TS – Tectonics & Structural Geology
TS1.1 – Temperature in sedimentary basins: a tool for geodynamics
EGU2020-2386 | Displays | TS1.1
DIAGENETIC HISTORY VS. THERMAL EVOLUTION OF PALAEZOIC RESERVOIR ROCKS IN THE ILLIZI BASIN (Algeria)Andrea Di Giulio, Chiara Nicola, Domenico Grigo, Paolo Scotti, Massimiliano Zattin, Chiara Amadori, Silvia Tamburelli, Alberto Consonni, and Andrea Ortenzi
Unravelling the time-space distribution of diagenetic events modifying the pore network of reservoir rocks is a classical task of hydrocarbon research. Nevertheless, it is not always easy to reach that picture, as it needs to constraint a number of variables driving that distribution along the geological history of sedimentary basins.
Here we present the results of an integrated study performed on 15 samples of Palaeozoic reservoir sandstones coming from 3 hydrocarbon wells in the Illizi Basin. In particular, the topic of debate that promoted this study is the possible thermal effect on the Illizi Basin reservoirs rocks of the Cenozoic magmatic activity occurred in Hoggar dome, south of the studied region, and in other sector of the basin as pointed out by several magmatic intrusions.
The study was performed by combining: i) the reconstruction of the relative diagenetic timing obtained by petrographic observations; ii) microthermometric analyses of fluid inclusions trapped in diagenetic minerals; iii) low-T thermochronology (both Fission tracks and U-Th/H analyses) on clastic apatite grains; iv) vitrinite reflectance analysis; v) geohistory analysis of sampled wells. These data were used to constrain different thermal models, focussing in particular to the possible evidence of a Tertiary thermal overprint.
The results of the study can be summarized as follows:
- Several diagenetic minerals precipitated in the pore network of the studied rocks; among these, precipitation conditions for quartz, calcite, ankerite and to a minor degree feldspars were constrained through fluid inclusion microthermometric analyses;
- All these phases precipitated in a relatively narrow range of temperatures nicely correlated with burial depth of samples, from fluids with quite homogenous salinity (78-113 °C and 9.2-14.5 NaCl eq. %) suggesting a relatively limited time in which most of cements precipitated;
- The data on the thermal maturity of organic matter (vitrinite reflectance along the Mesozoic sequence, and vitrinite reflectance equivalent, mainly from chitinozoans, for the Silurian-Devonian sequence) seem to suggest a heating higher than the one currently observed. This may be compatible both with an episode of magmatic activity or with a late Cretaceous-Tertiary burial now eroded (in the wells studied, no more than 500-700m);
- Thermochronology shows a continuous burial until temperatures compatible with those observed by vitrinite reflectance although a minor thermal episode (i.e. with a temperature variation of the order of 10°C) is allowed.
Based on this integrated data set, different thermal scenarios have been tested, excluding or including a Cenozoic additional heating, in order to estimate the effect of the adopted thermal model on the age of cement precipitation in the pore system of studied reservoir rocks.
How to cite: Di Giulio, A., Nicola, C., Grigo, D., Scotti, P., Zattin, M., Amadori, C., Tamburelli, S., Consonni, A., and Ortenzi, A.: DIAGENETIC HISTORY VS. THERMAL EVOLUTION OF PALAEZOIC RESERVOIR ROCKS IN THE ILLIZI BASIN (Algeria), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2386, https://doi.org/10.5194/egusphere-egu2020-2386, 2020.
Unravelling the time-space distribution of diagenetic events modifying the pore network of reservoir rocks is a classical task of hydrocarbon research. Nevertheless, it is not always easy to reach that picture, as it needs to constraint a number of variables driving that distribution along the geological history of sedimentary basins.
Here we present the results of an integrated study performed on 15 samples of Palaeozoic reservoir sandstones coming from 3 hydrocarbon wells in the Illizi Basin. In particular, the topic of debate that promoted this study is the possible thermal effect on the Illizi Basin reservoirs rocks of the Cenozoic magmatic activity occurred in Hoggar dome, south of the studied region, and in other sector of the basin as pointed out by several magmatic intrusions.
The study was performed by combining: i) the reconstruction of the relative diagenetic timing obtained by petrographic observations; ii) microthermometric analyses of fluid inclusions trapped in diagenetic minerals; iii) low-T thermochronology (both Fission tracks and U-Th/H analyses) on clastic apatite grains; iv) vitrinite reflectance analysis; v) geohistory analysis of sampled wells. These data were used to constrain different thermal models, focussing in particular to the possible evidence of a Tertiary thermal overprint.
The results of the study can be summarized as follows:
- Several diagenetic minerals precipitated in the pore network of the studied rocks; among these, precipitation conditions for quartz, calcite, ankerite and to a minor degree feldspars were constrained through fluid inclusion microthermometric analyses;
- All these phases precipitated in a relatively narrow range of temperatures nicely correlated with burial depth of samples, from fluids with quite homogenous salinity (78-113 °C and 9.2-14.5 NaCl eq. %) suggesting a relatively limited time in which most of cements precipitated;
- The data on the thermal maturity of organic matter (vitrinite reflectance along the Mesozoic sequence, and vitrinite reflectance equivalent, mainly from chitinozoans, for the Silurian-Devonian sequence) seem to suggest a heating higher than the one currently observed. This may be compatible both with an episode of magmatic activity or with a late Cretaceous-Tertiary burial now eroded (in the wells studied, no more than 500-700m);
- Thermochronology shows a continuous burial until temperatures compatible with those observed by vitrinite reflectance although a minor thermal episode (i.e. with a temperature variation of the order of 10°C) is allowed.
Based on this integrated data set, different thermal scenarios have been tested, excluding or including a Cenozoic additional heating, in order to estimate the effect of the adopted thermal model on the age of cement precipitation in the pore system of studied reservoir rocks.
How to cite: Di Giulio, A., Nicola, C., Grigo, D., Scotti, P., Zattin, M., Amadori, C., Tamburelli, S., Consonni, A., and Ortenzi, A.: DIAGENETIC HISTORY VS. THERMAL EVOLUTION OF PALAEZOIC RESERVOIR ROCKS IN THE ILLIZI BASIN (Algeria), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2386, https://doi.org/10.5194/egusphere-egu2020-2386, 2020.
EGU2020-4584 | Displays | TS1.1
Quantifying the Effects of Salt Structures on Source Rocks Thermal Evolution of the Marine Sedimentary BasinsShaowen Liu and Liangshu Wang
Evaporitic salt is prevailed in marine sedimentary basins, and the discovered hydrocarbon reservoirs are generally associated with salt structures in the world; accordingly salt structures have attracted much attention from academic and industry during the past decade. Tarim Basin that locates in northwest China, is the largest marine sedimentary basin in China with great hydrocarbon resources potential. Previous studies of salt structures in this basin mainly focus on its strong sealing capacity and structural traps created by salt structures. However, besides its extreme impermeability and low viscosity, rock salt has another unique thermal properties, featured by a large thermal conductivity as high as 5~6 W/(m.K), usually 2~3 times greater than that of other common sedimentary rocks, but a relatively low radiogenic heat production. This strong contrast in thermal properties could change the evolving thermal regime and associated thermal history of the source rocks around salt bodies, but has not been understood well. Herein based on the theoretical models and interpreted salt bearing seismic profiles from the Kuqa Foreland Basin, northern Tarim Basin, we use the 2D finite element numerical experiments to investigate the impacts of salt structures on basin geothermal regime and associated hydrocarbon thermal evolution. Our results show that, owing to its high efficiency in heat conduction, the salt rocks would result in obviously positive temperature anomalies (3~13%) above the salt body and negative temperature anomalies (11~35%) in the subsalt, enhancing and restraining the thermal maturation of source rocks above and below the salt body, respectively. The amplitude and extent of geothermal effects of salt structures depend on the thermal conductivity, geometry, thickness and burial depth of the salt bodies. The thermally affected area around the salt body can be 2 time of salt radius laterally and 2~3 times of salt thickness vertically. Salt structures in the Kuqa Foreland Basin can prominently cool the subsalt formation temperature and accordingly reduce the thermal maturity (Ro) of Jurassic source rocks as much as 18%, enabling the source rocks to be still of gas generation other than over-mature stage as expected previously, which is favor for deep hydrocarbon preservation below salt. In particular, salt structures in the west and east Kuqa Foreland Basin show strong differences in their thickness, geometric pattern, burial depth and composition, the thermal effects of salt structures on thermal maturation of subsalt source rocks should differ accordingly, which is supported by the observed tempo-spatial variation of Ro for Jurassic source rocks in this basin. Finally, we propose that the geothermal effects of salt structures will be of great importance in the deep hydrocarbon resources potential assessment and exploration in marine sedimentary basins in China.
How to cite: Liu, S. and Wang, L.: Quantifying the Effects of Salt Structures on Source Rocks Thermal Evolution of the Marine Sedimentary Basins, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4584, https://doi.org/10.5194/egusphere-egu2020-4584, 2020.
Evaporitic salt is prevailed in marine sedimentary basins, and the discovered hydrocarbon reservoirs are generally associated with salt structures in the world; accordingly salt structures have attracted much attention from academic and industry during the past decade. Tarim Basin that locates in northwest China, is the largest marine sedimentary basin in China with great hydrocarbon resources potential. Previous studies of salt structures in this basin mainly focus on its strong sealing capacity and structural traps created by salt structures. However, besides its extreme impermeability and low viscosity, rock salt has another unique thermal properties, featured by a large thermal conductivity as high as 5~6 W/(m.K), usually 2~3 times greater than that of other common sedimentary rocks, but a relatively low radiogenic heat production. This strong contrast in thermal properties could change the evolving thermal regime and associated thermal history of the source rocks around salt bodies, but has not been understood well. Herein based on the theoretical models and interpreted salt bearing seismic profiles from the Kuqa Foreland Basin, northern Tarim Basin, we use the 2D finite element numerical experiments to investigate the impacts of salt structures on basin geothermal regime and associated hydrocarbon thermal evolution. Our results show that, owing to its high efficiency in heat conduction, the salt rocks would result in obviously positive temperature anomalies (3~13%) above the salt body and negative temperature anomalies (11~35%) in the subsalt, enhancing and restraining the thermal maturation of source rocks above and below the salt body, respectively. The amplitude and extent of geothermal effects of salt structures depend on the thermal conductivity, geometry, thickness and burial depth of the salt bodies. The thermally affected area around the salt body can be 2 time of salt radius laterally and 2~3 times of salt thickness vertically. Salt structures in the Kuqa Foreland Basin can prominently cool the subsalt formation temperature and accordingly reduce the thermal maturity (Ro) of Jurassic source rocks as much as 18%, enabling the source rocks to be still of gas generation other than over-mature stage as expected previously, which is favor for deep hydrocarbon preservation below salt. In particular, salt structures in the west and east Kuqa Foreland Basin show strong differences in their thickness, geometric pattern, burial depth and composition, the thermal effects of salt structures on thermal maturation of subsalt source rocks should differ accordingly, which is supported by the observed tempo-spatial variation of Ro for Jurassic source rocks in this basin. Finally, we propose that the geothermal effects of salt structures will be of great importance in the deep hydrocarbon resources potential assessment and exploration in marine sedimentary basins in China.
How to cite: Liu, S. and Wang, L.: Quantifying the Effects of Salt Structures on Source Rocks Thermal Evolution of the Marine Sedimentary Basins, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4584, https://doi.org/10.5194/egusphere-egu2020-4584, 2020.
EGU2020-5815 | Displays | TS1.1
Unexpected thermal history of a syn-collisional basin revealed by geo- and thermochronology: the case of the Tertiary Piedmont Basin (Western Alps, Italy)Chiara Amadori, Antonio Langone, Mattina Marini, Reguzzi Simone, Barbara Carrapa, Matteo Maino, and Andrea Di Giulio
The Tertiary Piedmont Basin (TPB) in NW Italy represents an episutural basin developed since the Late Eocene in the retrobelt of the Western Alps and in the foreland of the Northern Apennine. During Oligo-Miocene time, up to 3 km-thick clastic deposits filled the basin recording the tectonics associated with the shift from the Alpine collisional thickening and the progressive NE-migration of the Apennine. The continental thickening was also accompanied by the opening of the Liguro-Provençal Basin and the drift of the Corsica-Sardinia block. Because of this key-position, the tectono-sedimentary and thermochronological history of the TPB has been the object of extensive investigations (Maino et al., 2013 and reference therein). However, several questions regarding its burial-exhumation history are still open. In order to define the thermal history of the source-sink system, we combined literature data with new detrital apatite fission-track analyses and zircon U-Pb dating from Upper Priabonian to Lower Miocene syn-tectonic deposits. Results from AFT analysis show: i) a single reset population at 24.8 ± 1.2 Ma (Late Chattian) in the lowermost Late Priabonian sample; ii) partially annealed apatite grains from Early Rupelian sample; iii) unannealed Late Rupelian-Miocene samples with AFT age populations spanning from Late Cretaceous to Late Oligocene in time. Data from the Ligurian Alps crystalline massifs report similar AFT cooling ages between 22.9 ± 5.3 - 24.0 ± 1.4 Ma. This, combined with our data, shows that the bottom of the TPB sequence experienced ~110 °C heating and subsequent cooling together with its nearby margin. The heating experienced by the basin combined with reconstructed sedimentary thickness (before the exhumation/cooling event) of ca. < 3 km, implies an elevated geothermal gradient of about 60 °C/Km, which is anomalous for a thickened orogenic crust. Furthermore, one sample from Upper Oligocene sedimentary rocks contains an AFT detrital population age (33.6 ± 2 Ma) consistent with a youngest U-Pb age peak of 33.6 Ma from co-magmatic zircon grains, which likely reflects the age of volcanites today buried under the Po Plain (Di Giulio et al., 2001). Detrital zircon U-Pb ages show two main populations at ca. 290 and ca. 460 Ma, which are expected products of a Variscan source now exposed in the Ligurian Alps and Southern Alps. Our new geo-thermochronological data overall suggests a distributed Oligocene thermal signal, the origin of which is discussed. Possible explanations are: 1) a > 3 km of focused erosion associated with tectonic deformation occurred in the TPB and nearby margin and/or 2) an anomalously high heat flow event driven by asthenospheric rise as a consequence of the Liguro-Provençal rifting.
Maino M., Decarlis A., Felletti F., Seno S. (2013) Tectono-sedimentary evolution of the Tertiary Piedmont Basin (NW Italy) within the Oligo–Miocene central Mediterranean geodynamics. Tectonics, 32, 593–619.
Di Giulio, A., Carrapa B., Fantoni R., Gorla L., Valdisturlo L. (2001) Middle Eocene to Early Miocene sedimentary evolution of the western segment of the South Alpine foredeep (Italy). Int. J. Earth Sci., 90, 534-548.
How to cite: Amadori, C., Langone, A., Marini, M., Simone, R., Carrapa, B., Maino, M., and Di Giulio, A.: Unexpected thermal history of a syn-collisional basin revealed by geo- and thermochronology: the case of the Tertiary Piedmont Basin (Western Alps, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5815, https://doi.org/10.5194/egusphere-egu2020-5815, 2020.
The Tertiary Piedmont Basin (TPB) in NW Italy represents an episutural basin developed since the Late Eocene in the retrobelt of the Western Alps and in the foreland of the Northern Apennine. During Oligo-Miocene time, up to 3 km-thick clastic deposits filled the basin recording the tectonics associated with the shift from the Alpine collisional thickening and the progressive NE-migration of the Apennine. The continental thickening was also accompanied by the opening of the Liguro-Provençal Basin and the drift of the Corsica-Sardinia block. Because of this key-position, the tectono-sedimentary and thermochronological history of the TPB has been the object of extensive investigations (Maino et al., 2013 and reference therein). However, several questions regarding its burial-exhumation history are still open. In order to define the thermal history of the source-sink system, we combined literature data with new detrital apatite fission-track analyses and zircon U-Pb dating from Upper Priabonian to Lower Miocene syn-tectonic deposits. Results from AFT analysis show: i) a single reset population at 24.8 ± 1.2 Ma (Late Chattian) in the lowermost Late Priabonian sample; ii) partially annealed apatite grains from Early Rupelian sample; iii) unannealed Late Rupelian-Miocene samples with AFT age populations spanning from Late Cretaceous to Late Oligocene in time. Data from the Ligurian Alps crystalline massifs report similar AFT cooling ages between 22.9 ± 5.3 - 24.0 ± 1.4 Ma. This, combined with our data, shows that the bottom of the TPB sequence experienced ~110 °C heating and subsequent cooling together with its nearby margin. The heating experienced by the basin combined with reconstructed sedimentary thickness (before the exhumation/cooling event) of ca. < 3 km, implies an elevated geothermal gradient of about 60 °C/Km, which is anomalous for a thickened orogenic crust. Furthermore, one sample from Upper Oligocene sedimentary rocks contains an AFT detrital population age (33.6 ± 2 Ma) consistent with a youngest U-Pb age peak of 33.6 Ma from co-magmatic zircon grains, which likely reflects the age of volcanites today buried under the Po Plain (Di Giulio et al., 2001). Detrital zircon U-Pb ages show two main populations at ca. 290 and ca. 460 Ma, which are expected products of a Variscan source now exposed in the Ligurian Alps and Southern Alps. Our new geo-thermochronological data overall suggests a distributed Oligocene thermal signal, the origin of which is discussed. Possible explanations are: 1) a > 3 km of focused erosion associated with tectonic deformation occurred in the TPB and nearby margin and/or 2) an anomalously high heat flow event driven by asthenospheric rise as a consequence of the Liguro-Provençal rifting.
Maino M., Decarlis A., Felletti F., Seno S. (2013) Tectono-sedimentary evolution of the Tertiary Piedmont Basin (NW Italy) within the Oligo–Miocene central Mediterranean geodynamics. Tectonics, 32, 593–619.
Di Giulio, A., Carrapa B., Fantoni R., Gorla L., Valdisturlo L. (2001) Middle Eocene to Early Miocene sedimentary evolution of the western segment of the South Alpine foredeep (Italy). Int. J. Earth Sci., 90, 534-548.
How to cite: Amadori, C., Langone, A., Marini, M., Simone, R., Carrapa, B., Maino, M., and Di Giulio, A.: Unexpected thermal history of a syn-collisional basin revealed by geo- and thermochronology: the case of the Tertiary Piedmont Basin (Western Alps, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5815, https://doi.org/10.5194/egusphere-egu2020-5815, 2020.
EGU2020-7205 | Displays | TS1.1 | Highlight
Repurposing Britain’s Coal Measures: insights from seismic and borehole-based mapping, and geothermal modellingLouis Howell, Stuart Egan, Bernard Besly, Graham Leslie, and Surika Sooriyathasan
As a consequence of 19th and 20th century coal mining, a vast quantity of subsurface data has been accumulated on Britain’s late Carboniferous Coal Measures and the basins in which they have accumulated. Here we discuss current understanding of the geological evolution of the British Isles during this period, as well as how these data can be repurposed as the UK seeks to reduce its greenhouse gas emissions.
It is widely assumed that Britain’s Coal Measures accumulated during a period of tectonically quiescent, thermally induced post-rift subsidence and that the lateral extent of the Variscan foreland in southern England and Wales was restricted. Burial history curves constructed from stratigraphic successions across the UK suggest, however, that during the late Carboniferous the UK was characterised by accelerated subsidence rates as far north as northern England and Scotland, beyond any perceivable flexure-induced foredeep. On local scales, seismic and borehole-based mapping shows that many individual depocentres were strongly influenced by syn-depositional faulting, folding and positive inversion. This influence is illustrated by repeated local unconformities within the late Carboniferous succession across England and Scotland as well as variable isochore thickness trends. We propose that this succession was influenced by a combination of both local tectonic controls and regional controls such as supralithospheric orogenic loading and sublithospheric dynamic loading. In this sense, we believe that the British Variscan foreland system, as the British Isles should be referred to as during the late Carboniferous, resembled a ‘broken’ foreland system such as that of Patagonia, South America.
Understanding the nature of Britain’s Coal Measures has gained renewed importance given the need to reduce carbon emissions and seek alternative sources of energy. Across the UK, there are a number of active projects aiming to harness latent heat from abandoned underground coalmines. In addition, coupled CO2 sequestration and enhanced coal bed methane recovery offers a further, if riskier, low carbon subsurface energy prospect. To aid deep geothermal exploration, subsurface data from northern England is being compiled in order to construct regional 3D geothermal models. Our models highlight hot areas within the subsurface more realistically than equivalent maps based on contouring around individual borehole temperature measurements that are skewed by sparsely distributed data points and, potentially, inaccurate measurements. Deep heat-producing granite bodies and the variable thickness of thermally resistive rock units, such as the Pennine Coal Measures Group, are highlighted as dominant controls on the distribution of deep geothermal energy in northern England.
How to cite: Howell, L., Egan, S., Besly, B., Leslie, G., and Sooriyathasan, S.: Repurposing Britain’s Coal Measures: insights from seismic and borehole-based mapping, and geothermal modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7205, https://doi.org/10.5194/egusphere-egu2020-7205, 2020.
As a consequence of 19th and 20th century coal mining, a vast quantity of subsurface data has been accumulated on Britain’s late Carboniferous Coal Measures and the basins in which they have accumulated. Here we discuss current understanding of the geological evolution of the British Isles during this period, as well as how these data can be repurposed as the UK seeks to reduce its greenhouse gas emissions.
It is widely assumed that Britain’s Coal Measures accumulated during a period of tectonically quiescent, thermally induced post-rift subsidence and that the lateral extent of the Variscan foreland in southern England and Wales was restricted. Burial history curves constructed from stratigraphic successions across the UK suggest, however, that during the late Carboniferous the UK was characterised by accelerated subsidence rates as far north as northern England and Scotland, beyond any perceivable flexure-induced foredeep. On local scales, seismic and borehole-based mapping shows that many individual depocentres were strongly influenced by syn-depositional faulting, folding and positive inversion. This influence is illustrated by repeated local unconformities within the late Carboniferous succession across England and Scotland as well as variable isochore thickness trends. We propose that this succession was influenced by a combination of both local tectonic controls and regional controls such as supralithospheric orogenic loading and sublithospheric dynamic loading. In this sense, we believe that the British Variscan foreland system, as the British Isles should be referred to as during the late Carboniferous, resembled a ‘broken’ foreland system such as that of Patagonia, South America.
Understanding the nature of Britain’s Coal Measures has gained renewed importance given the need to reduce carbon emissions and seek alternative sources of energy. Across the UK, there are a number of active projects aiming to harness latent heat from abandoned underground coalmines. In addition, coupled CO2 sequestration and enhanced coal bed methane recovery offers a further, if riskier, low carbon subsurface energy prospect. To aid deep geothermal exploration, subsurface data from northern England is being compiled in order to construct regional 3D geothermal models. Our models highlight hot areas within the subsurface more realistically than equivalent maps based on contouring around individual borehole temperature measurements that are skewed by sparsely distributed data points and, potentially, inaccurate measurements. Deep heat-producing granite bodies and the variable thickness of thermally resistive rock units, such as the Pennine Coal Measures Group, are highlighted as dominant controls on the distribution of deep geothermal energy in northern England.
How to cite: Howell, L., Egan, S., Besly, B., Leslie, G., and Sooriyathasan, S.: Repurposing Britain’s Coal Measures: insights from seismic and borehole-based mapping, and geothermal modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7205, https://doi.org/10.5194/egusphere-egu2020-7205, 2020.
EGU2020-13606 | Displays | TS1.1
A Bayesian approach for thermal history reconstruction in basin modelingAndrea Licciardi, Kerry Gallagher, and Stephen Anthony Clark
Vitrinite reflectance and apatite fission track) and borehole data (bottom hole temperature and porosi ty) for thermal history reconstruction in basin modeling. The approach implements a trans-dimensional and hierarchical Bayesian formulation with a reversible jump Markov chain Monte Carlo (rjMcMC) algorithm. The main objective of the inverse problem is to infer the heat flow history below a borehole given the data and a set of geological constraints (e.g. stratigraphy , burial histories and physical properties of the sediments). The algorithm incorporat es an adaptive, data-driven parametrization of the heat flow history, and allows for automatic estimation of relative importance of each data type in the inversion and for robust quantification of parameter uncertainties and trade-offs. In addition, the algorithm deals with uncertainties on the imposed geological constraints in two ways. First, the amount of erosion and timing of an erosional event are explicitly treated as independent parameters to be inferred from the data. Second, uncertainties on compaction parameters and surface temperature histo ry are directly propagated
into the final probabilistic solution.
How to cite: Licciardi, A., Gallagher, K., and Clark, S. A.: A Bayesian approach for thermal history reconstruction in basin modeling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13606, https://doi.org/10.5194/egusphere-egu2020-13606, 2020.
Vitrinite reflectance and apatite fission track) and borehole data (bottom hole temperature and porosi ty) for thermal history reconstruction in basin modeling. The approach implements a trans-dimensional and hierarchical Bayesian formulation with a reversible jump Markov chain Monte Carlo (rjMcMC) algorithm. The main objective of the inverse problem is to infer the heat flow history below a borehole given the data and a set of geological constraints (e.g. stratigraphy , burial histories and physical properties of the sediments). The algorithm incorporat es an adaptive, data-driven parametrization of the heat flow history, and allows for automatic estimation of relative importance of each data type in the inversion and for robust quantification of parameter uncertainties and trade-offs. In addition, the algorithm deals with uncertainties on the imposed geological constraints in two ways. First, the amount of erosion and timing of an erosional event are explicitly treated as independent parameters to be inferred from the data. Second, uncertainties on compaction parameters and surface temperature histo ry are directly propagated
into the final probabilistic solution.
How to cite: Licciardi, A., Gallagher, K., and Clark, S. A.: A Bayesian approach for thermal history reconstruction in basin modeling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13606, https://doi.org/10.5194/egusphere-egu2020-13606, 2020.
EGU2020-18462 | Displays | TS1.1 | Highlight
Middle Miocene onset of thrusting along the basal décollement of the Jura Mountains: Evidence from carbonate U-Pb dating and clumped isotope thermometryNathan Looser, Herfried Madritsch, Marcel Guillong, Oscar Laurent, Stephan Wohlwend, and Stefano M. Bernasconi
During its late-stage evolution, the European Alpine orogen witnessed a northwest-directed propagation of its deformation front along an evaporitic basal décollement into the foreland. This resulted in the decoupling of the northern Alpine Molasse Basin from its basement and the formation of the Jura fold-and-thrust belt. Here, we present the first absolute age and temperature constraints on deformation along this major décollement by using combined carbonate U-Pb dating by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and clumped isotope thermometry. We analyzed calcite veins associated with a secondary thrust fault branching off from the basal décollement in a deep borehole within the Swiss Molasse Basin providing evidence for three brittle deformation events related to Alpine contraction: Vein formation at ~14 Ma ago, thrust faulting with cataclasis ~13 Ma ago, and another vein formation event ~9 Ma ago. Clumped isotope data reveal vein calcite precipitation at temperatures of ~100 °C from fluids equilibrated with the host rock during all deformation intervals. These temperatures are in good agreement with temperature estimates from microfabrics of anhydrite mylonites in the basal décollement. Our data demonstrate that the propagation of Alpine deformation into its distal foreland occurred significantly earlier than previously inferred, at middle Miocene (Langhian) times at the latest, contributing to the debate about the late-stage geodynamics of the central Alps. The deformation sequence indicated by our results underpins fundamental kinematic models of viscous décollement-based foreland thrust belts. Beyond that, we demonstrate the potential of our methodological approach applied to foreland thrust systems in resolving the late-stage evolution of convergent orogens.
How to cite: Looser, N., Madritsch, H., Guillong, M., Laurent, O., Wohlwend, S., and Bernasconi, S. M.: Middle Miocene onset of thrusting along the basal décollement of the Jura Mountains: Evidence from carbonate U-Pb dating and clumped isotope thermometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18462, https://doi.org/10.5194/egusphere-egu2020-18462, 2020.
During its late-stage evolution, the European Alpine orogen witnessed a northwest-directed propagation of its deformation front along an evaporitic basal décollement into the foreland. This resulted in the decoupling of the northern Alpine Molasse Basin from its basement and the formation of the Jura fold-and-thrust belt. Here, we present the first absolute age and temperature constraints on deformation along this major décollement by using combined carbonate U-Pb dating by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and clumped isotope thermometry. We analyzed calcite veins associated with a secondary thrust fault branching off from the basal décollement in a deep borehole within the Swiss Molasse Basin providing evidence for three brittle deformation events related to Alpine contraction: Vein formation at ~14 Ma ago, thrust faulting with cataclasis ~13 Ma ago, and another vein formation event ~9 Ma ago. Clumped isotope data reveal vein calcite precipitation at temperatures of ~100 °C from fluids equilibrated with the host rock during all deformation intervals. These temperatures are in good agreement with temperature estimates from microfabrics of anhydrite mylonites in the basal décollement. Our data demonstrate that the propagation of Alpine deformation into its distal foreland occurred significantly earlier than previously inferred, at middle Miocene (Langhian) times at the latest, contributing to the debate about the late-stage geodynamics of the central Alps. The deformation sequence indicated by our results underpins fundamental kinematic models of viscous décollement-based foreland thrust belts. Beyond that, we demonstrate the potential of our methodological approach applied to foreland thrust systems in resolving the late-stage evolution of convergent orogens.
How to cite: Looser, N., Madritsch, H., Guillong, M., Laurent, O., Wohlwend, S., and Bernasconi, S. M.: Middle Miocene onset of thrusting along the basal décollement of the Jura Mountains: Evidence from carbonate U-Pb dating and clumped isotope thermometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18462, https://doi.org/10.5194/egusphere-egu2020-18462, 2020.
EGU2020-18533 | Displays | TS1.1
Metamorphosed Permian vertebrate fossils: geochemistry and mineralogy of “white” sharksAnthea Arns, Frank Tomaschek, Edith Alig, Katrin Weber, Hubert Vonhof, Jan Fischer, Sebastian Voigt, and Thomas Tütken
The intra-mountainous Saar-Nahe Basin (SNB), SW Germany, a strike-slip-fault basin formed during the Variscian orogeny, was filled by a large freshwater lake system during the Early Permian. The SNB experienced intense syn- and post-depositional magmatic activity, resulting in a complex volcano-sedimentary sequence of magmatic intrusions, lava flows and tephra deposits intercalating in continental red beds and limno-fluvial sediments. Fossils preserved in white color are found in Permo-Carboniferous fluvio-lacustrine siliciclastic floodplain sediments with thin intercalated limestone banks, of the Remigiusberg Formation in the SNB. The oldest amniote fossil of Germany and other partly articulated tetrapod remains were recovered from it at the Remigiusberg quarry near Kusel (e.g., Fröbisch et al., 2011; Voigt et al. 2014). These terrestrial tetrapods were discovered together with aquatic vertebrate fossils in close proximity (< 5 m; within the contact aureole) to an underlying decameter thick sill of kuselite, an auto-hydrothermally altered andesite. We aim to assess the thermal and chemical impact of post-depositional contact metamorphism and hydrothermal activity associated with this sill on the bioapatite of vertebrate skeletal remains by characterizing the elemental, isotopic and mineralogical composition of these fossils. White-colored, likely hydrothermally altered teeth of the freshwater shark Lebachacanthus were analyzed and compared to shark teeth of the same species retaining their original black color, from contemporaneous unmetamorphosed lacustrine black shale deposits in the SNB.
In situ Electron Microprobe analysis and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) elemental profiles reveal distinct diagenetic histories for the black- and white-colored shark teeth. This is further supported by apatite ẟ18O and ẟ13C values, which indicate different secondary alteration by fluids for both facies. Raman spectroscopy and X-ray diffraction on bulk powder samples identify fluorapatite as the major mineral phase in all teeth. Apatite crystallinity of both dentin and enameloid is higher in white- than in black-colored fossils, consistent with crystallite growth due to thermal overprint of > 500 °C. For both, white- and black-colored shark teeth, LA-ICP-MS U-Pb analyses yield inconclusive data and unexpectedly young ages inconsistent with known ages of deposition or metamorphism.
We are currently analyzing the petrology of the kuselite to constrain the metamorphic evolution of sediments in the contact aureole by modelling. Additionally, heating experiments of modern bioapatite samples are performed to further constrain the alteration temperature. Altogether, these data will enhance our understanding of the particular thermometamorphic/hydrothermal conditions required to form white-colored, recrystallized vertebrate fossils in the context of the magmatic-metamorphic evolution of the SNB.
References
FRÖBISCH, J., SCHOCH, R.R., MÜLLER, J., SCHINDLER, T. & SCHWEISS, D.J. (2011): The oldest amniote from Germany: a sphenacodontid synapsid from the Saar-Nahe Basin. Acta Palaeontologica Polonica, 56: 113–120.
VOIGT, S., FISCHER, J., SCHINDLER, T., WUTTKE, M., SPINDLER, F. & RINEHART, L. (2014): On a potential fossil hotspot for Pennsylvanian-Permian nonaquatic vertebrates in Europe. Freiberger Forschungshefte, C548: 39–44.
How to cite: Arns, A., Tomaschek, F., Alig, E., Weber, K., Vonhof, H., Fischer, J., Voigt, S., and Tütken, T.: Metamorphosed Permian vertebrate fossils: geochemistry and mineralogy of “white” sharks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18533, https://doi.org/10.5194/egusphere-egu2020-18533, 2020.
The intra-mountainous Saar-Nahe Basin (SNB), SW Germany, a strike-slip-fault basin formed during the Variscian orogeny, was filled by a large freshwater lake system during the Early Permian. The SNB experienced intense syn- and post-depositional magmatic activity, resulting in a complex volcano-sedimentary sequence of magmatic intrusions, lava flows and tephra deposits intercalating in continental red beds and limno-fluvial sediments. Fossils preserved in white color are found in Permo-Carboniferous fluvio-lacustrine siliciclastic floodplain sediments with thin intercalated limestone banks, of the Remigiusberg Formation in the SNB. The oldest amniote fossil of Germany and other partly articulated tetrapod remains were recovered from it at the Remigiusberg quarry near Kusel (e.g., Fröbisch et al., 2011; Voigt et al. 2014). These terrestrial tetrapods were discovered together with aquatic vertebrate fossils in close proximity (< 5 m; within the contact aureole) to an underlying decameter thick sill of kuselite, an auto-hydrothermally altered andesite. We aim to assess the thermal and chemical impact of post-depositional contact metamorphism and hydrothermal activity associated with this sill on the bioapatite of vertebrate skeletal remains by characterizing the elemental, isotopic and mineralogical composition of these fossils. White-colored, likely hydrothermally altered teeth of the freshwater shark Lebachacanthus were analyzed and compared to shark teeth of the same species retaining their original black color, from contemporaneous unmetamorphosed lacustrine black shale deposits in the SNB.
In situ Electron Microprobe analysis and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) elemental profiles reveal distinct diagenetic histories for the black- and white-colored shark teeth. This is further supported by apatite ẟ18O and ẟ13C values, which indicate different secondary alteration by fluids for both facies. Raman spectroscopy and X-ray diffraction on bulk powder samples identify fluorapatite as the major mineral phase in all teeth. Apatite crystallinity of both dentin and enameloid is higher in white- than in black-colored fossils, consistent with crystallite growth due to thermal overprint of > 500 °C. For both, white- and black-colored shark teeth, LA-ICP-MS U-Pb analyses yield inconclusive data and unexpectedly young ages inconsistent with known ages of deposition or metamorphism.
We are currently analyzing the petrology of the kuselite to constrain the metamorphic evolution of sediments in the contact aureole by modelling. Additionally, heating experiments of modern bioapatite samples are performed to further constrain the alteration temperature. Altogether, these data will enhance our understanding of the particular thermometamorphic/hydrothermal conditions required to form white-colored, recrystallized vertebrate fossils in the context of the magmatic-metamorphic evolution of the SNB.
References
FRÖBISCH, J., SCHOCH, R.R., MÜLLER, J., SCHINDLER, T. & SCHWEISS, D.J. (2011): The oldest amniote from Germany: a sphenacodontid synapsid from the Saar-Nahe Basin. Acta Palaeontologica Polonica, 56: 113–120.
VOIGT, S., FISCHER, J., SCHINDLER, T., WUTTKE, M., SPINDLER, F. & RINEHART, L. (2014): On a potential fossil hotspot for Pennsylvanian-Permian nonaquatic vertebrates in Europe. Freiberger Forschungshefte, C548: 39–44.
How to cite: Arns, A., Tomaschek, F., Alig, E., Weber, K., Vonhof, H., Fischer, J., Voigt, S., and Tütken, T.: Metamorphosed Permian vertebrate fossils: geochemistry and mineralogy of “white” sharks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18533, https://doi.org/10.5194/egusphere-egu2020-18533, 2020.
EGU2020-19279 | Displays | TS1.1
Structural styles of the External Rif and Flysch Domain (Rif belt, northern Morocco) through thermal maturity and structural dataAndrea Schito, Achraf Atouabat, Sveva Corrado, Faouziya Haissen, Geoffroy Mohn, and Dominique Frizon De Lamotte
Located in northern Morocco, the Rif belt represents the western edge of the Maghrebides system. This domain underwent a significant Cenozoic alpine compressional deformation, due to the collision between the North African margin and the south-western margin of the exotic Alboran Domain. This collision led to the development of a nappe stack during the Miocene.
This contribution aims to characterize the main tectonic mechanisms driving the evolution of the Rifain wedge, its burial-exhumation paths and to understand the former architecture of the North African paleo-margin. The work focuses mainly on the Flysch domain, originated from the Maghrebian branch of the Tethys and on the External domain (namely Intrarif, Mesorif and Prerif) that belong to the former north African margin. To define the thrust sheet stacking pattern and their burial-exhumation paths, a regional transect from Chefchaouen and Ouezzane towns (Central Rif), crossing the orogenic wedge from the Flysch to the Prerif Units is constructed.
The methodological approach consists in combining petrography and Raman micro-spectroscopy on organic matter and 1D thermal modelling, together with field structural data.
A new paleo-thermal data set of vitrinite reflectance (Ro%) and Raman micro-spectroscopy displays levels of thermal maturity between early and deep diagenetic conditions (Ro% ranges from 0.50% to 1.15%).
Preliminary results show an abrupt change in the thermal maturity and the rate of shortening in the Loukkos sub-unit (Intrarif Domain) that is structurally squeezed between Tangier sub-unit (Intrarif Domain) and the “Izzaren Duplex” (Mesorif).
Furthermore, previous studies show that the thickest crust below the Rif fold-and-thrust belt is located below the Izzaren area, suggesting a deep crustal imbrication at the transition between the Intrarif and the Mesorif. These observations joined with the thermal maturity data and 1D thermal modelling allow revisiting the structural evolution of the central part of the Rif belt, by defining the rate of shortening and proposing a new geological restoration with respect to the Mesozoic North African margin structural original setting.
How to cite: Schito, A., Atouabat, A., Corrado, S., Haissen, F., Mohn, G., and Frizon De Lamotte, D.: Structural styles of the External Rif and Flysch Domain (Rif belt, northern Morocco) through thermal maturity and structural data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19279, https://doi.org/10.5194/egusphere-egu2020-19279, 2020.
Located in northern Morocco, the Rif belt represents the western edge of the Maghrebides system. This domain underwent a significant Cenozoic alpine compressional deformation, due to the collision between the North African margin and the south-western margin of the exotic Alboran Domain. This collision led to the development of a nappe stack during the Miocene.
This contribution aims to characterize the main tectonic mechanisms driving the evolution of the Rifain wedge, its burial-exhumation paths and to understand the former architecture of the North African paleo-margin. The work focuses mainly on the Flysch domain, originated from the Maghrebian branch of the Tethys and on the External domain (namely Intrarif, Mesorif and Prerif) that belong to the former north African margin. To define the thrust sheet stacking pattern and their burial-exhumation paths, a regional transect from Chefchaouen and Ouezzane towns (Central Rif), crossing the orogenic wedge from the Flysch to the Prerif Units is constructed.
The methodological approach consists in combining petrography and Raman micro-spectroscopy on organic matter and 1D thermal modelling, together with field structural data.
A new paleo-thermal data set of vitrinite reflectance (Ro%) and Raman micro-spectroscopy displays levels of thermal maturity between early and deep diagenetic conditions (Ro% ranges from 0.50% to 1.15%).
Preliminary results show an abrupt change in the thermal maturity and the rate of shortening in the Loukkos sub-unit (Intrarif Domain) that is structurally squeezed between Tangier sub-unit (Intrarif Domain) and the “Izzaren Duplex” (Mesorif).
Furthermore, previous studies show that the thickest crust below the Rif fold-and-thrust belt is located below the Izzaren area, suggesting a deep crustal imbrication at the transition between the Intrarif and the Mesorif. These observations joined with the thermal maturity data and 1D thermal modelling allow revisiting the structural evolution of the central part of the Rif belt, by defining the rate of shortening and proposing a new geological restoration with respect to the Mesozoic North African margin structural original setting.
How to cite: Schito, A., Atouabat, A., Corrado, S., Haissen, F., Mohn, G., and Frizon De Lamotte, D.: Structural styles of the External Rif and Flysch Domain (Rif belt, northern Morocco) through thermal maturity and structural data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19279, https://doi.org/10.5194/egusphere-egu2020-19279, 2020.
EGU2020-20672 | Displays | TS1.1
A Pyrenean-like model for the Variscan belt in NW Africa : insights from thermometry-based Raman spectroscopy study in the Khenifra BasinRémi Leprêtre, Andrea Schito, Rachid Ouchaou, Mohamed El Houicha, and Francis Chopin
The Variscan belt in NW Africa is an intracontinental belt, resulting from far-field compressional stress during the closure of the Rheic Ocean between the Late Carboniferous and the Early Permian. In the classical view, this orogen building was preceded by a pre-orogenic stage, namely the Eo-variscan stage, suggested to have occurred at the Late Devonian-Early Carboniferous transition.
This view is now questioned, for multiple reasons. A first structural reason aims at re-interpreting the so-called Eovariscan features as extensional ones. Indeed, although many structures have been described, their integration into a compressional setting is not straightforward. A second reason is geodynamical, since this peculiar stage is bracketed between two general extensional phases recorded at the scale of NW Africa, and this leaves a very short time interval to proceed to a compressional phase that is geodynamically not integrated until today. At last, a third reason stems from early findings from metamorphic works in the Western Meseta that demonstrated the occurrences of previously unnoticed high geothermal gradients inside numerous Early Carboniferous basins (Chopin et al., 2014 ; Wernert et al., 2016 ; Delchini et al., 2018 ; Lahfid et al., 2019).
In this work, we sampled the Khenifra Basin within the easternmost part of the Western Meseta, where the Eovariscan deformation was defined (Allary et al., 1972). We carried on structural observations into the basement and sampled both the Ordovician basement and the Middle(?)-Late Visean series of the basin, which is thought the be extensional. Maximum temperatures reached by the 77 sampled rocks were obtained from the analysis of organic matter with the use of the Raman spectroscopy. The examination of this new dataset demonstrates that the Ordovician series acquired temperatures through a single event, consistently with their common record of the Eovariscan deformation. Instead, the unconformable Visean series on top of the basement show a pronounced basinal asymmetry, from low temperatures (< 160°C) to temperatures equivalent to the Ordovician ones (> 250°C). The Visean series do not record the Eovariscan deformation, and their thermal structure was acquired before the Variscan event, regarding their repartition within the basin. The examination of the different hypotheses for the timing of the maximal temperature acquisition (Variscan, compressional Eovariscan and extensional Eovariscan) leads to a single option only compatible with an extensional Eovariscan context.
The renewal on the knowledge about the early stages of the Variscan orogeny in NW Africa allows us to consider a Pyrenean-like model for the formation of this intraplate belt, resulting from the inversion of hot Early Carboniferous rifted basins.
How to cite: Leprêtre, R., Schito, A., Ouchaou, R., El Houicha, M., and Chopin, F.: A Pyrenean-like model for the Variscan belt in NW Africa : insights from thermometry-based Raman spectroscopy study in the Khenifra Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20672, https://doi.org/10.5194/egusphere-egu2020-20672, 2020.
The Variscan belt in NW Africa is an intracontinental belt, resulting from far-field compressional stress during the closure of the Rheic Ocean between the Late Carboniferous and the Early Permian. In the classical view, this orogen building was preceded by a pre-orogenic stage, namely the Eo-variscan stage, suggested to have occurred at the Late Devonian-Early Carboniferous transition.
This view is now questioned, for multiple reasons. A first structural reason aims at re-interpreting the so-called Eovariscan features as extensional ones. Indeed, although many structures have been described, their integration into a compressional setting is not straightforward. A second reason is geodynamical, since this peculiar stage is bracketed between two general extensional phases recorded at the scale of NW Africa, and this leaves a very short time interval to proceed to a compressional phase that is geodynamically not integrated until today. At last, a third reason stems from early findings from metamorphic works in the Western Meseta that demonstrated the occurrences of previously unnoticed high geothermal gradients inside numerous Early Carboniferous basins (Chopin et al., 2014 ; Wernert et al., 2016 ; Delchini et al., 2018 ; Lahfid et al., 2019).
In this work, we sampled the Khenifra Basin within the easternmost part of the Western Meseta, where the Eovariscan deformation was defined (Allary et al., 1972). We carried on structural observations into the basement and sampled both the Ordovician basement and the Middle(?)-Late Visean series of the basin, which is thought the be extensional. Maximum temperatures reached by the 77 sampled rocks were obtained from the analysis of organic matter with the use of the Raman spectroscopy. The examination of this new dataset demonstrates that the Ordovician series acquired temperatures through a single event, consistently with their common record of the Eovariscan deformation. Instead, the unconformable Visean series on top of the basement show a pronounced basinal asymmetry, from low temperatures (< 160°C) to temperatures equivalent to the Ordovician ones (> 250°C). The Visean series do not record the Eovariscan deformation, and their thermal structure was acquired before the Variscan event, regarding their repartition within the basin. The examination of the different hypotheses for the timing of the maximal temperature acquisition (Variscan, compressional Eovariscan and extensional Eovariscan) leads to a single option only compatible with an extensional Eovariscan context.
The renewal on the knowledge about the early stages of the Variscan orogeny in NW Africa allows us to consider a Pyrenean-like model for the formation of this intraplate belt, resulting from the inversion of hot Early Carboniferous rifted basins.
How to cite: Leprêtre, R., Schito, A., Ouchaou, R., El Houicha, M., and Chopin, F.: A Pyrenean-like model for the Variscan belt in NW Africa : insights from thermometry-based Raman spectroscopy study in the Khenifra Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20672, https://doi.org/10.5194/egusphere-egu2020-20672, 2020.
EGU2020-20718 | Displays | TS1.1
Joint application of fluid inclusion and clumped isotope (Δ47) thermometry to burial carbonate cements from Upper Triassic reservoirs of the Paris BasinNatalia Amanda Vergara, Marta Gasparrini, Sveva Corrado, and Stefano Bernasconi
A realistic reconstruction of the time-temperature history of sedimentary basins is critical to understand basin evolution and to predict oil maturation as well to assess reservoir quality. Carbonate rocks undergo diagenetic processes that modify their mineralogical and petrophysical properties. Understanding the temperature at which those processes occur and determining the geochemistry of the driving fluids is critical to constrain their occurrence and evolution in space and time.
Here, we put to the test the joint application of two independent techniques: the traditional fluid inclusion microthermometry (FIM) and the more recent clumped isotopes thermometer (∆47). We compare thermal information acquired by Δ47 thermometer and FIM on diagenetic carbonates having precipitated at temperatures between 60°C and 130°C in Upper Triassic reservoirs (depths of 1820-2450 m) from the well-known Paris Basin, and having suffered 120°C during maximum burial for about 20 Ma. A conventional diagenesis study (petrography, O-C isotope geochemistry) has been accomplished in samples from three different cores drilled in carbonate-cemented siliciclastic reservoir units of Norian age (Grés de Chaunoy Formation) and located in the northern part of the basin depocenter. A complete cement paragenesis was reconstructed highlighting three different burial cements: two non-ferroan blocky calcite phases (Cal1 and Cal2) and one non-ferroan dolomite phase of saddle type (Dol1). The progressively more negative δ18Ocarb suggests a possible increase in temperature, going from Cal1 to Dol1, whereas the consistently negative δ13C could indicate the involvement of continental fluids.
FIM indicates homogenization temperatures (Th) spanning from 60°C to 95°C (mode 67.5°C) for Cal1, 70°C to 110°C (mode 84°C) for Cal2, and 100°C to 130°C (mode 115°C) for Dol1. Δ47 measurements overall reveals lower temperatures for calcite cements, indicating probable thermal re-equilibration of the fluid inclusions, and a fairly similar temperature for the saddle dolomite cement. Uncertainties in the temperatures obtained through FIM and ∆47 thermometry and in the successively calculated δ18Ofluid, may lead to an erroneous assessment of the time of precipitation of the different diagenetic phases and to an erroneous thermal history and fluid-flow reconstruction.
This work emphasizes the necessity of better understanding the limitations and applicability fields of these thermometric tools, especially when applied to burial diagenetic phases precipitated at temperatures above 100°C and/or in reservoirs having experienced temperatures in the gas window.
How to cite: Vergara, N. A., Gasparrini, M., Corrado, S., and Bernasconi, S.: Joint application of fluid inclusion and clumped isotope (Δ47) thermometry to burial carbonate cements from Upper Triassic reservoirs of the Paris Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20718, https://doi.org/10.5194/egusphere-egu2020-20718, 2020.
A realistic reconstruction of the time-temperature history of sedimentary basins is critical to understand basin evolution and to predict oil maturation as well to assess reservoir quality. Carbonate rocks undergo diagenetic processes that modify their mineralogical and petrophysical properties. Understanding the temperature at which those processes occur and determining the geochemistry of the driving fluids is critical to constrain their occurrence and evolution in space and time.
Here, we put to the test the joint application of two independent techniques: the traditional fluid inclusion microthermometry (FIM) and the more recent clumped isotopes thermometer (∆47). We compare thermal information acquired by Δ47 thermometer and FIM on diagenetic carbonates having precipitated at temperatures between 60°C and 130°C in Upper Triassic reservoirs (depths of 1820-2450 m) from the well-known Paris Basin, and having suffered 120°C during maximum burial for about 20 Ma. A conventional diagenesis study (petrography, O-C isotope geochemistry) has been accomplished in samples from three different cores drilled in carbonate-cemented siliciclastic reservoir units of Norian age (Grés de Chaunoy Formation) and located in the northern part of the basin depocenter. A complete cement paragenesis was reconstructed highlighting three different burial cements: two non-ferroan blocky calcite phases (Cal1 and Cal2) and one non-ferroan dolomite phase of saddle type (Dol1). The progressively more negative δ18Ocarb suggests a possible increase in temperature, going from Cal1 to Dol1, whereas the consistently negative δ13C could indicate the involvement of continental fluids.
FIM indicates homogenization temperatures (Th) spanning from 60°C to 95°C (mode 67.5°C) for Cal1, 70°C to 110°C (mode 84°C) for Cal2, and 100°C to 130°C (mode 115°C) for Dol1. Δ47 measurements overall reveals lower temperatures for calcite cements, indicating probable thermal re-equilibration of the fluid inclusions, and a fairly similar temperature for the saddle dolomite cement. Uncertainties in the temperatures obtained through FIM and ∆47 thermometry and in the successively calculated δ18Ofluid, may lead to an erroneous assessment of the time of precipitation of the different diagenetic phases and to an erroneous thermal history and fluid-flow reconstruction.
This work emphasizes the necessity of better understanding the limitations and applicability fields of these thermometric tools, especially when applied to burial diagenetic phases precipitated at temperatures above 100°C and/or in reservoirs having experienced temperatures in the gas window.
How to cite: Vergara, N. A., Gasparrini, M., Corrado, S., and Bernasconi, S.: Joint application of fluid inclusion and clumped isotope (Δ47) thermometry to burial carbonate cements from Upper Triassic reservoirs of the Paris Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20718, https://doi.org/10.5194/egusphere-egu2020-20718, 2020.
EGU2020-21703 | Displays | TS1.1
Sedimentological features and thermal maturity signature of the upper Triassic Streppenosa and Noto Formations, source rocks in the Hyblean Plateau (SE Sicily, Italy)Rosanna Maniscalco, Sveva Corrado, Martina Balestra, Andrea Schito, Claudio Ivan Casciano, Martina Forzese, Sergio Montalbano, Alessandra Pellegrino, Andang Bachtiar, Giuseppe Palmeri, and Agata Di Stefano
The upper Triassic Streppenosa and Noto Formations are considered the main source rocks of the Hyblean Plateau in south-eastern Sicily, that represents the present-day deformed foreland of the Sicilian fold-and-thrust belt. This work focusses on the Upper Triassic Streppenosa and Noto Formations, penetrated by the Eureka 1 onshore well (south-eastern Sicily, Italy) in order to constrain the burial-thermal history of this basin of the western Tethys. According to previous paleogeographic reconstructions, starting from Norian, the palaeogeographic scenario consisted, moving from north to south, of a wide carbonate platform (Sciacca Fm.), adjacent to two different domains: the euxinic lagoon/basin of the Noto Formation, and, to the south, the basin of the Streppenosa Formation. Eureka 1 well is located in the inner portion of the platform-basin system and its Triassic succession consists of alternation of black shales and micritic, microbial dolomitic laminated limestones. A detailed description of the sedimentological facies from cores samples has been performed together with detailed organic petrography/Raman spectroscopy and clay mineralogy on fine grained sediments to assess thermal maturity of the Streppenosa and Noto Fms. The main facies consist of light-grey limestones (wackestone-mudstone) with scattered sub-angular intraclast, light grey finely laminated limestones, dark grey-black laminated mudstones, brownish undulated algal laminae saturated with bitumen. The cores are often bitumen saturated and interrupted by different sets of open microfractures, veins filled with calcite, and stylolites (parallel and vertical with respect to lamination) that may enhance and/or inhibit at places the fluid flow. Concerning thermal maturity, the studied interval falls in the lower-mid portion of the oil window, with robust agreement among the geothermometers derived from the three adopted techniques.
How to cite: Maniscalco, R., Corrado, S., Balestra, M., Schito, A., Casciano, C. I., Forzese, M., Montalbano, S., Pellegrino, A., Bachtiar, A., Palmeri, G., and Di Stefano, A.: Sedimentological features and thermal maturity signature of the upper Triassic Streppenosa and Noto Formations, source rocks in the Hyblean Plateau (SE Sicily, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21703, https://doi.org/10.5194/egusphere-egu2020-21703, 2020.
The upper Triassic Streppenosa and Noto Formations are considered the main source rocks of the Hyblean Plateau in south-eastern Sicily, that represents the present-day deformed foreland of the Sicilian fold-and-thrust belt. This work focusses on the Upper Triassic Streppenosa and Noto Formations, penetrated by the Eureka 1 onshore well (south-eastern Sicily, Italy) in order to constrain the burial-thermal history of this basin of the western Tethys. According to previous paleogeographic reconstructions, starting from Norian, the palaeogeographic scenario consisted, moving from north to south, of a wide carbonate platform (Sciacca Fm.), adjacent to two different domains: the euxinic lagoon/basin of the Noto Formation, and, to the south, the basin of the Streppenosa Formation. Eureka 1 well is located in the inner portion of the platform-basin system and its Triassic succession consists of alternation of black shales and micritic, microbial dolomitic laminated limestones. A detailed description of the sedimentological facies from cores samples has been performed together with detailed organic petrography/Raman spectroscopy and clay mineralogy on fine grained sediments to assess thermal maturity of the Streppenosa and Noto Fms. The main facies consist of light-grey limestones (wackestone-mudstone) with scattered sub-angular intraclast, light grey finely laminated limestones, dark grey-black laminated mudstones, brownish undulated algal laminae saturated with bitumen. The cores are often bitumen saturated and interrupted by different sets of open microfractures, veins filled with calcite, and stylolites (parallel and vertical with respect to lamination) that may enhance and/or inhibit at places the fluid flow. Concerning thermal maturity, the studied interval falls in the lower-mid portion of the oil window, with robust agreement among the geothermometers derived from the three adopted techniques.
How to cite: Maniscalco, R., Corrado, S., Balestra, M., Schito, A., Casciano, C. I., Forzese, M., Montalbano, S., Pellegrino, A., Bachtiar, A., Palmeri, G., and Di Stefano, A.: Sedimentological features and thermal maturity signature of the upper Triassic Streppenosa and Noto Formations, source rocks in the Hyblean Plateau (SE Sicily, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21703, https://doi.org/10.5194/egusphere-egu2020-21703, 2020.
TS2.3 – Deformation processes, microstructures and physical properties
EGU2020-2773 | Displays | TS2.3
When minerals fight back: The relationship between back stress and geometrically necessary dislocation densityChristopher Thom, David Goldsby, Kathryn Kumamoto, and Lars Hansen
The dynamics of several geophysical phenomena, such as post-seismic deformation and post-glacial isostatic readjustment, are inferred to be controlled by the transient rheology of olivine in Earth’s mantle. However, the physical mechanism(s) that underlie(s) this behavior remain(s) relatively unknown, and most experimental studies focus on quantifying steady-state rheology. Recent studies have suggested that back stresses caused by long-range elastic interactions among dislocations could play a role in transient deformation of olivine. Wallis et al. (2017) identified an internal back stress in olivine single crystals deforming at 1573 K, which gave rise to anelastic transient deformation in stress dip experiments. Hansen et al. (2019) quantified the room-temperature strain hardening of olivine deforming by low-temperature plasticity and measured a back stress that gave rise to a Bauschinger effect, a well-known phenomenon in materials science wherein the yield stress is reduced upon reversing the sense of direction of the deformation.
To explore deformation at very high dislocation density, we have developed a novel nanoindentation load drop method to measure the back stress in a material at sub-micron length scales. Using a self-similar Berkovich tip, we measure back stresses in single crystals of olivine, quartz, and plagioclase feldspar at a range of indentation depths from 100–1700 nm, corresponding to geometrically necessary dislocation (GND) densities of order 1014–1015 m-2. Our results reveal a power-law relationship between back stress and GND density with an exponent ranging from 0.44-0.55 for each material, with an average across all materials of 0.48. Normalizing back stress by the shear modulus measured during the indentation test results in a master curve with a power-law exponent of 0.44, in close agreement with the theoretical prediction (0.5) derived from the classical Taylor hardening equation (Taylor, 1934). For olivine, the extrapolation of our fit quantitatively agrees with other published data spanning over 5 orders of magnitude in GND density and temperatures ranging from 298-1573 K. This work provides the first experimental evidence in support of Taylor hardening in a geologic material, supports the assertion that strain hardening is an athermal process that can occur during high-temperature creep, and suggests that back stresses from long-range interactions among dislocations must be considered in rheological models of transient creep.
How to cite: Thom, C., Goldsby, D., Kumamoto, K., and Hansen, L.: When minerals fight back: The relationship between back stress and geometrically necessary dislocation density, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2773, https://doi.org/10.5194/egusphere-egu2020-2773, 2020.
The dynamics of several geophysical phenomena, such as post-seismic deformation and post-glacial isostatic readjustment, are inferred to be controlled by the transient rheology of olivine in Earth’s mantle. However, the physical mechanism(s) that underlie(s) this behavior remain(s) relatively unknown, and most experimental studies focus on quantifying steady-state rheology. Recent studies have suggested that back stresses caused by long-range elastic interactions among dislocations could play a role in transient deformation of olivine. Wallis et al. (2017) identified an internal back stress in olivine single crystals deforming at 1573 K, which gave rise to anelastic transient deformation in stress dip experiments. Hansen et al. (2019) quantified the room-temperature strain hardening of olivine deforming by low-temperature plasticity and measured a back stress that gave rise to a Bauschinger effect, a well-known phenomenon in materials science wherein the yield stress is reduced upon reversing the sense of direction of the deformation.
To explore deformation at very high dislocation density, we have developed a novel nanoindentation load drop method to measure the back stress in a material at sub-micron length scales. Using a self-similar Berkovich tip, we measure back stresses in single crystals of olivine, quartz, and plagioclase feldspar at a range of indentation depths from 100–1700 nm, corresponding to geometrically necessary dislocation (GND) densities of order 1014–1015 m-2. Our results reveal a power-law relationship between back stress and GND density with an exponent ranging from 0.44-0.55 for each material, with an average across all materials of 0.48. Normalizing back stress by the shear modulus measured during the indentation test results in a master curve with a power-law exponent of 0.44, in close agreement with the theoretical prediction (0.5) derived from the classical Taylor hardening equation (Taylor, 1934). For olivine, the extrapolation of our fit quantitatively agrees with other published data spanning over 5 orders of magnitude in GND density and temperatures ranging from 298-1573 K. This work provides the first experimental evidence in support of Taylor hardening in a geologic material, supports the assertion that strain hardening is an athermal process that can occur during high-temperature creep, and suggests that back stresses from long-range interactions among dislocations must be considered in rheological models of transient creep.
How to cite: Thom, C., Goldsby, D., Kumamoto, K., and Hansen, L.: When minerals fight back: The relationship between back stress and geometrically necessary dislocation density, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2773, https://doi.org/10.5194/egusphere-egu2020-2773, 2020.
EGU2020-21694 | Displays | TS2.3
The role of grain boundary energy anisotropy on the grain size evolution during normal grain growth.Hesham Salama, Katharina Marquardt, Julia Kundin, Oleg Shchyglo, and Ingo Steinbach
Many regions of the Earth’s mantle deform in grain size-sensitive creep regimes. The grain size right below the transition zone is believed to be very small, and the grain size should in subsequent depths be mainly controlled by normal grain growth. The grain size evolution is commonly predicted using either existing grain growth laws in combination with grain boundary diffusion coefficients or by extrapolating empirically determined grain growth laws. Effects of Zenner pinning and different ratios of second phases have been studied, while the role of anisotropic grain boundary properties is currently neglected1. The grain boundary energy varies with the orientation of the grain boundary plane, as expressed through the typical crystal habitae (Wulff-shapes). Individual crystals in a polycrystalline material maintain a grain boundary energy anisotropy during grain growth. Here we study how grain boundary anisotropy impacts grain boundary migration and normal grain growth rates by three-dimensional phase-field simulations2. We imply grain boundary energy minimization by faceting/varying the grain boundary plane to minimize the grain boundary energy. The ideal grain boundary energy anisotropy for the solid-solid interface is taken from experimentally investigated grain boundary plane distributions and grain boundary energy distributions on periclase (MgO). We compare the grain size evolution in simulations with isotropic and anisotropic grain boundary energy of cubic crystal symmetry. We found that the grain boundary energy anisotropy has a significant influence on grain boundary migration and grain growth kinetics2.
<r>2- <r0>2= kt
The change in grain size is given as variation between the initial and final average grain radius, r. The time is t, and a material-specific parameter that accounts for the grain boundary energy anisotropy is extracted from the simulations as
k = A·µgb·σgb
Where, the grain boundary energy, σgb varies with orientation, and the grain boundary mobility, µgb assumed to be isotropic. We found that the rate of grain growth for periclase, A is a factor of 3 smaller compared to an isotropic material.
These results are of three-fold importance:
A better prediction of grain size evolution will need to develop an anisotropic theory for grain growth, that address our lake in knowledge regarding pressure effects on both grain boundary energy anisotropy and diffusion.
1. Rohrer, G. S. Annu. Rev. Mater. Res. 2005
2. Salama et al. Acta Materialia 2020
How to cite: Salama, H., Marquardt, K., Kundin, J., Shchyglo, O., and Steinbach, I.: The role of grain boundary energy anisotropy on the grain size evolution during normal grain growth., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21694, https://doi.org/10.5194/egusphere-egu2020-21694, 2020.
Many regions of the Earth’s mantle deform in grain size-sensitive creep regimes. The grain size right below the transition zone is believed to be very small, and the grain size should in subsequent depths be mainly controlled by normal grain growth. The grain size evolution is commonly predicted using either existing grain growth laws in combination with grain boundary diffusion coefficients or by extrapolating empirically determined grain growth laws. Effects of Zenner pinning and different ratios of second phases have been studied, while the role of anisotropic grain boundary properties is currently neglected1. The grain boundary energy varies with the orientation of the grain boundary plane, as expressed through the typical crystal habitae (Wulff-shapes). Individual crystals in a polycrystalline material maintain a grain boundary energy anisotropy during grain growth. Here we study how grain boundary anisotropy impacts grain boundary migration and normal grain growth rates by three-dimensional phase-field simulations2. We imply grain boundary energy minimization by faceting/varying the grain boundary plane to minimize the grain boundary energy. The ideal grain boundary energy anisotropy for the solid-solid interface is taken from experimentally investigated grain boundary plane distributions and grain boundary energy distributions on periclase (MgO). We compare the grain size evolution in simulations with isotropic and anisotropic grain boundary energy of cubic crystal symmetry. We found that the grain boundary energy anisotropy has a significant influence on grain boundary migration and grain growth kinetics2.
<r>2- <r0>2= kt
The change in grain size is given as variation between the initial and final average grain radius, r. The time is t, and a material-specific parameter that accounts for the grain boundary energy anisotropy is extracted from the simulations as
k = A·µgb·σgb
Where, the grain boundary energy, σgb varies with orientation, and the grain boundary mobility, µgb assumed to be isotropic. We found that the rate of grain growth for periclase, A is a factor of 3 smaller compared to an isotropic material.
These results are of three-fold importance:
A better prediction of grain size evolution will need to develop an anisotropic theory for grain growth, that address our lake in knowledge regarding pressure effects on both grain boundary energy anisotropy and diffusion.
1. Rohrer, G. S. Annu. Rev. Mater. Res. 2005
2. Salama et al. Acta Materialia 2020
How to cite: Salama, H., Marquardt, K., Kundin, J., Shchyglo, O., and Steinbach, I.: The role of grain boundary energy anisotropy on the grain size evolution during normal grain growth., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21694, https://doi.org/10.5194/egusphere-egu2020-21694, 2020.
EGU2020-13710 | Displays | TS2.3
Relocated micas in marble – indicators for postdeformational microfabric modificationRebecca Kühn, Florian Duschl, Bernd Leiss, and Torben Schulze
A relocation of mica grains in marbles can be observed as trace of newly precipitated calcite material in cathodoluminescence microscopy analysis. Mica grains relocate by rotation and/or translation from foliation parallel to new irregular orientations. The mica grains can be either located at calcite grain boundaries or within large calcite grains.
The process erases deformed, inclusion-rich calcite material and creates undeformed and mostly inclusion-free grains and can therefore be regarded as postdeformational. Not every mica present relocates and the choice of whether a specific mica relocates cannot be related to a specific primary orientation. Furthermore, no significant difference in composition between relocated and non-relocated mica grains can be observed. Newly precipitated calcite has less Mg than the dissolved grain material.
The precipitation of new calcite material at the calcite-mica interface is supposed to be the initial trigger leading to dissolution of inclusion-rich, deformed calcite material at the opposite side of the mica grain. The newly precipitated calcite material inherits the already existing calcite grain‘s crystallographic orientation.
Assuming this process occurs to a larger extent in a material, it might modify a deformation-related microfabric. Therefore, an interpretation in terms of deformation conditions should be done carefully, considering postdeformational dissolution-precipitation processes.
How to cite: Kühn, R., Duschl, F., Leiss, B., and Schulze, T.: Relocated micas in marble – indicators for postdeformational microfabric modification, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13710, https://doi.org/10.5194/egusphere-egu2020-13710, 2020.
A relocation of mica grains in marbles can be observed as trace of newly precipitated calcite material in cathodoluminescence microscopy analysis. Mica grains relocate by rotation and/or translation from foliation parallel to new irregular orientations. The mica grains can be either located at calcite grain boundaries or within large calcite grains.
The process erases deformed, inclusion-rich calcite material and creates undeformed and mostly inclusion-free grains and can therefore be regarded as postdeformational. Not every mica present relocates and the choice of whether a specific mica relocates cannot be related to a specific primary orientation. Furthermore, no significant difference in composition between relocated and non-relocated mica grains can be observed. Newly precipitated calcite has less Mg than the dissolved grain material.
The precipitation of new calcite material at the calcite-mica interface is supposed to be the initial trigger leading to dissolution of inclusion-rich, deformed calcite material at the opposite side of the mica grain. The newly precipitated calcite material inherits the already existing calcite grain‘s crystallographic orientation.
Assuming this process occurs to a larger extent in a material, it might modify a deformation-related microfabric. Therefore, an interpretation in terms of deformation conditions should be done carefully, considering postdeformational dissolution-precipitation processes.
How to cite: Kühn, R., Duschl, F., Leiss, B., and Schulze, T.: Relocated micas in marble – indicators for postdeformational microfabric modification, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13710, https://doi.org/10.5194/egusphere-egu2020-13710, 2020.
EGU2020-7681 | Displays | TS2.3
Shear coupled grain boundary migration as a deformation mechanism in minerals.Gill Pennock and Martyn Drury
A grain boundary can move under stress by a mechanism called shear coupled grain boundary migration (SC GBM) and contribute to strain. SC GBM is considered to be a general property of all grain boundaries over a wide range of misorientation angles, although higher deformation temperatures favour grain boundary sliding. Apart from a structured boundary interface, SC also requires a critical shear stress. We examine evidence for SC GBM in ice. An extensive literature study showed that SC GBM of high angle boundaries does occur in ice bicrystals that were probably deformed under conditions close to those found in nature. We conclude that SC GBM is likely to be an important deformation mechanism for geological materials, where extensive GBM occurs and also in nano sized materials, such as fault gauges.
How to cite: Pennock, G. and Drury, M.: Shear coupled grain boundary migration as a deformation mechanism in minerals., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7681, https://doi.org/10.5194/egusphere-egu2020-7681, 2020.
A grain boundary can move under stress by a mechanism called shear coupled grain boundary migration (SC GBM) and contribute to strain. SC GBM is considered to be a general property of all grain boundaries over a wide range of misorientation angles, although higher deformation temperatures favour grain boundary sliding. Apart from a structured boundary interface, SC also requires a critical shear stress. We examine evidence for SC GBM in ice. An extensive literature study showed that SC GBM of high angle boundaries does occur in ice bicrystals that were probably deformed under conditions close to those found in nature. We conclude that SC GBM is likely to be an important deformation mechanism for geological materials, where extensive GBM occurs and also in nano sized materials, such as fault gauges.
How to cite: Pennock, G. and Drury, M.: Shear coupled grain boundary migration as a deformation mechanism in minerals., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7681, https://doi.org/10.5194/egusphere-egu2020-7681, 2020.
EGU2020-871 | Displays | TS2.3
The upper 2121 m at EastGRIP - Results from physical properties of NEGISNicolas Stoll, Ilka Weikusat, Johanna Kerch, Jan Eichler, Wataru Shigeyama, Tomoyuki Homma, Daniela Jansen, Steven Franke, Ernst-Jan Kuiper, David Wallis, Julien Westhoff, Tomotaka Saruya, Sérgio Henrique Faria, Sepp Kipfstuhl, Kumiko Goto Azuma, Nobuhiko Azuma, and Dorthe Dahl-Jensen
Here we present the ice microstructure and CPO (c-axes fabric) data from the upper 2121 m of the EastGRIP ice core, an on-going deep drilling project on the North East Greenland Ice Stream. Understanding ice flow behaviour of fast flowing ice streams is crucial for accurate projections of future global sea level rise, but is still poorly understood due to e.g. missing observational fabric data from ice streams.
The presented CPO patterns found at EastGRIP show (1) a rapid evolution of c-axes anisotropy compared to deep ice cores from less dynamic sites, (2) a CPO evolution towards a strong vertical girdle and (3) CPO patterns that have not previously been directly observed in ice. Furthermore, data regarding grain properties (e.g. grain size) and indications of dynamic recrystallization, already at shallow depths, are presented.
The ice CPO shows a clear evolution with depth. In the first measurements at 111 m depth a broad single maximum distribution is observed, which transforms into a crossed girdle CPO (196-294 m). With increasing depth, an evolution towards a vertical girdle c-axes distribution occurs. Below 1150 m the CPO evolves into a vertical girdle with a higher density of c-axes oriented horizontally, a novel CPO in ice. These CPO patterns indicate a depth-related change in deformation modes, from vertical compression to extensional deformation along flow.
Grain size values are similar to results from other Greenlandic deep ice cores. Grain size evolution is characterized by an increase until 500 m depth, a decrease until 1360 m depth and mainly constant values in the Glacial. These findings are accompanied by indications of an early onset of dynamic recrystallisation e.g. irregular grain shapes, protruding grains and island grains.
The presented high-resolution data enable, for the very first time, a detailed and data- based look into a fast-flowing ice stream and are an important step towards a better understanding of the rheology of ice and its flow behaviour.
How to cite: Stoll, N., Weikusat, I., Kerch, J., Eichler, J., Shigeyama, W., Homma, T., Jansen, D., Franke, S., Kuiper, E.-J., Wallis, D., Westhoff, J., Saruya, T., Faria, S. H., Kipfstuhl, S., Azuma, K. G., Azuma, N., and Dahl-Jensen, D.: The upper 2121 m at EastGRIP - Results from physical properties of NEGIS , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-871, https://doi.org/10.5194/egusphere-egu2020-871, 2020.
Here we present the ice microstructure and CPO (c-axes fabric) data from the upper 2121 m of the EastGRIP ice core, an on-going deep drilling project on the North East Greenland Ice Stream. Understanding ice flow behaviour of fast flowing ice streams is crucial for accurate projections of future global sea level rise, but is still poorly understood due to e.g. missing observational fabric data from ice streams.
The presented CPO patterns found at EastGRIP show (1) a rapid evolution of c-axes anisotropy compared to deep ice cores from less dynamic sites, (2) a CPO evolution towards a strong vertical girdle and (3) CPO patterns that have not previously been directly observed in ice. Furthermore, data regarding grain properties (e.g. grain size) and indications of dynamic recrystallization, already at shallow depths, are presented.
The ice CPO shows a clear evolution with depth. In the first measurements at 111 m depth a broad single maximum distribution is observed, which transforms into a crossed girdle CPO (196-294 m). With increasing depth, an evolution towards a vertical girdle c-axes distribution occurs. Below 1150 m the CPO evolves into a vertical girdle with a higher density of c-axes oriented horizontally, a novel CPO in ice. These CPO patterns indicate a depth-related change in deformation modes, from vertical compression to extensional deformation along flow.
Grain size values are similar to results from other Greenlandic deep ice cores. Grain size evolution is characterized by an increase until 500 m depth, a decrease until 1360 m depth and mainly constant values in the Glacial. These findings are accompanied by indications of an early onset of dynamic recrystallisation e.g. irregular grain shapes, protruding grains and island grains.
The presented high-resolution data enable, for the very first time, a detailed and data- based look into a fast-flowing ice stream and are an important step towards a better understanding of the rheology of ice and its flow behaviour.
How to cite: Stoll, N., Weikusat, I., Kerch, J., Eichler, J., Shigeyama, W., Homma, T., Jansen, D., Franke, S., Kuiper, E.-J., Wallis, D., Westhoff, J., Saruya, T., Faria, S. H., Kipfstuhl, S., Azuma, K. G., Azuma, N., and Dahl-Jensen, D.: The upper 2121 m at EastGRIP - Results from physical properties of NEGIS , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-871, https://doi.org/10.5194/egusphere-egu2020-871, 2020.
EGU2020-4983 | Displays | TS2.3
Phase mixing in upper mantle shear zones: Olivine nucleation during dynamic recrystallization of orthopyroxene and clinopyroxene porphyroclastsSören Tholen and Jolien Linckens
Small grain size and a well-mixed phase assemblage are key features of upper mantle (ultra)mylonitic layers. In those layers, Zener pinning inhibits grain growth, which could lead to diffusion creep. This increases the strain rate for a given stress significantly. Prerequisite is phase mixing which can occur by dynamic recrystallization (dynRXS) plus grain boundary sliding (GBS), metamorphic or melt/fluid-rock reactions, creep cavitation plus nucleation, or by a combination of those processes. In order to get insights into the interplay of phase mixing and dynRXS we investigate microfabrics (EBSD, optical microscopy) displaying the transition from clasts to mixed assemblages. Samples are taken from the Lanzo peridotite shear zone (Italy).
Olivine dynamically recrystallizes from protomylonitic to ultramylonitic samples. Its grain size varies systematically between monomineralic (~20µm) and polymineralic layers (~10µm). Olivine is the dominant mixing phase for both, dynamically recrystallizing orthopyroxene (ol~55vol.%) and clinopyroxene clasts (ol~45vol.%). In contrast, recrystallizing olivine clasts show little evidence of phase mixing. In phase mixtures, olivine neoblasts show weak (J-index ~1.8) C-Type and weak (J-Index ~1.5) B-type CPO’s. Both types suggest the presence of water during deformation.
Isolated, equiaxial orthopyroxene clasts are present in all samples. DynRXS of opx starts in mylonites. Some clasts and tips of extensively elongated opx bands (max. axial ratios 1:50) are bordered by fine-grained (min. ECD~5µm) mixtures of olivine, opx ± anorthite/ cpx/ pargasite. Mixing intensities seem to depend on the connection to the olivine-rich matrix. Clast grain boundaries are highly lobate with indentations of secondary phases (mostly olivine). Opx neoblasts have no internal deformation and show large misorientations close to their host clast (misorientation angle >45° at ~20µm distance). Their grain shape is either flat and elongated or equiaxial. Both shapes have lobate boundaries. Their CPO depends on the host clast orientation. In ultramylonites, opx bands disappeared completely.
Clinopyroxene porphyroclasts dynamically recrystallize in protomylonite to ultramylonite samples. Olivine is the dominant mixing phase (~45vol.%). Cpx mixed area grain sizes tend to be coarser (~10µm) than in corresponding opx areas (~6µm). Ultramylonitic cpx-ol assemblages have a higher mixing percentage (phase boundaries/grain boundaries ~70%) than mylonitic assemblages (~40%). In the mylonitic layers, clusters of cpx neoblasts form ‘walls’ parallel to their host grain borders. Olivine neoblasts between these clusters show no CPO. The overall cpx CPO varies from [001] perpendicular and [010] parallel to the foliation with (J -Index ~2.5) to [100] perpendicular and [001] parallel to the foliation (J-Index ~1.2).
Beside few thoroughly mixed areas, bands of cpx+ol and of opx+ol are still distinguishable in ultramylonitic layers. This suggests their origin to be dynamically recrystallized opx and cpx clasts. Therefore, phase mixing is assumed to occur simultaneously to clast recrystallization. Beside a small gradient of opx/cpx abundance depending on the distance from their host clast there is little evidence for phase mixing by dynRXS+GBS only. High abundances of olivine neoblasts at grain boundaries of recrystallizing clasts and their instant mixed assemblage with host phase neoblasts suggest phase mixing being strongly dependent on olivine nucleation during dynRXS of opx and cpx.
How to cite: Tholen, S. and Linckens, J.: Phase mixing in upper mantle shear zones: Olivine nucleation during dynamic recrystallization of orthopyroxene and clinopyroxene porphyroclasts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4983, https://doi.org/10.5194/egusphere-egu2020-4983, 2020.
Small grain size and a well-mixed phase assemblage are key features of upper mantle (ultra)mylonitic layers. In those layers, Zener pinning inhibits grain growth, which could lead to diffusion creep. This increases the strain rate for a given stress significantly. Prerequisite is phase mixing which can occur by dynamic recrystallization (dynRXS) plus grain boundary sliding (GBS), metamorphic or melt/fluid-rock reactions, creep cavitation plus nucleation, or by a combination of those processes. In order to get insights into the interplay of phase mixing and dynRXS we investigate microfabrics (EBSD, optical microscopy) displaying the transition from clasts to mixed assemblages. Samples are taken from the Lanzo peridotite shear zone (Italy).
Olivine dynamically recrystallizes from protomylonitic to ultramylonitic samples. Its grain size varies systematically between monomineralic (~20µm) and polymineralic layers (~10µm). Olivine is the dominant mixing phase for both, dynamically recrystallizing orthopyroxene (ol~55vol.%) and clinopyroxene clasts (ol~45vol.%). In contrast, recrystallizing olivine clasts show little evidence of phase mixing. In phase mixtures, olivine neoblasts show weak (J-index ~1.8) C-Type and weak (J-Index ~1.5) B-type CPO’s. Both types suggest the presence of water during deformation.
Isolated, equiaxial orthopyroxene clasts are present in all samples. DynRXS of opx starts in mylonites. Some clasts and tips of extensively elongated opx bands (max. axial ratios 1:50) are bordered by fine-grained (min. ECD~5µm) mixtures of olivine, opx ± anorthite/ cpx/ pargasite. Mixing intensities seem to depend on the connection to the olivine-rich matrix. Clast grain boundaries are highly lobate with indentations of secondary phases (mostly olivine). Opx neoblasts have no internal deformation and show large misorientations close to their host clast (misorientation angle >45° at ~20µm distance). Their grain shape is either flat and elongated or equiaxial. Both shapes have lobate boundaries. Their CPO depends on the host clast orientation. In ultramylonites, opx bands disappeared completely.
Clinopyroxene porphyroclasts dynamically recrystallize in protomylonite to ultramylonite samples. Olivine is the dominant mixing phase (~45vol.%). Cpx mixed area grain sizes tend to be coarser (~10µm) than in corresponding opx areas (~6µm). Ultramylonitic cpx-ol assemblages have a higher mixing percentage (phase boundaries/grain boundaries ~70%) than mylonitic assemblages (~40%). In the mylonitic layers, clusters of cpx neoblasts form ‘walls’ parallel to their host grain borders. Olivine neoblasts between these clusters show no CPO. The overall cpx CPO varies from [001] perpendicular and [010] parallel to the foliation with (J -Index ~2.5) to [100] perpendicular and [001] parallel to the foliation (J-Index ~1.2).
Beside few thoroughly mixed areas, bands of cpx+ol and of opx+ol are still distinguishable in ultramylonitic layers. This suggests their origin to be dynamically recrystallized opx and cpx clasts. Therefore, phase mixing is assumed to occur simultaneously to clast recrystallization. Beside a small gradient of opx/cpx abundance depending on the distance from their host clast there is little evidence for phase mixing by dynRXS+GBS only. High abundances of olivine neoblasts at grain boundaries of recrystallizing clasts and their instant mixed assemblage with host phase neoblasts suggest phase mixing being strongly dependent on olivine nucleation during dynRXS of opx and cpx.
How to cite: Tholen, S. and Linckens, J.: Phase mixing in upper mantle shear zones: Olivine nucleation during dynamic recrystallization of orthopyroxene and clinopyroxene porphyroclasts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4983, https://doi.org/10.5194/egusphere-egu2020-4983, 2020.
EGU2020-9953 | Displays | TS2.3
Strain localisation during diffusion creep: influence of grain coarsening and grain boundary slidingJohn Wheeler, Lynn Evans, Robyn Gardner, and Sandra Piazolo
Diffusion creep and the wet low temperature version, pressure solution, are major deformation mechanisms in the Earth. Pressure solution operates in many metamorphosing systems in the crust and may contribute to slow creep on fault surfaces. Diffusion creep prevails in areas of the upper mantle deforming slowly, and possibly in most of the lower mantle. Both mechanisms contribute to localisation since small grain sizes can deform faster.
However, there has been limited attention paid to the evolution of microstructure during diffusion creep. In some experiments grains coarsen; in some but not all experiments grains remain rather equant. We have developed a grain-scale numerical model for diffusion creep, which indicates that those processes are very important in influencing evolving strength. Our models illustrate three behaviours.
- Strain localises along slip surfaces formed by aligned grain boundaries on all scales. This affects overall strength.
- Diffusion creep is predicted to produce elongate grains and then the overall aggregate has intense mechanical anisotropy. Thus strength during diffusion creep, and localisation on weak zones, is influenced not just by grain size but by other aspects of microstructure.
- Grain coarsening increases grain size and strength. Our most recent work shows how it interacts with ongoing deformation. In particular grain growth can lead to particular grain shapes which are directly related to strain rate, and influence strength. Consequently, understanding localisation during diffusion creep must encompass the effects of diffusion itself, grain boundary sliding and grain coarsening.
How to cite: Wheeler, J., Evans, L., Gardner, R., and Piazolo, S.: Strain localisation during diffusion creep: influence of grain coarsening and grain boundary sliding, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9953, https://doi.org/10.5194/egusphere-egu2020-9953, 2020.
Diffusion creep and the wet low temperature version, pressure solution, are major deformation mechanisms in the Earth. Pressure solution operates in many metamorphosing systems in the crust and may contribute to slow creep on fault surfaces. Diffusion creep prevails in areas of the upper mantle deforming slowly, and possibly in most of the lower mantle. Both mechanisms contribute to localisation since small grain sizes can deform faster.
However, there has been limited attention paid to the evolution of microstructure during diffusion creep. In some experiments grains coarsen; in some but not all experiments grains remain rather equant. We have developed a grain-scale numerical model for diffusion creep, which indicates that those processes are very important in influencing evolving strength. Our models illustrate three behaviours.
- Strain localises along slip surfaces formed by aligned grain boundaries on all scales. This affects overall strength.
- Diffusion creep is predicted to produce elongate grains and then the overall aggregate has intense mechanical anisotropy. Thus strength during diffusion creep, and localisation on weak zones, is influenced not just by grain size but by other aspects of microstructure.
- Grain coarsening increases grain size and strength. Our most recent work shows how it interacts with ongoing deformation. In particular grain growth can lead to particular grain shapes which are directly related to strain rate, and influence strength. Consequently, understanding localisation during diffusion creep must encompass the effects of diffusion itself, grain boundary sliding and grain coarsening.
How to cite: Wheeler, J., Evans, L., Gardner, R., and Piazolo, S.: Strain localisation during diffusion creep: influence of grain coarsening and grain boundary sliding, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9953, https://doi.org/10.5194/egusphere-egu2020-9953, 2020.
About 50 years ago, John Ramsay and colleagues established the thorough foundation for the field-scale observational and mathematical description of the structures, deformation, and kinematics in ductile shear zones. Since then, these probably most important instabilities of the ductile lithosphere enjoyed an almost explosive growth in scientific attention. It is perhaps fair to say that this tremendous research effort featured four main themes:
[1] The historic scientific nucleus – quantification of shear-zone geometry, strain and associated kinematic history from field observations
[2] Qualitative and quantitative analysis of microphysical deformation mechanisms in the field and the laboratory
[3] Shear-zone rheology
[4] The development of physically consistent mathematical models for shear zones, mainly using continuum mechanics.
In concert, these four cornerstones of shear-zone research enabled tremendous progress in our understanding of why and how ductile shear zones form. So, what are some of the outstanding problems?
A truly comprehensive model for ductile shear zones must account for the vast range of length and time scales involved, each easily covering ten orders of magnitude, as well as the associated intimate coupling between thermal, hydraulic, mechanical, and chemical processes. The multi-scale and multi-physics nature of ductile shear zones generates scientific challenges for all four research themes named above. This presentation is dedicated to highlighting exciting challenges in themes 2, and 3 and 4.
In the microanalytical arena [2], the nano-scale is an exciting new frontier, especially when it comes to the interplay between metamorphism and ductile deformation. The nano-frontier can be tackled with new synchrotron methods. I showcase some applications to fossil shear-zone samples and discuss opportunities for in-situ experiments. In the domain of rheology [3], I present some simple experiments with strain-softening materials and field observations that support the notion: transient rheological behaviour is very important for shear localisation. In the modelling domain [4], some recent examples for the intriguing physical consequences predicted by new multi-physics and cross-scale coupling terms in ductile localisation problems are illustrated.
How to cite: Schrank, C.: Ductile shear zones – future perspectives, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4273, https://doi.org/10.5194/egusphere-egu2020-4273, 2020.
About 50 years ago, John Ramsay and colleagues established the thorough foundation for the field-scale observational and mathematical description of the structures, deformation, and kinematics in ductile shear zones. Since then, these probably most important instabilities of the ductile lithosphere enjoyed an almost explosive growth in scientific attention. It is perhaps fair to say that this tremendous research effort featured four main themes:
[1] The historic scientific nucleus – quantification of shear-zone geometry, strain and associated kinematic history from field observations
[2] Qualitative and quantitative analysis of microphysical deformation mechanisms in the field and the laboratory
[3] Shear-zone rheology
[4] The development of physically consistent mathematical models for shear zones, mainly using continuum mechanics.
In concert, these four cornerstones of shear-zone research enabled tremendous progress in our understanding of why and how ductile shear zones form. So, what are some of the outstanding problems?
A truly comprehensive model for ductile shear zones must account for the vast range of length and time scales involved, each easily covering ten orders of magnitude, as well as the associated intimate coupling between thermal, hydraulic, mechanical, and chemical processes. The multi-scale and multi-physics nature of ductile shear zones generates scientific challenges for all four research themes named above. This presentation is dedicated to highlighting exciting challenges in themes 2, and 3 and 4.
In the microanalytical arena [2], the nano-scale is an exciting new frontier, especially when it comes to the interplay between metamorphism and ductile deformation. The nano-frontier can be tackled with new synchrotron methods. I showcase some applications to fossil shear-zone samples and discuss opportunities for in-situ experiments. In the domain of rheology [3], I present some simple experiments with strain-softening materials and field observations that support the notion: transient rheological behaviour is very important for shear localisation. In the modelling domain [4], some recent examples for the intriguing physical consequences predicted by new multi-physics and cross-scale coupling terms in ductile localisation problems are illustrated.
How to cite: Schrank, C.: Ductile shear zones – future perspectives, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4273, https://doi.org/10.5194/egusphere-egu2020-4273, 2020.
EGU2020-5250 | Displays | TS2.3
Evidence that viscous shear zones spontaneously establish hydro-mechanical anisotropyJames Gilgannon, Marius Waldvogel, Thomas Poulet, Florian Fusseis, Alfons Berger, Auke Barnhoorn, and Marco Herwegh
We revisit large shear strain deformation experiments on Carrara marble and observe that anisotropic porous domains develop spontaneously during shearing. Specifically, as samples are deformed periodic porous sheets are documented to emerge and are found to transfer mass. These results imply that viscous shear zones may naturally partition fluids into highly anisotropic bands. As this hydro-mechanical anisotropy is produced by creep, each porous sheet is interpreted to represent a transient dynamic pathway for fluid transport. It is unclear how long each porous domain is uniquely sustained but it is clear that sheets are persistently present with increasing strain. Our results forward the idea that viscous shear zones have dynamic transport properties that are not related to fracturing or chemical reaction. We believe these new results provide experimental foundation for changing the paradigm of viscosity in rocks to include dynamic permeability. In our view making this change in perspective could alter many classical interpretations in natural banded mylonite zones, for example shear zone parallel syn-kinematic veining may be the result of pore sheet instability and ductile fracturing.
How to cite: Gilgannon, J., Waldvogel, M., Poulet, T., Fusseis, F., Berger, A., Barnhoorn, A., and Herwegh, M.: Evidence that viscous shear zones spontaneously establish hydro-mechanical anisotropy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5250, https://doi.org/10.5194/egusphere-egu2020-5250, 2020.
We revisit large shear strain deformation experiments on Carrara marble and observe that anisotropic porous domains develop spontaneously during shearing. Specifically, as samples are deformed periodic porous sheets are documented to emerge and are found to transfer mass. These results imply that viscous shear zones may naturally partition fluids into highly anisotropic bands. As this hydro-mechanical anisotropy is produced by creep, each porous sheet is interpreted to represent a transient dynamic pathway for fluid transport. It is unclear how long each porous domain is uniquely sustained but it is clear that sheets are persistently present with increasing strain. Our results forward the idea that viscous shear zones have dynamic transport properties that are not related to fracturing or chemical reaction. We believe these new results provide experimental foundation for changing the paradigm of viscosity in rocks to include dynamic permeability. In our view making this change in perspective could alter many classical interpretations in natural banded mylonite zones, for example shear zone parallel syn-kinematic veining may be the result of pore sheet instability and ductile fracturing.
How to cite: Gilgannon, J., Waldvogel, M., Poulet, T., Fusseis, F., Berger, A., Barnhoorn, A., and Herwegh, M.: Evidence that viscous shear zones spontaneously establish hydro-mechanical anisotropy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5250, https://doi.org/10.5194/egusphere-egu2020-5250, 2020.
EGU2020-12715 | Displays | TS2.3
Development of interconnected fine-grained polyphase networks during progressive exhumation of a shear zoneAlexander Lusk and John Platt
Present exposure of the ductile Caledonian retrowedge in northwestern Scotland records the evolution of a shear zone that was exhuming while actively deforming, providing a natural laboratory to study strain localization in a progressively cooling system. Examination of rocks from two detailed transects across this region consistently show a transition from microstructures that are dominated by interconnected phyllosilicate networks in a quartz-rich matrix with feldspar porphyroclasts, to interconnected fine-grained regions of mixed quartz + phyllosilicate + feldspar. These polyphase regions are demonstrably weaker than surrounding quartz layers and likely deform by grain-size sensitive mechanisms including diffusion-accommodated grain boundary sliding.
Microstructures characterized by a quartz-rich matrix and interconnected phyllosilicates undergo quartz recrystallization by high temperature grain boundary migration and are dominated by prism a slip. In contrast, fine-grained polyphase microstructures record quartz recrystallization dominated by subgrain rotation and activation of rhomb a and basal a slip systems. We propose transient hardening occurs in quartz-dominated regions as quartz with a strong Y-axis maximum undergoes the switch from prism a easy slip to basal a easy slip during cooling, and thus partitions strain into interconnected phyllosilicate layers. In response, interconnected phyllosilicate layers undergo mechanical comminution, becoming increasingly mixed by grain-size sensitive creep processes to form polyphase layers as they accommodate an increased proportion of strain. This transition from quartz-rich matrix with phyllosilicate interconnected weak layers to fine-grained, polyphase weak layers could be of first-order importance in strain localization within polyphase mylonitic and ultramylonitic rocks.
How to cite: Lusk, A. and Platt, J.: Development of interconnected fine-grained polyphase networks during progressive exhumation of a shear zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12715, https://doi.org/10.5194/egusphere-egu2020-12715, 2020.
Present exposure of the ductile Caledonian retrowedge in northwestern Scotland records the evolution of a shear zone that was exhuming while actively deforming, providing a natural laboratory to study strain localization in a progressively cooling system. Examination of rocks from two detailed transects across this region consistently show a transition from microstructures that are dominated by interconnected phyllosilicate networks in a quartz-rich matrix with feldspar porphyroclasts, to interconnected fine-grained regions of mixed quartz + phyllosilicate + feldspar. These polyphase regions are demonstrably weaker than surrounding quartz layers and likely deform by grain-size sensitive mechanisms including diffusion-accommodated grain boundary sliding.
Microstructures characterized by a quartz-rich matrix and interconnected phyllosilicates undergo quartz recrystallization by high temperature grain boundary migration and are dominated by prism a slip. In contrast, fine-grained polyphase microstructures record quartz recrystallization dominated by subgrain rotation and activation of rhomb a and basal a slip systems. We propose transient hardening occurs in quartz-dominated regions as quartz with a strong Y-axis maximum undergoes the switch from prism a easy slip to basal a easy slip during cooling, and thus partitions strain into interconnected phyllosilicate layers. In response, interconnected phyllosilicate layers undergo mechanical comminution, becoming increasingly mixed by grain-size sensitive creep processes to form polyphase layers as they accommodate an increased proportion of strain. This transition from quartz-rich matrix with phyllosilicate interconnected weak layers to fine-grained, polyphase weak layers could be of first-order importance in strain localization within polyphase mylonitic and ultramylonitic rocks.
How to cite: Lusk, A. and Platt, J.: Development of interconnected fine-grained polyphase networks during progressive exhumation of a shear zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12715, https://doi.org/10.5194/egusphere-egu2020-12715, 2020.
EGU2020-19297 | Displays | TS2.3
On the causes of brittle nucleation of shear zones: the example of Cap de Creus, Eastern Pyrenees (Spain)Claudio Rosenberg, Loïc Labrousse, Nicolas Landry, Elena Druguet, and Jordi Carreras
The area of Cap de Creus, at the eastern termination of the Axial Zone of the Pyrenean Belt, exposes some of the most famous outcrops of ductile shear zones and shear zone networks (Carreras, 2001). Recent studies proposed that the nucleation and growth of such shear zones may have taken place by brittle processes (Fusseis et al., 2006; Fusseis and Handy, 2008).
The present study investigates the geometrical relationships between fracture systems and some shear zones, the deformation temperature of these shear zones, and the processes leading to the nucleation and growth of shear zones along fracture planes. We selected two areas of the Cap de Creus, the Cala d’Agulles, and the Punta de Cap de Creus, because they are most intensely dissected by subparallel sets of shear zones and fractures. The orientation of the average shear zone planes is sub-parallel to the orientation of the major set of fractures, and the great extent and close spacing of some shear zones that we characterized by aerial photos from a drone, is similar to the distribution and extent of the fracture planes. These observations, in addition to those of Fusseis et al. (2006) suggest that the shear zones nucleated on previous fracture planes.
These fractures are surrounded by haloes of nearly 1 cm thickness affecting the fabric of the country rock, an amphibolite-facies, biotite-andalusite bearing schist. Microscopic observations show that the haloes correspond to the wide-spread presence of thin (less than 2µm thickness) phosphate seams coating the grain boundaries, preferentially those oriented at low angle to the fracture plane, and to the alteration of plagioclase to white mica and sericite, and to the growth of tourmaline, also related to grain boundaries and micro-fractures.
Deformation temperature in the shear zones is assessed by white mica thermometry and pseudosections. The calculated T of at least 350-400° C is consistent with qualitative observations showing the presence of stable biotite within very fine-grained (<< 10 µm) shear bands and the recrystallization of quartz by rotation of sub-grain boundaries.
In summary, fractures formed at high temperature, possibly associated with the intrusion of tourmaline-bearing pegmatites and fluids, which predate the ductile mylonitic event (Druguet, 2001; Van Lichtervelde et al., 2017). Fluids altered and weakened a volume of approximately 2 cm thickness all along the fracture planes, whose extent may reach > 100 m. The inferred, relatively high T of ca. 400° C indicates that fracturing is not due to the proximity of the brittle-ductile transition. In addition, no significant micro-fracturing of the mylonites is observed in thin sections. Therefore, fracturing precedes the ductile shear zones, which nucleate on some of the “inherited” sets of thin, planar, weakened structures, the large majority of which remains undeformed. These observations raise the question on whether nucleation and propagation of ductile shear zones is mechanically unrelated to brittle fracturing. Their weakening of planar structures would originate from fluid migration along fracture planes, but fracturing would no longer be active during ductile deformation.
How to cite: Rosenberg, C., Labrousse, L., Landry, N., Druguet, E., and Carreras, J.: On the causes of brittle nucleation of shear zones: the example of Cap de Creus, Eastern Pyrenees (Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19297, https://doi.org/10.5194/egusphere-egu2020-19297, 2020.
The area of Cap de Creus, at the eastern termination of the Axial Zone of the Pyrenean Belt, exposes some of the most famous outcrops of ductile shear zones and shear zone networks (Carreras, 2001). Recent studies proposed that the nucleation and growth of such shear zones may have taken place by brittle processes (Fusseis et al., 2006; Fusseis and Handy, 2008).
The present study investigates the geometrical relationships between fracture systems and some shear zones, the deformation temperature of these shear zones, and the processes leading to the nucleation and growth of shear zones along fracture planes. We selected two areas of the Cap de Creus, the Cala d’Agulles, and the Punta de Cap de Creus, because they are most intensely dissected by subparallel sets of shear zones and fractures. The orientation of the average shear zone planes is sub-parallel to the orientation of the major set of fractures, and the great extent and close spacing of some shear zones that we characterized by aerial photos from a drone, is similar to the distribution and extent of the fracture planes. These observations, in addition to those of Fusseis et al. (2006) suggest that the shear zones nucleated on previous fracture planes.
These fractures are surrounded by haloes of nearly 1 cm thickness affecting the fabric of the country rock, an amphibolite-facies, biotite-andalusite bearing schist. Microscopic observations show that the haloes correspond to the wide-spread presence of thin (less than 2µm thickness) phosphate seams coating the grain boundaries, preferentially those oriented at low angle to the fracture plane, and to the alteration of plagioclase to white mica and sericite, and to the growth of tourmaline, also related to grain boundaries and micro-fractures.
Deformation temperature in the shear zones is assessed by white mica thermometry and pseudosections. The calculated T of at least 350-400° C is consistent with qualitative observations showing the presence of stable biotite within very fine-grained (<< 10 µm) shear bands and the recrystallization of quartz by rotation of sub-grain boundaries.
In summary, fractures formed at high temperature, possibly associated with the intrusion of tourmaline-bearing pegmatites and fluids, which predate the ductile mylonitic event (Druguet, 2001; Van Lichtervelde et al., 2017). Fluids altered and weakened a volume of approximately 2 cm thickness all along the fracture planes, whose extent may reach > 100 m. The inferred, relatively high T of ca. 400° C indicates that fracturing is not due to the proximity of the brittle-ductile transition. In addition, no significant micro-fracturing of the mylonites is observed in thin sections. Therefore, fracturing precedes the ductile shear zones, which nucleate on some of the “inherited” sets of thin, planar, weakened structures, the large majority of which remains undeformed. These observations raise the question on whether nucleation and propagation of ductile shear zones is mechanically unrelated to brittle fracturing. Their weakening of planar structures would originate from fluid migration along fracture planes, but fracturing would no longer be active during ductile deformation.
How to cite: Rosenberg, C., Labrousse, L., Landry, N., Druguet, E., and Carreras, J.: On the causes of brittle nucleation of shear zones: the example of Cap de Creus, Eastern Pyrenees (Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19297, https://doi.org/10.5194/egusphere-egu2020-19297, 2020.
EGU2020-9155 | Displays | TS2.3
Carbon ordering in an aseismic shear zone: implications for crustal weakening and Raman spectroscopyLauren Kedar, Clare Bond, and David Muirhead
Multi-layered stratigraphic sequences present ample opportunity for the study of strain localization and its complexities. By constraining mechanisms of crustal weakening, it is possible to gain a sounder understanding of the dynamic evolution of the Earth’s crust, especially when applied to realistic, field-based scenarios. One such mechanism is that of strain-related carbon ordering. This is the process whereby the amorphous nanostructure of fossilized organic matter contained within the rock is progressively organized towards a more sheet-like structure, similar to that of graphite. One common method of studying this process is through Raman spectroscopy. This is a non-destructive tool which makes use of the relative positions and intensities of two key spectral peaks, where one peak represents graphitic carbon and the other disordered (or amorphous) carbon. The intensity ratio between these two peaks suggests the degree to which the carbon has progressed from its original kerogen-like structure towards that of graphite. This progression can be due to increasing temperature or increasing strain, and until now, these two contributory factors have been difficult to separate, particularly in field examples.
Previous field-based studies have focused on carbon ordering on fault planes, while experimental studies have monitored the effects of strain-related ordering in organic carbon on both fault surfaces and more distributed shear zones. These studies confirmed the occurrence of strain-related ordering at seismic rates, particularly in the form of graphitization of carbon. However, these experiments showed the effects of strain-related ordering at aseismic rates to be limited when distributed shear zones were considered, in part due to the geological timescales required to emulate true conditions.
In this study, Raman spectroscopy is used to compare the relative nanostructural order of organic carbon within a recumbent isoclinal fold formed of interbedded limestones and marls. The central, overturned fold limb forms a 170m wide, 1km long aseismic shear zone, with evidence of increased strain recorded in calcite grains relative to the upper and lower limbs. Raman spectroscopy intensity ratios (I[d]/I[g]) are compared across the fold, showing a marked 23% decrease in the overturned limb. Such a decrease in I[d]/I[g] suggests increased carbon ordering within the overturned limb, which in combination with evidence for increased strain in calcite, suggests that the carbon ordering here is derived directly from strain-related ordering. This has important implications. We infer, from previous studies, that strain-related carbon ordering encourages further strain partitioning in carbonaceous material, and may enhance zones of weakness in the rock. This ordering in aseismic shear zones has so far been unreported in nature, and so our field-based results are significant in supporting previous experimental evidence for this phenomenon. Our results also have implications for understanding dynamic crustal evolution, and will play an important role in the development of Raman thermobarometry, especially since current methods do not distinguish between strain-related and temperature-related ordering.
How to cite: Kedar, L., Bond, C., and Muirhead, D.: Carbon ordering in an aseismic shear zone: implications for crustal weakening and Raman spectroscopy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9155, https://doi.org/10.5194/egusphere-egu2020-9155, 2020.
Multi-layered stratigraphic sequences present ample opportunity for the study of strain localization and its complexities. By constraining mechanisms of crustal weakening, it is possible to gain a sounder understanding of the dynamic evolution of the Earth’s crust, especially when applied to realistic, field-based scenarios. One such mechanism is that of strain-related carbon ordering. This is the process whereby the amorphous nanostructure of fossilized organic matter contained within the rock is progressively organized towards a more sheet-like structure, similar to that of graphite. One common method of studying this process is through Raman spectroscopy. This is a non-destructive tool which makes use of the relative positions and intensities of two key spectral peaks, where one peak represents graphitic carbon and the other disordered (or amorphous) carbon. The intensity ratio between these two peaks suggests the degree to which the carbon has progressed from its original kerogen-like structure towards that of graphite. This progression can be due to increasing temperature or increasing strain, and until now, these two contributory factors have been difficult to separate, particularly in field examples.
Previous field-based studies have focused on carbon ordering on fault planes, while experimental studies have monitored the effects of strain-related ordering in organic carbon on both fault surfaces and more distributed shear zones. These studies confirmed the occurrence of strain-related ordering at seismic rates, particularly in the form of graphitization of carbon. However, these experiments showed the effects of strain-related ordering at aseismic rates to be limited when distributed shear zones were considered, in part due to the geological timescales required to emulate true conditions.
In this study, Raman spectroscopy is used to compare the relative nanostructural order of organic carbon within a recumbent isoclinal fold formed of interbedded limestones and marls. The central, overturned fold limb forms a 170m wide, 1km long aseismic shear zone, with evidence of increased strain recorded in calcite grains relative to the upper and lower limbs. Raman spectroscopy intensity ratios (I[d]/I[g]) are compared across the fold, showing a marked 23% decrease in the overturned limb. Such a decrease in I[d]/I[g] suggests increased carbon ordering within the overturned limb, which in combination with evidence for increased strain in calcite, suggests that the carbon ordering here is derived directly from strain-related ordering. This has important implications. We infer, from previous studies, that strain-related carbon ordering encourages further strain partitioning in carbonaceous material, and may enhance zones of weakness in the rock. This ordering in aseismic shear zones has so far been unreported in nature, and so our field-based results are significant in supporting previous experimental evidence for this phenomenon. Our results also have implications for understanding dynamic crustal evolution, and will play an important role in the development of Raman thermobarometry, especially since current methods do not distinguish between strain-related and temperature-related ordering.
How to cite: Kedar, L., Bond, C., and Muirhead, D.: Carbon ordering in an aseismic shear zone: implications for crustal weakening and Raman spectroscopy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9155, https://doi.org/10.5194/egusphere-egu2020-9155, 2020.
EGU2020-13110 | Displays | TS2.3
The flow-to-sliding transition in crystalline magmaZhipeng Qin and Jenny Suckale
Magmatic flows are rarely, if ever, entirely free of crystals. If these crystals distribute in an approximately homogeneous way, their impact on flow can be captured by defining a suitable effective viscosity for the suspension. A spatially heterogeneous crystal distribution, however, can build up to the degree that the flow behavior of the crystal-bearing magma becomes substantially different from that of a pure melt. One example is the transition from flow to sliding, in which the deformation in the crystalline magma is concentrated almost entirely in a thin interfacial layer as opposed to being distributed in a typical flow profile throughout the domain. The transition is particularly consequential for the large-scale dynamics of the system, because it can be associated with transport rates increasing by orders of magnitudes.
Most conduit models associate the flow-to-sliding transition with a critical crystal fraction, often in the 60% range. Here, we hypothesize that the flow to sliding transition can occur at crystal fraction as low as a few percents under certain conditions. We test our hypothesis by numerically reproducing existing laboratory measurements of the effective viscosity of plagioclase-bearing basalt in a rotational viscometer. We utilize a direct numerical method to resolve the interactions between the crystals and the magmatic melt at the scale of individual interfaces in 2D. Our numerical approach only requires assumptions about the pure phase including the crystal fraction and crystal shape. All phase interactions and their aggregate effect on the flow emerge self-consistently from the simulation itself.
Our simulations suggest that the behavior of multiphase suspensions at low fluid Reynolds number is highly variable and depends sensitively on the characteristics of the immersed phases and the geometry of the flow domain. We show that there is no meaningful dilute limit in which the phase interactions can be neglected or captured by adjusting the effective rheology of the suspension in a way that removes dependencies on the properties of the immersed phase. Since our models operate at the scale of individual crystals, our model results are testable in both field and laboratory settings. In fact, they suggest that observations of microstructure provide valuable constraints on the large scale flow dynamics at the time. Particularly important is the degree of preferential crystal alignment and the existence of force chains or crystal clusters.
How to cite: Qin, Z. and Suckale, J.: The flow-to-sliding transition in crystalline magma, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13110, https://doi.org/10.5194/egusphere-egu2020-13110, 2020.
Magmatic flows are rarely, if ever, entirely free of crystals. If these crystals distribute in an approximately homogeneous way, their impact on flow can be captured by defining a suitable effective viscosity for the suspension. A spatially heterogeneous crystal distribution, however, can build up to the degree that the flow behavior of the crystal-bearing magma becomes substantially different from that of a pure melt. One example is the transition from flow to sliding, in which the deformation in the crystalline magma is concentrated almost entirely in a thin interfacial layer as opposed to being distributed in a typical flow profile throughout the domain. The transition is particularly consequential for the large-scale dynamics of the system, because it can be associated with transport rates increasing by orders of magnitudes.
Most conduit models associate the flow-to-sliding transition with a critical crystal fraction, often in the 60% range. Here, we hypothesize that the flow to sliding transition can occur at crystal fraction as low as a few percents under certain conditions. We test our hypothesis by numerically reproducing existing laboratory measurements of the effective viscosity of plagioclase-bearing basalt in a rotational viscometer. We utilize a direct numerical method to resolve the interactions between the crystals and the magmatic melt at the scale of individual interfaces in 2D. Our numerical approach only requires assumptions about the pure phase including the crystal fraction and crystal shape. All phase interactions and their aggregate effect on the flow emerge self-consistently from the simulation itself.
Our simulations suggest that the behavior of multiphase suspensions at low fluid Reynolds number is highly variable and depends sensitively on the characteristics of the immersed phases and the geometry of the flow domain. We show that there is no meaningful dilute limit in which the phase interactions can be neglected or captured by adjusting the effective rheology of the suspension in a way that removes dependencies on the properties of the immersed phase. Since our models operate at the scale of individual crystals, our model results are testable in both field and laboratory settings. In fact, they suggest that observations of microstructure provide valuable constraints on the large scale flow dynamics at the time. Particularly important is the degree of preferential crystal alignment and the existence of force chains or crystal clusters.
How to cite: Qin, Z. and Suckale, J.: The flow-to-sliding transition in crystalline magma, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13110, https://doi.org/10.5194/egusphere-egu2020-13110, 2020.
EGU2020-13160 | Displays | TS2.3
Influence of initial preferred orientations on strain localisation and fold patterns in non-linear viscous anisotropic materialsTamara de Riese, Paul D. Bons, Enrique Gomez-Rivas, Albert Griera, Maria-Gema Llorens, and Ilka Weikusat
Deformation localisation in rocks can lead to a variety of structures, such as shear zones and shear bands that can range from grain to crustal scale, from discrete and isolated zones to anastomosing networks. The heterogeneous strain field can furthermore result in a wide range of highly diverse fold geometries.
We present a series of numerical simulations of the simple-shear deformation of an intrinsically anisotropic non-linear viscous material with a single maximum crystal preferred orientation (CPO) in dextral simple shear. We use the Viscoplastic Full-Field Transform (VPFFT) crystal plasticity code (e.g. Lebensohn & Rollett, 2020) coupled with the modelling platform ELLE (http://elle.ws) to achieve very high strains. The VPFFT-approach simulates viscoplastic deformation by dislocation glide, taking into account the different available slip systems and their critical resolved shear stresses. The approach is well suited for strongly non-linear anisotropic materials (de Riese et al., 2019). We vary the anisotropic behaviour of the material from isotropic to highly anisotropic (according to the relative critical resolved shear stress required to activate the different slip systems), as well as the orientation of the initial single maximum orientation, which we vary from parallel to perpendicular to the shear plane. To visualize deformation structures, we use passive markers, for which we also systematically vary the initial orientation.
At relatively low strains the amount of strain rate localisation and resulting deformation structures highly depend on the initial single maximum orientation in the material in all anisotropic models. Three regimes can be recognised: distributed shear localisation, synthetic shear bands and antithetic shear bands. However, at very high strains localisation behaviour always tends to converge to a similar state, independent of the initial orientation of the anisotropy.
In rocks, shear localisation is often detected by the deflection and/or folding of layers, which may be parallel to the anisotropy (e.g. cleavage formed by aligned mica), or by deflection/deformation of passive layering, such as original sedimentary layers. The resulting fold patterns vary strongly, depending on the original orientation of layering relative to the deformation field. This can even result in misleading structures that seem to indicate the opposite sense of shear. Most distinct deformation structures tend to form when the layering is originally parallel to the shear plane.
de Riese, T., Evans, L., Gomez-Rivas, E., Griera, A., Lebensohn, R.A., Llorens, M.-G., Ran, H., Sachau, T., Weikusat, I., Bons, P.D. 2019. Shear localisation in anisotropic, non-linear viscous materials that develop a CPO: A numerical study. J. Struct. Geol. 124, 81-90.
Lebensohn, R.A., Rollett, A.D. 2020. Spectral methods for full-field micromechanical modelling of polycrystalline materials. Computational Mat. Sci. 173, 109336.
How to cite: de Riese, T., Bons, P. D., Gomez-Rivas, E., Griera, A., Llorens, M.-G., and Weikusat, I.: Influence of initial preferred orientations on strain localisation and fold patterns in non-linear viscous anisotropic materials , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13160, https://doi.org/10.5194/egusphere-egu2020-13160, 2020.
Deformation localisation in rocks can lead to a variety of structures, such as shear zones and shear bands that can range from grain to crustal scale, from discrete and isolated zones to anastomosing networks. The heterogeneous strain field can furthermore result in a wide range of highly diverse fold geometries.
We present a series of numerical simulations of the simple-shear deformation of an intrinsically anisotropic non-linear viscous material with a single maximum crystal preferred orientation (CPO) in dextral simple shear. We use the Viscoplastic Full-Field Transform (VPFFT) crystal plasticity code (e.g. Lebensohn & Rollett, 2020) coupled with the modelling platform ELLE (http://elle.ws) to achieve very high strains. The VPFFT-approach simulates viscoplastic deformation by dislocation glide, taking into account the different available slip systems and their critical resolved shear stresses. The approach is well suited for strongly non-linear anisotropic materials (de Riese et al., 2019). We vary the anisotropic behaviour of the material from isotropic to highly anisotropic (according to the relative critical resolved shear stress required to activate the different slip systems), as well as the orientation of the initial single maximum orientation, which we vary from parallel to perpendicular to the shear plane. To visualize deformation structures, we use passive markers, for which we also systematically vary the initial orientation.
At relatively low strains the amount of strain rate localisation and resulting deformation structures highly depend on the initial single maximum orientation in the material in all anisotropic models. Three regimes can be recognised: distributed shear localisation, synthetic shear bands and antithetic shear bands. However, at very high strains localisation behaviour always tends to converge to a similar state, independent of the initial orientation of the anisotropy.
In rocks, shear localisation is often detected by the deflection and/or folding of layers, which may be parallel to the anisotropy (e.g. cleavage formed by aligned mica), or by deflection/deformation of passive layering, such as original sedimentary layers. The resulting fold patterns vary strongly, depending on the original orientation of layering relative to the deformation field. This can even result in misleading structures that seem to indicate the opposite sense of shear. Most distinct deformation structures tend to form when the layering is originally parallel to the shear plane.
de Riese, T., Evans, L., Gomez-Rivas, E., Griera, A., Lebensohn, R.A., Llorens, M.-G., Ran, H., Sachau, T., Weikusat, I., Bons, P.D. 2019. Shear localisation in anisotropic, non-linear viscous materials that develop a CPO: A numerical study. J. Struct. Geol. 124, 81-90.
Lebensohn, R.A., Rollett, A.D. 2020. Spectral methods for full-field micromechanical modelling of polycrystalline materials. Computational Mat. Sci. 173, 109336.
How to cite: de Riese, T., Bons, P. D., Gomez-Rivas, E., Griera, A., Llorens, M.-G., and Weikusat, I.: Influence of initial preferred orientations on strain localisation and fold patterns in non-linear viscous anisotropic materials , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13160, https://doi.org/10.5194/egusphere-egu2020-13160, 2020.
EGU2020-45 | Displays | TS2.3
Ultrahigh resolution 3D imaging and characterisation of nanoscale pore structure in shales and its control on gas transportMohamed Garum, Paul Glover, Piroska Lorinczi, and Ali Hassanpour
Cost-effective and environmentally sensitive shale gas production requires detailed knowledge of the petrophysical characteristics of the shale from which the gas is extracted. Parameters such as the kerogen fraction, pore size distributions, porosity, permeability, the frackability of the rock and the degree to which natural fracturing already occurs are required in order to be able to estimate potential gas reserves and how easily it can be extracted. Innovative imaging techniques, including Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) and Nanoscale X-Ray Tomography (nano-CT), can be used to characterise the microstructural properties of shale. Here we report using FIB-SEM serial sectioning and nano-CT on approximately cubic samples of side length about 25 µm. The resolution of the FIB-SEM scanning is approximately 20 nm, while that of the nano-CT is about 50 nm, providing between 125 and 1953 million voxels per scan. These ultra-high resolution techniques have been shown to be effective methods for the analysis and imaging of shale microstructure. Each technique can provide data over a different and separate range of scales, and with different resolutions. Results analysed so far indicate that pores which seem to be unconnected when imaged on a micrometre scale by micro-CT scanning, are connected by thin pathways when imaged at these higher resolutions. This nano-scale connectivity is responsible for the small but non-zero permeability of gas shales to gas flow, which is typically measured in the range 5 nD – 200 nD. The volume, size, aspect ratios, surface area to volume ratio and orientations have all been calculated from the scanned data as a function of scale. These data indicate an extremely complex, heterogeneous, anisotropic and multimodal pore nanostructure and microstructure for the shales, with structure at all scales contributing to both gas storage and gas flow. Further work analysing the connectivity of the microscale and nanoscale pore spaces within the rock is underway. We believe that the combination of nano-CT with FIB-SEM on the same sample has the potential for providing an enhanced understanding of shale microstructure, which is necessary for modelling elastic behaviour, gas storage, gas desorption and gas flow in gas shales.
Keywords: Gas shale, FIB-SEM, nano-CT, porosity, permeability, Kerogen, pore volume, size distribution, pore aspect ratio and surface area to pore volume.
How to cite: Garum, M., Glover, P., Lorinczi, P., and Hassanpour, A.: Ultrahigh resolution 3D imaging and characterisation of nanoscale pore structure in shales and its control on gas transport , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-45, https://doi.org/10.5194/egusphere-egu2020-45, 2020.
Cost-effective and environmentally sensitive shale gas production requires detailed knowledge of the petrophysical characteristics of the shale from which the gas is extracted. Parameters such as the kerogen fraction, pore size distributions, porosity, permeability, the frackability of the rock and the degree to which natural fracturing already occurs are required in order to be able to estimate potential gas reserves and how easily it can be extracted. Innovative imaging techniques, including Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) and Nanoscale X-Ray Tomography (nano-CT), can be used to characterise the microstructural properties of shale. Here we report using FIB-SEM serial sectioning and nano-CT on approximately cubic samples of side length about 25 µm. The resolution of the FIB-SEM scanning is approximately 20 nm, while that of the nano-CT is about 50 nm, providing between 125 and 1953 million voxels per scan. These ultra-high resolution techniques have been shown to be effective methods for the analysis and imaging of shale microstructure. Each technique can provide data over a different and separate range of scales, and with different resolutions. Results analysed so far indicate that pores which seem to be unconnected when imaged on a micrometre scale by micro-CT scanning, are connected by thin pathways when imaged at these higher resolutions. This nano-scale connectivity is responsible for the small but non-zero permeability of gas shales to gas flow, which is typically measured in the range 5 nD – 200 nD. The volume, size, aspect ratios, surface area to volume ratio and orientations have all been calculated from the scanned data as a function of scale. These data indicate an extremely complex, heterogeneous, anisotropic and multimodal pore nanostructure and microstructure for the shales, with structure at all scales contributing to both gas storage and gas flow. Further work analysing the connectivity of the microscale and nanoscale pore spaces within the rock is underway. We believe that the combination of nano-CT with FIB-SEM on the same sample has the potential for providing an enhanced understanding of shale microstructure, which is necessary for modelling elastic behaviour, gas storage, gas desorption and gas flow in gas shales.
Keywords: Gas shale, FIB-SEM, nano-CT, porosity, permeability, Kerogen, pore volume, size distribution, pore aspect ratio and surface area to pore volume.
How to cite: Garum, M., Glover, P., Lorinczi, P., and Hassanpour, A.: Ultrahigh resolution 3D imaging and characterisation of nanoscale pore structure in shales and its control on gas transport , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-45, https://doi.org/10.5194/egusphere-egu2020-45, 2020.
EGU2020-1516 | Displays | TS2.3
Impacts of mineralogy on micro-scale pore structure and fluid flow capacity of deeply buried sandstone reservoirsJuncheng Qiao, Jianhui Zeng, and Xiao Feng
Hydrocarbon exploration is extending from the shallowly buried to deeply buried strata with increasing demands for fossil fuels. The variable storage and percolation capacities that intrinsically depend on the pore geometry restrict the hydrocarbon recovery and displacement efficiency and trigger studies on the micro-scale pore structure, fluid flow capacity, and their controlling factors. Minerals within sandstone are the results of the coupling control of depositional factors and diagenetic alternations, which determine the microscopic pore geometry and subsequently affect the fluid flow capacity. In order to investigate the impacts of mineralogy on the pore structure and fluid flow capacity, integrated analyses including porosity and permeability measurements, casting thin section (CTS), scanning electron microscopy (SEM), pressure-controlled mercury porosimetry (PCP), rate-controlled mercury porosimetry (RCP), nuclear magnetic resonance (NMR), and X-ray diffraction (XRD) are conducted on the deeply buried sandstone samples in the Jurassic Sangonghe Formation of the Junggar Basin. Microscopic pore structure is characterized by the combination of SEM, CTS, PCP, and RCP and fractal theory. Fluid flow capacity is evaluated by the innovative application of film bound water model in NMR and mineralogy is quantitatively measured by XRD. The results indicate that the deeply buried sandstone is rich in quartz (54.2%), feldspar (25.1%), and clay (14.2%), with dominant kaolinite (5.04%) and chlorite (5.38%) cementation. The reservoir has a wide pore-throat diameter distribution with three peaks in the ranges 0.01–1, 10–80, and 200–1000 μm. Pores are tri-fractal and can be divided into micropores, mesopores, and macropores, with average porosity contributions of 50.11, 21.83, and 28.04%, respectively. The movable porosity of deeply buried sandstone ranges from 1.75 to 8.24%, primarily contributed by intergranular (avg. 2.34%) and intragranular pores (avg. 2.56%). Most of the fluids are movable in intergranular pores but are irreducible in intragranular pores. Correlation analyses between mineralogy and pore structure suggest that quartz provides preservation to intergranular porosity, which increases pore size and macropores porosity and reduces heterogeneity of the pore system. The influence of feldspar reverses and becomes poor owing to the simultaneous clay precipitation and complex roles of feldspar dissolution in microporosity. Chlorite, kaolinite, and illite, all act as destructions to intergranular porosity. They enhance the mesopores and micropores porosities, reduce the pore size, and increase the microscopic heterogeneities of the macropores, micropores, and whole pore system. The relationships between mineralogy and fluid flow capacity indicate that quartz is favorable for the fluid flow capacity, but feldspar and clay play negative roles. The reversed impacts of quartz and feldspar lay in their opposite controls on pore size. However, both pore size and hydrophilia should be taken into account when considering the effects of clay minerals. These negative effects are associated with types, contents, and hydrophilic degrees of clay minerals, in which I/S and illite exhibit the strongest negative impacts. The fluid flow in the intergranular and intragranular pores is generally enhanced by higher quartz content, but reduced by higher clay content. Irreducible fluids in the intergranular and intragranular pores are determined by chlorite and kaolinite contents, respectively.
How to cite: Qiao, J., Zeng, J., and Feng, X.: Impacts of mineralogy on micro-scale pore structure and fluid flow capacity of deeply buried sandstone reservoirs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1516, https://doi.org/10.5194/egusphere-egu2020-1516, 2020.
Hydrocarbon exploration is extending from the shallowly buried to deeply buried strata with increasing demands for fossil fuels. The variable storage and percolation capacities that intrinsically depend on the pore geometry restrict the hydrocarbon recovery and displacement efficiency and trigger studies on the micro-scale pore structure, fluid flow capacity, and their controlling factors. Minerals within sandstone are the results of the coupling control of depositional factors and diagenetic alternations, which determine the microscopic pore geometry and subsequently affect the fluid flow capacity. In order to investigate the impacts of mineralogy on the pore structure and fluid flow capacity, integrated analyses including porosity and permeability measurements, casting thin section (CTS), scanning electron microscopy (SEM), pressure-controlled mercury porosimetry (PCP), rate-controlled mercury porosimetry (RCP), nuclear magnetic resonance (NMR), and X-ray diffraction (XRD) are conducted on the deeply buried sandstone samples in the Jurassic Sangonghe Formation of the Junggar Basin. Microscopic pore structure is characterized by the combination of SEM, CTS, PCP, and RCP and fractal theory. Fluid flow capacity is evaluated by the innovative application of film bound water model in NMR and mineralogy is quantitatively measured by XRD. The results indicate that the deeply buried sandstone is rich in quartz (54.2%), feldspar (25.1%), and clay (14.2%), with dominant kaolinite (5.04%) and chlorite (5.38%) cementation. The reservoir has a wide pore-throat diameter distribution with three peaks in the ranges 0.01–1, 10–80, and 200–1000 μm. Pores are tri-fractal and can be divided into micropores, mesopores, and macropores, with average porosity contributions of 50.11, 21.83, and 28.04%, respectively. The movable porosity of deeply buried sandstone ranges from 1.75 to 8.24%, primarily contributed by intergranular (avg. 2.34%) and intragranular pores (avg. 2.56%). Most of the fluids are movable in intergranular pores but are irreducible in intragranular pores. Correlation analyses between mineralogy and pore structure suggest that quartz provides preservation to intergranular porosity, which increases pore size and macropores porosity and reduces heterogeneity of the pore system. The influence of feldspar reverses and becomes poor owing to the simultaneous clay precipitation and complex roles of feldspar dissolution in microporosity. Chlorite, kaolinite, and illite, all act as destructions to intergranular porosity. They enhance the mesopores and micropores porosities, reduce the pore size, and increase the microscopic heterogeneities of the macropores, micropores, and whole pore system. The relationships between mineralogy and fluid flow capacity indicate that quartz is favorable for the fluid flow capacity, but feldspar and clay play negative roles. The reversed impacts of quartz and feldspar lay in their opposite controls on pore size. However, both pore size and hydrophilia should be taken into account when considering the effects of clay minerals. These negative effects are associated with types, contents, and hydrophilic degrees of clay minerals, in which I/S and illite exhibit the strongest negative impacts. The fluid flow in the intergranular and intragranular pores is generally enhanced by higher quartz content, but reduced by higher clay content. Irreducible fluids in the intergranular and intragranular pores are determined by chlorite and kaolinite contents, respectively.
How to cite: Qiao, J., Zeng, J., and Feng, X.: Impacts of mineralogy on micro-scale pore structure and fluid flow capacity of deeply buried sandstone reservoirs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1516, https://doi.org/10.5194/egusphere-egu2020-1516, 2020.
EGU2020-6968 | Displays | TS2.3
Synchrotron multi-modal, multi-scale chemical and structural imaging of vein-bearing shalesChristoph E. Schrank, Michael W. M. Jones, Cameron M. Kewish, and Grant A. van Riessen
The coupling between fluid transport, chemical reactions, and deformation constitutes one of the frontiers of geoscientific research. From an analytical perspective, a fundamental challenge is posed by the fact that sub-nanometre- to micrometre-scale structures play a vital role in the macroscopic (centimetre- to metre-scale) response of deforming, reacting, fluid-bearing rocks. Sample analysis with conventional laboratory techniques quickly becomes prohibitively expensive and laborious when more than four orders of magnitude in length scales need to be resolved. This issue is particularly challenging in very fine-grained rocks such as mylonites and shales.
Here, we investigate calcite-vein-bearing shales to illustrate how synchrotron X-ray fluorescence microscopy, ptychography, and small- and wide-angle transmission scattering can be used for the quantitative multi-scale analysis of micro- and nano-textures in rock. These analytical techniques are applied to thin sections or thin rock slabs on the centimetre-scale and provide information on length scales from hundreds of micrometres down to angstroms. Therefore, the considered array of synchrotron techniques covers up to eight orders of magnitude in length scale in terms of chemical and structural information. In our case study, we demonstrate how this suite of analytical techniques can be employed to reveal, for example, the relative timing of mineralisation events, trace-element chemistry, texture, and the structural width of fluid pathways such as grain boundaries.
How to cite: Schrank, C. E., Jones, M. W. M., Kewish, C. M., and van Riessen, G. A.: Synchrotron multi-modal, multi-scale chemical and structural imaging of vein-bearing shales, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6968, https://doi.org/10.5194/egusphere-egu2020-6968, 2020.
The coupling between fluid transport, chemical reactions, and deformation constitutes one of the frontiers of geoscientific research. From an analytical perspective, a fundamental challenge is posed by the fact that sub-nanometre- to micrometre-scale structures play a vital role in the macroscopic (centimetre- to metre-scale) response of deforming, reacting, fluid-bearing rocks. Sample analysis with conventional laboratory techniques quickly becomes prohibitively expensive and laborious when more than four orders of magnitude in length scales need to be resolved. This issue is particularly challenging in very fine-grained rocks such as mylonites and shales.
Here, we investigate calcite-vein-bearing shales to illustrate how synchrotron X-ray fluorescence microscopy, ptychography, and small- and wide-angle transmission scattering can be used for the quantitative multi-scale analysis of micro- and nano-textures in rock. These analytical techniques are applied to thin sections or thin rock slabs on the centimetre-scale and provide information on length scales from hundreds of micrometres down to angstroms. Therefore, the considered array of synchrotron techniques covers up to eight orders of magnitude in length scale in terms of chemical and structural information. In our case study, we demonstrate how this suite of analytical techniques can be employed to reveal, for example, the relative timing of mineralisation events, trace-element chemistry, texture, and the structural width of fluid pathways such as grain boundaries.
How to cite: Schrank, C. E., Jones, M. W. M., Kewish, C. M., and van Riessen, G. A.: Synchrotron multi-modal, multi-scale chemical and structural imaging of vein-bearing shales, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6968, https://doi.org/10.5194/egusphere-egu2020-6968, 2020.
EGU2020-21109 | Displays | TS2.3
Weakening mechanisms and the role of easy slip horizons in thrust belt development: a microstructural approachAimee Guida Barroso, Eddie Dempsey, Bob Holdsworth, and Nicola De Paola
The Late Silurian Moine Thrust Zone (MTZ) of the NW Highlands of Scotland has long been fundamental to the understanding of the nature and processes that occur during thrust tectonics in the upper continental crust. This complex imbrication zone formed during final Scandian stages of the Caledonian orogeny when collision of Baltica and Laurentia led to WNW-ESE tectonic foreshortening of >100km. The MTZ juxtaposed greenschist to amphibolite facies Neoproterozoic metamorphic rocks of the Moine Supergroup over sequences of little metamorphosed Cambro-Ordovician and Neoproterozoic sedimentary rocks and their Neoarchean to Paleoproterozoic gneissic basement in a zone ranging from <1km to >20km wide.
The mechanical problems represented by thrust wedges being transported over such great distances without losing their internal cohesion has highlighted the role played by detachment structures and the need for mechanisms that create significant weakening along basal detachments that allow overthrusts to accommodate major horizontal displacements in the shallow crust. Field studies and use of section balancing techniques have highlighted that a substantial proportion of the displacement seems to be accommodated along detachments that follow specific stratigraphic levels.
Other than the Moine Thrust Mylonites and the mylonitised parts of the Cambrian Quartzites, relatively little is known about the grain scale deformation and potential weakening processes that have occurred in other parts of the MTZ. New lithological descriptions of the fault rocks and sedimentary protoliths observed in the Assynt, Durness and Eriboll areas are presented here and provide detailed microstructural evidence for the long-term weakening mechanisms that were operating at the time. These mechanisms are consistently related to the onset of grain size reduction, triggered by both chemical enhanced and geometric processes. These include feldspar alteration to fine phyllosilicates associated with cataclasis and dynamic recrystallization of quartz.
Pressure solution, evidenced by changes in the shape of minerals along cleavage surfaces and the presence of dissolution seams and caps, is widespread throughout the studied rock sequences. The profuse occurrence of this grain-scale mechanism makes it very likely that syn-deformational fluid-influx lead to the destruction of load bearing microstructural frameworks and the development of interconnected weak layers due to alteration, explaining the occurrence of detachments within impure layers of the predominantly quartzose Pipe Rock and Salterella Grit members. The progressive development of these interconnecting fine-grained weak layers resulting from incongruent diffusive mass transfer is enhanced in the more mineralogically heterogeneous units of the Cambro-Ordovician sedimentary sequence (in particular, Fucoid Beds dolomitic siltstones and Durness limestones) explaining the consistently observed slip localization in these horizons.
How to cite: Guida Barroso, A., Dempsey, E., Holdsworth, B., and De Paola, N.: Weakening mechanisms and the role of easy slip horizons in thrust belt development: a microstructural approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21109, https://doi.org/10.5194/egusphere-egu2020-21109, 2020.
The Late Silurian Moine Thrust Zone (MTZ) of the NW Highlands of Scotland has long been fundamental to the understanding of the nature and processes that occur during thrust tectonics in the upper continental crust. This complex imbrication zone formed during final Scandian stages of the Caledonian orogeny when collision of Baltica and Laurentia led to WNW-ESE tectonic foreshortening of >100km. The MTZ juxtaposed greenschist to amphibolite facies Neoproterozoic metamorphic rocks of the Moine Supergroup over sequences of little metamorphosed Cambro-Ordovician and Neoproterozoic sedimentary rocks and their Neoarchean to Paleoproterozoic gneissic basement in a zone ranging from <1km to >20km wide.
The mechanical problems represented by thrust wedges being transported over such great distances without losing their internal cohesion has highlighted the role played by detachment structures and the need for mechanisms that create significant weakening along basal detachments that allow overthrusts to accommodate major horizontal displacements in the shallow crust. Field studies and use of section balancing techniques have highlighted that a substantial proportion of the displacement seems to be accommodated along detachments that follow specific stratigraphic levels.
Other than the Moine Thrust Mylonites and the mylonitised parts of the Cambrian Quartzites, relatively little is known about the grain scale deformation and potential weakening processes that have occurred in other parts of the MTZ. New lithological descriptions of the fault rocks and sedimentary protoliths observed in the Assynt, Durness and Eriboll areas are presented here and provide detailed microstructural evidence for the long-term weakening mechanisms that were operating at the time. These mechanisms are consistently related to the onset of grain size reduction, triggered by both chemical enhanced and geometric processes. These include feldspar alteration to fine phyllosilicates associated with cataclasis and dynamic recrystallization of quartz.
Pressure solution, evidenced by changes in the shape of minerals along cleavage surfaces and the presence of dissolution seams and caps, is widespread throughout the studied rock sequences. The profuse occurrence of this grain-scale mechanism makes it very likely that syn-deformational fluid-influx lead to the destruction of load bearing microstructural frameworks and the development of interconnected weak layers due to alteration, explaining the occurrence of detachments within impure layers of the predominantly quartzose Pipe Rock and Salterella Grit members. The progressive development of these interconnecting fine-grained weak layers resulting from incongruent diffusive mass transfer is enhanced in the more mineralogically heterogeneous units of the Cambro-Ordovician sedimentary sequence (in particular, Fucoid Beds dolomitic siltstones and Durness limestones) explaining the consistently observed slip localization in these horizons.
How to cite: Guida Barroso, A., Dempsey, E., Holdsworth, B., and De Paola, N.: Weakening mechanisms and the role of easy slip horizons in thrust belt development: a microstructural approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21109, https://doi.org/10.5194/egusphere-egu2020-21109, 2020.
EGU2020-9086 | Displays | TS2.3
Graphitic material in fault zones: Implication for strain localization and rheological weakeningShuyun Cao, Franz Neubauer, and Meixia Lv
Graphitic carbon exhibits a large range of structures and chemical compositions, from amorphous-like compounds to crystalline graphite. The graphitic carbon-bearing rocks are widely occurred in low- to high- grade metamorphic massif and fault zone. The carbonaceous material in the rock will gradually transform from an amorphous into an ordered crystalline structure by thermal metamorphism, which is called graphitization. The degree of graphitization is believed to be a reliable indicator of peak temperature conditions in the metamorphic rock. In many low-grade metamorphic rocks, graphitic carbon (e.g., soot, low-grade coal) is often associated with brittle fault gouge whereas in high-grade metamorphic rocks, graphitic carbon (crystalline granite) are most commonly seen in marble, schist or gneiss. In recent years, graphitic carbon-bearing rocks have been reported from natural fault zones (reviwers paper see Cao and Neubauer 2019 and references therein). The graphitic carbon grains in our samples tend to enrich in slip-surface or micro-shear zone with strain localization in fault, performed as dislocation glide of deformation. The graphite LPO shows slip system in the direction of basil <a> combined basil <a> slip and weak prism <a> slip systems, suggesting a low-temperature to a medium to high temperature deformation conditions, which is in consistent with the results of Raman Spectra of Carbonaceous material (RSCM) thermometry. We also proposed that the graphitic carbon formed in the rocks can significantly affect the mechanical properties of the fault during the process of faulting. This process can effectively cause reaction weakening and strain localization, which is thought to play an important role as solid lubrication in fault weakening.
How to cite: Cao, S., Neubauer, F., and Lv, M.: Graphitic material in fault zones: Implication for strain localization and rheological weakening, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9086, https://doi.org/10.5194/egusphere-egu2020-9086, 2020.
Graphitic carbon exhibits a large range of structures and chemical compositions, from amorphous-like compounds to crystalline graphite. The graphitic carbon-bearing rocks are widely occurred in low- to high- grade metamorphic massif and fault zone. The carbonaceous material in the rock will gradually transform from an amorphous into an ordered crystalline structure by thermal metamorphism, which is called graphitization. The degree of graphitization is believed to be a reliable indicator of peak temperature conditions in the metamorphic rock. In many low-grade metamorphic rocks, graphitic carbon (e.g., soot, low-grade coal) is often associated with brittle fault gouge whereas in high-grade metamorphic rocks, graphitic carbon (crystalline granite) are most commonly seen in marble, schist or gneiss. In recent years, graphitic carbon-bearing rocks have been reported from natural fault zones (reviwers paper see Cao and Neubauer 2019 and references therein). The graphitic carbon grains in our samples tend to enrich in slip-surface or micro-shear zone with strain localization in fault, performed as dislocation glide of deformation. The graphite LPO shows slip system in the direction of basil <a> combined basil <a> slip and weak prism <a> slip systems, suggesting a low-temperature to a medium to high temperature deformation conditions, which is in consistent with the results of Raman Spectra of Carbonaceous material (RSCM) thermometry. We also proposed that the graphitic carbon formed in the rocks can significantly affect the mechanical properties of the fault during the process of faulting. This process can effectively cause reaction weakening and strain localization, which is thought to play an important role as solid lubrication in fault weakening.
How to cite: Cao, S., Neubauer, F., and Lv, M.: Graphitic material in fault zones: Implication for strain localization and rheological weakening, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9086, https://doi.org/10.5194/egusphere-egu2020-9086, 2020.
EGU2020-960 | Displays | TS2.3
Development of C- shear bands in brittle-ductile shear zones: Insights from analogue and numerical models.Arnab Roy, Nandan Roy, Puspendu Saha, and Nibir Mandal
Development of brittle and brittle-ductile shear zones involve partitioning of large shear strains in bands, called C-shear bands (C-SB) nearly parallel to the shear zone boundaries. Our present work aims to provide a comprehensive understanding of the rheological factors in controlling such SB growth in meter scale natural brittle- ductile shear zones observed in in Singbhum and Chotonagpur mobile belts. The shear zones show C- SB at an angle of 0°- 5° with the shear zone boundary. We used analogue models, based on Coulomb and Viscoplastic rheology to reproduce them in experimental conditions.
These models produce dominantly Riedel (R) shear bands. We show a transition from R-shearing in conjugate to single sets at angles of ~15o by changing model materials. However, none of the analogue models produced C-SB, as observed in the field. To reconcile the experimental and field findings, numeral models have been used to better constrain the geometrical and rheological parameters. We simulate model shear zones replicating those observed in the field, which display two distinct zones: drag zone where the viscous strains dominate and the core zone, where both viscous and plastic strains come into play. Numerical model results suggest the formation of C- SB for a specific rheological condition. We also show varying shear band patterns as a function of the thickness ratio between drag and core zones.
How to cite: Roy, A., Roy, N., Saha, P., and Mandal, N.: Development of C- shear bands in brittle-ductile shear zones: Insights from analogue and numerical models., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-960, https://doi.org/10.5194/egusphere-egu2020-960, 2020.
Development of brittle and brittle-ductile shear zones involve partitioning of large shear strains in bands, called C-shear bands (C-SB) nearly parallel to the shear zone boundaries. Our present work aims to provide a comprehensive understanding of the rheological factors in controlling such SB growth in meter scale natural brittle- ductile shear zones observed in in Singbhum and Chotonagpur mobile belts. The shear zones show C- SB at an angle of 0°- 5° with the shear zone boundary. We used analogue models, based on Coulomb and Viscoplastic rheology to reproduce them in experimental conditions.
These models produce dominantly Riedel (R) shear bands. We show a transition from R-shearing in conjugate to single sets at angles of ~15o by changing model materials. However, none of the analogue models produced C-SB, as observed in the field. To reconcile the experimental and field findings, numeral models have been used to better constrain the geometrical and rheological parameters. We simulate model shear zones replicating those observed in the field, which display two distinct zones: drag zone where the viscous strains dominate and the core zone, where both viscous and plastic strains come into play. Numerical model results suggest the formation of C- SB for a specific rheological condition. We also show varying shear band patterns as a function of the thickness ratio between drag and core zones.
How to cite: Roy, A., Roy, N., Saha, P., and Mandal, N.: Development of C- shear bands in brittle-ductile shear zones: Insights from analogue and numerical models., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-960, https://doi.org/10.5194/egusphere-egu2020-960, 2020.
Deformation of lithospheric rocks regularly localizes into high-strain shear zones that include fine-grained ultramylonites. Occurring as quasi-straight layers of intimately mixed phases that often describe sharp transitions with the host rock, these structures may channelize fluid flow[1,2] and could serve as precursors for deep earthquakes[3]. However, although intensively documented, ultramylonites originate from still unknown processes. Here I focus on a mylonitic complex that includes numerous mantle ultramylonites in the Ronda peridotite (Spain). Among them, I was able to highlight one of their precursors that I better describe as a long and straight grain boundary, along which four-grain junctions are observed with randomly oriented grains of olivine and pyroxenes. This precursor starts from a pyroxene porphyroclast and extends to an incipient, weakly undulated ultramylonite, where intimate phase mixing arises with asymmetrical grain size distribution. While the finer grain size locates on one side, describing a sharp – but continuous – transition with the host rock, the grain size gradually increases towards the other side, giving rise to a smooth transition. All phases have a very weak lattice preferred orientation (LPO) in the ultramylonite, which strongly differs from the host rock where olivine is highly deformed with evidence of high dislocation densities and a strong LPO. Altogether, these features shed light on the origin of mantle ultramylonites that I attribute to a migrating grain boundary, the sliding of which continuously produces new grains by phase nucleation, probably at the favor of transient four-grain junctions. Nucleated grains then grow and progressively detach from the precursor as it keeps on migrating depending on the dislocation densities in the host rock. Although such an unusual grain boundary remains to be understood in terms of source mechanism, these findings provide new constraints on the appearing and development of ultramylonites.
[1] Fusseis, F., Regenauer-Lieb, K., Liu, J., Hough, R. M. & De Carlo, F. Creep cavitation can establish a dynamic granular fluid pump in ductile shear zones. Nature 459: 974–977 (2009)
[2] Précigout, J., Prigent, C., Palasse, L. & Pochon, A. Water pumping in mantle shear zones. Nat. commun. 8: 15736, https://doi.org/10.1038/ncomms15736 (2017)
[3] White, J. C. Paradoxical pseudotachylyte – Fault melt outside the seismogenic zone. J. Struct. Geol. 38: 11-20 (2012)
How to cite: Précigout, J.: On the Origin of Ultramylonites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3938, https://doi.org/10.5194/egusphere-egu2020-3938, 2020.
Deformation of lithospheric rocks regularly localizes into high-strain shear zones that include fine-grained ultramylonites. Occurring as quasi-straight layers of intimately mixed phases that often describe sharp transitions with the host rock, these structures may channelize fluid flow[1,2] and could serve as precursors for deep earthquakes[3]. However, although intensively documented, ultramylonites originate from still unknown processes. Here I focus on a mylonitic complex that includes numerous mantle ultramylonites in the Ronda peridotite (Spain). Among them, I was able to highlight one of their precursors that I better describe as a long and straight grain boundary, along which four-grain junctions are observed with randomly oriented grains of olivine and pyroxenes. This precursor starts from a pyroxene porphyroclast and extends to an incipient, weakly undulated ultramylonite, where intimate phase mixing arises with asymmetrical grain size distribution. While the finer grain size locates on one side, describing a sharp – but continuous – transition with the host rock, the grain size gradually increases towards the other side, giving rise to a smooth transition. All phases have a very weak lattice preferred orientation (LPO) in the ultramylonite, which strongly differs from the host rock where olivine is highly deformed with evidence of high dislocation densities and a strong LPO. Altogether, these features shed light on the origin of mantle ultramylonites that I attribute to a migrating grain boundary, the sliding of which continuously produces new grains by phase nucleation, probably at the favor of transient four-grain junctions. Nucleated grains then grow and progressively detach from the precursor as it keeps on migrating depending on the dislocation densities in the host rock. Although such an unusual grain boundary remains to be understood in terms of source mechanism, these findings provide new constraints on the appearing and development of ultramylonites.
[1] Fusseis, F., Regenauer-Lieb, K., Liu, J., Hough, R. M. & De Carlo, F. Creep cavitation can establish a dynamic granular fluid pump in ductile shear zones. Nature 459: 974–977 (2009)
[2] Précigout, J., Prigent, C., Palasse, L. & Pochon, A. Water pumping in mantle shear zones. Nat. commun. 8: 15736, https://doi.org/10.1038/ncomms15736 (2017)
[3] White, J. C. Paradoxical pseudotachylyte – Fault melt outside the seismogenic zone. J. Struct. Geol. 38: 11-20 (2012)
How to cite: Précigout, J.: On the Origin of Ultramylonites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3938, https://doi.org/10.5194/egusphere-egu2020-3938, 2020.
EGU2020-3508 | Displays | TS2.3
Processes, properties, and microstructures in faults active at retrograde conditionsAke Fagereng, Christian Stenvall, Matt Ikari, Johann Diener, and Chris Harris
Faults that are active at retrograde conditions tend to contain metastable fault rock assemblages that are prone to undergo fluid-consuming reactions. These reactions typically lead to growth of minerals that are viscously and frictionally weaker than the reactants. This is illustrated in the well-studied Outer Hebrides Fault Zone (OHFZ) of Scotland, and we add observations from the Kuckaus Mylonite Zone (KMZ), Namibia. In both locations, deformation is localised in anastomosing networks of phyllosilicates that developed during deformation of amphibolite and/or granulite assemblages at greenschist facies conditions. Microstructures of these phyllonites show generally well aligned phyllosilicates wrapping around fractured feldspars and quartz with features indicating dislocation creep.
In the KMZ, further localization occurred in ultramylonites within the mylonite zone. These are characterised by a similar phyllosilicate proportion to surrounding mylonites, but lack interconnected phyllosilicate networks. Instead, they contain a very fine-grained assemblage of quartz, feldspar, and phyllosilicate, where both quartz and feldspar lack a CPO. We interpret this assemblage as having deformed through grain-size sensitive creep, at lower shear stress than the surrounding mylonite. It is possible that the ultramylonites developed by dismembering an earlier interconnected weak phase microstructure with increasing finite strain, as has been suggested experimentally by Cross and Skemer (2017).
Whereas these exhumed fault zones deformed at greenschist facies conditions, continued activity would exhume similar fault rocks to shallower depth. We explored frictional properties and microstructure of greenschist facies fault rock at low temperature conditions by deforming chlorite-amphibole-epidote assemblages in single-direct shear at room temperature and 10 MPa normal stress under fluid saturated conditions. As inferred at greater depth, presence of chlorite weakens and promotes aseismic creep along these experimental faults. Presence of chlorite also correlates with the development of striations on fault surfaces. Lack of chlorite, on the other hand, leads to velocity-weakening behaviour and, in epidotite, a fault surface containing very fine grains that do not develop when ≥ 50 % chlorite is present. We suggest that chlorite supresses wear at contact asperities between stronger minerals, and therefore also supresses velocity-weakening behaviour.
Overall, we see that growth of retrograde phyllosilicates lead to profound weakening, strain localisation, and frictional stabilisation of major shear zones, from greenschist facies to near-surface conditions. These processes and properties are, however, reliant on external fluids to allow hydration reactions in otherwise relatively dry host rocks. From scattered syn-deformational quartz veins, in the KMZ, such fluids appear to be of surface origin, whereas in the OHFZ, fluids were likely of a deeper, metamorphic or magmatic origin. Ready incorporation of such fluids into retrograde minerals would prevent substantial or widespread fluid overpressures from developing. These fluid sources are similar to present-day inferred fluid regimes in the Alpine and San Andreas Faults, respectively. We speculate that the variable slip behaviour seen on active retrograde faults relate to their degree of retrogression, and the development of time and strain-dependent microstructures with specific strengths and behaviours.
How to cite: Fagereng, A., Stenvall, C., Ikari, M., Diener, J., and Harris, C.: Processes, properties, and microstructures in faults active at retrograde conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3508, https://doi.org/10.5194/egusphere-egu2020-3508, 2020.
Faults that are active at retrograde conditions tend to contain metastable fault rock assemblages that are prone to undergo fluid-consuming reactions. These reactions typically lead to growth of minerals that are viscously and frictionally weaker than the reactants. This is illustrated in the well-studied Outer Hebrides Fault Zone (OHFZ) of Scotland, and we add observations from the Kuckaus Mylonite Zone (KMZ), Namibia. In both locations, deformation is localised in anastomosing networks of phyllosilicates that developed during deformation of amphibolite and/or granulite assemblages at greenschist facies conditions. Microstructures of these phyllonites show generally well aligned phyllosilicates wrapping around fractured feldspars and quartz with features indicating dislocation creep.
In the KMZ, further localization occurred in ultramylonites within the mylonite zone. These are characterised by a similar phyllosilicate proportion to surrounding mylonites, but lack interconnected phyllosilicate networks. Instead, they contain a very fine-grained assemblage of quartz, feldspar, and phyllosilicate, where both quartz and feldspar lack a CPO. We interpret this assemblage as having deformed through grain-size sensitive creep, at lower shear stress than the surrounding mylonite. It is possible that the ultramylonites developed by dismembering an earlier interconnected weak phase microstructure with increasing finite strain, as has been suggested experimentally by Cross and Skemer (2017).
Whereas these exhumed fault zones deformed at greenschist facies conditions, continued activity would exhume similar fault rocks to shallower depth. We explored frictional properties and microstructure of greenschist facies fault rock at low temperature conditions by deforming chlorite-amphibole-epidote assemblages in single-direct shear at room temperature and 10 MPa normal stress under fluid saturated conditions. As inferred at greater depth, presence of chlorite weakens and promotes aseismic creep along these experimental faults. Presence of chlorite also correlates with the development of striations on fault surfaces. Lack of chlorite, on the other hand, leads to velocity-weakening behaviour and, in epidotite, a fault surface containing very fine grains that do not develop when ≥ 50 % chlorite is present. We suggest that chlorite supresses wear at contact asperities between stronger minerals, and therefore also supresses velocity-weakening behaviour.
Overall, we see that growth of retrograde phyllosilicates lead to profound weakening, strain localisation, and frictional stabilisation of major shear zones, from greenschist facies to near-surface conditions. These processes and properties are, however, reliant on external fluids to allow hydration reactions in otherwise relatively dry host rocks. From scattered syn-deformational quartz veins, in the KMZ, such fluids appear to be of surface origin, whereas in the OHFZ, fluids were likely of a deeper, metamorphic or magmatic origin. Ready incorporation of such fluids into retrograde minerals would prevent substantial or widespread fluid overpressures from developing. These fluid sources are similar to present-day inferred fluid regimes in the Alpine and San Andreas Faults, respectively. We speculate that the variable slip behaviour seen on active retrograde faults relate to their degree of retrogression, and the development of time and strain-dependent microstructures with specific strengths and behaviours.
How to cite: Fagereng, A., Stenvall, C., Ikari, M., Diener, J., and Harris, C.: Processes, properties, and microstructures in faults active at retrograde conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3508, https://doi.org/10.5194/egusphere-egu2020-3508, 2020.
EGU2020-7480 | Displays | TS2.3
Microstructural evolution of amphibolite-eclogite facies quartz veins under low greenschist facies deformation conditionMichel Bestmann, Benjamin Huet, Bernhard Grasemann, and Giorgio Pennacchioni
Quartz veins in poly-metamorphic settings often accommodate the latest deformation state and therefore can provide important information. Identification of microfabric (microstructure and crystallographic preferred orientation, CPO) evolution of quartz during mylonitization, and especially of the grain-scale interplay between brittle and crystal-plastic processes, has different relevant implications: e.g., on understanding the efficiency of fluid mobility through deforming quartz that can dramatically influence the rheology and the degree of chemical exchange. However, in order to interpret the microstructure and the related deformation processes it is necessary to relate these especially to the deformation temperature. Particularly the CPO and the Ti-in-qtz geothermometry is used to constrain the deformation temperature. However, both methods have to be applied with great caution because even when many times used some fundamental processes are not fully understood yet.
Here we present results from deformed quartz veins from the Prijakt Nappe (Autroalpine Unit, Schober Mountains, Central Eastern Alps). These veins localized ductile shear and eventually seismic faulting (recorded by the occurrence of pseudotachylytes) within Eo-Alpine eclogite-facies shists. The veins formed shortly after the eclogitic peak, but the temperature of their deformation remains unconstrained. CL imaging reveals critical details for understanding the role of microfracturing and fluid-rock interaction during initial stages of shear localization, the onset of dynamic recrystallization and the resetting of the Ti-in-quartz geochemistry. Even when optical-light-microscopy and EBSD analysis indicate crystal plastic deformation by subgrain rotation CL and orientation contrast (OC) imaging gives evidence of brittle stage of deformation at least for some of the deformation microstructure. Microshear zones show a bulk dark-CL, but still bright tones in cores of new recrystallized grains similar to the CL signature of the host coarse quartz crystals. CL dark tones also match with the pattern of subgrain boundaries. This reflects fluid permeability pathways along subgrain and grain boundaries (identified by widespread fluid inclusions) and the associated partial resetting of Ti concentrations. The CPO of the new grains within the micro-shear zones rotate with the sense of shear around the kinematic Y-axis and cannot be related to the activity of specific slip systems. In contrast the partial single girdle of c-axis within the ultramylonite with its elongated substructured grains and its characteristic layered microstructure can be related to the activity of several slip systems. Misorientation axis analysis indicates that prism
How to cite: Bestmann, M., Huet, B., Grasemann, B., and Pennacchioni, G.: Microstructural evolution of amphibolite-eclogite facies quartz veins under low greenschist facies deformation condition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7480, https://doi.org/10.5194/egusphere-egu2020-7480, 2020.
Quartz veins in poly-metamorphic settings often accommodate the latest deformation state and therefore can provide important information. Identification of microfabric (microstructure and crystallographic preferred orientation, CPO) evolution of quartz during mylonitization, and especially of the grain-scale interplay between brittle and crystal-plastic processes, has different relevant implications: e.g., on understanding the efficiency of fluid mobility through deforming quartz that can dramatically influence the rheology and the degree of chemical exchange. However, in order to interpret the microstructure and the related deformation processes it is necessary to relate these especially to the deformation temperature. Particularly the CPO and the Ti-in-qtz geothermometry is used to constrain the deformation temperature. However, both methods have to be applied with great caution because even when many times used some fundamental processes are not fully understood yet.
Here we present results from deformed quartz veins from the Prijakt Nappe (Autroalpine Unit, Schober Mountains, Central Eastern Alps). These veins localized ductile shear and eventually seismic faulting (recorded by the occurrence of pseudotachylytes) within Eo-Alpine eclogite-facies shists. The veins formed shortly after the eclogitic peak, but the temperature of their deformation remains unconstrained. CL imaging reveals critical details for understanding the role of microfracturing and fluid-rock interaction during initial stages of shear localization, the onset of dynamic recrystallization and the resetting of the Ti-in-quartz geochemistry. Even when optical-light-microscopy and EBSD analysis indicate crystal plastic deformation by subgrain rotation CL and orientation contrast (OC) imaging gives evidence of brittle stage of deformation at least for some of the deformation microstructure. Microshear zones show a bulk dark-CL, but still bright tones in cores of new recrystallized grains similar to the CL signature of the host coarse quartz crystals. CL dark tones also match with the pattern of subgrain boundaries. This reflects fluid permeability pathways along subgrain and grain boundaries (identified by widespread fluid inclusions) and the associated partial resetting of Ti concentrations. The CPO of the new grains within the micro-shear zones rotate with the sense of shear around the kinematic Y-axis and cannot be related to the activity of specific slip systems. In contrast the partial single girdle of c-axis within the ultramylonite with its elongated substructured grains and its characteristic layered microstructure can be related to the activity of several slip systems. Misorientation axis analysis indicates that prism
How to cite: Bestmann, M., Huet, B., Grasemann, B., and Pennacchioni, G.: Microstructural evolution of amphibolite-eclogite facies quartz veins under low greenschist facies deformation condition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7480, https://doi.org/10.5194/egusphere-egu2020-7480, 2020.
EGU2020-12819 | Displays | TS2.3
The integrated stress-strain analysis of calcite twins: Consistent stress and strain determined from natural dataKei Wakamori and Atsushi Yamaji
Stress and strain are different physical entities. Do the stress and strain determined from e-twins in a sample of polycrystalline calcite have similar principal orientations and similar shape ratios? Köpping et al. (2019) tackled this question by applying Turner’s (1953) classical method of paleostress analysis to natural data. However, despite the assumption of the method, the orientations of P- and T-axes of an e-twin lamella do not have a one-to-one correspondence with the principal orientations of the stress that formed the lamella. And, the method cannot determine a shape ratio. Another difficulty arises when one tackles the question: Natural calcite has usually been subjected to polyphase tectonics with different stress conditions. One has to separate stresses and to evaluate corresponding strains from a sample. Once lamellae are grouped according to the stresses, the strain achieved by the formation of a group of twin lamellae is easily evaluated by the method of Conel (1962) if the total strain represented by a group is small.
The present authors tackled the question by combining Conel’s strain analysis method with a novel method of paleostress analysis of mechanical twins, which clusters the directional data of e-twins by means of a statistical mixture model and determines stresses for each group of data. And, the appropriate number of stresses is determined by means of Bayesian information criterion. The method also determines the probabilities of each lamella to be formed by the stresses, which are called the memberships of the lamella. The strain achieved under a stress condition can be computed using the memberships. We applied this integrated stress-strain analysis method to Data Sets I and II from two calcite veins in a Miocene forearc basin deposit in central Japan. Since the sampling area was close to a triple-trench junction, the young formation has experienced polyphase tectonics.
As a result, we obtained the consistent stress and strains from both of the data sets. Three stresses were obtained from Data Set I, and the corresponding strains were 0.17, 0.25 and 0.13%. Two stresses were obtained from Data Set II, and the strains were 0.39 and 0.42%. The stress and strain determined from the data sets for each deformation phase were consistent with each other. That is, the principal axes had difference as small as < 20 degrees, and the shape ratios of stress and strain had also similar values. It is not straightforward to generalize this result, but both the stress and strain analyses seem to give appropriate results, providing that polyphase deformations are coped with.
How to cite: Wakamori, K. and Yamaji, A.: The integrated stress-strain analysis of calcite twins: Consistent stress and strain determined from natural data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12819, https://doi.org/10.5194/egusphere-egu2020-12819, 2020.
Stress and strain are different physical entities. Do the stress and strain determined from e-twins in a sample of polycrystalline calcite have similar principal orientations and similar shape ratios? Köpping et al. (2019) tackled this question by applying Turner’s (1953) classical method of paleostress analysis to natural data. However, despite the assumption of the method, the orientations of P- and T-axes of an e-twin lamella do not have a one-to-one correspondence with the principal orientations of the stress that formed the lamella. And, the method cannot determine a shape ratio. Another difficulty arises when one tackles the question: Natural calcite has usually been subjected to polyphase tectonics with different stress conditions. One has to separate stresses and to evaluate corresponding strains from a sample. Once lamellae are grouped according to the stresses, the strain achieved by the formation of a group of twin lamellae is easily evaluated by the method of Conel (1962) if the total strain represented by a group is small.
The present authors tackled the question by combining Conel’s strain analysis method with a novel method of paleostress analysis of mechanical twins, which clusters the directional data of e-twins by means of a statistical mixture model and determines stresses for each group of data. And, the appropriate number of stresses is determined by means of Bayesian information criterion. The method also determines the probabilities of each lamella to be formed by the stresses, which are called the memberships of the lamella. The strain achieved under a stress condition can be computed using the memberships. We applied this integrated stress-strain analysis method to Data Sets I and II from two calcite veins in a Miocene forearc basin deposit in central Japan. Since the sampling area was close to a triple-trench junction, the young formation has experienced polyphase tectonics.
As a result, we obtained the consistent stress and strains from both of the data sets. Three stresses were obtained from Data Set I, and the corresponding strains were 0.17, 0.25 and 0.13%. Two stresses were obtained from Data Set II, and the strains were 0.39 and 0.42%. The stress and strain determined from the data sets for each deformation phase were consistent with each other. That is, the principal axes had difference as small as < 20 degrees, and the shape ratios of stress and strain had also similar values. It is not straightforward to generalize this result, but both the stress and strain analyses seem to give appropriate results, providing that polyphase deformations are coped with.
How to cite: Wakamori, K. and Yamaji, A.: The integrated stress-strain analysis of calcite twins: Consistent stress and strain determined from natural data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12819, https://doi.org/10.5194/egusphere-egu2020-12819, 2020.
EGU2020-13523 | Displays | TS2.3
Dissolution precipitation creep as a process for the strain localisation in gabbroAmicia Lee, Holger Stunitz, Matheus Ariel Battisti, and Jiri Konopasek
Strain localisation and fabric development in the lower crust is controlled by the active deformation mechanisms. Understanding the driving forces of such deformation aids in quantifying the stresses and rates of the deformation processes. Here we show that diffusion creep plays a major role in deformation of gabbro lenses at upper amphibolite facies conditions. The Kågen gabbro in the North Norwegian Caledonides intruded the Vaddas Nappe at 439 Ma at pressures of 7-9 kbar, temperatures of 650-900°C (depths of ∼26-34 km). The Kågen gabbro on south Arnøya is made up of undeformed gabbro lenses with sheared margins wrapping around them. This contribution analyses the evolution of the microstructures and fabric of the low strain gabbro to high strain margins. Microstructural and textural data indicate that preferential crystal growth of amphibole grains in the extension direction has produced the deformation microstructure and the CPO. Dissolution precipitation creep is inferred to be the dominant deformation mechanism, where dissolution of the gabbro took place in reacting phases of clinopyroxene and plagioclase, and precipitation took place in the form of new minerals: amphibole, garnet and zoisite. Synchronous deformation and mineral reactions of clinopyroxene suggests mafic rocks can become mechanically weak during the general transformation weakening process, i.e. the interaction of mineral reaction and deformation by diffusion creep. Deformation and metamorphic reaction were both important transformation processes during diffusion creep deformation of the margins of the gabbro lenses. The weakening is directly connected to a transformation process that facilitates diffusion creep deformation of strong minerals (pyroxene, garnet, zoisite) at far lower stresses than dislocation creep. Initially strong lithologies can become weak, provided that reactions can proceed during deformation, the transformation process itself is an important weakening mechanism in mafic (and other) rocks, facilitating deformation at low differential stresses.
How to cite: Lee, A., Stunitz, H., Battisti, M. A., and Konopasek, J.: Dissolution precipitation creep as a process for the strain localisation in gabbro, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13523, https://doi.org/10.5194/egusphere-egu2020-13523, 2020.
Strain localisation and fabric development in the lower crust is controlled by the active deformation mechanisms. Understanding the driving forces of such deformation aids in quantifying the stresses and rates of the deformation processes. Here we show that diffusion creep plays a major role in deformation of gabbro lenses at upper amphibolite facies conditions. The Kågen gabbro in the North Norwegian Caledonides intruded the Vaddas Nappe at 439 Ma at pressures of 7-9 kbar, temperatures of 650-900°C (depths of ∼26-34 km). The Kågen gabbro on south Arnøya is made up of undeformed gabbro lenses with sheared margins wrapping around them. This contribution analyses the evolution of the microstructures and fabric of the low strain gabbro to high strain margins. Microstructural and textural data indicate that preferential crystal growth of amphibole grains in the extension direction has produced the deformation microstructure and the CPO. Dissolution precipitation creep is inferred to be the dominant deformation mechanism, where dissolution of the gabbro took place in reacting phases of clinopyroxene and plagioclase, and precipitation took place in the form of new minerals: amphibole, garnet and zoisite. Synchronous deformation and mineral reactions of clinopyroxene suggests mafic rocks can become mechanically weak during the general transformation weakening process, i.e. the interaction of mineral reaction and deformation by diffusion creep. Deformation and metamorphic reaction were both important transformation processes during diffusion creep deformation of the margins of the gabbro lenses. The weakening is directly connected to a transformation process that facilitates diffusion creep deformation of strong minerals (pyroxene, garnet, zoisite) at far lower stresses than dislocation creep. Initially strong lithologies can become weak, provided that reactions can proceed during deformation, the transformation process itself is an important weakening mechanism in mafic (and other) rocks, facilitating deformation at low differential stresses.
How to cite: Lee, A., Stunitz, H., Battisti, M. A., and Konopasek, J.: Dissolution precipitation creep as a process for the strain localisation in gabbro, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13523, https://doi.org/10.5194/egusphere-egu2020-13523, 2020.
EGU2020-8851 | Displays | TS2.3
Microstructure evolution of plagioclase-hosted Fe-Ti-oxide microinclusions in oceanic gabbroOlga Ageeva, Olga Pilipenko, Alexey Pertsev, and Rainer Abart
Microinclusions of Fe-Ti-oxides in rock-forming plagioclase are protected from subsea-floor alterations by the silicate matrix and are stable carriers of the paleomagnetic record of oceanic gabbros. We studied plagioclase-hosted microinclusions in oceanic gabbro (“gabbro 1241” from the Vema Lithospheric section, Mid-Atlantic ridge, Pertsev et al., 2015) with a complex petrogenetic history. Important events in the gabbro evolution caused consecutive transformations of the micro-inclusions and presumably affected their paleomagnetic records.
The earliest generation of the microinclusions was present as ulvospinel and presumably titanomagnetite which were probably formed by sub-solidus oxidation exsolution of early-magmatic plagioclase (An#42-45). An increase of the anorthite component around the early generation of microinclusions to typical values of late-magmatic plagioclase (An#53) suggest involvement of the late-magmatic fluid accompanying residual melt at 800-900°С (Pertsev et al., 2015). Subsequently, the gabbro was locally affected by hydrothermal alteration at about 600°С as a result of interaction of the gabbro with reduced brine containing 20-21% NaCl. The reducing conditions of this process ensured a “non-oxidative” character and primarily cooling driven exsolution of the microinclusions and transformation of the titanomagnetite microinclusions into ulvospinel-magnetite (“Usp-Mt1”) intergrowths at about 500°С, which is close or higher than the Curie temperature (Tc) of the exsolving titanomagnetite but lower than the Tc of the newly forming Mt1, and the acquired magnetisation may be referred to chemical remanence. The further evolution of the micro-inclusions correlates with low-temperature hydrothermal alteration induced by inflow of seawater-derived fluids during tectonic unroofing of the lithospheric section (Pertsev et al., 2015). The homogeneous ulvospinel inclusions and ulvospinel of the “Usp-Mt1”-inclusions were replaced by “Ilm-Mt2” -aggregates under more oxidizing conditions: 3 Fe2TiO4(Ulv) + 0.5 O2= 3 FeTiO3(Ilm) + Fe3O4(Mt2). The Mt1 was more stable to increase of fO2 that resulted in simultaneous presence of the “Ilm-Mt2”-, “Mt1/Ilm-Mt2“- and “Usp-Mt1” -inclusions with two generations of magnetic phases (magnetite) within a single plagioclase grains.
Thus, despite of protection by silicate matrix the microinclusions of Fe-Ti-oxides in rock-forming plagioclases evolve under the influence of petrogenetic processes. It is important to note that bulk-rock AF demagnetization of 14 specimens (extracted from “gabbro-1241“) in the interval 100-250 Oersted (Oe) and 300-700 Oe revealed both moderately-grouped (k=27.4) and variable (deviated with angle 40-104°) directional components of magnetisation, which may have resulted from the presence of different generations of magnetite. Further magnetic investigation of separates of plagioclase single grains will allow to evaluate capacities of plagioclase-hosted Fe-Ti-micro-inclusions to save initial and “newfound” paleomagnetic information and to serve as stable sources of paleomagnetic record in regions of mid-oceanic ridges.
Funding by RFBR project 18-55-14003 and FWF project I 3998-N29 is acknowledged.
Pertsev, A. N., Aranovich, L. Y., Prokofiev, V. Y., Bortnikov, N. S., Cipriani, A., Simakin, S. S., & Borisovskiy, S. E. (2015). Signatures of residual melts, magmatic and seawater-derived fluids in oceanic lower-crust gabbro from the Vema lithospheric section, Central Atlantic. Journal of Petrology, 56(6), 1069-1088.
How to cite: Ageeva, O., Pilipenko, O., Pertsev, A., and Abart, R.: Microstructure evolution of plagioclase-hosted Fe-Ti-oxide microinclusions in oceanic gabbro, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8851, https://doi.org/10.5194/egusphere-egu2020-8851, 2020.
Microinclusions of Fe-Ti-oxides in rock-forming plagioclase are protected from subsea-floor alterations by the silicate matrix and are stable carriers of the paleomagnetic record of oceanic gabbros. We studied plagioclase-hosted microinclusions in oceanic gabbro (“gabbro 1241” from the Vema Lithospheric section, Mid-Atlantic ridge, Pertsev et al., 2015) with a complex petrogenetic history. Important events in the gabbro evolution caused consecutive transformations of the micro-inclusions and presumably affected their paleomagnetic records.
The earliest generation of the microinclusions was present as ulvospinel and presumably titanomagnetite which were probably formed by sub-solidus oxidation exsolution of early-magmatic plagioclase (An#42-45). An increase of the anorthite component around the early generation of microinclusions to typical values of late-magmatic plagioclase (An#53) suggest involvement of the late-magmatic fluid accompanying residual melt at 800-900°С (Pertsev et al., 2015). Subsequently, the gabbro was locally affected by hydrothermal alteration at about 600°С as a result of interaction of the gabbro with reduced brine containing 20-21% NaCl. The reducing conditions of this process ensured a “non-oxidative” character and primarily cooling driven exsolution of the microinclusions and transformation of the titanomagnetite microinclusions into ulvospinel-magnetite (“Usp-Mt1”) intergrowths at about 500°С, which is close or higher than the Curie temperature (Tc) of the exsolving titanomagnetite but lower than the Tc of the newly forming Mt1, and the acquired magnetisation may be referred to chemical remanence. The further evolution of the micro-inclusions correlates with low-temperature hydrothermal alteration induced by inflow of seawater-derived fluids during tectonic unroofing of the lithospheric section (Pertsev et al., 2015). The homogeneous ulvospinel inclusions and ulvospinel of the “Usp-Mt1”-inclusions were replaced by “Ilm-Mt2” -aggregates under more oxidizing conditions: 3 Fe2TiO4(Ulv) + 0.5 O2= 3 FeTiO3(Ilm) + Fe3O4(Mt2). The Mt1 was more stable to increase of fO2 that resulted in simultaneous presence of the “Ilm-Mt2”-, “Mt1/Ilm-Mt2“- and “Usp-Mt1” -inclusions with two generations of magnetic phases (magnetite) within a single plagioclase grains.
Thus, despite of protection by silicate matrix the microinclusions of Fe-Ti-oxides in rock-forming plagioclases evolve under the influence of petrogenetic processes. It is important to note that bulk-rock AF demagnetization of 14 specimens (extracted from “gabbro-1241“) in the interval 100-250 Oersted (Oe) and 300-700 Oe revealed both moderately-grouped (k=27.4) and variable (deviated with angle 40-104°) directional components of magnetisation, which may have resulted from the presence of different generations of magnetite. Further magnetic investigation of separates of plagioclase single grains will allow to evaluate capacities of plagioclase-hosted Fe-Ti-micro-inclusions to save initial and “newfound” paleomagnetic information and to serve as stable sources of paleomagnetic record in regions of mid-oceanic ridges.
Funding by RFBR project 18-55-14003 and FWF project I 3998-N29 is acknowledged.
Pertsev, A. N., Aranovich, L. Y., Prokofiev, V. Y., Bortnikov, N. S., Cipriani, A., Simakin, S. S., & Borisovskiy, S. E. (2015). Signatures of residual melts, magmatic and seawater-derived fluids in oceanic lower-crust gabbro from the Vema lithospheric section, Central Atlantic. Journal of Petrology, 56(6), 1069-1088.
How to cite: Ageeva, O., Pilipenko, O., Pertsev, A., and Abart, R.: Microstructure evolution of plagioclase-hosted Fe-Ti-oxide microinclusions in oceanic gabbro, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8851, https://doi.org/10.5194/egusphere-egu2020-8851, 2020.
EGU2020-5297 | Displays | TS2.3
A database for the seismic properties of slow spreading mid-ocean ridges gabbrosLuiz F. G. Morales, Maël Allard, and Benoit Ildefonse
Gabbros are the main component of the oceanic crust and represent ~2/3 of the total magmatic crustal thickness. At the interface between magmatic, tectonic and hydrothermal processes, gabbros from slow spreading ridges may have a complex mineralogy and microstructural evolution. This includes structures that vary from purely magmatic fabrics, with layering and magmatic alignment of minerals, to rocks deformed from subsolidus temperatures to the lower-T brittle-ductile conditions. Such a variation is normally accompanied with changes in mineralogy, microstructures and crystallographic preferred orientations (CPO) of the main phases of these rocks, which in turn affect their seismic properties. Here we present a database of the CPO-derived seismic properties of 70 samples collected during the IODP Expedition 360 (site U1473). Initial results show that the dominant phases are plagioclase and clinopyroxene[MOU1] , and different samples may have different contents of olivine, enstatite, magnetite, ilmenite, chlorite and amphibole. Maximum velocities can be either parallel to the strongest concentration of (010) poles of plagioclase or olivine/clinopyroxene [001], depending on the proportions between these phases. Anisotropy of P waves vary from ~5% in the more isotropic gabbros with weak magmatic fabric to a maximum of ~10% in more mylonitic terms. A similar effect is observed for the S-waves. Destructive interference between plagioclase CPO vs. clinopyroxene/olivine reducing anisotropy is possibly observed. This is because the maximum Vp in a foliated gabbro is parallel to the maximum concentration of poles to (010), and perpendicular to olivine and clinopyroxene. As the lineation in our gabbros is generally marked by olivine and clinopyroxene [001] (instead of the fast direction [100]), this possibly cause anisotropy reduction. When present in the more mylonitized gabbros, amphibole has strong CPOs and help to increase the general anisotropy of P and S waves. The elastic constants calculated from these aggregates will be used as input for more physically robust calculations using differential effective medium approaches to better understand the effect of melt inclusions in these rocks by the time of their deformation in the lower crust.
How to cite: Morales, L. F. G., Allard, M., and Ildefonse, B.: A database for the seismic properties of slow spreading mid-ocean ridges gabbros, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5297, https://doi.org/10.5194/egusphere-egu2020-5297, 2020.
Gabbros are the main component of the oceanic crust and represent ~2/3 of the total magmatic crustal thickness. At the interface between magmatic, tectonic and hydrothermal processes, gabbros from slow spreading ridges may have a complex mineralogy and microstructural evolution. This includes structures that vary from purely magmatic fabrics, with layering and magmatic alignment of minerals, to rocks deformed from subsolidus temperatures to the lower-T brittle-ductile conditions. Such a variation is normally accompanied with changes in mineralogy, microstructures and crystallographic preferred orientations (CPO) of the main phases of these rocks, which in turn affect their seismic properties. Here we present a database of the CPO-derived seismic properties of 70 samples collected during the IODP Expedition 360 (site U1473). Initial results show that the dominant phases are plagioclase and clinopyroxene[MOU1] , and different samples may have different contents of olivine, enstatite, magnetite, ilmenite, chlorite and amphibole. Maximum velocities can be either parallel to the strongest concentration of (010) poles of plagioclase or olivine/clinopyroxene [001], depending on the proportions between these phases. Anisotropy of P waves vary from ~5% in the more isotropic gabbros with weak magmatic fabric to a maximum of ~10% in more mylonitic terms. A similar effect is observed for the S-waves. Destructive interference between plagioclase CPO vs. clinopyroxene/olivine reducing anisotropy is possibly observed. This is because the maximum Vp in a foliated gabbro is parallel to the maximum concentration of poles to (010), and perpendicular to olivine and clinopyroxene. As the lineation in our gabbros is generally marked by olivine and clinopyroxene [001] (instead of the fast direction [100]), this possibly cause anisotropy reduction. When present in the more mylonitized gabbros, amphibole has strong CPOs and help to increase the general anisotropy of P and S waves. The elastic constants calculated from these aggregates will be used as input for more physically robust calculations using differential effective medium approaches to better understand the effect of melt inclusions in these rocks by the time of their deformation in the lower crust.
How to cite: Morales, L. F. G., Allard, M., and Ildefonse, B.: A database for the seismic properties of slow spreading mid-ocean ridges gabbros, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5297, https://doi.org/10.5194/egusphere-egu2020-5297, 2020.
EGU2020-10312 | Displays | TS2.3
Strain localization in abyssal peridotites from a magma-starved mid-ocean ridge: a microstructural studyManon Bickert, Mathilde Cannat, Andréa Tommasi, Suzon Jammes, and Luc Lavier
Detachment faults are large offset normal faults that exhume mantle-derived rocks on the seafloor at slow spreading ridges. They are assumed to root at the base of the brittle lithosphere. Magma, if present, can help localize strain at the base of the axial brittle lithosphere by its own presence or crystallization of weaker phases such as plagioclase. This is the case of the Mid-Atlantic Ridge, where ductile shear zones are preferentially formed in and next to magmatic veins (Boschi et al., 2006; Cannat, 1991; Cannat & Casey, 1995; Ceuleneer & Cannat, 1997; Dick et al., 2002; Hansen et al., 2013; Picazo et al., 2012, Schroeder & John, 2004).
Here we focus of a nearly amagmatic case, the eastern part of the Southwest Indian Ridge (SWIR). Partially serpentinized peridotites recovered from dredging on and off axis record variable degrees of a heterogeneous high stress deformation. Orthopyroxene is primarily brittle (kinks, fractures), while olivine displays a wide range of plastic to semi-brittle deformation, ranging from weak to strong with development of extensively recrystallized anastomosing microshear zones. These microshear zones, which are a few mm to cm wide, represent the highest strain localization recorded in these samples. No further evidence of high strain localization, such as high temperature mylonites, has been recovered in this area. The fine-grained microshear zones are preferentially located along orthopyroxene grains or around kinked olivines. Both represent stronger grains (rheological contrast at the grains scale) that produce stress concentrations. Rock-scale thermo-mechanical models using orthopyroxene and olivine flow laws reproduce the observations: ductile shear zones in olivine also initiate preferentially next to brittle orthopyroxene.
We propose that this deformation is linked to the rooting of the detachment faults at depth, where an anastomozed network of microshear zones localizes strain at the base of the lithosphere, allowing the exhumation of variably deformed rocks.
How to cite: Bickert, M., Cannat, M., Tommasi, A., Jammes, S., and Lavier, L.: Strain localization in abyssal peridotites from a magma-starved mid-ocean ridge: a microstructural study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10312, https://doi.org/10.5194/egusphere-egu2020-10312, 2020.
Detachment faults are large offset normal faults that exhume mantle-derived rocks on the seafloor at slow spreading ridges. They are assumed to root at the base of the brittle lithosphere. Magma, if present, can help localize strain at the base of the axial brittle lithosphere by its own presence or crystallization of weaker phases such as plagioclase. This is the case of the Mid-Atlantic Ridge, where ductile shear zones are preferentially formed in and next to magmatic veins (Boschi et al., 2006; Cannat, 1991; Cannat & Casey, 1995; Ceuleneer & Cannat, 1997; Dick et al., 2002; Hansen et al., 2013; Picazo et al., 2012, Schroeder & John, 2004).
Here we focus of a nearly amagmatic case, the eastern part of the Southwest Indian Ridge (SWIR). Partially serpentinized peridotites recovered from dredging on and off axis record variable degrees of a heterogeneous high stress deformation. Orthopyroxene is primarily brittle (kinks, fractures), while olivine displays a wide range of plastic to semi-brittle deformation, ranging from weak to strong with development of extensively recrystallized anastomosing microshear zones. These microshear zones, which are a few mm to cm wide, represent the highest strain localization recorded in these samples. No further evidence of high strain localization, such as high temperature mylonites, has been recovered in this area. The fine-grained microshear zones are preferentially located along orthopyroxene grains or around kinked olivines. Both represent stronger grains (rheological contrast at the grains scale) that produce stress concentrations. Rock-scale thermo-mechanical models using orthopyroxene and olivine flow laws reproduce the observations: ductile shear zones in olivine also initiate preferentially next to brittle orthopyroxene.
We propose that this deformation is linked to the rooting of the detachment faults at depth, where an anastomozed network of microshear zones localizes strain at the base of the lithosphere, allowing the exhumation of variably deformed rocks.
How to cite: Bickert, M., Cannat, M., Tommasi, A., Jammes, S., and Lavier, L.: Strain localization in abyssal peridotites from a magma-starved mid-ocean ridge: a microstructural study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10312, https://doi.org/10.5194/egusphere-egu2020-10312, 2020.
EGU2020-19034 | Displays | TS2.3
Reaction-induced strain localisation in garnet pyroxenites during mantle corner flow: an example from the Ulten Zone (Eastern Alps, N Italy)Stefano Zanchetta, Luca Menegon, Luca Pellegrino, Simone Tumiati, and Nadia Malaspina
In the Ulten Zone (Tonale nappe, Eastern Alps, N Italy), numerous peridotite bodies occur within high-grade crustal rocks. Peridotites show a transition from coarse protogranular spinel-lherzolites to fine-grained mylonitic garnet-amphibole peridotites (Obata and Morten, 1987). Pyroxenites veins and dikes, transposed along the peridotite foliation, show a similar evolution from coarse garnet-free websterites to fine-grained garnet + amphibole clinopyroxenites (Morten and Obata, 1983). This evolution has been interpreted to reflect cooling and pressure increase of pyroxenites and host peridotites from spinel- (1200 °C, 1.3-1.6 GPa) to garnet-facies conditions (850 °C and 2.8 GPa) within the mantle corner flow (Nimis and Morten, 2000).
The newly formed garnet occurs as exsolution within porphyroclastic, high-T pyroxenes, and crystallises along the pyroxenite and peridotite foliation.
Textural evidence and crystallographic orientation data indicate that the transition from spinel- to garnet-facies conditions was assisted by intense shearing and deformation. Pyroxene porphyroclasts in garnet clinopyroxenites show well-developed crystallographic preferred orientation (CPO), high frequency of low-angle misorientations, and non-random distribution of the low-angle misorientation axes. These features indicates that pyroxene porphyroclasts primarily deform by dislocation creep on the (100) [010] slip system. Dislocation creep is accompanied by subgrain rotation recrystallisation, which promotes the formation of new, smaller and equant pyroxene grains around porphyroclasts. The grain size reduction promotes a switch in the deformation mechanism from grain-size insensitive creep (i.e. dislocation creep) in the porphyroclasts to grain-size sensitive (GSS) creep in the small recrystallised grains. The switch from dislocation to GSS creep is accompanied not only by grain size reduction of pyroxenes, but also by the formation of garnet exsolutions in pyroxenes and garnet crystallisation along foliation. We suggest that garnet crystallisation triggers the pinning of the recrystallised matrix, stabilising the fine-grained microtexture for GSS creep process, and finally contributes to the rheological weakening of pyroxenites.
Pyroxenites and peridotites of Ulten Zone thus offer a unique opportunity to investigate the effects of mantle deformation and weakening on the processes that control the material exchange between crust and mantle at subduction zones.
Morten, L., & Obata, M. (1983). Bulletin de Minéralogie, 106(6), 775-780.
Nimis, P. & Morten, L. (2000). Journal of Geodynamics, 30(1-2), 93-115
Obata, M., & Morten, L. (1987). Journal of Petrology, 28(3), 599-623.
How to cite: Zanchetta, S., Menegon, L., Pellegrino, L., Tumiati, S., and Malaspina, N.: Reaction-induced strain localisation in garnet pyroxenites during mantle corner flow: an example from the Ulten Zone (Eastern Alps, N Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19034, https://doi.org/10.5194/egusphere-egu2020-19034, 2020.
In the Ulten Zone (Tonale nappe, Eastern Alps, N Italy), numerous peridotite bodies occur within high-grade crustal rocks. Peridotites show a transition from coarse protogranular spinel-lherzolites to fine-grained mylonitic garnet-amphibole peridotites (Obata and Morten, 1987). Pyroxenites veins and dikes, transposed along the peridotite foliation, show a similar evolution from coarse garnet-free websterites to fine-grained garnet + amphibole clinopyroxenites (Morten and Obata, 1983). This evolution has been interpreted to reflect cooling and pressure increase of pyroxenites and host peridotites from spinel- (1200 °C, 1.3-1.6 GPa) to garnet-facies conditions (850 °C and 2.8 GPa) within the mantle corner flow (Nimis and Morten, 2000).
The newly formed garnet occurs as exsolution within porphyroclastic, high-T pyroxenes, and crystallises along the pyroxenite and peridotite foliation.
Textural evidence and crystallographic orientation data indicate that the transition from spinel- to garnet-facies conditions was assisted by intense shearing and deformation. Pyroxene porphyroclasts in garnet clinopyroxenites show well-developed crystallographic preferred orientation (CPO), high frequency of low-angle misorientations, and non-random distribution of the low-angle misorientation axes. These features indicates that pyroxene porphyroclasts primarily deform by dislocation creep on the (100) [010] slip system. Dislocation creep is accompanied by subgrain rotation recrystallisation, which promotes the formation of new, smaller and equant pyroxene grains around porphyroclasts. The grain size reduction promotes a switch in the deformation mechanism from grain-size insensitive creep (i.e. dislocation creep) in the porphyroclasts to grain-size sensitive (GSS) creep in the small recrystallised grains. The switch from dislocation to GSS creep is accompanied not only by grain size reduction of pyroxenes, but also by the formation of garnet exsolutions in pyroxenes and garnet crystallisation along foliation. We suggest that garnet crystallisation triggers the pinning of the recrystallised matrix, stabilising the fine-grained microtexture for GSS creep process, and finally contributes to the rheological weakening of pyroxenites.
Pyroxenites and peridotites of Ulten Zone thus offer a unique opportunity to investigate the effects of mantle deformation and weakening on the processes that control the material exchange between crust and mantle at subduction zones.
Morten, L., & Obata, M. (1983). Bulletin de Minéralogie, 106(6), 775-780.
Nimis, P. & Morten, L. (2000). Journal of Geodynamics, 30(1-2), 93-115
Obata, M., & Morten, L. (1987). Journal of Petrology, 28(3), 599-623.
How to cite: Zanchetta, S., Menegon, L., Pellegrino, L., Tumiati, S., and Malaspina, N.: Reaction-induced strain localisation in garnet pyroxenites during mantle corner flow: an example from the Ulten Zone (Eastern Alps, N Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19034, https://doi.org/10.5194/egusphere-egu2020-19034, 2020.
EGU2020-18346 | Displays | TS2.3
Pressure dependence of olivine grain growth at upper mantle conditionsFilippe Ferreira, Marcel Thielmann, and Katharina Marquardt
The convective motion of Earth’s upper mantle is controlled by two main deformation mechanisms: grain size-insensitive dislocation creep and grain size sensitive diffusion creep. Grain size thus plays a key role in upper mantle deformation, as it has a significant impact on the viscosity of the upper mantle. Moreover, grain size also affects seismic velocities as well as seismic attenuation.
Despite the importance of grain size and its evolution during deformation, there is still a lack of experimental data on grain growth of olivine at upper mantle pressures. For this reason, we here investigate olivine grain growth at pressures ranging from 1 GPa to 12 GPa and temperatures from 1200 to 1400ºC. The experiments were done using piston cylinder and multi-anvil apparatuses. We used as a starting material olivine aggregates with small amounts of pyroxene (<10%) produced via sol-gel method.
Our results indicate that grain growth is reduced at increasing pressures. This suggests that the enhanced grain growth due to the temperature increase with depth may be offset, thus facilitating a change from dislocation to diffusion creep in the deep upper mantle. This might have an important impact on the dynamics of the upper mantle.
How to cite: Ferreira, F., Thielmann, M., and Marquardt, K.: Pressure dependence of olivine grain growth at upper mantle conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18346, https://doi.org/10.5194/egusphere-egu2020-18346, 2020.
The convective motion of Earth’s upper mantle is controlled by two main deformation mechanisms: grain size-insensitive dislocation creep and grain size sensitive diffusion creep. Grain size thus plays a key role in upper mantle deformation, as it has a significant impact on the viscosity of the upper mantle. Moreover, grain size also affects seismic velocities as well as seismic attenuation.
Despite the importance of grain size and its evolution during deformation, there is still a lack of experimental data on grain growth of olivine at upper mantle pressures. For this reason, we here investigate olivine grain growth at pressures ranging from 1 GPa to 12 GPa and temperatures from 1200 to 1400ºC. The experiments were done using piston cylinder and multi-anvil apparatuses. We used as a starting material olivine aggregates with small amounts of pyroxene (<10%) produced via sol-gel method.
Our results indicate that grain growth is reduced at increasing pressures. This suggests that the enhanced grain growth due to the temperature increase with depth may be offset, thus facilitating a change from dislocation to diffusion creep in the deep upper mantle. This might have an important impact on the dynamics of the upper mantle.
How to cite: Ferreira, F., Thielmann, M., and Marquardt, K.: Pressure dependence of olivine grain growth at upper mantle conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18346, https://doi.org/10.5194/egusphere-egu2020-18346, 2020.
EGU2020-9859 | Displays | TS2.3
The solid medium deformation apparatus – reloadedRenée Heilbronner, Holger Stunitz, Jacques Précigout, and Hugues Raimbourg
Rock deformation experiments are used to compile mechanical data sets for minerals and rocks and to study microstructure and texture development.
The Griggs apparatus, a solid medium piston cylinder machine was designed about 60 years ago to investigate rock deformation mechanisms and rheology at elevated confining pressures. In a typical experiment today, the confining medium is NaCl, with confining pressures up to 3 GPa, temperatures up to 1100°C, and displacement rates between 10-8 and 10-2 ms-1 (equivalent to strain rates of 10-7 to 10-3 s-1). In axial tests, the cylindrical samples are 12 to 15 mm long with a diameter of 0.625 mm. In shearing test, split cylinder assemblies are used with 0.5 to 1 mm thick samples introduced along the 45° pre-cut. Reasonable total strains are limited to 30% axial shortening or shear strains of gamma 4. (Higher strains can be attained but are difficult to analyse mechanically. Unlike for gas rigs, torsion is not available for solid medium machines).
As of now, the operational fleet of solid medium deformation apparatus comprises worldwide over 20 machines in different labs (mainly in Europe, U.S.A. and Japan), providing the scientific community with an ever-growing rheological and microstructural data base.
In view of numerous developments in experimental design, as well as improvements of hardware and software for data acquisition and processing, the experimental community was recently invited to a two-day workshop, hosted by the experimental group of Orléans University. The main goal was to discuss the following points:
- how to further improve the apparatus, increase its scope and improve calibrations;
- how to further improve data processing, and the precision and reliability of the results;
- how to maintain consistency among the labs and through time (backwards compatibility);
- how ensure compatibility of results from axial and shearing experiments;
- how to make the data available to the community.
The poster represents a condensed report of the meeting highlighting a few issues of special interest to the structural community. Visitors to the poster are invited to share their thoughts and to give us feed-back.
How to cite: Heilbronner, R., Stunitz, H., Précigout, J., and Raimbourg, H.: The solid medium deformation apparatus – reloaded, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9859, https://doi.org/10.5194/egusphere-egu2020-9859, 2020.
Rock deformation experiments are used to compile mechanical data sets for minerals and rocks and to study microstructure and texture development.
The Griggs apparatus, a solid medium piston cylinder machine was designed about 60 years ago to investigate rock deformation mechanisms and rheology at elevated confining pressures. In a typical experiment today, the confining medium is NaCl, with confining pressures up to 3 GPa, temperatures up to 1100°C, and displacement rates between 10-8 and 10-2 ms-1 (equivalent to strain rates of 10-7 to 10-3 s-1). In axial tests, the cylindrical samples are 12 to 15 mm long with a diameter of 0.625 mm. In shearing test, split cylinder assemblies are used with 0.5 to 1 mm thick samples introduced along the 45° pre-cut. Reasonable total strains are limited to 30% axial shortening or shear strains of gamma 4. (Higher strains can be attained but are difficult to analyse mechanically. Unlike for gas rigs, torsion is not available for solid medium machines).
As of now, the operational fleet of solid medium deformation apparatus comprises worldwide over 20 machines in different labs (mainly in Europe, U.S.A. and Japan), providing the scientific community with an ever-growing rheological and microstructural data base.
In view of numerous developments in experimental design, as well as improvements of hardware and software for data acquisition and processing, the experimental community was recently invited to a two-day workshop, hosted by the experimental group of Orléans University. The main goal was to discuss the following points:
- how to further improve the apparatus, increase its scope and improve calibrations;
- how to further improve data processing, and the precision and reliability of the results;
- how to maintain consistency among the labs and through time (backwards compatibility);
- how ensure compatibility of results from axial and shearing experiments;
- how to make the data available to the community.
The poster represents a condensed report of the meeting highlighting a few issues of special interest to the structural community. Visitors to the poster are invited to share their thoughts and to give us feed-back.
How to cite: Heilbronner, R., Stunitz, H., Précigout, J., and Raimbourg, H.: The solid medium deformation apparatus – reloaded, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9859, https://doi.org/10.5194/egusphere-egu2020-9859, 2020.
EGU2020-5595 | Displays | TS2.3
Effect of confining pressure on the strength of wet quartzite revisitedLucille Nègre, Holger Stünitz, Hugues Raimbourg, Jacques Précigout, Petr Jeřábek, and Petar Pongrac
The ability of water to enhance plastic deformation of a quartz aggregate has been experimentally demonstrated during the sixties (e.g. Griggs and Blacic 1965), however the processes involved are still questioned. Notably the processes combining the effect of water and pressure during the deformation are still not completely understood. Pressure strongly influences the strength of fine-grained (3.6 - 4.9 µm) wet quartz aggregates (Kronenberg and Tullis 1984), where diffusion creep operates (Fukuda et al. 2018) but its effect on coarser-grained material expected to deform only by dislocation creep is not well constrained. To re-assess the effect of pressure on quartz crystal plastic deformation, natural wet quartzite samples from the Tana quarry in northern Norway (grain size ≈ 150 µm) have been deformed using a Griggs-type apparatus at varying confining pressures (from 0.6 to 2.0 GPa). All the samples with 0.1 wt. % H2O added were shortened coaxially up to 30% strain at constant strain rate (≈10-6 s-1) and temperature (900°C).
All mechanical records show that quartzite flow stresses decrease systematically with increasing pressure. These results allow to determine the strength of quartzite as a function of water fugacity, such as introduced in the flow law by Kohlstedt et al. (1995) to account for both pressure and water effects. In our case, the fugacity coefficient is m≈1 when using a stress exponent of n=2.
Microstructure and image analyses of samples reveal that the bulk strain results mainly from crystal plastic deformation of original grains whereas the recrystallization processes are limited volumetrically (less than 5%) and restricted to the boundaries of original grains. Deformation is not strongly partitioned into recrystallized domains compared to flattened original grains. Optical and SEM-cathodoluminescence images revealed the presence of cracks in conjunction with recrystallization (even for high-pressure samples) and associated chemical/fluid interaction, but the cracks do not contribute significantly to the bulk strain of the samples.
In order to determine the amount of water used for the deformation and the redistribution of H2O during deformation, the H2O content of the quartzite has been calculated from FTIR (Fourier Transform InfraRed spectroscopy) measurements for both, grain interiors and grain boundaries. The H2O concentrations decrease inside grains with the onset of deformation with respect to the starting material. H2O is primarily stored in the grain boundary region. There is no systematic correlation with pressure. Thus, pressure dependence of H2O weakening is not restricted to fine-grained materials at high pressure and temperature. Deformation redistributes water from the grain interiors to their grain boundaries.
References:
Fukuda, J., Holyoke III, C.W., and Kronenberg, A.K. (2018). J. Geophysical Res.: Solid Earth, 123(6), 4676-4696.
Griggs, D. T., and Blacic J. D. (1965). Science, 147(3655), 292‑295.
Kohlstedt, D. L., Evans B., and Mackwell S. J. (1995). J. Geophysical Res.: Solid Earth, 100(B9), 17587-17602.
Kronenberg, A. K., and Tullis J. (1984). J. Geophysical Res.: Solid Earth, 89(B6), 4281‑4297.
How to cite: Nègre, L., Stünitz, H., Raimbourg, H., Précigout, J., Jeřábek, P., and Pongrac, P.: Effect of confining pressure on the strength of wet quartzite revisited, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5595, https://doi.org/10.5194/egusphere-egu2020-5595, 2020.
The ability of water to enhance plastic deformation of a quartz aggregate has been experimentally demonstrated during the sixties (e.g. Griggs and Blacic 1965), however the processes involved are still questioned. Notably the processes combining the effect of water and pressure during the deformation are still not completely understood. Pressure strongly influences the strength of fine-grained (3.6 - 4.9 µm) wet quartz aggregates (Kronenberg and Tullis 1984), where diffusion creep operates (Fukuda et al. 2018) but its effect on coarser-grained material expected to deform only by dislocation creep is not well constrained. To re-assess the effect of pressure on quartz crystal plastic deformation, natural wet quartzite samples from the Tana quarry in northern Norway (grain size ≈ 150 µm) have been deformed using a Griggs-type apparatus at varying confining pressures (from 0.6 to 2.0 GPa). All the samples with 0.1 wt. % H2O added were shortened coaxially up to 30% strain at constant strain rate (≈10-6 s-1) and temperature (900°C).
All mechanical records show that quartzite flow stresses decrease systematically with increasing pressure. These results allow to determine the strength of quartzite as a function of water fugacity, such as introduced in the flow law by Kohlstedt et al. (1995) to account for both pressure and water effects. In our case, the fugacity coefficient is m≈1 when using a stress exponent of n=2.
Microstructure and image analyses of samples reveal that the bulk strain results mainly from crystal plastic deformation of original grains whereas the recrystallization processes are limited volumetrically (less than 5%) and restricted to the boundaries of original grains. Deformation is not strongly partitioned into recrystallized domains compared to flattened original grains. Optical and SEM-cathodoluminescence images revealed the presence of cracks in conjunction with recrystallization (even for high-pressure samples) and associated chemical/fluid interaction, but the cracks do not contribute significantly to the bulk strain of the samples.
In order to determine the amount of water used for the deformation and the redistribution of H2O during deformation, the H2O content of the quartzite has been calculated from FTIR (Fourier Transform InfraRed spectroscopy) measurements for both, grain interiors and grain boundaries. The H2O concentrations decrease inside grains with the onset of deformation with respect to the starting material. H2O is primarily stored in the grain boundary region. There is no systematic correlation with pressure. Thus, pressure dependence of H2O weakening is not restricted to fine-grained materials at high pressure and temperature. Deformation redistributes water from the grain interiors to their grain boundaries.
References:
Fukuda, J., Holyoke III, C.W., and Kronenberg, A.K. (2018). J. Geophysical Res.: Solid Earth, 123(6), 4676-4696.
Griggs, D. T., and Blacic J. D. (1965). Science, 147(3655), 292‑295.
Kohlstedt, D. L., Evans B., and Mackwell S. J. (1995). J. Geophysical Res.: Solid Earth, 100(B9), 17587-17602.
Kronenberg, A. K., and Tullis J. (1984). J. Geophysical Res.: Solid Earth, 89(B6), 4281‑4297.
How to cite: Nègre, L., Stünitz, H., Raimbourg, H., Précigout, J., Jeřábek, P., and Pongrac, P.: Effect of confining pressure on the strength of wet quartzite revisited, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5595, https://doi.org/10.5194/egusphere-egu2020-5595, 2020.
EGU2020-13172 | Displays | TS2.3
Behaviour of wet quartzite: deformation experiments revisitedPetar Pongrac, Petr Jeřábek, Holger Stünitz, Hugues Raimbourg, Lucille Nègre, and Jacques Précigout
Since quartz is among the most abundant minerals in continental crust and one of the first to show plasticity with increasing pressure and temperature, understanding its mechanical behavior is crucial for estimates on crustal strength and modeling of geodynamic processes. Since discovery of significantly lower mechanical strength of quartz as a consequence of H2O presence in the crystal (Griggs & Blacic, 1965), remarkable amount of work has been done in order to improve knowledge about processes and mechanisms responsible for so called H2O weakening effect. As the weakening effect depends on molecular H2O, it is a disequilibrium weakening process that is difficult to incorporate into existing flaw laws.
In order to estimate mechanical behavior of quartz in presence of H2O, we performed deformation experiments in solid-medium Griggs-type apparatus in coaxial setting under controlled laboratory conditions using very pure natural quartzite from Tana quarry in northern Norway. Behavior of as-is and 0.1 wt% H2O added samples was studied in 1) eight shortening experiments at 900 °C, 1 GPa and constant strain rate of 10-6 s-1 reaching 5% and 30% strain, 2) six strain rate stepping experiments covering 10-5, 10-6 and 10-7 s-1, 3) two temperature stepping experiments covering 750, 850 and 950 °C and 4) one hot-pressing experiment maintaining the starting experimental conditions for 14 hours.
There is a negligible strength difference between the as-is and H2O added samples. Both H2O added and as-is strain rate steeping experiments had shown surprisingly low stress exponent, with the highest value of 2.26. Temperature stepping experiments gave activation energy values of 177 kJ/mol and 198 kJ/mol. In all studied samples, strain increases towards the sample centers exhibiting grain size decrease from initial 250 – 300 µm. Three principal deformation mechanisms contributing to the bulk strain were identified: 1) crystal plasticity of original grains manifested by flattening, undulatory extinction, and development of subgrains, 2) cracking of original grains demonstrated by fluid inclusion trails and minor grain offset and 3) dynamic recrystallization via subgrain rotation recrystallization indicated by misorientation analysis from EBSD data. FTIR spectroscopy was applied to evaluate H2O speciation, quantity and distribution. Regardless of added H2O, most of deformed original grains showed relative H2O concentration between 0 and 400 H/106Si, implying significant decrease of H2O content from original 600 to 2000 H/106Si measured in undeformed grains. Average H2O concentration in grain boundaries showed 750 H/106Si for as-is samples and 1300 H/106Si for H2O added. Plasticity is most visible in CL-images, as well as higher degree of grain fragmentation and crack density in samples with added H2O. Ubiquitous presence of fluid along the grain boundaries, demonstrated by FTIR results, may have facilitated sliding along grain boundaries which, in turn, could explain the low stress exponent derived from strain rate stepping experiments.
REFERENCES:
Griggs, D. T. & Blacic, J. D. (1965): Quartz: Anomalous Weakness of Synthetic Crystals. Science 147(3655):292-95.
How to cite: Pongrac, P., Jeřábek, P., Stünitz, H., Raimbourg, H., Nègre, L., and Précigout, J.: Behaviour of wet quartzite: deformation experiments revisited, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13172, https://doi.org/10.5194/egusphere-egu2020-13172, 2020.
Since quartz is among the most abundant minerals in continental crust and one of the first to show plasticity with increasing pressure and temperature, understanding its mechanical behavior is crucial for estimates on crustal strength and modeling of geodynamic processes. Since discovery of significantly lower mechanical strength of quartz as a consequence of H2O presence in the crystal (Griggs & Blacic, 1965), remarkable amount of work has been done in order to improve knowledge about processes and mechanisms responsible for so called H2O weakening effect. As the weakening effect depends on molecular H2O, it is a disequilibrium weakening process that is difficult to incorporate into existing flaw laws.
In order to estimate mechanical behavior of quartz in presence of H2O, we performed deformation experiments in solid-medium Griggs-type apparatus in coaxial setting under controlled laboratory conditions using very pure natural quartzite from Tana quarry in northern Norway. Behavior of as-is and 0.1 wt% H2O added samples was studied in 1) eight shortening experiments at 900 °C, 1 GPa and constant strain rate of 10-6 s-1 reaching 5% and 30% strain, 2) six strain rate stepping experiments covering 10-5, 10-6 and 10-7 s-1, 3) two temperature stepping experiments covering 750, 850 and 950 °C and 4) one hot-pressing experiment maintaining the starting experimental conditions for 14 hours.
There is a negligible strength difference between the as-is and H2O added samples. Both H2O added and as-is strain rate steeping experiments had shown surprisingly low stress exponent, with the highest value of 2.26. Temperature stepping experiments gave activation energy values of 177 kJ/mol and 198 kJ/mol. In all studied samples, strain increases towards the sample centers exhibiting grain size decrease from initial 250 – 300 µm. Three principal deformation mechanisms contributing to the bulk strain were identified: 1) crystal plasticity of original grains manifested by flattening, undulatory extinction, and development of subgrains, 2) cracking of original grains demonstrated by fluid inclusion trails and minor grain offset and 3) dynamic recrystallization via subgrain rotation recrystallization indicated by misorientation analysis from EBSD data. FTIR spectroscopy was applied to evaluate H2O speciation, quantity and distribution. Regardless of added H2O, most of deformed original grains showed relative H2O concentration between 0 and 400 H/106Si, implying significant decrease of H2O content from original 600 to 2000 H/106Si measured in undeformed grains. Average H2O concentration in grain boundaries showed 750 H/106Si for as-is samples and 1300 H/106Si for H2O added. Plasticity is most visible in CL-images, as well as higher degree of grain fragmentation and crack density in samples with added H2O. Ubiquitous presence of fluid along the grain boundaries, demonstrated by FTIR results, may have facilitated sliding along grain boundaries which, in turn, could explain the low stress exponent derived from strain rate stepping experiments.
REFERENCES:
Griggs, D. T. & Blacic, J. D. (1965): Quartz: Anomalous Weakness of Synthetic Crystals. Science 147(3655):292-95.
How to cite: Pongrac, P., Jeřábek, P., Stünitz, H., Raimbourg, H., Nègre, L., and Précigout, J.: Behaviour of wet quartzite: deformation experiments revisited, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13172, https://doi.org/10.5194/egusphere-egu2020-13172, 2020.
EGU2020-8179 | Displays | TS2.3
The effect of garnet and muscovite on the recrystallized grain size of quartz from general shear experimentsLeif Tokle, Greg Hirth, Luiz Morales, and Holger Stunitz
To investigate the role of strong and weak secondary phases on the recrystallized grain size of quartz, we performed grain size analyses on quenched samples from general shear experiments on quartz-garnet and quartz-muscovite mixtures. Six general shear experiments were conducted in the Griggs apparatus; three with mixtures of quartz-garnet (vol.% garnet 5, 15, 30) and three with mixtures of quartz-muscovite (vol.% muscovite 5, 10, 25). The starting powders for both set of experiments were synthetic mixtures of quartz-muscovite or quartz-garnet with 0.1 wt.% water added. The quartz-garnet experiments were conducted at 900°C, a pressure of 1.2 GPa, and a shear strain rate of ~10-5 s-1, while the quartz-muscovite experiments were conducted at 800°C, a pressure of 1.5 GPa, and a shear strain rate of ~10-5 s-1. At these deformation conditions quartz is stronger than muscovite and weaker than garnet. We observed that the bulk strength of the aggregate decreases with a greater volume percent of muscovite and increases with a greater volume percent of garnet. Garnet at these conditions does not deform plastically. The presence of secondary phases within the deforming aggregate causes stress concentrations and partitioning of strain rate between the different phases relative to the measured bulk stress and strain rate. The degree of partitioning is primarily related to the rheology and volume percent of the phases. Due to the piezometric relationship between recrystallized grain size and stress, we can use the quartz recrystallized grain size to determine the local stress of quartz in the experiments and compare it to the measured bulk stress. The results from these analyses will provide new insight into the effect of strain partitioning in general and of strong and weak secondary phases on quartz rheology.
How to cite: Tokle, L., Hirth, G., Morales, L., and Stunitz, H.: The effect of garnet and muscovite on the recrystallized grain size of quartz from general shear experiments , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8179, https://doi.org/10.5194/egusphere-egu2020-8179, 2020.
To investigate the role of strong and weak secondary phases on the recrystallized grain size of quartz, we performed grain size analyses on quenched samples from general shear experiments on quartz-garnet and quartz-muscovite mixtures. Six general shear experiments were conducted in the Griggs apparatus; three with mixtures of quartz-garnet (vol.% garnet 5, 15, 30) and three with mixtures of quartz-muscovite (vol.% muscovite 5, 10, 25). The starting powders for both set of experiments were synthetic mixtures of quartz-muscovite or quartz-garnet with 0.1 wt.% water added. The quartz-garnet experiments were conducted at 900°C, a pressure of 1.2 GPa, and a shear strain rate of ~10-5 s-1, while the quartz-muscovite experiments were conducted at 800°C, a pressure of 1.5 GPa, and a shear strain rate of ~10-5 s-1. At these deformation conditions quartz is stronger than muscovite and weaker than garnet. We observed that the bulk strength of the aggregate decreases with a greater volume percent of muscovite and increases with a greater volume percent of garnet. Garnet at these conditions does not deform plastically. The presence of secondary phases within the deforming aggregate causes stress concentrations and partitioning of strain rate between the different phases relative to the measured bulk stress and strain rate. The degree of partitioning is primarily related to the rheology and volume percent of the phases. Due to the piezometric relationship between recrystallized grain size and stress, we can use the quartz recrystallized grain size to determine the local stress of quartz in the experiments and compare it to the measured bulk stress. The results from these analyses will provide new insight into the effect of strain partitioning in general and of strong and weak secondary phases on quartz rheology.
How to cite: Tokle, L., Hirth, G., Morales, L., and Stunitz, H.: The effect of garnet and muscovite on the recrystallized grain size of quartz from general shear experiments , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8179, https://doi.org/10.5194/egusphere-egu2020-8179, 2020.
EGU2020-14067 | Displays | TS2.3
Do local kinematics have an effect on the recrystallized grain size piezometer?Rüdiger Kilian and Michael Stipp
The quartz recrystallized grain size piezometer was determined by axial shortening experiments on Black Hills quartzite in Griggs type triaxial deformation apparatus (Stipp & Tullis, 2003). The analysis of general shear experiments on Black Hills quartzite (Heilbronner & Kilian, 2017) reveal a striking discrepancy between both experimental setups; at a given differential stress, recrystallized grains are much larger in the general shear experiments than in axial shortening.
A major difference between both sets of experiments is, that the finite grain volume of quartz in the general shear experiments almost entirely consists of recrystallized grains while the here investigated axial shortening experiments have fractions of recrystallized grains in the range of 15 to 30% in the high stress experiments and up to 60% in the low stress experiments. Quartz in the general shear experiments developed a moderate to strong crystallographic preferred orientation (CPO) while, apart from a Dauphiné-induced ordering of poles to {10-11} and {01-11}, no overall significant CPO developed in the axial shortening experiments.
Based on the analysis of the EBSD data of Cross et al. (2017), we observed that the dispersion axes of large quartz grains in the axial shortening experiments correspond to the global kinematic reference frame. The dispersion axes of the fraction of small, recrystallized grains depend on the local kinematics between the porphyroclasts. Slip transparency indicates that boundaries between the largest grains are rather hard while recrystallized grains can accommodate strain induced by crystal plastic slip more effectively and homogeneously.
These results suggest that recrystallized grains in the axial shortening experiments, at least in those with low fractions of recrystallized grains, correspond to a material deforming at a rate higher than the imposed shortening rate while the axial load is predominantly supported by the porphyroclasts. In contrast, recrystallized grains in general shear experiments deform at the imposed (global) rate and derived stresses correspond on average to the deforming zone. Due to strain and strain rate inhomogeneities in the latter experiments, however, there is a systematic variation in recrystallized grain size across the general shear zone. We compare these local microstructural variations and discuss their significance for the recrystallized grain size piezometer calibration.
How to cite: Kilian, R. and Stipp, M.: Do local kinematics have an effect on the recrystallized grain size piezometer?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14067, https://doi.org/10.5194/egusphere-egu2020-14067, 2020.
The quartz recrystallized grain size piezometer was determined by axial shortening experiments on Black Hills quartzite in Griggs type triaxial deformation apparatus (Stipp & Tullis, 2003). The analysis of general shear experiments on Black Hills quartzite (Heilbronner & Kilian, 2017) reveal a striking discrepancy between both experimental setups; at a given differential stress, recrystallized grains are much larger in the general shear experiments than in axial shortening.
A major difference between both sets of experiments is, that the finite grain volume of quartz in the general shear experiments almost entirely consists of recrystallized grains while the here investigated axial shortening experiments have fractions of recrystallized grains in the range of 15 to 30% in the high stress experiments and up to 60% in the low stress experiments. Quartz in the general shear experiments developed a moderate to strong crystallographic preferred orientation (CPO) while, apart from a Dauphiné-induced ordering of poles to {10-11} and {01-11}, no overall significant CPO developed in the axial shortening experiments.
Based on the analysis of the EBSD data of Cross et al. (2017), we observed that the dispersion axes of large quartz grains in the axial shortening experiments correspond to the global kinematic reference frame. The dispersion axes of the fraction of small, recrystallized grains depend on the local kinematics between the porphyroclasts. Slip transparency indicates that boundaries between the largest grains are rather hard while recrystallized grains can accommodate strain induced by crystal plastic slip more effectively and homogeneously.
These results suggest that recrystallized grains in the axial shortening experiments, at least in those with low fractions of recrystallized grains, correspond to a material deforming at a rate higher than the imposed shortening rate while the axial load is predominantly supported by the porphyroclasts. In contrast, recrystallized grains in general shear experiments deform at the imposed (global) rate and derived stresses correspond on average to the deforming zone. Due to strain and strain rate inhomogeneities in the latter experiments, however, there is a systematic variation in recrystallized grain size across the general shear zone. We compare these local microstructural variations and discuss their significance for the recrystallized grain size piezometer calibration.
How to cite: Kilian, R. and Stipp, M.: Do local kinematics have an effect on the recrystallized grain size piezometer?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14067, https://doi.org/10.5194/egusphere-egu2020-14067, 2020.
EGU2020-8629 | Displays | TS2.3
HP/HT deformation experiments of garnet-omphacite aggregates – influence of volume fractions on deformation mechanisms.Stefanie Klackl, Katrin Kraus, Jörg Renner, Bernhard Grasemann, and Anna Rogowitz
Forming in oceanic and continental subduction zones during high to ultra-high-pressure metamorphism, eclogites play an important role in convergent settings. To improve our understanding of eclogite deformation behaviour with respect to its phase abundance of omphacite and garnet, synthetic eclogite samples containing 25, 50 and 75% volume fraction of garnet have been deformed in a modified Griggs-type solid-medium apparatus. Deformation conditions were set to a confining pressure of 2.5 GPa, 900 °C and 3*10-6 s-1. Detailed microstructure analysis via optical and electron microscope imaging (SE, BSE and EBSD) served for identification of the dominant active deformation mechanism.
All eclogite samples show a foliation which is defined by a shape preferred orientation (SPO) of omphacite and intercalated foliation sub-parallel garnet aggregates. Another common feature is a weak crystallographic preferred orientation (CPO) of omphacite which is present throughout all samples. In accordance to uniaxial shortening the CPO resembles an s-type texture with a point maximum of [001] axis parallel to the foliation and a maximum of [010] axis perpendicular to the foliation. The stereographic projection of garnet crystallographic orientation is almost distributed randomly. Nevertheless, both phases show an intracrystalline misorientation, indicating activation of crystal plastic processes. With increasing garnet content the grain average misorientation is increasing in both omphacite and garnet crystals. On the other hand, deformation twinning in omphacite is decreasing with increasing garnet content. Further, all samples show indication of brittle deformation of both garnet and omphacite, increasing with increasing garnet content. In samples with a 25% volume fraction of garnet micro-cracks are primarily orientated perpendicular to the foliation, getting more randomly distributed in samples with a 50 and 75% volume fraction of garnet.
In conclusion, all samples show similar microstructures and textures indicating that similar mechanism are active during deformation. However, the overall dominant deformation behaviour is switching from crystal plastic to brittle with increasing garnet content.
How to cite: Klackl, S., Kraus, K., Renner, J., Grasemann, B., and Rogowitz, A.: HP/HT deformation experiments of garnet-omphacite aggregates – influence of volume fractions on deformation mechanisms., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8629, https://doi.org/10.5194/egusphere-egu2020-8629, 2020.
Forming in oceanic and continental subduction zones during high to ultra-high-pressure metamorphism, eclogites play an important role in convergent settings. To improve our understanding of eclogite deformation behaviour with respect to its phase abundance of omphacite and garnet, synthetic eclogite samples containing 25, 50 and 75% volume fraction of garnet have been deformed in a modified Griggs-type solid-medium apparatus. Deformation conditions were set to a confining pressure of 2.5 GPa, 900 °C and 3*10-6 s-1. Detailed microstructure analysis via optical and electron microscope imaging (SE, BSE and EBSD) served for identification of the dominant active deformation mechanism.
All eclogite samples show a foliation which is defined by a shape preferred orientation (SPO) of omphacite and intercalated foliation sub-parallel garnet aggregates. Another common feature is a weak crystallographic preferred orientation (CPO) of omphacite which is present throughout all samples. In accordance to uniaxial shortening the CPO resembles an s-type texture with a point maximum of [001] axis parallel to the foliation and a maximum of [010] axis perpendicular to the foliation. The stereographic projection of garnet crystallographic orientation is almost distributed randomly. Nevertheless, both phases show an intracrystalline misorientation, indicating activation of crystal plastic processes. With increasing garnet content the grain average misorientation is increasing in both omphacite and garnet crystals. On the other hand, deformation twinning in omphacite is decreasing with increasing garnet content. Further, all samples show indication of brittle deformation of both garnet and omphacite, increasing with increasing garnet content. In samples with a 25% volume fraction of garnet micro-cracks are primarily orientated perpendicular to the foliation, getting more randomly distributed in samples with a 50 and 75% volume fraction of garnet.
In conclusion, all samples show similar microstructures and textures indicating that similar mechanism are active during deformation. However, the overall dominant deformation behaviour is switching from crystal plastic to brittle with increasing garnet content.
How to cite: Klackl, S., Kraus, K., Renner, J., Grasemann, B., and Rogowitz, A.: HP/HT deformation experiments of garnet-omphacite aggregates – influence of volume fractions on deformation mechanisms., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8629, https://doi.org/10.5194/egusphere-egu2020-8629, 2020.
EGU2020-11145 | Displays | TS2.3
Exploitation of unsuitably oriented foliation by localized mylonites and pseudotachylytes (Tauern Window, Eastern Alps)Giovanni Toffol, Giorgio Pennacchioni, Luiz Fernando Grafulha Morales, and Simone Papa
During exhumation, metamorphic rocks change their rheological behavior from dominantly ductile to brittle. Especially at the “brittle-ductile transition” at the bottom of the brittle crust, which coincides roughly with the domain where most “shallow” earthquakes nucleate, rocks exhibit a close interplay between ductile flow and fracturing.
In the Neves area (Tauern window, Eastern Alps) the exhumation across the brittle-ductile transition of amphibolite-facies meta-granitoids during the Alpine cycle is recorded by the association of pseudotachylyte veins and localized low-grade mylonites (stage-2 deformation). The stage-2 structures exploited the precursor amphibolite-facies foliation within meter-thick mylonites (stage-1 deformation) and were in turn overprinted by epidote-chlorite-bearing shear fractures and veins (stage-3 deformation). The kinematics and orientation of stage-1 and stage-3 structures indicate a slight rotation of the regional shortening direction from 345° to about 360°. This implies that stage-2 mylonites and pseudotachylytes developed at a high angle to the shortening direction.
The syn-kinematic metamorphic assemblage of stage-2 mylonites includes quartz, oligoclase (Ab75), biotite, epidote, and minor muscovite and K-feldspar; garnet was not stable. This assemblage constrains the deformation at upper greenschist facies condition and temperatures of around 400 °C. During mylonitization the coarse-grained (mm-sized) amphibolite-facies quartz recrystallized by subgrain rotation to ultra-fine (~ 3 µm average grain size determined from EBSD maps) aggregates. Such a small grain size yields differential stress > 200 MPa during stage-2 mylonitization, considering the piezometer of Cross et al., 2017 1.
Pseudotachylytes are in a close spatial association with stage-2 mylonites and share the same sense of shear. There is no evidence of a ductile overprint of pseudotachylytes. The stage-2 structures developed at a very high angle to the inferred shortening direction, which implies that the coseismic slip occurred on planes with a very low friction coefficient (estimated <0.3), contradicting the high differential stress estimated for the mylonites. We infer a genetic relationship between stage-2 mylonite and pseudotachylyte. Mylonites progressively formed the mica-rich foliation planes, continuous over large distances, that provided the weak mechanical anisotropy eventually leading to coseismic slip.
Reference:
1: Cross, et al., 2017, The recrystallized grain size piezometer for quartz: An EBSD‐based calibration. Geophys. Res. Lett., 44(13), 6667-6674.
How to cite: Toffol, G., Pennacchioni, G., Grafulha Morales, L. F., and Papa, S.: Exploitation of unsuitably oriented foliation by localized mylonites and pseudotachylytes (Tauern Window, Eastern Alps), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11145, https://doi.org/10.5194/egusphere-egu2020-11145, 2020.
During exhumation, metamorphic rocks change their rheological behavior from dominantly ductile to brittle. Especially at the “brittle-ductile transition” at the bottom of the brittle crust, which coincides roughly with the domain where most “shallow” earthquakes nucleate, rocks exhibit a close interplay between ductile flow and fracturing.
In the Neves area (Tauern window, Eastern Alps) the exhumation across the brittle-ductile transition of amphibolite-facies meta-granitoids during the Alpine cycle is recorded by the association of pseudotachylyte veins and localized low-grade mylonites (stage-2 deformation). The stage-2 structures exploited the precursor amphibolite-facies foliation within meter-thick mylonites (stage-1 deformation) and were in turn overprinted by epidote-chlorite-bearing shear fractures and veins (stage-3 deformation). The kinematics and orientation of stage-1 and stage-3 structures indicate a slight rotation of the regional shortening direction from 345° to about 360°. This implies that stage-2 mylonites and pseudotachylytes developed at a high angle to the shortening direction.
The syn-kinematic metamorphic assemblage of stage-2 mylonites includes quartz, oligoclase (Ab75), biotite, epidote, and minor muscovite and K-feldspar; garnet was not stable. This assemblage constrains the deformation at upper greenschist facies condition and temperatures of around 400 °C. During mylonitization the coarse-grained (mm-sized) amphibolite-facies quartz recrystallized by subgrain rotation to ultra-fine (~ 3 µm average grain size determined from EBSD maps) aggregates. Such a small grain size yields differential stress > 200 MPa during stage-2 mylonitization, considering the piezometer of Cross et al., 2017 1.
Pseudotachylytes are in a close spatial association with stage-2 mylonites and share the same sense of shear. There is no evidence of a ductile overprint of pseudotachylytes. The stage-2 structures developed at a very high angle to the inferred shortening direction, which implies that the coseismic slip occurred on planes with a very low friction coefficient (estimated <0.3), contradicting the high differential stress estimated for the mylonites. We infer a genetic relationship between stage-2 mylonite and pseudotachylyte. Mylonites progressively formed the mica-rich foliation planes, continuous over large distances, that provided the weak mechanical anisotropy eventually leading to coseismic slip.
Reference:
1: Cross, et al., 2017, The recrystallized grain size piezometer for quartz: An EBSD‐based calibration. Geophys. Res. Lett., 44(13), 6667-6674.
How to cite: Toffol, G., Pennacchioni, G., Grafulha Morales, L. F., and Papa, S.: Exploitation of unsuitably oriented foliation by localized mylonites and pseudotachylytes (Tauern Window, Eastern Alps), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11145, https://doi.org/10.5194/egusphere-egu2020-11145, 2020.
EGU2020-6714 | Displays | TS2.3
Quantitative texture analysis by neutron diffraction in deformed crystalline aggregates: Contín Shear Zone, Morais Complex, N Portugal.Manuela Durán Oreja, Jeremie Malecki, and Juan Gómez Barreiro
Two samples of mylonitic-ultramylonitic ortogneisses collected along the Contín shear zone were investigated for crystal preferred orientation and seismic anisotropy. Neutron diffraction data obtained at the D1B beamline at ILL (Institute Laue-Langevin, Grenoble) were analyzed with the Rietveld method as implemented in the code MAUD, to obtain the orientation distribution functions (ODF) of the principal phases (quartz, K-feldspar, plagioclase, phlogopite, muscovite and riebeckite). Texture and microstructure are compatible with the plastic deformation of the aggregates under medium to low-temperature conditions. Kinematic analysis supports a top-to-the SE sense of shear, suggesting a thrust character. Using preferred orientation data and single crystal elastic tensors, P and S-waves velocities and elastic anisotropy have been calculated. We have explored the role of several factors controlling the elastic properties of rocks, particularly the role of strain state and mineral changes in a shear zone. Those factors have a direct impact on the medium impedance and consequently on the interphase reflectivity. P-wave velocities, S-wave splitting and anisotropy increase with muscovite content. Seismic anisotropy is linked with the texture symmetry, which can result in large deviations between actual anisotropy and that measured along Cartesian XYZ sample directions (lineation/foliation reference frame). This is significant for the prediction and interpretation of seismic data. (Research support CGL2016-78560-P)
How to cite: Durán Oreja, M., Malecki, J., and Gómez Barreiro, J.: Quantitative texture analysis by neutron diffraction in deformed crystalline aggregates: Contín Shear Zone, Morais Complex, N Portugal., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6714, https://doi.org/10.5194/egusphere-egu2020-6714, 2020.
Two samples of mylonitic-ultramylonitic ortogneisses collected along the Contín shear zone were investigated for crystal preferred orientation and seismic anisotropy. Neutron diffraction data obtained at the D1B beamline at ILL (Institute Laue-Langevin, Grenoble) were analyzed with the Rietveld method as implemented in the code MAUD, to obtain the orientation distribution functions (ODF) of the principal phases (quartz, K-feldspar, plagioclase, phlogopite, muscovite and riebeckite). Texture and microstructure are compatible with the plastic deformation of the aggregates under medium to low-temperature conditions. Kinematic analysis supports a top-to-the SE sense of shear, suggesting a thrust character. Using preferred orientation data and single crystal elastic tensors, P and S-waves velocities and elastic anisotropy have been calculated. We have explored the role of several factors controlling the elastic properties of rocks, particularly the role of strain state and mineral changes in a shear zone. Those factors have a direct impact on the medium impedance and consequently on the interphase reflectivity. P-wave velocities, S-wave splitting and anisotropy increase with muscovite content. Seismic anisotropy is linked with the texture symmetry, which can result in large deviations between actual anisotropy and that measured along Cartesian XYZ sample directions (lineation/foliation reference frame). This is significant for the prediction and interpretation of seismic data. (Research support CGL2016-78560-P)
How to cite: Durán Oreja, M., Malecki, J., and Gómez Barreiro, J.: Quantitative texture analysis by neutron diffraction in deformed crystalline aggregates: Contín Shear Zone, Morais Complex, N Portugal., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6714, https://doi.org/10.5194/egusphere-egu2020-6714, 2020.
EGU2020-11703 | Displays | TS2.3
Quantitative microstructural analysis of western Mediterranean strike-slip kinematics: the Palmi Shear Zone, southern Calabria, ItalyGaetano Ortolano, Eugenio Fazio, Roberto Visalli, Ian G. Alsop, Mario Pagano, and Rosolino CIrrincione
We apply Quantitative Microstructural Analysis (QMA) to a selection of mylonitic rocks that originate from different protoliths, ranging from tonalite to skarn and passing through migmatitic paragneiss. These rocks, that at the end of Paleozoic originally belonged to the lower crustal portion of the southern European Variscan chain, were successively involved in deep-seated strike-slip kinematics of the western Mediterranean realm, created by the relative movement in the Paleocene of the African-European colliding plates. This geodynamics leads to the roto-translation of the Sardinia-Corsica block and the drifting of the kabilo-clabride microplate system (Cirrincione et al., 2015). Remnants of these high strain-rate strike-slip zones are characterized by rheological behaviours controlled by the selective activation of their specific interconnecting weakening phase, as well as by the rheology and abundance of porphyroclasts. QMA is generated by means of new semi-automated GIS-based tools that allow us to extrapolate statistically meaningful kinematic and rheological properties of this meso-Alpine strike-slip mylonitic shear zone (i.e. Palmi Shear Zone). This, in turn, constrains the Alpine evolutionary stages of southern Calabrian geodynamics (Ortolano et al., 2020). Semi-automated image analysis of mXRF maps, combined with high-resolution thin-section scans involving new GIS-based tools developed for structural analysis (e.g. Ortolano et al., 2018; Visalli, 2018), was performed on a selection of three different mylonitic rock-types. These tools permit the user to quantitatively extrapolate rock-fabric parameters such as grain size, aspect ratio and orientation, which allows the nature and relative percentage of the weakening vs. hardening layers, as well as their kinematics, to be derived. Our results allow us to distinguish the porphyroclastic domain levels constituted alternatively by feldspar, amphibole, pyroxene or scapolite, from the weakening phase ones dominated by quartz, biotite plus quartz, or by calcite when the weakening layer is controlled by skarns. Image analysis of porphyroclastic domains has been used to infer the dominant shear-type through Rigid Grain Analysis, revealing a pure shear component of 66 to 68 % for the mylonitic tonalites; 62 to 66 % for the mylonitic paragneisses; and 58 to 62 % for the mylonitic skarn. Image analysis conducted on quartz-rich domains allows an estimate of the shear strain rate, which ranges on average from 1.14*10-12 (1/s) for mylonitic paragneiss to 5.91*10-12 (1/s) for mylonitic tonalite, and is in accord with high strain zones in natural settings. Our results provide new insights into the kinematics and rheology of this exhumed relic of the deep-rooted early-Alpine strike-slip tectonics of the western Mediterranean.
References
Cirrincione R., Fazio E., Fiannacca P., Ortolano G. & Pezzino A., Punturo R. 2015. Period. Mineral., 84(3B), 701-749.
Ortolano G., Visalli R., Godard G. & Cirrincione R. 2018. Comput. Geosci., 115, 56-65.
Ortolano, G., Fazio, E., Visalli, R., Alsop, G.I., Pagano, M., Cirrincione, R. 2020. Journal of Structural Geology, 131, art. no. 103956.
Visalli R. 2018. Plinius, vol 44, DOI:10.19276/plinius.2018.01014.
How to cite: Ortolano, G., Fazio, E., Visalli, R., Alsop, I. G., Pagano, M., and CIrrincione, R.: Quantitative microstructural analysis of western Mediterranean strike-slip kinematics: the Palmi Shear Zone, southern Calabria, Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11703, https://doi.org/10.5194/egusphere-egu2020-11703, 2020.
We apply Quantitative Microstructural Analysis (QMA) to a selection of mylonitic rocks that originate from different protoliths, ranging from tonalite to skarn and passing through migmatitic paragneiss. These rocks, that at the end of Paleozoic originally belonged to the lower crustal portion of the southern European Variscan chain, were successively involved in deep-seated strike-slip kinematics of the western Mediterranean realm, created by the relative movement in the Paleocene of the African-European colliding plates. This geodynamics leads to the roto-translation of the Sardinia-Corsica block and the drifting of the kabilo-clabride microplate system (Cirrincione et al., 2015). Remnants of these high strain-rate strike-slip zones are characterized by rheological behaviours controlled by the selective activation of their specific interconnecting weakening phase, as well as by the rheology and abundance of porphyroclasts. QMA is generated by means of new semi-automated GIS-based tools that allow us to extrapolate statistically meaningful kinematic and rheological properties of this meso-Alpine strike-slip mylonitic shear zone (i.e. Palmi Shear Zone). This, in turn, constrains the Alpine evolutionary stages of southern Calabrian geodynamics (Ortolano et al., 2020). Semi-automated image analysis of mXRF maps, combined with high-resolution thin-section scans involving new GIS-based tools developed for structural analysis (e.g. Ortolano et al., 2018; Visalli, 2018), was performed on a selection of three different mylonitic rock-types. These tools permit the user to quantitatively extrapolate rock-fabric parameters such as grain size, aspect ratio and orientation, which allows the nature and relative percentage of the weakening vs. hardening layers, as well as their kinematics, to be derived. Our results allow us to distinguish the porphyroclastic domain levels constituted alternatively by feldspar, amphibole, pyroxene or scapolite, from the weakening phase ones dominated by quartz, biotite plus quartz, or by calcite when the weakening layer is controlled by skarns. Image analysis of porphyroclastic domains has been used to infer the dominant shear-type through Rigid Grain Analysis, revealing a pure shear component of 66 to 68 % for the mylonitic tonalites; 62 to 66 % for the mylonitic paragneisses; and 58 to 62 % for the mylonitic skarn. Image analysis conducted on quartz-rich domains allows an estimate of the shear strain rate, which ranges on average from 1.14*10-12 (1/s) for mylonitic paragneiss to 5.91*10-12 (1/s) for mylonitic tonalite, and is in accord with high strain zones in natural settings. Our results provide new insights into the kinematics and rheology of this exhumed relic of the deep-rooted early-Alpine strike-slip tectonics of the western Mediterranean.
References
Cirrincione R., Fazio E., Fiannacca P., Ortolano G. & Pezzino A., Punturo R. 2015. Period. Mineral., 84(3B), 701-749.
Ortolano G., Visalli R., Godard G. & Cirrincione R. 2018. Comput. Geosci., 115, 56-65.
Ortolano, G., Fazio, E., Visalli, R., Alsop, G.I., Pagano, M., Cirrincione, R. 2020. Journal of Structural Geology, 131, art. no. 103956.
Visalli R. 2018. Plinius, vol 44, DOI:10.19276/plinius.2018.01014.
How to cite: Ortolano, G., Fazio, E., Visalli, R., Alsop, I. G., Pagano, M., and CIrrincione, R.: Quantitative microstructural analysis of western Mediterranean strike-slip kinematics: the Palmi Shear Zone, southern Calabria, Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11703, https://doi.org/10.5194/egusphere-egu2020-11703, 2020.
EGU2020-15152 | Displays | TS2.3
Thermal history modelling of the western margin of the Bohemian Massif using high-resolution apatite fission-track thermochronologyLucie Novakova, Raymond Jonckheere, Bastian Wauschkuhn, and Lothar Ratchbacher
The Naab area is situated on the western border of the Bohemian Massif, 60 km south of the KTB (Kontinentalen Tiefbohrung). The main super-deep borehole of the KTB reached a depth of 9,101 meters in the Earth's continental crust. The fission-track data for the KTB and the Naab area present contrasting signatures. The apatite fission-track ages in the upper section of the KTB borehole and surrounding area are in the range 50-70 Ma (Wagner et al., 1994; Wauschkuhn et al., 2015). The apatite fission-track ages of the Naab basement are older than those of the KTB area, and span a broader range: 120-200 Ma (Vercoutere, 1994). The distributions of the confined-track lengths range from unimodal over skewed and mixed to bimodal, with mean lengths in the range 11-13 µm. In broad terms, this can be interpreted as that the Naab samples contain both an older and younger (in particular pre- and post-late Cretaceous) fission-track population. The aim of our research is to investigate the applicability of lab-based models to geological data, using improved measurement techniques.
We studied eighteen samples dated by Vercoutere (1994) from the Palaeozoic basement and seven large rock samples from the Rotliegend strata north of the Luhe fault. We intend to extend the confined-track length measurements of Vercoutere (1994), aiming to achieve higher resolution through methodological innovations made possible by computer-controlled motorized microscopes. Improved statistics increase the resolution of the modelled thermal histories, which permits to better distinguish systematic from statistical differences between the modelled palaeotemperatures and geological estimates. Experiments have shown that the rate of length increase permits to distinguish older from younger tracks (Jonckheere et al., 2017). This allows us to distinguish between tracks formed before and after the Late Cretaceous to Palaeocene exhumation. The etch rate of a confined track is also an indicator of its individual thermal history, supplementing the information gleaned from its etchable length under fixed conditions. We compiled a comprehensive, high-resolution confined-track-length dataset. The Naab thermal histories were determined using modern modelling algorithms, implementing the most recent empirical equations.
References
Jonckheere R., Tamer M., Wauschkuhn F., Wauschkuhn B., Ratschbacher L., 2017. Single-track length measurements of step-etched fission tracks in Durango apatite: Vorsprung durch Technik.American Mineralogist 102, 987-996.
Vercoutere C., 1994. The thermotectonic history of the Brabant Massif (Belgium) and the Naab Basement (Germany): an apatite fission track analysis. Ph. D. thesis, Universiteit Gent, pp. 191.
Wagner G.A., Hejl E., Van Den Haute P., 1994. The KTB fission-track project: Methodical aspects and geological implications. Radiation Measurements 23, 95-101.
Wauschkuhn B., Jonckheere R., Ratschbacher L., 2015. The KTB apatite fission-track profiles: building on a firm foundation? Geochimica et Cosmochimica Acta 167, 27-62.
How to cite: Novakova, L., Jonckheere, R., Wauschkuhn, B., and Ratchbacher, L.: Thermal history modelling of the western margin of the Bohemian Massif using high-resolution apatite fission-track thermochronology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15152, https://doi.org/10.5194/egusphere-egu2020-15152, 2020.
The Naab area is situated on the western border of the Bohemian Massif, 60 km south of the KTB (Kontinentalen Tiefbohrung). The main super-deep borehole of the KTB reached a depth of 9,101 meters in the Earth's continental crust. The fission-track data for the KTB and the Naab area present contrasting signatures. The apatite fission-track ages in the upper section of the KTB borehole and surrounding area are in the range 50-70 Ma (Wagner et al., 1994; Wauschkuhn et al., 2015). The apatite fission-track ages of the Naab basement are older than those of the KTB area, and span a broader range: 120-200 Ma (Vercoutere, 1994). The distributions of the confined-track lengths range from unimodal over skewed and mixed to bimodal, with mean lengths in the range 11-13 µm. In broad terms, this can be interpreted as that the Naab samples contain both an older and younger (in particular pre- and post-late Cretaceous) fission-track population. The aim of our research is to investigate the applicability of lab-based models to geological data, using improved measurement techniques.
We studied eighteen samples dated by Vercoutere (1994) from the Palaeozoic basement and seven large rock samples from the Rotliegend strata north of the Luhe fault. We intend to extend the confined-track length measurements of Vercoutere (1994), aiming to achieve higher resolution through methodological innovations made possible by computer-controlled motorized microscopes. Improved statistics increase the resolution of the modelled thermal histories, which permits to better distinguish systematic from statistical differences between the modelled palaeotemperatures and geological estimates. Experiments have shown that the rate of length increase permits to distinguish older from younger tracks (Jonckheere et al., 2017). This allows us to distinguish between tracks formed before and after the Late Cretaceous to Palaeocene exhumation. The etch rate of a confined track is also an indicator of its individual thermal history, supplementing the information gleaned from its etchable length under fixed conditions. We compiled a comprehensive, high-resolution confined-track-length dataset. The Naab thermal histories were determined using modern modelling algorithms, implementing the most recent empirical equations.
References
Jonckheere R., Tamer M., Wauschkuhn F., Wauschkuhn B., Ratschbacher L., 2017. Single-track length measurements of step-etched fission tracks in Durango apatite: Vorsprung durch Technik.American Mineralogist 102, 987-996.
Vercoutere C., 1994. The thermotectonic history of the Brabant Massif (Belgium) and the Naab Basement (Germany): an apatite fission track analysis. Ph. D. thesis, Universiteit Gent, pp. 191.
Wagner G.A., Hejl E., Van Den Haute P., 1994. The KTB fission-track project: Methodical aspects and geological implications. Radiation Measurements 23, 95-101.
Wauschkuhn B., Jonckheere R., Ratschbacher L., 2015. The KTB apatite fission-track profiles: building on a firm foundation? Geochimica et Cosmochimica Acta 167, 27-62.
How to cite: Novakova, L., Jonckheere, R., Wauschkuhn, B., and Ratchbacher, L.: Thermal history modelling of the western margin of the Bohemian Massif using high-resolution apatite fission-track thermochronology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15152, https://doi.org/10.5194/egusphere-egu2020-15152, 2020.
EGU2020-111 | Displays | TS2.3
Metamorphic micro-textural variations and their bearing on rock technical properties. A case study of the transition from greenschist- to high-pressure granulite-facies in the Eastern Segment, Sveconorwegian orogenCindy Urueña, Charlotte Möller, Jenny Andersson, Mattias Göransson, Jan Erik Lindqvist, and Urban Åkeson
The Precambrian shield in southern Sweden exposes a granitic bedrock segment that represents a part of an ancient eroded mountain belt and expose a gradual change in metamorphic grade from cold (<300°C), little affected by recrystallization, to hot (>800°C) and partially molten sections at the west coast (Möller and Andersson, 2018). This area – the Eastern Segment – offers a large scale study of the interdependence of metamorphism, deformation, partial melting, and functional properties of crushed rock aggregates.
In the petrological community, it is well-known that the evolution of a metamorphic unit (e.g. a high-pressure unit) with respect to pressure, temperature, time, and deformation holds key information on its tectonic history. It has rarely been emphasized, however, that the same factors determine the physical properties of the rock and thus, its technical properties. Basic research in metamorphic petrology thus contributes with a fundament to applied and technical science, e.g. by providing data that lead to quarrying of proper materials.
This study assesses the variations of technical properties with the metamorphic state, primarily metamorphic temperature and partial melting during metamorphism. Our first results show the correlation between the petrological characteristics and technical properties of felsic orthogneiss within a migmatized eclogite-bearing terrane and its high-pressure granulite-bearing footwall.
Measurements include the Los Angeles and Micro-Deval value tests. The Los Angeles value is a measure of the resistance to fragmentation (EN 1097-2, 2010). The Micro-Deval test measures the resistance to wear.
High values of the Los Angeles and Micro-Deval analyses for felsic orthogneiss in the eclogite-bearing domain reflect poor technical properties and are largely linked to that the rocks underwent partial melting. Orthogneisses in the footwall, which recrystallized under high-temperature, dry conditions, and without partial melting, tend to have lower values. This group includes high-quality rocks for the production of aggregates suitable for asphalt base courses and unbound road layers.
Micro-textures in the orthogneisses are linked with these metamorphic conditions. The clinopyroxene-bearing orthogneisses have complex grain boundaries and micro-perthitic feldspars, finer average grain size, lower biotite content, and absence of migmatitic segregation or penetrative veining. These textures in the footwall orthogneisses contrast with those in the migmatitic orthogneisses from the eclogite-bearing domain, which have a coarser average grain size, even-grained and granoblastic texture, and lack of perthitic texture in feldspars. Thus, these petrographic parameters govern the technical differences.
Our ongoing research addresses the relations between macro-fabric, micro-texture and technical properties of felsic orthogneiss and metagabbro, respectively, along 120 km profile across the metamorphic field gradient from greenschist- to high-pressure granulite-facies in the Eastern Segment.
How to cite: Urueña, C., Möller, C., Andersson, J., Göransson, M., Lindqvist, J. E., and Åkeson, U.: Metamorphic micro-textural variations and their bearing on rock technical properties. A case study of the transition from greenschist- to high-pressure granulite-facies in the Eastern Segment, Sveconorwegian orogen, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-111, https://doi.org/10.5194/egusphere-egu2020-111, 2020.
The Precambrian shield in southern Sweden exposes a granitic bedrock segment that represents a part of an ancient eroded mountain belt and expose a gradual change in metamorphic grade from cold (<300°C), little affected by recrystallization, to hot (>800°C) and partially molten sections at the west coast (Möller and Andersson, 2018). This area – the Eastern Segment – offers a large scale study of the interdependence of metamorphism, deformation, partial melting, and functional properties of crushed rock aggregates.
In the petrological community, it is well-known that the evolution of a metamorphic unit (e.g. a high-pressure unit) with respect to pressure, temperature, time, and deformation holds key information on its tectonic history. It has rarely been emphasized, however, that the same factors determine the physical properties of the rock and thus, its technical properties. Basic research in metamorphic petrology thus contributes with a fundament to applied and technical science, e.g. by providing data that lead to quarrying of proper materials.
This study assesses the variations of technical properties with the metamorphic state, primarily metamorphic temperature and partial melting during metamorphism. Our first results show the correlation between the petrological characteristics and technical properties of felsic orthogneiss within a migmatized eclogite-bearing terrane and its high-pressure granulite-bearing footwall.
Measurements include the Los Angeles and Micro-Deval value tests. The Los Angeles value is a measure of the resistance to fragmentation (EN 1097-2, 2010). The Micro-Deval test measures the resistance to wear.
High values of the Los Angeles and Micro-Deval analyses for felsic orthogneiss in the eclogite-bearing domain reflect poor technical properties and are largely linked to that the rocks underwent partial melting. Orthogneisses in the footwall, which recrystallized under high-temperature, dry conditions, and without partial melting, tend to have lower values. This group includes high-quality rocks for the production of aggregates suitable for asphalt base courses and unbound road layers.
Micro-textures in the orthogneisses are linked with these metamorphic conditions. The clinopyroxene-bearing orthogneisses have complex grain boundaries and micro-perthitic feldspars, finer average grain size, lower biotite content, and absence of migmatitic segregation or penetrative veining. These textures in the footwall orthogneisses contrast with those in the migmatitic orthogneisses from the eclogite-bearing domain, which have a coarser average grain size, even-grained and granoblastic texture, and lack of perthitic texture in feldspars. Thus, these petrographic parameters govern the technical differences.
Our ongoing research addresses the relations between macro-fabric, micro-texture and technical properties of felsic orthogneiss and metagabbro, respectively, along 120 km profile across the metamorphic field gradient from greenschist- to high-pressure granulite-facies in the Eastern Segment.
How to cite: Urueña, C., Möller, C., Andersson, J., Göransson, M., Lindqvist, J. E., and Åkeson, U.: Metamorphic micro-textural variations and their bearing on rock technical properties. A case study of the transition from greenschist- to high-pressure granulite-facies in the Eastern Segment, Sveconorwegian orogen, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-111, https://doi.org/10.5194/egusphere-egu2020-111, 2020.
EGU2020-5167 | Displays | TS2.3
Strain localization associated with brittle faulting in a natural clinoptilolite-tuff (open-pit mine Nižný Hrabovec, Slovak Republic)Zhaoliang Hou, A. Hugh N Rice, Cornelius Tschegg, Thomas Berger, and Bernhard Grasemann
Clinoptilolite, a micro-porous natural zeolite comprising tetrahedra of silica and alumina that commonly occurs in volcanic tuffs through devitrification of natural glasses, has numerous uses in the manufacturing, agriculture and building industries; it also has applications in veterinary and human medicines. Field observations and microstructural investigations in the natural clinoptilolite-tuff from Nižný Hrabovec (Slovak Republic) – one of the world’s economically most important high-quality clinoptilolite deposits – show evidence of strain localization. Brittle faults formed along pre-existing joints with plumose structures that had acted as a pathway for local infiltration of iron-, manganese- and potassium-rich fluids. Fault displacement formed structures that are indicative of both velocity hardening, with dissolution precipitation creep (SC/SCC’ foliation), and velocity weakening, with several phases of ultra-cataclasites forming along principal slip surfaces. Rock-fluid interaction is characterized by a high-mobility of K, with K-feldspar decorating SC/SCC’ foliations, infiltrating fractures in fault damage zones and precipitating as idiomorphic crystals in open cavities and along fault surfaces. Microstructures such as polished slickensides, injection of fluidized cataclasites, clast cortex grains in cataclasites and truncated grains along principal slip surfaces suggest that seismic slip probably occurred along some of the faults.
How to cite: Hou, Z., Rice, A. H. N., Tschegg, C., Berger, T., and Grasemann, B.: Strain localization associated with brittle faulting in a natural clinoptilolite-tuff (open-pit mine Nižný Hrabovec, Slovak Republic), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5167, https://doi.org/10.5194/egusphere-egu2020-5167, 2020.
Clinoptilolite, a micro-porous natural zeolite comprising tetrahedra of silica and alumina that commonly occurs in volcanic tuffs through devitrification of natural glasses, has numerous uses in the manufacturing, agriculture and building industries; it also has applications in veterinary and human medicines. Field observations and microstructural investigations in the natural clinoptilolite-tuff from Nižný Hrabovec (Slovak Republic) – one of the world’s economically most important high-quality clinoptilolite deposits – show evidence of strain localization. Brittle faults formed along pre-existing joints with plumose structures that had acted as a pathway for local infiltration of iron-, manganese- and potassium-rich fluids. Fault displacement formed structures that are indicative of both velocity hardening, with dissolution precipitation creep (SC/SCC’ foliation), and velocity weakening, with several phases of ultra-cataclasites forming along principal slip surfaces. Rock-fluid interaction is characterized by a high-mobility of K, with K-feldspar decorating SC/SCC’ foliations, infiltrating fractures in fault damage zones and precipitating as idiomorphic crystals in open cavities and along fault surfaces. Microstructures such as polished slickensides, injection of fluidized cataclasites, clast cortex grains in cataclasites and truncated grains along principal slip surfaces suggest that seismic slip probably occurred along some of the faults.
How to cite: Hou, Z., Rice, A. H. N., Tschegg, C., Berger, T., and Grasemann, B.: Strain localization associated with brittle faulting in a natural clinoptilolite-tuff (open-pit mine Nižný Hrabovec, Slovak Republic), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5167, https://doi.org/10.5194/egusphere-egu2020-5167, 2020.
EGU2020-9231 | Displays | TS2.3
Deformation history of the Marmara Granitoid and implications for a dextral shear zone in NW AnatoliaSalim Birkan Bayrak, Işıl Nur Güraslan, Alp Ünal, Ömer Kamacı, Şafak Altunkaynak, and Erdinç Yiğitbaş
Marmara granitoid (47 Ma) is a representative example of the Eocene post-collisional magmatism which produced several granitic plutons in NW Anatolia, Turkey. It is a W-E trending sill-like magmatic body which was concordantly emplaced into the metamorphic basement rocks of Erdek Complex and Saraylar Marble. The granitoid is represented by deformed granodiorite which displays well-developed lineation and foliation in meso-scale defined by the elongation of mica and feldspar crystals and recrystallization of quartz however, in some places, magmatic textures are preserved. Deformed granodiorite is broadly cut by aplitic and pegmatitic dikes and contains mafic enclaves which display the same deformation indicators with the main granitoid.
Microstructural analysis shows that the solid-state deformation of the Marmara granitoid is classified as ductile deformation with high temperatures and ductile-to-brittle deformation with relatively lower temperatures. Evidence for the ductile deformation of the granitoid is represented by chessboard extinction of quartz, grain boundary migration (GBM) and subgrain rotation recrystallisation (SGR) which exhibits that the deformation temperature changed from 600 oC to 400oC. Bulging recrystallization (BLG), grain size reduction of amphibole, biotite and plagioclases and microcracks on plagioclases were considered as overlying ductile-to-brittle deformation signatures which develop between 300-<250 oC temperatures.
All of these field and micro-structural data collectively suggest that the shear sense indicators such as micafish structures and δ type mantled porphyroclasts displayed stair-steppings pointing out to a right lateral movement, indicating that the structural evolution and deformation history of Marmara granitoid was controlled by a dextral shear zone.
How to cite: Bayrak, S. B., Güraslan, I. N., Ünal, A., Kamacı, Ö., Altunkaynak, Ş., and Yiğitbaş, E.: Deformation history of the Marmara Granitoid and implications for a dextral shear zone in NW Anatolia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9231, https://doi.org/10.5194/egusphere-egu2020-9231, 2020.
Marmara granitoid (47 Ma) is a representative example of the Eocene post-collisional magmatism which produced several granitic plutons in NW Anatolia, Turkey. It is a W-E trending sill-like magmatic body which was concordantly emplaced into the metamorphic basement rocks of Erdek Complex and Saraylar Marble. The granitoid is represented by deformed granodiorite which displays well-developed lineation and foliation in meso-scale defined by the elongation of mica and feldspar crystals and recrystallization of quartz however, in some places, magmatic textures are preserved. Deformed granodiorite is broadly cut by aplitic and pegmatitic dikes and contains mafic enclaves which display the same deformation indicators with the main granitoid.
Microstructural analysis shows that the solid-state deformation of the Marmara granitoid is classified as ductile deformation with high temperatures and ductile-to-brittle deformation with relatively lower temperatures. Evidence for the ductile deformation of the granitoid is represented by chessboard extinction of quartz, grain boundary migration (GBM) and subgrain rotation recrystallisation (SGR) which exhibits that the deformation temperature changed from 600 oC to 400oC. Bulging recrystallization (BLG), grain size reduction of amphibole, biotite and plagioclases and microcracks on plagioclases were considered as overlying ductile-to-brittle deformation signatures which develop between 300-<250 oC temperatures.
All of these field and micro-structural data collectively suggest that the shear sense indicators such as micafish structures and δ type mantled porphyroclasts displayed stair-steppings pointing out to a right lateral movement, indicating that the structural evolution and deformation history of Marmara granitoid was controlled by a dextral shear zone.
How to cite: Bayrak, S. B., Güraslan, I. N., Ünal, A., Kamacı, Ö., Altunkaynak, Ş., and Yiğitbaş, E.: Deformation history of the Marmara Granitoid and implications for a dextral shear zone in NW Anatolia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9231, https://doi.org/10.5194/egusphere-egu2020-9231, 2020.
EGU2020-2897 | Displays | TS2.3
Non-steady strain in the terrane boundary shear zone of the Ambaji Granulite, NW India: Implications for understanding towards the dynamics of emplacement of the lower-middle crustal rocks.Ragini Saraswati and Tapas Kumar Biswal
Shear zones in the high-grade terranes represent the tectonic- fossils of strain history. One such shear zones, namely Balaram-Jogdadi shear zones defining the terrane boundary of the Ambaji granulites of the South Delhi terrane Aravalli –Delhi Mobile belt, NW India, provide evidence for strain variation during exhumation of lower-middle crustal rocks. Compilation of field and microscopic analysis of various samples of mylonite from shear zones suggest that the part of shear zone contains high-grade mineral assemblages such as cordierite, sillimanite, spinel, garnet in quartzo-feldspathic mylonite rock and exhibit signature of thrusting in which garnet behaved as brittle phase and quartz and feldspar grain show ductile deformation. 2D and 3D strain analysis estimate a plane to flattening type of strain pattern. Principal strain planes are used to calculate the strain ratios for estimation of variation of strain along the shear zone. This study indicates high-grade mylonite accommodates high strain. The flow of rigid porphyroclasts estimates mean kinematic vorticity number varies from 0.47 to 0.68, which indicates the dominance of pure shear during shearing. Vorticity by the Rs/θ method in quartz grain estimates ranges from 0.7 to 0.95, suggesting a non-steady strain towards the end of deformation. High-grade mylonites were overprinted by low-temperature mylonitisation marked by minerals like quartz, feldspar, biotite in which feldspar porphyroclast shows brittle deformation and quartz, biotite show ductile deformation. Several shear kinematics indicate top-to-NW sinistral strike-slip shearing. Thus it has been interpreted that the shear zone had undergone non-steady strain. The initial thrusting phase was dominated by more pure shear component. The strike-slip shearing part was dominated by more simple shear component. Monazite geochronology sets the age of shearing at 834-778 Ma suggesting the exhumation was a transition event between Grenville to Pan-African orogeny.
Keywords: Shear zone, Deformation, Vorticity, 3D strain analysis, Monazite dating
How to cite: Saraswati, R. and Biswal, T. K.: Non-steady strain in the terrane boundary shear zone of the Ambaji Granulite, NW India: Implications for understanding towards the dynamics of emplacement of the lower-middle crustal rocks., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2897, https://doi.org/10.5194/egusphere-egu2020-2897, 2020.
Shear zones in the high-grade terranes represent the tectonic- fossils of strain history. One such shear zones, namely Balaram-Jogdadi shear zones defining the terrane boundary of the Ambaji granulites of the South Delhi terrane Aravalli –Delhi Mobile belt, NW India, provide evidence for strain variation during exhumation of lower-middle crustal rocks. Compilation of field and microscopic analysis of various samples of mylonite from shear zones suggest that the part of shear zone contains high-grade mineral assemblages such as cordierite, sillimanite, spinel, garnet in quartzo-feldspathic mylonite rock and exhibit signature of thrusting in which garnet behaved as brittle phase and quartz and feldspar grain show ductile deformation. 2D and 3D strain analysis estimate a plane to flattening type of strain pattern. Principal strain planes are used to calculate the strain ratios for estimation of variation of strain along the shear zone. This study indicates high-grade mylonite accommodates high strain. The flow of rigid porphyroclasts estimates mean kinematic vorticity number varies from 0.47 to 0.68, which indicates the dominance of pure shear during shearing. Vorticity by the Rs/θ method in quartz grain estimates ranges from 0.7 to 0.95, suggesting a non-steady strain towards the end of deformation. High-grade mylonites were overprinted by low-temperature mylonitisation marked by minerals like quartz, feldspar, biotite in which feldspar porphyroclast shows brittle deformation and quartz, biotite show ductile deformation. Several shear kinematics indicate top-to-NW sinistral strike-slip shearing. Thus it has been interpreted that the shear zone had undergone non-steady strain. The initial thrusting phase was dominated by more pure shear component. The strike-slip shearing part was dominated by more simple shear component. Monazite geochronology sets the age of shearing at 834-778 Ma suggesting the exhumation was a transition event between Grenville to Pan-African orogeny.
Keywords: Shear zone, Deformation, Vorticity, 3D strain analysis, Monazite dating
How to cite: Saraswati, R. and Biswal, T. K.: Non-steady strain in the terrane boundary shear zone of the Ambaji Granulite, NW India: Implications for understanding towards the dynamics of emplacement of the lower-middle crustal rocks., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2897, https://doi.org/10.5194/egusphere-egu2020-2897, 2020.
EGU2020-7397 | Displays | TS2.3
The kinematic vorticity analysis of ductile shear zones of Ambaji Granulite, NW India and its tectonic implicationsSudheer Kumar Tiwari, Anouk Beniest, and Tapas Kumar Biswal
The Neoproterozoic (834 – 778 Ma) Ambaji granulite witnessed four deformation phases (D1- D4), of which the D2 deformation phase was most significant for the exhumation of granulites in the ductile regime. We performed a field study to investigate the tectonic evolution of the D2 deformation phase and investigated the deformation evolution of the ductile extrusion of the Ambaji granulite by estimating the vorticity of flow (Wm) with the Rigid Grain Net and strain ratio/orientation techniques.
During the D2 deformation phase, the S1 fabric was folded by F2 folds that are coaxial with the F1 folds. The F2 folds were produced in response to NW-SE compression. Because the large shear zones are oriented parallel to the axial plane of the F2 folds, they likely formed simultaneously during the D2 deformation phase. Compression during the D2 deformation phase accommodated most of the exhumation of the granulite along the shear zones. D2 shearing was constrained between 834 ± 7 to 778 ± 8 Ma (Monazite ages).
The shear zones evolved from a high temperature (>700 °C) thrust-slip shearing event in the lower-middle crust to a low temperature (450 °C) retrograde sinistral shearing event at the brittle-ductile-transition (BDT). The Wm estimates of 0.32–0.40 and 0.60 coincide with the high temperature event and suggests pure shear dominated deformation. The low temperature phase coincides with Wm estimates of 0.64–0.87 and ~1.0, implying two flow regimes. The shear zone was first affected by general non-coaxial deformation and gradually became dominated by simple shearing.
We interpreted that the high temperature event happened in a compressive tectonic regime, which led to horizontal shortening and vertical displacement of the granulite to the BDT. The low temperature event occurred in a transpressive tectonic setting that caused the lateral displacement of the granulite body at BDT depth. The Wm values indicate a non-steady strain during the exhumation of granulite. From the BDT to surface, the Ambaji granulite exhumed through the NW-SE directed extension for normal faults via brittle exhumation through crustal extension and thinning.
How to cite: Tiwari, S. K., Beniest, A., and Biswal, T. K.: The kinematic vorticity analysis of ductile shear zones of Ambaji Granulite, NW India and its tectonic implications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7397, https://doi.org/10.5194/egusphere-egu2020-7397, 2020.
The Neoproterozoic (834 – 778 Ma) Ambaji granulite witnessed four deformation phases (D1- D4), of which the D2 deformation phase was most significant for the exhumation of granulites in the ductile regime. We performed a field study to investigate the tectonic evolution of the D2 deformation phase and investigated the deformation evolution of the ductile extrusion of the Ambaji granulite by estimating the vorticity of flow (Wm) with the Rigid Grain Net and strain ratio/orientation techniques.
During the D2 deformation phase, the S1 fabric was folded by F2 folds that are coaxial with the F1 folds. The F2 folds were produced in response to NW-SE compression. Because the large shear zones are oriented parallel to the axial plane of the F2 folds, they likely formed simultaneously during the D2 deformation phase. Compression during the D2 deformation phase accommodated most of the exhumation of the granulite along the shear zones. D2 shearing was constrained between 834 ± 7 to 778 ± 8 Ma (Monazite ages).
The shear zones evolved from a high temperature (>700 °C) thrust-slip shearing event in the lower-middle crust to a low temperature (450 °C) retrograde sinistral shearing event at the brittle-ductile-transition (BDT). The Wm estimates of 0.32–0.40 and 0.60 coincide with the high temperature event and suggests pure shear dominated deformation. The low temperature phase coincides with Wm estimates of 0.64–0.87 and ~1.0, implying two flow regimes. The shear zone was first affected by general non-coaxial deformation and gradually became dominated by simple shearing.
We interpreted that the high temperature event happened in a compressive tectonic regime, which led to horizontal shortening and vertical displacement of the granulite to the BDT. The low temperature event occurred in a transpressive tectonic setting that caused the lateral displacement of the granulite body at BDT depth. The Wm values indicate a non-steady strain during the exhumation of granulite. From the BDT to surface, the Ambaji granulite exhumed through the NW-SE directed extension for normal faults via brittle exhumation through crustal extension and thinning.
How to cite: Tiwari, S. K., Beniest, A., and Biswal, T. K.: The kinematic vorticity analysis of ductile shear zones of Ambaji Granulite, NW India and its tectonic implications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7397, https://doi.org/10.5194/egusphere-egu2020-7397, 2020.
TS2.5 – The energy budget of tectonic systems
EGU2020-10759 | Displays | TS2.5
Thermal energy pattern related with the temperature increasing due to intraplate and induced seismicity, Southern Norway, 2017-2018Rodrigo Estay
Small seismological events recorded in southern Norway in the period of 2017-2018 were used to calculate the sudden co-seismic temperature increase using a simple stress-drop model. In order to estimate the net production of thermal energy, both, industry explosions and natural events were included. The range of resultant average temperature rise, with a maximum of ~ 143 ° C for a Mw =3.5, is proposed as an additional constituent that explain the weakness areas related to the high amount of intracrustal seismicity, mainly regarding the anisotropic thermal expansion of rocks and the flash heating thermal process produced by historical earthquakes with magnitudes over . The temperature values were subsequently used to estimate the thermal energy in 2D and 3D cumulative patterns in the area, as well as the total amount of energy that is available regarding seismic activity. The results were correlated with existing geological information, considering lineaments and heat flux data. Areas with high values of thermal energy seems to be spatially linked with both high heat flux zones and high density of lineaments, mainly to the south of the Trøndelag Platform as well as to the south of the Møre basin.
How to cite: Estay, R.: Thermal energy pattern related with the temperature increasing due to intraplate and induced seismicity, Southern Norway, 2017-2018, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10759, https://doi.org/10.5194/egusphere-egu2020-10759, 2020.
Small seismological events recorded in southern Norway in the period of 2017-2018 were used to calculate the sudden co-seismic temperature increase using a simple stress-drop model. In order to estimate the net production of thermal energy, both, industry explosions and natural events were included. The range of resultant average temperature rise, with a maximum of ~ 143 ° C for a Mw =3.5, is proposed as an additional constituent that explain the weakness areas related to the high amount of intracrustal seismicity, mainly regarding the anisotropic thermal expansion of rocks and the flash heating thermal process produced by historical earthquakes with magnitudes over . The temperature values were subsequently used to estimate the thermal energy in 2D and 3D cumulative patterns in the area, as well as the total amount of energy that is available regarding seismic activity. The results were correlated with existing geological information, considering lineaments and heat flux data. Areas with high values of thermal energy seems to be spatially linked with both high heat flux zones and high density of lineaments, mainly to the south of the Trøndelag Platform as well as to the south of the Møre basin.
How to cite: Estay, R.: Thermal energy pattern related with the temperature increasing due to intraplate and induced seismicity, Southern Norway, 2017-2018, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10759, https://doi.org/10.5194/egusphere-egu2020-10759, 2020.
EGU2020-10795 | Displays | TS2.5
Simulation of frictional heat generation due to underground motionAndreas Uslar
Frictional energy generating during an earthquake has been well studied in the last decades and quite a few laboratory experiments have been carried out recently with the objective to quantify and describe this type of energy in a better way. In our research we modelled the temperature rise during a simulated seismic event and the consequent equivalent heat released using the ANSYS® Mechanical software. Our approach is using the Finite Element Method to model a symmetrical fault plane where several parameters such as density, pressure, structural and thermal material characteristics are set according the conditions of a compressional tri-axial test. Natural and forced models were explored applying the Mohr-Coulomb failure criteria. Using a temporal window similar to a realistic situation, we are capable to observe the differences that occur during the stick-slip behavior in the co-seismic rupture process. On the other hand, the time lapse allows us to observe model and infer how the heat is generated and transferred around the fault plane. As a preliminary result, a variation of approximately 1.5°C was obtained simulating the conditions for a laboratory induced micro-seismic event modelled as a tri-axial test under 10 MPa of confining pressure and 20 MPa as vertical pressure, with velocities in the order of 1.5 mm/s.
How to cite: Uslar, A.: Simulation of frictional heat generation due to underground motion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10795, https://doi.org/10.5194/egusphere-egu2020-10795, 2020.
Frictional energy generating during an earthquake has been well studied in the last decades and quite a few laboratory experiments have been carried out recently with the objective to quantify and describe this type of energy in a better way. In our research we modelled the temperature rise during a simulated seismic event and the consequent equivalent heat released using the ANSYS® Mechanical software. Our approach is using the Finite Element Method to model a symmetrical fault plane where several parameters such as density, pressure, structural and thermal material characteristics are set according the conditions of a compressional tri-axial test. Natural and forced models were explored applying the Mohr-Coulomb failure criteria. Using a temporal window similar to a realistic situation, we are capable to observe the differences that occur during the stick-slip behavior in the co-seismic rupture process. On the other hand, the time lapse allows us to observe model and infer how the heat is generated and transferred around the fault plane. As a preliminary result, a variation of approximately 1.5°C was obtained simulating the conditions for a laboratory induced micro-seismic event modelled as a tri-axial test under 10 MPa of confining pressure and 20 MPa as vertical pressure, with velocities in the order of 1.5 mm/s.
How to cite: Uslar, A.: Simulation of frictional heat generation due to underground motion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10795, https://doi.org/10.5194/egusphere-egu2020-10795, 2020.
EGU2020-14142 | Displays | TS2.5
Heat transfer through the nappes of the Lepontine DomeAlessia Tagliaferri, Filippo Luca Schenker, Stefan Markus Schmalholz, and Silvio Seno
The heat transfer through the nappes of the Lepontine Dome (Central Alps, Ticino, Switzerland) produced metamorphic amphibolite-facies isogrades that locally dissect the tectonic contacts. This large-scale observation, suggesting a thermal amphibolite-facies event after thrusting and nappe formation, is however at odd with the extremely pervasive mineral and stretching lineation (NW-SE directed) that attests non-coaxial deformation during shearing at similar metamorphic conditions.
To solve this apparent paradox we performed 2D thermo-kinematic simulations in which we investigated the relationships between nappe geometry and the geometries of isogrades. The numerical simulations are based on the finite difference method. We evaluate the relative importance of velocity, thermal diffusion and advection, and geometry of the thrust sheets, on the geometrical relation between tectonic contacts and isogrades. We calculate the thermal evolution and peak temperatures in order to compare the numerical results with field and petrological data collected along the Simano and Cima Lunga nappes.
In the field, the alternation of lithotypes is parallel to the nappe boundaries and constant over their whole length (order of kms). Passing from the Simano to the Cima-Lunga nappe, the transition between the nappes is marked by a progressive change in the texture of gneisses, in which the porphyroblasts become more stretched from the bottom to the top, and by the change in the constituent lithotypes. In the studied area, the Simano nappe is formed mainly by metagranitoids and by minor paragneisses. The Cima Lunga nappe is made of metasediments, mainly quartz-rich gneisses intercalated with amphibolite-gneisses, peridotitic lenses and local calcschists and/or marbles. Finally, the widespread paragneisses forming both the nappes frequently contain garnets of different sizes and internal microstructure. Published and own petrological data of these garnet-bearing rocks will be used to restrict the physical parameters of the numerical results.
We intend to test multiple geological scenarios related to different sources of heat production, such as: internal heat sources (radiogenic heating); additional heat flux at the bottom of the nappes, such in the case of a magmatic underplating, slab break-off, lower crust delamination; and in situ-produced heat due to shear heating mechanisms at the tectonic boundary between the nappes (thrust surface).
How to cite: Tagliaferri, A., Schenker, F. L., Schmalholz, S. M., and Seno, S.: Heat transfer through the nappes of the Lepontine Dome, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14142, https://doi.org/10.5194/egusphere-egu2020-14142, 2020.
The heat transfer through the nappes of the Lepontine Dome (Central Alps, Ticino, Switzerland) produced metamorphic amphibolite-facies isogrades that locally dissect the tectonic contacts. This large-scale observation, suggesting a thermal amphibolite-facies event after thrusting and nappe formation, is however at odd with the extremely pervasive mineral and stretching lineation (NW-SE directed) that attests non-coaxial deformation during shearing at similar metamorphic conditions.
To solve this apparent paradox we performed 2D thermo-kinematic simulations in which we investigated the relationships between nappe geometry and the geometries of isogrades. The numerical simulations are based on the finite difference method. We evaluate the relative importance of velocity, thermal diffusion and advection, and geometry of the thrust sheets, on the geometrical relation between tectonic contacts and isogrades. We calculate the thermal evolution and peak temperatures in order to compare the numerical results with field and petrological data collected along the Simano and Cima Lunga nappes.
In the field, the alternation of lithotypes is parallel to the nappe boundaries and constant over their whole length (order of kms). Passing from the Simano to the Cima-Lunga nappe, the transition between the nappes is marked by a progressive change in the texture of gneisses, in which the porphyroblasts become more stretched from the bottom to the top, and by the change in the constituent lithotypes. In the studied area, the Simano nappe is formed mainly by metagranitoids and by minor paragneisses. The Cima Lunga nappe is made of metasediments, mainly quartz-rich gneisses intercalated with amphibolite-gneisses, peridotitic lenses and local calcschists and/or marbles. Finally, the widespread paragneisses forming both the nappes frequently contain garnets of different sizes and internal microstructure. Published and own petrological data of these garnet-bearing rocks will be used to restrict the physical parameters of the numerical results.
We intend to test multiple geological scenarios related to different sources of heat production, such as: internal heat sources (radiogenic heating); additional heat flux at the bottom of the nappes, such in the case of a magmatic underplating, slab break-off, lower crust delamination; and in situ-produced heat due to shear heating mechanisms at the tectonic boundary between the nappes (thrust surface).
How to cite: Tagliaferri, A., Schenker, F. L., Schmalholz, S. M., and Seno, S.: Heat transfer through the nappes of the Lepontine Dome, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14142, https://doi.org/10.5194/egusphere-egu2020-14142, 2020.
EGU2020-18763 | Displays | TS2.5
From Elastic Deformation Loading Rates to Heat Flow Anomalies: Constraints on Seismic Efficiency and Friction CoefficientMalte J. Ziebarth, John G. Anderson, Sebastian von Specht, Oliver Heidbach, and Fabrice Cotton
A long standing debate in seismology revolves around the nonexistent heat flow anomaly across the San Andreas fault. Given the fault’s average slip rate and age, a strong San Andreas fault, i.e. characterized by a relatively high static friction coefficient of µ>=0.6, should produce a significant local heat flow anomaly across the fault [1]. Since the work of Lachenbruch and Sass [1], this anomaly has not been observed and although many possible causes for the lack of a heat flow anomaly have been explored, the static or dynamic weakness of the San Andreas fault remains a favorable explanation [2,3].
Recently, we have introduced the ENergy COnserving Seismicity (ENCOS) framework that relates elastic deformation energy loading rates to the long-term average energy release of the seismic process. Within the presented implementation of ENCOS for Southern California with an elastic loading rate between 300 MW and 1.9 GW, the two most significant parameters are the static friction coefficient and the average efficiency. In particular, they are the most significant sources of uncertainty in harnessing the GPS-derived strain rates and the stress data within the ENCOS framework.
Here, we show how ENCOS can be leveraged in combination with the constraints from heat flow measurements and observed seismicity to restrict the parameter space of the average efficiency and the static friction coefficient. This can help to reduce the uncertainty of the ENCOS model parameters, such as the elastic deformation energy loading rate, and opens a new viewpoint on the heat flow paradox.
[1] Lachenbruch, A. H., and Sass, J. H. (1980), Heat flow and energetics of the San Andreas Fault Zone, J. Geophys. Res., 85(B11), 6185–6222.
[2] Scholz, C. H. (2013). The Strength of the San Andreas Fault: A Critical Analysis. In Earthquakes: Radiated Energy and the Physics of Faulting (eds R. Abercrombie, A. McGarr, G. Di Toro and H. Kanamori).
[3] E. E. Brodsky et al. (2020), The State of Stress on the Fault Before, During, and After a Major Earthquake, Annu. Rev. Earth Planet. Sci. 48:2.1–2.26.
How to cite: Ziebarth, M. J., Anderson, J. G., von Specht, S., Heidbach, O., and Cotton, F.: From Elastic Deformation Loading Rates to Heat Flow Anomalies: Constraints on Seismic Efficiency and Friction Coefficient, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18763, https://doi.org/10.5194/egusphere-egu2020-18763, 2020.
A long standing debate in seismology revolves around the nonexistent heat flow anomaly across the San Andreas fault. Given the fault’s average slip rate and age, a strong San Andreas fault, i.e. characterized by a relatively high static friction coefficient of µ>=0.6, should produce a significant local heat flow anomaly across the fault [1]. Since the work of Lachenbruch and Sass [1], this anomaly has not been observed and although many possible causes for the lack of a heat flow anomaly have been explored, the static or dynamic weakness of the San Andreas fault remains a favorable explanation [2,3].
Recently, we have introduced the ENergy COnserving Seismicity (ENCOS) framework that relates elastic deformation energy loading rates to the long-term average energy release of the seismic process. Within the presented implementation of ENCOS for Southern California with an elastic loading rate between 300 MW and 1.9 GW, the two most significant parameters are the static friction coefficient and the average efficiency. In particular, they are the most significant sources of uncertainty in harnessing the GPS-derived strain rates and the stress data within the ENCOS framework.
Here, we show how ENCOS can be leveraged in combination with the constraints from heat flow measurements and observed seismicity to restrict the parameter space of the average efficiency and the static friction coefficient. This can help to reduce the uncertainty of the ENCOS model parameters, such as the elastic deformation energy loading rate, and opens a new viewpoint on the heat flow paradox.
[1] Lachenbruch, A. H., and Sass, J. H. (1980), Heat flow and energetics of the San Andreas Fault Zone, J. Geophys. Res., 85(B11), 6185–6222.
[2] Scholz, C. H. (2013). The Strength of the San Andreas Fault: A Critical Analysis. In Earthquakes: Radiated Energy and the Physics of Faulting (eds R. Abercrombie, A. McGarr, G. Di Toro and H. Kanamori).
[3] E. E. Brodsky et al. (2020), The State of Stress on the Fault Before, During, and After a Major Earthquake, Annu. Rev. Earth Planet. Sci. 48:2.1–2.26.
How to cite: Ziebarth, M. J., Anderson, J. G., von Specht, S., Heidbach, O., and Cotton, F.: From Elastic Deformation Loading Rates to Heat Flow Anomalies: Constraints on Seismic Efficiency and Friction Coefficient, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18763, https://doi.org/10.5194/egusphere-egu2020-18763, 2020.
EGU2020-13800 | Displays | TS2.5
Detailed statistical analysis of the Gole Larghe Fault Zone fracture network (Italian Southern Alps) improves estimates of the energy budget for intraplate earthquakes in basement rocksAndrea Bistacchi, Silvia Mittempergher, Steve A.F. Smith, Giulio Di Toro, and Stefan Nielsen
We present a study on the paleoseismic Gole Larghe Fault Zone (GLFZ), composed of hundreds of sub-parallel faults hosted in tonalites of the Adamello Massif (Italian Southern Alps), where we collected a complete transect across the fault zone, including the background host rocks, over a thickness of >1km.
Along this transect, we studied the correlation between fracture spacing (for “fracture” here we mean joints, veins, faults, shear fractures, and all other brittle structures) and position with a robust non-parametric approach. This analysis, new for fracture distribution studies, allows detecting volumes of the fault zone with clustering or a trend in spacing, versus volumes where the spatial distribution is stationary. The analysis reveals that the GLFZ can be subdivided in “stationary volumes” where fractures shows stationary statistical properties. Each one of these volumes can be completely characterized with scanline and/or scanarea surveys to obtain a complete and statistically sound estimate of all fracture parameters (spacing, intensity, density, length, height, orientation, topology, etc.).
Within the GLFZ we have two main classes of structures: (i) “master” faults that are sub-parallel to the fault zone and are always characterized by pseudotachylytes and/or cataclasites, and (ii) minor “fractures” (e.g. Riedel fractures, joints, veins, etc.) that are oblique to the fault zone and interconnect the former. Out of the GLFZ we observe a background fracturing that is associated to the cooling of the Adamello tonalites under deviatoric tectonic stress (“cooling joints”).
By comparing fracture statistics within and outside the fault zone, we demonstrated that master faults within the GLFZ were almost completely inherited from the “cooling joints” of the host rocks. The cooling joints just grew in length and became completely interconnected at the scale of the seismic rupture. This means that, at least in the case of the GLFZ, the large faults and fractures along which seismic ruptures were running do not add significantly to the earthquake energy budget, because they were already present in the system before the onset of seismic activity. The only fractures to be considered in this budget are the minor interconnecting fractures (e.g. Riedel fractures, joints, veins, etc.) that are coated with pseudotachylytes.
These observations confirm once again the classical assumption that seismic ruptures propagate along pre-existing discontinuities and do not, in general, tend to fracture intact rocks.
How to cite: Bistacchi, A., Mittempergher, S., Smith, S. A. F., Di Toro, G., and Nielsen, S.: Detailed statistical analysis of the Gole Larghe Fault Zone fracture network (Italian Southern Alps) improves estimates of the energy budget for intraplate earthquakes in basement rocks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13800, https://doi.org/10.5194/egusphere-egu2020-13800, 2020.
We present a study on the paleoseismic Gole Larghe Fault Zone (GLFZ), composed of hundreds of sub-parallel faults hosted in tonalites of the Adamello Massif (Italian Southern Alps), where we collected a complete transect across the fault zone, including the background host rocks, over a thickness of >1km.
Along this transect, we studied the correlation between fracture spacing (for “fracture” here we mean joints, veins, faults, shear fractures, and all other brittle structures) and position with a robust non-parametric approach. This analysis, new for fracture distribution studies, allows detecting volumes of the fault zone with clustering or a trend in spacing, versus volumes where the spatial distribution is stationary. The analysis reveals that the GLFZ can be subdivided in “stationary volumes” where fractures shows stationary statistical properties. Each one of these volumes can be completely characterized with scanline and/or scanarea surveys to obtain a complete and statistically sound estimate of all fracture parameters (spacing, intensity, density, length, height, orientation, topology, etc.).
Within the GLFZ we have two main classes of structures: (i) “master” faults that are sub-parallel to the fault zone and are always characterized by pseudotachylytes and/or cataclasites, and (ii) minor “fractures” (e.g. Riedel fractures, joints, veins, etc.) that are oblique to the fault zone and interconnect the former. Out of the GLFZ we observe a background fracturing that is associated to the cooling of the Adamello tonalites under deviatoric tectonic stress (“cooling joints”).
By comparing fracture statistics within and outside the fault zone, we demonstrated that master faults within the GLFZ were almost completely inherited from the “cooling joints” of the host rocks. The cooling joints just grew in length and became completely interconnected at the scale of the seismic rupture. This means that, at least in the case of the GLFZ, the large faults and fractures along which seismic ruptures were running do not add significantly to the earthquake energy budget, because they were already present in the system before the onset of seismic activity. The only fractures to be considered in this budget are the minor interconnecting fractures (e.g. Riedel fractures, joints, veins, etc.) that are coated with pseudotachylytes.
These observations confirm once again the classical assumption that seismic ruptures propagate along pre-existing discontinuities and do not, in general, tend to fracture intact rocks.
How to cite: Bistacchi, A., Mittempergher, S., Smith, S. A. F., Di Toro, G., and Nielsen, S.: Detailed statistical analysis of the Gole Larghe Fault Zone fracture network (Italian Southern Alps) improves estimates of the energy budget for intraplate earthquakes in basement rocks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13800, https://doi.org/10.5194/egusphere-egu2020-13800, 2020.
EGU2020-8030 | Displays | TS2.5 | Highlight
Impact of coseismic off-fault damage on the overall energy budget.Marion Y. Thomas and Harsha S. Bhat
In the brittle part of the crust, deformation is usually perceived to be the result of displacement along fault planes, whose behaviors are controlled by their frictional properties. However, fault zones not only consist of a narrow fault core where slip occurs, they are also surrounded by a complex structure which is of key importance in the mechanics of faulting, hence in determining the overall energy budget. Indeed, as pointed out by the numerous field, geophysical, mechanical and laboratory observations, if the behavior of fault zones is intrinsically linked to the properties of the main sliding plane, it also depends on those of the surrounding medium. In parallel, fault displacements may induce a substantial change in the physical properties of the surrounding medium. As a consequence, to improve our understanding of active fault zones, fault slip and the evolving physical properties must be studied as a unique system of stress accommodation and no longer as two distinct entities. To tackle this problem, we have developed a micromechanics-based constitutive model, thermodynamically argued, that can determine the inelastic behavior at macroscopic scale that arises from structural rearrangements at microscale. It is therefore the compulsory tool to emulate the strong coupling between the bulk and the fault that prevails during earthquakes. With this code, we can reproduce the strain rate sensitive, non-linear stress-strain relationship that leads to off-fault damage as a seismic event is propagating. We explore different scenarii and we show that there is a unique off-fault damage pattern associated with supershear transition of an earthquake rupture, that is also observed in the field. We define, in return, the impact of damage on the propagation of the earthquake in itself and the generated waves. We conclude by assessing the kinetic energy, the dissipated energy and the radiated energy to define how energy is consumed within crustal systems during seismic events.
How to cite: Thomas, M. Y. and Bhat, H. S.: Impact of coseismic off-fault damage on the overall energy budget., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8030, https://doi.org/10.5194/egusphere-egu2020-8030, 2020.
In the brittle part of the crust, deformation is usually perceived to be the result of displacement along fault planes, whose behaviors are controlled by their frictional properties. However, fault zones not only consist of a narrow fault core where slip occurs, they are also surrounded by a complex structure which is of key importance in the mechanics of faulting, hence in determining the overall energy budget. Indeed, as pointed out by the numerous field, geophysical, mechanical and laboratory observations, if the behavior of fault zones is intrinsically linked to the properties of the main sliding plane, it also depends on those of the surrounding medium. In parallel, fault displacements may induce a substantial change in the physical properties of the surrounding medium. As a consequence, to improve our understanding of active fault zones, fault slip and the evolving physical properties must be studied as a unique system of stress accommodation and no longer as two distinct entities. To tackle this problem, we have developed a micromechanics-based constitutive model, thermodynamically argued, that can determine the inelastic behavior at macroscopic scale that arises from structural rearrangements at microscale. It is therefore the compulsory tool to emulate the strong coupling between the bulk and the fault that prevails during earthquakes. With this code, we can reproduce the strain rate sensitive, non-linear stress-strain relationship that leads to off-fault damage as a seismic event is propagating. We explore different scenarii and we show that there is a unique off-fault damage pattern associated with supershear transition of an earthquake rupture, that is also observed in the field. We define, in return, the impact of damage on the propagation of the earthquake in itself and the generated waves. We conclude by assessing the kinetic energy, the dissipated energy and the radiated energy to define how energy is consumed within crustal systems during seismic events.
How to cite: Thomas, M. Y. and Bhat, H. S.: Impact of coseismic off-fault damage on the overall energy budget., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8030, https://doi.org/10.5194/egusphere-egu2020-8030, 2020.
EGU2020-16230 | Displays | TS2.5
Energy budget of laboratory earthquakes: a comparison between linear elastic fracture mechanics approach and experimental approach.Marie Violay, Federica Paglialunga, and François X. Passelègue
Earthquakes correspond to a sudden release of elastic energy stored during inter-seismic period by tectonic loading around fault. The earthquake energy budget consists of four non-independent terms: the energy release rate (by unit crack length), the fracture energy, the heat term and finally the radiated energy. These terms depend on the rupture and sliding velocities, the amount of slip and the stress drop. Because of the impossibility to access to stress and strain conditions at depth, the earthquake energy budget cannot be fully constrained from seismological data, limiting our understanding of its influence on rupture propagation.
To address this issue, we conducted stick-slip experiments with large samples in a biaxial configuration apparatus. By imposing constant normal load and increasing shear load, seismic events were produced on a 20 cm long fault, for which the energy budget was estimated using different methods.
Fracture energy was estimated by recording the strain field around the crack tip through high frequency (2 MHz) strain gage rosettes array and comparing it to the theoretical LEFM strain field predictions obtained for same conditions (i.e. rupture velocity, distance from the fault). Fracture energies were then inverted and found to range in between 1 and 10 J/m2. At the same time the energy partitioning was estimated through stress-slip evolution during rupture. The fracture energies obtained from this method are almost one order of magnitude larger than the ones inverted from LEFM and range in between 1 and 90 J/m2. Moreover, the energy partitioning shows the radiated energy ranging between 80 and 300 J/m2 and finally the heat/thermal energy as the largest fraction of the energy partitioning with values ranging from 200 to 2500 J/m2. Our preliminary results highlight the importance of understanding the contribution of heat energy in frictional processes, since this term cannot be estimated from seismological data.
How to cite: Violay, M., Paglialunga, F., and Passelègue, F. X.: Energy budget of laboratory earthquakes: a comparison between linear elastic fracture mechanics approach and experimental approach., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16230, https://doi.org/10.5194/egusphere-egu2020-16230, 2020.
Earthquakes correspond to a sudden release of elastic energy stored during inter-seismic period by tectonic loading around fault. The earthquake energy budget consists of four non-independent terms: the energy release rate (by unit crack length), the fracture energy, the heat term and finally the radiated energy. These terms depend on the rupture and sliding velocities, the amount of slip and the stress drop. Because of the impossibility to access to stress and strain conditions at depth, the earthquake energy budget cannot be fully constrained from seismological data, limiting our understanding of its influence on rupture propagation.
To address this issue, we conducted stick-slip experiments with large samples in a biaxial configuration apparatus. By imposing constant normal load and increasing shear load, seismic events were produced on a 20 cm long fault, for which the energy budget was estimated using different methods.
Fracture energy was estimated by recording the strain field around the crack tip through high frequency (2 MHz) strain gage rosettes array and comparing it to the theoretical LEFM strain field predictions obtained for same conditions (i.e. rupture velocity, distance from the fault). Fracture energies were then inverted and found to range in between 1 and 10 J/m2. At the same time the energy partitioning was estimated through stress-slip evolution during rupture. The fracture energies obtained from this method are almost one order of magnitude larger than the ones inverted from LEFM and range in between 1 and 90 J/m2. Moreover, the energy partitioning shows the radiated energy ranging between 80 and 300 J/m2 and finally the heat/thermal energy as the largest fraction of the energy partitioning with values ranging from 200 to 2500 J/m2. Our preliminary results highlight the importance of understanding the contribution of heat energy in frictional processes, since this term cannot be estimated from seismological data.
How to cite: Violay, M., Paglialunga, F., and Passelègue, F. X.: Energy budget of laboratory earthquakes: a comparison between linear elastic fracture mechanics approach and experimental approach., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16230, https://doi.org/10.5194/egusphere-egu2020-16230, 2020.
Earthquake ruptures are driven by the dynamic weakening of frictional strength along faults. This drop of frictional stress toward a residual level is at the origin of the slip-weakening model, which became a well-established framework to study seismic ruptures and their energy budget. In this framework, the part of frictional energy associated to the rupture propagation (i.e. the fracture energy) corresponds to the excess of frictional dissipation on top of the residual stress, also referred as the breakdown work.
In this study, we test this energy partition for friction models that do not impose the magnitude of the residual stress. For example, rate-and-state models are a class of generic friction laws for which the residual stress after the rupture emerges from the interplay with the bulk elastodynamics. In this context, we simulate a frictional rupture at the interface between two linearly elastic solids and study the energy balance driving its propagation. Using dynamic fracture mechanics, we independently measure throughout the rupture the energy release rate from the bulk elastic fields and the frictional dissipation along the interface. From the comparison between these two quantities, we identify the part of interface dissipation corresponding to the fracture energy and show how the latter can be significantly smaller than the total breakdown work.
In a second phase, we test the generality of these results along another type of interface representative of mature fault zones filled with gouge.
This study shines new light on the energy budget of frictional ruptures and finds implications in the estimation of the fracture energy during earthquakes.
How to cite: Barras, F.: On the energy balance behind frictional ruptures, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18255, https://doi.org/10.5194/egusphere-egu2020-18255, 2020.
Earthquake ruptures are driven by the dynamic weakening of frictional strength along faults. This drop of frictional stress toward a residual level is at the origin of the slip-weakening model, which became a well-established framework to study seismic ruptures and their energy budget. In this framework, the part of frictional energy associated to the rupture propagation (i.e. the fracture energy) corresponds to the excess of frictional dissipation on top of the residual stress, also referred as the breakdown work.
In this study, we test this energy partition for friction models that do not impose the magnitude of the residual stress. For example, rate-and-state models are a class of generic friction laws for which the residual stress after the rupture emerges from the interplay with the bulk elastodynamics. In this context, we simulate a frictional rupture at the interface between two linearly elastic solids and study the energy balance driving its propagation. Using dynamic fracture mechanics, we independently measure throughout the rupture the energy release rate from the bulk elastic fields and the frictional dissipation along the interface. From the comparison between these two quantities, we identify the part of interface dissipation corresponding to the fracture energy and show how the latter can be significantly smaller than the total breakdown work.
In a second phase, we test the generality of these results along another type of interface representative of mature fault zones filled with gouge.
This study shines new light on the energy budget of frictional ruptures and finds implications in the estimation of the fracture energy during earthquakes.
How to cite: Barras, F.: On the energy balance behind frictional ruptures, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18255, https://doi.org/10.5194/egusphere-egu2020-18255, 2020.
EGU2020-11253 | Displays | TS2.5
Predicting the propagation and interaction of frontal accretionary thrust faults with work optimizationMichele Cooke, Jess McBeck, and Laura Fattaruso
This study assesses the ability of work optimization to predict the spatial and temporal initiation of faults. We focus on the growth of flaws that develop into thrust faults at the toe of accretionary prisms because observations from physical laboratory accretion experiments provide rich data with which to validate the models, and the processes of accretionary thrust fault initiation remain unclear. In order to model these systems, we apply new implementations to the fault growth code GROW that improve its prediction of fault interaction using work optimization, including: 1) CPU parallelization, 2) a new growth algorithm that propagates only the most efficient fault in each growth increment, the single run mode, and 3) a new growth algorithm that only considers fault propagation from fault tips that host high sums of modes I and II stress intensity factors, KG, the limiting mode. The single and limiting mode produce the geometries that best match the observed geometries, rather than the previous algorithm that allows all the faults to propagate simultaneously, regardless of KG, the multiple and non-limiting mode. The single limiting models predict that frontal accretionary thrusts initiate at the midpack or shallower depths, consistent with findings of previous studies. The thrusts propagate upward, link with the surface, and then propagate downward and link with the detachment. The backthrust tends to propagate before the forethrust, and then influence the forethrust propagation. This temporal and spatial sequence of faulting arises from the lower compression, higher shear strain, higher Coulomb stress and higher strain energy density that develop near the wedge surface and the inflection of the wedge slope. The models reveal that the final slip distributions do not reliably indicate the initiation location of the faults, in contrast to the assumptions of previous analyses.
How to cite: Cooke, M., McBeck, J., and Fattaruso, L.: Predicting the propagation and interaction of frontal accretionary thrust faults with work optimization, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11253, https://doi.org/10.5194/egusphere-egu2020-11253, 2020.
This study assesses the ability of work optimization to predict the spatial and temporal initiation of faults. We focus on the growth of flaws that develop into thrust faults at the toe of accretionary prisms because observations from physical laboratory accretion experiments provide rich data with which to validate the models, and the processes of accretionary thrust fault initiation remain unclear. In order to model these systems, we apply new implementations to the fault growth code GROW that improve its prediction of fault interaction using work optimization, including: 1) CPU parallelization, 2) a new growth algorithm that propagates only the most efficient fault in each growth increment, the single run mode, and 3) a new growth algorithm that only considers fault propagation from fault tips that host high sums of modes I and II stress intensity factors, KG, the limiting mode. The single and limiting mode produce the geometries that best match the observed geometries, rather than the previous algorithm that allows all the faults to propagate simultaneously, regardless of KG, the multiple and non-limiting mode. The single limiting models predict that frontal accretionary thrusts initiate at the midpack or shallower depths, consistent with findings of previous studies. The thrusts propagate upward, link with the surface, and then propagate downward and link with the detachment. The backthrust tends to propagate before the forethrust, and then influence the forethrust propagation. This temporal and spatial sequence of faulting arises from the lower compression, higher shear strain, higher Coulomb stress and higher strain energy density that develop near the wedge surface and the inflection of the wedge slope. The models reveal that the final slip distributions do not reliably indicate the initiation location of the faults, in contrast to the assumptions of previous analyses.
How to cite: Cooke, M., McBeck, J., and Fattaruso, L.: Predicting the propagation and interaction of frontal accretionary thrust faults with work optimization, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11253, https://doi.org/10.5194/egusphere-egu2020-11253, 2020.
TS3.4 – Strain localisation, deformation, fluid flow and seismic activity in subduction zones
EGU2020-3373 | Displays | TS3.4 | Highlight
Hydration- and dehydration-induced rheological heterogeneities on the deep subduction interface, and possible relationships to episodic tremor and slow slipWhitney Behr, Carolyn Tewksbury-Christle, Alissa Kotowski, Claudio Cannizzaro, Robert Blass, and Taras Gerya
Episodic tremor and slow slip (ETS) is observed in several subduction zones down-dip of the locked megathrust, and may provide clues for preparatory processes before megathrust rupture. Exhumed rocks provide a unique opportunity to evaluate the sources of rheological heterogeneity on the subduction interface and their potential role in generating ETS-like behavior. We present data from two subduction interface shear zones representative of the down-dip extent of the megathrust: the Condrey Mountain Schist (CMS) in northern CA (greenschist to blueschist facies conditions) and the Cycladic Blueschist Unit (CBU) on Syros Island, Greece (blueschist to eclogite facies). Both complexes highlight the propensity for fluid-mediated metamorphic reactions to produce strong rheological heterogeneities:
In the CMW, hydration reactions led to progressive serpentinization of peridotite bodies that were entrained from the overriding plate and underplated along with oceanic-affinity sediments. The margins of each peridotite-serpentinite lens show extreme strain localization accommodated by dislocation glide and minor pressure solution in antigorite, whereas lens interiors show evidence for more distributed, alternating, frictional-viscous deformation, with abundant crack-seal veins occupied by antigorite, brucite and oxides that are in some places also ductilely sheared. Deformation in the surrounding metasedimentary matrix was purely viscous.
In the CBU on Syros Island, dehydration reactions in MORB-affinity basalts, subducted and underplated with oceanic and continental-affinity sediments, led to progressive development of strong eclogitic lenses within a weaker blueschist and metasedimentary matrix. The eclogite lenses are commonly coarse-grained and massive and show brittle deformation in the form of dilational and shear fractures/veins filled with quartz, white mica, glaucophane and/or chlorite. Brittle deformation in the eclogites is coeval with ductile deformation in the surrounding blueschist and metasedimentary matrix, indicating concurrent frictional-viscous flow.
Although we cannot easily distinguish transient deformation processes in exhumed rocks, we can use the following three approaches to assess whether these heterogeneities could have generated deformation behaviors similar to deep ETS: 1) We measure displacements within, and dimensions of the heterogeneities in outcrop/map-scale to estimate the maximum possible seismic moment that would be released when the frictional heterogeneities slip; 2) We compare deformation mechanisms inferred from field and microstructural observations to their expected mechanical behavior from rock deformation experiments; and 3) We use seismo-thermo-mechanical modeling to examine expected slip velocities and moment-duration ratios for frictional-viscous shear zones that are scaled to observations from nature and the lab.
All three approaches suggest that frictional-viscous heterogeneities of the types and length-scales we observe in the exhumed rock record are compatible with ETS as documented in modern subduction zones.
How to cite: Behr, W., Tewksbury-Christle, C., Kotowski, A., Cannizzaro, C., Blass, R., and Gerya, T.: Hydration- and dehydration-induced rheological heterogeneities on the deep subduction interface, and possible relationships to episodic tremor and slow slip, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3373, https://doi.org/10.5194/egusphere-egu2020-3373, 2020.
Episodic tremor and slow slip (ETS) is observed in several subduction zones down-dip of the locked megathrust, and may provide clues for preparatory processes before megathrust rupture. Exhumed rocks provide a unique opportunity to evaluate the sources of rheological heterogeneity on the subduction interface and their potential role in generating ETS-like behavior. We present data from two subduction interface shear zones representative of the down-dip extent of the megathrust: the Condrey Mountain Schist (CMS) in northern CA (greenschist to blueschist facies conditions) and the Cycladic Blueschist Unit (CBU) on Syros Island, Greece (blueschist to eclogite facies). Both complexes highlight the propensity for fluid-mediated metamorphic reactions to produce strong rheological heterogeneities:
In the CMW, hydration reactions led to progressive serpentinization of peridotite bodies that were entrained from the overriding plate and underplated along with oceanic-affinity sediments. The margins of each peridotite-serpentinite lens show extreme strain localization accommodated by dislocation glide and minor pressure solution in antigorite, whereas lens interiors show evidence for more distributed, alternating, frictional-viscous deformation, with abundant crack-seal veins occupied by antigorite, brucite and oxides that are in some places also ductilely sheared. Deformation in the surrounding metasedimentary matrix was purely viscous.
In the CBU on Syros Island, dehydration reactions in MORB-affinity basalts, subducted and underplated with oceanic and continental-affinity sediments, led to progressive development of strong eclogitic lenses within a weaker blueschist and metasedimentary matrix. The eclogite lenses are commonly coarse-grained and massive and show brittle deformation in the form of dilational and shear fractures/veins filled with quartz, white mica, glaucophane and/or chlorite. Brittle deformation in the eclogites is coeval with ductile deformation in the surrounding blueschist and metasedimentary matrix, indicating concurrent frictional-viscous flow.
Although we cannot easily distinguish transient deformation processes in exhumed rocks, we can use the following three approaches to assess whether these heterogeneities could have generated deformation behaviors similar to deep ETS: 1) We measure displacements within, and dimensions of the heterogeneities in outcrop/map-scale to estimate the maximum possible seismic moment that would be released when the frictional heterogeneities slip; 2) We compare deformation mechanisms inferred from field and microstructural observations to their expected mechanical behavior from rock deformation experiments; and 3) We use seismo-thermo-mechanical modeling to examine expected slip velocities and moment-duration ratios for frictional-viscous shear zones that are scaled to observations from nature and the lab.
All three approaches suggest that frictional-viscous heterogeneities of the types and length-scales we observe in the exhumed rock record are compatible with ETS as documented in modern subduction zones.
How to cite: Behr, W., Tewksbury-Christle, C., Kotowski, A., Cannizzaro, C., Blass, R., and Gerya, T.: Hydration- and dehydration-induced rheological heterogeneities on the deep subduction interface, and possible relationships to episodic tremor and slow slip, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3373, https://doi.org/10.5194/egusphere-egu2020-3373, 2020.
EGU2020-5646 | Displays | TS3.4
Rheological properties of the shallow subduction interface: insights from the Chugach Complex, AlaskaZoe Braden and Whitney Behr
The plate interface in subduction zones accommodates a wide range of seismic styles over different depths as a function of pressure-temperature conditions, compositional and fluid-pressure heterogeneities, deformation mechanisms, and degrees of strain localization. The shallow subduction interface (i.e. ~2-10 km subduction depths), in particular, can exhibit either slow slip events (e.g. Hikurangi) or megathrust earthquakes (e.g. Tohoku). To evaluate the factors governing these different slip behaviors, we need better constraints on the rheological properties of the shallow interface. Here we focus on exhumed rocks within the Chugach Complex of southern Alaska, which represents the Jurassic to Cretaceous shallow subduction interface of the Kula and North American plates. The Chugach is ideal because it exhibits progressive variations in subducted rock types through time, minimal post-subduction overprinting, and extensive along-strike exposure (~250 km). Our aims are to use field structural mapping, geochronology, and microstructural analysis to examine a) how strain is localized in different subducted protoliths, and b) the deformation processes, role of fluids, and strain localization mechanisms within each high strain zone. We interpret these data in the context of the relative ‘strengths’ of different materials on the shallow interface and possible styles of seismicity.
Thus far we have characterized deformation features along a 1.25-km-thick melange belt within the Turnagain Arm region southeast of Anchorage. The westernmost melange unit is sediment poor and consists of deep marine rocks with more chert, shale and mafic rocks than units to the east. The melange fabric is variably developed (weakly to strongly) throughout the unit and is steeply (sub-vertical) west-dipping with down-dip lineations. Quartz-calcite-filled dilational cracks are oriented perpendicular to the main melange fabric.
Drone imaging and structural mapping reveals 3 major discrete shear zones and 6-7 minor shear zones within the melange belt, all of which exhibit thrust kinematics. Major shear zones show a significant and observable strain gradient into a wide (~1 m) region of high strain and deform large blocks while minor shear zones are generally developed in narrow zones (~10-15 cm) of high strain between larger blocks. One major shear zone is developed in basalt and has closely-spaced, polished slip surfaces that define a facoidal texture; the basalt shear zone is ~1 m thick. Preserved pillows are observable in lower strain areas on either side of the shear zone but are deformed and indistinguishable within the high strain zone. The other two major shear zones are developed in shale and are matrix-supported with wispy, closely-spaced foliation and rotated porphyroclasts of chert and basalt; the shale shear zones are ~0.5-2 m thick.
Abundant quartz-calcite veins parallel to the melange fabric and within shale shear zones record multiple generations of fluid-flow; early veins appear to be more silicic and later fluid flow involved only calcite precipitation. At the west, trench-proximal end of the mélange unit there is a 5-10 m thick silicified zone of fluid injection that is bound on one side by the basalt shear zone. Fluid injection appears to pre-date or be synchronous with shearing.
How to cite: Braden, Z. and Behr, W.: Rheological properties of the shallow subduction interface: insights from the Chugach Complex, Alaska, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5646, https://doi.org/10.5194/egusphere-egu2020-5646, 2020.
The plate interface in subduction zones accommodates a wide range of seismic styles over different depths as a function of pressure-temperature conditions, compositional and fluid-pressure heterogeneities, deformation mechanisms, and degrees of strain localization. The shallow subduction interface (i.e. ~2-10 km subduction depths), in particular, can exhibit either slow slip events (e.g. Hikurangi) or megathrust earthquakes (e.g. Tohoku). To evaluate the factors governing these different slip behaviors, we need better constraints on the rheological properties of the shallow interface. Here we focus on exhumed rocks within the Chugach Complex of southern Alaska, which represents the Jurassic to Cretaceous shallow subduction interface of the Kula and North American plates. The Chugach is ideal because it exhibits progressive variations in subducted rock types through time, minimal post-subduction overprinting, and extensive along-strike exposure (~250 km). Our aims are to use field structural mapping, geochronology, and microstructural analysis to examine a) how strain is localized in different subducted protoliths, and b) the deformation processes, role of fluids, and strain localization mechanisms within each high strain zone. We interpret these data in the context of the relative ‘strengths’ of different materials on the shallow interface and possible styles of seismicity.
Thus far we have characterized deformation features along a 1.25-km-thick melange belt within the Turnagain Arm region southeast of Anchorage. The westernmost melange unit is sediment poor and consists of deep marine rocks with more chert, shale and mafic rocks than units to the east. The melange fabric is variably developed (weakly to strongly) throughout the unit and is steeply (sub-vertical) west-dipping with down-dip lineations. Quartz-calcite-filled dilational cracks are oriented perpendicular to the main melange fabric.
Drone imaging and structural mapping reveals 3 major discrete shear zones and 6-7 minor shear zones within the melange belt, all of which exhibit thrust kinematics. Major shear zones show a significant and observable strain gradient into a wide (~1 m) region of high strain and deform large blocks while minor shear zones are generally developed in narrow zones (~10-15 cm) of high strain between larger blocks. One major shear zone is developed in basalt and has closely-spaced, polished slip surfaces that define a facoidal texture; the basalt shear zone is ~1 m thick. Preserved pillows are observable in lower strain areas on either side of the shear zone but are deformed and indistinguishable within the high strain zone. The other two major shear zones are developed in shale and are matrix-supported with wispy, closely-spaced foliation and rotated porphyroclasts of chert and basalt; the shale shear zones are ~0.5-2 m thick.
Abundant quartz-calcite veins parallel to the melange fabric and within shale shear zones record multiple generations of fluid-flow; early veins appear to be more silicic and later fluid flow involved only calcite precipitation. At the west, trench-proximal end of the mélange unit there is a 5-10 m thick silicified zone of fluid injection that is bound on one side by the basalt shear zone. Fluid injection appears to pre-date or be synchronous with shearing.
How to cite: Braden, Z. and Behr, W.: Rheological properties of the shallow subduction interface: insights from the Chugach Complex, Alaska, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5646, https://doi.org/10.5194/egusphere-egu2020-5646, 2020.
EGU2020-3285 | Displays | TS3.4
Rock record constraints on the seismic signature of subduction interface shear zonesCarolyn Tewksbury-Christle, Whitney Behr, and Mark Helper
The low velocity layer (LVL) in modern subduction zones is a 3-5 km thick region that parallels the top of the downgoing slab and is characterized by anomalously high Vp/Vs ratios (1.8-2.5) consistent with 2.5-4% fracture porosity at near-lithostatic pore fluid pressures. The LVL has been previously interpreted as partially hydrated, relatively undeformed oceanic crust at the top of the downgoing slab, but collocation of the LVL with episodic tremor and slow slip events (ETS) in modern subduction zones suggests that the LVL may alternatively represent the seismic signature of a subduction interface shear zone.
To test this hypothesis, we use field & structural observations, geochronology, and seismic velocity calculations to compare and contrast the bulk seismic properties of a fossil subduction interface shear zone (Condrey Mountain Schist, CMS, northern CA) to properties of modern LVLs. Specifically, we 1) determined thicknesses of underplated packages (interpreted to represent the maximum thickness of the actively deforming interface) using depositional age discontinuities and high resolution structural mapping, 2) averaged the bulk rock seismic velocities weighted by mapped lithologic proportions and corrected for pressure-temperature effects, and 3) used field evidence of modifying factors (e.g., microcracks, fluid-filled veins, mineral anisotropy) to further refine the possible range of seismic velocities and effects on Vp/Vs ratio.
The CMS greenschist- to blueschist-facies units were subducted to ~25-35 km (450°C, 0.8-1.0 GPa) with limited retrogression or exhumational overprint. These rocks were underplated episodically at depth in three packages individually up to 4.5 km thick from 155-135 Ma, based on detrital zircon data. Each package is dominantly composed of metasedimentary rocks with m- to km-scale metamafic and serpentinized ultramafic lenses. Strain localization to ~1 km thick ductile shear zones between underplating episodes is collocated with km-scale serpentinized ultramafic lenses at the base of each package. Deformation was distributed and ductile with rare macro- or micro-scale prograde brittle failure in the metasedimentary or metamafic units. In the serpentinized ultramafics, ductile shear zones wrap massive blocks with prograde brittle fracture. Maximum fracture porosity estimated from relict veins is ~10%. Average Vp/Vs for the CMS is ~1.6 (lithology alone) but up to 3.0 (accounting for maximum fracture porosity).
The fossil subduction interface shear zone preserved in the CMS is consistent in both thickness and seismic signature with the LVL in modern subduction zones. Estimated Vp/Vs is higher than the LVL but assumes that all fractures are simultaneously open. The total thickness of the CMS (10+ km) is greater than the LVL, however, so previously underplated material must lose its anomalous seismic signature during underplating (e.g., due to fluid loss and transport up the slab during or after underplating). Our results support the hypothesis that LVLs in modern subduction zones represent the seismic signature of the subduction interface shear zone.
How to cite: Tewksbury-Christle, C., Behr, W., and Helper, M.: Rock record constraints on the seismic signature of subduction interface shear zones, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3285, https://doi.org/10.5194/egusphere-egu2020-3285, 2020.
The low velocity layer (LVL) in modern subduction zones is a 3-5 km thick region that parallels the top of the downgoing slab and is characterized by anomalously high Vp/Vs ratios (1.8-2.5) consistent with 2.5-4% fracture porosity at near-lithostatic pore fluid pressures. The LVL has been previously interpreted as partially hydrated, relatively undeformed oceanic crust at the top of the downgoing slab, but collocation of the LVL with episodic tremor and slow slip events (ETS) in modern subduction zones suggests that the LVL may alternatively represent the seismic signature of a subduction interface shear zone.
To test this hypothesis, we use field & structural observations, geochronology, and seismic velocity calculations to compare and contrast the bulk seismic properties of a fossil subduction interface shear zone (Condrey Mountain Schist, CMS, northern CA) to properties of modern LVLs. Specifically, we 1) determined thicknesses of underplated packages (interpreted to represent the maximum thickness of the actively deforming interface) using depositional age discontinuities and high resolution structural mapping, 2) averaged the bulk rock seismic velocities weighted by mapped lithologic proportions and corrected for pressure-temperature effects, and 3) used field evidence of modifying factors (e.g., microcracks, fluid-filled veins, mineral anisotropy) to further refine the possible range of seismic velocities and effects on Vp/Vs ratio.
The CMS greenschist- to blueschist-facies units were subducted to ~25-35 km (450°C, 0.8-1.0 GPa) with limited retrogression or exhumational overprint. These rocks were underplated episodically at depth in three packages individually up to 4.5 km thick from 155-135 Ma, based on detrital zircon data. Each package is dominantly composed of metasedimentary rocks with m- to km-scale metamafic and serpentinized ultramafic lenses. Strain localization to ~1 km thick ductile shear zones between underplating episodes is collocated with km-scale serpentinized ultramafic lenses at the base of each package. Deformation was distributed and ductile with rare macro- or micro-scale prograde brittle failure in the metasedimentary or metamafic units. In the serpentinized ultramafics, ductile shear zones wrap massive blocks with prograde brittle fracture. Maximum fracture porosity estimated from relict veins is ~10%. Average Vp/Vs for the CMS is ~1.6 (lithology alone) but up to 3.0 (accounting for maximum fracture porosity).
The fossil subduction interface shear zone preserved in the CMS is consistent in both thickness and seismic signature with the LVL in modern subduction zones. Estimated Vp/Vs is higher than the LVL but assumes that all fractures are simultaneously open. The total thickness of the CMS (10+ km) is greater than the LVL, however, so previously underplated material must lose its anomalous seismic signature during underplating (e.g., due to fluid loss and transport up the slab during or after underplating). Our results support the hypothesis that LVLs in modern subduction zones represent the seismic signature of the subduction interface shear zone.
How to cite: Tewksbury-Christle, C., Behr, W., and Helper, M.: Rock record constraints on the seismic signature of subduction interface shear zones, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3285, https://doi.org/10.5194/egusphere-egu2020-3285, 2020.
EGU2020-5472 | Displays | TS3.4
Record by quartz veins of earthquakes and slow slip eventsHugues Raimbourg, Vincent Famin, Kristijan Rajic, Saskia Erdmann, Benjamin Moris-Muttoni, and Donald Fisher
Veins that form contemporaneously with deformation are the best recorders of the fluids circulating in the depths of orogenic and subduction zones. We have analyzed syn-kinematic quartz veins from accretionary prisms (Shimanto Belt in Japan, Kodiak accretionary prism in Alaska) and tectonic nappes in collisional orogens (Flysch à Helminthoïdes in the Alps, the southern domain of the variscan Montagne Noire), which formed at temperature conditions between 250 and 350°C, i.e. spanning the downdip limit of large subduction earthquakes and the generation of slow slip events. In all geological domains, veins hosted in rocks with the lower temperature conditions (~250-300°C) show quartz grains with crystallographic facets and growth rims. Cathodoluminescence (CL) imaging of these growth rims shows two different colors, a short-lived blue color and a brown one, attesting to cyclic variations in precipitation conditions. In contrast, veins hosted in rocks with the higher temperature conditions (~350°C), show a homogeneous, CL-brown colored quartz, except for some very restricted domains of crack-seal structures of CL-blue quartz found in Japan, Kodiak and Montagne Noire. Based on laser ablation and electron microprobe mapping, the variations in CL colors appear correlated with the trace element content of quartz, the short-lived CL-blue being associated with the substitution of Si4+ by Al3++Li+/H+.
Due to their ubiquitous presence in various settings, the variations in CL colors in the lower T range reflect a common, general process. We interpret these cyclic growth structures as a reflection of deformation/fracturing events, which triggered transient changes in (1) the fluid pressure through fluid flow and (2) the chemistry of the fluid due to enhanced reactivity of the fractured material. The CL-blue growth rims delineate zones where quartz growth was rapid and crystals incorporated a large proportion of Al and Li. Crystal growth continued at a lower pace after fluid pressure and composition evolved to equilibrium conditions, leading to the formation of CL-brown quartz with few substitutions of tetrahedral Si. The variations in fluid pressure fluctuated at values close to lithostatic conditions, as indicated by growth in cavities that remained open.
The crack-seal microstructures have been interpreted as the result of slow-slip events near the base of the seismogenic zone (Fisher and Brantley, 2014; Ujiie et al., 2018). Our observations on quartz composition suggest that the quartz in crack-seal microstructures records episodic variation in fluid pressure and composition, similar to vein quartz at T<~300 °C. In contrast to the cooler and shallower domain, the variations are significantly smaller, as recorded by the very limited extent of the CL-blue domains, and most if not all of the quartz growth occurred under constant physico-chemical conditions, including a near lithostatic fluid pressure.
We conclude that quartz trace element content is a useful tool to track variations in fluid conditions. In particular, at seismogenic depths (i.e. near 250°C), fluid pressure varies significantly around a lithostatic value. In contrast, deeper, near the base of the seismogenic zone where slow slip events occur (i.e. near 350°C), the variations in fluid pressure conditions are smaller.
How to cite: Raimbourg, H., Famin, V., Rajic, K., Erdmann, S., Moris-Muttoni, B., and Fisher, D.: Record by quartz veins of earthquakes and slow slip events, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5472, https://doi.org/10.5194/egusphere-egu2020-5472, 2020.
Veins that form contemporaneously with deformation are the best recorders of the fluids circulating in the depths of orogenic and subduction zones. We have analyzed syn-kinematic quartz veins from accretionary prisms (Shimanto Belt in Japan, Kodiak accretionary prism in Alaska) and tectonic nappes in collisional orogens (Flysch à Helminthoïdes in the Alps, the southern domain of the variscan Montagne Noire), which formed at temperature conditions between 250 and 350°C, i.e. spanning the downdip limit of large subduction earthquakes and the generation of slow slip events. In all geological domains, veins hosted in rocks with the lower temperature conditions (~250-300°C) show quartz grains with crystallographic facets and growth rims. Cathodoluminescence (CL) imaging of these growth rims shows two different colors, a short-lived blue color and a brown one, attesting to cyclic variations in precipitation conditions. In contrast, veins hosted in rocks with the higher temperature conditions (~350°C), show a homogeneous, CL-brown colored quartz, except for some very restricted domains of crack-seal structures of CL-blue quartz found in Japan, Kodiak and Montagne Noire. Based on laser ablation and electron microprobe mapping, the variations in CL colors appear correlated with the trace element content of quartz, the short-lived CL-blue being associated with the substitution of Si4+ by Al3++Li+/H+.
Due to their ubiquitous presence in various settings, the variations in CL colors in the lower T range reflect a common, general process. We interpret these cyclic growth structures as a reflection of deformation/fracturing events, which triggered transient changes in (1) the fluid pressure through fluid flow and (2) the chemistry of the fluid due to enhanced reactivity of the fractured material. The CL-blue growth rims delineate zones where quartz growth was rapid and crystals incorporated a large proportion of Al and Li. Crystal growth continued at a lower pace after fluid pressure and composition evolved to equilibrium conditions, leading to the formation of CL-brown quartz with few substitutions of tetrahedral Si. The variations in fluid pressure fluctuated at values close to lithostatic conditions, as indicated by growth in cavities that remained open.
The crack-seal microstructures have been interpreted as the result of slow-slip events near the base of the seismogenic zone (Fisher and Brantley, 2014; Ujiie et al., 2018). Our observations on quartz composition suggest that the quartz in crack-seal microstructures records episodic variation in fluid pressure and composition, similar to vein quartz at T<~300 °C. In contrast to the cooler and shallower domain, the variations are significantly smaller, as recorded by the very limited extent of the CL-blue domains, and most if not all of the quartz growth occurred under constant physico-chemical conditions, including a near lithostatic fluid pressure.
We conclude that quartz trace element content is a useful tool to track variations in fluid conditions. In particular, at seismogenic depths (i.e. near 250°C), fluid pressure varies significantly around a lithostatic value. In contrast, deeper, near the base of the seismogenic zone where slow slip events occur (i.e. near 350°C), the variations in fluid pressure conditions are smaller.
How to cite: Raimbourg, H., Famin, V., Rajic, K., Erdmann, S., Moris-Muttoni, B., and Fisher, D.: Record by quartz veins of earthquakes and slow slip events, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5472, https://doi.org/10.5194/egusphere-egu2020-5472, 2020.
EGU2020-6845 | Displays | TS3.4
The coupling of dehydration and deformation results in localised fluid flow in the accretionary wedge – a novel study of calcite veinsIsmay Vénice Akker, Christoph E. Schrank, Michael W.M. Jones, Cameron M. Kewish, Alfons Berger, and Marco Herwegh
In plate-convergent settings, fluid-saturated sediments dehydrate during subduction. The sediments are subsequently accreted to the upper plate. Along their dehydration-deformation path, the initial unconsolidated soft marine sediments become thick, foliated, impermeable meta-sedimentary sequences. Fluid flow through such ‘non’-porous low-permeability rocks is concentrated in fracture networks, ranging from the mm- to the km-scale. We study the interplay between ductile and brittle deformation processes and fluid flow by investigating calcite veins in slates from the exhumed European Alpine accretionary wedge across scales (µm to km). These slates experienced peak metamorphic temperatures between 200°C and 330°C and represent the transition between the upper aseismic and seismic zone. With the use of Synchrotron X-ray Fluorescence Microscopy (SXFM), we investigate the slates by visualizing trace-element distributions. This technique shows that alternating cycles of slow pressure-dissolution processes and brittle fracturing persist over long time scales. At the micron-scale, pressure solution of the initial carbonate-rich slates is indicated by an enrichment of newly recrystallized phyllosilicates on cleavage planes and in pressure shadows. These ductile deformation features are mutually overprinted by calcite veins (aperture 10 µm), which are nicely visualized with Sr-SXFM maps. Increasing compaction and recrystallization in the slate-rich matrix leads to progressed dehydration resulting in an increased pore fluid pressure and subsequent hydrofracturing. The micron-sized fractures are immediately filled in with minerals, which are oversaturated at that time in the fluid, resulting in the formation of (i) micron-veinlets. Micron-veinlets collect (ii) into mm-cm sized veins, which themselves form (iii) vein arrays and (iv) mega-arrays, respectively at the 50-100 m and 300-400 m scale. This upscaling of fluid pathways indicates a localised fluid transport through the accretionary wedge, which has important implications for the understanding of the mechanical stability of the accretionary wedge and related seismic activity.
How to cite: Akker, I. V., Schrank, C. E., Jones, M. W. M., Kewish, C. M., Berger, A., and Herwegh, M.: The coupling of dehydration and deformation results in localised fluid flow in the accretionary wedge – a novel study of calcite veins, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6845, https://doi.org/10.5194/egusphere-egu2020-6845, 2020.
In plate-convergent settings, fluid-saturated sediments dehydrate during subduction. The sediments are subsequently accreted to the upper plate. Along their dehydration-deformation path, the initial unconsolidated soft marine sediments become thick, foliated, impermeable meta-sedimentary sequences. Fluid flow through such ‘non’-porous low-permeability rocks is concentrated in fracture networks, ranging from the mm- to the km-scale. We study the interplay between ductile and brittle deformation processes and fluid flow by investigating calcite veins in slates from the exhumed European Alpine accretionary wedge across scales (µm to km). These slates experienced peak metamorphic temperatures between 200°C and 330°C and represent the transition between the upper aseismic and seismic zone. With the use of Synchrotron X-ray Fluorescence Microscopy (SXFM), we investigate the slates by visualizing trace-element distributions. This technique shows that alternating cycles of slow pressure-dissolution processes and brittle fracturing persist over long time scales. At the micron-scale, pressure solution of the initial carbonate-rich slates is indicated by an enrichment of newly recrystallized phyllosilicates on cleavage planes and in pressure shadows. These ductile deformation features are mutually overprinted by calcite veins (aperture 10 µm), which are nicely visualized with Sr-SXFM maps. Increasing compaction and recrystallization in the slate-rich matrix leads to progressed dehydration resulting in an increased pore fluid pressure and subsequent hydrofracturing. The micron-sized fractures are immediately filled in with minerals, which are oversaturated at that time in the fluid, resulting in the formation of (i) micron-veinlets. Micron-veinlets collect (ii) into mm-cm sized veins, which themselves form (iii) vein arrays and (iv) mega-arrays, respectively at the 50-100 m and 300-400 m scale. This upscaling of fluid pathways indicates a localised fluid transport through the accretionary wedge, which has important implications for the understanding of the mechanical stability of the accretionary wedge and related seismic activity.
How to cite: Akker, I. V., Schrank, C. E., Jones, M. W. M., Kewish, C. M., Berger, A., and Herwegh, M.: The coupling of dehydration and deformation results in localised fluid flow in the accretionary wedge – a novel study of calcite veins, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6845, https://doi.org/10.5194/egusphere-egu2020-6845, 2020.
EGU2020-11961 | Displays | TS3.4
Heterogeneous stresses and deformation mechanisms at shallow crustal conditions, Hungaroa Fault Zone, Hikurangi Subduction Margin, New ZealandCarolyn Boulton, Marcel Mizera, Maartje Hamers, Inigo Müller, Martin Ziegler, André Niemeijer, and Timothy Little
The Hungaroa Fault Zone (HFZ), an inactive thrust fault along the Hikurangi Subduction Margin, accommodated large displacements (~4–10 km) at the onset of subduction in the early Miocene. Within a 40 m-wide high-strain fault core, calcareous mudstones and marls display evidence for mixed-mode viscous flow and brittle fracture, including: discrete faults; extensional veins containing stretched calcite fibers; shear veins with calcite slickenfibers; calcite foliation-boudinage structures; calcite pressure fringes; dark dissolution seams; stylolites; embayed calcite grains; and an anastomosing phyllosilicate foliation.
Multiple observations indicate a heterogeneous stress state within the fault core. Detailed optical and electron backscatter diffraction-based texture analysis of syntectonic calcite veins and isoclinally folded limestone layers within the fault core reveal that calcite grains have experienced intracrystalline plasticity and interface mobility, and local subgrain development and dynamic recrystallisation. The recrystallized grain size in two calcite veins of 6.0±3.9 µm (n=1339; 1SD; HFZ-H4-5.2m_A;) and 7.2±4.2µm (n=406; 1SD; HFZ-H4-19.9m) indicate high differential stresses (~76–134 MPa). Hydrothermal friction experiments on a foliated, calcareous mudstone yield a friction coefficient of μ≈0.35. Using this friction coefficient in the Mohr-Coulomb failure criterion yields a maximum differential stress of 55 MPa at 4 km depth, assuming a minimum principal stress equal to the vertical stress, an average sediment density of 2350 kg/m3, and hydrostatic pore fluid pressure. Interestingly, calcareous microfossils within the foliated mudstone matrix are undeformed. Moreover, calcite veins are oriented both parallel to and highly oblique to the foliation, indicating spatial and/or temporal variations in the maximum principle stress azimuth.
To further constrain HFZ deformation conditions, clumped isotope geothermometry was performed on six syntectonic calcite veins, yielding formation temperatures of 79.3±19.9°C (95% confidence interval). These temperatures are well below those at which dynamic recrystallisation of calcite is anticipated and exclude shear heating and the migration of hotter fluids as an explanation for dynamic recrystallisation of calcite at shallow crustal levels (<5 km depth).
Our results indicate that: (1) stresses are spatiotemporally heterogeneous in crustal fault zones containing mixtures of competent and incompetent minerals; (2) heterogeneous deformation mechanisms, including frictional sliding, pressure solution, dynamic recrystallization, and mixed-mode fracturing accommodate slip in shallow crustal fault zones; and (3) brittle fractures play a pivotal role in fault zone deformation by providing fluid pathways that promote fluid-enhanced recovery and dynamic recrystallisation in the deforming calcite at remarkably low temperatures. Together, field geology, microscopy, and clumped isotope geothermometry provide a powerful method for constraining the multiscale slip behavior of large-displacement fault zones.
How to cite: Boulton, C., Mizera, M., Hamers, M., Müller, I., Ziegler, M., Niemeijer, A., and Little, T.: Heterogeneous stresses and deformation mechanisms at shallow crustal conditions, Hungaroa Fault Zone, Hikurangi Subduction Margin, New Zealand, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11961, https://doi.org/10.5194/egusphere-egu2020-11961, 2020.
The Hungaroa Fault Zone (HFZ), an inactive thrust fault along the Hikurangi Subduction Margin, accommodated large displacements (~4–10 km) at the onset of subduction in the early Miocene. Within a 40 m-wide high-strain fault core, calcareous mudstones and marls display evidence for mixed-mode viscous flow and brittle fracture, including: discrete faults; extensional veins containing stretched calcite fibers; shear veins with calcite slickenfibers; calcite foliation-boudinage structures; calcite pressure fringes; dark dissolution seams; stylolites; embayed calcite grains; and an anastomosing phyllosilicate foliation.
Multiple observations indicate a heterogeneous stress state within the fault core. Detailed optical and electron backscatter diffraction-based texture analysis of syntectonic calcite veins and isoclinally folded limestone layers within the fault core reveal that calcite grains have experienced intracrystalline plasticity and interface mobility, and local subgrain development and dynamic recrystallisation. The recrystallized grain size in two calcite veins of 6.0±3.9 µm (n=1339; 1SD; HFZ-H4-5.2m_A;) and 7.2±4.2µm (n=406; 1SD; HFZ-H4-19.9m) indicate high differential stresses (~76–134 MPa). Hydrothermal friction experiments on a foliated, calcareous mudstone yield a friction coefficient of μ≈0.35. Using this friction coefficient in the Mohr-Coulomb failure criterion yields a maximum differential stress of 55 MPa at 4 km depth, assuming a minimum principal stress equal to the vertical stress, an average sediment density of 2350 kg/m3, and hydrostatic pore fluid pressure. Interestingly, calcareous microfossils within the foliated mudstone matrix are undeformed. Moreover, calcite veins are oriented both parallel to and highly oblique to the foliation, indicating spatial and/or temporal variations in the maximum principle stress azimuth.
To further constrain HFZ deformation conditions, clumped isotope geothermometry was performed on six syntectonic calcite veins, yielding formation temperatures of 79.3±19.9°C (95% confidence interval). These temperatures are well below those at which dynamic recrystallisation of calcite is anticipated and exclude shear heating and the migration of hotter fluids as an explanation for dynamic recrystallisation of calcite at shallow crustal levels (<5 km depth).
Our results indicate that: (1) stresses are spatiotemporally heterogeneous in crustal fault zones containing mixtures of competent and incompetent minerals; (2) heterogeneous deformation mechanisms, including frictional sliding, pressure solution, dynamic recrystallization, and mixed-mode fracturing accommodate slip in shallow crustal fault zones; and (3) brittle fractures play a pivotal role in fault zone deformation by providing fluid pathways that promote fluid-enhanced recovery and dynamic recrystallisation in the deforming calcite at remarkably low temperatures. Together, field geology, microscopy, and clumped isotope geothermometry provide a powerful method for constraining the multiscale slip behavior of large-displacement fault zones.
How to cite: Boulton, C., Mizera, M., Hamers, M., Müller, I., Ziegler, M., Niemeijer, A., and Little, T.: Heterogeneous stresses and deformation mechanisms at shallow crustal conditions, Hungaroa Fault Zone, Hikurangi Subduction Margin, New Zealand, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11961, https://doi.org/10.5194/egusphere-egu2020-11961, 2020.
EGU2020-17557 | Displays | TS3.4
Episodic fluid pressure cycling controls the interplay between Slow Slip Events and Large Megathrust EarthquakesClaudio Petrini, Luca Dal Zilio, and Taras Gerya
Slow slip events (SSEs) are part of a spectrum of aseismic processes that relieve tectonic stress on faults. Their occurrence in subduction zones have been suggested to trigger megathrust earthquakes due to perturbations in fluid pressure. However, examples to date have been poorly recorded and physical observations of temporal fluid pressure fluctuations through slow slip cycles remain elusive. Here, we use a newly developed two-phase flow numerical model — which couples solid rock deformation and pervasive fluid flow — to show how crustal stresses and fluid pressures within subducting megathrust evolve before and during slow slip and regular events. This unified 2D numerical framework couples inertial mechanical deformation and fluid flow by using finite difference methods, marker-in-cell technique, and poro-visco-elasto-plastic rheologies. Furthermore, an adaptive time stepping allows the correct resolution of both long- and short-time scales, ranging from years to milliseconds during the dynamic propagation of earthquake rupture.
Here we show how permeability and its spatial distribution control the degree of locking along the megathrust interface and the interplay between seismic and aseismic slip. While a constant permeability leads to more regular seismic cycles, a depth dependent permeability contributes substantially to the development of two distinct megathrust zones: a shallow, locked seismogenic zone and a deep, narrow aseismic segment characterized by SSEs. Furthermore, we show that without requiring any specific friction law, our model shows that permeability, episodic stress transfer and fluid pressure cycling control the predominant slip mode along the subduction megathrust. Specifically, we find that the up-dip propagation of episodic SSEs systematically decreases the fault strength due to a continuous accumulation and release of fluid pressure within overpressured subducting interface, thus affecting the timing of large megathrust earthquakes. These results contribute to improve our understanding of the physical driving forces underlying the interplay between seismic and aseismic slip, and demonstrate that slow slip events may prove useful for short-term earthquake forecasts.
How to cite: Petrini, C., Dal Zilio, L., and Gerya, T.: Episodic fluid pressure cycling controls the interplay between Slow Slip Events and Large Megathrust Earthquakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17557, https://doi.org/10.5194/egusphere-egu2020-17557, 2020.
Slow slip events (SSEs) are part of a spectrum of aseismic processes that relieve tectonic stress on faults. Their occurrence in subduction zones have been suggested to trigger megathrust earthquakes due to perturbations in fluid pressure. However, examples to date have been poorly recorded and physical observations of temporal fluid pressure fluctuations through slow slip cycles remain elusive. Here, we use a newly developed two-phase flow numerical model — which couples solid rock deformation and pervasive fluid flow — to show how crustal stresses and fluid pressures within subducting megathrust evolve before and during slow slip and regular events. This unified 2D numerical framework couples inertial mechanical deformation and fluid flow by using finite difference methods, marker-in-cell technique, and poro-visco-elasto-plastic rheologies. Furthermore, an adaptive time stepping allows the correct resolution of both long- and short-time scales, ranging from years to milliseconds during the dynamic propagation of earthquake rupture.
Here we show how permeability and its spatial distribution control the degree of locking along the megathrust interface and the interplay between seismic and aseismic slip. While a constant permeability leads to more regular seismic cycles, a depth dependent permeability contributes substantially to the development of two distinct megathrust zones: a shallow, locked seismogenic zone and a deep, narrow aseismic segment characterized by SSEs. Furthermore, we show that without requiring any specific friction law, our model shows that permeability, episodic stress transfer and fluid pressure cycling control the predominant slip mode along the subduction megathrust. Specifically, we find that the up-dip propagation of episodic SSEs systematically decreases the fault strength due to a continuous accumulation and release of fluid pressure within overpressured subducting interface, thus affecting the timing of large megathrust earthquakes. These results contribute to improve our understanding of the physical driving forces underlying the interplay between seismic and aseismic slip, and demonstrate that slow slip events may prove useful for short-term earthquake forecasts.
How to cite: Petrini, C., Dal Zilio, L., and Gerya, T.: Episodic fluid pressure cycling controls the interplay between Slow Slip Events and Large Megathrust Earthquakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17557, https://doi.org/10.5194/egusphere-egu2020-17557, 2020.
EGU2020-12087 | Displays | TS3.4
Episodic stress tensor and fluid pressure cycling in subducting oceanic crust during Northern Hikurangi slow slip eventsEmily Warren-Smith, Bill Fry, Laura Wallace, Enrique Chon, Stuart Henrys, Anne Sheehan, Kimihiro Mochizuki, Susan Schwartz, Katherine Woods, John Ristau, and Spahr Webb
The occurrence of slow slip events (SSEs) in subduction zones has been proposed to be linked to the presence of, and fluctuations in near-lithostatic fluid pressures (Pf) within the megathrust shear zone and subducting oceanic crust. In particular, the 'fault-valve' model is commonly used to describe occasional, repeated breaching of a low-permeability interface shear zone barrier, which caps an overpressured hydrothermal fluid reservoir. In this model, a precursory increase in fluid pressure may therefore be anticipated to precede megathrust rupture. Resulting activation of fractures during slip opens permeable pathways for fluid migration and fluid pressure decreases once more, until the system becomes sealed and overpressure can re-accumulate. While the priming conditions for cyclical valving behaviour have been observed at subduction zones globally, and evidence for post-megathrust rupture drainage exists, physical observations of precursory fluid pressure increases, and subsequent decreases, particularly within the subducting slab where hydrothermal fluids are sourced, remain elusive.
Here we use earthquake focal mechanisms recorded on an ocean-bottom seismic network to identify changes in the stress tensor within subducting oceanic crust during four SSEs in New Zealand’s Northern Hikurangi subduction zone. We show that the stress, or shape ratio, which describes the relative magnitudes of the principal compressive stress axes, shows repeated decreases prior to, and rapid increases during the occurrence of geodetically documented SSEs. We propose that these changes represent precursory accumulation and subsequent release of fluid pressure within overpressured subducting oceanic crust via a ‘valving’ model for megathrust slip behaviour. Our observations indicate that the timing of slow slip events on subduction megathrusts may be controlled by cyclical accumulation of fluid pressure within subducting oceanic crust.
Our model is further supported by observations of seismicity preceding a large SSE in the northern Hikurangi Margin in 2019, captured by ocean-bottom seismometers and absolute pressure recorders. Observations of microseismicity during this period indicate that a stress state conducive to vertical fluid flow was present in the downgoing plate prior to SSE initiation, before subsequently returning to a down-dip extensional state following the SSE. We propose this precursory seismicity is indicative of fluid migration towards the interface shear zone from the lower plate fluid reservoir, which may have helped triggering slip on the megathrust.
We also present preliminary results of a moment tensor study to investigate spatial and temporal patterns in earthquake source properties in SSE regions along the Hikurangi Margin. In particular, earthquakes near Porangahau – a region susceptible to dynamic triggering of tremor and where shallow SSEs occur every 5 years or so – exhibit distinctly lower double couple components than elsewhere along the margin. We attribute this to elevated fluid pressures within the crust here, which is consistent with recent observations of high seismic reflectivity from an autocorrelation study. Such high fluid pressure may control the broad range of seismic and aseismic phenomena observed at Porangahau.
How to cite: Warren-Smith, E., Fry, B., Wallace, L., Chon, E., Henrys, S., Sheehan, A., Mochizuki, K., Schwartz, S., Woods, K., Ristau, J., and Webb, S.: Episodic stress tensor and fluid pressure cycling in subducting oceanic crust during Northern Hikurangi slow slip events, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12087, https://doi.org/10.5194/egusphere-egu2020-12087, 2020.
The occurrence of slow slip events (SSEs) in subduction zones has been proposed to be linked to the presence of, and fluctuations in near-lithostatic fluid pressures (Pf) within the megathrust shear zone and subducting oceanic crust. In particular, the 'fault-valve' model is commonly used to describe occasional, repeated breaching of a low-permeability interface shear zone barrier, which caps an overpressured hydrothermal fluid reservoir. In this model, a precursory increase in fluid pressure may therefore be anticipated to precede megathrust rupture. Resulting activation of fractures during slip opens permeable pathways for fluid migration and fluid pressure decreases once more, until the system becomes sealed and overpressure can re-accumulate. While the priming conditions for cyclical valving behaviour have been observed at subduction zones globally, and evidence for post-megathrust rupture drainage exists, physical observations of precursory fluid pressure increases, and subsequent decreases, particularly within the subducting slab where hydrothermal fluids are sourced, remain elusive.
Here we use earthquake focal mechanisms recorded on an ocean-bottom seismic network to identify changes in the stress tensor within subducting oceanic crust during four SSEs in New Zealand’s Northern Hikurangi subduction zone. We show that the stress, or shape ratio, which describes the relative magnitudes of the principal compressive stress axes, shows repeated decreases prior to, and rapid increases during the occurrence of geodetically documented SSEs. We propose that these changes represent precursory accumulation and subsequent release of fluid pressure within overpressured subducting oceanic crust via a ‘valving’ model for megathrust slip behaviour. Our observations indicate that the timing of slow slip events on subduction megathrusts may be controlled by cyclical accumulation of fluid pressure within subducting oceanic crust.
Our model is further supported by observations of seismicity preceding a large SSE in the northern Hikurangi Margin in 2019, captured by ocean-bottom seismometers and absolute pressure recorders. Observations of microseismicity during this period indicate that a stress state conducive to vertical fluid flow was present in the downgoing plate prior to SSE initiation, before subsequently returning to a down-dip extensional state following the SSE. We propose this precursory seismicity is indicative of fluid migration towards the interface shear zone from the lower plate fluid reservoir, which may have helped triggering slip on the megathrust.
We also present preliminary results of a moment tensor study to investigate spatial and temporal patterns in earthquake source properties in SSE regions along the Hikurangi Margin. In particular, earthquakes near Porangahau – a region susceptible to dynamic triggering of tremor and where shallow SSEs occur every 5 years or so – exhibit distinctly lower double couple components than elsewhere along the margin. We attribute this to elevated fluid pressures within the crust here, which is consistent with recent observations of high seismic reflectivity from an autocorrelation study. Such high fluid pressure may control the broad range of seismic and aseismic phenomena observed at Porangahau.
How to cite: Warren-Smith, E., Fry, B., Wallace, L., Chon, E., Henrys, S., Sheehan, A., Mochizuki, K., Schwartz, S., Woods, K., Ristau, J., and Webb, S.: Episodic stress tensor and fluid pressure cycling in subducting oceanic crust during Northern Hikurangi slow slip events, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12087, https://doi.org/10.5194/egusphere-egu2020-12087, 2020.
EGU2020-20603 | Displays | TS3.4
Stress orientation variability along the Hikurangi Subduction Margin: Insights from borehole image loggingEffat Behboudi, Ivan Lokmer, David McNamara, Tom Manzocchi, Laura Wallace, Demian Saffer, Philip Barnes, Ingo Pecher, Hikweon Lee, Gil Young Kim, Hung-Yu Wu, Katerina Petronotis, Leah LeVay, Iodp Expedition372 Scientists, and Iodp Expedition375 Scientists
The Hikurangi Subduction Margin (HSM) of New Zealand is well-known for its variable seismic behaviour along strike, and across the Pacific-Australian subduction interface. Pacific-Australian plate motion is accommodated by a combination of slow slip and normal seismic events. The mechanics of slow slip earthquakes and their relationship to normal earthquakes are not well constrained, and so they represent a challenge to the development of hazard models for this region of New Zealand.Variability in a number of aspects of the stress state along the HSM may play a role in controlling the observed spatially variable seismic behaviour. Here we present preliminary analysis of stress orientation information from borehole image logs acquired from oil and gas exploration wells, and scientific wells drilled as part IODP Expedition 372. Orientations of borehole breakouts (BOs) and drilling-induced tensile fractures (DITFs) from these image logs are used to determine orientations of the minimum and maximum horizontal stress directions respectively within the upper 3 km of the over-riding Australian Plate (hanging wall of the HSM subduction interface). Our analysis reveals that present day maximum horizontal compressive stress orientation (SHmax) within the subduction hangingwall varies along the HSM strike, from NE-SW (oblique to Pacific-Australian plate motion, parallel to HSM strike) in the northern HSM, to NW-SE (oblique to Pacific-Australian plate motion and HSM strike) in the southern HSM. Some deviation from this trend can be observed in both regions. At the frontal thrust in the northern HSM, SHmax is oriented N-S, and in the southern HSM one well shows a shallow E-W oriented SHmax. The borehole image log SHmax orientations in the northern HSM are consistent with SHmax orientations derived from shallow focal mechanism inversion. In contrast, borehole image logs SHmax orientations in the south of HSM are oblique to focal mechanisms derived shallow SHmax orientations. Borehole SHmax orientations are compatible with the maximum horizontal contraction strain rate direction determined from campaign GPS surface velocities, though in the southern HSM multiple directions are determined from this technique. The difference in stress orientations along the HSM is consistent with the variation in seismic behaviour linked to changes in coupling at the subduction interface. Interestingly, it is the southern HSM, where the subduction interface is considered strongly coupled, that stress field orientations are not consistent with depth and show variability. In the northern HSM, where the subduction interface is considered to be weakly coupled, stress orientations appear broadly consistent with depth.
How to cite: Behboudi, E., Lokmer, I., McNamara, D., Manzocchi, T., Wallace, L., Saffer, D., Barnes, P., Pecher, I., Lee, H., Kim, G. Y., Wu, H.-Y., Petronotis, K., LeVay, L., Expedition372 Scientists, I., and Expedition375 Scientists, I.: Stress orientation variability along the Hikurangi Subduction Margin: Insights from borehole image logging, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20603, https://doi.org/10.5194/egusphere-egu2020-20603, 2020.
The Hikurangi Subduction Margin (HSM) of New Zealand is well-known for its variable seismic behaviour along strike, and across the Pacific-Australian subduction interface. Pacific-Australian plate motion is accommodated by a combination of slow slip and normal seismic events. The mechanics of slow slip earthquakes and their relationship to normal earthquakes are not well constrained, and so they represent a challenge to the development of hazard models for this region of New Zealand.Variability in a number of aspects of the stress state along the HSM may play a role in controlling the observed spatially variable seismic behaviour. Here we present preliminary analysis of stress orientation information from borehole image logs acquired from oil and gas exploration wells, and scientific wells drilled as part IODP Expedition 372. Orientations of borehole breakouts (BOs) and drilling-induced tensile fractures (DITFs) from these image logs are used to determine orientations of the minimum and maximum horizontal stress directions respectively within the upper 3 km of the over-riding Australian Plate (hanging wall of the HSM subduction interface). Our analysis reveals that present day maximum horizontal compressive stress orientation (SHmax) within the subduction hangingwall varies along the HSM strike, from NE-SW (oblique to Pacific-Australian plate motion, parallel to HSM strike) in the northern HSM, to NW-SE (oblique to Pacific-Australian plate motion and HSM strike) in the southern HSM. Some deviation from this trend can be observed in both regions. At the frontal thrust in the northern HSM, SHmax is oriented N-S, and in the southern HSM one well shows a shallow E-W oriented SHmax. The borehole image log SHmax orientations in the northern HSM are consistent with SHmax orientations derived from shallow focal mechanism inversion. In contrast, borehole image logs SHmax orientations in the south of HSM are oblique to focal mechanisms derived shallow SHmax orientations. Borehole SHmax orientations are compatible with the maximum horizontal contraction strain rate direction determined from campaign GPS surface velocities, though in the southern HSM multiple directions are determined from this technique. The difference in stress orientations along the HSM is consistent with the variation in seismic behaviour linked to changes in coupling at the subduction interface. Interestingly, it is the southern HSM, where the subduction interface is considered strongly coupled, that stress field orientations are not consistent with depth and show variability. In the northern HSM, where the subduction interface is considered to be weakly coupled, stress orientations appear broadly consistent with depth.
How to cite: Behboudi, E., Lokmer, I., McNamara, D., Manzocchi, T., Wallace, L., Saffer, D., Barnes, P., Pecher, I., Lee, H., Kim, G. Y., Wu, H.-Y., Petronotis, K., LeVay, L., Expedition372 Scientists, I., and Expedition375 Scientists, I.: Stress orientation variability along the Hikurangi Subduction Margin: Insights from borehole image logging, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20603, https://doi.org/10.5194/egusphere-egu2020-20603, 2020.
EGU2020-12631 | Displays | TS3.4
Stable and Unstable Shear in Altered Downgoing Slabs: Predicted Strain Localization in Magnesian Carbonates and Wadati-Benioff SeismicityAbhishek Prakash, Caleb W Holyoke III, Peter B Kelemen, William M Lamb, Stephen H Kirby, and Andreas K Kronenberg
Seismicity of subduction zones at upper-mantle depths is commonly explained by dehydration reactions of serpentine and hydrous silicates and reductions in effective pressure. However, the conditions of Wadati-Benioff zone seismicity do not strictly correspond to temperatures and depths of serpentine dehydration, and there is no independent evidence that seawater penetrates the lithosphere to form serpentine at depths >30km below the seafloor. Altered lithosphere may contain magnesian carbonates in addition to hydrous silicates, both at the top of plates, where CO2 of seawater reacts with mantle rocks and at the base of plates where CO2 is introduced by mantle plumes.
Adapting the thermal softening model of Kelemen and Hirth (2007), we model the strain localization and shear heating within magnesite horizons embedded within an olivine host using flow laws determined experimentally for dislocation creep and diffusion creep of the carbonate layer and olivine host (Hirth and Kohlstedt, 2003; Holyoke et al., 2014). Strain rates predicted within carbonate-rich layers of downgoing slabs are much higher than those of the surrounding olivine at all conditions. However, shearing may be either stable or unstable depending on the relative rates of shear heating and conductive heat loss from the shear zone. Localized strain rates reach a steady state when shear heating and heat flow are balanced, while unstable strain rates are calculated where shear heating exceeds heat flow. Modeled strain rates accelerate to 10+1 s-1, as temperatures reach melting conditions, and stresses drop, corresponding to a seismic event. Applications of this model to the double Benioff zones of the NE Japan trench predict unstable seismic shear for both upper and lower seismic zones to subduction depths of ~300 km. For cold downgoing slabs, such as the Tonga subduction system, unstable seismic shear is predicted for carbonate horizons of altered downgoing slabs to depths exceeding 400 km.
How to cite: Prakash, A., Holyoke III, C. W., Kelemen, P. B., Lamb, W. M., Kirby, S. H., and Kronenberg, A. K.: Stable and Unstable Shear in Altered Downgoing Slabs: Predicted Strain Localization in Magnesian Carbonates and Wadati-Benioff Seismicity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12631, https://doi.org/10.5194/egusphere-egu2020-12631, 2020.
Seismicity of subduction zones at upper-mantle depths is commonly explained by dehydration reactions of serpentine and hydrous silicates and reductions in effective pressure. However, the conditions of Wadati-Benioff zone seismicity do not strictly correspond to temperatures and depths of serpentine dehydration, and there is no independent evidence that seawater penetrates the lithosphere to form serpentine at depths >30km below the seafloor. Altered lithosphere may contain magnesian carbonates in addition to hydrous silicates, both at the top of plates, where CO2 of seawater reacts with mantle rocks and at the base of plates where CO2 is introduced by mantle plumes.
Adapting the thermal softening model of Kelemen and Hirth (2007), we model the strain localization and shear heating within magnesite horizons embedded within an olivine host using flow laws determined experimentally for dislocation creep and diffusion creep of the carbonate layer and olivine host (Hirth and Kohlstedt, 2003; Holyoke et al., 2014). Strain rates predicted within carbonate-rich layers of downgoing slabs are much higher than those of the surrounding olivine at all conditions. However, shearing may be either stable or unstable depending on the relative rates of shear heating and conductive heat loss from the shear zone. Localized strain rates reach a steady state when shear heating and heat flow are balanced, while unstable strain rates are calculated where shear heating exceeds heat flow. Modeled strain rates accelerate to 10+1 s-1, as temperatures reach melting conditions, and stresses drop, corresponding to a seismic event. Applications of this model to the double Benioff zones of the NE Japan trench predict unstable seismic shear for both upper and lower seismic zones to subduction depths of ~300 km. For cold downgoing slabs, such as the Tonga subduction system, unstable seismic shear is predicted for carbonate horizons of altered downgoing slabs to depths exceeding 400 km.
How to cite: Prakash, A., Holyoke III, C. W., Kelemen, P. B., Lamb, W. M., Kirby, S. H., and Kronenberg, A. K.: Stable and Unstable Shear in Altered Downgoing Slabs: Predicted Strain Localization in Magnesian Carbonates and Wadati-Benioff Seismicity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12631, https://doi.org/10.5194/egusphere-egu2020-12631, 2020.
EGU2020-11685 | Displays | TS3.4
Characterization of porosity from Cation Exchange Capacity and resistivity data at IODP Expedition 358 Site C0024: insights on compaction state, stress and deformation history at the frontal thrust of the Nankai marginJade Dutilleul, Marianne Conin, Sylvain Bourlange, and Yves Géraud and the Expedition 358 Science Party
In subduction zones, megathrust seismicity depends on the hydrogeological, thermal, physical and mechanical properties of the sediments before they enter the subduction zone and how these properties evolve through the subduction process. In particular, fluids are progressively released by compaction and/or mineral dehydration reactions as burial increases, resulting in the build-up of pore fluid pressure in low-permeability sediments that strongly affects fault behavior through its control on effective normal stress.
We use porosity, logging and chemical data to characterize compaction state and bound water content of sediments at Site C0024. This site was drilled in March 2019 during International Ocean Discovery Program Expedition 358 in the anticline overlying the frontal thrust of the Nankai margin, a few kilometers landward of Sites C0006 and C0007 that were previously drilled during the NanTroSEIZE project. Sites C0024, C0006 and C0007 transect the décollement and overlying accreted Upper Shikoku Basin and wedge slope deposits. At Site C0024, the main frontal thrust at ~820 mbsf, the top of its footwall (up to ~870 mbsf) and its hanging-wall were logged. Two intervals were cored in the hanging-wall (~0-320 mbsf and ~510-652 mbsf). Four sedimentary facies were identified : (1) the slope apron (~0-4 mbsf) composed of silty clay to clayey silt hemipelagites, (2) accreted trench wedge sediments (~4–519 mbsf) composed of hemipelagites with volcanic ash layers, silt and sand turbidites, (3) outer trench-wedge sediments (~519-555 mbsf) mainly composed of hemipelagites with rare silt turbidites and volcanic ash layers and (4) accreted Upper Shikoku Basin (>555mbsf) composed of hemipelagites and volcanic ash layers. The Pliocene to Miocene accreted Upper Shikoku Basin deposits at the frontal thrust are correlated with undeformed Upper Shikoku Basin deposits at reference Sites C0011 and C0012 seaward in the incoming Shikoku Basin.
Following previous studies, we use Cation Exchange Capacity (CEC) to determine bound water content and interstitial porosity in the cored interval. Unlike total porosity commonly measured onboard, interstitial porosity is representative of the compaction state of sediments. We use interstitial porosity data to calibrate resistivity-derived porosity through the hanging-wall, the décollement and below. Resistivity-derived porosity is obtained with a resistivity model accounting for the high surface conductivity of clays based on CEC, exchangeable cation composition, LWD resistivity and gamma ray logs. We also document the evolution of the structure of micro- to macropores with depth using low pressure nitrogen adsorption/desorption, mercury injection capillary pressure and nuclear magnetic resonance. Finally, we compare the porosity dataset at Site C0024 with that of Sites C0006 and C0007 in the frontal thrust and reference Sites C0011 and C0012 in the entering Shikoku Basin to characterize the evolution of the compaction state of sediments during accretion.
How to cite: Dutilleul, J., Conin, M., Bourlange, S., and Géraud, Y. and the Expedition 358 Science Party: Characterization of porosity from Cation Exchange Capacity and resistivity data at IODP Expedition 358 Site C0024: insights on compaction state, stress and deformation history at the frontal thrust of the Nankai margin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11685, https://doi.org/10.5194/egusphere-egu2020-11685, 2020.
In subduction zones, megathrust seismicity depends on the hydrogeological, thermal, physical and mechanical properties of the sediments before they enter the subduction zone and how these properties evolve through the subduction process. In particular, fluids are progressively released by compaction and/or mineral dehydration reactions as burial increases, resulting in the build-up of pore fluid pressure in low-permeability sediments that strongly affects fault behavior through its control on effective normal stress.
We use porosity, logging and chemical data to characterize compaction state and bound water content of sediments at Site C0024. This site was drilled in March 2019 during International Ocean Discovery Program Expedition 358 in the anticline overlying the frontal thrust of the Nankai margin, a few kilometers landward of Sites C0006 and C0007 that were previously drilled during the NanTroSEIZE project. Sites C0024, C0006 and C0007 transect the décollement and overlying accreted Upper Shikoku Basin and wedge slope deposits. At Site C0024, the main frontal thrust at ~820 mbsf, the top of its footwall (up to ~870 mbsf) and its hanging-wall were logged. Two intervals were cored in the hanging-wall (~0-320 mbsf and ~510-652 mbsf). Four sedimentary facies were identified : (1) the slope apron (~0-4 mbsf) composed of silty clay to clayey silt hemipelagites, (2) accreted trench wedge sediments (~4–519 mbsf) composed of hemipelagites with volcanic ash layers, silt and sand turbidites, (3) outer trench-wedge sediments (~519-555 mbsf) mainly composed of hemipelagites with rare silt turbidites and volcanic ash layers and (4) accreted Upper Shikoku Basin (>555mbsf) composed of hemipelagites and volcanic ash layers. The Pliocene to Miocene accreted Upper Shikoku Basin deposits at the frontal thrust are correlated with undeformed Upper Shikoku Basin deposits at reference Sites C0011 and C0012 seaward in the incoming Shikoku Basin.
Following previous studies, we use Cation Exchange Capacity (CEC) to determine bound water content and interstitial porosity in the cored interval. Unlike total porosity commonly measured onboard, interstitial porosity is representative of the compaction state of sediments. We use interstitial porosity data to calibrate resistivity-derived porosity through the hanging-wall, the décollement and below. Resistivity-derived porosity is obtained with a resistivity model accounting for the high surface conductivity of clays based on CEC, exchangeable cation composition, LWD resistivity and gamma ray logs. We also document the evolution of the structure of micro- to macropores with depth using low pressure nitrogen adsorption/desorption, mercury injection capillary pressure and nuclear magnetic resonance. Finally, we compare the porosity dataset at Site C0024 with that of Sites C0006 and C0007 in the frontal thrust and reference Sites C0011 and C0012 in the entering Shikoku Basin to characterize the evolution of the compaction state of sediments during accretion.
How to cite: Dutilleul, J., Conin, M., Bourlange, S., and Géraud, Y. and the Expedition 358 Science Party: Characterization of porosity from Cation Exchange Capacity and resistivity data at IODP Expedition 358 Site C0024: insights on compaction state, stress and deformation history at the frontal thrust of the Nankai margin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11685, https://doi.org/10.5194/egusphere-egu2020-11685, 2020.
EGU2020-3231 | Displays | TS3.4
Recent advances in GNSS-A observation technology and networks and latest observation results around Japan IslandsYusuke Yokota, Tadashi Ishikawa, Shun-ichi Watanabe, and Yuto Nakamura
Our research group has been studying advanced GNSS-A (Global Navigation Satellite System – Acoustic ranging combination) technique over two decades. In recent years, detection sensitivity of GNSS-A observations has been sophisticated by improving the accuracy and frequency of analysis technology and acoustic systems [e.g., Yokota et al., 2018, MGR; Ishikawa et al., in prep]. The current observation frequency is more than 4 times/year, the observation accuracy for each observation is less than 2 cm, and it can detect a steady deformation rate of 1 cm/year or less and an unsteady fluctuation of 5 cm or less. Also, efforts are being made to strengthen the observation network.
GNSS-A observations for the 2011 Tohoku-oki earthquake and its postseismic field revealed the details of the crustal deformation field on the Japan Trench side [Sato et al., 2011, Science; Watanabe et al., 2014, GRL]. The long-term observation data in the Nankai Trough region revealed the strain accumulation process at the interseismic period [Yokota et al., 2016, Nature; Watanabe et al., 2018, JGR; Nishimura et al., 2018, Geosphere]. Furthermore, detection and monitoring of large-scale slow slip events (SSEs) in the shallow part of the Nankai Trough was achieved by recent sensitivity improvements [Yokota & Ishikawa, 2020, Science Advances]. The detected postseismic fields, coupling condition and shallow SSEs contain universal features that should be shared in many subduction zones. Here, along with the latest observations, we discuss spatial and temporal relationships of these events, strain accumulations and releases along subduction zones around Japan by GNSS-A and its impact on slow earthquake science.
Recently, because of the need for continuous monitoring a shallow SSE, the monitoring ability of GNSS-A was also investigated. It was confirmed that relatively large-scale shallow SSE (surface deformation: > 5 cm) could be monitored. However, the ability to determine the time constant of an SSE is poor. For monitoring the detail of an SSE, it is essential to improve the observation frequency in the future. Here, we also discuss the technical issues to be considered and their solution plans (e.g., new platform and system).
How to cite: Yokota, Y., Ishikawa, T., Watanabe, S., and Nakamura, Y.: Recent advances in GNSS-A observation technology and networks and latest observation results around Japan Islands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3231, https://doi.org/10.5194/egusphere-egu2020-3231, 2020.
Our research group has been studying advanced GNSS-A (Global Navigation Satellite System – Acoustic ranging combination) technique over two decades. In recent years, detection sensitivity of GNSS-A observations has been sophisticated by improving the accuracy and frequency of analysis technology and acoustic systems [e.g., Yokota et al., 2018, MGR; Ishikawa et al., in prep]. The current observation frequency is more than 4 times/year, the observation accuracy for each observation is less than 2 cm, and it can detect a steady deformation rate of 1 cm/year or less and an unsteady fluctuation of 5 cm or less. Also, efforts are being made to strengthen the observation network.
GNSS-A observations for the 2011 Tohoku-oki earthquake and its postseismic field revealed the details of the crustal deformation field on the Japan Trench side [Sato et al., 2011, Science; Watanabe et al., 2014, GRL]. The long-term observation data in the Nankai Trough region revealed the strain accumulation process at the interseismic period [Yokota et al., 2016, Nature; Watanabe et al., 2018, JGR; Nishimura et al., 2018, Geosphere]. Furthermore, detection and monitoring of large-scale slow slip events (SSEs) in the shallow part of the Nankai Trough was achieved by recent sensitivity improvements [Yokota & Ishikawa, 2020, Science Advances]. The detected postseismic fields, coupling condition and shallow SSEs contain universal features that should be shared in many subduction zones. Here, along with the latest observations, we discuss spatial and temporal relationships of these events, strain accumulations and releases along subduction zones around Japan by GNSS-A and its impact on slow earthquake science.
Recently, because of the need for continuous monitoring a shallow SSE, the monitoring ability of GNSS-A was also investigated. It was confirmed that relatively large-scale shallow SSE (surface deformation: > 5 cm) could be monitored. However, the ability to determine the time constant of an SSE is poor. For monitoring the detail of an SSE, it is essential to improve the observation frequency in the future. Here, we also discuss the technical issues to be considered and their solution plans (e.g., new platform and system).
How to cite: Yokota, Y., Ishikawa, T., Watanabe, S., and Nakamura, Y.: Recent advances in GNSS-A observation technology and networks and latest observation results around Japan Islands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3231, https://doi.org/10.5194/egusphere-egu2020-3231, 2020.
EGU2020-864 | Displays | TS3.4
An investigation on possibilty of creep on the Makran subduction zone based on deformation dataHoma Ghadimi Moghaddam, Alireza Khodaverdian, and Hamid Zafarani
Long term crustal flow of the Makran subduction zone is computed with a kinematic finite element model based on iterated weighted least squares fits to data. Data include 91 fault traces, 56 fault offset rates, 76 geodetic velocities, 1962 principal stress azimuths, and velocity boundary conditions. Model provides long-term fault slip rates, velocity, and distributed permanent strain rates between faults in the Makran region from all available kinematic data. Due to low seismicity of western Makran compared to its eastern part we defined two models to evaluate the possibility of creep in the Iranian Makran subduction. One model assumes that geodetic velocities measured adjacent to the Makran subduction zone reflect a temporarily locked subduction zone will be referred to as the “seismic deformation model”. In contrast, another model called the “half creeping deformation model” assumes that the western part of Makran may creep smoothly without any locking. In order to verify the models, the estimates of fault slip rates are compared to slip rates from merely analysing geodetic benchmark velocities or paleoseismological studies or published geological rates which have not been used in the model. Our estimated rates are all in the range of geodetic rates and are even more consistent with geological rates than previous GPS-based estimates. Another verification for the model is comparison of the computed interseismic velocities at GPS benchmarks to GPS measurements. While neither model accurately predicts these interseismic velocities at benchmarks, the half creeping deformation model is more accurate for Chabahar station than the seismic deformation model. These results have important earthquake and tsunami hazard implications. For example, Fault slip rates are the main component of time-dependent seismic hazard studies and can be used to estimate activity rates for more sophisticated earthquake models.
How to cite: Ghadimi Moghaddam, H., Khodaverdian, A., and Zafarani, H.: An investigation on possibilty of creep on the Makran subduction zone based on deformation data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-864, https://doi.org/10.5194/egusphere-egu2020-864, 2020.
Long term crustal flow of the Makran subduction zone is computed with a kinematic finite element model based on iterated weighted least squares fits to data. Data include 91 fault traces, 56 fault offset rates, 76 geodetic velocities, 1962 principal stress azimuths, and velocity boundary conditions. Model provides long-term fault slip rates, velocity, and distributed permanent strain rates between faults in the Makran region from all available kinematic data. Due to low seismicity of western Makran compared to its eastern part we defined two models to evaluate the possibility of creep in the Iranian Makran subduction. One model assumes that geodetic velocities measured adjacent to the Makran subduction zone reflect a temporarily locked subduction zone will be referred to as the “seismic deformation model”. In contrast, another model called the “half creeping deformation model” assumes that the western part of Makran may creep smoothly without any locking. In order to verify the models, the estimates of fault slip rates are compared to slip rates from merely analysing geodetic benchmark velocities or paleoseismological studies or published geological rates which have not been used in the model. Our estimated rates are all in the range of geodetic rates and are even more consistent with geological rates than previous GPS-based estimates. Another verification for the model is comparison of the computed interseismic velocities at GPS benchmarks to GPS measurements. While neither model accurately predicts these interseismic velocities at benchmarks, the half creeping deformation model is more accurate for Chabahar station than the seismic deformation model. These results have important earthquake and tsunami hazard implications. For example, Fault slip rates are the main component of time-dependent seismic hazard studies and can be used to estimate activity rates for more sophisticated earthquake models.
How to cite: Ghadimi Moghaddam, H., Khodaverdian, A., and Zafarani, H.: An investigation on possibilty of creep on the Makran subduction zone based on deformation data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-864, https://doi.org/10.5194/egusphere-egu2020-864, 2020.
EGU2020-8315 | Displays | TS3.4
Sounds of the deep subduction zone plumbing system: modeling non-volcanic tremor activity in a fault-valve, pore-pressure diffusive systemGaspard Farge, Nikolai Shapiro, Claude Jaupart, and Édouard Kaminski
The activity of slow-earthquakes in subduction zones have been closely linked to fluid circulation processes — like hydro fracturation and pore-pressure pulses — on the one hand by geological observations and on the other hand by slow-earthquake triggering and interaction models. In deep fault zone environments, where slow slip events and various regimes of tremor are observed, fluids coming from metamorphic dehydration of slab sediments are channeled towards the surface. Geological observations indicate that fluid transport conditions vary significantly on short time scales, and along dip, strike and width of the fault zone. In homogeneously permeable systems where fluids transit under stable conditions, pore-pressure can be described by a diffusion equation. We use a time and space bimodal description of the transport properties to model a tremor generating, permeable fault zone. Thin zones of low permeability acting as valves are distributed along the 1D channel with a higher background permeability. When a threshold pore-pressure differential is reached, the valve permeability is brought to background levels, until the barrier is healed and closes again. In this model, the opening of a valve occurs at the same time as the source of a low-frequency earthquake (LFE) is triggered. In such a set up, sources interact uniquely due to the channeling of stress through pore-pressure diffusion, and the interaction characteristics in time/space are described in the framework of a diffusive system. When the number of sources is high, the model can reproduce clustering behaviours observed for LFE activity in subduction zones. The transition from a Poisson process description of seismicity to highly clustered, cascading events is governed by the source interaction distances, directly relating to the transport properties of the medium. In time, such a model is meant to diagnose the transport conditions in a subduction zone or a magmatic system, provided that it can be characterized by clustering statistics on the low-frequency seismicity it generates.
How to cite: Farge, G., Shapiro, N., Jaupart, C., and Kaminski, É.: Sounds of the deep subduction zone plumbing system: modeling non-volcanic tremor activity in a fault-valve, pore-pressure diffusive system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8315, https://doi.org/10.5194/egusphere-egu2020-8315, 2020.
The activity of slow-earthquakes in subduction zones have been closely linked to fluid circulation processes — like hydro fracturation and pore-pressure pulses — on the one hand by geological observations and on the other hand by slow-earthquake triggering and interaction models. In deep fault zone environments, where slow slip events and various regimes of tremor are observed, fluids coming from metamorphic dehydration of slab sediments are channeled towards the surface. Geological observations indicate that fluid transport conditions vary significantly on short time scales, and along dip, strike and width of the fault zone. In homogeneously permeable systems where fluids transit under stable conditions, pore-pressure can be described by a diffusion equation. We use a time and space bimodal description of the transport properties to model a tremor generating, permeable fault zone. Thin zones of low permeability acting as valves are distributed along the 1D channel with a higher background permeability. When a threshold pore-pressure differential is reached, the valve permeability is brought to background levels, until the barrier is healed and closes again. In this model, the opening of a valve occurs at the same time as the source of a low-frequency earthquake (LFE) is triggered. In such a set up, sources interact uniquely due to the channeling of stress through pore-pressure diffusion, and the interaction characteristics in time/space are described in the framework of a diffusive system. When the number of sources is high, the model can reproduce clustering behaviours observed for LFE activity in subduction zones. The transition from a Poisson process description of seismicity to highly clustered, cascading events is governed by the source interaction distances, directly relating to the transport properties of the medium. In time, such a model is meant to diagnose the transport conditions in a subduction zone or a magmatic system, provided that it can be characterized by clustering statistics on the low-frequency seismicity it generates.
How to cite: Farge, G., Shapiro, N., Jaupart, C., and Kaminski, É.: Sounds of the deep subduction zone plumbing system: modeling non-volcanic tremor activity in a fault-valve, pore-pressure diffusive system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8315, https://doi.org/10.5194/egusphere-egu2020-8315, 2020.
EGU2020-11486 | Displays | TS3.4
Methane hydrate saturations at the Southern Hikurangi margin (New Zealand) estimated from seismic and rock physics inversionFrancesco Turco, Andrew Gorman, Gareth Crutchley, Leonardo Azevedo, Dario Grana, and Ingo Pecher
Geophysical data indicate that the Hikurangi subduction margin on New Zealand’s East Coast contains a large gas hydrate province. Gas hydrates are widespread in shallow sediments across the margin, and locally intense fluid seepage associated with methane hydrate is observed in several areas. Glendhu and Honeycomb ridges lie at the toe of the Hikurangi deformation wedge at depths ranging from 2100 to 2800 m. These two parallel four-way closure systems host concentrated methane hydrate deposits. The control on hydrate formation at these ridges is governed by steeply dipping permeable strata and fractures, which allow methane to flow upwards into the gas hydrate stability zone. Hydrate recycling at the base of the hydrate stability zone may contribute to the accumulation of highly concentrated hydrate in porous layers.
To improve the characterisation of the hydrate systems at Glendhu and Honeycomb ridges, we estimate hydrate saturation and porosity of the concentrated hydrate deposits. We first estimate elastic properties (density, compressional and shear-wave velocities) of the gas hydrate stability zone through full-waveform inversion and iterative geostatistical seismic amplitude versus angle (AVA) inversion. We then perform a petrophysical inversion based on a rock physics model to predict gas hydrate saturation and porosity of the hydrate bearing sediments along the two ridges.
Our results indicate that the high seismic amplitudes correspond to the top interface of highly concentrated hydrate deposit, with peak saturations around 35%. Because of the resolution of the seismic data we assume that the estimated properties are averaged over layers of 10 to 20 meters thickness. These saturation values are in agreement with studies conducted in other areas of concentrated hydrate accumulations in similar geologic settings.
How to cite: Turco, F., Gorman, A., Crutchley, G., Azevedo, L., Grana, D., and Pecher, I.: Methane hydrate saturations at the Southern Hikurangi margin (New Zealand) estimated from seismic and rock physics inversion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11486, https://doi.org/10.5194/egusphere-egu2020-11486, 2020.
Geophysical data indicate that the Hikurangi subduction margin on New Zealand’s East Coast contains a large gas hydrate province. Gas hydrates are widespread in shallow sediments across the margin, and locally intense fluid seepage associated with methane hydrate is observed in several areas. Glendhu and Honeycomb ridges lie at the toe of the Hikurangi deformation wedge at depths ranging from 2100 to 2800 m. These two parallel four-way closure systems host concentrated methane hydrate deposits. The control on hydrate formation at these ridges is governed by steeply dipping permeable strata and fractures, which allow methane to flow upwards into the gas hydrate stability zone. Hydrate recycling at the base of the hydrate stability zone may contribute to the accumulation of highly concentrated hydrate in porous layers.
To improve the characterisation of the hydrate systems at Glendhu and Honeycomb ridges, we estimate hydrate saturation and porosity of the concentrated hydrate deposits. We first estimate elastic properties (density, compressional and shear-wave velocities) of the gas hydrate stability zone through full-waveform inversion and iterative geostatistical seismic amplitude versus angle (AVA) inversion. We then perform a petrophysical inversion based on a rock physics model to predict gas hydrate saturation and porosity of the hydrate bearing sediments along the two ridges.
Our results indicate that the high seismic amplitudes correspond to the top interface of highly concentrated hydrate deposit, with peak saturations around 35%. Because of the resolution of the seismic data we assume that the estimated properties are averaged over layers of 10 to 20 meters thickness. These saturation values are in agreement with studies conducted in other areas of concentrated hydrate accumulations in similar geologic settings.
How to cite: Turco, F., Gorman, A., Crutchley, G., Azevedo, L., Grana, D., and Pecher, I.: Methane hydrate saturations at the Southern Hikurangi margin (New Zealand) estimated from seismic and rock physics inversion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11486, https://doi.org/10.5194/egusphere-egu2020-11486, 2020.
TS3.5 – Faults and fractures in rocks : mechanics, occurrence, dating, stress history and fluid flow
EGU2020-18248 | Displays | TS3.5
Hydrofractures and crustal-scale fluid flowPaul D. Bons, Tamara de Riese, Enrique Gomez-Rivas, Isaac Naaman, and Till Sachau
Fluids can circulate in all levels of the crust, as veins, ore deposits and chemical alterations and isotopic shifts indicate. It is furthermore generally accepted that faults and fractures play a central role as preferred fluid conduits. Fluid flow is, however, not only passively reacting to the presence of faults and fractures, but actively play a role in their creation, (re-) activation and sealing by mineral precipitates. This means that the interaction between fluid flow and fracturing is a two-way process, which is further controlled by tectonic activity (stress field), fluid sources and fluxes, as well as the availability of alternative fluid conduits, such as matrix porosity. Here we explore the interaction between matrix permeability and dynamic fracturing on the spatial and temporal distribution of fluid flow for upward fluid fluxes. Envisaged fluid sources can be dehydration reactions, release of igneous fluids, or release of fluids due to decompression or heating.
Our 2D numerical cellular automaton-type simulations span the whole range from steady matrix-flow to highly dynamical flow through hydrofractures. Hydrofractures are initiated when matrix flow is insufficient to maintain fluid pressures below the failure threshold. When required fluid fluxes are high and/or matrix porosity low, flow is dominated by hydrofractures and the system exhibits self-organised critical phenomena. The size of fractures achieves a power-law distribution, as failure events may sometimes trigger avalanche-like amalgamation of hydrofractures. By far most hydrofracture events only lead to local fluid flow pulses within the source area. Conductive fracture networks do not develop if hydrofractures seal relatively quickly, which can be expected in deeper crustal levels. Only the larger events span the whole system and actually drain fluid from the system. We present the 10 square km hydrothermal Hidden Valley Mega-Breccia on the Paralana Fault System in South Australia as a possible example of large-scale fluid expulsion events. Although field evidence suggests that the breccia formed over a period of at least 150 Myrs, actual cumulative fluid duration may rather have been in the order of days only. This example illustrates the extreme dynamics that crustal-scale fluid flow in hydrofractures can achieve.
How to cite: Bons, P. D., de Riese, T., Gomez-Rivas, E., Naaman, I., and Sachau, T.: Hydrofractures and crustal-scale fluid flow, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18248, https://doi.org/10.5194/egusphere-egu2020-18248, 2020.
Fluids can circulate in all levels of the crust, as veins, ore deposits and chemical alterations and isotopic shifts indicate. It is furthermore generally accepted that faults and fractures play a central role as preferred fluid conduits. Fluid flow is, however, not only passively reacting to the presence of faults and fractures, but actively play a role in their creation, (re-) activation and sealing by mineral precipitates. This means that the interaction between fluid flow and fracturing is a two-way process, which is further controlled by tectonic activity (stress field), fluid sources and fluxes, as well as the availability of alternative fluid conduits, such as matrix porosity. Here we explore the interaction between matrix permeability and dynamic fracturing on the spatial and temporal distribution of fluid flow for upward fluid fluxes. Envisaged fluid sources can be dehydration reactions, release of igneous fluids, or release of fluids due to decompression or heating.
Our 2D numerical cellular automaton-type simulations span the whole range from steady matrix-flow to highly dynamical flow through hydrofractures. Hydrofractures are initiated when matrix flow is insufficient to maintain fluid pressures below the failure threshold. When required fluid fluxes are high and/or matrix porosity low, flow is dominated by hydrofractures and the system exhibits self-organised critical phenomena. The size of fractures achieves a power-law distribution, as failure events may sometimes trigger avalanche-like amalgamation of hydrofractures. By far most hydrofracture events only lead to local fluid flow pulses within the source area. Conductive fracture networks do not develop if hydrofractures seal relatively quickly, which can be expected in deeper crustal levels. Only the larger events span the whole system and actually drain fluid from the system. We present the 10 square km hydrothermal Hidden Valley Mega-Breccia on the Paralana Fault System in South Australia as a possible example of large-scale fluid expulsion events. Although field evidence suggests that the breccia formed over a period of at least 150 Myrs, actual cumulative fluid duration may rather have been in the order of days only. This example illustrates the extreme dynamics that crustal-scale fluid flow in hydrofractures can achieve.
How to cite: Bons, P. D., de Riese, T., Gomez-Rivas, E., Naaman, I., and Sachau, T.: Hydrofractures and crustal-scale fluid flow, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18248, https://doi.org/10.5194/egusphere-egu2020-18248, 2020.
EGU2020-14590 | Displays | TS3.5
Fault-controlled diagenesis and fluid circulation along a major syn-rift border fault system – insights from the Dombjerg Fault, Wollaston Forland Basin, NE GreenlandEric Salomon, Atle Rotevatn, Thomas Berg Kristensen, Sten-Andreas Grundvåg, Gijs Allard Henstra, Anna Nele Meckler, Axel Gerdes, and Richard Albert Roper
In marine rift basins, rift-climax deep-water clastics in the hanging wall of rift- or basin-bounding fault systems are commonly juxtaposed against crystalline basement rocks in the footwall. Displacing highly permeable, unconsolidated sediments against low-permeable rock distinguishes these faults significantly from others displacing hard rock. Due to limited surface exposure of such fault zones, studies elucidating their structure and evolution are rare. Consequently, their impact on fluid circulation and in-fault, near-fault, and hanging wall sediment diagenesis are also poorly understood. Motivated by this, we here investigate a well-exposed strand of a major basin-bounding fault system in the East Greenland rift system, namely the Dombjerg Fault which bounds the Wollaston Forland Basin, NE Greenland. Here, Upper Jurassic and Lower Cretaceous syn-rift deep-water clastics are juxtaposed against Caledonian metamorphic basement.
Previously, a ~1 km-wide zone of increased calcite cementation of the hanging wall sediments along the Dombjerg fault core was identified (Kristensen et al., 2016). Now, based on U/Pb calcite dating, we are able to show that cementation and formation of this zone started during the rift climax in Berrisian/Valanginian times. Using clumped isotope analysis, we determined cement formation temperatures of ~30-70˚C. Temperatures likely do not relate to the normal geothermal gradient, but to elevated fluid temperatures of upward directed circulation along the fault.
Vein formation within the cementation zone clusters between ~125-100 Ma in the post-rift stage, indicating that fracturing in the hanging wall is not directly related to the main phase of activity of the adjacent Dombjerg Fault. Vein formation temperatures range between ~30-80˚C, signifying a shallow burial depth of the hanging wall deposits. Further, similar minor element concentrations of veins and adjacent cements argue for diffusional mass transfer, which in turn infers a subdued fluid circulation and low permeability of the fracture network. These results imply that the chemical alteration zone formed an impermeable barrier quickly after sediment deposition and maintained this state even after fracture formation.
We argue that the existence of such a cementation zone should be considered in any assessments that target basin-bounding fault systems for, e.g., hydrocarbon, groundwater, geothermal energy, and carbon storage exploration. Our study highlights that the understanding fluid flow properties as well as fault-controlled diagenesis affecting the fault itself and/or adjacent basinal clastics is of great fundamental and economic importance.
References:
Kristensen, T. B., Rotevatn, A., Peacock, D. C. P., Henstra, G. A., Midtkandal, I., and Grundvag, S. A. (2016). Structure and flow properties of syn-rift border faults: The interplay between fault damage and fault-related chemical alteration (Dombjerg Fault, Wollaston Forland, NE Greenland), J. Struct. Geol., 92, 99-115, doi:10.1016/j.jsg.2016.09.012.
How to cite: Salomon, E., Rotevatn, A., Kristensen, T. B., Grundvåg, S.-A., Henstra, G. A., Meckler, A. N., Gerdes, A., and Roper, R. A.: Fault-controlled diagenesis and fluid circulation along a major syn-rift border fault system – insights from the Dombjerg Fault, Wollaston Forland Basin, NE Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14590, https://doi.org/10.5194/egusphere-egu2020-14590, 2020.
In marine rift basins, rift-climax deep-water clastics in the hanging wall of rift- or basin-bounding fault systems are commonly juxtaposed against crystalline basement rocks in the footwall. Displacing highly permeable, unconsolidated sediments against low-permeable rock distinguishes these faults significantly from others displacing hard rock. Due to limited surface exposure of such fault zones, studies elucidating their structure and evolution are rare. Consequently, their impact on fluid circulation and in-fault, near-fault, and hanging wall sediment diagenesis are also poorly understood. Motivated by this, we here investigate a well-exposed strand of a major basin-bounding fault system in the East Greenland rift system, namely the Dombjerg Fault which bounds the Wollaston Forland Basin, NE Greenland. Here, Upper Jurassic and Lower Cretaceous syn-rift deep-water clastics are juxtaposed against Caledonian metamorphic basement.
Previously, a ~1 km-wide zone of increased calcite cementation of the hanging wall sediments along the Dombjerg fault core was identified (Kristensen et al., 2016). Now, based on U/Pb calcite dating, we are able to show that cementation and formation of this zone started during the rift climax in Berrisian/Valanginian times. Using clumped isotope analysis, we determined cement formation temperatures of ~30-70˚C. Temperatures likely do not relate to the normal geothermal gradient, but to elevated fluid temperatures of upward directed circulation along the fault.
Vein formation within the cementation zone clusters between ~125-100 Ma in the post-rift stage, indicating that fracturing in the hanging wall is not directly related to the main phase of activity of the adjacent Dombjerg Fault. Vein formation temperatures range between ~30-80˚C, signifying a shallow burial depth of the hanging wall deposits. Further, similar minor element concentrations of veins and adjacent cements argue for diffusional mass transfer, which in turn infers a subdued fluid circulation and low permeability of the fracture network. These results imply that the chemical alteration zone formed an impermeable barrier quickly after sediment deposition and maintained this state even after fracture formation.
We argue that the existence of such a cementation zone should be considered in any assessments that target basin-bounding fault systems for, e.g., hydrocarbon, groundwater, geothermal energy, and carbon storage exploration. Our study highlights that the understanding fluid flow properties as well as fault-controlled diagenesis affecting the fault itself and/or adjacent basinal clastics is of great fundamental and economic importance.
References:
Kristensen, T. B., Rotevatn, A., Peacock, D. C. P., Henstra, G. A., Midtkandal, I., and Grundvag, S. A. (2016). Structure and flow properties of syn-rift border faults: The interplay between fault damage and fault-related chemical alteration (Dombjerg Fault, Wollaston Forland, NE Greenland), J. Struct. Geol., 92, 99-115, doi:10.1016/j.jsg.2016.09.012.
How to cite: Salomon, E., Rotevatn, A., Kristensen, T. B., Grundvåg, S.-A., Henstra, G. A., Meckler, A. N., Gerdes, A., and Roper, R. A.: Fault-controlled diagenesis and fluid circulation along a major syn-rift border fault system – insights from the Dombjerg Fault, Wollaston Forland Basin, NE Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14590, https://doi.org/10.5194/egusphere-egu2020-14590, 2020.
EGU2020-660 | Displays | TS3.5
Comb-veins as a marker for crustal-scale fluid circulation: insight from geochronological (U-Th dating), geochemical, and field to microstructural analyses along the seismogenic Val Roveto Fault (central Apennines, Italy)Luca Smeraglia, Stefano M. Bernasconi, Fabrizio Berra, Andrea Billi, Chiara Boschi, Antonio Caracausi, Eugenio Carminati, Francesca Castorina, Carlo Doglioni, Francesco Italiano, Andrea Luca Rizzo, Ibrahim Tonguç Uysal, and Jian-xin Zhao
Comb-veins are mineral-filled fractures oriented perpendicular to fault surfaces, with their intersection with the fault surface generating lineations that are perpendicular to the downdip slip direction. Despite the large occurrence along normal faults within seismogenic extensional tectonic settings (i.e. Greece, Turkey, Italy), their origin, geochemical signature, and kinematics are still poorly constrained. Here we present the first multidisciplinary study, combining field to microscale observations (optical microscope and cathodoluminescence) with geochemical-geochronological analyses (U-Th dating, stable-clumped isotopes, Strontium isotopes, whole-rock geochemistry, and fluid inclusions), on calcite-filled comb-veins cutting through the principal surface of the seismogenic Val Roveto Fault in the central Apennines, Italy. We show that comb-veins precipitated in Late Pleistocene time (between 300 ky and 140 ky) below the present-day outcrop level at a maximum depth of ∼350 m and temperatures between 32 and 64°C from deep-seated fluids modified by reactions with crustal rocks and with a mantle contribution (up to ∼39%). The observed geochemical signature and temperatures are not compatible which those of cold meteoric water and/or shallow groundwater (maximum temperature of 12 °C) circulating within shallow aquifers (≤ 500 m depth) in the study region. Therefore, we propose that deep-seated crust/mantle-derived warm fluids were squeezed upward during earthquakes and were hence responsible for calcite precipitation at shallow depths in co-seismic comb fractures. As comb-veins are rather common, particularly along seismogenic normal faults, we suggest that further studies are necessary to test whether these veins are often of co-seismic origin. If so, they may become a unique and irreplaceable tool to unravel the seismic history and crustal-scale fluid circulation of active faults.
How to cite: Smeraglia, L., Bernasconi, S. M., Berra, F., Billi, A., Boschi, C., Caracausi, A., Carminati, E., Castorina, F., Doglioni, C., Italiano, F., Rizzo, A. L., Uysal, I. T., and Zhao, J.: Comb-veins as a marker for crustal-scale fluid circulation: insight from geochronological (U-Th dating), geochemical, and field to microstructural analyses along the seismogenic Val Roveto Fault (central Apennines, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-660, https://doi.org/10.5194/egusphere-egu2020-660, 2020.
Comb-veins are mineral-filled fractures oriented perpendicular to fault surfaces, with their intersection with the fault surface generating lineations that are perpendicular to the downdip slip direction. Despite the large occurrence along normal faults within seismogenic extensional tectonic settings (i.e. Greece, Turkey, Italy), their origin, geochemical signature, and kinematics are still poorly constrained. Here we present the first multidisciplinary study, combining field to microscale observations (optical microscope and cathodoluminescence) with geochemical-geochronological analyses (U-Th dating, stable-clumped isotopes, Strontium isotopes, whole-rock geochemistry, and fluid inclusions), on calcite-filled comb-veins cutting through the principal surface of the seismogenic Val Roveto Fault in the central Apennines, Italy. We show that comb-veins precipitated in Late Pleistocene time (between 300 ky and 140 ky) below the present-day outcrop level at a maximum depth of ∼350 m and temperatures between 32 and 64°C from deep-seated fluids modified by reactions with crustal rocks and with a mantle contribution (up to ∼39%). The observed geochemical signature and temperatures are not compatible which those of cold meteoric water and/or shallow groundwater (maximum temperature of 12 °C) circulating within shallow aquifers (≤ 500 m depth) in the study region. Therefore, we propose that deep-seated crust/mantle-derived warm fluids were squeezed upward during earthquakes and were hence responsible for calcite precipitation at shallow depths in co-seismic comb fractures. As comb-veins are rather common, particularly along seismogenic normal faults, we suggest that further studies are necessary to test whether these veins are often of co-seismic origin. If so, they may become a unique and irreplaceable tool to unravel the seismic history and crustal-scale fluid circulation of active faults.
How to cite: Smeraglia, L., Bernasconi, S. M., Berra, F., Billi, A., Boschi, C., Caracausi, A., Carminati, E., Castorina, F., Doglioni, C., Italiano, F., Rizzo, A. L., Uysal, I. T., and Zhao, J.: Comb-veins as a marker for crustal-scale fluid circulation: insight from geochronological (U-Th dating), geochemical, and field to microstructural analyses along the seismogenic Val Roveto Fault (central Apennines, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-660, https://doi.org/10.5194/egusphere-egu2020-660, 2020.
EGU2020-970 | Displays | TS3.5
Deciphering orogenic and post-orogenic fluid-assisted deformations by coupling structural, mineralogical, geochemical, and geochronological investigation methods. An example from Zannone Island, ItalyManuel Curzi, Andrea Billi, Eugenio Carminati, Richard Albert, Luca Aldega, Stefano Bernasconi, Chiara Boschi, Antonio Caracausi, Luca Cardello, Alessia Conti, Kristian Drivenes, Stefania Franchini, Axel Gerdes, Andrea Luca Rizzo, Federico Rossetti, Luca Smeraglia, Bjørn Eske Sørensen, Roelant Van der Lelij, Gianluca Vignaroli, and Giulio Viola
Zannone is a very important island, located in the Neogene-Quaternary extensional domain of the Tyrrhenian back-arc basin, as it is the unique spot where the Paleozoic (?) crystalline basement is hypotesized to be exposed in central Apennines. The exposure of such hypothetical basement in the Zannone Island is very problematic as it implies very large normal displacements (> 3 km) along surrounding faults. No such displacements are known along faults close to Zannone Island.
In this work, we study the hypothetical Paleozoic crystalline basement exposed in the Zannone Island with the main aim of understanding its geological nature and relationships with the surrounding rocks. We use a multidisciplinary approach including 1) interpretation of seismic reflection profile; 2) field survey; 3) petro-textural observations; 4) microthermometry on fluid inclusions; 5) geochemical analyses of stable and clumped isotopes; 6) Illite crystallinity and mineralogical analyses of clays and host rocks; 7) analyses of minor gaseous species (He, Ne, and Ar concentrations and isotope ratios) in fluid inclusions; 8) U-Pb geochronology of syn-tectonic calcite, and 9) K-Ar dating of syn-kinematic clay minerals.
Our results show that the hypothetical Paleozoic (?) crystalline basement exposed on the Zannone Island is, instead, represented by siliciclastic rocks of very low metamorphic grade. This is testified by the quartzarenites nature of the rocks, the presence of chloritoid and by the observed incipient foliation marked by fine-grained white micas and disposed parallel to the bedding. The contact between such siliciclastic rocks and the overlapping Triassic Dolostone is represented by a low-angle thrust cut by sets of high-angle normal faults with associated calcite mineralizations. K-Ar dating on clay minerals in fault gouge reveals that at least one event of authigenesis (i.e. fluid-assisted tectonic activity) occurred in Zannone Island <22 Ma ago. U-Pb dating on sin-tectonic calcite mineralizations allowed to constrain the compressional deformation and subsequent normal faulting in the study area at around 7 Ma. This result is consistent with the 1) described emplacement of imbricate thrust sheets onshore close to Zannone Island and 2) syn-tectonic sediments-filling basins observed by seismic reflection studies. Microthermometry on fluid inclusions and stable isotopes analyses on syn-tectonic mineralizations highlighted the involvement of two different fluids during tectonic processes. One characterized by low salinity (as NaCl equivalent; i.e. meteoric-derived fluids) and one by high salinity (as NaCl equivalent; i.e. deep crustal-derived fluids). Microthermometry on fluid inclusions allowed to constrain a wide range of P-T entrapment conditions. For this reason, we highlighted a transition from lithostatic toward hydrostatic pressure during precipitation of syn-tectonic mineralizations.
How to cite: Curzi, M., Billi, A., Carminati, E., Albert, R., Aldega, L., Bernasconi, S., Boschi, C., Caracausi, A., Cardello, L., Conti, A., Drivenes, K., Franchini, S., Gerdes, A., Rizzo, A. L., Rossetti, F., Smeraglia, L., Sørensen, B. E., Van der Lelij, R., Vignaroli, G., and Viola, G.: Deciphering orogenic and post-orogenic fluid-assisted deformations by coupling structural, mineralogical, geochemical, and geochronological investigation methods. An example from Zannone Island, Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-970, https://doi.org/10.5194/egusphere-egu2020-970, 2020.
Zannone is a very important island, located in the Neogene-Quaternary extensional domain of the Tyrrhenian back-arc basin, as it is the unique spot where the Paleozoic (?) crystalline basement is hypotesized to be exposed in central Apennines. The exposure of such hypothetical basement in the Zannone Island is very problematic as it implies very large normal displacements (> 3 km) along surrounding faults. No such displacements are known along faults close to Zannone Island.
In this work, we study the hypothetical Paleozoic crystalline basement exposed in the Zannone Island with the main aim of understanding its geological nature and relationships with the surrounding rocks. We use a multidisciplinary approach including 1) interpretation of seismic reflection profile; 2) field survey; 3) petro-textural observations; 4) microthermometry on fluid inclusions; 5) geochemical analyses of stable and clumped isotopes; 6) Illite crystallinity and mineralogical analyses of clays and host rocks; 7) analyses of minor gaseous species (He, Ne, and Ar concentrations and isotope ratios) in fluid inclusions; 8) U-Pb geochronology of syn-tectonic calcite, and 9) K-Ar dating of syn-kinematic clay minerals.
Our results show that the hypothetical Paleozoic (?) crystalline basement exposed on the Zannone Island is, instead, represented by siliciclastic rocks of very low metamorphic grade. This is testified by the quartzarenites nature of the rocks, the presence of chloritoid and by the observed incipient foliation marked by fine-grained white micas and disposed parallel to the bedding. The contact between such siliciclastic rocks and the overlapping Triassic Dolostone is represented by a low-angle thrust cut by sets of high-angle normal faults with associated calcite mineralizations. K-Ar dating on clay minerals in fault gouge reveals that at least one event of authigenesis (i.e. fluid-assisted tectonic activity) occurred in Zannone Island <22 Ma ago. U-Pb dating on sin-tectonic calcite mineralizations allowed to constrain the compressional deformation and subsequent normal faulting in the study area at around 7 Ma. This result is consistent with the 1) described emplacement of imbricate thrust sheets onshore close to Zannone Island and 2) syn-tectonic sediments-filling basins observed by seismic reflection studies. Microthermometry on fluid inclusions and stable isotopes analyses on syn-tectonic mineralizations highlighted the involvement of two different fluids during tectonic processes. One characterized by low salinity (as NaCl equivalent; i.e. meteoric-derived fluids) and one by high salinity (as NaCl equivalent; i.e. deep crustal-derived fluids). Microthermometry on fluid inclusions allowed to constrain a wide range of P-T entrapment conditions. For this reason, we highlighted a transition from lithostatic toward hydrostatic pressure during precipitation of syn-tectonic mineralizations.
How to cite: Curzi, M., Billi, A., Carminati, E., Albert, R., Aldega, L., Bernasconi, S., Boschi, C., Caracausi, A., Cardello, L., Conti, A., Drivenes, K., Franchini, S., Gerdes, A., Rizzo, A. L., Rossetti, F., Smeraglia, L., Sørensen, B. E., Van der Lelij, R., Vignaroli, G., and Viola, G.: Deciphering orogenic and post-orogenic fluid-assisted deformations by coupling structural, mineralogical, geochemical, and geochronological investigation methods. An example from Zannone Island, Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-970, https://doi.org/10.5194/egusphere-egu2020-970, 2020.
EGU2020-2866 | Displays | TS3.5
Cyclicity of paleofluid infiltration in the active Mount Morrone Fault System (central Apennines, Italy) constrained by carbonate concretionsGianluca Vignaroli, Valentina Argante, Federico Rossetti, Lorenzo Petracchini, Michele Soligo, Mauro Brilli, Tsai-Luen Yu, and Chuan-Chou Shen
Active faults are characterized by creation/destruction of secondary (tectonic) permeability in response to a continuous interplay between deformation and fluid pressure fluctuations during the seismic cycle. The study of the paleofluid circulation in fault rocks can thus provide insights into the hydraulic and mechanical behavior of the seismogenic crust.
This work integrates data from field geology with geochemical and geochronological constraints to understand the spatio-temporal evolution of the paleofluid circulation in the Mount Morrone Fault System (MMFS), a ~25 km-long tectonic structure activated during the extensional Quaternary phase of the central Apennines (Italy). The MMFS cuts through a Mesozoic-Cenozoic multilayer carbonate succession for a cumulative stratigraphic offset of about 2 km. Fluvio-lacustrine and slope deposits (Middle-Late Pleistocene) occur at its hanging wall and are variably involved by faulting. The MMFS is currently classified as a silent seismic fault, with an estimated Mw= 6.5-7.0 potential magnitude and recurrence time at 2.4 ka for an expected earthquake.
The structural survey focused on the western strand of the MMFS cutting through a succession of Sinemurian dolomitized limestones. A composite network of NW-SE-striking, SW-dipping fault surfaces defines the structural architecture of the MMFS in the study outcrops, with high angle (dip > 55°) faults that systematically cut and displace medium-to-low angle (dip in the order of 30°-50°) faults. Both fault systems are characterized by dominant dip-slip movement and normal kinematics. Lenses of cm-thick cataclasites often occur along the slip surfaces. Cataclasites are made by sub-angular to sub-rounded carbonate clasts (up to 1 cm-wide) dispersed in a very fine-grained matrix. Layers of cm-thick carbonate concretions occur associated with the cataclasites, testifying for pulses of fluid discharge along the fault surface during the tectonic activity of the MMFS. Microstructural investigations document that: (i) carbonate concretions show an internal texture of fibrous vein having fiber growth direction roughly perpendicular to the vein wall, and (ii) the basal portions of the carbonate concretions are fractured and incorporated within the underlying cataclasites through the deposition of a new calcite cement. The geochemical (δ13C and δ18O stable isotope) analyses on selected samples attest for a progressive chemical shift of the mineralizing fluid from marine (in host rock and in cataclasites) to meteoric waters (in carbonate concretions). The U-Th dating of carbonate concretions and calcite slickenfibers constrains the fault-controlled fluid circulation to the Middle Pleistocene, with ages spanning from 270 to 180 ka. Significantly, the dating of carbonate concretions documents a 12-kyr cyclicity of the fluid infiltration in the fault zone.
The development of the secondary permeability in the MMFS thus corresponds to a combination of faulting and tensile fracturing, in response to a cyclic increasing of the shear stress and the pore pressure during the seismic cycle. The polyphasic deformation system of the MMFS constitutes a record of fault activation and reactivation episodes that could contribute to define the recurrence model of seismic events on regional-scale faults.
How to cite: Vignaroli, G., Argante, V., Rossetti, F., Petracchini, L., Soligo, M., Brilli, M., Yu, T.-L., and Shen, C.-C.: Cyclicity of paleofluid infiltration in the active Mount Morrone Fault System (central Apennines, Italy) constrained by carbonate concretions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2866, https://doi.org/10.5194/egusphere-egu2020-2866, 2020.
Active faults are characterized by creation/destruction of secondary (tectonic) permeability in response to a continuous interplay between deformation and fluid pressure fluctuations during the seismic cycle. The study of the paleofluid circulation in fault rocks can thus provide insights into the hydraulic and mechanical behavior of the seismogenic crust.
This work integrates data from field geology with geochemical and geochronological constraints to understand the spatio-temporal evolution of the paleofluid circulation in the Mount Morrone Fault System (MMFS), a ~25 km-long tectonic structure activated during the extensional Quaternary phase of the central Apennines (Italy). The MMFS cuts through a Mesozoic-Cenozoic multilayer carbonate succession for a cumulative stratigraphic offset of about 2 km. Fluvio-lacustrine and slope deposits (Middle-Late Pleistocene) occur at its hanging wall and are variably involved by faulting. The MMFS is currently classified as a silent seismic fault, with an estimated Mw= 6.5-7.0 potential magnitude and recurrence time at 2.4 ka for an expected earthquake.
The structural survey focused on the western strand of the MMFS cutting through a succession of Sinemurian dolomitized limestones. A composite network of NW-SE-striking, SW-dipping fault surfaces defines the structural architecture of the MMFS in the study outcrops, with high angle (dip > 55°) faults that systematically cut and displace medium-to-low angle (dip in the order of 30°-50°) faults. Both fault systems are characterized by dominant dip-slip movement and normal kinematics. Lenses of cm-thick cataclasites often occur along the slip surfaces. Cataclasites are made by sub-angular to sub-rounded carbonate clasts (up to 1 cm-wide) dispersed in a very fine-grained matrix. Layers of cm-thick carbonate concretions occur associated with the cataclasites, testifying for pulses of fluid discharge along the fault surface during the tectonic activity of the MMFS. Microstructural investigations document that: (i) carbonate concretions show an internal texture of fibrous vein having fiber growth direction roughly perpendicular to the vein wall, and (ii) the basal portions of the carbonate concretions are fractured and incorporated within the underlying cataclasites through the deposition of a new calcite cement. The geochemical (δ13C and δ18O stable isotope) analyses on selected samples attest for a progressive chemical shift of the mineralizing fluid from marine (in host rock and in cataclasites) to meteoric waters (in carbonate concretions). The U-Th dating of carbonate concretions and calcite slickenfibers constrains the fault-controlled fluid circulation to the Middle Pleistocene, with ages spanning from 270 to 180 ka. Significantly, the dating of carbonate concretions documents a 12-kyr cyclicity of the fluid infiltration in the fault zone.
The development of the secondary permeability in the MMFS thus corresponds to a combination of faulting and tensile fracturing, in response to a cyclic increasing of the shear stress and the pore pressure during the seismic cycle. The polyphasic deformation system of the MMFS constitutes a record of fault activation and reactivation episodes that could contribute to define the recurrence model of seismic events on regional-scale faults.
How to cite: Vignaroli, G., Argante, V., Rossetti, F., Petracchini, L., Soligo, M., Brilli, M., Yu, T.-L., and Shen, C.-C.: Cyclicity of paleofluid infiltration in the active Mount Morrone Fault System (central Apennines, Italy) constrained by carbonate concretions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2866, https://doi.org/10.5194/egusphere-egu2020-2866, 2020.
EGU2020-20149 | Displays | TS3.5
Isotope analysis of vein-hosted fluid inclusions: A case study on fracture-controlled fluid flow in the Albanian foreland fold-and-thrust beltStefan de Graaf, Casimir Nooitgedacht, Hubert Vonhof, Jeroen van der Lubbe, and John Reijmer
Vein-hosted fluid inclusions may represent remnants of subsurface paleo-fluids and therefore provide a valuable record of fracture-controlled fluid flow. Isotope data (δ2H and δ18O) of fluid inclusions are particularly useful for studying the provenance and type of paleo-fluids circulating in the subsurface. Although isotopic analysis of sub-microliter amounts of fluid inclusion water is not straightforward, major steps forward have been made over the past decade through the development of continuous-flow set-ups. These techniques make use of mechanical crushing at a relatively low-temperature (110˚C) and allow for on-line analysis of both δ2H and δ18O ratios of bulk fluid inclusion water. However, continuous-flow techniques have mostly been used in speleothem research, and have not yet found a widespread application on vein systems for hydrogeological reconstructions.
We used isotope data of fluid inclusions hosted in calcite vein cements to reconstruct regional fluid migration pathways in the Albanian foreland fold-and-thrust system. Tectonic forces during thrust emplacement typically instigate distinct phases of fracturing accompanied by complex fluid flow patterns. The studied calcite veins developed in a sequence of naturally fractured Cretaceous to Eocene carbonate rocks as a result of several fracturing events from the early stages of burial onward. Fluid inclusion isotope data of the veins reveal that fluids circulating in the carbonates were derived from an underlying reservoir, which consisted of a mixture of meteoric water and evolved marine fluids, probably derived from deep-seated evaporites. The meteoric fluids infiltrated in the hinterland before being driven outward into the foreland basin. The fluid inclusion isotope data furthermore show that meteoric water becomes increasingly dominant in the system through time as migration pathways shortened and marine formation fluids were progressively flushed out.
The diagenetic stability of fluid inclusions is of key interest in the study of their isotope ratios. Recrystallization, secondary fluid infiltration and isotope exchange processes could potentially drive alterations of fluid inclusion isotope signatures after entrapment. In this case, however, isotope signatures of fluid inclusions seem to have remained largely unaltered, despite the Cretaceous to Tertiary age of the vein system. Oxygen isotope exchange processes between the fluid inclusion water and host mineral could have been inhibited at the relatively low temperatures of vein formation (i.e. <80˚C). Although more research into the diagenetic stability of fluid inclusion isotope ratios is required, the fluid inclusion isotope record has potential as a powerful tool for fluid provenancing in subsurface fluid flow systems.
How to cite: de Graaf, S., Nooitgedacht, C., Vonhof, H., van der Lubbe, J., and Reijmer, J.: Isotope analysis of vein-hosted fluid inclusions: A case study on fracture-controlled fluid flow in the Albanian foreland fold-and-thrust belt, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20149, https://doi.org/10.5194/egusphere-egu2020-20149, 2020.
Vein-hosted fluid inclusions may represent remnants of subsurface paleo-fluids and therefore provide a valuable record of fracture-controlled fluid flow. Isotope data (δ2H and δ18O) of fluid inclusions are particularly useful for studying the provenance and type of paleo-fluids circulating in the subsurface. Although isotopic analysis of sub-microliter amounts of fluid inclusion water is not straightforward, major steps forward have been made over the past decade through the development of continuous-flow set-ups. These techniques make use of mechanical crushing at a relatively low-temperature (110˚C) and allow for on-line analysis of both δ2H and δ18O ratios of bulk fluid inclusion water. However, continuous-flow techniques have mostly been used in speleothem research, and have not yet found a widespread application on vein systems for hydrogeological reconstructions.
We used isotope data of fluid inclusions hosted in calcite vein cements to reconstruct regional fluid migration pathways in the Albanian foreland fold-and-thrust system. Tectonic forces during thrust emplacement typically instigate distinct phases of fracturing accompanied by complex fluid flow patterns. The studied calcite veins developed in a sequence of naturally fractured Cretaceous to Eocene carbonate rocks as a result of several fracturing events from the early stages of burial onward. Fluid inclusion isotope data of the veins reveal that fluids circulating in the carbonates were derived from an underlying reservoir, which consisted of a mixture of meteoric water and evolved marine fluids, probably derived from deep-seated evaporites. The meteoric fluids infiltrated in the hinterland before being driven outward into the foreland basin. The fluid inclusion isotope data furthermore show that meteoric water becomes increasingly dominant in the system through time as migration pathways shortened and marine formation fluids were progressively flushed out.
The diagenetic stability of fluid inclusions is of key interest in the study of their isotope ratios. Recrystallization, secondary fluid infiltration and isotope exchange processes could potentially drive alterations of fluid inclusion isotope signatures after entrapment. In this case, however, isotope signatures of fluid inclusions seem to have remained largely unaltered, despite the Cretaceous to Tertiary age of the vein system. Oxygen isotope exchange processes between the fluid inclusion water and host mineral could have been inhibited at the relatively low temperatures of vein formation (i.e. <80˚C). Although more research into the diagenetic stability of fluid inclusion isotope ratios is required, the fluid inclusion isotope record has potential as a powerful tool for fluid provenancing in subsurface fluid flow systems.
How to cite: de Graaf, S., Nooitgedacht, C., Vonhof, H., van der Lubbe, J., and Reijmer, J.: Isotope analysis of vein-hosted fluid inclusions: A case study on fracture-controlled fluid flow in the Albanian foreland fold-and-thrust belt, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20149, https://doi.org/10.5194/egusphere-egu2020-20149, 2020.
EGU2020-22180 | Displays | TS3.5
Influence of fluid-assisted micro-crack healing on fault permeability structureAlissar Yehya and James R. Rice
Micro-cracks in fault damage zones can heal through diffusive mass transfer driven by differences in chemical potential, with rates controlled by temperature and pressure. The diffusion of pore fluid pressure in fault damage zones accelerates mass diffusion and assists healing processes. In this work, we use fluid flow model coupled with heat transfer and crack healing to investigate, through different scenarios, the role of subsurface warm fluid migration, along damage zones, in enhancing healing and re-shaping the fault permeability structure. Our results show that if the flow communication exists between the bed and only one side of the damage zone and not the other side, it leads to an asymmetric permeability structure caused by healing in the side circulated by fluids (ex: Rapolano geothermal area, Italy). Another scenario is when the damage zone adjacent to the fault core is not the interval with the highest permeability, as conventionally expected, which is the case of the Alpine Fault, New Zealand. As shown by our simulations, this can be due to healing by diffusive mass transfer, favored by the localized high geothermal gradients and the upward fluid migration through the fault relay structure.
How to cite: Yehya, A. and Rice, J. R.: Influence of fluid-assisted micro-crack healing on fault permeability structure, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22180, https://doi.org/10.5194/egusphere-egu2020-22180, 2020.
Micro-cracks in fault damage zones can heal through diffusive mass transfer driven by differences in chemical potential, with rates controlled by temperature and pressure. The diffusion of pore fluid pressure in fault damage zones accelerates mass diffusion and assists healing processes. In this work, we use fluid flow model coupled with heat transfer and crack healing to investigate, through different scenarios, the role of subsurface warm fluid migration, along damage zones, in enhancing healing and re-shaping the fault permeability structure. Our results show that if the flow communication exists between the bed and only one side of the damage zone and not the other side, it leads to an asymmetric permeability structure caused by healing in the side circulated by fluids (ex: Rapolano geothermal area, Italy). Another scenario is when the damage zone adjacent to the fault core is not the interval with the highest permeability, as conventionally expected, which is the case of the Alpine Fault, New Zealand. As shown by our simulations, this can be due to healing by diffusive mass transfer, favored by the localized high geothermal gradients and the upward fluid migration through the fault relay structure.
How to cite: Yehya, A. and Rice, J. R.: Influence of fluid-assisted micro-crack healing on fault permeability structure, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22180, https://doi.org/10.5194/egusphere-egu2020-22180, 2020.
EGU2020-11638 | Displays | TS3.5
Fracture growth during exhumation in low-permeability rock formations—the role of fluid PVT propertiesPeter Eichhubl
Detailed fluid inclusion analyses of fracture cements in tightly cemented hydrocarbon-bearing sandstones and shales reveal that natural fractures tend to form under conditions approaching maximum burial, coinciding with hydrocarbon generation, and during incipient exhumation. Fluid inclusion analyses also reveal that these fractures form under abnormal (above-hydrostatic) pore fluid pressures. While compaction disequilibrium can account for elevated pore fluid pressures that promote fracture growth during early prograde burial, hydrocarbon maturation is likely the primary driver for fracture growth under peak burial conditions. Tectonic processes and thermal stresses provide secondary drivers. Thermal contraction with exhumation and cooling of the rock mass can promote fracture growth depending on the PVT properties of the fluid phase. The possible contribution of hydrocarbon generation after peak burial as a driver for fracture growth during incipient exhumation is discussed.
How to cite: Eichhubl, P.: Fracture growth during exhumation in low-permeability rock formations—the role of fluid PVT properties, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11638, https://doi.org/10.5194/egusphere-egu2020-11638, 2020.
Detailed fluid inclusion analyses of fracture cements in tightly cemented hydrocarbon-bearing sandstones and shales reveal that natural fractures tend to form under conditions approaching maximum burial, coinciding with hydrocarbon generation, and during incipient exhumation. Fluid inclusion analyses also reveal that these fractures form under abnormal (above-hydrostatic) pore fluid pressures. While compaction disequilibrium can account for elevated pore fluid pressures that promote fracture growth during early prograde burial, hydrocarbon maturation is likely the primary driver for fracture growth under peak burial conditions. Tectonic processes and thermal stresses provide secondary drivers. Thermal contraction with exhumation and cooling of the rock mass can promote fracture growth depending on the PVT properties of the fluid phase. The possible contribution of hydrocarbon generation after peak burial as a driver for fracture growth during incipient exhumation is discussed.
How to cite: Eichhubl, P.: Fracture growth during exhumation in low-permeability rock formations—the role of fluid PVT properties, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11638, https://doi.org/10.5194/egusphere-egu2020-11638, 2020.
EGU2020-6520 | Displays | TS3.5
Permeability contrasts of fault zones - from conceptual model to numerical simulationUlrich Kelka, Thomas Poulet, and Luk Peeters
Fault and fracture networks can govern fluid flow patterns in the subsurface and predicting fluid flow on a regional scale is of interest in a variety of fields like groundwater management, mining engineering, energy, and mineral resources. Especially the pore fluid pressure can have a strong impact on the strength of fault zones and might be one of the drivers for fault reactivation. Reliable simulations of the transient changes in fluid pressure need to account for the generic architecture of fault zones that comprises strong permeability contrast between the fault core and damage zone.
Particularly, the distribution and connectivity of large-scale fault zones can have a strong impact on the flow field. Yet, modelling numerically such features in their full complexity remains challenging. Often faults zones are conceptualized as forming exclusively either barriers or conduits to fluid flow. However, a generic architecture of fault zones often comprises a discrete fault core surrounded by a diffuse damage zone and conceptualizing large scale discontinuities simply as a barrier or conduit is unlikely to capture the regional scale fluid flow dynamics. It is known that if the fault zone is hosted in low-permeability strata, such as clays or crystalline rocks, a transversal flow barrier can form along the fault core whereas the fracture-rich fault damage zone represents a longitudinal conduit. In more permeable host-rocks (i.e. sandstones or carbonates) the reverse situation can occur, and the permeability distributions in the damage zones can be governed by the abundance of low-permeability deformation features. A reliable numerical model needs to account for the difference and strong contrasts in fluid flow properties of the core and the damage zone, both transversally and longitudinally, in order to make prediction about the regional fluid flow pattern.
Here, we present a numerical method that accounts for the generic fault zone architecture as lower dimensional interfaces in conforming meshes during fluid flow simulations in fault networks. With this method we aim to decipher the impact of fault zone architecture on subsurface flow pattern and fluid pressure evolution in fractures and faulted porous media. The method is implemented in a finite element framework for Multiphysics simulations. We demonstrate the impact of considering the more generic geological structure of individual faults on the flow field by conceptualizing discontinuities either as barriers, conduits or as a conduit-barrier system and show were these conceptualizations are applicable in natural systems. We further show that a reliable regional scale fluid flow simulation in faulted porous media needs to account for the generic fault zone architecture. The approach is finally used to evaluate the fluid flow response of statistically parameterised faulted media, in order to investigate the impact and sensitivity of each variable parameter.
How to cite: Kelka, U., Poulet, T., and Peeters, L.: Permeability contrasts of fault zones - from conceptual model to numerical simulation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6520, https://doi.org/10.5194/egusphere-egu2020-6520, 2020.
Fault and fracture networks can govern fluid flow patterns in the subsurface and predicting fluid flow on a regional scale is of interest in a variety of fields like groundwater management, mining engineering, energy, and mineral resources. Especially the pore fluid pressure can have a strong impact on the strength of fault zones and might be one of the drivers for fault reactivation. Reliable simulations of the transient changes in fluid pressure need to account for the generic architecture of fault zones that comprises strong permeability contrast between the fault core and damage zone.
Particularly, the distribution and connectivity of large-scale fault zones can have a strong impact on the flow field. Yet, modelling numerically such features in their full complexity remains challenging. Often faults zones are conceptualized as forming exclusively either barriers or conduits to fluid flow. However, a generic architecture of fault zones often comprises a discrete fault core surrounded by a diffuse damage zone and conceptualizing large scale discontinuities simply as a barrier or conduit is unlikely to capture the regional scale fluid flow dynamics. It is known that if the fault zone is hosted in low-permeability strata, such as clays or crystalline rocks, a transversal flow barrier can form along the fault core whereas the fracture-rich fault damage zone represents a longitudinal conduit. In more permeable host-rocks (i.e. sandstones or carbonates) the reverse situation can occur, and the permeability distributions in the damage zones can be governed by the abundance of low-permeability deformation features. A reliable numerical model needs to account for the difference and strong contrasts in fluid flow properties of the core and the damage zone, both transversally and longitudinally, in order to make prediction about the regional fluid flow pattern.
Here, we present a numerical method that accounts for the generic fault zone architecture as lower dimensional interfaces in conforming meshes during fluid flow simulations in fault networks. With this method we aim to decipher the impact of fault zone architecture on subsurface flow pattern and fluid pressure evolution in fractures and faulted porous media. The method is implemented in a finite element framework for Multiphysics simulations. We demonstrate the impact of considering the more generic geological structure of individual faults on the flow field by conceptualizing discontinuities either as barriers, conduits or as a conduit-barrier system and show were these conceptualizations are applicable in natural systems. We further show that a reliable regional scale fluid flow simulation in faulted porous media needs to account for the generic fault zone architecture. The approach is finally used to evaluate the fluid flow response of statistically parameterised faulted media, in order to investigate the impact and sensitivity of each variable parameter.
How to cite: Kelka, U., Poulet, T., and Peeters, L.: Permeability contrasts of fault zones - from conceptual model to numerical simulation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6520, https://doi.org/10.5194/egusphere-egu2020-6520, 2020.
EGU2020-22014 | Displays | TS3.5
Upscaled modelling of natural fracturing and leakage due to high overpressuresAne Elisabet Lothe, Arnt Grøver, and Ole-Andre Roli
In sedimentary basins highly overpressured formations and zones are observed worldwide. The high overpressures have been generated over millions of years due to sedimentation amount and rate, compaction, lateral fluid flow, diagenesis and other processes. The lateral fluid flow is often controlled by the fault pattern and sealing properties of the faults in the area, thus defining what is often termed pressure compartments. When high overpressures builds-up over time in such compartment, eventually natural hydraulic faulting and fracturing will start to develop to cease and relief the overpressure.
In this work we have aimed to simulate fracture generation, how they in an upscaled approach evolve and progress upwards, and how this will influence the water fluid flow and the pore pressure distribution. We use an in-house software (PressureAhead) to simulate three-dimensional water fluid pressure generation and dissipation over millions of years. Interpreted seismic horizons for the whole stratigraphy are back-stripped (decompaction) in order to provide the basin burial history as input to the forward simulator. Uplift and erosion events are included. For each timestep, the effect of pressure generation and dissipation is calculated. For the fault and failure development, the combined Griffith-Coulomb failure criteria are implemented to calculate when failure occurs, secondly, when the fracture has been formed and the cohesion is lost, the frictional sliding criteria is used. The fractures are in this approach working as a pressure valve, that will stay open as long as the pressure support is large enough. Compared to previous approach, the failure criteria is now evaluated for the whole stratigraphic column in 3D Using this approach, the effect of natural fracturing taking place in different parts of the basin at different geological events can be modelled.
The new simulation approach will be presented for a dataset from the deeper part of the Viking Graben, North Sea offshore Norway. The study area covers an NNE-SSW trending graben defined by large faults. Seventeen seismic horizons (resolution 50x50 m) from Middle Jurassic to seafloor have been used to set up the model. The modelling is carried out over the 150 My, with time steps of 250 000 years. Examples of varying key input parameters will be shown. Strength and weakness with such an upscaled modelling framework will be discussed.
How to cite: Lothe, A. E., Grøver, A., and Roli, O.-A.: Upscaled modelling of natural fracturing and leakage due to high overpressures , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22014, https://doi.org/10.5194/egusphere-egu2020-22014, 2020.
In sedimentary basins highly overpressured formations and zones are observed worldwide. The high overpressures have been generated over millions of years due to sedimentation amount and rate, compaction, lateral fluid flow, diagenesis and other processes. The lateral fluid flow is often controlled by the fault pattern and sealing properties of the faults in the area, thus defining what is often termed pressure compartments. When high overpressures builds-up over time in such compartment, eventually natural hydraulic faulting and fracturing will start to develop to cease and relief the overpressure.
In this work we have aimed to simulate fracture generation, how they in an upscaled approach evolve and progress upwards, and how this will influence the water fluid flow and the pore pressure distribution. We use an in-house software (PressureAhead) to simulate three-dimensional water fluid pressure generation and dissipation over millions of years. Interpreted seismic horizons for the whole stratigraphy are back-stripped (decompaction) in order to provide the basin burial history as input to the forward simulator. Uplift and erosion events are included. For each timestep, the effect of pressure generation and dissipation is calculated. For the fault and failure development, the combined Griffith-Coulomb failure criteria are implemented to calculate when failure occurs, secondly, when the fracture has been formed and the cohesion is lost, the frictional sliding criteria is used. The fractures are in this approach working as a pressure valve, that will stay open as long as the pressure support is large enough. Compared to previous approach, the failure criteria is now evaluated for the whole stratigraphic column in 3D Using this approach, the effect of natural fracturing taking place in different parts of the basin at different geological events can be modelled.
The new simulation approach will be presented for a dataset from the deeper part of the Viking Graben, North Sea offshore Norway. The study area covers an NNE-SSW trending graben defined by large faults. Seventeen seismic horizons (resolution 50x50 m) from Middle Jurassic to seafloor have been used to set up the model. The modelling is carried out over the 150 My, with time steps of 250 000 years. Examples of varying key input parameters will be shown. Strength and weakness with such an upscaled modelling framework will be discussed.
How to cite: Lothe, A. E., Grøver, A., and Roli, O.-A.: Upscaled modelling of natural fracturing and leakage due to high overpressures , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22014, https://doi.org/10.5194/egusphere-egu2020-22014, 2020.
EGU2020-8644 | Displays | TS3.5
Porosity channeling and fracturing in fluid over-pressure zonesDaniel Koehn, Sandra Piazolo, Till Sachau, and Renaud Toussaint
It is important to understand the effects of fluid over-pressure in rocks because gradients in over-pressure can lead to failure of rocks and expulsion of fluids. Examples are hydro-fracturing in engineering as well as fluid generation during hydrocarbon maturation, metamorphic reactions or over-pressure below seals in sedimentary basins. In order to have an understanding of the complexity of effective stress fields, fracture, failure and fluid drainage the process was studied with a dynamic hydro-mechanical numerical model. The evolution of fluid pressure build up, fracturing and the dynamic interaction between solid and fluid is modeled. Three scenarios are studied: fluid pressure build up in a sedimentary basin, in a confined zone and in a horizontal layer that is offset by a fault. Results indicate that the geometry of the fluid-overpressure zone has a first order control on the patterns including porosity evolution and fracturing. If the over-pressure develops below a seal in a sedimentary basin, the effective differential and mean stress approach zero and the horizontal and vertical effective stresses flip in orientation leading to horizontal hydro-factures or breccia zones. If the over-pressure zone is confined vertically as well, the standard effective stress model develops with the effective mean stress decreasing while the differential stress remains mainly constant. This leads to semi-vertically aligned extensional and conjugate shear failure at much lower over-pressures than in the sedimentary basin. A perfectly aligned horizontal layer that increases in fluid pressure internally leads to a horizontal hydro-fracture within the layer. A faulted layer develops complex multi-directional failure with the fault itself being a location of early fracturing followed by brecciation of the layer itself. All simulations undergo a phase transition in porosity evolution with an initially random porosity reducing its symmetry and forming a static porosity wave with an internal dilation zone and the development of dynamic porosity channels within this zone that drain the over-pressure. Our results show that patterns of fractures, hence fluid release, that form due to high fluid overpressures can only be successfully predicted if the geometry of the geological system is known, including the fluid overpressure source and the position of seals and faults that offset source layers and seals.
How to cite: Koehn, D., Piazolo, S., Sachau, T., and Toussaint, R.: Porosity channeling and fracturing in fluid over-pressure zones , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8644, https://doi.org/10.5194/egusphere-egu2020-8644, 2020.
It is important to understand the effects of fluid over-pressure in rocks because gradients in over-pressure can lead to failure of rocks and expulsion of fluids. Examples are hydro-fracturing in engineering as well as fluid generation during hydrocarbon maturation, metamorphic reactions or over-pressure below seals in sedimentary basins. In order to have an understanding of the complexity of effective stress fields, fracture, failure and fluid drainage the process was studied with a dynamic hydro-mechanical numerical model. The evolution of fluid pressure build up, fracturing and the dynamic interaction between solid and fluid is modeled. Three scenarios are studied: fluid pressure build up in a sedimentary basin, in a confined zone and in a horizontal layer that is offset by a fault. Results indicate that the geometry of the fluid-overpressure zone has a first order control on the patterns including porosity evolution and fracturing. If the over-pressure develops below a seal in a sedimentary basin, the effective differential and mean stress approach zero and the horizontal and vertical effective stresses flip in orientation leading to horizontal hydro-factures or breccia zones. If the over-pressure zone is confined vertically as well, the standard effective stress model develops with the effective mean stress decreasing while the differential stress remains mainly constant. This leads to semi-vertically aligned extensional and conjugate shear failure at much lower over-pressures than in the sedimentary basin. A perfectly aligned horizontal layer that increases in fluid pressure internally leads to a horizontal hydro-fracture within the layer. A faulted layer develops complex multi-directional failure with the fault itself being a location of early fracturing followed by brecciation of the layer itself. All simulations undergo a phase transition in porosity evolution with an initially random porosity reducing its symmetry and forming a static porosity wave with an internal dilation zone and the development of dynamic porosity channels within this zone that drain the over-pressure. Our results show that patterns of fractures, hence fluid release, that form due to high fluid overpressures can only be successfully predicted if the geometry of the geological system is known, including the fluid overpressure source and the position of seals and faults that offset source layers and seals.
How to cite: Koehn, D., Piazolo, S., Sachau, T., and Toussaint, R.: Porosity channeling and fracturing in fluid over-pressure zones , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8644, https://doi.org/10.5194/egusphere-egu2020-8644, 2020.
EGU2020-5538 | Displays | TS3.5
Permeability tensors of three-dimensional numerically grown geomechanical discrete fracture networksAdriana Paluszny, Robin N Thomas, and Robert W Zimmerman
The mechanics of fracture propagation and interaction influence the growth and permeability of developing fracture networks. A set of initial flaws grows quasi-statically in response to a remote tensile stress. A finite element, stress intensity factor-based approach grows these flaws into non-planar three-dimensional discrete fracture networks (GDFNs). Their extension and growth angle is a function of local stress intensity factors along a fracture tip. Stress concentration increase when proximal fractures are aligned, and decreases when they are sub-coplanar. These interactions can result in the reactivation of fractures that were initially inactive, and the arrest of fractures that become entrapped by proximal growing fractures. Interaction can cause growth away from an intersection front between two fractures, resulting in evolving fracture patterns that become non-uniform and non-planar, forming dense networks. These GDFNs provide representations of subsurface networks that numerically model the physical process of concurrent fracture growth. Permeability tensors of the geomechanical 3D networks are computed, assuming Darcy flow. Growth influences apertures, and in turn, the hydraulic properties of the network. GDFNs provide a promising way to model subsurface fracture networks, and their related hydro-mechanical processes, where fracture mechanics is the primary influence on the geometric and hydraulic properties of the networks.
How to cite: Paluszny, A., Thomas, R. N., and Zimmerman, R. W.: Permeability tensors of three-dimensional numerically grown geomechanical discrete fracture networks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5538, https://doi.org/10.5194/egusphere-egu2020-5538, 2020.
The mechanics of fracture propagation and interaction influence the growth and permeability of developing fracture networks. A set of initial flaws grows quasi-statically in response to a remote tensile stress. A finite element, stress intensity factor-based approach grows these flaws into non-planar three-dimensional discrete fracture networks (GDFNs). Their extension and growth angle is a function of local stress intensity factors along a fracture tip. Stress concentration increase when proximal fractures are aligned, and decreases when they are sub-coplanar. These interactions can result in the reactivation of fractures that were initially inactive, and the arrest of fractures that become entrapped by proximal growing fractures. Interaction can cause growth away from an intersection front between two fractures, resulting in evolving fracture patterns that become non-uniform and non-planar, forming dense networks. These GDFNs provide representations of subsurface networks that numerically model the physical process of concurrent fracture growth. Permeability tensors of the geomechanical 3D networks are computed, assuming Darcy flow. Growth influences apertures, and in turn, the hydraulic properties of the network. GDFNs provide a promising way to model subsurface fracture networks, and their related hydro-mechanical processes, where fracture mechanics is the primary influence on the geometric and hydraulic properties of the networks.
How to cite: Paluszny, A., Thomas, R. N., and Zimmerman, R. W.: Permeability tensors of three-dimensional numerically grown geomechanical discrete fracture networks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5538, https://doi.org/10.5194/egusphere-egu2020-5538, 2020.
EGU2020-4688 | Displays | TS3.5 | Highlight | TS Division Outstanding ECS Lecture
From Faults and Fluids to Mountain Belt DynamicsChristoph von Hagke
For understanding the formation of mountain belts it is necessary to gain quantitative insights on fault and fracture mechanics on multiple scales. In particular, for addressing the role of fluids on larger processes, it is inevitable to constrain fault and fracture geometries at depth, as well as gain insights on how fluids influence fault mechanics. At least partly, the future of such analyses lies in exploiting large data sets, as well as in multi- and interdisciplinary research.
In this talk I will present results from variety of geological settings, including dilatant faults at Mid-Ocean Ridges, the Oman Mountains, the Khao Kwang fold-trust belt in Thailand, and the European Alps. I will show how multi-scale studies and the use of large data sets helps constraining fluid migration in mountain belts, fault geometries, as well as possible feedbacks between fluid flow and strain localization. Results are then applied to discuss the role of mechanical stratigraphy on structural style in foreland fold-thrust belts.
How to cite: von Hagke, C.: From Faults and Fluids to Mountain Belt Dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4688, https://doi.org/10.5194/egusphere-egu2020-4688, 2020.
For understanding the formation of mountain belts it is necessary to gain quantitative insights on fault and fracture mechanics on multiple scales. In particular, for addressing the role of fluids on larger processes, it is inevitable to constrain fault and fracture geometries at depth, as well as gain insights on how fluids influence fault mechanics. At least partly, the future of such analyses lies in exploiting large data sets, as well as in multi- and interdisciplinary research.
In this talk I will present results from variety of geological settings, including dilatant faults at Mid-Ocean Ridges, the Oman Mountains, the Khao Kwang fold-trust belt in Thailand, and the European Alps. I will show how multi-scale studies and the use of large data sets helps constraining fluid migration in mountain belts, fault geometries, as well as possible feedbacks between fluid flow and strain localization. Results are then applied to discuss the role of mechanical stratigraphy on structural style in foreland fold-thrust belts.
How to cite: von Hagke, C.: From Faults and Fluids to Mountain Belt Dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4688, https://doi.org/10.5194/egusphere-egu2020-4688, 2020.
EGU2020-20161 | Displays | TS3.5
Scale discrepancy paradox between observation and modelling in fractured reservoir models in oil and gas industry.Pascal Richard and Loïc Bazalgette
Naturally fractured reservoirs represent one of the most challenging resource in the oil and gas industry. The understanding based on centimeter scale observations is upscaled and modeled at 100-meter scale.
In this paper, we will illustrate with case study examples of conceptual fracture model elaborated using static and dynamic data, the disconnect between the scale of observation and the scale of modelling. We will also discuss the potential disconnect between the detail of fundamental, but necessary, research work in universities against the coarse resolution of the models built in the oil industry, and how we can benefit of the differences in scales and approaches.
The appraisal and development of fractured reservoirs offer challenges due to the variations in reservoir quality and natural fracture distribution. Typically, the presence of open, connected fractures is one of the key elements to achieve a successful development. Fracture modelling studies are carried out routinely to support both appraisal and development strategies of these fractured reservoirs.
Overall fracture modelling workflow consists first of a fracture characterization phase concentrating on the understanding of the deformation history and the evaluation of the nature, type and distribution of the fractures; secondly of a fracture modelling part where fracture properties for the dynamic simulation are generated and calibrated against dynamic data. The pillar of the studies is the creation of 3D conceptual fracture diagrams/concepts which summarize both the understanding and the uncertainty of the fracture network of interest. These conceptual diagrams rely on detailed observations at the scale of the wellbore using core and borehole image data which are on contrasting scale compare to the 10’s of meters to 100’s of meter scale of the grid cells of the dynamic models used for the production history match and forecast. These contrasting scales will be the thread of the presentation.
How to cite: Richard, P. and Bazalgette, L.: Scale discrepancy paradox between observation and modelling in fractured reservoir models in oil and gas industry., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20161, https://doi.org/10.5194/egusphere-egu2020-20161, 2020.
Naturally fractured reservoirs represent one of the most challenging resource in the oil and gas industry. The understanding based on centimeter scale observations is upscaled and modeled at 100-meter scale.
In this paper, we will illustrate with case study examples of conceptual fracture model elaborated using static and dynamic data, the disconnect between the scale of observation and the scale of modelling. We will also discuss the potential disconnect between the detail of fundamental, but necessary, research work in universities against the coarse resolution of the models built in the oil industry, and how we can benefit of the differences in scales and approaches.
The appraisal and development of fractured reservoirs offer challenges due to the variations in reservoir quality and natural fracture distribution. Typically, the presence of open, connected fractures is one of the key elements to achieve a successful development. Fracture modelling studies are carried out routinely to support both appraisal and development strategies of these fractured reservoirs.
Overall fracture modelling workflow consists first of a fracture characterization phase concentrating on the understanding of the deformation history and the evaluation of the nature, type and distribution of the fractures; secondly of a fracture modelling part where fracture properties for the dynamic simulation are generated and calibrated against dynamic data. The pillar of the studies is the creation of 3D conceptual fracture diagrams/concepts which summarize both the understanding and the uncertainty of the fracture network of interest. These conceptual diagrams rely on detailed observations at the scale of the wellbore using core and borehole image data which are on contrasting scale compare to the 10’s of meters to 100’s of meter scale of the grid cells of the dynamic models used for the production history match and forecast. These contrasting scales will be the thread of the presentation.
How to cite: Richard, P. and Bazalgette, L.: Scale discrepancy paradox between observation and modelling in fractured reservoir models in oil and gas industry., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20161, https://doi.org/10.5194/egusphere-egu2020-20161, 2020.
EGU2020-20010 | Displays | TS3.5
Forecasting the propagation paths of fluid-driven fractures, particularly dikes and inclined sheetsAgust Gudmundsson, Kyriaki Drymoni, Mohsen Bazargan, and Kayode Adeoye-Akinde
It is of great importance in many fields to be able to forecast the likely propagation paths of fluid-driven factures. These include mineral veins, human-made hydraulic fractures, and dikes/inclined sheets. The physical principles that control the propagation of all fluid-driven fractures are the same. Here the focus is on dikes and inclined sheets where the selected path determines whether, where, and when a particular dike/sheet reaches the surface to erupt. Here we provide analytical and numerical models on dike/sheet paths in crustal segments (including volcanoes) that include layers of various types (lava flows, pyroclastic flows, tuff layers, soil layers, etc) as well as mechanically weak contacts and faults. The modelling results are then compared with, and tested on, actual data of two types. (a) Seismic data on the paths of dikes/sheets as well as human-made hydraulic fractures, and (b) field data on the actual propagation paths of dikes/sheets in layered and faulted rocks
The numerical results show that, particularly in stratovolcanoes, the paths are likely to be complex with common deflections along layer contacts, in agreement with field observations. Also, some dikes/sheets may use existing faults as parts of their paths, primarily steeply dipping and recently active normal faults. The propagation path is thus not entirely in pure mode I but rather partly in a mixed mode. The energy required to propagate the dike/sheet is mainly the surface energy needed to rupture the rock, to form two new surfaces and move them apart as the fracture propagates. The energy available to drive the fracture is the stored elastic energy in the hosting crustal segment.
From its point of initiation in the magma-chamber roof, a dike/sheet can, theoretically, select any one of an infinite number of paths to follow to its point of arrest or eruption. It is shown that the eventual path selected is the one of least action, that is, the path along which the time integral of the difference between the kinetic and potential energies is an extremum (normally a minimum) relative to all other possible paths with the same endpoints. If the kinetic energy is omitted, and there are no constraints, then least action becomes the minimum potential energy, which was postulated as a basis for understanding dike propagation by Gudmundsson (1986). Here it is shown how this theoretical framework can help us make reliable forecasts of dike/sheet paths and associated volcanic eruptions.
Gudmundsson, A., 1986. Formation of dykes, feeder-dykes, and the intrusion of dykes from magma chambers. Bulletin of Volcanology, 47, 537-550.
Gudmundsson, A., 2020. Volcanotectonics: Understanding the Structure, Deformation, and Dynamics of Volcanoes. Cambridge University Press, Cambridge.
Drymoni, K., Browning, J. Gudmundsson, A., 2020. Dyke-arrest scenarios in extensional regimes: insights from field observations and numerical models, Santorini, Greece. Journal of Volcanology and Geothermal Research (in press).
How to cite: Gudmundsson, A., Drymoni, K., Bazargan, M., and Adeoye-Akinde, K.: Forecasting the propagation paths of fluid-driven fractures, particularly dikes and inclined sheets , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20010, https://doi.org/10.5194/egusphere-egu2020-20010, 2020.
It is of great importance in many fields to be able to forecast the likely propagation paths of fluid-driven factures. These include mineral veins, human-made hydraulic fractures, and dikes/inclined sheets. The physical principles that control the propagation of all fluid-driven fractures are the same. Here the focus is on dikes and inclined sheets where the selected path determines whether, where, and when a particular dike/sheet reaches the surface to erupt. Here we provide analytical and numerical models on dike/sheet paths in crustal segments (including volcanoes) that include layers of various types (lava flows, pyroclastic flows, tuff layers, soil layers, etc) as well as mechanically weak contacts and faults. The modelling results are then compared with, and tested on, actual data of two types. (a) Seismic data on the paths of dikes/sheets as well as human-made hydraulic fractures, and (b) field data on the actual propagation paths of dikes/sheets in layered and faulted rocks
The numerical results show that, particularly in stratovolcanoes, the paths are likely to be complex with common deflections along layer contacts, in agreement with field observations. Also, some dikes/sheets may use existing faults as parts of their paths, primarily steeply dipping and recently active normal faults. The propagation path is thus not entirely in pure mode I but rather partly in a mixed mode. The energy required to propagate the dike/sheet is mainly the surface energy needed to rupture the rock, to form two new surfaces and move them apart as the fracture propagates. The energy available to drive the fracture is the stored elastic energy in the hosting crustal segment.
From its point of initiation in the magma-chamber roof, a dike/sheet can, theoretically, select any one of an infinite number of paths to follow to its point of arrest or eruption. It is shown that the eventual path selected is the one of least action, that is, the path along which the time integral of the difference between the kinetic and potential energies is an extremum (normally a minimum) relative to all other possible paths with the same endpoints. If the kinetic energy is omitted, and there are no constraints, then least action becomes the minimum potential energy, which was postulated as a basis for understanding dike propagation by Gudmundsson (1986). Here it is shown how this theoretical framework can help us make reliable forecasts of dike/sheet paths and associated volcanic eruptions.
Gudmundsson, A., 1986. Formation of dykes, feeder-dykes, and the intrusion of dykes from magma chambers. Bulletin of Volcanology, 47, 537-550.
Gudmundsson, A., 2020. Volcanotectonics: Understanding the Structure, Deformation, and Dynamics of Volcanoes. Cambridge University Press, Cambridge.
Drymoni, K., Browning, J. Gudmundsson, A., 2020. Dyke-arrest scenarios in extensional regimes: insights from field observations and numerical models, Santorini, Greece. Journal of Volcanology and Geothermal Research (in press).
How to cite: Gudmundsson, A., Drymoni, K., Bazargan, M., and Adeoye-Akinde, K.: Forecasting the propagation paths of fluid-driven fractures, particularly dikes and inclined sheets , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20010, https://doi.org/10.5194/egusphere-egu2020-20010, 2020.
EGU2020-12447 | Displays | TS3.5
U-Th Dating of Syntectonic Calcite Veins Reveals the Dynamic Nature of Fracture Cementation and Healing in FaultsRandolph Williams, Peter Mozley, Warren Sharp, and Laurel Goodwin
Fracture cementation is an important control on the recovery of prefailure levels of permeability and strength in faults and reservoir rock. The timescales of this process, however, are almost entirely unknown from direct analysis of the rock record. We report U‐Th dating results that quantify rates of fracture cementation in syntectonic calcite veins from the Loma Blanca fault, New Mexico, USA. Measured cementation rates vary from ~0.05 to 0.80 mm/ka and exhibit a power function correlation with minimum fracture apertures. We argue that this correlation is the result of crystal growth in a transport‐limited system, where cementation rates were proportional to rates of fluid flow in individual fractures. We argue that such transport‐limited growth necessarily leads to a heterogeneous distribution of cementation rates as fluids migrate through fracture networks of variable and changing aperture. For this reason, individual fractures are not expected to seal at monotonic rates through time but could instead experience order‐of‐magnitude increases or decreases in sealing rate depending on their geometric properties (e.g., aperture, length/width, and orientation) and position within a continually evolving fracture network. We further argue that such transport‐limited, flux‐dependent cementation necessarily leads to a heterogeneous distribution of permeability and strength recovery as fluids migrate through fault‐zone fracture networks. These heterogeneities may influence rupture propagations pathways and the continual development of fault‐zone architecture/complexity.
How to cite: Williams, R., Mozley, P., Sharp, W., and Goodwin, L.: U-Th Dating of Syntectonic Calcite Veins Reveals the Dynamic Nature of Fracture Cementation and Healing in Faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12447, https://doi.org/10.5194/egusphere-egu2020-12447, 2020.
Fracture cementation is an important control on the recovery of prefailure levels of permeability and strength in faults and reservoir rock. The timescales of this process, however, are almost entirely unknown from direct analysis of the rock record. We report U‐Th dating results that quantify rates of fracture cementation in syntectonic calcite veins from the Loma Blanca fault, New Mexico, USA. Measured cementation rates vary from ~0.05 to 0.80 mm/ka and exhibit a power function correlation with minimum fracture apertures. We argue that this correlation is the result of crystal growth in a transport‐limited system, where cementation rates were proportional to rates of fluid flow in individual fractures. We argue that such transport‐limited growth necessarily leads to a heterogeneous distribution of cementation rates as fluids migrate through fracture networks of variable and changing aperture. For this reason, individual fractures are not expected to seal at monotonic rates through time but could instead experience order‐of‐magnitude increases or decreases in sealing rate depending on their geometric properties (e.g., aperture, length/width, and orientation) and position within a continually evolving fracture network. We further argue that such transport‐limited, flux‐dependent cementation necessarily leads to a heterogeneous distribution of permeability and strength recovery as fluids migrate through fault‐zone fracture networks. These heterogeneities may influence rupture propagations pathways and the continual development of fault‐zone architecture/complexity.
How to cite: Williams, R., Mozley, P., Sharp, W., and Goodwin, L.: U-Th Dating of Syntectonic Calcite Veins Reveals the Dynamic Nature of Fracture Cementation and Healing in Faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12447, https://doi.org/10.5194/egusphere-egu2020-12447, 2020.
EGU2020-5387 | Displays | TS3.5
Dating faults, fractures and fluids with U-Pb calcite geochronology: Application to contrasting fracture and fluid-flow modes of the Cleveland BasinJack Lee, Nick Roberts, Robert Holdworth, Andrew Aplin, Richard Haslam, and Cedric John
Fractures and faults act as important permeable pathways in the subsurface and are of great significance to the petroleum industry and for future Carbon Capture and Storage. Fractures allow fluid-flow through impermeable units such as mudrocks and can affect how these lithologies act as top seals, source rocks and/or unconventional reservoirs. Natural fractures within mudrocks can strongly influence top seal integrity, primary migration and the performance of unconventional (e.g. shale gas) reservoirs. This project studies the exhumed, early-mature, Jurassic mudrock succession of the Cleveland Basin, NE England, combining structural geology with isotope geochemistry and geochronology. The primary objective is to provide an absolute chronology of faulting and fracturing through novel U-Pb geochronology of fracture-fill calcite. The abundance of well-exposed, natural fractures with different orientations and failure modes provides an opportunity to investigate the properties of these fractures, and provide a basin-wide temporal and spatial framework of evolving deformation. The second objective is to use trace element, stable isotope, and clumped isotope analyses, to constrain fluid composition and temperature. In combination, these objectives will provide an integrated understanding of fracturing, faulting and fluid migration during burial and exhumation of a sedimentary basin.
Current fracture-fill dates from U-Pb geochronology provide intriguing insights into the history of the Cleveland Basin. We have identified and dated three phases of deformation and associated fluid-flow that have contrasting kinematics and fluid-flow regimes. The E-W trending Flamborough Head Fault Zone (FHFZ) bounds the basin to the south, and calcite preserved in one of the major extensional faults provides ages of 64-56 Ma. Calcite from N-S to NNW-SSE trending normal faults and associated fractures in the north of the Cleveland Basin provide ages of 44-25 Ma, revealing a previously unknown phase of Cenozoic faulting, which we speculatively relate to salt-related deformation. Structural and petrographic information suggest that the E-W and N-S trending faults have contrasting fracture-fluid-flow systems. Large (up to 30 cm), chalk hosted, vuggy calcite cements with geopetal sediment-fills in the E-W fault zone suggest it acted as an open fluid conduit with voluminous fluid-flow, linking the shallow sub-surface with deeper levels of the stratigraphy. In contrast, typically thin (<5 mm) vein fills with varying crack-seal-slip type textures in the N-S mudstone-hosted fractures of the Cleveland Basin provide evidence of episodic slip of variable displacement (44-40 Ma); these fracture openings may partly be controlled by pore fluid pressures and pre-date fault movement along the regional Peak Fault and smaller scales N-S faults (40-25 Ma) which are characterised by damage zone calcite mineralisation and extensional jog structures. Initial stable isotopic results are giving indications of fluid temperatures and sourcing which will be built on further by clumped isotope and fluid inclusions work.
How to cite: Lee, J., Roberts, N., Holdworth, R., Aplin, A., Haslam, R., and John, C.: Dating faults, fractures and fluids with U-Pb calcite geochronology: Application to contrasting fracture and fluid-flow modes of the Cleveland Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5387, https://doi.org/10.5194/egusphere-egu2020-5387, 2020.
Fractures and faults act as important permeable pathways in the subsurface and are of great significance to the petroleum industry and for future Carbon Capture and Storage. Fractures allow fluid-flow through impermeable units such as mudrocks and can affect how these lithologies act as top seals, source rocks and/or unconventional reservoirs. Natural fractures within mudrocks can strongly influence top seal integrity, primary migration and the performance of unconventional (e.g. shale gas) reservoirs. This project studies the exhumed, early-mature, Jurassic mudrock succession of the Cleveland Basin, NE England, combining structural geology with isotope geochemistry and geochronology. The primary objective is to provide an absolute chronology of faulting and fracturing through novel U-Pb geochronology of fracture-fill calcite. The abundance of well-exposed, natural fractures with different orientations and failure modes provides an opportunity to investigate the properties of these fractures, and provide a basin-wide temporal and spatial framework of evolving deformation. The second objective is to use trace element, stable isotope, and clumped isotope analyses, to constrain fluid composition and temperature. In combination, these objectives will provide an integrated understanding of fracturing, faulting and fluid migration during burial and exhumation of a sedimentary basin.
Current fracture-fill dates from U-Pb geochronology provide intriguing insights into the history of the Cleveland Basin. We have identified and dated three phases of deformation and associated fluid-flow that have contrasting kinematics and fluid-flow regimes. The E-W trending Flamborough Head Fault Zone (FHFZ) bounds the basin to the south, and calcite preserved in one of the major extensional faults provides ages of 64-56 Ma. Calcite from N-S to NNW-SSE trending normal faults and associated fractures in the north of the Cleveland Basin provide ages of 44-25 Ma, revealing a previously unknown phase of Cenozoic faulting, which we speculatively relate to salt-related deformation. Structural and petrographic information suggest that the E-W and N-S trending faults have contrasting fracture-fluid-flow systems. Large (up to 30 cm), chalk hosted, vuggy calcite cements with geopetal sediment-fills in the E-W fault zone suggest it acted as an open fluid conduit with voluminous fluid-flow, linking the shallow sub-surface with deeper levels of the stratigraphy. In contrast, typically thin (<5 mm) vein fills with varying crack-seal-slip type textures in the N-S mudstone-hosted fractures of the Cleveland Basin provide evidence of episodic slip of variable displacement (44-40 Ma); these fracture openings may partly be controlled by pore fluid pressures and pre-date fault movement along the regional Peak Fault and smaller scales N-S faults (40-25 Ma) which are characterised by damage zone calcite mineralisation and extensional jog structures. Initial stable isotopic results are giving indications of fluid temperatures and sourcing which will be built on further by clumped isotope and fluid inclusions work.
How to cite: Lee, J., Roberts, N., Holdworth, R., Aplin, A., Haslam, R., and John, C.: Dating faults, fractures and fluids with U-Pb calcite geochronology: Application to contrasting fracture and fluid-flow modes of the Cleveland Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5387, https://doi.org/10.5194/egusphere-egu2020-5387, 2020.
EGU2020-2192 | Displays | TS3.5
Full paleostress tensor determination: case of the Panasqueira Mine, Portugal.Christophe Pascal, Luís Jaques, and Atsushi Yamaji
The quantification of tectonic forces or, alternatively, stresses represents a significant step towards the understanding of the natural processes governing plate tectonics and deformation at all scales. However, paleostress reconstructions based on the observation and measurement of natural fractures are traditionally limited to the determination of four out of the six parameters of the stress tensor. In the present study, we attempt to reconstruct full paleostress tensors by extending the methodologies advanced by previous authors. We selected Panasqueira Mine, Central Portugal, as natural laboratory, and focused on the measurement of sub-horizontal quartz veins, which are favorably exposed in three dimensions in the underground galleries of the mine. Inversion of the vein data allowed for quantifying the respective orientations of the stress axes and the shape ratio of the stress ellipsoid. In order to reconstruct an additional stress parameter, namely pressure, we extensively sampled vein material and combined fluid inclusion analyses on quartz samples with geothermometric analyses on sulphide minerals. Finally, we adjusted the radius of the obtained Mohr circle with the help of rupture laws, and obtained the six parameters of the paleostress tensor that prevailed during vein formation. Our results suggests a NW-SE reverse stress regime with a shape ratio equal to ~0.6, lithostatic pore pressures of ~300 MPa and differential stress lower than ~20 MPa.
How to cite: Pascal, C., Jaques, L., and Yamaji, A.: Full paleostress tensor determination: case of the Panasqueira Mine, Portugal., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2192, https://doi.org/10.5194/egusphere-egu2020-2192, 2020.
The quantification of tectonic forces or, alternatively, stresses represents a significant step towards the understanding of the natural processes governing plate tectonics and deformation at all scales. However, paleostress reconstructions based on the observation and measurement of natural fractures are traditionally limited to the determination of four out of the six parameters of the stress tensor. In the present study, we attempt to reconstruct full paleostress tensors by extending the methodologies advanced by previous authors. We selected Panasqueira Mine, Central Portugal, as natural laboratory, and focused on the measurement of sub-horizontal quartz veins, which are favorably exposed in three dimensions in the underground galleries of the mine. Inversion of the vein data allowed for quantifying the respective orientations of the stress axes and the shape ratio of the stress ellipsoid. In order to reconstruct an additional stress parameter, namely pressure, we extensively sampled vein material and combined fluid inclusion analyses on quartz samples with geothermometric analyses on sulphide minerals. Finally, we adjusted the radius of the obtained Mohr circle with the help of rupture laws, and obtained the six parameters of the paleostress tensor that prevailed during vein formation. Our results suggests a NW-SE reverse stress regime with a shape ratio equal to ~0.6, lithostatic pore pressures of ~300 MPa and differential stress lower than ~20 MPa.
How to cite: Pascal, C., Jaques, L., and Yamaji, A.: Full paleostress tensor determination: case of the Panasqueira Mine, Portugal., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2192, https://doi.org/10.5194/egusphere-egu2020-2192, 2020.
EGU2020-8688 | Displays | TS3.5
Fault slip envelope: A new parametric investigation tool for fault system strength and slipRoger Soliva, Frantz Maerten, Laurent Maerten, and Jussi Mattila
The fact that inherited fault systems show strong variability in their 3D shape provides good reasons to consider the strength of the Earth’s brittle crust as variably anisotropic. In this work we quantify this strength anisotropy as a function of fault system complexity by combining 3D boundary element model, frictional slip theory and fast iterative computation method. This method allows to analyze together a very large number of scenarios of stress and fault mechanical properties variations through space and time. Using both synthetic and real fault system geometries we analyze a very large number of numerical simulations (125,000) to define for the first time macroscopic rupture envelopes for fault systems, referred to as “fault slip envelopes”. Fault slip envelopes are defined using variable friction, cohesion and stress state, and their shape is directly related to the fault system 3D geometry and the friction coefficient on fault surfaces. The obtained fault slip envelopes shows that very complex fault geometry implies low and isotropic strength of the fault system compared to geometry having limited fault orientations relative to the remote stresses, providing strong strength anisotropy. This technique is applied to the realistic geological conditions of the Olkiluoto high-level nuclear waste repository (Finland). The model results suggests that Olkiluoto fault system has a better probability to slip under the present day Andersonian thrust stress regime, than for the strike-slip and normal stress regimes expected in the future due to the probable presence of an ice sheet. This new tool allows to quantify the anisotropy of strength and probability of slip of 3D real fault networks as a function of a wide range of possible geological conditions an mechanical properties. This significantly helps to define the most conservative fault slip hazard case or to account for potential uncertainties in the input data for slip. This technique therefore applies to earthquakes hazard studies, geological storage, geothermal resources along faults and fault leaks/seals in geological reservoirs.
How to cite: Soliva, R., Maerten, F., Maerten, L., and Mattila, J.: Fault slip envelope: A new parametric investigation tool for fault system strength and slip, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8688, https://doi.org/10.5194/egusphere-egu2020-8688, 2020.
The fact that inherited fault systems show strong variability in their 3D shape provides good reasons to consider the strength of the Earth’s brittle crust as variably anisotropic. In this work we quantify this strength anisotropy as a function of fault system complexity by combining 3D boundary element model, frictional slip theory and fast iterative computation method. This method allows to analyze together a very large number of scenarios of stress and fault mechanical properties variations through space and time. Using both synthetic and real fault system geometries we analyze a very large number of numerical simulations (125,000) to define for the first time macroscopic rupture envelopes for fault systems, referred to as “fault slip envelopes”. Fault slip envelopes are defined using variable friction, cohesion and stress state, and their shape is directly related to the fault system 3D geometry and the friction coefficient on fault surfaces. The obtained fault slip envelopes shows that very complex fault geometry implies low and isotropic strength of the fault system compared to geometry having limited fault orientations relative to the remote stresses, providing strong strength anisotropy. This technique is applied to the realistic geological conditions of the Olkiluoto high-level nuclear waste repository (Finland). The model results suggests that Olkiluoto fault system has a better probability to slip under the present day Andersonian thrust stress regime, than for the strike-slip and normal stress regimes expected in the future due to the probable presence of an ice sheet. This new tool allows to quantify the anisotropy of strength and probability of slip of 3D real fault networks as a function of a wide range of possible geological conditions an mechanical properties. This significantly helps to define the most conservative fault slip hazard case or to account for potential uncertainties in the input data for slip. This technique therefore applies to earthquakes hazard studies, geological storage, geothermal resources along faults and fault leaks/seals in geological reservoirs.
How to cite: Soliva, R., Maerten, F., Maerten, L., and Mattila, J.: Fault slip envelope: A new parametric investigation tool for fault system strength and slip, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8688, https://doi.org/10.5194/egusphere-egu2020-8688, 2020.
EGU2020-18032 | Displays | TS3.5
Scale dependency of segmentation along the strike of normal faults.Vincent Roche, Tom Manzocchi, Giovanni Camanni, Conrad Childs, and Vasileios Papanikolaou
The present study provides insights on the segmented nature of normal faults as a function of scale, and attempts to identify whether segmentation is scale invariant, scale dependent or hierarchical. This is a topic of critical importance for studies of fault development and in modelling exercises where one needs to extrapolate observations at one scale to other scales.
Results are based on data observed in the Blue Lias in Somerset (UK), in Fumanya mine (Spain) and in a 3D seismic reflection survey in the Bonaparte Basin (Australia). Fault segmentation is investigated quantitatively based on previously established methodologies and we focus on neutral relay zones observed between fault segments along the strike of the normal faults.
We found that there are quantitative indications that the shape of the relay zones, the breaching of the relays and the degree of segmentation are all scale independent in Kilve and Fumanya. We propose that this is related to the low variability across scales in the geological parameters controlling segmentation, due to the relative homogeneity of the rock medium across the studied scales, the lack of influence of pre-existing faults or fractures, and the similar deformation histories for all studied faults. By contrast, faults show scale dependency in the Bonaparte Basin where large faults are under the influence of an oblique reactivation of pre-existing faults. Independently of the area, segmentation observed continuously through scale stresses the need to take into account resolution of observation in discussing fault development.
How to cite: Roche, V., Manzocchi, T., Camanni, G., Childs, C., and Papanikolaou, V.: Scale dependency of segmentation along the strike of normal faults., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18032, https://doi.org/10.5194/egusphere-egu2020-18032, 2020.
The present study provides insights on the segmented nature of normal faults as a function of scale, and attempts to identify whether segmentation is scale invariant, scale dependent or hierarchical. This is a topic of critical importance for studies of fault development and in modelling exercises where one needs to extrapolate observations at one scale to other scales.
Results are based on data observed in the Blue Lias in Somerset (UK), in Fumanya mine (Spain) and in a 3D seismic reflection survey in the Bonaparte Basin (Australia). Fault segmentation is investigated quantitatively based on previously established methodologies and we focus on neutral relay zones observed between fault segments along the strike of the normal faults.
We found that there are quantitative indications that the shape of the relay zones, the breaching of the relays and the degree of segmentation are all scale independent in Kilve and Fumanya. We propose that this is related to the low variability across scales in the geological parameters controlling segmentation, due to the relative homogeneity of the rock medium across the studied scales, the lack of influence of pre-existing faults or fractures, and the similar deformation histories for all studied faults. By contrast, faults show scale dependency in the Bonaparte Basin where large faults are under the influence of an oblique reactivation of pre-existing faults. Independently of the area, segmentation observed continuously through scale stresses the need to take into account resolution of observation in discussing fault development.
How to cite: Roche, V., Manzocchi, T., Camanni, G., Childs, C., and Papanikolaou, V.: Scale dependency of segmentation along the strike of normal faults., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18032, https://doi.org/10.5194/egusphere-egu2020-18032, 2020.
EGU2020-491 | Displays | TS3.5
Factors controlling fracture distribution within a carbonate-hosted relay ramp: insights from the Tre Monti fault (Central Apennines)Marco Mercuri, Eugenio Carminati, Maria Chiara Tartarello, Marco Brandano, Paolo Mazzanti, Alessandro Brunetti, Ken J. W. McCaffrey, and Cristiano Collettini
Fractures constitute the main pathway for fluids in fault damage zones hosted in low-porosity rocks. Understanding the factors controlling fracture distribution is hence fundamental to better assess fluids circulation in fault damage zones, with evident implications for fault mechanics, hydrogeology and hydrocarbon exploration. Being usually characterized by a strong damage and structural complexity, this is of particularly importance for relay zones.
We integrated classical and modern structural geology techniques to investigate the factors controlling fracture distribution within a portion of a relay ramp damage zone pertaining to the Tre Monti fault (Central Italy). The damage zone is hosted within peritidal carbonates and located at the footwall of the relay ramp front segment. We analysed the distribution of the fracture density in the outcrop through (1) scanlines measured in the field, (2) oriented rock samples, and (3) scan-areas performed on a virtual outcrop model obtained by aerial structure-from-motion.
Our results highlight structural and lithological control on fracture distribution. Scanlines and virtual scan-areas show that fracture density increases with the distance from the front segment of the relay ramp. Moreover, all the methods highlight that supratidal and intertidal carbonate facies exhibit higher fracture density than subtidal limestones.
This apparently anomalous trend of fracture density, that increases moving away from a main fault segment, has two main explanations. (1) The damage is associated with the relay ramp development: approaching the centre of the relay ramp (i.e., moving away from the front segment) an increase in the number of subsidiary faults with their associated damage zones promotes high fracture densities. (2) The increase in fracture density can be attributed to the increasing content in supratidal and intertidal carbonate facies that are more abundant in the centre of the relay ramp.
Our results provide important suggestions for factors controlling fracture distribution and fluid flow within relay ramps hosted by shallow water limestones. We show that the trend of fracture distribution with respect to a main fault is not easily predictable in presence of a relay ramp, because it can be modulated by the subsidiary faults formation and slip during the relay ramp development. Moreover, carbonate facies play a non-negligible role in fracture distribution within fault zones hosted in shallow-water carbonates.
How to cite: Mercuri, M., Carminati, E., Tartarello, M. C., Brandano, M., Mazzanti, P., Brunetti, A., McCaffrey, K. J. W., and Collettini, C.: Factors controlling fracture distribution within a carbonate-hosted relay ramp: insights from the Tre Monti fault (Central Apennines), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-491, https://doi.org/10.5194/egusphere-egu2020-491, 2020.
Fractures constitute the main pathway for fluids in fault damage zones hosted in low-porosity rocks. Understanding the factors controlling fracture distribution is hence fundamental to better assess fluids circulation in fault damage zones, with evident implications for fault mechanics, hydrogeology and hydrocarbon exploration. Being usually characterized by a strong damage and structural complexity, this is of particularly importance for relay zones.
We integrated classical and modern structural geology techniques to investigate the factors controlling fracture distribution within a portion of a relay ramp damage zone pertaining to the Tre Monti fault (Central Italy). The damage zone is hosted within peritidal carbonates and located at the footwall of the relay ramp front segment. We analysed the distribution of the fracture density in the outcrop through (1) scanlines measured in the field, (2) oriented rock samples, and (3) scan-areas performed on a virtual outcrop model obtained by aerial structure-from-motion.
Our results highlight structural and lithological control on fracture distribution. Scanlines and virtual scan-areas show that fracture density increases with the distance from the front segment of the relay ramp. Moreover, all the methods highlight that supratidal and intertidal carbonate facies exhibit higher fracture density than subtidal limestones.
This apparently anomalous trend of fracture density, that increases moving away from a main fault segment, has two main explanations. (1) The damage is associated with the relay ramp development: approaching the centre of the relay ramp (i.e., moving away from the front segment) an increase in the number of subsidiary faults with their associated damage zones promotes high fracture densities. (2) The increase in fracture density can be attributed to the increasing content in supratidal and intertidal carbonate facies that are more abundant in the centre of the relay ramp.
Our results provide important suggestions for factors controlling fracture distribution and fluid flow within relay ramps hosted by shallow water limestones. We show that the trend of fracture distribution with respect to a main fault is not easily predictable in presence of a relay ramp, because it can be modulated by the subsidiary faults formation and slip during the relay ramp development. Moreover, carbonate facies play a non-negligible role in fracture distribution within fault zones hosted in shallow-water carbonates.
How to cite: Mercuri, M., Carminati, E., Tartarello, M. C., Brandano, M., Mazzanti, P., Brunetti, A., McCaffrey, K. J. W., and Collettini, C.: Factors controlling fracture distribution within a carbonate-hosted relay ramp: insights from the Tre Monti fault (Central Apennines), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-491, https://doi.org/10.5194/egusphere-egu2020-491, 2020.
EGU2020-924 | Displays | TS3.5
Characterization of fracture networking and connectivity: Insights from Discrete Fracture Network Model and Multi-Scale analysis from the Buxa Dolomite of the Main Boundary thrust sheet, Siang widow, Arunachal Himalayan Fold thrust beltFarzan Ahmed and Kathakali Bhattacharyya
Fracture systems develop at different stages of progressive deformation and are often genetically associated with folding. The frontal Main Boundary thrust (MBT) sheet is folded in a fault bend fold (Ahmed et al., 2018) and is exposed in Siang window in far eastern Arunachal Himalayan fold-thrust belt (FTB). The Buxa dolomite of the Lesser Himalayan sequence forms part of the MBT sheet and records four different sets of fractures (Basa et al., 2019). We present results from Discrete Fracture Network (DFN) model from the Buxa dolomite. Integrating fold test, cross-cutting, offset and abutting relationships, we have established that the low-angle fracture set (0°-20°) formed as a result of early layer parallel shortening. These low-angle and the two sets of medium angle fractures (20°-60°) formed prior to the fault-bend folding. The late stage, high-angle fractures (60°-90°) developed synchronous to the fault-bend fold (Basa et al., 2019). We model the fractures formed before and during the folding event using 3D MOVE’s Fracture Modeling module to evaluate how the properties of secondary porosity and permeability, induced by fracture sets, fracture area/unit volume (P32) and overall connectivity are affected by the folding event. The input parameters of fracture orientation, intensity, length and aperture were measured from the field. For the aspect ratio, theoretical value of 1:2 (Olding, 1997; Olson, 2003) was considered.
Results from DFN analysis indicate that the average porosity increases from pre-folding (model-1) (~0.0028) to syn- to post-folding (model-2) (~0.0071). The permeability also increases from ~231 Darcy in model-1 to ~3988 Darcy in model-2. There is also a significant rise in P32 (~2.8m2/m3 to ~4.3m2/m3) value from model-1 to model-2. The late high-angle fracture set led to increase in overall connectivity, including porosity, permeability and fracture intensity. This is also corroborated from the field results that reveal high-angle fractures are more conducive to vein formation (~41%) compared to the lower angle fracture-sets (~15 %).
How to cite: Ahmed, F. and Bhattacharyya, K.: Characterization of fracture networking and connectivity: Insights from Discrete Fracture Network Model and Multi-Scale analysis from the Buxa Dolomite of the Main Boundary thrust sheet, Siang widow, Arunachal Himalayan Fold thrust belt, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-924, https://doi.org/10.5194/egusphere-egu2020-924, 2020.
Fracture systems develop at different stages of progressive deformation and are often genetically associated with folding. The frontal Main Boundary thrust (MBT) sheet is folded in a fault bend fold (Ahmed et al., 2018) and is exposed in Siang window in far eastern Arunachal Himalayan fold-thrust belt (FTB). The Buxa dolomite of the Lesser Himalayan sequence forms part of the MBT sheet and records four different sets of fractures (Basa et al., 2019). We present results from Discrete Fracture Network (DFN) model from the Buxa dolomite. Integrating fold test, cross-cutting, offset and abutting relationships, we have established that the low-angle fracture set (0°-20°) formed as a result of early layer parallel shortening. These low-angle and the two sets of medium angle fractures (20°-60°) formed prior to the fault-bend folding. The late stage, high-angle fractures (60°-90°) developed synchronous to the fault-bend fold (Basa et al., 2019). We model the fractures formed before and during the folding event using 3D MOVE’s Fracture Modeling module to evaluate how the properties of secondary porosity and permeability, induced by fracture sets, fracture area/unit volume (P32) and overall connectivity are affected by the folding event. The input parameters of fracture orientation, intensity, length and aperture were measured from the field. For the aspect ratio, theoretical value of 1:2 (Olding, 1997; Olson, 2003) was considered.
Results from DFN analysis indicate that the average porosity increases from pre-folding (model-1) (~0.0028) to syn- to post-folding (model-2) (~0.0071). The permeability also increases from ~231 Darcy in model-1 to ~3988 Darcy in model-2. There is also a significant rise in P32 (~2.8m2/m3 to ~4.3m2/m3) value from model-1 to model-2. The late high-angle fracture set led to increase in overall connectivity, including porosity, permeability and fracture intensity. This is also corroborated from the field results that reveal high-angle fractures are more conducive to vein formation (~41%) compared to the lower angle fracture-sets (~15 %).
How to cite: Ahmed, F. and Bhattacharyya, K.: Characterization of fracture networking and connectivity: Insights from Discrete Fracture Network Model and Multi-Scale analysis from the Buxa Dolomite of the Main Boundary thrust sheet, Siang widow, Arunachal Himalayan Fold thrust belt, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-924, https://doi.org/10.5194/egusphere-egu2020-924, 2020.
EGU2020-2195 | Displays | TS3.5
Impact of multiphase fracture sequence in folded carbonates on the evolution of naturally fractured reservoir types. An outcrop case study from Mirabeau Anticline (SE France)Juliette Lamarche, Nicolas Espurt, Tassadit Kaci, Marié Lionel, and Richard P. Pascal
Fractures in rocks are sensitive cursers that may enhance porosity and permeability. This is particularly true in carbonates because background fractures might be ubiquitous after embrittlement at early burial (Lavenu & Lamarche, 2018). Barren fractures at depth are susceptible to chemical reactions with underground fluids and cementation that might totally or partially reduce porosity and permeability (Laubach et al., 2019; Aubert et al., 2019). Hence, early background fractures with long lasting tectonic history and structural diagenesis, in addition to fractures neo-formed at any time during burial, tectonic inversion and folding join the game of matrix/fracture permeability and porosity modification. To predict the fractures contribution to flow in Naturally Fractured Reservoirs, it is fundamental to know the fracture sequence and geometry resulting from the geological history in folded carbonates, from the host-rock embrittlement to the present-day situation. At any step, we intent quantifying the fracture geometry and estimating their contribution to the host reservoir properties.
The study is performed in Upper Jurassic to Lower Cretaceous carbonates (Oxfordian, Tithonian, Berriasian) formed in the South-Provençal Basin. From deposition to present-day, the platform carbonates underwent alternating subsidence, uplift, erosion and folding. We sampled a scan-line along a horizontal path across both flanks of the Mirabeau Anticline (SE France). We measured all tectonic and stratigraphic features crossed by the line, checked their nature and position. We deciphered their chronological relationships with respect to each other and to the bed tilting. We compiled all cross-cutting relationships into a coherent sequence of deformation of pre-, syn- and post-fold structures and correlated it to burial, uplift and folding of the host rock. At each brittle stage, the fracture pattern was characterized in terms of architecture, mechanical stratigraphy and reservoir properties in order to draw a time-path in a matrix versus fracture permeability and porosity table (Nelson Reservoir types) during 150My. After embrittlement, the host-rocks bear fractures, pressure-solution, faulting, folding and erosion. If it was a reservoir, its Nelson type would have evolved from IV to III during the burial and initial brittle deformation. The tectonic inversion and onset of multiple-scale brittle structures would have increased and decreased the fracture and matrix contribution respectively and the reservoir evolved to types II and I. During the 150My history, fracture porosity and permeability depends on their geometry (veins versus tension gashes) and cementation. This results in several switches from type II to I as a function of the fracture timing, geometry, connectivity and diagenesis.
Aubert I. et al. (2019). Imbricated structure and hydraulic path induced by strike-slip reactivation of a normal fault in carbonates. Fifth International Conference on Fault and Top Seals, 8-12 September 2019, Palermo, Italy.
Bestani L.et al. (2016) Reconstruction of the Provence Chain evolution, southeastern France., Tectonics Vol: 35, p.1506–1525
Laubach, S. E. et al. (2019) The role of chemistry in fracture pattern development and opportunities to advance interpretations of geological materials. Reviews Geophysics, 57.
Lavenu A.P.C., Lamarche J. (2018) What controls diffuse fractures in platform carbonates? Insights from Provence (France) and Apulia (Italy), JSG 108, p. 94-107
How to cite: Lamarche, J., Espurt, N., Kaci, T., Lionel, M., and P. Pascal, R.: Impact of multiphase fracture sequence in folded carbonates on the evolution of naturally fractured reservoir types. An outcrop case study from Mirabeau Anticline (SE France), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2195, https://doi.org/10.5194/egusphere-egu2020-2195, 2020.
Fractures in rocks are sensitive cursers that may enhance porosity and permeability. This is particularly true in carbonates because background fractures might be ubiquitous after embrittlement at early burial (Lavenu & Lamarche, 2018). Barren fractures at depth are susceptible to chemical reactions with underground fluids and cementation that might totally or partially reduce porosity and permeability (Laubach et al., 2019; Aubert et al., 2019). Hence, early background fractures with long lasting tectonic history and structural diagenesis, in addition to fractures neo-formed at any time during burial, tectonic inversion and folding join the game of matrix/fracture permeability and porosity modification. To predict the fractures contribution to flow in Naturally Fractured Reservoirs, it is fundamental to know the fracture sequence and geometry resulting from the geological history in folded carbonates, from the host-rock embrittlement to the present-day situation. At any step, we intent quantifying the fracture geometry and estimating their contribution to the host reservoir properties.
The study is performed in Upper Jurassic to Lower Cretaceous carbonates (Oxfordian, Tithonian, Berriasian) formed in the South-Provençal Basin. From deposition to present-day, the platform carbonates underwent alternating subsidence, uplift, erosion and folding. We sampled a scan-line along a horizontal path across both flanks of the Mirabeau Anticline (SE France). We measured all tectonic and stratigraphic features crossed by the line, checked their nature and position. We deciphered their chronological relationships with respect to each other and to the bed tilting. We compiled all cross-cutting relationships into a coherent sequence of deformation of pre-, syn- and post-fold structures and correlated it to burial, uplift and folding of the host rock. At each brittle stage, the fracture pattern was characterized in terms of architecture, mechanical stratigraphy and reservoir properties in order to draw a time-path in a matrix versus fracture permeability and porosity table (Nelson Reservoir types) during 150My. After embrittlement, the host-rocks bear fractures, pressure-solution, faulting, folding and erosion. If it was a reservoir, its Nelson type would have evolved from IV to III during the burial and initial brittle deformation. The tectonic inversion and onset of multiple-scale brittle structures would have increased and decreased the fracture and matrix contribution respectively and the reservoir evolved to types II and I. During the 150My history, fracture porosity and permeability depends on their geometry (veins versus tension gashes) and cementation. This results in several switches from type II to I as a function of the fracture timing, geometry, connectivity and diagenesis.
Aubert I. et al. (2019). Imbricated structure and hydraulic path induced by strike-slip reactivation of a normal fault in carbonates. Fifth International Conference on Fault and Top Seals, 8-12 September 2019, Palermo, Italy.
Bestani L.et al. (2016) Reconstruction of the Provence Chain evolution, southeastern France., Tectonics Vol: 35, p.1506–1525
Laubach, S. E. et al. (2019) The role of chemistry in fracture pattern development and opportunities to advance interpretations of geological materials. Reviews Geophysics, 57.
Lavenu A.P.C., Lamarche J. (2018) What controls diffuse fractures in platform carbonates? Insights from Provence (France) and Apulia (Italy), JSG 108, p. 94-107
How to cite: Lamarche, J., Espurt, N., Kaci, T., Lionel, M., and P. Pascal, R.: Impact of multiphase fracture sequence in folded carbonates on the evolution of naturally fractured reservoir types. An outcrop case study from Mirabeau Anticline (SE France), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2195, https://doi.org/10.5194/egusphere-egu2020-2195, 2020.
EGU2020-3118 | Displays | TS3.5
Combining Ground-Penetrating Radar profiles with geomechanical and petrophysical in situ measurements to characterize sub-seismic resolution structural and diagenetic heterogeneities in porous sandstones (Northern Apennines, Italy)Leonardo Del Sole, Antonino Calafato, and Marco Antonellini
Deformation bands and structurally-related diagenetic heterogeneities, here named Structural Diagenetic Heterogeneities (SDH), have been recognized to affect subsurface fluid flow on a range of scales and potentially promoting reservoir compartmentalization, altering flow paths, influencing flow buffering, and sealing during production. Their impact on reservoir hydraulic properties depends on many factors, such as their permeability contrast with respect to the undeformed reservoir rock, their anisotropy, thickness, geometry as well as their physical connectivity and arrangement in the subsurface. Deformation bands offsets (from a few mm to 20-40 mm) and diagenetic heterogeneities (carbonate nodules) dimensions (from 0.2 to 15 m in length; from 0.1 to 1.0 m in thickness) make them SDH below seismic resolution.
We used Ground Penetrating Radar (GPR) for detection and analysis of the assemblage “deformation bands - carbonate nodules”, in high-porosity arkose sandstone of the Northern Apennines (Italy). Petrophysical (air-permeability) and mechanical (uniaxial compressive strength) properties of host rock, deformation bands, and calcite-cement nodules were evaluated along a 30-meters thick stratigraphic log to characterize the permeability and strength variations of those features. 2D GPR surveys allowed the description of the SDH spatial organization, geometry, and continuity in the subsurface. The assemblage “deformation bands – nodules” decreases porosity and permeability and produces a strengthening effect of the rock volume, inducing a strong mechanical and petrophysical heterogeneity to the pristine rock. Different textural, petrophysical, and geomechanical properties of deformation bands, nodules, and host rock result in different GPR response (dielectric permittivity; instantaneous attributes). We show that GPR can be useful to characterize variations in petrophysical and geomechanical properties other than characterize the geometry and spatial distribution of flow baffles and small-scale flow barriers in the subsurface such as deformation bands and cement-nodules. GPR showed its worth as a high-resolution and non-invasive tool to extend outcrop information (petrophysical and geomechanical data) to 3D subsurface volumes in a way to reconstruct realistic and detailed outcrop analogues. Such potential could be critical in assisting and improving the characterization of SDH networks in the study of faulted aquifers and reservoirs in porous sandstones.
How to cite: Del Sole, L., Calafato, A., and Antonellini, M.: Combining Ground-Penetrating Radar profiles with geomechanical and petrophysical in situ measurements to characterize sub-seismic resolution structural and diagenetic heterogeneities in porous sandstones (Northern Apennines, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3118, https://doi.org/10.5194/egusphere-egu2020-3118, 2020.
Deformation bands and structurally-related diagenetic heterogeneities, here named Structural Diagenetic Heterogeneities (SDH), have been recognized to affect subsurface fluid flow on a range of scales and potentially promoting reservoir compartmentalization, altering flow paths, influencing flow buffering, and sealing during production. Their impact on reservoir hydraulic properties depends on many factors, such as their permeability contrast with respect to the undeformed reservoir rock, their anisotropy, thickness, geometry as well as their physical connectivity and arrangement in the subsurface. Deformation bands offsets (from a few mm to 20-40 mm) and diagenetic heterogeneities (carbonate nodules) dimensions (from 0.2 to 15 m in length; from 0.1 to 1.0 m in thickness) make them SDH below seismic resolution.
We used Ground Penetrating Radar (GPR) for detection and analysis of the assemblage “deformation bands - carbonate nodules”, in high-porosity arkose sandstone of the Northern Apennines (Italy). Petrophysical (air-permeability) and mechanical (uniaxial compressive strength) properties of host rock, deformation bands, and calcite-cement nodules were evaluated along a 30-meters thick stratigraphic log to characterize the permeability and strength variations of those features. 2D GPR surveys allowed the description of the SDH spatial organization, geometry, and continuity in the subsurface. The assemblage “deformation bands – nodules” decreases porosity and permeability and produces a strengthening effect of the rock volume, inducing a strong mechanical and petrophysical heterogeneity to the pristine rock. Different textural, petrophysical, and geomechanical properties of deformation bands, nodules, and host rock result in different GPR response (dielectric permittivity; instantaneous attributes). We show that GPR can be useful to characterize variations in petrophysical and geomechanical properties other than characterize the geometry and spatial distribution of flow baffles and small-scale flow barriers in the subsurface such as deformation bands and cement-nodules. GPR showed its worth as a high-resolution and non-invasive tool to extend outcrop information (petrophysical and geomechanical data) to 3D subsurface volumes in a way to reconstruct realistic and detailed outcrop analogues. Such potential could be critical in assisting and improving the characterization of SDH networks in the study of faulted aquifers and reservoirs in porous sandstones.
How to cite: Del Sole, L., Calafato, A., and Antonellini, M.: Combining Ground-Penetrating Radar profiles with geomechanical and petrophysical in situ measurements to characterize sub-seismic resolution structural and diagenetic heterogeneities in porous sandstones (Northern Apennines, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3118, https://doi.org/10.5194/egusphere-egu2020-3118, 2020.
EGU2020-4123 | Displays | TS3.5
Controlling factors and formation mechanism of fractures in the tight-gas sandstones of the Upper Triassic Xujiahe Formation, western Sichuan Basin, ChinaWenya Lyu, Lianbo Zeng, Shuangquan Chen, Lei Tang, and Yunzhao Zhang
Based on cores, image logs and thin sections, five sets of fractures are developed in the study area, where faults are developed. Most of fractures are open without fillings, and some fractures are filled with calcite, quartz, bitumen, pyrite and mud. Fractures are mainly controlled by lithology, mechanical stratigraphy and faults. Based on mutual crosscutting relationships of fractures, mineral filling sequence of fracture fillings, fluid inclusion and carbon-oxygen isotope analysis of calcite fillings in fractures, and quartz spintronic resonance analysis of quartz fillings in fractures, in combination with thermal and burial history, the formation sequence and time of fractures were analyzed. The results show that fractures mainly formed over three period, that is, the late Triassic, Middle to Late Jurassic, and Late Cretaceous to Paleogene. Then,combined with the paleostress evolution and fracture characteristics of the study area, the formation mechanism of fractures was discussed.
How to cite: Lyu, W., Zeng, L., Chen, S., Tang, L., and Zhang, Y.: Controlling factors and formation mechanism of fractures in the tight-gas sandstones of the Upper Triassic Xujiahe Formation, western Sichuan Basin, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4123, https://doi.org/10.5194/egusphere-egu2020-4123, 2020.
Based on cores, image logs and thin sections, five sets of fractures are developed in the study area, where faults are developed. Most of fractures are open without fillings, and some fractures are filled with calcite, quartz, bitumen, pyrite and mud. Fractures are mainly controlled by lithology, mechanical stratigraphy and faults. Based on mutual crosscutting relationships of fractures, mineral filling sequence of fracture fillings, fluid inclusion and carbon-oxygen isotope analysis of calcite fillings in fractures, and quartz spintronic resonance analysis of quartz fillings in fractures, in combination with thermal and burial history, the formation sequence and time of fractures were analyzed. The results show that fractures mainly formed over three period, that is, the late Triassic, Middle to Late Jurassic, and Late Cretaceous to Paleogene. Then,combined with the paleostress evolution and fracture characteristics of the study area, the formation mechanism of fractures was discussed.
How to cite: Lyu, W., Zeng, L., Chen, S., Tang, L., and Zhang, Y.: Controlling factors and formation mechanism of fractures in the tight-gas sandstones of the Upper Triassic Xujiahe Formation, western Sichuan Basin, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4123, https://doi.org/10.5194/egusphere-egu2020-4123, 2020.
EGU2020-19401 | Displays | TS3.5
Stress-based tomography: potential, open-questions and future developmentsPeter Bayer, Mohammad Javad Afshari Moein, Márk Somogyvári, Lisa Ringel, and Mohammadreza Jalali
Fracture network characterization is critical for many subsurface engineering problems in petroleum, mining, nuclear waste disposal and Enhanced Geothermal Systems (EGS). Due to limited exposure, direct measurement of fracture network properties at great depth is not possible and geophysical imaging techniques cannot resolve the fractures. Therefore, tomographic imaging techniques have been proposed and applied to reconstruct the structural discontinuities of rock mass. Stress-based tomography is a novel concept aiming at probabilistic imaging of the fracture network using the stress perturbations along deep boreholes. Currently, this approach has only been successfully tested on two-dimensional fracture networks. However, its great potential to unravel the heterogeneous structure of fractured rocks at great depth motivates further scientific effort. Here, we present the potential, open questions, current challenges and necessary future developments in order to apply this methodology to image three-dimensional multiscale structure of the rock mass in the field. Other tomographic approaches such as tracer and hydraulic tomography invert tracer breakthrough curves (BTCs) and pressure response in an observational well. We suggest a joint and comparative tomographic analysis in a Bayesian inversion framework to reconstruct Discrete Fracture Networks (DFN). This is expected to provide a new view of the strengths of each tomographic variant.
How to cite: Bayer, P., Afshari Moein, M. J., Somogyvári, M., Ringel, L., and Jalali, M.: Stress-based tomography: potential, open-questions and future developments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19401, https://doi.org/10.5194/egusphere-egu2020-19401, 2020.
Fracture network characterization is critical for many subsurface engineering problems in petroleum, mining, nuclear waste disposal and Enhanced Geothermal Systems (EGS). Due to limited exposure, direct measurement of fracture network properties at great depth is not possible and geophysical imaging techniques cannot resolve the fractures. Therefore, tomographic imaging techniques have been proposed and applied to reconstruct the structural discontinuities of rock mass. Stress-based tomography is a novel concept aiming at probabilistic imaging of the fracture network using the stress perturbations along deep boreholes. Currently, this approach has only been successfully tested on two-dimensional fracture networks. However, its great potential to unravel the heterogeneous structure of fractured rocks at great depth motivates further scientific effort. Here, we present the potential, open questions, current challenges and necessary future developments in order to apply this methodology to image three-dimensional multiscale structure of the rock mass in the field. Other tomographic approaches such as tracer and hydraulic tomography invert tracer breakthrough curves (BTCs) and pressure response in an observational well. We suggest a joint and comparative tomographic analysis in a Bayesian inversion framework to reconstruct Discrete Fracture Networks (DFN). This is expected to provide a new view of the strengths of each tomographic variant.
How to cite: Bayer, P., Afshari Moein, M. J., Somogyvári, M., Ringel, L., and Jalali, M.: Stress-based tomography: potential, open-questions and future developments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19401, https://doi.org/10.5194/egusphere-egu2020-19401, 2020.
EGU2020-19487 | Displays | TS3.5
High-resolution 3D seismic investigation of fine scale faults and fractures along the Vestnesa Ridge, western Svalbard MarginFrances Cooke, Andreia Plaza-Faverola, Stefan Bünz, and Sunny Singhroha
Methane seepage on continental margins derived from shallow gas reserves and gas hydrate stores is significant globally, with initial observations most commonly derived from pockmark expressions on the seafloor. The processes driving fluid flow (liquids and gases) through upper (200m) marine sediments is not well understood. Pockmarks signify present or past seepage events, and are prominent across Vestnesa Ridge. Not all pockmarks are active (venting), suggesting that the mechanism behind fluid flow varies across the ridge. The main structures observed in the seismic are gas chimneys, faults and fractures. Here we study the characteristics of the observed features through attribute analysis at three significant horizons (age estimates: <0.2Ma, ~0.2Ma and ~1.5Ma). We extract fault orientations through the generation of 3D fault attributes and analysis of fault detect volumes. Attribute extracts at horizons, using amplitude and edge detection methods, together with spectral decomposition and RGB blending, have revealed fine-scale (<10m) faults. High amplitude lineaments at multiple depths match fault trends and radial fracturing is observed around gas chimneys. Small faults propagate outwards from gas chimneys and feed into larger tectonically derived faults, suggesting horizontal inter-connectivity at specific depths. Enhanced imaging of gas chimneys and small scale features, contribute to our understanding of how fluids migrate through the sediment column. We hypothesize that the connecting fractures, forming between main fault zones may suggest sediment overpressure and restricted flow through tectonically induced faults resulting in horizontal fluid transport.
How to cite: Cooke, F., Plaza-Faverola, A., Bünz, S., and Singhroha, S.: High-resolution 3D seismic investigation of fine scale faults and fractures along the Vestnesa Ridge, western Svalbard Margin , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19487, https://doi.org/10.5194/egusphere-egu2020-19487, 2020.
Methane seepage on continental margins derived from shallow gas reserves and gas hydrate stores is significant globally, with initial observations most commonly derived from pockmark expressions on the seafloor. The processes driving fluid flow (liquids and gases) through upper (200m) marine sediments is not well understood. Pockmarks signify present or past seepage events, and are prominent across Vestnesa Ridge. Not all pockmarks are active (venting), suggesting that the mechanism behind fluid flow varies across the ridge. The main structures observed in the seismic are gas chimneys, faults and fractures. Here we study the characteristics of the observed features through attribute analysis at three significant horizons (age estimates: <0.2Ma, ~0.2Ma and ~1.5Ma). We extract fault orientations through the generation of 3D fault attributes and analysis of fault detect volumes. Attribute extracts at horizons, using amplitude and edge detection methods, together with spectral decomposition and RGB blending, have revealed fine-scale (<10m) faults. High amplitude lineaments at multiple depths match fault trends and radial fracturing is observed around gas chimneys. Small faults propagate outwards from gas chimneys and feed into larger tectonically derived faults, suggesting horizontal inter-connectivity at specific depths. Enhanced imaging of gas chimneys and small scale features, contribute to our understanding of how fluids migrate through the sediment column. We hypothesize that the connecting fractures, forming between main fault zones may suggest sediment overpressure and restricted flow through tectonically induced faults resulting in horizontal fluid transport.
How to cite: Cooke, F., Plaza-Faverola, A., Bünz, S., and Singhroha, S.: High-resolution 3D seismic investigation of fine scale faults and fractures along the Vestnesa Ridge, western Svalbard Margin , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19487, https://doi.org/10.5194/egusphere-egu2020-19487, 2020.
EGU2020-22583 | Displays | TS3.5
Quantitative fracture characterization in the damage zone of the Victoria Fault, MaltaAnna Losa, Mattia Martinelli, and Andrea Bistacchi
Fault damage zones can be preferential conduits for geofluids, depending on the secondary permeability developed with fracturing. Large-scale outcrop analogues allow a complete characterization of fracture networks, that cannot be satisfactorily imaged in the subsurface (e.g. with seismics). In this project we mapped fractures in the damage zone of the Victoria Fault, a major normal fault crosscutting Miocene shallow-water carbonates of Malta, combining field analysis and a high resolution photogrammetric Digital Outcrop Model (DOM). This allowed characterizing (i) the damage zone width, (ii) its spatial organization, (iii) geometrical parameters of the fracture network and (iv) its connectivity, and (v) the variability of these parameters in different stratigraphic units.
How to cite: Losa, A., Martinelli, M., and Bistacchi, A.: Quantitative fracture characterization in the damage zone of the Victoria Fault, Malta, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22583, https://doi.org/10.5194/egusphere-egu2020-22583, 2020.
Fault damage zones can be preferential conduits for geofluids, depending on the secondary permeability developed with fracturing. Large-scale outcrop analogues allow a complete characterization of fracture networks, that cannot be satisfactorily imaged in the subsurface (e.g. with seismics). In this project we mapped fractures in the damage zone of the Victoria Fault, a major normal fault crosscutting Miocene shallow-water carbonates of Malta, combining field analysis and a high resolution photogrammetric Digital Outcrop Model (DOM). This allowed characterizing (i) the damage zone width, (ii) its spatial organization, (iii) geometrical parameters of the fracture network and (iv) its connectivity, and (v) the variability of these parameters in different stratigraphic units.
How to cite: Losa, A., Martinelli, M., and Bistacchi, A.: Quantitative fracture characterization in the damage zone of the Victoria Fault, Malta, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22583, https://doi.org/10.5194/egusphere-egu2020-22583, 2020.
The present contribution focuses on carbonates fault cores exposed in central and southern Italy, which crosscut Mesozoic limestones and dolostones, pertain to 10’s of m- to 100’s of m-throw extensional fault zones, and include two main domains named as inner and outer fault cores, respectively. The inner fault cores are made up of main slip surfaces (MSS), matrix-supported cataclasites, and fault breccia. Cement-supported cataclasites, if present in the limestone-hosted fault cores, localize around the MSS. The outer fault cores mainly include grain-supported cataclasites, subsidiary slip surfaces, and lithons of fragmented host rocks. In order to assess the fluid flow properties of the carbonate fault cores, the results of microstructural, petrophysical, and ultrasonic studies are first presented, and then discussed in terms of pore type, geometry, textural anisotropy, and poro-perm relationships. Overall, the documented pore distribution is mainly function of both deformation micro-mechanisms and diagenetic processes, which took place in the carbonate fault cores during faulting and fault rock exhumation from depth. In the limestone-hosted fault cores, the experimental results show that the cross-fault fluid flow properties are affected by the the irregular geometry of the cement fronts. These fronts, which depart from the MSS, are due to calcite precipitation in vadose environments from meteoric-derived fault fluids. At depths of about 1 km, these fluids merge with the local freshwater aquifers, and cement the whole fault cores. Overall, these fault cores include a stiff pore networks, and are thought to behave like a granular medium. There, it is proposed that the cross-fault permeability can be computed by applying the Kozeny-Carmen correlation. For any given value of effective porosity, the value of permeability is therefore proportional to the average value of the pore throat, which characterize the aperture of capillary tubes with a geometrical tortuosity of ca. 2.5. On the contrary, the dolostone-hosted fault cores include a soft pore network made up of elongated pores, and are thought to behave like an elastic cracked medium. Accordingly, it is proposed that the cross-fault permeability can be computed by following percolation theory by considering the values of dynamic elastic moduli measured during ultrasonic tests at Pc=30 MPa, and almost isotropic fracture networks. Results of this work could be helpful during appraisal and development operations of hydrocarbon reservoirs, for freshwater aquifer protection, and activities of CO2 storage in depleted carbonate reservoirs.
How to cite: Agosta, F.: Permeability models for carbonate fault cores, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3360, https://doi.org/10.5194/egusphere-egu2020-3360, 2020.
The present contribution focuses on carbonates fault cores exposed in central and southern Italy, which crosscut Mesozoic limestones and dolostones, pertain to 10’s of m- to 100’s of m-throw extensional fault zones, and include two main domains named as inner and outer fault cores, respectively. The inner fault cores are made up of main slip surfaces (MSS), matrix-supported cataclasites, and fault breccia. Cement-supported cataclasites, if present in the limestone-hosted fault cores, localize around the MSS. The outer fault cores mainly include grain-supported cataclasites, subsidiary slip surfaces, and lithons of fragmented host rocks. In order to assess the fluid flow properties of the carbonate fault cores, the results of microstructural, petrophysical, and ultrasonic studies are first presented, and then discussed in terms of pore type, geometry, textural anisotropy, and poro-perm relationships. Overall, the documented pore distribution is mainly function of both deformation micro-mechanisms and diagenetic processes, which took place in the carbonate fault cores during faulting and fault rock exhumation from depth. In the limestone-hosted fault cores, the experimental results show that the cross-fault fluid flow properties are affected by the the irregular geometry of the cement fronts. These fronts, which depart from the MSS, are due to calcite precipitation in vadose environments from meteoric-derived fault fluids. At depths of about 1 km, these fluids merge with the local freshwater aquifers, and cement the whole fault cores. Overall, these fault cores include a stiff pore networks, and are thought to behave like a granular medium. There, it is proposed that the cross-fault permeability can be computed by applying the Kozeny-Carmen correlation. For any given value of effective porosity, the value of permeability is therefore proportional to the average value of the pore throat, which characterize the aperture of capillary tubes with a geometrical tortuosity of ca. 2.5. On the contrary, the dolostone-hosted fault cores include a soft pore network made up of elongated pores, and are thought to behave like an elastic cracked medium. Accordingly, it is proposed that the cross-fault permeability can be computed by following percolation theory by considering the values of dynamic elastic moduli measured during ultrasonic tests at Pc=30 MPa, and almost isotropic fracture networks. Results of this work could be helpful during appraisal and development operations of hydrocarbon reservoirs, for freshwater aquifer protection, and activities of CO2 storage in depleted carbonate reservoirs.
How to cite: Agosta, F.: Permeability models for carbonate fault cores, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3360, https://doi.org/10.5194/egusphere-egu2020-3360, 2020.
EGU2020-3370 | Displays | TS3.5
Fracture stratigraphy, fault architecture and DFN modeling of both diffuse and localized fracture networksFabrizio Agosta
Quantification of the geometry, distribution, and dimension of fracture networks is key to fully understand the petrophysical properties of outcrop-to-reservoir scales rock volumes. On these regards, Discrete Fracture Network (DFN) modeling is a very useful tool to compute the values of fracture porosity and equivalent permeability of geo-cellular volumes populated with stochastic or deterministic fracture networks. Independently of their size and cell dimensions, the single geocelullar volumes are populated by inputting the following parameters for each fracture set: (i) length; (ii) aspect ratio; (iii) mechanical and hydraulic apertures; (iv) fracture intensity, and (v) attitude. A sensitivity analysis is always carried out in order to test the seeding procedure of the employed software, and to check the validity of the fracture aperture values employed as input data. The latter values, in fact, are the most critical to assess from outcrop and laboratory analyses. The present contribution focuses on the results of recent works performed on the fractured limestone rocks of the Apulian Platform, which are widely exposed along the Italian peninsula. Outcrops are first introduced in order to define the fracture stratigraphy and fault architecture of the Meso-Cenozoic limestone rocks. Then, the criteria behind the construction of DFN models are illustrated. Methods employed for the build of individual fracture units and single fault damage zone domains are illustrated. Finally, the computed values of fracture porosity and equivalent horizontal permeability obtained for multiple DFN models are presented. Discussion of the data focuses on the fluid accumulation and migration properties of the fractured limestone rocks by considering their amount of exhumation experienced during Plio-Quaternary times. Results of DFN modeling could be helpful to optimize the appraisal and development operations of hydrocarbon reservoirs, and minimize the pollution of freshwater aquifer. In fact, the Apulian carbonates host in the underground significant amounts of freshwater of the Mediterranean Region, and the largest oil and gas reserves of continental Europe. Furthermore, the results could shed new lights into the role exerted by faults and fractures on subsurface CO2 storage in depleted carbonate reservoirs, a practice that envisioned to decrease the greenhouse gas concentration in the atmosphere in the next future.
How to cite: Agosta, F.: Fracture stratigraphy, fault architecture and DFN modeling of both diffuse and localized fracture networks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3370, https://doi.org/10.5194/egusphere-egu2020-3370, 2020.
Quantification of the geometry, distribution, and dimension of fracture networks is key to fully understand the petrophysical properties of outcrop-to-reservoir scales rock volumes. On these regards, Discrete Fracture Network (DFN) modeling is a very useful tool to compute the values of fracture porosity and equivalent permeability of geo-cellular volumes populated with stochastic or deterministic fracture networks. Independently of their size and cell dimensions, the single geocelullar volumes are populated by inputting the following parameters for each fracture set: (i) length; (ii) aspect ratio; (iii) mechanical and hydraulic apertures; (iv) fracture intensity, and (v) attitude. A sensitivity analysis is always carried out in order to test the seeding procedure of the employed software, and to check the validity of the fracture aperture values employed as input data. The latter values, in fact, are the most critical to assess from outcrop and laboratory analyses. The present contribution focuses on the results of recent works performed on the fractured limestone rocks of the Apulian Platform, which are widely exposed along the Italian peninsula. Outcrops are first introduced in order to define the fracture stratigraphy and fault architecture of the Meso-Cenozoic limestone rocks. Then, the criteria behind the construction of DFN models are illustrated. Methods employed for the build of individual fracture units and single fault damage zone domains are illustrated. Finally, the computed values of fracture porosity and equivalent horizontal permeability obtained for multiple DFN models are presented. Discussion of the data focuses on the fluid accumulation and migration properties of the fractured limestone rocks by considering their amount of exhumation experienced during Plio-Quaternary times. Results of DFN modeling could be helpful to optimize the appraisal and development operations of hydrocarbon reservoirs, and minimize the pollution of freshwater aquifer. In fact, the Apulian carbonates host in the underground significant amounts of freshwater of the Mediterranean Region, and the largest oil and gas reserves of continental Europe. Furthermore, the results could shed new lights into the role exerted by faults and fractures on subsurface CO2 storage in depleted carbonate reservoirs, a practice that envisioned to decrease the greenhouse gas concentration in the atmosphere in the next future.
How to cite: Agosta, F.: Fracture stratigraphy, fault architecture and DFN modeling of both diffuse and localized fracture networks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3370, https://doi.org/10.5194/egusphere-egu2020-3370, 2020.
EGU2020-4902 | Displays | TS3.5
Linking direct and continuum fluid flow models for fractured media: The intersection problemMaximilian O. Kottwitz, Anton A. Popov, Steffen Abe, and Boris J. P. Kaus
Finding an adequate bridge between direct and continuum modeling approaches has been the fundamental issue of upscaling fluid flow in rock masses. Typically, numerical simulations of direct fluid flow (e.g. Stokes or Lattice-Boltzmann) in fractured or porous media serve as small-scale building blocks for larger-scale continuum flow simulations (e.g. Darcy). For fractured rock masses, the discrete-fracture-network (DFN) modeling approach is often used as an initial step to upscale flow properties by parameterizing the permeability of each fracture with its hydraulic aperture and solving steady-state flow equations within the fracture system. However, numerical simulations of Stokes flow in small fracture networks (FN) indicate that, depending on the orientation of the applied pressure gradient, fluid flow tends to localize at places where fractures intersect. This effect causes discrepancies between direct and equivalent continuum flow modeling approaches, which ought to be taken into account when modeling flow at the network scale.
In this study, we compare direct flow simulations of small fracture networks to their continuum representation obtained with several techniques in order to find an upscaling approach that takes these intersection effects into account. Direct flow simulations are conducted by solving the Stokes equations in 3D using our open-source finite-difference software LaMEM. Continuum flow simulations are realized with a newly developed parallel finite-element code, which solves fully anisotropic 3D Darcy flow with specific permeability tensors for each voxel. The direct flow simulations serve as benchmarks to optimize the continuum flow models by comparing resulting permeabilities. We tested two different schemes to generate the equivalent continuum representation:
(1) Fully resolved isotropic permeability discretizations (fracture permeability is obtained from a refined cubic law) where voxel sizes are a fraction of the minimal hydraulic aperture of the FN or
(2) coarse anisotropic permeability discretizations (permeability tensors are rotated according to fracture orientation) with voxel sizes larger than the minimal hydraulic aperture of the FN.
We then assess different scenarios to incorporate the intersection effects by adding, averaging and/or multiplying the permeabilities of the intersecting fractures within intersection voxels. Preliminary results for scheme 1 suggest that a simple addition of both intersecting fracture permeabilities delivers the best fit to the results of the direct flow simulations, if the voxel size is about 68% of the minimal hydraulic aperture. Scheme 2 systematically underestimates the direct flow permeabilities by about 26%.
How to cite: Kottwitz, M. O., Popov, A. A., Abe, S., and Kaus, B. J. P.: Linking direct and continuum fluid flow models for fractured media: The intersection problem, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4902, https://doi.org/10.5194/egusphere-egu2020-4902, 2020.
Finding an adequate bridge between direct and continuum modeling approaches has been the fundamental issue of upscaling fluid flow in rock masses. Typically, numerical simulations of direct fluid flow (e.g. Stokes or Lattice-Boltzmann) in fractured or porous media serve as small-scale building blocks for larger-scale continuum flow simulations (e.g. Darcy). For fractured rock masses, the discrete-fracture-network (DFN) modeling approach is often used as an initial step to upscale flow properties by parameterizing the permeability of each fracture with its hydraulic aperture and solving steady-state flow equations within the fracture system. However, numerical simulations of Stokes flow in small fracture networks (FN) indicate that, depending on the orientation of the applied pressure gradient, fluid flow tends to localize at places where fractures intersect. This effect causes discrepancies between direct and equivalent continuum flow modeling approaches, which ought to be taken into account when modeling flow at the network scale.
In this study, we compare direct flow simulations of small fracture networks to their continuum representation obtained with several techniques in order to find an upscaling approach that takes these intersection effects into account. Direct flow simulations are conducted by solving the Stokes equations in 3D using our open-source finite-difference software LaMEM. Continuum flow simulations are realized with a newly developed parallel finite-element code, which solves fully anisotropic 3D Darcy flow with specific permeability tensors for each voxel. The direct flow simulations serve as benchmarks to optimize the continuum flow models by comparing resulting permeabilities. We tested two different schemes to generate the equivalent continuum representation:
(1) Fully resolved isotropic permeability discretizations (fracture permeability is obtained from a refined cubic law) where voxel sizes are a fraction of the minimal hydraulic aperture of the FN or
(2) coarse anisotropic permeability discretizations (permeability tensors are rotated according to fracture orientation) with voxel sizes larger than the minimal hydraulic aperture of the FN.
We then assess different scenarios to incorporate the intersection effects by adding, averaging and/or multiplying the permeabilities of the intersecting fractures within intersection voxels. Preliminary results for scheme 1 suggest that a simple addition of both intersecting fracture permeabilities delivers the best fit to the results of the direct flow simulations, if the voxel size is about 68% of the minimal hydraulic aperture. Scheme 2 systematically underestimates the direct flow permeabilities by about 26%.
How to cite: Kottwitz, M. O., Popov, A. A., Abe, S., and Kaus, B. J. P.: Linking direct and continuum fluid flow models for fractured media: The intersection problem, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4902, https://doi.org/10.5194/egusphere-egu2020-4902, 2020.
EGU2020-5677 | Displays | TS3.5
Modeling fluid flow through complex fracture network in geological media by using hierarchical hydraulic propertiesKyung Won Chang, Gungor Beskardes, and Chester Weiss
Hydraulic stimulation is the process of initiating fractures in a target reservoir for subsurface energy resource management with applications in unconventional oil/gas and enhanced geothermal systems. The fracture characteristics (i.e., number, size and orientation with respect to the wellbore) determines the modified permeability field of the host rock and thus, numerical simulations of flow in fractured media are essential for estimating the anticipated change in reservoir productivity. However, numerical modeling of fluid flow in highly fractured media is challenging due to the explosive computational cost imposed by the explicit discretization of fractures at multiple length scales. A common strategy for mitigating this extreme cost is to crudely simplify the geometry of fracture network, thereby neglecting the important contributions made by all elements of the complex fracture system.
The proposed “Hierarchical Finite Element Method” (Hi-FEM; Weiss, Geophysics, 2017) reduces the comparatively insignificant dimensions of planar- and curvilinear-like features by translating them into integrated hydraulic conductivities, thus enabling cost-effective simulations with requisite solutions at material discontinuities without defining ad-hoc, heuristic, or empirically-estimated boundary conditions between fractures and the surrounding formation. By representing geometrical and geostatistical features of a given fracture network through the Hi-FEM computational framework, geometrically- and geomechanically-dependent fluid flow properly can now be modeled economically both within fractures as well as the surrounding medium, with a natural “physics-informed” coupling between the two.
SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.
How to cite: Chang, K. W., Beskardes, G., and Weiss, C.: Modeling fluid flow through complex fracture network in geological media by using hierarchical hydraulic properties , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5677, https://doi.org/10.5194/egusphere-egu2020-5677, 2020.
Hydraulic stimulation is the process of initiating fractures in a target reservoir for subsurface energy resource management with applications in unconventional oil/gas and enhanced geothermal systems. The fracture characteristics (i.e., number, size and orientation with respect to the wellbore) determines the modified permeability field of the host rock and thus, numerical simulations of flow in fractured media are essential for estimating the anticipated change in reservoir productivity. However, numerical modeling of fluid flow in highly fractured media is challenging due to the explosive computational cost imposed by the explicit discretization of fractures at multiple length scales. A common strategy for mitigating this extreme cost is to crudely simplify the geometry of fracture network, thereby neglecting the important contributions made by all elements of the complex fracture system.
The proposed “Hierarchical Finite Element Method” (Hi-FEM; Weiss, Geophysics, 2017) reduces the comparatively insignificant dimensions of planar- and curvilinear-like features by translating them into integrated hydraulic conductivities, thus enabling cost-effective simulations with requisite solutions at material discontinuities without defining ad-hoc, heuristic, or empirically-estimated boundary conditions between fractures and the surrounding formation. By representing geometrical and geostatistical features of a given fracture network through the Hi-FEM computational framework, geometrically- and geomechanically-dependent fluid flow properly can now be modeled economically both within fractures as well as the surrounding medium, with a natural “physics-informed” coupling between the two.
SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.
How to cite: Chang, K. W., Beskardes, G., and Weiss, C.: Modeling fluid flow through complex fracture network in geological media by using hierarchical hydraulic properties , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5677, https://doi.org/10.5194/egusphere-egu2020-5677, 2020.
EGU2020-6577 | Displays | TS3.5
Computational framework for discontinuity network characterizationThomas Poulet, Ulrich Kelka, Stefan Westerlund, and Luk Peeters
The topological and geometrical description of fault and fracture networks is an essential first step in any investigation of fractured or faulted media. The spatial arrangement, density, connectivity, and geometry of the discontinuities strongly impact the physical properties of the media such as resilience and permeability. Obtaining reliable metrics for characterizing fault and fracture networks is of interest for mining engineering, reservoir characterization, groundwater management, and studies on the regional fluid flow history. During large-scale studies, we mostly rely on two-dimensional lineaments obtained through structural mapping, outcrop analysis, or remote sensing. An efficient and widely applicable framework for discontinuity network characterization should therefore be based on the analysis of the frequently available two-dimensional data sets.
Here, we present an automated framework for efficient and robust characterization of the geometric and topologic parameters of discontinuity networks. The geometry of the lineaments is characterised based on orientation, length, and sinuosity. The underlying distribution of these parameters are determined, and representative probability density functions are reported. The connection between the geometric parameters is validated, e.g. correlation between orientation and length. The spatial arrangement is determined by classical line- and window-sampling, by assessing the fractal dimension, and via graph-based topology analysis.
In addition to the statistical analysis of lineament networks, we show how the graph data structure can be utilized for further characterization by linking it to raster data such as magnetic, gravimetric, or elevation. This procedure not only yields an additional means for lineament characterization but also allows users to assess dominant pathways based, for instance, on hydraulic gradients. We demonstrate the applicability of our algorithm on synthetic data sets and real-world case studies on mapped fault and fracture networks.
We finally show how our framework can also be utilized to design detailed numerical studies on the fluid flow properties of analysed networks by conditioning mesh refinement on the type and number of intersections. In addition, due to known scaling relationships our framework can help to determine appropriate parameters for the simulations. We provide examples of statistically parametrized fluid flow simulations in natural discontinuity networks and show the impact of conceptualizing the lineaments as conduits, barriers or conduit-barrier systems.
How to cite: Poulet, T., Kelka, U., Westerlund, S., and Peeters, L.: Computational framework for discontinuity network characterization , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6577, https://doi.org/10.5194/egusphere-egu2020-6577, 2020.
The topological and geometrical description of fault and fracture networks is an essential first step in any investigation of fractured or faulted media. The spatial arrangement, density, connectivity, and geometry of the discontinuities strongly impact the physical properties of the media such as resilience and permeability. Obtaining reliable metrics for characterizing fault and fracture networks is of interest for mining engineering, reservoir characterization, groundwater management, and studies on the regional fluid flow history. During large-scale studies, we mostly rely on two-dimensional lineaments obtained through structural mapping, outcrop analysis, or remote sensing. An efficient and widely applicable framework for discontinuity network characterization should therefore be based on the analysis of the frequently available two-dimensional data sets.
Here, we present an automated framework for efficient and robust characterization of the geometric and topologic parameters of discontinuity networks. The geometry of the lineaments is characterised based on orientation, length, and sinuosity. The underlying distribution of these parameters are determined, and representative probability density functions are reported. The connection between the geometric parameters is validated, e.g. correlation between orientation and length. The spatial arrangement is determined by classical line- and window-sampling, by assessing the fractal dimension, and via graph-based topology analysis.
In addition to the statistical analysis of lineament networks, we show how the graph data structure can be utilized for further characterization by linking it to raster data such as magnetic, gravimetric, or elevation. This procedure not only yields an additional means for lineament characterization but also allows users to assess dominant pathways based, for instance, on hydraulic gradients. We demonstrate the applicability of our algorithm on synthetic data sets and real-world case studies on mapped fault and fracture networks.
We finally show how our framework can also be utilized to design detailed numerical studies on the fluid flow properties of analysed networks by conditioning mesh refinement on the type and number of intersections. In addition, due to known scaling relationships our framework can help to determine appropriate parameters for the simulations. We provide examples of statistically parametrized fluid flow simulations in natural discontinuity networks and show the impact of conceptualizing the lineaments as conduits, barriers or conduit-barrier systems.
How to cite: Poulet, T., Kelka, U., Westerlund, S., and Peeters, L.: Computational framework for discontinuity network characterization , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6577, https://doi.org/10.5194/egusphere-egu2020-6577, 2020.
EGU2020-19664 | Displays | TS3.5
Predictive DFN modelling for the Upper Muschelkalk aquifer in the northernmost Swiss Molasse Basin based on vertical and horizontal borehole recordsRaphael Schneeberger, Bill Lanyon, Alan Herbert, Mario Habermüller, and Herfried Madritsch
The exploration of the underground is a complex, but common task. Structural characterisation of a given sub-surface volume is of interest, for many purposes including deep geological repositories for radioactive waste, exploitation of mineral resources and geothermal energy production. One major challenge in this regard relates to the identification of sub-seismic scale faults and fractures. Discrete fracture network modelling is one possible technique for this purpose. Ideally, it is supported by borehole data. Even so, the results of stochastic models require critical verification to determine resulting uncertainties and model robustness.
We present a case-study from the village of Schlattingen, located the northernmost Molasse Basin in Switzerland, that is devoted to such a verification aimed at improvement of the DFN modelling workflows. Two boreholes were drilled at this location, a vertical cored borehole reaching into the crystalline basement and a deviated borehole running sub-horizontally for 464 m in the Schinznach Formation (Upper Muschelkalk), a potential geothermal reservoir (Frieg et al. 2015). This borehole layout allows testing the workflow for discrete fracture network modelling from a single borehole and assessment of the the added value of a deviated borehole (and vice versa).
The modelling workflow used borehole data and outcrop descriptions from a range of locations as input data. The spatial distribution of features was simulated using a Poisson distribution. The aims of the study were to investigate the workflow’s ability to account for the different orientation biases in the two boreholes and develop understanding of spatial variability in fracture orientation and frequency.
It was found that reasonable consistency in orientation and overall frequency could be achieved using the borehole orientation distributions but that the spatial variability in fracture frequency and clustering of fractures were significant. It was also necessary to critically evaluate the borehole imagery from the deviated borehole.
Current efforts are focused on better constrain the spatial fracture distribution along the deviated borehole using correlation analysis (Marett et al. 2018, Gale at al. 2018) and assess its influence on the discrete fracture network model. In addition, it is anticipated to integrate observation from nearby outcrops into the modelling strategy.
References:
Frieg, B., Grob, H., Hertrich, M., Madritsch, H., Müller, H., Vietor, T., Vogt, T., and Weber, H.P. (2015). Novel Approach for the Extrapolation of the Muschelkalk Aquifer in Switzerland for the CO2-free production of vegetables. Proceedings World Geothermal Congress, Melbourne, Australia
Gale, J. F. W., Ukar, E., & Laubach, S. E. (2018). Gaps in DFN models and how to fill them. 2nd International Discrete Fracture Network Engineering Conference, DFNE 2018.
Marrett, R., Gale, J. F. W., Gómez, L. A., & Laubach, S. E. (2018). Correlation analysis of fracture arrangement in space. Journal of Structural Geology, 108, 16–33. https://doi.org/10.1016/j.jsg.2017.06.012
How to cite: Schneeberger, R., Lanyon, B., Herbert, A., Habermüller, M., and Madritsch, H.: Predictive DFN modelling for the Upper Muschelkalk aquifer in the northernmost Swiss Molasse Basin based on vertical and horizontal borehole records , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19664, https://doi.org/10.5194/egusphere-egu2020-19664, 2020.
The exploration of the underground is a complex, but common task. Structural characterisation of a given sub-surface volume is of interest, for many purposes including deep geological repositories for radioactive waste, exploitation of mineral resources and geothermal energy production. One major challenge in this regard relates to the identification of sub-seismic scale faults and fractures. Discrete fracture network modelling is one possible technique for this purpose. Ideally, it is supported by borehole data. Even so, the results of stochastic models require critical verification to determine resulting uncertainties and model robustness.
We present a case-study from the village of Schlattingen, located the northernmost Molasse Basin in Switzerland, that is devoted to such a verification aimed at improvement of the DFN modelling workflows. Two boreholes were drilled at this location, a vertical cored borehole reaching into the crystalline basement and a deviated borehole running sub-horizontally for 464 m in the Schinznach Formation (Upper Muschelkalk), a potential geothermal reservoir (Frieg et al. 2015). This borehole layout allows testing the workflow for discrete fracture network modelling from a single borehole and assessment of the the added value of a deviated borehole (and vice versa).
The modelling workflow used borehole data and outcrop descriptions from a range of locations as input data. The spatial distribution of features was simulated using a Poisson distribution. The aims of the study were to investigate the workflow’s ability to account for the different orientation biases in the two boreholes and develop understanding of spatial variability in fracture orientation and frequency.
It was found that reasonable consistency in orientation and overall frequency could be achieved using the borehole orientation distributions but that the spatial variability in fracture frequency and clustering of fractures were significant. It was also necessary to critically evaluate the borehole imagery from the deviated borehole.
Current efforts are focused on better constrain the spatial fracture distribution along the deviated borehole using correlation analysis (Marett et al. 2018, Gale at al. 2018) and assess its influence on the discrete fracture network model. In addition, it is anticipated to integrate observation from nearby outcrops into the modelling strategy.
References:
Frieg, B., Grob, H., Hertrich, M., Madritsch, H., Müller, H., Vietor, T., Vogt, T., and Weber, H.P. (2015). Novel Approach for the Extrapolation of the Muschelkalk Aquifer in Switzerland for the CO2-free production of vegetables. Proceedings World Geothermal Congress, Melbourne, Australia
Gale, J. F. W., Ukar, E., & Laubach, S. E. (2018). Gaps in DFN models and how to fill them. 2nd International Discrete Fracture Network Engineering Conference, DFNE 2018.
Marrett, R., Gale, J. F. W., Gómez, L. A., & Laubach, S. E. (2018). Correlation analysis of fracture arrangement in space. Journal of Structural Geology, 108, 16–33. https://doi.org/10.1016/j.jsg.2017.06.012
How to cite: Schneeberger, R., Lanyon, B., Herbert, A., Habermüller, M., and Madritsch, H.: Predictive DFN modelling for the Upper Muschelkalk aquifer in the northernmost Swiss Molasse Basin based on vertical and horizontal borehole records , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19664, https://doi.org/10.5194/egusphere-egu2020-19664, 2020.
EGU2020-4799 | Displays | TS3.5
An alternative method to evaluate fracture network efficiency to fluid flowGiampaolo Proietti, Valentina Romano, Alessia Conti, Maria Chiara Tartarello, and Sabina Bigi
Fracture networks exist at a wide range of scale in the earth crust and strongly influence the hydraulic behaviour of rocks, providing either pathways or barriers for fluid flow. Many oil, gas, geothermal and water supply reservoirs form in fractured rocks. The main challenge is the development of numerical models that describe adequately the fracture networks and the constitutive equations governing the physical processes in fractured reservoir. The hydraulic properties of fracture networks, derived from Discrete Fracture Network (DFN), models are commonly used to populate continuum equivalent models at reservoir scale, to reduce the computational cost and the numerical complexity. However, the efficiency of fracture networks to fluid flow is strongly tied to their connectivity and spatial distribution, that continuum models are not able to capture explicitly.In this work we used field data and synthetic models to introduce a new parameter to evaluate the efficiency of fracture networks to fluid flow, reflecting a range of variability in fracture network characteristics (e.g. P32, number of fractures, stress field). This alternative method allows to model fractured systems at reservoir scale, in a variety of geological settings, using exclusively a DFN approach.
How to cite: Proietti, G., Romano, V., Conti, A., Tartarello, M. C., and Bigi, S.: An alternative method to evaluate fracture network efficiency to fluid flow , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4799, https://doi.org/10.5194/egusphere-egu2020-4799, 2020.
Fracture networks exist at a wide range of scale in the earth crust and strongly influence the hydraulic behaviour of rocks, providing either pathways or barriers for fluid flow. Many oil, gas, geothermal and water supply reservoirs form in fractured rocks. The main challenge is the development of numerical models that describe adequately the fracture networks and the constitutive equations governing the physical processes in fractured reservoir. The hydraulic properties of fracture networks, derived from Discrete Fracture Network (DFN), models are commonly used to populate continuum equivalent models at reservoir scale, to reduce the computational cost and the numerical complexity. However, the efficiency of fracture networks to fluid flow is strongly tied to their connectivity and spatial distribution, that continuum models are not able to capture explicitly.In this work we used field data and synthetic models to introduce a new parameter to evaluate the efficiency of fracture networks to fluid flow, reflecting a range of variability in fracture network characteristics (e.g. P32, number of fractures, stress field). This alternative method allows to model fractured systems at reservoir scale, in a variety of geological settings, using exclusively a DFN approach.
How to cite: Proietti, G., Romano, V., Conti, A., Tartarello, M. C., and Bigi, S.: An alternative method to evaluate fracture network efficiency to fluid flow , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4799, https://doi.org/10.5194/egusphere-egu2020-4799, 2020.
EGU2020-4712 | Displays | TS3.5
Fluid flow through rock fractures undergoing chemical interactions: A look at pressure solution from an experimental perspectiveHarald Milsch and Chaojie Cheng
Fluid transport within the Earth’s crust is predominantly controlled by planar void space like fractures and crack networks. Characterizing the time dependent hydro-mechanical properties of these rock-structural elements therefore is of paramount importance for natural geosystem understanding and geotechnical applications alike.
In this contribution we outline the protocol and results of a long term flow-through experiment of more than 4 months conducted with one single-fractured, pure quartz, and centimeter-sized Fontainebleau sandstone sample displaying very low matrix permeability.
The cylindrical sample was axially split to generate one single and rough tensile fracture and the obtained sample halves were manually offset in axial direction by 200 µm resulting in geometric mismatch of the two fracture faces yielding asperity contacts and high contact stresses upon loading.
The experiment was conducted at constant temperature (333 K) and pore fluid pressure (1 MPa), three different confining pressure levels (2, 18, and 30 MPa), and with two different fluids (deionized water and 0.3 mM SiO2 solution).
The sample was continuously flown through and the experimental procedure consisted of several successive stages during which confining pressure and fluid type were systematically varied in time intervals of several weeks each.
The experiment yielded results of continuous sample and fracture permeability measurements, the derivation of time dependent changes in hydraulic fracture aperture, a complete ICP-OES chemical analysis of Si concentrations in the effluent in one day time intervals, and a full before/after microstructural investigation of mechanical aperture, contact area ratio, as well as asperity and free fracture face morphology.
Overall, this experiment yields evidenced insights into the low-temperature dynamics of fracture permeability when, concurrently, chemical interactions between fluid and rock are taking place. Moreover, the investigations emphasize the role of pressure solution (creep) in this context as opposed to, e.g., free face dissolution or subcritical crack growth. Finally, conclusions are drawn on the rate-limiting sub-process of pressure solution with possible implications for fluid history matching in quartz-rich fractured rock masses.
How to cite: Milsch, H. and Cheng, C.: Fluid flow through rock fractures undergoing chemical interactions: A look at pressure solution from an experimental perspective, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4712, https://doi.org/10.5194/egusphere-egu2020-4712, 2020.
Fluid transport within the Earth’s crust is predominantly controlled by planar void space like fractures and crack networks. Characterizing the time dependent hydro-mechanical properties of these rock-structural elements therefore is of paramount importance for natural geosystem understanding and geotechnical applications alike.
In this contribution we outline the protocol and results of a long term flow-through experiment of more than 4 months conducted with one single-fractured, pure quartz, and centimeter-sized Fontainebleau sandstone sample displaying very low matrix permeability.
The cylindrical sample was axially split to generate one single and rough tensile fracture and the obtained sample halves were manually offset in axial direction by 200 µm resulting in geometric mismatch of the two fracture faces yielding asperity contacts and high contact stresses upon loading.
The experiment was conducted at constant temperature (333 K) and pore fluid pressure (1 MPa), three different confining pressure levels (2, 18, and 30 MPa), and with two different fluids (deionized water and 0.3 mM SiO2 solution).
The sample was continuously flown through and the experimental procedure consisted of several successive stages during which confining pressure and fluid type were systematically varied in time intervals of several weeks each.
The experiment yielded results of continuous sample and fracture permeability measurements, the derivation of time dependent changes in hydraulic fracture aperture, a complete ICP-OES chemical analysis of Si concentrations in the effluent in one day time intervals, and a full before/after microstructural investigation of mechanical aperture, contact area ratio, as well as asperity and free fracture face morphology.
Overall, this experiment yields evidenced insights into the low-temperature dynamics of fracture permeability when, concurrently, chemical interactions between fluid and rock are taking place. Moreover, the investigations emphasize the role of pressure solution (creep) in this context as opposed to, e.g., free face dissolution or subcritical crack growth. Finally, conclusions are drawn on the rate-limiting sub-process of pressure solution with possible implications for fluid history matching in quartz-rich fractured rock masses.
How to cite: Milsch, H. and Cheng, C.: Fluid flow through rock fractures undergoing chemical interactions: A look at pressure solution from an experimental perspective, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4712, https://doi.org/10.5194/egusphere-egu2020-4712, 2020.
EGU2020-5791 | Displays | TS3.5
Stylolites:when they became conduits for fluid pathway ?Giuseppe Repetto, Silvana Magni, Paul Sardini, Marja Siitari Sattari, Juuso Sammaljärvi, and Arnaud Mazurier
Dissolution process is a complex phenomenon controlled by several factors such as the nature of chemical dissolution, lithology, porosity, stress orientation, environmental conditions, networks of fractures. In the karst field, however, compressional tectonic structures, as like stylolites, are never been taken into consideration for fluid flow. Stylolites are formed by a pressure solution processes that dissolves the soluble particles and leads to an enrichment in insolvable, non-carbonate particles (NCP) along their surfaces. Potentially they play an important role in fluid circulation during carbonate deformation.
Although they seem macroscopically planar, stylolites have an extremely variable shape from the meso- to microscale, with variable porosity and permeability. Because of this, they have a strong effect on regional fluid flow and the formation of reservoirs since they can act as barriers or conduits for flow.
In this research we investigated the distribution of voids and pores present both within and near the stylolites.This task is challenging because the pore sizes are small and therefore difficult to investigate. To determine which role the NCP and these structures have on fluid circulation, a comparison is herein presented between two different methods used to map the submicroscopic arrangement of pores and voids in and around stylolites. Because the investigated stylolites are relatively narrow, around 30-50 µm, we decided to use a classical micro Computed Tomography (µCT) technique supported by the 14C-PMMA impregnation method on two marble samples. These two comprelementary methods characterize the spatial distribution of connected voids in and around stylolites. µCT analysis provide adequate information on the 3D distribution of voids even if nanometer scale pores and small fractures are difficult to observe using µCT.
14C-PMMA method is however able to reveal connected porosities from mineral areas that consist of nanometer scale pores. Methylmethacrylate intrudes into nanometer scale pores, and autoradiography is used to visualize the porosities thanks to 14C beta emissions. Combining these two techniques, CT tomography and PMMA autoradiography we can visualize the 3D pore structures of the studied samples.
The results show that the micro CT technique supported by the PMMA autoradiography technique provides a useful tool to characterize the voids and pore structures of geomaterials.
The results allowed a more accurate description of the behavior of stylolites in fluid-rock interaction.
Key words: stylolites, permeability, microCT and 14C-PMMA impregnation
How to cite: Repetto, G., Magni, S., Sardini, P., Sattari, M. S., Sammaljärvi, J., and Mazurier, A.: Stylolites:when they became conduits for fluid pathway ?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5791, https://doi.org/10.5194/egusphere-egu2020-5791, 2020.
Dissolution process is a complex phenomenon controlled by several factors such as the nature of chemical dissolution, lithology, porosity, stress orientation, environmental conditions, networks of fractures. In the karst field, however, compressional tectonic structures, as like stylolites, are never been taken into consideration for fluid flow. Stylolites are formed by a pressure solution processes that dissolves the soluble particles and leads to an enrichment in insolvable, non-carbonate particles (NCP) along their surfaces. Potentially they play an important role in fluid circulation during carbonate deformation.
Although they seem macroscopically planar, stylolites have an extremely variable shape from the meso- to microscale, with variable porosity and permeability. Because of this, they have a strong effect on regional fluid flow and the formation of reservoirs since they can act as barriers or conduits for flow.
In this research we investigated the distribution of voids and pores present both within and near the stylolites.This task is challenging because the pore sizes are small and therefore difficult to investigate. To determine which role the NCP and these structures have on fluid circulation, a comparison is herein presented between two different methods used to map the submicroscopic arrangement of pores and voids in and around stylolites. Because the investigated stylolites are relatively narrow, around 30-50 µm, we decided to use a classical micro Computed Tomography (µCT) technique supported by the 14C-PMMA impregnation method on two marble samples. These two comprelementary methods characterize the spatial distribution of connected voids in and around stylolites. µCT analysis provide adequate information on the 3D distribution of voids even if nanometer scale pores and small fractures are difficult to observe using µCT.
14C-PMMA method is however able to reveal connected porosities from mineral areas that consist of nanometer scale pores. Methylmethacrylate intrudes into nanometer scale pores, and autoradiography is used to visualize the porosities thanks to 14C beta emissions. Combining these two techniques, CT tomography and PMMA autoradiography we can visualize the 3D pore structures of the studied samples.
The results show that the micro CT technique supported by the PMMA autoradiography technique provides a useful tool to characterize the voids and pore structures of geomaterials.
The results allowed a more accurate description of the behavior of stylolites in fluid-rock interaction.
Key words: stylolites, permeability, microCT and 14C-PMMA impregnation
How to cite: Repetto, G., Magni, S., Sardini, P., Sattari, M. S., Sammaljärvi, J., and Mazurier, A.: Stylolites:when they became conduits for fluid pathway ?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5791, https://doi.org/10.5194/egusphere-egu2020-5791, 2020.
EGU2020-5851 | Displays | TS3.5
Textural evolution and fluid-rock interaction during upper crustal, seismic deformation: Insights from the carbonate-dominated fault rock suite of the Belluno Thrust, Italian Southern AlpsRenato Diamanti, Costantino Zuccari, Selina Bonini, Gianluca Vignaroli, and Giulio Viola
A multi-scalar, multi-methodological approach has been used to characterize the deformation mechanisms and fluid-rock interaction processes within the Belluno Thrust (BT), a regional-scale thrust cutting through Mesozoic carbonates of the eastern Southern Alps of Italy. We report the first results of a systematic analysis of the deformation mechanisms that steered strain localization within the BT fault zone during seismogenic faulting. The WSW-ENE-striking BT contributed to development of the south-verging thrust-and-fold belt of the Southern Alps during the Late Oligocene – present time interval. We studied an outstanding exposure of the BT in the greater Feltre region, where the BT juxtaposes an Early Jurassic oolitic and micritic limestone (the Calcari Grigi Group) in the hanging wall against an Upper Jurassic-Early Cretaceous pelagic and cherty limestone (the Maiolica Fm.). The BT is defined by a 2 m-thick damage zone formed at the expense of both the hanging wall and footwall blocks. Atop the damage zone is a millimetric principal slip surface (PSS) that strikes WSW-ENE and dips 40° to the NNW. Kinematic analysis confirms the top-to-the SSE transport along the BT. Several structural facies have been identified by means of detailed structural mapping and sampled from the damage zone (from within both the hanging- and the footwall blocks) and the PSS. The outcrop structural characterization has revealed a number of physically juxtaposed, yet different, structural facies: i) cohesive, weakly foliated proto- to ultracataclasite; ii) uncohesive, clay-rich gouge; iii) foliated domains with SC-C’ structures. Relatively unstrained host rock lithons are wrapped by these variably strained domains. Petrographic and microstructural analyses show evidence of pervasive pressure solution, with abundant stylolites, slickolites and foliated domains indicating an overall ductile behaviour. Calcite veins are also common in all recognised structural facies showing mutual cross-cutting relationships with the pressure-solution seams. This structural characterization has provided the basis for detailed image analysis of selected cataclastic textures to calculate fractal parameters for the particle size distribution (Ds) and morphology (Dr) of the clasts aiming at better understanding the cataclastic flow active in the BT fault rocks. Results from a range of representative samples suggest corrosive wear to be the main cataclastic process (Ds 1,41 ÷ 2,00; Dr 1,51 ÷ 1,88). Cathodoluminescence imaging revealed multiple generations of cement and permitted discriminating the first-order chemical characteristics of parental fluids and constraining the relationships between calcite veining and cementation. Two syn-tectonic cements have been identified: i) a bright-orange cement, preferentially surrounding carbonate clasts with highly irregular margins, indicative of the involvement of carbonate-reactive fluids; ii) a dull, homogeneous brown/black cement coexisting with a siliceous matrix, mantled clasts and local sigmoidal structures. The latter is at times observed as thin injections and fluidized structures. Our preliminary results suggest that overall deformation was accommodated by creep and low-T crystal-plastic deformation possibly during inter-seismic phases as indicated by the presence of pressure-solution seams and foliated fabrics. Transient spikes of coseismic rupturing possibly promoted by multiple batches of overpressured fluids were accompanied by significant cataclasis and brittle strain localization.
How to cite: Diamanti, R., Zuccari, C., Bonini, S., Vignaroli, G., and Viola, G.: Textural evolution and fluid-rock interaction during upper crustal, seismic deformation: Insights from the carbonate-dominated fault rock suite of the Belluno Thrust, Italian Southern Alps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5851, https://doi.org/10.5194/egusphere-egu2020-5851, 2020.
A multi-scalar, multi-methodological approach has been used to characterize the deformation mechanisms and fluid-rock interaction processes within the Belluno Thrust (BT), a regional-scale thrust cutting through Mesozoic carbonates of the eastern Southern Alps of Italy. We report the first results of a systematic analysis of the deformation mechanisms that steered strain localization within the BT fault zone during seismogenic faulting. The WSW-ENE-striking BT contributed to development of the south-verging thrust-and-fold belt of the Southern Alps during the Late Oligocene – present time interval. We studied an outstanding exposure of the BT in the greater Feltre region, where the BT juxtaposes an Early Jurassic oolitic and micritic limestone (the Calcari Grigi Group) in the hanging wall against an Upper Jurassic-Early Cretaceous pelagic and cherty limestone (the Maiolica Fm.). The BT is defined by a 2 m-thick damage zone formed at the expense of both the hanging wall and footwall blocks. Atop the damage zone is a millimetric principal slip surface (PSS) that strikes WSW-ENE and dips 40° to the NNW. Kinematic analysis confirms the top-to-the SSE transport along the BT. Several structural facies have been identified by means of detailed structural mapping and sampled from the damage zone (from within both the hanging- and the footwall blocks) and the PSS. The outcrop structural characterization has revealed a number of physically juxtaposed, yet different, structural facies: i) cohesive, weakly foliated proto- to ultracataclasite; ii) uncohesive, clay-rich gouge; iii) foliated domains with SC-C’ structures. Relatively unstrained host rock lithons are wrapped by these variably strained domains. Petrographic and microstructural analyses show evidence of pervasive pressure solution, with abundant stylolites, slickolites and foliated domains indicating an overall ductile behaviour. Calcite veins are also common in all recognised structural facies showing mutual cross-cutting relationships with the pressure-solution seams. This structural characterization has provided the basis for detailed image analysis of selected cataclastic textures to calculate fractal parameters for the particle size distribution (Ds) and morphology (Dr) of the clasts aiming at better understanding the cataclastic flow active in the BT fault rocks. Results from a range of representative samples suggest corrosive wear to be the main cataclastic process (Ds 1,41 ÷ 2,00; Dr 1,51 ÷ 1,88). Cathodoluminescence imaging revealed multiple generations of cement and permitted discriminating the first-order chemical characteristics of parental fluids and constraining the relationships between calcite veining and cementation. Two syn-tectonic cements have been identified: i) a bright-orange cement, preferentially surrounding carbonate clasts with highly irregular margins, indicative of the involvement of carbonate-reactive fluids; ii) a dull, homogeneous brown/black cement coexisting with a siliceous matrix, mantled clasts and local sigmoidal structures. The latter is at times observed as thin injections and fluidized structures. Our preliminary results suggest that overall deformation was accommodated by creep and low-T crystal-plastic deformation possibly during inter-seismic phases as indicated by the presence of pressure-solution seams and foliated fabrics. Transient spikes of coseismic rupturing possibly promoted by multiple batches of overpressured fluids were accompanied by significant cataclasis and brittle strain localization.
How to cite: Diamanti, R., Zuccari, C., Bonini, S., Vignaroli, G., and Viola, G.: Textural evolution and fluid-rock interaction during upper crustal, seismic deformation: Insights from the carbonate-dominated fault rock suite of the Belluno Thrust, Italian Southern Alps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5851, https://doi.org/10.5194/egusphere-egu2020-5851, 2020.
EGU2020-19184 | Displays | TS3.5
Long-term burial history and orogenic-scale fluid flow depicted from stable isotopes and stylolite paleopiezometry in the Umbria-Marches arcuate belt (Northern Apennines, Italy).Nicolas Beaudoin, Aurélie Labeur, Olivier Lacombe, Guilhem Hoareau, Marta Marchegiano, Cédric John, Daniel Koehn, Andrea Billi, Adrian Boyce, Christophe Pecheyran, and Jean-Paul Callot
Faults, joints and stylolites are ubiquitous features in fold-and-thrust belts, and have been used for decades to reconstruct the past fluid flow (or plumbing system) at the scale of folded reservoirs/basins. The textural and geochemical study of the minerals filling the fractures makes it possible to unravel the history of fluid flow in an orogen, when combined with a knowledge of the burial history and/or of the paleothermal gradient. In most cases, the latter derives from the former, itself often argued over, limiting the interpretations of past fluid temperatures. Yet, recent methodological developments applied to carbonates and calcite fillings provide new perspectives for a more accurate reconstruction of the temperature, pressure and timing of the fluids that were present in the strata at the time they deformed, at every stage of fold development. Indeed, the temperature at which fluids precipitated can be obtained by Δ47CO2 clumped isotopes while the timing of calcite precipitation in veins and faults is given by U-Pb absolute dating. Also, the maximum burial depth of strata before contraction can be estimated using sedimentary stylolite paleopiezometry, hence in a way free of any consideration about the geothermal gradient.
These techniques were jointly applied at the scale of the Umbria-Marches arcuate belt (UMAR, Northen Apennines, Italy). Mesoscale faults and vein sets were measured and sampled in the Cretaceous-Eocene rocks. Focusing on those fractures that developed during Layer Parallel Shortening (LPS, i.e. oriented NE-SW to E-W) and during folding (i.e. oriented parallel to local fold axis), paleofluid sources, temperatures and timing were reconstructed using U-Pb absolute dating, Δ47CO2 clumped isotopes as well as δ18O, δ13C, and 87/86Sr signatures of calcite veins. Results show a regional divide in the fluid system, with most of the belt including the foreland recording a fluid system involving basinal brines resulting at various degree from fluid-rock interactions (FRI) between pristine marine fluids (δ18Ofluid= 0‰ SMOW) and surrounding limestones (δ18Ofluid= 10‰ SMOW). Precipitation temperatures (35°C to 75°C) appear consistent with the burial history unraveled by sedimentary stylolite roughness paleopiezometry (600 m to 1500m in the range) and estimated geothermal gradient (23°C/km, Caricchi et al., 2004). As the degree of FRI increases forelandward, we propose a lateral, strata-bound, squeegee-type migration of fluids during folding and thrusting. In the western hinterland however, the fluid system rather involves hydrothermal fluids with a higher degree of FRI, the corresponding precipitation temperatures (100°C to 130°C) of which are inconsistent with local maximum burial (1500m). As the Sr radiogenic signatures preclude any deep origin of the fluids, we propose that the fluid system prevailing in the hinterland during LPS reflects the eastward migration of formational fluids originating from the Tuscan basin, located west from the UMAR, where studied Cretaceous rocks were buried under more than 4 km of sediments during the Miocene.
Beyond being the first combination of paleofluid geochemistry and burial estimates through paleopiezometry, this fluid flow model illustrates how the large scale structures may control the fluid system at the scale of a mountain belt.
How to cite: Beaudoin, N., Labeur, A., Lacombe, O., Hoareau, G., Marchegiano, M., John, C., Koehn, D., Billi, A., Boyce, A., Pecheyran, C., and Callot, J.-P.: Long-term burial history and orogenic-scale fluid flow depicted from stable isotopes and stylolite paleopiezometry in the Umbria-Marches arcuate belt (Northern Apennines, Italy)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19184, https://doi.org/10.5194/egusphere-egu2020-19184, 2020.
Faults, joints and stylolites are ubiquitous features in fold-and-thrust belts, and have been used for decades to reconstruct the past fluid flow (or plumbing system) at the scale of folded reservoirs/basins. The textural and geochemical study of the minerals filling the fractures makes it possible to unravel the history of fluid flow in an orogen, when combined with a knowledge of the burial history and/or of the paleothermal gradient. In most cases, the latter derives from the former, itself often argued over, limiting the interpretations of past fluid temperatures. Yet, recent methodological developments applied to carbonates and calcite fillings provide new perspectives for a more accurate reconstruction of the temperature, pressure and timing of the fluids that were present in the strata at the time they deformed, at every stage of fold development. Indeed, the temperature at which fluids precipitated can be obtained by Δ47CO2 clumped isotopes while the timing of calcite precipitation in veins and faults is given by U-Pb absolute dating. Also, the maximum burial depth of strata before contraction can be estimated using sedimentary stylolite paleopiezometry, hence in a way free of any consideration about the geothermal gradient.
These techniques were jointly applied at the scale of the Umbria-Marches arcuate belt (UMAR, Northen Apennines, Italy). Mesoscale faults and vein sets were measured and sampled in the Cretaceous-Eocene rocks. Focusing on those fractures that developed during Layer Parallel Shortening (LPS, i.e. oriented NE-SW to E-W) and during folding (i.e. oriented parallel to local fold axis), paleofluid sources, temperatures and timing were reconstructed using U-Pb absolute dating, Δ47CO2 clumped isotopes as well as δ18O, δ13C, and 87/86Sr signatures of calcite veins. Results show a regional divide in the fluid system, with most of the belt including the foreland recording a fluid system involving basinal brines resulting at various degree from fluid-rock interactions (FRI) between pristine marine fluids (δ18Ofluid= 0‰ SMOW) and surrounding limestones (δ18Ofluid= 10‰ SMOW). Precipitation temperatures (35°C to 75°C) appear consistent with the burial history unraveled by sedimentary stylolite roughness paleopiezometry (600 m to 1500m in the range) and estimated geothermal gradient (23°C/km, Caricchi et al., 2004). As the degree of FRI increases forelandward, we propose a lateral, strata-bound, squeegee-type migration of fluids during folding and thrusting. In the western hinterland however, the fluid system rather involves hydrothermal fluids with a higher degree of FRI, the corresponding precipitation temperatures (100°C to 130°C) of which are inconsistent with local maximum burial (1500m). As the Sr radiogenic signatures preclude any deep origin of the fluids, we propose that the fluid system prevailing in the hinterland during LPS reflects the eastward migration of formational fluids originating from the Tuscan basin, located west from the UMAR, where studied Cretaceous rocks were buried under more than 4 km of sediments during the Miocene.
Beyond being the first combination of paleofluid geochemistry and burial estimates through paleopiezometry, this fluid flow model illustrates how the large scale structures may control the fluid system at the scale of a mountain belt.
How to cite: Beaudoin, N., Labeur, A., Lacombe, O., Hoareau, G., Marchegiano, M., John, C., Koehn, D., Billi, A., Boyce, A., Pecheyran, C., and Callot, J.-P.: Long-term burial history and orogenic-scale fluid flow depicted from stable isotopes and stylolite paleopiezometry in the Umbria-Marches arcuate belt (Northern Apennines, Italy)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19184, https://doi.org/10.5194/egusphere-egu2020-19184, 2020.
EGU2020-8850 | Displays | TS3.5
Thermochronology and REE analyses as new tools to track thermal anomaly and fluid flow along a crustal scale fault (Têt fault, French Pyrenees)Gaétan Milesi, Monié Patrick, Philippe Münch, Roger Soliva, Sylvain Mayolle, Audrey Taillefer, Olivier Bruguier, Mathieu Bellanger, Michaël Bonno, and Céline Martin
The Têt fault is a crustal scale major fault in the eastern Pyrenees that displays about 30 hot springs along its surface trace with temperatures between 29°C and 73°C. The regional process of fluid circulation at depth has previously been highlighted by thermal numerical modelling supported by hydrochemical analyses and tectonic study. Numerical modelling suggests the presence of a strong subsurface anomaly of temperature along-fault (locally > 90°C/km), governed by topography-driven meteoric fluid upflow through the fault damage zone (advection). On the basis of this modelling, we focused our thermochronological study on 30 samples collected close and between two hot spring clusters in both the hanging wall and the footwall of the Têt fault, where the most important thermal anomaly is recorded by models. We analysed apatite using (U-Th)/He (AHe) dating combined with REE analyses on the same dated grains.
Along the fault, AHe ages are in a range of 26 to 8 Ma in the footwall and 43 and 18 Ma in the hanging wall, and only few apatite grains have been impacted by hydrothermalism near the St-Thomas hot spring cluster. By contrast, particularly young AHe ages below 6 Ma, correlated to REE depletion, are found around the Thuès-les-bains hot spring cluster. These very young ages are therefore interpreted as thermal resetting due to an important hydrothermal activity. A thermal anomaly can be mapped and appears restricted to 1 km around this cluster of hot springs, i.e. more restricted than the size of the anomaly predicted by numerical models. These results reveal that AHe dating and REE analyses can be used to highlight neo- or paleo-hydrothermal anomaly recorded by rocks along faults.
This study brings new elements to discuss the onset of the hydrothermal circulations and consequences on AHe and REE mobilisation, and suggest a strong heterogeneity of the hydrothermal flow pattern into the fault damage zone. Moreover, this study suggests that crustal scale faults adjacent to reliefs can localise narrow high hydrothermal flow and important geothermal gradient. Besides these results, this study provides new constraints for geothermal exploration around crustal faults, as well as a discussion on the use of thermochronometers into fault damage zones.
How to cite: Milesi, G., Patrick, M., Münch, P., Soliva, R., Mayolle, S., Taillefer, A., Bruguier, O., Bellanger, M., Bonno, M., and Martin, C.: Thermochronology and REE analyses as new tools to track thermal anomaly and fluid flow along a crustal scale fault (Têt fault, French Pyrenees), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8850, https://doi.org/10.5194/egusphere-egu2020-8850, 2020.
The Têt fault is a crustal scale major fault in the eastern Pyrenees that displays about 30 hot springs along its surface trace with temperatures between 29°C and 73°C. The regional process of fluid circulation at depth has previously been highlighted by thermal numerical modelling supported by hydrochemical analyses and tectonic study. Numerical modelling suggests the presence of a strong subsurface anomaly of temperature along-fault (locally > 90°C/km), governed by topography-driven meteoric fluid upflow through the fault damage zone (advection). On the basis of this modelling, we focused our thermochronological study on 30 samples collected close and between two hot spring clusters in both the hanging wall and the footwall of the Têt fault, where the most important thermal anomaly is recorded by models. We analysed apatite using (U-Th)/He (AHe) dating combined with REE analyses on the same dated grains.
Along the fault, AHe ages are in a range of 26 to 8 Ma in the footwall and 43 and 18 Ma in the hanging wall, and only few apatite grains have been impacted by hydrothermalism near the St-Thomas hot spring cluster. By contrast, particularly young AHe ages below 6 Ma, correlated to REE depletion, are found around the Thuès-les-bains hot spring cluster. These very young ages are therefore interpreted as thermal resetting due to an important hydrothermal activity. A thermal anomaly can be mapped and appears restricted to 1 km around this cluster of hot springs, i.e. more restricted than the size of the anomaly predicted by numerical models. These results reveal that AHe dating and REE analyses can be used to highlight neo- or paleo-hydrothermal anomaly recorded by rocks along faults.
This study brings new elements to discuss the onset of the hydrothermal circulations and consequences on AHe and REE mobilisation, and suggest a strong heterogeneity of the hydrothermal flow pattern into the fault damage zone. Moreover, this study suggests that crustal scale faults adjacent to reliefs can localise narrow high hydrothermal flow and important geothermal gradient. Besides these results, this study provides new constraints for geothermal exploration around crustal faults, as well as a discussion on the use of thermochronometers into fault damage zones.
How to cite: Milesi, G., Patrick, M., Münch, P., Soliva, R., Mayolle, S., Taillefer, A., Bruguier, O., Bellanger, M., Bonno, M., and Martin, C.: Thermochronology and REE analyses as new tools to track thermal anomaly and fluid flow along a crustal scale fault (Têt fault, French Pyrenees), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8850, https://doi.org/10.5194/egusphere-egu2020-8850, 2020.
EGU2020-15407 | Displays | TS3.5
Tectonic control on crustal degassing in continental region: the role of rock fracturationDario Buttitta, Antonio Caracausi, Rocco Favara, Lauro Chiaraluce, Maurizio Gasparo Morticelli, and Attilio Sulli
Degassing of volatiles across the Earth crust towards the atmosphere is mainly controlled by long last diffusion. However, it can also be episodic. In fact, tectonic control of solid phase release of radiogenic helium (4He) due to, e.g. fracturing, may contribute to explain variance of the continental 4He degassing flux over multiple time and space scales. Rock rheology have a controlling influence on a wide range of crustal-scale processes including fluid flow, tectonic deformations and seismicity. Though faults comprise a small volume of the crust, they influence the mechanical and fluid flow properties of the crust, and are mechanisms for accommodating most of the elastic strain in the crust through a variety of slip-behaviours. Helium isotopes (3He,4He) are useful tracers for investigating many important geological processes because helium is a stable and conservative nuclide that does not take part in any chemical or biological process. Indeed, 4He released from rocks in the porefluid can be used to trace the deformation of rocks in a field of stress [Bauer 2017; Torgersen and O’Donnell 1991]. In fact, a volume of rock starts to be affected by micro-fractures from since it is subjected to stress conditions exceeding about half its yield strength [Bauer, 2017]. Hence, the network of fractures evolves in a volume of rock progressively increase as a function of the evolution of deformation, improving the release of 4He that is trapped since its production. Consequently, 4He in natural fluids that outgas in a region of active tectonic can record the evolution of the field of stress and this volatile component could be used to trace changes in stress and deformation field. For the purpose of quantifying the amount of 4He present in the geological traps that feed the mud volcanoes of Regnano-Nirano mud volcanoes systems (Bonini et al., 2007), in the north Italy, in our study we have reconstructed the 3D geological model of the reservoirs, and proceeded to estimate the gas contained in them. Fluids emitted from these systems are thermogenic-CH4 rich, which vertically migrates towards the surface. Helium is in traces and its isotopic signature (≈0.01-0.02Ra, Ra is the 3He/4He in air) shows that 4He is mainly produced in the crust by U-Th decay. We have found that the present 4He is greater than what should be available taking into account only the steady-state crustal production. Therefore, we compared the excess helium present in the reservoirs with the contribution coming from the seismic activity of the area, which is sufficient to explain this excess. Our study highlights that an intense fracturing of a volume of rock, due to the recent seismicity below the studied area, may explain the accumulation of helium in the reservoir higher than the steady-state condition. Therefore, the effective vertical rate of fluid transport in the Earth's continental crust can be characterized by episodic events controlled by fracturing.
Bonini (2007) - JGRes Solid Earth
Torgersen & O’Donnell (1991) - GRL, vol.18
Bauer (2017) - SAND2017-9438
How to cite: Buttitta, D., Caracausi, A., Favara, R., Chiaraluce, L., Gasparo Morticelli, M., and Sulli, A.: Tectonic control on crustal degassing in continental region: the role of rock fracturation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15407, https://doi.org/10.5194/egusphere-egu2020-15407, 2020.
Degassing of volatiles across the Earth crust towards the atmosphere is mainly controlled by long last diffusion. However, it can also be episodic. In fact, tectonic control of solid phase release of radiogenic helium (4He) due to, e.g. fracturing, may contribute to explain variance of the continental 4He degassing flux over multiple time and space scales. Rock rheology have a controlling influence on a wide range of crustal-scale processes including fluid flow, tectonic deformations and seismicity. Though faults comprise a small volume of the crust, they influence the mechanical and fluid flow properties of the crust, and are mechanisms for accommodating most of the elastic strain in the crust through a variety of slip-behaviours. Helium isotopes (3He,4He) are useful tracers for investigating many important geological processes because helium is a stable and conservative nuclide that does not take part in any chemical or biological process. Indeed, 4He released from rocks in the porefluid can be used to trace the deformation of rocks in a field of stress [Bauer 2017; Torgersen and O’Donnell 1991]. In fact, a volume of rock starts to be affected by micro-fractures from since it is subjected to stress conditions exceeding about half its yield strength [Bauer, 2017]. Hence, the network of fractures evolves in a volume of rock progressively increase as a function of the evolution of deformation, improving the release of 4He that is trapped since its production. Consequently, 4He in natural fluids that outgas in a region of active tectonic can record the evolution of the field of stress and this volatile component could be used to trace changes in stress and deformation field. For the purpose of quantifying the amount of 4He present in the geological traps that feed the mud volcanoes of Regnano-Nirano mud volcanoes systems (Bonini et al., 2007), in the north Italy, in our study we have reconstructed the 3D geological model of the reservoirs, and proceeded to estimate the gas contained in them. Fluids emitted from these systems are thermogenic-CH4 rich, which vertically migrates towards the surface. Helium is in traces and its isotopic signature (≈0.01-0.02Ra, Ra is the 3He/4He in air) shows that 4He is mainly produced in the crust by U-Th decay. We have found that the present 4He is greater than what should be available taking into account only the steady-state crustal production. Therefore, we compared the excess helium present in the reservoirs with the contribution coming from the seismic activity of the area, which is sufficient to explain this excess. Our study highlights that an intense fracturing of a volume of rock, due to the recent seismicity below the studied area, may explain the accumulation of helium in the reservoir higher than the steady-state condition. Therefore, the effective vertical rate of fluid transport in the Earth's continental crust can be characterized by episodic events controlled by fracturing.
Bonini (2007) - JGRes Solid Earth
Torgersen & O’Donnell (1991) - GRL, vol.18
Bauer (2017) - SAND2017-9438
How to cite: Buttitta, D., Caracausi, A., Favara, R., Chiaraluce, L., Gasparo Morticelli, M., and Sulli, A.: Tectonic control on crustal degassing in continental region: the role of rock fracturation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15407, https://doi.org/10.5194/egusphere-egu2020-15407, 2020.
EGU2020-15861 | Displays | TS3.5
Faults controlling geothermal fluid flow in a karst geothermal system (Western Alpine Molasse Basin, France and Switzerland)Giovanni Luca Cardello and Michel Meyer
Karst geothermal systems fluid flow is dominated by structurally controlled porosity, which constrains the paths of aquifer recharge and the upwell of geothermal fluids. In fold-and-thrust belt settings associated with continental collision, geothermal fields occur within basins generally interested by low-enthalpy geothermal systems. Despite that, the deeper and warmer levels of multiply stratified aquifers within the detached sedimentary covers are vertically connected to shallower depths by high-angle faults, thus making of them interesting targets for exploration.
In the frame of the geothermal exploration steered by the Geneva Canton, this work aims at determining how fracture connectivity, orientation and permeability anisotropy has implications on fluid flow within high-angle faults. Recent software development (e.g., FracPaQ) allows to quantify such interconnection providing insights into spatial variation of multiscale fault-controlled porosity in order to have dynamic feedbacks between fluid flow, permeability rise/fall. We use the inner Jura fold-and-thrust belt and the other carbonate relieves surrounding Geneva as an outcrop analogue for the deeper carbonate reservoir, lying at depth beneath the siliciclastic Molasse deposits. Hereby, we present new structural and morphostructural lineament maps and scan box analyses from outcrops that provide a multiscale analysis on fracturing across the study area. The sampling sites are representative of fractured fold hinges constituted of Mesozoic carbonates crossed by high-angle faults.
The map analysis show that the late Oligocene-early Miocene growing carbonate anticlines are shaped by a series of fore- and back-thrusts resulting in salient-and-recess curvy thrusts accommodating different amount of shortening across high-angle tear-faults. With the support of high-resolution LIDAR images, we observe that at the large scale (e.g., five kilometers), as fault zone broadens across transfer zones, the background fracture network is more intense at the salient flanks. Major faults occur as segmented, thus not providing near-surface structure capable of giving any earthquake significantly larger than the already measured ones (e.g., ML 5.3, Epagny earthquake 1996). Our preliminary results identify the W- and the NNW- striking systems strike-slip faults as the preferred patterns of fluid flow. Cross-cutting relationships vary with their position into the bended belt, thus making them suitable to be multiply reactivated during the Jura arc indentation. At the outcrop scale, the most mature fault zones associated with larger displacement are characterized by high fracture intensity and connectivity. Field evidences show that NNW- and W/NW- striking systems are vein-rich whereas N- and NE-striking systems are accompanied by open fracture sets although they may work with opposite fluid-flow vertical directivity. Mechanical and regional chronological development of the fracture network is also discussed as related to the regional fault evolution.
How to cite: Cardello, G. L. and Meyer, M.: Faults controlling geothermal fluid flow in a karst geothermal system (Western Alpine Molasse Basin, France and Switzerland), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15861, https://doi.org/10.5194/egusphere-egu2020-15861, 2020.
Karst geothermal systems fluid flow is dominated by structurally controlled porosity, which constrains the paths of aquifer recharge and the upwell of geothermal fluids. In fold-and-thrust belt settings associated with continental collision, geothermal fields occur within basins generally interested by low-enthalpy geothermal systems. Despite that, the deeper and warmer levels of multiply stratified aquifers within the detached sedimentary covers are vertically connected to shallower depths by high-angle faults, thus making of them interesting targets for exploration.
In the frame of the geothermal exploration steered by the Geneva Canton, this work aims at determining how fracture connectivity, orientation and permeability anisotropy has implications on fluid flow within high-angle faults. Recent software development (e.g., FracPaQ) allows to quantify such interconnection providing insights into spatial variation of multiscale fault-controlled porosity in order to have dynamic feedbacks between fluid flow, permeability rise/fall. We use the inner Jura fold-and-thrust belt and the other carbonate relieves surrounding Geneva as an outcrop analogue for the deeper carbonate reservoir, lying at depth beneath the siliciclastic Molasse deposits. Hereby, we present new structural and morphostructural lineament maps and scan box analyses from outcrops that provide a multiscale analysis on fracturing across the study area. The sampling sites are representative of fractured fold hinges constituted of Mesozoic carbonates crossed by high-angle faults.
The map analysis show that the late Oligocene-early Miocene growing carbonate anticlines are shaped by a series of fore- and back-thrusts resulting in salient-and-recess curvy thrusts accommodating different amount of shortening across high-angle tear-faults. With the support of high-resolution LIDAR images, we observe that at the large scale (e.g., five kilometers), as fault zone broadens across transfer zones, the background fracture network is more intense at the salient flanks. Major faults occur as segmented, thus not providing near-surface structure capable of giving any earthquake significantly larger than the already measured ones (e.g., ML 5.3, Epagny earthquake 1996). Our preliminary results identify the W- and the NNW- striking systems strike-slip faults as the preferred patterns of fluid flow. Cross-cutting relationships vary with their position into the bended belt, thus making them suitable to be multiply reactivated during the Jura arc indentation. At the outcrop scale, the most mature fault zones associated with larger displacement are characterized by high fracture intensity and connectivity. Field evidences show that NNW- and W/NW- striking systems are vein-rich whereas N- and NE-striking systems are accompanied by open fracture sets although they may work with opposite fluid-flow vertical directivity. Mechanical and regional chronological development of the fracture network is also discussed as related to the regional fault evolution.
How to cite: Cardello, G. L. and Meyer, M.: Faults controlling geothermal fluid flow in a karst geothermal system (Western Alpine Molasse Basin, France and Switzerland), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15861, https://doi.org/10.5194/egusphere-egu2020-15861, 2020.
EGU2020-4762 | Displays | TS3.5 | Highlight
U-Pb calcite dating and isotopic fluid signatures of extensional fault gouges affecting the Penninic Frontal Thrust : implications for exhumation of the seismogenic zone.Antonin Bilau, Yann Rolland, Stéphane Schwartz, Thierry Dumont, Benjamin Brigaud, Cécile Gautheron, Rosella Pinna-Jamme, Pierre Deschamps, Nicolas Godeau, Abel Guihou, and Jérémie Melleton
Coupled fluid characterization and absolute dating of fracture networks may provide insights into the understanding of critical stages of evolution of a growing orogen. As a result of the collision between the European and Apulian plates, the Alps have experienced several evolutionary stages comprising continental subduction, nappe stacking, thick- to thin-skin tectonics in relation with the frontal propagation of a fold and thrust belt, and extensional reactivation of the major Penninic Frontal Thrust (PFT). Current evolution of the orogen (Tricart et al., 2001, 2007 and Sue et al., 2007) shows an ongoing extensional seismic activity along PFT while borders of the orogenic system remain in compression. The transition from compression to extension along the PFT remains unconstrained.
This study aims to constrain the time of the PFT inversion and provide a characterization of the tectonic structures through time during the formation of upper Durance normal fault system. For this, we applied several novel dating techniques (in-situ U-Pb calcite and (U-Th)/He hematite dating techniques). In addition, we determined the geochemical signature of the fluids trapped (calcite crystallization) deformation by δ13C and δ18O stable isotope analysis of calcites to constrain the fluid reservoirs, and thus the size of the involved tectonic structures. Stable isotopes show that the fluids associated with the early extensive structures bear isotopic signatures close to those of their host rocks, indicating a fluid at equilibrium and thus a close system in agreement with the small (mm-cm) size of mostly ductile structures. In a second stage, connection of veins and fractures lead to major fault formation (metric to kilometric scale structures) show isotopic signatures in agreement with ascending metamorphic fluids, featuring an open system along the PFT.
U-Pb dating on calcite was successful on several samples despite high common lead concentrations. Two fault gouge samples associated with kilometric scale faults gave ages between 3.5 Ma and 2.5 Ma. These structures are a signature of the paleoseismic activity wich occured some 2.5-3.5 Ma ago when the wall domain of PFT was few km depth. Moreover, (U-Th)/He hematite dating was used on slickensides of the same fault system. Preliminary ages of 2.5, 1.5 and 15 Ma were obtained. The 15 Ma age is interpreted as a minimum age inversion of the PFT, while other ages overlap with the U-Pb calcite ages. This multidisciplinary inverstigation in the Western Alps helps to constrain the exhumation history of the paleo-seismogenic zone related to the inversion of the PFT.
How to cite: Bilau, A., Rolland, Y., Schwartz, S., Dumont, T., Brigaud, B., Gautheron, C., Pinna-Jamme, R., Deschamps, P., Godeau, N., Guihou, A., and Melleton, J.: U-Pb calcite dating and isotopic fluid signatures of extensional fault gouges affecting the Penninic Frontal Thrust : implications for exhumation of the seismogenic zone., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4762, https://doi.org/10.5194/egusphere-egu2020-4762, 2020.
Coupled fluid characterization and absolute dating of fracture networks may provide insights into the understanding of critical stages of evolution of a growing orogen. As a result of the collision between the European and Apulian plates, the Alps have experienced several evolutionary stages comprising continental subduction, nappe stacking, thick- to thin-skin tectonics in relation with the frontal propagation of a fold and thrust belt, and extensional reactivation of the major Penninic Frontal Thrust (PFT). Current evolution of the orogen (Tricart et al., 2001, 2007 and Sue et al., 2007) shows an ongoing extensional seismic activity along PFT while borders of the orogenic system remain in compression. The transition from compression to extension along the PFT remains unconstrained.
This study aims to constrain the time of the PFT inversion and provide a characterization of the tectonic structures through time during the formation of upper Durance normal fault system. For this, we applied several novel dating techniques (in-situ U-Pb calcite and (U-Th)/He hematite dating techniques). In addition, we determined the geochemical signature of the fluids trapped (calcite crystallization) deformation by δ13C and δ18O stable isotope analysis of calcites to constrain the fluid reservoirs, and thus the size of the involved tectonic structures. Stable isotopes show that the fluids associated with the early extensive structures bear isotopic signatures close to those of their host rocks, indicating a fluid at equilibrium and thus a close system in agreement with the small (mm-cm) size of mostly ductile structures. In a second stage, connection of veins and fractures lead to major fault formation (metric to kilometric scale structures) show isotopic signatures in agreement with ascending metamorphic fluids, featuring an open system along the PFT.
U-Pb dating on calcite was successful on several samples despite high common lead concentrations. Two fault gouge samples associated with kilometric scale faults gave ages between 3.5 Ma and 2.5 Ma. These structures are a signature of the paleoseismic activity wich occured some 2.5-3.5 Ma ago when the wall domain of PFT was few km depth. Moreover, (U-Th)/He hematite dating was used on slickensides of the same fault system. Preliminary ages of 2.5, 1.5 and 15 Ma were obtained. The 15 Ma age is interpreted as a minimum age inversion of the PFT, while other ages overlap with the U-Pb calcite ages. This multidisciplinary inverstigation in the Western Alps helps to constrain the exhumation history of the paleo-seismogenic zone related to the inversion of the PFT.
How to cite: Bilau, A., Rolland, Y., Schwartz, S., Dumont, T., Brigaud, B., Gautheron, C., Pinna-Jamme, R., Deschamps, P., Godeau, N., Guihou, A., and Melleton, J.: U-Pb calcite dating and isotopic fluid signatures of extensional fault gouges affecting the Penninic Frontal Thrust : implications for exhumation of the seismogenic zone., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4762, https://doi.org/10.5194/egusphere-egu2020-4762, 2020.
EGU2020-7405 | Displays | TS3.5
Large-scale intraplate deformation caused the cementation of Jurassic carbonates in the eastern Paris BasinThomas Blaise, Benjamin Brigaud, and Cédric Carpentier
In the eastern Paris Basin, the Oxfordian (Upper Jurassic) and Bathonian to Bajocian (Middle Jurassic) carbonate platforms have been intensively cemented, despite rather low burial (< 1000 m). These limestone units are separated from each other by a 150 m thick succession of Callovian - Oxfordian clay-rich rocks. These claystones are currently under investigation by the French national radioactive waste management agency (Andra).
Most of the initial porosity in the Middle and Upper Jurassic limestones is now sealed by successive stages of calcite precipitation, which have been thoroughly characterized both petrographically and geochemically over the last fifteen years (Buschaert et al., 2004; Vincent et al., 2007; Brigaud et al., 2009; André et al., 2010; Carpentier et al., 2014). However, despite these research efforts, the timing and temperature of the fluids involved in the cementation of these carbonate rocks were still uncertain.
Here, we present and discuss newly acquired ∆47 temperatures and U-Pb ages of calcite cements filling the intergranular pore space, as well as vugs and microfractures.
The Middle Jurassic limestones were largely cemented during the Late Jurassic / Early Cretaceous period, as shown by our new LA-ICP-MS U-Pb ages that agree with the previous Isotope Dilution-TIMS U-Pb age of 147.8 ± 3.8 Ma from Pisapia et al. (2017). This event is believed to be associated to the Bay of Biscay rifting. Our data also reveal a second and more discrete crystallization event during the Late Eocene / Oligocene period, related to the European Cenozoic Rift System (ECRIS). In both cases, calcite was precipitated from fluids in thermal disequilibrium with the host rocks.
By contrast, the Upper Jurassic limestones were largely affected by the successive deformation events that occurred during the Late Mesozoic / Cenozoic period. New LA-ICP-MS U-Pb ages acquired in ca. 200 µm-thick fractures reveal that calcite crystallized during three successive periods corresponding to the Pyrenean compression, the ECRIS extension and, finally, during the Alpine compression. These compression phases generated late stylolitization and subsequent dissolution/recrystallization in the Upper Jurassic limestones, while such tectonic features are rare in the Middle Jurassic.
Therefore, as opposed to the more conventional « burial-induced » model, our study highlights the role of stress propagation in the cementation of carbonate rocks hundreds of kilometers away from the rifting or collisional areas.
References:
Buschaert et al., 2004. Applied Geochemistry 19, 1201 – 1215. Vincent et al., 2007. Sedimentary Geology 197, 267 – 289. Brigaud et al., 2009. Sedimentary Geology 222, 161 – 180. André et al., 2010. Tectonophysics 490, 214 – 228. Carpentier et al., 2014. Marine and Petroleum Geology 53, 44 – 70. Pisapia et al., 2017. Journal of the Geological Society of London 175, 60 – 70.
How to cite: Blaise, T., Brigaud, B., and Carpentier, C.: Large-scale intraplate deformation caused the cementation of Jurassic carbonates in the eastern Paris Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7405, https://doi.org/10.5194/egusphere-egu2020-7405, 2020.
In the eastern Paris Basin, the Oxfordian (Upper Jurassic) and Bathonian to Bajocian (Middle Jurassic) carbonate platforms have been intensively cemented, despite rather low burial (< 1000 m). These limestone units are separated from each other by a 150 m thick succession of Callovian - Oxfordian clay-rich rocks. These claystones are currently under investigation by the French national radioactive waste management agency (Andra).
Most of the initial porosity in the Middle and Upper Jurassic limestones is now sealed by successive stages of calcite precipitation, which have been thoroughly characterized both petrographically and geochemically over the last fifteen years (Buschaert et al., 2004; Vincent et al., 2007; Brigaud et al., 2009; André et al., 2010; Carpentier et al., 2014). However, despite these research efforts, the timing and temperature of the fluids involved in the cementation of these carbonate rocks were still uncertain.
Here, we present and discuss newly acquired ∆47 temperatures and U-Pb ages of calcite cements filling the intergranular pore space, as well as vugs and microfractures.
The Middle Jurassic limestones were largely cemented during the Late Jurassic / Early Cretaceous period, as shown by our new LA-ICP-MS U-Pb ages that agree with the previous Isotope Dilution-TIMS U-Pb age of 147.8 ± 3.8 Ma from Pisapia et al. (2017). This event is believed to be associated to the Bay of Biscay rifting. Our data also reveal a second and more discrete crystallization event during the Late Eocene / Oligocene period, related to the European Cenozoic Rift System (ECRIS). In both cases, calcite was precipitated from fluids in thermal disequilibrium with the host rocks.
By contrast, the Upper Jurassic limestones were largely affected by the successive deformation events that occurred during the Late Mesozoic / Cenozoic period. New LA-ICP-MS U-Pb ages acquired in ca. 200 µm-thick fractures reveal that calcite crystallized during three successive periods corresponding to the Pyrenean compression, the ECRIS extension and, finally, during the Alpine compression. These compression phases generated late stylolitization and subsequent dissolution/recrystallization in the Upper Jurassic limestones, while such tectonic features are rare in the Middle Jurassic.
Therefore, as opposed to the more conventional « burial-induced » model, our study highlights the role of stress propagation in the cementation of carbonate rocks hundreds of kilometers away from the rifting or collisional areas.
References:
Buschaert et al., 2004. Applied Geochemistry 19, 1201 – 1215. Vincent et al., 2007. Sedimentary Geology 197, 267 – 289. Brigaud et al., 2009. Sedimentary Geology 222, 161 – 180. André et al., 2010. Tectonophysics 490, 214 – 228. Carpentier et al., 2014. Marine and Petroleum Geology 53, 44 – 70. Pisapia et al., 2017. Journal of the Geological Society of London 175, 60 – 70.
How to cite: Blaise, T., Brigaud, B., and Carpentier, C.: Large-scale intraplate deformation caused the cementation of Jurassic carbonates in the eastern Paris Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7405, https://doi.org/10.5194/egusphere-egu2020-7405, 2020.
EGU2020-4391 | Displays | TS3.5
Fault tectonic analysis of aftershocks of the 2011 Tohoku, Japan, earthquake: interaction between three different tectonic domains and approximation of stress magnitudePom-yong Choi
In order to elucidate the regional variation of stress field in the eastern part of Japan after the 2011 Tohoku earthquake of M=9.3, we tried to analyze focal mechanism data of earthquakes that occurred in 2011, presented by the Japan Meteorological Agency (JMA). Although earthquakes (aftershocks) occurred largely in the offshore area along the subduction zone of the Pacific plate under the North American and Eurasian plates, focal mechanism data presented by JMA are mainly those on land. For fault tectonic analysis, the suggested focal mechanism data are classified into appropriate populations on the basis of clusters and focal depths to reduce the bias and errors of stress tensors resulting from areal stress variation and varying vertical load. According to the results, the stress types of determined stress tensors consist of reverse, wrench and normal faulting ones. As for reverse faulting stresses in which the vertical load is the minimum principal stress axis, those of NW-SE compression prevail, which may be tightly related to northwestward movement of the Pacific plate. Those of E-W compression are determined in the continental crust deeper than about 9 km around Yamagata and in the lower part of subducting oceanic crust. In the Kanagawa and Chiba areas, determined stress tensors display NNW-SSE compression as well as NW-SE and E-W compressions. The NNW-SSE compression seems to be related to the movement of the Philippine Sea plate. Stress tensors of wrench faulting type are found in the continental crust far from the subduction zone of the Pacific plate, displaying NW-SE and E-W compressions in the shallower and deeper parts of crust, respectively. The E-W compression is presumably associated with the Himalayan tectonic domain. Determined stress tensors of normal faulting type show diverse extension directions: NW-SE extension in the coastal area, parallel to the Pacific compression, and E-W or NE-SW extension elsewhere. Especially, numerous focal mechanism data showing normal faulting stresses are present in the coastal area of Fukushima and Ibaraki, from which Poisson’s ratio of shallow crust was determined to be 0.25 to 0.27 using friction lines on Mohr’s circles and focal depths (or corresponding vertical loads). Additional horizontal stress related to the northwestward motion of the Pacific plate was estimated to be 46, 122 and 286 MPa in three groups of 0 to1.5, 1.5 to 4.5 and 3.5 to 11.5 kilometers in depth, respectively.
How to cite: Choi, P.: Fault tectonic analysis of aftershocks of the 2011 Tohoku, Japan, earthquake: interaction between three different tectonic domains and approximation of stress magnitude, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4391, https://doi.org/10.5194/egusphere-egu2020-4391, 2020.
In order to elucidate the regional variation of stress field in the eastern part of Japan after the 2011 Tohoku earthquake of M=9.3, we tried to analyze focal mechanism data of earthquakes that occurred in 2011, presented by the Japan Meteorological Agency (JMA). Although earthquakes (aftershocks) occurred largely in the offshore area along the subduction zone of the Pacific plate under the North American and Eurasian plates, focal mechanism data presented by JMA are mainly those on land. For fault tectonic analysis, the suggested focal mechanism data are classified into appropriate populations on the basis of clusters and focal depths to reduce the bias and errors of stress tensors resulting from areal stress variation and varying vertical load. According to the results, the stress types of determined stress tensors consist of reverse, wrench and normal faulting ones. As for reverse faulting stresses in which the vertical load is the minimum principal stress axis, those of NW-SE compression prevail, which may be tightly related to northwestward movement of the Pacific plate. Those of E-W compression are determined in the continental crust deeper than about 9 km around Yamagata and in the lower part of subducting oceanic crust. In the Kanagawa and Chiba areas, determined stress tensors display NNW-SSE compression as well as NW-SE and E-W compressions. The NNW-SSE compression seems to be related to the movement of the Philippine Sea plate. Stress tensors of wrench faulting type are found in the continental crust far from the subduction zone of the Pacific plate, displaying NW-SE and E-W compressions in the shallower and deeper parts of crust, respectively. The E-W compression is presumably associated with the Himalayan tectonic domain. Determined stress tensors of normal faulting type show diverse extension directions: NW-SE extension in the coastal area, parallel to the Pacific compression, and E-W or NE-SW extension elsewhere. Especially, numerous focal mechanism data showing normal faulting stresses are present in the coastal area of Fukushima and Ibaraki, from which Poisson’s ratio of shallow crust was determined to be 0.25 to 0.27 using friction lines on Mohr’s circles and focal depths (or corresponding vertical loads). Additional horizontal stress related to the northwestward motion of the Pacific plate was estimated to be 46, 122 and 286 MPa in three groups of 0 to1.5, 1.5 to 4.5 and 3.5 to 11.5 kilometers in depth, respectively.
How to cite: Choi, P.: Fault tectonic analysis of aftershocks of the 2011 Tohoku, Japan, earthquake: interaction between three different tectonic domains and approximation of stress magnitude, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4391, https://doi.org/10.5194/egusphere-egu2020-4391, 2020.
EGU2020-5438 | Displays | TS3.5
Multiphase brittle tectonic evolution of the Mid-Norwegian margin, central Norway, reconstructed by remote sensing, paleostress inversion and K-Ar fault rock datingGiulia Tartaglia, Giulio Viola, Alberto Ceccato, Stefano Bernasconi, Roelant van der Lelij, and Thomas Scheiber
Basement terranes commonly contain complex fault networks developed during repeated episodes of brittle deformation. The Mid-Norwegian margin (from 62 to 63.8 °N) exposes a complexly fractured terrane formed mainly by Caledonian basement rocks. The margin recorded a prolonged brittle deformation history spanning the Devonian to Paleogene time interval. It is characterised by a pervasive NE-SW structural grain due to the ductile-brittle multiphase activity of the Møre-Trøndelag Fault Complex (MTFC).
In order to develop a time-constrained tectonic model of the area, we applied a multidisciplinary approach combining remote sensing, field work, paleostress inversion, microstructural analysis, mineralogical characterization, clumped isotope thermometry on carbonates and K-Ar dating of fault rocks from key representative faults. We present herein the preliminary structural-geochronological data of a still ongoing study of two regions along the Mid-Norwegian margin, the Hitra-Frøya and Kråkenes-Runde areas. These key areas represent the intersection regions between the Mid-Norwegian- and the other sectors of the margin.
The brittle structural record of the entire Mid-Norwegian margin was analysed by remote sensing of lineaments using high resolution LiDAR data followed by ground-truthing of the obtained results during field work. Three main sets of lineaments were identified: i) (E)NE-(W)SW-trending lineaments, parallel to the coastline and to the MTFC; ii) N(NW)-S(SE)-trending lineaments; iii) WNW-ESE-trending lineaments. The main sets of faults and fractures were further characterised by their fault rock association and coating. All generations of faults contain thin coatings of chlorite, variably thick epidote and quartz mineralisations and calcite veins and coatings, locally associated with acicular zeolite. Samples of calcite and related gouges were collected from different sets of faults. Carbonate clumped isotope thermometry constrains the range of temperature of calcite growth between 140 and 30 °C, indicating that calcite precipitated at different thermal conditions during a multiphase structural evolution. K-Ar data collected so far from synkinematic illite separated from fault gouges yield Jurassic-Paleogene ages.
The structural network of the margin is interpreted as reflecting a sequence of different deformation episodes. In order to resolve the orientation of the stress field for each recorded event, we applied paleostress inversion with the Win-Tensor software [1]. The preliminary results suggest that at least three tectonic stages affected the margin. A NE-SW strike-slip dominated transpression possibly reflects the late stages of the Caledonian orogenic cycle. A pure and oblique extensional (E)NE-(W)SW stage is associated with the Jurassic North Sea rifting, followed by a NW-SE Paleogene extensional reactivation observable throughout the margin.
To conclude, a new multidisciplinary database for the reconstruction of the brittle deformation history of the Mid-Norwegian margin is presented. The proposed approach aims to define the temporal and structural characterisation of each single tectonic episode. Such an approach is also pivotal toward the correlation with the deformation history of the corresponding offshore domains, as well as the comparison in time with other segments of the Norwegian margin.
[1] Delvaux, D. and Sperner, B. (2003). Stress tensor inversion from fault kinematic indicators and focal mechanism data: the TENSOR program. Geological Society, London, Special Publications, 212: 75-100
How to cite: Tartaglia, G., Viola, G., Ceccato, A., Bernasconi, S., van der Lelij, R., and Scheiber, T.: Multiphase brittle tectonic evolution of the Mid-Norwegian margin, central Norway, reconstructed by remote sensing, paleostress inversion and K-Ar fault rock dating, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5438, https://doi.org/10.5194/egusphere-egu2020-5438, 2020.
Basement terranes commonly contain complex fault networks developed during repeated episodes of brittle deformation. The Mid-Norwegian margin (from 62 to 63.8 °N) exposes a complexly fractured terrane formed mainly by Caledonian basement rocks. The margin recorded a prolonged brittle deformation history spanning the Devonian to Paleogene time interval. It is characterised by a pervasive NE-SW structural grain due to the ductile-brittle multiphase activity of the Møre-Trøndelag Fault Complex (MTFC).
In order to develop a time-constrained tectonic model of the area, we applied a multidisciplinary approach combining remote sensing, field work, paleostress inversion, microstructural analysis, mineralogical characterization, clumped isotope thermometry on carbonates and K-Ar dating of fault rocks from key representative faults. We present herein the preliminary structural-geochronological data of a still ongoing study of two regions along the Mid-Norwegian margin, the Hitra-Frøya and Kråkenes-Runde areas. These key areas represent the intersection regions between the Mid-Norwegian- and the other sectors of the margin.
The brittle structural record of the entire Mid-Norwegian margin was analysed by remote sensing of lineaments using high resolution LiDAR data followed by ground-truthing of the obtained results during field work. Three main sets of lineaments were identified: i) (E)NE-(W)SW-trending lineaments, parallel to the coastline and to the MTFC; ii) N(NW)-S(SE)-trending lineaments; iii) WNW-ESE-trending lineaments. The main sets of faults and fractures were further characterised by their fault rock association and coating. All generations of faults contain thin coatings of chlorite, variably thick epidote and quartz mineralisations and calcite veins and coatings, locally associated with acicular zeolite. Samples of calcite and related gouges were collected from different sets of faults. Carbonate clumped isotope thermometry constrains the range of temperature of calcite growth between 140 and 30 °C, indicating that calcite precipitated at different thermal conditions during a multiphase structural evolution. K-Ar data collected so far from synkinematic illite separated from fault gouges yield Jurassic-Paleogene ages.
The structural network of the margin is interpreted as reflecting a sequence of different deformation episodes. In order to resolve the orientation of the stress field for each recorded event, we applied paleostress inversion with the Win-Tensor software [1]. The preliminary results suggest that at least three tectonic stages affected the margin. A NE-SW strike-slip dominated transpression possibly reflects the late stages of the Caledonian orogenic cycle. A pure and oblique extensional (E)NE-(W)SW stage is associated with the Jurassic North Sea rifting, followed by a NW-SE Paleogene extensional reactivation observable throughout the margin.
To conclude, a new multidisciplinary database for the reconstruction of the brittle deformation history of the Mid-Norwegian margin is presented. The proposed approach aims to define the temporal and structural characterisation of each single tectonic episode. Such an approach is also pivotal toward the correlation with the deformation history of the corresponding offshore domains, as well as the comparison in time with other segments of the Norwegian margin.
[1] Delvaux, D. and Sperner, B. (2003). Stress tensor inversion from fault kinematic indicators and focal mechanism data: the TENSOR program. Geological Society, London, Special Publications, 212: 75-100
How to cite: Tartaglia, G., Viola, G., Ceccato, A., Bernasconi, S., van der Lelij, R., and Scheiber, T.: Multiphase brittle tectonic evolution of the Mid-Norwegian margin, central Norway, reconstructed by remote sensing, paleostress inversion and K-Ar fault rock dating, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5438, https://doi.org/10.5194/egusphere-egu2020-5438, 2020.
EGU2020-7788 | Displays | TS3.5
Estimation of paleostress from pore fluid pressure of the quartz veins and its significance in the Cu-Pb-Zn mineralization (Ambaji, Aravalli-Delhi mobile belt, NW India)Neeraj Kumar Sharma and Tapas Kumar Biswal
Quartz veins are produced from the crystallization of the last silica enriched hydrothermal phase from granitic magma circulating along the pre-existing fracture of rock. In many instances, these hydrothermal fluid act as a carrier for the ore minerals. The intrusion of quartz veins along fractures depends upon the tectonic stress conditions in the area. Fluid pressure (Pf) of these ascending liquids should be higher than the normal compressive stress (σn) to dilate the fractures. We are studying the quartz vein intrusion in the Cu‒Pb‒Zn mineralization belt of Ambaji, South Delhi terrane, Aravalli- Delhi mobile belt, NW India. The host rocks include mica schist, amphibolite, calc schist, talc tremolite schist, and four phases of granite intrusion (G0‒G3). The age of G0, G1, G2 and G3 granite are 960, 860, 800, and 750 Ma respectively. The rocks underwent three phases of folding (F1‒F3) and show greenschist to amphibolite facies metamorphism. The quartz vein intrusion is related to syn to post F3 folding and G3 granite magmatism. This final phase hydrothermal fluid extremely altered host rock and formed biotite-tourmaline-quartz and tremolite-actinolite-talc-chlorite greisen along the contact. The greisen host chalcopyrite-pyrite-galena-sphalerite mineralization suggesting the ore minerals were transported by the quartz vein. Vein orientation, stress condition, fluid pressure fluctuation, and fluid temperature can decide the fracture dilation and mineralization processes. Therefore, this work concentrates on the geometrical distribution of the vein orientation data. From this we deduced (i) girdle distribution pattern of vein data (ii) σ1 = 120º/75º, σ2 = 052º/07º, σ3 = 323º/07º indicate maximum extension was NW-SE and σ1σ2 plane strikes was N52ºE, (iii) θ2 =12º, θ3 = 40º and (iv) R'(driving pressure ratio) = 0.95, ϕ (tectonic stress ratio) = 0.90 indicates high value for R' leading to dilation of wide range of fractures. Further, the high ϕ value suggests uniaxial extension. Microscopic petrography of fluid inclusions shows three generations of inclusion like primary inclusion, secondary inclusion, and pseudosecondary inclusion. Most of the inclusion has aqueous and vapour phase and some inclusions show solid halite phase. We observed different types of trail bound of inclusion like intragranular inclusion, intergranular inclusion and transgranular inclusion, which suggest deformation and recrystallization in the rock. We are studying microthermometry analysis of fluid inclusion present in the quartz vein and trying to estimate the fluid pressure. With the help of fluid pressure, the 3D Mohr circle will be constructed and paleostress will be quantified. That will help in understanding the stress condition and mineralization in the rock.
Keywords: Veins, Fractures, Paleostress, 3D Mohr Circle, Mineralisation, Fluid Inclusion, Microthermometry
How to cite: Sharma, N. K. and Biswal, T. K.: Estimation of paleostress from pore fluid pressure of the quartz veins and its significance in the Cu-Pb-Zn mineralization (Ambaji, Aravalli-Delhi mobile belt, NW India) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7788, https://doi.org/10.5194/egusphere-egu2020-7788, 2020.
Quartz veins are produced from the crystallization of the last silica enriched hydrothermal phase from granitic magma circulating along the pre-existing fracture of rock. In many instances, these hydrothermal fluid act as a carrier for the ore minerals. The intrusion of quartz veins along fractures depends upon the tectonic stress conditions in the area. Fluid pressure (Pf) of these ascending liquids should be higher than the normal compressive stress (σn) to dilate the fractures. We are studying the quartz vein intrusion in the Cu‒Pb‒Zn mineralization belt of Ambaji, South Delhi terrane, Aravalli- Delhi mobile belt, NW India. The host rocks include mica schist, amphibolite, calc schist, talc tremolite schist, and four phases of granite intrusion (G0‒G3). The age of G0, G1, G2 and G3 granite are 960, 860, 800, and 750 Ma respectively. The rocks underwent three phases of folding (F1‒F3) and show greenschist to amphibolite facies metamorphism. The quartz vein intrusion is related to syn to post F3 folding and G3 granite magmatism. This final phase hydrothermal fluid extremely altered host rock and formed biotite-tourmaline-quartz and tremolite-actinolite-talc-chlorite greisen along the contact. The greisen host chalcopyrite-pyrite-galena-sphalerite mineralization suggesting the ore minerals were transported by the quartz vein. Vein orientation, stress condition, fluid pressure fluctuation, and fluid temperature can decide the fracture dilation and mineralization processes. Therefore, this work concentrates on the geometrical distribution of the vein orientation data. From this we deduced (i) girdle distribution pattern of vein data (ii) σ1 = 120º/75º, σ2 = 052º/07º, σ3 = 323º/07º indicate maximum extension was NW-SE and σ1σ2 plane strikes was N52ºE, (iii) θ2 =12º, θ3 = 40º and (iv) R'(driving pressure ratio) = 0.95, ϕ (tectonic stress ratio) = 0.90 indicates high value for R' leading to dilation of wide range of fractures. Further, the high ϕ value suggests uniaxial extension. Microscopic petrography of fluid inclusions shows three generations of inclusion like primary inclusion, secondary inclusion, and pseudosecondary inclusion. Most of the inclusion has aqueous and vapour phase and some inclusions show solid halite phase. We observed different types of trail bound of inclusion like intragranular inclusion, intergranular inclusion and transgranular inclusion, which suggest deformation and recrystallization in the rock. We are studying microthermometry analysis of fluid inclusion present in the quartz vein and trying to estimate the fluid pressure. With the help of fluid pressure, the 3D Mohr circle will be constructed and paleostress will be quantified. That will help in understanding the stress condition and mineralization in the rock.
Keywords: Veins, Fractures, Paleostress, 3D Mohr Circle, Mineralisation, Fluid Inclusion, Microthermometry
How to cite: Sharma, N. K. and Biswal, T. K.: Estimation of paleostress from pore fluid pressure of the quartz veins and its significance in the Cu-Pb-Zn mineralization (Ambaji, Aravalli-Delhi mobile belt, NW India) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7788, https://doi.org/10.5194/egusphere-egu2020-7788, 2020.
EGU2020-13864 | Displays | TS3.5
Determination of stress condition and friction coefficient from orientation distribution of outcrop-scale faultsKatsushi Sato
Friction coefficients along faults control the brittle strength of the earth's upper crust, although it is difficult to estimate them especially of ancient geological faults. This study proposes to estimate the friction coefficient of faults with stress condition which activated them by the following procedure. Stress tensor inversion using fault-slip data can calculate principal stress axes and a stress ratio, which allows us to draw a normalized Mohr’s circle. Assuming that faulting occurs when the ratio of shear stress to normal stress on the fault (the slip tendency) exceeds the friction coefficient, a linear boundary of distribution of points corresponding to the observed population of faults should be found on the Mohr diagram. The slope of the boundary (friction envelope) provides the friction coefficient. Since this method has a difficulty in the graphical recognition of the linear boundary, this study automated it by considering the fluctuations of fluid pressure and differential stress. The fluctuations yield a density distribution of points representing faults on the Mohr diagram according to the friction coefficient. Then we can find the optimal value of friction coefficient so as to explain the density distribution.
The method was applied to some examples of natural outcrop-scale faults. The first example is from the Pleistocene Kazusa Group, central Japan, which filled a forearc basin of the Sagami Trough. Stress inversion analysis showed WNW-ENE trending tensional stress with a low stress ratio. The friction coefficient was calculated to be about 0.7, which is typical value for sandstone.
Another example is from an underplated tectonic mélange in the Cretaceous to Paleogene Shimanto accretionary complex in southwest Japan along the Nankai Trough. The stress condition was determined to be an axial compression perpendicular to the foliation of shale matrix. The friction coefficient ranges from 0.1 to 0.3, which is extremely low indicating a weak plate boundary under the accretionary wedge.
How to cite: Sato, K.: Determination of stress condition and friction coefficient from orientation distribution of outcrop-scale faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13864, https://doi.org/10.5194/egusphere-egu2020-13864, 2020.
Friction coefficients along faults control the brittle strength of the earth's upper crust, although it is difficult to estimate them especially of ancient geological faults. This study proposes to estimate the friction coefficient of faults with stress condition which activated them by the following procedure. Stress tensor inversion using fault-slip data can calculate principal stress axes and a stress ratio, which allows us to draw a normalized Mohr’s circle. Assuming that faulting occurs when the ratio of shear stress to normal stress on the fault (the slip tendency) exceeds the friction coefficient, a linear boundary of distribution of points corresponding to the observed population of faults should be found on the Mohr diagram. The slope of the boundary (friction envelope) provides the friction coefficient. Since this method has a difficulty in the graphical recognition of the linear boundary, this study automated it by considering the fluctuations of fluid pressure and differential stress. The fluctuations yield a density distribution of points representing faults on the Mohr diagram according to the friction coefficient. Then we can find the optimal value of friction coefficient so as to explain the density distribution.
The method was applied to some examples of natural outcrop-scale faults. The first example is from the Pleistocene Kazusa Group, central Japan, which filled a forearc basin of the Sagami Trough. Stress inversion analysis showed WNW-ENE trending tensional stress with a low stress ratio. The friction coefficient was calculated to be about 0.7, which is typical value for sandstone.
Another example is from an underplated tectonic mélange in the Cretaceous to Paleogene Shimanto accretionary complex in southwest Japan along the Nankai Trough. The stress condition was determined to be an axial compression perpendicular to the foliation of shale matrix. The friction coefficient ranges from 0.1 to 0.3, which is extremely low indicating a weak plate boundary under the accretionary wedge.
How to cite: Sato, K.: Determination of stress condition and friction coefficient from orientation distribution of outcrop-scale faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13864, https://doi.org/10.5194/egusphere-egu2020-13864, 2020.
EGU2020-21186 | Displays | TS3.5
Strike-slip fault stress detected by paleostress analysis in paleoforearc basin: an example of the Miocene Tanabe Group, Southwest JapanNoriaki Abe and Katsushi Sato
The Miocene plate configuration along southwest Japan arc has been controversial as follows. According to Hall (1996), the Pacific Plate subducted dextrally against the Eurasia Plate before 15 Ma, whereas Seno and Maruyama (1984) suggested the Philippines Sea Plate subducted sinistrally. The shear sense of oblique subduction is possibly recorded as the deformation of forearc basin fill. This study performed a series of paleostress analyses by using outcrop-scale structures in the Miocene Tanabe Group to examine whether strike-slip fault stress conditions were detected or not and which sense of shear is expected along trench-parallel faults.
The study area extends roughly 10 km along the coastal area of the Shirahama Formation, the upper part of the Tanabe Group, Kii Peninsula, southwest Japan. The measured structures consist of outcrop-scale faults and veins. Fault displacements range from about several mm to 1 m. The thicknesses of veins are about several mm.
In total, 245 faults and 245 veins were observed. They were analyzed by the stress inversion methods (Sato, 2006; Yamaji and Sato, 2011), which can detect multiple stress conditions from a dataset.
As the result, normal fault stresses were dominant in the whole Tanabe Group. The horizontal extension directions was spatially variable. It trends roughly N-S in southern area and E-W in northern area. This spatial variation is consistent with the report from the present-day forearc basin offshore the Kii Peninsula (Lin et al., 2010). In several areas, strike-slip fault stresses were detected. In these area, some map-scale faults subparallel to the ENE-WSW trending present-day trench were reported (Tanabe Research Group, 1984). Detected strike-slip fault stresses can induce dextral shear deformations on these map-scale faults, which is consistent with the dextral oblique subduction model of the Pacific Plate.
Hall, R., 1996. Reconstructing cenozoic SE Asia. Geological Society of London Special Publication, 106, 153-184.
Lin, W., M. L. Doan, J. C. Moore, L. McNeill, T. B. Byrne, T. Ito, D. Saffer, M. Conin, M. Kinoshita, Y. Sanada and others, 2010. Present-day principal horizontal stress orientations in the Kumano forearc basin of the southwest Japan subduction zone determined from IODP NanTroSEIZE drilling Site C0009. Geophysical Research Letters, 37.
Sato, K., 2006. Incorporation of incomplete fault-slip data into stress tensor inversion. Tectonophysics, 421, 319-330.
Seno, T., S. Maruyama, 1984. Paleogeographic reconstruction and origin of the Philippine Sea. Tectonophysics, 102, 53-84.
Tanabe Research Group, 1984. Stratigraphy and geological structure of the Tanabe Group in the Kii Peninsula, Southwest Japan. Earth Science (Chikyu Kagaku), 38, 249-263.
Yamaji, A., Sato, K., 2011. Clustering of fracture orientations using a mixed Bingham distribution and its application to paleostress analysis from dike or vein orientations. Journal of Structural Geology, 33, 1148-1157.
How to cite: Abe, N. and Sato, K.: Strike-slip fault stress detected by paleostress analysis in paleoforearc basin: an example of the Miocene Tanabe Group, Southwest Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21186, https://doi.org/10.5194/egusphere-egu2020-21186, 2020.
The Miocene plate configuration along southwest Japan arc has been controversial as follows. According to Hall (1996), the Pacific Plate subducted dextrally against the Eurasia Plate before 15 Ma, whereas Seno and Maruyama (1984) suggested the Philippines Sea Plate subducted sinistrally. The shear sense of oblique subduction is possibly recorded as the deformation of forearc basin fill. This study performed a series of paleostress analyses by using outcrop-scale structures in the Miocene Tanabe Group to examine whether strike-slip fault stress conditions were detected or not and which sense of shear is expected along trench-parallel faults.
The study area extends roughly 10 km along the coastal area of the Shirahama Formation, the upper part of the Tanabe Group, Kii Peninsula, southwest Japan. The measured structures consist of outcrop-scale faults and veins. Fault displacements range from about several mm to 1 m. The thicknesses of veins are about several mm.
In total, 245 faults and 245 veins were observed. They were analyzed by the stress inversion methods (Sato, 2006; Yamaji and Sato, 2011), which can detect multiple stress conditions from a dataset.
As the result, normal fault stresses were dominant in the whole Tanabe Group. The horizontal extension directions was spatially variable. It trends roughly N-S in southern area and E-W in northern area. This spatial variation is consistent with the report from the present-day forearc basin offshore the Kii Peninsula (Lin et al., 2010). In several areas, strike-slip fault stresses were detected. In these area, some map-scale faults subparallel to the ENE-WSW trending present-day trench were reported (Tanabe Research Group, 1984). Detected strike-slip fault stresses can induce dextral shear deformations on these map-scale faults, which is consistent with the dextral oblique subduction model of the Pacific Plate.
Hall, R., 1996. Reconstructing cenozoic SE Asia. Geological Society of London Special Publication, 106, 153-184.
Lin, W., M. L. Doan, J. C. Moore, L. McNeill, T. B. Byrne, T. Ito, D. Saffer, M. Conin, M. Kinoshita, Y. Sanada and others, 2010. Present-day principal horizontal stress orientations in the Kumano forearc basin of the southwest Japan subduction zone determined from IODP NanTroSEIZE drilling Site C0009. Geophysical Research Letters, 37.
Sato, K., 2006. Incorporation of incomplete fault-slip data into stress tensor inversion. Tectonophysics, 421, 319-330.
Seno, T., S. Maruyama, 1984. Paleogeographic reconstruction and origin of the Philippine Sea. Tectonophysics, 102, 53-84.
Tanabe Research Group, 1984. Stratigraphy and geological structure of the Tanabe Group in the Kii Peninsula, Southwest Japan. Earth Science (Chikyu Kagaku), 38, 249-263.
Yamaji, A., Sato, K., 2011. Clustering of fracture orientations using a mixed Bingham distribution and its application to paleostress analysis from dike or vein orientations. Journal of Structural Geology, 33, 1148-1157.
How to cite: Abe, N. and Sato, K.: Strike-slip fault stress detected by paleostress analysis in paleoforearc basin: an example of the Miocene Tanabe Group, Southwest Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21186, https://doi.org/10.5194/egusphere-egu2020-21186, 2020.
EGU2020-14540 | Displays | TS3.5
Impact of elastic material properties and discontinuities on the stress orientationKarsten Reiter
The in-situ stress state in the upper crust is an important issue for diverse economic purposes and scientific questions as well. Several methods have been established in the last decades to estimate the present-day orientation of the maximum compressive horizontal stress (SHmax) in the crust. It has been assumed, that the SHmax orientation on a regional scale is governed by the same forces that drive plate motion too. The SHmax orientation data, compiled by the World Stress Map (WSM) project, confirmed that for many regions in the world. Due to the increasing amount of data, it is now possible to identify several areas in the world, where stress orientation deviates from the expected orientation due to plate boundary forces (first order stress sources), or the plate wide pattern. In some of this regions a gradual rotation of the SHmax orientation is observed.
Several second and third order stress sources have been identified which may explain stress rotation in the upper crust. For example, lateral heterogeneities in the crust, such as density, petrophysical or petrothermal properties and discontinuities, like faults are identified. Apparently, there are just a few studies, that deal with the potential extend of stress rotation as a function of second and third order stress sources. For that reason, generic geomechanical numerical models have been developed, consisting of up to five different units oriented at an angle of 60 degrees to the direction of contraction. These units have variable elastic material properties, such as Young’s modulus, Poisson ratio and density. In addition, an identical model geometry allows the units to be separated by contact surfaces that allow them so slide along the faults, depending on a selected coefficient of friction.
The model results indicate, that a density contrast or the variation of the Poisson’s ratio alone sparsely rotates the horizontal stress orientation. Conversely, a contrast of the Young’s modulus allows significant stress rotations. Not only areas in the vicinity of the material transition are affected by the stress rotation, but the entire blocks. Low friction discontinuities do not change the stress pattern when viewed over a wide area in homogeneous models. This also applies to models with alternating stiff and soft blocks - the stress orientation is determined solely by the boundary conditions, not the material transitions. This indicates that material contrasts are capable of producing significant stress rotation for larger areas in the crust. Active faults that separates such material contrasts have the opposite effect, they compensate for stress rotations.
How to cite: Reiter, K.: Impact of elastic material properties and discontinuities on the stress orientation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14540, https://doi.org/10.5194/egusphere-egu2020-14540, 2020.
The in-situ stress state in the upper crust is an important issue for diverse economic purposes and scientific questions as well. Several methods have been established in the last decades to estimate the present-day orientation of the maximum compressive horizontal stress (SHmax) in the crust. It has been assumed, that the SHmax orientation on a regional scale is governed by the same forces that drive plate motion too. The SHmax orientation data, compiled by the World Stress Map (WSM) project, confirmed that for many regions in the world. Due to the increasing amount of data, it is now possible to identify several areas in the world, where stress orientation deviates from the expected orientation due to plate boundary forces (first order stress sources), or the plate wide pattern. In some of this regions a gradual rotation of the SHmax orientation is observed.
Several second and third order stress sources have been identified which may explain stress rotation in the upper crust. For example, lateral heterogeneities in the crust, such as density, petrophysical or petrothermal properties and discontinuities, like faults are identified. Apparently, there are just a few studies, that deal with the potential extend of stress rotation as a function of second and third order stress sources. For that reason, generic geomechanical numerical models have been developed, consisting of up to five different units oriented at an angle of 60 degrees to the direction of contraction. These units have variable elastic material properties, such as Young’s modulus, Poisson ratio and density. In addition, an identical model geometry allows the units to be separated by contact surfaces that allow them so slide along the faults, depending on a selected coefficient of friction.
The model results indicate, that a density contrast or the variation of the Poisson’s ratio alone sparsely rotates the horizontal stress orientation. Conversely, a contrast of the Young’s modulus allows significant stress rotations. Not only areas in the vicinity of the material transition are affected by the stress rotation, but the entire blocks. Low friction discontinuities do not change the stress pattern when viewed over a wide area in homogeneous models. This also applies to models with alternating stiff and soft blocks - the stress orientation is determined solely by the boundary conditions, not the material transitions. This indicates that material contrasts are capable of producing significant stress rotation for larger areas in the crust. Active faults that separates such material contrasts have the opposite effect, they compensate for stress rotations.
How to cite: Reiter, K.: Impact of elastic material properties and discontinuities on the stress orientation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14540, https://doi.org/10.5194/egusphere-egu2020-14540, 2020.
EGU2020-18815 | Displays | TS3.5
Tectonic evolution of the seismically active western continental margin of the Indian plate: Implications for kinematic history and fluid flowMohamedharoon Shaikh, Deepak Maurya, Mukherjee Soumyajit, Naimisha Vanik, Abhishek Kumar, and Laxman Chamyal
The deformation history along the E-W trending Kachchh rift basin at the western continental margin of the Indian plate located in the state of Gujarat, India, has been controlled by activation of NW-SE, NE-SW and E-W trending, 0.25–50 km long oblique-slip and dip-slip faults.
The study is an attempt to establish the kinematic framework along sub-parallel, NW-SE striking group of intra-uplift, striated, high-angle reverse faults, consisting of, Vigodi Fault (VF) and its bifurcation – West Vigodi Fault (WVF), Gugriana Fault (GUF) and its bifurcation – Khirasra fault (KHIF) from the western part of the Kachchh basin in the northern part of Gujarat state in western India. They meet the E-W trending master faults – the Kachchh Mainland Fault (KMF) to the north and the Katrol Hill Fault (KHF) to the south at an acute angle.
Fault-slip data consisting of fault plane and slickenside attitudes along with other kinematic indicators were recorded along the faults at 69 structural stations. A total of 1258 fault-slip data were used to carry out paleostress analysis using Win-Tensor (v.5.8.8) and T-Tecto Studio X5 by executing the Right Dihedral Method.
The NW-SE trending fault system exposes highly porous and permeable deformed sandstones belonging to the Jhuran and Bhuj Formation. The pure compaction bands, cataclastic deformation band clusters, slipped deformation bands and deformation band faults are documented. These tabular structures are densely populated in the fault damage zones of VF, WVF, GUF and KHIF. The field observations related to fluid flow conduits are discussed. We also present the field characteristics and petrographic evidences of chemical bleaching caused by fluid-rock interaction found in the Bhuj and the Jhuran sandstones. The change in the coloration pattern of deformation bands in comparison with the host rock color, presence of iron concretions, iron rinds and liesegang rings are important records of the diagenetic control over the fluid flow. The study is an attempt to the link the tectonic activity and simultaneous chemical reactions that affect the fluid flow transport.
We attribute the deformation history in the western continental margin of the Indian plate has been dominantly controlled by intraplate compressional stresses induced by anticlockwise rotation and collision of the Indian plate with the Eurasian plate at ~55 Ma. This correlates well with the Kachchh basin where rifting aborted during the Late Cretaceous, accommodated syn-rifting extensional component in the intra-uplift VF, GUF and KHIF. It has then undergone inversion phase due to onset of compressive stresses during the Post-Deccan Trap time up to the present. The NW-SE trending intra-uplift faults reactivated multiple times and generated deformation bands having high porosity contrast with the host Bhuj sandstone.
How to cite: Shaikh, M., Maurya, D., Soumyajit, M., Vanik, N., Kumar, A., and Chamyal, L.: Tectonic evolution of the seismically active western continental margin of the Indian plate: Implications for kinematic history and fluid flow, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18815, https://doi.org/10.5194/egusphere-egu2020-18815, 2020.
The deformation history along the E-W trending Kachchh rift basin at the western continental margin of the Indian plate located in the state of Gujarat, India, has been controlled by activation of NW-SE, NE-SW and E-W trending, 0.25–50 km long oblique-slip and dip-slip faults.
The study is an attempt to establish the kinematic framework along sub-parallel, NW-SE striking group of intra-uplift, striated, high-angle reverse faults, consisting of, Vigodi Fault (VF) and its bifurcation – West Vigodi Fault (WVF), Gugriana Fault (GUF) and its bifurcation – Khirasra fault (KHIF) from the western part of the Kachchh basin in the northern part of Gujarat state in western India. They meet the E-W trending master faults – the Kachchh Mainland Fault (KMF) to the north and the Katrol Hill Fault (KHF) to the south at an acute angle.
Fault-slip data consisting of fault plane and slickenside attitudes along with other kinematic indicators were recorded along the faults at 69 structural stations. A total of 1258 fault-slip data were used to carry out paleostress analysis using Win-Tensor (v.5.8.8) and T-Tecto Studio X5 by executing the Right Dihedral Method.
The NW-SE trending fault system exposes highly porous and permeable deformed sandstones belonging to the Jhuran and Bhuj Formation. The pure compaction bands, cataclastic deformation band clusters, slipped deformation bands and deformation band faults are documented. These tabular structures are densely populated in the fault damage zones of VF, WVF, GUF and KHIF. The field observations related to fluid flow conduits are discussed. We also present the field characteristics and petrographic evidences of chemical bleaching caused by fluid-rock interaction found in the Bhuj and the Jhuran sandstones. The change in the coloration pattern of deformation bands in comparison with the host rock color, presence of iron concretions, iron rinds and liesegang rings are important records of the diagenetic control over the fluid flow. The study is an attempt to the link the tectonic activity and simultaneous chemical reactions that affect the fluid flow transport.
We attribute the deformation history in the western continental margin of the Indian plate has been dominantly controlled by intraplate compressional stresses induced by anticlockwise rotation and collision of the Indian plate with the Eurasian plate at ~55 Ma. This correlates well with the Kachchh basin where rifting aborted during the Late Cretaceous, accommodated syn-rifting extensional component in the intra-uplift VF, GUF and KHIF. It has then undergone inversion phase due to onset of compressive stresses during the Post-Deccan Trap time up to the present. The NW-SE trending intra-uplift faults reactivated multiple times and generated deformation bands having high porosity contrast with the host Bhuj sandstone.
How to cite: Shaikh, M., Maurya, D., Soumyajit, M., Vanik, N., Kumar, A., and Chamyal, L.: Tectonic evolution of the seismically active western continental margin of the Indian plate: Implications for kinematic history and fluid flow, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18815, https://doi.org/10.5194/egusphere-egu2020-18815, 2020.
EGU2020-19230 | Displays | TS3.5
Tectonic evolution of shallow water carbonates: the Lastoni di Formin platform (Dolomites - Italy)Riccardo Inama, Niccolò Menegoni, and Cesare Perotti
Carbonate rocks are among the most important targets for hydrocarbon exploration, and are considered of particular interest also for gas storage and carbon dioxide sequestration. The development of complex fracture networks in carbonates have a significant influence in fluid circulation, enhancing porosity and permeability and, therefore, modifying their storage capacity. The middle-Triassic Lastoni di Formin platform (Italian Dolomites) was studied by combining field measurements and photogrammetric techniques. The reconstruction of the Digital Model of the buildup allowed the analysis at the outcrop scale with a resolution of 5-10 cm, and gave the opportunity to focus on the behavior of sub-seismic (<10 m) structural elements. Even though their influence on the reservoir quality has been documented, heterogeneities of this order of dimensions are considered as part of the matrix properties in reservoir modeling: outcrop analogues represents a very good source of data that can help to fill this resolution gap. Many generations of fractures and faults can be distinguished at seismic and sub-seismic scale in the present-day fracture pattern of Lastoni di Formin, that is the result of different successive deformational events. In particular, the outcrop records the presence of two different tectonic phases: an E-W extension (Jurassic), that generate N-S trending joints and normal faults, and the Alpine compression (Neogene), that forms conjugate strike slip faults and flower structures. Moreover, an early fracturing gravitational event can be observed: is represented by opening-mode fractures and extensional faults sub-orthogonal to the direction of progradation of the buildup. The presence of platform-derived materials (oncoids) in the fracture fills allows to time-constrain the genesis of these fractures shortly after the deposition. Bed-perpendicular diffuse fractures, which are often strata-bound or terminate on bed-parallel stilolythes, were also detected. Both the margin-parallel early fractures and the Jurassic structures underwent strike-slip reactivations during the Alpine orogeny, which indicates a N-S to NNW-SSE shortening. Evidence of these movements can be inferred from riedel structures, en-chelon arrays, splays and fault jogs that can be observed at different scale. Reactivation of early structures can indicate that they influenced the distribution of subsequent faults and fractures affecting the platform.
How to cite: Inama, R., Menegoni, N., and Perotti, C.: Tectonic evolution of shallow water carbonates: the Lastoni di Formin platform (Dolomites - Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19230, https://doi.org/10.5194/egusphere-egu2020-19230, 2020.
Carbonate rocks are among the most important targets for hydrocarbon exploration, and are considered of particular interest also for gas storage and carbon dioxide sequestration. The development of complex fracture networks in carbonates have a significant influence in fluid circulation, enhancing porosity and permeability and, therefore, modifying their storage capacity. The middle-Triassic Lastoni di Formin platform (Italian Dolomites) was studied by combining field measurements and photogrammetric techniques. The reconstruction of the Digital Model of the buildup allowed the analysis at the outcrop scale with a resolution of 5-10 cm, and gave the opportunity to focus on the behavior of sub-seismic (<10 m) structural elements. Even though their influence on the reservoir quality has been documented, heterogeneities of this order of dimensions are considered as part of the matrix properties in reservoir modeling: outcrop analogues represents a very good source of data that can help to fill this resolution gap. Many generations of fractures and faults can be distinguished at seismic and sub-seismic scale in the present-day fracture pattern of Lastoni di Formin, that is the result of different successive deformational events. In particular, the outcrop records the presence of two different tectonic phases: an E-W extension (Jurassic), that generate N-S trending joints and normal faults, and the Alpine compression (Neogene), that forms conjugate strike slip faults and flower structures. Moreover, an early fracturing gravitational event can be observed: is represented by opening-mode fractures and extensional faults sub-orthogonal to the direction of progradation of the buildup. The presence of platform-derived materials (oncoids) in the fracture fills allows to time-constrain the genesis of these fractures shortly after the deposition. Bed-perpendicular diffuse fractures, which are often strata-bound or terminate on bed-parallel stilolythes, were also detected. Both the margin-parallel early fractures and the Jurassic structures underwent strike-slip reactivations during the Alpine orogeny, which indicates a N-S to NNW-SSE shortening. Evidence of these movements can be inferred from riedel structures, en-chelon arrays, splays and fault jogs that can be observed at different scale. Reactivation of early structures can indicate that they influenced the distribution of subsequent faults and fractures affecting the platform.
How to cite: Inama, R., Menegoni, N., and Perotti, C.: Tectonic evolution of shallow water carbonates: the Lastoni di Formin platform (Dolomites - Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19230, https://doi.org/10.5194/egusphere-egu2020-19230, 2020.
EGU2020-19461 | Displays | TS3.5
Outcrop Fracture Pattern and Paleostress Analysis of the Ghumanwan Dome, Hazara Basin, NW Himalayas, PakistanNaveed Ahsan, Muhammad Armaghan Faisal Miraj, Hamza Tariq, and Abdul Qayyum
Hazara Basin is a NE-SW trending fold and thrust belt, emerged as a consequence of ongoing collision between the Indian and Eurasian plates. Hazara Basin is bounded by Panjal Thrust (PT) in the North and Main Boundary Thrust (MBT) is located in the South. The present work deals with the paleostresses and outcrop fracture pattern (orientations, opening, fracture density) in different rock units exposed in Ghumanwan area located in the vicinity of Abbottabad, in Hazara Basin. PT and MBT juxtapose various lithological units along the Hazara Kashmir Syntaxes (HKS). The imbricate fault system between these two faults indicates a sinistral relative movement. We adopted circle inventory method in the field and collected data (fracture length, width, orientations and dip azimuth) from diverse rock units at 11 visited outcrop stations of the Ghumanwan Dome. These rock units include Upper Cretaceous (Kawagarh Formation) and Paleogene carbonates (Lockhart Formation and Margalla Hill Limestone). We observed highly dense, non-systematic fracture pattern in which mostly fractures are oriented in N-W direction normal to the bedding. Moreover, MOVETM 2018 (Midland Valley) Stress Analysis module (Stereonet Plot) was used for paleostresses analysis. The results show that the Slip Tendency (ratio of shear stress to normal stress) magnitude of σ2 lies closer to the σ3 (on Stereonet) and suggests compressional stresses in which NW-SE oriented fractures developed. The N-S compressive stresses which have mainly affected the concerned area are presumably linked to be late Eocene-Oligocene tectonic event.
How to cite: Ahsan, N., Armaghan Faisal Miraj, M., Tariq, H., and Qayyum, A.: Outcrop Fracture Pattern and Paleostress Analysis of the Ghumanwan Dome, Hazara Basin, NW Himalayas, Pakistan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19461, https://doi.org/10.5194/egusphere-egu2020-19461, 2020.
Hazara Basin is a NE-SW trending fold and thrust belt, emerged as a consequence of ongoing collision between the Indian and Eurasian plates. Hazara Basin is bounded by Panjal Thrust (PT) in the North and Main Boundary Thrust (MBT) is located in the South. The present work deals with the paleostresses and outcrop fracture pattern (orientations, opening, fracture density) in different rock units exposed in Ghumanwan area located in the vicinity of Abbottabad, in Hazara Basin. PT and MBT juxtapose various lithological units along the Hazara Kashmir Syntaxes (HKS). The imbricate fault system between these two faults indicates a sinistral relative movement. We adopted circle inventory method in the field and collected data (fracture length, width, orientations and dip azimuth) from diverse rock units at 11 visited outcrop stations of the Ghumanwan Dome. These rock units include Upper Cretaceous (Kawagarh Formation) and Paleogene carbonates (Lockhart Formation and Margalla Hill Limestone). We observed highly dense, non-systematic fracture pattern in which mostly fractures are oriented in N-W direction normal to the bedding. Moreover, MOVETM 2018 (Midland Valley) Stress Analysis module (Stereonet Plot) was used for paleostresses analysis. The results show that the Slip Tendency (ratio of shear stress to normal stress) magnitude of σ2 lies closer to the σ3 (on Stereonet) and suggests compressional stresses in which NW-SE oriented fractures developed. The N-S compressive stresses which have mainly affected the concerned area are presumably linked to be late Eocene-Oligocene tectonic event.
How to cite: Ahsan, N., Armaghan Faisal Miraj, M., Tariq, H., and Qayyum, A.: Outcrop Fracture Pattern and Paleostress Analysis of the Ghumanwan Dome, Hazara Basin, NW Himalayas, Pakistan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19461, https://doi.org/10.5194/egusphere-egu2020-19461, 2020.
EGU2020-4878 | Displays | TS3.5
On the straight and narrow: extreme localization of brittle fault damage and displacement along the Glade Fault Zone, Eastern Fiordland, New ZealandMichael Ofman and Steven Smith
The southern Glade Fault Zone is a crustal-scale, subvertical dextral strike-slip fault zone on the eastern margin of Fiordland, New Zealand. For a distance of c. 40 km between Lake Te Anau and the Hollyford Valley, the fault cuts plutonic host rocks and has an estimated total dextral separation of c. 6-8 km. We report previously unidentified mylonites, cataclasites, pseudotachylites and fault gouge subparallel to pervasive sets of planar cooling joints in the Hut Creek-Mistake Creek area plutonic suites. The outcropping assemblage of joints and fault rocks record thermal, seismic and rheological conditions in the southern Glade Fault. Here we integrate methods to characterise the fault rocks and fracture damage zone of the southern Glade Fault from Glade Pass to Mt Aragorn. We use (i) EDS (Energy Dispersive x-ray Spectroscopy), XRD (X-Ray Diffraction) and EBSD (Electron Backscatter Diffraction) analysis to describe the mineralogy, kinematics and microstructures of fault rocks and, (ii) drone orthophotography and traditional structural measurements to detail geometrical relationships between structural features. Field mapping of glacially polished outcrops identifies the zone of brittle fault-related damage (i.e. damage zone + fault rock sequence) is up to one order of magnitude narrower than documented along other strike-slip faults with similar displacements, suggesting that the Glade Fault Zone represents an “end-member” of extreme localization of brittle deformation and fault displacement. This is interpreted to result from linkage of pre-existing cooling joints (and mylonitic shear zones), which allowed the younger brittle fault zone to establish its length and planarity relatively efficiently compared to the case of fault nucleation and growth in more isotropic host rocks.
How to cite: Ofman, M. and Smith, S.: On the straight and narrow: extreme localization of brittle fault damage and displacement along the Glade Fault Zone, Eastern Fiordland, New Zealand, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4878, https://doi.org/10.5194/egusphere-egu2020-4878, 2020.
The southern Glade Fault Zone is a crustal-scale, subvertical dextral strike-slip fault zone on the eastern margin of Fiordland, New Zealand. For a distance of c. 40 km between Lake Te Anau and the Hollyford Valley, the fault cuts plutonic host rocks and has an estimated total dextral separation of c. 6-8 km. We report previously unidentified mylonites, cataclasites, pseudotachylites and fault gouge subparallel to pervasive sets of planar cooling joints in the Hut Creek-Mistake Creek area plutonic suites. The outcropping assemblage of joints and fault rocks record thermal, seismic and rheological conditions in the southern Glade Fault. Here we integrate methods to characterise the fault rocks and fracture damage zone of the southern Glade Fault from Glade Pass to Mt Aragorn. We use (i) EDS (Energy Dispersive x-ray Spectroscopy), XRD (X-Ray Diffraction) and EBSD (Electron Backscatter Diffraction) analysis to describe the mineralogy, kinematics and microstructures of fault rocks and, (ii) drone orthophotography and traditional structural measurements to detail geometrical relationships between structural features. Field mapping of glacially polished outcrops identifies the zone of brittle fault-related damage (i.e. damage zone + fault rock sequence) is up to one order of magnitude narrower than documented along other strike-slip faults with similar displacements, suggesting that the Glade Fault Zone represents an “end-member” of extreme localization of brittle deformation and fault displacement. This is interpreted to result from linkage of pre-existing cooling joints (and mylonitic shear zones), which allowed the younger brittle fault zone to establish its length and planarity relatively efficiently compared to the case of fault nucleation and growth in more isotropic host rocks.
How to cite: Ofman, M. and Smith, S.: On the straight and narrow: extreme localization of brittle fault damage and displacement along the Glade Fault Zone, Eastern Fiordland, New Zealand, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4878, https://doi.org/10.5194/egusphere-egu2020-4878, 2020.
EGU2020-8497 | Displays | TS3.5
Microfaulting by early diagenesis of micritic continental carbonates - dilatant and compactive shear localization (Montpellier area, France)Grégory Ballas, Flavia Girard, Yannick Caniven, Roger Soliva, Bernard Celerier, Sylvain Mayolle, Romain Hemelsdael, Didier Loggia, Aurélien Gay, Michel Lopez, and Michel Seranne
Microfaults formed in continental carbonates reveal poorly known mechanisms of shear localization induced by early diagenesis during compaction. These faults are characterized by sinuous shape, bed-controlled, pervasive distribution, no calcite precipitation, and mainly disaggregation processes. Two main sets were described: (1) The first set is composed by normal-sense, high-angle microfaults affecting the top of carbonate beds showing undulating pedogenic bed surface. They show porosity increase and are sometimes organized in polygonal patterns. Their occurrence seems related to overconsolidation of pedogenic surface and density inversion – phreatic loading – fluid expulsion processes in the surficial carbonate bed. (2) The second set is composed by low-angle compactive microfaults with large slickenlines and incipient shear-offset. Their organization within two conjugate systems (normal-sense set and strike-slip set) almost contemporaneous is consistent with a NS extension following the slope induced by the basin subsidence to the south. Their occurrence seems related to vertical loading below few meters depth and occurred by shear-enhanced compaction and incipient pressure-solution process. The presence of such structures gives news information concerning dilatant or compactive shear processes and rheological properties of micritic carbonates during early diagenesis.
How to cite: Ballas, G., Girard, F., Caniven, Y., Soliva, R., Celerier, B., Mayolle, S., Hemelsdael, R., Loggia, D., Gay, A., Lopez, M., and Seranne, M.: Microfaulting by early diagenesis of micritic continental carbonates - dilatant and compactive shear localization (Montpellier area, France), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8497, https://doi.org/10.5194/egusphere-egu2020-8497, 2020.
Microfaults formed in continental carbonates reveal poorly known mechanisms of shear localization induced by early diagenesis during compaction. These faults are characterized by sinuous shape, bed-controlled, pervasive distribution, no calcite precipitation, and mainly disaggregation processes. Two main sets were described: (1) The first set is composed by normal-sense, high-angle microfaults affecting the top of carbonate beds showing undulating pedogenic bed surface. They show porosity increase and are sometimes organized in polygonal patterns. Their occurrence seems related to overconsolidation of pedogenic surface and density inversion – phreatic loading – fluid expulsion processes in the surficial carbonate bed. (2) The second set is composed by low-angle compactive microfaults with large slickenlines and incipient shear-offset. Their organization within two conjugate systems (normal-sense set and strike-slip set) almost contemporaneous is consistent with a NS extension following the slope induced by the basin subsidence to the south. Their occurrence seems related to vertical loading below few meters depth and occurred by shear-enhanced compaction and incipient pressure-solution process. The presence of such structures gives news information concerning dilatant or compactive shear processes and rheological properties of micritic carbonates during early diagenesis.
How to cite: Ballas, G., Girard, F., Caniven, Y., Soliva, R., Celerier, B., Mayolle, S., Hemelsdael, R., Loggia, D., Gay, A., Lopez, M., and Seranne, M.: Microfaulting by early diagenesis of micritic continental carbonates - dilatant and compactive shear localization (Montpellier area, France), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8497, https://doi.org/10.5194/egusphere-egu2020-8497, 2020.
EGU2020-8516 | Displays | TS3.5
The effect of pre-existing faults on the development of extensional basins: insights from wet clay experimentsLorenzo Bonini, Roberto Basili, Nicolò Bertone, Umberto Fracassi, Francesco Emanuele Maesano, and Gianluca Valensise
Most of the present-day extensional systems formed in areas that already experienced an older phase of tectonic activity. Therefore, understanding how a pre-existing structural setting may affect the development of an extensional basin is a crucial interplay to decipher. Depending on the kinematics of these phases, the resulting inherited faults can be extensional, contractional, or transcurrent. Consequently, a new extensional basin forms atop or across pre-existing faults that can dip at a low- (e.g., inherited thrust faults) or high-angle (e.g., inherited extensional faults). Furthermore, the inherited structures can have a non-optimal attitude with respect to the new extensional stress field, thereby determining different instances for reactivation. In this study, we analyzed the impact of dip and strike of inherited faults on the development of an extensional basin using wet clay (kaolin) analogue modeling. We reproduced sixteen different setups by varying the dip (30°, 45°, 60°) and the strike (15°, 30°, 45°, 60°, 75°) of the pre-existing faults that we introduced in the experiments before applying extension. The results show that the orientation of pre-existing faults has a direct effect onto the shape of the new extensional basins. When the pre-existing faults are reused to accommodate the new extensional phase, the formed basins are asymmetric and the rate of growth of the new faults is lower.
How to cite: Bonini, L., Basili, R., Bertone, N., Fracassi, U., Maesano, F. E., and Valensise, G.: The effect of pre-existing faults on the development of extensional basins: insights from wet clay experiments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8516, https://doi.org/10.5194/egusphere-egu2020-8516, 2020.
Most of the present-day extensional systems formed in areas that already experienced an older phase of tectonic activity. Therefore, understanding how a pre-existing structural setting may affect the development of an extensional basin is a crucial interplay to decipher. Depending on the kinematics of these phases, the resulting inherited faults can be extensional, contractional, or transcurrent. Consequently, a new extensional basin forms atop or across pre-existing faults that can dip at a low- (e.g., inherited thrust faults) or high-angle (e.g., inherited extensional faults). Furthermore, the inherited structures can have a non-optimal attitude with respect to the new extensional stress field, thereby determining different instances for reactivation. In this study, we analyzed the impact of dip and strike of inherited faults on the development of an extensional basin using wet clay (kaolin) analogue modeling. We reproduced sixteen different setups by varying the dip (30°, 45°, 60°) and the strike (15°, 30°, 45°, 60°, 75°) of the pre-existing faults that we introduced in the experiments before applying extension. The results show that the orientation of pre-existing faults has a direct effect onto the shape of the new extensional basins. When the pre-existing faults are reused to accommodate the new extensional phase, the formed basins are asymmetric and the rate of growth of the new faults is lower.
How to cite: Bonini, L., Basili, R., Bertone, N., Fracassi, U., Maesano, F. E., and Valensise, G.: The effect of pre-existing faults on the development of extensional basins: insights from wet clay experiments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8516, https://doi.org/10.5194/egusphere-egu2020-8516, 2020.
EGU2020-9747 | Displays | TS3.5
Stratigraphic control on damage zone width in faulted platform carbonates: an example from the Gozo Island, MaltaMattia Martinelli, Andrea Bistaccchi, and Riccardo Castellanza
Fault damage zones (DZ) are fractured volumes of rock that surround the fault core(s), and their structure can have an important role on the control of fault mechanics and of the hydraulic properties of the fault zone, with impact on groundwater flow, ore-deposits, hydrocarbon reservoirs, nuclear waste disposal and contaminant transport in the subsurface. It is generally accepted that DZ width is controlled by fault displacement, and that it increases with increasing offset. However, published data on DZ width in faulted carbonates show a scattering over two orders of magnitude, suggesting that this parameter is controlled also by other factors. Here we present the results of a study performed on two units of the platform carbonates of the Malta and Gozo Islands. These two units, that are cross-cut by normal faults, are characterize by different petrographical, petrophysical and mechanical properties and have completely different Damage Zone width along faults characterized by the same tectonic history and with comparable displacement. More competent and rigid grain-dominated carbonates show DZ thickness of several hundreds of meters, while fracturing in the less competent and more elastic micrite-dominated rocks is developed only very close to the fault core, with a DZ width of few tens of meters. In order to explain this counterintuitive facies-controlled behavior, we performed petrophysical (porosity, density, permeability) and geo-mechanical (Uniaxial, Brazilian, Triaxial tests) analyses to characterize the mechanical stratigraphy and develop a numerical modelling study. Results highlight the heterogeneous stress distribution in a multilayer with variable elastic parameters subjected to horizontal extension. The more elastic unit can more easily expand laterally with respect to the less elastic one with the consequence that σ3 decrease faster in the last one and this can yield before the more compliant one even if it is stronger. Also the width of the yielding zone is increased in the stiffer layers, leading to a wider DZ.
How to cite: Martinelli, M., Bistaccchi, A., and Castellanza, R.: Stratigraphic control on damage zone width in faulted platform carbonates: an example from the Gozo Island, Malta, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9747, https://doi.org/10.5194/egusphere-egu2020-9747, 2020.
Fault damage zones (DZ) are fractured volumes of rock that surround the fault core(s), and their structure can have an important role on the control of fault mechanics and of the hydraulic properties of the fault zone, with impact on groundwater flow, ore-deposits, hydrocarbon reservoirs, nuclear waste disposal and contaminant transport in the subsurface. It is generally accepted that DZ width is controlled by fault displacement, and that it increases with increasing offset. However, published data on DZ width in faulted carbonates show a scattering over two orders of magnitude, suggesting that this parameter is controlled also by other factors. Here we present the results of a study performed on two units of the platform carbonates of the Malta and Gozo Islands. These two units, that are cross-cut by normal faults, are characterize by different petrographical, petrophysical and mechanical properties and have completely different Damage Zone width along faults characterized by the same tectonic history and with comparable displacement. More competent and rigid grain-dominated carbonates show DZ thickness of several hundreds of meters, while fracturing in the less competent and more elastic micrite-dominated rocks is developed only very close to the fault core, with a DZ width of few tens of meters. In order to explain this counterintuitive facies-controlled behavior, we performed petrophysical (porosity, density, permeability) and geo-mechanical (Uniaxial, Brazilian, Triaxial tests) analyses to characterize the mechanical stratigraphy and develop a numerical modelling study. Results highlight the heterogeneous stress distribution in a multilayer with variable elastic parameters subjected to horizontal extension. The more elastic unit can more easily expand laterally with respect to the less elastic one with the consequence that σ3 decrease faster in the last one and this can yield before the more compliant one even if it is stronger. Also the width of the yielding zone is increased in the stiffer layers, leading to a wider DZ.
How to cite: Martinelli, M., Bistaccchi, A., and Castellanza, R.: Stratigraphic control on damage zone width in faulted platform carbonates: an example from the Gozo Island, Malta, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9747, https://doi.org/10.5194/egusphere-egu2020-9747, 2020.
EGU2020-8709 | Displays | TS3.5
Fault Damage Scaling: Insights from field data in carbonate rocks and analogue modellingSylvain Mayolle, Roger Soliva, Stephane Dominguez, Yannick Caniven, Christopher Wibberley, and Gregory Ballas
Fault damage zones present a renewal of interest to better understand stress perturbations around faults, earthquake’s ground motions and fluid flow in the upper crust. Although numerous studies provide significant amounts of data from a broad variety of rocks, the processes controlling fault damage development are not clearly understood and scaling properties in carbonate rocks remain poorly studied. D-T (displacement - DZ thickness) data compilations show strong scattering and are acquired using different methods and at different places along the faults (including tip, wall, link, or inner and outer damages), therefore rendering difficult a proper definition of the scaling relationship.
First, we analyse fault/fracture systems at the outcrop and map scale and define displacement - thickness (D-T) scaling of fault damage zones using scanlines, in carbonate rocks in France and Spain. We determine fault displacement and damage zone thickness perpendicular to fault planes and far from fault tips for 12 selected faults in four study sites. The data show a logarithmic decrease of fracture frequency from the fault cores. This decrease is characterized by local frequency peaks corresponding to variably-linked secondary fault segments and abandoned tips within the fault damage zone. D-T data comprised between 0 and 100 m of net fault displacement show a nearly linear scaling with very little scattering. Including two additional data for D > 100 m, the best fit corresponds better to a power law. The linear scaling is explained by well-known processes of fault growth such as stress perturbations around faults and fault segment linkage. The non-linear trend shown by the largest faults suggests that at this scale the faults become restricted at their lower tips by the base of the brittle crust.
Secondly, we analyse fault damage growth using analogue modelling of normal faults in a sand box. The model is composed by a 5 cm thick layer of dry sand deposited above a 2 cm thick ductile “kinetic sand” (sand and silicone) layer. The experiment is analysed in cross-section using image correlation allowing to calculate the velocity field and strain tensor over the fault zones including their damage pattern. Fault damage thickness obtained using the strain field appears to grow linearly with respect to shear displacement when the fault is contained into the dry sand layer. When the fault lower tip reaches the kinetic sand, fault damage begins to growth non-linearly with shear displacement, revealing that the brittle layer thickness is the main parameter governing the non-linear scaling.
How to cite: Mayolle, S., Soliva, R., Dominguez, S., Caniven, Y., Wibberley, C., and Ballas, G.: Fault Damage Scaling: Insights from field data in carbonate rocks and analogue modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8709, https://doi.org/10.5194/egusphere-egu2020-8709, 2020.
Fault damage zones present a renewal of interest to better understand stress perturbations around faults, earthquake’s ground motions and fluid flow in the upper crust. Although numerous studies provide significant amounts of data from a broad variety of rocks, the processes controlling fault damage development are not clearly understood and scaling properties in carbonate rocks remain poorly studied. D-T (displacement - DZ thickness) data compilations show strong scattering and are acquired using different methods and at different places along the faults (including tip, wall, link, or inner and outer damages), therefore rendering difficult a proper definition of the scaling relationship.
First, we analyse fault/fracture systems at the outcrop and map scale and define displacement - thickness (D-T) scaling of fault damage zones using scanlines, in carbonate rocks in France and Spain. We determine fault displacement and damage zone thickness perpendicular to fault planes and far from fault tips for 12 selected faults in four study sites. The data show a logarithmic decrease of fracture frequency from the fault cores. This decrease is characterized by local frequency peaks corresponding to variably-linked secondary fault segments and abandoned tips within the fault damage zone. D-T data comprised between 0 and 100 m of net fault displacement show a nearly linear scaling with very little scattering. Including two additional data for D > 100 m, the best fit corresponds better to a power law. The linear scaling is explained by well-known processes of fault growth such as stress perturbations around faults and fault segment linkage. The non-linear trend shown by the largest faults suggests that at this scale the faults become restricted at their lower tips by the base of the brittle crust.
Secondly, we analyse fault damage growth using analogue modelling of normal faults in a sand box. The model is composed by a 5 cm thick layer of dry sand deposited above a 2 cm thick ductile “kinetic sand” (sand and silicone) layer. The experiment is analysed in cross-section using image correlation allowing to calculate the velocity field and strain tensor over the fault zones including their damage pattern. Fault damage thickness obtained using the strain field appears to grow linearly with respect to shear displacement when the fault is contained into the dry sand layer. When the fault lower tip reaches the kinetic sand, fault damage begins to growth non-linearly with shear displacement, revealing that the brittle layer thickness is the main parameter governing the non-linear scaling.
How to cite: Mayolle, S., Soliva, R., Dominguez, S., Caniven, Y., Wibberley, C., and Ballas, G.: Fault Damage Scaling: Insights from field data in carbonate rocks and analogue modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8709, https://doi.org/10.5194/egusphere-egu2020-8709, 2020.
EGU2020-14084 | Displays | TS3.5
Linking the mechanics of polygonal faults with hydrothermal activity and marine biosphere – the Guadeloupe geothermal systemChristoph von Hagke, Katharina Leu, Elco Luijendijk, Melody Philippon, Stefan Back, Jean-Frederic Lebrun, Sebastien Cordonnier, Olivier Gros, Silvina Gonzalez-Rizzo, and Aurelien Gay
Polygonal faults are ubiquitous features, commonly observed in seismic images of fine-grained sedimentary successions along many passive margins. They are characterized by covering large parts of the basin with a typical polygonal pattern. In the last decade, different mechanical models for the generation of polygonal faults have been proposed; however, as they are commonly formed at depth and not directly observable at the surface, their formation remains a matter of debate. As part of the GEOTREF Program (ADEME – Investissement d’avenir) we found polygonal fault structures exposed close to the surface in marine soft sediments at 5 m water depth at the western coast of Guadeloupe. The structures are associated with fault-bound thermal springs and clearly visible at the sea bottom due to preferential precipitation of sulfur minerals and concentration of diatoms. In a multidisciplinary study involving a team of hydrogeologists, marine micro-biologists, and structural geologists, we study the genesis of polygonal faults in this setting. We analyzed the sediments in which the polygonal faults formed structurally and geochemically. First results suggest that SiO2 precipitated from hydrothermal fluids increases the cohesion of the most permeable soft sediments. Dewatering of the underlying layers causes the formation of polygonal faults at a depth of <1 m. These polygonal faults then act as channels for hot fluids, resulting in accumulation of sulfur favoring the establishment of diatoms at the surface. This study offers the unique opportunity to study the formation of polygonal faults in situ. We compare the observed geometries of polygonal faults with GEOTREF cruise 2-D seismic data offshore Guadeloupe, and 3-D seismic data of polygonal faults in New Zealand and Australia with the goal to understand the variability of polygonal fault geometries, as well as their comparability across different scales of observation. On a more local scale, this study provides insights how fracture dynamics guides fluid flow, which in turn interacts with the marine biosphere.
How to cite: von Hagke, C., Leu, K., Luijendijk, E., Philippon, M., Back, S., Lebrun, J.-F., Cordonnier, S., Gros, O., Gonzalez-Rizzo, S., and Gay, A.: Linking the mechanics of polygonal faults with hydrothermal activity and marine biosphere – the Guadeloupe geothermal system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14084, https://doi.org/10.5194/egusphere-egu2020-14084, 2020.
Polygonal faults are ubiquitous features, commonly observed in seismic images of fine-grained sedimentary successions along many passive margins. They are characterized by covering large parts of the basin with a typical polygonal pattern. In the last decade, different mechanical models for the generation of polygonal faults have been proposed; however, as they are commonly formed at depth and not directly observable at the surface, their formation remains a matter of debate. As part of the GEOTREF Program (ADEME – Investissement d’avenir) we found polygonal fault structures exposed close to the surface in marine soft sediments at 5 m water depth at the western coast of Guadeloupe. The structures are associated with fault-bound thermal springs and clearly visible at the sea bottom due to preferential precipitation of sulfur minerals and concentration of diatoms. In a multidisciplinary study involving a team of hydrogeologists, marine micro-biologists, and structural geologists, we study the genesis of polygonal faults in this setting. We analyzed the sediments in which the polygonal faults formed structurally and geochemically. First results suggest that SiO2 precipitated from hydrothermal fluids increases the cohesion of the most permeable soft sediments. Dewatering of the underlying layers causes the formation of polygonal faults at a depth of <1 m. These polygonal faults then act as channels for hot fluids, resulting in accumulation of sulfur favoring the establishment of diatoms at the surface. This study offers the unique opportunity to study the formation of polygonal faults in situ. We compare the observed geometries of polygonal faults with GEOTREF cruise 2-D seismic data offshore Guadeloupe, and 3-D seismic data of polygonal faults in New Zealand and Australia with the goal to understand the variability of polygonal fault geometries, as well as their comparability across different scales of observation. On a more local scale, this study provides insights how fracture dynamics guides fluid flow, which in turn interacts with the marine biosphere.
How to cite: von Hagke, C., Leu, K., Luijendijk, E., Philippon, M., Back, S., Lebrun, J.-F., Cordonnier, S., Gros, O., Gonzalez-Rizzo, S., and Gay, A.: Linking the mechanics of polygonal faults with hydrothermal activity and marine biosphere – the Guadeloupe geothermal system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14084, https://doi.org/10.5194/egusphere-egu2020-14084, 2020.
EGU2020-7192 | Displays | TS3.5
Signature of coseismic slip in unconsolidated Quaternary gravels, Campo Imperatore, ItalyMatteo Demurtas, Fabrizio Balsamo, and Mattia Pizzati
Faulting in seismically active regions commonly involves the deformation of unconsolidated to poorly lithified sediments. The seldom occurrence of seismic slip within these deposits appears to be counterintuitive if compared to classic crustal strength profiles that predict a velocity-strengthening behaviour for the first few km of depth. Therefore, the investigation of geological evidence for coseismic faulting within unconsolidated deposits is a key step towards a broader understanding of mechanisms of strain accommodation at shallow to near-surface depth.
Here we document the occurrence of minor faults within an unconsolidated colluvial fan at the hanging wall of the Vado di Corno Fault Zone (VCFZ) in the Central Apennines, Italy. The VCFZ is part of the active Campo Imperatore Fault System and accommodated 1-2 km of displacement since Early-Pleistocene. The deposits lie in direct contact with the master fault surface, are Late-Pleistocene to Holocene in age, and consist of angular carbonatic clasts, up to tens of centimetres in size, derived from the dismantling of the VCFZ footwall.
Studied faults are organised in two main sets: (i) subvertical, N-S trending dip-slip faults, parallel to the fan long axis, and (ii) WNW-ESE striking faults, synthetic and antithetic to the VCFZ master fault surface (N195/55°). Both fault sets are striated and commonly have positive relief with respect to the host deposits. Some of these faults show a fault core up to 5-6 cm thick, bounded by discrete and well-developed polished surfaces. Locally, particularly in fine-grained gravel levels, the occurrence of extreme strain localisation (i.e. millimetric ultracataclastic layers with truncated clasts) along mirror-like fault surfaces is observed. Grain size analysis of undeformed and faulted gravels shows an increase of the power-law exponent (fractal dimension) from values of D = 1.65-2.2 in the undeformed host rocks up to D = 2.9 in the cataclastic slip zones. Microstructural analysis suggests cataclasis is the main deformation mechanism leading to grain size reduction along faults, whereas intergranular pressure solution becomes widespread moving away from the slip zone where fluid circulation was present.
Collectively, our observations provide new insights into the mechanics of faulting and strain accommodation in the shallowest part of the crust (< 1 km) and new evidence to understand the propagation of seismic ruptures within shallow unconsolidated deposits.
How to cite: Demurtas, M., Balsamo, F., and Pizzati, M.: Signature of coseismic slip in unconsolidated Quaternary gravels, Campo Imperatore, Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7192, https://doi.org/10.5194/egusphere-egu2020-7192, 2020.
Faulting in seismically active regions commonly involves the deformation of unconsolidated to poorly lithified sediments. The seldom occurrence of seismic slip within these deposits appears to be counterintuitive if compared to classic crustal strength profiles that predict a velocity-strengthening behaviour for the first few km of depth. Therefore, the investigation of geological evidence for coseismic faulting within unconsolidated deposits is a key step towards a broader understanding of mechanisms of strain accommodation at shallow to near-surface depth.
Here we document the occurrence of minor faults within an unconsolidated colluvial fan at the hanging wall of the Vado di Corno Fault Zone (VCFZ) in the Central Apennines, Italy. The VCFZ is part of the active Campo Imperatore Fault System and accommodated 1-2 km of displacement since Early-Pleistocene. The deposits lie in direct contact with the master fault surface, are Late-Pleistocene to Holocene in age, and consist of angular carbonatic clasts, up to tens of centimetres in size, derived from the dismantling of the VCFZ footwall.
Studied faults are organised in two main sets: (i) subvertical, N-S trending dip-slip faults, parallel to the fan long axis, and (ii) WNW-ESE striking faults, synthetic and antithetic to the VCFZ master fault surface (N195/55°). Both fault sets are striated and commonly have positive relief with respect to the host deposits. Some of these faults show a fault core up to 5-6 cm thick, bounded by discrete and well-developed polished surfaces. Locally, particularly in fine-grained gravel levels, the occurrence of extreme strain localisation (i.e. millimetric ultracataclastic layers with truncated clasts) along mirror-like fault surfaces is observed. Grain size analysis of undeformed and faulted gravels shows an increase of the power-law exponent (fractal dimension) from values of D = 1.65-2.2 in the undeformed host rocks up to D = 2.9 in the cataclastic slip zones. Microstructural analysis suggests cataclasis is the main deformation mechanism leading to grain size reduction along faults, whereas intergranular pressure solution becomes widespread moving away from the slip zone where fluid circulation was present.
Collectively, our observations provide new insights into the mechanics of faulting and strain accommodation in the shallowest part of the crust (< 1 km) and new evidence to understand the propagation of seismic ruptures within shallow unconsolidated deposits.
How to cite: Demurtas, M., Balsamo, F., and Pizzati, M.: Signature of coseismic slip in unconsolidated Quaternary gravels, Campo Imperatore, Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7192, https://doi.org/10.5194/egusphere-egu2020-7192, 2020.
EGU2020-7993 | Displays | TS3.5
The research of Meinong earthquake induced hydrological anomalies and increased vertical permeability in southwestern TaiwanYan-Yao Lin, Shih-Jung Wang, and Wen-Chi Lai
Hydrological anomalies induced by the earthquakes are valuable research data to understand the hydrogeology structure. At the same time, a complete hydrogeological data is the key to the study of earthquake hydrology. In this research, we collected the anomalous hydrological data after the Mw 6.4 2016 Meinong Earthquake in Taiwan. The main purpose is to know the mechanism of hydrological changes triggered by earthquake and understand the local hydrogeological characteristics in the southern Taiwan.
From the distribution of the groundwater level change in the same location but different depths of aquifer, as well as the location of the rupture and liquefaction, it could be found that the co-seismic groundwater level change is large in Chianan Plain in the northwest of the epicenter and accompanied with a lot of ruptures and liquefactions located along the Hsinhua Fault. However, the observations in several wells around the Hsinhua Fault show a different water level change pattern compared with the other wells in Chianan Plain. Actually, these wells show that the co-seismic groundwater level decreases in the deep aquifer and increase in the shallow aquifer. It is shown that the Meinong Earthquake may enhance the connectivity between different aquifers near the fault zone and produce an increased vertical pressure gradient. The anomalous hydrological phenomenon also reflected in the river flow. Based on the river flow data we collected from five stations in the Zengwun River watershed, the river flow at two stations in the upstream dose not change after earthquake. There is a little increase at the midstream station. However, a large river flow increase is observed at the downstream station. After excluding the influence of rainfall, we think that the large amount of anomalous flow is caused by the rise of the co-seismic groundwater level between the middle and downstream sections, and a large amount of liquefaction in this area can prove this hypothesis.
The hypothesis of connectivity changes between different aquifers can be verified by analyzing the tidal response of different aquifers. Many studies have used the tide analysis to obtain the aquifer permeability and compressibility, and compared the changes in the analysis results before and after the earthquake. We think that if different aquifers are vertically connected after earthquake, the tidal analysis results should show a consistent permeability. Tidal analysis is executing now and the results will be provided at conference.
How to cite: Lin, Y.-Y., Wang, S.-J., and Lai, W.-C.: The research of Meinong earthquake induced hydrological anomalies and increased vertical permeability in southwestern Taiwan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7993, https://doi.org/10.5194/egusphere-egu2020-7993, 2020.
Hydrological anomalies induced by the earthquakes are valuable research data to understand the hydrogeology structure. At the same time, a complete hydrogeological data is the key to the study of earthquake hydrology. In this research, we collected the anomalous hydrological data after the Mw 6.4 2016 Meinong Earthquake in Taiwan. The main purpose is to know the mechanism of hydrological changes triggered by earthquake and understand the local hydrogeological characteristics in the southern Taiwan.
From the distribution of the groundwater level change in the same location but different depths of aquifer, as well as the location of the rupture and liquefaction, it could be found that the co-seismic groundwater level change is large in Chianan Plain in the northwest of the epicenter and accompanied with a lot of ruptures and liquefactions located along the Hsinhua Fault. However, the observations in several wells around the Hsinhua Fault show a different water level change pattern compared with the other wells in Chianan Plain. Actually, these wells show that the co-seismic groundwater level decreases in the deep aquifer and increase in the shallow aquifer. It is shown that the Meinong Earthquake may enhance the connectivity between different aquifers near the fault zone and produce an increased vertical pressure gradient. The anomalous hydrological phenomenon also reflected in the river flow. Based on the river flow data we collected from five stations in the Zengwun River watershed, the river flow at two stations in the upstream dose not change after earthquake. There is a little increase at the midstream station. However, a large river flow increase is observed at the downstream station. After excluding the influence of rainfall, we think that the large amount of anomalous flow is caused by the rise of the co-seismic groundwater level between the middle and downstream sections, and a large amount of liquefaction in this area can prove this hypothesis.
The hypothesis of connectivity changes between different aquifers can be verified by analyzing the tidal response of different aquifers. Many studies have used the tide analysis to obtain the aquifer permeability and compressibility, and compared the changes in the analysis results before and after the earthquake. We think that if different aquifers are vertically connected after earthquake, the tidal analysis results should show a consistent permeability. Tidal analysis is executing now and the results will be provided at conference.
How to cite: Lin, Y.-Y., Wang, S.-J., and Lai, W.-C.: The research of Meinong earthquake induced hydrological anomalies and increased vertical permeability in southwestern Taiwan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7993, https://doi.org/10.5194/egusphere-egu2020-7993, 2020.
EGU2020-17943 | Displays | TS3.5
Post-emplacement fluid-driven intrusion fracturing and quartz-sand injections at the basal shear zone of the Esla Nappe (Cantabrian Zone, NW Iberia)Manuel Ignacio de Paz Álvarez, Sergio Llana Fúnez, and Juan Luis Alonso
The Esla Nappe is located in the external foreland and thrust belt of the Variscan Orogen in the NW Iberian Massif (Cantabrian Zone, NW Iberia). It is formed by a near-complete Palaeozoic sedimentary succession. With a displacement of around 19 km, the nappe was emplaced along a thin (<2–3 m) basal shear zone (ENBSZ) located at an estimated minimum depth of 4 km. Emplacement took place during the Moscovian (ca. 312 Ma). Fault-rock assemblages record a variety of alternating deformation mechanisms and processes, including cataclastic flow, pressure solution and hydrofracturing and vein precipitation. All these processes are considered evidence of an aseismic stable behaviour of the ENBSZ, where deformation was influenced by secular variations in the fluid pore pressure.
Following emplacement, the ENBSZ was breached by clastic dykes and sills which were intruded following re-opened previous anisotropies, including bedding planes, thrust surfaces, joints and stylolites. Together, they constitute an interconnected network of quartz sand-rich lithosomes reaching structural heights occasionally exceeding 20 m above the ENBSZ. The orientation of the dykes suggests that the injection process took place under low differential stress conditions in the hangingwall, and near-lithostatic fluid pore overpressure conditions in the footwall. The injected slurry consisted of overpressured pore fluid, quartz-sand grains derived from the footwall and entrained host-derived fragments. Depending on fracture aperture and slurry composition, a variety of fluid velocities can be inferred in the order of 15–30 cm/s. Thin pure injections of quartz grains (ca. <1 cm) were characterised by a laminar flow (Re<2100), whereas the thickest quartz and host-derived mixed injections (~1 m) displayed a fully turbulent flow (Re~2 x 104).
The causes for the fluids to reach near-lithostatic fluid overpressures within the uppermost footwall remain unknown. It is not possible to rule out a seismic trigger, but the absence of extreme shear localization structures typical of seismic slip suggests that the injection process was driven by fluid progressive accumulation, possibly related with clay dehydration reactions, tectonic loading, pore compaction or fluid migration from underlying formations. Actual breaching and injection may have been allowed by a decrease in bedding-parallel compressive stresses in the Esla Nappe associated with the subsequent evolution of the thrust-wedge.
How to cite: de Paz Álvarez, M. I., Llana Fúnez, S., and Alonso, J. L.: Post-emplacement fluid-driven intrusion fracturing and quartz-sand injections at the basal shear zone of the Esla Nappe (Cantabrian Zone, NW Iberia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17943, https://doi.org/10.5194/egusphere-egu2020-17943, 2020.
The Esla Nappe is located in the external foreland and thrust belt of the Variscan Orogen in the NW Iberian Massif (Cantabrian Zone, NW Iberia). It is formed by a near-complete Palaeozoic sedimentary succession. With a displacement of around 19 km, the nappe was emplaced along a thin (<2–3 m) basal shear zone (ENBSZ) located at an estimated minimum depth of 4 km. Emplacement took place during the Moscovian (ca. 312 Ma). Fault-rock assemblages record a variety of alternating deformation mechanisms and processes, including cataclastic flow, pressure solution and hydrofracturing and vein precipitation. All these processes are considered evidence of an aseismic stable behaviour of the ENBSZ, where deformation was influenced by secular variations in the fluid pore pressure.
Following emplacement, the ENBSZ was breached by clastic dykes and sills which were intruded following re-opened previous anisotropies, including bedding planes, thrust surfaces, joints and stylolites. Together, they constitute an interconnected network of quartz sand-rich lithosomes reaching structural heights occasionally exceeding 20 m above the ENBSZ. The orientation of the dykes suggests that the injection process took place under low differential stress conditions in the hangingwall, and near-lithostatic fluid pore overpressure conditions in the footwall. The injected slurry consisted of overpressured pore fluid, quartz-sand grains derived from the footwall and entrained host-derived fragments. Depending on fracture aperture and slurry composition, a variety of fluid velocities can be inferred in the order of 15–30 cm/s. Thin pure injections of quartz grains (ca. <1 cm) were characterised by a laminar flow (Re<2100), whereas the thickest quartz and host-derived mixed injections (~1 m) displayed a fully turbulent flow (Re~2 x 104).
The causes for the fluids to reach near-lithostatic fluid overpressures within the uppermost footwall remain unknown. It is not possible to rule out a seismic trigger, but the absence of extreme shear localization structures typical of seismic slip suggests that the injection process was driven by fluid progressive accumulation, possibly related with clay dehydration reactions, tectonic loading, pore compaction or fluid migration from underlying formations. Actual breaching and injection may have been allowed by a decrease in bedding-parallel compressive stresses in the Esla Nappe associated with the subsequent evolution of the thrust-wedge.
How to cite: de Paz Álvarez, M. I., Llana Fúnez, S., and Alonso, J. L.: Post-emplacement fluid-driven intrusion fracturing and quartz-sand injections at the basal shear zone of the Esla Nappe (Cantabrian Zone, NW Iberia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17943, https://doi.org/10.5194/egusphere-egu2020-17943, 2020.
EGU2020-1784 | Displays | TS3.5
Study on the hydrocarbon accumulation models of the upper Es3 in the gentle slope belt of Chexi DepressionShan Zhao and Hua Liu
Based on the analysis of hydrocarbon source, reservoir forming period, composition and classification of transportation system, and the reasons of failure well in Chexi Depression of Bohai Bay Basin,Two types of hydrocarbon accumulation models in gentle slope belt of Chexi area are established and the main controlling factors of hydrocarbon accumulation are defined. There are three sets of source rocks(Es1、middle and lover submember of Es3、Es4)in Chexi area, the different strata of source rocks have great differences in the Pr/Ph and the content of gammacerane. It has been found that the crude oil of Es3 has a good geochemical correspondence with the middle and lower of Es3 source rocks, and has the characteristics of near source accumulation. The hydrocarbon accumulation in the study area exists in the sedimentary period of the Dongying formation and the sedimentary period of the Guantao formation to the present two stages, which is dominated by late filling. There are two stages of oil and gas filling in the inner and middle belts, and only late stage hydrocarbon filling in the outer slope belt. The hydrocarbon transportation system is mainly composed of faults and sand bodies. The effective source rocks in the middle and lover submember of Es3 are connected with the upper reservoir of Es3 in a small area, which can be directly migrated to the upper sandstone reservoir of Es3 to form lithologic oil and gas reservoir. However, most of the oil and gas in the upper Es3 reservoir need to be vertically migrated by means of oil source fault, and then through the contact of sand bodies such as main channel and fan body, the main oil and gas reservoir will gradually move up with the distance from the source rock. The area with direct contact source reservoir configuration relationship is a "sand body lateral migration" reservoir formation mode, and the main controlling factors of reservoir formation are sand body connectivity and reservoir porosity and permeability. The source reservoir configuration area with fault connection type is a "fault sand combination T-type migration" reservoir forming mode, and the main controlling factors of reservoir forming are migration convergence facies (structural ridge and cross-section ridge).The area of passive reservoir contact is "fault sand combination step migration" reservoir forming mode, and the main controlling factors of reservoir forming are migration convergence facies (structural ridge) and lateral sealing of faults in preservation conditions.
Key words: Chexi Depression; Source of hydrocarbon; Accumulation period; Fault sand transport combination; Reservoir forming mode
How to cite: Zhao, S. and Liu, H.: Study on the hydrocarbon accumulation models of the upper Es3 in the gentle slope belt of Chexi Depression, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1784, https://doi.org/10.5194/egusphere-egu2020-1784, 2020.
Based on the analysis of hydrocarbon source, reservoir forming period, composition and classification of transportation system, and the reasons of failure well in Chexi Depression of Bohai Bay Basin,Two types of hydrocarbon accumulation models in gentle slope belt of Chexi area are established and the main controlling factors of hydrocarbon accumulation are defined. There are three sets of source rocks(Es1、middle and lover submember of Es3、Es4)in Chexi area, the different strata of source rocks have great differences in the Pr/Ph and the content of gammacerane. It has been found that the crude oil of Es3 has a good geochemical correspondence with the middle and lower of Es3 source rocks, and has the characteristics of near source accumulation. The hydrocarbon accumulation in the study area exists in the sedimentary period of the Dongying formation and the sedimentary period of the Guantao formation to the present two stages, which is dominated by late filling. There are two stages of oil and gas filling in the inner and middle belts, and only late stage hydrocarbon filling in the outer slope belt. The hydrocarbon transportation system is mainly composed of faults and sand bodies. The effective source rocks in the middle and lover submember of Es3 are connected with the upper reservoir of Es3 in a small area, which can be directly migrated to the upper sandstone reservoir of Es3 to form lithologic oil and gas reservoir. However, most of the oil and gas in the upper Es3 reservoir need to be vertically migrated by means of oil source fault, and then through the contact of sand bodies such as main channel and fan body, the main oil and gas reservoir will gradually move up with the distance from the source rock. The area with direct contact source reservoir configuration relationship is a "sand body lateral migration" reservoir formation mode, and the main controlling factors of reservoir formation are sand body connectivity and reservoir porosity and permeability. The source reservoir configuration area with fault connection type is a "fault sand combination T-type migration" reservoir forming mode, and the main controlling factors of reservoir forming are migration convergence facies (structural ridge and cross-section ridge).The area of passive reservoir contact is "fault sand combination step migration" reservoir forming mode, and the main controlling factors of reservoir forming are migration convergence facies (structural ridge) and lateral sealing of faults in preservation conditions.
Key words: Chexi Depression; Source of hydrocarbon; Accumulation period; Fault sand transport combination; Reservoir forming mode
How to cite: Zhao, S. and Liu, H.: Study on the hydrocarbon accumulation models of the upper Es3 in the gentle slope belt of Chexi Depression, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1784, https://doi.org/10.5194/egusphere-egu2020-1784, 2020.
EGU2020-6519 | Displays | TS3.5
Characteristics of fluid-flow migration(bleached rock) around major structures in a reservoir-cap rock system, SE Utah, USAKyoungtae Ko
Bleached rocks are commonly formed from CO2-saturated water leakage to the surface. It could provide opportunities to understand the mechanisms and controlling factors associated with injected and sequestrated CO2 leakages as well as fluid flow in the subsurface. In this study, we investigated the various bleaching patterns and their related structures in order to understand the characteristics of fluid-flow migration around the major structures. Also, we examined the effects of lithology and structural characteristics on fluid flow in detail along and around the major structures. For this purpose, we analyzed bleaching characteristics of multiple layered sedimentary rocks around two major faults (Moab and Salt Wash Faults) and fold axes (Green river anticline system) based on field observations and quantitative measurements (scanline survey and permeability) in the exhumed reservoir-cap rock systems in SE Utah, USA. The results showed that strongly bleached layers of sedimentary rock have a higher density of deformation bands compared to unbleached layers. This is consistent with the general property of deformation bands that frequently develop in layers with higher porosity and permeability. Although almost all fault zones act as conduits for fluid flow, some fault zones filled with clay-rich gouges could impede fluid flow. In addition, the internal sealing characteristics of the layer boundaries such as bedding planes could be important factors as they can act either as a pathway or a barrier for lateral fluid flow depending on the existence of filling materials such as calcite or kerogen. Our research may be useful for assessing CO2 leakage in oil reservoirs or CO2 sequestration sites located in a reservoir-cap rock system of sedimentary basins.
How to cite: Ko, K.: Characteristics of fluid-flow migration(bleached rock) around major structures in a reservoir-cap rock system, SE Utah, USA, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6519, https://doi.org/10.5194/egusphere-egu2020-6519, 2020.
Bleached rocks are commonly formed from CO2-saturated water leakage to the surface. It could provide opportunities to understand the mechanisms and controlling factors associated with injected and sequestrated CO2 leakages as well as fluid flow in the subsurface. In this study, we investigated the various bleaching patterns and their related structures in order to understand the characteristics of fluid-flow migration around the major structures. Also, we examined the effects of lithology and structural characteristics on fluid flow in detail along and around the major structures. For this purpose, we analyzed bleaching characteristics of multiple layered sedimentary rocks around two major faults (Moab and Salt Wash Faults) and fold axes (Green river anticline system) based on field observations and quantitative measurements (scanline survey and permeability) in the exhumed reservoir-cap rock systems in SE Utah, USA. The results showed that strongly bleached layers of sedimentary rock have a higher density of deformation bands compared to unbleached layers. This is consistent with the general property of deformation bands that frequently develop in layers with higher porosity and permeability. Although almost all fault zones act as conduits for fluid flow, some fault zones filled with clay-rich gouges could impede fluid flow. In addition, the internal sealing characteristics of the layer boundaries such as bedding planes could be important factors as they can act either as a pathway or a barrier for lateral fluid flow depending on the existence of filling materials such as calcite or kerogen. Our research may be useful for assessing CO2 leakage in oil reservoirs or CO2 sequestration sites located in a reservoir-cap rock system of sedimentary basins.
How to cite: Ko, K.: Characteristics of fluid-flow migration(bleached rock) around major structures in a reservoir-cap rock system, SE Utah, USA, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6519, https://doi.org/10.5194/egusphere-egu2020-6519, 2020.
TS4.2 – Three- and four-dimensional aspects of faulting
EGU2020-19731 | Displays | TS4.2
Do pre-existing basement structures influence the geometry and growth of normal faults and rifts?Christopher Jackson, Luca Collanega, Thomas Phillips, Antje Lenhart, Edoseghe Osagiede, Catherine Siuda, Matthew Reeve, Oliver Duffy, Rebecca Bell, Atle Rotevatn, Craig Magee, Robert Gawthorpe, Alexander Coleman, Paul Whipp, Thomas Kristensen, Haakon Fossen, Anna Breda, and Nicola Marsh
Rifts often evolve on a template of crystalline basement that may contain strong lithological and mechanical heterogeneities related to complex pre-rift tectonic histories. Numerous studies argue that reactivation of such pre-existing structures can influence the geometry and evolution of normal faults and rift physiography. However, in many cases: (i) it is unclear where, if at all, structures at the rift margin continue along-strike below the rift axis; and (ii) the precise geometric and kinematic relationship between pre-existing structures and newly formed normal faults is not well understood. These uncertainties reflect the fact that: (i) potential field data are typically of low-resolution, and thus cannot resolve the detailed morphology of shallow fault networks; (ii) field data cannot provide an accurate 3D image of intra-basement structures and the overlying rift; and (iii) seismic reflection data typically do not image deeply buried intra-basement structures. Understanding the kinematic as well as geometric relationship between intra-basement structures and rift-related fault networks is important for understanding plate motions and for undertaking stress inversions, given that paleo-extension directions (and sigma 3) are, in many rifted provinces, typically thought to lie normal to the dominant fault strike.
We here tackle these problems using subsurface data from the Taranaki Basin, offshore New Zealand, and the northern North Sea, offshore west Norway. Our data provide excellent imaging of shallowly buried intra-basement structures, as well as cover-hosted normal faults and their associated pre- and syn-growth strata. We identify a range of intra-basement structures, both extensional and contractional,, and a range of geometric and kinematic interactions between intra-basement structures and cover normal faults. For example, some of the normal faults are physically connected to intra-basement structures oriented oblique to the regional extension direction. It is notable that, even in cases, intra-basement structures were apparently not extensionally reactivated during the later rift phase. Displacement maxima on cover faults occur at 100-200 m above the crystalline basement-cover interface, suggesting the former did not form due to simple extensional reactivation and upward propagation of pre-existing structures; rather, ‘passive’ basement structures somehow perturbed the regional stress field, leading to the development of normal faults whose strikes mimic those of the underlying pre-existing basement structures. Cover normal faults can also display a range of complex geometries related to the linkage of numerous, originally separate slip surfaces, and upward-bifurcation of strongly segmented fault systems. We also show that the timing of physical linkage between basement and cover structures can be recorded in the geometry of related growth strata, which document the switch from non-rotational to rotational faulting.
Our analyses show that km-scale, intra-basement structures can control the nucleation and development of newly formed, rift-related normal faults, most likely due to a local perturbation of the regional stress field. Because of this, simply inverting fault strike for causal extension direction may be incorrect, especially in provinces where pre-existing, intra-basement structures occur. We also show that a detailed kinematic analysis is key to deciphering the temporal as well as the geometric relationships between structures developed at multiple structural levels.
How to cite: Jackson, C., Collanega, L., Phillips, T., Lenhart, A., Osagiede, E., Siuda, C., Reeve, M., Duffy, O., Bell, R., Rotevatn, A., Magee, C., Gawthorpe, R., Coleman, A., Whipp, P., Kristensen, T., Fossen, H., Breda, A., and Marsh, N.: Do pre-existing basement structures influence the geometry and growth of normal faults and rifts?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19731, https://doi.org/10.5194/egusphere-egu2020-19731, 2020.
Rifts often evolve on a template of crystalline basement that may contain strong lithological and mechanical heterogeneities related to complex pre-rift tectonic histories. Numerous studies argue that reactivation of such pre-existing structures can influence the geometry and evolution of normal faults and rift physiography. However, in many cases: (i) it is unclear where, if at all, structures at the rift margin continue along-strike below the rift axis; and (ii) the precise geometric and kinematic relationship between pre-existing structures and newly formed normal faults is not well understood. These uncertainties reflect the fact that: (i) potential field data are typically of low-resolution, and thus cannot resolve the detailed morphology of shallow fault networks; (ii) field data cannot provide an accurate 3D image of intra-basement structures and the overlying rift; and (iii) seismic reflection data typically do not image deeply buried intra-basement structures. Understanding the kinematic as well as geometric relationship between intra-basement structures and rift-related fault networks is important for understanding plate motions and for undertaking stress inversions, given that paleo-extension directions (and sigma 3) are, in many rifted provinces, typically thought to lie normal to the dominant fault strike.
We here tackle these problems using subsurface data from the Taranaki Basin, offshore New Zealand, and the northern North Sea, offshore west Norway. Our data provide excellent imaging of shallowly buried intra-basement structures, as well as cover-hosted normal faults and their associated pre- and syn-growth strata. We identify a range of intra-basement structures, both extensional and contractional,, and a range of geometric and kinematic interactions between intra-basement structures and cover normal faults. For example, some of the normal faults are physically connected to intra-basement structures oriented oblique to the regional extension direction. It is notable that, even in cases, intra-basement structures were apparently not extensionally reactivated during the later rift phase. Displacement maxima on cover faults occur at 100-200 m above the crystalline basement-cover interface, suggesting the former did not form due to simple extensional reactivation and upward propagation of pre-existing structures; rather, ‘passive’ basement structures somehow perturbed the regional stress field, leading to the development of normal faults whose strikes mimic those of the underlying pre-existing basement structures. Cover normal faults can also display a range of complex geometries related to the linkage of numerous, originally separate slip surfaces, and upward-bifurcation of strongly segmented fault systems. We also show that the timing of physical linkage between basement and cover structures can be recorded in the geometry of related growth strata, which document the switch from non-rotational to rotational faulting.
Our analyses show that km-scale, intra-basement structures can control the nucleation and development of newly formed, rift-related normal faults, most likely due to a local perturbation of the regional stress field. Because of this, simply inverting fault strike for causal extension direction may be incorrect, especially in provinces where pre-existing, intra-basement structures occur. We also show that a detailed kinematic analysis is key to deciphering the temporal as well as the geometric relationships between structures developed at multiple structural levels.
How to cite: Jackson, C., Collanega, L., Phillips, T., Lenhart, A., Osagiede, E., Siuda, C., Reeve, M., Duffy, O., Bell, R., Rotevatn, A., Magee, C., Gawthorpe, R., Coleman, A., Whipp, P., Kristensen, T., Fossen, H., Breda, A., and Marsh, N.: Do pre-existing basement structures influence the geometry and growth of normal faults and rifts?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19731, https://doi.org/10.5194/egusphere-egu2020-19731, 2020.
EGU2020-4581 | Displays | TS4.2
Structural Characteristics and Mechanism of the Horsetail Structure in China Offshore Basins: Case Studies from Liaodong Bay Area, Bohai Bay Basin and Weixinan Area, Beibuwan BasinJie Zhang, Zhiping Wu, and Yanjun Cheng
The horsetail structure, also named brush structure, generally refers to a sets of secondary faults converged to the primary fault on the plane. Based on 2-D and 3-D seismic data, the structural characteristics, evolution and mechanism of the horsetail structure of Liaodong Bay area in Bohai Bay Basin and Weixinan area in Beibuwan Basin are analyzed. In the Liaodong Bay area, the primary fault of the horsetail structure is the NNE-striking branch fault of Tan-Lu strike-slip fault zone. The NE-striking secondary extensional faults converged to the primary strike-slip fault. Fault activity analysis shows that both the primary and secondary faults intensively activated during the third Member of the Shahejie Formation (42~38 Ma). In the Weixinan area, the NE-striking Weixinan fault is the primary fault of the horsetail structure, which is an extensional fault. A large amount of EW-striking secondary extensional faults converged to the primary NE-striking Weixinan fault. Fault activity analysis shows that NE-striking primary fault intensively activated during the second Member of the Liushagang Formation (48.6~40.4 Ma), whereas the EW-striking secondary faults intensively activated during the Weizhou Formation (33.9~23 Ma). The different structure and evolution of the horsetail structure in the Liaodong Bay area and Weixinan area are mainly resulted from the regional tectonic settings. About 42 Ma, the change of subduction direction of the Pacific plate and the India-Eurasian collision resulted in the right-lateral strike-slip movement of NNE-striking Tan-Lu fault and the formation of NE-striking extensional faults along the bend of the strike-slip fault, therefore, the horsetail structure of Liaodong Bay area formed. However, the formation of the horsetail structure of Weixinan area is related to the clockwise rotation of extension stress in the South China Sea (SCS): 1) During Paleocene to M. Eocene (65~37.8 Ma), the retreat of Pacific plate subduction zone resulted in the formation of NW-SE extensional stress field in the north margin of the SCS, NE-striking primary fault of horsetail structure formed; 2) During L. Eocene to E. Oligocene (37.8~28.4 Ma), the change of subduction direction of the Pacific plate and the India-Eurasian collision resulted in the clockwise rotation of extension direction from NW-SE to N-S in the north margin of the SCS, a large amount of EW-striking secondary faults of horsetail structure formed, and the horsetail structure was totally formed in the Weixinan area until this stage.
How to cite: Zhang, J., Wu, Z., and Cheng, Y.: Structural Characteristics and Mechanism of the Horsetail Structure in China Offshore Basins: Case Studies from Liaodong Bay Area, Bohai Bay Basin and Weixinan Area, Beibuwan Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4581, https://doi.org/10.5194/egusphere-egu2020-4581, 2020.
The horsetail structure, also named brush structure, generally refers to a sets of secondary faults converged to the primary fault on the plane. Based on 2-D and 3-D seismic data, the structural characteristics, evolution and mechanism of the horsetail structure of Liaodong Bay area in Bohai Bay Basin and Weixinan area in Beibuwan Basin are analyzed. In the Liaodong Bay area, the primary fault of the horsetail structure is the NNE-striking branch fault of Tan-Lu strike-slip fault zone. The NE-striking secondary extensional faults converged to the primary strike-slip fault. Fault activity analysis shows that both the primary and secondary faults intensively activated during the third Member of the Shahejie Formation (42~38 Ma). In the Weixinan area, the NE-striking Weixinan fault is the primary fault of the horsetail structure, which is an extensional fault. A large amount of EW-striking secondary extensional faults converged to the primary NE-striking Weixinan fault. Fault activity analysis shows that NE-striking primary fault intensively activated during the second Member of the Liushagang Formation (48.6~40.4 Ma), whereas the EW-striking secondary faults intensively activated during the Weizhou Formation (33.9~23 Ma). The different structure and evolution of the horsetail structure in the Liaodong Bay area and Weixinan area are mainly resulted from the regional tectonic settings. About 42 Ma, the change of subduction direction of the Pacific plate and the India-Eurasian collision resulted in the right-lateral strike-slip movement of NNE-striking Tan-Lu fault and the formation of NE-striking extensional faults along the bend of the strike-slip fault, therefore, the horsetail structure of Liaodong Bay area formed. However, the formation of the horsetail structure of Weixinan area is related to the clockwise rotation of extension stress in the South China Sea (SCS): 1) During Paleocene to M. Eocene (65~37.8 Ma), the retreat of Pacific plate subduction zone resulted in the formation of NW-SE extensional stress field in the north margin of the SCS, NE-striking primary fault of horsetail structure formed; 2) During L. Eocene to E. Oligocene (37.8~28.4 Ma), the change of subduction direction of the Pacific plate and the India-Eurasian collision resulted in the clockwise rotation of extension direction from NW-SE to N-S in the north margin of the SCS, a large amount of EW-striking secondary faults of horsetail structure formed, and the horsetail structure was totally formed in the Weixinan area until this stage.
How to cite: Zhang, J., Wu, Z., and Cheng, Y.: Structural Characteristics and Mechanism of the Horsetail Structure in China Offshore Basins: Case Studies from Liaodong Bay Area, Bohai Bay Basin and Weixinan Area, Beibuwan Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4581, https://doi.org/10.5194/egusphere-egu2020-4581, 2020.
EGU2020-12844 | Displays | TS4.2
Field-based fault architecture of fold-thrust belts: an example from the Qaidam basin, northeast Tibetan PlateauYangwen Pei
Understanding the detailed fault architecture of reverse faulting is not only critical for revealing the processes involved in fold-thrust belts as well as predicting the relationship between folds and faults, the distribution of strain, and sub-seismic faulting deformation, but also important for understanding fault related compartmentalisation and fluid flow behaviour both along and/or across thrust fault zones. The Lenghu5 fold-thrust belt, provides an exceptionally well-exposed outcrop example of a reverse fault-related fold. Detailed stratigraphic logging coupled with high-resolution cross-sections provides a unique insight into the 3D geometry of a thrust fault at both basin and outcrop scale.
In this study we observed 85 - 90% of the estimated throw is accommodated on the main fault zone (i.e., the Lenghu5 thrust fault), which has sufficient throw to be imaged on a seismic profile, while 15-20% of the throw is accommodated on smaller scale folds and faults that are beyond seismic resolution. The Lenghu5 thrust fault, a seismically resolvable fault with up to ~800m of throw, exhibits a large variation of fault architecture and strain distribution along the fault zone. As meso-scale (1-100 m) structural features are normally beyond the seismic resolution, high-resolution outcrop in-situ mapping (5-10 cm resolution) was employed to study the deformation features of the Lenghu5 thrust fault zone. The excellent exposure of outcrops enables detailed investigation of its fault zone architecture. Multiple structural domains with different levels of strain were observed and are associated with the fault throw distribution across the fault. Based on previously proposed models and high-resolution outcrop mapping, an updated fault zone model was constructed to characterize the structural features and evolution of the Lenghu5 thrust fault.
The possible parameters that impact fault architecture and strain distribution, including fault throw, bed thickness, lithology and mechanical heterogeneity were evaluated. Fault throw distributions and linkages control the strain distribution across a thrust fault zone, with local folding processes contributing important elements in the Lenghu5 thrust fault especially where more incompetent beds dominate the stratigraphy. Mechanical heterogeneity, induced by different layer stacking patterns, controls the details of the fault architecture in the thrust zone. The variations in bed thicknesses and mechanical property contrasts are likely to control the initial fault dips and fault/fracture density. Large fault throws are associated with wide strain accommodation and damage zones, although the relationship between the development and width of the fault zone with the throw accumulation remains to be assessed.
By presenting the high resolution mapping of fault architecture this study provides an insight into the sub-seismic fault zone geometry and strain distributions possible in thrust faults and reviews their application to assessing fault zone behaviour.
How to cite: Pei, Y.: Field-based fault architecture of fold-thrust belts: an example from the Qaidam basin, northeast Tibetan Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12844, https://doi.org/10.5194/egusphere-egu2020-12844, 2020.
Understanding the detailed fault architecture of reverse faulting is not only critical for revealing the processes involved in fold-thrust belts as well as predicting the relationship between folds and faults, the distribution of strain, and sub-seismic faulting deformation, but also important for understanding fault related compartmentalisation and fluid flow behaviour both along and/or across thrust fault zones. The Lenghu5 fold-thrust belt, provides an exceptionally well-exposed outcrop example of a reverse fault-related fold. Detailed stratigraphic logging coupled with high-resolution cross-sections provides a unique insight into the 3D geometry of a thrust fault at both basin and outcrop scale.
In this study we observed 85 - 90% of the estimated throw is accommodated on the main fault zone (i.e., the Lenghu5 thrust fault), which has sufficient throw to be imaged on a seismic profile, while 15-20% of the throw is accommodated on smaller scale folds and faults that are beyond seismic resolution. The Lenghu5 thrust fault, a seismically resolvable fault with up to ~800m of throw, exhibits a large variation of fault architecture and strain distribution along the fault zone. As meso-scale (1-100 m) structural features are normally beyond the seismic resolution, high-resolution outcrop in-situ mapping (5-10 cm resolution) was employed to study the deformation features of the Lenghu5 thrust fault zone. The excellent exposure of outcrops enables detailed investigation of its fault zone architecture. Multiple structural domains with different levels of strain were observed and are associated with the fault throw distribution across the fault. Based on previously proposed models and high-resolution outcrop mapping, an updated fault zone model was constructed to characterize the structural features and evolution of the Lenghu5 thrust fault.
The possible parameters that impact fault architecture and strain distribution, including fault throw, bed thickness, lithology and mechanical heterogeneity were evaluated. Fault throw distributions and linkages control the strain distribution across a thrust fault zone, with local folding processes contributing important elements in the Lenghu5 thrust fault especially where more incompetent beds dominate the stratigraphy. Mechanical heterogeneity, induced by different layer stacking patterns, controls the details of the fault architecture in the thrust zone. The variations in bed thicknesses and mechanical property contrasts are likely to control the initial fault dips and fault/fracture density. Large fault throws are associated with wide strain accommodation and damage zones, although the relationship between the development and width of the fault zone with the throw accumulation remains to be assessed.
By presenting the high resolution mapping of fault architecture this study provides an insight into the sub-seismic fault zone geometry and strain distributions possible in thrust faults and reviews their application to assessing fault zone behaviour.
How to cite: Pei, Y.: Field-based fault architecture of fold-thrust belts: an example from the Qaidam basin, northeast Tibetan Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12844, https://doi.org/10.5194/egusphere-egu2020-12844, 2020.
EGU2020-11814 | Displays | TS4.2
Structural Complexity and Mechanics of a shallow crustal Seismogenic Source (Vado di Corno Fault Zone, Italy)Michele Fondriest, Fabrizio Balsamo, Andrea Bistacchi, Luca Clemenzi, Matteo Demurtas, Fabrizio Storti, and Giulio Di Toro
The mechanics and seismogenic behaviour of fault zones are strongly influenced by their internal structure, intended as three-dimensional geometry and topology of the fault/fracture network and distribution of the fault zone rocks with related physical properties. In this perspective, the internal structure of the extensional seismically active Vado di Corno Fault Zone (Central Apennines, Italy) was quantified by combining high-resolution structural mapping with modern techniques of 3D fault network modelling over ∼2 km along fault strike. The fault zone is hosted in carbonate host rocks, was exhumed from ∼2 km depth, accommodated a normal slip of ∼1.5-2 km since Early-Pleistocene and cuts through the Pliocene Omo Morto Thrust Zone that was partially reactivated in extension.
The exceptional exposure of the Vado di Corno Fault Zone footwall block allowed us to reconstruct with extreme detail the geometry of the older Omo Morto Thrust Zone and quantify the spatial arrangement of master and subsidiary faults, and fault zone rocks within the Vado di Corno Fault Zone. The combined analysis of the structural map and of a realistic 3D fault network model with kinematic, topological and slip tendency analyses, pointed out the crucial role of the older Omo Morto Thrust Zone geometry (i.e. the occurrence and position of lateral ramps) in controlling the along-strike segmentation and slip distribution of the active Vado di Corno normal fault zone. These findings were tested with a boundary element mechanical model that highlights the effect of inherited compressional features on the Vado di Corno Fault Zone internal structure and returns distributions and particularly partitioning of slip comparable with those measured in the field.
Lastly, we discuss the exhumed Vado di Corno Fault Zone as an analogue for the shallow structure of many seismic sources in the Central Apennines. The mechanical interaction of the inherited Omo Morto Thrust Zone and the extensional Vado di Corno Fault Zone generated along-strike and down-dip geometrical asperities. Similar settings could play first-order control on the complex spatio-temporal evolution and rupture heterogeneity of earthquakes in the region (e.g. 2009 Mw 6.1 L’Aquila earthquake).
How to cite: Fondriest, M., Balsamo, F., Bistacchi, A., Clemenzi, L., Demurtas, M., Storti, F., and Di Toro, G.: Structural Complexity and Mechanics of a shallow crustal Seismogenic Source (Vado di Corno Fault Zone, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11814, https://doi.org/10.5194/egusphere-egu2020-11814, 2020.
The mechanics and seismogenic behaviour of fault zones are strongly influenced by their internal structure, intended as three-dimensional geometry and topology of the fault/fracture network and distribution of the fault zone rocks with related physical properties. In this perspective, the internal structure of the extensional seismically active Vado di Corno Fault Zone (Central Apennines, Italy) was quantified by combining high-resolution structural mapping with modern techniques of 3D fault network modelling over ∼2 km along fault strike. The fault zone is hosted in carbonate host rocks, was exhumed from ∼2 km depth, accommodated a normal slip of ∼1.5-2 km since Early-Pleistocene and cuts through the Pliocene Omo Morto Thrust Zone that was partially reactivated in extension.
The exceptional exposure of the Vado di Corno Fault Zone footwall block allowed us to reconstruct with extreme detail the geometry of the older Omo Morto Thrust Zone and quantify the spatial arrangement of master and subsidiary faults, and fault zone rocks within the Vado di Corno Fault Zone. The combined analysis of the structural map and of a realistic 3D fault network model with kinematic, topological and slip tendency analyses, pointed out the crucial role of the older Omo Morto Thrust Zone geometry (i.e. the occurrence and position of lateral ramps) in controlling the along-strike segmentation and slip distribution of the active Vado di Corno normal fault zone. These findings were tested with a boundary element mechanical model that highlights the effect of inherited compressional features on the Vado di Corno Fault Zone internal structure and returns distributions and particularly partitioning of slip comparable with those measured in the field.
Lastly, we discuss the exhumed Vado di Corno Fault Zone as an analogue for the shallow structure of many seismic sources in the Central Apennines. The mechanical interaction of the inherited Omo Morto Thrust Zone and the extensional Vado di Corno Fault Zone generated along-strike and down-dip geometrical asperities. Similar settings could play first-order control on the complex spatio-temporal evolution and rupture heterogeneity of earthquakes in the region (e.g. 2009 Mw 6.1 L’Aquila earthquake).
How to cite: Fondriest, M., Balsamo, F., Bistacchi, A., Clemenzi, L., Demurtas, M., Storti, F., and Di Toro, G.: Structural Complexity and Mechanics of a shallow crustal Seismogenic Source (Vado di Corno Fault Zone, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11814, https://doi.org/10.5194/egusphere-egu2020-11814, 2020.
EGU2020-13914 | Displays | TS4.2
Characteristics of episodic fault growth and off-fault deformation structuresSimon Preuss, Jean Paul Ampuero, Luca Dal Zilio, Taras Gerya, and Ylona van Dinther
Natural fault networks are geometrically complex systems that evolve through time. The growth and evolution of faults and their off-fault damage pattern are influenced by both dynamic earthquake ruptures and aseismic deformation during the interseismic period. To better understand each of their contributions to faulting we simulate both earthquake rupture dynamics and long-term deformation in a visco-elasto-plastic crust subjected to rate-and-state-dependent friction [1,2]. The continuum mechanics-based numerical model presented here includes three new features. First, a 2.5-D approximation to incorporate effects of a viscoelastic lower crustal substrate below a finite depth. Second, we introduce a dynamically adaptive (slip-velocity-dependent) measure of fault width to ensure grid size convergence of fault angles for evolving faults. Third, fault localisation is facilitated by plastic strain weakening of bulk rate-and-state friction parameters as motivated by laboratory experiments. This allows us to for the first time simulate sequences of episodic fault growth due to earthquakes and aseismic creep. Localized fault growth is simulated for four bulk rheologies ranging from persistent velocity-weakening to velocity-strengthening. Yet, episodic fault growth is only obtained for a bulk rheology that transitions from velocity-strengthening friction to velocity-weakening friction. Interestingly, in each of these bulk rheologies, faults predominantly localise [LDZ1] and grow in the inter-seismic period due to aseismic deformation. However, [LDZ2] off-fault deformation - both distributed and localised - is typically formed during dynamic earthquake ruptures. Simulated off-fault deformation structures range from fan-shaped distributed deformation to localized Riedel splay faults and antithetic conjugate [LDZ3] Riedel shear faults [LDZ4] and towards wing cracks. We observe that the fault-normal width of the outer damage zone saturates with increasing fault length due to the finite depth of the seismogenic zone. We also observe that dynamically and statically evolving stress fields from neighbouring fault strands affects first and secondary fault growth. Finally, we find that the amount of off-fault deformation distinctly depends on the degree of optimality of a fault with respect to the prevailing but dynamically changing stress field. Typically, we simulate off-fault deformation on faults parallel to the loading direction. This produces a 6.5-fold higher off-fault energy dissipation than on an optimally oriented fault, which in turn has a 1.5-fold larger stress drop. The misalignment of the fault with respect to the static stress field thus facilitates off-fault deformation. These results imply that fault geometries bend [2], individual fault strands interact and that optimal orientations and off-fault deformation vary through space and time. With our work we establish the basis for simulations and analyses of complex evolving fault networks subject to both long-term and short-term dynamics. Currently, we are using this basis to simulate and explain orthogonal faulting observed in the 2019 M6.4-M7.1 Ridgecrest earthquake sequence.
How to cite: Preuss, S., Ampuero, J. P., Dal Zilio, L., Gerya, T., and van Dinther, Y.: Characteristics of episodic fault growth and off-fault deformation structures, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13914, https://doi.org/10.5194/egusphere-egu2020-13914, 2020.
Natural fault networks are geometrically complex systems that evolve through time. The growth and evolution of faults and their off-fault damage pattern are influenced by both dynamic earthquake ruptures and aseismic deformation during the interseismic period. To better understand each of their contributions to faulting we simulate both earthquake rupture dynamics and long-term deformation in a visco-elasto-plastic crust subjected to rate-and-state-dependent friction [1,2]. The continuum mechanics-based numerical model presented here includes three new features. First, a 2.5-D approximation to incorporate effects of a viscoelastic lower crustal substrate below a finite depth. Second, we introduce a dynamically adaptive (slip-velocity-dependent) measure of fault width to ensure grid size convergence of fault angles for evolving faults. Third, fault localisation is facilitated by plastic strain weakening of bulk rate-and-state friction parameters as motivated by laboratory experiments. This allows us to for the first time simulate sequences of episodic fault growth due to earthquakes and aseismic creep. Localized fault growth is simulated for four bulk rheologies ranging from persistent velocity-weakening to velocity-strengthening. Yet, episodic fault growth is only obtained for a bulk rheology that transitions from velocity-strengthening friction to velocity-weakening friction. Interestingly, in each of these bulk rheologies, faults predominantly localise [LDZ1] and grow in the inter-seismic period due to aseismic deformation. However, [LDZ2] off-fault deformation - both distributed and localised - is typically formed during dynamic earthquake ruptures. Simulated off-fault deformation structures range from fan-shaped distributed deformation to localized Riedel splay faults and antithetic conjugate [LDZ3] Riedel shear faults [LDZ4] and towards wing cracks. We observe that the fault-normal width of the outer damage zone saturates with increasing fault length due to the finite depth of the seismogenic zone. We also observe that dynamically and statically evolving stress fields from neighbouring fault strands affects first and secondary fault growth. Finally, we find that the amount of off-fault deformation distinctly depends on the degree of optimality of a fault with respect to the prevailing but dynamically changing stress field. Typically, we simulate off-fault deformation on faults parallel to the loading direction. This produces a 6.5-fold higher off-fault energy dissipation than on an optimally oriented fault, which in turn has a 1.5-fold larger stress drop. The misalignment of the fault with respect to the static stress field thus facilitates off-fault deformation. These results imply that fault geometries bend [2], individual fault strands interact and that optimal orientations and off-fault deformation vary through space and time. With our work we establish the basis for simulations and analyses of complex evolving fault networks subject to both long-term and short-term dynamics. Currently, we are using this basis to simulate and explain orthogonal faulting observed in the 2019 M6.4-M7.1 Ridgecrest earthquake sequence.
How to cite: Preuss, S., Ampuero, J. P., Dal Zilio, L., Gerya, T., and van Dinther, Y.: Characteristics of episodic fault growth and off-fault deformation structures, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13914, https://doi.org/10.5194/egusphere-egu2020-13914, 2020.
EGU2020-989 | Displays | TS4.2
Factors controlling shear rupture roughness: An insight from field and laboratory experimentsManaska Mukhopadhyay, Uddalak Biswas, Nibir Mandal, and Santanu Misra
Faults and fracture surfaces record the history of slip events through a range of structural features in tectonically active zones. Slickensides, among them, prove to be the most prominent evidences of such slip movements. These linear features give us crucial information about the mechanical processes associated with shear surface roughness formation. We conducted extensive field survey in the Singhbhum Shear Zone, Eastern India, and report shear fractures of varying surface roughness from deformed quartzites. Shear surfaces encountered in the field study varied from very smooth, devoid of any lineation to strongly rough with prominent slickenlines.
For better understanding of the varied surface roughness, we performed analogue laboratory experiments. The experimental results suggest that the fracture orientation and the mode of shear failure are potential factors that control the fracture roughness. We used cohesive sand-talc models for the analogue experiments with varying sand:talc volume ratio, ranging from pure sand to pure talc variant. Experimental models with pure sand composition underwent Coulomb failure in the brittle regime. With subsequent increase in talc content, the behavior of failure switched to plastic yielding in the ductile regime. This transition from coulomb failure to plastic yielding produced a remarkable variation in the shear surface roughness characteristics. Shear surfaces formed by Coulomb failure are smooth and devoid any slickenlines, whereas, those formed by plastic yielding show prominent presence strongly linear roughness, defined by cylindrical ridge-grooves along the slip direction.
Shear surface roughness defined by linear irregularities become more prominent with increasing fracture orientation (θ) to the compression direction (θ = 30° to 60°). Increase in θ promotes the formation of smooth slickenlines at the cost of rough zones. For critical analysis and understanding of these features we develop a new computational technique. The technique is based on controlled optical images to map the shear surface geometry from field casts and laboratory samples. Binarization of the irregular surface images (cantor set) provides 1D fractal dimension (D), which is used to quantify the roughness variability, and the degree of their anisotropy in terms of ΔD (difference in D across and along the slip direction). From numerical models, we finally show onset of wave instability in the mechanically distinct rupture zone as an alternative mechanism for slickenlines formation.
How to cite: Mukhopadhyay, M., Biswas, U., Mandal, N., and Misra, S.: Factors controlling shear rupture roughness: An insight from field and laboratory experiments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-989, https://doi.org/10.5194/egusphere-egu2020-989, 2020.
Faults and fracture surfaces record the history of slip events through a range of structural features in tectonically active zones. Slickensides, among them, prove to be the most prominent evidences of such slip movements. These linear features give us crucial information about the mechanical processes associated with shear surface roughness formation. We conducted extensive field survey in the Singhbhum Shear Zone, Eastern India, and report shear fractures of varying surface roughness from deformed quartzites. Shear surfaces encountered in the field study varied from very smooth, devoid of any lineation to strongly rough with prominent slickenlines.
For better understanding of the varied surface roughness, we performed analogue laboratory experiments. The experimental results suggest that the fracture orientation and the mode of shear failure are potential factors that control the fracture roughness. We used cohesive sand-talc models for the analogue experiments with varying sand:talc volume ratio, ranging from pure sand to pure talc variant. Experimental models with pure sand composition underwent Coulomb failure in the brittle regime. With subsequent increase in talc content, the behavior of failure switched to plastic yielding in the ductile regime. This transition from coulomb failure to plastic yielding produced a remarkable variation in the shear surface roughness characteristics. Shear surfaces formed by Coulomb failure are smooth and devoid any slickenlines, whereas, those formed by plastic yielding show prominent presence strongly linear roughness, defined by cylindrical ridge-grooves along the slip direction.
Shear surface roughness defined by linear irregularities become more prominent with increasing fracture orientation (θ) to the compression direction (θ = 30° to 60°). Increase in θ promotes the formation of smooth slickenlines at the cost of rough zones. For critical analysis and understanding of these features we develop a new computational technique. The technique is based on controlled optical images to map the shear surface geometry from field casts and laboratory samples. Binarization of the irregular surface images (cantor set) provides 1D fractal dimension (D), which is used to quantify the roughness variability, and the degree of their anisotropy in terms of ΔD (difference in D across and along the slip direction). From numerical models, we finally show onset of wave instability in the mechanically distinct rupture zone as an alternative mechanism for slickenlines formation.
How to cite: Mukhopadhyay, M., Biswas, U., Mandal, N., and Misra, S.: Factors controlling shear rupture roughness: An insight from field and laboratory experiments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-989, https://doi.org/10.5194/egusphere-egu2020-989, 2020.
EGU2020-4557 | Displays | TS4.2
Fault interactions, fault kinematics, and evolution of the structural framework in the Irish Lower CarboniferousKoen Torremans, John Conneally, John Güven, Robert Doyle, jiulin Guo, Eoin Dunlevy, and John Walsh
Fault systems in the Irish Lower Carboniferous are important in relation to its subsurface groundwater, geothermal and mineral resources. For example, major base metal deposits in the world-class Irish Orefield occur in association with normal faults. Despite their economic importance, however, the fault networks and structural framework at depth are still poorly constrained. The Irish Carboniferous Basin is an excellent area to study the extensional fault systems and evolution of rift basins, given the relatively low amounts of later compressional deformation and metamorphism, and because high-quality subsurface datasets exist from several decades of mineral exploration. Our work aimed at developing a coherent structural framework for the Lower Carboniferous in Ireland, to unravel the geometries and kinematics of faulting in a carbonate-dominated rift basin that developed on top of a strong pre-existing structural template in the underlying basement rocks.
We have defined the geometry of key fault systems in the rift across a wide range of scales, using three-dimensional integrated analysis of large datasets. These datasets include public and proprietary onshore 2D reflection seismic, mapping, drillhole, micro-palaeontological, aeromagnetic, electromagnetic, and ground gravity data. Our work has revealed the nature of segmentation patterns and interactions of normal faults, including synthetic and conjugate relay zones. Quantification of fault parameters, kinematic analysis and kinematic restoration have allowed us to gain insights into the distribution of extension during rifting in time and space, using growth sequences and facies changes on faults. The analysis of this structural framework in relation to several mineral deposits, and in combination with lithofacies distribution and the development of bathymetry during basin formation, allows us to better understand current and past fluid flow pathways, especially in relation to base metal mineralising events.
How to cite: Torremans, K., Conneally, J., Güven, J., Doyle, R., Guo, J., Dunlevy, E., and Walsh, J.: Fault interactions, fault kinematics, and evolution of the structural framework in the Irish Lower Carboniferous, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4557, https://doi.org/10.5194/egusphere-egu2020-4557, 2020.
Fault systems in the Irish Lower Carboniferous are important in relation to its subsurface groundwater, geothermal and mineral resources. For example, major base metal deposits in the world-class Irish Orefield occur in association with normal faults. Despite their economic importance, however, the fault networks and structural framework at depth are still poorly constrained. The Irish Carboniferous Basin is an excellent area to study the extensional fault systems and evolution of rift basins, given the relatively low amounts of later compressional deformation and metamorphism, and because high-quality subsurface datasets exist from several decades of mineral exploration. Our work aimed at developing a coherent structural framework for the Lower Carboniferous in Ireland, to unravel the geometries and kinematics of faulting in a carbonate-dominated rift basin that developed on top of a strong pre-existing structural template in the underlying basement rocks.
We have defined the geometry of key fault systems in the rift across a wide range of scales, using three-dimensional integrated analysis of large datasets. These datasets include public and proprietary onshore 2D reflection seismic, mapping, drillhole, micro-palaeontological, aeromagnetic, electromagnetic, and ground gravity data. Our work has revealed the nature of segmentation patterns and interactions of normal faults, including synthetic and conjugate relay zones. Quantification of fault parameters, kinematic analysis and kinematic restoration have allowed us to gain insights into the distribution of extension during rifting in time and space, using growth sequences and facies changes on faults. The analysis of this structural framework in relation to several mineral deposits, and in combination with lithofacies distribution and the development of bathymetry during basin formation, allows us to better understand current and past fluid flow pathways, especially in relation to base metal mineralising events.
How to cite: Torremans, K., Conneally, J., Güven, J., Doyle, R., Guo, J., Dunlevy, E., and Walsh, J.: Fault interactions, fault kinematics, and evolution of the structural framework in the Irish Lower Carboniferous, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4557, https://doi.org/10.5194/egusphere-egu2020-4557, 2020.
EGU2020-5092 | Displays | TS4.2 | Highlight
3D fault network development at the Galicia magma-poor margin, North-AtlanticDerren Cresswell, Gaël Lymer, and Tim Reston
We investigate the structures of hyper-extended continental crust and the 3D nature of the development of syn-rift fault networks at the Galicia margin, West of Spain, based on observations from a 3D multi-channel seismic reflection dataset acquired in 2013. This seismic volume provides, for the first time, 3D high-resolution imaging of a fault network geometry above a detachment fault (The “S reflector”) in the distal setting of a continental margin. The Galicia margin is sediment-starved, magma-poor and salt-free, thus providing optimal observations of the structures through seismic data.
We use the 3D data to observe the geometries of the faults, to analyse the fault heaves at different levels of the litho-stratigraphic sequence (i.e. at the top of the crystalline basement, at the top of the pre-rift/early syn-rift sediments and at the top of the syn-kinematic sediments), and to make a stratigraphic analysis to constrain the dynamics and the kinematics of fault activity within the successive half-grabens.
Our 3D interpretations demonstrate that the continental crust thins to zero during the rifting by the simultaneous development of initially individual fault planes, which progressively link with adjacent faults to form a network of active faults. The linked roots of the faults altogether form the surface of the S at depth, and allow the oceanward propagation of the detachment fault during the rifting. The faults throughout the network remained active and progressively rotated with further extension, until their deactivation when they acquired an angle of ~30°. Whereupon, a new network of active, initially isolated, faults developed and linked one step (~10 km) oceanward. The system repeats until the break-up of the continental crust, resulting in the progressive focussing of the locus of the extension toward the ocean, where the continental crust is the thinnest.
Given the similitude of the features observed at the Galicia margin with other magma poor continental margins, we expect that most margins worldwide might have formed following similar processes, thus representing a paradigm shift in the global understanding of late fault network development at rifted margins during continental break-up.
How to cite: Cresswell, D., Lymer, G., and Reston, T.: 3D fault network development at the Galicia magma-poor margin, North-Atlantic , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5092, https://doi.org/10.5194/egusphere-egu2020-5092, 2020.
We investigate the structures of hyper-extended continental crust and the 3D nature of the development of syn-rift fault networks at the Galicia margin, West of Spain, based on observations from a 3D multi-channel seismic reflection dataset acquired in 2013. This seismic volume provides, for the first time, 3D high-resolution imaging of a fault network geometry above a detachment fault (The “S reflector”) in the distal setting of a continental margin. The Galicia margin is sediment-starved, magma-poor and salt-free, thus providing optimal observations of the structures through seismic data.
We use the 3D data to observe the geometries of the faults, to analyse the fault heaves at different levels of the litho-stratigraphic sequence (i.e. at the top of the crystalline basement, at the top of the pre-rift/early syn-rift sediments and at the top of the syn-kinematic sediments), and to make a stratigraphic analysis to constrain the dynamics and the kinematics of fault activity within the successive half-grabens.
Our 3D interpretations demonstrate that the continental crust thins to zero during the rifting by the simultaneous development of initially individual fault planes, which progressively link with adjacent faults to form a network of active faults. The linked roots of the faults altogether form the surface of the S at depth, and allow the oceanward propagation of the detachment fault during the rifting. The faults throughout the network remained active and progressively rotated with further extension, until their deactivation when they acquired an angle of ~30°. Whereupon, a new network of active, initially isolated, faults developed and linked one step (~10 km) oceanward. The system repeats until the break-up of the continental crust, resulting in the progressive focussing of the locus of the extension toward the ocean, where the continental crust is the thinnest.
Given the similitude of the features observed at the Galicia margin with other magma poor continental margins, we expect that most margins worldwide might have formed following similar processes, thus representing a paradigm shift in the global understanding of late fault network development at rifted margins during continental break-up.
How to cite: Cresswell, D., Lymer, G., and Reston, T.: 3D fault network development at the Galicia magma-poor margin, North-Atlantic , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5092, https://doi.org/10.5194/egusphere-egu2020-5092, 2020.
EGU2020-21550 | Displays | TS4.2 | Highlight
Three-dimensional analysis of normal faults in the Horda Platform (North Sea): the possible influence of stress perturbations on fault geometriesLuca Collanega, Donatella Mellere, Matteo Massironi, and Anna Breda
Rift-related faults often display non-rectilinear geometries, which have been interpreted as (i) the result of linkage between different fault segments -developed during a single or more tectonic phases-, (ii) as curvilinear faults due to gravitational collapse, (iii) as inherited basement trends. Disentangling these processes is generally difficult, with multi-phase rifting and reactivation of pre-existing structures being the most intuitive and commonly adopted explanations.
Here, we use 3D seismic data to reconstruct the evolution of a couple of intersecting, curvilinear faults in the Horda Platform (Northern North Sea), which is characterised by a complex history of reactivation and multi-phase extension during the Jurassic-Cretaceous rifting. By reconstructing the three-dimensional geometry of the fault planes, we highlight that one fault follows the trend of the Permian-Triassic rift along its entire length, whereas the other, strongly curvilinear, fault appears to be partially deflected from it. By using time-thickness maps and kinematic analyses, we show that the partially deflected fault initiated in the Late Jurassic, soon after the other one (which activated in the Middle Jurassic). Notably, the younger fault flexes from the inherited Permian-Triassic trend as it approaches the other, more mature, fault, getting perpendicular to -and finally crosscutting- it. Hence, the curvilinear geometry developed during the upward propagation of the fault plane during the Jurassic-Cretaceous rifting, suggesting that such change of strike was driven by the influence of the more mature fault and is not due to structural inheritance. Similar deflections can be observed also in other areas of the dataset, with incipient faults flexing towards more mature structures.
More generally, newer faults have been shown to deflect perpendicularly to pre-existing faults both in analogue and numerical models, suggesting we are facing a general process. These strike deflections suggest a stress re-orientation in the vicinity of well-developed structures, and not just simply a stress-drop as widely indicated by fault spacing and throw distribution of parallel faults. This is consistent with observations on deflected normal faults developing in correspondence to oblique basement fabrics as well as with the numerical model of the stress field by Homberg et al. (1997). Hence, our three-dimensional analysis of fault geometries suggests that the well-established concept of “fault-related stress-drop” should be broadened into the concept of “fault-related stress-reorientation”.
References
Homberg, C., Hu, J.C., Angelier, J., Bergerat, F., Lacombe, O., 1997. Characterization of stress perturbations near major fault zones: insights from 2-D distinct-element numerical modelling and field studies (Jura mountains). Journal of Structural Geology 19, 703–718. https://doi.org/10.1016/S0191-8141(96)00104-6
How to cite: Collanega, L., Mellere, D., Massironi, M., and Breda, A.: Three-dimensional analysis of normal faults in the Horda Platform (North Sea): the possible influence of stress perturbations on fault geometries, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21550, https://doi.org/10.5194/egusphere-egu2020-21550, 2020.
Rift-related faults often display non-rectilinear geometries, which have been interpreted as (i) the result of linkage between different fault segments -developed during a single or more tectonic phases-, (ii) as curvilinear faults due to gravitational collapse, (iii) as inherited basement trends. Disentangling these processes is generally difficult, with multi-phase rifting and reactivation of pre-existing structures being the most intuitive and commonly adopted explanations.
Here, we use 3D seismic data to reconstruct the evolution of a couple of intersecting, curvilinear faults in the Horda Platform (Northern North Sea), which is characterised by a complex history of reactivation and multi-phase extension during the Jurassic-Cretaceous rifting. By reconstructing the three-dimensional geometry of the fault planes, we highlight that one fault follows the trend of the Permian-Triassic rift along its entire length, whereas the other, strongly curvilinear, fault appears to be partially deflected from it. By using time-thickness maps and kinematic analyses, we show that the partially deflected fault initiated in the Late Jurassic, soon after the other one (which activated in the Middle Jurassic). Notably, the younger fault flexes from the inherited Permian-Triassic trend as it approaches the other, more mature, fault, getting perpendicular to -and finally crosscutting- it. Hence, the curvilinear geometry developed during the upward propagation of the fault plane during the Jurassic-Cretaceous rifting, suggesting that such change of strike was driven by the influence of the more mature fault and is not due to structural inheritance. Similar deflections can be observed also in other areas of the dataset, with incipient faults flexing towards more mature structures.
More generally, newer faults have been shown to deflect perpendicularly to pre-existing faults both in analogue and numerical models, suggesting we are facing a general process. These strike deflections suggest a stress re-orientation in the vicinity of well-developed structures, and not just simply a stress-drop as widely indicated by fault spacing and throw distribution of parallel faults. This is consistent with observations on deflected normal faults developing in correspondence to oblique basement fabrics as well as with the numerical model of the stress field by Homberg et al. (1997). Hence, our three-dimensional analysis of fault geometries suggests that the well-established concept of “fault-related stress-drop” should be broadened into the concept of “fault-related stress-reorientation”.
References
Homberg, C., Hu, J.C., Angelier, J., Bergerat, F., Lacombe, O., 1997. Characterization of stress perturbations near major fault zones: insights from 2-D distinct-element numerical modelling and field studies (Jura mountains). Journal of Structural Geology 19, 703–718. https://doi.org/10.1016/S0191-8141(96)00104-6
How to cite: Collanega, L., Mellere, D., Massironi, M., and Breda, A.: Three-dimensional analysis of normal faults in the Horda Platform (North Sea): the possible influence of stress perturbations on fault geometries, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21550, https://doi.org/10.5194/egusphere-egu2020-21550, 2020.
EGU2020-15764 | Displays | TS4.2
Three-dimensional geometries of relay zones in normal faultsGiovanni Camanni, Vincent Roche, Conrad Childs, Tom Manzocchi, John Walsh, John Conneally, Muhammad Mudasar Saqab, and Efstratios Delogkos
Individual normal faults are rarely single planar surfaces and often comprise arrays of fault segments arising from the earliest stages of fault propagation. Current models for the geometry and formation of relay zones between adjacent fault segments have been informed mainly by 2D analysis from either maps or cross-sections observed in outcrop and, to a lesser extent, by the analysis of relay zones from 3D seismic reflection data. Using high quality 3D seismic reflection datasets from a selection of sedimentary basins, we investigate fundamental characteristics of segmentation from the analysis of 67 normal faults with modest displacements (< ca. 190 m) which preserve the 3D geometry of 532 relay zones. Our analysis shows that relay zones most often develop by bifurcation from a single fault surface but can also arise from the formation of segments which are disconnected in 3D. Relay zones generally occur between fault segments that step in either the dip or strike direction, and oblique relay zones with an intermediate orientation are less frequent. This is attributed to the influence of mechanical stratigraphy, and to a tendency for faults to locally propagate laterally and vertically rather than obliquely. Cross-sectional stepping of relay zones typically forms contractional rather than extensional relay zones, a configuration which is attributed to the development of early stage Riedel shears associated with fault localisation. Comparing datasets from different geological settings suggests that the mechanical heterogeneity of the faulted sequence and the influence of pre-existing structure are the underlying controls on the geometrical characteristics of relay zones in normal faults, and different combinations of these two controls can account for the variation in fault zone structure observed between datasets.
How to cite: Camanni, G., Roche, V., Childs, C., Manzocchi, T., Walsh, J., Conneally, J., Saqab, M. M., and Delogkos, E.: Three-dimensional geometries of relay zones in normal faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15764, https://doi.org/10.5194/egusphere-egu2020-15764, 2020.
Individual normal faults are rarely single planar surfaces and often comprise arrays of fault segments arising from the earliest stages of fault propagation. Current models for the geometry and formation of relay zones between adjacent fault segments have been informed mainly by 2D analysis from either maps or cross-sections observed in outcrop and, to a lesser extent, by the analysis of relay zones from 3D seismic reflection data. Using high quality 3D seismic reflection datasets from a selection of sedimentary basins, we investigate fundamental characteristics of segmentation from the analysis of 67 normal faults with modest displacements (< ca. 190 m) which preserve the 3D geometry of 532 relay zones. Our analysis shows that relay zones most often develop by bifurcation from a single fault surface but can also arise from the formation of segments which are disconnected in 3D. Relay zones generally occur between fault segments that step in either the dip or strike direction, and oblique relay zones with an intermediate orientation are less frequent. This is attributed to the influence of mechanical stratigraphy, and to a tendency for faults to locally propagate laterally and vertically rather than obliquely. Cross-sectional stepping of relay zones typically forms contractional rather than extensional relay zones, a configuration which is attributed to the development of early stage Riedel shears associated with fault localisation. Comparing datasets from different geological settings suggests that the mechanical heterogeneity of the faulted sequence and the influence of pre-existing structure are the underlying controls on the geometrical characteristics of relay zones in normal faults, and different combinations of these two controls can account for the variation in fault zone structure observed between datasets.
How to cite: Camanni, G., Roche, V., Childs, C., Manzocchi, T., Walsh, J., Conneally, J., Saqab, M. M., and Delogkos, E.: Three-dimensional geometries of relay zones in normal faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15764, https://doi.org/10.5194/egusphere-egu2020-15764, 2020.
EGU2020-19706 | Displays | TS4.2
The three-dimensional geometries of segmented normal faultsJohn Walsh, Vincent Roche, Giovanni Camanni, Conrad Childs, Tom Manzocchi, John Conneally, Muhammad Mudasar Saqab, and Efstratios Delogkos
Normal faults are often complex three dimensional structures comprising multiple sub-parallel segments separated by intervening relay zones. In this study we outline geometrical characterisations capturing this 3D complexity and providing a semi-quantitative basis for the comparison of faults and for defining the factors controlling their geometrical evolution.
Individual relay zones can be assigned to one of four types according to their form (i.e. whether the bounding segments are unconnected in 3D or merge into a single surface) and their orientation (i.e. whether they are slip-parallel or slip-perpendicular). From the detailed analysis of 84 fault arrays mapped from 3D seismic reflection surveys (including 63 from our mapping of 8 different study areas and 21 derived from the literature), we show that the 3D geometry of fault arrays can be quantitatively defined on the basis of the relative numbers of these types of relay zones.
Detailed mapping of fault zones indicates that whilst they can individually contain all four types of relay zone, their relative proportions varies between different study areas. Differences in the proportions of relay zone types are attributed to two primary controls, the mechanical heterogeneity of the faulted sequence and the presence of basement structure. For example, relay zones with an upward bifurcating geometry are prevalent in faults that reactivate deeper structures, whereas the formation of laterally bifurcating relays is promoted by heterogeneous mechanical stratigraphy.
Fault arrays in the literature generally do not contain the full range of possible relay zone type but tend to comprise either all bifurcating relay zones or all unconnected relay zones. These end-member fault geometries have led to contrasting conceptual models for the growth of faults. The mapping conducted here suggests that the proportion of bifurcating relay zones increases as data resolution increases and that fault surface bifurcation is ubiquitous. Models for the geometrical evolution of fault arrays must account for the full range of relay zone geometries that appears to be a characteristic of all faults.
How to cite: Walsh, J., Roche, V., Camanni, G., Childs, C., Manzocchi, T., Conneally, J., Saqab, M. M., and Delogkos, E.: The three-dimensional geometries of segmented normal faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19706, https://doi.org/10.5194/egusphere-egu2020-19706, 2020.
Normal faults are often complex three dimensional structures comprising multiple sub-parallel segments separated by intervening relay zones. In this study we outline geometrical characterisations capturing this 3D complexity and providing a semi-quantitative basis for the comparison of faults and for defining the factors controlling their geometrical evolution.
Individual relay zones can be assigned to one of four types according to their form (i.e. whether the bounding segments are unconnected in 3D or merge into a single surface) and their orientation (i.e. whether they are slip-parallel or slip-perpendicular). From the detailed analysis of 84 fault arrays mapped from 3D seismic reflection surveys (including 63 from our mapping of 8 different study areas and 21 derived from the literature), we show that the 3D geometry of fault arrays can be quantitatively defined on the basis of the relative numbers of these types of relay zones.
Detailed mapping of fault zones indicates that whilst they can individually contain all four types of relay zone, their relative proportions varies between different study areas. Differences in the proportions of relay zone types are attributed to two primary controls, the mechanical heterogeneity of the faulted sequence and the presence of basement structure. For example, relay zones with an upward bifurcating geometry are prevalent in faults that reactivate deeper structures, whereas the formation of laterally bifurcating relays is promoted by heterogeneous mechanical stratigraphy.
Fault arrays in the literature generally do not contain the full range of possible relay zone type but tend to comprise either all bifurcating relay zones or all unconnected relay zones. These end-member fault geometries have led to contrasting conceptual models for the growth of faults. The mapping conducted here suggests that the proportion of bifurcating relay zones increases as data resolution increases and that fault surface bifurcation is ubiquitous. Models for the geometrical evolution of fault arrays must account for the full range of relay zone geometries that appears to be a characteristic of all faults.
How to cite: Walsh, J., Roche, V., Camanni, G., Childs, C., Manzocchi, T., Conneally, J., Saqab, M. M., and Delogkos, E.: The three-dimensional geometries of segmented normal faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19706, https://doi.org/10.5194/egusphere-egu2020-19706, 2020.
EGU2020-22497 | Displays | TS4.2
3D geometry of outcrop-scale normal faults from Taranaki, New ZealandInbar Vaknin, Andy Nicol, and Conrad Childs
Fault surfaces and fault zones have been shown to have complex geometries comprising a range of morphologies including, segmentation, tip-line splays and slip-surface corrugations (e.g., Childs et al., 2009*). The three-dimensional (3D) geometries of faults (and fault zones) is difficult to determine from outcrop data which are typically 2D and limited in size. In this poster we examine the small-scale geometries of faults from normal faults cropping out in well bedded parts of the Mount Messenger and Mahakatino formations in Taranaki, New Zealand. We present two main datasets; i) measurements and maps of 2D vertical and horizontal sections for in excess of 200 faults and, ii) 3D fault model of a small-fault (vertical displacement ~1 cm) produced by serial fault-perpendicular sections of a block 10x10x13 cm. The sectioned block contains a single fault that offsets sand and silt layers, and comprises two main dilational bends; in the 3D model we map displacement, bedding and fault geometry for the sectioned fault zone. Faults in the 2D dataset comprise a range of geometries including, vertical segmentation, bends, splays and fault-surface corrugations. Although we have little information on the local magnitudes and orientations of stresses during faulting, geometric analysis of the fault zones provides information on the relationships between bed characteristics (e.g., thickness, induration and composition) and fault-surface orientations. The available data supports the view that the strike and dip of fault surfaces vary by up to 25° producing undulations or corrugations on fault surfaces over a range of scales from millimetres to metres and in both horizontal and vertical directions. Preliminary analysis of the available data suggests that these corrugations appear to reflect fault refractions due to changing bed lithologies (unexpectedly the steepest sections of faults are in mudstone beds), breaching of relays and development of conjugate fault sets. The relative importance of these factors and their importance for fault geometry will be explored further in the poster.
*Childs, C., Walsh, J.J., Manzocchi, T., Bonson, C., Nicol A., Schöpfer, M.P.J. 2009. A geometric model of fault zone and fault rock thickness variations. Journal of Structural Geology 31, 117-127.
How to cite: Vaknin, I., Nicol, A., and Childs, C.: 3D geometry of outcrop-scale normal faults from Taranaki, New Zealand, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22497, https://doi.org/10.5194/egusphere-egu2020-22497, 2020.
Fault surfaces and fault zones have been shown to have complex geometries comprising a range of morphologies including, segmentation, tip-line splays and slip-surface corrugations (e.g., Childs et al., 2009*). The three-dimensional (3D) geometries of faults (and fault zones) is difficult to determine from outcrop data which are typically 2D and limited in size. In this poster we examine the small-scale geometries of faults from normal faults cropping out in well bedded parts of the Mount Messenger and Mahakatino formations in Taranaki, New Zealand. We present two main datasets; i) measurements and maps of 2D vertical and horizontal sections for in excess of 200 faults and, ii) 3D fault model of a small-fault (vertical displacement ~1 cm) produced by serial fault-perpendicular sections of a block 10x10x13 cm. The sectioned block contains a single fault that offsets sand and silt layers, and comprises two main dilational bends; in the 3D model we map displacement, bedding and fault geometry for the sectioned fault zone. Faults in the 2D dataset comprise a range of geometries including, vertical segmentation, bends, splays and fault-surface corrugations. Although we have little information on the local magnitudes and orientations of stresses during faulting, geometric analysis of the fault zones provides information on the relationships between bed characteristics (e.g., thickness, induration and composition) and fault-surface orientations. The available data supports the view that the strike and dip of fault surfaces vary by up to 25° producing undulations or corrugations on fault surfaces over a range of scales from millimetres to metres and in both horizontal and vertical directions. Preliminary analysis of the available data suggests that these corrugations appear to reflect fault refractions due to changing bed lithologies (unexpectedly the steepest sections of faults are in mudstone beds), breaching of relays and development of conjugate fault sets. The relative importance of these factors and their importance for fault geometry will be explored further in the poster.
*Childs, C., Walsh, J.J., Manzocchi, T., Bonson, C., Nicol A., Schöpfer, M.P.J. 2009. A geometric model of fault zone and fault rock thickness variations. Journal of Structural Geology 31, 117-127.
How to cite: Vaknin, I., Nicol, A., and Childs, C.: 3D geometry of outcrop-scale normal faults from Taranaki, New Zealand, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22497, https://doi.org/10.5194/egusphere-egu2020-22497, 2020.
EGU2020-20580 | Displays | TS4.2
Transfer of displacement between faults of opposed dipConrad Childs, Robert Worthington, John Walsh, and Vincent Roche
The transfer of displacement between faults that dip in the same direction is well understood and relay ramps between adjacent fault segments have been frequently described. Perhaps counterintuitively, displacement can also be transferred between faults that dip in opposite directions but the structure at the boundaries between opposed dipping faults is not well understood. We constrain the mechanism by which displacement is transferred between opposed-dipping faults by examining the geometries of faulted horizons and fault throw distributions at these ‘conjugate relay zones’.
Structure contour maps of horizons offset by overlapping opposed-dipping faults from different extensional settings display a consistent pattern. Above the line of intersection between the conjugate faults the deformed horizon is flat between converging faults and displacement transfer is reflected in changes in footwall elevation. Below the line of fault intersection the mutual footwall is flat and elevation changes occur in the hanging walls of the divergent faults. These elevation changes can be explained as a simple superposition of the deformation fields of two faults that have retarded lateral propagation due to the presence of the other synchronous fault, irrespective of whether the two faults actually intersect. The observed patterns of horizon elevation strongly resemble those seen at boundaries between adjacent basin-scale half-graben of opposed polarity.
How to cite: Childs, C., Worthington, R., Walsh, J., and Roche, V.: Transfer of displacement between faults of opposed dip, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20580, https://doi.org/10.5194/egusphere-egu2020-20580, 2020.
The transfer of displacement between faults that dip in the same direction is well understood and relay ramps between adjacent fault segments have been frequently described. Perhaps counterintuitively, displacement can also be transferred between faults that dip in opposite directions but the structure at the boundaries between opposed dipping faults is not well understood. We constrain the mechanism by which displacement is transferred between opposed-dipping faults by examining the geometries of faulted horizons and fault throw distributions at these ‘conjugate relay zones’.
Structure contour maps of horizons offset by overlapping opposed-dipping faults from different extensional settings display a consistent pattern. Above the line of intersection between the conjugate faults the deformed horizon is flat between converging faults and displacement transfer is reflected in changes in footwall elevation. Below the line of fault intersection the mutual footwall is flat and elevation changes occur in the hanging walls of the divergent faults. These elevation changes can be explained as a simple superposition of the deformation fields of two faults that have retarded lateral propagation due to the presence of the other synchronous fault, irrespective of whether the two faults actually intersect. The observed patterns of horizon elevation strongly resemble those seen at boundaries between adjacent basin-scale half-graben of opposed polarity.
How to cite: Childs, C., Worthington, R., Walsh, J., and Roche, V.: Transfer of displacement between faults of opposed dip, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20580, https://doi.org/10.5194/egusphere-egu2020-20580, 2020.
EGU2020-1187 | Displays | TS4.2 | Highlight
The temporal evolution of syn-sedimentary normal faults and the possible role of tip retreatBailey Lathrop, Christopher Jackson, Rebecca Bell, and Atle Rotevatn
We need to understand how normal faults grow in order to better determine the tectono-stratigraphic evolution of rifts, and the distribution and size of potentially hazardous earthquakes. The growth of normal faults is commonly described by two models: 1) the propagating fault model (isolated growth model), and 2) the constant-length model. The propagating fault model envisages a sympathetic increase between fault lengthening (L) and displacement (D), whereas the constant-length model states that faults reach their near-final length before accumulating significant displacement (Walsh et al., 2002). Several relatively recent studies agree that faults generally follow a constant-length model, or a “hybrid model” of the two, where most faults reach their near final length within the first 20-30% of their lives, and accrue displacement throughout. Furthermore, in the past 20 years, much research has focused on how faults grow; relatively few studies have questioned what happens to the fault geometry as it becomes inactive, i.e. do faults abruptly die, or do they more gradually become inactive by so-called tip retreat. We here use a 3D seismic reflection dataset from the Exmouth Plateau, offshore Australia to support a hybrid fault growth model for normal faults, and to also determine the relationship between length and displacement as a fault dies. We show that the studied faults grew in three distinct stages: a lengthening stage (<30% of the faults life), a displacement accrual stage (30-75%), and a possible tip retreat stage (75%-end). This work has important implications in our understanding of the temporal evolution of normal faults, both how they grow and how they die.
How to cite: Lathrop, B., Jackson, C., Bell, R., and Rotevatn, A.: The temporal evolution of syn-sedimentary normal faults and the possible role of tip retreat, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1187, https://doi.org/10.5194/egusphere-egu2020-1187, 2020.
We need to understand how normal faults grow in order to better determine the tectono-stratigraphic evolution of rifts, and the distribution and size of potentially hazardous earthquakes. The growth of normal faults is commonly described by two models: 1) the propagating fault model (isolated growth model), and 2) the constant-length model. The propagating fault model envisages a sympathetic increase between fault lengthening (L) and displacement (D), whereas the constant-length model states that faults reach their near-final length before accumulating significant displacement (Walsh et al., 2002). Several relatively recent studies agree that faults generally follow a constant-length model, or a “hybrid model” of the two, where most faults reach their near final length within the first 20-30% of their lives, and accrue displacement throughout. Furthermore, in the past 20 years, much research has focused on how faults grow; relatively few studies have questioned what happens to the fault geometry as it becomes inactive, i.e. do faults abruptly die, or do they more gradually become inactive by so-called tip retreat. We here use a 3D seismic reflection dataset from the Exmouth Plateau, offshore Australia to support a hybrid fault growth model for normal faults, and to also determine the relationship between length and displacement as a fault dies. We show that the studied faults grew in three distinct stages: a lengthening stage (<30% of the faults life), a displacement accrual stage (30-75%), and a possible tip retreat stage (75%-end). This work has important implications in our understanding of the temporal evolution of normal faults, both how they grow and how they die.
How to cite: Lathrop, B., Jackson, C., Bell, R., and Rotevatn, A.: The temporal evolution of syn-sedimentary normal faults and the possible role of tip retreat, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1187, https://doi.org/10.5194/egusphere-egu2020-1187, 2020.
EGU2020-9046 | Displays | TS4.2
Geometrical comparison of outcrop data and discrete element models of extensional fault zones in layered carbonatesHagen Deckert, Steffen Abe, and Wolfgang Bauer
In the course of hydrocarbon or geothermal exploration the characterisation of fault zone architectures is of interest for fluid flow modelling and geomechanical studies. Seismic data normally offer the best information for the identification of fault zone geometries in sedimentary basins. However, the internal structure or the damage zone of a fault can be hardly resolved with seismic data as displacements along single fault strands or fractures are by far too small. Thus, it is not possible to directly map small scale faults with seismic methods, though these structures might significantly influence fluid flow. We try to examine the architecture of extensional fault zones in carbonate rocks at subseismic scales by using discrete element method (DEM) techniques to numerically simulate the evolution of fault zones including their associated damage zones.
As a case study we have analysed the geometry, displacement and fault width of normal faults in fine grained jurassic limestones in a quarry in Franconia, Germany. The quarry shows a rather simple set of conjugated 60deg dipping normal faults. Displacement is rather small and varies between c. 5cm up to c. 2m, some faults show almost no offset. The fault thickness varies between 2cm and c. 1m. A closer investigation of the fault geometries reveals, next to planar parts, sometimes complex fault zone structures including restraining and releasing bends, multiple fault strands as well as lenses and associated riedel shears. Analysis of high resolution photogrammetric data revealed a high number of small scale fractures between neighbouring discrete fault surfaces which are interpreted as highly fractured damage zones. Some faults with rather small displacement suggest that the overall inclination of the fault is a result of small subvertical sections which are connected in a staircase like appearance.
The DEM models simulate normal faulting in a layered marl-limestone sequence driven by the displacement of an underlying basement fault. Different layer geometries and effective vertical stresses in the range of 15-45 MPa, equivalent to an overburden thickness of c. 1000-3000m, have been used in the models. The stress range covers the maximum burial depth of the carbonates, which is assumed to be c. 1500m. Material properties used in the DEM were calibrated based on laboratory data, i.e. results of triaxial deformation tests on the studied limestones.
Results of the models show fault geometries which resemble those observed in the studied outcrop. In particularly under low stress, small offsets and with strongly decoupled layers we observe steeply dipping faults (>70deg) which also show staircase structures composed of sub-vertical fractures within each of the layers and horizontal offsets along the layer interfaces. We also observe the development of multiple fault strands and associated damage zones.
Our study shows that the DEM models are capable to reproduce observed fault geometries and damage zones. The results help to understand fault zone architectures and depict highly fractured areas in a sub-seismic scale.
How to cite: Deckert, H., Abe, S., and Bauer, W.: Geometrical comparison of outcrop data and discrete element models of extensional fault zones in layered carbonates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9046, https://doi.org/10.5194/egusphere-egu2020-9046, 2020.
In the course of hydrocarbon or geothermal exploration the characterisation of fault zone architectures is of interest for fluid flow modelling and geomechanical studies. Seismic data normally offer the best information for the identification of fault zone geometries in sedimentary basins. However, the internal structure or the damage zone of a fault can be hardly resolved with seismic data as displacements along single fault strands or fractures are by far too small. Thus, it is not possible to directly map small scale faults with seismic methods, though these structures might significantly influence fluid flow. We try to examine the architecture of extensional fault zones in carbonate rocks at subseismic scales by using discrete element method (DEM) techniques to numerically simulate the evolution of fault zones including their associated damage zones.
As a case study we have analysed the geometry, displacement and fault width of normal faults in fine grained jurassic limestones in a quarry in Franconia, Germany. The quarry shows a rather simple set of conjugated 60deg dipping normal faults. Displacement is rather small and varies between c. 5cm up to c. 2m, some faults show almost no offset. The fault thickness varies between 2cm and c. 1m. A closer investigation of the fault geometries reveals, next to planar parts, sometimes complex fault zone structures including restraining and releasing bends, multiple fault strands as well as lenses and associated riedel shears. Analysis of high resolution photogrammetric data revealed a high number of small scale fractures between neighbouring discrete fault surfaces which are interpreted as highly fractured damage zones. Some faults with rather small displacement suggest that the overall inclination of the fault is a result of small subvertical sections which are connected in a staircase like appearance.
The DEM models simulate normal faulting in a layered marl-limestone sequence driven by the displacement of an underlying basement fault. Different layer geometries and effective vertical stresses in the range of 15-45 MPa, equivalent to an overburden thickness of c. 1000-3000m, have been used in the models. The stress range covers the maximum burial depth of the carbonates, which is assumed to be c. 1500m. Material properties used in the DEM were calibrated based on laboratory data, i.e. results of triaxial deformation tests on the studied limestones.
Results of the models show fault geometries which resemble those observed in the studied outcrop. In particularly under low stress, small offsets and with strongly decoupled layers we observe steeply dipping faults (>70deg) which also show staircase structures composed of sub-vertical fractures within each of the layers and horizontal offsets along the layer interfaces. We also observe the development of multiple fault strands and associated damage zones.
Our study shows that the DEM models are capable to reproduce observed fault geometries and damage zones. The results help to understand fault zone architectures and depict highly fractured areas in a sub-seismic scale.
How to cite: Deckert, H., Abe, S., and Bauer, W.: Geometrical comparison of outcrop data and discrete element models of extensional fault zones in layered carbonates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9046, https://doi.org/10.5194/egusphere-egu2020-9046, 2020.
EGU2020-10293 | Displays | TS4.2
Investigating fault sinuosity using discrete element modelling in 3DJanis Aleksans, Conrad Childs, and Martin Schöpfer
Scaled numerical models of faults are useful complements to geological data and by providing insights into fault dynamics they can improve our understanding of the different stages of development of normal fault systems, from nucleation through to localisation and maturity.
In this work, we use Particle Flow Code in three dimensions, which implements the Distinct Element Method (DEM), to study the development of systems of normal faults. The modelling is based on spherical particles that interact via a linear force-displacement law. Cohesion is modelled by adding linear elastic bonds to particle-particle contacts. These bonds break if the critical normal or shear strength is exceeded, thus creating a fracture surface within the rock volume. Model boundaries are represented by rigid and frictionless walls enclosing the modelled volume vertically and at the ends, with periodic lateral boundaries. Extension is replicated by slowly moving the end walls away from the centre while maintaining a constant confining pressure.
The DEM models replicate many aspects of the geometry and dynamics of natural fault systems with stages of fault nucleation, propagation, interaction and linkage. Here we focus on the sinuosity of model fault map traces which show a similar variability to that seen in nature. In the models, fault trace sinuosity is negatively correlated with the Young’s modulus of the rock, so that faults become less sinuous as the stiffness of the solid medium increases. This relationship supports a model in which the lengths of fault segments formed at the early stages of extension are smaller in rocks with lower Young’s modulus than in rocks with higher Young’s modulus. Longer initial fault segments become connected as displacement increases, to give lower sinuosity faults.
How to cite: Aleksans, J., Childs, C., and Schöpfer, M.: Investigating fault sinuosity using discrete element modelling in 3D, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10293, https://doi.org/10.5194/egusphere-egu2020-10293, 2020.
Scaled numerical models of faults are useful complements to geological data and by providing insights into fault dynamics they can improve our understanding of the different stages of development of normal fault systems, from nucleation through to localisation and maturity.
In this work, we use Particle Flow Code in three dimensions, which implements the Distinct Element Method (DEM), to study the development of systems of normal faults. The modelling is based on spherical particles that interact via a linear force-displacement law. Cohesion is modelled by adding linear elastic bonds to particle-particle contacts. These bonds break if the critical normal or shear strength is exceeded, thus creating a fracture surface within the rock volume. Model boundaries are represented by rigid and frictionless walls enclosing the modelled volume vertically and at the ends, with periodic lateral boundaries. Extension is replicated by slowly moving the end walls away from the centre while maintaining a constant confining pressure.
The DEM models replicate many aspects of the geometry and dynamics of natural fault systems with stages of fault nucleation, propagation, interaction and linkage. Here we focus on the sinuosity of model fault map traces which show a similar variability to that seen in nature. In the models, fault trace sinuosity is negatively correlated with the Young’s modulus of the rock, so that faults become less sinuous as the stiffness of the solid medium increases. This relationship supports a model in which the lengths of fault segments formed at the early stages of extension are smaller in rocks with lower Young’s modulus than in rocks with higher Young’s modulus. Longer initial fault segments become connected as displacement increases, to give lower sinuosity faults.
How to cite: Aleksans, J., Childs, C., and Schöpfer, M.: Investigating fault sinuosity using discrete element modelling in 3D, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10293, https://doi.org/10.5194/egusphere-egu2020-10293, 2020.
EGU2020-20632 | Displays | TS4.2
Estimation of Carbon Dioxide emissions along an active fault by using geoelectrical measurementsEster Piegari, Rosa Di Maio, Rosanna Salone, and Claudio De Paola
In the last twenty years, a growing interest is noticed in quantifying non-volcanic degassing, which could represent a significant input of CO2 into the atmosphere. Large emissions of non-volcanic carbon dioxide usually take place in seismically active zones, where the existence of a positive spatial correlation between gas discharges and extensional tectonic regimes has been confirmed by seismic data. Extensional stress plays a key role in creating pathways for the rising of gases at micro- and macro-scales, increasing the rock permeability and connecting the deep crust to the earth surface. Geoelectrical investigations, which are very sensitive to permeability changes, provide accurate volumetric reconstructions of the physical properties of the rocks and, therefore, are fundamental not only for the definition of the seismic-active zone geometry, but also for understanding the processes that govern the flow of fluids along the damage zone. In this framework, we present the results of an integrated approach where geoelectrical and passive seismic data are used to construct a 3D geological model, whose simulated temporal evolution allowed the estimation of CO2 flux along an active fault in the area of Matese Ridge (Southern Apennines, Italy). By varying the geometry of the source system and the permeability values of the damage zone, characteristic times for the upward migration of CO2 through a thick layer of silts and clays have been estimated and CO2 fluxes comparable with the observed values in the investigated area have been predicted. These findings are promising for gas hazard, as they suggest that numerical simulations of different CO2 degassing scenarios could forecast possible critical variations in the amount of CO2 emitted near the fault.
How to cite: Piegari, E., Di Maio, R., Salone, R., and De Paola, C.: Estimation of Carbon Dioxide emissions along an active fault by using geoelectrical measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20632, https://doi.org/10.5194/egusphere-egu2020-20632, 2020.
In the last twenty years, a growing interest is noticed in quantifying non-volcanic degassing, which could represent a significant input of CO2 into the atmosphere. Large emissions of non-volcanic carbon dioxide usually take place in seismically active zones, where the existence of a positive spatial correlation between gas discharges and extensional tectonic regimes has been confirmed by seismic data. Extensional stress plays a key role in creating pathways for the rising of gases at micro- and macro-scales, increasing the rock permeability and connecting the deep crust to the earth surface. Geoelectrical investigations, which are very sensitive to permeability changes, provide accurate volumetric reconstructions of the physical properties of the rocks and, therefore, are fundamental not only for the definition of the seismic-active zone geometry, but also for understanding the processes that govern the flow of fluids along the damage zone. In this framework, we present the results of an integrated approach where geoelectrical and passive seismic data are used to construct a 3D geological model, whose simulated temporal evolution allowed the estimation of CO2 flux along an active fault in the area of Matese Ridge (Southern Apennines, Italy). By varying the geometry of the source system and the permeability values of the damage zone, characteristic times for the upward migration of CO2 through a thick layer of silts and clays have been estimated and CO2 fluxes comparable with the observed values in the investigated area have been predicted. These findings are promising for gas hazard, as they suggest that numerical simulations of different CO2 degassing scenarios could forecast possible critical variations in the amount of CO2 emitted near the fault.
How to cite: Piegari, E., Di Maio, R., Salone, R., and De Paola, C.: Estimation of Carbon Dioxide emissions along an active fault by using geoelectrical measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20632, https://doi.org/10.5194/egusphere-egu2020-20632, 2020.
EGU2020-1073 | Displays | TS4.2
Bayesian Finite-fault inversion for determination of rupture geometry and slip functionHamed Davari, Anooshiravan Ansari, Sanaz Vajedian, and Navid Kheirdast
In the finite-fault modelling we aim to invert the observed data to image the earthquake rupture inside the solid crust medium. The common finite fault inversion methods usually take a planar geometry for the ruptured area, however, evidences show more complicated geometries (e.g. 2016 Mw7.8 Kaikura) can causes the seismic event. Having the advanced remote sensing technologies (e.g. InSAR), with a high data resolution in the near fault area, we can increase the accuracy for determination of rupture geometry. In this study, we consider a large three dimensional ensemble of point sources in the solid crust medium, each point source can trigger six moment tensor components that makes the model space of the problem. We then find the most probable geometry of the ruptured area by inverting the interferometric observation for moment tensor components. Using the Bayesian inversion with MCMC (Markov Chain Monte Carlo) simulation the fault geometry and static slip deformation is determined from moment tensor to have a ruptured zone that maximizes the posteriori likelihood. The proposed method would be applied to 2019 M5.9 Torkamanchay earthquake in Iran and the preliminary results is presented.
How to cite: Davari, H., Ansari, A., Vajedian, S., and Kheirdast, N.: Bayesian Finite-fault inversion for determination of rupture geometry and slip function , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1073, https://doi.org/10.5194/egusphere-egu2020-1073, 2020.
In the finite-fault modelling we aim to invert the observed data to image the earthquake rupture inside the solid crust medium. The common finite fault inversion methods usually take a planar geometry for the ruptured area, however, evidences show more complicated geometries (e.g. 2016 Mw7.8 Kaikura) can causes the seismic event. Having the advanced remote sensing technologies (e.g. InSAR), with a high data resolution in the near fault area, we can increase the accuracy for determination of rupture geometry. In this study, we consider a large three dimensional ensemble of point sources in the solid crust medium, each point source can trigger six moment tensor components that makes the model space of the problem. We then find the most probable geometry of the ruptured area by inverting the interferometric observation for moment tensor components. Using the Bayesian inversion with MCMC (Markov Chain Monte Carlo) simulation the fault geometry and static slip deformation is determined from moment tensor to have a ruptured zone that maximizes the posteriori likelihood. The proposed method would be applied to 2019 M5.9 Torkamanchay earthquake in Iran and the preliminary results is presented.
How to cite: Davari, H., Ansari, A., Vajedian, S., and Kheirdast, N.: Bayesian Finite-fault inversion for determination of rupture geometry and slip function , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1073, https://doi.org/10.5194/egusphere-egu2020-1073, 2020.
EGU2020-2426 | Displays | TS4.2
Cockade-bearing breccias, cataclasites and gouges in a single fault zone: Microstructures and geochemistyAlfons Berger and Marco Herwegh
The seismic-interseismic cycle strongly relates to the interplay between dilation owing to fracturing and frictional granular flow on one hand side and hydrothermal cementation processes on the other side. This study investigates different fault rocks of a crustal-scale fault zone in the Central Alps (Switzerland). We combine microstructural with geochemical approaches to decipher the interaction of grain size reduction via frictional processes with precipitation and resulting particle size increases. The three major fault rocks, i.e. (1) cockade-bearing breccias, (2) cataclasites, and (3) fault gouges, differ in their microstructure. The chemical data clearly demonstrate a decreasing gain of volume along this group of tectonites. Their different precipitation volumes most likely relate to dynamic changed of the local permeability of these rocks. The fluid pathways control the precipitation at different localities and times, which affect the healing of these fault rocks inducing a gain in rock strength. During the next deformation event, the extent of healing therefore directly controls the mechanical behavior of the rock. The estimated volume gain (~+110%) in cockade-bearing breccias is consistent with the seismic dilatant behavior of these frictional rocks as already proposed from other arguments (Berger and Herwegh 2019). This is in contrast to the fault-gouges with only minor gains in volume and mass resulting in a predominantly non-cohesive deformation style. This example indicates that permeability evolution (and related hydrothermal processes) strongly influences the mechanical behavior of such faults. This shows the highly dynamic behavior with time in long-lived fault systems. These dynamic changes in precipitation and resulting different strengths occur at different timescales from minutes (seismic events) to thousands of years.
Ref.: Berger, A., Herwegh, M., 2019. Cockade structures as a paleo-earthquake proxy in upper crustal hydrothermal systems. Nature Scientific Reports, 9, 9209.
How to cite: Berger, A. and Herwegh, M.: Cockade-bearing breccias, cataclasites and gouges in a single fault zone: Microstructures and geochemisty, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2426, https://doi.org/10.5194/egusphere-egu2020-2426, 2020.
The seismic-interseismic cycle strongly relates to the interplay between dilation owing to fracturing and frictional granular flow on one hand side and hydrothermal cementation processes on the other side. This study investigates different fault rocks of a crustal-scale fault zone in the Central Alps (Switzerland). We combine microstructural with geochemical approaches to decipher the interaction of grain size reduction via frictional processes with precipitation and resulting particle size increases. The three major fault rocks, i.e. (1) cockade-bearing breccias, (2) cataclasites, and (3) fault gouges, differ in their microstructure. The chemical data clearly demonstrate a decreasing gain of volume along this group of tectonites. Their different precipitation volumes most likely relate to dynamic changed of the local permeability of these rocks. The fluid pathways control the precipitation at different localities and times, which affect the healing of these fault rocks inducing a gain in rock strength. During the next deformation event, the extent of healing therefore directly controls the mechanical behavior of the rock. The estimated volume gain (~+110%) in cockade-bearing breccias is consistent with the seismic dilatant behavior of these frictional rocks as already proposed from other arguments (Berger and Herwegh 2019). This is in contrast to the fault-gouges with only minor gains in volume and mass resulting in a predominantly non-cohesive deformation style. This example indicates that permeability evolution (and related hydrothermal processes) strongly influences the mechanical behavior of such faults. This shows the highly dynamic behavior with time in long-lived fault systems. These dynamic changes in precipitation and resulting different strengths occur at different timescales from minutes (seismic events) to thousands of years.
Ref.: Berger, A., Herwegh, M., 2019. Cockade structures as a paleo-earthquake proxy in upper crustal hydrothermal systems. Nature Scientific Reports, 9, 9209.
How to cite: Berger, A. and Herwegh, M.: Cockade-bearing breccias, cataclasites and gouges in a single fault zone: Microstructures and geochemisty, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2426, https://doi.org/10.5194/egusphere-egu2020-2426, 2020.
EGU2020-20861 | Displays | TS4.2
Characteristics and evolution process of strike-slip fault in Halahatang area, North Tarim Basin, NW ChinaDebo Ma
Characteristics and evolution process of strike-slip fault is a key issue restricting further exploration in Halahatang area, North Tarim Basin, NW China. This paper uses the new-acquired 3D seismic data and applies fault structural analysis method to study the characteristics of Halahatang area, and discusses evolution process of the faults.
The data used in this paper include 1960 km2 3D seismic data in prestack time migration in Halahatang area, and 4 wells logging data used to calibrate seismic horizon. The bin size of 3D seismic is 25 m×25 m with sampling rate of 4ms, and data length of 7000 ms. Firstly, the Eigen-structure coherency and SO semblance are used to identify the distribution of the strike-slip fault. Secondly, the segmentation of Ordovician strike-slip fault in the study area is studied and the control effect of segmentation on reservoir development and oil and gas enrichment is discussed.
The slip distance of strike-slip fault is very small, the maximum is no more than 2 km. They are typical cratonic strike-slip faults which are developed inside the craton. There are four kinds of structural styles on the profile, which are vertical and steep, positive flower structure, negative flower structure and semi-flower structure. Five structural styles of linear extension, X type, braided structure, horsetail structure, and en-echelon structure are developed on the plane. There are obvious segmentation along the fault trend.
According to the strata subjected to strike-slip deformation and the structural styles in different strata, it is determined that the strike-slip faults have three stages of activity in Halahatang area.
In the Late Ordovician, NNE, NNW, NE, and NEE strike-slip faults are mainly developed in the study area. The faults on the seismic profile are steep and upright, with small displacements. Faults generally only break into the Ordovician, and later activities will cause faults to go up to the Silurian and even the upper Palaeozoic, which have different tectonic styles with that of the Ordovician faults. The NNE and NNW strike-slip faults form an “X”-type conjugate strike-slip fault, reflecting the conjugate strike-slip fault is generated by near north-south compression.
In the Late Permian, 4 NNW transtensional strike-slip faults are generated by the activation of some Ordovician strike-slip faults. In the Late Cretaceous-Palaeocene, the study area mainly develop several groups of NNE, near SN transtensional strike-slip faults. These transtensional strike-slip faults appear as graben and horst or stepped faults on the section. These transtensional strike-slip faults are R-shear faults in the Mesozoic and Cenozoic strata formed by the Ordovician NNE faults slip dextrally under the tectonic stress.
How to cite: Ma, D.: Characteristics and evolution process of strike-slip fault in Halahatang area, North Tarim Basin, NW China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20861, https://doi.org/10.5194/egusphere-egu2020-20861, 2020.
Characteristics and evolution process of strike-slip fault is a key issue restricting further exploration in Halahatang area, North Tarim Basin, NW China. This paper uses the new-acquired 3D seismic data and applies fault structural analysis method to study the characteristics of Halahatang area, and discusses evolution process of the faults.
The data used in this paper include 1960 km2 3D seismic data in prestack time migration in Halahatang area, and 4 wells logging data used to calibrate seismic horizon. The bin size of 3D seismic is 25 m×25 m with sampling rate of 4ms, and data length of 7000 ms. Firstly, the Eigen-structure coherency and SO semblance are used to identify the distribution of the strike-slip fault. Secondly, the segmentation of Ordovician strike-slip fault in the study area is studied and the control effect of segmentation on reservoir development and oil and gas enrichment is discussed.
The slip distance of strike-slip fault is very small, the maximum is no more than 2 km. They are typical cratonic strike-slip faults which are developed inside the craton. There are four kinds of structural styles on the profile, which are vertical and steep, positive flower structure, negative flower structure and semi-flower structure. Five structural styles of linear extension, X type, braided structure, horsetail structure, and en-echelon structure are developed on the plane. There are obvious segmentation along the fault trend.
According to the strata subjected to strike-slip deformation and the structural styles in different strata, it is determined that the strike-slip faults have three stages of activity in Halahatang area.
In the Late Ordovician, NNE, NNW, NE, and NEE strike-slip faults are mainly developed in the study area. The faults on the seismic profile are steep and upright, with small displacements. Faults generally only break into the Ordovician, and later activities will cause faults to go up to the Silurian and even the upper Palaeozoic, which have different tectonic styles with that of the Ordovician faults. The NNE and NNW strike-slip faults form an “X”-type conjugate strike-slip fault, reflecting the conjugate strike-slip fault is generated by near north-south compression.
In the Late Permian, 4 NNW transtensional strike-slip faults are generated by the activation of some Ordovician strike-slip faults. In the Late Cretaceous-Palaeocene, the study area mainly develop several groups of NNE, near SN transtensional strike-slip faults. These transtensional strike-slip faults appear as graben and horst or stepped faults on the section. These transtensional strike-slip faults are R-shear faults in the Mesozoic and Cenozoic strata formed by the Ordovician NNE faults slip dextrally under the tectonic stress.
How to cite: Ma, D.: Characteristics and evolution process of strike-slip fault in Halahatang area, North Tarim Basin, NW China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20861, https://doi.org/10.5194/egusphere-egu2020-20861, 2020.
EGU2020-237 | Displays | TS4.2
Fault kinematic investigations along the Panchkula-Morni region, NW Himalaya, IndiaAjay Kumar, Soumyajit Mukherjee, Mohamedharoon A. Shaikh, and Seema Singh
The Morni hills located in the north-western Himalaya in Panchkula district, Haryana has undergone poly-phase deformation owing to its complex tectonic history. In order to better understand the kinematic evolution of study area, detailed structural analyses of the fault system at regional-scale is carried out. We perform paleostress analyses on the collected fault-slip data to derive the paleostress tensors. The fault-slip data includes attitudes of fault planes and slickenside lineations, and the sense of slip along the fault plane determined by observing various kinematic indicators. The study area mainly exposes compacted, fine- to medium-grained calcareous sandstones belonging to the lower Siwalik formation in the Himalayan foreland basin. The exposed sandstones contain numerous striated slip planes of varying slip-sense. As the fault planes are intra-formational and exposed in uniform lithology, sense of slip cannot be determined through offset markers. In such cases, the sense of slip of the fault plane is determined solely by observing various slickenside kinematic indicators and fracture types developed on the faulted surface. The slickenside kinematic indicators e.g., calcite mineral steps were found useful in deciphering the sense of movement of each of the slip plane. The paleostress inversion of fault-slip data was carried out by applying the open source software T-Tecto studio X5 to obtain the reduced stress tensor. The Paleostress inversion algorithm called the Right Dihedral Method (RDM) is executed to estimate the principal stress axes orientations. Temporally, the slip planes may have reactivated multiple times preserving multiple slickenside orientations superimposing one another. Such fault-slip data are called heterogeneous and therefore, multiple stress states are deduced to explain the heterogeneous fault-slip data. The paleostress analysis results indicate stress regime index (R’) range 1.25–2.25 and 0.20–1.00 suggesting pure strike-slip to transpressive and pure extensive to transtensive stress regime respectively prevailing in the study area.
How to cite: Kumar, A., Mukherjee, S., Shaikh, M. A., and Singh, S.: Fault kinematic investigations along the Panchkula-Morni region, NW Himalaya, India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-237, https://doi.org/10.5194/egusphere-egu2020-237, 2020.
The Morni hills located in the north-western Himalaya in Panchkula district, Haryana has undergone poly-phase deformation owing to its complex tectonic history. In order to better understand the kinematic evolution of study area, detailed structural analyses of the fault system at regional-scale is carried out. We perform paleostress analyses on the collected fault-slip data to derive the paleostress tensors. The fault-slip data includes attitudes of fault planes and slickenside lineations, and the sense of slip along the fault plane determined by observing various kinematic indicators. The study area mainly exposes compacted, fine- to medium-grained calcareous sandstones belonging to the lower Siwalik formation in the Himalayan foreland basin. The exposed sandstones contain numerous striated slip planes of varying slip-sense. As the fault planes are intra-formational and exposed in uniform lithology, sense of slip cannot be determined through offset markers. In such cases, the sense of slip of the fault plane is determined solely by observing various slickenside kinematic indicators and fracture types developed on the faulted surface. The slickenside kinematic indicators e.g., calcite mineral steps were found useful in deciphering the sense of movement of each of the slip plane. The paleostress inversion of fault-slip data was carried out by applying the open source software T-Tecto studio X5 to obtain the reduced stress tensor. The Paleostress inversion algorithm called the Right Dihedral Method (RDM) is executed to estimate the principal stress axes orientations. Temporally, the slip planes may have reactivated multiple times preserving multiple slickenside orientations superimposing one another. Such fault-slip data are called heterogeneous and therefore, multiple stress states are deduced to explain the heterogeneous fault-slip data. The paleostress analysis results indicate stress regime index (R’) range 1.25–2.25 and 0.20–1.00 suggesting pure strike-slip to transpressive and pure extensive to transtensive stress regime respectively prevailing in the study area.
How to cite: Kumar, A., Mukherjee, S., Shaikh, M. A., and Singh, S.: Fault kinematic investigations along the Panchkula-Morni region, NW Himalaya, India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-237, https://doi.org/10.5194/egusphere-egu2020-237, 2020.
EGU2020-2829 | Displays | TS4.2
Fault System Evolution and Its Influences on Buried-hills Formation in Tanhai Area of Jiyang Depression, Bohai Bay Basin, ChinaMeng Zhang, Zhiping Wu, and Shiyong Yan
Buried-hills, paleotopographic highs covered by younger sediments, become the focused area of exploration in China in pace with the reduction of hydrocarbon resources in the shallow strata. A number of buried-hill fields have been discovered in Tanhai area located in the northeast of Jiyang Depression within Bohai Bay Basin, which provides an excellent case study for better understanding the structural evolution and formation mechanism of buried-hills. High-quality 3-D seismic data calibrated by well data makes it possible to research deeply buried erosional remnants. In this study, 3-D visualization of key interfaces, seismic cross-sections, fault polygons maps and thickness isopach maps are shown to manifest structural characteristics of buried-hills. Balanced cross-sections and fault growth rates are exhibited to demonstrate the forming process of buried-hills. The initiation and development of buried-hills are under the control of fault system. According to strike variance, main faults are grouped into NW-, NNE- and near E-trending faults. NW-trending main faults directly dominate the whole mountain range, while NNE- and near E-trending main faults have an effect on dissecting mountain range and controlling the single hill. In addition, secondary faults with different nature complicate internal structure of buried-hills. During Late Triassic, NW-trending thrust faults formed in response to regional compressional stress field, preliminarily building the fundamental NW-trending structural framework. Until Late Jurassic-Early Cretaceous, rolling-back subduction of Pacific Plate and sinistral movement of Tan-Lu Fault Zone (TLFZ) integrally converted NW-trending thrust faults into normal faults. The footwall of NW-trending faults quickly rose and became a large-scale NW-trending mountain range. The intense movement of TLFZ simultaneously induced a series of secondary NNE-trending strike-slip faults, among which large-scale ones divided the mountain range into northern, middle and southern section. After entry into Cenozoic, especially Middle Eocene, the change of subduction direction of Pacific Plate induced the transition of regional stress field. Near E-trending basin-controlling faults developed and dissected previous tectonic framework. The middle section of mountain range was further separated into three different single hill. Subsequently, the mountain range was gradually submerged and buried by overlying sediments, due to regional thermal subsidence. Through multiphase structural evolution, the present-day geometry of buried-hills is eventually taken shape.
How to cite: Zhang, M., Wu, Z., and Yan, S.: Fault System Evolution and Its Influences on Buried-hills Formation in Tanhai Area of Jiyang Depression, Bohai Bay Basin, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2829, https://doi.org/10.5194/egusphere-egu2020-2829, 2020.
Buried-hills, paleotopographic highs covered by younger sediments, become the focused area of exploration in China in pace with the reduction of hydrocarbon resources in the shallow strata. A number of buried-hill fields have been discovered in Tanhai area located in the northeast of Jiyang Depression within Bohai Bay Basin, which provides an excellent case study for better understanding the structural evolution and formation mechanism of buried-hills. High-quality 3-D seismic data calibrated by well data makes it possible to research deeply buried erosional remnants. In this study, 3-D visualization of key interfaces, seismic cross-sections, fault polygons maps and thickness isopach maps are shown to manifest structural characteristics of buried-hills. Balanced cross-sections and fault growth rates are exhibited to demonstrate the forming process of buried-hills. The initiation and development of buried-hills are under the control of fault system. According to strike variance, main faults are grouped into NW-, NNE- and near E-trending faults. NW-trending main faults directly dominate the whole mountain range, while NNE- and near E-trending main faults have an effect on dissecting mountain range and controlling the single hill. In addition, secondary faults with different nature complicate internal structure of buried-hills. During Late Triassic, NW-trending thrust faults formed in response to regional compressional stress field, preliminarily building the fundamental NW-trending structural framework. Until Late Jurassic-Early Cretaceous, rolling-back subduction of Pacific Plate and sinistral movement of Tan-Lu Fault Zone (TLFZ) integrally converted NW-trending thrust faults into normal faults. The footwall of NW-trending faults quickly rose and became a large-scale NW-trending mountain range. The intense movement of TLFZ simultaneously induced a series of secondary NNE-trending strike-slip faults, among which large-scale ones divided the mountain range into northern, middle and southern section. After entry into Cenozoic, especially Middle Eocene, the change of subduction direction of Pacific Plate induced the transition of regional stress field. Near E-trending basin-controlling faults developed and dissected previous tectonic framework. The middle section of mountain range was further separated into three different single hill. Subsequently, the mountain range was gradually submerged and buried by overlying sediments, due to regional thermal subsidence. Through multiphase structural evolution, the present-day geometry of buried-hills is eventually taken shape.
How to cite: Zhang, M., Wu, Z., and Yan, S.: Fault System Evolution and Its Influences on Buried-hills Formation in Tanhai Area of Jiyang Depression, Bohai Bay Basin, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2829, https://doi.org/10.5194/egusphere-egu2020-2829, 2020.
EGU2020-7290 | Displays | TS4.2
Surface and subsurface fault mapping in the Yorkshire Wolds, UKRowan Vernon, Jon Ford, Katie Watkinson, Richard Haslam, Mark Woods, Andrew Farrant, Helen Burke, Alice Davis, Jennifer Lear, Harris Tarnanas, and Edward Wrathmell
The Flamborough Head Fault Zone (FHFZ) marks the southern extent of the Cleveland Basin and the northern margin of the Market Weighton Block, England. It is a regionally-significant structural zone which has undergone a complex history of Mesozoic-Cenozoic extension and compression. It is predominantly comprised of east-west trending faults which form a graben that is dissected by north-south trending faults, including the southern extension to the Peak Trough, the Hunmanby Fault. To the west, FHFZ links with the Howardian Fault System and offshore, in the east, it is truncated by the north-south trending Dowsing Fault. The FHFZ is well exposed and described from coastal cliff sections at Flamborough Head but the inland development of the faults have hitherto been poorly explored predominantly due to limited inland-exposure.
The region around the FHFZ is underlain by the Chalk Group, a 500 m thick limestone succession. The Chalk Group is a principal aquifer that is the main source of water supply in East Yorkshire. The geometry and physical characteristics of the Chalk succession, including the effects of faulting, influence groundwater flow across the region. A range of modern data and recent geological research highlight that considerable changes can be made to the region’s current geological maps and subsurface understanding. Ensuring these features are better-documented is key for up-dating groundwater models to enable more confident decisions about land-use, water management and environmental regulation.
A multi-faceted approach to geological mapping has been undertaken in the region by the British Geological Survey (BGS), in collaboration with the Environment Agency. Remote sensing and field mapping of the superficial deposits has better characterised the extent and nature of these deposits and identified potential recharge ‘windows’ into the bedrock. Remote sensing, targeted field mapping, palaeontological analysis, passive seismic and 2D onshore seismic interpretation have been integrated to produce a new map of the Chalk succession, which reveals the inland extension of the FHFZ in unprecedented detail. Combining these techniques has enabled us to bridge the gap between the surface geology and deeper subsurface structure, increase our understanding of the geology of the region and produce an improved conceptual model at a range of depths which will be used to better manage water resources.
How to cite: Vernon, R., Ford, J., Watkinson, K., Haslam, R., Woods, M., Farrant, A., Burke, H., Davis, A., Lear, J., Tarnanas, H., and Wrathmell, E.: Surface and subsurface fault mapping in the Yorkshire Wolds, UK, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7290, https://doi.org/10.5194/egusphere-egu2020-7290, 2020.
The Flamborough Head Fault Zone (FHFZ) marks the southern extent of the Cleveland Basin and the northern margin of the Market Weighton Block, England. It is a regionally-significant structural zone which has undergone a complex history of Mesozoic-Cenozoic extension and compression. It is predominantly comprised of east-west trending faults which form a graben that is dissected by north-south trending faults, including the southern extension to the Peak Trough, the Hunmanby Fault. To the west, FHFZ links with the Howardian Fault System and offshore, in the east, it is truncated by the north-south trending Dowsing Fault. The FHFZ is well exposed and described from coastal cliff sections at Flamborough Head but the inland development of the faults have hitherto been poorly explored predominantly due to limited inland-exposure.
The region around the FHFZ is underlain by the Chalk Group, a 500 m thick limestone succession. The Chalk Group is a principal aquifer that is the main source of water supply in East Yorkshire. The geometry and physical characteristics of the Chalk succession, including the effects of faulting, influence groundwater flow across the region. A range of modern data and recent geological research highlight that considerable changes can be made to the region’s current geological maps and subsurface understanding. Ensuring these features are better-documented is key for up-dating groundwater models to enable more confident decisions about land-use, water management and environmental regulation.
A multi-faceted approach to geological mapping has been undertaken in the region by the British Geological Survey (BGS), in collaboration with the Environment Agency. Remote sensing and field mapping of the superficial deposits has better characterised the extent and nature of these deposits and identified potential recharge ‘windows’ into the bedrock. Remote sensing, targeted field mapping, palaeontological analysis, passive seismic and 2D onshore seismic interpretation have been integrated to produce a new map of the Chalk succession, which reveals the inland extension of the FHFZ in unprecedented detail. Combining these techniques has enabled us to bridge the gap between the surface geology and deeper subsurface structure, increase our understanding of the geology of the region and produce an improved conceptual model at a range of depths which will be used to better manage water resources.
How to cite: Vernon, R., Ford, J., Watkinson, K., Haslam, R., Woods, M., Farrant, A., Burke, H., Davis, A., Lear, J., Tarnanas, H., and Wrathmell, E.: Surface and subsurface fault mapping in the Yorkshire Wolds, UK, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7290, https://doi.org/10.5194/egusphere-egu2020-7290, 2020.
EGU2020-9569 | Displays | TS4.2
3D reconstructions of fault surfaces and key stratigraphic horizons to define recent tectonic activity in the northern Apennines outer fronts and foredeep (northern Adriatic Sea, Italy)Yuri Panara, Francesco Emanuele Maesano, Roberto Basili, Giacomo Losi, Jakub Fedorik, and Giovanni Toscani
Fault plane attitude and dimension are important parameters for deriving seismotectonic information or input data for earthquake hazard assessment and in this sense a complete 3D view and characterization of geological and structural elements is essential. However, there is always a trade-off between structural complexity and data availability at the scale of the designed application.
In the last few years, merging public and confidential seismic reflection profiles and borehole data, were used in order to carry out a 3D reconstruction of fault planes and Plio-Pleistocene stratigraphic horizons in the northern Adriatic Sea, at the front of the northern Apennine fold-and-thrust belt and associated foredeep. The study area straddles the Italian coastline and subsurface data interpretation allowed us to reconstruct the structural setting of both onshore and offshore structures. Although it is known that this area has low rates of active tectonic deformation, it hosts important seismogenic faults associated with instrumental seismicity and historical earthquakes.
The dense distribution of seismic reflection profiles allowed us to perform an accurate 3D reconstruction of almost 50 fault planes, of different dimensions and order of importance. Their geometrical and structural features helped to define the most recent tectonic phases. To this end, we also mapped several Plio-Pleistocene regional unconformities and integrated them with previously published reconstructions of key horizons.
In some cases, where further published data were available, it was also possible to perform detailed cross sections whose restoration allowed us to reconstruct the post-Miocene (5.33 Ma) slip-rate history of some important tectonic structures with a detail of ~1 Ma. The 3D geological model revealed several structural features like fault continuity and terminations, level of connectivity, presence of lateral ramps, along strike variations of displacement that could not be fully addressed using cross sections alone.
How to cite: Panara, Y., Maesano, F. E., Basili, R., Losi, G., Fedorik, J., and Toscani, G.: 3D reconstructions of fault surfaces and key stratigraphic horizons to define recent tectonic activity in the northern Apennines outer fronts and foredeep (northern Adriatic Sea, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9569, https://doi.org/10.5194/egusphere-egu2020-9569, 2020.
Fault plane attitude and dimension are important parameters for deriving seismotectonic information or input data for earthquake hazard assessment and in this sense a complete 3D view and characterization of geological and structural elements is essential. However, there is always a trade-off between structural complexity and data availability at the scale of the designed application.
In the last few years, merging public and confidential seismic reflection profiles and borehole data, were used in order to carry out a 3D reconstruction of fault planes and Plio-Pleistocene stratigraphic horizons in the northern Adriatic Sea, at the front of the northern Apennine fold-and-thrust belt and associated foredeep. The study area straddles the Italian coastline and subsurface data interpretation allowed us to reconstruct the structural setting of both onshore and offshore structures. Although it is known that this area has low rates of active tectonic deformation, it hosts important seismogenic faults associated with instrumental seismicity and historical earthquakes.
The dense distribution of seismic reflection profiles allowed us to perform an accurate 3D reconstruction of almost 50 fault planes, of different dimensions and order of importance. Their geometrical and structural features helped to define the most recent tectonic phases. To this end, we also mapped several Plio-Pleistocene regional unconformities and integrated them with previously published reconstructions of key horizons.
In some cases, where further published data were available, it was also possible to perform detailed cross sections whose restoration allowed us to reconstruct the post-Miocene (5.33 Ma) slip-rate history of some important tectonic structures with a detail of ~1 Ma. The 3D geological model revealed several structural features like fault continuity and terminations, level of connectivity, presence of lateral ramps, along strike variations of displacement that could not be fully addressed using cross sections alone.
How to cite: Panara, Y., Maesano, F. E., Basili, R., Losi, G., Fedorik, J., and Toscani, G.: 3D reconstructions of fault surfaces and key stratigraphic horizons to define recent tectonic activity in the northern Apennines outer fronts and foredeep (northern Adriatic Sea, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9569, https://doi.org/10.5194/egusphere-egu2020-9569, 2020.
EGU2020-14014 | Displays | TS4.2
Taking up the challenge of identifying active faults for seismic hazard assessment of the city of Ulaanbaatar (Mongolia)Abeer Al Ashkar, Antoine Schlupp, Matthieu Ferry, and Munkhuu Ulziibat
Ulaanbaatar, capital city of Mongolia (1.5 M inhabitants, i.e. half of the country’s population), is located in Central Mongolia where seismic activity and deformation rates are low (< 1mm/yr.). In contrast, Western Mongolia has experienced four great earthquakes (M ≥ 8) between 1905 and 1957 as well as numerous moderate ones. Some (e.g. the 1957 Bogd earthquake) have been felt at the capital located more than 500 km away. During the last decades, several active faults, located 10 km to 45 km away from Ulaanbaatar, have been discovered and studied. Tectonic Geomorphology and Paleoseismology studies indicate that these faults are able to generate earthquakes of M ≥ 6 with average recurrence times ranging from 1 kyr to 10 kyr (e.g. 1195 ± 157 yr for the Sharkhai fault). Furthermore, since 2005 very dense microseismicity swarms located 10 km NW of the City have been monitored by the Seismic Observatory of Mongolia (IAG). Further studies showed the swarms are produced by the previously undetected Emeelt fault zone along three parallel branches. Due to their proximity to a key population and economic center, all these active structures contribute significantly to increasing Seismic Hazard. During the course of these studies, we documented Quaternary activity along several supplementary faults, which demonstrates that the knowledge of active faults in the region is still incomplete and suggests seismic hazard levels should be revised. Therefore, we undertook to map, as exhaustively as possible, all active tectonic structures in a radius of 300 km around Ulaanbaatar. Here we present preliminary results based on the combined analysis of multi-source and multi-sensor data from satellite images (e.g. Pleiades, Sentinel-2, Landsat8), UAV photographs, and digital elevation models (TanDEM-X and UAV photogrammetric DEMs) in order to extract the most relevant information at various scales. We performed a detailed Tectonic Geomorphology analysis of alluvial and slope landforms to identify recent deformation affecting stream channels and associated deposits (ponds, fans and terraces). On that basis, we document segmentation, deformation patterns and kinematics, as well as relationships between faults at regional scale. Finally, we identify potential sites for future paleoseismic investigations along the main structures. Though this project is in a preliminary stage, our long-term goal is to build a comprehensive database of sources of seismic hazard to the City of Ulaanbaatar and integrate these results into seismic hazard calculations.
How to cite: Al Ashkar, A., Schlupp, A., Ferry, M., and Ulziibat, M.: Taking up the challenge of identifying active faults for seismic hazard assessment of the city of Ulaanbaatar (Mongolia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14014, https://doi.org/10.5194/egusphere-egu2020-14014, 2020.
Ulaanbaatar, capital city of Mongolia (1.5 M inhabitants, i.e. half of the country’s population), is located in Central Mongolia where seismic activity and deformation rates are low (< 1mm/yr.). In contrast, Western Mongolia has experienced four great earthquakes (M ≥ 8) between 1905 and 1957 as well as numerous moderate ones. Some (e.g. the 1957 Bogd earthquake) have been felt at the capital located more than 500 km away. During the last decades, several active faults, located 10 km to 45 km away from Ulaanbaatar, have been discovered and studied. Tectonic Geomorphology and Paleoseismology studies indicate that these faults are able to generate earthquakes of M ≥ 6 with average recurrence times ranging from 1 kyr to 10 kyr (e.g. 1195 ± 157 yr for the Sharkhai fault). Furthermore, since 2005 very dense microseismicity swarms located 10 km NW of the City have been monitored by the Seismic Observatory of Mongolia (IAG). Further studies showed the swarms are produced by the previously undetected Emeelt fault zone along three parallel branches. Due to their proximity to a key population and economic center, all these active structures contribute significantly to increasing Seismic Hazard. During the course of these studies, we documented Quaternary activity along several supplementary faults, which demonstrates that the knowledge of active faults in the region is still incomplete and suggests seismic hazard levels should be revised. Therefore, we undertook to map, as exhaustively as possible, all active tectonic structures in a radius of 300 km around Ulaanbaatar. Here we present preliminary results based on the combined analysis of multi-source and multi-sensor data from satellite images (e.g. Pleiades, Sentinel-2, Landsat8), UAV photographs, and digital elevation models (TanDEM-X and UAV photogrammetric DEMs) in order to extract the most relevant information at various scales. We performed a detailed Tectonic Geomorphology analysis of alluvial and slope landforms to identify recent deformation affecting stream channels and associated deposits (ponds, fans and terraces). On that basis, we document segmentation, deformation patterns and kinematics, as well as relationships between faults at regional scale. Finally, we identify potential sites for future paleoseismic investigations along the main structures. Though this project is in a preliminary stage, our long-term goal is to build a comprehensive database of sources of seismic hazard to the City of Ulaanbaatar and integrate these results into seismic hazard calculations.
How to cite: Al Ashkar, A., Schlupp, A., Ferry, M., and Ulziibat, M.: Taking up the challenge of identifying active faults for seismic hazard assessment of the city of Ulaanbaatar (Mongolia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14014, https://doi.org/10.5194/egusphere-egu2020-14014, 2020.
EGU2020-21089 | Displays | TS4.2
The formation model of neotectonic fault zone in the Ulsan Fault Zone, Gyeongsang basin, KoreaJi-Hoon Kang
The Yangsan Fault Zone (YFZ) of NNE trend and Ulsan Fault Zone (UFZ) of NNW trend are developed in the Gyeongsang Basin, the southern part of the Korean Peninsula, and many active faults and Quaternary faults (ATV and QTY Fs) have been found in these fault zones. The tectonic movement of the YFZ can be explained at least by two different strike-slip movements, named as D1 sinistral strike-slip and D2 dextral strike-slip, and then two different dip-slip movements, named as D3 conjugate reverse-slip and D4 Quaternary reverse-slip. The surfaces of D3 fault in basement rocks are extended those of D4 fault in the covering Quaternary deposits, like the other Quaternary faults within the YFZ. The D3 and D4 faults were formed under the same compression of (N)NW-(S)SE direction. After that, the active faults occurred in the Korean Peninsula under the compression of E-W direction. The ATV and QTY Fs thrust the Bulguksa igneous rocks of Late Cretaceous-Early Tertiary upon the Quaternary deposits or are developed within the Quaternary deposits in the UFZ, showing the reverse-slip sense of top-to-the west movement. This presentation is suggested the formation model of neotectonic fault zone in the UFZ on the basis of the various trends [(W)NW, N-S, (E)NE trends] of fault surfaces of the ATV and QTY Fs found in the UFZ, and the zigzag-form connecting line of their outcrop sites, and the deformation history (the N-S trending 1st reverse-slip faulting by the 1st E-W compression and associated the E-W trending strike-slip tear faulting, the N-S trending 2nd reverse-slip faulting by the 2nd E-W compression) of neotectonic fault zone in the Singye-ri valley around the UFZ, and the compressive arc-shaped lineaments which convex to the west reported in the YFZ.
Acknowledgements: This research was financially supported by a grant (2017-MPSS31-006) from the Research and Development of Active fault of Korean Peninsula funded by the Korean Ministry of the Interior and Safety, and by Ministry of public Administration and Security as Disaster Prevention Safety Human resource development Project.
How to cite: Kang, J.-H.: The formation model of neotectonic fault zone in the Ulsan Fault Zone, Gyeongsang basin, Korea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21089, https://doi.org/10.5194/egusphere-egu2020-21089, 2020.
The Yangsan Fault Zone (YFZ) of NNE trend and Ulsan Fault Zone (UFZ) of NNW trend are developed in the Gyeongsang Basin, the southern part of the Korean Peninsula, and many active faults and Quaternary faults (ATV and QTY Fs) have been found in these fault zones. The tectonic movement of the YFZ can be explained at least by two different strike-slip movements, named as D1 sinistral strike-slip and D2 dextral strike-slip, and then two different dip-slip movements, named as D3 conjugate reverse-slip and D4 Quaternary reverse-slip. The surfaces of D3 fault in basement rocks are extended those of D4 fault in the covering Quaternary deposits, like the other Quaternary faults within the YFZ. The D3 and D4 faults were formed under the same compression of (N)NW-(S)SE direction. After that, the active faults occurred in the Korean Peninsula under the compression of E-W direction. The ATV and QTY Fs thrust the Bulguksa igneous rocks of Late Cretaceous-Early Tertiary upon the Quaternary deposits or are developed within the Quaternary deposits in the UFZ, showing the reverse-slip sense of top-to-the west movement. This presentation is suggested the formation model of neotectonic fault zone in the UFZ on the basis of the various trends [(W)NW, N-S, (E)NE trends] of fault surfaces of the ATV and QTY Fs found in the UFZ, and the zigzag-form connecting line of their outcrop sites, and the deformation history (the N-S trending 1st reverse-slip faulting by the 1st E-W compression and associated the E-W trending strike-slip tear faulting, the N-S trending 2nd reverse-slip faulting by the 2nd E-W compression) of neotectonic fault zone in the Singye-ri valley around the UFZ, and the compressive arc-shaped lineaments which convex to the west reported in the YFZ.
Acknowledgements: This research was financially supported by a grant (2017-MPSS31-006) from the Research and Development of Active fault of Korean Peninsula funded by the Korean Ministry of the Interior and Safety, and by Ministry of public Administration and Security as Disaster Prevention Safety Human resource development Project.
How to cite: Kang, J.-H.: The formation model of neotectonic fault zone in the Ulsan Fault Zone, Gyeongsang basin, Korea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21089, https://doi.org/10.5194/egusphere-egu2020-21089, 2020.
TS5.1 – Seismic analysis and geodetic modelling: multi-disciplinary approach to problem-solving
EGU2020-11146 | Displays | TS5.1
Using Seismic and Geodetic Observations in a Simultaneous Kinematic Model of the 2019 Ridgecrest, California EarthquakesDara Goldberg, Diego Melgar, Valerie Sahakian, Amanda Thomas, Xiaohua Xu, Brendan Crowell, and Jianghui Geng
The July 4, 2019 Mw6.4 and subsequent July 6, 2019 Mw7.1 Ridgecrest Sequence earthquakes in California, USA, ruptured orthogonal fault planes in the Little Lake Fault Zone, a low slip rate (1 mm/year) dextral fault zone in the region linking the Eastern California Shear Zone (ECSZ) and Walker Lane. This region is tectonically interesting because it accommodates approximately one fourth of plate boundary motion and has been proposed to be an incipient transform fault system that could eventually become the main tectonic boundary, replacing the San Andreas Fault. Additionally, large ruptures of such low slip rate faults are important to understand from the context of seismic hazard. We investigate the interaction within this fault system and demonstrate a novel kinematic slip method that inverts for both earthquakes simultaneously, allowing us to use Interferometric Synthetic Aperture Radar (InSAR) data that spans both earthquakes, along with seismic (strong-motion accelerometer) and geodetic (high-rate Global Navigation Satellite Systems (GNSS) and GNSS static offset) datasets that recorded each earthquake separately. We also present results of Coulomb stress change modeling to evaluate how the Mw6.4 earthquake may have affected the subsequent Mw7.1 event. Our findings suggest a complex rupture process and interactions between several fault structures, including dynamic and static triggering between splays involved in the July 4th Mw6.4 and July 6th Mw7.1 events. The integration of seismic and geodetic datasets provides constraints on rupture continuation through stepovers, as well as important context for regional models of seismic source characterization and hazard.
How to cite: Goldberg, D., Melgar, D., Sahakian, V., Thomas, A., Xu, X., Crowell, B., and Geng, J.: Using Seismic and Geodetic Observations in a Simultaneous Kinematic Model of the 2019 Ridgecrest, California Earthquakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11146, https://doi.org/10.5194/egusphere-egu2020-11146, 2020.
The July 4, 2019 Mw6.4 and subsequent July 6, 2019 Mw7.1 Ridgecrest Sequence earthquakes in California, USA, ruptured orthogonal fault planes in the Little Lake Fault Zone, a low slip rate (1 mm/year) dextral fault zone in the region linking the Eastern California Shear Zone (ECSZ) and Walker Lane. This region is tectonically interesting because it accommodates approximately one fourth of plate boundary motion and has been proposed to be an incipient transform fault system that could eventually become the main tectonic boundary, replacing the San Andreas Fault. Additionally, large ruptures of such low slip rate faults are important to understand from the context of seismic hazard. We investigate the interaction within this fault system and demonstrate a novel kinematic slip method that inverts for both earthquakes simultaneously, allowing us to use Interferometric Synthetic Aperture Radar (InSAR) data that spans both earthquakes, along with seismic (strong-motion accelerometer) and geodetic (high-rate Global Navigation Satellite Systems (GNSS) and GNSS static offset) datasets that recorded each earthquake separately. We also present results of Coulomb stress change modeling to evaluate how the Mw6.4 earthquake may have affected the subsequent Mw7.1 event. Our findings suggest a complex rupture process and interactions between several fault structures, including dynamic and static triggering between splays involved in the July 4th Mw6.4 and July 6th Mw7.1 events. The integration of seismic and geodetic datasets provides constraints on rupture continuation through stepovers, as well as important context for regional models of seismic source characterization and hazard.
How to cite: Goldberg, D., Melgar, D., Sahakian, V., Thomas, A., Xu, X., Crowell, B., and Geng, J.: Using Seismic and Geodetic Observations in a Simultaneous Kinematic Model of the 2019 Ridgecrest, California Earthquakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11146, https://doi.org/10.5194/egusphere-egu2020-11146, 2020.
EGU2020-13379 | Displays | TS5.1
Joint seismic and geodetic transdimensional earthquake source optimization guided by multi-array teleseismic backprojectionAndreas Steinberg, Henriette Sudhaus, Frank Krüger, Hannes Vasyura-Bathke, Simon Daout, and Marius Paul Isken
Earthquakes have been observed to initiate and terminate near geometrical irregularities (bends, step-overs, branching of secondary faults). Rupture segmentationinfluences the seismic radiation and therefore, the related seismic hazard. Good imaging of rupture segmentation helps to characterize fault geometries at depth for follow-up tectonic, stress-field or other analyses. From reported earthquake source models it appears that large earthquakes with magnitudes above 7 are most often segmented, while earthquakes with magnitudes below 6.5 most often are not. If this observationreflects nature or if it is rather an artifact of our abilities to well observe and infer earthquake sources can not be answered without an objective strategy to constrain rupture complexity. However, data-driven analyses of rupture segmentation are not often conducted in source modeling as it is mostly pre-defined through a given and fixed number of sources.
We, here, propose a segmentation-sensitive source analysis by combining a model-independent teleseismic back-projection and image segmentation methods with a kinematic fault inversion. Our approach is twofold. We first develop a time-domain multi-array back-projection of teleseismic data with robust estimations of uncertainties based on bootstrapping of the travel-time models and array weights (Palantiri software, https://braunfuss.github.io/Palantiri/). Backprojection has proven to be a powerful tool to infer rupture propagation from teleseismic data and identify irregularities of the rupture process over time.
We then model the earthquake sources with the results obtained from the backprojection and additional information obtained from the application of image segmentation methods to the InSAR displacement maps. For this second step, we use a combination of different observations (teleseismic waveforms and surface displacement maps based on InSAR) to increase the resolution on the spatio-temporal evolution of fault slip. We develop a novel Informational criterion based transdimensional optimization scheme to model an adequate representation of the source complexity. We present our method on two cases study: the 2016 Muji Mw 6.7 earthquake (Pamir) and the 2008-2009 Qaidam (Tibet) sequence of earthquakes. We find that the 2008 Qaidam earthquake ruptures one segment, the 2016 Muji earthquake on two segments and the Qaidam 2009 earthquake on two or three segments.
This work is based on the open-source, python-based Pyrocko toolbox and is conducted within the project “Bridging Geodesy and Seismology” (www.bridges.uni-kiel.de<http://www.bridges.uni-kiel.de>) funded by the DFG through an Emmy-Noether grant.
How to cite: Steinberg, A., Sudhaus, H., Krüger, F., Vasyura-Bathke, H., Daout, S., and Isken, M. P.: Joint seismic and geodetic transdimensional earthquake source optimization guided by multi-array teleseismic backprojection, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13379, https://doi.org/10.5194/egusphere-egu2020-13379, 2020.
Earthquakes have been observed to initiate and terminate near geometrical irregularities (bends, step-overs, branching of secondary faults). Rupture segmentationinfluences the seismic radiation and therefore, the related seismic hazard. Good imaging of rupture segmentation helps to characterize fault geometries at depth for follow-up tectonic, stress-field or other analyses. From reported earthquake source models it appears that large earthquakes with magnitudes above 7 are most often segmented, while earthquakes with magnitudes below 6.5 most often are not. If this observationreflects nature or if it is rather an artifact of our abilities to well observe and infer earthquake sources can not be answered without an objective strategy to constrain rupture complexity. However, data-driven analyses of rupture segmentation are not often conducted in source modeling as it is mostly pre-defined through a given and fixed number of sources.
We, here, propose a segmentation-sensitive source analysis by combining a model-independent teleseismic back-projection and image segmentation methods with a kinematic fault inversion. Our approach is twofold. We first develop a time-domain multi-array back-projection of teleseismic data with robust estimations of uncertainties based on bootstrapping of the travel-time models and array weights (Palantiri software, https://braunfuss.github.io/Palantiri/). Backprojection has proven to be a powerful tool to infer rupture propagation from teleseismic data and identify irregularities of the rupture process over time.
We then model the earthquake sources with the results obtained from the backprojection and additional information obtained from the application of image segmentation methods to the InSAR displacement maps. For this second step, we use a combination of different observations (teleseismic waveforms and surface displacement maps based on InSAR) to increase the resolution on the spatio-temporal evolution of fault slip. We develop a novel Informational criterion based transdimensional optimization scheme to model an adequate representation of the source complexity. We present our method on two cases study: the 2016 Muji Mw 6.7 earthquake (Pamir) and the 2008-2009 Qaidam (Tibet) sequence of earthquakes. We find that the 2008 Qaidam earthquake ruptures one segment, the 2016 Muji earthquake on two segments and the Qaidam 2009 earthquake on two or three segments.
This work is based on the open-source, python-based Pyrocko toolbox and is conducted within the project “Bridging Geodesy and Seismology” (www.bridges.uni-kiel.de<http://www.bridges.uni-kiel.de>) funded by the DFG through an Emmy-Noether grant.
How to cite: Steinberg, A., Sudhaus, H., Krüger, F., Vasyura-Bathke, H., Daout, S., and Isken, M. P.: Joint seismic and geodetic transdimensional earthquake source optimization guided by multi-array teleseismic backprojection, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13379, https://doi.org/10.5194/egusphere-egu2020-13379, 2020.
EGU2020-3704 | Displays | TS5.1
Post-Seismic Deformation in the Northern Antarctic Peninsula Following the 2013 Magnitude 7.7 Scotia Sea EarthquakeGrace Nield, Matt King, Achraf Koulali, Nahidul Samrat, and Rebekka Steffen
Large earthquakes in the vicinity of Antarctica have the potential to cause post-seismic deformation on the continent, affecting measurements of displacement and gravity field change from GRACE or those attempting to constrain models of glacial isostatic adjustment.
In November 2013 a magnitude 7.7 strike-slip earthquake occurred in the Scotia Sea around 650 km from the northern tip of the Antarctic Peninsula. GPS coordinate time series from the Peninsula region show a change in rate after this event indicating a far-field post-seismic deformation signal is present. At these far-field locations, the effects of fault after-slip are likely negligible and hence we consider the deformation to be due to post-seismic viscoelastic deformation. Here we use a global spherical finite element model to investigate the extent of post-seismic viscoelastic deformation in the northern Antarctic Peninsula. We investigate possible 1D earth models that can fit the GPS data and consider the effect of including a simple 3D earth structure in the region. These results, combined with previous results showing East Antarctica is still deforming following 1998 Mw 8.2 intraplate earthquake, suggest that much of Antarctica is deforming due to recent post-seismic deformation.
How to cite: Nield, G., King, M., Koulali, A., Samrat, N., and Steffen, R.: Post-Seismic Deformation in the Northern Antarctic Peninsula Following the 2013 Magnitude 7.7 Scotia Sea Earthquake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3704, https://doi.org/10.5194/egusphere-egu2020-3704, 2020.
Large earthquakes in the vicinity of Antarctica have the potential to cause post-seismic deformation on the continent, affecting measurements of displacement and gravity field change from GRACE or those attempting to constrain models of glacial isostatic adjustment.
In November 2013 a magnitude 7.7 strike-slip earthquake occurred in the Scotia Sea around 650 km from the northern tip of the Antarctic Peninsula. GPS coordinate time series from the Peninsula region show a change in rate after this event indicating a far-field post-seismic deformation signal is present. At these far-field locations, the effects of fault after-slip are likely negligible and hence we consider the deformation to be due to post-seismic viscoelastic deformation. Here we use a global spherical finite element model to investigate the extent of post-seismic viscoelastic deformation in the northern Antarctic Peninsula. We investigate possible 1D earth models that can fit the GPS data and consider the effect of including a simple 3D earth structure in the region. These results, combined with previous results showing East Antarctica is still deforming following 1998 Mw 8.2 intraplate earthquake, suggest that much of Antarctica is deforming due to recent post-seismic deformation.
How to cite: Nield, G., King, M., Koulali, A., Samrat, N., and Steffen, R.: Post-Seismic Deformation in the Northern Antarctic Peninsula Following the 2013 Magnitude 7.7 Scotia Sea Earthquake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3704, https://doi.org/10.5194/egusphere-egu2020-3704, 2020.
EGU2020-10569 | Displays | TS5.1
Seismic and geodetic response to crustal deformation in Krísuvík volcanic system, southwest IcelandRevathy M. Parameswaran, Ingi Th. Bjarnason, and Freysteinn Sigmundsson
The Reykjanes Peninsula (RP) is a transtensional plate boundary in southwest Iceland that marks the transition of the Mid-Atlantic Ridge (MAR) from the offshore divergent Reykjanes Ridge (RR) in the west to the South Iceland Seismic Zone (SISZ) in the east. The seismicity here trends ~N80°E in central RP and bends to ~N45°E at its western tip as it joins RR. Seismic surveys, geodetic studies, and recent GPS-based kinematic models indicate that the seismic zone is a collection of strike-slip and normal faults (e.g., Keiding et al., 2008). Meanwhile, the tectonic processes in the region also manifest as NE-SW trending volcanic fissures and normal faults, and N-S oriented dextral faults (e.g., Clifton and Kattenhorn, 2006). The largest of these fissure and normal-fault systems in RP is the Krísuvík-Trölladyngja volcanic system, which is a high-energy geothermal zone. The seismicity here predominantly manifests RP’s transtentional tectonics; however, also hosts triggered events such as those following the 17 June 2000 Mw6.5 earthquake in the SISZ (Árnadottir et al., 2004) ~80 km east of Krísuvík. Stress inversions of microearthquakes from 1997-2006 in the RP indicate that the current stress state is mostly strike-slip with increased normal component to the west, indicating that the seismicity is driven by plate diverging motion (Keiding et al., 2009). However, the geothermal system in Krísuvík is a potential secondary source for triggered seismicity and deformation. This study uses seismic and geodetic data to evaluate the activity in the Krísuvík-Trölladyngja volcanic system. The seismic data is used to identify specific areas of focused activity and evaluate variations in the stress field associated with plate motion and/or geothermal activity over space and time. The data used, within the time period 2007-2016, was collected by the the South Icelandic Lowland (SIL) seismic network operated and managed by the Iceland Meterological Office (IMO). Furthermore, variations in seismicity are compared to crustal deformation observed with TerraSAR-X images from 2009-2019. Crustal changes in the Krísuvík area are quantified to develop a model for corresponding deformation sources. These changes are then correlated with the stress-field variations determined with seismic analysis.
How to cite: M. Parameswaran, R., Th. Bjarnason, I., and Sigmundsson, F.: Seismic and geodetic response to crustal deformation in Krísuvík volcanic system, southwest Iceland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10569, https://doi.org/10.5194/egusphere-egu2020-10569, 2020.
The Reykjanes Peninsula (RP) is a transtensional plate boundary in southwest Iceland that marks the transition of the Mid-Atlantic Ridge (MAR) from the offshore divergent Reykjanes Ridge (RR) in the west to the South Iceland Seismic Zone (SISZ) in the east. The seismicity here trends ~N80°E in central RP and bends to ~N45°E at its western tip as it joins RR. Seismic surveys, geodetic studies, and recent GPS-based kinematic models indicate that the seismic zone is a collection of strike-slip and normal faults (e.g., Keiding et al., 2008). Meanwhile, the tectonic processes in the region also manifest as NE-SW trending volcanic fissures and normal faults, and N-S oriented dextral faults (e.g., Clifton and Kattenhorn, 2006). The largest of these fissure and normal-fault systems in RP is the Krísuvík-Trölladyngja volcanic system, which is a high-energy geothermal zone. The seismicity here predominantly manifests RP’s transtentional tectonics; however, also hosts triggered events such as those following the 17 June 2000 Mw6.5 earthquake in the SISZ (Árnadottir et al., 2004) ~80 km east of Krísuvík. Stress inversions of microearthquakes from 1997-2006 in the RP indicate that the current stress state is mostly strike-slip with increased normal component to the west, indicating that the seismicity is driven by plate diverging motion (Keiding et al., 2009). However, the geothermal system in Krísuvík is a potential secondary source for triggered seismicity and deformation. This study uses seismic and geodetic data to evaluate the activity in the Krísuvík-Trölladyngja volcanic system. The seismic data is used to identify specific areas of focused activity and evaluate variations in the stress field associated with plate motion and/or geothermal activity over space and time. The data used, within the time period 2007-2016, was collected by the the South Icelandic Lowland (SIL) seismic network operated and managed by the Iceland Meterological Office (IMO). Furthermore, variations in seismicity are compared to crustal deformation observed with TerraSAR-X images from 2009-2019. Crustal changes in the Krísuvík area are quantified to develop a model for corresponding deformation sources. These changes are then correlated with the stress-field variations determined with seismic analysis.
How to cite: M. Parameswaran, R., Th. Bjarnason, I., and Sigmundsson, F.: Seismic and geodetic response to crustal deformation in Krísuvík volcanic system, southwest Iceland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10569, https://doi.org/10.5194/egusphere-egu2020-10569, 2020.
EGU2020-2059 | Displays | TS5.1
Quantitative analysis for amplitude anomalies at the seabed in the Laminaria High North West Shelf of Austuralia from 2D (1992 Caulerpa) and 3D (1995, Laminaria) pre-stack seismic dataLamees Abdulkareem
Variation in seismic amplitudes provides different information from the subsurface such as evidence of hydrocarbon accumulation or changes in the lithologies. Furthermore, amplitude anomalies may also be created by thin layers. However, amplitude anomalies are affected by various factors that may not be caused by changes in the lithology or the existence of hydrocarbons such as those caused by acquisition or processing of the seismic data. Hence, these effects need to be understood, eliminated or reduced to background noise levels. Reprocessing of 2D (1992, Caulerpa) and 3D (1995, Laminaria) pre-stack seismic data were applied to examine the veracity of amplitude anomalies at the seabed in the Laminaria High NW Shelf of Australia. This study showed that by applying simple but similar processing steps to that applied to the 3D seismic volume that were used in previous studies; it is possible to produce similar amplitude anomalies at the seabed. However, it was noted that amplitude anomalies at the seabed are sensitive to the velocity model; in particular, when applying radon demultiple to suppress the multiple energy in the seismic data. The result of reprocessing these data suggested that the different results of mapping the seabed reflector in this study and previous studies could result from the different processing parameters applied to each data set. Furthermore, reprocessing of the 2D (1992, Caulerpa) that covered the Laminaria High showed similar but not identical amplitude anomalies compared with the original 3D seismic volume (1995), and it is proposed that these difference could be related to the processing applied on each data set. It is concluded in this study, that amplitude anomalies at the seabed are frequency dependent so any manipulation in the frequency filters could affect these amplitude anomalies.
How to cite: Abdulkareem, L.: Quantitative analysis for amplitude anomalies at the seabed in the Laminaria High North West Shelf of Austuralia from 2D (1992 Caulerpa) and 3D (1995, Laminaria) pre-stack seismic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2059, https://doi.org/10.5194/egusphere-egu2020-2059, 2020.
Variation in seismic amplitudes provides different information from the subsurface such as evidence of hydrocarbon accumulation or changes in the lithologies. Furthermore, amplitude anomalies may also be created by thin layers. However, amplitude anomalies are affected by various factors that may not be caused by changes in the lithology or the existence of hydrocarbons such as those caused by acquisition or processing of the seismic data. Hence, these effects need to be understood, eliminated or reduced to background noise levels. Reprocessing of 2D (1992, Caulerpa) and 3D (1995, Laminaria) pre-stack seismic data were applied to examine the veracity of amplitude anomalies at the seabed in the Laminaria High NW Shelf of Australia. This study showed that by applying simple but similar processing steps to that applied to the 3D seismic volume that were used in previous studies; it is possible to produce similar amplitude anomalies at the seabed. However, it was noted that amplitude anomalies at the seabed are sensitive to the velocity model; in particular, when applying radon demultiple to suppress the multiple energy in the seismic data. The result of reprocessing these data suggested that the different results of mapping the seabed reflector in this study and previous studies could result from the different processing parameters applied to each data set. Furthermore, reprocessing of the 2D (1992, Caulerpa) that covered the Laminaria High showed similar but not identical amplitude anomalies compared with the original 3D seismic volume (1995), and it is proposed that these difference could be related to the processing applied on each data set. It is concluded in this study, that amplitude anomalies at the seabed are frequency dependent so any manipulation in the frequency filters could affect these amplitude anomalies.
How to cite: Abdulkareem, L.: Quantitative analysis for amplitude anomalies at the seabed in the Laminaria High North West Shelf of Austuralia from 2D (1992 Caulerpa) and 3D (1995, Laminaria) pre-stack seismic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2059, https://doi.org/10.5194/egusphere-egu2020-2059, 2020.
EGU2020-548 | Displays | TS5.1
The detection of seismo-ionospheric anomalies using the deep neural networkHamidreza Bagheri, Hamid Farzaneh, and Hadi Amin
Total Electron Content (TEC) measured by the Global Positioning System (GPS) is useful to register the pre-earthquake ionospheric anomalies appearing before a large earthquake. In this paper, the TEC value was predicted using the deep neural network. Also, the anomaly is detected utilizing this predicted value and the definition of the threshold value, leading to the use of the anomaly as a precursor. In neural networks, Convolutional Neural Network (ConvNets or CNNs) is one of the main categories to do images recognition, image classifications, object detections, facial recognition, etc. In this study, the CNNs has been applied to the ionospheric TEC of the Global Ionosphere Maps (GIM) data on a powerful earthquake in Chile on the 1st of April in 2014. In this method, a two-hour TEC observation is converted into a time series for this region for several consecutive days before and after the occurrence of an earthquake. The prediction of the non-linear time series is formulated as a method for specific pattern recognition in the input data using ConvNets. Results indicate that under suitable conditions the TEC values can be estimated properly in the aforementioned days and hours by ConvNets. In order to show the efficiency of this method in predicting the time series, the results obtained from this research were compared with those from other researches.
How to cite: Bagheri, H., Farzaneh, H., and Amin, H.: The detection of seismo-ionospheric anomalies using the deep neural network, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-548, https://doi.org/10.5194/egusphere-egu2020-548, 2020.
Total Electron Content (TEC) measured by the Global Positioning System (GPS) is useful to register the pre-earthquake ionospheric anomalies appearing before a large earthquake. In this paper, the TEC value was predicted using the deep neural network. Also, the anomaly is detected utilizing this predicted value and the definition of the threshold value, leading to the use of the anomaly as a precursor. In neural networks, Convolutional Neural Network (ConvNets or CNNs) is one of the main categories to do images recognition, image classifications, object detections, facial recognition, etc. In this study, the CNNs has been applied to the ionospheric TEC of the Global Ionosphere Maps (GIM) data on a powerful earthquake in Chile on the 1st of April in 2014. In this method, a two-hour TEC observation is converted into a time series for this region for several consecutive days before and after the occurrence of an earthquake. The prediction of the non-linear time series is formulated as a method for specific pattern recognition in the input data using ConvNets. Results indicate that under suitable conditions the TEC values can be estimated properly in the aforementioned days and hours by ConvNets. In order to show the efficiency of this method in predicting the time series, the results obtained from this research were compared with those from other researches.
How to cite: Bagheri, H., Farzaneh, H., and Amin, H.: The detection of seismo-ionospheric anomalies using the deep neural network, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-548, https://doi.org/10.5194/egusphere-egu2020-548, 2020.
EGU2020-12670 | Displays | TS5.1
Using rigid microplate motions to detect the stress buildup preceding large earthquakes: a feasibility test based on synthetic modelsGiampiero Iaffaldano and Juan Martin de Blas
Assessing the temporal evolution of stresses along seismogenic faults is typically done by combining geodetic observations collected near the locations of previous large earthquakes with modeling of the interseismic, coseismic, and postseismic deformation. Here we explore whether it is feasible to link the charge phase of large earthquakes to rigid microplate motions, which can be inferred from geodetic observations that are instead collected further away from crustal faults. We use numerical simulations of the dynamics and associated kinematics of an idealized, rigid microplate subject to stress buildups and drop-offs from a series of earthquakes. Simulations span the charging cycle of a single 6.5 < MW < 8 earthquake. Several MW < 6.5 earthquakes distributed according to the Gutenberg-Richter law occur meanwhile. We use large ensembles of simulations featuring randomly-generated earthquake hypocenters and make statistical assessments of the fraction of model time needed for the microplate motions to depart from the initial one to a degree that is larger than typical geodetic uncertainties, and for at least 90% of the remaining time before the large earthquake occurs. We find such a fraction (i) to be only one tenth in simulations that do feature a large earthquake, (ii) to be longer in simulations that do not, and (iii) to remain small for realistic microplate geometries and asthenosphere viscosity/thickness values. Our inferences hold also when we simulate geodetic time series shorter than the large-earthquake cycle, and even when we assume that only half of the stress buildup affects the microplate rigid motion.
How to cite: Iaffaldano, G. and Martin de Blas, J.: Using rigid microplate motions to detect the stress buildup preceding large earthquakes: a feasibility test based on synthetic models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12670, https://doi.org/10.5194/egusphere-egu2020-12670, 2020.
Assessing the temporal evolution of stresses along seismogenic faults is typically done by combining geodetic observations collected near the locations of previous large earthquakes with modeling of the interseismic, coseismic, and postseismic deformation. Here we explore whether it is feasible to link the charge phase of large earthquakes to rigid microplate motions, which can be inferred from geodetic observations that are instead collected further away from crustal faults. We use numerical simulations of the dynamics and associated kinematics of an idealized, rigid microplate subject to stress buildups and drop-offs from a series of earthquakes. Simulations span the charging cycle of a single 6.5 < MW < 8 earthquake. Several MW < 6.5 earthquakes distributed according to the Gutenberg-Richter law occur meanwhile. We use large ensembles of simulations featuring randomly-generated earthquake hypocenters and make statistical assessments of the fraction of model time needed for the microplate motions to depart from the initial one to a degree that is larger than typical geodetic uncertainties, and for at least 90% of the remaining time before the large earthquake occurs. We find such a fraction (i) to be only one tenth in simulations that do feature a large earthquake, (ii) to be longer in simulations that do not, and (iii) to remain small for realistic microplate geometries and asthenosphere viscosity/thickness values. Our inferences hold also when we simulate geodetic time series shorter than the large-earthquake cycle, and even when we assume that only half of the stress buildup affects the microplate rigid motion.
How to cite: Iaffaldano, G. and Martin de Blas, J.: Using rigid microplate motions to detect the stress buildup preceding large earthquakes: a feasibility test based on synthetic models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12670, https://doi.org/10.5194/egusphere-egu2020-12670, 2020.
EGU2020-13090 | Displays | TS5.1
Strain patterns of Sichuan and Yunnan, China from GPS data and comparison between seismic and geodetic moment releaseJingyang Zhao, Yanqiang Wu, Hongbao Liang, and Kaifu Du
We processed data from ~600 GPS stations, covering the period 1999-2018, to provide new insights into the crustal motion and deformation of Sichuan and Yunnan, China. We used the derived velocity field to evaluate two-dimensional strain rate tensors, and mapped the main, maximum shear, dilatation, east-west and north-south strain rates.The spatial distribution of the main strain rate in the Sichuan-Yunnan region generally shows an orderly deflection. The minimum principal strain rate is northeastward in the west of the Sichuan-Yunnan block boundary, gradually deflects eastward and southeastward toward the east and south, and returns to the northeast direction until the southwestern edge of Sichuan-Yunnan. This reflects the complex tectonic dynamics background of the study area. The high value of the maximum shear strain rate is mainly distributed along the eastern boundary of the Sichuan-Yunnan block, especially near the Xianshuihe-Xiaojiang fault, where the maximum shear strain rate exceeds 4.0 × 10-8 / a. The area strain rate in the study region shows that the areas of compression and expansion are comparable, with weak tensions prevailing in the interior and compression in the marginal areas. The strain rate result also shows that the east-west strain rate component in the southern Sichuan-Yunnan is dominated by positive value, and the north is dominated by negative value. It indicates that the east-west deformation in the south of the Sichuan-Yunnan is dominated by expansion, and in the north is dominated by contraction. The north-south component strain rate shows that there is a significant positive high-value zone in and around the Xianshuihe fault zone, while southern Sichuan-Yunnan is a more significant negative-value zone, and the distribution of negative high-value zones is controlled by the south boundary of the Sichuan-Yunnan block. Based on the fault activity and focal mechanism data, the study area was divided into several seismic source zones. We translated the geodetic strain rates into rates of seismic moment release in each zone and compared them with earthquake catalog-based moment rates, to evaluate the potential of seismic activity of the region. The analysis shows the geodetic strain is completely released seismically for most of the study area. However, for the southern Yunnan,the geodesy-based moment rates are more than 2 times higher than the earthquake-based rates. This result indicates that at least a large earthquake may occur in southern Yunnan in the future.
How to cite: Zhao, J., Wu, Y., Liang, H., and Du, K.: Strain patterns of Sichuan and Yunnan, China from GPS data and comparison between seismic and geodetic moment release, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13090, https://doi.org/10.5194/egusphere-egu2020-13090, 2020.
We processed data from ~600 GPS stations, covering the period 1999-2018, to provide new insights into the crustal motion and deformation of Sichuan and Yunnan, China. We used the derived velocity field to evaluate two-dimensional strain rate tensors, and mapped the main, maximum shear, dilatation, east-west and north-south strain rates.The spatial distribution of the main strain rate in the Sichuan-Yunnan region generally shows an orderly deflection. The minimum principal strain rate is northeastward in the west of the Sichuan-Yunnan block boundary, gradually deflects eastward and southeastward toward the east and south, and returns to the northeast direction until the southwestern edge of Sichuan-Yunnan. This reflects the complex tectonic dynamics background of the study area. The high value of the maximum shear strain rate is mainly distributed along the eastern boundary of the Sichuan-Yunnan block, especially near the Xianshuihe-Xiaojiang fault, where the maximum shear strain rate exceeds 4.0 × 10-8 / a. The area strain rate in the study region shows that the areas of compression and expansion are comparable, with weak tensions prevailing in the interior and compression in the marginal areas. The strain rate result also shows that the east-west strain rate component in the southern Sichuan-Yunnan is dominated by positive value, and the north is dominated by negative value. It indicates that the east-west deformation in the south of the Sichuan-Yunnan is dominated by expansion, and in the north is dominated by contraction. The north-south component strain rate shows that there is a significant positive high-value zone in and around the Xianshuihe fault zone, while southern Sichuan-Yunnan is a more significant negative-value zone, and the distribution of negative high-value zones is controlled by the south boundary of the Sichuan-Yunnan block. Based on the fault activity and focal mechanism data, the study area was divided into several seismic source zones. We translated the geodetic strain rates into rates of seismic moment release in each zone and compared them with earthquake catalog-based moment rates, to evaluate the potential of seismic activity of the region. The analysis shows the geodetic strain is completely released seismically for most of the study area. However, for the southern Yunnan,the geodesy-based moment rates are more than 2 times higher than the earthquake-based rates. This result indicates that at least a large earthquake may occur in southern Yunnan in the future.
How to cite: Zhao, J., Wu, Y., Liang, H., and Du, K.: Strain patterns of Sichuan and Yunnan, China from GPS data and comparison between seismic and geodetic moment release, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13090, https://doi.org/10.5194/egusphere-egu2020-13090, 2020.
EGU2020-18250 | Displays | TS5.1
On the cause of enhanced landward motion of the overriding plate after a major subduction earthquakeMario D'Acquisto, Matthew Herman, and Rob Govers
During and after a large megathrust earthquake, the overriding plate above the rupture zone moves oceanward. Enigmatically, the post-seismic motion of the overriding plate after several recent large earthquakes, further along strike from the rupture zone, was faster in the landward direction than before the event. Previous studies interpreted these changes as the result of increased mechanical coupling along the megathrust interface, transient slab acceleration, or bulk postseismic deformation with elastic bending mentioned as a possible underlying mechanism. Before invoking additional mechanisms, it is important to understand the contribution of postseismic deformation processes that are inherent features of megathrust earthquakes. We thus aim to quantify and analyse the deformation that produces landward motion during afterslip and viscous relaxation.
We use velocity-driven 3D mechanical finite element models, in which large megathrust earthquakes occur periodically on the finite plate interface. The model geometry is similar to most present-day subduction zones, but does not exactly match any specific subduction zone.
The results show increased post-seismic landward motion at (trench-parallel) distances greater than 450 km from the middle of the ruptured asperity. Similar patterns of landward motion are generated by viscous relaxation in the mantle wedge and by deep afterslip on the shear zone downdip of the brittle megathrust interface. Landward displacement due to postseismic relaxation largely accumulates at exponentially decaying rates until ~6 Maxwell relaxation times after the earthquake. The spatial distribution and magnitude of the velocity changes is broadly consistent with observations related to both the 2010 Maule and the 2011 Tohoku-oki earthquakes.
Further model experiments show that patterns of landward motion due to afterslip and to viscous relaxation are insensitive to the locking pattern of the megathrust. However, the locking distribution does affect the magnitudes of the displacements and velocities. Results show that the increased landward displacement due to postseismic deformation scales directly proportionally to seismic moment.
We conclude that the landward motion results from in-plane horizontal bending of the overriding plate and mantle. This bending is an elastic response to oceanward tractions near the base of the plate around the ruptured asperity, causing extension locally and compression further away along-trench. This elastic in-plate bending consistently contributes to earthquake-associated changes in surface velocities for the biggest megathrust earthquakes, producing landward motion along strike from the rupture zone.
How to cite: D'Acquisto, M., Herman, M., and Govers, R.: On the cause of enhanced landward motion of the overriding plate after a major subduction earthquake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18250, https://doi.org/10.5194/egusphere-egu2020-18250, 2020.
During and after a large megathrust earthquake, the overriding plate above the rupture zone moves oceanward. Enigmatically, the post-seismic motion of the overriding plate after several recent large earthquakes, further along strike from the rupture zone, was faster in the landward direction than before the event. Previous studies interpreted these changes as the result of increased mechanical coupling along the megathrust interface, transient slab acceleration, or bulk postseismic deformation with elastic bending mentioned as a possible underlying mechanism. Before invoking additional mechanisms, it is important to understand the contribution of postseismic deformation processes that are inherent features of megathrust earthquakes. We thus aim to quantify and analyse the deformation that produces landward motion during afterslip and viscous relaxation.
We use velocity-driven 3D mechanical finite element models, in which large megathrust earthquakes occur periodically on the finite plate interface. The model geometry is similar to most present-day subduction zones, but does not exactly match any specific subduction zone.
The results show increased post-seismic landward motion at (trench-parallel) distances greater than 450 km from the middle of the ruptured asperity. Similar patterns of landward motion are generated by viscous relaxation in the mantle wedge and by deep afterslip on the shear zone downdip of the brittle megathrust interface. Landward displacement due to postseismic relaxation largely accumulates at exponentially decaying rates until ~6 Maxwell relaxation times after the earthquake. The spatial distribution and magnitude of the velocity changes is broadly consistent with observations related to both the 2010 Maule and the 2011 Tohoku-oki earthquakes.
Further model experiments show that patterns of landward motion due to afterslip and to viscous relaxation are insensitive to the locking pattern of the megathrust. However, the locking distribution does affect the magnitudes of the displacements and velocities. Results show that the increased landward displacement due to postseismic deformation scales directly proportionally to seismic moment.
We conclude that the landward motion results from in-plane horizontal bending of the overriding plate and mantle. This bending is an elastic response to oceanward tractions near the base of the plate around the ruptured asperity, causing extension locally and compression further away along-trench. This elastic in-plate bending consistently contributes to earthquake-associated changes in surface velocities for the biggest megathrust earthquakes, producing landward motion along strike from the rupture zone.
How to cite: D'Acquisto, M., Herman, M., and Govers, R.: On the cause of enhanced landward motion of the overriding plate after a major subduction earthquake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18250, https://doi.org/10.5194/egusphere-egu2020-18250, 2020.
EGU2020-18393 | Displays | TS5.1
Fault stressing in the overriding plate due to megathrust coupling along the Nankai trough, JapanAkinori Hashima, Hiroshi Sato, Tatsuya Ishiyama, Andrew Freed, and Thorsten Becker
The Nankai trough has hosted ~M8 interplate earthquakes with the interval of 100-200 years. The crustal activity in southwest (SW) Japan in the overriding plate was relatively quiet after the last coupled megathrust ruptures occurred in 1944 and 1946. In the recent 20 years, however, SW Japan has experienced ~M7 earthquakes such as the 2016 Kumamoto earthquake. Similar activation of crustal earthquakes in the later stage of the megathrust earthquake cycles can be found in the historical earthquake occurrence based on paleographical studies. Such a change cannot be resolved by the probabilistic approaches, which usually rely on paleo-seismological data on longer timescales. Here, we show a deterministic way to quantify the current stressing state on the source faults due to megathrust coupling at the Nankai trough, making use of the data captured by the dense, modern geodetic network in Japan.
We constructed a 3-D finite element model (FEM) around the Japanese islands including the viscoelastic feature in the asthenosphere. The geometry of plate boundary on the Philippine Sea slab is based on earthquake distributions determined by the previous studies. In particular, the bended geometry at the junction of the Nankai trough and the Ryukyu trench is crucial for calculating stress. The plate boundary is divided into 8 x 27 patches to generate Green’s functions. The model region is divided into about 1000,000 tetrahedral elements with dimension of 5-100 km. We revised the source fault model by the Headquarters for Earthquake Research Promotion based on recent geophysical and geological data and added new faults in the Sea of Japan.
Our inter-seismic inversion suggests ~8 cm/year slip-rate deficit, which is consistent with the previous studies. Using the slip distribution, we calculate stressing rates on the source faults over SW Japan. In particular, positive Coulomb stressing rate on the source faults of the 2016 Kumamoto earthquake and the other M7 earthquakes is consistent with their occurrence. The crustal earthquakes before the 1944 and 1946 megathrust events also occurred in the region with source faults with positive Coulomb stressing rate.
How to cite: Hashima, A., Sato, H., Ishiyama, T., Freed, A., and Becker, T.: Fault stressing in the overriding plate due to megathrust coupling along the Nankai trough, Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18393, https://doi.org/10.5194/egusphere-egu2020-18393, 2020.
The Nankai trough has hosted ~M8 interplate earthquakes with the interval of 100-200 years. The crustal activity in southwest (SW) Japan in the overriding plate was relatively quiet after the last coupled megathrust ruptures occurred in 1944 and 1946. In the recent 20 years, however, SW Japan has experienced ~M7 earthquakes such as the 2016 Kumamoto earthquake. Similar activation of crustal earthquakes in the later stage of the megathrust earthquake cycles can be found in the historical earthquake occurrence based on paleographical studies. Such a change cannot be resolved by the probabilistic approaches, which usually rely on paleo-seismological data on longer timescales. Here, we show a deterministic way to quantify the current stressing state on the source faults due to megathrust coupling at the Nankai trough, making use of the data captured by the dense, modern geodetic network in Japan.
We constructed a 3-D finite element model (FEM) around the Japanese islands including the viscoelastic feature in the asthenosphere. The geometry of plate boundary on the Philippine Sea slab is based on earthquake distributions determined by the previous studies. In particular, the bended geometry at the junction of the Nankai trough and the Ryukyu trench is crucial for calculating stress. The plate boundary is divided into 8 x 27 patches to generate Green’s functions. The model region is divided into about 1000,000 tetrahedral elements with dimension of 5-100 km. We revised the source fault model by the Headquarters for Earthquake Research Promotion based on recent geophysical and geological data and added new faults in the Sea of Japan.
Our inter-seismic inversion suggests ~8 cm/year slip-rate deficit, which is consistent with the previous studies. Using the slip distribution, we calculate stressing rates on the source faults over SW Japan. In particular, positive Coulomb stressing rate on the source faults of the 2016 Kumamoto earthquake and the other M7 earthquakes is consistent with their occurrence. The crustal earthquakes before the 1944 and 1946 megathrust events also occurred in the region with source faults with positive Coulomb stressing rate.
How to cite: Hashima, A., Sato, H., Ishiyama, T., Freed, A., and Becker, T.: Fault stressing in the overriding plate due to megathrust coupling along the Nankai trough, Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18393, https://doi.org/10.5194/egusphere-egu2020-18393, 2020.
TS5.2 – Advances in understanding earthquake sequences and (a)seismic slip across scales
EGU2020-18554 | Displays | TS5.2
Going from stable creep to aseismic slow slip events in the ductile realmMarcel Thielmann and Thibault Duretz
The accommodation of motion on faults spans a large spectrum of slip modes, ranging from stable creep to earthquakes. While seismic slip modes certainly have the largest impact on the surface due to the induced ground shaking, it has been recognized that slow aseismic slip modes relax most of the accumulated stresses on a fault. It has also been suggested that aseismic slip controls seismic events, thus making this kind of slip mode key for earthquake prediction.
Despite the importance of aseismic slow slip, its underlying physical mechanisms are still unclear. Commonly, slow slip events are modeled in terms of frictional failure, employing a rate-and-state model of fault friction, often also invoking fluids that alter frictional properties on the fault. However, at larger depths, frictional processes become increasingly difficult to activate due to the increase in ambient pressure and ductile processes are more likely to dominate deformation.
Here we therefore investigate deep aseismic slip processes governed by ductile deformation mechanisms using 2D numerical models, where we employ a composite viscoelastic rheology combined with grain size reduction and shear heating as weakening processes. We show that the collaborative action of these two weakening mechanisms is sufficient to create the entire spectrum of aseismic slip, ranging from stable creep to long-term slow slip events. The results show that ductile deformation does not necessarily result in stable slip and induces slip modes with considerably larger velocities than the far-field plate velocities. Moreover, the propagation of ductile ruptures induces large stresses in front of the rupture tip which may also trigger short-term seismic events.
How to cite: Thielmann, M. and Duretz, T.: Going from stable creep to aseismic slow slip events in the ductile realm, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18554, https://doi.org/10.5194/egusphere-egu2020-18554, 2020.
The accommodation of motion on faults spans a large spectrum of slip modes, ranging from stable creep to earthquakes. While seismic slip modes certainly have the largest impact on the surface due to the induced ground shaking, it has been recognized that slow aseismic slip modes relax most of the accumulated stresses on a fault. It has also been suggested that aseismic slip controls seismic events, thus making this kind of slip mode key for earthquake prediction.
Despite the importance of aseismic slow slip, its underlying physical mechanisms are still unclear. Commonly, slow slip events are modeled in terms of frictional failure, employing a rate-and-state model of fault friction, often also invoking fluids that alter frictional properties on the fault. However, at larger depths, frictional processes become increasingly difficult to activate due to the increase in ambient pressure and ductile processes are more likely to dominate deformation.
Here we therefore investigate deep aseismic slip processes governed by ductile deformation mechanisms using 2D numerical models, where we employ a composite viscoelastic rheology combined with grain size reduction and shear heating as weakening processes. We show that the collaborative action of these two weakening mechanisms is sufficient to create the entire spectrum of aseismic slip, ranging from stable creep to long-term slow slip events. The results show that ductile deformation does not necessarily result in stable slip and induces slip modes with considerably larger velocities than the far-field plate velocities. Moreover, the propagation of ductile ruptures induces large stresses in front of the rupture tip which may also trigger short-term seismic events.
How to cite: Thielmann, M. and Duretz, T.: Going from stable creep to aseismic slow slip events in the ductile realm, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18554, https://doi.org/10.5194/egusphere-egu2020-18554, 2020.
EGU2020-13690 | Displays | TS5.2
On the scaling between precursory moment release and earthquake magnitude: Insights from the laboratory.Mateo Acosta, Francois Passelègue, Alexandre Schubnel, Raúl Madariaga, and Marie Violay
Recent seismological observations highlighted that both aseismic silent slip and/or foreshock sequences can precede large earthquake ruptures (Tohoku-Oki, 2011, Mw 9.0 (Kato et al., 2012); Iquique, 2014, Mw 8.1 (Ruiz et al, 2014; Socquet et al., 2017); Illapel, 2015, Mw 8.3 (Huang and Meng, 2018); Nicoya, 2012, Mw 7.6 (Voss et al., 2018)). However, the evolution of such precursory markers during earthquake nucleation remains poorly understood. Here, we report for the first time, experimental results regarding the nucleation of laboratory earthquakes (stick slip events) conducted on Westerly Granite saw-cut samples under both dry and fluid pressure conditions. Experiments were conducted under stress conditions representative of the upper continental crust, i.e confining pressures from 50 to 95 MPa; fluid pressures (water) ranging from 0 to 45 MPa.
At a given effective confining pressure, different precursory slip behaviors are observed. In dry conditions, we observe that slip evolves exponentially up to the main instability and is escorted by an exponential increase of acoustic emissions. With pressurized fluids, precursory slip evolves first exponentially then switches to a power law of time. There, precursory slip remains silent, independently of the fluid pressure level. The temporal evolution of precursory fault slip and seismicity are controlled by the fault’s environment, limiting its prognostic value. Nevertheless, we show that, independently of the fault conditions, the total precursory moment release scales with the co-seismic moment of the main instability. The relation follows a semi- empirical scaling relationship between precursory and co-seismic moment release by combining nucleation theory (Ida, 1972; Campillo and Ionescu, 1992) with the scaling between fracture energy and co-seismic slip which has been demonstrated experimentally (Nielsen et al., 2016; Passelègue et al., 2016), theoretically (Viesca and Garagash; 2015) and by natural observations (Abercrombie and Rice; 2005). We then compile data from natural earthquakes, and show that, over a range of Mw6.0 to Mw9.0 the proposed scaling law holds for natural observations. In summary, the amount of moment released prior to an earthquake is directly related to its magnitude, increasing therefore the detectability of large earthquakes. The scaling relationship between precursory and co-seismic moment should motivate detailed studies of precursory deformation of moderate to large earthquakes.
How to cite: Acosta, M., Passelègue, F., Schubnel, A., Madariaga, R., and Violay, M.: On the scaling between precursory moment release and earthquake magnitude: Insights from the laboratory., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13690, https://doi.org/10.5194/egusphere-egu2020-13690, 2020.
Recent seismological observations highlighted that both aseismic silent slip and/or foreshock sequences can precede large earthquake ruptures (Tohoku-Oki, 2011, Mw 9.0 (Kato et al., 2012); Iquique, 2014, Mw 8.1 (Ruiz et al, 2014; Socquet et al., 2017); Illapel, 2015, Mw 8.3 (Huang and Meng, 2018); Nicoya, 2012, Mw 7.6 (Voss et al., 2018)). However, the evolution of such precursory markers during earthquake nucleation remains poorly understood. Here, we report for the first time, experimental results regarding the nucleation of laboratory earthquakes (stick slip events) conducted on Westerly Granite saw-cut samples under both dry and fluid pressure conditions. Experiments were conducted under stress conditions representative of the upper continental crust, i.e confining pressures from 50 to 95 MPa; fluid pressures (water) ranging from 0 to 45 MPa.
At a given effective confining pressure, different precursory slip behaviors are observed. In dry conditions, we observe that slip evolves exponentially up to the main instability and is escorted by an exponential increase of acoustic emissions. With pressurized fluids, precursory slip evolves first exponentially then switches to a power law of time. There, precursory slip remains silent, independently of the fluid pressure level. The temporal evolution of precursory fault slip and seismicity are controlled by the fault’s environment, limiting its prognostic value. Nevertheless, we show that, independently of the fault conditions, the total precursory moment release scales with the co-seismic moment of the main instability. The relation follows a semi- empirical scaling relationship between precursory and co-seismic moment release by combining nucleation theory (Ida, 1972; Campillo and Ionescu, 1992) with the scaling between fracture energy and co-seismic slip which has been demonstrated experimentally (Nielsen et al., 2016; Passelègue et al., 2016), theoretically (Viesca and Garagash; 2015) and by natural observations (Abercrombie and Rice; 2005). We then compile data from natural earthquakes, and show that, over a range of Mw6.0 to Mw9.0 the proposed scaling law holds for natural observations. In summary, the amount of moment released prior to an earthquake is directly related to its magnitude, increasing therefore the detectability of large earthquakes. The scaling relationship between precursory and co-seismic moment should motivate detailed studies of precursory deformation of moderate to large earthquakes.
How to cite: Acosta, M., Passelègue, F., Schubnel, A., Madariaga, R., and Violay, M.: On the scaling between precursory moment release and earthquake magnitude: Insights from the laboratory., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13690, https://doi.org/10.5194/egusphere-egu2020-13690, 2020.
EGU2020-4192 | Displays | TS5.2
Temperature and fluid activation of contact healing and fault lubrication in rate-and-state frictionSylvain Barbot
The frictional behavior of rocks under shear offers tremendous complexity depending among others on rock type, temperature, fluid content, and sliding velocity. A large body of laboratory experiments documents these effects, but a unifying theoretical framework linking these observations is still missing. Here, I present a constitutive law based on multiple temperature and fluid activated healing processes and a fluid lubrication phase to capture fault behavior in the brittle field in all conditions relevant to the seismic cycle. Distinct healing processes are activated at different temperatures, pore fluid pressures, and depths based on their respective activation enthalpy. A fluid phase is rapidly formed at the high temperatures facilitated by shear heating, allowing strong weakening at high slip velocity. The model explains the intricate change of frictional behavior of carbonate rocks at various temperatures, including simultaneous velocity-strengthening and temperature-weakening at temperatures lower than 70ºC, transitioning to simultaneous velocity-weakening and temperature-hardening at higher temperatures. With different parameters, the model explains the frictional properties of quartz and granitic rocks in hydrothermal conditions with velocity-strengthening behavior in nominally dry conditions, transitioning to velocity-weakening between 100ºC and 350ºC in wet conditions. Inclusion of a lubrication phase formed between the solidus and the liquidus of the host rocks explains the strong weakening at high slip velocity in a variety of rocks. The unified constitutive framework allows modeling of faults in varying temperature and pore pressure conditions, including for example injection of pore fluids in natural faults or shear heating of the host rocks.
How to cite: Barbot, S.: Temperature and fluid activation of contact healing and fault lubrication in rate-and-state friction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4192, https://doi.org/10.5194/egusphere-egu2020-4192, 2020.
The frictional behavior of rocks under shear offers tremendous complexity depending among others on rock type, temperature, fluid content, and sliding velocity. A large body of laboratory experiments documents these effects, but a unifying theoretical framework linking these observations is still missing. Here, I present a constitutive law based on multiple temperature and fluid activated healing processes and a fluid lubrication phase to capture fault behavior in the brittle field in all conditions relevant to the seismic cycle. Distinct healing processes are activated at different temperatures, pore fluid pressures, and depths based on their respective activation enthalpy. A fluid phase is rapidly formed at the high temperatures facilitated by shear heating, allowing strong weakening at high slip velocity. The model explains the intricate change of frictional behavior of carbonate rocks at various temperatures, including simultaneous velocity-strengthening and temperature-weakening at temperatures lower than 70ºC, transitioning to simultaneous velocity-weakening and temperature-hardening at higher temperatures. With different parameters, the model explains the frictional properties of quartz and granitic rocks in hydrothermal conditions with velocity-strengthening behavior in nominally dry conditions, transitioning to velocity-weakening between 100ºC and 350ºC in wet conditions. Inclusion of a lubrication phase formed between the solidus and the liquidus of the host rocks explains the strong weakening at high slip velocity in a variety of rocks. The unified constitutive framework allows modeling of faults in varying temperature and pore pressure conditions, including for example injection of pore fluids in natural faults or shear heating of the host rocks.
How to cite: Barbot, S.: Temperature and fluid activation of contact healing and fault lubrication in rate-and-state friction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4192, https://doi.org/10.5194/egusphere-egu2020-4192, 2020.
EGU2020-17441 | Displays | TS5.2
Systematic characterization of slow slip events along the Mexican subduction zone from 2000 to 2019Mathilde Radiguet, Ekaterina Kazachkina, Louise Maubant, Nathalie Cotte, Vladimir Kostoglodov, Adriano Gualandi, and Kristel Chanard
Slow slip events (SSEs) represent a significant mechanism of strain release along several subduction zones, and understanding their occurrence and relations with major earthquake asperities is essential for a comprehensive understanding of the seismic cycle. Here, we focus on the Mexican subduction zone, characterized by the occurrence of recurrent large slow slip events (SSEs), both in the Guerrero region, where the SSEs are among the largest observed worldwide, and in the Oaxaca region, where smaller, more frequent SSEs occur. Up to now, most slow slip studies in the Mexican subduction zone focused either on the detailed analysis of a single event, were limited to a small area (Guerrero or Oaxaca), or were limited to data before 2012 [e.g.1-4]. In this study, our aim is to build an updated and consistent catalog of major slow slip events in the Guerrero-Oaxaca region.
We use an approach similar to Michel et al. 2018 [5]. We analyze the GPS time series from 2000 to 2019 using Independent Component Analysis (ICA), in order to separate temporally varying sources of different origins (seasonal signals, SSEs and afterslip of major earthquakes). We are able to isolate a component corresponding to seasonal loading, which matches the temporal evolution of displacement modeled from the GRACE data. The sources (independent components) identified as tectonic sources of deep origin are inverted for slip on the subduction interface. We thus obtain a model of the spatio-temporal evolution of aseismic slip on the subduction interface over 19 years, from which we can isolate around 30 individual slow slip events of Mw > 6.2.
The obtained catalog is coherent with previous studies (in terms of number of events detected, magnitude and duration) which validates the methodology. The observed moment-duration scaling is close to M0~T3 as recently suggested by Michel [6] for Cascadia SSEs, and our study extends the range of magnitude considered in their analysis. Finally, we also investigate the spatio-temporal relations between the SSEs occurring in the adjacent regions of Guerrero and Oaxaca, and their interaction with local and distant earthquakes.
References:
- Kostoglodov, V. et al. A large silent earthquake in the Guerrero seismic gap, Mexico. Geophys. Res. Lett 30, 1807 (2003).
- Graham, S. et al. Slow Slip History for the Mexico Subduction Zone: 2005 Through 2011. Pure and Applied Geophysics 1–21 (2015). doi:10.1007/s00024-015-1211-x
- Larson, K. M., Kostoglodov, V. & Shin’ichi Miyazaki, J. A. S. The 2006 aseismic slow slip event in Guerrero, Mexico: New results from GPS. Geophys. Res. Lett. 34, L13309 (2007).
- Radiguet, M. et al. Slow slip events and strain accumulation in the Guerrero gap, Mexico. J. Geophys. Res. 117, B04305 (2012).
- Michel, S., Gualandi, A. & Avouac, J.-P. Interseismic Coupling and Slow Slip Events on the Cascadia Megathrust. Pure Appl. Geophys. (2018). doi:10.1007/s00024-018-1991-x
- Michel, S., Gualandi, A. & Avouac, J. Similar scaling laws for earthquakes and Cascadia slow-slip events. Nature 574, 522–526 (2019) doi:10.1038/s41586-019-1673-6
How to cite: Radiguet, M., Kazachkina, E., Maubant, L., Cotte, N., Kostoglodov, V., Gualandi, A., and Chanard, K.: Systematic characterization of slow slip events along the Mexican subduction zone from 2000 to 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17441, https://doi.org/10.5194/egusphere-egu2020-17441, 2020.
Slow slip events (SSEs) represent a significant mechanism of strain release along several subduction zones, and understanding their occurrence and relations with major earthquake asperities is essential for a comprehensive understanding of the seismic cycle. Here, we focus on the Mexican subduction zone, characterized by the occurrence of recurrent large slow slip events (SSEs), both in the Guerrero region, where the SSEs are among the largest observed worldwide, and in the Oaxaca region, where smaller, more frequent SSEs occur. Up to now, most slow slip studies in the Mexican subduction zone focused either on the detailed analysis of a single event, were limited to a small area (Guerrero or Oaxaca), or were limited to data before 2012 [e.g.1-4]. In this study, our aim is to build an updated and consistent catalog of major slow slip events in the Guerrero-Oaxaca region.
We use an approach similar to Michel et al. 2018 [5]. We analyze the GPS time series from 2000 to 2019 using Independent Component Analysis (ICA), in order to separate temporally varying sources of different origins (seasonal signals, SSEs and afterslip of major earthquakes). We are able to isolate a component corresponding to seasonal loading, which matches the temporal evolution of displacement modeled from the GRACE data. The sources (independent components) identified as tectonic sources of deep origin are inverted for slip on the subduction interface. We thus obtain a model of the spatio-temporal evolution of aseismic slip on the subduction interface over 19 years, from which we can isolate around 30 individual slow slip events of Mw > 6.2.
The obtained catalog is coherent with previous studies (in terms of number of events detected, magnitude and duration) which validates the methodology. The observed moment-duration scaling is close to M0~T3 as recently suggested by Michel [6] for Cascadia SSEs, and our study extends the range of magnitude considered in their analysis. Finally, we also investigate the spatio-temporal relations between the SSEs occurring in the adjacent regions of Guerrero and Oaxaca, and their interaction with local and distant earthquakes.
References:
- Kostoglodov, V. et al. A large silent earthquake in the Guerrero seismic gap, Mexico. Geophys. Res. Lett 30, 1807 (2003).
- Graham, S. et al. Slow Slip History for the Mexico Subduction Zone: 2005 Through 2011. Pure and Applied Geophysics 1–21 (2015). doi:10.1007/s00024-015-1211-x
- Larson, K. M., Kostoglodov, V. & Shin’ichi Miyazaki, J. A. S. The 2006 aseismic slow slip event in Guerrero, Mexico: New results from GPS. Geophys. Res. Lett. 34, L13309 (2007).
- Radiguet, M. et al. Slow slip events and strain accumulation in the Guerrero gap, Mexico. J. Geophys. Res. 117, B04305 (2012).
- Michel, S., Gualandi, A. & Avouac, J.-P. Interseismic Coupling and Slow Slip Events on the Cascadia Megathrust. Pure Appl. Geophys. (2018). doi:10.1007/s00024-018-1991-x
- Michel, S., Gualandi, A. & Avouac, J. Similar scaling laws for earthquakes and Cascadia slow-slip events. Nature 574, 522–526 (2019) doi:10.1038/s41586-019-1673-6
How to cite: Radiguet, M., Kazachkina, E., Maubant, L., Cotte, N., Kostoglodov, V., Gualandi, A., and Chanard, K.: Systematic characterization of slow slip events along the Mexican subduction zone from 2000 to 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17441, https://doi.org/10.5194/egusphere-egu2020-17441, 2020.
EGU2020-4288 | Displays | TS5.2
Effect of Rheology on Afterslip and Viscoelastic Patterns Following the 2010 Mw 8.8 Maule, Chile, EarthquakeCarlos Peña, Oliver Heidbach, Marcos Moreno, Jonathan Bedford, Moritz Ziegler, Andrés Tassara, and Onno Oncken
After large earthquakes at subduction zones, the plate interface continues moving due to mostly frictional afterslip processes. Below depths of 60 km, little frictional afterslip is to be expected on the plate interface due to low shear strength, lack of apparent geodetic interseismic locking, and low seismic moment release from aftershocks. However, inversion models that consider an elastic crust above a mantle with viscoelastic rheology result in a significant portion of afterslip at depths > 60 km. In this study, we present a forward 3D geomechanical-numerical model with power-law rheology that simulates dislocation creep processes for the crust and upper mantle in combination with an afterslip inversion. The linear rheology case is also considered for comparison. We estimate the cumulative viscoelastic relaxation and the afterslip distribution for the first six years following the 2010 Mw 8.8 Maule earthquake in Chile. The cumulative afterslip distribution is obtained from the inversion of the residual surface displacements between continuous GPS (cGPS) observations and predicted displacements from viscoelastic forward modelling. We investigate three simulations: two with the same dislocation creep parameters in the slab and upper mantle but different ones in the continental crust, and another with elastic properties in the crust and slab and a linear viscoelastic upper mantle. Our preferred simulation is the one with power-law rheology in the crust and upper mantle with a weak continental crust since the corresponding afterslip distribution shows the best overall fit to the cGPS displacements (cumulative and time series) as well as having a good correlation with aftershock activity. In this simulation, most of the viscoelastic relaxation occurs in the continental lower crust beneath the volcanic arc due to dislocation creep processes. The resulting afterslip pattern from the inversion is reduced at depths > 60 km, which correlates well with the spatial distribution of cumulative seismic moment release from aftershocks. We conclude that by allowing for non-linear stress relaxation in the continental lower crust due to dislocation creep processes, the resulting afterslip distribution is in better agreement with the physical constraints from the shear strength of the plate interface at depth, the predicted locking degree, and the aftershock activity.
How to cite: Peña, C., Heidbach, O., Moreno, M., Bedford, J., Ziegler, M., Tassara, A., and Oncken, O.: Effect of Rheology on Afterslip and Viscoelastic Patterns Following the 2010 Mw 8.8 Maule, Chile, Earthquake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4288, https://doi.org/10.5194/egusphere-egu2020-4288, 2020.
After large earthquakes at subduction zones, the plate interface continues moving due to mostly frictional afterslip processes. Below depths of 60 km, little frictional afterslip is to be expected on the plate interface due to low shear strength, lack of apparent geodetic interseismic locking, and low seismic moment release from aftershocks. However, inversion models that consider an elastic crust above a mantle with viscoelastic rheology result in a significant portion of afterslip at depths > 60 km. In this study, we present a forward 3D geomechanical-numerical model with power-law rheology that simulates dislocation creep processes for the crust and upper mantle in combination with an afterslip inversion. The linear rheology case is also considered for comparison. We estimate the cumulative viscoelastic relaxation and the afterslip distribution for the first six years following the 2010 Mw 8.8 Maule earthquake in Chile. The cumulative afterslip distribution is obtained from the inversion of the residual surface displacements between continuous GPS (cGPS) observations and predicted displacements from viscoelastic forward modelling. We investigate three simulations: two with the same dislocation creep parameters in the slab and upper mantle but different ones in the continental crust, and another with elastic properties in the crust and slab and a linear viscoelastic upper mantle. Our preferred simulation is the one with power-law rheology in the crust and upper mantle with a weak continental crust since the corresponding afterslip distribution shows the best overall fit to the cGPS displacements (cumulative and time series) as well as having a good correlation with aftershock activity. In this simulation, most of the viscoelastic relaxation occurs in the continental lower crust beneath the volcanic arc due to dislocation creep processes. The resulting afterslip pattern from the inversion is reduced at depths > 60 km, which correlates well with the spatial distribution of cumulative seismic moment release from aftershocks. We conclude that by allowing for non-linear stress relaxation in the continental lower crust due to dislocation creep processes, the resulting afterslip distribution is in better agreement with the physical constraints from the shear strength of the plate interface at depth, the predicted locking degree, and the aftershock activity.
How to cite: Peña, C., Heidbach, O., Moreno, M., Bedford, J., Ziegler, M., Tassara, A., and Oncken, O.: Effect of Rheology on Afterslip and Viscoelastic Patterns Following the 2010 Mw 8.8 Maule, Chile, Earthquake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4288, https://doi.org/10.5194/egusphere-egu2020-4288, 2020.
EGU2020-17101 | Displays | TS5.2
Reconstructing 10 years of spatio-temporal aseismic slip history along the San Andreas FaultSylvain Michel, Romain Jolivet, Adriano Gualandi, Blandine Guardonio, Olivier Lengliné, Manon Dalaison, and Angélique Benoit
The San Andreas Fault creeping section is generally considered as slipping continuously and aseismically, at a rate of about 35 mm/yr. However, recent studies, using either Global Positioning System (GPS) network or Interferometric Synthetic Aperture Radar (InSAR) data, have highlighted spatial and temporal variations of slip rate. Here, we combine GPS, InSAR, creepmeter and seismicity data over the 2008-2018 period, taking advantage of their complementary spatial and temporal resolutions, to detail a comprehensive picture of episodic acceleration and deceleration slip patterns. For this purpose, we use a variational Bayesian Independent Component Analysis (vbICA) decomposition to separate geodetic deformation due to non-tectonic sources from signals of tectonic origin. The fault slip kinematics is reconstructed by linear inversion of each Independent Component related to transient tectonic activity. We document aseismic slip acceleration transients and discuss their origin.
How to cite: Michel, S., Jolivet, R., Gualandi, A., Guardonio, B., Lengliné, O., Dalaison, M., and Benoit, A.: Reconstructing 10 years of spatio-temporal aseismic slip history along the San Andreas Fault, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17101, https://doi.org/10.5194/egusphere-egu2020-17101, 2020.
The San Andreas Fault creeping section is generally considered as slipping continuously and aseismically, at a rate of about 35 mm/yr. However, recent studies, using either Global Positioning System (GPS) network or Interferometric Synthetic Aperture Radar (InSAR) data, have highlighted spatial and temporal variations of slip rate. Here, we combine GPS, InSAR, creepmeter and seismicity data over the 2008-2018 period, taking advantage of their complementary spatial and temporal resolutions, to detail a comprehensive picture of episodic acceleration and deceleration slip patterns. For this purpose, we use a variational Bayesian Independent Component Analysis (vbICA) decomposition to separate geodetic deformation due to non-tectonic sources from signals of tectonic origin. The fault slip kinematics is reconstructed by linear inversion of each Independent Component related to transient tectonic activity. We document aseismic slip acceleration transients and discuss their origin.
How to cite: Michel, S., Jolivet, R., Gualandi, A., Guardonio, B., Lengliné, O., Dalaison, M., and Benoit, A.: Reconstructing 10 years of spatio-temporal aseismic slip history along the San Andreas Fault, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17101, https://doi.org/10.5194/egusphere-egu2020-17101, 2020.
EGU2020-18166 | Displays | TS5.2 | Highlight
Reversals in geodetically observed surface motions suggests enhanced slab pull in the months preceding Maule Mw 8.8 and Tohoku-oki Mw 9.0 earthquakesJonathan Bedford, Marcos Moreno, Zhiguo Deng, Onno Oncken, Bernd Schurr, Timm John, Juan Carlos Báez, and Michael Bevis
It is increasingly apparent that the progression to eventual failure of large subduction earthquakes can be captured by continuous networks that record anomalous seismic and geodetic signals in the late interseismic period. Such precursory signals are generally understood to be related to a gradual decoupling of the mainshock area of the fault and can last from days to years. These natural observations are consistent with various numerical and laboratory models in which similar late-interseismic signals are generated.
Here we analyse the continuous GNSS records of the final 5 years leading to the 2010 Mw 8.8 Maule, Chile and 2011 Mw 9.0 Tohoku-oki, Japan earthquakes. We implement the Greedy Automatic Signal Decomposition - a regression approach that builds upon existing tectonic trajectory models - to model the daily GNSS displacement time series as the sum of background seasonal oscillations, step functions, linear (1st order polynomial) motion, and a sparse number of multi-transient functions. The multi-transient functions are simply the sum of decay functions (e.g. exponential, logarithmic) that begin at the same time but have different characteristic decay constants. The inclusion of these versatile multi-transients allows the model to capture a variety of transient motion. We see that both subduction margins exhibit variability in their interseismic velocities. The most striking of these motions occur in the 5-7 months directly before both the Maule and Tohoku-oki earthquakes during which the sense of motion reverses in the trench-perpendicular component. These reversals manifest themselves as wobbles in the displacement time series with a peak-to-peak displacement between 4-8 mm and occur on a spatial scale in the order of thousands of kilometres. After investigating fluid loading and possible reference frame artifacts, we conclude that the wobbles are most likely of a tectonic origin.
In the pre-Tohoku-oki case, for which we have a much denser surface coverage, kinematic models indicate an initial extension in the Philippine Sea Plate followed by a viscoelastic rebound. The spatial scale and approximate onset of this apparent extension are in agreement with the anomalous GRACE gravity signals reported in earlier work of Panet et al. (2018, Nature Geoscience). Furthermore, the speed that the trench-wards transient migrates along-strike of the subduction zone before Tohoku-oki indicates that deep slow-slip is also occurring. In the pre-Maule case, we see a similar reversal but lack the number of measurements to track any migration of the velocity front. Nevertheless, from inclusion of vertical displacement in analyses of both networks, we suspect that these late interseismic reversal signals are caused by a sudden enhanced slab pulling. Such an enhanced slab pull might be caused by sudden densification of metastable slab. Therefore, a main message of this work is that large asperities, while they might fail gradually local to the mainshock region, might also brought to failure by changes in the slab pull boundary conditions that can be several hundreds of km deep.
How to cite: Bedford, J., Moreno, M., Deng, Z., Oncken, O., Schurr, B., John, T., Báez, J. C., and Bevis, M.: Reversals in geodetically observed surface motions suggests enhanced slab pull in the months preceding Maule Mw 8.8 and Tohoku-oki Mw 9.0 earthquakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18166, https://doi.org/10.5194/egusphere-egu2020-18166, 2020.
It is increasingly apparent that the progression to eventual failure of large subduction earthquakes can be captured by continuous networks that record anomalous seismic and geodetic signals in the late interseismic period. Such precursory signals are generally understood to be related to a gradual decoupling of the mainshock area of the fault and can last from days to years. These natural observations are consistent with various numerical and laboratory models in which similar late-interseismic signals are generated.
Here we analyse the continuous GNSS records of the final 5 years leading to the 2010 Mw 8.8 Maule, Chile and 2011 Mw 9.0 Tohoku-oki, Japan earthquakes. We implement the Greedy Automatic Signal Decomposition - a regression approach that builds upon existing tectonic trajectory models - to model the daily GNSS displacement time series as the sum of background seasonal oscillations, step functions, linear (1st order polynomial) motion, and a sparse number of multi-transient functions. The multi-transient functions are simply the sum of decay functions (e.g. exponential, logarithmic) that begin at the same time but have different characteristic decay constants. The inclusion of these versatile multi-transients allows the model to capture a variety of transient motion. We see that both subduction margins exhibit variability in their interseismic velocities. The most striking of these motions occur in the 5-7 months directly before both the Maule and Tohoku-oki earthquakes during which the sense of motion reverses in the trench-perpendicular component. These reversals manifest themselves as wobbles in the displacement time series with a peak-to-peak displacement between 4-8 mm and occur on a spatial scale in the order of thousands of kilometres. After investigating fluid loading and possible reference frame artifacts, we conclude that the wobbles are most likely of a tectonic origin.
In the pre-Tohoku-oki case, for which we have a much denser surface coverage, kinematic models indicate an initial extension in the Philippine Sea Plate followed by a viscoelastic rebound. The spatial scale and approximate onset of this apparent extension are in agreement with the anomalous GRACE gravity signals reported in earlier work of Panet et al. (2018, Nature Geoscience). Furthermore, the speed that the trench-wards transient migrates along-strike of the subduction zone before Tohoku-oki indicates that deep slow-slip is also occurring. In the pre-Maule case, we see a similar reversal but lack the number of measurements to track any migration of the velocity front. Nevertheless, from inclusion of vertical displacement in analyses of both networks, we suspect that these late interseismic reversal signals are caused by a sudden enhanced slab pulling. Such an enhanced slab pull might be caused by sudden densification of metastable slab. Therefore, a main message of this work is that large asperities, while they might fail gradually local to the mainshock region, might also brought to failure by changes in the slab pull boundary conditions that can be several hundreds of km deep.
How to cite: Bedford, J., Moreno, M., Deng, Z., Oncken, O., Schurr, B., John, T., Báez, J. C., and Bevis, M.: Reversals in geodetically observed surface motions suggests enhanced slab pull in the months preceding Maule Mw 8.8 and Tohoku-oki Mw 9.0 earthquakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18166, https://doi.org/10.5194/egusphere-egu2020-18166, 2020.
EGU2020-21477 | Displays | TS5.2
Revisiting the deformation transients before the 2011 Tohoku-Oki Megathrust Earthquake with GPSAnne Socquet, Lou Marill, David Marsan, Baptiste Rousset, Mathilde Radiguet, Roland Burgmann, Nathalie Cotte, and Michel Bouchon
The precursory activity leading up to the Tohoku-Oki earthquake of 2011 has been suggested to feature both long- and short-term episodes of decoupling and suggests a particularly complex slow slip history. The analysis of the F3 solution of the Japanese GPS network suggested that an accelerated slip occurred in the deeper part of the seismogenic zone during the 10 years preceding the earthquake (Heki & Mitsui, EPSL 2013; Mavrommatis et al., GRL 2014; Yokota & Koketsu, Nat. Com. 2015). During the two months preceding the earthquake, no anomaly in the GPS position time series has been revealed so far, although several anomalous geophysical signals have been reported (an extended foreshock crisis near the future hypocenter (Kato et al., Science 2012), a synchronized increase of intermediate-depth background seismicity (Bouchon et al., Nat Geosc. 2016), a signal in ocean-bottom pressure gauges and on-land strainmeter time series (Ito et al., Tectonoph. 2013), and large scale gravity anomalies that suggest deep-seated slab deformation processes (Panet et al., Nat. Geosc. 2018 ; Wang & Burgmann, GRL 2019)).
We present novel results based on an independent analysis of the Japanese GPS data set. We perform a full reprocessing of the raw data with a double-difference approach, a systematic analysis of the obtained time-series, including noise characterization and network filtering, and make a robust assessment of long- and short-term tectonic aseismic transients preceding the Tohoku-Oki earthquake. An accelerated slip on the lower part of the seismogenic zone over the last decade is confirmed, not only below the epicenter of Tohoku-Oki earthquake but also further south, offshore Boso peninsula, which is a worrying sign of an on-going slow decoupling east of Tokyo. At shorter time-scale, first results seem compatible with a slow slip close to the epicenter initiating ~ 2 months before the mainshock.
How to cite: Socquet, A., Marill, L., Marsan, D., Rousset, B., Radiguet, M., Burgmann, R., Cotte, N., and Bouchon, M.: Revisiting the deformation transients before the 2011 Tohoku-Oki Megathrust Earthquake with GPS , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21477, https://doi.org/10.5194/egusphere-egu2020-21477, 2020.
The precursory activity leading up to the Tohoku-Oki earthquake of 2011 has been suggested to feature both long- and short-term episodes of decoupling and suggests a particularly complex slow slip history. The analysis of the F3 solution of the Japanese GPS network suggested that an accelerated slip occurred in the deeper part of the seismogenic zone during the 10 years preceding the earthquake (Heki & Mitsui, EPSL 2013; Mavrommatis et al., GRL 2014; Yokota & Koketsu, Nat. Com. 2015). During the two months preceding the earthquake, no anomaly in the GPS position time series has been revealed so far, although several anomalous geophysical signals have been reported (an extended foreshock crisis near the future hypocenter (Kato et al., Science 2012), a synchronized increase of intermediate-depth background seismicity (Bouchon et al., Nat Geosc. 2016), a signal in ocean-bottom pressure gauges and on-land strainmeter time series (Ito et al., Tectonoph. 2013), and large scale gravity anomalies that suggest deep-seated slab deformation processes (Panet et al., Nat. Geosc. 2018 ; Wang & Burgmann, GRL 2019)).
We present novel results based on an independent analysis of the Japanese GPS data set. We perform a full reprocessing of the raw data with a double-difference approach, a systematic analysis of the obtained time-series, including noise characterization and network filtering, and make a robust assessment of long- and short-term tectonic aseismic transients preceding the Tohoku-Oki earthquake. An accelerated slip on the lower part of the seismogenic zone over the last decade is confirmed, not only below the epicenter of Tohoku-Oki earthquake but also further south, offshore Boso peninsula, which is a worrying sign of an on-going slow decoupling east of Tokyo. At shorter time-scale, first results seem compatible with a slow slip close to the epicenter initiating ~ 2 months before the mainshock.
How to cite: Socquet, A., Marill, L., Marsan, D., Rousset, B., Radiguet, M., Burgmann, R., Cotte, N., and Bouchon, M.: Revisiting the deformation transients before the 2011 Tohoku-Oki Megathrust Earthquake with GPS , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21477, https://doi.org/10.5194/egusphere-egu2020-21477, 2020.
EGU2020-1373 | Displays | TS5.2
Cross-comparing GPS and seismic data in advance and after great earthquakesTai Liu and Vladimir Kossobokov
With the accumulation of seismic and other geophysical data and update of methodologies, the accuracy and reliability of seismic risk assessment can be improved. In particular, the introduction of GPS observation data leads to better understanding of earthquake origins and sequences. For this, we cross-compare the pre- and post-seismic deformation of the 2011 Tohoku Mw9.1 earthquake in Japan, the 2010 off shore Maule Mw8.8 earthquake in Chile, the 2018 Kodiak Mw7.9 earthquake in the Gulf of Alaska, and the 2016 Kaikoura Mw7.8 earthquake in New Zealand derived from GPS observations with integral characteristics of the regional seismic regime, including the accumulated length of seismic sources derived from the catalogs of earthquake hypocenter parameters. We found that (a) the area on top the 2011 Tohoku mega-thrust keeps moving at speed of about 10 cm per year, (b) eventually, the 2016 Kaikoura unidirectional strike-slip resulted in the current position retreat nearby epicenter and steady increase on the opposite edge of its rupture zone, (c) the four cases show up different deformation vs seismicity correlation patterns in advance and after the catastrophic event, and (d) GPS data confirm the existence of intermittent long periods of regionally stable levels of seismic regime controlled by the Unified Scaling Law for Earthquakes that may switch as the result of mid- or even short-term bursts of activity associated with major catastrophic earthquakes.
The study supported from the RFBR Project No. 19-35-50059 “Study of pre- and post-seismic displacements in the areas of the strongest earthquakes in the world".
How to cite: Liu, T. and Kossobokov, V.: Cross-comparing GPS and seismic data in advance and after great earthquakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1373, https://doi.org/10.5194/egusphere-egu2020-1373, 2020.
With the accumulation of seismic and other geophysical data and update of methodologies, the accuracy and reliability of seismic risk assessment can be improved. In particular, the introduction of GPS observation data leads to better understanding of earthquake origins and sequences. For this, we cross-compare the pre- and post-seismic deformation of the 2011 Tohoku Mw9.1 earthquake in Japan, the 2010 off shore Maule Mw8.8 earthquake in Chile, the 2018 Kodiak Mw7.9 earthquake in the Gulf of Alaska, and the 2016 Kaikoura Mw7.8 earthquake in New Zealand derived from GPS observations with integral characteristics of the regional seismic regime, including the accumulated length of seismic sources derived from the catalogs of earthquake hypocenter parameters. We found that (a) the area on top the 2011 Tohoku mega-thrust keeps moving at speed of about 10 cm per year, (b) eventually, the 2016 Kaikoura unidirectional strike-slip resulted in the current position retreat nearby epicenter and steady increase on the opposite edge of its rupture zone, (c) the four cases show up different deformation vs seismicity correlation patterns in advance and after the catastrophic event, and (d) GPS data confirm the existence of intermittent long periods of regionally stable levels of seismic regime controlled by the Unified Scaling Law for Earthquakes that may switch as the result of mid- or even short-term bursts of activity associated with major catastrophic earthquakes.
The study supported from the RFBR Project No. 19-35-50059 “Study of pre- and post-seismic displacements in the areas of the strongest earthquakes in the world".
How to cite: Liu, T. and Kossobokov, V.: Cross-comparing GPS and seismic data in advance and after great earthquakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1373, https://doi.org/10.5194/egusphere-egu2020-1373, 2020.
EGU2020-2550 | Displays | TS5.2
Enhancement of Interplate Coupling after Recent Megathrust EarthquakesMohammad Yuzariyadi and Kosuke Heki
Enhanced interplate coupling has been found for segments adjacent along-strike to megathrust faults after the 2003 Tokachi-Oki and the 2011 Tohoku-Oki earthquakes, NE Japan, and was interpreted as acceleration of the subducting Pacific Plate slab. A similar enhanced coupling was also reported for the segments to the north of the rupture area of the 2010 Maule earthquake, central Chile. We utilize available GNSS data to find such enhanced coupling in worldwide subduction zones including NE Japan, central and northern Chile, Sumatra, and Mexico to investigate their common features. Our study revealed that the accelerations of landward movement of 2.1-9.0 mm per year appeared in adjacent segments following the 2014 Iquique (Chile), the 2007 Bengkulu (Sumatra), and the 2012 Oaxaca (Mexico) earthquakes. We also confirmed that the enhanced coupling is associated with the increase of seismicity for all these six cases. We found that the degree of enhancement depends on the length of the slab and the magnitude of the earthquake, which is consistent with the simple 2-dimensional model proposed earlier.
How to cite: Yuzariyadi, M. and Heki, K.: Enhancement of Interplate Coupling after Recent Megathrust Earthquakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2550, https://doi.org/10.5194/egusphere-egu2020-2550, 2020.
Enhanced interplate coupling has been found for segments adjacent along-strike to megathrust faults after the 2003 Tokachi-Oki and the 2011 Tohoku-Oki earthquakes, NE Japan, and was interpreted as acceleration of the subducting Pacific Plate slab. A similar enhanced coupling was also reported for the segments to the north of the rupture area of the 2010 Maule earthquake, central Chile. We utilize available GNSS data to find such enhanced coupling in worldwide subduction zones including NE Japan, central and northern Chile, Sumatra, and Mexico to investigate their common features. Our study revealed that the accelerations of landward movement of 2.1-9.0 mm per year appeared in adjacent segments following the 2014 Iquique (Chile), the 2007 Bengkulu (Sumatra), and the 2012 Oaxaca (Mexico) earthquakes. We also confirmed that the enhanced coupling is associated with the increase of seismicity for all these six cases. We found that the degree of enhancement depends on the length of the slab and the magnitude of the earthquake, which is consistent with the simple 2-dimensional model proposed earlier.
How to cite: Yuzariyadi, M. and Heki, K.: Enhancement of Interplate Coupling after Recent Megathrust Earthquakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2550, https://doi.org/10.5194/egusphere-egu2020-2550, 2020.
EGU2020-20862 | Displays | TS5.2
Build seismic cycle balance deformation with InSAR in Northen ChileLauriane Bayle, Romain Jolivet, Nadaya Cubas, and Laetitia Le Pourhiet
Lauriane Baylé (1), Romain Jolivet (2), Nadaya Cubas (1) and Laetitia Le
Pourhiet (1)
(1) Institut des Sciences de la Terre de Paris, UMR 7193, UPMC UniversitéParis 6, CNRS, Paris,
France
(2) Laboratoire de Géologie, Département de Géosciences, École Normale Supérieure, CNRS UMR 8538,
PSL ResearchUniversity, Paris, France
Recent studies have pointed out to a discrepancy between the short- and long-
term deformation of overriding plates in subduction zones. This led to debates
about when and how permanent deformation is acquired. This contradiction
has notably been observed along the Central Andes Subduction Zone, where
the coast subsides during and shortly after major earthquakes while a coastal
uplift with rates ranging between 0.1 and 0.3 mm/yr has been inferred the
last 4000 ky. For instance, during the 15th September 2015 Mw 8.3 Illapel
earthquake the geodetics (GPS and InSAR) data show a coastal subsidence
along the line-of-sight of 20 cm in InSAR.
To reconcile the seemingly contradictory observations, we here propose to
provide a seismic cycle uplift balance by constrainning inter-, co- and post-
seismic vertical velocities from InSAR time series. The study focuses on La
Serena peninsula (71.3°W, 30°S, Chile) along which the Illapel earthquake
occurred and for which long-term uplift rates have been provided by previous
geomorphological studies.
To build this seismic cycle balance, we use InSAR data (Sentinel-1) acqui-
red between the September 15, 2015 and January 19, 2019. The time series
for the ascendant orbite is calculated and the accumulated vertical displace-
ment extracted providing co- and post-seismic displacement. The co-seismic
displacement are similar to those previously obtain. To constrain the displa-
cement during the inter-seismic period, data on both sides of the peninsula
are used. In that respect, we aim determining when, during the seismic cycle,
and where, along the coast, the uplift occurs.
The deduced time series will then be confronted to numerical modelling
to provide the short- and long-term mechanics reproducing the short- and
long-term observations.
How to cite: Bayle, L., Jolivet, R., Cubas, N., and Le Pourhiet, L.: Build seismic cycle balance deformation with InSAR in Northen Chile, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20862, https://doi.org/10.5194/egusphere-egu2020-20862, 2020.
Lauriane Baylé (1), Romain Jolivet (2), Nadaya Cubas (1) and Laetitia Le
Pourhiet (1)
(1) Institut des Sciences de la Terre de Paris, UMR 7193, UPMC UniversitéParis 6, CNRS, Paris,
France
(2) Laboratoire de Géologie, Département de Géosciences, École Normale Supérieure, CNRS UMR 8538,
PSL ResearchUniversity, Paris, France
Recent studies have pointed out to a discrepancy between the short- and long-
term deformation of overriding plates in subduction zones. This led to debates
about when and how permanent deformation is acquired. This contradiction
has notably been observed along the Central Andes Subduction Zone, where
the coast subsides during and shortly after major earthquakes while a coastal
uplift with rates ranging between 0.1 and 0.3 mm/yr has been inferred the
last 4000 ky. For instance, during the 15th September 2015 Mw 8.3 Illapel
earthquake the geodetics (GPS and InSAR) data show a coastal subsidence
along the line-of-sight of 20 cm in InSAR.
To reconcile the seemingly contradictory observations, we here propose to
provide a seismic cycle uplift balance by constrainning inter-, co- and post-
seismic vertical velocities from InSAR time series. The study focuses on La
Serena peninsula (71.3°W, 30°S, Chile) along which the Illapel earthquake
occurred and for which long-term uplift rates have been provided by previous
geomorphological studies.
To build this seismic cycle balance, we use InSAR data (Sentinel-1) acqui-
red between the September 15, 2015 and January 19, 2019. The time series
for the ascendant orbite is calculated and the accumulated vertical displace-
ment extracted providing co- and post-seismic displacement. The co-seismic
displacement are similar to those previously obtain. To constrain the displa-
cement during the inter-seismic period, data on both sides of the peninsula
are used. In that respect, we aim determining when, during the seismic cycle,
and where, along the coast, the uplift occurs.
The deduced time series will then be confronted to numerical modelling
to provide the short- and long-term mechanics reproducing the short- and
long-term observations.
How to cite: Bayle, L., Jolivet, R., Cubas, N., and Le Pourhiet, L.: Build seismic cycle balance deformation with InSAR in Northen Chile, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20862, https://doi.org/10.5194/egusphere-egu2020-20862, 2020.
EGU2020-12165 | Displays | TS5.2
Deep structure of the Central-Chile continental wedge and its implications for large megathrust earthquakesAndrei Maksymowicz, Daniela Montecinos, and Daniel Díaz
subduction zone ruptured by the high slip patch of the 1960 Mw9.5 Valdivia earthquake. The density structure of the upper plate was generated by using a 2-D forward modeling schema (GGrad) offshore, and 3D inversion onshore (GRAV3D) with a database composed by a recompilation of previous marine and onshore gravity measurements, complemented by 113 new gravimetric station acquired by our group. The modelling was constrained by independent seismological data, active seismic information and electromagnetic soundings registered during the project. The joint analyze of the obtained density model with magnetic data and seismic models, provide new insight about the structure of the upper plate forearc, where an East-West segmentation of physical parameters (perpendicular to the margin) is associated with first order changes in the surface geology, deep structural style and seismotectonics characteristics of the margin. The systematical comparison of the results observed in this segment with surrounding regions of the Chilean margin, suggests a causal link between complex sequence of large earthquakes ruptures and changes of rheology/lithology along the interplate boundary, determined in turn, by the long term tectonic and geodynamic evolution of the subduction zone.
How to cite: Maksymowicz, A., Montecinos, D., and Díaz, D.: Deep structure of the Central-Chile continental wedge and its implications for large megathrust earthquakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12165, https://doi.org/10.5194/egusphere-egu2020-12165, 2020.
subduction zone ruptured by the high slip patch of the 1960 Mw9.5 Valdivia earthquake. The density structure of the upper plate was generated by using a 2-D forward modeling schema (GGrad) offshore, and 3D inversion onshore (GRAV3D) with a database composed by a recompilation of previous marine and onshore gravity measurements, complemented by 113 new gravimetric station acquired by our group. The modelling was constrained by independent seismological data, active seismic information and electromagnetic soundings registered during the project. The joint analyze of the obtained density model with magnetic data and seismic models, provide new insight about the structure of the upper plate forearc, where an East-West segmentation of physical parameters (perpendicular to the margin) is associated with first order changes in the surface geology, deep structural style and seismotectonics characteristics of the margin. The systematical comparison of the results observed in this segment with surrounding regions of the Chilean margin, suggests a causal link between complex sequence of large earthquakes ruptures and changes of rheology/lithology along the interplate boundary, determined in turn, by the long term tectonic and geodynamic evolution of the subduction zone.
How to cite: Maksymowicz, A., Montecinos, D., and Díaz, D.: Deep structure of the Central-Chile continental wedge and its implications for large megathrust earthquakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12165, https://doi.org/10.5194/egusphere-egu2020-12165, 2020.
EGU2020-12150 | Displays | TS5.2
Investigating seismic segmentation and recurrence patterns of great earthquakes along the Chilean megathrust.Diego Molina, Andres Tassara, Jean-Paul Ampuero, and Daniel Melnick
Megathrust earthquakes at subduction zones are one of the most devastating natural phenomena. Understanding the relationships between their temporal recurrence, spatial segmentation and the frictional structure of the megathrust is of primary relevance. We analyzed the common spatial variability of gravity anomalies, geodetic locking and wedge taper basal friction (three independent proxies for megathrust frictional structure) along the Chilean margin. A marked along-strike segmentation has emerged that is organized into three hierarchical levels. At a subcontinental-scale (103 km), we observe a first-order difference between Central (18-32°S) and Southern (32°-46°S) Andes. This is marked by a dominance of positive/negative gravity, high/low locking, high/low friction along the Central/Southern segments. We explain this as mainly reflecting the combined effect on effective normal stress (σeff) of a high/low density forearc and low/high pore pressure along both megathrust segments, in agreement with the geological structure of the forearc, sediment input at the trench and the long-term architecture of the Andes. Inside this large-scale subdivision, we identify a number of segments (102 km) that are limited by marked small-scale (101 km) changes in the first-order tendency of the three proxies coinciding with geological features of both plates. When we compare this against the paleoseismic, historic and instrumental record of past earthquakes in Chile, we note that segments largely coincide with seismic asperities, i.e. those regions of the megathrust concentrating the largest fraction of coseismic slip. Bridging these two scales, the rupture length of giant (Mw 8.5-9.5) earthquakes, which encompassed several asperities, define an intermediate hierarchic level of organization (102-103 km). Considering this segmentation into the conceptual framework of the rate-and-state friction (RSF) law, we infer that asperities inside the rate-weakening seismogenic zone of the Central Andean megathrust are dominantly unstable (i.e. σeff>σc = the critical stress defined by RSF parameters) and therefore prone to initiate and concentrate the coseismic rupture. In contrast, most of the asperities along the Southern mega-segment are likely characterized by a conditionally-stable behavior (σeff<σc) that allows a rich and complex seismogenic behavior where interseismic creep and locking are both possible and large coseismic slip propagation is dominant. This can explain the apparent difference in the recurrence of giant earthquakes along both mega-segments, since the synchronization of unstable asperities in the Central Andean megathrust (2000-3000 yr recurrence time) is less probable than in the case of conditionally-stable asperities in the Southern segment (300-500 yrs). We will test these hypothesis developing numerical simulations of multiple seismic cycles with setups representing the inferred contrast on the physical properties of the megathrust along the Chilean margin, and we will present preliminary results of this exercise.
How to cite: Molina, D., Tassara, A., Ampuero, J.-P., and Melnick, D.: Investigating seismic segmentation and recurrence patterns of great earthquakes along the Chilean megathrust. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12150, https://doi.org/10.5194/egusphere-egu2020-12150, 2020.
Megathrust earthquakes at subduction zones are one of the most devastating natural phenomena. Understanding the relationships between their temporal recurrence, spatial segmentation and the frictional structure of the megathrust is of primary relevance. We analyzed the common spatial variability of gravity anomalies, geodetic locking and wedge taper basal friction (three independent proxies for megathrust frictional structure) along the Chilean margin. A marked along-strike segmentation has emerged that is organized into three hierarchical levels. At a subcontinental-scale (103 km), we observe a first-order difference between Central (18-32°S) and Southern (32°-46°S) Andes. This is marked by a dominance of positive/negative gravity, high/low locking, high/low friction along the Central/Southern segments. We explain this as mainly reflecting the combined effect on effective normal stress (σeff) of a high/low density forearc and low/high pore pressure along both megathrust segments, in agreement with the geological structure of the forearc, sediment input at the trench and the long-term architecture of the Andes. Inside this large-scale subdivision, we identify a number of segments (102 km) that are limited by marked small-scale (101 km) changes in the first-order tendency of the three proxies coinciding with geological features of both plates. When we compare this against the paleoseismic, historic and instrumental record of past earthquakes in Chile, we note that segments largely coincide with seismic asperities, i.e. those regions of the megathrust concentrating the largest fraction of coseismic slip. Bridging these two scales, the rupture length of giant (Mw 8.5-9.5) earthquakes, which encompassed several asperities, define an intermediate hierarchic level of organization (102-103 km). Considering this segmentation into the conceptual framework of the rate-and-state friction (RSF) law, we infer that asperities inside the rate-weakening seismogenic zone of the Central Andean megathrust are dominantly unstable (i.e. σeff>σc = the critical stress defined by RSF parameters) and therefore prone to initiate and concentrate the coseismic rupture. In contrast, most of the asperities along the Southern mega-segment are likely characterized by a conditionally-stable behavior (σeff<σc) that allows a rich and complex seismogenic behavior where interseismic creep and locking are both possible and large coseismic slip propagation is dominant. This can explain the apparent difference in the recurrence of giant earthquakes along both mega-segments, since the synchronization of unstable asperities in the Central Andean megathrust (2000-3000 yr recurrence time) is less probable than in the case of conditionally-stable asperities in the Southern segment (300-500 yrs). We will test these hypothesis developing numerical simulations of multiple seismic cycles with setups representing the inferred contrast on the physical properties of the megathrust along the Chilean margin, and we will present preliminary results of this exercise.
How to cite: Molina, D., Tassara, A., Ampuero, J.-P., and Melnick, D.: Investigating seismic segmentation and recurrence patterns of great earthquakes along the Chilean megathrust. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12150, https://doi.org/10.5194/egusphere-egu2020-12150, 2020.
EGU2020-9831 | Displays | TS5.2
Continual interaction between the Minahassa subduction interface and the Palu-Koro strike-slip fault in Sulawesi, Indonesia.Nicolai Nijholt, Wim Simons, and Riccardo Riva
Two major fault systems host Mw>7 earthquakes in Central and Northern Sulawesi, Indonesia: the Minahassa subduction interface and the Palu-Koro strike-slip fault. The Celebes Sea oceanic lithosphere subducts beneath the north arm of Sulawesi at the Minahassa subduction zone. At the western termination of the Minahassa subduction zone, it connects to the left-lateral Palu-Koro strike-slip fault zone. This fault strikes onshore at Palu Bay and then crosses Sulawesi. Interseismic GNSS velocities indicate that the Palu-Koro fault zone accommodates about 4 cm/yr of relative motion in the Palu Bay area, with a ~10 km locking depth. This shallowly locked segment of the Palu-Koro fault around the Palu Bay area ruptured during the devastating, tsunami-generating, 2018 Mw7.5 Palu earthquake. This complex event highlights the high seismic hazard for the island of Sulawesi.
We have a >20-year record of GNSS velocities on Sulawesi, where the densest cluster of monument sites surrounds the Palu-Koro fault, specifically around Palu Bay, whereas the rest of the island is less densely covered. High quality estimates of interseismic velocities reveal second-order complex patterns of transient deformation in the wake of major earthquakes: the velocities in northern Sulawesi and around the Palu-Koro fault do not follow their interseismic trends after a major subduction earthquake has occurred, for several years after the event. This effect of transient deformation reaches more than 400km away from the epicentre of the major earthquakes. Surprisingly, a deviation from the background slip rate on the Palu-Koro fault is not accompanied by a deviation from the background (micro)seismic activity.
We construct a 3D numerical model based on the structural and seismological data in the Sulawesi region. We investigate the post-seismic relaxation pattern from a subduction earthquake and determine whether the slip rate on the Palu-Koro fault changes due to this earthquake through forward model calculations. With a modelling focus on the 1996 Mw7.9 and 2008 Mw7.4 earthquakes that ruptured the Minahassa subduction interface, this study outlines the triggering of transient deformation and continual interaction between the Minahassa subduction interface and the Palu-Koro strike-slip fault.
How to cite: Nijholt, N., Simons, W., and Riva, R.: Continual interaction between the Minahassa subduction interface and the Palu-Koro strike-slip fault in Sulawesi, Indonesia., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9831, https://doi.org/10.5194/egusphere-egu2020-9831, 2020.
Two major fault systems host Mw>7 earthquakes in Central and Northern Sulawesi, Indonesia: the Minahassa subduction interface and the Palu-Koro strike-slip fault. The Celebes Sea oceanic lithosphere subducts beneath the north arm of Sulawesi at the Minahassa subduction zone. At the western termination of the Minahassa subduction zone, it connects to the left-lateral Palu-Koro strike-slip fault zone. This fault strikes onshore at Palu Bay and then crosses Sulawesi. Interseismic GNSS velocities indicate that the Palu-Koro fault zone accommodates about 4 cm/yr of relative motion in the Palu Bay area, with a ~10 km locking depth. This shallowly locked segment of the Palu-Koro fault around the Palu Bay area ruptured during the devastating, tsunami-generating, 2018 Mw7.5 Palu earthquake. This complex event highlights the high seismic hazard for the island of Sulawesi.
We have a >20-year record of GNSS velocities on Sulawesi, where the densest cluster of monument sites surrounds the Palu-Koro fault, specifically around Palu Bay, whereas the rest of the island is less densely covered. High quality estimates of interseismic velocities reveal second-order complex patterns of transient deformation in the wake of major earthquakes: the velocities in northern Sulawesi and around the Palu-Koro fault do not follow their interseismic trends after a major subduction earthquake has occurred, for several years after the event. This effect of transient deformation reaches more than 400km away from the epicentre of the major earthquakes. Surprisingly, a deviation from the background slip rate on the Palu-Koro fault is not accompanied by a deviation from the background (micro)seismic activity.
We construct a 3D numerical model based on the structural and seismological data in the Sulawesi region. We investigate the post-seismic relaxation pattern from a subduction earthquake and determine whether the slip rate on the Palu-Koro fault changes due to this earthquake through forward model calculations. With a modelling focus on the 1996 Mw7.9 and 2008 Mw7.4 earthquakes that ruptured the Minahassa subduction interface, this study outlines the triggering of transient deformation and continual interaction between the Minahassa subduction interface and the Palu-Koro strike-slip fault.
How to cite: Nijholt, N., Simons, W., and Riva, R.: Continual interaction between the Minahassa subduction interface and the Palu-Koro strike-slip fault in Sulawesi, Indonesia., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9831, https://doi.org/10.5194/egusphere-egu2020-9831, 2020.
EGU2020-11940 | Displays | TS5.2
Using P- to S- wave conversions from controlled sources to determine the shear-wave velocity structure along Hikurangi Margin Forearc, New ZealandPasan Herath, Tim Stern, Martha Savage, Dan Bassett, Stuart Henrys, Dan Barker, Harm Van Avendonk, Nathan Bangs, Adrian Arnulf, Ryuta Arai, Shuichi Kodaira, and Kimihiro Mochizuki
The Hikurangi subduction margin offshore of the east coast of New Zealand displays along-strike variations in subduction-thrust slip behavior. Geodetic observations show that the subduction-thrust of the southern segment of the margin is locked on the 30-100 year scale and the northern segment displays periodic slow-slip on the 1-2 year scale. It is hypothesised that spatial variations in pore-pressure may play a role in this contrasting phenomenon. Higher pore-pressures would result in lower effective stresses, which promote slow-slip of the subduction-thrust. In addition, the presence of a sedimentary wedge with very low shear wave-speeds in the northern Hikurangi margin has been proposed to fit the ultra-long duration of ground motions observed following the 2016 Kaikoura earthquake. Compressional (P-) wave velocities (Vp) of the subsurface provide useful information about the lithological composition. Combined with shear (S-) wave velocities (Vs), the Vp/Vs ratio which is directly related to Poisson’s ratio can be obtained. This is a diagnostic property of a rock’s consolidation and porosity. Typical Vp/Vs ratio of consolidated and crystalline rocks range from 1.6 to 1.9 and that of unconsolidated sediments can range from 2.0 to 4.0.
We use the controlled sources of R/V Marcus G Langseth recorded by a profile of 49 multi-component ocean bottom seismometers (OBS) along the Hikurangi margin forearc for the Seismogenesis at Hikurangi Integrated Research Experiment (SHIRE) to derive the Vs structure and estimate the Vp/Vs ratio. The orientations of the horizontal components of each OBS are found by a hodogram analysis and by an eigenvalue-decomposition of the covariance matrix. Using the orientations, the horizontal components of each OBS are rotated into radial and transverse components. P to S converted phases are identified on the radial and transverse components considering their linear moveout, polarisation angle, and ellipticity. We confirm incoming S-waves to OBSs by comparing them with their hydrophone components. We identify both PPS (up-going P-wave after reflection or refraction converts to an S-wave at an interface) and PSS (down-going P-wave from the controlled source converts to an S-wave at an interface) type conversions. The identified conversion interfaces are the sediment-basement interface and the top of the subducting crust. The travel-time delay of a PPS type conversion relative to its P-wave arrival is indicative of Vs above the converting interface. The linear-moveout of PSS type conversions are indicative of Vs along the raypath after the conversion. Preliminary results from the southern Hikurangi margin suggest Vp/Vs ratios of ~1.70 for the basement rocks above the subducting crust and ~1.90 for the sediments overlying the basement rocks. These values indicate that the basement rocks are consolidated and less porous than the overlying sediments.
We expect to estimate the Vp/Vs ratios in the northern Hikurangi margin to assess the role played by pore-pressure in the along-strike variation in subduction-thrust slip behavior. We also expect to ascertain the presence and estimate the thickness of the low-velocity sediment wedge in the northern Hikurangi margin.
How to cite: Herath, P., Stern, T., Savage, M., Bassett, D., Henrys, S., Barker, D., Van Avendonk, H., Bangs, N., Arnulf, A., Arai, R., Kodaira, S., and Mochizuki, K.: Using P- to S- wave conversions from controlled sources to determine the shear-wave velocity structure along Hikurangi Margin Forearc, New Zealand, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11940, https://doi.org/10.5194/egusphere-egu2020-11940, 2020.
The Hikurangi subduction margin offshore of the east coast of New Zealand displays along-strike variations in subduction-thrust slip behavior. Geodetic observations show that the subduction-thrust of the southern segment of the margin is locked on the 30-100 year scale and the northern segment displays periodic slow-slip on the 1-2 year scale. It is hypothesised that spatial variations in pore-pressure may play a role in this contrasting phenomenon. Higher pore-pressures would result in lower effective stresses, which promote slow-slip of the subduction-thrust. In addition, the presence of a sedimentary wedge with very low shear wave-speeds in the northern Hikurangi margin has been proposed to fit the ultra-long duration of ground motions observed following the 2016 Kaikoura earthquake. Compressional (P-) wave velocities (Vp) of the subsurface provide useful information about the lithological composition. Combined with shear (S-) wave velocities (Vs), the Vp/Vs ratio which is directly related to Poisson’s ratio can be obtained. This is a diagnostic property of a rock’s consolidation and porosity. Typical Vp/Vs ratio of consolidated and crystalline rocks range from 1.6 to 1.9 and that of unconsolidated sediments can range from 2.0 to 4.0.
We use the controlled sources of R/V Marcus G Langseth recorded by a profile of 49 multi-component ocean bottom seismometers (OBS) along the Hikurangi margin forearc for the Seismogenesis at Hikurangi Integrated Research Experiment (SHIRE) to derive the Vs structure and estimate the Vp/Vs ratio. The orientations of the horizontal components of each OBS are found by a hodogram analysis and by an eigenvalue-decomposition of the covariance matrix. Using the orientations, the horizontal components of each OBS are rotated into radial and transverse components. P to S converted phases are identified on the radial and transverse components considering their linear moveout, polarisation angle, and ellipticity. We confirm incoming S-waves to OBSs by comparing them with their hydrophone components. We identify both PPS (up-going P-wave after reflection or refraction converts to an S-wave at an interface) and PSS (down-going P-wave from the controlled source converts to an S-wave at an interface) type conversions. The identified conversion interfaces are the sediment-basement interface and the top of the subducting crust. The travel-time delay of a PPS type conversion relative to its P-wave arrival is indicative of Vs above the converting interface. The linear-moveout of PSS type conversions are indicative of Vs along the raypath after the conversion. Preliminary results from the southern Hikurangi margin suggest Vp/Vs ratios of ~1.70 for the basement rocks above the subducting crust and ~1.90 for the sediments overlying the basement rocks. These values indicate that the basement rocks are consolidated and less porous than the overlying sediments.
We expect to estimate the Vp/Vs ratios in the northern Hikurangi margin to assess the role played by pore-pressure in the along-strike variation in subduction-thrust slip behavior. We also expect to ascertain the presence and estimate the thickness of the low-velocity sediment wedge in the northern Hikurangi margin.
How to cite: Herath, P., Stern, T., Savage, M., Bassett, D., Henrys, S., Barker, D., Van Avendonk, H., Bangs, N., Arnulf, A., Arai, R., Kodaira, S., and Mochizuki, K.: Using P- to S- wave conversions from controlled sources to determine the shear-wave velocity structure along Hikurangi Margin Forearc, New Zealand, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11940, https://doi.org/10.5194/egusphere-egu2020-11940, 2020.
EGU2020-12063 | Displays | TS5.2 | Highlight
Studies of seismic velocities in subduction zones from continuous OBS dataWeiwei Wang, Martha Savage, Alec Yates, Shu-Huei Hung, Yinhe Luo, Tim Stern, Pei-Ying Patty Lin, Hsin-Ying Yang, Ban-Yuan Kuo, Bill Fry, and Spahr Webb
In recent years, Ocean Bottom Seismometers (OBSs) have become widely used to expand the coverage of seismic networks onto the ocean. This study takes advantage of offshore observations at the northern end of the Hikurangi margin and southwestern Okinawa Trough to study the tectonics in both regions.
In the Hikurangi subduction zone, slow slip events (SSEs) have been observed, which are caused by the subduction of the Pacific Plate under New Zealand. The behaviour of SSEs and how they influence the physical properties of Earth materials are open to question. From 2014 to 2015, 15 OBSs were deployed offshore Gisborne, New Zealand on the Hikurangi margin. Ambient noise data from the OBSs are used to study velocity changes related to SSEs. Single station cross-component correlations and auto-correlations are computed, from which coda waves are used to monitor the velocity changes before, during and after the SSEs in 2014 and 2015 to analyse the slow earthquake behaviour and its relation to stress changes. Different rotation on horizontal components is tested by rotating horizontal components to N-E direction and parallel-perpendicular to the coastline. The dv/v computed by different components or rotation show different changes. The averaged dv/v displays a 0.1% velocity decrease during the SSE in October 2014.
The southwestern Okinawa Trough tapers towards Taiwan. How the back-arc crust accommodates the narrowing processing remains to be understood. At various times between 2010 and 2017, 22 OBSs on a small scale (~0.2°×0.3°) were deployed in Southwestern Okinawa Trough offshore northeast Taiwan. Ambient noise recorded on vertical velocity and pressure sensors is used to retrieve Scholte waves for studying shear wave velocity structure. Phase velocities are forward-modeled according to a model proposed by Kuo et al. 2015 and shear strength and density results from ODP1202. Phase velocity dispersion curves are measured from cross-correlations and unwrapped according to the modeled phase velocities. The fundamental mode phase velocities averaged from different station pairs are 0.62 km/s at 3 s period and 1.56 km/s at 6.5 s period. A 3D inversion will be conducted for a shear wave velocity structure from the basin center to the edge.
How to cite: Wang, W., Savage, M., Yates, A., Hung, S.-H., Luo, Y., Stern, T., Lin, P.-Y. P., Yang, H.-Y., Kuo, B.-Y., Fry, B., and Webb, S.: Studies of seismic velocities in subduction zones from continuous OBS data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12063, https://doi.org/10.5194/egusphere-egu2020-12063, 2020.
In recent years, Ocean Bottom Seismometers (OBSs) have become widely used to expand the coverage of seismic networks onto the ocean. This study takes advantage of offshore observations at the northern end of the Hikurangi margin and southwestern Okinawa Trough to study the tectonics in both regions.
In the Hikurangi subduction zone, slow slip events (SSEs) have been observed, which are caused by the subduction of the Pacific Plate under New Zealand. The behaviour of SSEs and how they influence the physical properties of Earth materials are open to question. From 2014 to 2015, 15 OBSs were deployed offshore Gisborne, New Zealand on the Hikurangi margin. Ambient noise data from the OBSs are used to study velocity changes related to SSEs. Single station cross-component correlations and auto-correlations are computed, from which coda waves are used to monitor the velocity changes before, during and after the SSEs in 2014 and 2015 to analyse the slow earthquake behaviour and its relation to stress changes. Different rotation on horizontal components is tested by rotating horizontal components to N-E direction and parallel-perpendicular to the coastline. The dv/v computed by different components or rotation show different changes. The averaged dv/v displays a 0.1% velocity decrease during the SSE in October 2014.
The southwestern Okinawa Trough tapers towards Taiwan. How the back-arc crust accommodates the narrowing processing remains to be understood. At various times between 2010 and 2017, 22 OBSs on a small scale (~0.2°×0.3°) were deployed in Southwestern Okinawa Trough offshore northeast Taiwan. Ambient noise recorded on vertical velocity and pressure sensors is used to retrieve Scholte waves for studying shear wave velocity structure. Phase velocities are forward-modeled according to a model proposed by Kuo et al. 2015 and shear strength and density results from ODP1202. Phase velocity dispersion curves are measured from cross-correlations and unwrapped according to the modeled phase velocities. The fundamental mode phase velocities averaged from different station pairs are 0.62 km/s at 3 s period and 1.56 km/s at 6.5 s period. A 3D inversion will be conducted for a shear wave velocity structure from the basin center to the edge.
How to cite: Wang, W., Savage, M., Yates, A., Hung, S.-H., Luo, Y., Stern, T., Lin, P.-Y. P., Yang, H.-Y., Kuo, B.-Y., Fry, B., and Webb, S.: Studies of seismic velocities in subduction zones from continuous OBS data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12063, https://doi.org/10.5194/egusphere-egu2020-12063, 2020.
EGU2020-20374 | Displays | TS5.2
Bridging Long- and Short-term Behavior Shows Fault Strength as a Strain-averageYlona van Dinther
The strength of faults is subject of an important debate throughout various Earth Scientific disciplines. Different scientific communities have different perspectives with respect to appropriate values for friction coefficients μ. Geodynamicists with a long-term perspective require very low effective strengths (μ<0.05), while at the same time realizing mountains need to be sustained as well. Geologists and seismologists typically start from Byerlee friction coefficients of 0.6<μ<0.85, whereas rock mechanics experiments at high seismic slip rates show short-term low dynamic friction values of 0.03<μ<0.3. Here I show that both long- and short-term approaches can be made more compatible through considering that a regional or global frictional strength should be approached as a strain-averaged quantity. Doing this accounts for large variations of strain in both time and space. What matters for large-scale models is that most deformation occurs over a very small space and time during which friction is exceptionally low, thus making the representative long-term strength low. This is supported by seismo-thermo-mechanical models that self-consistently simulate the dynamics of both long-term subduction and short-term seismogenesis. The latter sustain mountain building, while representative earthquake-like events occur on faults with pore fluid pressure-effective static friction coefficients between 0.125 and 0.005 (or 0.75<Pf/Ps<0.99). These low friction values suggest faults are weak and suggest the dominant role of fluid pressures in weakening faults in subduction zones. This is confirmed in analytical considerations based on mechanical energy dissipation, which provide an equation to calculate the long-term fault strength as a strain-average quantity. Constraining the four parameters in this equation by observations confirms that fluid weakening is more important for long-term weakening than dynamic frictional weakening and low static friction coefficients. From the short-term perspective of modeling earthquake rupture dynamics it is now also becoming evident that fluid overpressured faults are preferable. They namely facilitate the incorporation of laboratory-observed dynamic weakening (70-90%) by limiting the stress drop to reasonable values. In summary, this cross-scale perspective supports long-term effective friction values in the range of about 0.03 to 0.2.
How to cite: van Dinther, Y.: Bridging Long- and Short-term Behavior Shows Fault Strength as a Strain-average, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20374, https://doi.org/10.5194/egusphere-egu2020-20374, 2020.
The strength of faults is subject of an important debate throughout various Earth Scientific disciplines. Different scientific communities have different perspectives with respect to appropriate values for friction coefficients μ. Geodynamicists with a long-term perspective require very low effective strengths (μ<0.05), while at the same time realizing mountains need to be sustained as well. Geologists and seismologists typically start from Byerlee friction coefficients of 0.6<μ<0.85, whereas rock mechanics experiments at high seismic slip rates show short-term low dynamic friction values of 0.03<μ<0.3. Here I show that both long- and short-term approaches can be made more compatible through considering that a regional or global frictional strength should be approached as a strain-averaged quantity. Doing this accounts for large variations of strain in both time and space. What matters for large-scale models is that most deformation occurs over a very small space and time during which friction is exceptionally low, thus making the representative long-term strength low. This is supported by seismo-thermo-mechanical models that self-consistently simulate the dynamics of both long-term subduction and short-term seismogenesis. The latter sustain mountain building, while representative earthquake-like events occur on faults with pore fluid pressure-effective static friction coefficients between 0.125 and 0.005 (or 0.75<Pf/Ps<0.99). These low friction values suggest faults are weak and suggest the dominant role of fluid pressures in weakening faults in subduction zones. This is confirmed in analytical considerations based on mechanical energy dissipation, which provide an equation to calculate the long-term fault strength as a strain-average quantity. Constraining the four parameters in this equation by observations confirms that fluid weakening is more important for long-term weakening than dynamic frictional weakening and low static friction coefficients. From the short-term perspective of modeling earthquake rupture dynamics it is now also becoming evident that fluid overpressured faults are preferable. They namely facilitate the incorporation of laboratory-observed dynamic weakening (70-90%) by limiting the stress drop to reasonable values. In summary, this cross-scale perspective supports long-term effective friction values in the range of about 0.03 to 0.2.
How to cite: van Dinther, Y.: Bridging Long- and Short-term Behavior Shows Fault Strength as a Strain-average, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20374, https://doi.org/10.5194/egusphere-egu2020-20374, 2020.
EGU2020-10210 | Displays | TS5.2
Dynamic and quasi-dynamic modelling of earthquake sequences from zero to three dimensions: choose model complexity as neededMeng Li, Casper Pranger, Luca Dal Zilio, and Ylona van Dinther
Earthquake sequences reflect the repetitive dynamic processes of stress accumulation and release on a fault. Understanding earthquake sequences is fundamental for the research of induced and natural earthquakes and may ultimately help to better assess long-term seismic hazard. Numerical models are well-suited to overcome limited spatiotemporal observations and improve our understanding on this topic. However, large models in 3D are still computational time and memory consuming. Moreover, this may not be optimal if the aspects of lateral or depth variations within the results are not needed to answer a particular objective. This motivated us to investigate the advantages and limitations of various dimensional models by simulating earthquake sequences in 0D, 1D, 2D and ultimately 3D. We applied a C++ numerical library GARNET [1] to deal with the various dimensional models in one simulator. This library uses a fully staggered finite difference scheme with a rectilinear adaptive grid. It also incorporates an automatic discretization algorithm and combines different physical ingredients such as visco-elasto-plastic rheology and quasi- and fully dynamic approaches into one algorithm.
Here we present numerical experiments of a strike-slip fault under rate-and-state friction, surrounded by an elastic medium with constant tectonic loading and, test them under different parameters and initial conditions. By adding one dimension at a time, we simulate a more detailed structure of the seismic cycle. The higher dimensional models present both the validity and the limitations of the lower dimensional ones. For example, inertial waves are not possible to present in 0D while a quasi-dynamic radiation damping term can be added here instead. Another example is that due to lack of grid extension along the fault, both 0D and 1D model fail to reveal an earthquake nucleation phase. However, some important observables, such as the seismic cycle period, maximum/minimum stress and slip rates, are calculated accurately in lower dimensional models, which are much faster than higher dimensional models. We also implemented and compared quasi- and fully dynamic models in the same way. Our results indicate that both the size of simulated seismic events and their interval are reduced in quasi-dynamic models. This could provide us with guidance to identify the appropriate model complexity for various problems. We will also present 3D modeling results, which will be compared to their 2D equivalent. Finally, we present our results for the SCEC SEAS benchmarks [2] and compare them to other participating codes.
[1] Pranger, C. C., L. Le Pourhiet, D. May, Y. van Dinther, and T. Gerya (2016). “Self- consistent seismic cycle simulation in a three-dimensional continuum model: method- ology and examples.” AGU Fall Meeting Abstracts.
[2] Erickson, B. A., et al. (2019). The Community Code Verification Exercise for Simulating Sequences of Earthquakes and Aseismic Slip (SEAS). Poster Presentation at 2019 SCEC Annual Meeting.
How to cite: Li, M., Pranger, C., Dal Zilio, L., and van Dinther, Y.: Dynamic and quasi-dynamic modelling of earthquake sequences from zero to three dimensions: choose model complexity as needed , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10210, https://doi.org/10.5194/egusphere-egu2020-10210, 2020.
Earthquake sequences reflect the repetitive dynamic processes of stress accumulation and release on a fault. Understanding earthquake sequences is fundamental for the research of induced and natural earthquakes and may ultimately help to better assess long-term seismic hazard. Numerical models are well-suited to overcome limited spatiotemporal observations and improve our understanding on this topic. However, large models in 3D are still computational time and memory consuming. Moreover, this may not be optimal if the aspects of lateral or depth variations within the results are not needed to answer a particular objective. This motivated us to investigate the advantages and limitations of various dimensional models by simulating earthquake sequences in 0D, 1D, 2D and ultimately 3D. We applied a C++ numerical library GARNET [1] to deal with the various dimensional models in one simulator. This library uses a fully staggered finite difference scheme with a rectilinear adaptive grid. It also incorporates an automatic discretization algorithm and combines different physical ingredients such as visco-elasto-plastic rheology and quasi- and fully dynamic approaches into one algorithm.
Here we present numerical experiments of a strike-slip fault under rate-and-state friction, surrounded by an elastic medium with constant tectonic loading and, test them under different parameters and initial conditions. By adding one dimension at a time, we simulate a more detailed structure of the seismic cycle. The higher dimensional models present both the validity and the limitations of the lower dimensional ones. For example, inertial waves are not possible to present in 0D while a quasi-dynamic radiation damping term can be added here instead. Another example is that due to lack of grid extension along the fault, both 0D and 1D model fail to reveal an earthquake nucleation phase. However, some important observables, such as the seismic cycle period, maximum/minimum stress and slip rates, are calculated accurately in lower dimensional models, which are much faster than higher dimensional models. We also implemented and compared quasi- and fully dynamic models in the same way. Our results indicate that both the size of simulated seismic events and their interval are reduced in quasi-dynamic models. This could provide us with guidance to identify the appropriate model complexity for various problems. We will also present 3D modeling results, which will be compared to their 2D equivalent. Finally, we present our results for the SCEC SEAS benchmarks [2] and compare them to other participating codes.
[1] Pranger, C. C., L. Le Pourhiet, D. May, Y. van Dinther, and T. Gerya (2016). “Self- consistent seismic cycle simulation in a three-dimensional continuum model: method- ology and examples.” AGU Fall Meeting Abstracts.
[2] Erickson, B. A., et al. (2019). The Community Code Verification Exercise for Simulating Sequences of Earthquakes and Aseismic Slip (SEAS). Poster Presentation at 2019 SCEC Annual Meeting.
How to cite: Li, M., Pranger, C., Dal Zilio, L., and van Dinther, Y.: Dynamic and quasi-dynamic modelling of earthquake sequences from zero to three dimensions: choose model complexity as needed , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10210, https://doi.org/10.5194/egusphere-egu2020-10210, 2020.
EGU2020-8854 | Displays | TS5.2
The role of the fault-block structure of the continental margin in the generation of the strongest subduction earthquakesIrina Vladimirova, Yury Gabsatarov, Dmitry Alekseev, and Leopold Lobkovsky
Modern seismotectonic studies are aimed at obtaining a self-consistent explanation of fault zone heterogeneity, the rupture process, recurrence times and rupture mode of large earthquake sequences. In subduction regions large earthquakes are often characterized by very long source zones and complex long-term postseismic processes following the coseismic release of accumulated elastic stresses. A set of mechanical models was proposed to describe the generation of strongest earthquakes based on the idea of the synchronous failure of several adjacent asperities.
In this study we propose a model which is based on verified numerical schemes, which allows us to quantitatively characterize the process of generation of strong earthquakes. The model takes into account the fault-block structure of the continental margin and combined the ideas of a possible synchronous destruction of several adjacent asperities, mutual sliding along a fault plane with a variable coefficient of friction and subsequent healing of medium defects under high pressure conditions.
The applicability of the proposed model is shown by the example of the recent seismic history of the Kuril subduction zone. Kuril island arc is one of the most tectonically active regions of the world due to very high plate convergence rate. Heterogeneities in the mechanical coupling of the interplate interface in this region lead to the formation of the block structure of the continental margin, which is confirmed by various geological and seismological studies.
GPS observations recorded at different stages of seismic cycle related to the 2006–2007 Simushir earthquakes allow us to model geodynamic processes of slow strain accumulation and its rapid release during the earthquake and the subsequent posteseismic process. We use parameters describing the regional tectonic structure and rheology obtained from the inversion of geodetic data to construct a 2D model of generation of large earthquakes in central Kurils. Analysis of paleoseismic data on dates and rupture characteristics of previous major earthquakes shows a good agreement between the modeled and observed seismic cycle features. The predicted horizontal displacements of the seismogenic block at the coseismic stage are consistent with satellite geodetic data recorded during the 2006 Simushir earthquake.
The proposed model provides new insights into the geodynamic processes controlling the occurrence of strong subduction earthquakes.
How to cite: Vladimirova, I., Gabsatarov, Y., Alekseev, D., and Lobkovsky, L.: The role of the fault-block structure of the continental margin in the generation of the strongest subduction earthquakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8854, https://doi.org/10.5194/egusphere-egu2020-8854, 2020.
Modern seismotectonic studies are aimed at obtaining a self-consistent explanation of fault zone heterogeneity, the rupture process, recurrence times and rupture mode of large earthquake sequences. In subduction regions large earthquakes are often characterized by very long source zones and complex long-term postseismic processes following the coseismic release of accumulated elastic stresses. A set of mechanical models was proposed to describe the generation of strongest earthquakes based on the idea of the synchronous failure of several adjacent asperities.
In this study we propose a model which is based on verified numerical schemes, which allows us to quantitatively characterize the process of generation of strong earthquakes. The model takes into account the fault-block structure of the continental margin and combined the ideas of a possible synchronous destruction of several adjacent asperities, mutual sliding along a fault plane with a variable coefficient of friction and subsequent healing of medium defects under high pressure conditions.
The applicability of the proposed model is shown by the example of the recent seismic history of the Kuril subduction zone. Kuril island arc is one of the most tectonically active regions of the world due to very high plate convergence rate. Heterogeneities in the mechanical coupling of the interplate interface in this region lead to the formation of the block structure of the continental margin, which is confirmed by various geological and seismological studies.
GPS observations recorded at different stages of seismic cycle related to the 2006–2007 Simushir earthquakes allow us to model geodynamic processes of slow strain accumulation and its rapid release during the earthquake and the subsequent posteseismic process. We use parameters describing the regional tectonic structure and rheology obtained from the inversion of geodetic data to construct a 2D model of generation of large earthquakes in central Kurils. Analysis of paleoseismic data on dates and rupture characteristics of previous major earthquakes shows a good agreement between the modeled and observed seismic cycle features. The predicted horizontal displacements of the seismogenic block at the coseismic stage are consistent with satellite geodetic data recorded during the 2006 Simushir earthquake.
The proposed model provides new insights into the geodynamic processes controlling the occurrence of strong subduction earthquakes.
How to cite: Vladimirova, I., Gabsatarov, Y., Alekseev, D., and Lobkovsky, L.: The role of the fault-block structure of the continental margin in the generation of the strongest subduction earthquakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8854, https://doi.org/10.5194/egusphere-egu2020-8854, 2020.
TS5.3 – The Mechanics of Earthquake Faulting: a multiscale approach
EGU2020-2890 | Displays | TS5.3
Highly stressed lower crust: Evidence from dry pseudotachylytes in granulites, Lofoten, NorwayKristina G. Dunkel, Xin Zhong, Luiz F. G. Morales, and Bjørn Jamtveit
Due to the high confining pressures in the lower crust, the generating mechanisms of lower crustal earthquakes, occurring below the standard seismogenic zone, are puzzling. Their investigation is difficult because the records of such earthquakes, pseudotachylytes, are typically reacted and/or deformed. Here we describe exceptionally pristine pseudotachylytes in lower crustal granulites from the Lofoten Vesterålen Archipelago, Norway. The pseudotachylytes have essentially the same mineralogical composition as their host (plagioclase, alkali feldspar, orthopyroxene) and contain microstructures indicative of rapid cooling (microlites, spherulites, ‘cauliflower’ garnet). Neither the wall rock nor the pseudotachylytes themselves contain hydrous minerals, and no mylonites are associated with the pseudotachylytes. This excludes the most commonly suggested weakening mechanisms that may cause earthquakes below the brittle-ductile transition: dehydration- or reaction-induced embrittlement, plastic instability, thermal runaway, and downward propagation of seismic rupture from shallow faults into their deeper ductile extensions. Hence, we suggest that transient stress pulses caused by shallower earthquakes are the most likely explanation for the occurrence of fossil earthquakes in the analysed rocks from Lofoten.
Earthquakes are short events, but their effects on the tectonic and metamorphic development of their host can be long-lasting. The initial deformation features related to seismic events, which potentially determine these effects, are often overprinted by metamorphism driven by fluids infiltrating the rock along the seismic fault. Because of the anhydrous conditions in the present case, those structures are preserved. The wall rocks to the investigated pseudotachylytes appear undamaged in optical and backscatter electron observation; however, cathodoluminescence imaging of feldspar and quartz reveals healed fractures and alteration zones. Those areas are further investigated with electron backscatter diffraction and transmission electron microscopy to better understand the microstructural and chemical changes during and after the seismic event.
How to cite: Dunkel, K. G., Zhong, X., Morales, L. F. G., and Jamtveit, B.: Highly stressed lower crust: Evidence from dry pseudotachylytes in granulites, Lofoten, Norway, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2890, https://doi.org/10.5194/egusphere-egu2020-2890, 2020.
Due to the high confining pressures in the lower crust, the generating mechanisms of lower crustal earthquakes, occurring below the standard seismogenic zone, are puzzling. Their investigation is difficult because the records of such earthquakes, pseudotachylytes, are typically reacted and/or deformed. Here we describe exceptionally pristine pseudotachylytes in lower crustal granulites from the Lofoten Vesterålen Archipelago, Norway. The pseudotachylytes have essentially the same mineralogical composition as their host (plagioclase, alkali feldspar, orthopyroxene) and contain microstructures indicative of rapid cooling (microlites, spherulites, ‘cauliflower’ garnet). Neither the wall rock nor the pseudotachylytes themselves contain hydrous minerals, and no mylonites are associated with the pseudotachylytes. This excludes the most commonly suggested weakening mechanisms that may cause earthquakes below the brittle-ductile transition: dehydration- or reaction-induced embrittlement, plastic instability, thermal runaway, and downward propagation of seismic rupture from shallow faults into their deeper ductile extensions. Hence, we suggest that transient stress pulses caused by shallower earthquakes are the most likely explanation for the occurrence of fossil earthquakes in the analysed rocks from Lofoten.
Earthquakes are short events, but their effects on the tectonic and metamorphic development of their host can be long-lasting. The initial deformation features related to seismic events, which potentially determine these effects, are often overprinted by metamorphism driven by fluids infiltrating the rock along the seismic fault. Because of the anhydrous conditions in the present case, those structures are preserved. The wall rocks to the investigated pseudotachylytes appear undamaged in optical and backscatter electron observation; however, cathodoluminescence imaging of feldspar and quartz reveals healed fractures and alteration zones. Those areas are further investigated with electron backscatter diffraction and transmission electron microscopy to better understand the microstructural and chemical changes during and after the seismic event.
How to cite: Dunkel, K. G., Zhong, X., Morales, L. F. G., and Jamtveit, B.: Highly stressed lower crust: Evidence from dry pseudotachylytes in granulites, Lofoten, Norway, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2890, https://doi.org/10.5194/egusphere-egu2020-2890, 2020.
EGU2020-7295 | Displays | TS5.3
Deciphering deformation mechanisms during seismic slip along wet carbonate faultsMarkus Ohl, Helen E. King, Andre Niemeijer, Jianye Chen, Martyn Drury, and Oliver Plümper
Strong dynamic weakening at seismic slip velocities in experiments on calcite has been attributed to a combination of grain-size reduction and nanoscale diffusion. However, these experiments were performed mostly dry and it is unknown how fluid-rock interactions affect the deformation mechanisms. The resulting physico-chemical interactions are key in deciphering deformation mechanisms and rheological changes during and after (seismic) faulting in the presence of a fluid phase. It is the interaction of the nanoscale of granular fault materials with fluids that may drive changes in rheological behaviour and fault stability. Considering that faults in the upper crust are major fluid pathways, there is a particular need for deformation experiments under wet conditions that focus on the nanoscale interaction between gouge material and pore fluid.
In order to track and quantify potential fluid – mineral interaction processes in carbonate faults, we have conducted deformation experiments on calcite gouge with water enriched in 18O (97 at%) as pore fluid. The fault gouge was deformed in a rotary shear apparatus at v = 1 m/s and a normal load of σn = 2 and 4 MPa. Raman spectroscopy and nanoscale secondary ion mass spectrometry (nanoSIMS) were used to analyse isotope distribution in the post-experiment samples. The nanostructure was characterised in electron transparent thin foils, prepared in a focused ion beam – scanning electron microscope (FIB-SEM), using transmission electron microscopy (TEM).
Raman analyses confirm the incorporation of 18O into the calcite crystal structure, as well as the presence of amorphous carbon. We identify three new band positions relating to the possible isotopologues of CO32- (reflecting 16O substitution by 18O). In addition, we detected portlandite (Ca(OH)2), pointing to the hydration reaction of lime (CaO) with water. Raman and NanoSIMS maps reveal that 18O is incorporated throughout the deformed volume, implying that calcite breakdown and isotope exchange affected the entire fault gouge.
Considering the oxygen self-diffusion rates in calcite (Farver, 1994) we conclude that solid-state 18O – isotope exchange cannot explain the observed incorporation of 18O into the calcite crystals during wet, seismic deformation. The hydration of portlandite and, calcite containing 18O implies the breakdown and decarbonation of the starting calcite and the nucleation of new calcite grains. Our results question the state and nature of calcite gouges during seismic deformation and challenge our knowledge of the rheological properties of wet calcite fault gouges at high strain rates. The observations suggest that the physico-chemical changes are a crucial part of the deformation mechanism and have implications for the development of microphysical models that allow us to quantitatively predict fault rheology.
References
John R. Farver, Oxygen self-diffusion in calcite: Dependence on temperature and water fugacity, Earth and Planetary Science Letters, Volume 121, Issues 3–4, 1994, Pages 575-587, doi:10.1016/0012-821X(94)90092-2.
How to cite: Ohl, M., King, H. E., Niemeijer, A., Chen, J., Drury, M., and Plümper, O.: Deciphering deformation mechanisms during seismic slip along wet carbonate faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7295, https://doi.org/10.5194/egusphere-egu2020-7295, 2020.
Strong dynamic weakening at seismic slip velocities in experiments on calcite has been attributed to a combination of grain-size reduction and nanoscale diffusion. However, these experiments were performed mostly dry and it is unknown how fluid-rock interactions affect the deformation mechanisms. The resulting physico-chemical interactions are key in deciphering deformation mechanisms and rheological changes during and after (seismic) faulting in the presence of a fluid phase. It is the interaction of the nanoscale of granular fault materials with fluids that may drive changes in rheological behaviour and fault stability. Considering that faults in the upper crust are major fluid pathways, there is a particular need for deformation experiments under wet conditions that focus on the nanoscale interaction between gouge material and pore fluid.
In order to track and quantify potential fluid – mineral interaction processes in carbonate faults, we have conducted deformation experiments on calcite gouge with water enriched in 18O (97 at%) as pore fluid. The fault gouge was deformed in a rotary shear apparatus at v = 1 m/s and a normal load of σn = 2 and 4 MPa. Raman spectroscopy and nanoscale secondary ion mass spectrometry (nanoSIMS) were used to analyse isotope distribution in the post-experiment samples. The nanostructure was characterised in electron transparent thin foils, prepared in a focused ion beam – scanning electron microscope (FIB-SEM), using transmission electron microscopy (TEM).
Raman analyses confirm the incorporation of 18O into the calcite crystal structure, as well as the presence of amorphous carbon. We identify three new band positions relating to the possible isotopologues of CO32- (reflecting 16O substitution by 18O). In addition, we detected portlandite (Ca(OH)2), pointing to the hydration reaction of lime (CaO) with water. Raman and NanoSIMS maps reveal that 18O is incorporated throughout the deformed volume, implying that calcite breakdown and isotope exchange affected the entire fault gouge.
Considering the oxygen self-diffusion rates in calcite (Farver, 1994) we conclude that solid-state 18O – isotope exchange cannot explain the observed incorporation of 18O into the calcite crystals during wet, seismic deformation. The hydration of portlandite and, calcite containing 18O implies the breakdown and decarbonation of the starting calcite and the nucleation of new calcite grains. Our results question the state and nature of calcite gouges during seismic deformation and challenge our knowledge of the rheological properties of wet calcite fault gouges at high strain rates. The observations suggest that the physico-chemical changes are a crucial part of the deformation mechanism and have implications for the development of microphysical models that allow us to quantitatively predict fault rheology.
References
John R. Farver, Oxygen self-diffusion in calcite: Dependence on temperature and water fugacity, Earth and Planetary Science Letters, Volume 121, Issues 3–4, 1994, Pages 575-587, doi:10.1016/0012-821X(94)90092-2.
How to cite: Ohl, M., King, H. E., Niemeijer, A., Chen, J., Drury, M., and Plümper, O.: Deciphering deformation mechanisms during seismic slip along wet carbonate faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7295, https://doi.org/10.5194/egusphere-egu2020-7295, 2020.
EGU2020-7926 | Displays | TS5.3
Bridging the Gap Between Seismic and Sub-seismic Mirror-Slip Surfaces in Carbonate Fault GougeMilo Trainor Moss, Berend A. Verberne, Miki Takahashi, and Andre R. Niemeijer
Specularly light reflective fault plane interfaces known as Mirror-Slip Surfaces (MSS’s) are common in seismically active fault zones around the world and thus their role in controlling fault strength and stability is of great interest. MSS’s have been experimentally produced in simulated carbonate faults at relatively high (10-1-100 m/s) and low (10-7-10-5 m/s) sliding velocities (resp. HV and LV). However, their role in controlling fault mechanical properties at sub-seismic vs seismic fault-slip velocities remains enigmatic. With the aim to unravel the structural development of MSS’s with increasing shear displacement (rate) and effective normal stress, we conducted HV and LV shear deformation experiments on simulated faults composed of granular calcite. We employed a ring shear set-up in a HV rotary shear apparatus as well as a saw-cut assembly mounted in a triaxial cell, which enabled fault-slip tests under a wide range of slip velocities (v = 10-7 - 10-1 m/s) and effective normal stresses (σn ≈ 10 – 170 MPa). All experiments were carried out under room-dry conditions, at room temperature. Post-mortem microstructure analysis of recovered fragments was carried out through visual inspection, incident light and scanning electron microscopy, as well as using Raman spectroscopy.
MSSs develop at sub-seismic slip velocities (v = 10-7 m/s) initially as visibly striated patches after 0.0062 m (σn ≈ 10 MPa), 0.004 m (σn ≈ 50 MPa) and 0.0026 m (σn ≈ 170 MPa) of shear displacement. The area covered by MSSs systematically increases with displacement to form continuous coatings after 0.042 (σn ≈ 10 MPa), 0.0062 m (σn ≈ 50 MPa) and 0.0036 m (σn ≈ 10 MPa). As displacement rate is increased (10-5 – 10-4 m/s) MSSs are no longer observed however continuous MSSs are visible again at seismic slip velocities (>10-1 m/s). Our microstructural analysis revealed that MSSs are layers of (nano)crystalline calcite some of which contain elongated nanofibrous structures. In addition, discrete, 3 - 20 micron-sized patches of amorphous carbon are produced at seismic slip velocities, and at sub-seismic velocities under high normal stresses (σn > 160 MPa). We could not however identify any microstructural characteristics that are diagnostics of MSSs produced at certain slip rates or normal stress.
Our interpretation is that MSSs form by sintering of nm-sized particles within ultrafine-grained shear bands. With increasing shear displacement, MSS patches connect into continuous veneers. The formation of (continuous) MSSs at low as well as high sliding velocities in our experiments implies that natural MSSs are unreliable indicators for palaeoseismicity.
How to cite: Trainor Moss, M., Verberne, B. A., Takahashi, M., and Niemeijer, A. R.: Bridging the Gap Between Seismic and Sub-seismic Mirror-Slip Surfaces in Carbonate Fault Gouge, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7926, https://doi.org/10.5194/egusphere-egu2020-7926, 2020.
Specularly light reflective fault plane interfaces known as Mirror-Slip Surfaces (MSS’s) are common in seismically active fault zones around the world and thus their role in controlling fault strength and stability is of great interest. MSS’s have been experimentally produced in simulated carbonate faults at relatively high (10-1-100 m/s) and low (10-7-10-5 m/s) sliding velocities (resp. HV and LV). However, their role in controlling fault mechanical properties at sub-seismic vs seismic fault-slip velocities remains enigmatic. With the aim to unravel the structural development of MSS’s with increasing shear displacement (rate) and effective normal stress, we conducted HV and LV shear deformation experiments on simulated faults composed of granular calcite. We employed a ring shear set-up in a HV rotary shear apparatus as well as a saw-cut assembly mounted in a triaxial cell, which enabled fault-slip tests under a wide range of slip velocities (v = 10-7 - 10-1 m/s) and effective normal stresses (σn ≈ 10 – 170 MPa). All experiments were carried out under room-dry conditions, at room temperature. Post-mortem microstructure analysis of recovered fragments was carried out through visual inspection, incident light and scanning electron microscopy, as well as using Raman spectroscopy.
MSSs develop at sub-seismic slip velocities (v = 10-7 m/s) initially as visibly striated patches after 0.0062 m (σn ≈ 10 MPa), 0.004 m (σn ≈ 50 MPa) and 0.0026 m (σn ≈ 170 MPa) of shear displacement. The area covered by MSSs systematically increases with displacement to form continuous coatings after 0.042 (σn ≈ 10 MPa), 0.0062 m (σn ≈ 50 MPa) and 0.0036 m (σn ≈ 10 MPa). As displacement rate is increased (10-5 – 10-4 m/s) MSSs are no longer observed however continuous MSSs are visible again at seismic slip velocities (>10-1 m/s). Our microstructural analysis revealed that MSSs are layers of (nano)crystalline calcite some of which contain elongated nanofibrous structures. In addition, discrete, 3 - 20 micron-sized patches of amorphous carbon are produced at seismic slip velocities, and at sub-seismic velocities under high normal stresses (σn > 160 MPa). We could not however identify any microstructural characteristics that are diagnostics of MSSs produced at certain slip rates or normal stress.
Our interpretation is that MSSs form by sintering of nm-sized particles within ultrafine-grained shear bands. With increasing shear displacement, MSS patches connect into continuous veneers. The formation of (continuous) MSSs at low as well as high sliding velocities in our experiments implies that natural MSSs are unreliable indicators for palaeoseismicity.
How to cite: Trainor Moss, M., Verberne, B. A., Takahashi, M., and Niemeijer, A. R.: Bridging the Gap Between Seismic and Sub-seismic Mirror-Slip Surfaces in Carbonate Fault Gouge, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7926, https://doi.org/10.5194/egusphere-egu2020-7926, 2020.
EGU2020-18129 | Displays | TS5.3
On the loading conditions for pore fluid stabilization of failure in crustal rockFranciscus Aben and Nicolas Brantut
During shear failure in rock, fracture damage created within the failure zone causes localized dilation, which, under partially drained conditions, results in a localized pore fluid pressure drop. The effective normal stress within the failure zone therefore increases, and with it the fracture and frictional strengths. This effect is known as dilatancy hardening. Dilatancy hardening may suppress rupture propagation and slip rates sufficiently to stabilize the rupture and postpone or prevent dynamic failure. Here, we study the loading conditions at which the rate of dilatancy hardening is sufficiently high to stabilize failure. We do so by measuring the local pore fluid pressure during failure and the rate of dilatancy with slip at a range of confining and pore fluid pressures.
We performed shear failure experiments on thermally treated intact Westerly granite under triaxial loading conditions. The samples were saturated with water and contained notches to force the location of the shear failure zone. For each experiment, we imposed a different combination of confining pressure and pore fluid pressure, so that the overall effective pressure was either 40 MPa or 80 MPa prior to axial deformation at 10-6 s-1 strain rate. Dynamic shear failure was recognized by a sudden audible stress drop, whereas the stress drop during stabilized shear failure took longer and was inaudible. Local pore fluid pressure was measured with in-house developed pressure transducers placed on the trajectory of the prospective failure.
At effective pressures of 40 MPa and 80 MPa, we observe stabilized failure for a ratio λ (imposed pore fluid pressure over confining pressure) > 0.5. For λ < 0.5, we observe dynamic failure. Of two experiments performed at λ = 0.5 and 80 MPa effective pressure, one showed stabilized failure and one failed dynamically. For λ > 0.5, we observe pore fluid pressure drops in the failure zone of 30-45 MPa for 40 MPa effective pressure, and 60 MPa for 80 MPa confining pressure. The local pore fluid pressure during dynamic failure (λ < 0.5) is 0 MPa, strongly suggesting local fluid vaporization. Of the two experiments at λ = 0.5, the dilation rate with slip is higher for the dynamic failure relative to the stabilized failure.
We show that with increasing effective pressure, dilatancy hardening increases as the local pore fluid pressure drop during failure becomes larger. For λ < 0.5, dilatancy hardening is insufficient to stabilize failure because the local pore fluid pressure drop is larger than the absolute imposed pore fluid pressure. Near λ = 0.5, small variations in dilatancy control rupture stability. For λ > 0.5, dilatancy hardening is sufficient to suppress dynamic failure.
How to cite: Aben, F. and Brantut, N.: On the loading conditions for pore fluid stabilization of failure in crustal rock, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18129, https://doi.org/10.5194/egusphere-egu2020-18129, 2020.
During shear failure in rock, fracture damage created within the failure zone causes localized dilation, which, under partially drained conditions, results in a localized pore fluid pressure drop. The effective normal stress within the failure zone therefore increases, and with it the fracture and frictional strengths. This effect is known as dilatancy hardening. Dilatancy hardening may suppress rupture propagation and slip rates sufficiently to stabilize the rupture and postpone or prevent dynamic failure. Here, we study the loading conditions at which the rate of dilatancy hardening is sufficiently high to stabilize failure. We do so by measuring the local pore fluid pressure during failure and the rate of dilatancy with slip at a range of confining and pore fluid pressures.
We performed shear failure experiments on thermally treated intact Westerly granite under triaxial loading conditions. The samples were saturated with water and contained notches to force the location of the shear failure zone. For each experiment, we imposed a different combination of confining pressure and pore fluid pressure, so that the overall effective pressure was either 40 MPa or 80 MPa prior to axial deformation at 10-6 s-1 strain rate. Dynamic shear failure was recognized by a sudden audible stress drop, whereas the stress drop during stabilized shear failure took longer and was inaudible. Local pore fluid pressure was measured with in-house developed pressure transducers placed on the trajectory of the prospective failure.
At effective pressures of 40 MPa and 80 MPa, we observe stabilized failure for a ratio λ (imposed pore fluid pressure over confining pressure) > 0.5. For λ < 0.5, we observe dynamic failure. Of two experiments performed at λ = 0.5 and 80 MPa effective pressure, one showed stabilized failure and one failed dynamically. For λ > 0.5, we observe pore fluid pressure drops in the failure zone of 30-45 MPa for 40 MPa effective pressure, and 60 MPa for 80 MPa confining pressure. The local pore fluid pressure during dynamic failure (λ < 0.5) is 0 MPa, strongly suggesting local fluid vaporization. Of the two experiments at λ = 0.5, the dilation rate with slip is higher for the dynamic failure relative to the stabilized failure.
We show that with increasing effective pressure, dilatancy hardening increases as the local pore fluid pressure drop during failure becomes larger. For λ < 0.5, dilatancy hardening is insufficient to stabilize failure because the local pore fluid pressure drop is larger than the absolute imposed pore fluid pressure. Near λ = 0.5, small variations in dilatancy control rupture stability. For λ > 0.5, dilatancy hardening is sufficient to suppress dynamic failure.
How to cite: Aben, F. and Brantut, N.: On the loading conditions for pore fluid stabilization of failure in crustal rock, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18129, https://doi.org/10.5194/egusphere-egu2020-18129, 2020.
EGU2020-6217 | Displays | TS5.3
Dilatancy hardening, rupture stabilization and instability in hydraulically isolated faultsDavid Lockner, Brooks Proctor, Brian Kilgore, Tom Mitchell, and Nick Beeler
Delayed failure or slip stabilization are expected outcomes of transient dilatancy and associated loss of pore pressure in isolated faults during rupture nucleation. Segall and Rice (1995), for example, developed relationships for pore pressure transients in the rate and state (r-s) friction formalism. They considered pore volume changes that were log(velocity) dependent and, depending on the hydraulic diffusivity and fault/fluid compressibility, could significantly change fault stability and rupture nucleation properties. Despite the theoretical importance of transient pore pressure effects, few laboratory experiments exist that show the effect of variable pore pressure in hydraulically isolated faults. This is due in large part to the difficulties involved in measuring pore pressure directly in isolated faults. We report on triaxial deformation of model sawcut faults in Westerly granite at normal stresses to 197 MPa. Samples were 76.2 mm-diameter cylinders with a fault inclined 30° to the sample axis. Tests were performed on bare surface granite and on faults containing 1 mm quartz gouge. Fault pore pressure was measured directly with a miniature pressure transducer with fast frequency response. Velocity-stepping experiments showed log(velocity) pressure drops as large as 4 MPa that are consistent with Segall and Rice (1995) and often larger than intrinsic r-s dependent strength changes. However, for large velocity steps the initial pressure response was a rapid increase that led to either slow slip or dynamic failure. We attribute this sudden pore pressure increase to rapid compaction as the open pore structure in the gouge became unstable and collapsed. Since this effect is only observed during rapid velocity increase, it is most likely to occur as a rupture front propagates along the fault. In this case, the pore collapse and associated weakening could contribute to an overall stress drop and is likely to slow rupture propagation. For example, a 4 MPa pore pressure rise on a fault with 40 MPa effective normal stress could result in a 2 to 3 MPa loss of shear strength, a strength loss much larger than would be predicted from typical r-s parameters.
How to cite: Lockner, D., Proctor, B., Kilgore, B., Mitchell, T., and Beeler, N.: Dilatancy hardening, rupture stabilization and instability in hydraulically isolated faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6217, https://doi.org/10.5194/egusphere-egu2020-6217, 2020.
Delayed failure or slip stabilization are expected outcomes of transient dilatancy and associated loss of pore pressure in isolated faults during rupture nucleation. Segall and Rice (1995), for example, developed relationships for pore pressure transients in the rate and state (r-s) friction formalism. They considered pore volume changes that were log(velocity) dependent and, depending on the hydraulic diffusivity and fault/fluid compressibility, could significantly change fault stability and rupture nucleation properties. Despite the theoretical importance of transient pore pressure effects, few laboratory experiments exist that show the effect of variable pore pressure in hydraulically isolated faults. This is due in large part to the difficulties involved in measuring pore pressure directly in isolated faults. We report on triaxial deformation of model sawcut faults in Westerly granite at normal stresses to 197 MPa. Samples were 76.2 mm-diameter cylinders with a fault inclined 30° to the sample axis. Tests were performed on bare surface granite and on faults containing 1 mm quartz gouge. Fault pore pressure was measured directly with a miniature pressure transducer with fast frequency response. Velocity-stepping experiments showed log(velocity) pressure drops as large as 4 MPa that are consistent with Segall and Rice (1995) and often larger than intrinsic r-s dependent strength changes. However, for large velocity steps the initial pressure response was a rapid increase that led to either slow slip or dynamic failure. We attribute this sudden pore pressure increase to rapid compaction as the open pore structure in the gouge became unstable and collapsed. Since this effect is only observed during rapid velocity increase, it is most likely to occur as a rupture front propagates along the fault. In this case, the pore collapse and associated weakening could contribute to an overall stress drop and is likely to slow rupture propagation. For example, a 4 MPa pore pressure rise on a fault with 40 MPa effective normal stress could result in a 2 to 3 MPa loss of shear strength, a strength loss much larger than would be predicted from typical r-s parameters.
How to cite: Lockner, D., Proctor, B., Kilgore, B., Mitchell, T., and Beeler, N.: Dilatancy hardening, rupture stabilization and instability in hydraulically isolated faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6217, https://doi.org/10.5194/egusphere-egu2020-6217, 2020.
EGU2020-22160 | Displays | TS5.3
Imaging laboratory rupture nucleation at the source: A friction experiment using ultrafast ultrasoundJohannes Aichele, Soumaya Latour, Stefan Catheline, and Philippe Roux
At the field scale and in most laboratory studies the rupture nucleation mechanism of an earthquake, landslide or glacier stick-slip cannot be directly imaged. Near-field and source effects are thus difficult to observe. We use correlation of highspeed ultrasound images to track shear wave propagation at the rupture nucleation source and in its near-field. The particle velocity and accumulated displacement of the shear wave field emitted by the rupture are observed in-situ on a very dense grid. The grid consists of the ultrasonic imaging plane inside the frictional body and resolution is defined by the ultrasonic wavelenth (0.3 mm). The rupture process is generated by controlling a driving slab through a motor and a granular layer of sand or gravel constitutes the stick-slip behavior. The frictional body is a homemade Poly-Vinyl-Alcohol hydrogel. Although its properties are differing from those of classically investigated rocks, it constitutes a linear elastic material and reproduces rupture processes that are known from the field and rock physics. Through the elastic wave field we observe microslips which precede supershear rupture propagation along the frictional interface. We experimentally show that the source mechanism of a breaking asperity depends on the material contrast of the adjacent halfspaces. Neither a double-couple nor a single-force mechanism perfectly reproduce the experimental data of a rupturing asperity, while micro-slips are well reproduced by a singular shear point force.
How to cite: Aichele, J., Latour, S., Catheline, S., and Roux, P.: Imaging laboratory rupture nucleation at the source: A friction experiment using ultrafast ultrasound , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22160, https://doi.org/10.5194/egusphere-egu2020-22160, 2020.
At the field scale and in most laboratory studies the rupture nucleation mechanism of an earthquake, landslide or glacier stick-slip cannot be directly imaged. Near-field and source effects are thus difficult to observe. We use correlation of highspeed ultrasound images to track shear wave propagation at the rupture nucleation source and in its near-field. The particle velocity and accumulated displacement of the shear wave field emitted by the rupture are observed in-situ on a very dense grid. The grid consists of the ultrasonic imaging plane inside the frictional body and resolution is defined by the ultrasonic wavelenth (0.3 mm). The rupture process is generated by controlling a driving slab through a motor and a granular layer of sand or gravel constitutes the stick-slip behavior. The frictional body is a homemade Poly-Vinyl-Alcohol hydrogel. Although its properties are differing from those of classically investigated rocks, it constitutes a linear elastic material and reproduces rupture processes that are known from the field and rock physics. Through the elastic wave field we observe microslips which precede supershear rupture propagation along the frictional interface. We experimentally show that the source mechanism of a breaking asperity depends on the material contrast of the adjacent halfspaces. Neither a double-couple nor a single-force mechanism perfectly reproduce the experimental data of a rupturing asperity, while micro-slips are well reproduced by a singular shear point force.
How to cite: Aichele, J., Latour, S., Catheline, S., and Roux, P.: Imaging laboratory rupture nucleation at the source: A friction experiment using ultrafast ultrasound , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22160, https://doi.org/10.5194/egusphere-egu2020-22160, 2020.
EGU2020-7109 | Displays | TS5.3
Signature of supershear transition seen in damage and aftershock patternHarsha Bhat, Jorge Jara, Lucile Bruhat, Solene Antoine, Kurama Okubo, Marion Thomas, Esteban Rougier, Ares Rosakis, Charles Sammis, Yann Klinger, and Romain Jolivet
Supershear earthquakes are rare but powerful ruptures with devastating consequences. How quickly an earthquake rupture attains this speed, or for that matter decelerates from it, strongly affects high-frequency ground motion and the spatial extent of coseismic off-fault damage. Traditionally, studies of supershear earthquakes have focused on determining which fault segments sustained fully-grown supershear ruptures. Knowing that the rupture first propagated at subshear rupture speeds, these studies usually guessed an approximate location for the transition from subshear to supershear regimes. The rarity of confirmed supershear ruptures, combined with the fact that conditions for supershear transition are still debated, complicates the investigation of supershear transition in real earthquakes. Here, we find a unique signature of the location of a supershear transition: we show that, when a rupture accelerates towards supershear speed, the stress concentration abruptly shrinks, limiting the off-fault damage and aftershock productivity. First, we use theoretical fracture mechanics to demonstrate that, before transitioning to supershear, the stress concentration around the rupture tip shrinks, confining the region where damage & aftershocks are expected. Then, employing two different dynamic rupture modeling approaches, we confirm such reduction in stress concentration, further validating the expected signature in the transition region. We contrast these numerical and theoretical results with high-resolution aftershock catalogs for three natural supershear earthquakes, where we identify a small region with lower aftershock density near the supershear transition. Finally, using satellite optical image correlation techniques, we show that, for a fourth event, the transition zone is characterized by a diminution in the width of the damage zone. Our results demonstrate that the transition from subshear to supershear rupture can be clearly identified by a localized absence of aftershocks, and a decrease in off-fault damage, due to a transient reduction of the stress intensity at the rupture tip.
How to cite: Bhat, H., Jara, J., Bruhat, L., Antoine, S., Okubo, K., Thomas, M., Rougier, E., Rosakis, A., Sammis, C., Klinger, Y., and Jolivet, R.: Signature of supershear transition seen in damage and aftershock pattern, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7109, https://doi.org/10.5194/egusphere-egu2020-7109, 2020.
Supershear earthquakes are rare but powerful ruptures with devastating consequences. How quickly an earthquake rupture attains this speed, or for that matter decelerates from it, strongly affects high-frequency ground motion and the spatial extent of coseismic off-fault damage. Traditionally, studies of supershear earthquakes have focused on determining which fault segments sustained fully-grown supershear ruptures. Knowing that the rupture first propagated at subshear rupture speeds, these studies usually guessed an approximate location for the transition from subshear to supershear regimes. The rarity of confirmed supershear ruptures, combined with the fact that conditions for supershear transition are still debated, complicates the investigation of supershear transition in real earthquakes. Here, we find a unique signature of the location of a supershear transition: we show that, when a rupture accelerates towards supershear speed, the stress concentration abruptly shrinks, limiting the off-fault damage and aftershock productivity. First, we use theoretical fracture mechanics to demonstrate that, before transitioning to supershear, the stress concentration around the rupture tip shrinks, confining the region where damage & aftershocks are expected. Then, employing two different dynamic rupture modeling approaches, we confirm such reduction in stress concentration, further validating the expected signature in the transition region. We contrast these numerical and theoretical results with high-resolution aftershock catalogs for three natural supershear earthquakes, where we identify a small region with lower aftershock density near the supershear transition. Finally, using satellite optical image correlation techniques, we show that, for a fourth event, the transition zone is characterized by a diminution in the width of the damage zone. Our results demonstrate that the transition from subshear to supershear rupture can be clearly identified by a localized absence of aftershocks, and a decrease in off-fault damage, due to a transient reduction of the stress intensity at the rupture tip.
How to cite: Bhat, H., Jara, J., Bruhat, L., Antoine, S., Okubo, K., Thomas, M., Rougier, E., Rosakis, A., Sammis, C., Klinger, Y., and Jolivet, R.: Signature of supershear transition seen in damage and aftershock pattern, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7109, https://doi.org/10.5194/egusphere-egu2020-7109, 2020.
EGU2020-2213 | Displays | TS5.3
Rupture speed of supershear slip instabilitiesDavid Kammer, Ilya Svetlizky, and Jay Fineberg
Shear ruptures propagating along natural faults or simulated faults in analog laboratory experiments present a wide range of rupture velocities. Most ruptures propagate at velocities below the Rayleigh wave speed and Linear Elastic Fracture Mechanics (LEFM) theory has been shown to predict quantitatively well the observed propagation speed. However, early theoretical and numerical work suggested that ruptures may surpass the shear wave speed and propagate at velocities that can reach the longitudinal wave speed. This was later confirmed in laboratory experiments and observed as supershear earthquakes in nature. While the transition from sub-Rayleigh to supershear propagation has been studied extensively, current knowledge of propagation speed in the supershear regime is limited to a couple of idealistic set-ups. Here, we analyse the propagation speed of supershear ruptures along various nonuniform interfaces using simulations and experiments. We show that an approximate fracture mechanics theory describes well supershear rupture speeds as observed in our experiments and simulations. Furthermore, the theory uncovers a critical rupture length below which supershear propagation is impossible. Beyond this critical length, a rupture can sustain supershear propagation for arbitrarily low prestress levels if local non-uniformities cause transition. The presented theory provides a tool to better understand the potential for supershear ruptures in more realistic heterogeneous systems.
How to cite: Kammer, D., Svetlizky, I., and Fineberg, J.: Rupture speed of supershear slip instabilities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2213, https://doi.org/10.5194/egusphere-egu2020-2213, 2020.
Shear ruptures propagating along natural faults or simulated faults in analog laboratory experiments present a wide range of rupture velocities. Most ruptures propagate at velocities below the Rayleigh wave speed and Linear Elastic Fracture Mechanics (LEFM) theory has been shown to predict quantitatively well the observed propagation speed. However, early theoretical and numerical work suggested that ruptures may surpass the shear wave speed and propagate at velocities that can reach the longitudinal wave speed. This was later confirmed in laboratory experiments and observed as supershear earthquakes in nature. While the transition from sub-Rayleigh to supershear propagation has been studied extensively, current knowledge of propagation speed in the supershear regime is limited to a couple of idealistic set-ups. Here, we analyse the propagation speed of supershear ruptures along various nonuniform interfaces using simulations and experiments. We show that an approximate fracture mechanics theory describes well supershear rupture speeds as observed in our experiments and simulations. Furthermore, the theory uncovers a critical rupture length below which supershear propagation is impossible. Beyond this critical length, a rupture can sustain supershear propagation for arbitrarily low prestress levels if local non-uniformities cause transition. The presented theory provides a tool to better understand the potential for supershear ruptures in more realistic heterogeneous systems.
How to cite: Kammer, D., Svetlizky, I., and Fineberg, J.: Rupture speed of supershear slip instabilities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2213, https://doi.org/10.5194/egusphere-egu2020-2213, 2020.
EGU2020-2565 | Displays | TS5.3
Yield and shear of rough interlocked faults: analytical solution and experimental observationsAmir Sagy, Vladimir Lyakhovsky, and Yossef H. Hatzor
Natural fault surfaces are interlocked, partly cohesive, and display multiscale geometric irregularities. Here we examine the nucleation of deformation and the evolution of shear in such interlocked surfaces using a closed-form analytical solution and a series of laboratory experiments. The analytical model considers an interlocked interface with multiscale roughness between two linear elastic half-space blocks. The interface geometry is based on three-dimensional fault surfaces imaging. It is represented by a Fourier series and the plane strain solution for the elastic stress distribution is represented as a sum of the constant background stress generated by a uniform far-field loading and perturbations associated with the interface roughness. The model predicts the critical stress necessary for failure and the location of failure nucleation sites across the surface, as function of the initial surface geometry.
A similar configuration is adopted in laboratory experiments as carbonate blocks with rough interlocked surfaces generated by tensional fracturing are sheared in a servo-controlled direct shear apparatus. Resistance to shear and surface roughness evolution are measured under variable normal stresses, slip distances and slip rates. We find that the evolution of surface morphology with shear is closely related to the loading configuration. Initially rough, interlocked, surfaces become rougher when normal stress and displacement rate are increased. Under a fixed, relatively low normal stress and fixed displacement rate however, the surfaces become smoother with increasing displacement distance.
The shear of the interlocked slip surfaces is associated with volumetric deformation, wear and frictional slip, all of which are typically observed across natural fault zones. We suggest that their intensities and partitioning are strongly affected by the initial surface roughness characteristics, the background stress, and the rate and magnitude of shear displacement.
How to cite: Sagy, A., Lyakhovsky, V., and Hatzor, Y. H.: Yield and shear of rough interlocked faults: analytical solution and experimental observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2565, https://doi.org/10.5194/egusphere-egu2020-2565, 2020.
Natural fault surfaces are interlocked, partly cohesive, and display multiscale geometric irregularities. Here we examine the nucleation of deformation and the evolution of shear in such interlocked surfaces using a closed-form analytical solution and a series of laboratory experiments. The analytical model considers an interlocked interface with multiscale roughness between two linear elastic half-space blocks. The interface geometry is based on three-dimensional fault surfaces imaging. It is represented by a Fourier series and the plane strain solution for the elastic stress distribution is represented as a sum of the constant background stress generated by a uniform far-field loading and perturbations associated with the interface roughness. The model predicts the critical stress necessary for failure and the location of failure nucleation sites across the surface, as function of the initial surface geometry.
A similar configuration is adopted in laboratory experiments as carbonate blocks with rough interlocked surfaces generated by tensional fracturing are sheared in a servo-controlled direct shear apparatus. Resistance to shear and surface roughness evolution are measured under variable normal stresses, slip distances and slip rates. We find that the evolution of surface morphology with shear is closely related to the loading configuration. Initially rough, interlocked, surfaces become rougher when normal stress and displacement rate are increased. Under a fixed, relatively low normal stress and fixed displacement rate however, the surfaces become smoother with increasing displacement distance.
The shear of the interlocked slip surfaces is associated with volumetric deformation, wear and frictional slip, all of which are typically observed across natural fault zones. We suggest that their intensities and partitioning are strongly affected by the initial surface roughness characteristics, the background stress, and the rate and magnitude of shear displacement.
How to cite: Sagy, A., Lyakhovsky, V., and Hatzor, Y. H.: Yield and shear of rough interlocked faults: analytical solution and experimental observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2565, https://doi.org/10.5194/egusphere-egu2020-2565, 2020.
EGU2020-21610 | Displays | TS5.3
Stress triggering and the mechanics of fault slip behaviorMarco Maria Scuderi and Cristiano Collettini
Dynamic changes in the stress field during the seismic cycle of tectonic faults can control frictional stability and the mode of fault slip. Small perturbation in the stress field, like those produced by tidal stresses can influence the evolution of frictional strength and fault stability with the potential of triggering a variety of slip behaviors. However, an open question that remains still poorly understood is how amplitude and frequency of stress changes influence the triggering of an instability and the associated slip behavior, i.e. slow or fast slip.
Here we reproduce in the laboratory the spectrum of fault slip behaviors, from slow-slip to dynamic stick-slip, by matching the critical fault rheologic stiffness (kc) with the surrounding stiffness (k). We investigate the influence of normal stress variations on the slip style of a quartz rich fault gouge at the stability boundary, i.e. k/kc slightly less than one, by adopting two techniques: 1) instantaneous step-like changes and 2) sinusoidal variations in normal stress. For the latter case, modulations of normal stress were chosen to have amplitudes greater, less or equal to the typical stress drop observed during unperturbed experiments. Also, the period was varied to be greater, less or equal to the typical recurrence time of laboratory slow-slip events. During the experiments, we continuously record ultrasonic wave velocity to monitor the microphysical state of the fault. We find that frictional stability is profoundly affected by variation in normal stress giving rise to a variety of slip behaviors. Furthermore, during strain accumulation and fabric development, changes in normal stress permanently influence the microphysical state of the fault gouge increasing kc and producing a switch from slow to fast stick-slip. Our results indicate that perturbations in the stress state can trigger a variety of slip behaviors along the same fault patch. These results have important implications for the formulation of constitutive laws in the framework of rate- and state- friction, highlighting the necessity to account for the microphysical state of the fault in order to improve our understanding of frictional stability.
How to cite: Scuderi, M. M. and Collettini, C.: Stress triggering and the mechanics of fault slip behavior, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21610, https://doi.org/10.5194/egusphere-egu2020-21610, 2020.
Dynamic changes in the stress field during the seismic cycle of tectonic faults can control frictional stability and the mode of fault slip. Small perturbation in the stress field, like those produced by tidal stresses can influence the evolution of frictional strength and fault stability with the potential of triggering a variety of slip behaviors. However, an open question that remains still poorly understood is how amplitude and frequency of stress changes influence the triggering of an instability and the associated slip behavior, i.e. slow or fast slip.
Here we reproduce in the laboratory the spectrum of fault slip behaviors, from slow-slip to dynamic stick-slip, by matching the critical fault rheologic stiffness (kc) with the surrounding stiffness (k). We investigate the influence of normal stress variations on the slip style of a quartz rich fault gouge at the stability boundary, i.e. k/kc slightly less than one, by adopting two techniques: 1) instantaneous step-like changes and 2) sinusoidal variations in normal stress. For the latter case, modulations of normal stress were chosen to have amplitudes greater, less or equal to the typical stress drop observed during unperturbed experiments. Also, the period was varied to be greater, less or equal to the typical recurrence time of laboratory slow-slip events. During the experiments, we continuously record ultrasonic wave velocity to monitor the microphysical state of the fault. We find that frictional stability is profoundly affected by variation in normal stress giving rise to a variety of slip behaviors. Furthermore, during strain accumulation and fabric development, changes in normal stress permanently influence the microphysical state of the fault gouge increasing kc and producing a switch from slow to fast stick-slip. Our results indicate that perturbations in the stress state can trigger a variety of slip behaviors along the same fault patch. These results have important implications for the formulation of constitutive laws in the framework of rate- and state- friction, highlighting the necessity to account for the microphysical state of the fault in order to improve our understanding of frictional stability.
How to cite: Scuderi, M. M. and Collettini, C.: Stress triggering and the mechanics of fault slip behavior, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21610, https://doi.org/10.5194/egusphere-egu2020-21610, 2020.
EGU2020-3396 | Displays | TS5.3
Quantifying effects of laboratory-simulated diagenetic sediment lithification on frictional slip behaviorMatt Ikari and Andre Hüpers
On major plate-boundary fault zones, it is generally observed that large-magnitude earthquakes tend to nucleate within a discrete depth range in the crust known as the seismogenic zone. This is generally explained by the contrast between frictionally stable, velocity strengthening sediments at shallow depths and lithified, velocity-weakening rocks at seismogenic (10’s of km) depth. Thus, it is hypothesized that diagenetic and low-grade metamorphic processes are responsible for the development of velocity-weakening frictional behavior in sediments that make up fault gouges. Previous laboratory studies comparing the frictional properties of intact rocks and powdered versions of the same rocks generally support this hypothesis, however controlling lithification in the laboratory and systematically quantifying frictional behavior as a function of lithification and remains a challenge.
Here, we simulate the lithification process in the laboratory by using mixtures of halite and shale powders with halite-saturated brine, which we consolidate under 10 MPa normal stress and subsequently desiccate. The desiccation allows precipitation of halite as cement, creating synthetic rocks. We vary the proportion of salt to shale in our samples, which we use as a proxy for degree of lithification. We measure the frictional properties of our lithified samples, and equivalent powdered versions of these samples, with velocity-step tests in the range 10-7 – 3x10-5 m/s. We quantify lithification by two methods: (1) direct measurement of cohesion, and (2) measuring the porosity reduction of lithified samples compared to powders. Using these measurements, we systematically investigate the relationship between lithification and frictional slip behavior.
We observe that powdered samples of every halite-shale proportion exhibits predominantly velocity-strengthening friction, whereas lithified samples exhibit a combination of velocity strengthening and significant velocity weakening when halite constitutes at least 30 wt% of the sample. Larger velocity weakening generally coincides with friction coefficients of > 0.62, cohesion of > ~1 MPa, and porosity reduction of > ~50 vol%. Although none of our lithified samples exhibit strictly velocity-weakening friction, this is consistent with the frictional behavior of pure halite under our experimental conditions. Scanning electron microscopy images do not show any clear characteristics attributable to velocity-weakening, but did reveal that the shear surfaces for powders tends to exhibit small cracks not seen in the lithified sample shear surfaces. These results suggest that lithification via cementation and porosity loss may facilitate slip instability, but that microstructural indicators are subtle.
How to cite: Ikari, M. and Hüpers, A.: Quantifying effects of laboratory-simulated diagenetic sediment lithification on frictional slip behavior, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3396, https://doi.org/10.5194/egusphere-egu2020-3396, 2020.
On major plate-boundary fault zones, it is generally observed that large-magnitude earthquakes tend to nucleate within a discrete depth range in the crust known as the seismogenic zone. This is generally explained by the contrast between frictionally stable, velocity strengthening sediments at shallow depths and lithified, velocity-weakening rocks at seismogenic (10’s of km) depth. Thus, it is hypothesized that diagenetic and low-grade metamorphic processes are responsible for the development of velocity-weakening frictional behavior in sediments that make up fault gouges. Previous laboratory studies comparing the frictional properties of intact rocks and powdered versions of the same rocks generally support this hypothesis, however controlling lithification in the laboratory and systematically quantifying frictional behavior as a function of lithification and remains a challenge.
Here, we simulate the lithification process in the laboratory by using mixtures of halite and shale powders with halite-saturated brine, which we consolidate under 10 MPa normal stress and subsequently desiccate. The desiccation allows precipitation of halite as cement, creating synthetic rocks. We vary the proportion of salt to shale in our samples, which we use as a proxy for degree of lithification. We measure the frictional properties of our lithified samples, and equivalent powdered versions of these samples, with velocity-step tests in the range 10-7 – 3x10-5 m/s. We quantify lithification by two methods: (1) direct measurement of cohesion, and (2) measuring the porosity reduction of lithified samples compared to powders. Using these measurements, we systematically investigate the relationship between lithification and frictional slip behavior.
We observe that powdered samples of every halite-shale proportion exhibits predominantly velocity-strengthening friction, whereas lithified samples exhibit a combination of velocity strengthening and significant velocity weakening when halite constitutes at least 30 wt% of the sample. Larger velocity weakening generally coincides with friction coefficients of > 0.62, cohesion of > ~1 MPa, and porosity reduction of > ~50 vol%. Although none of our lithified samples exhibit strictly velocity-weakening friction, this is consistent with the frictional behavior of pure halite under our experimental conditions. Scanning electron microscopy images do not show any clear characteristics attributable to velocity-weakening, but did reveal that the shear surfaces for powders tends to exhibit small cracks not seen in the lithified sample shear surfaces. These results suggest that lithification via cementation and porosity loss may facilitate slip instability, but that microstructural indicators are subtle.
How to cite: Ikari, M. and Hüpers, A.: Quantifying effects of laboratory-simulated diagenetic sediment lithification on frictional slip behavior, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3396, https://doi.org/10.5194/egusphere-egu2020-3396, 2020.
EGU2020-4205 | Displays | TS5.3
Laboratory observations of frictional stability and fault zone evolution under heterogeneous friction, rheology, and stress conditionsChun-Yu Ke, Sara Beth Leach Cebry, Srisharan Shreedharan, Chris Marone, David S. Kammer, and Gregory C. McLaskey
Natural faults experience a variety of frictional, rheological, and stress heterogeneities. To investigate the effects of these heterogeneities on seismic stability and the mode of fault slip behavior, laboratory experiments were conducted using a biaxial shearing apparatus with a 0.76 m by 0.076 m simulated fault where 2.5 to 5 mm thick gouge layers were sheared at applied normal stresses of 7 to 12 MPa for 25 mm of cumulative slip. Laboratory faults consisted of uniform layers of gouge, homogeneous mixtures, and/or heterogeneous patches of talc, quartz, and gypsum minerals. Experiments with a uniform layer of velocity weakening fault gouge revealed the development of two asperities at the highly stressed ends of the fault that could fail independently, and creep fronts that facilitated interaction between asperities. This behavior was also reproduced with simple numerical simulations that employ rate- and state-dependent friction. In other experiments, the fault consisted of patches of alternating velocity strengthening and velocity weakening fault gouges. Patch size and location were varied to understand how earthquake ruptures accelerate or decelerate in this heterogeneous environment. These experiments revealed that a velocity weakening fault patch was more likely to remain stable if located next to a velocity strengthening fault patch. However, stability was dependent on the patch sizes and location relative to where the load is applied. In certain cases, some sections of the fault slipped unstably while others slid stably. These experiments, and matching numerical models, highlight the complexity that can arise on natural faults due to frictional, rheological, and stress heterogeneities.
How to cite: Ke, C.-Y., Leach Cebry, S. B., Shreedharan, S., Marone, C., Kammer, D. S., and McLaskey, G. C.: Laboratory observations of frictional stability and fault zone evolution under heterogeneous friction, rheology, and stress conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4205, https://doi.org/10.5194/egusphere-egu2020-4205, 2020.
Natural faults experience a variety of frictional, rheological, and stress heterogeneities. To investigate the effects of these heterogeneities on seismic stability and the mode of fault slip behavior, laboratory experiments were conducted using a biaxial shearing apparatus with a 0.76 m by 0.076 m simulated fault where 2.5 to 5 mm thick gouge layers were sheared at applied normal stresses of 7 to 12 MPa for 25 mm of cumulative slip. Laboratory faults consisted of uniform layers of gouge, homogeneous mixtures, and/or heterogeneous patches of talc, quartz, and gypsum minerals. Experiments with a uniform layer of velocity weakening fault gouge revealed the development of two asperities at the highly stressed ends of the fault that could fail independently, and creep fronts that facilitated interaction between asperities. This behavior was also reproduced with simple numerical simulations that employ rate- and state-dependent friction. In other experiments, the fault consisted of patches of alternating velocity strengthening and velocity weakening fault gouges. Patch size and location were varied to understand how earthquake ruptures accelerate or decelerate in this heterogeneous environment. These experiments revealed that a velocity weakening fault patch was more likely to remain stable if located next to a velocity strengthening fault patch. However, stability was dependent on the patch sizes and location relative to where the load is applied. In certain cases, some sections of the fault slipped unstably while others slid stably. These experiments, and matching numerical models, highlight the complexity that can arise on natural faults due to frictional, rheological, and stress heterogeneities.
How to cite: Ke, C.-Y., Leach Cebry, S. B., Shreedharan, S., Marone, C., Kammer, D. S., and McLaskey, G. C.: Laboratory observations of frictional stability and fault zone evolution under heterogeneous friction, rheology, and stress conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4205, https://doi.org/10.5194/egusphere-egu2020-4205, 2020.
EGU2020-16538 | Displays | TS5.3
Exploring frictional velocity dependence as a mechanism for slow earthquake ruptureJulia Krogh and Chris Marone
Earthquakes fail through a spectrum of slip modes ranging from slow slip to fast elastodynamic rupture. Slow earthquakes, or slow-slip events, represent fault slip behaviors that involve quasi-dynamic, self-sustained rupture propagation. To better understand the mechanisms that limit the slip speed and propagation rates of slow slip, we focus on a particular parameter: the critical frictional weakening rate of the fault surface, kc. When kc is approximately equal to k, the elastic loading stiffness of the fault, complex fault slip behaviors including slow-slip events are observed. If kc has a negative dependence on slip velocity, acceleration during the coseismic phase could decrease kc until it approximates k, terminating in a slow earthquake. Here, we describe the results of laboratory experiments designed to quantify the dependence of kc on frictional slip velocity. We conducted double-direct shear experiments in a biaxial shearing apparatus with 3 mm-thick fault zones composed of quartz powder to simulate fault gouge. We focus on step decreases in slip velocity from 300 to 3 m/s that were performed for a range of normal stresses, from 10 to 20 MPa, which we know to be near the stability transition from stable to unstable sliding defined by k/kc ~ 1.0. Under stable conditions, rate-state friction modeling was used to determine kc for each velocity step. Our data provide direct insight on the stability transition associated with kc(V), including experiments for which slow-slip instabilities grew larger and faster throughout velocity-step sequences. Ultimately, both numerical modeling and observational data indicate that the velocity dependence of kc is an important parameter when considering the mechanisms of slow earthquake nucleation.
How to cite: Krogh, J. and Marone, C.: Exploring frictional velocity dependence as a mechanism for slow earthquake rupture, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16538, https://doi.org/10.5194/egusphere-egu2020-16538, 2020.
Earthquakes fail through a spectrum of slip modes ranging from slow slip to fast elastodynamic rupture. Slow earthquakes, or slow-slip events, represent fault slip behaviors that involve quasi-dynamic, self-sustained rupture propagation. To better understand the mechanisms that limit the slip speed and propagation rates of slow slip, we focus on a particular parameter: the critical frictional weakening rate of the fault surface, kc. When kc is approximately equal to k, the elastic loading stiffness of the fault, complex fault slip behaviors including slow-slip events are observed. If kc has a negative dependence on slip velocity, acceleration during the coseismic phase could decrease kc until it approximates k, terminating in a slow earthquake. Here, we describe the results of laboratory experiments designed to quantify the dependence of kc on frictional slip velocity. We conducted double-direct shear experiments in a biaxial shearing apparatus with 3 mm-thick fault zones composed of quartz powder to simulate fault gouge. We focus on step decreases in slip velocity from 300 to 3 m/s that were performed for a range of normal stresses, from 10 to 20 MPa, which we know to be near the stability transition from stable to unstable sliding defined by k/kc ~ 1.0. Under stable conditions, rate-state friction modeling was used to determine kc for each velocity step. Our data provide direct insight on the stability transition associated with kc(V), including experiments for which slow-slip instabilities grew larger and faster throughout velocity-step sequences. Ultimately, both numerical modeling and observational data indicate that the velocity dependence of kc is an important parameter when considering the mechanisms of slow earthquake nucleation.
How to cite: Krogh, J. and Marone, C.: Exploring frictional velocity dependence as a mechanism for slow earthquake rupture, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16538, https://doi.org/10.5194/egusphere-egu2020-16538, 2020.
We model mechanics of an aseismic fault creep propagation and conditions when it may lead to the initiation of seismic slip. We do so by considering fault bounding medium to be elastically deformable and fault's interfacial strength to be slip rate- and state-dependent characterized by the steady-state rate-weakening. The fault is considered to be initially locked: a state of slip when interfacial slip velocity is considerably low and arbitrarily less than the steady-state sliding rate for given uniformly distributed prestress.
We find solutions for creep penetration into the fault under geologically relevant loading scenarios (e.g., that of a plate-bounding strike-slip faulting driven by the slip at depth, or that of a rate-weakening patch of a fault loaded by a creep on an adjacent rate-strengthening part due to, e.g., anthropogenic fluid injection). In all the cases, the creep makes its way as a self-similar traveling front characterized by high stress owed to the direct effect; however, the remaining creep profile exhibits a near steady-state sliding. This may imply that a choice from a set of rules for the evolution of state variable—with identical linearizations about steady-state sliding—has no bearing on the creep penetration. Further, we find that the prestress, close to or far from steady-state sliding stress, controls the rate and manner of the creep penetration.
We study slip propagation from an imposed dislocation accrued at a constant rate at one end of a homogeneous fault with the other end either at (1) the free surface of an elastic half-space or (2) strictly locked (buried) in the elastic full space. In both scenarios, no slip instability takes place over aseismic creep propagation distances relatable to the usual elasto-frictional nucleation lengthscale (e.g. Rubin & Ampuero 2005). Instead, in the first case creep propagation leads to the nucleation of the first and all subsequent dynamic events of the emerging cycle at/near the free surface after the creep traversed the entire length of the fault. In the second case, the creep front traverses nearly the entire length of the fault, but, instead of nucleating a dynamic event, the front arrests at some distance from the buried fault end, followed by the continual accumulation of aseismic slip without ever nucleating a dynamic event. These results may be owed to the physical and geometrical invariance of the considered homogeneous fault and may signal the essential role of fault strength heterogeneity, either that of the normal stress and/or frictional properties (Ray & Viesca, 2017, 2019), in defining its seismogenic character, i.e. under which conditions and where on the fault the earthquake slip instability can take place.
How to cite: Ray, S. and Garagash, D.: How fault creep makes its way!, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21286, https://doi.org/10.5194/egusphere-egu2020-21286, 2020.
We model mechanics of an aseismic fault creep propagation and conditions when it may lead to the initiation of seismic slip. We do so by considering fault bounding medium to be elastically deformable and fault's interfacial strength to be slip rate- and state-dependent characterized by the steady-state rate-weakening. The fault is considered to be initially locked: a state of slip when interfacial slip velocity is considerably low and arbitrarily less than the steady-state sliding rate for given uniformly distributed prestress.
We find solutions for creep penetration into the fault under geologically relevant loading scenarios (e.g., that of a plate-bounding strike-slip faulting driven by the slip at depth, or that of a rate-weakening patch of a fault loaded by a creep on an adjacent rate-strengthening part due to, e.g., anthropogenic fluid injection). In all the cases, the creep makes its way as a self-similar traveling front characterized by high stress owed to the direct effect; however, the remaining creep profile exhibits a near steady-state sliding. This may imply that a choice from a set of rules for the evolution of state variable—with identical linearizations about steady-state sliding—has no bearing on the creep penetration. Further, we find that the prestress, close to or far from steady-state sliding stress, controls the rate and manner of the creep penetration.
We study slip propagation from an imposed dislocation accrued at a constant rate at one end of a homogeneous fault with the other end either at (1) the free surface of an elastic half-space or (2) strictly locked (buried) in the elastic full space. In both scenarios, no slip instability takes place over aseismic creep propagation distances relatable to the usual elasto-frictional nucleation lengthscale (e.g. Rubin & Ampuero 2005). Instead, in the first case creep propagation leads to the nucleation of the first and all subsequent dynamic events of the emerging cycle at/near the free surface after the creep traversed the entire length of the fault. In the second case, the creep front traverses nearly the entire length of the fault, but, instead of nucleating a dynamic event, the front arrests at some distance from the buried fault end, followed by the continual accumulation of aseismic slip without ever nucleating a dynamic event. These results may be owed to the physical and geometrical invariance of the considered homogeneous fault and may signal the essential role of fault strength heterogeneity, either that of the normal stress and/or frictional properties (Ray & Viesca, 2017, 2019), in defining its seismogenic character, i.e. under which conditions and where on the fault the earthquake slip instability can take place.
How to cite: Ray, S. and Garagash, D.: How fault creep makes its way!, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21286, https://doi.org/10.5194/egusphere-egu2020-21286, 2020.
EGU2020-5204 | Displays | TS5.3
Lower crustal earthquake facilitated by overpressurized frictional meltsXin Zhong, Arianne Petley-Ragan, Sarah Incel, Marcin Dabrowski, Niels Andersen, Håkon Austrheim, and Bjørn Jamtveit
Earthquakes are among the most catastrophic geological events that last only several to tens of seconds. During earthquakes, many processes may occur including rupturing, frictional sliding, pore fluid pressurization and occasionally frictional melting. However, little direct records of these fast processes remain preserved through geological time. During rapid shearing, frictional melt may form that lubricates the rocks and facilitates further sliding. The frictional melt layer may quench quickly within seconds to minutes depending on its thickness. After quenching, the product pseudotachylyte preserves valuable information about the conditions when the frictional melt was generated. Here, we study pseudotachylyte from Holsnøy Island in the Bergen Arcs of Western Norway, an exhumed portion of the lower continental crust. The investigated pseudotachylyte vein is ca. 1-2 cm thick and free of injection veins along the 2 m visible length of the fault. The pseudotachylyte matrix is made up of fine-grained omphacite (Jd38), sodic plagioclase (Ab83) and kyanite with minor rutile and sulphides. Many dendritic garnets are found within the pseudotachylyte showing gradual grain size reduction towards the wall rock. This suggests that the garnets crystallized during rapid quenching. The stability of epidote, kyanite and quartz in the wall rock plagioclase, and omphacite and albitic plagioclase together with quartz in the pseudotachylyte matrix constrains the ambient P ca. 1.5-1.7 GPa and T ca. 650-750°C. Using Raman elastic barometry, the constrained pressure condition from quartz inclusions in the dendritic garnets in the pseudotachylyte is > 2 GPa. Based on an elastic model (Eshelby’s solution), it is not possible to maintain 0.5 GPa overpressure within a thin melt layer by thermal pressurization or melting expansion. A potential explanation is that GPa level differential stress was present in the wall rocks and the melt pressure approached the normal stress when shear rigidity vanished during frictional melting. Our study illustrates how overpressure can be created within frictional melt veins under conditions of high differential stress, and offers a mechanism that facilitates co-seismic weakening during lower crustal earthquakes.
How to cite: Zhong, X., Petley-Ragan, A., Incel, S., Dabrowski, M., Andersen, N., Austrheim, H., and Jamtveit, B.: Lower crustal earthquake facilitated by overpressurized frictional melts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5204, https://doi.org/10.5194/egusphere-egu2020-5204, 2020.
Earthquakes are among the most catastrophic geological events that last only several to tens of seconds. During earthquakes, many processes may occur including rupturing, frictional sliding, pore fluid pressurization and occasionally frictional melting. However, little direct records of these fast processes remain preserved through geological time. During rapid shearing, frictional melt may form that lubricates the rocks and facilitates further sliding. The frictional melt layer may quench quickly within seconds to minutes depending on its thickness. After quenching, the product pseudotachylyte preserves valuable information about the conditions when the frictional melt was generated. Here, we study pseudotachylyte from Holsnøy Island in the Bergen Arcs of Western Norway, an exhumed portion of the lower continental crust. The investigated pseudotachylyte vein is ca. 1-2 cm thick and free of injection veins along the 2 m visible length of the fault. The pseudotachylyte matrix is made up of fine-grained omphacite (Jd38), sodic plagioclase (Ab83) and kyanite with minor rutile and sulphides. Many dendritic garnets are found within the pseudotachylyte showing gradual grain size reduction towards the wall rock. This suggests that the garnets crystallized during rapid quenching. The stability of epidote, kyanite and quartz in the wall rock plagioclase, and omphacite and albitic plagioclase together with quartz in the pseudotachylyte matrix constrains the ambient P ca. 1.5-1.7 GPa and T ca. 650-750°C. Using Raman elastic barometry, the constrained pressure condition from quartz inclusions in the dendritic garnets in the pseudotachylyte is > 2 GPa. Based on an elastic model (Eshelby’s solution), it is not possible to maintain 0.5 GPa overpressure within a thin melt layer by thermal pressurization or melting expansion. A potential explanation is that GPa level differential stress was present in the wall rocks and the melt pressure approached the normal stress when shear rigidity vanished during frictional melting. Our study illustrates how overpressure can be created within frictional melt veins under conditions of high differential stress, and offers a mechanism that facilitates co-seismic weakening during lower crustal earthquakes.
How to cite: Zhong, X., Petley-Ragan, A., Incel, S., Dabrowski, M., Andersen, N., Austrheim, H., and Jamtveit, B.: Lower crustal earthquake facilitated by overpressurized frictional melts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5204, https://doi.org/10.5194/egusphere-egu2020-5204, 2020.
EGU2020-7425 | Displays | TS5.3
Field and experimental evidence of frictional melting in fluid-rich faultsGiulio Di Toro, Michele Fondriest, Tom Mitchell, Rodrigo Gomila, Erik Jensen, Simone Masoch, Andrea Bistacchi, Giulia Magnarini, Dan Faulkner, José Cembrano, Silvia Mittempergher, and Elena Spagnuolo
Pseudotachylytes (solidified friction melts produced during seismic slip) are considered to be rare in the geological record because they should be typical of particular seismogenic environments characterized by water-deficient cohesive rocks. Here we present field and experimental evidence that frictional melting can occur in “fluid-rich” faults hosted in the continental crust.
Pseudotachylytes were found in the >40 km long Bolfin Fault Zone of the Atacama Fault System (Northern Chile). The pseudotachylytes (1) are associated with a ~1 m thick ultracataclastic fault core which accommodated > 5 km of strike-slip displacement at 6-8 km depth and 280-350°C ambient temperature, (2) cut a ca. 50 m thick damage zone made of sub-greenschists facies hydrothermally altered diorites and gabbros, (3) cut and are cut by epidote+chlorite+calcite bearing veins. The microstructure of the pseudotachylytes include (1) tabular microlites of feldspar hosted in a glassy-like matrix and (2) vesicles filled by post-seismic sub-greenschist facies minerals hosted in a strongly altered matrix of albite, chlorite, and epidote crystals.
Experiments reproducing seismic slip in the presence of pressurized water and conducted with the rotary shear apparatus SHIVA on experimental faults made of the sub-greenschists (hydrothermally altered) facies damage zone rocks from the Bolfin Fault Zone, resulted in the production of vesiculated pseudotachylytes. In these experiments, fault weakening mainly occurred by melt lubrication rather than by pore fluid thermal pressurization.
The identification of pseudotachylytes and its association with intense pre- and post-seismic hydrothermal alteration challenges the common belief that pseudotachylytes are rare. Consistent with the experimental evidence, pseudotachylytes (1) could be a common coseismic fault product in the continental crust, (2) may easily be produced in fluid-rich hydrothermal environments but, (3) are easily lost from the geological record because they are prone to alteration.
How to cite: Di Toro, G., Fondriest, M., Mitchell, T., Gomila, R., Jensen, E., Masoch, S., Bistacchi, A., Magnarini, G., Faulkner, D., Cembrano, J., Mittempergher, S., and Spagnuolo, E.: Field and experimental evidence of frictional melting in fluid-rich faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7425, https://doi.org/10.5194/egusphere-egu2020-7425, 2020.
Pseudotachylytes (solidified friction melts produced during seismic slip) are considered to be rare in the geological record because they should be typical of particular seismogenic environments characterized by water-deficient cohesive rocks. Here we present field and experimental evidence that frictional melting can occur in “fluid-rich” faults hosted in the continental crust.
Pseudotachylytes were found in the >40 km long Bolfin Fault Zone of the Atacama Fault System (Northern Chile). The pseudotachylytes (1) are associated with a ~1 m thick ultracataclastic fault core which accommodated > 5 km of strike-slip displacement at 6-8 km depth and 280-350°C ambient temperature, (2) cut a ca. 50 m thick damage zone made of sub-greenschists facies hydrothermally altered diorites and gabbros, (3) cut and are cut by epidote+chlorite+calcite bearing veins. The microstructure of the pseudotachylytes include (1) tabular microlites of feldspar hosted in a glassy-like matrix and (2) vesicles filled by post-seismic sub-greenschist facies minerals hosted in a strongly altered matrix of albite, chlorite, and epidote crystals.
Experiments reproducing seismic slip in the presence of pressurized water and conducted with the rotary shear apparatus SHIVA on experimental faults made of the sub-greenschists (hydrothermally altered) facies damage zone rocks from the Bolfin Fault Zone, resulted in the production of vesiculated pseudotachylytes. In these experiments, fault weakening mainly occurred by melt lubrication rather than by pore fluid thermal pressurization.
The identification of pseudotachylytes and its association with intense pre- and post-seismic hydrothermal alteration challenges the common belief that pseudotachylytes are rare. Consistent with the experimental evidence, pseudotachylytes (1) could be a common coseismic fault product in the continental crust, (2) may easily be produced in fluid-rich hydrothermal environments but, (3) are easily lost from the geological record because they are prone to alteration.
How to cite: Di Toro, G., Fondriest, M., Mitchell, T., Gomila, R., Jensen, E., Masoch, S., Bistacchi, A., Magnarini, G., Faulkner, D., Cembrano, J., Mittempergher, S., and Spagnuolo, E.: Field and experimental evidence of frictional melting in fluid-rich faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7425, https://doi.org/10.5194/egusphere-egu2020-7425, 2020.
EGU2020-5568 | Displays | TS5.3
Raman Spectroscopy of Carbonaceous Material record in pseudotachylytes: heating or deformation?Benjamin Moris-Muttoni, Romain Augier, Hugues Raimbourg, and Abdeltif Lahfid
The Raman Spectroscopy of Carbonaceous Materials (RSCM) permits to quantify the degree of crystallinity of carbonaceous materials (CM), which increases upon geological heating. First believed to be a reliable indicator of metamorphic grade (Pasteris and Wopenka, 1991 ; Wada et al., 1996), the quantitative evolution of crystallinity of CM has been proposed as new geothermometers for a wide range of temperature between 200 and 650°C (Beyssac et al., 2002 ; Rahl et al., 2005 ; Lahfid et al., 2010 ; Kouketsu et al., 2014).
According to recent studies, RSCM approach has been used to detect evidence of frictional heating during seismic events from pseudotachylites (Ito et al., 2017) or on fault gouges and breccia (Furuichi et al., 2015 ; Kuo et al., 2018). This new application assumes that CM spectra reflect only the thermal record irrespectively of the potential impact of geological strain on CM crystallinity (Tagiri and Tsuboi, 1979 ; Bonijoly et al., 1982 ; Ross et al., 1991 ; Bustin et al., 1995).
The aim of this study is to reconsider this postulate by using RSCM method in order to understand the effects of seismic deformation on the structure of the carbonaceous material. For this purpose, we analyzed three pseuydotachylyte veins from the Shimanto Belt (Southwest Japan), one from a drilling in the Nobeoka Tectonic Line, another from Okitsu area and a last one from the Mugi area, with RSCM method through high-resolution cross-sections perpendicular to the structure. Samples are composed of weakly foliated tectonic melanges troncated by a millimetric shear plane filled by fine black vitreous material accompanied by injection veins. Filling material presents an important grain-size reduction and embayment structures of sandstones clasts, scattered iron sulfides while element maps show flow textures. These microstructure features are described as characteristics of melt-origin pseudotachylytes (Hasegawa et al., 2019) but could also be produced by an intense comminution along with fluids circulation. Area ratio show a large evolution of CM spectra inside the pseudotachylyte compare to the host rock. In addition, intensity ratio (i.e. R1 in Beyssac et al., 2002) drastically increases inside the pseudotachylyte as expected. However, intensity ratio values are higher than expected values at this temperature, from your own calibration on undeformed samples, and highest values are observed on each rim of the pseudotachylyte. This result suggest that structural evolution of CM is not only controlled by temperature, but also by deformation, in a broad sense. More importantly, these parameters shows a very sharp evolution in few microns along cross-sections, which is at variance with thermal diffusivity models applicable for others intrusive bodies (Aoya et al., 2010 ; Hilchie and Jamieson, 2014).
These observations of step-wise evolution of CM raman parameters suggest that deformation is the principal influencing factor of the evolution of CM crystallinity in fault cores. It therefore questions the maximum temperature reached fault zones, possibly much lower than previously estimated.
How to cite: Moris-Muttoni, B., Augier, R., Raimbourg, H., and Lahfid, A.: Raman Spectroscopy of Carbonaceous Material record in pseudotachylytes: heating or deformation? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5568, https://doi.org/10.5194/egusphere-egu2020-5568, 2020.
The Raman Spectroscopy of Carbonaceous Materials (RSCM) permits to quantify the degree of crystallinity of carbonaceous materials (CM), which increases upon geological heating. First believed to be a reliable indicator of metamorphic grade (Pasteris and Wopenka, 1991 ; Wada et al., 1996), the quantitative evolution of crystallinity of CM has been proposed as new geothermometers for a wide range of temperature between 200 and 650°C (Beyssac et al., 2002 ; Rahl et al., 2005 ; Lahfid et al., 2010 ; Kouketsu et al., 2014).
According to recent studies, RSCM approach has been used to detect evidence of frictional heating during seismic events from pseudotachylites (Ito et al., 2017) or on fault gouges and breccia (Furuichi et al., 2015 ; Kuo et al., 2018). This new application assumes that CM spectra reflect only the thermal record irrespectively of the potential impact of geological strain on CM crystallinity (Tagiri and Tsuboi, 1979 ; Bonijoly et al., 1982 ; Ross et al., 1991 ; Bustin et al., 1995).
The aim of this study is to reconsider this postulate by using RSCM method in order to understand the effects of seismic deformation on the structure of the carbonaceous material. For this purpose, we analyzed three pseuydotachylyte veins from the Shimanto Belt (Southwest Japan), one from a drilling in the Nobeoka Tectonic Line, another from Okitsu area and a last one from the Mugi area, with RSCM method through high-resolution cross-sections perpendicular to the structure. Samples are composed of weakly foliated tectonic melanges troncated by a millimetric shear plane filled by fine black vitreous material accompanied by injection veins. Filling material presents an important grain-size reduction and embayment structures of sandstones clasts, scattered iron sulfides while element maps show flow textures. These microstructure features are described as characteristics of melt-origin pseudotachylytes (Hasegawa et al., 2019) but could also be produced by an intense comminution along with fluids circulation. Area ratio show a large evolution of CM spectra inside the pseudotachylyte compare to the host rock. In addition, intensity ratio (i.e. R1 in Beyssac et al., 2002) drastically increases inside the pseudotachylyte as expected. However, intensity ratio values are higher than expected values at this temperature, from your own calibration on undeformed samples, and highest values are observed on each rim of the pseudotachylyte. This result suggest that structural evolution of CM is not only controlled by temperature, but also by deformation, in a broad sense. More importantly, these parameters shows a very sharp evolution in few microns along cross-sections, which is at variance with thermal diffusivity models applicable for others intrusive bodies (Aoya et al., 2010 ; Hilchie and Jamieson, 2014).
These observations of step-wise evolution of CM raman parameters suggest that deformation is the principal influencing factor of the evolution of CM crystallinity in fault cores. It therefore questions the maximum temperature reached fault zones, possibly much lower than previously estimated.
How to cite: Moris-Muttoni, B., Augier, R., Raimbourg, H., and Lahfid, A.: Raman Spectroscopy of Carbonaceous Material record in pseudotachylytes: heating or deformation? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5568, https://doi.org/10.5194/egusphere-egu2020-5568, 2020.
EGU2020-7928 | Displays | TS5.3
Simulating melting of fault gouge at the local scaleGuilhem Mollon, Jerôme Aubry, and Alexandre Schubnel
Melting of fault gouge during fast co-seismic slip has been widely documented in laboratory studies. Because the real-time observation and local probing of this phenomenon is experimentally out of reach at the present time, the implication of melting on fault weakening are not yet fully understood,. Physics-based numerical modelling of a synthetic sliding interface could thus be a way to bring a better understanding of this physico-mechanical process.
In this study, we present a numerical work paving the way towards such an understanding. It is implemented in MELODY, a numerical tool combining Discrete Element Method (DEM) and a Multibody Meshfree Approach (i.e. highly deformable DEM). In this model, a small patch of seismic fault filled with granular gouge (composed of perfectly rigid and incrompressible grains with realistic angular shapes) is simulated. By shearing this simulated fault, we produce highly deformable gouge particles within a melted layer.
Numerical results show that melting processes have strong consequences on the fault rheology, by reducing shear stress and favouring the localization of the deformation on the sliding interface. Results are compared with experimental observations on saw-cut faults deformed in triaxial conditions in the laboratory. Future developments including thermal diffusion within the gouge and in the surrounding medium are described.
How to cite: Mollon, G., Aubry, J., and Schubnel, A.: Simulating melting of fault gouge at the local scale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7928, https://doi.org/10.5194/egusphere-egu2020-7928, 2020.
Melting of fault gouge during fast co-seismic slip has been widely documented in laboratory studies. Because the real-time observation and local probing of this phenomenon is experimentally out of reach at the present time, the implication of melting on fault weakening are not yet fully understood,. Physics-based numerical modelling of a synthetic sliding interface could thus be a way to bring a better understanding of this physico-mechanical process.
In this study, we present a numerical work paving the way towards such an understanding. It is implemented in MELODY, a numerical tool combining Discrete Element Method (DEM) and a Multibody Meshfree Approach (i.e. highly deformable DEM). In this model, a small patch of seismic fault filled with granular gouge (composed of perfectly rigid and incrompressible grains with realistic angular shapes) is simulated. By shearing this simulated fault, we produce highly deformable gouge particles within a melted layer.
Numerical results show that melting processes have strong consequences on the fault rheology, by reducing shear stress and favouring the localization of the deformation on the sliding interface. Results are compared with experimental observations on saw-cut faults deformed in triaxial conditions in the laboratory. Future developments including thermal diffusion within the gouge and in the surrounding medium are described.
How to cite: Mollon, G., Aubry, J., and Schubnel, A.: Simulating melting of fault gouge at the local scale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7928, https://doi.org/10.5194/egusphere-egu2020-7928, 2020.
EGU2020-3771 | Displays | TS5.3
Frictional strength, stability, and healing properties of basalt faults for CO2 storage purposesPiercarlo Giacomel, Roberta Ruggieri, Marco Scuderi, Elena Spagnuolo, Giulio Di Toro, and Cristiano Collettini
Despite the numerous advantages of storing CO2 into basalts by dissolving carbon dioxide into water prior to its injection, the large amount of H2O required for this operation poses an increased risk of fluid overpressure into the fault/fracture networks, and renders the seismicity analysis pivotal to upscale this storage method to voluminous basaltic occurrences diffused worldwide.
To deepen our knowledge on the frictional strength, stability, and the healing properties of basalt-built faults, we carried out friction tests on basalts from Mt. Etna using the biaxial deformation machine, BRAVA, and the rotary-shear apparatus, SHIVA (HP-HT laboratory of INGV-Rome, Italy). Specimens were selected for their relative abundance of olivine and pyroxene crystals, i.e. the main sources of divalent cations in silicate rocks necessary to trap CO2 into basalts.
Experiments were performed both on synthetic powdered samples and bare surfaces, at room-dry and water drained-saturated conditions, at room temperature and pressure. Bare surfaces consisted in basalt slabs and hollowed cylinders, which were mounted on BRAVA and SHIVA apparatus, respectively. Samples were subjected to 5 to 30 MPa normal stress (σn) for powdered samples and in the range 5 to 10 MPa for bare surfaces.
At the investigated normal stresses, frictional sliding data obey Byerlee’s law for friction, with the friction coefficient µ = 0.59 – 0.78. Differences in μ mainly reflect sample variability, different experimental configurations, sample geometry, and, to a lesser extent, the boundary conditions (dry/wet). However, in detail, basalt slabs are generally characterized by the highest friction coefficient and hollow cylinders exhibit a slight increase in friction coefficient with increasing shear displacement, due to the progressive slip hardening resulting from gouge production during frictional sliding.
Velocity step increases were conducted on BRAVA after steady values of friction were attained (~ 6.5-7.5 mm for gouge and ~ 3 mm slip for bare surfaces) and consisted in velocity sequences from 0.1 to 300 µm s-1, with ~ 500 μm displacement for each step. Rate-and-state friction experiments show opposite mechanical behavior between bare surfaces and synthetic fault gouge: while bare surfaces experience a transition from rate-weakening at low sliding velocity (V) to rate-strengthening behavior at higher V without any clear dependence on the applied σn, gouge revealed a negative trend of (a-b) with shear velocity at σn > 5 MPa and a velocity-weakening behavior at V ≥ 30 µm s-1, regardless of experimental conditions. We ascribe this different behavior to shear delocalization owing to frictional wear production in bare surfaces, and to shear localization accompanied by grain size reduction along the Riedel R1 and boundary B shear zones in fault gouges, as also confirmed by microstructural analysis.
The velocity weakening behavior of fault gouge, coupled with the fast healing rates retrieved from slide-hold-slide experiments (500 µm displacement cumulated at V = 10 µm/s followed by hold times from 30 to 3000 s), define high strength zones that are potentially seismogenic. Conversely, velocity strengthening behavior of bare surfaces promotes aseismic creep at V ≥ 100 µm s-1, regardless of the faster restrengthening compared to fault gouge.
How to cite: Giacomel, P., Ruggieri, R., Scuderi, M., Spagnuolo, E., Di Toro, G., and Collettini, C.: Frictional strength, stability, and healing properties of basalt faults for CO2 storage purposes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3771, https://doi.org/10.5194/egusphere-egu2020-3771, 2020.
Despite the numerous advantages of storing CO2 into basalts by dissolving carbon dioxide into water prior to its injection, the large amount of H2O required for this operation poses an increased risk of fluid overpressure into the fault/fracture networks, and renders the seismicity analysis pivotal to upscale this storage method to voluminous basaltic occurrences diffused worldwide.
To deepen our knowledge on the frictional strength, stability, and the healing properties of basalt-built faults, we carried out friction tests on basalts from Mt. Etna using the biaxial deformation machine, BRAVA, and the rotary-shear apparatus, SHIVA (HP-HT laboratory of INGV-Rome, Italy). Specimens were selected for their relative abundance of olivine and pyroxene crystals, i.e. the main sources of divalent cations in silicate rocks necessary to trap CO2 into basalts.
Experiments were performed both on synthetic powdered samples and bare surfaces, at room-dry and water drained-saturated conditions, at room temperature and pressure. Bare surfaces consisted in basalt slabs and hollowed cylinders, which were mounted on BRAVA and SHIVA apparatus, respectively. Samples were subjected to 5 to 30 MPa normal stress (σn) for powdered samples and in the range 5 to 10 MPa for bare surfaces.
At the investigated normal stresses, frictional sliding data obey Byerlee’s law for friction, with the friction coefficient µ = 0.59 – 0.78. Differences in μ mainly reflect sample variability, different experimental configurations, sample geometry, and, to a lesser extent, the boundary conditions (dry/wet). However, in detail, basalt slabs are generally characterized by the highest friction coefficient and hollow cylinders exhibit a slight increase in friction coefficient with increasing shear displacement, due to the progressive slip hardening resulting from gouge production during frictional sliding.
Velocity step increases were conducted on BRAVA after steady values of friction were attained (~ 6.5-7.5 mm for gouge and ~ 3 mm slip for bare surfaces) and consisted in velocity sequences from 0.1 to 300 µm s-1, with ~ 500 μm displacement for each step. Rate-and-state friction experiments show opposite mechanical behavior between bare surfaces and synthetic fault gouge: while bare surfaces experience a transition from rate-weakening at low sliding velocity (V) to rate-strengthening behavior at higher V without any clear dependence on the applied σn, gouge revealed a negative trend of (a-b) with shear velocity at σn > 5 MPa and a velocity-weakening behavior at V ≥ 30 µm s-1, regardless of experimental conditions. We ascribe this different behavior to shear delocalization owing to frictional wear production in bare surfaces, and to shear localization accompanied by grain size reduction along the Riedel R1 and boundary B shear zones in fault gouges, as also confirmed by microstructural analysis.
The velocity weakening behavior of fault gouge, coupled with the fast healing rates retrieved from slide-hold-slide experiments (500 µm displacement cumulated at V = 10 µm/s followed by hold times from 30 to 3000 s), define high strength zones that are potentially seismogenic. Conversely, velocity strengthening behavior of bare surfaces promotes aseismic creep at V ≥ 100 µm s-1, regardless of the faster restrengthening compared to fault gouge.
How to cite: Giacomel, P., Ruggieri, R., Scuderi, M., Spagnuolo, E., Di Toro, G., and Collettini, C.: Frictional strength, stability, and healing properties of basalt faults for CO2 storage purposes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3771, https://doi.org/10.5194/egusphere-egu2020-3771, 2020.
EGU2020-6691 | Displays | TS5.3
In-situ petrophysical and geomechanical characterization and 3D modelling of a mature normal fault zone (Goddo fault, Bømlo – Norway)Alberto Ceccato, Giulio Viola, Marco Antonellini, Giulia Tartaglia, and Eric James Ryan
The detailed characterization of internal fault zone architecture and petrophysical and geomechanical properties of fault rocks is fundamental to understanding the flow and mechanical behaviour of mature fault zones. The Goddo normal fault (Bømlo – Norway) accommodated c. E-W extension related to North Sea Rifting from Permian to Early Cretaceous times [1]. It represents a good example of a mature, iteratively reactivated and thus long-lived (seismogenic?) fault zone, developed in a pervasively fractured granitoid basement at upper crustal conditions in a regional extensional setting.
Field characterization of the fault zone’s structural facies and analysis of background fracture patterns in the protolith have been integrated with in-situ petrophysical and geomechanical surveys of the recognized fault zone architectural components. In-situ air-permeability and mechanical directional tests (performed with NER TinyPerm III air-minipermeameter and DRC GeoHammer, L-type Schmidt hammer, respectively) have allowed for the quantification of the permeability tensor and mechanical properties (UCS and elastic modulus) within each brittle structural facies. Mechanical properties measured parallel to fault rock fabric of cataclasite- and gouge-bearing structural facies differ by up to one order of magnitude from those measured perpendicularly to it (~10 MPa vs. 100-200 MPa in UCS, respectively). Accordingly, permeability of cataclasite- and gouge-bearing facies is several orders of magnitude larger when measured parallel to fault-rock fabric than that perpendicular to it (10-0-10-1 D vs. 10-2-10-3 D, respectively). Virtual outcrop models (VOMs) of the fault zone were obtained from high-resolution UAV-photogrammetry. Field measurements of fracture orientations were used for calibration of the VOMs to construct a statistically robust fracture dataset. The results of VOMs structural analysis allowed for the quantification of fracture intensity and geometrical characteristics of mesoscopic fracture patterns within the different domains of the fault zone architecture.
Results from field, VOMs structural analysis, and in-situ petrophysical investigations have been integrated into a realistic 3D fault zone model with the software 3DMove (Petex). This model can be used to investigate the influence of mesoscopic fracture patterns, related to either the fault zone or the background fracturing, on the hydro-mechanical behaviour of a mature fault zone. In addition, the evolution of the hydro-mechanical properties through time can be assessed by integrating the progressive development of brittle structural facies and fracture sets developed during the incremental strain and stress history into the model. This contribution proposes a geologically-constrained method to quantify the geometry of 3D fault zones, as a possible tool for models to be adopted in stress-strain analysis, hydraulic characterization and in the mechanical analysis of fault zones.
[1] Viola, G., Scheiber, T., Fredin, O., Zwingmann, H., Margreth, A., & Knies, J. (2016). Deconvoluting complex structural histories archived in brittle fault zones. Nature communications, 7, 13448.
How to cite: Ceccato, A., Viola, G., Antonellini, M., Tartaglia, G., and Ryan, E. J.: In-situ petrophysical and geomechanical characterization and 3D modelling of a mature normal fault zone (Goddo fault, Bømlo – Norway), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6691, https://doi.org/10.5194/egusphere-egu2020-6691, 2020.
The detailed characterization of internal fault zone architecture and petrophysical and geomechanical properties of fault rocks is fundamental to understanding the flow and mechanical behaviour of mature fault zones. The Goddo normal fault (Bømlo – Norway) accommodated c. E-W extension related to North Sea Rifting from Permian to Early Cretaceous times [1]. It represents a good example of a mature, iteratively reactivated and thus long-lived (seismogenic?) fault zone, developed in a pervasively fractured granitoid basement at upper crustal conditions in a regional extensional setting.
Field characterization of the fault zone’s structural facies and analysis of background fracture patterns in the protolith have been integrated with in-situ petrophysical and geomechanical surveys of the recognized fault zone architectural components. In-situ air-permeability and mechanical directional tests (performed with NER TinyPerm III air-minipermeameter and DRC GeoHammer, L-type Schmidt hammer, respectively) have allowed for the quantification of the permeability tensor and mechanical properties (UCS and elastic modulus) within each brittle structural facies. Mechanical properties measured parallel to fault rock fabric of cataclasite- and gouge-bearing structural facies differ by up to one order of magnitude from those measured perpendicularly to it (~10 MPa vs. 100-200 MPa in UCS, respectively). Accordingly, permeability of cataclasite- and gouge-bearing facies is several orders of magnitude larger when measured parallel to fault-rock fabric than that perpendicular to it (10-0-10-1 D vs. 10-2-10-3 D, respectively). Virtual outcrop models (VOMs) of the fault zone were obtained from high-resolution UAV-photogrammetry. Field measurements of fracture orientations were used for calibration of the VOMs to construct a statistically robust fracture dataset. The results of VOMs structural analysis allowed for the quantification of fracture intensity and geometrical characteristics of mesoscopic fracture patterns within the different domains of the fault zone architecture.
Results from field, VOMs structural analysis, and in-situ petrophysical investigations have been integrated into a realistic 3D fault zone model with the software 3DMove (Petex). This model can be used to investigate the influence of mesoscopic fracture patterns, related to either the fault zone or the background fracturing, on the hydro-mechanical behaviour of a mature fault zone. In addition, the evolution of the hydro-mechanical properties through time can be assessed by integrating the progressive development of brittle structural facies and fracture sets developed during the incremental strain and stress history into the model. This contribution proposes a geologically-constrained method to quantify the geometry of 3D fault zones, as a possible tool for models to be adopted in stress-strain analysis, hydraulic characterization and in the mechanical analysis of fault zones.
[1] Viola, G., Scheiber, T., Fredin, O., Zwingmann, H., Margreth, A., & Knies, J. (2016). Deconvoluting complex structural histories archived in brittle fault zones. Nature communications, 7, 13448.
How to cite: Ceccato, A., Viola, G., Antonellini, M., Tartaglia, G., and Ryan, E. J.: In-situ petrophysical and geomechanical characterization and 3D modelling of a mature normal fault zone (Goddo fault, Bømlo – Norway), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6691, https://doi.org/10.5194/egusphere-egu2020-6691, 2020.
EGU2020-7243 | Displays | TS5.3
The rupture process of the Peru intermediate and deep earthquakesCarolina López Sánchez, Elisa Buforn, Maurizio Mattesini, and Hernando Tavera
The seismicity of Peru is associated with the subduction process of the Nazca plate under South America and characterized by the occurrence of shallow, intermediate and deep earthquakes. In this study, we focus our attention on the rupture process of earthquakes (Mw>6.0 ) that occurred during the period 2018-2019 at intermediate depth (50<h<200 km) and deep depth (500<h<700 km). Focal mechanisms have been estimated from slip inversion of body waves at teleseismic distances (Kikuchi and Kanamori, 1991). We investigate possible differences in the moment rate functions at different focal depths using our results and those provided by SCARDEC database. Furthermore, an estimation of the radiated seismic energy (ER) was provided from the direct integration of the velocity P wave recorded at teleseismic and regional distances, getting values between 1015 to 1016 J. The data were corrected by geometrical spreading, anelastic attenuation, and free surface effect. These results are interpreted in terms of the seismotectonics of the region
How to cite: López Sánchez, C., Buforn, E., Mattesini, M., and Tavera, H.: The rupture process of the Peru intermediate and deep earthquakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7243, https://doi.org/10.5194/egusphere-egu2020-7243, 2020.
The seismicity of Peru is associated with the subduction process of the Nazca plate under South America and characterized by the occurrence of shallow, intermediate and deep earthquakes. In this study, we focus our attention on the rupture process of earthquakes (Mw>6.0 ) that occurred during the period 2018-2019 at intermediate depth (50<h<200 km) and deep depth (500<h<700 km). Focal mechanisms have been estimated from slip inversion of body waves at teleseismic distances (Kikuchi and Kanamori, 1991). We investigate possible differences in the moment rate functions at different focal depths using our results and those provided by SCARDEC database. Furthermore, an estimation of the radiated seismic energy (ER) was provided from the direct integration of the velocity P wave recorded at teleseismic and regional distances, getting values between 1015 to 1016 J. The data were corrected by geometrical spreading, anelastic attenuation, and free surface effect. These results are interpreted in terms of the seismotectonics of the region
How to cite: López Sánchez, C., Buforn, E., Mattesini, M., and Tavera, H.: The rupture process of the Peru intermediate and deep earthquakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7243, https://doi.org/10.5194/egusphere-egu2020-7243, 2020.
EGU2020-9369 | Displays | TS5.3
Slip modes and interaction in a simplified strike-slip fault system with increasing geometrical complexityMichael Rudolf, Joscha Podlesny, Matthias Rosenau, Ralf Kornhuber, and Onno Oncken
The release of elastic energy along an active fault is accommodated by a wide range of slip modes. It ranges from long-term slow slip events (SSEs) and creep to short-term tremors and earthquakes. They vary not only in their characteristic duration but also in their magnitude, spatial extend and slip velocities. As all slip modes are related to earthquakes, the understanding of the relationships between the different slip modes and the underlying mechanisms is crucial to assess earthquake hazards in various regions. The exact relation is unclear, as in some regions many slip modes occur simultaneously (e.g. Tohoku-Oki) and in others certain slip modes are completely absent (e.g. Cascadia).
One of the driving factors in the generation of this large variety of slip modes is the interplay of fault heterogeneity and geometrical complexity of the fault system. Using a scaled physical model we test various settings in terms of fault heterogeneity and geometrical complexity. The experimental results are then validated and benchmarked using multi-scale numerical simulations. We describe the system using the rate-and-state frictional framework and introduce the on-fault heterogeneity with variable frictional properties. All properties are the same for analogue and simulation as far as they can be determined or realized experimentally (a-b, vload, Shmax, Shmin, etc...). As analogue material we use segmented, decimetre sized neoprene foam blocks in multiple configurations (e.g. biaxial shear at forces <1 kN) to simulate the elastic upper crust. The contact surfaces are spray-painted with acrylic paint to generate velocity weakening characteristics in between the blocks. The major advantage of using neoprene over other materials, such as gelatine or polyurethane foams, is that it has closed pores and thus exhibits a more favourable Poisson’s ratio in comparison with rocks and shows better elastic strain propagation in the block. Furthermore, all used materials are inert and do not change their properties over time.
We are able to reliably generate frequent stick-slip events of variable size and recurrence intervals. The slip characteristics, such as slip distribution, are in good agreement with analytical solutions of fault slip in elastic media. In this contribution we will highlight the material properties, experimental results and used methodologies to monitor and process the experimental data. Additionally, we are going to give an outlook on the interaction behaviour of multiple faults in dependence of their geometric configuration and the generation of power-law type magnitude scaling relations.
How to cite: Rudolf, M., Podlesny, J., Rosenau, M., Kornhuber, R., and Oncken, O.: Slip modes and interaction in a simplified strike-slip fault system with increasing geometrical complexity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9369, https://doi.org/10.5194/egusphere-egu2020-9369, 2020.
The release of elastic energy along an active fault is accommodated by a wide range of slip modes. It ranges from long-term slow slip events (SSEs) and creep to short-term tremors and earthquakes. They vary not only in their characteristic duration but also in their magnitude, spatial extend and slip velocities. As all slip modes are related to earthquakes, the understanding of the relationships between the different slip modes and the underlying mechanisms is crucial to assess earthquake hazards in various regions. The exact relation is unclear, as in some regions many slip modes occur simultaneously (e.g. Tohoku-Oki) and in others certain slip modes are completely absent (e.g. Cascadia).
One of the driving factors in the generation of this large variety of slip modes is the interplay of fault heterogeneity and geometrical complexity of the fault system. Using a scaled physical model we test various settings in terms of fault heterogeneity and geometrical complexity. The experimental results are then validated and benchmarked using multi-scale numerical simulations. We describe the system using the rate-and-state frictional framework and introduce the on-fault heterogeneity with variable frictional properties. All properties are the same for analogue and simulation as far as they can be determined or realized experimentally (a-b, vload, Shmax, Shmin, etc...). As analogue material we use segmented, decimetre sized neoprene foam blocks in multiple configurations (e.g. biaxial shear at forces <1 kN) to simulate the elastic upper crust. The contact surfaces are spray-painted with acrylic paint to generate velocity weakening characteristics in between the blocks. The major advantage of using neoprene over other materials, such as gelatine or polyurethane foams, is that it has closed pores and thus exhibits a more favourable Poisson’s ratio in comparison with rocks and shows better elastic strain propagation in the block. Furthermore, all used materials are inert and do not change their properties over time.
We are able to reliably generate frequent stick-slip events of variable size and recurrence intervals. The slip characteristics, such as slip distribution, are in good agreement with analytical solutions of fault slip in elastic media. In this contribution we will highlight the material properties, experimental results and used methodologies to monitor and process the experimental data. Additionally, we are going to give an outlook on the interaction behaviour of multiple faults in dependence of their geometric configuration and the generation of power-law type magnitude scaling relations.
How to cite: Rudolf, M., Podlesny, J., Rosenau, M., Kornhuber, R., and Oncken, O.: Slip modes and interaction in a simplified strike-slip fault system with increasing geometrical complexity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9369, https://doi.org/10.5194/egusphere-egu2020-9369, 2020.
EGU2020-12831 | Displays | TS5.3
Time variations of the temperature depth profile in a scientific-drilling borehole penetrated through the Futagawa Fault, JapanWeiren Lin, Susumu Shibutani, Nana Kamiya, Koichiro Sado, Tatsuhiro Sugimoto, Yuzuru Yamamoto, Xiaoqiu Yang, and Masataka Kinoshita
A scientific vertical borehole (borehole FDB) was rapidly drilled down to 691.7 m during September 2017 – March 2018 after the Mw 7.0 Kumamoto earthquake (mainshock), Japan occurred on 16th April 2016. This borehole penetrated the seismogenic fault called Futagawa Fault which ruptured during the mainshock. Temperature measurements across a newly ruptured fault enable us to detect the frictional heat induced by the high-speed fault slipping, and then to estimate the fault frictional resistance which controls earthquake dynamics. To investigate the frictional heat of its coseismic rupturing, we started temperature measurements in the borehole FDB from May 2018, i.e. two years after the mainshock. We are still repeating the temperature measurements once per two or three months; and have conducted seven times of the measurements until the end of November 2019.
At the drilling site located at Mashiki town, Kumamoto Pref, a ~2.5 m dextral strike-slip coseismic displacement which is the largest displacement of the mainshock was observed on the surface rupture in this area. The borehole FDB consists of a cased interval from the surface down to a depth of ~300 m, and an open hole interval below that, down to the bottom of the borehole. In this borehole, the groundwater level is ~42 m, we measure the water temperature below the groundwater level and assume that the water temperature is the same as that of the formation after they became an equilibrium state after several months after the drilling operation. We measured the temperature and pressure while putting down and pulling up high resolution temperature and pressure sensors at an approximately constant rate of 3 m/min. A positive temperature peak around a fault where resistivity and P-wave velocity obtained from borehole logging abruptly dropped. The temperature depth profile showed time variation possibly including dissipation of the coseismic frictional heat caused by the fault rupturing and the other natural reasons e.g. groundwater flow.
How to cite: Lin, W., Shibutani, S., Kamiya, N., Sado, K., Sugimoto, T., Yamamoto, Y., Yang, X., and Kinoshita, M.: Time variations of the temperature depth profile in a scientific-drilling borehole penetrated through the Futagawa Fault, Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12831, https://doi.org/10.5194/egusphere-egu2020-12831, 2020.
A scientific vertical borehole (borehole FDB) was rapidly drilled down to 691.7 m during September 2017 – March 2018 after the Mw 7.0 Kumamoto earthquake (mainshock), Japan occurred on 16th April 2016. This borehole penetrated the seismogenic fault called Futagawa Fault which ruptured during the mainshock. Temperature measurements across a newly ruptured fault enable us to detect the frictional heat induced by the high-speed fault slipping, and then to estimate the fault frictional resistance which controls earthquake dynamics. To investigate the frictional heat of its coseismic rupturing, we started temperature measurements in the borehole FDB from May 2018, i.e. two years after the mainshock. We are still repeating the temperature measurements once per two or three months; and have conducted seven times of the measurements until the end of November 2019.
At the drilling site located at Mashiki town, Kumamoto Pref, a ~2.5 m dextral strike-slip coseismic displacement which is the largest displacement of the mainshock was observed on the surface rupture in this area. The borehole FDB consists of a cased interval from the surface down to a depth of ~300 m, and an open hole interval below that, down to the bottom of the borehole. In this borehole, the groundwater level is ~42 m, we measure the water temperature below the groundwater level and assume that the water temperature is the same as that of the formation after they became an equilibrium state after several months after the drilling operation. We measured the temperature and pressure while putting down and pulling up high resolution temperature and pressure sensors at an approximately constant rate of 3 m/min. A positive temperature peak around a fault where resistivity and P-wave velocity obtained from borehole logging abruptly dropped. The temperature depth profile showed time variation possibly including dissipation of the coseismic frictional heat caused by the fault rupturing and the other natural reasons e.g. groundwater flow.
How to cite: Lin, W., Shibutani, S., Kamiya, N., Sado, K., Sugimoto, T., Yamamoto, Y., Yang, X., and Kinoshita, M.: Time variations of the temperature depth profile in a scientific-drilling borehole penetrated through the Futagawa Fault, Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12831, https://doi.org/10.5194/egusphere-egu2020-12831, 2020.
TS5.4 – Seismic and Aseismic Slip on Seismogenic Faults
EGU2020-15091 | Displays | TS5.4
The influence of loading path on fault reactivation: a laboratory perspectiveCarolina Giorgetti and Marie Violay
Despite natural faults are variably oriented to the Earth's surface and to the local stress field, the mechanics of fault reactivation and slip under variable loading paths (sensu Sibson, 1993) is still poorly understood. Nonetheless, different loading paths commonly occur in natural faults, from load-strengthening when the increase in shear stress is coupled with an increase in normal stress (e.g., reverse faults in absence of the fluid pressure increase) to load-weakening when the increase in shear stress is coupled with a decrease in normal stress (e.g., normal faults). According to the Mohr-Coulomb theory, the reactivation of pre-existing faults is only influenced by the fault orientation to the stress field, the fault friction, and the principal stresses magnitude. Therefore, the stress path the fault experienced is often neglected when evaluating the potential for reactivation. Yet, in natural faults characterized by thick, incohesive fault zone and highly fractured damage zone, the loading path could not be ruled out. Here we propose a laboratory approach aimed at reproducing the typical tectonic loading paths for reverse and normal faults. We performed triaxial saw-cut experiments, simulating the reactivation of well-oriented (i.e., 30° to the maximum principal stress) and misoriented (i.e., 50° to the maximum principal stress), normal and reverse gouge-bearing faults under dry and water-saturated conditions. We find that load-strengthening versus load-weakening path results in clearly different hydro-mechanical behavior. Particularly, prior to reactivation, reverse faults undergo compaction even at differential stresses well below the value required for reactivation. Contrarily, normal faults experience dilation, most of which occurs only near the differential stress values required for reactivation. Moreover, when reactivating at comparable normal stress, normal faults (load-weakening path) are more prone to slip seismically than reverse fault (load-strengthening path). Indeed, the higher mean stress that normal fault experienced before reactivation compacts more efficiently the gouge layer, thus increasing the fault stiffness and favoring seismic slip. This contrasting fault zone compaction and dilation prior to reactivation may occur in different natural tectonic settings, affecting the fault hydro-mechanical behavior. Thus, to take into account the loading path the fault experienced is fundamental in evaluating both natural and induced fault reactivation and the related seismic risk assessment.
How to cite: Giorgetti, C. and Violay, M.: The influence of loading path on fault reactivation: a laboratory perspective, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15091, https://doi.org/10.5194/egusphere-egu2020-15091, 2020.
Despite natural faults are variably oriented to the Earth's surface and to the local stress field, the mechanics of fault reactivation and slip under variable loading paths (sensu Sibson, 1993) is still poorly understood. Nonetheless, different loading paths commonly occur in natural faults, from load-strengthening when the increase in shear stress is coupled with an increase in normal stress (e.g., reverse faults in absence of the fluid pressure increase) to load-weakening when the increase in shear stress is coupled with a decrease in normal stress (e.g., normal faults). According to the Mohr-Coulomb theory, the reactivation of pre-existing faults is only influenced by the fault orientation to the stress field, the fault friction, and the principal stresses magnitude. Therefore, the stress path the fault experienced is often neglected when evaluating the potential for reactivation. Yet, in natural faults characterized by thick, incohesive fault zone and highly fractured damage zone, the loading path could not be ruled out. Here we propose a laboratory approach aimed at reproducing the typical tectonic loading paths for reverse and normal faults. We performed triaxial saw-cut experiments, simulating the reactivation of well-oriented (i.e., 30° to the maximum principal stress) and misoriented (i.e., 50° to the maximum principal stress), normal and reverse gouge-bearing faults under dry and water-saturated conditions. We find that load-strengthening versus load-weakening path results in clearly different hydro-mechanical behavior. Particularly, prior to reactivation, reverse faults undergo compaction even at differential stresses well below the value required for reactivation. Contrarily, normal faults experience dilation, most of which occurs only near the differential stress values required for reactivation. Moreover, when reactivating at comparable normal stress, normal faults (load-weakening path) are more prone to slip seismically than reverse fault (load-strengthening path). Indeed, the higher mean stress that normal fault experienced before reactivation compacts more efficiently the gouge layer, thus increasing the fault stiffness and favoring seismic slip. This contrasting fault zone compaction and dilation prior to reactivation may occur in different natural tectonic settings, affecting the fault hydro-mechanical behavior. Thus, to take into account the loading path the fault experienced is fundamental in evaluating both natural and induced fault reactivation and the related seismic risk assessment.
How to cite: Giorgetti, C. and Violay, M.: The influence of loading path on fault reactivation: a laboratory perspective, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15091, https://doi.org/10.5194/egusphere-egu2020-15091, 2020.
EGU2020-9568 | Displays | TS5.4
The role of heterogeneity in fault zone weakening and stabilityJohn Bedford, Daniel Faulkner, and Nadia Lapusta
Heterogeneity is abundant in crustal fault zones from the micron-scale to the plate interface scale. Despite this, it is still uncertain how different scales of heterogeneity interact and influence the mechanical properties of natural faults. Here we present experimental results where heterogeneous faults are simulated in the laboratory by placing patches of different fault gouge materials next to each other in a direct shear arrangement. These laterally heterogeneous experimental faults (50 mm in total length) are then sheared and the frictional strength evolution is measured with increasing displacement. Two types of fault gouge are used: (1) a fine-grained quartz gouge which obeys Byerlee friction (coefficient of friction = 0.6-0.7) and is rate weakening, and (2) a clay gouge comprised predominantly of kaolinite which has a low friction coefficient (approx. 0.25) and is rate strengthening. We find that with the addition of only a small amount of clay gouge the bulk fault strength weakens considerably after only a few millimetres of slip. Although clay is preferentially smeared along localized Y-shear bands, the observed weakening cannot be explained by clay smear as the total displacement on the fault is far too small for the clay to be smeared through the entire length of the quartz patches. Instead we propose stress concentrations at the boundary between clay and quartz patches, driven by slip on the weaker clay patch, produce enhanced weakening and shear at an overall low stress within the quartz patches.
The scale of heterogeneity also controls the frictional stability of the experimental fault. When clay patches are small and comprise <20% of the total fault area, instabilities occur within the unstable quartz gouge leading to stick-slip behaviour. However when patches of clay comprise >20% of the total sliding area, instabilities within the quartz are supressed leading to stable sliding. In this case, the bulk fault also becomes increasingly rate-strengthening with slip, tending towards the behaviour of a fault comprised of 100% clay. These results demonstrate how natural geological heterogeneity and the interplay between different geologic materials can help explain fault weakness and also control the seismogenic potential of tectonic faults.
How to cite: Bedford, J., Faulkner, D., and Lapusta, N.: The role of heterogeneity in fault zone weakening and stability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9568, https://doi.org/10.5194/egusphere-egu2020-9568, 2020.
Heterogeneity is abundant in crustal fault zones from the micron-scale to the plate interface scale. Despite this, it is still uncertain how different scales of heterogeneity interact and influence the mechanical properties of natural faults. Here we present experimental results where heterogeneous faults are simulated in the laboratory by placing patches of different fault gouge materials next to each other in a direct shear arrangement. These laterally heterogeneous experimental faults (50 mm in total length) are then sheared and the frictional strength evolution is measured with increasing displacement. Two types of fault gouge are used: (1) a fine-grained quartz gouge which obeys Byerlee friction (coefficient of friction = 0.6-0.7) and is rate weakening, and (2) a clay gouge comprised predominantly of kaolinite which has a low friction coefficient (approx. 0.25) and is rate strengthening. We find that with the addition of only a small amount of clay gouge the bulk fault strength weakens considerably after only a few millimetres of slip. Although clay is preferentially smeared along localized Y-shear bands, the observed weakening cannot be explained by clay smear as the total displacement on the fault is far too small for the clay to be smeared through the entire length of the quartz patches. Instead we propose stress concentrations at the boundary between clay and quartz patches, driven by slip on the weaker clay patch, produce enhanced weakening and shear at an overall low stress within the quartz patches.
The scale of heterogeneity also controls the frictional stability of the experimental fault. When clay patches are small and comprise <20% of the total fault area, instabilities occur within the unstable quartz gouge leading to stick-slip behaviour. However when patches of clay comprise >20% of the total sliding area, instabilities within the quartz are supressed leading to stable sliding. In this case, the bulk fault also becomes increasingly rate-strengthening with slip, tending towards the behaviour of a fault comprised of 100% clay. These results demonstrate how natural geological heterogeneity and the interplay between different geologic materials can help explain fault weakness and also control the seismogenic potential of tectonic faults.
How to cite: Bedford, J., Faulkner, D., and Lapusta, N.: The role of heterogeneity in fault zone weakening and stability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9568, https://doi.org/10.5194/egusphere-egu2020-9568, 2020.
EGU2020-2761 | Displays | TS5.4 | Highlight
Fault healing plays a key role in creating the spectrum of tectonic faulting styles from seismic to aseismic slipChris Marone
Tectonic faults fail in a broad spectrum of modes ranging from aseismic creep to fast, ordinary, earthquakes modulated by elastodynamic rupture processes. Laboratory friction experiments with repetitive stick-slip failure have reproduced this complete range of modes with failure durations spanning several orders of magnitude. These works show that the frictional weakening rate with slip (i.e., the rheological critical stiffness kc =σn(b-a)/Dc, where σn is effective fault normal stress, Dc is the friction critical slip distance and (b-a) represents the friction rate parameter) is the primary control on the mode of slip, but higher-order effects are also important including variation of kc with slip velocity. Far from the stability boundary, stick-slip occurs when the rate of elastic unloading with slip k is small compared to the frictional weakening rate (i.e., k<<kc). Potential energy, in the form of stored elastic strain, drives rapid fault acceleration. Near the stability boundary, when k ~ kc, lab experiments document slow and quasi-dynamic failure events, consistent with the observation that earthquake stress drop is negligible for slow earthquakes. Lab data show that stick-slip stress drop decreases systematically as k/kc approaches 1 from below. There are two possible scenarios for slow slip near the stability boundary, although they are degenerate in most cases. 1) Fault slip relieves elastic stresses prior to failure and thus the potential energy needed to drive fast rupture is absent. 2) Elastic strain accumulates but the fault rheology is velocity strengthening or otherwise inconsistent with rapid slip, for example because the frictional weakening rate kc is low. In Scenario 1, slip can occur early in the seismic cycle, as creep, or later in the cycle when shear stress reaches a critical value for precursory slip. In either case, slip occurs because the rate of fault healing is low compared to the stressing rate. A low rate of fault healing can also explain Scenario 2 because the friction state evolution parameter b scales directly with the rate of fault healing and kc. Given that the friction parameter a is positive definite, the frictional healing rate (b) sets the scale of kc for a given value of Dc. Thus, while these two scenarios for slow slip appear distinct they both derive from the rate of fault healing. Exceptions would involve faults that are strongly velocity weakening (b-a) >>0 yet have negligible healing rates (b ~ 0), which is indeed rare. The rate of fault healing is expected to vary with mineralogy, effective stress, temperature and other factors. Thus, while we expect a systematic variation of seismic style with depth, associated with changes in kc, we should not be surprised to find a spectrum of faulting styles throughout the lithosphere, including a range of styles at a given location. Discoveries of seismic tremor, low frequency earthquakes, and other modes of fault slip are challenging our views of tectonic faulting and they highlight the need for close connections between field observations, detailed laboratory work and theoretical studies of friction and faulting.
How to cite: Marone, C.: Fault healing plays a key role in creating the spectrum of tectonic faulting styles from seismic to aseismic slip, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2761, https://doi.org/10.5194/egusphere-egu2020-2761, 2020.
Tectonic faults fail in a broad spectrum of modes ranging from aseismic creep to fast, ordinary, earthquakes modulated by elastodynamic rupture processes. Laboratory friction experiments with repetitive stick-slip failure have reproduced this complete range of modes with failure durations spanning several orders of magnitude. These works show that the frictional weakening rate with slip (i.e., the rheological critical stiffness kc =σn(b-a)/Dc, where σn is effective fault normal stress, Dc is the friction critical slip distance and (b-a) represents the friction rate parameter) is the primary control on the mode of slip, but higher-order effects are also important including variation of kc with slip velocity. Far from the stability boundary, stick-slip occurs when the rate of elastic unloading with slip k is small compared to the frictional weakening rate (i.e., k<<kc). Potential energy, in the form of stored elastic strain, drives rapid fault acceleration. Near the stability boundary, when k ~ kc, lab experiments document slow and quasi-dynamic failure events, consistent with the observation that earthquake stress drop is negligible for slow earthquakes. Lab data show that stick-slip stress drop decreases systematically as k/kc approaches 1 from below. There are two possible scenarios for slow slip near the stability boundary, although they are degenerate in most cases. 1) Fault slip relieves elastic stresses prior to failure and thus the potential energy needed to drive fast rupture is absent. 2) Elastic strain accumulates but the fault rheology is velocity strengthening or otherwise inconsistent with rapid slip, for example because the frictional weakening rate kc is low. In Scenario 1, slip can occur early in the seismic cycle, as creep, or later in the cycle when shear stress reaches a critical value for precursory slip. In either case, slip occurs because the rate of fault healing is low compared to the stressing rate. A low rate of fault healing can also explain Scenario 2 because the friction state evolution parameter b scales directly with the rate of fault healing and kc. Given that the friction parameter a is positive definite, the frictional healing rate (b) sets the scale of kc for a given value of Dc. Thus, while these two scenarios for slow slip appear distinct they both derive from the rate of fault healing. Exceptions would involve faults that are strongly velocity weakening (b-a) >>0 yet have negligible healing rates (b ~ 0), which is indeed rare. The rate of fault healing is expected to vary with mineralogy, effective stress, temperature and other factors. Thus, while we expect a systematic variation of seismic style with depth, associated with changes in kc, we should not be surprised to find a spectrum of faulting styles throughout the lithosphere, including a range of styles at a given location. Discoveries of seismic tremor, low frequency earthquakes, and other modes of fault slip are challenging our views of tectonic faulting and they highlight the need for close connections between field observations, detailed laboratory work and theoretical studies of friction and faulting.
How to cite: Marone, C.: Fault healing plays a key role in creating the spectrum of tectonic faulting styles from seismic to aseismic slip, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2761, https://doi.org/10.5194/egusphere-egu2020-2761, 2020.
EGU2020-15224 | Displays | TS5.4
Complexity of low-frequency earthquakes activity in western ShikokuNatalia Poiata, Jean-Pierre Vilotte, Nikolai Shapiro, Mariano Supino, and Kazushige Obara
Short-duration transient seismic events known as low-frequency earthquakes (LFEs) are a component of the slow earthquakes family observed in the transition zone, at the root of seismogenic regions of the subduction zones or active faults. LFEs are the signature of impulse seismic energy radiation associated to and often mixed within complex tectonic tremor signal. Detailed analysis and characterization of LFE space-time activity in relation to other slow earthquake phenomena can provide important information about the state and the processes of fault interface.
We derive a catalog of LFEs in western Shikoku (Japan) by applying a full waveform coherency-based detection and location method to the 4-year continuous data covering the period of 2013-2016 and recorded at Hi-net seismic stations of NIED. The obtained catalog of over 150,000 detected events allows looking into the details of LFE space-time activity during the tectonic tremor sequences and inter-sequence periods.
We use this catalogue of LFEs to perform a systematic statistical analysis of the event occurrence patterns by applying correlation and clustering analysis to infer the large-scale (long temporal ~ 1-2 day duration) space-time characteristics and interaction patterns of activity and its potential relation to the structural complexity of the subducting plate. We also analyze the correlation between the migration of clustered LFE activity during energetic tremor sequences and short-term slow slip events occurring in the area during the analyzed period.
How to cite: Poiata, N., Vilotte, J.-P., Shapiro, N., Supino, M., and Obara, K.: Complexity of low-frequency earthquakes activity in western Shikoku, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15224, https://doi.org/10.5194/egusphere-egu2020-15224, 2020.
Short-duration transient seismic events known as low-frequency earthquakes (LFEs) are a component of the slow earthquakes family observed in the transition zone, at the root of seismogenic regions of the subduction zones or active faults. LFEs are the signature of impulse seismic energy radiation associated to and often mixed within complex tectonic tremor signal. Detailed analysis and characterization of LFE space-time activity in relation to other slow earthquake phenomena can provide important information about the state and the processes of fault interface.
We derive a catalog of LFEs in western Shikoku (Japan) by applying a full waveform coherency-based detection and location method to the 4-year continuous data covering the period of 2013-2016 and recorded at Hi-net seismic stations of NIED. The obtained catalog of over 150,000 detected events allows looking into the details of LFE space-time activity during the tectonic tremor sequences and inter-sequence periods.
We use this catalogue of LFEs to perform a systematic statistical analysis of the event occurrence patterns by applying correlation and clustering analysis to infer the large-scale (long temporal ~ 1-2 day duration) space-time characteristics and interaction patterns of activity and its potential relation to the structural complexity of the subducting plate. We also analyze the correlation between the migration of clustered LFE activity during energetic tremor sequences and short-term slow slip events occurring in the area during the analyzed period.
How to cite: Poiata, N., Vilotte, J.-P., Shapiro, N., Supino, M., and Obara, K.: Complexity of low-frequency earthquakes activity in western Shikoku, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15224, https://doi.org/10.5194/egusphere-egu2020-15224, 2020.
EGU2020-19639 | Displays | TS5.4 | Highlight
Towards Slow Earthquakes ForecastingAdriano Gualandi, Jean-Philippe Avouac, Sylvain Michel, and Davide Faranda
Slow Slip Events (SSEs) are episodic slip events that play a significant role in the moment budget along subduction megathrust. They share many similarities with regular earthquakes, and have been observed in major subduction regions like, for example, Cascadia, Japan, Mexico, New Zealand. They show striking regularity, suggesting that it might be possible to forecast their size and timing, but the prediction of their extension and exact timing is still yet to come. They certainly are a great natural system to study how friction works at scale of the order of hundreds or thousands of km, and their recurrence time being much shorter than that of regular earthquakes, they give us the possibility to study multiple cycles and test their predictability.
Here we focus on the Cascadia region, where SSEs recur every about 1 or 2 years, depending on the latitude. The study of GPS position time series during the time span ranging from 2007 to 2017 has revealed a low-dimensional (< 5) non-linear chaotic dynamics with a predictable horizon (calculated as the inverse of the metric entropy) in the order of days to months for causally filtered data. It is notable that the increase of instantaneous dimensionality of the attractor seems to constitute a reliable precursor of the large SSEs. The causal filter adopted to reach this conclusion introduces a group delay larger than the predictability horizon time, meaning that this approach cannot be used for real-time forecasting. We thus test alternative filters and data driven approaches (e.g., dynamic mode decomposition) for real-time characterization of the attractor’s properties and evolution. In any case, we conclude that SSEs in Cascadia can be described as a deterministic, albeit chaotic, system rather than as a random process. As SSEs might be regarded as earthquakes in slow motion, regular earthquakes might be similarly chaotic and predictable for short amount of times. If the relation between predictability horizon and the duration of the instability (i.e., slipping event duration) holds also for regular earthquakes, this would imply that earthquakes long-term predictions are intrinsically impossible, and the predictable horizon would be only a fraction of the regular earthquakes typical duration (10-100 s for M>6 earthquakes).
How to cite: Gualandi, A., Avouac, J.-P., Michel, S., and Faranda, D.: Towards Slow Earthquakes Forecasting, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19639, https://doi.org/10.5194/egusphere-egu2020-19639, 2020.
Slow Slip Events (SSEs) are episodic slip events that play a significant role in the moment budget along subduction megathrust. They share many similarities with regular earthquakes, and have been observed in major subduction regions like, for example, Cascadia, Japan, Mexico, New Zealand. They show striking regularity, suggesting that it might be possible to forecast their size and timing, but the prediction of their extension and exact timing is still yet to come. They certainly are a great natural system to study how friction works at scale of the order of hundreds or thousands of km, and their recurrence time being much shorter than that of regular earthquakes, they give us the possibility to study multiple cycles and test their predictability.
Here we focus on the Cascadia region, where SSEs recur every about 1 or 2 years, depending on the latitude. The study of GPS position time series during the time span ranging from 2007 to 2017 has revealed a low-dimensional (< 5) non-linear chaotic dynamics with a predictable horizon (calculated as the inverse of the metric entropy) in the order of days to months for causally filtered data. It is notable that the increase of instantaneous dimensionality of the attractor seems to constitute a reliable precursor of the large SSEs. The causal filter adopted to reach this conclusion introduces a group delay larger than the predictability horizon time, meaning that this approach cannot be used for real-time forecasting. We thus test alternative filters and data driven approaches (e.g., dynamic mode decomposition) for real-time characterization of the attractor’s properties and evolution. In any case, we conclude that SSEs in Cascadia can be described as a deterministic, albeit chaotic, system rather than as a random process. As SSEs might be regarded as earthquakes in slow motion, regular earthquakes might be similarly chaotic and predictable for short amount of times. If the relation between predictability horizon and the duration of the instability (i.e., slipping event duration) holds also for regular earthquakes, this would imply that earthquakes long-term predictions are intrinsically impossible, and the predictable horizon would be only a fraction of the regular earthquakes typical duration (10-100 s for M>6 earthquakes).
How to cite: Gualandi, A., Avouac, J.-P., Michel, S., and Faranda, D.: Towards Slow Earthquakes Forecasting, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19639, https://doi.org/10.5194/egusphere-egu2020-19639, 2020.
EGU2020-3556 | Displays | TS5.4
Analysis of the foreshock sequences preceding two moderate (Mw4.7 and Mw5.8) earthquakes in the Sea of Marmara offshore Istanbul, Turkey.Virginie Durand, Stephan Bentz, Grzegorz Kwiatek, Georg Dresen, Christopher Wollin, Oliver Heidbach, Patricia Martinez-Garzon, Fabrice Cotton, Murat Nurlu, and Marco Bohnhoff
In September 2019 a sequence of two moderate earthquakes (Mw4.7 and Mw5.8) occurred in the central Sea of Marmara (Turkey), SW of Istanbul. These events took place ate the transition between a creeping and a locked segment of the North Anatolian Fault. To investigate in detail the spatiotemporal evolution of the seismicity, we apply a matched-filter technique to continuous waveforms, thus reducing the magnitude threshold for detection. Sequences of foreshocks preceding the two mainshocks are clearly seen, exhibiting different behaviors: a migration of the seismicity along the entire fault segment on the long-term (several days before the mainshocks) and a concentration around the epicenters of the large events on the short-term (during the few hours preceding the mainshocks). We infer that both seismic and aseismic slip during the foreshock sequences change the stress state on the fault, bringing it closer to failure. Our observations also suggest that the Mw 4.7 event contributed to weaken the fault as part of the preparation process of the Mw 5.8 earthquake.
How to cite: Durand, V., Bentz, S., Kwiatek, G., Dresen, G., Wollin, C., Heidbach, O., Martinez-Garzon, P., Cotton, F., Nurlu, M., and Bohnhoff, M.: Analysis of the foreshock sequences preceding two moderate (Mw4.7 and Mw5.8) earthquakes in the Sea of Marmara offshore Istanbul, Turkey., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3556, https://doi.org/10.5194/egusphere-egu2020-3556, 2020.
In September 2019 a sequence of two moderate earthquakes (Mw4.7 and Mw5.8) occurred in the central Sea of Marmara (Turkey), SW of Istanbul. These events took place ate the transition between a creeping and a locked segment of the North Anatolian Fault. To investigate in detail the spatiotemporal evolution of the seismicity, we apply a matched-filter technique to continuous waveforms, thus reducing the magnitude threshold for detection. Sequences of foreshocks preceding the two mainshocks are clearly seen, exhibiting different behaviors: a migration of the seismicity along the entire fault segment on the long-term (several days before the mainshocks) and a concentration around the epicenters of the large events on the short-term (during the few hours preceding the mainshocks). We infer that both seismic and aseismic slip during the foreshock sequences change the stress state on the fault, bringing it closer to failure. Our observations also suggest that the Mw 4.7 event contributed to weaken the fault as part of the preparation process of the Mw 5.8 earthquake.
How to cite: Durand, V., Bentz, S., Kwiatek, G., Dresen, G., Wollin, C., Heidbach, O., Martinez-Garzon, P., Cotton, F., Nurlu, M., and Bohnhoff, M.: Analysis of the foreshock sequences preceding two moderate (Mw4.7 and Mw5.8) earthquakes in the Sea of Marmara offshore Istanbul, Turkey., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3556, https://doi.org/10.5194/egusphere-egu2020-3556, 2020.
EGU2020-18295 | Displays | TS5.4 | Highlight
The November 11 2019 Le Teil, France M5 earthquake: a triggered event in nuclear countryJean-Paul Ampuero, Jérémy Billant, Florent Brenguier, Olivier Cavalié, Francoise Courboulex, Anne Deschamps, Bertrand Delouis, Raphaël Grandin, Romain Jolivet, Chao Liang, Aurélien Mordret, and Elif Oral
An earthquake of magnitude 5 (Mw 4.9) occurred near the town of Le Teil, France on November 11 2019, causing damage locally and concern due to its proximity to nuclear facilities. Despite its moderate magnitude, this earthquake offers unique opportunities to advance basic and applied research on earthquakes in general, including our understanding of the largest and most destructive earthquakes and induced seismicity. We present here an overview of the source characteristics of this event and, based on analysis of InSAR and seismological observations and optical images, we discuss its potential relation to human activity. We also discuss the emerging unique research opportunities.
The Le Teil earthquake occurred in a low seismicity region, a moderate hazard zone that has nevertheless experienced damaging earthquakes in the past. Its hypocentral depth is particularly shallow, less than 1.5 km. Radar images delineate the surface rupture and constrain well the coseismic slip distribution. The surface rupture corresponds to the previously mapped La Rouvière fault, an ancient normal fault reactivated as reverse-faulting by the Le Teil earthquake. Slip is predominantly confined in the top ~1 km and extends along ~4.5 km along-strike with two main slip asperities and stress drop of a few MPa. A large cement quarry sits on top of the deep edge of the rupture area, ~1 km above the fault. Based on optical images we estimate the distribution of mass extracted from the nearby quarry since 1947. We then compute the induced Coulomb stresses on the fault: they are favorable for reverse faulting and reach about 150 kPa, within the range of stresses that have been previously reported to trigger earthquakes, but substantially smaller than the coseismic stress drop. Analysis of the mainshock and quarry blast signals on the nearest stations (8.5 to 45 km distance) places the mainshock epicenter within the area of influence of the quarry-induced stresses.
These analyses so far indicate that the Le Teil event is likely a triggered earthquake: its initiation was favored by the quarry-induced stresses, but the bulk of its rupture propagation was enabled by naturally pre-existing stresses. We also report on directivity analyses based on various data subsets, which remain to be reconciled, possibly pointing to a non-trivial rupture path.
The characteristics of the Le Teil earthquake bear on important questions: how can earthquakes nucleate at such shallow depth? what confines slip at such shallow depth? do structural features control the patchy distribution of slip? how do elongated ruptures stop? It also offers a unique opportunity to study directly, by drilling at seismogenic depth, the three key spots of an earthquake: its hypocenter, its large slip area and its arrest area. The high aspect ratio of the rupture, comparable to that of the largest earthquakes, opens a window into the physics of very large earthquakes. Continued research would also address implications for seismic hazard in low-seismicity areas, including the safety of nearby nuclear power plants, especially by monitoring the unbroken sections of the fault system.
How to cite: Ampuero, J.-P., Billant, J., Brenguier, F., Cavalié, O., Courboulex, F., Deschamps, A., Delouis, B., Grandin, R., Jolivet, R., Liang, C., Mordret, A., and Oral, E.: The November 11 2019 Le Teil, France M5 earthquake: a triggered event in nuclear country, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18295, https://doi.org/10.5194/egusphere-egu2020-18295, 2020.
An earthquake of magnitude 5 (Mw 4.9) occurred near the town of Le Teil, France on November 11 2019, causing damage locally and concern due to its proximity to nuclear facilities. Despite its moderate magnitude, this earthquake offers unique opportunities to advance basic and applied research on earthquakes in general, including our understanding of the largest and most destructive earthquakes and induced seismicity. We present here an overview of the source characteristics of this event and, based on analysis of InSAR and seismological observations and optical images, we discuss its potential relation to human activity. We also discuss the emerging unique research opportunities.
The Le Teil earthquake occurred in a low seismicity region, a moderate hazard zone that has nevertheless experienced damaging earthquakes in the past. Its hypocentral depth is particularly shallow, less than 1.5 km. Radar images delineate the surface rupture and constrain well the coseismic slip distribution. The surface rupture corresponds to the previously mapped La Rouvière fault, an ancient normal fault reactivated as reverse-faulting by the Le Teil earthquake. Slip is predominantly confined in the top ~1 km and extends along ~4.5 km along-strike with two main slip asperities and stress drop of a few MPa. A large cement quarry sits on top of the deep edge of the rupture area, ~1 km above the fault. Based on optical images we estimate the distribution of mass extracted from the nearby quarry since 1947. We then compute the induced Coulomb stresses on the fault: they are favorable for reverse faulting and reach about 150 kPa, within the range of stresses that have been previously reported to trigger earthquakes, but substantially smaller than the coseismic stress drop. Analysis of the mainshock and quarry blast signals on the nearest stations (8.5 to 45 km distance) places the mainshock epicenter within the area of influence of the quarry-induced stresses.
These analyses so far indicate that the Le Teil event is likely a triggered earthquake: its initiation was favored by the quarry-induced stresses, but the bulk of its rupture propagation was enabled by naturally pre-existing stresses. We also report on directivity analyses based on various data subsets, which remain to be reconciled, possibly pointing to a non-trivial rupture path.
The characteristics of the Le Teil earthquake bear on important questions: how can earthquakes nucleate at such shallow depth? what confines slip at such shallow depth? do structural features control the patchy distribution of slip? how do elongated ruptures stop? It also offers a unique opportunity to study directly, by drilling at seismogenic depth, the three key spots of an earthquake: its hypocenter, its large slip area and its arrest area. The high aspect ratio of the rupture, comparable to that of the largest earthquakes, opens a window into the physics of very large earthquakes. Continued research would also address implications for seismic hazard in low-seismicity areas, including the safety of nearby nuclear power plants, especially by monitoring the unbroken sections of the fault system.
How to cite: Ampuero, J.-P., Billant, J., Brenguier, F., Cavalié, O., Courboulex, F., Deschamps, A., Delouis, B., Grandin, R., Jolivet, R., Liang, C., Mordret, A., and Oral, E.: The November 11 2019 Le Teil, France M5 earthquake: a triggered event in nuclear country, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18295, https://doi.org/10.5194/egusphere-egu2020-18295, 2020.
EGU2020-215 | Displays | TS5.4
From Corinth gulf extension to Ionian subduction/collision (W. Greece): micro-seismicity survey to constrain local tectonics and regional geodynamicsValentine Lefils, Alexis Rigo, and Efthimios Sokos
The North-Eastern zone of the Gulf of Corinth in Greece is characterized by the rotation of a micro-plate in formation. The Island Akarnanian Block (IAB) have been progressively individualized since the Pleistocene (less than ~ 1.5 My ago). This micro-plate is the result of a larger-scale tectonic context with, on one side the N-S extension of the Gulf of Corinth to the East, and on the other side the Hellenic subduction to the South and the Apulian collision to the West. To the Northeast, the IAB micro-plate is bounded by a large North-South sinistral strike-slip fault system, the Katouna-Stamna Fault (KSF) and by several normal faults. To the North, normal faults reach the limit between Apulian and Eurasian plates and to the East, they form the East-West graben of Trichonis lake.
Although the structures and dynamics behind the Gulf of Corinth extension are today relatively known, nevertheless, the set of faults linking the Gulf of Corinth to the Western subduction structures remain poorly studied. The seismicity recorded by the Greek national network shows discrepancies regarding to the faults mapped on the surface.
At the end of 2015, a new micro-seismicity campaign started with the deployment of a temporary seismological network in an area ranging from the Gulf of Patras to the Amvrakikos Gulf toward the North. This network includes 17 seismic stations, recording continuously, added to the permanent stations of the Corinth Rift Laboratory (CRL) and of the Hellenic Unified Seismic Network (HUSN).
The analysis of the seismological records is still in process for the 2016 and 2017 years. Our study consists first in picking the P- and S- waves, and then to precisely localize the seismic events recorded by our temporary seismological network combined with the permanent ones. We will present here the event location map obtained for the 2016-2017 period, a new seismic velocity model, and focal mechanisms. The seismic activity including thousands of events, is characterized by the presence of numerous clusters of few days to few weeks duration. The clusters are analysed in detail by relative relocations in order to appraise their physical processes and their implications in the fault activity. We will discuss the deformation mode of the region and build a seismotectonic model consistent with the regional geodynamics and observations.
How to cite: Lefils, V., Rigo, A., and Sokos, E.: From Corinth gulf extension to Ionian subduction/collision (W. Greece): micro-seismicity survey to constrain local tectonics and regional geodynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-215, https://doi.org/10.5194/egusphere-egu2020-215, 2020.
The North-Eastern zone of the Gulf of Corinth in Greece is characterized by the rotation of a micro-plate in formation. The Island Akarnanian Block (IAB) have been progressively individualized since the Pleistocene (less than ~ 1.5 My ago). This micro-plate is the result of a larger-scale tectonic context with, on one side the N-S extension of the Gulf of Corinth to the East, and on the other side the Hellenic subduction to the South and the Apulian collision to the West. To the Northeast, the IAB micro-plate is bounded by a large North-South sinistral strike-slip fault system, the Katouna-Stamna Fault (KSF) and by several normal faults. To the North, normal faults reach the limit between Apulian and Eurasian plates and to the East, they form the East-West graben of Trichonis lake.
Although the structures and dynamics behind the Gulf of Corinth extension are today relatively known, nevertheless, the set of faults linking the Gulf of Corinth to the Western subduction structures remain poorly studied. The seismicity recorded by the Greek national network shows discrepancies regarding to the faults mapped on the surface.
At the end of 2015, a new micro-seismicity campaign started with the deployment of a temporary seismological network in an area ranging from the Gulf of Patras to the Amvrakikos Gulf toward the North. This network includes 17 seismic stations, recording continuously, added to the permanent stations of the Corinth Rift Laboratory (CRL) and of the Hellenic Unified Seismic Network (HUSN).
The analysis of the seismological records is still in process for the 2016 and 2017 years. Our study consists first in picking the P- and S- waves, and then to precisely localize the seismic events recorded by our temporary seismological network combined with the permanent ones. We will present here the event location map obtained for the 2016-2017 period, a new seismic velocity model, and focal mechanisms. The seismic activity including thousands of events, is characterized by the presence of numerous clusters of few days to few weeks duration. The clusters are analysed in detail by relative relocations in order to appraise their physical processes and their implications in the fault activity. We will discuss the deformation mode of the region and build a seismotectonic model consistent with the regional geodynamics and observations.
How to cite: Lefils, V., Rigo, A., and Sokos, E.: From Corinth gulf extension to Ionian subduction/collision (W. Greece): micro-seismicity survey to constrain local tectonics and regional geodynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-215, https://doi.org/10.5194/egusphere-egu2020-215, 2020.
EGU2020-230 | Displays | TS5.4
Mixed-Mode Seismic Slip and Aseismic Creep on a Highly Active Low-Angle Normal Fault System in Papua New GuineaJames Biemiller, Laura Wallace, and Luc Lavier
Whether low-angle normal faults (LANFs; dip < 30°) slip in large earthquakes or creep aseismically is a longstanding problem in fault mechanics. Although abundant in the geologic record, active examples of these enigmatic ‘misoriented’ structures are rare and extension rates across them are typically less than a few mm/yr. As such, geodetic and seismological observations of LANFs are sparse and can be difficult to interpret in terms of earthquake cycles. With a long-term slip rate of ~1 cm/yr, the Mai’iu fault in Papua New Guinea may be the world’s most active LANF and thus offers an outstanding natural laboratory to evaluate seismic vs. aseismic behavior of LANFs. Here, we use new results from a campaign GPS network to determine the degree of locking vs. aseismic creep on the Mai’iu fault and evaluate these results in the context of geological evidence for mixed seismic and aseismic slip in exhumed Mai’iu fault rocks.
We derive velocities from GPS measurements with 3-4 km station spacing above the shallowest portions of the fault, which dips 21-25° at the surface. Dislocation modeling of these velocities is consistent with 6-8 mm/yr of horizontal extension, corresponding to ~1 cm/yr dip-slip rates on a 27-35°-dipping fault. Strain rates and vertical derivatives of horizontal stress rates derived from these velocities confirm localized extension across the fault. We compare and evaluate two interseismic locking models that fit the data best: one in which the fault deforms by shallow near-surface creep updip of a deeper zone of increased interseismic coupling which soles into a steadily creeping shear zone at depth, and one in which the fault creeps steadily downdip of a shallowly locked patch. These results combined with field and microstructural evidence from the exhumed fault rocks suggest that the fault slips by a mixture of brittle frictional (seismic slip, fracturing, and cataclastic creep) and viscous (stress-driven dissolution-precipitation creep, or pressure solution) processes. Using depth-constrained mechanical properties and stress conditions inferred from exhumed fault rocks, we model the time-dependent competition between frictional slip and viscous creep to assess where and how elastic strain accumulates along the Mai’iu fault, and whether the fault is capable of hosting or nucleating earthquakes.
How to cite: Biemiller, J., Wallace, L., and Lavier, L.: Mixed-Mode Seismic Slip and Aseismic Creep on a Highly Active Low-Angle Normal Fault System in Papua New Guinea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-230, https://doi.org/10.5194/egusphere-egu2020-230, 2020.
Whether low-angle normal faults (LANFs; dip < 30°) slip in large earthquakes or creep aseismically is a longstanding problem in fault mechanics. Although abundant in the geologic record, active examples of these enigmatic ‘misoriented’ structures are rare and extension rates across them are typically less than a few mm/yr. As such, geodetic and seismological observations of LANFs are sparse and can be difficult to interpret in terms of earthquake cycles. With a long-term slip rate of ~1 cm/yr, the Mai’iu fault in Papua New Guinea may be the world’s most active LANF and thus offers an outstanding natural laboratory to evaluate seismic vs. aseismic behavior of LANFs. Here, we use new results from a campaign GPS network to determine the degree of locking vs. aseismic creep on the Mai’iu fault and evaluate these results in the context of geological evidence for mixed seismic and aseismic slip in exhumed Mai’iu fault rocks.
We derive velocities from GPS measurements with 3-4 km station spacing above the shallowest portions of the fault, which dips 21-25° at the surface. Dislocation modeling of these velocities is consistent with 6-8 mm/yr of horizontal extension, corresponding to ~1 cm/yr dip-slip rates on a 27-35°-dipping fault. Strain rates and vertical derivatives of horizontal stress rates derived from these velocities confirm localized extension across the fault. We compare and evaluate two interseismic locking models that fit the data best: one in which the fault deforms by shallow near-surface creep updip of a deeper zone of increased interseismic coupling which soles into a steadily creeping shear zone at depth, and one in which the fault creeps steadily downdip of a shallowly locked patch. These results combined with field and microstructural evidence from the exhumed fault rocks suggest that the fault slips by a mixture of brittle frictional (seismic slip, fracturing, and cataclastic creep) and viscous (stress-driven dissolution-precipitation creep, or pressure solution) processes. Using depth-constrained mechanical properties and stress conditions inferred from exhumed fault rocks, we model the time-dependent competition between frictional slip and viscous creep to assess where and how elastic strain accumulates along the Mai’iu fault, and whether the fault is capable of hosting or nucleating earthquakes.
How to cite: Biemiller, J., Wallace, L., and Lavier, L.: Mixed-Mode Seismic Slip and Aseismic Creep on a Highly Active Low-Angle Normal Fault System in Papua New Guinea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-230, https://doi.org/10.5194/egusphere-egu2020-230, 2020.
EGU2020-232 | Displays | TS5.4
2017-2019 SSE sequence and its interaction with large earthquakes in MexicoEkaterina Kazachkina, Mathilde Radiguet, Nathalie Cotte, Jorge Jara, Andrea Walpersdorf, and Vladimir Kostoglodov
An intriguing sequence of a 2-stage SSE in Guerrero and a simultaneous SSE in Oaxaca took place in Mexico in 2017-2019. Three large earthquakes occur during these SSEs adding complexity to the observed surface deformations. The objective of this work is to explain the interaction between the overlapping seismic and aseismic events through the analysis of continuous GPS observations.
We perform kinematic inversion of the GPS time series solving for the cumulative slip distribution on the subduction interface due to two SSEs, using Independent Component Analysis Inversion Method (ICAIM, Gualandi, 2015). The daily position time series for 2017-2019 are obtained by processing continuous data using GAMIT/GLOBK 10.7 (Herring et al, 2018). Strong postseismic signals generated by the following earthquakes 08/09/2017 Mw8.2 in Tehuantepec, 19/09/2017 Mw7.1 in Puebla-Morelos and 16/02/2018 Mw7.2 in Pinotepa are removed using the ICA decomposition.
Our results show complex slip evolution on the subduction interface. We observe a clear change of cumulative seismic moment release rate after large seismic events of 2017 and after the earthquake in Pinotepa in 2018. The occurrence of Mw8.2 and Mw7.1 events notably slowed down the slip propagation of the Guerrero SSE. Continuous SSE in Oaxaca propagates from the northeast near the city of Oaxaca (-97.00°E, 16.70°N) towards the southwest approaching Pinotepa (-98.00°E, 17.00°N). Guerrero SSE migrates from the origin of its 1st phase near Tecpan (-100.50°E, 17.50°N) southeastwards to Acapulco (-99.50°E, 17.20°N) where the 2nd stage develops. Therefore the stress changes induced by the two aseismic events likely triggered the Mw7.2 Pinotepa earthquake (-98.01°E, 16.22°N).
How to cite: Kazachkina, E., Radiguet, M., Cotte, N., Jara, J., Walpersdorf, A., and Kostoglodov, V.: 2017-2019 SSE sequence and its interaction with large earthquakes in Mexico, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-232, https://doi.org/10.5194/egusphere-egu2020-232, 2020.
An intriguing sequence of a 2-stage SSE in Guerrero and a simultaneous SSE in Oaxaca took place in Mexico in 2017-2019. Three large earthquakes occur during these SSEs adding complexity to the observed surface deformations. The objective of this work is to explain the interaction between the overlapping seismic and aseismic events through the analysis of continuous GPS observations.
We perform kinematic inversion of the GPS time series solving for the cumulative slip distribution on the subduction interface due to two SSEs, using Independent Component Analysis Inversion Method (ICAIM, Gualandi, 2015). The daily position time series for 2017-2019 are obtained by processing continuous data using GAMIT/GLOBK 10.7 (Herring et al, 2018). Strong postseismic signals generated by the following earthquakes 08/09/2017 Mw8.2 in Tehuantepec, 19/09/2017 Mw7.1 in Puebla-Morelos and 16/02/2018 Mw7.2 in Pinotepa are removed using the ICA decomposition.
Our results show complex slip evolution on the subduction interface. We observe a clear change of cumulative seismic moment release rate after large seismic events of 2017 and after the earthquake in Pinotepa in 2018. The occurrence of Mw8.2 and Mw7.1 events notably slowed down the slip propagation of the Guerrero SSE. Continuous SSE in Oaxaca propagates from the northeast near the city of Oaxaca (-97.00°E, 16.70°N) towards the southwest approaching Pinotepa (-98.00°E, 17.00°N). Guerrero SSE migrates from the origin of its 1st phase near Tecpan (-100.50°E, 17.50°N) southeastwards to Acapulco (-99.50°E, 17.20°N) where the 2nd stage develops. Therefore the stress changes induced by the two aseismic events likely triggered the Mw7.2 Pinotepa earthquake (-98.01°E, 16.22°N).
How to cite: Kazachkina, E., Radiguet, M., Cotte, N., Jara, J., Walpersdorf, A., and Kostoglodov, V.: 2017-2019 SSE sequence and its interaction with large earthquakes in Mexico, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-232, https://doi.org/10.5194/egusphere-egu2020-232, 2020.
EGU2020-2770 | Displays | TS5.4
Role of the creeping segment in the synchronization of earthquake cycles on oceanic transform faults revealed by numerical simulations in the framework of rate-and-state frictionMeng Wei and Pengcheng Shi
Synchronization behavior of large earthquakes, rupture of nearby faults close in time for many cycles, has been reported in many fault systems. The general idea is that the faults in the system have similar repeating interval and are positively coupled through stress interaction. However, many details of such synchronization remain unknown. Here, we built numerical models in the framework of rate-and-state friction to simulate earthquake cycles on the west Gofar fault, an oceanic transform fault in the East Pacific Rise. Our model is consisted of two seismic segments, separated by a creeping segment, for which the size and location is constrained by seismic data. The parameters in the seismic segments were set to reproduce M6 earthquakes every 5 years, to be consistent with observation. We varied the parameters in the creeping segment to understand its role on earthquake synchronization. We found that the width and the strength of the creeping segment will determine the synchronization of earthquake cycles on the two seismic segments. When the creeping segment is relatively narrow or weak, the system will become synchronized quickly and the synchronization remains for many cycles. When it is relatively wide or strong, the earthquake cycles on the two segments are not related but could be synchronized by chance. In both cases, earthquakes tend to rupture the entire seismic segment. Between these two end-member situations, the system fluctuated between synchronization and non-synchronization on the time scale of 5-10 cycles. The switch always happens when the partial rupture of the seismic segment occurs, resulting in moderate size earthquakes (M4-5) and earthquake cycle shift, which is likely caused by stress interaction through the creeping segment. Here, we conclude that the co-seismic slip and aseismic after slip in the creeping segment could promote the synchronization of earthquake cycles on oceanic transform faults, and likely in other tectonic systems. In addition, the average seismic ratio of the entire fault can be quite low, ranging between 0.2-0.4 because of the barrier segment. We suggest that the existence of creep segments contributed significantly to the well-observed low seismic ratio on oceanic transform faults.
How to cite: Wei, M. and Shi, P.: Role of the creeping segment in the synchronization of earthquake cycles on oceanic transform faults revealed by numerical simulations in the framework of rate-and-state friction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2770, https://doi.org/10.5194/egusphere-egu2020-2770, 2020.
Synchronization behavior of large earthquakes, rupture of nearby faults close in time for many cycles, has been reported in many fault systems. The general idea is that the faults in the system have similar repeating interval and are positively coupled through stress interaction. However, many details of such synchronization remain unknown. Here, we built numerical models in the framework of rate-and-state friction to simulate earthquake cycles on the west Gofar fault, an oceanic transform fault in the East Pacific Rise. Our model is consisted of two seismic segments, separated by a creeping segment, for which the size and location is constrained by seismic data. The parameters in the seismic segments were set to reproduce M6 earthquakes every 5 years, to be consistent with observation. We varied the parameters in the creeping segment to understand its role on earthquake synchronization. We found that the width and the strength of the creeping segment will determine the synchronization of earthquake cycles on the two seismic segments. When the creeping segment is relatively narrow or weak, the system will become synchronized quickly and the synchronization remains for many cycles. When it is relatively wide or strong, the earthquake cycles on the two segments are not related but could be synchronized by chance. In both cases, earthquakes tend to rupture the entire seismic segment. Between these two end-member situations, the system fluctuated between synchronization and non-synchronization on the time scale of 5-10 cycles. The switch always happens when the partial rupture of the seismic segment occurs, resulting in moderate size earthquakes (M4-5) and earthquake cycle shift, which is likely caused by stress interaction through the creeping segment. Here, we conclude that the co-seismic slip and aseismic after slip in the creeping segment could promote the synchronization of earthquake cycles on oceanic transform faults, and likely in other tectonic systems. In addition, the average seismic ratio of the entire fault can be quite low, ranging between 0.2-0.4 because of the barrier segment. We suggest that the existence of creep segments contributed significantly to the well-observed low seismic ratio on oceanic transform faults.
How to cite: Wei, M. and Shi, P.: Role of the creeping segment in the synchronization of earthquake cycles on oceanic transform faults revealed by numerical simulations in the framework of rate-and-state friction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2770, https://doi.org/10.5194/egusphere-egu2020-2770, 2020.
EGU2020-3296 | Displays | TS5.4
Imaging fine seismic structures of faults with fault-zone trapped wavesHui Su and Yuanze Zhou
A fault is a low-velocity zone with widely distributed scatterers compared to the surrounding uniform materials because of the highly damaged rocks in its core. When seismic waves travel through faults, they will reflect on boundaries multiply and be trapped in the fault zones which cause the energy redistribution and generate coda waves with complicated characteristics after the direct P- and S- waves. The coda is named fault-zone trapped waves (FZTWs) (Li et al., 1990). The amplitude and duration characteristics of FZTWs (Li et al., 2016) can be used to constrain the geometric features of the fault and the physical parameters of the scatterers, so the fine structure of the fault can be finally obtained. We observed some FZTWs at several Hi-net stations in Japan, which were generated by low magnitude aftershocks following large earthquakes. Relatively strong FZTWs can be recorded by the seismic stations near or on the fault where the events happened. In this study, we simulate the theoretic envelops of FZTWs with radiative transport theory (Sanborn et al., 2017) for possible velocity models with scatterers described with von Karman distribution (Sato et al., 2012). While the theoretical envelops of FZTWs fit the observed ones well, the fine fault model is determined. The FZTWs from different events before and after the main shock can be used to determine the physical properties of faults and their adjoint area varied in the seismogenic process, then we can deeply understand the fault evolutions before and after earthquakes. The varying properties of faults can provide a new perspective for earthquake preparation and a new reference for earthquake prediction and promotes the development of earthquake prediction.
Li, Y. G., R. D. Catchings, and M. R. Goldman. 2016, Subsurface Fault Damage Zone of the 2014Mw 6.0 South Napa, California, Earthquake Viewed from Fault‐Zone Trapped Waves. Bulletin of the Seismological Society of America, 106, no. 6,2747-2763. doi: 10.1785/0120160039.
Li, Y. G., P. Leary, K. Aki, and P. Malin. 1990, Seismic Trapped Modes in the Oroville and San-Andreas Fault Zones. Science, 249, no. 4970,763-766. doi: 10.1126/science.249.4970.763.
Sanborn, C. J., V. F. Cormier, and M. Fitzpatrick. 2017, Combined Effects of Deterministic and Statistical Structure on High-frequency Regional Seismograms. Geophysical Journal International, 210, no. 2,1143-1159. doi: 10.1093/gji/ggx219.
Sato H., Fehler M.C. 2012, Seismic Wave Propagation and Scattering in the Heterogeneous Earth, 2nd edn, Springer-Verlag.
How to cite: Su, H. and Zhou, Y.: Imaging fine seismic structures of faults with fault-zone trapped waves, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3296, https://doi.org/10.5194/egusphere-egu2020-3296, 2020.
A fault is a low-velocity zone with widely distributed scatterers compared to the surrounding uniform materials because of the highly damaged rocks in its core. When seismic waves travel through faults, they will reflect on boundaries multiply and be trapped in the fault zones which cause the energy redistribution and generate coda waves with complicated characteristics after the direct P- and S- waves. The coda is named fault-zone trapped waves (FZTWs) (Li et al., 1990). The amplitude and duration characteristics of FZTWs (Li et al., 2016) can be used to constrain the geometric features of the fault and the physical parameters of the scatterers, so the fine structure of the fault can be finally obtained. We observed some FZTWs at several Hi-net stations in Japan, which were generated by low magnitude aftershocks following large earthquakes. Relatively strong FZTWs can be recorded by the seismic stations near or on the fault where the events happened. In this study, we simulate the theoretic envelops of FZTWs with radiative transport theory (Sanborn et al., 2017) for possible velocity models with scatterers described with von Karman distribution (Sato et al., 2012). While the theoretical envelops of FZTWs fit the observed ones well, the fine fault model is determined. The FZTWs from different events before and after the main shock can be used to determine the physical properties of faults and their adjoint area varied in the seismogenic process, then we can deeply understand the fault evolutions before and after earthquakes. The varying properties of faults can provide a new perspective for earthquake preparation and a new reference for earthquake prediction and promotes the development of earthquake prediction.
Li, Y. G., R. D. Catchings, and M. R. Goldman. 2016, Subsurface Fault Damage Zone of the 2014Mw 6.0 South Napa, California, Earthquake Viewed from Fault‐Zone Trapped Waves. Bulletin of the Seismological Society of America, 106, no. 6,2747-2763. doi: 10.1785/0120160039.
Li, Y. G., P. Leary, K. Aki, and P. Malin. 1990, Seismic Trapped Modes in the Oroville and San-Andreas Fault Zones. Science, 249, no. 4970,763-766. doi: 10.1126/science.249.4970.763.
Sanborn, C. J., V. F. Cormier, and M. Fitzpatrick. 2017, Combined Effects of Deterministic and Statistical Structure on High-frequency Regional Seismograms. Geophysical Journal International, 210, no. 2,1143-1159. doi: 10.1093/gji/ggx219.
Sato H., Fehler M.C. 2012, Seismic Wave Propagation and Scattering in the Heterogeneous Earth, 2nd edn, Springer-Verlag.
How to cite: Su, H. and Zhou, Y.: Imaging fine seismic structures of faults with fault-zone trapped waves, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3296, https://doi.org/10.5194/egusphere-egu2020-3296, 2020.
EGU2020-4534 | Displays | TS5.4
A Pump-Probe Analysis of Nonlinear Elastic Behavior on the San Andreas FaultAndrew Delorey
Fracture networks in the subsurface influence nearly every aspect of earthquakes and natural hazards. These aspects, including stress, permeability and material failure, and are important for hazard assessment. However, our ability to monitor fracture behavior in the Earth is insufficient for any type of decision-making regarding hazard avoidance. I propose a new method for probing the evolution of fracture networks in situ to inform public safety decisions and understand natural systems.
In heterogeneous, fractured materials, like those found in the Earth, the relationship between stress and strain is highly nonlinear. This nonlinearity in the upper crust is almost entirely due to fractures. By measuring to what extent Earth materials exhibit nonlinear elastic behavior, we can learn more information about them. Directly, measuring physical properties may be more useful than just detecting that fractures are present or how they are shaped and oriented. We measure nonlinearity by measuring the apparent modulus at different strains.
In this study we use a pump-probe analysis, which involves continuously probing velocity (as a proxy for modulus) while systematically straining the material. We will use solid Earth tides as a strain pump and empirical Green’s functions (EGF) as a velocity probe. We apply this analysis to the San Andreas Fault near Parkfield, California. We chose Parkfield because there is a long-term deployment of borehole seismic instruments that recorded before and after a M6 earthquake. We find evidence that nonlinear behavior is correlated with the seismic cycle and therefore it may contain information on the both the evolution and current state of stress on faults.
How to cite: Delorey, A.: A Pump-Probe Analysis of Nonlinear Elastic Behavior on the San Andreas Fault, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4534, https://doi.org/10.5194/egusphere-egu2020-4534, 2020.
Fracture networks in the subsurface influence nearly every aspect of earthquakes and natural hazards. These aspects, including stress, permeability and material failure, and are important for hazard assessment. However, our ability to monitor fracture behavior in the Earth is insufficient for any type of decision-making regarding hazard avoidance. I propose a new method for probing the evolution of fracture networks in situ to inform public safety decisions and understand natural systems.
In heterogeneous, fractured materials, like those found in the Earth, the relationship between stress and strain is highly nonlinear. This nonlinearity in the upper crust is almost entirely due to fractures. By measuring to what extent Earth materials exhibit nonlinear elastic behavior, we can learn more information about them. Directly, measuring physical properties may be more useful than just detecting that fractures are present or how they are shaped and oriented. We measure nonlinearity by measuring the apparent modulus at different strains.
In this study we use a pump-probe analysis, which involves continuously probing velocity (as a proxy for modulus) while systematically straining the material. We will use solid Earth tides as a strain pump and empirical Green’s functions (EGF) as a velocity probe. We apply this analysis to the San Andreas Fault near Parkfield, California. We chose Parkfield because there is a long-term deployment of borehole seismic instruments that recorded before and after a M6 earthquake. We find evidence that nonlinear behavior is correlated with the seismic cycle and therefore it may contain information on the both the evolution and current state of stress on faults.
How to cite: Delorey, A.: A Pump-Probe Analysis of Nonlinear Elastic Behavior on the San Andreas Fault, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4534, https://doi.org/10.5194/egusphere-egu2020-4534, 2020.
EGU2020-6559 | Displays | TS5.4
Temporal variation of fault slip rate in southern Taiwan by integrating GPS and InSAR observationsLi-Yang Hsiao and Wu-Lung Chang
Due to the rapid convergence of Philippine Sea Plate toward the continental margin of Eurasian Plate, the southern Taiwan has a high number of 8 active faults published by the Taiwan Central Geological Survey. We inverted the Global Positioning System (GPS) velocity measurements to investigate the slip rates on these faults and how these values could change with time, especially before and after large seismic events. In this study we employed TDEFNODE to first evaluate two fault-slip models before and after the 2016 Mw 6.4 Meinong earthquake within the periods of 2002 to 2016 (model 1) and 2016 to 2018 (model 2). Our results from these two models show that some long-term average fault slip rates were changed with time, such as the Zuozhen, Chishan and Hengchun faults that have values 30.2, 27.0 and 29.7 mm/yr in 2002-2016 and 15.2, 6.6 and 14.2 mm/yr in 2016-2018, respectively. In addition, we focused on the Mw 7.0 and Mw 6.9 2006 Hengchun doublet earthquakes by integrating the Permanent Scattered Interferometric Synthetic Aperture Radar (PS-InSAR) data collected by ALOS from 2007 to 2011 with the GPS velocities for a joint inversion for fault slip model (model 3). The results show that the average long-term slip rates of the Chishan and Hengchun faults are 12.5 and 16.8 mm/yr, respectively, which are significantly lower than the rates of 2002-2016 (model 1). More fault models with different time spans are on the way to affirm these temporal rate changes and explore their implications on earthquake hazard analysis.
How to cite: Hsiao, L.-Y. and Chang, W.-L.: Temporal variation of fault slip rate in southern Taiwan by integrating GPS and InSAR observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6559, https://doi.org/10.5194/egusphere-egu2020-6559, 2020.
Due to the rapid convergence of Philippine Sea Plate toward the continental margin of Eurasian Plate, the southern Taiwan has a high number of 8 active faults published by the Taiwan Central Geological Survey. We inverted the Global Positioning System (GPS) velocity measurements to investigate the slip rates on these faults and how these values could change with time, especially before and after large seismic events. In this study we employed TDEFNODE to first evaluate two fault-slip models before and after the 2016 Mw 6.4 Meinong earthquake within the periods of 2002 to 2016 (model 1) and 2016 to 2018 (model 2). Our results from these two models show that some long-term average fault slip rates were changed with time, such as the Zuozhen, Chishan and Hengchun faults that have values 30.2, 27.0 and 29.7 mm/yr in 2002-2016 and 15.2, 6.6 and 14.2 mm/yr in 2016-2018, respectively. In addition, we focused on the Mw 7.0 and Mw 6.9 2006 Hengchun doublet earthquakes by integrating the Permanent Scattered Interferometric Synthetic Aperture Radar (PS-InSAR) data collected by ALOS from 2007 to 2011 with the GPS velocities for a joint inversion for fault slip model (model 3). The results show that the average long-term slip rates of the Chishan and Hengchun faults are 12.5 and 16.8 mm/yr, respectively, which are significantly lower than the rates of 2002-2016 (model 1). More fault models with different time spans are on the way to affirm these temporal rate changes and explore their implications on earthquake hazard analysis.
How to cite: Hsiao, L.-Y. and Chang, W.-L.: Temporal variation of fault slip rate in southern Taiwan by integrating GPS and InSAR observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6559, https://doi.org/10.5194/egusphere-egu2020-6559, 2020.
EGU2020-6777 | Displays | TS5.4
Afterslip and slow slip events in the postseismic deformation of the 2016 Pedernales earthquake, EcuadorFrederique Rolandone, Jean-Mathieu nocquet, Patricia Mothes, Paul Jarrin, and Mathilde Vergnolle
In subduction zones, slip along the plate interface occurs in various modes including earthquakes, steady slip, and transient accelerated aseismic slip during either Slow Slip Events (SSE) or afterslip. We analyze continuous GPS measurements along the central Ecuador subduction segment to illuminate how the different slip modes are organized in space and time in the zone of the 2016 Mw 7.8 Pedernales earthquake. The early post-seismic period (1 month after the earthquake) shows large and rapid afterslip developing at discrete areas of the megathrust and a slow slip event remotely triggered (∼100 km) south of the rupture of the Pedernales earthquake. We find that areas of large and rapid early afterslip correlate with areas of the subduction interface that had hosted SSEs in years prior to the 2016 earthquake. Areas along the Ecuadorian margin hosting regular SSEs and large afterslip had a dominant aseismic slip mode that persisted throughout the earthquake cycle during several years and decades: they regularly experienced SSEs during the interseismic phase, they did not rupture during the 2016 Pedernales earthquake, they had large aseismic slip after it. Four years after the Pedernales earthquake, postseismic deformation is still on-going. Afterslip and SSEs are both involved in the postseimsic deformation. Two large aftershocks (Mw 6.7 & 6.8) occurred after the first month of postseismic deformation in May 18, and later in July 7 2016 two other large aftershocks (Mw 5.9 & 6.3) occurred, all were located north east of the rupture. They may have triggered their own postseismic deformation. Several seismic swarms were identified south and north of the rupture area by a dense network of seismic stations installed during one year after the Pedernales earthquakes, suggesting the occurrence of SSEs. Geodetically, several SSEs were detected during the postseismic deformation either in areas where no SSEs were detected previously, or in areas where regular seismic swarms and repeating earthquakes were identified. The SSEs may have been triggered by the stress increment due to aftershocks or due to afterslip.
How to cite: Rolandone, F., nocquet, J.-M., Mothes, P., Jarrin, P., and Vergnolle, M.: Afterslip and slow slip events in the postseismic deformation of the 2016 Pedernales earthquake, Ecuador, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6777, https://doi.org/10.5194/egusphere-egu2020-6777, 2020.
In subduction zones, slip along the plate interface occurs in various modes including earthquakes, steady slip, and transient accelerated aseismic slip during either Slow Slip Events (SSE) or afterslip. We analyze continuous GPS measurements along the central Ecuador subduction segment to illuminate how the different slip modes are organized in space and time in the zone of the 2016 Mw 7.8 Pedernales earthquake. The early post-seismic period (1 month after the earthquake) shows large and rapid afterslip developing at discrete areas of the megathrust and a slow slip event remotely triggered (∼100 km) south of the rupture of the Pedernales earthquake. We find that areas of large and rapid early afterslip correlate with areas of the subduction interface that had hosted SSEs in years prior to the 2016 earthquake. Areas along the Ecuadorian margin hosting regular SSEs and large afterslip had a dominant aseismic slip mode that persisted throughout the earthquake cycle during several years and decades: they regularly experienced SSEs during the interseismic phase, they did not rupture during the 2016 Pedernales earthquake, they had large aseismic slip after it. Four years after the Pedernales earthquake, postseismic deformation is still on-going. Afterslip and SSEs are both involved in the postseimsic deformation. Two large aftershocks (Mw 6.7 & 6.8) occurred after the first month of postseismic deformation in May 18, and later in July 7 2016 two other large aftershocks (Mw 5.9 & 6.3) occurred, all were located north east of the rupture. They may have triggered their own postseismic deformation. Several seismic swarms were identified south and north of the rupture area by a dense network of seismic stations installed during one year after the Pedernales earthquakes, suggesting the occurrence of SSEs. Geodetically, several SSEs were detected during the postseismic deformation either in areas where no SSEs were detected previously, or in areas where regular seismic swarms and repeating earthquakes were identified. The SSEs may have been triggered by the stress increment due to aftershocks or due to afterslip.
How to cite: Rolandone, F., nocquet, J.-M., Mothes, P., Jarrin, P., and Vergnolle, M.: Afterslip and slow slip events in the postseismic deformation of the 2016 Pedernales earthquake, Ecuador, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6777, https://doi.org/10.5194/egusphere-egu2020-6777, 2020.
EGU2020-7992 | Displays | TS5.4
Polished slickensides preserved in the Obir Caves (Austria) close to the Periadriatic Fault SystemStefanie Koppensteiner, Harald Bauer, Lukas Plan, and Bernhard Grasemann
We studied polished slickensides, which are perfectly preserved in the Obir Caves (Northern Karavanke Mountains, Austria) situated in the Middle Triassic Wetterstein limestone of the Hochobir massif. The investigated area is located close to the seismogenic ESE-trending Periadriatic Fault System, which is the border between the Eastern and Southern Alps. The polished slickensides observed on a block between two major left-lateral NE-SW trending slickensides record a range of polishing from none to highly-reflective fault surfaces. A classification of the different polishing grades of the fault surfaces inside the cave compared with their spatial orientation shows that there is no relationship between the degree of polishing and fault orientation. Associated cataclastically deformed brittle fault zones and partly polished slickensides at the cave entrance and on the Eastern slope of the Hochobir massif where the fault zone localizes in shattered dolomitic rocks, show similar kinematics and spatial orientation to the faults inside the Obir Caves.
Thin section analysis identified the smooth fault mirror surfaces as principal slip surfaces. Cataclastic grains are truncated along the principal slip surfaces and along secondary Riedel faults. Five different stages of cataclastic deformation can be distinguished: I) Undeformed carbonate host rock. II) Isolated fractures in the host rock with injected ultracataclastic material. III) Dilation cataclasites containing jigsaw breccia. IV) Ultracataclasite with angular-to-rounded host rock fragments and jigsaw breccia. V) Ultracataclasite with isolated clasts and truncated grains close to the mirror surfaces.
The microstructures including polished slickensides, injected cataclasites and truncated grains along principal slip surfaces as well as the geological position close to the seismogenic Periadriatic Fault System suggest that the investigated fault surfaces in the Obir Caves formed during seismic slip.
How to cite: Koppensteiner, S., Bauer, H., Plan, L., and Grasemann, B.: Polished slickensides preserved in the Obir Caves (Austria) close to the Periadriatic Fault System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7992, https://doi.org/10.5194/egusphere-egu2020-7992, 2020.
We studied polished slickensides, which are perfectly preserved in the Obir Caves (Northern Karavanke Mountains, Austria) situated in the Middle Triassic Wetterstein limestone of the Hochobir massif. The investigated area is located close to the seismogenic ESE-trending Periadriatic Fault System, which is the border between the Eastern and Southern Alps. The polished slickensides observed on a block between two major left-lateral NE-SW trending slickensides record a range of polishing from none to highly-reflective fault surfaces. A classification of the different polishing grades of the fault surfaces inside the cave compared with their spatial orientation shows that there is no relationship between the degree of polishing and fault orientation. Associated cataclastically deformed brittle fault zones and partly polished slickensides at the cave entrance and on the Eastern slope of the Hochobir massif where the fault zone localizes in shattered dolomitic rocks, show similar kinematics and spatial orientation to the faults inside the Obir Caves.
Thin section analysis identified the smooth fault mirror surfaces as principal slip surfaces. Cataclastic grains are truncated along the principal slip surfaces and along secondary Riedel faults. Five different stages of cataclastic deformation can be distinguished: I) Undeformed carbonate host rock. II) Isolated fractures in the host rock with injected ultracataclastic material. III) Dilation cataclasites containing jigsaw breccia. IV) Ultracataclasite with angular-to-rounded host rock fragments and jigsaw breccia. V) Ultracataclasite with isolated clasts and truncated grains close to the mirror surfaces.
The microstructures including polished slickensides, injected cataclasites and truncated grains along principal slip surfaces as well as the geological position close to the seismogenic Periadriatic Fault System suggest that the investigated fault surfaces in the Obir Caves formed during seismic slip.
How to cite: Koppensteiner, S., Bauer, H., Plan, L., and Grasemann, B.: Polished slickensides preserved in the Obir Caves (Austria) close to the Periadriatic Fault System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7992, https://doi.org/10.5194/egusphere-egu2020-7992, 2020.
EGU2020-18617 | Displays | TS5.4
Post-seismic deformation of the 2010 M w 7.4 Ogasawara Islands outer-rise earthquake evidenced by Repeating Earthquakes.Blandine Gardonio, Aitaro Kato, Sylvain Michel, and Alexandre Schubnel
Although far from the Japanese main island of Honshu, the Izu-Bonin area is a very active seismic zone. It experienced two major earthquakes in the past decade: (i) the 2010 Mw 7.4 Ogasawara Islands intraplate earthquake that occurred on the 2010/12/22 in a normal-fault, in the outer-rise of the trench of the Pacific plate that subduct underneath the Philippine Sea plate, (ii) the Mw 7.9 Bonin island very-deep focus earthquake that occurred on the 2015/05/30 that was preceded by an acceleration of the seismicity at large depth. The aftershocks of the outer-rise earthquake were distributed in a NW-SE belt and formed subparallel lines along a fracture zone in the Pacific plate. The aftershocks were first located in the surroundings of the main shock rupture and migrated over the following days beyond or into the Ogasawara Plateau and the Uyeda Ridge. Due to its location in the sea and with only a few GPS and seismic stations around, it is difficult to assess the extent of the post-seismic deformation of this earthquake.
In that context, the analysis of repeating earthquakes as a proxy for slip on the fault is very useful. Using ten seismic stations, we detected 130 repeating earthquakes. Their number inscreased in the next few days following the main shock and are located in the northern branch of the fault. Ten days later, another increase of repeating earthquakes occurs on the subduction interface concomitent with a displacement to the east seen by GPS stations, indicating that the outer-rise earthquake might have triggered a slow slip event on the subduction interface. The main shock was also followed by an extremely rapid migration of the seismicity at depths up to 80km showing that it perturbed the entire outer-rise structure of the slab at depth.
How to cite: Gardonio, B., Kato, A., Michel, S., and Schubnel, A.: Post-seismic deformation of the 2010 M w 7.4 Ogasawara Islands outer-rise earthquake evidenced by Repeating Earthquakes., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18617, https://doi.org/10.5194/egusphere-egu2020-18617, 2020.
Although far from the Japanese main island of Honshu, the Izu-Bonin area is a very active seismic zone. It experienced two major earthquakes in the past decade: (i) the 2010 Mw 7.4 Ogasawara Islands intraplate earthquake that occurred on the 2010/12/22 in a normal-fault, in the outer-rise of the trench of the Pacific plate that subduct underneath the Philippine Sea plate, (ii) the Mw 7.9 Bonin island very-deep focus earthquake that occurred on the 2015/05/30 that was preceded by an acceleration of the seismicity at large depth. The aftershocks of the outer-rise earthquake were distributed in a NW-SE belt and formed subparallel lines along a fracture zone in the Pacific plate. The aftershocks were first located in the surroundings of the main shock rupture and migrated over the following days beyond or into the Ogasawara Plateau and the Uyeda Ridge. Due to its location in the sea and with only a few GPS and seismic stations around, it is difficult to assess the extent of the post-seismic deformation of this earthquake.
In that context, the analysis of repeating earthquakes as a proxy for slip on the fault is very useful. Using ten seismic stations, we detected 130 repeating earthquakes. Their number inscreased in the next few days following the main shock and are located in the northern branch of the fault. Ten days later, another increase of repeating earthquakes occurs on the subduction interface concomitent with a displacement to the east seen by GPS stations, indicating that the outer-rise earthquake might have triggered a slow slip event on the subduction interface. The main shock was also followed by an extremely rapid migration of the seismicity at depths up to 80km showing that it perturbed the entire outer-rise structure of the slab at depth.
How to cite: Gardonio, B., Kato, A., Michel, S., and Schubnel, A.: Post-seismic deformation of the 2010 M w 7.4 Ogasawara Islands outer-rise earthquake evidenced by Repeating Earthquakes., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18617, https://doi.org/10.5194/egusphere-egu2020-18617, 2020.
EGU2020-9996 | Displays | TS5.4
Study of the early postseismic phase of Tohoku-Oki earthquake (2011) with kinematics solutionsAxel Periollat, Mathilde Radiguet, Jérôme Weiss, Cédric Twardzik, Nathalie Cotte, and Anne Socquet
Stress accumulation and relaxation occur on fault zones throughout the seismic cycle. In particular, the postseismic phase, which directly follows the earthquake rupture is a combination of different processes among which aseismic slip on the fault zone (called afterslip), viscoelastic deformation of the surrounding material, poroelastic relaxation and aftershocks. However, little work has been done on the early stage of the transition from the co- to the postseismic phase, and the physical processes explaining this transition.
In this study, we focus on the few minutes to the few days following the mainshock, where the deformation is assumed to be dominated by afterslip, for the Mw 9.0 Tohoku-Oki earthquake, one of the largest and most instrumented recent earthquake (2011). Here, GEONET GPS data are used to study its early stage.
Based on the method developed by Twardzik et al. (2019), we obtain kinematics position time series (30-s), which we use to characterize the fast displacements rates which typically occur during the early stages of this postseismic phase. For that, we use the GipsyX 1.2 software developed by JPL. Then, we apply a sidereal filter to remove the multi-path effect and obtained clean displacement time series.
This poster shows the preliminary results of our kinematics solutions analysis. In particular, we highlight study the differences between the standard and high rate estimation of the co-seismic offsets. We also characterize the temporal evolution of the early postseismic phase and study its spatial pattern with respect to that of the coseismic slip.
References:
Twardzik Cedric, Mathilde Vergnolle, Anthony Sladen and Antonio Avallone (2019), Unravelling the contribution of early postseismic deformation using sub-daily GNSS positioning. Scientific Report 9, n°1 doi.org/10.1038/s41598-019-39038-z
How to cite: Periollat, A., Radiguet, M., Weiss, J., Twardzik, C., Cotte, N., and Socquet, A.: Study of the early postseismic phase of Tohoku-Oki earthquake (2011) with kinematics solutions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9996, https://doi.org/10.5194/egusphere-egu2020-9996, 2020.
Stress accumulation and relaxation occur on fault zones throughout the seismic cycle. In particular, the postseismic phase, which directly follows the earthquake rupture is a combination of different processes among which aseismic slip on the fault zone (called afterslip), viscoelastic deformation of the surrounding material, poroelastic relaxation and aftershocks. However, little work has been done on the early stage of the transition from the co- to the postseismic phase, and the physical processes explaining this transition.
In this study, we focus on the few minutes to the few days following the mainshock, where the deformation is assumed to be dominated by afterslip, for the Mw 9.0 Tohoku-Oki earthquake, one of the largest and most instrumented recent earthquake (2011). Here, GEONET GPS data are used to study its early stage.
Based on the method developed by Twardzik et al. (2019), we obtain kinematics position time series (30-s), which we use to characterize the fast displacements rates which typically occur during the early stages of this postseismic phase. For that, we use the GipsyX 1.2 software developed by JPL. Then, we apply a sidereal filter to remove the multi-path effect and obtained clean displacement time series.
This poster shows the preliminary results of our kinematics solutions analysis. In particular, we highlight study the differences between the standard and high rate estimation of the co-seismic offsets. We also characterize the temporal evolution of the early postseismic phase and study its spatial pattern with respect to that of the coseismic slip.
References:
Twardzik Cedric, Mathilde Vergnolle, Anthony Sladen and Antonio Avallone (2019), Unravelling the contribution of early postseismic deformation using sub-daily GNSS positioning. Scientific Report 9, n°1 doi.org/10.1038/s41598-019-39038-z
How to cite: Periollat, A., Radiguet, M., Weiss, J., Twardzik, C., Cotte, N., and Socquet, A.: Study of the early postseismic phase of Tohoku-Oki earthquake (2011) with kinematics solutions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9996, https://doi.org/10.5194/egusphere-egu2020-9996, 2020.
EGU2020-10070 | Displays | TS5.4
The strength inversion origin of non-volcanic tremor: models and observationsJason P. Morgan, Albert de Montserrat Navarro, Paola Vannucchi, Alexander Peter Clarke, Audrey Ougier-Simonin, and Luca Aldega
Non-volcanic tremor remains a poorly understood form of seismic activity. In its most common subduction zone setting, tremor typically occurs within the plate interface at or near the shallow and deep edges of the interseismically locked zone. Detailed seismic observations have shown that tremor is composed of repeating small low-frequency earthquakes (LFE), often accompanied by very-low-frequency earthquakes (VLF), all involving shear failure and slip. However, LFEs and VLFs within each cluster show nearly constant source durations for all observed magnitudes. This implies asperities of near-constant size, with recent seismic observations hinting that the failure size is of order ~200m.
We propose that geological observations and geomechanical lab measurements on heterogeneous rock assemblages representative of the shallow tremor region are most consistent with LFEs and VLFs involving the seismic failure of relatively weaker blocks within a stronger matrix. Furthermore, in the shallow subducting rocks within a subduction shear channel, hydrothermal fluids and diagenesis have led to a strength inversion from the initial weak matrix with relatively stronger blocks to a stronger matrix with embedded relatively weaker blocks. In this case, tremor will naturally occur as the now-weaker blocks fail seismically while their more competent surrounding matrix has not yet reached a state of general seismic failure, and instead only fails at local stress-concentrations around the tremorgenic blocks.
Here we use the recently developed code LaCoDe (de Monserrat et al., 2019) to create and explore a wide range of numerical experiments. These experiments are designed to characterize the likely stress and strain accumulations that can develop in a heterogeneous subduction shear channel, and their implications for the genesis of tremor and its spatially associated seismic events. In our previous modeling efforts we did not strongly vary either the block volume-fraction or the initial block and matrix geometry. Here we do both, and also explore a range of rock compressibilities ranging from seismically-inferred values to nearly incompressible behavior. We also explore models with irregular 'quasi-geological' initial block/matrix geometries. Drucker-Prager plasticity is used to characterize a fault-like mode of shear failure. This suite of experiments demonstrate that, for a wide range of block and matrix conditions, the proposed strength-inversion mechanism can generate a mode of shallow tectonic tremor that clusters in spatially discontinuous swarms along the plate interface. At the deeper edge of the interseismically locked zone, channelised dehydration associated with subduction along a plate interface could induce a similar relative strength inversion, and thereby generate deep seated tremor.
How to cite: Morgan, J. P., de Montserrat Navarro, A., Vannucchi, P., Clarke, A. P., Ougier-Simonin, A., and Aldega, L.: The strength inversion origin of non-volcanic tremor: models and observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10070, https://doi.org/10.5194/egusphere-egu2020-10070, 2020.
Non-volcanic tremor remains a poorly understood form of seismic activity. In its most common subduction zone setting, tremor typically occurs within the plate interface at or near the shallow and deep edges of the interseismically locked zone. Detailed seismic observations have shown that tremor is composed of repeating small low-frequency earthquakes (LFE), often accompanied by very-low-frequency earthquakes (VLF), all involving shear failure and slip. However, LFEs and VLFs within each cluster show nearly constant source durations for all observed magnitudes. This implies asperities of near-constant size, with recent seismic observations hinting that the failure size is of order ~200m.
We propose that geological observations and geomechanical lab measurements on heterogeneous rock assemblages representative of the shallow tremor region are most consistent with LFEs and VLFs involving the seismic failure of relatively weaker blocks within a stronger matrix. Furthermore, in the shallow subducting rocks within a subduction shear channel, hydrothermal fluids and diagenesis have led to a strength inversion from the initial weak matrix with relatively stronger blocks to a stronger matrix with embedded relatively weaker blocks. In this case, tremor will naturally occur as the now-weaker blocks fail seismically while their more competent surrounding matrix has not yet reached a state of general seismic failure, and instead only fails at local stress-concentrations around the tremorgenic blocks.
Here we use the recently developed code LaCoDe (de Monserrat et al., 2019) to create and explore a wide range of numerical experiments. These experiments are designed to characterize the likely stress and strain accumulations that can develop in a heterogeneous subduction shear channel, and their implications for the genesis of tremor and its spatially associated seismic events. In our previous modeling efforts we did not strongly vary either the block volume-fraction or the initial block and matrix geometry. Here we do both, and also explore a range of rock compressibilities ranging from seismically-inferred values to nearly incompressible behavior. We also explore models with irregular 'quasi-geological' initial block/matrix geometries. Drucker-Prager plasticity is used to characterize a fault-like mode of shear failure. This suite of experiments demonstrate that, for a wide range of block and matrix conditions, the proposed strength-inversion mechanism can generate a mode of shallow tectonic tremor that clusters in spatially discontinuous swarms along the plate interface. At the deeper edge of the interseismically locked zone, channelised dehydration associated with subduction along a plate interface could induce a similar relative strength inversion, and thereby generate deep seated tremor.
How to cite: Morgan, J. P., de Montserrat Navarro, A., Vannucchi, P., Clarke, A. P., Ougier-Simonin, A., and Aldega, L.: The strength inversion origin of non-volcanic tremor: models and observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10070, https://doi.org/10.5194/egusphere-egu2020-10070, 2020.
EGU2020-10727 | Displays | TS5.4
Co-location of the downdip end of seismic locking and the continental shelf breakLuca C. Malatesta, Lucile Bruhat, Noah J. Finnegan, and Jean-Arthur L. Olive
Along subduction margins, the morphology of the near shore domain records the combined action of erosion from ocean waves and permanent tectonic deformation from the convergence of plates. We observe that at subduction margins around the globe, the edge of continental shelves tends to be located above the downdip end of seismic coupling on the megathrust (locking depth). Coastlines lie farther landward at variable distances. This observation stems from a compilation of well-resolved coseismic and interseismic coupling datasets. The permanent interseismic uplift component of the total tectonic deformation can explain the localization of the shelf break. It contributes a short wave-length gradient in vertical deformation on top of the structural and isostatic deformation of the margin. This places a hinge line between seaward subsidence and landward uplift above the locking depth. Landward of the hinge line, rocks are uplifted in the domain of wave-base erosion and a shelf is maintained by the competition of rock uplift and wave erosion. Wave erosion then sets the coastline back from the tectonically meaningful shelf break. We combine a wave erosion model with an elastic deformation model to show how the locking depth pins the location of the shelf break. In areas where the shelf is wide, onshore geodetic constraints on seismic coupling is limited and could be advantageously complemented by considering the location of the shelf break. Subduction margin morphology integrates hundreds of seismic cycles and could inform seismic coupling stability through time.
How to cite: Malatesta, L. C., Bruhat, L., Finnegan, N. J., and Olive, J.-A. L.: Co-location of the downdip end of seismic locking and the continental shelf break, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10727, https://doi.org/10.5194/egusphere-egu2020-10727, 2020.
Along subduction margins, the morphology of the near shore domain records the combined action of erosion from ocean waves and permanent tectonic deformation from the convergence of plates. We observe that at subduction margins around the globe, the edge of continental shelves tends to be located above the downdip end of seismic coupling on the megathrust (locking depth). Coastlines lie farther landward at variable distances. This observation stems from a compilation of well-resolved coseismic and interseismic coupling datasets. The permanent interseismic uplift component of the total tectonic deformation can explain the localization of the shelf break. It contributes a short wave-length gradient in vertical deformation on top of the structural and isostatic deformation of the margin. This places a hinge line between seaward subsidence and landward uplift above the locking depth. Landward of the hinge line, rocks are uplifted in the domain of wave-base erosion and a shelf is maintained by the competition of rock uplift and wave erosion. Wave erosion then sets the coastline back from the tectonically meaningful shelf break. We combine a wave erosion model with an elastic deformation model to show how the locking depth pins the location of the shelf break. In areas where the shelf is wide, onshore geodetic constraints on seismic coupling is limited and could be advantageously complemented by considering the location of the shelf break. Subduction margin morphology integrates hundreds of seismic cycles and could inform seismic coupling stability through time.
How to cite: Malatesta, L. C., Bruhat, L., Finnegan, N. J., and Olive, J.-A. L.: Co-location of the downdip end of seismic locking and the continental shelf break, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10727, https://doi.org/10.5194/egusphere-egu2020-10727, 2020.
EGU2020-12085 | Displays | TS5.4
Strike-variable coseismic and postseismic slips of the 12 December 2017 Mw 6.0 Hojedk (Iran) earthquake revealed by Sentinel-1/2 images: Implications for the local lithospheric structureYingwen Zhao, Caijun Xu, and Yangmao Wen
On 12 December 2017, a shallow reverse earthquake ruptured an unrecognized fault located in a transpressional relay zone between Lakar Kuh and Gowk faults. Four tracks of Sentinel-1A/B interferometric wide swath SAR images are used to generate coseismic interferograms. The retrieved maximum line-of-sight (LOS) displacement is up to ~1 m toward the satellite for descending data. An offset tracking method within GAMMA software is used to generate range and azimuth offsets based on Sentinel-1 SAR images. Two Sentinel-2 images are processed with the COSI-Corr package to generate horizontal displacements. The calculated three-dimension deformation field shows that the east-west displacements have motions in different directions, the north-south shortening near the fault trace approaches ~2 m and the maximum uplift is over 1 m. Based on the rupture trace in Sentinel-2 image, a strike-variable fault is constructed to explain the LOS displacements. The estimated slip distribution shows that the peak slip is ~2.5 m located at a depth of ~1.5 km and the depth extent of rupture is 0-3 km with the length of rupture on the surface approaching ~7 km. There are both right-lateral and left-lateral slips occurring on the fault, which are consistent with field observations. The one year of postseismic displacements are estimated by a short baseline subset technique based on two tracks (ascending and descending) of Sentinel-1 SAR images. The maximum LOS displacements is up to ~7 cm toward the satellite for the descending data. The forward displacements show that the poro-elastic rebound in the upper crust does not explain the LOS data. The data can be fitted well in terms of afterslip. The estimated postseismic slip on this strike-variable fault is found to occur in portions of the fault where small slips on these patches are obtained in the coseismic slip inversion. Most of patches related to the postseismic slip are located below the main coseismic patches with the depth extent of rupture being 0.5-4 km. The cumulative slip distribution during one year has the peak slip of ~20 cm, releasing ~12% of the moment of coseismic rupture. Taking into account aftershock depths, the shallow postseismic slip is considered to occur aseismically and cause the most of postseismic deformation. The afterslip may result from some response to a stress concentration located at the periphery of main coseismic rupture. After the analysis on Coulomb stress change, it is possible that the former two Mw ~6 earthquakes occurred on 1 and 12 December cause stress perturbations in the seismogenic zone of this earthquake, which further may bring the local prestressed lithosphere to rupture. For this shallow event, a small shear modulus (less than 30 GPa) is needed to make the moment more comparable to seismic results. This earthquake can be interpreted as the accommodation of the northward motion in the form of oblique-slip reverse fault between right-lateral strike-slip fault systems. The unusually deformation patterns caused by the coseismic and postseismic slips of this earthquake may be indicative of differently local lithosphere structure in this transpressional relay zone.
How to cite: Zhao, Y., Xu, C., and Wen, Y.: Strike-variable coseismic and postseismic slips of the 12 December 2017 Mw 6.0 Hojedk (Iran) earthquake revealed by Sentinel-1/2 images: Implications for the local lithospheric structure, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12085, https://doi.org/10.5194/egusphere-egu2020-12085, 2020.
On 12 December 2017, a shallow reverse earthquake ruptured an unrecognized fault located in a transpressional relay zone between Lakar Kuh and Gowk faults. Four tracks of Sentinel-1A/B interferometric wide swath SAR images are used to generate coseismic interferograms. The retrieved maximum line-of-sight (LOS) displacement is up to ~1 m toward the satellite for descending data. An offset tracking method within GAMMA software is used to generate range and azimuth offsets based on Sentinel-1 SAR images. Two Sentinel-2 images are processed with the COSI-Corr package to generate horizontal displacements. The calculated three-dimension deformation field shows that the east-west displacements have motions in different directions, the north-south shortening near the fault trace approaches ~2 m and the maximum uplift is over 1 m. Based on the rupture trace in Sentinel-2 image, a strike-variable fault is constructed to explain the LOS displacements. The estimated slip distribution shows that the peak slip is ~2.5 m located at a depth of ~1.5 km and the depth extent of rupture is 0-3 km with the length of rupture on the surface approaching ~7 km. There are both right-lateral and left-lateral slips occurring on the fault, which are consistent with field observations. The one year of postseismic displacements are estimated by a short baseline subset technique based on two tracks (ascending and descending) of Sentinel-1 SAR images. The maximum LOS displacements is up to ~7 cm toward the satellite for the descending data. The forward displacements show that the poro-elastic rebound in the upper crust does not explain the LOS data. The data can be fitted well in terms of afterslip. The estimated postseismic slip on this strike-variable fault is found to occur in portions of the fault where small slips on these patches are obtained in the coseismic slip inversion. Most of patches related to the postseismic slip are located below the main coseismic patches with the depth extent of rupture being 0.5-4 km. The cumulative slip distribution during one year has the peak slip of ~20 cm, releasing ~12% of the moment of coseismic rupture. Taking into account aftershock depths, the shallow postseismic slip is considered to occur aseismically and cause the most of postseismic deformation. The afterslip may result from some response to a stress concentration located at the periphery of main coseismic rupture. After the analysis on Coulomb stress change, it is possible that the former two Mw ~6 earthquakes occurred on 1 and 12 December cause stress perturbations in the seismogenic zone of this earthquake, which further may bring the local prestressed lithosphere to rupture. For this shallow event, a small shear modulus (less than 30 GPa) is needed to make the moment more comparable to seismic results. This earthquake can be interpreted as the accommodation of the northward motion in the form of oblique-slip reverse fault between right-lateral strike-slip fault systems. The unusually deformation patterns caused by the coseismic and postseismic slips of this earthquake may be indicative of differently local lithosphere structure in this transpressional relay zone.
How to cite: Zhao, Y., Xu, C., and Wen, Y.: Strike-variable coseismic and postseismic slips of the 12 December 2017 Mw 6.0 Hojedk (Iran) earthquake revealed by Sentinel-1/2 images: Implications for the local lithospheric structure, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12085, https://doi.org/10.5194/egusphere-egu2020-12085, 2020.
EGU2020-13980 | Displays | TS5.4
Earthquakes without aftershocks: Is there a link to fluid-absent geodynamics?Thanushika Gunatilake and Stephen A. Miller
One question that remains unanswered is why some earthquakes are preceded by foreshocks and generate aftershocks by the thousands, while other similarly-sized (or larger) earthquakes produce few, if any, foreshocks or aftershocks. Current understanding equates large magnitude earthquakes with hundreds or even thousands of aftershocks, however a magnitude 7.1 earthquake in Mexico in 2017 and a magnitude 8.0 earthquake in 2019 in Peru generated no foreshocks and no aftershocks (M>4), while the 2020 M6.4 earthquake in Puerto Rico was preceded by ten foreshocks (M>4) and more than sixty aftershocks (M>4) in the first week. The 2019 Ridgecrest earthquake (M7.1) in California was preceded by a M6.4 foreshock and thousands of aftershocks, and this is relevant because this sequence occurred in the fluid-rich Coso hydrothermal/volcanic region. Other examples include the 2001 Kunlun (Tibet) earthquake (M=7.8) that generated a mere 12 aftershocks (M>4) in the first three weeks, while the tectonically similar 2002 Denali earthquake (M=7.9) spawned nearly 160 aftershocks (M>4) in the first three weeks. We attribute this contrasting behaviour to the geodynamic setting; subduction (and thus devolitization) underlies Denali, while a fluid-absent thickened crust (from the Himalayan orogeny) underlies Tibet.
In this work, we performed a global inventory of large earthquakes and their aftershocks, and find strong evidence that aftershock productivity correlates with the geodynamic and petrological settings hosting the earthquakes. In cases where deep fluid sources are likely (using geodynamic arguments), we find that earthquakes are sometimes preceded by foreshocks, and always produce rich aftershock sequences. On the contrary, using the same geodynamic arguments, we show that regions without an obvious deep fluid source produce few, if any, aftershocks. From this study, we hypothesize that, in general, fluid-absent geodynamic environments generate a dearth of aftershocks, while fluid-rich environments generate aftershock sequences that follow the typical Gutenberg-Richter, Bath and Omori Laws.
How to cite: Gunatilake, T. and Miller, S. A.: Earthquakes without aftershocks: Is there a link to fluid-absent geodynamics?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13980, https://doi.org/10.5194/egusphere-egu2020-13980, 2020.
One question that remains unanswered is why some earthquakes are preceded by foreshocks and generate aftershocks by the thousands, while other similarly-sized (or larger) earthquakes produce few, if any, foreshocks or aftershocks. Current understanding equates large magnitude earthquakes with hundreds or even thousands of aftershocks, however a magnitude 7.1 earthquake in Mexico in 2017 and a magnitude 8.0 earthquake in 2019 in Peru generated no foreshocks and no aftershocks (M>4), while the 2020 M6.4 earthquake in Puerto Rico was preceded by ten foreshocks (M>4) and more than sixty aftershocks (M>4) in the first week. The 2019 Ridgecrest earthquake (M7.1) in California was preceded by a M6.4 foreshock and thousands of aftershocks, and this is relevant because this sequence occurred in the fluid-rich Coso hydrothermal/volcanic region. Other examples include the 2001 Kunlun (Tibet) earthquake (M=7.8) that generated a mere 12 aftershocks (M>4) in the first three weeks, while the tectonically similar 2002 Denali earthquake (M=7.9) spawned nearly 160 aftershocks (M>4) in the first three weeks. We attribute this contrasting behaviour to the geodynamic setting; subduction (and thus devolitization) underlies Denali, while a fluid-absent thickened crust (from the Himalayan orogeny) underlies Tibet.
In this work, we performed a global inventory of large earthquakes and their aftershocks, and find strong evidence that aftershock productivity correlates with the geodynamic and petrological settings hosting the earthquakes. In cases where deep fluid sources are likely (using geodynamic arguments), we find that earthquakes are sometimes preceded by foreshocks, and always produce rich aftershock sequences. On the contrary, using the same geodynamic arguments, we show that regions without an obvious deep fluid source produce few, if any, aftershocks. From this study, we hypothesize that, in general, fluid-absent geodynamic environments generate a dearth of aftershocks, while fluid-rich environments generate aftershock sequences that follow the typical Gutenberg-Richter, Bath and Omori Laws.
How to cite: Gunatilake, T. and Miller, S. A.: Earthquakes without aftershocks: Is there a link to fluid-absent geodynamics?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13980, https://doi.org/10.5194/egusphere-egu2020-13980, 2020.
EGU2020-17399 | Displays | TS5.4
Mixed-mode Slip Behavior and Strength Evolution of an Actively Exhuming Low-Angle Normal Fault, Woodlark Rift, SE Papua New GuineaMarcel Mizera, Timothy Little, Carolyn Boulton, James Biemiller, and David Prior
Rapid dip-slip (11.7±3.5 mm/yr) on the active Mai'iu low-angle normal fault in SE Papua New Guinea enabled the preservation of early formed microstructures in mid to shallow crustal rocks. The corrugated, convex-upward shaped fault scarp dips as low as 16°–20° near its trace close to sea level and forms a continuous landscape surface traceable for at least 28 km in the NNE slip-direction. Structurally, offset on the Mai'iu fault has formed a metamorphic core complex and has exhumed a metabasaltic footwall during 30–45 km of dip slip on a rolling-hinge style detachment fault. The exhumed crustal section records the spatiotemporal evolution of fault rock deformation mechanisms and the differential stresses that drive slip on this active low-angle normal fault.
The Mai'iu fault exposes a <3 m-thick fault core consisting of gouges and cataclasites. These deformed units overprint a structurally underlying carapace of metabasaltic mylonites that are locally >60 m-thick. Detailed microstructural, textural and geochemical data combined with chlorite-based geothermometry of these fault rocks reveal a variety of deformation processes operating within the Mai'iu fault zone. A strong crystallographic preferred orientation of non-plastically deformed actinolite in a pre-existing, fine-grained (6–33 µm) mafic assemblage indicates that mylonitic deformation was controlled by diffusion-accommodated grain-boundary sliding together with syn-tectonic chlorite precipitation at >270–370°C. At shallower crustal levels on the fault (T≈150–270°C), fluid-assisted mass transfer and metasomatic reactions created a foliated cataclasite fabric during inferred periods of aseismic creep. Pseudotachylites and ultracataclasites mutually cross-cut both the foliations and one another, recording repeated episodes of seismic slip. In these fault rocks, paleopiezometry based on calcite twinning yields peak differential stresses of ~140–185 MPa at inferred depths of 8–12 km. These differential stresses were high enough to drive continued slip on a ~35° dipping segment of the Mai'iu fault, and to cause new brittle yielding of strong mafic rocks in the exhuming footwall of that fault. In the uppermost crust (<8 km; T<150°C), where the Mai'iu fault dips shallowly and is most severely misoriented for slip, actively deforming fault rocks are clay-rich gouges containing abundant saponite, a frictionally weak mineral (µ<0.28).
In summary, these results combined with fault dislocation models of GPS velocities from campaign stations in this region suggest a combination of brittle frictional and viscous flow processes within the Mai'iu fault zone. Gouges of the Mai'iu fault have been strongly altered by fluids and are frictionally weak near the surface, where the fault is most strongly misoriented. At greater depths (8–12 km) the fault is stronger and slips both by aseismic creep and episodic earthquakes (a mixture of fast and slow slip) in response to locally high differential stresses.
How to cite: Mizera, M., Little, T., Boulton, C., Biemiller, J., and Prior, D.: Mixed-mode Slip Behavior and Strength Evolution of an Actively Exhuming Low-Angle Normal Fault, Woodlark Rift, SE Papua New Guinea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17399, https://doi.org/10.5194/egusphere-egu2020-17399, 2020.
Rapid dip-slip (11.7±3.5 mm/yr) on the active Mai'iu low-angle normal fault in SE Papua New Guinea enabled the preservation of early formed microstructures in mid to shallow crustal rocks. The corrugated, convex-upward shaped fault scarp dips as low as 16°–20° near its trace close to sea level and forms a continuous landscape surface traceable for at least 28 km in the NNE slip-direction. Structurally, offset on the Mai'iu fault has formed a metamorphic core complex and has exhumed a metabasaltic footwall during 30–45 km of dip slip on a rolling-hinge style detachment fault. The exhumed crustal section records the spatiotemporal evolution of fault rock deformation mechanisms and the differential stresses that drive slip on this active low-angle normal fault.
The Mai'iu fault exposes a <3 m-thick fault core consisting of gouges and cataclasites. These deformed units overprint a structurally underlying carapace of metabasaltic mylonites that are locally >60 m-thick. Detailed microstructural, textural and geochemical data combined with chlorite-based geothermometry of these fault rocks reveal a variety of deformation processes operating within the Mai'iu fault zone. A strong crystallographic preferred orientation of non-plastically deformed actinolite in a pre-existing, fine-grained (6–33 µm) mafic assemblage indicates that mylonitic deformation was controlled by diffusion-accommodated grain-boundary sliding together with syn-tectonic chlorite precipitation at >270–370°C. At shallower crustal levels on the fault (T≈150–270°C), fluid-assisted mass transfer and metasomatic reactions created a foliated cataclasite fabric during inferred periods of aseismic creep. Pseudotachylites and ultracataclasites mutually cross-cut both the foliations and one another, recording repeated episodes of seismic slip. In these fault rocks, paleopiezometry based on calcite twinning yields peak differential stresses of ~140–185 MPa at inferred depths of 8–12 km. These differential stresses were high enough to drive continued slip on a ~35° dipping segment of the Mai'iu fault, and to cause new brittle yielding of strong mafic rocks in the exhuming footwall of that fault. In the uppermost crust (<8 km; T<150°C), where the Mai'iu fault dips shallowly and is most severely misoriented for slip, actively deforming fault rocks are clay-rich gouges containing abundant saponite, a frictionally weak mineral (µ<0.28).
In summary, these results combined with fault dislocation models of GPS velocities from campaign stations in this region suggest a combination of brittle frictional and viscous flow processes within the Mai'iu fault zone. Gouges of the Mai'iu fault have been strongly altered by fluids and are frictionally weak near the surface, where the fault is most strongly misoriented. At greater depths (8–12 km) the fault is stronger and slips both by aseismic creep and episodic earthquakes (a mixture of fast and slow slip) in response to locally high differential stresses.
How to cite: Mizera, M., Little, T., Boulton, C., Biemiller, J., and Prior, D.: Mixed-mode Slip Behavior and Strength Evolution of an Actively Exhuming Low-Angle Normal Fault, Woodlark Rift, SE Papua New Guinea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17399, https://doi.org/10.5194/egusphere-egu2020-17399, 2020.
EGU2020-18382 | Displays | TS5.4
Effect of grain fracture on stick-slip dynamics of granular fault gougeDi Wang, Omid Dorostkar, Wei Zhou, Chris Marone, and Jan Carmeliet
Fault gouge is produced by comminution, wear and other shearing processes that take place during geological tectonic movements. The frictional properties and stick-slip dynamics of granular fault show similar patterns as geophysical phenomena like earthquakes and landslides. In this work, we introduce a particle breakage model in a granular fault system to study the effect of grain fracture on the stick-slip dynamics. Our results show that particle breakage changes the macroscopic friction and the characteristics of slip events. By statistical analyses on a large number of slip events, we find that grain fracture changes the distribution of slip event size. During the evolution of crushable fault gouge, particle breakage does not lead to large slip events but triggers many small slips that partly dissipate the accumulated energy. On the other hand, the grain fracture is also influenced by the slip dynamics: it is shown that larger slip events will lead to a series of particle breakage due to localized high stresses during the rearrangement of granular gouge. Our findings in this study show that in faults with granular gouge particle breakage significantly changes the characteristics of frictional instabilities and affects the dynamics of fault system.
How to cite: Wang, D., Dorostkar, O., Zhou, W., Marone, C., and Carmeliet, J.: Effect of grain fracture on stick-slip dynamics of granular fault gouge, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18382, https://doi.org/10.5194/egusphere-egu2020-18382, 2020.
Fault gouge is produced by comminution, wear and other shearing processes that take place during geological tectonic movements. The frictional properties and stick-slip dynamics of granular fault show similar patterns as geophysical phenomena like earthquakes and landslides. In this work, we introduce a particle breakage model in a granular fault system to study the effect of grain fracture on the stick-slip dynamics. Our results show that particle breakage changes the macroscopic friction and the characteristics of slip events. By statistical analyses on a large number of slip events, we find that grain fracture changes the distribution of slip event size. During the evolution of crushable fault gouge, particle breakage does not lead to large slip events but triggers many small slips that partly dissipate the accumulated energy. On the other hand, the grain fracture is also influenced by the slip dynamics: it is shown that larger slip events will lead to a series of particle breakage due to localized high stresses during the rearrangement of granular gouge. Our findings in this study show that in faults with granular gouge particle breakage significantly changes the characteristics of frictional instabilities and affects the dynamics of fault system.
How to cite: Wang, D., Dorostkar, O., Zhou, W., Marone, C., and Carmeliet, J.: Effect of grain fracture on stick-slip dynamics of granular fault gouge, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18382, https://doi.org/10.5194/egusphere-egu2020-18382, 2020.
EGU2020-4174 | Displays | TS5.4
A unified numerical model for the simulation of the seismic cycle for normal and reverse fault earthquakes in ItalyMatteo Albano, Salvatore Barba, Christian Bignami, Carlo Doglioni, Eugenio Carminati, Michele Saroli, Marco Moro, Salvatore Stramondo, and Sergey Samsonov
Earthquakes are the result of the strain accumulation in the earth's crust over a variable decade to millennial period, i.e., the interseismic stage, followed by a sudden stress release at a crustal discontinuity, i.e., the coseismic stage, finally evolving in a postseismic stage.
Commonly, the seismic cycle is modelled with analytical and numerical approaches. Analytical methods simulate the interseismic, coseismic and postseismic phases independently. These models impose the slip of single or multiple planar sources to infer fault geometry, slip distribution and regional deformations to fit the available geodetic or seismological measurements, often regardless of the magnitude and orientation of the interseismic gravitational and tectonic forces. Numerical approaches allow simulating complex geometries in heterogeneous media and at different modelling scales, assuming various constitutive laws. Such models often impose the slip on the fault plane to simulate the observed coseismic dislocation or the propagation of the seismic waves, or they adopt ad-hoc boundary conditions to investigate the interseismic stress accumulation or the postseismic relaxation for specific cases.
We contribute to the understanding of the seismic cycle associated to a single fault by developing a numerical model to simulate the long-term crustal interseismic deformation, the coseismic brittle episodic dislocation, and the postseismic relaxation of the upper crust within a unified environment for both normal and reverse fault earthquakes in Italy, including the forces acting during the interseismic period, i.e., the lithostatic load and the horizontal stress field, the latter simulated with the application of a shear traction a the model’s base. We adjusted the setup of our model to simulate the interseismic, coseismic and postseismic phases for two seismic events: the Mw 6.1 L’Aquila 2009 normal fault earthquake and the Mw 5.9 Emilia-Romagna 2012 reverse fault earthquake.
The simulation results show that the applied basal shear traction is fundamental to model the large-scale interseismic pattern since it allows for a first-order simulation of the ongoing crustal interseismic extension of the Central Apennines and compression of the Adriatic foreland and the north-eastern part of the Italian territory. The action of shear tractions and lithostatic forces generates a local concentration of stresses and strains in the presence of local heterogeneities or discontinuities, i.e., at the transition between the brittle locked fault and the ductile unlocked slipping fault during the interseismic stage. Such an interseismic strain partitioning provides maximum horizontal stress sufficient to exceed the friction on the locked brittle part of the fault, with the subsequent collapse of the hangingwall in case of extensional earthquakes or the expulsion of the hangingwall in case of compressional earthquakes. The instantaneous slip of the hangingwall perturbs the crustal pore fluid pressures, triggering groundwater flow in the postseismic phase from regions of higher pore pressures, which further compress, to regions of lower pore pressures, which further dilate. As a result, displacements gradually accumulate in the postseismic phase, according to the dissipation of pore pressure excess. Once the postseismic phase terminates, a new cycle of interseismic loading can start again.
How to cite: Albano, M., Barba, S., Bignami, C., Doglioni, C., Carminati, E., Saroli, M., Moro, M., Stramondo, S., and Samsonov, S.: A unified numerical model for the simulation of the seismic cycle for normal and reverse fault earthquakes in Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4174, https://doi.org/10.5194/egusphere-egu2020-4174, 2020.
Earthquakes are the result of the strain accumulation in the earth's crust over a variable decade to millennial period, i.e., the interseismic stage, followed by a sudden stress release at a crustal discontinuity, i.e., the coseismic stage, finally evolving in a postseismic stage.
Commonly, the seismic cycle is modelled with analytical and numerical approaches. Analytical methods simulate the interseismic, coseismic and postseismic phases independently. These models impose the slip of single or multiple planar sources to infer fault geometry, slip distribution and regional deformations to fit the available geodetic or seismological measurements, often regardless of the magnitude and orientation of the interseismic gravitational and tectonic forces. Numerical approaches allow simulating complex geometries in heterogeneous media and at different modelling scales, assuming various constitutive laws. Such models often impose the slip on the fault plane to simulate the observed coseismic dislocation or the propagation of the seismic waves, or they adopt ad-hoc boundary conditions to investigate the interseismic stress accumulation or the postseismic relaxation for specific cases.
We contribute to the understanding of the seismic cycle associated to a single fault by developing a numerical model to simulate the long-term crustal interseismic deformation, the coseismic brittle episodic dislocation, and the postseismic relaxation of the upper crust within a unified environment for both normal and reverse fault earthquakes in Italy, including the forces acting during the interseismic period, i.e., the lithostatic load and the horizontal stress field, the latter simulated with the application of a shear traction a the model’s base. We adjusted the setup of our model to simulate the interseismic, coseismic and postseismic phases for two seismic events: the Mw 6.1 L’Aquila 2009 normal fault earthquake and the Mw 5.9 Emilia-Romagna 2012 reverse fault earthquake.
The simulation results show that the applied basal shear traction is fundamental to model the large-scale interseismic pattern since it allows for a first-order simulation of the ongoing crustal interseismic extension of the Central Apennines and compression of the Adriatic foreland and the north-eastern part of the Italian territory. The action of shear tractions and lithostatic forces generates a local concentration of stresses and strains in the presence of local heterogeneities or discontinuities, i.e., at the transition between the brittle locked fault and the ductile unlocked slipping fault during the interseismic stage. Such an interseismic strain partitioning provides maximum horizontal stress sufficient to exceed the friction on the locked brittle part of the fault, with the subsequent collapse of the hangingwall in case of extensional earthquakes or the expulsion of the hangingwall in case of compressional earthquakes. The instantaneous slip of the hangingwall perturbs the crustal pore fluid pressures, triggering groundwater flow in the postseismic phase from regions of higher pore pressures, which further compress, to regions of lower pore pressures, which further dilate. As a result, displacements gradually accumulate in the postseismic phase, according to the dissipation of pore pressure excess. Once the postseismic phase terminates, a new cycle of interseismic loading can start again.
How to cite: Albano, M., Barba, S., Bignami, C., Doglioni, C., Carminati, E., Saroli, M., Moro, M., Stramondo, S., and Samsonov, S.: A unified numerical model for the simulation of the seismic cycle for normal and reverse fault earthquakes in Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4174, https://doi.org/10.5194/egusphere-egu2020-4174, 2020.
EGU2020-10197 | Displays | TS5.4
On the Nature of Fault Slip: From the Field to the LabFrancois Passelegue, Michelle Almakari, Pierre Dublanchet, Fabian Barras, and Marie Violay
Modern geophysics highlights that the slip behaviour response of faults is variable in space and time and can result in slow or fast ruptures. Despite geodetical, seismological, experimental and field observations, the origin of this variation of the rupture velocity in nature, as well as the physics behind it, is still debated. Here, we first discuss the scaling relationships existing for the different types of fault slip observed in nature and we highlight how they appear to stem from the same physical mechanism. Second, we reproduce at the scale of the laboratory the complete spectrum of rupture velocities observed in nature. Our results show that when the nucleation length is within the fault length, the rupture velocity can range from a few millimetres to kilometres per second, depending on the available energy at the onset of slip. Our results are analysed in the framework of linear elastic fracture mechanics and highlight that the nature of seismicity is governed mostly by the initial stress level along the faults. Our results reveal that faults presenting similar frictional properties can rupture at both slow and fast rupture velocities. This combined set of field and experimental observations bring a new explanation of the dominance of slow rupture fronts in the shallow part of the crust and in areas presenting large fluid pressure, where initial stresses are expected to remain relatively low during the seismic cycle.
How to cite: Passelegue, F., Almakari, M., Dublanchet, P., Barras, F., and Violay, M.: On the Nature of Fault Slip: From the Field to the Lab, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10197, https://doi.org/10.5194/egusphere-egu2020-10197, 2020.
Modern geophysics highlights that the slip behaviour response of faults is variable in space and time and can result in slow or fast ruptures. Despite geodetical, seismological, experimental and field observations, the origin of this variation of the rupture velocity in nature, as well as the physics behind it, is still debated. Here, we first discuss the scaling relationships existing for the different types of fault slip observed in nature and we highlight how they appear to stem from the same physical mechanism. Second, we reproduce at the scale of the laboratory the complete spectrum of rupture velocities observed in nature. Our results show that when the nucleation length is within the fault length, the rupture velocity can range from a few millimetres to kilometres per second, depending on the available energy at the onset of slip. Our results are analysed in the framework of linear elastic fracture mechanics and highlight that the nature of seismicity is governed mostly by the initial stress level along the faults. Our results reveal that faults presenting similar frictional properties can rupture at both slow and fast rupture velocities. This combined set of field and experimental observations bring a new explanation of the dominance of slow rupture fronts in the shallow part of the crust and in areas presenting large fluid pressure, where initial stresses are expected to remain relatively low during the seismic cycle.
How to cite: Passelegue, F., Almakari, M., Dublanchet, P., Barras, F., and Violay, M.: On the Nature of Fault Slip: From the Field to the Lab, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10197, https://doi.org/10.5194/egusphere-egu2020-10197, 2020.
EGU2020-12694 | Displays | TS5.4
The 2016 Mw 7.8 Kaikoura earthquake and its relationship to tremors.Pierre Romanet, Florent Aden-Antoniow, and Satoshi Ide
The relationship between slow earthquake and regular earthquake is fundamental question in seismology. It was already shown that some slow slip event may have led to some megathrust event. In return, passing surface wave from earthquake may also trigger tremors and slow slip event. Documenting these possible triggering effects between slow and fast events is of primary importance to understand them.
In this study we will focus more particularly on Marlborough region, in a region that was subject to the Mw 7.8 2016 Kaikoura earthquake. Two years before Kaikoura earthquake, we observed a Northeast to Southwest migration of tremors, getting closer to the hypocenter of Kaikoura earthquake. Despite being speculative, this may indicate that a slow slip event is happening shortly before Kaikoura earthquake, which is also supported by a small signal in two GPS stations nearby. After the earthquake, the rate of tremors increased in the region. Studying the relationship between tremors and the Kaikoura earthquake may provide some information on the role of the subduction in the region, as well as provide a new documented interaction of slow earthquakes with a crustal earthquake.
To detect and locate tremors, we use broadband and shortband velocity traces from the GeoNet network. The traces are bandpass filtered between 2-8Hz, and transform into envelope. Then we apply a classic cross-correlation technic to detect and locate the events. To remove unexpected events (i.e.: earthquakes), we used a criteria base on seismic energy and duration. Finally, we manually check each velocity traces and spectrograms.
How to cite: Romanet, P., Aden-Antoniow, F., and Ide, S.: The 2016 Mw 7.8 Kaikoura earthquake and its relationship to tremors., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12694, https://doi.org/10.5194/egusphere-egu2020-12694, 2020.
The relationship between slow earthquake and regular earthquake is fundamental question in seismology. It was already shown that some slow slip event may have led to some megathrust event. In return, passing surface wave from earthquake may also trigger tremors and slow slip event. Documenting these possible triggering effects between slow and fast events is of primary importance to understand them.
In this study we will focus more particularly on Marlborough region, in a region that was subject to the Mw 7.8 2016 Kaikoura earthquake. Two years before Kaikoura earthquake, we observed a Northeast to Southwest migration of tremors, getting closer to the hypocenter of Kaikoura earthquake. Despite being speculative, this may indicate that a slow slip event is happening shortly before Kaikoura earthquake, which is also supported by a small signal in two GPS stations nearby. After the earthquake, the rate of tremors increased in the region. Studying the relationship between tremors and the Kaikoura earthquake may provide some information on the role of the subduction in the region, as well as provide a new documented interaction of slow earthquakes with a crustal earthquake.
To detect and locate tremors, we use broadband and shortband velocity traces from the GeoNet network. The traces are bandpass filtered between 2-8Hz, and transform into envelope. Then we apply a classic cross-correlation technic to detect and locate the events. To remove unexpected events (i.e.: earthquakes), we used a criteria base on seismic energy and duration. Finally, we manually check each velocity traces and spectrograms.
How to cite: Romanet, P., Aden-Antoniow, F., and Ide, S.: The 2016 Mw 7.8 Kaikoura earthquake and its relationship to tremors., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12694, https://doi.org/10.5194/egusphere-egu2020-12694, 2020.
TS5.5 – Active Tectonics and Geodynamics of Eastern Mediterranean
EGU2020-11156 | Displays | TS5.5
Measuring Anatolian plate velocity and strain with Sentinel-1 InSAR and GNSS data: implications for fault locking, seismic hazard, and crustal dynamicsJonathan Weiss, Richard Walters, Tim Wright, Yu Morishita, Milan Lazecky, Hua Wang, Ekbal Hussain, and Andrew Hooper
Geodetic measurements of small rates of interseismic crustal motion made at high spatial resolutions and over large areas are crucial for understanding the earthquake cycle, characterizing spatial variations in lithosphere rheology and fault frictional properties, illuminating the mechanics of large-scale continental deformation, and improving earthquake hazard models. The densification of Global Navigation Satellite System (GNSS) networks has provided an unprecedented view of the kinematics of deforming regions. However, large gaps in spatial coverage still hamper our ability to fully characterize patterns of surface deformation. Interferometric synthetic aperture radar (InSAR), and the Sentinel-1 (S-1) satellites in particular, have the potential to overcome this obstacle by providing spatially continuous measurements of surface motions, without instruments on the ground, with precision approaching that obtained from GNSS, and at a resolution of a few tens of meters. In order to manage and process the large data volumes produced by S-1, we have developed open-source, automated workflows to efficiently generate interferograms and line-of-sight (LOS) velocity fields. These outputs are valuable for a range of applications, from earthquake rapid-response to investigating human-induced ground-level changes. In this talk, we demonstrate our ability to measure plate-scale interseismic deformation using data from the first ~5 years of the S-1 mission. We estimate LOS velocities for the Anatolian microplate, an area encompassing ~800,000 km2 and including the highly seismogenic North Anatolian Fault Zone (NAFZ). By combining S-1 InSAR and GNSS data, we create high-resolution surface velocity and strain rate fields for the region, which illuminate horizontal deformation patterns dominated by the westward motion of Anatolia relative to Eurasia, localized strain accumulation along the NAFZ, and rapid vertical signals associated with groundwater extraction. Relatively low levels of strain characterize other active regions including the East and Central Anatolian Fault Zones and the Western Anatolian Extensional Province. We find that GNSS data alone are insufficient for characterizing key details of the strain rate field that are critical for understanding the relationship between strain accumulation and release in earthquakes. We highlight two important results stemming from our work including probabilistic estimates of the recurrence times of earthquakes of varying magnitudes for the region and a new NAFZ locking distribution that shows close correspondence to the surface rupture extents of large 20th century earthquakes.
How to cite: Weiss, J., Walters, R., Wright, T., Morishita, Y., Lazecky, M., Wang, H., Hussain, E., and Hooper, A.: Measuring Anatolian plate velocity and strain with Sentinel-1 InSAR and GNSS data: implications for fault locking, seismic hazard, and crustal dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11156, https://doi.org/10.5194/egusphere-egu2020-11156, 2020.
Geodetic measurements of small rates of interseismic crustal motion made at high spatial resolutions and over large areas are crucial for understanding the earthquake cycle, characterizing spatial variations in lithosphere rheology and fault frictional properties, illuminating the mechanics of large-scale continental deformation, and improving earthquake hazard models. The densification of Global Navigation Satellite System (GNSS) networks has provided an unprecedented view of the kinematics of deforming regions. However, large gaps in spatial coverage still hamper our ability to fully characterize patterns of surface deformation. Interferometric synthetic aperture radar (InSAR), and the Sentinel-1 (S-1) satellites in particular, have the potential to overcome this obstacle by providing spatially continuous measurements of surface motions, without instruments on the ground, with precision approaching that obtained from GNSS, and at a resolution of a few tens of meters. In order to manage and process the large data volumes produced by S-1, we have developed open-source, automated workflows to efficiently generate interferograms and line-of-sight (LOS) velocity fields. These outputs are valuable for a range of applications, from earthquake rapid-response to investigating human-induced ground-level changes. In this talk, we demonstrate our ability to measure plate-scale interseismic deformation using data from the first ~5 years of the S-1 mission. We estimate LOS velocities for the Anatolian microplate, an area encompassing ~800,000 km2 and including the highly seismogenic North Anatolian Fault Zone (NAFZ). By combining S-1 InSAR and GNSS data, we create high-resolution surface velocity and strain rate fields for the region, which illuminate horizontal deformation patterns dominated by the westward motion of Anatolia relative to Eurasia, localized strain accumulation along the NAFZ, and rapid vertical signals associated with groundwater extraction. Relatively low levels of strain characterize other active regions including the East and Central Anatolian Fault Zones and the Western Anatolian Extensional Province. We find that GNSS data alone are insufficient for characterizing key details of the strain rate field that are critical for understanding the relationship between strain accumulation and release in earthquakes. We highlight two important results stemming from our work including probabilistic estimates of the recurrence times of earthquakes of varying magnitudes for the region and a new NAFZ locking distribution that shows close correspondence to the surface rupture extents of large 20th century earthquakes.
How to cite: Weiss, J., Walters, R., Wright, T., Morishita, Y., Lazecky, M., Wang, H., Hussain, E., and Hooper, A.: Measuring Anatolian plate velocity and strain with Sentinel-1 InSAR and GNSS data: implications for fault locking, seismic hazard, and crustal dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11156, https://doi.org/10.5194/egusphere-egu2020-11156, 2020.
EGU2020-7656 | Displays | TS5.5
Contemporary Kinematics of the South Aegean Area (Greece) Detected with Continuous GNSS MeasurementsVassilis Sakkas, Chrysa Doxa, Andreas Tzanis, and Haralambos Kranis
We examine the kinematic characteristics of the crustal deformation in the broader southern Aegean region using 47 permanent GNNS stations distributed across the eastern Peloponnesus, Attica, Cyclades, Dodecanese, Crete and the coast of western Anatolia. Our analysis is based on the study of velocity vectors relative to local reference points at the western and eastern halves of the study area, as well as on the strain field calculated from absolute velocity vectors across the study area. We demonstrate that the South Aegean region undergoes complex distributed block deformation.
At the eastern end of the study area this varies from N210°-N220° extension and with crustal thinning across NE Peloponnesus – Attica, to N210°-N220° compression between the central-eastern Peloponnesus and western Crete, both consistent with the geodynamic setting of the Hellenic Subduction System.
A principal feature of the S. Aegean crust appears to be a broad shear zone extending between the islands of Samos/Ikaria and Kalymnos, Paros/Naxos and Amorgos and Milos – Santorini; It exhibits left-lateral kinematics and its southern boundary appears to coincide with the Amorgos – Santorini ridge and comprise the Anhydros basin and associated volcanic field (including Columbo and Santorini). Significant WNW-ESE crustal thinning is observed within the zone.
The area of the Dodecanese, to the south of Kalymnos and east of Astypalaea and north of Rhodes appears to undergo severe crustal thinning in the NW-SE direction while the SE rim of the Aegean Plate appears to undergo thinning in the NE-SW direction. Finally, the abrupt increase in velocity between eastern Crete and Karpathos island indicates the presence of a very significant N-S tectonic boundary of unknown as yet nature, extending between 35°N and 36°N at least.
In order to assign some values to the above qualitative description, we note that with respect to a reference point at Anavyssos, Attica, the distribution of velocities allows identification of four and possibly five major tectonic blocks with different kinematics, whose location, direction of motion and average velocities respectively are:
- Samos – Ikaria and Naxos-Paros-Amorgos group of islands, N220° and 1.5mm/yr respectively.
- The south-western Cyclades (Anafi, Ios, Antiparos, Milos, Folegandros, Sikinos and Santorini group of islands, N210° and 3.3 mm/yr.
- The northern Dodecanese (Kalymnos, Kos, Astypalaea group), N150° and 3.0 mm/yr.
- The southern Dodecanese (Nisyros, Telos, Rhodes, Karpathos group), N120° and 7.4 mm/yr respectively.
- The Cretan Sea and Crete, N160° and 2.0 mm/yr respectively.
An interpretation of the nature and kinematics of the boundaries between these blocks will be presented and discussed. Overall, the south Aegean appears to undergo distributed block deformation associated with a rather complex kinematic pattern, the nature of which remains to be confirmed, validated and explained with future research.
Acknowledgements. This presentation was financially supported by the Special Account for Research Grants of the National & Kapodistrian University of Athens.
How to cite: Sakkas, V., Doxa, C., Tzanis, A., and Kranis, H.: Contemporary Kinematics of the South Aegean Area (Greece) Detected with Continuous GNSS Measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7656, https://doi.org/10.5194/egusphere-egu2020-7656, 2020.
We examine the kinematic characteristics of the crustal deformation in the broader southern Aegean region using 47 permanent GNNS stations distributed across the eastern Peloponnesus, Attica, Cyclades, Dodecanese, Crete and the coast of western Anatolia. Our analysis is based on the study of velocity vectors relative to local reference points at the western and eastern halves of the study area, as well as on the strain field calculated from absolute velocity vectors across the study area. We demonstrate that the South Aegean region undergoes complex distributed block deformation.
At the eastern end of the study area this varies from N210°-N220° extension and with crustal thinning across NE Peloponnesus – Attica, to N210°-N220° compression between the central-eastern Peloponnesus and western Crete, both consistent with the geodynamic setting of the Hellenic Subduction System.
A principal feature of the S. Aegean crust appears to be a broad shear zone extending between the islands of Samos/Ikaria and Kalymnos, Paros/Naxos and Amorgos and Milos – Santorini; It exhibits left-lateral kinematics and its southern boundary appears to coincide with the Amorgos – Santorini ridge and comprise the Anhydros basin and associated volcanic field (including Columbo and Santorini). Significant WNW-ESE crustal thinning is observed within the zone.
The area of the Dodecanese, to the south of Kalymnos and east of Astypalaea and north of Rhodes appears to undergo severe crustal thinning in the NW-SE direction while the SE rim of the Aegean Plate appears to undergo thinning in the NE-SW direction. Finally, the abrupt increase in velocity between eastern Crete and Karpathos island indicates the presence of a very significant N-S tectonic boundary of unknown as yet nature, extending between 35°N and 36°N at least.
In order to assign some values to the above qualitative description, we note that with respect to a reference point at Anavyssos, Attica, the distribution of velocities allows identification of four and possibly five major tectonic blocks with different kinematics, whose location, direction of motion and average velocities respectively are:
- Samos – Ikaria and Naxos-Paros-Amorgos group of islands, N220° and 1.5mm/yr respectively.
- The south-western Cyclades (Anafi, Ios, Antiparos, Milos, Folegandros, Sikinos and Santorini group of islands, N210° and 3.3 mm/yr.
- The northern Dodecanese (Kalymnos, Kos, Astypalaea group), N150° and 3.0 mm/yr.
- The southern Dodecanese (Nisyros, Telos, Rhodes, Karpathos group), N120° and 7.4 mm/yr respectively.
- The Cretan Sea and Crete, N160° and 2.0 mm/yr respectively.
An interpretation of the nature and kinematics of the boundaries between these blocks will be presented and discussed. Overall, the south Aegean appears to undergo distributed block deformation associated with a rather complex kinematic pattern, the nature of which remains to be confirmed, validated and explained with future research.
Acknowledgements. This presentation was financially supported by the Special Account for Research Grants of the National & Kapodistrian University of Athens.
How to cite: Sakkas, V., Doxa, C., Tzanis, A., and Kranis, H.: Contemporary Kinematics of the South Aegean Area (Greece) Detected with Continuous GNSS Measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7656, https://doi.org/10.5194/egusphere-egu2020-7656, 2020.
EGU2020-3167 | Displays | TS5.5
Bivergent extension in the overriding plate above a slab tear (Dodecanese, Greece)Bernhard Grasemann, David A. Schneider, Konstantinos Soukis, and Vincent Roche
Tearing in the Hellenic slab below the transition between the Aegean and Anatolian plate is considered to have significantly affected Miocene tectonic and magmatic evolution of the eastern Mediterranean by causing a toroidal flow of asthenosphere and a lateral gradient of extension in the upper plate. Some studies suggest that this lateral gradient is accommodated by a distributed sinistral lithospheric-scale shear zone whereas other studies favor a localized NE-SW striking transfer zone. Recent studies in the northern Dodecanese demonstrate that the transition zone between the Aegean and Anatolian plate is characterized by Miocene extension with a constant NNE-SSW sense of shear accommodating the difference in finite extension rates in the middle-lower crust. Neither localized or distributed strike-slip faults nor rotation of blocks about a vertical axis have been observed.
In this work we focus on the geology Kalymnos located in the central Dodecanese. Based on our new geological map, three major tectonic units can be distinguished: (i) Low-grade, fossil-rich late Paleozoic marbles, which have been deformed into S-vergent folds and out-of-sequence thrusts. This fold-and-thrust belt is sealed by an up to 200 m thick wildflysch-type deposit consisting of low-grade metamorphic radiolarites and conglomerates with tens of meters-scale marbles and ultramafics blocks. (ii) Above this unit, amphibolite facies schists, quartzites and amphibolites are tectonically juxtaposed along a several meter-thick thrust fault with low-grade ultramylonites and cohesive ultracataclasites/pseudotachylites with top-to-N kinematics. (iii) At highest structural levels, a major cataclastic low-angle normal fault zone localized in Verrucano-type violet slates separates Mesozoic unmetamorphosed limestones in the hanging wall. The sense of shear of the normal fault is top-to-SSW. All units are cut by brittle high-angle normal faults shaping the geomorphology of Kalymnos, which is characterized by three major NNW-SSE trending graben systems.
New white mica Ar-Ar ages suggests that the middle units represent relics of a Variscan basement, which was thrusted on top of a fold-and-thrust belt during an Eo-Cimmerian event. Zircon (U-Th)/He ages from the Variscan basement are c. 28 Ma, indicating that the lower units were exhumed below the Mesozoic carbonates during the Oligocene-Miocene. Since Miocene extension in the northern Dodecanese records top-to-NNE kinematics, we suggest that back-arc extension in the whole Aegean realm and transition to the Anatolian plate is bivergent, and tearing in the Hellenic slab did not significantly affected the extension pattern in the upper crust.
How to cite: Grasemann, B., Schneider, D. A., Soukis, K., and Roche, V.: Bivergent extension in the overriding plate above a slab tear (Dodecanese, Greece), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3167, https://doi.org/10.5194/egusphere-egu2020-3167, 2020.
Tearing in the Hellenic slab below the transition between the Aegean and Anatolian plate is considered to have significantly affected Miocene tectonic and magmatic evolution of the eastern Mediterranean by causing a toroidal flow of asthenosphere and a lateral gradient of extension in the upper plate. Some studies suggest that this lateral gradient is accommodated by a distributed sinistral lithospheric-scale shear zone whereas other studies favor a localized NE-SW striking transfer zone. Recent studies in the northern Dodecanese demonstrate that the transition zone between the Aegean and Anatolian plate is characterized by Miocene extension with a constant NNE-SSW sense of shear accommodating the difference in finite extension rates in the middle-lower crust. Neither localized or distributed strike-slip faults nor rotation of blocks about a vertical axis have been observed.
In this work we focus on the geology Kalymnos located in the central Dodecanese. Based on our new geological map, three major tectonic units can be distinguished: (i) Low-grade, fossil-rich late Paleozoic marbles, which have been deformed into S-vergent folds and out-of-sequence thrusts. This fold-and-thrust belt is sealed by an up to 200 m thick wildflysch-type deposit consisting of low-grade metamorphic radiolarites and conglomerates with tens of meters-scale marbles and ultramafics blocks. (ii) Above this unit, amphibolite facies schists, quartzites and amphibolites are tectonically juxtaposed along a several meter-thick thrust fault with low-grade ultramylonites and cohesive ultracataclasites/pseudotachylites with top-to-N kinematics. (iii) At highest structural levels, a major cataclastic low-angle normal fault zone localized in Verrucano-type violet slates separates Mesozoic unmetamorphosed limestones in the hanging wall. The sense of shear of the normal fault is top-to-SSW. All units are cut by brittle high-angle normal faults shaping the geomorphology of Kalymnos, which is characterized by three major NNW-SSE trending graben systems.
New white mica Ar-Ar ages suggests that the middle units represent relics of a Variscan basement, which was thrusted on top of a fold-and-thrust belt during an Eo-Cimmerian event. Zircon (U-Th)/He ages from the Variscan basement are c. 28 Ma, indicating that the lower units were exhumed below the Mesozoic carbonates during the Oligocene-Miocene. Since Miocene extension in the northern Dodecanese records top-to-NNE kinematics, we suggest that back-arc extension in the whole Aegean realm and transition to the Anatolian plate is bivergent, and tearing in the Hellenic slab did not significantly affected the extension pattern in the upper crust.
How to cite: Grasemann, B., Schneider, D. A., Soukis, K., and Roche, V.: Bivergent extension in the overriding plate above a slab tear (Dodecanese, Greece), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3167, https://doi.org/10.5194/egusphere-egu2020-3167, 2020.
EGU2020-4857 | Displays | TS5.5
Persistent earthquake-rupture segmentation due to variable interseismic slip accumulation within the southern Hellenic subduction plate-interface zone in GreeceVasso Saltogianni, Vasiliki Mouslopoulou, Onno Oncken, Andrew Nicol, Michael Gianniou, and Stelios Mertikas
Increasing evidence suggests that large thrust-faults that splay from the plate-interface to extend within the upper-plate have a significant impact on subduction seismogenesis. The manner in which these two elements, the plate-interface itself and its splay-thrust faults, interact with one another during the earthquake cycle remains, however, poorly explored. Here, we use GPS velocities, constrained by millennial fault slip-rates, to quantify the accumulation (and partitioning) of strain on individual faults of the plate-interface zone and capture their possible interactions. We zoom into the southern Hellenic Subduction System (HSS), where the greatest (M8.3) earthquake and tsunami ever recorded in the Mediterranean was produced by slip on a splay-thrust fault. Our analysis shows that the HSS is kinematically segmented and strain is accumulated at spatially variable rates along individual structures of the plate-interface zone. We find that insterseismic locking reaches up to ~85% and ~45% on the western and eastern segments, respectively, and on structures different to those that ruptured historically. Although the western HSS has been more active recently (e.g. 365 BC), the eastern HSS carries currently higher potential for large-magnitude (M>6) earthquakes andits interface-zone appears to be closer to failure. Elastic fault-interactions are responsible for both significant inter-segment variability in strain-accumulation and millennial uniformity in earthquake rupture-segmentation between eastern and western HSS.
How to cite: Saltogianni, V., Mouslopoulou, V., Oncken, O., Nicol, A., Gianniou, M., and Mertikas, S.: Persistent earthquake-rupture segmentation due to variable interseismic slip accumulation within the southern Hellenic subduction plate-interface zone in Greece , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4857, https://doi.org/10.5194/egusphere-egu2020-4857, 2020.
Increasing evidence suggests that large thrust-faults that splay from the plate-interface to extend within the upper-plate have a significant impact on subduction seismogenesis. The manner in which these two elements, the plate-interface itself and its splay-thrust faults, interact with one another during the earthquake cycle remains, however, poorly explored. Here, we use GPS velocities, constrained by millennial fault slip-rates, to quantify the accumulation (and partitioning) of strain on individual faults of the plate-interface zone and capture their possible interactions. We zoom into the southern Hellenic Subduction System (HSS), where the greatest (M8.3) earthquake and tsunami ever recorded in the Mediterranean was produced by slip on a splay-thrust fault. Our analysis shows that the HSS is kinematically segmented and strain is accumulated at spatially variable rates along individual structures of the plate-interface zone. We find that insterseismic locking reaches up to ~85% and ~45% on the western and eastern segments, respectively, and on structures different to those that ruptured historically. Although the western HSS has been more active recently (e.g. 365 BC), the eastern HSS carries currently higher potential for large-magnitude (M>6) earthquakes andits interface-zone appears to be closer to failure. Elastic fault-interactions are responsible for both significant inter-segment variability in strain-accumulation and millennial uniformity in earthquake rupture-segmentation between eastern and western HSS.
How to cite: Saltogianni, V., Mouslopoulou, V., Oncken, O., Nicol, A., Gianniou, M., and Mertikas, S.: Persistent earthquake-rupture segmentation due to variable interseismic slip accumulation within the southern Hellenic subduction plate-interface zone in Greece , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4857, https://doi.org/10.5194/egusphere-egu2020-4857, 2020.
EGU2020-10755 | Displays | TS5.5
Neogene and active brittle deformation on Amorgos Island (Greece)Jan Behrmann, Jakob Schneider, and Benjamin Zitzow
Amorgos is the south-eastern outpost of the Cyclades Islands in the Aegean Sea, which forms part of the Neogene-Quaternary zone of crustal and lithospheric N-S upper plate extension northward of the Hellenic subduction zone and deep sea trench. Apart from subduction-related earthquakes further south, the southern Aegean is affected by frequent earthquakes sourced in the upper plate. The twin earthquakes of 9 July 1956, followed by a strong tsunami, were the strongest events of this kind in the past Century. Hypocenters are related to a NE-SW oriented normal fault bounding the Amorgos-Santorini Graben System. There are questions in the literature regarding the seismic source and fault plane solutions, especially the contribution of a transcurrent faulting component.
We have analyzed the kinematics of brittle faults exposed on Amorgos Island itself that could be related to Neogene and active extensional and/or transcurrent deformation. Seismic slip often occurs on previously existing faults. Thus, their orientations and kinematics may help shed light on the structure of seismic sources at depth. We present evidence for a complex history of faulting. Early normal detachment faults and shear zones overprint older (rare) reverse faults, and are themselves overprinted by several sets of dominantly dextral NE and SE trending strike slip faults. Youngest is a conjugate set of NE trending high-angle normal faults. These are especially frequent along the SE coast of the island, suggesting a clear spatial relationship with the 1956 rupture. They can be fitted to a moment tensor solution similar to the published solutions for the 1956 Amorgos earthquake. The kinematic solution for the population of early normal faults suggests that the whole of Amorgos Island may have experienced a 15° NNW tilt during later extension, which lets us suspect that the island could be a tilted block of a much larger fault system. Regarding long-term late Neogene to Quaternary kinematics, dextrally transtensive fault slip is required to fit the regional pattern of extensional deformation in the Aegean, and this is reflected by small-scale brittle faulting on Amorgos.
How to cite: Behrmann, J., Schneider, J., and Zitzow, B.: Neogene and active brittle deformation on Amorgos Island (Greece), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10755, https://doi.org/10.5194/egusphere-egu2020-10755, 2020.
Amorgos is the south-eastern outpost of the Cyclades Islands in the Aegean Sea, which forms part of the Neogene-Quaternary zone of crustal and lithospheric N-S upper plate extension northward of the Hellenic subduction zone and deep sea trench. Apart from subduction-related earthquakes further south, the southern Aegean is affected by frequent earthquakes sourced in the upper plate. The twin earthquakes of 9 July 1956, followed by a strong tsunami, were the strongest events of this kind in the past Century. Hypocenters are related to a NE-SW oriented normal fault bounding the Amorgos-Santorini Graben System. There are questions in the literature regarding the seismic source and fault plane solutions, especially the contribution of a transcurrent faulting component.
We have analyzed the kinematics of brittle faults exposed on Amorgos Island itself that could be related to Neogene and active extensional and/or transcurrent deformation. Seismic slip often occurs on previously existing faults. Thus, their orientations and kinematics may help shed light on the structure of seismic sources at depth. We present evidence for a complex history of faulting. Early normal detachment faults and shear zones overprint older (rare) reverse faults, and are themselves overprinted by several sets of dominantly dextral NE and SE trending strike slip faults. Youngest is a conjugate set of NE trending high-angle normal faults. These are especially frequent along the SE coast of the island, suggesting a clear spatial relationship with the 1956 rupture. They can be fitted to a moment tensor solution similar to the published solutions for the 1956 Amorgos earthquake. The kinematic solution for the population of early normal faults suggests that the whole of Amorgos Island may have experienced a 15° NNW tilt during later extension, which lets us suspect that the island could be a tilted block of a much larger fault system. Regarding long-term late Neogene to Quaternary kinematics, dextrally transtensive fault slip is required to fit the regional pattern of extensional deformation in the Aegean, and this is reflected by small-scale brittle faulting on Amorgos.
How to cite: Behrmann, J., Schneider, J., and Zitzow, B.: Neogene and active brittle deformation on Amorgos Island (Greece), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10755, https://doi.org/10.5194/egusphere-egu2020-10755, 2020.
EGU2020-8478 | Displays | TS5.5
Co-seismic deformation and preliminary fault model of the M6.4 Durres (Albania) Nov. 26, 2019 earthquake, based on space geodesy observationsAthanassios Ganas, Varvara Tsironi, Flavio Cannavo, Pierre Briole, Panagiotis Elias, Sotiris Valkaniotis, Ioannis Koukouvelas, and Efthimios Sokos
We report the mapping the co-seismic deformation in the coastal region of Durres (Albania) following the Mw=6.4 shallow earthquake on Nov. 26, 2019, 02:54 UTC. The tectonics of western and northern Albania is characterised by on-going compression due to collision between Eurasian and Adriatic plates. Crustal deformation is characterised by shortening directed at NNE-SSW to E-W orientation. We analysed co-seismic interferograms of the Sentinel-1 (ESA) satellites (ascending orbit; relative orbit 175, slice numbers 14 & 15) and GPS observations (30-s interval) recorded at two stations (DUR2 and TIR2). The raw GPS data were processed with the GIPSY-OASIS II software, using the Precise Point Positioning (PPP) methodology with Final JPL products, to obtain daily static solutions defined in ITRF14. The coseismic offsets were computed as differences between the mean positions, respectively 5 days before and after the earthquake day. Uncertainties associated with the displacements were calculated by propagating the errors in GPS solutions. For DUR2 the displacement is significant in all three components (East=-1.3 cm, North=-2.1 cm, Up= +1.4 cm), while for TIR2 seems reasonable (0.4 cm on the horizontal components) but within the error bar. The SAR images were processed by the open-source SNAP software and they were obtained on Nov. 14, 2019 20:59 UTC (master scene) and on Nov. 26, 2019 16:31 UTC (slave scene). Each frame (slice) was processed independently and the wrapped phase was mosaicked in order to reveal the full deformation extent. The InSAR fringe pattern shows a 45-km long, NW-SE arrangement of three (3) fringes with a maximum LOS displacement of about +8.4 cm near the village Hamallaj (15 km NE of Durres). Assuming a half-space elastic model with uniform slip along a rectangular fault surface, the source of the ground deformation was inverted using the available geodetic data (GNSS and InSAR). The mean scatter value between data and the model is 2.4 mm. The inversion modelling indicates that the 2019 Durres (Albania) earthquakes ruptured a low-angle fault (24 km long by 9 km wide) dipping 23° towards east with the fault plane top at 16 km. The geodetic fault-model is in agreement with published moment tensor solutions showing a NNW-SSE fault plane (for example the USGS solution has attributes 337°/27°/91°; strike/dip-angle/rake angle). This geometry is compatible with a blind thrust fault that may root on the main basal thrust i.e. along the main Ionian thrust front that separates Adria-Apulia from Eurasia.
Acknowledgement: This research is supported by HELPOS (“Hellenic Plate Observing System” - MIS 5002697) which is implemented under the Action “Reinforcement of the Research and Innovation Infrastructure”, funded by the Operational Programme "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund). We also thank The Institute of GeoSciences, Energy, Water and Environment of Albania for providing GNSS data.
How to cite: Ganas, A., Tsironi, V., Cannavo, F., Briole, P., Elias, P., Valkaniotis, S., Koukouvelas, I., and Sokos, E.: Co-seismic deformation and preliminary fault model of the M6.4 Durres (Albania) Nov. 26, 2019 earthquake, based on space geodesy observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8478, https://doi.org/10.5194/egusphere-egu2020-8478, 2020.
We report the mapping the co-seismic deformation in the coastal region of Durres (Albania) following the Mw=6.4 shallow earthquake on Nov. 26, 2019, 02:54 UTC. The tectonics of western and northern Albania is characterised by on-going compression due to collision between Eurasian and Adriatic plates. Crustal deformation is characterised by shortening directed at NNE-SSW to E-W orientation. We analysed co-seismic interferograms of the Sentinel-1 (ESA) satellites (ascending orbit; relative orbit 175, slice numbers 14 & 15) and GPS observations (30-s interval) recorded at two stations (DUR2 and TIR2). The raw GPS data were processed with the GIPSY-OASIS II software, using the Precise Point Positioning (PPP) methodology with Final JPL products, to obtain daily static solutions defined in ITRF14. The coseismic offsets were computed as differences between the mean positions, respectively 5 days before and after the earthquake day. Uncertainties associated with the displacements were calculated by propagating the errors in GPS solutions. For DUR2 the displacement is significant in all three components (East=-1.3 cm, North=-2.1 cm, Up= +1.4 cm), while for TIR2 seems reasonable (0.4 cm on the horizontal components) but within the error bar. The SAR images were processed by the open-source SNAP software and they were obtained on Nov. 14, 2019 20:59 UTC (master scene) and on Nov. 26, 2019 16:31 UTC (slave scene). Each frame (slice) was processed independently and the wrapped phase was mosaicked in order to reveal the full deformation extent. The InSAR fringe pattern shows a 45-km long, NW-SE arrangement of three (3) fringes with a maximum LOS displacement of about +8.4 cm near the village Hamallaj (15 km NE of Durres). Assuming a half-space elastic model with uniform slip along a rectangular fault surface, the source of the ground deformation was inverted using the available geodetic data (GNSS and InSAR). The mean scatter value between data and the model is 2.4 mm. The inversion modelling indicates that the 2019 Durres (Albania) earthquakes ruptured a low-angle fault (24 km long by 9 km wide) dipping 23° towards east with the fault plane top at 16 km. The geodetic fault-model is in agreement with published moment tensor solutions showing a NNW-SSE fault plane (for example the USGS solution has attributes 337°/27°/91°; strike/dip-angle/rake angle). This geometry is compatible with a blind thrust fault that may root on the main basal thrust i.e. along the main Ionian thrust front that separates Adria-Apulia from Eurasia.
Acknowledgement: This research is supported by HELPOS (“Hellenic Plate Observing System” - MIS 5002697) which is implemented under the Action “Reinforcement of the Research and Innovation Infrastructure”, funded by the Operational Programme "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund). We also thank The Institute of GeoSciences, Energy, Water and Environment of Albania for providing GNSS data.
How to cite: Ganas, A., Tsironi, V., Cannavo, F., Briole, P., Elias, P., Valkaniotis, S., Koukouvelas, I., and Sokos, E.: Co-seismic deformation and preliminary fault model of the M6.4 Durres (Albania) Nov. 26, 2019 earthquake, based on space geodesy observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8478, https://doi.org/10.5194/egusphere-egu2020-8478, 2020.
EGU2020-18053 | Displays | TS5.5
Present Seismotectonic Behavior of the EAF from Improved Seismicity Catalog and Earthquake Source Mechanism SolutionsSezim Ezgi Guvercin, Hayrullah Karabulut, Ugur Dogan, Ziyadin Cakir, Semih Ergintav, Cengiz Zabci, Alpay Ozdemir, Seda Ozarpaci, Ali Ozgun Konca, and Mehmet Kokum
The seismotectonic behavior of the Eastern Anatolia is predominantly controlled by the East Anatolian Fault (EAF). Together with the North Anatolian Fault (NAF), this ~400 km long sinistral transform fault, accommodates the westward motion of Anatolia between Anatolian and Arabian plates with a slip rate of ~10 mm/yr which is significantly slower than the motion of the NAF (25 mm/yr). Although this two major faults are similar in terms of the migration of the large earthquakes from east to west, the present seismicity of the EAF is high compared to the NAF. Except for the several earthquakes with Mw > 5, there were no devastating earthquakes during the instrumental period along the EAF. The absence of large earthquakes during the last ~50 years along the EAF indicates presence of significant seismic gaps and potential seismic hazard in the region. Recent studies indicate segmentation of the EAF with varying lengths of creeping and locked segments. Some details of the geometries and the slip rates of these segments have been estimated by the InSAR observations. Both InSAR and GPS observations indicate that the maximum creep along this the EAF is ~10 mm/yr, approximately the slip rate of the EAF.
While both geodetic data verify the existence of creep from surface deformation, its relation to the seismic behavior of the EAF is less clear. There is a ~30 km long creeping segment to the north-east of Lake Hazar which generates no significant seismicity. On the other hand, another creeping segment to the south-west of Lake Hazar, there are repeating events, below the depth of 10 km, with a horizontal extent of 15 km. The highly fractured and complex structure of this fault zone is also confirmed by the available focal mechanisms which shows significant variety.
In this study, we update seismicity catalog with improved locations to date and present a uniform and high quality focal mechanism catalog down to M4 completeness, using regional waveforms. The seismicity catalog is used to estimate the geometry of the segmentation while the novel earthquake source mechanisms are used to understand the kinematics of the segments and interactions. Moreover, we present the latest M4.9, 2019, Sivrice earthquake, pointing out a location where the stress is perturbed due to a transition from creeping segment to locked segment. (Supported by TUBITAK no: 118Y435 project)
How to cite: Guvercin, S. E., Karabulut, H., Dogan, U., Cakir, Z., Ergintav, S., Zabci, C., Ozdemir, A., Ozarpaci, S., Konca, A. O., and Kokum, M.: Present Seismotectonic Behavior of the EAF from Improved Seismicity Catalog and Earthquake Source Mechanism Solutions , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18053, https://doi.org/10.5194/egusphere-egu2020-18053, 2020.
The seismotectonic behavior of the Eastern Anatolia is predominantly controlled by the East Anatolian Fault (EAF). Together with the North Anatolian Fault (NAF), this ~400 km long sinistral transform fault, accommodates the westward motion of Anatolia between Anatolian and Arabian plates with a slip rate of ~10 mm/yr which is significantly slower than the motion of the NAF (25 mm/yr). Although this two major faults are similar in terms of the migration of the large earthquakes from east to west, the present seismicity of the EAF is high compared to the NAF. Except for the several earthquakes with Mw > 5, there were no devastating earthquakes during the instrumental period along the EAF. The absence of large earthquakes during the last ~50 years along the EAF indicates presence of significant seismic gaps and potential seismic hazard in the region. Recent studies indicate segmentation of the EAF with varying lengths of creeping and locked segments. Some details of the geometries and the slip rates of these segments have been estimated by the InSAR observations. Both InSAR and GPS observations indicate that the maximum creep along this the EAF is ~10 mm/yr, approximately the slip rate of the EAF.
While both geodetic data verify the existence of creep from surface deformation, its relation to the seismic behavior of the EAF is less clear. There is a ~30 km long creeping segment to the north-east of Lake Hazar which generates no significant seismicity. On the other hand, another creeping segment to the south-west of Lake Hazar, there are repeating events, below the depth of 10 km, with a horizontal extent of 15 km. The highly fractured and complex structure of this fault zone is also confirmed by the available focal mechanisms which shows significant variety.
In this study, we update seismicity catalog with improved locations to date and present a uniform and high quality focal mechanism catalog down to M4 completeness, using regional waveforms. The seismicity catalog is used to estimate the geometry of the segmentation while the novel earthquake source mechanisms are used to understand the kinematics of the segments and interactions. Moreover, we present the latest M4.9, 2019, Sivrice earthquake, pointing out a location where the stress is perturbed due to a transition from creeping segment to locked segment. (Supported by TUBITAK no: 118Y435 project)
How to cite: Guvercin, S. E., Karabulut, H., Dogan, U., Cakir, Z., Ergintav, S., Zabci, C., Ozdemir, A., Ozarpaci, S., Konca, A. O., and Kokum, M.: Present Seismotectonic Behavior of the EAF from Improved Seismicity Catalog and Earthquake Source Mechanism Solutions , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18053, https://doi.org/10.5194/egusphere-egu2020-18053, 2020.
EGU2020-10185 | Displays | TS5.5
Contrasting seismogenic behaviors on the North Anatolian Fault in the Sea of MarmaraPierre Henry, Céline Grall, M Sinan Özeren, Volkan Özbey, Gülsen Uçarkus, Louis Géli, Valérie Ballu, Ziyadin Çakir, Semih Ergintav, Dietrich Lange, and Jean-Yves Royer
Since the 1999 Izmit-Kocaeli earthquake, the Main Marmara Fault (MMF) of the North Anatolian Fault system in the Sea of Marmara has been considered at an imminent risk for a large earthquake. Land geodesy has difficulties characterizing the distribution of interseismic loading, and hence of slip deficit, on the offshore faults, and notably on the Istanbul-Silivri segment of the NAF. The need to clarify the status of offshore fault segments has motivated seafloor monitoring experiments and marine geophysical and sedimentological studies, notably in the framework of EMSO consortium and MARSITE and MAREGAMI projects. Results from cross-disciplinary projects have shown that aseismic creep, spatially correlated to active gas venting at the seafloor, occurs on the Western segment of the MMF. This segment is also capable to large earthquake ruptures such as the 1912 event. On the eastern part of the Sea of Marmara, the Istanbul-Silivri and Prince Island segments appear essentially locked. Moreover, the base of the seismogenic zone and locking depth appears to shallow (from 15-20 to 10-15 km) from west to east.
On one hand, we propose to further evaluate fault slip rates and distribution of locking ratio on individual fault segments using an elastic block model constrained by land geodesy data and marine observations (long-term fault slip rate estimates, local acoustic ranging results). On the other hand, we evaluate the temperature at the seismogenic depths by basin modelling. Results suggest that spatial variations of fault behavior in the Sea of Marmara may result from a combination of factors. First, thermogenic gas generation within the > 6 km thick sedimentary cover in the Western Sea of Marmara may contribute to unlock the shallow part of the fault by generating overpressures. Second, heterogeneity of the crust composition could be a factor as the North Anatolian Fault system follows the intra-pontide ophiolitic suture. For instance, long term post-seismic creep onland at Ismet Paşa has been related to the presence of serpentinite in the fault zone. Moreover, high-density magnetic bodies have been identified along the MMF. Third, varying thermal regimes between the Western and Eastern parts of the Sea of Marmara may account for variations in the seismogenic depths. Seafloor heat flow in the Sea of Marmara is strongly affected by sediment blanketing and basin modeling considering this process suggests that the crustal heat flow is about 20 mW/m2 higher in the eastern part than in western part of the Sea of Marmara. This difference may be explained by a more spread out crustal extension in the western Sea of Marmara.
How to cite: Henry, P., Grall, C., Özeren, M. S., Özbey, V., Uçarkus, G., Géli, L., Ballu, V., Çakir, Z., Ergintav, S., Lange, D., and Royer, J.-Y.: Contrasting seismogenic behaviors on the North Anatolian Fault in the Sea of Marmara, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10185, https://doi.org/10.5194/egusphere-egu2020-10185, 2020.
Since the 1999 Izmit-Kocaeli earthquake, the Main Marmara Fault (MMF) of the North Anatolian Fault system in the Sea of Marmara has been considered at an imminent risk for a large earthquake. Land geodesy has difficulties characterizing the distribution of interseismic loading, and hence of slip deficit, on the offshore faults, and notably on the Istanbul-Silivri segment of the NAF. The need to clarify the status of offshore fault segments has motivated seafloor monitoring experiments and marine geophysical and sedimentological studies, notably in the framework of EMSO consortium and MARSITE and MAREGAMI projects. Results from cross-disciplinary projects have shown that aseismic creep, spatially correlated to active gas venting at the seafloor, occurs on the Western segment of the MMF. This segment is also capable to large earthquake ruptures such as the 1912 event. On the eastern part of the Sea of Marmara, the Istanbul-Silivri and Prince Island segments appear essentially locked. Moreover, the base of the seismogenic zone and locking depth appears to shallow (from 15-20 to 10-15 km) from west to east.
On one hand, we propose to further evaluate fault slip rates and distribution of locking ratio on individual fault segments using an elastic block model constrained by land geodesy data and marine observations (long-term fault slip rate estimates, local acoustic ranging results). On the other hand, we evaluate the temperature at the seismogenic depths by basin modelling. Results suggest that spatial variations of fault behavior in the Sea of Marmara may result from a combination of factors. First, thermogenic gas generation within the > 6 km thick sedimentary cover in the Western Sea of Marmara may contribute to unlock the shallow part of the fault by generating overpressures. Second, heterogeneity of the crust composition could be a factor as the North Anatolian Fault system follows the intra-pontide ophiolitic suture. For instance, long term post-seismic creep onland at Ismet Paşa has been related to the presence of serpentinite in the fault zone. Moreover, high-density magnetic bodies have been identified along the MMF. Third, varying thermal regimes between the Western and Eastern parts of the Sea of Marmara may account for variations in the seismogenic depths. Seafloor heat flow in the Sea of Marmara is strongly affected by sediment blanketing and basin modeling considering this process suggests that the crustal heat flow is about 20 mW/m2 higher in the eastern part than in western part of the Sea of Marmara. This difference may be explained by a more spread out crustal extension in the western Sea of Marmara.
How to cite: Henry, P., Grall, C., Özeren, M. S., Özbey, V., Uçarkus, G., Géli, L., Ballu, V., Çakir, Z., Ergintav, S., Lange, D., and Royer, J.-Y.: Contrasting seismogenic behaviors on the North Anatolian Fault in the Sea of Marmara, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10185, https://doi.org/10.5194/egusphere-egu2020-10185, 2020.
EGU2020-8809 | Displays | TS5.5
The slip deficit along the North Anatolian Fault (Turkey) in the Marmara Sea: Insights from paleoseismicity, seismicity and geodetic dataErsen Aksoy, Mustapha Meghraoui, and Renaud Toussaint
The North Anatolian Fault experienced large earthquakes with 250 to 400 years recurrence time. In the Marmara Sea region the 1999 (Mw = 7.4) and the 1912 (Mw = 7.4) earthquake ruptures bound the Central Marmara Sea fault segment. Using historical-instrumental catalogue and paleoseismic results (≃ 2000-year database), the mapped fault segments, fault kinematic and GPS data, we compute the paleoseismic-seismic moment rate and geodetic moment rate. The geodetic moment rate is obtained by projecting the measured surface displacements to estimate the strain rate, and evaluating the associated elastic stress rate over a regular spatial grid. The paleoseismic-seismic moment rate is obtained by summing the moment tensors over regions of the spatial grid and periods of time. A clear discrepancy appears between the moment rates and implies a significant delay in the seismic slip along the fault. The rich database allows us to identify the size of the seismic gap and related fault segment and estimate the moment rate deficit. Our modeling suggest that the locked Central Marmara Sea fault segment even including a creeping section bears a moment rate deficit = 6.4*1017 N.m./yr. that corresponds to Mw ≃ 7.4 for a future earthquake with an average ≃ 3.25 m coseismic slip. Taking into account the uncertainty in the strain accumulation along the 130-km-long Central fault segment, our estimate of the seismic slip deficit being ≃ 10 mm/yr implies the size of the future earthquake ranges between Mw = 7.4 and 7.5.
How to cite: Aksoy, E., Meghraoui, M., and Toussaint, R.: The slip deficit along the North Anatolian Fault (Turkey) in the Marmara Sea: Insights from paleoseismicity, seismicity and geodetic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8809, https://doi.org/10.5194/egusphere-egu2020-8809, 2020.
The North Anatolian Fault experienced large earthquakes with 250 to 400 years recurrence time. In the Marmara Sea region the 1999 (Mw = 7.4) and the 1912 (Mw = 7.4) earthquake ruptures bound the Central Marmara Sea fault segment. Using historical-instrumental catalogue and paleoseismic results (≃ 2000-year database), the mapped fault segments, fault kinematic and GPS data, we compute the paleoseismic-seismic moment rate and geodetic moment rate. The geodetic moment rate is obtained by projecting the measured surface displacements to estimate the strain rate, and evaluating the associated elastic stress rate over a regular spatial grid. The paleoseismic-seismic moment rate is obtained by summing the moment tensors over regions of the spatial grid and periods of time. A clear discrepancy appears between the moment rates and implies a significant delay in the seismic slip along the fault. The rich database allows us to identify the size of the seismic gap and related fault segment and estimate the moment rate deficit. Our modeling suggest that the locked Central Marmara Sea fault segment even including a creeping section bears a moment rate deficit = 6.4*1017 N.m./yr. that corresponds to Mw ≃ 7.4 for a future earthquake with an average ≃ 3.25 m coseismic slip. Taking into account the uncertainty in the strain accumulation along the 130-km-long Central fault segment, our estimate of the seismic slip deficit being ≃ 10 mm/yr implies the size of the future earthquake ranges between Mw = 7.4 and 7.5.
How to cite: Aksoy, E., Meghraoui, M., and Toussaint, R.: The slip deficit along the North Anatolian Fault (Turkey) in the Marmara Sea: Insights from paleoseismicity, seismicity and geodetic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8809, https://doi.org/10.5194/egusphere-egu2020-8809, 2020.
EGU2020-4264 | Displays | TS5.5
3-D lithospheric-scale rheological model of the Sea of MarmaraErshad Gholamrezaie, Magdalena Scheck-Wenderoth, Judith Bott, Oliver Heidbach, Marco Bohnhoff, and Manfred R. Strecker
The North Anatolian Fault (NAF) below the Sea of Marmara, also known as the Main Marmara Fault (MMF), has repeatedly produced major (M>7) earthquakes in the past. Currently, the MMF corresponds to a seismic gap between the locus of the most recent M>7 ruptures of the 1912 Ganos (M 7.3) and 1999 Izmit (M 7.4) earthquakes. This seismic gap has a recurrence time of approximately 250 years and has not ruptured since 1766. Consequently, it poses a major seismic hazard to the Marmara region, including the megacity Istanbul. The Marmara seismic gap is considered to be locked in the eastern and central segments of the MMF, while the western segment is partly creeping. In the context of seismic hazard and risk assessment, one of the main questions is, if either the Marmara seismic gap will rupture in a single large earthquake or in several ones due to segmentation along the MMF. In part this depends on the physical properties of the lithosphere below the Sea of Marmara as they are a key control of the contemporary stress state. To contribute to this discussion, we present 3‑D lithospheric-scale thermal and rheological models of the Sea of Marmara. These models are based on published 3‑D density models that indicate lateral and vertical crustal heterogeneities below the Sea of Marmara (Gholamrezaie et al., 2019). The density models consist of two layers of sediments, upper and lower crystalline crustal layers, and two crustal dome-shaped, high-density bodies that spatially correlate with major bends along the MMF. We show that these crustal heterogeneities may cause the lithospheric strength to vary significantly along the MMF, supporting the hypothesis that the fault is mechanically segmented. In addition, our results indicate a spatial correlation between observed aseismic fault patches (Wollin et al., 2018) and the location of the high-density bodies. These bodies are colder and stronger than the surrounding crystalline crust, and may thus represent the lateral bounds of the locked MMF segment.
How to cite: Gholamrezaie, E., Scheck-Wenderoth, M., Bott, J., Heidbach, O., Bohnhoff, M., and Strecker, M. R.: 3-D lithospheric-scale rheological model of the Sea of Marmara, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4264, https://doi.org/10.5194/egusphere-egu2020-4264, 2020.
The North Anatolian Fault (NAF) below the Sea of Marmara, also known as the Main Marmara Fault (MMF), has repeatedly produced major (M>7) earthquakes in the past. Currently, the MMF corresponds to a seismic gap between the locus of the most recent M>7 ruptures of the 1912 Ganos (M 7.3) and 1999 Izmit (M 7.4) earthquakes. This seismic gap has a recurrence time of approximately 250 years and has not ruptured since 1766. Consequently, it poses a major seismic hazard to the Marmara region, including the megacity Istanbul. The Marmara seismic gap is considered to be locked in the eastern and central segments of the MMF, while the western segment is partly creeping. In the context of seismic hazard and risk assessment, one of the main questions is, if either the Marmara seismic gap will rupture in a single large earthquake or in several ones due to segmentation along the MMF. In part this depends on the physical properties of the lithosphere below the Sea of Marmara as they are a key control of the contemporary stress state. To contribute to this discussion, we present 3‑D lithospheric-scale thermal and rheological models of the Sea of Marmara. These models are based on published 3‑D density models that indicate lateral and vertical crustal heterogeneities below the Sea of Marmara (Gholamrezaie et al., 2019). The density models consist of two layers of sediments, upper and lower crystalline crustal layers, and two crustal dome-shaped, high-density bodies that spatially correlate with major bends along the MMF. We show that these crustal heterogeneities may cause the lithospheric strength to vary significantly along the MMF, supporting the hypothesis that the fault is mechanically segmented. In addition, our results indicate a spatial correlation between observed aseismic fault patches (Wollin et al., 2018) and the location of the high-density bodies. These bodies are colder and stronger than the surrounding crystalline crust, and may thus represent the lateral bounds of the locked MMF segment.
How to cite: Gholamrezaie, E., Scheck-Wenderoth, M., Bott, J., Heidbach, O., Bohnhoff, M., and Strecker, M. R.: 3-D lithospheric-scale rheological model of the Sea of Marmara, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4264, https://doi.org/10.5194/egusphere-egu2020-4264, 2020.
EGU2020-13052 | Displays | TS5.5
How Has GPS Velocity Field Changed Along the 1999 Izmit Rupture 20 Years After the 1999 Izmit, Turkey Earthquake?Seda Özarpacı, Uğur Doğan, Semih Ergintav, Ziyadin Çakır, Alpay Özdemir, Michael Floyd, and Robert Reilinger
A seismic gap along the western segment of the North Anatolian Fault, in the Marmara-Izmit region, was identified before the 1999 M7.6, Izmit and M7.4 Duzce earthquakes, so the region along the coseismic fault has been monitored with geodetic techniques for decades, providing well defined pre-, co- and post-seismic deformations. Here, we report new continuous and survey GPS measurements with near-fault (~2 – 10 km to the fault) and far-fault (~50 – 70 km from the fault) stations, including 7 years (2013 – 2019) of continuous observations, and 5 near-fault campaigns (every six months between 2014 – 2016) to further investigate postseismic deformation. GPS observations were processed with the GAMIT/GLOBK (v10.7) GNSS software. We used these observations to estimate the spatial distribution of current aseismic after-slip, along the 1999 Izmit rupture. We also searched for spatiotemporal changes of shallow creep events along the surface trace. With elastic models and GPS observations, we determined a shallow creep rate that reaches a maximum around the epicenter of the 1999 Izmit earthquake of about 12.7 ± 1.2 mm/yr, consistent with published InSAR results. Creep rates decrease both east and west of the epicentral region. Moreover, we show that broad-scale postseismic effects that diminish logarithmically, continue at present. (This study is supported by TUBITAK 1001 project no: 113Y102 and 117Y278)
How to cite: Özarpacı, S., Doğan, U., Ergintav, S., Çakır, Z., Özdemir, A., Floyd, M., and Reilinger, R.: How Has GPS Velocity Field Changed Along the 1999 Izmit Rupture 20 Years After the 1999 Izmit, Turkey Earthquake?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13052, https://doi.org/10.5194/egusphere-egu2020-13052, 2020.
A seismic gap along the western segment of the North Anatolian Fault, in the Marmara-Izmit region, was identified before the 1999 M7.6, Izmit and M7.4 Duzce earthquakes, so the region along the coseismic fault has been monitored with geodetic techniques for decades, providing well defined pre-, co- and post-seismic deformations. Here, we report new continuous and survey GPS measurements with near-fault (~2 – 10 km to the fault) and far-fault (~50 – 70 km from the fault) stations, including 7 years (2013 – 2019) of continuous observations, and 5 near-fault campaigns (every six months between 2014 – 2016) to further investigate postseismic deformation. GPS observations were processed with the GAMIT/GLOBK (v10.7) GNSS software. We used these observations to estimate the spatial distribution of current aseismic after-slip, along the 1999 Izmit rupture. We also searched for spatiotemporal changes of shallow creep events along the surface trace. With elastic models and GPS observations, we determined a shallow creep rate that reaches a maximum around the epicenter of the 1999 Izmit earthquake of about 12.7 ± 1.2 mm/yr, consistent with published InSAR results. Creep rates decrease both east and west of the epicentral region. Moreover, we show that broad-scale postseismic effects that diminish logarithmically, continue at present. (This study is supported by TUBITAK 1001 project no: 113Y102 and 117Y278)
How to cite: Özarpacı, S., Doğan, U., Ergintav, S., Çakır, Z., Özdemir, A., Floyd, M., and Reilinger, R.: How Has GPS Velocity Field Changed Along the 1999 Izmit Rupture 20 Years After the 1999 Izmit, Turkey Earthquake?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13052, https://doi.org/10.5194/egusphere-egu2020-13052, 2020.
EGU2020-18112 | Displays | TS5.5
A geodetic exploration of the behavior of aseismic slip along the central section of the North Anatolian faultJorge Jara, Alpay Ozdemir, Angelique Benoit, Romain Jolivet, Ziyadin Çakir, Semih Ergintav, and Ugur Dogan
Many geodetic evidence suggest aseismic slip along active faults is more common than previously thought. Furthermore, aseismic slip during the interseismic period seems to be made of intermittent slow slip events, corresponding to episodes of loading and releasing of tectonic stress over time. However, although our capabilities of detection and location of aseismic deformation have significantly increased together with the growth in available geodetic data, the physical mechanisms governing slow slip remain unknown.
We explore the spatial and temporal behavior of aseismic deformation in the vicinity of the small town of Ismetpasa, located along the central section of the North Anatolian Fault (Turkey). We combine InSAR and GNSS data acquired over the last 10 years to locate and quantify aseismic slip in the subsurface. We process SAR images (ALOS and Sentinel-1) acquired from 2007 to 2018 to build time series of ground deformation and maps of ground velocity. We confirm the presence of a 100 km-long creeping section, at rates of 10-20 mm/yr. Along this section, slip is not constant and decreases over time as formerly observed over the last 60 years. Furthermore, via a detailed analysis of our geodetic time series, we detect 3 major episodes of aseismic slip between 2015 and 2018, with durations ranging from 6 months to 1 year and magnitudes between 4.6 - 5.2. These results are compared with time series obtained from a network of GNSS permanent stations we have installed in the region (17 stations, period 2016 - 2019). As a conclusion, aseismic slip along this section of the North Anatolian Fault is characterized by slow slip events rather than by a constant, steady-state aseismic slip rate. We discuss the potential implications in terms of mechanics of slow slip along the NAF.
How to cite: Jara, J., Ozdemir, A., Benoit, A., Jolivet, R., Çakir, Z., Ergintav, S., and Dogan, U.: A geodetic exploration of the behavior of aseismic slip along the central section of the North Anatolian fault, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18112, https://doi.org/10.5194/egusphere-egu2020-18112, 2020.
Many geodetic evidence suggest aseismic slip along active faults is more common than previously thought. Furthermore, aseismic slip during the interseismic period seems to be made of intermittent slow slip events, corresponding to episodes of loading and releasing of tectonic stress over time. However, although our capabilities of detection and location of aseismic deformation have significantly increased together with the growth in available geodetic data, the physical mechanisms governing slow slip remain unknown.
We explore the spatial and temporal behavior of aseismic deformation in the vicinity of the small town of Ismetpasa, located along the central section of the North Anatolian Fault (Turkey). We combine InSAR and GNSS data acquired over the last 10 years to locate and quantify aseismic slip in the subsurface. We process SAR images (ALOS and Sentinel-1) acquired from 2007 to 2018 to build time series of ground deformation and maps of ground velocity. We confirm the presence of a 100 km-long creeping section, at rates of 10-20 mm/yr. Along this section, slip is not constant and decreases over time as formerly observed over the last 60 years. Furthermore, via a detailed analysis of our geodetic time series, we detect 3 major episodes of aseismic slip between 2015 and 2018, with durations ranging from 6 months to 1 year and magnitudes between 4.6 - 5.2. These results are compared with time series obtained from a network of GNSS permanent stations we have installed in the region (17 stations, period 2016 - 2019). As a conclusion, aseismic slip along this section of the North Anatolian Fault is characterized by slow slip events rather than by a constant, steady-state aseismic slip rate. We discuss the potential implications in terms of mechanics of slow slip along the NAF.
How to cite: Jara, J., Ozdemir, A., Benoit, A., Jolivet, R., Çakir, Z., Ergintav, S., and Dogan, U.: A geodetic exploration of the behavior of aseismic slip along the central section of the North Anatolian fault, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18112, https://doi.org/10.5194/egusphere-egu2020-18112, 2020.
EGU2020-8100 | Displays | TS5.5
Present-day crustal deformation of Georgia (Caucasus)Giorgi Sokhadze, Galaktion Hahubia, Manana Kachakhidze, and Giorgi Khazaradze
The republic of Georgia is located in the Caucasus, between the Black and Caspian seas from the west and the east, and Greater and Lesser Caucasus mountains from the north and the south. Tectonically, the region belongs to the Alpine-Himalayan collisional zone, formed during the late Cenozoic period as a result of a collision between the Arabian and Eurasian plates. The deformation zone due to this collision is broad and extends from Zagros mountains in southern Iran to the Greater Caucasus in the north. The GPS studies conducted during the last decade suggest a convergence rate of 18 mm/yr between the Arabia and Eurasia plates. Although majority of this convergence occurs in the southern part of the deformation zone, important part of this convergence takes place in Georgia, implying an elevated seismic risk in the region. This is corroborated by a presence of significant historical and instrumental earthquakes in the country.
As part of the project dealing with the detection of possible low frequency electromagnetic emissions proceeding earthquakes, in summer of 2016 we have installed a continuous GNSS station MTSK between Mtskheta and Tbilisi. The station consists of Leica GRX1200 GNSS receiver with an AS10 antenna. It is mounted on top of the building, anchored to the existing brick wall. In contrast, principal convergence between the Lesser and Greater Caucasus across the Tbilisi segment, occurs along the northern boundary of the Lesser Caucasus. To constrain the velocity gradient to the northern boundary of the lesser Caucasus, in 2019 an additional continuous GNSS station MKRN was installed in this deformation zone by the GTDI near the settlement of Mukhrani. It consists of Trimble 5700 receiver with a Zephyr Geodetic antenna.
The analysis of the data is performed using the Gamit/Globk software package from MIT and it is processed in conjunction with 26 continuous GNSS stations of the GEO-CORS network operated by National Agency of Public Registry of Georgia (geocors.napr.gov.ge). In addition, we analyze data form the stations located on Eurasia, Arabia and Africa plates. The principle objective of the given work is to monitor millimeter level deformation of the crust due to the collision of Arabia and Eurasia tectonic plates and identify the regions of higher deformation and relate them to individual faults.
This work has been partially supported by Shota Rustaveli National Science Foundation of Georgia (grant DI/21/9-140/13) and PROMONTEC (CGL2017-84720-R AEI/FEDER, UE) project, financed by the Spanish MINEICO. We are grateful to the Andronikashvili Institute of Physics (www.aiphysics.tsu.ge) for letting us use their facility for the installation of the GNSS station.
How to cite: Sokhadze, G., Hahubia, G., Kachakhidze, M., and Khazaradze, G.: Present-day crustal deformation of Georgia (Caucasus), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8100, https://doi.org/10.5194/egusphere-egu2020-8100, 2020.
The republic of Georgia is located in the Caucasus, between the Black and Caspian seas from the west and the east, and Greater and Lesser Caucasus mountains from the north and the south. Tectonically, the region belongs to the Alpine-Himalayan collisional zone, formed during the late Cenozoic period as a result of a collision between the Arabian and Eurasian plates. The deformation zone due to this collision is broad and extends from Zagros mountains in southern Iran to the Greater Caucasus in the north. The GPS studies conducted during the last decade suggest a convergence rate of 18 mm/yr between the Arabia and Eurasia plates. Although majority of this convergence occurs in the southern part of the deformation zone, important part of this convergence takes place in Georgia, implying an elevated seismic risk in the region. This is corroborated by a presence of significant historical and instrumental earthquakes in the country.
As part of the project dealing with the detection of possible low frequency electromagnetic emissions proceeding earthquakes, in summer of 2016 we have installed a continuous GNSS station MTSK between Mtskheta and Tbilisi. The station consists of Leica GRX1200 GNSS receiver with an AS10 antenna. It is mounted on top of the building, anchored to the existing brick wall. In contrast, principal convergence between the Lesser and Greater Caucasus across the Tbilisi segment, occurs along the northern boundary of the Lesser Caucasus. To constrain the velocity gradient to the northern boundary of the lesser Caucasus, in 2019 an additional continuous GNSS station MKRN was installed in this deformation zone by the GTDI near the settlement of Mukhrani. It consists of Trimble 5700 receiver with a Zephyr Geodetic antenna.
The analysis of the data is performed using the Gamit/Globk software package from MIT and it is processed in conjunction with 26 continuous GNSS stations of the GEO-CORS network operated by National Agency of Public Registry of Georgia (geocors.napr.gov.ge). In addition, we analyze data form the stations located on Eurasia, Arabia and Africa plates. The principle objective of the given work is to monitor millimeter level deformation of the crust due to the collision of Arabia and Eurasia tectonic plates and identify the regions of higher deformation and relate them to individual faults.
This work has been partially supported by Shota Rustaveli National Science Foundation of Georgia (grant DI/21/9-140/13) and PROMONTEC (CGL2017-84720-R AEI/FEDER, UE) project, financed by the Spanish MINEICO. We are grateful to the Andronikashvili Institute of Physics (www.aiphysics.tsu.ge) for letting us use their facility for the installation of the GNSS station.
How to cite: Sokhadze, G., Hahubia, G., Kachakhidze, M., and Khazaradze, G.: Present-day crustal deformation of Georgia (Caucasus), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8100, https://doi.org/10.5194/egusphere-egu2020-8100, 2020.
EGU2020-2825 | Displays | TS5.5
Active Tectonics of the Mt. Muşgüneyi: Implications for Western Part of the Turkish Iranian PlateauTaylan Sançar
The Eastern Turkish High Plateau (ETHP) presents one of the most critical areas of Turkish-Iranian Plateau, where active slip rates and kinematics of the faults have been used in models that aim to describe the overall deformation characteristics (such as; the beginning of the collision and convergence velocity) of the Arabian-Eurasian collision. However, lack of the spatial distribution of horizontal slip and rock uplift rates of the Bitlis-Zağros Mountain Range (BZMR) prevent our understandings about active deformation of Turkish-Iranian Plateau. Mt. Muşgüneyi that constitute the NW part of BZMR and southern margin of the ETHP is critically important because conflicting viewpoints related to the active tectonics of both the ETHP, Turkish-Iranian Plateau and Arabian-Eurasian collision zone currently being adopted in research into it. In this study, I extracted spatial distribution of the fault geometry in the Mt. Muşgüneyi and river networks from DEM, satellite images and aerial photo in order to understand faulting mechanism and measure their cumulative offsets, respectively. Geomorphic indexes (mountain-front sinuosity, valley floor width to valley height ratio, transverse topographic symmetry factor, asymmetry factor, hypsometric curve and integral) and drainage pattern analysis (channel concavity, integral analyses and knick point analyses) have been used to isolate the tectonic activity of the region. The results of this study reveal that although dozens of dextral faults accommodate the strain in the region, the 260 km length dextral Kavakbaşı Fault is the most important structure in the NW part of BZMR and it takes 60% of overall deformation. Previous studies suggest that 3–4.5 Ma is needed to account for the measured 9 km cumulative offset in this region, however, I measured c.a. 24 km cumulative horizontal offset on Kavakbaşı Fault that indicates c.a. 12 Ma needed to account for the offset. Morphometric studies point out sustaining significant uplift within the Mt. Muşgüneyi and signify the uplift rate is larger than horizontal slip rate moreover my results contradict the idea that change in the nature of the collision zone 5 ± 2 Ma ago. Furthermore, I propose that NW part of BZMR is extremely important to understand when the modern configuration of the boundary faults of the Anatolian Scholle did form? Considering similarities between the Kavakbaşı and the Nazımiye fault, which located at c.a. 70 km south of the North Anatolian Fault Zone in the Anatolian Scholle, in terms of their ages, orientations, slip senses and cumulative offset, I suggest that they belonged to the earlier dextral deformation zone along the southern margin of the collision that sinistrally offset by the East Anatolian Fault Zone (EAFZ) about 33±3 km. This offset estimate dived by calculated long-term slip rate of the EAFZ and Na-alkali basaltic activity in the Plio-Pleistocene that emplaced at the eastern part of the Anatolian Scholle yields that age of the EAFZ is 6 Ma. This study supported by TÜBİTAK Project No:115Y684.
How to cite: Sançar, T.: Active Tectonics of the Mt. Muşgüneyi: Implications for Western Part of the Turkish Iranian Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2825, https://doi.org/10.5194/egusphere-egu2020-2825, 2020.
The Eastern Turkish High Plateau (ETHP) presents one of the most critical areas of Turkish-Iranian Plateau, where active slip rates and kinematics of the faults have been used in models that aim to describe the overall deformation characteristics (such as; the beginning of the collision and convergence velocity) of the Arabian-Eurasian collision. However, lack of the spatial distribution of horizontal slip and rock uplift rates of the Bitlis-Zağros Mountain Range (BZMR) prevent our understandings about active deformation of Turkish-Iranian Plateau. Mt. Muşgüneyi that constitute the NW part of BZMR and southern margin of the ETHP is critically important because conflicting viewpoints related to the active tectonics of both the ETHP, Turkish-Iranian Plateau and Arabian-Eurasian collision zone currently being adopted in research into it. In this study, I extracted spatial distribution of the fault geometry in the Mt. Muşgüneyi and river networks from DEM, satellite images and aerial photo in order to understand faulting mechanism and measure their cumulative offsets, respectively. Geomorphic indexes (mountain-front sinuosity, valley floor width to valley height ratio, transverse topographic symmetry factor, asymmetry factor, hypsometric curve and integral) and drainage pattern analysis (channel concavity, integral analyses and knick point analyses) have been used to isolate the tectonic activity of the region. The results of this study reveal that although dozens of dextral faults accommodate the strain in the region, the 260 km length dextral Kavakbaşı Fault is the most important structure in the NW part of BZMR and it takes 60% of overall deformation. Previous studies suggest that 3–4.5 Ma is needed to account for the measured 9 km cumulative offset in this region, however, I measured c.a. 24 km cumulative horizontal offset on Kavakbaşı Fault that indicates c.a. 12 Ma needed to account for the offset. Morphometric studies point out sustaining significant uplift within the Mt. Muşgüneyi and signify the uplift rate is larger than horizontal slip rate moreover my results contradict the idea that change in the nature of the collision zone 5 ± 2 Ma ago. Furthermore, I propose that NW part of BZMR is extremely important to understand when the modern configuration of the boundary faults of the Anatolian Scholle did form? Considering similarities between the Kavakbaşı and the Nazımiye fault, which located at c.a. 70 km south of the North Anatolian Fault Zone in the Anatolian Scholle, in terms of their ages, orientations, slip senses and cumulative offset, I suggest that they belonged to the earlier dextral deformation zone along the southern margin of the collision that sinistrally offset by the East Anatolian Fault Zone (EAFZ) about 33±3 km. This offset estimate dived by calculated long-term slip rate of the EAFZ and Na-alkali basaltic activity in the Plio-Pleistocene that emplaced at the eastern part of the Anatolian Scholle yields that age of the EAFZ is 6 Ma. This study supported by TÜBİTAK Project No:115Y684.
How to cite: Sançar, T.: Active Tectonics of the Mt. Muşgüneyi: Implications for Western Part of the Turkish Iranian Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2825, https://doi.org/10.5194/egusphere-egu2020-2825, 2020.
EGU2020-8438 | Displays | TS5.5 | Highlight
2019 Mw5.8 Silivri Earthquake Reveals the Complexity of the Main Marmara Shear ZoneA. Ozgun Konca, Sezim Ezgi Guvercin, Hayrullah Karabulut, Figen Eskikoy, and Semih Ergintav
The North Anatolian Fault (NAF) is a 1600 km dextral transform fault accommodating the motion between Anatolia and Eurasia Plates. The segments beneath the Marmara Sea, are the only part of the NAF that did not break since the 20thcentury. Recent studies show that this 150 km seismic gap is characterized by heterogeneous interseismic behavior and significantly high background seismicity with respect to the other parts of the NAF.
On September 24 2019, an activity started north of the Main Marmara Fault (MMF) including a Mw4.7 earthquake, which led to the Mw5.8 mainshock several days later. The 2019 Mw5.8 Silivri earthquake is the largest since 1963 Mw6.3 Cinarcik earthquake in the Marmara Sea. This sequence occurred at a location that is immediate north west of the Central Basin; between a zone that is possibly partially creeping (Central Basin) to the west and a possibly locked segment to the east (Kumburgaz Basin).
In this study we used template search for detection of earthquakes, relocated the earthquakes, obtained focal mechanism solutions of earthquakes that are M>4 and obtained a finite-fault slip model of the Mw5.8 mainshock. Using template cross-correlation, a total of 400 earthquakes were detected in this sequence. The activity started in a relatively narrow zone and spread to larger distances following the Mw4.7 mainshock. The depth distribution shows that the earthquakes are confined to a narrow zone between the depths of 9-13 km. The focal mechanisms show that there are two clusters; the cluster to the northwest show a ~70°north dipping fault with rake angles about ~160°, while the activity toward east converges to the Main Marmara Fault and dip angle is close to ~70°with rake angles of ~140°. The finite-fault model shows a bilateral rupture that propagated down-dip from the hypocenter.
We conclude that the seismic activity occurred on a fault that is within the Main Marmara Shear Zone beneath the sedimentary basin. This secondary fault possibly connects to the Main Marmara Fault to the east. There is no evidence that the causative fault continues up-dip into the basin. Another characteristic of this sequence is that all of the focal mechanisms show significant thrust component in addition to the expected right-lateral motion. The January 2020 Mw4.7 earthquake that occurred in the same zone between the two clusters have predominantly thrust mechanism, confirming that this zone is under local compression. The observed thrust component is possibly related to change of the width of the shear zone with narrowing from Central Basin to the west to Central High to the east and/or the change of the interseismic behavior of the fault from partially creeping Central Basin and locked Kumburgaz Basin segments.
How to cite: Konca, A. O., Guvercin, S. E., Karabulut, H., Eskikoy, F., and Ergintav, S.: 2019 Mw5.8 Silivri Earthquake Reveals the Complexity of the Main Marmara Shear Zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8438, https://doi.org/10.5194/egusphere-egu2020-8438, 2020.
The North Anatolian Fault (NAF) is a 1600 km dextral transform fault accommodating the motion between Anatolia and Eurasia Plates. The segments beneath the Marmara Sea, are the only part of the NAF that did not break since the 20thcentury. Recent studies show that this 150 km seismic gap is characterized by heterogeneous interseismic behavior and significantly high background seismicity with respect to the other parts of the NAF.
On September 24 2019, an activity started north of the Main Marmara Fault (MMF) including a Mw4.7 earthquake, which led to the Mw5.8 mainshock several days later. The 2019 Mw5.8 Silivri earthquake is the largest since 1963 Mw6.3 Cinarcik earthquake in the Marmara Sea. This sequence occurred at a location that is immediate north west of the Central Basin; between a zone that is possibly partially creeping (Central Basin) to the west and a possibly locked segment to the east (Kumburgaz Basin).
In this study we used template search for detection of earthquakes, relocated the earthquakes, obtained focal mechanism solutions of earthquakes that are M>4 and obtained a finite-fault slip model of the Mw5.8 mainshock. Using template cross-correlation, a total of 400 earthquakes were detected in this sequence. The activity started in a relatively narrow zone and spread to larger distances following the Mw4.7 mainshock. The depth distribution shows that the earthquakes are confined to a narrow zone between the depths of 9-13 km. The focal mechanisms show that there are two clusters; the cluster to the northwest show a ~70°north dipping fault with rake angles about ~160°, while the activity toward east converges to the Main Marmara Fault and dip angle is close to ~70°with rake angles of ~140°. The finite-fault model shows a bilateral rupture that propagated down-dip from the hypocenter.
We conclude that the seismic activity occurred on a fault that is within the Main Marmara Shear Zone beneath the sedimentary basin. This secondary fault possibly connects to the Main Marmara Fault to the east. There is no evidence that the causative fault continues up-dip into the basin. Another characteristic of this sequence is that all of the focal mechanisms show significant thrust component in addition to the expected right-lateral motion. The January 2020 Mw4.7 earthquake that occurred in the same zone between the two clusters have predominantly thrust mechanism, confirming that this zone is under local compression. The observed thrust component is possibly related to change of the width of the shear zone with narrowing from Central Basin to the west to Central High to the east and/or the change of the interseismic behavior of the fault from partially creeping Central Basin and locked Kumburgaz Basin segments.
How to cite: Konca, A. O., Guvercin, S. E., Karabulut, H., Eskikoy, F., and Ergintav, S.: 2019 Mw5.8 Silivri Earthquake Reveals the Complexity of the Main Marmara Shear Zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8438, https://doi.org/10.5194/egusphere-egu2020-8438, 2020.
EGU2020-6144 | Displays | TS5.5
Converting InSAR- and GNSS-derived strain rate maps into earthquake hazard models for AnatoliaChris Rollins, Tim Wright, Jonathan Weiss, Andrew Hooper, and Richard Walters
Geodetic measurements of crustal deformation rates can provide important constraints on a region’s earthquake hazard that purely seismicity-based hazard models may miss. For example, geodesy might show that strain (or a deficit of seismic moment) is accumulating faster than the total rate at which known earthquakes have released it, implying that the long-term hazard may include larger earthquakes with long recurrence intervals (and/or temporal increases in seismicity rates). Conversely, the moment release rate in recent earthquakes might surpass the geodetic moment buildup rate, suggesting that the long-term-average earthquake activity and hazard may in fact may be more quiescent than might be estimated using the earthquake history alone. Such geodetic constraints, however, have traditionally been limited by poor spatial and/or temporal sampling, resulting in ambiguities about how the lithosphere accommodates strain in space and time that can bias estimates of the resulting hazard. High-resolution deformation maps address this limitation by imaging (rather than presuming and/or modelling) where and how deformation takes place. These maps are now within reach for the Alpine-Himalayan Belt – one of the most populous and seismically hazardous regions on Earth – thanks to the COMET-LiCSAR InSAR processing system, which performs large-scale automated processing and timeseries analysis of Sentinel-1 data provided by the EU’s Copernicus programme. We are pairing LiCSAR products with GNSS data to generate high-resolution maps of interseismic surface motion (velocity) and strain rate for the Anatolia region. Here we quantitively investigate what these strain rate distributions imply for seismic hazard in this region, using two approaches in parallel.
First, building on previous work, we develop a fully probability-based method to pair geodesy and seismic catalogs to estimate the recurrence times of large, moderate and small earthquakes in a given region. We assume that earthquakes 1) obey a power-law magnitude-frequency distribution up to a maximum magnitude and 2) collectively release seismic moment at the same rate that we estimate it is accumulating from the strain rate maps. Iterating over various magnitude-frequency distributions and their governing parameters, and formally incorporating uncertainties in moment buildup rate and the magnitudes of recorded earthquakes, we build a probabilistic long-term-average earthquake model for Anatolia as a whole, including the most likely maximum earthquake magnitude. Second, we estimate how seismic hazard may vary from place to place within Anatolia. Using insights from dislocation models, we identify two key signatures of a locked fault in a strain rate field, allowing us to convert the newly developed strain maps to “effective fault maps.” Additionally, we explore how characteristics of earthquake magnitude-frequency distributions may scale with the rate of strain (or moment) buildup, and what these scaling relations imply for the distribution of hazard in Anatolia, using the seismic catalog to evaluate these hypotheses. We also explore the implications of our findings for seismic hazard and address how to expand these approaches to the Alpine-Himalaya Belt as a whole.
How to cite: Rollins, C., Wright, T., Weiss, J., Hooper, A., and Walters, R.: Converting InSAR- and GNSS-derived strain rate maps into earthquake hazard models for Anatolia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6144, https://doi.org/10.5194/egusphere-egu2020-6144, 2020.
Geodetic measurements of crustal deformation rates can provide important constraints on a region’s earthquake hazard that purely seismicity-based hazard models may miss. For example, geodesy might show that strain (or a deficit of seismic moment) is accumulating faster than the total rate at which known earthquakes have released it, implying that the long-term hazard may include larger earthquakes with long recurrence intervals (and/or temporal increases in seismicity rates). Conversely, the moment release rate in recent earthquakes might surpass the geodetic moment buildup rate, suggesting that the long-term-average earthquake activity and hazard may in fact may be more quiescent than might be estimated using the earthquake history alone. Such geodetic constraints, however, have traditionally been limited by poor spatial and/or temporal sampling, resulting in ambiguities about how the lithosphere accommodates strain in space and time that can bias estimates of the resulting hazard. High-resolution deformation maps address this limitation by imaging (rather than presuming and/or modelling) where and how deformation takes place. These maps are now within reach for the Alpine-Himalayan Belt – one of the most populous and seismically hazardous regions on Earth – thanks to the COMET-LiCSAR InSAR processing system, which performs large-scale automated processing and timeseries analysis of Sentinel-1 data provided by the EU’s Copernicus programme. We are pairing LiCSAR products with GNSS data to generate high-resolution maps of interseismic surface motion (velocity) and strain rate for the Anatolia region. Here we quantitively investigate what these strain rate distributions imply for seismic hazard in this region, using two approaches in parallel.
First, building on previous work, we develop a fully probability-based method to pair geodesy and seismic catalogs to estimate the recurrence times of large, moderate and small earthquakes in a given region. We assume that earthquakes 1) obey a power-law magnitude-frequency distribution up to a maximum magnitude and 2) collectively release seismic moment at the same rate that we estimate it is accumulating from the strain rate maps. Iterating over various magnitude-frequency distributions and their governing parameters, and formally incorporating uncertainties in moment buildup rate and the magnitudes of recorded earthquakes, we build a probabilistic long-term-average earthquake model for Anatolia as a whole, including the most likely maximum earthquake magnitude. Second, we estimate how seismic hazard may vary from place to place within Anatolia. Using insights from dislocation models, we identify two key signatures of a locked fault in a strain rate field, allowing us to convert the newly developed strain maps to “effective fault maps.” Additionally, we explore how characteristics of earthquake magnitude-frequency distributions may scale with the rate of strain (or moment) buildup, and what these scaling relations imply for the distribution of hazard in Anatolia, using the seismic catalog to evaluate these hypotheses. We also explore the implications of our findings for seismic hazard and address how to expand these approaches to the Alpine-Himalaya Belt as a whole.
How to cite: Rollins, C., Wright, T., Weiss, J., Hooper, A., and Walters, R.: Converting InSAR- and GNSS-derived strain rate maps into earthquake hazard models for Anatolia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6144, https://doi.org/10.5194/egusphere-egu2020-6144, 2020.
EGU2020-17589 | Displays | TS5.5
Analysis of the complexity of the Mw 5.8, 26 September 2019 Silivri Eq. in the Sea of Marmara, Turkey, constrained from geodetic datasetsSemih Ergintav, Alpay Ödemir, Seda Özarpacı, Hilmi Erkoç, Efe T. Ayruk, Uğur Doğan, Hayrullah Karabulut, Ali Özgün Konca, Thomas Walter, and Hannes Vasyura-Bathke
Based on >20 years of GPS observations and seismological works, direct constraints on the strain accumulation along the Main Marmara Fault (MMF) show different characteristics from Princess Islands to Ganos Fault. Ganos and Princess Island segments identified as locked based on GPS and seismological observations while the part of the Central Marmara segment show partially creeping behaviour. Moreover, around the Kumburgaz Basin, GPS data could be explained by creep models in contrast to fully locked seismic models. Clearly, there are many puzzling questions on the nature of strain accumulation on the MMF, under the constrain of various data sets. In order to contribute to a better understanding of this fault the observation capacity of geodesic network has been increased along the northern coast of the Marmara Sea and supported by seismological stations as well as Marine Geodesy.
In September, 2019, an intense earthquake activity started between Central Marmara and Kumburgaz Basin. The mainshock occurred on 26 September 2019 (Mw5.8) as a largest earthquake, since 1963 Mw6.3 Cinarcik earthquake, in the Marmara Sea. A foreshock activity started 4 days before the mainshock and the largest one (Mw4.7) observed on September 24, close to the mainshock. The mechanisms of the mainshock and the large aftershocks as well as foreshocks are dominantly strike-slip with a significant reverse component. The aftershocks are located on the north of the MMF trace.
Here we investigate the geodetic data related to this event, with the aim to shed some light on the complexly segmented MMF. We observed co-seismic offsets at the nearest 6 GPS stations (~12-20 km far to the epicenter) along the northern coastline of the Sea of Marmara. The estimated offsets are not big and change between 1-3 mm on horizontal and 1-10 mm on vertical components. All of the stations are located on the northern part of the hypocenter and exhibit predominant NS-direction movement, which is inconsistent with a primarily E-W right lateral transform system. Instead, the co-seismic pattern can be explained with a complex earthquake mechanism which has a dominant reverse component while the strike-slip component is relatively insignificant, based on Okada-type elastic models and geodetic moment magnitude obtained as ~6.2. The total cumulative moment using geodesy is much higher than the total seismic cumulative moment of earthquake activity (~M5.9), and the thrust component is also more dominant in comparison the focal mechanisms from regional data. Obviously, geodetic co-seismic offsets estimated from daily-based data and they include pre-and post-earthquake deformations. In addition, the tide-gauge data (station distance is 25 km far to epicenter) was analyzed and it shows the strong variations after Mw 4.7 and they faded out after Mw5.8. This sea level change, which temporally correlates with the seismic activity, gives important evidence about the possibilities of pre-earthquake activity. Using GPS time series, we intend to explore the pre-earthquake anomalies and, to reduce the discrepancy between seismological and geodetic models. (This study is supported by TUBITAK 1001 Project no: 117Y278).
How to cite: Ergintav, S., Ödemir, A., Özarpacı, S., Erkoç, H., Ayruk, E. T., Doğan, U., Karabulut, H., Konca, A. Ö., Walter, T., and Vasyura-Bathke, H.: Analysis of the complexity of the Mw 5.8, 26 September 2019 Silivri Eq. in the Sea of Marmara, Turkey, constrained from geodetic datasets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17589, https://doi.org/10.5194/egusphere-egu2020-17589, 2020.
Based on >20 years of GPS observations and seismological works, direct constraints on the strain accumulation along the Main Marmara Fault (MMF) show different characteristics from Princess Islands to Ganos Fault. Ganos and Princess Island segments identified as locked based on GPS and seismological observations while the part of the Central Marmara segment show partially creeping behaviour. Moreover, around the Kumburgaz Basin, GPS data could be explained by creep models in contrast to fully locked seismic models. Clearly, there are many puzzling questions on the nature of strain accumulation on the MMF, under the constrain of various data sets. In order to contribute to a better understanding of this fault the observation capacity of geodesic network has been increased along the northern coast of the Marmara Sea and supported by seismological stations as well as Marine Geodesy.
In September, 2019, an intense earthquake activity started between Central Marmara and Kumburgaz Basin. The mainshock occurred on 26 September 2019 (Mw5.8) as a largest earthquake, since 1963 Mw6.3 Cinarcik earthquake, in the Marmara Sea. A foreshock activity started 4 days before the mainshock and the largest one (Mw4.7) observed on September 24, close to the mainshock. The mechanisms of the mainshock and the large aftershocks as well as foreshocks are dominantly strike-slip with a significant reverse component. The aftershocks are located on the north of the MMF trace.
Here we investigate the geodetic data related to this event, with the aim to shed some light on the complexly segmented MMF. We observed co-seismic offsets at the nearest 6 GPS stations (~12-20 km far to the epicenter) along the northern coastline of the Sea of Marmara. The estimated offsets are not big and change between 1-3 mm on horizontal and 1-10 mm on vertical components. All of the stations are located on the northern part of the hypocenter and exhibit predominant NS-direction movement, which is inconsistent with a primarily E-W right lateral transform system. Instead, the co-seismic pattern can be explained with a complex earthquake mechanism which has a dominant reverse component while the strike-slip component is relatively insignificant, based on Okada-type elastic models and geodetic moment magnitude obtained as ~6.2. The total cumulative moment using geodesy is much higher than the total seismic cumulative moment of earthquake activity (~M5.9), and the thrust component is also more dominant in comparison the focal mechanisms from regional data. Obviously, geodetic co-seismic offsets estimated from daily-based data and they include pre-and post-earthquake deformations. In addition, the tide-gauge data (station distance is 25 km far to epicenter) was analyzed and it shows the strong variations after Mw 4.7 and they faded out after Mw5.8. This sea level change, which temporally correlates with the seismic activity, gives important evidence about the possibilities of pre-earthquake activity. Using GPS time series, we intend to explore the pre-earthquake anomalies and, to reduce the discrepancy between seismological and geodetic models. (This study is supported by TUBITAK 1001 Project no: 117Y278).
How to cite: Ergintav, S., Ödemir, A., Özarpacı, S., Erkoç, H., Ayruk, E. T., Doğan, U., Karabulut, H., Konca, A. Ö., Walter, T., and Vasyura-Bathke, H.: Analysis of the complexity of the Mw 5.8, 26 September 2019 Silivri Eq. in the Sea of Marmara, Turkey, constrained from geodetic datasets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17589, https://doi.org/10.5194/egusphere-egu2020-17589, 2020.
EGU2020-18364 | Displays | TS5.5
Probabilistic constraints on lithospheric forces, fault tractions, and rheology in the eastern Mediterranean regionMatthew Herman, Rob Govers, Lukas van de Wiel, and Nicolai Nijholt
The Aegean Sea region sits in a complex deformation zone between the African, Eurasian, and Anatolian plates. It contains the Hellenic subduction zone, where African oceanic lithosphere descends under the Aegean Sea. The subducting slab may be torn or fragmented at both its eastern (Pliny-Strabo zone) and western (Kefalonia fault) edges. The overriding Aegean Sea is cut by numerous active normal faults accommodating north-south extension. On top of this, the collision of Arabia with Anatolia farther east drives Anatolia and the connected Aegean Sea westward, resulting in the left lateral North Anatolian fault (and its extension into the Aegean), as well as greater relative velocities between the subducting slab and the overriding plate. These geodynamic processes and geological features all affect the present-day kinematics of the Aegean region.
Surface velocities measured at Global Navigation Satellite System stations throughout the Aegean provide important constraints on these underlying geodynamic forces. Previous studies have attributed the surface motions to some combination of plate boundary interactions, lateral variations in gravitational potential energy (GPE), subduction and slab tearing, internal faulting, and mantle tractions. The expected imprint of these processes also varies with the rheology of the lithosphere. Up to this point, there has been little effort to systematically evaluate the relative contributions of these different forces. In this study, we implement a Markov Chain Monte Carlo approach to efficiently and precisely determine the likely values and uncertainties of these geodynamic forces and the lithospheric rheology. We also identify trade-offs between processes that produce similar surface signals.
Preliminary results indicate that the dominant imprint on surface velocities comes from the southwestward rollback of the Hellenic slab and the westward escape of Anatolia. Although lateral variations in GPE also have an effect on the velocities, these are generally less important than slab rollback and Anatolian escape. At a lithospheric scale, the North Anatolian fault has little shear resistance to allow a relatively sharp velocity transition across it. Including resistive tractions on intraplate faults within the Aegean Sea has a smaller effect on the modeled velocity field. By using the velocity field to guide a statistical analysis of the geodynamic drivers, we have been able to better constrain the primary drivers of deformation in the eastern Mediterranean.
How to cite: Herman, M., Govers, R., van de Wiel, L., and Nijholt, N.: Probabilistic constraints on lithospheric forces, fault tractions, and rheology in the eastern Mediterranean region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18364, https://doi.org/10.5194/egusphere-egu2020-18364, 2020.
The Aegean Sea region sits in a complex deformation zone between the African, Eurasian, and Anatolian plates. It contains the Hellenic subduction zone, where African oceanic lithosphere descends under the Aegean Sea. The subducting slab may be torn or fragmented at both its eastern (Pliny-Strabo zone) and western (Kefalonia fault) edges. The overriding Aegean Sea is cut by numerous active normal faults accommodating north-south extension. On top of this, the collision of Arabia with Anatolia farther east drives Anatolia and the connected Aegean Sea westward, resulting in the left lateral North Anatolian fault (and its extension into the Aegean), as well as greater relative velocities between the subducting slab and the overriding plate. These geodynamic processes and geological features all affect the present-day kinematics of the Aegean region.
Surface velocities measured at Global Navigation Satellite System stations throughout the Aegean provide important constraints on these underlying geodynamic forces. Previous studies have attributed the surface motions to some combination of plate boundary interactions, lateral variations in gravitational potential energy (GPE), subduction and slab tearing, internal faulting, and mantle tractions. The expected imprint of these processes also varies with the rheology of the lithosphere. Up to this point, there has been little effort to systematically evaluate the relative contributions of these different forces. In this study, we implement a Markov Chain Monte Carlo approach to efficiently and precisely determine the likely values and uncertainties of these geodynamic forces and the lithospheric rheology. We also identify trade-offs between processes that produce similar surface signals.
Preliminary results indicate that the dominant imprint on surface velocities comes from the southwestward rollback of the Hellenic slab and the westward escape of Anatolia. Although lateral variations in GPE also have an effect on the velocities, these are generally less important than slab rollback and Anatolian escape. At a lithospheric scale, the North Anatolian fault has little shear resistance to allow a relatively sharp velocity transition across it. Including resistive tractions on intraplate faults within the Aegean Sea has a smaller effect on the modeled velocity field. By using the velocity field to guide a statistical analysis of the geodynamic drivers, we have been able to better constrain the primary drivers of deformation in the eastern Mediterranean.
How to cite: Herman, M., Govers, R., van de Wiel, L., and Nijholt, N.: Probabilistic constraints on lithospheric forces, fault tractions, and rheology in the eastern Mediterranean region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18364, https://doi.org/10.5194/egusphere-egu2020-18364, 2020.
EGU2020-10682 | Displays | TS5.5
Locking Behavior of Main Marmara Fault in Western Turkey During Interseismic PeriodZeynep Yılmaz, Ali Özgün Konca, and Semih Ergintav
The North Anatolian Fault (NAF) produced multiple earthquakes of M>7 throughout the 20th century, while the part of NAF beneath Sea of Marmara did not rupture during this period. Analysis of the Main Marmara Fault's interseismic behavior, the most active branch of the North Anatolian Fault in this region, in terms of locking depth and fault slip rate is critical for evaluating the region's seismic risk with a population of more than 20 million, as it provides information about the seismic moment deficit that may release in a potential future earthquake.
In this study, we modeled the Main Marmara Fault's interseismic locking with realistic geometry and 3D structure including sedimentary basins, by implementing a 3D finite element approach and using interseismic GPS velocities. We have optimized the fits with GPS data by evaluating cases where each fault segment is constrained by a fault slip rate below a predefined locking depth ranging from 0 to 20 km. Preliminary models reveal that a difference in locking depth is required between the Western Marmara and the eastern end of the Ganos Segment entering the Sea of Marmara. This result, which is consistent with seismicity studies and other previous studies using 1D profiles shows that the strain accumulation under Western Marmara is less and that the locking depths or couplings are not similar in these two segments. For the Princes' Islands Segment, further analysis is required due to complexity in the GPS data. Recent earthquakes along Silivri also indicate that the strain accumulation is complex with most mechanisms showing significant thrust component. We have also calculated various possible strain accumulation patterns and compared the strain rate field around the Main Marmara Fault. Our results show that in most cases the change in the seismicity of each segment is consistent with the interseismic behavior associated with its fault locking.
(This research has been supported by Boğaziçi University Scientific Research Projects Coordination Unit. Project Number: 15022, 2019)
How to cite: Yılmaz, Z., Konca, A. Ö., and Ergintav, S.: Locking Behavior of Main Marmara Fault in Western Turkey During Interseismic Period, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10682, https://doi.org/10.5194/egusphere-egu2020-10682, 2020.
The North Anatolian Fault (NAF) produced multiple earthquakes of M>7 throughout the 20th century, while the part of NAF beneath Sea of Marmara did not rupture during this period. Analysis of the Main Marmara Fault's interseismic behavior, the most active branch of the North Anatolian Fault in this region, in terms of locking depth and fault slip rate is critical for evaluating the region's seismic risk with a population of more than 20 million, as it provides information about the seismic moment deficit that may release in a potential future earthquake.
In this study, we modeled the Main Marmara Fault's interseismic locking with realistic geometry and 3D structure including sedimentary basins, by implementing a 3D finite element approach and using interseismic GPS velocities. We have optimized the fits with GPS data by evaluating cases where each fault segment is constrained by a fault slip rate below a predefined locking depth ranging from 0 to 20 km. Preliminary models reveal that a difference in locking depth is required between the Western Marmara and the eastern end of the Ganos Segment entering the Sea of Marmara. This result, which is consistent with seismicity studies and other previous studies using 1D profiles shows that the strain accumulation under Western Marmara is less and that the locking depths or couplings are not similar in these two segments. For the Princes' Islands Segment, further analysis is required due to complexity in the GPS data. Recent earthquakes along Silivri also indicate that the strain accumulation is complex with most mechanisms showing significant thrust component. We have also calculated various possible strain accumulation patterns and compared the strain rate field around the Main Marmara Fault. Our results show that in most cases the change in the seismicity of each segment is consistent with the interseismic behavior associated with its fault locking.
(This research has been supported by Boğaziçi University Scientific Research Projects Coordination Unit. Project Number: 15022, 2019)
How to cite: Yılmaz, Z., Konca, A. Ö., and Ergintav, S.: Locking Behavior of Main Marmara Fault in Western Turkey During Interseismic Period, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10682, https://doi.org/10.5194/egusphere-egu2020-10682, 2020.
EGU2020-4639 | Displays | TS5.5
3-D density structure of the upper-mantle from gravity inversion constrained by seismic velocity model: A case study of the Mediterranean Sea and surrounding regionFayez Harash
Harash Fayez1, Chao Chen1,2, Qing Liang1,2, Chenming Tu1
1Institute of Geophysics & Geomatics, China University of Geosciences, Wuhan 430074, P.R. China (Corresponding author: Harash Fayez).
2Subsurface Multi-Scale Imaging Lab, Institute of Geophysics & Geomatics, China University of Geosciences,
Wuhan 430074, P.R. China.
Summary
A 3-D density structure of the lithosphere and upper-mantle beneath the Mediterranean Sea and adjacent region was constructed based on inversion of gravity anomaly constrained by seismic tomography model. In this study, we have removed the terrain and crustal effects from the observed gravity field (EIGEN-6C4), in order to obtain the mantle gravity anomaly which was used to investigate the lithospheric and the upper-mantle density distribution. The 3-D inversion process is constrained by a reference density model estimated from shear-wave velocity model (SL2013sv). Our result shows some characteristics of density distribution in the lithosphere and upper-mantle that might be related to the tectonic signification beneath the Mediterranean Sea and adjacent region. A low-density zone dominates the lithosphere beneath the Mediterranean Sea except the area around Arabia shield and North Anatolian fault belt. A thinner high-density layer appears beneath the southwest of Mediterranean Sea, and it may be related to the older oceanic lithosphere fragments. The high-density anomalies appear below depth of 280 km beneath the Mediterranean Sea and the Turkish Aegean Sea Plate. However, the low-density anomalies appears at the top of the upper-mantle beneath trenches of the southwestern of Mediterranean Sea, the eastern of Aegean Sea, the Red Sea, the Black Sea and the middle of Arabia shield. It may indicate the intensity and origination of tectonic movement referring the deep structure below the Eratosthenes seamount in the Mediterranean Sea. Furthermore, the convergence region of two low-density anomaly zones may be interpreted as a significant tectonic unit.
How to cite: Harash, F.: 3-D density structure of the upper-mantle from gravity inversion constrained by seismic velocity model: A case study of the Mediterranean Sea and surrounding region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4639, https://doi.org/10.5194/egusphere-egu2020-4639, 2020.
Harash Fayez1, Chao Chen1,2, Qing Liang1,2, Chenming Tu1
1Institute of Geophysics & Geomatics, China University of Geosciences, Wuhan 430074, P.R. China (Corresponding author: Harash Fayez).
2Subsurface Multi-Scale Imaging Lab, Institute of Geophysics & Geomatics, China University of Geosciences,
Wuhan 430074, P.R. China.
Summary
A 3-D density structure of the lithosphere and upper-mantle beneath the Mediterranean Sea and adjacent region was constructed based on inversion of gravity anomaly constrained by seismic tomography model. In this study, we have removed the terrain and crustal effects from the observed gravity field (EIGEN-6C4), in order to obtain the mantle gravity anomaly which was used to investigate the lithospheric and the upper-mantle density distribution. The 3-D inversion process is constrained by a reference density model estimated from shear-wave velocity model (SL2013sv). Our result shows some characteristics of density distribution in the lithosphere and upper-mantle that might be related to the tectonic signification beneath the Mediterranean Sea and adjacent region. A low-density zone dominates the lithosphere beneath the Mediterranean Sea except the area around Arabia shield and North Anatolian fault belt. A thinner high-density layer appears beneath the southwest of Mediterranean Sea, and it may be related to the older oceanic lithosphere fragments. The high-density anomalies appear below depth of 280 km beneath the Mediterranean Sea and the Turkish Aegean Sea Plate. However, the low-density anomalies appears at the top of the upper-mantle beneath trenches of the southwestern of Mediterranean Sea, the eastern of Aegean Sea, the Red Sea, the Black Sea and the middle of Arabia shield. It may indicate the intensity and origination of tectonic movement referring the deep structure below the Eratosthenes seamount in the Mediterranean Sea. Furthermore, the convergence region of two low-density anomaly zones may be interpreted as a significant tectonic unit.
How to cite: Harash, F.: 3-D density structure of the upper-mantle from gravity inversion constrained by seismic velocity model: A case study of the Mediterranean Sea and surrounding region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4639, https://doi.org/10.5194/egusphere-egu2020-4639, 2020.
EGU2020-22071 | Displays | TS5.5
Constraining Source Properties of the 1894 Istanbul EarthquakeNesrin Yenihayat, Eser Çakti, and Karin Şeşetyan
The Marmara region is one of the most active tectonic regions with its high population and rapid but irregularly growing cities in Turkey. Located in this active zone, Istanbul has always been under the danger of being hit by destructive earthquakes, which in the past have caused serious damage in the city more than once. Major earthquakes to affect Istanbul during the Ottoman period took place in 1509, 1766 and 1894. As the latest one, we have relatively rich knowledge about the 10 July 1894 earthquake. The 1894 earthquake resulted in 474 losses of life and 482 injuries. Around 21,000 dwellings were damaged, which is a number that corresponds to 1/7 of the total dwellings of the city at that time. Without any doubt the exact loss of life was higher. Because of the censorship the exact loss numbers remained unknown. Researchers have been split in opinion about the intensity, epicenter, magnitude, and rupture length of this event. The main target of this study is to have a better insight on the possible location of the 1894 earthquake with the help of damage analysis and ground motion modeling. Ottoman Empire archive records, scientific reports and papers, newspapers, government correspondence, letters, notes of voyagers and diaries are the major sources to make an evaluation on the type and extent of damage. An intensity map associated with the 1894 earthquake is prepared based on macro-seismic information, and damage analysis and classification. Various information types contained in the old city maps, municipal boundaries, and the population information have contributed to this assessment. Obtained damage information is presented, evaluated and interpreted. For earthquake modelling the ELER (Earthquake Loss Assessment Routine) software is used. Using the ground motion module of ELER, several scenarios are modeled having different source, path, and site parameters. The resulting ground motion distributions are compared with the damage and intensity maps to provide a first-order assessment of the earthquake source parameters of the 1894 earthquake.
How to cite: Yenihayat, N., Çakti, E., and Şeşetyan, K.: Constraining Source Properties of the 1894 Istanbul Earthquake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22071, https://doi.org/10.5194/egusphere-egu2020-22071, 2020.
The Marmara region is one of the most active tectonic regions with its high population and rapid but irregularly growing cities in Turkey. Located in this active zone, Istanbul has always been under the danger of being hit by destructive earthquakes, which in the past have caused serious damage in the city more than once. Major earthquakes to affect Istanbul during the Ottoman period took place in 1509, 1766 and 1894. As the latest one, we have relatively rich knowledge about the 10 July 1894 earthquake. The 1894 earthquake resulted in 474 losses of life and 482 injuries. Around 21,000 dwellings were damaged, which is a number that corresponds to 1/7 of the total dwellings of the city at that time. Without any doubt the exact loss of life was higher. Because of the censorship the exact loss numbers remained unknown. Researchers have been split in opinion about the intensity, epicenter, magnitude, and rupture length of this event. The main target of this study is to have a better insight on the possible location of the 1894 earthquake with the help of damage analysis and ground motion modeling. Ottoman Empire archive records, scientific reports and papers, newspapers, government correspondence, letters, notes of voyagers and diaries are the major sources to make an evaluation on the type and extent of damage. An intensity map associated with the 1894 earthquake is prepared based on macro-seismic information, and damage analysis and classification. Various information types contained in the old city maps, municipal boundaries, and the population information have contributed to this assessment. Obtained damage information is presented, evaluated and interpreted. For earthquake modelling the ELER (Earthquake Loss Assessment Routine) software is used. Using the ground motion module of ELER, several scenarios are modeled having different source, path, and site parameters. The resulting ground motion distributions are compared with the damage and intensity maps to provide a first-order assessment of the earthquake source parameters of the 1894 earthquake.
How to cite: Yenihayat, N., Çakti, E., and Şeşetyan, K.: Constraining Source Properties of the 1894 Istanbul Earthquake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22071, https://doi.org/10.5194/egusphere-egu2020-22071, 2020.
EGU2020-2220 | Displays | TS5.5
Design and implementation of the seismotectonic Atlas of Greece v1.0Ioannis Kassaras, Vasilis Kapetanidis, Athanassios Ganas, Andreas Tzanis, Panayotis Papadimitriou, Vicki Kouskouna, Andreas Karakonstantis, Sotirios Valkaniotis, Stylianos Chailas, Vasileios Sakkas, Chrysanthi Kosma, George Bozionelos, Varvara Tsironi, and Georgia Giannaraki
Knowledge of the present-day relationships between earthquakes, active tectonics, and crustal deformation is a key for understanding the geodynamics, ongoing surface processes (i.e. erosion, sedimentation, etc.) and is also essential for the risk assessment and management of geo-reservoirs for energy and waste.
Greece is characterized by the most tectonically active regime in the eastern Mediterranean, involving (a) intense crustal deformation and thickening, with an uplift rate of a few mm/yr along the Hellenic Arc due to accretion of sediments of the African plate beneath the overriding Aegean plate, (b) wide-spread extension in the back-arc region (for example in the Gulf of Corinth) due to retreat of the African slab and (c) significant strike-slip motions due to offset between oceanic-continental subduction in the west and the westward propagation of Anatolia in the east. Study of the complexity of the contemporary Greek tectonics has been the subject of intense efforts of our working group during the last decade, employing multidisciplinary state-of-the-art methodologies regarding geological mapping, seismological and geodetic surveying and numerical analyses at various scales. The products of these studies are the pieces of a puzzle that we aim to merge with existing data (topography, bathymetry, land-use, etc) in order to compose the digital version of the modern Seismotectonic Atlas of Greece.
It has been over 30 years since the first edition of the seismotectonic map was published by Greece's Geological Institute in 1989, which emerges the need for an update, as soon as dozens of strong earthquakes have occurred both on mainland and offshore, whose locations and fault kinematics have been studied and this information has to be taken into account in city and infrastructure planning. Moreover, the patterns of active tectonics and stress, the tectonic strain distribution, the annual ratio between seismic and geodetic moment release, the precise location of onshore active faults and the slip-rates of major faults are much better known today than they were 30 years ago.
Open-source mapping software and GIS tools are being used to showcase important up-to-date seismotectonic features together with critical geospatial information (motorways, railways, gas pipelines, electricity plants, etc) at a nationwide scale of 1:500,000. This updated product aims to reveal a comprehensive image of the regional crustal deformation in a useful manner for scientists, students, and stakeholders to obtain a first-order perception of seismic risk in the Greek territory, but, also, to be used as a basis for other applications in Geosciences.
How to cite: Kassaras, I., Kapetanidis, V., Ganas, A., Tzanis, A., Papadimitriou, P., Kouskouna, V., Karakonstantis, A., Valkaniotis, S., Chailas, S., Sakkas, V., Kosma, C., Bozionelos, G., Tsironi, V., and Giannaraki, G.: Design and implementation of the seismotectonic Atlas of Greece v1.0, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2220, https://doi.org/10.5194/egusphere-egu2020-2220, 2020.
Knowledge of the present-day relationships between earthquakes, active tectonics, and crustal deformation is a key for understanding the geodynamics, ongoing surface processes (i.e. erosion, sedimentation, etc.) and is also essential for the risk assessment and management of geo-reservoirs for energy and waste.
Greece is characterized by the most tectonically active regime in the eastern Mediterranean, involving (a) intense crustal deformation and thickening, with an uplift rate of a few mm/yr along the Hellenic Arc due to accretion of sediments of the African plate beneath the overriding Aegean plate, (b) wide-spread extension in the back-arc region (for example in the Gulf of Corinth) due to retreat of the African slab and (c) significant strike-slip motions due to offset between oceanic-continental subduction in the west and the westward propagation of Anatolia in the east. Study of the complexity of the contemporary Greek tectonics has been the subject of intense efforts of our working group during the last decade, employing multidisciplinary state-of-the-art methodologies regarding geological mapping, seismological and geodetic surveying and numerical analyses at various scales. The products of these studies are the pieces of a puzzle that we aim to merge with existing data (topography, bathymetry, land-use, etc) in order to compose the digital version of the modern Seismotectonic Atlas of Greece.
It has been over 30 years since the first edition of the seismotectonic map was published by Greece's Geological Institute in 1989, which emerges the need for an update, as soon as dozens of strong earthquakes have occurred both on mainland and offshore, whose locations and fault kinematics have been studied and this information has to be taken into account in city and infrastructure planning. Moreover, the patterns of active tectonics and stress, the tectonic strain distribution, the annual ratio between seismic and geodetic moment release, the precise location of onshore active faults and the slip-rates of major faults are much better known today than they were 30 years ago.
Open-source mapping software and GIS tools are being used to showcase important up-to-date seismotectonic features together with critical geospatial information (motorways, railways, gas pipelines, electricity plants, etc) at a nationwide scale of 1:500,000. This updated product aims to reveal a comprehensive image of the regional crustal deformation in a useful manner for scientists, students, and stakeholders to obtain a first-order perception of seismic risk in the Greek territory, but, also, to be used as a basis for other applications in Geosciences.
How to cite: Kassaras, I., Kapetanidis, V., Ganas, A., Tzanis, A., Papadimitriou, P., Kouskouna, V., Karakonstantis, A., Valkaniotis, S., Chailas, S., Sakkas, V., Kosma, C., Bozionelos, G., Tsironi, V., and Giannaraki, G.: Design and implementation of the seismotectonic Atlas of Greece v1.0, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2220, https://doi.org/10.5194/egusphere-egu2020-2220, 2020.
EGU2020-15127 | Displays | TS5.5
High resolution seismicity catalog of the Marmara Sea region during the 2009-2014 period using template matchingHayrullah Karabulut, Olivier Lengliné, Jean Schmittbuhl, Emanuela Matrullo, and Michel Bouchon
A massive template-matching approach is successfully applied in Marmara Sea region along the North Anatolian Fault, during the 2009-2014 period to enrich the description of the time and space evolution of the seismicity. Detection of events are performed on the continuous data recorded from 2009 to 2014 combining two types of catalogs as templates: a finely constructed catalog for the three first year (2009-2011) (Schmittbuhl et al, 2016) and a raw catalog from KOERI for the last three years (2012-2014). Magnitudes (Ml) are estimated for all detected events using relative amplitudes of the highly coherent waveforms between new events and template events. The template database provides a nearly threefold increase of the number of small events (more than 15000 earthquakes compare to the 4673 events of the initial catalog). Combined with a double-difference relocation based on cross-correlation differential travel-time data, the database is shown to be a relevant framework for the long term monitoring of specific remanent structures like seismic swarms or repeating earthquakes. The obtained catalog confirms the strong contrast of behaviors along the Main Marmara Fault (MMF): deep creeping to the west (Central Basin), fully locked in the center (Kumburgaz Basin) and dominated by fluid and off-fault activity to the east (Cinarcik Basin).
How to cite: Karabulut, H., Lengliné, O., Schmittbuhl, J., Matrullo, E., and Bouchon, M.: High resolution seismicity catalog of the Marmara Sea region during the 2009-2014 period using template matching, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15127, https://doi.org/10.5194/egusphere-egu2020-15127, 2020.
A massive template-matching approach is successfully applied in Marmara Sea region along the North Anatolian Fault, during the 2009-2014 period to enrich the description of the time and space evolution of the seismicity. Detection of events are performed on the continuous data recorded from 2009 to 2014 combining two types of catalogs as templates: a finely constructed catalog for the three first year (2009-2011) (Schmittbuhl et al, 2016) and a raw catalog from KOERI for the last three years (2012-2014). Magnitudes (Ml) are estimated for all detected events using relative amplitudes of the highly coherent waveforms between new events and template events. The template database provides a nearly threefold increase of the number of small events (more than 15000 earthquakes compare to the 4673 events of the initial catalog). Combined with a double-difference relocation based on cross-correlation differential travel-time data, the database is shown to be a relevant framework for the long term monitoring of specific remanent structures like seismic swarms or repeating earthquakes. The obtained catalog confirms the strong contrast of behaviors along the Main Marmara Fault (MMF): deep creeping to the west (Central Basin), fully locked in the center (Kumburgaz Basin) and dominated by fluid and off-fault activity to the east (Cinarcik Basin).
How to cite: Karabulut, H., Lengliné, O., Schmittbuhl, J., Matrullo, E., and Bouchon, M.: High resolution seismicity catalog of the Marmara Sea region during the 2009-2014 period using template matching, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15127, https://doi.org/10.5194/egusphere-egu2020-15127, 2020.
EGU2020-4668 | Displays | TS5.5
Crustal scattering and intrinsic attenuation of S-waves in southern Aegean derived using envelope inversionPratul Ranjan and Konstantinos I. Konstantinou
Southern Aegean is the major part of the Eurasian plate overriding the subduction of African plate in eastern Mediterranean region. In this study, shallow depth (< 40 km) events recorded by temporary and permanent seismic networks in southern Aegean are used to study the crustal scattering attenuation (Qs-1) and intrinsic attenuation (Qi-1) of S-waves. The 3 component S-waveforms are filtered in 1-2, 2-4, 4-8, and 8-16 Hz bands and envelopes are calculated by smoothing the root mean square of individual components. The envelopes are modeled using the approximate analytical solution of 3D isotropic radiative transfer equation. The fitting is performed using grid search approach to obtain Qs-1 and then linear inversion is used to calculate Qi-1 for each source station pair. The results obtained from each source-station pair are assigned to an ellipsoid region and robust mean technique is used to map the results in each 0.20o x 0.20o bin. The final results indicate consistently high Qs-1 in western Crete in all 4 frequency bands. Also, high Qs-1 is observed in western Peloponnese in 1-2 and 2-4 Hz frequency bands. High Qi-1 is observed along the volcanic arc in all 4 frequency bands. Our results compare well with the recent S-wave scattering study in the region. They are also consistent with the geodynamics of southern Aegean subduction zone. Our study provides useful insight about the attenuation in the southern Aegean crust which has implications for ground motion and seismic hazard.
How to cite: Ranjan, P. and Konstantinou, K. I.: Crustal scattering and intrinsic attenuation of S-waves in southern Aegean derived using envelope inversion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4668, https://doi.org/10.5194/egusphere-egu2020-4668, 2020.
Southern Aegean is the major part of the Eurasian plate overriding the subduction of African plate in eastern Mediterranean region. In this study, shallow depth (< 40 km) events recorded by temporary and permanent seismic networks in southern Aegean are used to study the crustal scattering attenuation (Qs-1) and intrinsic attenuation (Qi-1) of S-waves. The 3 component S-waveforms are filtered in 1-2, 2-4, 4-8, and 8-16 Hz bands and envelopes are calculated by smoothing the root mean square of individual components. The envelopes are modeled using the approximate analytical solution of 3D isotropic radiative transfer equation. The fitting is performed using grid search approach to obtain Qs-1 and then linear inversion is used to calculate Qi-1 for each source station pair. The results obtained from each source-station pair are assigned to an ellipsoid region and robust mean technique is used to map the results in each 0.20o x 0.20o bin. The final results indicate consistently high Qs-1 in western Crete in all 4 frequency bands. Also, high Qs-1 is observed in western Peloponnese in 1-2 and 2-4 Hz frequency bands. High Qi-1 is observed along the volcanic arc in all 4 frequency bands. Our results compare well with the recent S-wave scattering study in the region. They are also consistent with the geodynamics of southern Aegean subduction zone. Our study provides useful insight about the attenuation in the southern Aegean crust which has implications for ground motion and seismic hazard.
How to cite: Ranjan, P. and Konstantinou, K. I.: Crustal scattering and intrinsic attenuation of S-waves in southern Aegean derived using envelope inversion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4668, https://doi.org/10.5194/egusphere-egu2020-4668, 2020.
EGU2020-20421 | Displays | TS5.5
Three Approaches to Interseismic Slip Rates on the Marmara Faults and Their Tensorial Correlations with the Kostrov-Based Strain RatesVolkan Özbey, Mehmet Sinan Özeren, Pierre Henry, Elliot Klein, Gerald Galgana, Dietrich Lange, Jean-Yves Royer, Valerie Ballu, and Ziyadin Çakır
The interseismic slip distribution in the Marmara fault system represents both observational and modelling challenges. The observational challenge is obvious: the faults are under water and to understand their interseismic behavior (creeping versus locked) requires expensive and logistically difficult underwater geodetic measurements, alongside those on land. Up to now, two such underwater studies have been conducted and they suggest that the segment to the south of Istanbul zone (so-called Central segment) is locked while some creep is probably going on along the neighboring segment to the west. Given these two important findings, the slip distribution problem is still non-trivial due to the fact that our experiments so far demonstrate that the block-based slip inversions and those that only consider a single fault (with the same geometry as one of the boundaries of the blocks) give significantly different results. In this study we approach the problem using three methodologies: block models with spatially non-varying strains within individual blocks, a boundary element approach and a continuum kinematic approach. Although the block model does not give spatially varying strains, the inversion results from the block model can be used as an input to model strain field in the vicinity of the fault. We constract a formulation to correlate the results from these with the strain rates obtained using focal mechanism summations.
GPS velocities are taken from previous studies around the Marmara Sea such as Reilinger et al., (2006), Aktuğ et al., (2009), Ergintav et al., (2014), Özdemir et al., (2016) and Özdemir and Karslıoğlu, (2019). Since all studies have different processing strategies or by choosing different reference frames, the GPS velocity fields could not be combined directly. Hence, we combined all velocity fields by minimizing the residuals between the velocities of the common sites in the studies. For this purpose VELROT program (Herring et al 2015) was used. Reilinger et al., (2006) was selected the reference field and other velocity fields were aligned one by one on it. If the combined sigma of the pairs of velocity estimates in the residuals are greater than 2 mm yr-1, that sites are excluded from the final velocity field. As a result, 127 GPS velocities were used in the developed models.
How to cite: Özbey, V., Özeren, M. S., Henry, P., Klein, E., Galgana, G., Lange, D., Royer, J.-Y., Ballu, V., and Çakır, Z.: Three Approaches to Interseismic Slip Rates on the Marmara Faults and Their Tensorial Correlations with the Kostrov-Based Strain Rates , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20421, https://doi.org/10.5194/egusphere-egu2020-20421, 2020.
The interseismic slip distribution in the Marmara fault system represents both observational and modelling challenges. The observational challenge is obvious: the faults are under water and to understand their interseismic behavior (creeping versus locked) requires expensive and logistically difficult underwater geodetic measurements, alongside those on land. Up to now, two such underwater studies have been conducted and they suggest that the segment to the south of Istanbul zone (so-called Central segment) is locked while some creep is probably going on along the neighboring segment to the west. Given these two important findings, the slip distribution problem is still non-trivial due to the fact that our experiments so far demonstrate that the block-based slip inversions and those that only consider a single fault (with the same geometry as one of the boundaries of the blocks) give significantly different results. In this study we approach the problem using three methodologies: block models with spatially non-varying strains within individual blocks, a boundary element approach and a continuum kinematic approach. Although the block model does not give spatially varying strains, the inversion results from the block model can be used as an input to model strain field in the vicinity of the fault. We constract a formulation to correlate the results from these with the strain rates obtained using focal mechanism summations.
GPS velocities are taken from previous studies around the Marmara Sea such as Reilinger et al., (2006), Aktuğ et al., (2009), Ergintav et al., (2014), Özdemir et al., (2016) and Özdemir and Karslıoğlu, (2019). Since all studies have different processing strategies or by choosing different reference frames, the GPS velocity fields could not be combined directly. Hence, we combined all velocity fields by minimizing the residuals between the velocities of the common sites in the studies. For this purpose VELROT program (Herring et al 2015) was used. Reilinger et al., (2006) was selected the reference field and other velocity fields were aligned one by one on it. If the combined sigma of the pairs of velocity estimates in the residuals are greater than 2 mm yr-1, that sites are excluded from the final velocity field. As a result, 127 GPS velocities were used in the developed models.
How to cite: Özbey, V., Özeren, M. S., Henry, P., Klein, E., Galgana, G., Lange, D., Royer, J.-Y., Ballu, V., and Çakır, Z.: Three Approaches to Interseismic Slip Rates on the Marmara Faults and Their Tensorial Correlations with the Kostrov-Based Strain Rates , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20421, https://doi.org/10.5194/egusphere-egu2020-20421, 2020.
EGU2020-6589 | Displays | TS5.5
Seismotectonic setting of Santorini-Amorgos zone and the surrounding area revealed from crustal earthquakes relocation and Vp/Vs distributionRatri Andinisari, Konstantinos I. Konstantinou, Pratul Ranjan, and Qori F. Hermawan
The Santorini-Amorgos zone represents right-lateral transtensional regime from NE of Santorini to the south of Amorgos which also hosts Kolumbo submarine volcano. A total number of 1869 crustal events from 2002 to 2019 were recorded by permanent and temporal seismic networks deployed in southern Aegean. Absolute locations of these events were obtained by utilizing the probabilistic nonlinear algorithm NonLinLoc. Precise relative relocation by using double-difference algorithm with catalog and cross-correlation differential times was later performed, resulting in 1455 locations with horizontal and vertical uncertainties of less than 0.3 km. Clusters of earthquakes relocated between Naxos and Paros as well as north of Astypalaia do not coincide with any fault in the area. Similarly, the relocated crustal events across Santorini-Amorgos zone show that most of the earthquake clusters do not coincide with any of the existing faults. The distribution of Vp/Vs ratios in the area were investigated based on the P and S-wave travel times of all the events. Vp/Vs ratios in the area vary between 1.67 and 2.03 with errors less than 0.04. The highest Vp/Vs values were found to be distributed in the area between Naxos and Paros. Other areas with notably high Vp/Vs ratio are north of Santorini, Anydros, west of Amorgos, offshore area south of the easternmost tip of Amorgos, and the island of Astypalaia. These mentioned areas were also rich in seismic activities during the period of study. The high Vp/Vs ratios in the region of high seismicity signifies that these events were likely related to the migration of magmatic fluids to the surface and may not be caused by the existing faults.
How to cite: Andinisari, R., Konstantinou, K. I., Ranjan, P., and Hermawan, Q. F.: Seismotectonic setting of Santorini-Amorgos zone and the surrounding area revealed from crustal earthquakes relocation and Vp/Vs distribution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6589, https://doi.org/10.5194/egusphere-egu2020-6589, 2020.
The Santorini-Amorgos zone represents right-lateral transtensional regime from NE of Santorini to the south of Amorgos which also hosts Kolumbo submarine volcano. A total number of 1869 crustal events from 2002 to 2019 were recorded by permanent and temporal seismic networks deployed in southern Aegean. Absolute locations of these events were obtained by utilizing the probabilistic nonlinear algorithm NonLinLoc. Precise relative relocation by using double-difference algorithm with catalog and cross-correlation differential times was later performed, resulting in 1455 locations with horizontal and vertical uncertainties of less than 0.3 km. Clusters of earthquakes relocated between Naxos and Paros as well as north of Astypalaia do not coincide with any fault in the area. Similarly, the relocated crustal events across Santorini-Amorgos zone show that most of the earthquake clusters do not coincide with any of the existing faults. The distribution of Vp/Vs ratios in the area were investigated based on the P and S-wave travel times of all the events. Vp/Vs ratios in the area vary between 1.67 and 2.03 with errors less than 0.04. The highest Vp/Vs values were found to be distributed in the area between Naxos and Paros. Other areas with notably high Vp/Vs ratio are north of Santorini, Anydros, west of Amorgos, offshore area south of the easternmost tip of Amorgos, and the island of Astypalaia. These mentioned areas were also rich in seismic activities during the period of study. The high Vp/Vs ratios in the region of high seismicity signifies that these events were likely related to the migration of magmatic fluids to the surface and may not be caused by the existing faults.
How to cite: Andinisari, R., Konstantinou, K. I., Ranjan, P., and Hermawan, Q. F.: Seismotectonic setting of Santorini-Amorgos zone and the surrounding area revealed from crustal earthquakes relocation and Vp/Vs distribution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6589, https://doi.org/10.5194/egusphere-egu2020-6589, 2020.
EGU2020-4689 | Displays | TS5.5
The Crustal Structure of the Eastern Marmara Region Using Receiver Function AnalysisPınar Büyükakpınar and Mustafa Aktar
This study focuses on the crust of the Eastern Marmara in order to understand of how much the structure is influenced by the tectonic history and also by the activity of the NAF. Recent studies have claimed that the crustal thickness varies significantly on the north and south of the NAF, which is assumed to indicate the separation line between Eurasian and Anatolian Plates. The present study aims to reevaluate the claim above, using newly available data and recently developed tools. The methods used during the study are the receiver function analysis and surface wave analysis. The first one is more intensively applied, since the second one only serves to introduce stability constraint in the inversions. Data are obtained from the permanent network of KOERI and from PIRES arrays. The main result of the study indicates that the receiver functions for the stations close to the fault zone are essentially very different from the rest and should be treated separately. They show signs of complex 3D structures of which two were successfully analyzed by forward modeling (HRTX and ADVT). A dipping shallow layer is seen to satisfy the major part of the azimuthal variation at these two stations. For the stations off the fault on the other hand, the receiver functions show a more stable behavior and are analyzed successfully by classical methods. CCP stacking, H-k estimation, single and joint inversion with surface waves, are used for that purpose. The results obtained from these totally independent approaches are remarkably consistent with each other. It is observed that the crustal thickness does not vary significantly neither in the NS, nor in the SW direction. A deeper Moho can only be expected on two most NE stations where a gradual transition is more likely than a sharp boundary (SILT and KLYT). The structural trends, although not significant, are generally aligned in the EW direction. In particular, a slower lower crust is observed in the southern stations, which is possibly linked to the mantle upwelling and thermal transient of the Aegean extension. Otherwise neither the velocity, nor the thickness of the crust does not imply any significant variation across the fault zone, as was previously claimed.
How to cite: Büyükakpınar, P. and Aktar, M.: The Crustal Structure of the Eastern Marmara Region Using Receiver Function Analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4689, https://doi.org/10.5194/egusphere-egu2020-4689, 2020.
This study focuses on the crust of the Eastern Marmara in order to understand of how much the structure is influenced by the tectonic history and also by the activity of the NAF. Recent studies have claimed that the crustal thickness varies significantly on the north and south of the NAF, which is assumed to indicate the separation line between Eurasian and Anatolian Plates. The present study aims to reevaluate the claim above, using newly available data and recently developed tools. The methods used during the study are the receiver function analysis and surface wave analysis. The first one is more intensively applied, since the second one only serves to introduce stability constraint in the inversions. Data are obtained from the permanent network of KOERI and from PIRES arrays. The main result of the study indicates that the receiver functions for the stations close to the fault zone are essentially very different from the rest and should be treated separately. They show signs of complex 3D structures of which two were successfully analyzed by forward modeling (HRTX and ADVT). A dipping shallow layer is seen to satisfy the major part of the azimuthal variation at these two stations. For the stations off the fault on the other hand, the receiver functions show a more stable behavior and are analyzed successfully by classical methods. CCP stacking, H-k estimation, single and joint inversion with surface waves, are used for that purpose. The results obtained from these totally independent approaches are remarkably consistent with each other. It is observed that the crustal thickness does not vary significantly neither in the NS, nor in the SW direction. A deeper Moho can only be expected on two most NE stations where a gradual transition is more likely than a sharp boundary (SILT and KLYT). The structural trends, although not significant, are generally aligned in the EW direction. In particular, a slower lower crust is observed in the southern stations, which is possibly linked to the mantle upwelling and thermal transient of the Aegean extension. Otherwise neither the velocity, nor the thickness of the crust does not imply any significant variation across the fault zone, as was previously claimed.
How to cite: Büyükakpınar, P. and Aktar, M.: The Crustal Structure of the Eastern Marmara Region Using Receiver Function Analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4689, https://doi.org/10.5194/egusphere-egu2020-4689, 2020.
EGU2020-5418 | Displays | TS5.5
Reprocessing, depth conversion and structural restoration of vintage seismic data: New insights into the volcano-tectonic evolution of the Christiana-Santorini-Kolumbo marine volcanic zoneChristian Huebscher and Jonas Preine
Located on the Hellenic Volcanic Arc, the Christiana-Santorini-Kolumbo (CSK) marine volcanic zone is notorious for its catastrophic volcanic eruptions, earthquakes and tsunamis. Here, not only the largest volcanic eruption in human history, the so-called “Minoan” eruption took place in the Late Bronze age 3600 years ago, but also the largest 20th-century shallow earthquake in Europe of magnitude 7.4 in 1956. Although the region is heavily populated and a fully developed touristic region, the acting tectonic forces are not fully understood to this day aggravating the necessary assessment of geohazards.
Recent bathymetric and seismic studies revealed that the CSK zone comprises a system of neotectonic horst and graben structures with extended internal faulting that is thought to be the result of the ongoing extension in the southern Aegean. The NE-SW alignment of volcanic edifices within the CSK underlines the tectonic control of volcanism in this area. In this study, we show how advanced reprocessing of selected seismic lines leads to significantly improved seismic images revealing new details of the complex rift system. Moreover, using a unique diffraction-based approach for velocity model building, we perform pre-stack depth migration (PSDM) and present for the first time depth-converted seismic sections from the CSK zone. This allows for the proper estimation of fault angles, sedimentary thicknesses and performing structural restoration in order to reconstruct and measure the amount of extension in the individual rift basins. We revise the previous seismostratigraphic scheme and propose a new correlation between the horst and graben units.
Structural restoration indicates an extension of approx. 3 km along the Santorini-Anafi basin while PSDM indicates the sedimentary strata to be of maximum 1500 m thickness. According to the new stratigraphic model, we infer a four-stage evolution of this basin in which early marine deposition, syn-rift deposition, complex infill deposition and neotectonic syn-rift deposition are distinguished. Moreover, we identify negative flower structures within the basin centre indicating the presence of a strike-slip component, which superimposes the dominant NW-SE directed extension. Based on these findings, we are confident that by applying the proposed workflow to the complete regional dataset, the understanding of the relationship between tectonics and volcanism in the CSK zone will be significantly improved, and, consequently, will lead to an improved risk assessment of the central Aegean Sea.
How to cite: Huebscher, C. and Preine, J.: Reprocessing, depth conversion and structural restoration of vintage seismic data: New insights into the volcano-tectonic evolution of the Christiana-Santorini-Kolumbo marine volcanic zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5418, https://doi.org/10.5194/egusphere-egu2020-5418, 2020.
Located on the Hellenic Volcanic Arc, the Christiana-Santorini-Kolumbo (CSK) marine volcanic zone is notorious for its catastrophic volcanic eruptions, earthquakes and tsunamis. Here, not only the largest volcanic eruption in human history, the so-called “Minoan” eruption took place in the Late Bronze age 3600 years ago, but also the largest 20th-century shallow earthquake in Europe of magnitude 7.4 in 1956. Although the region is heavily populated and a fully developed touristic region, the acting tectonic forces are not fully understood to this day aggravating the necessary assessment of geohazards.
Recent bathymetric and seismic studies revealed that the CSK zone comprises a system of neotectonic horst and graben structures with extended internal faulting that is thought to be the result of the ongoing extension in the southern Aegean. The NE-SW alignment of volcanic edifices within the CSK underlines the tectonic control of volcanism in this area. In this study, we show how advanced reprocessing of selected seismic lines leads to significantly improved seismic images revealing new details of the complex rift system. Moreover, using a unique diffraction-based approach for velocity model building, we perform pre-stack depth migration (PSDM) and present for the first time depth-converted seismic sections from the CSK zone. This allows for the proper estimation of fault angles, sedimentary thicknesses and performing structural restoration in order to reconstruct and measure the amount of extension in the individual rift basins. We revise the previous seismostratigraphic scheme and propose a new correlation between the horst and graben units.
Structural restoration indicates an extension of approx. 3 km along the Santorini-Anafi basin while PSDM indicates the sedimentary strata to be of maximum 1500 m thickness. According to the new stratigraphic model, we infer a four-stage evolution of this basin in which early marine deposition, syn-rift deposition, complex infill deposition and neotectonic syn-rift deposition are distinguished. Moreover, we identify negative flower structures within the basin centre indicating the presence of a strike-slip component, which superimposes the dominant NW-SE directed extension. Based on these findings, we are confident that by applying the proposed workflow to the complete regional dataset, the understanding of the relationship between tectonics and volcanism in the CSK zone will be significantly improved, and, consequently, will lead to an improved risk assessment of the central Aegean Sea.
How to cite: Huebscher, C. and Preine, J.: Reprocessing, depth conversion and structural restoration of vintage seismic data: New insights into the volcano-tectonic evolution of the Christiana-Santorini-Kolumbo marine volcanic zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5418, https://doi.org/10.5194/egusphere-egu2020-5418, 2020.
EGU2020-11174 | Displays | TS5.5
Detecting Transient Creep Events on the Ismetpasa Segment of the North Anatolian Fault with Continous GNSS Time SeriesAlpay Özdemir, Uğur Doğan, Jorge Jara, Ziyadin Çakır, Romain Jolivet, Semih Ergintav, Seda Özarpacı, and Angélique Benoit
Twenty six years after the Mw 7.3 Gerede Earthquake in1944, Ambraseys (1970) first recognized, in the offset of a manmade wall, the signature of slow aseismic slip along the central segment of the North Anatolian Fault (NAF). Following this discovery, many studies characterized the behavior of aseismic slip with land-and space-based geodetic techniques, including creepmeters. It is now well recognized that the aseismic slip rate decreases logarithmically from more than 3 cm/yr in the years following the Gerede Earthquake to approximately 6±2 mm/yr today. In the last two decades, InSAR allowed deriving maps of ground velocities suggesting that aseismic slip extends along a 100-km-long section of the fault. Furthermore, aseismic slip rate varies in space along strike, reaching its peak value approximately 15-24 km east of the city of Ismetpasa. Furthermore, creepmeter measurements and InSAR time series indicate that aseismic slip in the region of Ismetpasa behaves episodically rather than continuously, alternating quiescent periods and transient episodes of relatively rapid aseismic slip. These observations raise questions about how slip accommodates tectonic stress along the fault with significant implications in terms of hazard along the seismogenic zone.
In order to monitore spatial and temporal variations in the aseismic slip rate and to detect slow slip events along the fault, we have established ISMENET -Ismetpasa Continuous GNSS Network- in July 2016. ISMENET stations are distributed over approximately 120 km along strike. In order to explore the shallow, fine spatio-temporal behavior of aseismic slip, stations are located within 200 m to 10 km of the fault. We process GNSS data with the Bernese (V5.2) and GAMIT/GLOBK (V10.7) GNSS software. We analyze the GNSS time series to extract the signature of aseismic slip using a principal component analysis to reduce the influence of non-tectonic noises.
Keywords: Ismetpasa, Aseismic slip, GNSS, PCA, Time Series Analysis, NAFZ
How to cite: Özdemir, A., Doğan, U., Jara, J., Çakır, Z., Jolivet, R., Ergintav, S., Özarpacı, S., and Benoit, A.: Detecting Transient Creep Events on the Ismetpasa Segment of the North Anatolian Fault with Continous GNSS Time Series, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11174, https://doi.org/10.5194/egusphere-egu2020-11174, 2020.
Twenty six years after the Mw 7.3 Gerede Earthquake in1944, Ambraseys (1970) first recognized, in the offset of a manmade wall, the signature of slow aseismic slip along the central segment of the North Anatolian Fault (NAF). Following this discovery, many studies characterized the behavior of aseismic slip with land-and space-based geodetic techniques, including creepmeters. It is now well recognized that the aseismic slip rate decreases logarithmically from more than 3 cm/yr in the years following the Gerede Earthquake to approximately 6±2 mm/yr today. In the last two decades, InSAR allowed deriving maps of ground velocities suggesting that aseismic slip extends along a 100-km-long section of the fault. Furthermore, aseismic slip rate varies in space along strike, reaching its peak value approximately 15-24 km east of the city of Ismetpasa. Furthermore, creepmeter measurements and InSAR time series indicate that aseismic slip in the region of Ismetpasa behaves episodically rather than continuously, alternating quiescent periods and transient episodes of relatively rapid aseismic slip. These observations raise questions about how slip accommodates tectonic stress along the fault with significant implications in terms of hazard along the seismogenic zone.
In order to monitore spatial and temporal variations in the aseismic slip rate and to detect slow slip events along the fault, we have established ISMENET -Ismetpasa Continuous GNSS Network- in July 2016. ISMENET stations are distributed over approximately 120 km along strike. In order to explore the shallow, fine spatio-temporal behavior of aseismic slip, stations are located within 200 m to 10 km of the fault. We process GNSS data with the Bernese (V5.2) and GAMIT/GLOBK (V10.7) GNSS software. We analyze the GNSS time series to extract the signature of aseismic slip using a principal component analysis to reduce the influence of non-tectonic noises.
Keywords: Ismetpasa, Aseismic slip, GNSS, PCA, Time Series Analysis, NAFZ
How to cite: Özdemir, A., Doğan, U., Jara, J., Çakır, Z., Jolivet, R., Ergintav, S., Özarpacı, S., and Benoit, A.: Detecting Transient Creep Events on the Ismetpasa Segment of the North Anatolian Fault with Continous GNSS Time Series, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11174, https://doi.org/10.5194/egusphere-egu2020-11174, 2020.
EGU2020-4070 | Displays | TS5.5
Geodynamic Evolution of Datça Basin Since the PlioceneÖkmen Sümer, Fatih Seçkin Şiş, Meryem Dilan İnce, Çağlar Özkaymak, Levent Tosun, Bora Uzel, Marius Stoica, Cor Langereis, and Nuretdin Kaymakci
The slab edge processes related to the subduction of the African slab along the Aegean-Cyprian trench, beneath Anatolia, played a significant role in Cenozoic extension in western Anatolia. The Datça Basin, which includes various Late Miocene depositional environments characterised by continental to marine transitions, is a WSW-ESE trending asymmetric depression developed on the Datça Peninsula, which separates the Aegean and Eastern Mediterranean Seas at the SW corner of Anatolia. Presently, the region is seismically active and is dominated by the E-W-trending Gökova Graben in the north and the NE-SW-trending Pliny-Strabo Trench in the south. Here, we conduct high resolution integrated stratigraphic study, that includes biostratigraphy, magnetostratigraphy as well as kinematic studies involving paleostress analysis to unravel geodynamic evolution of the region within the context of Africa-Eurasia convergence.
Three prominent sequences separated by unconformities are recognised in the Datça Basin; i) facies associations related to alluvial fan to fluvio-lacustrine deposits of Pliocene age, ii) facies extending from alluvial fan to fluvio-deltaic to marine incursions interlayered with two air-fall ash deposits of Pleistocene age, and iii) alluvial fan to fluvial to marine coastal facies of the modern basin infill. Integration of available information and our findings indicate that the basin experienced three distinct deformation phases associated with reactivation of pre-existing structures since Pliocene. First, the Datça Basin was initially developed as a transtensional basin in Pliocene possibly due to strike-slip deformation related to the Pliny-Strabo Trench, then orthogonal extensional deformation dominated and the basin evolved into a superimposed half-graben as a result of NNE to NNW directed extensional strain and subsequently became a full graben under N-S directed extension by the late Pliocene onwards.
This research is supported by The Scientific and Technological Research Council of Turkey (TUBITAK) with Grant Number of 117R012.
Keywords: Integrated stratigraphy, kinematics, basin evolution, Datça Basin, Southwestern Anatolia
How to cite: Sümer, Ö., Şiş, F. S., İnce, M. D., Özkaymak, Ç., Tosun, L., Uzel, B., Stoica, M., Langereis, C., and Kaymakci, N.: Geodynamic Evolution of Datça Basin Since the Pliocene, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4070, https://doi.org/10.5194/egusphere-egu2020-4070, 2020.
The slab edge processes related to the subduction of the African slab along the Aegean-Cyprian trench, beneath Anatolia, played a significant role in Cenozoic extension in western Anatolia. The Datça Basin, which includes various Late Miocene depositional environments characterised by continental to marine transitions, is a WSW-ESE trending asymmetric depression developed on the Datça Peninsula, which separates the Aegean and Eastern Mediterranean Seas at the SW corner of Anatolia. Presently, the region is seismically active and is dominated by the E-W-trending Gökova Graben in the north and the NE-SW-trending Pliny-Strabo Trench in the south. Here, we conduct high resolution integrated stratigraphic study, that includes biostratigraphy, magnetostratigraphy as well as kinematic studies involving paleostress analysis to unravel geodynamic evolution of the region within the context of Africa-Eurasia convergence.
Three prominent sequences separated by unconformities are recognised in the Datça Basin; i) facies associations related to alluvial fan to fluvio-lacustrine deposits of Pliocene age, ii) facies extending from alluvial fan to fluvio-deltaic to marine incursions interlayered with two air-fall ash deposits of Pleistocene age, and iii) alluvial fan to fluvial to marine coastal facies of the modern basin infill. Integration of available information and our findings indicate that the basin experienced three distinct deformation phases associated with reactivation of pre-existing structures since Pliocene. First, the Datça Basin was initially developed as a transtensional basin in Pliocene possibly due to strike-slip deformation related to the Pliny-Strabo Trench, then orthogonal extensional deformation dominated and the basin evolved into a superimposed half-graben as a result of NNE to NNW directed extensional strain and subsequently became a full graben under N-S directed extension by the late Pliocene onwards.
This research is supported by The Scientific and Technological Research Council of Turkey (TUBITAK) with Grant Number of 117R012.
Keywords: Integrated stratigraphy, kinematics, basin evolution, Datça Basin, Southwestern Anatolia
How to cite: Sümer, Ö., Şiş, F. S., İnce, M. D., Özkaymak, Ç., Tosun, L., Uzel, B., Stoica, M., Langereis, C., and Kaymakci, N.: Geodynamic Evolution of Datça Basin Since the Pliocene, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4070, https://doi.org/10.5194/egusphere-egu2020-4070, 2020.
EGU2020-6168 | Displays | TS5.5
Spatio-temporal variations on the vertical deformation rate of the NW Anatolian Block: Luminescence chronology of the Sakarya River terracesM. Korhan Erturac, Eren Şahiner, Azad Sağlam Selçuk, Alper Gürbüz, Hilal Okur, Cengiz Zabcı, Niyazi Meriç, Sinan Özeren, and Gürsel Sunal
The study area (40-40.45°N and 30-32.15° E) exhibits a high topography (1200-1800 m elevation) and bounded by the Galatean Massif at east, Pontide Mountain Range to the north, the Central Anatolian Plateau to the south and the Marmara Sea to the west. The region is actively been deformed and dissected by the active branches of the dextral strike slip North Anatolian Fault Zone (NAFZ) and the Sakarya River (SR) system. We have investigated the depositional terraces formed along the main course and the major tributaries of the SR to reveal the dynamics of the terrace formation by climate, sea level changes and also to quantify the variations in rate of vertical deformation within the current geodynamics of the NW Anatolian Block. The geometry of the main river (1) and its tributaries (4) allow us to determine the spatio-temporal variations in four vertical (100 km) and three along fault sections (200 km) since the last ~150 ka.
Up to date, we have mapped 23 distinct evenly scattered multi-step terrace staircases along the main river course and its 6 major tributaries. Mapping is aided with high precision rtk-GPS profiling and SfM photogrammetry using UAV. The dating is carried by luminescence geochronology (OSL and p-IRIR) to constrain the timing of the formation and also abandonment of each depositional terrace step.
The results show that the focus region is under control of vertical deformation at a rate of 0.6-0.7 mm/year regardless from the distance to the main strand of the NAFZ. There is also evidence that this rate has been decelerated from ~1.0-1.1 mm/year since the last 100 ka. The distinct variations in the calculated uplift rates along the profiles reveal apperant southwards tilting in between the active branches of the NAFZ and also within the block.
This study is funded by TUBITAK 117Y426 project grant.
How to cite: Erturac, M. K., Şahiner, E., Sağlam Selçuk, A., Gürbüz, A., Okur, H., Zabcı, C., Meriç, N., Özeren, S., and Sunal, G.: Spatio-temporal variations on the vertical deformation rate of the NW Anatolian Block: Luminescence chronology of the Sakarya River terraces, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6168, https://doi.org/10.5194/egusphere-egu2020-6168, 2020.
The study area (40-40.45°N and 30-32.15° E) exhibits a high topography (1200-1800 m elevation) and bounded by the Galatean Massif at east, Pontide Mountain Range to the north, the Central Anatolian Plateau to the south and the Marmara Sea to the west. The region is actively been deformed and dissected by the active branches of the dextral strike slip North Anatolian Fault Zone (NAFZ) and the Sakarya River (SR) system. We have investigated the depositional terraces formed along the main course and the major tributaries of the SR to reveal the dynamics of the terrace formation by climate, sea level changes and also to quantify the variations in rate of vertical deformation within the current geodynamics of the NW Anatolian Block. The geometry of the main river (1) and its tributaries (4) allow us to determine the spatio-temporal variations in four vertical (100 km) and three along fault sections (200 km) since the last ~150 ka.
Up to date, we have mapped 23 distinct evenly scattered multi-step terrace staircases along the main river course and its 6 major tributaries. Mapping is aided with high precision rtk-GPS profiling and SfM photogrammetry using UAV. The dating is carried by luminescence geochronology (OSL and p-IRIR) to constrain the timing of the formation and also abandonment of each depositional terrace step.
The results show that the focus region is under control of vertical deformation at a rate of 0.6-0.7 mm/year regardless from the distance to the main strand of the NAFZ. There is also evidence that this rate has been decelerated from ~1.0-1.1 mm/year since the last 100 ka. The distinct variations in the calculated uplift rates along the profiles reveal apperant southwards tilting in between the active branches of the NAFZ and also within the block.
This study is funded by TUBITAK 117Y426 project grant.
How to cite: Erturac, M. K., Şahiner, E., Sağlam Selçuk, A., Gürbüz, A., Okur, H., Zabcı, C., Meriç, N., Özeren, S., and Sunal, G.: Spatio-temporal variations on the vertical deformation rate of the NW Anatolian Block: Luminescence chronology of the Sakarya River terraces, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6168, https://doi.org/10.5194/egusphere-egu2020-6168, 2020.
EGU2020-1068 | Displays | TS5.5
Small scale fault interactions in Southwestern Anatolia as revealed from Seismology & InSARFigen Eskikoy, Semih Ergintav, Ali Özgün Konca, Ziyadin Çakır, Hannes Vasyura-Bathke, Marius Isken, and Hayrullah Karabulut
Southwestern Anatolia is part of a N-S extensional regime mainly driven by rollback along the Hellenic subduction zone beneath the Aegean Sea. This seismically active area is controlled primarily by normal fault systems. The fault structures in the region are segmented and in many cases seismic interaction between these segments can be observed.
2017 seismic activity along the Eastern and Western edges of Gökova Bay. Within the same year, three separate moderate sized (Mw~5) events took place near the town of Ula (Muğla) on the eastern edge of Gökova Bay. One of these earthquakes occurred in April before the Bodrum-Kos earthquake while the other pair occurred in November within two days.
We relocated all the events that occurred in Ula region in 2017 and remodeled the source mechanisms from regional seismic waveforms by using Bayesian Earthquake Analysis Tool (BEAT). The surface deformations can also be clearly observed from InSAR tracks of both ascending and descending orbits. Because of the large noise margins of the interferograms, atmospheric noise corrections and high resolution DEM data were used.
Due to temporal and spatial proximity of the two Mw~5 events during the November sequence, InSAR yields only cumulative deformation of the earthquakes. Therefore, we determined the contribution of each event to the cumulative static displacements observed by InSAR data, using the source models from seismic waveforms. The locations and the source mechanisms of the two Mw~5 earthquake are consistent and explain the observed surface deformation.
Our results imply that these earthquakes occurred on a previously unknown normal fault rather than the southeastern branches of the nearby Muğla Fault as proposed earlier. The results are consistent with the recently mapped fault structure by Akyüz et al. (2018). The November activity implies EW trending, south dipping normal faulting system and the change in the strike direction of the fault on the eastern edge can be clearly seen both InSAR and waveform modelling results of April activity.
Co-seismic and post-seismic InSAR analysis shows that the seismic activity following the 2017 Mw6.6 Bodrum-Kos propagated from western Gökova Bay where rupture occurred toward east including the Ula region. A long term comparison of seismicity beneath Gökova Bay and Ula region shows that the seismicity in these two regions are temporally correlated. Hence, while the aforementioned moderate sized earthquakes are not directly triggered by the Bodrum-Kos earthquake, increased seismic activity following Bodrum-Kos earthquake shows that the stress changes in these two regions affect each other. The location errors of the events especially the depth errors in the catalogs and the active fault structure in the area cannot be realized without any geodetic or seismic data analysis. This study claims that the interpretations of the moderate size earthquakes should be studied by using multidisciplinary data sets.
ACKNOWLEDGEMENTS
This work is supported by the Turkish Directorate of Strategy and Budget under the TAM Project number DPT2007K120610.
How to cite: Eskikoy, F., Ergintav, S., Konca, A. Ö., Çakır, Z., Vasyura-Bathke, H., Isken, M., and Karabulut, H.: Small scale fault interactions in Southwestern Anatolia as revealed from Seismology & InSAR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1068, https://doi.org/10.5194/egusphere-egu2020-1068, 2020.
Southwestern Anatolia is part of a N-S extensional regime mainly driven by rollback along the Hellenic subduction zone beneath the Aegean Sea. This seismically active area is controlled primarily by normal fault systems. The fault structures in the region are segmented and in many cases seismic interaction between these segments can be observed.
2017 seismic activity along the Eastern and Western edges of Gökova Bay. Within the same year, three separate moderate sized (Mw~5) events took place near the town of Ula (Muğla) on the eastern edge of Gökova Bay. One of these earthquakes occurred in April before the Bodrum-Kos earthquake while the other pair occurred in November within two days.
We relocated all the events that occurred in Ula region in 2017 and remodeled the source mechanisms from regional seismic waveforms by using Bayesian Earthquake Analysis Tool (BEAT). The surface deformations can also be clearly observed from InSAR tracks of both ascending and descending orbits. Because of the large noise margins of the interferograms, atmospheric noise corrections and high resolution DEM data were used.
Due to temporal and spatial proximity of the two Mw~5 events during the November sequence, InSAR yields only cumulative deformation of the earthquakes. Therefore, we determined the contribution of each event to the cumulative static displacements observed by InSAR data, using the source models from seismic waveforms. The locations and the source mechanisms of the two Mw~5 earthquake are consistent and explain the observed surface deformation.
Our results imply that these earthquakes occurred on a previously unknown normal fault rather than the southeastern branches of the nearby Muğla Fault as proposed earlier. The results are consistent with the recently mapped fault structure by Akyüz et al. (2018). The November activity implies EW trending, south dipping normal faulting system and the change in the strike direction of the fault on the eastern edge can be clearly seen both InSAR and waveform modelling results of April activity.
Co-seismic and post-seismic InSAR analysis shows that the seismic activity following the 2017 Mw6.6 Bodrum-Kos propagated from western Gökova Bay where rupture occurred toward east including the Ula region. A long term comparison of seismicity beneath Gökova Bay and Ula region shows that the seismicity in these two regions are temporally correlated. Hence, while the aforementioned moderate sized earthquakes are not directly triggered by the Bodrum-Kos earthquake, increased seismic activity following Bodrum-Kos earthquake shows that the stress changes in these two regions affect each other. The location errors of the events especially the depth errors in the catalogs and the active fault structure in the area cannot be realized without any geodetic or seismic data analysis. This study claims that the interpretations of the moderate size earthquakes should be studied by using multidisciplinary data sets.
ACKNOWLEDGEMENTS
This work is supported by the Turkish Directorate of Strategy and Budget under the TAM Project number DPT2007K120610.
How to cite: Eskikoy, F., Ergintav, S., Konca, A. Ö., Çakır, Z., Vasyura-Bathke, H., Isken, M., and Karabulut, H.: Small scale fault interactions in Southwestern Anatolia as revealed from Seismology & InSAR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1068, https://doi.org/10.5194/egusphere-egu2020-1068, 2020.
EGU2020-18856 | Displays | TS5.5
Deformation of continental blocks within convergent plates: Anatolia as a case studyCengiz Zabcı, Taylan Sançar, Müge Yazıcı, Anke M. Friedrich, and Naki Akçar
Anatolia is part of the west-central Alpide plate-boundary zone, particularly where the deformation is characterized by the westward extrusion of this continental block between the Arabian-Eurasian collision in the east and the Hellenic Subduction in the west. Although, this motion mostly happens along the boundary structures, i.e., the North Anatolian and East Anatolian shear zones, there are multiple studies documenting the active deformation along NE-striking sinistral and NW-striking dextral strike-slip faults within the central and eastern parts of Anatolia. These secondary faults slice Anatolia into several pieces giving formation of the Malatya-Erzincan, Cappadocian and Central Anatolian slices from east to west, where their boundary geometries are strongly controlled by the weak zones, the Tethyan Suture Zones.
We compiled all geological slip-rate and palaeoseismological studies, which point out inhomogeneous magnitude of deformation along different sections of these secondary structures. The Central Anatolian Fault Zone, the westernmost NE-striking sinistral strike-slip structure and the western boundary between the Central Anatolia and Cappadocian slices, has an average horizontal slip-rate of about 1 to 1.5 mm/a for the last few tens of thousands of years. The earthquake recurrence of about 4500 years between two events revealed on the northern sections of the CAFZ also support this rate of deformation. However, the Malatya-Ovacık Fault Zone has a bimodal behaviour in terms of deformation rate, which is 2.5 times higher along its northern member, the Ovacık Fault (OF) than the southern one, the Malatya Fault (MF) (2.5 to 1 mm/a), respectively. This velocity difference between two distinct members of the same fault zone can be explained by the relative westward motion of slices where the OF makes the direct contact between the Central Anatolian and Malatya-Erzincan, and the MF delimits Cappadocian and Malatya-Erzincan slices. Although these structures, which are shallow and probably deform only the upper crust, are of having secondary importance, yet they are still capable of producing infrequent but strong earthquakes within this highly deforming convergent setting. This study is supported by TÜBİTAK projects no. 114Y227 and 114Y580.
How to cite: Zabcı, C., Sançar, T., Yazıcı, M., Friedrich, A. M., and Akçar, N.: Deformation of continental blocks within convergent plates: Anatolia as a case study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18856, https://doi.org/10.5194/egusphere-egu2020-18856, 2020.
Anatolia is part of the west-central Alpide plate-boundary zone, particularly where the deformation is characterized by the westward extrusion of this continental block between the Arabian-Eurasian collision in the east and the Hellenic Subduction in the west. Although, this motion mostly happens along the boundary structures, i.e., the North Anatolian and East Anatolian shear zones, there are multiple studies documenting the active deformation along NE-striking sinistral and NW-striking dextral strike-slip faults within the central and eastern parts of Anatolia. These secondary faults slice Anatolia into several pieces giving formation of the Malatya-Erzincan, Cappadocian and Central Anatolian slices from east to west, where their boundary geometries are strongly controlled by the weak zones, the Tethyan Suture Zones.
We compiled all geological slip-rate and palaeoseismological studies, which point out inhomogeneous magnitude of deformation along different sections of these secondary structures. The Central Anatolian Fault Zone, the westernmost NE-striking sinistral strike-slip structure and the western boundary between the Central Anatolia and Cappadocian slices, has an average horizontal slip-rate of about 1 to 1.5 mm/a for the last few tens of thousands of years. The earthquake recurrence of about 4500 years between two events revealed on the northern sections of the CAFZ also support this rate of deformation. However, the Malatya-Ovacık Fault Zone has a bimodal behaviour in terms of deformation rate, which is 2.5 times higher along its northern member, the Ovacık Fault (OF) than the southern one, the Malatya Fault (MF) (2.5 to 1 mm/a), respectively. This velocity difference between two distinct members of the same fault zone can be explained by the relative westward motion of slices where the OF makes the direct contact between the Central Anatolian and Malatya-Erzincan, and the MF delimits Cappadocian and Malatya-Erzincan slices. Although these structures, which are shallow and probably deform only the upper crust, are of having secondary importance, yet they are still capable of producing infrequent but strong earthquakes within this highly deforming convergent setting. This study is supported by TÜBİTAK projects no. 114Y227 and 114Y580.
How to cite: Zabcı, C., Sançar, T., Yazıcı, M., Friedrich, A. M., and Akçar, N.: Deformation of continental blocks within convergent plates: Anatolia as a case study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18856, https://doi.org/10.5194/egusphere-egu2020-18856, 2020.
EGU2020-4116 | Displays | TS5.5
Strain Partitioning Between the Izmir-Balikesir Transfer Zone and the North Anatolian Fault Zone, NW TurkeyLevent Tosun, Elif Çakır, Bora Uzel, Ökmen Sümer, Atilla Arda Özacar, Nuretdin Kaymakcı, and Cor Langereis
The present tectonic framework of the Western Anatolia has been dominated by two major deformations. The first one is the product of the slab-edge processes related to the convergence between Eurasian and African plates along with the Aegean-Cyprean subduction system since the Oligocene, and the second one is the westwards escape of Anatolian Block along the North Anatolian Fault Zone (NAFZ) since the late Miocene. The first one resulted in a widespread extensional deformation in the Western Anatolia and the Aegean region and is associated with slab-detachment and slab-tear processes that gave rise to the development of dynamic topography and various core-complexes (e.g., Cyclades and Menderes). Recent studies have shown that the deferential extensional strain between the core complexes in the region has been accommodated by strike-slip dominated transfer zones, the İzmir-Balıkesir Transfer Zone (İBTZ), which developed (sub)parallel to the extension direction and accommodate differential extension and rotational deformation in the region. The second one gave way to the development of a complex strike-slip deformation pattern and an array of pull-apart basin complexes throughout the northern margin of the Anatolian Block. The NAFZ and İBTZ interact around the Balıkesir-Bursa region resulting in a very peculiar deformation style due to partitioning of strain between these major structures.
This study aims at unraveling how the strain partitioning operates between İBTZ and NAFZ and to reveal the kinematic constraints that produced the present tectonic scheme in the region. The geometry and kinematics of the faults are determined by analyzing 2773 fault slip data obtained from 49 sites evenly distributed throughout the study area. The preliminary results show that the İzmir-Balıkesir Transfer Zone localized after Miocene with the decoupling of strike-slip faults, and to the episodic exhumation of the metamorphic core complexes. The focal mechanism solutions of the recent earthquakes support this decoupling and manifest the seismic activity of the İBTZ. This study is supported by a Tübitak Project, Grant Number of 117R011.
How to cite: Tosun, L., Çakır, E., Uzel, B., Sümer, Ö., Özacar, A. A., Kaymakcı, N., and Langereis, C.: Strain Partitioning Between the Izmir-Balikesir Transfer Zone and the North Anatolian Fault Zone, NW Turkey, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4116, https://doi.org/10.5194/egusphere-egu2020-4116, 2020.
The present tectonic framework of the Western Anatolia has been dominated by two major deformations. The first one is the product of the slab-edge processes related to the convergence between Eurasian and African plates along with the Aegean-Cyprean subduction system since the Oligocene, and the second one is the westwards escape of Anatolian Block along the North Anatolian Fault Zone (NAFZ) since the late Miocene. The first one resulted in a widespread extensional deformation in the Western Anatolia and the Aegean region and is associated with slab-detachment and slab-tear processes that gave rise to the development of dynamic topography and various core-complexes (e.g., Cyclades and Menderes). Recent studies have shown that the deferential extensional strain between the core complexes in the region has been accommodated by strike-slip dominated transfer zones, the İzmir-Balıkesir Transfer Zone (İBTZ), which developed (sub)parallel to the extension direction and accommodate differential extension and rotational deformation in the region. The second one gave way to the development of a complex strike-slip deformation pattern and an array of pull-apart basin complexes throughout the northern margin of the Anatolian Block. The NAFZ and İBTZ interact around the Balıkesir-Bursa region resulting in a very peculiar deformation style due to partitioning of strain between these major structures.
This study aims at unraveling how the strain partitioning operates between İBTZ and NAFZ and to reveal the kinematic constraints that produced the present tectonic scheme in the region. The geometry and kinematics of the faults are determined by analyzing 2773 fault slip data obtained from 49 sites evenly distributed throughout the study area. The preliminary results show that the İzmir-Balıkesir Transfer Zone localized after Miocene with the decoupling of strike-slip faults, and to the episodic exhumation of the metamorphic core complexes. The focal mechanism solutions of the recent earthquakes support this decoupling and manifest the seismic activity of the İBTZ. This study is supported by a Tübitak Project, Grant Number of 117R011.
How to cite: Tosun, L., Çakır, E., Uzel, B., Sümer, Ö., Özacar, A. A., Kaymakcı, N., and Langereis, C.: Strain Partitioning Between the Izmir-Balikesir Transfer Zone and the North Anatolian Fault Zone, NW Turkey, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4116, https://doi.org/10.5194/egusphere-egu2020-4116, 2020.
EGU2020-843 | Displays | TS5.5
Contributions of fault gouge mineralogy on aseismic creep of active faults: the East Anatolian Fault (Eastern Turkey) as a case studyMüge Yazıcı, Mehran Basmenji, Mehmet Köküm, Ugur Dogan, Cengiz Zabcı, and Semih Ergintav
In the complex tectonic setting of the Eastern Mediterranean, the westward motion of the Anatolian Block is accommodated mainly along its boundary faults, the North Anatolian Shear Zone (NASZ) and the East Anatolian Shear Zone (EASZ). Although there are relatively limited studies on the active tectonics of the EASZ, horizontal slip rate is suggested to be of about 10 mm/yr, using geodetic data. In terms of instrumental and historical seismicity, this sinistral strike-slip fault generated surface rupturing earthquakes along almost its entire length except two segments, Palu in the northeast and Turkoglu in the southwest, creating two seismic gaps on the East Anatolian Fault (EAF), the most prominent member of the EASZ. In spite of the fact that there are some off-fault seismic activities such as the 2010 Kovancılar Earthquake (M 6.1) in the vicinity of Palu Seismic Gap, recent geodetic measurements show significant aseismic creep, almost retaining the full far plate velocity (~10 mm/yr) for about 100 km-long section of the fault. Hence, the region is continuously monitored by various types of techniques, such as GNSS, InSAR, creepmeter, seismology, and high-resolution photogrammetry.
In addition to monitoring, we investigated the mechanical signature of the creep in the fault zone using fault rocks along the Palu Segment. We collected several samples directly from the deformation zone of the EAF, which makes the boundary between limestones of the Kirkgecit Formation and the chaotic alternation of volcanics, mudstones, and limestones of the Maden Complex, at two locations. The Underground Railway Tunnel Section (39.9504°N, 38.6976°E) is cut by the fault zone where the creep signals are recorded by a creepmeter. The X-Ray Diffraction (XRD) analyses of collected samples of this locality suggest the presence of montmorillonite (smectite group) as the main clay mineral in addition to chlorite-kaolinite with a negligible amount of illite-mica minerals within the fault rocks. This preliminary result suggests a linkage between the creeping and petrophysical properties of fault rocks, which are made of the weak smectite mineral and show no-frictional healing as the expected characteristics of the creep. However, the preliminary analyses of fault gouge samples from the Murat River Section (39.9696°N, 38.7043°E) yield a small amount of smectite group clays. We are going to extend our study at different locations in order to increase the spatial resolution on the relation between the fault rocks and creep motion. This study is supported by the TUBITAK Project no. 118Y435.
How to cite: Yazıcı, M., Basmenji, M., Köküm, M., Dogan, U., Zabcı, C., and Ergintav, S.: Contributions of fault gouge mineralogy on aseismic creep of active faults: the East Anatolian Fault (Eastern Turkey) as a case study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-843, https://doi.org/10.5194/egusphere-egu2020-843, 2020.
In the complex tectonic setting of the Eastern Mediterranean, the westward motion of the Anatolian Block is accommodated mainly along its boundary faults, the North Anatolian Shear Zone (NASZ) and the East Anatolian Shear Zone (EASZ). Although there are relatively limited studies on the active tectonics of the EASZ, horizontal slip rate is suggested to be of about 10 mm/yr, using geodetic data. In terms of instrumental and historical seismicity, this sinistral strike-slip fault generated surface rupturing earthquakes along almost its entire length except two segments, Palu in the northeast and Turkoglu in the southwest, creating two seismic gaps on the East Anatolian Fault (EAF), the most prominent member of the EASZ. In spite of the fact that there are some off-fault seismic activities such as the 2010 Kovancılar Earthquake (M 6.1) in the vicinity of Palu Seismic Gap, recent geodetic measurements show significant aseismic creep, almost retaining the full far plate velocity (~10 mm/yr) for about 100 km-long section of the fault. Hence, the region is continuously monitored by various types of techniques, such as GNSS, InSAR, creepmeter, seismology, and high-resolution photogrammetry.
In addition to monitoring, we investigated the mechanical signature of the creep in the fault zone using fault rocks along the Palu Segment. We collected several samples directly from the deformation zone of the EAF, which makes the boundary between limestones of the Kirkgecit Formation and the chaotic alternation of volcanics, mudstones, and limestones of the Maden Complex, at two locations. The Underground Railway Tunnel Section (39.9504°N, 38.6976°E) is cut by the fault zone where the creep signals are recorded by a creepmeter. The X-Ray Diffraction (XRD) analyses of collected samples of this locality suggest the presence of montmorillonite (smectite group) as the main clay mineral in addition to chlorite-kaolinite with a negligible amount of illite-mica minerals within the fault rocks. This preliminary result suggests a linkage between the creeping and petrophysical properties of fault rocks, which are made of the weak smectite mineral and show no-frictional healing as the expected characteristics of the creep. However, the preliminary analyses of fault gouge samples from the Murat River Section (39.9696°N, 38.7043°E) yield a small amount of smectite group clays. We are going to extend our study at different locations in order to increase the spatial resolution on the relation between the fault rocks and creep motion. This study is supported by the TUBITAK Project no. 118Y435.
How to cite: Yazıcı, M., Basmenji, M., Köküm, M., Dogan, U., Zabcı, C., and Ergintav, S.: Contributions of fault gouge mineralogy on aseismic creep of active faults: the East Anatolian Fault (Eastern Turkey) as a case study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-843, https://doi.org/10.5194/egusphere-egu2020-843, 2020.
EGU2020-3161 | Displays | TS5.5
Paleoseismic and morphometric manifestation of the transition between the Western Anatolian extensional regime and the North Anatolian Fault strike-slip zoneVolkan Karabacak, Taylan Sançar, and Yusuf Büyükdeniz
The strike-slip dominated North Anatolian Fault Zone (NAFZ) prolongs to the west and furcates into several branches where shear is distributed to multiple parallel/subparallel segments. The earlier structures that resulted from the ongoing Western Anatolian extension had a key role in the fact that the western part of the NAFZ has a wider deformation zone. Although the southern boundary of this zone is controversial, it is proposed that there is a strong interaction between the deformation zones of the NAFZ and Western Anatolian Extensional Province (WAEP) along the northern margin of the Uludag Range. Since this pivotal region marks the transition between the extensional regime and continental strike-slip zone, it is necessary to increase knowledge thereof. Within this ongoing study, we focused on the morphotectonic and paleoseismologic properties of the Ulubat and Bursa faults that delimits the northern boundary of the Uludag Range. The results of the morphometric analyses (topographic symmetry factor, asymmetry factor, hypsometric curve and integral, channel concavity, and integral analyses) that performed on 79 drainage basin to the south of these faults suggested that the vertical motion in the northeastern part of the Uludag Range changes abruptly to strike-slip dominated deformation, along with Ulubat Fault, towards the west of the Bursa basin.
The 50 km length, dextral Ulubat Fault was mapped in the field by using offset physiographic features and geological evidence. We divided the ENE–WSW striking Ulubat Fault into three segments that present the releasing double-bend geometry. There are two major changes in trends up to 20 degrees between each segment. The western segment has a length of 17 km in the E-W direction. The middle segment extends toward NE with a length of 20 km. The eastern segment stretches eastward for 13 km with a southward arc-shape geometry. We conducted the first paleoseismological trench studies on middle and eastern segments of the Ulubat Fault and identified at least 6 paleoearthquakes for the last 16 ka on both segments. The paleoseismic behavioral results which are consistent with the geometric segmentation show individual ruptures on each segment. Dated surface ruptures history show that the fault has used the same single trace in Holocene and the last events occurred in 1143 AD and 170 AD along the middle and eastern segments respectively.
Although further studies are needed to evaluate the paleoseismic recurrence interval, our results show that the Ulubat Fault takes over a considerable activity in the north of Uludag Range. The field evidence and morphometric analyses around the Uludag Range sign out that the Ulubat Fault forms the southernmost member of the NAFZ strike-slip domain. The eastern segment of the dextral Ulubat Fault has vertical component while the Bursa Fault exhibits the characteristics of the WAEP towards further east. This research was supported by the Disaster & Emergency Management Authority of Turkey (UDAP project; G-18-01).
How to cite: Karabacak, V., Sançar, T., and Büyükdeniz, Y.: Paleoseismic and morphometric manifestation of the transition between the Western Anatolian extensional regime and the North Anatolian Fault strike-slip zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3161, https://doi.org/10.5194/egusphere-egu2020-3161, 2020.
The strike-slip dominated North Anatolian Fault Zone (NAFZ) prolongs to the west and furcates into several branches where shear is distributed to multiple parallel/subparallel segments. The earlier structures that resulted from the ongoing Western Anatolian extension had a key role in the fact that the western part of the NAFZ has a wider deformation zone. Although the southern boundary of this zone is controversial, it is proposed that there is a strong interaction between the deformation zones of the NAFZ and Western Anatolian Extensional Province (WAEP) along the northern margin of the Uludag Range. Since this pivotal region marks the transition between the extensional regime and continental strike-slip zone, it is necessary to increase knowledge thereof. Within this ongoing study, we focused on the morphotectonic and paleoseismologic properties of the Ulubat and Bursa faults that delimits the northern boundary of the Uludag Range. The results of the morphometric analyses (topographic symmetry factor, asymmetry factor, hypsometric curve and integral, channel concavity, and integral analyses) that performed on 79 drainage basin to the south of these faults suggested that the vertical motion in the northeastern part of the Uludag Range changes abruptly to strike-slip dominated deformation, along with Ulubat Fault, towards the west of the Bursa basin.
The 50 km length, dextral Ulubat Fault was mapped in the field by using offset physiographic features and geological evidence. We divided the ENE–WSW striking Ulubat Fault into three segments that present the releasing double-bend geometry. There are two major changes in trends up to 20 degrees between each segment. The western segment has a length of 17 km in the E-W direction. The middle segment extends toward NE with a length of 20 km. The eastern segment stretches eastward for 13 km with a southward arc-shape geometry. We conducted the first paleoseismological trench studies on middle and eastern segments of the Ulubat Fault and identified at least 6 paleoearthquakes for the last 16 ka on both segments. The paleoseismic behavioral results which are consistent with the geometric segmentation show individual ruptures on each segment. Dated surface ruptures history show that the fault has used the same single trace in Holocene and the last events occurred in 1143 AD and 170 AD along the middle and eastern segments respectively.
Although further studies are needed to evaluate the paleoseismic recurrence interval, our results show that the Ulubat Fault takes over a considerable activity in the north of Uludag Range. The field evidence and morphometric analyses around the Uludag Range sign out that the Ulubat Fault forms the southernmost member of the NAFZ strike-slip domain. The eastern segment of the dextral Ulubat Fault has vertical component while the Bursa Fault exhibits the characteristics of the WAEP towards further east. This research was supported by the Disaster & Emergency Management Authority of Turkey (UDAP project; G-18-01).
How to cite: Karabacak, V., Sançar, T., and Büyükdeniz, Y.: Paleoseismic and morphometric manifestation of the transition between the Western Anatolian extensional regime and the North Anatolian Fault strike-slip zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3161, https://doi.org/10.5194/egusphere-egu2020-3161, 2020.
EGU2020-11072 | Displays | TS5.5
Spatio-temporal variations of surface creep along the Hazar-Palu Segment of the East Anatolian Fault, TurkeyUgur Dogan, Semih Ergintav, Seda Ozarpaci, Alpay Ozdemir, M. Hilmi Erkoç, Alper Yigitoglu, Efe T. Ayruk, Ziyadin Çakir, Hayrullah Karabulut, Bulent Bayram, Cengiz Zabci, and Roger Bilham
Aseismic creep is detected and started to be monitored along the 100 km-long Palu-Hazar Segment of the Eastern Anatolian Fault (EAF) in Turkey, a major plate boundary between Anatolia and Arabia. We used creepmeters, InSAR, GPS, and seismic observations to document the extent and magnitude of this motion in order to increase our knowledge on the spatiotemporal variation of creep along the EAF, its relationship with the lithology and tectonic structures, and the stress change on the neighboring fault segments. Until now, we observed the region with continuous GPS and survey GPS measurements with near (~ 0.1- 4 km to the fault) and far-field (~25 – 225 km from the fault) stations to determine the depth of the creep zone and its velocity along the EAF. We processed 6 years (2014 – 2019) of continuous and 7 campaign (2015 – 2019) GPS data with GAMIT/GLOBK software. With elastic models, we determined a creep rate that reaches about 5 ± 0.3 mm/yr from GPS observations (50% of secular velocity). In addition to surface control of the creeping zone, we analyzed the deformations, by using three Terrestrial Laser Scanner (TLS) survey, in the Palu railway tunnel that crosses the fault where the walls of the tunnel have been offset by 15 ± 2 mm since the construction in the middle of the last century. Also, two creepmeters were installed inside the tunnel and transient creep anomalies are detected. These results are correlated with seismic and InSAR data (This study is supported by TUBITAK 1001 projects 114Y250 and 118Y450).
Keywords: Hazar-Palu, Creep, East Anatolian Fault, Earthquake, GPS, InSAR, TLS
How to cite: Dogan, U., Ergintav, S., Ozarpaci, S., Ozdemir, A., Erkoç, M. H., Yigitoglu, A., Ayruk, E. T., Çakir, Z., Karabulut, H., Bayram, B., Zabci, C., and Bilham, R.: Spatio-temporal variations of surface creep along the Hazar-Palu Segment of the East Anatolian Fault, Turkey, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11072, https://doi.org/10.5194/egusphere-egu2020-11072, 2020.
Aseismic creep is detected and started to be monitored along the 100 km-long Palu-Hazar Segment of the Eastern Anatolian Fault (EAF) in Turkey, a major plate boundary between Anatolia and Arabia. We used creepmeters, InSAR, GPS, and seismic observations to document the extent and magnitude of this motion in order to increase our knowledge on the spatiotemporal variation of creep along the EAF, its relationship with the lithology and tectonic structures, and the stress change on the neighboring fault segments. Until now, we observed the region with continuous GPS and survey GPS measurements with near (~ 0.1- 4 km to the fault) and far-field (~25 – 225 km from the fault) stations to determine the depth of the creep zone and its velocity along the EAF. We processed 6 years (2014 – 2019) of continuous and 7 campaign (2015 – 2019) GPS data with GAMIT/GLOBK software. With elastic models, we determined a creep rate that reaches about 5 ± 0.3 mm/yr from GPS observations (50% of secular velocity). In addition to surface control of the creeping zone, we analyzed the deformations, by using three Terrestrial Laser Scanner (TLS) survey, in the Palu railway tunnel that crosses the fault where the walls of the tunnel have been offset by 15 ± 2 mm since the construction in the middle of the last century. Also, two creepmeters were installed inside the tunnel and transient creep anomalies are detected. These results are correlated with seismic and InSAR data (This study is supported by TUBITAK 1001 projects 114Y250 and 118Y450).
Keywords: Hazar-Palu, Creep, East Anatolian Fault, Earthquake, GPS, InSAR, TLS
How to cite: Dogan, U., Ergintav, S., Ozarpaci, S., Ozdemir, A., Erkoç, M. H., Yigitoglu, A., Ayruk, E. T., Çakir, Z., Karabulut, H., Bayram, B., Zabci, C., and Bilham, R.: Spatio-temporal variations of surface creep along the Hazar-Palu Segment of the East Anatolian Fault, Turkey, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11072, https://doi.org/10.5194/egusphere-egu2020-11072, 2020.
EGU2020-13045 | Displays | TS5.5
Interseismic Deformation in the Gulf of Aqaba Inferred from GPS MeasurementsNicolas Castro-Perdomo, Renier Viltres, Frédéric Masson, Patrice Ulrich, Jean-Daniel Bernard, Maher Dhahry, Shaozhuo Liu, Abdulaziz Alothman, Hani Zahran, P. Martin Mai, and Sigurjón Jónsson
The Dead Sea Transform fault forms the boundary between the Arabian plate and the Sinai-Levant subplate. Several aspects of this fault system have been extensively studied during the last century. However, the present-day kinematics and deformation along its southern end in the Gulf of Aqaba remain poorly understood. Here we present a crustal motion velocity field based on three GPS surveys conducted between 2015 and 2019 at 30 campaign sites, complemented by 12 permanent stations operating near the gulf. We constrained a pole of rotation for the Sinai-Levant subplate based on five selected stations on the Sinai Peninsula. This Euler pole predicts a left-lateral slip rate of ~4.5 mm/yr on the fault system in the gulf, consistent with earlier findings. We find that standard models of interseismic deformation, such as back-slip and screw dislocation models do not provide a reasonable constraint on fault locking depths due to limited near-fault measurements. Despite this, our results reveal a small (~1 mm/yr) but systematic left-lateral residual motion across the gulf that cannot be resolved by elastic models of strain accumulation. We further find that the orientation of these residuals agrees with modelled postseismic transient motions caused by the 1995 MW 7.2 Nuweiba earthquake in the NE and SW quadrants relative to the gulf trend. Combined, these observations suggest that postseismic deformation caused by the Nuweiba earthquake may still be ongoing. We anticipate our findings to be a starting point for future geodetic studies in the northern Red Sea region where large-scale infrastructure mega-projects, such as the NEOM city and the King Salman bridge across the gulf are being developed. Future studies would benefit from incorporating additional GPS stations on the Sinai side of the gulf, refined finite-fault models, seafloor geodetic measurements and better information about past earthquakes.
How to cite: Castro-Perdomo, N., Viltres, R., Masson, F., Ulrich, P., Bernard, J.-D., Dhahry, M., Liu, S., Alothman, A., Zahran, H., Mai, P. M., and Jónsson, S.: Interseismic Deformation in the Gulf of Aqaba Inferred from GPS Measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13045, https://doi.org/10.5194/egusphere-egu2020-13045, 2020.
The Dead Sea Transform fault forms the boundary between the Arabian plate and the Sinai-Levant subplate. Several aspects of this fault system have been extensively studied during the last century. However, the present-day kinematics and deformation along its southern end in the Gulf of Aqaba remain poorly understood. Here we present a crustal motion velocity field based on three GPS surveys conducted between 2015 and 2019 at 30 campaign sites, complemented by 12 permanent stations operating near the gulf. We constrained a pole of rotation for the Sinai-Levant subplate based on five selected stations on the Sinai Peninsula. This Euler pole predicts a left-lateral slip rate of ~4.5 mm/yr on the fault system in the gulf, consistent with earlier findings. We find that standard models of interseismic deformation, such as back-slip and screw dislocation models do not provide a reasonable constraint on fault locking depths due to limited near-fault measurements. Despite this, our results reveal a small (~1 mm/yr) but systematic left-lateral residual motion across the gulf that cannot be resolved by elastic models of strain accumulation. We further find that the orientation of these residuals agrees with modelled postseismic transient motions caused by the 1995 MW 7.2 Nuweiba earthquake in the NE and SW quadrants relative to the gulf trend. Combined, these observations suggest that postseismic deformation caused by the Nuweiba earthquake may still be ongoing. We anticipate our findings to be a starting point for future geodetic studies in the northern Red Sea region where large-scale infrastructure mega-projects, such as the NEOM city and the King Salman bridge across the gulf are being developed. Future studies would benefit from incorporating additional GPS stations on the Sinai side of the gulf, refined finite-fault models, seafloor geodetic measurements and better information about past earthquakes.
How to cite: Castro-Perdomo, N., Viltres, R., Masson, F., Ulrich, P., Bernard, J.-D., Dhahry, M., Liu, S., Alothman, A., Zahran, H., Mai, P. M., and Jónsson, S.: Interseismic Deformation in the Gulf of Aqaba Inferred from GPS Measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13045, https://doi.org/10.5194/egusphere-egu2020-13045, 2020.
EGU2020-20404 | Displays | TS5.5
Seismogenic source model of the 2019 Mw 5.9 East-Azerbaijan earthquake (NW Iran) through Sentinel-1 DInSAR measurementsEmanuela Valerio, Francesco Casu, Vincenzo Convertito, Claudio De Luca, Vincenzo De Novellis, Michele Manunta, Mariarosaria Manzo, Fernando Monterroso, and Riccardo Lanari
On 7 November 2019 (22:47 UTC) a Mw 5.9 earthquake struck the East-Azerbaijan region, in the north-western Iran, about 100 km east of Tabriz, the fourth largest city of Iran with a population of over two million. This seismic event caused both widespread damage to the surrounding villages and casualties, killing about 5 people and injuring hundreds. The occurrence of this earthquake is related to the main geodynamic regime controlled by the oblique Arabia-Eurasia convergence and, in particular, this event is inserted in the tectonic context of the East-Azerbaijan Plateau, a complex mountain belt that contains internal major fold-and-thrust belts.
In this work, we first generate the coseismic deformation maps by applying the Differential Synthetic Aperture Radar Interferometry (DInSAR) technique to SAR data collected along ascending and descending orbits by the Sentinel-1 constellation of the European Copernicus Programme. Then, we invert them through analytical modeling in order to better constrain the geometry and characteristics of the main source. The retrieved fault model revealed a shallow seismic source approximately NE–SW-striking and characterized by a left-lateral strike-slip, southeast-dipping faulting mechanism. Our retrieved solution reveals a new minor fault never mapped in geological maps before, whose kinematics is compatible with that of the surrounding structures and with the local and regional stress states. Moreover, we also use the preferred fault model to calculate the Coulomb Failure Function at the nearby receiver faults; taking into account the surrounding geological structures reported in literature, we show that all the considered receiver faults have been positively stressed by the main event. This is also confirmed by the distribution of the aftershocks that occurred near the considered faults. The analysis of the earthquake nucleated along these left-lateral strike-slip minor fault is essential to improve our knowledge of the East-Azerbaijan Plateau; therefore, further studies are required to evaluate their role in seismic hazard definition of northwest of Iran, in order to help in the mitigation of the seismic hazard in seismogenic regions unprepared for the occurrence of seismic events.
This work is supported by: the 2019-2021 IREA-CNR and Italian Civil Protection Department agreement, H2020 EPOS-SP (GA 871121), ENVRI-FAIR (GA 824068) projects, and the I-AMICA (PONa3_00363) project.
How to cite: Valerio, E., Casu, F., Convertito, V., De Luca, C., De Novellis, V., Manunta, M., Manzo, M., Monterroso, F., and Lanari, R.: Seismogenic source model of the 2019 Mw 5.9 East-Azerbaijan earthquake (NW Iran) through Sentinel-1 DInSAR measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20404, https://doi.org/10.5194/egusphere-egu2020-20404, 2020.
On 7 November 2019 (22:47 UTC) a Mw 5.9 earthquake struck the East-Azerbaijan region, in the north-western Iran, about 100 km east of Tabriz, the fourth largest city of Iran with a population of over two million. This seismic event caused both widespread damage to the surrounding villages and casualties, killing about 5 people and injuring hundreds. The occurrence of this earthquake is related to the main geodynamic regime controlled by the oblique Arabia-Eurasia convergence and, in particular, this event is inserted in the tectonic context of the East-Azerbaijan Plateau, a complex mountain belt that contains internal major fold-and-thrust belts.
In this work, we first generate the coseismic deformation maps by applying the Differential Synthetic Aperture Radar Interferometry (DInSAR) technique to SAR data collected along ascending and descending orbits by the Sentinel-1 constellation of the European Copernicus Programme. Then, we invert them through analytical modeling in order to better constrain the geometry and characteristics of the main source. The retrieved fault model revealed a shallow seismic source approximately NE–SW-striking and characterized by a left-lateral strike-slip, southeast-dipping faulting mechanism. Our retrieved solution reveals a new minor fault never mapped in geological maps before, whose kinematics is compatible with that of the surrounding structures and with the local and regional stress states. Moreover, we also use the preferred fault model to calculate the Coulomb Failure Function at the nearby receiver faults; taking into account the surrounding geological structures reported in literature, we show that all the considered receiver faults have been positively stressed by the main event. This is also confirmed by the distribution of the aftershocks that occurred near the considered faults. The analysis of the earthquake nucleated along these left-lateral strike-slip minor fault is essential to improve our knowledge of the East-Azerbaijan Plateau; therefore, further studies are required to evaluate their role in seismic hazard definition of northwest of Iran, in order to help in the mitigation of the seismic hazard in seismogenic regions unprepared for the occurrence of seismic events.
This work is supported by: the 2019-2021 IREA-CNR and Italian Civil Protection Department agreement, H2020 EPOS-SP (GA 871121), ENVRI-FAIR (GA 824068) projects, and the I-AMICA (PONa3_00363) project.
How to cite: Valerio, E., Casu, F., Convertito, V., De Luca, C., De Novellis, V., Manunta, M., Manzo, M., Monterroso, F., and Lanari, R.: Seismogenic source model of the 2019 Mw 5.9 East-Azerbaijan earthquake (NW Iran) through Sentinel-1 DInSAR measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20404, https://doi.org/10.5194/egusphere-egu2020-20404, 2020.
TS6.1 – The Afro-Arabian Rift System
EGU2020-21127 | Displays | TS6.1
Constraining strain and magmatism patterns between the Ethiopian and East African plateaux from new seismic and geodetic dataCynthia Ebinger, Weston Harding, Christian Kakonkwe, Ellen Knappe, Ian Bastow, Rebecca Bendick, Mary Muthoni, Gladys Kianji, Nicholas Mariita, and Atalay Ayele
Lateral heterogeneities in crust and mantle structure influence the distribution of strain and magmatism in continental rift zones. Sutures between Archaean cratons and younger orogenic belts represent some of Earth’s largest lateral heterogeneities: > 170 km-thick, buoyant and relatively dry lithosphere juxtaposed to ~120 km-thick, more volatile-rich mantle lithosphere. The seismically and volcanically active Turkana Depression between the Ethiopian and East African plateau magma-rich Eastern rift formed near the eastern edge of the Archaean Tanzania craton. This area was affected by rifting in Mesozoic and Paleogene time, and may have been a thin zone when magmatism started at ~40 Ma. Several hypotheses had been proposed to explain the unusual ~300 km-breadth of the Turkana Depression. We use new data from the Turkana Rift Arrays to Investigate Lithospheric Structure (TRAILS) is to evaluate spatial variations in the location of strain, and in the direction and magnitude of seismic anisotropy, which is strongly influenced by mantle flow patterns along lithosphere-asthenosphere topography, fluid-filled cracks (e.g., dikes), and pre-existing mantle lithosphere strain fabrics. Complementary data sets provide a strong contextual framework. Our results and those of regional studies show that strain is currently localized to ~100 km-wide section of the Depression, and the western sectors are inactive. We suggest that the original location of strain and magmatism was near the eastern edge of the Tanzania craton above a steep lithosphere-asthenosphere gradient, and that rifting has migrated eastward to form a more contiguous zone between the Main Ethiopian and Eastern rift zones.
How to cite: Ebinger, C., Harding, W., Kakonkwe, C., Knappe, E., Bastow, I., Bendick, R., Muthoni, M., Kianji, G., Mariita, N., and Ayele, A.: Constraining strain and magmatism patterns between the Ethiopian and East African plateaux from new seismic and geodetic data , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21127, https://doi.org/10.5194/egusphere-egu2020-21127, 2020.
Lateral heterogeneities in crust and mantle structure influence the distribution of strain and magmatism in continental rift zones. Sutures between Archaean cratons and younger orogenic belts represent some of Earth’s largest lateral heterogeneities: > 170 km-thick, buoyant and relatively dry lithosphere juxtaposed to ~120 km-thick, more volatile-rich mantle lithosphere. The seismically and volcanically active Turkana Depression between the Ethiopian and East African plateau magma-rich Eastern rift formed near the eastern edge of the Archaean Tanzania craton. This area was affected by rifting in Mesozoic and Paleogene time, and may have been a thin zone when magmatism started at ~40 Ma. Several hypotheses had been proposed to explain the unusual ~300 km-breadth of the Turkana Depression. We use new data from the Turkana Rift Arrays to Investigate Lithospheric Structure (TRAILS) is to evaluate spatial variations in the location of strain, and in the direction and magnitude of seismic anisotropy, which is strongly influenced by mantle flow patterns along lithosphere-asthenosphere topography, fluid-filled cracks (e.g., dikes), and pre-existing mantle lithosphere strain fabrics. Complementary data sets provide a strong contextual framework. Our results and those of regional studies show that strain is currently localized to ~100 km-wide section of the Depression, and the western sectors are inactive. We suggest that the original location of strain and magmatism was near the eastern edge of the Tanzania craton above a steep lithosphere-asthenosphere gradient, and that rifting has migrated eastward to form a more contiguous zone between the Main Ethiopian and Eastern rift zones.
How to cite: Ebinger, C., Harding, W., Kakonkwe, C., Knappe, E., Bastow, I., Bendick, R., Muthoni, M., Kianji, G., Mariita, N., and Ayele, A.: Constraining strain and magmatism patterns between the Ethiopian and East African plateaux from new seismic and geodetic data , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21127, https://doi.org/10.5194/egusphere-egu2020-21127, 2020.
EGU2020-2620 | Displays | TS6.1
Multiphase rotational extension and marginal flexure along a developing passive margin: the Western Afar Margin, East AfricaFrank Zwaan, Giacomo Corti, Derek Keir, Federico Sani, Ameha Muluneh, Finnigan Illsley-Kemp, and Mauro Papini
This multidisciplinary study focuses on the tectonics of the Western Afar Margin (WAM), which is situated between the Ethiopian Plateau and Afar Depression in East Africa. The WAM represents a developing passive margin in a highly volcanic setting, thus offering unique opportunities for the study of rifting and (magma-rich) continental break-up, and our results have both regional and global implications.
Earthquake analysis shows that the margin is still deforming under a ca. E-W extension regime (a result also obtained by analysis on fault measurements from recent field campaigns), whereas Afar itself undergoes a more SW-NE extension. Together with GPS data, we see Afar currently opening in a rotational fashion. This opening is however a relatively recent and local phenomenon, due to the rotation of the Danakil microcontinent modifying the regional stress field (since 11 Ma). Regional tectonics is otherwise dominated by the rotation of Arabia since 25 Ma and should cause SW-NE (oblique) extension along the WAM. This oblique motion is indeed recorded in the large-scale en echelon fault patterns along the margin, which were reactivated in the current E-W extension regime. We thus have good evidence of a multiphase rotational history of the WAM and Afar.
Furthermore, analysis of the margin’s structural architecture reveals large-scale flexure towards Afar, likely representing the developing seaward-dipping reflectors that are typical for magma-rich margins. Detailed fault mapping and earthquake analysis show that recent faulting is dominantly antithetic (dipping away from the rift), bounding remarkable marginal grabens, although a large but older synthetic escarpment fault system is present as well. By means of analogue modelling efforts we find that marginal flexure indeed initially develops a large escarpment, whereas the currently active structures only form after significant flexure. Moreover, these models show that marginal grabens do not develop under oblique extension conditions. Instead, the latter model boundary conditions create the large-scale en echelon fault arrangement typical of the WAM. We derive that the recent structures of the margin could have developed only after a shift to local orthogonal extension. These modeling results support the multiphase extension scenario as described above.
Altogether, our findings are highly relevant for our understanding of the structural evolution of (magma-rich) passive margins. Indeed, seismic sections of such margins show very similar structures to those of the WAM. However, the general lack of marginal grabens, which are so obvious along the WAM, can be explained by the fact that most rift systems undergo or have undergone oblique extension, often in multiple phases during which structures from older phases control subsequent deformation.
How to cite: Zwaan, F., Corti, G., Keir, D., Sani, F., Muluneh, A., Illsley-Kemp, F., and Papini, M.: Multiphase rotational extension and marginal flexure along a developing passive margin: the Western Afar Margin, East Africa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2620, https://doi.org/10.5194/egusphere-egu2020-2620, 2020.
This multidisciplinary study focuses on the tectonics of the Western Afar Margin (WAM), which is situated between the Ethiopian Plateau and Afar Depression in East Africa. The WAM represents a developing passive margin in a highly volcanic setting, thus offering unique opportunities for the study of rifting and (magma-rich) continental break-up, and our results have both regional and global implications.
Earthquake analysis shows that the margin is still deforming under a ca. E-W extension regime (a result also obtained by analysis on fault measurements from recent field campaigns), whereas Afar itself undergoes a more SW-NE extension. Together with GPS data, we see Afar currently opening in a rotational fashion. This opening is however a relatively recent and local phenomenon, due to the rotation of the Danakil microcontinent modifying the regional stress field (since 11 Ma). Regional tectonics is otherwise dominated by the rotation of Arabia since 25 Ma and should cause SW-NE (oblique) extension along the WAM. This oblique motion is indeed recorded in the large-scale en echelon fault patterns along the margin, which were reactivated in the current E-W extension regime. We thus have good evidence of a multiphase rotational history of the WAM and Afar.
Furthermore, analysis of the margin’s structural architecture reveals large-scale flexure towards Afar, likely representing the developing seaward-dipping reflectors that are typical for magma-rich margins. Detailed fault mapping and earthquake analysis show that recent faulting is dominantly antithetic (dipping away from the rift), bounding remarkable marginal grabens, although a large but older synthetic escarpment fault system is present as well. By means of analogue modelling efforts we find that marginal flexure indeed initially develops a large escarpment, whereas the currently active structures only form after significant flexure. Moreover, these models show that marginal grabens do not develop under oblique extension conditions. Instead, the latter model boundary conditions create the large-scale en echelon fault arrangement typical of the WAM. We derive that the recent structures of the margin could have developed only after a shift to local orthogonal extension. These modeling results support the multiphase extension scenario as described above.
Altogether, our findings are highly relevant for our understanding of the structural evolution of (magma-rich) passive margins. Indeed, seismic sections of such margins show very similar structures to those of the WAM. However, the general lack of marginal grabens, which are so obvious along the WAM, can be explained by the fact that most rift systems undergo or have undergone oblique extension, often in multiple phases during which structures from older phases control subsequent deformation.
How to cite: Zwaan, F., Corti, G., Keir, D., Sani, F., Muluneh, A., Illsley-Kemp, F., and Papini, M.: Multiphase rotational extension and marginal flexure along a developing passive margin: the Western Afar Margin, East Africa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2620, https://doi.org/10.5194/egusphere-egu2020-2620, 2020.
EGU2020-539 | Displays | TS6.1
Seismicity induced by fluid migration in the Main Ethiopian RiftMartina Raggiunti, Derek Keir, Carolina Pagli, and Aude Lavayssiere
Faults can act as preferential degassing pathways for fluids of deep origin. Their migration and consequently variation of fluid pore pressure can cause a reduction of normal stress on the fault planes and trigger earthquakes. This can generate not only microseismicity but also events with significant magnitude. To understand this phenomenon, we studied the spatial, temporal and waveform characteristics of local seismicity from the northern sector of Main Ethiopian Rift (MER) of East Africa near Fentale and Dofen volcanoes. The seismic database contains events occurred in the MER from October 2001 to January 2003, and acquired by the Ethiopia Afar Geoscientific Experiment (EAGLE Project). The recorded events have been relocated with NLLoc using a new 3D velocity model derived from a wide-angle controlled source experiment. The relocated catalog contains a total of 1543 events with magnitudes between 0 and 4. The seismicity is mainly concentrated in two areas: near the border faults of the Ethiopian plateau and within the rift. On the border faults, events mostly occur down to 20 km depth, with an average depth of ~ 12 km. Within the rift, the events mostly happen down to 15 km depth, with an average depth of ~ 9 km. The seismicity is divided into several clusters aligned parallel to the rift direction, and in profile sections the clusters are mostly dipping steeply sub-vertical and dipping consistent with Andersonian normal faults. The analysis of the temporal-spatial distribution of earthquakes shows that some of the clusters are strongly concentrated in time and in space, and therefore swarm-like. To understand if the different clusters have been conditioned by fluid migration we have also analyzed the frequency content, release of seismic moment, and b-val is cut out. The link between earthquakes and fluid migration has also been explored by interpreting the distribution of seismicity using remote sensing mapping of faults, fumaroles and hydrothermal springs. Understanding where and how the fluid migration occurs will aid geothermal exploration efforts in the region, also improved knowledge of where geothermal activity is linked to seismicity has implications for seismic hazard estimation, which is very important for this densely and economically active areas.
How to cite: Raggiunti, M., Keir, D., Pagli, C., and Lavayssiere, A.: Seismicity induced by fluid migration in the Main Ethiopian Rift, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-539, https://doi.org/10.5194/egusphere-egu2020-539, 2020.
Faults can act as preferential degassing pathways for fluids of deep origin. Their migration and consequently variation of fluid pore pressure can cause a reduction of normal stress on the fault planes and trigger earthquakes. This can generate not only microseismicity but also events with significant magnitude. To understand this phenomenon, we studied the spatial, temporal and waveform characteristics of local seismicity from the northern sector of Main Ethiopian Rift (MER) of East Africa near Fentale and Dofen volcanoes. The seismic database contains events occurred in the MER from October 2001 to January 2003, and acquired by the Ethiopia Afar Geoscientific Experiment (EAGLE Project). The recorded events have been relocated with NLLoc using a new 3D velocity model derived from a wide-angle controlled source experiment. The relocated catalog contains a total of 1543 events with magnitudes between 0 and 4. The seismicity is mainly concentrated in two areas: near the border faults of the Ethiopian plateau and within the rift. On the border faults, events mostly occur down to 20 km depth, with an average depth of ~ 12 km. Within the rift, the events mostly happen down to 15 km depth, with an average depth of ~ 9 km. The seismicity is divided into several clusters aligned parallel to the rift direction, and in profile sections the clusters are mostly dipping steeply sub-vertical and dipping consistent with Andersonian normal faults. The analysis of the temporal-spatial distribution of earthquakes shows that some of the clusters are strongly concentrated in time and in space, and therefore swarm-like. To understand if the different clusters have been conditioned by fluid migration we have also analyzed the frequency content, release of seismic moment, and b-val is cut out. The link between earthquakes and fluid migration has also been explored by interpreting the distribution of seismicity using remote sensing mapping of faults, fumaroles and hydrothermal springs. Understanding where and how the fluid migration occurs will aid geothermal exploration efforts in the region, also improved knowledge of where geothermal activity is linked to seismicity has implications for seismic hazard estimation, which is very important for this densely and economically active areas.
How to cite: Raggiunti, M., Keir, D., Pagli, C., and Lavayssiere, A.: Seismicity induced by fluid migration in the Main Ethiopian Rift, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-539, https://doi.org/10.5194/egusphere-egu2020-539, 2020.
EGU2020-9219 | Displays | TS6.1
Imaging segmentation in early stage rifting (prior to breakup) using a joint inversion of Rayleigh waves from teleseisms and ambient noise tomography in the northern East African RiftEmma L. Chambers, Nicholas Harmon, Derek Keir, Catherine Rychert, and Ryan Gallacher
Within the melt-rich northern East African Rift system, extension progresses from continental rifting in the Ethiopian rift to near continental breakup in Afar. Multiple models have been proposed to understand the evolution of lithospheric stretching and magmatism, but previous studies do not provide a single absolute seismic velocity model of the crust and upper mantle for all stages of the rift. Here we jointly invert surface waves from ambient noise and teleseismic Rayleigh waves to obtain shear velocity maps from 10 to 210 km depth, enabling us to analyse variations in crustal and upper mantle shear wave velocity structure spatially and in depth. Using one model allows us to interpret and understand the pattern of crustal and lithospheric thinning from the rift flanks into the rift, the depth and locus of melt generation, and how these processes vary as a rift evolves towards incipient seafloor spreading.
We observe in areas unaffected by rifting, a fast lid (>0.1 km/s faster than surroundings) at lithosphere-asthenosphere-boundary depths (~60 - 80 km). The fast-lid is not visible directly beneath the rift and we instead observe slow velocities (slow enough to contain partial melt (3.95 – 4.10 ± 0.03 km/s)), which we interpret as evidence for melt infiltration into the uppermost mantle beneath the rift. In addition, the fast lid thins into the rift, until it is no longer observed, suggesting the rift is more stretched than the surrounding plate (~18% thinner). The slow velocities in the asthenosphere beneath the rift are segmented, ~110 km wide, ~60 – 120 km deep with ~70 km spacing between segments. The shallowest and slowest anomalies occur beneath Afar, which is at later stage rifting. At crustal depths we observe a broadening in the slow velocity zones along the length of the Main Ethiopian Rift. Furthermore, the slow crustal velocities laterally spread to beneath areas of the Ethiopian Plateau that were affected by flood basalt volcanism (velocities of 3.30 – 3.80 ± 0.04 km/s). We interpret the broadening of the slow velocity as the Moho acting as a barrier causing lateral migration of melt into areas of pre-existing weakness. Our model provides the first comprehensive seismic model of the northern East African Rift allowing us to interpret rift structure. The segmented slow velocities in the asthenosphere suggest discrete melt-rich upwelling may drive the early the breakup process, with shallowing of the top of the melt-rich zone as the rift evolves and the lithosphere is modified by melt infiltration, with the Moho and lithosphere thinning later in the rifting process.
How to cite: Chambers, E. L., Harmon, N., Keir, D., Rychert, C., and Gallacher, R.: Imaging segmentation in early stage rifting (prior to breakup) using a joint inversion of Rayleigh waves from teleseisms and ambient noise tomography in the northern East African Rift, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9219, https://doi.org/10.5194/egusphere-egu2020-9219, 2020.
Within the melt-rich northern East African Rift system, extension progresses from continental rifting in the Ethiopian rift to near continental breakup in Afar. Multiple models have been proposed to understand the evolution of lithospheric stretching and magmatism, but previous studies do not provide a single absolute seismic velocity model of the crust and upper mantle for all stages of the rift. Here we jointly invert surface waves from ambient noise and teleseismic Rayleigh waves to obtain shear velocity maps from 10 to 210 km depth, enabling us to analyse variations in crustal and upper mantle shear wave velocity structure spatially and in depth. Using one model allows us to interpret and understand the pattern of crustal and lithospheric thinning from the rift flanks into the rift, the depth and locus of melt generation, and how these processes vary as a rift evolves towards incipient seafloor spreading.
We observe in areas unaffected by rifting, a fast lid (>0.1 km/s faster than surroundings) at lithosphere-asthenosphere-boundary depths (~60 - 80 km). The fast-lid is not visible directly beneath the rift and we instead observe slow velocities (slow enough to contain partial melt (3.95 – 4.10 ± 0.03 km/s)), which we interpret as evidence for melt infiltration into the uppermost mantle beneath the rift. In addition, the fast lid thins into the rift, until it is no longer observed, suggesting the rift is more stretched than the surrounding plate (~18% thinner). The slow velocities in the asthenosphere beneath the rift are segmented, ~110 km wide, ~60 – 120 km deep with ~70 km spacing between segments. The shallowest and slowest anomalies occur beneath Afar, which is at later stage rifting. At crustal depths we observe a broadening in the slow velocity zones along the length of the Main Ethiopian Rift. Furthermore, the slow crustal velocities laterally spread to beneath areas of the Ethiopian Plateau that were affected by flood basalt volcanism (velocities of 3.30 – 3.80 ± 0.04 km/s). We interpret the broadening of the slow velocity as the Moho acting as a barrier causing lateral migration of melt into areas of pre-existing weakness. Our model provides the first comprehensive seismic model of the northern East African Rift allowing us to interpret rift structure. The segmented slow velocities in the asthenosphere suggest discrete melt-rich upwelling may drive the early the breakup process, with shallowing of the top of the melt-rich zone as the rift evolves and the lithosphere is modified by melt infiltration, with the Moho and lithosphere thinning later in the rifting process.
How to cite: Chambers, E. L., Harmon, N., Keir, D., Rychert, C., and Gallacher, R.: Imaging segmentation in early stage rifting (prior to breakup) using a joint inversion of Rayleigh waves from teleseisms and ambient noise tomography in the northern East African Rift, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9219, https://doi.org/10.5194/egusphere-egu2020-9219, 2020.
EGU2020-14917 | Displays | TS6.1
Evaporites reveal Pleistocene basin dynamics in the Danakil depression (northern Afar, Ethiopia)Valentin Rime, Anneleen Foubert, Robin Fentimen, Haileyesus Negga, Afifé El Korh, Thierry Adatte, Irka Hajdas, Balemwal Atnafu, and Tesfaye Kidane
The Danakil depression (Afar, Ethiopia) is a rift valley forming the southernmost part of the Red Sea rift. It is situated between the Ethiopian plateau and the Danakil block and is thought to represent an advanced stage of rifting, characterized by important tectonic and volcanic activity. Its floor is situated 120 meters below sea level and is covered by salt pans.
This study focuses on a 625 m deep borehole drilled in the central part of the basin. It mainly consists of evaporites dominated by halite along with clastic and carbonate sediments. Lithostratigraphy and facies description were completed by micropaleontological, geochemical, mineralogical and organic matter analysis. They reveal the complex history of this rift basin. Two marine Red Sea incursions are identified. Strong water stratification during the older marine incursion led to the formation of sapropel layers and magnesite. The restriction of the basin and the strong aridity led to the formation of evaporites, culminating in the deposition of potash salts. Between the two marine events, continental evaporites contributed to several hundreds of meters of basin fill. The younger marine incursion was probably characterized by wetter environments, resulting in the deposition of smaller volumes of evaporites. Since then, hypersaline lakes and salt pans filled the basin. Ongoing radiocarbon and U/Th datings will constrain further the Pleistocene stratigraphy and timing of the marine incursions.
These findings shed a new light on the basin history. The successive flooding and desiccation events are a consequence of sea-level variations but also important tectonic activity. Rift margin uplift prevented flooding during the Holocene sea-level highstand and contributed to the restriction of the depression. Significant basin subsidence at very short time scales created accommodation space for the voluminous sediment infill. This implies very active rifting during the last 250 ka.
How to cite: Rime, V., Foubert, A., Fentimen, R., Negga, H., El Korh, A., Adatte, T., Hajdas, I., Atnafu, B., and Kidane, T.: Evaporites reveal Pleistocene basin dynamics in the Danakil depression (northern Afar, Ethiopia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14917, https://doi.org/10.5194/egusphere-egu2020-14917, 2020.
The Danakil depression (Afar, Ethiopia) is a rift valley forming the southernmost part of the Red Sea rift. It is situated between the Ethiopian plateau and the Danakil block and is thought to represent an advanced stage of rifting, characterized by important tectonic and volcanic activity. Its floor is situated 120 meters below sea level and is covered by salt pans.
This study focuses on a 625 m deep borehole drilled in the central part of the basin. It mainly consists of evaporites dominated by halite along with clastic and carbonate sediments. Lithostratigraphy and facies description were completed by micropaleontological, geochemical, mineralogical and organic matter analysis. They reveal the complex history of this rift basin. Two marine Red Sea incursions are identified. Strong water stratification during the older marine incursion led to the formation of sapropel layers and magnesite. The restriction of the basin and the strong aridity led to the formation of evaporites, culminating in the deposition of potash salts. Between the two marine events, continental evaporites contributed to several hundreds of meters of basin fill. The younger marine incursion was probably characterized by wetter environments, resulting in the deposition of smaller volumes of evaporites. Since then, hypersaline lakes and salt pans filled the basin. Ongoing radiocarbon and U/Th datings will constrain further the Pleistocene stratigraphy and timing of the marine incursions.
These findings shed a new light on the basin history. The successive flooding and desiccation events are a consequence of sea-level variations but also important tectonic activity. Rift margin uplift prevented flooding during the Holocene sea-level highstand and contributed to the restriction of the depression. Significant basin subsidence at very short time scales created accommodation space for the voluminous sediment infill. This implies very active rifting during the last 250 ka.
How to cite: Rime, V., Foubert, A., Fentimen, R., Negga, H., El Korh, A., Adatte, T., Hajdas, I., Atnafu, B., and Kidane, T.: Evaporites reveal Pleistocene basin dynamics in the Danakil depression (northern Afar, Ethiopia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14917, https://doi.org/10.5194/egusphere-egu2020-14917, 2020.
EGU2020-11138 | Displays | TS6.1
Mantle Plume – Spreading Ridge Interaction: A Comparative Study of the Red Sea and Reykjanes RidgesZachary Molitor, Oliver Jagoutz, Leigh Royden, Stephanie Brown, Guido Port, Ali Dogru, and Joao Keller
As a young, mid ocean ridge, the Red Sea is a unique natural laboratory for studying the processes that drive continental rifting and breakup. The role of hot spots, frequently attributed to mantle plumes, in triggering or driving breakup and their impact on crustal structure and topography is not well understood. We have found that the Red Sea ridge bears a resemblance to the Reykjanes ridge in terms of bathymetry, morphology, geophysical properties, basalt chemistry, and modelled melting temperature and pressure of primary basalts. The results of modelling basalt melting temperature call into question the role of mantle temperature on generating excess melt beneath the Red Sea and Reykjanes ridges. Within 300 kilometers of a hotspot center, determined by seismic tomography, mantle excess temperatures are as high as 300 degrees relative to an ambient mantle temperature of about 1300 C. Outside of this radius excess temperatures are not significant (less than 50 C), and unlikely to cause significant melting anomalies. It is likely that the southern Red Sea and northern Reykjanes ridge are directly affected by hot, buoyant upwelling from the Afar and Iceland mantle plumes, and the central Red Sea and southern Reykjanes ridge may be affected by dynamic pressure related to actively upwelling mantle around the mantle plumes.
How to cite: Molitor, Z., Jagoutz, O., Royden, L., Brown, S., Port, G., Dogru, A., and Keller, J.: Mantle Plume – Spreading Ridge Interaction: A Comparative Study of the Red Sea and Reykjanes Ridges, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11138, https://doi.org/10.5194/egusphere-egu2020-11138, 2020.
As a young, mid ocean ridge, the Red Sea is a unique natural laboratory for studying the processes that drive continental rifting and breakup. The role of hot spots, frequently attributed to mantle plumes, in triggering or driving breakup and their impact on crustal structure and topography is not well understood. We have found that the Red Sea ridge bears a resemblance to the Reykjanes ridge in terms of bathymetry, morphology, geophysical properties, basalt chemistry, and modelled melting temperature and pressure of primary basalts. The results of modelling basalt melting temperature call into question the role of mantle temperature on generating excess melt beneath the Red Sea and Reykjanes ridges. Within 300 kilometers of a hotspot center, determined by seismic tomography, mantle excess temperatures are as high as 300 degrees relative to an ambient mantle temperature of about 1300 C. Outside of this radius excess temperatures are not significant (less than 50 C), and unlikely to cause significant melting anomalies. It is likely that the southern Red Sea and northern Reykjanes ridge are directly affected by hot, buoyant upwelling from the Afar and Iceland mantle plumes, and the central Red Sea and southern Reykjanes ridge may be affected by dynamic pressure related to actively upwelling mantle around the mantle plumes.
How to cite: Molitor, Z., Jagoutz, O., Royden, L., Brown, S., Port, G., Dogru, A., and Keller, J.: Mantle Plume – Spreading Ridge Interaction: A Comparative Study of the Red Sea and Reykjanes Ridges, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11138, https://doi.org/10.5194/egusphere-egu2020-11138, 2020.
EGU2020-19491 | Displays | TS6.1
An up-to-date Mapping for the Movement and the Deformation of the Sinai Micro-plate from a Combined GPS Velocity FieldMohamed Saleh, Frederic Masson, Nadia Abou-Aly, and Abdel-Monem Mohamed
We use combined GPS velocities covering Sinai peninsula to estimate the current rates across the Sinai micro-plate boundaries. New GPS velocities were estimated for 67 sites located within and around Sinai (Arabia, Eurasia and Nubia plates) covering the time span 1999-2018 using GAMIT/GLOBK 10.6 (Herring et al., 2015). We have combined our velocity field with two other recent solutions of GPS sites located around Sinai area. We used the VELROT tool from GAMIT/GLOBK package to combine all solutions resulting in a velocity field of 265 GPS sites in ITRF2018. Then, we selected 61 sites that represent the Sinai plate interior to estimate the Euler pole of Sinai micro-plate. Our computed the Euler pole parameters, latitude, longitude, and angular velocity for Sinai are 53.3±1.8°, -7.8±2.2°, and 0.451±0.014°/Ma, respectively, which are comparable to previous estimates, but with better uncertainties. The relative block motions at the Sinai plate boundaries are estimated using the DEFNODE code (McCaffrey, 2002) by minimizing the GPS residual motions within the blocks in a least squares sense. Our block motion model for Sinai sub-plate shows a fault-parallel velocity at the Gulf of Aqaba of 4.7-4.5 mm/yr, associated with negligible fault-normal component, which decreased toward the north direction along the Dead Sea Transform Fault. On the other hand, an opening rate of 3 mm/yr is estimated at the southern part of the Gulf of Suez with negligible fault-parallel component. At central and northern parts of the Gulf of Suez, the opening rate decreases until it vanished at the northern part of the Suez Canal while the fault-parallel component increases.
How to cite: Saleh, M., Masson, F., Abou-Aly, N., and Mohamed, A.-M.: An up-to-date Mapping for the Movement and the Deformation of the Sinai Micro-plate from a Combined GPS Velocity Field , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19491, https://doi.org/10.5194/egusphere-egu2020-19491, 2020.
We use combined GPS velocities covering Sinai peninsula to estimate the current rates across the Sinai micro-plate boundaries. New GPS velocities were estimated for 67 sites located within and around Sinai (Arabia, Eurasia and Nubia plates) covering the time span 1999-2018 using GAMIT/GLOBK 10.6 (Herring et al., 2015). We have combined our velocity field with two other recent solutions of GPS sites located around Sinai area. We used the VELROT tool from GAMIT/GLOBK package to combine all solutions resulting in a velocity field of 265 GPS sites in ITRF2018. Then, we selected 61 sites that represent the Sinai plate interior to estimate the Euler pole of Sinai micro-plate. Our computed the Euler pole parameters, latitude, longitude, and angular velocity for Sinai are 53.3±1.8°, -7.8±2.2°, and 0.451±0.014°/Ma, respectively, which are comparable to previous estimates, but with better uncertainties. The relative block motions at the Sinai plate boundaries are estimated using the DEFNODE code (McCaffrey, 2002) by minimizing the GPS residual motions within the blocks in a least squares sense. Our block motion model for Sinai sub-plate shows a fault-parallel velocity at the Gulf of Aqaba of 4.7-4.5 mm/yr, associated with negligible fault-normal component, which decreased toward the north direction along the Dead Sea Transform Fault. On the other hand, an opening rate of 3 mm/yr is estimated at the southern part of the Gulf of Suez with negligible fault-parallel component. At central and northern parts of the Gulf of Suez, the opening rate decreases until it vanished at the northern part of the Suez Canal while the fault-parallel component increases.
How to cite: Saleh, M., Masson, F., Abou-Aly, N., and Mohamed, A.-M.: An up-to-date Mapping for the Movement and the Deformation of the Sinai Micro-plate from a Combined GPS Velocity Field , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19491, https://doi.org/10.5194/egusphere-egu2020-19491, 2020.
EGU2020-1935 | Displays | TS6.1
Modelling constraints on rifting in the Afar region: the birth of a triple junctionHany Khalil, Fabio Capitanio, Peter Betts, and Alexander Cruden
Rifting in the Afar region is considered to be the only known example of the formation of an incipient divergent triple junction. Taking the Afar region as an example, we use three-dimensional (3D) laboratory experiments to test hypotheses for the formation and evolution of divergent triple junctions. We systematically evaluate the role of mechanical weakening due to plume impingement versus inherited weak linear structures in lithospheric mantle under both far-field orthogonal and rotational extensional boundary conditions. The interaction between far-field boundary forces and inherited rheological heterogeneities results in a range of complex rift propagation geometries and structural features, such as rift segmentation and ridge jumps, which are comparable to those observed in the Afar region. The combination of rotational boundary conditions and inherited linear heterogeneities favours the formation of rifts that connect at high-angles. Lithospheric weakening associated with a mantle plume triggers different rifting styles but has little influence on large-scale continental breakup. When compared to the Afar region, our results suggest that the rotation of the Arabian plate since the Oligocene led to rifting of the Red Sea and the Gulf of Aden, which are distinct from the formation of the Main Ethiopian Rift. We suggest that rifting in the Afar region is not consistent with the incipient divergent triple junction hypothesis. Rather, the Afar triple junction formed as a result of complex multi-phase rifting events driven by far-field tectonic forces.
How to cite: Khalil, H., Capitanio, F., Betts, P., and Cruden, A.: Modelling constraints on rifting in the Afar region: the birth of a triple junction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1935, https://doi.org/10.5194/egusphere-egu2020-1935, 2020.
Rifting in the Afar region is considered to be the only known example of the formation of an incipient divergent triple junction. Taking the Afar region as an example, we use three-dimensional (3D) laboratory experiments to test hypotheses for the formation and evolution of divergent triple junctions. We systematically evaluate the role of mechanical weakening due to plume impingement versus inherited weak linear structures in lithospheric mantle under both far-field orthogonal and rotational extensional boundary conditions. The interaction between far-field boundary forces and inherited rheological heterogeneities results in a range of complex rift propagation geometries and structural features, such as rift segmentation and ridge jumps, which are comparable to those observed in the Afar region. The combination of rotational boundary conditions and inherited linear heterogeneities favours the formation of rifts that connect at high-angles. Lithospheric weakening associated with a mantle plume triggers different rifting styles but has little influence on large-scale continental breakup. When compared to the Afar region, our results suggest that the rotation of the Arabian plate since the Oligocene led to rifting of the Red Sea and the Gulf of Aden, which are distinct from the formation of the Main Ethiopian Rift. We suggest that rifting in the Afar region is not consistent with the incipient divergent triple junction hypothesis. Rather, the Afar triple junction formed as a result of complex multi-phase rifting events driven by far-field tectonic forces.
How to cite: Khalil, H., Capitanio, F., Betts, P., and Cruden, A.: Modelling constraints on rifting in the Afar region: the birth of a triple junction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1935, https://doi.org/10.5194/egusphere-egu2020-1935, 2020.
EGU2020-149 | Displays | TS6.1
How isostasy explains continental rifting in East Africa?Mohammad Bagherbandi and Nureldin A. A. Gido
The principle of isostasy plays an important role to understand the relation between different geodynamic processes. Although, it is difficult to find an exact method that delivers a complete image of the Earth structure. However, gravimetric methods are alternative to provide images of the interior of the Earth. The Earth’s crust parameters, i.e. crustal depth and crust-mantle density contrast, can reveal adequate information about the solid Earth system such as volcanic activity, earthquake and continental rifting. Hence, in this study, a combine Moho model using seismic and gravity data is determined to investigate the relationship between the isostatic state of the lithosphere and seismic activities in East Africa. Our results show that isostatic equilibrium and compensation states are closely correlated to the seismicity patterns in the study area. For example, several studies suggest that African superplume causes the rift valley, and consequently differences in crustal and mantle densities occur. This paper presents a method to determine the crustal thickness and crust-mantle density contrast and consequently one can observe low-density contrast (about 200 kg/m3 ) and thin crust (about 30 km) near the triple junction plate tectonics in East Africa (Afar Triangle), which confirms the state of overcompensation in the rift valley areas. Furthermore, the density structure of the lithosphere shows a large correlation with the earthquake activity, sub-crustal stress and volcanic distribution across East Africa.
How to cite: Bagherbandi, M. and Gido, N. A. A.: How isostasy explains continental rifting in East Africa?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-149, https://doi.org/10.5194/egusphere-egu2020-149, 2020.
The principle of isostasy plays an important role to understand the relation between different geodynamic processes. Although, it is difficult to find an exact method that delivers a complete image of the Earth structure. However, gravimetric methods are alternative to provide images of the interior of the Earth. The Earth’s crust parameters, i.e. crustal depth and crust-mantle density contrast, can reveal adequate information about the solid Earth system such as volcanic activity, earthquake and continental rifting. Hence, in this study, a combine Moho model using seismic and gravity data is determined to investigate the relationship between the isostatic state of the lithosphere and seismic activities in East Africa. Our results show that isostatic equilibrium and compensation states are closely correlated to the seismicity patterns in the study area. For example, several studies suggest that African superplume causes the rift valley, and consequently differences in crustal and mantle densities occur. This paper presents a method to determine the crustal thickness and crust-mantle density contrast and consequently one can observe low-density contrast (about 200 kg/m3 ) and thin crust (about 30 km) near the triple junction plate tectonics in East Africa (Afar Triangle), which confirms the state of overcompensation in the rift valley areas. Furthermore, the density structure of the lithosphere shows a large correlation with the earthquake activity, sub-crustal stress and volcanic distribution across East Africa.
How to cite: Bagherbandi, M. and Gido, N. A. A.: How isostasy explains continental rifting in East Africa?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-149, https://doi.org/10.5194/egusphere-egu2020-149, 2020.
EGU2020-1658 | Displays | TS6.1
Study on the inversion structure of rift system in central and west AfricaXiyuan Li, Wangshui Hu, Zhongying Lei, Chijun Huang, and Silin Yin
In the process of plate tectonic movement, extensional faults and conversion faults occur.In the process of studying the rift system of central and west Africa, by comparing the basin types and fault plane distribution characteristics of Africa and South America on both sides of the Atlantic ocean, it can be seen that the main continental fault on both sides of the Atlantic ocean and the fault developed at the mid-ocean ridge on the bottom of the Atlantic ocean belong to the conversion fault.The function of conversion faults is to regulate the difference in the moving speed between blocks in the contemporaneous structure. Therefore, the conversion faults developed in these three regions are similar and interrelated in terms of structure type, structure style, block movement mode and direction.The main transference faults in various regions play a role in regulating the differences of continental extension and inversion tectonic rates in the Atlantic ocean, Africa and South America.
There are two transition fault systems in the rift system of central Africa and west Africa. Under the joint action of these two transition fault systems, extensional basins and transition basins are mainly developed in the rift system of central and west Africa. Moreover, these two transition fault systems play different roles in different stages of the tectonic movement of the whole African plate.
After detailed interpretation of seismic data, it can be found that there are mainly fault-controlled inversion structures in Doseo basin and Doba basin.
As a representative of transition basins, fault-controlled inversion structures are widely developed in the Doseo basin, but they have different distribution characteristics.Among them, fault-controlled inversion structures with large inversion ranges are distributed near large faults in the basin, while fault-controlled inversion structures with small inversion ranges are far away from the structural units of the main controlled faults, the inversion structures have a small amplitude, and the stratigraphic reconstruction fragmentation degree is relatively weak. The inversion structures with weak inversion are mainly developed in the middle, western depression and southern uplift of Doseo basin.And as the representative of the extensional basin. In Doba basin, fault-controlled inversion structures are mainly developed, and the structures with high inversion rate are distributed in the central depression zone of the basin. The low inversion rate structures are distributed in the uplift and slope areas in the western part of the basin. By studying the development types and distribution locations of inversion structures in basins, it can be known that different types of basins have different transformation conditions during inversion.
Therefore, by comparing the differences in the plane and vertical characteristics of the inversion tectonic development of Doseo and Doba basins, as well as the studies on the eastern and western and non-other basins, it can be concluded that during the tectonic evolution of the rift system in central and west Africa, especially during the transition inversion stage, there were significant differences between the transition basin and the extensional basin.
How to cite: Li, X., Hu, W., Lei, Z., Huang, C., and Yin, S.: Study on the inversion structure of rift system in central and west Africa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1658, https://doi.org/10.5194/egusphere-egu2020-1658, 2020.
In the process of plate tectonic movement, extensional faults and conversion faults occur.In the process of studying the rift system of central and west Africa, by comparing the basin types and fault plane distribution characteristics of Africa and South America on both sides of the Atlantic ocean, it can be seen that the main continental fault on both sides of the Atlantic ocean and the fault developed at the mid-ocean ridge on the bottom of the Atlantic ocean belong to the conversion fault.The function of conversion faults is to regulate the difference in the moving speed between blocks in the contemporaneous structure. Therefore, the conversion faults developed in these three regions are similar and interrelated in terms of structure type, structure style, block movement mode and direction.The main transference faults in various regions play a role in regulating the differences of continental extension and inversion tectonic rates in the Atlantic ocean, Africa and South America.
There are two transition fault systems in the rift system of central Africa and west Africa. Under the joint action of these two transition fault systems, extensional basins and transition basins are mainly developed in the rift system of central and west Africa. Moreover, these two transition fault systems play different roles in different stages of the tectonic movement of the whole African plate.
After detailed interpretation of seismic data, it can be found that there are mainly fault-controlled inversion structures in Doseo basin and Doba basin.
As a representative of transition basins, fault-controlled inversion structures are widely developed in the Doseo basin, but they have different distribution characteristics.Among them, fault-controlled inversion structures with large inversion ranges are distributed near large faults in the basin, while fault-controlled inversion structures with small inversion ranges are far away from the structural units of the main controlled faults, the inversion structures have a small amplitude, and the stratigraphic reconstruction fragmentation degree is relatively weak. The inversion structures with weak inversion are mainly developed in the middle, western depression and southern uplift of Doseo basin.And as the representative of the extensional basin. In Doba basin, fault-controlled inversion structures are mainly developed, and the structures with high inversion rate are distributed in the central depression zone of the basin. The low inversion rate structures are distributed in the uplift and slope areas in the western part of the basin. By studying the development types and distribution locations of inversion structures in basins, it can be known that different types of basins have different transformation conditions during inversion.
Therefore, by comparing the differences in the plane and vertical characteristics of the inversion tectonic development of Doseo and Doba basins, as well as the studies on the eastern and western and non-other basins, it can be concluded that during the tectonic evolution of the rift system in central and west Africa, especially during the transition inversion stage, there were significant differences between the transition basin and the extensional basin.
How to cite: Li, X., Hu, W., Lei, Z., Huang, C., and Yin, S.: Study on the inversion structure of rift system in central and west Africa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1658, https://doi.org/10.5194/egusphere-egu2020-1658, 2020.
EGU2020-676 | Displays | TS6.1
High intensity ignimbritic activity in the Central sector of the Main Ethiopian RiftZara Franceschini, Stéphane Scaillet, Raffaello Cioni, Giacomo Corti, Federico Sani, Gaëlle Prouteau, Bruno Scaillet, and Abate Assen Melaku
The volcano-tectonic evolution of the Main Ethiopian Rift (MER) is punctuated with periods of intense silicic volcanism, characterized by large explosive caldera-forming eruptions and the production of several ignimbrite deposits. These volcanic paroxysms require large volume of evolved silicic magma accumulated in shallow chambers into the continental crust; however, the relations between magmatism and tectonics during rifting, and the influence of the distribution and timing of regional tectonics on the ascent of magma and its stalling in large magmatic reservoirs remain poorly defined.
We present new geochronological data (40Ar/39Ar dataset of 29 samples) providing new constraints on the timing, evolution and characteristics of volcanism in the Central sector of the MER, where large ignimbrite deposits and remnants of several calderas testify the recurrence of silicic flare-ups. Specifically, we investigate in detail the eastern margin of the rift, where a voluminous, widespread, crystal-rich ignimbrite (Munesa Crystal Tuff, MCT) has been described. This deposit has been correlated to a thick ignimbrite occurring at the bottom of geothermal wells in the rift, pointing to a giant eruptive event attributed to a huge caldera structure, presumably buried beneath the rift floor. At least other two widespread ignimbrite units are present along the same margin for several tens of kilometres, testifying the high volcanicity of this sector of the MER.
Our survey and analyses suggest that, at least in the eastern margin of the rift, activity was clustered in periods of large magma production and emission, resulting in the recurrence of intense volcanic phases interspersed with periods of rest of volcanism. Ignimbrites and other volcanic deposits occur in the investigated area, spanning an age interval from 3.5 Ma to as recent as 150 ka. The MCT emission, around 3.5 Ma, was followed, after a long quiescence, by an important phase with the emplacement of both mafic (lava flows and scoria cone) and evolved (ignimbrites) products between 1.9-1.6 Ma. After that, volcanism occurred more frequently, possibly with a lower amount of erupted magma and still alternating with quiescent periods, with volcanism clusters at ~ 1.3-1.2 Ma, ~ 0.8-0.7 Ma and ~ 0.3-0.2 Ma. This clustered volcanic activity will be compared with the episodic rifting of this sector of the Main Ethiopian Rift.
How to cite: Franceschini, Z., Scaillet, S., Cioni, R., Corti, G., Sani, F., Prouteau, G., Scaillet, B., and Assen Melaku, A.: High intensity ignimbritic activity in the Central sector of the Main Ethiopian Rift, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-676, https://doi.org/10.5194/egusphere-egu2020-676, 2020.
The volcano-tectonic evolution of the Main Ethiopian Rift (MER) is punctuated with periods of intense silicic volcanism, characterized by large explosive caldera-forming eruptions and the production of several ignimbrite deposits. These volcanic paroxysms require large volume of evolved silicic magma accumulated in shallow chambers into the continental crust; however, the relations between magmatism and tectonics during rifting, and the influence of the distribution and timing of regional tectonics on the ascent of magma and its stalling in large magmatic reservoirs remain poorly defined.
We present new geochronological data (40Ar/39Ar dataset of 29 samples) providing new constraints on the timing, evolution and characteristics of volcanism in the Central sector of the MER, where large ignimbrite deposits and remnants of several calderas testify the recurrence of silicic flare-ups. Specifically, we investigate in detail the eastern margin of the rift, where a voluminous, widespread, crystal-rich ignimbrite (Munesa Crystal Tuff, MCT) has been described. This deposit has been correlated to a thick ignimbrite occurring at the bottom of geothermal wells in the rift, pointing to a giant eruptive event attributed to a huge caldera structure, presumably buried beneath the rift floor. At least other two widespread ignimbrite units are present along the same margin for several tens of kilometres, testifying the high volcanicity of this sector of the MER.
Our survey and analyses suggest that, at least in the eastern margin of the rift, activity was clustered in periods of large magma production and emission, resulting in the recurrence of intense volcanic phases interspersed with periods of rest of volcanism. Ignimbrites and other volcanic deposits occur in the investigated area, spanning an age interval from 3.5 Ma to as recent as 150 ka. The MCT emission, around 3.5 Ma, was followed, after a long quiescence, by an important phase with the emplacement of both mafic (lava flows and scoria cone) and evolved (ignimbrites) products between 1.9-1.6 Ma. After that, volcanism occurred more frequently, possibly with a lower amount of erupted magma and still alternating with quiescent periods, with volcanism clusters at ~ 1.3-1.2 Ma, ~ 0.8-0.7 Ma and ~ 0.3-0.2 Ma. This clustered volcanic activity will be compared with the episodic rifting of this sector of the Main Ethiopian Rift.
How to cite: Franceschini, Z., Scaillet, S., Cioni, R., Corti, G., Sani, F., Prouteau, G., Scaillet, B., and Assen Melaku, A.: High intensity ignimbritic activity in the Central sector of the Main Ethiopian Rift, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-676, https://doi.org/10.5194/egusphere-egu2020-676, 2020.
EGU2020-821 | Displays | TS6.1 | Highlight
The Buried Grand Canyon in Egypt: Structural controls on the Neogene River NileAli Abdelkhalek, Jonas Kley, Mohamed Hammed, and Ahmed Saied Ali
The origin and intricate history of the River Nile are still widely disputed. Some studies have claimed that the present course of the Nile has formed at ~7-5 Ma, while others have suggested a much longer evolution. We proposed earlier that the southern and central segments of the River Nile in Egypt have originally evolved along a NW trending short-lived rift that was formed by NE-SW extension at ~25-23 Ma, and abandoned at an early stage. Here we focus on the development of the northern segment of the river, which we interpret as having both a relatively young age (~7-6 Ma) and different tectonic evolution. Gravity models and 3D seismic and well data show the presence of a deeply buried canyon west of the northern modern River Nile, 120 km southwest of Cairo, and approximately parallel to its present-day valley with a predominant NNE-NE course. The U-shaped canyon is up to 13 km wide and attains a maximum depth of around 1,900 meters, about as deep as the Grand Canyon of the Colorado River in Arizona, USA. The canyon was cut into a rising plateau along deep-seated NNE to NE-striking faults that formed at ~90-80 Ma as secondary shears to the main structures of the WNW oriented Cretaceous Beni-Suef rift and possibly have been reactivated at ~14 Ma with the origin of the Gulf of Aqaba-Dead Sea NNE sinistral transform plate boundary. The deeply incised canyon formed as a result of severe erosion due to significant sea level drop and desiccation of the Mediterranean in late Miocene time (Messinian Crisis ~7-6 Ma), which was accompanied by continued progressive uplift of the north-eastern Egyptian terrain[KJ1] . [2] The ancestral river excavated and widened a vast braided channel[3] that cut deeply into Turonian-Campanian sediments in the Beni-Suef basin. The canyon attained its maximum depth by ~5 Ma, and subsequently it was filled by six successive clastic-dominated units of different fluvial facies.[4]
How to cite: Abdelkhalek, A., Kley, J., Hammed, M., and Ali, A. S.: The Buried Grand Canyon in Egypt: Structural controls on the Neogene River Nile, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-821, https://doi.org/10.5194/egusphere-egu2020-821, 2020.
The origin and intricate history of the River Nile are still widely disputed. Some studies have claimed that the present course of the Nile has formed at ~7-5 Ma, while others have suggested a much longer evolution. We proposed earlier that the southern and central segments of the River Nile in Egypt have originally evolved along a NW trending short-lived rift that was formed by NE-SW extension at ~25-23 Ma, and abandoned at an early stage. Here we focus on the development of the northern segment of the river, which we interpret as having both a relatively young age (~7-6 Ma) and different tectonic evolution. Gravity models and 3D seismic and well data show the presence of a deeply buried canyon west of the northern modern River Nile, 120 km southwest of Cairo, and approximately parallel to its present-day valley with a predominant NNE-NE course. The U-shaped canyon is up to 13 km wide and attains a maximum depth of around 1,900 meters, about as deep as the Grand Canyon of the Colorado River in Arizona, USA. The canyon was cut into a rising plateau along deep-seated NNE to NE-striking faults that formed at ~90-80 Ma as secondary shears to the main structures of the WNW oriented Cretaceous Beni-Suef rift and possibly have been reactivated at ~14 Ma with the origin of the Gulf of Aqaba-Dead Sea NNE sinistral transform plate boundary. The deeply incised canyon formed as a result of severe erosion due to significant sea level drop and desiccation of the Mediterranean in late Miocene time (Messinian Crisis ~7-6 Ma), which was accompanied by continued progressive uplift of the north-eastern Egyptian terrain[KJ1] . [2] The ancestral river excavated and widened a vast braided channel[3] that cut deeply into Turonian-Campanian sediments in the Beni-Suef basin. The canyon attained its maximum depth by ~5 Ma, and subsequently it was filled by six successive clastic-dominated units of different fluvial facies.[4]
How to cite: Abdelkhalek, A., Kley, J., Hammed, M., and Ali, A. S.: The Buried Grand Canyon in Egypt: Structural controls on the Neogene River Nile, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-821, https://doi.org/10.5194/egusphere-egu2020-821, 2020.
EGU2020-18075 | Displays | TS6.1
Are abandoned rifts tectonically active? Morphotectonic evidence from the Gulf of SuezDavid Fernández-Blanco, Gino de Gelder, and Christopher A-L. Jackson
Intra-continental abandoned rifts can fail for many reasons and are typically considered to be tectonically inactive. It is widely thought that the Oligo-Miocene Suez Rift, Egypt, which is located at the propagating northern end of the Red Sea spreading ridge, was abandoned in the Pliocene when motion between the African and Arabian plates was accommodated instead by the sinistral Dead Sea transform fault. However, local evidence for Plio-Quaternary normal faulting, the presence of uplifted Quaternary shorelines along the rift margins, and low-magnitude but widespread seismicity, together suggest the Suez Rift is tectonically active. Here, we present the first detailed analysis of this post-“abandonment” tectonic activity. We analyze the fluvial and tectonic geomorphology of the rift using freely available, 30 m-horizontal resolution digital elevation models (DEMs). These data reveal widespread normal fault offsets of Plio-Quaternary rocks at outcrop-to-basin scale, even in rift sectors >250 km north of the southern terminus of the rift. River morphology, tectonic knickpoints, normalized steepness indexes (ksn), and chi (χ) maps also provide evidence for relatively young faulting. Uplifted Quaternary shorelines show that active normal faults have footwall uplift rates of up to 0.125 mm/yr, even in locations >200 km north of the rift terminus, with these rates being relatively consistent for both rift margins. Our preliminary results provide clear evidence for young and ongoing tectonic activity in the Suez Rift and thus question the notion that this evolving plate boundary is currently in a state of complete tectonic quiescence. We speculate that the present tectonic activity in the Suez Rift results from the translation of far-field stresses imposed by the Afar plume, or by a recent change in the Eulerian pole of rotation between the African and the Arabian plates. Our results call for further analyses of the recent rifting in the Suez Rift and the exploration of recent activity in other “abandoned” rifts.
How to cite: Fernández-Blanco, D., de Gelder, G., and Jackson, C. A.-L.: Are abandoned rifts tectonically active? Morphotectonic evidence from the Gulf of Suez , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18075, https://doi.org/10.5194/egusphere-egu2020-18075, 2020.
Intra-continental abandoned rifts can fail for many reasons and are typically considered to be tectonically inactive. It is widely thought that the Oligo-Miocene Suez Rift, Egypt, which is located at the propagating northern end of the Red Sea spreading ridge, was abandoned in the Pliocene when motion between the African and Arabian plates was accommodated instead by the sinistral Dead Sea transform fault. However, local evidence for Plio-Quaternary normal faulting, the presence of uplifted Quaternary shorelines along the rift margins, and low-magnitude but widespread seismicity, together suggest the Suez Rift is tectonically active. Here, we present the first detailed analysis of this post-“abandonment” tectonic activity. We analyze the fluvial and tectonic geomorphology of the rift using freely available, 30 m-horizontal resolution digital elevation models (DEMs). These data reveal widespread normal fault offsets of Plio-Quaternary rocks at outcrop-to-basin scale, even in rift sectors >250 km north of the southern terminus of the rift. River morphology, tectonic knickpoints, normalized steepness indexes (ksn), and chi (χ) maps also provide evidence for relatively young faulting. Uplifted Quaternary shorelines show that active normal faults have footwall uplift rates of up to 0.125 mm/yr, even in locations >200 km north of the rift terminus, with these rates being relatively consistent for both rift margins. Our preliminary results provide clear evidence for young and ongoing tectonic activity in the Suez Rift and thus question the notion that this evolving plate boundary is currently in a state of complete tectonic quiescence. We speculate that the present tectonic activity in the Suez Rift results from the translation of far-field stresses imposed by the Afar plume, or by a recent change in the Eulerian pole of rotation between the African and the Arabian plates. Our results call for further analyses of the recent rifting in the Suez Rift and the exploration of recent activity in other “abandoned” rifts.
How to cite: Fernández-Blanco, D., de Gelder, G., and Jackson, C. A.-L.: Are abandoned rifts tectonically active? Morphotectonic evidence from the Gulf of Suez , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18075, https://doi.org/10.5194/egusphere-egu2020-18075, 2020.
EGU2020-9401 | Displays | TS6.1
Tectonics of the Northern Red Sea, insights from multibeam bathymetric mapping of Mabahiss Deep.Daniele Trippanera, Margherita Fittipaldi, Nico Augustin, Froukje M. van der Zwan, and Sigurjón Jónsson
The Red Sea is a unique place to study the birth of an oceanic rift basin and the interplay between magma and tectonics at a young divergent plate boundary. The Red Sea is a NNW-SSE oriented and 2000 km long rift system with a spreading rate decreasing from ~16 mm/yr in the south to ~7 mm/yr in the north. The morphology also changes along the rift axis: the south portion is a continuous and well-developed rift, clearly exposing oceanic crust, the central portion is characterized by deeps made by oceanic crust separated by shallower inter-trough zones, and the northern part contains more widely spaced and less obvious deeps with the transition to the continental crust not well defined. While the central Red Sea morphology has been extensively studied, the structure of the northern Red Sea and its link to the central Red Sea are still unclear. Indeed, the northern Red Sea rift is offset by 100 km to the central Red Sea axis by the still poorly understood Zabargad fracture zone.
Here we aim at improving the understanding of the volcano-tectonic structure of the axial part of the southern tip of the northern Red Sea that corresponds to the Mabahiss Deep. To this aim, we carried out multiple multibeam surveys with R/V Thuwal and R/V Kobi Ruegg to map the sea bottom to add to what had been done in earlier surveys. In addition, we obtained several sub-bottom profiling lines across and along the deep to better constrain the shallow sedimentary structure.
Our results show that the 15 km long, 9 km wide and 2250 m deep Mabahiss Deep along with the 800 m high and 5 km wide central volcano are the key prominent structures of the area. The deep is bordered by a series of Red Sea parallel normal faults on two sides forming a graben-like structure and thus suggesting a rift-like morphology. The central volcano is well preserved and has a 2 km wide summit caldera containing several volcanic cones and thus suggesting a permanent magmatic source underneath of a relatively young age. The ocean floor outside the deep and the volcanic edifice is mostly covered by salt flows, limiting structural analysis of the surrounding areas.
A comparison between the northern and central Red Sea suggests, although in both areas thick salt covers most of the ocean floor, that the axes have similar rift-like structures with stable axial volcanism. However, in the central Red Sea larger portions of the oceanic crust are free of salt and the deformation seems larger with more prominent faults that also affect the floor of the deeps and split apart volcanic edifices, enhancing the occurrence of diffused monogenic volcanic cones. Therefore, this might suggest, despite the central and northern Red Sea sharing the same structure and evolution, that the less volcanic and tectonic activity in the north probably reflects the decreasing spreading rate from south to north along the Red Sea.
How to cite: Trippanera, D., Fittipaldi, M., Augustin, N., van der Zwan, F. M., and Jónsson, S.: Tectonics of the Northern Red Sea, insights from multibeam bathymetric mapping of Mabahiss Deep., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9401, https://doi.org/10.5194/egusphere-egu2020-9401, 2020.
The Red Sea is a unique place to study the birth of an oceanic rift basin and the interplay between magma and tectonics at a young divergent plate boundary. The Red Sea is a NNW-SSE oriented and 2000 km long rift system with a spreading rate decreasing from ~16 mm/yr in the south to ~7 mm/yr in the north. The morphology also changes along the rift axis: the south portion is a continuous and well-developed rift, clearly exposing oceanic crust, the central portion is characterized by deeps made by oceanic crust separated by shallower inter-trough zones, and the northern part contains more widely spaced and less obvious deeps with the transition to the continental crust not well defined. While the central Red Sea morphology has been extensively studied, the structure of the northern Red Sea and its link to the central Red Sea are still unclear. Indeed, the northern Red Sea rift is offset by 100 km to the central Red Sea axis by the still poorly understood Zabargad fracture zone.
Here we aim at improving the understanding of the volcano-tectonic structure of the axial part of the southern tip of the northern Red Sea that corresponds to the Mabahiss Deep. To this aim, we carried out multiple multibeam surveys with R/V Thuwal and R/V Kobi Ruegg to map the sea bottom to add to what had been done in earlier surveys. In addition, we obtained several sub-bottom profiling lines across and along the deep to better constrain the shallow sedimentary structure.
Our results show that the 15 km long, 9 km wide and 2250 m deep Mabahiss Deep along with the 800 m high and 5 km wide central volcano are the key prominent structures of the area. The deep is bordered by a series of Red Sea parallel normal faults on two sides forming a graben-like structure and thus suggesting a rift-like morphology. The central volcano is well preserved and has a 2 km wide summit caldera containing several volcanic cones and thus suggesting a permanent magmatic source underneath of a relatively young age. The ocean floor outside the deep and the volcanic edifice is mostly covered by salt flows, limiting structural analysis of the surrounding areas.
A comparison between the northern and central Red Sea suggests, although in both areas thick salt covers most of the ocean floor, that the axes have similar rift-like structures with stable axial volcanism. However, in the central Red Sea larger portions of the oceanic crust are free of salt and the deformation seems larger with more prominent faults that also affect the floor of the deeps and split apart volcanic edifices, enhancing the occurrence of diffused monogenic volcanic cones. Therefore, this might suggest, despite the central and northern Red Sea sharing the same structure and evolution, that the less volcanic and tectonic activity in the north probably reflects the decreasing spreading rate from south to north along the Red Sea.
How to cite: Trippanera, D., Fittipaldi, M., Augustin, N., van der Zwan, F. M., and Jónsson, S.: Tectonics of the Northern Red Sea, insights from multibeam bathymetric mapping of Mabahiss Deep., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9401, https://doi.org/10.5194/egusphere-egu2020-9401, 2020.
EGU2020-4641 | Displays | TS6.1
Movements of thick evaporites on the flanks of a mid-ocean ridge: the central Red Sea Miocene evaporitesNeil Mitchell, Wen Shi, Ay Izzeldin, and Ian Stewart
Thick evaporites ("salt") were deposited in the South and North Atlantic, and Gulf of Mexico basins, in some parts deposited onto the flanks of nascent oceanic spreading centres. Unfortunately, knowledge of the history of evaporite movements is complicated in such places by their inaccessibility and subsequent diapirism. This is less of a problem in the Red Sea, a young rift basin that is transitioning to an ocean basin and where the evaporites are less affected by diapirism. In this study, we explore the vertical movements of the evaporite surface imaged with deep seismic profiling. The evaporites have moved towards the spreading axis of the basin during and after their deposition, which ended at the 5.3 Ma Miocene-Pliocene boundary. We quantify the evaporite surface deflation needed to balance the volume of evaporites overflowing oceanic crust of 5.3 Ma age, thermal subsidence of the lithosphere and loss of halite through pore water diffusion, allowing for isostatic effects. The reconstructed evaporite surface lies within the range of estimated global sea level towards the end of the Miocene. Therefore, the evaporites appear to have filled the basin almost completely at the end of the Miocene. Effects of shunting by terrigenous sediments and carbonates near the coast and contributions of hydrothermal salt are too small to be resolved by this reconstruction.
How to cite: Mitchell, N., Shi, W., Izzeldin, A., and Stewart, I.: Movements of thick evaporites on the flanks of a mid-ocean ridge: the central Red Sea Miocene evaporites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4641, https://doi.org/10.5194/egusphere-egu2020-4641, 2020.
Thick evaporites ("salt") were deposited in the South and North Atlantic, and Gulf of Mexico basins, in some parts deposited onto the flanks of nascent oceanic spreading centres. Unfortunately, knowledge of the history of evaporite movements is complicated in such places by their inaccessibility and subsequent diapirism. This is less of a problem in the Red Sea, a young rift basin that is transitioning to an ocean basin and where the evaporites are less affected by diapirism. In this study, we explore the vertical movements of the evaporite surface imaged with deep seismic profiling. The evaporites have moved towards the spreading axis of the basin during and after their deposition, which ended at the 5.3 Ma Miocene-Pliocene boundary. We quantify the evaporite surface deflation needed to balance the volume of evaporites overflowing oceanic crust of 5.3 Ma age, thermal subsidence of the lithosphere and loss of halite through pore water diffusion, allowing for isostatic effects. The reconstructed evaporite surface lies within the range of estimated global sea level towards the end of the Miocene. Therefore, the evaporites appear to have filled the basin almost completely at the end of the Miocene. Effects of shunting by terrigenous sediments and carbonates near the coast and contributions of hydrothermal salt are too small to be resolved by this reconstruction.
How to cite: Mitchell, N., Shi, W., Izzeldin, A., and Stewart, I.: Movements of thick evaporites on the flanks of a mid-ocean ridge: the central Red Sea Miocene evaporites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4641, https://doi.org/10.5194/egusphere-egu2020-4641, 2020.
TS6.2 – Tectono-magmatic-sedimentary process of the marginal basins in the West Pacific: from convergent to divergent
EGU2020-6456 | Displays | TS6.2 | Highlight
Western Pacific marginal basin plate tectonics: overview, questions, and insights from mantle structureJonny Wu and John Suppe
EGU2020-1600 | Displays | TS6.2 | Highlight
Seismic Imaging, Arc Magamtism and Megathrust Earthquake under the Western Pacific Subduction ZoneZhi Wang and Jian Wang
Arc magmatism and megathrust earthquake occurrence in a subduction zone are deemed to attribute to many factors, including structural heterogeneities, fluid contents, temperature, depth of subducting oceanic crust, and etc. However, how these factors affect them is unclear. The extensive arc magmatism observed on the island arcs is considered to be an indicator on chemical exchange between the wedge mantle and the surface in a subduction zone. Megathrust earthquake frequently occurrence is also considered to be attributed to the slab melting and associated interplate coupling of the subducting plate. The Western Pacific subduction zone is regarded as one of the best Laboratory for seismologists to examine these processes due to the densest seismic networks recording numerous earthquakes. Some of the previous studies suggest that the island-arc magmatism is mainly contributed to the melting of peridotite in the mantle wedge due to fluids intrusion from the dehydration process associated with the subducting oceanic crust. They further argued that the oceanic plate could only provide water to the overlying mantle wedge for arc magmatism, but not melt itself due to that it is too cold to melt at a depth between 100 and 200km. However, some of other studies revealed that the hydrated basalt derived from the mid-ocean ridge will be melted with high T and water saturated on the upper interface of the sbuducting plate in the mantle wedge. We consider that the three-dimensional (3-D) P- and S- wave velocity (Vp, Vs) and Poisson’s ratio (σ) structures of the subduction zone, synthesized from a large-quantity of high-quality direct P-, and S-wave arrival times of source-recive pairs from the well located suboceanic events with sP depth phase data could provide a compelling evidence for structural heterogeneity, highly hydrated and serpentinized forearc mantle and dehydrated fluids in the subduction zones. In this study, we combined seismic velocities and Poisson’s ratio images under the entire-arc region of the Western Pacific subduction zone to reveal their effects on megathrust earthquake generation and arc magmatism. We find that a ~10 km-thick low-velocity layer with high-V and high-Poisson’s ratio anomalies is clearly imaged along the upper interface of the subducting Pacific slab. This distinct layer implies partial melting of the oceanic crust due to the deep-seated metamorophic reactions depending on the source of fluids and temperature regime. Such a process could refertilize the overlying mantle wedge and enrich the peridotite sources of basalts under the island arc. Significant low-V and high-Poisson’s ratio anomalies were observed in the mantle wedge along the volcanic front, indicating melting or partial melting of peridotite-rich mantle and then yield tholeiitic magma there. The present study demonstrates that the combined factors of fluid content, mineral composition and thermal regime play a crucial role in both slab melting and arc-magmatism under the Western Pacific subduction zone.
How to cite: Wang, Z. and Wang, J.: Seismic Imaging, Arc Magamtism and Megathrust Earthquake under the Western Pacific Subduction Zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1600, https://doi.org/10.5194/egusphere-egu2020-1600, 2020.
Arc magmatism and megathrust earthquake occurrence in a subduction zone are deemed to attribute to many factors, including structural heterogeneities, fluid contents, temperature, depth of subducting oceanic crust, and etc. However, how these factors affect them is unclear. The extensive arc magmatism observed on the island arcs is considered to be an indicator on chemical exchange between the wedge mantle and the surface in a subduction zone. Megathrust earthquake frequently occurrence is also considered to be attributed to the slab melting and associated interplate coupling of the subducting plate. The Western Pacific subduction zone is regarded as one of the best Laboratory for seismologists to examine these processes due to the densest seismic networks recording numerous earthquakes. Some of the previous studies suggest that the island-arc magmatism is mainly contributed to the melting of peridotite in the mantle wedge due to fluids intrusion from the dehydration process associated with the subducting oceanic crust. They further argued that the oceanic plate could only provide water to the overlying mantle wedge for arc magmatism, but not melt itself due to that it is too cold to melt at a depth between 100 and 200km. However, some of other studies revealed that the hydrated basalt derived from the mid-ocean ridge will be melted with high T and water saturated on the upper interface of the sbuducting plate in the mantle wedge. We consider that the three-dimensional (3-D) P- and S- wave velocity (Vp, Vs) and Poisson’s ratio (σ) structures of the subduction zone, synthesized from a large-quantity of high-quality direct P-, and S-wave arrival times of source-recive pairs from the well located suboceanic events with sP depth phase data could provide a compelling evidence for structural heterogeneity, highly hydrated and serpentinized forearc mantle and dehydrated fluids in the subduction zones. In this study, we combined seismic velocities and Poisson’s ratio images under the entire-arc region of the Western Pacific subduction zone to reveal their effects on megathrust earthquake generation and arc magmatism. We find that a ~10 km-thick low-velocity layer with high-V and high-Poisson’s ratio anomalies is clearly imaged along the upper interface of the subducting Pacific slab. This distinct layer implies partial melting of the oceanic crust due to the deep-seated metamorophic reactions depending on the source of fluids and temperature regime. Such a process could refertilize the overlying mantle wedge and enrich the peridotite sources of basalts under the island arc. Significant low-V and high-Poisson’s ratio anomalies were observed in the mantle wedge along the volcanic front, indicating melting or partial melting of peridotite-rich mantle and then yield tholeiitic magma there. The present study demonstrates that the combined factors of fluid content, mineral composition and thermal regime play a crucial role in both slab melting and arc-magmatism under the Western Pacific subduction zone.
How to cite: Wang, Z. and Wang, J.: Seismic Imaging, Arc Magamtism and Megathrust Earthquake under the Western Pacific Subduction Zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1600, https://doi.org/10.5194/egusphere-egu2020-1600, 2020.
EGU2020-1404 | Displays | TS6.2 | Highlight
Crustal structure and evolution of the Niuafo'ou Microplate in the northeastern Lau Basin, Southwestern PacificFlorian Schmid, Heidrun Kopp, Michael Schnabel, Anke Dannowski, Ingo Heyde, Michael Riedel, Martin Engels, Anouk Beniest, Ingo Klaucke, Nico Augustin, Philipp Brandl, Colin Devey, and Mark Hannington
The northeastern Lau Basin is one of the fastest opening and magmatically most active back-arc regions on Earth. Although the current pattern of plate boundaries and motions in this complex mosaic of microplates is fairly well understood, the structure and evolution of the back-arc crust are not. We present refraction seismic, multichannel seismic and gravity data from a 300 km long east-west oriented transect crossing the Niuafo’ou Microplate (back-arc), the Fonualei Rift and Spreading Centre (FRSC) and the Tofua Volcanic Arc at 17°20’S. Our P wave tomography model shows strong lateral variations in the thickness and velocity-depth distribution of the crust. The thinnest crust is present in the Fonualei Rift and Spreading Center, suggesting active seafloor spreading there. In the much thicker crust of the volcanic arc we identify a region of anomalously low velocities, indicative of partial melts. Surprisingly, the melt reservoir is located at ~17 km distance to the volcanic front, supporting the hypothesis that melts are deviated from the volcanic arc towards the FRSC in sub-crustal domains. We identify two distinct regions in the back-arc crust, representing different opening phases of the northeastern Lau Basin. During initial extension, likely dominated by rifting, crust of generally lower upper-crustal velocities formed. During an advanced opening phase, likely dominated by seafloor spreading, crust of higher upper-crustal velocities formed and is now up to 11 km thick. This thickening is the result of magmatic underplating, which is supported by elevated upper mantle temperatures in this region.
How to cite: Schmid, F., Kopp, H., Schnabel, M., Dannowski, A., Heyde, I., Riedel, M., Engels, M., Beniest, A., Klaucke, I., Augustin, N., Brandl, P., Devey, C., and Hannington, M.: Crustal structure and evolution of the Niuafo'ou Microplate in the northeastern Lau Basin, Southwestern Pacific, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1404, https://doi.org/10.5194/egusphere-egu2020-1404, 2020.
The northeastern Lau Basin is one of the fastest opening and magmatically most active back-arc regions on Earth. Although the current pattern of plate boundaries and motions in this complex mosaic of microplates is fairly well understood, the structure and evolution of the back-arc crust are not. We present refraction seismic, multichannel seismic and gravity data from a 300 km long east-west oriented transect crossing the Niuafo’ou Microplate (back-arc), the Fonualei Rift and Spreading Centre (FRSC) and the Tofua Volcanic Arc at 17°20’S. Our P wave tomography model shows strong lateral variations in the thickness and velocity-depth distribution of the crust. The thinnest crust is present in the Fonualei Rift and Spreading Center, suggesting active seafloor spreading there. In the much thicker crust of the volcanic arc we identify a region of anomalously low velocities, indicative of partial melts. Surprisingly, the melt reservoir is located at ~17 km distance to the volcanic front, supporting the hypothesis that melts are deviated from the volcanic arc towards the FRSC in sub-crustal domains. We identify two distinct regions in the back-arc crust, representing different opening phases of the northeastern Lau Basin. During initial extension, likely dominated by rifting, crust of generally lower upper-crustal velocities formed. During an advanced opening phase, likely dominated by seafloor spreading, crust of higher upper-crustal velocities formed and is now up to 11 km thick. This thickening is the result of magmatic underplating, which is supported by elevated upper mantle temperatures in this region.
How to cite: Schmid, F., Kopp, H., Schnabel, M., Dannowski, A., Heyde, I., Riedel, M., Engels, M., Beniest, A., Klaucke, I., Augustin, N., Brandl, P., Devey, C., and Hannington, M.: Crustal structure and evolution of the Niuafo'ou Microplate in the northeastern Lau Basin, Southwestern Pacific, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1404, https://doi.org/10.5194/egusphere-egu2020-1404, 2020.
EGU2020-20752 | Displays | TS6.2 | Highlight
Origin of the Caroline mantle plume and its interaction with the Caroline basinGuoliang Zhang, Ji Zhang, and Shuai Wang
The Caroline Rise has played an important role in the tectonic frame of the western Pacific, however, the nature and origin of the Caroline Rise has long been unclear. The boundary between the Pacific plate and the Caroline plate has long been unclear, thus, it unclear which plate is underneath the Caroline Rise. In this study, we confirmed that the Caroline Rise represents an oceanic plateau formed as a large igneous province based on seafloor sampling. In this study, we have age-dated and analyzed the whole-rock major and trace elements and Sr-Nd-Pb-Hf isotopes of the basalt samples from the Caroline Plateau. The basalt samples are classified into two groups, the alkali group and the tholeiite group. The results of age-dating indicate older ages for the tholeiite group than the alkali group. The tholeiite group basalts are apparently older than the Caroline Islands and are close to the basalts of Ontong Java Plateau in trace element compositions. We suggest that the tholeiite group basalts represent the main stage volcanism and the alkali group basalts represent the late stage volcanism of the Caroline Plateau. The alkali group basalts show trace element and isotope compositions similar to those of the Caroline Islands to the east. The tholeiitie group basalts have involved significant amount of depleted asthenosphere components, which suggests interactions of the Caroline plume with the Caroline basin spreading center. The MORB-like depleted geochemical nature of the Caroline tholeiite group basalts indicates formation of the Caroline Plateau under the young and thin Caroline plate lithosphere. Our results of age and geochemistry of the Caroline Plateau/Seamount system could be explained by the activities of the Caroline hotspot. This work was financially supported by the National Natural Science Foundation of China (91858206, 41876040).
How to cite: Zhang, G., Zhang, J., and Wang, S.: Origin of the Caroline mantle plume and its interaction with the Caroline basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20752, https://doi.org/10.5194/egusphere-egu2020-20752, 2020.
The Caroline Rise has played an important role in the tectonic frame of the western Pacific, however, the nature and origin of the Caroline Rise has long been unclear. The boundary between the Pacific plate and the Caroline plate has long been unclear, thus, it unclear which plate is underneath the Caroline Rise. In this study, we confirmed that the Caroline Rise represents an oceanic plateau formed as a large igneous province based on seafloor sampling. In this study, we have age-dated and analyzed the whole-rock major and trace elements and Sr-Nd-Pb-Hf isotopes of the basalt samples from the Caroline Plateau. The basalt samples are classified into two groups, the alkali group and the tholeiite group. The results of age-dating indicate older ages for the tholeiite group than the alkali group. The tholeiite group basalts are apparently older than the Caroline Islands and are close to the basalts of Ontong Java Plateau in trace element compositions. We suggest that the tholeiite group basalts represent the main stage volcanism and the alkali group basalts represent the late stage volcanism of the Caroline Plateau. The alkali group basalts show trace element and isotope compositions similar to those of the Caroline Islands to the east. The tholeiitie group basalts have involved significant amount of depleted asthenosphere components, which suggests interactions of the Caroline plume with the Caroline basin spreading center. The MORB-like depleted geochemical nature of the Caroline tholeiite group basalts indicates formation of the Caroline Plateau under the young and thin Caroline plate lithosphere. Our results of age and geochemistry of the Caroline Plateau/Seamount system could be explained by the activities of the Caroline hotspot. This work was financially supported by the National Natural Science Foundation of China (91858206, 41876040).
How to cite: Zhang, G., Zhang, J., and Wang, S.: Origin of the Caroline mantle plume and its interaction with the Caroline basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20752, https://doi.org/10.5194/egusphere-egu2020-20752, 2020.
EGU2020-6525 | Displays | TS6.2 | Highlight
Chemical variations in hydrothermal systems recorded by epidote in altered oceanic crust of South China SeaLiyan Tian, Si-Yu Hu, and Xuan-Ce Wang
The circulation of seawater within the oceanic crust promotes the extensive chemical variations of the lithosphere prior to its entering subduction zones as well as the development of the biosphere. A good understanding of the chemical variations during hydrothermal circulation is essential to further decipher the biological activities in such extreme environments. Epidote is a common byproduct, but a good indicator for hydrothermal activities during the hydrothermal alteration of oceanic crust.
This study presents the petrographic and geochemical features of epidote from depth of 850-910 m (below the surface) in the northern South China Sea margin to provide insights into the possible chemical variations in hydrothermal systems in subsurface. Eight samples with obvious epidote veins were chosen from the altered basalts in Hole 1502B of IODP Expedition 368. They cover a range with different depth and occurrences, including epidote veins, composite epidote-calcite veins, and composite epidote-silica veins. Sulfide mineralization is widespread and dominated with pyrite, chalcopyrite and sphalerite. Scanning Electron Microscopy images show that the epidote-calcite vein samples display obvious zonation structure in epidote, and the others not. The major element concentrations of Fe also show variations with epidote zonation. We further carried out in situ trace element concentration measurement on epidote minerals by Laser Ablation-Induced Coupled Plasma-Mass Spectrometry. In Chondrite-normalized diagrams, all epidote mineral samples show flat patterns with significant positive Eu anomalies, which may relate to highly oxidized conditions maximising Eu3+ incorporation. We therefore propose that the zonation of epidote may reflect the pulse of hydrothermal activities, one of which is likely to be associated with the precipitation of chalcopyrite and sphalerite.
How to cite: Tian, L., Hu, S.-Y., and Wang, X.-C.: Chemical variations in hydrothermal systems recorded by epidote in altered oceanic crust of South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6525, https://doi.org/10.5194/egusphere-egu2020-6525, 2020.
The circulation of seawater within the oceanic crust promotes the extensive chemical variations of the lithosphere prior to its entering subduction zones as well as the development of the biosphere. A good understanding of the chemical variations during hydrothermal circulation is essential to further decipher the biological activities in such extreme environments. Epidote is a common byproduct, but a good indicator for hydrothermal activities during the hydrothermal alteration of oceanic crust.
This study presents the petrographic and geochemical features of epidote from depth of 850-910 m (below the surface) in the northern South China Sea margin to provide insights into the possible chemical variations in hydrothermal systems in subsurface. Eight samples with obvious epidote veins were chosen from the altered basalts in Hole 1502B of IODP Expedition 368. They cover a range with different depth and occurrences, including epidote veins, composite epidote-calcite veins, and composite epidote-silica veins. Sulfide mineralization is widespread and dominated with pyrite, chalcopyrite and sphalerite. Scanning Electron Microscopy images show that the epidote-calcite vein samples display obvious zonation structure in epidote, and the others not. The major element concentrations of Fe also show variations with epidote zonation. We further carried out in situ trace element concentration measurement on epidote minerals by Laser Ablation-Induced Coupled Plasma-Mass Spectrometry. In Chondrite-normalized diagrams, all epidote mineral samples show flat patterns with significant positive Eu anomalies, which may relate to highly oxidized conditions maximising Eu3+ incorporation. We therefore propose that the zonation of epidote may reflect the pulse of hydrothermal activities, one of which is likely to be associated with the precipitation of chalcopyrite and sphalerite.
How to cite: Tian, L., Hu, S.-Y., and Wang, X.-C.: Chemical variations in hydrothermal systems recorded by epidote in altered oceanic crust of South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6525, https://doi.org/10.5194/egusphere-egu2020-6525, 2020.
EGU2020-3557 | Displays | TS6.2
Remote predictive geological mapping as a tool for the reconstruction of the complex geodynamic evolution of MelanesiaPhilipp Brandl, Anna Kraetschell, Justin Emberley, Mark Hannington, Margaret Stewart, Sven Petersen, and Alan Baxter
The offshore regions of Eastern Papua New Guinea and the Solomon Islands include several active and remnant arc and backarc systems that formed in response to complex plate tectonic adjustments following subduction initiation in the Eocene. Although there has been extensive exploration for offshore petroleum resources, and more than 54 research cruises have investigated or transited the region since 1993, a comprehensive regional geological map, including the deep marine areas, has not been available at a scale that permits quantitative analysis of the basin history. We present the first map that depicts interpreted assemblage- and formation-level lithostratigraphic units correlated across the marine basins and adjacent land masses. The mapped assemblages and large-scale formations are based on a compilation of land-based geological maps, marine geophysical data (hydroacoustics, magnetics, and gravity) integrated with the results of geological sampling, ocean drilling, seismic surveys, and seabed observations.
More than 400,000 km2 of the map area covered by ship-based multibeam and other geophysical data were inspected to derive the offshore geological units. In areas with limited data, the units were extrapolated from well-documented formations in adjacent regions with more complete information, including on land. This approach follows closely the techniques used for remote predictive mapping in other regions of the Earth where geological information is sparse. Geological boundaries were constrained by ship-based multibeam data reprocessed at 35-m to 50-m resolution and integrated with the Global Multi-Resolution Topography (GMRT) gridded at 100 m. Lithotectonic assemblages were assigned on the basis of plate structure, crustal type and thickness, age, composition, and sedimentary cover and further refined by bathymetric and geophysical data from the literature and cruise reports. The final compilation is generalized and presented here at 1:1 М. Our new approach integrates conventional mapping on land with remote predictive mapping of the ocean floor.
The newly compiled geological map illustrates the diversity of assemblages in the region and its complex geodynamic evolution. The resolution of our map allows to perform quantitative analyses of area-age relationships and thus crustal growth. Further geoscientific analyses may allow to estimate the regional mineral potential and to delineate permissive areas as future exploration targets.
How to cite: Brandl, P., Kraetschell, A., Emberley, J., Hannington, M., Stewart, M., Petersen, S., and Baxter, A.: Remote predictive geological mapping as a tool for the reconstruction of the complex geodynamic evolution of Melanesia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3557, https://doi.org/10.5194/egusphere-egu2020-3557, 2020.
The offshore regions of Eastern Papua New Guinea and the Solomon Islands include several active and remnant arc and backarc systems that formed in response to complex plate tectonic adjustments following subduction initiation in the Eocene. Although there has been extensive exploration for offshore petroleum resources, and more than 54 research cruises have investigated or transited the region since 1993, a comprehensive regional geological map, including the deep marine areas, has not been available at a scale that permits quantitative analysis of the basin history. We present the first map that depicts interpreted assemblage- and formation-level lithostratigraphic units correlated across the marine basins and adjacent land masses. The mapped assemblages and large-scale formations are based on a compilation of land-based geological maps, marine geophysical data (hydroacoustics, magnetics, and gravity) integrated with the results of geological sampling, ocean drilling, seismic surveys, and seabed observations.
More than 400,000 km2 of the map area covered by ship-based multibeam and other geophysical data were inspected to derive the offshore geological units. In areas with limited data, the units were extrapolated from well-documented formations in adjacent regions with more complete information, including on land. This approach follows closely the techniques used for remote predictive mapping in other regions of the Earth where geological information is sparse. Geological boundaries were constrained by ship-based multibeam data reprocessed at 35-m to 50-m resolution and integrated with the Global Multi-Resolution Topography (GMRT) gridded at 100 m. Lithotectonic assemblages were assigned on the basis of plate structure, crustal type and thickness, age, composition, and sedimentary cover and further refined by bathymetric and geophysical data from the literature and cruise reports. The final compilation is generalized and presented here at 1:1 М. Our new approach integrates conventional mapping on land with remote predictive mapping of the ocean floor.
The newly compiled geological map illustrates the diversity of assemblages in the region and its complex geodynamic evolution. The resolution of our map allows to perform quantitative analyses of area-age relationships and thus crustal growth. Further geoscientific analyses may allow to estimate the regional mineral potential and to delineate permissive areas as future exploration targets.
How to cite: Brandl, P., Kraetschell, A., Emberley, J., Hannington, M., Stewart, M., Petersen, S., and Baxter, A.: Remote predictive geological mapping as a tool for the reconstruction of the complex geodynamic evolution of Melanesia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3557, https://doi.org/10.5194/egusphere-egu2020-3557, 2020.
EGU2020-6710 | Displays | TS6.2
Magmatic evolution in a sedimented margin and implications for lithospheric breakup: insights from high-resolution seismic data from the South China SeaCuimei Zhang, Xiong Pang, Ming Su, Jinyun Zheng, Hongbo Li, Yale Gu, Jiangyang Zhang, and Yanghui Zhao
The interaction between magmatic and extensional processes related to the formation of rifted margins has been and still is highly debated. The interpretation of magmatic additions, timing of onset and budget of magma during rifting and lithospheric breakup remain controversial and poorly understood. In contrast, the emplacement of magmatic additions in rift systems with high sedimentation rates provides an exceptional perspective towards resolving some of these problems.
In this paper, we present two new high-resolution seismic profiles imaging the complete transition from the hyperextended crust to oceanic crust in the northern South China Sea (SCS). Based on the observation of magma-related structures and the interrelationship with the sedimentary sequence, we define forms and timing of magmatic additions. We show that magmatic activity initiated during necking and then propagated together with the seaward formation of “new” basement , as indicated by the occurrence of sills and laccoliths during hyperextension, and ENE striking cone-shaped volcanos during the final breakup stage before the establishment of an embryonic and then steady-state oceanic crust.
First order estimations of the magmatic budget in order to decipher the magmatic evolution show that it strikingly increased during final hyperextension and the breakup stage and lasted until 23.8 Ma. Thus, magmatic activity continued even after cessation of rifting. This study enables for the first time to provide a semi-quantitative estimate of when, where and how much magma formed during final rifting and breakup at a magma-intermediate margin.
How to cite: Zhang, C., Pang, X., Su, M., Zheng, J., Li, H., Gu, Y., Zhang, J., and Zhao, Y.: Magmatic evolution in a sedimented margin and implications for lithospheric breakup: insights from high-resolution seismic data from the South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6710, https://doi.org/10.5194/egusphere-egu2020-6710, 2020.
The interaction between magmatic and extensional processes related to the formation of rifted margins has been and still is highly debated. The interpretation of magmatic additions, timing of onset and budget of magma during rifting and lithospheric breakup remain controversial and poorly understood. In contrast, the emplacement of magmatic additions in rift systems with high sedimentation rates provides an exceptional perspective towards resolving some of these problems.
In this paper, we present two new high-resolution seismic profiles imaging the complete transition from the hyperextended crust to oceanic crust in the northern South China Sea (SCS). Based on the observation of magma-related structures and the interrelationship with the sedimentary sequence, we define forms and timing of magmatic additions. We show that magmatic activity initiated during necking and then propagated together with the seaward formation of “new” basement , as indicated by the occurrence of sills and laccoliths during hyperextension, and ENE striking cone-shaped volcanos during the final breakup stage before the establishment of an embryonic and then steady-state oceanic crust.
First order estimations of the magmatic budget in order to decipher the magmatic evolution show that it strikingly increased during final hyperextension and the breakup stage and lasted until 23.8 Ma. Thus, magmatic activity continued even after cessation of rifting. This study enables for the first time to provide a semi-quantitative estimate of when, where and how much magma formed during final rifting and breakup at a magma-intermediate margin.
How to cite: Zhang, C., Pang, X., Su, M., Zheng, J., Li, H., Gu, Y., Zhang, J., and Zhao, Y.: Magmatic evolution in a sedimented margin and implications for lithospheric breakup: insights from high-resolution seismic data from the South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6710, https://doi.org/10.5194/egusphere-egu2020-6710, 2020.
EGU2020-1553 | Displays | TS6.2
Structure and stratigraphic framework of the basins along the Chinese Continental Margins: new constraints on the Cenozoic plates’ reorganization in Eastern and Southeastern AsiaJianye Ren, Chao Lei, and Junxia Zhang
Bohai Bay, East China Sea and South China Sea are three of the largest-scale Cenozoic petroleum-rich sedimentary basins along the Chinese continental margin. For the past decades, the wealth of geological and geophysical data was acquired by the petroleum industries, which provide an opportunity to have a synthetic study on these basins.
(1) Structure and stratigraphic framework for the Cenozoic basins in the Bohai Bay, the East China Sea and the South China Sea are revealed to be different. The Bohai Bay basin was imaged to be a pull-apart basin, through which a regional-scale strike-slip fault went. The South China Sea was controlled by extension, which generated a serial of deepwater basins on the hyper-extended crust adjacent to the oceanic crust, most of which was controlled by the detachment faults. Between the Bohai Bay basin and East China Sea is the East China Sea, at the deep level of which a serial of thrust faults occurred. It indicated the regional compression from the pacific plate toward the East China.
(2) Based on the different structure and stratigraphic sequence in the basins along the Chinese continental margin, the basins evolutions were reconstructed. In Late Paleocene to Middle Eocene, distributed faulting occurred along the Chinese continental margin. Subsequently, in Late Eocene the evolution of these three basins were observed to be different. The Bohai Bay Basin was strongly influenced by the oblique strike-slip faulting, and lasted to the latest Late Oligocene, followed by the thermal subsidence in Miocene and a pulse of acceleration subsidence since Pliocene. In contrast to Bohai Bay basin, the continental shelf basin of the East China Sea experienced a long-time compression in the context of back-arc setting, and subsequently has a regional subsidence since Early Pliocene. The continental crust of the South China Sea was thinned since Late Eocene and eventually broke apart in Oligocene to form oceanic crust, where detachment faults bounded a serial of deepwater basins.
The different in basin structures and evolutions since Late Eocene was consistent with the event of plate organization in the western Pacific at that time. Before the event, Chinese continental margin was influenced by the interaction of Eurasian and Pacific plates, e.g. double-plate system. The subduction and related retreat of Pacific plate led to the back-arc extension of the Chinese continental margin, generating widely distributed grabens and half grabens filled with sediments. After this event, the Chinese continental margin was deformed by the interaction between India, Eurasian, Pacific and Philippine Sea plates, e.g. multi-plate system. In this context, several dynamic forces affected the evolution of the Chinese continental margins was observed, e.g. the collision between India and Eurasia, the change of the subduction direction of the Pacific plate, the subduction collision of the proto-South China Sea, the northward movement of the Philippine Sea plate. These complex plate reorganizations lead to the different genetic type of basins in Chinese continental margin.
How to cite: Ren, J., Lei, C., and Zhang, J.: Structure and stratigraphic framework of the basins along the Chinese Continental Margins: new constraints on the Cenozoic plates’ reorganization in Eastern and Southeastern Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1553, https://doi.org/10.5194/egusphere-egu2020-1553, 2020.
Bohai Bay, East China Sea and South China Sea are three of the largest-scale Cenozoic petroleum-rich sedimentary basins along the Chinese continental margin. For the past decades, the wealth of geological and geophysical data was acquired by the petroleum industries, which provide an opportunity to have a synthetic study on these basins.
(1) Structure and stratigraphic framework for the Cenozoic basins in the Bohai Bay, the East China Sea and the South China Sea are revealed to be different. The Bohai Bay basin was imaged to be a pull-apart basin, through which a regional-scale strike-slip fault went. The South China Sea was controlled by extension, which generated a serial of deepwater basins on the hyper-extended crust adjacent to the oceanic crust, most of which was controlled by the detachment faults. Between the Bohai Bay basin and East China Sea is the East China Sea, at the deep level of which a serial of thrust faults occurred. It indicated the regional compression from the pacific plate toward the East China.
(2) Based on the different structure and stratigraphic sequence in the basins along the Chinese continental margin, the basins evolutions were reconstructed. In Late Paleocene to Middle Eocene, distributed faulting occurred along the Chinese continental margin. Subsequently, in Late Eocene the evolution of these three basins were observed to be different. The Bohai Bay Basin was strongly influenced by the oblique strike-slip faulting, and lasted to the latest Late Oligocene, followed by the thermal subsidence in Miocene and a pulse of acceleration subsidence since Pliocene. In contrast to Bohai Bay basin, the continental shelf basin of the East China Sea experienced a long-time compression in the context of back-arc setting, and subsequently has a regional subsidence since Early Pliocene. The continental crust of the South China Sea was thinned since Late Eocene and eventually broke apart in Oligocene to form oceanic crust, where detachment faults bounded a serial of deepwater basins.
The different in basin structures and evolutions since Late Eocene was consistent with the event of plate organization in the western Pacific at that time. Before the event, Chinese continental margin was influenced by the interaction of Eurasian and Pacific plates, e.g. double-plate system. The subduction and related retreat of Pacific plate led to the back-arc extension of the Chinese continental margin, generating widely distributed grabens and half grabens filled with sediments. After this event, the Chinese continental margin was deformed by the interaction between India, Eurasian, Pacific and Philippine Sea plates, e.g. multi-plate system. In this context, several dynamic forces affected the evolution of the Chinese continental margins was observed, e.g. the collision between India and Eurasia, the change of the subduction direction of the Pacific plate, the subduction collision of the proto-South China Sea, the northward movement of the Philippine Sea plate. These complex plate reorganizations lead to the different genetic type of basins in Chinese continental margin.
How to cite: Ren, J., Lei, C., and Zhang, J.: Structure and stratigraphic framework of the basins along the Chinese Continental Margins: new constraints on the Cenozoic plates’ reorganization in Eastern and Southeastern Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1553, https://doi.org/10.5194/egusphere-egu2020-1553, 2020.
EGU2020-5610 | Displays | TS6.2
From Mesozoic subduction to Cenozoic extension: what controlled the tectonic process of South China Sea?Zhen Sun, Fucheng Li, Ning Qiu, and Longtao Sun
The South China Sea (SCS) is one of the largest marginal seas in the western Pacific. Widespread onshore outcrops of the late Mesozoic granitic and volcanic rocks suggest that the SCS was once an active margin associated with Paleo-Pacific or proto South China Sea subducted toward South China in the late Mesozoic. It transitioned into rifting after late Cretaceous and then spreading in Oligocene. IODP drilling indicates that SCS transitioned from subduction into sea spreading in a short time (no more than 30 Myrs) and show diachronous breakup both temporally and spatially. What controlled this tectonic process? In order to answer these questions, we used a combination of data sources, including reprocessed magnetic data, drilling/dredging samples, depositional environment and deformation style on multi-channel seismic profiles to constrain the possible spatial distribution of the Mesozoic volcanic arc first and found that the southwest part of the Mesozoic volcanic arc distributes on both sides of the southwest SCS sub-basin, while the northeast part remains nearly in its original location. The results suggest that the initial breakup sites for the SCS margin might be arc area in the southwest and fore-arc area in the northeast during the opening of SCS basin. Mathematical modeling experiments suggest that several circumstances may cause fore-arc breakup, including: steepening of the subducting plate, a pre-existing rheologically/tectonically weak zone in the arc-front/fore-arc in the subduction plate, seamount or plateau subduction and damaging of the fore-arc area. Also if the subducting slab is young or the subduction time is short, fore-arc breakup will occur. Further analysis suggested that along with the rifting, two sources of magma may have contributed to the rifting. One is supposed to be decompressive melting, the other one is deep sourced and constitute the high velocity lower crustal magmatic underplating, which is supposed to be related with the subduction slab break off.
How to cite: Sun, Z., Li, F., Qiu, N., and Sun, L.: From Mesozoic subduction to Cenozoic extension: what controlled the tectonic process of South China Sea?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5610, https://doi.org/10.5194/egusphere-egu2020-5610, 2020.
The South China Sea (SCS) is one of the largest marginal seas in the western Pacific. Widespread onshore outcrops of the late Mesozoic granitic and volcanic rocks suggest that the SCS was once an active margin associated with Paleo-Pacific or proto South China Sea subducted toward South China in the late Mesozoic. It transitioned into rifting after late Cretaceous and then spreading in Oligocene. IODP drilling indicates that SCS transitioned from subduction into sea spreading in a short time (no more than 30 Myrs) and show diachronous breakup both temporally and spatially. What controlled this tectonic process? In order to answer these questions, we used a combination of data sources, including reprocessed magnetic data, drilling/dredging samples, depositional environment and deformation style on multi-channel seismic profiles to constrain the possible spatial distribution of the Mesozoic volcanic arc first and found that the southwest part of the Mesozoic volcanic arc distributes on both sides of the southwest SCS sub-basin, while the northeast part remains nearly in its original location. The results suggest that the initial breakup sites for the SCS margin might be arc area in the southwest and fore-arc area in the northeast during the opening of SCS basin. Mathematical modeling experiments suggest that several circumstances may cause fore-arc breakup, including: steepening of the subducting plate, a pre-existing rheologically/tectonically weak zone in the arc-front/fore-arc in the subduction plate, seamount or plateau subduction and damaging of the fore-arc area. Also if the subducting slab is young or the subduction time is short, fore-arc breakup will occur. Further analysis suggested that along with the rifting, two sources of magma may have contributed to the rifting. One is supposed to be decompressive melting, the other one is deep sourced and constitute the high velocity lower crustal magmatic underplating, which is supposed to be related with the subduction slab break off.
How to cite: Sun, Z., Li, F., Qiu, N., and Sun, L.: From Mesozoic subduction to Cenozoic extension: what controlled the tectonic process of South China Sea?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5610, https://doi.org/10.5194/egusphere-egu2020-5610, 2020.
EGU2020-6436 | Displays | TS6.2
Sedimentary Dispersal and Accumulation in the oceanic basin, South China Sea, revealed by Sediment BudgetFei Wang and Weiwei Ding
South China Sea (SCS) is not only the crucial pathway for transporting terrigenous materials from Eurasia to the Western Pacific Ocean since the early Oligocene, but also the dominant accumulation and preservation place as a result of limited material exchange between the semi-closed oceanic basin and the open ocean since the middle Miocene. Diverse factors, including global climate changes, eustatic sea level change, regional and local tectonic events, et al., controlled the sedimentary dispersal and accumulational patterns in the oceanic basin of the SCS, which can be revealed by the calculation of sediment budget at different geological times, as the sediment budget can illustrate directly the sediment influx, storage, loss in a basin system (Hapke et.al, 2010).
By interpreting the multichannel seismic profiles covering the whole oceanic basin with constraints from International Ocean Discovery Program (IODP) Expeditions 349, 367 and 368, we reconstructed the sequence stratigraphy framework of the study area, and then calculated the sedimentary budget at different geological time. This work aims to quantitate the sedimentary dispersal and accumulation in the oceanic basin for the first time.
Until now we have completed the sequence boundary identification and dating, as well as the division of sedimentary units of all multichannel seismic profiles. The grid data of different sequence boundaries have been obtained and posted on the bathymetric map, and by the time-depth conversion with appropriate function in different region referred from the drilling results of IODP expeditions, we have figured out the thickness of each sedimentary unit. In the following we will do the decompaction correction before calculating the sedimentary budget of the whole oceanic basin at different times. This work could increase our understandings on the major controlling factors and possible material sources of the deposition process.
How to cite: Wang, F. and Ding, W.: Sedimentary Dispersal and Accumulation in the oceanic basin, South China Sea, revealed by Sediment Budget, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6436, https://doi.org/10.5194/egusphere-egu2020-6436, 2020.
South China Sea (SCS) is not only the crucial pathway for transporting terrigenous materials from Eurasia to the Western Pacific Ocean since the early Oligocene, but also the dominant accumulation and preservation place as a result of limited material exchange between the semi-closed oceanic basin and the open ocean since the middle Miocene. Diverse factors, including global climate changes, eustatic sea level change, regional and local tectonic events, et al., controlled the sedimentary dispersal and accumulational patterns in the oceanic basin of the SCS, which can be revealed by the calculation of sediment budget at different geological times, as the sediment budget can illustrate directly the sediment influx, storage, loss in a basin system (Hapke et.al, 2010).
By interpreting the multichannel seismic profiles covering the whole oceanic basin with constraints from International Ocean Discovery Program (IODP) Expeditions 349, 367 and 368, we reconstructed the sequence stratigraphy framework of the study area, and then calculated the sedimentary budget at different geological time. This work aims to quantitate the sedimentary dispersal and accumulation in the oceanic basin for the first time.
Until now we have completed the sequence boundary identification and dating, as well as the division of sedimentary units of all multichannel seismic profiles. The grid data of different sequence boundaries have been obtained and posted on the bathymetric map, and by the time-depth conversion with appropriate function in different region referred from the drilling results of IODP expeditions, we have figured out the thickness of each sedimentary unit. In the following we will do the decompaction correction before calculating the sedimentary budget of the whole oceanic basin at different times. This work could increase our understandings on the major controlling factors and possible material sources of the deposition process.
How to cite: Wang, F. and Ding, W.: Sedimentary Dispersal and Accumulation in the oceanic basin, South China Sea, revealed by Sediment Budget, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6436, https://doi.org/10.5194/egusphere-egu2020-6436, 2020.
EGU2020-2273 | Displays | TS6.2
Extension discrepancy distribution of the hyper-thinned continental crust in the Baiyun Rift, northern margin of the South China SeaYanghui Zhao, Weiwei Ding, Jianye Ren, Jiabiao Li, Dianjun Tong, and Jiangyang Zhang
It has been widely reported that extension of the upper crust measured from faulting is far less than the lower crustal thinning at rifted continental margins. This phenomenon is referred to as “extension discrepancy”. However, recent studies found out not all rifted margins had experienced a crustal thinning increasing with depth. Here, we use observations from 3D seismic reflection data that cover the Baiyun Rift, to explore the extension discrepancy between the brittle extension and crustal thinning when the crust of the Northern South China Sea margin thinned from 30km to <12km. To achieve this, first, we restored the rift system of the Baiyun Rift in the absence of post-rift sediments and water loading. Subsequently, we applied alternative methods based on the fault geometries and the crustal thickness ratios to compare the deformation of the brittle crust and the whole crust. Results show (1) the upper crustal faulting was sufficient to explain the whole crust thinning in the basin center, indicating no extension discrepancy; (2) near the rift flanks, the upper crustal faulting is greater than the whole crustal thinning, indicating inverse discrepancy. In the northeast of the Baiyun Rift where detachment faulting occurred, magmas passively upwelled and thickened the crust due to isostasy. Consequently, the lower crust was exhumed locally during the detachment faulting. These results indicate the hyper-thinning process of the continental crust in the Northern South China Sea was substantially dominated by tectonic extension rather than thermal thinning.
How to cite: Zhao, Y., Ding, W., Ren, J., Li, J., Tong, D., and Zhang, J.: Extension discrepancy distribution of the hyper-thinned continental crust in the Baiyun Rift, northern margin of the South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2273, https://doi.org/10.5194/egusphere-egu2020-2273, 2020.
It has been widely reported that extension of the upper crust measured from faulting is far less than the lower crustal thinning at rifted continental margins. This phenomenon is referred to as “extension discrepancy”. However, recent studies found out not all rifted margins had experienced a crustal thinning increasing with depth. Here, we use observations from 3D seismic reflection data that cover the Baiyun Rift, to explore the extension discrepancy between the brittle extension and crustal thinning when the crust of the Northern South China Sea margin thinned from 30km to <12km. To achieve this, first, we restored the rift system of the Baiyun Rift in the absence of post-rift sediments and water loading. Subsequently, we applied alternative methods based on the fault geometries and the crustal thickness ratios to compare the deformation of the brittle crust and the whole crust. Results show (1) the upper crustal faulting was sufficient to explain the whole crust thinning in the basin center, indicating no extension discrepancy; (2) near the rift flanks, the upper crustal faulting is greater than the whole crustal thinning, indicating inverse discrepancy. In the northeast of the Baiyun Rift where detachment faulting occurred, magmas passively upwelled and thickened the crust due to isostasy. Consequently, the lower crust was exhumed locally during the detachment faulting. These results indicate the hyper-thinning process of the continental crust in the Northern South China Sea was substantially dominated by tectonic extension rather than thermal thinning.
How to cite: Zhao, Y., Ding, W., Ren, J., Li, J., Tong, D., and Zhang, J.: Extension discrepancy distribution of the hyper-thinned continental crust in the Baiyun Rift, northern margin of the South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2273, https://doi.org/10.5194/egusphere-egu2020-2273, 2020.
EGU2020-9137 | Displays | TS6.2
Partitioning between strike-slip and orthogonal extension in the western South China SeaPan Luo, Jianye Ren, Xi He, Chao Lei, Junjie Xu, Gianreto Manatschal, Nick Kusznir, and Peng Chao
Our study focuses on the Zhongjianna (ZJN) (Phu Kham) Basin, located at the western termination of the South China Sea (SCS) and separated from the Indochina continent by the N-S striking East Vietnam Boundary Fault Zone, which is a large scale strike-slip fault system. The sedimentary infill history of the ZJN basin records the complete evolution and interaction of the Indochina-SCS system and allows the tectonic and kinematic evolution of the basin to be understood.. The discovery of hyper-extended continental crust and mantle exhumation in this basin leads to the question of what is the relative role of large-scale strike-slip and orthogonal faulting in controlling crustal thinning in the ZJN basin.
Our preliminary results confirm the existence of hyperextended continental crust flooring the ZJN basin. Two different types of structures can be identified in this area: extension related deformation in the eastern part and strike-slip related deformation in the western part. The analysis of fault geometries and kinematics linked to timing and subsidence rates suggest that the N-S-orientated strike-slip structures dominated the continental shelf and slope area on the west side of the basin. In the basin, however, most faults strike NE-SW and are parallel to the mid-ocean ridge. Thus, it appears that the ZJN basin resulted from the partitioning between strike-slip and orthogonal extension.
In our presentation we show the results of our seismic interpretation, strain and subsidence analysis and discuss the interaction between strike-slip and orthogonal extension in setting up the hyper-extended ZJN basin and its implications for the large scale tectonic and geodynamic framework.
How to cite: Luo, P., Ren, J., He, X., Lei, C., Xu, J., Manatschal, G., Kusznir, N., and Chao, P.: Partitioning between strike-slip and orthogonal extension in the western South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9137, https://doi.org/10.5194/egusphere-egu2020-9137, 2020.
Our study focuses on the Zhongjianna (ZJN) (Phu Kham) Basin, located at the western termination of the South China Sea (SCS) and separated from the Indochina continent by the N-S striking East Vietnam Boundary Fault Zone, which is a large scale strike-slip fault system. The sedimentary infill history of the ZJN basin records the complete evolution and interaction of the Indochina-SCS system and allows the tectonic and kinematic evolution of the basin to be understood.. The discovery of hyper-extended continental crust and mantle exhumation in this basin leads to the question of what is the relative role of large-scale strike-slip and orthogonal faulting in controlling crustal thinning in the ZJN basin.
Our preliminary results confirm the existence of hyperextended continental crust flooring the ZJN basin. Two different types of structures can be identified in this area: extension related deformation in the eastern part and strike-slip related deformation in the western part. The analysis of fault geometries and kinematics linked to timing and subsidence rates suggest that the N-S-orientated strike-slip structures dominated the continental shelf and slope area on the west side of the basin. In the basin, however, most faults strike NE-SW and are parallel to the mid-ocean ridge. Thus, it appears that the ZJN basin resulted from the partitioning between strike-slip and orthogonal extension.
In our presentation we show the results of our seismic interpretation, strain and subsidence analysis and discuss the interaction between strike-slip and orthogonal extension in setting up the hyper-extended ZJN basin and its implications for the large scale tectonic and geodynamic framework.
How to cite: Luo, P., Ren, J., He, X., Lei, C., Xu, J., Manatschal, G., Kusznir, N., and Chao, P.: Partitioning between strike-slip and orthogonal extension in the western South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9137, https://doi.org/10.5194/egusphere-egu2020-9137, 2020.
EGU2020-8920 | Displays | TS6.2
The stratigraphic and magmatic tape recorder of crustal thinning and lithospheric breakup: insights from the NW South China SeaPeng Chao, Gianreto Manatschal, Nick Kusznir, Pauline Chenin, Jianye Ren, and Xiong Pang
In the last two decades, knowledge of the South China Sea (SCS) rifted margins has significantly evolved. However, there are still many open questions related to when, how, and under what conditions major crustal thinning (necking) and lithospheric breakup occurred and how these processes are recorded in the stratigraphic and magmatic tape recorder. In this study, we aim to explore the tectono-sedimentary-magmatic evolution of rift systems during crustal thinning and lithospheric breakup. Our study is based on observation of conjugate margins architecture along high resolution long offset reflection seismic sections through the Northwest SCS. We focus on crustal thinning and lithospheric breakup, and the transition to first oceanic crust and the birth of an oceanic spreading centre. We describe the Northwest SCS crustal architecture, define extensional domains (proximal, necking, hyper-extended, OCT, oceanic domain) and margin architecture (upper and lower plate). We determine the tectono-sedimentary evolution and discuss the evolution of deformation modes through time and space by linking the tectono-stratigraphic-magma evolution with the observed crustal thinning. These results have important implications for understanding the deformation history and processes in time and space, and enable the analysis and linkage of the tectono-stratigraphic evolution of rift systems with the observed crustal thinning and breakup processes.
How to cite: Chao, P., Manatschal, G., Kusznir, N., Chenin, P., Ren, J., and Pang, X.: The stratigraphic and magmatic tape recorder of crustal thinning and lithospheric breakup: insights from the NW South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8920, https://doi.org/10.5194/egusphere-egu2020-8920, 2020.
In the last two decades, knowledge of the South China Sea (SCS) rifted margins has significantly evolved. However, there are still many open questions related to when, how, and under what conditions major crustal thinning (necking) and lithospheric breakup occurred and how these processes are recorded in the stratigraphic and magmatic tape recorder. In this study, we aim to explore the tectono-sedimentary-magmatic evolution of rift systems during crustal thinning and lithospheric breakup. Our study is based on observation of conjugate margins architecture along high resolution long offset reflection seismic sections through the Northwest SCS. We focus on crustal thinning and lithospheric breakup, and the transition to first oceanic crust and the birth of an oceanic spreading centre. We describe the Northwest SCS crustal architecture, define extensional domains (proximal, necking, hyper-extended, OCT, oceanic domain) and margin architecture (upper and lower plate). We determine the tectono-sedimentary evolution and discuss the evolution of deformation modes through time and space by linking the tectono-stratigraphic-magma evolution with the observed crustal thinning. These results have important implications for understanding the deformation history and processes in time and space, and enable the analysis and linkage of the tectono-stratigraphic evolution of rift systems with the observed crustal thinning and breakup processes.
How to cite: Chao, P., Manatschal, G., Kusznir, N., Chenin, P., Ren, J., and Pang, X.: The stratigraphic and magmatic tape recorder of crustal thinning and lithospheric breakup: insights from the NW South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8920, https://doi.org/10.5194/egusphere-egu2020-8920, 2020.
EGU2020-1727 | Displays | TS6.2
Chemical Geodynamics of Asthenospheric Outflow in the western Pacific: Philippine Sea Back-arc Basin Mantle Source of the Yap Trench Forearc LavasLimei Tang and Ling Chen
We present new major and trace element chemistry and Sr, Nd, and Pb isotope data from basalts, recovered from the forearc setting of the Yap Trench in the western Pacific, and discuss their melt evolution and petrogenesis within the framework of the geodynamic interactions among the Caroline Plate, the Caroline ridge, and the Philippine Sea plate. These rocks have mid-ocean ridge basalt (MORB)-like geochemical features, including medium Fe contents, tholeiitic affinity, high TiO2 values at a given Fe2O3/MgO ratio, Ti/V, Nb/Y, Ba/Yb, and Ba/Th ratios similar to those of back-arc basin basalts (BABB), and trace element patterns commonly displayed by MORB and BABB lavas. However, these basalts are characterized by highly radiogenic Sr and Pb contents, reminiscent of western Pacific sediments. We suggest that forearc magmatism was responsible for the origin and petrogenesis of these rocks. Forearc magmatism was induced by the shrinking of the Philippine Sea plate, which squeezed out the underlying back-arc basin asthenosphere with Indian–type ambient mantle characteristics to invade the forearc mantle of the Yap Trench and causes lithospheric extension. Upwelling and decompression melting of this mantle produced MORB-like lavas in the narrow forearc setting. An apparent slab tear or gap in the subducting plate facilitate the penetration of the mantle outflow. The collision of the Caroline Ridge subducted more sediments into the mantle wedge. Melting of the subducted sediments and the invasion of the Indian-type asthenosphere into the forearc account for the highly radioactive Sr and Pb isotopes of the MORB-like lavas.
How to cite: Tang, L. and Chen, L.: Chemical Geodynamics of Asthenospheric Outflow in the western Pacific: Philippine Sea Back-arc Basin Mantle Source of the Yap Trench Forearc Lavas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1727, https://doi.org/10.5194/egusphere-egu2020-1727, 2020.
We present new major and trace element chemistry and Sr, Nd, and Pb isotope data from basalts, recovered from the forearc setting of the Yap Trench in the western Pacific, and discuss their melt evolution and petrogenesis within the framework of the geodynamic interactions among the Caroline Plate, the Caroline ridge, and the Philippine Sea plate. These rocks have mid-ocean ridge basalt (MORB)-like geochemical features, including medium Fe contents, tholeiitic affinity, high TiO2 values at a given Fe2O3/MgO ratio, Ti/V, Nb/Y, Ba/Yb, and Ba/Th ratios similar to those of back-arc basin basalts (BABB), and trace element patterns commonly displayed by MORB and BABB lavas. However, these basalts are characterized by highly radiogenic Sr and Pb contents, reminiscent of western Pacific sediments. We suggest that forearc magmatism was responsible for the origin and petrogenesis of these rocks. Forearc magmatism was induced by the shrinking of the Philippine Sea plate, which squeezed out the underlying back-arc basin asthenosphere with Indian–type ambient mantle characteristics to invade the forearc mantle of the Yap Trench and causes lithospheric extension. Upwelling and decompression melting of this mantle produced MORB-like lavas in the narrow forearc setting. An apparent slab tear or gap in the subducting plate facilitate the penetration of the mantle outflow. The collision of the Caroline Ridge subducted more sediments into the mantle wedge. Melting of the subducted sediments and the invasion of the Indian-type asthenosphere into the forearc account for the highly radioactive Sr and Pb isotopes of the MORB-like lavas.
How to cite: Tang, L. and Chen, L.: Chemical Geodynamics of Asthenospheric Outflow in the western Pacific: Philippine Sea Back-arc Basin Mantle Source of the Yap Trench Forearc Lavas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1727, https://doi.org/10.5194/egusphere-egu2020-1727, 2020.
EGU2020-4396 | Displays | TS6.2 | Highlight
Sediment gravity flow deposits triggered by typhoon, East China Sea Shelf, Western North PacificXin Shan, Xuefa Shi, and Shuqing Qiao
Hybrid event beds and a debrite are identified in a core on the mid-shelf of East China Sea. Four units are divided according to abrupt boundary identification, with assistance of grain size analysis. The hybrid event beds typically comprise four internal divisions from the base to the top: (1) structureless muddy sand (H1a, high density turbidite); (2) massive muddy sand with mud clasts (H1b, higher density turbidite); (3) linked debrite (H3); (4) homogeneous mud (H5, fluid mud). The radiocarbon ages of the core were in the range of 3890–8526 yr BP. Based on correlation with other surrounding cores, the depositional age of hybrid event beds and the debrite may be less than 500 yr BP. The TOC and δ13C values in event beds suggest a local erosional regime. The average δ13C value for turbidite (H1a and H1b) is similar to the H3 division in the hybrid event beds, implying that the organic matter in the H1a, H1b and H3 may come from the same source area. The REE data reveals the sediment source is initially from Korean rivers. Bi-plots of (La/Lu)UCC vs. (La/Y)UCC, (La/Y)UCC vs. (Gd/Lu)UCC, (La/Yb)UCC vs. (Gd/Yb)UCC and (La/Yb)UCC vs. (Sm/Nd)UCC of four units in the core are concentrated in the similar range, indicating these event beds have the same source area. Both regimes that partial transformation from a debris flow and erosional bulking are suggested. It is unlikely that the debris flow is triggered by a hyperpycnal flow or a tsunami, because both can carry continental and/or coastal signals which have not been recognized in the core. Typhoon can be a probable triggering mechanism.
Acknowledgements
This paper was supported by National Program on Global Change and Air-Sea Interaction (Grant No. GASI-GEOGE-03), National Natural Science Foundation of China (Grants No U1606401 and No. 41706063) and the Taishan Scholar Program of Shandong.
How to cite: Shan, X., Shi, X., and Qiao, S.: Sediment gravity flow deposits triggered by typhoon, East China Sea Shelf, Western North Pacific, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4396, https://doi.org/10.5194/egusphere-egu2020-4396, 2020.
Hybrid event beds and a debrite are identified in a core on the mid-shelf of East China Sea. Four units are divided according to abrupt boundary identification, with assistance of grain size analysis. The hybrid event beds typically comprise four internal divisions from the base to the top: (1) structureless muddy sand (H1a, high density turbidite); (2) massive muddy sand with mud clasts (H1b, higher density turbidite); (3) linked debrite (H3); (4) homogeneous mud (H5, fluid mud). The radiocarbon ages of the core were in the range of 3890–8526 yr BP. Based on correlation with other surrounding cores, the depositional age of hybrid event beds and the debrite may be less than 500 yr BP. The TOC and δ13C values in event beds suggest a local erosional regime. The average δ13C value for turbidite (H1a and H1b) is similar to the H3 division in the hybrid event beds, implying that the organic matter in the H1a, H1b and H3 may come from the same source area. The REE data reveals the sediment source is initially from Korean rivers. Bi-plots of (La/Lu)UCC vs. (La/Y)UCC, (La/Y)UCC vs. (Gd/Lu)UCC, (La/Yb)UCC vs. (Gd/Yb)UCC and (La/Yb)UCC vs. (Sm/Nd)UCC of four units in the core are concentrated in the similar range, indicating these event beds have the same source area. Both regimes that partial transformation from a debris flow and erosional bulking are suggested. It is unlikely that the debris flow is triggered by a hyperpycnal flow or a tsunami, because both can carry continental and/or coastal signals which have not been recognized in the core. Typhoon can be a probable triggering mechanism.
Acknowledgements
This paper was supported by National Program on Global Change and Air-Sea Interaction (Grant No. GASI-GEOGE-03), National Natural Science Foundation of China (Grants No U1606401 and No. 41706063) and the Taishan Scholar Program of Shandong.
How to cite: Shan, X., Shi, X., and Qiao, S.: Sediment gravity flow deposits triggered by typhoon, East China Sea Shelf, Western North Pacific, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4396, https://doi.org/10.5194/egusphere-egu2020-4396, 2020.
EGU2020-4608 | Displays | TS6.2
The significance and tectonic evolution of Huatung basinMinghui Zhao, Jean-Claude Sibuet, Jonny Wu, Longtao Sun, and Jiazheng Zhang
The Huatung basin (HB), located between the Philippine Sea plate (PSP) and the South China Sea (SCS), has likely existed near tectonically-active plate boundaries since the early Cenozoic. It may record SCS evolution from the SCS rifting phase to today, and is a key region to understand the broad geodynamic interactions between the SCS and PSP. A left-lateral shear plate boundary between the SCS and PSP followed the Gagua ridge and was active before 56 Ma. A slight compressive component along the Gagua ridge might have occurred from 40 to 30 Ma, giving rise to the topographic uplift of Gagua ridge and adjacent ridges with possibly some underthrusting of the PSP below the HB. A significant compressive episode also occurred along a second fracture zone around 23 Ma ago. The Manila trench inception occurred along the PSP-SCS plate boundary before the end of SCS spreading, involving the subduction of the younger SCS beneath the older HB. Later the intra-oceanic Luzon arc formed and collided in a sub-parallel fashion with the Eurasian continent around 5-6 Ma ago to form Taiwan. The PSP/EU motion was oblique with respect to this plate boundary during SCS opening. However, we have no direct evidence of the HB age (early Cenozoic or early Cretaceous) and if the PSP underthrusted below the HB. We propose to carry a deep seismic refraction survey and dredge sampling of basement units to clarify this problem. This work is supported by the Chinese National Natural Science Foundation (contracts 91958212, 41730532, 41576070 and 41676043).
How to cite: Zhao, M., Sibuet, J.-C., Wu, J., Sun, L., and Zhang, J.: The significance and tectonic evolution of Huatung basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4608, https://doi.org/10.5194/egusphere-egu2020-4608, 2020.
The Huatung basin (HB), located between the Philippine Sea plate (PSP) and the South China Sea (SCS), has likely existed near tectonically-active plate boundaries since the early Cenozoic. It may record SCS evolution from the SCS rifting phase to today, and is a key region to understand the broad geodynamic interactions between the SCS and PSP. A left-lateral shear plate boundary between the SCS and PSP followed the Gagua ridge and was active before 56 Ma. A slight compressive component along the Gagua ridge might have occurred from 40 to 30 Ma, giving rise to the topographic uplift of Gagua ridge and adjacent ridges with possibly some underthrusting of the PSP below the HB. A significant compressive episode also occurred along a second fracture zone around 23 Ma ago. The Manila trench inception occurred along the PSP-SCS plate boundary before the end of SCS spreading, involving the subduction of the younger SCS beneath the older HB. Later the intra-oceanic Luzon arc formed and collided in a sub-parallel fashion with the Eurasian continent around 5-6 Ma ago to form Taiwan. The PSP/EU motion was oblique with respect to this plate boundary during SCS opening. However, we have no direct evidence of the HB age (early Cenozoic or early Cretaceous) and if the PSP underthrusted below the HB. We propose to carry a deep seismic refraction survey and dredge sampling of basement units to clarify this problem. This work is supported by the Chinese National Natural Science Foundation (contracts 91958212, 41730532, 41576070 and 41676043).
How to cite: Zhao, M., Sibuet, J.-C., Wu, J., Sun, L., and Zhang, J.: The significance and tectonic evolution of Huatung basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4608, https://doi.org/10.5194/egusphere-egu2020-4608, 2020.
EGU2020-6264 | Displays | TS6.2
Influences of tropical monsoon climatology on the delivery and dispersal of organic carbon over the Upper Gulf of Thailand, SE AsiaBin Wu, Xiaodan Wu, Xuefa Shi, Shuqing Qiao, Shengfa Liu, Limin Hu, Jihua Liu, Yazhi Bai, Aimei Zhu, Narumol Kornkanitnan, and Somkiat Khokiattiwong
The seasonal reversal of monsoon climatology modulates precipitation, currents, river influx and a variety of biogeochemical processes. In the present study, we evaluated the role of tropical monsoon pertaining to fluvial discharge, sediment load, coastal current and water stratification on seasonal organic carbon dynamics during four sampling campaigns in the Upper Gulf of Thailand (UGoT), SE Asia. This study demonstrates that particulate organic carbon (POC) is closely correlated with the river influx of suspended sediment, which is generally regulated by the local rainfall. Higher POC is found near the large estuarine section (Chao Phraya River, CHAO) during southwest monsoon period and the small estuarine section (Mae Klong River, MK) during the tropical cyclones impacted November 2013. POC in the estuarine sections is influenced more by the seasonal shift than the coastal sections. Land-derived organic matter prevails in the small estuarine and coastal sections, while marine-derived organic matter dominates in the CHAO and MK impacted estuarine sections. Total organic carbon (TOC) however displays less significant seasonal monsoon variations than POC. Further, TOC tends to accumulate in the sub-silt fraction of sediments, which mainly occurs in the small estuarine and eastern coastal sections and is obviously influenced more by marine-derived factors. TOC in surface sediment of the CHAO and MK influenced sections however displays more seasonal variations with prevailing river input as evidenced by coarser sediment and higher C/N ratios. Moreover, the almost year round water stratification across the region acts as the barrier in retaining organic carbon in the estuaries and their vicinities from dispersal into the lower portion of Gulf of Thailand. High sedimentation rate (~1.1 cm·yr-1) further facilitates the organic carbon burial in the study area. The delivery, dispersal and burial of organic carbon are closely associated with the climate controlled precipitation, and thus the tropical monsoon climatology under the global warming in particular is an important factor influencing the organic carbon in the UGoT.
Acknowledgements
This study was supported by National Programme on Global Change and Air-Sea Interaction (GASI-02-IND-CJ05, GASI-GEOGE-03), the Natural Science Foundation of China (U1606401), the Qingdao National Laboratory for Marine Science and Technology (2016ASKJ13), the China-Thailand cooperation project “Research on Vulnerability of Coastal Zones”, and the Taishan Scholar Program of Shandong.
How to cite: Wu, B., Wu, X., Shi, X., Qiao, S., Liu, S., Hu, L., Liu, J., Bai, Y., Zhu, A., Kornkanitnan, N., and Khokiattiwong, S.: Influences of tropical monsoon climatology on the delivery and dispersal of organic carbon over the Upper Gulf of Thailand, SE Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6264, https://doi.org/10.5194/egusphere-egu2020-6264, 2020.
The seasonal reversal of monsoon climatology modulates precipitation, currents, river influx and a variety of biogeochemical processes. In the present study, we evaluated the role of tropical monsoon pertaining to fluvial discharge, sediment load, coastal current and water stratification on seasonal organic carbon dynamics during four sampling campaigns in the Upper Gulf of Thailand (UGoT), SE Asia. This study demonstrates that particulate organic carbon (POC) is closely correlated with the river influx of suspended sediment, which is generally regulated by the local rainfall. Higher POC is found near the large estuarine section (Chao Phraya River, CHAO) during southwest monsoon period and the small estuarine section (Mae Klong River, MK) during the tropical cyclones impacted November 2013. POC in the estuarine sections is influenced more by the seasonal shift than the coastal sections. Land-derived organic matter prevails in the small estuarine and coastal sections, while marine-derived organic matter dominates in the CHAO and MK impacted estuarine sections. Total organic carbon (TOC) however displays less significant seasonal monsoon variations than POC. Further, TOC tends to accumulate in the sub-silt fraction of sediments, which mainly occurs in the small estuarine and eastern coastal sections and is obviously influenced more by marine-derived factors. TOC in surface sediment of the CHAO and MK influenced sections however displays more seasonal variations with prevailing river input as evidenced by coarser sediment and higher C/N ratios. Moreover, the almost year round water stratification across the region acts as the barrier in retaining organic carbon in the estuaries and their vicinities from dispersal into the lower portion of Gulf of Thailand. High sedimentation rate (~1.1 cm·yr-1) further facilitates the organic carbon burial in the study area. The delivery, dispersal and burial of organic carbon are closely associated with the climate controlled precipitation, and thus the tropical monsoon climatology under the global warming in particular is an important factor influencing the organic carbon in the UGoT.
Acknowledgements
This study was supported by National Programme on Global Change and Air-Sea Interaction (GASI-02-IND-CJ05, GASI-GEOGE-03), the Natural Science Foundation of China (U1606401), the Qingdao National Laboratory for Marine Science and Technology (2016ASKJ13), the China-Thailand cooperation project “Research on Vulnerability of Coastal Zones”, and the Taishan Scholar Program of Shandong.
How to cite: Wu, B., Wu, X., Shi, X., Qiao, S., Liu, S., Hu, L., Liu, J., Bai, Y., Zhu, A., Kornkanitnan, N., and Khokiattiwong, S.: Influences of tropical monsoon climatology on the delivery and dispersal of organic carbon over the Upper Gulf of Thailand, SE Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6264, https://doi.org/10.5194/egusphere-egu2020-6264, 2020.
EGU2020-8782 | Displays | TS6.2
Spatial and temporal distributions of clay minerals in mud deposits on the inner shelf of the East China Sea: Implications for paleoenvironmental changes in the HoloceneShengfa Liu, Xuefa Shi, Xisheng Fang, Yanguang Dou, Yanguang Liu, and Xuchen Wang
We present a paleoclimatic reconstruction for the Holocene by clay mineral analyses of sediments from core MZ02 retrieved from the mud area of the inner continental shelf of the East China Sea (ECS). The clay minerals mainly consist of illite (66%-79%) and chlorite (12%-19%), with minor kaolinite (7%-13%) and smectite (0-6%). Provenance analysis suggests that the illite-dominated clay minerals were derived mainly from the detrital outputs of the Changjiang, Minjiang, and small rivers from Taiwan Island. Our study indicates that the sea level rise since the last glacial, the strength of the Taiwan Warm Current (TWC) and Chinese Coastal Current (CCC) have controlled the dispersal and deposition of clay minerals on the ECS, that in turn determined the clay mineral compositions in the core sediments. During 13,000-9500 BP, due to the lower sea level and shorter distance between these three estuaries and core MZ02, fine sediments on the inner shelf of the ECS were primarily supplied by mixed provenances from the Changjiang, Taiwanese, and Minjiang rivers. During the early Holocene (9500-6200 BP), stronger sediment reworking and erosion at the shelf edge was responsible for the increased lateral transport of fine sediments in the ECS, which lead to a dominance of the sediment source from the Changjiang, while the Taiwanese and Minjiang rivers only provided minor components of detrital sediment to the shelf. Increased strength of TWC might have played an important role in the sediment dispersal and deposition on the inner shelf of the ECS during 6200-2400 BP, with a dominance of more than 60% sediments transported from Taiwanese rivers. Furthermore, our study implies that the Asian monsoon and the weakening of TWC were linked to the abrupt increase of Changjiang and Minjiang derived terrigenous detritus materials since 2400 BP.
Acknowledgments
This work was supported by National Nature Science Foundation of China (No.41106063), Science and Technology Basic Special Program of China (No.2008FY220300), Marine Public Welfare Research Project of China (No.200805063), China Postdoctoral Science Foundation (No.20100481304) and Coastal Investigation and Research Project of China (No. 908-01-CJ12).
How to cite: Liu, S., Shi, X., Fang, X., Dou, Y., Liu, Y., and Wang, X.: Spatial and temporal distributions of clay minerals in mud deposits on the inner shelf of the East China Sea: Implications for paleoenvironmental changes in the Holocene, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8782, https://doi.org/10.5194/egusphere-egu2020-8782, 2020.
We present a paleoclimatic reconstruction for the Holocene by clay mineral analyses of sediments from core MZ02 retrieved from the mud area of the inner continental shelf of the East China Sea (ECS). The clay minerals mainly consist of illite (66%-79%) and chlorite (12%-19%), with minor kaolinite (7%-13%) and smectite (0-6%). Provenance analysis suggests that the illite-dominated clay minerals were derived mainly from the detrital outputs of the Changjiang, Minjiang, and small rivers from Taiwan Island. Our study indicates that the sea level rise since the last glacial, the strength of the Taiwan Warm Current (TWC) and Chinese Coastal Current (CCC) have controlled the dispersal and deposition of clay minerals on the ECS, that in turn determined the clay mineral compositions in the core sediments. During 13,000-9500 BP, due to the lower sea level and shorter distance between these three estuaries and core MZ02, fine sediments on the inner shelf of the ECS were primarily supplied by mixed provenances from the Changjiang, Taiwanese, and Minjiang rivers. During the early Holocene (9500-6200 BP), stronger sediment reworking and erosion at the shelf edge was responsible for the increased lateral transport of fine sediments in the ECS, which lead to a dominance of the sediment source from the Changjiang, while the Taiwanese and Minjiang rivers only provided minor components of detrital sediment to the shelf. Increased strength of TWC might have played an important role in the sediment dispersal and deposition on the inner shelf of the ECS during 6200-2400 BP, with a dominance of more than 60% sediments transported from Taiwanese rivers. Furthermore, our study implies that the Asian monsoon and the weakening of TWC were linked to the abrupt increase of Changjiang and Minjiang derived terrigenous detritus materials since 2400 BP.
Acknowledgments
This work was supported by National Nature Science Foundation of China (No.41106063), Science and Technology Basic Special Program of China (No.2008FY220300), Marine Public Welfare Research Project of China (No.200805063), China Postdoctoral Science Foundation (No.20100481304) and Coastal Investigation and Research Project of China (No. 908-01-CJ12).
How to cite: Liu, S., Shi, X., Fang, X., Dou, Y., Liu, Y., and Wang, X.: Spatial and temporal distributions of clay minerals in mud deposits on the inner shelf of the East China Sea: Implications for paleoenvironmental changes in the Holocene, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8782, https://doi.org/10.5194/egusphere-egu2020-8782, 2020.
EGU2020-8919 | Displays | TS6.2
Sedimentation at different time scales in Yellow River delta in response to course shift and water-sediment regulationQiao Shuqing, Shi Xuefa, Yonggui Yu, Limin Hu, Lin Zhou, Guangbo Ren, Gang Yang, Zhengquan Yao, and Naishuang Bi
The fluvial sediment to the sea is the base of coastal geomorphology and biogeochemical processes, and its transport is an important pathway to the global biogeochemical cycle. The Yellow River is one of globally well-known large rivers because of high sediment load and Chinese Mother River. Its channel shifts frequently because of high sediment load and steep river-channel gradient in the lower reaches . The terminal channel has shifted more than 50 times since 1855 and the last two changes in 1976 and 1996. Furthermore, Yellow River Conservancy Commission has began to implement Water-Sediment Regulation Scheme (WSRS) since 2002, to increase the main channel discharge capacity and to reduce deposition in the reservoirs and river channel. Surface sediment, multi-core and gravity sediment cores, remote sensing images and bathymetric data near the Yellow River delta were collected to study the impact of WSRS and river terminal change together with the water and sediment discharge at the gauging station. Especially, 7Be, 210Pb and 137Cs, grain size, sediment color and TOC/TN was measured to show sedimentary record of WSRS and channel shift on inter-and intra-annual time scale. The results show that the fresh sediment from Yellow River during 2014 WSRS period can be transported eastward more than 80 km off the rivermouth, while cannot pass 38° easily. Meanwhile the sediment can penetrate as deep as 12 cm. The subaerial delta area is mostly stable after 2002, and its balance is mainly controlled by the surrounding artificial coastline. The subaqueous delta changed from trapping about 4.6×108 t to being eroded ~ 3.1×108 t and 1.1×108 t each year during the three stages of 1976-1996, 1996-2002 and 2002-2014. It is proposed that the subaerial delta area will change little except for the Q8 outlet area, while the subaqueous delta evolution mostly depend on the Huanghe material besides the hydrodynamic conditions. In addition, the aim of WSRS to scour the lower riverbed will recede in future. This study deepens our understanding of the fluvial sediment disperse pattern and sedimentation under the influence of human activities and hydrodynamic conditions.
How to cite: Shuqing, Q., Xuefa, S., Yu, Y., Hu, L., Zhou, L., Ren, G., Yang, G., Yao, Z., and Bi, N.: Sedimentation at different time scales in Yellow River delta in response to course shift and water-sediment regulation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8919, https://doi.org/10.5194/egusphere-egu2020-8919, 2020.
The fluvial sediment to the sea is the base of coastal geomorphology and biogeochemical processes, and its transport is an important pathway to the global biogeochemical cycle. The Yellow River is one of globally well-known large rivers because of high sediment load and Chinese Mother River. Its channel shifts frequently because of high sediment load and steep river-channel gradient in the lower reaches . The terminal channel has shifted more than 50 times since 1855 and the last two changes in 1976 and 1996. Furthermore, Yellow River Conservancy Commission has began to implement Water-Sediment Regulation Scheme (WSRS) since 2002, to increase the main channel discharge capacity and to reduce deposition in the reservoirs and river channel. Surface sediment, multi-core and gravity sediment cores, remote sensing images and bathymetric data near the Yellow River delta were collected to study the impact of WSRS and river terminal change together with the water and sediment discharge at the gauging station. Especially, 7Be, 210Pb and 137Cs, grain size, sediment color and TOC/TN was measured to show sedimentary record of WSRS and channel shift on inter-and intra-annual time scale. The results show that the fresh sediment from Yellow River during 2014 WSRS period can be transported eastward more than 80 km off the rivermouth, while cannot pass 38° easily. Meanwhile the sediment can penetrate as deep as 12 cm. The subaerial delta area is mostly stable after 2002, and its balance is mainly controlled by the surrounding artificial coastline. The subaqueous delta changed from trapping about 4.6×108 t to being eroded ~ 3.1×108 t and 1.1×108 t each year during the three stages of 1976-1996, 1996-2002 and 2002-2014. It is proposed that the subaerial delta area will change little except for the Q8 outlet area, while the subaqueous delta evolution mostly depend on the Huanghe material besides the hydrodynamic conditions. In addition, the aim of WSRS to scour the lower riverbed will recede in future. This study deepens our understanding of the fluvial sediment disperse pattern and sedimentation under the influence of human activities and hydrodynamic conditions.
How to cite: Shuqing, Q., Xuefa, S., Yu, Y., Hu, L., Zhou, L., Ren, G., Yang, G., Yao, Z., and Bi, N.: Sedimentation at different time scales in Yellow River delta in response to course shift and water-sediment regulation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8919, https://doi.org/10.5194/egusphere-egu2020-8919, 2020.
EGU2020-9119 | Displays | TS6.2
Seismic stratigraphy and tectonic structure from a long multi-channel seismic profile across the southern of South China Seawu zhaocai
In order to grasp the Cenozoic extension and tectonic deformation characteristics of the crust in the southern of the South China Sea, a newly acquired multi-channel seismic profile (DZ02) acrossing the conjugate continental margin of the Southwest Subbasin, Nansha block, and Nansha Trough is explained. Four stratigraphic units (syn-rift unit, drift unit1, drift unit2 and post-rift unit) were determined with six sequence boundaries (Tg, T70, T60, T40, T20, T10). Based on the differences in tectonic units and the features of stratigraphic and structural in the southern of the South China Sea, it is divided into five structural belts from northwest to southeast, which are the northern continental margin extension zone, the Southwest Subbasin, the Nansha intracontinental extension zone, the Nansha forebulge zone, and the Nansha trough. The fault derived and whole crustal extension factors of the Nansha block are also calculated. The results show that in time, the Nansha block has undergone two phases of extension, namely the syn-rift period and the seafloor spreading period. The syn-rifting stage accounted for about 69% of the total extension, and the seafloor spreading stage of the South China Sea accounted for about 26%. In space, the whole crust extension factor is greater than the fault derived extension factor in most areas. By comparing with the multi-channel seismic profile of the eastern part of the Nansha block imply that the crustal extension process is synchronous, but the extent of the extension in the western of Nansha is always greater.
How to cite: zhaocai, W.: Seismic stratigraphy and tectonic structure from a long multi-channel seismic profile across the southern of South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9119, https://doi.org/10.5194/egusphere-egu2020-9119, 2020.
In order to grasp the Cenozoic extension and tectonic deformation characteristics of the crust in the southern of the South China Sea, a newly acquired multi-channel seismic profile (DZ02) acrossing the conjugate continental margin of the Southwest Subbasin, Nansha block, and Nansha Trough is explained. Four stratigraphic units (syn-rift unit, drift unit1, drift unit2 and post-rift unit) were determined with six sequence boundaries (Tg, T70, T60, T40, T20, T10). Based on the differences in tectonic units and the features of stratigraphic and structural in the southern of the South China Sea, it is divided into five structural belts from northwest to southeast, which are the northern continental margin extension zone, the Southwest Subbasin, the Nansha intracontinental extension zone, the Nansha forebulge zone, and the Nansha trough. The fault derived and whole crustal extension factors of the Nansha block are also calculated. The results show that in time, the Nansha block has undergone two phases of extension, namely the syn-rift period and the seafloor spreading period. The syn-rifting stage accounted for about 69% of the total extension, and the seafloor spreading stage of the South China Sea accounted for about 26%. In space, the whole crust extension factor is greater than the fault derived extension factor in most areas. By comparing with the multi-channel seismic profile of the eastern part of the Nansha block imply that the crustal extension process is synchronous, but the extent of the extension in the western of Nansha is always greater.
How to cite: zhaocai, W.: Seismic stratigraphy and tectonic structure from a long multi-channel seismic profile across the southern of South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9119, https://doi.org/10.5194/egusphere-egu2020-9119, 2020.
EGU2020-13579 | Displays | TS6.2
Reconstruction of sediment transported patterns since the late Miocene in the Qiongdongnan Basin, northern South China SeaMing Su, Zhixuan Lin, Ce Wang, Hui Chen, Shan Liu, and Kunwen Luo
Late Miocene-to-present sedimentary succession, consisting of deep-water channels, submarine canyons, shelf-edge delta and clinoform, mass transport complex (MTC), turbidites, pelagic sediments and so on, has accumulated in the Qiongdongnan Basin (QDNB) and supplied from several sediment potential provenances, including surrounding tectonic uplifts and drainage system (e.g. Hainan island, Red River system and Shenhu Uplift). This multiple sediment source system with a variety of space-time distribution is more likely to result in different transported pathways to connect with accumulated zone of the QDNB. To investigate spatial and temporal variation of sediment transported patterns since the late Miocene, the primary dataset in this study is high-resolution 2D seismic profiles that are used to interpret several types of sedimentary features and to determine the distribution within the basin. Integrated analysis of core samples and well log data summarized from previous studies is allow for acquiring high-resolution vertical information about physical and chemical properties of different types of sedimentary features. Depended on characterization and spatial distribution of depositional models, the sediment delivered pattern could be classified into three major types. (1) the downslope transports suggest that sediments were transported by gravity flows and slope failures from high topographic areas to deposit at the basinfloor, and basinward prograding deposition at the shelf or tectonic uplifts, channels/canyons developed along the slope and submarine fans formed at the lower slope are the products of downslope transports shown in the SE-trending seismic profiles; (2) the canyon-axial transports are associated with geomorphology of the Central Canyon System (CCS) across the QDNB from SWW to NEE. Abundant sediments originated at the Red River system were supplied from the west, resulting in dominantly onlap-filling turbidites with a series of erosional discordance within the head area and western segment of the CCS; (3) the combined transport is a mixture of downslope and canyon-axial sediment transports. A large volume of MTDs source from the Hainan Island in the north was transported southward and impeded by the Southern Uplift, so they tended to widen the canyon and continuously deliver eastward along CCS. These three types of sediment transported patterns since the late Miocene in the QDNB might be helpful for predicting distribution of different sedimentary characteristics, which has economic significance in the industrial field.
How to cite: Su, M., Lin, Z., Wang, C., Chen, H., Liu, S., and Luo, K.: Reconstruction of sediment transported patterns since the late Miocene in the Qiongdongnan Basin, northern South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13579, https://doi.org/10.5194/egusphere-egu2020-13579, 2020.
Late Miocene-to-present sedimentary succession, consisting of deep-water channels, submarine canyons, shelf-edge delta and clinoform, mass transport complex (MTC), turbidites, pelagic sediments and so on, has accumulated in the Qiongdongnan Basin (QDNB) and supplied from several sediment potential provenances, including surrounding tectonic uplifts and drainage system (e.g. Hainan island, Red River system and Shenhu Uplift). This multiple sediment source system with a variety of space-time distribution is more likely to result in different transported pathways to connect with accumulated zone of the QDNB. To investigate spatial and temporal variation of sediment transported patterns since the late Miocene, the primary dataset in this study is high-resolution 2D seismic profiles that are used to interpret several types of sedimentary features and to determine the distribution within the basin. Integrated analysis of core samples and well log data summarized from previous studies is allow for acquiring high-resolution vertical information about physical and chemical properties of different types of sedimentary features. Depended on characterization and spatial distribution of depositional models, the sediment delivered pattern could be classified into three major types. (1) the downslope transports suggest that sediments were transported by gravity flows and slope failures from high topographic areas to deposit at the basinfloor, and basinward prograding deposition at the shelf or tectonic uplifts, channels/canyons developed along the slope and submarine fans formed at the lower slope are the products of downslope transports shown in the SE-trending seismic profiles; (2) the canyon-axial transports are associated with geomorphology of the Central Canyon System (CCS) across the QDNB from SWW to NEE. Abundant sediments originated at the Red River system were supplied from the west, resulting in dominantly onlap-filling turbidites with a series of erosional discordance within the head area and western segment of the CCS; (3) the combined transport is a mixture of downslope and canyon-axial sediment transports. A large volume of MTDs source from the Hainan Island in the north was transported southward and impeded by the Southern Uplift, so they tended to widen the canyon and continuously deliver eastward along CCS. These three types of sediment transported patterns since the late Miocene in the QDNB might be helpful for predicting distribution of different sedimentary characteristics, which has economic significance in the industrial field.
How to cite: Su, M., Lin, Z., Wang, C., Chen, H., Liu, S., and Luo, K.: Reconstruction of sediment transported patterns since the late Miocene in the Qiongdongnan Basin, northern South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13579, https://doi.org/10.5194/egusphere-egu2020-13579, 2020.
EGU2020-11862 | Displays | TS6.2
Research progress on the Zhongnan-Liyue Fault Zone in the South China Sea BasinZiying Xu, Jun Wang, Hongfang Gao, and Yongjian Yao
We give a review of the up-to-date research situation about The Zhongnan-Liyue Fault Zone (ZLFZ), than analyze the spatial distribution and tectonic deformation feature of the ZLFZ based on the geophysical data including topographic, seismic, gravity and magnetic data. The results show that the ZLFZ has obvious north-south segmentation characteristics in in the South China Sea Basin. The north section, which is between northwest sub-basin and east sub-basin, is a narrow zone with the width of ~16 km, and is NNW trend from 18°N,115.5°E to 17.5°N,116°E. Meanwhile ,the south section, which is between southwest sub-basin and east sub-basin, is a wide zone with the width of 60-80 km, and is NNW trend from the east of ZhongshaBank to the west of LiyueBank. The main fault of the ZLFZ is NNW trend along the seamounts ridge of Zhongnan. the ZLFZ of transition region is NNE trend from the north section to the south section. According the sub-basin’s sedimentary thickness and oceanic crust thickness exist obvious difference, on both sides of the ZLFZ, we speculate that the ZLFZ play an important role on geological structure of sub-basin. According to the chang of crustal structure, We speculate that the ZLFZ is at least a crustal fracture zone.
Key words: South China Sea Basin; Zhongnan-Liyue Fault Zone; Spatial distribution; Tectonic deformation
Foundation item: National Natural Science Foundation of China (41606080, 41576068); The China Geological Survey Program (GZH201400202, 1212011220117, DD20160138, 1212011220116).
How to cite: Xu, Z., Wang, J., Gao, H., and Yao, Y.: Research progress on the Zhongnan-Liyue Fault Zone in the South China Sea Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11862, https://doi.org/10.5194/egusphere-egu2020-11862, 2020.
We give a review of the up-to-date research situation about The Zhongnan-Liyue Fault Zone (ZLFZ), than analyze the spatial distribution and tectonic deformation feature of the ZLFZ based on the geophysical data including topographic, seismic, gravity and magnetic data. The results show that the ZLFZ has obvious north-south segmentation characteristics in in the South China Sea Basin. The north section, which is between northwest sub-basin and east sub-basin, is a narrow zone with the width of ~16 km, and is NNW trend from 18°N,115.5°E to 17.5°N,116°E. Meanwhile ,the south section, which is between southwest sub-basin and east sub-basin, is a wide zone with the width of 60-80 km, and is NNW trend from the east of ZhongshaBank to the west of LiyueBank. The main fault of the ZLFZ is NNW trend along the seamounts ridge of Zhongnan. the ZLFZ of transition region is NNE trend from the north section to the south section. According the sub-basin’s sedimentary thickness and oceanic crust thickness exist obvious difference, on both sides of the ZLFZ, we speculate that the ZLFZ play an important role on geological structure of sub-basin. According to the chang of crustal structure, We speculate that the ZLFZ is at least a crustal fracture zone.
Key words: South China Sea Basin; Zhongnan-Liyue Fault Zone; Spatial distribution; Tectonic deformation
Foundation item: National Natural Science Foundation of China (41606080, 41576068); The China Geological Survey Program (GZH201400202, 1212011220117, DD20160138, 1212011220116).
How to cite: Xu, Z., Wang, J., Gao, H., and Yao, Y.: Research progress on the Zhongnan-Liyue Fault Zone in the South China Sea Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11862, https://doi.org/10.5194/egusphere-egu2020-11862, 2020.
EGU2020-12566 | Displays | TS6.2
Subsidence discrepancy in the Valencia Trough revealed from reflection seismic observations and backstripping resultsPenggao Fang, Geoffroy Mohn, Julie Tugend, and Nick Kusznir
The Valencia Trough is commonly included as part of the set of western Mediterranean Cenozoic extensional basins that formed in relation with the Tethyan oceanic slab rollback during the latest Oligocene to early Miocene. It lies in a complex tectonic setting between the Gulf of Lions to the North-West, the Catalan Coastal Range and the Iberian chain to the West, the Balearic promontory to the East and the Betic orogenic system to the South. This rifting period is coeval with or directly followed by the development of the external Betics fold and thrust belts at the southern tip of the Valencia Trough. Recent investigations suggest that the Valencia Trough is segmented into two main domains exhibiting different geological and geophysical characteristics between its northeastern and southwestern parts. The presence of numerous Cenozoic normal faults and the well-studied subsidence pattern evolution of the NE part of the Valencia Trough suggest that it mainly formed coevally with the rifting of Gulf of Lion. However, if a significant post-Oligocene subsidence is also evidenced in its SW part; fewer Cenozoic rift structures are observed suggesting that the subsidence pattern likely results from the interference of different processes.
In this presentation, we quantify the post-Oligocene subsidence history of the SW part of the Valencia Trough with the aim of evaluating the potential mechanisms explaining this apparent subsidence discrepancy. We analyzed the spatial and temporal distribution of the post-Oligocene subsidence using the interpretation of a dense grid of high-quality multi-channel seismic profiles, also integrating drill-hole results and velocity information from expanding spread profiles (ESP). We used the mapping of the main unconformities, especially the so-called Oligocene unconformity, to perform a 3D flexural backstripping, which permits the prediction of the post-Oligocene water-loaded subsidence. Our results confirm that the post-Oligocene subsidence of the SW part of the Valencia Trough cannot be explained by the rifting of the Gulf of Lions. Previous works already showed that the extreme crustal thinning observed to the SW is related to a previous Mesozoic rift event. Here, we further highlight that if few Cenozoic extensional structures are observed, they can be interpreted as gravitational features rooting at the regionally identified Upper Triassic evaporite level. Backstripping results combined with the mapping of the first sediments deposited on top of the Oligocene unconformity show that they are largely controlled by the shape of Betic front with a possible additional effect of preserved Mesozoic structures. At larger scale, we compare the mechanisms accounting for the origin and subsidence at the SW part of the Valencia Trough with those responsible for the subsidence of its NE part and the Gulf of Lions.
How to cite: Fang, P., Mohn, G., Tugend, J., and Kusznir, N.: Subsidence discrepancy in the Valencia Trough revealed from reflection seismic observations and backstripping results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12566, https://doi.org/10.5194/egusphere-egu2020-12566, 2020.
The Valencia Trough is commonly included as part of the set of western Mediterranean Cenozoic extensional basins that formed in relation with the Tethyan oceanic slab rollback during the latest Oligocene to early Miocene. It lies in a complex tectonic setting between the Gulf of Lions to the North-West, the Catalan Coastal Range and the Iberian chain to the West, the Balearic promontory to the East and the Betic orogenic system to the South. This rifting period is coeval with or directly followed by the development of the external Betics fold and thrust belts at the southern tip of the Valencia Trough. Recent investigations suggest that the Valencia Trough is segmented into two main domains exhibiting different geological and geophysical characteristics between its northeastern and southwestern parts. The presence of numerous Cenozoic normal faults and the well-studied subsidence pattern evolution of the NE part of the Valencia Trough suggest that it mainly formed coevally with the rifting of Gulf of Lion. However, if a significant post-Oligocene subsidence is also evidenced in its SW part; fewer Cenozoic rift structures are observed suggesting that the subsidence pattern likely results from the interference of different processes.
In this presentation, we quantify the post-Oligocene subsidence history of the SW part of the Valencia Trough with the aim of evaluating the potential mechanisms explaining this apparent subsidence discrepancy. We analyzed the spatial and temporal distribution of the post-Oligocene subsidence using the interpretation of a dense grid of high-quality multi-channel seismic profiles, also integrating drill-hole results and velocity information from expanding spread profiles (ESP). We used the mapping of the main unconformities, especially the so-called Oligocene unconformity, to perform a 3D flexural backstripping, which permits the prediction of the post-Oligocene water-loaded subsidence. Our results confirm that the post-Oligocene subsidence of the SW part of the Valencia Trough cannot be explained by the rifting of the Gulf of Lions. Previous works already showed that the extreme crustal thinning observed to the SW is related to a previous Mesozoic rift event. Here, we further highlight that if few Cenozoic extensional structures are observed, they can be interpreted as gravitational features rooting at the regionally identified Upper Triassic evaporite level. Backstripping results combined with the mapping of the first sediments deposited on top of the Oligocene unconformity show that they are largely controlled by the shape of Betic front with a possible additional effect of preserved Mesozoic structures. At larger scale, we compare the mechanisms accounting for the origin and subsidence at the SW part of the Valencia Trough with those responsible for the subsidence of its NE part and the Gulf of Lions.
How to cite: Fang, P., Mohn, G., Tugend, J., and Kusznir, N.: Subsidence discrepancy in the Valencia Trough revealed from reflection seismic observations and backstripping results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12566, https://doi.org/10.5194/egusphere-egu2020-12566, 2020.
EGU2020-21429 | Displays | TS6.2
Multi-phase volcanisms along a stretched continental crust: insights from Xisha massif, northwestern of the South China Sea marginLijie Wang, Fuyuan Li, Baojin Zhang, Ziying Xu, and Zhe Wang
Volcanism occurs close to the rifting active areas, especially in the passive continental margins. Their occurrence can have considerable impacts on the continental lithosphere breakup process, hydrocarbon accumulation system in a basin, and regional heat flows. The Xisha massif surrounded by two hyper-extended continental crust and three oceanic basins that the area is underlain by stretched continental crust in the northwestern South China Sea margin. Sporadic Cenozoic volcanic samples and structures from wells, seismic data, and multi-beam data in the Xisha massif have been previously recognized. This study focuses on describing the igneous structures and mapping the volcanic distributions. With the use of drilled wells with lithologic and stratigraphic information, 2D multiple channel seismic data, and multi-beam data, the occurrence of three phases Cenozoic volcanism were mapped. The first episodic volcanism during the rifting to spreading stage in the South China Sea occurred together with Mesozoic granitic pluton. The drilling samples in the well CK-2 show that Late Eocene to Early Miocene basaltic pyroclastic rocks beneath the thick Miocene reefal limestone. Only five mound shaped structures from seismic profiles located on the basement highs and entirely overlapped by the following carbonates. The second episodic volcanism occurred during Middle Miocene that features volcanic group, isolated volcanic mounds, lava flows, and hydrothermal vents associated with sills in the northwestern Xisha massif. The volcanic groups are mainly present above a NE-SW trended sag and the long axis trends NW, the same as the Middle Miocene active fault orientation in the Qiongdongnan basin. The volume of the largest volcanic group is ca. 504 km3. From the intruded strata and deformational structures of volcanic mounds, sills, and laccolith, we found the third episodic volcanism occurred during Pliocene on a small scale. The igneous bodies mainly distributed in the southern Xisha massif. Distribution and volume of igneous bodies show that Middle Miocene stage magmatic activity is more intense than the others, where volcanism is dominant. Comparing with tectonic stress filed, continental crust structures, and sediment thickness, we found the distribution of volcanos is probably related to NE-SW stretching stress filed during Middle Miocene. A high vertical pressure caused by 20-25 km’s crust thickness and only ca. 1-3 km thickness sediment layer may build a good vertical gradient for magma transport. We indicate the intense Middle Miocene volcanism in Xisha massif is also related to the high velocity layers in the lower crust and cased the high heat flows. These phenomena probably coincided with more magma intruded in the lower crust when plenty of post spreading magmatism emplacement in the SCS margin.
How to cite: Wang, L., Li, F., Zhang, B., Xu, Z., and Wang, Z.: Multi-phase volcanisms along a stretched continental crust: insights from Xisha massif, northwestern of the South China Sea margin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21429, https://doi.org/10.5194/egusphere-egu2020-21429, 2020.
Volcanism occurs close to the rifting active areas, especially in the passive continental margins. Their occurrence can have considerable impacts on the continental lithosphere breakup process, hydrocarbon accumulation system in a basin, and regional heat flows. The Xisha massif surrounded by two hyper-extended continental crust and three oceanic basins that the area is underlain by stretched continental crust in the northwestern South China Sea margin. Sporadic Cenozoic volcanic samples and structures from wells, seismic data, and multi-beam data in the Xisha massif have been previously recognized. This study focuses on describing the igneous structures and mapping the volcanic distributions. With the use of drilled wells with lithologic and stratigraphic information, 2D multiple channel seismic data, and multi-beam data, the occurrence of three phases Cenozoic volcanism were mapped. The first episodic volcanism during the rifting to spreading stage in the South China Sea occurred together with Mesozoic granitic pluton. The drilling samples in the well CK-2 show that Late Eocene to Early Miocene basaltic pyroclastic rocks beneath the thick Miocene reefal limestone. Only five mound shaped structures from seismic profiles located on the basement highs and entirely overlapped by the following carbonates. The second episodic volcanism occurred during Middle Miocene that features volcanic group, isolated volcanic mounds, lava flows, and hydrothermal vents associated with sills in the northwestern Xisha massif. The volcanic groups are mainly present above a NE-SW trended sag and the long axis trends NW, the same as the Middle Miocene active fault orientation in the Qiongdongnan basin. The volume of the largest volcanic group is ca. 504 km3. From the intruded strata and deformational structures of volcanic mounds, sills, and laccolith, we found the third episodic volcanism occurred during Pliocene on a small scale. The igneous bodies mainly distributed in the southern Xisha massif. Distribution and volume of igneous bodies show that Middle Miocene stage magmatic activity is more intense than the others, where volcanism is dominant. Comparing with tectonic stress filed, continental crust structures, and sediment thickness, we found the distribution of volcanos is probably related to NE-SW stretching stress filed during Middle Miocene. A high vertical pressure caused by 20-25 km’s crust thickness and only ca. 1-3 km thickness sediment layer may build a good vertical gradient for magma transport. We indicate the intense Middle Miocene volcanism in Xisha massif is also related to the high velocity layers in the lower crust and cased the high heat flows. These phenomena probably coincided with more magma intruded in the lower crust when plenty of post spreading magmatism emplacement in the SCS margin.
How to cite: Wang, L., Li, F., Zhang, B., Xu, Z., and Wang, Z.: Multi-phase volcanisms along a stretched continental crust: insights from Xisha massif, northwestern of the South China Sea margin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21429, https://doi.org/10.5194/egusphere-egu2020-21429, 2020.
TS6.4 – Rift to ridge: the record of continental breakup processes
EGU2020-378 | Displays | TS6.4 | Highlight
3D structures and sedimentary infill across the continent-ocean transition of the northern South China Sea: constraint by the drilling results from IODP Expeditions 367, 368 and 368XChao Lei, Jianye Ren, Geoffroy Mohn, Michael Nirrengarten, Xiong Pang, Jinyun Zheng, and Bowen Liu
Apart from the Iberia-Newfoundland margins, the South China Sea (SCS) represents another passive margin where continent-ocean transition basement was sampled by deep drilling. Drilling data from IODP Expedition 367-368 and 368X combined with seismic profiles revealed a narrow continent-ocean transition (COT) between the Distal High sampled at Site U1501 and the Ridge B sampled at Site U1500. Results suggested that major Eocene lithospheric thinning triggered Mid-Ocean Ridge type melt production which emplaced within hyperextended continental crust leading eventually to continental breakup.
Because of available dense seismic survey consisting of deep-penetrated seismic data imaging as deep as 12 s TWT, as well as drilling results from IODP Expeditions 367-368 and 368X, the COT in the northern SCS enables us to investigate the 3D propagation of continental breakup and the interactions between tectonic extension and magmatism. The top of acoustic basement can be consistently interpreted through all of our seismic survey and reveal various types of reliefs and nature from hyperextended continental crust to oceanic crust. In the basement, deep-penetrated seismic profiles present series of densely sub-parallel high-amplitude reflections that occurred within the lower crust. The lower boundary of these reflections is often characterized by double continual and high reflections interpreted as the Moho. Across the COT, the basement structure is characterized by: 1) Series of tilted blocks bounded by high angle faults on the Distal High and filled by syn-tectonic sedimentary wedges, 2) Rounded mounds of the basement with chaotic seismic reflection and sedimentary onlaps on these structures, 3) Series of ridges delimited by high-angle normal faults with no sedimentary wedge on the first oceanic crust.
Based on the detail stratigraphic framework constraint by drilling results from IODP Expeditions, the nature and timing of formation of these basement highs can be investigated. Some of these highs are limited by extensional faults while the nature of mounded structures located on the thinnest continental crust remain mysterious. Our detailed analyses emphasize the occurrence and local control of syn-rift magmatism in order to build such structures. At larger scale, the hyperextended continental crust is characterized by significant 3D morphological variations both observed on dip and strike profiles. In contrast, the initial oceanic crust is characterized by a more homogenous structure and consistently juxtaposed to continental crust over a sharp and narrow zone.
How to cite: Lei, C., Ren, J., Mohn, G., Nirrengarten, M., Pang, X., Zheng, J., and Liu, B.: 3D structures and sedimentary infill across the continent-ocean transition of the northern South China Sea: constraint by the drilling results from IODP Expeditions 367, 368 and 368X, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-378, https://doi.org/10.5194/egusphere-egu2020-378, 2020.
Apart from the Iberia-Newfoundland margins, the South China Sea (SCS) represents another passive margin where continent-ocean transition basement was sampled by deep drilling. Drilling data from IODP Expedition 367-368 and 368X combined with seismic profiles revealed a narrow continent-ocean transition (COT) between the Distal High sampled at Site U1501 and the Ridge B sampled at Site U1500. Results suggested that major Eocene lithospheric thinning triggered Mid-Ocean Ridge type melt production which emplaced within hyperextended continental crust leading eventually to continental breakup.
Because of available dense seismic survey consisting of deep-penetrated seismic data imaging as deep as 12 s TWT, as well as drilling results from IODP Expeditions 367-368 and 368X, the COT in the northern SCS enables us to investigate the 3D propagation of continental breakup and the interactions between tectonic extension and magmatism. The top of acoustic basement can be consistently interpreted through all of our seismic survey and reveal various types of reliefs and nature from hyperextended continental crust to oceanic crust. In the basement, deep-penetrated seismic profiles present series of densely sub-parallel high-amplitude reflections that occurred within the lower crust. The lower boundary of these reflections is often characterized by double continual and high reflections interpreted as the Moho. Across the COT, the basement structure is characterized by: 1) Series of tilted blocks bounded by high angle faults on the Distal High and filled by syn-tectonic sedimentary wedges, 2) Rounded mounds of the basement with chaotic seismic reflection and sedimentary onlaps on these structures, 3) Series of ridges delimited by high-angle normal faults with no sedimentary wedge on the first oceanic crust.
Based on the detail stratigraphic framework constraint by drilling results from IODP Expeditions, the nature and timing of formation of these basement highs can be investigated. Some of these highs are limited by extensional faults while the nature of mounded structures located on the thinnest continental crust remain mysterious. Our detailed analyses emphasize the occurrence and local control of syn-rift magmatism in order to build such structures. At larger scale, the hyperextended continental crust is characterized by significant 3D morphological variations both observed on dip and strike profiles. In contrast, the initial oceanic crust is characterized by a more homogenous structure and consistently juxtaposed to continental crust over a sharp and narrow zone.
How to cite: Lei, C., Ren, J., Mohn, G., Nirrengarten, M., Pang, X., Zheng, J., and Liu, B.: 3D structures and sedimentary infill across the continent-ocean transition of the northern South China Sea: constraint by the drilling results from IODP Expeditions 367, 368 and 368X, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-378, https://doi.org/10.5194/egusphere-egu2020-378, 2020.
EGU2020-4998 | Displays | TS6.4
Mapping the continent-ocean transition in the Eastern Black Sea BasinTim Minshull, Vanessa Monteleone, Hector Marin Moreno, and Donna Shillington
The transition from continental to oceanic crust at rifted margins is characterised by changes in a variety of parameters including crustal thickness, basement morphology and magnetisation. Rifted margins also vary significantly in the degree of magmatism that is associated with breakup. The Eastern Black Sea Basin formed by backarc extension in late Cretaceous to early Cenozoic times, by the rotation of Shatsky Ridge relative to the Mid Black Sea High. Wide-angle seismic data show that anomalously thick oceanic crust is present in the southeast of the basin, while further to the northwest the crust is thinner in the centre of the basin. This thinner crust has seismic velocities that are anomalously low for oceanic crust, but is significantly magnetised and has a similar basement morphology to the thicker crust to the southeast. We synthesise constraints from wide-angle seismic data, magnetic anomaly data and new long-offset seismic reflection data into an integrated interpretation of the location and nature of the continent-ocean transition within the basin. Northwest to southeast along the axis of the basin, we infer a series of transitions from mildly stretched continental crust at the Mid Black Sea High to hyper-thinned continental crust, then to thin oceanic crust, and finally to anomalously thick oceanic crust. We explore the geodynamic processes that may have led to this configuration.
How to cite: Minshull, T., Monteleone, V., Marin Moreno, H., and Shillington, D.: Mapping the continent-ocean transition in the Eastern Black Sea Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4998, https://doi.org/10.5194/egusphere-egu2020-4998, 2020.
The transition from continental to oceanic crust at rifted margins is characterised by changes in a variety of parameters including crustal thickness, basement morphology and magnetisation. Rifted margins also vary significantly in the degree of magmatism that is associated with breakup. The Eastern Black Sea Basin formed by backarc extension in late Cretaceous to early Cenozoic times, by the rotation of Shatsky Ridge relative to the Mid Black Sea High. Wide-angle seismic data show that anomalously thick oceanic crust is present in the southeast of the basin, while further to the northwest the crust is thinner in the centre of the basin. This thinner crust has seismic velocities that are anomalously low for oceanic crust, but is significantly magnetised and has a similar basement morphology to the thicker crust to the southeast. We synthesise constraints from wide-angle seismic data, magnetic anomaly data and new long-offset seismic reflection data into an integrated interpretation of the location and nature of the continent-ocean transition within the basin. Northwest to southeast along the axis of the basin, we infer a series of transitions from mildly stretched continental crust at the Mid Black Sea High to hyper-thinned continental crust, then to thin oceanic crust, and finally to anomalously thick oceanic crust. We explore the geodynamic processes that may have led to this configuration.
How to cite: Minshull, T., Monteleone, V., Marin Moreno, H., and Shillington, D.: Mapping the continent-ocean transition in the Eastern Black Sea Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4998, https://doi.org/10.5194/egusphere-egu2020-4998, 2020.
EGU2020-637 | Displays | TS6.4
The seismic structure of the West Iberian continent-ocean transitionIrene Merino Perez, Manel Prada, César R. Ranero, Valenti Sallares, Ingo Grevemeyer, Alcinoe Calahorrano, Alejandra L. Cameselle, and Marta Neres
The West Iberian margin has been studied since the 1980 to mid 1990’s when some of the most emblematic geophysical cross-sections and borehole samples were collected in the area. Despite of this wealth of information, there is little understanding on how the transitional domain, commonly interpreted as exhumed mantle, transitions into oceanic crust. The lack of appropriate geophysical data makes the nature of the basement, and thus the origin of the structures, still debated. Also, the mechanisms of thinning occurring in the continental-ocean transition are poorly constrained due to data quality or methodological limitations.
Here, we present spatially coincident multichannel seismic (MCS) and wide angle seismic (WAS) data collected during the FRAME-2018 survey across the Tagus Abyssal Plain, South-West the Iberian margin. The MCS data were recorded with a 6-km-long streamer, while 17 Ocean Bottom Seismometers and 18 Ocean Bottom Hydrophones were deployed each 10 km and used to record the WAS data, both along a 350 km-long, E-W trending profile located at 38º N, and crossing the Tagus Abyssal Plain.
The MCS time-migrated seismic section provides a high-quality image from which we interpret the tectono-stratigraphic structure from the continent to the ocean, ~180 km eastwards from the J-anomaly. The seismic image shows three main domains: a first domain closest to the continent with tilted fault blocks with possible syn-rift sediments and a possibly continental basement. In this domain, there is high-reflectivity reflections at 1-2 s TWT from the top of the basement. Then, westwards, a domain displays gentle basement-top topography, high intra-basement complex reflectivity and deep-penetrating landward dipping reflections. No clear Moho reflection occurs. A third domain to the west correspond to a very smooth and highly reflective top of basement coincident with the magnetic J-anomaly. Further west top basement shows an irregular topography with comparatively numerous short tilted blocks.
We use refracted and reflected travel-times (TT) WAS and MCS field data to jointly invert for P-wave velocity (Vp) and the geometry of interfaces in the sediment, the top of the basement, and Moho. Combining MCS TT with WAS TT allows retrieving the Vp structure of the shallow part of the model and the geometry of seismic interfaces with a level of resolution that is beyond what can be obtained with WAS TT alone. The result of this joint WAS-MCS tomography is a Vp model of the margin that is fully consistent with the MCS image along the whole profile. The preliminary models show that the crustal structure is laterally more complex than previously modelled, presenting sharp boundaries between at least 5 different domains from the base of the continental slope to the ocean basin.
How to cite: Merino Perez, I., Prada, M., R. Ranero, C., Sallares, V., Grevemeyer, I., Calahorrano, A., L. Cameselle, A., and Neres, M.: The seismic structure of the West Iberian continent-ocean transition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-637, https://doi.org/10.5194/egusphere-egu2020-637, 2020.
The West Iberian margin has been studied since the 1980 to mid 1990’s when some of the most emblematic geophysical cross-sections and borehole samples were collected in the area. Despite of this wealth of information, there is little understanding on how the transitional domain, commonly interpreted as exhumed mantle, transitions into oceanic crust. The lack of appropriate geophysical data makes the nature of the basement, and thus the origin of the structures, still debated. Also, the mechanisms of thinning occurring in the continental-ocean transition are poorly constrained due to data quality or methodological limitations.
Here, we present spatially coincident multichannel seismic (MCS) and wide angle seismic (WAS) data collected during the FRAME-2018 survey across the Tagus Abyssal Plain, South-West the Iberian margin. The MCS data were recorded with a 6-km-long streamer, while 17 Ocean Bottom Seismometers and 18 Ocean Bottom Hydrophones were deployed each 10 km and used to record the WAS data, both along a 350 km-long, E-W trending profile located at 38º N, and crossing the Tagus Abyssal Plain.
The MCS time-migrated seismic section provides a high-quality image from which we interpret the tectono-stratigraphic structure from the continent to the ocean, ~180 km eastwards from the J-anomaly. The seismic image shows three main domains: a first domain closest to the continent with tilted fault blocks with possible syn-rift sediments and a possibly continental basement. In this domain, there is high-reflectivity reflections at 1-2 s TWT from the top of the basement. Then, westwards, a domain displays gentle basement-top topography, high intra-basement complex reflectivity and deep-penetrating landward dipping reflections. No clear Moho reflection occurs. A third domain to the west correspond to a very smooth and highly reflective top of basement coincident with the magnetic J-anomaly. Further west top basement shows an irregular topography with comparatively numerous short tilted blocks.
We use refracted and reflected travel-times (TT) WAS and MCS field data to jointly invert for P-wave velocity (Vp) and the geometry of interfaces in the sediment, the top of the basement, and Moho. Combining MCS TT with WAS TT allows retrieving the Vp structure of the shallow part of the model and the geometry of seismic interfaces with a level of resolution that is beyond what can be obtained with WAS TT alone. The result of this joint WAS-MCS tomography is a Vp model of the margin that is fully consistent with the MCS image along the whole profile. The preliminary models show that the crustal structure is laterally more complex than previously modelled, presenting sharp boundaries between at least 5 different domains from the base of the continental slope to the ocean basin.
How to cite: Merino Perez, I., Prada, M., R. Ranero, C., Sallares, V., Grevemeyer, I., Calahorrano, A., L. Cameselle, A., and Neres, M.: The seismic structure of the West Iberian continent-ocean transition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-637, https://doi.org/10.5194/egusphere-egu2020-637, 2020.
EGU2020-2658 | Displays | TS6.4 | Highlight | Stephan Mueller Medal Lecture
On spreading modes and magma supply at slow and ultraslow mid-ocean ridgesMathilde Cannat
The availability of magma is a key to understand mid-ocean ridge tectonics, and specifically the distribution of the two contrasted spreading modes displayed at slow and ultraslow ridges (volcanically-dominated, and detachment fault-dominated). The part of the plate divergence that is not accommodated by magma emplaced as gabbros or basaltic dikes is taken up by normal faults that exhume upper mantle rocks, in many instances all the way to the seafloor.
Magma is, however, more than just a material that is, or is not, available to fill the gap between two diverging plates. It is the principal carrier of heat into the axial region and as such it may contribute to thin the axial lithosphere, hence diminishing the volume of new plate material formed at each increment of plate separation. Magma as a heat carrier may also, however, if emplaced in the more permeable upper lithosphere, attract and fuel vigorous hydrothermal circulation and contribute instead to overcooling the newly formed upper plate (Cochran and Buck, JGR 2001).
Magma is also a powerful agent for strain localization in the axial region: magma and melt-crystal mushes are weak; gabbros that crystallize from these melts are weaker than peridotites because they contain abundant plagioclase; and hydrothermally-altered gabbros, and gabbro-peridotite mixtures, are weaker than serpentinites because of minerals such as chlorite and talc. As a result, detachment-dominated ridge regions that receive very little magma probably have a stronger axial lithosphere than detachment-dominated ridge regions that receive a little more magma.
Because magma has this triple role (building material, heat carrier, and strain localization agent), and because it is highly mobile (through porosity, along permeability barriers, in fractures and dikes), it is likely that variations in magma supply to the ridge, in time and space, and variations in where this magma gets emplaced in the axial plate, cause a greater diversity of spreading modes, and of the resulting slow and ultraslow lithosphere composition and structure, than suggested by the first order dichotomy between volcanically-dominated and detachment-dominated spreading.
In this talk I illustrate these points using results of recent studies at the Mid-Atlantic and Southwest Indian ridges.
How to cite: Cannat, M.: On spreading modes and magma supply at slow and ultraslow mid-ocean ridges, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2658, https://doi.org/10.5194/egusphere-egu2020-2658, 2020.
The availability of magma is a key to understand mid-ocean ridge tectonics, and specifically the distribution of the two contrasted spreading modes displayed at slow and ultraslow ridges (volcanically-dominated, and detachment fault-dominated). The part of the plate divergence that is not accommodated by magma emplaced as gabbros or basaltic dikes is taken up by normal faults that exhume upper mantle rocks, in many instances all the way to the seafloor.
Magma is, however, more than just a material that is, or is not, available to fill the gap between two diverging plates. It is the principal carrier of heat into the axial region and as such it may contribute to thin the axial lithosphere, hence diminishing the volume of new plate material formed at each increment of plate separation. Magma as a heat carrier may also, however, if emplaced in the more permeable upper lithosphere, attract and fuel vigorous hydrothermal circulation and contribute instead to overcooling the newly formed upper plate (Cochran and Buck, JGR 2001).
Magma is also a powerful agent for strain localization in the axial region: magma and melt-crystal mushes are weak; gabbros that crystallize from these melts are weaker than peridotites because they contain abundant plagioclase; and hydrothermally-altered gabbros, and gabbro-peridotite mixtures, are weaker than serpentinites because of minerals such as chlorite and talc. As a result, detachment-dominated ridge regions that receive very little magma probably have a stronger axial lithosphere than detachment-dominated ridge regions that receive a little more magma.
Because magma has this triple role (building material, heat carrier, and strain localization agent), and because it is highly mobile (through porosity, along permeability barriers, in fractures and dikes), it is likely that variations in magma supply to the ridge, in time and space, and variations in where this magma gets emplaced in the axial plate, cause a greater diversity of spreading modes, and of the resulting slow and ultraslow lithosphere composition and structure, than suggested by the first order dichotomy between volcanically-dominated and detachment-dominated spreading.
In this talk I illustrate these points using results of recent studies at the Mid-Atlantic and Southwest Indian ridges.
How to cite: Cannat, M.: On spreading modes and magma supply at slow and ultraslow mid-ocean ridges, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2658, https://doi.org/10.5194/egusphere-egu2020-2658, 2020.
EGU2020-14296 | Displays | TS6.4
Tectono-magmatic and thermal evolution of the SE China margin-NW Palawan breakupGeoffroy Mohn, Michael Nirrengarten, Andrea Schito, Nick Kusznir, Sveva Corrado, Stephen Bowden, Manuel Pubellier, François Sapin, and Hans-Christian Larsen
Continent Ocean Transitions (COTs) record the processes leading to continental breakup and localized oceanic accretion initiation. The recent IODP Expeditions 367-368 and 368X at the SE China margins combined with high quality multi-channel seismic profiles provide a unique dataset to explore the tectono-magmatic and thermal evolution from final rifting to early seafloor spreading. To investigate these issues, we developed a multi-disciplinary approach combining reflection seismic interpretations with geophysical quantitative analysis calibrated thanks to drilling results, from which we measured and modelled the thermal maturity in pre-/syn- to post-rift sediments.
Drilling results show that the transition from the most thinned continental crust to new, largely igneous crust is narrow (~20 km). During final rifting, decompression melting forming Mid-Ocean Ridge type magmatism emplaced within thinned continental crust as deep intrusions and shallow extrusive rocks concomitant with continued deformation by extensional faults. The initial igneous crust of the conjugate margins is asymmetric in width and morphology. The wider and faulted newly accreted domain on the SE China side indicates that magmatic accretion was associated with tectonic faulting during the formation of initial oceanic lithosphere, a feature not observed on the conjugate Palawan side. We suggest that deformation and magmatism were not symmetrically distributed between the conjugate margins during the initiation of seafloor spreading but evolved asymmetrically prior to the spreading ridge stabilising.
Organic matter from post-rift sediments has low thermal maturities due to limited burial and the absence of late post-rift magmatism. In contrast, pre to syn-rift sediments show significant variability in thermal maturities across the COT. Localised high thermal maturities for the pre- to syn-rift sediments requires that significant additional heat be imparted at shallow depths during breakup, likely related to magmatic intrusion or subsurface expressions of volcanism. The heterogeneous variation in thermal maturity observed across the COT reflects localised thermal perturbations caused by magmatic additions.
How to cite: Mohn, G., Nirrengarten, M., Schito, A., Kusznir, N., Corrado, S., Bowden, S., Pubellier, M., Sapin, F., and Larsen, H.-C.: Tectono-magmatic and thermal evolution of the SE China margin-NW Palawan breakup, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14296, https://doi.org/10.5194/egusphere-egu2020-14296, 2020.
Continent Ocean Transitions (COTs) record the processes leading to continental breakup and localized oceanic accretion initiation. The recent IODP Expeditions 367-368 and 368X at the SE China margins combined with high quality multi-channel seismic profiles provide a unique dataset to explore the tectono-magmatic and thermal evolution from final rifting to early seafloor spreading. To investigate these issues, we developed a multi-disciplinary approach combining reflection seismic interpretations with geophysical quantitative analysis calibrated thanks to drilling results, from which we measured and modelled the thermal maturity in pre-/syn- to post-rift sediments.
Drilling results show that the transition from the most thinned continental crust to new, largely igneous crust is narrow (~20 km). During final rifting, decompression melting forming Mid-Ocean Ridge type magmatism emplaced within thinned continental crust as deep intrusions and shallow extrusive rocks concomitant with continued deformation by extensional faults. The initial igneous crust of the conjugate margins is asymmetric in width and morphology. The wider and faulted newly accreted domain on the SE China side indicates that magmatic accretion was associated with tectonic faulting during the formation of initial oceanic lithosphere, a feature not observed on the conjugate Palawan side. We suggest that deformation and magmatism were not symmetrically distributed between the conjugate margins during the initiation of seafloor spreading but evolved asymmetrically prior to the spreading ridge stabilising.
Organic matter from post-rift sediments has low thermal maturities due to limited burial and the absence of late post-rift magmatism. In contrast, pre to syn-rift sediments show significant variability in thermal maturities across the COT. Localised high thermal maturities for the pre- to syn-rift sediments requires that significant additional heat be imparted at shallow depths during breakup, likely related to magmatic intrusion or subsurface expressions of volcanism. The heterogeneous variation in thermal maturity observed across the COT reflects localised thermal perturbations caused by magmatic additions.
How to cite: Mohn, G., Nirrengarten, M., Schito, A., Kusznir, N., Corrado, S., Bowden, S., Pubellier, M., Sapin, F., and Larsen, H.-C.: Tectono-magmatic and thermal evolution of the SE China margin-NW Palawan breakup, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14296, https://doi.org/10.5194/egusphere-egu2020-14296, 2020.
EGU2020-19478 | Displays | TS6.4
Tectonic evolution of the East Vietnam-Southwest Borneo margin breakupSung-Ping Chang, Manuel Pubellier, Matthias Delescluse, Michael Nirrengarten, Geoffroy Mohn, Nicolas Chamot-Rooke, and Yan Qiu
We investigate the extensional processes occurring during the rifting of a marginal basin to use long-streamer multichannel seismic transects across the entire southwestern South China Sea (SCS). The basin is characterized by space and time propagating breakup followed by seafloor spreading during Cenozoic. Stretching and thinning of the continental crust were accompanied by ubiquitous large extensional detachment faults. In the proximal E Vietnam margin, rifted basins are filled with lower syn-rift sedimentation (syn-rift I). These sediments pinch out towards the distal margin. On the conjugate NW Borneo margin, the same coeval syn-rift I is truncated at the top, suggesting a period of crustal uplift affecting solely the southern margin. To illustrate the pre-breakup geometries of the southwestern SCS margins, we restore two conjugate sections near the first oceanic magnetic anomaly (20.1 Ma, C6n). The result highlights a thick pre-breakup succession (syn-rift II) offset slightly by several seaward-dipping normal faults above the exhumed basement. The magmatism intruded this hyper-extended basin and proceeded to break up the continental lithosphere eventually. The COT configuration not only illustrates asymmetrical hyper-extension but also appears in map view to have a rhombic shape controlled by N-S abrupt segments and E-W hyper-extended ones. The spatial variation of the crustal structures suggests an initial N-S extension contemporaneous with the first phase of seafloor spreading in the eastern SCS. The extensional direction significantly changed later (circa 23Ma) to NW-SE in relation to a well-documented ridge jump. Interestingly, this change in the direction of opening is coeval with the collision and the counterclockwise rotation in Borneo, thus suggesting that those events are linked. Therefore, we propose that collision was responsible for significant change in the far-field stress and influenced the extensional regime in the SCS.
How to cite: Chang, S.-P., Pubellier, M., Delescluse, M., Nirrengarten, M., Mohn, G., Chamot-Rooke, N., and Qiu, Y.: Tectonic evolution of the East Vietnam-Southwest Borneo margin breakup, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19478, https://doi.org/10.5194/egusphere-egu2020-19478, 2020.
We investigate the extensional processes occurring during the rifting of a marginal basin to use long-streamer multichannel seismic transects across the entire southwestern South China Sea (SCS). The basin is characterized by space and time propagating breakup followed by seafloor spreading during Cenozoic. Stretching and thinning of the continental crust were accompanied by ubiquitous large extensional detachment faults. In the proximal E Vietnam margin, rifted basins are filled with lower syn-rift sedimentation (syn-rift I). These sediments pinch out towards the distal margin. On the conjugate NW Borneo margin, the same coeval syn-rift I is truncated at the top, suggesting a period of crustal uplift affecting solely the southern margin. To illustrate the pre-breakup geometries of the southwestern SCS margins, we restore two conjugate sections near the first oceanic magnetic anomaly (20.1 Ma, C6n). The result highlights a thick pre-breakup succession (syn-rift II) offset slightly by several seaward-dipping normal faults above the exhumed basement. The magmatism intruded this hyper-extended basin and proceeded to break up the continental lithosphere eventually. The COT configuration not only illustrates asymmetrical hyper-extension but also appears in map view to have a rhombic shape controlled by N-S abrupt segments and E-W hyper-extended ones. The spatial variation of the crustal structures suggests an initial N-S extension contemporaneous with the first phase of seafloor spreading in the eastern SCS. The extensional direction significantly changed later (circa 23Ma) to NW-SE in relation to a well-documented ridge jump. Interestingly, this change in the direction of opening is coeval with the collision and the counterclockwise rotation in Borneo, thus suggesting that those events are linked. Therefore, we propose that collision was responsible for significant change in the far-field stress and influenced the extensional regime in the SCS.
How to cite: Chang, S.-P., Pubellier, M., Delescluse, M., Nirrengarten, M., Mohn, G., Chamot-Rooke, N., and Qiu, Y.: Tectonic evolution of the East Vietnam-Southwest Borneo margin breakup, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19478, https://doi.org/10.5194/egusphere-egu2020-19478, 2020.
EGU2020-7223 | Displays | TS6.4
The seismic structure of the Galicia Interior Basin from new seismic images: Implications for the West Iberia margin formationAlejandra L. Cameselle, César R. Ranero, Luis M. Pinheiro, and Valentí Sallarès
The Galicia Interior Basin (GIB) off West Iberia, is considered an aborted rift formed in the context of opening of the North Atlantic rift system. Despite the Galicia Interior Basin being located in one of the best studied examples of magma-poor rifted margins (i.e., the West Iberia continental margin), its 3D structural variability and its role during continental rifting in the regional geodynamic context remains poorly understood. In this sense, Galicia Interior Basin represents the necessary link to understand the mechanisms of extension from the little extended shelf to the areas where continental breakup finally occurred.
Here we present new multichannel seismic data collected during FRAME cruise carried out onboard the Spanish “R/V Sarmiento de Gamboa” during summer 2018. The structure of the Galicia Interior Basin has been imaged using a 6-km-long solid-state digital multichannel streamer with 480 channels and two G-II gun arrays with a total volume of 3920 cu.in. fired every 37.5 m at 140 bar (2000 p.s.i.) pressure. The new post-stack time migrations of multichannel seismic profiles show the complex basement structure and deep sedimentary units across the region with an unprecedented detail. Additionally, we used state-of-the-art techniques to reprocessed a complementary set of vintage multichannel seismic profiles collected across the GIB. The integration of new and reprocessed seismic profiles provides the opportunity to study for the first time the 3D tectonic crustal-scale structure of the GIB.
Our images reveal syn- and post-rift sediment, tilted fault blocks, well-defined top-of-the-basement reflections, and also intra-basement and Moho reflections that offer new information about the variations in tectonic structural style during rifting. The data display an asymmetric structure and variations in the amount and distribution of crustal extension across the GIB. At the center of the basin – about 150 km landward from the continent-ocean transition – the continental basement has been thinned to 6-8 km associated with listric (in two-way travel time) normal faults without final breakup. Further offshore, the continental basement thickens again until ~20 km under the Galicia Bank, before entering the Deep Galicia Margin where continental basement thins laterally continuously to mantle exhumation and final breakup. The observed crustal structure and margin configuration represents a challenge to current models of rifting and continent-ocean transition structure, and allow to speculate on the possible causes for rift failure at the GIB in the context of the opening of the West Iberia margin.
How to cite: Cameselle, A. L., Ranero, C. R., Pinheiro, L. M., and Sallarès, V.: The seismic structure of the Galicia Interior Basin from new seismic images: Implications for the West Iberia margin formation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7223, https://doi.org/10.5194/egusphere-egu2020-7223, 2020.
The Galicia Interior Basin (GIB) off West Iberia, is considered an aborted rift formed in the context of opening of the North Atlantic rift system. Despite the Galicia Interior Basin being located in one of the best studied examples of magma-poor rifted margins (i.e., the West Iberia continental margin), its 3D structural variability and its role during continental rifting in the regional geodynamic context remains poorly understood. In this sense, Galicia Interior Basin represents the necessary link to understand the mechanisms of extension from the little extended shelf to the areas where continental breakup finally occurred.
Here we present new multichannel seismic data collected during FRAME cruise carried out onboard the Spanish “R/V Sarmiento de Gamboa” during summer 2018. The structure of the Galicia Interior Basin has been imaged using a 6-km-long solid-state digital multichannel streamer with 480 channels and two G-II gun arrays with a total volume of 3920 cu.in. fired every 37.5 m at 140 bar (2000 p.s.i.) pressure. The new post-stack time migrations of multichannel seismic profiles show the complex basement structure and deep sedimentary units across the region with an unprecedented detail. Additionally, we used state-of-the-art techniques to reprocessed a complementary set of vintage multichannel seismic profiles collected across the GIB. The integration of new and reprocessed seismic profiles provides the opportunity to study for the first time the 3D tectonic crustal-scale structure of the GIB.
Our images reveal syn- and post-rift sediment, tilted fault blocks, well-defined top-of-the-basement reflections, and also intra-basement and Moho reflections that offer new information about the variations in tectonic structural style during rifting. The data display an asymmetric structure and variations in the amount and distribution of crustal extension across the GIB. At the center of the basin – about 150 km landward from the continent-ocean transition – the continental basement has been thinned to 6-8 km associated with listric (in two-way travel time) normal faults without final breakup. Further offshore, the continental basement thickens again until ~20 km under the Galicia Bank, before entering the Deep Galicia Margin where continental basement thins laterally continuously to mantle exhumation and final breakup. The observed crustal structure and margin configuration represents a challenge to current models of rifting and continent-ocean transition structure, and allow to speculate on the possible causes for rift failure at the GIB in the context of the opening of the West Iberia margin.
How to cite: Cameselle, A. L., Ranero, C. R., Pinheiro, L. M., and Sallarès, V.: The seismic structure of the Galicia Interior Basin from new seismic images: Implications for the West Iberia margin formation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7223, https://doi.org/10.5194/egusphere-egu2020-7223, 2020.
EGU2020-5559 | Displays | TS6.4
Imaging the Deep Galicia margin using three-dimensional full waveform inversionBhargav Boddupalli, Tim Minshull, Joanna Morgan, and Gaye Bayrakci
Imaging of hyperextended zone and exhumed continental mantle rocks can improve our understanding of the tectonics of the final stages of rifting. In the Deep Galicia margin, the upper and lower crust are coupled allowing the normal faults to cut through the brittle crust and penetrate to the mantle leading to serpentinization of the mantle. Localized extensional forces caused extreme thinning and elongation of crystalline continental crust causing the continental blocks to slip over a lithospheric-scale detachment fault called the S-reflector.
A high-resolution velocity model obtained using seismic full waveform inversion gives us deeper insights into the rifting process. In this study, we present results from three dimensional acoustic full waveform inversion performed using wide-angle seismic data acquired in the deep water environments of the Deep Galicia margin using ocean bottom seismometers. We performed full waveform inversion in the time domain, starting with a velocity model obtained using travel-time tomography, of dimensions 78.5 km x 22.1 km and depth 12 km. The high-resolution modelling shows short-wavelength variations in the velocity, adding details to the travel-time model. We superimposed our final model, converted to two-way time, on pre-stack time-migrated three-dimensional reflection data from the same survey. Compared to the starting model, our model shows improved alignment of the velocity variations along the steeply dipping normal faults and a sharp velocity contrast across the S-reflector. We validated our result using checkerboard tests, by tracking changes in phases of the first arrivals during the inversion and by comparing the observed and the synthetic waveforms. We observe a clear evidence for preferential serpentinization (45 %) of the mantle with lower velocities in the mantle correlating with the fault intersections with the S-reflector.
How to cite: Boddupalli, B., Minshull, T., Morgan, J., and Bayrakci, G.: Imaging the Deep Galicia margin using three-dimensional full waveform inversion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5559, https://doi.org/10.5194/egusphere-egu2020-5559, 2020.
Imaging of hyperextended zone and exhumed continental mantle rocks can improve our understanding of the tectonics of the final stages of rifting. In the Deep Galicia margin, the upper and lower crust are coupled allowing the normal faults to cut through the brittle crust and penetrate to the mantle leading to serpentinization of the mantle. Localized extensional forces caused extreme thinning and elongation of crystalline continental crust causing the continental blocks to slip over a lithospheric-scale detachment fault called the S-reflector.
A high-resolution velocity model obtained using seismic full waveform inversion gives us deeper insights into the rifting process. In this study, we present results from three dimensional acoustic full waveform inversion performed using wide-angle seismic data acquired in the deep water environments of the Deep Galicia margin using ocean bottom seismometers. We performed full waveform inversion in the time domain, starting with a velocity model obtained using travel-time tomography, of dimensions 78.5 km x 22.1 km and depth 12 km. The high-resolution modelling shows short-wavelength variations in the velocity, adding details to the travel-time model. We superimposed our final model, converted to two-way time, on pre-stack time-migrated three-dimensional reflection data from the same survey. Compared to the starting model, our model shows improved alignment of the velocity variations along the steeply dipping normal faults and a sharp velocity contrast across the S-reflector. We validated our result using checkerboard tests, by tracking changes in phases of the first arrivals during the inversion and by comparing the observed and the synthetic waveforms. We observe a clear evidence for preferential serpentinization (45 %) of the mantle with lower velocities in the mantle correlating with the fault intersections with the S-reflector.
How to cite: Boddupalli, B., Minshull, T., Morgan, J., and Bayrakci, G.: Imaging the Deep Galicia margin using three-dimensional full waveform inversion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5559, https://doi.org/10.5194/egusphere-egu2020-5559, 2020.
EGU2020-5060 | Displays | TS6.4
Magma at rifted margins: when, where and how much?Gianreto Manatschal, Simon Tomasi, Nick Kusznir, Cuimei Zhang, Daniel Sauter, Chao Peng, Marc Ulrich, and Pauline Chenin
Rifted margins are either classified as volcanic vs. non-volcanic or magma-rich vs. magma-poor. While such classifications are essentially based on the magmatic budget observed at rifted margins, they do not take into account the relative timing of magmatic activity with respect to tectonic activity, i.e. when and where first magma forms. High-quality reflection and refraction seismic surveys combined with drill hole data and field observations show that such a binary classification is unable to satisfactorily describe the magmatic processes related to rifting and lithospheric breakup.
Our results show that the magmatic evolution of rifted margins is complex and cannot be characterized based on the volume of observed magma alone. On one hand, so-called “non-volcanic” margins are not amagmatic, as shown by the results of ODP drilling along the Iberia-Newfoundland rifted margins and field observations in fossil analogues. On the other hand, magma-rich margins, such as the Norwegian, NW Australian or the Namibia rifted margins show evidence for hyper-extension prior to magmatic activity. These observations suggest that the magmatic budget and the timing of magma production do not only depend on the amount of crustal/lithospheric extension but also on the composition and temperature of the decompressing mantle and the occurrence of mantle plumes. However, the fact that the magmatic budget may change very abruptly along strike is difficult to reconcile with the occurrence of plumes or other deep-seated, large-scale mantle phenomena only. These observations prompted us to re-examine the magmatic and tectonic processes and their interactions during rifting and lithospheric breakup and how far inheritance, rifting rates and plume-related activity may control the magmatic budget during rifting.
In our presentation we will review results from the global margins and will discuss the structural and magmatic evolution of so-called magma-rich, magma-poor and -intermediate rifted margins. In particular, we will try to examine when, where and how much magma forms during rifting and lithospheric breakup. The key questions that we aim to address are: 1) to what extent is melting directly related to decompression and extension , 2) how far is the magmatic budget controlled by inherited mantle composition, and 3) how important is magma storage in the mantle lithosphere during initial stages of magma production. Answering to these questions will allow to discuss to what extent the magmatic evolution of rift systems reflect the interplay between inheritance (innate/"genetic code"), actual physical processes (acquired/external factors) and plume induced processes.
How to cite: Manatschal, G., Tomasi, S., Kusznir, N., Zhang, C., Sauter, D., Peng, C., Ulrich, M., and Chenin, P.: Magma at rifted margins: when, where and how much?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5060, https://doi.org/10.5194/egusphere-egu2020-5060, 2020.
Rifted margins are either classified as volcanic vs. non-volcanic or magma-rich vs. magma-poor. While such classifications are essentially based on the magmatic budget observed at rifted margins, they do not take into account the relative timing of magmatic activity with respect to tectonic activity, i.e. when and where first magma forms. High-quality reflection and refraction seismic surveys combined with drill hole data and field observations show that such a binary classification is unable to satisfactorily describe the magmatic processes related to rifting and lithospheric breakup.
Our results show that the magmatic evolution of rifted margins is complex and cannot be characterized based on the volume of observed magma alone. On one hand, so-called “non-volcanic” margins are not amagmatic, as shown by the results of ODP drilling along the Iberia-Newfoundland rifted margins and field observations in fossil analogues. On the other hand, magma-rich margins, such as the Norwegian, NW Australian or the Namibia rifted margins show evidence for hyper-extension prior to magmatic activity. These observations suggest that the magmatic budget and the timing of magma production do not only depend on the amount of crustal/lithospheric extension but also on the composition and temperature of the decompressing mantle and the occurrence of mantle plumes. However, the fact that the magmatic budget may change very abruptly along strike is difficult to reconcile with the occurrence of plumes or other deep-seated, large-scale mantle phenomena only. These observations prompted us to re-examine the magmatic and tectonic processes and their interactions during rifting and lithospheric breakup and how far inheritance, rifting rates and plume-related activity may control the magmatic budget during rifting.
In our presentation we will review results from the global margins and will discuss the structural and magmatic evolution of so-called magma-rich, magma-poor and -intermediate rifted margins. In particular, we will try to examine when, where and how much magma forms during rifting and lithospheric breakup. The key questions that we aim to address are: 1) to what extent is melting directly related to decompression and extension , 2) how far is the magmatic budget controlled by inherited mantle composition, and 3) how important is magma storage in the mantle lithosphere during initial stages of magma production. Answering to these questions will allow to discuss to what extent the magmatic evolution of rift systems reflect the interplay between inheritance (innate/"genetic code"), actual physical processes (acquired/external factors) and plume induced processes.
How to cite: Manatschal, G., Tomasi, S., Kusznir, N., Zhang, C., Sauter, D., Peng, C., Ulrich, M., and Chenin, P.: Magma at rifted margins: when, where and how much?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5060, https://doi.org/10.5194/egusphere-egu2020-5060, 2020.
EGU2020-8215 | Displays | TS6.4
Emplacement mechanisms of a dyke swarm across the Brittle-Ductile transitionHans Jørgen Kjøll, Olivier Galland, Loic Labrousse, and Torgeir B. Andersen
Dykes are the main magma transport pathways through the Earth’s crust and, in volcanic rifts, they are considered the main mechanism to accommodate tectonic extension. Most models consider dykes as hydro-fractures propagating as brittle tensile, mode I cracks opening perpendicular to the least principal stress. This implies that dykes emplaced in rifts are expected to be sub-vertical and accommodate crustal extension. Here we present detailed field observations of a well-exposed dyke swarm that formed near the brittle-ductile transition at a magma-rich rifted margin during opening of the Iapetus Ocean. It was related to a ca 600 million year-old large igneous province. Our observations show that dykes were not systematically emplaced by purely brittle deformation and that dyke orientation may differ from the typical mode 1 pattern. Distinct dyke morphologies related to different emplacement mechanisms have been recognized including: 1) Brittle dykes that exhibit straight contacts with the host rock, sharp tips, and en-echelon segments with bridges exhibiting angular fragments; 2) Brittle-ductile dykes with undulating contacts, rounded tips, folding of the host rock and contemporaneous brittle and ductile features; 3) Ductile “dykes” with rounded shapes and mingling between partially molten host rock and the intruding mafic magma. The brittle dykes exhibit two distinct orientations separated by ~30° that are mutually cross-cutting, demonstrating that the dyke swam did not consist of only vertical sheets oriented perpendicular to regional extension, as expected in rifts. By using the host-rock layers as markers, a kinematic restoration to quantify the average strain accommodating the emplacement of the dyke complex was performed. This strain estimate shows that the dyke swarm accommodated >100% horizontal extension, but also 27% vertical thickening. This suggests that the magma influx rate was higher than the tectonic stretching rate, which imply that magma was emplaced forcefully, as supported by field observations of the host-rock deformation. Finally, observations of typical “brittle” dykes that were subsequently deformed by ductile mechanisms as well as dykes that were emplaced by purely ductile mechanisms suggest that the fast emplacement of the dyke swarm triggered a rapid shallowing of the brittle-ductile transition. The abrupt dyke emplacement and associated heating resulted in weakening of the crust that probably facilitated the continental break-up, which culminated with opening of the Iapetus Ocean.
How to cite: Kjøll, H. J., Galland, O., Labrousse, L., and Andersen, T. B.: Emplacement mechanisms of a dyke swarm across the Brittle-Ductile transition , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8215, https://doi.org/10.5194/egusphere-egu2020-8215, 2020.
Dykes are the main magma transport pathways through the Earth’s crust and, in volcanic rifts, they are considered the main mechanism to accommodate tectonic extension. Most models consider dykes as hydro-fractures propagating as brittle tensile, mode I cracks opening perpendicular to the least principal stress. This implies that dykes emplaced in rifts are expected to be sub-vertical and accommodate crustal extension. Here we present detailed field observations of a well-exposed dyke swarm that formed near the brittle-ductile transition at a magma-rich rifted margin during opening of the Iapetus Ocean. It was related to a ca 600 million year-old large igneous province. Our observations show that dykes were not systematically emplaced by purely brittle deformation and that dyke orientation may differ from the typical mode 1 pattern. Distinct dyke morphologies related to different emplacement mechanisms have been recognized including: 1) Brittle dykes that exhibit straight contacts with the host rock, sharp tips, and en-echelon segments with bridges exhibiting angular fragments; 2) Brittle-ductile dykes with undulating contacts, rounded tips, folding of the host rock and contemporaneous brittle and ductile features; 3) Ductile “dykes” with rounded shapes and mingling between partially molten host rock and the intruding mafic magma. The brittle dykes exhibit two distinct orientations separated by ~30° that are mutually cross-cutting, demonstrating that the dyke swam did not consist of only vertical sheets oriented perpendicular to regional extension, as expected in rifts. By using the host-rock layers as markers, a kinematic restoration to quantify the average strain accommodating the emplacement of the dyke complex was performed. This strain estimate shows that the dyke swarm accommodated >100% horizontal extension, but also 27% vertical thickening. This suggests that the magma influx rate was higher than the tectonic stretching rate, which imply that magma was emplaced forcefully, as supported by field observations of the host-rock deformation. Finally, observations of typical “brittle” dykes that were subsequently deformed by ductile mechanisms as well as dykes that were emplaced by purely ductile mechanisms suggest that the fast emplacement of the dyke swarm triggered a rapid shallowing of the brittle-ductile transition. The abrupt dyke emplacement and associated heating resulted in weakening of the crust that probably facilitated the continental break-up, which culminated with opening of the Iapetus Ocean.
How to cite: Kjøll, H. J., Galland, O., Labrousse, L., and Andersen, T. B.: Emplacement mechanisms of a dyke swarm across the Brittle-Ductile transition , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8215, https://doi.org/10.5194/egusphere-egu2020-8215, 2020.
EGU2020-9029 | Displays | TS6.4
Feedbacks between magmatic intrusions, faulting, and surface processes at continental riftsThomas Morrow, Jean-Arthur Olive, Mark Behn, and Paris Smalls
During continental rifting, faulting, magmatic injection, and surface processes collectively shape the landscape. Although feedbacks between surface processes and faulting at rifts have been explored, the relationship between shallow magmatic intrusions, topography, and surface processes is poorly understood. Magmatic injection is controlled in part by lithospheric stress, and should therefore respond to rift-associated perturbations to the stress field. Along with normal fault formation and evolution, surficial mass redistribution via erosion, sediment transport, and deposition alters lithospheric stresses and has the potential to influence dike emplacement and long-term rift structure. Here we present a series of two-dimensional (2-D) numerical model runs utilizing the particle-in-cell, finite difference code SiStER to quantify the feedbacks between tectonic, magmatic, and surface processes that shape continental rifts. In our models, extension is accommodated through a combination of magmatic intrusion and tectonic stretching. Magmatic intrusion occurs within a narrow region when and where the sum of horizontal deviatoric stress and magmatic overpressure exceeds the tensile strength of the lithosphere. Magmatic overpressure is thus a key parameter that strongly modulates the sensitivity of dike emplacement to faulting, bending, and topographically-induced variations in lithosphere stress. Our results first probe the relationships between fault-related stresses and the timing and depth-distribution of magmatic intrusions at a rift with no active surface processes. In these cases, the locus of magmatic spreading migrates vertically in response to the evolving stress field. The 2-D tectonic model is then coupled to a 1-D landscape evolution model, which modifies topography concurrent with extension. In the simplest case, topographic diffusion effectively redistributes the topographic load, contributing to variations in injection-controlling lithospheric stresses. We compare our tectonic-responsive results with models that incorporate active surface processes to constrain the conditions under which surface processes modulate magmatic injection. Our simulations suggest that the development and redistribution of topography exerts an important control on the partitioning of tectonic and magmatic strain at extensional plate boundaries.
How to cite: Morrow, T., Olive, J.-A., Behn, M., and Smalls, P.: Feedbacks between magmatic intrusions, faulting, and surface processes at continental rifts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9029, https://doi.org/10.5194/egusphere-egu2020-9029, 2020.
During continental rifting, faulting, magmatic injection, and surface processes collectively shape the landscape. Although feedbacks between surface processes and faulting at rifts have been explored, the relationship between shallow magmatic intrusions, topography, and surface processes is poorly understood. Magmatic injection is controlled in part by lithospheric stress, and should therefore respond to rift-associated perturbations to the stress field. Along with normal fault formation and evolution, surficial mass redistribution via erosion, sediment transport, and deposition alters lithospheric stresses and has the potential to influence dike emplacement and long-term rift structure. Here we present a series of two-dimensional (2-D) numerical model runs utilizing the particle-in-cell, finite difference code SiStER to quantify the feedbacks between tectonic, magmatic, and surface processes that shape continental rifts. In our models, extension is accommodated through a combination of magmatic intrusion and tectonic stretching. Magmatic intrusion occurs within a narrow region when and where the sum of horizontal deviatoric stress and magmatic overpressure exceeds the tensile strength of the lithosphere. Magmatic overpressure is thus a key parameter that strongly modulates the sensitivity of dike emplacement to faulting, bending, and topographically-induced variations in lithosphere stress. Our results first probe the relationships between fault-related stresses and the timing and depth-distribution of magmatic intrusions at a rift with no active surface processes. In these cases, the locus of magmatic spreading migrates vertically in response to the evolving stress field. The 2-D tectonic model is then coupled to a 1-D landscape evolution model, which modifies topography concurrent with extension. In the simplest case, topographic diffusion effectively redistributes the topographic load, contributing to variations in injection-controlling lithospheric stresses. We compare our tectonic-responsive results with models that incorporate active surface processes to constrain the conditions under which surface processes modulate magmatic injection. Our simulations suggest that the development and redistribution of topography exerts an important control on the partitioning of tectonic and magmatic strain at extensional plate boundaries.
How to cite: Morrow, T., Olive, J.-A., Behn, M., and Smalls, P.: Feedbacks between magmatic intrusions, faulting, and surface processes at continental rifts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9029, https://doi.org/10.5194/egusphere-egu2020-9029, 2020.
EGU2020-11228 | Displays | TS6.4
Kinematics and extent of the Liguro-Piemont OceanEline Le Breton, Sascha Brune, Kamil Ustaszewski, Sabin Zahirovic, Maria Seton, and R. Dietmar Müller
Assessing the extent of a former ocean, of which only remnants are found in mountain belts, is challenging but crucial to understand subduction and exhumation processes. Here we present new constraints on the opening and width of the Liguro-Piemont (LP) Ocean (or Alpine Tethys) in Mesozoic time using plate kinematic reconstructions of the Western Mediterranean-Alpine area.
Our kinematic model is based on a compilation of geological-geophysical data and published reconstructions of the opening of the Atlantic for the motion of Europe, Africa and Iberia, and of the Cenozoic deformation along fold-and-thrust belts (Alps, Apennines, Dinarides, Provence) and extensional basins (Liguro-Provencal Basin and Sicily Channel Rift Zone) for the motion of the Adriatic plate (Adria) and Sardinia-Corsica. For Jurassic and Cretaceous times, our main assumption is to avoid significant convergence or divergence between Adria and Africa and between Iberia and Sardinia-Corsica, as there is no geological evidence for such deformation. This implies in return strike-slip motion between southern France and Iberia-Sardinia-Corsica and within the Adriatic plate.
Our model shows that the LP basin opened in three phases: (1) first a slow extensional phase of c. 4 mm/yr (full rate) in Lower-Middle Jurassic between 200-165 Ma, followed by (2) a faster (up to 1.5 cm/yr) oblique extension in Middle-Upper Jurassic between 165-154 Ma, which coincides with emplacement ages of gabbros and pillow-lavas, and (3) a final main extensional phase in Upper Jurassic between 154 and 145 Ma, with rates up to 2.3 cm/yr. At 145 Ma, Iberia starts to move relative to Europe and thus extension in the LP domain decreases rapidly till it ceases completely at about 130 Ma. We interpret the first phase as rifting of the proximal part of the continental margins (200-165 Ma) followed by hyper-extension and formation of the ocean-continent transition zone (165-154 Ma), and break-up and ultra-slow oceanic spreading during the final third phase (mainly 154-145 Ma). Along a NW-SE transect between Corsica and northern Adria, we estimate the width of the LP Ocean to a maximum of ~ 240 km (oceanic domain) and the extent of the whole rifted margins to ~ 500 km, subdivided into ~380 km for the proximal and necking zones, and ~120 km for the hyper-extended and ocean-continent transition zones. Our results are supported by high-resolution thermo-mechanical modelling of the rifting phase that, using our kinematic constraints, reproduces very well the geometry of the Adriatic margin, as obtained by published geological reconstructions of the Southern Alps.
We test other kinematic scenarios for the motion of Sardinia-Corsica and for the opening of the Ionian Basin which would increase the obliquity of rifting and reduce even more the width of the extended domain. Therefore, our calculated extent of the LP Ocean constitutes a maximum estimate providing crucial constraints for geodynamic modelling and a better understanding of subduction processes during the Alpine Orogeny.
How to cite: Le Breton, E., Brune, S., Ustaszewski, K., Zahirovic, S., Seton, M., and Müller, R. D.: Kinematics and extent of the Liguro-Piemont Ocean , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11228, https://doi.org/10.5194/egusphere-egu2020-11228, 2020.
Assessing the extent of a former ocean, of which only remnants are found in mountain belts, is challenging but crucial to understand subduction and exhumation processes. Here we present new constraints on the opening and width of the Liguro-Piemont (LP) Ocean (or Alpine Tethys) in Mesozoic time using plate kinematic reconstructions of the Western Mediterranean-Alpine area.
Our kinematic model is based on a compilation of geological-geophysical data and published reconstructions of the opening of the Atlantic for the motion of Europe, Africa and Iberia, and of the Cenozoic deformation along fold-and-thrust belts (Alps, Apennines, Dinarides, Provence) and extensional basins (Liguro-Provencal Basin and Sicily Channel Rift Zone) for the motion of the Adriatic plate (Adria) and Sardinia-Corsica. For Jurassic and Cretaceous times, our main assumption is to avoid significant convergence or divergence between Adria and Africa and between Iberia and Sardinia-Corsica, as there is no geological evidence for such deformation. This implies in return strike-slip motion between southern France and Iberia-Sardinia-Corsica and within the Adriatic plate.
Our model shows that the LP basin opened in three phases: (1) first a slow extensional phase of c. 4 mm/yr (full rate) in Lower-Middle Jurassic between 200-165 Ma, followed by (2) a faster (up to 1.5 cm/yr) oblique extension in Middle-Upper Jurassic between 165-154 Ma, which coincides with emplacement ages of gabbros and pillow-lavas, and (3) a final main extensional phase in Upper Jurassic between 154 and 145 Ma, with rates up to 2.3 cm/yr. At 145 Ma, Iberia starts to move relative to Europe and thus extension in the LP domain decreases rapidly till it ceases completely at about 130 Ma. We interpret the first phase as rifting of the proximal part of the continental margins (200-165 Ma) followed by hyper-extension and formation of the ocean-continent transition zone (165-154 Ma), and break-up and ultra-slow oceanic spreading during the final third phase (mainly 154-145 Ma). Along a NW-SE transect between Corsica and northern Adria, we estimate the width of the LP Ocean to a maximum of ~ 240 km (oceanic domain) and the extent of the whole rifted margins to ~ 500 km, subdivided into ~380 km for the proximal and necking zones, and ~120 km for the hyper-extended and ocean-continent transition zones. Our results are supported by high-resolution thermo-mechanical modelling of the rifting phase that, using our kinematic constraints, reproduces very well the geometry of the Adriatic margin, as obtained by published geological reconstructions of the Southern Alps.
We test other kinematic scenarios for the motion of Sardinia-Corsica and for the opening of the Ionian Basin which would increase the obliquity of rifting and reduce even more the width of the extended domain. Therefore, our calculated extent of the LP Ocean constitutes a maximum estimate providing crucial constraints for geodynamic modelling and a better understanding of subduction processes during the Alpine Orogeny.
How to cite: Le Breton, E., Brune, S., Ustaszewski, K., Zahirovic, S., Seton, M., and Müller, R. D.: Kinematics and extent of the Liguro-Piemont Ocean , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11228, https://doi.org/10.5194/egusphere-egu2020-11228, 2020.
EGU2020-22080 | Displays | TS6.4
Conjunction between diachronic volcanic processes and transform margin leads to the unusual structure of the Demerara transform marginal plateau and its three different margins.Thomas Museur, David Graindorge, Frauke Klingelhoefer, Walter Roest, Christophe Basile, Lies Loncke, and François Sapin
The Demerara plateau (offshore Suriname and French Guiana) is an original transform marginal plateau located at the junction between the central and the equatorial Atlantic domains. New results combining the interpretation of several datasets of high-penetration industrial MCS, academic MCS and wide-angle seismic data image a 30 km thick crust in the plateau, evolving towards three different margins to the two adjacent oceanic domains.
This work shows that this oceanic relief is a Jurassic volcanic margin located at the southern termination of the Central Atlantic rifting, and forming the divergent western margin of the Demerara plateau. New result from dredges also show the influence of a hotspot in this rifting phase. The resulting transitional domain is unusual, characterized by a progressive thinning of the margin toward the west and the presence of SDRs outer bodies on a reworked unit probably of continental origin. Unambiguous oceanic crust is identified at about 100 km from the slope break of the shelf. Toward the plateau, the outer SDR body let place to several thick superimposed inner SDR.
Then, this Jurassic domain was remarkably reworked during the Cretaceous rifting phase linked to the opening of the Equatorial Atlantic. This second event restructured this volcanic object, forming a transform northern margin and a divergent eastern margin, each with a specific transitional domain.
The presence of a volcanic margin which subsequently undergoes a non-coaxial opening with transform constraints is relatively unusual. Our data help to better constrain the transitional domains and the TOC of the Equatorial Atlantic Cretaceous margins.
The characterization of the northern and eastern extension limit of the SDRs formations and of the high velocity lower crust observed in the plateau is an important regional issue. This knowledge is necessary in particular to characterize the volumes and structures associated with the Jurassic volcanic episode, which control the thermo-structural Cretaceous evolution of the plateau and the adjacent domains.
How to cite: Museur, T., Graindorge, D., Klingelhoefer, F., Roest, W., Basile, C., Loncke, L., and Sapin, F.: Conjunction between diachronic volcanic processes and transform margin leads to the unusual structure of the Demerara transform marginal plateau and its three different margins., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22080, https://doi.org/10.5194/egusphere-egu2020-22080, 2020.
The Demerara plateau (offshore Suriname and French Guiana) is an original transform marginal plateau located at the junction between the central and the equatorial Atlantic domains. New results combining the interpretation of several datasets of high-penetration industrial MCS, academic MCS and wide-angle seismic data image a 30 km thick crust in the plateau, evolving towards three different margins to the two adjacent oceanic domains.
This work shows that this oceanic relief is a Jurassic volcanic margin located at the southern termination of the Central Atlantic rifting, and forming the divergent western margin of the Demerara plateau. New result from dredges also show the influence of a hotspot in this rifting phase. The resulting transitional domain is unusual, characterized by a progressive thinning of the margin toward the west and the presence of SDRs outer bodies on a reworked unit probably of continental origin. Unambiguous oceanic crust is identified at about 100 km from the slope break of the shelf. Toward the plateau, the outer SDR body let place to several thick superimposed inner SDR.
Then, this Jurassic domain was remarkably reworked during the Cretaceous rifting phase linked to the opening of the Equatorial Atlantic. This second event restructured this volcanic object, forming a transform northern margin and a divergent eastern margin, each with a specific transitional domain.
The presence of a volcanic margin which subsequently undergoes a non-coaxial opening with transform constraints is relatively unusual. Our data help to better constrain the transitional domains and the TOC of the Equatorial Atlantic Cretaceous margins.
The characterization of the northern and eastern extension limit of the SDRs formations and of the high velocity lower crust observed in the plateau is an important regional issue. This knowledge is necessary in particular to characterize the volumes and structures associated with the Jurassic volcanic episode, which control the thermo-structural Cretaceous evolution of the plateau and the adjacent domains.
How to cite: Museur, T., Graindorge, D., Klingelhoefer, F., Roest, W., Basile, C., Loncke, L., and Sapin, F.: Conjunction between diachronic volcanic processes and transform margin leads to the unusual structure of the Demerara transform marginal plateau and its three different margins., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22080, https://doi.org/10.5194/egusphere-egu2020-22080, 2020.
EGU2020-9586 | Displays | TS6.4
Obliquity favours propagation pulses during continental break-upAnthony Jourdon, Laetitia Le Pourhiet, Frédéric Mouthereau, and Dave A. May
V-shaped propagators are ubiquist and the seafloor age map is often sufficient to unravel the first order features of the timing of continental break-up at regional or more global scale. Some propagators show pulses in the rate of continental break-up propagation highlighted by the geometry of magnetic anomalies. These pulses, which were first introduced by Courtillot (1982) in the Gulf of Aden, represent a major element of plate tectonics. Despite the well documented geological record of these changes of rate, and their implications for plate kinematic reconstructions or the thermal regime of oblique margins, the dynamics of ridge and rift propagation at long/geodynamic timescale remains poorly studied nor understood. To date, despite the large progress made in understanding lithospheric dynamics and continental break-up, no lithospheric scale dynamic models has been able to produce self consistently pulse of ridgepropagation followed by a phase of stagnation. One obvious reason for this lack of dynamic ground stands from the fact that this problem mandates 3D thermo-mechanically coupled simulation approach that is just starting to emerge. In this work we chose to adopt a numerical modelling set-up after Le Pourhiet et al. (2018) to produce V-shaped propagators. Simulations investigate the influence of both kinematic and rheology of the lithosphere on the propagation trend and rate. The tectonic evolution of these margins shows 3 different modes of continental break-up propagation and a major change of deformation regime between phases of propagations and phases of stagnation.
How to cite: Jourdon, A., Le Pourhiet, L., Mouthereau, F., and May, D. A.: Obliquity favours propagation pulses during continental break-up , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9586, https://doi.org/10.5194/egusphere-egu2020-9586, 2020.
V-shaped propagators are ubiquist and the seafloor age map is often sufficient to unravel the first order features of the timing of continental break-up at regional or more global scale. Some propagators show pulses in the rate of continental break-up propagation highlighted by the geometry of magnetic anomalies. These pulses, which were first introduced by Courtillot (1982) in the Gulf of Aden, represent a major element of plate tectonics. Despite the well documented geological record of these changes of rate, and their implications for plate kinematic reconstructions or the thermal regime of oblique margins, the dynamics of ridge and rift propagation at long/geodynamic timescale remains poorly studied nor understood. To date, despite the large progress made in understanding lithospheric dynamics and continental break-up, no lithospheric scale dynamic models has been able to produce self consistently pulse of ridgepropagation followed by a phase of stagnation. One obvious reason for this lack of dynamic ground stands from the fact that this problem mandates 3D thermo-mechanically coupled simulation approach that is just starting to emerge. In this work we chose to adopt a numerical modelling set-up after Le Pourhiet et al. (2018) to produce V-shaped propagators. Simulations investigate the influence of both kinematic and rheology of the lithosphere on the propagation trend and rate. The tectonic evolution of these margins shows 3 different modes of continental break-up propagation and a major change of deformation regime between phases of propagations and phases of stagnation.
How to cite: Jourdon, A., Le Pourhiet, L., Mouthereau, F., and May, D. A.: Obliquity favours propagation pulses during continental break-up , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9586, https://doi.org/10.5194/egusphere-egu2020-9586, 2020.
EGU2020-17271 | Displays | TS6.4
Impact of crustal rheology on oblique rift development and geometry: a numerical studyGuillaume Duclaux, Ritske Huismans, and Dave May
Fault network orientations and three-dimensional geometries of oblique rift systems and oblique passive margins vary widely at the surface of the Earth. In fact, rift width and conjugate passive margins asymmetries also evolve along-strike oblique extensional systems. This evolution can be linked to either changes in tectonic forces and plate motion direction, or transitions between contrasting geological provinces such as mobile belts and cratons.
Here, we use high-resolution 3D forward thermo-mechanical modelling with non-linear viscoplastic rheologies to assess the importance of crustal rheology on low to moderate oblique rifts and non-volcanic passive margins deformation patterns and finite geometries. We compare two crustal end-members model series, one with a stiff crust, and the second with a weak crust. We find that the rheology of the crust strongly controls the width and timing of formation of oblique rifts and passive margins. Coupling between the frictional plastic crust and upper mantle in the stiff models promotes narrow rift systems, while decoupling in the weak models promotes wide rifts. In these wide rifts, strain partitioning in the upper crust favours the development of an interconnected wide anastomosed shear zones network with a long lifespan. While stiff crustal rheology promotes Type I narrow margins, weak crustal rheology promotes the development of Type II margins, with a delayed continental crust breakup compared with the lithospheric mantle breakup. With increasing obliquity this transition in rifting style is accompanied by an evolution of the mantle lithosphere necking behaviour from cylindrical at low obliquity to segmented at higher obliquity. We compare these results with natural oblique rift systems and passive margins in order to decipher the relative impact of crustal rheology along different terrains.
How to cite: Duclaux, G., Huismans, R., and May, D.: Impact of crustal rheology on oblique rift development and geometry: a numerical study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17271, https://doi.org/10.5194/egusphere-egu2020-17271, 2020.
Fault network orientations and three-dimensional geometries of oblique rift systems and oblique passive margins vary widely at the surface of the Earth. In fact, rift width and conjugate passive margins asymmetries also evolve along-strike oblique extensional systems. This evolution can be linked to either changes in tectonic forces and plate motion direction, or transitions between contrasting geological provinces such as mobile belts and cratons.
Here, we use high-resolution 3D forward thermo-mechanical modelling with non-linear viscoplastic rheologies to assess the importance of crustal rheology on low to moderate oblique rifts and non-volcanic passive margins deformation patterns and finite geometries. We compare two crustal end-members model series, one with a stiff crust, and the second with a weak crust. We find that the rheology of the crust strongly controls the width and timing of formation of oblique rifts and passive margins. Coupling between the frictional plastic crust and upper mantle in the stiff models promotes narrow rift systems, while decoupling in the weak models promotes wide rifts. In these wide rifts, strain partitioning in the upper crust favours the development of an interconnected wide anastomosed shear zones network with a long lifespan. While stiff crustal rheology promotes Type I narrow margins, weak crustal rheology promotes the development of Type II margins, with a delayed continental crust breakup compared with the lithospheric mantle breakup. With increasing obliquity this transition in rifting style is accompanied by an evolution of the mantle lithosphere necking behaviour from cylindrical at low obliquity to segmented at higher obliquity. We compare these results with natural oblique rift systems and passive margins in order to decipher the relative impact of crustal rheology along different terrains.
How to cite: Duclaux, G., Huismans, R., and May, D.: Impact of crustal rheology on oblique rift development and geometry: a numerical study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17271, https://doi.org/10.5194/egusphere-egu2020-17271, 2020.
EGU2020-20576 | Displays | TS6.4
Massive High-Angle Normal Faulting at distal magma-poor margins: examples from South AtlanticMichaël Denis and Jean-François Ballard
Seismic imaging of very distal margins enabled to evidence seaward-verging normal faults with slip displacements up to 6000 meters, in several areas of both African & Brazilian magma-poor margins.
Interpretation of deep seismic profiles, including 3D seismic, time- & depth-migrated, evidence sharp depth variations of the Moho, close to areas where subcontinental mantle exhumed further to successive activation of Low-Angle Normal Faults and large detachement faults.
The sharp Moho depth variations are related to giant High-Angle Normal Faults (HANF) which had offset the Moho itself and may have rooted close to the base of the serpentinized mantle. The faults are sealed within the salt, enabling to date it Late Aptian in age.
The close synchronicity between HANF activity and salt deposition reflects some dramatic changes of depositional environments, subsidence and deformation processes at the scale of the margin, especially as salt deposition is also closely related to significant increase of magmatic additions in the ultra-distal parts of the margin.
These changes are very likely related to the lithospheric break-up process and support the post-detachement timing of activation of the HANF interpreted from cross-cutting relationships on the seismics.
The evolutionary model for HANF proposed is supported by field evidence, seismic analogs and thermomechanical models: it invokes thermal, isostatic, rheologic, tectono-magmatic processes, and documents the context of South Atlantic salt deposition.
How to cite: Denis, M. and Ballard, J.-F.: Massive High-Angle Normal Faulting at distal magma-poor margins: examples from South Atlantic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20576, https://doi.org/10.5194/egusphere-egu2020-20576, 2020.
Seismic imaging of very distal margins enabled to evidence seaward-verging normal faults with slip displacements up to 6000 meters, in several areas of both African & Brazilian magma-poor margins.
Interpretation of deep seismic profiles, including 3D seismic, time- & depth-migrated, evidence sharp depth variations of the Moho, close to areas where subcontinental mantle exhumed further to successive activation of Low-Angle Normal Faults and large detachement faults.
The sharp Moho depth variations are related to giant High-Angle Normal Faults (HANF) which had offset the Moho itself and may have rooted close to the base of the serpentinized mantle. The faults are sealed within the salt, enabling to date it Late Aptian in age.
The close synchronicity between HANF activity and salt deposition reflects some dramatic changes of depositional environments, subsidence and deformation processes at the scale of the margin, especially as salt deposition is also closely related to significant increase of magmatic additions in the ultra-distal parts of the margin.
These changes are very likely related to the lithospheric break-up process and support the post-detachement timing of activation of the HANF interpreted from cross-cutting relationships on the seismics.
The evolutionary model for HANF proposed is supported by field evidence, seismic analogs and thermomechanical models: it invokes thermal, isostatic, rheologic, tectono-magmatic processes, and documents the context of South Atlantic salt deposition.
How to cite: Denis, M. and Ballard, J.-F.: Massive High-Angle Normal Faulting at distal magma-poor margins: examples from South Atlantic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20576, https://doi.org/10.5194/egusphere-egu2020-20576, 2020.
EGU2020-21717 | Displays | TS6.4
Synrift subsidence and magmatism of the Central South Atlantic passive margins based on long term 2-D thermo-mechanical modellingThomas Theunissen, Ritske Huismans, Frank Despinois, Jean-Claude Ringenbach, and François Sapin
Here we use observations from the central South Atlantic conjugate margins to constrain the structural style of rifting and its relation with sedimentary basin evolution during the syn and early post-rift. Three synthetics transects from North (Gabon-Brazil) to South (Angola-Brazil) are used to constrain fault distribution, margin width, crustal thickness, distribution of magmatism, syn-rift sedimentary section thickness and paleo-environment from the start of rifting in the Berriasian (145 Ma) until the early post rift in the Aptian (113 Ma). This integrated study aims to understand variations in along strike structural style, magmatic output, and sedimentary basin evolution to assess the contribution of mantle processes on topography using forward 2-D thermo-mechanical modelling. We design a model setup that reproduces South Atlantic central segment main characteristics before rifting. We then explore scenarios of lithospheric thinning where strain weakening mechanisms, degree of depletion of lithopsheric mantle and crustal rheology are the main variables. The model accounts for decompression melting with feedbacks on temperature, viscosity and density of the mantle. The subsidence in the thermo-mechanical models is calibrated with a reference ridge elevation, where a 6 km thick oceanic crust is predicted, and explained by the different contributions on buoyancy of rifted passive margin during rifting. We discuss conditions to get magma-poor margins with/without exhumed mantle at the seafloor and conditions to reach a small topographic gradient and shallow water environment between the proximal and distal domains over more than 200 km of the wide margin during most of the syn-rift.
How to cite: Theunissen, T., Huismans, R., Despinois, F., Ringenbach, J.-C., and Sapin, F.: Synrift subsidence and magmatism of the Central South Atlantic passive margins based on long term 2-D thermo-mechanical modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21717, https://doi.org/10.5194/egusphere-egu2020-21717, 2020.
Here we use observations from the central South Atlantic conjugate margins to constrain the structural style of rifting and its relation with sedimentary basin evolution during the syn and early post-rift. Three synthetics transects from North (Gabon-Brazil) to South (Angola-Brazil) are used to constrain fault distribution, margin width, crustal thickness, distribution of magmatism, syn-rift sedimentary section thickness and paleo-environment from the start of rifting in the Berriasian (145 Ma) until the early post rift in the Aptian (113 Ma). This integrated study aims to understand variations in along strike structural style, magmatic output, and sedimentary basin evolution to assess the contribution of mantle processes on topography using forward 2-D thermo-mechanical modelling. We design a model setup that reproduces South Atlantic central segment main characteristics before rifting. We then explore scenarios of lithospheric thinning where strain weakening mechanisms, degree of depletion of lithopsheric mantle and crustal rheology are the main variables. The model accounts for decompression melting with feedbacks on temperature, viscosity and density of the mantle. The subsidence in the thermo-mechanical models is calibrated with a reference ridge elevation, where a 6 km thick oceanic crust is predicted, and explained by the different contributions on buoyancy of rifted passive margin during rifting. We discuss conditions to get magma-poor margins with/without exhumed mantle at the seafloor and conditions to reach a small topographic gradient and shallow water environment between the proximal and distal domains over more than 200 km of the wide margin during most of the syn-rift.
How to cite: Theunissen, T., Huismans, R., Despinois, F., Ringenbach, J.-C., and Sapin, F.: Synrift subsidence and magmatism of the Central South Atlantic passive margins based on long term 2-D thermo-mechanical modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21717, https://doi.org/10.5194/egusphere-egu2020-21717, 2020.
EGU2020-18622 | Displays | TS6.4
How syn-rift sedimentation promotes the formation of hyper-extended marginsSusanne Buiter
Seismic observations show that some rifted continental margins may have substantial amounts of offshore sediments. For example, sediment layers of several kilometres thick are found on the margins of Mid Norway, Namibia and Angola. Intriguingly, these margins are wide, being characterised by distances of several hundreds of kilometres from typical continental crustal thicknesses of 30-40 km to clearly identifiable oceanic crust. On the other hand, some margins that are sediment-starved, such as Goban Spur, Flemish Cap and Northern Norway, have short onshore-to-offshore transitions. Variations in the amount of sediments not only impact the development of offshore sedimentary basins, but the changes in mass balance by erosion and sedimentation can also interact with extensional tectonic processes. In convergent settings, such feedback relationships between erosion and tectonic deformation have long been highlighted: Erosion reduces the elevation and width of mountain belts and in turn tectonic activity and exhumation are focused at regions of enhanced erosion. But what is the role played by surface processes during formation of rifted continental margins?
I use geodynamic finite-element experiments to explore the response of continental rifts to erosion and sedimentation from initial rifting to continental break-up. The experiments predict that rifted margins with thick syn-rift sedimentary packages are more likely to form hyper-extended crust and require more stretching to achieve continental break-up than sediment-starved margins. These findings imply that surface processes can control the style of continental break-up and that the role of sedimentation in rifted margin evolution goes far beyond the simple exertion of a passive weight.
How to cite: Buiter, S.: How syn-rift sedimentation promotes the formation of hyper-extended margins, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18622, https://doi.org/10.5194/egusphere-egu2020-18622, 2020.
Seismic observations show that some rifted continental margins may have substantial amounts of offshore sediments. For example, sediment layers of several kilometres thick are found on the margins of Mid Norway, Namibia and Angola. Intriguingly, these margins are wide, being characterised by distances of several hundreds of kilometres from typical continental crustal thicknesses of 30-40 km to clearly identifiable oceanic crust. On the other hand, some margins that are sediment-starved, such as Goban Spur, Flemish Cap and Northern Norway, have short onshore-to-offshore transitions. Variations in the amount of sediments not only impact the development of offshore sedimentary basins, but the changes in mass balance by erosion and sedimentation can also interact with extensional tectonic processes. In convergent settings, such feedback relationships between erosion and tectonic deformation have long been highlighted: Erosion reduces the elevation and width of mountain belts and in turn tectonic activity and exhumation are focused at regions of enhanced erosion. But what is the role played by surface processes during formation of rifted continental margins?
I use geodynamic finite-element experiments to explore the response of continental rifts to erosion and sedimentation from initial rifting to continental break-up. The experiments predict that rifted margins with thick syn-rift sedimentary packages are more likely to form hyper-extended crust and require more stretching to achieve continental break-up than sediment-starved margins. These findings imply that surface processes can control the style of continental break-up and that the role of sedimentation in rifted margin evolution goes far beyond the simple exertion of a passive weight.
How to cite: Buiter, S.: How syn-rift sedimentation promotes the formation of hyper-extended margins, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18622, https://doi.org/10.5194/egusphere-egu2020-18622, 2020.
EGU2020-5130 | Displays | TS6.4
Seismic wide-angle constrains on the structure of the northern Sicily margin and Vavilov Basin: implications for the opening of the Tyrrhenian back-arc basinIngo Grevemeyer, Cesar Ranero, Nevio Zitellini, Valenit Sallares, and Manel Prada
The Tyrrhenian Sea in the central Mediterranean Sea was form by Neogene slab roll-back of the retreating Ionian slab about 6 to 2 Myr ago. Yet, little is known about the structure of its southern margin off Sicily as well as back-arc extension and spreading in the southern Tyrrhenian Sea to the north of Sicily. The Sicilian margin is generally classified as a passive margin bounding a young back-arc basin. However, focal mechanisms from regional earthquakes suggest that the margins suffers presently from compressional tectonics. New seismic refraction and wide-angle data were collected along seismic profile WAS4 during the CHIANTI survey of the Spanish research vessel Sarmiento de Gamboa in 2015. The profile runs from the centre of the Tyrrhenian Sea – the Vavilov Basin – across the margin of Sicily, approaching the Gulf of Castellammare to the northwest of Sicily. Reanalyzed multi-channel seismic data supports compressional tectonics across a small basin paralleling the coastline of Sicily, revealing recent inversion of the Tyrrhenian Basin. Offshore of Sicily WAS4 indicates a roughly 120-140 km wide domain showing seismic P-wave velocities characteristic for continental crust (Vp ~4-6.7 km/s) and a base of crust defined by a wide-angle Moho reflection. Continental crust reaches a maximum thickness of 22 km to the north of the Gulf of Castellammare and is thinning to ~9 km to the north of the Ustica Ridge. The compressional belt occurs in continental crust to the south of Ustica Ridge. In the Vavilov Basin, a lithosphere was sample where seismic P-wave velocity increases from approx. 3-4 km/s to 7.5 km/s. This velocity depth-distribution clearly shows profound similarities to serpentinized mantle and hence un-roofed mantle. Thus, seismic constrains support results from Ocean Drilling Program (ODP) hole 651A, which sample serpentinized peridotites in the Vavilov Basin. The transition between serpentinized mantle and continental crust is rather abrupt. Thus, within a ~10 km wide transitional domain, continental crust with a thickness of~ 9 km is juxtaposed against un-roofed mantle. All available data from the Tyrrhenian Sea support wide-spread mantle exhumation in the Vavilov Basin. Therefore, the Tyrrhenian Sea provides a rather different structure when compared to marginal basins in the Western Pacific and hence may not have supported a mid-ocean ridge-type spreading system opening the basin.
How to cite: Grevemeyer, I., Ranero, C., Zitellini, N., Sallares, V., and Prada, M.: Seismic wide-angle constrains on the structure of the northern Sicily margin and Vavilov Basin: implications for the opening of the Tyrrhenian back-arc basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5130, https://doi.org/10.5194/egusphere-egu2020-5130, 2020.
The Tyrrhenian Sea in the central Mediterranean Sea was form by Neogene slab roll-back of the retreating Ionian slab about 6 to 2 Myr ago. Yet, little is known about the structure of its southern margin off Sicily as well as back-arc extension and spreading in the southern Tyrrhenian Sea to the north of Sicily. The Sicilian margin is generally classified as a passive margin bounding a young back-arc basin. However, focal mechanisms from regional earthquakes suggest that the margins suffers presently from compressional tectonics. New seismic refraction and wide-angle data were collected along seismic profile WAS4 during the CHIANTI survey of the Spanish research vessel Sarmiento de Gamboa in 2015. The profile runs from the centre of the Tyrrhenian Sea – the Vavilov Basin – across the margin of Sicily, approaching the Gulf of Castellammare to the northwest of Sicily. Reanalyzed multi-channel seismic data supports compressional tectonics across a small basin paralleling the coastline of Sicily, revealing recent inversion of the Tyrrhenian Basin. Offshore of Sicily WAS4 indicates a roughly 120-140 km wide domain showing seismic P-wave velocities characteristic for continental crust (Vp ~4-6.7 km/s) and a base of crust defined by a wide-angle Moho reflection. Continental crust reaches a maximum thickness of 22 km to the north of the Gulf of Castellammare and is thinning to ~9 km to the north of the Ustica Ridge. The compressional belt occurs in continental crust to the south of Ustica Ridge. In the Vavilov Basin, a lithosphere was sample where seismic P-wave velocity increases from approx. 3-4 km/s to 7.5 km/s. This velocity depth-distribution clearly shows profound similarities to serpentinized mantle and hence un-roofed mantle. Thus, seismic constrains support results from Ocean Drilling Program (ODP) hole 651A, which sample serpentinized peridotites in the Vavilov Basin. The transition between serpentinized mantle and continental crust is rather abrupt. Thus, within a ~10 km wide transitional domain, continental crust with a thickness of~ 9 km is juxtaposed against un-roofed mantle. All available data from the Tyrrhenian Sea support wide-spread mantle exhumation in the Vavilov Basin. Therefore, the Tyrrhenian Sea provides a rather different structure when compared to marginal basins in the Western Pacific and hence may not have supported a mid-ocean ridge-type spreading system opening the basin.
How to cite: Grevemeyer, I., Ranero, C., Zitellini, N., Sallares, V., and Prada, M.: Seismic wide-angle constrains on the structure of the northern Sicily margin and Vavilov Basin: implications for the opening of the Tyrrhenian back-arc basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5130, https://doi.org/10.5194/egusphere-egu2020-5130, 2020.
EGU2020-18473 | Displays | TS6.4
Extensional tectonics during the Tyrrhenian back-arc basin formation synthetized in a new morpho-tectonic mapMaria Filomena Loreto, Nevio Zitellini, César Rodriguez Ranero, Camilla Palmiotto, and Manel Prada
A new tectonic map is presented focused upon the extensional style accompanying the formation of the Tyrrhenian back-arc basin. Our basin-wide analysis synthetizes the interpretation of vintage multichannel and single channel seismic profiles integrated with modern seismic images and P-wave velocity models, and with a new morpho-tectonic map of the Tyrrhenian (Palmiotto & Loreto, 2019). Four distinct evolutionary opening stages have been constrained: 1) the initial Langhian(?)/Serravallian opening phase actives offshore central/southern Sardinia and offshore western Calabria; 2) the Tortonian/Messinian phase dominated by extension offshore North Sardinia-Corsica, and by oceanic accretion in the Cornaglia and Campania Terraces; 3) the Pliocene phase, dominated by mantle exhumation which was active mainly in the central Tyrrhenian and led to the full opening of Vavilov Basin; and 4) the Quaternary phase characterized by the opening of the Marsili back-arc basin. Listric and planar normal faults and their conjugates bound a series of horst and graben, half-graben and triangular basins. Distribution of extensional faults, active since Middle Miocene, throughout the basin allowed us to define a faults arrangement in the northern / central Tyrrhenian mainly related to in a pure shear which evolved a simple shear opening of continental margins. At depth, faults accommodate over a Ductile-Brittle Transitional zone cut by a low-angle detachment fault possibly responsible for mantle exhumation in the Vavilov and Magnaghi abyssal plains. In the southern Tyrrhenian, normal, inverse and transcurrent faults appear to be related to a large shear zone located along the continental margin of the northern Sicily. Extensional style variationthroughout the back-arc basin combined with wide-angle seismic velocity models, from Prada et al. (2014; 2015), allow to explore the relationship between shallow deformation, represented by faults distribution throughout the basin, and crustal-scale processes, subduction of Ionian slab and exhumation.
REFERENCES
Palmiotto, C., & Loreto, M. F., (2019). Regional scale morphological pattern of the Tyrrhenian Sea: New insights from EMODnet bathymetry. Geomorphology, 332, 88-99.
Prada, M., Sallarès, V., Ranero, C.R., Vendrell, M.G., Grevemeyer, I., Zitellini, N. & De Franco, R., 2014. Seismic structure of the Central Tyrrhenian basin: Geophysical constraints on the nature of the main crustal domains. J. Geophys. Res.: Solid Earth, 119(1), 52-70.
Prada, M., Sallarès, V., Ranero, C.R., Vendrell, M.G., Grevemeyer, I., Zitellini, N. & De Franco, R., 2015. The complex 3-D transition from continental crust to backarc magmatism and exhumed mantle in the Central Tyrrhenian basin. Geophys. J. Int., 203(1), 63-78.
How to cite: Loreto, M. F., Zitellini, N., Ranero, C. R., Palmiotto, C., and Prada, M.: Extensional tectonics during the Tyrrhenian back-arc basin formation synthetized in a new morpho-tectonic map, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18473, https://doi.org/10.5194/egusphere-egu2020-18473, 2020.
A new tectonic map is presented focused upon the extensional style accompanying the formation of the Tyrrhenian back-arc basin. Our basin-wide analysis synthetizes the interpretation of vintage multichannel and single channel seismic profiles integrated with modern seismic images and P-wave velocity models, and with a new morpho-tectonic map of the Tyrrhenian (Palmiotto & Loreto, 2019). Four distinct evolutionary opening stages have been constrained: 1) the initial Langhian(?)/Serravallian opening phase actives offshore central/southern Sardinia and offshore western Calabria; 2) the Tortonian/Messinian phase dominated by extension offshore North Sardinia-Corsica, and by oceanic accretion in the Cornaglia and Campania Terraces; 3) the Pliocene phase, dominated by mantle exhumation which was active mainly in the central Tyrrhenian and led to the full opening of Vavilov Basin; and 4) the Quaternary phase characterized by the opening of the Marsili back-arc basin. Listric and planar normal faults and their conjugates bound a series of horst and graben, half-graben and triangular basins. Distribution of extensional faults, active since Middle Miocene, throughout the basin allowed us to define a faults arrangement in the northern / central Tyrrhenian mainly related to in a pure shear which evolved a simple shear opening of continental margins. At depth, faults accommodate over a Ductile-Brittle Transitional zone cut by a low-angle detachment fault possibly responsible for mantle exhumation in the Vavilov and Magnaghi abyssal plains. In the southern Tyrrhenian, normal, inverse and transcurrent faults appear to be related to a large shear zone located along the continental margin of the northern Sicily. Extensional style variationthroughout the back-arc basin combined with wide-angle seismic velocity models, from Prada et al. (2014; 2015), allow to explore the relationship between shallow deformation, represented by faults distribution throughout the basin, and crustal-scale processes, subduction of Ionian slab and exhumation.
REFERENCES
Palmiotto, C., & Loreto, M. F., (2019). Regional scale morphological pattern of the Tyrrhenian Sea: New insights from EMODnet bathymetry. Geomorphology, 332, 88-99.
Prada, M., Sallarès, V., Ranero, C.R., Vendrell, M.G., Grevemeyer, I., Zitellini, N. & De Franco, R., 2014. Seismic structure of the Central Tyrrhenian basin: Geophysical constraints on the nature of the main crustal domains. J. Geophys. Res.: Solid Earth, 119(1), 52-70.
Prada, M., Sallarès, V., Ranero, C.R., Vendrell, M.G., Grevemeyer, I., Zitellini, N. & De Franco, R., 2015. The complex 3-D transition from continental crust to backarc magmatism and exhumed mantle in the Central Tyrrhenian basin. Geophys. J. Int., 203(1), 63-78.
How to cite: Loreto, M. F., Zitellini, N., Ranero, C. R., Palmiotto, C., and Prada, M.: Extensional tectonics during the Tyrrhenian back-arc basin formation synthetized in a new morpho-tectonic map, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18473, https://doi.org/10.5194/egusphere-egu2020-18473, 2020.
EGU2020-6950 | Displays | TS6.4
Investigations of the Oligocene-Miocene opening of the Ligurian Basin using refraction seismic dataHeidrun Kopp, Anke Dannowski, Ingo Grevemeyer, Dietrich Lange, Martin Thorwart, Grazia Caielli, Roberto Franco, Florian Petersen, Felix Noah Wolf, and Bettina Schramm
The Ligurian Basin is located north-west of Corsica at the transition from the western Alpine orogen to the Apennine system. The Back-arc basin was generated by the southeast trench retreat of the Apennines-Calabrian subduction zone. The opening took place from late Oligocene to Miocene. While the extension led to extreme continental thinning and un-roofing of mantle material little is known about the style of back-arc rifting.
To shed light on the present day crustal and lithospheric architecture of the Ligurian Basin, active seismic data have been recorded on short period ocean bottom seismometers in the framework of SPP2017 4D-MB, the German component of AlpArray. An amphibious refraction seismic profile was shot across the Ligurian Basin in an E-W direction from the Gulf of Lion to Corsica. The profile extends onshore Corsica to image the necking zone of continental thinning.
The majority of the refraction seismic data show mantle phases at offsets up to 70 km. The arrivals of seismic phases were picked and inverted in a travel time tomography. The results show a crust-mantle boundary in the central basin at ~12 km depth below sea surface. The mantle shows rather high velocities >7.8 km/s. The crust-mantle boundary deepens from ~12 km to ~18 km within 25 - 30 km towards Corsica. The results do not map an axial valley as expected for oceanic spreading. However, an extremely thinned continental crust indicates a long lasting rifting process that possibly does not initiated oceanic spreading before the opening of the Ligurian Basin stopped.
How to cite: Kopp, H., Dannowski, A., Grevemeyer, I., Lange, D., Thorwart, M., Caielli, G., Franco, R., Petersen, F., Wolf, F. N., and Schramm, B.: Investigations of the Oligocene-Miocene opening of the Ligurian Basin using refraction seismic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6950, https://doi.org/10.5194/egusphere-egu2020-6950, 2020.
The Ligurian Basin is located north-west of Corsica at the transition from the western Alpine orogen to the Apennine system. The Back-arc basin was generated by the southeast trench retreat of the Apennines-Calabrian subduction zone. The opening took place from late Oligocene to Miocene. While the extension led to extreme continental thinning and un-roofing of mantle material little is known about the style of back-arc rifting.
To shed light on the present day crustal and lithospheric architecture of the Ligurian Basin, active seismic data have been recorded on short period ocean bottom seismometers in the framework of SPP2017 4D-MB, the German component of AlpArray. An amphibious refraction seismic profile was shot across the Ligurian Basin in an E-W direction from the Gulf of Lion to Corsica. The profile extends onshore Corsica to image the necking zone of continental thinning.
The majority of the refraction seismic data show mantle phases at offsets up to 70 km. The arrivals of seismic phases were picked and inverted in a travel time tomography. The results show a crust-mantle boundary in the central basin at ~12 km depth below sea surface. The mantle shows rather high velocities >7.8 km/s. The crust-mantle boundary deepens from ~12 km to ~18 km within 25 - 30 km towards Corsica. The results do not map an axial valley as expected for oceanic spreading. However, an extremely thinned continental crust indicates a long lasting rifting process that possibly does not initiated oceanic spreading before the opening of the Ligurian Basin stopped.
How to cite: Kopp, H., Dannowski, A., Grevemeyer, I., Lange, D., Thorwart, M., Caielli, G., Franco, R., Petersen, F., Wolf, F. N., and Schramm, B.: Investigations of the Oligocene-Miocene opening of the Ligurian Basin using refraction seismic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6950, https://doi.org/10.5194/egusphere-egu2020-6950, 2020.
EGU2020-10040 | Displays | TS6.4
Structure and evolution of the Jan Mayen MicrocontinentAnke Dannowski, Michael Schnabel, Udo Barckhausen, Dieter Franke, Martin Thorwart, Thomas Funck, Martin Engels, and Christian Berndt
The Jan Mayen Ridge (JMR) is a 150-km-long and 10–30 km wide seafloor expression in N-S direction in the centre of the North Atlantic and part of the Jan Mayen Microcontinent (JMMC). Previous studies show that the eastern flank of the JMR was formed during the breakup of the Norway Basin along today’s Aegir Ridge, prior to magnetic anomaly C23 (~50 Ma). The western margin of the JMMC is conjugate to East Greenland. Rifting gradually propagated northward, likely from Chron C21 (~46 Ma) onward. Fan-shaped magnetic anomalies in the Norway Basin suggest that the JMMC must have rotated counter-clockwise. The JMR is likely underlain by continental crust. Volcanic flows have been observed within the sediments in the Jan Mayen Basin (JMB). While a relatively uniform upper crust was observed throughout the JMMC, the thickness of the lower continental crust varies significantly from up to 15 km below the JMR down to almost zero thickness towards the western part of the JMB. However, the character of the lower crust and the development of the conjugate East Greenland – JMMC margins during Oligocene are still disputed.
Here, we investigate the crustal structure of the JMMC using a new 265-km-long seismic refraction line crossing the JMMC at 69.7°N in E-W direction, which was acquired on board of RV Maria S. Merian during cruise MSM67. The profile consists of 30 ocean bottom seismometers (OBS) with a spacing of 9.5 km. The dataset was complemented by on-board gravity measurements and a magnetometer array towed behind the vessel during shooting. The line extends from oceanic crust in the Norway Basin, across the microcontinent and into oceanic crust that formed at the presently active mid-oceanic Kolbeinsey Ridge. The magnetic profile shows old seafloor spreading anomalies in the east (likely anomaly 24, ~52 Ma), then low amplitude magnetic anomalies in the central portion of the profile, which are typical for many plutonic continental rocks. On the western part of the profile, high amplitude anomalies of younger oceanic crust (likely anomalies C5C trough C6, ~19–16 Ma) are recognized near the western termination of the JMB. The seismic velocity distribution and crustal thickness vary strongly along the profile, with velocities typical for oceanic crust at either end of the profile and a thickened crust (12–13 km) underneath the JMR. This suggests that the JMMC consists of thinned continental crust with a total width of 100 km.
How to cite: Dannowski, A., Schnabel, M., Barckhausen, U., Franke, D., Thorwart, M., Funck, T., Engels, M., and Berndt, C.: Structure and evolution of the Jan Mayen Microcontinent, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10040, https://doi.org/10.5194/egusphere-egu2020-10040, 2020.
The Jan Mayen Ridge (JMR) is a 150-km-long and 10–30 km wide seafloor expression in N-S direction in the centre of the North Atlantic and part of the Jan Mayen Microcontinent (JMMC). Previous studies show that the eastern flank of the JMR was formed during the breakup of the Norway Basin along today’s Aegir Ridge, prior to magnetic anomaly C23 (~50 Ma). The western margin of the JMMC is conjugate to East Greenland. Rifting gradually propagated northward, likely from Chron C21 (~46 Ma) onward. Fan-shaped magnetic anomalies in the Norway Basin suggest that the JMMC must have rotated counter-clockwise. The JMR is likely underlain by continental crust. Volcanic flows have been observed within the sediments in the Jan Mayen Basin (JMB). While a relatively uniform upper crust was observed throughout the JMMC, the thickness of the lower continental crust varies significantly from up to 15 km below the JMR down to almost zero thickness towards the western part of the JMB. However, the character of the lower crust and the development of the conjugate East Greenland – JMMC margins during Oligocene are still disputed.
Here, we investigate the crustal structure of the JMMC using a new 265-km-long seismic refraction line crossing the JMMC at 69.7°N in E-W direction, which was acquired on board of RV Maria S. Merian during cruise MSM67. The profile consists of 30 ocean bottom seismometers (OBS) with a spacing of 9.5 km. The dataset was complemented by on-board gravity measurements and a magnetometer array towed behind the vessel during shooting. The line extends from oceanic crust in the Norway Basin, across the microcontinent and into oceanic crust that formed at the presently active mid-oceanic Kolbeinsey Ridge. The magnetic profile shows old seafloor spreading anomalies in the east (likely anomaly 24, ~52 Ma), then low amplitude magnetic anomalies in the central portion of the profile, which are typical for many plutonic continental rocks. On the western part of the profile, high amplitude anomalies of younger oceanic crust (likely anomalies C5C trough C6, ~19–16 Ma) are recognized near the western termination of the JMB. The seismic velocity distribution and crustal thickness vary strongly along the profile, with velocities typical for oceanic crust at either end of the profile and a thickened crust (12–13 km) underneath the JMR. This suggests that the JMMC consists of thinned continental crust with a total width of 100 km.
How to cite: Dannowski, A., Schnabel, M., Barckhausen, U., Franke, D., Thorwart, M., Funck, T., Engels, M., and Berndt, C.: Structure and evolution of the Jan Mayen Microcontinent, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10040, https://doi.org/10.5194/egusphere-egu2020-10040, 2020.
EGU2020-1147 | Displays | TS6.4
Physical modeling of the formation of the microcontinent Jan MayenGrigory Agranov, Eugene Dubinin, Andrey Grokholsky, and Anna Makushkina
The split between the North American and Eurasian plates began in the Late Pleistocene - Early Eocene (58-60 million years). As the stretching took place, overlapping rift cracks formed. With further evolution, the crack that came from the north fully formed, while the south at that time died out, forming the axis of paleospreading (early Ypresian Age, 49.7 Ma). A hot spot was already functioning near Greenland at that time. In the Priabonian Age (33.1 million years), the hot spot ended under the axis of paleospreading. As a result, the spreading axis jumped (Peron-Pinvidic et al., 2012) creating the Jan Mine main microcontinent and the Kolbeinsain spreading ridge. In addition, the northern branch of the spreading ridge died out and the Aegir paleospreading ridge formed. These raises a number of questions arise:
-What is the mechanism for the separation of the Jan Mine continental block?
-Why did the spreading axis jumped and the Aegir Ridge wither away?
-What is the effect of the Icelandic hot spot on microblock formation?
-Are there similar structures in the world formed through a similar mechanism?
To answer these questions, a physical simulation was performed. Some of these issues were considered in (Muller et al., 2001, Gaina et al., 2003, Mjelde et al., 2008, Mjelde, Faleide, 2009).
Modelling was based on the initial geometry of rift cracks, known oldest magnetic anomalies and existing reconstructions. It showed two possibilities for the formation of the Jan Mayen microcontinent.
The first model is associated with parallel or oblique strike of rift cracks, the oncoming movement of which leads to their overlap, isolation of the microcontinental block, which experienced deformation and rotation.
The second model is associated with the presence of a local heat source (hot spot), the influence of which led to a jump of one branch of the rift towards the hot spot, and to the generation of a significant amount of magmatic material, which could significantly change the initial continental structure of the microblock. The second method, which combines the influence of the overlap zone and the hot spot, showed the best correlation with natural structures.
How to cite: Agranov, G., Dubinin, E., Grokholsky, A., and Makushkina, A.: Physical modeling of the formation of the microcontinent Jan Mayen, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1147, https://doi.org/10.5194/egusphere-egu2020-1147, 2020.
The split between the North American and Eurasian plates began in the Late Pleistocene - Early Eocene (58-60 million years). As the stretching took place, overlapping rift cracks formed. With further evolution, the crack that came from the north fully formed, while the south at that time died out, forming the axis of paleospreading (early Ypresian Age, 49.7 Ma). A hot spot was already functioning near Greenland at that time. In the Priabonian Age (33.1 million years), the hot spot ended under the axis of paleospreading. As a result, the spreading axis jumped (Peron-Pinvidic et al., 2012) creating the Jan Mine main microcontinent and the Kolbeinsain spreading ridge. In addition, the northern branch of the spreading ridge died out and the Aegir paleospreading ridge formed. These raises a number of questions arise:
-What is the mechanism for the separation of the Jan Mine continental block?
-Why did the spreading axis jumped and the Aegir Ridge wither away?
-What is the effect of the Icelandic hot spot on microblock formation?
-Are there similar structures in the world formed through a similar mechanism?
To answer these questions, a physical simulation was performed. Some of these issues were considered in (Muller et al., 2001, Gaina et al., 2003, Mjelde et al., 2008, Mjelde, Faleide, 2009).
Modelling was based on the initial geometry of rift cracks, known oldest magnetic anomalies and existing reconstructions. It showed two possibilities for the formation of the Jan Mayen microcontinent.
The first model is associated with parallel or oblique strike of rift cracks, the oncoming movement of which leads to their overlap, isolation of the microcontinental block, which experienced deformation and rotation.
The second model is associated with the presence of a local heat source (hot spot), the influence of which led to a jump of one branch of the rift towards the hot spot, and to the generation of a significant amount of magmatic material, which could significantly change the initial continental structure of the microblock. The second method, which combines the influence of the overlap zone and the hot spot, showed the best correlation with natural structures.
How to cite: Agranov, G., Dubinin, E., Grokholsky, A., and Makushkina, A.: Physical modeling of the formation of the microcontinent Jan Mayen, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1147, https://doi.org/10.5194/egusphere-egu2020-1147, 2020.
EGU2020-16107 | Displays | TS6.4 | Highlight
Upper mantle conditions during the opening of the North Atlantic OceanZsófia Zalai, Jenny Collier, Gareth Roberts, and Thomas Funck
Mantle conditions during the opening of the North Atlantic Ocean and specifically the presence or otherwise of a deep mantle plume have been much debated. Current models fall into two groups: the plume impingement and the plate-driven models. The plume impingement model associates the arrival of the Icelandic plume with continental break-up of the North Atlantic and the observed excess magmatism is associated with passive upwelling and elevated mantle potential temperatures. However, the plate-driven model associates this excess magmatism with increased mantle fertility due to inherited lithospheric structure and/or small-scale convection induced by sub-lithospheric topography.
We examine the spatial and temporal variation of upper mantle conditions at the time of continental break-up using an inventory of 40 published seismic refraction velocity-depth profiles acquired between the Charlie Gibbs and the East Greenland Fracture Zones. We make use of the Hc-Vp method to estimate mantle potential temperature and the ratio of active to passive upwelling by extracting igneous crustal thickness, Hc, and its mean p-wave velocity, Vp. Finally, we compare the spatial and temporal patterns obtained to those predicted by previously proposed models of mantle conditions around the time of break-up.
Our results indicate an asymmetry in mantle potential temperature between the Greenland and the European side, the latter being 100°C hotter. The temperature anomaly also varies on a wavelength of 300-500 km along strike both margins. In most profiles, the mantle potential temperature decreases with time, with normal temperatures of 1300°C being reached 5-10 Ma after the onset of seafloor spreading at 55 Ma. This temperature appears to be “steady state” once reached. The exception to this is the Greenland-Iceland-Faroes Ridge where the “steady state” temperature is 100°C higher. However, the decreasing trend of mantle potential temperature with time is not uniform across the whole North Atlantic region: the temperature decreases by a 60°C/Ma rate at the Hatton margin, while at the Møre and Vøring margins it is considerably slower, at only 20°C/Ma. A 100°C lower than normal mantle potential temperature anomaly was found at the now extinct Aegir Ridge spreading centre even though it was located less than 300 km away from the proposed reconstructed position of the Icelandic plume. Nevertheless, the plume’s position coincides well with the highest calculated upwelling ratios. The NE Greenland margin is also characterised by moderate upwelling compared to the purely passive European side.
Overall the spatial distribution of high active upwelling ratios and widespread elevated mantle potential temperatures support the plume impingement model for the opening of the North Atlantic Ocean. This thermal anomaly was exhausted at a varying rate on the different margins in 5-10 Ma. Furthermore, the 300-500 km wide localised thermal anomalies and the proximity of the proposed plume location to a low temperature anomaly indicate moderation by local complexities that might be a manifestation of upper mantle flow induced by structural inheritance or plate tectonic processes.
How to cite: Zalai, Z., Collier, J., Roberts, G., and Funck, T.: Upper mantle conditions during the opening of the North Atlantic Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16107, https://doi.org/10.5194/egusphere-egu2020-16107, 2020.
Mantle conditions during the opening of the North Atlantic Ocean and specifically the presence or otherwise of a deep mantle plume have been much debated. Current models fall into two groups: the plume impingement and the plate-driven models. The plume impingement model associates the arrival of the Icelandic plume with continental break-up of the North Atlantic and the observed excess magmatism is associated with passive upwelling and elevated mantle potential temperatures. However, the plate-driven model associates this excess magmatism with increased mantle fertility due to inherited lithospheric structure and/or small-scale convection induced by sub-lithospheric topography.
We examine the spatial and temporal variation of upper mantle conditions at the time of continental break-up using an inventory of 40 published seismic refraction velocity-depth profiles acquired between the Charlie Gibbs and the East Greenland Fracture Zones. We make use of the Hc-Vp method to estimate mantle potential temperature and the ratio of active to passive upwelling by extracting igneous crustal thickness, Hc, and its mean p-wave velocity, Vp. Finally, we compare the spatial and temporal patterns obtained to those predicted by previously proposed models of mantle conditions around the time of break-up.
Our results indicate an asymmetry in mantle potential temperature between the Greenland and the European side, the latter being 100°C hotter. The temperature anomaly also varies on a wavelength of 300-500 km along strike both margins. In most profiles, the mantle potential temperature decreases with time, with normal temperatures of 1300°C being reached 5-10 Ma after the onset of seafloor spreading at 55 Ma. This temperature appears to be “steady state” once reached. The exception to this is the Greenland-Iceland-Faroes Ridge where the “steady state” temperature is 100°C higher. However, the decreasing trend of mantle potential temperature with time is not uniform across the whole North Atlantic region: the temperature decreases by a 60°C/Ma rate at the Hatton margin, while at the Møre and Vøring margins it is considerably slower, at only 20°C/Ma. A 100°C lower than normal mantle potential temperature anomaly was found at the now extinct Aegir Ridge spreading centre even though it was located less than 300 km away from the proposed reconstructed position of the Icelandic plume. Nevertheless, the plume’s position coincides well with the highest calculated upwelling ratios. The NE Greenland margin is also characterised by moderate upwelling compared to the purely passive European side.
Overall the spatial distribution of high active upwelling ratios and widespread elevated mantle potential temperatures support the plume impingement model for the opening of the North Atlantic Ocean. This thermal anomaly was exhausted at a varying rate on the different margins in 5-10 Ma. Furthermore, the 300-500 km wide localised thermal anomalies and the proximity of the proposed plume location to a low temperature anomaly indicate moderation by local complexities that might be a manifestation of upper mantle flow induced by structural inheritance or plate tectonic processes.
How to cite: Zalai, Z., Collier, J., Roberts, G., and Funck, T.: Upper mantle conditions during the opening of the North Atlantic Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16107, https://doi.org/10.5194/egusphere-egu2020-16107, 2020.
EGU2020-900 | Displays | TS6.4
Magnetic modeling of the West Iberian Margin constrained by new geophysical dataMarta Neres, César Ranero, Ingo Grevemeyer, Irene Merino, Valenti Sallares, Manel Prada, Alcinoe Calahorrano, and Alejandra Cameselle
The nature of the J magnetic anomaly off West Iberia and its implications on the kinematic and geodynamic evolution of the margin has been addressed by several studies, with several distinct interpretations and resulting models. The main reason for this is that one single geophysical dataset (the IAM-9 seismic profile on the Iberia Abyssal Plain) has until now imaged the respective crust and was available as constraint, leaving a large degree of uncertainty for interpretation and modeling. New geophysical imaging of the structure of J anomaly and nearby domains, preferably in different margin sectors, would then be essential to cast new light on the discussion on the Iberian margin evolution. We here present new constrained magnetic modeling for two profiles across the J anomaly off Iberia, in the Tagus and in the Iberia Abyssal Plain, respectively. These profiles were recently surveyed for wide angle and reflection seismics and for magnetic data, during the FRAME-2018 survey. The joint processing of wide angle and reflection seismic data revealed with unprecedented detail the velocity structure and the tectono-stratigraphy along the profiles. Here, we use these results as constraints for magnetic modeling of the measured anomalies, namely for detailed definition of the basement topography and identification of the different domains. Magnetic modeling allowed inferring the relative contribution of each layer and the existence of additional magnetic sources, such as intrusive bodies in exhumed mantle domains. Regarding the J anomaly, we show that it cannot be attributed only to magnetization contrasts between different layers. The J anomaly is rather the result of an anomalous highly magnetized source body, associated with a locally thicker crust, which claims for an abnormal magmatic composition with strong enrichment in iron oxides. We discuss possible origins for the found structure and composition of the J anomaly off Iberia, as well as implications of the new magnetic modeled profiles for the margin conjugation and kinematics.
The author would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL.
How to cite: Neres, M., Ranero, C., Grevemeyer, I., Merino, I., Sallares, V., Prada, M., Calahorrano, A., and Cameselle, A.: Magnetic modeling of the West Iberian Margin constrained by new geophysical data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-900, https://doi.org/10.5194/egusphere-egu2020-900, 2020.
The nature of the J magnetic anomaly off West Iberia and its implications on the kinematic and geodynamic evolution of the margin has been addressed by several studies, with several distinct interpretations and resulting models. The main reason for this is that one single geophysical dataset (the IAM-9 seismic profile on the Iberia Abyssal Plain) has until now imaged the respective crust and was available as constraint, leaving a large degree of uncertainty for interpretation and modeling. New geophysical imaging of the structure of J anomaly and nearby domains, preferably in different margin sectors, would then be essential to cast new light on the discussion on the Iberian margin evolution. We here present new constrained magnetic modeling for two profiles across the J anomaly off Iberia, in the Tagus and in the Iberia Abyssal Plain, respectively. These profiles were recently surveyed for wide angle and reflection seismics and for magnetic data, during the FRAME-2018 survey. The joint processing of wide angle and reflection seismic data revealed with unprecedented detail the velocity structure and the tectono-stratigraphy along the profiles. Here, we use these results as constraints for magnetic modeling of the measured anomalies, namely for detailed definition of the basement topography and identification of the different domains. Magnetic modeling allowed inferring the relative contribution of each layer and the existence of additional magnetic sources, such as intrusive bodies in exhumed mantle domains. Regarding the J anomaly, we show that it cannot be attributed only to magnetization contrasts between different layers. The J anomaly is rather the result of an anomalous highly magnetized source body, associated with a locally thicker crust, which claims for an abnormal magmatic composition with strong enrichment in iron oxides. We discuss possible origins for the found structure and composition of the J anomaly off Iberia, as well as implications of the new magnetic modeled profiles for the margin conjugation and kinematics.
The author would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL.
How to cite: Neres, M., Ranero, C., Grevemeyer, I., Merino, I., Sallares, V., Prada, M., Calahorrano, A., and Cameselle, A.: Magnetic modeling of the West Iberian Margin constrained by new geophysical data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-900, https://doi.org/10.5194/egusphere-egu2020-900, 2020.
EGU2020-11068 | Displays | TS6.4
Uncertainties in breakup markers along the Iberian Newfoundland margin: The need for a new North Atlantic plate modelAnnabel Causer, Lucía Pérez-Díaz, Graeme Eagles, and Jürgen Adam
The Iberian-Newfoundland conjugate margins are one of the most extensively studied non-volcanic rifted margins in the world. In recent years, researchers have focused their efforts at better understanding the earliest stages of continental rifting, often relying heavily on the identification of so-called “break-up features” imaged in seismic profiles or interpreted from potential field data. Along the Iberian-Newfoundland margins, widely used break-up markers include interpretations of old magnetic anomalies from the M-Series, as well as the J-anomaly, believed to mark the occurrence and spatial extent of first oceanic lithosphere. However, uncertainties in the location and interpretation of these features have led to discrepancies between modelled depictions of the palaeopositions of Iberia and Newfoundland during the early Cretaceous as well as the timing of first seafloor spreading between the two.
Using new seismic data from the Southern Newfoundland Basin (SNB) we are able to illustrate the unsuitability of “break-up” features along the Iberian – Newfoundland Margin for plate kinematic reconstructions. Our data shows that basement associated with the younger M-Series magnetic anomalies is comprised of exhumed mantle and magmatic additions, and most likely represents transitional domains and not true oceanic lithosphere. Magmatic activity in the SNB as early as M4 times (128 Ma), and the presence of SDR packages onlapping onto basement faults suggest that, at this time, plate divergence was still being accommodated by tectonic faulting. Therefore, young M-series anomalies (including the J-anomaly) are not suitable basis on which to reconstruct plate positions during the early stages of continental separation.
We instead follow an alternative modelling approach, not reliant on the identification of extended continental margin features, to robustly constrain North Atlantic tectonics pre-M0 (~121 Ma) times. We do this by using seafloor spreading data and a statistically robust inversion method as the basis for a number of purpose built two-plate models for Africa, Iberia, Eurasia, Greenland and North America, with quantified uncertainties. Together, these models will provide an invaluable framework within to study the evolution of the extended continental margins immediately prior to and during continental separation.
How to cite: Causer, A., Pérez-Díaz, L., Eagles, G., and Adam, J.: Uncertainties in breakup markers along the Iberian Newfoundland margin: The need for a new North Atlantic plate model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11068, https://doi.org/10.5194/egusphere-egu2020-11068, 2020.
The Iberian-Newfoundland conjugate margins are one of the most extensively studied non-volcanic rifted margins in the world. In recent years, researchers have focused their efforts at better understanding the earliest stages of continental rifting, often relying heavily on the identification of so-called “break-up features” imaged in seismic profiles or interpreted from potential field data. Along the Iberian-Newfoundland margins, widely used break-up markers include interpretations of old magnetic anomalies from the M-Series, as well as the J-anomaly, believed to mark the occurrence and spatial extent of first oceanic lithosphere. However, uncertainties in the location and interpretation of these features have led to discrepancies between modelled depictions of the palaeopositions of Iberia and Newfoundland during the early Cretaceous as well as the timing of first seafloor spreading between the two.
Using new seismic data from the Southern Newfoundland Basin (SNB) we are able to illustrate the unsuitability of “break-up” features along the Iberian – Newfoundland Margin for plate kinematic reconstructions. Our data shows that basement associated with the younger M-Series magnetic anomalies is comprised of exhumed mantle and magmatic additions, and most likely represents transitional domains and not true oceanic lithosphere. Magmatic activity in the SNB as early as M4 times (128 Ma), and the presence of SDR packages onlapping onto basement faults suggest that, at this time, plate divergence was still being accommodated by tectonic faulting. Therefore, young M-series anomalies (including the J-anomaly) are not suitable basis on which to reconstruct plate positions during the early stages of continental separation.
We instead follow an alternative modelling approach, not reliant on the identification of extended continental margin features, to robustly constrain North Atlantic tectonics pre-M0 (~121 Ma) times. We do this by using seafloor spreading data and a statistically robust inversion method as the basis for a number of purpose built two-plate models for Africa, Iberia, Eurasia, Greenland and North America, with quantified uncertainties. Together, these models will provide an invaluable framework within to study the evolution of the extended continental margins immediately prior to and during continental separation.
How to cite: Causer, A., Pérez-Díaz, L., Eagles, G., and Adam, J.: Uncertainties in breakup markers along the Iberian Newfoundland margin: The need for a new North Atlantic plate model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11068, https://doi.org/10.5194/egusphere-egu2020-11068, 2020.
EGU2020-13177 | Displays | TS6.4
Segmentation and structural style evolution during continental breakup: observations from the Northern Bay of Biscay passive margin (offshore France)Julie Tugend, Emmanuel Masini, Sylvie Leroy, and Laurent Jolivet
The extension and thinning of the continental lithosphere during rifting may eventually lead to continental breakup. Related mechanisms are recorded within the Continent-Ocean Transitions (COT) of distal passive margins, showing different, often complex, tectono-magmatic interactions as revealed by the variability of basement architectures imaged by seismic data. Different extensional structures are interpreted in the COT, including high-angle or low-angle extensional faults dipping either oceanward or continentward. This variability appears mainly controlled by the initial rheological stratification of the lithosphere and its evolution during rifting. As a result, the relative influence between lower crustal ductility, crustal embrittlement, and serpentinization of the underlying mantle are the main parameters considered to explain the structural variability observed in the COT.
In this contribution, we document the tectonic evolution of the northern Bay of Biscay passive margin and show the impact of passive margin segmentation in controlling along strike changes in structural style during rifting and continental breakup. The Bay of Biscay is a V-shaped oceanic basin, which opened during the northward propagation of the North Atlantic Ocean. Its bordering magma-poor passive margins formed subsequently to a Late Jurassic to Early Cretaceous oblique rifting and Aptian-Albian oceanic spreading onset. A large number of studies already focused on this margin revealing a first-order along strike segmentation, but the structures accommodating the passage from one to the other segment remained poorly constrained.
We used a series of reflection seismic sections and complementary marine data sets such as dredges and drilling results from the Deep Sea Drilling Project to map the structural pattern and stratigraphic evolution related to this segment transition. Our seismic interpretations and mapping of the main rift structures define a relatively loose segment transition marked by a progressive change in structural style expressed differently between the COT and the rest of the passive margin. The differences observed between the proximal and distal parts of the margin can be explained by an evolution of the nature and depth of the main fault décollement level; crustal embrittlement and serpentinization becoming important controlling parameters oceanward. However, the progressive change in structural style observed in the distal margin from west to east from oceanward dipping to mainly continentward dipping faults is more likely to be related a different accommodation of extensional deformation across the transfer zone. This segmentation occurs near major pre-existing structures identified further continentward, suggesting a key role of inheritance.
Results of this work reveal the impact of margin segmentation in controlling changes in structural style at the end of rifting. If this soft transfer zones do not seem to be observed as far as the first oceanic crust, further work is required to determine how far it can control different interplay between tectonic and magmatic processes further oceanward in the COT.
How to cite: Tugend, J., Masini, E., Leroy, S., and Jolivet, L.: Segmentation and structural style evolution during continental breakup: observations from the Northern Bay of Biscay passive margin (offshore France), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13177, https://doi.org/10.5194/egusphere-egu2020-13177, 2020.
The extension and thinning of the continental lithosphere during rifting may eventually lead to continental breakup. Related mechanisms are recorded within the Continent-Ocean Transitions (COT) of distal passive margins, showing different, often complex, tectono-magmatic interactions as revealed by the variability of basement architectures imaged by seismic data. Different extensional structures are interpreted in the COT, including high-angle or low-angle extensional faults dipping either oceanward or continentward. This variability appears mainly controlled by the initial rheological stratification of the lithosphere and its evolution during rifting. As a result, the relative influence between lower crustal ductility, crustal embrittlement, and serpentinization of the underlying mantle are the main parameters considered to explain the structural variability observed in the COT.
In this contribution, we document the tectonic evolution of the northern Bay of Biscay passive margin and show the impact of passive margin segmentation in controlling along strike changes in structural style during rifting and continental breakup. The Bay of Biscay is a V-shaped oceanic basin, which opened during the northward propagation of the North Atlantic Ocean. Its bordering magma-poor passive margins formed subsequently to a Late Jurassic to Early Cretaceous oblique rifting and Aptian-Albian oceanic spreading onset. A large number of studies already focused on this margin revealing a first-order along strike segmentation, but the structures accommodating the passage from one to the other segment remained poorly constrained.
We used a series of reflection seismic sections and complementary marine data sets such as dredges and drilling results from the Deep Sea Drilling Project to map the structural pattern and stratigraphic evolution related to this segment transition. Our seismic interpretations and mapping of the main rift structures define a relatively loose segment transition marked by a progressive change in structural style expressed differently between the COT and the rest of the passive margin. The differences observed between the proximal and distal parts of the margin can be explained by an evolution of the nature and depth of the main fault décollement level; crustal embrittlement and serpentinization becoming important controlling parameters oceanward. However, the progressive change in structural style observed in the distal margin from west to east from oceanward dipping to mainly continentward dipping faults is more likely to be related a different accommodation of extensional deformation across the transfer zone. This segmentation occurs near major pre-existing structures identified further continentward, suggesting a key role of inheritance.
Results of this work reveal the impact of margin segmentation in controlling changes in structural style at the end of rifting. If this soft transfer zones do not seem to be observed as far as the first oceanic crust, further work is required to determine how far it can control different interplay between tectonic and magmatic processes further oceanward in the COT.
How to cite: Tugend, J., Masini, E., Leroy, S., and Jolivet, L.: Segmentation and structural style evolution during continental breakup: observations from the Northern Bay of Biscay passive margin (offshore France), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13177, https://doi.org/10.5194/egusphere-egu2020-13177, 2020.
EGU2020-21580 | Displays | TS6.4
Mechanisms of continental break-up : tectonic, stratigraphic and structural constraints from a preserved distal rifted margin (Agly massif, eastern Pyrenees)Martin Motus, Yoann Denèle, Frédéric Mouthereau, and Élise Nardin
The Agly massif and its neighboring Mesozoic basins altogether form part of the Pyrenean Cretaceous rift preserved in the retro-wedge of the Pyrenean mountain belt. The relationships between the tectonic evolution of these syn-rift basins and the crustal-scale tectonic processes allows us to investigate the strain partitioning, the rheology and the sequence of deformation associated with the thinning of the deep crust leading to continental break-up.
Based on structural, microstructural and thermochronological studies of the deep crust of the Agly massif and the revised stratigraphy and depositional environments of the pre- and syn-rift sedimentary rocks, we propose a tectonic reconstruction of the eastern segment of the Pyrenean rift at the time of continental break-up. Two parallel cross sections allow us to discuss about the mechanical behavior of the deep crust and the control by lateral rheological heterogeneities on the spatial and temporal evolution of rifting. We emphasize the role of low-angle (decollement) and high-angle (detachment) extensional structures in the deep crust that collectively accommodate thinning and exhumation, respectively. Structural relationships between the Variscan basement and the Mesozoic basins are highlighted, such as a major extensional detachment fault system exhuming the mantle at the contact between the Agly massif and the Boucheville basin in the south. We further discuss the origin of tectono-sedimentary breccias in the context of crustal-scale thinning/exhumation processes and basins evolution.
Our different results are finally integrated in a 3D tectonic model of the distal margin, illustrating a crustal scale space-time vision of the mechanisms leading to continental break-up.
How to cite: Motus, M., Denèle, Y., Mouthereau, F., and Nardin, É.: Mechanisms of continental break-up : tectonic, stratigraphic and structural constraints from a preserved distal rifted margin (Agly massif, eastern Pyrenees), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21580, https://doi.org/10.5194/egusphere-egu2020-21580, 2020.
The Agly massif and its neighboring Mesozoic basins altogether form part of the Pyrenean Cretaceous rift preserved in the retro-wedge of the Pyrenean mountain belt. The relationships between the tectonic evolution of these syn-rift basins and the crustal-scale tectonic processes allows us to investigate the strain partitioning, the rheology and the sequence of deformation associated with the thinning of the deep crust leading to continental break-up.
Based on structural, microstructural and thermochronological studies of the deep crust of the Agly massif and the revised stratigraphy and depositional environments of the pre- and syn-rift sedimentary rocks, we propose a tectonic reconstruction of the eastern segment of the Pyrenean rift at the time of continental break-up. Two parallel cross sections allow us to discuss about the mechanical behavior of the deep crust and the control by lateral rheological heterogeneities on the spatial and temporal evolution of rifting. We emphasize the role of low-angle (decollement) and high-angle (detachment) extensional structures in the deep crust that collectively accommodate thinning and exhumation, respectively. Structural relationships between the Variscan basement and the Mesozoic basins are highlighted, such as a major extensional detachment fault system exhuming the mantle at the contact between the Agly massif and the Boucheville basin in the south. We further discuss the origin of tectono-sedimentary breccias in the context of crustal-scale thinning/exhumation processes and basins evolution.
Our different results are finally integrated in a 3D tectonic model of the distal margin, illustrating a crustal scale space-time vision of the mechanisms leading to continental break-up.
How to cite: Motus, M., Denèle, Y., Mouthereau, F., and Nardin, É.: Mechanisms of continental break-up : tectonic, stratigraphic and structural constraints from a preserved distal rifted margin (Agly massif, eastern Pyrenees), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21580, https://doi.org/10.5194/egusphere-egu2020-21580, 2020.
EGU2020-18950 | Displays | TS6.4
The kinematic evolution of the Demerara plateau and Guyana-Suriname marginsJúlia Gómez-Romeu, Emmanuel Masini, Nick Kusznir, and Sylvain Calassou
The Caribbean region has undergone a complex plate kinematics evolution due to the interaction between Central Atlantic pre-subduction paleogeography and Caribbean subduction dynamics. To better understand the initiation and dynamics of the Caribbean subduction it is important to determine the pre-subduction template. However, this template cannot be easily recognized as it either suffered from pervasive tectonic overprinting or has been consumed by subduction. To address this problem, it may be valuable to first unravel the structure and deformation history of the surrounding areas of the Caribbean region.
Here we investigate the kinematic evolution of the Triassic-Jurassic Demerara plateau and Guyana-Suriname (i.e Dp and G-S) margins which are present-day located to the south of the Caribbean subduction. To achieve our aim, we use seismic, gravity and magnetic data and apply a gravity anomaly inversion technique to determine Moho depth, crustal basement thickness and crustal thinning factor.
The Dp and G-S margins avoided subduction and consequently preserve the divergent history of Early Jurassic to Early Cretaceous rifting related to the opening of the Central Atlantic and Equatorial Atlantic respectively. This is inferred by a complex architecture of the Dp and G-S margins characterized by a set of transfer zones that crosscut each other.
By unravelling the kinematic evolution of the Dp and G-S margins we attempt to determine the pre-subduction template of the surrounding area of the Caribbean region.
How to cite: Gómez-Romeu, J., Masini, E., Kusznir, N., and Calassou, S.: The kinematic evolution of the Demerara plateau and Guyana-Suriname margins, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18950, https://doi.org/10.5194/egusphere-egu2020-18950, 2020.
The Caribbean region has undergone a complex plate kinematics evolution due to the interaction between Central Atlantic pre-subduction paleogeography and Caribbean subduction dynamics. To better understand the initiation and dynamics of the Caribbean subduction it is important to determine the pre-subduction template. However, this template cannot be easily recognized as it either suffered from pervasive tectonic overprinting or has been consumed by subduction. To address this problem, it may be valuable to first unravel the structure and deformation history of the surrounding areas of the Caribbean region.
Here we investigate the kinematic evolution of the Triassic-Jurassic Demerara plateau and Guyana-Suriname (i.e Dp and G-S) margins which are present-day located to the south of the Caribbean subduction. To achieve our aim, we use seismic, gravity and magnetic data and apply a gravity anomaly inversion technique to determine Moho depth, crustal basement thickness and crustal thinning factor.
The Dp and G-S margins avoided subduction and consequently preserve the divergent history of Early Jurassic to Early Cretaceous rifting related to the opening of the Central Atlantic and Equatorial Atlantic respectively. This is inferred by a complex architecture of the Dp and G-S margins characterized by a set of transfer zones that crosscut each other.
By unravelling the kinematic evolution of the Dp and G-S margins we attempt to determine the pre-subduction template of the surrounding area of the Caribbean region.
How to cite: Gómez-Romeu, J., Masini, E., Kusznir, N., and Calassou, S.: The kinematic evolution of the Demerara plateau and Guyana-Suriname margins, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18950, https://doi.org/10.5194/egusphere-egu2020-18950, 2020.
EGU2020-10862 | Displays | TS6.4
Crustal Thickness and Composition of the São Paulo Plateau and Florianópolis Ridge, SE Brazilian MarginMichelle Graça, Leanne Cowie, Nick Kusznir, and Natasha Stanton
The São Paulo Plateau (SPP) and the Florianópolis Ridge (FR), located on the Santos segment of the SE Brazilian margin in the South Atlantic, are large positive bathymetric features with a combined lateral dimension of approximately 500 km. An important question is whether they are underlain by thinned continental crust or by anomalously thick magmatic crust. Each hypothesis has implications for the breakup of the South Atlantic and the evolution of the overlying saline Santos basin.
Integrated quantitative analysis consisting of gravity inversion, RDA (residual depth anomaly) analysis and flexural subsidence analysis has been applied to a deep long-offset seismic reflection line running NW-SE across the SPP and FR. Gravity inversion predicts crustal basement thicknesses in the range of 12 to 15 km for the SPP and FR, deceasing to 7-8 km thickness at the extreme SE end of the profile. The SPP and FR are separated by a region of thinner crust approximately 80 km wide. Thinning factors from subsidence analysis for SPP and FR are typically between 0.6 and 0.7.
RDA values close to zero and a thinning factor of 1 were obtained for the region with 7-8 km thick crust at the SE end of the profile which are all consistent with normal oceanic crust rather than previously interpreted exhumed mantle. This oceanic crust is highly tectonised and corresponds to the location of the Florianópolis Fracture Zone.
Flexural backstripping and reverse thermal subsidence modelling were performed to calculate palaeo-bathymetry at breakup and give 2.5 km below sea level at the SE end of the profile consistent with this region being oceanic crust. Flexural subsidence analysis applied to base salt shows that the observed base salt subsidence requires a component of syn-tectonic subsidence as well as post-rift thermal subsidence, and that the salt was deposited while the crust was still thinning.
Joint inversion of time seismic reflection and gravity data to determine the lateral variation in basement density by comparing seismic and gravity Moho in the time domain gives a basement density under the SPP and FR of between 2600 and 2700 kg/m3. The same method gives a basement density of 900kg/m3 for the oceanic crust at the SE end of the profile. The FR basement in the NW shows a basement density similar to that of the SPP while in its SE the basement density is much higher approaching 2950 kg/m3. We interpret the relatively low basement densities of the SPP with respect to that of oceanic crust as indicating a continental rather than magmatic composition. A similar analysis to determine basement density applied to the Evain et al. (2015) seismic refraction profile in the same location also gives a SPP basement density that supports a continental composition.
How to cite: Graça, M., Cowie, L., Kusznir, N., and Stanton, N.: Crustal Thickness and Composition of the São Paulo Plateau and Florianópolis Ridge, SE Brazilian Margin , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10862, https://doi.org/10.5194/egusphere-egu2020-10862, 2020.
The São Paulo Plateau (SPP) and the Florianópolis Ridge (FR), located on the Santos segment of the SE Brazilian margin in the South Atlantic, are large positive bathymetric features with a combined lateral dimension of approximately 500 km. An important question is whether they are underlain by thinned continental crust or by anomalously thick magmatic crust. Each hypothesis has implications for the breakup of the South Atlantic and the evolution of the overlying saline Santos basin.
Integrated quantitative analysis consisting of gravity inversion, RDA (residual depth anomaly) analysis and flexural subsidence analysis has been applied to a deep long-offset seismic reflection line running NW-SE across the SPP and FR. Gravity inversion predicts crustal basement thicknesses in the range of 12 to 15 km for the SPP and FR, deceasing to 7-8 km thickness at the extreme SE end of the profile. The SPP and FR are separated by a region of thinner crust approximately 80 km wide. Thinning factors from subsidence analysis for SPP and FR are typically between 0.6 and 0.7.
RDA values close to zero and a thinning factor of 1 were obtained for the region with 7-8 km thick crust at the SE end of the profile which are all consistent with normal oceanic crust rather than previously interpreted exhumed mantle. This oceanic crust is highly tectonised and corresponds to the location of the Florianópolis Fracture Zone.
Flexural backstripping and reverse thermal subsidence modelling were performed to calculate palaeo-bathymetry at breakup and give 2.5 km below sea level at the SE end of the profile consistent with this region being oceanic crust. Flexural subsidence analysis applied to base salt shows that the observed base salt subsidence requires a component of syn-tectonic subsidence as well as post-rift thermal subsidence, and that the salt was deposited while the crust was still thinning.
Joint inversion of time seismic reflection and gravity data to determine the lateral variation in basement density by comparing seismic and gravity Moho in the time domain gives a basement density under the SPP and FR of between 2600 and 2700 kg/m3. The same method gives a basement density of 900kg/m3 for the oceanic crust at the SE end of the profile. The FR basement in the NW shows a basement density similar to that of the SPP while in its SE the basement density is much higher approaching 2950 kg/m3. We interpret the relatively low basement densities of the SPP with respect to that of oceanic crust as indicating a continental rather than magmatic composition. A similar analysis to determine basement density applied to the Evain et al. (2015) seismic refraction profile in the same location also gives a SPP basement density that supports a continental composition.
How to cite: Graça, M., Cowie, L., Kusznir, N., and Stanton, N.: Crustal Thickness and Composition of the São Paulo Plateau and Florianópolis Ridge, SE Brazilian Margin , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10862, https://doi.org/10.5194/egusphere-egu2020-10862, 2020.
EGU2020-15222 | Displays | TS6.4
Evidence of tectonic reactivation after continental breakup in the Ceará Terrace, Equatorial margin of Brazil, from 2D reflection seismicsAline Cristine Tavares, David Lopes de Castro, Ole Rønø Clausen, Diógenes Custódio de Oliveira, Francisco Hilario R. Bezerra, and Helenice Vital
The Brazilian equatorial margin has its origin in the fragmentation of the supercontinent Pangea with the separation of the South American and African continents and is composed of divergent oblique and transform segments related to large oceanic fracture zones, which are typical of the Equatorial Atlantic (e.g., Saint Paul, Romanche, and Chain). The dynamic evolution of this margin is related to the generation of marginal ridges, which are basement highs that follow the same trend of the continental-oceanic boundary in a transform margin.
The Ceará Terrace (CT), the main target of this investigation, is an E-W-striking marginal ridge located south of the western end of the Romanche Fracture Zone (RFZ) in the continental margin of Brazil. The CT has a counterpart in the African margin, the Ivory Coast-Ghana Ridge (ICGR), which is located north of the eastern termination of the RFZ. Earlier studies show that the evolution of both marginal ridges (CT and ICGR) was mainly influenced by (1) tectonic uplift due to Late Albian-Cenomanian transpressional tectonics and (2) flexural uplift due to erosion and thermal changes caused by the passage of the oceanic spreading center.
While ICGR is the most intensely studied marginal ridge in the Atlantic equatorial margin, the CT still needs further analysis to unravel its evolutionary process. The objective of the present study is thus to map and analyze the CT to understand its time and spatial evolution. Therefore, we have used and interpreted 2D reflection seismic sections and boreholes from the Brazilian Agency of Oil and Gas.
Our study shows that the CT is an intensely deformed Lower Cretaceous structure, which originates from the Atlantic opening process. The CT is controlled by the RZF and preexisting fault zones in the continent such as the Transbrasiliano lineament (TB). The interpretation of the seismic sections shows an intense ductile and brittle deformation of the CT paleo structure (syn-rift sequence) and the sedimentary units deposited after it (drift sequence). It indicates that tectonic reactivation occurred in the period where the transform movements were already restricted to the furthest spreading center. There is also evidence that some faults affect the whole rift sequence suggesting a possible brittle reactivation of the offshore continuation of the TB due to changes in plate movements in the Late Albian. This plate shifts agrees with previous works that show compressional features concentrated in continental shelf near of CT and half-grabens linked with the offshore TB prolongation. On the other hand, there is no evidence of the influence of weakness zones in the CIGR, where the Kandi lineament (the prolongation of the TB in the African continent) is far more than 300 km of that marginal ridge.
Acknowledgments:
This research was supported by Programa Institucional de Internacionalização - Coordenação de Aperfeiçoamento de Pessoal (PRINT-CAPES) and Aarhus University (AU). Brazilian Agency of Oil and Natural Gas (ANP) is thanked for providing the seismic and borehole data. We also thank Schlumberger for giving access to Petrel.
How to cite: Tavares, A. C., de Castro, D. L., Clausen, O. R., de Oliveira, D. C., Bezerra, F. H. R., and Vital, H.: Evidence of tectonic reactivation after continental breakup in the Ceará Terrace, Equatorial margin of Brazil, from 2D reflection seismics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15222, https://doi.org/10.5194/egusphere-egu2020-15222, 2020.
The Brazilian equatorial margin has its origin in the fragmentation of the supercontinent Pangea with the separation of the South American and African continents and is composed of divergent oblique and transform segments related to large oceanic fracture zones, which are typical of the Equatorial Atlantic (e.g., Saint Paul, Romanche, and Chain). The dynamic evolution of this margin is related to the generation of marginal ridges, which are basement highs that follow the same trend of the continental-oceanic boundary in a transform margin.
The Ceará Terrace (CT), the main target of this investigation, is an E-W-striking marginal ridge located south of the western end of the Romanche Fracture Zone (RFZ) in the continental margin of Brazil. The CT has a counterpart in the African margin, the Ivory Coast-Ghana Ridge (ICGR), which is located north of the eastern termination of the RFZ. Earlier studies show that the evolution of both marginal ridges (CT and ICGR) was mainly influenced by (1) tectonic uplift due to Late Albian-Cenomanian transpressional tectonics and (2) flexural uplift due to erosion and thermal changes caused by the passage of the oceanic spreading center.
While ICGR is the most intensely studied marginal ridge in the Atlantic equatorial margin, the CT still needs further analysis to unravel its evolutionary process. The objective of the present study is thus to map and analyze the CT to understand its time and spatial evolution. Therefore, we have used and interpreted 2D reflection seismic sections and boreholes from the Brazilian Agency of Oil and Gas.
Our study shows that the CT is an intensely deformed Lower Cretaceous structure, which originates from the Atlantic opening process. The CT is controlled by the RZF and preexisting fault zones in the continent such as the Transbrasiliano lineament (TB). The interpretation of the seismic sections shows an intense ductile and brittle deformation of the CT paleo structure (syn-rift sequence) and the sedimentary units deposited after it (drift sequence). It indicates that tectonic reactivation occurred in the period where the transform movements were already restricted to the furthest spreading center. There is also evidence that some faults affect the whole rift sequence suggesting a possible brittle reactivation of the offshore continuation of the TB due to changes in plate movements in the Late Albian. This plate shifts agrees with previous works that show compressional features concentrated in continental shelf near of CT and half-grabens linked with the offshore TB prolongation. On the other hand, there is no evidence of the influence of weakness zones in the CIGR, where the Kandi lineament (the prolongation of the TB in the African continent) is far more than 300 km of that marginal ridge.
Acknowledgments:
This research was supported by Programa Institucional de Internacionalização - Coordenação de Aperfeiçoamento de Pessoal (PRINT-CAPES) and Aarhus University (AU). Brazilian Agency of Oil and Natural Gas (ANP) is thanked for providing the seismic and borehole data. We also thank Schlumberger for giving access to Petrel.
How to cite: Tavares, A. C., de Castro, D. L., Clausen, O. R., de Oliveira, D. C., Bezerra, F. H. R., and Vital, H.: Evidence of tectonic reactivation after continental breakup in the Ceará Terrace, Equatorial margin of Brazil, from 2D reflection seismics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15222, https://doi.org/10.5194/egusphere-egu2020-15222, 2020.
EGU2020-20540 | Displays | TS6.4
Brazilian Equatorial Margin: evidences of magmatic intrusion and alteration of host rock from well dataAndre Aquino da Silva, Yoe Alain Reyes Perez, and Helenice Vital
The mechanisms of magmatic intrusion is very complex and are commonly associated to pristine unconformities (weak spots) on the crust that ease its emplacement on the form of sills or dikes. When occurring on the Oceanic crust these weak spots may led to the formation of volcanic islands (such as Fernando de Noronha, on the Brazilian Equatorial Margin-BEM), submarine highs. Alignment of such features are related to Plate motion and the set of volcanos of Fernando de Noronha Ridge are considered a consequence of the westward motion of the South American Plate. Occurrence of magmatic rocks were found on a set of offshore wells at different depths and away of submarine highs. These magmatic emplacement suggests be related to a deep plume-fed mechanism which is the source of all sills found on the wells, as well as the volcanic highs occurring of the BEM. The lateral extents of the sills is greatly influenced by the presence of faults when preceding the intrusion, during which also occurred incorporation of parts of the host rock as xenoliths. On the well logs it is possible to observe changes on sonic slowness for the same lithotype when close to the sills, which indicates rock alteration due to the magmatic intrusion.
How to cite: Aquino da Silva, A., Reyes Perez, Y. A., and Vital, H.: Brazilian Equatorial Margin: evidences of magmatic intrusion and alteration of host rock from well data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20540, https://doi.org/10.5194/egusphere-egu2020-20540, 2020.
The mechanisms of magmatic intrusion is very complex and are commonly associated to pristine unconformities (weak spots) on the crust that ease its emplacement on the form of sills or dikes. When occurring on the Oceanic crust these weak spots may led to the formation of volcanic islands (such as Fernando de Noronha, on the Brazilian Equatorial Margin-BEM), submarine highs. Alignment of such features are related to Plate motion and the set of volcanos of Fernando de Noronha Ridge are considered a consequence of the westward motion of the South American Plate. Occurrence of magmatic rocks were found on a set of offshore wells at different depths and away of submarine highs. These magmatic emplacement suggests be related to a deep plume-fed mechanism which is the source of all sills found on the wells, as well as the volcanic highs occurring of the BEM. The lateral extents of the sills is greatly influenced by the presence of faults when preceding the intrusion, during which also occurred incorporation of parts of the host rock as xenoliths. On the well logs it is possible to observe changes on sonic slowness for the same lithotype when close to the sills, which indicates rock alteration due to the magmatic intrusion.
How to cite: Aquino da Silva, A., Reyes Perez, Y. A., and Vital, H.: Brazilian Equatorial Margin: evidences of magmatic intrusion and alteration of host rock from well data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20540, https://doi.org/10.5194/egusphere-egu2020-20540, 2020.
EGU2020-9187 | Displays | TS6.4
Imaging magma storage in the Main Ethiopian Rift with 3-D MagnetotelluricsJuliane Huebert, Kathy Whaler, Shimeles Fisseha, Fiona Iddon, and Colin Hogg
The Main Ethiopian Rift (MER) as part of the large East African continental break-up zone is characterized by lateral extension and active volcanism. Rifting in the MER is magma assisted, with surface expressions of magmatism concentrated at en echelon Quaternary magmatic segments and off-axis linear features, but questions still remain about their respective roles in rifting.
The storage and pathways of magma ascent are of great interest for the assessment of both geohazard and geothermal energy potential. Imaging magma storage throughout the crust and in the upper mantle can be achieved by geophysical deep sounding techniques such as magnetotellurics (MT). Through MT measurements it is possible to access the electrical conductivity of the subsurface, a parameter that is greatly sensitive to the melt and water content. We present new MT data from the Central MER and a three-dimensional model of conductivity of the crust, imaging across-rift magma storage not only under the well-developed central-axis silicic volcanic complex Aluto, but also under several off-axis basaltic monogenetic volcanic fields. The conductivity model supports the idea of bi-modal magma storage in the CMER and helps constrain the melt and water content in the crust through the use of petrological melt-mixing models. Integrating our findings with the results from seismic tomography and receiver functions as well as Bouguer gravity data and petrological observations allows a comprehensive picture of magma storage and pathways in the MER.
How to cite: Huebert, J., Whaler, K., Fisseha, S., Iddon, F., and Hogg, C.: Imaging magma storage in the Main Ethiopian Rift with 3-D Magnetotellurics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9187, https://doi.org/10.5194/egusphere-egu2020-9187, 2020.
The Main Ethiopian Rift (MER) as part of the large East African continental break-up zone is characterized by lateral extension and active volcanism. Rifting in the MER is magma assisted, with surface expressions of magmatism concentrated at en echelon Quaternary magmatic segments and off-axis linear features, but questions still remain about their respective roles in rifting.
The storage and pathways of magma ascent are of great interest for the assessment of both geohazard and geothermal energy potential. Imaging magma storage throughout the crust and in the upper mantle can be achieved by geophysical deep sounding techniques such as magnetotellurics (MT). Through MT measurements it is possible to access the electrical conductivity of the subsurface, a parameter that is greatly sensitive to the melt and water content. We present new MT data from the Central MER and a three-dimensional model of conductivity of the crust, imaging across-rift magma storage not only under the well-developed central-axis silicic volcanic complex Aluto, but also under several off-axis basaltic monogenetic volcanic fields. The conductivity model supports the idea of bi-modal magma storage in the CMER and helps constrain the melt and water content in the crust through the use of petrological melt-mixing models. Integrating our findings with the results from seismic tomography and receiver functions as well as Bouguer gravity data and petrological observations allows a comprehensive picture of magma storage and pathways in the MER.
How to cite: Huebert, J., Whaler, K., Fisseha, S., Iddon, F., and Hogg, C.: Imaging magma storage in the Main Ethiopian Rift with 3-D Magnetotellurics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9187, https://doi.org/10.5194/egusphere-egu2020-9187, 2020.
EGU2020-2904 | Displays | TS6.4
New approaches regarding the geodynamic constraints of Late Cretaceous magmatism in Carpathian areaMihai Tatu and Elena Luisa Iatan
During the Meso-Cretaceous compressive tectonic event (marked by the subduction of the East European Platform under Gondwana, and the initiation of the creation of accretionary prism in front of the orogen) the absence of related magmatism, and implicitly, the lack of an "arc" is similar to that of the Alps (McCarthy et al., 2018). Afterward, in the Upper Cretaceous, the Carpathian area has evolved in an extensional geodynamic context, specific to post-collisional periods, marked by the appearance of sedimentary basins with complex evolution and Gosau type molasses (Schuller, 2004; Schuller et al., 2009). In connection to the above, or not, it has evolved a complex magmatism, from a compositional point of view and as manifestation, largely calc-alkaline, known in the geological literature as banatitic (von Cotta, 1864). Banatitic magmatism is the first such manifestation in the Carpathians, post-subduction and post-collision and the most reliable age data (using U-Pb on zircon and Re-Os on molybdenite methods) suggest a very narrow range of evolution (70.2 - 83.98 Ma, Nicolescu et al., 1999; Galhofer, 2015; 72.36 - 80.63 Ma, Ciobanu et al., 2002; Zimmerman et al., 2008), that is characteristic to short-lived magmatism. Comparatively, in Serbia (Bor-Madjanpek district), the same magmatism occurs between 86-84 Ma, in Bulgaria in the Srednogorie massif between 92-86 Ma and Rhodope massif at 67-70 Ma (von Quadt et al., 2007). The geodynamic models discussed for this type of magmatism suggest, almost all without exception, the existence of subductions that would have extended as activity from the Middle Cretaceous to the Paleogene. Or, the realities of the terrain show that this magmatism seals the mesocretacic compressive structures (napes), as Nicolescu et al. (1999) exposed for the first time in Banat region. The situation is similar in the Apuseni Mountains. From the presumption of the generation of subductions for this magmatism, the idea of an "L" form magmatic belt ("arc"), from the Apuseni Mountains to Bulgaria, was forced. If we look closely at the spatial distribution of intrusive and effusive bodies, aspect also revealed by gravimetry studies (Andrei et al. 1989), we observe that they occupy areas with specific geometries, linked to or close to the Gosau-type basins, but strictly controlled by strike-slip fractures, similar to those that have controlled the appearance of Gosau basins (Drew, 2006). The metallogenesis associated with this magmatism is represented by metalliferous accumulations of Fe, Cu, Pb, Zn, with Au, Ag and W, Mo, B, Mg, Te, Bi, Sb, with a great typological variety, spatially controlled by the same type of fractures. It is evident that the transpressive-transtensive regime worked throughout the entire range of magmatic and metallogenetic activity, controlling it. In Banat region, as well as in the Apuseni Mountains, the end of the magmatic activity ceases with mineralizing and/or bearing mineralization lamprophyres. Being so, probably the lamprophyres attend or announce the metallogenetic event.
Acknowledgments
This work was supported by two grants of the Romanian Ministry of Research and Innovation, project number PN-III-P4-ID-PCCF-2016-4-0014, and project number PN-III-P1-1.2-PCCDI-2017-0346/29, both within PNCDI III
How to cite: Tatu, M. and Iatan, E. L.: New approaches regarding the geodynamic constraints of Late Cretaceous magmatism in Carpathian area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2904, https://doi.org/10.5194/egusphere-egu2020-2904, 2020.
During the Meso-Cretaceous compressive tectonic event (marked by the subduction of the East European Platform under Gondwana, and the initiation of the creation of accretionary prism in front of the orogen) the absence of related magmatism, and implicitly, the lack of an "arc" is similar to that of the Alps (McCarthy et al., 2018). Afterward, in the Upper Cretaceous, the Carpathian area has evolved in an extensional geodynamic context, specific to post-collisional periods, marked by the appearance of sedimentary basins with complex evolution and Gosau type molasses (Schuller, 2004; Schuller et al., 2009). In connection to the above, or not, it has evolved a complex magmatism, from a compositional point of view and as manifestation, largely calc-alkaline, known in the geological literature as banatitic (von Cotta, 1864). Banatitic magmatism is the first such manifestation in the Carpathians, post-subduction and post-collision and the most reliable age data (using U-Pb on zircon and Re-Os on molybdenite methods) suggest a very narrow range of evolution (70.2 - 83.98 Ma, Nicolescu et al., 1999; Galhofer, 2015; 72.36 - 80.63 Ma, Ciobanu et al., 2002; Zimmerman et al., 2008), that is characteristic to short-lived magmatism. Comparatively, in Serbia (Bor-Madjanpek district), the same magmatism occurs between 86-84 Ma, in Bulgaria in the Srednogorie massif between 92-86 Ma and Rhodope massif at 67-70 Ma (von Quadt et al., 2007). The geodynamic models discussed for this type of magmatism suggest, almost all without exception, the existence of subductions that would have extended as activity from the Middle Cretaceous to the Paleogene. Or, the realities of the terrain show that this magmatism seals the mesocretacic compressive structures (napes), as Nicolescu et al. (1999) exposed for the first time in Banat region. The situation is similar in the Apuseni Mountains. From the presumption of the generation of subductions for this magmatism, the idea of an "L" form magmatic belt ("arc"), from the Apuseni Mountains to Bulgaria, was forced. If we look closely at the spatial distribution of intrusive and effusive bodies, aspect also revealed by gravimetry studies (Andrei et al. 1989), we observe that they occupy areas with specific geometries, linked to or close to the Gosau-type basins, but strictly controlled by strike-slip fractures, similar to those that have controlled the appearance of Gosau basins (Drew, 2006). The metallogenesis associated with this magmatism is represented by metalliferous accumulations of Fe, Cu, Pb, Zn, with Au, Ag and W, Mo, B, Mg, Te, Bi, Sb, with a great typological variety, spatially controlled by the same type of fractures. It is evident that the transpressive-transtensive regime worked throughout the entire range of magmatic and metallogenetic activity, controlling it. In Banat region, as well as in the Apuseni Mountains, the end of the magmatic activity ceases with mineralizing and/or bearing mineralization lamprophyres. Being so, probably the lamprophyres attend or announce the metallogenetic event.
Acknowledgments
This work was supported by two grants of the Romanian Ministry of Research and Innovation, project number PN-III-P4-ID-PCCF-2016-4-0014, and project number PN-III-P1-1.2-PCCDI-2017-0346/29, both within PNCDI III
How to cite: Tatu, M. and Iatan, E. L.: New approaches regarding the geodynamic constraints of Late Cretaceous magmatism in Carpathian area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2904, https://doi.org/10.5194/egusphere-egu2020-2904, 2020.
EGU2020-4336 | Displays | TS6.4
Vein-plus-wall rock melting model for the origin of Early Paleozoic alkali diabases in South Qinling Belt, Central ChinaFangyi Zhang and Shaocong Lai
Early Paleozoic mafic dykes are widespread in South Qinling Belt, central China. In this study, we present new major element, trace element, zircon U–Pb age and Sr–Nd–Hf isotopic results of Early Paleozoic diabases dykes in the South Qinling Belt to explore nature of the mantle source. The South Qinling Belt diabases have low SiO2 (42.1–49.5 wt%) high TiO2 (2.89–5.17 wt%), variable MgO (4.0–9.4 wt%) contents. In primitive mantle normalized multielement diagrams, all samples are strongly enriched in the majority of incompatible trace elements but systematic depletion in Rb, K, Pb, Zr and Hf. The negative K and Rb anomaly together with high TiO2 and high Na2O/K2O character suggest magma was derived from a source rich in amphibole. Partial melting modelling indicate 20–36% partial melting of amphibole-clinopyroxene-phlogopite veins with subsequent dissolution of ~30% orthopyroxene from the wall-rock peridotite within spinel stability field can produce the observed compositions of diabases. Additionally, South Qinling Belt diabases are characterized by moderately depleted Nd (εNd(t)= +2.2 to 3.3) and Hf (εHf(t)= +6.2 to 7.2) isotopic compositions without pronounced isotope decoupling, indicating mantle metasomatism occurred shortly prior to Early Paleozoic magmatism. It is proposed that low-degree silicate melts released from asthenosphere infiltrated and solidified within lithospheric mantle, forming non-peridotitic lithologies rich in amphibole clinopyroxene and phlogopite. Subsequent lithosphere extension caused the melting of the most easily fusible material in the lithosphere, which gave rise to the Early Paleozoic alkaline magmatism in South Qinling.
How to cite: Zhang, F. and Lai, S.: Vein-plus-wall rock melting model for the origin of Early Paleozoic alkali diabases in South Qinling Belt, Central China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4336, https://doi.org/10.5194/egusphere-egu2020-4336, 2020.
Early Paleozoic mafic dykes are widespread in South Qinling Belt, central China. In this study, we present new major element, trace element, zircon U–Pb age and Sr–Nd–Hf isotopic results of Early Paleozoic diabases dykes in the South Qinling Belt to explore nature of the mantle source. The South Qinling Belt diabases have low SiO2 (42.1–49.5 wt%) high TiO2 (2.89–5.17 wt%), variable MgO (4.0–9.4 wt%) contents. In primitive mantle normalized multielement diagrams, all samples are strongly enriched in the majority of incompatible trace elements but systematic depletion in Rb, K, Pb, Zr and Hf. The negative K and Rb anomaly together with high TiO2 and high Na2O/K2O character suggest magma was derived from a source rich in amphibole. Partial melting modelling indicate 20–36% partial melting of amphibole-clinopyroxene-phlogopite veins with subsequent dissolution of ~30% orthopyroxene from the wall-rock peridotite within spinel stability field can produce the observed compositions of diabases. Additionally, South Qinling Belt diabases are characterized by moderately depleted Nd (εNd(t)= +2.2 to 3.3) and Hf (εHf(t)= +6.2 to 7.2) isotopic compositions without pronounced isotope decoupling, indicating mantle metasomatism occurred shortly prior to Early Paleozoic magmatism. It is proposed that low-degree silicate melts released from asthenosphere infiltrated and solidified within lithospheric mantle, forming non-peridotitic lithologies rich in amphibole clinopyroxene and phlogopite. Subsequent lithosphere extension caused the melting of the most easily fusible material in the lithosphere, which gave rise to the Early Paleozoic alkaline magmatism in South Qinling.
How to cite: Zhang, F. and Lai, S.: Vein-plus-wall rock melting model for the origin of Early Paleozoic alkali diabases in South Qinling Belt, Central China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4336, https://doi.org/10.5194/egusphere-egu2020-4336, 2020.
TS7.1 – Apennines tectonics, sedimentation and magmatism from Permian to Present
EGU2020-11301 | Displays | TS7.1 | Highlight
Kinematic reconstructions of the Western Mediterranean area since Triassic time: possible scenarios and their implications for the ApenninesEline Le Breton
The Western Mediterranean-Alpine belt is remarkable for its tectonic complexity, i.e. strong arcuation of plate boundaries, fast trench retreat, upper-plate extension and switch of subduction/collision polarity around the Adriatic plate (Adria). The kinematic evolution of the Western Mediterranean area is enigmatic due to the intermittently motion of small continental plates (Adria, Iberia and Sardinia-Corsica) that are caught between two major plates (Africa and Europe), converging since Cretaceous time. Reconstructing the past motion of these micro-plates is challenging due to the strong deformation of their boundaries but is key to understand the geodynamic evolution of the whole area.
The Neogene tectonic evolution is well constrained using magnetic anomalies and transform zones in the Atlantic Ocean for the motion of Europe, Iberia and Africa, and by reconstructing the amount of convergence along fold-and-thrust belts (Apennines, Alps, Dinarides, Provence) and coeval divergence along extensional basins (Liguro-Provencal and Tyrrhenian basins, Sicily Channel Rift Zone) for the motion of Adria and Sardinia-Corsica. Those reconstructions show that Adria had a slight independent motion from Africa and rotated counter-clockwise of about 5º relative to Europe since 20 Ma. However, uncertainties increase and debates arise as one goes back in time. The main debates concern the past motion of Iberia and where its motion relative to Europe is being accommodated in Mesozoic time. Different kinematic scenarios have been proposed depending on the interpretation of paleomagnetic dataset of Iberia, magnetic anomalies in the North Atlantic, and geological-geophysical record of deformation in the Pyrenees and between Iberia and Sardinia-Corsica. Those scenarios have different implications for the tectonic evolution of the Apennines, especially for the Permian-Triassic paleo-tectonic setting of Sardinia, Calabria and Adria, and for the extent and timing of closure of the Liguro-Piemont Ocean. It is important to discuss those implications to better understand subduction processes in the Apennines and their driving forces.
How to cite: Le Breton, E.: Kinematic reconstructions of the Western Mediterranean area since Triassic time: possible scenarios and their implications for the Apennines, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11301, https://doi.org/10.5194/egusphere-egu2020-11301, 2020.
The Western Mediterranean-Alpine belt is remarkable for its tectonic complexity, i.e. strong arcuation of plate boundaries, fast trench retreat, upper-plate extension and switch of subduction/collision polarity around the Adriatic plate (Adria). The kinematic evolution of the Western Mediterranean area is enigmatic due to the intermittently motion of small continental plates (Adria, Iberia and Sardinia-Corsica) that are caught between two major plates (Africa and Europe), converging since Cretaceous time. Reconstructing the past motion of these micro-plates is challenging due to the strong deformation of their boundaries but is key to understand the geodynamic evolution of the whole area.
The Neogene tectonic evolution is well constrained using magnetic anomalies and transform zones in the Atlantic Ocean for the motion of Europe, Iberia and Africa, and by reconstructing the amount of convergence along fold-and-thrust belts (Apennines, Alps, Dinarides, Provence) and coeval divergence along extensional basins (Liguro-Provencal and Tyrrhenian basins, Sicily Channel Rift Zone) for the motion of Adria and Sardinia-Corsica. Those reconstructions show that Adria had a slight independent motion from Africa and rotated counter-clockwise of about 5º relative to Europe since 20 Ma. However, uncertainties increase and debates arise as one goes back in time. The main debates concern the past motion of Iberia and where its motion relative to Europe is being accommodated in Mesozoic time. Different kinematic scenarios have been proposed depending on the interpretation of paleomagnetic dataset of Iberia, magnetic anomalies in the North Atlantic, and geological-geophysical record of deformation in the Pyrenees and between Iberia and Sardinia-Corsica. Those scenarios have different implications for the tectonic evolution of the Apennines, especially for the Permian-Triassic paleo-tectonic setting of Sardinia, Calabria and Adria, and for the extent and timing of closure of the Liguro-Piemont Ocean. It is important to discuss those implications to better understand subduction processes in the Apennines and their driving forces.
How to cite: Le Breton, E.: Kinematic reconstructions of the Western Mediterranean area since Triassic time: possible scenarios and their implications for the Apennines, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11301, https://doi.org/10.5194/egusphere-egu2020-11301, 2020.
EGU2020-5328 | Displays | TS7.1
Magmatism and mantle evolution in the Northern Apennines: a tale of rifting, oceanization and subductionAlessandra Montanini
The Apennine magmatism from Early Permian to present may be considered as the result of a Wilson cycle. Here, the main stages of this magmatic activity will be reviewed from a mantle source perspective in the framework of the Alpine-Apennine system. The oldest magmatic event is represented by gabbro-derived granulites of Late Variscan age, now occurring as blocks in Late Cretaceous orogenic melanges. Their protholiths were recognized as deep crustal cumulates derived from MOR-type tholeiitic liquids. This event may be related to the extensive magmatic underplating affecting SW Europe in conjuction with lithospheric thinning and orogenic collapse of the Variscan belt. The subsequent Mesozoic continental rifting preceding the opening of the Jurassic Ligurian Tethys was mostly amagmatic. Nevertheless, widespread evidence of melt migration in the ascending lithosphere during passive asthenospheric upwelling is testified in the exhumed mantle bodies from the Northern Apennine ophiolites. Mantle rocks showing a considerable geochemical and isotope heterogeneity were a dominant component of the Ligurian Tethys oceanic lithosphere. In contrast, the short-lived magmatism of the Ligurian Tethys (ca. 160-165 Ma) was characterized by uniform N-MORB signatures, both in marginal and oceanward domains of the basin, which were related to embryonic and slow-spreading ridge type oceanic lithosphere, respectively. The Nd-Hf isotopic contrast between magmatic products and associated mantle rocks (Rampone et al., 1998; Mc Carthy et al., 2015; Barry et al., 2017; this work) is a debated issue, which could reflect the occurrence of inherited subcontinental mantle or ancient depleted domains in the convecting upper mantle. The subduction initiation in the Northern Apennine was not related to igneous activity. No record of island-arc magmatism linked to the Alpine east-dipping subduction stage has been recognized, possibly due to dry, mantle-dominated, subducted lithosphere (Mc Carthy et al., 2018). On the other hand, the collisional calc-alkaline magmatism coheval with the west-dipping Apennine subduction system was found only as clasts in sediments from the nascent orogen (Aveto-Petrignacola Formation). Ancient modifications of mantle sources, possibly related to the previous subduction event, have been proposed for the origin of this magmatism (Mattioli et al., 2012). The imprint of Apennine subduction on mantle sources is strikingly attested by the recent volcanism (< 5 Ma), which includes the unique magmatic associations from Tuscany and Roman provinces. Here, leucite-free (lamproites, shoshonites) and leucite-bearing (kamafugite, leucitite, plagioleucitite) K-rich magmas, were erupted in the former domains, and locally hybridized with anatectic melts. Mantle melting was triggered by post-orogenic extension following the eastward migration of the Adriatic slab. Mantle source modification through recycling of different sedimentary lithologies from the subducted slab may explain the extreme incompatible trace element enrichments and Sr-Pb-Nd-Hf isotopic signatures of the ultrapotassic magmas, coupled with their subduction-related geochemical affinity (Conticelli et al., 2015).
References
Barry et al., 2017. Sci. Reports 7, 1870
Conticelli et al., 2015. Lithos 232, 174–196
Mattioli et al., 2012. Lithos 134-135, 201–220.
Mc Carthy and Muntener, 2015. Geology 43, 255–258
Mc Carthy et al., 2018. Geology 46, 1059–1062
Rampone et al., 1998. Earth Planet. Sci. Lett. 163, 175–189
How to cite: Montanini, A.: Magmatism and mantle evolution in the Northern Apennines: a tale of rifting, oceanization and subduction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5328, https://doi.org/10.5194/egusphere-egu2020-5328, 2020.
The Apennine magmatism from Early Permian to present may be considered as the result of a Wilson cycle. Here, the main stages of this magmatic activity will be reviewed from a mantle source perspective in the framework of the Alpine-Apennine system. The oldest magmatic event is represented by gabbro-derived granulites of Late Variscan age, now occurring as blocks in Late Cretaceous orogenic melanges. Their protholiths were recognized as deep crustal cumulates derived from MOR-type tholeiitic liquids. This event may be related to the extensive magmatic underplating affecting SW Europe in conjuction with lithospheric thinning and orogenic collapse of the Variscan belt. The subsequent Mesozoic continental rifting preceding the opening of the Jurassic Ligurian Tethys was mostly amagmatic. Nevertheless, widespread evidence of melt migration in the ascending lithosphere during passive asthenospheric upwelling is testified in the exhumed mantle bodies from the Northern Apennine ophiolites. Mantle rocks showing a considerable geochemical and isotope heterogeneity were a dominant component of the Ligurian Tethys oceanic lithosphere. In contrast, the short-lived magmatism of the Ligurian Tethys (ca. 160-165 Ma) was characterized by uniform N-MORB signatures, both in marginal and oceanward domains of the basin, which were related to embryonic and slow-spreading ridge type oceanic lithosphere, respectively. The Nd-Hf isotopic contrast between magmatic products and associated mantle rocks (Rampone et al., 1998; Mc Carthy et al., 2015; Barry et al., 2017; this work) is a debated issue, which could reflect the occurrence of inherited subcontinental mantle or ancient depleted domains in the convecting upper mantle. The subduction initiation in the Northern Apennine was not related to igneous activity. No record of island-arc magmatism linked to the Alpine east-dipping subduction stage has been recognized, possibly due to dry, mantle-dominated, subducted lithosphere (Mc Carthy et al., 2018). On the other hand, the collisional calc-alkaline magmatism coheval with the west-dipping Apennine subduction system was found only as clasts in sediments from the nascent orogen (Aveto-Petrignacola Formation). Ancient modifications of mantle sources, possibly related to the previous subduction event, have been proposed for the origin of this magmatism (Mattioli et al., 2012). The imprint of Apennine subduction on mantle sources is strikingly attested by the recent volcanism (< 5 Ma), which includes the unique magmatic associations from Tuscany and Roman provinces. Here, leucite-free (lamproites, shoshonites) and leucite-bearing (kamafugite, leucitite, plagioleucitite) K-rich magmas, were erupted in the former domains, and locally hybridized with anatectic melts. Mantle melting was triggered by post-orogenic extension following the eastward migration of the Adriatic slab. Mantle source modification through recycling of different sedimentary lithologies from the subducted slab may explain the extreme incompatible trace element enrichments and Sr-Pb-Nd-Hf isotopic signatures of the ultrapotassic magmas, coupled with their subduction-related geochemical affinity (Conticelli et al., 2015).
References
Barry et al., 2017. Sci. Reports 7, 1870
Conticelli et al., 2015. Lithos 232, 174–196
Mattioli et al., 2012. Lithos 134-135, 201–220.
Mc Carthy and Muntener, 2015. Geology 43, 255–258
Mc Carthy et al., 2018. Geology 46, 1059–1062
Rampone et al., 1998. Earth Planet. Sci. Lett. 163, 175–189
How to cite: Montanini, A.: Magmatism and mantle evolution in the Northern Apennines: a tale of rifting, oceanization and subduction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5328, https://doi.org/10.5194/egusphere-egu2020-5328, 2020.
EGU2020-17862 | Displays | TS7.1
Oligocene-Miocene tectonics of the SW Alps and western Apennines coupled orogenic belts, as recorded by their internal and external syn-orogenic basinsLuca Barale, Piana Fabrizio, Bertok Carlo, d'Atri Anna, Irace Andrea, and Martire Luca
The Oligocene-Miocene evolution of the westernmost part of the Northern Apennines was constrained firstly by Oligocene E-W regional sinistral shearing and then by Early Miocene shortening and Middle to Late Miocene NW-SE dextral transpression affecting the southern termination of the Western Alps arc (Maritime and Ligurian Alps) and the substrate of the Tertiary Piemonte Basin (TPB), which started to be incorporated, in the same time span, in the Northern Apennines belt
In other words, the dynamics accommodating the different motion of the WNW-directed Adria and SW Alps with respect to the ENE-directed Ligurian-Corso-Sardinian block also controlled the evolution of TPB and its Ligurian substrate since at least the Aquitanian, when a regional conterclockwise rotation began and a deep reshaping of the basin occurred, due to predominant NE-SW shortening concomitant with the Northern Apennines thrust fronts propagation (Burdigalian). On the other side, the infilling of the SW Alps foreland basin was partially controlled also by the resedimentation of non-metamorphic Cretaceous-Paleocene Ligurian units previously deposited along the Briançonnais-Dauphinois continental margin. The subsequent Late Burdigalian to Serravallian extension in the internal side of the SW Alps allowed the creation of accomodation space and the deposition of relevant thickness of sediments in the TPB, during the coeval progressive uplifting of Alpine crystalline and metamorphic units (e.g. the Argentera Massif and Dora-Maira Unit). This Alpine process constrained the shape and evolution of the TPB syn-orogenic sub-basins and their subsequent tectonic paths within the NW Apennines belt, while it was being built. The steps of this Alps-Apennines evolution have been clearly recorded by a set of regional scale, Oligocene to Pleistocene unconformities that can be continuously traced at surface in the southern part of the Piemonte region and in the subsurface of the western Po plain.
We thus remark that the evolution of the westernmost part of the Apennines can be studied largely referring to the Alpine geodynamics, since, although the Alps and the Apennines are two distinct geomorphologic and geophysical entities at the scale of the Western Mediterranean area, they share common synorogenic basins and consistent kinematic evolution in their junction zone of NW Italy.
How to cite: Barale, L., Fabrizio, P., Carlo, B., Anna, D., Andrea, I., and Luca, M.: Oligocene-Miocene tectonics of the SW Alps and western Apennines coupled orogenic belts, as recorded by their internal and external syn-orogenic basins, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17862, https://doi.org/10.5194/egusphere-egu2020-17862, 2020.
The Oligocene-Miocene evolution of the westernmost part of the Northern Apennines was constrained firstly by Oligocene E-W regional sinistral shearing and then by Early Miocene shortening and Middle to Late Miocene NW-SE dextral transpression affecting the southern termination of the Western Alps arc (Maritime and Ligurian Alps) and the substrate of the Tertiary Piemonte Basin (TPB), which started to be incorporated, in the same time span, in the Northern Apennines belt
In other words, the dynamics accommodating the different motion of the WNW-directed Adria and SW Alps with respect to the ENE-directed Ligurian-Corso-Sardinian block also controlled the evolution of TPB and its Ligurian substrate since at least the Aquitanian, when a regional conterclockwise rotation began and a deep reshaping of the basin occurred, due to predominant NE-SW shortening concomitant with the Northern Apennines thrust fronts propagation (Burdigalian). On the other side, the infilling of the SW Alps foreland basin was partially controlled also by the resedimentation of non-metamorphic Cretaceous-Paleocene Ligurian units previously deposited along the Briançonnais-Dauphinois continental margin. The subsequent Late Burdigalian to Serravallian extension in the internal side of the SW Alps allowed the creation of accomodation space and the deposition of relevant thickness of sediments in the TPB, during the coeval progressive uplifting of Alpine crystalline and metamorphic units (e.g. the Argentera Massif and Dora-Maira Unit). This Alpine process constrained the shape and evolution of the TPB syn-orogenic sub-basins and their subsequent tectonic paths within the NW Apennines belt, while it was being built. The steps of this Alps-Apennines evolution have been clearly recorded by a set of regional scale, Oligocene to Pleistocene unconformities that can be continuously traced at surface in the southern part of the Piemonte region and in the subsurface of the western Po plain.
We thus remark that the evolution of the westernmost part of the Apennines can be studied largely referring to the Alpine geodynamics, since, although the Alps and the Apennines are two distinct geomorphologic and geophysical entities at the scale of the Western Mediterranean area, they share common synorogenic basins and consistent kinematic evolution in their junction zone of NW Italy.
How to cite: Barale, L., Fabrizio, P., Carlo, B., Anna, D., Andrea, I., and Luca, M.: Oligocene-Miocene tectonics of the SW Alps and western Apennines coupled orogenic belts, as recorded by their internal and external syn-orogenic basins, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17862, https://doi.org/10.5194/egusphere-egu2020-17862, 2020.
EGU2020-22549 | Displays | TS7.1
Structural analysis and 3D geological modelling of the Santerno transect in the Northern Apennines (Italy)Griso Lorenzo, Bistacchi Andrea, and Storti Fabrizio
We present preliminary results of a structural analysis and 3D modelling project carried out along a transect in the Santerno Valley, between Firenzuola (Tuscany) and the outskirts of Imola. The aim of the project is to combine surface geological and structural data (available thanks to the national geological mapping CARG project and original surveys), with the available subsurface data (2D seismics and a few wells), and obtain a comprehensive 3D framework for deformation in this key area of the Northern Apennines. In addition, by combining geodetic, seismicity and interferometric data with the 3D structural model, we are able to obtain a better picture of the active structures in the area.
Our analysis shows that the studied transect is at the northern periclinal hinge of a regional anticline/window where the Marnoso-Arenacea Formation crops out and is crosscut by several regional-scale thrusts. Subsurface data suggest that these relatively shallow thrusts are rooted at the top of Mesozoic carbonates, that do not crop out in the area. Different balancing algorithms confirm a relevant along-strike variation of slip along these thrusts, that reduce their offset towards the periclinal hinge to the west.
In the more external part of the transect, towards the lower hills and the plain around Imola, a regional-scale pop-up, evidenced by the late-Messinian unconformity, is the main feature in subsurface datasets. This structure is rooted at the base of Mesozoic carbonates and is characterized by large and continuous ramps that can be considered candidates for recent earthquakes in the area.
How to cite: Lorenzo, G., Andrea, B., and Fabrizio, S.: Structural analysis and 3D geological modelling of the Santerno transect in the Northern Apennines (Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22549, https://doi.org/10.5194/egusphere-egu2020-22549, 2020.
We present preliminary results of a structural analysis and 3D modelling project carried out along a transect in the Santerno Valley, between Firenzuola (Tuscany) and the outskirts of Imola. The aim of the project is to combine surface geological and structural data (available thanks to the national geological mapping CARG project and original surveys), with the available subsurface data (2D seismics and a few wells), and obtain a comprehensive 3D framework for deformation in this key area of the Northern Apennines. In addition, by combining geodetic, seismicity and interferometric data with the 3D structural model, we are able to obtain a better picture of the active structures in the area.
Our analysis shows that the studied transect is at the northern periclinal hinge of a regional anticline/window where the Marnoso-Arenacea Formation crops out and is crosscut by several regional-scale thrusts. Subsurface data suggest that these relatively shallow thrusts are rooted at the top of Mesozoic carbonates, that do not crop out in the area. Different balancing algorithms confirm a relevant along-strike variation of slip along these thrusts, that reduce their offset towards the periclinal hinge to the west.
In the more external part of the transect, towards the lower hills and the plain around Imola, a regional-scale pop-up, evidenced by the late-Messinian unconformity, is the main feature in subsurface datasets. This structure is rooted at the base of Mesozoic carbonates and is characterized by large and continuous ramps that can be considered candidates for recent earthquakes in the area.
How to cite: Lorenzo, G., Andrea, B., and Fabrizio, S.: Structural analysis and 3D geological modelling of the Santerno transect in the Northern Apennines (Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22549, https://doi.org/10.5194/egusphere-egu2020-22549, 2020.
EGU2020-6923 | Displays | TS7.1
Cyclic brittle-ductile behaviour recorded in exhuming high-pressure continental units of the Northern Apennines.Francesco Giuntoli and Giulio Viola
Exhumation of subducted high-pressure units is favoured by relatively narrow, high-strain shear zones, where most metamorphic and deformational processes occur. Unfortunately, these are commonly overprinted and/or partly or fully obliterated along the exhumation path by younger fabrics or by metamorphic re-equilibration. Their identification and characterization are, therefore, of primary importance when aiming at reconstructing the deepest (and thus earliest) tectonometamorphic history of high-pressure crustal units.
The Northern Apennines (Italy) offer the opportunity to study a unique setting where continental units (Tuscan Metamorphic Units) were subducted to high-pressure conditions and then exhumed and juxtaposed against non-metamorphic units (Tuscan Nappe). We have studied a well exposed section in the Monticiano-Roccastrada Unit of the Mid Tuscan Ridge (MTR), where a mesoscopic (~20 m length and 5 m high) compressional duplex deforms the Palaeozoic-Triassic quartz-rich metasandstones, metaconglomerates and minor metapelites of the Monte Quoio - Montagnola Senese Unit with a top-to-the-NE sense of shear (Arenarie di Poggio al Carpino Formation; Casini et al., 2007).
Our approach is based on detailed fieldwork, microstructural and petrological investigations. Field observations reveal severe strain partitioning within the duplex between metapelite levels, corresponding to 10-50 cm thick high-strain zones, and metasandstone levels, which form relatively strain-free metric horses. Early generations of quartz veins are highly transposed (sheath folds occur) parallel to the metapelitic high-strain shear zones. Veins are composed of iso-oriented quartz, forming up to several centimetre long single-grain ribbons, Mg-carpholite (XMg~ 0.65) needles and K-white mica marking the stretching lineation. Carpholite in the transposed veins invariably defines the stretching direction of shear zones. These high-P veins coexist with a later generation of less deformed, oblique quartz veins. The mylonitic foliation in the metapelites is defined by quartz, chloritoid, pyrophyllite and K-white mica forming a stretching lineation coherent with the one visible in the veins. Geometrical, cross-cutting and petrographic relations suggest that there has occurred cyclic deformation between brittle and viscous conditions, with the veins forming broadly syn-mylonitic shearing. Thermodynamic modeling results suggest >0.8 GPa and ~350°C for the formation of both the high-pressure veins and the mylonitic foliation.
Shear zones were subsequently folded about the NNW-SSE axis of the regional antiform associated with the MTR. Later brittle overprinting is represented by quart-filled tension gashes and localized C’ planes, mostly within the more competent metasandstone levels, indicating top-to-the-SW reactivation. In summary, our results suggest a cyclic brittle-ductile behaviour occurring at high pressure conditions. This could potentially reflect the repeated alternation between aseismic creep (viscous) and coseismic slip (brittle) during the first stages of the exhumation history of this portion of the northern Apennines, from lower to middle crustal levels in a compressional top-to-the-NE setting. Dating of K-white mica is ongoing to constrain the geodynamic scenario of such shear zone.
Casini, G., Decandia, F.A., Tavarnelli, E., 2007. Analysis of a mesoscopic duplex in SW Tuscany, Italy: implications for thrust system development during positive tectonic inversion. Geol. Soc. London, Spec. Publ. 272, 437–446.
How to cite: Giuntoli, F. and Viola, G.: Cyclic brittle-ductile behaviour recorded in exhuming high-pressure continental units of the Northern Apennines., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6923, https://doi.org/10.5194/egusphere-egu2020-6923, 2020.
Exhumation of subducted high-pressure units is favoured by relatively narrow, high-strain shear zones, where most metamorphic and deformational processes occur. Unfortunately, these are commonly overprinted and/or partly or fully obliterated along the exhumation path by younger fabrics or by metamorphic re-equilibration. Their identification and characterization are, therefore, of primary importance when aiming at reconstructing the deepest (and thus earliest) tectonometamorphic history of high-pressure crustal units.
The Northern Apennines (Italy) offer the opportunity to study a unique setting where continental units (Tuscan Metamorphic Units) were subducted to high-pressure conditions and then exhumed and juxtaposed against non-metamorphic units (Tuscan Nappe). We have studied a well exposed section in the Monticiano-Roccastrada Unit of the Mid Tuscan Ridge (MTR), where a mesoscopic (~20 m length and 5 m high) compressional duplex deforms the Palaeozoic-Triassic quartz-rich metasandstones, metaconglomerates and minor metapelites of the Monte Quoio - Montagnola Senese Unit with a top-to-the-NE sense of shear (Arenarie di Poggio al Carpino Formation; Casini et al., 2007).
Our approach is based on detailed fieldwork, microstructural and petrological investigations. Field observations reveal severe strain partitioning within the duplex between metapelite levels, corresponding to 10-50 cm thick high-strain zones, and metasandstone levels, which form relatively strain-free metric horses. Early generations of quartz veins are highly transposed (sheath folds occur) parallel to the metapelitic high-strain shear zones. Veins are composed of iso-oriented quartz, forming up to several centimetre long single-grain ribbons, Mg-carpholite (XMg~ 0.65) needles and K-white mica marking the stretching lineation. Carpholite in the transposed veins invariably defines the stretching direction of shear zones. These high-P veins coexist with a later generation of less deformed, oblique quartz veins. The mylonitic foliation in the metapelites is defined by quartz, chloritoid, pyrophyllite and K-white mica forming a stretching lineation coherent with the one visible in the veins. Geometrical, cross-cutting and petrographic relations suggest that there has occurred cyclic deformation between brittle and viscous conditions, with the veins forming broadly syn-mylonitic shearing. Thermodynamic modeling results suggest >0.8 GPa and ~350°C for the formation of both the high-pressure veins and the mylonitic foliation.
Shear zones were subsequently folded about the NNW-SSE axis of the regional antiform associated with the MTR. Later brittle overprinting is represented by quart-filled tension gashes and localized C’ planes, mostly within the more competent metasandstone levels, indicating top-to-the-SW reactivation. In summary, our results suggest a cyclic brittle-ductile behaviour occurring at high pressure conditions. This could potentially reflect the repeated alternation between aseismic creep (viscous) and coseismic slip (brittle) during the first stages of the exhumation history of this portion of the northern Apennines, from lower to middle crustal levels in a compressional top-to-the-NE setting. Dating of K-white mica is ongoing to constrain the geodynamic scenario of such shear zone.
Casini, G., Decandia, F.A., Tavarnelli, E., 2007. Analysis of a mesoscopic duplex in SW Tuscany, Italy: implications for thrust system development during positive tectonic inversion. Geol. Soc. London, Spec. Publ. 272, 437–446.
How to cite: Giuntoli, F. and Viola, G.: Cyclic brittle-ductile behaviour recorded in exhuming high-pressure continental units of the Northern Apennines., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6923, https://doi.org/10.5194/egusphere-egu2020-6923, 2020.
EGU2020-3258 | Displays | TS7.1
Hematite (U-Th)/He constraints on Plio-Pleistocene deformation and hydrothermalism in the eastern Island of Elba, northern Apennines (Italy)Giulio Viola, Alexis Derycke, Cécile Gautheron, Francesco Mazzarini, Giovanni Musumeci, and Paolo Stefano Garofalo
The northern Tyrrhenian Sea and the inner northern Apennines (NA) are classically regarded as a late Miocene–Pleistocene back-arc system characterized by crustal extension and acidic magmatism coeval with shortening farther east at the front of the belt. The orogenic prism of the NA, which is well exposed in the easternmost Island of Elba, formed by eastward thrusting, stacking and folding of oceanic and continental units from the Eocene down to the late Miocene. Eastern Elba hosts the historically and economically most important Fe district of Italy, which, in the study area, consists of sulphide- and Fe-rich veins and breccias, in addition to minor massive Fe ore bodies of hydrothermal origin emplaced in actively deforming upper crustal conditions (Mazzarini et al., JSG, 2019). The Zuccale fault (ZF) on Elba is generally interpreted as a major normal fault, which would have greatly facilitated regional E-W extension during the late Miocene. It is an east-dipping low angle fault that displaces the nappe pile by up to 6 km. The fault architecture is complex, although it can be approximated by an exclusively brittle, flat-lying component dated to < c. 5 Ma by K-Ar on illite from fault gouge that cuts through steeper, brittle-ductile and earlier top-to-the E thrust related fabrics (Viola et al., Tectonics, 2018).
Aiming at directly constraining the syn- to post Pliocene evolution of the ZF and the age of the hydrothermal Fe deposits of the historic mining district, we performed hematite (U-Th)/He dating of the low-angle, hematite-decorated principal slip surface of the ZF at the famous Terra Nera section. Hematite samples examined in this study comprise platelet-shaped crystals (specularite), fine aggregates coating fault slip surfaces, massive veins, the fine matrix of breccias, and euhedral millimetric crystals from low strain domains. Ages from the ZF striated fault plane span the ~4.2±0.4 to 3.6±0.4 Ma time interval, fully consistent with available fault gouge illite K-Ar dates. Later NNE-SSW strike-slip faulting, associated with centimetric specularite veins, is constrained to between 2.1±0.2 and 1.7±0.2 Ma, roughly coeval with transient and local reactivation of the ZF as indicated by 1.9±0.2-1.5±0.2 Ma old euhedral, millimetric hematite infilling dilational jogs within the foliated ZF fault zone. Farther north, in the Rio Albano area, mineralised hematite breccias genetically associated with top-to-the E spectacular extensional faults are dated to between 1.6±0.2 and 0.9±0.1 Ma and postdate older ~2.7-2.6 Ma quartz-hematite veins associated with a discrete phase of top-to-the W shearing.
All obtained dates fit our independently built structural model of the investigated area, where clear crosscutting relationships and structural/metamorphic considerations have permitted establishing a sequence of kinematically constrained deformation events. For the first time we have defined the exact timing of deformation in the study area, contributing to the unravelling of the local, long and complex tectonic and mineralization history and to a better constrained regional picture.
How to cite: Viola, G., Derycke, A., Gautheron, C., Mazzarini, F., Musumeci, G., and Garofalo, P. S.: Hematite (U-Th)/He constraints on Plio-Pleistocene deformation and hydrothermalism in the eastern Island of Elba, northern Apennines (Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3258, https://doi.org/10.5194/egusphere-egu2020-3258, 2020.
The northern Tyrrhenian Sea and the inner northern Apennines (NA) are classically regarded as a late Miocene–Pleistocene back-arc system characterized by crustal extension and acidic magmatism coeval with shortening farther east at the front of the belt. The orogenic prism of the NA, which is well exposed in the easternmost Island of Elba, formed by eastward thrusting, stacking and folding of oceanic and continental units from the Eocene down to the late Miocene. Eastern Elba hosts the historically and economically most important Fe district of Italy, which, in the study area, consists of sulphide- and Fe-rich veins and breccias, in addition to minor massive Fe ore bodies of hydrothermal origin emplaced in actively deforming upper crustal conditions (Mazzarini et al., JSG, 2019). The Zuccale fault (ZF) on Elba is generally interpreted as a major normal fault, which would have greatly facilitated regional E-W extension during the late Miocene. It is an east-dipping low angle fault that displaces the nappe pile by up to 6 km. The fault architecture is complex, although it can be approximated by an exclusively brittle, flat-lying component dated to < c. 5 Ma by K-Ar on illite from fault gouge that cuts through steeper, brittle-ductile and earlier top-to-the E thrust related fabrics (Viola et al., Tectonics, 2018).
Aiming at directly constraining the syn- to post Pliocene evolution of the ZF and the age of the hydrothermal Fe deposits of the historic mining district, we performed hematite (U-Th)/He dating of the low-angle, hematite-decorated principal slip surface of the ZF at the famous Terra Nera section. Hematite samples examined in this study comprise platelet-shaped crystals (specularite), fine aggregates coating fault slip surfaces, massive veins, the fine matrix of breccias, and euhedral millimetric crystals from low strain domains. Ages from the ZF striated fault plane span the ~4.2±0.4 to 3.6±0.4 Ma time interval, fully consistent with available fault gouge illite K-Ar dates. Later NNE-SSW strike-slip faulting, associated with centimetric specularite veins, is constrained to between 2.1±0.2 and 1.7±0.2 Ma, roughly coeval with transient and local reactivation of the ZF as indicated by 1.9±0.2-1.5±0.2 Ma old euhedral, millimetric hematite infilling dilational jogs within the foliated ZF fault zone. Farther north, in the Rio Albano area, mineralised hematite breccias genetically associated with top-to-the E spectacular extensional faults are dated to between 1.6±0.2 and 0.9±0.1 Ma and postdate older ~2.7-2.6 Ma quartz-hematite veins associated with a discrete phase of top-to-the W shearing.
All obtained dates fit our independently built structural model of the investigated area, where clear crosscutting relationships and structural/metamorphic considerations have permitted establishing a sequence of kinematically constrained deformation events. For the first time we have defined the exact timing of deformation in the study area, contributing to the unravelling of the local, long and complex tectonic and mineralization history and to a better constrained regional picture.
How to cite: Viola, G., Derycke, A., Gautheron, C., Mazzarini, F., Musumeci, G., and Garofalo, P. S.: Hematite (U-Th)/He constraints on Plio-Pleistocene deformation and hydrothermalism in the eastern Island of Elba, northern Apennines (Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3258, https://doi.org/10.5194/egusphere-egu2020-3258, 2020.
EGU2020-5987 | Displays | TS7.1
The cooling, deformation and exhumation history of the late Miocene syn-tectonic Porto Azzurro pluton in a regional transfer zone (Elba Island, Italy)Andrea Brogi, Richard Spiess, Alfredo Caggianelli, Antonio Langone, Fin Stuart, Martina Zucchi, Caterina Bianco, and Domenico Liotta
In extensional tectonic settings, stretched terrains are often associated to lithosphere partial melting and widespread magmatism with plutons emplaced in the thinned crust. Emplacement of felsic magmas, at upper crustal levels, represents the final stage of the magma transfer from profound to shallow depth. In this framework, a mostly vertical permeability controls the magma uprising migration, as induced by dominant transcurrent crustal structures. Nevertheless, the interplay between extension and prolonged heat transfer favors uplift and progressive exhumation of the magmatic bodies, during their cooling.
In this presentation, we show an example of a felsic magmatic intrusion, the Porto Azzurro pluton (inner northern Apennines), emplaced in an extensional tectonic setting and mainly controlled by a regional transfer zone related to the opening of the Tyrrhenian Basin. This is exposed in the eastern Elba Island (Tuscan Archipelago). The hosting rocks of the Porto Azzurro pluton are mainly represented by micaschist, paragneiss and quartzite, affected by contact metamorphism and intense fluid circulation. We have analysed the structures that assisted the pluton emplacement and the ones that deformed the pluton itself during its cooling, from melt-present to brittle conditions, based on the integration among fieldwork, micro-structural, petrological and EBSD analyses. Furthermore, new U/Pb geochronological data on zircons and (U-Th)/He on apatite fission track refined the age of the pluton emplacement and its cooling, adding new data about the pluton history. Existing petrological analyses of the hosting rocks allowed us to better constrain the time-evolution of the thermal perturbation, permitting to frame the deformation and exhumation history of the Porto Azzurro monzogranite in the context of the Neogene extensional tectonics affecting the inner Northern Apennines.
How to cite: Brogi, A., Spiess, R., Caggianelli, A., Langone, A., Stuart, F., Zucchi, M., Bianco, C., and Liotta, D.: The cooling, deformation and exhumation history of the late Miocene syn-tectonic Porto Azzurro pluton in a regional transfer zone (Elba Island, Italy) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5987, https://doi.org/10.5194/egusphere-egu2020-5987, 2020.
In extensional tectonic settings, stretched terrains are often associated to lithosphere partial melting and widespread magmatism with plutons emplaced in the thinned crust. Emplacement of felsic magmas, at upper crustal levels, represents the final stage of the magma transfer from profound to shallow depth. In this framework, a mostly vertical permeability controls the magma uprising migration, as induced by dominant transcurrent crustal structures. Nevertheless, the interplay between extension and prolonged heat transfer favors uplift and progressive exhumation of the magmatic bodies, during their cooling.
In this presentation, we show an example of a felsic magmatic intrusion, the Porto Azzurro pluton (inner northern Apennines), emplaced in an extensional tectonic setting and mainly controlled by a regional transfer zone related to the opening of the Tyrrhenian Basin. This is exposed in the eastern Elba Island (Tuscan Archipelago). The hosting rocks of the Porto Azzurro pluton are mainly represented by micaschist, paragneiss and quartzite, affected by contact metamorphism and intense fluid circulation. We have analysed the structures that assisted the pluton emplacement and the ones that deformed the pluton itself during its cooling, from melt-present to brittle conditions, based on the integration among fieldwork, micro-structural, petrological and EBSD analyses. Furthermore, new U/Pb geochronological data on zircons and (U-Th)/He on apatite fission track refined the age of the pluton emplacement and its cooling, adding new data about the pluton history. Existing petrological analyses of the hosting rocks allowed us to better constrain the time-evolution of the thermal perturbation, permitting to frame the deformation and exhumation history of the Porto Azzurro monzogranite in the context of the Neogene extensional tectonics affecting the inner Northern Apennines.
How to cite: Brogi, A., Spiess, R., Caggianelli, A., Langone, A., Stuart, F., Zucchi, M., Bianco, C., and Liotta, D.: The cooling, deformation and exhumation history of the late Miocene syn-tectonic Porto Azzurro pluton in a regional transfer zone (Elba Island, Italy) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5987, https://doi.org/10.5194/egusphere-egu2020-5987, 2020.
EGU2020-9351 | Displays | TS7.1
Eastward Tectonic Escape of Sicily Microplate: preliminary resultsGiulia Penza, Chiara Macchiavelli, Pietro Paolo Pierantoni, and Eugenio Turco
The complex processes affecting the Tyrrhenian-Apennine System are inevitably reflected in Sicily, here considered as an independent plate starting from 5 Ma and located between Europe and Africa plates and Calabria microplate.
In particular the retreat of the Adriatic-Ionian slab and its fragmentation involve Sicily in a process of escape towards east-southeast due to the space that the slab is creating. At the same time Africa acts as an intender during its convergence with the European plate.
We show here the preliminary results of a study that aims to reconstruct the kinematic evolution of Sicily and its role in the framework of the Tyrrhenian-Apennine System.
First of all we found the margins of the plate, searching for lithospheric structures that can be considered as plate boundaries, using different types of data (high resolution bathymetric maps, seismic sections, geodetic data, focal mechanism of recent earthquakes, gravimetric maps, lithosphere thickness maps…) together with the literature.
The margins are:
-The Sicily Channel, characterized by a series of pull-apart basins related to a dextral trascurrent zone (Sicily-Africa margin);
-The Malta escarpment and the Taormina Line characterized by transpression (Sicily-Calabria margin);
-The Drepano-Ustica seamount also characterized by transpression (Sicily Europe margin).
Starting from the structures in the Sicily Channel, we found the Euler pole of rotation between Sicily and Africa using the GPlates software. Thanks to the software we were able to find also Sicily-Europe and Sicily-Calabria poles and the velocity vectors.
Finally, we compared the Euler poles and the velocity vectors with the geological data, trying the best fit of the two and better refine the model.
Key Words: Sicily microplate, Sicily Channel, Malta Escarpment, Tyrrhenian-Apennine System.
How to cite: Penza, G., Macchiavelli, C., Pierantoni, P. P., and Turco, E.: Eastward Tectonic Escape of Sicily Microplate: preliminary results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9351, https://doi.org/10.5194/egusphere-egu2020-9351, 2020.
The complex processes affecting the Tyrrhenian-Apennine System are inevitably reflected in Sicily, here considered as an independent plate starting from 5 Ma and located between Europe and Africa plates and Calabria microplate.
In particular the retreat of the Adriatic-Ionian slab and its fragmentation involve Sicily in a process of escape towards east-southeast due to the space that the slab is creating. At the same time Africa acts as an intender during its convergence with the European plate.
We show here the preliminary results of a study that aims to reconstruct the kinematic evolution of Sicily and its role in the framework of the Tyrrhenian-Apennine System.
First of all we found the margins of the plate, searching for lithospheric structures that can be considered as plate boundaries, using different types of data (high resolution bathymetric maps, seismic sections, geodetic data, focal mechanism of recent earthquakes, gravimetric maps, lithosphere thickness maps…) together with the literature.
The margins are:
-The Sicily Channel, characterized by a series of pull-apart basins related to a dextral trascurrent zone (Sicily-Africa margin);
-The Malta escarpment and the Taormina Line characterized by transpression (Sicily-Calabria margin);
-The Drepano-Ustica seamount also characterized by transpression (Sicily Europe margin).
Starting from the structures in the Sicily Channel, we found the Euler pole of rotation between Sicily and Africa using the GPlates software. Thanks to the software we were able to find also Sicily-Europe and Sicily-Calabria poles and the velocity vectors.
Finally, we compared the Euler poles and the velocity vectors with the geological data, trying the best fit of the two and better refine the model.
Key Words: Sicily microplate, Sicily Channel, Malta Escarpment, Tyrrhenian-Apennine System.
How to cite: Penza, G., Macchiavelli, C., Pierantoni, P. P., and Turco, E.: Eastward Tectonic Escape of Sicily Microplate: preliminary results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9351, https://doi.org/10.5194/egusphere-egu2020-9351, 2020.
EGU2020-9727 | Displays | TS7.1
The opening of the Tyrrhenian basin and the Apennine chain formation in the kinematic context of Africa - Europe collisionEugenio Turco, Chiara Macchiavelli, Pietro Paolo Pierantoni, Giulia Penza, and Antonio Schettino
The Africa Europe collision, which produces the formation of the Alpine arc, in the Mediterranean area is accompanied by passive subduction processes, resulting from the sinking of the remnant Alpine Tethys and the Ionian lithosphere, and from the fragmentation of the Adriatic plate. In this complex deformation, back-arc basins (Alboran, Balearic, Tyrrhenian and Hellenic) and circum - Mediterranean mountain ranges are formed.
In this work we focus our attention on the opening of the Tyrrhenian basin and the contemporary formation of the Apennine chain.
In order to describe the evolution of the geodynamic processes that guided the formation of the Tyrrhenian basin and the Apennine chain we used the plate kinematics technique. Through careful observation of the regional structures we have divided the area of the Apennine Chain and the Tyrrhenian basin into polygons (crustal blocks or microplates) distinguished on the basis of the direction of the Tyrrhenian extension. The boundary between the polygons has been placed coinciding with the large structures that characterize the Tyrrhenian-Apennine area. The rotation poles of the individual polygons, in the frame of reference of the Sardo-Corso block, are based on the Tyrrhenian extension directions that characterize them. The velocity ratio between the polygons was determined by the slip vector of the structure (plate boundary) that separates them. To determine the rotation time of the polygons we used the stratigraphic records of the syn-rift sequences, while the rotation angle of the polygons is obtained comparing the crustal balance with the speed ratios.
Finally, the kinematic framework obtained, included in the global rotation model, allowed us to reconstruct the tectonic evolution of the central Mediterranean during the opening of the Tyrrhenian basin.
Key Words: Tyrrhenian-Apennine System, Non-rigid plate kinematics.
How to cite: Turco, E., Macchiavelli, C., Pierantoni, P. P., Penza, G., and Schettino, A.: The opening of the Tyrrhenian basin and the Apennine chain formation in the kinematic context of Africa - Europe collision, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9727, https://doi.org/10.5194/egusphere-egu2020-9727, 2020.
The Africa Europe collision, which produces the formation of the Alpine arc, in the Mediterranean area is accompanied by passive subduction processes, resulting from the sinking of the remnant Alpine Tethys and the Ionian lithosphere, and from the fragmentation of the Adriatic plate. In this complex deformation, back-arc basins (Alboran, Balearic, Tyrrhenian and Hellenic) and circum - Mediterranean mountain ranges are formed.
In this work we focus our attention on the opening of the Tyrrhenian basin and the contemporary formation of the Apennine chain.
In order to describe the evolution of the geodynamic processes that guided the formation of the Tyrrhenian basin and the Apennine chain we used the plate kinematics technique. Through careful observation of the regional structures we have divided the area of the Apennine Chain and the Tyrrhenian basin into polygons (crustal blocks or microplates) distinguished on the basis of the direction of the Tyrrhenian extension. The boundary between the polygons has been placed coinciding with the large structures that characterize the Tyrrhenian-Apennine area. The rotation poles of the individual polygons, in the frame of reference of the Sardo-Corso block, are based on the Tyrrhenian extension directions that characterize them. The velocity ratio between the polygons was determined by the slip vector of the structure (plate boundary) that separates them. To determine the rotation time of the polygons we used the stratigraphic records of the syn-rift sequences, while the rotation angle of the polygons is obtained comparing the crustal balance with the speed ratios.
Finally, the kinematic framework obtained, included in the global rotation model, allowed us to reconstruct the tectonic evolution of the central Mediterranean during the opening of the Tyrrhenian basin.
Key Words: Tyrrhenian-Apennine System, Non-rigid plate kinematics.
How to cite: Turco, E., Macchiavelli, C., Pierantoni, P. P., Penza, G., and Schettino, A.: The opening of the Tyrrhenian basin and the Apennine chain formation in the kinematic context of Africa - Europe collision, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9727, https://doi.org/10.5194/egusphere-egu2020-9727, 2020.
EGU2020-19985 | Displays | TS7.1
3D Architecture and Plio-Quaternary evolution of the Paola Basin: Insights into the Forearc of the Tyrrhenian-Ionian Subduction SystemMarta Corradino, Fabrizio Pepe, Giovanni Bertotti, Vincenzo Picotti, Carmelo Monaco, and Rinaldo Nicolich
Fore-arc basins form structurally in response to a variety of subduction zone processes. The sedimentary infill records the tectono-stratigraphic evolution of the basin, and thus, provides information on the dynamic of the fore-arc region. Using seismic reflection profiles and bathymetric data, we analysed the stratigraphy and tectonics of the Paola Basin, deciphering the tectono-sedimentary mechanisms that acted in the forearc of the Tyrrhenian‐Ionian subduction system during the Plio-Quaternary. The Paola Basin is a NNW-SSE trending syncline, bounded by the Coastal Chain to the east and a regional-scale anticline, here called Paola Anticline, to the west. There are no major normal faults bordering the basin. It hosts up to 5.2 km thick Plio-Quaternary deposits, most of them supplied from Apenninic/Sila entry points and transported by longshore currents. The total subsidence reaches the value of ∼5 km. The sedimentary load varies from 60% to 75% of the total subsidence. The Pliocene to Lower Pleistocene sedimentary infill of the syncline displays a strata growth geometry consistent with a continuous rotation of the eastern limb of the Paola Anticline. Crustal folding is the mechanism that better explains the lack of significant normal faults bordering the Paola Basin, its tectonic subsidence and the uplift of the Paola Anticline. During the Late Pliocene - Early Pleistocene, contractional deformation continued, and also strike-slip movements affected both the Paola Anticline and the eastern sector of the basin. This resulted in the growth of the central sector of the Coastal Chain, leading to the definition of the Paola and Crati basins, previously connected in a larger proto basin. Also, strike-slip faults with associated releasing and restraining bends formed in the hinge zone of the Paola Anticline. The bathymetric expression of the strike-slip zone consists of structural highs and depressions that overall form the Paola Ridge. The development of strike-slip tectonics is associated to the trench-parallel component of the upper plate motion occurring in the oblique subduction setting. The growth of the Paola Anticline and Paola Basin was coeval with the opening of the Vavilov and Marsili back arc basins. Thus, extensional and contractional tectonics spatially coexisted along sectors of the upper plate of the Tyrrhenian-Ionian subduction system from Early Pliocene to Early Pleistocene. Since the Middle Pleistocene, the growth of the Paola Anticline and Paola Basin came to an end, and extensional tectonics controlled the evolution of the forearc region.
How to cite: Corradino, M., Pepe, F., Bertotti, G., Picotti, V., Monaco, C., and Nicolich, R.: 3D Architecture and Plio-Quaternary evolution of the Paola Basin: Insights into the Forearc of the Tyrrhenian-Ionian Subduction System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19985, https://doi.org/10.5194/egusphere-egu2020-19985, 2020.
Fore-arc basins form structurally in response to a variety of subduction zone processes. The sedimentary infill records the tectono-stratigraphic evolution of the basin, and thus, provides information on the dynamic of the fore-arc region. Using seismic reflection profiles and bathymetric data, we analysed the stratigraphy and tectonics of the Paola Basin, deciphering the tectono-sedimentary mechanisms that acted in the forearc of the Tyrrhenian‐Ionian subduction system during the Plio-Quaternary. The Paola Basin is a NNW-SSE trending syncline, bounded by the Coastal Chain to the east and a regional-scale anticline, here called Paola Anticline, to the west. There are no major normal faults bordering the basin. It hosts up to 5.2 km thick Plio-Quaternary deposits, most of them supplied from Apenninic/Sila entry points and transported by longshore currents. The total subsidence reaches the value of ∼5 km. The sedimentary load varies from 60% to 75% of the total subsidence. The Pliocene to Lower Pleistocene sedimentary infill of the syncline displays a strata growth geometry consistent with a continuous rotation of the eastern limb of the Paola Anticline. Crustal folding is the mechanism that better explains the lack of significant normal faults bordering the Paola Basin, its tectonic subsidence and the uplift of the Paola Anticline. During the Late Pliocene - Early Pleistocene, contractional deformation continued, and also strike-slip movements affected both the Paola Anticline and the eastern sector of the basin. This resulted in the growth of the central sector of the Coastal Chain, leading to the definition of the Paola and Crati basins, previously connected in a larger proto basin. Also, strike-slip faults with associated releasing and restraining bends formed in the hinge zone of the Paola Anticline. The bathymetric expression of the strike-slip zone consists of structural highs and depressions that overall form the Paola Ridge. The development of strike-slip tectonics is associated to the trench-parallel component of the upper plate motion occurring in the oblique subduction setting. The growth of the Paola Anticline and Paola Basin was coeval with the opening of the Vavilov and Marsili back arc basins. Thus, extensional and contractional tectonics spatially coexisted along sectors of the upper plate of the Tyrrhenian-Ionian subduction system from Early Pliocene to Early Pleistocene. Since the Middle Pleistocene, the growth of the Paola Anticline and Paola Basin came to an end, and extensional tectonics controlled the evolution of the forearc region.
How to cite: Corradino, M., Pepe, F., Bertotti, G., Picotti, V., Monaco, C., and Nicolich, R.: 3D Architecture and Plio-Quaternary evolution of the Paola Basin: Insights into the Forearc of the Tyrrhenian-Ionian Subduction System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19985, https://doi.org/10.5194/egusphere-egu2020-19985, 2020.
EGU2020-5266 | Displays | TS7.1
The upper Messinian-lowermost Pliocene out-of-sequence event in the southern Apennines (Italy): a study about the kinematics of the major thrust faultsSabatino Ciarcia, Ernesto Paolo Prinzi, Francesco D’Assisi Tramparulo, and Stefano Vitale
The southern Apennines are a fold-and-thrust belt formed since the lower Miocene until the middle Pleistocene (e.g., Vitale and Ciarcia, 2013). Although a wide literature exists about the geology of this orogenic chain, few are the studies about the kinematics of the major thrusts. With this in mind, this work is aimed to investigate the out-of-sequence regional thrust system exposed in the Campania region. This system is characterized by a frontal ramp exposed along the N-NE side of the platform carbonate ridge forming the regional mountain backbone. The main structure is also exposed as a flat thrust in the Campagna and Giffoni tectonic windows located in the internal sector of the chain. We analyzed several outcrops; in some of them, we observed the Mesozoic carbonates superposed onto the upper Miocene wedge-top basin deposits of the Castelvetere Group. The kinematic analysis of major and minor structures suggests the occurrence of two thrust fault sets: (i) the oldest indicates an eastward tectonic vergence, whereas (ii) the youngest, and more developed, toward the north. In the external zones, the N-S shortening was synchronous with the deposition of the upper Messinian-lowermost Pliocene Altavilla Fm. The origin of this out-of-sequence regional deformation is still matter of debate (e.g., Vitale et al., 2017). In our opinion it was the shallow expression of a deep-seated thrusting episode within the buried Apulian slab. It was dominated by thrust ramps (thick-skinned tectonics) mainly verging to East, and by the N-verging structures associated to lateral ramps.
References
Vitale Stefano and Ciarcia Sabatino (2013) - Tectono-stratigraphic and kinematic evolution of the southern Apennines/Calabria-Peloritani Terrane system (Italy). Tectonophysics, 583, 164–182.
Vitale Stefano, Tramparulo Francesco d'Assisi, Ciarcia Sabatino, Amore F. Ornella, Prinzi Ernesto Paolo and Laiena Fabio (2017) - The northward tectonic transport in the southern Apennines: examples from the Capri Island and western Sorrento Peninsula (Italy). International Journal of Earth Sciences (Geologische Rundschau), 106, 97–113.
How to cite: Ciarcia, S., Prinzi, E. P., Tramparulo, F. D., and Vitale, S.: The upper Messinian-lowermost Pliocene out-of-sequence event in the southern Apennines (Italy): a study about the kinematics of the major thrust faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5266, https://doi.org/10.5194/egusphere-egu2020-5266, 2020.
The southern Apennines are a fold-and-thrust belt formed since the lower Miocene until the middle Pleistocene (e.g., Vitale and Ciarcia, 2013). Although a wide literature exists about the geology of this orogenic chain, few are the studies about the kinematics of the major thrusts. With this in mind, this work is aimed to investigate the out-of-sequence regional thrust system exposed in the Campania region. This system is characterized by a frontal ramp exposed along the N-NE side of the platform carbonate ridge forming the regional mountain backbone. The main structure is also exposed as a flat thrust in the Campagna and Giffoni tectonic windows located in the internal sector of the chain. We analyzed several outcrops; in some of them, we observed the Mesozoic carbonates superposed onto the upper Miocene wedge-top basin deposits of the Castelvetere Group. The kinematic analysis of major and minor structures suggests the occurrence of two thrust fault sets: (i) the oldest indicates an eastward tectonic vergence, whereas (ii) the youngest, and more developed, toward the north. In the external zones, the N-S shortening was synchronous with the deposition of the upper Messinian-lowermost Pliocene Altavilla Fm. The origin of this out-of-sequence regional deformation is still matter of debate (e.g., Vitale et al., 2017). In our opinion it was the shallow expression of a deep-seated thrusting episode within the buried Apulian slab. It was dominated by thrust ramps (thick-skinned tectonics) mainly verging to East, and by the N-verging structures associated to lateral ramps.
References
Vitale Stefano and Ciarcia Sabatino (2013) - Tectono-stratigraphic and kinematic evolution of the southern Apennines/Calabria-Peloritani Terrane system (Italy). Tectonophysics, 583, 164–182.
Vitale Stefano, Tramparulo Francesco d'Assisi, Ciarcia Sabatino, Amore F. Ornella, Prinzi Ernesto Paolo and Laiena Fabio (2017) - The northward tectonic transport in the southern Apennines: examples from the Capri Island and western Sorrento Peninsula (Italy). International Journal of Earth Sciences (Geologische Rundschau), 106, 97–113.
How to cite: Ciarcia, S., Prinzi, E. P., Tramparulo, F. D., and Vitale, S.: The upper Messinian-lowermost Pliocene out-of-sequence event in the southern Apennines (Italy): a study about the kinematics of the major thrust faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5266, https://doi.org/10.5194/egusphere-egu2020-5266, 2020.
EGU2020-21568 | Displays | TS7.1
A critical revision of the Liguride complex in the Pollino area (Southern Apennines)Francesco Cavalcante, Rita Catanzariti, and Giacomo Prosser
The geodynamic reconstructions of the Apennine-Tyrrhenian system strongly rely on chronological and P-T data derived from the study of ophiolite-bearing units accreted in orogenic belts, frequently affected by HP-LT metamorphic overprint. Consequently, we carried out a detailed geological survey, combined with the study of calcareous nannofossils and the analysis of mineralogical and petrographic features of low-grade metamorphic rocks, in order to reconstruct the tectono-stratigraphic relationships among different formations of the Liguride Complex and perform a critical review of the existing literature on the P-T evolution of the Liguride accretionary wedge exposed in the Pollino area of the Southern Apennines.
A geological-structural survey allowed us to distinguish four major tectonic units, characterized by an overall decrease of metamorphic grade from top to bottom. The tectonic units consist of: i) slices of continental crust rocks consisting of Albitic gneisses, Garnet gneisses and Amphibolites; ii) the Frido Unit Auctorum p.p. with a variable intensity of deformation and HP/LT metamorphic grade. This unit consist of a typical ophiolitic assemblage, including serpentinites with metadoleretites or alterated peridotites, pillow lavas, foliated metabasites, metalimestones and metabreccias, quarzites, and jaspers. The upper part of the succession is made up of calcschists and low-grade metapelites, displaying variable PT conditions from about 7 kbar and 200 °C to 12 kbar and 350 °C. A wide variation of P-T conditions suggests that the Frido Unit consists of different thrust sheets, showing a progressive increase of the metamorphic grade moving from north to south; iii) the Seluci-Cogliandrino Unit, consisting mainly of metapelites and slices of an upper Jurassic seafloor succession with pillow lavas; iv) the non-metamorphic Nord Calabrian Unit represented, from the bottom, by ophiolites, shales with pencil cleavage (Crete Nere Formation) and by a prevailing calciclastic unit (Saraceno Formation), topped by thrust top deposits (Albidona Formation).
Calcareous nannofossil assemblages were studied in samples coming from the main successions of the investigated area, in order to provide age constraints for the deformation of the Liguride accretionary wedge. Results show that Frido Unit did not preserve calcareous nannofossils in all analyzed samples, because of the strong deformation produced during the HP-LT metamorphic overprint. In the upper part of the Seluci-Cogliandrino Unit, Eocene inf. CNE4 biozone has been documented. On the other hand, in the lower part of the Saraceno Fm a late Albian age (CC9 p.p.) was documented, based on the occurrence of Eiffellithus turriseiffelii and Hayesites irregularis. Moreover, the occurrence of Discoaster lodoensis, Reticulofenestra dictyoda and Toweius callosus framed the lower stratigraphic interval of the Albidona Fm to the early Eocene (Ypresian; CNE4 p.p.). Based on the above data, the current views on the Cretaceous-Paleogene geodinamic evolution of the southern Apennine thrust and fold belt should be substantially revised.
How to cite: Cavalcante, F., Catanzariti, R., and Prosser, G.: A critical revision of the Liguride complex in the Pollino area (Southern Apennines), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21568, https://doi.org/10.5194/egusphere-egu2020-21568, 2020.
The geodynamic reconstructions of the Apennine-Tyrrhenian system strongly rely on chronological and P-T data derived from the study of ophiolite-bearing units accreted in orogenic belts, frequently affected by HP-LT metamorphic overprint. Consequently, we carried out a detailed geological survey, combined with the study of calcareous nannofossils and the analysis of mineralogical and petrographic features of low-grade metamorphic rocks, in order to reconstruct the tectono-stratigraphic relationships among different formations of the Liguride Complex and perform a critical review of the existing literature on the P-T evolution of the Liguride accretionary wedge exposed in the Pollino area of the Southern Apennines.
A geological-structural survey allowed us to distinguish four major tectonic units, characterized by an overall decrease of metamorphic grade from top to bottom. The tectonic units consist of: i) slices of continental crust rocks consisting of Albitic gneisses, Garnet gneisses and Amphibolites; ii) the Frido Unit Auctorum p.p. with a variable intensity of deformation and HP/LT metamorphic grade. This unit consist of a typical ophiolitic assemblage, including serpentinites with metadoleretites or alterated peridotites, pillow lavas, foliated metabasites, metalimestones and metabreccias, quarzites, and jaspers. The upper part of the succession is made up of calcschists and low-grade metapelites, displaying variable PT conditions from about 7 kbar and 200 °C to 12 kbar and 350 °C. A wide variation of P-T conditions suggests that the Frido Unit consists of different thrust sheets, showing a progressive increase of the metamorphic grade moving from north to south; iii) the Seluci-Cogliandrino Unit, consisting mainly of metapelites and slices of an upper Jurassic seafloor succession with pillow lavas; iv) the non-metamorphic Nord Calabrian Unit represented, from the bottom, by ophiolites, shales with pencil cleavage (Crete Nere Formation) and by a prevailing calciclastic unit (Saraceno Formation), topped by thrust top deposits (Albidona Formation).
Calcareous nannofossil assemblages were studied in samples coming from the main successions of the investigated area, in order to provide age constraints for the deformation of the Liguride accretionary wedge. Results show that Frido Unit did not preserve calcareous nannofossils in all analyzed samples, because of the strong deformation produced during the HP-LT metamorphic overprint. In the upper part of the Seluci-Cogliandrino Unit, Eocene inf. CNE4 biozone has been documented. On the other hand, in the lower part of the Saraceno Fm a late Albian age (CC9 p.p.) was documented, based on the occurrence of Eiffellithus turriseiffelii and Hayesites irregularis. Moreover, the occurrence of Discoaster lodoensis, Reticulofenestra dictyoda and Toweius callosus framed the lower stratigraphic interval of the Albidona Fm to the early Eocene (Ypresian; CNE4 p.p.). Based on the above data, the current views on the Cretaceous-Paleogene geodinamic evolution of the southern Apennine thrust and fold belt should be substantially revised.
How to cite: Cavalcante, F., Catanzariti, R., and Prosser, G.: A critical revision of the Liguride complex in the Pollino area (Southern Apennines), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21568, https://doi.org/10.5194/egusphere-egu2020-21568, 2020.
EGU2020-19622 | Displays | TS7.1
Ductile shearing of Apennine allochtonous units and Messinian terrigenous deposits on top of the Inner Apulian Platform (Monte Alpi, Southern Italy)Giacomo Prosser, Fabrizio Agosta, Alessandro Giuffrida, Claudia Belviso, and Francesco Cavalcante
Mylonites are common structural elements in basement complexes. There, strain localization within shear zones occurs at amphibolite to greenschist facieses. More rarely, it also takes place at low-grade to anchizonal conditions in the external portions of orogenic belts. In the present contribution, we document the large-scale architecture, micro-structure, and mineralogy of a prominent shear zone exposed along the southern flank of the Monte Alpi Unit, southern Apennines, Italy. Deformation localized within the Messinian sedimentary protolith topping the carbonates of the Apulian Platform, and in the lowermost tectonic units of the Apennine allochton. Integration of results achieved after field geological mapping, outcrop structural analyses, optical and SEM micropscopy, and X-Ray diffrattometry permits to assess the time-space evolution of the main deformation mechanisms in the aforementioned shear zone. The shear zone involved Messinian shale, sandstones and conglomerates originally deposited in a foreland basin system, and Mesozoic claystones, limestones, and marls that formed in deep basinal environments. Now days, the mylonitic foliation is sub-parallel to the tectonic contact between the Messinian sedimentary cover of the Apulian carbonates and the overlying allochton. Shear-related deformation produced a foliated mylonitic fabric dipping ca. 20° S, and a well-developed, east-trending stretching lineation defined by aligned quartz and/or calcite grains. The conglomeratic levels were boudinaged, and the individual elongated pebbles re-oriented along slip direction. The microstructure of mylonites is characterized by a fine-grained calcite matrix, which shows an intense foliation due to dark bands made up of oxides, organic matter, and minor phyllosilicates. X-ray diffraction data performed on the Messinian shales and Mesozoic claystones, indicate the presence of mixed layer illite/smectite with 80-90% of illite and R1/R3 ordering thus suggesting an high digenetic grade (temperature: 120-140 °C). The two analyzed lithologies mainly differ in the presence of kaolinite, which occurs in the more proximal Messinian facies. Altogether, outcrop-scale kinematic markers such as shear bands, rootles folds and asymmetric porphyroclasts show a consistent top-to-the-east shear sense. Mineralogical and microstructural data indicate that shearing took place at a depth of 6-7 km during the Early Pliocene emplacement of the Apennine allochton on the Apulian Platform, and then exhumed by Late Pliocene low-angle normal faulting, Lower Pleistocene transpression, and Middle-Pleistocene-Holocene high-angle extensional faulting. In summary, the eastward motion of the allochton produced intense and localized low-temperature shearing in sediments on top of the Apulian Platform and in the overlying allochton. A subsequent reactivation of this shear zones as low-angle normal fault during late Pliocene exhumation is envisioned.
How to cite: Prosser, G., Agosta, F., Giuffrida, A., Belviso, C., and Cavalcante, F.: Ductile shearing of Apennine allochtonous units and Messinian terrigenous deposits on top of the Inner Apulian Platform (Monte Alpi, Southern Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19622, https://doi.org/10.5194/egusphere-egu2020-19622, 2020.
Mylonites are common structural elements in basement complexes. There, strain localization within shear zones occurs at amphibolite to greenschist facieses. More rarely, it also takes place at low-grade to anchizonal conditions in the external portions of orogenic belts. In the present contribution, we document the large-scale architecture, micro-structure, and mineralogy of a prominent shear zone exposed along the southern flank of the Monte Alpi Unit, southern Apennines, Italy. Deformation localized within the Messinian sedimentary protolith topping the carbonates of the Apulian Platform, and in the lowermost tectonic units of the Apennine allochton. Integration of results achieved after field geological mapping, outcrop structural analyses, optical and SEM micropscopy, and X-Ray diffrattometry permits to assess the time-space evolution of the main deformation mechanisms in the aforementioned shear zone. The shear zone involved Messinian shale, sandstones and conglomerates originally deposited in a foreland basin system, and Mesozoic claystones, limestones, and marls that formed in deep basinal environments. Now days, the mylonitic foliation is sub-parallel to the tectonic contact between the Messinian sedimentary cover of the Apulian carbonates and the overlying allochton. Shear-related deformation produced a foliated mylonitic fabric dipping ca. 20° S, and a well-developed, east-trending stretching lineation defined by aligned quartz and/or calcite grains. The conglomeratic levels were boudinaged, and the individual elongated pebbles re-oriented along slip direction. The microstructure of mylonites is characterized by a fine-grained calcite matrix, which shows an intense foliation due to dark bands made up of oxides, organic matter, and minor phyllosilicates. X-ray diffraction data performed on the Messinian shales and Mesozoic claystones, indicate the presence of mixed layer illite/smectite with 80-90% of illite and R1/R3 ordering thus suggesting an high digenetic grade (temperature: 120-140 °C). The two analyzed lithologies mainly differ in the presence of kaolinite, which occurs in the more proximal Messinian facies. Altogether, outcrop-scale kinematic markers such as shear bands, rootles folds and asymmetric porphyroclasts show a consistent top-to-the-east shear sense. Mineralogical and microstructural data indicate that shearing took place at a depth of 6-7 km during the Early Pliocene emplacement of the Apennine allochton on the Apulian Platform, and then exhumed by Late Pliocene low-angle normal faulting, Lower Pleistocene transpression, and Middle-Pleistocene-Holocene high-angle extensional faulting. In summary, the eastward motion of the allochton produced intense and localized low-temperature shearing in sediments on top of the Apulian Platform and in the overlying allochton. A subsequent reactivation of this shear zones as low-angle normal fault during late Pliocene exhumation is envisioned.
How to cite: Prosser, G., Agosta, F., Giuffrida, A., Belviso, C., and Cavalcante, F.: Ductile shearing of Apennine allochtonous units and Messinian terrigenous deposits on top of the Inner Apulian Platform (Monte Alpi, Southern Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19622, https://doi.org/10.5194/egusphere-egu2020-19622, 2020.
EGU2020-20774 | Displays | TS7.1
Late Miocene thrust tectonics of the Latin Valley: insights from seismic lines (Central Apennines, Italy)Giuseppe Vico and Giovanni Luca Cardello
In west-directed subduction zones, as the compression moves towards the foreland, the accretionary prism progressively expands to follow the hinge migration towards the east. Although late Miocene foreland propagation implies the shift of the thrust front, in the central Apennines, the effects of the Messinian compression can be observed on a much broader area, implying out-of-sequence thrusting in the rear.
In order to understand the Messinian involvement of the previously formed Tortonian belt-foredeep system, a regional reinterpretation is here provided. The analysis of publicly available 2D seismic reflection lines across the upper and middle Latin Valley and 10 wells enables the identification of two main seismostratigraphic units: i) the Meso-Cenozoic neritic carbonates and ii) the upper Tortonian siliciclastic pelitic and arenaceous turbiditic associations of the Frosinone Formation.
The most evident reflectors are the upper Cretaceous and upper Serravallian top paraconformities, which, due to tectonic repetition can be followed at different depths. We find that minor reflectors can be attributed to the several thrusts affecting folded Meso-Cenozoic neritic carbonates. This observation allows us, together with field and well evidences, to trace several thrust sheets characterized by a general top-to-the NE sense of shear. In a few sections from the Latin Valley (e.g. Line FR-309-80), we recognized the Meso-Cenozoic neritic carbonates being thrusted together with the Tortonian Frosinone Formation, on top of a laterally variably thick siliciclastic succession. This further syn-orogenic unit could be related to the early Messinian sandstones of the Torrice Formation, implying that out-of-sequence thrusting took place in the Latin Valley during the wedge-top sedimentation. The thin-skinned fold-and-thrust fabric is defined by en-échelon distributed thrusts, NNE- and ENE striking tear faults and minor pop-up structures often determining ideal traps for hydrocarbon and geothermal fluids. Finally, conjugated NW-striking high-angle normal faults crosscut the orogenic heritage and sets a horst and graben structure associated with continental deposition and the Volsci Volcanic Field.
The limited oil exploitation over the past century has targeted only the shallower siliciclastic traps and some evidences in the shallower neritic carbornate thrust sheets. At the light of our new interpretation, the deeper carbonate units could be a new focus for hydrocarbon accumulation and may furnish targets for geothermal and/or hydrocarbon research in the area. Future work aims at quantify the Tortonian and Messinian amount of shortening by taking into consideration the adjoining Volsci Range. Finally, our findings bear implications on geodynamic reconstructions and may represent an example of the geometry and kinematic evolution of platform derived thrust sheets and similar belts worldwide associated with W-directed subduction zones.
How to cite: Vico, G. and Cardello, G. L.: Late Miocene thrust tectonics of the Latin Valley: insights from seismic lines (Central Apennines, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20774, https://doi.org/10.5194/egusphere-egu2020-20774, 2020.
In west-directed subduction zones, as the compression moves towards the foreland, the accretionary prism progressively expands to follow the hinge migration towards the east. Although late Miocene foreland propagation implies the shift of the thrust front, in the central Apennines, the effects of the Messinian compression can be observed on a much broader area, implying out-of-sequence thrusting in the rear.
In order to understand the Messinian involvement of the previously formed Tortonian belt-foredeep system, a regional reinterpretation is here provided. The analysis of publicly available 2D seismic reflection lines across the upper and middle Latin Valley and 10 wells enables the identification of two main seismostratigraphic units: i) the Meso-Cenozoic neritic carbonates and ii) the upper Tortonian siliciclastic pelitic and arenaceous turbiditic associations of the Frosinone Formation.
The most evident reflectors are the upper Cretaceous and upper Serravallian top paraconformities, which, due to tectonic repetition can be followed at different depths. We find that minor reflectors can be attributed to the several thrusts affecting folded Meso-Cenozoic neritic carbonates. This observation allows us, together with field and well evidences, to trace several thrust sheets characterized by a general top-to-the NE sense of shear. In a few sections from the Latin Valley (e.g. Line FR-309-80), we recognized the Meso-Cenozoic neritic carbonates being thrusted together with the Tortonian Frosinone Formation, on top of a laterally variably thick siliciclastic succession. This further syn-orogenic unit could be related to the early Messinian sandstones of the Torrice Formation, implying that out-of-sequence thrusting took place in the Latin Valley during the wedge-top sedimentation. The thin-skinned fold-and-thrust fabric is defined by en-échelon distributed thrusts, NNE- and ENE striking tear faults and minor pop-up structures often determining ideal traps for hydrocarbon and geothermal fluids. Finally, conjugated NW-striking high-angle normal faults crosscut the orogenic heritage and sets a horst and graben structure associated with continental deposition and the Volsci Volcanic Field.
The limited oil exploitation over the past century has targeted only the shallower siliciclastic traps and some evidences in the shallower neritic carbornate thrust sheets. At the light of our new interpretation, the deeper carbonate units could be a new focus for hydrocarbon accumulation and may furnish targets for geothermal and/or hydrocarbon research in the area. Future work aims at quantify the Tortonian and Messinian amount of shortening by taking into consideration the adjoining Volsci Range. Finally, our findings bear implications on geodynamic reconstructions and may represent an example of the geometry and kinematic evolution of platform derived thrust sheets and similar belts worldwide associated with W-directed subduction zones.
How to cite: Vico, G. and Cardello, G. L.: Late Miocene thrust tectonics of the Latin Valley: insights from seismic lines (Central Apennines, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20774, https://doi.org/10.5194/egusphere-egu2020-20774, 2020.
EGU2020-10031 | Displays | TS7.1
The “syn” and “post” depositional evolution of a foredeep basin segmented by orogen-transversal tectonic structures: the case of the Cervarola Sandstones Formation, Miocene, Northern Apennines, ItalyAlberto Piazza, Roberto Tinterri, and Andrea Artoni
In collisional belts, foredeep turbidites are tracers of the evolution of the orogenic wedge. Syn-depositional tectonics affects the sedimentary facies distribution of the turbidite deposits, while post-depositional tectonics generates the major structures that deform the foredeep basins. The Aquitanian to Burdigalian Cervarola turbiditic succession is one of the main Oligo-Miocene foredeep units that characterize the northwestern portion of the Northern Apennines. The reconstructed sin and post depositional evolution of the Cervarola succession reveals that orogen-transversal tectonic structures strongly and persistently controlled this turbiditic succession, from the time turbidites were infilling the foredeep basin (Aquitanian-Burdigalian) to the time this foredeep deposits became a major and complex thrust sheet of the Northern Apennines orogenic wedge (post-Burdigalian-Present). The syn-depositional history of the Cervarola turbiditic succession has been defined through a detailed facies analysis that has allowed the basin morphology to be accurately constrained. Then, the post-depositional history has been addressed to define the multi-scale deformations preserved in the Cervarola succession through the following approaches: 1) analysis of published geological maps, 2) detailed field mapping, 3) construction of geological cross sections across the major folds, 4) analysis of meso-scale structures and 5) analysis of a seismic reflection profile. The study has outlined that the foredeep basin morphology was tectonically controlled and segmented by compressive structures transversal to the NW-SE basin elongation. The same structures were also present during the post-depositional compressive phases that built up the orogenic wedge and they have been even reactivated in the latest extensional events that have dismembered the mountain range. These orogeny-transversal and long-lasting (~23Myrs) lineaments cross-cut the entire tectonic stacking of the Northern Apennines, affecting tectonic units which suffered different amount of translation during the mountain building, making the reconstruction of the geological evolution possible only with an integrated approach as performed in this work.
How to cite: Piazza, A., Tinterri, R., and Artoni, A.: The “syn” and “post” depositional evolution of a foredeep basin segmented by orogen-transversal tectonic structures: the case of the Cervarola Sandstones Formation, Miocene, Northern Apennines, Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10031, https://doi.org/10.5194/egusphere-egu2020-10031, 2020.
In collisional belts, foredeep turbidites are tracers of the evolution of the orogenic wedge. Syn-depositional tectonics affects the sedimentary facies distribution of the turbidite deposits, while post-depositional tectonics generates the major structures that deform the foredeep basins. The Aquitanian to Burdigalian Cervarola turbiditic succession is one of the main Oligo-Miocene foredeep units that characterize the northwestern portion of the Northern Apennines. The reconstructed sin and post depositional evolution of the Cervarola succession reveals that orogen-transversal tectonic structures strongly and persistently controlled this turbiditic succession, from the time turbidites were infilling the foredeep basin (Aquitanian-Burdigalian) to the time this foredeep deposits became a major and complex thrust sheet of the Northern Apennines orogenic wedge (post-Burdigalian-Present). The syn-depositional history of the Cervarola turbiditic succession has been defined through a detailed facies analysis that has allowed the basin morphology to be accurately constrained. Then, the post-depositional history has been addressed to define the multi-scale deformations preserved in the Cervarola succession through the following approaches: 1) analysis of published geological maps, 2) detailed field mapping, 3) construction of geological cross sections across the major folds, 4) analysis of meso-scale structures and 5) analysis of a seismic reflection profile. The study has outlined that the foredeep basin morphology was tectonically controlled and segmented by compressive structures transversal to the NW-SE basin elongation. The same structures were also present during the post-depositional compressive phases that built up the orogenic wedge and they have been even reactivated in the latest extensional events that have dismembered the mountain range. These orogeny-transversal and long-lasting (~23Myrs) lineaments cross-cut the entire tectonic stacking of the Northern Apennines, affecting tectonic units which suffered different amount of translation during the mountain building, making the reconstruction of the geological evolution possible only with an integrated approach as performed in this work.
How to cite: Piazza, A., Tinterri, R., and Artoni, A.: The “syn” and “post” depositional evolution of a foredeep basin segmented by orogen-transversal tectonic structures: the case of the Cervarola Sandstones Formation, Miocene, Northern Apennines, Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10031, https://doi.org/10.5194/egusphere-egu2020-10031, 2020.
EGU2020-19557 | Displays | TS7.1
New insight on the sedimentary record related to the late-Quaternary tectonics of the western segment of the “Livorno-Sillaro” (Northern Tuscany, Italy).Giovanni Sarti, Vito Gerardo Giannico, Daniele Pittaro, and Lorenzo Porta
The “Livorno-Sillaro” line represents one of the most important transversal structure of the inner Northern Apennines. It has been described in the literature as a major strike-slip fault (e.g., Bortolotti, 1966; Carmignani et al., 1994; Pascucci, 2005; Pascucci et al., 2007), and it is divided into two segments, eastern and western.
A stratigraphic-sequence frame for the late-Quaternary deposits has been developed by using the different facies associations defined through a large subsurface database analysis. Moreover, a correlation has been done between subsoil deposits and the outcropping sediments on the hilly areas (Livorno, Pisa and Cerbaie hills) surrounding the Arno valley.
Additionally, a morphotectonic analysis of the hydrographic networks and relief distribution has been done the Lidar data (DTM), supplied by the Tuscany Region, at the 2 m and 10 m of resolution. Specifically, the river system is particularly sensitive to deformation processes. The fluvial streams are in fact characterized by low geomorphological inertia and, therefore, by response times of a few hundred thousand years to the tectonic processes in progress.
As a result of the integrated multidisciplinary analysis, it was possible to highlight a tectonic activity in the middle Pleistocene -Holocene interval of the western portion of the "Livorno-Sillaro" lineament neglected in the geological literature until now.
References
Bortolotti V. (1966) – La tettonica trasversale dell’Appennino – La linea Livorno-Sillaro. Bollettino della Società Geologica Italiana, Vol.85, pp. 529-540, 3 ff., 1 tav.
Carmignani L., Decandia F.A., Fantozzi P.L., Lazzarotto A., Liotta D. & Meccheri M. (1994) – Tertiary extensional tectonics in Tuscany (Northern Apennines, Italy). Tectonophysics. Vol. 238, pp. 295-315.
Pascucci V. (2005) – Neogene evolution of the Viareggio Basin, Northern Tuscany (Italy). GeoActa. Vol. 4, pp. 123-128.
Pascucci V., Martini I.P., Sagri M. & Sandrelli F. (2007) – Effects of transverse structural lineaments on the Neogene-Quaternary basins of Tuscany (inner Northern Apennines, Italy). Sedimentary Processes, Environments, and Basins: A Tribute to Peter Friend.
How to cite: Sarti, G., Giannico, V. G., Pittaro, D., and Porta, L.: New insight on the sedimentary record related to the late-Quaternary tectonics of the western segment of the “Livorno-Sillaro” (Northern Tuscany, Italy)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19557, https://doi.org/10.5194/egusphere-egu2020-19557, 2020.
The “Livorno-Sillaro” line represents one of the most important transversal structure of the inner Northern Apennines. It has been described in the literature as a major strike-slip fault (e.g., Bortolotti, 1966; Carmignani et al., 1994; Pascucci, 2005; Pascucci et al., 2007), and it is divided into two segments, eastern and western.
A stratigraphic-sequence frame for the late-Quaternary deposits has been developed by using the different facies associations defined through a large subsurface database analysis. Moreover, a correlation has been done between subsoil deposits and the outcropping sediments on the hilly areas (Livorno, Pisa and Cerbaie hills) surrounding the Arno valley.
Additionally, a morphotectonic analysis of the hydrographic networks and relief distribution has been done the Lidar data (DTM), supplied by the Tuscany Region, at the 2 m and 10 m of resolution. Specifically, the river system is particularly sensitive to deformation processes. The fluvial streams are in fact characterized by low geomorphological inertia and, therefore, by response times of a few hundred thousand years to the tectonic processes in progress.
As a result of the integrated multidisciplinary analysis, it was possible to highlight a tectonic activity in the middle Pleistocene -Holocene interval of the western portion of the "Livorno-Sillaro" lineament neglected in the geological literature until now.
References
Bortolotti V. (1966) – La tettonica trasversale dell’Appennino – La linea Livorno-Sillaro. Bollettino della Società Geologica Italiana, Vol.85, pp. 529-540, 3 ff., 1 tav.
Carmignani L., Decandia F.A., Fantozzi P.L., Lazzarotto A., Liotta D. & Meccheri M. (1994) – Tertiary extensional tectonics in Tuscany (Northern Apennines, Italy). Tectonophysics. Vol. 238, pp. 295-315.
Pascucci V. (2005) – Neogene evolution of the Viareggio Basin, Northern Tuscany (Italy). GeoActa. Vol. 4, pp. 123-128.
Pascucci V., Martini I.P., Sagri M. & Sandrelli F. (2007) – Effects of transverse structural lineaments on the Neogene-Quaternary basins of Tuscany (inner Northern Apennines, Italy). Sedimentary Processes, Environments, and Basins: A Tribute to Peter Friend.
How to cite: Sarti, G., Giannico, V. G., Pittaro, D., and Porta, L.: New insight on the sedimentary record related to the late-Quaternary tectonics of the western segment of the “Livorno-Sillaro” (Northern Tuscany, Italy)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19557, https://doi.org/10.5194/egusphere-egu2020-19557, 2020.
EGU2020-3871 | Displays | TS7.1
Mesozoic palaeogeography and tectono-stratigraphic features of the northern Amerini Mts. (Central Apennines, Italy): new constraints on their Jurassic and Cretaceous evolutionCostantino Zuccari, Angelo Cipriani, and Massimo Santantonio
A geological mapping project was performed on the 1:10,000 scale in the northern Amerini Mts. (Narni–Amelia Ridge, Central Apennines), coupled with facies analysis and multidisciplinary outcrop characterisation. This project was focused on the Jurassic-Lower Cretaceous succession, in order to reconstruct the Mesozoic palaeogeography and tectono-sedimentary evolution of the study area. This sector of the Apenninic Chain (i.e. Umbria-Marche-Sabina palaeogeographic domain) experienced the Early Jurassic rifting phase, which dismembered the vast Calcare Massiccio carbonate platform. The development of a rugged submarine topography, coupled with drowning of the benthic factories, were the main effects of this normal faulting. The complex submarine physiography, made of structural highs and lows, is highlighted by facies and thickness variations of the Jurassic and Lower Cretaceous deposits. The hangingwall blocks hosted thick (hundreds of metres) pelagic successions, with variable volumes of admixed gravity-flow deposits. These successions onlapped the horst blocks along escarpments, rooted in the rift faults, where the pre-rift Calcare Massiccio was exposed. The tops of footwall blocks (Pelagic Carbonate Platforms or PCPs) were capped by thin (few tens of metres or less), fossil-rich and chert-free, condensed pelagic successions. This rift architecture was evened out at a domain scale in the Early Cretaceous. Successively, Miocene orogenic and Plio-Pleistocene extensional faulting caused uplift and exhumation of the Mesozoic rocks.
In the study area, geothematic mapping associated with the analysis of basin-margin unconformities and successions revealed a narrow and elongated Jurassic structural high (Mt. Croce di Serra - Mt. Alsicci structural high), surrounded by Jurassic basinal pelagites. The PCP-top condensed succession is not preserved. The chert-rich basinal units rest on the horst-block Calcare Massiccio through unconformity surfaces (palaeoescarpments), as marked by the silicification of the (otherwise chert-free) shallow-water limestone. The onlap successions embed megablocks of Calcare Massiccio (hundreds of metres across), detached from their parent palaeoescarpments. Very thin, condensed deposits form discontinuous veneers on the olistoliths of Calcare Massiccio (epi-olistolith deposits) and are onlapped by younger basin-fill pelagites. The beds surrounding the olistoliths are characteristically bent due to differential compaction, as their (newly acquired) strikes mimic the outline of the stiff objects they were burying.
Indirect evidence for a Toarcian, post-rift, tectonic pulse can be locally mapped, and is documented by angular unconformities between the Pliensbachian and Toarcian pelagites, as well as by mass-transport deposits found in the Rosso Ammonitico (Toarcian).
The same goes for millimetric to centimetric neptunian dykes made of Maiolica pelagites cross-cutting the Corniola Fm. (Sinemurian-Pliensbachian). These dykes, coupled with the occurrence of unconformities between Aptian-Albian pelagites (Marne a Fucoidi Fm.) and Lower Jurassic rocks (Calcare Massiccio and Corniola formations), provide evidence for a further Early Cretaceous tectonic phase, recently reported from the southern sectors of Narni-Amelia ridge.
How to cite: Zuccari, C., Cipriani, A., and Santantonio, M.: Mesozoic palaeogeography and tectono-stratigraphic features of the northern Amerini Mts. (Central Apennines, Italy): new constraints on their Jurassic and Cretaceous evolution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3871, https://doi.org/10.5194/egusphere-egu2020-3871, 2020.
A geological mapping project was performed on the 1:10,000 scale in the northern Amerini Mts. (Narni–Amelia Ridge, Central Apennines), coupled with facies analysis and multidisciplinary outcrop characterisation. This project was focused on the Jurassic-Lower Cretaceous succession, in order to reconstruct the Mesozoic palaeogeography and tectono-sedimentary evolution of the study area. This sector of the Apenninic Chain (i.e. Umbria-Marche-Sabina palaeogeographic domain) experienced the Early Jurassic rifting phase, which dismembered the vast Calcare Massiccio carbonate platform. The development of a rugged submarine topography, coupled with drowning of the benthic factories, were the main effects of this normal faulting. The complex submarine physiography, made of structural highs and lows, is highlighted by facies and thickness variations of the Jurassic and Lower Cretaceous deposits. The hangingwall blocks hosted thick (hundreds of metres) pelagic successions, with variable volumes of admixed gravity-flow deposits. These successions onlapped the horst blocks along escarpments, rooted in the rift faults, where the pre-rift Calcare Massiccio was exposed. The tops of footwall blocks (Pelagic Carbonate Platforms or PCPs) were capped by thin (few tens of metres or less), fossil-rich and chert-free, condensed pelagic successions. This rift architecture was evened out at a domain scale in the Early Cretaceous. Successively, Miocene orogenic and Plio-Pleistocene extensional faulting caused uplift and exhumation of the Mesozoic rocks.
In the study area, geothematic mapping associated with the analysis of basin-margin unconformities and successions revealed a narrow and elongated Jurassic structural high (Mt. Croce di Serra - Mt. Alsicci structural high), surrounded by Jurassic basinal pelagites. The PCP-top condensed succession is not preserved. The chert-rich basinal units rest on the horst-block Calcare Massiccio through unconformity surfaces (palaeoescarpments), as marked by the silicification of the (otherwise chert-free) shallow-water limestone. The onlap successions embed megablocks of Calcare Massiccio (hundreds of metres across), detached from their parent palaeoescarpments. Very thin, condensed deposits form discontinuous veneers on the olistoliths of Calcare Massiccio (epi-olistolith deposits) and are onlapped by younger basin-fill pelagites. The beds surrounding the olistoliths are characteristically bent due to differential compaction, as their (newly acquired) strikes mimic the outline of the stiff objects they were burying.
Indirect evidence for a Toarcian, post-rift, tectonic pulse can be locally mapped, and is documented by angular unconformities between the Pliensbachian and Toarcian pelagites, as well as by mass-transport deposits found in the Rosso Ammonitico (Toarcian).
The same goes for millimetric to centimetric neptunian dykes made of Maiolica pelagites cross-cutting the Corniola Fm. (Sinemurian-Pliensbachian). These dykes, coupled with the occurrence of unconformities between Aptian-Albian pelagites (Marne a Fucoidi Fm.) and Lower Jurassic rocks (Calcare Massiccio and Corniola formations), provide evidence for a further Early Cretaceous tectonic phase, recently reported from the southern sectors of Narni-Amelia ridge.
How to cite: Zuccari, C., Cipriani, A., and Santantonio, M.: Mesozoic palaeogeography and tectono-stratigraphic features of the northern Amerini Mts. (Central Apennines, Italy): new constraints on their Jurassic and Cretaceous evolution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3871, https://doi.org/10.5194/egusphere-egu2020-3871, 2020.
EGU2020-10374 | Displays | TS7.1
Permian sporomorphs from upper Palaeozoic succession of Southern Tuscany (Italy): new constraints for the stratigraphy and palaeogeographic setting of the Tuscan DomainAmalia Spina, Andrea Brogi, Enrico Capezzuoli, Simonetta Cirilli, and Domenico Liotta
Recent biostratigraphic, sedimentological and petrological studies in the inner Northern Apennines (Italy) permit to refine the upper Palaeozoic successions of southern Tuscany, allowing new hypothesis to frame these formations in the Permian palaeogeographical scenario of the western Mediterranean domain. The Tuscan pre-Triassic deposits, belonging to the Monticiano-Roccastrada Unit, are generally barren or scarce in term of biomineralized fossiliferous content. They were mostly affected by HP-LT to LP-HT metamorphism that, together with the limited distribution of deposits, made difficult their stratigraphic correlation.
The present study is focused on two metamorphic units (i.e. Filladi e metacalcari di Fosso della Falsacqua Formation and Filladi e quarziti del Torrente Mersino Formation) which age attribution and correlation was strongly debated in the literature.
The Filladi e metacalcari di Fosso della Falsacqua Formation (minimum estimated thickness of about 150 m), cropping out in Monte Leoni area, is mainly characterized by black to dark-grey phyllite, metasiltstones and metasandstones with dark limestone intercalations. Due to the lack of biomineralized fossil content, by lithostratigraphic correlation with other formations cropping out in Tuscany, this formation was differently assigned to late Carboniferous-early Permian or Devonian.
The Filladi e quarziti del Torrente Mersino Formation (minimum estimated thickness of about 200 m) crops out in the Boccheggiano mining area and mainly consists of black to dark-grey quartz-phyllite, quartz metaconglomerates, light-grey quartzites, green phyllites and quartzites and light-grey phyllites. This formation resulted barren of fossil content and has been differently assigned to Ordovician-Silurian, Silurian-Devonian, late Carboniferous-Permian and Triassic by lithostratigraphic correlation with other Tuscan-Sardinian successions.
In the present study, the first finding of a middle Permian well-preserved microflora adds more constrains to the age attribution of these studied formations. This new age assignment permits to correlate the investigated formations with the coheval ones belonging to southern Tuscany (i.e. Farma Formation) and Elba Island (Rio Marina Formation) characterized by a similar microfloral content. Moreover, the occurrence of Gondwana-related sporomorphs, in all the studied formations, points to a new palaeogeographic scenario of the upper Palaeozoic successions from the northern Gondwana margin. The results of this integrated study inclines to consider the fragmentation of the northern margin of Gondwana as a result of several transtensional (pull-apart) basins where different laterally-related depositional environments leaded the sedimentation of these Tuscan middle Permian formations.
How to cite: Spina, A., Brogi, A., Capezzuoli, E., Cirilli, S., and Liotta, D.: Permian sporomorphs from upper Palaeozoic succession of Southern Tuscany (Italy): new constraints for the stratigraphy and palaeogeographic setting of the Tuscan Domain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10374, https://doi.org/10.5194/egusphere-egu2020-10374, 2020.
Recent biostratigraphic, sedimentological and petrological studies in the inner Northern Apennines (Italy) permit to refine the upper Palaeozoic successions of southern Tuscany, allowing new hypothesis to frame these formations in the Permian palaeogeographical scenario of the western Mediterranean domain. The Tuscan pre-Triassic deposits, belonging to the Monticiano-Roccastrada Unit, are generally barren or scarce in term of biomineralized fossiliferous content. They were mostly affected by HP-LT to LP-HT metamorphism that, together with the limited distribution of deposits, made difficult their stratigraphic correlation.
The present study is focused on two metamorphic units (i.e. Filladi e metacalcari di Fosso della Falsacqua Formation and Filladi e quarziti del Torrente Mersino Formation) which age attribution and correlation was strongly debated in the literature.
The Filladi e metacalcari di Fosso della Falsacqua Formation (minimum estimated thickness of about 150 m), cropping out in Monte Leoni area, is mainly characterized by black to dark-grey phyllite, metasiltstones and metasandstones with dark limestone intercalations. Due to the lack of biomineralized fossil content, by lithostratigraphic correlation with other formations cropping out in Tuscany, this formation was differently assigned to late Carboniferous-early Permian or Devonian.
The Filladi e quarziti del Torrente Mersino Formation (minimum estimated thickness of about 200 m) crops out in the Boccheggiano mining area and mainly consists of black to dark-grey quartz-phyllite, quartz metaconglomerates, light-grey quartzites, green phyllites and quartzites and light-grey phyllites. This formation resulted barren of fossil content and has been differently assigned to Ordovician-Silurian, Silurian-Devonian, late Carboniferous-Permian and Triassic by lithostratigraphic correlation with other Tuscan-Sardinian successions.
In the present study, the first finding of a middle Permian well-preserved microflora adds more constrains to the age attribution of these studied formations. This new age assignment permits to correlate the investigated formations with the coheval ones belonging to southern Tuscany (i.e. Farma Formation) and Elba Island (Rio Marina Formation) characterized by a similar microfloral content. Moreover, the occurrence of Gondwana-related sporomorphs, in all the studied formations, points to a new palaeogeographic scenario of the upper Palaeozoic successions from the northern Gondwana margin. The results of this integrated study inclines to consider the fragmentation of the northern margin of Gondwana as a result of several transtensional (pull-apart) basins where different laterally-related depositional environments leaded the sedimentation of these Tuscan middle Permian formations.
How to cite: Spina, A., Brogi, A., Capezzuoli, E., Cirilli, S., and Liotta, D.: Permian sporomorphs from upper Palaeozoic succession of Southern Tuscany (Italy): new constraints for the stratigraphy and palaeogeographic setting of the Tuscan Domain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10374, https://doi.org/10.5194/egusphere-egu2020-10374, 2020.
EGU2020-19978 | Displays | TS7.1
Origin and metamorphic reworking of the Buca della Vena Tl-rich orebody (Alpi Apuane, Italy)Simone Vezzoni, Diego Pieruccioni, Andrea Dini, Giancarlo Molli, and Cristian Biagioni
The origin and evolution of an orebody hosted in metamorphic terrane is a prime topic in economic geology because they have implications on exploration as well as on related potential geo-environmental health hazards. The Alpi Apuane orebodies has long been known; however, their ore genesis and the relationships with the Apenninic age deformation and metamorphism is still a matter of debate. Indeed, they are still an interesting field of research, as proved by the recent discovery of a remarkable Tl anomaly associated to the baryte ± pyrite ± Fe-oxides ores of southern Alpi Apuane, northern Tuscany, Italy [1]. The present work reports a new detailed field and underground geological-structural investigation, performed from cartographic- to microscopic-scale, integrated by available drill-logs data, of one of these Tl-rich orebodies - the Buca della Vena ore.
The present study gives new insights on some aspect of the ore-forming events and discusses previous interpretations. According to our investigations, the ore settings were acquired during successive geological events related to an early hydrothermal-magmatic phase, likely of Permian age, and to the more recent Apenninic deformations. We suggest that the proto-ore was produced by hydrothermal activity related to the post-Variscan magmatic cycle (documented by the Permian age “Fornovolasco metarhyolite” Fm [2]), causing ore-formation, tourmalinization and hydrothermal alteration halo in the Cambrian-Lower Ordovician phyllites host-rocks. In our model, the ores were then partially exhumed suffering supergene alteration with development of minor Fe-oxides sedimentary mineralizations during the upper Norian-Hettangian. Finally, the previous hydrothermal and sedimentary ores, along with the host-rocks, were involved in the Apenninic orogenesis, and were recrystallized, and partially remobilized acquiring the current mineralogical, textural, and structural settings.
References:
[1] Biagioni, C., D’Orazio, M., Vezzoni, S., Dini, A., Orlandi, P., 2013. Mobilization of Tl-Hg-As-Sb-(Ag,Cu)-Pb sulfosalt melts during low-grade metamorphism in the Alpi Apuane (Tuscany, Italy). Geology, 41, 747-750.
[2] Vezzoni, S., Biagioni, C., D’Orazio, M., Pieruccioni, D., Galanti, Y., Petrelli, M., Molli, G., 2018. Evidence of Permian magmatism in the Alpi Apuane metamorphic complex (Northern Apennines, Italy): New hints for the geological evolution of the basement of the Adria plate. Lithos, 318-319, 104-123.
How to cite: Vezzoni, S., Pieruccioni, D., Dini, A., Molli, G., and Biagioni, C.: Origin and metamorphic reworking of the Buca della Vena Tl-rich orebody (Alpi Apuane, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19978, https://doi.org/10.5194/egusphere-egu2020-19978, 2020.
The origin and evolution of an orebody hosted in metamorphic terrane is a prime topic in economic geology because they have implications on exploration as well as on related potential geo-environmental health hazards. The Alpi Apuane orebodies has long been known; however, their ore genesis and the relationships with the Apenninic age deformation and metamorphism is still a matter of debate. Indeed, they are still an interesting field of research, as proved by the recent discovery of a remarkable Tl anomaly associated to the baryte ± pyrite ± Fe-oxides ores of southern Alpi Apuane, northern Tuscany, Italy [1]. The present work reports a new detailed field and underground geological-structural investigation, performed from cartographic- to microscopic-scale, integrated by available drill-logs data, of one of these Tl-rich orebodies - the Buca della Vena ore.
The present study gives new insights on some aspect of the ore-forming events and discusses previous interpretations. According to our investigations, the ore settings were acquired during successive geological events related to an early hydrothermal-magmatic phase, likely of Permian age, and to the more recent Apenninic deformations. We suggest that the proto-ore was produced by hydrothermal activity related to the post-Variscan magmatic cycle (documented by the Permian age “Fornovolasco metarhyolite” Fm [2]), causing ore-formation, tourmalinization and hydrothermal alteration halo in the Cambrian-Lower Ordovician phyllites host-rocks. In our model, the ores were then partially exhumed suffering supergene alteration with development of minor Fe-oxides sedimentary mineralizations during the upper Norian-Hettangian. Finally, the previous hydrothermal and sedimentary ores, along with the host-rocks, were involved in the Apenninic orogenesis, and were recrystallized, and partially remobilized acquiring the current mineralogical, textural, and structural settings.
References:
[1] Biagioni, C., D’Orazio, M., Vezzoni, S., Dini, A., Orlandi, P., 2013. Mobilization of Tl-Hg-As-Sb-(Ag,Cu)-Pb sulfosalt melts during low-grade metamorphism in the Alpi Apuane (Tuscany, Italy). Geology, 41, 747-750.
[2] Vezzoni, S., Biagioni, C., D’Orazio, M., Pieruccioni, D., Galanti, Y., Petrelli, M., Molli, G., 2018. Evidence of Permian magmatism in the Alpi Apuane metamorphic complex (Northern Apennines, Italy): New hints for the geological evolution of the basement of the Adria plate. Lithos, 318-319, 104-123.
How to cite: Vezzoni, S., Pieruccioni, D., Dini, A., Molli, G., and Biagioni, C.: Origin and metamorphic reworking of the Buca della Vena Tl-rich orebody (Alpi Apuane, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19978, https://doi.org/10.5194/egusphere-egu2020-19978, 2020.
EGU2020-2341 | Displays | TS7.1
Upper Carboniferous-Permian tectonics in Central Mediterranean: an updated revisionGiancarlo Molli, Andrea Brogi, Alfredo Caggianelli, Enrico Capezzuoli, Domenico Liotta, Amalia Spina, and Ivan Zibra
An updated revision of the upper Carboniferous-Permian tectonics recorded in Corsica, Calabria and Tuscany is here proposed. We combine our and literature data to document how the sedimentary, tectono-metamorphic and magmatic upper Carboniferous-Permian record fits with a regional-scale tectonic scenario characterized by trascurrent fault systems associated with stretched crustal domains in which extensional regional structures, magmatism and transtensional basins developed. In Corsica, altogether with well-known effusive and intrusive Permian magmatism, the alpine S.Lucia nappe exposes a kilometer-scale portion of the Permian lower to mid-crust, with many similarities to the Ivrea-Verbano zone. The two distinct Mafic and Leucogranitic complexes, which characterize this crustal domain are juxtposed by an oblique-slip shear zone named as S.Lucia Shear Zone. Structural and petrological data document interaction between magmatism, metamorphism and shearing during Permian in the c. 800-400 °C temperature range. In Calabria (Sila, Serre and Aspromonte), a continuous pre-Mesozoic crustal section is exposed. The lower crust portion of such section is mainly made up of granulites and migmatitic paragneisses with subordinate marbles and metabasites. The mid-crustal section includes an up to 13 km thick sequence of granitoids of tonalitic to granitic composition, emplaced between 306 and 295 Ma and progressively deformed during retrograde extensional shearing to end with a final magmatic activity between 295 and 277 Ma, consisting in the injection of shallower dykes in a transtensional regime. The section is completed by an upper crustal portion mainly formed by a Paleozoic succession deformed as a low-grade fold and thrust belt, locally overlaying medium-grade paragneiss units, and therefore as a whole reminiscent of the external/nappe zone domains of Sardinia Hercynian orogen. In Tuscany we document, how late Carboniferous/Permian shallow marine to continental sedimentary basins characterized by unconformity and abrupt change in sedimentary facies (coal-measures, red fanglomerate deposits) and acid magmatism well fit a transtensional setting with a mid-crustal shear zone linked with a system of E-W trending (in present orientation) upper crust splay faults. We will frame the whole dataset in a regional framework of first-order transcurrent shear zones network which includes a westernmost S.Lucia Shear Zone and an easternmost East Tuscan Shear Zone, with intervening crustal domains in which extensional to transtensional shearing occured.
How to cite: Molli, G., Brogi, A., Caggianelli, A., Capezzuoli, E., Liotta, D., Spina, A., and Zibra, I.: Upper Carboniferous-Permian tectonics in Central Mediterranean: an updated revision, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2341, https://doi.org/10.5194/egusphere-egu2020-2341, 2020.
An updated revision of the upper Carboniferous-Permian tectonics recorded in Corsica, Calabria and Tuscany is here proposed. We combine our and literature data to document how the sedimentary, tectono-metamorphic and magmatic upper Carboniferous-Permian record fits with a regional-scale tectonic scenario characterized by trascurrent fault systems associated with stretched crustal domains in which extensional regional structures, magmatism and transtensional basins developed. In Corsica, altogether with well-known effusive and intrusive Permian magmatism, the alpine S.Lucia nappe exposes a kilometer-scale portion of the Permian lower to mid-crust, with many similarities to the Ivrea-Verbano zone. The two distinct Mafic and Leucogranitic complexes, which characterize this crustal domain are juxtposed by an oblique-slip shear zone named as S.Lucia Shear Zone. Structural and petrological data document interaction between magmatism, metamorphism and shearing during Permian in the c. 800-400 °C temperature range. In Calabria (Sila, Serre and Aspromonte), a continuous pre-Mesozoic crustal section is exposed. The lower crust portion of such section is mainly made up of granulites and migmatitic paragneisses with subordinate marbles and metabasites. The mid-crustal section includes an up to 13 km thick sequence of granitoids of tonalitic to granitic composition, emplaced between 306 and 295 Ma and progressively deformed during retrograde extensional shearing to end with a final magmatic activity between 295 and 277 Ma, consisting in the injection of shallower dykes in a transtensional regime. The section is completed by an upper crustal portion mainly formed by a Paleozoic succession deformed as a low-grade fold and thrust belt, locally overlaying medium-grade paragneiss units, and therefore as a whole reminiscent of the external/nappe zone domains of Sardinia Hercynian orogen. In Tuscany we document, how late Carboniferous/Permian shallow marine to continental sedimentary basins characterized by unconformity and abrupt change in sedimentary facies (coal-measures, red fanglomerate deposits) and acid magmatism well fit a transtensional setting with a mid-crustal shear zone linked with a system of E-W trending (in present orientation) upper crust splay faults. We will frame the whole dataset in a regional framework of first-order transcurrent shear zones network which includes a westernmost S.Lucia Shear Zone and an easternmost East Tuscan Shear Zone, with intervening crustal domains in which extensional to transtensional shearing occured.
How to cite: Molli, G., Brogi, A., Caggianelli, A., Capezzuoli, E., Liotta, D., Spina, A., and Zibra, I.: Upper Carboniferous-Permian tectonics in Central Mediterranean: an updated revision, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2341, https://doi.org/10.5194/egusphere-egu2020-2341, 2020.
TS7.2 – Fold-thrust belts as linking elements between orogen and foreland deformation - nature, models, processes
EGU2020-5607 | Displays | TS7.2
Numerical modelling of tectonic underplating in accretionary wedgesJonas B. Ruh
Accretionary wedge systems result from scraping clastic sedimentary sequences off a descending oceanic plate at subduction zones. Sediments covering the incoming, subducting oceanic plate may be accreted at the wedge front forming a typical imbricate fan. Buried parts of the stratigraphic sequence may underthrust the wedge body and get subsequently accreted at its base (underplating) or even descend further into the mantle. Tectonic underplating requires a step-down of the major décollement horizon representing in fact the subduction plate interface. Intense underplating at the rear of accretionary wedges ultimately leads to antiformal stacking and, in combination of surface erosion, to the uplift of sediments formerly accreted at the base of wedges. In the present study, I try to determine and quantify the main features leading to tectonic underplating and subsequent uplift of underthrust incoming sediments at subduction zones. To do so, a numerical model is set up defined by a downgoing rigid plate, an overlying sedimentary sequence and a rigid backstop resulting in sediment accretion. The implementation of two weak décollement layers allows for the potential development of tectonic underplating. Tested parameters for the tectonic evolution of such systems include décollement strength, surface erosion, elastic stiffness of the downgoing plate and geometry of the rigid backstop. The applied numerical code is based on the finite difference marker-in-cell technique with a visco-elasto-plastic rheology. Results indicate that underplating is intensified when i) the stratigraphically lower décollement is strengthened with respect to the upper one, ii) surface erosion is increased, or iii) the downgoing plate becomes stiffer. Modelling results are compared to natural cases of accrretionary wedges where sediments have been underplated (and eventually exhumed) as in the Makran, the Franciscan, or the Appalachians.
How to cite: Ruh, J. B.: Numerical modelling of tectonic underplating in accretionary wedges, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5607, https://doi.org/10.5194/egusphere-egu2020-5607, 2020.
Accretionary wedge systems result from scraping clastic sedimentary sequences off a descending oceanic plate at subduction zones. Sediments covering the incoming, subducting oceanic plate may be accreted at the wedge front forming a typical imbricate fan. Buried parts of the stratigraphic sequence may underthrust the wedge body and get subsequently accreted at its base (underplating) or even descend further into the mantle. Tectonic underplating requires a step-down of the major décollement horizon representing in fact the subduction plate interface. Intense underplating at the rear of accretionary wedges ultimately leads to antiformal stacking and, in combination of surface erosion, to the uplift of sediments formerly accreted at the base of wedges. In the present study, I try to determine and quantify the main features leading to tectonic underplating and subsequent uplift of underthrust incoming sediments at subduction zones. To do so, a numerical model is set up defined by a downgoing rigid plate, an overlying sedimentary sequence and a rigid backstop resulting in sediment accretion. The implementation of two weak décollement layers allows for the potential development of tectonic underplating. Tested parameters for the tectonic evolution of such systems include décollement strength, surface erosion, elastic stiffness of the downgoing plate and geometry of the rigid backstop. The applied numerical code is based on the finite difference marker-in-cell technique with a visco-elasto-plastic rheology. Results indicate that underplating is intensified when i) the stratigraphically lower décollement is strengthened with respect to the upper one, ii) surface erosion is increased, or iii) the downgoing plate becomes stiffer. Modelling results are compared to natural cases of accrretionary wedges where sediments have been underplated (and eventually exhumed) as in the Makran, the Franciscan, or the Appalachians.
How to cite: Ruh, J. B.: Numerical modelling of tectonic underplating in accretionary wedges, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5607, https://doi.org/10.5194/egusphere-egu2020-5607, 2020.
EGU2020-5256 | Displays | TS7.2
Buckle fold growth in the western Northern Calcareous Alps fold-and-thrust belt of Austria– finite element modelling and field observationsSinah Kilian, Hugo Ortner, and Barbara Schneider-Muntau
We studied the Karwendel mountains of the Northern Calcareous Alps fold-and-thrust belt, that formed during the Upper Cretaceous. The study area exposes one of the principal thrusts that emplaces Triassic sediments on the top of Cretaceous rocks. Based on a detailed structural analysis (Kilian and Ortner, 2019) it has been demonstrated that the folds above the thrust are buckle folds.
With the finite element modelling, we aimed to create folds with wavelengths comparable to those observed in the field. The model set up is a simple layer cake model based on the stratigraphy of the western Northern Calcareous Alps. We used ABAQUS a finite element software to create the model. The material model is linear elasticity. During modelling, we tested different material characteristics and layer thickness. In all model runs a very weak décollement (possibly salt) is necessary to produce folds. We further tested the influence of erosion and re-sedimentation on the development of structures. We concluded that the growth of folds having wavelengths comparable to the field examples depends on the thickness of the competent layer, whereas the thickness of the incompetent layer has negligible influence.
We suggest that fold development in this part of the Northern Calcareous Alps is dependent on the interplay between the growth of evaporite-cored anticlines and surface erosion.
Reference
Kilian, S., Ortner, H.: Structural evidence of in-sequence and out-of-sequence thrusting in the Karwendel mountains and the tectonic subdivision of the western Northern Calcareous Alps. Austrian Journal of Earth Sciences, Vienna, 2019, V.112/1, p.62-83, DOI: 10.17738/ajes.2019.0005.
How to cite: Kilian, S., Ortner, H., and Schneider-Muntau, B.: Buckle fold growth in the western Northern Calcareous Alps fold-and-thrust belt of Austria– finite element modelling and field observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5256, https://doi.org/10.5194/egusphere-egu2020-5256, 2020.
We studied the Karwendel mountains of the Northern Calcareous Alps fold-and-thrust belt, that formed during the Upper Cretaceous. The study area exposes one of the principal thrusts that emplaces Triassic sediments on the top of Cretaceous rocks. Based on a detailed structural analysis (Kilian and Ortner, 2019) it has been demonstrated that the folds above the thrust are buckle folds.
With the finite element modelling, we aimed to create folds with wavelengths comparable to those observed in the field. The model set up is a simple layer cake model based on the stratigraphy of the western Northern Calcareous Alps. We used ABAQUS a finite element software to create the model. The material model is linear elasticity. During modelling, we tested different material characteristics and layer thickness. In all model runs a very weak décollement (possibly salt) is necessary to produce folds. We further tested the influence of erosion and re-sedimentation on the development of structures. We concluded that the growth of folds having wavelengths comparable to the field examples depends on the thickness of the competent layer, whereas the thickness of the incompetent layer has negligible influence.
We suggest that fold development in this part of the Northern Calcareous Alps is dependent on the interplay between the growth of evaporite-cored anticlines and surface erosion.
Reference
Kilian, S., Ortner, H.: Structural evidence of in-sequence and out-of-sequence thrusting in the Karwendel mountains and the tectonic subdivision of the western Northern Calcareous Alps. Austrian Journal of Earth Sciences, Vienna, 2019, V.112/1, p.62-83, DOI: 10.17738/ajes.2019.0005.
How to cite: Kilian, S., Ortner, H., and Schneider-Muntau, B.: Buckle fold growth in the western Northern Calcareous Alps fold-and-thrust belt of Austria– finite element modelling and field observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5256, https://doi.org/10.5194/egusphere-egu2020-5256, 2020.
EGU2020-21901 | Displays | TS7.2
Mapping strain in the footwall of a thrust: Preliminary results from 3D bulk fabric of illite.Charles Aubourg, Gracia-Puzo Francho, Casas-Sainz Antonio, Izquierdo-Llavall Esther, Boiron Tiphaine, and Saur Hugo
The Sigues fold (Aragon, Spain) presents an exceptional outcrop where 1) the footwall is largely exposed, 2) it is constituted of homogenous shales, 3) the strain varies at distance from the emergent thrust, with all steps of cleavage development. The best model to explain the strain distribution is the trishear propagation of a thrust with a P/S ratio of 1. However, from East to West, the thrust geometry is changing progressively from blind thrust to flat ramp. The topographic surface as well as the position of the emerging part of the thrust determine the geometry of the structure. This is, therefore, a place with variable geometries, which allow us to describe the different geometric stages of the ramp-and-flat model that we are used to find in major orogenic thrusts.
To map the strain, we measured the magnetic fabric of hundreds of shale fragments (weighting a few grams) in dozens of localities. The magnetic fabric is governed primarily by illite. Hence, the magnetic fabric represents a 3D view of illite organization, i.e. the matrix of those shales (see Gracia-Puzo et al., EGU, EMRP3.8). The measurement of 3D fabric of illite takes about a minute per fragment and is non-destructive.
Magnetic fabric of shale fragments provides three useful parameters, the degree of anisotropy, the shape parameter from oblate to prolate, and the length of the confidence angle of the minimum axis of tensor. We show that all these three parameters are highly sensitive to strain. While each locality provides homogenous results from ~15 fragments (covering few square meters each), it is statistically different from one site to the other, with trends consistent with distance to the main thrust. Assuming rigid rotation of illite particles, we calculate the strain using Eigen values of magnetic fabric tensor.
Our preliminary maps shows: 1) that the strain increases considerably (from units to tens in %) when approaching the main thrust, 2) at a distance of more than 1 km, several strain gradients are detected, suggesting that blind thrusts propagate in the footwall. Serial N-S cross-sections are expected to describe the lateral variability on the structure, the deformation accumulated on the footwall and also establishing the portion of the hanging wall which is being affected and the décollement of the thrust. Our approach is thus promising to map strain in shales from deformed regions, both from natural outcrops, or from boreholes.
How to cite: Aubourg, C., Francho, G.-P., Antonio, C.-S., Esther, I.-L., Tiphaine, B., and Hugo, S.: Mapping strain in the footwall of a thrust: Preliminary results from 3D bulk fabric of illite. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21901, https://doi.org/10.5194/egusphere-egu2020-21901, 2020.
The Sigues fold (Aragon, Spain) presents an exceptional outcrop where 1) the footwall is largely exposed, 2) it is constituted of homogenous shales, 3) the strain varies at distance from the emergent thrust, with all steps of cleavage development. The best model to explain the strain distribution is the trishear propagation of a thrust with a P/S ratio of 1. However, from East to West, the thrust geometry is changing progressively from blind thrust to flat ramp. The topographic surface as well as the position of the emerging part of the thrust determine the geometry of the structure. This is, therefore, a place with variable geometries, which allow us to describe the different geometric stages of the ramp-and-flat model that we are used to find in major orogenic thrusts.
To map the strain, we measured the magnetic fabric of hundreds of shale fragments (weighting a few grams) in dozens of localities. The magnetic fabric is governed primarily by illite. Hence, the magnetic fabric represents a 3D view of illite organization, i.e. the matrix of those shales (see Gracia-Puzo et al., EGU, EMRP3.8). The measurement of 3D fabric of illite takes about a minute per fragment and is non-destructive.
Magnetic fabric of shale fragments provides three useful parameters, the degree of anisotropy, the shape parameter from oblate to prolate, and the length of the confidence angle of the minimum axis of tensor. We show that all these three parameters are highly sensitive to strain. While each locality provides homogenous results from ~15 fragments (covering few square meters each), it is statistically different from one site to the other, with trends consistent with distance to the main thrust. Assuming rigid rotation of illite particles, we calculate the strain using Eigen values of magnetic fabric tensor.
Our preliminary maps shows: 1) that the strain increases considerably (from units to tens in %) when approaching the main thrust, 2) at a distance of more than 1 km, several strain gradients are detected, suggesting that blind thrusts propagate in the footwall. Serial N-S cross-sections are expected to describe the lateral variability on the structure, the deformation accumulated on the footwall and also establishing the portion of the hanging wall which is being affected and the décollement of the thrust. Our approach is thus promising to map strain in shales from deformed regions, both from natural outcrops, or from boreholes.
How to cite: Aubourg, C., Francho, G.-P., Antonio, C.-S., Esther, I.-L., Tiphaine, B., and Hugo, S.: Mapping strain in the footwall of a thrust: Preliminary results from 3D bulk fabric of illite. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21901, https://doi.org/10.5194/egusphere-egu2020-21901, 2020.
EGU2020-1916 | Displays | TS7.2
Formation and forward propagation of the Indosinian Nanpanjiang foreland basin and foreland thrust belt in SW ChinaWen-Xin Yang, Dan-Ping Yan, Liang Qiu, Michael. L Wells, Jian-Meng Dong, Tian Gao, and Zhi Zhang
Nanpanjiang Basin (also called the Youjiang Basin or Dian-Qian-Gui Basin in literatures), the foreland basin of the Indosinian orogenic belt, is located on the boundary belt between the South China and Indochina Blocks. This foreland basin is characterized by a transition from the Early Triassic shallow-marine carbonate platforms to Middle and Upper Triassic continental facies clastic rocks and reworked by the subsequent Indosinian foreland thrusting and deformations. The development of the Indosinian foreland fold-and-thrust belt remains underappreciated in part because of the loose constraints of the transition from basin deposition to deformation and erosion. In this study, we present two geological cross-sections that synthesized field geological investigations, together with the structural interpretation of three seismic profiles, and LA-ICP-MS detrital zircon age constraints. The results reveal that the thrust belt is characterized by fault-related folds with duplex and imbricate thrusts, which yield the NNE-trending regional shortening estimate of ~36%. The new constraints indicate that the Nanpanjiang foreland basin formed before 237 Ma (D11) was overridden by the following NNE-ward progressive deformations, including 237-225 Ma thick-skinned thrusts (D12), 223-183 Ma thin-skinned thrusts (D13), and after that entire basin-involved deformation (D14). Subsequently, D1 was re-deformed and superimposed by the Middle to Late Jurassic NNE-striking fault-related fold system (D2). D11-4 reveals a NNE-verging propagation in-sequence foreland thrusting which overrode the foreland basin and the corresponded NNE-ward progressive foreland basin during the Indosinian.
How to cite: Yang, W.-X., Yan, D.-P., Qiu, L., Wells, M. L., Dong, J.-M., Gao, T., and Zhang, Z.: Formation and forward propagation of the Indosinian Nanpanjiang foreland basin and foreland thrust belt in SW China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1916, https://doi.org/10.5194/egusphere-egu2020-1916, 2020.
Nanpanjiang Basin (also called the Youjiang Basin or Dian-Qian-Gui Basin in literatures), the foreland basin of the Indosinian orogenic belt, is located on the boundary belt between the South China and Indochina Blocks. This foreland basin is characterized by a transition from the Early Triassic shallow-marine carbonate platforms to Middle and Upper Triassic continental facies clastic rocks and reworked by the subsequent Indosinian foreland thrusting and deformations. The development of the Indosinian foreland fold-and-thrust belt remains underappreciated in part because of the loose constraints of the transition from basin deposition to deformation and erosion. In this study, we present two geological cross-sections that synthesized field geological investigations, together with the structural interpretation of three seismic profiles, and LA-ICP-MS detrital zircon age constraints. The results reveal that the thrust belt is characterized by fault-related folds with duplex and imbricate thrusts, which yield the NNE-trending regional shortening estimate of ~36%. The new constraints indicate that the Nanpanjiang foreland basin formed before 237 Ma (D11) was overridden by the following NNE-ward progressive deformations, including 237-225 Ma thick-skinned thrusts (D12), 223-183 Ma thin-skinned thrusts (D13), and after that entire basin-involved deformation (D14). Subsequently, D1 was re-deformed and superimposed by the Middle to Late Jurassic NNE-striking fault-related fold system (D2). D11-4 reveals a NNE-verging propagation in-sequence foreland thrusting which overrode the foreland basin and the corresponded NNE-ward progressive foreland basin during the Indosinian.
How to cite: Yang, W.-X., Yan, D.-P., Qiu, L., Wells, M. L., Dong, J.-M., Gao, T., and Zhang, Z.: Formation and forward propagation of the Indosinian Nanpanjiang foreland basin and foreland thrust belt in SW China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1916, https://doi.org/10.5194/egusphere-egu2020-1916, 2020.
EGU2020-11748 | Displays | TS7.2
Contractional inheritance and rheology controls in a FTB: the Argentinian Precordillera, Central Andes (30°S)Matthieu Branellec, Nuria Carrera, Josep Anton Munoz, Jean-Claude Ringenbach, and Jean-Paul Callot
The Central Andes (12°S-36°S) stretches over more than 2400km. They are characterized by strong longitudinal and latitudinal segmentation (Sierra Pampeanas, Precordillera, Cordillera Frontal, Cordillera Principal from east to west), each domain having distinctive basement involvement and showing different structural styles. The Argentinian Precordillera, located at 30°S, has long been interpreted as a thin-skinned wedge detached below into the lower part of Paleozoic succession. It makes up a typical Coulomb foreland thrust belt system. However, the impact of the Paleozoic inheritance derived from the various orogenic stages on the current structural style has been overlooked. The Chanic structures that developed in Silurian / Devonian times have been reactivated by the Andean deformation that took place from Oligocene to Plio-Pleistocene times. The current structure of the Precordillera has been the subject of numerous studies in the last decades. Thanks to compilation of this literature and fieldwork, we present a new cross-section considering these 2 superimposed events. This cross-section can be divided into 2 different zones depending on the dominant structures. The western Precordillera involves an Ordovician succession characterized by Chanic superimposed folding phases with cleavage development. On the contrary, in the eastern part, most of the observed structures were developed during Andean orogeny. The structural style is characterized by thrusts faults and penetrative deformation is absent. The Sierras Pampeanas in the East are a Miocene thick-skinned system that makes up a typical broken foreland system. The association of both systems of Precordillera and Sierras Pampeanas delineate an inheritance-controlled original orogenic thin-skinned system that turns to the east into a broad thick-skinned system involving up to Precambrian rocks.
How to cite: Branellec, M., Carrera, N., Munoz, J. A., Ringenbach, J.-C., and Callot, J.-P.: Contractional inheritance and rheology controls in a FTB: the Argentinian Precordillera, Central Andes (30°S), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11748, https://doi.org/10.5194/egusphere-egu2020-11748, 2020.
The Central Andes (12°S-36°S) stretches over more than 2400km. They are characterized by strong longitudinal and latitudinal segmentation (Sierra Pampeanas, Precordillera, Cordillera Frontal, Cordillera Principal from east to west), each domain having distinctive basement involvement and showing different structural styles. The Argentinian Precordillera, located at 30°S, has long been interpreted as a thin-skinned wedge detached below into the lower part of Paleozoic succession. It makes up a typical Coulomb foreland thrust belt system. However, the impact of the Paleozoic inheritance derived from the various orogenic stages on the current structural style has been overlooked. The Chanic structures that developed in Silurian / Devonian times have been reactivated by the Andean deformation that took place from Oligocene to Plio-Pleistocene times. The current structure of the Precordillera has been the subject of numerous studies in the last decades. Thanks to compilation of this literature and fieldwork, we present a new cross-section considering these 2 superimposed events. This cross-section can be divided into 2 different zones depending on the dominant structures. The western Precordillera involves an Ordovician succession characterized by Chanic superimposed folding phases with cleavage development. On the contrary, in the eastern part, most of the observed structures were developed during Andean orogeny. The structural style is characterized by thrusts faults and penetrative deformation is absent. The Sierras Pampeanas in the East are a Miocene thick-skinned system that makes up a typical broken foreland system. The association of both systems of Precordillera and Sierras Pampeanas delineate an inheritance-controlled original orogenic thin-skinned system that turns to the east into a broad thick-skinned system involving up to Precambrian rocks.
How to cite: Branellec, M., Carrera, N., Munoz, J. A., Ringenbach, J.-C., and Callot, J.-P.: Contractional inheritance and rheology controls in a FTB: the Argentinian Precordillera, Central Andes (30°S), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11748, https://doi.org/10.5194/egusphere-egu2020-11748, 2020.
EGU2020-22109 | Displays | TS7.2
A mountain of folds: triangle zone in the fold-and-thrust belt of the External Pamir, KyrgyzstanThomas Voigt, Jonas Kley, and Christoph Wehner
Triangle zones are thrust sheets or stacks of thrust sheets underlain by foreland-directed thrusts and overlain by a kinematically linked “passive” roof thrust - a backthrust - directed towards the hinterland. They are not uncommon in thin-skinned fold-and-thrust belts. Most triangle zones are known from seismic data and drilling. We describe a km-scale example exposed on a flank of the Altyn Dara valley near the thrust front of the Pamir mountains in Kyrgyzstan. The External Pamir is a high-level thrust belt built from non-metamorphic strata of Permian to Neogene age. It is bounded on its internal, southern side by the Main Pamir thrust with metamorphic rocks in its hanging-wall and in the north by the Pamir Frontal thrust which juxtaposes it with undeformed foreland strata of the Alai valley.
The triangle zone has formed where the basal detachment of the External Pamir ramps up from Lower Cretaceous redbeds into a succession of Upper Cretaceous marine pelites with a few intercalated limestone horizons. The strongly deformed Upper Cretaceous strata are contained between a north-directed thrust and a south-directed backthrust, both of which carry Lower Cretaceous rocks in their hanging-walls. In stark contrast to classical models, the core of the triangle zone is occupied by a bundle of essentially unfaulted, isoclinal upright folds. The subvertical axial planes diverge slightly upwards and changing elevations of the synclinal troughs suggest an anticlinorium. This structure is exposed over a vertical distance of 1 km in the steep flank of Pik Sverdlova. The folds involve four shaly packages and three limestone horizons. The initial total thickness of this succession was about 500 m. A strong slaty cleavage is developed in the shales, but the limestones do not show marked thickness variations between the long, straight fold limbs and the tight but rounded hinges. Assuming negligible penetrative strain in the limestones, unfolding the sinuous bed length suggests 10 km of horizontal shortening accommodated by folding.
Its overall geometry suggests that the triangle zone originated as a wide zone of detachment folding above a thrust fault propagating at the base of the weak Upper Cretaceous shales. The strong contraction may indicate some kind of buttress towards the foreland such as a syndepositional fault against which the Cenomanian-Turonian succession thinned or terminated, or the backthrust itself if it initiated early on. At any rate, the highly shortened bundle of folds was at some point bypassed along a deeper detachment in Lower Cretaceous strata into which the backthrust merges.
The internal structure of the Pik Sverdlova triangle zone would be difficult to image by conventional seismic techniques. Vertical drilling would also be unlikely to fully reveal the folded architecture. We speculate that in many triangle zones folding may be a more important mechanism than incorporated in the prevailing thrust-stacking models.
How to cite: Voigt, T., Kley, J., and Wehner, C.: A mountain of folds: triangle zone in the fold-and-thrust belt of the External Pamir, Kyrgyzstan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22109, https://doi.org/10.5194/egusphere-egu2020-22109, 2020.
Triangle zones are thrust sheets or stacks of thrust sheets underlain by foreland-directed thrusts and overlain by a kinematically linked “passive” roof thrust - a backthrust - directed towards the hinterland. They are not uncommon in thin-skinned fold-and-thrust belts. Most triangle zones are known from seismic data and drilling. We describe a km-scale example exposed on a flank of the Altyn Dara valley near the thrust front of the Pamir mountains in Kyrgyzstan. The External Pamir is a high-level thrust belt built from non-metamorphic strata of Permian to Neogene age. It is bounded on its internal, southern side by the Main Pamir thrust with metamorphic rocks in its hanging-wall and in the north by the Pamir Frontal thrust which juxtaposes it with undeformed foreland strata of the Alai valley.
The triangle zone has formed where the basal detachment of the External Pamir ramps up from Lower Cretaceous redbeds into a succession of Upper Cretaceous marine pelites with a few intercalated limestone horizons. The strongly deformed Upper Cretaceous strata are contained between a north-directed thrust and a south-directed backthrust, both of which carry Lower Cretaceous rocks in their hanging-walls. In stark contrast to classical models, the core of the triangle zone is occupied by a bundle of essentially unfaulted, isoclinal upright folds. The subvertical axial planes diverge slightly upwards and changing elevations of the synclinal troughs suggest an anticlinorium. This structure is exposed over a vertical distance of 1 km in the steep flank of Pik Sverdlova. The folds involve four shaly packages and three limestone horizons. The initial total thickness of this succession was about 500 m. A strong slaty cleavage is developed in the shales, but the limestones do not show marked thickness variations between the long, straight fold limbs and the tight but rounded hinges. Assuming negligible penetrative strain in the limestones, unfolding the sinuous bed length suggests 10 km of horizontal shortening accommodated by folding.
Its overall geometry suggests that the triangle zone originated as a wide zone of detachment folding above a thrust fault propagating at the base of the weak Upper Cretaceous shales. The strong contraction may indicate some kind of buttress towards the foreland such as a syndepositional fault against which the Cenomanian-Turonian succession thinned or terminated, or the backthrust itself if it initiated early on. At any rate, the highly shortened bundle of folds was at some point bypassed along a deeper detachment in Lower Cretaceous strata into which the backthrust merges.
The internal structure of the Pik Sverdlova triangle zone would be difficult to image by conventional seismic techniques. Vertical drilling would also be unlikely to fully reveal the folded architecture. We speculate that in many triangle zones folding may be a more important mechanism than incorporated in the prevailing thrust-stacking models.
How to cite: Voigt, T., Kley, J., and Wehner, C.: A mountain of folds: triangle zone in the fold-and-thrust belt of the External Pamir, Kyrgyzstan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22109, https://doi.org/10.5194/egusphere-egu2020-22109, 2020.
EGU2020-13310 | Displays | TS7.2
Evolution of the Aure-Moresby Foreland FTB (Papua New Guinea): Constraints from balanced crustal scale cross-section and forward modeling.charlie kergaravat, jean-claude ringenbach, and Jaume Verges
The New Guinea Orogen evolved by the accretion of volcanic arcs onto the northern Australian margin during the Cenozoic arc-continent collision. Since that time, the northern Australian margin has undergone oblique convergence with Pacific plate involving volcanic arcs and intra-oceanic basin in between. The resulting FTBs are the Papuan FTB, the Mobile Belt and the Aure-Moresby FTB belonging to the curved shape New Guinea Highlands.
Previous regional structural studies were focus to the Central Papuan FTB. Concerning the Aure-Moresby FTB, few studies based mainly on field work describe a highly deformed Neogene underfilled foreland basin with mixed carbonate-siliciclastic deposits. One regional cross-section through the onshore Aure-Moresby FTB is proposed by Kugler during his PhD in 1967. In this regard, some lack of consistency about the regional structural style can be highlighted such as the different timing and amount of shortening between the Papuan and Aure-Moresby FTBs and the large N-S positive flower structure to explain the uplift of the Aure FTB.
The main goals of this study on the Aure-Moresby Foreland FTB are: (i) to discuss the impact of the mechanical stratigraphy on structural style, (ii) to estimate the significance of basement involvement and its morphology, (iii) to determine the shortening by comparing the regional balanced and restored cross sections, (iv) to estimate the relative ages of tectonic deformation and to propose a 2D kinematic model illustrating the evolution of the orogenic system since the Late Cretaceous.
For this purpose, 2D seismic profiles, chronostratigraphic synthesis, remote sensing mapping, wells and gravimetric data have been integrated in order to construct a consistent structural evolutionary model of the Aure FTB. This study is mainly focused on the interpretation of NE-SW trending 2D seismic lines in Move software to build a balanced cross-section from the hinterland to the foreland Aure foredeep.
This study shows that the Aure-Moresby FTB structure is the result of thin-skinned deformation along Late Cretaceous, Miocene and Pliocene detachment levels affected by recent thick-skinned deformation. The section is characterized by multiple fault-propagation folds detached at various level within the Mesozoic and Cenozoic. In the central Aure FTB, two main structural steps show major uplifts that correspond to the wide Dude Anticlinorium and the Kapau Margin interpreted as crustal scale thrusting rooted at the brittle/ductile transition and connected with the Cretaceous décollement level. Crustal scale deformation seems to be transmitted into Mesozoic and Cenozoic decollements and disharmonic levels forming the frontal folded zone. In the frontal Aure FTB, Miocene carbonate may be involved in the deformation forming potentially Pleistocene structural traps. Based on flexural slip restoration technique, 28 km of shortening have been calculated within the sedimentary cover along 250 km that correspond to a ratio of 11,2 %.
How to cite: kergaravat, C., ringenbach, J., and Verges, J.: Evolution of the Aure-Moresby Foreland FTB (Papua New Guinea): Constraints from balanced crustal scale cross-section and forward modeling., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13310, https://doi.org/10.5194/egusphere-egu2020-13310, 2020.
The New Guinea Orogen evolved by the accretion of volcanic arcs onto the northern Australian margin during the Cenozoic arc-continent collision. Since that time, the northern Australian margin has undergone oblique convergence with Pacific plate involving volcanic arcs and intra-oceanic basin in between. The resulting FTBs are the Papuan FTB, the Mobile Belt and the Aure-Moresby FTB belonging to the curved shape New Guinea Highlands.
Previous regional structural studies were focus to the Central Papuan FTB. Concerning the Aure-Moresby FTB, few studies based mainly on field work describe a highly deformed Neogene underfilled foreland basin with mixed carbonate-siliciclastic deposits. One regional cross-section through the onshore Aure-Moresby FTB is proposed by Kugler during his PhD in 1967. In this regard, some lack of consistency about the regional structural style can be highlighted such as the different timing and amount of shortening between the Papuan and Aure-Moresby FTBs and the large N-S positive flower structure to explain the uplift of the Aure FTB.
The main goals of this study on the Aure-Moresby Foreland FTB are: (i) to discuss the impact of the mechanical stratigraphy on structural style, (ii) to estimate the significance of basement involvement and its morphology, (iii) to determine the shortening by comparing the regional balanced and restored cross sections, (iv) to estimate the relative ages of tectonic deformation and to propose a 2D kinematic model illustrating the evolution of the orogenic system since the Late Cretaceous.
For this purpose, 2D seismic profiles, chronostratigraphic synthesis, remote sensing mapping, wells and gravimetric data have been integrated in order to construct a consistent structural evolutionary model of the Aure FTB. This study is mainly focused on the interpretation of NE-SW trending 2D seismic lines in Move software to build a balanced cross-section from the hinterland to the foreland Aure foredeep.
This study shows that the Aure-Moresby FTB structure is the result of thin-skinned deformation along Late Cretaceous, Miocene and Pliocene detachment levels affected by recent thick-skinned deformation. The section is characterized by multiple fault-propagation folds detached at various level within the Mesozoic and Cenozoic. In the central Aure FTB, two main structural steps show major uplifts that correspond to the wide Dude Anticlinorium and the Kapau Margin interpreted as crustal scale thrusting rooted at the brittle/ductile transition and connected with the Cretaceous décollement level. Crustal scale deformation seems to be transmitted into Mesozoic and Cenozoic decollements and disharmonic levels forming the frontal folded zone. In the frontal Aure FTB, Miocene carbonate may be involved in the deformation forming potentially Pleistocene structural traps. Based on flexural slip restoration technique, 28 km of shortening have been calculated within the sedimentary cover along 250 km that correspond to a ratio of 11,2 %.
How to cite: kergaravat, C., ringenbach, J., and Verges, J.: Evolution of the Aure-Moresby Foreland FTB (Papua New Guinea): Constraints from balanced crustal scale cross-section and forward modeling., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13310, https://doi.org/10.5194/egusphere-egu2020-13310, 2020.
EGU2020-7670 | Displays | TS7.2
Varying thrust geometry along the Central Atlas fronts: structural criteria for 3-D reconstructionAntonio M. Casas, Pablo Calvín, Pablo Santolaria, Tania Mochales, Hmidou El-Ouardi, ESther Izquierdo, Teresa Román-Berdiel, Sara Torres, Andrés Pocoví, Belén Oliva-Urcia, Bennacer Moussaid, Marcos Marcén, Andrés Gil-Imaz, Vicente Carlos Ruiz, María Felicidad Bógalo, Elisa Sánchez, Ángela Herrejón, Ángela Jiménez, Juan José Villalaín, and Irene Falcón
Multiple constraints, including poorly known parameters, determine along-strike changes of frontal thrust structures in fold-and-thrust belts. Along the 400 km long, continuous Central Moroccan Atlas belt, structural style shows significant changes, preserving similar figures of shortening. This implies the absence of large-scale vertical-axes rotations, as demonstrated by paleomagnetic studies accomplished during the development of this project. The main factors controlling thrust geometry are:
- the geometry of Triassic-Jurassic extensional basins subsequently inverted during Cenozoic compression, with especial mention to changes of cover thickness and orientation of structures
- transfer of displacement between the northern and southern thrust systems
- transfer of displacement between the basement (Paleozoic) units and the Mesozoic cover through the Upper Triassic detachment. This factor strongly determines the width of the belt in each transect, as it occurs in other basement-and-cover fold-and-thrust belts
- cover/detachment thickness ratio.
- localization and partitioning of deformation between different structures in the inner part and the borders of the massif
- amount of superposition between different cover thrust sheets, including folded thrusts
- structural style, changing from thin-skinned style to large recumbent folds along strike, probably depending on P-T conditions and cover thickness
- backthrusts related to low cover thickness/detachment thickness ratio, especially frequent in the northern Atlas thrusts
- differential shortening between sections related to layer-parallel shortening and folds associated with cleavage development in the central part of the chain
- influence of previous structures, such as individual diapirs, salt walls or igneous intrusions that modify the pre-compressional geometry of the detachment level, nucleate structures and favor buttressing. This feature can also be a source of errors in the calculation of shortening.
All these factors result in strong along-strike changes such as branching of thrust surfaces, progression of deformation towards the foreland and differential cleavage development. Influence of structures developed during the basinal/diapiric/igneous stage results in a variability of trends that varies between from less than 10° to more than 30°, what allows in some cases to distinguish between structures controlled by basinal features and newly formed thrusts.
In spite of the different techniques for cross-sections reconstruction, and in some cases, the different interpretations for the origin of structures, the shortening figures obtained along the chain are remarkably constant, on the range of 35 km, thus implying a 18 to 30% of shortening for most of the transects what attests for the reliability of the results.
Recognition and quantification of factors controlling the development of structures is the fundamental step to determine the main thrust surfaces, and the secondary backthrusts in a region where basin inversion is one of the main constraints. Structural criteria point to a dominant southward vergence and secondary northwards-directed thrusts. Minor strike-slip components were probably localized in the core of the chain. Present-day 3-D reconstruction of the Atlas is currently being done considering all these inputs as well as those obtained from merging the vast dataset obtained.
How to cite: Casas, A. M., Calvín, P., Santolaria, P., Mochales, T., El-Ouardi, H., Izquierdo, E., Román-Berdiel, T., Torres, S., Pocoví, A., Oliva-Urcia, B., Moussaid, B., Marcén, M., Gil-Imaz, A., Ruiz, V. C., Bógalo, M. F., Sánchez, E., Herrejón, Á., Jiménez, Á., Villalaín, J. J., and Falcón, I.: Varying thrust geometry along the Central Atlas fronts: structural criteria for 3-D reconstruction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7670, https://doi.org/10.5194/egusphere-egu2020-7670, 2020.
Multiple constraints, including poorly known parameters, determine along-strike changes of frontal thrust structures in fold-and-thrust belts. Along the 400 km long, continuous Central Moroccan Atlas belt, structural style shows significant changes, preserving similar figures of shortening. This implies the absence of large-scale vertical-axes rotations, as demonstrated by paleomagnetic studies accomplished during the development of this project. The main factors controlling thrust geometry are:
- the geometry of Triassic-Jurassic extensional basins subsequently inverted during Cenozoic compression, with especial mention to changes of cover thickness and orientation of structures
- transfer of displacement between the northern and southern thrust systems
- transfer of displacement between the basement (Paleozoic) units and the Mesozoic cover through the Upper Triassic detachment. This factor strongly determines the width of the belt in each transect, as it occurs in other basement-and-cover fold-and-thrust belts
- cover/detachment thickness ratio.
- localization and partitioning of deformation between different structures in the inner part and the borders of the massif
- amount of superposition between different cover thrust sheets, including folded thrusts
- structural style, changing from thin-skinned style to large recumbent folds along strike, probably depending on P-T conditions and cover thickness
- backthrusts related to low cover thickness/detachment thickness ratio, especially frequent in the northern Atlas thrusts
- differential shortening between sections related to layer-parallel shortening and folds associated with cleavage development in the central part of the chain
- influence of previous structures, such as individual diapirs, salt walls or igneous intrusions that modify the pre-compressional geometry of the detachment level, nucleate structures and favor buttressing. This feature can also be a source of errors in the calculation of shortening.
All these factors result in strong along-strike changes such as branching of thrust surfaces, progression of deformation towards the foreland and differential cleavage development. Influence of structures developed during the basinal/diapiric/igneous stage results in a variability of trends that varies between from less than 10° to more than 30°, what allows in some cases to distinguish between structures controlled by basinal features and newly formed thrusts.
In spite of the different techniques for cross-sections reconstruction, and in some cases, the different interpretations for the origin of structures, the shortening figures obtained along the chain are remarkably constant, on the range of 35 km, thus implying a 18 to 30% of shortening for most of the transects what attests for the reliability of the results.
Recognition and quantification of factors controlling the development of structures is the fundamental step to determine the main thrust surfaces, and the secondary backthrusts in a region where basin inversion is one of the main constraints. Structural criteria point to a dominant southward vergence and secondary northwards-directed thrusts. Minor strike-slip components were probably localized in the core of the chain. Present-day 3-D reconstruction of the Atlas is currently being done considering all these inputs as well as those obtained from merging the vast dataset obtained.
How to cite: Casas, A. M., Calvín, P., Santolaria, P., Mochales, T., El-Ouardi, H., Izquierdo, E., Román-Berdiel, T., Torres, S., Pocoví, A., Oliva-Urcia, B., Moussaid, B., Marcén, M., Gil-Imaz, A., Ruiz, V. C., Bógalo, M. F., Sánchez, E., Herrejón, Á., Jiménez, Á., Villalaín, J. J., and Falcón, I.: Varying thrust geometry along the Central Atlas fronts: structural criteria for 3-D reconstruction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7670, https://doi.org/10.5194/egusphere-egu2020-7670, 2020.
EGU2020-13016 | Displays | TS7.2
New Versus Conventional Approach for Modeling Flexure of Foreland BasinsMortaza Pirouz, Jean-Philippe Avouac, Adriano Gualandi, Muhammad Hassan Quddusi, and Weitong Huang
We constrain foreland basins geometry to assess the equivalent elastic thickness of the lithosphere and the loads that have originated due to the collisional process. Geometry of the foreland relates to the topography loading and hidden subsurface load based on simple 2D flexural models have been done for many foreland basins during 80 and 90s (for example for Zagros, Taiwan, and Colville foreland in Alaska) and most of them highlighted that present topographic and basin loads are not enough to provide such a deflection and extra buried loads are expected. Recent 3D flexure models using conventional approaches are used to estimate the elastic thickness of the lithosphere and may highlight a need for the buried loads. In the conventional approach, we apply topographic and basin loads and use the common assumption that the space created due to the deflection is filled with material of crustal density. This takes place in the deflection function by Δρ=ρmantle-ρcruct. The conventional approach thus includes the static subsurface load associated with the buoyancy of the crustal root. In the new approach, we assume that the deflection is filled with air Δρ=ρmantle-ρair and the sub-surface load is proportional to the topographic load. The load from topography and sub-surface loads is then simply λ times the topographic load. This approach allows accounting for quantifying all sub-surface loads correlated with topography, including the effect of the crustal root. In the new approach the Moho depth, representing the ratio between the root and topographic height, can be considered and the results give more clue about recognizing and quantifying buried load or mantle dynamics loads. With the new approach, we investigated Zagros, Taiwan, and Colville basin-Alaska foreland basins and obtained very precise models with less than 5% misfit between observations and predictions. Previous studies highlight that the buried loads are needed to obtain comparable results to the observations. However, our results show that the best models do not need extra buried loads with a reasonable ratio between topographic relief and crustal root using the new modeling approach.
Abbreviations: Tc, thickness of undeformed lithosphere; wt, deflection due to topographic load; Pt, topographic load; ρm, density of Mantle; ρc, density of crust; ρa, density of air; g, gravity acceleration; β, flexural parameter; Hr, root thickness; Ht, topographic height, and λ, ratio between root thickness and topographic height.
How to cite: Pirouz, M., Avouac, J.-P., Gualandi, A., Quddusi, M. H., and Huang, W.: New Versus Conventional Approach for Modeling Flexure of Foreland Basins, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13016, https://doi.org/10.5194/egusphere-egu2020-13016, 2020.
We constrain foreland basins geometry to assess the equivalent elastic thickness of the lithosphere and the loads that have originated due to the collisional process. Geometry of the foreland relates to the topography loading and hidden subsurface load based on simple 2D flexural models have been done for many foreland basins during 80 and 90s (for example for Zagros, Taiwan, and Colville foreland in Alaska) and most of them highlighted that present topographic and basin loads are not enough to provide such a deflection and extra buried loads are expected. Recent 3D flexure models using conventional approaches are used to estimate the elastic thickness of the lithosphere and may highlight a need for the buried loads. In the conventional approach, we apply topographic and basin loads and use the common assumption that the space created due to the deflection is filled with material of crustal density. This takes place in the deflection function by Δρ=ρmantle-ρcruct. The conventional approach thus includes the static subsurface load associated with the buoyancy of the crustal root. In the new approach, we assume that the deflection is filled with air Δρ=ρmantle-ρair and the sub-surface load is proportional to the topographic load. The load from topography and sub-surface loads is then simply λ times the topographic load. This approach allows accounting for quantifying all sub-surface loads correlated with topography, including the effect of the crustal root. In the new approach the Moho depth, representing the ratio between the root and topographic height, can be considered and the results give more clue about recognizing and quantifying buried load or mantle dynamics loads. With the new approach, we investigated Zagros, Taiwan, and Colville basin-Alaska foreland basins and obtained very precise models with less than 5% misfit between observations and predictions. Previous studies highlight that the buried loads are needed to obtain comparable results to the observations. However, our results show that the best models do not need extra buried loads with a reasonable ratio between topographic relief and crustal root using the new modeling approach.
Abbreviations: Tc, thickness of undeformed lithosphere; wt, deflection due to topographic load; Pt, topographic load; ρm, density of Mantle; ρc, density of crust; ρa, density of air; g, gravity acceleration; β, flexural parameter; Hr, root thickness; Ht, topographic height, and λ, ratio between root thickness and topographic height.
How to cite: Pirouz, M., Avouac, J.-P., Gualandi, A., Quddusi, M. H., and Huang, W.: New Versus Conventional Approach for Modeling Flexure of Foreland Basins, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13016, https://doi.org/10.5194/egusphere-egu2020-13016, 2020.
EGU2020-11043 | Displays | TS7.2
Western Europe tectonic evolution : probing the relative role of inheritance and sub-lithospheric processesFrédéric Mouthereau, Paul Angrand, Juliette Rat, and Maxime Daudet
Abstract : The heterogeneous continental lithosphere of Western Europe inherits billion of years of tectonic evolution, mineral transformation and magmatic addition. Its deformation over broad regions form collisional orogens and large forelands basins, which tectonic evolution is controlled by the interactions between its inherited properties, large-scale plate convection and smaller-scale plate subduction. How these first-order interactions are connected through time and space to control collision evolution is however largely unknown. Here we explore the evolution of the Alpine collision along a transect stretching between northern Africa and Europe. We show that the complex patterns of Alpine deformation from the Rif-Betic, Pyrenean collision and Europe primarily reflects continental fragmentation and drastic weakening of the lithosphere that occurred during the Late Permian-Triassic. Subsequent rifting episodes from Jurassic to Early Cretaceous left imprints on the thermal evolution of sedimentary basins, together with significant increase of Iberia topography, asthenospheric flow, and plate-scale dispersion of terrigenous sediments. The lack of large oceanic domain, at the transition between Atlantic and western Tethys, resulted in the distributed of shortening over a broad region from north Africa, Iberia and Europe, in the upper Cretaceous (~70 Ma). Detailed contraints on the sequence of shortening throughout West Europe from Late Cretaceous to the Tortonian reveals that the overall evolution of the west-alpine orogenic domain is primarily controlled by the nature and architecture of the continental lithosphere but became progressively controlled by sub-lithospheric processes associated with late/post-orogenic tectonic evolution.
How to cite: Mouthereau, F., Angrand, P., Rat, J., and Daudet, M.: Western Europe tectonic evolution : probing the relative role of inheritance and sub-lithospheric processes , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11043, https://doi.org/10.5194/egusphere-egu2020-11043, 2020.
Abstract : The heterogeneous continental lithosphere of Western Europe inherits billion of years of tectonic evolution, mineral transformation and magmatic addition. Its deformation over broad regions form collisional orogens and large forelands basins, which tectonic evolution is controlled by the interactions between its inherited properties, large-scale plate convection and smaller-scale plate subduction. How these first-order interactions are connected through time and space to control collision evolution is however largely unknown. Here we explore the evolution of the Alpine collision along a transect stretching between northern Africa and Europe. We show that the complex patterns of Alpine deformation from the Rif-Betic, Pyrenean collision and Europe primarily reflects continental fragmentation and drastic weakening of the lithosphere that occurred during the Late Permian-Triassic. Subsequent rifting episodes from Jurassic to Early Cretaceous left imprints on the thermal evolution of sedimentary basins, together with significant increase of Iberia topography, asthenospheric flow, and plate-scale dispersion of terrigenous sediments. The lack of large oceanic domain, at the transition between Atlantic and western Tethys, resulted in the distributed of shortening over a broad region from north Africa, Iberia and Europe, in the upper Cretaceous (~70 Ma). Detailed contraints on the sequence of shortening throughout West Europe from Late Cretaceous to the Tortonian reveals that the overall evolution of the west-alpine orogenic domain is primarily controlled by the nature and architecture of the continental lithosphere but became progressively controlled by sub-lithospheric processes associated with late/post-orogenic tectonic evolution.
How to cite: Mouthereau, F., Angrand, P., Rat, J., and Daudet, M.: Western Europe tectonic evolution : probing the relative role of inheritance and sub-lithospheric processes , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11043, https://doi.org/10.5194/egusphere-egu2020-11043, 2020.
EGU2020-2601 | Displays | TS7.2
Inversion tectonics, intracontinental fold-and-thrust belts and complex stress fields in central Europe: the history of the Franconian Basin revealed by paleostress analysis, geological maps and field observations.Saskia Köhler, Florian Duschl, Hamed Fazlikhani, and Daniel Köhn
The Franconian Basin in SE Germany has seen a complex stress history indicative of several extensional and compressional phases e.g. the Iberia-Europe collision acting on a pre-faulted Variscan basement. Early Cretaceous extension is followed by Late Cretaceous inversion with syntectonic sedimentation and deformation increasing progressively from SW to NE culminating in the Franconian Line where basement rocks are thrusted over the Mesozoic cover. The development of this intracontinental fold-and-thrust belt is followed by Paleogene extension associated with the formation of the Eger Graben, which is then succeeded by a new compressional event as a consequence of the Alpine orogeny.
We use existing data from literature and geological maps and new field data to construct balanced cross-sections in order to reveal the architecture of the Cretaceous fold-and-thrust belt. In addition, we undertake paleostress analysis using a combination of fault slip information, veins and tectonic and sedimentary stylolites to identify stress events in the study area, as well as their nature and timing. Furthermore, we try to understand how basement faults influence younger faults in the cover sequence.
Our paleostress data indicates that at least five different stress events existed in Mesozoic to Cenozoic times (from old to young): (1) an N-S directed extensional stress field with E-W striking normal faults, (2) a NNE-SSW directed compressional stress field causing thrusting and folding of the cover sequence, (3) a strike slip regime with NE-SW compression and NW-SE extension, (4) an extensional event with NW-SE extension and the formation of ENE-WSW striking faults according to the formation of the Eger Graben in the E, and finally (5) a strike slip regime with NW-SE compression and NE-SW extension related to Alpine stresses. The geometry of faulting and deformation varies significantly over the regions with respect to the influence of and distance to inherited Variscan structures.
We argue that the extensional event of stress field (1) provides spacing for Early Cretaceous sedimentation in the Franconian Basin. This is followed by the creation of an intracontinental fold-and-thrust belt during stress fields (2) and (3) with a slight rotation of the main compressive stress during these events in Late Cretaceous. We associate the following extension to the development of the Eger Graben in Miocene time. Finally, a NW-SE directed compression related to Alpine stresses in an intracontinental strike-slip regime is following. Reconstruction of the Cretaceous fold-and-thrust belt reveals mainly fault propagation folding with deep detachments sitting below the cover sequence indicating thick-skinned tectonics. We argue that the Franconian Line is a thrust with a steeply dipping root that belongs to the same fold-and-thrust belt.
How to cite: Köhler, S., Duschl, F., Fazlikhani, H., and Köhn, D.: Inversion tectonics, intracontinental fold-and-thrust belts and complex stress fields in central Europe: the history of the Franconian Basin revealed by paleostress analysis, geological maps and field observations. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2601, https://doi.org/10.5194/egusphere-egu2020-2601, 2020.
The Franconian Basin in SE Germany has seen a complex stress history indicative of several extensional and compressional phases e.g. the Iberia-Europe collision acting on a pre-faulted Variscan basement. Early Cretaceous extension is followed by Late Cretaceous inversion with syntectonic sedimentation and deformation increasing progressively from SW to NE culminating in the Franconian Line where basement rocks are thrusted over the Mesozoic cover. The development of this intracontinental fold-and-thrust belt is followed by Paleogene extension associated with the formation of the Eger Graben, which is then succeeded by a new compressional event as a consequence of the Alpine orogeny.
We use existing data from literature and geological maps and new field data to construct balanced cross-sections in order to reveal the architecture of the Cretaceous fold-and-thrust belt. In addition, we undertake paleostress analysis using a combination of fault slip information, veins and tectonic and sedimentary stylolites to identify stress events in the study area, as well as their nature and timing. Furthermore, we try to understand how basement faults influence younger faults in the cover sequence.
Our paleostress data indicates that at least five different stress events existed in Mesozoic to Cenozoic times (from old to young): (1) an N-S directed extensional stress field with E-W striking normal faults, (2) a NNE-SSW directed compressional stress field causing thrusting and folding of the cover sequence, (3) a strike slip regime with NE-SW compression and NW-SE extension, (4) an extensional event with NW-SE extension and the formation of ENE-WSW striking faults according to the formation of the Eger Graben in the E, and finally (5) a strike slip regime with NW-SE compression and NE-SW extension related to Alpine stresses. The geometry of faulting and deformation varies significantly over the regions with respect to the influence of and distance to inherited Variscan structures.
We argue that the extensional event of stress field (1) provides spacing for Early Cretaceous sedimentation in the Franconian Basin. This is followed by the creation of an intracontinental fold-and-thrust belt during stress fields (2) and (3) with a slight rotation of the main compressive stress during these events in Late Cretaceous. We associate the following extension to the development of the Eger Graben in Miocene time. Finally, a NW-SE directed compression related to Alpine stresses in an intracontinental strike-slip regime is following. Reconstruction of the Cretaceous fold-and-thrust belt reveals mainly fault propagation folding with deep detachments sitting below the cover sequence indicating thick-skinned tectonics. We argue that the Franconian Line is a thrust with a steeply dipping root that belongs to the same fold-and-thrust belt.
How to cite: Köhler, S., Duschl, F., Fazlikhani, H., and Köhn, D.: Inversion tectonics, intracontinental fold-and-thrust belts and complex stress fields in central Europe: the history of the Franconian Basin revealed by paleostress analysis, geological maps and field observations. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2601, https://doi.org/10.5194/egusphere-egu2020-2601, 2020.
EGU2020-6742 | Displays | TS7.2
Late-Stage Alpine Continent-Continent Collision: Implications from Exhumation of the External Crystalline MassifsMarco Herwegh, Alfons Berger, Edi Kissling, Nicolas Bellahsen, and Yann Rolland
Late stage Alpine collision is the result of collision of the European and Adriatic continental plates. For this stage, particularly the External Crystalline Massifs (ECM) and their forelands provide information on deformation style/kinematics, exhumation history and geodynamic driving forces. Using the ECMs as marker for the non-thinned European passive continental margin, the margin’s paleogeography with its curved geometries controls in parts later compressional tectonics. During closure of the Valaisan in Eocene times, a major NW-SE trending sinistral transfer zone must have acted as lateral ramp between the NNW migrating Penninic front and the westerly situated European margin units (Argentera and Maritime Alps, stage 1 of Schmid et al. 2017). Hence, first transpressive movements were documented by transpressional strike-slip faults in the case of Argentera and southern Belledonne s.l. Massifs. The SW-NE trending ECMs became affected during a first stage of horizontal tectonics in Oligocene, when first the margin sediments were scrapped off their substratum (Helvetics, Chaînes Subalpines, Dauphinois) followed by thick-skinned thrusting. Transport directions gradually changed from W to N from the Western towards the Eastern ECMs. This spread in transport direction is the consequence of an Alp-internal vertical uplift (Internal Crystalline Massifs (ICM), Lepontine dome) induced by indentation of Adriatic mantle into European lithosphere (stage 2 of Schmid et al. 2017). With further down-bending of the European crust, a major change to a vertical tectonic deformation style occurred in Mid to Late Miocene. Steep reverse faults in the ECMs, in parts with oblique slip components (Mont Blanc), witness this stage with its enhanced vertical rock uplift component. The latter is most pronounced in the Aar Massif and gradually decreases towards the West (Belledonne s.l.). With continuous ICM exhumation in Late Miocene, deformation style switches again to horizontal tectonics, leading to ‘en bloc’ exhumation above basement thrusts of all massifs (Belledonne to Aar Massifs). Progressive shortening induced thrust propagation into the foreland sediments as well as the Jura mountains. In the case of the Argentera Massif, oroclinal bending probably led to a substantial anticlockwise rotation, which goes in hand with the rotation of the entire SW Alpine arc (stage 3 of Schmid et al. 2017). In a geodynamic context, the ‘Adriatic push model’ could explain aforementioned stages of classical horizontal tectonics. Not so, however, the observed severe components of vertical tectonics in the case of ECMs. Here, lower crustal delamination, with a loss of lithospheric negatively buoyant forcing and consequent strong increase in positive buoyancy explains generation and activity of steep reverse faulting in the ECMs. In this context, the ‘orogeny slab rollback’ model provides a physically more consistent framework to explain the observed deformation sequences of late-stage continent-continent collision.
Schmid, S.M., Kissling, E., Diehl, T., van Hinsbergen, D.J., Molli, G., 2017. Ivrea mantle wedge, arc of the Western Alps, and kinematic evolution of the Alps–Apennines orogenic system. Swiss Journal of Geosciences 110, 581-612.
How to cite: Herwegh, M., Berger, A., Kissling, E., Bellahsen, N., and Rolland, Y.: Late-Stage Alpine Continent-Continent Collision: Implications from Exhumation of the External Crystalline Massifs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6742, https://doi.org/10.5194/egusphere-egu2020-6742, 2020.
Late stage Alpine collision is the result of collision of the European and Adriatic continental plates. For this stage, particularly the External Crystalline Massifs (ECM) and their forelands provide information on deformation style/kinematics, exhumation history and geodynamic driving forces. Using the ECMs as marker for the non-thinned European passive continental margin, the margin’s paleogeography with its curved geometries controls in parts later compressional tectonics. During closure of the Valaisan in Eocene times, a major NW-SE trending sinistral transfer zone must have acted as lateral ramp between the NNW migrating Penninic front and the westerly situated European margin units (Argentera and Maritime Alps, stage 1 of Schmid et al. 2017). Hence, first transpressive movements were documented by transpressional strike-slip faults in the case of Argentera and southern Belledonne s.l. Massifs. The SW-NE trending ECMs became affected during a first stage of horizontal tectonics in Oligocene, when first the margin sediments were scrapped off their substratum (Helvetics, Chaînes Subalpines, Dauphinois) followed by thick-skinned thrusting. Transport directions gradually changed from W to N from the Western towards the Eastern ECMs. This spread in transport direction is the consequence of an Alp-internal vertical uplift (Internal Crystalline Massifs (ICM), Lepontine dome) induced by indentation of Adriatic mantle into European lithosphere (stage 2 of Schmid et al. 2017). With further down-bending of the European crust, a major change to a vertical tectonic deformation style occurred in Mid to Late Miocene. Steep reverse faults in the ECMs, in parts with oblique slip components (Mont Blanc), witness this stage with its enhanced vertical rock uplift component. The latter is most pronounced in the Aar Massif and gradually decreases towards the West (Belledonne s.l.). With continuous ICM exhumation in Late Miocene, deformation style switches again to horizontal tectonics, leading to ‘en bloc’ exhumation above basement thrusts of all massifs (Belledonne to Aar Massifs). Progressive shortening induced thrust propagation into the foreland sediments as well as the Jura mountains. In the case of the Argentera Massif, oroclinal bending probably led to a substantial anticlockwise rotation, which goes in hand with the rotation of the entire SW Alpine arc (stage 3 of Schmid et al. 2017). In a geodynamic context, the ‘Adriatic push model’ could explain aforementioned stages of classical horizontal tectonics. Not so, however, the observed severe components of vertical tectonics in the case of ECMs. Here, lower crustal delamination, with a loss of lithospheric negatively buoyant forcing and consequent strong increase in positive buoyancy explains generation and activity of steep reverse faulting in the ECMs. In this context, the ‘orogeny slab rollback’ model provides a physically more consistent framework to explain the observed deformation sequences of late-stage continent-continent collision.
Schmid, S.M., Kissling, E., Diehl, T., van Hinsbergen, D.J., Molli, G., 2017. Ivrea mantle wedge, arc of the Western Alps, and kinematic evolution of the Alps–Apennines orogenic system. Swiss Journal of Geosciences 110, 581-612.
How to cite: Herwegh, M., Berger, A., Kissling, E., Bellahsen, N., and Rolland, Y.: Late-Stage Alpine Continent-Continent Collision: Implications from Exhumation of the External Crystalline Massifs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6742, https://doi.org/10.5194/egusphere-egu2020-6742, 2020.
EGU2020-19638 | Displays | TS7.2
Reconstructing orogen dynamics from detrital geo-thermochronological signals in pro- and retro-foreland basins: A case sudy of the Pyrenees, FranceSébastien Ternois, Julien Léger, Raphaël Pik, and Mary Ford
A bivergent orogenic belt and its foreland basins form an intimately coupled system for which cause-effect relationships have generated much debate. This is the case in the Pyrenees, where the contemporaneity of crustal thermal events (cooling) with foreland tectonic events (subsidence) during convergence has, until recent years, remained unclear due to little quantification of processes during early orogenesis. Over the last 5 years, the development of new tools for generating, manipulating and modelling data and processes in geo-thermochronology has been stimulating new research that challenged established paradigms in both Pyrenean pro- and retro-foreland systems. Results obtained for these systems must now be compared and integrated into a reconstruction of the Pyrenean orogen history.
In this study we first review published detrital geo-thermochronology data in the eastern to central Pyrenees, harmonizing the way by which they are inverted for the inference of sediment provenance with use of current statistical modelling methods. Second, we re-interpret these detrital data in terms of provenance for both Pyrenean pro- and retro-foreland systems. Last, we compare the geo-thermochronological signals in both foreland basins to reconstruct orogen dynamics in the Pyrenees. We critically assess the implications of this newly proposed reconstruction for the validity of conceptual models for orogenic evolution and of plate kinematic models in the northwestern Mediterranean region.
How to cite: Ternois, S., Léger, J., Pik, R., and Ford, M.: Reconstructing orogen dynamics from detrital geo-thermochronological signals in pro- and retro-foreland basins: A case sudy of the Pyrenees, France, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19638, https://doi.org/10.5194/egusphere-egu2020-19638, 2020.
A bivergent orogenic belt and its foreland basins form an intimately coupled system for which cause-effect relationships have generated much debate. This is the case in the Pyrenees, where the contemporaneity of crustal thermal events (cooling) with foreland tectonic events (subsidence) during convergence has, until recent years, remained unclear due to little quantification of processes during early orogenesis. Over the last 5 years, the development of new tools for generating, manipulating and modelling data and processes in geo-thermochronology has been stimulating new research that challenged established paradigms in both Pyrenean pro- and retro-foreland systems. Results obtained for these systems must now be compared and integrated into a reconstruction of the Pyrenean orogen history.
In this study we first review published detrital geo-thermochronology data in the eastern to central Pyrenees, harmonizing the way by which they are inverted for the inference of sediment provenance with use of current statistical modelling methods. Second, we re-interpret these detrital data in terms of provenance for both Pyrenean pro- and retro-foreland systems. Last, we compare the geo-thermochronological signals in both foreland basins to reconstruct orogen dynamics in the Pyrenees. We critically assess the implications of this newly proposed reconstruction for the validity of conceptual models for orogenic evolution and of plate kinematic models in the northwestern Mediterranean region.
How to cite: Ternois, S., Léger, J., Pik, R., and Ford, M.: Reconstructing orogen dynamics from detrital geo-thermochronological signals in pro- and retro-foreland basins: A case sudy of the Pyrenees, France, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19638, https://doi.org/10.5194/egusphere-egu2020-19638, 2020.
EGU2020-18993 | Displays | TS7.2
Structural relief across the NW segment of the Zagros Mountain Front Flexure in the Kurdistan Region of Iraq: implications for basement thrustingMjahid Zebari, Christoph Grützner, Philipp Balling, and Kamil Ustaszewski
Within the NW segment of the Zagros belt in the Kurdistan Region of Iraq, the Zagros Mountain Front Flexure separates the High Folded Zone from the Foothill Zone and forms a pronounced topographic and structural step. Due to the lack of outcrops and subsurface data, balanced and kinematic valid geometrical interpretations for the subsurface deformation associated with this step are not well constrained yet. To solve this, we estimated the structural relief across seven regional transects crossing the Mountain Front Flexure and we constrained the geometry of deformation from deformed-state and forward-modeled balanced cross-sections. The calculated structural relief for six out of seven transects ranges from 2 to 3 km. By using forward modeling, we show that predominantly thick-skinned deformation is needed to explain this amount of relief across the Mountain Front Flexure. Our best-fitting result suggests c. 6.5 km of displacement along a basement thrust fault that dips c. 25° at the top of the basement and that is shallowing downwards. About 4.2 km of this displacement on the basement fault were accommodated up-section by thrust-related and detachment folding of the Triassic and younger units within two prominent anticlines. About 2.3 km of displacement was transferred to the Foothill Zone, forming detachment folds above the Triassic detachment level. Inclined river terraces on the flank of anticlines within the Foothill Zone indicate ongoing displacement on this basement fault. The amount of shortening within the low topographic part of the belt from the deformation front to the limit of seismogenic thrusting within the Imbricated Zone, implies that the Late Miocene to Quaternary shortening rates there were much lower than the present-day geodetically derived convergence rates for this part of belt. These results shed new light on the geometry of the Zagros and its structural evolution.
How to cite: Zebari, M., Grützner, C., Balling, P., and Ustaszewski, K.: Structural relief across the NW segment of the Zagros Mountain Front Flexure in the Kurdistan Region of Iraq: implications for basement thrusting, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18993, https://doi.org/10.5194/egusphere-egu2020-18993, 2020.
Within the NW segment of the Zagros belt in the Kurdistan Region of Iraq, the Zagros Mountain Front Flexure separates the High Folded Zone from the Foothill Zone and forms a pronounced topographic and structural step. Due to the lack of outcrops and subsurface data, balanced and kinematic valid geometrical interpretations for the subsurface deformation associated with this step are not well constrained yet. To solve this, we estimated the structural relief across seven regional transects crossing the Mountain Front Flexure and we constrained the geometry of deformation from deformed-state and forward-modeled balanced cross-sections. The calculated structural relief for six out of seven transects ranges from 2 to 3 km. By using forward modeling, we show that predominantly thick-skinned deformation is needed to explain this amount of relief across the Mountain Front Flexure. Our best-fitting result suggests c. 6.5 km of displacement along a basement thrust fault that dips c. 25° at the top of the basement and that is shallowing downwards. About 4.2 km of this displacement on the basement fault were accommodated up-section by thrust-related and detachment folding of the Triassic and younger units within two prominent anticlines. About 2.3 km of displacement was transferred to the Foothill Zone, forming detachment folds above the Triassic detachment level. Inclined river terraces on the flank of anticlines within the Foothill Zone indicate ongoing displacement on this basement fault. The amount of shortening within the low topographic part of the belt from the deformation front to the limit of seismogenic thrusting within the Imbricated Zone, implies that the Late Miocene to Quaternary shortening rates there were much lower than the present-day geodetically derived convergence rates for this part of belt. These results shed new light on the geometry of the Zagros and its structural evolution.
How to cite: Zebari, M., Grützner, C., Balling, P., and Ustaszewski, K.: Structural relief across the NW segment of the Zagros Mountain Front Flexure in the Kurdistan Region of Iraq: implications for basement thrusting, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18993, https://doi.org/10.5194/egusphere-egu2020-18993, 2020.
EGU2020-11758 | Displays | TS7.2
Inheritance processes of active extensional deformation in ocean-continent subduction zones: the example of the northern Andes compressional margin in EcuadorCédric Bulois, François Michaud, Marianne Saillard, Nicolas Espurt, Marc Regnier, María-José Hernandez Salazar, Yvonne Font, Pedro Reyes Benítez, Jean-Yves Collot, Jean-Noël Proust, Elia D'Acremont, Laure Schenini, and Diego Barba
Over the last 23 Myr, the roughly east-directed subduction of the Nazca Plate beneath South America led to the formation of several mountain ranges associated with the overall northern Andes evolution. Along the active southwestern Ecuadorian margin, the compressional setting involves the Cretaceous-Miocene Chongón-Colonche / Santa Elena terranes, overlain by recent sedimentary basins. This geological setting, generally interpreted as an onshore-offshore forearc system, evolves in close relation with the active tectonic escape of the North Andean Sliver and the opening of the Gulf of Guayaquil. This region is characterised by a widespread extensional deformation in the upper plate that overprints moderate subduction and crustal earthquakes.
To better document such extensional processes, we specifically explore the offshore shelf and the littoral area of the Santa Elena Peninsula using academic and industrial 2D seismic profiles calibrated with local wells and field observations. We document a trench-parallel fault network, composed of >20km-long normal faults that take place on top of the former Chongón-Colonche accretionary wedge. These faults are linearly-steep along the trench, and are listric toward the continent where they clearly control fault-block rotation. They separate flexural basins developing on the platform ahead the Chongón-Colonche Cordillera, and are associated with immerged terraces most likely formed during the Last Glacial Maximum. They also may link to further onshore marine terraces developing since the Pleistocene across the coastline.
These observations suggest a peculiar dismantlement of the margin, mainly affected by tectonic erosion involving reactivation of former compressional features. Normal faults are specifically interpreted as a regional syn-orogenic collapse of the Chongón-Colonche Cordillera, which may result from transecting subducting ridges, fracture zones and seamounts controlling, at least partially, the geometry and the nature of the deformation along the southwestern Ecuadorian margin. This deformation pattern is likely linked to a weak interseismic coupling along the subduction interface to which the active opening of the Gulf of Guayaquil overlaps. This project is funded by the project ANR MARACAS ANR-18-CE31-0022 (MARine terraces along the northern Andean Coast as a proxy for seismic hazard ASsessment).
How to cite: Bulois, C., Michaud, F., Saillard, M., Espurt, N., Regnier, M., Hernandez Salazar, M.-J., Font, Y., Reyes Benítez, P., Collot, J.-Y., Proust, J.-N., D'Acremont, E., Schenini, L., and Barba, D.: Inheritance processes of active extensional deformation in ocean-continent subduction zones: the example of the northern Andes compressional margin in Ecuador, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11758, https://doi.org/10.5194/egusphere-egu2020-11758, 2020.
Over the last 23 Myr, the roughly east-directed subduction of the Nazca Plate beneath South America led to the formation of several mountain ranges associated with the overall northern Andes evolution. Along the active southwestern Ecuadorian margin, the compressional setting involves the Cretaceous-Miocene Chongón-Colonche / Santa Elena terranes, overlain by recent sedimentary basins. This geological setting, generally interpreted as an onshore-offshore forearc system, evolves in close relation with the active tectonic escape of the North Andean Sliver and the opening of the Gulf of Guayaquil. This region is characterised by a widespread extensional deformation in the upper plate that overprints moderate subduction and crustal earthquakes.
To better document such extensional processes, we specifically explore the offshore shelf and the littoral area of the Santa Elena Peninsula using academic and industrial 2D seismic profiles calibrated with local wells and field observations. We document a trench-parallel fault network, composed of >20km-long normal faults that take place on top of the former Chongón-Colonche accretionary wedge. These faults are linearly-steep along the trench, and are listric toward the continent where they clearly control fault-block rotation. They separate flexural basins developing on the platform ahead the Chongón-Colonche Cordillera, and are associated with immerged terraces most likely formed during the Last Glacial Maximum. They also may link to further onshore marine terraces developing since the Pleistocene across the coastline.
These observations suggest a peculiar dismantlement of the margin, mainly affected by tectonic erosion involving reactivation of former compressional features. Normal faults are specifically interpreted as a regional syn-orogenic collapse of the Chongón-Colonche Cordillera, which may result from transecting subducting ridges, fracture zones and seamounts controlling, at least partially, the geometry and the nature of the deformation along the southwestern Ecuadorian margin. This deformation pattern is likely linked to a weak interseismic coupling along the subduction interface to which the active opening of the Gulf of Guayaquil overlaps. This project is funded by the project ANR MARACAS ANR-18-CE31-0022 (MARine terraces along the northern Andean Coast as a proxy for seismic hazard ASsessment).
How to cite: Bulois, C., Michaud, F., Saillard, M., Espurt, N., Regnier, M., Hernandez Salazar, M.-J., Font, Y., Reyes Benítez, P., Collot, J.-Y., Proust, J.-N., D'Acremont, E., Schenini, L., and Barba, D.: Inheritance processes of active extensional deformation in ocean-continent subduction zones: the example of the northern Andes compressional margin in Ecuador, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11758, https://doi.org/10.5194/egusphere-egu2020-11758, 2020.
EGU2020-9494 | Displays | TS7.2
Tectonic subdivisions in thrust belts – cleaning up the western Northern Calcareous Alps (NCA)Hugo Ortner and Sinah Kilian
Tectonic subdivisions of larger geologic units reflect the geologic knowledge at the time of creation. In many thrust belts the original subdivisions had been created during the first comprehensive mapping campaigns at the end of the 19th to early 20th century and reflect the geologic knowledge at that time. Even if many thrusts were identified correctly, no formal framework existed to give guidelines of how to distinguish tectonic units. Nevertheless, these subdivisions are still in use.
We analyze the thrust sheets of the Northern Calcareous Alps of western Austria and southern Germany and test the implicit assumptions underlying most tectonic subdivisions against field observations:
Assumption 1: Thrust transport is large and thrusts do not end laterally. However, several major thrusts do loose stratgraphic offset and end laterally.
Assumption 2: Allochthons are surrounded by thrusts on all sides. Unfortunately, any fault has been used to delimit allochthons.
Assumption 3: Thrusting should bring old on young rocks. In some cases, allochthons have been delimited by out-of-sequence thrusts, that stack young on old rocks. In other cases, the allochthon is a mountain-size glide block that was buried by younger sediments, and the trace of the thrust is an unconformity in the field.
As a consequence we propose a revised tectonic subdivision of the western part of the NCA, that avoids some of the problems discussed here, and is entirely based on the emplacement of old-on-young rocks across thrusts.
How to cite: Ortner, H. and Kilian, S.: Tectonic subdivisions in thrust belts – cleaning up the western Northern Calcareous Alps (NCA), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9494, https://doi.org/10.5194/egusphere-egu2020-9494, 2020.
Tectonic subdivisions of larger geologic units reflect the geologic knowledge at the time of creation. In many thrust belts the original subdivisions had been created during the first comprehensive mapping campaigns at the end of the 19th to early 20th century and reflect the geologic knowledge at that time. Even if many thrusts were identified correctly, no formal framework existed to give guidelines of how to distinguish tectonic units. Nevertheless, these subdivisions are still in use.
We analyze the thrust sheets of the Northern Calcareous Alps of western Austria and southern Germany and test the implicit assumptions underlying most tectonic subdivisions against field observations:
Assumption 1: Thrust transport is large and thrusts do not end laterally. However, several major thrusts do loose stratgraphic offset and end laterally.
Assumption 2: Allochthons are surrounded by thrusts on all sides. Unfortunately, any fault has been used to delimit allochthons.
Assumption 3: Thrusting should bring old on young rocks. In some cases, allochthons have been delimited by out-of-sequence thrusts, that stack young on old rocks. In other cases, the allochthon is a mountain-size glide block that was buried by younger sediments, and the trace of the thrust is an unconformity in the field.
As a consequence we propose a revised tectonic subdivision of the western part of the NCA, that avoids some of the problems discussed here, and is entirely based on the emplacement of old-on-young rocks across thrusts.
How to cite: Ortner, H. and Kilian, S.: Tectonic subdivisions in thrust belts – cleaning up the western Northern Calcareous Alps (NCA), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9494, https://doi.org/10.5194/egusphere-egu2020-9494, 2020.
EGU2020-9969 | Displays | TS7.2
Prediction uncertainties in salt detached fold and thrust belts – examples from the surface and subsurface of the Northern Calcareous Alps (Austria)Klaus Pelz, Pablo Granado, Michael König, Elizabeth P. Wilson, Philipp Strauss, Eduard Roca, Wolfgang Thöny, and Josep Anton Muñoz
As shown for fold and thrust belts worldwide and for the Northern Calcareous Alps (NCA) in particular, the initial thickness and spatial distribution of autochthonous salt exerts fundamental control on deformation localization and structural style. The initial sedimentary geometries of mini-basins formed by downbuilding into or rafting on salt do influence the geometries of thrust sheets during subsequent shortening. The lateral extent and spacing of individual thrust sheets and the overall cylindricity of structures is governed by initial facies changes and thickness variations within and across mini-basins and salt ridges between them. During convergence, remaining inflated salt localizes shortening whereas mini-basins may react as rather rigid blocks. As deformation culminates at these secondary welds that eventually become thrusted and squeezed, apparent structural closures might become exploration targets but potentially yield more complex internal geometries and less predictable facies distribution.
In this contribution we show several cross sections constrained by surface and subsurface data in the eastern NCA and below the Vienna Basin. We compare areas with abrupt changes in stratigraphic thickness, limited lateral extent of individual thrust sheets and highly non-cylindrical structural style along strike to areas where thrust sheets extend over several tens of kilometers along strike with remarkably cylindrical structures, little thickness variations and less abrupt facies changes. Predictive capabilities in underconstrained areas (i.e., insufficient seismic imaging and/or resolution, lack of well control, bad outcrop conditions) are analyzed and compared to closures with well control and pre-drill expectations. Evidently, culminations can be predicted with more confidence in areas with little variation in facies and sedimentary thicknesses. Reliability of predictions generally degrades with decreasing thrust sheet size, observable non-cylindricity within and in between thrust sheets, and with increased complexities at the edges of mini-basins (e.g., squeezed and thrusted flaps). Internal geometries of mini-basins need to be imaged and analyzed properly to narrow down these uncertainties at potential culminations along the edges.
How to cite: Pelz, K., Granado, P., König, M., Wilson, E. P., Strauss, P., Roca, E., Thöny, W., and Muñoz, J. A.: Prediction uncertainties in salt detached fold and thrust belts – examples from the surface and subsurface of the Northern Calcareous Alps (Austria), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9969, https://doi.org/10.5194/egusphere-egu2020-9969, 2020.
As shown for fold and thrust belts worldwide and for the Northern Calcareous Alps (NCA) in particular, the initial thickness and spatial distribution of autochthonous salt exerts fundamental control on deformation localization and structural style. The initial sedimentary geometries of mini-basins formed by downbuilding into or rafting on salt do influence the geometries of thrust sheets during subsequent shortening. The lateral extent and spacing of individual thrust sheets and the overall cylindricity of structures is governed by initial facies changes and thickness variations within and across mini-basins and salt ridges between them. During convergence, remaining inflated salt localizes shortening whereas mini-basins may react as rather rigid blocks. As deformation culminates at these secondary welds that eventually become thrusted and squeezed, apparent structural closures might become exploration targets but potentially yield more complex internal geometries and less predictable facies distribution.
In this contribution we show several cross sections constrained by surface and subsurface data in the eastern NCA and below the Vienna Basin. We compare areas with abrupt changes in stratigraphic thickness, limited lateral extent of individual thrust sheets and highly non-cylindrical structural style along strike to areas where thrust sheets extend over several tens of kilometers along strike with remarkably cylindrical structures, little thickness variations and less abrupt facies changes. Predictive capabilities in underconstrained areas (i.e., insufficient seismic imaging and/or resolution, lack of well control, bad outcrop conditions) are analyzed and compared to closures with well control and pre-drill expectations. Evidently, culminations can be predicted with more confidence in areas with little variation in facies and sedimentary thicknesses. Reliability of predictions generally degrades with decreasing thrust sheet size, observable non-cylindricity within and in between thrust sheets, and with increased complexities at the edges of mini-basins (e.g., squeezed and thrusted flaps). Internal geometries of mini-basins need to be imaged and analyzed properly to narrow down these uncertainties at potential culminations along the edges.
How to cite: Pelz, K., Granado, P., König, M., Wilson, E. P., Strauss, P., Roca, E., Thöny, W., and Muñoz, J. A.: Prediction uncertainties in salt detached fold and thrust belts – examples from the surface and subsurface of the Northern Calcareous Alps (Austria), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9969, https://doi.org/10.5194/egusphere-egu2020-9969, 2020.
EGU2020-2583 | Displays | TS7.2
Contractional rejuvenation of syn-rift salt-bearing minibasins by numerical simulationsPablo Granado and Jonas B. Ruh
Contractional rejuvenation of syn-rift salt-bearing minibasins by numerical simulations
Pablo Granado1, Jonas B. Ruh2
1 Institut de Recerca Geomodels, Departament de Dinàmica de la Terra i de l'Oceà, Universitat de Barcelona, Martí i Franquès s/n, 08028 Barcelona, Spain
2 Structural Geology and Tectonics Group, Geological Institute, Department of Earth Sciences, ETH Zurich, Switzerland
This work presents numerical experiments of contractional rejuvenation of passive margin minibasins and related diapiric structures and the involvement in inverted rift and fold-and-thrust belt systems. We use 2D finite difference numerical experiments with a temperature-dependent Maxwell-type visco-elasto-plastic rheology. Our experiments consist of a first phase of extension controlled by basement faults overlaid by a thick salt-bearing unit covered by a pre-kinematic layer. Extension led to forced folding and stretching of the pre-kinematic layer triggering diapirism, fixing the lateral dimensions of minibasins, whereas syn-rift accommodation space was controlled by extension of the basement faults plus salt evacuation provided by sediment load. Rate of extension controlled: i) internal growth geometries of minibasins; ii) the amount of downbuilding, and iii) the timing and extent of primary welds. Contractional reactivation was then carried out as end member modes of thin-skinned shortening over the basement steps, full inversion of extensional faults (i.e. thick-skinned), and combinations of both, always including erosion and syn-contractional sedimentation. Results provide an extensive template of structural styles and related kinematic evolutions including minibasin rotation and imbrication, squeezing of salt structures and surface flaring, and development of deep contractional growth synclines. Modelling results will be compared to natural case studies.
How to cite: Granado, P. and B. Ruh, J.: Contractional rejuvenation of syn-rift salt-bearing minibasins by numerical simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2583, https://doi.org/10.5194/egusphere-egu2020-2583, 2020.
Contractional rejuvenation of syn-rift salt-bearing minibasins by numerical simulations
Pablo Granado1, Jonas B. Ruh2
1 Institut de Recerca Geomodels, Departament de Dinàmica de la Terra i de l'Oceà, Universitat de Barcelona, Martí i Franquès s/n, 08028 Barcelona, Spain
2 Structural Geology and Tectonics Group, Geological Institute, Department of Earth Sciences, ETH Zurich, Switzerland
This work presents numerical experiments of contractional rejuvenation of passive margin minibasins and related diapiric structures and the involvement in inverted rift and fold-and-thrust belt systems. We use 2D finite difference numerical experiments with a temperature-dependent Maxwell-type visco-elasto-plastic rheology. Our experiments consist of a first phase of extension controlled by basement faults overlaid by a thick salt-bearing unit covered by a pre-kinematic layer. Extension led to forced folding and stretching of the pre-kinematic layer triggering diapirism, fixing the lateral dimensions of minibasins, whereas syn-rift accommodation space was controlled by extension of the basement faults plus salt evacuation provided by sediment load. Rate of extension controlled: i) internal growth geometries of minibasins; ii) the amount of downbuilding, and iii) the timing and extent of primary welds. Contractional reactivation was then carried out as end member modes of thin-skinned shortening over the basement steps, full inversion of extensional faults (i.e. thick-skinned), and combinations of both, always including erosion and syn-contractional sedimentation. Results provide an extensive template of structural styles and related kinematic evolutions including minibasin rotation and imbrication, squeezing of salt structures and surface flaring, and development of deep contractional growth synclines. Modelling results will be compared to natural case studies.
How to cite: Granado, P. and B. Ruh, J.: Contractional rejuvenation of syn-rift salt-bearing minibasins by numerical simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2583, https://doi.org/10.5194/egusphere-egu2020-2583, 2020.
EGU2020-14942 | Displays | TS7.2
The pre-Mesozoic basement underneath the Jura Mountains fold-and-thrust belt: an overview from models and mapsMarc Schori, Anna Sommaruga, and Jon Mosar
The Jura Mountains are a thin-skinned fold-and-thrust belt (FTB) in the northern foreland of the European Alps, extending over northern and western Switzerland and eastern France. The Jura FTB was detached in Triassic evaporites during Late Miocene and Pliocene compression. Prior to this, the pre-Mesozoic basement was intensely pre-structured by inherited faults that had been reactivated under changing stress fields during the Mesozoic and Cenozoic structural evolution of continental Europe. In order to understand the connection between thin-skinned FTB formation and pre-existing basement structures, we compiled boreholes and geological cross-sections across the Northern Alpine Foreland and derived elevation, thickness and erosion models of defined Mesozoic units and the top of the pre-Mesozoic basement.
Our models confirm the presence of basement faults concealed underneath the detached cover of the Jura Mountains. The pre-Mesozoic basement shows differences in structural altitudes resulting from partially overlapping lithospheric processes. They include graben formation during evolution of the European Cenozoic Rift System (ECRIS), flexural subsidence during Alpine forebulge development and lithospheric long-wavelength buckle folding. Faults in connection with these processes follow structural trends that suggest the reactivation of inherited Variscan and post-Variscan fault systems. We discuss the spatio-temporal imprint of lithospheric signatures on the pre-Mesozoic basement and their consequence on the formation of the Jura Mountains FTB. Untangling structures within the pre-Mesozoic basement leads us to a modern understanding of the long-term evolution of the detached Mesozoic cover. Furthermore, it allows us to improve the prediction of ages that are potentially preserved within the Mesozoic cover of the Jura FTB.
How to cite: Schori, M., Sommaruga, A., and Mosar, J.: The pre-Mesozoic basement underneath the Jura Mountains fold-and-thrust belt: an overview from models and maps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14942, https://doi.org/10.5194/egusphere-egu2020-14942, 2020.
The Jura Mountains are a thin-skinned fold-and-thrust belt (FTB) in the northern foreland of the European Alps, extending over northern and western Switzerland and eastern France. The Jura FTB was detached in Triassic evaporites during Late Miocene and Pliocene compression. Prior to this, the pre-Mesozoic basement was intensely pre-structured by inherited faults that had been reactivated under changing stress fields during the Mesozoic and Cenozoic structural evolution of continental Europe. In order to understand the connection between thin-skinned FTB formation and pre-existing basement structures, we compiled boreholes and geological cross-sections across the Northern Alpine Foreland and derived elevation, thickness and erosion models of defined Mesozoic units and the top of the pre-Mesozoic basement.
Our models confirm the presence of basement faults concealed underneath the detached cover of the Jura Mountains. The pre-Mesozoic basement shows differences in structural altitudes resulting from partially overlapping lithospheric processes. They include graben formation during evolution of the European Cenozoic Rift System (ECRIS), flexural subsidence during Alpine forebulge development and lithospheric long-wavelength buckle folding. Faults in connection with these processes follow structural trends that suggest the reactivation of inherited Variscan and post-Variscan fault systems. We discuss the spatio-temporal imprint of lithospheric signatures on the pre-Mesozoic basement and their consequence on the formation of the Jura Mountains FTB. Untangling structures within the pre-Mesozoic basement leads us to a modern understanding of the long-term evolution of the detached Mesozoic cover. Furthermore, it allows us to improve the prediction of ages that are potentially preserved within the Mesozoic cover of the Jura FTB.
How to cite: Schori, M., Sommaruga, A., and Mosar, J.: The pre-Mesozoic basement underneath the Jura Mountains fold-and-thrust belt: an overview from models and maps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14942, https://doi.org/10.5194/egusphere-egu2020-14942, 2020.
EGU2020-18669 | Displays | TS7.2 | Highlight
Low-temperature thermochronology and vitrinite reflectance data reveal longwavelength uplift in the Alpine foreland basinSarah Louis, Elco Luijendijk, Christoph von Hagke, István Dunkl, Ralf Littke, and Jonas Kley
Foreland basin sediments mirror the history of an orogeny. Deformation and geodynamic processes in low spatial extend (e.g. dozens of km) can be quantified using kinematic restoration. Processes happening deep underneath an orogen show a large spatial manifestation that is difficult to quantify in time and space. Marine units at surface outcrops show 900 m of net uplift since deposition in undeformed parts of the alpine foreland basin. Existing low-temperature thermochronology data from the Swiss part of the Molasse Basin show a thermal overprint that indicates exhumation of more than 1.5 km. We quantify the wavelength of deep seated processes of the Alpine orogen by generating and analyzing a holistic dataset of the entire alpine foreland basin. In addition to compiling existing data from the western part of the basin we have generated a new apatite (U-Th)/He and vitrinite reflectance data set from the central and eastern part of the basin. The new apatite (U-Th)/He ages in the German part of the basin show exhumation below or close to the detection limit (~1.5 km). Within the folded and thrusted Molasse, exhumation is localized along thrusts and the thermochronological data indicates thrusting between 10 to 20 Ma. Vitrinite reflectance data reveals a trend of exhumation increasing from East to West. Parts of the central German Molasse basin have been exhumed as well. Thus, on the large scale we can see longwave exhumation patterns in the western part of the basin that affect both the deformed and undeformed parts of the basin which cannot only be related to Jura thrusting.
How to cite: Louis, S., Luijendijk, E., von Hagke, C., Dunkl, I., Littke, R., and Kley, J.: Low-temperature thermochronology and vitrinite reflectance data reveal longwavelength uplift in the Alpine foreland basin , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18669, https://doi.org/10.5194/egusphere-egu2020-18669, 2020.
Foreland basin sediments mirror the history of an orogeny. Deformation and geodynamic processes in low spatial extend (e.g. dozens of km) can be quantified using kinematic restoration. Processes happening deep underneath an orogen show a large spatial manifestation that is difficult to quantify in time and space. Marine units at surface outcrops show 900 m of net uplift since deposition in undeformed parts of the alpine foreland basin. Existing low-temperature thermochronology data from the Swiss part of the Molasse Basin show a thermal overprint that indicates exhumation of more than 1.5 km. We quantify the wavelength of deep seated processes of the Alpine orogen by generating and analyzing a holistic dataset of the entire alpine foreland basin. In addition to compiling existing data from the western part of the basin we have generated a new apatite (U-Th)/He and vitrinite reflectance data set from the central and eastern part of the basin. The new apatite (U-Th)/He ages in the German part of the basin show exhumation below or close to the detection limit (~1.5 km). Within the folded and thrusted Molasse, exhumation is localized along thrusts and the thermochronological data indicates thrusting between 10 to 20 Ma. Vitrinite reflectance data reveals a trend of exhumation increasing from East to West. Parts of the central German Molasse basin have been exhumed as well. Thus, on the large scale we can see longwave exhumation patterns in the western part of the basin that affect both the deformed and undeformed parts of the basin which cannot only be related to Jura thrusting.
How to cite: Louis, S., Luijendijk, E., von Hagke, C., Dunkl, I., Littke, R., and Kley, J.: Low-temperature thermochronology and vitrinite reflectance data reveal longwavelength uplift in the Alpine foreland basin , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18669, https://doi.org/10.5194/egusphere-egu2020-18669, 2020.
EGU2020-9889 | Displays | TS7.2
3D geological model of the Po Plain subsurface: an example of open geological base data for basin analysisChiara D'Ambrogi, Maurizio Marino, Fabio Carlo Molinari, Michele Morelli, Andrea Irace, Luca Barale, Fabrizio Piana, Gianfranco Fioraso, Pio Di Manna, and Pietro Mosca
The Po Plain is a one-of-a-kind place where to study the evolution of the orogen-foreland pair. It is a complex geological system consisting mainly of Triassic to Quaternary sedimentary successions that have recorded the tectonic evolution of the paleoAdriatic continental margin during the Middle-Late Triassic and Jurassic time interval, as well as the development and mutual interaction of the Western Alps, Southern Alps and Northern Apennines orogenic belts, and related synorogenic basins, during the Cenozoic.
These peculiarities allow for achieving analyses on several topics (e.g., the relations between opposite-verging thrust systems, the role of the inherited paleogeography, the geometry and evolution of the foredeep and thrust-top basins, the presence and the activity of seismogenic faults), individually treated by previous studies, with focus on limited time-intervals, or detailed 3D models of limited areas.
Nevertheless, a comprehensive and accessible 3D model of the general framework of the entire Po Plain subsurface is still unavailable.
In this respect, the HotLime Project (GeoERA Programme) will fill the gap providing a publicly accessible 3D framework model of the geometry of some stratigraphic horizons, focusing on crucial stratigraphic intervals, extended from Piemonte to Emilia-Romagna Region - Adriatic coastline, covering an area larger than 21,000 km2. In the HotLime Project, the model will be used as input for the geothermal assessment of carbonate reservoirs.
The 3D model, built as a whole, will include five regional-wide stratigraphic horizons (e.g. top or unconformity surface), from Triassic to Pleistocene, plus additional less extended horizons, and the 3D geometry of more than 150 faults (i.e., Mesozoic extensional faults and Paleogene to Neogene thrusts).
This comprehensive 3D geological model of the Po Plain subsurface is based on an integrated analysis of surface and subsurface geological/geophysical data (the latter provided by ENI SpA), that allows for better interpreting and correlating the key horizons. The input dataset includes: 305 well data; 799 2D seismic profiles, with a mean spacing of 5 km; detailed surface data from geological maps at different scales. The final 3D model benefits from the comprehensive and coherent interpretation of the overall input dataset, and the time-depth conversion of the 3D model as a whole through a 3D velocity model.
The objective of this work is to build a general-purpose 3D geological model that will serve a multiplicity of specific topics, and provide a powerful 3D image of this complex foreland basin. It highlights the position and geometry of inherited structures and allows for analyzing their relations with stratigraphic variations of the sedimentary infill (e.g., unit thickness); besides, the comparison of the mutual relations of the compressional faults with the pre-existing discontinuities. The fault distribution and clustering will be also compared with the deformations observed on the highly-detail modeled Pliocene and Pleistocene horizons, giving a fundamental input for the calculation of slip/uplift rates and definition of the activity of the faults.
This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 731166
How to cite: D'Ambrogi, C., Marino, M., Molinari, F. C., Morelli, M., Irace, A., Barale, L., Piana, F., Fioraso, G., Di Manna, P., and Mosca, P.: 3D geological model of the Po Plain subsurface: an example of open geological base data for basin analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9889, https://doi.org/10.5194/egusphere-egu2020-9889, 2020.
The Po Plain is a one-of-a-kind place where to study the evolution of the orogen-foreland pair. It is a complex geological system consisting mainly of Triassic to Quaternary sedimentary successions that have recorded the tectonic evolution of the paleoAdriatic continental margin during the Middle-Late Triassic and Jurassic time interval, as well as the development and mutual interaction of the Western Alps, Southern Alps and Northern Apennines orogenic belts, and related synorogenic basins, during the Cenozoic.
These peculiarities allow for achieving analyses on several topics (e.g., the relations between opposite-verging thrust systems, the role of the inherited paleogeography, the geometry and evolution of the foredeep and thrust-top basins, the presence and the activity of seismogenic faults), individually treated by previous studies, with focus on limited time-intervals, or detailed 3D models of limited areas.
Nevertheless, a comprehensive and accessible 3D model of the general framework of the entire Po Plain subsurface is still unavailable.
In this respect, the HotLime Project (GeoERA Programme) will fill the gap providing a publicly accessible 3D framework model of the geometry of some stratigraphic horizons, focusing on crucial stratigraphic intervals, extended from Piemonte to Emilia-Romagna Region - Adriatic coastline, covering an area larger than 21,000 km2. In the HotLime Project, the model will be used as input for the geothermal assessment of carbonate reservoirs.
The 3D model, built as a whole, will include five regional-wide stratigraphic horizons (e.g. top or unconformity surface), from Triassic to Pleistocene, plus additional less extended horizons, and the 3D geometry of more than 150 faults (i.e., Mesozoic extensional faults and Paleogene to Neogene thrusts).
This comprehensive 3D geological model of the Po Plain subsurface is based on an integrated analysis of surface and subsurface geological/geophysical data (the latter provided by ENI SpA), that allows for better interpreting and correlating the key horizons. The input dataset includes: 305 well data; 799 2D seismic profiles, with a mean spacing of 5 km; detailed surface data from geological maps at different scales. The final 3D model benefits from the comprehensive and coherent interpretation of the overall input dataset, and the time-depth conversion of the 3D model as a whole through a 3D velocity model.
The objective of this work is to build a general-purpose 3D geological model that will serve a multiplicity of specific topics, and provide a powerful 3D image of this complex foreland basin. It highlights the position and geometry of inherited structures and allows for analyzing their relations with stratigraphic variations of the sedimentary infill (e.g., unit thickness); besides, the comparison of the mutual relations of the compressional faults with the pre-existing discontinuities. The fault distribution and clustering will be also compared with the deformations observed on the highly-detail modeled Pliocene and Pleistocene horizons, giving a fundamental input for the calculation of slip/uplift rates and definition of the activity of the faults.
This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 731166
How to cite: D'Ambrogi, C., Marino, M., Molinari, F. C., Morelli, M., Irace, A., Barale, L., Piana, F., Fioraso, G., Di Manna, P., and Mosca, P.: 3D geological model of the Po Plain subsurface: an example of open geological base data for basin analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9889, https://doi.org/10.5194/egusphere-egu2020-9889, 2020.
EGU2020-7685 | Displays | TS7.2
Timing and magnitude of vertical-axis rotations in the eastwards-flanking synorogenic sediments of the South-Pyrenean fold-and-thrust belt. Kinematics and origin of the salient curvature.Charlotte Peigney, Elisabet Beamud, Óscar Gratacós, Luis Valero, Ruth Soto, Eduard Roca, and Josep Anton Muñoz
The South-Pyrenean fold-and-thrust belt consists of three major thin-skinned thrust sheets (Bóixols, Montsec and Serres Marginals) made up of uppermost Triassic to Oligocene cover rocks emplaced during Late Cretaceous-Oligocene times. In its central part, it forms a major salient (the Pyrenean South-Central Unit) whose geometry is controlled by the areal distribution of the pre-orogenic Upper Triassic and synorogenic Eocene salt décollement layers. Both westwards and eastwards, the salient is fringed by Paleogene synorogenic deposits that are deformed by detachment folds with orientations ranging from N-S to E-W. In the western edge of the salient, the varying trend of the folds is a result of synorogenic vertical axis rotations (VAR) which caused the clockwise rotation of the folds from an initial predominant E-W trend to the current NW-SE to NNW-SSE trend. The salient, at least on its western part, developed from a progressive curve originated from divergent thrust transport directions and distributed shortening.
The aim of our study is to get a better understanding of the whole salient, by studying the kinematics of the deformation on the most frontal part of its eastern edge. Here, some sparse anticlockwise rotations have been reported but their origin and their possible relationship with the distribution of the salt décollements has not yet been addressed. For this purpose, 78 paleomagnetic sites have been sampled on the synorogenic upper Eocene-Oligocene materials of the NE Ebro foreland Basin, in the Artesa de Segre area, focusing on the limbs of oblique salt-cored anticlines (Ponts, Vilanova de l’Aguda, Cardona) which are detached above the synorogenic Eocene-Oligocene evaporites of the Cardona and the Barbastro formations. VAR analyses principally show anticlockwise rotations similar to those previously identified to the North in the Oliana Anticline, although a small number of clockwise rotations were also detected.
In addition to the VAR analysis, a magnetostratigraphic study of the Eocene-Oligocene continental materials of the northern limb of the Sanaüja Anticline has been conducted in order to constrain the age of these rotations from stratigraphic correlations. The demagnetization of 104 samples from a ca. 1100 m thick magnetostratigraphic section shows Priabonian to Rupelian ages for this succession. The integration of our results on timing, direction and magnitude of foreland VAR with previous paleomagnetic and structural data from both the western and eastern boundaries of the frontal thrust of the Pyrenean South-Central Unit will allow the understanding of the kinematics of the thrust salient as a whole.
How to cite: Peigney, C., Beamud, E., Gratacós, Ó., Valero, L., Soto, R., Roca, E., and Muñoz, J. A.: Timing and magnitude of vertical-axis rotations in the eastwards-flanking synorogenic sediments of the South-Pyrenean fold-and-thrust belt. Kinematics and origin of the salient curvature., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7685, https://doi.org/10.5194/egusphere-egu2020-7685, 2020.
The South-Pyrenean fold-and-thrust belt consists of three major thin-skinned thrust sheets (Bóixols, Montsec and Serres Marginals) made up of uppermost Triassic to Oligocene cover rocks emplaced during Late Cretaceous-Oligocene times. In its central part, it forms a major salient (the Pyrenean South-Central Unit) whose geometry is controlled by the areal distribution of the pre-orogenic Upper Triassic and synorogenic Eocene salt décollement layers. Both westwards and eastwards, the salient is fringed by Paleogene synorogenic deposits that are deformed by detachment folds with orientations ranging from N-S to E-W. In the western edge of the salient, the varying trend of the folds is a result of synorogenic vertical axis rotations (VAR) which caused the clockwise rotation of the folds from an initial predominant E-W trend to the current NW-SE to NNW-SSE trend. The salient, at least on its western part, developed from a progressive curve originated from divergent thrust transport directions and distributed shortening.
The aim of our study is to get a better understanding of the whole salient, by studying the kinematics of the deformation on the most frontal part of its eastern edge. Here, some sparse anticlockwise rotations have been reported but their origin and their possible relationship with the distribution of the salt décollements has not yet been addressed. For this purpose, 78 paleomagnetic sites have been sampled on the synorogenic upper Eocene-Oligocene materials of the NE Ebro foreland Basin, in the Artesa de Segre area, focusing on the limbs of oblique salt-cored anticlines (Ponts, Vilanova de l’Aguda, Cardona) which are detached above the synorogenic Eocene-Oligocene evaporites of the Cardona and the Barbastro formations. VAR analyses principally show anticlockwise rotations similar to those previously identified to the North in the Oliana Anticline, although a small number of clockwise rotations were also detected.
In addition to the VAR analysis, a magnetostratigraphic study of the Eocene-Oligocene continental materials of the northern limb of the Sanaüja Anticline has been conducted in order to constrain the age of these rotations from stratigraphic correlations. The demagnetization of 104 samples from a ca. 1100 m thick magnetostratigraphic section shows Priabonian to Rupelian ages for this succession. The integration of our results on timing, direction and magnitude of foreland VAR with previous paleomagnetic and structural data from both the western and eastern boundaries of the frontal thrust of the Pyrenean South-Central Unit will allow the understanding of the kinematics of the thrust salient as a whole.
How to cite: Peigney, C., Beamud, E., Gratacós, Ó., Valero, L., Soto, R., Roca, E., and Muñoz, J. A.: Timing and magnitude of vertical-axis rotations in the eastwards-flanking synorogenic sediments of the South-Pyrenean fold-and-thrust belt. Kinematics and origin of the salient curvature., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7685, https://doi.org/10.5194/egusphere-egu2020-7685, 2020.
EGU2020-5585 | Displays | TS7.2
Relief rejuvenation in response to intraplate neotectonics in the Betics foreland (southern Spain)Inmaculada Expósito, Alejandro Jiménez-Bonilla, José Luís Yanes, Juan Carlos Balanyá, and Francisco Moral
How to cite: Expósito, I., Jiménez-Bonilla, A., Yanes, J. L., Balanyá, J. C., and Moral, F.: Relief rejuvenation in response to intraplate neotectonics in the Betics foreland (southern Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5585, https://doi.org/10.5194/egusphere-egu2020-5585, 2020.
How to cite: Expósito, I., Jiménez-Bonilla, A., Yanes, J. L., Balanyá, J. C., and Moral, F.: Relief rejuvenation in response to intraplate neotectonics in the Betics foreland (southern Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5585, https://doi.org/10.5194/egusphere-egu2020-5585, 2020.
EGU2020-438 | Displays | TS7.2
Syn-tectonic sand intrusions - an added complexity to a highly deformed fold and thrust belt and implication for subsurface structural interpretation: Eastern Carpathians Bend Zone, RomaniaDan Mircea Tamas, Alexandra Tamas, Zsolt Schleder, and Csaba Krezsek
Fold and thrust belts are a notorious challenging environment when it comes to providing structural models for the subsurface, and the Eastern Carpathians Bend Zone (ECBZ) is no exception.
Hosting the largest onshore oil fields in Romania, this is a highly mature hydrocarbon area, with most of the fields producing since the late nineteenth century. Characterise by superimposed tectonic events, most notably the mid-Miocene compression (when most of the shortening occurred) the area is also well known for multiple detachment levels and salt tectonics. As a consequence, the reservoirs, especially the Oligocene - lower Miocene (sub-salt), thought very prolific are structurally complex, heterogeneous and compartmentalised. It is a constant struggle for the geologist to create structural maps of these reservoirs due to complex deformation, inconsistent data and poor seismic resolution. Some of the most significant issues are related to scattering of dip data and the overall difficulties in correlating well logs. In some cases, even the logs of the side-track well do not correlate with the initial log.
In order to get a better understanding of these complex structures, we used the nearby Oligocene - lower Miocene surface exposures. First, detailed fieldwork coupled with drone photogrammetry and interpretation of 3D virtual outcrop models revealed that upright, gently plunging folds as well as overturned and recumbent folding occurs at these stratigraphic levels. Fold limbs are occasionally cross-cut by forethrust or backthrust. Also, parasitic folding and fold-accommodation faults have been identified. Apart from this rather complex but typical tectonic structures, a network of sand intrusions is also present in the Oligocene - lower Miocene sequence. The injectites, dykes, sills or composite intrusions are sourced from the quartz-rich sandstones and injected into the adjacent rocks. The dyke networks are intersecting the adjacent rocks at high angles and appear to follow fold-related fractures. Also, some preserved fluidized layers respond to fold tightening by thickness redistribution and intrusion. Injection is therefore considered to be syn-kinematic with the mid-Miocene tectonic stage when most of the shortening in the area occurred. Intrusion was most likely driven by the fluid overpressures built up due to active contractional tectonics, with intrusion events potentially triggered by associated seismicity.
Their presence can explain some of the reservoir heterogeneities and challenges in well correlation. For example, one well through a misinterpreted dyke will provide misleading information regarding reservoir architecture, including dip data and highlighting that not every change in dip is due to folding or faulting. Finally, as the dykes commonly follow fold-related fractures, it is highly possible to intrude fault planes as well, thus potentially influencing the shale gouge ratio and fault seal capacity.
The outcrops in the ECBZ are good surface analogues for global examples of hydrocarbon reservoirs affected by remobilized sand intrusions. A better understanding of these complex structures, especially in a compressional setting, can improve both subsurface structural interpretation and reservoir characterisation.
How to cite: Tamas, D. M., Tamas, A., Schleder, Z., and Krezsek, C.: Syn-tectonic sand intrusions - an added complexity to a highly deformed fold and thrust belt and implication for subsurface structural interpretation: Eastern Carpathians Bend Zone, Romania, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-438, https://doi.org/10.5194/egusphere-egu2020-438, 2020.
Fold and thrust belts are a notorious challenging environment when it comes to providing structural models for the subsurface, and the Eastern Carpathians Bend Zone (ECBZ) is no exception.
Hosting the largest onshore oil fields in Romania, this is a highly mature hydrocarbon area, with most of the fields producing since the late nineteenth century. Characterise by superimposed tectonic events, most notably the mid-Miocene compression (when most of the shortening occurred) the area is also well known for multiple detachment levels and salt tectonics. As a consequence, the reservoirs, especially the Oligocene - lower Miocene (sub-salt), thought very prolific are structurally complex, heterogeneous and compartmentalised. It is a constant struggle for the geologist to create structural maps of these reservoirs due to complex deformation, inconsistent data and poor seismic resolution. Some of the most significant issues are related to scattering of dip data and the overall difficulties in correlating well logs. In some cases, even the logs of the side-track well do not correlate with the initial log.
In order to get a better understanding of these complex structures, we used the nearby Oligocene - lower Miocene surface exposures. First, detailed fieldwork coupled with drone photogrammetry and interpretation of 3D virtual outcrop models revealed that upright, gently plunging folds as well as overturned and recumbent folding occurs at these stratigraphic levels. Fold limbs are occasionally cross-cut by forethrust or backthrust. Also, parasitic folding and fold-accommodation faults have been identified. Apart from this rather complex but typical tectonic structures, a network of sand intrusions is also present in the Oligocene - lower Miocene sequence. The injectites, dykes, sills or composite intrusions are sourced from the quartz-rich sandstones and injected into the adjacent rocks. The dyke networks are intersecting the adjacent rocks at high angles and appear to follow fold-related fractures. Also, some preserved fluidized layers respond to fold tightening by thickness redistribution and intrusion. Injection is therefore considered to be syn-kinematic with the mid-Miocene tectonic stage when most of the shortening in the area occurred. Intrusion was most likely driven by the fluid overpressures built up due to active contractional tectonics, with intrusion events potentially triggered by associated seismicity.
Their presence can explain some of the reservoir heterogeneities and challenges in well correlation. For example, one well through a misinterpreted dyke will provide misleading information regarding reservoir architecture, including dip data and highlighting that not every change in dip is due to folding or faulting. Finally, as the dykes commonly follow fold-related fractures, it is highly possible to intrude fault planes as well, thus potentially influencing the shale gouge ratio and fault seal capacity.
The outcrops in the ECBZ are good surface analogues for global examples of hydrocarbon reservoirs affected by remobilized sand intrusions. A better understanding of these complex structures, especially in a compressional setting, can improve both subsurface structural interpretation and reservoir characterisation.
How to cite: Tamas, D. M., Tamas, A., Schleder, Z., and Krezsek, C.: Syn-tectonic sand intrusions - an added complexity to a highly deformed fold and thrust belt and implication for subsurface structural interpretation: Eastern Carpathians Bend Zone, Romania, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-438, https://doi.org/10.5194/egusphere-egu2020-438, 2020.
EGU2020-2564 | Displays | TS7.2
Structure of the Gare Kakheti foothills using seismic reflection profiles: implications for kinematic evolution of the Georgian part of Kura foreland fold-and-thrust beltAlexander Razmadze
Gare Kakheti foothills are located between Lesser Caucasus and Kakheti Ridge and are mainly represented by the series of NEN dipping thrust faults, most of which are associated with fault‐related folds. Gare Kakheti foothills as a part of the Kura foreland fold-and-thrust belt developed formerly as a foreland basin (Oligocene-Lower Miocene) (e.g. Alania et al., 2017). Neogene shallow marine and continental sediments in the Gare Kakheti foothills keep the record on the stratigraphy and structural evolution of the study area during the compressive deformation. Interpreted seismic profiles and structural cross-sections across the Udabno, Tsitsmatiani, and Berebisseri synclines show that they are thrust-top basins. Seismic reflection data reveal the presence of growth fault-propagation folds and some structural wedges (or duplex). The evolution of the Udabno, Tsitsmatiani, and Berebisseri basins is compared with simple models of thrust-top basins whose development is controlled by the kinematics of competing for growth anticlines. Growth anticlines are mainly represented by fault-propagation folds. The geometry of growth strata in associated footwall synclines and the sedimentary infill of thrust-top basins provide information on the thrusting activity in terms of location, geometry, and age.
This work was supported by Shota Rustaveli National Science Foundation (SRNSF - #PHDF-19-268).
How to cite: Razmadze, A.: Structure of the Gare Kakheti foothills using seismic reflection profiles: implications for kinematic evolution of the Georgian part of Kura foreland fold-and-thrust belt, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2564, https://doi.org/10.5194/egusphere-egu2020-2564, 2020.
Gare Kakheti foothills are located between Lesser Caucasus and Kakheti Ridge and are mainly represented by the series of NEN dipping thrust faults, most of which are associated with fault‐related folds. Gare Kakheti foothills as a part of the Kura foreland fold-and-thrust belt developed formerly as a foreland basin (Oligocene-Lower Miocene) (e.g. Alania et al., 2017). Neogene shallow marine and continental sediments in the Gare Kakheti foothills keep the record on the stratigraphy and structural evolution of the study area during the compressive deformation. Interpreted seismic profiles and structural cross-sections across the Udabno, Tsitsmatiani, and Berebisseri synclines show that they are thrust-top basins. Seismic reflection data reveal the presence of growth fault-propagation folds and some structural wedges (or duplex). The evolution of the Udabno, Tsitsmatiani, and Berebisseri basins is compared with simple models of thrust-top basins whose development is controlled by the kinematics of competing for growth anticlines. Growth anticlines are mainly represented by fault-propagation folds. The geometry of growth strata in associated footwall synclines and the sedimentary infill of thrust-top basins provide information on the thrusting activity in terms of location, geometry, and age.
This work was supported by Shota Rustaveli National Science Foundation (SRNSF - #PHDF-19-268).
How to cite: Razmadze, A.: Structure of the Gare Kakheti foothills using seismic reflection profiles: implications for kinematic evolution of the Georgian part of Kura foreland fold-and-thrust belt, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2564, https://doi.org/10.5194/egusphere-egu2020-2564, 2020.
EGU2020-2325 | Displays | TS7.2 | Highlight
Structure of the south-central Taiwan fold-and-thrust beltDennis Brown, Joaquina Alvarez-Marron, Hao Kuo-Chen, Yih-Min Wu, Giovanni Camanni, and Cristina Biete
Studies of mountain belts worldwide have shown that the structural, mechanical, and kinematic evolution of their foreland fold-and-thrust belts are strongly influenced by the structure of the continental margins that are involved in the deformation. The area on and around the island of Taiwan provides an unparalleled opportunity to investigate this because the entire profile of the SE margin of the Eurasian plate, from the shelf in the north to the slope and continent-ocean transition in the south and the offshore, is currently involved in a collision with the Luzon arc on the Philippine Sea plate. Taiwan can, then, provide key insights into how such features as rift basins on the shelf, the extensional faults that form the shelf-slope break in the basement, or the structure of the extended crust and morphology of the sedimentary carapace of the slope can be directly reflected in the structural architecture, the location and pattern of seismicity, topography, and the contemporaneous stress and strain fields of a fold-and-thrust belt. For example, east-northeast striking faults that have been mapped on the necking zone of the Eurasian margin can be traced into the island of Taiwan where they are causing important along-strike changes in various aspects of the structural, mechanical, kinematic, and morphological behavior of the fold-and-thrust belt. In particular, across the upper part of the necking zone there is an abrupt north-south change in structure, an increase in the amount of seismicity, an increase in topography, a rotation of the direction of maximum compressive horizontal stress, of the GPS displacement vectors, the compressional strain rate, and the maximum shear strain rate. These changes are interpreted to be caused by east-northeast striking, dextral strike-slip faulting in the basement that is taking place as a result of the reactivation of pre-existing faults along the upper part of the necking zone. The abrupt southeastward increase in topography across the upper part of the necking zone is the surface expression of the basal thrust of the fold-and-thrust belt ramping down into the basement, with maximum elevations reached in the basement-involved thrust sheets, suggesting a causal link between basement involvement in the thrusting and high topography. On the shelf, the roughly northeast-oriented Hsuehshan Trough is inverting along almost north-south striking basin bounding faults that penetrate into the middle crust and have well-clustered, deep seismicity. There are no substantial differences in the contemporaneous stress and strain field. There is, however, a clear relationship between basement involvement in the thrusting and the development of high topography in the Hsuehshan Range. Only the upper part of the slope is involved in the fold-and-thrust belt in southernmost Taiwan. In this area, there is a reduction of the amount of seismicity and lower topography. The largest part of the corresponding thrust wedge developed in the lower slope is offshore. This work is funded by the Spanish Ministerio de Ciencia, Innovación y Universidades grant PGC2018-094227-B-I00.
How to cite: Brown, D., Alvarez-Marron, J., Kuo-Chen, H., Wu, Y.-M., Camanni, G., and Biete, C.: Structure of the south-central Taiwan fold-and-thrust belt, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2325, https://doi.org/10.5194/egusphere-egu2020-2325, 2020.
Studies of mountain belts worldwide have shown that the structural, mechanical, and kinematic evolution of their foreland fold-and-thrust belts are strongly influenced by the structure of the continental margins that are involved in the deformation. The area on and around the island of Taiwan provides an unparalleled opportunity to investigate this because the entire profile of the SE margin of the Eurasian plate, from the shelf in the north to the slope and continent-ocean transition in the south and the offshore, is currently involved in a collision with the Luzon arc on the Philippine Sea plate. Taiwan can, then, provide key insights into how such features as rift basins on the shelf, the extensional faults that form the shelf-slope break in the basement, or the structure of the extended crust and morphology of the sedimentary carapace of the slope can be directly reflected in the structural architecture, the location and pattern of seismicity, topography, and the contemporaneous stress and strain fields of a fold-and-thrust belt. For example, east-northeast striking faults that have been mapped on the necking zone of the Eurasian margin can be traced into the island of Taiwan where they are causing important along-strike changes in various aspects of the structural, mechanical, kinematic, and morphological behavior of the fold-and-thrust belt. In particular, across the upper part of the necking zone there is an abrupt north-south change in structure, an increase in the amount of seismicity, an increase in topography, a rotation of the direction of maximum compressive horizontal stress, of the GPS displacement vectors, the compressional strain rate, and the maximum shear strain rate. These changes are interpreted to be caused by east-northeast striking, dextral strike-slip faulting in the basement that is taking place as a result of the reactivation of pre-existing faults along the upper part of the necking zone. The abrupt southeastward increase in topography across the upper part of the necking zone is the surface expression of the basal thrust of the fold-and-thrust belt ramping down into the basement, with maximum elevations reached in the basement-involved thrust sheets, suggesting a causal link between basement involvement in the thrusting and high topography. On the shelf, the roughly northeast-oriented Hsuehshan Trough is inverting along almost north-south striking basin bounding faults that penetrate into the middle crust and have well-clustered, deep seismicity. There are no substantial differences in the contemporaneous stress and strain field. There is, however, a clear relationship between basement involvement in the thrusting and the development of high topography in the Hsuehshan Range. Only the upper part of the slope is involved in the fold-and-thrust belt in southernmost Taiwan. In this area, there is a reduction of the amount of seismicity and lower topography. The largest part of the corresponding thrust wedge developed in the lower slope is offshore. This work is funded by the Spanish Ministerio de Ciencia, Innovación y Universidades grant PGC2018-094227-B-I00.
How to cite: Brown, D., Alvarez-Marron, J., Kuo-Chen, H., Wu, Y.-M., Camanni, G., and Biete, C.: Structure of the south-central Taiwan fold-and-thrust belt, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2325, https://doi.org/10.5194/egusphere-egu2020-2325, 2020.
EGU2020-3800 | Displays | TS7.2
Foreland basin sediment archives: highlighting their use in documenting deformation of the orogenic hinterland and foreland.Yani Najman
Interrogation of sediment archives allows for documentation of both hinterland and foreland deformation. Examples of their use as an archive of Himalayan foreland deformation include the work of Govin et al. (Geology, 2018) in which determination of the timing of drainage rerouting of the palaeo-Brahmaputra has allowed us to date the timing of surface uplift of the Shillong Plateau, and the work of Najman et al (Tectonics, 2018) in which the presence of the major Paleogene unconformity previously recognised in the Himalayan foreland basin, was shown to extend much further south into the foreland, allowing for a broader range of possible causal mechanisms to be discussed. There are numerous examples of the use of the Himalayan foreland basin sediment record to determine orogenic tectonics, this being a complementary approach to bedrock studies of the orogen. For example, Govin et al. (in review) and Lang et al (GSAB 2016), used detrital mineral lag time studies targeted to the Siwalik Himalayan foreland sediment archive, to demonstrate when the rapid exhumation of the eastern Himalayan syntaxis commenced. Comparison with a similar dataset derived from a more distal sediment archive of the Bengal Fan (Najman et al. GSAB 2019), shows the advantages (as well as disadvantages) in the use of proximal sediment archives.
How to cite: Najman, Y.: Foreland basin sediment archives: highlighting their use in documenting deformation of the orogenic hinterland and foreland., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3800, https://doi.org/10.5194/egusphere-egu2020-3800, 2020.
Interrogation of sediment archives allows for documentation of both hinterland and foreland deformation. Examples of their use as an archive of Himalayan foreland deformation include the work of Govin et al. (Geology, 2018) in which determination of the timing of drainage rerouting of the palaeo-Brahmaputra has allowed us to date the timing of surface uplift of the Shillong Plateau, and the work of Najman et al (Tectonics, 2018) in which the presence of the major Paleogene unconformity previously recognised in the Himalayan foreland basin, was shown to extend much further south into the foreland, allowing for a broader range of possible causal mechanisms to be discussed. There are numerous examples of the use of the Himalayan foreland basin sediment record to determine orogenic tectonics, this being a complementary approach to bedrock studies of the orogen. For example, Govin et al. (in review) and Lang et al (GSAB 2016), used detrital mineral lag time studies targeted to the Siwalik Himalayan foreland sediment archive, to demonstrate when the rapid exhumation of the eastern Himalayan syntaxis commenced. Comparison with a similar dataset derived from a more distal sediment archive of the Bengal Fan (Najman et al. GSAB 2019), shows the advantages (as well as disadvantages) in the use of proximal sediment archives.
How to cite: Najman, Y.: Foreland basin sediment archives: highlighting their use in documenting deformation of the orogenic hinterland and foreland., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3800, https://doi.org/10.5194/egusphere-egu2020-3800, 2020.
EGU2020-18768 | Displays | TS7.2
Geological structure and active deformation in the fold-thrust belt of southern Taiwan in relation to crustal-scale structureMaryline Le Béon, John Suppe, Yu-Huan Hsieh, Mong-Han Huang, Hsin-Hua Huang, and Chih-Tung Chen
The fold-thrust belt of southern Taiwan currently accommodates rapid westward shortening in the order of 4.5 mm/a and is estimated to have developed since the Late Pliocene. It is the locus of the 2016 Mw6.4 Meinong earthquake, which involved fault slip at multiple levels in the mid-to-upper crust. It nucleated at ~15 km depth and also triggered shallow structures that reach the surface or nearly. To characterize the structure of the piedmont and investigate the broader tectonic setting of the event, we build two east-west regional balanced cross-sections based on surface geology, subsurface data, coseismic and interseismic geodetic data, and published nanno- and magneto-stratigraphy. We also document the first-order evolution of the piedmont and how the piedmont structures relate to the inner part of the mountain belt based on the cross-section restoration and the analysis of the seismic velocity structure of the plate boundary.
From the Coastal Plain towards the east, we propose a series of three active west-dipping backthrusts, rooted on a ~4.0-km-deep detachment, the Tainan detachment. The detachment lies within the base of the 3-km-thick Plio-Pleistocene Gutingkeng mudstone, which represents the initial foreland basin sediments. Syntectonic sediments and rapid shortening and uplift observed from geodetic measurements attest for the activity of these structures since the Late Pleistocene. Further east, the Tainan detachment ramps down to ~7 km depth, allowing the east-dipping Lungchuan and Pingchi thrusts to bring Upper Miocene continental-shelf formations to the surface. The cross-section restoration indicates less than 10 km shortening since ~450 ka or less on the Tainan detachment and the frontal backthrusts, while the east-dipping Lungchuan and Pingchi thrusts each consumed ~10 km shortening. Another ramp from ~7 to ~11 km depth is expected further east based on older sediments and slates exposed on the hanging wall of faults in the inner part of the mountain belt. This ~11-km-depth detachment seems to correspond with an inversion in seismic velocities at ~12 km depth beneath the slates belt, interpreted as slates over-riding lower-velocity passive margin sediments. Therefore, the detachment and thrusts system proposed from our cross-section appears to correspond to the main plate interface, where significant shortening was consumed in a thin-skinned deformation style, involving only foreland basin sediments near the deformation front.
The Meinong earthquake coseismic surface deformation suggests that, in addition to the deepest (15-20 km) main fault plane, the ~4-7-km-depth ramp, the Tainan detachment and the backthrusts slipped aseismically during after the earthquake. In contrast, the earthquake nucleated below the main detachment and, based on tomographic models, there is no clear structural connection between deep and shallower structures. The Meinong event locates near the interface between Cenozoic basement rocks and post-rifting sediments, similarly to the 2010 Mw6.3 Jiashian event. We propose that this interface is the locus of moderate-magnitude events, which seismic waves triggered limited slip on shallower faults, rooted within the weak, fluid-rich Gutingkeng mudstone. This interface may have developed as a secondary detachment level with limited total shortening.
How to cite: Le Béon, M., Suppe, J., Hsieh, Y.-H., Huang, M.-H., Huang, H.-H., and Chen, C.-T.: Geological structure and active deformation in the fold-thrust belt of southern Taiwan in relation to crustal-scale structure, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18768, https://doi.org/10.5194/egusphere-egu2020-18768, 2020.
The fold-thrust belt of southern Taiwan currently accommodates rapid westward shortening in the order of 4.5 mm/a and is estimated to have developed since the Late Pliocene. It is the locus of the 2016 Mw6.4 Meinong earthquake, which involved fault slip at multiple levels in the mid-to-upper crust. It nucleated at ~15 km depth and also triggered shallow structures that reach the surface or nearly. To characterize the structure of the piedmont and investigate the broader tectonic setting of the event, we build two east-west regional balanced cross-sections based on surface geology, subsurface data, coseismic and interseismic geodetic data, and published nanno- and magneto-stratigraphy. We also document the first-order evolution of the piedmont and how the piedmont structures relate to the inner part of the mountain belt based on the cross-section restoration and the analysis of the seismic velocity structure of the plate boundary.
From the Coastal Plain towards the east, we propose a series of three active west-dipping backthrusts, rooted on a ~4.0-km-deep detachment, the Tainan detachment. The detachment lies within the base of the 3-km-thick Plio-Pleistocene Gutingkeng mudstone, which represents the initial foreland basin sediments. Syntectonic sediments and rapid shortening and uplift observed from geodetic measurements attest for the activity of these structures since the Late Pleistocene. Further east, the Tainan detachment ramps down to ~7 km depth, allowing the east-dipping Lungchuan and Pingchi thrusts to bring Upper Miocene continental-shelf formations to the surface. The cross-section restoration indicates less than 10 km shortening since ~450 ka or less on the Tainan detachment and the frontal backthrusts, while the east-dipping Lungchuan and Pingchi thrusts each consumed ~10 km shortening. Another ramp from ~7 to ~11 km depth is expected further east based on older sediments and slates exposed on the hanging wall of faults in the inner part of the mountain belt. This ~11-km-depth detachment seems to correspond with an inversion in seismic velocities at ~12 km depth beneath the slates belt, interpreted as slates over-riding lower-velocity passive margin sediments. Therefore, the detachment and thrusts system proposed from our cross-section appears to correspond to the main plate interface, where significant shortening was consumed in a thin-skinned deformation style, involving only foreland basin sediments near the deformation front.
The Meinong earthquake coseismic surface deformation suggests that, in addition to the deepest (15-20 km) main fault plane, the ~4-7-km-depth ramp, the Tainan detachment and the backthrusts slipped aseismically during after the earthquake. In contrast, the earthquake nucleated below the main detachment and, based on tomographic models, there is no clear structural connection between deep and shallower structures. The Meinong event locates near the interface between Cenozoic basement rocks and post-rifting sediments, similarly to the 2010 Mw6.3 Jiashian event. We propose that this interface is the locus of moderate-magnitude events, which seismic waves triggered limited slip on shallower faults, rooted within the weak, fluid-rich Gutingkeng mudstone. This interface may have developed as a secondary detachment level with limited total shortening.
How to cite: Le Béon, M., Suppe, J., Hsieh, Y.-H., Huang, M.-H., Huang, H.-H., and Chen, C.-T.: Geological structure and active deformation in the fold-thrust belt of southern Taiwan in relation to crustal-scale structure, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18768, https://doi.org/10.5194/egusphere-egu2020-18768, 2020.
EGU2020-4172 | Displays | TS7.2
Mechanics and paleo geomorphy of the platform margin of Dengying formation in the Jiulongshan field, Sichuan Basin, ChinaLining Wang
The northwestern Sichuan region experienced the evolutionary process of a marine Craton basin in the Sinian-Middle Triassic and a continental basin in the Mesozoic-Cenozoic. Several regional tectonic activities cause the complicated stratigraphic distribution and structural deformations in deep layers. During key tectonic periods, the characteristic sedimentary and deformation structures were formed, including the platform margin of Dengying formation, the western palaeohigh at the end of Silurian, and the passive continental margin of late Paleozoic-middle Triassic. The Meso-Cenozoic intra-continental compressional tectonic processes since the late Triassic controlled the formation of complex thrusting structures surrounding and inside the basin. The northern Longmenshan fold-thrust belt has footwall in-situ thrust structures, controlled by two sets of detachments in the Lower Triassic and the Lower Cambrian, presenting a multi-level deformation structure with shallow folds, the middle thin-skin thrusts and the deeper basement-involved folds. From the perspective of structural geology, the Dengying formation of the Upper Sinian is mainly distributed in the eastern and northern areas of the northwest Sichuan basin where the Jiulongshan fold is the favorable exploration belts. Using the three-dimensional seismic reflection data, we recognize the structural characteristics of the platform margin of Dengying formation. Meanwhile, we apply new methods of two-dimensional and structural restoration based on mechanical constrains to gain insights into the development of the Jiulongshan anticline which forms the trap for the Jiulongshan field. The result of structural restoration indicates that, the formation of the Jiulongshan anticline is controlled by two-stage contractional thrusts. In the early days, there was no significant relief in Jiulongshan area, and the southwestern top of the Sinian Dengying formation was the paleo-high. The anticline was gradually formed in the Late Jurassic-the Early Cretaceous, presenting an approximately E-W strike structure. This structure was transformed by the N-E contractional stress to become an anticline in NE-SW direction.
How to cite: Wang, L.: Mechanics and paleo geomorphy of the platform margin of Dengying formation in the Jiulongshan field, Sichuan Basin, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4172, https://doi.org/10.5194/egusphere-egu2020-4172, 2020.
The northwestern Sichuan region experienced the evolutionary process of a marine Craton basin in the Sinian-Middle Triassic and a continental basin in the Mesozoic-Cenozoic. Several regional tectonic activities cause the complicated stratigraphic distribution and structural deformations in deep layers. During key tectonic periods, the characteristic sedimentary and deformation structures were formed, including the platform margin of Dengying formation, the western palaeohigh at the end of Silurian, and the passive continental margin of late Paleozoic-middle Triassic. The Meso-Cenozoic intra-continental compressional tectonic processes since the late Triassic controlled the formation of complex thrusting structures surrounding and inside the basin. The northern Longmenshan fold-thrust belt has footwall in-situ thrust structures, controlled by two sets of detachments in the Lower Triassic and the Lower Cambrian, presenting a multi-level deformation structure with shallow folds, the middle thin-skin thrusts and the deeper basement-involved folds. From the perspective of structural geology, the Dengying formation of the Upper Sinian is mainly distributed in the eastern and northern areas of the northwest Sichuan basin where the Jiulongshan fold is the favorable exploration belts. Using the three-dimensional seismic reflection data, we recognize the structural characteristics of the platform margin of Dengying formation. Meanwhile, we apply new methods of two-dimensional and structural restoration based on mechanical constrains to gain insights into the development of the Jiulongshan anticline which forms the trap for the Jiulongshan field. The result of structural restoration indicates that, the formation of the Jiulongshan anticline is controlled by two-stage contractional thrusts. In the early days, there was no significant relief in Jiulongshan area, and the southwestern top of the Sinian Dengying formation was the paleo-high. The anticline was gradually formed in the Late Jurassic-the Early Cretaceous, presenting an approximately E-W strike structure. This structure was transformed by the N-E contractional stress to become an anticline in NE-SW direction.
How to cite: Wang, L.: Mechanics and paleo geomorphy of the platform margin of Dengying formation in the Jiulongshan field, Sichuan Basin, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4172, https://doi.org/10.5194/egusphere-egu2020-4172, 2020.
EGU2020-7817 | Displays | TS7.2
Indentation tectonics of the Zhongtiaoshan Block in the Trans-North China OrogenJiawei Cui
The North China (NCC) is one of the oldest cratons in the world. The tectonic evolution processes of the NCC have been debated for decades (Zhao and Zhai, 2013; Zhao, 2007; Zhao et al., 2002, 2003, 2005, 2009; Zhai et al., 2005; Zhai and Santosh, 2011; Wilde et al., 2002, 2005; Kroner et al., 2005; Kusky et al., 2001, 2007; Kusky and Li, 2003; Faure et al., 2007; Trap et al., 2012; Hu et al., 2013; Zhao et al.,2019). The controversy focuses on the time of the formation of the NCC is in the late Paleoproterozoic or the late Archean. The key point of the controversy is that there are serious disagreement about the nature and implications of the late Paleoproterozoic orogen in the NCC. Some researchers thought the NCC underwent compression in 1.85 Ga according to previous researchers (Zhai et al., 2005; Zhai and Santosh, 2011; Zhao et al., 2019). Some researchers even thought that the NCC was finally formed resulted from the collision of the east block and the west block (Kusky et al., 2001, 2007; Kusky and Li, 2003; Trap et al., 2012; Zhao et al., 2002a, 2003a, 2005, 2009;). Recently, we found that NE-NEE trending extensional ductile shear zones developed in the Paleoproterozoic granitic gneiss (2.4Ga) in the northern margin of the Zhongtiaoshan, the middle part of the NCC. The ductile shear zone was unconformity covered by the Changcheng System and the deformation ages according to the 40Ar/39Ar dating results is 1.92 Ga, which indicate that the deformation time was in the late Paleoproterozoic. Therefore, We propose that that the NCC was in the post-collision extension environment or lateral and vertical extrusion of blocks might have happened after the orogeny in late Paleoproterozioc.
How to cite: Cui, J.: Indentation tectonics of the Zhongtiaoshan Block in the Trans-North China Orogen, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7817, https://doi.org/10.5194/egusphere-egu2020-7817, 2020.
The North China (NCC) is one of the oldest cratons in the world. The tectonic evolution processes of the NCC have been debated for decades (Zhao and Zhai, 2013; Zhao, 2007; Zhao et al., 2002, 2003, 2005, 2009; Zhai et al., 2005; Zhai and Santosh, 2011; Wilde et al., 2002, 2005; Kroner et al., 2005; Kusky et al., 2001, 2007; Kusky and Li, 2003; Faure et al., 2007; Trap et al., 2012; Hu et al., 2013; Zhao et al.,2019). The controversy focuses on the time of the formation of the NCC is in the late Paleoproterozoic or the late Archean. The key point of the controversy is that there are serious disagreement about the nature and implications of the late Paleoproterozoic orogen in the NCC. Some researchers thought the NCC underwent compression in 1.85 Ga according to previous researchers (Zhai et al., 2005; Zhai and Santosh, 2011; Zhao et al., 2019). Some researchers even thought that the NCC was finally formed resulted from the collision of the east block and the west block (Kusky et al., 2001, 2007; Kusky and Li, 2003; Trap et al., 2012; Zhao et al., 2002a, 2003a, 2005, 2009;). Recently, we found that NE-NEE trending extensional ductile shear zones developed in the Paleoproterozoic granitic gneiss (2.4Ga) in the northern margin of the Zhongtiaoshan, the middle part of the NCC. The ductile shear zone was unconformity covered by the Changcheng System and the deformation ages according to the 40Ar/39Ar dating results is 1.92 Ga, which indicate that the deformation time was in the late Paleoproterozoic. Therefore, We propose that that the NCC was in the post-collision extension environment or lateral and vertical extrusion of blocks might have happened after the orogeny in late Paleoproterozioc.
How to cite: Cui, J.: Indentation tectonics of the Zhongtiaoshan Block in the Trans-North China Orogen, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7817, https://doi.org/10.5194/egusphere-egu2020-7817, 2020.
EGU2020-20903 | Displays | TS7.2
Multiple detachments of thin-skinned fold-and-thrust belts in the eastern Sichuan Basin, ChinaZhidong Gu
The eastern Sichuan Basin, South China, is characterized by approximately parallel thin-skinned fold-and-thrust belts with exposed narrow anticlines and wide synclines. The structural deformation, however, has remained controversial due to the previous poor seismic data. In this study, the new collected pre-stack long-offset 2D- and 3D seismic data have been applied, and a 200-km long cross section perpendicular to the fold-and-thrust belts has been constructed to analyze the structural style and geometric and kinematic evolution. The stratigraphic succession is composed of competent layers separated by three main incompetent layers being multiple detachments, which are the Cambrian evaporites, the Lower Silurian shales, and the Middle-Lower Triassic evaporites, respectively. The basal detachment, the Cambrian evaporites, played a dominant role in the structural deformation, above which the fold-and-thrust belts were generated, and the middle and top detachments accommodated the displacement during the deformation. The main structural styles are detachment folds, fault propagation folds, back thrusts and basement-involved folds. The evolution succession of the fold-and-thrust belts should be kink band, detachment folds, and sequential thrusts of the forelimb and backlimb of the folds. The style of deformation is dependent on the mechanical characters of stratigraphic succession, i.e., the thickness variation of competent and incompetent layers in the stratigraphic units.
How to cite: Gu, Z.: Multiple detachments of thin-skinned fold-and-thrust belts in the eastern Sichuan Basin, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20903, https://doi.org/10.5194/egusphere-egu2020-20903, 2020.
The eastern Sichuan Basin, South China, is characterized by approximately parallel thin-skinned fold-and-thrust belts with exposed narrow anticlines and wide synclines. The structural deformation, however, has remained controversial due to the previous poor seismic data. In this study, the new collected pre-stack long-offset 2D- and 3D seismic data have been applied, and a 200-km long cross section perpendicular to the fold-and-thrust belts has been constructed to analyze the structural style and geometric and kinematic evolution. The stratigraphic succession is composed of competent layers separated by three main incompetent layers being multiple detachments, which are the Cambrian evaporites, the Lower Silurian shales, and the Middle-Lower Triassic evaporites, respectively. The basal detachment, the Cambrian evaporites, played a dominant role in the structural deformation, above which the fold-and-thrust belts were generated, and the middle and top detachments accommodated the displacement during the deformation. The main structural styles are detachment folds, fault propagation folds, back thrusts and basement-involved folds. The evolution succession of the fold-and-thrust belts should be kink band, detachment folds, and sequential thrusts of the forelimb and backlimb of the folds. The style of deformation is dependent on the mechanical characters of stratigraphic succession, i.e., the thickness variation of competent and incompetent layers in the stratigraphic units.
How to cite: Gu, Z.: Multiple detachments of thin-skinned fold-and-thrust belts in the eastern Sichuan Basin, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20903, https://doi.org/10.5194/egusphere-egu2020-20903, 2020.
EGU2020-7785 | Displays | TS7.2
Geometrical and chronological constraints for magnetic signatures in the Central High AtlasTania Mochales, Ahmed Manar, Antonio María Casas-Sainz, Pablo Calvin, Pablo Santolaria, Juan José Villalaín, Vicente Carlos Ruiz, Andrés Gil-Imaz, Sara Torres, Andrés Pocoví, Bennacer Moussaid, Teresa Román-Berdiel, Hmidou El Ouardi, Esther Izquierdo-Llavall, Belén Oliva-Urcía, Marcos Marcén, María Felicidad Bógalo, Elisa Sánchez-Moreno, Ángela Herrejón, and Ángela Jiménez and the CHA Team
New residual magnetic map is presented to help decipher the magnetic imprints in the Central High Atlas (CHA) fold-and-thrust belt. The total intensity map shows a main direction mimicking the N070 trend which features the Atlas range. Detailed structural and paleomagnetic studies performed in the selected area demonstrate that similar shortening figures are observed in western and eastern portions. Differences in structural style are the consequence of (i) the inherited structure from the Triassic-Jurassic rifting stage, to Cenozoic inversion, (ii) the differential displacement through the Upper Triassic detachment level and (iii) superposition of cover thrust sheets.
Remarkable magnetic anomalies are recorded, from negative values (<-400 nT) in the southern foreland, to positive (>500 nT) in the core of the range. The western sector of the chain is defined by intermediate to high anomalies, probably related to NE-SW basement structures, which favored the emplacement of Triassic CAMP basalts and/or Jurassic gabbro bodies, within the syn-rift sequence. The central part of the range is characterized by high and very high positive anomalies with an irregular distribution, probably linked to Middle-Late Jurassic diapirism produced during extension and intrusion of gabbroid bodies at the core of diapirs, whose structure nucleated NE-SW anticlinal ridges. The eastern sector is characterized by intermediate to low intensity anomalies, likely associated to thick series of basinal Jurassic limestones, whose sequences were stacked (during the Cenozoic compressional stage) by means of kilometer-scale thrusts. Very high positive, linear anomalies seem to be related to Jurassic gabbro intruding directly into the carbonate facies in the eastern sector. Widespread negative anomalies are detected in the foreland southern basin. In this case, the remanent signature could be related to the Paleozoic magmatic provinces.
How to cite: Mochales, T., Manar, A., Casas-Sainz, A. M., Calvin, P., Santolaria, P., Villalaín, J. J., Ruiz, V. C., Gil-Imaz, A., Torres, S., Pocoví, A., Moussaid, B., Román-Berdiel, T., El Ouardi, H., Izquierdo-Llavall, E., Oliva-Urcía, B., Marcén, M., Bógalo, M. F., Sánchez-Moreno, E., Herrejón, Á., and Jiménez, Á. and the CHA Team: Geometrical and chronological constraints for magnetic signatures in the Central High Atlas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7785, https://doi.org/10.5194/egusphere-egu2020-7785, 2020.
New residual magnetic map is presented to help decipher the magnetic imprints in the Central High Atlas (CHA) fold-and-thrust belt. The total intensity map shows a main direction mimicking the N070 trend which features the Atlas range. Detailed structural and paleomagnetic studies performed in the selected area demonstrate that similar shortening figures are observed in western and eastern portions. Differences in structural style are the consequence of (i) the inherited structure from the Triassic-Jurassic rifting stage, to Cenozoic inversion, (ii) the differential displacement through the Upper Triassic detachment level and (iii) superposition of cover thrust sheets.
Remarkable magnetic anomalies are recorded, from negative values (<-400 nT) in the southern foreland, to positive (>500 nT) in the core of the range. The western sector of the chain is defined by intermediate to high anomalies, probably related to NE-SW basement structures, which favored the emplacement of Triassic CAMP basalts and/or Jurassic gabbro bodies, within the syn-rift sequence. The central part of the range is characterized by high and very high positive anomalies with an irregular distribution, probably linked to Middle-Late Jurassic diapirism produced during extension and intrusion of gabbroid bodies at the core of diapirs, whose structure nucleated NE-SW anticlinal ridges. The eastern sector is characterized by intermediate to low intensity anomalies, likely associated to thick series of basinal Jurassic limestones, whose sequences were stacked (during the Cenozoic compressional stage) by means of kilometer-scale thrusts. Very high positive, linear anomalies seem to be related to Jurassic gabbro intruding directly into the carbonate facies in the eastern sector. Widespread negative anomalies are detected in the foreland southern basin. In this case, the remanent signature could be related to the Paleozoic magmatic provinces.
How to cite: Mochales, T., Manar, A., Casas-Sainz, A. M., Calvin, P., Santolaria, P., Villalaín, J. J., Ruiz, V. C., Gil-Imaz, A., Torres, S., Pocoví, A., Moussaid, B., Román-Berdiel, T., El Ouardi, H., Izquierdo-Llavall, E., Oliva-Urcía, B., Marcén, M., Bógalo, M. F., Sánchez-Moreno, E., Herrejón, Á., and Jiménez, Á. and the CHA Team: Geometrical and chronological constraints for magnetic signatures in the Central High Atlas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7785, https://doi.org/10.5194/egusphere-egu2020-7785, 2020.
EGU2020-8036 | Displays | TS7.2
3-D geological model of the Central High Atlas fold-and-thrust beltPablo Santolaria, Antonio M. Casas, Pablo Calvín, Tania Mochales, Hmidou El-Ouardi, Esther Izquierdo, Teresa Román-Berdiel, Sara Torres, Andrés Pocoví, Belén Oliva-Urcia, Bennacer Moussaid, Marcos Marcén, Andrés Gil-Imaz, Vicente Carlos Ruiz, María Felicidad Bógalo, Elisa M. Sánchez-Moreno, Ángela Herrejón, Ángela Jiménez, Juan José Villalaín, and Irene Falcón
The Atlas system, an ENE-WSW intracontinental chain in the NW of Africa, grew because of the inversion of Mesozoic extensional basins during the Cenozoic convergence between the African and European plates. The Central High Atlas (CHA) is located in the mid-western sector of the chain and is characterized by (i) the presence of an Upper Triassic décollement, (ii) thick Lower-Middle Jurassic sedimentary sequences, and (iii) the occurrence of diapirs and igneous bodies which are especially common in the central part of the chain. The northern and southern borders are characterized by fold-and-thrust-systems involving the Paleozoic basement and the Mesozoic cover and showing significant displacements, especially towards the South.
Framed on a multidisciplinary structural project aiming to reconstruct the 4-D structure of the CHA, the purpose of this work is to gather a vast constraining dataset into a present-day, regional, 3-D geological model of the CHA fold-and-thrust belt. This 3-D reconstruction gives special weight to along- and across-strike variations of the geometry of the basement and cover structures and the distribution of salt and igneous bodies. The 3-D model is founded by 23 serial cross-sections, constrained by surface geology and more than 1900 structural data and complemented by geophysical modelling. The model considers regional structures having enough lateral continuity and so we ruled out minor, local features. Stratigraphically, we considered 5 horizons: (1) the top of the Triassic located below the detachment level, and partially equivalent to the top of the basement, (2) the base of the Jurassic succession (i.e. the top of the detachment level), (3) the Lower-Middle Jurassic limit and, towards the southern and northern fronts and foreland basins, (4) the bases of the Cretaceous and (5) the Cenozoic succession.
The reconstruction of the 3-D model entailed a strong feedback between the model and the cross-sections. The incipient 3-D model helped to refine the lateral consistency between cross-sections regarding branch and tip lines, cut-offs, fault angles, etc., and so to improve and further constrain them.
Thick to thin skinned deformation dominates the eastern, central and northwestern areas of the chain while thick skinned deformation occurs in the westernmost transects. The chain is defined as an asymmetric, doubly verging fold-and-thrust belt. A north-dipping, basement regional fault represents the main rooting structure of the CHA. Its geometry varies from and almost horizontal (West), to a 10°-12° (Centre) and 15° (East) thrust ramp surface. As this fault intersects the cover, it splits into a regional thrust front with several thrust branches. To the north, antithetic basement faults change to a thrust relay system as they intersect the Mesozoic sequence. Along the core of the chain, the structural style is characterized by open salt bodies, welded diapirs and steep thrusts having relatively limited lateral continuation. The Toundoute Unit, located in the central-western sector represents a basement-and-cover thrust stack where the basement is exhumed and crops out.
This 3-D structural model provides the bases for further 4-D reconstruction of the CHA and, at the same time, served as a constraining approach for cross-section construction.
How to cite: Santolaria, P., Casas, A. M., Calvín, P., Mochales, T., El-Ouardi, H., Izquierdo, E., Román-Berdiel, T., Torres, S., Pocoví, A., Oliva-Urcia, B., Moussaid, B., Marcén, M., Gil-Imaz, A., Carlos Ruiz, V., Felicidad Bógalo, M., Sánchez-Moreno, E. M., Herrejón, Á., Jiménez, Á., Villalaín, J. J., and Falcón, I.: 3-D geological model of the Central High Atlas fold-and-thrust belt, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8036, https://doi.org/10.5194/egusphere-egu2020-8036, 2020.
The Atlas system, an ENE-WSW intracontinental chain in the NW of Africa, grew because of the inversion of Mesozoic extensional basins during the Cenozoic convergence between the African and European plates. The Central High Atlas (CHA) is located in the mid-western sector of the chain and is characterized by (i) the presence of an Upper Triassic décollement, (ii) thick Lower-Middle Jurassic sedimentary sequences, and (iii) the occurrence of diapirs and igneous bodies which are especially common in the central part of the chain. The northern and southern borders are characterized by fold-and-thrust-systems involving the Paleozoic basement and the Mesozoic cover and showing significant displacements, especially towards the South.
Framed on a multidisciplinary structural project aiming to reconstruct the 4-D structure of the CHA, the purpose of this work is to gather a vast constraining dataset into a present-day, regional, 3-D geological model of the CHA fold-and-thrust belt. This 3-D reconstruction gives special weight to along- and across-strike variations of the geometry of the basement and cover structures and the distribution of salt and igneous bodies. The 3-D model is founded by 23 serial cross-sections, constrained by surface geology and more than 1900 structural data and complemented by geophysical modelling. The model considers regional structures having enough lateral continuity and so we ruled out minor, local features. Stratigraphically, we considered 5 horizons: (1) the top of the Triassic located below the detachment level, and partially equivalent to the top of the basement, (2) the base of the Jurassic succession (i.e. the top of the detachment level), (3) the Lower-Middle Jurassic limit and, towards the southern and northern fronts and foreland basins, (4) the bases of the Cretaceous and (5) the Cenozoic succession.
The reconstruction of the 3-D model entailed a strong feedback between the model and the cross-sections. The incipient 3-D model helped to refine the lateral consistency between cross-sections regarding branch and tip lines, cut-offs, fault angles, etc., and so to improve and further constrain them.
Thick to thin skinned deformation dominates the eastern, central and northwestern areas of the chain while thick skinned deformation occurs in the westernmost transects. The chain is defined as an asymmetric, doubly verging fold-and-thrust belt. A north-dipping, basement regional fault represents the main rooting structure of the CHA. Its geometry varies from and almost horizontal (West), to a 10°-12° (Centre) and 15° (East) thrust ramp surface. As this fault intersects the cover, it splits into a regional thrust front with several thrust branches. To the north, antithetic basement faults change to a thrust relay system as they intersect the Mesozoic sequence. Along the core of the chain, the structural style is characterized by open salt bodies, welded diapirs and steep thrusts having relatively limited lateral continuation. The Toundoute Unit, located in the central-western sector represents a basement-and-cover thrust stack where the basement is exhumed and crops out.
This 3-D structural model provides the bases for further 4-D reconstruction of the CHA and, at the same time, served as a constraining approach for cross-section construction.
How to cite: Santolaria, P., Casas, A. M., Calvín, P., Mochales, T., El-Ouardi, H., Izquierdo, E., Román-Berdiel, T., Torres, S., Pocoví, A., Oliva-Urcia, B., Moussaid, B., Marcén, M., Gil-Imaz, A., Carlos Ruiz, V., Felicidad Bógalo, M., Sánchez-Moreno, E. M., Herrejón, Á., Jiménez, Á., Villalaín, J. J., and Falcón, I.: 3-D geological model of the Central High Atlas fold-and-thrust belt, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8036, https://doi.org/10.5194/egusphere-egu2020-8036, 2020.
EGU2020-8342 | Displays | TS7.2
Why do triangle zones exist? Insights from numerical modelsBetti Hegyi, Zoltan Erdos, Ritske S. Huismans, and Christoph von Hagke
Triangle zones in fold and thrust belts are enigmatic structures bound by foreland verging thrust zones and back-thrusts verging towards the hinterland. The geometry as well as kinematic evolution of these structures has been the subject of a wide range of studies over the last few decades. The understanding of triangle zone mechanics is incomplete although different driving mechanisms for their formation have been proposed. So far few – mostly analogue – modeling studies have focused on understanding the primary factors controlling their formation. Factors suggested to have a first order control on the formation of triangle zones include the rheological properties of the detachment and overburden rocks, the thickness of the overburden rocks, syn-tectonic erosion and sedimentation rate, fluid over-pressure conditions, and the angle of the detachment. Here we use the arbitrary Lagrangian-Eularian finite element code FANTOM to examine the development of triangle zones. We focus especially on the effect of the angle and rheology of the detachment, the rheology of the overburden strata, and syn-tectonic deposition.
How to cite: Hegyi, B., Erdos, Z., Huismans, R. S., and von Hagke, C.: Why do triangle zones exist? Insights from numerical models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8342, https://doi.org/10.5194/egusphere-egu2020-8342, 2020.
Triangle zones in fold and thrust belts are enigmatic structures bound by foreland verging thrust zones and back-thrusts verging towards the hinterland. The geometry as well as kinematic evolution of these structures has been the subject of a wide range of studies over the last few decades. The understanding of triangle zone mechanics is incomplete although different driving mechanisms for their formation have been proposed. So far few – mostly analogue – modeling studies have focused on understanding the primary factors controlling their formation. Factors suggested to have a first order control on the formation of triangle zones include the rheological properties of the detachment and overburden rocks, the thickness of the overburden rocks, syn-tectonic erosion and sedimentation rate, fluid over-pressure conditions, and the angle of the detachment. Here we use the arbitrary Lagrangian-Eularian finite element code FANTOM to examine the development of triangle zones. We focus especially on the effect of the angle and rheology of the detachment, the rheology of the overburden strata, and syn-tectonic deposition.
How to cite: Hegyi, B., Erdos, Z., Huismans, R. S., and von Hagke, C.: Why do triangle zones exist? Insights from numerical models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8342, https://doi.org/10.5194/egusphere-egu2020-8342, 2020.
EGU2020-18590 | Displays | TS7.2
Role of structural inheritances in the development of the Mountain Front Flexure in the Lurestan region of the Zagros beltStefano Tavani, Giovanni Camanni, Michele Nappo, Marco Snidero, Alessandra Ascione, Ettore Valente, Gholamreza Gharabeigli, Davoud Morsalnejad, and Stefano Mazzoli
The Mountain Front Flexure is a major structure of the Zagros orogenic system, and is underlain by the deeply rooted and seismically active Mountain Front Fault system. These coupled structural features divide the belt from its foreland and their trace is sinuous, forming salients and recesses. The origin and tectonic significance of the Mountain Front Fault system and its sinuosity are still unclear, with most of hypotheses pointing to a strong structural control exerted by geological inheritances. In this work we combine interpretation of seismic reflection profiles, earthquake data, geomorphic analysis, and geological observations, to build a balanced cross section across the Mountain Front Flexure in the Lurestan region. Our data are suggestive of a hybrid tectonic style for the Lurestan region, characterised by a major and newly developed crustal ramp in the frontal portion of the belt (i.e the Mountain Front Fault) and by the reactivation of steeply dipping pre-existing basin-bounding faults, along with a minor amount of shortening, in the inner area. Specifically, the integration of our results with previous knowledge indicates that the Mountain Front Fault system developed in the necking domain of the Jurassic rift system, ahead of an array of inverted Jurassic extensional faults, in a structural fashion which resembles that of a crustal-scale footwall shortcut. Within this structural context, the sinusoidal shape of the Mountain Front Flexure in the Lurestan area arises from the re-use of the original segmentation of the inverted Jurassic rift system.
How to cite: Tavani, S., Camanni, G., Nappo, M., Snidero, M., Ascione, A., Valente, E., Gharabeigli, G., Morsalnejad, D., and Mazzoli, S.: Role of structural inheritances in the development of the Mountain Front Flexure in the Lurestan region of the Zagros belt, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18590, https://doi.org/10.5194/egusphere-egu2020-18590, 2020.
The Mountain Front Flexure is a major structure of the Zagros orogenic system, and is underlain by the deeply rooted and seismically active Mountain Front Fault system. These coupled structural features divide the belt from its foreland and their trace is sinuous, forming salients and recesses. The origin and tectonic significance of the Mountain Front Fault system and its sinuosity are still unclear, with most of hypotheses pointing to a strong structural control exerted by geological inheritances. In this work we combine interpretation of seismic reflection profiles, earthquake data, geomorphic analysis, and geological observations, to build a balanced cross section across the Mountain Front Flexure in the Lurestan region. Our data are suggestive of a hybrid tectonic style for the Lurestan region, characterised by a major and newly developed crustal ramp in the frontal portion of the belt (i.e the Mountain Front Fault) and by the reactivation of steeply dipping pre-existing basin-bounding faults, along with a minor amount of shortening, in the inner area. Specifically, the integration of our results with previous knowledge indicates that the Mountain Front Fault system developed in the necking domain of the Jurassic rift system, ahead of an array of inverted Jurassic extensional faults, in a structural fashion which resembles that of a crustal-scale footwall shortcut. Within this structural context, the sinusoidal shape of the Mountain Front Flexure in the Lurestan area arises from the re-use of the original segmentation of the inverted Jurassic rift system.
How to cite: Tavani, S., Camanni, G., Nappo, M., Snidero, M., Ascione, A., Valente, E., Gharabeigli, G., Morsalnejad, D., and Mazzoli, S.: Role of structural inheritances in the development of the Mountain Front Flexure in the Lurestan region of the Zagros belt, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18590, https://doi.org/10.5194/egusphere-egu2020-18590, 2020.
TS7.4 – Dynamics and Structures of the Tethyan realm: Collisions and back-arcs from the Mediterranean to the Himalayas
EGU2020-18224 | Displays | TS7.4
Tectonic evolution of the Mediterranean region from a global plate kinematics perspective: insights from a new deformable tectonic modelSimone Agostini, Simon Otto, John Watson, and Roy Howgate
The tectonic evolution of the Mediterranean is well studied, but the models often cover a limited period of geological time and are not always placed in a wider context. Its evolution is linked to the surrounding African and Eurasian continents and their relative movements.
A new fully deformable tectonic model of the Mediterranean has been created as part of a proprietary plate model. This work has led to the identification of key global tectonic events influencing the development of the Mediterranean from the Early Permian to the present day. This first fully-deformable plate model of the Mediterranean enables to account for the shortening and extension that occurred in the area at a temporal resolution of 1 Ma. In most available plate models, plates are rigidly rotated back to their paleo-position, meaning they preserve their present-day size and shape. In some recent papers, the extent of deformation has been illustrated for selected time-slices, but these models cannot be considered to be ‘deformable’ because the deformation is not modelled in a continuous manner.
Following Hercynian orogenesis and until the break-up of Pangea, the Mediterranean was dominated by extensional tectonics along its southern margin, as a series small continental blocks rifted from the northern margin of Gondwana. The opening of the Central Atlantic in the Late Triassic-Early Jurassic led to displacement between Eurasia and Africa south of Iberia and the development of the Alpine Tethys, as the Atlantic initially propagated northwards to the east of Iberia. Rotation of Africa caused by the opening of the South Atlantic in the Late Jurassic-Early Cretaceous led to a ‘jump’ in spreading to the west, at the Iberia-Newfoundland margin. These larger scale plate motions overprinted the more local impacts of continued extension along the northern margin of Africa (e.g. Pindos Ocean). Opening of the North Atlantic once again changed the relative motion of Eurasia and Africa, and initiated a period of oceanic subduction and collision that culminated in the Alpine orogeny. Crucial to this story is the paleo-position of Apulia/Adria, which remained attached to Africa and was able to act as an indenter into Eurasia during the Alpine compression. Evidence for this connection will be presented and discussed.
How to cite: Agostini, S., Otto, S., Watson, J., and Howgate, R.: Tectonic evolution of the Mediterranean region from a global plate kinematics perspective: insights from a new deformable tectonic model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18224, https://doi.org/10.5194/egusphere-egu2020-18224, 2020.
The tectonic evolution of the Mediterranean is well studied, but the models often cover a limited period of geological time and are not always placed in a wider context. Its evolution is linked to the surrounding African and Eurasian continents and their relative movements.
A new fully deformable tectonic model of the Mediterranean has been created as part of a proprietary plate model. This work has led to the identification of key global tectonic events influencing the development of the Mediterranean from the Early Permian to the present day. This first fully-deformable plate model of the Mediterranean enables to account for the shortening and extension that occurred in the area at a temporal resolution of 1 Ma. In most available plate models, plates are rigidly rotated back to their paleo-position, meaning they preserve their present-day size and shape. In some recent papers, the extent of deformation has been illustrated for selected time-slices, but these models cannot be considered to be ‘deformable’ because the deformation is not modelled in a continuous manner.
Following Hercynian orogenesis and until the break-up of Pangea, the Mediterranean was dominated by extensional tectonics along its southern margin, as a series small continental blocks rifted from the northern margin of Gondwana. The opening of the Central Atlantic in the Late Triassic-Early Jurassic led to displacement between Eurasia and Africa south of Iberia and the development of the Alpine Tethys, as the Atlantic initially propagated northwards to the east of Iberia. Rotation of Africa caused by the opening of the South Atlantic in the Late Jurassic-Early Cretaceous led to a ‘jump’ in spreading to the west, at the Iberia-Newfoundland margin. These larger scale plate motions overprinted the more local impacts of continued extension along the northern margin of Africa (e.g. Pindos Ocean). Opening of the North Atlantic once again changed the relative motion of Eurasia and Africa, and initiated a period of oceanic subduction and collision that culminated in the Alpine orogeny. Crucial to this story is the paleo-position of Apulia/Adria, which remained attached to Africa and was able to act as an indenter into Eurasia during the Alpine compression. Evidence for this connection will be presented and discussed.
How to cite: Agostini, S., Otto, S., Watson, J., and Howgate, R.: Tectonic evolution of the Mediterranean region from a global plate kinematics perspective: insights from a new deformable tectonic model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18224, https://doi.org/10.5194/egusphere-egu2020-18224, 2020.
EGU2020-4929 | Displays | TS7.4
Deep seated density anomalies across the Iberia-Africa plate boundary and its topographic responseIvone Jiménez-Munt, Montserrat Torne, Manel Fernàndez, Jaume Vergés, Ajay Kumar, Alberto Carballo, and Daniel Garcia-Castellanos
The modes in which the lithosphere deforms during continental collision and the mechanisms involved are not well understood. While continental subduction and mantle delamination are often invoked in tectonophysical studies, these processes are difficult to be confirmed in more complex tectonic regions such as the Gibraltar Arc. We study the present-day density and compositional structure of the lithosphere along a transect running from S Iberia to N Africa crossing the western Gibraltar Arc. This region is located in the westernmost continental segment of the African-Eurasian plates, characterized by a diffuse transpressive plate boundary. An integrated and self-consistent geophysical-petrological methodology is used to model the lithosphere structure variations and the thermophysical properties of the upper mantle. The crustal structure is mainly constrained by seismic experiments and geological data, whereas the composition of the lithospheric mantle is constrained by xenolith data. The results show large lateral variations in the topography of the lithosphere-asthenosphere boundary (LAB). We distinguish different chemical lithospheric mantle domains that reproduce the main trends of the geophysical observables and the modelled P- and S-wave seismic velocities. A sublithospheric body colder than the surrounding mantle is needed beneath the Betics-Rif to adjust the measured potential fields. We link this body to the Iberian slab localized just to the east of the profile and having some effect on the geoid and Bouguer anomalies. Local isostasy allows explaining most of the topography, but an elastic thickness higher than 10 km is needed to explain local misfits between the Atlas and the Rif Mountains. This work has been supported by Spanish Ministry by the projects MITE (CGL2014-59516) and GeoCAM (PGC2018-095154-B-100).
How to cite: Jiménez-Munt, I., Torne, M., Fernàndez, M., Vergés, J., Kumar, A., Carballo, A., and Garcia-Castellanos, D.: Deep seated density anomalies across the Iberia-Africa plate boundary and its topographic response, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4929, https://doi.org/10.5194/egusphere-egu2020-4929, 2020.
The modes in which the lithosphere deforms during continental collision and the mechanisms involved are not well understood. While continental subduction and mantle delamination are often invoked in tectonophysical studies, these processes are difficult to be confirmed in more complex tectonic regions such as the Gibraltar Arc. We study the present-day density and compositional structure of the lithosphere along a transect running from S Iberia to N Africa crossing the western Gibraltar Arc. This region is located in the westernmost continental segment of the African-Eurasian plates, characterized by a diffuse transpressive plate boundary. An integrated and self-consistent geophysical-petrological methodology is used to model the lithosphere structure variations and the thermophysical properties of the upper mantle. The crustal structure is mainly constrained by seismic experiments and geological data, whereas the composition of the lithospheric mantle is constrained by xenolith data. The results show large lateral variations in the topography of the lithosphere-asthenosphere boundary (LAB). We distinguish different chemical lithospheric mantle domains that reproduce the main trends of the geophysical observables and the modelled P- and S-wave seismic velocities. A sublithospheric body colder than the surrounding mantle is needed beneath the Betics-Rif to adjust the measured potential fields. We link this body to the Iberian slab localized just to the east of the profile and having some effect on the geoid and Bouguer anomalies. Local isostasy allows explaining most of the topography, but an elastic thickness higher than 10 km is needed to explain local misfits between the Atlas and the Rif Mountains. This work has been supported by Spanish Ministry by the projects MITE (CGL2014-59516) and GeoCAM (PGC2018-095154-B-100).
How to cite: Jiménez-Munt, I., Torne, M., Fernàndez, M., Vergés, J., Kumar, A., Carballo, A., and Garcia-Castellanos, D.: Deep seated density anomalies across the Iberia-Africa plate boundary and its topographic response, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4929, https://doi.org/10.5194/egusphere-egu2020-4929, 2020.
EGU2020-5332 | Displays | TS7.4
Comparison of the crust and upper mantle structure of the Alboran and Algerian domains (Western Mediterranean): Tectonic significanceAjay Kumar, Manel Fernàndez, Jaume Vergés, Montserrat Torne, and Ivone Jimenez-Munt
We present a comparison of the present-day crust to upper-mantle structure in the Western Mediterranean along two NW-SE oriented geo-transects in the Alboran and Algerian basins. The Alboran domain geo-transect traverses the Iberian Massif, the Betics, the Alboran Basin and ends in the northern margin of Africa between the Tell and Rif mountains. The Algerian domain geo-transect traverses the Catalan Coast Ranges, the Valencia Trough, the Balearic Promontory, the Algerian basin, the Greater Kabylies and ends in the Tell-Atlas Mountains in the northern margin of Africa. We model the thermal, density (i.e. compositional) and seismic velocity structure by integrating geophysical and geochemical dataset in a self-consistent thermodynamic framework. The crustal structure is constrained by seismic experiments and geological cross-sections, whereas seismic tomography models and mantle xenoliths constrain the upper mantle structure and composition. The Algerian Basin lithosphere shows a typical oceanic lithosphere composition, whereas the Alboran Basin lithosphere is slightly fertile. The lithospheric mantle beneath the Betics and Greater Kabylies are also fertile compared to the Iberian and African lithospheres showing the involvement of the fertile sublithosphere mantle during the later stages of subduction. In the Valencia Trough, the lithosphere is fertile in comparison to the Balearic Promontory lithosphere, which is similar to Iberian lithosphere. A lithosphere-scale thickening is observed in the Betics, and the Greater Kabylies, and thinning follows towards the Alboran and Algerian back-arc basins. Detached slabs with anomalous temperature of-320 oC, with oceanic lithosphere composition beneath the Greater Kabylies, and Iberian lithosphere composition beneath the Betics, are required to fit the geoid height. Our results impose important constraints for the geodynamic evolution models of the Western Mediterranean.
This work has been supported by SUBTETIS (PIE-201830E039) project, EU Marie Curie Initial Training Network ‘SUBITOP’ (674899-SUBITOP-H2020-MSCA-ITN-2015), the Agencia Estatal de Investigación through projects MITE (CGL2014-59516) and GeoCAM (PGC2018-095154-B-100), and the Agency for Management of University and Research Grants of Catalonia (AGAUR-2017-SGR-847).
How to cite: Kumar, A., Fernàndez, M., Vergés, J., Torne, M., and Jimenez-Munt, I.: Comparison of the crust and upper mantle structure of the Alboran and Algerian domains (Western Mediterranean): Tectonic significance, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5332, https://doi.org/10.5194/egusphere-egu2020-5332, 2020.
We present a comparison of the present-day crust to upper-mantle structure in the Western Mediterranean along two NW-SE oriented geo-transects in the Alboran and Algerian basins. The Alboran domain geo-transect traverses the Iberian Massif, the Betics, the Alboran Basin and ends in the northern margin of Africa between the Tell and Rif mountains. The Algerian domain geo-transect traverses the Catalan Coast Ranges, the Valencia Trough, the Balearic Promontory, the Algerian basin, the Greater Kabylies and ends in the Tell-Atlas Mountains in the northern margin of Africa. We model the thermal, density (i.e. compositional) and seismic velocity structure by integrating geophysical and geochemical dataset in a self-consistent thermodynamic framework. The crustal structure is constrained by seismic experiments and geological cross-sections, whereas seismic tomography models and mantle xenoliths constrain the upper mantle structure and composition. The Algerian Basin lithosphere shows a typical oceanic lithosphere composition, whereas the Alboran Basin lithosphere is slightly fertile. The lithospheric mantle beneath the Betics and Greater Kabylies are also fertile compared to the Iberian and African lithospheres showing the involvement of the fertile sublithosphere mantle during the later stages of subduction. In the Valencia Trough, the lithosphere is fertile in comparison to the Balearic Promontory lithosphere, which is similar to Iberian lithosphere. A lithosphere-scale thickening is observed in the Betics, and the Greater Kabylies, and thinning follows towards the Alboran and Algerian back-arc basins. Detached slabs with anomalous temperature of-320 oC, with oceanic lithosphere composition beneath the Greater Kabylies, and Iberian lithosphere composition beneath the Betics, are required to fit the geoid height. Our results impose important constraints for the geodynamic evolution models of the Western Mediterranean.
This work has been supported by SUBTETIS (PIE-201830E039) project, EU Marie Curie Initial Training Network ‘SUBITOP’ (674899-SUBITOP-H2020-MSCA-ITN-2015), the Agencia Estatal de Investigación through projects MITE (CGL2014-59516) and GeoCAM (PGC2018-095154-B-100), and the Agency for Management of University and Research Grants of Catalonia (AGAUR-2017-SGR-847).
How to cite: Kumar, A., Fernàndez, M., Vergés, J., Torne, M., and Jimenez-Munt, I.: Comparison of the crust and upper mantle structure of the Alboran and Algerian domains (Western Mediterranean): Tectonic significance, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5332, https://doi.org/10.5194/egusphere-egu2020-5332, 2020.
EGU2020-9535 | Displays | TS7.4
The Westernmost Mediterranean evolution: A review of the Alboran and Algero-Balearic basins stratigraphyLaura Gómez de la Peña, César Ranero, Eulàlia Gràcia, and Guillermo Booth-Rea
The Alboran Basin is the westernmost of the Mediterranean basins. It is composed of different sub-basins and connects toward the east with the Algero-Balearic Basin. Regional studies of these basins are mainly from the ´90s, but the restricted seismic coverage and generally low quality (old acquisition and processing methods) of the seismic profiles were not enough to perform a detailed analysis of the entire sediment infill. More recent works characterize in detail a particular area, but the correlation between the different sub-basins remained beyond the scope of those works. Furthermore, these recent works are usually focused only on the Messinian and younger stratigraphy. Thus, the correlation of the sediment history across the entire region and its integration with the regional tectonic evolution has not been achieved. This results in a bunch of models, different for each sub-basin and not always coherent among them, which makes difficult the understanding of the geodynamic evolution of the region
Based on ~4500 km of new and reprocessed multichannel seismic profiles, together with well and dredge data, we are able to review the westernmost Mediterranean stratigraphy at a regional scale. We have correlated the sediment units deposited since the beginning of the formation of the different sub-basins, and we present for the first time a coherent stratigraphy and large-scale tectonic evolution of the whole region. The results provide the information to test and refine models of the geodynamic evolution of the westernmost Mediterranean.
The main objectives are: (i) To define a seismostratigraphy framework for the entire region, integrating previous interpretations and correlating the sedimentary units among depocentres; (ii) To propose an evolutionary model for each sub-basin; and (iii) To integrate all sub-basins results in an updated general kinematic model for the westernmost Mediterranean region.
Main results shed light on the particular evolution of each sub-basin as well as in the entire basin evolution. The Late Oligocene - Miocene represents the formation stage of the basins, controlled by the evolution of the Gibraltar subduction system. During this period, each sub-basin shows different sedimentary units, supporting differences in their evolution. The Plio-Quaternary corresponds to the deformation stage, driven by the Eurasian-African plates convergence. The Plio-Quaternary sediments are covering the entire area, instead of being restricted to the sub-basins. This latter period is characterized by contractional and strike-slip deformation, accommodated mainly by re-activation of pre-existing crustal structures.
How to cite: Gómez de la Peña, L., Ranero, C., Gràcia, E., and Booth-Rea, G.: The Westernmost Mediterranean evolution: A review of the Alboran and Algero-Balearic basins stratigraphy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9535, https://doi.org/10.5194/egusphere-egu2020-9535, 2020.
The Alboran Basin is the westernmost of the Mediterranean basins. It is composed of different sub-basins and connects toward the east with the Algero-Balearic Basin. Regional studies of these basins are mainly from the ´90s, but the restricted seismic coverage and generally low quality (old acquisition and processing methods) of the seismic profiles were not enough to perform a detailed analysis of the entire sediment infill. More recent works characterize in detail a particular area, but the correlation between the different sub-basins remained beyond the scope of those works. Furthermore, these recent works are usually focused only on the Messinian and younger stratigraphy. Thus, the correlation of the sediment history across the entire region and its integration with the regional tectonic evolution has not been achieved. This results in a bunch of models, different for each sub-basin and not always coherent among them, which makes difficult the understanding of the geodynamic evolution of the region
Based on ~4500 km of new and reprocessed multichannel seismic profiles, together with well and dredge data, we are able to review the westernmost Mediterranean stratigraphy at a regional scale. We have correlated the sediment units deposited since the beginning of the formation of the different sub-basins, and we present for the first time a coherent stratigraphy and large-scale tectonic evolution of the whole region. The results provide the information to test and refine models of the geodynamic evolution of the westernmost Mediterranean.
The main objectives are: (i) To define a seismostratigraphy framework for the entire region, integrating previous interpretations and correlating the sedimentary units among depocentres; (ii) To propose an evolutionary model for each sub-basin; and (iii) To integrate all sub-basins results in an updated general kinematic model for the westernmost Mediterranean region.
Main results shed light on the particular evolution of each sub-basin as well as in the entire basin evolution. The Late Oligocene - Miocene represents the formation stage of the basins, controlled by the evolution of the Gibraltar subduction system. During this period, each sub-basin shows different sedimentary units, supporting differences in their evolution. The Plio-Quaternary corresponds to the deformation stage, driven by the Eurasian-African plates convergence. The Plio-Quaternary sediments are covering the entire area, instead of being restricted to the sub-basins. This latter period is characterized by contractional and strike-slip deformation, accommodated mainly by re-activation of pre-existing crustal structures.
How to cite: Gómez de la Peña, L., Ranero, C., Gràcia, E., and Booth-Rea, G.: The Westernmost Mediterranean evolution: A review of the Alboran and Algero-Balearic basins stratigraphy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9535, https://doi.org/10.5194/egusphere-egu2020-9535, 2020.
EGU2020-448 | Displays | TS7.4
Subduction of a rifted passive continental margin: the Pohorje case of Eastern Alps - constraints from geochronology and geochemistryRuihong Chang, Franz Neubauer, Johann Genser, Yongjiang Liu, and Sihua Yuan
A-type subduction is considered to occur at the final stage of continent-continent collision. In many cases, the UHP/HP metamorphic conditions are well known but data on the type of subducted continental crust is lacking. In terms of end members, the type of subducted crust is either (1) normal thick continental crust or (2) the crust from the center of a rift zone, which is influenced by strong extension, high-temperature metamorphism due to thinning of even the continental mantle lithosphere and strong magmatism. To resolve these alternative scenarios, we investigated the southernmost part of the Eclogite-Gneiss Unit (EGU) of Cretaceous metamorphic age exposed in the Pohorje Mountains in Eastern Alps. There, UHP eclogites and ultramafic mantle rocks are exposed in a matrix of paragneiss and hitherto undated granitic orthogneises (Kirst et al., 2010). This study presents, for the first time, geochronological and geochemical data from newly discovered Permian granitic orthogneisses in this area. LA-ICP-MS zircon U–Pb ages of the orthogneisses are 255±2.2 Ma and 260±0.81 Ma, which are interpreted as the age of zircon crystallization in a magma. In contrast, all rounded zircons from paragneissic rocks give Cretaceous ages (89.34±0.69 Ma and 90.8±1.2 Ma), considered as the age of UHP/HP metamorphism. These zircons overgrew older zircons of Permian and rare older ages tentatively indicating that the metasedimentary could be not older than latest Permian. Zircon εHf(t) values of the four ortho- and paragneisses with (176Hf/177Hf) initial from 0.282201 to 0.282562, TDM2 are Proterozoic (1390~1970 Ma). The granitic orthogneisses show the geochemical features (high (La/Lu) N ratios (160.3–307.3), strong negative Eu anomalies) of an evolved granite molten from continental crust. This type of orthogneisses could be considered as the source magma of seemingly rootless Late Permian to Triassic pegmatites (Knoll et al., 2018) widespread within the EGU further to the north. The paragneisses are heterogeneously composed and are associated with eclogites and ultramafic cumulates of oceanic affinity (De Hoog et al., 2011). We argue that the Permian granitic orthogneisses might be derived from partial melting of lower crust in a rift zone. We consider, therefore, this segment of the EGU as part of the distal Late Permian rift zone, which finally led to the opening of the Meliata Ocean during Middle Triassic times. If true, the new data also imply that the stretched continental crust was potentially not much wider than ca. 100 km, was subducted and then rapidly exhumed during early Late Cretaceous times.
References
De Hoog, J.C.M., Janák, M., Vrabec, M., Hatton, K.H., 2011. In: Dobrzhinetskaya, L., Faryad, S.W., Wallis, S., Cuthbert, S. (Eds.), Ultrahigh-pressure Metamorphism: 25 Years After the Discovery of Coesite and Diamond. Elsevier Insights, pp. 399–439.
Janák, M., Froitzheim, N., Yoshida, K., Sasinková, V., Nosko, M., Kobayashi, T., Hirajima, T., Vrabec, M., 2015. Journal of Metamorphic Geology 33, 495–512.
Kirst, F., Sandmann. S., Nagel. T., et al. 2010. Geologica Carpathica 61(6), 451-461.
Knoll, T., Schuster, R., Huet, B., Mali, H., Onuk, P., Horschinegg, M., Ertl, A., Giester, G., 2018. Canadian Mineralogist 56, 489-528.
How to cite: Chang, R., Neubauer, F., Genser, J., Liu, Y., and Yuan, S.: Subduction of a rifted passive continental margin: the Pohorje case of Eastern Alps - constraints from geochronology and geochemistry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-448, https://doi.org/10.5194/egusphere-egu2020-448, 2020.
A-type subduction is considered to occur at the final stage of continent-continent collision. In many cases, the UHP/HP metamorphic conditions are well known but data on the type of subducted continental crust is lacking. In terms of end members, the type of subducted crust is either (1) normal thick continental crust or (2) the crust from the center of a rift zone, which is influenced by strong extension, high-temperature metamorphism due to thinning of even the continental mantle lithosphere and strong magmatism. To resolve these alternative scenarios, we investigated the southernmost part of the Eclogite-Gneiss Unit (EGU) of Cretaceous metamorphic age exposed in the Pohorje Mountains in Eastern Alps. There, UHP eclogites and ultramafic mantle rocks are exposed in a matrix of paragneiss and hitherto undated granitic orthogneises (Kirst et al., 2010). This study presents, for the first time, geochronological and geochemical data from newly discovered Permian granitic orthogneisses in this area. LA-ICP-MS zircon U–Pb ages of the orthogneisses are 255±2.2 Ma and 260±0.81 Ma, which are interpreted as the age of zircon crystallization in a magma. In contrast, all rounded zircons from paragneissic rocks give Cretaceous ages (89.34±0.69 Ma and 90.8±1.2 Ma), considered as the age of UHP/HP metamorphism. These zircons overgrew older zircons of Permian and rare older ages tentatively indicating that the metasedimentary could be not older than latest Permian. Zircon εHf(t) values of the four ortho- and paragneisses with (176Hf/177Hf) initial from 0.282201 to 0.282562, TDM2 are Proterozoic (1390~1970 Ma). The granitic orthogneisses show the geochemical features (high (La/Lu) N ratios (160.3–307.3), strong negative Eu anomalies) of an evolved granite molten from continental crust. This type of orthogneisses could be considered as the source magma of seemingly rootless Late Permian to Triassic pegmatites (Knoll et al., 2018) widespread within the EGU further to the north. The paragneisses are heterogeneously composed and are associated with eclogites and ultramafic cumulates of oceanic affinity (De Hoog et al., 2011). We argue that the Permian granitic orthogneisses might be derived from partial melting of lower crust in a rift zone. We consider, therefore, this segment of the EGU as part of the distal Late Permian rift zone, which finally led to the opening of the Meliata Ocean during Middle Triassic times. If true, the new data also imply that the stretched continental crust was potentially not much wider than ca. 100 km, was subducted and then rapidly exhumed during early Late Cretaceous times.
References
De Hoog, J.C.M., Janák, M., Vrabec, M., Hatton, K.H., 2011. In: Dobrzhinetskaya, L., Faryad, S.W., Wallis, S., Cuthbert, S. (Eds.), Ultrahigh-pressure Metamorphism: 25 Years After the Discovery of Coesite and Diamond. Elsevier Insights, pp. 399–439.
Janák, M., Froitzheim, N., Yoshida, K., Sasinková, V., Nosko, M., Kobayashi, T., Hirajima, T., Vrabec, M., 2015. Journal of Metamorphic Geology 33, 495–512.
Kirst, F., Sandmann. S., Nagel. T., et al. 2010. Geologica Carpathica 61(6), 451-461.
Knoll, T., Schuster, R., Huet, B., Mali, H., Onuk, P., Horschinegg, M., Ertl, A., Giester, G., 2018. Canadian Mineralogist 56, 489-528.
How to cite: Chang, R., Neubauer, F., Genser, J., Liu, Y., and Yuan, S.: Subduction of a rifted passive continental margin: the Pohorje case of Eastern Alps - constraints from geochronology and geochemistry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-448, https://doi.org/10.5194/egusphere-egu2020-448, 2020.
EGU2020-11134 | Displays | TS7.4 | Highlight
Using geodynamic modeling to test plate tectonic scenarios of the Mediterranean-Alpine areaBoris Kaus, Eline Le Breton, Georg Reuber, and Christian Schuler
Using geological and geophysical data, it is possible to reconstruct the past motion of tectonic plates involved in the Alpine orogeny and propose possible scenarios for their geological evolution. However, those scenarios have not yet been tested for geodynamic consistency.
Here, we perform 3D thermomechanical geodynamic simulations of the Mediterranean-Alpine area starting with a plate tectonic reconstruction at 20 Ma based on the work of Le Breton et al. (2017). The models include viscoelastoplastic rheologies and a free surface, and thus simulate the spontaneous occurrence of shear zones as well as the development of topography. Whereas some aspects of the tectonic reconstruction are well constrained (i.e. past position of the plates and subduction-collision fronts), many details such as the dip and length of the subducted plates, their thermal structure as well as their rheology, are unknown. The models are run forward in time to see to which extent they are consistent with the kinematic reconstructions. Perhaps unsurprisingly, our initial modelling attempts show a wide variety of behavior, including slab break off events and slab rollbacks in the wrong directions. Yet, in all cases tested so far, the model evolution does not reproduce the present-day geological setting, with Adria frequently moving too far towards the east and breaking apart internally, frequently no Alpine chain forming and in some cases new subduction zones developing within the Western Mediterranean that swallow Sardinia and Corsica.
Reproducing geological scenarios with thermomechanical geodynamic modelling thus requires substantial additional work, both from the modelling side (testing the effect of uncertain parameters on the behaviour of plates and subduction zones), as well as from the plate reconstruction side (assessing which parameters are well constrained and need to be reproduced). Nevertheless, interesting insights can already be obtained from our models, and in our presentation, we will highlight some of the links between interacting subducting plates and plate motion.
Le Breton E, Handy MR, Molli G, Ustaszewski K (2017) Post-20 Ma Motion of the Adriatic Plate: New Constraints From Surrounding Orogens and Implications for Crust-Mantle Decoupling. Tectonics 36:3135–3154. doi: 10.1002/2016TC004443
How to cite: Kaus, B., Le Breton, E., Reuber, G., and Schuler, C.: Using geodynamic modeling to test plate tectonic scenarios of the Mediterranean-Alpine area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11134, https://doi.org/10.5194/egusphere-egu2020-11134, 2020.
Using geological and geophysical data, it is possible to reconstruct the past motion of tectonic plates involved in the Alpine orogeny and propose possible scenarios for their geological evolution. However, those scenarios have not yet been tested for geodynamic consistency.
Here, we perform 3D thermomechanical geodynamic simulations of the Mediterranean-Alpine area starting with a plate tectonic reconstruction at 20 Ma based on the work of Le Breton et al. (2017). The models include viscoelastoplastic rheologies and a free surface, and thus simulate the spontaneous occurrence of shear zones as well as the development of topography. Whereas some aspects of the tectonic reconstruction are well constrained (i.e. past position of the plates and subduction-collision fronts), many details such as the dip and length of the subducted plates, their thermal structure as well as their rheology, are unknown. The models are run forward in time to see to which extent they are consistent with the kinematic reconstructions. Perhaps unsurprisingly, our initial modelling attempts show a wide variety of behavior, including slab break off events and slab rollbacks in the wrong directions. Yet, in all cases tested so far, the model evolution does not reproduce the present-day geological setting, with Adria frequently moving too far towards the east and breaking apart internally, frequently no Alpine chain forming and in some cases new subduction zones developing within the Western Mediterranean that swallow Sardinia and Corsica.
Reproducing geological scenarios with thermomechanical geodynamic modelling thus requires substantial additional work, both from the modelling side (testing the effect of uncertain parameters on the behaviour of plates and subduction zones), as well as from the plate reconstruction side (assessing which parameters are well constrained and need to be reproduced). Nevertheless, interesting insights can already be obtained from our models, and in our presentation, we will highlight some of the links between interacting subducting plates and plate motion.
Le Breton E, Handy MR, Molli G, Ustaszewski K (2017) Post-20 Ma Motion of the Adriatic Plate: New Constraints From Surrounding Orogens and Implications for Crust-Mantle Decoupling. Tectonics 36:3135–3154. doi: 10.1002/2016TC004443
How to cite: Kaus, B., Le Breton, E., Reuber, G., and Schuler, C.: Using geodynamic modeling to test plate tectonic scenarios of the Mediterranean-Alpine area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11134, https://doi.org/10.5194/egusphere-egu2020-11134, 2020.
EGU2020-20638 | Displays | TS7.4
Geodynamic evolution of the East Carpathian Foreland Basin since the Middle Miocene: Implications for sediment supply to the Black Sea and Dacian BasinArjan de Leeuw, Stephen Vincent, Anton Matoshko, Andrei Matoshko, Marius Stoica, and Igor Nicoara
The Carpathian orogen is part of the Alpine-Himalayan collision zone and formed as the result of the collision of the Tisza-Dacia and ALCAPA mega-units with the European southern margin, following a protracted phase of subduction, slab roll-back and accretionary wedge formation. The foreland basin of the East Carpathians is 800 km long and stretches out across Poland, Ukraine, Moldova and Romania. We use the results of our intensive field research to unravel the sedimentary architecture of this basin and reveal how it responded to the final phases of foreland vergent thrusting, continental collision and subsequent slab detachment. We discuss the asymmetry in the basins evolution and eventual inversion and relate this to the diachronous evolution of the Carpathian orogen. We also address the impact of changing subsidence patterns and base-level changes on connectivity with the Central and Eastern Paratethys, important for faunal exchange and patterns of endemism. We finally show that continental collision led to the establishment of a Late Miocene NW-SE prograding axial drainage system in the foreland supplying abundant sediment to the NW Black Sea, thus triggering large-scale shelf edge progradation.
How to cite: de Leeuw, A., Vincent, S., Matoshko, A., Matoshko, A., Stoica, M., and Nicoara, I.: Geodynamic evolution of the East Carpathian Foreland Basin since the Middle Miocene: Implications for sediment supply to the Black Sea and Dacian Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20638, https://doi.org/10.5194/egusphere-egu2020-20638, 2020.
The Carpathian orogen is part of the Alpine-Himalayan collision zone and formed as the result of the collision of the Tisza-Dacia and ALCAPA mega-units with the European southern margin, following a protracted phase of subduction, slab roll-back and accretionary wedge formation. The foreland basin of the East Carpathians is 800 km long and stretches out across Poland, Ukraine, Moldova and Romania. We use the results of our intensive field research to unravel the sedimentary architecture of this basin and reveal how it responded to the final phases of foreland vergent thrusting, continental collision and subsequent slab detachment. We discuss the asymmetry in the basins evolution and eventual inversion and relate this to the diachronous evolution of the Carpathian orogen. We also address the impact of changing subsidence patterns and base-level changes on connectivity with the Central and Eastern Paratethys, important for faunal exchange and patterns of endemism. We finally show that continental collision led to the establishment of a Late Miocene NW-SE prograding axial drainage system in the foreland supplying abundant sediment to the NW Black Sea, thus triggering large-scale shelf edge progradation.
How to cite: de Leeuw, A., Vincent, S., Matoshko, A., Matoshko, A., Stoica, M., and Nicoara, I.: Geodynamic evolution of the East Carpathian Foreland Basin since the Middle Miocene: Implications for sediment supply to the Black Sea and Dacian Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20638, https://doi.org/10.5194/egusphere-egu2020-20638, 2020.
EGU2020-7531 | Displays | TS7.4
The Neotethys suture in the eastern Bulgarian RhodopesJan Pleuger, Zlatka Cherneva, Linus Klug, Elis Hoffmann, Michael Schmidtke, Nikolaus Froitzheim, Neven Georgiev, Kalin Naydenov, Kristoph Stegmann, Alexandra Pohl, Marisa Germer, Alexander Borchert, and Martina Menneken
Following a tectonic scheme proposed by Janák et al. (2011; Journal of Metamorphic Geology 29, 317-332) and Pleuger et al. (2011; Zeitschrift der Deutschen Gesellschaft für Geowissenschaften 162, 171-192), the Rhodopes are composed of four nappe complexes, from bottom to top the Lower, Middle, and Upper Allochthon and the Circum-Rhodope Belt. Rocks derived from Adria and/or Pelagonia (Lower Allochthon) are separated from rocks of European origin (Upper Allochthon) by lithologically variegated thrust sheets containing sporadic occurrences of ophiolites (Middle Allochthon). These ophiolites typically yield magmatic protolith ages of c. 160 Ma and were metamorphosed under amphibolite- to eclogite-facies conditions. They represent Neotethyan lithosphere subducted below Europe in the Late Cretaceous to Palaeogene whereas the Circum-Rhodope Belt contains ophiolites of the same protolith age but with lower metamorphic grade (greenschist facies at most) and was obducted onto the former European margin in the Jurassic. We present LA-ICP-MS U-Pb zircon and additional geochemical data from the Luda Reka Unit in the Bulgarian Eastern Rhodopes. This unit consists mostly of amphibolite, metagabbro, and metadiorite that yielded two protolith ages of 163.5±2.6 Ma and 154.2±1.0 Ma. The trace element patterns resemble those of typical back-arc basalts and lower oceanic crustal cumulates. Initial epsilon Nd values of six samples calculated to 154 Ma were +10.8 ±0.8 (2σ; n = 6), in agreement with average basalts derived from depleted ambient mantle. A pegmatite crosscutting the Luda Reka Unit yielded a magmatic age of 52.04±1.1 Ma. Such pegmatites are widespread in the Luda Reka Unit (Middle Allochthon) suggesting that emplacement of this unit over the Bjala Reka Orthogneiss Unit (Lower Allochthon) where such pegmatites are lacking happened only after c. 52 Ma. The Bjala Reka Orthogneiss Unit forms the footwall of the top-to-the-SSW Bjala Reka Detachment that became active in the Late Eocene. Where the Luda Reka Unit is lacking, the Bjala Reka Orthogneiss Unit is overlain by rocks that were collectively described as “Low-grade Mesozoic Unit” (e.g. Bonev & Stampfli 2008; Lithos 100, 210-233). Based on peak temperatures determined by Raman spectroscopy of organic matter, two tectonic units can be distinguished in the “Low-grade Mesozoic Unit”. The temperature peak was at c. 530 °C in the Mandrica Unit below and at c. 285 °C in the Maglenica Unit above. For the Mandrica Unit, minimum peak pressures of c. 1.4 GPa were obtained by Raman spectroscopy of quartz inclusions in garnet, indicating that this unit underwent subduction-related metamorphism. Because of this marked difference in peak metamorphic grade, we attribute only the anchimetamorphic Maglenica Unit to the Circum-Rhodope Belt while the high-pressure Mandrica Unit probably represents the Upper Allochthon. Both units are presently separated by the top-to-the-NW Mandrica Detachment that was active before the Bjala Reka Detachment. Our new findings show that the easternmost Rhodopes expose a condensed section through all four nappe complexes, notably including the Neotethys suture.
How to cite: Pleuger, J., Cherneva, Z., Klug, L., Hoffmann, E., Schmidtke, M., Froitzheim, N., Georgiev, N., Naydenov, K., Stegmann, K., Pohl, A., Germer, M., Borchert, A., and Menneken, M.: The Neotethys suture in the eastern Bulgarian Rhodopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7531, https://doi.org/10.5194/egusphere-egu2020-7531, 2020.
Following a tectonic scheme proposed by Janák et al. (2011; Journal of Metamorphic Geology 29, 317-332) and Pleuger et al. (2011; Zeitschrift der Deutschen Gesellschaft für Geowissenschaften 162, 171-192), the Rhodopes are composed of four nappe complexes, from bottom to top the Lower, Middle, and Upper Allochthon and the Circum-Rhodope Belt. Rocks derived from Adria and/or Pelagonia (Lower Allochthon) are separated from rocks of European origin (Upper Allochthon) by lithologically variegated thrust sheets containing sporadic occurrences of ophiolites (Middle Allochthon). These ophiolites typically yield magmatic protolith ages of c. 160 Ma and were metamorphosed under amphibolite- to eclogite-facies conditions. They represent Neotethyan lithosphere subducted below Europe in the Late Cretaceous to Palaeogene whereas the Circum-Rhodope Belt contains ophiolites of the same protolith age but with lower metamorphic grade (greenschist facies at most) and was obducted onto the former European margin in the Jurassic. We present LA-ICP-MS U-Pb zircon and additional geochemical data from the Luda Reka Unit in the Bulgarian Eastern Rhodopes. This unit consists mostly of amphibolite, metagabbro, and metadiorite that yielded two protolith ages of 163.5±2.6 Ma and 154.2±1.0 Ma. The trace element patterns resemble those of typical back-arc basalts and lower oceanic crustal cumulates. Initial epsilon Nd values of six samples calculated to 154 Ma were +10.8 ±0.8 (2σ; n = 6), in agreement with average basalts derived from depleted ambient mantle. A pegmatite crosscutting the Luda Reka Unit yielded a magmatic age of 52.04±1.1 Ma. Such pegmatites are widespread in the Luda Reka Unit (Middle Allochthon) suggesting that emplacement of this unit over the Bjala Reka Orthogneiss Unit (Lower Allochthon) where such pegmatites are lacking happened only after c. 52 Ma. The Bjala Reka Orthogneiss Unit forms the footwall of the top-to-the-SSW Bjala Reka Detachment that became active in the Late Eocene. Where the Luda Reka Unit is lacking, the Bjala Reka Orthogneiss Unit is overlain by rocks that were collectively described as “Low-grade Mesozoic Unit” (e.g. Bonev & Stampfli 2008; Lithos 100, 210-233). Based on peak temperatures determined by Raman spectroscopy of organic matter, two tectonic units can be distinguished in the “Low-grade Mesozoic Unit”. The temperature peak was at c. 530 °C in the Mandrica Unit below and at c. 285 °C in the Maglenica Unit above. For the Mandrica Unit, minimum peak pressures of c. 1.4 GPa were obtained by Raman spectroscopy of quartz inclusions in garnet, indicating that this unit underwent subduction-related metamorphism. Because of this marked difference in peak metamorphic grade, we attribute only the anchimetamorphic Maglenica Unit to the Circum-Rhodope Belt while the high-pressure Mandrica Unit probably represents the Upper Allochthon. Both units are presently separated by the top-to-the-NW Mandrica Detachment that was active before the Bjala Reka Detachment. Our new findings show that the easternmost Rhodopes expose a condensed section through all four nappe complexes, notably including the Neotethys suture.
How to cite: Pleuger, J., Cherneva, Z., Klug, L., Hoffmann, E., Schmidtke, M., Froitzheim, N., Georgiev, N., Naydenov, K., Stegmann, K., Pohl, A., Germer, M., Borchert, A., and Menneken, M.: The Neotethys suture in the eastern Bulgarian Rhodopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7531, https://doi.org/10.5194/egusphere-egu2020-7531, 2020.
EGU2020-7529 | Displays | TS7.4
Role of dextral strike slip faulting in the distribution of Aegean extension since Miocene times inferred from receiver function analysisAgathe Faucher, Christel Tiberi, Frédéric Gueydan, and Alexandrine Gesret
Aegean plate is marked since Eocene by widespread NE-SW extension induced by the African slab roll-back. In Miocene times, E-W shortening created by the westward Anatolian extrusion overlays the extension, with the formation of Miocene dextral strike slip faults in addition to normal faults. We propose to quantify the role of large dextral strike slip faults in accommodating Aegean extension, using receiver functions to image Moho geometry.
Aegean extension is particularly evidenced by a topographic difference between the emerged continental Greece and the submerged Cyclades. In this study we characterize the associated Moho geometry with a particular focus on the transition between these two domains. From a geological point of view, the transition between continental Greece and the Cyclades is marked by two dextral strike slip faults: the Pelagonian fault (onshore) and the South Evvia fault (offshore). Our objective is also to show a potential Moho signature of these strike slip faults. We processed receiver functions (RF) from the MEDUSA stations located in Attic and Evvia.
Our results show that the Moho is deeper beneath continental Greece (~27km) than beneath the Cyclades (~25km). A detailed azimuthal study of RF distribution shows a flat Moho underneath Continental Greece. The crustal thickness is also almost constant inside the Cyclades, as already suggested by previous studies. However, the transition between the Cyclades and Continental Greece is not continuous. These two crustal blocks are separated by the Pelagonian and the South Evvia strike slip faults in a narrow transition zone (~75km). In this zone (South Evvia/Attica), dip and strike of the Moho vary and suggest a crustal signature of the strike slip structures observed at the surface. These strike slip faults therefore accommodate in a narrow zone the inferred variations in crustal thicknesses between the Cyclades and Continental Greece.
Our data show that differences in topography between Continental Greece and the Cyclades are isostatically compensated, reflecting various amount of crustal thinning larger in the Cyclades than in Continental Greece. Inside these two crustal blocks, we imaged a flat Moho, suggesting a wide rift extension process associated with the formation of numerous Miocene and Plio-Quaternary basins. The dextral strike slip faults at the edges of the continental blocks (Continental Greece and Cyclades) accommodated the inferred variations in the amount of crustal thinning, suggesting that they act as continental transfer zones at crustal-scale during Miocene Aegean Extension.
How to cite: Faucher, A., Tiberi, C., Gueydan, F., and Gesret, A.: Role of dextral strike slip faulting in the distribution of Aegean extension since Miocene times inferred from receiver function analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7529, https://doi.org/10.5194/egusphere-egu2020-7529, 2020.
Aegean plate is marked since Eocene by widespread NE-SW extension induced by the African slab roll-back. In Miocene times, E-W shortening created by the westward Anatolian extrusion overlays the extension, with the formation of Miocene dextral strike slip faults in addition to normal faults. We propose to quantify the role of large dextral strike slip faults in accommodating Aegean extension, using receiver functions to image Moho geometry.
Aegean extension is particularly evidenced by a topographic difference between the emerged continental Greece and the submerged Cyclades. In this study we characterize the associated Moho geometry with a particular focus on the transition between these two domains. From a geological point of view, the transition between continental Greece and the Cyclades is marked by two dextral strike slip faults: the Pelagonian fault (onshore) and the South Evvia fault (offshore). Our objective is also to show a potential Moho signature of these strike slip faults. We processed receiver functions (RF) from the MEDUSA stations located in Attic and Evvia.
Our results show that the Moho is deeper beneath continental Greece (~27km) than beneath the Cyclades (~25km). A detailed azimuthal study of RF distribution shows a flat Moho underneath Continental Greece. The crustal thickness is also almost constant inside the Cyclades, as already suggested by previous studies. However, the transition between the Cyclades and Continental Greece is not continuous. These two crustal blocks are separated by the Pelagonian and the South Evvia strike slip faults in a narrow transition zone (~75km). In this zone (South Evvia/Attica), dip and strike of the Moho vary and suggest a crustal signature of the strike slip structures observed at the surface. These strike slip faults therefore accommodate in a narrow zone the inferred variations in crustal thicknesses between the Cyclades and Continental Greece.
Our data show that differences in topography between Continental Greece and the Cyclades are isostatically compensated, reflecting various amount of crustal thinning larger in the Cyclades than in Continental Greece. Inside these two crustal blocks, we imaged a flat Moho, suggesting a wide rift extension process associated with the formation of numerous Miocene and Plio-Quaternary basins. The dextral strike slip faults at the edges of the continental blocks (Continental Greece and Cyclades) accommodated the inferred variations in the amount of crustal thinning, suggesting that they act as continental transfer zones at crustal-scale during Miocene Aegean Extension.
How to cite: Faucher, A., Tiberi, C., Gueydan, F., and Gesret, A.: Role of dextral strike slip faulting in the distribution of Aegean extension since Miocene times inferred from receiver function analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7529, https://doi.org/10.5194/egusphere-egu2020-7529, 2020.
EGU2020-7260 | Displays | TS7.4
Formation of a Late Cretaceous continental margin arc and an Early Cenozoic back-arc basin in the Kyrenia Range, northern Cyprus related to S-Neotethyan subductionGuohui Chen and Alastair Robertson
Field, geochemical and geochronological research on Late Cretaceous and Early Cenozoic volcanic rocks in Kyrenia Range provide constraints on the tectono-magmatic evolution of the northerly, active continental margin of the Southern Neotethys. Field mapping in the western Kyrenia Range demonstrates that frontal (southerly) thrust sheets are dominated by felsic volcanogenic rocks. U-Pb zircon dating indicates that the felsic volcanics erupted at 72.9 ± 1.0 Ma (Late Campanian). These volcanics are interpreted as the products of sub-aqueous continental margin arc volcanism based on geochemical evidence. The exposed arc volcanics are somewhat younger than arc-derived volcaniclastic sediments in W Cyprus (80.1 ± 1.1 Ma), and are also younger than arc-related granitic rocks (88-82 Ma) cutting the Tauride active continental margin (Malatya-Keban platform) in SE Turkey. Structurally higher (more northerly) imbricate thrust sheets include Late Cretaceous (Maastrichtian) and Early Cenozoic basalts that are underlain by a Mesozoic continental carbonate platform (metamorphosed), and interbedded with pelagic and redeposited carbonates that formed in an active continental margin setting. The basalts have within-plate geochemical characteristics, although with a variable subduction influence in some areas (e.g., western Kyrenia Range) that could be either be contemporaneous or inherited from Late Cretaceous (c. 70-80 Ma) subduction. Modern and ancient comparisons (e.g., Tyrrhenian Sea) suggest that the basaltic rocks represent incipient, extensional marginal basin formation. Integration with comparable evidence of continental margin arc magmatism in SE Turkey and elsewhere provides a picture of arc magmatism and marginal basin formation along an active continental margin, prior to collision during the Miocene.
How to cite: Chen, G. and Robertson, A.: Formation of a Late Cretaceous continental margin arc and an Early Cenozoic back-arc basin in the Kyrenia Range, northern Cyprus related to S-Neotethyan subduction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7260, https://doi.org/10.5194/egusphere-egu2020-7260, 2020.
Field, geochemical and geochronological research on Late Cretaceous and Early Cenozoic volcanic rocks in Kyrenia Range provide constraints on the tectono-magmatic evolution of the northerly, active continental margin of the Southern Neotethys. Field mapping in the western Kyrenia Range demonstrates that frontal (southerly) thrust sheets are dominated by felsic volcanogenic rocks. U-Pb zircon dating indicates that the felsic volcanics erupted at 72.9 ± 1.0 Ma (Late Campanian). These volcanics are interpreted as the products of sub-aqueous continental margin arc volcanism based on geochemical evidence. The exposed arc volcanics are somewhat younger than arc-derived volcaniclastic sediments in W Cyprus (80.1 ± 1.1 Ma), and are also younger than arc-related granitic rocks (88-82 Ma) cutting the Tauride active continental margin (Malatya-Keban platform) in SE Turkey. Structurally higher (more northerly) imbricate thrust sheets include Late Cretaceous (Maastrichtian) and Early Cenozoic basalts that are underlain by a Mesozoic continental carbonate platform (metamorphosed), and interbedded with pelagic and redeposited carbonates that formed in an active continental margin setting. The basalts have within-plate geochemical characteristics, although with a variable subduction influence in some areas (e.g., western Kyrenia Range) that could be either be contemporaneous or inherited from Late Cretaceous (c. 70-80 Ma) subduction. Modern and ancient comparisons (e.g., Tyrrhenian Sea) suggest that the basaltic rocks represent incipient, extensional marginal basin formation. Integration with comparable evidence of continental margin arc magmatism in SE Turkey and elsewhere provides a picture of arc magmatism and marginal basin formation along an active continental margin, prior to collision during the Miocene.
How to cite: Chen, G. and Robertson, A.: Formation of a Late Cretaceous continental margin arc and an Early Cenozoic back-arc basin in the Kyrenia Range, northern Cyprus related to S-Neotethyan subduction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7260, https://doi.org/10.5194/egusphere-egu2020-7260, 2020.
EGU2020-8898 | Displays | TS7.4 | Highlight
The Slab Puzzle of the Alpine-Mediterranean Region: Insights from a new, High-Resolution, Shear-Wave Velocity Model of the Upper MantleAmr El-Sharkawy, Thomas Meier, Sergei Lebedev, Jan Behrmann, Mona Hamada, Luigia Cristiano, Christian Weidle, and Daniel Köhn
The fascinatingly complex tectonic make-up of the Mediterranean region comprises small, strongly-curved retreating subduction zones, associated back-arc basins, and the continental collisions along the northern and eastern margins of the Adriatic microplate. It remains a challenge to resolve the geometry of the subducted slabs in the Mediterranean upper mantle. Here, we present new evidence for the location and lateral and vertical extent of slab segments from a new, high-resolution, Rayleigh-wave tomography. The tomographic model spans the depth range from the crust down to 300 km and is complemented by intermediate-deep seismicity data in the circum-Mediterranean region.
An automated procedure to measure inter-station Rayleigh wave phase velocities is applied to a large, heterogeneous dataset from all publically available stations around the Mediterranean in the time period from 1990 to 2015. Furthermore, for the first time, data from the Egyptian National Seismological Network (ENSN) are used regional seismic tomography. The resulting large set of about 200,000 inter-station phase velocity measurements is inverted for a set of phase-velocity maps spanning a very broad period range (8 - 350 s). The maps are then inverted, point by point, for a 3D, S-velocity model using a stochastic, particle-swarm-optimization inversion.
We distinguish between attached slab segments reaching down to the bottom of the model and shallow slabs of shorter length or detached slab segments resulting both from horizontal tearing. We discuss evidence for continental subduction east of Cyprus, for continuous NE-dipping subduction in the Antalyan region and NW dipping subduction in the SE Aegean in the area of Rhodes. An attached slab is imaged beneath the Hellenides reaching down to at least 300 km depth whereas beneath the Dinarides a short slab is found down to about 150 km depth above a slab tear. The slab in the southern Carpathians seems to be partly detached. A south-dipping slab is imaged in the central Alps but shallow bivergent subduction is favoured in the eastern Alps. In the western Alps, a shallow slab east-dipping Eurasian slab segment is in close proximity to the nearly vertically dipping attached slab segment beneath the northern Apennines and the southern Po plain. In the central Apennines a slab gap is found whereas the NE-dipping Calabrian Slab seems to partly detached along the northern Sicilian coast. The Kabylides Slab that appears to be attached along the North African coast but detached along the margin of the shelf in the Sicily Channel, is clearly separated from the Calabrian Slab in the NE and the Alboran-Betics Slab in the west. According to our model, the latter slab consists of two segments: a shallow Alboran one and a detached Betics slab segment. We summarize our interpretations in a map of the Mediterranean slab segments and indicate open questions.
How to cite: El-Sharkawy, A., Meier, T., Lebedev, S., Behrmann, J., Hamada, M., Cristiano, L., Weidle, C., and Köhn, D.: The Slab Puzzle of the Alpine-Mediterranean Region: Insights from a new, High-Resolution, Shear-Wave Velocity Model of the Upper Mantle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8898, https://doi.org/10.5194/egusphere-egu2020-8898, 2020.
The fascinatingly complex tectonic make-up of the Mediterranean region comprises small, strongly-curved retreating subduction zones, associated back-arc basins, and the continental collisions along the northern and eastern margins of the Adriatic microplate. It remains a challenge to resolve the geometry of the subducted slabs in the Mediterranean upper mantle. Here, we present new evidence for the location and lateral and vertical extent of slab segments from a new, high-resolution, Rayleigh-wave tomography. The tomographic model spans the depth range from the crust down to 300 km and is complemented by intermediate-deep seismicity data in the circum-Mediterranean region.
An automated procedure to measure inter-station Rayleigh wave phase velocities is applied to a large, heterogeneous dataset from all publically available stations around the Mediterranean in the time period from 1990 to 2015. Furthermore, for the first time, data from the Egyptian National Seismological Network (ENSN) are used regional seismic tomography. The resulting large set of about 200,000 inter-station phase velocity measurements is inverted for a set of phase-velocity maps spanning a very broad period range (8 - 350 s). The maps are then inverted, point by point, for a 3D, S-velocity model using a stochastic, particle-swarm-optimization inversion.
We distinguish between attached slab segments reaching down to the bottom of the model and shallow slabs of shorter length or detached slab segments resulting both from horizontal tearing. We discuss evidence for continental subduction east of Cyprus, for continuous NE-dipping subduction in the Antalyan region and NW dipping subduction in the SE Aegean in the area of Rhodes. An attached slab is imaged beneath the Hellenides reaching down to at least 300 km depth whereas beneath the Dinarides a short slab is found down to about 150 km depth above a slab tear. The slab in the southern Carpathians seems to be partly detached. A south-dipping slab is imaged in the central Alps but shallow bivergent subduction is favoured in the eastern Alps. In the western Alps, a shallow slab east-dipping Eurasian slab segment is in close proximity to the nearly vertically dipping attached slab segment beneath the northern Apennines and the southern Po plain. In the central Apennines a slab gap is found whereas the NE-dipping Calabrian Slab seems to partly detached along the northern Sicilian coast. The Kabylides Slab that appears to be attached along the North African coast but detached along the margin of the shelf in the Sicily Channel, is clearly separated from the Calabrian Slab in the NE and the Alboran-Betics Slab in the west. According to our model, the latter slab consists of two segments: a shallow Alboran one and a detached Betics slab segment. We summarize our interpretations in a map of the Mediterranean slab segments and indicate open questions.
How to cite: El-Sharkawy, A., Meier, T., Lebedev, S., Behrmann, J., Hamada, M., Cristiano, L., Weidle, C., and Köhn, D.: The Slab Puzzle of the Alpine-Mediterranean Region: Insights from a new, High-Resolution, Shear-Wave Velocity Model of the Upper Mantle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8898, https://doi.org/10.5194/egusphere-egu2020-8898, 2020.
EGU2020-189 | Displays | TS7.4
Western Anatolian Record of Subduction Initiation through CollisionMegan Mueller, Alexis Licht, Faruk Ocakoğlu, Clay Campbell, Mustafa Kaya, Begüm Kurtoğlu, Gui Akşit, Michael Taylor, Grégoire Métais, Pauline Coster, and K. Christopher Beard
The 1,700-km-long Izmir-Ankara-Erzincan suture (IAES) in Anatolia (Turkey) marks where Gondwanan and Laurasian microcontinents collided during the Cretaceous and Paleogene. The timing and dynamics of subduction and collision along the IAES are poorly constrained resulting in competitive paleogeographic scenarios requiring unique geodynamic and biogeographic reconstructions of the Mediterranean domain and broader Alpine-Zagros-Himalayan orogen. In western Anatolia, orogenic development following subduction initiation has been poorly documented. The timing of collision is debated: sometime in the Late Cretaceous to Early Eocene. Eocene slab breakoff is inferred from geochemical data but is either not supported or unresolved in mantle tomography and has not been tested using other techniques.
We use the Saricakaya and Central Sakarya Basins in western Anatolia to appraise models of subduction initiation, intercontinental collision and slab breakoff in northwest Turkey and to discuss the implications of our results for geodynamic evolution of the IAES. From measured sections, volcanic zircon geochronology, and sedimentary provenance proxies, we demonstrate that there was little topographic development associated with early subduction stages. We refine the age of intercontinental collision to the Maastrichtian-middle Paleocene. We challenge the interpretation of Eocene slab breakoff and provide a new model of syncollisional evolution in western Anatolia in which convergence, underthrusting, and accommodation space creation dominate during the early Eocene.
Finally, we compare results in western Anatolia to central Anatolia to determine that there was a synchronous magmatic history and onset of deformation along the IAES, thus supporting synchronous collision models of the IAES. The location, chronology and style of deformation and topographic development in western Anatolia is an important counterpoint to popular orogenic cyclicity models.
How to cite: Mueller, M., Licht, A., Ocakoğlu, F., Campbell, C., Kaya, M., Kurtoğlu, B., Akşit, G., Taylor, M., Métais, G., Coster, P., and Beard, K. C.: Western Anatolian Record of Subduction Initiation through Collision, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-189, https://doi.org/10.5194/egusphere-egu2020-189, 2020.
The 1,700-km-long Izmir-Ankara-Erzincan suture (IAES) in Anatolia (Turkey) marks where Gondwanan and Laurasian microcontinents collided during the Cretaceous and Paleogene. The timing and dynamics of subduction and collision along the IAES are poorly constrained resulting in competitive paleogeographic scenarios requiring unique geodynamic and biogeographic reconstructions of the Mediterranean domain and broader Alpine-Zagros-Himalayan orogen. In western Anatolia, orogenic development following subduction initiation has been poorly documented. The timing of collision is debated: sometime in the Late Cretaceous to Early Eocene. Eocene slab breakoff is inferred from geochemical data but is either not supported or unresolved in mantle tomography and has not been tested using other techniques.
We use the Saricakaya and Central Sakarya Basins in western Anatolia to appraise models of subduction initiation, intercontinental collision and slab breakoff in northwest Turkey and to discuss the implications of our results for geodynamic evolution of the IAES. From measured sections, volcanic zircon geochronology, and sedimentary provenance proxies, we demonstrate that there was little topographic development associated with early subduction stages. We refine the age of intercontinental collision to the Maastrichtian-middle Paleocene. We challenge the interpretation of Eocene slab breakoff and provide a new model of syncollisional evolution in western Anatolia in which convergence, underthrusting, and accommodation space creation dominate during the early Eocene.
Finally, we compare results in western Anatolia to central Anatolia to determine that there was a synchronous magmatic history and onset of deformation along the IAES, thus supporting synchronous collision models of the IAES. The location, chronology and style of deformation and topographic development in western Anatolia is an important counterpoint to popular orogenic cyclicity models.
How to cite: Mueller, M., Licht, A., Ocakoğlu, F., Campbell, C., Kaya, M., Kurtoğlu, B., Akşit, G., Taylor, M., Métais, G., Coster, P., and Beard, K. C.: Western Anatolian Record of Subduction Initiation through Collision, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-189, https://doi.org/10.5194/egusphere-egu2020-189, 2020.
EGU2020-322 | Displays | TS7.4
Geochronology and Lu-Hf isotopic study of the granodioritic pulse in the Qaradagh batholith (NW Iran)Vartan Simmonds, Mohssen Moazzen, Gültekin Topuz, and Ali Mohammadi
The Qaradagh batholith in northwest Iran mainly comprises granodioritic rocks, which makes more than 50% of the batholith. This lithology is the first intrusive pulse within this batholith and the oldest Tertiary magmatism in the region, though other younger pulses of granite, diorite, quartz-diorite, syenite, quartz-syenite, monzonite, quartz-monzonite, quartz monzodiorite, monzogranite and gabbro intruded the main body. These magmatic rocks have intruded the Upper Cretaceous and Paleogene sedimentary, volcano-sedimentary and igneous rocks.
The Qaradagh batholith hosts vein-type and some local stock-work type Cu–Au–Mo mineralization, especially in its central parts, while skarn-type deposits have been formed at its contacts with peripheral carbonate rocks. Its extension towards the north into the neighboring south Armenia (which is part of the South Armenian Block) is known as the Meghri–Ordubad pluton (MOP), which hosts several large porphyry Cu–Mo deposits and other precious and base metal mineralizations. U–Pb geochronology on the zircons separated from the granodioritic unit yielded a weighted 206Pb/238U mean age of 43.81 ± 0.18 (MSWD=1.38) and a Pb*/U concordia age of 44.04 ± 1.00 Ma (MSWD= 24), which correspond to Middle Eocene.
Since the Qaradagh batholith and especially its earliest magmatic phase are considered as the oldest plutonic event of the Cenozoic age in northwest Iran, thus this investigation testifies to the fact that intrusive activities of Tertiary in this region has commenced in Middle Eocene, contrary to the opinion of the majority of authors who believe that plutonism in this region occurred during Oligocene.
However, this age is much older than the molybdenite Re–Os ages of quartz-sulfide veins hosted by granodioritic rocks (25.19 ± 0.19 to 31.22 ± 0.28 Ma), indicating that mineralization in this batholith is related to another much younger intrusive phase, and even to several phases, as the published ages of molybdenites from various veins and mineralized zones show a large interval. Comparing the obtained age with those from the MOP in southern Armenia indicate that southern part of the MOP is almost coeval with the emplacement of the granodioritic rocks in Qaradagh batholith.
The U and Th contents of the zircons range from 17.1 to 1534.0 and from 4.9 to 641.0 ppm, respectively, with Th/U ratios between 0.66 and 5.82 (mean of 1.26), indicating a magmatic source. Meanwhile, the εHf(t) values of the zircons range from 8.7 to 11.1 with the mean of 9.5, which are plotted between the CHUR and the Depleted Mantle evolution lines, indicating a juvenile and homogeneous magmatic source and the predominance of mantle-derived magmas with limited crustal assimilation.
How to cite: Simmonds, V., Moazzen, M., Topuz, G., and Mohammadi, A.: Geochronology and Lu-Hf isotopic study of the granodioritic pulse in the Qaradagh batholith (NW Iran), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-322, https://doi.org/10.5194/egusphere-egu2020-322, 2020.
The Qaradagh batholith in northwest Iran mainly comprises granodioritic rocks, which makes more than 50% of the batholith. This lithology is the first intrusive pulse within this batholith and the oldest Tertiary magmatism in the region, though other younger pulses of granite, diorite, quartz-diorite, syenite, quartz-syenite, monzonite, quartz-monzonite, quartz monzodiorite, monzogranite and gabbro intruded the main body. These magmatic rocks have intruded the Upper Cretaceous and Paleogene sedimentary, volcano-sedimentary and igneous rocks.
The Qaradagh batholith hosts vein-type and some local stock-work type Cu–Au–Mo mineralization, especially in its central parts, while skarn-type deposits have been formed at its contacts with peripheral carbonate rocks. Its extension towards the north into the neighboring south Armenia (which is part of the South Armenian Block) is known as the Meghri–Ordubad pluton (MOP), which hosts several large porphyry Cu–Mo deposits and other precious and base metal mineralizations. U–Pb geochronology on the zircons separated from the granodioritic unit yielded a weighted 206Pb/238U mean age of 43.81 ± 0.18 (MSWD=1.38) and a Pb*/U concordia age of 44.04 ± 1.00 Ma (MSWD= 24), which correspond to Middle Eocene.
Since the Qaradagh batholith and especially its earliest magmatic phase are considered as the oldest plutonic event of the Cenozoic age in northwest Iran, thus this investigation testifies to the fact that intrusive activities of Tertiary in this region has commenced in Middle Eocene, contrary to the opinion of the majority of authors who believe that plutonism in this region occurred during Oligocene.
However, this age is much older than the molybdenite Re–Os ages of quartz-sulfide veins hosted by granodioritic rocks (25.19 ± 0.19 to 31.22 ± 0.28 Ma), indicating that mineralization in this batholith is related to another much younger intrusive phase, and even to several phases, as the published ages of molybdenites from various veins and mineralized zones show a large interval. Comparing the obtained age with those from the MOP in southern Armenia indicate that southern part of the MOP is almost coeval with the emplacement of the granodioritic rocks in Qaradagh batholith.
The U and Th contents of the zircons range from 17.1 to 1534.0 and from 4.9 to 641.0 ppm, respectively, with Th/U ratios between 0.66 and 5.82 (mean of 1.26), indicating a magmatic source. Meanwhile, the εHf(t) values of the zircons range from 8.7 to 11.1 with the mean of 9.5, which are plotted between the CHUR and the Depleted Mantle evolution lines, indicating a juvenile and homogeneous magmatic source and the predominance of mantle-derived magmas with limited crustal assimilation.
How to cite: Simmonds, V., Moazzen, M., Topuz, G., and Mohammadi, A.: Geochronology and Lu-Hf isotopic study of the granodioritic pulse in the Qaradagh batholith (NW Iran), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-322, https://doi.org/10.5194/egusphere-egu2020-322, 2020.
EGU2020-3709 | Displays | TS7.4
Migration of post-collisional volcanism in northwestern Iran at plate tectonic velocitiesAxel Schmitt, Jalil Ghalamghash, Razieh Chaharlang, Jamshid Hassanzadeh, and Seyed Mousavi
Post-collisional magmatism of Neogene-Quaternary age is manifested in a long but disjointed belt of volcanoes broadly paralleling the Arabia-Eurasia suture zone. Volcanic compositions in this belt share geochemical characteristics with subduction-related magmas, yet they postdate subduction and formed in the wake of continental collision. Potential mechanisms for melt generation in the absence of subduction include slab break-off, lithospheric mantle delamination, or incorporation of fusible crustal rocks or sediment into the mantle through subduction or collision, leading to volcanism seemingly randomly distributed in time and space. In northwestern Iran, the two largest post-collisional volcanic centers are Sahand and Sabalan stratocones, which are located at distances of 150 and 300 km on a line perpendicular to the strike of the suture zone, where they overlie rocks of the Eocene-Oligocene Urumieh-Dokhtar magmatic arc. Here, we present U-Pb zircon ages for intermediate lavas and pyroclastic rocks from Sabalan volcano which complement published data for the Sahand and Sabalan systems [1, 2]. In both sample suites, inherited zircon from the basement is scarce and restricted to Cretaceous and Eocene-Oligocene ages for Sahand, and Archean, late Proterozoic and Oligocene-Miocene ages for Sabalan. Individual samples display coherent young populations that likely crystallized shortly before eruption. In addition, many samples show evidence of antecrystic zircon, indicating a long-lived subvolcanic reservoir where older intrusive rocks became recycled. Because of this recycling, the overall zircon age distribution of each volcano better represents the duration of magmatic activity than a compilation of eruption ages would. Based on the oldest antecrystic zircon ages, the onset of magmatism is constrained to ca. 10 Ma for Sahand, and ca. 5 Ma for Sabalan. This age difference shows a progression in the onset of magmatism that is consistent with plate tectonic velocities of ~30 mm/a. This rate and the northeastward direction of the volcanic migration also matches the reconstructed convergence of the Neotethyan oceanic lithosphere towards Eurasia. Apparent pulses in zircon production for both, Sahand and Sabalan, as well as a tailing off in the frequency of older ages are likely due to sampling bias of the volcanic stratigraphy, where younger eruptive products may have destroyed or obscured older units. Regardless of this bias, U-Pb and U-Th disequilibrium zircon ages from both volcanoes consistently indicate late Pleistocene eruptions as young as <173 ka and <110 ka for Sahand and Sabalan, respectively. The systematic younging of the onset of volcanism for these two volumetric dominant volcanic centers in northwestern Iran suggests that passage of a detached oceanic slab following closure of the Neotethys is a viable mechanism for post-collisional magmatism in the region.
[1] Ghalamghash, J., Schmitt, A. K., & Chaharlang, R. (2019), Lithos, 344, 265-279.
[2] Ghalamghash, J., Mousavi, S. Z., Hassanzadeh, J., & Schmitt, A. K. (2016), J Volc Geotherm Res, 327, 192-207.
How to cite: Schmitt, A., Ghalamghash, J., Chaharlang, R., Hassanzadeh, J., and Mousavi, S.: Migration of post-collisional volcanism in northwestern Iran at plate tectonic velocities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3709, https://doi.org/10.5194/egusphere-egu2020-3709, 2020.
Post-collisional magmatism of Neogene-Quaternary age is manifested in a long but disjointed belt of volcanoes broadly paralleling the Arabia-Eurasia suture zone. Volcanic compositions in this belt share geochemical characteristics with subduction-related magmas, yet they postdate subduction and formed in the wake of continental collision. Potential mechanisms for melt generation in the absence of subduction include slab break-off, lithospheric mantle delamination, or incorporation of fusible crustal rocks or sediment into the mantle through subduction or collision, leading to volcanism seemingly randomly distributed in time and space. In northwestern Iran, the two largest post-collisional volcanic centers are Sahand and Sabalan stratocones, which are located at distances of 150 and 300 km on a line perpendicular to the strike of the suture zone, where they overlie rocks of the Eocene-Oligocene Urumieh-Dokhtar magmatic arc. Here, we present U-Pb zircon ages for intermediate lavas and pyroclastic rocks from Sabalan volcano which complement published data for the Sahand and Sabalan systems [1, 2]. In both sample suites, inherited zircon from the basement is scarce and restricted to Cretaceous and Eocene-Oligocene ages for Sahand, and Archean, late Proterozoic and Oligocene-Miocene ages for Sabalan. Individual samples display coherent young populations that likely crystallized shortly before eruption. In addition, many samples show evidence of antecrystic zircon, indicating a long-lived subvolcanic reservoir where older intrusive rocks became recycled. Because of this recycling, the overall zircon age distribution of each volcano better represents the duration of magmatic activity than a compilation of eruption ages would. Based on the oldest antecrystic zircon ages, the onset of magmatism is constrained to ca. 10 Ma for Sahand, and ca. 5 Ma for Sabalan. This age difference shows a progression in the onset of magmatism that is consistent with plate tectonic velocities of ~30 mm/a. This rate and the northeastward direction of the volcanic migration also matches the reconstructed convergence of the Neotethyan oceanic lithosphere towards Eurasia. Apparent pulses in zircon production for both, Sahand and Sabalan, as well as a tailing off in the frequency of older ages are likely due to sampling bias of the volcanic stratigraphy, where younger eruptive products may have destroyed or obscured older units. Regardless of this bias, U-Pb and U-Th disequilibrium zircon ages from both volcanoes consistently indicate late Pleistocene eruptions as young as <173 ka and <110 ka for Sahand and Sabalan, respectively. The systematic younging of the onset of volcanism for these two volumetric dominant volcanic centers in northwestern Iran suggests that passage of a detached oceanic slab following closure of the Neotethys is a viable mechanism for post-collisional magmatism in the region.
[1] Ghalamghash, J., Schmitt, A. K., & Chaharlang, R. (2019), Lithos, 344, 265-279.
[2] Ghalamghash, J., Mousavi, S. Z., Hassanzadeh, J., & Schmitt, A. K. (2016), J Volc Geotherm Res, 327, 192-207.
How to cite: Schmitt, A., Ghalamghash, J., Chaharlang, R., Hassanzadeh, J., and Mousavi, S.: Migration of post-collisional volcanism in northwestern Iran at plate tectonic velocities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3709, https://doi.org/10.5194/egusphere-egu2020-3709, 2020.
EGU2020-304 | Displays | TS7.4
The Durkan Complex in the western Makran Accretionary Prism (SE Iran): Evidence for a Late Cretaceous tectonically disrupted oceanic seamountEdoardo Barbero, Morteza Delavari, Asghar Dolati, Luca Pandolfi, Emilio Saccani, Michele Marroni, Marco Chiari, Valeria Luciani, and Rita Catanzariti
The Makran Accretionary Prism (SE of Iran) represents the less known segment of the Alpine-Himalayan orogenic system. It results from the Cretaceous to present-day convergence between the Arabian and Eurasian plates that was accommodated by the northward subduction of the Neotethys Ocean below the southern margin of Eurasia. As a peculiar feature, the Makran is the only segment of the Alpine-Himalayan orogenic system, in which subduction is still active. The North Makran is the innermost structural domain of the accretionary wedge. It consists of distinct complexes and tectonic units representing remnants of the Cretaceous-Paleocene accretionary-subduction phases. Among these, the Durkan Complex consists of several tectonic units, which include deformed Early Cretaceous-Paleocene carbonatic and volcanic successions, as well as rare Carboniferous, Permian and Jurassic slices of platform limestones. The Durkan Complex is commonly interpreted as representing the disrupted sedimentary cover of the passive margin of a micro-continent known in literature as the Bajgan-Durkan Complex. However, its stratigraphic succession, as well as the age and geochemistry of the volcanic rocks are still poorly known. Nevertheless, such data are fundamental for constraining its meaning for the pre-Eocene geodynamic evolution of the Makran Accretionary Prism. For this reason, we present new stratigraphic and petrological data on the westernmost sector of the Durkan Complex.
Our data show that the Durkan Complex includes distinct tectonic slices showing both slightly metamorphic and non-metamorphic highly-deformed stratigraphic successions. Stratigraphic data allow us to recognize three main types of successions. Type I consists of an alternation of pillow lavas and Albian-Cenomanian pelagic shales and radiolarites. Type II consists of pillow and massive lavas with minor volcaniclastic arenites grading up to an alternation of volcanic and volcaniclastic rocks and Cenomanian pelagic limestones and shales. Local intercalations of mass-transport deposits are common, particularly in the upper part of the sequence. Type III consists of pillow lava flows, volcanic breccia, and volcaniclastic sandstone overlain by an Albian-Cenomanian carbonatic platform. All these successions are stratigraphically overlain by a post-Cenomanian pelagic and hemipelagic sequence. Ages were determined by foraminifera and radiolarian biostratigraphy. The volcanic rocks in the distinct successions show similar geochemical features. They consist of basalt and minor trachybasalt showing alkaline affinity with high Nb/Y ratios (0.62 – 4.4), as well as marked LREE/HREE enrichment. The overall geochemical features of the rocks are comparable with those of alkaline oceanic within-plate basalts and plume-type MORBs.
In summary, our data show that the rock assemblages of the Durkan Complex represent the remnants of a seamount rather than remnants of continental margin successions, as it was previously described. The distinct successions of the Durkan Complex show tectono-stratigraphic features that can be reconciled to the cap (Type III), the slope (Type II), and the foothill (Type I) of a typical seamount environment. Finally, our new findings and regional-scale comparisons suggest that the Late Cretaceous alkaline magmatic pulse recorded in the Durkan Complex was likely related to mantle plume activity in the Makran sector of the Neotethys.
How to cite: Barbero, E., Delavari, M., Dolati, A., Pandolfi, L., Saccani, E., Marroni, M., Chiari, M., Luciani, V., and Catanzariti, R.: The Durkan Complex in the western Makran Accretionary Prism (SE Iran): Evidence for a Late Cretaceous tectonically disrupted oceanic seamount, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-304, https://doi.org/10.5194/egusphere-egu2020-304, 2020.
The Makran Accretionary Prism (SE of Iran) represents the less known segment of the Alpine-Himalayan orogenic system. It results from the Cretaceous to present-day convergence between the Arabian and Eurasian plates that was accommodated by the northward subduction of the Neotethys Ocean below the southern margin of Eurasia. As a peculiar feature, the Makran is the only segment of the Alpine-Himalayan orogenic system, in which subduction is still active. The North Makran is the innermost structural domain of the accretionary wedge. It consists of distinct complexes and tectonic units representing remnants of the Cretaceous-Paleocene accretionary-subduction phases. Among these, the Durkan Complex consists of several tectonic units, which include deformed Early Cretaceous-Paleocene carbonatic and volcanic successions, as well as rare Carboniferous, Permian and Jurassic slices of platform limestones. The Durkan Complex is commonly interpreted as representing the disrupted sedimentary cover of the passive margin of a micro-continent known in literature as the Bajgan-Durkan Complex. However, its stratigraphic succession, as well as the age and geochemistry of the volcanic rocks are still poorly known. Nevertheless, such data are fundamental for constraining its meaning for the pre-Eocene geodynamic evolution of the Makran Accretionary Prism. For this reason, we present new stratigraphic and petrological data on the westernmost sector of the Durkan Complex.
Our data show that the Durkan Complex includes distinct tectonic slices showing both slightly metamorphic and non-metamorphic highly-deformed stratigraphic successions. Stratigraphic data allow us to recognize three main types of successions. Type I consists of an alternation of pillow lavas and Albian-Cenomanian pelagic shales and radiolarites. Type II consists of pillow and massive lavas with minor volcaniclastic arenites grading up to an alternation of volcanic and volcaniclastic rocks and Cenomanian pelagic limestones and shales. Local intercalations of mass-transport deposits are common, particularly in the upper part of the sequence. Type III consists of pillow lava flows, volcanic breccia, and volcaniclastic sandstone overlain by an Albian-Cenomanian carbonatic platform. All these successions are stratigraphically overlain by a post-Cenomanian pelagic and hemipelagic sequence. Ages were determined by foraminifera and radiolarian biostratigraphy. The volcanic rocks in the distinct successions show similar geochemical features. They consist of basalt and minor trachybasalt showing alkaline affinity with high Nb/Y ratios (0.62 – 4.4), as well as marked LREE/HREE enrichment. The overall geochemical features of the rocks are comparable with those of alkaline oceanic within-plate basalts and plume-type MORBs.
In summary, our data show that the rock assemblages of the Durkan Complex represent the remnants of a seamount rather than remnants of continental margin successions, as it was previously described. The distinct successions of the Durkan Complex show tectono-stratigraphic features that can be reconciled to the cap (Type III), the slope (Type II), and the foothill (Type I) of a typical seamount environment. Finally, our new findings and regional-scale comparisons suggest that the Late Cretaceous alkaline magmatic pulse recorded in the Durkan Complex was likely related to mantle plume activity in the Makran sector of the Neotethys.
How to cite: Barbero, E., Delavari, M., Dolati, A., Pandolfi, L., Saccani, E., Marroni, M., Chiari, M., Luciani, V., and Catanzariti, R.: The Durkan Complex in the western Makran Accretionary Prism (SE Iran): Evidence for a Late Cretaceous tectonically disrupted oceanic seamount, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-304, https://doi.org/10.5194/egusphere-egu2020-304, 2020.
EGU2020-7360 | Displays | TS7.4
Slip-sense inversion in Iran: Implications for Eurasian tectonicsBernard Guest
The left-lateral Doruneh Fault System (DFS) bounds the north margin of the Central Iranian microplate, and has played an important role in the structural evolution of the Turkish-Iranian Plateau and of Afghanistan. The western termination of the DFS is a sinistral synthetic branch fault array that shows clear kinematic evidence of having undergone recent slip sense inversion from a dextral array to a sinistral array in the latest Neogene or earliest Quaternary. Similarly, kinematic evidence from the Anarak Metamorphic complex at the southwestern most branch of the DFS terminal fault array suggests that this core complex formed at a transpressive left stepping termination and that it was inverted in the latest Neogene to a transtensional fault termination. The recognition that the DFS and possibly other faults in NE Iran were inverted from dextral to sinistral strike slip in the latest Neogene, and the likely connection between the DFS and the Herat Fault of Afghanistan suggests that the evolutions of Afghanistan and the Indo-Asian collisional system are linked to the tectonic evolution of the Turkish-Iranian Plateau. This speculative model explains the Late Neogene tectonic realignment of the Arabia-Eurasia collision zone in terms of the interaction between the Afghan blocks that were extruding west from the Indo-Asian collision and the Turkish Iranian collision zone that was evolving to the east as Arabia sutured diachronously with Eurasia. The collision of the Afghan blocks with East Iran effectively locked the respective eastern and western free boundaries for the Arabia-Eurasia, and Indo-Asian collisional belts and forced them to diverge away from one another. If confirmed, this explains the Late Miocene to Pliocene tectonic reorganization that is recognized across the Middle East and has implications for geologic process models across the region. Regional tectonic reorganization and/or inversion may (1) invert and possibly breach older Cenozoic structures while forming a younger generation of post-Miocene structures, (2) reorganize drainage and sediment supply networks, and sealing and obscuring older structural and stratigraphic bodies under younger sediments, (3) rejuvenate existing structures and trigger secondary fluid migration, and (4) increase exhumation, sediment supply, and subsidence in late Neogene basins across the region.
How to cite: Guest, B.: Slip-sense inversion in Iran: Implications for Eurasian tectonics , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7360, https://doi.org/10.5194/egusphere-egu2020-7360, 2020.
The left-lateral Doruneh Fault System (DFS) bounds the north margin of the Central Iranian microplate, and has played an important role in the structural evolution of the Turkish-Iranian Plateau and of Afghanistan. The western termination of the DFS is a sinistral synthetic branch fault array that shows clear kinematic evidence of having undergone recent slip sense inversion from a dextral array to a sinistral array in the latest Neogene or earliest Quaternary. Similarly, kinematic evidence from the Anarak Metamorphic complex at the southwestern most branch of the DFS terminal fault array suggests that this core complex formed at a transpressive left stepping termination and that it was inverted in the latest Neogene to a transtensional fault termination. The recognition that the DFS and possibly other faults in NE Iran were inverted from dextral to sinistral strike slip in the latest Neogene, and the likely connection between the DFS and the Herat Fault of Afghanistan suggests that the evolutions of Afghanistan and the Indo-Asian collisional system are linked to the tectonic evolution of the Turkish-Iranian Plateau. This speculative model explains the Late Neogene tectonic realignment of the Arabia-Eurasia collision zone in terms of the interaction between the Afghan blocks that were extruding west from the Indo-Asian collision and the Turkish Iranian collision zone that was evolving to the east as Arabia sutured diachronously with Eurasia. The collision of the Afghan blocks with East Iran effectively locked the respective eastern and western free boundaries for the Arabia-Eurasia, and Indo-Asian collisional belts and forced them to diverge away from one another. If confirmed, this explains the Late Miocene to Pliocene tectonic reorganization that is recognized across the Middle East and has implications for geologic process models across the region. Regional tectonic reorganization and/or inversion may (1) invert and possibly breach older Cenozoic structures while forming a younger generation of post-Miocene structures, (2) reorganize drainage and sediment supply networks, and sealing and obscuring older structural and stratigraphic bodies under younger sediments, (3) rejuvenate existing structures and trigger secondary fluid migration, and (4) increase exhumation, sediment supply, and subsidence in late Neogene basins across the region.
How to cite: Guest, B.: Slip-sense inversion in Iran: Implications for Eurasian tectonics , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7360, https://doi.org/10.5194/egusphere-egu2020-7360, 2020.
EGU2020-4012 | Displays | TS7.4
Crustal Structure and Earthquakes beneath the Jammu and Kashmir HimalayaSupriyo Mitra, Swati Sharma, Debarchan Powali, Keith Priestley, and Sunil Wanchoo
We use P-wave receiver function (P-RF) analysis of broadband teleseismic data recorded at twenty two stations spanning the Jammu-Kishtwar Himalaya, Pir Panjal Ranges, Kashmir Valley, and Zanskar Ranges in Northwest Himalaya to model the seismic velocity structures of the crust and the uppermost mantle. Our network extends from the Shiwalik Himalaya (S) to the Tethyan Himalaya (N), across the major Himalayan thrust systems and litho-tectonic units. We perform Vp/Vs-Depth stacking of P-RF and joint inversion with surface wave dispersion data. Our analysis show that the underthrust Indian crust, beneath the Jammu-Kishtwar Himalaya, has an average thickness of ~40 km and dips northward at ~7-9º. The overlying Himalayan wedge increases in thickness northward from the Shiwalik Himalaya (~8–10 km) to the Tethyan Himalaya (~25–30 km). The underthrust Indian crust Moho is marked by a large positive impedance contrast and lies at a depth of ~45 km beneath the Shiwalik Himalaya and ~65 km beneath the Higher Himalaya, deepening northward beneath the Tethyan Himalaya. We observe Moho flexure across the Mandli-Kishanpur Thrust (MKT), in the Shiwalik Himalaya, and beneath the Kishtwar window. Each time to Moho deepens by ~10 km, from ~45 km to ~55 km, and from ~55 km to ~65 km, respectively. The Moho is remarkably flat at ~56 km beneath the Pir Panjal Ranges, from its southern foothills to the northern flank in the Kashmir Valley. North of the Kashmir Valley the Moho dips steeply underneath the Zanskar Ranges from ~56 km to ~62 km. Along the Jammu-Kishtwar common conversion point (CCP) profile the Main Himalayan Thrust (MHT) is highlighted by the low velocity layer (LVL) at a depth of ~8 km beneath the Shiwalik Himalaya to ~25 km beneath the Higher Himalaya. The average dip on the MHT is ~9º and has a frontal ramp beneath the Kishtwar window. The MKT, MBT and MCT are marked by LVLs which splays updip from the MHT. Average crustal Vp/Vs shows that beneath the Shiwalik Himalaya, west of the MFT anticline the crust is mafic in nature while towards the east the crust is felsic in nature. Beneath the Lesser Himalaya the crust is largely felsic, while beneath the Pir Panjal range the crust is intermediate to mafic. North of the Kashmir Valley, beneath the Zanskar range the crust is felsic to intermediate in nature. We compare the source mechanism of the 2013 Kishtwar earthquake (Mw 5.7) and hypocentral location of small-to-moderate earthquake beneath Kishtwar region with the CCP profile. Our results show that these earthquakes occurred on or above the MHT in the unlocking zone, between the frictionally locked shallow segment and deeper creeping segment of the MHT. This marks the zone of stress build-up on the MHT in the interseismic period and is possibly the zone of megathrust initiation.
How to cite: Mitra, S., Sharma, S., Powali, D., Priestley, K., and Wanchoo, S.: Crustal Structure and Earthquakes beneath the Jammu and Kashmir Himalaya, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4012, https://doi.org/10.5194/egusphere-egu2020-4012, 2020.
We use P-wave receiver function (P-RF) analysis of broadband teleseismic data recorded at twenty two stations spanning the Jammu-Kishtwar Himalaya, Pir Panjal Ranges, Kashmir Valley, and Zanskar Ranges in Northwest Himalaya to model the seismic velocity structures of the crust and the uppermost mantle. Our network extends from the Shiwalik Himalaya (S) to the Tethyan Himalaya (N), across the major Himalayan thrust systems and litho-tectonic units. We perform Vp/Vs-Depth stacking of P-RF and joint inversion with surface wave dispersion data. Our analysis show that the underthrust Indian crust, beneath the Jammu-Kishtwar Himalaya, has an average thickness of ~40 km and dips northward at ~7-9º. The overlying Himalayan wedge increases in thickness northward from the Shiwalik Himalaya (~8–10 km) to the Tethyan Himalaya (~25–30 km). The underthrust Indian crust Moho is marked by a large positive impedance contrast and lies at a depth of ~45 km beneath the Shiwalik Himalaya and ~65 km beneath the Higher Himalaya, deepening northward beneath the Tethyan Himalaya. We observe Moho flexure across the Mandli-Kishanpur Thrust (MKT), in the Shiwalik Himalaya, and beneath the Kishtwar window. Each time to Moho deepens by ~10 km, from ~45 km to ~55 km, and from ~55 km to ~65 km, respectively. The Moho is remarkably flat at ~56 km beneath the Pir Panjal Ranges, from its southern foothills to the northern flank in the Kashmir Valley. North of the Kashmir Valley the Moho dips steeply underneath the Zanskar Ranges from ~56 km to ~62 km. Along the Jammu-Kishtwar common conversion point (CCP) profile the Main Himalayan Thrust (MHT) is highlighted by the low velocity layer (LVL) at a depth of ~8 km beneath the Shiwalik Himalaya to ~25 km beneath the Higher Himalaya. The average dip on the MHT is ~9º and has a frontal ramp beneath the Kishtwar window. The MKT, MBT and MCT are marked by LVLs which splays updip from the MHT. Average crustal Vp/Vs shows that beneath the Shiwalik Himalaya, west of the MFT anticline the crust is mafic in nature while towards the east the crust is felsic in nature. Beneath the Lesser Himalaya the crust is largely felsic, while beneath the Pir Panjal range the crust is intermediate to mafic. North of the Kashmir Valley, beneath the Zanskar range the crust is felsic to intermediate in nature. We compare the source mechanism of the 2013 Kishtwar earthquake (Mw 5.7) and hypocentral location of small-to-moderate earthquake beneath Kishtwar region with the CCP profile. Our results show that these earthquakes occurred on or above the MHT in the unlocking zone, between the frictionally locked shallow segment and deeper creeping segment of the MHT. This marks the zone of stress build-up on the MHT in the interseismic period and is possibly the zone of megathrust initiation.
How to cite: Mitra, S., Sharma, S., Powali, D., Priestley, K., and Wanchoo, S.: Crustal Structure and Earthquakes beneath the Jammu and Kashmir Himalaya, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4012, https://doi.org/10.5194/egusphere-egu2020-4012, 2020.
EGU2020-22472 | Displays | TS7.4
Lower crustal recycling: Reconciling Petrological and Numerical Constraints from the PamirRyan Stoner, Mark Behn, and Bradley Hacker
Geochronological and thermobarometric data from a lower crustal xenolith suite in the Pamir offer a unique record of the transport of lower crust to mantle depths after an episode of slab breakoff. We compare petrologically constrained pressure-temperature-time paths from the xenoliths to pressure-temperature-time (P-T-t) paths of tracked markers in 2-D numerical geodynamic models of density foundering with thermodynamically calculated densities. We investigate whether gravitational “drip” instabilities or the peeling back of a dense layer—delamination—can reproduce the P-T-t paths seen in the xenoliths, with the ancillary goal of capturing the positive feedback between mechanical thickening and densification of the lower crust. Key thermobarometric observations from the xenoliths we try to match in our numerical study are: (1) initial heating at near-constant pressure followed by (2) a sharp increase in pressure with continued heating. We find that thick crustal sections develop P-T-t paths in numerical models of delamination that match the observations from xenoliths: the lower crust initially heats due to return flow from upwelling asthenosphere, and then foundering mantle lithosphere and crust show a marked increase in pressure with additional heating. Initial gravitational drip instabilities founder with relatively little heating yet may thin the mantle lithosphere sufficiently to allow for subsequent delamination or asymmetric drips to nucleate in the region of hotter, thinner mantle lithosphere. Such subsequent asymmetric drips or delamination entrain crust that closely follows the P-T-t path from xenoliths. This suggests that the xenoliths were not derived from an initial drip instability, but instead from later instabilities or delamination enabled by thinning of the lithosphere. In all models where density foundering occurs, the positive feedback between contraction and densification of the lower crust leads to the loss of initially positively buoyant lower crust. The combination of geological and numerical methods constrains the geometry and triggers of lower crustal foundering during collision. Contraction alone does not match the record of foundering; the lithosphere must have also been asymmetrically thinned.
How to cite: Stoner, R., Behn, M., and Hacker, B.: Lower crustal recycling: Reconciling Petrological and Numerical Constraints from the Pamir, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22472, https://doi.org/10.5194/egusphere-egu2020-22472, 2020.
Geochronological and thermobarometric data from a lower crustal xenolith suite in the Pamir offer a unique record of the transport of lower crust to mantle depths after an episode of slab breakoff. We compare petrologically constrained pressure-temperature-time paths from the xenoliths to pressure-temperature-time (P-T-t) paths of tracked markers in 2-D numerical geodynamic models of density foundering with thermodynamically calculated densities. We investigate whether gravitational “drip” instabilities or the peeling back of a dense layer—delamination—can reproduce the P-T-t paths seen in the xenoliths, with the ancillary goal of capturing the positive feedback between mechanical thickening and densification of the lower crust. Key thermobarometric observations from the xenoliths we try to match in our numerical study are: (1) initial heating at near-constant pressure followed by (2) a sharp increase in pressure with continued heating. We find that thick crustal sections develop P-T-t paths in numerical models of delamination that match the observations from xenoliths: the lower crust initially heats due to return flow from upwelling asthenosphere, and then foundering mantle lithosphere and crust show a marked increase in pressure with additional heating. Initial gravitational drip instabilities founder with relatively little heating yet may thin the mantle lithosphere sufficiently to allow for subsequent delamination or asymmetric drips to nucleate in the region of hotter, thinner mantle lithosphere. Such subsequent asymmetric drips or delamination entrain crust that closely follows the P-T-t path from xenoliths. This suggests that the xenoliths were not derived from an initial drip instability, but instead from later instabilities or delamination enabled by thinning of the lithosphere. In all models where density foundering occurs, the positive feedback between contraction and densification of the lower crust leads to the loss of initially positively buoyant lower crust. The combination of geological and numerical methods constrains the geometry and triggers of lower crustal foundering during collision. Contraction alone does not match the record of foundering; the lithosphere must have also been asymmetrically thinned.
How to cite: Stoner, R., Behn, M., and Hacker, B.: Lower crustal recycling: Reconciling Petrological and Numerical Constraints from the Pamir, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22472, https://doi.org/10.5194/egusphere-egu2020-22472, 2020.
EGU2020-16977 | Displays | TS7.4
Eocene post-collisional magmatism in Himalaya orogenic belt: evidence from petrography, zircon U-Pb age and Sr-Nd-Hf isotope of the Mayum alkaline complex, southern Lhasa subterraneXiaoshuang Chen and Haijin Xu
Alkaline magmatism is commonly generated in extensional settings, playing an important role in constraining the timing of slab breakoff. Eocene post-collisional magmatism is widely distributed along the Gangdese belt of southern Tibet. However, few Eocene post-collisional alkaline magmatism has been identified. Here, we present a comprehensive study of whole-rock geochemistry, zircon U-Pb ages and Sr-Nd-Hf isotopes of the Mayum alkaline complex from the Southern Lhasa Subterrane, providing an insight into the timing of breakoff of the Neo-Tethyan slab. The alkaline complex is composed of amphibolite syenite, quartz syenite and alkaline granite. The mafic microgranular enclaves are ubiquitous in the syenites. Zircon U-Pb analyses indicates that the alkaline rocks were generated in Early Eocene (ca. 53-50 Ma). These ages suggest that the alkaline rocks emplaced shortly (10-15Ma) after the continental collision between the Indian and Eurasian plates. The alkaline rocks have high SiO2 (64.32-77.36 wt.%), Na2O + K2O (6.63-9.03 wt.%) contents, low MgO (0.14-2.52 wt.%) contents. These rocks show obvious arc-like geochemical features in trace elements, i.e., enrichment in LILEs (e.g., Rb, K), LREEs, Th and U, and depletion in HFSEs (e.g., Nb, Ta, Ti), HREEs with strongly to moderately negative Eu anomalies (δEu=0.28–0.72). These features together with high FeOT/MgO, Ga/Al, Ce/Nb and Y/Nb values, and low Ba, Sr contents, suggesting that the Mayum alkaline rocks belong to an A2-type granitoids. Besides, the alkaline rocks have homogeneous initial 87Sr/86Sr ratios (0.7052-0.7059) and negative εNd(t) values (-2.1 to -0.9) for whole-rock, and positive zircon εHf(t) values (+0.73 to +11.16). Nd-Hf isotope decoupling suggests that the alkaline was likely produced by mixing of mantle- and crust-derived magmas under a post-collisional extensional setting. Combined with previous published results, we propose that the slab breakoff of the subducting Neo-Tethyan oceanic lithosphere at least prior to Early Eocene (ca. 53Ma). The Eocene Mayum alkaline complex might be related to asthenosphere upwelling trigged by the slab breakoff.
How to cite: Chen, X. and Xu, H.: Eocene post-collisional magmatism in Himalaya orogenic belt: evidence from petrography, zircon U-Pb age and Sr-Nd-Hf isotope of the Mayum alkaline complex, southern Lhasa subterrane, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16977, https://doi.org/10.5194/egusphere-egu2020-16977, 2020.
Alkaline magmatism is commonly generated in extensional settings, playing an important role in constraining the timing of slab breakoff. Eocene post-collisional magmatism is widely distributed along the Gangdese belt of southern Tibet. However, few Eocene post-collisional alkaline magmatism has been identified. Here, we present a comprehensive study of whole-rock geochemistry, zircon U-Pb ages and Sr-Nd-Hf isotopes of the Mayum alkaline complex from the Southern Lhasa Subterrane, providing an insight into the timing of breakoff of the Neo-Tethyan slab. The alkaline complex is composed of amphibolite syenite, quartz syenite and alkaline granite. The mafic microgranular enclaves are ubiquitous in the syenites. Zircon U-Pb analyses indicates that the alkaline rocks were generated in Early Eocene (ca. 53-50 Ma). These ages suggest that the alkaline rocks emplaced shortly (10-15Ma) after the continental collision between the Indian and Eurasian plates. The alkaline rocks have high SiO2 (64.32-77.36 wt.%), Na2O + K2O (6.63-9.03 wt.%) contents, low MgO (0.14-2.52 wt.%) contents. These rocks show obvious arc-like geochemical features in trace elements, i.e., enrichment in LILEs (e.g., Rb, K), LREEs, Th and U, and depletion in HFSEs (e.g., Nb, Ta, Ti), HREEs with strongly to moderately negative Eu anomalies (δEu=0.28–0.72). These features together with high FeOT/MgO, Ga/Al, Ce/Nb and Y/Nb values, and low Ba, Sr contents, suggesting that the Mayum alkaline rocks belong to an A2-type granitoids. Besides, the alkaline rocks have homogeneous initial 87Sr/86Sr ratios (0.7052-0.7059) and negative εNd(t) values (-2.1 to -0.9) for whole-rock, and positive zircon εHf(t) values (+0.73 to +11.16). Nd-Hf isotope decoupling suggests that the alkaline was likely produced by mixing of mantle- and crust-derived magmas under a post-collisional extensional setting. Combined with previous published results, we propose that the slab breakoff of the subducting Neo-Tethyan oceanic lithosphere at least prior to Early Eocene (ca. 53Ma). The Eocene Mayum alkaline complex might be related to asthenosphere upwelling trigged by the slab breakoff.
How to cite: Chen, X. and Xu, H.: Eocene post-collisional magmatism in Himalaya orogenic belt: evidence from petrography, zircon U-Pb age and Sr-Nd-Hf isotope of the Mayum alkaline complex, southern Lhasa subterrane, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16977, https://doi.org/10.5194/egusphere-egu2020-16977, 2020.
EGU2020-904 | Displays | TS7.4
Reconciling plate convergence and orogeny: The influence of India-Asia convergence rate on the formation of the HimalayasBen S. Knight, Fabio A. Capitanio, and Roberto F. Weinberg
The collision of India and Eurasia since ~50 Ma has resulted in a broad range of deformation along the Himalaya-Tibetan orogeny, accommodating >2700 km of convergence. The region is characterised by the Tibetan Plateau, the Himalayan internal units and fold-and-thrust belt from North to South. These formed as a consequence of a convergence history characterised by a progressive decrease in velocity, from ~10 cm/yr 50 Ma, to ~8 cm/yr 42.5 Ma and to present-day values of ~4 cm/yr around 20 Ma. Here, we test the controls of such a convergence velocity history on the orogeny of a viscoplastic wedge during collision, above a subducting continental lithosphere. We compare numerical models simulating India-Asia plate convergence and collision, comparing the structures observed throughout the evolution with those observed in the Himalayan-Tibetan region. The models display distinct phases of growth and structural style evolution in the Himalayan-Tibetan region that are a result of the change in convergence velocity and long-term collision. After an initial stacking, the high convergence velocity forces deformation migration towards the upper plate, where a plateau forms, while late stage slowdown of collision favours the formation of the Himalayan fold-and-thrust belt. While the latter is in agreement with the structuring of the southermost domains and the South Tibetan Detachment (STD) fault, the former provide constraints to the initial uplift of the Tibetan Plateau.
How to cite: Knight, B. S., Capitanio, F. A., and Weinberg, R. F.: Reconciling plate convergence and orogeny: The influence of India-Asia convergence rate on the formation of the Himalayas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-904, https://doi.org/10.5194/egusphere-egu2020-904, 2020.
The collision of India and Eurasia since ~50 Ma has resulted in a broad range of deformation along the Himalaya-Tibetan orogeny, accommodating >2700 km of convergence. The region is characterised by the Tibetan Plateau, the Himalayan internal units and fold-and-thrust belt from North to South. These formed as a consequence of a convergence history characterised by a progressive decrease in velocity, from ~10 cm/yr 50 Ma, to ~8 cm/yr 42.5 Ma and to present-day values of ~4 cm/yr around 20 Ma. Here, we test the controls of such a convergence velocity history on the orogeny of a viscoplastic wedge during collision, above a subducting continental lithosphere. We compare numerical models simulating India-Asia plate convergence and collision, comparing the structures observed throughout the evolution with those observed in the Himalayan-Tibetan region. The models display distinct phases of growth and structural style evolution in the Himalayan-Tibetan region that are a result of the change in convergence velocity and long-term collision. After an initial stacking, the high convergence velocity forces deformation migration towards the upper plate, where a plateau forms, while late stage slowdown of collision favours the formation of the Himalayan fold-and-thrust belt. While the latter is in agreement with the structuring of the southermost domains and the South Tibetan Detachment (STD) fault, the former provide constraints to the initial uplift of the Tibetan Plateau.
How to cite: Knight, B. S., Capitanio, F. A., and Weinberg, R. F.: Reconciling plate convergence and orogeny: The influence of India-Asia convergence rate on the formation of the Himalayas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-904, https://doi.org/10.5194/egusphere-egu2020-904, 2020.
EGU2020-14987 | Displays | TS7.4
The Mechanism and Dynamics of N-S trends normal faults in Tibetan Plateau: Insight From Thermochronology, Magnetotellurics, Magmatism and GPS MeasurementsHan-Ao Li, in-Gen Dai, Le-Tian Zhang, Ya-Lin Li, Guang-Hao Ha, and Cheng-Shan Wang
The N-S trends normal faults are widespread through the whole Tibetan Plateau. It records key information for the growth and uplift of the Tibetan Plateau. Numerous models are provided to explain the causes of rifting in the Tibetan Plateau based on the low-temperature thermochronology1. With the developments of the geophysical and magmatic geochemistry methods and its applications on the Tibetan Plateau, we could gain more profound understanding on the sphere structure of the Tibetan Plateau. This would give us more clues on how the deep process affect the formation and evolution of the shallow normal faults. However, few researchers pay attention on this and the relationship between the surface evolution and deep process of these faults. In order to solve these puzzles, we collected the published thermochronology data, magnetotelluric data, faults-related ultrapotassic, potassic and the adakitic rocks ages and present-day GPS measurements. We find that the distribution of the N-S trends normal faults are closely related to the weak zones in the middle to lower crust (15-50 km) revealed by the magmatism and magnetotelluric data2. Besides, the present-day GPS data show that the E-W extension rates match well with the eastward movements speeds interior Tibetan Plateau3. Combined with the thermochronology data (25-4 Ma), we concluded that 1.The weak zone in the middle to lower crust influence the developments and evolution of the N-S trends normal faults. 2. The material eastward flow enhance the N-S normal faults developments. 3. The timing of the middle to lower crustal flow may begin in the Miocene.
Key words: N-S trends normal faults; Thermochronology; Magnetotellurics; Magmatism; GPS Measurements; middle to lower crustal flow
References:
1Lee, J., Hager, C., Wallis, S.R., Stockli, D.F., Whitehouse, M.J., Aoya, M. and Wang, Y., 2011. Middle to Late Miocene Extremely Rapid Exhumation and Thermal Reequilibration in the Kung Co Rift, Southern Tibet. Tectonics, 30(2).
2Pang, Y., Zhang, H., Gerya, T.V., Liao, J., Cheng, H. and Shi, Y., 2018. The Mechanism and Dynamics of N-S Rifting in Southern Tibet: Insight from 3-D Thermomechanical Modeling. Journal of Geophysical Research: Solid Earth.
3Zhang, P.-Z., Shen, Z., Wang, M., Gan, W., Bürgmann, R., Molnar, P., Wang, Q., Niu, Z., Sun, J., Wu, J., Hanrong, S. and Xinzhao, Y., 2004. Continuous Deformation of the Tibetan Plateau from Global Positioning System Data. Geology, 32(9).
Acknowledgements:
We thank Shi-Ying Xu, Xu Han, Bo-Rong Liu for collecting data. Special thanks are given to Dr. Guang-Hao Ha and Professors Jin-Gen Dai, Le-Tian Zhang,Ya-Lin Li and Cheng-Shan Wang for many critical and constructive comments.
How to cite: Li, H.-A., Dai, I.-G., Zhang, L.-T., Li, Y.-L., Ha, G.-H., and Wang, C.-S.: The Mechanism and Dynamics of N-S trends normal faults in Tibetan Plateau: Insight From Thermochronology, Magnetotellurics, Magmatism and GPS Measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14987, https://doi.org/10.5194/egusphere-egu2020-14987, 2020.
The N-S trends normal faults are widespread through the whole Tibetan Plateau. It records key information for the growth and uplift of the Tibetan Plateau. Numerous models are provided to explain the causes of rifting in the Tibetan Plateau based on the low-temperature thermochronology1. With the developments of the geophysical and magmatic geochemistry methods and its applications on the Tibetan Plateau, we could gain more profound understanding on the sphere structure of the Tibetan Plateau. This would give us more clues on how the deep process affect the formation and evolution of the shallow normal faults. However, few researchers pay attention on this and the relationship between the surface evolution and deep process of these faults. In order to solve these puzzles, we collected the published thermochronology data, magnetotelluric data, faults-related ultrapotassic, potassic and the adakitic rocks ages and present-day GPS measurements. We find that the distribution of the N-S trends normal faults are closely related to the weak zones in the middle to lower crust (15-50 km) revealed by the magmatism and magnetotelluric data2. Besides, the present-day GPS data show that the E-W extension rates match well with the eastward movements speeds interior Tibetan Plateau3. Combined with the thermochronology data (25-4 Ma), we concluded that 1.The weak zone in the middle to lower crust influence the developments and evolution of the N-S trends normal faults. 2. The material eastward flow enhance the N-S normal faults developments. 3. The timing of the middle to lower crustal flow may begin in the Miocene.
Key words: N-S trends normal faults; Thermochronology; Magnetotellurics; Magmatism; GPS Measurements; middle to lower crustal flow
References:
1Lee, J., Hager, C., Wallis, S.R., Stockli, D.F., Whitehouse, M.J., Aoya, M. and Wang, Y., 2011. Middle to Late Miocene Extremely Rapid Exhumation and Thermal Reequilibration in the Kung Co Rift, Southern Tibet. Tectonics, 30(2).
2Pang, Y., Zhang, H., Gerya, T.V., Liao, J., Cheng, H. and Shi, Y., 2018. The Mechanism and Dynamics of N-S Rifting in Southern Tibet: Insight from 3-D Thermomechanical Modeling. Journal of Geophysical Research: Solid Earth.
3Zhang, P.-Z., Shen, Z., Wang, M., Gan, W., Bürgmann, R., Molnar, P., Wang, Q., Niu, Z., Sun, J., Wu, J., Hanrong, S. and Xinzhao, Y., 2004. Continuous Deformation of the Tibetan Plateau from Global Positioning System Data. Geology, 32(9).
Acknowledgements:
We thank Shi-Ying Xu, Xu Han, Bo-Rong Liu for collecting data. Special thanks are given to Dr. Guang-Hao Ha and Professors Jin-Gen Dai, Le-Tian Zhang,Ya-Lin Li and Cheng-Shan Wang for many critical and constructive comments.
How to cite: Li, H.-A., Dai, I.-G., Zhang, L.-T., Li, Y.-L., Ha, G.-H., and Wang, C.-S.: The Mechanism and Dynamics of N-S trends normal faults in Tibetan Plateau: Insight From Thermochronology, Magnetotellurics, Magmatism and GPS Measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14987, https://doi.org/10.5194/egusphere-egu2020-14987, 2020.
EGU2020-18249 | Displays | TS7.4
The structure of the Central-Eastern Rif (Morocco) and the disregarded subduction of the North-West African paleo-marginOriol Gimeno, Dominique Frizon de Lamotte, Rémi Leprêtre, Faouziya Haissen, Achraf Atouabat, and Geoffroy Mohn
The Rif Belt (Northern Morocco) forms the western edge of the Alpine-Himalayan orogenic system developed during the convergence between the Africa and Eurasia plates. Compared to other mountains belts, the External Rif, which preserves remnants of the North African paleo-margin, presents two unusual features: (1) the presence of metamorphic massifs [External Metamorphic Massifs (EMMs)] and (2) the existence of large allochthonous thrust-sheets that travelled far away [the Higher Nappes]. In this contribution, we combined structural, stratigraphic and metamorphic data, complemented by new field observation and thermochronology results, to revisit the structure of the External Rif and to review its Cenozoic evolution. The External Rif was the site of a poly-phased tectonic evolution recorded before and after of a major unconformity: the so-called “Mesorif Unconformity” postdating an important Midde-Late Eocene deformation. This tectonic event is well-preserved in the North-African paleo-margin because of its under-thrusting (“subduction”) below the Maghrebian Tethys, the former oceanic domain separating Iberia from Africa. The MP-LT metamorphism, recorded in the EMMs (Temsamane Units in Morocco), is a direct vestige of this process. By contrast, traces of this event are absent in the oceanic units of the Intrarif Domain, element of the Maghrebian Tethys. After the “Mesorif Unconformity”, i.e. during the Miocene, the regional geodynamics is dominated by the westward translation of the Alboran Domain and the coeval deformation of the Ketama Unit (Intrarif) in front of it. This process results directly from the subduction of the Maghrebian Tethys, which happened at that time. The docking of the Ketama Unit against the already exhumed EMMs allowed an uplift and the subsequent detachment of the top of its lithostratigraphic pile, individualizing the Higher Nappes. During their gravity-driven travel towards the foredeep basin, they dragged at their floor the already exhumed Senhadja Nappes, inherited from the distal-most part of the NW African margin. All these elements are integrated in a coherent model integrating the External Rif in the geodynamics of the West Mediterranean.
How to cite: Gimeno, O., Frizon de Lamotte, D., Leprêtre, R., Haissen, F., Atouabat, A., and Mohn, G.: The structure of the Central-Eastern Rif (Morocco) and the disregarded subduction of the North-West African paleo-margin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18249, https://doi.org/10.5194/egusphere-egu2020-18249, 2020.
The Rif Belt (Northern Morocco) forms the western edge of the Alpine-Himalayan orogenic system developed during the convergence between the Africa and Eurasia plates. Compared to other mountains belts, the External Rif, which preserves remnants of the North African paleo-margin, presents two unusual features: (1) the presence of metamorphic massifs [External Metamorphic Massifs (EMMs)] and (2) the existence of large allochthonous thrust-sheets that travelled far away [the Higher Nappes]. In this contribution, we combined structural, stratigraphic and metamorphic data, complemented by new field observation and thermochronology results, to revisit the structure of the External Rif and to review its Cenozoic evolution. The External Rif was the site of a poly-phased tectonic evolution recorded before and after of a major unconformity: the so-called “Mesorif Unconformity” postdating an important Midde-Late Eocene deformation. This tectonic event is well-preserved in the North-African paleo-margin because of its under-thrusting (“subduction”) below the Maghrebian Tethys, the former oceanic domain separating Iberia from Africa. The MP-LT metamorphism, recorded in the EMMs (Temsamane Units in Morocco), is a direct vestige of this process. By contrast, traces of this event are absent in the oceanic units of the Intrarif Domain, element of the Maghrebian Tethys. After the “Mesorif Unconformity”, i.e. during the Miocene, the regional geodynamics is dominated by the westward translation of the Alboran Domain and the coeval deformation of the Ketama Unit (Intrarif) in front of it. This process results directly from the subduction of the Maghrebian Tethys, which happened at that time. The docking of the Ketama Unit against the already exhumed EMMs allowed an uplift and the subsequent detachment of the top of its lithostratigraphic pile, individualizing the Higher Nappes. During their gravity-driven travel towards the foredeep basin, they dragged at their floor the already exhumed Senhadja Nappes, inherited from the distal-most part of the NW African margin. All these elements are integrated in a coherent model integrating the External Rif in the geodynamics of the West Mediterranean.
How to cite: Gimeno, O., Frizon de Lamotte, D., Leprêtre, R., Haissen, F., Atouabat, A., and Mohn, G.: The structure of the Central-Eastern Rif (Morocco) and the disregarded subduction of the North-West African paleo-margin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18249, https://doi.org/10.5194/egusphere-egu2020-18249, 2020.
EGU2020-7704 | Displays | TS7.4
Superposition of nappe stacking and extensional exhumation in the Sierra de los Filabres (Southeast Spain)Kristóf Porkoláb, Jasper Hupkes, Liviu Matenco, Ernst Willingshofer, and Jan Wijbrans
The Sierra de los Filabres mountain range in the Betics system of SE Spain is one of the best natural laboratory to investigate processes associated with nappe stacking and subsequent exhumation of metamorphic rocks during the orogenic evolution. Existing research separates the Iberia-derived high-pressure, amphibolite facies Nevado-Fillabrides complex in a lower tectonic plate position from the lower grade ALCAPECA microcontinent-derived Alpujárride complex in an upper tectonic plate position. Their nappe-stack contact is also defined as an extensional detachment that controls the exhumation of the higher grade Nevado-Fillabrides complex. We have tested this model with a detailed (micro-)structural and lithological analysis complemented by 40Ar/39Ar white mica dating of key shear zones. We aim to define key shear zones that separate different tectonic units, to determine the kinematics and timing of main deformation phases, and to understand the interplay between burial and exhumation structures. The results show that shearing related to the subduction burial up to the amphibolite facies is ~ top-NW in present-day coordinates. Three amphibolite facies nappe units are distinguished, which may correspond to proximal and more distal parts of the former hyper-extended Iberian margin. The bottom and top nappes consist of continental material, while the middle nappe is largely made of mafic and ultramafic rocks. Top-NW shearing was coeval with the isoclinal and tight asymmetric folding of the formations. These structures were overprinted by upright folds and greenschist facies shear zones that still developed under compression. These contractional structures are cross-cut by ~ top-W shear zones associated with exhumation that show evidences of gradually decreasing P-T conditions during extension from ductile shearing to normal faulting. We show that the same protolith can be followed in amphibolite grade below and in low greenschists grade above the main extensional detachment. This demonstrates that the extensional detachment did not follow and reactivate exactly the former nappe contact between the Nevado-Fillabrides and Alpujárride complexes. Our single grain fusion 40Ar/39Ar ages on white micas show a range of 10 to 20 Ma in case of nappe contacts or extensional shear zones, while yield a significantly older, 25-40 Ma age cluster in case of a sample far away from the main shear zones in the core of the Nevado-Fillabrides dome. This age cluster could either represent excess Ar in the sample, or resetting due to a distinct tectono-metamorphic event that occurred prior to the Early Miocene subduction of the Nevado-Fillabrides complex. The latter case would require the reconsideration of recent tectonic reconstructions of the region.
How to cite: Porkoláb, K., Hupkes, J., Matenco, L., Willingshofer, E., and Wijbrans, J.: Superposition of nappe stacking and extensional exhumation in the Sierra de los Filabres (Southeast Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7704, https://doi.org/10.5194/egusphere-egu2020-7704, 2020.
The Sierra de los Filabres mountain range in the Betics system of SE Spain is one of the best natural laboratory to investigate processes associated with nappe stacking and subsequent exhumation of metamorphic rocks during the orogenic evolution. Existing research separates the Iberia-derived high-pressure, amphibolite facies Nevado-Fillabrides complex in a lower tectonic plate position from the lower grade ALCAPECA microcontinent-derived Alpujárride complex in an upper tectonic plate position. Their nappe-stack contact is also defined as an extensional detachment that controls the exhumation of the higher grade Nevado-Fillabrides complex. We have tested this model with a detailed (micro-)structural and lithological analysis complemented by 40Ar/39Ar white mica dating of key shear zones. We aim to define key shear zones that separate different tectonic units, to determine the kinematics and timing of main deformation phases, and to understand the interplay between burial and exhumation structures. The results show that shearing related to the subduction burial up to the amphibolite facies is ~ top-NW in present-day coordinates. Three amphibolite facies nappe units are distinguished, which may correspond to proximal and more distal parts of the former hyper-extended Iberian margin. The bottom and top nappes consist of continental material, while the middle nappe is largely made of mafic and ultramafic rocks. Top-NW shearing was coeval with the isoclinal and tight asymmetric folding of the formations. These structures were overprinted by upright folds and greenschist facies shear zones that still developed under compression. These contractional structures are cross-cut by ~ top-W shear zones associated with exhumation that show evidences of gradually decreasing P-T conditions during extension from ductile shearing to normal faulting. We show that the same protolith can be followed in amphibolite grade below and in low greenschists grade above the main extensional detachment. This demonstrates that the extensional detachment did not follow and reactivate exactly the former nappe contact between the Nevado-Fillabrides and Alpujárride complexes. Our single grain fusion 40Ar/39Ar ages on white micas show a range of 10 to 20 Ma in case of nappe contacts or extensional shear zones, while yield a significantly older, 25-40 Ma age cluster in case of a sample far away from the main shear zones in the core of the Nevado-Fillabrides dome. This age cluster could either represent excess Ar in the sample, or resetting due to a distinct tectono-metamorphic event that occurred prior to the Early Miocene subduction of the Nevado-Fillabrides complex. The latter case would require the reconsideration of recent tectonic reconstructions of the region.
How to cite: Porkoláb, K., Hupkes, J., Matenco, L., Willingshofer, E., and Wijbrans, J.: Superposition of nappe stacking and extensional exhumation in the Sierra de los Filabres (Southeast Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7704, https://doi.org/10.5194/egusphere-egu2020-7704, 2020.
EGU2020-10358 | Displays | TS7.4
Late stage of the Gibraltar arc subduction system (western Mediterranean): from slab-tearing to continental-edge delaminationAna M. Negredo, Flor de Lis Mancilla, Carlos Clemente, Jose Morales, and Javier Fullea
The Gibraltar arc subduction system is the result of the fast westward roll-back of the Alboran slab at the westernmost end of the Mediterranean Sea. This westward motion is controlled, at its northern edge, by slab tearing along a so called STEP (Subduction-Transform-Edge-Propagator) fault under the Betics orogen. The Alboran subduction process is in its last evolutionary stage, where the oceanic lithosphere has been fully consumed and the continental lithosphere attached to it collides with the overriding plate. In this situation the continued slow convergence between Iberia and Africa could lead to a short stage of continental subduction. However, the particular setup after slab tearing, characterized by a sharp lateral contrast between the orogenic Betic lithosphere and the adjacent thinned lithosphere of the overriding Alboran domain, is also prone to trigger continental delamination, i.e. the detachment between the crust and the lithospheric mantle. Several lines of evidence indicate that northwards mantle delamination is likely occurring in the central Betics. The fast average topographic uplift during the last 8 Ma together with the lack of spatial correspondence between the highest topography (Sierra Nevada Mountains) and the thickest crust indicate that the topography could be partly supported by asthenospheric upwelling due to continental delamination. In this study we take advantage of an unprecedented resolution seismic receiver functions lithospheric mapping in the Betic orogen to investigate the conditions for, and consequences of, edge delamination in the Iberian margin after slab tearing. We show that given a weak enough Iberian lower crust the delaminated lithospheric mantle peels off the crust and adopts a geometry consistent with the imaged southward dipping Iberian lithosphere in the central Betics. In contrast, the thinned lower crust beneath the Iberian margin in the eastern Betics prevented mantle delamination via asthenospheric inflow into the lower crust.
How to cite: Negredo, A. M., Mancilla, F. D. L., Clemente, C., Morales, J., and Fullea, J.: Late stage of the Gibraltar arc subduction system (western Mediterranean): from slab-tearing to continental-edge delamination , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10358, https://doi.org/10.5194/egusphere-egu2020-10358, 2020.
The Gibraltar arc subduction system is the result of the fast westward roll-back of the Alboran slab at the westernmost end of the Mediterranean Sea. This westward motion is controlled, at its northern edge, by slab tearing along a so called STEP (Subduction-Transform-Edge-Propagator) fault under the Betics orogen. The Alboran subduction process is in its last evolutionary stage, where the oceanic lithosphere has been fully consumed and the continental lithosphere attached to it collides with the overriding plate. In this situation the continued slow convergence between Iberia and Africa could lead to a short stage of continental subduction. However, the particular setup after slab tearing, characterized by a sharp lateral contrast between the orogenic Betic lithosphere and the adjacent thinned lithosphere of the overriding Alboran domain, is also prone to trigger continental delamination, i.e. the detachment between the crust and the lithospheric mantle. Several lines of evidence indicate that northwards mantle delamination is likely occurring in the central Betics. The fast average topographic uplift during the last 8 Ma together with the lack of spatial correspondence between the highest topography (Sierra Nevada Mountains) and the thickest crust indicate that the topography could be partly supported by asthenospheric upwelling due to continental delamination. In this study we take advantage of an unprecedented resolution seismic receiver functions lithospheric mapping in the Betic orogen to investigate the conditions for, and consequences of, edge delamination in the Iberian margin after slab tearing. We show that given a weak enough Iberian lower crust the delaminated lithospheric mantle peels off the crust and adopts a geometry consistent with the imaged southward dipping Iberian lithosphere in the central Betics. In contrast, the thinned lower crust beneath the Iberian margin in the eastern Betics prevented mantle delamination via asthenospheric inflow into the lower crust.
How to cite: Negredo, A. M., Mancilla, F. D. L., Clemente, C., Morales, J., and Fullea, J.: Late stage of the Gibraltar arc subduction system (western Mediterranean): from slab-tearing to continental-edge delamination , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10358, https://doi.org/10.5194/egusphere-egu2020-10358, 2020.
EGU2020-9221 | Displays | TS7.4
Neogene-to-Quaternary post-orogenic tectonic evolution and CaCO3-rich fluids from the Tabernas basin (eastern Betics, Spain) reveal control by deep-seated processes in the mantleMarine Larrey, Frédéric Mouthereau, Emmanuel Masini, Sylvain Calassou, Aurélien Virgone, Eric Gaucher, Damien Huyghe, and Nicolas Beaudoin
Since Miocene times, the crustal thinning in eastern Betics and the Alboran region associated with westward slab retreat led to the formation and exhumation of metamorphic domes and EW-directed narrow basins.
The Tabernas basin preserves a sedimentary records of the last stages of metamorphic domes exhumation (14 to 8 Ma). Structural constraints from fault patterns and sedimentary archives show evidence in the field for E-W strike-slip faults that developed close to dome-basin contacts. The evolution of strike-slip faulting and extensional basins reveals strain partitioning during the late Miocene that is consistent with the present-day regional NNW-directed compression and WSW-directed/orogen-parallel extension that result from the NW-SE Africa-Europe plate convergence. A regional cross-section further emphasizes the role of crustal-scale strike-slip faulting and slab detachment and delamination under the Alboran domain.
Calcite veins that developed during the orogen-parallel extension in the metamorphic basement and the Tortonian sedimentary rocks show a wide variety of stable isotopes ratios. Calcite cements have δ18O values ranging from -17.23‰ to -5.30‰ for, and from -15.77‰ to -1.6‰ for δ13C isotopic ratios. This patterns is interpreted to reflect the increase of freshwater input buffered by the composition of host carbonate rocks.
Continental carbonates of Quaternary ages are widespread in the Tabernas basin. Travertines show a close structural relationship with N170 and N50 normal faults, implying tectonically-controlled Ca/CO2 leakages. Their δ13C values are compatible with a hydrothermal origin from a deep-seated carbon source (δ18O median of -7.5‰, δ13C median of 2.1‰). Degassing associated with regional volcanism from the Serravallian until the Tortonian-Messinian ages is likely to be also the main vector of recent CO2 storages in rocks. The U-Th ages of travertines, ranging from 8ka ± 0.2 to 354ka ±76, further outline interactions with captive aquifer from 350ka and subsequent Ca/CO2 leakages due to geodynamic changes.
How to cite: Larrey, M., Mouthereau, F., Masini, E., Calassou, S., Virgone, A., Gaucher, E., Huyghe, D., and Beaudoin, N.: Neogene-to-Quaternary post-orogenic tectonic evolution and CaCO3-rich fluids from the Tabernas basin (eastern Betics, Spain) reveal control by deep-seated processes in the mantle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9221, https://doi.org/10.5194/egusphere-egu2020-9221, 2020.
Since Miocene times, the crustal thinning in eastern Betics and the Alboran region associated with westward slab retreat led to the formation and exhumation of metamorphic domes and EW-directed narrow basins.
The Tabernas basin preserves a sedimentary records of the last stages of metamorphic domes exhumation (14 to 8 Ma). Structural constraints from fault patterns and sedimentary archives show evidence in the field for E-W strike-slip faults that developed close to dome-basin contacts. The evolution of strike-slip faulting and extensional basins reveals strain partitioning during the late Miocene that is consistent with the present-day regional NNW-directed compression and WSW-directed/orogen-parallel extension that result from the NW-SE Africa-Europe plate convergence. A regional cross-section further emphasizes the role of crustal-scale strike-slip faulting and slab detachment and delamination under the Alboran domain.
Calcite veins that developed during the orogen-parallel extension in the metamorphic basement and the Tortonian sedimentary rocks show a wide variety of stable isotopes ratios. Calcite cements have δ18O values ranging from -17.23‰ to -5.30‰ for, and from -15.77‰ to -1.6‰ for δ13C isotopic ratios. This patterns is interpreted to reflect the increase of freshwater input buffered by the composition of host carbonate rocks.
Continental carbonates of Quaternary ages are widespread in the Tabernas basin. Travertines show a close structural relationship with N170 and N50 normal faults, implying tectonically-controlled Ca/CO2 leakages. Their δ13C values are compatible with a hydrothermal origin from a deep-seated carbon source (δ18O median of -7.5‰, δ13C median of 2.1‰). Degassing associated with regional volcanism from the Serravallian until the Tortonian-Messinian ages is likely to be also the main vector of recent CO2 storages in rocks. The U-Th ages of travertines, ranging from 8ka ± 0.2 to 354ka ±76, further outline interactions with captive aquifer from 350ka and subsequent Ca/CO2 leakages due to geodynamic changes.
How to cite: Larrey, M., Mouthereau, F., Masini, E., Calassou, S., Virgone, A., Gaucher, E., Huyghe, D., and Beaudoin, N.: Neogene-to-Quaternary post-orogenic tectonic evolution and CaCO3-rich fluids from the Tabernas basin (eastern Betics, Spain) reveal control by deep-seated processes in the mantle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9221, https://doi.org/10.5194/egusphere-egu2020-9221, 2020.
EGU2020-10520 | Displays | TS7.4
Image of the Iberian Tethys paleomargin beneath the eastern Betic mountain rangeFlor de Lis Mancilla, Jose Morales, Antonio Molina-Aguilera, Daniel Stich, Jose Miguel Azañon, Teresa Teixido, Benjamin Heit, and Xiaohui Yuan
We obtain P-wave receiver functions from recordings at a dense seismic broadband transect, deployed along 170 km across the eastern Betic orogen in south Spain. Migrated images show the crustal structure of the orogen in detail. In particular, they reveal the situation of the subducted Iberian paleomargin, with full preservation of the proximal domain and the ~50 km wide necking domain. Crustal thinning affects the lower continental crust. The Variscan crust of the Tethys margin is bending downward beneath the Betics, reaching ~45 km depth, and terminates abruptly at a major slab tear fault. The distal domain of the paleomargin cannot be reconstructed, but the migrated section suggests that material has been exhumed through the subduction channel and integrated into the Betic Orogene. This supports an origin of the HP-LT Nevado-Filabride units from subducted, hyperextended Variscan crust.
How to cite: Mancilla, F. D. L., Morales, J., Molina-Aguilera, A., Stich, D., Azañon, J. M., Teixido, T., Heit, B., and Yuan, X.: Image of the Iberian Tethys paleomargin beneath the eastern Betic mountain range, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10520, https://doi.org/10.5194/egusphere-egu2020-10520, 2020.
We obtain P-wave receiver functions from recordings at a dense seismic broadband transect, deployed along 170 km across the eastern Betic orogen in south Spain. Migrated images show the crustal structure of the orogen in detail. In particular, they reveal the situation of the subducted Iberian paleomargin, with full preservation of the proximal domain and the ~50 km wide necking domain. Crustal thinning affects the lower continental crust. The Variscan crust of the Tethys margin is bending downward beneath the Betics, reaching ~45 km depth, and terminates abruptly at a major slab tear fault. The distal domain of the paleomargin cannot be reconstructed, but the migrated section suggests that material has been exhumed through the subduction channel and integrated into the Betic Orogene. This supports an origin of the HP-LT Nevado-Filabride units from subducted, hyperextended Variscan crust.
How to cite: Mancilla, F. D. L., Morales, J., Molina-Aguilera, A., Stich, D., Azañon, J. M., Teixido, T., Heit, B., and Yuan, X.: Image of the Iberian Tethys paleomargin beneath the eastern Betic mountain range, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10520, https://doi.org/10.5194/egusphere-egu2020-10520, 2020.
EGU2020-10681 | Displays | TS7.4
Cenozoic multiphase orogenic deformations in Northern Calabria Arc: hints from geological mapping in the Longobucco BasinGiulia Innamorati, Simone Fabbi, and Massimo Santantonio
The Meso/Cenozoic geodynamic evolution of the Calabria Peloritani Arc (CPA) has been, and is still, hotly debated, this sector of the Apennine chain being an exotic continental ribbon scraped off from its original position (European Plat