EGU General Assembly 2022  

The physical cause, or origin, or generation of plate tectonics, especially how it arises from a convecting mantle on Earth (and not apparently on our solar system's other terrestrial planets) is one of the big questions in geophysics, and has  haunted (or taunted) the author  for the last 30+ years.  Although he's tried to drive the question to basic physical causes for plate boundary formation in a cold stiff lithosphere,  he's certainly taken his share of wrong turns.  His earliest attempts to understand these processes from fluid lab experiments (while a postdoc at WHOI) only achieved (1) making gallons of fluids that look much like mucus, and (2) proof that he was a lousy experimentalist.  But in the intervening decades, he's burrowed deeper into smaller and smaller scales to understand how microscale physics of mineral grains influence plate boundary formation at large scales.  This led to the most recent theory of grain damage that allows for formation of weak boundaries, corresponds to field and laboratory observations of mylonitic behavior, and has applications from the onset of early plate tectonics, to passive margin collapse, to slab segmentation and necking.   The most recent theory incorporates how mineral phases (olivine and pyroxene) mix with each other at the grain scale, and this has allowed a close comparison to new rock deformation experiments on grain mixing and shear localization, which opens up many new questions and predictions for more experiments and observations.  

How to cite: Bercovici, D.: Searching for the origin of plate tectonics, leaving no grain unturned, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9705, https://doi.org/10.5194/egusphere-egu22-9705, 2022.

Earthquakes provide a crucial way of probing the deformation style, strength, and stress state of the lithosphere.  In this talk, I will outline ways in which we can use careful analysis and precise seismological observations of earthquakes, particularly those at moderate magnitudes (M ~5-6), to map out how stress is supported in the lithosphere, and how the rheology of the lithosphere can vary in both space and time, summarising our current understanding of the controls on the distribution of earthquakes.  I will draw on examples from a range of regional studies, and outline what conclusions we can draw about the geological and geodynamic controls on the distribution of earthquakes in each region, and the variation on the style of deformation within the lithosphere.  I will also discuss areas in which our current understanding of the distribution of earthquakes remains unable to explain some observations, and challenges for the future.

How to cite: Craig, T.: Probing the rheology of the lithosphere using earthquake seismology, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13373, https://doi.org/10.5194/egusphere-egu22-13373, 2022.

This presentation describes the structure and morphologies associated with seafloor spreading in the Red Sea inferred from bathymetric, gravity, magnetic and seismic data. We show that the orientation of the structures is consistent with an Arabia-Nubia Euler pole located within the 95% confidence of Ar-Rajehi et al, (2010) Euler pole and with the tectonic model initially proposed by Girdler (1984). At the Red Sea scale, our model shows that a spreading axis extends along its entire length, even though it is mostly covered by allochthonous Middle Miocene salt and Late Miocene minibasins flowing inward from the margins. In the northern Red Sea, oceanic basement is only exposed through small windows within the salt, forming a series of deeps. The seafloor segments symmetrically bisect the new ocean in the south. Right-stepping transform faults that cluster near Jeddah, Zabargad and Ikhwan Islands offset the ridge axis as spreading is getting more oblique towards the Euler Pole. The northern, central and southern Red Sea segments display a well-developed mid-ocean ridge flanked by landward-dipping volcanic basement, typical of slow spreading ridges. In the northern magma poor spreading segment, mantle exhumation is likely at the transition between continental and oceanic crust. Transpression and transtension along transform faults accounts for the exhumation of the mantle on Zabargad Island as well as the collapse of a pull-apart basin in the Conrad deep.

We propose a new structural model for the Red Sea constrained by the geodetic rules of tectonic plates movements on a sphere. Finally, we discuss the effect of the Danakil microplate on the ridge morphology and show that the Arabia-Nubia-Danakil triple junction is likely located further north than previously described, around 18±0.5°N, where we observe a shift in the ridge axis orientation as well as in the spreading orientation.

How to cite: Delaunay, A., Alafifi, A., Baby, G., Fedorik, J., Tapponnier, P., and Dyment, J.: Structure and Morphology of the Mid-Ocean-Ridge in the Red Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1405, https://doi.org/10.5194/egusphere-egu22-1405, 2022.

How to cite: Jolivet, L., Allanic, C., Becker, T., Bellahsen, N., Briais, J., Davaille, A., Faccenna, C., Lasseur, E., and Romanowicz, B.: Continental rifts and mantle convection: Insights from the East African Rift and a new model of the West European Rift System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1696, https://doi.org/10.5194/egusphere-egu22-1696, 2022.

Corrugated detachments are fundamental crustal structures found in many extensional systems and plate tectonic boundaries, including mid-oceanic ridges and rifted margins. Direct observations of the complete geometry of extensional detachments are rare and our understanding of detachment fault structures and the mechanisms of development of high-angle normal faults and their rotation to lower angles mainly relies on proxy observations, for example seismicity trends, and numerical modelling.

We present interpretations of a high-resolution 3D seismic reflection survey from the hyperextended domain of the Porcupine Basin, Offshore West of Ireland. The 3D data image a highly reflective corrugated surface, the P reflector, that we interpret as an extensional detachment preserved in its slip position that likely developed at the top mantle surface during Jurassic hyperextension of the basin. Within the 3D data, the P reflector covers an area 95 km long and 35 km wide and has a domal shape that is elongate in the N-S direction with a crest at ~6.3 s two way travel time. It is the first time to our knowledge that 3D seismic data has imaged a complete detachment in the hyperextended area of a rifted margin, including its domal shape, the breakaway structures, and the linkage between the steep and shallow segments of the detachment. The resolved texture and geometry of the detachment and its relationship with overlying faults provide a basis for refining current models of detachment formation accommodating extreme extension.

Steep west-dipping faults mark the western frontal margin of the detachment. The steep faults pass eastward into shallower, predominantly west-dipping faults that appear to merge downwards with the P reflector. The P reflector has pronounced E-W corrugations, interpreted to indicate the detachment slip vector. The reflector is also characterised by abrupt changes in dip across N-S transverse ridges. These ridges are spaced on average 10 km apart, they coincide with lines of intersection between the P reflector and large overlying faults, and they often mark the termination of detachment corrugations. We interpret these ridges as recording former locations of the western boundary of the detachment so that they indicate a step-wise westward propagation of the P reflector. While it is generally accepted that detachments develop by oceanward propagation, we suggest that the faceted nature of the detachment indicates that this process is a punctuated one and that the clearly imaged transverse ridges record the oceanward stepping of the detachment with the initiation of a new family of steep faults.

We propose a new concept for the growth of detachments that may be applicable to other detachments that accommodate extreme extension, for example at mid-oceanic slow and ultra-slow spreading ridges.

How to cite: Lymer, G., Childs, C., and Walsh, J.: Punctuated propagation of a corrugated extensional detachment offshore West of Ireland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1799, https://doi.org/10.5194/egusphere-egu22-1799, 2022.

The Afar Depression forms a triple junction between three rift systems: the Red Sea Rift, the Gulf of Aden Rift and the Main Ethiopian Rift. Rifting began in the Oligocene after the eruption of the Ethiopian Flood Basalts. It represents a unique modern example of hotspot-influenced continental breakup. Its emerged position allows detailed field and remote sensing investigations. Important mapping efforts in the area during the 60s and 70s provided very valuable input for the understanding of the local geology but also for the development of global tectonic, volcanological and sedimentary concepts in continental rift settings.

This study presents the compilation of a new geological map which covers the complete Afar depression and includes its Phanerozoic sedimentary and magmatic cover. The map is based on extensive literature research, remote sensing and fieldwork. The geological history of the Afar Depression has also been reviewed. The map evidences the complexity of the rift system with the interaction of distinct tectonic plates, blocks, rift segments, sedimentary basins and volcanic areas that evolve through time and space. This integrative geological map and review is used to reassess and discuss aspects of the style, evolution, kinematics and dynamics of this rift system. Studying this unique modern example of active rifting will help in the better comprehension of rift processes and passive margin development worldwide.

How to cite: Rime, V., Foubert, A., Atnafu, B., and Kidane, T.: New mapping of the Afar Depression: towards the better understanding of rift dynamics in a hotspot-influenced continental rift zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2208, https://doi.org/10.5194/egusphere-egu22-2208, 2022.

Rifting in Ethiopia is predominantly driven by magmatic intrusion into the rifting crust. Unravelling the dynamics of lithospheric melt migration and storage is paramount to understanding the late-stage development of continental rifts. In particular, extensive geophysical observations of the structure and composition of rifting crust must be supported by petrology to provide a complete picture of rift-related magmatism. We present major element, trace element, and volatile element compositional data for olivine-hosted melt inclusions from the Boku Volcanic Complex (BVC), a monogenetic cone field in the north Main Ethiopian Rift. Through combined CO₂-density-calibrated Raman spectroscopy and secondary ion mass spectrometry we assess the total CO₂ concentrations within the melt inclusions allowing us to estimate pressures of entrapment via CO₂-H₂O solubility models. Our results show that primitive BVC melts carry up to 0.58 wt% CO₂ (mean ~0.2 wt%), with as much as half of the CO₂ in the melt inclusion present within shrinkage bubbles. Volatile solubility models suggest that these melts are stored over a narrow range of depths (10-15 km), consistent with geophysical data and implying the existence of focussed zone of magma intrusion at mid-crustal depths. The expansive range of trace element concentrations in the inclusions illustrate that, at the time of entrapment, compositional heterogeneity remains extant, and melts must therefore be stored in discrete magmatic bodies with limited mixing. Our results have implications for understanding the interplay between magma intrusion and extensional tectonics during continental break-up, such as magmatic compensation of crustal thinning and the thermo-mechanical effects of melt emplacement into the rifting crust.

How to cite: Wong, K., Ferguson, D., Wieser, P., Morgan, D., Edmonds, M., Tadesse, A. Z., and Yirgu, G.: Petrological evidence for focussed mid-crustal magma intrusion in the Main Ethiopian Rift, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2290, https://doi.org/10.5194/egusphere-egu22-2290, 2022.

The continental deposits of the Triassic basins developed along the eastern margin of the Central and North Atlantic show a similar sedimentological evolution, as those of the western margin resulting from the interaction of various processes.

The examples chosen in this work are those of the Mohammedia-Benslimane-ElGara-Berrechid basin MBEB in the Moroccan meseta that we studied in detail in the field, and that we tried to compare with Portugal which is on the same East Atlantic margin.

At the begininig of the Mesozoic, the northwestern part of the African continent was affected by an initial fracturing associated with the early stages of the opening of the Central Atlantic (Atlantic rift) during which several Moroccan Triassic basins are open.

The Mohammedia-Benslimane-ElGara-Berrechid basin is part of the Moroccan western Triassic province, which corresponds to all the basins of the Moroccan Atlantic margin in direct relation with the Atlantic rift. In this basin, an asymmetric rift is set up on the old Hercynian structures during the Carnien-Norien, the paroxysm is reached at the Trias-Lias passage with the installation of basalts (CAMP: Central Atlantique Magmatic Province).

During rifting (syn-rift stage in the Upper Triassic), the MBEB basin experienced three major phases of sediment filling. The first phase is purely continental, the first deposits to arrive in the opening basin are of proximal fluvial origin. Subsequently, the decrease of the paleopente and the rise of the base level generated paleoenvironmental changes in the basin (2nd phase), and the deposition system evolved towards distal environments. During the third phase, the syn-rift sedimentary series recorded a marine incursion in the late Triassic with saliferous sedimentation. This marine intervention is deduced from the presence of a thick saliferous series with a large lateral extension and whose isotopic ratios of sulfur and bromine contents indicate their marine origin. These marine waters are probably of Tethysian origin and are also linked to the opening of the Proto-Atlantic.

In Portugal, the Upper Triassic is represented by two formations in the north of the Lusitanian basin (Palain, 1976): Silves Fm which is fluvial sandstone and Dagorda Fm which includes first dolomites and then evaporites. In this Portuguese basin, the proximal-distal fluvial transition took place at the Norien-Rhétien limit. This also rift-type basin was filled with continental fluvial and alluvial clastic rocks of the Silves Formation, largely derived from the adjacent Iberian highlands of the Meseta. Locally, black shales are present at the top of the Silves and may represent the first marine incursion into the basin.

The comparison between the two basins shows that they followed a similar evolution at the base and in the middle of the series but at the top the MBEB basin presented thick layers of evaporites while that of Portugal presented mainly dolomites attributed to paralic facies.

Palain, C., 1976. Une série détritique terrigene; 'les grès de silves'; Trias et Lias inférieur du Portugal. Mem. Serv. Geol. Portugal, p. 25 (377 pp.)

How to cite: Essamoud, R., Afenzar, A., and Belqadi, A.: Triassic sedimentation on the Eastern Atlantic margin: two examples from Moroccan Meseta and Portugal, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3259, https://doi.org/10.5194/egusphere-egu22-3259, 2022.

Multiple geoscientific studies along the Main Ethiopian and Eastern rifts have revealed that extension via magma intrusion now prevails over plate stretching as the primary mechanism for strain accommodation throughout the crust and mantle lithosphere. However, problematic in this picture is where the Main Ethiopian and Eastern rifts meet, across the low-lying, broadly-rifted, and as-yet poorly-studied Turkana Depression which separates the elevated Ethiopian and East African plateaus. We have so far revealed through body-wave tomography (Kounoudis et al., 2021), that the Depression does not lack mantle dynamic support in comparison to the plateaus, suggesting a significantly thinned crust, resulting from superposed Mesozoic and Cenozoic rifting, most likely explains its low elevations. Slow uppermost-mantle wavespeeds imply the presence of either melt-intruded mantle lithosphere or ponded asthenospheric material below lithospheric thin-spots induced by the region’s multiple rifting phases. To better illuminate the Depression’s lithosphere-asthenosphere system, we conduct a surface-wave analysis to image crust and uppermost-mantle structure using data from the NSF-NERC funded Turkana Rift Arrays Investigating Lithospheric Structure (TRAILS) project broadband seismic network. In particular, we investigate the presence of melt, whether the lithosphere is melt-rich, melt-poor, and/or if ponded zones of asthenosphere exist below variably thinned lithosphere. Group velocity dispersion curves, measured using data from local and regional earthquakes, yield the first high resolution fundamental mode Rayleigh-wave group velocity maps for periods between 4 and 40s for the Turkana Depression. In collaboration with the ongoing TRAILS GPS project, we explore how these results relate to present-day versus past episodes of extension.

Kounoudis, R., Bastow, I.D., Ebinger, C.J., Ogden, C.S., Ayele, A., Bendick, R., Mariita, N., Kiangi, G., Wigham, G., Musila, M. & Kibret, B. (2021). Body-wave tomographic imaging of the Turkana Depression: Implications for rift development and plume-lithosphere interactions. G3, 22, doi:10.1029/2021GC009782.

How to cite: Kounoudis, R., Bastow, I., Ebinger, C., Ogden, C., Ayele, A., Bendick, R., Mariita, N., Kianji, G., Musila, M., and Sullivan, G.: The Crust and Uppermost-Mantle Structure of the Turkana Depression: Insights from Surface-Wave Analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4683, https://doi.org/10.5194/egusphere-egu22-4683, 2022.

During the formation of rifted continental margins, a rift evolves through a number of stages that produce major sedimentary basins and distinct rifted margin domains. While these domains have been classified based on the resulting structures and crustal thickness seen in geophysical data, the evolution of the fault network that produces these domains is not as well understood. Further, margin architecture may be influenced by erosion and sedimentation. Previous studies have qualitatively examined how faults respond to sedimentation during rifting, but there has not been a quantitative study on how variable surface processes efficiency affects fault network properties and the effect this has on rift evolution.

In this study we use a two-way coupling between the geodynamic code ASPECT (Kronbichler et al., 2012) and the surface processes code FastScape (Braun and Willett, 2013) to run 12 high-resolution 2D rift models that represent asymmetric, symmetric, and wide rift types (Neuharth et al., in review). For each rift type, we vary the surface process efficiency by altering the bedrock erodibility (K_f) from no surface processes to low (K_f = 10^-6 m^0.2/yr), medium (10^-5), and high efficiency (10^-4). To analyze these models, we use a novel quantitative fault analysis toolbox that extracts discrete faults from our continuum models and correlates them through space and time (https://github.com/thilowrona/fatbox). This toolbox allows us to track faults and their properties such as the number of faults, their displacement, and cumulative length, to see how they evolve through time, as well as how these properties change given different rifting types and surface processes efficiency.

Based on the evolution of fault network properties, we find that rift fault networks evolve through 5 major phases: 1) distributed deformation and coalescence, 2) fault system growth, 3) fault system decline and basinward localization, 4) rift migration, and 5) continental breakup. Each of these phases can be correlated to the rifted margin domains defined from geophysical data (e.g., proximal, necking, hyperextended, and oceanic). We find that surface processes do not have a large impact on the overall evolution of a rift, but they do affect fault network properties by enhancing strain localization, increasing fault longevity, and reducing the total length of a fault system. Through these changes, they can prolong rift phases and delay continental breakup with increasing surface process efficiency. To summarize, we find that surface processes do not change the overall evolution of rifts, but they do affect fault growth and as a result the timing of rifting.

Braun, J., and Willett, S.D., 2013, A very efficient O(n), implicit and parallel method to solve the stream power equation governing fluvial incision and landscape evolution: Geomorphology, v. 180–181, p. 170–179, doi:10.1016/j.geomorph.2012.10.008.

Kronbichler, M., Heister, T., and Bangerth, W., 2012, High Accuracy Mantle Convection Simulation through Modern Numerical Methods.: Geophysical Journal International, v. 191, doi:doi:10.1111/j.1365-246x.2012.05609.x.

Neuharth, D., Brune, S., Wrona, T., Glerum, A., Braun, J., and Yuan, X.P., (in review at  Tectonics), Evolution of rift systems and their fault networks in response to surface processes, [preprint], doi: https://doi.org/10.31223/X5Q333

How to cite: Neuharth, D., Brune, S., Wrona, T., Glerum, A., Braun, J., and Yuan, X.: Evolution of rift systems and their fault networks in response to surface processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5758, https://doi.org/10.5194/egusphere-egu22-5758, 2022.

The palaeobathymetric evolution of rifted margins during continental breakup is complex. We investigate the subsidence of Late Triassic to Early Jurassic evaporitic sequences in the proximal and distal parts of the Scotian margin that formed during the opening of the Central Atlantic Ocean.

We use a 3D flexural backstripping technique, which incorporates decompaction and post-breakup reverse thermal subsidence modelling applied to key stratigraphic intervals through the Jurassic down to the Late Triassic base salt. The isostatic evolution of rifted margins depends on crustal thinning, lithosphere thermal perturbation and melt production during rifting and breakup. Quantitative analysis of seismic reflection and gravity anomaly data together with subsidence analysis have also been used to determine crustal thickness variations and ocean–continent transition structure, and to constrain the along strike variability in breakup related magmatism and crustal composition.

Reverse post-breakup subsidence modelling to the Late Triassic base salt restores this horizon at breakup time to near sea level in the proximal domains of the Scotian margin where the continental crust was only slightly thinned during rifting. In contrast, predicted palaeobathymetry of the base salt surface restored to breakup time is greater than 2 to 3 km in the distal parts of the margin where the continental crust was highly thinned (<10km) close to the ocean-continent-transition. One possible interpretation of this is that while the proximal salt underwent post-rift thermal subsidence only, the distal salt was deposited during the latest stage of rifting focused along the distal domains of the Scotian margin, where it underwent additional tectonic subsidence from crustal thinning. This observed difference between the subsidence of proximal and distal salt has been observed elsewhere on the South Atlantic margins (e.g., the Angolan Kwanza margin) and illustrates the complexity of the subsidence and palaeobathymetric evolution of distal rifted margins during breakup.

The deposition of Triassic evaporites occurred before and after the emplacement of the Central Atlantic Magmatic Province (CAMP). The impact of the CAMP on rifting, crustal structure and palaeobathymetric evolution of the Nova Scotia remains to be determined. We do not exclude an additional positive dynamic topography effect at breakup time related to the CAMP magmatic event.

How to cite: Tugend, J., Kusznir, N., Mohn, G., Deptuck, M., Kendell, K., Keppie, F., Morrison, N., and Dmytriw, R.: Palaeobathymetric evolution of the Nova Scotia rifted margin during the Central Atlantic Ocean opening, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5938, https://doi.org/10.5194/egusphere-egu22-5938, 2022.

Early Carboniferous igneous rocks are widespread in the Southern Urals. We have obtained new stratigraphic and isotopic data on plutonic and volcanic complexes, allowing us to determine correlation of their age and to construct a new geodynamic model.

The prevailing tectonic setting in the Southern Urals during the Early Carboniferous was sinistral transtension. Volcanic and plutonic complexes in transtensional zones were synchronously formed along large submeridional orogen-parallel strike-slip faults, but are particularly abundant within two N–S-trending zones: Magnitogorsk and East Ural.

The upper Tournaisian–lower Visean sequence in the Magnitogorsk zone consists mainly of moderately alkaline volcanic rocks, basalt and rhyolite are predominant, but pyroclastic, volcano-sedimentary, terrigenous, and carbonate rocks are also widespread. The middle Visean sequence consists of moderately alkaline basalt, andesite, dacite including lavas, tuffs and tuffites. The thickness of the Lower Carboniferous volcanic group varies from 1200 to 5500 m. The age of the volcanic rocks has been proved by findings of foraminifera in limestone interbeds. The oldest volcanic rocks appear in upper Tournaisian, while the youngest are found in the middle upper Visean. New U–Pb zircon dating using SHRIMP is now in progress.

Volcanic rocks in the East Ural zone occur within a few tectonic sheets. The sequence consists of lavas and tuffs of basalt, basaltic andesite, andesite and rhyolite. The total thickness of the sequence varies from 800 to 1500 m. The age of the sequence is determined by findings of fossil plants as middle Visean.

We studied eight plutons in the Magnitogorsk and six in the East Ural zones. Most of them record several intrusive phases. The composition of the rocks varies from gabbro to granodiorites and granites from normal to moderately alkaline series. We combined our new isotopic data on zircons (SHRIMP) with published ages and came to the following conclusions.

• Two main stages of Early Carboniferous plutonism can be distinguished in the Southern Ural. The first began simultaneously in both zones at the Devonian/Carboniferous boundary (ca. 356–357 Ma) and then changed to volcanic activity at around 346 Ma in the Magnitogosk zone and at around 340 Ma in the East Ural zone, respectively. The second stage began after the termination of volcanic activity and corresponds to 334–327 Ma interval in both zones. So, stages of active volcanism and plutonism alternate in time.
• Early Carboniferous rifting began with intrusion of plutons, usually associated with transtensional zones under oblique collision. The subsequent volcanic stage corresponds to local extension. The next stage of plutonism began just after volcanism termination and marked a cessation of tectonic activity.

The reported study was funded by RFBR and Czech Science Foundation according to the research project № 19-55-26009. Centre of collective usage ‘Geoportal’, Lomonosov Moscow State University (MSU), provided access to remote sensing data.

How to cite: Pravikova, N., Tevelev, A., Kazansky, A., Kosheleva, I., Sobolev, I., Borisenko, A., Koptev, E., Shestakov, P., and Žák, J.: Early Carboniferous rifting in the Southern Urals: New isotopic dating of plutonic and volcanic complexes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6172, https://doi.org/10.5194/egusphere-egu22-6172, 2022.

The East African Rift System (EARS) is the largest active continental rift on Earth. Inherited lithospheric strength variations have played a large role in forming the system’s current geometry. The partly overlapping eastern and western EARS branches encompass the large Victoria continental microplate that rotates counter-clockwise with respect to Nubia, in striking contrast to its neighboring plates.

Both the forces driving rifting in the EARS as a whole and the rotation of Victoria in particular are debated. Whereas some studies largely ascribe the rifting to horizontal mantle tractions deriving from plume-induced flow patterns (e.g., Ghosh et al., 2013), or to more equal contributions of mantle tractions and gravitational potential energy (e.g., Kendall and Lithgow-Bertelloni, 2016), recent work by Rajaonarison et al. (2021) points to a dominant role for lithospheric buoyancy forces in the opening of the rift system. Similarly, other numerical modeling (Glerum et al., 2020) has shown that Victoria’s rotation can be induced through drag of the major plates along the edges of the microplate transmitted along stronger lithospheric zones, with weaker regions facilitating the rotation, without the need for plume-lithosphere interactions (e.g., Koptev et al., 2015; Calais et al., 2006).

With unprecedented data-driven, regional spherical geodynamic numerical models spanning the EARS and the upper 660 km of mantle, we aim to identify the individual contributions of lithosphere and mantle drivers of deformation in the EARS and of Victoria’s rotation. Observational data informs the model setup in terms of crustal and lithospheric thickness, sublithospheric mantle density structure and plate motions. Comparison to separate observations of the high-resolution model evolution of strain localization, melting conditions, horizontal stress directions, topography and horizontal plate motions allows us to identify the geodynamic drivers at play and quantify the contributions of large-scale upper mantle flow to the local deformation of the East African crust.

Calais et al. (2006). GSL Special Publications, 259(1), 9–22.

Ghosh et al. (2013). J. Geophys. Res. 118, 346–368.

Glerum et al. (2020). Nature Communications 11 (1), 2881.

Koptev et al. (2015). Nat. Geosci. 8, 388–392.

Rajaonarison et al. (2021). Geophys. Res. Letters, 48(6), 1–10.

How to cite: Glerum, A., Brune, S., and Ben Mansour, W.: Geodynamic Drivers of the East African Rift System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7155, https://doi.org/10.5194/egusphere-egu22-7155, 2022.

Fossil carbonate reefs are common along rifts and rifted passive margins. They provide valuable paleoecological and paleogeographical information. Moreover, porous reef buildups are targeted as potential oil and gas reservoirs and sites for gas storage.

The Red Sea and Gulf of Suez contain several generations of reef deposits: (1) syn-rift Early and Middle Miocene reefs that formed along the eroded footwalls of normal faults, and (2) post-rift Pliocene-Holocene coastal reefs that split apart, subsided, and aggraded to form carbonate platforms by salt-driven raft tectonics. The Late Miocene lacks reefs due to evaporitic conditions. This study focuses on the uplifted Early-Middle Miocene reef deposits, which outcrop sporadically along the Arabian and African margins of the Red Sea, particularly the northern half, over a distance of ~1000 km. They are exhumed along the coastal plain at elevations of 50-150 meters. We studied several reefs on the Arabian side and carried out age determination implementing a revised planktonic foraminifera zonation and paleoenvironmental interpretation. We also used satellite images to identify and map similar exhumed reefs on the African side.

The Miocene reefs are located along the eroded footwalls of normal fault scarps that form the first or second marginal half grabens, usually sitting unconformably over the basement. The flat reef and back-reef lagoonal facies are often removed by erosion, but the dipping thick fore-reef talus breccias are preserved. The breccias are an unsorted mix of coral reef and back reef debris and also contain basement clasts. The linear fore-reef talus deposits follow along the fault scarps, revealing paleo-valleys incised into the hanging wall. Placing the reef on the basin-scale helps us distinguish the tectonic influence, accompanied by climate and eustatic sea-level variation, on shallow marine carbonates during rifting.

Mapping all published, newly discovered, and inferred outcrops along the African and Arabian coast of the Red Sea allow us to develop a new tectono-sedimentary model for reef evolution in the syn-rift setting. The proposed model explains the absence of the reef outcrops in the southern areas of the Arabian Red Sea and predicts subsurface zones where reef growth possibly took place. Nature of the contact between reef carbonates and the underlying Precambrian basement in conjunction with the consistently preserved fore-reef zone disclose the uplift history and erosion events prior and post reef growth. In addition, following the reef distribution, we developed a syn-rift paleogeographic model of the Red Sea.

How to cite: Pensa, T., Afifi, A., Delaunay, A., and Baby, G.: Tectonic control on the reef evolution in the Red Sea syn-rift basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7186, https://doi.org/10.5194/egusphere-egu22-7186, 2022.

Within rifted margins, the necking domain corresponds to the area where drastic reduction in basement thickness leads the crust to attain a wedge-shape. The crustal thinning occurs along detachment fault systems typically recording displacements in the order of 10s of kilometers. These systems commonly shape the crustal taper and eventually the taper break, where crustal thickness is thinned to 10 km or less. In recent years, it has become clear that evolutionary models for detachment fault systems remain unsatisfactory as the well-known principles for smaller magnitude fault systems are not fully applicable to these large-magnitude systems. Consequently, the detailed responses in the foot- and hanging walls and associated basin sedimentation within detachment fault systems and necking domains remain poorly understood compared to those observed in extensional half-graben basins.

We use interpretation of 3D- and 2D seismic reflection data from the Mid-Norwegian rifted margin to discuss the effects of lateral interaction and linkage of extensional detachment faults on the necking domain configuration. We investigate how the structural evolution of these detachment faults interact with the effects of isostatic rollback to produce complex 3D geometries and control the configuration of the associated supradetachment basins. The study area demonstrates how successive incision may induce a complex structural relief in response to faulting and folding. In the proximal parts of the south Vøring and northeastern Møre basins, the Klakk and Main Møre Fault Complexes form the outer necking breakaway complex and the western boundary of the Frøya High. We interpret the previously identified metamorphic core complex within the central Frøya High as an extension-parallel turtleback-structure. The now eroded turtleback is flanked by a supradetachment basin with two synclinal depocenters resting at the foot of the necking domain above the taper break. We attribute footwall and turtleback exhumation to Jurassic-Early Cretaceous detachment faulting along the Klakk and Main Møre Fault Complexes. The study area further demonstrates how detachment fault evolution may lead to the formation of younger, successively incising fault splays locally. Consequently, displacement may occur along laterally linked fault segments generated at different stages in time. Implicitly, the detachment fault system may continue to change configuration and therefore re-iterate itself and its geometry during its evolution.

How to cite: Gresseth, J. L. S., Osmundsen, P. T., and Péron-Pinvidic, G.: Evolution of detachment fault systems within necking domains: insights from the Frøya and Gossa Highs, mid-Norwegian margin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8003, https://doi.org/10.5194/egusphere-egu22-8003, 2022.

How to cite: Ferrante, G., Rivalta, E., and Maccaferri, F.: Spatio-temporal evolution of rift volcanism driven by progressive crustal unloading, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8663, https://doi.org/10.5194/egusphere-egu22-8663, 2022.

Marginal Seas are extensional basins formed in a convergent setting near active subduction zones. They are characterized by a short life (<25 Ma), as well as unstable and changing directions of seafloor spreading. However, the underlying processes involved in their formation from rifting to seafloor spreading initiation are still debated (supra-subduction convection/extension, slab-pull). This problem is further compounded by the fact that our understanding of continental breakup is primarily derived from the evolution of magma-poor and magma-rich Continent-Ocean Transitions (COT) of the Atlantic margins.

In this contribution, we characterize the tectono-magmatic processes acting during continental breakup by investigating the COT structures of three main Marginal Seas located in the Western Pacific, namely the South China Sea, the Coral Sea and the Woodlark Basin. All three examples formed under rapid extension rates and propagation of seafloor spreading. Although each marginal basin has its uniqueness, we show that these three marginal basins are characterized by a narrow COT (typically <~20 km), documenting the sharp juxtaposition of continental crust against igneous oceanic crust. The COT of the three basins shows that final extension is accommodated by the activity of one major low-angle normal fault. This extension is contemporaneous with important magmatic activity expressed by volcanic edifices, dykes and sills emplaced in the distalmost part of these margins. Such narrow COT suggests that a rapid shift from rifting to spreading.

The rapid localization of extensional deformation in a narrow area has major implications for partial melting generation. The evolution of extensional structures is controlled by the interplay of lithospheric thinning, asthenosphere upwelling and decompression melting. High extension rate prevents conductive cooling and lead to focus volcanic activity in a narrow area evolving rapidly in space and time to magmatic accretion. Causes for the fast extensions rates of Marginal Sea rifting are likely controlled by kinematic boundary conditions directly or indirectly controlled by nearby subduction zones. Such mode of breakup is probably not limited to marginal Seas but only enhanced in such settings.

How to cite: Mohn, G., Ringenbach, J.-C., Nirrengarten, M., Tugend, J., McCarthy, A., and Lei, C.: Continental breakup style of Marginal Seas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8715, https://doi.org/10.5194/egusphere-egu22-8715, 2022.

Breakup volcanism along rifted passive margins is highly variable in time and space. The factors controlling magmatic activity during continental rifting and breakup are not resolved and controversial. Here we use numerical models to investigate melt generation at rifted margins with contrasting rifting styles corresponding to those observed in natural systems. Our results demonstrate a surprising correlation of enhanced magmatism with margin width. This relationship is explained by depth-dependent extension, during which the lithospheric mantle ruptures earlier than the crust, and is confirmed by a semi-analytical prediction of melt volume over margin width. The results presented here show that the effect of increased mantle temperature at wide volcanic margins is likely over-estimated, and demonstrate that the large volumes of magmatism at volcanic rifted margin can be explained by depth-dependent extension and very moderate excess mantle potential temperature in the order of 50-80 °C, significantly smaller than previously suggested.

How to cite: Lu, G. and Huismans, R.: Melt volume at Atlantic volcanic rifted margins controlled by depth-dependent extension and mantle temperature, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9420, https://doi.org/10.5194/egusphere-egu22-9420, 2022.

Permian-Triassic rifts of the West Siberian basin compose one of the largest continental rift systems in the world. The Koltogor-Urengoy and Khudosey rifts of meridional strike are the main structures in the eastern part of the basin and are filled mainly by basaltic lavas with clastic sediments. However, in the central part of the West Siberian plate felsic lavas are widespread along with mafic volcanics. Here we present the detailed data on composition of lavas, whole-rock geochemistry, geophysical features and U-Pb ages from the Frolov-Krasnoleninsky region in the central part of the West Siberian basin.

Within the studied region, Permian-Triassic rifts of NW and NE strike are predominant. The main structure is Rogozhnikov-Nazym graben of NW strike, composed of rhyolite-dacitic lavas.  According to the seismic data, this volcanic area comprises multiple local eruptive centers (1-5 km in diameter). Lavas constitute the major part of the volcanic pile, while tuffs are subordinate (up to 15%). Deep boreholes did not reach the base of volcanic sequence, but its thickness exceed 0.5 km.

The main geochemical features of the Rogozhnikov-Nazym volcanics are: 1) acidic composition and increased alkali content; 2) signs of supra-subduction setting: Ta-Nb and Pb anomalies; 3) high ratios of all incompatible trace elements. According to these features, volcanic rocks of the Rogozhnikov-Nazym graben were formed in the setting of post-collisional extension. Furthermore, coeval felsic lavas are widespread in smaller structures of the Frolov-Krasnoleninskiy region and demonstrate similar geochemical characteristics.

We obtained 9 U-Pb (SHRIMP) ages from felsic lavas of the Rogozhnikov-Nazym graben and other rift structures. All samples yielded ages in the range from 254±2 to 248.2±1.3 Ma (Late Permian – Early Triassic). Thus, volcanic activity in the Frolov-Krasnoleninsky region was nearly synchronous to the main phase of Siberian Traps magmatism in the Siberian platform.

Volcanic rocks of the Frolov-Krasnoleninsky region constitute rifts of NW strike (mainly felsic lavas, including the Rogozhnikov-Nazym graben) and NE strike (mainly mafic lavas, geochemically similar to the Siberian Traps basalts). We suggest that orientation of rifts inherits two conjugate strike-slip fault systems, which mark the W-E compression during the preceding collisional event in the Early-Middle Permian, and the mechanism of extension is similar to pull-apart model. The contrasting composition of volcanics can be caused by different-depth zones of magma generation.

The Permian-Triassic volcanics are overlain by continental coal-bearing coarse-grained volcanoclastic sediments of the Chelyabinsk Group (Middle Triassic – Early Jurassic). These deposits fill the local depressions in the paleotopography. The Middle Jurassic clastic Tyumen Formation overlays both volcanic rocks and Chelyabinsk Group, covers almost the entire territory of the Frolov-Krasnoleninsky region and marks the initiation of post-rift subsidence in the West Siberian basin.

How to cite: Smirnova, M., Latyshev, A., Panchenko, I., Kulikov, P., Khotylev, A., and Garipov, R.: Permian-Triassic rifts of the West Siberian basin: evidence of voluminous felsic volcanic activity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9480, https://doi.org/10.5194/egusphere-egu22-9480, 2022.

NE Brazil is scarred by a number of aborted rift basins that developed from the same extensional stresses that lead to the opening of the South Atlantic. Extension started in Late Jurassic times, with the formation of an AfroBrazilian Depression south of the Patos Lineament, and continued through the Early Berriasian along two NS trending axes of deformation: Recôncavo-Tucano-Jatobá (RTJ) and Gabon-Sergipe-Alagoas (GSA). In the Late Berriasian - Early Barremian, rifting jumped North of the Pernambuco Lineament to progress along the NE-SW trending Cariri-Potiguar (CP) axis. In the Late Barremian, approximately coinciding with the opening of the Equatorial Atlantic, rifting aborted along the RTJ and CP axes and continued along the GBA trend eventually resulting in continental break-up. Extension-related magmatic activity seems to have been restricted to break-up along the marginal basins, although dyke swarms bordering the Potiguar basin (Rio Ceará-Mirim) seem to be associated to early extension stages in NE Brazil and three subparallel dolerite dykes, with K-Ar dates of 105±9 Ma, were inferred indirectly from aeromagnetic and outcrop data East of the RTJ axis. Aiming at better understanding the structure and evolution of the syn-rift basins of NE Brazil, a total of 20 seismic stations were deployed between October 2018 and January 2021 along the CP and RTJ trends. The deployment, funded by the national oil company Petrobras, included both broadband and short-period stations borrowed from the Pool de Equipamentos Geofísicos do Brasil. These stations complemented a number of permanent broadband stations belonging to the Rede Sismográfica do Brasil. Receiver functions were obtained for each of the seismic stations from teleseismic P-wave recordings and S-wave velocity models were developed from their joint inversion with dispersion velocities from an independent tomographic study. In the RTJ basins, our results show that the crust is about 41 km thick and displays a thick (5-8 km) layer of fast-velocity material (> 4.0 km/s) at its bottom; in the Potiguar basin, our results show a thinner crust of about 30-35 km underlain by an anomalously slow (4.3-4.4 km/s) uppermost mantle. We argue that those anomalous layers are the result of syn-rift and/or post-rift magmatic intrusions, which would have had the effect of increasing velocity at lower crustal levels under the RTJ basins and decreasing velocity at uppermost mantle depths under the Potiguar basin. If correct, ou interpretation would imply that, in spite of an overall lack of evidence at shallow levels, deep magmatic processes have played a role in the formation and evolution of the syn-rift basins of NE Brazil.

How to cite: Julià, J., Döring, M., and Barbosa, T.: Crustal architecture under the NE Brazil syn-rift basins from receiver functions: Evidence of deep magmatic processes., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9962, https://doi.org/10.5194/egusphere-egu22-9962, 2022.

Since the middle Triassic the long-lived convergent margin of western Gondwana evolved from a relatively steeply inclined into a flat lying slab setting that combined an extensional regime on the backarc side with the telescoping of crustal slices at the continental margin. In the Northern Andes the opening of Late Triassic basins is practically contemporaneous with the outwedging of lower crustal slices, that often alternate with intrusive sheets of S-type granites and mark the limit to a  non-metamorphic roof. A tectonic coupling between backarc collapse and the escape of lower crustal slices can be examined in detail in the northwestern flank of the Sierra Nevada de Santa Marta, a northern-most outlier of the North Andean basement. Remnants of a Late Triassic graben fill attest here to a block tilted toward the hinterland. Its tri-partite sedimentary sequence recycled material sourced from external parts of the continental margin. The basement of a more foreland-oriented block of the Sevilla belt is affected by outward-verging folds, which have formed under greenschist facies conditions in its upper and lower amphibolite conditions in its lower part. The succeeding Inner Santa Marta Metamorphic Belt consists of a stack of high-grade metamorphic basement slices separated by siliciclastic wedges metamorphosed under lower amphibolite conditions. The soles of the basement slices consist of migmatites with remobilized granitic pods and resulting folds oriented in a dip-slip direction. These structures are overprinted by a flattening and a second migmatitic event, which records peak P-T conditions of a lowest crustal level. Accordingly, they contain inclusions of ultramafic rocks. The time-equivalent correspondence between a supracrustal  backarc extension and a foreland-directed stacking of crustal slices suggests some similarity to the model  of a low-viscosity channel of a thickened orogenic crust. An important difference of this flat-slab setting resides, however, in a wholesale mobility of a strongly heated crust that constitutes the backarc and frontal position of this active margin.

How to cite: Avila Paez, M. A., Kammer, A., Conde Carvajal, C. A., Piraquive Bermudez, A., and Gomez Plata, C. N.: Backarc rifting as a response to a crustal collapse at the western Gondwana margin: The Triassic tectonic setting of the Sierra Nevada de Santa Marta, Northern Andes of Colombia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10866, https://doi.org/10.5194/egusphere-egu22-10866, 2022.

Rifted margins are the result of the successful process of thinning and breakup of continents leading to the formation of new oceanic lithosphere. Observations on rifted margins are now integrating an increasing amount of multi-channel seismic data and drilling of several Continent-Ocean Transitions. Based on large scale geometries and domains observed on high-quality long-offset seismic lines, we illustrate a simple classification based on mechanical behavior and magmatic production. Therefore, rifted margins are not divided into opposing types, but described as a combination and continuum that can evolve through time and space from ductile to brittle mechanical behavior on one hand and from magma-poor to magma-rich on the other hand.

For instance, margins such as the Mauritania-Senegal Basin evolve north to south from a magma-poor to a magma-rich margin. Margins such as the Vøring one suffered different rifting episodes evolving from ductile deformation in the Devonian to more brittle and magma-poor rifting in the Cretaceous prior to a final magma-rich breakup in the Paleogene.

Thanks to these examples and to some others, we show the variability of the rifted margins worldwide but also along strike of a single segment and through time along a single margin in order to explore and illustrate some of the forcing parameters that can control the initial rifting conditions but also their evolution through time.

How to cite: Sapin, F.: Rifted margins classification and forcing parameters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11260, https://doi.org/10.5194/egusphere-egu22-11260, 2022.

The breakup of Pangaea in Early Mesozoic times initiated first in the Central Atlantic region, where Triassic to Early Jurassic lithosphere extension led to continental breakup and oceanic accretion. The Central Atlantic rifted margins of NW Africa and eastern North America exhibit complex along-strike variations in structural configuration, crustal geometries, and magmatic budget at breakup. Quantifying these lateral changes is essential to understand the tectonic and geodynamic processes that dominated rifting and continental breakup. The existing seismic refraction lines along the African side and its American conjugate provide good constraints on the 2D crustal architecture of several Central Atlantic margins. However, they are insufficient to quantify the ambiguous lateral variations.

This work examines the central segment of the Moroccan Atlantic margin, which is named here the Sidi Ifni-Tan Tan margin. Using 2D seismic reflection and well data, we quantify the stratigraphic and structural architecture of the margin. We then use this to constrain 2D and 3D gravity models, to predict crustal thickness and types. Ultimately, our results are integrated with previous findings from the conjugate Nova Scotia margin, on the Canadian side, to propose a rift to drift model for this segment of the Central Atlantic and discuss the tectonic processes that dominated rifting and decided the fate of continental breakup.

How to cite: Gouiza, M.: Rift to drift evolution and crustal structure of the Central Atlantic: the Sidi Ifni-Nova Scotia conjugate margins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11336, https://doi.org/10.5194/egusphere-egu22-11336, 2022.

The East African Rift System (EARS) is the classic example of an active continental rift associated with extension, deformation, lithosphere thinning, and generation of magmas from different mantle domains and depths. Magmatism and tectonics have always been closely linked and their mutual relationships concern many processes such as the kinematics and rates of extension, the passive versus active role of mantle upwelling and magma genesis. In addition, the spatial and temporal variations of the geochemical signature of magmas varies in response to different mantle domains contributing to their genesis (subcontinental lithosphere, asthenosphere and deeper mantle sources).

In this study we carefully screened an exhaustive geochemical database of basalts (including authors’ unpublished data) emplaced in the EARS to decipher the possible connection between different mantle domains, and the evolution and tectonic characteristics of the EARS. The geochemical data were subdivided according to spatial and temporal criteria: from a spatial point of view, the samples were ascribed to five groups, namely Afar, Ethiopia, Turkana depression, Kenya and Tanzania. From a temporal point of view, the magmatic activity of the EARS was subdivided into three main temporal sequences: 45-25 Ma, 25-10 Ma and 10-0 Ma.

The geochemical signature and radiogenic isotopes (Sr, Nd, Pb) of the selected basalts reveal significant spatial and temporal variations and permits to place important constraints on the contribution of subcontinental lithosphere, asthenosphere, and lower mantle in magma genesis

How to cite: Braschi, E., Tommasini, S., Corti, G., and Orlando, A.: Spatial and temporal variation of magmatism in the East African Rift System: influence of tectonics and different mantle domains, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11973, https://doi.org/10.5194/egusphere-egu22-11973, 2022.

When continental lithosphere is extended to break-up it forms two conjugate passive margins. In many instances, these margins are asymmetric: while one is wide and extensively faulted, the conjugate thins more abruptly and exhibits little faulting. Recent studies have suggested that this asymmetry results from the formation of an oceanward-dipping sequential normal fault array and rift migration leading to the observed geometry of asymmetric margins. Numerical models have shown that fault sequentiality arises as a result of asymmetric uplift of the hot mantle towards the hanging wall of the active fault. The preferential localization of strain reinforced by strain weakening effects is random and can happen on either conjugate. However, along the long stretch of the South Atlantic margins, from the Camamu-Gabon to the North Santos-South Kwanza conjugates, the polarity can be very well correlated with the distance of the rift to nearby cratonic lithosphere. Here, we use numerical experiments to show that the presence of a thick cratonic root inhibits asthenospheric flow from underneath the craton towards the adjacent fold belt, while flow from underneath the fold belt towards the craton is favoured. This enhances and promotes sequential faulting and rift migration towards the craton and resulting in a wide faulted margin on the fold belt and a narrow conjugate margin on the craton side, thereby determining the polarity of asymmetry, as observed in nature.

How to cite: Gudipati, R., Pérez-Gussinyé, M., Andres-Martinez, M., Neto-Araujo, M., and Phipps Morgan, J.: Passive margin asymmetry and its polarity in the presence of a craton, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12619, https://doi.org/10.5194/egusphere-egu22-12619, 2022.

The choice of crustal and mantle densities in numerical geodynamic models is usually based on convention. The isostatic component of the topography is, however, in most if not all cases not calibrated to fit observations resulting in not very well constrained elevations. The density distribution on Earth is not easy to constrain because it involves multiple variables (temperature, pressure, composition, and deformation). We provide a review and global analysis of the topography of the Earth showing that elevation of stable continents and active mid-ocean ridges far from hotspots on average is +400 m and -2750 m respectively. We show that density values for the crust and mantle, commonly used for isostatic modeling result in highly inaccurate prediction of topography. We use thermodynamic calculations to constrain the density distribution of the continental lithospheric mantle, sub-lithospheric mantle, the mid-ocean ridge mantle, and review data on crustal density. We couple the thermo-dynamic consistent density calculations with 2-D forward geodynamic modelling including melt prediction and calibrate crustal and mantle densities that match the observed elevation difference. Our results can be used as a reference case for geodynamic modeling that accurately fits the relative elevation between continents and mid-ocean ridges consistent with geophysical observations and thermodynamic calculations. 

How to cite: Theunissen, T., Huismans, R. S., Lu, G., and Riel, N.: Relative continent/mid-ocean ridge elevation: a reference case for isostasy in geodynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12955, https://doi.org/10.5194/egusphere-egu22-12955, 2022.

A holistic understanding of rift initiation, evolution, and variation is made complicated by the difficulties of deep seismic imaging, limited modern examples of continental rifting, and few accessible outcrops of fossil rifted margins. In particular, The temporal structural and rheological evolution of the mantle lithosphere during riftingis poorly constrained. The mantle lithosphere rheology controls lithospheric strength at initiation, but how deformation is partitioned between the crust and mantle,  and how the paths for melt migration from the asthenosphere to the rift surface evolve during rifting is fundamental for our understanding of the rift-to-drift evolution .
Here, we use elastoplastic-viscoelastoplastic modeling in concert with published deep seismic profiles of Atlantic rifted margins and geological insights from the Lanzo peridotite outcrops in the Alps to propose a new mode of extensional tectonics in the subcontinental mantle. We run a series of dynamic models varying initial conditions and mechanisms of deformation localization in the mantle lithosphere consistent with mechanisms of ductile shear zone formation observed at slow spreading centers. Models and geophysical surveys show homologous, sigmoidal reflectors in the mantle, a reversal of fault vergence as seafloor spreading develops, exhumation of the mantle, and increasing magmatic accretion. Geological evidence, along with the coincidence of magmatic accretion and extensional structures in the mantle, suggests that faults in the mantle may serve as conduits for melt, resulting in bright reflectors on seismic profiles.

How to cite: Montiel, N., Massini, E., Lavier, L., and Müntener, O.: Characterizing mantle deformation processes during the rift-to-drift transition at magma-poor margins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13043, https://doi.org/10.5194/egusphere-egu22-13043, 2022.

A common observation in plate tectonics is the successive stages of rifting and associated crustal and lithospheric thinning, and subsequent convergence and inversion of sedimentary basins. Rates and style of inversion often vary across the sedimentary basins, influenced by changing stress and thermal fields, different convergence directions, and also controlled by inherited structures, all of which determine the localization and style of the resulting deformation. However, the dynamic feedbacks between lithospheric tectonics and surface processes, and their 3D expressions have not been studied in details by previous models, even though erosion and sediment distribution exerts a significant control on differential vertical movements and thermal evolution.

In this study, we investigate strain partitioning during extension and subsequent structural inversion, and tackle the coupling between tectonics, mantle melting and surface processes. To do so, we apply the 3D thermo-mechanical code I3ELVIS (Gerya 2015; Munch et al. 2020), which is based on staggered finite differences and marker-in-cell techniques to solve the mass, momentum and energy conservation equations for incompressible media. The models also take into account simplified melting processes, as well as erosion and sedimentation by diffusion.

We compare the modeling results with seismic and well data from the Mediterranean back-arc basins, such as the Alboran, Tyrrhenian and Pannonian Basins. The temporal variation of different plate convergence and slab retreat velocities lead to the extensional formation, recent structural inversion and related differential vertical motions of these basins. In fossil extensional basins, plate convergence has ultimately overprinted the former basin structure, and lead to the rise of young orogens, i.e. the Pyrenees or Great Caucasus.

How to cite: Oravecz, É., Balázs, A., Gerya, T., May, D., and Fodor, L.: Structural inversion of sedimentary basins: insights from 3D coupled thermo-mechanical and surface processes models and observations from the Mediterranean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-542, https://doi.org/10.5194/egusphere-egu22-542, 2022.

The Troodos ophiolite of Cyprus hosts a fossil spreading ridge at the Solea graben, whose last magmatic activity has been previously dated to 94.3±0.5 Ma. To study the evolution of a dying ridge, we collected structural geologic data and oriented specimens from the mantle section (serpentinized peridotites, pegmatitic dykes, pyroxenite and wehrlite intrusions) and lower crust (layered gabbros and massive gabbros) for paleomagnetic and rock magnetic analyses. Our results revealed a systematic pattern of horizontal axis rotations (i.e., tilt) in the region to the west of the Solea spreading axis, involving upper crust, lower crust, and upper mantle. Horizontal axis rotations vary in magnitude between ~20° to ~90° within the studied area, with the largest tilts observed to the west of the exposed mantle section at Mt. Olympus, and the smallest tilts observed near the NNW-SSE trending Troodos Forest-Amiandos fault system. This rotation pattern conflicts with previous interpretations considering the Troodos Forest-Amiandos fault as an oceanic detachment, and rather indicates the existence of deep-rooted listric faults that dismembered the Solea spreading ridge after the final phase of spreading.

Paleomagnetic directions from serpentinized peridotites indicate that serpentinization occurred both before and during dismemberment of the ridge by listric faulting. As these directions also record a well-studied regional 90° counter-clock-wise rotation of the Troodos ophiolite, we constrained the timing of ridge dismemberment and associated serpentinization between ~94 Ma and the beginning of the regional microplate rotation in the Turonian, hence encompassing a relatively short period of time of 2-4 Myr that well coincides with hydrothermal alteration in nearby plagiogranites dated at ~92–90 Ma.

How to cite: Advokaat, E., Maffione, M., Burton-Johnson, A., and Dekkers, M.: Anatomy of a dying spreading ridge: paleomagnetic evidence for horizontal axis rotations in the Troodos Ophiolite, Cyprus, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-957, https://doi.org/10.5194/egusphere-egu22-957, 2022.

Continental extension at mature rifts systems focuses along spreading segments where dominant magmatic activity, diking and minor faulting assist plate divergence. Such processes make adjacent spreading segments grow but also interact at zones where the spreading is transferred from one segment to another. A great variety of tectonic structures has been observed at transfer zones, encompassing parallel strike-slip faults (bookshelf faulting) or conjugate systems of en-echelon oblique faults. Transfer zones can also become transform plate boundaries once continental breakup occurs. However, the role of magma in influencing the deformation at rift-rift transfer zones is unclear as direct observations are rare. In this study, we address this open question by exploiting high-resolution Pléiades-1 tri-stereo imagery to produce the first 1 m DEM of the Afrera Plain transfer zone, between the Erta Ale and Tat Ali spreading segments in Northern Afar. This dataset has been used to conduct a detailed structural analysis of both tectonic and magmatic features and explore their geometrical and spatial relationships. We observed different trends and kinematics: Dikes opens with an extension oriented ~N65°E, consistent with the regional extension; tectonic features have instead an extensional component with direction varying between ~N46°E and ~N68°E. Riedel shears and measurements of fractures opening directions indicate that tectonic deformation occurs along two families of NW-SE- and NS-striking oblique faults having right-lateral and left-lateral components, respectively. At the same time, spatial relationships between faults and lava flows also indicate that magmatic and tectonic activity co-exist in the transfer zone. We explain these observations by two different strain fields acting in the Afrera Plain during magmatic and amagmatic phases. During magmatic phases, dikes open orthogonal to the spreading direction responding to the regional extension. Conversely, during amagmatic phases, the transfer zone is dominated by the interaction between the two spreading segments with counterclockwise rotations of the strain field and shear motions accommodated by conjugate fault systems.

How to cite: La Rosa, A., Pagli, C., Hurman, G., and Keir, D.: Analysis of high-resolution Digital Elevation Model (DEM) of the Afrera Plain (Afar) reveals relationship between magmatism and tectonics in a rift transfer zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1175, https://doi.org/10.5194/egusphere-egu22-1175, 2022.

        The tectonic evolution of the North Atlantic Ocean has been extensively studied using a variety of geological, geophysical, and plate reconstruction techniques. Recently, deformable plate tectonic reconstructions, built using the GPlates software, have become an increasingly used method for studying the plate kinematics, deformation, and subsequent crustal thickness evolution of tectonic regimes. For the North Atlantic Ocean in particular, deformable plate models have proven to be useful for studying the kinematic evolution of continental blocks (e.g. Flemish Cap and Galicia Bank) and the partitioning of strain within sedimentary basins (e.g. Orphan Basin). However, despite these advancements, previously published deformable plate models have included limitations that can be geologically unsatisfying. Some notable examples include, but are not limited to, uniform crustal thickness assumptions at model start times, and the rigid nature of continental blocks and model boundaries that define the limits of where deformation takes place.  

        Using the interplay of GPlates and its python programming module, pyGPlates, we present a new deformable plate modelling strategy and application within the North Atlantic Ocean. In contrast to previous studies, this approach considers deformation within continental blocks and the reconstruction of present day crustal thickness estimates calculated via gravity inversion. In addition, we also demonstrate the minimized impact of rigid landward model boundaries using this approach and the resultant ability to reconstruct rift domain boundaries a priori. The results of this study provide insight into the pre-rift (200 Ma) crustal thickness template of the North Atlantic and the evolution of relevant continental blocks during rift-related deformation. Furthermore, this work also highlights the potential impact of Appalachian and Caledonian terrane boundaries on the distribution and extent of rifting experienced along the Newfoundland, Ireland, and West Iberian offshore rifted margins.  

How to cite: King, M. and Welford, J. K.: Reconstructing deformable continental blocks and crustal thicknesses back through time within the North Atlantic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1310, https://doi.org/10.5194/egusphere-egu22-1310, 2022.

With increased geophysical scrutiny of the NE Newfoundland-Irish margin pair (North Atlantic), the previously assumed conjugate relationship and rift-perpendicular extension between the Flemish Cap and Goban Spur are increasingly questioned. We present multichannel reflection profiles along the Flemish Cap, the Porcupine Bank, and the Goban Spur, along which structural domains (proximal, necking, hyperextended, and/or exhumed mantle domains included) are defined. Features of each structural domain along these profiles on the Flemish Cap and the Goban Spur are strikingly different, whereas similar structural features are observed in the necking domains along seismic profiles on the Porcupine Bank and the Flemish Cap. The variability in basement features suggests oblique rifting between the Flemish Cap and the Goban Spur-Porcupine Bank region, as well as a connection between the Porcupine Bank and the Flemish Cap during Early Jurassic rifting. This understanding is consistent with crustal thickness evolution calculated from a deformable plate reconstruction model that is locally updated based on seismic interpretation constraints and previously published plate reconstructions. The updated deformable plate model shows varying extension obliquity between the Porcupine Bank, Goban Spur, and Flemish Cap, which are strongly influenced by inherited Caledonian and Variscan structures, resulting in the conclusion that the Flemish Cap and the Goban Spur were not conjugate margins prior to the opening of the modern North Atlantic Ocean.

How to cite: Yang, P. and Welford, J. K.: Conjugate no more: redefining the pre-rift relationship between the Flemish Cap and the Goban Spur prior to the North Atlantic opening, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2780, https://doi.org/10.5194/egusphere-egu22-2780, 2022.

The Wilson Cycle of closing and opening of oceans is often schematically portrayed with ‘empty’ oceanic basins. However, bathymetric and geophysical observations outline anomalous topographic features, such as microcontinents and oceanic plateaus, that can be accreted when oceans close in subduction. This implies that numerous rifted margins have formed in regions characterized by the presence of previously accreted continental terranes. The main factors controlling where and how such continental rifts localize in relation to the inherited compressional structures is yet to be explored properly. Potential factors that can influence the evolution and structural style of a rift in such a tectonic setting include the thermo-tectonic age of the accretionary orogen, the number and type (size, rheology) of accreted terranes, the nature of terrane boundaries, as well as the velocity of rifting.

We use 2D finite-element thermo-mechanical models to investigate how the number and size of accreted terranes as well as the duration of tectonic quiescence between orogenesis and extension (i.e., the amount of time available for the thermal re-equilibration of the thickened lithosphere) affect the style of continental rifting. Our results can further understanding of how rifted margins formed after accretionary orogenesis are influenced by the compressional stage such as the Norwegian rifted margin, where the late-Paleozoic to Mesozoic rifting occurred after the early Paleozoic Caledonian orogeny.

We test two hypotheses. According to our first hypothesis, the location of the rift is dependent on the age of the accretion. If extension directly follows accretion, we expect the thick lithosphere of the orogen to be strong in a brittle sense, causing extension to localise adjacent to the orogen. In contrast, if the onset of extension happens after a period of tectonic quiescence, the accretionary orogen has time to heat up and viscously weaken, allowing it to localize deformation more efficiently. We test this hypothesis by varying the amount of time available for thermal re-equilibration.

Secondly, we hypothesize that the degree to which the compressional structures such as terrane boundaries in the accretionary stack reactivate depends on the size and complexity of the accreted assembly (through the number and size of the accreted terrains) as well as the strength of shear zones. We test this hypothesis by varying the number of terranes accreted prior to rifting.

Our preliminary results show that the subduction interface is reactivated in an extensional regime, but without a period of quiescence the reactivation is temporary and rifting occurs in the unthickened foreland basin area.

How to cite: Erdős, Z., Buiter, S., and Tetreault, J.: The influence of accretionary orogenesis on rift dynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3220, https://doi.org/10.5194/egusphere-egu22-3220, 2022.

The intracontinental belt of the High Atlas is an aborted rift system along NW Africa, which formed during the Mesozoic break-up of Pangaea and was inverted during the Alpine Orogeny. Although the inversion and orogeny build-up have been extensively studied, the Triassic to Jurassic rifting, synchronous to the opening of the Atlantic and the Tethys, is still poorly understood. True orthogonal rifting is proposed to occur in the Triassic to Early Jurassic, while the end of rifting is controversial and believed to be controlled by oblique extension. Restoration of the Atlantic-Tethys triple junction suggests sinistral motion between Iberia and Africa being active during the Middle Jurassic, which reactivated pre-existing NE-SW trending Hercynian weaknesses in transtension mode. This led to the formation of a series of pull-apart basins involving the basement and localised volcanic activity.

The Atlas system is an excellent field analogue to analyse the role of strike-slip tectonics in extensional systems, especially in the early stages of rifting. Despite the late Cenozoic (Alpine) inversion, the well-exposed syn-rift structures and sediments have been weakly affected by the broad contractional event.

Our study aims to investigate the kinematic and geometry of the oblique rifting phase, the strain variation lengthwise in the Atlas rift system, the relationship between the orthogonal rift structures, the strike-slip structures, and the synchronous volcanism. In this contribution, we will highlight the fieldwork results, which we used to constrain the restoration of the rift sytem, quantify extension vs. transtension, and produce a conceptual model of how strike-slip tectonics can influence the early stages of a rift system.

How to cite: Vasileiou, A., Gouiza, M., Mortimer, E., and Coliier, R.: Analysis of strike-slip tectonics in extensional systems: the case of the Moroccan Atlas system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3597, https://doi.org/10.5194/egusphere-egu22-3597, 2022.

Quantifying the spatial and temporal evolution of fault systems is crucial in understanding plate boundary deformation and the associated seismic hazard, as well as to help georesources exploration in sedimentary basins. During the last decade, 3D lithospheric-scale geodynamic models have become capable of simulating the evolution of complex fault systems, from the onset of rifting to sea-floor spreading. But since these models describe faults as finite-width shear zones within a deforming continuum, additional efforts are needed to isolate and analyse individual faults, so we can understand the entire life span of normal fault networks.

Here we present 3D numerical forward models using the open-source community software ASPECT. Our thermo-mechanical models include visco-plastic rheology, strain softening as well as lithospheric and asthenospheric layers to capture rift evolution from inception to continental break-up. We quantify normal fault evolution at the surface of the model with a method that describes fault systems as 2D networks consisting of nodes and edges. Building on standard image analysis tools such as skeletonization and edge detection, we establish a hierarchical network structure that groups nodes and edges into components that make up individual evolving faults. This allows us to track fault geometries and kinematics through time enabling us to analyse the growth, linkage and disintegration of faults.

We find that the initial fault network is formed by rapid fault growth and linkage, followed by competition between neighbouring faults and coalescence into a mature fault network. At this stage, faults accumulate displacement without a further increase in length. Upon necking and basin-ward localisation, the first generation of faults shrink and disintegrate successively while being replaced by newly emerging faults in the rift centre. These new faults undergo a localisation process similar to the initial rift stage. We identify several of these basin-ward localisation phases, which all feature this pattern. In oblique rift models, where the extension direction is not parallel to the rift trend, we observe strain partitioning between the rift borders and the centre, with strike-slip faults emerging in the centre even at moderate obliquity. Analysing the spatio-temporal evolution of modelled faults thus allows us to map their entire life span to observed stages of rift system evolution.

How to cite: Brune, S., Wrona, T., Neuharth, D., Glerum, A., and Naliboff, J.: Life and Death of Normal Faults: Quantitative Analysis of Fault Network Evolution in 3D Rift Models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6294, https://doi.org/10.5194/egusphere-egu22-6294, 2022.

The northwestern margin of the Iberian Peninsula (western Bay of Biscay) is a unique place that gathers several outstanding geological features in a relatively reduced area. Here, a former hyperextended continental margin developed in proximity to a triple point, underwent a subsequent partial tectonic inversion yielding the present Cantabrian margin. For all these reasons, the northwest area of ​​Iberia can be considered as a natural laboratory for the study of the role of tectonic inheritance in the evolution of the extensional continental margins and their subsequent inversion. However, and largely due to the lack of interest from exploration companies, the northwestern margin of Iberia presented a great deficit of geophysical and geological information. Both scientific interest and the lack of information provided the main reasons for the MARIBNO amphibious project (2019-2022). This project is being carried out by a multidisciplinary geoscientific team leaded by the Complutense University of Madrid with the acquisition of offshore and onshore data. The main objectives are focused on the study of the crustal structure, the tectonic control by the structure prior to the alpine stages and the mapping and characterization of the crustal domains, combining geological and geophysical criteria.

A one month-long geophysical cruise was carried out aboard the BO Sarmiento de Gamboa (Spanish Research Council, CSIC) in September-October of 2021. Data acquisition was divided in two cruise legs: The WAS Leg consisted in the acquisition wide-angle seismic data (WAS) along 3 transects with simultaneous offshore-onshore recording in 3 component short-period instruments: Transect WAS-1 (∼320 km) recorded in 14 OBS and 11 land seismometers, Transect WAS-2 (∼260 km) recorded in 12 OBS and 10 land seismometers and Transect WAS-3 (∼255 km) recorded in 9 OBS and 12 land seismometers. The seismic source consisted in an airgun array with 4660 ci and 90 seconds of shot interval. The MCS leg consisted in the acquisition of 2D multichannel seismic reflection data (MCS) along 14 transects (∼1500 km) recorded on a digital streamer with a 12.5 m channel-interval. Several streamer configurations were deployed with 480, 240 and 168 channels and the seismic source consisted in an airgun array with 1960 ci. During both legs, continuous marine acquisition of multibeam bathymetry, gravity, geomagnetics and ultra-high resolution seismic data also were carried out. MARIBNO project is still underway, and the data are being processed and interpreted. Acquired information will be complemented and combined with the additional acquisition of onshore gravity and magnetic data and the information from several geological field mapping studies on seismic transects throughout the Cantabrian Mountains. Here we show some preliminary results and the current development of the MARIBNO amphibious project.

How to cite: Muñoz-Martín, A., Granja-Bruña, J.-L., De la Fuente-Oliver, M. A., Druet, M., De Vicente, G., Gallastegui Suárez, J., and Maestro, A. and the MARIBNO WORKING GROUP: MARIBNO amphibious project: Structure of the northwestern Iberian margin and role of the inherited tectonics in the Alpine extension and inversion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6886, https://doi.org/10.5194/egusphere-egu22-6886, 2022.

Extensional detachment faults, core complexes and supradetachment basins play major roles in the evolution of 3D rifted margin architecture. The successive incision of basement from early to late stages in the margin evolution is rarely explained in 3D. One reason for this is likely the lack of a unifying model for how very large faults grow and link laterally, and how this, in turn, links to the temporal evolution of the margin. As fault shape exerts a fundamental control on syn-rift basin architecture, the 3D evolution of detachment faults is critical to understand sedimentation in associated basins.

In the proximal margin offshore Norway, one control on lateral variation appears to be the differential exploitation of `extraction´ structures that evolved above the ductile crust. This controlled flips in fault polarity under the proximal margin, and lateral transitions from supradetachment- to half-graben style, Late Paleozoic-Triassic basins. Extensional culminations and core complexes were associated with this deformation pattern at depth.

The growth of an extensional fault past a displacement of a few kilometers will involve a change in 3D fault shape related to the isostatic rollback of parts of the fault plane. As displacement magnitude varies along the fault plane, so will the amount of extensional unloading and associated isostatic compensation. With increasing extension this will enforce a particular shape on the fault plane, with an extensional culmination developing in the area of maximum displacement, and synclinal recesses evolving on the flanks. With continued extension, the culmination evolves into a core complex. Necking domains, where faults propagate into the ductile middle crust appear to be prime locations for this type of faulting. As large-magnitude faults combine into domain-bounding breakaway complexes, this results in intermittent occurrences of core complexes along the main breakaways and lateral transitions into steeper megafaults and fault arrays. At the Mid-Norwegian margin, we interpret the Jurassic-Cretaceous North Møre and south Vøring basins to illustrate this type of evolution. Components of strike-slip may modify this type of pattern, as illustrated by  continental core complexes exposed in areas such as Death Valley and western Norway.

How to cite: Osmundsen, P. T., Péron-Pinvidic, G., Gresseth, J. L., and Braathen, A.: 3D evolution of extensional detachment faults and their effect on the architecture of rifts and rifted margins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7480, https://doi.org/10.5194/egusphere-egu22-7480, 2022.

The Neuquén Basin is a major Mesozoic sedimentary depocenter located in the foreland of the Andes Mountains in Argentina. The basin hosts world renown inversion systems that have been the target of georesource exploration for the last three decades. The Huincul High is a structurally and economically prominent ~270km long, E-W trending feature that formed by the accretion of exotic Paleozoic terranes influencing subsequent Mesozoic deformation in the basin. Exploration in Huincul High has been mainly focused on the shallow part of the inversion structures leaving a limited understanding of  deep structural architecture and early tectonic evolution. With this research, for the first time a set of 4 3D seismic reflection surveys covering an area of 1400km2 have been analysed and integrated with stratigraphic information from 15 exploratory wells to provide new insights into the tectonostratigraphic and kinematic evolution of the western reaches of the Huincul High.

Detailed horizon and fault interpretation revealed Late Triassic, isolated, 10-50km long NE-SW to NW-SE trending half grabens. These extensional systems are attributed to the Late Triassic cessation of the Andean subduction to the west and intraplate extension regime ensuing. Thickness map of the Lower Jurassic Los Molles unit shows the development of an extensive ~50km  long ~15km wide NE-SW depocentre at that time. It is proposed that Andean subduction was renewed at that time, moving the Neuquén Basin into a backarc environment with hotter, weaker continental lithosphere thinned by mantle underflow which might have caused ductile flexural sag and minimal brittle faulting.

Prominent NE-SW cylindrical inversion anticlines ~17km across and well-developed harpoon structures are observed in the hangingwall of reactivated  ~50km long, NE-SW trending, extensional faults. Growth strata analysis shows thinning of Middle to Lower Cretaceous strata over the crest of these folds suggesting a phase of  NW-SE compression at this time. This compressional phase is attributed to the increase in Andean subduction rate and shallowing of the subduction dip, as the Neuquén Basin is moved into a foreland setting. Fault displacement analysis suggests that the reactivated faults were formed as separate fault segments at the time of extension in the Late Triassic. Additionally, analysis indicates that faults segments with increased reactivation show prominent hangingwall inversion anticlines.

Dip-steered coherency extractions along the Early Cretaceous Vaca Muerta Formation showed en echelon NW-SE transtensional faults occurring directly above Late Triassic non inverted faults; decoupled by the underlying shaly and mechanically weak Los Molles unit. These observations point to a post-inversion tectonic event that might coincide with reconfiguration of subducted plates changing the principal stress orientation and causing strike slip reactivation.

These results highlight the importance of  structural inheritance of a pre-existing  fault architecture in the development of  consequent inversion, and how mechanically weak units can inhibit fault propagation during the later compressional events, acting as a decoupling layer.  A detailed evolutionary model is proposed for the western reaches of the Huincul High which envisages crustal weakening and thermal sag to explain the thickening of the Early Jurassic strata previous to the main Cretaceous inversion.

How to cite: Antonov, I., Scarselli, N., and Adam, J.: Tectonic and geometric assessment of inversion systems in the Huincul High, Neuquén Basin (Argentina) – the role of structural inheritance and mechanical stratigraphy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8244, https://doi.org/10.5194/egusphere-egu22-8244, 2022.

Footwall fault scarp-degradation produces sediments resulting in gravity-driven syn-rift wedge-shaped deposits located on the immediate hangingwall. To understand which aspects control footwall scarp-degradation we propose a model suggesting where, why, and how degradation occurs. We compare five offshore 3D seismic surveys acquired on the Northern Carnarvon Basin (North West Shelf of Australia) calibrated with well data to assess these questions. Two 3D seismic surveys (i.e., Panaeus 2001 East and Fortuna) are located on the Dampier Sub-basin, proximal to the Western Australia coastline and three (i.e., Thebe, Bonaventure and Agrippina) in a more distal position on the Exmouth Plateau. Data show that degradation is more pronounced on the distal surveys compared to the proximal ones. On the proximal surveys, the sedimentation rate is greater than in the distal ones, and footwall scarp-degradation is less pronounced. Answering these questions will help us to predict the style and the amount of footwall scarp-degradation in similar extensional settings.

How to cite: Martinez, C., Chiarella, D., Jackson, C. A.-L., and Scarselli, N.: Regional-scale proximal to distal footwall scarp-degradation variability of extensional faults, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8726, https://doi.org/10.5194/egusphere-egu22-8726, 2022.

Throughout Earth’s history, the movement, suturing, and rifting of tectonic plates in the Wilson cycle often takes advantage of lithospheric weaknesses and pre-existing plate boundaries. Continental rifting and subduction initiation represent arduous phases of this cycle for plate divergence and convergence, respectively, where strain is not yet focused into a narrow and mature plate boundary. Here we present an analysis of the Puysegur margin to demonstrate how past tectonic regimes create inherited lithospheric structures that facilitate subsequent stages of the Wilson cycle.

The Puysegur margin is a young subduction zone and forms the northern segment of the Australian-Pacific plate boundary south of New Zealand, which has evolved from divergence to strike-slip and recently to oblique convergence, all in the last ~45 million years. Magnetic anomalies and curved fracture zones located south of the Puysegur segment show the divergent phase involved seafloor spreading and the formation of new oceanic lithosphere. However, these features are not present in the upper Pacific plate at the latitudes of the Puysegur margin, and the lack of quality seismic images in this region hampered our understanding of the local crustal structure, which was assumed to be a northward extension of the oceanic domain. A deep penetrating multichannel reflection (MCS) and ocean-bottom seismometer (OBS) dataset was acquired in 2018 with the R/V Langseth and provided new high-quality seismic images of the crustal structure along the Puysegur margin.

Our seismic images reveal that the overriding Pacific plate contains stretched continental crust with magmatic intrusions, which formed from rifting between Zealandia continental plateaus during AUS-PAC plate divergence. This stretching phase was highly asymmetric and resulted in the opening of the Solander Basin. Rifting was more advanced to the south, yet never proceeded to breakup and seafloor spreading as previously thought. A new southern continent-ocean transition is inferred from potential field data, marking the boundary between stretched continental crust and new oceanic crust formed during the extensional phase.

Along-strike heterogeneity with mixed continental and oceanic domains and asymmetric rift architecture along the Puysegur margin were critical features for following tectonic regimes. Increasingly oblique plate motions sparked strike-slip motion, which localized near the pre-existing spreading center in the south, but along the western edge of the rift zone in relatively unstretched crust at the Puysegur margin in the north. Translational motion juxtaposed weak ~10 Myr old oceanic lithosphere with buoyant continental crust across the strike-slip boundary. Incipient subduction transpired as oceanic lithosphere from the south forcibly underthrust continent lithosphere at an oblique collision zone.

We suggest that subduction initiation at the Puysegur Trench was enabled by inherited buoyancy contrasts and structural weaknesses that were imprinted into the lithosphere during earlier phases of continental rifting and strike-slip along the plate boundary. In the global evolution of plate tectonics, strike-slip might be the key component to achieving the Wilson cycle, as it is the most efficient mechanism to offset terranes and juxtapose lithospheric domains of contrasting properties across broad regions, thus generating advantageous conditions for subduction initiation and subsequent closure of oceanic basins.

How to cite: Shuck, B., Van Avendonk, H., Gulick, S., Gurnis, M., Sutherland, R., Stock, J., and Hightower, E.: A Cenozoic Wilson cycle along the Puysegur Margin, New Zealand: The role of rift architecture and strike-slip dynamics enabling subduction initiation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10197, https://doi.org/10.5194/egusphere-egu22-10197, 2022.

The Gulf of Mexico opened as a Late Triassic-Mid Jurassic continental rift that was first largely covered by the Mid-Jurassic Louann Salt and later split apart by a triangular-shaped oceanic crust. Salt in the Gulf of Mexico largely hampers the imaging and interpretation of underlying pre-salt and crustal geometries, which are fundamental for assessing the early kinematic evolution of the margin. To better define these deep geometries and their lateral variations, we built three seismic-based crustal-scale cross-sections across the Florida-Yucatan conjugate margins, in the areas where the Mid-Jurassic salt unit is thinner.

Seismic-based cross-sections image the architecture of rifting and the geometries of the continental and oceanic crusts and the transition between them (ocean-continent transition, OCT). They show a meaningful along-strike variation: the South Florida-East Yucatan area is characterized by a narrower rifted continental crust that evolves sharply to oceanic crust whereas in the North Florida and central-western Yucatan areas, the rifted continental crust is wider and the transition to the oceanic crust corresponds to a narrow magmatic or exhumed mantle domain. In the rifted continental crust, seismic profiles image doubly-verging basement faults organized into decoupled and coupled rift domains. The geometrical and cross-cutting relationships between these basement faults, the Louann Salt and the underlying pre-salt sequence indicates a progressive migration of rifting from proximal to distal domains and from the central and north-eastern to the south-eastern Gulf of Mexico.  

Bulk continental crust extension was determined using the area balancing method. Estimated horizontal extension values vary from a minimum of ∼120 km in the South Florida-East Yucatan conjugate to a minimum of ∼240 km in the North Florida-Central Yucatan conjugate, being systematically larger in the northern margin. Crustal domains identified in the cross-sections were laterally correlated and westwards extended considering gravity and magnetic anomalies data to build a regional-scale, crustal domains map of the Gulf of Mexico. This map, together with the crustal extension estimates, has been used as the reference to carry out a plate-scale reconstruction of the Gulf of Mexico from the early rifting stages to the end of oceanic spreading.

Based on our observations and considering previous models, we propose that the study area evolved from an early rift involving magmatism, to a magma-poor margin, with continental break-up (OCT formation) being characterized by mantle exhumation and associated magmatism along the North Florida and central-western Yucatan areas.

How to cite: Izquierdo-Llavall, E., Ringenbach, J. C., Sapin, F., Rives, T., Callot, J.-P., and Nielsen, C.: Crustal structure and along-strike variations in the Gulf of Mexico conjugate margins: From early rifting to oceanic spreading, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11453, https://doi.org/10.5194/egusphere-egu22-11453, 2022.

Rift-related inheritance plays a key role in orogenic building, by controlling the thermal state and the position of major sedimentary and crustal decollement levels. As recognized by various authors, a switch from thin- to thick-skinned style of deformation in reactivated rifted-margin during convergence occurs where the necking domain of the margin is involved in the subduction. This is observed in the External Crystalline Massifs (Aar, Mont-Blanc, Belledonne, Pelvoux, Argentera) located at the transition between the external and the internal domains of the western Alps corresponding also to the proximal-distal transition (necking domain) of the former Jurassic margin. Necking reactivation during Alpine convergence is accommodated by shear zones, rooted in the ductile middle crust, propagating  the deformation toward the external domain.  This Alpine overprint, which led to a lower greenschist metamorphism (ca. 330°C) in the External Crystalline Massifs, raise the question of the preservation of the rift-related, pre-alpine structures in the western Alps, and their use as fossil-analogues of present-day necking domains.

A case study is the internal Mont-Blanc massif, where preserved pre-rift to syn-rift (Triassic to Mid-Jurassic) cover is observed below the internal nappes, and on top the crustal basement (Mont-Blanc granite). The contact between these deposits and the underlying basement is a fault zone, made of a cataclastic basement overlaid by a black gouge. Above the contact, remnants of allochthonous pre-rift deposits and delaminated carbonates are observed. The syn-rift sandstones (Grès Singuliers Fm), which are either in contact with the fault or located above the pre-rift deposits, contain reworked clasts of cataclasite. Above the contact, in the cataclastic basement, some crinoid-rich sediments of likely Pliensbachian age fill open cracks. Taken together, these observations strongly point to the preservation of a pre-alpine, rift-related detachment fault of Jurassic age.

The petrographical and geochemical analysis of the exhumed fault indicates strong hydration-assisted deformation. In the cataclasite, feldspars breakdown and important element transfer (especially Ba, F, Si, Pb, Zn and REE) suggest fluid circulation in an open system. The black gouge matrix is mostly made of illite, likely recrystallized during the Alpine overprint. In addition, different generations of syn-kinematic veins are observed in the detachment. The first type, composed of graphite precipitated at ~400°C in the cataclasite. Syn-kinematic quartz and quartz hyalophane (Ba-rich feldspars) in the cataclasite and gouge were formed from a fluid above 170°C a salinity of ~9 wt.% NaCl-equivalent. The mobilized elements are the same as those involved in pre-alpine Pb-Zn (Ba-F) ore-deposits of the internal Mont-Blanc (Amône, Mont-Chemin, Catogne), suggesting a genetic link between rift-related faults and mineralisations.

Despite partial Alpine metamorphic overprint, the early tectonic, sedimentary and geochemical records of this rift-related detachment fault are very well preserved, making a good analogue of present-day necking domains. The example of Mont-Blanc massif gives an opportunity to study all these aspects in detail, in particular to understand fluid-mediated element mobility during rifting. Finally, it can be used to better understand the final stages of reactivation of the necking domain in a mature orogenic system.

How to cite: Dall'asta, N., Hoareau, G., Manatschal, G., and Ribes, C.: Preservation of the necking domain in orogens: a case study of the Mont-Blanc massif (Western Alps, France), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11778, https://doi.org/10.5194/egusphere-egu22-11778, 2022.

Late Miocene calc-alkaline intrusions in the back-arc of Southern Patagonia mark an eastward migration of the arc due to accelerated subduction velocity of the Nazca plate or slab flattening preceding active ridge subduction. Amongst these intrusions are the emblematic Torres del Paine (51°S) and Fitz Roy (49°S) plutonic complexes, crystalised at ca. 12.5 and ca. 16.5 Ma, respectively (Leuthold et al., 2012; Ramírez de Arellano et al., 2012). Both intrusions are located at the eastern boundary of the Southern Patagonian Icefield and form prominent peaks with steep slopes that are ~3 km higher in elevation than the surrounding low-relief foreland. Their exhumation has been proposed as a response to glacial erosion and associated glacial rebound since ca. 7 Ma (Fosdick et al., 2013), and/or by regional dynamic uplift between 14 and 6 Ma due to the northward migration of subducting spreading ridges (Guillaume et al., 2009). Here we present a new data set of apatite and zircon (U-Th)/He from both plutonic complexes, numerically modelled to unravel their late-Neogene to Quaternary thermal histories. Our results show three rapid cooling periods for the Fitz Roy intrusion: at ca. 9.5 Ma, at ca. 7.5 Ma, and since ca. 1 Ma. For Torres del Paine, inverse thermal modelling reveals short and rapid cooling at ca. 6.5 Ma followed by late-Quaternary final cooling. The 10 Ma cooling signal only evidenced in the northern plutonic complex (Fitz Roy) may represent an exhumation response to the northward migrating subduction of spreading ridge segments, causing localized dynamic uplift. Thus, the absence of exhumation signal before 6.5 Ma in the southern part (Torres del Paine) suggest that the spreading ridge subduction must have occurred before its 12.5 Ma emplacement. On the other hand, rapid cooling by similar magnitude in both plutonic complexes between ca. 7.5–6.5 Ma, likely reflects the onset of late-Cenozoic glaciations in Southern Patagonia. Finally, the late-stage Quaternary cooling signals differ between Torres del Paine and Fitz Roy, likely highlighting different exhumation responses (i.e. relief development vs. uniform exhumation) to mid-Pleistocene climate cooling. We thus identify and distinguish the causes of rapid exhumation periods in the Southern Patagonian Andes, and propose a first Late Miocene exhumation pulse due to subduction of spreading ridge dynamics, and two Late Cenozoic exhumation episodes due to regional climate changes that have shaped alpine landscapes in this region.

References:

Leuthold J., et al. 2012. Time resolved construction of a bimodal laccolith (Torres del Paine, Patagonia). EPSL.

Ramírez de Arellano C., et al. 2012. High precision U/Pb zircon dating of the Chaltén Plutonic Complex (Cerro Fitz Roy, Patagonia) and its relationship to arc migration in the southernmost Andes. Tectonics.

Fosdick J. C., et al. 2013. Retroarc deformation and exhumation near the end of the Andes, southern Patagonia. EPSL.

Guillaume B. 2009. Neogene uplift of central eastern Patagonia: Dynamic response to active spreading ridge subduction? Tectonics.

How to cite: Paiva Muller, V. A., Sue, C., Valla, P., Sternai, P., Simon-Labric, T., Martinod, J., Ghiglione, M., Baumgartner, L., Herman, F., Reiners, P., Gautheron, C., Grujic, D., Shuster, D., and Braun, J.: Exhumation signals and forcing mechanisms in the Southern Patagonian Andes (Torres del Paine and Fitz Roy plutonic complexes), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-226, https://doi.org/10.5194/egusphere-egu22-226, 2022.

How to cite: Tien, C.-Y., White, N., Maclennan, J., and Conway-Jones, B.: Constraining Neogene Mantle Dynamics of Western Mediterranean Region Encompassing Iberia by Quantitative Modeling of Basalt Geochemistry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-354, https://doi.org/10.5194/egusphere-egu22-354, 2022.

Mantle convection generates transient vertical motion at the surface, which is referred to as dynamic topography. The bulk of topography and bathymetry is isostatically supported by variations in the thickness and density of both the crust and the lithosphere which means that dynamic topography generated by sub-plate density anomalies needs to be isolated from these dominant isostatic signals. Australia’s isolation from plate boundaries and its rapid northwards translation suggest that long-wavelength dynamic topography is primarily controlled by the interplay between plate motion and sub-plate convection. Along the eastern seaboard of Australia, the coincidence of elevated topography, positive long-wavelength free-air gravity anomalies and Cenozoic basaltic magmatism imply that a combination of asthenospheric temperature anomalies and thinned lithosphere generate and maintain regional topography. Distributions of onshore and offshore intraplate magmatism reflect both plate motion and convective instabilities. Compilations of deep seismic reflection profiles, wide-angle surveys and receiver function analyses are used to determine crustal velocity structure across Australia. Residual (i.e. dynamic) topographic signals are isolated by isostatically correcting local crustal structure with respect to a reference column that sits at sea level. The resultant pattern of dynamic topography is consistent with residual bathymetric anomalies from oceanic lithosphere surrounding Australia. Significant positive dynamic topography occurs along the eastern seaboard and in southwest Australia (e.g. Yilgarn Craton). These signals are corroborated by independent geologic evidence for regional uplift.

How to cite: Slay, P., White, N., and Stephenson, S.: Dynamic Topography of the Australian Continent and its Margins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-373, https://doi.org/10.5194/egusphere-egu22-373, 2022.

Lithosphere removal beneath orogenic plateaus are transient events that must often be inferred from the absence of evidence: for example, unexplained topographic uplift in the geologic record, or the absence of high-velocity mantle lithosphere. Even when foundering events do leave traces of their occurrence on the surface, the low preservation potential of such evidence leaves incomplete and ambiguous records. Distinctive features include isotopically juvenile magmatism and transient surface subsidence that form localized, internally drained hinterland basins and playas. However, basaltic volcanism and related lacustrine sediments are rarely well preserved, and this limits our ability to evaluate the role of lithosphere removal in orogenesis to only select localities. To develop a more comprehensive record of this process, and facilitate comparisons between regions with copious surface and/or geophysical evidence of lithospheric foundering with regions where the evidence is scant, whether poorly preserved or not yet recognized, we present the detrital record from young strata in internally-drained hinterland basins as a proxy for foundering-related magmatism. The detrital samples include unconsolidated to poorly consolidated lacustrine sediment of the Bidahochi paleolake from the Colorado Plateau, which is associated with the isotopically juvenile (positive epsilon Nd) Hopi Buttes Volcanic field; Oligocene siltstone from the Pamir Plateau with juvenile isotopic signature (positive epsilon Hf); and Eocene-Oligocene sandstone from several localities on the Tibetan Plateau. Integration of isotope geochemistry, trace element geochemistry, and thermochronology of detrital zircon and apatite presents a promising approach to reconstruct a continuous record of low-volume magmatism, both eroded and preserved. Ti-in-zircon thermometry, Ce-U-Ti oxybarometry, and REE proxies for depth of magmatic differentiation potentially provide a means of distinguishing zircon crystals associated with hinterland magmatism from that associated with arc magmatism. Using these datasets, we consider whether lithospheric foundering can be associated with recognizable patterns that are similar across orogens, and whether geochemical shifts in hinterland magmatism reveal first-order differences in the temporal scale of lithosphere removal in different orogens. 

How to cite: He, J. and Kapp, P.: Evaluating scant surface evidence of deep lithosphere removal: Towards a more comprehensive record, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-443, https://doi.org/10.5194/egusphere-egu22-443, 2022.

Although seismic tomography has provided important constraints on the long-wavelength structure of the mantle and its planform of convection, much is yet not well understood about the dynamic interaction of tectonic plates and deep mantle circulation at intermediate wavelengths (i.e., below plate-scale). In particular, a better understanding of the seismic structure of the oceanic upper mantle could potentially help unraveling the relationships between different scales of mantle convection, hotspot volcanism, and surface observables (e.g., MORB geochemistry, gravity gradients and bathymetry). We here present a new tomographic model of the shear-wave velocity and radial anisotropy structure beneath the central and southern Atlantic ocean constructed from the inversion of surface and body waves waveforms down to 30s period. Preliminary results confirm the existence of quasi-periodically distributed low-velocity regions in the upper mantle (200–350 km depth) organized in horizontally elongated bands some of which are parallel to the direction of absolute plate motion, as previously found in a lower resolution global tomographic models SEMum2 (French et al., 2013) and SEMUCB_WM1 (French and Romanowicz, 2014). Many of these elongated structures overlie vertically elongated plumelike conduits that appear to be rooted in the lower mantle, located, when projected vertically to the surface, in the vicinity of major hotspots.  However, there is no direct vertical correspondence between the imaged plumelike conduits and hotspots locations suggesting a complex interaction between the upwelling flow and the lithosphere/asthenosphere system. We discuss possible relations of this structure with trace element geochemistry of the corresponding hotspots.

How to cite: Romanowicz, B., Munch, F., Rudolph, M., and Mukhopadhyay, S.: Imaging the meso-scale structure of the upper mantle beneath the southern and central Atlantic ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2113, https://doi.org/10.5194/egusphere-egu22-2113, 2022.

Age-progressive volcanic “hotspot” chains result from the passage of a tectonic plate over a thermochemical mantle plume, thereby sampling the otherwise-inaccessible lowermost mantle. A common feature in oceanic hotspot tracks is the occurrence of two parallel volcanic chains with an average separation of ~50 km (e.g., Loa and Kea chains in Hawaii). Some other tracks (including Tristan-Gough, Shona, the Line Islands, Wake seamounts, Tuvalu and Cook-Austral) feature a 200-400 km spacing, but the origin of such widely-spaced melting zones in the mantle remains unknown. Here, we explore 3D Cartesian geodynamic models of thermochemical plume ascent through the upper mantle. We explore various distributions of intrinsically-dense eclogitic material across the plume stem. For a wide range of eclogite distributions, the plume pools in the depth range of 300~410 km, where the excess density of eclogite is greater than above and below, as also predicted by Ballmer et al., EPSL 2013. This “Deep Eclogitic Pool” then splits up into two lobes that feed two separate shallow plumelets, particularly at high eclogite contents in the center of the underlying plume stem. The two plumelets feed two separate melting zones at the base of the lithosphere, which are elongated in the direction of plate motion due to interaction with small-scale convection. This “forked plume” morphology can account for hotspot chains with two widely-spaced (250~400 km) tracks and with long-lived (>5 My) coeval activity along each track. Forked plumes may also provide an ideal opportunity to study geochemical zonation of the lower-mantle plume stem, as each plumelet ultimately samples the opposite side of a deep plume conduit that potentially preserves spatial heterogeneity from the lowermost mantle. We compare this model to geochemical asymmetry evident along the Wake, Tuvalu and Cook-Austral double-chain segments, which make up the extensive (>100 Ma) Rurutu-Arago hotspot track. The preservation of a long-lived NE-SW geochemical asymmetry along the Rurutu-Arago double chain indicates a deep origin, likely from the southern boundary of the Pacific large low shear-velocity province. Our findings highlight the potential of the hotspot geochemical record to map lower-mantle structure over space and time, complementing the seismic-tomography snapshot.

How to cite: Ballmer, M. and Finlayson, V.: Widely-spaced Double Hotspot Chains due to Forked Plumes sample Lower Mantle Geochemical Structure, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3461, https://doi.org/10.5194/egusphere-egu22-3461, 2022.

It has been hypothesized that Australia is experiencing long-wavelength uplift and subsidence in response to intraplate stresses and/or dynamic topography (e.g. Beekman et al., 1997; Czarnota et al., 2013). In central Australia, intraplate stresses are of particular interest due to the presence of several enigmatically long-lived (500+ Myr) Bouguer anomalies of magnitude + 150 mgal. Additionally, a recent study by Jansen et al. (2022) showed that the Finke river, which drains away from a large gravity high, is actively responding to cyclic changes in uplift. Here, transient uplift and subsidence of up to ~150 m may be driven by the the flexural response to variable in-plane stresses in the presence of large loads embedded within the lithosphere.  The in-plane stress changes may be associated with shear at the base of the lithosphere and therefore inherently linked to plate velocity and mantle dynamics.
     Here, we explore mechanisms of uplift in central Australia and investigate their signatures within the geomorphic record through numerical modeling and χ analysis. We observe strong χ variations across drainage divides associated with gravity anomalies, which we link to episodic transitions from exorheic to endorheic drainage during periods of uplift and subsidence.  Landscape evolution models that incorporate flexural uplift in response to time-transient variations in horizontal stresses suggest that depositional patterns, spatial χ variations, and river profiles can be explained by this uplift mechanism.  In a more general sense, these results demonstrate that the cyclic loss and gain of drainage area during periods of endorheism and exorheism can result in drastic, sudden changes in χ which correspond to waxing and waning of basinal areas.

How to cite: Ruetenik, G., Jansen, J., Sandiford, M., and Moucha, R.: Large-scale drainage disequilibrium in central Australia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3756, https://doi.org/10.5194/egusphere-egu22-3756, 2022.

Mid-plate volcanoes are well known as hotspots. They represent the surface signature of mantle plumes, nevertheless their origin and their role in geodynamics are still a challenge in the Earth sciences. Even though plate tectonics and mantle plumes were discovered at the same time, the latter cannot be explained by the former. Plumes’ birth, life and death play a fundamental role on the evolution of life on Earth and on plate-tectonic reorganization. La Réunion hotspot is known as one of the largest on the Earth, that created the Deccan volcanic traps in India (almost 2 million km²) and the death of more than 90% of life on the Earth including dinosaurs ~65Ma ago. So far the origin of the mantle plumes and their role in geodynamics are still unclear in Earth sciences. In that respect, we use the dataset from the French-German RHUM-RUM experiment around La Réunion hotspot (2012-2013), from IRIS data center and FDSN to extensively investigate the deep structure of the plume along its complete track from its birth to its present stage, as well as from the upper mantle to the lowermost mantle. Several shear-wave anomalies are resolved underneath Indian Ocean and the upper mantle beneath this region is fed by mantle plume rising from the core-mantle boundary. The lower mantle thermochemical dome associated to the South-African Large Low-Shear Velocity Province (LLSVP) is found to be composed of several conduits. Plume branches are highlighted at ~900 km depth. Thermal instability and thermochemical heterogeneities in the D" layer are likely the principal reasons of the plumes birth at the core-mantle boundary, and therefore an indicator of long-life of the Réunion hotspot.

How to cite: Dongmo Wamba, M., Romanowicz, B., Montagner, J.-P., and Simons, F.: Plume conduits rooted at the core-mantle boundary beneath the Réunion hotspot, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5259, https://doi.org/10.5194/egusphere-egu22-5259, 2022.

Geodynamic models based on seismic tomography have been utilized to understand a wide range of physical processes in the Earth's mantle ranging from lithospheric stress states to plate-mantle interactions. However, the influence of various model components and the associated physical properties of the mantle on the observed surface deformation is still an open question and requires further research. In this study, we develop global mantle flow models based on high-resolution seismic tomography to quantify the relative importance of the plate driving and resisting forces on the surface motions. Our models include temperature and density variations based on seismic tomography, lithospheric structure, and the observed locations of subducted slabs, using the geodynamics software ASPECT. We use a diffusion/dislocation creep rheology with different parameters for the major mantle phases. To facilitate plate-like deformation, we prescribe weak plate boundaries at the locations given by global fault databases. We resolve the resulting strong viscosity variations using adaptive mesh refinement such that our global models have a minimum resolution of <10 km in the lithosphere. We analyze the influence of slab viscosity, plate boundary friction, asthenospheric viscosity, and plate boundary geometry on reproducing the observed GPS surface velocities. Our parameter study identifies model configurations that have up to 85% directional correlation and a global velocity mean within 10% difference with the observed surface motions. Our results also suggest that the modeled velocities are very sensitive to the plate boundary friction, particularly to variations in viscosity, dip angles, and the plate boundary geometry, i.e., open vs closed boundaries, or localized vs. diffused deformation zones. These models show the relative influence of plate-driving forces on the surface motions in general, and in particular the importance of using accurate models of plate boundary friction for reproducing observed plate motions. In addition, they can be used as a starting point to separate the influences of lithospheric structure and mantle convection on surface observables like strain rate, stress field, and topography.

How to cite: Saxena, A., Dannberg, J., and Gassmoeller, R.: Investigating the effects of plate-driving forces on observed surface deformation using global mantle flow models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5561, https://doi.org/10.5194/egusphere-egu22-5561, 2022.

Most orogenic belts are close to convergent plate margins. However, some orogens are formed far away from plate boundaries, as a result of compressional stress propagating within plates, basal loading, or a combination of thereof. We focus on the Atlas of Morocco, which is such an intraplate orogeny and shows evidence of mantle driven uplift, and plume-related volcanism. How these processes interact each other is still poorly constrained and it provides clues about intraplate stress propagation, strain localization, and lithospheric weakening due to mantle dynamics. 

We present three sets of observations constructed by integrating previous data with new analyses. Crustal and thermal evolution constraints are combined with new analyses of topographic evolution and petrological and geochemical data from the Anti-Atlas volcanic fields. Our findings reveal that: i) crustal deformation and exhumation started during middle/late Miocene, contemporaneous with the onset of volcanism; ii) volcanism has an anorogenic signature with a deep source; iii) a dynamic deep mantle source supports the high topography. Lastly, we conducted simple numerical tests to investigate the connections between mantle dynamics and crustal deformation. This leads us to propose a model where mantle upwelling and related volcanism weaken the lithosphere and favor the localization of crustal shortening along pre-existing structures due to plate convergence.

How to cite: Lanari, R., Faccenna, C., Natali, C., Sengul, E., Fellin, G., Becker, T., Gogus, O., Youbi, N., and Conticelli, S.: Mantle dynamics and intraplate orogeny: The Atlas of Morocco, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5992, https://doi.org/10.5194/egusphere-egu22-5992, 2022.

Deep mantle plumes are buoyant upwellings rising from the Earth’s core-mantle boundary to its surface, and describing most hotspot chains. Mechanisms to explain dual chains of hotspot volcanoes for the Hawaiian-Emperor and Yellowstone chains fail to explain the geochemical similarity and large distances between contemporaneous volcanoes of the Tasmantid and Lord Howe chains in the SW Pacific. Using numerical models of mantle convection, we demonstrate how slab-plume interaction can lead to sustained plume branching over a period of >40 million years to produce parallel volcanic chains that track plate motion. We propose a three-part model: first, slabs stagnate in the upper mantle, explaining fast upper mantle P-wave velocity anomalies; second, deflection of a plume conduit by a stagnating slab splits it into two branches 650-900 km apart, aligning to the orientation of the trench axis; third, plume branches heat the stagnating slab causing partial melting and release of volatiles which percolate to the surface forming two contemporaneous volcanic chains with slab-influenced EM1 signatures. Our results highlight the critical role of long-lived subduction on the evolution and behaviour of intraplate volcanism.

How to cite: Mather, B., Seton, M., Williams, S., Whittaker, J., Carey, R., Arnould, M., Coltice, N., Rogers, A., Ruttor, S., and Nebel, O.: Parallel volcanic chains generated by plume-slab interaction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6571, https://doi.org/10.5194/egusphere-egu22-6571, 2022.

The north Andean block evidences by its shallow to intermediate seismicity a juxtaposition of a southern, relatively steeply dipping slab segment with a correlating volcanic arc and a northern flat slab domain, where a margin-parallel volcanic arc became extinct since the Late Miocene. The clear-cut offset of the seismic pattern suggests the presence of a slab tear, which has its correlative morphological expression by a distinct lineament in the Cauca Valley and separates, within the Eastern Cordillera of Colombia, a southern narrow antiformal cordilleran tract from a northern composite belt with an axial depression that constitutes the High Plain of Bogotá. Faults are consistently blind and associated with tight, basement-cored folds with inverted limbs at the mountain front and distinct domes separated by marginal synclines. These structures belong to a young deformation phase as they were superposed on older cylindrical fold trains. Their ductile deformation style may be associated with a thermal anomaly as evidenced by abnormally high Ro data. In order to assess the age of this folding we extracted zircons from a rhyolitic dike that straddles a marginal syncline of a major dome. U-Pb age data indicate a recycling of these crystals from a Neoproterozoic volcanoclastic sequence that composes the basement of this marginal part of the Cordillera. Euhedral overgrowths yield, however, Quaternary ages that we tentatively associate to the advance of the outer bend of the flat slab to its present position.

How to cite: Conde-Carvajal, C., Kammer, A., Avila-Paez, M., Cubillos, S., Piraquive, A., and von Quadt, A.: Quaternary magmatism above a slab tear, Northern Andes of Colombia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9038, https://doi.org/10.5194/egusphere-egu22-9038, 2022.

Typically, the change in lithospheric thickness associated with fracture zones relates directly to the vigor of secondary convection or mantle flow patterns. Therefore, one might expect that mantle flow considerably boosted by the presence of a mantle plume would easily overcome the lithospheric steps created at fracture zone locations. However, to date, there are no studies to verify this assumption. Numerical models based on an example from the SW Indian Ridge suggest that the axial flow driven by a plume (the Marion plume) is indeed likely to be curtailed by the long-offset fracture zones¹.

We have investigated the interactions between the Jan Mayen fracture zone and Iceland mantle plume in the NE Atlantic by considering (a) the lithospheric and asthenospheric regional configuration and (b) the geochemistry of rocks produced by submarine volcanism.

Several global lithospheric models indicate a thinning of the lithosphere on both sides of the Jan Mayen Fracture transform, despite the difference in age of the two adjacent oceanic basins. However, the tomographic models indicate a gap in the asthenospheric flow at the lithosphere-asthenosphere depth under Jan Mayen transform fault, and only a narrow northward channel of this flow is visible under the westernmost part of the fracture zone.

Vesteris seamount is an alkaline seamount placed in the central part of the Greenland Basin, located ca. 480 km west from slow-spreading Mohn's ridge and ca. 250 km north from the Jan Mayen Fracture Zone. Vesteris is a solitary volcanic center far away from an active ridge regime with an eruptive age ranging from 650 – 10 ka ². Here we report new results from geochemical analysis of several samples dredged during the East Greenland Sampling campaign EGS-2012 from the flanks of Vesteris. Whole-rock major and trace elements, together with isotopes and olivine phenocryst mineral data, are used to decipher the source of volcanism at Vesteris Seamount.

The Sr-Nd-Pb isotopic signatures indicate that Vesteris volcanism is unrelated to the Iceland mantle plume. Low NiO concentrations in highly forsteritic olivines from Vesteris alkali basalt suggest that the source was dominantly peridotitic. Rare Earth Elements profiles indicate very low degrees of partial melting of a deep mantle source in the presence of residual garnet.

Vesteris seamount was formed in a location of a relatively steep gradient of the lithospheric-asthenospheric boundary and close to the northward mantle flow that is carving the Greenland thick lithosphere. The results suggest that the Iceland mantle flow may not have crossed the Jan Mayen Transform Fault; instead, the seamount tapped into a mantle reservoir in the Greenland Basin that preserved the complex history of the Greenland craton and adjacent terranes.   REFS. (1) Georgen and Lin, 2003, Plume-transform interactions at ultra-slow spreading ridges: Implications for the SW Indian Ridge, G-cubed, doi:10.1029/2003GC000542; (2) Mertz & Renne, 1995, Quaternary multi-stage alkaline volcanism at Vesteris Seamount (Norwegian—Greenland Sea): evidence from laser step heating 40Ar/39Ar experiments, Journal of Geodynamics, doi:10.1016/0264-3707(94)E0001-B.

How to cite: Beloša, L., Gaina, C., Callegaro, S., Mazzini, A., Meyzen, C., Polteau, S., and Bizimis, M.: Plume-Fracture Zone interactions in the NE Atlantic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9199, https://doi.org/10.5194/egusphere-egu22-9199, 2022.

Earth's surface moves in response to a combination of tectonic forces from the thermally convective mantle and plate boundary forces. Plate motion changes are increasingly well documented in the geologic record and they hold important constraints. However, the underlying forces that initiate such plate motion changes remain poorly understood. I have developed a novel 3-D spherical numerical scheme of mantle and lithosphere dynamics, aiming to exploit information of past plate motion changes in quantitative terms. In order to validate the models and single out those most representative of the recent tectonic evolution of Earth, model results are compared to global plate kinematic reconstructions. Additionally, over the past years a pressure driven, so-called Poiseuille flow, model for upper mantle flux in the asthenosphere has gained increasing geodynamic attention–for a number of fluid dynamic arguments. This elegantly simple model makes a powerful testable prediction: Plate motion changes should coincide with regional scale mantle convection induced elevation changes (i.e., dynamic topography). For this the histories of large scale vertical lithosphere motion recorded in the sedimentary record holds important information.

Here, I will present analytical results that help to better understand driving and resisting forces of plate tectonics – in particular the plume push force. Moreover, numerical results indicate that mantle convection plays an active role in driving plate motions through pressure driven upper mantle flow. Altogether, theoretical and observational constrains provide powerful insights for geodynamic forward and inverse models of past mantle convection.

How to cite: Stotz, I., Vilacís, B., Hayek, J. N., Bunge, H.-P., and Friedrich, A. M.: Plume push force: a relevant driver of plate tectonics that can be constrained by horizontal and vertical plate motions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12422, https://doi.org/10.5194/egusphere-egu22-12422, 2022.

Constraining the dynamic topography of Antarctica and its surrounding seas is required in order to gauge the pattern of mantle convection beneath this continent. However, such studies are limited by this continent’s geographical remoteness, by the lack of bedrock exposure and by extensive glaciation. Oceanic residual depth measurements provide a well-established proxy for offshore dynamic topography. Here, over 400 seismic reflection profiles have been interpreted to calculate residual depth measurements throughout the oceans that surround Antarctica. These measurements have been carefully corrected for sedimentary loading and, where possible, for crustal thickness variations. When combined with previous global compilations, these new residual depths significantly improve spatial resolution across the region, providing excellent constraints on dynamic topographic basins and swells. In the continental realm, an improved understanding of dynamic topography will help to quantify temporal and spatial variations in ice sheet stability. Volcanism and slow shear wave velocity anomalies beneath the continent indicate dynamic support.  By mapping offshore dynamic topography to a higher resolution, greater context is provided for future onshore studies.

How to cite: Dunn, A., White, N., Holdt, M., and Larter, R.: Dynamic topographic observations of Antarctica and its fringing oceanic basins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13092, https://doi.org/10.5194/egusphere-egu22-13092, 2022.

First ⁴⁰Ar/³⁹Ar isotopic age data for gold hydrothermal veinlet-vein mineralization of the late Mesozoic Ketkap-Yuna igneous province (KYuIP) of the Aldan shield (AS) confirm the geological relation of this type of mineralization with the early Cretaceous sub-alkali magmatism. The combination of geological characteristics and U-Pb dating of magmatites indirectly enabled us to determine the age and highly productive bi-metasomatic «massif-skarn» type of mineralization associated with sub-alkali magmatogenic formations of the province.

Isotopic datings of magmatites and gold mineralization of the KYuIP and other late Mesozoic igneous provinces of the Aldan shield show age conformity of ore-bearing magmatites and ores accompanying them (fig. 1, 2). A relative, in comparison to provinces of the tectonic-magmatic activation (TMA) of the Western and Central Aldan, delay in time of occurrences of the KYuIP late Mesozoic magmatism and gold mineralization related to it, and the difference in volume ratios of formational types of magmatic formations in different provinces can be explained by the characteristics of tectonic structure of the region.