Content:

GMPV – Geochemistry, Mineralogy, Petrology & Volcanology

GMPV1.1 – Advances in nano- to micro-analytical tools to understand Earth processes

EGU21-14614 | vPICO presentations | GMPV1.1 | Highlight

Grain boundary character information via individual imaging or statistical analyses: complexion transitions and grain boundary segregation

Katharina Marquardt, David Dobson, Simon Hunt, and Ulrich Faul

Grain boundaries affect bulk properties of polycrystalline materials, such as electrical conductivity, melting or bulk viscosity. In the past two decades, observations of marked bulk material property changes have been associated with changes in the structure and composition of grain boundaries. This led to the term “grain boundary complexions” to mark the phase-like behaviour of grain boundaries while differing from phases in the sense of Gibbs (Cantwell 2014).

Here we introduce the principles of grain boundary structure to property relations and potent methods to study these. The focus is on the combination of structural, chemical and statistical analysis as obtainable using transmission electron microscopy and electron backscatter diffraction. Data from these complementary methods will be discussed on two systems; garnet and olivine polycrystals.

Past elasticity measurements showed that the Youngs modulus of garnet polycrystals changes as a function of sintering pressure (Hunt et al. 2016). Here we used high resolution transmission electron microscopy to study the structure of grain boundaries from polycrystals synthesized at low (4-8 GPa) and high (8-15) GPa sintering pressure. The HRTEM data were acquired using an image-corrected JEOL ARM 300 to achieve the highest resolution at low electron doses using a OneView camera. Our data indicate a grain boundary structural change occurs from “low-pressure” to “high pressure” grain boundaries, where the grain boundary facets change from >100 nm – 20 nm to 3-7 nm length scale, respectively. We conclude that sintering pressure affects grain-boundary strength and we will evaluate how this may influence anelastic energy loss of seismic waves through elastic or diffusional accommodation of grain-boundary sliding.

Polycrystalline olivine samples show different viscosity related to grain boundary segregation of impurities. To investigate if the distribution of grain boundaries is affected by grain boundary chemistry, we analysed grain orientation data from over 4x104 grains, corresponding to more than 6000 mm grain boundary length per sample. Using stereology, we extract the geometry of the interfacial network. The thus obtained grain boundary character distribution (GBCD) is discussed in relation to bulk viscosity.

How to cite: Marquardt, K., Dobson, D., Hunt, S., and Faul, U.: Grain boundary character information via individual imaging or statistical analyses: complexion transitions and grain boundary segregation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14614, https://doi.org/10.5194/egusphere-egu21-14614, 2021.

EGU21-6581 | vPICO presentations | GMPV1.1 | Highlight

Atom probe as a tool for understanding mineral physics and rock deformation: a case study of deformed wehrlite

Joseph Cukjati, Reid Cooper, Stephen Parman, Ningli Zhao, Austin Akey, and Fernando Laiginhas

Here we report Atom Probe Tomography (APT) analyses of grain and phase boundaries of laboratory-deformed, fine-grained mixtures of clinopyroxene and olivine (Zhao, et al., 2019).  The experiments show that the mixtures deform much more rapidly than either mineral endmember.  This enhanced deformation in the two-phase material is due to stress-driven reactions at the phase boundaries. Lower effective viscosities of phase mixtures may be critical to the initiation of plate tectonics and the formation of mantle shear zones.

The hypothesis presented here is that the ‘bulk rock’ – a wehrlite – deforms rapidly because conversion of one phase to the other occurs at phase boundaries (e.g., Sundberg & Cooper, 2008).  In this model, grain-scale transport of the shared (slowly-diffusing) mineralogical component Si4+ is not required.  The near-boundary gradients of olivine-insoluble ions are presented as evidence of the phase transformation which either dissolves olivine into clinopyroxene or vice versa.  

The resolving power of the APT makes it a promising tool for investigating the microphysics of rock deformation, bridging the atomic scale all the way to the plate-tectonic scale.

References:
Sundberg M, Cooper RF (2008) Crystallographic preferred orientation produced by diffusional creep of harzburgite: effects of chemical interactions among phases during plastic flow. J Geophys Res Solid Earth 113(12):B12208.
Zhao N, Hirth G, Cooper RF, Kruckenberg SC, Cukjati J (2019) Low viscosity of mantle rocks linked to phase boundary sliding. Earth Planet Sci Lett 517:83–94.

How to cite: Cukjati, J., Cooper, R., Parman, S., Zhao, N., Akey, A., and Laiginhas, F.: Atom probe as a tool for understanding mineral physics and rock deformation: a case study of deformed wehrlite, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6581, https://doi.org/10.5194/egusphere-egu21-6581, 2021.

EGU21-2432 | vPICO presentations | GMPV1.1 | Highlight

Atomic scale structure of a plagioclase – magnetite interface

Ge Bian, Olga Ageeva, Gerlinde Habler, Vladimir Roddatis, and Rainer Abart

Magnetite (Mt) is the foremost carrier of rock natural remanent magnetization (NRM). Needle- and lath shaped Mt micro-inclusions in plagioclase (Pl) from gabbro often have systematic crystallographic- and shape orientation relationships (CORs, SORs) with the Pl host. The SORs of Mt leads to magnetic anisotropy which may bias the NRM of the Mt-Pl inclusion-host assemblage. Thus, the origin of the CORs and SORs between Mt and Pl is important for paleomagnetic reconstructions. In this context, the atomic structures of Mt-Pl interfaces are of particular interest.

The CORs and SORs between Mt and Pl were reported earlier and the underlying systematics was revealed from correlated optical and scanning electron microscopy (SEM) including electron back scattered diffraction (EBSD) analyses [1] (and references therein). The so-called plane normal type Mt micro-inclusions extend parallel to the Mt<111> direction, which is perpendicular to the densely packed Mt{222} oxygen layers that are parallel to one of seven Pl lattice planes with nearly identical d-spacings, namely Pl(112), Pl(-312), Pl(1-50), Pl(150), Pl(100), Pl(31-2) and Pl(1-12). Direct imaging of Mt-Pl interfaces has rarely been reported due to the beam sensitivity of Pl. Here we present the microscopic structure of a Mt-Pl interface along the inclusion elongation direction using high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and integrated differential phase contrast STEM (iDPC-STEM) techniques.

The TEM foil was prepared using a focused Ga-ion beam (Ga-FIB) from a lath-shaped Mt micro-inclusion of 23 μm x 17 μm x 0.1 μm extending perpendicular to Mt{111}/Pl(-312). The foil is oriented so that the Mt<111>/Pl(-312)-pole are parallel and Mt{110}/Pl(150) planes are perpendicular to the foil.

The STEM images show that the Mt-Pl interface is perfectly straight and parallel to Mt{110}/Pl(150) and that it is devoid of steps. Electron diffraction patterns confirm that the elongation direction of the micro-inclusions is determined by the good fit of oxygen layers across the Pl-Mt interface. A 2.4% difference in the d-spacings between Pl(-312) and Mt{222} is likely accommodated by every about 42'nd Mt{222} plane forming an edge dislocation at the Mt-Pl interface. In addition, elastic strain is indicated by a deviation of d111/d110 of Mt from the strain free reference lattice. Moreover, lattice fringes in iDPC-STEM images reveal coherence between Pl(22-1) and Mt{111} planes without misfit dislocations. This additional coherence may explain the particularly strong alignment of Mt{111} and Pl(-312) reflected by the EBSD data.

In summary, the elongation directions of the Mt inclusions are determined by the alignment of important oxygen layers of both phases across the Mt-Pl interface, which is parallel to oxygen-rich lattice planes in both phases. Misfit dislocations are presumably introduced to compensate the 2.4% lattice misfit along the elongation direction. The well-organized interface structure ensures a low interfacial energy and is a viable explanation for the observed Mt-Pl CORs and SORs.  

Acknowledgement

Funding by FWF project I 3998-N29 and RFBR project 18-55-14003 is acknowledged.

Reference

[1] Ageeva et al (2020) Contrib. Mineral. Petrol. 175(10), 1-16.

How to cite: Bian, G., Ageeva, O., Habler, G., Roddatis, V., and Abart, R.: Atomic scale structure of a plagioclase – magnetite interface, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2432, https://doi.org/10.5194/egusphere-egu21-2432, 2021.

EGU21-124 | vPICO presentations | GMPV1.1

TEM and LA-ICP-MS constraints on fluid-induced alteration of a zircon-xenotime intergrowth in pegmatite from Piława Górna (the Góry Sowie Block, SW Poland)

Fabian Tramm, Richard Wirth, Bartosz Budzyń, Jiří Sláma, Anja Schreiber, and Łukasz Birski

An intergrowth of zircon and xenotime, formed at ca. 2.09 Ga, was significantly altered after incorporation as a restite into pegmatite at ca. 370 Ma (Piława Górna, Góry Sowie Block, SW Poland; Budzyń et al., 2018). Alteration involved fluid-induced coupled dissolution-reprecipitation processes, which resulted in compositional alteration and development of patchy zoning and porosity in the xenotime and the rim of zircon. Diffusion-reaction processes affected the metamict core of zircon and resulted in nano- to microscale patchy zoning and submicron-scale porosity. This study evaluates the alteration processes with respect to structural and compositional characteristics by using TEM and LA-ICPMS trace element analysis.

Nanoscale observations revealed nanoporosity in the metamict core of zircon and a continuation of patchy zoning on a submicron level, which resulted from heterogeneous metamictization correlating with variation in U and Th contents. The altered xenotime and the zircon rim are dominated by microporosity filled with a variety of secondary phases such as U, Th, Pb and Fe rich oxides and silicates. In rare cases, secondary PbS formed nano inclusions in zircon, occasionally surrounded by amorphous apatite. Aside of known substitution mechanisms in xenotime, such as thorite and cheralite components, a correlation of Zr with LREE and Si contents indicates substitution of the zircon component. Furthermore, the zircon-xenotime interface revealed dissolution pits, filled with secondary zircon that formed at the expense of primary xenotime via coupled dissolution-reprecipitation reactions. This indicates local penetration of the fluid-mineral reaction front into xenotime. Major (Si, Zr and P) and trace elements, including U, Th and Pb, which are geochronologically relevant, have been mobilized in the metamict core of zircon due to alteration induced by an alkali-rich fluid with high activities of F, Na and Ca. The altered xenotime and porous rim of zircon were affected by alteration induced by a fluid containing Fe, which resulted in precipitation of Fe-rich phases, such as Fe-oxides and silicates often accompanied by relevant contents of Pb. In conclusion, nanoscale structural observations and LA-ICP-MS trace element data support the complex geochronological implications of the altered zircon-xenotime intergrowth, emphasising the necessity of understanding alteration processes of zircon and xenotime taking into account element transport and thus the disturbance of their geochronological clock.

Acknowledgements: This work was supported by the National Science Centre grant no. 2017/27/B/ST10/00813.

References:

BudzyńB., Sláma J., Kozub-Budzyń G.A., Konečný P., HolickýI., RzepaG.,Jastrzębski M. (2018) Lithos 310-311, 65-85.

How to cite: Tramm, F., Wirth, R., Budzyń, B., Sláma, J., Schreiber, A., and Birski, Ł.: TEM and LA-ICP-MS constraints on fluid-induced alteration of a zircon-xenotime intergrowth in pegmatite from Piława Górna (the Góry Sowie Block, SW Poland), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-124, https://doi.org/10.5194/egusphere-egu21-124, 2021.

EGU21-9404 | vPICO presentations | GMPV1.1

Trace-element migration during crystal-plastic deformation in UHP rutile: dislocations in low-angle boundaries as high-diffusivity pathways.

Rick Verberne, Hugo van Schrojenstein Lantman, Steven Reddy, Matteo Alvaro, David Wallis, Denis Fougerouse, Antonio Langone, Marco Scambelluri, David Saxey, and William Rickard

The trace-element composition of rutile is commonly used to constrain P-T-t conditions for a wide range of metamorphic systems. Recent studies have highlighted the importance of micro- and nanostructures in the redistribution of trace elements in rutile via high-diffusivity pathways and dislocation-impurity associations. In this contribution, we investigate the effect of crystal-plastic deformation of rutile on its composition by combining microstructural and petrological analyses with atom probe tomography. The studied sample is from an omphacite vein of the ultrahigh-pressure metamorphic Lago di Cignana unit, Western Alps, Italy. Zr-in-rutile thermometry and inclusions of quartz in rutile and of coesite in omphacite constrain rutile deformation to around the prograde HP-UHP boundary at 500–550 °C. Crystal-plastic deformation of a large rutile grain resulted in low-angle boundaries that generate a total misorientation of ~25°. Dislocations constituting the low-angle boundary are enriched in common (Fe, Zr) and uncommon trace elements (Ca). The Ca is interpreted to be derived from the grain exterior, suggesting diffusion of trace elements along the dislocation cores. The potential for dislocation microstructures to act as fast diffusion pathways must be evaluated when applying traditional geochemical analyses as compositional disturbances caused by the presence of dislocation might lead to erroneous interpretations.

How to cite: Verberne, R., van Schrojenstein Lantman, H., Reddy, S., Alvaro, M., Wallis, D., Fougerouse, D., Langone, A., Scambelluri, M., Saxey, D., and Rickard, W.: Trace-element migration during crystal-plastic deformation in UHP rutile: dislocations in low-angle boundaries as high-diffusivity pathways., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9404, https://doi.org/10.5194/egusphere-egu21-9404, 2021.

EGU21-3100 | vPICO presentations | GMPV1.1

Zircon recrystallisation microstructures andthe implications for U-Pb dating

Jasper Huijsmans, Maartje Hamers, Martyn Drury, and Jim Lee

Uranium-lead dating of zircon has been used extensively in geochronological studies based on the widespread occurrence of zircon and its resistance to chemical and physical weathering. Previous research has shown that despite their apparent robustness, many zircons contain evidence for recrystallisation, such as the replacement of the primary oscillatory zoning by unzoned zircon. This replacement is characterised by rims, patches and embayments of unzoned zircon which can either completely replace the primary zoning or preserve faint remnants within the unzoned zircon.  In some samples, the unzoned zircon contains lower U and Pb concentrations, implying that the zircon U-Pb age may be reset during the replacement (Pidgeon, 1992). Interestingly, zircons have also been found in which there is no apparent difference in U-Pb age between the zoned and unzoned zircon (Schaltegger et al., 1999). To better understand the replacement of zoned by unzoned zircon, it is important to study the microstructures present within recrystallised zircon to understand possible mechanisms causing recrystallisation. Multiple mechanisms may explain the trace element distribution within (partially) recrystallised zircon: annealing of radiation damaged (metamict) zircon, annealing of lattice strain imposed by alternating U concentrations in oscillatory zoning, enhanced diffusion along fast-diffusivity pathways (such as low-angle subgrain boundaries or fractures) and coupled dissolution-reprecipitation.  The mechanism(s) by which zircons recrystallise remain poorly understood, as well as the effect of the formation of different microstructures on corresponding zircon U-Pb dates. Understanding these phenomena is therefore of vital importance for correctly interpreting U-Pb ages in zircon.

This work focusses on investigating the microstructures that are present within recrystallised zircons from both metamorphic and igneous environments from the Jack Hills, Australia (Pidgeon, 1992) and the island of Lewis and Harris, Scotland (Van  Breemen  et  al.   1971). Suites of zircons from these areas have been imaged with cathodoluminescence, which is a powerful tool for obtaining high resolution images of the internal structures of zircons. Within these suites, zircons are present which show complex zoning patterns and (partial) recrystallisation; these will be studied in greater detail using EDS, EBSD and SHRIMP. Preliminary results of EDS on the inclusions show that inclusions are composed of feldspars, thorite, quartz and apatite, which were most likely included during the primary crystallisation of the zircon. EBSD measurements will provide additional data on the crystallographic orientation of recrystallized zones and the state of metamictization of the zircons, and may show if zircon has deformed crystal-plastically forming subgrain boundaries.

 

References

Pidgeon, R. T. (1992). Recrystallisation of oscillatory zoned zircon: some geochronological and petrological implications. Contributions to Mineralogy and Petrology, 110(4), 463-472.

Schaltegger, U., Fanning, C. M., Günther, D., Maurin, J. C., Schulmann, K., & Gebauer, D. (1999). Growth, annealing and recrystallization of zircon and preservation of monazite in high-grade metamorphism: conventional and in-situ U-Pb isotope, cathodoluminescence and microchemical evidence. Contributions to Mineralogy and Petrology, 134(2-3), 186-201.

Van Breemen, O., Aftalion, M., & Pidgeon, R. (1971). The age of the granitic injection complex of harris,outer hebrides.Scottish Journal of Geology,7(2), 139–152.

How to cite: Huijsmans, J., Hamers, M., Drury, M., and Lee, J.: Zircon recrystallisation microstructures andthe implications for U-Pb dating, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3100, https://doi.org/10.5194/egusphere-egu21-3100, 2021.

EGU21-7327 | vPICO presentations | GMPV1.1

Insights into chemical mobility in titanite driven by low-temperature crystal-plastic deformation

Nicholas Udy and Michael Stearns

The U-Pb system in titanite has been shown to be reset during a variety of high-temperature processes including high-temperature deformation, but post-deformation modification and recovery of crystal-lattice strain have so far made U-Pb equilibration mechanism from deformed titanites equivocal. Microstructures, including mechanical twinning and subgrain rotation recrystallization are more likely to be preserved at low-temperatures, but the systematics of chemical equilibration have not been established for these conditions. This study identifies progressive crystallographic misorientation and deformation twins in titanite porphyroclasts from the Wasatch Fault Zone, Utah, USA. The microstructures, mapped using electron backscatter diffraction (EBSD), developed at ~11 km depth during 300–400 ºC crystal-plastic deformation within the ductile fault zone. These microstructural maps were used to guide laser ablation-split stream ICP-MS analysis: U-Pb isotopes measured in tandem with major and trace element contents. Despite the low temperature, U-Pb and trace element contents in titanite equilibrated, at least partially, during deformation. Both major and trace elements in titanite also likely partitioned with a fluid and in response to the (re)crystallization of other mineral phases in the fault zone. Chemical zoning and crystal lattice recovery suggestive of fluid-aided recrystallization are absent, and the main mechanism for this resetting may instead be an enhancement of element mobility along microstructure dislocations. These processes are interpreted to record complex open-system behavior of titanite caused by crystal-plastic deformation during the initiation of the WFZ. This presentation will summarize the comparative analysis of microstructure by EBSD and titanite chemistry by LASS-ICP-MS, and how it bears on the understanding of elemental mobility in titanite during low-temperature crystal-plastic deformation.

How to cite: Udy, N. and Stearns, M.: Insights into chemical mobility in titanite driven by low-temperature crystal-plastic deformation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7327, https://doi.org/10.5194/egusphere-egu21-7327, 2021.

EGU21-10775 | vPICO presentations | GMPV1.1

Meyer-Neldel Rule on thermal stability parameters (trap depth and frequency factor) of luminescence signals in quartz

Zuzanna Kabacińska, Alida Timar-Gabor, and Benny Guralnik

Thermally activated processes can be described mathematically by the Arrhenius equation. The Meyer-Neldel Rule (MNR), or compensation law, linearly relates the pre-exponent term to the logarithm of the excitation enthalpy for processes that are thermally driven in an Arrhenian manner. This empirical rule was observed in many areas of materials science, in physics, chemistry, and biology. In geosciences it was found to uphold in hydrogen diffusion (Jones 2014a) and proton conduction (Jones 2014b) in minerals.

Trapped charge dating methods that use electron spin resonance (ESR) or optically or thermally stimulated luminescence (OSL and TL) are based on the dose-dependent accumulation of defects in minerals such as quartz and feldspar. The thermal stability of these defects in the age range investigated is a major prerequisite for accurate dating, while the accurate determination of the values of the trap depths and frequency factors play a major role in thermochronometry applications. 

The correlation of kinetic parameters for diffusion has been very recently established for irradiated oxides (Kotomin et al. 2018). A correlation between the activation energy and the frequency factor that satisfied the Meyer–Neldel rule was reported when the thermal stability of [AlO4/h+]0 and [TiO4/M+]0 ESR signals in quartz was studied as function of dose (Benzid and Timar-Gabor 2020). Here we compiled the optically stimulated luminescence (OSL) data published so far in this regard, and investigated experimentally the thermal stability of OSL signals for doses ranging from 10 to 10000 Gy in sedimentary quartz samples. We report a linear relationship between the natural logarithm of the preexponent term (the frequency factor) and the activation energy E, corresponding to a Meyer-Neldel energy of 45 meV, and a deviation from first order kinetics in the high dose range accompanied by an apparent decrease in thermal stability. The implications of these observations and the atomic and physical mechanisms are currently studied.

 

References

Benzid, K., Timar Gabor, A. 2020. The compensation effect (Meyer–Neldel rule) on [AlO4/h+]0 and [TiO4/M+]0 paramagnetic centers in irradiated sedimentary quartz. AIP Advances 10, 075114.

Kotomin, E., Kuzovkov, V., Popov, A. I., Maier, J., and Vila, R. 2018. Anomalous kinetics of diffusion-controlled defect annealing in irradiated ionic solids. J. Phys. Chem. A 122(1), 28–32

Jones, A. G. (2014a), Compensation of the Meyer-Neldel Compensation Law for H diffusion in minerals, Geochem. Geophys. Geosyst., 15, 2616–2631

Jones, A. G. (2014b), Reconciling different equations for proton conduction using the Meyer-Neldel compensation rule, Geochem. Geophys. Geosyst., 15, 337–349

How to cite: Kabacińska, Z., Timar-Gabor, A., and Guralnik, B.: Meyer-Neldel Rule on thermal stability parameters (trap depth and frequency factor) of luminescence signals in quartz, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10775, https://doi.org/10.5194/egusphere-egu21-10775, 2021.

Inclusions in garnets from the river Lešnica alluvion (Cer mountain area, Serbia),  were investigated in an effort to study their distribution within the garnet host and to estimate the mechanism of their origin. Garnets are often occurring in the Lešnica alluvion in a form of loosely separated crystals with preserved crystalline forms and as mildly rounded broken grains [1]. Their mineralogical determination was previously published by Milošević et al, [1]. Crystals, that have been extracted and separated from the sandy fraction, have exhibited the presence of various types of inclusions in their structure. Single and multiphase inclusions in the garnets were examined optically by petrographic methods followed by SEM-EDS method, applied for the chemical analyses of the individual inclusion, and LA-ICP-MS applied to determine distribution and content of trace elements in the host garnet.

Results from SEM-EDS method show that garnets are of the spessartine-almandine type with the incorporation of irregular inclusions determined as rare earth elements (REE) minerals (monazite, xenotime, columbite-tantalite) and accessory minerals that usually incorporate REE (titanite, apatite, and zircon) together with uranium oxide minerals. Other single-phase inclusions are often quartz and rutile. Size of inclusion varieties from grain to grain, between 5 and 40 µm, while their distribution doesn’t follow any pattern, random distribution. It has been noted that zircon and uranium oxide minerals are often found coupled and as multiphase inclusions while monazite, xenotime and columbite-tantalite minerals are observed as separate, single, inclusions. Chondrite normalized REE in the host garnets plotted on spider diagram show extreme depletions of large ion lithophile elements (LILE) and enrichment in high field strength elements (HFSE), with negative Ce, Nd and Eu anomaly. Single-phase and multiphase inclusions that are occurring in the same garnet host with a random distribution are suggesting different genetic relations.

[1] Milošević M., Kostić B., Vulić P., Jelić I. 2019. Garnets from river Lešnica alluvion, mountain Cer. II Kongres Geologa Bosne i Hercegovine sa medjunarodnim učešćem, Pp. 306-311

How to cite: Milošević, M. and Kostić, B.: Single and multi-phase inclusions in garnets from the Lešnica alluvion in the Internal Dinarides, Serbia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2423, https://doi.org/10.5194/egusphere-egu21-2423, 2021.

The proliferation of modern techniques available for petrologists has resulted in an explosion of detailed information on mineral compositions and processes over the last decade. One area of research that is undergoing dramatic advances is the non-destructive interrogation of samples in three dimensions through X-ray microscopy (XRM). Techniques such as ZEISS Versa and Ultra XRM can be performed at a variety of scales and resolutions, resulting in micro-to-nano scale information on geological samples. Such techniques can be correlated with each other i.e. expanding nanoscale resolution to a large sample or internal calibration of X-ray intensity to identify mineral assemblages, or even correlation with other techniques such as electron microscopy (EM). X-ray techniques are also particularly adaptable to digital resolution enhancements through software processes such as machine learning algorithms.

Collecting 3D information for petrological investigations can often require ground truthing of mineralogical and compositional interpretations. The more developed the 3D microscopy becomes, the more we are increasingly interested in features that are deeply buried within our samples. This means the corresponding techniques for excavating a region of interest also need to advance in both speed and accuracy.

The ZEISS Crossbeam-Laser (XBL) system provides a unique capability of rapidly excavating to a point of interest within a 3D sample volume. The XBL is already seeing use in material sciences, with a standard XB chamber with focussed Ion Beam (FIB) and Electron Microscopy (EM), and a correlated femtosecond laser chamber for rapid material removal. Sample data collected through XRM can be correlated to the XBL stage so that any internal features located by XRM have their coordinates automatically available in three dimensions. The femtosecond laser can excavate to a region of interest (RoI) within the sample within seconds or minutes, dramatically reducing preparation time compared to standard FIB/PFIB. The laser cut surface can be used for analysis techniques such as energy dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD), even prior to final polishing with the focussed ion beam (FIB).

Here we show the XRM-XBL workflow in high grade metamorphic rocks for identifying minerals in context for geochronology and micro-to-nano scale textures.

How to cite: Taylor, R.: Advances in 3D characterisation for correlative microscopy in geosciences, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9597, https://doi.org/10.5194/egusphere-egu21-9597, 2021.

Geochemical, petrographic, and spectroscopic indices that vary with compositional changes in petroliferous organic matter (OM) during thermal maturation are key petroleum system parameters used to understand petroleum generation. In unconventional shale source-rock reservoirs, where multiple, highly dispersed OM types may be present in intimate contact with surrounding mineral phases, OM molecular composition (e.g., aromaticity) is especially useful for informing structure-reactivity relationships representative of different OM types. Here, we employ microscale, in situ, and correlative Raman and reflectance approaches to evaluate aromaticity evolution for a suite of OM types (i.e., liptinite, micrinite, solid bitumen, vitrinite, and inertinite) at the single particle level across an artificial thermal gradient. Our samples include a marginally mature (vitrinite reflectance ~0.5%) Late Cretaceous Boquillas Shale from south Texas, United States, and two hydrous pyrolysis (HP) residues following reaction of the raw Boquillas Shale sample at 300°C and 330°C for 72 hours. Our data indicate that: (i) liptinite, micrinite, solid bitumen, vitrinite, and inertinite particles exhibit different aromatic signatures in the raw shale sample and (ii) these OM types, with the exception of inertinite, effectively experience similar changes in aromatic structure with thermal advance. Data also reinforce the concept that reservoir temperature may be a secondary factor in controlling the molecular composition of inertinite. These findings inform a broader understanding of how different petroliferous OM types evolve throughout thermal reactions and further demonstrate that correlative Raman spectroscopy and reflection analyses, combined with careful organic petrography, can provide complimentary estimates of OM molecular composition and thermal maturity.

How to cite: Jubb, A., Birdwell, J., and Hackley, P.: Evaluating aromaticity changes with thermal stress at the single particle level for a suite of organic matter types from the Boquillas Shale (Texas, United States) via correlative Raman and reflection analyses, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-259, https://doi.org/10.5194/egusphere-egu21-259, 2021.

EGU21-1528 | vPICO presentations | GMPV1.1

A Raman spectroscopic study of the natural carbonophosphates Na3MCO3PO4 (M = Mn, Fe, and Mg)

Ekaterina Fomina, Evgeniy Kozlov, Mikhail Sidorov, and Vladimir Bocharov

Along with some other Na-minerals, carbonophosphates indicate a high initial Na activity in carbonatite and kimberlite melts, which is beneficial for petrological reconstructions. Because carbonophosphates are capable of incorporating large-ion lithophile and rare earth elements (REEs) in their structure, they can participate in the transport of these elements. Moreover, due to the presence of both [PO4]3− and [CO3]2− groups in carbonophosphates, these mineral phases play an important role in the Earth's global carbon and phosphate cycles. With all these properties, carbonophosphates have long attracted the attention of geologists. Raman spectroscopy appears to be one of the most suitable tools for their diagnosis, since they commonly present in rocks as small inclusions in other mineral grains. Despite this profit, only a few publications contain Raman characteristics of either natural or synthetic carbonophosphates.

We studied and compared Raman spectra of three natural carbonophosphate phases (sidorenkite, bonshtedtite, and bradleyite) with the general formula Na3MCO3PO4 (M = Mn, Fe, and Mg, correspondingly). These spectra showed from 21 to 24 vibrational bands, of which the two most intense (963±5 cm-1 и 1074±3 cm-1) correspond to the ν1(P–O) and ν1(C–O) modes. These two bands split due to the occurrence of isomorphic impurities. It was found that the crystallographic orientation of the sample influences the intensity of most bands. A natural increase in the Raman shift was observed for most bands assigned to the same vibrations (the smallest shift in the spectrum is characteristic of sidorenkite, an intermediate - of bonshtedtite, and the largest - of bradleyite).

We propose the following algorithm for the diagnosis of carbonophosphates:

  • Checking minerals for belonging to the group of carbonophosphates by the main bands and the characteristic profile of the spectrum;
  • Testing the hypothesis that the mineral of question is bradleyite based on the analysis of the estimated shift of the main bands;
  • Diagnosis of a mineral species by peaks located between the main bands;
  • Validation of the diagnostics by considering the position of the bands at 185±9 cm-1, 208±7 cm-1, 255±5 cm-1, and 725±6 cm-1.

The proposed algorithm allows one to perform Raman diagnostics of carbonophosphates in inclusions even in the absence of EPMA data. In the study of carbonatites, kimberlites, and other rocks, the diagnostics of the mineral species of the carbonophosphate group can be important in the petrological aspect.

This research was funded by the Russian Science Foundation, grant number 19-77-10039.

How to cite: Fomina, E., Kozlov, E., Sidorov, M., and Bocharov, V.: A Raman spectroscopic study of the natural carbonophosphates Na3MCO3PO4 (M = Mn, Fe, and Mg), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1528, https://doi.org/10.5194/egusphere-egu21-1528, 2021.

EGU21-2626 | vPICO presentations | GMPV1.1 | Highlight

The Potential Applications of Raman Spectroscopy in Unravelling Complex Palaeowildfire Ecosystems

Thomas Theurer, David Muirhead, David Jolley, and Dmitri Mauquoy

Raman spectroscopy represents a novel methodology of characterising plant-fire interactions through geological history, with enormous potential. Applications of Raman spectroscopy to charcoal have shown that this is an effective method of understanding intensity changes across palaeofire regimes. Such analyses have relied on the determination of appropriate Raman parameters, given their relationship with temperature of formation and microstructural changes in reference charcoals. Quantitative assessments of charcoal microstructure have also been successfully applied to the assessment of carbonaceous maturation under alternate thermal regimes, such as pyroclastic volcanism. Palaeowildfire systems in association with volcanism may present a complex history of thermal maturation, given interactions between detrital charcoals and volcanogenic deposition. However, whilst palaeofire and volcanic maturation of carbonaceous material are well understood individually, their interaction has yet to be characterised. Here we present the first analysis of palaeofire charcoals derived from volcanic ignition utilising Raman spectroscopy. Our results indicate that complex interactions between volcanism and palaeofire systems may be better understood by the characterisation of charcoal microstructure, alongside palaeobotanical and ecosystem studies. Understanding the unique relationship between wildfires and volcanism, and the impact that this has on the fossil record, may better assist our understanding of wildfire systems in deep history. Further still, this highlights the potential for better understanding the socioecological impacts of modern and future wildfire systems closely associated with volcanic centres. 

How to cite: Theurer, T., Muirhead, D., Jolley, D., and Mauquoy, D.: The Potential Applications of Raman Spectroscopy in Unravelling Complex Palaeowildfire Ecosystems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2626, https://doi.org/10.5194/egusphere-egu21-2626, 2021.

Over the last two decades, Raman microspectroscopy has known a spectacular development in various research fields of petrology opening new avenues for studies in sedimentology, metamorphism or magmatism and cosmochemistry. This has been made possible thanks to major technological improvements (e.g., Raman hyperspectral mapping) and a better theoretical approach (e.g., data processing and interpretation). Raman spectra are actually sensitive to even minor (chemical or structural) perturbations within chemical bonds in (even amorphous) solids, liquids, and gases. They can, thus, help identify, characterize, and differentiate between individual minerals, fluid inclusions, glasses, carbonaceous materials, solid solution phases, strain in minerals, and dissolved species in multi-component solutions. Such sensitivity and versatility make Raman a unique tool for petrology. Yet, it relies on a weak and subtle signal and a cautious approach is required to avoid pitfalls during the analysis and/or the interpretation of data. Some recent scientific milestones will be presented and discussed in various fields like geothermobarometry of metamorphic rocks, geochemistry of meteorites, speciation of deep fluids involved in fluid-rock interactions or the characterization of organic/mineral assemblages of astrobiological interest. For the particular c       ase of petrology, Raman microspectroscopy has the immense advantage that it requires minimal sample preparation, thus it can be performed in situ preserving the original microtexture of the sample with a rather high spatial resolution for analysis, typically 1 mm at 532 nm for modern systems. Therefore, this technique is now increasingly used to study poorly crystalline and chemically heterogeneous materials involved for instance in geochemical processes occuring at Earth surface. But it faces numerous challenges due to the reactivity of such phases making them fragile under the laser beam, or due to the quasi-systematic presence of intense backgrounds in the spectra overwhelming the Raman signal. The source of this background can be multiple as it can be observed with fine-grained samples and/or it can be generated by the presence of luminescence/fluorescence emission centers. More generally such background is not well understood although it is a major issue for Raman spectroscopy in many petrological applications. However, there too, recent technological developments, sometimes based on old ideas, offer new possibilities to investigate safely and accurately such materials : time-resolved spectroscopy and surface-enhanced Raman spectroscopy (SERS) will be presented as well as some applications for petrology of complex samples.

How to cite: Beyssac, O.: Raman spectroscopy for petrology : recent scientific milestones, technological trends and challenges, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3416, https://doi.org/10.5194/egusphere-egu21-3416, 2021.

In recent decades increasing evidence was found for life under extreme conditions, e.g., near black smokers on the ocean floor. The synthesis and stability of vital molecules like adenosine triphosphate (ATP) and adenosine diphosphate (ADP) are essential to maintain the metabolism of all known organisms. The lifetime of these molecules in water is limited by the non-enzymatic hydrolysis reaction that becomes dominant at elevated temperatures. A better understanding of this mechanism will provide us insights of life at extreme conditions.

Previous studies determined the hydrolysis rate constants of ATP for several compositions, temperatures and pressures using quench experiments and subsequent analysis. So far, it was not tested whether quench artefacts might have affected those results. Therefore, the current study was performed to develop a method to follow the reaction in-situ with a high sampling rate at elevated temperatures. A confocal micro-Raman spectrometer and a hydrothermal diamond anvil cell were used to perform experiments at elevated temperatures and vapour pressure. Spectra were obtained in the range of 660 cm-1 to 1157 cm-1 as a function of time. Different solutions of ATP and ADP were measured at 353 K, 373 K, and 393 K, at starting pH values of 3 and 7. First findings are consistent with previous studies and show that with decreasing pH value the hydrolysis rate increases. The data indicate hydrolysis rate constants in the magnitude of 10-3 s-1 by 393 K, 10-4 s-1 by 373 K and 10-5 s-1 by 353 K. These initial observations show that this technique produces reliable kinetic data on this reaction. It also provides much better sampling statistics than quench experiments. 

The high reaction rates suggest that a mechanism exists to regulate this reaction at higher temperatures, which is necessary to allow metabolism under extreme conditions. Moreover, it is commonly known that ATP interacts with various metal ions with different effects on the reaction rate. An application of this method would be the quantification of the hydrolysis rate constant in chemically more complex systems.

How to cite: Moeller, C., Schmidt, C., Guyot, F., and Wilke, M.: A new in-situ method to determine the hydrolysis rate constant of adenosine triphosphate (ATP) by application of Raman spectroscopy in a hydrothermal diamond anvil cell, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3419, https://doi.org/10.5194/egusphere-egu21-3419, 2021.

EGU21-7459 | vPICO presentations | GMPV1.1

An insight on the polyphase thermal history of the Ghomarides and Upper Sebtides in the Internal Rif (North Morocco) by means of Raman spectroscopy on organic matter

Andrea Schito, Achraf Atouabat, Rocco Calcagni, Sveva Corrado, David Muirhead, Claudia Romano, Alessandro Pozzi, Roberto Galimberti, and Amalia Spina

The correct assessment of maximum temperatures experienced by rocks is an essential tool to unravel the evolution of the thermal structure of the crust during the main phases of an orogenesis. Given to broad P-T stability field of classical metamorphic mineralogical indicators, maximum temperatures derived from the analyses of carbonaceous material dispersed in rocks by means of Raman spectroscopy has shown to be a suitable alternative to classical geothermometer. Initially developed for high metamorphic rocks the use of this tools has recently been extended also at lower metamorphic degree and diagenesis. This allowed us to extend the analyses of paleotemperatures experienced by rocks from Ghomarides and Sebtides from the Internal Rif in North Morocco with respect to previous works. Ghomaride and Sebtides in this portion of the Rif-Betic-Tell chain, represent respectively the upper and lower plates of a metamorphic core complex  and are composed, the first, by Paleozoic rocks with a partially preserved Mesozoic-Cenozoic cover and the second by lower Paleozoic to Triassic deep-crustal mica-schists, migmatites and granulites associated with peridotites (Beni Bousera complex).

Our data suggest that the uppermost Tiszgarine Unit of the Upper Sebtides experienced warmer condition than previously observed. Moreover, we calculate the maximum temperatures experienced by the Ghomarides  during both the Eo and Late Variscan cycles showing that differences in temperature exist among the vary units that compose the complex. Finally, in the southern area our data suggest a less severe alpine heating related to the emplacement of the Beni Bousera peridotite, than previously calculated.

How to cite: Schito, A., Atouabat, A., Calcagni, R., Corrado, S., Muirhead, D., Romano, C., Pozzi, A., Galimberti, R., and Spina, A.: An insight on the polyphase thermal history of the Ghomarides and Upper Sebtides in the Internal Rif (North Morocco) by means of Raman spectroscopy on organic matter, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7459, https://doi.org/10.5194/egusphere-egu21-7459, 2021.

EGU21-7530 | vPICO presentations | GMPV1.1

In situ Raman spectroscopic technique for high-pressure studies of mineral and fluid inclusions formation 

Nadezda Chertkova, Anna Spivak, Egor Zakharchenko, Yuriy Litvin, Oleg Safonov, and Anastasiia Burova

Rapid development of in situ experimental techniques provides researchers with new opportunities to model geological processes, which take place deep in the Earth’s interior. Raman spectroscopy is considered a powerful analytical tool for investigation of the samples subjected to high pressures in a diamond anvil cell, since in such experiments phase assemblages can be determined in real time using measured Raman spectra.

In this study, we describe experimental methods for in situ observation and spectroscopic analysis of fluids and minerals, which constitute environment for diamond growth, at the upper mantle pressure conditions. Experiments were conducted in the externally heated, “piston-cylinder” type diamond anvil cell at pressures exceeding 6 GPa and temperatures up to 600 degree C. Phase relationships and fluid speciation were monitored during experiments to reconstruct the environment and mechanism of inclusions formation. Compared to other analytical tools, commonly used in combination with diamond anvil cell apparatus, Raman spectroscopy offers several advantages, such as short sample preparation time, non-destructive characterization of the phases observed in the sample chamber and relatively short measurement time.

This work was supported by grant No. 20-77-00079 from the Russian Science Foundation.

How to cite: Chertkova, N., Spivak, A., Zakharchenko, E., Litvin, Y., Safonov, O., and Burova, A.: In situ Raman spectroscopic technique for high-pressure studies of mineral and fluid inclusions formation , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7530, https://doi.org/10.5194/egusphere-egu21-7530, 2021.

EGU21-7939 | vPICO presentations | GMPV1.1

Raman Spectral Trends in ‘low-temperature’ Carbonaceous Materials.

David Muirhead

Amorphous carbonaceous materials are typically those that would be considered immature, at temperatures below 300°C, in a typical sedimentary basin burial setting. Only recently has there been much discussion on the efficacy of Raman spectroscopy on amorphous carbon at temperatures below 300°C. Here we present data from a variety of published sources alongside our own data reviewing the apparent trends in amorphous carbon with some discussion related to thermal regime (intensity, duration), with case studies including intruded host rocks, fold and thrust belts and wildfires. We conclude that Raman spectroscopy can be applied successfully to ‘low-temperature’ carbonaceous material whilst noting the challenges faced to fully understand the physio-chemical mechanisms at these temperature ranges.

How to cite: Muirhead, D.: Raman Spectral Trends in ‘low-temperature’ Carbonaceous Materials., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7939, https://doi.org/10.5194/egusphere-egu21-7939, 2021.

Carotenoid compounds such as β-carotene are some of the most prevalent organic molecules on Earth and are key biomarkers as there is no known abiogenic source. During diagenesis and thermal alteration, carbon undergoes well-documented changes in Raman spectra.

There has been little research into the transitional degradation of carotenoid spectra to where they are fully replaced by the carbon spectra as the main identifier of thermal maturity under Raman spectroscopy. This is an overlooked regime when discussing the search for life, terrestrial and extra-terrestrial, where current research (using Raman spectroscopy) either focuses on finding living organisms displaying common organic molecules, or looks for the elemental carbon evidence of extinct fossil life. The real world is not usually so polarised, so covering the transition between these modes of life detection will improve any detection analysis.

For this study the volcanic thermal spring system in Viterbo, Italy was used as a field-based laboratory. The high rate of carbonate precipitation in these thermal springs, the wide range of thermal regimes (58°C to 25°C), and the prevalence of fast-growing algae in the run-off streams, give excellent preservation of a range of organic matter states at directly measurable temperatures.

The results demonstrate how the Raman spectra of the carotenoid compounds change with hydration, death of the organism, and thermal alteration of the organic material. The relationship between the spectra of the carotenoid compound and the elemental carbon spectra in the transition zone is also shown.

This study expands on the use of Raman spectroscopy of carbon as a low-temperature geothermometer, and provides a framework for the spectral response of organic matter in an often-overlooked geological regime. It is anticipated that the fields of geothermal energy, climatology, geobiology and astrogeobiology, could all benefit from this study, incorporating this enhanced thermal alteration data into existing and future work.

How to cite: O'Donnell, A.: Searching for life in volcanic carbonate systems and the effect of temperature on organic molecules, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9659, https://doi.org/10.5194/egusphere-egu21-9659, 2021.

Organic carbon in rocks undergoes nanostructural changes when exposed to increased temperatures or strain. These changes can be identified using Raman spectroscopy, giving information about thermal maturity and strain conditions. However, it is well documented that in a heterogeneous rock, strain can be highly localised, evident in microstructural variations such as strain shadows, sub-grain development, twinning, and the rotation and alignment of crystal axes. In this study we map microstructural textures in deformed calcite through optical microscopy and EBSD of calcite crystal axes. This textural map is compared to mapped Raman spectral parameters of organic carbon particles in the same thin section. A comparison of the maps allows assessment of the extent to which Raman spectral parameters and hence carbon nanostructure is influenced by strain at a sub-mm scale. The study highlights the sensitivity of organic carbon nanostructure to sub-mm scale changes in strain localisation within a single deformed carbonate sample.

How to cite: Kedar, L., Bond, C., and Muirhead, D.: Strain-related carbon ordering on a sub-mm scale: a comparison of carbonate microfabrics and organic carbon nanostructure within a single sample., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9921, https://doi.org/10.5194/egusphere-egu21-9921, 2021.

EGU21-11092 | vPICO presentations | GMPV1.1

Raman Spectroscopy as a potential strain gauge

Clare Bond, Lauren Kedar, and David Muirhead

Raman Spectroscopy is increasingly being used to better understand a range of Earth Science processes. Notable recently is the application of Raman Spectroscopy to carbonaceous material in strained rocks. Here we investigate the changes in Raman Spectral response in strained material relative to an unstrained equivalent, drawing on examples from the published literature and our own work. We consider inconsistencies in the relative changes in Raman Spectral parameters of strained material and their potential causes. In doing so we look at some of the current methods for determining Raman Spectral parameters in rocks and what they might tell us about the strain state of carbon in a single rock sample. Finally, we consider the implications for use of Raman Spectroscopy of carbonaceous material as a geothermometer as well as a future potential strain gauge. 

How to cite: Bond, C., Kedar, L., and Muirhead, D.: Raman Spectroscopy as a potential strain gauge, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11092, https://doi.org/10.5194/egusphere-egu21-11092, 2021.

GMPV4.1 – Evolution of the Earth's upper mantle: a petrological, geochemical and geodynamic perspective on lithospheric mantle xenoliths, orogenic and ophiolitic peridotites

EGU21-8450 | vPICO presentations | GMPV4.1

Depletion, metasomatism and refertilisation in the Sub-Continental Lithospheric Mantle beneath northern Victoria Land (Antarctica): a review

Massimo Coltorti, Costanza Bonadiman, Federico Casetta, Barbara Faccini, Pier Paolo Giacomoni, Beatrice Pelorosso, and Cristina Perinelli

Assessing the nature and evolution of the Sub-Continental Lithospheric Mantle (SCLM) is crucial to understand the dynamics of Earth’s interior and the global scale tectono-magmatic processes. The study of ultramafic xenoliths brought to the surface in specific context, such as northern Victoria Land (Antarctica), is a key to investigate how the SCLM bear witness of large-scale geodynamic episodes. Indeed, the Antarctica lithosphere was involved into three main tectono-magmatic episodes since Paleozoic, i.e. the 550-110 Ma Ross subduction, the Jurassic (~182 Ma) Ferrar magmatism and the Cenozoic alkaline magmatism responsible for the opening of the West Antarctic Rift System (WARS).

In this study, a review of the petrological and geochemical features of >200 mantle-derived and cumulate xenoliths brought to the surface at Baker Rocks, Greene Point, Handler Ridge, Harrow Peaks, Browning Pass and Mount Overlord enabled us to reconstruct the main depletion and enrichment processes that took place in the Antarctica SCLM. Strong depletion is recorded by Greene Point lherzolites and harzburgites (18-21%), which likely began melting in the garnet facies and terminated in the spinel facies (Perinelli et al. 2006), whereas mild melt extraction in the spinel stability field was hypothesized at Baker Rocks and Handler Ridge (12-16% and 7-13% melting, respectively). The onset of the Jurassic Ferrar large magmatic event is testified by both the refertilisation in Greene Point-Baker Rocks peridotites and the appearance of cumulate orthopyroxenites/olivine-websterites at Harrow Peaks and Baker Rocks. Late enrichment process/es took place in concomitance with the Cenozoic alkaline magmatism of the WARS, resulting in both cryptic and modal metasomatism and overprinting earlier chemical modifications. This metasomatism was particularly effective at Baker Rocks, as shown by the increase of clinopyroxene abundance, its trace element enrichment and the formation of amphibole disseminated and in veins. Clinopyroxene composition in Cenozoic cumulate rocks matches the enrichment path observed in the peridotites, supporting the link between the last metasomatic process and the recent alkaline magmatism.

Among mantle xenoliths populations, Greene Point record the highest T-P (870-1059 °C; 0.8-1.6 GPa) and the least oxidized conditions (fO2 down to -2/-3 ΔFMQ). Cumulate rocks yield the highest fO2 (up to +1.5 ΔFMQ), at T varying between 900 and 1150°C, approximating the conditions of crystallizing melts. No discrepancies in fO2 emerged between amphibole-bearing and amphibole-free peridotites, ruling out a strict correlation between amphibole stability, H2O activity and fO2. Nevertheless, the alkaline metasomatic event, which led to amphibole formation, caused a remarkable increase in the H2O content of the system. In fact, anhydrous peridotites preserve bulk H2O contents ≤128 ppm, while lherzolites with disseminated amphibole and hornblendites have H2O contents as up to 354-1120 ppm and 1.42 wt%, respectively.

 

Perinelli, C., et al. 2006. Geochemical and O-isotope constraints on the evolution of lithospheric mantle in the Ross Sea rift area (Antarctica). Contributions to Mineralogy and Petrology, 151(3), 245-266.

How to cite: Coltorti, M., Bonadiman, C., Casetta, F., Faccini, B., Giacomoni, P. P., Pelorosso, B., and Perinelli, C.: Depletion, metasomatism and refertilisation in the Sub-Continental Lithospheric Mantle beneath northern Victoria Land (Antarctica): a review, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8450, https://doi.org/10.5194/egusphere-egu21-8450, 2021.

EGU21-10603 | vPICO presentations | GMPV4.1

Geochemical and petrophysical characterization of mantle metasomatism beneath the North Tanzanian Divergence, East African rift.

Adeline Clutier, Fleurice Parat, Michel Gregoire, Benoit Gibert, Stéphanie Gautier, and Christel Tiberi

The North Tanzanian Divergence (NTD) is the prolongation of the eastern branch of the East African Rift and is a place of intense volcanism. Numerous volcanoes erupted deep subalkaline to highly alkaline magmas, including the particular active natrocarbonatite Oldoinyo Lengai. On the North-South axis (Natron to Manyara basins), three highly alkaline volcanoes, Pello Hills, Lashaine and Labait, erupted melilite magmas that originated from low degree of partial melting of asthenospheric mantle (depth > 120 km). The particularity of these volcanoes is that they sampled numerous mantle xenoliths during ascent. This represents a unique opportunity to study the composition and the rheology of lithospheric mantle. Mantle xenoliths are deep garnet-bearing peridotites (120 km depth), amphibole and phlogopite peridotites and phlogopitites. They contain abundant hydrous minerals as isolated crystals or veins that attest to an important metasomatism beneath the NTD. Previous geochemical and petrological studies have highlighted interactions of alkaline magmas and the thick cratonic lithosphere as metasomatic agent. However, the presence and composition of magmas, the degree of metasomatism, and the role of metasomatism on mantle rheology below the NTD is still debated.

To characterize these previous parameters, in this study we performed geochemical and petrophysical analyses on metasomatized, fertile and refractory mantle xenoliths from Labait (on-craton volcano) and Pello Hills (in-rift volcano). Using mineral compositions and thermobarometer calibrations, we estimated the depth of mantle xenoliths between 40 and 140 km (14 to 47 kbar) and temperatures from 930 to 1340°C. EBSD analysis on thin sections indicate that peridotites and amphibole/phlogopite-bearing mantle xenoliths display a moderate to strong deformation induced crystal preferred orientation. In contrast, weak mineral orientations have been observed in phlogopite-amphibole-clinopyroxene-bearing veins. Calculation of seismic properties using MTEX program show that peridotites are seismically anisotropic, up to 12.4% for P-wave velocity (Vp) and 6.8% for S-wave velocity (Vs). The Vp and Vs in hydrous veins are lower than in peridotites (Vp: 7.5-7.9 and 8.3-9.6 km/s; Vs: 4.4-4.6 and 5.0-5.3 km/s respectively) and therefore the Vp and Vs velocities decrease with the increasing proportion of metasomatic minerals. We estimate that a peridotite with 20 vol.% metasomatic vein has a velocity decrease of 3.5% for Vp and 2.9% for Vs, compared to a fertile peridotite.

These geochemical and petrophysical approaches are important to understand P- and S-wave propagation in the lithospheric mantle beneath the NTD and more specifically in metasomatized lithospheric mantle. The new in situ data and models from mantle xenoliths will be compared to tomographic acquisition and discussed in term of temperature, presence of melt or metasomatism processes. Both petrophysical and geophysical data will help to precisely determine the structure and rheology of the lithospheric mantle, which may control the propagation of the rift at early stage rifting between the Tanzanian craton and the mobile Proterozoic belts.

How to cite: Clutier, A., Parat, F., Gregoire, M., Gibert, B., Gautier, S., and Tiberi, C.: Geochemical and petrophysical characterization of mantle metasomatism beneath the North Tanzanian Divergence, East African rift., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10603, https://doi.org/10.5194/egusphere-egu21-10603, 2021.

EGU21-1670 | vPICO presentations | GMPV4.1

Evolution of lithospheric mantle beneath mobile belt between two cratons: An example from the Oku Massif, Cameroon Volcanic Line (W Africa)

Jacek Puziewicz, Sylvin S. T. Tedonkenfack, Sonja Aulbach, Theodoros Ntaflos, Mary-Alix Kaczmarek, Anna Kukula, Magdalena Matusiak-Małek, and Małgorzata Ziobro

Cameroon Volcanic Line (CVL) is located in the western part of equatorial Africa and consists of volcanoes which were active from Eocene to recent, stretching ca. 1700 km from the Atlantic in the SW into the African continent in the NE. The continental part of the CVL is located on the Neoproterozoic Central African Orogenic Belt and is situated between the Congo craton and Sahara/Western Africa craton. Mantle peridotite xenoliths which occur locally in lavas of the CVL come from the spinel facies only, suggesting a relatively shallow lithosphere-asthenosphere boundary (LAB). This is supported by seismic studies, showing the LAB at 90-100 km.

In order to understand better the evolution of the lithospheric mantle beneath the CVL, we studied xenolith suite (16 xenoliths) from Befang in the Oku Massif (Tedonkenfack et al., submitted). The Befang xenoliths are almost entirely lherzolites which have cataclastic to weakly porphyroclastic texture. Harzburgites and websterites occur subordinately. Spinel is interstitial and has amoeboidal shape. The studied peridotites (14 lherzolites, 1 harzburgite) consist of minerals with almost constant composition (olivine Fo88.7-90.3, orthopyroxene Al 0.17-0.19 atoms per formula unit (a pfu), clinopyroxene Al 0.28-0.30 a pfu, spinel Cr# dominantly 0.09-0.11). Spinel of Cr# 0.15 occurs in one of the lherzolites, whereas that occurring in harzburgite has Cr# 0.19. Clinopyroxene REE patterns are similar to those of Depleted MORB Mantle (DMM) except LREEs, which vary from depleted to enriched. The A-type olivine fabric occurs in the EBSD-studied subset of 8 samples (one harzburgite and 7 lherzolites). Orthopyroxene shows deformation consistent with olivine. The fabric of LREE-enriched clinopyroxene is equivalent to those of orthopyroxene and olivine, whereas spinel and LREE-depleted clinopyroxene are oriented independently of the fabric of host rock.

These data, thermometry, phase relationships and phase equilibria diagrams suggest that the Befang mantle section was refertilised by MORB-like melt at pressures 1.0-1.4 GPa and temperatures slightly above 1200 – 1275 ºC. The olivine-orthopyroxene framework and LREE-enriched clinopyroxene preserve the fabric of protolith. On the other hand, the LREE-depleted clinopyroxene shows discordant orientation relative to olivine-orthopyroxene protolith framework, and amoeboidal spinel crystallized from the melt. The major element and REEs composition of pyroxenes occurring in the Befang peridotites indicate chemical reequilibration at temperatures 930 – 1000 ºC. Trace element modeling shows that websterites can be linked to Cenozoic volcanism. We speculate that they form veins in the lithospheric mantle. Our study therefore supports the origin of fertile SCLM via refertilization rather than by extraction of small melt fractions, and further emphasizes the involvement of depleted melts in this process, which contrasts with the incompatible element-enriched melts typically invoked in within-plate settings.

This study originated thanks to the project of Polish National Centre of Research NCN 2017/27/B/ST10/00365 to JP. The bilateral Austrian-Polish project WTZ PL 08/2018 enabled extensive microprobe work.

References:

Tedonkenfack SST, Puziewicz J, Aulbach S, Ntaflos T., Kaczmarek M-A, Matusiak-Małek M, Kukuła A, Ziobro M: Lithospheric mantle refertilization by DMM-derived melts beneath the Cameroon Volcanic Line – a case study of the Befang xenolith suite (Oku Volcanic Group, Cameroon). Submitted.

How to cite: Puziewicz, J., Tedonkenfack, S. S. T., Aulbach, S., Ntaflos, T., Kaczmarek, M.-A., Kukula, A., Matusiak-Małek, M., and Ziobro, M.: Evolution of lithospheric mantle beneath mobile belt between two cratons: An example from the Oku Massif, Cameroon Volcanic Line (W Africa), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1670, https://doi.org/10.5194/egusphere-egu21-1670, 2021.

EGU21-5234 | vPICO presentations | GMPV4.1

Lithospheric mantle beneath the Vogelsberg volcanic field (Central Germany) 

Małgorzata Ziobro, Jacek Puziewicz, Sonja Aulbach, Theodoros Ntaflos, Magdalena Matusiak-Małek, and Michel Grégoire

Vogelsberg is a Cenozoic volcanic field situated at the northern tip of the Upper Rhine Graben. It stretches over two major Variscan basement units: the Rheno-Hercynian Zone in the NW and the Saxo-Thuringian Zone in the SE. We studied peridotite xenoliths from Breitenborn, Nidda and Dreihausen (SE, central and NW part of Vogelsberg, respectively) in order to reveal the evolution of the subcontinental lithospheric mantle (SCLM) rejuvenated during a Cenozoic rifting episode.

The Vogelsberg xenoliths are spinel harzburgites and clinopyroxene-poor spinel lherzolites. Most samples show grain size reduction leading to serial or porphyroclastic texture, or slight to well-defined foliation. All studied sites have similar major elements chemistry: olivine Fo 89.3-91.7%; orthopyroxene (opx) Mg# 0.89-0.92 and 0.06-0.25 atoms of Al pfu (per formula unit); clinopyroxene (cpx) Mg# 0.89-0.93 and 0.10-0.33 atoms of Al pfu. Spinel Cr# is highly variable: 0.18-0.45 for Breitenborn, 0.14-0.57 for Nidda and 0.11-0.61 for Dreihausen.

Vogelsberg peridotites exhibit a diversity of REE patterns:

(1) opx with a sinusoidal pattern, no cpx (Nidda, Dreihausen);

(2) cpx with flat patterns; coexisting opx with strong LREE-depletion, (La/Lu)N ~0.02 (Nidda, Dreihausen)

(3) cpx with flat, spoon-shaped patterns with La-Ce-enrichment (La/Pr)N ~4.3; opx similar to (2) but partly spoon-like, (Nd/Lu)N ~0.02 (Nidda, Breitenborn)

(4) cpx with different degree of LREE-enrichment, (La/Lu)N­ of 4-21.4; coexisting opx with mild LREE-depletion, (La/Lu)N of 0.1-0.3 (Breitenborn, Nidda, Dreihausen)

(5) cpx with flat HREE pattern and strongly LREE-depleted, (La/Eu)N ~0.03; coexisting opx similar to (2) but with (Ce/Lu)N ~0.001 (Breitenborn)

Temperatures calculated using REE content (TREE) [1] for the Breitenborn peridotites exhibit two ranges: 930-990°C and 1050-1130°C, for the Nidda ones: 880-930°C, 1000-1050°C and 1110-1150°C and for Dreihausen ones: 1140-1190°C. Temperatures calculated on the basis of pyroxene major element contents (TBKN) [2] are 40-90°C lower than TREE in Breitenborn and Nidda and lower by 10-55°C in Dreihausen.

The most common pyroxene REE patterns (type 4) are products of two-phase metasomatism: by Vogelsberg alkali basalt followed by a highly LREE-rich melt that further increased LREE contents in cpx, up to observed abundances. Strongly LREE-depleted opx (types 2, 3, 5) and cpx (type 5) patterns could be residues after partial melting of a fertile protolith, or products of metasomatism by melts derived from depleted MORB mantle. Cpx patterns of type 2 and 3 might have been once similar to type 5 but were later affected by the second phase of metasomatism: highly LREE-rich melt that increased chromatographically their LREE contents to variable degrees. The diversity of REE patterns and calculated temperatures shows that the SCLM beneath Vogelsberg is highly heterogeneous, probably due to spatial variability of deformation and percolation of hot melts connected with Cenozoic rifting.

 

This study was funded by Polish National Science Centre to MZ (UMO-2018/29/N/ST10/00259) and JP (UMO-2014/15/B/ST10/00095). EPMA analyses were done thanks to the Polish-Austrian projects WTZ PL/16 and WTZ PL 08/2018. MZ acknowledges the DAAD fellowship at Goethe University Frankfurt.

References

[1] Liang Y. et al. (2013). GeochimCosmochimActa 102, 246–260.

[2] Brey G. & Köhler T. (1990). JPetrol 31, 1353–1378.

How to cite: Ziobro, M., Puziewicz, J., Aulbach, S., Ntaflos, T., Matusiak-Małek, M., and Grégoire, M.: Lithospheric mantle beneath the Vogelsberg volcanic field (Central Germany) , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5234, https://doi.org/10.5194/egusphere-egu21-5234, 2021.

EGU21-15992 | vPICO presentations | GMPV4.1

Metal enrichment as a result of SCLM metasomatism? Insight from ultramafic xenoliths from SW Poland.

Hubert Mazurek, Jakub Ciazela, Magdalena Matusiak-Małek, Bartosz Pieterek, Jacek Puziewicz, Marina Lazarov, Ingo Horn, and Theodoros Ntaflos

Migration of metals such as gold, silver and copper through the subcontinental lithospheric mantle (SCLM) can be tracked by the investigation of sulfides in mantle xenoliths. Therefore, to understand relations between the metal migration and metasomatism of silicate phases in the SCLM beneath SW Poland we studied sulfides in a set of mantle ultramafic xenoliths with variable metasomatic history. The xenoliths occur in the Cenozoic alkaline mafic volcanic rocks from the SW Poland (N Bohemian Massif).  

The studied sulfides occur in mantle rocks of variable history: 1) strongly depleted (group A0) to weakly metasomatized peridotites (Group A1); 2) strongly melt-metasomatized peridotites (Group B); 3) pyroxenites (Group C; for details of group definition see Matusiak-Małek et al., 2014, JoP). The metasomatism was of mixed silicate/carbonatite nature. The sulfides are either interstitial or enclosed in the silicates and form mostly globular monosulfide solid solution-chalcopyrite (mss-Ccp) assemblages typical of igneous sulfides separated and crystallized from mafic magmas, with mss partially re-equilibrated to exsolutions of pentlandite (Pn) and pyrrhotite (Po) when temperature dropped to <600°C (e.g., Craig and Kullerud, 1969, Econ. Geol. Monogr.).

The sulfide abundances increase from Group A (≤ 0.008 vol.‰) through Group B (up to 0.060 vol. ‰) to Group C (up to 0.963 vol.‰) xenoliths. The sulfides of Groups C (Po15–99Pn0–20Ccp0–70)and B (Po0–85Pn14–100Ccp0–27) are generally poorer in Ni compared to Group A (Po0–74Pn24–100Ccp0–35). Consequently, Ni/(Ni+Fe) in the Group C pentlandites (0.41–0.52) is lower than in those in Group A (0.45–0.69). Moreover, the sulfide grains of Group B are enriched in chalcophile elements (e.g., the median content of Zn is 90 ppm) compared to sulfides from Groups C (52 ppm Zn) and A (51 ppm of Zn). The same relations occur in PGE contents, e.g., Pt in Group B is 1.6 ppm, while in Groups C and A it is 0.1 and 1.3 ppm, respectively.  Observed differences in δ56Fe between the Groups are probably due to modal composition of bulk sulfide grains between Groups A (Ni-rich), B and C (Fe-Cu-rich). As no difference is observed between the grains of the same composition, any fractionation of Fe isotopes in sulfide melt seems to be possible only upon its differentiation from Ni-rich to Fe-Cu-rich.

The host peridotites were affected by strong depletion as the degree of partial melting was possibly ~30%. Thus, the observed enhanced sulfide modes in the metasomatized peridotites (Groups A1 and B) are most likely brought by the metasomatic melt. This is also evidenced by their Fe-Cu-rich composition, similar to that of the sulfides from the pyroxenites. In this view, melt metasomatism likely affects the chalcophile and highly-siderophile metal budget of the continental lithosphere.

 

The measurements of Fe isotopic ratios were financed from funds for years 2020-2024 within program “Diamond Grant” (DI2019 0093 49), the LAICPMS measurements were financed from 2016/23/N/ST10/00288 to J.C., and the EPMA analyses were done within the frame of the Polish-Austrian project WTZ PL/16 and WTZ PL 08/2018.

How to cite: Mazurek, H., Ciazela, J., Matusiak-Małek, M., Pieterek, B., Puziewicz, J., Lazarov, M., Horn, I., and Ntaflos, T.: Metal enrichment as a result of SCLM metasomatism? Insight from ultramafic xenoliths from SW Poland., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15992, https://doi.org/10.5194/egusphere-egu21-15992, 2021.

EGU21-12817 | vPICO presentations | GMPV4.1

First assessment of the noble gas and CO2 isotopic composition of fluid inclusions hosted in mantle xenoliths from El Hierro (Canary Islands) 

Andres Sandoval Velasquez, Andrea Luca Rizzo, Alessandro Aiuppa, Maria Luce Frezzotti, Samantha Remigi, Eleazar Padrón, and Nemesio Pérez

Studying the isotopic composition of fluids trapped in mantle xenoliths opens avenues to understanding the origin and cycling of volatiles in the Earth’s upper mantle. Here, we present the first isotopic results for noble gases and CO2 in fluid inclusions (FI) trapped in mantle xenoliths from El Hierro the youngest island of the Canarian archipelago. Our results are based on 6 mantle xenolith samples (3 Spinel-lherzolites and 3 Spinel-harzburgites) collected from the El Julan cliff valley (Oglialoro et al., 2017), from which we hand-picked crystals of Ol, Opx, and Cpx. Isotopic determinations were performed at the INGV (Sezione di Palermo) noble gas and stable isotopes laboratories, following the preparation methods and analytical procedures described in Rizzo et al. (2018 and references therein).

The Ne-Ar isotopic compositions reveal the presence of an atmospheric component in the FI. Most of the samples exhibit 4He/20Ne ratios > 60, 20Ne/22Ne ratios between 9.84 and 10.49, 21Ne/22Ne ratios from 0.0295 to 0.0330, and 40Ar/36Ar > 800, suggesting mixing between MORB-like mantle fluids and an air-derived component. We argue this latter may (at least in part) derive from upper mantle recycling of atmospheric fluids via paleo-subduction event(s). Excluding samples possibly affected by diffusive fractionation processes, the average Rc/Ra ratio (3He/4He ratio corrected for atmospheric contamination) measured in El Hierro xenoliths is ~7.45 + 0.26 Ra, within the MORB range (8 + 1 Ra; Graham, 2002). The He homogeneous signature of these xenoliths agrees well with the 3He/4He compositions previously reported in lava phenocrysts and cumulates (Day and Hilton, 2011) and is slightly below the maximum ratios measured in groundwater samples during the 2012 volcanic unrest (~8.2 Ra; Padron et al., 2013). All these pieces of evidence argue against a primordial source involved in the local lithospheric mantle. Putting these data in the context of previous literature results for FI and surface gases in the Canary Islands (La Palma, La Gomera, Tenerife, Gran Canaria, and Lanzarote), we identify an eastward 3He/4He decreasing trend that parallels a corresponding increase of the oceanic crust thickness. In addition to the mantle heterogeneity, we propose that part of the 3He/4He east-to-west variation along the archipelago is caused by the variable thickness of the oceanic crust (and hence, different interactions with 4He-rich crustal fluids during emplacement).

The FI δ13C(CO2) isotopic composition ranges from -2.38 to -1.23‰ in pyroxenes and -0.2 to +2.0‰ in olivine. These unusually positive δ13C compositions support the existence of a recycled crustal carbon component in the local source mantle, likely pointing to mantle metasomatism (Oglialoro et al., 2017) from fluids carrying carbon from subducted sediments and/or altered oceanic crust (AOC).

How to cite: Sandoval Velasquez, A., Rizzo, A. L., Aiuppa, A., Frezzotti, M. L., Remigi, S., Padrón, E., and Pérez, N.: First assessment of the noble gas and CO2 isotopic composition of fluid inclusions hosted in mantle xenoliths from El Hierro (Canary Islands) , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12817, https://doi.org/10.5194/egusphere-egu21-12817, 2021.

EGU21-8810 | vPICO presentations | GMPV4.1

Pyroxenitic xenoliths from southern Scotland and what they tell us.

Magdalena Matusiak-Małek, Piotr Matczuk, Brian G.J. Upton, Theodoros Ntaflos, Sonja Aulbach, Jacek Puziewicz, and Anna Kukuła

Late Carboniferous/early Permian mafic volcanic rocks occurring in Scotland carry a broad spectrum of peridotitic and pyroxenitic xenoliths. The latter provide evidence of magmatic processes in the lower crust and the lithospheric mantle. In this study we present textural and compositional data on twenty-eight pyroxenitic xenoliths from six localities from southern Scotland (Midland Valley and Southern Uplands Terranes).

Most are interpreted as adcumulates (varying in grain size from fine to coarse) although some others are mesocumulates. They include both clinopyroxenites and websterites with variable amounts of olivine; phlogopite is present in only one sample. Cores of greenish clinopyroxene in three of the olivine clinopyroxenites are enveloped by brownish clinopyroxene, while one composite xenolith comprising coarse-grained olivine clinopyroxenite in sharp contact with harzburgite. Five groups, based on textural and mineralogical features were distinguished. Representatives of more than one group can be present in a single locality.

Most of the samples from the same textural group share similar chemical composition. In general, the clinopyroxenes are Ti,Al-diopside/augite with Mg#=0.74-0.86; where clinopyroxenes are zoned the rims have lower Mg# and higher Al content. The orthopyroxene is an Al (±Cr)-enstatite with Mg#=0.78-0.89, olivine (Fo76-77) is relatively NiO-rich (0.16-0.29 wt.%). In clinopyroxenites the pyroxenes are LREE-enriched (LaN/LuN=1.31-3.17) with convex-upward REE patterns (SmN/LuN=2.48-7.37).

The temperatures and pressures of clinopyroxene crystallization in most of the clinopyroxenites are 1220-1300°C and 1.08–1.30 GPa (Putirka, 2008), respectively. Only the composite xenolith and the coarse-grained clinopyroxenites recorded higher pressures (1.42 and 1.65-2.03 GPa, respectively). As the Moho beneath S Scotland is located at ~35 km (corresponding to ~1 GPa; Davis et al., 2012), most of the clinopyroxenites are considered to come from the uppermost portions of lithospheric mantle or lowermost continental crust; the coarse-grained clinopyroxenites and the composite xenolith sample lithospheric mantle.

Clinopyroxenites from the southern Scotland crystallized from alkaline basaltic magmas similar to those that entrained  them. Whilst Downes et al. (2007, 2001) had previously suggested this for clinopyroxenites from Midland Valley localities, our studies show that crystallization of mafic melts was more widespread. Strong chemical and textural variations in the pyroxenites together with relatively constant PT conditions of crystallization suggest that they formed either from melts of slightly different composition, perhaps in response to magma chamber processes such as magma replenishment and/ or mixing. While, the presence of mafic cumulates points to possible crustal underplating beneath S Scotland, the presence of a high-pressure clinopyroxenites and composite clinopyroxenitic-peridotitic xenolith imply that some of the pyroxenites originated in the lithospheric mantle.

Davis et al. (2012). Geoph.J. Int., 190, 705-725.

Downes et al., (2007). J. Geol. Soc., 164, 1217-1231.

Downes et al. (2001). Lithos, 58, 105-124.

Putirka et al. (2008). Rev. Min. Petr., 69, 61-120.

This study was funded by Polish National Science Centre to MMM no. DEC-2016/23/B/ST10/01905. EPMA analyses were done within the frame of the Polish-Austrian project WTZ PL/16 and WTZ PL 08/2018.

 

How to cite: Matusiak-Małek, M., Matczuk, P., Upton, B. G. J., Ntaflos, T., Aulbach, S., Puziewicz, J., and Kukuła, A.: Pyroxenitic xenoliths from southern Scotland and what they tell us., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8810, https://doi.org/10.5194/egusphere-egu21-8810, 2021.

EGU21-10496 | vPICO presentations | GMPV4.1

Long-lived low Th/U Pacific-type isotopic mantle domain

Xijun Liu, Zhiguo Zhang, Pengde Liu, Yujia Song, and Yao Xiao

    The presence of Pacific-type and Indian-type mid-ocean ridge (MORB) isotopic source domains in the upper mantle is a clear manifestation of global-scale mantle compositional heterogeneities. The Indian-type mantle domain is a long-lived feature that can be traced back to, at least, the Palaeozoic Tethyan mantle domain. Little temporal constraints currently exist, however, regarding the longevity of Pacific-type mantle domain. The extinct Paleo-Asia Ocean (PAO), a subsidiary ocean of the Panthalassic Ocean that formed during the breakup of the Rodinia Supercontinent in Mesoproterozoic to Neoproterozoic, can provide a solution to this dilemma. Here, we report the first complete geochemical and Sr, Nd and high-precision Pb isotopic data set for representative mafic rock samples from ophiolites representing remnants of the PAO basement ranging in age from 275 to 624Ma to constrain the composition of their mantle provenance. Data suggest that the sub-PAO mantle has a similar long time-integrated, high Sm/Nd ratio as the global depleted upper mantle, but also shows typical Pacific MORB-like Pb isotopic compositions with lower 207Pb/204Pb(t) and 208Pb/204Pb(t) for given 206Pb/204Pb(t) ratios, and low radiogenic 208Pb*/206Pb*, indicating a long time-integrated, low Th/U ratios. Thus, the Pacific-type mantle domain, like the Indian-type mantle domain, is a long-lived secular mantle domain that can be traced back to early Paleozoic or even to the Neoproterozoic. Data further indicate that the Nd and Pb isotopic distinction between such two large-scale and long-term mantle domains is due to the different evolutionary and tectonic histories of the circum-Pacific (PAO, Paleo- and modern Pacific) and sub-Tethys-Indian oceanic mantle realms. The Panthalassic-Pacific ocean realm had remarkable permanency existing as a big ocean at lease throughout the Phanerozoic, that implies that continental materials were limit to recycle into underlying mantle, thus the underlying mantle was relative free of the continental material contamination and then produce the low time-integrated Th/U Pacific-type mantle domain. In contrast, the break-up of the Gondwana supercontinent makes the Tethys realms to experience repeated opening and closures, which transferred large volume of continental materials into the underlying mantle and then produce the high Th/U Indian-type mantle domain. Our results indicate that the high Sm/Nd and low Th/U ratio of Pacific-type mantle domain most likely are an inherited, long-standing intrinsic feature of the depleted upper mantle derived from the Earth's primordial mantle with less contamination of continental materials. In contrast, the large-scale and long-lived Indian-type mantle heterogeneity is produced by plate tectonic-driven continental material circulation in the upper mantle. Such a genetic link between plate tectonics and mantle chemical geodynamics is crucial to our understanding of how the Earth system works.

    This study was financially supported by the National Natural Science Foundation of China (92055208,41772059) and the CAS “Light of West China” Program (2018-XBYJRC-003).

How to cite: Liu, X., Zhang, Z., Liu, P., Song, Y., and Xiao, Y.: Long-lived low Th/U Pacific-type isotopic mantle domain, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10496, https://doi.org/10.5194/egusphere-egu21-10496, 2021.

EGU21-14751 | vPICO presentations | GMPV4.1

Pristine metasomatic melt preserved in mantle rocks of the Bohemian Massif

Alessia Borghini, Silvio Ferrero, Patrick J. O'Brien, Bernd Wunder, and Oscar Laurent

Melt inclusions of very unusual nature occur in garnets of eclogites of the Granulitgebirge, Bohemian Massif. This is one of the first direct characterization of a preserved metasomatic melt responsible for the formation of eclogites enclosed in garnet peridotites. The inclusions are micrometric, from glassy to fully crystalized as nanogranitoids and randomly distributed in the garnet core. Nanogranitoids contain kumdykolite/albite, phlogopite, osumilite and kokchetavite with a variable amount of quartz, pyroxene, carbonate and rare white mica. The melt has a granitic composition rather than basaltic or tonalitic/trondhjemitic as would be expected from the partial melting of ultramafic or mafic rocks and it is as well hydrous and peraluminous. The trace elements composition is also unusual for melts in mantle rocks with elements typical of continental crust (Cs, Li, B, Pb and Rb) and subduction zone (Th and U). Similar signatures, i.e. continental crust and subduction, are visible also in the whole rock trace elements in the form of high amounts of LILE and U. The eclogite major elements composition is similar to a Ca- and Fe - rich mafic rock akin more to the crust than to the mantle.

The peculiar melt composition and the lack of a clear residue of a melting reaction in the eclogites suggest that this melt is external, i.e. metasomatic. It infiltered the peridotites during subduction of the continental crust at mantle depth and aided the transformation of basic layers, already in the peridotite, to eclogite. In addition, similar trace elements patterns to the melt reported here can be found in the so-called durbachite -ultrapotassic melanosyenite present in the high-grade Variscan basement- and in the garnet peridotites and garnet pyroxenites of the T-7 borehole. In both case metasomatism was suggested but the agent was just inferred based on the geochemical signature. All these occurrences suggest that mantle contaminated by melts from deeply subducted continental crust is widespread beneath the Bohemian Massif.

How to cite: Borghini, A., Ferrero, S., O'Brien, P. J., Wunder, B., and Laurent, O.: Pristine metasomatic melt preserved in mantle rocks of the Bohemian Massif, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14751, https://doi.org/10.5194/egusphere-egu21-14751, 2021.

EGU21-11060 | vPICO presentations | GMPV4.1

Multiple stages of serpentinization in mantle derived peridotites of the South Armorican Variscan suture zone

Geoffrey Aertgeerts, Didier Lahondère, Christophe Monnier, and Jean-Pierre Lorand

South Armorican mantle peridotites represent a great diversity of protoliths from supra-subduction zone to arc-fore arc ophiolites. In this study, we investigate the serpentinization of these protoliths. Numerous samples were collected in five different units, which represent ophiolitic dismembered pieces (Ty-Lan Peridotites (TLP) from the Audierne Complex, and Pont de Barel Peridotites (PBP), Folies Siffait Peridotites (FSP), l’Orgerais Peridotites (LOP) and Drain Peridotites (DP) from the Champtoceaux Complex). Field and microscopic observations together with Raman spectroscopy and electronic microprobe analysis (EMPA) allowed to identify several stages of serpentinization. All samples display a high rate of serpentinization, up to 80-90 %. Primary assemblage is represented by spinel (TLP, PBP, DP and LOP), olivine (TLP and FSP) and Ti-poor or Cr-rich pargasite (TLP and PBP). In all the samples, lizardite from olivine and bastites from pyroxene and amphibole characterize the first stage of serpentinization. It is associated with magnetite crystallization. No Al-rich lizardite meshe is identified by EMPA suggesting a low temperature (< 340°C) event. This serpentinization is followed by two generations of veins (V1 and V2). The V1 are Al-poor lizardite shear veins and crack-seal chrysotile veins characterize the V2. In PBP, microprobe mapping shows that V2 displays heterogeneous chemical chrysotile composition with significant variations of Al, Fe and Mg contents, suggesting metasomatism and/or variation of fluid composition during serpentinization. All these observations are closely similar to those of oceanic serpentinized peridotites. In the TLP, we identified a second stage of serpentinization characterized by antigorite after lizardite suggesting a high temperature event. In the OP, antigorite after lizardite was also identified. However, compared to the TLP ones, LOP antigorite is related to ductile (i.e., ultramylonite) deformations. This clearly indicates a high temperature stage of serpentinization (up to 500 °C). Furthermore, LOP ultramylonitized samples display one more chrysotile veins generation (V3) characterized by three distinct vein networks. The first one (V3a) is a crack-seal type vein network opened parallel to the main foliation. The second one (V3b) is perpendicular to the first one, whereas the third one (V3c) corresponds to tension gashes connected to C’ plans. This latter is perpendicular to V3a and V3b networks. The mylonitic foliation of LOP is similar to the surrounding micaschists schistosity, suggesting an orogenic high temperature stage of serpentinization. In the FSP, σ-type polycrystalline structures were identified. Lizardite meshes are progressively transposed and recrystallized into the foliation plan. This stage is associated with the crystallization of chlorite after tremolite, suggesting a retrograde stage of serpentinization during serpentinites exhumation. Finally, despite a great diversity of mantle-derived protoliths, our study shows that South-Armorican peridotites recorded a similar first low temperature oceanic stage of serpentinization. According to the Variscan history, it could have started during the Cambro-Ordovician for TLP, and during the Late Devonian for PBP, DP, LOP, FSP. Furthermore, some of these peridotites also recorded an orogenic serpentinization (LOP and FLP). Such observations provide new constraints that could be useful to a better understanding of the tectonometamorphic evolution of the South Armorican suture zones during the Variscan orogeny. 

How to cite: Aertgeerts, G., Lahondère, D., Monnier, C., and Lorand, J.-P.: Multiple stages of serpentinization in mantle derived peridotites of the South Armorican Variscan suture zone, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11060, https://doi.org/10.5194/egusphere-egu21-11060, 2021.

EGU21-3319 | vPICO presentations | GMPV4.1

Rodingitization of mafic rocks from Central Evia (Greece) associated with serpentinite exhumation: Evidence from Petrological, Geochemical and Isotopic data 

Christos Karkalis, Andreas Magganas, Petros Koutsovitis, and Theodoros Ntaflos

In Central Evia island (Aegean-Greece) serpentinized ultramafic rocks appear as elongated thrust sheets or in the form of olistostromes incorporated within Maestrichtian-Paleocene flysch. These are crosscut by well-developed rodingite dykes that were derived from four main protoliths that include i) Boninites, ii) Island-arc Tholeiitic Basalts and Gabbros, iii) Alkaline basalts and iv) Calc-alkaline basalts. They mainly comprise of minerals that include (hydro)garnet + chlorite + clinopyroxene ± vesuvianite. Accessory minerals include spinel ± calcite ± prehnite ± amphibole ± orthopyroxene ± olivine ± quartz ± opaque Fe-Ti oxides. Rodingites that were formed at the expense of boninites and island-arc tholeiitic rocks were likely formed within a single rodingitization stage, since garnet is mainly grossular-rich and relict primary clinopyroxene has been preserved. The rodingitization of the alkaline and calc-alkaline basalts seems to have occurred as a multi-stage metasomatic process that occurred during the exhumation of the mafic-ultramafic mantle wedge complex. This resulted in the development of late-stage andradite, vesuvianite and in some cases of chlorite during derodingitization. In this case, successive reaction zones with variability in the participating mineral phases were developed.  Geochemical results reveal remarkable rare earth element (REE) enrichments, especially in the inner zones, likely being the result of successive diffusion and element transfer. Few rodingites are characterized as calcite-bearing, whose stable 13C-18O isotopic data points to the restricted involvement of late-stage mixed hydrothermal and seawater-related carbonation processes.

How to cite: Karkalis, C., Magganas, A., Koutsovitis, P., and Ntaflos, T.: Rodingitization of mafic rocks from Central Evia (Greece) associated with serpentinite exhumation: Evidence from Petrological, Geochemical and Isotopic data , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3319, https://doi.org/10.5194/egusphere-egu21-3319, 2021.

Extensive magmatic activities were developed in  Central and Western Anatolia,  since middle miocene to quaternary times,   the most primitive lavas are situated in eastern end of Central (Sivas) and also western (Kula) Anatolia, besides Kula basalts are  one of the most recent basaltic rocks together with  basalts  from south-central Anatolia.   Although the magmatism is generally   observed at several different  locations, the recent   basaltic rocks in both of the regions   seem to be derived from  the melting  of the peridotite and pyroxenite  source  domains and the latter one  was ignored in previous studies as source component.

 The previous studies indicate that many of the basaltic rocks from Central and Western Anatolia  are related with spinel-garnet transition, but typical Tb/Yb(N) (>1.8; [1]) and Zn/Fe   (separates peridotite-derived (Zn/Fe <12; [2]) and pyroxenite-derived (Zn/Fe 13-20); [2] melts)  Co/Fe  ratios of the basaltic rocks from  several volcanic centers from Central and Western Anatolia  reveal that   melting from the single  source component  are not solely capable of  the producing  basaltic  rocks. 

 Sr-Nd and Pb isotopic  compositions  clearly display the distinction  of samples which are  linked to    asthenospheric source. The lead isotopic systematic  shows  no siginificant differences  among the Central and Western Anatolian basalts,  of all the samples are above the NHRL line and close to EM II  mantle component,  Sr- Nd  isotopes  also display similar compositions as well, the majority of the samples are in and close to mantle array,   but the  Sr isotopic composition   of  Miocene aged  Gediz and Simav lavas have high radiogenic values. 

Tb/Yb(N),  Zn/Fe ratios  and   as well as the Pb isotopic  compositions and REE-based melting model reveal  that Sivas, Erciyes Hasandağ, and Develidağ samples in central Anatolia,  and Kula, Gediz basalt in western Anatolia  seem to be  derived from the amalgamated melting of  pyroxenite and peridotite sources,   besides,  the sources melting is capable of  the producing     elemental variations in  basaltic rocks related with either lithospheric delamination or lithospheric  unstability

  • 1.Wang et al., 2002, J.Geophys.Res.vol:107,ECV 5 1-21
  • 2 .Le Roux, et al.,2011,EPSL, vol:307, 395-408

This study is financially supported by Hacettepe University, BAB project no: FHD-2018-17283

 

How to cite: Kurkcuoglu, B. and Yürür, T.: Sr-Nd-Pb isotopic significance of mantle source components from Central and Western Anatolia:  Melting  evidences   from peridotite and pyroxenite source  domains, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12162, https://doi.org/10.5194/egusphere-egu21-12162, 2021.

EGU21-14209 | vPICO presentations | GMPV4.1

A new tool to probe lithosphere evolution: OH signatures of pyroxenes

Jannick Ingrin

Four OH stretching bands in the frequency range 3300 – 3700 cm-1 dominate the infrared spectra of lithospheric pyroxenes. Depending on their metasomatic history or geodynamic origin, they have characteristic OH signatures. Pyroxenes from continental lithosphere that undergone “wet” metasomatism have distinct signature of those having undergone “dry” metasomatism. Pyroxenes from oceanic lithosphere have yet a third type of signature. Our most recent analyses of xenoliths and a critical review of the literature show that the phenomenon is widely distributed among continents and oceans. The phenomenon affects simultaneously opx and cpx from the same rock and various lithologies: peridotites, pyroxenites and granulites. In continental lithosphere, pyroxenes affected by “wet” metasomatism are dominated by OH bands at 3600 and 3415 cm-1 for opx and 3635 and 3445 cm-1 for cpx . Whereas pyroxenes affected by “dry” metasomatism are dominated by OH bands at 3570 and 3515 cm-1 for opx and 3595 and 3515 cm-1 for cpx. Opxs from oceanic lithosphere have OH spectra dominated by the band at 3415 cm-1, and with a smaller by bands at 3520 and 3570 cm-1 (Fig. 1).

In all these observations it was not possible to correlate the signatures with a specific major, minor or trace element. Therefore, the exact nature of the observed signatures remains unidentified. Notwithstanding, these OH signatures are representative of specific lithospheric events and offer a potential new benchmark for the study of lithospheric processes.

Fig.1 : Schematic diagram showing the 3 types of signatures for opx. Spectra from opxs in oceanic lithosphere are from Gose, J., Schmadicke, E. and Beran A.: Geology, 37, 543-546, 2009. Drawing of subduction is from WangZ-Z., Liu,J., Xia, Q-K., Hao Y_T. and Wang Q-Y.: Lithos, 360-361, 2020.

How to cite: Ingrin, J.: A new tool to probe lithosphere evolution: OH signatures of pyroxenes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14209, https://doi.org/10.5194/egusphere-egu21-14209, 2021.

EGU21-8372 | vPICO presentations | GMPV4.1

Ophiolitic peridotites in Xigaze (Tibet): Constraints on modes of melt transport in the mantle

Lingquan Zhao, Sumit Chakraborty, and Hans-Peter Schertl

The Xigaze ophiolite (Tibet), which occurs in the central segment of the Yarlung Zangbo Suture Zone, exposes a complete portion of a mantle sequence that consists essentially of fresh as well as serpentinized peridotites. We studied a sequence beneath the crustal section that exposes fresh, Cpx-bearing harzburgites and dunites that are underlain by serpentinized Cpx-bearing harzburgites and dunites. The rocks at the bottom are crosscut by dykes that have undergone different degrees of rodingitization. The modal compositions of peridotite from both fresh and serpentinized sections plot in abyssal upper mantle fields, with clinopyroxene modes less than 5 vol. %. Although harzburgites and dunites indicate that melt has been lost relative to primitive mantle compositions, the trace element patterns carry signatures of enrichment in incompatible elements, such as (i) “bowl-shaped” patterns of trace elements in silicate-Earth normalized spider diagrams, (ii) positive anomalies in highly incompatible trace elements such as Rb, Th, U, Ta, and (iii) enrichment of LREE in the clinopyroxenes from dunites and harzburgites. These features are indicative of complex melt transfer processes and cannot be produced by simple melt extraction. Petrographic studies reveal that harzburgite and dunite contain interstitial polyphase aggregates of olivine + Cpx + spinel + Opx and olivine + Cpx + Spinel, respectively. Experimental studies (e.g. Morgan and Liang, 2003) suggest that these aggregates represent frozen melt-rich components, indicating that fertile melt was percolating through the depleted harzburgite – dunite matrix. Presence of such “melt pods” would explain the trace element enrichment patterns of the bulk rock, as well as features such as reverse zoning (core: Cr, Fe2+ rich, rim: Al, Mg rich) of spinels in polyphase aggregates in fresh dunites. These results show that melt extraction from the mantle is not a single stage process, and that evidence of multiple melt pulses that propagated through a rock are preserved in the petrographic features as well as in the form of chemical signatures that indicate refertilization of initially depleted rocks.

How to cite: Zhao, L., Chakraborty, S., and Schertl, H.-P.: Ophiolitic peridotites in Xigaze (Tibet): Constraints on modes of melt transport in the mantle, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8372, https://doi.org/10.5194/egusphere-egu21-8372, 2021.

EGU21-15299 | vPICO presentations | GMPV4.1

Supra-subduction mantle pyroxenites in an infant subduction system: the New Caledonia ophiolite record.

Elisa Ferrari, Arianna Secchiari, Alessandra Montanini, and Dominique Cluzel

Pyroxenites constitute the major form of heterogeneity in the upper mantle. Their occurrence in supra-subduction zone settings is mostly testified by veins and layers in refractory ophiolitic peridotites, where they represent a crucial witness of melt migration in the forearc/subarc environment [1,2]. The New Caledonia ophiolite hosts one of the largest forearc mantle section worldwide, providing a unique perspective into upper mantle processes. The sequence is dominated by ultra-depleted harzburgites [3], locally overlain by mafic-ultramafic cumulates [4,5,6]. The harzburgites are highly refractory residues that register a multi-phase evolution, including fluid-assisted melting in a forearc environment and contamination by fluid- and melt inputs triggered by Eocene subduction [1]. Pyroxenitic rocks intruding the harzburgites are only known in the Bogota peninsula shear zone, which records HT deformation along a paleotransform fault [7]. In this contribution, we report a comprehensive petrological and geochemical characterization on a new set of pyroxenites from this locality. The pyroxenites (~5-15 cm-thick) generally cut the peridotite foliation at variable angles, but concordant, locally boudinaged, layers also occur. Pyroxenite textures range from cumulitic to porphyroclastic or granoblastic-polygonal. The studied samples mostly consist of amphibole-bearing (5-44 vol.%) websterites, with variable amounts of orthopyroxene (27-67 vol.%) and almost constant clinopyroxene contents (~ 25-29 vol.%). Minor olivine-bearing orthopyroxenites are also present. Accessory phases include high-Ca (An= 82-86 mol%) plagioclase, Cr-rich spinel (Cr# = 50-61), sulfides and, occasionally, apatite. Pyroxenes displays high Mg# (Mg# Opx= 91-92; Mg# Cpx= 84-93), coupled with low Al2O3 contents (0.97-1.92 wt% and 1-2.42 wt% for orthopyroxene and clinopyroxene, respectively). Amphibole is high Mg# edenite. Application of conventional pyroxene thermometry yield equilibration temperatures ranging between 930-1040°C, comparable to the enclosing harzburgites (~ 950°C), whereas amphibole-plagioclase geothermometer provides lower temperatures (~ 800°C). Bulk rock composition of the websterites show variable Mg# (82-91) and REE concentrations ranging between 1 to 10 times chondritic values. They are characterized by flat to LREE-depleted (LaN/SmN 0.28-0.92) patterns, coupled to weak MREE-HREE fractionation (GdN/YbN = 1.73-1.92) and Eu negative anomalies. By contrast, orthopyroxenites display notably lower concentrations (0.1≤REE≤1 chondrite abundances). As a whole, clinopyroxene REE patterns of the websterites mirror bulk rocks at higher absolute values. Putative melts in equilibrium with clinopyroxene indicate strongly enriched compositions (up to 300 times chondritic values) coupled to variable LREE-HREE fractionation (LaN/LuN = 3-19) and flat to fractionated HREE (GdN/LuN 1-2). Such enriched liquids, which show some analogies with pre-obduction adakite-like dikes [8], have never been recorded in the MTZ cumulitic sequence of the New Caledonia ophiolite and shed new light on the magmatic activity in the early stage of subduction. 

[1] Varfalvy, Canad Mineral, 1997, 35 (2), 543-570.
[2] Berly et al., J. Petrol., 2006, 47(8), 1531-1555.
[3] Secchiari et al., Geosc. Front., 2020, 11(1), 37–55. [4]. 
[4] Marchesi et al., Chem. Geol., 2009, 266, 171-186.
[5] Pirard et al., J. Petrol., 2013, 54, 1759–1792.
[6] Secchiari et al., Contrib. Mineral. Petrol., 2018, 173(8), 66.
[7] Chatzaras et al., Geology, 2020, 48 (6): 569–573.
[8] Cluzel et al., Terra Nova, 2006, 6, 395–402.

How to cite: Ferrari, E., Secchiari, A., Montanini, A., and Cluzel, D.: Supra-subduction mantle pyroxenites in an infant subduction system: the New Caledonia ophiolite record., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15299, https://doi.org/10.5194/egusphere-egu21-15299, 2021.

EGU21-15136 | vPICO presentations | GMPV4.1

Pyroxenites of Kukesi Massif, Mirdita Ophiolite – geological record for magmatic system in SSZ environment – preliminary results

Jakub Mikrut, Magdalena Matusiak-Małek, Jacek Puziewicz, and Kujtim Onuzi

Kukesi massif is located in the eastern part of the Mirdita Ophiolite (northern Albania), which marks suture after Neo-Thetyan ocean closure. It is formed of well-preserved mantle and crustal sections which exhibit Supra-Subduction Zone affinity (e.g. Dilek and Furnes 2009, Lithos). Lower part of the mantle section of the Kukesi massif consist mainly of harzburgites, whereas dunites are located close to Moho. Crustal section records transition from lower part formed by peridotites and pyroxenites (so called intermediate zone after Hoxha and Boullier 1995, Tectonophysics) to gabbros. In this study we focus on composition and origin of pyroxenites occurring in the mantle and lower crustal parts of the Kukesi massif.

In this study we studied 9 samples. They have composition of olivine websterite, clinopyroxenite, orthopyroxenite, hornblende-clinopyroxenite and websterite. Five of the analyzed samples have mantle origin (M): we studied (M)-olivine websterites and (M)-clinopyroxenite from harzburgitic part, as well as two (M)-orthopyroxenitic veins (one with clinopyroxenitic central part - composite vein) with minor amphibole cross-cutting dunites from one locality. From intermediate zone in crustal (C) part we collected (C)-hornblende-clinopyroxenites and (C)-websterite. 

Clinopyroxene composition is homogeneous in (M)-olivine-websterites (Mg#=84.5-87 and 88.8-90.5; Al=0.07-0.1 and 0.05-0.07, respectively), (M)-clinopyroxenite (Mg#=84-86, Al=0.04-0.08), (C)-hornblende-clinopyroxenites (Mg#=88.5-91, Al=0.08-0.12a.p.f.u.) and (C)-websterite (Mg#=87-88; Al=0.13-0.16a.p.f.u.). It differs widely between (M)-orthopyroxenitic veins: from Mg#=85-94 and Al=0.02-0.08 a.p.f.u  in clinopyroxenitic part of composite vein to Mg#=93.6-95 and Al=0.01-0.03 in the purely orthopyroxenitic one. Orthopyroxene from two samples of  (M)-olivine websterites have either Mg#=83 and Al~0.07 a.p.f.u (Foolivine=81.5) or Mg#=87  and Al~0.04 a.p.f.u (Foolivine=86). Orthopyroxene composition in composite(M)-vein varies in wide ranges (Mg#=83-89; Al=0.04-0.08 a.p.f.u.); the other vein is homogeneous (Mg#=90-91, Al=0.02-0.03 a.p.f.u, Foolivine=86.8-90); in (C)-websterite orthopyroxene has Mg#=82.4-84 and Al=0.12-0.14 a.p.f.u. Amphibole has composition of tremolite-actinolite. Spinel, where present, is highly chromian (Cr#=0.59-0.80).

Clinopyroxene is LREE-depleted in most of the samples, the (La/Lu)N=0.03-0.08. It is also LREE-depleted in (M)-clinopyroxenite ((La/Lu)N=0.05-0.23), but the contents of trace elements are higher than in other samples (eg. LuN=0.79-2.75 vs. 0.40-0.85). In (M)-veins the LREE contents are approximately at primitive mantle level ((La/Lu)N=0.28-1.66).  Clinopyroxene in all samples has positive Th-U, Pb and Sr anomalies and negative Ta and Zr anomalies, but concentrations of trace elements is significantly higher in (M) clinopyroxenite and veins.

The presence of tremolite and actinolite points to a retrogressive metamorphism which affected the rocks. The LREE-depleted nature of clinopyroxene forming all the pyroxenites and presence of orthopyroxene  point to crystallization of the rocks from tholeiitic melt, but variations in Mg# and REE content in clinopyroxene may reflect formation either from different generations of melts or from melts fractionated due to reactive percolation.  Variations in composition of the parental melts is visible even in a scale of one outcrop, which is demonstrated by (M)-orthopyroxenite veins with various modal composition and mineral major and trace elements compositions.

This study was financed from scientific funds for years 2018-2022 as a project within program “Diamond Grant” (DI 024748).

How to cite: Mikrut, J., Matusiak-Małek, M., Puziewicz, J., and Onuzi, K.: Pyroxenites of Kukesi Massif, Mirdita Ophiolite – geological record for magmatic system in SSZ environment – preliminary results, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15136, https://doi.org/10.5194/egusphere-egu21-15136, 2021.

The Masirah ophiolite is one of the few true ocean ridge ophiolites that have been preserved (Rollinson, 2017) and lacks any indication that it formed in a subduction environment. The Masirah ophiolite in south-eastern Oman is a different and older ophiolite from the more famous northern Oman ophiolite. Chromite and copper ores comprise large deposits in the Samail ophiolite, northern Oman. In comparison, chromite and copper deposits have not been described in previous reports or previous exploration in Masirah ophiolite. Rollinson (2017) has proposed that the apparent absence of chromitites in the mantle section of Masirah ophiolite is an important discriminant between subduction related and ocean ridge ophiolites.  However, during recent studies on the Batain ophiolite mélange, and Masirah ophiolite, several chromitite pods have been discovered. The chromitites occur as separated small concordant, lenticular pods (3–10 m in thickness), which have been extensively altered and deformed, with the host pyroxenite serpentinites serpentinized harzburgites and dunites. The largest chromitite pods found within the pyroxenite and dunite of Masirah are up to 10 m across.  Unusual minerals and mineral inclusions (orthopyroxene, clinopyroxene, amphibole, phlogopite, serpentine, native Fe, FeO, alloy, sulfide, calcite, laurite, celestine and halite) within chromite have been observed in the chromitites from the  Masirah ophiolites.  The existence of hydrous silicate inclusions in the chromite calls for a role of hydration during chromite genesis. Both  phlogopite and hornblende were possibly formed from alkali-rich hydrous fluids/melts trapped within the chromite during the chromitite formation. High-T green hornblende and phlogopite included in the chromites is evidence of the introduction of water in the magma at the end of the chromite crystallization. Such paragenesis points to the presence of hydrous fluids during the activity of the shear bands. The chromitites parental magmas are rich in K, Na, LREE, B, Cs, Pb, Sr, Li, Rb and U relative to HREE, reflecting the alkalic fluids/melts that prevailed during the chromitites genesis.

The mineral inclusions  in association with host peridotites may have been brought by the uprising asthenosphere at mid-oceanic ridges due to the mantle convection. It appears that this chromite has been formed through reaction between amid-ocean-ridge basalt-melt with depleted harzburgite in the uppermost mantle.  The chromitite deposits have similar cr# (55-62% Al-chromitites), mg# Al2O3 and TiO2 contents to spinels found in MORB, and have been interpreted as having formed in amid-ocean ridge setting.  This suggests that this chromitites is residual from lower degree, partial melting of peridotite, which produced low-Cr# chromitites at the Moho transition zone, possibly in a mid-ocean-ridge setting. The chemistry of both mineral inclusions and chromite   suggests MORB-related tectonic setting for the chromitites that were crystallized at 1000 °C–1300 °C under pressures <3 GPa . The host peridotites were generated during the proto-Indian Ocean MORB extension and emplaced as a result of the obduction of the ophiolite over the Oman Continental margin during Late Cretaceous-Early Paleocene.

Rollinson, H., 2017. Geoscience Frontiers, 8: 1253–1262.

How to cite: Nasir, S.: New  podiform chromitites Occurrence from the Masirah Ophiolite, Oman, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-72, https://doi.org/10.5194/egusphere-egu21-72, 2021.

EGU21-15840 | vPICO presentations | GMPV4.1

Sequential geochemical extractions and mineralogy of Fe-bearing minerals in carbonatized mantle rocks in the Samail Ophiolite, Oman 

Zena Severin, Jessica L. Till, and Oman Drilling Project Phase 1 Science Party

Within the Samail Ophiolite, Oman, there are intervals of listvenite outcrops between layers of serpentinite zones above the basal thrust zone, atop the metamorphic sole. Near the base of the ophiolite mantle section, some peridotites underwent 100% carbonation from metasomatic introduction of CO2-bearing fluids <200°C to form listvenites during the time of emplacement (97 ± 29 Ma, Falk and Kelemen, 2015). The carbonate rocks comprise mostly magnesite and/or dolomite, quartz, Cr-spinel, and Fe-(hydr)oxides; with carbonates as the sole Mg-minerals and quartz as the only silicate phase. The aim of this study is to chemically and petrographically investigate the Fe-bearing minerals within the fluid-altered mantle rocks in drill core samples from hole BT1B of the ICDP Oman Drilling Project. Sequential chemical extractions are useful for recognizing iron pools based on the minerology. We investigated the quantities of Fe-oxide/hydroxide phases through a series of chemical extractions (Poulton and Canfield, 2005) via atomic absorption spectroscopy in addition to optical microscope, SEM/EDS, EPMA/WDS and ICP analysis. Extractions performed at room temperature and one at 50°C included: carbonate-associated Fe (sodium acetate) targeting siderite, HCl-extractable Fe(II), reducible oxides (citrate-dithionite) targeting hematite and possible goethite, and magnetite (oxalate). Carbonate-based Fe in the listvenites from a sodium acetate extraction ranges from 12-28 mg/g, while the same extraction performed at 50°C for twice as long resulted in higher proportions of carbonate-associated Fe (15-35 mg/g). Easily reducible iron quantities from the diluted HCl solution extraction display the lowest overall Fe fractions (0.75-5.5 mg/g) following the room temperature acetate and 0.63-1.7 mg/g after the 50°C acetate extraction. Fe in reducible oxides extracted by dithionite ranged from 1.4-15 mg/g with similar result after both a room-temperature acetate and a 50°C acetate step. Oxalate extraction succeeding the room-temperature acetate yielded magnetite concentrations of 1.9-8.0 mg/g, while the increased temperature and time in the first step (acetate extraction) were followed by significantly lower amounts of Fe extracted by oxalate (0.47- 3.6 mg/g). Additionally, the same extractions were performed on a pure siderite sample from Greenland. For siderite samples crushed a week prior to analysis, the carbonate-associated Fe in sodium acetate extract was 165±17 mg/g; the sidenote yielded 42 wt% of overall extracted Fe (392±33 mg/g). This is only slightly lower than the expected 48.2 wt% of Fe for a pure siderite sample. Dilute HCl extractions display results of 126±5.4 mg/g, dithionite solution extracted 25±0.5 mg/g and oxalate proportions were 76±9 mg/g. Due to possible oxidation of siderite to magnetite occurring during the time between powdering the samples and analysis, the full dissolution of siderite may not be fully represented in only the acetate. Microprobe data shows a total amount of FeO in carbonates as 1.3-10.8 wt%. This is more than or similar to the acetate and HCl proportions of Fe which represent carbonate associated minerals in the listvenites. Data obtained from EMPA and ICP will additionally be discussed in relation to the Fe-oxide phases with relation to the listvenites minerology.

How to cite: Severin, Z., Till, J. L., and Phase 1 Science Party, O. D. P.: Sequential geochemical extractions and mineralogy of Fe-bearing minerals in carbonatized mantle rocks in the Samail Ophiolite, Oman , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15840, https://doi.org/10.5194/egusphere-egu21-15840, 2021.

EGU21-14475 | vPICO presentations | GMPV4.1

Trace element composition of clinopyroxene in gabbros and dolerites of the Tortuga Ophiolitic Complex, southernmost Patagonia.

Fernanda Torres Garcia, Mauricio Calderón, Leonardo Fadel Cury, Thomas Theye, Joachim Opitz, Diego Rojo, Joaquín Hopfenblatt, and Francisco Fuentes

During the Upper Jurassic-Lower Cretaceous times the western margin of Gondwana in southern Patagonia experienced extreme lithospheric extension and generation of rift and marginal back-arc basins. The ophiolitic complexes of the Rocas Verdes basin comprises incomplete ophiolite pseudostratigraphy lacking ultramafic rocks. The Tortuga Ophiolitic Complex, the southernmost seafloor remnant of the Rocas Verdes basin, record the most advanced evolutionary stage of the back-arc basin evolution in a mid-ocean ridge-type setting. The base of the Tortuga Complex consists of massive and layered gabbros, most of which are two pyroxene and olivine gabbros, leucogabbros, and clinopyroxene troctolites intruded by dikes of basalt and diabase with chilled margins. We present new major and trace element composition of clinopyroxene from the gabbros and sheeted dikes complexes to assess the geochemical affinity of parental basaltic magmas. Clinopyroxene in gabbros is mostly augite and have Al contents of 0.06-0.14 a.p.f.u. and Mg# of 80-92. Clinopyroxene in dolerites in the sheeted dike unit (augite and diopside) have Al content of 0.11-0.12 a.p.f.u. and Mg# of 85-92. Some immobile trace elements (e.g. Zr, Ti, Y) are sensitive to the degree of partial melting and mantle source composition, and can be used as a proxy for distinguishing tectonic environments. The Ti+Cr vs. Ca diagram, coupled with moderate-high TiO2 content of clinopyroxene (0.4-1.4 wt.%) suggests their generation in mid-oceanic ridge-type environment (cf. Beccaluva et al., 1989).  The high Ti/Zr ratios (of ~4-11) coupled with low Zr contents (~0.2-1.1) are expected for higher degrees of partial melting or for melting of more depleted mantle sources. Conversely, low Zr/Y ratios (0.05-0.13) plot between the range of arc basalts. Chondrite-normalized REE patterns in clinopyroxene display a strong depletion of LREE compared to HREE and have an almost flat pattern in the MREE to HREE with a positive Eu (Eu*= 0.9-1.1) anomaly, indicating that clinopyroxene crystallized from a strongly depleted mid-ocean-ridge-type basalt, formed by extensive fractional melting of the mantle source and/or fractional crystallization and accumulation of anhydrous phases. The general trend of the incompatible trace elements patterns exhibit depletion in LILEs, minor HFSEs depletion, positive anomaly of Rb and negative anomalies in Ba, Zr, Ti and Nb, consistent with their generation from a refractory mantle source barely influenced by subduction components derived from the oceanic slab. This agrees with basalt generation in a back-arc basin located far away from the convergent margin. This study was supported by the Fondecyt grant 1161818 and the Anillo Project ACT-105.

How to cite: Torres Garcia, F., Calderón, M., Fadel Cury, L., Theye, T., Opitz, J., Rojo, D., Hopfenblatt, J., and Fuentes, F.: Trace element composition of clinopyroxene in gabbros and dolerites of the Tortuga Ophiolitic Complex, southernmost Patagonia., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14475, https://doi.org/10.5194/egusphere-egu21-14475, 2021.

EGU21-5975 | vPICO presentations | GMPV4.1

Spatial variability in Karoo dolerites

Arnold Kotze and R. James Roberts

AD Kotze and RJ Roberts

Department of Geology, University of Pretoria, Hatfield, Pretoria, South Africa; u04541686@tuks.co.za

The Karoo Large Igneous Province (KLIP) in South Africa consists of both a spatially limited extrusive basalt suite (Drakensberg Group) and a spatially extensive dolerite suite, both generally considered to be remarkable homogenous and of a “low-Ti” character (Luttinen, 2018). The homogeneity of the rocks requires that statistical analysis is necessary to look for spatial and geochemical trends in the data, which may yield clues to the mantle processes producing the 60 000 km2 expanse of basaltic magma. In this project, data derived from several locations are used as proxies to check for lateral variability in the Karoo dolerites. A principal component analysis (PCA) on trace element data using a covariance matrix was performed, and comparisons based on variables that are 1) common to the Karoo dolerites and Lesotho basalts and, 2) responsible for the most amount of variation to the data set are made. Trace element modelling is then used to test different mantle melting scenarios possibly responsible for the variation seen in the dolerites.

Principal component analyses revealed several trace elements are responsible for most of the variability in the dolerites. Cr and Ni has the strongest positive loading on Component 1 whereas Cr and Ba has the strongest positive loading on Component 2. Ba has a strong negative loading on Component 1. Cu, Sr, V and Zr do impart an appreciable amount of variation to the data, but all four variables have weak negative loadings on both components. Interestingly, the activity of Cu and V seems to be the inverse of that of Cr and Ni.

Due to the nature of a PCA, this work is afforded an opportunity to place the geochemistry of the Karoo dolerites within a larger geodynamic context without bias. From the observed variation, the activity of Ba and Cr is interpreted as an assimilation-oxidation process, whereas the Ni signature reflects the mantle origin of the magmas. Further modelling of these processes will allow the testing of suggested mechanisms for the formation of the KLIP, especially whether the magmatism is plume-related or related to the foundering of crustal blocks.

Luttinen, A., 2018. Bilateral geochemical asymmetry in the Karoo large igneous province. Scientific Reports, 8(5223).

How to cite: Kotze, A. and Roberts, R. J.: Spatial variability in Karoo dolerites, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5975, https://doi.org/10.5194/egusphere-egu21-5975, 2021.

GMPV4.2 – Understanding planetary crusts and mantles: Recent advances in planetary sciences

EGU21-10624 | vPICO presentations | GMPV4.2

Modelling the ascent of picritic lunar magmas

Marissa Lo, Giuseppe La Spina, Katherine Joy, Margherita Polacci, and Mike Burton

Quantifying the volatile content of the lunar interior is valuable for understanding the formation, thermal evolution, and magmatic evolution of the Earth and Moon. Petrological modelling and geochemical measurements have been used to study the volatile composition of the lunar interior. Improvements to analytical instruments have facilitated more precise measurements of the volatile content of lunar samples and meteorites, however, several problems remain with these measurements, hence, the volatile content of lunar magmas has yet to be constrained with certainty. We propose a volcanological approach for inferring the volatile contents of different lunar magmas.

            A terrestrial magma ascent model has been modified for lunar applications. Numerous parameters were adjusted for lunar conditions, including: magma major element composition, from low-Ti (green and yellow glasses) to high-Ti (orange, red, and black glasses); H2O content; CO content; gravity; and pressure. The model calculated values for gas exsolution, viscosity, mass flow rate, and several other ascent processes, from a depth of 10 km to the surface. Using these results, we will assess the effect of varying magmatic volatile content on lunar magma ascent processes. We will also compare and contrast our results with existing models for lunar magma ascent, as well as models for magma ascent on other planetary bodies. Future work will involve modelling eruptions, using results from the magma ascent model, and verifying the results of the models using images and digital elevation models of the lunar surface.

How to cite: Lo, M., La Spina, G., Joy, K., Polacci, M., and Burton, M.: Modelling the ascent of picritic lunar magmas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10624, https://doi.org/10.5194/egusphere-egu21-10624, 2021.

EGU21-1123 | vPICO presentations | GMPV4.2

The behaviour of MgO in a giant impact setting

Tim Bögels and Razvan Caracas

The Earth-Moon system and its formation is a topic of great scientific interest, and great debate over the past decades. The giant impact hypothesis is the currently accepted model to explain the formation of our moon. Accordingly, a mars-sized impactor collides with the proto-earth. This giant impact vaporized a significant portion of the impactor and the proto-earth, creating a large accretionary disk from which the moon subsequently formed. Currently, there is a large effort to build reliable thermodynamic descriptors for the building materials of the two bodies involved in the impact. Understanding the behavior of major rock-forming minerals under these extreme conditions is vital for increasing the accuracy of these models.

Magnesium oxide, MgO, is one of the fundamental building blocks for rocky planets. It is an archetype material of ionic solids and a well-known refractory material. Because of its relevance it has been studied extensively; experimental and theoretical results have been produced up to pressures of 800 GPa and temperatures reaching 20000 K. These pressure and temperature regions are of great interest for the planetary sciences, studying planetary interiors. The transformation of the face-centered B1 phase to the body-centered B2 phase and the associated melting curve have been modelled numerous times. In contrast, we know very little of the liquid behaviour of MgO under pressure, let alone at the low pressures found in accretionary disks.

Here we investigate the low-density high-temperature regime characteristic of after-shock isentropic release. We explore the subcritical and the supercritical regimes of MgO using ab initio molecular dynamics. We determine the position of the critical point and examine the structural and transport properties in the sub- and supercritical regimes. We find an elevated critical temperature in comparison with previously studied magnesium-silicates, in agreement to the refractory nature of MgO. Furthermore, we provide insight into the speciation of liquid MgO and the liquid-gas separation. We see a shift in Mg-O speciation towards lower degrees of coordination as the temperature is increased from 4000K to 10000K. This shift in speciation is less pronounced at higher densities. The majority of the chemical species forming the incipient gas phase consist of isolated Mg and O ions and some MgO and O2.

This research was supported by the European Research Council under EU Horizon 2020 research and innovation program (grant agreement 681818 – IMPACT to RC). We acknowledge access to supercomputing facilities via eDARI stl2816, PRACE RA4947, and Uninet2 NN9697K grants.

How to cite: Bögels, T. and Caracas, R.: The behaviour of MgO in a giant impact setting, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1123, https://doi.org/10.5194/egusphere-egu21-1123, 2021.

EGU21-1145 | vPICO presentations | GMPV4.2

Partial core vaporization during giant impacts inferred from the entropy and the critical point of iron

Zhi Li, Razvan Caracas, and François Soubiran

The prevailing theory of the origin of the Moon is the giant impact hypothesis, in which a Mars-sized impactor collides with the proto-Earth in the late stage of accretion, and the Moon is subsequently formed from the proto-lunar disk made of the ejected materials. As the laboratory-scale experiments are not able to simulate planetary-scale impacts, our understanding of the giant impact mostly comes from hydrodynamic simulations. However, the results of these simulations heavily depend upon the available equation of state to describe the thermodynamic response of the constituent materials of the proto-Earth and impactor to shock waves.

 

Iron as a building block material of the terrestrial planets naturally received significant attention. But the major effort has been put to determine its phase diagram up to the Earth’s core conditions (126-360 GPa and 3000-7000 K) and beyond. The studies of iron at low densities are still scarce and the position of the critical point (CP) is uncertain. As the liquid-vapor dome ends at CP, the position of the latter determines the time evolution of the proto-lunar disk during its condensation.

 

In order to assess whether the core of the planets undergoes significant vaporization during a giant impact, we employ ab initio molecular-dynamics simulations to explore iron over a wide density region encompassing the critical point (CP) and the Hugoniot lines of the shocked iron cores. We determine the critical point of iron in the temperature range of 9000-9350 K, and the density range of 1.85-2.40 g/cm3, corresponding to a pressure range of 4-7 kbars [1]. This implies that the iron core of the proto-Earth may become supercritical after giant impacts. We show that the iron core of Theia partially vaporized during the Giant Impact. Part of this vapour may have remained in the disk, to eventually participate in the Moon’s small core. Similarly, during the late veneer stage a large fraction of the planetesimals have their cores undergoing partial vaporization. This would help to mix the highly siderophile elements into magma ponds or oceans.

 

References:

[1] Z. Li, R. Caracas, F. Soubiran, Partial core vaporization during Giant Impacts inferred from the entropy and the critical point of iron, Earth Planet. Sci. Letters, 2020, https://doi.org/10.1016/j.epsl.2020.116463

 

How to cite: Li, Z., Caracas, R., and Soubiran, F.: Partial core vaporization during giant impacts inferred from the entropy and the critical point of iron, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1145, https://doi.org/10.5194/egusphere-egu21-1145, 2021.

EGU21-12352 | vPICO presentations | GMPV4.2

Trace and minor element variations in lunar granulites: Insights into lunar metamorphic conditions.

John Pernet-Fisher, Margaret Hartley, and Kathrine Joy

Metamorphic rocks on the Moon are an important yet under-studied suite of lunar lithologies that have been identified in the Apollo and lunar meteorite collections [1]. These rocks, with granoblastic textures, are generally referred to as granulites; however, unlike their terrestrial counterparts, they are considered to represent the products of only high-temperature (> 1000 oC) thermal metamorphism that completely re-crystallised their protolith(s). Lunar granulites are commonly sub-divided into two main compositional groups related to their protolith lithologies. The Fe-granulites, found at most Apollo landing sites, are generally accepted to derive from metamorphosed plagioclase-rich igneous cumulates, termed the ferroan anorthosite (FAN) suite. The FAN suite are important lithologies as they represent products of the primary lunar crust. The Mg-granulites are found mostly at the Apollo 16 landing site and within lunar meteorite samples; the protolith(s) of this latter group is not well understood [2].  Early studies have linked the protolith to secondary magmatic intrusions into the primary anorthositic crust (termed the Mg-suite); however, recent studies have tentatively connected the protolith to a Mg-rich variation of the primary crustal plagioclase cumulates (termed the MAN suite). The occurrence of MANs is controversial, it is unclear how the MAN suite fits into canonical lunar crustal formation models [3]. To investigate the protoliths of the granulite suites, we report in situ trace- and minor-element abundances for olivine and pyroxene grains within Fe- and Mg-granulites, determined by LA-ICP-MS and EPMA respectively. Trace-element data presented here indicate that the Mg-granulites are compositionally similar to the MAN suite. Furthermore, by comparing plagioclase trace-element data with peak metamorphic temperatures (calculated using two-pyroxene thermometers [4]), we find no relationship between metamorphic temperature and diagnostic trace-element signatures suggesting that both granulite suites experienced similar thermal metamorphic conditions. Additionally, we estimate the duration of metamorphic heating using experimentally derived diffusion rates of minor elements in minerals,  (such as Ca in olivine [5]). Both the calculated cooling rates and peak metamorphic temperatures can set constraints on the metamorphic heat source responsible for thermally annealing the Fe- and Mg-granulites. Specifically, we are able to assess whether the granulites formed as a result of shallow (<1 km) burial of the protolith by impact melt sheets or hot, impact-generated fall-back breccias [6]; or deep (> 1km) contact metamorphism of the protolith due to the emplacement of magma chambers or upwelling plutons within the lunar crust [7].

 

[1] Lindstrom & Lindstrom, 1986, JGR, 91(B4), 263-276 [2] Treiman et al. 2010. MaPS, 45, 163-180. [3] Gross et al. 2014, EPSL, 388, 318-328. [4] Brey & Köhler, 1990, J Pet, 31, 1353-1378. [5] Dohmen et al, 2007, PCM, 34, 389-407. [6] Cushing et al. 1999, MaPS, 34, 185-195. [7] Hudgins et al. 2011, Am Min, 96, 1673-1685.

How to cite: Pernet-Fisher, J., Hartley, M., and Joy, K.: Trace and minor element variations in lunar granulites: Insights into lunar metamorphic conditions., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12352, https://doi.org/10.5194/egusphere-egu21-12352, 2021.

EGU21-12247 | vPICO presentations | GMPV4.2

Origins and Implications of the Apollo 16 Breccia Noble Gas Suite

Mark C. Nottingham, Natalie M. Curran, John Pernet-Fisher, Ray Burgess, and Katherine H. Joy

The Apollo 16 landing site is dominated by regolith breccias; consolidated regolith palaeo-soils [5,7,8]. Each regolith soil (and, by extension, each regolith breccia) is composed of fragments of rock sourced from different impacts and lithological units [e.g. 2,3]. Because of this, these samples probe the impact history of the lunar surface across a wide range of time. McKay et al. (1986) reported the trapped argon isotope ratios (i.e., 40Ar/36ArTr) values of regolith breccias and used these values to semi-quantitatively model breccia formation ages [see also 4]. Two groups of regolith breccias were identified at the Apollo 16 landing site: (i) the ‘ancient’ group, lithified immature regolith (i.e., <30 Is/FeO), and (ii) a ‘younger’ group that generally have higher levels of maturity. Joy et al. (2011) used the 40Ar/36ArTr ratios to model that: (i) the ancient samples closed from soils to breccias between ~3.8 and 3.4 Ga, consistent with regolith developed and consolidated after the Imbrium basin-forming event, and during a time of declining basin-forming impacts, and (ii) that the young breccias were assembled in the Eratosthenian period between ~2.5 and 1.7 Ga, providing insight into post-basin bombardment impact processes.

A third set of regolith breccias identified by Jerde et al. (1987, 1990), (the soil-like breccias), have no reported noble gas or exposure age information. Joy et al. (2011) inferred that these samples were likely consolidated into breccias in the last 2 Ga (based on their Is/FeO maturity being similar to the Apollo 16 soils). They, therefore, may extend the current archive of impact and regolith processes into the Eratosthenian and Copernican periods.

Whole-rock samples were laser step heated and the extracted gases were measured using a Thermo Scientific Helix-MC noble gas magnetic sector mass spectrometer. Preliminary analysis of our data shows these breccias are dominated by a solar wind composition component, with minor spallation and radiogenic contributions. The concentrations of evolved gases suggest the samples are more similar in terms of noble gas budget to the present day Apollo 16 soil samples (based on analysis using data collated by Curran et al. 2020), than the ancient gas-poor Apollo 16 regolith breccias (McKay et al. 1986). Thus, these noble gas data are consistent with the petrological characterisation and Is/FeO classification [5,6] of these breccias being comparable to present day Apollo 16 soil samples. Solar wind composition gas concentrations comparable to present day soil samples suggest these new breccias represent consolidated regolith of comparable maturity, perhaps suggesting these soil-like breccias were formed around the same time period as the ‘younger’ group.

References: [1] Curran, N.M., et al., 2020, PSS, 182, 104823. [2] Donohue, P.H., et al., 2013, 44th LPSC, A#2897.; [3] Fagan, A.L., et al., 2013, GCA, 106, 429-445.; [4] Fagan, A.L., et al., 2014, Earth Moon Planets, 112, 59–71.; [5] Jerde, E.A., et al., 1987, J. Geophys. Res., 92(B4), E526– E536.; [6] Jerde, E.A., et al., 1990, EPSL, 98(1), 90-108.; [7] Joy, K.H., et al., 2011, GCA, 75(22), 7208-7225.; [8] McKay, D.S., et al., (1986), J. Geophys. Res., 91(B4), 277– 303.

How to cite: Nottingham, M. C., Curran, N. M., Pernet-Fisher, J., Burgess, R., and Joy, K. H.: Origins and Implications of the Apollo 16 Breccia Noble Gas Suite, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12247, https://doi.org/10.5194/egusphere-egu21-12247, 2021.

EGU21-10792 | vPICO presentations | GMPV4.2

Combined microstructural analysis and in-situ U-Pb chronology of baddeleyite within shergottites Northwest Africa (NWA) 7257, NWA 8679 and Zagami 

Leanne Staddon, James Darling, Winfried Schwarz, Natasha Stephen, Sheila Schuindt, Joseph Dunlop, and Kim Tait

Baddeleyite (monoclinic; m-ZrO2) is an important U-Pb chronometer within mafic lithologies from many planetary bodies. Recent in-situ U-Pb dating of micro-baddeleyite within shergottites has been key in confirming recent magmatic activity on Mars. However, despite a high U-Pb closure temperature (≥900 °C) and the retention of robust U-Pb isotope systematics to ~57 GPa within experimental studies, up to 80% Pb loss within baddeleyite has been reported from the highly-shocked shergottite Northwest Africa (NWA) 5298. Significantly, U-Pb isotopic disturbance has been shown to be strongly linked with baddeleyite internal microstructure, generated by partial to complete reversion from meta-stable, high P-T zirconia polymorphs during shock metamorphism. NWA 5298 has experienced elevated shock metamorphism, and particularly post-shock temperatures, in comparison to many other shergottites; in the absence of microstructural analyses, the magnitude of baddeleyite U-Pb isotopic disturbance within more moderately shocked shergottites remains unknown.

To address this, we combine electron backscatter diffraction (EBSD) microstructural analysis and in-situ U-Pb chronology of baddeleyite within three enriched shergottites: NWA 7257, NWA 8679 and Zagami. Studied samples have undergone shock conditions typical of shergottites, with complete transformation of plagioclase to maskelynite and pervasive fracturing of pyroxene, phosphates and oxides. Small veinlets of shock melt cross-cut NWA 8679 and Zagami, and shock melt pockets are present in all samples. Baddeleyite is abundant and ubiquitously associated with late-stage igneous assemblages, rather than shock melt.

We document a wide range of baddeleyite microstructures. These include crystal-plastically deformed magmatic twins, domains with a marked decrease in crystallinity, and complex, nanostructured domains with orthogonal orientation relationships that are interpreted to have resulted from complete reversion from high P-T polymorphs. Magmatic twins are only locally preserved due to shock heterogeneity. Despite this, and in contrast to NWA 5298, we find no link between baddeleyite microstructure and U-Pb isotope systematics. Analyses fall along well-defined discordia within Tera-Wasserburg plots for each sample, with the U-Pb isotopic composition of analyses controlled by overlap with surrounding phases and fractures rather than baddeleyite microstructure. We therefore determine two new, microstructurally constrained ages from discordia lower intercepts: 195 ± 15 Ma (95% confidence; MSWD 5.6) for NWA 7257 and 220 ± 23 Ma (95% confidence; MSWD 2.2) for NWA 8679. For Zagami, our findings support the previously reported magmatic crystallisation age of ~180 Ma. These results provide further confirmation that high post-shock temperatures are required to induce resolvable U-Pb isotopic disturbance baddeleyite, even within highly shocked samples, and that reversion from high P-T zirconia polymorphs alone does not necessitate U-Pb isotopic disturbance. While we caution the continued requirement for detailed microstructural analyses of baddeleyite prior to isotopic analyses, this study underlines the utility of baddeleyite chronology within martian meteorites and other shocked planetary materials.

How to cite: Staddon, L., Darling, J., Schwarz, W., Stephen, N., Schuindt, S., Dunlop, J., and Tait, K.: Combined microstructural analysis and in-situ U-Pb chronology of baddeleyite within shergottites Northwest Africa (NWA) 7257, NWA 8679 and Zagami , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10792, https://doi.org/10.5194/egusphere-egu21-10792, 2021.

EGU21-12820 | vPICO presentations | GMPV4.2

Volatile depletion and evolution of Vesta from coupled Cu-Zn isotope systematics

Jasmeet K. Dhaliwal, James M.D. Day, John B. Creech, and Frederic Moynier

The moderately volatile elements, Cu and Zn, are not strongly affected by magmatic differentiation [1, 2] and are important tracers of volatile depletion in planetary bodies, particularly low-mass, airless bodies [3]. New isotopic ratio and abundance measurements for both Cu and Zn are presented for eucrites to more fully understand volatile depletion processes that affected the parent-body of the howardite-eucrite-diogenite (HED) meteorites, the asteroid 4-Vesta. Zinc isotope ratios are reported for twenty-eight eucrite samples, which along with prior data [4] yield a range of δ66Zn from -1.8 to +6.3 ‰, excluding one outlier, PCA 82502 (δ66Zn = -7.8 ‰) and a Zn concentration range from 0.3 to 3.8 p.p.m. Heavy Zn isotopic ratios (positive δ66Zn compositions) in eucrites form a negative trend with Zn concentration, reflecting volatile depletion processes on Vesta that are similar to the Moon [5, 6]. Within the combined sample set, eleven eucrites have light Zn isotopic compositions from δ66Zn of -0.02 to -7.8 ‰, with the majority having more negative compositions than likely chondritic precursors (maximum δ66Zn of ~ -0.2 ‰ [7]). These samples are interpreted to reflect condensates formed subsequent to surface volatilization and outgassing, such as during impact bombardment. Measurements of Cu compositions are also reported for nineteen of the samples, yielding a range of δ65Cu from -1.6 to +0.9 ‰, and range of Cu concentrations from 0.2 to 2.8 p.p.m., with the exception of Stannern (Cu > 10 ppm). As with Zn, negative Cu isotopic ratios that are lighter than chondritic compositions (δ65Cu ~ -0.5 ‰ [8]) are attributed to recondensation that occurred following impact-induced vaporization (cf. [9]). Within the wide ranges of Zn and Cu isotopic compositions measured in eucrites, most samples cluster within ~ 0 ‰ < δ66Zn < +3 ‰ and ~ 0.2 ‰ < δ65Cu < +0.9 ‰. This range is interpreted to reflect volatile depletion processes similar to those that affected the Moon (BSM: δ66Zn +1.4 ± 0.5‰ [5, 6, 10, 11] and δ65Cu = +0.92 ± 0.16‰ [9-11]). The greater heterogeneity in eucrite Zn and Cu isotopic compositions compared to lunar samples can be attributed to the smaller size of the HED parent asteroid, which may have experienced more limited homogenization of these signatures following volatile depletion and for eucrites which have experienced complex impact addition and metamorphic processes.  

[1] Chen et al. (2013) EPSL, 369, 34-42. [2] Savage et al. (2015) Geochemical Perspective Letters, 1, 53-64. [3] Day and Moynier (2014) Philisophical Transactions of the Royal Society A, 372, p.20130259. [4] Paniello et al. (2012) GCA, 86, 76-87. [5] Paniello et al. (2012) Nature, 490, 376-379. [6] Kato et al. 2015 Nature Communications, 6, 1-4. [7] Luck et al. (2005) GCA 69, 5351-5363. [8] Luck et al. (2003) GCA, 67¸143-151. [9] Day et al. (2019) GCA, 266, 131-143. [10] Moynier et al. (2006) GCA, 70, 6103-6117. [11] Herzog et al. (2009) GCA, 73, 5884-5904.

How to cite: Dhaliwal, J. K., Day, J. M. D., Creech, J. B., and Moynier, F.: Volatile depletion and evolution of Vesta from coupled Cu-Zn isotope systematics, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12820, https://doi.org/10.5194/egusphere-egu21-12820, 2021.

EGU21-1230 | vPICO presentations | GMPV4.2

Superheating and cooling rates effects on olivine growth in chondritic liquid: experimental and petrographic approach

Marion Auxerre, François Faure, and Delphine Lequin

Chondrules - major constituent of chondrites (primitive meteorites) - belong to the first object formed in the solar system. They are millimetre-sized igneous objects resulting from partial to complete fusion and are divided into main families: non-porphyritic and porphyritic (Gooding and Keil, 1981); the latter one is more abundant in chondrites. This study aims to reproduce thermal histories of macro-porphyritic olivine chondrules (PO) and to better constrain (thermal, temporal) the conditions reigning in the early solar system.

In general, PO chondrules are composed of numerous euhedral crystals of olivine and/or pyroxene suggesting an initially melting below their liquidus temperatures. By contrast, in our study, the macro-porphyritic olivine chondrule displays only one large euhedral olivine. The low number of olivine crystals indicates that chondrule suffered an initial step of superheating, limiting nucleation process (Lofgren, 1988; Hewins et al., 1988). Moreover, embayments observed in euhedral olivine show that olivine crystal began to growth rapidly and then the growth-rate decreased during the cooling. Therefore, our petrographic investigation proposes a first high temperature stage (ΔTliq = +10 °C) followed by a slow cooling.

To test this thermal history, experiments are performed to determine degree of superheating and cooling rate effect (i) on nucleation rate and (ii) on morphology of olivines formed during cooling. Preliminary results seem to confirm that macro-porphyritic olivine chondrules result from the slow cooling of a superheated initial chondritic liquid (Varela et al., 2006). Then these results allow to precise the beginning of the igneous processes (minimum thermal temperature and cooling rate) and to discuss the complete thermal evolution of the chondrule, by considering all other reaction textures observed in this chondrule: peritectic and oxidation reactions, quench texture and aqueous alteration.

 

References:

Gooding et al., (1981) Meteoritics, 16, No. I; Hewins et al., (1988) Meteoritics, 25, 309-318; Lofgren, (1988) Geochim. & Cosmochim. Ada, 50, 1715-1726; Varela et al., (2006) Icarus, 178 (2), 553–569.

How to cite: Auxerre, M., Faure, F., and Lequin, D.: Superheating and cooling rates effects on olivine growth in chondritic liquid: experimental and petrographic approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1230, https://doi.org/10.5194/egusphere-egu21-1230, 2021.

EGU21-1751 | vPICO presentations | GMPV4.2

A rare free silica-bearing micrometeorite

Dafilgo Fernandes

Extraterrestrial dust that reaches the Earth’s surface has shown to represent the diverse types of samples from different precursors, namely, asteroid complexes and cometary bodies from the solar system. A substantial amount of this dust that strikes the upper atmosphere is believed to have been lost due to frictional heating with air molecules. Cosmic spherules that are melted particles are some of the widely recognized micrometeorites that survived this catastrophic entry process; however, their primordial characteristics are altered from their precursors making it difficult to identify the precursors. An individual peculiar spherule MS-I35-P204 recovered from the Antarctica blue ice has been identified. The spherule has been segregated using magnetic separation method, mounted in epoxy, and examined using SEM, subsequently analysed under electron microprobe. It is surrounded by a thin magnetite rim, and also holds a single kamacite bead that protrudes out at its top. The interior mineralogy mostly constitutes of a bulk pyroxene normative glass (MnO>2wt%) with several vesicles. The rare mineral phase is a skeletal aggregate of free silica, bearing Fe nuggets embedded in a glass. An isolated narrow lath of forsterite appears to be chondritic and is observed as relict grain that is associated with an anomalous low Ca pyroxene (MnO ~1.3 wt%, FeO~13 wt%). Earlier, free silica has been reported in some chondritic meteorites particularly the Enstatite and Ordinary group, and also in some carbonaceous chondrites such as CM, CR, CH, and K. It profoundly forms a pod that encloses the ferromagnesian silicate in silica-bearing chondrules. The unusual mineral assemblage seen in this spherule thereby appears to constrain probably the unique type of its contributor which need to be studied.

How to cite: Fernandes, D.: A rare free silica-bearing micrometeorite, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1751, https://doi.org/10.5194/egusphere-egu21-1751, 2021.

GMPV5.1 – Solving geoscience problems using mineralogy

Nitrogen cycling between the Earth’s surface and interior influences atmosphere evolution, climate and habitability of our planet. Nitrogen transport process in the Earth’s interior is a key part of the cycling, which remains enigmatic. Silicate minerals are the main carriers of nitrogen mainly in the form of ammonium. Thus, untangling interactions of ammonium and lattice of the host minerals at the deep Earth’s conditions, is essential for understanding nitrogen transport process.

Feldspar, the most abundant mineral in the Earth’s crust, is a carrier of nitrogen to the deep Earth. Nitrogen is incorporated as ammonium in the M site of feldspar framework. To investigate interactions of ammonium and lattice at high temperatures, we conducted FTIR, Raman and XRD spectra measurements at high temperatures to 1000 oC on an ammonium-bearing feldspar, and revealed ammonium diffusivities and impacts on the lattice. The results show that diffusivities of ammonium at 800, 900 and 1000 oC are comparable to those of hydroxyl in feldspar, but much slower than structural molecular water. Importantly, ammonium in the M site of feldspar seems more stable than that in the layered site of phengite previously reported. Moreover, ammonium-bearing feldspar has smaller temperature-induced Raman mode wavenumber shifts and thermal expansion coefficients, as compared with ammonium-free feldspar.

The above results suggest interactions of ammonium and lattice of the silicate minerals at high temperatures. Thermal stabilities of ammonium depend on structure of the host silicates, and thermal stabilities of the host silicates are in turn affected by ammonium incorporated.

How to cite: Yang, Y.: Interactions of ammonium and lattice of feldspar at high temperatures, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13827, https://doi.org/10.5194/egusphere-egu21-13827, 2021.

EGU21-13814 | vPICO presentations | GMPV5.1

Topotaxial intergrowth and origin of antiperthite in monzogranite 

Yueting Song and Shanrong Zhao

The crystallographic orientation of antiperthite (squared alkali feldspar inclusions grow inside plagioclase host) in Tiantangzai monzogranite from Dabie Mountain was investigated. The morphology of alkali feldspar inclusions is hexahedron, three pairs of parallel faces are controlled by the (010), (001) and (110) planes of the host plagioclase, respectively. Some plagioclase develops albite polysynthetic twin, defined the twinned individuals as Pl(1) and Pl(2), respectively; some alkali feldspar inclusions are related by Carlsbad twin, the twinned individuals are also defined as Kfs(1) and Kfs(2), respectively. Pl(1) is oriented similarly to Kfs(1). The topotaxial relationship between Pl(2) and Kfs(1) is similar to albite-twin. The topotaxial relationship between Kfs(2) and Pl(1) is similar to Carlsbad-twin. Kfs(2) and Pl(2) would form a topotaxial relationship similar to Carlsbad-albite-twin. Pl(1) generally becomes thinner or disappears in the regions where alkali feldspar inclusions developed. The development sequence of the alkali feldspar inclusions and the polysynthetic albite twin needs to be further investigated. Electron microprobe line scanning shows a homogeneous K, Ca and Na distribution in a single plagioclase grain with inclusions developed, suggesting that the origin of alkali feldspar inclusion may not be related to exsolution. The fractures in the host plagioclase are well developed, but most fractures do not pass through the embedded alkali feldspar. The precipitated alkali feldspar may be a result of alkali-bearing fluids penetrating through fractures and replacing plagioclase. The rim of some larger anhedral alkali feldspar inclusions has many voids, the local average misorientation map indicates there is a rectangular area with low misorientation difference inside the anhedral inclusions. The anhedral alkali feldspar inclusions are presumed to form by secondary replacement on top of the original rectangular inclusions.

How to cite: Song, Y. and Zhao, S.: Topotaxial intergrowth and origin of antiperthite in monzogranite , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13814, https://doi.org/10.5194/egusphere-egu21-13814, 2021.

EGU21-12665 | vPICO presentations | GMPV5.1

Orientation relationships between magnetite micro-inclusions and plagioclase host 

Olga Ageeva, Ge Bian, Gerlinde Habler, and Rainer Abart

Magnetite micro-inclusions in silicate minerals are important carriers of the remanent magnetization of rocks. Their shape orientation relationships (SOR) and crystallographic orientation relationships (COR) to the host crystal are of interest in the context of the bulk magnetic properties of the inclusion-host assemblage. We investigated the SOR and COR of magnetite (MT) micro-inclusions in plagioclase (PL) from oceanic gabbro using correlated optical microscopy, scanning electron microscopy, Electron backscatter diffraction analysis and Transmission electron microscopy.

In the mm-sized PL crystals of the investigated gabbros MT is present as equant, needle- and lath-shaped (sub)micrometer sized inclusions. More than 95% of the needle-shaped inclusions show SOR and specific COR to the plagioclase host. Most of the needles are elongated perpendicular to one of the MT{111} planes, which is aligned parallel to one of the (112), (1-12), (-312), (-3-12), (150), (1-50) or (100) planes of plagioclase. These inclusions are classified as “plane-normal type”. The needle elongation parallel to MT<111>, which is the easy direction of magnetization, ensures high magnetic susceptibility of these inclusions. The underlying formation mechanism is related to the parallel alignment of oxygen layers with similar lattice spacing across the MT-PL interfaces that are parallel to the elongation direction [1].

Apart from the SOR and the alignment of a MT{111} with one of the PL low index planes, the MT crystals rotate about the needle elongation direction. The rotation angles are statistically distributed with several maxima representing specific orientation relationships. In some cases one of the MT<001> axes is aligned with PL[14 10 7] or PL[-14 10 -7], which ensures that FeO6 octahedra of MT well fit into channels // [001] of PL, which are formed by six membered rings of SiO4 and AlO4 tetrahedra [2]. This COR is referred to as the “nucleation orientation” of magnetite with respect to PL. There are several other possibilities to fit FeO6 octahedra into the [001] channels of PL, but the alignment stated above allows for the additional parallel alignment of one of the MT{111} with one of the above mentioned low index lattice planes of PL. MT crystals with one of these nucleation orientations can undergo directional growth to develop laths and needles. MT crystals with other nucleation orientations that do not allow for the parallel alignment of MT{111} with the above mentioned PL lattice planes, do not significantly grow and form the equant inclusions.

For some needles one or more of the MT{011} planes that are parallel to the needle elongation direction, are aligned with low-index planes of plagioclase such as PL (112), PL(150), PL(1-50) etc., and form MT facets. This situation corresponds to achievement of the best possible match between the two crystal lattices. This can either be generated during primary growth or during re-equilibration of the micro-inclusions and the plagioclase host.

Funding by RFBR project 18-55-14003 and Austrian Science fund (FWF): I 3998-N29 is acknowledged.

Reference

[1] Ageeva et al (2020) Contrib. Mineral. Petrol. 175(10), 1-16.

[2] Wenk et al (2011) Am. Min. 96, 1316-1324

How to cite: Ageeva, O., Bian, G., Habler, G., and Abart, R.: Orientation relationships between magnetite micro-inclusions and plagioclase host , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12665, https://doi.org/10.5194/egusphere-egu21-12665, 2021.

EGU21-10116 | vPICO presentations | GMPV5.1

Using electron backscatter diffraction to determine the formation mechanism of mineral inclusions in garnet

Thomas Griffiths, Victoria Kohn, Rainer Abart, and Gerlinde Habler

Determining the origin of mineral inclusions is a key problem in petrology. Assuming different inclusion formation mechanisms can lead to dramatically different petrological interpretations. Crystallographic orientation relationships (CORs), systematic relationships between the crystallographic orientations of crystals sharing boundary segments, are sensitive to the mechanisms of inclusion formation. Electron backscatter diffraction (EBSD) in the scanning electron microscope yields highly spatially resolved information about host-inclusion CORs. EBSD point analyses allow collection of large COR datasets, while retaining a link to the location of every measured inclusion and any shape preferred orientation (SPO) relative to host crystallography and microstructures. Based on combined COR, SPO and location information, we can differentiate between multiple origin hypotheses where COR formation is predicted, and the large number of measurements achievable allows observation of the relative frequency of different CORs.

Acicular rutile inclusions in garnet with SPOs parallel to garnet crystal directions are often interpreted based on microstructures alone as products of exsolution, implying the existence of precursor Ti-bearing garnet. We studied rutile needles from metapegmatite garnets from two localities with separate geological histories. Rutile needles occur in zones that extend parallel to garnet {112} (both localities) and {110} (one locality) crystal planes. Needles are elongated parallel to <111> (both localities) and <100> (one locality) directions in the garnet hosts. The majority of needles show a “specific” (completely fixed) COR to the garnet host. Several different CORs can be found within a single garnet domain and the frequency of different CORs varies both between domains from the same locality and between localities. Despite the existence of several CORs, there is a systematic link between the rutile-garnet COR exhibited by a given needle inclusion and its elongation direction relative to the crystallography of both garnet and rutile.

A comparison with literature datasets of CORs from garnets with acicular rutile inclusions reveals that both the type and frequencies of rutile-garnet CORs found in metapegmatite garnets differ strongly from those found in garnets of purely metamorphic origin. CORs judged to result in a poor alignment between rutile and garnet structures are considerably more frequent in the metapegmatite samples.

In garnets from one locality, the SPO of rutile needles does not favour all crystallographically equivalent garnet <111> directions equally. Instead, needles are preferentially elongated parallel to garnet <111> directions at high angles to the garnet facets defined by inclusion zoning. SPO and COR of the rutile needles thus depend on the orientation of the growing garnet interface, which is incompatible with an exsolution origin for these inclusions. Oriented nucleation of rutile at the garnet interface and subsequent simultaneous growth of both phases can account for these observations.

These results show the power of combining spatially resolved COR data with SPO information. An exsolution origin for rutile needles cannot be proposed based on needle SPO alone, and specific CORs are not necessarily indicative of an exsolution origin for rutile needles even if they occur together with an SPO relative to the garnet host.

We acknowledge funding by the Austrian Science Fund (FWF): I4285-N37.

How to cite: Griffiths, T., Kohn, V., Abart, R., and Habler, G.: Using electron backscatter diffraction to determine the formation mechanism of mineral inclusions in garnet, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10116, https://doi.org/10.5194/egusphere-egu21-10116, 2021.

EGU21-5066 | vPICO presentations | GMPV5.1

High-pressure crystal chemistry of four natural REE(As,P)O4 minerals from Mt. Cervandone, Italy

Francesco Pagliaro, Paolo Lotti, Alessandro Guastoni, Davide Comboni, G. Diego Gatta, Nicola Rotiroti, and Sula Milani

REE orthoarsenates and orthophosphates are common accessory minerals characterized by the general chemical formula REEXO4, where REE represents one of the lanthanides (La-Lu series), Y, Sc, Ca or Th, whereas X stands for As, P or Si. In the framework of a long-term project on the high-T/high-P crystal-chemistry and phase-stability of REE-bearing minerals, the high-pressure behavior of chernovite-(Y) (nominally YAsO4), xenotime-(Y) (nominally YPO4) gasparite-(Ce) (nominally CeAsO4) and monazite-(Ce) (nominally CePO4), has been studied. Chernovite-(Y) and xenotime-(Y) show a HREE- (Gd-Lu series) and Y-enrichment, and the same tetragonal symmetry (space group I41/amd), whereas gasparite-(Ce) and monazite-(Ce) share the same LREE (La-Eu) enrichment and monoclinic cell (space group P21/n). All these minerals occur at Mt. Cervandone (Western Alps, Italy), a renowned Alpine REE-bearing mineral deposit. The crystal chemistry of the four minerals has been studied via EPM-WDS analysis. Excluding gasparite-(Ce), which formation is bound to the replacement of the mineral synchisite-(Ce) (CaCe(CO3)2F), a sensible enrichment in Gd and Ho is observed. Moreover, the majority of the chernovite-(Y) show a variable amount of ThO2, up to 13 wt%, and phosphorous as substitute for arsenic in almost every proportion. In the case of the monoclinic series between monazite-(Ce) and gaparite-(Ce), no solid solution has been observed. Experiments at high-pressure were performed by in situ synchrotron X-ray diffraction using a diamond anvil cell. The high-pressure behavior of single crystals of xenotime-(Y), gasparite-(Ce) and monazite-(Ce) has been studied up to ~20 GPa, whereas that of chernovite-(Y) has been studied by powder diffraction up to 8.20(5) GPa. A II-order Birch-Murnaghan equation of state was fitted to the V-P data, within the phase stability field of the minerals, yielding the following bulk moduli: KP0,T0 = 125(3) GPa (βV0 = 0.0080(2) GPa-1) for chernovite-(Y); KP0,T0 = 145(2) GPa (βV0 = 0.0069(1) GPa-1) for xenotime-(Y);  KP0,T0 = 106.7(9) GPa (βV0 = 0.0094(1) GPa-1) for gasparite-(Ce), KP0,T0 = 121(2) GPa (βV0 = 0.0083(1) GPa-1) for monazite-(Ce). K’ = ∂KV/∂P = 4 (fixed) for all the minerals. Deformation mechanisms, at the atomic scale, were described on the basis of structure refinements.  

Acknowledgments: This research was partly funded by the PRIN2017 project “Mineral reactivity, a key to understand large-scale processes” (2017L83S77).

How to cite: Pagliaro, F., Lotti, P., Guastoni, A., Comboni, D., Gatta, G. D., Rotiroti, N., and Milani, S.: High-pressure crystal chemistry of four natural REE(As,P)O4 minerals from Mt. Cervandone, Italy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5066, https://doi.org/10.5194/egusphere-egu21-5066, 2021.

EGU21-10129 | vPICO presentations | GMPV5.1

Nano-sized particles and semimetal-rich melts in PGE-rich magmatic mineral systems 

José María González-Jiménez, Joaquín A. Proenza, Fernando Gervilla, and Rubén Piña

The results of several high temperature experiments predict that nanoparticles and nanomelts enriched in noble metals indeed exist in magmatic systems. Nanoparticles of Ru-Os-Ir or P-bearing sulfides alloys have been synthetized from S-free or S-undersaturated basaltic silicate melts at > 1000 °C at > 1000 °C. Pt-rich arsenide nanoparticles have also been synthesized in high-temperature sulfide melts well before the melt had reached a Pt–As concentration at which discrete Pt arsenide minerals become stable phases. More recently, the immiscibility of PGE-rich bismuthide melts within Ni-Fe-Cu sulfide liquids have also observed in high-temperature experiments, evidencing the key role played by nanomelts in controlling the PGE partitioning in magmatic mineral systems and their necessary existence for the formation of PGE-rich nanoparticles. However, many researches still remain convinced that these nanoparticles represent artifacts produced during quenching of experimental runs. The combination of focused ion beam micro-sampling techniques with high-resolution transmission electron microscopy (HRTEM) observations allowed the identification of PGE nanoparticles and nanominerals in magmatic base-metal sulfides from the PGE-Cr deposits from the Bushveld Complex in South Africa  and the eastern Cuban ophiolites. Moreover, nanometer sized of all six PGEs (Os, Ir, Rh, Ru, Pt, Pd) are relatively frequent natural quenched silicate melts preserved in mantle xenoliths. Collectively, all these observations made on natural rocks confirm the predictions of previous experiments on the possible formation of PGE mineral nanoparticles in magmatic systems rather to be result of low-temperature subsolidus re-equilibrium of magmatic minerals.

 

 

How to cite: González-Jiménez, J. M., Proenza, J. A., Gervilla, F., and Piña, R.: Nano-sized particles and semimetal-rich melts in PGE-rich magmatic mineral systems , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10129, https://doi.org/10.5194/egusphere-egu21-10129, 2021.

EGU21-10025 | vPICO presentations | GMPV5.1

Evaluating the effects of deformation on the chemistry of composite magnesioferrite-magnetite crystals by means of EBSD

Igor González-Pérez, Samuel Noval-Ruiz, Jose María González-Jímenez, Fernando Gervilla, Isabel Fanlo, and Fernando Tornos

Chemical signatures of magnetite are commonly used to track the evolution of mineralizing systems in many geological settings. However, the impact of deformation processes on magnetite chemistry remains still underexplored. Here, we report a rare case of composite crystals consisting of magnetite and magnesioferrite recording different degrees and styles of deformation in order to evaluate how deformation promotes chemical modification. The samples employed in this study come from two different Mg-skarn iron deposits (i.e., El Robledal and San Manuel) from the Serranía de Ronda (SW Spain). Chemical data acquired by Electron Probe Microprobe Analyzer (EPMA) and Field Emission Scanning Microscopy (FESEM) are contrasted against microstructural data obtained by using Electron Back-Scattered Diffraction (EBSD). Our results show that magnesioferrite crystals [Fe2+# (Fe2+/Fe2++Mg2+) = 0.22-0.46 and Fe3+# (Fe3+/Fe3++Al3+) = 0.99-1.00] from El Robledal deposit are characterized by a ductile deformation that led to different crystallographic orientation domains along with the replacement of magnesioferrite by magnetite (Fe2+# (Fe2+/Fe2++Mg2+) = 0.51-0.99 and Fe3+ (Fe3+/Fe3++Al3+) =0.98-1.00] via coupled dissolution – reprecipitation. A replacement of magnesioferrite [Fe2+# (Fe2+/Fe2++Mg2+) = 0.43-0.64 and Fe3+ (Fe3+/Fe3++Al3+) = 0.99-1.00] by magnetite Fe2+# (Fe2+/Fe2++Mg2+) = 0.78-1.00 and Fe3+# (Fe3+/Fe3++Al3+) = 0.98-1.00] via a coupled dissolution – reprecipitation mechanism is also preserved in the composite (i.e., zoned) crystals from the San Manuel deposit, which was additionally overprinted by an additional recrystallization event as a result of grain boundary migration recrystallization. Our results show that deformation in a fluid-assisted deformation regime has induced chemical modification of the original magnesioferrite aggregates as well as strain localization. This close physicochemical link offers new avenues of interpreting the chemical signatures of Mg-Fe oxides, utilizing their microstructurally controlled variation or lack thereof.

How to cite: González-Pérez, I., Noval-Ruiz, S., González-Jímenez, J. M., Gervilla, F., Fanlo, I., and Tornos, F.: Evaluating the effects of deformation on the chemistry of composite magnesioferrite-magnetite crystals by means of EBSD, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10025, https://doi.org/10.5194/egusphere-egu21-10025, 2021.

EGU21-61 | vPICO presentations | GMPV5.1

Mechanisms of bastnasite formation: replacement of calcite by rare earth carbonates.

Adrienn Maria Szucs, Alexandra Stavropoulou, Claire O'Donnell, Seana Davis, and Juan Diego Rodriguez-Blanco

The interaction of rare earth bearing (La, Nd, Dy) aqueous solutions with calcite crystals at was studied at ambient and hydrothermal conditions (25-220 °C) and resulted in the solvent-mediated surface precipitation and subsequent pseudomorphic mineral replacement of calcite by rare earth carbonates. Calcite grains were replaced from their periphery inwards, and the newly formed REE-bearing carbonates follow the crystallisation sequence lanthanite [REE2(CO3)3·8H2O] → kozoite [orthorhombic REECO3(OH)] → hydroxylbastnasite [hexagonal REECO3(OH)]. The specific rare earth involved in these processes and the temperature have a significant role in the polymorph selection, crystallisation pathways and kinetics of mineral replacement. La- and Nd-bearing kozoite, grows oriented onto the calcite surface, forming an epitaxy, due to their structural similarities. This phase forms elongated crystals on [100], with the {011} and {0-11} as major forms. The epitaxial relationship is (104) [010]cc ║(001) [100]koz and is strongly dependent on the ionic radius of the rare earth in the structure of kozoite. These results have strong implications for the understanding of mineralisation reactions occurring in REE-bearing carbonatite deposits, the most important resources of rare earths in the world.

How to cite: Szucs, A. M., Stavropoulou, A., O'Donnell, C., Davis, S., and Rodriguez-Blanco, J. D.: Mechanisms of bastnasite formation: replacement of calcite by rare earth carbonates., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-61, https://doi.org/10.5194/egusphere-egu21-61, 2021.

EGU21-11559 | vPICO presentations | GMPV5.1

Tourmalinisation in peraluminous granitic context : from experiment to thermodynamic modelling

Julien Fort, Stanislas Sizaret, Michel Pichavant, Arnault Lassin, Johann Tuduri, and Olivier Blein

Tourmaline records the physico chemical conditions during its cristallisation, as its primary chemical zonations are generally unbalanced, its occurrence as alteration product could be used to decipher the physicochemical properties of mineralizing fluids. However, the role of the tourmalinisation in hydrothermal processes remains little studied, if not poorly understood.  The complexity of its thermodynamic properties is related to the presence of four cationic sites allowing the accommodation of a wide variety of elements (Henry and Dutrow, 2018). Moreover the phenomena of deprotonation, Si-IVB and valence state, make the approach of solid solution properties complex (Hughes et al., 2001; Henry et al., 2011; Bačík, 2015; Morgan, 2016). Thus, thermodynamic properties are most often estimated  (Garofalo et al., 2000; Hinsberg and Schumacher, 2007) and only a few measurements could be carried out on a reduced number of near-endmembers crystals (Kuyunko et al., 1984; Ogorodova et al., 2012).

This study aims to investigate experimentally the stability field of schorl (Na-Fe) – dravite (Na-Mg) solid solution at 2 kbar total pressure between 400° and 600°C as a function of the boron content of the fluid and fO2 condition, using an internally heated gas apparatus. Those metasomatic experiments have been conducted on a mixture of naturals crystals of cordierite + albite, representing a peraluminous granite composition in a Na-Mg-Fe-Al-Si-B-O-H system, characterized by a high-Mg, low-Fe content. These experiments were performed in order to simulate a classic aluminous host of these tourmaline alterations in granitic context. The results will be studied, in terms of stability of the tourmaline species, chemistry variation and texture. They will be compared with thermodynamic models build using data from the literature (Korges et al., 2018; Pan et al., 2019 among others) . Ultimately, the objective is to characterize in a P, T, W/R space, the chemical evolution of fluids, the alteration sequence of rocks and the variations in volumes related to the successive reactions.

How to cite: Fort, J., Sizaret, S., Pichavant, M., Lassin, A., Tuduri, J., and Blein, O.: Tourmalinisation in peraluminous granitic context : from experiment to thermodynamic modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11559, https://doi.org/10.5194/egusphere-egu21-11559, 2021.

EGU21-16170 | vPICO presentations | GMPV5.1

Multi-Element Correlation Analysis of Cu-bearing Tourmaline using LA-ICP-Time-Of-Flight-MS

Hao A.O. Wang, Michael S. Krzemnicki, Susanne Büche, Sarah Degen, Leander Franz, and Rainer Schultz-Guttler

Major, minor and trace element analysis using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been applied to a broad range of mineral samples for characterization, mineral resources prospection, tracing and provenance determination, radiometric dating and studies on mineral formation conditions. In this study, we present a state-of-the-art LA-ICP-Time-Of-Flight-MS (LA-ICP-TOF-MS) technique for multi-element analysis of gem-quality Cu-bearing tourmaline from Brazil, Mozambique and Nigeria, with a special focus on elemental correlation among and within various provenances.

A TOF-MS obtains a full mass spectrum from 7Li+ to 238U+ simultaneously with an improved mass resolving power. These advantages over other conventional ICP-MS setups allow the TOF users to apply a novel concept of “first measure, then determine” which elements are of interest for the analysis of geological samples. Since the TOF-MS technique requires no/limited a priori knowledge about the sample before measurement, this technique can be beneficial for studying elements which occur infrequently in the minerals and for analysing full elemental composition in unidentified inclusions.

Multi-element composition of more than 400 Cu-bearing tourmaline samples (majority elbaite, Na-rich) was analysed using LA-ICP-TOF-MS that cover various colors, qualities and provenances available in the gem and jewellery trade. In order to investigate the elemental correlation, a non-linear unsupervised dimension reduction was performed on the high dimensional multi-element dataset using t-distributed stochastic neighbor embedding (t-SNE) algorithm. An unsupervised calculation works solely with the elemental concentrations and without labels of data points, for example color or provenance. The clusters in the geochemical data visualization indicates elemental similarity of various samples. We found that t-SNE algorithm is better than principle component analysis (PCA) algorithm in maintaining intrinsic elemental correlation from the original high dimensional space and embedding such information onto low dimensional datasets for visualization. Therefore, the t-SNE method excels in distinguishing within-group elemental similarities from between-group similarities. The separation of subgroups achieved with t-SNE is in agreement with the confirmed geographic provenances.

Additionally, a unique type of Cu-bearing liddicoatite (Ca and REE-rich) was recently discovered near Maraca in Mozambique (Nampula area). Since they have been reported so far only from this occurrence, this type of tourmaline is especially interesting to study how elements correlated during tourmaline formation. Applying t-SNE calculation on these samples, we have found two groups (or four subgroups) of these tourmaline samples. When multi-element concentration was plotted, it can be seen that light-REEs (La to Nd) have an apparent correlation with Ca concentration, however a negative correlation was observed between mid-REEs (Sm to Ho) and Ca. A correlation of Na to Bi and Th was also observed.

In a rare four-color (pink, purple, blue, green) Cu-bearing tourmaline sample from Quintos mine in the state of Rio Grande do Norte, Brazil, multi-element analysis was conducted along a profile across the entire color variation, from the core of the crystal (pink) to the rim of the crystal (green) to monitor elemental variations and correlations throughout the crystal growth process of this tourmaline within the pegmatite.

How to cite: Wang, H. A. O., Krzemnicki, M. S., Büche, S., Degen, S., Franz, L., and Schultz-Guttler, R.: Multi-Element Correlation Analysis of Cu-bearing Tourmaline using LA-ICP-Time-Of-Flight-MS, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16170, https://doi.org/10.5194/egusphere-egu21-16170, 2021.

EGU21-16379 | vPICO presentations | GMPV5.1

Magnetite (U-Th-Sm)/He dating: analytical challenges and application

Marianna Corre, Martine Lanson, Arnaud Agranier, Stephane Schwartz, Fabrice Brunet, Cécile Gautheron, and Rosella Pinna

Magnetite (U-Th-Sm)/He dating method has a strong geodynamic significance, since it provides geochronological constraints on serpentinization episodes, which are associated to important geological processes such as ophiolite obductions, subduction zones, transform faults and fluid circulations. Although helium content that range from 0.1 pmol/g to 20 pmol/g can routinely be measured, the application of this dating technique however is still limited due to major analytical obstacles. The dissolution of a single magnetite crystal and the measurement of the U, Th and Sm present at the ppb level in the corresponding solution, remains highly challenging, especially because of the absence of magnetite standard. In order to overcome these analytical issues, two strategies have been followed, and tested on magnetite from high-pressure rocks from the Western Alps (Schwartz et al., 2020). Firstly, we purified U, Th and Sm (removing Fe and other major elements) using ion exchange columns in order to analyze samples, using smaller dilution. Secondly, we performed in-situ analyzes by laser-ablation-ICPMS. Since no solid magnetite certified standard is yet available, we synthetized our own by precipitating magnetite nanocrystals. The first quantitative results obtained by LA-ICP-MS using this synthetic material along with international glass standards, are promising. The laser-ablation technique overcomes the analytical difficulties related to sample dissolution and purification. It thus opens the path to the dating of magnetite (and also spinels) in various ultramafic rocks such as mantle xenoliths or serpentinized peridotites in ophiolites.

Schwartz S., Gautheron C., Ketcham R.A., Brunet F., Corre M., Agranier A., Pinna-Jamme R., Haurine F., Monvoin G., Riel N., 2020, Unraveling the exhumation history of high-press ure ophiolites using magnetite (U-Th-Sm)/He thermochronometry. Earth and Planetary Science Letters 543 (2020) 116359.

How to cite: Corre, M., Lanson, M., Agranier, A., Schwartz, S., Brunet, F., Gautheron, C., and Pinna, R.: Magnetite (U-Th-Sm)/He dating: analytical challenges and application, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16379, https://doi.org/10.5194/egusphere-egu21-16379, 2021.

Stability relations of the REE-bearing accessory phases and alteration processes in the cancrinite-bearing nepheline syenite from the Čistá pluton (the center of the upper-crustal Tepla–Barrandian unit, Bohemian Massif, Czech Republic) were studied. Observations of rock microtextures, quantitative analyses of minerals and compositional X-ray mapping were performed using electron probe microanalysis (EPMA). The primary REE-bearing accessory minerals assemblage includes monazite-(Ce) associated with gadolinite-group minerals (i.e. gadolinite-(Ce) and gadolinite-(Y)), which were partially replaced by britholite-(Ce), bastnäsite-(Ce), aggregates of fine-grained REE-bearing phases (possibly fluorapatite and/or britholite-(Ce)) and, rarely, cerianite. K-feldspar and albite form intergrowths or symplectites with REE-phases in the investigated reaction microtextures. Furthermore, the zircon crystals demonstrate oscillatory zoning and/or extensive patchy zoning due to alteration processes. The alteration of accessory minerals are interpreted as driven by K- and Na-bearing alkali fluids with high CO2 activity during late- to post-magmatic processes.

Acknowledgements: This work was supported by the National Science Centre research grant no. 2017/27/B/ST10/00813.

How to cite: Jaranowski, M., Budzyń, B., Kozub-Budzyń, G. A., Sláma, J., and Klomínský, J.: Stability relations of monazite-(Ce), gadolinite-(Ce), gadolinite-(Y), britholite-(Ce) and bastnäsite-(Ce) during late- to post-magmatic processes in nepheline syenite (Čistá pluton, Czech Republic), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-820, https://doi.org/10.5194/egusphere-egu21-820, 2021.

The pressure-temperature conditions are transient in time and space during tectonic processes. To understand the complete P-T history of crustal domains examining the mineral paragenetic sequences and zoning profiles of minerals from diverse lithologies in the domain is necessary. But in highly tectonised crustal domains establishing time equivalence between far-spaced samples is difficult. To overcome this, a mylonite sample with closely spaced layers of different mineralogy collected from the South Maharashtra Shear Zone located along the north of Western Dharwar Craton (Rekha and Bhattacharya, 2014) was studied. The mylonite has four mineralogically distinct layers of few millimeters width containing garnet porphyroblasts of distinct zoning pattern separated by quartz layers. Layer-1 has two domains on the basis of the relative abundance of quartz; Layer-1A with more quartz and less flaky minerals and Layer-1B with less quartz and more flaky minerals. Layer-1A is composed of quartz>biotite>plagioclase>chlorite>K-feldspar with syn- to post-tectonic garnet porphyroblasts and the fabric is defined by shape preferred biotite-chlorite aggregates, recrystallized plagioclase and quartz ribbons.Layer-1B is relatively quartz poor and plagioclase>biotite>chlorite>K-feldspar aggregates rich domain as compared to L1A with biotite-chlorite aggregates and recrystallized plagioclase defined fabric.Prehnite elongated parallel to schistosity present but not very common. Layer-2 is very thin with amphibole-biotite±chlorite defined foliation and consists of plagioclase-K-feldspar-quartz with large garnet porphyroblast ofsyn to post-tectonic origin. Chlorites are mainly present near to garnet. Layer-3 is composed of biotite-calcite-plagioclase-chlorite-quartz with syn/post-tectonic garnet porphyroblast and the foliation is defined by biotite-chlorite aggregates, recrystallize plagioclase, calcite grains aligned parallel to the foliation and elongated quartz grains.Layer-3 is separated from the quartz layers on both sides by the formation of thin hornblende layers arranged parallel to the foliation. Very few hornblende grains found within the layer aligned parallel with the fabric defining minerals. Large pre-tectonic muscovite grains are preserved in Layer-3 and are altered to epidote along the margins of the grain. Layer-4 consists of hornblende, calcite, quartz with few plagioclase, K-feldspar and post tectonic garnet porphyroblast. The fabric is defined by the long axis of amphibole and calcite grains aligned parallel to it. Later biotite-prehnite grains formed at high angle to the fabric defining minerals. Conventional geothermobarometers were used for P-T estimation and it varies from 450-560°C and 6 kbar for Layer-1A, 445-550°C and 7 kbar for Layer-1B, 475-570°C and 6 kbar for Layer-2, 450-575°C and 7-8 kbar for Layer-3 and 450-5500°C and 7-9 kbar for Layer-4 at reference temperature of 500°C and pressure of 6kbar. Though different layers have distinctly different mineral assemblages there is hardly any variation in the P-T conditions which implies the original bulk rock composition was different for different layers not the P-T conditions of deformation.

Keywords: Mylonite, Western Dharwar Craton, Geothermobarometry

How to cite: Praharaj, P. and Rekha, S.: Role of P-T conditions and bulk rock composition in the mineralogical variations in millimeter scale: a study from South Maharashtra Shear Zone, western India , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9966, https://doi.org/10.5194/egusphere-egu21-9966, 2021.

EGU21-4392 | vPICO presentations | GMPV5.1

Monitoring mineral precipitation sequence of Lake Magadi soda lake: A multi-technical approach

Melese Getenet, Juan Manuel García-Ruiz, Franziska Emmerling, Dominik Al-Sabbagh, Fermín Otálora, and Cristóbal Verdugo-Escamilla

Lake Magadi is a saline soda lake in East African Rift Valley, occupying the axial trough of Southern Kenyan Rift. Its fed by perennial saline hot/warm springs, which evolve into the soda and saline chemistry of the lake. The main processes thought to cause the enrichment of the lake in Na+, CO32-, Cl-, HCO3- and SO42- are evaporative concentration, mineral precipitation and fractional dissolution [1]. Lake Magadi is considered an analogous environment to the early Earth [2]. The high pH, silica and carbonate content of Lake Magadi allows the formation of silica and carbonate induced self-assembled mineral structures [3,4]. Revealing the mineral precipitation sequence of Lake Magadi have implications in understanding the geochemistry of evaporative rift settings and soda oceans. We have experimentally investigated the mineral precipitation sequence during evaporation at 25 °C. The sequence of mineral precipitation was recorded by using in-situ video microscopy. The mineral patterns observed in video microscopies were identified by spectroscopic, diffraction and electron microscopy techniques. The mineralogy and elemental composition of the precipitates were determined by using Raman spectroscopy, powder X-ray diffractions and scanning electron microscopy coupled with energy dispersive X-ray analyser. The results of the ex-situ analyses were compared with the in-situ X-ray diffraction. In-situ X-ray diffractions were performed on acoustically levitated droplets in the μSpot beamline at BESSY II synchrotron (Berlin, Germany). Finally, thermodynamic evaporation simulation was performed by using PHREEQC code with Pitzer database. Ex-situ and in-situ experiments revealed that mineral precipitation begins with trona, followed by halite and finally thermonatrite. In PHREEQC simulations, natron was observed instead of thermonatrite, suggesting the role of kinetics in the mineral assemblages. This multi-technical approach of in-situ monitoring and ex-situ characterization is a powerful approach to unveil mineral precipitation patterns and the resulting geochemical evolution in evaporative rift settings.

Acknowledgments: We acknowledge funding from the European Research Council under grant agreement no. 340863, from the Ministerio de Economía y Competitividad of Spain through the project CGL2016-78971-P and Junta de Andalucía for financing the project P18-FR-5008. M.G. acknowledges Grant No. BES-2017-081105 of the Ministerio de Ciencia, Innovacion y Universidades of the Spanish government.

References:

[1] Eugster, H.P. (1970). Chemistry and origin of the brines of Lake Magadi, Kenya. Mineralogical Society of America Special Papers, 3, 213–235.

[2] Kempe, S.; Degens, E.T. (1985). An early soda ocean?. Chem. Geol.  53, 95–108

[3] Getenet, M.; García-Ruiz, J.M.; Verdugo-Escamilla, C.; Guerra-Tschuschke, I (2020). Mineral Vesicles and Chemical Gardens from Carbonate-Rich Alkaline Brines of Lake Magadi, Kenya, Crystals, 10, 467.

[4] García-Ruiz J.M., van Zuilen M.A., Bach W. (2020) Mineral self-organization on a lifeless planet. Phys Life Rev, 34–35,62–82

How to cite: Getenet, M., García-Ruiz, J. M., Emmerling, F., Al-Sabbagh, D., Otálora, F., and Verdugo-Escamilla, C.: Monitoring mineral precipitation sequence of Lake Magadi soda lake: A multi-technical approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4392, https://doi.org/10.5194/egusphere-egu21-4392, 2021.

EGU21-12619 | vPICO presentations | GMPV5.1

Comparison of Microporous Minerals for Potential Contaminant Uptake

Marvin Osorio, Christopher Oze, and Aaron Celestian

Microporous minerals have many industrial applications, from filtration to contaminant immobilization. Natural and synthetic minerals, including zeolites, clays, and silica aerogel, represent a few examples of microporous minerals with distinctive structures, surface charges, and porosity. Analysis and comparison of their crystal structures are necessary to determine how each mineral may be suited for contaminant uptake. Here we assessed the structure of microporous minerals, specifically rowleyite, clinoptilolite, vermiculite, and silica aerogel.  Raman spectroscopy, X-ray fluorescence, and X-ray powder diffraction were used to create and model atomic mineral structures to visualize atomic and macroscope features. Taking into account pore size and surface charge each mineral was reviewed to find the best fit with regards to heavy metal uptake, mainly Pb (lead). Overall, we provide a comparative framework to assess microporous minerals that will inform future flow-through experiments for heavy metal uptake.

How to cite: Osorio, M., Oze, C., and Celestian, A.: Comparison of Microporous Minerals for Potential Contaminant Uptake, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12619, https://doi.org/10.5194/egusphere-egu21-12619, 2021.

EGU21-870 | vPICO presentations | GMPV5.1

Reach of pollution and sediment correlation with the tailings in Šibenik Bay (Croatia)

Laura Huljek, Hana Fajković, and Željko Kwokal

To determine the influence of the historic factory of electrodes and ferroalloys on the Šibenik bay sediments, XRPD analysis were carried out. The factory was established in the city of Šibenik, on the coast of the Krka River estuary, and produced calcium carbide, and later electrodes and ferroalloys. It was active from 1900 until 1995 [1]. During that time, a large amount of produced tailings were stored nearby and on the shore of the estuary. Due to the presence of the strong winds (bora and sirocco), which can reach up to 130 km/h, the tailings material could be transported to long distances [2].

Samples of tailing were collected at the location of the former factory, which is a tailing hill today, samples of dust were collected from the rooftop of the factory in the 1980s. Other samples were taken on a 1 km distant beach in the Šibenik bay  (Beach A) and a 19 km distant beach on the island in the outer Šibenik archipelago (Beach B). Both beaches are located south-west of the factory. The samples from the beaches were taken with a corer at different depths: 0 – 3 cm, 3 – 5 cm, around 5 cm. The sample from 3 – 5 cm depth was not analysed.

Bulk sample and a fraction <63 µm were analysed on X-Ray Diffractometer. The XRPD analysis of the sediments from Beach B in the outer Šibenik archipelago shows that calcite and quartz are the most abundant phases. This mineral composition shows that distant islands were not affected by aeolian transportation of the factory dust and tailing. In the bulk samples from Beach A, in the uppermost part (0 – 3 cm depth) mineral components are calcite, aragonite, calcium manganite, bustamite ferroan and carbon, while calcite, quartz, aragonite, calcium manganite and manganosite are present in the fraction <63 µm. The sample from the depth of 5 cm at the same beach, shows calcite, aragonite and Mn-oxide, while fraction <63 µm lacks in Mn-oxide.

A bulk sample of tailings shows mineral components: calcite, quartz, calcium manganite, bustamite ferroan and gypsum which corresponds to the previous research [3], and there is also manganese silicon, manganese silicide, carbon and amorphous phase [4]. A fraction <63 µm of the tailing, shows the following mineral phases: calcite, quartz, calcium manganite and bustamite ferroan, as presented in previous research [3]. Analysis of the rooftop dust shows three phases: carbon, bustamite ferroan and manganosite, which does not correspond to the data given from the factory [3].

From the presented results, it could be concluded that the historic factory influenced sediments in the Šibenik bay, however, its influence was not detected on the Beach B 19 km to the SW, which opens the question of reach and distance to which tailings can be transported by sea and/or wind.

This work has been supported in part (samples collection) by Croatian Science Foundation under the project lP-2019-04-5832.

How to cite: Huljek, L., Fajković, H., and Kwokal, Ž.: Reach of pollution and sediment correlation with the tailings in Šibenik Bay (Croatia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-870, https://doi.org/10.5194/egusphere-egu21-870, 2021.

EGU21-7462 | vPICO presentations | GMPV5.1

Minerals of Bolshoi Semiachik geothermal fields (Central Kamchatka, Russia)

Elena Zhitova, Rezeda Ismagilova, Anastasia Sergeeva, Maria Nazarova, Anton Nuzhdaev, Ruslan Kuznetsov, Ilya Bolshakov, and Daria Bukhanova

The volcanic complex Bolshoi Semiachik is characterized by intensive hydrothermal activity which is expressed by presence of thermal fields with gas-steam jets (T up to ~ 140 ºC), boiling pots (T up to ~ 100 ºC), warm lakes (T up to ~ 90 ºC) and ground (T up to ~ 97 ºC) . The circulating hydrothermal solution is rich in ammonium, sulfate and locally in carbonate. To date, little is known about surface mineralogy that occurs at the geothermal fields of the volcanic complex Bolshoi Semiachik. The major geological expeditions were carried out there in the 1960`s, and there was also some additional research carried out in the 1980`s. The study of minerals occurring at the surface of geothermal fields is relevant for planetary science since similar minerals are suggested for Mars and Europa (Jupiter moon) and geochemistry since such environments of mineral formation are very specific.

In the summer 2020 the expedition of the Institute of volcanology and seismology has been organized in order to monitor thermal fields and to conduct mineral and water samples for study. Here we report the first data on mineral identification of processed samples (at about 50). At that moment, minerals have been identified by powder X-ray diffraction and electron-microprobe analyses.

The surface of Bolshoi Semiachik geothermal fields is covered by clay minerals with montmorillonite that is rich in disseminated pyrite being the most abundant. Among salt minerals the common phases are sulfates: halotrichite-, copiapite and voltaite-group minerals, alunogen, gypsum and native sulphur. The SiO2 polymorphs: tridymite, cristobalite are also found at the geothermal field surface. In the zone called Central Crater chalcantite has been found in association with rhomboclase and tridymite. Some samples with zeolite-group mineral - laumontite were also found, which at the moment is identified less reliably. The central (high temperature) part of deposits around steam-gas jet is composed of dickite in association with sulphur and quartz covered by alunogen and halotrichite efflorescent. The rim (at about 1 meter from the center) is composed of smectites, marcasite and natroalunite. This zonation is likely caused by pH which is lower at the central part where the steam unloads and increases at the peripheral area around the steam-gas jet.

Acknowledgment. The study has been supported by RFBR project # 20-35-70008. We are grateful to Volcanoes of Kamchatka for letting us to conduct the field works at Bolshoi Semiachik thermal fields. Experimental works on mineral identification have been carried out using Analytical Centre of IViS and Research Park of SPbU.

How to cite: Zhitova, E., Ismagilova, R., Sergeeva, A., Nazarova, M., Nuzhdaev, A., Kuznetsov, R., Bolshakov, I., and Bukhanova, D.: Minerals of Bolshoi Semiachik geothermal fields (Central Kamchatka, Russia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7462, https://doi.org/10.5194/egusphere-egu21-7462, 2021.

EGU21-14392 | vPICO presentations | GMPV5.1

Ca, Cu and Pb solubilization and biomineralization by microorganisms: case study from Kamchatka, Russia

Irina Chernyshova, Oleg Vereshchagin, Zelenskaya Marina, Himelbrant Dmitry, Vlasov Dmitry, and Frank-Kamenetskaya Olga

The role of microorganisms (lichens, micromycetes and bacteria) in the formation of biominerals is widely known (Purvis, 2008; Vlasov et al., 2020). In the fall of 2019, we organized an expedition to the area of Tolbachik volcano (cones 1, 2, 3 and Mount 1004), Kamchatka, Russia, and collected 120 samples of volcanic rocks with biofilms. The volcanic cones of Tolbachik concentrate a wide variety of elements and are a type-locality of more than 300 minerals (Vergasova and Filatov, 2012; Siidra et al., 2017; Pekov et al., 2018). Lichen species are widespread in the volcanic fields of Kamchatka, Russia (Kukwa et al., 2014).  The goal of this work was to search for and study biominerals associated with lichens.

As a result of our research, calcium oxalates (whewellite and weddellite) and copper oxalates (moolooite) associated with lichens were found. Whewellite was found in the lichens Psylolechia leprosa and Sarcogyne hypophaea. Whewellite and weddellite were found together in the lichen Rinodina gennarii. Pyroxene (diopside) and plagioclase (anorthite) sourced calcium for the oxalates formation. Whewellite accumulates in apothecia in the form of whitish masses, consisting of lamellar crystals of 5-6 microns in size and their stacked intergrowths. Weddellite forms bipyramidal crystals of 2-10 microns in size. Moolooite was found in lichens Acarospora squamulosa and Lecanora polytropa (together with whewellite). The source of copper is tenorite, atacamite and copper-rich silicates (products of basalt processing by fumaroles). Moolooite forms lamellar crystals and intergrowths up to 5-6 microns in size. An interesting feature of oxalate formations in the Lecanora polytropa lichen is a high lead content, which has never been previously recorded in natural oxalates. Linarite and pyromorphite are most likely the source of lead. Chemical analysis showed that "nests" of calcium oxalates can contain up to 6 wt% PbO, while "nests" of copper oxalate - no more than 1 wt% PbO. The results obtained indicate the possibility selective sorption of lead and suggest the possibility of replacing calcium with lead in the oxalates. The studies of the location forms of lead in biofilms are in progress. The exact form of lead has not yet been established. Linarite and pyromorphite are most likely the source of lead. This research was supported by Russian Science Foundation grant (19-17-00141) and performed at the resource centers of St. Petersburg State University (MM, XRD, Geomodel).

Fedotov S.A. (ed.). Great fissure Tolbachik eruption (1975-1976, Kamchatka) // Moscow: Nauka. 1984. 637 p.

Kukwa M. et al. // The Lichenologist. 2014. 46. 1. P. 129–131.

Pekov I.V. et al. // Acta Cryst. 2018. B74. P. 502–518.

Purvis O.W. et al. // Mineralogical Magazine. 2008. 72. 2. P. 607–616.

Siidra O.I. et al. // European Journal of Mineralogy. 2017. 29. 3. P. 499–510.

Vergasova L.P. and Filatov S.K. // Volcanology and Seismology. 2012. 5. P. 3–12.

Vlasov D.Yu. et al. In: Aspergillus niger: pathogenicity, cultivation and uses, Nova Science Publishers, New York. 2020. P. 2-121.

How to cite: Chernyshova, I., Vereshchagin, O., Marina, Z., Dmitry, H., Dmitry, V., and Olga, F.-K.: Ca, Cu and Pb solubilization and biomineralization by microorganisms: case study from Kamchatka, Russia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14392, https://doi.org/10.5194/egusphere-egu21-14392, 2021.

EGU21-6901 | vPICO presentations | GMPV5.1

Influence of temperature on the hydrothermal clay soils' shear strength of the Nizhne-Koshelevsky and Verkhne-Pauzhetsky thermal fields.

Ruslan Kuznetsov, Mikhail Chernov, Victoria Krupskaya, and Ruslan Khamidov

Nizhne-Koshelevskoe and Verkhne-Pauzhetskoe thermal fields are located in the south of Kamchatka, the first - within the Koshelevsky volcanic massif, the second - on the territory of the Pauzhetsky geothermal field. The first horizon from the surface in these fields is formed by clayey soils, that have been formed as a result of hydrothermal alteration of volcanic rocks. And in the natural conditions clayey soils are at temperatures reaching 100 °C.

Samples of undisturbed clay soils were taken within the thermal fields. The samples are characterized by a density of 1.29 - 1.42 g/cm3, rather high values of the weight moisture (90-110%), and temperatures of 50 - 70 °C.

The samples are dominated by clay minerals: kaolinite and mixed-layer - kaolinite-smectite, their content is about 75%. The other 25% are microcline, cristobalite, anatase, gypsum, pyrite, marcasite, quartz and alunite.

For samples of undisturbed clay soils, direct shear tests were carried out at a temperature of 20 °C and at a temperatures of the samples close to their natural temperatures (50–70 °C). Thus, the values of cohesion and the angle of internal friction of the samples were determined.

The obtained results can be interfered as follows: as a result of an increase in the temperature of clayey soils, the thickness of electric double layer on the surface of clay particles decreases. On the one hand, it leads to a decrease of cohesion value between the clay particles and the beginning of shear deformations at lower vertical loads. On the other hand, a smaller thickness of electric double layer brings particles closer to each other, which is the reason for an increasing angle of internal friction and shear resistance at higher vertical loads.

How to cite: Kuznetsov, R., Chernov, M., Krupskaya, V., and Khamidov, R.: Influence of temperature on the hydrothermal clay soils' shear strength of the Nizhne-Koshelevsky and Verkhne-Pauzhetsky thermal fields., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6901, https://doi.org/10.5194/egusphere-egu21-6901, 2021.

The most famous of natural occurring iron-nickel alloys are kamacite, taenite and tetrataenite, forming iron meteorites. Normally, they have significant platinum-group elements (PGE) content being a result of high siderophile behaviour of the latter. In spite of native iron and nickel having been described in terrestrial rocks, the most abundant Fe-Ni mineral in Earth’s crust is awaruite (Ni3Fe). Current work represents the preliminary results of testing the ability of awaruite to concentrate PGE.

Awaruite is a widespread accessory mineral of ultramafic complexes. Its formation is usually assessed to the serpentinization of olivine which produces reductive fluid. The latter reacts with nickel sulfides and produces awaruite. Several reports of awaruite occurring together with platinum-group minerals (PGM) are present in the literature. In the Ural-Alaskan type complexes of Koryak Highlands (Far East Russia), such cases are abundant. Textural investigations of such complexes discovered a diverse array of serpentine–related mineralization, including isoferroplatinum in chlorite matrix, isoferroplatinum–amphibole intergrowths, and a wide range of PGE, Fe and Cu alloys formed in serpentine veinlets together with awaruite and base metal sulfides. This provides evidence of the relation between awaruite and platinum mineralization.

LA-ICP-MS has been used to reveal the PGE content in awaruite and coexisting sulfides. Grains from the placers related to the Galmoenan complex of Ural-Alaskan type were used for this study. The analysis revealed that sulfides may bear significant PGE admixture. Unexpectedly, the most abundant impurity is Os. Its content varies from 0.7 to 538 ppm. The shape of the time-resolved spectra of some samples indicates the possible presence of solid inclusions which concentrate Os. However, most of them, including those with 538 ppm Os, exhibit plain time-resolved spectra suggesting homogeneous Os distribution. Contents of other PGE are moderate: up to 8.3 ppm Pt, 1.4 ppm Pd, 4.3 ppm Ru, 0.25 ppm Rh and 2.6 ppm Ir.

Some awaruite grains also show relatively high Os content (up to 89 ppm), but time-resolved spectra of them exhibit clear evidence of mineral inclusions presence. In one case, Os spike coincides with the S spike, suggesting that Os is incorporated into the sulfide phase. In the case of spikeless spectra, Os content is always below the detection limit (b.d.l.). Rhodium content also is always b.d.l., while Ru content reaches 0.44 ppm, Ir – 0.08 ppm, and Pt – 0.03 ppm. The only element explicitly showing significant and homogenous presence in the awaruite is Pd, that content reaches 5.8 ppm in one analysis and 0.2–1.1 in many others.

These data indicate that in the studied case, awaruite mineralization is accompanied by the formation of PGM, while its role as a direct PGE concentrator is moderate and restricted to the first tenths ppm of Ru and Pd. Sulfides have shown much more impressive ability in concentrating PGE. Their selective enrichment in Os is a novelty and demands explanation.

 

Author thanks Evgeniy Sidorov and Dima Kamenetsky for the assistance. CODES of UTAS is greatly acknowledged for the LA-ICP-MS analyses. This work was supported by the Russian Foundation for Basic Research (RFBR) grant No 20-05-00290 A.

How to cite: Kutyrev, A.: Awaruite (Ni3Fe) as a platinum-group elements concentrator: Preliminary data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5432, https://doi.org/10.5194/egusphere-egu21-5432, 2021.

EGU21-160 | vPICO presentations | GMPV5.1

Geochemical specialization of geological complexes in the northern part of the Kamchatka Peninsula

Liubov Kononova, Marina Ladygina, and Angelina Maltseva

The study area (4350 km2; 58°00'-58°40'N 161°00'-162°00'E) is located within the Kamchatka-Olyutorsk integumentary fold zone. The eastern part of the area is occupied by structures of the Litken rift; formations of the superimposed Neogene-Quaternary Central Kamchatka volcanic belt are developed in the central and western parts. Volcanic rocks of the Umuvayam complex (N1um; α, ζ, λζN1um) are widespread in the study territory, Tolyatovayam (N1-2tl; λζ N1-2tl), Veemgetver (N2vm; ζN2vm), Emiyayam ( νδ,δ,qδ, δπ, μ-γδ, qμ, qμ-qδ, γδ, εγ-δ N1e) volcanic complexes, lava sheets and intrusions of the basic composition of the Quaternary age spread to a less extent. Geological formations and associated ore objects were developed during three mineragenic epochs: Late Cretaceous-Middle Paleogene (volcanic intraoceanic sediments and terrigenous complex of the oceanic shelf), Middle Paleogene-Neogene (terrigenous complex of the oceanic shelf) and Quaternary (andesite complex of the back-arc rift zone, island-arc complex and terrigenous complex of the back-arc basin of the active continental margin). Mineragenic epochs correspond to five structural-facies zones: Mid-Kamchatka-Koryak, Litken-Central-Kamchatka (QE-I-QH), Central Kamchatka, Litken (₽2-Q), Kamchatka-Olyutorsk (K2-₽2). 

In order to identify geochemical criteria for the ore content and potential metallotects for all geological formations.

In general, the structural-material complexes show the chalcophilic type of geochemical specialization. Mid-Kamchatka-Koryak structural-facies zone has a spectrum W5,0Ag4,4Bi2,8Mo2,5Sn2,2Zn2,0Cu1,8, Litken-Central-Kamchatka As11,0Mo5,0Ag2,9Co1,5, Central Kamchatka Ag6,0W5,2(Bi,Mo)3,3Cr2,2Cu1,9(PbSeSn)1,8V1,7Zn1,6, Litken (SnV)3,0Cr2,4Sc2,0Cu1,9(SeZnGa)1,8Ag1,7Pb1,6(CoGe)1,6, Kamchatka Olyutorsk Ag4,2Cr3,8V2,5Sc1,7Cu1,6(ZnGa)1,5.

The following metallotects can be distinguished in the study area: 

The rocks of the Umuvayam, Emivayam, and Tolyatovyam complexes are part of the Central Kamchatka structural-facies zone, which occupies the largest central part of the study area. Epithermal silver-gold objects of the adularia-quartz formation are formed due to the invasion of intermediate and acidic phases of these complexes, postmagmatic activity, and metasomatic transformations of rocks. The averaged spectrum of accumulation of chemical elements, derived for the rocks that make up the Central Kamchatka structural-facies zone, is characterized by a wide range and demonstrates the siderophilic-lithophilic-chalcophilic type of geochemical specialization. Silver, copper, lead, and zinc included in the spectrum are indicators of the known and predicted mineralization of silver-gold adularia-quartz and polysulfide formations, and the presence of molybdenum indicates the possibility of detecting copper-molybdenum-porphyry ore objects. Thus, the geochemical data fully confirm that the Central Kamchatka structural-facies zone is highly promising.

How to cite: Kononova, L., Ladygina, M., and Maltseva, A.: Geochemical specialization of geological complexes in the northern part of the Kamchatka Peninsula, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-160, https://doi.org/10.5194/egusphere-egu21-160, 2021.

GMPV5.2 – Mineral deposits: systems, settings and processes

EGU21-7903 | vPICO presentations | GMPV5.2

Modeling the sulfide saturation in continuously assimilating magmatic systems with the Magma Chamber Simulator

Ville Virtanen, Jussi Heinonen, Nicholas Barber, and Ferenc Molnár

The timing and degree of immiscible sulfide precipitation in a magma effectively controls the formation of magmatic sulfide deposits and the budget of degassing sulfur species in volcanic systems. Besides the absolute sulfur (S) content, sulfide precipitation is strongly affected by the sulfur content at sulfide saturation (SCSS) in the host silicate melt. Assimilation of S-rich wall-rocks, such as black shales, effectively increases the S content in the magma, while simultaneously lowering the SCSS. Accordingly, assimilation has been identified as the most important process in the formation of many economically significant magmatic base metal sulfide deposit, especially in continental tectonic settings. Detailed understanding of the relation between wall-rock assimilation and sulfide saturation requires accurate thermodynamic models for open magmatic systems experiencing assimilation-fractional crystallization (AFC).

The Magma Chamber Simulator (MCS) is currently the only geochemical modeling software that considers the thermodynamic phase equilibria in open magmatic systems involving magma and wall-rock (and recharge) subsystems. We utilized the MCS to explore how assimilation affects the SCSS and S content of the magma. With the current lack of thermodynamic data for sulfides, we tentatively modeled S as a trace element and varied its compatibility to wall-rock in the different models. For a case study, we chose the mafic layered intrusions of Duluth Complex, Minnesota, which host some of the largest Cu-Ni sulfide deposits in the world. Assimilation of the adjacent black shale has been established as the main source for S in the deposits.

Our MCS models show in detail how continuous assimilation of the black shale lowers the SCSS of the melt. Partial melt from the black shale enriches the magma in SiO2, Al2O3, K2O, and H2O, while depleting FeO, MgO, CaO, and Na2O, which causes a first order decrease in the SCSS. The compositional change also replaces troctolitic cumulates (plagioclase, olivine ± clinopyroxene) with norite (plagioclase and orthopyroxene), which leads to more pronounced FeO depletion in the melt, further lowering the SCSS. On the other hand, the assimilated partial melt also increases the melt mass in the magma subsystem, which counteracts the S enrichment. Accordingly, in the model where S is compatible to the wall-rock residual, the degree of sulfide saturation only slightly increases relative to the same magma experiencing FC without assimilation.

More than half of the wall-rock S must partition to the assimilated partial melt in order to meet the S isotopic criteria of the modeled Cu-Ni-deposits. The main stage of sulfide precipitation is associated with ~30 wt.% crystallization of the assimilating host magma. The proportion of sulfides relative to silicates in these models is smaller than observed in the Duluth Complex deposits, which underlines the role of dynamic processes in concentrating sulfides from the silicate magma.

How to cite: Virtanen, V., Heinonen, J., Barber, N., and Molnár, F.: Modeling the sulfide saturation in continuously assimilating magmatic systems with the Magma Chamber Simulator, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7903, https://doi.org/10.5194/egusphere-egu21-7903, 2021.

EGU21-12593 | vPICO presentations | GMPV5.2

Geochemical study in situ (LA-ICP-MS) of ore minerals from Paleoproterozoic layered PGE intrusions in the north-eastern Fennoscandian Shield

Svetlana Drogobuzhskaya, Tamara Bayanova, and Andrey Novikov

The laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) is a unique method for local analysis that allows studying mineral grains in situ. The aims of these geochemical researches are to estimate concentrations and distributions of PGE and other siderophilic and chalcophilic elements in ore minerals from complex deposits in the Arctic region (Fennoscandian Shield), using the LA-ICP-MS local analysis of trace elements. Pyrite, pentlandite, pyrrhotite and other sulfides are important for determining platinum-group elements.

In situ analyses of sulfide crystals were carried out on polished thin sections by ICP-MS. The electron (LEO-1415) and optic (LEICA OM 2500 P, camera DFC 290) spectroscopy was applied to study the morphology of the samples. Analytical points on sulfide minerals were selected using microelectronic and optical images.

PGE and other elements (As, Bi, Cd, Cr, Co, CuFe, Ni, Se, S, Sn, Sb, Pb, Re, Te, Tl, Zn, Hf, Th, U, REE) were measured by ICP-MS, using an ELAN 9000 DRC-e (Perkin Elmer) quadrupole mass spectrometer equipped with a 266 nm UP-266 MAСRO laser (New Wave Research). NIST 610, NIST 612 and tandem graduation (using solutions), considering sensitivity coefficients of isotopes were used to check the accuracy of estimations. Fe, Ni and Cu were used as internal standards, being most evenly distributed elements in minerals, when concentrations of elements in sulfides were calculated. The estimates were carried out, using inter-laboratory standards of chalcopyrite, pentlandite and pyrrhotite, which had been preliminarily prepared and studied using microprobe analysis (Cameca MS-46).

Data on concentrations of PGE, Au and Ag in sulfides, including data on their distribution in minerals, are crucial in studying the origin of noble metals in sulfide ores and interpreting formation settings of complex deposits. Estimated concentrations of other trace elements provide an essential supplement to geochemical data. Received data are new data (LA-ICP-MS) of Pt-Pd and Cu-Ni reefs of the Monchegorsk ore areas (2.5 Ga) with prospected commercial deposits. Elaborated LA-ICP-MS techniques were applied to provide in situ measurements of noble metals (PGE, Au, Ag), as well as siderophilic and chalcophilic elements, in sulfide minerals in order to study their distributions in chalcopyrite, pentlandite and pyrite from the Pechenga and Allarechka Cu-Ni deposits (1.98 Ga), Fedorova Tundra and Severny Kamennik PGE deposits (2.5 Ga).

 

The scientific researches are supported by RFBR Grant No 18-05-70082, scientific themes 0226-2019-0032 and 0226-2019-0053.

How to cite: Drogobuzhskaya, S., Bayanova, T., and Novikov, A.: Geochemical study in situ (LA-ICP-MS) of ore minerals from Paleoproterozoic layered PGE intrusions in the north-eastern Fennoscandian Shield, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12593, https://doi.org/10.5194/egusphere-egu21-12593, 2021.

EGU21-1987 | vPICO presentations | GMPV5.2

Trace element geochemistry of iron oxides from the Per Geijer apatite iron ores in the Kiruna district, northern Sweden: Implications for ore genesis

Patrick Krolop, Kari Niiranen, Sabine Gilbricht, Bernhard Schulz, Marcus Oelze, and Thomas Seifert

Iron oxide-apatite (IOA) deposits are an important source of iron ore based on the modal abundance of magnetite > 90 vol.%. Further interest is generated due to the high variability of apatite and hematite in some of these ores. The origin of the so-called Kiruna-type deposits has been subject to controversy for more than a century. Models range from a purely magmatic origin to ore-forming processes that involve variable stages of hydrothermal fluid involvement to a not widely accepted sedimentary-exhalative origin. In contribution of understanding ore-forming processes of this deposit type, we performed mineral chemistry and trace element analyses on samples from the Per Geijer deposits. They account for the lesser studied deposits in the Kiruna district of northern Sweden. A comprehensive mineral-chemical dataset of magnetite and hematite obtained by electron microprobe analysis (EPMA) and LA-ICP-MS from representative drill core samples is presented. Magnetite and four different types of hematite constitute the massive orebodies: Primary and pristine magnetite with moderate to high concentrations of Ti (∼61–2180 ppm), Ni (∼11–480 ppm), Co (∼5–300 ppm) and V (∼553–1831 ppm) indicate a magmatic origin for magnetite. Hematite type I appears as a replacement of magnetite with high Ti (∼15,700–42,300 ppm), relatively constant V (∼1460–2160 ppm) and moderate Sn (∼29–105 ppm) concentrations. Moderate and variable Ti (∼369–12,490 ppm) and low Sn (∼1.4–19 ppm) concentrations are representative for hematite type II. Hematite type III has lowest Ti (∼99–1250 ppm) concentrations. Significantly high Ti concentrations (∼12,100–78,700 ppm), low V (∼132–381 ppm) and high Sn (∼129–456 ppm) concentrations account for type IV. The presence of fluorapatite and disseminated pyrite with high Co:Ni ratios (> 1–10) in massive magnetite ores are consistent with a high temperature (∼ 800°C) genesis for the deposit. The different and abundant types of hematite state subsequent hydrothermal events.

How to cite: Krolop, P., Niiranen, K., Gilbricht, S., Schulz, B., Oelze, M., and Seifert, T.: Trace element geochemistry of iron oxides from the Per Geijer apatite iron ores in the Kiruna district, northern Sweden: Implications for ore genesis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1987, https://doi.org/10.5194/egusphere-egu21-1987, 2021.

Carbonatitic magmatism and metasomatism are rare in Great Britain & Ireland. However, REE-Nb minerals were identified in impure marbles and calc-silicates on the Aird of Shin and Arscaig near Lairg, Scotland. They belong to the Palaeoproterozoic Shin Group, a supercrustal succession of amphibolites, banded silicic gneisses, marbles and calc-silicates. The Shin Group is one of several Palaeoproterozoic to Neoproterozoic marble inliers in the North Highlands of Scotland that present evidence of Caledonian orogen carbonatitic metasomatism. The Proterozoic Bayan Obo ore complex in China was similarly deposited as a dolomite-limestone and later subject to alkali intrusions and carbonatitic metasomatism during the Caledonian orogeny. The Bayan Obo complex hosts REE-Nb-Fe carbonatitic fine-grained dolomites, REE-Nb deficient coarse dolomites, carbonatitic dykes, limestones and dolostones. The Aird of Shin marble mineralogy comprises niobium and tantalum Ca-bearing oxides, scheelite, strontian barite, ilmenite, REE-bearing monazite, REE-epidote and Fe-Mo sulphides in an impure Na-Fe-K calcite fabric. The Arscaig Qtz-Na-K calc-silicates are enriched in REE-bearing monazite, Mg-Fe chlorite and Fe-oxides, with minor REE-bearing xenotime, Mn-Fe garnet and strontian barite. The REE-Nb Aird of Shin marble and the REE-phosphate bearing Arscaig calc-silicates are comparable with carbonatitic mineral phases in the Bayan Obo complex. This study adds support to previous recognition of Caledonian carbonatitic magmatism and carbonatitic metasomatism of Proterozoic limestones and calc-silicates in Scotland. 

How to cite: Heptinstall, E. and Parnell, J.: Carbonatitic REE-Nb-Fe mineralisation in the Palaeoproterozoic Shin Group marble and calc-silicates, Loch Shin, Scotland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1190, https://doi.org/10.5194/egusphere-egu21-1190, 2021.

EGU21-851 | vPICO presentations | GMPV5.2 | Highlight

Petrological and zircon chemical record of arc magma evolution from long-lived batholith construction to giant porphyry copper deposit formation 

Chetan Nathwani, Adam Simmons, Simon Large, Jamie Wilkinson, Yannick Buret, and Christian Ihlenfeld

Porphyry Cu ore deposits are a rare product of arc magmatism that often form spatiotemporal clusters in magmatic arcs. The petrogenetic evolution of igneous rocks that cover the temporal window prior to and during porphyry Cu deposit formation may provide critical insights into magmatic processes that are key in generating these systems. This study documents the magmatic evolution of the Palaeocene-Eocene Yarabamba Batholith, Southern Peru, that was incrementally assembled between ~67 and ~59 Ma and hosts three, nearly contemporaneous, giant porphyry Cu-Mo deposits that formed at 57-54 Ma (Quellaveco, Toquepala and Cuajone). Whole-rock geochemistry, U-Pb geochronology and zircon trace element chemistry are reported from Yarabamba rocks that span the duration of plutonic activity, and from six porphyry intrusions at Quellaveco that bracket mineralisation. A change in whole-rock chemistry in Yarabamba intrusive rocks to high Sr/Y, high La/Yb and high Eu/Eu* is observed at ~60 Ma which is broadly coincident with a change in vector of the converging Nazca plate and the onset of regional compression and crustal thickening during the first stage of the Incaic orogeny. The geochemical changes are interpreted to reflect a deepening of the locus of lower crustal magma evolution in which amphibole ± garnet are stabilised as early and abundant fractionating phases and plagioclase is suppressed. Zircons in these rocks show a marked change towards higher Eu/Eu* (>0.3) and lower Ti (<9 ppm) compositions after ~60 Ma. Numerical modelling of melt Eu systematics and zircon-melt partitioning indicates that the time series of zircon Eu/Eu* in these rocks can be explained by a transition from shallower, plagioclase-dominated fractionation to high-pressure amphibole-dominated fractionation at deep crustal levels from ~60 Ma. Our modelling suggests that any redox effects on zircon Eu/Eu* are subordinate compared to changes in melt composition controlled by the fractionating mineral assemblage. We suggest that growth and intermittent recharge of the lower crustal magma reservoir from ~60 Ma produced a significant volume of hydrous and metallogenically fertile residual melt which ascended to the upper crust and eventually generated the three giant porphyry Cu-Mo deposits at Quellaveco, Toquepala and Cuajone from ~57 Ma. Our study highlights the importance of high-pressure magma differentiation fostered by strongly compressive tectonic regimes in generating world-class porphyry Cu deposits.

How to cite: Nathwani, C., Simmons, A., Large, S., Wilkinson, J., Buret, Y., and Ihlenfeld, C.: Petrological and zircon chemical record of arc magma evolution from long-lived batholith construction to giant porphyry copper deposit formation , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-851, https://doi.org/10.5194/egusphere-egu21-851, 2021.

EGU21-249 | vPICO presentations | GMPV5.2

Metallogeny of the Zahedan-Nehbandan magmatic belt and implications to porphyry Cu exploration in southeastern Iran

Majid Soleymani, Shojaeddin Niroomand, Abdorrahman Rajabi, Thomas Monecke, and Soroush Modabberi

The Late Cretaceous to Eocene Sistan suture zone in southeastern Iran separates the Lut continental block in the west from the Afghan continental block in the east. A major belt of Oligocene to Miocene igneous rocks occurs between the cities of Zahedan and Nehbandan, stretching for ~200 km from south to north parallel to the border with Pakistan and Afghanistan. Known porphyry Cu mineralization is associated with the intrusions and intrusive complexes at Kuh-e Janja (16.5+2.0 Ma), Kuh-e Seyasteragi (19.2+ 1.4 Ma), Kuh-e Assagie (27.5+2.0 Ma), and Kuh-e Lar (32.8+3.0 Ma).

Small intrusions and intrusive complexes in the Zahedan-Nehbandan magmatic belt are mostly intermediate to felsic in composition and have calc-alkaline or shoshonitic affinities. Associated volcanic and volcaniclastic rocks are common. The igneous rocks are hosted by deformed late Cretaceous to Eocene flysch sequences that formed in the Sefidabeh forearc basin developed during the subduction and closure of the Sistan ocean. The geochemical composition of the intrusive rocks and their ages suggest that igneous activity and related mineralization in the Zahedan-Nehbandan magmatic belt may have formed as a result of post-collisional processes. The locations of the intrusive centers in the Kuh-e Assagie and Kuh-e Lar may be controlled by strike-slip faults, which are major post-collisional structures.

The recent discovery of the Janja porphyry Cu-Au-Mo deposit below Quaternary alluvial terraces highlights the exploration potential of the Zahedan-Nehbandan magmatic belt. In addition to post-collisional porphyry deposits, other deposit types such as skarns, polymetallic veins, or epithermal deposits may be hidden below the regionally extensive Quaternary cover.

How to cite: Soleymani, M., Niroomand, S., Rajabi, A., Monecke, T., and Modabberi, S.: Metallogeny of the Zahedan-Nehbandan magmatic belt and implications to porphyry Cu exploration in southeastern Iran, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-249, https://doi.org/10.5194/egusphere-egu21-249, 2021.

EGU21-3318 | vPICO presentations | GMPV5.2

The effect of the trisulfur radical ion on molybdenum transport by hydrothermal fluids

Maria A. Kokh, Clement Laskar, and Gleb S. Pokrovski

Knowledge of molybdenum (Mo) speciation under hydrothermal conditions is a key for understanding the formation of porphyry deposits which are the primary source of Mo. Existing experimental and theoretical studies have revealed a complex speciation, solubility and partitioning behavior of Mo in fluid-vapor-melt systems, depending on conditions, with the (hydrogen)molybdate (HMoO4-, MoO42-) ions and their ion pairs with alkalis in S and Cl-poor fluids [1-3], mixed oxy-chloride species in strongly acidic saline fluids [4, 5], and (hydrogen)sulfide complexes (especially, MoS42-) in reduced H2S-bearing fluids and vapors [6-8]. However, these available data yet remain discrepant and are unable to account for the observed massive transport of Mo in porphyry-related fluids revealed by fluid inclusion analyses demonstrating 100s ppm of Mo (e.g., [9]). A potential missing ligand for Mo may be the recently discovered trisulfur radical ion (S3•-), which is predicted to be abundant in sulfate-sulfide rich acidic-to-neutral porphyry-like fluids [10]. We performed exploratory experiments of MoS2 solubility in model sulfate-sulfide-S3•--bearing aqueous solutions at 300°C and 450 bar. We demonstrate that Mo can be efficiently transported by S3•--bearing fluids at concentrations ranging from several 10s ppm to 100s ppm, depending on the fluid pH and redox, whereas the available data on OH-Cl-S complexes cited above predict negligibly small (<100 ppb) Mo concentrations at our conditions. Work is in progress to extend the experiments to wider T-P-composition range of porphyry fluids and to quantitatively assess the role of S3•- in Mo transport by geological fluids.

  • 1. Kudrin A.V. (1989) Geochem. Int. 26, 87–99.
  • 2. Minubayeva Z. and Seward T.M. (2010) Geochim. Cosmochim. Acta 74, 4365–4374.
  • 3. Shang L.B. et al. (2020) Econ. Geol. 115, 661–669.
  • 4. Ulrich T. and Mavrogenes J. (2008) Geochim. Cosmochim. Acta 72, 2316-2330.
  • 5. Borg S. et al. (2012) Geochim. Cosmochim. Acta 92, 292–307.
  • 6. Zhang L. et al. (2012) Geochim. Cosmochim. Acta 77, 175–185.
  • 7. Kokh M.A. et al. (2016) Geochim. Cosmochim. Acta 187, 311–333.
  • 8. Liu W. et al. (2020) Geochim. Cosmochim. Acta 290, 162–179.
  • 9. Kouzmanov K. and Pokrovski G.S. (2012) Soc. Econ. Geol. Spec. Pub. 16, 573–618.
  • 10. Pokrovski G.S. and Dubessy J. (2015) Earth Planet. Sci. Lett. 411, 298–309.

How to cite: Kokh, M. A., Laskar, C., and Pokrovski, G. S.: The effect of the trisulfur radical ion on molybdenum transport by hydrothermal fluids, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3318, https://doi.org/10.5194/egusphere-egu21-3318, 2021.

EGU21-4813 | vPICO presentations | GMPV5.2

The occurrence of gold in Voia deposit, South Apuseni Mountains, Romania

Elena-Luisa Iatan

Voia deposit belongs to the Săcărâmb-Cetraș-Cordurea Miocene volcano-tectonic alignment of the South Apuseni Mountains, Romania. This large volcanic complex represents a Sarmatian-Pannonian magmatic-hydrothemal mega-system of around 5 km2 with an estimated 3–4 Ma time-space evolution, consisting of seven andesitic volcanic structures grouped in a circle, three subvolcanic andesite-quartz porphyry microdiorite and associated porphyry Cu-Au(Mo), pyrite Ca-Mg skarns and epithermal Au-Ag-Pb-Zn-Cu mineralizations.

The mineral assemblages of alteration and mineralization processes belong to several mineralized zones on a vertical scale, according to sampling evidence and laboratory studies. HS products are found in the upper part of the structure (300-500 m), with dominant advanced and intermediate argillic alterations and sulfide-sulfate gold-poor veins (pyrite, marcasite, base metal sulfides, Fe-Ti oxides, vuggy quartz, alunite, gypsum, anhydrite). Within the 500-1200 m depth, the HS mineral assemblages gradually decrease in favor of IS and LS products. It is characterized by the coexistence of gold-rich LS assemblage (native gold, base metal sulfide, adularia, sericite-illite, chlorite, carbonates ± anhydrite veins), with the IS assemblage (iron oxides, chalcopyrite, pyrite, quartz, anhydrite). These assemblages overprint the HS mineral associations, resulting in a transition zone characterized by gold - pyrite - chalcopyrite - iron oxides - quartz - anhydrite mineral assemblage characteristic for HS and native gold - pyrite - base metal sulfides - carbonates - quartz mineral assemblage corresponding to IS+LS type.

Gold is present in all of the identified mineralization forms: porphyry-epithermal Cu-Au, epi-mesothermal carbonate veins with gold - base metal sulfides, quartz veins with pyrite - chalcopyrite - magnetite ± hematite ± anhydrite, anhydrite veins with base metal sulfides and sulfosalts, anhydrite veins with pyrite - anhydrite ± quartz, vuggy quartz (silica residue) with gold-poor pyrite veins and impregnations in porphyry systems.

Drilling core samples revealed that in Voia deposit, gold is concentrated in chalcopyrite (drills no. 7, 19, 37) along with pyrite - magnetite - hematite - quartz assemblage from the late potassic stage. The major amount of gold associated with chalcopyrite tends to be mainly submicroscopic. Pyrite from anhydrite veins of the early potassic stage ± phyllic alteration is relatively poor in gold (drills no. 1-6, 8-14). However, the highest gold contents are present in pentagonal dodecahedron pyrites (drills no. 33, 38, 39) of pyrite-chalcopyrite-magnetite ± hematite-quartz assemblage from late potassic stage ± phyllic alteration. Pyrite associated with magnetite from anhydrite veins tends to be poor in gold (drills no. 8, 11, 15, 28, 29). A carbonate vein containing gold-bearing base metal sulfides that was intercepted at 960,00-960,30m depth by drill no. 17 is one of the richest in gold.

Native gold occurs as fine inclusions in ore minerals (5-20 μm). Large irregular grains of native gold (>50 μm) appear at mineral boundaries and along the fissures. The gold color is bright yellow and has a measured Au:Ag ratio of 5:1, suggesting that native gold has been formed at a relatively high temperature.

Acknowledgments: This work was supported by two Romanian Ministry of Research and Innovation grants: PN-III-P4-ID-PCCF-2016-4-0014 and PN-III-P1-1.2-PCCDI-2017-0346/29.

How to cite: Iatan, E.-L.: The occurrence of gold in Voia deposit, South Apuseni Mountains, Romania, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4813, https://doi.org/10.5194/egusphere-egu21-4813, 2021.

EGU21-11150 | vPICO presentations | GMPV5.2

Gold fingerprint of the SCLM beneath a metallogenic province

Erwin Schettino, Claudio Marchesi, José María González-Jiménez, Edward Saunders, Károly Hidas, Fernando Gervilla, and Carlos Jesús Garrido

Magmatic-hydrothermal gold deposits form clusters in the Earth’s crust and are heterogeneously distributed within lithospheric blocks. A global assessment of whole-rock gold abundances in mantle lithologies worldwide indicates that Au concentrations increase with increasing fertility of mantle peridotites, with median Au contents ranging from 0.50 ppb in dunites, 1.00 ppb in harzburgites, and up to 1.26 ppb in lherzolites. Of particular interest are those volumes of fertile Subcontinental Lithospheric Mantle (SCLM) veined by pyroxenites and wehrlites, usually the Au-richest lithologies in the mantle as they have 2.05 ppb median Au concentrations. Partial melting of SCLM domains endowed in gold seems to play a key role in the genesis of gold-enriched magmas parental to magmatic-hydrothermal gold deposits in continental arc settings. The mineralogical expressions of gold inventory in such fertile mantle rocks are accessory Ni-Fe-Cu sulfides and discrete micron-to-nano-sized Au mineral particles that control the extraction and transport of gold in the mantle. Mantle xenoliths from the Neogene Volcanic Province (NVP) of southeast Spain represent an excellent example of SCLM refertilized by gold-sulfide-rich silicate melts underlying a gold metallogenic province. Here we present mineralogical and compositional data of sulfides in mantle xenoliths from this area (Tallante volcanic center), which are anomalously rich in gold (up to 46 ppm) compared to sulfides from SCLM not associated with Au-metallogenic provinces. We propose that these gold-rich, fertile mantle sources may have melted during the Cenozoic evolution of the westernmost Mediterranean subduction system and fed the ore-productive volcanic activity in southeast Spain.

How to cite: Schettino, E., Marchesi, C., González-Jiménez, J. M., Saunders, E., Hidas, K., Gervilla, F., and Garrido, C. J.: Gold fingerprint of the SCLM beneath a metallogenic province, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11150, https://doi.org/10.5194/egusphere-egu21-11150, 2021.

EGU21-12132 | vPICO presentations | GMPV5.2

Ore fluid characteristics at Gadag Gold Field, Dharwar Craton, southern India: Evidences from tourmaline chemistry and fluid inclusion study

Debasis Pal, Sakthi Saravanan Chinnasamy, and Sukumari Rekha

Dharwar Craton in southern India hosts several gold bearing greenstone belts including the well-known Kolar and Hutti. Among them, the Gadag greenstone belt in the western part of Dharwar Craton contains many potential gold mines. It has three different lode systems named western, central and eastern lodes. These lodes are spatially distributed as linear groups along the shear zone with distinct lithological assemblages. Tourmaline is one of the most common hydrothermal minerals present in the alteration zones apart from chlorite, muscovite and sericite. These tourmalines show two textural association (i) occur as isolated, euhedral grains along the mylonitic foliation defined by chlorite, muscovite, sericite, quartz and carbonates (ii) occurrences of anhedral bizarre shaped tourmaline grains along with carbonate and quartz. Though texturally different, compositionally both the tourmalines are similar. They are dravite in nature with high Altot (6.02 to 6.56 apfu), low Na (0.42 to 0.88 apfu) and medium X-vacancies (0.08 to 0.57 apfu). The predominance of Fe2+ (high Fe2+/Fe3+) and low Na in the tourmaline crystal structure indicates low saline, reduced ore fluid of metamorphic origin that is responsible for gold mineralization in Gadag.

Microthermometric study of aqueous, carbonic and aqueous-carbonic inclusions from the auriferous lodes at Gadag reveal low to medium saline (0.04 to 9.59 NaCl equiv.)  H2O-NaCl-CO2±CH4 ore forming fluid. Presence of trace amount of methane content within the carbonic inclusion indicates mineralization occurred at reducing environment. Thus, fluid inclusion results consistent with the tourmaline chemistry and strongly supports the metamorphic origin of ore fluids that responsible for gold mineralization at Gadag.

How to cite: Pal, D., Chinnasamy, S. S., and Rekha, S.: Ore fluid characteristics at Gadag Gold Field, Dharwar Craton, southern India: Evidences from tourmaline chemistry and fluid inclusion study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12132, https://doi.org/10.5194/egusphere-egu21-12132, 2021.

EGU21-14847 | vPICO presentations | GMPV5.2

Ore-controlling dike complexes of the gold-rare metal deposit Vladimirskoe (Eastern Sayan)

Brian Nharara, Eugenia Airiyants, Ol'ga Kiseleva, Dmitriy Belyanin, Petr Roshchektaev, and Sergey Zhmodik

Vladimirskoe gold-rare metal deposits are located in the Urik-Kitoiskaya gold zone, at the edges of the Neoarchean age Gargan microcontinent, in the southeastern part of the Eastern Sayan. Gold mineralization is localized in sheared, beresitised mineralized zones among granite gneiss of the Gargan Group (NARg). The width of the zones is 3-10 m and the length is up to 800 m. The material composition of the ores is sulfide-carbonate-quartz. The main ore minerals are pyrite, chalcopyrite, pyrrhotite, galena, sphalerite, as well as tellurides and sulfosalts of silver, lead, and bismuth. The main minerals at the deposit are gold, associated - silver, and bismuth, associated with sulfide mineralization. Average gold grades in ores are 7-12 g / t.

Mineralized ore zones are associated with faults, and are often localized at their intersection with dike complexes. Several fault systems are identified in the deposit. The first-order fault system is a right-lateral dip-slip with a submeridional strike. The second-order system has a northwest strike and represents zones of viscous faults, expressed by zones of cleavage, beresitisation, silicification, and sulfidization, which are associated with gold mineralization.

There are two types of dike complexes within the region. The first dike complex of the barun-holba subvolcanic complex (O-S) has basic composition. Dikes are widespread throughout the entire area and are characterized by diabase porphyrites, metabasalts, and more rarely, basaltic andesite porphyrites. The rocks have a porphyry structure with phenocrysts (1-3 cm) characterized by plagioclase, altered to form epidote and muscovite. Large porphyry segregations up to 10 cm, bearing traces of deformation processes are observed in some cases. The groundmass has a fine-grained, microlepidogranoblastic structure and is composed of a secondary epidote-chlorite-albite aggregate.

The second dike complex is less pronounced and is characterized by felsic dikes belonging to the Early Paleozoic Holba complex. It is located in the southeastern part of the region and is characterized by granite-porphyries, leucocratic pegmatoid granites, and dacites. Dikes of felsic composition have a felsic structure caused by microliths of albitised plagioclase, biotite, and secondary minerals (chlorite, epidote, amphibole, calcite).

Dikes and dike belts are the ore-controlling structures of gold mineralization. In intersecting zones of a northwestern strike, gold mineralization is concentrated near dikes and gradually fades away as we move from them. The greatest development of mineralized zones and the associated quartz-vein ore mineralization can be observed at the intersection of fault zones with dikes. In this case, ore columns with a thickness of 20-50 m formed, extending to a depth of 3 km. Vladimirskoe deposits belong to vein-dike ore-magmatic systems, their source of ore matter is of deep origin.

This work is supported by RFBR grants: No. 19-05-00764 and the Russian Ministry of Education and Science. 

References:

Gordienko I.V. et al., // Geology Ore Deposits. 2016. V. 58, № 5, P. 405-429.

Seminsky Zh. V. et al. // Proceedings of the Siberian Branch of the Section of Earth Sciences of the Russian Academy of Sciences. T. 45, N. 2. 2014. P. 19-34.

How to cite: Nharara, B., Airiyants, E., Kiseleva, O., Belyanin, D., Roshchektaev, P., and Zhmodik, S.: Ore-controlling dike complexes of the gold-rare metal deposit Vladimirskoe (Eastern Sayan), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14847, https://doi.org/10.5194/egusphere-egu21-14847, 2021.

EGU21-2806 | vPICO presentations | GMPV5.2

Shear zone development and structurally-controlled skarn ore mineralization in the Rosas district, SW Sardinia.

Matteo Luca Deidda, Antonio Attardi, Fabrizio Cocco, Dario Fancello, Antonio Funedda, and Stefano Naitza

The Rosas Shear Zone (RSZ) is a 1 km thick brittle-ductile shear zone that outcrops in the Variscan fold and thrust belt foreland of SW Sardinia, where several important ore deposits were mined in the last century. The RSZ lies in the footwall and strikes parallel to the NE-dipping regional thrust that separates the Variscan foreland from the nappe zone. Two thrusts that developed along the limbs of two km-scale overturned antiforms, with NE-dipping axial plane, bound the RSZ. The folds show a SW-facing direction and a well-developed axial plane cleavage, and affect a lower Cambrian-upper Ordovician stratigraphic succession mainly made, from bottom to top, by a sequence about 200 m thick of dolostones and massive limestone followed by 50 m of marly limestones overlain by about 150 m of sandstones, pelites and siltstones, finally unconformable capped by conglomerates and siltstones, ranging in thickness from a few to 200 m. Differently, within the RSZ the bedding is completely transposed along the cleavage and its internal structure is characterized by anastomosing thrusts that affect the stratigraphic succession defining map-scale slices mainly consisting of dolostones and limestones embedded into the siliciclastic formations. It is noteworthy the occurrence of a NE-dipping, up to 100 m thick gabbro-dyke that postdates the deformation phases and that can be related to the exhumation of the chain during late Carboniferous-Permian times.

In the whole area, contact metamorphic and metasomatic processes selectively affected the Cambrian carbonate tectonic slices, originating several skarn-type orebodies. Mineralized rocks display the mineralogical assemblages and textures of Fe-Cu-Zn skarns, with relicts of anhydrous calcic phases related to the prograde metamorphic stage (garnet, clinopyroxene, wollastonite), frequently enclosed in a mass of hydrous silicates (actinolitic amphibole, epidote) and magnetite related to the retrograde metasomatic stage, in turn followed by chlorite, sulfides, quartz and calcite associated to the hydrothermal stage. Metasomatic reactions also involved mafic rocks, producing a mineral association marked by clinopyroxene, amphibole, epidote, prehnite and Ba-rich K-feldspar. Sulfide ores are made of prevailing sphalerite, chalcopyrite and galena, with abundant pyrite and pyrrhotite and minor tetrahedrite and Ag-sulfosalts. Garnets are andraditic/grossularitic, distinctly zoned and optically anisotropic. Field surveys pointed out the tight structural controls on skarn and ore formation. On a local scale, the gabbro emplacement along high- to low-angle NNW-SSE structures bordering the carbonate tectonic slices accentuate the effects of contact metamorphism, and metric to decametric mineralogical zonation (garnet→pyroxene→wollastonite) are recognized. On a larger scale, extensive hydrothermal fluid circulations involved the structures of the RSZ. Infilling of metasomatic fluids in carbonate tectonic slices is fault-controlled and aided by the increase in permeability due to the alteration of prograde silicates. The causative intrusion related to skarn ores belongs to the early Permian (289±1 Ma) ilmenite-series, ferroan granite suite which intrudes the RSZ about 3 km east from the studied area. The Fe-Cu-Zn skarn ores of Rosas are best interpreted as distal, structurally-controlled orebodies, connected to large-scale circulation of granite-related fluids in the km-sized plumbing system represented by the RSZ.

How to cite: Deidda, M. L., Attardi, A., Cocco, F., Fancello, D., Funedda, A., and Naitza, S.: Shear zone development and structurally-controlled skarn ore mineralization in the Rosas district, SW Sardinia., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2806, https://doi.org/10.5194/egusphere-egu21-2806, 2021.

EGU21-1584 | vPICO presentations | GMPV5.2

Constraining the time-span of magmatic-hydrothermal activity in the Variscan Orogenic Belt – U-Pb geochronology of skarn-related garnet from the Schwarzenberg district, Erzgebirge, Germany

Nils Reinhardt, Axel Gerdes, Aratz Beranoaguirre, Max Frenzel, Lawrence D. Meinert, Jens Gutzmer, and Mathias Burisch

Europe´s major Sn and W resources are hosted by magmatic-hydrothermal ore deposits of the Variscan Belt: e.g. in Cornwall, the Erzgebirge, the Iberian Massif, and the French Massif Central. In the Erzgebirge, several major skarn bodies are located in the Schwarzenberg district (12 x 15 km). Although recent geochronological data relates (skarn) ore-formation to late- and post-orogenic magmatic-hydrothermal activity, details on the nature and duration of mineralization events remain insufficiently understood.

In this study we present innovative in-situ LA-ICP-MS U-Pb geochronology of garnet from several skarn prospects in the Schwarzenberg district, which is complemented with available geochronological data on intrusions and mineralization in order to constrain the timing of skarn formation within the Variscan orogenic cycle.

Eighteen garnet dates range from 338.2 ± 2.5 to 294 ± 8.3 Ma. Associated errors are in the range of 2.5 to 8.4 Ma, but generally tend to be <7 Ma. The oldest ages (338-331 Ma, stage I) are related to metasomatic garnets of the Globenstein skarn (n=5) – a skarn that is exceptionally enriched in W compared to the other skarn prospects in the same district. Conversely, the other skarns (Antonsthal, Breitenbrunn, Hämmerlein) are younger and range from 327 to 313 Ma (stage II) and 304 to 294 Ma (stage III), respectively. Stage I and II garnets lie within the range of available zircon ages of major intrusive bodies in this area (Aue-Schwarzenberg granite suite: 334-322 Ma; Eibenstock granite: 326-311 Ma). The third stage, in contrast, does not overlap with the age of any known granite intrusions in the Schwarzenberg district. However, it coincides with widespread early Permian volcanic rocks, which presumably have intrusive roots that are not yet exposed in the Erzgebirge region.

The distribution of garnet ages implies that skarn formation occurred episodically during the ~45 Ma life-time of the Variscan orogen, with the onset of magmatic-hydrothermal activity occurring significantly earlier than previously assumed – at 338 Ma, immediately after the peak of regional metamorphism. Tin and W deposits (skarn, greisen and vein-type) seem to have formed episodically over the entire 45 Ma orogenic cycle of the Erzgebirge – this is consistent with the age range of available geochronological data related to magmatic-hydrothermal ore deposits from other internal parts of the European Variscan Belt.

How to cite: Reinhardt, N., Gerdes, A., Beranoaguirre, A., Frenzel, M., Meinert, L. D., Gutzmer, J., and Burisch, M.: Constraining the time-span of magmatic-hydrothermal activity in the Variscan Orogenic Belt – U-Pb geochronology of skarn-related garnet from the Schwarzenberg district, Erzgebirge, Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1584, https://doi.org/10.5194/egusphere-egu21-1584, 2021.

EGU21-2137 | vPICO presentations | GMPV5.2

Spatiotemporal zonation of the Freiberg Ag-Pb-Zn-(Cu) epithermal system

Laura Swinkels, Jan Schulz-Isenbeck, Max Frenzel, Jens Gutzmer, and Mathias Burisch

The Freiberg district, located in the eastern part of the Erzgebirge, Germany, hosts one of the largest series of epithermal polymetallic vein deposits in Europe. The present study aims to decipher mineralogical and geochemical zoning on the vein- and district-scale and to constrain the underlying ore-forming processes. Detailed petrographic investigations, geochemical analyses and fluid inclusion studies are carried out on several vertical vein profiles within the Freiberg district in order to develop a district-scale metallogenic model. Five different mineral associations related to Permian magmatic-hydrothermal activity have been recognized within the Freiberg epithermal vein system exhibiting a distinct district-scale and vein-scale zonation. The central part of the Freiberg district is dominated by sphalerite-pyrite-quartz and galena-quartz±carbonate associations with a mean silver grade of 769 g/t (n=65). Similar base metal-rich assemblages also predominate the deepest vein intersections (>300 m below ground level) in the peripheral sectors of the Freiberg District. Vein infill at intermediate depth and peripheral positions in the district is, in contrast, dominated by a sphalerite-Ag-sulfides-carbonate association. This association is marked by an abundance of carbonate gangue and significantly higher silver grades (mean = 4800 g/t; n=25). Veins in the shallowest and most peripheral parts (depth <150 m b.g.l.) of the Freiberg district are dominated by a Ag-sulfide-quartz association with a mean Ag concentration of 4900 g/t (n= 56). Silver is mainly hosted by sulfosalts and fahlore but significant concentrations may also be associated to Ag-sulfide inclusions in galena. Even shallower, the veins comprise a stibnite-quartz association with distinctly low Ag contents (410 g/t Ag, n=4). Fluid inclusions related to the various associations yield consistent salinities in the range of 0.1 to 6.0 % eq. w(NaCl). The homogenization temperature, however, progressively decreases from about 320°C for quartz associated with proximal sphalerite-pyrite-quartz mineralization, down to ~170°C for quartz related to distal Ag-sulfide-quartz association. The general formation of the Freiberg epithermal veins is related to the continuous evolution of a magmatic-hydrothermal system in time and space. Silver deposition is most likely triggered by boiling and associated cooling and volatile-loss, which results in a distinct carbonate horizon (typically at ~500 m depth b.g.l. for peripheral parts) with significantly elevated Ag grades (sphalerite-Ag-sulfides-carbonate association).

How to cite: Swinkels, L., Schulz-Isenbeck, J., Frenzel, M., Gutzmer, J., and Burisch, M.: Spatiotemporal zonation of the Freiberg Ag-Pb-Zn-(Cu) epithermal system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2137, https://doi.org/10.5194/egusphere-egu21-2137, 2021.

EGU21-3156 | vPICO presentations | GMPV5.2

LA-ICP-MS U-Pb geochronology of carbonates from Ag-Bi-Co-Ni-As±U veins in the Erzgebirge (Germany and Czech Republic): New insights into the timing of mineralization

Marie Guilcher, Richard Albert, Axel Gerdes, Jens Gutzmer, and Mathias Burisch

Hydrothermal Ag-Bi-Co-Ni-As±U (five-element) veins are particularly prevalent across Central Europe, where this type of mineralization has been mined throughout the ages for its high-grade resources of Ag, Co, Ni, and U. The timing and the detailed geodynamic setting in which this style of mineralization formed remains, however, insufficiently understood due to the limited amount of geochronological data. In this contribution, we report the results of innovative LA-ICP-MS U-Pb geochronology on the carbonate gangue of Ag-Bi-Co-Ni-As±U mineralization from six districts in the Erzgebirge/Krušné Hory metallogenic province of Germany and the Czech Republic, with the goal to constrain the timing of ore formation in the context of Central Europe's geodynamic framework.

In-situ U-Pb ages of twelve samples, including dolomite-ankerite, calcite, and siderite cogenetic with Co-Ni-Fe-arsenides, range from 129.4 ± 8.2 to 85.93 ± 3.4 Ma. The ages of Ag-Bi-Co-Ni-As±U and fluorite-barite-Pb-Zn veins from the same occurrence (Annaberg-Buchholz district) overlap each other, suggesting that these two styles of mineralization are genetically related and may form coevally. The compilation of geochronological data from other Ag-Bi-Co-Ni-As±U occurrences in Europe suggests that the origin of this style of mineralization in Central Europe can be related to continental rifting associated with the Mesozoic opening of the Atlantic and/or the Alpine Tethys (200-100 Ma). This provides for the first time evidence for the formation of Ag-Bi-Co-Ni-As±U vein mineralization across Central Europe in response to continental rifting.

How to cite: Guilcher, M., Albert, R., Gerdes, A., Gutzmer, J., and Burisch, M.: LA-ICP-MS U-Pb geochronology of carbonates from Ag-Bi-Co-Ni-As±U veins in the Erzgebirge (Germany and Czech Republic): New insights into the timing of mineralization, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3156, https://doi.org/10.5194/egusphere-egu21-3156, 2021.

EGU21-15930 | vPICO presentations | GMPV5.2

Quantitative texture analysis of alluvial gold: primary and secondary signatures

Juan Gómez-Barreiro, Santos Barrios-Sánchez, José Manuel Compaña Prieto, Juan Morales Sánchez-Migallón, Kelvin dos Santos Alves, Magdalena Tettamanti, and Inés Puente Orench

The origin of gold nuggets (Au‐Ag alloys) is not completely understood. They crop out in placer deposits, potentially derived from a primary source (hydrothermal/magmatic). Meteorization, erosion and transport of primary gold deposits result in the liberation of a variety of particle size. Recent investigations suggest that both primary and secondary microstructural features may be preserved and could be related to deformation during transport, recrystallization and primary formation. Besides, the contribution of biological mechanisms (biomineralization) may have played an important role during secondary growth in some nuggets. In many cases, there is no clear evidence to distinguish between supergenic and hypogenic gold, so texture information could be excellent information to constrain the origin. Besides, it has been demonstrated that crystallography controls the de‐alloying processes in gold nuggets. This mechanism, that transforms the primary Au–Ag alloys into pure gold by preferential dissolution of Ag along crystal boundaries, could be determined by variations on texture, a factor never explored before, which may explain the dispersion in de‐alloying values in the same deposit.

 

In this case we have explored a selection of gold nuggets collected in the W sector of the Iberian Massif (Spain), representing the principal morphological types. As a non-destructive technique neutron diffraction appears as the technique of choice in this case. Beside, neutrons absorption is very low so that large samples could be investigated. Samples were analyzed in transmission at ILL (Grenoble) for texture. Quantitative texture and gold crystallinity was calculated using Rietveld method as implemented in Maud software (EWIMV). Mono- and polycrystalline nuggets and alloy composition were clearly identified in each particle with this technique. Our results show a close correlation between the morphology (i.e. transport length) of the particle and the crystallographic results, particularly for fibrous and discoid shapes (i.e. Zingg, Corey shape factor), what could be used to develop better transport models (distance-to-bedrock sources) and understand multisource gold placer assemblages. 

How to cite: Gómez-Barreiro, J., Barrios-Sánchez, S., Compaña Prieto, J. M., Morales Sánchez-Migallón, J., dos Santos Alves, K., Tettamanti, M., and Puente Orench, I.: Quantitative texture analysis of alluvial gold: primary and secondary signatures, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15930, https://doi.org/10.5194/egusphere-egu21-15930, 2021.

EGU21-12077 | vPICO presentations | GMPV5.2

Primary and Secondary Gold Sources of Quaternary Placers of Western Spain: a Morphotextural and Compositional Analysis of the Fresnedoso Deposit.

Kelvin Dos Santos Alves, Santos Barrios Sánchez, Juan Gómez Barreiro, Raul Merinero Palomares, Rafael Pablo Lozano Fernández, and José Manuel Compaña Prieto

In this contribution we have investigated the Fresnedoso Quaternary gold placer (Western Spain), analyzing the morphotextural and microchemical evolution of gold particles. The statistical analysis has revealed the presence of two populations of particles being consistent with primary sources situated at a distal [20 - 50 km] and a proximal [2.5 - 10 km] range. The gold morphology and chemistry point to a recycling (and potentially undiscovered) Tertiary paleoplacers. The discovery of primary laminar morphologies points to lode deposits in small-flat veins hosted in Precambrian metasediments (Schist Greywacke Complex). All these findings suggest that the Fresnedoso gold deposit is formed by mono and polycyclic particles. We have tested previous transport distance vs Flattening indexes (CFI, Shilo) models resulting in useful framework for exploration of undiscovered ores, even with a small sample dimension. Chemical analysis of the different gold morphologies depicted that the Fresnedoso gold is a AuAg bimetallic alloy. Three groups were identified based on the texture and composition of the gold particles: Type 1 (Au1= Au89-94Ag11-6), Type 2 (Au2= Au99 Ag1) and Type 3 (Au3~ Au >99). Particle's cores (gold Type 1) show a compositional range that could be interpreted as differences in primary sources, spatial dispersion of sources or the actuation of secondary processes, probably in an orogenic gold context. Microchemical heterogeneity in the particles is probably due to secondary processes. A conceptual model has been elaborated to explain particle's microchemical domains represented by gold Type 2 (rim) and Type 3 (micro-aggregates) as the result of two different de-alloying stages: A) initial Ag-leaching at the rim and/or through microcracks and grainboundaries (Type 2), B) Total reset of the primary chemical fingerprint, with porous microtexture and the precipitation of gold with iron oxyhydroxides and clays (Type 3). This model suggests a silver de-alloying mechanism favored in a chlorine-iron-rich environment as in the case of laterites. Deformation and eventually recrystallization mechanisms associated with the fluvial transport (mechanical cold-work), cooperated in the evolution of the particles (Dos Santos et al. 2020).

References 

Dos Santos Alves, K., Barrios Sánchez, S., Gómez Barreiro, J., Merinero Palomares,R. and Compaña Prieto, J.M. (2020). "Morphological and compositional analysis of alluvial gold: The Fresnedoso gold placer (Spain)." Ore Geology Reviews : 103489.

How to cite: Dos Santos Alves, K., Barrios Sánchez, S., Gómez Barreiro, J., Merinero Palomares, R., Pablo Lozano Fernández, R., and Manuel Compaña Prieto, J.: Primary and Secondary Gold Sources of Quaternary Placers of Western Spain: a Morphotextural and Compositional Analysis of the Fresnedoso Deposit., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12077, https://doi.org/10.5194/egusphere-egu21-12077, 2021.

EGU21-13358 | vPICO presentations | GMPV5.2 | Highlight

Tracing gold nuggets back to the source: a microchemical analysis of tertiary gold placers in Central Spain.

Santos Barrios, Juan Gómez Barreiro, Rafael Pablo Lozano Fernández, Raúl Merinero Palomares, Mercedes Suárez Barrios, Kelvin dos Santos Alves, Juan Morales Sánchez-Migallón, and Jeremi Malecki

Gold placers are abundant and intensively surveyed in western Iberia since antiquity. Three Cenozoic gold placers covering Neoproterozoic-Lower Paleozoic basement rocks have recently been revealed, which stand out for the number and size of the samples recovered: Salvatierra de Tormes (ST), Santibáñez el Alto (SA) and Casas de Don Pedro-Talarrubias (CSDP). To date, primary sources remain undiscovered. We have combined microchemical, inclusion analysis and morphology of gold nuggets to define the placer gold signature and its relationship with bedrock primary sources and infer mineralization styles. Coarse gold particles prevent secondary resetting of source signature and increase the chances to investigate mineral assemblages. Nuggets morphology analysis have reveled that ST and SA deposit are fluvial "trunk" placers, while CSDP represents an autochthon or colluvial placer type. Four different types of gold have been defined in nuggets: core gold (T1), rim gold (T2) fine grained gold in Fe-oxyhydroxides aggregates (T3) and "mustard" gold (Au+Sb-Pb-Fe-oxides) (T4).

Based on those categories we have explored primary and secondary signatures in the deposits. Lode signature is observed in the core of nuggets (T1) with a fineness between 800 and 1000. Alloy composition ranges from binary (Au:Ag) in SA to ternary (Au:Ag:Cu) in ST and CSDP. Sulphides and sulfarsenides dominates inclusions association in ST, while Sb- and Sb-Pb-Fe phases appear in ST and CSDP respectively. CSDP primary gold shows a distinct Hg content. The identification of mineral phases non-compatible with supergene conditions in gold and textural remnants of annealing microstructures, point to an hypogenic origin of T1 in all deposits and coul be compatible with a mesothermal system (<400ºC) in which, CSDP represents the higher T and SA the lower T end. A hybrid hydrothermal-magmatic system is proposed.

Secondary signature is complex and reveals several stages. Older evidence of in-situ modification of primary gold was found in CSDP gold-bearing quart fragments, with pervasive alteration under oxidizing and alkaline conditions. This process liberated gold from T1 and primary phases (e.g., aurostibite), leading to the formation of auroatimonades and "mustard" gold (T4), showing a complex textural pattern. Gold particles were subsequently modified during fluvial transport and deposition through the interaction with fluids, which activated Ag-leaching processes, resulting in the development of gold-rich rims (T2). Partial dissolution and re-precipitation of gold in reduction conditions formed very fineness gold particles embedded in Fe oxy-hydroxides (T3).

How to cite: Barrios, S., Gómez Barreiro, J., Lozano Fernández, R. P., Merinero Palomares, R., Suárez Barrios, M., dos Santos Alves, K., Morales Sánchez-Migallón, J., and Malecki, J.: Tracing gold nuggets back to the source: a microchemical analysis of tertiary gold placers in Central Spain., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13358, https://doi.org/10.5194/egusphere-egu21-13358, 2021.

EGU21-905 | vPICO presentations | GMPV5.2

Geochemical characteristics of Croatian prospective Bauxite deposit Mamutovac

Dominik Teskera, Hana Fajković, Nikolina Ilijanić, Nenad Tomašić, Nikola Gizdavec, Čobić Andrea, and Miko Slobodan

High demand for specific chemical elements from the group of rare earth elements (REE) has led to a detailed prospection and geochemical analysis of a previously known but unexploited bauxite deposit. The Upper Eocene karst bauxite within exploitation field Mamutovac, located in the municipality of Promina in the Dalmatian Hinterland (Croatia), is such a deposit, with estimated reserves of 112,000 tone.

In order to determine REE distribution pattern in the Mamutovac Ia deposit, a 25meter core was obtained by exploration drilling, down to the deposit footwall that is composed of Upper Cretaceous rudist limestone. For this study 23 subsamples were singled out, on average, per each meter of a core. 

The degree of lateritization is determined by the Al2O3–SiO2–Fe2O3 composition diagram (after Schellman, 1986), and lateritization varies from moderate to strong, with a lower degree of lateritization in a lower part of the core, down from 15 m.  Two different genetic classification systems indicate the origin of the bauxite is mafic, basaltic igneous rocks.            

Main mineral phases in the bauxite core samples were determined using X-ray powder diffraction (XRPD) analysis. The mineral phases through the whole core are similar, with boehmite, gibbsite, hematite, and anatase as the main phases. Additional mineral phases determined in the core are kaolinite, goethite, and rutile. 

Results of geochemical analysis obtained by inductively coupled plasma emission/mass spectrometry (ICP-ES/MS) indicate an inhomogeneous distribution of REE through the core, with two main trends: from 0-15m and from 15-25m, with some elevation of REE abundances in the lower part of the core. In the upper part of the core,  total REE content (∑REE), including Y and Sc, ranges between 352 and 630 ppm (average 500 ppm) and light REE (La-Sm) to heavy REE (Eu-Lu) (∑LREE/∑HREE) ratios reach up to 10.2. For lower part ∑REE (including Y and Sc) ranges between 569 and 813 ppm (average 676 ppm) and light REE (La-Sm) to heavy REE (Eu-Lu) (∑LREE/∑HREE) ratios are up to 9.82. Singificant enrichment of LREE compared to HREE is present due to the fact that HREE are highly mobile in an alkalic karst environment and consequently removed through drainage channels. The most abundant REE is Ce. Within interval, 0-15m Ce ranges between 149.3-264.9 ppm (average 210.7 ppm), while within the interval 15-25m Ce ranges 152.7-301.7 ppm (average 219.56 ppm).

Correlation analysis shows no correlation between Sc and other REE and no significant correlation between Ce and other REE or potential bearing oxides. The correlation between Sc and Al2O3 or Fe2O3 suggests that Sc is likely bound to Al-oxyhydroxides and Fe-oxyhydroxides. Correlation between REE (Sc free) and P2O5 indicates REE (Sc free) are probably contained in REE-bearing phosphates. 

This activity has received funding from the European Institute of Innovation and Technology (EIT), a body of the European Union, under the Horizon 2020, the EU Framework Programme and Research and Innovation.

How to cite: Teskera, D., Fajković, H., Ilijanić, N., Tomašić, N., Gizdavec, N., Andrea, Č., and Slobodan, M.: Geochemical characteristics of Croatian prospective Bauxite deposit Mamutovac, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-905, https://doi.org/10.5194/egusphere-egu21-905, 2021.

EGU21-11122 | vPICO presentations | GMPV5.2

Tauride Carbonate Platform Bauxite Deposits (Turkey) as an Alternative Source for Gallium

Hatice Nur Bayram, Ali Erdem Bakkalbasi, Zeynep Doner, Ali Tugcan Unluer, Huseyın Kocaturk, Demet Yıldırım, and Murat Budakoğlu

Mediterranean type karstic bauxite deposits are considered as the primary source for aluminum (Al) production in Europe. During the Al production, Gallium (Ga) is extracted from the so called Bayer-liquor during the processing of bauxite to alumina. Ga, a rare metal, is widely used in modern chemistry and electronic industry. During the past decades, the worldwide demand for Ga has been continuously increasing. In Turkey, karstic bauxite deposits are generally found with shallow marine carbonate rocks which were deposited during Mesozoic period and located in Tauride Carbonate platform. Most of these karstic bauxite deposits can be hosted considerable Ga enrichments, with other immobile elements such as rare earth elements (REE), titanium (Ti), lithium (Li), and iron (Fe). This work focuses on the revealing of the potential Ga enrichments in bauxides from different deposits of Turkey (Mortaş-Doğankuzu, Konya; Küçükkoraş, Karaman; Acıelma-Yoğunoluk, Kahramanmaraş bauxite deposits). Geochemical data of major and trace elements of studied bauxite deposits show that these deposits have significant Ga enrichments (up to 72.6 ppm), as well as the REE (up to 580 ppm), Ti (up to 1.8%), and Li (up to 428 ppm) enrichments. In addition, the Ga enrichments show strong positive correlation with heavy rare earth elements (HREE) and moderate positive correlation with Al, Fe, Ti, Li and Sn elements. In this context, it can be concluded that the most probable source for Ga is rock forming aluminosilicates of the source rock due to the substitution with Al3+ and Fe3+. During weathering process Ga exhibiting immobile behavior much like Al and Fe. Gallium is than incorporated into Al-bearing phases and thus enriched in the bauxite. Presence of Li content can be also interpreted as a contribution from micaceous source such as meta-carbonate rocks of Tauride platform. Moreover, geochemical association between Ga, Ti, Li, tin (Sn) and HREE can be explained by the redox and pH conditions causing other ions seperated from shallow environments.

How to cite: Bayram, H. N., Bakkalbasi, A. E., Doner, Z., Unluer, A. T., Kocaturk, H., Yıldırım, D., and Budakoğlu, M.: Tauride Carbonate Platform Bauxite Deposits (Turkey) as an Alternative Source for Gallium, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11122, https://doi.org/10.5194/egusphere-egu21-11122, 2021.

GMPV6.1 – From the nano- to the orogen-scale: metamorphism, deformation and fluid-rock interaction

EGU21-425 | vPICO presentations | GMPV6.1 | Highlight

Serpentine crack-seal veins: a unique record of fluid conditions during faulting

Matthew S. Tarling, Steven A.F. Smith, Jeremy S. Rooney, Cecilia Viti, and Keith C. Gordon

Serpentine veins are ubiquitous in hydrated and deformed ultramafic rocks, and have previously been used to track fault kinematics and understand the evolution of environmental conditions during vein formation. However, difficulties in unambiguously identifying and mapping serpentine types at sub-micron to mm scales has limited our understanding of vein precipitation kinetics and growth histories. Using recently developed techniques of Raman spectroscopy mapping, combined with scanning- and transmission-electron microscopy, we describe a new type of mineralogically banded serpentine crack-seal vein in six samples from different settings around the world. In all of the studied samples, individual bands comprise a thin layer (~0.4–2 µm) dominated by chrysotile and a much thicker layer (~0.5–30 µm) dominated by polygonal serpentine/lizardite. Existing field and experimental data suggest that disequilibrium conditions immediately following crack opening may favour rapid precipitation of chrysotile along one of the crack margins. Subsequently, diffusional transport of elements favours slower precipitation of polygonal serpentine/lizardite which leads to crack sealing. The similarities in layer thicknesses and mineralogy exhibited by samples collected from extension and shear veins, dilational jogs, foliation surfaces, and the margins of phacoids, suggest that a common set of processes involving crack opening and sealing are active in a range of different structural sites within serpentinite-dominated shear zones, potentially associated with frequent and repetitive stress drops such as those recorded during episodic tremor and slow slip.

How to cite: Tarling, M. S., Smith, S. A. F., Rooney, J. S., Viti, C., and Gordon, K. C.: Serpentine crack-seal veins: a unique record of fluid conditions during faulting, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-425, https://doi.org/10.5194/egusphere-egu21-425, 2021.

Geophysical observations show that the Alpine Fault in New Zealand is characterised by mid-crustal off-fault recurring tremor events and off-fault regions of continuous deformation. While geodesy indicates that deformation is distributed across the South Island, evidence from the rock record shows deformation accommodated in a region within several km from the fault. This zone is characterized by a 100-300 m wide mylonitised central fault zone and an approximately 8--10km, wide deformation region marked by the presence of Alpine foliation. Magnetotelluric surveys of the Southern Alps indicate a mid-crustal, high signal area coinciding with the location of the recurring tremors.  

While the mylonites and their associated mechanisms have been extensively studied in the field area, the wider off-fault deformation region has not had the same scrutiny. In the latter region, we observe frequent layer parallel, folded and crosscutting quartz veins. Quartz vein orientation and geometries are consistent with fracturing in the presence of fluid within an overall tectonic stress regime. The observed overprinting of older veins by younger vein generations, as well as their successive reorientations, indicate recurring fracturing within a continuously deforming region. Quantitative analysis of vein geometries including their width and displacement shows that vein formation may trigger the observed mid-crustal tremor signal. Microstructural signatures within the host rock are consistent with dissolution-precipitation creep as the main deformation mechanism in the host rock and pre-existing veins.  

In summary, according to field evidence both geophysically observed transient and continuous deformation take place in the presence of fluid and occur contemporaneously. This implies that strain accommodation in the host rock facilitated by dissolution-precipitation creep is insufficient; consequently, stress is build-up over time triggering intermittent fracturing.  

How to cite: McGrath, J., Piazolo, S., Morgan, R., and Elliott, J.: Field evidence for fluid facilitated fracturing and Dissolution-Precipitaion creep explains observed off-fault tremor and continuous deformation: Field examples from the Alpine Fault, New Zealand , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8214, https://doi.org/10.5194/egusphere-egu21-8214, 2021.

EGU21-1053 | vPICO presentations | GMPV6.1

From static alteration to mylonitization: a nano- to micrometric study of chloritization in granitoids with implications for equilibrium and fluid percolation length scales

Laura Airaghi, Benoit Dubacq, Anne Verlaguet, Franck Bourdelle, Nicolas Bellahsen, and Alexandre Gloter

Strain accommodation in upper crustal rocks is often accompanied by fluid-mediated crystallization of phyllosilicates, which influence rock strength and shear zone formation. The composition of these phyllosilicates is commonly used for pressure-temperature-time constraints of deformation events, although it is often highly heterogeneous. This study investigates the reactions producing a phyllosilicate, chlorite, in and below greenschist-facies conditions and the variations in chlorite composition, along a strain gradient in the Bielsa granitoid (Axial Zone, Pyrenees). Compositional maps of chlorite (including iron speciation) are compared to nanostructures observed by transmission electron microscopy in increasingly-strained samples and related to mechanisms of fluid percolation and scales of compositional homogenisation. In the Bielsa granitoid, altered at the late Variscan, Alpine-age shear zones are found with high strain gradients. The undeformed granitoid exhibits local equilibria, pseudomorphic replacement and high compositional heterogeneities in chlorite. This is attributed to: (i) variable element supply and reaction mechanisms observed at nanoscale and (ii) little interconnected intra- and inter-grain nanoporosity causing isolation of fluid evolving in local reservoirs. In samples with discrete and mm-sized fractures, channelized fluid triggered the precipitation of homogeneous Alpine chlorite in fractures, preserving late-Variscan chlorite within the matrix. In low-grade mylonites, where brittle-ductile deformation is observed, micro-, nano-cracks and defects allows the fluid percolating into the matrix at the scale of hundreds of µm. This results in a more pervasive replacement of late-Variscan chlorite by Alpine chlorite. Local equilibria and high compositional heterogeneities in phyllosilicates as chlorite are therefore preserved according (i) matrix-fracture porosity contrasts at nanoscale and (ii) the location and interconnection of nanoporosity between crystallites of phyllosilicates that control reaction mechanisms and element mobility. In low grade mylonites, mineral and compositional replacement remains incomplete despite the high strain.

How to cite: Airaghi, L., Dubacq, B., Verlaguet, A., Bourdelle, F., Bellahsen, N., and Gloter, A.: From static alteration to mylonitization: a nano- to micrometric study of chloritization in granitoids with implications for equilibrium and fluid percolation length scales, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1053, https://doi.org/10.5194/egusphere-egu21-1053, 2021.

EGU21-13793 | vPICO presentations | GMPV6.1

Elastic strains of quartz inclusions and microstructures from pressure solution in garnet reveal orientation and low magnitude of differential stress during subduction metamorphism

Hugo van Schrojenstein Lantman, David Wallis, Mattia Gilio, Marco Scambelluri, and Matteo Alvaro

Determining the stress state during metamorphism is a key challenge in metamorphic petrology as the effect of differential stress on metamorphic reactions is currently debated. Conventional piezometry generally gives stresses that correspond to overprinting deformation rather than to mineral growth of high-grade metamorphism, so an alternative approach is required. Garnetite lenses from the ultrahigh-pressure, low-temperature metamorphic Lago di Cignana unit (Western Alps, Italy) record compaction by a high degree of mineral dissolution in the fluid-rich environment of a cold subduction zone. This work combines microstructural analysis of deformed garnet with elastic strains of quartz inclusions to study the stresses in these metasedimentary rocks.

Garnet exhibits abundant evidence for incongruent pressure solution (IPS), most notably as truncated zones that mismatch across grain boundaries, interlocking structures, and shape-preferred orientation (SPO). The gap in garnet compositions represented by overgrown truncated zonation corresponds to undeformed garnet with inclusions of quartz and coesite, indicating that IPS operated during prograde to peak metamorphism. The distribution of aspect ratios in the garnet grain population suggests that pressure solution preferentially affected smaller grains. SPO analysis of many subregions across a garnetite sample reveals a complex distribution, however the local SPO is consistent with the stress orientation expected for local microstructures such as layering, garnet stacks, or fine-grained internal fluid pathways. Locally, two different preferential orientations are observed, interpreted as the result of two subsequent deformation stages under different stress configurations.

Quartz inclusions in prograde euhedral garnet, grown on the outer margin of coevally deformed garnetite, were analysed with Raman spectroscopy. Elastic strains obtained for these inclusions are in agreement with predicted strains for entrapment along the prograde P-T path for the Lago di Cignana unit (~1.5–2.0 GPa; ~450–500 °C), whereas significant differential stress during entrapment is expected to result in deviating strain components.

By combining microstructural analysis of garnet with elastic-strain analysis of quartz inclusions, stress orientations obtained from deformed garnet are combined with the stress magnitude for coeval garnet growth. The results indicate that the garnetite lenses were deformed and metamorphosed under low differential stress of variable orientation during subduction. These results are in agreement with a system where garnet is wet by a fluid phase that allows IPS.

 

Acknowledgements: This project has received funding from the European Research Council under the H2020 research and innovation program (N. 714936 TRUE DEPTHS to M. Alvaro)

How to cite: van Schrojenstein Lantman, H., Wallis, D., Gilio, M., Scambelluri, M., and Alvaro, M.: Elastic strains of quartz inclusions and microstructures from pressure solution in garnet reveal orientation and low magnitude of differential stress during subduction metamorphism, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13793, https://doi.org/10.5194/egusphere-egu21-13793, 2021.

EGU21-9762 | vPICO presentations | GMPV6.1

Crustal fluid pressure gradients and permeability evolutions estimated from metamorphic fluid-rock reaction zones (Sør Rondane Mountains, East Antarctica)

Masaoki Uno, Diana Mindaleva, Atsushi Okamoto, and Noriyoshi Tsuchiya

Fluid activity in the crust is a key process controlling the generations of earthquakes, magmas, ore deposition formation and deep geothermal activities. Although high pore fluid pressure has been recognized by geophysical observations and geological observations of mineral filled fractures, the actual fluid pressure, their durations and associated permeability are controversial and remain largely unknown. Here we propose a new methodology estimating the duration, fluid pressure gradients and permeability recorded in fluid-rock reaction zones, by utilizing thermodynamic analyses in conjunction with halogen (Cl, F) profiles along the reaction zones.

We have analyzed exceptionally well-exposed crustal fluid–rock reaction zones at Sør Rodane mountains, East Antarctica. The thermodynamic analyses of granitic dike–granulite-facies crust reaction zone at 0.5 GPa, 700°C (Uno et al., 2017) and amphibolite-facies hydration reaction zones around mineral-filled fractures at ~0.3 GPa, 450°C (Mindaleva et al., 2020) reveals extremely high fluid pressure gradients of ~100 MPa/10cm or ~1 MPa/mm across the reaction zones. The reactive transport analysis suggest that fluid activity lasted for 100–250 days and ~10 hours, respectively. These extremely high fluid pressure gradients represent the low permeability of the intact amphibolite and granulite host rocks without fractures. The estimated permeabilities of the host rocks are 10−20–10−22 m2, and are several orders smaller than the widely accepted crustal permeability model (~10−18 m2; e.g., Ingebritsen and Manning, 2010). On the other hand, permeability along the fractures are estimated as high as 10−11–10−16 m2, which is analogous to the permeability estimated for the hypocenter migration for the crustal earthquake swarms (~10−14–15 m2; e.g., Nakajima and Uchida, 2018). Our observation supports that low permeability of intact crust promotes fluid accumulation and subsequent fracturing in the crust and/or underlying plate boundaries.

 

[References]

Nakajima, J., Uchida, N., 2018. Nature Geoscience 11, 351–356.

Ingebritsen, S.E., Manning, C.E., 2010. Geofluids 10, 193–205.

Uno, M., Okamoto, A., Tsuchiya, N., 2017. Lithos 284–285, 625–641.

Mindaleva, D., Uno, M., Higashino, F. et al., 2020. Lithos 372–373, 105521.

How to cite: Uno, M., Mindaleva, D., Okamoto, A., and Tsuchiya, N.: Crustal fluid pressure gradients and permeability evolutions estimated from metamorphic fluid-rock reaction zones (Sør Rondane Mountains, East Antarctica), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9762, https://doi.org/10.5194/egusphere-egu21-9762, 2021.

The Proterozoic gneisses of the Bamble lithotectonic domain (south Norway) underwent intense scapolitisation caused by K- and Mg-rich fluids and extensive albitisation with formation of numerous ore deposits.

By detailed studies of mineral reaction fabrics we document release of the chemical active Mg, K and Fe-components forming the metasomatic fluid: Breakdown of biotite to muscovite releases K, Mg, Fe, Si and H2O. As reaction products tiny Fe-oxide needles are present in the transforming rock. H2O is reacting with K-feldspar to produce additional amounts of white mica and quartz. During a subsequent reaction muscovite is replaced to sillimanite again releasing quartz and a K-rich fluid. The reactions form the peculiar sillimanite-nodular quartzite, but also well-foliated sillimanite-mica gneiss.

Optical and EBSD microfabric studies reveal a shape preferred orientation for quartz, but despite of a pronounced foliation, quartz does not show a crystallographic preferred orientation. A crystallographic preferred orientation is present for mica and sillimanite. Coarse micas show sutured boundaries to quartz, implying low nucleation rates, no crystallographic or surface-energy control during growth and no obvious crystallographic relationship to quartz.

Our study illustrates the transformation of a quartzofeldspatic lithology into sillimanite-bearing quartzite. The mineral replacement and deformation show ongoing metamorphic reactions during deformation. The microfabric data indicates reaction at non-isostatic stress condition. The deduced mineral replacement reactions document a source of K-, Mg- and Fe-rich metasomatic fluids necessary to cause the pervasive scapolitisation and Fe-deposition in the area. The mineral reactions and deformation produce rocks with a new mineralogy and structure; an increased understanding of these processes is important for the modelling of crustal building and geological history.

How to cite: Engvik, A. K., Trepmann, C. A., and Austrheim, H.: Mg-K-Fe fluid producing mineral reactions, metasomatism and microfabric development during formation of nodular sillimanite-gneiss in the middle crust, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2909, https://doi.org/10.5194/egusphere-egu21-2909, 2021.

EGU21-8633 | vPICO presentations | GMPV6.1

Feedback mechanisms in mineral replacement networks: an experimental investigation of the ultramafic model system

Ingvild Aarrestad, Oliver Plümper, Desiree Roerdink, and Andreas Beinlich

The overall rates of multi-component reaction networks are known to be controlled by feedback mechanisms. Feedback mechanisms represent loop systems where the output of the system is conveyed back as input and the system is either accelerated or regulated (positive and negative feedback respectively). In other words, feedback mechanisms control the rate of a reaction network without external influences. Feedback mechanisms are well-studied in a variety of reaction networks (e.g. bio-chemical, atmospheric); however, in fluid-rock interaction systems they are not researched as such. Still, indirect evidence, theoretical considerations and direct observations attest to their existence [e.g. 1, 2, 3]. It remains unknown how mass and energy transport between distinct reaction sites affect the overall reaction rate and outcome through feedback mechanisms. We propose that feedback mechanisms are a missing critical ingredient to understand reaction progress and timescales of fluid-rock interactions. We apply the serpentinization of ultramafic silicates as a relatively simple reaction network to investigate feedback mechanisms during fluid-rock interactions. Recent studies show that theoretical timescale-predictions appear inconsistent with natural observations [e.g. 4, 5]. The ultramafic silicate system is ideal for investigating feedback mechanisms as it is relevant to natural processes, is reactive on timescales that can be explored in the laboratory, and natural peridotite typically consists of less than four phases. Our preliminary observations indicate a feedback between pyroxene dissolution and olivine serpentinization. Olivine serpentinization appears to proceed faster in the presence of pyroxene. Furthermore, the bulk system reaction rate increases with increasing fluid salinity, which is opposite to the salinity effect on the monomineralic olivine system. Dunite (>90% olivine) is rare, which is why it is crucial to explore the more common pyroxene-bearing systems. The salinity effect is important to investigate due to the inevitable increase in fluid salinity from the boiling-induced phase separation and OH-uptake in the formation of serpentine. Here we present preliminary textural and chemical observations, which will subsequently be used for kinetic modelling of feedback.

[1] Ortoleva P., Merino, E., Moore, C. & Chadam, J. (1987). American Journal of Science 287, 997-1007.

[2] Centrella, S., Austrheim, H., & Putnis, A. (2015). Lithos 236–237, 245–255.

[3] Nakatani, T. & Nakamura, M. (2016). Geochemistry, Geophysics, Geosystems 17, 3393-3419.

[4] Ingebritsen, S. E. & Manning, C. E. (2010). Geofluids 10, 193-205.

[5] Beinlich, A., John, T., Vrijmoed, J.C., Tominaga, M., Magna, T. & Podladchikov, Y.Y. (2020). Nature Geoscience 13, 307–311.

How to cite: Aarrestad, I., Plümper, O., Roerdink, D., and Beinlich, A.: Feedback mechanisms in mineral replacement networks: an experimental investigation of the ultramafic model system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8633, https://doi.org/10.5194/egusphere-egu21-8633, 2021.

EGU21-10766 | vPICO presentations | GMPV6.1

Molecular dynamics study of confined water in the periclase-brucite system under conditions of reaction-induced fracturing

Marthe Grønlie Guren, Henrik Andersen Sveinsson, Anders Hafreager, Bjørn Jamtveit, Anders Malthe-Sørenssen, and François Renard

Reaction-induced fracturing may occur when dry rocks are exposed to water and undergo mineral transformations that involve a volume change. The volume increase associated with hydration reactions in rocks, like the hydration of periclase to brucite, requires a stable water film to be present at reactive grain boundaries. Recent experiments on the hydration of periclase observed that the replacement reaction slows down dramatically when the effective mean stress exceeds 30 MPa. We hypothesise that a stable fluid film is required for the brucite-forming reaction to progress, and when the applied pressure overcome the hydration force, the fluid film will collapse and be squeezed out of the grain contacts which will prevent formation of brucite. To quantify this effect, we run molecular dynamics simulations where our setup consists of two interfaces of either periclase or brucite surrounded by water, and we study the behaviour of the water film confined between two surfaces subject to compressive stress. The simulations are carried out using the ClayFF force field and the single point charge (SPC) water model in the molecular dynamics simulation program LAMMPS. Our simulations show that when the pressure reaches a few tens of MPa, the water film collapses. The process reduces the water film thickness to one or two water layers and reduces the self-diffusion coefficient of the water molecules by a factor of eight. When the water film thickness is less than two water layers, the water film thickness is smaller than the hydration shell around Mg2+-ions, which will limit the ion-transportation. The observed collapse of the water film to a single layer at a normal pressure of 25-30 MPa might explain the observed slow-down of reaction-induced fracturing in the periclase-brucite system.

How to cite: Guren, M. G., Sveinsson, H. A., Hafreager, A., Jamtveit, B., Malthe-Sørenssen, A., and Renard, F.: Molecular dynamics study of confined water in the periclase-brucite system under conditions of reaction-induced fracturing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10766, https://doi.org/10.5194/egusphere-egu21-10766, 2021.

EGU21-9044 | vPICO presentations | GMPV6.1

Crystallization via non-classical pathways: Nanoscale imaging of mineral surfaces 

Christine V. Putnis, Lijun Wang, Encarnación Ruiz-Agudo, Cristina Ruiz-Agudo, and François Renard

The advancement in analytical imaging techniques, including atomic force microscopy (AFM) and scanning and transmission electron microscopies (SEM and TEM), has allowed us to observe processes occurring at mineral surfaces in situ at a nanoscale in real space and time and hence giving the possibility to elucidate reaction mechanisms. Classical crystal growth theories have been established for well over 100 years and while they can still be applied to explain crystal growth in many growth scenarios, we now know that these models are not always an accurate description of the mechanism of all crystal/mineral growth processes, especially where nanoparticle formation is observed. Consequently there is a current challenge at the forefront of understanding crystal/mineral growth mechanisms. This work describes experimental observations of non-classical crystallization processes at the nanoscale. Using AFM as well as SEM and TEM imaging, we demonstrate that many minerals commonly grow by the attachment of nanoparticles on an existing mineral surface, often resulting from the coupling of dissolution of a parent phase and the precipitation of a new product mineral. Through varied examples of crystal/mineral growth, including calcite and other carbonates, barite, brucite, and apatite, we define the importance of the mineral-fluid interface and the aqueous fluid interfacial (boundary) layer in the control of crystal growth. Whether a crystal will grow by classical monomer attachment resulting in step advancement or by the formation, aggregation and merging of nanoparticles, will be controlled by the aqueous fluid composition at the mineral-fluid interface. The processes described also allow for the development of porosity within the new mineral and hence have important consequences for fluid movement and element mobility within the Earth. Additionally an understanding of natural mineral growth has implications for geomimetic applications for the manufacture of functional engineered materials.

How to cite: Putnis, C. V., Wang, L., Ruiz-Agudo, E., Ruiz-Agudo, C., and Renard, F.: Crystallization via non-classical pathways: Nanoscale imaging of mineral surfaces , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9044, https://doi.org/10.5194/egusphere-egu21-9044, 2021.

EGU21-2025 | vPICO presentations | GMPV6.1

Rodingitization of mafic and ultramafic rocks in ophiolites from Northern Greece, seen by non-traditional stable isotopes, such as Cu, Fe and Zn.

Nina Zaronikola, Vinciane Debaille, Aikaterini Rogkala, Petros Petrounias, Ryan Mathur, Panagiotis Pomonis, Konstantin Hatzipanagiotou, and Basilios Tsikouras

Rodingites are metasomatic rocks, frequently found in ophiolitic complexes. They offer important information about the interaction between ultramafic-mafic rocks and metasomatizing fluids, as well as about the post-magmatic evolution of ophiolitic suites (Tsikouras et al., 2009; Hu & Santosh, 2017; Surour, 2019; Laborda-Lopez et al., 2020). Metasomatism, such as rodingitization, is a very intricate process, which depends on the mineralogy of the initial rock, the nature of the metasomatic agent, the fluid/rock ratio, the duration of metasomatism and the chemical disequilibrium at the time of metasomatism between the host rock and the metasomatic medium (Poitrasson et al., 2013). Rodingites from the Veria-Naousa and Edessa ophiolites, in Northern Greece, were geochemically analyzed and characterized by substantial overprint of primary textures. Their field observation, their neoblastic mineral assemblages and metasomatic textures reveal that they derived from ultramafic and mafic protoliths. The mineral phases in the ultramafic derived rodingites (UDR) include mainly diopside, garnet, chlorite, epidote, tremolite and Fe-Ti oxides whereas mafic derived rodingites (MDR) consist of diopside, garnet, vesuvianite, chlorite, quartz, prehnite and actinolite. The studied rodingites present δ65Cu values varying from -0.17‰ to 0.62‰ and for ultramafic and mafic parent-rocks from -0.49‰ to +0.50‰. The UDR and MDR from both ophiolites display δ66Zn range from -0.06‰ to 0.74‰ and their photoliths present a narrower range from +0.04‰ to +0.41‰. Rodingitization affects in different way UDR and MDR samples. On one hand, Cu isotope ratios are systematically heavier in rodingites compared to their respective protoliths, except for one rodingite sample that requires confirmation due to large error bar. On the other hand, Zn isotopes show enrichment in light isotopes (group 1: comprising all UDR and some MDR samples), or in heavy isotopes (group 2, only MDR samples). Intriguingly, the same protolith can lead to both group 1 and 2 rodingites, as defined here.  No mineralogical or geochemical trend can be found to understand the dual behavior of Zn stable isotopes during rodingitization so far. Fe isotopes do not show any significant fractionation of δ56Fe, ranging from +0.07‰ to +0.19‰ for the rodingites and from +0.12‰ to +0.23‰ for their protoliths, indicating that Fe isotopes are highly resistant to rodingitization. Our study shows that rodingitization enriches metasomatized samples in heavy Cu isotopes and has no impact on Fe isotopes. It remains unclear why Zn isotopes can be affected both ways.

How to cite: Zaronikola, N., Debaille, V., Rogkala, A., Petrounias, P., Mathur, R., Pomonis, P., Hatzipanagiotou, K., and Tsikouras, B.: Rodingitization of mafic and ultramafic rocks in ophiolites from Northern Greece, seen by non-traditional stable isotopes, such as Cu, Fe and Zn., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2025, https://doi.org/10.5194/egusphere-egu21-2025, 2021.

Multi-stage tourmalines are widely developed in granitic gneisses and hydrothermal veins from the Laojunshan metamorphic dome, Southwest China. These tourmalines exhibit variable petrographic characteristics and microstructures by ductile deformation to brittle deformation, which offers a great opportunity to understand the fluid and structural evolution during exhumation of the Laojunshan metamorphic dome. Three types of tourmalines have been recognized, including disseminated tourmaline distributed in granitic gneisses (Tur-G), elongated and broken tourmalines in quartz veins (Tur-QV), needle-columnar and fine-grained tourmaline with micro-shear zone in tourmaline veins (Tur-TV). All the tourmalines belong to the alkali group representing dravite-schorl solid solution series. The former two types belong to schorl and the latte type contains more Mg-rich components. Models of occurrence and chemical varieties including Al-occupation at the Y-site suggest that the Tur-G type and Tur-QV type tourmalines crystallized from magmatic fluids and the Tur-TV type tourmalines are hydrothermal origin. Hydrothermal tourmalines are characterized by higher Mg/(Mg + Fe) ratios, more pronounced positive Eu anomalies, higher Li, Sr, HREE contents and lower Na/(Na + Ca) ratios, lower Nb, Zr, Hf, LREE contents compared with magmatic tourmalines. The increase of Mg/(Mg+Fe) ratios from the Tur-QV to Tur-TV type tourmalines is associated with the crystallization of Fe-rich mineral during hydrothermal stage. In the Tur-QV types, the decrease of Mg/(Mg+Fe) ratios and increase of Al and LREE contents from core to rim suggest the contamination from surrounding strata. The δ11B values of Tur-G, Tur-QV, Tur-TV type tourmalines are ranging from -13~-7.9‰, -15.5~-7.5‰, -18.6~-11.6‰ respectively, which suggests that the boron was mainly derived from granitic melt and exsolved hydrothermal fluid. Boron isotopic variations of tourmaline are mainly controlled by temperature and exsolved fluid. All the results of observations from outcrop to thin section scales and chemical analysis indicate the formation of disseminated tourmaline distributed in granitic gneisses (Tur-G) should have been associated with late stage of magma evolution before regional exhumation, while tourmalines in hydrothermal veins (Tur-QV and Tur-TV) have been formed by the magmatic-hydrothermal events during exhumation of Laojunshan metamorphic dome. The primary tourmalines experienced shearing and fracturing, and then were replaced by chlorite, potassium feldspar and epidote. The ductile-brittle deformation of tourmalines was produced by progressive strain localization accompanied by the alkaline, B-undersaturated fluids, indicating episodes of brittle fracturing, possibly as a consequence of faulting at depths and subsequent fluid flow during exhumation of the dome.

How to cite: Li, W., Cao, S., Nakamura, E., Ota, T., Kunihiro, T., and Liu, Z.: Chemical and boron isotopic variations of deformed tourmaline in the Laojunshan metamorphic dome, Southwest China: Implication for magmatic-hydrothermal evolution during exhumation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11830, https://doi.org/10.5194/egusphere-egu21-11830, 2021.

EGU21-1595 | vPICO presentations | GMPV6.1

Geochemistry of Chromium-Silicate Minerals

Jacqueline Dall, Christopher Oze, Aaron Celestian, and George Rossman

Water-rock interactions at elevated pressures and temperatures may mobilize chromium from chromite to produce a variety of Cr-silicate minerals. Common Cr-silicates include fuchsite (KCr2(AlSi3O10)(OH)2), kämmererite ((Mg5Cr)(AlSi3)O10(OH)8), tawmawite (Ca2CrAl2Si3O12(OH)), and uvarovite (Ca3Cr2Si3O12). Here we assess the geochemistry and calculate the thermodynamic properties of a variety of Cr-silicates to elucidate their formation as well as how they may contribute chromium to the environment. Chromium-silicates follow an idealized 1:1 relationship with regards to Cr(III) and octahedral Al, except for kämmererite. Kämmererite can have Al in excess of 1:1 to Cr(III), substituting into the Mg site. FTIR and Raman analyses demonstrate that Cr(III) enrichment is distinguishable between respective end member minerals. Thermodynamic properties were calculated using established estimation algorithms and unit-cell measurements.  Overall, we provide an extensive assessment of Cr-silicates that addresses the formation of Cr-silicates and fate of chromium in the environment.

How to cite: Dall, J., Oze, C., Celestian, A., and Rossman, G.: Geochemistry of Chromium-Silicate Minerals, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1595, https://doi.org/10.5194/egusphere-egu21-1595, 2021.

EGU21-1469 | vPICO presentations | GMPV6.1 | Highlight

How much energy for life (H2) is generated by serpentinization at passive continental margins?

Elmar Albers, Wolfgang Bach, Marta Pérez-Gussinyé, Catherine McCammon, and Thomas Frederichs

Molecular hydrogen (H2) released during serpentinization of oceanic mantle is one of the main fuels for chemosynthetic-based deep life. Hydrogen is produced during the oxidation of ferrous to ferric iron, and the amount of H2 generated strongly depends on rock type, fluid composition, alteration temperature, and water-to-rock ratio.

Progress has been made in understanding serpentinization and related H2 production at slow-spreading mid-ocean ridges (MORs). Less attention has been paid to the hydration of mantle rocks at passive continental margins where different rock types are involved (lherzolite instead of harzburgite/dunite at MORs) and the alteration temperatures tend to be lower (<200°C vs. >200°C). To close this knowledge gap we investigated serpentinization and H2 production using drill core samples from the West Iberia margin (Ocean Drilling Program Leg 103, Hole 637A).

Lherzolitic compositions indicate that the exhumed peridotites represent sub-continental lithospheric mantle. The rocks are strongly serpentinized and mainly consist of serpentine with little magnetite and are generally brucite-free. Serpentine can be uncommonly Fe-rich, with XMg = Mg/(Mg+Fe) < 0.8, and shows distinct compositional trends towards a cronstedtite endmember. Bulk rock and silicate fraction Fe(III)/∑Fe ratios range from 0.6–0.92 and 0.58–0.8, respectively. Our data show that more than 2/3 of the ferric Fe is accounted for by Fe(III)-serpentine. Mass balance and thermodynamic calculations suggest that the initial serpentinization of the samples at temperatures of <200°C likely produced about 100–250 mmol H2 per kg rock, which is 2–3 times more than previously estimated.

These results lead us to suggest that the generation potential of H2 evolves from continental break-up to ultraslow and eventually slow MOR spreading. The observed metamorphic phase assemblages systematically vary between these different settings, which has consequences for H2 yields during serpentinization. At passive margins and ultraslow-spreading MORs, the main phase hosting Fe(III) appears to be serpentine, and H2 yields of 100–250 mmol and 50–150 mmol H2 per kg rock, respectively, may be expected at temperatures of <200°C. At slow-spreading MORs, in contrast, serpentinization of harzburgite may produce 200–350 mmol H2 per kg most of which is related to the formation of magnetite at >200°C. Within the same (low) temperature range, larger volumes of serpentinite should form at passive margins than at slow-spreading MORs, owing to lower geothermal gradients. Relative to both slow- and ultraslow-spreading MORs, serpentinization at passive margins likely produces more H2 and under conditions closer to/within the habitable zone. These sites may hence be suitable environments for hydrogenotrophic microbial life.

How to cite: Albers, E., Bach, W., Pérez-Gussinyé, M., McCammon, C., and Frederichs, T.: How much energy for life (H2) is generated by serpentinization at passive continental margins?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1469, https://doi.org/10.5194/egusphere-egu21-1469, 2021.

EGU21-16307 | vPICO presentations | GMPV6.1

Permian rifting and detachment faults and their role in Alpine collisional tectonics

Nikolaus Froitzheim and Linus Klug

The Permian was a time of strong crustal extension in the area of the later-formed Alpine orogen. This involved extensional detachment faulting and the formation of metamorphic core complexes. We describe (1) an area in the Southern Alps (Valsassina, Orobic chain) where a metamorphic core complex and detachment fault have been preserved and only moderately overprinted by Alpine collisional shortening, and (2) an area in the Austroalpine (Schneeberg) where Alpine deformation and metamorphism are intense but a Permian low-angle normal fault is reconstructed from the present-day tectonometamorphic setting. In the Southern Alps case, the Grassi Detachment Fault represents a low-angle detachment capping a metamorphic core complex in the footwall which was affected by upward‐increasing, top‐to‐the‐southeast mylonitization. Two granitoid intrusions occur in the core complex, c. 289 Ma and c. 287 Ma, the older of which was syn-tectonic with respect to the extensional mylonites (Pohl, Froitzheim, et al., 2018, Tectonics). Consequently, detachment‐related mylonitic shearing took place during the Early Permian and ended at ~288 Ma, but kinematically coherent brittle faulting continued. Considering 30° anticlockwise rotation of the Southern Alps since Early Permian, the extension direction of the Grassi Detachment Fault was originally ~N‐S and the sense of transport top-South. In this area, there is no evidence of Permian strike-slip faulting but only of extension. In the Schneeberg area of the Austroalpine, a unit of Early Paleozoic metasediments with only Eoalpine (Cretaceous) garnet, the Schneeberg Complex, overlies units with two-phased (Variscan plus Eoalpine) garnet both to the North (Ötztal Complex) and to the South (Texel Complex). The basal contact of the Schneeberg Complex was active as a north-directed thrust during the Eoalpine orogeny. It reactivated a pre-existing, post-Variscan but pre-Mesozoic, i.e. Permian low-angle normal fault. This normal fault had emplaced the Schneeberg Complex with only low Variscan metamorphism (no Variscan garnet) on an amphibolite-facies metamorphic Variscan basement. The original normal fault dipped south or southeast, like the Grassi detachment in the Southern Alps. As the most deeply subducted units of the Eoalpine orogen (e.g. Koralpe, Saualpe, Pohorje) are also the ones showing the strongest Permian rift-related magmatism, we hypothesize that the Eoalpine subduction was localized in a deep Permian rift system within continental crust.

How to cite: Froitzheim, N. and Klug, L.: Permian rifting and detachment faults and their role in Alpine collisional tectonics, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16307, https://doi.org/10.5194/egusphere-egu21-16307, 2021.

EGU21-1750 | vPICO presentations | GMPV6.1

How high to ultra-high temperature terranes form

Bénédicte Cenki-Tok, Patrice F. Rey, and Diane Arcay

Long-lived high- to ultra-high temperature (HT-UHT) terranes formed mostly during the Paleo-Proterozoic and are often associated to supercontinent cycles. Yet the detailed processes and conditions involved in their formation remain largely unresolved. Here we highlight the importance of the specific geothermal conditions necessary to form migmatitic to granulitic crusts. An analytical resolution of the heat equation highlights the interdependency of the thermal parameters controlling the crustal geotherm, i.e. the Moho temperature, when deformation occurs at thermal equilibrium. We further perform thermo-mechanical experiments mimicking an orogenic cycle, from shortening to gravitational collapse, to study the effect of deformation velocity that affects the crustal thermal equilibrium. We show that the formation of HT-UHT terranes is promoted by an elevated radiogenic heat production in the crust. Finally, the interplay between the thermal parameters and the orogenic cycle duration explain the difference in orogenic style through time and why some terranes are preferentially granulitic or migmatitic.

How to cite: Cenki-Tok, B., Rey, P. F., and Arcay, D.: How high to ultra-high temperature terranes form, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1750, https://doi.org/10.5194/egusphere-egu21-1750, 2021.

EGU21-14165 | vPICO presentations | GMPV6.1

Partial Melting of Bimineralic Eclogite by Clinopyroxene Breakdown 

Zhuocheng Wang, Lu Wang, Michael Brown, and Timothy Johnson

The generation of melt during exhumation of UHP–HP metamorphic rocks is an important variable in our full understanding of the fluid–melt-fluid evolution during the subduction cycle and the exhumation mechanism of deeply subducted continental crust (Wang et al., 2020; Sizova et al., 2012). It is generally believed that the partial melting of deeply subducted eclogite is controlled by the mineral assemblage, particularly the presence of any hydrous minerals, and the metamorphic P–T path. Here we report results from the Sulu belt, which was formed by the deep subduction of the passive margin of the Yangtze Craton under the North China Craton, with exhumation occurring during the Mesozoic (240–210 Ma). Recent studies in this belt have shown that phengite-bearing UHP eclogites can develop a solute-rich supercritical fluid or melt along grain boundaries by dehydroxylation of nominally anhydrous minerals during the early stage of decompression and/or trigger partial melting by breakdown of phengite and/or omphacite during the later stage of exhumation (Wang et al., 2014; Wang et al., 2020; Feng et al., 2021). However, the capacity of bimineralic eclogite to melt remains enigmatic due to the anhydrous mineral assemblage, indicating a low primary bulk water content, and the absence of studies reporting evidence of melting.

To determine whether bimineralic eclogite can produce melt during exhumation we undertook a comprehensive study, including petrology, microstructure and geochronology, on a bimineralic eclogite boudin within gneiss from a locality in the northeast of the Sulu belt. The margin of the eclogite boudin is extensively retrogressed, whereas the core is well preserved with distinctive garnet-rich and pyroxene-rich layers. The Ca-rich clinopyroxene in the boudin core exhibits abundant exsolved quartz formed during exhumation. In the pyroxene-rich layers micrometer-scale intergranular pockets composed of euhedral Ca-rich hornblende and Ca-rich plagioclase, and accessory barite and apatite, are interpreted as leucosome. Comparing the calculated bulk composition of the leucosome pockets, which is diorite, with the clinopyroxene, garnet and accessory mineral compositions from the host, suggests that the melt formation is dominated by the breakdown of clinopyroxene rather than garnet or the accessory minerals, based on the trace element characteristics. Symplectitic intergrowths of hornblende and plagioclase occur along boundaries between the garnet-rich and pyroxene-rich layers and extend into both. 

LA-ICP–MS analysis of metamorphic zircon from the eclogite with leucosome pockets yields an age range of 230–210 Ma. Ti-in-zircon thermometry yields a wide range of temperatures from 800 to 500°C. By contrast, temperatures calculated from the rock-forming minerals yield 890–830°C (Grt–Cpx thermometry at 3 GPa), 880–820°C (Amp–Pl (from leucosome pocket) thermometry at 1 GPa), and 700–650°C (Amp–Pl (from symplectite) thermometry at 1.0–0.5 GPa). Overall, we interpret the partial melting of the bimineralic eclogite in the northeastern Sulu belt to record breakdown of clinopyroxene during decompression from UHP–HP metamorphic conditions. This represents the first detailed micro-scale study of in situ melting of UHP bimineralic eclogite.

 

How to cite: Wang, Z., Wang, L., Brown, M., and Johnson, T.: Partial Melting of Bimineralic Eclogite by Clinopyroxene Breakdown , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14165, https://doi.org/10.5194/egusphere-egu21-14165, 2021.

EGU21-7433 | vPICO presentations | GMPV6.1

Documenting isobaric cooling in the lower crust using cordierite breakdown textures (Mont Mary nappe, Western Alps)

Michel Ballèvre, Marc Poujol, Selim Rousseau, and Paola Manzotti

Intracrystalline diffusion is an efficient mechanism in high-grade rocks. Therefore, growth zoning in garnet is erased and the evidence for prograde path is lost. However, information recorded by the textures may store significant clues for deciphering part of the P-T path. An example is provided here from the migmatitic paragneisses from the Mont Mary nappe (Western Alps).

The latter is made of a pre-Alpine basement consisting of an upper and a lower unit. The upper unit is made of paragneisses, marbles and amphibolites similar to those of the Valpelline Unit and of the Ivrea Zone. The lower unit displays granitic orthogneisses, paraschists (with muscovite, biotite, garnet with local occurrences of staurolite, kyanite and andalusite) (Dal Piaz et al. 2015). In this unit, we discovered a hectometre-sized volume with no Alpine overprint, preserving migmatitic paragneisses, the topic of this study.

The paragneisses display quartzo-feldspathic leucocratic layers interpreted as crystallized melts. The leucosomes are separated by biotite- and sillimanite-rich layers, with conspicuous garnet porphyroblasts. In addition, fresh cordierite crystals are found in these layers. Sillimanite included in garnet rims has the same orientation than the one in the matrix. There, the foliation is defined by the shape fabric of biotite and sillimanite, wrapping both garnet and cordierite crystals.

Such textures may be used to propose a P-T path. A sequence of prograde reactions, including dehydration-melting of muscovite, then biotite, result in the production of a large amount of sillimanite. Garnet growth was continuing during incongruent melting. However, intracrystalline diffusion has erased the prograde chemical zoning, as well as the distribution and shape of mineral inclusions. The late replacement of garnet and cordierite by biotite and sillimanite indicates near-isobaric cooling, also recorded by chemical zoning along garnet rims.

Chemical data on coexisting minerals will be used to provide quantitative constraints on the P-T path. In addition, preliminary geochronological data suggest that detrital zircons grains were significantly reset during the HT metamorphism, which could have taken place c. 270 Ma ago. To conclude, the studied paragneisses offer another example of Permian near-isobaric cooling in the middle crust of the Adriatic plate.

Dal Piaz G.V., Bistacchi A., Gianotti F., Monopoli B., Passeri L., Schiavo A. & collaboratori (2015) – Note illustrative della carta Geologica d’Italia alla scala 1:50.000. Foglio 070, Monte Cervino. ISPRA, Servizio Geologico d’Italia, 070, 1-431.

How to cite: Ballèvre, M., Poujol, M., Rousseau, S., and Manzotti, P.: Documenting isobaric cooling in the lower crust using cordierite breakdown textures (Mont Mary nappe, Western Alps), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7433, https://doi.org/10.5194/egusphere-egu21-7433, 2021.

EGU21-1827 | vPICO presentations | GMPV6.1

Characterization of P-T conditions and age of the mid-crustal material involved in the Alpine continental subduction (Dora Maira Massif)

Francesco Nosenzo, Paola Manzotti, Marc Poujol, Michel Ballèvre, and Jessica Langlade

The basement units of the Alps offer an excellent example to study how the Palaeozoic continental crust was recycled during the Alpine orogeny. The reconstruction of the pre-Alpine evolution of the continental basement is challenging and mainly relies on information provided by low-strain volumes, where mineralogical relics and isotopic data on accessory minerals can be safely investigated.

The knowledge of the pre-Alpine history of the Palaeozoic basement places severe constraints on its behaviour during the Alpine continental subduction. Firstly, its location in the (lower, middle, or upper) crust has implications for material balance during the Alpine orogeny. Secondly, its mineral content will determine how much water is needed for its transformation into an equilibrium eclogite-facies assemblage, with major implications for its metastability, hence its density and rheology during the Alpine history.

Here we investigate the pre-Alpine continental basement of the Dora Maira Massif (Western Alps), worldwide renowned for its Alpine quartz- to coesite-eclogite facies metamorphism. However, little is known about its pre-Alpine history. Spectacular polycyclic garnet-staurolite micaschists associated with garnet-biotite orthogneisses represent exceptional witnesses for reconstructing the Palaeozoic evolution of this region. Both lithologies contain mineralogical relics, such as a first generations of garnet, staurolite, muscovite and biotite indicative of a regional pre-Alpine amphibolite-facies metamorphism. Thermodynamic modelling on the micaschists constrains this pre-Alpine metamorphism at 640-660 °C, 6-7 kbar. Detrital zircon geochronology indicates that the youngest age population in the micaschists ranges from 450 Ma to 600 Ma and represents the maximal depositional age for the Palaeozoic sediment. U-Pb zircon geochronology in the garnet-biotite orthogneisses points to crystallization of the magma in the earliest Silurian (442 ± 2 Ma).

Detrital zircons in the micaschists display metamorphic overgrowths, characterized by high U content and very low Th/U ratios, as reported previously in amphibolite to granulite facies rocks. These metamorphic overgrowths yield U-Pb ages of 303 ± 2 Ma. These data constrain the timing of the Barrovian metamorphism in the Dora Maira Massif and confirm the hypothesis of a genetic link between this metamorphic episode and the Variscan orogeny.

The eclogite-facies polycyclic rocks from the Dora-Maira Massif therefore derive from upper crustal late Carboniferous lithologies, similar to those found in the Gran Paradiso and Monte Rosa, but different from the granulite-facies, lower crustal, rocks found in the Sesia Zone.

How to cite: Nosenzo, F., Manzotti, P., Poujol, M., Ballèvre, M., and Langlade, J.: Characterization of P-T conditions and age of the mid-crustal material involved in the Alpine continental subduction (Dora Maira Massif), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1827, https://doi.org/10.5194/egusphere-egu21-1827, 2021.

EGU21-1974 | vPICO presentations | GMPV6.1

Investigating heat transfer through the Lepontine Dome (Central European Alps) with a combined petrological, structural, dating and modelling approach

Alessia Tagliaferri, Stefan Markus Schmalholz, and Filippo Luca Schenker

Heat transfer during and after the emplacement of tectonic nappes within an orogeny is controlled by three fundamental processes: advection, diffusion and production of heat. Production is mainly caused by radioactive decay and shear heating. The relative importance and timing of these processes is often contentious. For example, in the Lepontine Dome of the Central European Alps the timing of the thermal evolution and the relative importance of advection, diffusion and shear heating is disputed. To better constrain and understand heat transfer in the Lepontine Dome, we apply a combined approach of petrological and structural analysis, zircon dating of migmatites and theoretical modelling.

We use data from an almost vertical transect (in the Ticino’s valleys) cutting from bottom-to-top the Simano, Cima Lunga and Maggia gneissic nappes. These nappes show an extremely pervasive mineral and stretching lineation (NW-SE directed) indicating non-coaxial deformation during shearing at amphibolite facies metamorphic conditions. The transition from the Simano to the Cima-Lunga nappe is marked by a progressive change in the texture of gneisses, in which the porphyroblasts become more stretched from the bottom to the top. Locally, at the tectonic contacts, syn-tectonic migmatites have been found. Their leucosomes contain metamorphic zircons with ages spreading from 40 to 31 Ma (U-Pb dating).
The widespread paragneisses frequently contain garnets of different sizes and internal microstructure. Published and own petrological data of these garnet-bearing rocks attest an inverted metamorphic gradient from ca. 700°C to 650-600 °C at intermediate pressures below the Cima Lunga unit during the peak-T amphibolite facies condition.

Overall, the field data depict a major km-scale shear zone that generated an inverted metamorphic gradient during the peak-T amphibolite facies condition between 40 and 31 Ma. These results hint that fast advection of heat or shear heating (or both component contempraneously) contributed to imprint the regional amphibolite facies metamorphism during nappe emplacement.

To take another step towards unravelling the controlling heat transfer processes in the Lepontine Dome and to test the relative importance of production, diffusion and advection, we employ three theoretical approaches with increasing complexity. First, we perform a dimensional analysis estimating dimensionless numbers, such as Peclet and Brinkman, for a range of reasonable parameters for the Lepontine Dome. Second, we apply numerical 2D thermo-kinematic simulations of trishear thrust-ramp evolution to test, for example, the impact of temperature-dependent viscosity and the geometrical relationship between temperature isogrades and nappe boundaries. Third, we apply state-of-the-art numerical 2D thermo-mechanical simulations of subduction and collision to investigate heat transfer and the resulting metamorphic facies distribution during the formation of an orogenic wedge.

Finally, we combine our modelling results with the available structural, age and metamorphic results to discuss potential scenarios for the heat transfer through the Lepontine dome.

How to cite: Tagliaferri, A., Schmalholz, S. M., and Schenker, F. L.: Investigating heat transfer through the Lepontine Dome (Central European Alps) with a combined petrological, structural, dating and modelling approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1974, https://doi.org/10.5194/egusphere-egu21-1974, 2021.

EGU21-12571 | vPICO presentations | GMPV6.1

New insights into the age and metamorphic evolution of the Irumide orogeny in Malawi

Sofia C. Böhme and Steven D. Boger

Metapelitic rocks of the Irumide Domain in central Malawi contain detrital and metamorphic zircons. U-Pb zircon geochronology yielded two age populations, which have been dated at c. 1995 Ma and 1050 Ma. The ages demonstrate that the precursor sediments to these rocks were derived from erosion of the Palaeoproterozoic Ubendian Domain, which is adjacent to the north, and at a later stage were affected by the Irumide orogeny. The metapelitic rocks are characterised by garnet + sillimanite + biotite ± muscovite ± K-feldspar mineral assemblages. Phase equilibria modelling shows that they equilibrated under pressure-temperature conditions of about 7 kbar and 700–740˚C.  In combination with the metamorphic ages this is interpreted to record late Mesoproterozoic (c. 1050 Ma) accretion of a juvenile island arc, the South Irumide Domain, to the southern margin of the Tanzania-Congo Craton.

How to cite: Böhme, S. C. and Boger, S. D.: New insights into the age and metamorphic evolution of the Irumide orogeny in Malawi, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12571, https://doi.org/10.5194/egusphere-egu21-12571, 2021.

EGU21-11159 | vPICO presentations | GMPV6.1

Deciphering the coupling between tectonic and metamorphic processes in the Monte Rosa nappe (Western Alps)

Joshua D Vaughan Hammon, Cindy Luisier, Lorenzo G Candioti, Stefan M Schmalholz, and Lukas P Baumgartner

Our refined ability to estimate metamorphic conditions incurred by rocks has increased our understanding of the dynamic earth. Calculating pressure (P), temperature (T) and time (t) histories of these rocks is vital for reconstructing tectonic movements within subduction zones. However, large disparities in peak P within a structurally coherent tectonic unit poses difficulties when attempting to resolve a tectono-metamorphic history, if a depth dependant lithostatic P is assumed. However, what is clear is that pressure, or mean stress, in a rock cannot exactly be lithostatic during an orogeny due to differential stress, required to drive rock deformation or to balance lateral variations in gravitational potential energy. Deviations from lithostatic P is commonly termed tectonic pressure, and both its magnitude and impact on metamorphic reactions in disputed.

For the ‘Queen of the Alps’ (the Monte Rosa massif), estimates for the maximum P recorded during Alpine orogenesis remain enigmatic. Large disparities in published estimates for peak P exist, ranging between 1.2 and 2.7 GPa. Moreover, the highest P estimates (2.2 - 2.7 GPa) are for rocks that comprise only a small percentage (< 1%) of the total volume of the nappe (whiteschist bodies and eclogitic mafic boudins). We present newly discovered whiteschist lithologies that persistently exhibit higher P conditions (c. 2.2 GPa) compared to metagranitic and metapelitic lithologies (c. 1.4 - 1.6 GPa). Detailed mapping and structural analysis in these regions lack evidence for tectonic mixing. Therefore, we suggest that a ΔP 0.6 ± 0.2 GPa during peak Alpine metamorphism could potentially represent tectonic pressure. Furthermore, we outline possible mechanisms that facilitate ΔP, namely mechanically- and/or reaction-induced. We present data from numerical models that exhibit significant ΔP (c. 0.4 GPa) during a transient period of high differential stress prior to buckling and subsequent exhumation of viscous fold nappes, similar to exhumation mechanisms suggested for the Monte Rosa nappe. As well as this, we present new routines for calculating metamorphic facies distribution within numerical models of subduction zones that agree with natural distributions within orogens.

The maximum burial depth of the Monte Rosa unit was likely significantly less than 80 km (based on the lithostatic pressure assumption and minor volumes of whiteschist at c. 2.2 GPa). Rather, the maximum burial depth of the Monte Rosa unit was presumably equal to or less than c. 60 km, estimated from pressures of 1.4 - 1.6 GPa recorded frequently in metagranite and metapelitic lithologies. In order to understanding, more completely, a rocks metamorphic history, consideration of the interplay between tectonic and metamorphic processes should not be overlooked.

How to cite: Vaughan Hammon, J. D., Luisier, C., Candioti, L. G., Schmalholz, S. M., and Baumgartner, L. P.: Deciphering the coupling between tectonic and metamorphic processes in the Monte Rosa nappe (Western Alps), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11159, https://doi.org/10.5194/egusphere-egu21-11159, 2021.

The eclogites from Vårdalneset, Western Gneiss Region, Norway, show an exceptional large variety of reaction and deformation microfabrics that document the processes and conditions during burial and exhumation. Coarse grained eclogites comprise about 35% omphacite, 25% garnet and 20% amphibole with various amounts of white mica, zoisite, kyanite, rutile, zircon and pyrite. Their fabric is characterized by few mm long and several hundred µm wide amphibole and omphacite grains aligned in the foliation plane with zoned garnet porphyroblasts up to several mm in diameter. In contrast, finer-grained mylonitic eclogites with grain diameters of few hundred µm comprise systematically higher amounts of garnet (45%) and omphacite (35%) and generally less amphibole (< 5%) but similar amounts of zoisite, white mica, rutile and quartz. In the coarse-grained eclogite, amphibole shows evidence of dislocation creep as indicated by undulatory extinction, subgrains and recrystallized grains in necks of boudinaged coarse amphibole layers as well as in contact to garnet. The large garnet porphyroblasts generally show a complex zonation with an inclusion-rich Fe-poor and Mg-rich inner core surrounded by a zone with Fe- and Ca-rich patches and a broad Mg-rich, Ca- and Fe-poor rim. Only at contact to coarse amphibole an additional, a few tens of µm thin serrated rim further enriched in Mg can occur. At the direct contact to such serrated Mg-rich rims, amphibole is partly replaced by a fine-grained quartz-kyanite ± rutile aggregate, indicating dehydration reactions of amphibole. Quartz - kyanite ± rutile aggregates are surrounding garnet also in contact to omphacite, zoisite and to other garnet crystals. The microstructures suggest that deformation and dehydration of amphibole are coupled and played an important role during deformation of the eclogites finally leading to the mylonitic eclogites with higher amounts of garnet and omphacite. Deformation is suggested to have triggered the dehydration reaction by a slight and local increase in temperature. Furthermore, deformation provided additional pathways for the escaping fluids along the increased grain and phase boundary area, as indicated by commonly present quartz within interstitials between recrystallized amphibole grains. In all samples, few µm wide amphibole rims replacing garnets document restricted rehydration-reactions at a later stage. The large variety of the deformation and reaction microfabrics exemplarily show that both deformation and metamorphic reactions did not proceed at long-term continuous conditions, but that both are coupled and occurred episodically.

How to cite: Trepmann, C. A., Engvik, A. K., and Prince Gutierrez, E. G.: Deformation and reaction fabrics in eclogites from the Western Gneiss Region (Norway) - evidence of dehydration reactions attributed to episodic deformation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2303, https://doi.org/10.5194/egusphere-egu21-2303, 2021.

EGU21-1154 | vPICO presentations | GMPV6.1

Retrograde carbon sequestration in orogenic complexes: a case study from the Chinese Southwestern Tianshan

Han Hu, Alberto Vitale Brovarone, Lifei Zhang, Francesca Piccoli, Weigang Peng, and Tingting Shen

The interaction between ascending carbonic fluids and rocks at shallow depths in orogenic systems plays an important role in carbon flux regulation. In subduction zones, most works have focused on processes related to carbon release from the subducting slab or sequestration via high-pressure (HP) carbonation of mafic or ultramafic lithologies. A significant fraction of the carbonic fluids released by deep metamorphic reactions can also reach orogenic complexes and react with crustal and exhumed metamorphic rocks. However, the amount of fluid-mediated carbonation that may take place at crustal depths in orogenic complexes is still poorly constrained.

We report the occurrence of retrograde mafic eclogites and metasomatic marbles in UHP units in the Chinese Tianshan orogenic belt. The mafic eclogites recorded two successive, superimposed metamorphic–metasomatic stages: graphite precipitation along fractures and veins at eclogite facies (Stage#1) and pervasive rock carbonation (i.e., Stage#2: silicate dissolution and carbonate precipitation) at retrograde amphibolite to greenschist facies. This work focuses on Stage#2 carbonation, which consists of the transformation of Stage#1 graphite-bearing eclogites into carbonate + paragonite (± zoisite) + quartz. We present field, microstructural, petrological, and geochemical results of carbonic fluid–rock interactions affecting exhumed mafic eclogites. These results are supported by thermodynamic modeling for low-pressure carbonation of mafic eclogite obtained by means of EQ3/6 and the Deep Earth Water model. Carbon and oxygen isotopic data and thermodynamic modeling suggest an external metasedimentary source for the Stage#2 carbonation. This deep carbon sequestration event can be referred to retrograde, greenschist-facies conditions at about 10 kbar and 450 °C, and redox conditions similar or more oxidized than the quartz–fayalite–magnetite (QFM) buffer. Our findings provide new insights into the reactivity of metastable, exhumed metamafic rocks with ascending carbonic fluids in orogenic systems. We conclude that retrograde, fluid-mediated rock carbonation can significantly impact on carbon fluxes from active collisional belts. 

How to cite: Hu, H., Vitale Brovarone, A., Zhang, L., Piccoli, F., Peng, W., and Shen, T.: Retrograde carbon sequestration in orogenic complexes: a case study from the Chinese Southwestern Tianshan, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1154, https://doi.org/10.5194/egusphere-egu21-1154, 2021.

EGU21-1734 | vPICO presentations | GMPV6.1

Model-derived uncertainties in the calculation of geological phase equilibria

Eleanor Green and Roger Powell

Phase equilibrium modelling offers a welcome window onto rock-forming processes. It underpins the principles of geothermobarometry, which today is commonly carried out via pseudosection calculations in software such as THERMOCALC and Perple_X. Increasingly, phase equilibrium modelling is combined with complementary approaches such as diffusion or geodynamical calculations, in order to simulate Earth processes.

However, as anyone with experience of pseudosection calculations will know, it is not always easy to make sense of a rock through phase equilibrium modelling. Problems may relate to: (1) in what way the assumption of thermodynamic equilibrium may, or may not, be applied; (2) uncertainties in compositional analysis; and (3) uncertainties in the composition-dependent equations of state (x-eos). The x-eos are the building blocks of the modelling – one x-eos is needed to represent each of the mineral and fluid phases in the calculation. 

Of the problems listed above, (3) is the most opaque for the user. In this talk I will discuss the uncertainties associated with the x-eos, and the implications of those uncertainties for thermobarometry and the simulation of Earth processes. I will describe two tools, currently in development, for investigating x-eos-derived uncertainty in thermobarometry.

How to cite: Green, E. and Powell, R.: Model-derived uncertainties in the calculation of geological phase equilibria, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1734, https://doi.org/10.5194/egusphere-egu21-1734, 2021.

EGU21-639 | vPICO presentations | GMPV6.1

The volume conjugate in progressive metamorphism

Timothy Chapman, Geoffrey Clarke, Luke Milan, and Julie Vry

Volume changes during metamorphic reactions are key contributors to the physical changes of crystalline rocks. Assessing dehydration or hydration reactions in terms of conjugate V–T pseudosections provides indicators of transient departures in hydrostatic pressure and their impact on observed mineral equilibria. The expansion in volume of major dehydration events such as the breakdown of lawsonite or chlorite delineate zones of fluid overpressure that generate connectivity via fracturing. Net compressional reactions represent sinks for fluid consumption and the focussing of strain. The capacity of metamorphic rocks to generate or consume fluid along portions of the P–T–V path exerts a fundamental control on the distribution of stresses in the crust and the observed mineral assemblages. Coupling a phase equilibria approach to mechanical modelling provides a quantitative framework to assess these changes in fluid pressure that can be compared to prominent case studies in rocks from New Caledonia and New Zealand.

How to cite: Chapman, T., Clarke, G., Milan, L., and Vry, J.: The volume conjugate in progressive metamorphism, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-639, https://doi.org/10.5194/egusphere-egu21-639, 2021.

EGU21-10651 | vPICO presentations | GMPV6.1

A new methodology for considering minor elements of geologic importance in phase equilibria modelling

Sean Hoffman, Matthew Mayne, and Gary Stevens

The development of activity-composition models for melt in phase equilibria modelling has enabled the study of crustal differentiation processes through partial melting. A number of minor and trace elements are not accommodated in the melt models relevant to aluminous sediments, but are of considerable petrological importance (e.g. Zr, P, Ti).  In this study, a new methodology is presented for handling minor and trace components that are currently unable to be thermodynamically constrained in supersolidus conditions. A new feature is built into the thermodynamic modelling software Rcrust (Mayne, Moyen, Stevens, et al., 2016), called Component Packet, that can manipulate chemical components that are not accommodated within the activity composition models. Using this functionality, any such element of interest can be modelled for each PT point in Rcrust and partitioned between specified phases. In this study, the usefulness of this new functionality has been demonstrated using the behaviour of Ti. Ti is critical in stabilizing biotite at high temperature. Thus, the lack of Ti in some solution models for melt in aluminous systems, result in a reduced stability of biotite in magma modelled as having fractionated from the residuum. In order to overcome this, a component packet is employed to investigate the proportion of Titanium that would be partitioned to melt during the anatexis of an average amphibolite-facies metapelite. In this scenario, Titanium contents in melt are estimated by linear regression to titanium versus maficity in a global compilation of S-type granites generated for this purpose. The results are compared to that of an internally consistent thermodynamic model, which does include TiO2. The linear regression method produces trends that agree with the internally consistent model under certain conditions and produces TiO2 contents for “melt” that are within the lower range of S-type granites and matches the correlation of TiO2 vs FeO+MgO of S-type granites, indicating that it is built on a strong relation. Melts are extracted once 7 vol% is accumulated, with 1 vol% retained in the residuum. The phase assemblages in extracted melts were investigated through cooling at 3 kbar and 650°C. The presence of Titanium in melt via Component packet results in a biotite mode of up to 2.5 wt% greater than melts formed without TiO2 at high temperatures, but on average less than 1 wt%. In addition, extracted melts with Ti from Component Packet allow ilmenite to be a liquidus phase. This shows that the component packet can be used to more accurately model titanium in melt, which greatly affects the stability of Ti phases at emplacement. Furthermore, the petrological applicability of the Component Packet is such that the methodology used here could be applied to the approximation of other minor components that thermodynamic models are currently unable to handle for crustal melting, such as P2O5.

REFERENCES
Mayne, M.J., Moyen, J.F., Stevens, G. & Kaislaniemi, L. 2016. Rcrust: a tool for calculating path-dependent open system processes and application to melt loss. Journal of Metamorphic Geology. 34(7):663–682.

How to cite: Hoffman, S., Mayne, M., and Stevens, G.: A new methodology for considering minor elements of geologic importance in phase equilibria modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10651, https://doi.org/10.5194/egusphere-egu21-10651, 2021.

EGU21-7938 | vPICO presentations | GMPV6.1

Petrogeochemical tools for simulating fluid-rock interaction processes in high-pressure metamorphic terrains

Pierre Lanari, Thomas Bovay, Daniela Rubatto, Hugo Dominguez, Thorsten Markmann, Nicolas Riel, and Alice Vho

Petrological models based on equilibrium thermodynamics have proven critical in assessing how mineral assemblages evolve with pressure (P) and temperature (T) conditions. Still, they remain limited for the investigation and simulation of fluid-rock interaction processes in open systems. The interaction between a reacting aqueous fluid and a (already water-saturated) rock at eclogite facies conditions, for example, can have no or very limited effects on the mineral assemblage—beyond eventually triggering re-equilibration. Therefore, pervasive fluid flows that are not associated to intense metasomatism cannot be modeled using phase diagrams and often remain hardly noticeable even to experienced petrologists. Unlike major and minor elements used for thermodynamic modeling, stable isotopes (e.g. oxygen) are known to be more sensitive for recording interaction with a fluid in isotopic disequilibrium.

In order to extend the existing modeling capabilities, an integrated modeling framework was developed applicable to multi-rock open systems combining thermodynamic and oxygen isotope fractionation modeling based on internally consistent databases (Vho et al. 2019, 2020). The petrological model quantifies the effect of dehydration reactions on the bulk δ18O of a rock during prograde metamorphism and can simulate different degrees of fluid-rock interaction with the surrounding rocks. This approach, in combination with the measurement of isotopic composition in key minerals, can be used for characterizing the behavior of open vs closed systems in natural settings and quantify the degree of fluid-rock interaction. Estimation of integrated fluid fluxes across geologic units of the Western Alps then allows permeability changes to be quantified along with the metamorphic conditions under which these changes occurred. Such results open the door to the dynamic simulation of reactive fluid flows in high-pressure environmentthat are controlled by the compaction pressure of the rock matrix.

This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 850530).

References:

  • Vho, A., Lanari, P., Rubatto, D. (2019). An internally-consistent database for oxygen isotope fractionation between minerals. Journal of Petrology, 60, 2101–2129
  • Vho, A., Lanari, P., Rubatto, D., Herman, J. (2020). Tracing fluid transfers in subduction zones: an integrated thermodynamic and δ18O fractionation modelling. Solid Earth, 11, 307-328

How to cite: Lanari, P., Bovay, T., Rubatto, D., Dominguez, H., Markmann, T., Riel, N., and Vho, A.: Petrogeochemical tools for simulating fluid-rock interaction processes in high-pressure metamorphic terrains, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7938, https://doi.org/10.5194/egusphere-egu21-7938, 2021.

Corona texture between olivine-plagioclase is a common phenomenon in metabasic rocks and has been reported from different geological terrane of the world. However, the documented coronal phases from these terrane show significant variation in terms of number and composition. In this study, we have tried to explore the effect of different parameters like pressure, temperature, reactant bulk composition, availability of fluid, chemical potential gradient etc. on the genesis of such distinct coronal minerals. To address this question, we have compared three coronal assemblages developed between olivine and plagioclase from published literature (Gallien et al. 2012; Banerjee et al. 2019; Adak & Dutta, 2020). These three samples represent different terrane and have distinctly separate geological evolutionary history that led in formation of the texture. The samples are – i) #CGGC, a mafic intrusive from Chotanagpur Granite Gneissic Complex, India (Adak & Dutta, 2020); ii) #GTSI, an olivine bearing mafic dyke from Granulite Terrane of South India (Banerjee et al. 2019); and iii) #VFH, a troctolitic gabbro from Valle Fértil and La Huerta range, Argentina (Gallien et al. 2012). The layers in coronae of #CGGC and #GTSI are defined by three phases of separate composition; orthopyroxene and amphibole are common, but #CGGC contains spinel and #GTSI contains magnetite. Whereas, #VFH contains four phases, clinopyroxene in addition to orthopyroxene, spinel and amphibole. Besides evaluation of reactant composition and their effect, our methodology also incorporates Schrienemaker’s analysis through P-T and chemical potential diagrams. Considering the chemistry of both the reactant and product phases we have used a simplified CMASH system and calculated μCaO–μH2O, μMgO–μH2O, μCaO–μMgO diagram along with petrogenetic grid for each sample. The results show that along with change in P-T, factors like initial composition of the reactant minerals, behaviour of the system during reaction (open/closed) and P-T-t path of evolution also play significant role in determining the products in coronae formed from the reactant olivine and plagioclase.

 

How to cite: Banerjee, M., Adak, V., and Dutta, U.: Identifying parameters on genesis of coronal phases at olivine-plagioclase contact: A comparison from different geological terrane, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16052, https://doi.org/10.5194/egusphere-egu21-16052, 2021.

EGU21-6328 | vPICO presentations | GMPV6.1

Estimating compositions of the deep continental crust

Laura Sammon, William McDonough, and Walter Mooney

The deep continental crust's chemical makeup is central to the debate of crustal formation, evolution, strength, and bulk composition. The impenetrable depths and pressures of the deep (roughly > 10 km) crust force geoscientists to rely on indirect sampling methods, studying medium- to high-grade metamorphic terrains and xenoliths to ascertain the composition of the middle and lower continental crust. Analyzing the deep crust in situ requires geophysical data, such as seismic velocities: Vp, Vs, and the Vp/Vs ratio. Each method provides a different perspective on deep crustal composition, but alone, neither is definitive. 

To address the nonuniqueness in crust composition modeling, we use thermodynamic modeling software (i.e. Perple_X) to relate observed seismic velocities to bulk compositions and mineralogies. We present a multidisciplinary model for the composition of Earth's deep crust, using geochemical and geophysical data. Through a Monte Carlo modeling approach, we determine the best-fit geochemical model for bulk middle and lower crustal compositions. For 12 different tectonic regimes, we quantify uncertainties in crustal composition, temperature, and seismic velocity while recognizing our own scientific biases. We present a global model of deep crustal composition conclude that regional scale geological variations benefit from a higher resolution model. Overall, our model forecasts 77% of the deepest continental crust has 45 to 55 wt.% SiO2; 15% 55 to 65 wt.% SiO2; 8% may have > 65 wt.% SiO2. Of perhaps equal or greater importance, however, we present a scalable, modular program that can be altered to incorporate additional petrological and geophysical constraints, allowing geoscientists to more easily compare different scenarios for the deep crust.

How to cite: Sammon, L., McDonough, W., and Mooney, W.: Estimating compositions of the deep continental crust, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6328, https://doi.org/10.5194/egusphere-egu21-6328, 2021.

Modern quantitative phase equilibria modelling techniques utilizing internally consistent datasets and activity-composition models have been successfully applied to a number of problems in metamorphic geology from hand sample to outcrop scale. Attesting to this the term “phase equilibria” appears in 1 548 articles in the Journal of Metamorphic Geology and one third of those are within the last 10 years. These techniques traditionally proceed either through the manual solution of non-linear equations or by a more automated Gibbs free energy minimization approach. However in order for these techniques to be scaled up to deal with crustal or planetary scale problems a number of hurdles still need to be overcome.

Spatial dimensions in a crustal or planetary model are estimated by grids with modelling conducted on individual cells. This allows processes within cells to effect chemical change to partner cells and thereby approximate open or conditionally open systems. Compositional constraints to the chemical system such as oxygen fugacity are pressure and temperature dependent therefore in order to model a planet wide set of conditions oxygen fugacity buffers are enabled that are dependent on the pressures and temperature of the individual grid cells. Stratigraphic layering is introduced by automating the procedure for setting the initial composition of cells and dependence relations determine the hierarchy of compositional change induced within crustal columns. Phase manipulations such as fluid, melt or crystal addition or extraction are defined by mechanistic parameters that simulate boundary conditions for example melt accumulation thresholds, fluid porosity threshold, rheological lockup conditions etc. Since certain key chemical parameters used in identifying crustal processes such as trace element ratios cannot be traditionally modelled due to their absence from the internally consistent thermodynamic datasets new methods of component approximation are introduced following the methods of trace element partitioning and accessory phase saturation for supersolidus systems.

Finally the increased complexity and number of calculations required to scale up phase equilibria modelling systems to the crustal or planetary scale provides an increased computational challenge therefore new potential strategies are explored for the optimizing of calculation load via parallel processing.

How to cite: Mayne, M.: Adapting phase equilibria modelling to crustal and planetary scale problems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8190, https://doi.org/10.5194/egusphere-egu21-8190, 2021.

GMPV7.1 – Metamorphic minerals: the building blocks of geological paradigms

EGU21-13449 | vPICO presentations | GMPV7.1

Dating polymetamorphism using titanite: Linking trace elements, textures, and ages

Jesse Walters, Alicia Cruz-Uribe, Won Joon Song, Joshua Stone, Hanna Brooks, and Kimberley Biela

Here we present titanite U-Pb dates from two banded calc silicate gneisses (SSP18-1A and 1B) from western Maine. Mineral textures and compositions display multiple phases of metamorphism. The peak lower granulite facies assemblage is Di + Kfs + Pl + Ttn, with little to no calcite present. Late Czo + Tr replaces Di + Pl, suggesting an influx of XH2O > 0.90 fluids. Nearby metapelites show the transition from sillimanite-bearing to muscovite-bearing assemblages, indicating that fluid infiltration may be widespread. Compositional maps of clinopyroxene in SSP18-1B show fracturing and rehealing of early Fe-rich diopside with late Mg-rich diopside. Both samples exhibit overprinting of An-rich plagioclase by increasingly Ab-rich plagioclase. Titanite grains in both samples exhibit BSE textures and compositional variation consistent with multiple phases of growth and dissolution-reprecipitation reactions.

Titanite trace element and U-Pb data were collected by LA-ICP-MS at the University of Maine using an ESI NWR193UC excimer laser ablation system coupled to an Agilent 8900 ICP-MS. Single spot ages range from 280 to 400 Ma with 12-20 Ma propagated 2SE. Four composition-date domains are identified in SSP18-1B: A. 400 ± 8 Ma (dark BSE cores), B. 372 ± 4 Ma (bright BSE cores), C. 342 ± 6 Ma (bright BSE cores, no Eu anomaly), and D. 302 ± 3 Ma (dark BSE rims, low LREE). Titanite Fe and Y concentrations increase with decreasing date, whereas Sr concentrations decrease. In clinopyroxene, Fe and Y decrease between high Fe-diopside and late Mg-diopside, placing the fracturing and rehealing events between 400 and 372 Ma. Strontium concentrations in titanite decrease between subsequent generations of plagioclase, diopside, and titanite, suggesting a continual fractionation of Sr from the reactive bulk composition. Low LREE in ca. 300 Ma titanite domains in both samples are consistent with the formation of texturally late allanite and clinozoisite, thus constraining the timing of the high XH2O fluid infiltration event. Zr-in-titanite temperatures for rims in the quartz-bearing SSP18-1B give a weighted mean T of 764 °C at 4.5 GPa, consistent with the muscovite-absent sillimanite-bearing assemblage in garnet cores from metapelite samples. However, the 100-150 °C lower Grt-Bt temperatures for metapelites are not consistent with peak metamorphic phase equilibria. Our data demonstrate the utility of linking titanite textures and trace element concentrations with those of other minerals to reveal past metamorphic and deformational events. Additionally, we show that titanite may reliably preserve U and Pb isotopic ratios, trace elements, and textures over subsequent high-T metamorphic events.

How to cite: Walters, J., Cruz-Uribe, A., Song, W. J., Stone, J., Brooks, H., and Biela, K.: Dating polymetamorphism using titanite: Linking trace elements, textures, and ages, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13449, https://doi.org/10.5194/egusphere-egu21-13449, 2021.

EGU21-3036 | vPICO presentations | GMPV7.1

Nanoscale evidence of metamorphism – insights from natural and experimentally-treated zircon 

Emily Peterman, Steven Reddy, David Saxey, Denis Fougerouse, and Zakaria Quadir

Nanoscale analyses of zircon have demonstrated that trace elements, including Pb, can be mobilized to discrete sites in radiation damaged zircon. Although several mechanisms for trace element mobility and segregation in zircon have been proposed, most of this work has been conducted on zircon grains with complex geologic histories, making it difficult to directly determine the mechanisms driving trace element mobility and segregation in zircon. To test among the existing hypotheses for mechanisms driving trace element mobility and segregation, we analyzed both untreated and experimentally heated (1450°C for 24h) Archean zircon using atom probe tomography and transmission electron microscopy (TEM). The sample has a simple, well-characterized thermal history, with no significant thermal events since original crystallization. Despite a high calculated radiation dose (>4 x 1018 a/g), the untreated zircon does not contain anomalous nanoscale features. In contrast, the experimentally heated zircon contains abundant clusters of Y, Mg, Al, Pb + Yb that range from 5 nm to 25 nm in diameter with toroidal polyhedral morphologies. The 207Pb/206Pb measured from Pb atoms located within these features is consistent with present-day segregation, thus confirming that these nanoscale features were produced by experimental heating in the laboratory. TEM analysis determined that the clusters are dislocation loops, and that cluster morphology is therefore crystallographically controlled. The largest loops are located in {100} and contain high concentrations of Mg and Al.

These experimentally induced, trace-element-enriched clusters are similar in size, morphology, composition, and crystallographic orientation to clusters observed in zircon affected by natural geologic processes (cf. Valley et al., 2015; Peterman et al., 2016). Although the calculated radiation doses for all analyzed grains are high, comparison of the nanoscale features indicates no apparent correlation between the radiation dose and the density or distribution of clusters. We also observe that trace-element-enriched clusters are conspicuously absent from zircon grains that lack younger igneous or metamorphic rims. These findings suggest that the pressure-temperature-time (P-T-t) history and the dT/dt significantly impact both the nanoscale redistribution of trace elements and the density of these features within zircon. Systematic evaluation of the composition and distribution of these features provides a framework for understanding the nanoscale record of metamorphism.

 

References:

Peterman, E.M., Reddy, S.M, Saxey, D.W., Snoeyenbos, D.R., Rickard, W.D.A., Fougerouse, D., and Kylander-Clark, A.R.C. (2016) Nanogeochronology of discordant zircon measured by atom probe microscopy of Pb-enriched dislocation loops. Science Advances, 2, e:1601218.

Valley, J.W., Reinhard, D.A., Cavosie, A.J., Ushikubo, T., Lawrence, D.F., Larson, D.J., Kelly, T.F., Snoeyenbos, DR., and Strickland, A. (2015) Nano-and micro-geochronology in Hadean and Archean zircons by atom-probe tomography and SIMS: New tools for old minerals. American Mineralogist, 100, 1355-1377.

How to cite: Peterman, E., Reddy, S., Saxey, D., Fougerouse, D., and Quadir, Z.: Nanoscale evidence of metamorphism – insights from natural and experimentally-treated zircon , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3036, https://doi.org/10.5194/egusphere-egu21-3036, 2021.

EGU21-6050 | vPICO presentations | GMPV7.1

Growth, replacement and element diffusion in metamorphic garnet revealed by trace element mapping 

Daniela Rubatto, Lanari Pierre, Marcel Burger, Bodo Hattendorf, Gunnar Schwarz, Detlef Günther, Jörg Hermann, Thomas Bovay, Alice Vho, and Francesca Piccoli

Garnet is one of the most robust and ubiquitous minerals that record element zoning during crustal metamorphism. In addition to major element distribution, zoning in trace elements can provide a wealth of information to document the changing conditions of garnet growth and modification. Trace element distribution in garnet grains was mapped in 2D in thin section with laser ablation inductively coupled plasma time of flight mass spectrometry (LA-ICP-TOFMS) and conventional LA-ICP-MS to achieve a lateral resolution of 15-5 µm and limits of detection for the heavy rare earth elements (REE) down to 0.2 µg/g (Rubatto et al. 2020).

In granulite-facies garnet, major elements show diffusional resetting, whereas trace elements still largely document the growth history. Enrichment of trace elements in the garnet mantle is attributed to the consumption of biotite (V, Cr) and the dissolution of zircon (Zr) and monazite (Y+REE) in the coexisting melt. Lu is notably enriched in the garnet mantle with implications for geochronology. The gradual zoning of Y+HREE between mantle and core is reconcilable with diffusion over ~200 µm in 10 My at temperatures of 750–800°C

In amphibolite facies garnet, Y+REE trace element zoning closely matches the growth zoning in Ca with no notable diffusive modification. Y+REE zoning is dominated by Rayleigh fractionation in the core and in the outer zones it shows annuli that mark the sporadic breakdown of accessory phases.

Garnet in eclogite facies samples that underwent fluid-rock interaction show growth zoning in major and trace elements, with local oscillations and sectors. In certain samples, the overall distribution of REE can be reconciled with diffusion-limited uptake. Where garnet displays fluid-related veinlets, visible in major elements, that cross-cut the primary growth zoning, the regular Y+REE and Cr growth zoning is not affected by the veinlets. This indicates that the veinlets did not form by a crack-seal mechanism but are rather related to a selective replacement process.

 

References

Rubatto D, Burger M, Lanari P, Hattendorf B, Schwarz G, Neff C, Keresztes Schmidt P, Hermann J, Vho A, Günther D (2020) Identification of growth mechanisms in metamorphic garnet by high-resolution trace element mapping with LA-ICP-TOFMS. Contrib Mineral Petrol 175:61 doi.org/10.1007/s00410-020-01700-5

How to cite: Rubatto, D., Pierre, L., Burger, M., Hattendorf, B., Schwarz, G., Günther, D., Hermann, J., Bovay, T., Vho, A., and Piccoli, F.: Growth, replacement and element diffusion in metamorphic garnet revealed by trace element mapping , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6050, https://doi.org/10.5194/egusphere-egu21-6050, 2021.

EGU21-14155 | vPICO presentations | GMPV7.1

Even the low-T garnet from the iconic Barrow’s zone is tetragonal

Bernardo Cesare and Fabrizio Nestola

Common (anhydrous) Fe-Mg-Ca-Mn garnet, the archetypal cubic mineral, has been recently discovered to be tetragonal in metapelites and metabasites from low-temperature regional metamorphic terranes (Cesare et al., 2018).

Despite the differences in bulk rock composition and pressure conditions, such low-T tetragonal garnets share common chemical features, namely high grossular (>25 mol%) and low pyrope (<7 mol%) contents. Similar compositions are documented in other contexts worldwide, both in blueschists-eclogites and in phyllites, including the metapelites from the garnet zone of the iconic Barrovian metamorphism of the Scottish highlands (Viete et al., 2011).

We have analysed a garnet crystal from a chlorite-biotite schist collected at the Barrow’s garnet zone in Glen Esk. The unit cell parameters were refined using diffraction reflections between 1.20 and 0.55 Å providing a tetragonal cell with a = 11.5731(5) Å and c = 11.5887(8) Å and volume V = 1552.15(15) Å3. Systematic absences analysis on complete intensity data collected up to 2theta = 80° indicated I41/acd space group confirming the cell parameters refinement.

Therefore, the garnet is tetragonal and not cubic, as suggested by its weak birefringence under crossed polarizers.

These results show that the tetragonal structure of common Fe-Mg-Ca-Mn garnet is verified whenever this mineral displays the Ca-rich, Mg-poor composition often observed in low-T metamorphic rocks. And support the hypothesis that the lowering of symmetry is composition-dependent.

 

References

Cesare, B., et al. Garnet, the archetypal cubic mineral, grows tetragonal. Sci Rep 9, 14672 (2019).

Viete, D.R., et al. The nature and origin of the Barrovian metamorphism, Scotland: Diffusion length scales in garnet and inferred thermal time scales. J. Geol. Soc. London 168, 115–132 (2011).

 

How to cite: Cesare, B. and Nestola, F.: Even the low-T garnet from the iconic Barrow’s zone is tetragonal, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14155, https://doi.org/10.5194/egusphere-egu21-14155, 2021.

EGU21-1508 | vPICO presentations | GMPV7.1

Elastic geobarometry of quartz inclusions in garnet at high temperature

Mattia Gilio, Nicola Campomenosi, Kira A. Musiyachenko, Ross J. Angel, Bernardo Cesare, and Matteo Alvaro

Elastic geo-thermobarometry allows the retrieval of the pressure and temperature of entrapment of an inclusion within a host (Zhang, 1998; Angel et al., 2014; Angel et al., 2015). So far, quartz-in-garnet elastic geobarometry has mainly dealt with rocks with inclusions entrapped at high pressure and low temperature conditions, such as eclogite. This is because, at high-temperature (HT) and low-to-medium-pressure conditions (T > 700 °C and P < 1.0 GPa), the rock might cross the α–β quartz transition, changing the elastic properties of quartz inclusions. Here we will show some preliminary results of HT elastic geobarometry in quartz inclusions entrapped (or re-equilibrated) within the β–quartz stability field.
The analysed samples come from three HT-LP terranes: the Athabasca granulite terrane in Canada (Dumond et al., 2015), the Jubrique Unit in the Beltic Cordilliera in Spain (Barich et al., 2014), and the Aus granulite terrane from the Namaqua metamorphic complex in Southern Namibia (Diener et al., 2013). These terrains include crustal rocks such as garnet-bearing gneisses and felsic and mafic granulites that equilibrated at low pressures and high temperatures, near or within the β-quartz stability field. Within these samples, Cesare et al. (2020) described post-entrapment shape change of quartz inclusion in garnet. The quartz inclusions have Raman spectra with peaks shifted to lower wavenumbers with respect to the unstrained reference quartz crystal. The changes in Raman peak shifts of the inclusions were converted into strains using the software StRAinMAN (Angel et al., 2019) and have positive volume strains with ε1>0 and ε3<0. The quartz EoS by Angel et al. (2017), which includes the α–β quartz transition, allowed the entrapment isomekes crossing the phase transition to be calculated and the entrapment pressures of quartz inclusions at HT to be estimated. The results of elastic geobarometry for the set of samples in question are consistent with the PT estimates by classic geothermobarometry, suggesting entrapment or re-equilibration at HT within the β–quartz stability field.
This work was supported by ERC-StG TRUE DEPTHS grant (number 714936) to M. Alvaro

References
Angel et al. (2014) - Am. Mineral. 99, 2146-2149. Angel et al. (2015) - J. Metamorph. Geol. 33, 801-813. Angel et al. (2017) - Contrib. Mineral. Petr. 172, 29. Angel et al. (2019) - Z. Krist.-Cryst. Mater. 234, 129-140. Barich et al. (2014) - Lithos 206, 303-320. Cesare et al. (2020) - Earth Planet. Sc. Lett. 555, 116708. Diener et al. (2013) - Precambrian Res. 224, 629-652. Dumond et al. (2015) - J. Metamorph. Geol. 33, 735-762. Zhang (1998) - Earth Planet. Sc. Lett. 157, 209-222.

How to cite: Gilio, M., Campomenosi, N., Musiyachenko, K. A., Angel, R. J., Cesare, B., and Alvaro, M.: Elastic geobarometry of quartz inclusions in garnet at high temperature, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1508, https://doi.org/10.5194/egusphere-egu21-1508, 2021.

In recent years, elastic thermobarometry has gained wider acceptance and utility within the petrologic community and beyond. In particular, quartz-in-garnet (qtz-in-grt) elastic barometry is widely used because of the ubiquity of garnet in metamorphic rocks. The technique is based on using Raman spectroscopy to quantify strains recorded by inclusions, and modeling the elastic evolution of the inclusion-host pair to constrain the initial conditions of inclusion entrapment. Recent studies have validated the technique experimentally by comparing pressures from the qtz-in-grt barometer with experimental conditions of garnet growth and entrapment of quartz, and have shown that the barometer can provide reliable pressure conditions of garnet growth. However, current experimental studies fail to capture the reliability of the technique under disparate pressure (P), temperature (T) and deformation conditions, and studies that systematically compare qtz-in-grt barometry and conventional thermobarometry are lacking. 

In this work, we compare P conditions from qtz-in-grt barometry and conventional thermobarometry from the following locations: spatially and temporally variant high P/T subduction zone eclogite blocks from the Franciscan Complex in California, high P/T subduction zone rocks of varying compositions from Syros, Greece, high P/T and low P/T rocks of varying compositions from the Betics system in Spain, low P/T schists from the Jajarkot and Karnali klippen in the Himalaya, high-P rocks from the Alps, and low P/T metapelites from northeast Nevada. Qtz-in-grt barometry constraints from the Franciscan and Syros show good agreement with some reference P-T conditions, but disagree with some thermodynamic equilibria constraints and subsets of multi-mineral thermobarometry calibrations. Qtz-in-grt barometry constraints from the Himalaya are in excellent agreement with reference P constraints. Measurements of samples from other localities are currently in progress. This set of quartz inclusion analyses further allows us to evaluate the effects of inclusion geometry, anisotropy, P and T conditions of garnet growth, and P and T paths on the ultimate P conditions recorded by the qtz-in-grt barometer. The data-set also provides insights into the possible limitations of other techniques (e.g., conventional thermobarometry).

How to cite: Cisneros, M. and Behr, W.: Quartz-in-garnet elastic barometry vs. conventional thermobarometers: a comparison across diverse tectonic settings, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3822, https://doi.org/10.5194/egusphere-egu21-3822, 2021.

EGU21-10229 | vPICO presentations | GMPV7.1

The corundum conundrum: Constraining the compositions of fluids involved in metasomatic corundum formation.

Vincent van Hinsberg, Chris Yakymchuk, Christopher Kirkland, and Kristoffer Szilas

Corundum, including the variety ruby, is found in numerous locations in the Archaean North Atlantic Craton of southern Greenland. Corundum owes its occurrence to fluid-induced interaction among high-grade metamorphic lithologies of contrasting chemistry. Here, we present constraints on the conditions of corundum formation and the compositions of the fluids involved for the Storø and Maniitsoq ruby localities. We use thermodynamic modelling of mineral and mineral-fluid equilibria, and complement these with experimentally obtained data on mineral solubility to show that metasomatism took place at 650-725˚C and 7 kbar, involving a boron-rich, acidic fluid of low fO2 and low X(CO2). Aqueous concentrations of aluminium are low and indicate that corundum saturation is the result of residual aluminium enrichment rather than aluminium mobilisation. Intrusion of the ca. 2.55 Ga Qôrqut granite and associated fluid release is the likely source of boron, and U-Pb dating of rutile inclusions is consistent with a temporal link between ruby formation and granite emplacement. Interaction with meta-dunite and Fe-sulfides modified the oxidized magmatic fluid, introduced SO4, and produced the reduced, high XMg and K-rich fluid recorded by the corundum-bearing samples. These results highlight a complex interplay among lithologies involved in corundum-formation, but also demonstrate that corundum formation is a predictable part of the geological history where a magmatic intrusion expels a pulse of fluid through its lithologically heterogeneous carapace.

How to cite: van Hinsberg, V., Yakymchuk, C., Kirkland, C., and Szilas, K.: The corundum conundrum: Constraining the compositions of fluids involved in metasomatic corundum formation., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10229, https://doi.org/10.5194/egusphere-egu21-10229, 2021.

EGU21-2291 | vPICO presentations | GMPV7.1

Generation of highly silicic magmas at ultra-high temperature conditions : evidence from melt inclusions in peritectic garnet

Bruna B. Carvalho, Omar Bartoli, Madhusoodhan Satish-Kumar, Tetsuo Kawakami, Tomokazu Hokada, Mattia Gilio, Matteo Alvaro, and Bernardo Cesare

Metamorphism at ultra-high temperature (UHT) conditions (i.e., T >900°C and pressures from 7 to 13 kbar) is now recognized as a fundamental process of Earth’s crust, and although progress has been achieved on its understanding, constraining melt generation and fluid regime at such extreme conditions is still poorly explored.

In this study we use former melt inclusions found in peritectic garnet to investigate anatexis and fluid regime of metapelitic granulites in samples from the Rundvågshetta area, the thermal axis of the Lützow-Holm Complex (East Antarctica). Peak P-T estimates are 925-1039°C at 11.5-15 kbar. The studied rock is a coarse-grained heterogeneous metapelitic granulite with a predominant mafic residual domain and a relatively more felsic, melt-rich domain. The mineral association in the mafic domain typically contains orthopyroxene (Al2O36-8.1 wt.%) + sillimanite + quartz + garnet (Prp42-55Alm40-52Grs3-4Sps0.2-1; XMg0.5) + K-feldspar (Kfs) + cordierite (XMg0.86) + rutile ± sapphirine ±biotite (XMg0.75; TiO23.7-5.8 wt.%) ±plagioclase (An35-46). Interstitial Kfs and quartz with low dihedral angles are often present, in particular as thin films between sillimanite and quartz; these features are interpreted as evidence for the presence of former melt along the grain boundaries. In contrast, the more felsic, melt-rich domain is composed of mesoperthite + quartz + garnet + sillimanite + brown biotite (XMg0.7; TiO23.7-5.4 wt.%) + rutile, but is free of orthopyroxene. Cores of garnet porphyroblasts (0.2-0.8 cm, Prp54-57Alm39-42Grs3-4Sps0.2-0.6, XMg0.57) in the melt-rich domains contain clusters of primary glassy inclusions (GI) and crystallized melt inclusions (nanogranitoids; NI) together with multiphase fluid inclusions (MFI) and accessory phases (mainly rutile and apatite).

The GI (5-20 µm) have negative crystal shapes and contain shrinkage bubbles with or without CO2and N2. In some cases, GI may have trapped apatite and rutile. Micro-Raman investigation suggest that the H2O contents of these glasses range from 0 to 3.4 wt.%. Glasses are weakly peraluminous (ASI=1-1.1), have high SiO2(76-78 wt.%), very high K2O (6.5-10 wt.%) and extremely low CaO and FeO+MgO contents.

The NI have variable sizes (10-150 µm) and often contains intergrowth of plagioclase + quartz, K-feldspar (Kfs) and biotite (Bt). Less frequently NI may have euhedral to subhedral grains of Kfs and Bt. Trapped phases are apatite and rutile, except for one inclusion that contains the sapphirine + quartz pair indicating that melt inclusions were trapped at UHT conditions.

The MFI are composed of CO2(with densities from 0.23 to 0.93 g/cm3) and step-daughter magnesite, pyrophyllite. Methane, N2or H2O were not detected.

Our results show that anatexis of metapelites at extremely hot conditions occurred in the presence of COHfluids and generated highly silicic, weakly peraluminous, mildly to strongly potassic magmas with low H2O contents. Additional trace element data will be acquired to shed light on further geochemical fingerprints of these peculiar magmas.

How to cite: Carvalho, B. B., Bartoli, O., Satish-Kumar, M., Kawakami, T., Hokada, T., Gilio, M., Alvaro, M., and Cesare, B.: Generation of highly silicic magmas at ultra-high temperature conditions : evidence from melt inclusions in peritectic garnet, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2291, https://doi.org/10.5194/egusphere-egu21-2291, 2021.

EGU21-10650 | vPICO presentations | GMPV7.1

Partial melting as an efficient mechanism to produce rare metal granite?

Alexis Plunder, Eric Gloaguen, Saskia Erdmann, Fabrice Gaillard, Josselyn Garde, and Jérémie Melleton

Rare metal (HFSE such Sn, W, Ta, Nb and LILLE such Li, Rb) granite represent the most enriched magmatic rocks on Earth. This is especially true for some elements that belongs either to the European list of critical raw materials and/or the conflict minerals (eg. Li, Sn, W, Nb, Ta). Rare metal granites generally emplace in the vincinity of S-type granites during late orogenic stages. The fraction crystallisation mechanism is postulated to be the unique way to produce enriched silicate melt that later leads to ore deposits due to a combination of magmatic/hydrothermal processes. However, some problems persist in the explanation of the genesis of rare metal granite: crystal fractionation alone does not lead to the very high rare metal concentrations; field discrepancies exist between rare metal granites and their supposed parent peraluminous granites that in some cases are unknown. An alternative model - based on the integration of geochemical, experimental, paleogeographical and structural studies – suggests that low degree partial melting could be an efficient mechanism to produce critical metals enriched silicate melts enriched. To test whether this hypothesis makes sense, we present a study of the behaviour of W, Sn, Nb and Ta in metamorphic minerals from various metapelitic rocks. The selected samples do not present anomalous bulk concentrations of these elements with respect to an average continental crust. They formed at different pressure temperature conditions, in different orogenic belts. The rock collection comprises (i) amphibolite-facies staurolite bearing rocks, (ii) sillimanite-bearing rocks and (iii) granulite-facies orthopyroxene-bearing rocks. These samples represent the three main stages of the classical evolution of a collisional gradient leading to partial melting: they respectively belong to the muscovite + biotite domain, the muscovite-out reaction and the biotite-out reaction. We first estimate pressure-temperature conditions of formation of the rocks using pseudosection modelling. We then expose a set of LA-ICP-MS data to identify the critical metal carriers minerals in our samples. Meanwhile, we investigate the behaviour of W, Sn, Nb and Ta during the muscovite out reaction with two piston cylinder experiments (a partial melting experiment and a crystallization experiment). The protolith consists of a staurolite-bearing metapelite that did not suffer partial melting. In the light of these new data, we discuss the framework of the production of critical metal enriched silicate melts. We show that the main carrier of W is muscovite (up to 30 ppm) and that biotite handle Sn at high temperature (up to 40ppm). Using both the data from the natural sample and the experiments, we highlight that muscovite releases W during its destabilisation ant that Sn enters in biotite until the mineral breaks. We finally discuss the implication of multiple low degree partial melting / melt extraction as efficient way to produce enriched silicate melts.

How to cite: Plunder, A., Gloaguen, E., Erdmann, S., Gaillard, F., Garde, J., and Melleton, J.: Partial melting as an efficient mechanism to produce rare metal granite?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10650, https://doi.org/10.5194/egusphere-egu21-10650, 2021.

EGU21-837 | vPICO presentations | GMPV7.1

On the possible analogy between the Dizi Series of the Southern slope zone of the Greater Caucasus and the folded basement of the plain Crimea: composition, metamorphism, magmatism and age

Irakli Javakhishvili, David Shengelia, Tamara Tsutsunava, Giorgi Chichinadze, Giorgi Beridze, and Leonid Shumlyanskyy

The Dizi Series is exposed within the Southern slope zone of the Greater Caucasus that occurs as a complex geological structure, which constitutes an integral part of the Mediterranean (Alpine-Himalayan) collisional orogenic belt. It is built up of terrigenous and volcanogenic-sedimentary rocks faunistically dated from the Devonian to Triassic inclusive (Somin, 1971; Somin, Belov, 1976; Kutelia 1983). Most of them are metamorphosed under conditions of chlorite-sericite subfacies of the greenschist facies of regional metamorphism (chlorite-phengite-albite±quartz, graphite-sericite-quartz phyllites and marbleized limestones), and only a minor part represented by clay-carbonaceous, phengite-chlorite-carbonaceous and prehnite-chlorite-carbonate schists underwent anchimetamorphism (Shengelia et al., 2015). The Dizi Series is intruded by numerous magmatic bodies of gabbro-diabases, diabases, diorites, diorite-porphyries, syenites, monzo-syenites and granitoids. The age of the intrusions was defined by K-Ar method at 176-165 Ma (Dudauri, Togonidze, 1998) and by U-Pb LA-ICP-MS zircon dating at 166.5 ± 4.6 Ma (authors` unpublished data) and corresponds to the Bathonian orogeny. The Middle Jurassic intrusions caused intense contact metamorphism of the rocks of the Dizi Series resulted in the formation of various hornfelses containing andalusite, cordierite, corundum, biotite, plagioclase, potassium feldspar, clinozoisite, hornblende, cummingtonite, clinopyroxene, wollastonite and scapolite. These rocks correspond to albite-epidote-hornfels, andalusite-biotite-muscovite-chlorite-hornfels and andalusite-biotite-muscovite-hornfels subfacies of the contact metamorphism (Javakhishvili et al., 2020). The analogues of the Dizi Series rocks have not previously been established either in the Greater Caucasus or in the neighboring regions. In our view, Paleozoic rocks similar to the Dizi Series occur under the Cretaceous and Jurassic deposits within the folded basement of the plain Crimea where they were recovered by wells. Most of these rocks, as in the Dizi Series, underwent metamorphism of chlorite subfacies of the greenschist facies and, to a lesser extent, deep epigenesis (clayey-carbonaceous, sericite-carbonaceous, actinolite-chlorite-prehnite, muscovite-albite-chlorite, epidote-actinolite-chlorite and graphite-talc-quartz schists) (Chernyak, 1969). These rocks are also intruded by Middle Jurassic igneous rocks, including gabbro-diabases, diabases, diorites, syenites, monzo-syenites, granite-porphyries, etc. (Shniukova, 2016; Shumlyanskyy, 2019). As a result of the contact metamorphism of the basement rocks, muscovite-quartz-cordierite and cordierite-quartz-feldspar micaceous hornfelses were formed. Quartz syenite yielded a K-Ar age of 158 Ma (Scherbak, 1981), while monzo-syenite was dated at 170 ± 5 Ma applying 40Ar/39Ar method (Meijers, 2010). Thus, based on the rock associations, the nature of metamorphism, the age of the metamorphic and igneous rocks, and on the spatial position of the Dizi Series and folded basement of the plain Crimea we assume that these units developed coevally in similar environment and geological conditions.

Acknowledgements.This work was supported by Shota Rustaveli National Science Foundation (SRNSF) [PHDF-19-159, Regional and Contact Metamorphism of the Dizi Series].

How to cite: Javakhishvili, I., Shengelia, D., Tsutsunava, T., Chichinadze, G., Beridze, G., and Shumlyanskyy, L.: On the possible analogy between the Dizi Series of the Southern slope zone of the Greater Caucasus and the folded basement of the plain Crimea: composition, metamorphism, magmatism and age, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-837, https://doi.org/10.5194/egusphere-egu21-837, 2021.

EGU21-16049 | vPICO presentations | GMPV7.1

High-grade metamorphism in metapelites from the western East European Craton, western Lithuania: challenges of deciphering and dating multi-stage metamorphism

Grazina Skridlaite, Jolanta Putnaite, Boguslaw Baginski, Agnieszka Huc, and Laurynas Siliauskas

The Precambrian basement of the western East European Craton (EEC) in western Lithuania is covered by ca 2 km thick sediments. The rocks are mostly charnockitoids and granitoids with a large area of metasedimentary rocks crosscut by the Lk1-5, Pc1-7, Sh3, Ls1-3, Ml1, Tr11, and other drillings. The metasediments are mostly Fe-rich pelites with subordinate calcic-silicic and mafic rocks.

The rocks were metamorphosed in granulite facies with a variable degree of partial melting resulting in domain-like structure. Most of the granulites contain garnet, biotite, sillimanite, plagioclase, K-feldspar, quartz, and opaque minerals with or without cordierite and hercynite spinel. The earlier geothermobarometry investigations in several drillings have revealed a complex nature of the granulite facies metamorphism. Peak conditions of 800-850o C at 8.5 -9 kbar (samples Tr11, Lk2, 5, Pc1) were obtained from large garnet, biotite, and plagioclase grains with the presence of sillimanite. A second stage of 600-770oC at 6-7 kbar was recorded mainly by the second garnet and cordierite. It was followed by a stage of 550-600oC at 4-5 kbar (Skridlaite et al., 2014).

Using a pseudosection approach (Thermocalc 3.5.0), the preliminary modelling results are the following: in Lk5 sample, the T increases from 790oC at 5.5 kbar to 840oC at 5 kbar; in Tr11 sample, the garnet is stable at 800oC and 7 kbar; in Pc1 sample, a drop of P from 6.5 7.5 to 5 kbar at 760-770oC is prominent.

No metamorphic zircon was produced during the peak metamorphism except for a single metamorphic grain of ca. 1.80 Ga in Lk 2 sample (Bogdanova et al., 2015). Metamorphic overgrowths were too thin to date them. Instead, numerous monazite grains seemed to be promising for dating metamorphic peaks and distinct stages. Two age groups of monazites were distinguished from the preliminary EPMA dating results in Lk1, 2, and 5 samples: 1.79-1.77 Ga and 1.66 Ga - 1.63 Ga. In Tr11 sample, the cores of 1.80-1.79 Ga monazites were overgrown by 1.77-1.76 Ga rims.

After preliminary attempts to model and date distinct stages of metamorphism, we could evaluate advantages of all the methods applied and to look after some solutions of the arising problems. First, the whole-rock chemistry of distinct domains might be helpful to model PT evolution of those domains. More careful mineral analysis in a greater number of samples should be helpful for finding peak and other assemblages in a local equilibrium. HREE, especially Y-content investigations in monazite grains might provide some clues on monazite and garnet behavior during the distinct stage of metamorphism. Some other solutions would be very welcome.

Bogdanova, S. et al., 2015. Precambrian Research, 259, 5–33.

Skridlaite, G. et al., 2014. Gondwana Research, 25, 649-667.

How to cite: Skridlaite, G., Putnaite, J., Baginski, B., Huc, A., and Siliauskas, L.: High-grade metamorphism in metapelites from the western East European Craton, western Lithuania: challenges of deciphering and dating multi-stage metamorphism, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16049, https://doi.org/10.5194/egusphere-egu21-16049, 2021.

EGU21-13256 | vPICO presentations | GMPV7.1

Unraveling potential biases in U-Pb detrital zircon record induced by high-temperature metamorphism (> 850 ºC)

Mahyra Tedeschi, Humberto Reis, Laura Stutenbecker, Matheus Kuchenbecker, Bruno Ribeiro, Vitor Barrote, Pedro Leonardo Vieira, and Cristiano Lana

Detrital zircon records are prone to several sources of bias that can compromise sediment provenance investigations based on U-Pb ages. High-temperature metamorphism (>850 ºC) is herewith addressed as a natural cause of bias since U-Pb zircon data from rocks submitted to these extreme, often prolonged conditions, frequently display protracted apparent concordant geochronological U-Pb records. The resulting spectrum can originate from disturbance of the primary U-Pb zircon system, likewise from subsequent recrystallization and crystallization processes during multiple and/or prolonged metamorphic events. Consequently, a high-grade metamorphosed igneous rock can exhibit a zircon age spectrum similar to that produced by polymict sedimentary rocks, thereby inducing provenance misinterpretations if this rock becomes a source for a sediment. A polymict sedimentary source that undergoes such high temperatures could potentially generate an even more intricate spectrum. Archean, Neoproterozoic and Paleozoic metamorphic rocks from the literature, dated by different techniques (SIMS and LA-ICP-MS), are employed as examples to demonstrate the resulting complications.  The compilation shows that (1) high-temperature metamorphism may generate age peaks of unclear or lacking geological meaning, and (2) the interpretation of detrital zircon age spectra depends on the timing of the metamorphic event (pre- or post-depositional). When high-temperature metamorphic rocks are eroded in uplifted areas, the youngest population of a detrital spectrum represents the maximum depositional age through metamorphic zircon from the source. If a sedimentary succession was subjected to high-temperature metamorphic conditions after deposition, its youngest zircon population more likely records the metamorphism, and the maximum depositional age, as well as older sources cannot be directly accessed. To evaluate the presence of high-temperature metamorphism-related bias in a given detrital zircon sample, we suggest a workflow for data acquisition and interpretation, combining a multi-proxy approach with: in situ U-Pb dating coupled with Hf analyses to retrieve the isotopic composition of the sources, and the integration of a petrochronological investigation to typify fingerprints of the (ultra)high-temperature metamorphic event.

How to cite: Tedeschi, M., Reis, H., Stutenbecker, L., Kuchenbecker, M., Ribeiro, B., Barrote, V., Vieira, P. L., and Lana, C.: Unraveling potential biases in U-Pb detrital zircon record induced by high-temperature metamorphism (> 850 ºC), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13256, https://doi.org/10.5194/egusphere-egu21-13256, 2021.

The Zr content of rutile coexisting with zircon and quartz is mainly a function of the temperature condition and is calibrated as Zr-in-rutile geothermometers. Because of their robustness under high-temperature conditions, they have been applied to granulite facies rocks instead of the conventional Fe-Mg exchange type geothermometers to estimate more reliable temperature conditions. However, it is recently pointed out that in order for rutile to retain the primary Zr content, rutile must be chemically isolated from zircon and quartz during cooling. In this context, inclusion rutile separately enclosed in garnet can be considered to retain the primary Zr content at the time of entrapment, only if rutile, zircon, and quartz are all enclosed in a contemporaneous domain of the garnet.

In this study, we re-examined the pressure-temperature (P-T) conditions of high-grade pelitic gneisses from selected regions (Akarui Point, Skarvsnes, Skallen, and Rundvågshetta) of the Lützow-Holm Complex (LHC), East Antarctica. The LHC has been divided into the upper-amphibolite facies zone, the transitional zone, and the granulite facies zone, based on matrix mineral assemblages of mafic- to intermediate gneisses. Akarui Point is located in the transitional zone and others in the granulite facies zone.

While previous studies commonly applied the conventional Fe-Mg exchange type geothermometers, we applied the Zr-in-rutile geothermometer of Tomkins et al. (2007) to rutile grains enclosed in garnet that also encloses zircon, quartz, and Al2SiO5 minerals. By utilizing the phosphorus zoning in garnet, we defined contemporaneous domains of the garnet and identified coexisting inclusion minerals in each domain. In this way, coexisting Al2SiO5 minerals and rutile grains were utilized to constrain the P-T condition of each domain of the garnet.

As a result, samples from Akarui Point, Skarvsnes, and Skallen were shown to have experienced almost the same P-T conditions around the kyanite/sillimanite transition boundary (~ 830-850 °C/~ 11 kbar). This is significantly higher than the previously estimated peak condition of 770-790 °C/7.7-9.8 kbar based on the conventional garnet-biotite geothermometer in the case of Akarui Point. From Rundvågshetta, where ultrahigh-T metamorphism is reported by previous studies, higher-T condition (850 ± 15 °C/0.1 kbar to 927 ± 16 °C/12.5 kbar) than those of other three regions was confirmed from inclusion rutile in garnet enclosing sillimanite. Therefore, the traditional metamorphic zone mapping, which classified Akarui Point as belonging to the transitional zone, does not reflect the highest metamorphic grade attained. It should be noted that the regional P-T conditions estimated from inclusion minerals in this study is that of earlier higher-P metamorphic stage than the regional P-T conditions determined by the metamorphic zone mapping utilizing matrix mineral assemblages. This result indicates that the Zr-in-rutile geothermometer is a powerful tool to reveal the P-T evolution of high-grade metamorphic terrains, when combined with detailed microstructural observations focusing on the relationship between rutile, zircon, and quartz.

How to cite: Suzuki, K. and Kawakami, T.: Metamorphic pressure-temperature conditions of the Lützow-Holm Complex of East Antarctica deduced from Zr-in-rutile geothermometer and Al2SiO5 minerals enclosed in garnet, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-776, https://doi.org/10.5194/egusphere-egu21-776, 2021.

The Mt. Medvednica is located north of Zagreb, a capital of Croatia, reaching 1033 m in height. It belongs to a complex geological unit located in the border area between Alps, Tisia (crystalline basement of the Pannonian Basin) and Dinarides, that are separated with large and regionally significant tectonic zones. Such geological position inevitably resulted with preservation of characteristics inherited from those large tectonic units, as well as those related to the local scale geological processes. Despite the significant tectonism, the Cretaceous metamorphism of Mt. Medvednica did not exceed P-T conditions of a low-grade metamorphism, as a typical metamorphic rock present is greenschist originated from the mafic igneous rock protolith.

The investigated Mt. Medvednica greenschists are characterized with weak schistosity, granoblastic to granolepidoblastic texture and typically comprise chlorite (40 vol.%), albite (35 vol.%), opaques (up to 15 vol.%), epidote (5 vol.%) and quartz (5 vol.%) that do not exceed 0.5 mm in size, with accessory minerals like titanite, apatite, zircon and calcite, together with rare finding of pumpellyite. The pumpellyite was so far just sporadically reported in the greenschists and was not investigated in detail. On the contrary, pumpellyite was almost regularly reported in the basic rocks from Jurassic ophiolite mélange that tectonically overly greenschists. Pumpellyite can be found there as a secondary hydrous silicate occurring in the altered extrusive rocks that undergone low-temperature ocean floor hydrothermal metasomatism addressed to the ophiolite emplacement.

Since blasts of pumpellyite (ca. 0.2‒0.3 mm in size) that we have found in the greenschists are possible indicators for a polyphase metamorphic evolution, we have conducted microtextural analyses combined with a phase equilibrium modeling approach through the construction of P-T pseudosections. Chemical composition of greenschists suggested an origin from the altered calc-alkaline basalt. Therefore, P-T pseudosections in the range of 100‒1000 MPa and 250‒450 °C were constructed with PERPLEX software in the complex MnNCKFMASHTO chemical system, and contoured by isopleths for the mode and chemical composition of major rock-forming minerals.

Pumpellyite chemistry is characterized with SiO2=36.77‒38.38 wt.%, Al2O3=18.56‒21.00 wt.%, CaO=20.69‒22.89 wt.% and FeO=14.50‒16.85 wt.% that classify this mineral as a pumpellyite-(Fe2+). Metamorphic P-T conditions for pumpellyite-(Fe2+) blasts in the assemblage with chlorite and albite were modeled to 500 MPa and 270°C. Those values correspond well with the theoretically expected values, as well as with previously obtained peak P-T values for greenschist metamorphism of Mt. Medvednica obtained on the metapelites and metabasites with aid of a classical geothermobarometry. For comparison, different pumpellyite chemistry and slightly higher P-T values obtained in this research with pressures (up to +300 MPa) and temperatures (approx. +40°C) point to metamorphic mineral different from pumpellyite related to Jurassic ophiolite mélange altered basic rocks. Microtextural relations between major mineral assemblage and assemblage with pumpellyite show that prograde part of Cretaceous metamorphism, as a consequence of closure of the Neo-Tethys oceanic crust, preceded the growth of pumpellyite that may be ascribed to the retrograde part of a clockwise P-T path.

How to cite: Balen, D. and Schneider, P.: Occurrence and significance of pumpellyite blasts from the greenschists of the Mt. Medvednica (Croatia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10224, https://doi.org/10.5194/egusphere-egu21-10224, 2021.

EGU21-4865 | vPICO presentations | GMPV7.1

Serpentinite Mud Volcanism and Exhumation of Forearc- and Lower Plate Material in the Mariana Convergent Margin System (IODP Expedition 366)

Irena Miladinova, Walter Kurz, Arianna V. Del Gaudio, and Werner Piller

Serpentine seamounts located in the forearc region of a subduction zone represent an excellent natural laboratory for studying the geochemical processes acting along convergent plate margins as well as the forearc structure and the related fault patterns. Active serpentinite mud volcanoes are currently restricted only to the Izu-Bonin-Mariana system, where old (presumably Cretaceous) oceanic lithosphere is subducting in the absence of an accretionary prism.

IODP Expedition 366 recovered cores from three serpentinite mud volcanoes at increasing distances from the Mariana trench (Yinazao, Fantangisña and Asùt Tesoro). Most of the material consists of serpentinite mud containing lithic clasts from the underlying forearc crust and mantle as well as from the subducting Pacific plate. Pelagic sediments and volcanic ash deposits underlying the mud volcanoes were also recovered. Recycled materials from the subducted slab are found at all three mud volcanoes and consist of metavolcanics, metamorphosed pelagic sediments including cherty limestone as well as fault rocks.

Preliminary investigation of lithic clasts from the furthest Asùt Tesoro Seamount revealed metavolcanics as well as serpentinized ultramafics with well-preserved primary mineral assemblages containing olivine, orthopyroxene and spinel.

Recovered clasts from the summit of the adjacent Fantangisña Seamount contain mainly sedimentary rocks of probable Pacific plate provenance. These consist of red cherty limestone breccia, red shale and mud-siltstone transected by a network of carbonate veins. In contrast, recovered material from the flank shows a wider variety including ultramafic rocks with various degrees of serpentinization and matrix composed of mesh and bastite textures, mafic metavolcanics as well as low-grade metasediments (cherty limestones). Interestingly, garnet with andradite composition occurs throughout the matrix of the ultramafics, indicating serpentinization temperatures of at least 225 °C.

Petrological analysis of metabasalt clasts from the flank of Fantangisña shows changes in the mineral composition within the different core intervals. The composition of clinopyroxene varies between aegirine-augite and omphacite, but augite and diopside are also present. The presence of phengite with Si content of up to 3.5 a.p.f.u. as well as the Na-content in pyroxene indicate minimum pressure of 0.7 GPa at ~250 °C. Additionaly, this estimation is supported by the presence of prehnite, chlorite and pumpellyite. 

Furthermore, providing a detailed characterization of the fluids composition and transport would allow the better constraining of the tectonic and metamorphic history as well as the physical properties of the subducting Pacific Plate. Additional data on that will be presented.

How to cite: Miladinova, I., Kurz, W., Del Gaudio, A. V., and Piller, W.: Serpentinite Mud Volcanism and Exhumation of Forearc- and Lower Plate Material in the Mariana Convergent Margin System (IODP Expedition 366), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4865, https://doi.org/10.5194/egusphere-egu21-4865, 2021.

EGU21-2473 | vPICO presentations | GMPV7.1

Brittle deformation during eclogitization: a perspective from a cold, early Paleozoic subduction zone

Michał Bukała, Christopher Barnes, Iwona Klonowska, Károly Hidas, Kathrin Fassmer, and Jarosław Majka

The Tsäkkok Lens (northern Scandinavian Caledonides) represents the outermost part of the rifted passive Baltica margin and consists of sediments and pillow basalts of MORB affinity that were metamorphosed under eclogite facies conditions. Fieldwork and further multidisciplinary analytical approach (including e.g. X-ray and EBSD mapping, and μ-CT imaging) revealed that eclogites record brittle deformation on the μm-to-m scale. This deformation is expressed as a set of microfractures (single-grain rupture) and mesofractures (sealed by garnet- and omphacite-veins). Phase equilibrium thermodynamic modeling of phengite-bearing and phengite-free eclogites performed in NCKFMMnASHT and NCFMMnASHT systems predict profuse dehydration related to lawsonite and amphibole breakdown at ~2.35 GPa and ~600°C, close to the peak conditions of ~2.55 GPa and ~640°C. These estimates are in line with conventional thermobarometry and Zr-in-rutile thermometry results. The evidence for dehydration is also provided by the  occurrence of relic glaucophane in matrix and polyphase inclusions in garnet consisting of clinozoisite + quartz ± kyanite ± paragonite that are interpreted as pseudomorphs after lawsonite. Dehydration reactions were responsible for producing fluid, which facilitated brittle fracturing of the eclogites at HP conditions due to increased pore-fluid pressure (also promoted by the volume changes during eclogitization) on the microscale. Altogether, micro- and mesofracturing acted as migration pathways for released fluid, whereas the microfractures are likely precursors of the mesoscale fractures. Garnet-WR Lu-Hf geochronology provided ages of 487.7 ± 4.6, 486.2 ± 3.2, and 484.6 ± 4.5 Ma. LA-ICP-MS trace element profiles of garnet revealed a well-pronounced peak of Lu content in the garnet cores that decreased towards the rims, indicating these dates represent the age of prograde metamorphism. Therefore, the early Paleozoic Tsäkkok Lens eclogites constitute the oldest documented natural example of HP brittle deformation during eclogitization of blueschist.

Research funded by NCN project no. 2019/33/N/ST10/01479 (M. Bukała) and no. 2014/14/E/ST10/00321 (J. Majka), as well as the Polish National Agency for the Academic Exchange scholarship no. PPN/IWA/2018/1/00046/U/0001 given to M. Bukała.

How to cite: Bukała, M., Barnes, C., Klonowska, I., Hidas, K., Fassmer, K., and Majka, J.: Brittle deformation during eclogitization: a perspective from a cold, early Paleozoic subduction zone, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2473, https://doi.org/10.5194/egusphere-egu21-2473, 2021.

EGU21-3061 | vPICO presentations | GMPV7.1

Decoupled oscillatory and O-isotope zonation in high pressure low temperature garnet: records of heterogeneous fluid transfer processes

Freya R. George, Daniel R. Viete, Janaína Ávila, and Gareth G. E. Seward

High pressure garnet porpyhroblasts formed in subduction zones serve as a witness to an integrated history of fluid flow, deformation, metamorphic reaction, and exhumation processes. Seemingly ubiquitous within garnet from a heterogeneous suite of eclogite and blueschist units is primary oscillatory elemental zoning—rhythmic, short wavelength (< 10 µm) concentric fluctuations concentrated near the rims of porphyroblasts—which has been documented using a combined major element X-ray mapping and trace element LA-ICP-MS mapping approach. This oscillatory zoning must reflect some fundamental petrogenetic process operating during subduction zone metamorphism. While longer length scale (> 50 µm) oscillations have been interpreted to reflect rock-wide P–T changes during physical cycling through the subduction channel, these short wavelength oscillations have typically been interpreted to reflect changes in the effective grain boundary chemistry induced by fluid fluxing during mineral growth.

Here, we present secondary ion mass spectrometry (SIMS) O-isotope data across the oscillatory zoning in garnet from six subduction settings. A lack of spatial covariance between the elemental and δ18O records is inconsistent with the interpretation that oscillatory zoning is directly linked to infiltration of chemically and isotopically distinct fluids. However, in most samples, vascillations in δ18O of < 2 ‰ (over 20–50 µm) in the mantle and rim, coupled with < 1 ‰ net core-to-rim change may point to the predominance of: (a) an internally-controlled grain boundary fluid and relatively stagnant fluid conditions, with grain boundaries that may experience transient opening, heterogeneous and locally-derived fluid fluxing, and then re-sealing, or (b) a rock-buffered oxygen isotope composition during garnet growth between  450 ˚C and 550 ˚C. However, several samples exhibit a systematic 2.5–4 ‰ change in δ18O across oscillatory major and trance element zoning, accompanied by a 2–3 mol% decrease in andradite content. This change, outside that predicted via closed system crystallization and fractionation, is suggested to reflect the relatively uncommon and sudden transient passage of a reduced external fluid. While this dataset does not reveal the mystery of the oscillatory zoning, it demonstrates spatial and temporal heterogeneity of fluid transfer in subduction zones.

How to cite: George, F. R., Viete, D. R., Ávila, J., and Seward, G. G. E.: Decoupled oscillatory and O-isotope zonation in high pressure low temperature garnet: records of heterogeneous fluid transfer processes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3061, https://doi.org/10.5194/egusphere-egu21-3061, 2021.

EGU21-8095 | vPICO presentations | GMPV7.1

Rapid, paced metamorphism of blueschists from laser-based Lu-Hf garnet-domain geochronology and LA-ICMPS trace element mapping

Lorraine Tual, Matthijs Smit, Jamie Cutts, Ellen Kooijman, Melanie Kielman-Schmitt, and Ian Foulds

Unravelling the timing and rate of subduction-zone metamorphism requires linking the composition of petrogenetic indicator minerals in blueschists and eclogites to time. Garnet is a key mineral in this regard, not in the least because it best records P-T conditions and changes therein and can be dated, using either Lu-Hf or Sm-Nd chronology. Bulk-grain garnet ages are the norm and can provide important and precise time constraints on reactions across both facies. Domain dating, i.e., dating of individual growth zones, moves beyond that. Domain dating by combining mechanical micro-milling and Sm-Nd chronology yielded important constraints on garnet-growth and fluid-release rates for blueschists (e.g., Dragovic et al., 2015). Developing this method for Lu-Hf chronology and, importantly, for "common-sized" garnet (≤1 cm) provides an important opportunity to further explore the potential of this approach.

We combined a low-loss micro-sampling technique in laser cutting with a refined Lu-Hf routine to precisely date multiple growth zones of a sub-cm-sized garnet in a blueschist. The targeted grain from a glaucophane-bearing micaschist from Syros Island, Greece, was chemically characterized by major- and trace-element mapping (EPMA, LA-ICPMS) and five zones were extracted using a laser mill. The three core and inner mantle zones are chemically comparable and identical in age within a 0.1 Myr precision (2σ). The outer two zones are chemically distinct and are resolvably younger (0.2-0.8 Myr). The timing of these two major garnet-growth episodes, together with the variations in trace-element chemistry, constrain important fluid-release reactions, such as chloritoid-breakdown. The data show that the integral history of garnet growth in subduction zones may be extremely short (<1 Myr), but may, even in that short timeframe, consist of multiple short pulses. Garnet-forming reactions clearly are localized and, thus, associated with focussed high-flux fluid flow. Beyond subduction-zone processes, our new protocol for zoned garnet Lu-Hf geochronology of "common-sized" garnet opens possibilities for constraining the causes and rates of garnet growth and in turn, the pace of tectonic processes in general.

 

Dragovic, B., Baxter, E.F. and Caddick, M.J., 2015. Pulsed dehydration and garnet growth during subduction revealed by zoned garnet geochronology and thermodynamic modeling, Sifnos, Greece. Earth and Planetary Science Letters, 413, pp.111-122.

How to cite: Tual, L., Smit, M., Cutts, J., Kooijman, E., Kielman-Schmitt, M., and Foulds, I.: Rapid, paced metamorphism of blueschists from laser-based Lu-Hf garnet-domain geochronology and LA-ICMPS trace element mapping, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8095, https://doi.org/10.5194/egusphere-egu21-8095, 2021.

Metamorphic minerals in the Brusque Complex of the northern Dom Feliciano Belt, Brazil, provide new insights into the timing and mode of regional convergence, challenging a long-lived subduction-collision model for orogenesis. The key evidence for subduction is an extensive linear belt of granitic rocks (the Granite Belt) that intruded the length of the hinterland of the Dom Feliciano Belt between ~630─580 Ma, and that is inferred to represent arc magmatism above the subducting Adamastor Ocean prior to continental collision. The study area comprises supracrustal units of a foreland fold-and-thrust belt outcropping along the western edge of the symmetric Kaoko─Dom Feliciano orogenic system. The integrated study of primary metamorphic mineral assemblages and associated deformation fabrics support the interpretation of a fold-and-thrust belt environment, with early tectonic movement top-to-NW away from the hinterland. P─T estimates constrained by garnet compositions indicate peak metamorphic conditions of 540─570°C and 5.5─6.5kbar, in line with typical geothermal gradients associated with orogenic metamorphism. The timing of early garnet growth, and by inference the early stages of crustal thickening in the foreland, is constrained by Lu─Hf garnet geochronology at ~660─650 Ma. The data indicate that the onset of metamorphism and deformation in the orogenic foreland occurred ~20–30 m.y. prior to intrusion of extensive granitic magmatism into the orogenic hinterland. The timing of early orogenic thickening in the foreland precludes the interpretation of the Granite Belt as an arc above a large-scale subduction zone in the lead up to orogenesis. Instead, it is interpreted to represent syn-orogenic magmatism typical for hinterland domains in other ancient and recent orogenic systems.

We appreciate financial support from Diku Norway and CAPES Brazil (project UTF-2018-10004), and from the Czech Science Foundation (project no. 18-24281S). This work was partly supported by the Research Council of Norway through the funding to The Norwegian Research School on Dynamics and Evolution of Earth and Planets, project number 249040/F60.

How to cite: Percival, J., Konopásek, J., and Anczkiewicz, R.: Constraining the timing of crustal thickening using garnet geochronology – An argument against subduction-driven orogenesis in the Dom Feliciano Belt, Brazil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9547, https://doi.org/10.5194/egusphere-egu21-9547, 2021.

EGU21-9515 | vPICO presentations | GMPV7.1

Determining the speed of intracontinental subduction – preliminary results of zoned garnet geochronology in micaschists from the Schneeberg and Radenthein Complexes, Eastern Alps

Kathrin Fassmer, Peter Tropper, Hannah Pomella, Thomas Angerer, Gerald Degenhart, Christoph Hauzenberger, Carsten Münker, Axel K. Schmitt, and Bernhard Fügenschuh

In collisional orogens continental crust is subducted to (ultra-)high-pressure (HP/UHP) conditions as constrained by petrologic, tectonic and geophysical observations. Despite a wealth of studies on the subduction and exhumation of UHP rocks, the duration of prograde metamorphism during subduction is still not well constrained.

We plan to apply Lu-Hf and Sm-Nd geochronology on metamorphic rock samples to date the duration of garnet growth, which represents a major part of prograde metamorphism from the greenschist-facies onward. Micaschist samples from the Schneeberg and Radenthein Units in the Eoalpine high-pressure belt (Eastern Alps) will be used for dating as they contain cm- to dm-sized garnet blasts, which experienced only one subduction-exhumation cycle. With dating different parts of big garnet grains, we test whether (1) it is possible to resolve the duration of garnet growth within single crystals, and (2) Lu-Hf and Sm-Nd systems date the same events in the PT-path or yield complementary information. Additionally, we will perform U-Pb geochronology on titanite in order to obtain the age of the first stages of exhumation; in addition, dating of rutile inclusions as well as matrix rutiles will be used to test Eoalpine prograde age. We will also apply U-Th-Pb monazite dating (EPMA and LA-ICPMS) to some of the samples. Collectively, these data will allow us to compare the duration of subduction and the timing of initial exhumation in a single sample. We then will constrain the PT-path of the dated samples by pseudosection modeling combined with Zr-in-rutile, quartz-in-garnet, and carbonaceous material geothermo(baro)metry. We already have preliminary results for Zr-in-rutile thermometry of rutile inclusions in garnets and matrix rutiles for samples from both locations. We measured Zr content with an EPMA and used the calibrations of Tomkins et al. (2007) and Kohn (2020). The calibration of Kohn (2020) gives overall slightly lower temperatures, but all obtained temperatures lay in a range of c. 500-600 °C in accordance with previously published data. In addition, EPMA, µ-XRF, LA-ICPMS, and µCT will be used to control if garnets preserved major and trace elemental growth zoning and to provide spatial 3D information on inclusion patterns. µCT analyses were already successfully used to obtain the chemical centre of the garnet grains in order to be able to cut them directly through there center. This is important for all in-situ chemical analyses. With dating different parts of single garnet crystals separately with Lu-Hf and Sm-Nd geochronology, we will add tight time constraints to the PT-path and constrain the duration of garnet growth.

With this contribution we formulate the working hypothesis that prograde subduction together with exhumation is a fast process. The basis for testing the idea of fast prograde metamorphism is that many geochronological studies propose a prograde duration of < 10 Ma and studies using geospeedometry sometimes propose an even shorter duration, which is the impetus for this investigation.

References:

Kohn, M.J. (2020). A refined zirconium-in-rutile thermometer. American Mineralogist(105), 963-971.

Tomkins, H.S., Powell, R. & Ellis, D.J. (2007). The pressure dependence of the zirconium-in-rutile thermometer. Journal of Metamorphic Geology(25), 703-713.

How to cite: Fassmer, K., Tropper, P., Pomella, H., Angerer, T., Degenhart, G., Hauzenberger, C., Münker, C., Schmitt, A. K., and Fügenschuh, B.: Determining the speed of intracontinental subduction – preliminary results of zoned garnet geochronology in micaschists from the Schneeberg and Radenthein Complexes, Eastern Alps, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9515, https://doi.org/10.5194/egusphere-egu21-9515, 2021.

EGU21-9657 | vPICO presentations | GMPV7.1

High pressure, halogen-bearing melt in ultra-high temperature felsic granulites of the Central Maine Terrane, Connecticut (US)

Silvio Ferrero, Jay J. Ague, Patrick J. O'Brien, Bernd Wunder, Laurent Remusat, Martin A. Ziemann, and Jennifer Axler

Inclusions of relic high pressure melts provide information on the fate of crustal rocks in the deep roots of orogens during collision and crustal thickening, including at extreme temperature conditions exceeding 1000°C. However, discoveries of high pressure melt inclusions are still a relative rarity among case studies of inclusions in metamorphic minerals. Here we present the results of experimental and microchemical investigations of nanogranitoids in garnets from the felsic granulites of the Central Maine Terrane (Connecticut, US). Their successful experimental re-homogenization at ~2 GPa confirms that they originally were trapped portions of deep melts and makes them the first direct evidence of high pressure during peak metamorphism and melting for these felsic granulites. The trapped melt has a hydrous, granitic, and peraluminous character typical of crustal melts from metapelites. This melt is higher in mafic components (FeO and MgO) than most of the nanogranitoids investigated previously, likely the result of the extreme melting temperatures – well above 1000°C. This is the first natural evidence of the positive correlation between temperature and mafic character of the melt, a trend previously supported only by experimental evidence. Moreover, it poses a severe caveat against the common assumption that partial melts from metasediments at depth are always leucogranitic in composition. NanoSIMS measurement on re-homogenized inclusions show significant amounts of CO2, Cl and F. Halogen abundance in the melt is considered to be a proxy for the presence of brines (strongly saline fluids) at depth. Brines are known to shift the melting temperatures of the system toward higher values, and may have been responsible for delaying melt production via biotite dehydration melting until these rocks reached extreme temperatures of more than 1000°C, rather than 800-850°C as commonly observed for these reactions.

How to cite: Ferrero, S., Ague, J. J., O'Brien, P. J., Wunder, B., Remusat, L., Ziemann, M. A., and Axler, J.: High pressure, halogen-bearing melt in ultra-high temperature felsic granulites of the Central Maine Terrane, Connecticut (US), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9657, https://doi.org/10.5194/egusphere-egu21-9657, 2021.

EGU21-2251 | vPICO presentations | GMPV7.1

Syn-deformational melt percolation through a high-pressure orthogneiss and the exhumation of a subducted continental wedge (Orlica-Śnieżnik Dome, NE Bohemian Massif)

Carmen Aguilar, Pavla Štípská, Francis Chopin, Karel Schulmann, Pavel Pitra, Prokop Závada, Pavlína Hasalová, and Jean-Emmanuel Martelat

High-pressure granitic orthogneiss of the south-eastern Orlica–Śnieżnik Dome (NE Bohemian Massif) shows relics of a shallow-dipping S1 foliation, reworked by upright F2 folds and a mostly pervasive N-S trending subvertical axial planar S2 foliation. Based on macroscopic observations, a gradual transition perpendicular to the subvertical S2 foliation from banded to schlieren and nebulitic orthogneiss was distinguished. All rock types comprise plagioclase, K-feldspar, quartz, white mica, biotite and garnet. The transition is characterized by increasing presence of interstitial phases along like-like grain boundaries and by progressive replacement of recrystallized K-feldspar grains by fine-grained myrmekite. These textural changes are characteristic for syn-deformational grain-scale melt percolation, which is in line with the observed enrichment of the rocks in incompatible elements such as REEs, Ba, Sr, and K, suggesting open-system behaviour with melt passing through the rocks. The P–T path deduced from the thermodynamic modelling indicates decompression from ~15−16 kbar and ~650–740 ºC to ~6 kbar and ~640 ºC. Melt was already present at the P–T peak conditions as indicated by the albitic composition of plagioclase in films, interstitial grains and in myrmekite. The variably re-equilibrated garnet suggests that melt content may have varied along the decompression path, involving successively both melt gain and loss. The 6–8 km wide zone of vertical foliation and migmatite textural gradients is interpreted as vertical crustal-scale channel where the grain-scale melt percolation was associated with horizontal shortening and vertical flow of partially molten crustal wedge en masse.

How to cite: Aguilar, C., Štípská, P., Chopin, F., Schulmann, K., Pitra, P., Závada, P., Hasalová, P., and Martelat, J.-E.: Syn-deformational melt percolation through a high-pressure orthogneiss and the exhumation of a subducted continental wedge (Orlica-Śnieżnik Dome, NE Bohemian Massif), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2251, https://doi.org/10.5194/egusphere-egu21-2251, 2021.

EGU21-6976 | vPICO presentations | GMPV7.1

High-pressure granulite facies metamorphism of Archean Bastar craton at the interface of Eastern Ghats Belt: Implications for cratonic subduction/underthrusting

Padmaja Jayalekshmi, Tapabrato Sarkar, Somnath Dasgupta, and Rajneesh Bhutani

The Bastar Craton at the interface of Eastern Ghats Belt (EGB) contains a mélange of rocks from both the Archean cratonic domain and the adjacent Proterozoic mobile belt domain marking a broad shear zone, known as the Terrane Boundary Shear Zone (TBSZ). The TBSZ preserves a very rare occurrence of high-grade metamorphosed Archean cratonic rocks, whose ancestry has been constrained by Nd model ages. This study presents the petrological and geochemical characterization of mafic granulites and orthopyroxene bearing granitoids from the shear zone and its implications on the tectonic evolution of the craton – mobile belt boundary. Detailed petrographic, geothermobarometric and P-T pseudosection studies indicate that the Bastar cratonic rocks underwent high-pressure granulite facies metamorphism along a clockwise P-T path, reaching ~900°C and 9-10 kbar. The originally amphibolite facies rocks, metamorphosed through dehydration-melting of hornblende (mafic rocks) and biotite (felsic rocks), to attain the peak P-T conditions. We suggest that this high-grade metamorphism was due to the subduction/underthrusting of the Bastar Craton beneath the EGB, supported by the available seismic data, which resulted from far-field stress related to the Kuunga orogeny in an intraplate setting.

How to cite: Jayalekshmi, P., Sarkar, T., Dasgupta, S., and Bhutani, R.: High-pressure granulite facies metamorphism of Archean Bastar craton at the interface of Eastern Ghats Belt: Implications for cratonic subduction/underthrusting, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6976, https://doi.org/10.5194/egusphere-egu21-6976, 2021.

EGU21-9122 | vPICO presentations | GMPV7.1

Sapphire-bearing magmatic rocks as indicators of the continental collision tectonic events: a case study of Uralian orogenic belt

Elena Sorokina, Roman Botcharnikov, Yuriy Kostitsyn, Delia Rösel, Tobias Häger, Mikhail Rassomakhin, Nataliya Kononkova, Alina Somsikova, Jasper Berndt, Tomas Lüdwig, Elena Medvedeva, and Wolfgang Hofmeister

Gem corundum (mainly ruby) occurrences are commonly associated with orogenic belts. Corundum deposits of metamorphic origin are known as robust indicators of continent-continent collision tectonic events. Although sapphire-bearing primary magmatic deposits are also found in orogenic belts, their link to continental collision process remains poorly understood. Here we show that primary igneous blue sapphire occurrences in the Ilmenogorsky alkaline complex of Ilmen Mountains in Uralian orogenic belt are indicative of the continent-continent collision processes among Kazakhstania, Laurussia, and Siberia 330 – 250 Ma ago (Sorokina et al. 2017).

The results of geochemical, mineralogical, and geochronological research of corundum syenite pegmatites demonstrate that in situ primary magmatic corundum-bearing mineral assemblages can be used to evaluate the formation conditions and the time constraints of magmatic processes imposed by tectonic activity during orogenesis.

Thus, the corundum syenite pegmatites have recorded a multistage evolution of the Ilmenogorsky complex. They crystallized at temperatures of 700 – 750°C at 275 and 295 Ma ago (in situ LA-ICP-MS U-Pb zircon dating) within the timeframe of the continental collision of the Uralian orogeny. The isotopic signatures show a geochemical link of these deposits to nepheline syenites – miaskites of the main igneous body in Ilmenogorsky complex. While, some corundum syenite-pegmatites express the metamorphic overprint at temperatures of 700 – 780°C occurred 249 ± 2Ma ago (TISM Rb-Sr isotopy) during limited post-collision stretching period in the area of Ilmenogorsky complex (Sorokina et al. 2021). Hence, these results imply that primary magmatic corundum deposits can be used as an important indicator of continental collision events.

References:

1.              Sorokina E.S., Botcharnikov R., Kostitsyn Yu.A., Rösel D., Häger T., Rassomakhin M.A., Kononkova N.N., Somsikova A.V., Berndt J., Ludwig T., Medvedeva E.V., Hofmeister W. (2021). Sapphire-bearing magmatic rocks trace the boundary between paleo-continents: a case study of Ilmenogorsky alkaline complex, Uralian collision zone of Russia. Gondwana research 2021 (in press).

2.  Sorokina, E.S., Karampelas, S., Nishanbaev, T.P., Nikandrov, S.N., Semiannikov, B.S., (2017). Sapphire Megacrysts in Syenite Pegmatites from the Ilmen Mountains, South Urals, Russia: New Mineralogical Data. Canadian Mineralogist 55, 823–843

How to cite: Sorokina, E., Botcharnikov, R., Kostitsyn, Y., Rösel, D., Häger, T., Rassomakhin, M., Kononkova, N., Somsikova, A., Berndt, J., Lüdwig, T., Medvedeva, E., and Hofmeister, W.: Sapphire-bearing magmatic rocks as indicators of the continental collision tectonic events: a case study of Uralian orogenic belt, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9122, https://doi.org/10.5194/egusphere-egu21-9122, 2021.

Numerous lenses of garnet amphibolite occur in the garnet-bearing biotite-plagioclase gneiss belt in the Baishan area of the Beishan Orogen, which connects the Tianshan Orogen to the west and the Mongolia-Xing’anling Orogen to the east. According to the microstructures, mineral relationships, and geothermobarometry, four stages of mineral assemblages have been identified as follows: (1) a pre-peak stage, which is recorded by the cores of garnet together with core-inclusions of plagioclase (Pl1); (2) a peak stage, which is recorded by the mantles of garnet together with mantle-inclusions of plagioclase (Pl2) + amphibole (Amp1) + Ilmenite (Ilm1) + biotite (Bt1), developed at temperature-pressure (P-T) conditions of 818.9–836.5 °C and 7.3–9.2 kbar; (3) a retrograde stage, which is recorded by garnet rims + plagioclase (Pl3) + amphibole (Amp2) + orthopyroxene (Opx1) + biotite (Bt2) + Ilmenite (Ilm2), developed at P-T conditions of 796.1–836.9 °C and 5.6–7.5 kbar; (4) a symplectitic stage, which is recorded by plagioclase (Pl4) + orthopyroxene (Opx2) + amphibole (Amp3) + biotite (Bt3) symplectites, developed at P-T conditions of 732 ± 59.6 °C and 6.1 ± 0.6 kbar. Moreover, the U-Pb dating of the Beishan garnet amphibolite indicates an age of 301.9 ± 4.7 Ma for the protolith and 281.4 ± 8.5 Ma for the peak metamorphic age. Therefore, the mineral assemblage, P-T conditions, and zircon U-Pb ages of the Beishan garnet amphibolite define a near-isothermal decompression of a clockwise P-T-t (Pressure-Temperature-time) path, indicating the presence of over thickened continental crust in the Huaniushan arc until the Early Permian, then the southern Beishan area underwent a continental crust tectonic thinning process.

How to cite: Kang, W. and Li, W.: Metamorphism and geochronology of garnet amphibolite from the Beishan Orogen, southern Central Asian Orogenic Belt: Constraints from P-T path and zircon U-Pb dating, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2, https://doi.org/10.5194/egusphere-egu21-2, 2021.

A part of Palaeoproterozoic granite-gneiss complex, commonly known as Wangtu Gneissic Complex (WGC), exposed in Wangtu-Karcham-Akpa region along the Sutlej valley, northwest lesser Himalaya, India. The core part of this gneissic complex is exposed as the undeformed granitoid body. The basement of WGC is still more or less in its primeval condition. The Paleoproterozoic thermal evolution of the North Indian Continental Margin is uncertain as the Lesser Himalayan granites are viewed either as a subduction-zone volcanic arc or rift-related magmatism during the Columbia assembly or disintegration process. Integrated mineralogical, geochemical analyses, temperature calculations of Ti solubility in biotite and zircon, and computational phase equilibria modelling of the Wangtu Gneissic Complex (WGC), Himachal Himalaya show a peraluminous existence for most WGC rocks that crystallize at a temperature of ~650°C at a pressure of ~1.0-1.1 GPa. The WGC magmatic zircons' U-Pb ages indicate two significant age groups at 1867 Ma and 2487 Ma.

The U-Pb zircon data and model phase equilibria for metasedimentary rock show the generation of S-type peraluminous magma parental to the WGC, by melting pre-existing supracrustal rocks at ~ 1800 Ma, at temperature ~ 850-900 ° C and pressure 1.1-1.2 GPa, identical to P-T conditions found in modern-day subduction zone settings. Also, TDM model ages vary between 3.07 Ga and 2.28 Ga, and f Sm/Nd values (-0.4930 to -0.3510) of the studied samples suggest a contribution of Achaean crust. This study shows that the North Indian Continental Margin was an active subduction zone during the Paleoproterozoic Columbia supercontinent assembly.

How to cite: Hifzurrahman, , Nasipuri, P., Raza, M. B., and Ganaie, A. M.: Evolution of Wangtu Gneissic Complex and its paleogeographic implications in Columbia assembly: insights from geochemistry, geochronology, and computational phase-equilibria study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14868, https://doi.org/10.5194/egusphere-egu21-14868, 2021.

EGU21-5612 | vPICO presentations | GMPV7.1

Barrovian-type metamorphism in the western domain of the Cordillera Darwin Metamorphic Complex, Fuegian Andes

Mauricio Calderon, Catalina Zúñiga, Francisco Hervé, Thomas Theye, Gonzalo Galaz, Diego Rojo, and Rodrigo Suárez

The Cordillera de Darwin Metamorphic Complex (CDMC) comprise metamorphosed supracrustal rocks and metaplutonic suites which records a unique tectonic evolution among the metamorphic complexes of the southernmost Andes. The pressure (P) and temperature (T) conditions determined in garnet-bearing schists in the Central Domain of the CDMC indicate a clockwise P-T path of metamorphism reaching burial depth as high as 12 kbar at ca. 620°C. This metamorphic event has been related to the closure of a marginal back-arc basin (Rocas Verdes Basin) and collision of an ensialic magmatic arc with the continent in the late Cretaceous. We focus on garnet-biotite schists intercalated within a huge block consisting of repeated sequences of metabasalts and amphibolites (Rocas Verdes Ophiolites), located in the Western Domain of the CDMC, at Seno Martínez. The chemical zonation of small garnet porphyroblasts (diameter of ca. 300 um) record two stages of metamorphism. Garnet is almost almandine in composition with lesser amounts of Ca, Mn and Mg.  The concentric zonation is characterized by relatively lower contents of Fe-Mg and higher contents of Ca-Mn in the core. Garnet bear tiny inclusions of clinozoisite, which is also present as isolated grains in the foliated matrix. Laths of biotite define the main foliation and have a nearly constant composition characterized by XFe of ca. 0.6. Two generations of phengitic white mica are identified on basis of Si content (a.pf.u.) varying between 3.20-3.30 (early generation) and of ca. 3.15 (late generation). To reconstruct the P-T conditions of metamorphism through thermodynamic modeling using the Perple_X software package, the bulk rock and mineral composition were considered. Using compositional isopleths of XFe, XMg, XCa and XMn in zoned garnet, Si content in white mica and XFe in biotite allow the constrain two stages of metamorphism (M1 and M2). The P-T conditions of M1, represented by the composition of the garnet core, are restricted to ca. 8 kbar and 400°C. M2 is restricted to ca. 7.5 kbar at 480°C, determined with the composition of the garnet rim, XFe in biotite and Si content in late phengitic white mica. Our preliminary results indicate that ophiolitic rocks and interleaved garnet-bearing schists were tectonically buried and metamorphosed in a relatively hot subduction interface characterized by a geothermal gradient of ca. 16°C/km, prior to the collision of the ensialic magmatic arc. Acknowledgements. This study was supported by the Fondecyt grant 1161818.

How to cite: Calderon, M., Zúñiga, C., Hervé, F., Theye, T., Galaz, G., Rojo, D., and Suárez, R.: Barrovian-type metamorphism in the western domain of the Cordillera Darwin Metamorphic Complex, Fuegian Andes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5612, https://doi.org/10.5194/egusphere-egu21-5612, 2021.

The Pakhal basin occurs as two parallel NW-SE trending sub-basins (Western and Eastern) located at the East-Dharwar Craton (EDC) and the Bastar Craton junction. The metasedimentary rocks exposed at the western side of the basin are known as the Pakhal belt, whereas those exposed on the eastern sides are known as the Albaka belt. The aggregate thickness of the sediments is nearly 6000 meters. Researchers have studied the geochemical affinities of Pakhal and Albaka rock, which proved to be crucial to understand the basin-architecture, source of sediments, and basin evolution in the context of rifting of the Dharwar and the Bastar craton However, the timing of inversion of tectonics and subsequent basin convergence is not studied.

Xenoliths of metasedimentary rocks are exposed within the EDC granites near the Pakhal basin. Aggregates of biotite, muscovite, plagioclase, and quartz constitute these metasedimentary rocks. Monazite, zircon, and iron-oxide are present as accessory minerals. The XMg Biotite (22 Opfu) varies from 0.86-0.10 and Ti content of biotite varies between 0.26-0.34 apfu. The mica is mostly muscovite with mean Si (22 Opfu.) content of 6.28 apfu. The XAb of plagioclase is constrained to be 0.97 apfu. The P-T conditions of metasedimentary xenoliths are constrained by using conventional geothermobarometers and P-T pseudosection analysis. The Ti content in biotite yield peak temperature 6500C for the stabilization of biotite. The P-T pseudosection analysis and subsequent modeling of compositional parameters imply a temperature window of 600-700 0C and pressure 0.6-1.0 GPa for the stability of biotite-muscovite-plagioclase-quartz assemblages. ~ 50 μm monazites grains are dispersed throughout the studied sample. The ThO2 content in the monazite grains varies between 1.7-5.8 wt%. Compositionally, the monazite grains are mostly La-Ce-Nd monazite in a tripartite classification. In a histogram distribution, the U-Th-Pb total spot ages exhibit two prominent peaks, at ~ 1295 Ma and ~ 1111 Ma. When combined with the P-T pseudosection analysis, the monazite ages imply rifting and opening the basin at ~ 1295 Ma. The ~ 1111 Ma monazite growth is correlated with granite emplacement and amalgamation of the Dharwar and the Bastar craton during Neoproterozoic Rodinia assembly.

How to cite: Ganaie, A. M., Hifzurrahman, , Nasipuri, P., and Satpathi, K.: Petrology, phase equilibria and In-situ U-Th-Pbtotal monazite geochronology of metasedimentary rocks from Pranhita-Godavari Basin and its implication in Mesoproterozoic-Neoproterozoic Supercontinent Assembly, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14948, https://doi.org/10.5194/egusphere-egu21-14948, 2021.

  The Kuruqtag area, located at the northeastern margin of the Tarim Craton, where the Precambrian metamorphic basement exposed, is ideal for studying the Precambrian geological evolution of the Tarim Craton. Previous zircon U-Pb chronology studies revealed that the metamorphic basement recorded a Paleoproterozoic tectonothermal event and suggested it associates with the Paleoproterozoic Nuna/Columbian supercontinent convergence event. However, the extensive range of metamorphic ages obtained from different studies (ranging from 1750-2000 Ma) and the lack of detailed P-T path corresponding to different metamorphic ages make it difficult to constrain the evolutionary framework of the Tarim craton during the Paleoproterozoic, which in turn affects future comparative regional studies.

  To constrain the P-T path, in this study, we performed detailed petrography, mineral chemical, and phase equilibrium modeling of metapelite collected from the khondalite series in the western part of the Kuruqtag (a garnet-sillimanite-cordierite-biotite gneiss with metamorphic age ~1850 Ma) and obtained the following results.

  Through petrographic studies, at least three phases of mineral assemblages can be used to invert the P-T path experienced by the metapelite. They are    M1 (peak metamorphic stage):represented by fine-grained biotite remnant (Bi Ⅰ) + fine-grained plagioclase(Pl Ⅰ) and quartz+ Ilmenite + , occurring as inclusions within the metamorphic garnet, and equilibrated mineral assemblages is: Grt(core) + Bi Ⅰ + Sill + Kfs + Pl Ⅰ + Qz + Ilm. M2 (isothermal depression stage), represented by cordierite occurring in the garnet rim or with spinel in the matrix, inferred equilibrated mineral assemblages is Grt(rim)+Bi Ⅰ +Cd+Kfs+Pl ⅠⅠ+Ilm+Sp.M3 (isothermal depression stage), is marked by the appearance of new growth of biotite(Bi ⅠⅠ) and the conversion of Sill to And. 

The P-T conditions for the mineral assemblage evolution (M1 → M3) are constrained by a P-T pseudosection constructed in the Na2O -CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O- TiO2-O2 chemical system. The resulting P-T path is clockwise from the M1 stage (840°C, 4 Kbar) through the isothermal depression path to M2 (840-850°C,5 Kbar) and then through the near-isobaric cooling path to the M3 stage (650°C, 3.5-4 Kbar).

How to cite: Guo, Y.: Petrography and phase equilibrium modeling of Paleoproterozoic metapelite in the Kuluktag area of Tarim Craton, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11000, https://doi.org/10.5194/egusphere-egu21-11000, 2021.

GMPV8.1 – The Dynamics of Magmatic Plumbing Systems

EGU21-880 | vPICO presentations | GMPV8.1

Formation and evolution of a magma reservoir at a slow-spreading center (Atlantis Bank, Southwest Indian Ridge)

Marine Boulanger, Lydéric France, Jeremy Deans, Carlotta Ferrando, Johan Lissenberg, and Anette von der Handt

The heterogeneous presence of ephemeral magmatic systems below the ridge axis and their complexity mostly account for the heterogeneous character of the oceanic crust accreted at (ultra) slow-spreading ridges. In order to better understand the magmatic processes involved in slow-spreading lower oceanic crust formation, we studied a drilled section of an oceanic core complex (OCC) interpreted as an exhumed portion of lower crust close to the ridge axis. We focused on ODP Hole 735B which presents the most primitive lithologies sampled at Atlantis Bank OCC (Southwest Indian Ridge) in a ~250 m thick section previously interpreted as a single crustal intrusion.

We combined detailed structural and petrographic data with whole-rock and in situ mineral analyses to determine the processes of emplacement and differentiation of melts within this section. The lower half of the unit is comprised of alternating troctolites and olivine gabbros showing intrusive contacts, and both magmatic and crystal-plastic fabrics. Such features are lacking in the upper half, rather uniform, gabbroic sequence. Whole-rock compositions highlight the cumulative character of both lower and upper units, and a great compositional variability in the lower sequence, whereas the upper sequence is rather homogeneous and differentiates up-section. In situ analyses of mineral phases document magma emplacement processes and provide evidence for ubiquitous reactive porous flow during differentiation. Comparison between both units' geochemistry also led us to strongly favor a model of formation of the reservoir that genetically links melts from the lower and the upper unit.

We show that the whole section, and related geochemical units, likely constitutes a single magmatic reservoir, in which the lower unit formed by emplacement of primitive sills related to the continuous recharge of primitive melts. Recharge led to partial assimilation of the crystallizing primitive mush, and related hybridization with interstitial melts. Hybrid melts were progressively collected in the overlying mushy part of the reservoir (upper unit), whereas the sills' residual melt differentiated by reactive porous flow processes under a predominantly crystallization regime. Similarly, hybrid melts’ evolution in the upper unit was governed by upward reactive porous flow and progressive differentiation and accumulation of evolved melts at the top of the reservoir. Our results provide the first integrated model for magma reservoir formation in the lower slow-spreading oceanic crust, and have potential implications regarding the lower crust structure and the composition of MORBs.

How to cite: Boulanger, M., France, L., Deans, J., Ferrando, C., Lissenberg, J., and von der Handt, A.: Formation and evolution of a magma reservoir at a slow-spreading center (Atlantis Bank, Southwest Indian Ridge), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-880, https://doi.org/10.5194/egusphere-egu21-880, 2021.

EGU21-6157 | vPICO presentations | GMPV8.1

Accretion of fast-spread lower oceanic crust: drill core GT1 from the ICDP Oman Drilling Project

Dominik Mock, David Axford Neave, Samuel Müller, Dieter Garbe-Schönberg, Benoit Ildefonse, Jürgen Koepke, and Oman Drilling Project Science Team

The Sumail Ophiolite at the northeastern coast of the Sultanate of Oman provides an ideal field laboratory for studies on fast-spread oceanic crust on land. Based on numerous campaigns in the past, the Oman Drilling Project (OmanDP) of the International Continental Scientific Drilling Program (ICDP) obtained nine 300 to 400 m long drill cores covering sections from the upper mantle to the dyke/gabbro transition zone. Drill core GT1 is located in the layered gabbros between ~1200 and ~800 m above the Moho transition zone (m.a.M.) and comprises of modally layered gabbro with cm-scale coherent bands of troctolite, anorthosite, and wehrlite. We prepared thin-sections with a small average spacing of <2 m and analyzed them by petrological, microstructural and geochemical methods. Clinopyroxene reveals Mg# (where Mg# = Mg/Mg+Fe x 100; molar basis) between 74 and 86, with some heavily altered olivine relicts between 70 and 83, and Ca# (where Ca# = Ca/Ca+Na x 100; molar basis) of plagioclase range from 68 to 87. The plots of these data show clear and consistently decreasing trends from the base of the drill core up section to a crustal height of 1070 m.a.M. where all fractionation indices show significant minima. Above 1070 m.a.M., the indices increase to their maxima. Clinopyroxene shows core/rim zonation in Mg# and TiO2 content with more primitive core compositions. However, distinct zonation is only observed above the minima mentioned above. Besides this general fractionation trend from the core base to 1070 m.a.M., individual fractionation trends on the scale of several decameters can be defined along the core (e.g., 820 to 895, 890 to 970, and 1085 to 1110 m.a.M.). As a quantifier of the plagioclase fabric symmetry, we used the BA index which ranges from 0 for a purely foliated to 1 for a purely lineated fabric. We found that the rock fabric changes parallel the observed fractionation trend with significant lineation at the base of the core and evolving towards almost purely foliated fabrics up section to 1070 m.a.M., indicating either an intense compaction or weaker shearing, or both at 1070 m.a.M. A possible scenario creating the observed trends is an evolved melt entering the more primitive crystal mush at 1070 m.a.M.  and crystallizing primary phases with significantly more evolved compositions. In such an environment, where the liquid/solid ratio is increased, minerals may be more sensitive to compaction and less affected by shearing which is possibly induced by convection of the upper mantle. Magmatic deformation would therefore lead to a strong foliation with only a limited lineation component. Moreover, we interpret the observed decameter-scale fractionation trends, also being accompanied by slight changes in the fabric, as results of individual magma reservoirs crystallizing in-situ and leading to the accretion of the lower gabbros in Oman (e.g., [1]).

 

[1] Kelemen, P. B., Koga, K., & Shimizu, N. (1997). Geochemistry of gabbro sills in the crust-mantle transition zone of the Oman ophiolite: Implications for the origin of the oceanic lower crust. Earth and Planetary Science Letters, 146(3-4), 475-488.

How to cite: Mock, D., Neave, D. A., Müller, S., Garbe-Schönberg, D., Ildefonse, B., Koepke, J., and Science Team, O. D. P.: Accretion of fast-spread lower oceanic crust: drill core GT1 from the ICDP Oman Drilling Project, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6157, https://doi.org/10.5194/egusphere-egu21-6157, 2021.

EGU21-14613 | vPICO presentations | GMPV8.1

Constraints on the pre-eruption thermal and fO2 conditions in the magma reservoir of Ciomadul (SE Carpathians, Romania) based on Fe-Ti oxide geochemistry

Máté Szemerédi, Katalin Mészáros, Réka Lukács, Zoltán Kovács, and Szabolcs Harangi

Ciomadul is the southernmost eruptive centre of the post-collisional Călimani-Gurghiu-Harghita andesitic-dacitic volcanic chain (SE Carpathians, Romania) and represents the latest manifestation of the Neogene to Quaternary volcanism in the Carpathian-Pannonian Region. Ciomadul consists of older, peripheral shoshonitic to dacitic lava domes formed episodically between 1 Ma and 300 ka and a voluminous, central volcanic complex developed within the last 200 ka. Although several lines of evidence (based on petrology, geophysics and gas monitoring) suggest a long-lived magmatic plumbing system holding a potentially active magma storage (“PAMS” volcano) beneath Ciomadul, the pre-eruptive conditions of the upper crustal magma reservoir (including temperature, oxygen fugacity and TiO2 activity) are not completely explored so far. In this study 23 rock samples, representing the whole volcanic activity of Ciomadul in time, were involved. Fe-Ti oxide (magnetite-ilmenite) grains were selected from magnetic heavy minerals, but only a few of the samples contained both magnetite and ilmenite crystals. Equilibrium between Ti-magnetite and ilmenite was tested by their chemical composition (Mg/Mn ratios).

Various geothermobarometer calibrations, including Andersen and Lindsley (1985, 1988) as well as Ghiorso and Evans (2008), were applied to calculate temperature and oxygen fugacity from Fe-Ti oxide compositions. Our results show that, in case of dacitic pyroclastic rocks, temperature values gained by the method of Ghiorso and Evans are significantly lower (640–780 °C) than those obtained by the geothermometers of Andersen and Lindsley (1985, 1988), showing 750–830 and 710–790°C temperatures, respectively. On the other hand, andesitic lava dome rocks of Dealul Mare show higher, 800–900 °C temperature according to all of these methods. The obtained temperature was compared with amphibole-plagioclase thermometry results and this shows a better agreement with the values yielded by the Andersen and Lindsley (1985) Fe-Ti oxide thermometry, particularly for the pumice samples.

In case of oxygen fugacity, the Ghiorso and Evans (2008) and Andersen and Lindsley (1985) methods showed fairly similar values (fO2=0.9–1.8) whereas the Andersen and Lindsley (1988) calculations gave higher oxygen fugacity (fO2=1.1–2.5). Nevertheless, these results, irrespective the applied calculation methods, suggest relatively oxidized conditions (ΔNNO>1) what is comparable with many other andesitic to dacitic volcanic systems (e.g. Mount St. Helens, Mount Unzen, Santorini). Values of TiO2 activity was calculated and obtained a range between 0.76 and 0.98 what is consistent with the common presence of titanite.

 

This study was financed by NKFIH K135179 project.

 

Andersen, D.J. & Lindsley, D.H. (1985). EOS Transactions of the American Geophysical Union, 66, 416.

Andersen, D.J. & Lindsley, D.H. (1988). Amer Miner 73:714–726.

Ghiorso, M.S. & Evans, B.W. (2008). Amer J Sci 308:957–1039.

How to cite: Szemerédi, M., Mészáros, K., Lukács, R., Kovács, Z., and Harangi, S.: Constraints on the pre-eruption thermal and fO2 conditions in the magma reservoir of Ciomadul (SE Carpathians, Romania) based on Fe-Ti oxide geochemistry, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14613, https://doi.org/10.5194/egusphere-egu21-14613, 2021.

EGU21-13667 | vPICO presentations | GMPV8.1

Trace element partition coefficients and petrogenesis of the 154 ka dacitic Haramul Mic lava dome (Ciomadul, Romania)

Emese Pánczél, Maurizio Petrelli, Réka Lukács, and Szabolcs Harangi

Haramul Mic is a ~0.15 km3 volume, crystal-rich, homogeneous, high-K dacite lava dome, which is one of the oldest ones in the Ciomadul Volcanic Complex (Romania, eastern-central Europe). The eruption that formed the lava dome occurred after about 200.000 years of quiescence. Eruption age of the dome determined by (U-Th)/He dating on zircon gave 154 +/- 16 ka that is in agreement with the youngest zircon U-Th outer rim date (142 +18/-16 ka). The apparently continuous crystallization of zircon between the eruption age and the 306 +/- 37 ka oldest zircon core date records a long-living magmatic plumbing system.

The Haramul Mic lava dome rock has 35-40% average crystal content and consists of plagioclase, amphibole, biotite and accessory zircon, apatite, titanite and Fe-Ti oxides. The groundmass is mainly built up by perlitic glass with some microlites and sheared vesicles. The dacite contains sparse mafic enclaves with K-rich, shoshonitic bulk composition, composed of plagioclase and biotite in addition to less amount of amphibole. Felsic crystal clots are more common and they comprise plagioclase, amphibole, biotite and interstitial vesicular glass.

Trace element content of the mineral phases and the groundmass glass was determined by LA-ICP-MS. All of the studied phases show homogeneous trace element compositions and along with the textural characteristics these imply general equilibrium state in the magma storage system before the eruption. Amphibole-plagioclase geothermometer and geobarometer calculations result in 700-800 oC crystallization temperature and 200-300 MPa crystallization pressure.

In order to reveal the magma chamber processes that triggered the eruption and formed the Haramul Mic lava dome after long quiescence time, it is necessary to understand better the behaviour of trace elements as the most sensitive indicators of magma reservoir mechanisms. We determined mineral-liquid trace element partition coefficients and evaluated the result in the context of crystal lattice strain model. They show many similarities with those proposed for the Fish Canyon Tuff dacite except for Li and Sc. The anomalous behaviour of Sc is clearly expressed by the elevated concentration in the glass phase and many times, there are some zonation in Sc from crystal core to rim. This could be explained either by inherently higher Sc content of the melt reflecting the nature of the primary magmas or by partial remelting of biotite just before the eruption. Significant positive anomaly of Li content can be observed in biotite crystals of the mafic enclave compared with the dacitic host rock. Li content of plagioclase varies between 15-30 ppm with slight rimward depletion.

Eruption initiation cannot be explained by physical mixing of mafic recharge magma, but rather by volatile transfer or second boiling. The water-rich nature of the melt is reflected by the abundant vesicles in the glassy groundmass. Furthermore, the amphibole phenocrysts have sharp margin without resorption rim, which suggest hydrous melt phase and relatively fast magma ascent.

This research belongs to the NKFIH-OTKA K135179 project and was supported by the ÚNKP-19-1 New National Excellence Program of the Ministry for Innovation and Technology.

How to cite: Pánczél, E., Petrelli, M., Lukács, R., and Harangi, S.: Trace element partition coefficients and petrogenesis of the 154 ka dacitic Haramul Mic lava dome (Ciomadul, Romania), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13667, https://doi.org/10.5194/egusphere-egu21-13667, 2021.

EGU21-10054 | vPICO presentations | GMPV8.1

The transitions from mildly explosive to caldera-forming eruptions at Colli Albani volcano (Italy)

Mónica Ágreda López, Luca Caricchi, Corin Jorgenson, Alessandro Musu, and Guido Giordano

The Colli Albani volcano is an ultrapotassic caldera complex located 30 km to the SE of Rome and has displayed a wide range of eruptive behaviors, ranging from effusive activity to highly explosive and large volume eruptions (up to 63 km3 dense rock equivalent per eruption) despite its mafic nature.

We combine physical volcanology, petrology, and geochemistry to focus on the mildly explosive to effusive products of two sections (Tuscolo and Artemisio) which are located on opposite sides of the main caldera and stratigraphically between the last large ignimbrite, Villa Senni. The target of this study is to identify the processes responsible for the transition from the smaller explosions to the larger caldera-forming ignimbrite eruptions, and eventually trace how the magmatic system rebuilds in the interim.

Whole rock analyses, mineral chemistry, and petrography of fall deposits from both field localities are compared with an existing dataset for the Villa Senni ignimbrites. We will use unsupervised and supervised machine learning approaches to identify similarities and differences between large caldera-forming eruptions and mild-explosive to effusive activity and identify the processes modulating the transition between these two behaviours.

How to cite: Ágreda López, M., Caricchi, L., Jorgenson, C., Musu, A., and Giordano, G.: The transitions from mildly explosive to caldera-forming eruptions at Colli Albani volcano (Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10054, https://doi.org/10.5194/egusphere-egu21-10054, 2021.

EGU21-7852 | vPICO presentations | GMPV8.1

A model for multicomponent diffusive bubble growth in magmas

Simone Colucci, Federico Brogi, and Chiara Montagna

Bubble growth is one of the key processes that govern the degassing of magmatic systems and drive volcanic eruptions. Typically, the gas exsolution process begins with the nucleation of bubbles in an oversaturated melt and continues with bubble growth. Bubbles grow by mass diffusion, when the silicate melt is oversaturated in volatiles, and by mechanical expansion as a response to pressure decrease. The viscosity of the surrounding melt and the surface tension oppose a resistance to bubble growth and control the mechanical disequilibrium between the bubbles and the melt itself. The combination of the Rayleigh-Plesset equation with a diffusion equation represents a common approach to describe diffusive bubble growth. A number of models have been developed for describing bubble growth dynamics in magmas, most of them accounting for a single volatile specie. Nevertheless, the multicomponent nature of magmatic volatiles has long been recognised to play a major role in controlling magmatic exsolution process. Here we present a model describing bubble growth in magmas in the presence of multiple volatile species through a fully non-ideal multicomponent saturation model.  Numerical simulations show the role of the different species (e.g., water and carbon dioxide) in the dynamics of diffusive bubble growth for different melt compositions. The new model is implemented in the MagmaFOAM library,  a dedicated computational tool to solve multiphase flows characterizing magmatic systems that extends the open-source library OpenFOAM. Within the MagmaFOAM framework it is possible to combine the bubble growth model with fluid solvers in order to fully capture the multi-scale nature of liquid and gas phases in magmatic systems.

How to cite: Colucci, S., Brogi, F., and Montagna, C.: A model for multicomponent diffusive bubble growth in magmas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7852, https://doi.org/10.5194/egusphere-egu21-7852, 2021.

EGU21-10936 | vPICO presentations | GMPV8.1

The effect of melt water content and isothermal annealing time on the formation and evolution of clinopyroxene-titanomagnetite clusters

Stefano Peres, Thomas Griffiths, Matteo Masotta, and Alessio Pontesilli

Crystal clustering influences the formation of crystal mushes and the rheology and differentiation of magmas. Heterogeneous nucleation is known to be an important cluster-forming mechanism, but there has been little systematic experimental study of cluster formation and evolution.

In this study, we analysed dynamic crystallization experiments from Pontesilli et al. (2019), focusing on clusters of clinopyroxene (cpx) and titanomagnetite (tmt). These experiments aimed to reproduce the crystallisation behaviour of dry (nominally 0 wt.% H2O) and hydrous (2 wt.% H2O added) Etnean trachybasalt at mid-crustal storage conditions (400 MPa, 1100°C, NNO+1 oxygen buffer, corresponding to undercooling of 120°C and 80°C respectively). After superheating at 1300°C for 30 minutes, samples were cooled at 80°C/min to 1100°C and annealed for dwell times ranging from 0.5h to 8h.

Electron backscatter diffraction (EBSD) maps and image analysis were used to quantify clustering parameters such as tmt number density, “shared perimeter fraction” (“SPF”, the fraction of total tmt boundary length shared between cpx and tmt), “fraction of touching tmt” (“FTT”, the fraction of all tmt grains that are touching cpx), and the crystallographic orientation relationships (CORs) between cpx and tmt. Dry samples generally show a higher number density of tmt crystals than wet samples. SPF and FTT are highest (≥ 0.40 and ≥ 0.93 respectively) in the 0.5h duration dry experiments. Both parameters fall to ≤ 0.25 and ≤ 0.75 respectively after 4h of annealing. In wet experiments, SPF and FFT are lower (≤ 0.33 and ≤ 0.79 respectively) at 0.5h annealing time and do not decrease strongly with annealing.

EBSD maps reveal that > 70 % of tmt grains are in contact with cpx in all analysed samples. Tmt exhibits two closely related CORs to cpx. More than 60% of total tmt-cpx boundary length in all samples follows COR 1 ([-110]tmt[010]cpx, [111]tmt(100)*cpx, [-1-12]tmt[001]cpx) or  COR 2 ([-110]tmt[010]cpx, [-1-11]tmt(-101)*cpx, [112]tmt[101]cpx). COR frequencies suggest a strong influence of water content and annealing time on their formation. In the 0.5h duration dry experiment, tmt-cpx boundaries following COR 1 are twice as frequent by length as those following COR 2, whereas in the 0.5h duration wet experiment, COR 2 boundaries are 5 times more frequent by length than COR 1 boundaries. In both wet and dry experiments the length ratio of COR 1 : COR 2 boundaries approaches 1 with longer annealing times.

The degree of undercooling (as imposed by the different water contents) is the most important influence on the microstructural clustering parameters, leading to lower overall number densities of tmt as well as affecting the SPF and FTT values at short durations and the subsequent evolution of these parameters with increasing annealing time. The high frequency of tmt-cpx CORs is consistent with heterogeneous nucleation. However, the mechanisms controlling which CORs develop are unclear. Annealing does not fully erase CORs or microstructural signatures of clustering, suggesting that crystal clusters erupted in volcanic products could still preserve signs of their formation.  

Pontesilli et al. (2019), Chem Geol 510:113-129. 10.1016/j.chemgeo.2019.02.015

Funded by the Austrian Science Fund (FWF): P 33227-N

How to cite: Peres, S., Griffiths, T., Masotta, M., and Pontesilli, A.: The effect of melt water content and isothermal annealing time on the formation and evolution of clinopyroxene-titanomagnetite clusters, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10936, https://doi.org/10.5194/egusphere-egu21-10936, 2021.

EGU21-10053 | vPICO presentations | GMPV8.1

Crystal zoning patterns: competition between crystal growth and elements diffusion

Alessandro Musu, Luca Caricchi, Diego Perugini, Rosa Anna Corsaro, Francesco Vetere, and Maurizio Petrelli

Magma reservoirs represent areas of large variation in the physico-chemical properties of magmas and are directly associated with volcanic activity. Understanding the processes acting at inaccessible depths is of crucial importance to interpret monitoring signals and to develop quantitative models to forecast volcanic activity. Minerals are witnesses of the temporal evolution of the physico-chemical conditions within magma reservoirs recording variations of intensive parameters as chemical signals. However, the competition between crystal growth and elements diffusion in the melt phase can also modulate the chemical zoning of minerals, therefore complicating the interpretation of chemical zoning patterns. To disentangle this complexity, chemically zoned minerals are synthetically grown at the Petro-Volcanology Research Group of the University of Perugia, under controlled conditions. For these experiments tephra from 2002-03 Mt. Etna eruption is used as starting material. The zonation in minerals is been forced inside a high-temperature furnace by oscillating the temperature with three different setups: static conditions, using a controlled deformation gradient (Concentric Cylinder Apparatus) and using a chaotic mixing regime (Chaotic Magma Mixing Device). The zoned crystals are analysed for major and trace elements by Electron Probe Micro Analyzer (EPMA) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), respectively. High spatial resolution elemental maps (0.5 micrometres) are also collected to characterise the zoning of selected crystals. The data are analysed using a series of custom-built machine learning algorithms to disentangle zoning related to variations of the thermodynamic conditions of crystal growth from the effects of the competition between diffusion and growth. The main target of this project is to provide quantitative tools to distinguish between chemical zoning forced by thermodynamic conditions of growth and chemical zoning produced by competition between crystal growth and element diffusion.

How to cite: Musu, A., Caricchi, L., Perugini, D., Corsaro, R. A., Vetere, F., and Petrelli, M.: Crystal zoning patterns: competition between crystal growth and elements diffusion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10053, https://doi.org/10.5194/egusphere-egu21-10053, 2021.

EGU21-13305 | vPICO presentations | GMPV8.1

Volcanic forces inferred from EBSD and µXRD analyses of Yellowstone quartz

Omero Felipe Orlandini and Kenneth Befus

The magnitude of forces at play in active magmatic systems is poorly constrained because direct observation is difficult. Additional complications include short time scales and the likelihood of overprinting signatures of deeper processes by the catastrophic nature of eruption. Deformation of crystal lattices is one signature of magmatic force common to all crystals that survive eruption. Quartz crystals have documented residual elastic stresses in the hundreds of MPa measured using synchrotron µXRD. These stresses may be caused by several processes: crystal-crystal impingement in a crystal mush, explosive fragmentation, or shear in flowing lavas. To better unravel when these stresses were imparted relative to the ultimate eruption, we combine µXRD with new EBSD measurements. EBSD helps constrain subgrain and twin boundary relationships, geometrically-necessary dislocation density (GND), and plastic deformation.

We target quartz grains from a violent Yellowstone super-eruption and from a large-volume rhyolitic obsidian lava flow (Huckleberry Ridge Tuff and Summit Lake lava, respectively). We use ‘Herkimer diamonds’ as a comparative baseline for deformation. Herkimer diamonds are quartz crystals, famous in the mineral specimen community, that grew into vugs and have experienced no tectonic or volcanic stresses. Samples from both Yellowstone eruptions preserve roughly the indistinguishable amounts of elastic residual stresses, ranging from 100 to 150 MPa. EBSD indicates a GND density of ca. 4E12, with slightly higher values in the Summit Lake Lava. Diffraction peak broadening provides a record of plastic deformation using µXRD. Diffraction peaks are significantly more smeared in Summit Lake lava (0 to 0.15 degrees) than in Huckleberry Ridge Tuff (~0.06 degrees). Subgrain formation in both samples is documented by both µXRD and EBSD. By isolating processes we conclude that elastic residual stresses record pre-eruptive magmatic environment. Viscous shear during lava emplacement generates the majority of plastic deformation, which swamps the signal of lesser amounts of plastic deformation produced in the reservoir or conduit. Pre-eruption processes are likely the source of elevated elastic residual stresses, and we favor an interpretation where the stresses arise from force-chain impingements within crystal mushes prior to eruption.

Finally, EBSD and µXRD provide complementary and overlapping results. Because µXRD peak smearing is sampling both geometrically-necessary and statistically-stored dislocations (SSD; dislocations which contribute no net lattice bending but do contribute to strain hardening), and EBSD only GNDs via relative lattice curvature, the relative proportion of both types of dislocation may be calculated. Huckleberry Ridge Tuff grains preserve up to 20% GNDs, and Summit Lake lavas less than 10%, potentially reflecting the greater total stresses of the Summit Lake samples.

How to cite: Orlandini, O. F. and Befus, K.: Volcanic forces inferred from EBSD and µXRD analyses of Yellowstone quartz, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13305, https://doi.org/10.5194/egusphere-egu21-13305, 2021.

EGU21-13439 | vPICO presentations | GMPV8.1

A message from the depth: the origin of the amphibole crystal clots with pyroxene cores in the Late Pleistocene Ciomadul dacites, Romania

Barbara Cserép, Zoltán Kovács, Kristóf Fehér, and Szabolcs Harangi

Identification of trans-crustal magma reservoir processes beneath volcanoes is a crucial task to better understand the behaviour and possible future activities of volcanic systems. Detailed petrological investigations have a fundamental role in such studies. Dacitic magmas are usually formed in an upper crustal magma reservoir by complex open-system processes including crystal fractionation and magma mixing following recharge events. Conditions of such processes are usually constrained by crystal-scale studies, whereas there is much less information about the petrogenetic processes occurring in the lower crustal hot zone. Here we provide insight into such processes by new results on amphibole crystal clots found in dacitic pumices from an explosive volcanic suite of the Ciomadul volcano, the youngest one in eastern-central Europe.

Amphibole is a common mineral phase of the Ciomadul dacites, occuring as phenocrysts and antecrysts, but occasionally they also form crystal clots with an inner core of either pyroxene or olivine with high Mg-numbers. Olivine is observed mostly in the 160-130 ka lava dome rocks, whereas the younger explosive eruption products are characterised by orthopyroxene and clinopyroxene. Such mafic crystal clots are most common in the pumices of the earliest explosive eruptions, which occurred after long quiescence at 56-45 ka. The most common appearance has high-Mg pyroxene core (mg#: 0.76-0.92) rimmed by amphibole. Two types of amphibole are found in such clots: irregular zone of actinolite to magnesio-hornblende directly around orthopyroxene and high Mg-Al pargasitic amphibole as the outer zone. Several crystal clots contain smaller amphibole crystals with diffuse transition to clinopyroxene at the inner part and complexly zoned amphibole with biotite inclusions in the outer part. These amphibole and pyroxene have lower Mg-number (< 0.80), and higher MnO content (up to 0.52 wt%) than the most common type. In both cases, amphibole could be a peritectic product of earlier-formed pyroxenes, which reacted with water-rich melt at higher and lower temperatures, respectively. Actinolite to magnesio-hornblende at the contact represents a transitional phase between pyroxene and the newly formed amphibole. In a few cases, crystal clots contain amphibole inclusions in pyroxene macrocrysts. These amphiboles have a particular composition not yet reproduced by experiments: they have high mg# (>0.86), but low tetrahedral Al (0.9-1.0 apfu) and usually high Cr content (Cr2O3 is up to 0.9 wt%), similar to the orthopyroxene and clinopyroxene hosts (0.26-0.71 and 0.78-0.89 wt%, respectively). We interpret these amphiboles as an early formed liquidus phase crystallized along with pyroxene from an ultra-hydrous mafic magma. Occasionally, crystal clots are complexly zoned amphibole macrocrysts with dispersed clinopyroxene inclusions. The amphibole has a wide compositional range, usually with high Mg-Al pargasitic core. These amphiboles could have formed by peritectic reaction between clinopyroxene and a water-rich melt.

The observed mafic crystal clots in the dacites indicate the presence of strongly hydrous mafic magmas accumulated probably at the crust-mantle boundary. During mafic recharge, volatile transfer may contribute to the crystal mush rejuvenation at shallow depth and triggering explosive eruptions.

This research was financed by the Hungarian National Research, Development and Innovation Fund (NKFIH) within K135179 project.

How to cite: Cserép, B., Kovács, Z., Fehér, K., and Harangi, S.: A message from the depth: the origin of the amphibole crystal clots with pyroxene cores in the Late Pleistocene Ciomadul dacites, Romania, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13439, https://doi.org/10.5194/egusphere-egu21-13439, 2021.

EGU21-14918 | vPICO presentations | GMPV8.1

Rejuvenation events recorded in alkali feldspar from the Tuolumne Intrusive Complex

Susanne Seitz, Guilherme Gualda, and Luca Caricchi

EGU21-5970 | vPICO presentations | GMPV8.1

Evolution of the crystallisation conditions in the Wellington Lake Pegmatite in the Pikes Peak Granite, Colorado (USA)

Ludmila Maria Fonseca Teixeira, Julien Allaz, and Olivier Bachmann

Pegmatites are texturally, mineralogically, and geochemically zoned rocks that show distinctive features such as graphic granite in the wall zones, coarse-crystalline material in the centre, and unusual mineralisation sometimes of economic significance. They are usually considered to be derived from silicate melts, but a significant fluid supply is also required to reproduce their unique characteristics. These fluids are commonly enriched in flux anions such as F-, Cl-, CO32-, and BO33- . Many studies have investigated the petrogenetic processes that led to pegmatite crystallisation, yet not all aspects of pegmatite formation have been fully understood. Notably, the nature of the precipitating medium remains uncertain for the different zones of the pegmatite. In order to better understand the transition from a silicate-melt-dominated crystallisation to fluid-dominated precipitation, we aimed to produce a temperature profile across the pegmatite and its host granite. We analysed quartz crystals from the different zones of the Wellington Lake Pegmatite and the host rock, a syenogranite of the Pikes Peak Batholith, in Colorado (USA). This NYF-type pegmatite consists of a fine-grained graphic granite wall zone, a coarse-grained quartz and albite intermediate zone, and pure blocky quartz core zone with REE-dominated mineralisation including fluocerite, bastnäsite, thorite, columbite, zircon, and cassiterite. Quartz trace element data (Al, Ti, Ge) suggest that the granite crystallized over a range of conditions, with Ti-in-quartz temperatures varying from 800 to 550°C. The wall zone of the pegmatite crystallised over a more constricted range, with temperatures on the order of ~660 to 630°C, just below the experimentally determined H2O-saturated haplogranite solidus. Finally, the intermediate and core zones of the pegmatite show much colder conditions, with fluid inclusion homogenisation temperatures calibrated for typical pegmatite pressures ranging from 450°C (for 300 MPa) or 380°C (for 200 MPa) for the intermediate zone to 380°C (for 300 MPa) or 325°C (for 200 MPa) for the core. These results suggest crystallisation from a range of conditions transitioning from hydrous silicate melt-based mineral precipitation at the high temperature end (in the core of quartz crystals in the granite) to sub-solidus Al-Si-Na-enriched fluid precipitation in the interstitial quartz of the granite and in the pegmatite. Textural and geochemical zoning in the pegmatite records the transition from near-magmatic conditions in the borders to colder and more hydrothermal conditions in the core.

 

How to cite: Fonseca Teixeira, L. M., Allaz, J., and Bachmann, O.: Evolution of the crystallisation conditions in the Wellington Lake Pegmatite in the Pikes Peak Granite, Colorado (USA), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5970, https://doi.org/10.5194/egusphere-egu21-5970, 2021.

EGU21-16304 | vPICO presentations | GMPV8.1

Zooming in on crystal mush: recent advances in volcano tomography

Michele Paulatto, Joanna Morgan, Kajetan Chrapkiewicz, Emilie Hooft, Doug Toomey, Costas Papazachos, Paraskevi Nomikou, and Ben Heath

The lack of direct seismological evidence for large molten magma chambers is considered to be one of the most important arguments in support of the mush paradigm. However, most published melt fraction estimates based on interpretation of seismological data are associated with large uncertainties because of two limitations: i) inherent limits to resolution of seismic tomography and, ii) trade-offs in the constitutive relationships that tie seismic properties to melt fraction. Low-velocity volumes associated with magma storage are particularly difficult to image with conventional travel-time tomography due to limited resolution and wavefront healing, resulting in blurred images and a high velocity bias. We tackle these limitation by applying full waveform inversion to active source seismic data collected over the Kolumbo submarine volcano (Greece). We recover a previously undetected Vp anomaly of –50% beneath the volcano and interpret this as a shallow magmatic intrusion. Extension of this approach to the wider Santorini volcanic system is ongoing. Concurrently, we are tackling the second limitation, which is the result of the dependence of elastic properties on the microgeometry of the melt. Seismological melt estimates rely on the assumption that the melt pore space can be represented by simple geometrical shapes, usually ellipsoids, with a given aspect ratio. Since the aspect ratio is poorly constrained, this results in a trade-off between melt fraction and melt geometry. We have adapted a method for the homogenisation of the elastic properties of multi-phase composites and applied it to calculating the elastic properties of partially molten rocks starting from the melt microstructure determined by X-ray CT scanning. The microgeometry of the mush can be inferred from the study of glomerocrysts: crystal mush inclusions with quenched interstitial melt that are carried to the surface by erupted lava. After the sample is digitized and segmented into its constitutive phases (crystals, melt, vesicles), the average elastic properties are determined by numerical homogenisation which consists of numerically simulating the deformation of the sample under load and predicting its elastic response. The results are compared to a semi analytical solution for ellipsoidal inclusions. We apply this approach to a plutonic nodule from St Kitts and show that the melt microstructure leads to an elastic response equivalent to that of ellipsoidal melt inclusions with an aspect ratio of 0.1 (oblate spheroids). This equivalent aspect ratio is used to refine melt estimates for Montserrat, Santorini and Kolumbo volcano.

How to cite: Paulatto, M., Morgan, J., Chrapkiewicz, K., Hooft, E., Toomey, D., Papazachos, C., Nomikou, P., and Heath, B.: Zooming in on crystal mush: recent advances in volcano tomography, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16304, https://doi.org/10.5194/egusphere-egu21-16304, 2021.

EGU21-2237 | vPICO presentations | GMPV8.1

Interpretation of volcanic surface deformation using a 3D multi-source approach

Jose Fernandez, Antonio G. Camacho, Sergey V. Samsonov, Kristy F. Tiampo, and Mimmo Palano

Volcano geodetic observation is a valuable tool to infer location, strength and geometry of magmatic plumbing systems. The availability of high precision and spatial resolution, spanning decades, deformation data from satellite radar observation and Global Navigation Satellite Systems (GNSS) can give us important information for detecting and characterizing their temporal variations as well as other possible geodynamic sources acting in the volcanic area. For this objective inversion techniques are necessary which help us to obtain the maximum of information from these new datasets. We present a new, original methodology to carry out a multi-source inversion of ground deformation data to better understand the subsurface causative processes (Camacho et al., 2020). The methodology uses a nonlinear approach which permits the determination of location, size and three-dimensional configuration, without any a priori assumption as to the number, nature or shape of the potential sources. The proposed method identifies a combination of pressure bodies and different types of dislocation sources (dip-slip, strike-slip and tensile) representing magmatic sources and other processes such as earthquakes, landslides or groundwater-induced subsidence through the aggregation of elemental cells. This approach carries out a simultaneous inversion of the deformation components and/or line-of-sight (LOS) data; and a simultaneous determination of diverse structures such as pressure bodies or dislocation sources, representing local and regional effects. Both things are done in a fully 3D context and without any initial hypothesis about the number, geometry or types of the causative sources is necessary. We show results from the application of this new methodology to synthetic and real test cases (e.g., Mt. Etna).

This research has been primarily supported by the Spanish Ministerio de Ciencia, Innovación and Universidades research project DEEP-MAPS (RTI2018-093874-B-I00) and is part of the CSIC-PTIs TELEDETEC and POLARCSIC activities.

References
Camacho, A.G., Fernández, J., Samsonov, S.V., Tiampo K.F., Palano, M., 2020. Multisource 3D modelling of elastic volcanic ground deformations. Earth and Planetary Science Letters, 547C, 116445. https://doi.org/10.1016/j.epsl.2020.116445.

How to cite: Fernandez, J., Camacho, A. G., Samsonov, S. V., Tiampo, K. F., and Palano, M.: Interpretation of volcanic surface deformation using a 3D multi-source approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2237, https://doi.org/10.5194/egusphere-egu21-2237, 2021.

EGU21-3591 | vPICO presentations | GMPV8.1

Anatomy of a volcanic island inferred from a multiphysics approach

Marceau Gresse, Makoto Uyeshima, Takao Koyama, Hideaki Hase, Koki Aizawa, Yusuke Yamaya, Yuichi Morita, Derek Weller, Tawat Rung-Arunwan, Takayuki Kaneko, Yoichi Sasai, Jacques Zlotnicki, Tsuneo Ishido, Hideki Ueda, and Maki Hata

Phreatic and phreatomagmatic eruptions are difficult to predict with accuracy on volcanoes due to complex interactions at depth between heat, water, and magmatic fluids. To better understand such multifaceted interactions, we present here a multidisciplinary geophysical approach performed on Miyakejima, a 10-km wide stratovolcano in the Izu Bonin arc. Its plumbing system was highlighted by combining four geophysical methods: magnetotellurics, seismicity (hypocenters), self-potential, and thermal image (remote sensing). We thus propose the first large-scale interpretation of the volcanic structure in terms of rock properties, temperature, fluid content, and fluid flow. Our findings indicate that hot volatiles released from a deep magmatic reservoir (> 350°C, 2.5–4.5 km depth) rise through a narrow permeable path, interact with the conductive hydrothermal system beneath the 2000 A.D. caldera (<250°C, 0–2 km depth). This mixture of fluid is finally released in the fumarolic area in the southern part of the caldera at 181°C. This combined approach allow us to: 1) delineate the water table of the volcano (300–700 m depth), 2) determine the general fluid flow circulation beneath the island, 3) characterize seismic signatures of long-period and volcano-tectonic events, and 4) elucidate the origin of the high water content of fumaroles developed since the last eruption in A.D. 2000.

How to cite: Gresse, M., Uyeshima, M., Koyama, T., Hase, H., Aizawa, K., Yamaya, Y., Morita, Y., Weller, D., Rung-Arunwan, T., Kaneko, T., Sasai, Y., Zlotnicki, J., Ishido, T., Ueda, H., and Hata, M.: Anatomy of a volcanic island inferred from a multiphysics approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3591, https://doi.org/10.5194/egusphere-egu21-3591, 2021.

EGU21-16010 | vPICO presentations | GMPV8.1

The permeability of magma mush assembled from anisotropic tabular crystals

Eloïse Bretagne, Fabian B. Wadsworth, Katherine J. Dobson, Jérémie Vasseur, and Jason P. Coumans

The extraction of melt from a mush in a magma reservoir is of wide interest. All models for melt extraction from a mush require knowledge of mush permeability, and yet this remains poorly constrained. This permeability is typically calculated using the Kozeny-Carman model or variants thereof, which require a priori knowledge of the microstructural geometry. Such models are not calibrated or tested for packs of crystals of a range of shapes found in natural mush piles, leading to the potential for oversimplification of complex natural systems.

Essentially, a magma mush with minimal crystal-crystal intergrowth is composed of packed crystals where the pore space is filled with interstitial melt. Therefore, this can be studied as a granular medium. We use numerical methods to create domains of closely packed, randomly oriented cuboids in which we keep the short and intermediate axes lengths equal (i.e. square cross section) and vary the long axis magnitude. Our synthetic ‘crystals’ therefore cover the range from oblate to prolate, passing through a cubic shape. We supplement these with 3D numerical packs of spherical particles in cubic lattice arrangements or random arrangements. For the sphere packs we use various polydispersivity of sphere sizes. The permeability of all of these pack types is calculated using a numerical simulation (both LBflow and Avizo-based algorithms) with imposed periodic boundary conditions. The preliminary results suggest that the permeability of a granular medium scales with the specific surface area exclusively, without requiring prior knowledge of the geometry and size distribution of the particles.

We suggest that the model toward which we are working will allow magma mush permeability to be modelled more accurately. If our approach is embedded in existing continuum models for mush compaction and melt extraction, then more accurate estimates of melt accumulation rates prior to very large eruptions could be found.

Keywords: melt segregation, compaction, granular media, fluid flow, numerical simulation

How to cite: Bretagne, E., Wadsworth, F. B., Dobson, K. J., Vasseur, J., and Coumans, J. P.: The permeability of magma mush assembled from anisotropic tabular crystals, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16010, https://doi.org/10.5194/egusphere-egu21-16010, 2021.

EGU21-5703 | vPICO presentations | GMPV8.1

Felsic melt migration via porous flow – a numerical modeling approach

Petra Maierová, Pavlína Hasalová, and Karel Schulmann

Melting of the continental crust and subsequent melt transport has been most thoroughly described in the case of metasedimentary rocks. In these rocks segregation and migration of melt occur either through an interconnected network of veins and melt-rich layers (leucosome) or in form of diapirs. For these rocks, porous flow of melt at grain scale is mostly regarded only as a transient stage of separation of melt from the solid rock.

An entirely different style of melting and melt transport occurs in the case of felsic metaigneous rocks. We use the example from the Bohemian Massif, the eastern European Variscan belt, where metaigneous migmatites were studied in large detail. Here, melt did not segregate from the solid rock but migrated pervasively along most of the grain boundaries and equilibrated with the host rock. This equilibration resulted in formation of a continuous sequence of texturally, geochemically and compositionally different migmatites.

The question arises, what are the conditions and driving forces for this unusual behavior. We attempt to address this question by means of numerical modeling of two-phase flow (i.e. flow of porous solid matrix and melt), using the open-source finite-element ASPECT code (aspect.geodynamics.org). Most previous numerical studies of this process were either purely generic or focused on the melting of the mantle. In order to study this process in crustal conditions, we set up a 2D crustal-scale thermo-mechanical model that includes melting and freezing. We investigate the role of material properties (viscosity, solidus and liquidus temperatures, solid matrix permeability, melt composition) and thermal and velocity boundary conditions, as well as the effect of grid resolution. The results are discussed in terms of realistic parameter values and possible styles of melt migration and deformation of the matrix.

How to cite: Maierová, P., Hasalová, P., and Schulmann, K.: Felsic melt migration via porous flow – a numerical modeling approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5703, https://doi.org/10.5194/egusphere-egu21-5703, 2021.

Volcanism is the surface expression of extensive magmatic systems, with their intrusive counterpart representing ~80% of the total magma budget. Our knowledge of igneous processes therefore largely relies on our understanding of deep plutonic processes. In continental or oceanic environments, most of the intrusive igneous rocks bear geochemical cumulate signatures (e.g., depletion in incompatible elements, enrichment in compatible ones) that are commonly explained by minerals-melt segregation during differentiation. Nevertheless, in many cases the processes aiding melt segregation still need to be further constrained.

In oceanic environments, deformation-assisted compaction aided by melt buoyancy is the main process involved in melt extraction. However, a number of cumulative rocks are lacking any clear compaction evidence, opening the potential for the involvement of other processes. Here, relying on current descriptions of melt dynamics within oceanic magma reservoirs, i.e. the mushy nature of the reservoirs and inferred cyclic replenishment by primitive melts, we propose the involvement of a new igneous process. In the "melt flush" model, repeatedly injected fresh melts hybridize within the injected mush triggering mineral dissolution and crystallization, and concurrent partial extraction of the former interstitial melt forced out of the system by the incoming melts aided by buoyancy.

This model is consistent with the widespread occurrence of reactive porous flow (RPF) identified in oceanic igneous systems, and matches the petrographical (e.g., olivine and plagioclase dissolution) and geochemical constraints (trace element signatures) brought by natural oceanic samples. More specifically, it has been shown that RPF proceeds following melt consuming reactions that ultimately result in a progressive closure of the mush porosity. The extraction of the evolved interstitial melts replaced by more primitive ones, and the porosity closure are here proposed to account for some of the cumulative signatures observed in igneous rocks. The "melt flush" model we describe eventually adds to the other processes involved in cumulates formation from various settings like magma compaction or crystal settling.

How to cite: France, L. and Boulanger, M.: A new perspective on cumulate formation and melt extraction from mushy reservoirs: the "melt flush" model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-912, https://doi.org/10.5194/egusphere-egu21-912, 2021.

Understanding the geometry of magma chambers plays a critical role in determining the igneous petrogenic processes that occur as intrusions cool. Quantitative fabric analysis methods, such as anisotropy of magnetic susceptibility (AMS), are routinely used to measure magma flow dynamics and determine the mechanism of magma transport and emplacement. However, magma mushes typically experience multiple flow events; e.g. emplacement, convection, and interstitial melt percolation. There is thus a need to develop a more a sophisticated approach to unravelling complex rock fabrics that record more than one magmatic state process. This study uses novel rock magnetic datasets to untangle the evolution of the 1163 Ma Younger Giant Dyke Complex (YGDC) of SW Greenland, a multi-sheeted troctolite dyke system that attains widths up to 800 m and encloses several evolved and/or modally layered ovoid pods.

Field results identify that ovoid pods occur in the thickest dyke segments. Several pods are defined by gently inward dipping modal layers and/or a parallel mineral foliations, and in-phase AMS magnetic foliations lie parallel to the observed field fabrics. Critically, imbricated plagioclase crystals record a magma transport direction toward the center of each pod, and this observation is substantiated by in-phase AMS lineations that plunge down dip of the foliation and shallow toward the center of each pod. These observations are interpreted to show gravitational settling under a convective flow regime.

In addition, 66% of out-of-phase AMS fabrics are non-parallel with in-phase AMS results. Out-of-phase AMS is a relatively new technique and is thought to reflect anisotropy controlled by a restrictive group of ferromagnetic minerals such as single domain magnetite and pyrrhotite. Out-of-phase lineations in layered pods are relatively steeply inclined and do not shallow towards the center, we therefore hypothesize that these lineations record a late stage filter-pressing process within the crystal mush. To test this hypothesis, anisotropy of anhysteretic remanent magnetism (AARM) data were collected from 15 samples. Results show that the AARM and out-of-phase AMS tensor axes are parallel, indicating that the sub-fabric detected by out-of-phase AMS is normal and most likely controlled by single domain magnetite.

Our results show that the application of rock magnetic techniques is effective in unravelling magma convection fabrics from later melt migration fabrics in mushy magmas.

How to cite: Koopmans, L. and McCarthy, W.: Using rock magnetics to resolve composite magmatic state fabrics: a case study from the Younger Giant Dyke Complex, SW Greenland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12041, https://doi.org/10.5194/egusphere-egu21-12041, 2021.

EGU21-3002 | vPICO presentations | GMPV8.1

Magma and hydrothermal fluids exploiting similar crustal traps at Gavorrano (Tuscany)

Luca Tinagli, Simone Vezzoni, Sergio Rocchi, and Andrea Dini

The 3D reconstruction of magmatic, metasomatic and/or ore bodies plays a major role in understanding the emplacement mechanisms for magmas and hydrothermal fluids in the upper crust.

The Gavorrano Intrusive-Hydrothermal Complex (GIHC, Tuscany, Italy) is an excellent case study in which intrusive and hydrothermal rocks, as well as sulphides ore bodies are spatially associated.

The evolution of the GIHC starts in the early Pliocene with the sequential emplacement, at the contact between the Paleozoic basement (metapelites) and the overlying Mesozoic limestone-dolostone formations, of a cordierite-biotite monzogranite and a tourmaline microgranite. The monzogranite is highly porphyritic with megacrysts of K-feldspar and phenocrysts of quartz, plagioclase, biotite, and cordierite. The microgranite is characterised by a huge number of euhedral microliths (10-500 µm) of black tourmaline set in a quartz-feldspars groundmass. The small size of the Gavorrano intrusion (ca. 3 x 1 km) and its shallow emplacement level (ca. 5 km) resulted in a thin contact aureole (< 100 m thick) made of phlogopite-olivine marble and biotite-andalusite pelitic hornfels. Isoclinal folds in marble are indicative of dynamic crystallization during contact metamorphism and point out an outward sense of movement of the aureole rocks with respect to the granite intrusion. At the contact with the intrusion, marbles were overprinted by a discontinuous (0.1-10 m thick) layer of vesuvianite-garnet exoskarn. Exoskarn, contact aureole and undisturbed host rocks, were subsequently affected by hydraulic brecciation. The closing stage of the evolution of the complex is characterized by mineralizing fluid circulation, producing widespread chloritization-silicification and decametric pyrite bodies (with adularia, fluorite, and base metal sulfides). 

Surface and underground mapping integrated by mining reports and drill logs allow us gave way to the reconstruction of the attitude and shape of magmatic and hydrothermal bodies. The NW-SE elongated intrusion is characterised by a pronounced asymmetry: the eastern part is made of sub-horizontal multiple bodies, locally with both roof and bottom contacts exposed; the western part has an overall sub-vertical, west-dipping attitude. Such an asymmetry is shown by each of the two intrusive units and highlighted by second order features: the monzogranite unit reaches its maximum thickness (0.8 km) in the central-western subvertical zone while in the subhorizontal eastern branches is few hundred meters thick, and the subhorizontal microgranite bodies display steep west-dipping offshoots. The GIHC asymmetry is also exhibited by the hydrothermal system: the pyrite orebodies mantle the top and the western flank of the intrusion, with the two main masses displaying, in vertical section, a sigmoidal shape with a steep west-dipping thick portion connecting upper and lower tails gently dipping to the west.

The collected data indicate the west side of the GIHC as the focus zone for both magmas and hydrothermal fluids. The overall geometries of the intrusive units and pyrite bodies suggest a sense of movement top-down-to-the-west. This close spatial and shape relationship between intrusive rocks and hydrothermal bodies suggests a common extensional tectono-magmatic regime capable to produce asymmetric crustal traps (dilational structures) for magmas and fluids.

How to cite: Tinagli, L., Vezzoni, S., Rocchi, S., and Dini, A.: Magma and hydrothermal fluids exploiting similar crustal traps at Gavorrano (Tuscany), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3002, https://doi.org/10.5194/egusphere-egu21-3002, 2021.

EGU21-14654 | vPICO presentations | GMPV8.1

Are dykes just filled hydraulic fractures? - Inelastic deformation and emplacement mechanisms of igneous tabular intrusions

Olivier Galland, Tobias Schmiedel, Håvard Bertelsen, Frank Guldstrand, Øystein Haug, and Alban Souche

Igneous tabular (sheet) intrusions such as dykes, sills and cone sheets, are fundamental elements of volcanic plumbing systems, as they represent the dominant pathways for magma transport and the main feeders of volcanic eruptions. When magma is intruded in the Earth’s crust, it makes its space by pushing and breaking the host rock, which can result in intense inelastic damage and fracturing. To understandand quantify the distribution of such intrusion-induced deformation patterns in the host rock is thus essential to resolve magma emplacement dynamics.

Sheet intrusions with their low thickness-to-length aspect ratios, resemble fractures. Based on this resemblance, tabular intrusions have been expected to form like (hydraulic) fractures propagating as tensile cracks with sharp and pointy tips, and assuming purely elastic deformation of the host rock. Even if some field observations support this theory, there is growing evidence that other mechanisms, involving significant inelastic deformation of the host rock, accommodate dyke and sill emplacement.

This contributionprovidesa summary review onthe role of inelastic deformation on the emplacement of tabular intrusions. (1) Field observations show that intrusion tips can be rounded, blunt, and the host deformation accommodating their propagation exhibits inelastic, compressional deformation, in drastic contradiction with theoretical predictions. (2) 3D and 2D laboratory experimentsof magma emplacement in a cohesive Mohr-Coulomb crusthighlightthat magma-induced inelastic deformation, in the form of shear damage and faulting, are first-order transient mechanical precursors for the propagating magma. In addition, these experiments show that the cohesion and friction properties of the model host rock are first-order parameters controlling the formation of intrusions of various shapes, including dykes, plugs, cone sheets, sills and laccoliths. (3) Elasto-plastic numerical models highlight that shear failure is the dominant mechanism to accommodate intrusion growth as soon as heterogeneities are introduced. We conclude that heterogeneities within the host-rock may locally "seed" shear faults ahead of the magmatic intrusion in the propagating direction, in good agreement with field observations. Given that rocks are naturally heterogeneous at multiple scale, these models suggest that shear failure is likely to be a common mechanism for accommodating magma propagation.

Overall, our field observations andmodelresultsshow that the brittle Coulomb properties of rocks, and their heterogeneities,must be accounted for revealing the nature and distribution of fractures and inelastic damage accommodating the emplacement of igneous tabular intrusions.

How to cite: Galland, O., Schmiedel, T., Bertelsen, H., Guldstrand, F., Haug, Ø., and Souche, A.: Are dykes just filled hydraulic fractures? - Inelastic deformation and emplacement mechanisms of igneous tabular intrusions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14654, https://doi.org/10.5194/egusphere-egu21-14654, 2021.

EGU21-2797 | vPICO presentations | GMPV8.1

Time-window into the transcrustal plumbing system dynamics of Dominica (Lesser Antilles)

Léa Ostorero, Georges Boudon, Hélène Balcone-Boissard, Daniel J. Morgan, Thiebaut d'Augustin, and Clara Solaro

A transcrustal mush system has been recognized beneath Dominica (Lesser Antilles) with different magma ponding zones that generated a series of pumiceous eruptions from Morne Trois Pitons–Micotrin volcano. Here, the latest, large, pumiceous eruption (Grand Fond - 24 kyrs cal BP) and four, smaller, Plinian eruptions (18-9 kyrs cal BP) are investigated. Pre-eruptive magma dynamics within the mush are unraveled through orthopyroxene phenocrysts by combining a Crystal System Analysis approach (on unzoned and zoned orthopyroxenes) and timescale estimates derived by intracrystalline Fe-Mg interdiffusion modeling. Two magmatic environments are recognized in the mush and have mixed, more or less vigorously, before the successive eruptions. Few interactions between the two magmas began 15-34 years prior to the small Plinian eruptions, but the sustained mixing occurred in the last 2 years. This contrasts with longer timescales (2-80 years) obtained for the larger eruption of Grand Fond with magmas stored deeper. These magma mixing timescales have significant implications for volcanic risk mitigation, with a growing reactivation signal that could be registered at the surface few years prior to the eruptions.

How to cite: Ostorero, L., Boudon, G., Balcone-Boissard, H., Morgan, D. J., d'Augustin, T., and Solaro, C.: Time-window into the transcrustal plumbing system dynamics of Dominica (Lesser Antilles), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2797, https://doi.org/10.5194/egusphere-egu21-2797, 2021.

EGU21-3172 | vPICO presentations | GMPV8.1

Insights into timescales of magmatic processes during the 2013-17 eruption at Volcán de Colima, Mexico

Gerallt Hughes, Chiara Petrone, Hilary Downes, Nick Varley, Samantha Hammond, and Katrina Kerr

Volcán de Colima is an active stratovolcano in western Mexico. Its 2013-17 eruptive phase was characterised by transitions between effusive and explosive events. This persistent activity, comprising vulcanian explosions, pyroclastic flows, lava flows and ashfall present significant hazards to ~750,000 people near the volcano.

Tracing patterns of magma storage, recharge and mixing through volcanic systems is key to accurately interpreting monitoring data and understanding potential future hazards. However, at many volcanoes, including Colima, these patterns are poorly constrained and the link between monitoring data and magmatic processes is unclear. To better understand the magmatic plumbing system at Colima, mineral chemistry and textural studies were undertaken on representative 2013-17 samples to constrain different magmatic environments and mixing between them.

These samples contain plagioclase, orthopyroxene, clinopyroxene, Fe-Ti oxides, and rare resorbed olivine and amphibole, typical of Colima andesites. Pyroxene phenocrysts have varied core compositions (Mg#~69-88), zoning and textural patterns, reflecting crystallisation from melts within a heterogeneous magma mush. Whilst we interpret the bulk of the system to be relatively evolved, the presence of disequilibrium textures and high-Cr mafic bands and rims reflect periodic recharge of mafic melts and remobilisation of both evolved and mafic mush material prior to eruption.

The mineral chemistry and petrography indicate the presence of two broad magmatic environments crystallising these pyroxenes. An evolved end-member, crystallising Mg#69-75 pyroxene at between 980-1000°C, comprises the bulk of the system. By contrast, the mafic end-member crystallises high-Mg# pyroxene at a temperature typically between 1020-1080°C. Pressure estimates typically vary between 4-6 kbar or c. 12-20 km depth, in agreement with geophysical evidence suggesting a melt-rich mushy body at this depth.

Zoning patterns range from diffuse zoning in normal zoned pyroxenes to sharper core-rim boundaries in reverse zoned phenocrysts. We applied elemental diffusion modelling to constrain the timescales of pre-eruptive magmatic processes. The modelling indicates relative differences in residence times with long residence timescales typically of decades to centuries for diffuse, normally zoned phenocrysts versus shorter residence timescales of weeks to months in reverse-zoned phenocrysts.

Most notably, an increased frequency of reverse zoned pyroxenes was recorded in lavas erupted after an intense VEI 3 eruption in July 2015. Timescale estimates suggest a recharge and mixing event occurred at approximately this time and estimates from 2016 lavas indicate multiple injection events leading up to the eruption. This suggests that the July 2015 eruption may have been directly linked to this mafic injection.

Despite both eruptions being associated with mafic recharge, the difference in the style of activity between the explosive 2015 and effusive 2016 eruptions suggest other controls on activity. These may include the volume of magmatic recharge, the frequency of injections, ascent rate, or the supply of volatiles from the mafic magmas. Further refinement of the storage timescales and recharge events, and comparison of timescales to monitoring data, also will help clarify the effect of these processes on the eruption timing and style.

How to cite: Hughes, G., Petrone, C., Downes, H., Varley, N., Hammond, S., and Kerr, K.: Insights into timescales of magmatic processes during the 2013-17 eruption at Volcán de Colima, Mexico, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3172, https://doi.org/10.5194/egusphere-egu21-3172, 2021.

EGU21-3125 | vPICO presentations | GMPV8.1

Timescales of plutonic-subvolcanic-volcanic connection in a Mio-Pliocene long-lived igneous system (Tuscany): zircon CA-ID-TIMS dating

Gabriele Paoli, Andrea Dini, Maria Ovtcharova, and Sergio Rocchi

The genetic link between plutonic and volcanic realms is a key for understanding timescales of igneous plumbing systems, and precise geochronological records are pivotal in estimating the duration of processes at different levels in such plumbing systems. The Campiglia igneous complex, Tuscany, offers exposures of the full range of emplacement levels (plutonic, subvolcanic, volcanic) of mantle- and crust-derived magmas. Magma emplacement occurred astride the Miocene-Pliocene boundary. New high-precision U-Pb CA-ID-TIMS, zircon geochronological data, coupled with LA-HR-ICP-MS zircon dates for the whole Campiglia system define a short crystallization time span for zircon from the peraluminous granite pluton (~100 ka), intermediate for the shallow-level mafic porphyry (~450 ka), and longer for the rhyolite (~700 ka), at odd with what commonly expected. The oldest ages for the three units are the same, leading to hypothesize the occurrence of a bimodal deep reservoir remaining in melt-present conditions for some 700 ka. In this framework, early-crystallized zircons were cannibalized by younger melt batches that were sequentially extracted from the reservoir.

How to cite: Paoli, G., Dini, A., Ovtcharova, M., and Rocchi, S.: Timescales of plutonic-subvolcanic-volcanic connection in a Mio-Pliocene long-lived igneous system (Tuscany): zircon CA-ID-TIMS dating, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3125, https://doi.org/10.5194/egusphere-egu21-3125, 2021.

       Studying magma reservoir processes is one of the keys to understand the evolution of igneous systems. One of the main processes, magma differentiation, governs the thermal evolution and chemical composition of the melt-crystal assemblage (magma or mush depending on the relative proportions), and therefore exerts a first order control over its physical properties (density, viscosity), and thus on reservoir dynamics. Various approaches have been implemented to model differentiation in an attempt to benchmark all the involved variables like initial and phase compositions, temperature, pressure, and oxygen fugacity (C0, X, T, P, fO2). Those approaches are among others mass balance calculations considering partition coefficients (D) values, experimental studies, thermodynamic models or a combination of those. In any of those cases, the evolution of trace elements is governed by the value of the D that is known to be dependent on (P, T, X, fO2). However, most of the present-day studies still use fixed values of D to provide first order estimates.

      Here, we present an approach combining thermodynamic modeling (relying on Rhyolite-MELTS, Gualda et al., 2012), that integrates X-T-P-fO2-dependent D for Rare Earth Elements (REE). We applied this new approach to a MORB system, with olivine, clinopyroxene and plagioclase as main mineral phases, and compared results to more classical approaches. D are derived from the models of Sun & Liang (2012, 2013, 2014) and Sun et al. (2017). The resulting model highlights that T & X effects on the D values can add or counterbalance each other depending on the mineral considered. In any cases our results emphasize the gain of using thermodynamic models along with both T- & X-dependent D values to properly model the evolution of igneous systems. Relying on our results, and on the corresponding thermodynamics constraints, we were also able to provide D for any mineral composition crystallized from this MORB system. Results bring to light that an error of ~1 order of magnitude of the Dmineral-melt value could be introduced when considering a fixed value of D.

 

Gualda et al. (2012) Journal of Petrology, 53-5, 875-890; Sun & Liang (2012) Contrib Mineral Petrol 163-5: 807-823; (2013) Chem Geol 358: 23-36; (2014) Chem Geol 372: 80-91; Sun et al. (2017) Geochim Cosmochim Acta 206: 273-295.

 

How to cite: Toussaint, A. and France, L.: Modeling differentiation in igneous systems: On the importance of considering temperature & composition dependent partition coefficients, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1222, https://doi.org/10.5194/egusphere-egu21-1222, 2021.

EGU21-13867 | vPICO presentations | GMPV8.1

Tracking reservoir dynamics across a complete caldera cycle at Rabaul, Papua New Guinea

Gareth N. Fabbro, Chris O. McKee, Mikhail E. Sindang, Jeffrey A. Oalmann, and Caroline Bouvet De La Maisonneuve

Caldera-forming eruptions are some of the most devastating events on Earth; however, the volcanoes that produce these eruptions frequently have much more minor activity. Knowing if a restless caldera is currently primed for a large eruption, therefore, has important implications for hazard assessment and risk management. Many calderas, including Rabaul in Papua New Guinea, show cycles of activity with multiple caldera-forming eruptions interspersed with more minor activity. We present data that spans an entire cycle, from one caldera-forming eruption to the next and estimate the storage conditions for each eruption. The last complete caldera cycle of Rabaul started at ~10.5 ka, with the eruption of the dacitic Vunabugbug Ignimbrite. Following the Vunabugbug, little volcanic activity was preserved until ~4.4 ka, suggesting either a period quiescence or destruction and burial during the subsequent caldera-forming eruptions of the region. From 4.4 ka, there is an increase in the volume and SiO2 contents of volcanic deposits that are preserved, which culminated in the eruption of the dacitic Memorial Ignimbrite at ~4.1 ka. The Memorial Ignimbrite was smaller than the Vunabugbug Ignimbrite and Rabaul Pyroclastics and may not have formed a caldera; however, it does appear to have altered the plumbing system and allowed deeper, hotter basalts to reach the surface. Following the eruption of these basalts, the system gradually evolves towards more silicic magmas, until the eruption of the dacitic Rabaul Pyroclastics at ~1.4 ka. After the Rabaul Pyroclastics hotter, more mafic magmas can again reach the surface, both as more mafic lava flows and as hybrid andesites that contain crystal cargos transported from deeper in the system.

Two-pyroxene, clinopyroxene–liquid and plagioclase–liquid thermobarometers suggest that the dacites, including those erupted during the caldera-forming eruptions, were stored at pressures of ~1 kbar (~4 km depth) and at temperatures of ~930 °C. There is a tight relationship between the temperature and the SiO2 content of the magmas, with the basalts erupted after the large ignimbrites recording temperatures of up to 1100 °C. Some of the more mafic magmas also record deeper storage, at pressures of 3–4 kbar (11–15 km). Plagioclase–liquid pairs suggest melt H2O contents of ~2.8 wt.% for the dacites, although some of the more mafic magmas have slightly higher melt H2O contents (3.2–4.0 wt.%)—this may be because the basalts were saturated and stored at greater pressures. Magnetite–liquid pairs record relatively constant oxygen fugacities of ~1.2 log units above the FMQ buffer.

At Rabaul it would take on the order of a few millennia to differentiate or accumulate enough dacitic magma to produce a large explosive eruption. The eruption of highly evolved, crystal-poor, cold, hydrous magmas geochemically similar to those erupted prior to the Memorial Ignimbrite and Rabaul Pyroclastics may provide a warning of an impending large explosive eruption.

How to cite: Fabbro, G. N., McKee, C. O., Sindang, M. E., Oalmann, J. A., and Bouvet De La Maisonneuve, C.: Tracking reservoir dynamics across a complete caldera cycle at Rabaul, Papua New Guinea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13867, https://doi.org/10.5194/egusphere-egu21-13867, 2021.

EGU21-12471 | vPICO presentations | GMPV8.1

Magmatic processes leading to the 1650 CE explosive eruption at the Kolumbo submarine volcano, Greece.

Filippo Mastroianni, Iacopo Fantozzi, Chiara Maria Petrone, Georgios E. Vougioukalakis, Eleonora Braschi, and Lorella Francalanci

Kolumbo is the largest of twenty submarine volcanic cones, tectonically aligned in the transtentional Anydros basin, one of the most seismically active zones in the South Aegean Volcanic Arc, whose magmatism is related to the subduction of the African Plate beneath the Aegean microplate. Kolumbo explosively erupted in 1650 CE, causing the death of 70 people on Santorini, which is only 7 km SW of Kolumbo. Explorative cruises employing ROVs discovered a high temperature (220°C) hydrothermal field with CO2-rich discharges and accumulation of acidic water at the bottom of the crater (505 m b.s.l.), increasing the related hazard. A possible magma chamber was recognized below the crater at depth 9-6 km by seismic data [Dimitriadis et al. 2009]. Geochemical data [Klaver et al. 2016] suggest that Kolumbo have a different mantle source and storage system from Santorini. It is fundamental to understand the behaviour of this volcano, and how its storage and plumbing system works, to correctly assess risk for nearby islands.

We present petrographic, geochemical and isotopic data of samples collected during the cruises and by divers. Most samples represent the juvenile products of the 1650 CE activity, characterizing different magmas interacting before the eruption. They consist of white rhyolitic pumices with grey and black bands, also including basaltic-andesitic enclaves. Plagioclase, biotite, pyroxenes are the main mineral phases; olivine is found in the mafic enclaves. Minerals show quite complex zoning and a large compositional variability. Fresh lithic lavas were sampled; they also have amphibole and can be subdivided in three groups with distinctive petrographic textures that are well reflected in their different chemical compositions. They give information on the early history of the volcano and on how the rhyolitic magma could have been generated.

Our data suggest the presence of a complex storage system where the most evolved magma differentiated by assimilation and fractional crystallization, undergoing several inputs of mafic magmas. Early batches of new melts initially mixed with the resident ones, whereas later arrivals only mingled with the rhyolitic magma, thus possibly representing the final trigger of the eruption.

How to cite: Mastroianni, F., Fantozzi, I., Petrone, C. M., Vougioukalakis, G. E., Braschi, E., and Francalanci, L.: Magmatic processes leading to the 1650 CE explosive eruption at the Kolumbo submarine volcano, Greece., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12471, https://doi.org/10.5194/egusphere-egu21-12471, 2021.

EGU21-6713 | vPICO presentations | GMPV8.1

A highly diverse silicic end member of a bimodal magma suite formed in an active continental back arc, Okinawa Trough

Arran Murch, Kenichiro Tani, Takashi Sano, and Shigekazu Yoneda

The Okinawa Trough (OT) is an incipient continental back-arc basin that extends from Kyushu in the north to Taiwan in the south. The Okinawa Trough can be split in to three segments, the Northern (NOT), Middle (MOT), and Southern (SOT) with active back-arc volcanism restricted to volcanic centres located in en-echelon grabens the MOT and SOT. Previous studies have shown magmatism in the OT is bimodal (basaltic to rhyolitic), with at least two types of silicic melts inferred to form through pure fractional crystallisation from basalt and by fractional crystallisation along with minor crustal assimilation (Shinjo and Kato, 2000).

Here we present petrological descriptions, along with major, trace element and Sr–Nd isotopic data for 75 silicic end member samples recovered as both lava and pumice, collected during the R/V Sonne HYDROMIN1 and 2 cruises in 1988 and 1990, respectively. Samples were dredged from various seafloor knolls and ridges located in the Io and Iheya grabens and from Izena Hole in the MOT, and from a single volcanic ridge in the Yaeyama graben and a single isolated knoll in the SOT.

Results show a chemically highly diverse silicic end member magmas, with at least four identifiable groups based on differences in the degree of enrichment of incompatible elements (LREE, K, Rb, Ba, etc.). Each group contains at least one dense lava sample suggesting the chemical diversity is a primary feature of magmatism in the Okinawa Trough rather than a result of the floating in of pumiceous material from various locations.

Using petrological descriptions and the chemistry of samples along with MELTS modelling we plan to calculate magma formation conditions and identify any evidence of magma mixing or crustal assimilation. In doing so we hope to provide a model to explain the diversity of silicic magma chemistry in the MOT and SOT.

 

Shinjo, R., and Kato, Y. (2000). Geochemical constraints on the origin of bimodal magmatism at the Okinawa Trough, an incipient back-arc basin. Lithos 54, 117–137. doi:10.1016/S0024-4937(00)00034-7.

How to cite: Murch, A., Tani, K., Sano, T., and Yoneda, S.: A highly diverse silicic end member of a bimodal magma suite formed in an active continental back arc, Okinawa Trough, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6713, https://doi.org/10.5194/egusphere-egu21-6713, 2021.

Understanding the causes of major and trace element variations of granite samples as well as their isotopic signatures is central to attempts to place these rocks in the context of broader geologic processes and continent evolution. For the granites of the Lachlan and New England Fold Belts (LFB and NEFB) of Australia there has been great debate between competing petrogenetic models. The open-system view that the isotopic variability and within-suite compositional trends can be accounted for by magma mixing and fractional crystallisation stands in contrast to the restite unmixing model, in which the geochemical features of certain granites are inherited from protoliths that underwent partial melting to produce magmas entraining varying proportions of residual material. Reconciling all aspects of the geochemical data in a mixing model is contingent on a plausible fractionation regime to produce the observed consistently linear (or near-linear) trends on Harker diagrams; however, the plausibility of existing fractional crystallisation models for LFB granites has not previously been tested with consideration of phase equilibria.

The Magma Chamber Simulator (MCS) models fractional crystallisation alone or with assimilation (AFC), constraining phase equilibria using MELTS and accounting for the thermal budget. This sophisticated modelling tool was used to conduct a case study of the I-type Jindabyne Suite of granites from the LFB, testing whether thermodynamically feasible geochemical trends matching the observed linear variations can arise through fractional crystallisation (with or without assimilation of supracrustal material). The results of 112 MCS models show (1) that for major elements liquid lines of descent (LLDs) may be sensibly linear over limited compositional ranges, (2) that the involvement of assimilation extends the range in which trends are relatively simple and near-linear, and (3) that, despite these observations, neither fractional crystallisation nor AFC are able to correctly reproduce the geochemical evolution of the I-type Jindabyne Suite granitoids as an LLD (contrary to existing models), instead persistently producing curved and kinked trends. The output of these simulations were further used to explore models in which: (a) crystal-bearing magmas evolve via fractional crystallisation or AFC (with chemical isolation assumed to be achieved through crystal zoning) and undergo varying degrees of melt-crystal segregation at different stages to produce the sample compositions; and (b) in situ crystallisation occurs via fractional crystallisation within the crystallisation zone, driving the evolution of a liquid resident magma, which the samples represent. These models are able to reproduce the Jindabyne Suite trends reasonably well. The modelling implies that fractional crystallisation, or some variant thereof, is a viable explanation for the linear trends in Jindabyne; however, tendency for grossly non-linear LLDs highlights that it should not be assumed that fractional crystallisation can generally explain linear trends in granites without careful modelling such as shown here.

How to cite: Iles, K. and Heinonen, J.: Modelling the production of linear trends in granitoids using the Magma Chamber Simulator: a case study of the Jindabyne Suite from the Lachlan Fold Belt, Australia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2570, https://doi.org/10.5194/egusphere-egu21-2570, 2021.

The parental magmas of massif-type anorthosites are suggested to originate from either the mantle or lower crust. If the source is the mantle, the magmas are presumed to have undergone crustal assimilation prior to plagioclase crystallization, which has produced melt compositions similar to anorthosite parental magmas (high-Al gabbros/basalts). If the source is the lower crust, the produced anorthosite parental melts are presumed to be monzodioritic (jotunitic) in composition. However, many studies have suggested that the monzodioritic rocks related to massif-type anorthosites rather represent residual melt compositions left after anorthosite fractionation. In this study, we have used the most recent thermodynamic modeling tools, Magma Chamber Simulator (MCS) and Rhyolite-MELTS to conduct partial melting, assimilation-fractional crystallization (AFC), and fractional crystallization (FC) models to address the unresolved questions about the source and compositional evolution of the anorthosite parental magmas.

AFC models were conducted at high lower crustal pressures (1000 MPa) by using MCS. In the models, we used four different sublithospheric mantle partial melt compositions and 11 different assimilants with representative average lower crustal compositions compiled from literature. In addition, equilibrium partial melting of the same lower crustal compositions was modeled separately by using rhyolite-MELTS. The melt major element compositions produced by both modeling tools were compared to suggested natural anorthosite parental magma compositions. Finally, to further study the evolution of these melts after their generation, FC models were run at different crustal pressures (1000-100 MPa) by using MCS. These differentiated melt compositions were compared to a global array of monzodioritic rocks presumed to represent residual melts left after anorthosite fractionation.

The preliminary modeling results point towards the mantle being a more suitable candidate for the source of the anorthosite parental magmas and that the parental magma compositions are better represented by high-Al gabbros than monzodioritic rocks: assimilation of mafic lower crustal material by mantle-derived magmas produces melts that are the most fitting analogues. Somewhat similar melts can also be produced by directly melting the lower crust, but this requires the crust to melt completely, which we consider improbable. The models further suggest fractional crystallization of high-Al gabbroic parental magmas produce residual melt evolution trends similar to the array of anorthosite-related monzodioritic rocks.

How to cite: Fred, R., Heinonen, A., and Heinonen, J. S.: The Origin and Melt Evolution of Massif-type Anorthosite Parental Magmas: Thermodynamically Controlled Major Element Constraints, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6922, https://doi.org/10.5194/egusphere-egu21-6922, 2021.

EGU21-13662 | vPICO presentations | GMPV8.1

The role of shallow open system processes in the evolution of South Tepeldag Pluton (NW Turkey): insights and constraints from thermodynamic modelling

Tunahan Arık, Ömer Kamacı, Işıl Nur Güraslan, and Şafak Altunkaynak

Eocene granitoids in NW Anatolia occurred following the continental collision between Sakarya Continent and Tauride-Anatolide Platform and mark the onset of post-collisional magmatism in the region. One of the representative members of the Eocene granitoids, the Tepeldağ pluton crops out as two isolated granitic bodies and is intruded into the Cretaceous blueschist assemblages (Kocasu formation) and ophiolitic rocks within the Izmir-Ankara-Erzincan suture zone (IAESZ). South Tepeldağ pluton (STP) is composed mainly of granodiorite with subordinate quartz diorite, which show transitional contacts. Aplitic dykes crosscut the pluton as well as the country rocks. STP includes a number of mafic microgranular enclaves (MME) of gabbro/diorite composition.

Geochemically, STP shows distinct I-type affinity with a metaluminous to slightly peraluminous (ASI ≤1.02) nature. The samples are medium-K to high-K calc-alkaline in character. They exhibit depletion in HFSE (Ti, Hf, Zr, Nb and Ta) compared to large ion lithophile elements (Rb, Ba, Th, U, K) and presents negative Nb, P, Ti anomalies. STP displays slight negative Eu anomalies (Eu/Eu* = 0.7–1.2), enrichment in LREE and flat HREE patterns in chondrite-normalized spider diagrams. MELTS modeling (with initial parameters of 1–3 kbar pressure, 2–3% water and QFM-NNO oxygen fugacity buffers) indicate that compositional variations in STP samples can be interpreted as a result of open system processes (assimilation fractional crystallization) rather than a reflection of fractional crystallization in the upper crustal magma chamber. All thermodynamic simulations dictate a crustal assimilation, especially in the late stages of the magmatic process, with a MgO, Na2O and Al2O3-rich assimilant similar to the suture zone (IAESZ) rocks.

How to cite: Arık, T., Kamacı, Ö., Güraslan, I. N., and Altunkaynak, Ş.: The role of shallow open system processes in the evolution of South Tepeldag Pluton (NW Turkey): insights and constraints from thermodynamic modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13662, https://doi.org/10.5194/egusphere-egu21-13662, 2021.

EGU21-2749 | vPICO presentations | GMPV8.1

Insights into the petrogenesis and petrophysics of vein magmatism in the Lamas de Olo region, northern Portugal

António Oliveira, Helena Martins, and Helena Sant'Ovaia

The onset of the final stages of the Variscan orogeny in the Central Iberian Zone (CIZ) is marked by the emplacement of several late to post-tectonic granite melts. The following transition into an extensional regime is associated with subvolcanic magmatism, commonly represented by veins and masses of rhyolitic porphyries, dolerites, and lamprophyres. In Portugal and Spain, these hypabyssal lithologies are fairly abundant.

The Lamas de Olo region of northern Portugal is located about 100 km to the ENE of Porto. Here, the most significant geological body is the composite, post-tectonic Lamas de Olo pluton. Several fracture systems, whose average trends are NNW-SSE, NNE-SSW, and WSW-ENE, cut through this pluton. The composing facies are known as the Lamas de Olo (LO), Alto dos Cabeços (AC), and Barragem (BA) granites. To the east of the pluton, there are two veins: a microgranite and a lamprophyre. While the microgranite is E-W trending, the lamprophyre is N53°E trending.

The felsic vein is rich in quartz and K-feldspar, which are frequently intergrown in granophyric texture, while muscovite, apatite, biotite, and ilmenite are accessories. The feldspars are intensely kaolinized and muscovitized, and biotite is mostly altered in chlorite and brookite/anatase. Compositionally, the microgranite is identical to the BA facies. It is subalkaline, highly felsic peraluminous, and associated with post-orogenic to transitional settings.

Biotite, K-feldspar, plagioclase, pyroxene, and amphibole are the main minerals composing the lamprophyre. Quartz, hematite, goethite, apatite, monazite, zircon, and magnetite are accessories. Pyroxene uralitization, amphibole biotitization, and biotite chloritization evidence the altered state of this vein. Geochemically, the pluton and lamprophyre have nothing in common. This lithology is metaluminous to weakly peraluminous, shoshonitic, alkaline, and associated with within-plate and post-collisional uplift settings. Zircon SHRIMP U-Pb analyses yield a concordia age of 295 ± 2 Ma (MSWD = 2.1) and the Nd isotopic signature is εNd = -0.05.

Considering the geochemistry, the microgranite is more evolved than the LO and AC granites. Most likely, it derived from a plagioclase-rich, crustal source, which was uncontaminated by mantle or young crustal materials. The microgranite melt was presumably derived from the same source that generated the BA granite, and its emplacement was controlled by WSW-ENE trending fractures. The mineral assemblage is mostly diamagnetic, and the post-magmatic alterations were mainly triggered by meteoric fluids, thus generating an ambiguous magnetic fabric. The microgranite is also associated with a subhorizontal magma flow and shallow roots. On the other hand, the lamprophyre was presumably derived from the lithospheric mantle and strongly contaminated by lower crustal materials. Geochemically, the lamprophyre is unrelated to the pluton, but structurally the NNE-SSW trending fractures probably influenced its emplacement. The petrophysical results point out a ferromagnetic behavior and influence of hydrothermal fluids. Based on our results, the lamprophyre was seemingly generated and emplaced after the microgranite.

This work was supported by the Portuguese Foundation for Science and Technology (FCT), through the project reference UIDB/04683/2020 and ICT (Institute of Earth Sciences). The main author is also financially supported by FCT through an individual Ph.D. grant (reference SFRH/BD/138818/2018).

How to cite: Oliveira, A., Martins, H., and Sant'Ovaia, H.: Insights into the petrogenesis and petrophysics of vein magmatism in the Lamas de Olo region, northern Portugal, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2749, https://doi.org/10.5194/egusphere-egu21-2749, 2021.

EGU21-1496 | vPICO presentations | GMPV8.1

Origin and Evolution of Silicified Rocks in the Etili - Çanakkale, Turkey

Hatice Ünal Ercan, Ömer Işık Ece, Paul A. Schroeder, and Fatma Gülmez

There are many well-known geothermal systems linked to magmatic activity on Earth, many of which eventually express a surface manifestation of the below ground magmatism. The Oligo-Miocene was a period of very active magmatism that took place in Western Anatolia, where granitoidic plutons were emplaced within crust while calcalkaline to alkaline lavas and associated pyroclastics produced by volcanoes under the control of extensional tectonism. Progressive deformation of the crust due to the extension resulted since that time resulting in the development of a E/NE-W/SW trending fault system and of fracture zones that run perpendicular to main faults.

The mineralogical composition of the Hamamtepe and Muratdağı silica sinter deposits is comprised of kaolinite, alunite, and quartz. Microlithofacies of these deposits were defined as, i) massive, ii) laminated, iii) breccia, and iv) porous. δ18O stable isotope analysis on silicified rocks and δ34S with 40Ar/39Ar radiometric age analysis on alunite minerals were performed with the aim of constraining the origin and timing of the silica deposits. We obtained results from δ18O ranging from 12.3 to 18.4 ‰, δ34S ranging from 9.2 and 16.6 ‰, and radiometric age analysis, which all suggest that the silica sinter deposits formed in a steam heated, low pH, oxidizing epithermal environments., coeval with prominent volcanic activity in the region.

How to cite: Ünal Ercan, H., Ece, Ö. I., Schroeder, P. A., and Gülmez, F.: Origin and Evolution of Silicified Rocks in the Etili - Çanakkale, Turkey, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1496, https://doi.org/10.5194/egusphere-egu21-1496, 2021.

EGU21-10222 | vPICO presentations | GMPV8.1

Reconstruction of the Jurassic to Early Cretaceous tectono-magmatic evolution of the Northern Andean Arc from their Crustal Thickness and Thermobarometry

Luisa Chavarria, Camilo Bustamante, Agustín Cardona, and Germán Bayona

Igneous rocks in magmatic arcs record variations in composition, thermal flux, and subduction dynamics through time. In the Northern Andes, arc magmatism of the Jurassic age registers a complicated history, including the fragmentation of Pangea at the end of the Triassic and the beginning of a new subduction zone in the Jurassic located at the western margin of South America.

We characterized the crustal thickness variations of the Early Jurassic to Early Cretaceous (194-130 Ma) in plutonic and volcanic rocks of the Northern Andes of Colombia and Ecuador, using trace elements signatures and analyzed the implications of the emplacement conditions during the last stage of the magmatism using Al-in-hornblende thermobarometry and mineral chemistry. Moderate rare earth elements (REE) slopes and depleted heavy REE patterns show that the primary residual magma source was amphibole, but plagioclase and pyroxene were also significant residual phases indicating that the magma source was formed in a crust that varied in thickness from 35-50 km. The La/Yb and Sr/Y crustal quantifications variations indicate that the arc underwent two thickening episodes. The first episode (190 to 180 Ma) is associated with a magmatic event. The second episode (165 to 154 Ma) is related to the shift to an oblique subduction setting and a subsequent collisional event that produced medium P-T metamorphic rocks. In the Late Jurassic to Early Cretaceous (154-130 Ma), the crust became thinner and, in this scenario, was emplaced the last stage of plutonism with depths that varied from shallow to deep level (until 25.5 km) in the crust.

How to cite: Chavarria, L., Bustamante, C., Cardona, A., and Bayona, G.: Reconstruction of the Jurassic to Early Cretaceous tectono-magmatic evolution of the Northern Andean Arc from their Crustal Thickness and Thermobarometry, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10222, https://doi.org/10.5194/egusphere-egu21-10222, 2021.

EGU21-13269 | vPICO presentations | GMPV8.1

Petrogenesis and emplacement depths of the Petite Pluton during the closure of the Rocas Verdes basin, southern Patagonia - preliminary results

Gianfranco Gregorina, Maria Fernanda Torres García, Mauricio Calderón, Thomas Theye, Francisco Hervé, Cristobal Ramírez de Arellano, and Francisco Fuentes

The Petite Pluton is a Cretaceous intrusion covering an area of nearly 136 km2 located in Isla Capitán Aracena, southernmost Patagonia, Chile. This pluton and other stocks are located outside of the margins the Early Cretaceous-Paleogene Fuegian Batholith. The Petite Pluton intrudes the Capitán Aracena ophiolitic complex, interpreted as supracrustal remnants generated during the rifting stage of the Rocas Verdes marginal basin (Late Jurassic- Early Cretaceous; cf. Calderón et al., 2013, Geochem. J.) overlain by hemi-pelagic sedimentary basin infill (Yahgan Formation). These units are locally deformed and exposed in the southern limit of the NW-SE-trending Magallanes fold-and-thrust belt. The satellite plutons consist of amphibole-bearing diorites and quartzdiorites (48-55 wt.% SiO2) with calc-alkaline compositional trends consistent with their generation in a subduction environment. On N-MORB normalized incompatible elements pattern, the rocks show peaks in LILE (Rb, Ba, Sr) and subtle throughs in Ti, Zr, Nb, Ta and Y. Chondrite-normalized REE pattern is concave upwards with enrichment of LREE relative to HREE without Eu anomaly. The mineral compositions of diorites of Petite pluton consist of amphibole (magnesio-hornblende and tschermakitic hornblende), plagioclase is labradorite and andesine (An44-59), with Ca-rich composition in small grains included within poikilitic amphibole, biotite (annite), quartz, minor contents of K-feldspar, titanite, magnetite-ilmenite pairs and traces of apatite and zircon. Amphibole composition can be used as a proxy of the amount of H2O-rich fluids involved in magma evolution and could potentially be used to constrain the crustal depths of pluton emplacement in magmatic plumbing systems (Yavuz & Döner, 2017, P. di Mineralogia; Torres García et al., 2020, Lithos). The calculated pressure and temperature of 3 kbar and 800-850°C, indicate the emplacement and crystallization of magma batches in the upper crust. Oxygen fugacity [log (ƒO2)] varies between -9.9 and -10.7 (NNO), indicating amphibole crystallization from basaltic-andesitic melts under moderately oxidizing conditions. The moderately Mg# (60-72) of amphibole is consistent with their crystallization from mafic-intermediate melt-dominated crystal mushes with residual melts generated after the fractionational crystallization of olivine and clinopyroxene at deeper crustal depths. The amphibole composition constraint an amount of 6 wt% of H2O in the residual melts. The subtle negative Eu anomaly in amphibole indicates its partially simultaneous fractionation with plagioclase, suggesting rapid undercooling. The emplacement of the Petite Pluton at ~10 km depth occurred during and/or lately after the tectonic emplacement of ophiolitic complexes within an accretionary wedge, governed by a NE tectonic transport (Muller et al., 2021, Tectonophysics). Late Cretaceous satellite plutons suggest a continentward migration of the magmatic arc, related to the flattening of the subducted oceanic lithosphere of the proto-Pacific Ocean.

Acknowledgements. The study is supported by  Fondecyt grant 1161818.

How to cite: Gregorina, G., Torres García, M. F., Calderón, M., Theye, T., Hervé, F., Ramírez de Arellano, C., and Fuentes, F.: Petrogenesis and emplacement depths of the Petite Pluton during the closure of the Rocas Verdes basin, southern Patagonia - preliminary results, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13269, https://doi.org/10.5194/egusphere-egu21-13269, 2021.

EGU21-13377 | vPICO presentations | GMPV8.1

Resolving changes in arc magma volatile budgets over Myr timescales leading up to porphyry Cu formation 

Simon Large, Chetan Nathwani, Yannick Buret, Tom Knott, and Jamie Wilkinson

The crustal-scale magmatic systems of Andean-style arcs produce thick volcanic deposits and abundant plutons that are emplaced into the crust. They can also generate spatially- and temporally-restricted, economically-important porphyry Cu deposits. These deposits are formed at the magmatic-hydrothermal transition and require significant amounts of volatiles and metals to be concentrated in the sub-volcanic environment. Thus, understanding the magmatic and tectonic processes acting within an arc segment and their effect on the volatile budgets of crustal magmas could be essential for identifying the constraining factors controlling the potential of a magmatic system to produce a porphyry deposit.

In this study we examine the magmatic evolution of the Rio Blanco-Los Bronces district, ~30 km northeast of Santiago, Chile, which is host to the Earth’s largest resource of Cu. Eocene to Early Miocene volcanic rocks were intruded by the Miocene San Francisco Batholith that, in turn, partially hosts intrusions related to the Late Miocene to Early Pliocene Rio Blanco-Los Bronces porphyry deposit cluster. We apply a combination of whole-rock, apatite and zircon geochemistry and zircon geochronology to the intrusive rock suite of the district to provide temporally- constrained geochemical information over the entire duration of batholith assembly and ore formation.

U-Pb geochronology reveals incremental assembly of the San Francisco Batholith by individual magma batches over >14Myr (~18 – 4 Ma), with ore formation occurring in discrete pulses in the last 3 Myr before cessation of intrusive activity within the district. Progressive changes in the trace element chemistry indicate crustal thickening and deeper magma evolution within the arc segment as a result of the subduction of the Juan Fernandez ridge. A temporal shift to elevated SO3 and Cl contents is recorded by zircon-hosted apatite inclusions from the intrusions with highest values occurring in porphyry intrusions directly associated with the ore forming events. These data suggest variable volatile budgets of magmas during zircon crystallisation and hint at crustal-scale controls on the porphyry ore-forming potential of an arc segment.

 

How to cite: Large, S., Nathwani, C., Buret, Y., Knott, T., and Wilkinson, J.: Resolving changes in arc magma volatile budgets over Myr timescales leading up to porphyry Cu formation , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13377, https://doi.org/10.5194/egusphere-egu21-13377, 2021.

EGU21-12995 | vPICO presentations | GMPV8.1

Contribution to the study of carbonatite complex of the Richat Dome (Mauritania)

Eboubekrine Sedigh Maham, Houssa Ouali, Michel jébrak, and Muhammed Ouabid

The Richat Dome is a huge circular, slightly elliptical depression (~ 40 km in diameter) in the Proterozoic to Cambro-Ordovician sedimentary series of the NE part of the Mauritanian Taoudeni basin. This structure consists of a central zone that corresponds to a complex of dolomitic limestones and sedimentary rocks of Neoproterozoic age, cut by breccia silica and felsic volcanic rocks. A peripheral zone comprising Neoproterozoic to Late Ordovician sandstones and pelites into which carbonatite veins and two gabbroic annular dykes are injected.

Generally, the carbonatites represent a relatively rare type of igneous rock composed mainly of primary carbonate minerals (calcite and/or dolomite > 50 vol % of the rock) associated with phosphate minerals, silicates, and oxides. They contain the highest concentrations of rare earth elements (REE) of all igneous rocks. The carbonatites are also the main source of REE especially the light REE (La, Ce, Pr and Nd) as well as some critical metals such as Nb and Ta.

The aim of this study is to present a preliminary work on the carbonatite dykes of the Richat Dome: (1) detailed geological mapping of the various dykes, (2) petrographic, (3) mineralogical and (4) geochemical characterizations. The results obtained will be cross-referenced with other strategic deposits around the world

How to cite: Maham, E. S., Ouali, H., jébrak, M., and Ouabid, M.: Contribution to the study of carbonatite complex of the Richat Dome (Mauritania), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12995, https://doi.org/10.5194/egusphere-egu21-12995, 2021.

GMPV9.1 – Multi-disciplinary volcano monitoring and imaging with networks

EGU21-3447 | vPICO presentations | GMPV9.1

Observation of gliding tremors from the Gulf of Guinea might help solve over 50 year old mystery

Charlotte Bruland, Sarah Mader, and Céline Hadziioannou

In the 1960's a peak in the seismic amplitude spectra around 26 s was discovered and detected on stations worldwide. The source was located in the Gulf of Guinea, with approximate coordinates (0,0), and was believed to be generated continuously. A source with similar spectral characteristics was discovered near the Vanuatu Islands, at nearly the antipodal location of the Gulf of Guinea source. Since it was located close to the volcanoes in Vanuatu, this source is commonly attributed to magmatic processes. The physical cause of the 26 s microseism, however, remains unclear.

We investigate the source location and evolution of the 26 s microseim using data from permanent broadband stations in Germany, France and Algeria and temporary arrays in Morocco, Cameroon and Botswana for spectral analysis and 3-C beamforming to get closer to resolving the source mechanism responsible for this enigmatic signal. We find that the signal modulates over time and is not always detectable, but occasionally it becomes so energetic it can be observed on stations worldwide. Such a burst can last for hours or days. The signal is visible on stations globally approximately 30 percent of the time. Our beamforming analysis confirms that the source is located in the Gulf of Guinea, as shown in previous studies, and that the location is temporally stable. Whenever the signal is detectable, both Love and Rayleigh waves are generated. We discover a spectral glide effect associated with the bursts, that so far has not been reported in the literature. 

The spectral glides last for about two days and are observed on stations globally. Although at higher frequencies, very long period tremors and gliding tremors are also observed on volcanoes as Redoubt in Alaska and Arenal in Costa Rica, suggesting that the origin of the 26 s tremor is also volcanic. However, there is no reported volcanic activity in the area where the source appears to be located.

 

How to cite: Bruland, C., Mader, S., and Hadziioannou, C.: Observation of gliding tremors from the Gulf of Guinea might help solve over 50 year old mystery, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3447, https://doi.org/10.5194/egusphere-egu21-3447, 2021.

EGU21-11140 | vPICO presentations | GMPV9.1

Crustal structure of La Palma and Tenerife (Canary Islands) from receiver function analysis.

Víctor Ortega, Luca D'Auria, Iván Cabrera-Pérez, José Barrancos, Germán D. Padilla, and Nemesio M. Pérez

The receiver function analysis (RF) is a commonly used and well-established method to investigate crustal and mantle structures, removing the source, ray-path and instrument signatures. RF gives the unique signature of sharp seismic discontinuities and information about P and S wave velocities beneath a seismic station. In particular, using the direct P wave as a reference arrival time, and the relative arrival time of P-to-S (Ps) conversions and multiple reflections allow constraining the principal crustal structures and studying the effects of dipping interfaces and crustal layering.

We have applied RF analysis to the active volcanic islands of Tenerife and La Palma (Canary Islands). In recent years, both islands have increased their seismic activity and showed variation in geochemical parameters attributed to a magmatic-hydrothermal activity. Previous studies evidenced in La Palma and Tenerife a seismic Moho depth at 14 km and 12 and 15 km, respectively, but it is not clear because there are some others discontinuities under the stations (Lodge et al., 2012). Other RF studies indicated a depth of seismic Moho discontinuity between 16 and 30 km beneath the eastern islands to 11-15 km under the western isles, observing a thinning of the crust towards the west (Martinez-Arévalo et al., 2013). 

We processed 313 teleseisms recorded by 17 stations for Tenerife and 252 teleseisms recorded by six stations for La Palma. Since the receiver functions display a significant complexity, as expected in oceanic volcanic islands, we applied a transdimensional inversion approach to image the 1D velocity structure beneath each station. We observe at least three discontinuities related with the oceanic crust and the overlying volcanic rocks layer. We compare the retrieved crustal structure with the seismicity recorded in recent years, showing how earthquakes have a radically different origin on these two islands. While in Tenerife they seem to be related to the dynamics of a shallow hydrothermal system, in La Palma they are related to magmatic intrusions in the upper mantle beneath the island.

References

Lodge, A., Nippress, S. E. J., Rietbrock, A., García-Yeguas, A., & Ibáñez, J. M. (2012). Evidence for magmatic underplating and partial melt beneath the Canary Islands derived using teleseismic receiver functions. Physics of the Earth and Planetary Interiors, 212, 44-54.

Martinez-Arevalo, C., de Lis Mancilla, F., Helffrich, G., & Garcia, A. (2013). Seismic evidence of a regional sublithospheric low velocity layer beneath the Canary Islands. Tectonophysics, 608, 586-599.

How to cite: Ortega, V., D'Auria, L., Cabrera-Pérez, I., Barrancos, J., Padilla, G. D., and Pérez, N. M.: Crustal structure of La Palma and Tenerife (Canary Islands) from receiver function analysis., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11140, https://doi.org/10.5194/egusphere-egu21-11140, 2021.

EGU21-7871 | vPICO presentations | GMPV9.1

Imaging seismovolcanic tremor sources distribution with seismic network-based methods reveals fluid pressure pathways within Klyuchevskoy Volcanic Group magmatic system

Cyril Journeau, Nikolai Shapiro, Léonard Seydoux, Jean Soubestre, Ivan Koulakov, Andrei Jakovlev, Ilyas Abkadyrov, Evgeny Gordeev, Danila Chebrov, Christoph Sens-Schönfelder, Birger Luehr, Francis Tong, Gaspard Farge, and Claude Jaupart

The Klyuchevskoy Volcanic Group (KVG) located in Kamchatka, Russia is one of the World’s most active clusters of subduction volcanoes. In order to investigate its structure and very intense seismovolcanic activity, an international collaboration designed the KISS experiment operating a dense temporary seismic network between August 2015 and July 2016. During this period, the main volcano of KVG – Kyuchevskoy entered into eruption in the spring 2016. The preparation and eruptive periods have been characterized by a large number of volcanic earthquakes and tremors.

We applied in this study three cross-correlations network-based methods to detect and locate seismovolcanic tremor sources. From these three methods we extract simple 1D functions: spectral width (averaging in the 0.5-5 Hz frequency band the width of the network covariance matrix eigenvalue distribution), network response function (performing the 3D back-projection of the inter-station cross-correlations) and correlation coefficient function (averaging correlation coefficient functions computed at single station that characterize the stability in time of the single-station intercomponent cross‐correlation function). The simultaneous application of these network features allowed us to classify the wavefield recorded by the dense seismic network. We then computed inter-station cross-correlations extracted from the first eigenvector filtered covariance matrix and generate time series of 3D spatial likelihood functions. Using output of our classification approach, we stack over time these 3D spatial likelihood functions for time windows containing tremor and we finally obtain a 3D Density Likelihood function imaging the seismovolcanic tremor sources distribution within KVG.

The addition of the temporary seismic stations from the KISS network greatly increased our detection and location resolution and thus allowed us to refine our knowledge about seismovolcanic tremor at KVG. Our results highlight a large distribution of tremor sources connecting different volcanoes and different depth levels. Most of tremor sources are located below the Klyuchevskoy volcano in a narrow zone vertically extended from the surface to the crust-mantle boundary and exhibit a highly intermittent behavior characterized by burst of activities and rapid upward and downward migrations between deep and shallow locations. Several tremor sources are also located along a SW-NE structure extending from Tolbachik to Klyuchevskoy volcanoes. We thus image the near-vertical quasi-open main conduit connecting the deep magmatic reservoir to Klyuchevskoy volcano in which very rapid pressure transfers might occur as well as a possible secondary conduit that links the marginal part of the deep reservoir to the Tolbachik volcanic system in which the system overpressure may be sometimes evacuated.

How to cite: Journeau, C., Shapiro, N., Seydoux, L., Soubestre, J., Koulakov, I., Jakovlev, A., Abkadyrov, I., Gordeev, E., Chebrov, D., Sens-Schönfelder, C., Luehr, B., Tong, F., Farge, G., and Jaupart, C.: Imaging seismovolcanic tremor sources distribution with seismic network-based methods reveals fluid pressure pathways within Klyuchevskoy Volcanic Group magmatic system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7871, https://doi.org/10.5194/egusphere-egu21-7871, 2021.

We analyze data from one tiltmeter and twelve broadband seismic stations recorded at the beginning of the 2018 Kilauea eruption, to provide an integrated view of distinct tremor sources that preceded and accompanied this eruption. Studying the beginning of the eruption is challenging because of the diversity and complexity of signals that were recorded during this phase. But such undertaking represents a key aspect for understanding the dynamics of the different processes that took place at the start of the lava lake withdrawal on May 2 and during the twelve major collapses that occurred in Halema‘uma‘u Crater through May 26. The application of a network-based method to automatically detect and locate seismic tremor, combined with physical modeling of the underlying source processes, enables a characterization of these tremor sources in unprecedented detail.

Our analyses document one tremor source active during the period preceding the eruption, which is attributed to the quasi-steady radiation from a shallow hydrothermal system located at the south-southwest edge of Halema‘uma‘u Crater. These analyses further document two newly described sequences of gliding tremor. The first sequence is attributed to progressive jerky intrusions of a rock piston into a shallow hydrothermal reservoir between May 7 and May 17. The second sequence is attributed to the gradual degassing of a bubbly magma within an east striking dike below Halema‘uma‘u Crater, impacted by repeated roof collapses, and resulting in a quasi to totally degassed magma by May 26.

How to cite: Soubestre, J., Chouet, B., and Dawson, P.: Characterizing volcanic tremor sources associated with collapses in Halema‘uma‘u Crater at the beginning of the 2018 Kilauea eruption, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10723, https://doi.org/10.5194/egusphere-egu21-10723, 2021.

EGU21-7968 | vPICO presentations | GMPV9.1

Investigation of the bedrock (metamorphic basement) geometry of Santorini island using single-station ambient noise data 

Nikolaos Chatzis, Constantinos Papazachos, Nikolaos Theodulidis, Panagiotis Hatzidimitriou, Marios Anthymidis, George Vougioukalakis, Dimitrios Panagiotopoulos, Emilie Hooft, Ben Heath, Doug Toomey, Michelle Paulatto, Joanna Morgan, and Mike Warner

We investigate the geometry of the metamorphic basement of the Santorini volcanic island using ambient noise data to determine the pre-Alpine/pre-volcanic bedrock structure. The geometry of pre-volcanic Santorini is important in order to constrain the recent volcanic history of the island and also to study the site-effect of the volcanic formations on seismic motions. Santorini is the most active volcano of the Southern Aegean Volcanic Arc and is the southernmost island of the Cyclades islands metamorphic complex. As a result, the volcanic material that has accumulated during the last 600+ Kyrs has been superimposed on the pre-volcanic Santorini (Cycladic) island. To map the thickness of volcanic material, we have performed a large number (>200) of single-station noise measurements in the Santorini area.  Measurements were mainly performed using conventional acquisition systems (Guralp-40T 30sec seismometer and Reftek-130A digitizer). We also employed additional single-station noise data from several previous studies (Dimitriadis et al. 2006, PROTEUS Project 2015), as well as permanent stations from the Hellenic Seismological Network in the same region. HVSR curves were calculated using single-station noise data and were used to estimate the fundamental frequency, f0, as well as the corresponding maximum HVSR amplitude, A0HVSR. The majority of HVSR curves showed prominent peaks (A0HVSR locally larger than 7-8), indicating a clear impedance contrast between volcanics and metamorphic formations. To map the bedrock depth, we estimated the thickness of the upper volcanic formations using the quarter-wavelength approximation for each site. For this assessment, the average shear-wave velocity (Vs) of the volcanic formations was estimated from the inversion of several passive ambient noise array data, as well as additional constraints from selected MASW measurements. Where possible, the reliability of the spatial variation of volcanic formation thickness was checked with independent geological information. Using the digital elevation model and the volcanic formation thickness for each site of the single-station noise data, we estimated the spatial distribution of the pre-Alpine, metamorphic bedrock depth. The resulting geometry of the pre-volcanic Santorini island shows very deep basins (now filled with volcanic formations) around the pre-Alpine bedrock outcrop in the southern part of Santorini (Profitis Ilias), increasing to 100+ meters in the Kamari-Perissa basin area (southeastern Santorini) and to more than 400+ in the central (Fira-Imerovigli) and the north Santorini areas (Oia), in agreement with recent larger-scale tomographic results (Heath et al., 2019). The results are also in very good agreement with the pre-Alpine bedrock geometry independently inferred from gravity data inversion (Tzanis et al., 2019.)

This research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme «Human Resources Development, Education and Lifelong Learning» in the context of the project “Strengthening Human Resources Research Potential via Doctorate Research” (MIS-5000432), implemented by the State Scholarships Foundation (ΙΚΥ), the Hellenic Foundation for Research and Innovation (HFRI) under the “First Call for HFRI Research Projects to support Faculty members and Researchers and the procurement of high-cost research equipment grant” (Project Number: 2924) and the Institute for the Study and Monitoring Of the SAntorini Volcano (ISMOSAV).

How to cite: Chatzis, N., Papazachos, C., Theodulidis, N., Hatzidimitriou, P., Anthymidis, M., Vougioukalakis, G., Panagiotopoulos, D., Hooft, E., Heath, B., Toomey, D., Paulatto, M., Morgan, J., and Warner, M.: Investigation of the bedrock (metamorphic basement) geometry of Santorini island using single-station ambient noise data , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7968, https://doi.org/10.5194/egusphere-egu21-7968, 2021.

EGU21-10957 | vPICO presentations | GMPV9.1

Ambient noise tomography of Gran Canaria island (Canary Islands)

Iván Cabrera Pérez, Jean Soubestre, Luca D'Auria, Germán Cervigón-Tomico, David Martínez van Dorth, José Barrancos, Germán D. Padilla, and Nemesio M. Pérez

The island of Gran Canaria is located in the Canarian Archipelago, with an area of 1560 km2 and a maximum altitude of 1956 m.a.s.l., being the third island of the archipelago in terms of extension and altitude. The island has two very well differentiated geological domains: the southwest domain or Paleo-Canarias, which is the geologically oldest part, and the northeast domain or Neo-Canarias, where are located the vents of the most recent Holocene eruptions. This volcanic island hosted Holocene eruptions. Therefore, apart from being affected by volcanic risk, it potentially hosts geothermal resources that could be exploited to increase the percentage of renewable energy in the Canary Islands.

The main objective of this work is to use Ambient Noise Tomography (ANT) for retrieving a high-resolution seismic velocity model of the first few kilometres of the crust, to improve local earthquake location and detect anomalies potentially related to active geothermal reservoirs. Currently, the 1-D velocity model of the island does not allow a correct determination of the hypocenters, being unable to take into account the substantial horizontal velocity contrasts correctly.

To realize the ANT, we deployed 28 temporary broadband seismic stations in two phases. Each campaign lasted at least one month. We also exploited data recorded by the permanent seismic network Red Sísmica Canaria (C7) operated by INVOLCAN. After applying standard data processing to retrieve Green’s functions from ambient noise cross-correlations, we retrieved the dispersion curves using the FTAN (Frequency Time ANalysis) technique. The inversion of dispersion curves to obtain group velocity maps was realized using a novel non-linear multiscale tomographic approach (MAnGOSTA, Multiscale Ambient NOiSe TomogrAphy). The forward modelling of surface waves traveltimes was implemented using a shortest-path algorithm that allows the topography to be taken into account. The MANgOSTA method consists of successive non-linear inversion steps on progressively finer grids. This technique allows retrieving 2-D group velocity models in the presence of substantial velocity contrasts with up to 100% of the relative variation. Then, we performed a depth inversion of the Rayleigh wave dispersion curves using a transdimensional Bayesian formulation. The final result is a 3-D model of P- and S-wave velocities of the island. The preliminary results show the presence of a low-velocity zone in the eastern part of the island that coincides spatially with anomalies observed in previous geophysical and geochemical studies and which could be related to actual or fossil geothermal reservoirs. Furthermore, the model shows the presence of high-velocity anomalies that are associated with the mafic core of the island.

How to cite: Cabrera Pérez, I., Soubestre, J., D'Auria, L., Cervigón-Tomico, G., Martínez van Dorth, D., Barrancos, J., Padilla, G. D., and Pérez, N. M.: Ambient noise tomography of Gran Canaria island (Canary Islands), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10957, https://doi.org/10.5194/egusphere-egu21-10957, 2021.

EGU21-13437 | vPICO presentations | GMPV9.1 | Highlight

Ambient noise waveform imaging of Yellowstone's magmatic system

Ross Maguire, Min Chen, Brandon Schmandt, Chengxin Jiang, Justin Wilgus, and Jiaqi Li

Understanding important characteristics of Yellowstone's magmatic system such as the melt fraction, composition, and geometric organization of melt are critical for improving our knowledge of volcanic processes and assessing the potential for future eruptions.  While previous tomographic images have provided much insight into the magmatic system, imaging results are complicated by an incomplete understanding of how large crustal magmatic systems affect seismic waveforms. In particular, tomographic studies based on asymptotic methods may underestimate the seismic wave speed anomaly of the magma reservoir because first arriving energy may be diffracted around strong low wave speed anomalies. Here, we present a high-resolution shear wave speed model of Yellowstone’s crust and uppermost mantle structure, based on the most up to date dataset of ambient noise correlation functions from broadband stations deployed in the Yellowstone region over the past two decades. This model serves as the starting point for an adjoint inversion, which has potential to improve resolution by incorporating more accurate sensitivity kernels based on realistic wave propagation physics. We discuss our adjoint tomography methodology and present the first model iterations. Continued iterations promise to sharpen features in the model which can provide new inferences into the present state of Yellowstone’s magmatic system.

How to cite: Maguire, R., Chen, M., Schmandt, B., Jiang, C., Wilgus, J., and Li, J.: Ambient noise waveform imaging of Yellowstone's magmatic system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13437, https://doi.org/10.5194/egusphere-egu21-13437, 2021.

In May 2018, a seismic crisis started in the Comoros archipelago, East of Mayotte, which was widely felt on the Island. The related discovery of a new, 800-m high, submarine edifice 50 km East of Mayotte showed that the seismicity was caused by the birth of a volcano. The eruption is still on going at the time of writing and has sparked a large interest in the scientific community.

The seismicity is still active and is being continuously monitored thanks to several seismic stations installed on the island of Mayotte. The oceanographic campaigns that were carried out since the beginning of the crisis deployed a number of ocean bottom seismometers directly above the seismicity, to accurately understand the crisis and particularly its location. A new technique of automatic detection based on Machine Learning enabled to considerably increase the number of earthquakes that can be used to constrain the extent of the seismicity. Furthermore, the development of a new velocity model for the region allowed a precise location of these earthquakes.

These new developments permitted to reconstruct the seismicity evolution during two years of this seismic crisis and to complete the seismicity map associated with the new seismic activity. These results provide more details on the active structures to study the evolution in time as well as their precise spacial variations, allowing the analysis of the daily-to-yearly timescales of this unprecedented eruption. This is crucial to understand the dynamics of the volcanic and magmatic processes beneath Mayotte island. Linking these spatial and time variations with the real-time data, as well as the deformation and petrology evolutions, will provide crucial details on the dynamics of submarine eruptions.

How to cite: Lavayssière, A. and Retailleau, L.: Short- and long-term evolution of the seismicity associated with the New Volcanic Edifice offshore Mayotte island, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2769, https://doi.org/10.5194/egusphere-egu21-2769, 2021.

EGU21-15902 | vPICO presentations | GMPV9.1

A REal-time TREmor Analysis Tool for seismic and infrasonic arrays

Patrick Smith and Chris Bean

The EUROVOLC project aims to promote an integrated and harmonised European volcanological community, with one of its main themes focusing on understanding sub-surface processes. Early identification of magma moving towards the surface is very important for the mitigation of risks from volcanic hazards, and joint research activities within the project aim to develop and improve schemes for detecting pre-eruptive unrest. Volcanic tremor is a sustained seismic signal that is often associated with such volcanic unrest, and has been linked to the movement of magmatic fluids in the subsurface. However, signals with similar spectral content can be generated by other surface processes such as flooding, rockfalls or lahars. Hence, one of the best ways of distinguishing between different possible mechanisms for generating tremor is by tracking the location of its source, which is also important for mitigating volcanic risk. Due to its emergent nature, tremor cannot be located using travel-time based methods, and therefore alternatives such as amplitude-based techniques or array analysis must be used. Dense, small-aperture arrays are particularly suited for analyzing volcanic tremor, yet costs associated with installation and maintenance have meant few long-term or permanent seismic arrays in use for routine monitoring.

Given the potential for wider usage of arrays, this work presents a freely available python-based software tool, developed as part of the EUROVOLC project, that uses array data and array processing techniques to analyze and locate volcanic tremor signals. RETREAT utilizes existing routines from the open-source ObsPy framework to carry out analysis of array data in real-time and performs either f-k (frequency-wavenumber) analysis, or alternatively Least-Squares beamforming, to calculate the backazimuth and slowness in overlapping time windows, which can help track the location of volcanic tremor sources. A graphical, or web-based, interface is used to configure a set of input parameters, before fetching chunks of waveform data and performing the array analysis. On each update the tool returns several plots, including timeseries of the backazimuth and slowness, a polar representation of the relative power and a map of the array with the dominant backazimuth overlaid.

The tool has been tested using real-time seismic data from the small-aperture SPITS array in Spitsbergen, as well as on data from a small aperture seismic array deployed during the 2014 eruption of Bárðarbunga volcano, Iceland. Although designed specifically for seismic array data (with a particular focus on volcanic tremor), RETREAT can also be used with infrasound sensors and has been successfully tested on infrasonic array data of explosive activity recorded at Mt. Etna, Italy, in 2019.

Although RETREAT has been designed for deployment as part of volcano monitoring systems and provides the ability to track tremor sources in real-time, it also has the capability to analyse existing datasets for testing, comparison and research purposes. However, RETREAT is primarily intended for use in real-time monitoring settings and it is hoped that it will facilitate wider use of arrays in tracking volcanic tremor or infrasonic sources in real-time, thereby enhancing monitoring capabilities.

How to cite: Smith, P. and Bean, C.: A REal-time TREmor Analysis Tool for seismic and infrasonic arrays, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15902, https://doi.org/10.5194/egusphere-egu21-15902, 2021.

EGU21-1752 | vPICO presentations | GMPV9.1

Seismic Tomography of Southern Tyrrhenian by means of teleseismic data

Giuseppe Pucciarelli

The topic of my work is a seismic tomography which has as object the investigation of Southern Tyrrhenian. This tomography has been obtained by means of inversion of teleseismic data to investigate subduction zones in the Southern Tyrrhenian oceanic back-arc basin. The subducting lithosphere has been mostly consumed along the Tyrrhenian-Apennine system has been consumed with the exception of the Calabrian arc sector. This kind of inversion could provide a good resolution to depth of 500-600 km, whereas previous local tomographies of Southern Tyrrhenian show results to depth of 250-300 km. The adopted database consists of 1929 teleseisms  recorded in period 1990-2012 by 122 southern Italian seismic station directly connected to ISC (International Seismological Centre). The software FMTT was employed for the inversion of these arrival times. I have implemented a grid of 0-500 km in depth, 7°E-20°E in longitude and 35°-48° in latitude, with a grid spacing of 50 km in depth, 0.8 degrees in longitude and 0.4 degrees in latitude. I have made 10 horizontal sections of final model from 50 km of depth to 500 km of depth, with an interval of 50 km of depth from each other. I have made 8 vertical sections, 4 NS vertical sections at fixed longitude and 4 WE vertical sections at fixed latitude. Finally, I have made 3 transversal sections. Summarising, the horizontal sections show an evolution of the high velocity body that represents the Ionian slab. It is visible both at depth of 50 km and at depth of 100 km, beneath the Calabrian arc and extends to northern Sicily beneath the Aeolian arc with a maximum of 0.6-0.8 km/s. At depth of 250 km, the tomography evidences a sort of “transition” due to the absence of the Southern Tyrrhenian HVA and the occurrence of a low velocity region with maximum of -0.5 km/s scattered between the Aeolian Islands and Calabria. In the depth interval from 250 km to 400 km, there are two impressive high velocity areas in northern Sicily and along southern Campania with a value of 0.3 km/s, separated by a low velocity area (LVA) along the Calabrian arc and the Aeolian Islands in the range [0.4 ; 0.6] km/s. Extensions of HVAs and LVAs previously mentioned have been estimated by means of vertical and transversal sections. This evidence could be interpreted as the effect of a three-dimensional circulation of astenospheric flow provoked by slab roll-back. A new evidence from the tomography is the presence of a LVA in the [250 ; 400] km depth interval with an extension of 100-150 km that practically splits the Tyrrhenian slab into two parts, in Neapolitan region and in the southern Calabria-northern Sicily region. The presence of this “window slab” could be interpreted as a tear in which unperturbed mantle insert itself.

How to cite: Pucciarelli, G.: Seismic Tomography of Southern Tyrrhenian by means of teleseismic data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1752, https://doi.org/10.5194/egusphere-egu21-1752, 2021.

EGU21-12812 | vPICO presentations | GMPV9.1

Investigation of the pre-eruptive processes of the 2014/15 Holuhraun eruption based on extracted volcanic tremor signals

Zahra Zali, Eva Eibl, Matthias Ohrnberger, and Frank Scherbaum

During volcanic unrest, multiple subsurface processes can happen simultaneously and may lead to an eruption. The analysis of seismic records in an unrest period before an eruption reveals information about the pre-eruptive processes and might be able to provide hints for a possible future eruption.

The 2014–2015 Holuhraun eruption was the largest one in Iceland in 230 years. It was extensively monitored and studied in a variety of multidisciplinary research approaches. Intense seismicity and ground deformation were interpreted as magma propagation from Bárðarbunga volcano 48 km laterally at ∼6 km depth over two weeks before an eruption started at Holuhraun. Different processes including vertical and lateral magma migration, dike propagation, caldera subsidence, and subglacial eruptions happened in this period and some models linking these processes are suggested. In the two-week interval preceding the eruption, there is still no clear connection between the observed tremor and pre-eruptive processes. Both the tremor source location and tremor generation process are not well understood yet. While cauldrons as a sign of subglacial eruptions were identified on the glacier surface from aerial photos, these cauldrons might have been formed earlier and there is hence an uncertainty of a few days. A tremor location might help to constrain these dates. However, the simultaneous occurrence of intense seismicity and tremor hinders the study and location of tremor. Here, we use a recent volcanic tremor extraction algorithm (Zali et al., 2020) and extract pre-eruptive tremor signals in order to better locate them using the Seismic Amplitude Ratio Analysis (SARA) method. Furthermore, the occurrence of the tremor could open new insights into ascending magma and fluid migration as well as the timing and duration of the subglacial eruptions.

We also observed short-lived tremors before the eruptions on August 29 and 31, which could be considered as eruption precursors. The primary investigation on the extracted tremor signals is promising while further analysis is on-going.

How to cite: Zali, Z., Eibl, E., Ohrnberger, M., and Scherbaum, F.: Investigation of the pre-eruptive processes of the 2014/15 Holuhraun eruption based on extracted volcanic tremor signals, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12812, https://doi.org/10.5194/egusphere-egu21-12812, 2021.

EGU21-14433 | vPICO presentations | GMPV9.1

Episodic earthquake mechanisms and intervening seismicity during the 2018 summit collapse at Kilauea caldera 

Celso Alvizuri, Robin Matoza, and Paul Okubo

The 2018 rift zone eruption of Kilauea volcano was accompanied by a remarkable and episodic collapse of its summit. Between May-August the eruption and collapse sequence included over 70,000 earthquakes (M≥0) and 54 major earthquakes (M≥5). We analyzed the seismicity in the Kilauea summit region and estimated seismic full moment tensors with their uncertainties for the 54 M≥5 events. These events occurred at almost daily intervals and were accompanied by intense seismicity which was concentrated between 0-3 km depths beneath the Halema‘uma‘u pit crater. The hypocenters reveal partial elliptical patterns (map view) that migrated downward by ∼200 m. The moment tensors reveal remarkably consistent mechanisms, with negative isotropic source types and localized uncertainties, and vertical P-axis orientations. From the moment tensors we derived Poisson’s ratios which are variable (ν = 0.1 − 0.3) for the first half of the collapse events and converged to ν ∼ 0.28 from June 26 onward.

How to cite: Alvizuri, C., Matoza, R., and Okubo, P.: Episodic earthquake mechanisms and intervening seismicity during the 2018 summit collapse at Kilauea caldera , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14433, https://doi.org/10.5194/egusphere-egu21-14433, 2021.

EGU21-16134 | vPICO presentations | GMPV9.1

Volcano-seismic 2020 unrest in Reykjanes Iceland: The MAGIC multi-parametric rapid response during Covid-19 lockdown

Philippe Jousset, Gylfi P. Hersir, Alina Shevchenko, Kristjan Agustsson, Egill A. Gudnason, Claus Milkereit, Achim Morschhauser, Eva Eibl, Thomas Walter, Thomas Reinsch, Kemal Erbas, Christopher Wollin, Anna Schantz, Friedemann Samrock, Thorbjorg Agustsdottir, Torsten Dahm, Olafur Flovenz, and Charlotte Krawczyk

The plate boundary between the American and Eurasian plates runs in southwest Iceland along a 5-10 km wide seismicity zone on the Reykjanes Peninsula. There, tectonic spreading events take place as continuous seismic release and seismic episodes (swarms and individual large events) with recurrence interval of about 40 years and volcanic episodes at intervals of 800-1000 years. The crust in Reykjanes is, therefore, particularly thin and hot and geothermal energy is currently harnesses in two areas on the western part of the peninsula in Reykjanes and Svartsengi.

Since January 2020, earthquake swarms with larger events up to M5.6 have been occurring frequently over the entire Reykjanes Peninsula, accompanied by unusual uplift (up to 12 cm) and subsidence cycles in the Svartsengi-Eldvörp fissure swarm. This raises the question whether we might be at the beginning of a new volcanic episode. In order to classify such processes at an early stage, multidisciplinary geophysical measurements are particularly valuable.

The Icelandic Meteorological Office (IMO), University of Iceland as well as ISOR and several partners responded immediately after the unrest began. As soon as January 2020, GFZ proposed a rapid response field campaign (MAGIC: MultidisciplinAry imaGIng and Characterization of the magma/fluid reservoir beneath Svartsengi). Only one week after the uplift start and first earthquake swarm, we connected a Distributed Acoustic Sensing interrogator to a 21 km long telecommunication fibre optic cable which crosses the uplift and swarm area. In addition, while we complied to strict constraints due to the Covid-19 pandemic, the rapid response activities comprised deployment of several additional sensors including broadband seismology, rotational seismology and we performed repeated surveys including gas-, gravity-, electromagnetic-, airborne and ground magnetic- measurements.

We present preliminary results from various techniques and discuss their role in discriminating different scenarios aiming at explaining the magma-tectonic unrest phase. In particular, we analyze how the combination of airborne snapshots of ground morphology can be combined with the high temporal and spatial resolution deformation fields along the fibre optic cable.

How to cite: Jousset, P., Hersir, G. P., Shevchenko, A., Agustsson, K., Gudnason, E. A., Milkereit, C., Morschhauser, A., Eibl, E., Walter, T., Reinsch, T., Erbas, K., Wollin, C., Schantz, A., Samrock, F., Agustsdottir, T., Dahm, T., Flovenz, O., and Krawczyk, C.: Volcano-seismic 2020 unrest in Reykjanes Iceland: The MAGIC multi-parametric rapid response during Covid-19 lockdown, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16134, https://doi.org/10.5194/egusphere-egu21-16134, 2021.

EGU21-276 | vPICO presentations | GMPV9.1

Combining multi-sensor infrared satellite and laboratory measurements to estimate the lava discharge rate of 2018 Kilauea Volcano, Hawai'i eruption

Simon Plank, Francesco Massimetti, Arianna Soldati, Kai-Uwe Hess, Michael Nolde, Sandro Martinis, and Donald B. Dingwell

Kīlauea Volcano, Hawai’i, is one of the world’s most active volcanoes. From 1983 to 2018 the magmatic system was in near continuous eruptions. This eruption ended on 30 April 2018 when the deflation of Kīlauea caldera began and a dike intrusion from the Middle East Rift Zone of Kīlauea Volcano downrift towards the Lower East Rift Zone (LERZ) was observed in seismic data. On 3 May 2018, the first of final 24 eruptive fissures opened at the LERZ. This was the beginning of the largest effusive event of the last two centuries at the LERZ. Here, we present Time-Averaged Discharge Rate (TADR) and lava eruption volume estimations based on a joint analysis of multi-sensor infrared (IR) Visible Infrared Imaging Radiometer Suite (VIIRS) and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite Earth observation data together with laboratory viscosity measurements to investigate this large eruption event at the LERZ. First, the TADR measurements were performed independently for each sensor data to cross-check the results against each other. Second, a joint timeseries of the VIIRS and MODIS TADR estimates was created to obtain more frequent measurements. This joint analysis of VIIRS and MODIS data resulted in an erupted lava volume of 0.924 ± 0.462 km³. Independent measurements based on airborne Synthetic Aperture Radar Interferometry (InSAR) and LIDAR topography changes are within the range of the IR data-based estimates of the erupted lava volume. The 2018 LERZ eruption could be differentiated into four main phases based on major element compositions of the eruptive products. The VIIRS and MODIS-based TADR estimation showed a relatively low Mean Output Rate (MOR) of 2.82 ± 1.41 m³/s during early Phase I. MOR then almost doubled to 4.94 ± 2.47 m³/s in late Phase I. A strong increase of MOR to 64.97 ± 32.48 m³/s occurred during Phase II. In Phase III, MOR again doubled to 137.67 ± 68.83 m³/s. This strong increase of the MOR during the different phases of the 2018 LERZ eruption agrees well with the evolution of the lava from low-temperature, highly differentiated sluggish ‘a‘ā lava flows in the beginning to high-temperature mafic more fluid pāhoehoe lava from Phase II onwards, as observed in the field by the USGS.

How to cite: Plank, S., Massimetti, F., Soldati, A., Hess, K.-U., Nolde, M., Martinis, S., and Dingwell, D. B.: Combining multi-sensor infrared satellite and laboratory measurements to estimate the lava discharge rate of 2018 Kilauea Volcano, Hawai'i eruption, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-276, https://doi.org/10.5194/egusphere-egu21-276, 2021.

Vulcanian explosions are hazardous and are often spontaneous and direct observations are therefore challenging. Ebeko is an active volcano on Paramushir Island, northern Kuril Islands, showing characteristic Vulcanian-type activity. In 2019, we started a comprehensive survey using a combination of geophysical field station records and repeated unoccupied aircraft system (UAS) surveys to describe the geomorphological features of the edifice and its evolution during ongoing activity. Seismic data revealed the activity of the volcano and were complemented by monitoring cameras, showing a mean explosion interval of 34 min. Digital terrain data generated from UAS quadcopter photographs allowed for the identification of the dimensions of the craters, a structural architecture and the tephra deposition at cm-scale resolution. The UAS was equipped with a thermal camera, which in combination with the terrain data, allowed it to identify fumaroles, volcano-tectonic structures and vents and generate a catalog of 282 thermal spots. The data provide details on a nested crater complex, aligned NNE-SSW, erupting on the northern rim of the former North Crater. Our catalog of thermal spots also follows a similar alignment on the edifice-scale and is also affected by topography on a local scale. New analysis are included in this presentation as well as a long term change analysis based on remote sensing data.

How to cite: Walter, T. R. and Belousov, A. A. M.:  The 2019 Eruption Dynamics and Morphology at Ebeko Volcano Monitored by geophysical instrument networks and Unoccupied Aircraft Systems (UAS), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-687, https://doi.org/10.5194/egusphere-egu21-687, 2021.

EGU21-7870 | vPICO presentations | GMPV9.1

The possible role of magma and geothermal fluid in the episodic uplift cycles and intense seismicity beneath the Svartsengi high temperature geothermal field, Iceland 

Ólafur Flóvenz, Rongjiang Wang, Gylfi Páll Hersir, Kristján Ágústsson, Magdalena Vassileva, Vincent Drouin, Sebastian Heimann, Marius Isken, Sebastian Hainzl, Egill Árni Gudnason, Thorbjörg Ágústsdóttir, Ingvar Magnússon, Josef Horalec, Claus Milkereit, Mahdi Motagh, Thomas Walter, Eleonora Rivalta, Philippe Jousset, and Torsten Dahm

The highly productive high temperature geothermal fields in Iceland are located within active volcanic systems on the plate boundaries. When an earthquake swarm or an unusual surface uplift or subsidence occur, it is important to assess the hazards and whether the unrest is triggered or controlled by volcanic or anthropogenic processes, or a combination of both.

On January 22nd, 2020, a rapid, large-scale uplift (14 km x 12 km) started at the Svartsengi geothermal field on the plate boundary of the Reykjanes Peninsula, along with an intense earthquake swarm that began simultaneously about 3 km east of the centre of uplift. The centre of uplift was located about 1 km west of Mt. Thorbjörn, in the middle of the Svartsengi geothermal field, close to the reinjection wells. Over a period of 6 months, three such uplift cycles occurred, each lasting for several weeks and followed by periods of relatively rapid subsidence. The duration and timing of the uplift-subsidence cycles appears to follow a clear trend where the successive inflation episodes lasted longer but with lower inflation rate.

The centres of uplift and the deflation cycles are the same and remained stationary. The accompanied intense earthquake swarms migrated along the 40 km long oblique plate boundary of the Reykjanes Peninsula, demonstrating a major plate tectonic event. The maximum depth of earthquakes was close to 4.5 km directly above the centre of uplift but extending to 6-7 km in the surroundings where the maximum magnitudes reached MW 4.8.

A few weeks after the onset of the unrest, nine additional seismic stations were deployed to densify the local seismic network in place. In addition, complimentary data from an existing 21 km long fibre optics cable were used to monitor high-frequency linear strain rates. Both measures led to a significant improvement in the earthquake detection and location which predominantly occurred in swarms. Likewise, InSAR data analysis of temporal uplift cycles was performed, repeated gravity measurements at permanent sites were performed, and resistivity was remeasured at chosen sites.  

Multiple different elementary models were developed and tested to explain the cyclic excitation of the uplift, subsidence, and seismicity. While the individual unrest episodes might be controlled by possible magma intrusions into the lower crust, our favoured model explains the spatio-temporal pattern of ground uplift by the rise and diffusion of pore pressure in a 4-5 km deep geothermal aquifer. To distinguish between different models, we use multi-disciplinary geophysical datasets, such as deformation, seismicity, and gravity.

How to cite: Flóvenz, Ó., Wang, R., Hersir, G. P., Ágústsson, K., Vassileva, M., Drouin, V., Heimann, S., Isken, M., Hainzl, S., Gudnason, E. Á., Ágústsdóttir, T., Magnússon, I., Horalec, J., Milkereit, C., Motagh, M., Walter, T., Rivalta, E., Jousset, P., and Dahm, T.: The possible role of magma and geothermal fluid in the episodic uplift cycles and intense seismicity beneath the Svartsengi high temperature geothermal field, Iceland , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7870, https://doi.org/10.5194/egusphere-egu21-7870, 2021.

EGU21-8796 | vPICO presentations | GMPV9.1

Inferring a shallow degassing model for Villarrica Volcano from seismic explosion signals and SO2 flux

Johanna Lehr, Stefan Bredemeyer, and Wolfgang Rabbel

Villarrica is a basaltic volcano with an active lava lake in South Central Chile. The lava lake displays a variety of degassing styles from gentle seething to more violent Strombolian explosions. This activity is accompanied by sequences of transient seismic waveforms suggesting the presence of discrete gas bubbles in the upper magma column. Gas bubbles flow through liquid-filled pipes according to distinct patterns depending on viscosity of the liquid and volumetric gas flow rate. Laboratory experiments indicate that these regimes are characterized by distinct frequency distributions of bubble sizes and spacings. By assuming that these parameters are reflected by the magnitude of the transients and the time between them, we compared their statistical distributions to infer a flow regime for the shallow conduit of Villarrica. The approximately log-normal distributions indicate a sustained slug flow regime in which the gas ascends in trains of conduit-wide gas slugs. The event catalog for our analysis contained about 20,000 events and was generated from 12 days of seismic data from March 2012 acquired by a dense local network. A well-known problem in earthquake statistics is the incompleteness of event catalogs towards low magnitudes due to decreasing detectability in the ambient noise. We estimated the actual distribution of magnitudes by using a Monte Carlo simulation of the event detection based on the statistical properties of the observed seismic noise. The unknown source depth and mechanism introduce further ambiguity regarding the distributions. Nevertheless, we hope to refine the degassing model by taking into account degassing rates, magma properties and more detailed analysis of the nature of the seismic events.

How to cite: Lehr, J., Bredemeyer, S., and Rabbel, W.: Inferring a shallow degassing model for Villarrica Volcano from seismic explosion signals and SO2 flux, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8796, https://doi.org/10.5194/egusphere-egu21-8796, 2021.

EGU21-1866 | vPICO presentations | GMPV9.1

Understanding Magmatic System of Unzen Volcano (Nagasaki, Southwest Japan) Inferred from Broad-band Magnetotelluric Observation

Agnis Triahadini, Koki Aizawa, Tasuku Hashimoto, Kazunari Uchida, Yuto Yamamoto, Keita Chiba, Dan Muramatsu, Kanta Miyano, Yuta Kawamura, and Aniya Satoru

Unzen Volcano is located in Shimabara Peninsula, Nagasaki, Japan. After 198 years of dormancy, the volcano erupted throughout 1990-1995 and resulted the emergence of new lava dome called Heisei-Shinzan. Following the eruption, numerous studies have been intensively conducted in Unzen volcano to assess the eruption mechanism and the magma plumbing system. Regarding to the magmatic system, the most preferred model is that the primary supply of magma is stored beneath Chijiwa bay. This magma chamber is located about 15 km west of the active dome at vertical depth approximately 15 km, and followed by subordinate shallower magma chambers beneath the volcano (e.g. Nakamura 1995; Kohno et al 2008). Upon the eruption, the magma ascended obliquely towards the summit in east direction (e.g. Umakoshi et al 2001). However, how main magma chamber  and shallower chambers are connected to the summit via oblique pathway is poorly imaged in terms of structure.
As widely known, Magnetotelluric method is highly sensitive to low resistivity zone caused by interconnected fluids. Low resistivity zone detected in the volcanic area usually can be interpreted as hydrothermal/magmatic fluid and or magma chamber containing partial melt (e.g. Aizawa et al 2014; Hill et al 2015). Thus, by using broadband Magnetotelluric method, we aim to investigate resistivity structure of Unzen volcano associated with magmatic system and its controlling structure (e.g. pathway and faults).
Although the shallow structures around Unzen volcano are estimated by the 2017-2019 campaigns (Triahadini et al 2019; Hashimoto et al 2020), we are unable to image deeper structure around the proposed location of magma chambers and magma pathway. To achieve our goals, during November-December 2020, we installed 35 new sites to cover whole area in Shimabara Peninsula. In total, deployed 99 Magnetotelluric stations covering Unzen volcano and Shimabara Peninsula. On this meeting, we would like to present our resistivity structure derived from all dataset.

How to cite: Triahadini, A., Aizawa, K., Hashimoto, T., Uchida, K., Yamamoto, Y., Chiba, K., Muramatsu, D., Miyano, K., Kawamura, Y., and Satoru, A.: Understanding Magmatic System of Unzen Volcano (Nagasaki, Southwest Japan) Inferred from Broad-band Magnetotelluric Observation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1866, https://doi.org/10.5194/egusphere-egu21-1866, 2021.

EGU21-4291 | vPICO presentations | GMPV9.1

Detection and monitoring of hydrothermal alteration by Principal Component Analysis applied on UAS derived optical data, Vulcano Island - Italy

Daniel Müller, Stefan Bredemeyer, Edgar Zorn, Erica De Paolo, and Thomas Walter

Modern UAS (unmanned aircraft system), light weight sensor systems and new processing routines allow us to gather optical data of volcanoes at a high resolution. However, due to the typically poor colorization, our ability to investigate and interpret such data is limited. Further, the information stored in the red, green and blue channel (RGB) is correlated. This makes any analysis a 3 dimensional task. Principal Component Analysis (PCA) helps us to overcome these problems by decorrelating the original band information and generating a variance representation of the original data. Therefore PCA is a suitable tool to detect optical anomalies, as might be caused by volcanic degassing and associated processes.

Applied in a case study at La Fossa Cone (Vulcano Island - Italy), the PCA showed a high efficiency for the detection and pixel based extraction of areas subject to hydrothermal alteration and sulfur deposition. We observed a broad alteration zone surrounding the active fumarole field, but also heterogeneities within, indicating a segmentation. Systematic variations in color and density distribution of sulfur deposits have implications for structural controls on the degassing system.

Combining the efficiency of PCA with the high resolution of UAS derived data, this methodology has a high potential to be employed in the spatio-temporal monitoring of volcanic hydrothermal systems and processes at surface.

 

How to cite: Müller, D., Bredemeyer, S., Zorn, E., De Paolo, E., and Walter, T.: Detection and monitoring of hydrothermal alteration by Principal Component Analysis applied on UAS derived optical data, Vulcano Island - Italy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4291, https://doi.org/10.5194/egusphere-egu21-4291, 2021.

The ability to accurately and reliably obtain images of shallow subsurface anomalies within the Earth is important for hazard monitoring at many geologic structures, such as volcanic edifices. In recent years, the use of machine learning as a novel, data-driven approach to addressing complex inverse problems in the geosciences has gained increasing attention, particularly in the field of seismology. Here we present a physics-based, machine learning method to integrate disparate geophysical datasets for shallow subsurface imaging. We develop a methodology for imaging static density variations at a volcano with well-characterized topography by pairing synthetic cosmic-ray muon and gravity datasets. We use an artificial neural network (ANN) to interpret noisy synthetic datasets generated using theoretical knowledge of the forward kernels that relate these datasets to density. The deep learning model is trained with synthetic data from a suite of possible anomalous density structures and its accuracy is determined by comparing against the known forward calculation. 

In essence, we have converted a traditional inversion problem into a pattern recognition tool, where the ANN learns to predict discrete anomalous patterns within a target structure. Given a comprehensive suite of possible patterns and an appropriate amount of added noise to the synthetic data, the ANN can then interpolate the best-fit anomalous pattern given data it has never seen before, such as those obtained from field measurements. The power of this approach is its generality, and our methodology may be applied to a range of observables, such as seismic travel times and electrical conductivity. Our method relies on physics-based forward kernels that connect observations to physical parameters, such as density, temperature, composition, porosity, and saturation. The key benefit in using a physics-based approach as opposed to a data-driven one is the ability to get accurate predictions in cases where the amount of data may be too sparse or difficult to obtain to reliably train a neural network. We compare our approach to a traditional inversion, where appropriate, and highlight the (dis)advantages of the deep learning model.

How to cite: Cosburn, K. and Roy, M.: Using artificial neural networks with joint muon-gravity datasets for shallow subsurface density prediction at volcanoes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-717, https://doi.org/10.5194/egusphere-egu21-717, 2021.

EGU21-14994 | vPICO presentations | GMPV9.1

Temporal evolution of 3He/4He isotopic ratio at Dos Aguas cold mineral spring, La Palma, Canary Islands

Eleazar Padrón, Nemesio M. Pérez, Gladys V. Melián, Hirochika Sumino, Mar Alonso, Guillermo Recio, María Asensio-Ramos, Fátima Rodríguez, and Luca D’Auria

Recent volcanic activity of La Palma island, the fifth in extension (706 km2) and the second in elevation (2,423 m a.s.l.) of the Canarian archipelago, has taken place exclusively in the last 123 ka at the southern part of the island, where Cumbre Vieja volcano, the most active basaltic volcano in the Canaries, has been constructed. A total of seven volcanic eruptions have been reported along the main north-south rift zone of Cumbre Vieja in the last 500 years. On October 7th and 13rd, 2017, two remarkable seismic swarms interrupted a seismic silence of 46 years in Cumbre Vieja volcano with earthquakes located beneath Cumbre Vieja volcano at depths ranging between 14 and 28 km with a maximum magnitude of 2.7. Five more seismic swarms were registered in 2020.

3He/4He ratio has been monitored at Dos Aguas cold mineral spring in La Palma Island since 1991 to date as an important volcano monitoring tool able to provide early warning signal of future volcanic unrest episodes. Magmatic helium emission studies have demonstrated to be sensitive and excellent precursors of magmatic processes occurring at depth. The highest 3He/4He ratio reported to date from the Canarian archipelago has been measured at Dos Aguas: 10.24 RA (being RA the ratio in atmospheric helium) (Padrón et al., 2015). This value is higher than any value found either in the lavas or terrestrial fluid in the Canary Islands, and indicates an important mantle contribution.  According to the temporal evolution of the magmatic component of helium at Dos Aguas, we suggest the occurrence of aseismic magma rising episodes beneath La Palma within the upper mantle towards an ephemeral magma reservoir in the period 2007-2017. However, in the period 2017-2020, magma rising have produced seismic swarms that were accompanied also by the highest 3He/4He ratio measured at Dos Aguas (10.42 RA); both geochemical and geophysical signals confirm an upward magma migration towards a subcrustal magma reservoir beneath La Palma island.

 

Padrón et al., (2015). Bull Volcanol 77:28. DOI 10.1007/s00445-015-0914-2

How to cite: Padrón, E., Pérez, N. M., Melián, G. V., Sumino, H., Alonso, M., Recio, G., Asensio-Ramos, M., Rodríguez, F., and D’Auria, L.: Temporal evolution of 3He/4He isotopic ratio at Dos Aguas cold mineral spring, La Palma, Canary Islands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14994, https://doi.org/10.5194/egusphere-egu21-14994, 2021.

EGU21-15073 | vPICO presentations | GMPV9.1

Geochemical evidence of volcanic plumbing system processes from fumarolic gases and diffuse CO2 degassing of Taal volcano, Philippines, prior to the January 2020 eruption 

Pedro A. Hernández, Gladys Melian, María Asensio-Ramos, Eleazar Padron, Hirochicka Sumino, Nemesio M. Perez, German Padilla, Jose Barrancos, Mª Criselda Baldago, Fatima Rodriguez, Mar Alonso, Cecilia Amonte, Carlo Arcilla, and Mahar Lagmay

Significant temporal variations in the chemical and isotopic composition of Taal fumarolic gas as well as in diffuse CO2 emission from Taal Main Crater Lake (TMLC) have been observed across the ~12 years of geochemical monitoring (Arpa et al., 2013; Hernández et a., 2017), with significant high CO2 degassing rates, typical of plume degassing volcanoes, measured in 2011 and 2017. In addition to these CO2 surveys at the TCML, soil CO2 efflux continuous monitoring was implemented at Taal volcano since 2016 and a clear increasing trend of the soil CO2 efflux in 2017 was also observed. Increasing trends on the fumarolic CO2/St, He/CO2, CO/CO2 and CO2/CH4 ratios were recorded during the period 2010-2011 whereas increasing SO2/H2S, H2/CO2 ratios were recorded during the period 2017-2018. A decreasing on the CO2/CH4 and CO2/St ratios was observed for 2017-2018. These changes are attributed to an increased contribution of magmatic fluids to the hydrothermal system in both periods. Observed changes in H2 and CO contents suggest increases in temperature and pressure in the upper parts of the hydrothermal system of Taal volcano. The 3He/4He ratios corrected (Rc/Ra), and δ13C of fumarolic gases also increased during the periods 2010-2011 and 2017-2018 before the eruption onset. During this study, diffuse CO2 emission values measured at TMCL showed a wide range of values from >0.5 g m−2 d−1 up to 84,902 g m−2 d−1. The observed relatively high and anomalous diffuse CO2 emission rate across the ~12 years reached values of 4,670 ± 159 t d-1 on March 24, 2011, and 3,858 ± 584 t d-1 on November 11, 2017. The average value of the soil CO2 efflux data measured by the geochemical station showed oscillations around background values until 14 March, 2017. Since then at 22:00 hours, a sharp increase of soil CO2 efflux from ~0.1 up to 1.1 kg m-2 d-1 was measured in 9 hours and continued to show a sustained increase in time up to 2.9 kg m-2 d-1 in 2 November, that represents the main long-term variation of the soil CO2 emission time series. All the above variations might be produced by two episodes of magmatic intrusion which favored degassing of a gas-rich magma at depth. During the 2010-2011 the magmatic intrusion of volatile-rich magma might have occurred from the mid-crustal storage region at shallower depths producing important changes in pressure and temperature conditions, whereas a new injection of more degassed magma into the deepest zone of the hydrothermal system occurring in 2017-2018 might have favored the accumulation of gases in the subsurface, promoting conditions leading to a phreatic eruption. These geochemical observations are most simply explained by magma recharge to the system, and represent the earliest warning precursor signals to the January 2020 eruptive activity.

Arpa, M.C., et al., 2013. Bull. Volcanol. 75, 747. https://doi.org/10.1007/s00445-013-0747-9.

Hernández, P.A., et al.,  2017. Geol. Soc. Lond. Spec. Publ. 437:131–152. https://doi.org/10.1144/SP437.17.

How to cite: Hernández, P. A., Melian, G., Asensio-Ramos, M., Padron, E., Sumino, H., Perez, N. M., Padilla, G., Barrancos, J., Baldago, M. C., Rodriguez, F., Alonso, M., Amonte, C., Arcilla, C., and Lagmay, M.: Geochemical evidence of volcanic plumbing system processes from fumarolic gases and diffuse CO2 degassing of Taal volcano, Philippines, prior to the January 2020 eruption , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15073, https://doi.org/10.5194/egusphere-egu21-15073, 2021.

EGU21-14763 | vPICO presentations | GMPV9.1

Insights from fumarole gas geochemistry on the recent volcanic unrest of Pico do Fogo, Cape Verde

Gladys V. Melián, Pedro A. Hernández, María Asensio-Ramos, Nemesio M. Pérez, Eleazar Padrón, Mar Alonso, Germán D. Padilla, José Barrancos, Francesco Sortino, Hirochicka Sumino, Fátima Rodríguez, Cecilia Amonte, Sonia Silva, Nadir Cardoso, and José M. Pereira

The Cape Verde islands are located about 800 km west of Senegal, at 14°-17° latitude and 21°-25° longitude. The archipelago consists of a volcanic chain of 10 major islands and eight minor islands The only currently active volcano in the Cape Verde archipelago is Pico do Fogo, which is located on the island of Fogo. Rising to 2829 m a.s.l., it is the most active volcano of the Cabo Verde Island. We report the results of the geochemical monitoring of the fumarolic discharges at the Pico do Fogo volcano in Cape Verde from 2007 to 2016. During this period Pico do Fogo experienced a volcanic eruption (November 23, 2014) that lasted 77 days. Two fumaroles were sampled, a low (F1~100ºC) and a medium (F2~300ºC) temperature. The variations observed in the δ18O and δ2H in F1 and F2 suggest different fluid source contributions and/or fractionation processes. Although no significant changes were observed in the outlet fumarole temperatures, two clear increases were observed in the vapor fraction of fumarolic discharges during the periods 2008-2009 and 2013-2014. Also, two sharp peaks were observed in CO2/CH4 ratios at both fumaroles, in November 2008 and November 2013, coinciding with significant increases in the emission rate of diffuse CO2 and He, and heat flow measured in the crater of Pico do Fogo volcano. This confirms that gases with a strong magmatic component rose towards the surface within the Pico do Fogo system during 2008 and 2013. Further, F2 showed two CO2/St peaks, the first in late 2010 and the second after eruption onset, suggesting the occurrence of magmatic pulses into the volcanic system. Time series of He/CO2, H2/CO2 and CO/CO2 ratios are low in 2008-2009, and high in 2013-2014 period, supporting the hypothesis of fluid input from a deeper magmatic source. Regarding to the isotopic composition, increases in 3He/4He (R/RA)cor are observed in both fumaroles; F1 showed a peak in 2010 from a minima in 2009 during the first magmatic reactivation onset and another in late 2013, while F2 displayed a slower rise to its maximum in late 2013. The high 3He/4He ratios in both fumaroles are close to the magmatic end-member, indicating that He is predominantly of upper mantle origin. This work supports that monitoring of the chemical and isotopic composition of the fumaroles of the Pico do Fogo volcano is a very important tool to understand the processes that take place in the magmatic-hydrothermal system and to be able to predict future episodes of volcanic unrest and to mitigate volcanic risk.

How to cite: Melián, G. V., Hernández, P. A., Asensio-Ramos, M., Pérez, N. M., Padrón, E., Alonso, M., Padilla, G. D., Barrancos, J., Sortino, F., Sumino, H., Rodríguez, F., Amonte, C., Silva, S., Cardoso, N., and Pereira, J. M.: Insights from fumarole gas geochemistry on the recent volcanic unrest of Pico do Fogo, Cape Verde, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14763, https://doi.org/10.5194/egusphere-egu21-14763, 2021.

EGU21-13506 | vPICO presentations | GMPV9.1

Geochemistry of gas emissions in the volcano-tectonic environment of the Eastern Carpathians

Boglarka-Mercedesz Kis, Laszlo Palcsu, Andreea-Rebeka Zsigmond, Dan Mircea Tamas, Istvan Szollosi, Roland Szalay, and Szabolcs Harangi

The Eastern Carpathians are characterized by intense gas emissions starting from the Neogene to Quaternary volcanic structures, especially the youngest dormant volcano, Ciomadul, but occurring also far away from these, in the Cretaceous flysch units. This is the most intensive degassing area from Romania. The gas emissions appear in different forms: dry gas, named mofettes and bubbling gas when they are accompanied by groundwater. The major components of these gas emissions are: CO2, CH4, N2 and sometimes H2S. Recent studies reveal a magmatic contribution up to 60% in these emissions (Vaselli et al., 2002, Kis et al., 2019). Gases are also present dissolved in groundwater and transported to the surface by CO2-rich springs. Besides these visible emissions, the gases come to the surface as diffuse degassing from the soil. We started a systematic geochemical investigation of the gas emissions in the volcano-tectonic environment of the southern part of the Eastern Carpathians, together with a 5-year monitoring of the gas emissions. Our primary aims are to constrain the flux of CO2, the origin of the different gas species, their interaction, and their relationship with the geodynamic background. Our findings could be integrated to the global carbon estimations, currently missing from the worldwide evaluations and could help the establishment of a long-term monitoring system of the gases in the area.

This work was supported by a grant of the Romanian Ministry of Education and Research, CNCS - UEFISCDI, project number PN-III-P1-1.1-TE-2019-1908, within PNCDI III and the project GTC 32144 supported by Babes-Bolyai University, Romania.

How to cite: Kis, B.-M., Palcsu, L., Zsigmond, A.-R., Tamas, D. M., Szollosi, I., Szalay, R., and Harangi, S.: Geochemistry of gas emissions in the volcano-tectonic environment of the Eastern Carpathians, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13506, https://doi.org/10.5194/egusphere-egu21-13506, 2021.

EGU21-9440 | vPICO presentations | GMPV9.1

First noble gas results from fluid inclusions of the Late Miocene-Pleistocene Macedonian volcanics

Kata Molnár, Marjan Temovski, and László Palcsu

Late Miocene to Pleistocene volcanism within the Vardar zone (N. Macedonia) covers a large area, has a wide range in composition and it is largely connected to the tectonic evolution of the South Balkan extensional system, the northern part of the Aegean extensional regime. A recent study indicated an increasing rate of mantle metasomatism towards the younger centers in the region [1]. During the last stage of activity, ultrapotassic (UK) centers that formed between ca. 3.2 and 1.5 Ma originated from the lithospheric mantle beneath the region [2]. Although there are no reported mantle xenoliths from these centers, the erupted mafic rocks contain abundant olivine as phenocrysts [3]. Noble gas isotopic characteristics of fluid inclusions in olivine can reveal important information about the origin of the fluid and the metasomatic state of the lithospheric mantle. We analyzed for the first time the noble gas composition of fluid inclusions of olivine phenocrysts from the Mlado Nagoričane volcanic center, the northernmost member of the UK centers with an eruption age of 1.8 ± 0.1 Ma [2]. The R/RA ratios give a range of 3.1-4.5 with 4He/20Ne values of 11.7-14.6. These R/RA values are lower than the MORB and the averaged subcontinental lithospheric values, and considering the negligible amount of atmospheric contribution, imply a more metasomatized character for the underlying lithospheric mantle beneath the region. Mantle-derived noble gases were detected in a recent geochemical study on the thermal springs and gas exhalations in the region, with up to 20% of mantle contribution calculated based on their noble gas composition using the MORB R/RA value [4]. These new Mlado Nagoričane fluid inclusion noble gas values indicate that the mantle contribution in the recent gas emissions in the region could be higher than what was thought.

This research was supported by the European Union and the State of Hungary, financed by the European Regional and Development Fund in the project of GINOP-2.3.2-15-2016-00009 ‘ICER’ project

[1] Molnár et al. 2020 – EGU2020-13101.

[2] Yanev et al., 2008 – Mineralogy and Petrology, 94(1-2), 45-60.

[3] Yanev et al., 2008 – Geochemistry, Mineralogy and Petrology, Sofia, 46, 35-67.

[4] Temovski et al. 2020 – EGU2020-2763.

How to cite: Molnár, K., Temovski, M., and Palcsu, L.: First noble gas results from fluid inclusions of the Late Miocene-Pleistocene Macedonian volcanics, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9440, https://doi.org/10.5194/egusphere-egu21-9440, 2021.

EGU21-5758 | vPICO presentations | GMPV9.1

A review of petrological monitoring procedures: suggestion of best practice protocols for eruption monitoring

Giuseppe Re, Rosa Anna Corsaro, Claudia D'Oriano, and Massimo Pompilio

Volcano monitoring is commonly performed through acquisition and interpretation of real-time signals able to track changes in the magmatic system and the eventual migration of magma toward the surface. Petrological monitoring, in particular,  focus on magma history in terms of depth of storage zones, transport pathways, mechanisms of differentiation, and timescales of involved processes with aim to extrapolate information about the trigger of magma ascent and the eruptive behaviour, and its possible variation over the course of an eruption.

In the present study, conducted in the framework of the EUROVOLC project, we developed a questionnaire that aims to survey the most common petrological monitoring procedures performed by volcano monitoring institutions, in order to identify prevailing techniques and most critical issues, and to rate the suitability of specific investigations in terms of costs versus benefit. The final goal is to identify essential and mandatory petrologic techniques to accomplish for an efficient petrological monitoring during ongoing eruptions, so that can be assessed the minimum logistic requirements (e.g., facilities, infrastructures, operators) and can be defined operative best practices protocols to achieve petrologic results in a timeframe short enough to be well of use for monitoring purposes.

The surveyed information, which resulted from a sample of eighteen interviewed institutions that deal with monitoring of active volcanoes with a variety of eruptive behaviour, provide insights about the whole steps of petrologic monitoring including sampling, sample preparations and analyses, data interpretation and dissemination. The survey reveals that efforts have been made to organize petrological monitoring with standardized procedures similarly to the other monitoring disciplines. For example, some institutions suffer lack of dedicated staff that can be operative with short forewarning. The objects of petrological investigation include all the types of volcanic products from lava to pyroclastic and there are attempts to deal with fixed sampling schedule. Moreover, there is consciousness that the capability to acquire and to interpret the most valuable analytical results at in situ institutions provide a quick image of ongoing eruptive processes and improve the interaction with other disciplines. Therefore, concerning the analytical procedures, which is the core of petrological monitoring, an important results is the cross correlation between the analyses that are easy to acquire (in terms of resources, equipment and time availability) and their effective role for the petrological monitoring.

The expectations include an augmented perception of the benefits that petrologic monitoring brings in the comprehension of eruptive processes. Filling the gap of the primary needs required to accomplish the identified best practices within a short timeframe is a compelling need to lead advancement of the volcano monitoring science.

How to cite: Re, G., Corsaro, R. A., D'Oriano, C., and Pompilio, M.: A review of petrological monitoring procedures: suggestion of best practice protocols for eruption monitoring, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5758, https://doi.org/10.5194/egusphere-egu21-5758, 2021.

EGU21-15427 | vPICO presentations | GMPV9.1

Monitoring of diffuse CO2 degassing at NERZ, NWRZ and NSRZ volcanic systems of Tenerife, Canary Islands

Fátima Rodríguez, Eleazar Padrón, Gladys Melián, María Asensio-Ramos, Mar Alonso, Cecilia Amonte, Alba Martín, Pedro A. Hernández, Nemesio M. Pérez, José Barrancos, Germán Padilla, and Luca D'Auria

One of the main volcano-structural and geomorphological feature in Tenerife (2,034 km2) is the triple rift system, formed by aligned of hundreds of monogenetic eruptive products of shield basaltic volcanism. At the intersection of this triple rift system rises the Teide-Pico Viejo volcanic complex. These volcanic rifts are considered as active volcanic edifices. The North East volcanic Rift Zone (NERZ, 210 km2) form a main NE-SW structure. The North West volcanic Rift Zone (NWRZ, 72 km2) is oriented in NW-SE direction and the North South volcanic Rift Zone (NSRZ, 325 km2) comprises a more scattered area on the south of these monogenetic cones. The most recent eruptive activity of Tenerife has taken place in these rift systems. NERZ host the fissural eruption of Arafo-Fasnia-Siete Fuentes (1704-1705). NWRZ host two historical eruptions: Arenas Negras in 1706 and Chinyero in 1909. Recently the eruption of Boca Cangrejo (1492) has been added to the historical register through 14C dating. NSRZ does not host historical volcanism, although it is recent, up to 10,000 years old.

In order to provide a multidisciplinary approach to monitor potential volcanic activity changes at the NERZ, NWRZ and NSRZ, diffuse CO2 emission surveys have been undertaken since 2000, in general in a yearly basis, but with a higher frequency when seismic swarms have occurred in and around NWRZ volcano. Each study area for NERZ, NWRZ and NSRZ comprises hundreds of sampling sites homogenously distributed. Soil CO2 efflux measurements at each sampling site were conducted at the surface environment by means of a portable non-dispersive infrared spectrophotometer (NDIR) LICOR Li820 following the accumulation chamber method. To quantify the CO2 emission rate from the NERZ, NWRZ and NSRZ a sequential Gaussian simulation (sGs) was used as interpolation method.

The diffuse CO2 emission rate for the NERZ ranged from 532 up to 2823 t d-1 between 2001 and 2020, with the highest value measured in 2020. In the case of NWRZ, the diffuse CO2 emission rate ranged from 52 up to 867 t d-1 between 2000 and 2020, with the highest value measured in one of the surveys of 2005. Finally, and for NSRZ, the diffuse CO2 emission rate ranged from 78 up to 819 t d-1 between 2002 and 2020, with the highest value measured in 2019. The temporal evolution of diffuse CO2 emission at the NERZ, NWRZ and NSRZ shows a nice and clear relationship with the volcanic seismicity in and around Tenerife Island, which started to take place from the end of 2016. The good temporal correlation between the volcanic seismicity and the increase trend observed in the time series of diffuse CO2 emission rates at NERZ, NWRZ and NSRZ is also coincident with the observed increase of diffuse CO2 emission rate at the summit crater of Teide. This work demonstrates the importance of performing soil CO2 efflux surveys at active rift systems in volcanic oceanic islands as an effective geochemical monitoring tool.

How to cite: Rodríguez, F., Padrón, E., Melián, G., Asensio-Ramos, M., Alonso, M., Amonte, C., Martín, A., Hernández, P. A., Pérez, N. M., Barrancos, J., Padilla, G., and D'Auria, L.: Monitoring of diffuse CO2 degassing at NERZ, NWRZ and NSRZ volcanic systems of Tenerife, Canary Islands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15427, https://doi.org/10.5194/egusphere-egu21-15427, 2021.

EGU21-15492 | vPICO presentations | GMPV9.1

Gas-sensors-equipped drone measurements of volcanic plume gas composition and flux at Pisciarelli, Campi Flegrei, Italy

Giancarlo Tamburello, Enrica Marotta, Pasquale Belviso, Gala Avvisati, Tullio Ricci, Dmitri Rouwet, Rosario Avino, and Stefano Caliro

The fumarolic field of Pisciarelli is the most active vent of the Campi Flegrei caldera, a volcano in the metropolitan area of Naples (Italy) in a current state of unrest. Recent studies have identified a clear escalation of degassing activity at Pisciarelli since 2012, raising concern on a possible acceleration of the unrest. The absence of sulfur dioxide prevents UV spectroscopy from determining the volcanic gas flux, and researchers have tried alternative techniques for measuring CO2 and H2S fluxes. Here we report observations of CO2, H2S, and H2O concentrations in the plume of Pisciarelli derived on December 2019 and October 2020 with a hexacopter drone equipped with miniaturized diffusive gas sensors. The drone flew at a constant altitude (~50 m above ground level), transecting the gas plume multiple times. This technique allowed us to calculate the CO2, H2S, and H2O gas fluxes by combining the georeferenced gas concentrations with the plume vertical rising speed derived from thermal and visible camera footages. Similar to previous gas composition and flux measurements, our results suggest that gas-sensors-equipped drones are a cost-effective technique for monitoring gas fluxes on active volcanoes, where UV spectroscopy cannot be used, and that can be made from safe distances.

How to cite: Tamburello, G., Marotta, E., Belviso, P., Avvisati, G., Ricci, T., Rouwet, D., Avino, R., and Caliro, S.: Gas-sensors-equipped drone measurements of volcanic plume gas composition and flux at Pisciarelli, Campi Flegrei, Italy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15492, https://doi.org/10.5194/egusphere-egu21-15492, 2021.

EGU21-15484 | vPICO presentations | GMPV9.1

Noble gases and carbon isotopes in natural gas samples from seismic active areas of southern Apennines (Italy)

Dario Buttitta and Michele Paternoster

In seismic active areas, the primary composition of natural gas emissions can be modified upon migration to the surface and storage in crustal reservoirs as the result of secondary chemical processes at shallow levels that can change the pristine composition of the fluids creating misunderstanding in the evaluation of the contributions due to different sources. Noble gases are among the most powerful indicators of such natural processes.  In particular, Helium (hereafter He) is a reliable geochemical tracer for discriminating the crustal and mantle components in the outgassing gases due to the different origin of its two isotopes (3He has a primordial origin, whereas 4He is continuously produced by radioactive α-decay of 235,238U and 232Th).  Therefore, the 3He/4He ratio is considered one of the most efficient geochemical tracers, whose variations can be directly ascribed to magmatic/crustal dynamics and therefore it is of primary importance in volcanic and seismic forecasting. In this study, we report chemical and isotopic (helium and carbon) data of gases and water emitted from three areas characterized by a high seismic hazard and located within the southern Apennines seismogenic belt. Through two fieldwork campaigns in 2019-2020, about 15 sites were inspected. Carbon dioxide is the main component in most of investigated sites (> 90 vol.%), except for Pozzo Tramutola, that is CH4-dominated. He and N2 concentrations are significantly variable (from 6 to 260 ppm and from 0.22 to 12.78 vol%, respectively). In agreement to previous investigations (Italiano et al., 2001; Caracausi and Paternoster, 2015), the sites in the Matese area are characterised by typical metamorphic [MOU1] N2 values and low content of He and Ar and seem to be the result of mixing processes between crustal and/or metamorphic and atmospheric or ASW end-member. The sampled fluids have 3He/4He ratios from 0.02 to 2.92 Ra with corresponding He/Ne ratios in the range of 0.353-508.10. These 4He/20Ne ratios are much higher than the same ratio in the atmosphere (He/Ne=0.318; Ozima-Podosek, 2002) supporting that atmospheric He component in the sampled fluids is negligible for most sites. In general, we recognized that 3He/4He ratios indicate mixing between radiogenic and mantle end-members and Mefite site has highest mantle values that are close to the ratio at Mt Vesuvio and Pleghreian volcanic systems (< 60 from the study area). The 40Ar/36Ar ratios show a small range from values close to atmosphere up to 40Ar/36Ar = 325. We also investigated the carbon species and their isotopes. To investigate the genetic origins of the methane we have used web-based machine learning tool that determines the origin of natural gases (Snodgrass-Milkov, 2020) and the results shown that methane is mainly thermogenic even if we also recognized an abiotic component in a few of sites. This study will provide data for the reconstruction of a basic model for interpreting the relationships between outgassing and tectonics, and further for interpreting possible seismic-induced variation

Ozima & Podosek. 2002. Noble Gas Geochemistry.

Tsunogai & Wakita. 1995. Science

Snodgrass and Milkov, 2020. Comput. Geosci

How to cite: Buttitta, D. and Paternoster, M.: Noble gases and carbon isotopes in natural gas samples from seismic active areas of southern Apennines (Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15484, https://doi.org/10.5194/egusphere-egu21-15484, 2021.

EGU21-15098 | vPICO presentations | GMPV9.1

Hydrogeochemical temporal variations related to changes of seismic activity at Tenerife, Canary Islands

Cecilia Amonte, María Asensio-Ramos, Gladys V. Melián, Nemesio M. Pérez, Eleazar Padrón, Pedro A. Hernández, Fátima Rodríguez, Luca D'Auria, and Dina López

The oceanic active volcanic island of Tenerife (2034 km2) is the largest of the Canarian archipelago. There are more than 1,000 galleries (horizontal drillings) in the island, which are used for groundwater exploitation and allow reaching the aquifer at different depths and elevations. During a two-year period (July 2016 to July 2018), a hydrogeochemical study was carried out in two galleries on Tenerife (Fuente del Valle and San Fernando) for volcanic monitoring purposes with weekly sampling. Physicochemical parameter of water, such us temperature (ºC), pH and electrical conductivity (E.C., µS·cm-1), were measured in-situ at each sampling point and chemical/isotopic composition of the water determined later in the laboratory.

Temperature values showed mean values of 28.1 ºC and 19.0 ºC for Fuente del Valle and San Fernando galleries, respectively. According to the average pH values, which were 6.30 for Fuente del Valle and 7.13 for San Fernando, and based on the chemical composition, both galleries are sodium-bicarbonate (Na-HCO3) type. E.C. values in both galleries presented high ranges, with mean values of 975 and 1648 µS·cm-1 for Fuente del Valle and San Fernando, respectively. The total alkalinity mean value of groundwater from Fuente del Valle gallery was 11.3 mEq·L-1 HCO3-, while that from San Fernando was 17.3 mEq·L-1 HCO3-. The SO42-/Cl molar ratio was 0.59 and 3.4 for the samples from Fuente del Valle and San Fernando galleries, respectively.

The δ18O and δD isotopic analyses showed a meteoric origin of groundwaters, with mean values of -6.2‰ and -26‰ vs. VSMOW for Fuente del Valle and -6.2‰ and -21 ‰ vs. VSMOW for San Fernando. The isotopic data showed a strong interaction with endogenous gases such as CO2, H2S, H2, etc. Regarding the isotopic composition of total dissolved carbon species, expressed as δ13CTDIC, average values of -0.17‰ and 0.26‰ were obtained for Fuente del Valle and San Fernando galleries, respectively. These results show an endogenous origin CO2 signature, heavier for Fuente del Valle gallery groundwater compared to that of San Fernando.

Groundwater physicochemical parameters exhibited stable values throughout the study period, while significant temporal variations were observed in the total alkalinity, SO42-/Cl- molar ratio, δ18O and δD. Changes in isotopic ratios coincided with variations observed in the alkalinity and the SO42-/Cl- molar ratio. On October 2, 2016, a seismic swarm of long-period events was recorded on Tenerife followed by a general increase of the seismic activity in and around the island. A correlation was observed between some hydrogeochemical parameters in the groundwaters of the galleries, related to observed changes of the seismic activity. This study demonstrates the suitability of monitoring the chemical and isotopic composition of groundwater from Fuente del Valle and San Fernando galleries, as they are sensitive to changes in volcanic activity on Tenerife island. The study of groundwaters associated to a volcanic system can provide information about the magmatic gas input in the aquifer, modelling how the groundwaters flow through the edifice, and offer important geochemical information that could herald a future eruption.

How to cite: Amonte, C., Asensio-Ramos, M., Melián, G. V., Pérez, N. M., Padrón, E., Hernández, P. A., Rodríguez, F., D'Auria, L., and López, D.: Hydrogeochemical temporal variations related to changes of seismic activity at Tenerife, Canary Islands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15098, https://doi.org/10.5194/egusphere-egu21-15098, 2021.

EGU21-11088 | vPICO presentations | GMPV9.1

Geochemical composition of Casaglia geothermal fluids and its relationships with the tectonic regime (Emilia-Romagna Region, Italy) 

Silvia Balzan, Antonio Caracausi, Giacomo Ferretti, Anna Saroni, Giovanni Martinelli, Francesco Italiano, and Massimo Coltorti

In this study the geochemical composition of the fluids belonging to the geothermic reservoir of Casaglia is presented. The site is located few kilometers northward of Ferrara, probably the only city in Italy whose heating system is fed by the geothermal heat near the top of the Dorsale Ferrarese, a structural anticline raising the Mesozoic limestones up to few hundred meters below the surface. Measurements of the chemical and isotopic composition of the gas phase (e.g., CO2 and noble gas) were carried out, together with a full characterization of the physico-chemical parameters and the chemistry of the water phase.

Fluids derive from a well at a depth of about 322+15meters and the temperature of the emerging water is of 78,6 °C, pH of 6.29 and Eh of -470 mV. Salinity is up to 115.6 mS/cm with a TDS varying between 71024 mg/L and 73718 mg/L. The hydrochemical facies is identified as clorurato-alkaline and the Cl/Br ratio suggest mixing with fossil brines. dD and d18O vary from 4.70 to 5.02 and from -12.0 to -12.2 respectively. The volatile phase is mainly composed of N2 (24.9-40.5 %),CH4 (21.1-29.5 %) and CO2 (37.1-18.6 %), with d13C(CO2), d13C(CH4) and dD(CH4) varying from -4.4 to -3.7 ‰, from -41.7 to 41.2 ‰ and from -152 to -171 ‰, respectively.  The He amounts are extraordinary high (up to 3956 ppm)  with a 3He/4He of 0.02Ra unequivocally pointing to a crustal origin (e.g., Caracausi & Sulli, 2019). The 40Ar/36Ar ratios span the range 300-374, being very close to the same ratio in atmosphere.

Such high He concentration cannot be explained by a simple steady-state crustal degassing, taking into account the Th and U contents of the sedimentary cover and the metamorphic basement (Coltorti et al. 2011) which lead also to consider that the thermal state of the Casaglia reservoir involve the entire crustal thickness and not only the Mesozoic carbonate succession that hosts the reservoir itself.

It is inferred that under an active tectonic regime, as it is that where Casaglia is located, the formation of micro-fracturation, due to the field of stress generated by the local seismicity, increases the He release from the rocks and can contribute to the observed He excess in the geothermal reservoirs (e.g., Buttitta et al., 2020). In this respect, the fault system of Dorsale Ferrarese contributes to generate a preferential pathway for rising fluids with consequent mixing phenomena and provides a reasonable explanation about the presence of this high He content in the reservoir.

References:

Buttitta D. et al. (2020). Continental degassing of helium in an active tectonic setting (northern Italy): the role of seismicity. Scientific Reports, 10(1), 1–13.

Caracausi A. & Sulli A. (2019). Outgassing of Mantle Volatiles in Compressional Tectonic Regime Away From Volcanism: The Role of Continental Delamination. Geochemistry, Geophysics, Geosystems, 20(4), 2007–2020.

Coltorti M. et al. 2011. U and Th content in the Central Apennines continental crust: a contribution to the determination of the geo-neutrinos flux at LNGS. Geoch. Cosmoch. Acta 75, 2271-2294.

How to cite: Balzan, S., Caracausi, A., Ferretti, G., Saroni, A., Martinelli, G., Italiano, F., and Coltorti, M.: Geochemical composition of Casaglia geothermal fluids and its relationships with the tectonic regime (Emilia-Romagna Region, Italy) , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11088, https://doi.org/10.5194/egusphere-egu21-11088, 2021.

EGU21-151 | vPICO presentations | GMPV9.1

The influence of hydrothermal alteration on volcano stability: a case study of La Soufrière de Guadeloupe (France)

Michael Heap, Tobias Baumann, Marina Rosas-Carbajal, Jean-Christophe Komorowski, H. Albert Gilg, Marlène Villeneuve, Roberto Moretti, Patrick Baud, Lucille Carbillet, Claire Harnett, and Thierry Reuschlé

Volcanoes are inherently unstable structures that spread and frequently experience mass wasting events (such as slope failure, rockfalls, and debris flows). Hydrothermal alteration, common to many volcanoes, is often invoked as a mechanism that contributes significantly to volcano instability. We present here a study that combines laboratory deformation experiments, geophysical data, and large-scale numerical modelling to better understand the influence of hydrothermal alteration on volcano stability. La Soufrière de Guadeloupe (France) is a hazardous andesitic volcano that hosts a large hydrothermal system and therefore represents an ideal natural laboratory for our study. Uniaxial and triaxial deformation experiments were performed on samples prepared from 17 variably-altered (alteration minerals include quartz, cristobalite, tridymite, hematite, pyrite, alunite, natro-alunite, gypsum, kaolinite, and talc) blocks collected from La Soufrière de Guadeloupe. Our uniaxial compressive strength experiments show that strength and Young’s modulus decrease as a function of increasing porosity and increasing alteration. Triaxial deformation experiments show that cohesion decreases as a function of increasing alteration, but that the angle of internal friction does not change systematically. We first combined recent muon tomography data with our laboratory data to create a 3D strength map of La Soufrière de Guadeloupe. The low-strength zone beneath the southern flank of the volcano exposed by our 3D strength map is coincident with the hydrothermal system. We then assigned laboratory-scale and upscaled mechanical properties (e.g., Young’s modulus, cohesion, and angle of internal friction) to zones identified by a recent electrical survey of the dome of La Soufrière de Guadeloupe. Numerical modelling (using the software LaMEM) was then performed on a cross-section of the volcano informed by the recent electrical data, and on a cross-section in which we artificially increased the size of the hydrothermally altered zone. Our modelling shows (1) the importance of using upscaled values in large-scale models and (2) that hydrothermal alteration significantly increases the surface velocity and strain rate of the volcanic slope. We therefore conclude, using models informed by experimental data, that hydrothermal alteration decreases volcano stability and thus expedites volcano spreading and increases the likelihood of mass wasting events and associated volcanic hazards. Hydrothermal alteration, and its evolution, should therefore be monitored at active volcanoes worldwide.

How to cite: Heap, M., Baumann, T., Rosas-Carbajal, M., Komorowski, J.-C., Gilg, H. A., Villeneuve, M., Moretti, R., Baud, P., Carbillet, L., Harnett, C., and Reuschlé, T.: The influence of hydrothermal alteration on volcano stability: a case study of La Soufrière de Guadeloupe (France), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-151, https://doi.org/10.5194/egusphere-egu21-151, 2021.

EGU21-10392 | vPICO presentations | GMPV9.1

Monitoring of Merapi volcano, Indonesia based on Sentinel-1 data

Virginie Pinel, François Beauducel, Raditya Putra, Sulis Sulistiyani, Gusti Made Agung Nandaka, Aisyah Nurnaning, Agus Budi Santoso, Hanik Humaida, Marie-Pierre Doin, Franck Thollard, and Christophe Laurent

Despite the well-established interest of Synthetic Aperture Radar data for volcanoes study and monitoring, their integration to operational monitoring activities in volcanoes observatories remains limited so far. We here describe the effort in progress to integrate in near real time the information derived from Sentinel-1 satellites into the monitoring devices at BBPTKG in charge of Merapi volcano survey as well as the use of Sentinel-1 data during the recent period of  unrest. Merapi (7°32.5’ S and 110°26.5’ E) located in the densely populated Province of Yogyakarta in Central Java is one of the most active volcanoes in Indonesia. The eruptive history of Merapi is characterized by two eruptive styles: 1) recurrent effusive growth of viscous lava domes, with gravitational collapses producing pyroclastic flows known as « Merapi-type nuées ardentes » (VEI 2); 2) more exceptional explosive eruptions of relatively large size (VEI 3-4), associated with column collapse pyroclastic flows reaching distances larger than 15 km from the summit. The eruptive periodicity is 4 to 5 years for the effusive events and 50 to 100 years for the explosive ones. The last explosive events (VEI 3-4) occurred in November 2010 and was followed by a period of limited activity. In August 2018, a new dome was observed inside the summit crater, thus marking the start of a new phase of effusive activity. A new period of unrest then started in mid-October 2020, characterized by an increase in seismic activity as well as large and localized displacements in the summit area. Magma finally reached the surface on 4  January 2021. Deformation is currently recorded by EDM and tiltmeters together with a network of 10 permanent GNSS stations. GNSS data are automatically processed and inverted for a pressure source at depth. Both displacement time series as well as spatial probability distribution are directly available through WebObs (Beauducel et al., Frontiers, 2020), an integrated web-based system for monitoring. Sentinel-1 data are acquired over the volcano every 12 days on descending track 76 and every 6 days on ascending track 127. Since mid 2017, Sentinel-1 data are automatically downloaded on a local server at BPPTKG. Interferograms and coherence images are then produced using the NSBAS processing chain (Doin et al, 2012) and automatically integrated to WebObs to enable detection of potential rapid and significant changes in signal. Mean velocity maps are also produced as well as time series of surface displacement at given location enabling direct comparison with GNSS measurements. The descending InSAR time series shows a strong displacement away from the satellite in a 1.5 km wide area located on the north-eastern part  of the crater. This signal became significant in September 2020. It is consistent with field measurements recorded and allows to map the affected area. In mid-November 2020, Sentinel-1 data thus provided the first information on the spatial extent of the ongoing surface displacements, which was useful for crisis management.

How to cite: Pinel, V., Beauducel, F., Putra, R., Sulistiyani, S., Nandaka, G. M. A., Nurnaning, A., Budi Santoso, A., Humaida, H., Doin, M.-P., Thollard, F., and Laurent, C.: Monitoring of Merapi volcano, Indonesia based on Sentinel-1 data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10392, https://doi.org/10.5194/egusphere-egu21-10392, 2021.

EGU21-970 | vPICO presentations | GMPV9.1

Broadening volcanic eruption forecasting using transfer machine learning

David Dempsey, Shane Cronin, Andreas Kempa-Liehr, and Martin Letourneur

Sudden steam-driven eruptions at tourist volcanoes were the cause of 63 deaths at Mt Ontake (Japan) in 2014, and 22 deaths at Whakaari (New Zealand) in 2019. Warning systems that can anticipate these eruptions could provide crucial hours for evacuation or sheltering but these require reliable forecasting. Recently, machine learning has been used to extract eruption precursors from observational data and train forecasting models. However, a weakness of this data-driven approach is its reliance on long observational records that span multiple eruptions. As many volcano datasets may only record one or no eruptions, there is a need to extend these techniques to data-poor locales.

Transfer machine learning is one approach for generalising lessons learned at data-rich volcanoes and applying them to data-poor ones. Here, we tackle two problems: (1) generalising time series features between seismic stations at Whakaari to address recording gaps, and (2) training a forecasting model for Mt Ruapehu augmented using data from Whakaari. This required that we standardise data records at different stations for direct comparisons, devise an interpolation scheme to fill in missing eruption data, and combine volcano-specific feature matrices prior to model training.

We trained a forecast model for Whakaari using tremor data from three eruptions recorded at one seismic station (WSRZ) and augmented by data from two other eruptions recorded at a second station (WIZ). First, the training data from both stations were standardised to a unit normal distribution in log space. Then, linear interpolation in feature space was used to infer missing eruption features at WSRZ. Under pseudo-prospective testing, the augmented model had similar forecasting skill to one trained using all five eruptions recorded at a single station (WIZ). However, extending this approach to Ruapehu, we saw reduced performance indicating that more work is needed in standardisation and feature selection.

How to cite: Dempsey, D., Cronin, S., Kempa-Liehr, A., and Letourneur, M.: Broadening volcanic eruption forecasting using transfer machine learning, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-970, https://doi.org/10.5194/egusphere-egu21-970, 2021.

EGU21-5089 | vPICO presentations | GMPV9.1

Mapping the Bubble Trap Feeding Eruptions of Strokkur Geyser, Iceland

Eva P. S. Eibl, Daniel Müller, Thomas R. Walter, Masoud Allahbakhshi, Philippe Jousset, Gylfi P. Hersir, and Torsten Dahm

Geysers are characterized by regular eruptions of hot water fountains. Their internal system consists of a heat source at depth, an often complex crack system and a conduit linking it to the surface. The conduit and crack system is filled with water, steam and gases similar to a volcano. Bubble traps are sometimes and rarely mapped and alternative heat-driven models for geyser eruptions exist.

Using a multidisciplinary, dense and close network of video cameras, seismometers, water pressure sensors and a tiltmeter we studied pool geyser Strokkur in June 2018. These multidisciplinary observations and particle-motion based tremor locations enabled us to derive a schematic cross section describing the driving mechanisms and the fluid dynamic processes within the bubble trap, crack system and conduit. We imaged a bubble trap at 23.7+-4.4 m depth, 13 to 23 m west of the conduit. We divide the eruptive cycle into eruption, refilling of the conduit, gas accumulation in the bubble trap and a trail of bubbles from the bubble trap into the conduit where they collapse at depth and have gained novel insights in understanding the gas accumulation, migration and collapse in such hot geyser systems in different phases of the eruptive cycle.

The dataset of this experiment can be accessed here:

- Eibl, E. P. S., Müller, D., Allahbakhshi, M., Walter, T. R., Jousset, P., Hersir, G. P., Dahm, T., (2020) ' Multidisciplinary dataset at the Strokkur Geyser, Iceland, allows to study internal processes and to image a bubble trap.' GFZ Data Services. DOI: 10.5880/GFZ.2.1.2020.007

- Eibl, E. P. S.; Walter, T.; Jousset, P.; Dahm, T.; Allahbakhshi, M.; Müller, D.; Hersir, G.P. (2020): 1 year seismological experiment at Strokkur in 2017/18. GFZ Data Services. Other/Seismic Network. DOI:10.14470/2Y7562610816

How to cite: Eibl, E. P. S., Müller, D., Walter, T. R., Allahbakhshi, M., Jousset, P., Hersir, G. P., and Dahm, T.: Mapping the Bubble Trap Feeding Eruptions of Strokkur Geyser, Iceland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5089, https://doi.org/10.5194/egusphere-egu21-5089, 2021.

EGU21-11315 | vPICO presentations | GMPV9.1

The challenge of monitoring volcanic unrest processes in small oceanic islands: the case of Tagoro volcano (Canary Islands)  

Carmen del Fresno, Alicia Felpeto, Itahiza Domínguez Cerdeña, Laura García-Cañada, Stavros Meletlidis, Elena González-Alonso, Pedro A. Torres, Natividad Luengo-Oroz, Sergio Sainz-Maza, Rubén López-Díaz, David Moure, and Benito Casas

Monitoring the activity of a volcanic unrest in an archipelago is always a challenging task. Difficulties are even greater if we are also dealing with monogenetic volcanism, without a defined magma chamber, where each unrest can be related to a different magma intrusion, following different ascending paths towards an eruptive vent that can arise both on land or at sea. Moreover, if the repose time between eruptions is long, the historical eruptive record contains very few eruptions, and hence few data that allow an in-depth characterization of the dynamics of the volcanism in the area. 

This year marks the tenth anniversary of the beginning of the last eruption in the Canary Islands (submarine eruption of Tagoro volcano, 2011-2012). In this work we review the main difficulties, concerns and uncertainties that arose in the monitoring of this phenomenon. Some of these problems were solved during the crisis, throughout a multiparametric monitoring and the collaboration of different institutions; others would not be a major problem today, thanks to recent technological advances. On the other hand, there are still some unsolved monitoring difficulties when studying an event similar  to the one which lead to Tagoro volcano ten years ago. Part of the complexity is inherent to the spatial distribution of the islands in the archipelago and the limitations on the knowledge of the volcanic phenomenon. It is in these last challenges where the key to improve the volcano monitoring in oceanic islands is. 

How to cite: del Fresno, C., Felpeto, A., Domínguez Cerdeña, I., García-Cañada, L., Meletlidis, S., González-Alonso, E., Torres, P. A., Luengo-Oroz, N., Sainz-Maza, S., López-Díaz, R., Moure, D., and Casas, B.: The challenge of monitoring volcanic unrest processes in small oceanic islands: the case of Tagoro volcano (Canary Islands)  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11315, https://doi.org/10.5194/egusphere-egu21-11315, 2021.

EGU21-12299 | vPICO presentations | GMPV9.1

Testing the application of Permutation Entropy to characterize the precursory phase of volcanic eruptions

Maria Sudibyo, Eva Eibl, and Sebastian Hainzl

Permutation Entropy (PE) has been suggested to be a promising tool for the prediction of volcanic eruptions. It is a robust yet simple tool to quantify the complexity of time series. The application has been used in the biomedical and econophysics fields and recently was adopted to find precursors of volcano eruptions and to identify tremor episodes. However, in the different eruption cases, the temporal variation of PE was found behaving in different ways. For example, a gradual drop of PE was observed few days prior to the 1996 Gjalp eruption while it remained high prior to the 2012 Copahua eruption. Our final aim is to quantify what features in the PE can be interpreted as eruption precursors and whether this is applicable to different eruptions from the same or different volcanoes. In calculating the PE, the determination of two key inputs, namely the delay time and the embedding dimension, is crucial as PE depends strongly on those parameters. Here we present several tests on different types of synthetic signals with different signal to noise ratios to determine the most suitable input parameters. We found that when the delay time is much shorter than or equal to the dominant period of the signal, the value of PE will be strongly influenced by the noise. Thus, the value of the delay time should be chosen in between. Furthermore, the embedding dimension should not be smaller than 5 to be able to identify the characteristic of the underlying signal. Finally, we show the application of this method to the seismic data during the dike formation and the effusive eruption at Holuhraun, Iceland, in 2014-2015.

How to cite: Sudibyo, M., Eibl, E., and Hainzl, S.: Testing the application of Permutation Entropy to characterize the precursory phase of volcanic eruptions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12299, https://doi.org/10.5194/egusphere-egu21-12299, 2021.

EGU21-15542 | vPICO presentations | GMPV9.1

Ranking Icelandic volcanoes by threat and prioritizing their monitoring requirements 

Sara Barsotti, Michelle Parks, Pfeffer Melissa, Kristín Jónsdóttir, Kristín Vogfjorð, and Benedikt Ófeigsson

How well are our volcanoes monitored? When and why should we review and enhance the monitoring setup for volcano surveillance? These questions are often raised at Volcano Observatories or at those Institutions in charge of monitoring volcanoes and their associated hazards. The Icelandic Meteorological Office (IMO) is responsible for monitoring natural hazards in Iceland, including volcanoes and volcanic eruptions. IMO operates an extended multidisciplinary monitoring network which comprises seismometers, cGPS, gas sensors, MultiGAS and DOASes, hydrological stations, strainmeters and tiltmeters, infrasound networks and webcams, with the aim of detecting in a timely manner potential unrest at any of the 32 active volcanoes in the country. Limited resources and funding opportunities often pose limitations on how extensive (in terms of number of sensors and their variety) a volcano monitoring network can be. Therefore, the Volcano Observatories are often required to decide how to prioritize the monitoring needs and find a balance in sensitivity, reliability, and efficacy of the network.  

In this contribution, we will present the results of the analysis performed at the IMO to rank the Icelandic active volcanoes by their threat and, consequently, to prioritize their monitoring needs. Some criteria (based on eruption frequency, potential hazards, infrastructure exposure and current status) are defined as guidelines and they are used to drive decisions regarding when and how to alter the monitoring setup. The specific case of Hekla volcano is used here to evaluate the validity of such criteria and to perform an analysis of the current capability of issuing a timely warning for one of the most dangerous volcanoes in Iceland. 

How to cite: Barsotti, S., Parks, M., Melissa, P., Jónsdóttir, K., Vogfjorð, K., and Ófeigsson, B.: Ranking Icelandic volcanoes by threat and prioritizing their monitoring requirements , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15542, https://doi.org/10.5194/egusphere-egu21-15542, 2021.

EGU21-14271 | vPICO presentations | GMPV9.1

The application of geodetic observations for near-real time monitoring of Icelandic volcanoes

Michelle Parks, Benedikt Ófeigsson, Halldór Geirsson, Vincent Drouin, Freysteinn Sigmundsson, Andrew Hooper, Sigrún Hreinsdóttir, Siqi Li, Cécile Ducrocq, Erik Sturkell, Kristín Vogfjord, Ásta Rut Hjartardóttir, Hildur María Fridriksdóttir, Ragnar Þrastarson, Sara Barsotti, Melissa Pfeffer, and Matthew Roberts

Ground deformation is frequently one of the first detectable precursors alerting scientists to changes in behavior or the onset of unrest at active volcanoes. GNSS, InSAR, strain and tilt measurements are routinely used by volcano observatories for monitoring pre-eruptive, co-eruptive and post-eruptive deformation. In addition to monitoring signals related to magma migration, deformation observations are used as an input into geodetic modeling to determine the location and rate of magma accumulation and help define the structure of magma plumbing systems beneath active volcanoes.

This presentation will provide an update of how geodetic observations are being used in conjunction with seismicity and gas measurements, for the near-real time monitoring of key Icelandic volcanoes; to determine their current status, identify the onset and likely cause of unrest, locate magmatic intrusions, determine magma volumes and supply rates and assess the likelihood of eruption. An overview of the current status of the following active volcanoes will be provided: Hekla, Bárðarbunga and Grímsvötn, along with an update of the recent volcano-tectonic unrest on the Reykjanes Peninsula.

Hekla is one of the most active and dangerous volcanoes in Iceland with approximately 18 eruptions since 1104. Over the past few decades, Hekla erupted at almost regular ~10 year intervals, with the last four eruptions occurring in 1970, 1980–1981, 1991 and 2000. Previous geodetic studies have suggested magma storage at depths of 12-25 km directly beneath the volcanic edifice. However, recent InSAR analysis has detected a localized inflation signal to the west of the volcano. A regional borehole strain meter network has proven instrumental for real-time eruption forecasting at Hekla.

In the Bárðarbunga volcanic system, the six-month long effusive 2014-2015 Holuhraun eruption was accompanied by gradual caldera collapse of up to 65 m and was preceded by a two-week period of 48 km long lateral dyke propagation with extensive seismicity and deformation. Geodetic observations indicate that Bárðarbunga began to slowly inflate in July 2015. This may be explained by a combination of renewed magma inflow and viscoelastic readjustment of the volcano.

The Grímsvötn subglacial volcano is the most frequently erupting volcano in Iceland, with eruptions in 1998, 2004 and 2011. A GPS station shows a prominent inflation cycle prior to eruptions. Observations during the 2011 eruption suggest a pressure drop at a surprisingly shallow level (about 2 km depth) during the eruption, in a similar location as in previous eruptions. Deformation at this volcano has now surpassed that observed prior to historic eruptions and its aviation color code is currently elevated to yellow.

In December 2019, the Reykjanes Peninsula entered a phase of volcano-tectonic unrest characterized by seismic swarms, followed in late January 2020 by inflation detected in near-real time by GNSS and InSAR observations. At the time of writing (mid-January 2021) there have been three magmatic intrusions in the vicinity of Svartsengi, an intrusion beneath Krýsuvík and indications of magma migration at depth along the entirety of the Peninsula.

How to cite: Parks, M., Ófeigsson, B., Geirsson, H., Drouin, V., Sigmundsson, F., Hooper, A., Hreinsdóttir, S., Li, S., Ducrocq, C., Sturkell, E., Vogfjord, K., Hjartardóttir, Á. R., Fridriksdóttir, H. M., Þrastarson, R., Barsotti, S., Pfeffer, M., and Roberts, M.: The application of geodetic observations for near-real time monitoring of Icelandic volcanoes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14271, https://doi.org/10.5194/egusphere-egu21-14271, 2021.

GMPV9.2 – Long-term observation of volcanic degassing: methods, findings and challenges

EGU21-7577 | vPICO presentations | GMPV9.2 | Highlight

The NOVAC database of volcanic SO2 emissions

Bo Galle and the The NOVAC Collaboration

We present a detailed global data-set of volcanic sulphur dioxide (SO2) emissions during the period 2005-2017. Measurements were obtained by scanning-DOAS instruments of the NOVAC network at 32 volcanoes, and processed using a standardized procedure. We reveal the daily statistics of volcanic gas emissions under a variety of volcanological and meteorological conditions. Data from several volcanoes are presented for the first time. Our results  are compared with yearly averages derived from measurements from space by the Aura/OMI instrument and with historical inventories of GEIA. This comparison shows some interesting differences which reasons are briefly discussed. Data is openly available through the web repository at https://novac.chalmers.se/.

How to cite: Galle, B. and the The NOVAC Collaboration: The NOVAC database of volcanic SO2 emissions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7577, https://doi.org/10.5194/egusphere-egu21-7577, 2021.

EGU21-3529 | vPICO presentations | GMPV9.2

The July 2019 explosive activity of Ubinas Volcano, Peru

Fredy Apaza, Christoph Kern, Mayra Ortega, and Rafael Miranda

Ubinas is a stratovolcano located in the Central Volcanic Zone of the Andes. It is one of the most active volcanoes in Peru, with more than 26 eruptive episodes recorded in the last 500 years (VEI 1-3). Its latest eruption began in early 2019, whit the occurrence of some distal VT seismicity accompanied by low levels of LP seismicity and in sometimes high frequency seismic signals associated with rockfalls. Concurrently, SO2 emissions increased from a few hundred to over 1,000 t/d between January and June while no significant ground deformation could be detected. Throughout the month of June, SO2 emissions climbed further to over 4,000 t/d, proximal VT swarms began to occur beneath the volcanic edifice, and deformation measurements indicated a pressurization of the system. This ramp-up in activity culminated with an explosive eruption on 19 July 2019 (07:28:49 UTC). The eruption released a cumulative energy of 336 MJ and vented an estimated 4.6x106 m3 of volcanic ash, making this one of the most energetic eruptive events of the last decade. Filled with hot gas and ash, the eruptive column reached 6,500 meters above the volcanic vent, with blocks and ballistic projectiles that reached 3.5 km from the crater and fragments up to 2.5 cm in diameter reported in the Ubinas town, 6.5 km to the southeast. By the time the eruption ended, up to 4 kg/m2 of tephra had fallen at this distance. Most of the plume was dispersed in east to southeast directions, crossing the regions of Moquegua, Puno. Ashfall was observed as far as Oruro, Bolivia, some 180 km from the volcano. Subsequent analyses of monitoring data and eruptive products allow classification of this event as a VEI 2 eruption caused by a rapid magmatic intrusion to shallow depths below the volcanic edifice.

How to cite: Apaza, F., Kern, C., Ortega, M., and Miranda, R.: The July 2019 explosive activity of Ubinas Volcano, Peru, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3529, https://doi.org/10.5194/egusphere-egu21-3529, 2021.

EGU21-10300 | vPICO presentations | GMPV9.2

Multiparametric monitoring of the ongoing eruption of Sangay volcano, Ecuador

Francisco Javier Vasconez, Silvana Hidalgo, Stephen Hernández, Josué Salgado, Sébastien Valade, Pedro Espín, Benjamin Bernard, Daniel Cárdenas, Jean Battaglia, Pablo Samaniego, and Diego Coppola

During the last two decades, Sangay has been one of the most active Ecuadorian volcanoes. However, because of its remote location and logistically difficult access, monitoring Sangay is a challenging task. The IG-EPN tackled this problem by expanding its terrestrial monitoring network and complementing it with the available satellite data. On 7th May 2019, the most recent and ongoing eruptive episode commenced. Compared to the previously monitored and observed eruptive activity at Sangay since the 2000’s, this episode is by far the most intense and the first to affect populated areas due to ash fallouts and numerous lahars. Surface activity is generally characterized by frequent low-to-moderate magnitude ash emissions and a semi-continuous viscous lava flow extrusion. This activity is punctuated by occasional lava flow collapse events, probably associated with pulses of high lava extrusion and that produced long-runout pyroclastic density currents towards the southeastern flank.

Here, we present the most complete data set of long-term instrumental observations performed at Sangay. SO2 degassing, seismic activity, ground deformation, ash emissions and thermal anomalies are depicted as a multiparametric sequence to better understand the link between these parameters and the dynamism and eruptive style of this isolated volcano.  

Correlations between the depicted parameters are not straight-forward, making it hard to identify patterns that might lead to enhanced eruptive activity. High values of SO2 recorded by the DOAS instruments as well as the TROPOMI satellite sensor seem to coincide with periods of increased eruption rate. Nevertheless, increases in SO2 flux do not occur systematically before or after these episodes. Seismic activity, characterized by daily counts of individual seismic events, does not demonstrated a clear precursory pattern either. These results indicate that none of the available monitoring parameters currently allow for a timely forecast of the largest and potentially most dangerous eruptions. However, looking at the entire time series we are able to distinguish a slightly but progressive change in the ground deformation displacement associated with a higher number of earthquakes per day prior to the 20 September 2020 paroxysmic event. This eruption produced regional ash fallout which affected significant swaths of farming lands and livestock. Since then, a different ground deformation pattern has taken hold, and coincides with a step decrease in the number of daily earthquakes and a significant increase in the SO2 mass measured by TROPOMI.

This behavior matches an open-vent system, where punctual increases in eruptive activity show few precursory signals. The observed increase in all the parameters compared to previous eruptions before 2019 allows us to propose that this eruptive phase is fed by batches of deep and volatile-rich magma which rise to the surface at high ascent rates. The interpretations presented here are an important step towards a better understanding of the dynamism and eruptive style of this very active and isolated volcano. Moreover, the various monitoring parameters from terrestrial to satellite provide a better picture of the behavior of Sangay that could be applied to other remote and open-system volcanoes.

How to cite: Vasconez, F. J., Hidalgo, S., Hernández, S., Salgado, J., Valade, S., Espín, P., Bernard, B., Cárdenas, D., Battaglia, J., Samaniego, P., and Coppola, D.: Multiparametric monitoring of the ongoing eruption of Sangay volcano, Ecuador, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10300, https://doi.org/10.5194/egusphere-egu21-10300, 2021.

EGU21-3711 | vPICO presentations | GMPV9.2

Continuous monitoring of SO2 emissions from Sinabung Volcano, Indonesia

Syegi Kunrat, Hilma Alfianti, Christoph Kern, Sofyan Primulyana, Allan Lerner, Moh. Nurul Asrori, Armen Putra, and Deri Al Hidayat

After more than 800 years of dormancy, phreatic explosions occurred at Sinabung Volcano in North Sumatra, Indonesia, on August 27, 2010. These marked the beginning of a period of unrest at Sinabung that continues through the present. Phreatic activity temporarily ceased in September 2010, however a more explosive phase of the eruption began again in September 2013, sending ash columns as high as 9 km above the volcano’s summit. A lava dome breached the surface on 17-18 December 2013 and subsequent collapses of this dome have produced numerous pyroclastic density currents reaching up to 5 km from the vent. Eruptive activity has waxed and waned since 2013, and the eruption entered period of especially vigorous activity beginning in February 2019 that is continuing through the present.

Between 2010 and 2013, the Indonesian Center for Volcanology and Geological Hazard Mitigation (CVGHM) significantly ramped up its monitoring efforts at Sinabung by installing seismometers, GPS instruments and electronic distance measuring benchmarks. In August 2016, the volcano observatory then installed a network of 3 scanning Differential Optical Absorption Spectrometers (DOAS) on the eastern side of Sinabung at distances between 4 and 6 km from the volcano’s summit. These DOAS instruments are part of the Network for Observation of Volcanic and Atmospheric Change (NOVAC), and autonomously measure the emission rate of sulfur dioxide (SO2) from Sinabung during typical west-wind conditions.

Since its installation, the DOAS network has provided useful monitoring information at Sinabung. The collected data indicate that the average SO2 emission rate lies between 100 and 400 metric tons per day (t/d), but emissions up to 2,400 t/d are common throughout the measurement period. The maximum emission rate recorded since 2016 was 4,500 t/d, measured in July 2019. However, the NOVAC instruments are not able to accurately capture the SO2 emissions associated with large explosive eruptions, and satellite data indicate that plumes associated with such events have sometimes contained significantly more SO2 than during the more typical passive degassing behavior. Here, we present excerpts of the long-term SO2 data from Sinabung and compare these with complimentary records of the timing and frequency of explosions, gas exhalations, rockfalls, and pyroclastic flows. These combined datasets provide insights into the active volcanic processes ongoing at Sinabung.

How to cite: Kunrat, S., Alfianti, H., Kern, C., Primulyana, S., Lerner, A., Asrori, Moh. N., Putra, A., and Al Hidayat, D.: Continuous monitoring of SO2 emissions from Sinabung Volcano, Indonesia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3711, https://doi.org/10.5194/egusphere-egu21-3711, 2021.

EGU21-4606 | vPICO presentations | GMPV9.2

Variation of SO2 and CO2 in the volcanic gas plumes of Santa Ana and San Miguel volcanoes: an overview by real-time measurements 

Xochilt Gutiérrez, Nicole Bobrowski, Thorsten Hoffmann, Eduardo Gutiérrez, Florian Dinger, Francisco Montalvo, and Demetrio Escobar

Volcanic degassing plays an important role in a volcano’s behavior. Going from large emissions at craters and fumaroles, to invisible degassing at vents and soil; a volcano releases H2O, CO2, SO2, HCl, HF, H2S, CO, H2, HBr, HI, Hg and noble gases.

SO2 emissions are considered a basic monitoring tool, mainly measured by remote-sensing techniques. The Differential Optical Absorption Spectroscopy (DOAS) is a well-established method currently used to regularly measure volcanic SO2 emission rates with about 80 scanning DOAS operating in 37 volcanoes within the framework of the global "Network for Observation of Volcanic and Atmospheric Change" (NOVAC) (Galle et al., 2010). Typically, SO2fluxes are often combined with in-situ gas measurements of SO2 and other volatiles (CO2, H2S), to evaluate the degassing regime. In-situ sampling can be made by collecting the gases directly in evacuated flasks or solution-filled bottles (alkaline traps), or by sampling with a multi-sensor instrument (MultiGAS) that enables real-time measurements of several gases at once (Aiuppa et al. 2005b; Shinohara 2005, Roberts et al. 2017).

Santa Ana and San Miguel are the most active volcanoes in El Salvador, with an average SO2 emission rate of 220 and 326 t/d, respectively during 2018. Both volcanoes arise along the Central American Volcanic Arc – CAVA, where the magmatism, fundamentally basaltic, is related to the convergence of the Caribbean Plate and the subducting Cocos Plate (Leeman and Carr 1995). Also, Santa Ana and San Miguel are part of the NOVAC group since 2008 with just a few published gas data (Rodriguez et al. 2004, Cartagena et al. 2004, Olmos et al. 2007, Colvin et al. 2013, Laiolo et al. 2017). The most recent studies were performed by Granieri et al. 2015 and Hasselle et al. 2019. The first, reported CO2/SO2, HCl/SO2 and HF/SO2 mass ratios (0.95, 0.13 and 0.016, respectively) measured at San Miguel volcano in early 2014; while the second, presented CO2/SO2, H2S/SO2 and H2O/SO2 ratios (<3-37.9, 0.03-0.1 and 32-205, respectively), measured in 2017-2018 at Santa Ana’s crater lake and rim.

In this study, we present an SO2 long-time data series (2008-2018) for San Miguel and Santa Ana obtained from the DOAS stations of each volcano, and complement with data collected during regular monitoring (2018-2020) and field campaigns in El Salvador (2019 and 2020) by means of MultiGAS devices. The aim of the study is to extend the characterization of these two volcanoes in El Salvador and the establishment of SO2 and CO2 baselines and inventories for them.

How to cite: Gutiérrez, X., Bobrowski, N., Hoffmann, T., Gutiérrez, E., Dinger, F., Montalvo, F., and Escobar, D.: Variation of SO2 and CO2 in the volcanic gas plumes of Santa Ana and San Miguel volcanoes: an overview by real-time measurements , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4606, https://doi.org/10.5194/egusphere-egu21-4606, 2021.

EGU21-12242 | vPICO presentations | GMPV9.2 | Highlight

Long-term evolution of the gas composition of Popocatepetl's plume

Noemie Taquet, Wolfgang Stremme, Claudia Rivera, Alejandro Bezanilla, Michel Grutter, Robin Campion, Sebastien Valade, Thomas Boulesteix, Denis Legrand, Thomas Blumenstock, and Frank Hase

Changes in the eruptive dynamics are mainly controlled by the magma gas content, and the degassing processes impacting the magma viscosity and ascending speed. The progressive exsolution of the gas species, their release at different depths, their mutual interaction and the eventual assimilation of crustal rocks are reflected in the volcanic plume composition changes. Combining long-term ground-based FTIR and UV remote measurements of the Popocatepetl's plume, seismic data and visual monitoring, we explore the relationship between the gas composition changes in the volcanic plume and the transition between extrusive and passive degassing regimes.

SO2, HCl, HF, BrO, SiF4 and CO2 are simultaneously measured in the volcanic plume since 2013 from the Altzomoni observatory, located 12 km north of the crater. We capture several phases of lava dome growth, different types of explosions and passive degassing periods. The evolution of the gas species ratios through these events allows deciphering the degassing processes.

How to cite: Taquet, N., Stremme, W., Rivera, C., Bezanilla, A., Grutter, M., Campion, R., Valade, S., Boulesteix, T., Legrand, D., Blumenstock, T., and Hase, F.: Long-term evolution of the gas composition of Popocatepetl's plume, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12242, https://doi.org/10.5194/egusphere-egu21-12242, 2021.

EGU21-3470 | vPICO presentations | GMPV9.2

Gas emissions from the resumption of eruptive activity at Kīlauea Volcano’s summit in December 2020.

Christoph Kern, Patricia Nadeau, Tamar Elias, Peter Kelly, Allan Lerner, Laura Clor, Miki Warren, Hannah Dietterich, and Taryn Lopez

Kīlauea Volcano (Hawaii, USA) had been in a state of quiescence since the end of the historic 2018 eruption on its lower East Rift Zone. Tapping the volcanic plumbing system at elevations around 300 m well below the volcano’s 1200 m summit, the 2018 eruption drained magma from the volcano’s summit reservoir and East Rift Zone, causing the drainage of a decade-old subaerial lava lake followed by widespread caldera collapse. Two years later, on the evening of 20 December 2020, the Hawaiian Volcano Observatory (HVO) once again detected a glow within the now vastly deepened Halemaʻumaʻu Crater at Kīlauea’s summit. A new eruption had begun. Observations over the next few days revealed lava flowing from three vents in the wall of the crater and into its base. A water lake, which had formed in 2019 – 2020 from groundwater infiltration, boiled off within hours and the crater began rapidly filling with lava. Over the first 3 days of the eruption, the new lava lake filled the lowermost ~150 m of the summit crater, and sulfur dioxide (SO2) emission rates sometimes exceeded 30,000 metric tons per day (t/d) as measured by Differential Optical Absorption Spectroscopy (DOAS) traverses recorded both from the ground and by helicopter. These vigorous SO2 emissions were also clearly detected by the Tropospheric Monitoring Instrument (TROPOMI) aboard the Sentinal-5 Precursor satellite, and comparisons of the ground-based data with those collected by TROPOMI are the topic of ongoing research. Lava effusion and gas emission rates then tailed off and, from 26 December to 2 January, DOAS measurements indicated SO2 emissions of ~5,000 t/d, similar to the average emission rate from Kīlauea’s summit lava lake throughout most of the volcano’s 2008-2018 eruption. Data from a continuous Multiple Gas Analyzer System (MultiGAS) installed approximately 1.3 km downwind of the active vents indicate that the carbon dioxide (CO2) to SO2 molar ratio of the emitted gas is low (0.3 ± 0.1), consistent with a model in which the erupted lava has been previously degassed in carbon dioxide but is only now degassing the more soluble sulfur as it reaches the surface. Further MultiGAS measurements performed with an unoccupied aircraft system (UAS) show that the gas composition varies throughout the emitted plume, but that the primary constituents are water vapor (~80-90% molar), carbon dioxide (~3%), and sulfur dioxide (~7-16%), while hydrogen sulfide is below the detection limit of the instrumentation. As of 11 January 2021, lava effusion and gas emissions appear to be slowly decreasing in vigor, but it is as yet unclear whether the eruption will continue to weaken and end within the coming weeks, or whether Kīlauea Volcano will once again harbor a sustained subaerial lava lake for months or years to come.

How to cite: Kern, C., Nadeau, P., Elias, T., Kelly, P., Lerner, A., Clor, L., Warren, M., Dietterich, H., and Lopez, T.: Gas emissions from the resumption of eruptive activity at Kīlauea Volcano’s summit in December 2020., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3470, https://doi.org/10.5194/egusphere-egu21-3470, 2021.

EGU21-4069 | vPICO presentations | GMPV9.2

Quantification of SO2 emission rates from the Kilauea volcano in Hawaii by the divergence of the SO2 flux using S5P-TROPOMI satellite measurements

Adrian Jost, Steffen Beirle, Steffen Dörner, and Thomas Wagner

With a nearly continuously effusive eruption since 1983, the Kilauea volcano (Hawaii, USA) is one of the most active volcanoes in the world. At the beginning of May 2018, a sequence of eruptions on the Lower East Rift Zone (LERZ) caused an enhanced outbreak of volcanic gases and aerosols, releasing them into the troposphere. Since these gases and particles affect climate, environment, traffic, and health on regional to global scales, a continuos monitoring of the emission rates is essential.

As satellites provide the opportunity to observe and quantify the emissions remotely from space, their contribution to the monitoring of volcanoes is significant. The TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor satellite was successfully launched by the end of 2017 and provides measurements with unprecedented level of details with a resolution of 3.5 x 7 km2. This also allows for an accurate retrieval of trace gas species such as volcanic SO2.

Here, it will be shown that the location and strength of SO2 emissions from Kilauea can be determined by the divergence of the temporal mean SO2 flux. This approach, which is based on the continuity equation, has been demonstrated to work for NOX emissions of individual power plants (Beirle et al., Sci. Adv., 2019).

The present state of our work indicates that emission maps of SO2 can be derived by the combination of satellite measurements and wind fields on high spatial resolution. As the divergence is highly sensitive on point sources like the erupting fissures in the 2018 Kilauea eruption, they can be localized very precisely. The obtained emission rates are slightly lower than the ones reported from ground-based measurements in other studies like the one from Kern et al. (Bull. Volcanol., 2020). The effects of suboptimal conditions like high cloud fractions on the method probably affect the derived emission rates and have to be further analyzed.

How to cite: Jost, A., Beirle, S., Dörner, S., and Wagner, T.: Quantification of SO2 emission rates from the Kilauea volcano in Hawaii by the divergence of the SO2 flux using S5P-TROPOMI satellite measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4069, https://doi.org/10.5194/egusphere-egu21-4069, 2021.

EGU21-9992 | vPICO presentations | GMPV9.2

Gas and heat fluxes during multiple effusive eruptions of Piton de la Fournaise (Réunion) and their implications for magmatic processes

Pauline Verdurme, Simon Carn, Andrew Harris, Diego Coppola, Andrea Di Muro, Santiago Arellano, and Lucia Gurioli

Piton de la Fournaise (La Réunion, France) is one of the most active volcanoes in the world, producing frequent effusive basaltic eruptions of varying duration. These eruptions are accompanied by strong thermal infrared (TIR) signals and significant sulfur dioxide (SO2) emissions detected by satellite instruments. The high frequency of eruptions provides an extensive dataset, which allows us to explore the relationships between eruptive heat, mass and gas fluxes. Five eruptions with different temporal trends of erupted mass flux have been selected for this study: April 2007, May 2015, August-October 2015, February 2019 and April 2020. For each of them, we estimated SO2 emission from three ultraviolet satellite instruments (the Ozone Monitoring Instrument OMI, the Ozone Mapping and Profiler Suite OMPS and the Tropospheric Monitoring Instrument TROPOMI). The total SO2 emission for each eruption has been estimated for an extensive range of sulfur (S) content within melt inclusions and the matrix using a petrological approach and the erupted magma masses obtained from MODIS TIR satellite data. Preliminary results show that, assuming the estimated SO2 emission falls within the 30% error of the SO2 mass detected by each satellite instrument, the implied magmatic sulfur contents are in good agreement with expected values for basaltic eruptions. Given pre-eruptive S contents between 200 and 750 ppm, estimated SO2 emissions for the May 2015 eruption are consistent with an eruption largely fed by degassed magma. However, for the February 2019 eruption, there is a discrepancy between the three satellite sensors. Whereas the TROPOMI and the OMI instruments provide almost the same range of magmatic sulfur content (300-1100 ppm), the OMPS gives a higher range (700 to 1900 ppm) suggesting that fresh, undegassed magma was also involved in this eruption. Petrologic analysis of the pre-eruptive sulfur content will allow us to validate the satellite data and, in turn, to validate the ground-based SO2 data from the NOVAC network operated by the Observatoire Volcanologique du Piton de la Fournaise (OVPF). Our approach yields insights into the characteristics of the magma reservoir supplying effusive events (e.g., eruptive degassing processes and the ratio of intrusive to extrusive magma) from space-based sensors.

How to cite: Verdurme, P., Carn, S., Harris, A., Coppola, D., Di Muro, A., Arellano, S., and Gurioli, L.: Gas and heat fluxes during multiple effusive eruptions of Piton de la Fournaise (Réunion) and their implications for magmatic processes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9992, https://doi.org/10.5194/egusphere-egu21-9992, 2021.

EGU21-1696 | vPICO presentations | GMPV9.2 | Highlight

A global perspective on Bromine monoxide composition in volcanic plumes derived from three years of S5-P/TROPOMI data

Simon Warnach, Holger Sihler, Christian Borger, Nicole Bobrowski, Stefan Schmitt, Moritz Schöne, Steffen Beirle, Ulrich Platt, and Thomas Wagner

Bromine monoxide (BrO) is a halogen radical capable of influencing atmospheric chemical processes, in particular the abundance of ozone, e. g. in the troposphere of polar regions, the stratosphere as well as in volcanic plumes. Furthermore, the molar bromine to sulphur ratio in volcanic gas emissions is a proxy for the magmatic composition of a volcano and potentially an eruption forecast parameter.

The high spatial resolution of the S5-P/TROPOMI instrument (up to 3.5x5.5km2) and its daily global coverage offer the potential to detect BrO even during minor eruptions and also to determine BrO/SO2 ratios during continuous passive degassing.

Here, we present a global overview of BrO/SO2 molar ratios in volcanic plumes derived from a systematic long-term investigation of three years of TROPOMI data.

We retrieved column densities of BrO and SO2 using Differential Optical Absorption Spectroscopy (DOAS) and calculated mean BrOSO2 molar ratios for each volcano. As expected, the calculated BrO/SO2 molar ratios differ strongly between different volcanoes ranging from several 10-5 up to several 10-4. In our study of three years of S5P/TROPOMI data we successfully recorded elevated BrO column densities for more than 100 volcanic events and were able to derive meaningful (coefficient of determination, R2 exceeding 0.5) BrO/SO2 ratios for multiple volcanoes.

How to cite: Warnach, S., Sihler, H., Borger, C., Bobrowski, N., Schmitt, S., Schöne, M., Beirle, S., Platt, U., and Wagner, T.: A global perspective on Bromine monoxide composition in volcanic plumes derived from three years of S5-P/TROPOMI data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1696, https://doi.org/10.5194/egusphere-egu21-1696, 2021.

EGU21-14092 | vPICO presentations | GMPV9.2 | Highlight

Trends in volcanic degassing through eruption cycles: insights from satellite measurements

Simon Carn, Vitali Fioletov, Chris McLinden, Nickolay Krotkov, and Can Li

Effective use of volcanic gas measurements for eruption forecasting and hazard mitigation at active volcanoes requires an understanding of long-term degassing behavior as context. Much recent progress has been made in quantifying global volcanic emissions of sulfur dioxide (SO2) and other gas species by expanding the coverage of ground-based sensor networks and through analysis of decadal-scale satellite datasets. Combined, these advances have provided valuable constraints on the magnitude and variability of SO2 emissions at over 120 actively degassing volcanoes worldwide. Being less constrained by the style or location of volcanic activity, satellite measurements can provide greater insight into trends in volcanic degassing during eruption cycles. Here, we present an analysis of ~15 years of volcanic SO2 measurements by the ultraviolet (UV) Ozone Monitoring Instrument (OMI) aboard NASA’s Aura satellite, focused on observed trends in SO2 emissions spanning eruptions of varying magnitude. The Aura/OMI measurements have been used to estimate annual mean SO2 emissions at ~100 volcanoes active between 2005 and 2020, around 80 of which erupted during the 15-year period. Superposed epoch analysis (SEA) of SO2 emission trends for the erupting volcanoes (with eruption magnitudes ranging from Volcanic Explosivity Index [VEI] 2 to 4) provides evidence that volcanoes exhibiting higher levels of SO2 emission in the years prior to eruption typically produce eruptions of lower magnitude, and vice versa. Post-eruptive SO2 degassing exceeds pre-eruptive emissions for several years after eruptions with VEI 3-4 and may scale with eruption size; perhaps consistent with larger eruptions being supplied by larger magma intrusions which continue to degas in subsequent years. The SEA is most robust for eruptions of intermediate magnitude (VEI 3) which are the most common events in the recent global eruption record covered by the OMI measurements. Limited observations of larger eruptions (VEI 5+) suggest significant differences in degassing trends during these larger events. Future work will extend the satellite-based estimates of volcanic SO2 emissions both forward and backward in time using other UV satellite instruments, generating longer records of SO2 degassing (extending back to 1978 for the strongest volcanic sources of SO2) that will be used to further explore and constrain these relationships.  

How to cite: Carn, S., Fioletov, V., McLinden, C., Krotkov, N., and Li, C.: Trends in volcanic degassing through eruption cycles: insights from satellite measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14092, https://doi.org/10.5194/egusphere-egu21-14092, 2021.

EGU21-9010 | vPICO presentations | GMPV9.2 | Highlight

Long-term gas observations track the early unrest phases of open-vent basaltic volcanoes 

Dario Delle Donne, Alessandro Aiuppa, Marcello Bitetto, Francesco Paolo La Monica, Giancarlo Tamburello, Diego Coppola, Giorgio Lacanna, Marco Laiolo, Mauro Coltelli, Emilio Pecora, and Maurizio Ripepe

At open-vent basaltic volcanoes, resolving the activity escalation that heralds larger, potentially harmful eruptions is challenged by the persistent mild ordinary activity, which often masks the precursory unrest signals related to heightened magma transport from depth. Gas (SO2 and CO2) fluxes at surface are controlled by rate of magma transport and degassing within the magma plumbing system, and thus constitute key parameters to infer deep magma budget and dynamics.

Here, we use several year-long (2014-present) gas observations at Etna and Stromboli volcanoes, in Sicily, to provide new evidence for the utility of long-term instrumental gas monitoring in real-time detecting the early phase of unrest prior eruption, and for characterizing syn-eruptive dynamics. To this aim, we use information from a gas monitoring network of permanent ultraviolet (UV) cameras and automatic Multi-Gas instruments that, combined with geophysical observations, allow characterizing changes in degassing and eruptive dynamics at high temporal/spatial resolution.

Our results show that the paroxysmal (lava fountaining) explosions that periodically interrupted persistent open-vent activity on Etna (during 2014-2020) were accompanied by systematic, repetitive SO2 emission patterns prior, during, and after eruptions. These allow us identifying the characteristic pre- syn- and post- eruptive degassing regimes, and to establish thresholds in the SO2 flux record that mark phases of unrest.

On Stromboli, the much improved temporal/spatial resolution of UV cameras allows resolving the escalation of regular strombolian activity, and its concentration toward its North-east crater, that heralds onset of effusive eruptions. During effusive eruption, although magma level drops in the conduit and explosive summit activity ceases, UV camera observations can still detect explosive gas bursts deep in the conduit while no infrasonic activity is detected. Combining the UV camera-derived SO2 fluxes with CO2/SO2 ratio records measured by the Multi-Gas, the CO2 flux can be inferred. We find that such CO2 flux time-series can allow tracking degassing of deeply stored mafic magma months before Stromboli’s eruptions. We finally show that remotely sensed gas emission and thermal activity can be combined together to characterize the dynamics of shallow magmatic system prior to and during unrest, ultimately helping to define timing of magma re-charging events driving the eruptions.

How to cite: Delle Donne, D., Aiuppa, A., Bitetto, M., La Monica, F. P., Tamburello, G., Coppola, D., Lacanna, G., Laiolo, M., Coltelli, M., Pecora, E., and Ripepe, M.: Long-term gas observations track the early unrest phases of open-vent basaltic volcanoes , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9010, https://doi.org/10.5194/egusphere-egu21-9010, 2021.

EGU21-14767 | vPICO presentations | GMPV9.2

Long-term variations of diffuse CO2, He and H2 at the summit crater of Teide volcano, Tenerife, Canary Islands

María Asensio-Ramos, Gladys Melián, Fátima Rodríguez, Nemesio M. Pérez, Mar Alonso, Alba Martín-Lorenzo, Cecilia Amonte, Pedro A. Hernández, Eleazar Padrón, and Luca D'Auria

Tenerife (2,034 km2) is the largest of the Canary Islands. Its structure is controlled by a volcano-tectonic rift-system with NW, NE and NS directions, with the volcanic system Teide-Pico Viejo located in the intersection. Teide is 3,718 m.a.s.l. high and its last eruption occurred in 1798 through an adventive cone of Teide-Pico Viejo volcanic complex. Persistent degassing activity, both visible and diffuse, takes place at the summit cone of the volcano, being the diffuse degassing the principle mechanism.

During the period 1999-2020, more than 200 diffuse CO2 efflux surveys have been performed in the summit crater of Teide Volcano. For each survey, 38 sampling sites homogeneously distributed inside the crater covering an area of 6,972 m2 were selected. Diffuse CO2 emission was estimated in each point by means of a portable non dispersive infrared (NDIR) CO2 fluxmeter using the accumulation chamber method. Additionally, soil gas samples were taken at 40 cm depth and analyzed later in the lab for the He and H2 content by means of quadrupole mass spectrometry and micro-gas chromatography, respectively. To estimate the He and H2 emission rates at each sampling point, the diffusive component was estimated following the Fick’s law and the convective emission component model was estimated following the Darcy’s law. In all cases, spatial distribution maps were constructed averaging the results of 100 simulations following the sequential Gaussian simulation (sGs) algorithm, in order to determine CO2, He and H2 emission rates.

During the study period, CO2 emissions ranged from 2.2 to 176.1 t/d, He emissions between 0.013 and 4.1 kg/d and H2 between 1.3 and 35.6 kg/d. On October 2, 2016, a seismic swarm of long-period events was recorded on Tenerife followed by a general increase of the seismic activity in and around the island (D’Auria et al., 2019). Since then, relatively high values have been obtained in the diffuse CO2, He and H2 emission rate the crater of Teide. This increase reflects a process of pressurization of the volcanic-hydrothermal system.

The variations in CO2, He and H2 emissions indicate changes in the activity of the system and can be useful to understand the behaviour of the volcanic system and to forecast future volcanic activity. Monitoring the diffuse degassing rates at Teide volcano has demonstrated to be an essential tool for predicting future seismic–volcanic unrest, and has become important to reduce volcanic risk in Tenerife (Melián et al., 2012; Pérez et al., 2013).

D'Auria .L, Barrancos J., Padilla G.D., Pérez N.M., Hernández P.A., Melián G., Padron E., Asensio-Ramos M., García‐Hernández R. (2019). J. Geophys. Res. 124, 8739-8752

Pérez N. M., Hernández P. A., Padrón E., Melián G., Nolasco D., Barrancos J., Padilla G., Calvo D., Rodríguez F., Dionis S. and Chiodini G. (2013). J. Geol. Soc., 170(4), 585-592.

Melián G., Tassi F., Pérez N. M., Hernández P., Sortino F., Vaselli O., Padrón E., Nolasco D., Barrancos J., Padilla G., Rodriguez F., Dionis S., Calvo D., Notsu K., Sumino H. (2012).  Bull. Volcanol, 74(6), 1465-1483.

 

How to cite: Asensio-Ramos, M., Melián, G., Rodríguez, F., Pérez, N. M., Alonso, M., Martín-Lorenzo, A., Amonte, C., Hernández, P. A., Padrón, E., and D'Auria, L.: Long-term variations of diffuse CO2, He and H2 at the summit crater of Teide volcano, Tenerife, Canary Islands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14767, https://doi.org/10.5194/egusphere-egu21-14767, 2021.

EGU21-8391 | vPICO presentations | GMPV9.2

Gas monitoring of a hydrothermal-magmatic volcano in a tropical environment: the example of La Soufriere de Guadeloupe (FWI)

Severine Moune, Roberto Moretti, Arnaud Burtin, David Jessop, Tristan Didier, Vincent Robert, Magali Bonifacie, Giancarlo Tamburello, and Jean-Christophe Komorowski

Fumarolic gas survey of dormant volcanoes is fundamental because the compositional and flux changes in gas emissions are recognised signals of unrest and may even be precursors of eruptions on several dormant volcanoes in hydrothermal unrest [1-5].

Here we report on the chemical compositions (CO2, H2S, SO2, H2) and mass fluxes of fumarolic gas emissions from the low-temperature (from 97° to 104°C) volcanic-hydrothermal system of La Soufrière de Guadeloupe (Lesser Antilles). This present study covers the period 2016 to present, encompassing the peak activity of April 2018. Long-term trends are acquired from both portable MultiGAS measurements (performed monthly) and two permanent MultiGAS stations (4 automated 20’ measurements per day). These MultiGAS data are discussed along with other geochemical and geophysical parameters monitored at OVSG, such as complete fumarole chemistry via Giggenbach bottles, fumarole temperatures, volcanic seismicity and deformation in order to track the deep-sourced magmatic signal contribution compared to the one of the hydrothermal system and detect potential signs of unrest [6].

Dealing with MultiGAS data from a low-T fumarolic system in a tropical environment is not straightforward due to external forcing effect of meteoric water on gas composition. Hence, interpretation of the observed chemical changes must consider (i) the role of water-gas-rock interactions and gas scrubbing processes by the hydrothermal system and the perched volcanic pond [7], which particularly affect sulphur precipitation and remobilization and (ii) how these processes vary with rainfall and groundwater circulation (i.e. rainy vs non-rainy seasons, extreme events).

[1] Giggenbach and Sheppard, 1989; [2] Symonds et al., 1994; [3] Hammouya et al., 1998; [4] De Moor et al., 2016; [5] Allard et al., 2014; [6] Moretti et al., submitted; [7] Symonds et al., 2001

How to cite: Moune, S., Moretti, R., Burtin, A., Jessop, D., Didier, T., Robert, V., Bonifacie, M., Tamburello, G., and Komorowski, J.-C.: Gas monitoring of a hydrothermal-magmatic volcano in a tropical environment: the example of La Soufriere de Guadeloupe (FWI), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8391, https://doi.org/10.5194/egusphere-egu21-8391, 2021.

EGU21-15149 | vPICO presentations | GMPV9.2

Monitoring diffuse CO2 emissions by means of an automatic geochemical station at Cumbre Vieja volcano, La Palma, Canary Islands.

José Barrancos, Claudia Rodríguez, Eleazar Padrón, Pedro A. Hernández, Germán D. Padilla, Luca D’Auria, and Nemesio M. Pérez

La Palma Island (708.3 km2) is located at the north-west and is one of the youngest (~2.0My) of the Canarian Archipelago. Volcanic activity has taken place exclusively at the southern part of the island, where Cumbre Vieja volcano, the most active basaltic volcano in the Canaries, has been constructed in the last 123 ky. Cumbre Vieja has suffered seven eruptions in the last 500 years, being the last in 1971 (Teneguía volcano). Since the last eruptive episode, Cumbre Vieja volcano has remained in a relative seismic calm that was interrupted on October 7th and 13rd, 2017, by two remarkable seismic swarms with earthquakes located beneath Cumbre Vieja volcano at depths ranging between 14 and 28 km with a maximum magnitude of 2.7. The frequency of these seismic episodes increased in 2020 with the occurrence of five more seismic swarms

As part of the volcano monitoring program of Cumbre Vieja, diffuse degassing of CO2 has been continuously monitored since 2005 at the southernmost part of Cumbre Vieja according to the accumulation chamber method. The monitoring site (LPA04) was selected because it shows anomalous diffuse CO2 degassing emission values with respect to the background values that had been measured in different surveys (Padrón et al., 2015). Meteorological and soil physical variables are also measured in an hourly basis and transmitted to ITER facilities about 150 Km far away.

Since its installation, CO2 emissions ranged from non-detectable (<1.5 gm-2d-1) to 1,464.0 gm-2d-1. The time series was characterized by a strong variability in the measured values that are modulated mainly by the atmospheric and soil parameters. Soil moisture is the monitored parameter that explains the highest variability of the data, being the dry season (spring y summer) the period with the highest observed diffuse emission values. This behavior in the time series has changed after 2017 as an increasing trend in being observed in a good temporal agreement with the increase of seismic activity recorded. The observed diffuse CO2 emissions trend in the LPA04 geochemical station support the occurrence of an upward magma migration towards a subcrustal magma reservoir beneath La Palma island.

Padrón et al., (2015). Bull Volcanol 77:28. DOI 10.1007/s00445-015-0914-2

How to cite: Barrancos, J., Rodríguez, C., Padrón, E., Hernández, P. A., Padilla, G. D., D’Auria, L., and Pérez, N. M.: Monitoring diffuse CO2 emissions by means of an automatic geochemical station at Cumbre Vieja volcano, La Palma, Canary Islands., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15149, https://doi.org/10.5194/egusphere-egu21-15149, 2021.

EGU21-12446 | vPICO presentations | GMPV9.2 | Highlight

Twenty years of CO2-emission monitoring at Cava dei Selci, Colli Albani volcano (Central Italy)

Luca Tarchini, Maria Luisa Carapezza, Domenico Granieri, and Massimo Ranaldi

Carbon dioxide flux from the soil has been monitored for 20 years at Cava dei Selci, the main degassing site of Colli Albani quiescent volcano. Cava dei Selci gas discharge occurs at the north-western periphery of the volcano, within an old stone quarry crossed by a NW-SE volcano-tectonic lineament. The area around the manifestation has been densely urbanized and lethal accidents by gas inhalation have occurred to a man and to dozens of animals including cows and sheep. Some houses had to be permanently evacuated because of hazardous indoor gas concentrations. Emitted gas is dominated by CO2 (>90 vol.%) with <1 vol.% of H2S. Isotopic composition (δ13C and 3He/4He) suggests a deep magmatic origin. No significant compositional variations have been recorded during the observation period.

Surveyed area includes a fixed grid of 130 points, regularly distributed over an area of about 5500 m2, where soil CO2 flux surveys have been carried out 55 times from May 2000 to August 2020 by accumulation chamber. Collected data have been reprocessed by sequential Gaussian simulation. The total diffuse CO2 output is highly fluctuating, with a maximum rate of 24.8 t*d−1 in January 2006 and a minimum value of 5.6 t*d−1 in December 2003; the estimated mean±1σ is 12.1±4.5 t*d−1. All the flux maps show typically a highly emissive area in the internal sector of the investigated grid, with NW-SE elongation. Another anomalous zone, with the same elongation, is found in the SW of the survey area. Diffuse degassing rate (total flux normalized by survey area) is similar to that of active volcanic zones.

In the same zone an automatic permanent station continuously measured the soil CO2 flux and environmental parameters (which may influence the soil gas flux) from 2004 to 2008 and from 2019 to present. Results of timeseries processing by Multiple Linear regression and Principal Component analysis, commonly used to filtrate and clear data from atmospheric inferences (for example at Stromboli and Campi Flegrei), were unsatisfying for Cava dei Selci. Therefore, we reprocessed the timeseries by the stochastic Gradient Boosting Trees regression technique. This allowed to explain up to 55 % of the CO2 variance by environmental variations; 45 % of the variance therefore reflects deep-seated processes. This technique looks promising for the regression of soil CO2 flux timeseries. The results of 20 years monitoring confirm that Cava dei Selci is a convenient site for both monitoring a potential unrest of the volcano and assessing the gas hazard in the nearby inhabited zone.

How to cite: Tarchini, L., Carapezza, M. L., Granieri, D., and Ranaldi, M.: Twenty years of CO2-emission monitoring at Cava dei Selci, Colli Albani volcano (Central Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12446, https://doi.org/10.5194/egusphere-egu21-12446, 2021.

EGU21-15190 | vPICO presentations | GMPV9.2

Temporal variations of CO2 efflux continuous monitoring at the summit cone of Teide volcano (Tenerife, Canary Islands) during the period1999-2021

Germán D. Padilla, Nemesio M. Perez, Pedro A. Hernández, Eleazar Padrón, José Barrancos, Luca D’Auria, Gladys Melián, Fátima Rodríguez, and Matthew J. Pankhurst

Tenerife Island (2034 km2), the largest of the Canarian archipelago, is characterized by three main volcano-tectonic axes: the NS, NE and NW rifts and a central caldera, Las Cañadas, hosting the twin stratovolcanoes Pico Viejo and Teide. Although Teide volcano hosts a weak fumarolic system, volcanic gas emissions from the summit cone consist mostly of diffuse CO2 degassing. The first continuous automatic geochemical station in Canary Islands was installed at the south-eastern foot of summit cone of Teide volcano in 1999, with the aim of improving the volcanic monitoring system and providing a multidisciplinary approach to the surveillance program of Teide volcano. The 1999-2020 time series shows diffuse CO2 emission values ranging between 0 and 62.8 kgm-2d-1, with a mean value of 4.3 kgm-2d-1. Inspection of the CO2 efflux time series shows significant temporal variations with anomalous values of more than 20 kgm-2d-1 centred at years 2000, 2003, 2005, 2007, 2008, 2012, 2015 and 2016, always before a significant increase in the seismic activity beneath Tenerife Island. With the aim to filter out environmental variables, a multiple regression analysis (MRA) was applied to the first 12 years of the diffuse CO2 flux time series (1999-2011), recorder on an hourly basis by the station, and we found that soil temperature, soil water content, wind speed and barometric pressure explained 16.7% of variability. The comparison between filtered CO2 efflux (continuous, hourly, automated station) versus the temporal evolution of diffuse CO2 emission estimated by ground CO2 efflux surveys of summit cone of Teide (during summer season on an area of around 0.11 km2) for the period 1999-2011 (Pérez et al., 2013), shows a nearly coincident marked peak in December 2001 and a similar shaped evolution from each sampling type as the increase from ~2005 to 2009 and the subsequent decrease from ~2009 to 2011, reaching maximum values of 161.6 and 179.9 t d-1, respectively. Seismic activity displayed as of monthly earthquakes (M>1) occurring in and around Tenerife island is well correlated with diffuse CO2 efflux relevant peaks. In average, the seismicity recorded during the study period was mainly preceded by geochemical anomalies of the registered surface CO2 efflux by about one year. After we analysed the CO2 efflux time series by using the Continuous Wavelet Transform (Ricker wavelet) to detect relevant time-frequency patterns in the signal, we found at low frequencies quasi-periodical oscillations with periods of 3-4 years, which might reflect the internal dynamics of the magmatic-hydrothermal system. Moreover, during the intervals of highest levels of CO2 efflux, the analysis evidenced also oscillations with a period of about 6 months during the interval 1999-2011. Our study reveals that continuous geochemical monitoring data is representative of the same trends in flux that are quantitatively captured by annual surveys, and provides the basis for accurate determination of background values. This combined approach offers a useful template for application to other volcanic systems for the purposes of constructing quantitative dynamic models of hydrothermal systems and identifying processes at depth in near-real-time.

How to cite: Padilla, G. D., Perez, N. M., Hernández, P. A., Padrón, E., Barrancos, J., D’Auria, L., Melián, G., Rodríguez, F., and Pankhurst, M. J.: Temporal variations of CO2 efflux continuous monitoring at the summit cone of Teide volcano (Tenerife, Canary Islands) during the period1999-2021, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15190, https://doi.org/10.5194/egusphere-egu21-15190, 2021.

GMPV9.4 – Volcano-glacier interactions: Arctic, Antarctic, and globally

EGU21-736 | vPICO presentations | GMPV9.4 | Highlight

Using glaciers to identify, monitor, and predict volcanic activity

Michael Martin, Iestyn Barr, Benjamin Edwards, Elias Symeonakis, and Matteo Spagnolo

Many (about 250) volcanoes worldwide are occupied by glaciers. Often glaciers are regarded as problematic for volcano monitoring, since glacier ice potentially masks evidence of volcanic activity. The most devastating volcanic eruptions of the last 100 years involved volcano-glacier interactions. The 1985 eruption of Nevado del Ruiz killed 23000 people, and the 2010 eruption of Eyjafjallajökull led to the closure of many European airports. Therefore, it is imperative to minimize these impacts on society by improving methods for monitoring of glacier-clad volcanoes. Amongst several methods, optical satellite remote sensing techniques are perhaps most auspicious, since they frequently have a relatively high temporal and spatial resolution, and are mostly freely available. They often clearly show the effects of volcanic activity on glaciers, including ice cauldron formation, ice fracturing and glacier terminus changes potentially due to subglacial melt or subglacial dome growth. This study has the objective to link pre-, syn- and post-eruption glacier behaviour to the type and timing of volcanic activity, and to develop a satellite based predictive tool for monitoring future eruptions. Despite several studies that link volcanic activity and changing glacier behaviour, the potential of using the latter to predict the former has yet to be systematically tested. Our approach is to observe how glaciers responded to past volcanic events using mostly, but not exclusively optical satellite imagery, and to build a database of examples for potential automated detection and forecasting on a global scale.

How to cite: Martin, M., Barr, I., Edwards, B., Symeonakis, E., and Spagnolo, M.: Using glaciers to identify, monitor, and predict volcanic activity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-736, https://doi.org/10.5194/egusphere-egu21-736, 2021.

EGU21-142 | vPICO presentations | GMPV9.4

Dwindling impact of large volcanic eruptions on global glacier changes in the Anthropocene

Michael Zemp and Ben Marzeion

Large volcanic eruptions impact climate through the injection of ash and sulfur gas into the atmosphere. While the ash particles fall out rapidly, the gas is converted to sulfate aerosols, which reflect solar radiation in the stratosphere and cause a cooling of the global mean surface temperature. Earlier studies suggested that major volcanic eruptions resulted in positive mass balances and advances of glaciers. Here we perform a multivariate analysis to decompose global glacier mass changes from 1961 to 2005 into components associated with anthropogenic influences, volcanic and solar activity, and El Niño Southern Oscillation (ENSO). We find that the global glacier mass loss was mainly driven by the anthropogenic forcing, interrupted by a few years of intermittent mass gains following large volcanic eruptions. The relative impact of volcanic eruptions is dwindling due to strongly increasing greenhouse gas concentrations since the mid of the 20th century. Furthermore, our study indicates that solar activity and ENSO have limited impacts on climate conditions at glacier locations and that volcanic eruptions alone can hardly explain decadal periods of glacier advances documented since the 16th century.

How to cite: Zemp, M. and Marzeion, B.: Dwindling impact of large volcanic eruptions on global glacier changes in the Anthropocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-142, https://doi.org/10.5194/egusphere-egu21-142, 2021.

EGU21-6821 | vPICO presentations | GMPV9.4

Modelling the formation and evolution of glaciovolcanic caves and chimneys.

Tryggvi Unnsteinsson, Gwenn Flowers, and Glyn Williams-Jones

Localised elevated subglacial or subnivean geothermal activity has the potential to influence the morphology and flow of glaciers. Under conditions where the meltwater produced by these glaciovolcanic interactions is effectively drained away from the geothermal source, glaciovolcanic voids may form. These voids can only exist if the influx of geothermal vapours/gases provides more heat for melting than can be compensated by the inflow of ice. We identify two distinct glaciovolcanic void morphologies: horizontal passageways or chambers beneath the ice/snow, termed caves, and vertical shafts, termed chimneys. Both transient and long-lived caves and chimneys have been observed, with their formation sometimes being precursory or concurrent expressions of volcanic unrest. A better understanding of these features can therefore aid volcano monitoring programs and volcanic hazard assessments. Here we investigate the relationships between glaciological and geothermal conditions and their effects on the formation and evolution of glaciovolcanic caves and chimneys. We adapt existing analytical models, originally developed to describe subglacial hydrology, to derive and balance expressions for the radial melt-opening and creep-closure to find steady-state solutions for cave and chimney geometries. The effects of localised geothermal heat fluxes on fully drained glaciovolcanic voids are further investigated using a numerical full-Stokes ice-flow model. Idealised voids, subject to a prescribed geothermally induced mass balance, are inserted within synthetic glaciers of variable bed slope and thickness. Transient simulations are then used to map out the parameter space that influences the formation and evolution of glaciovolcanic caves and chimneys.

How to cite: Unnsteinsson, T., Flowers, G., and Williams-Jones, G.: Modelling the formation and evolution of glaciovolcanic caves and chimneys., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6821, https://doi.org/10.5194/egusphere-egu21-6821, 2021.

EGU21-2402 | vPICO presentations | GMPV9.4

Completing the eruptive record of Deception Island (South Shetland Islands, Antarctica) by characterizing ash layers in proximal marine sediments cores.

Antonio Polo Sánchez, Joaquín Hopfenblatt, Adelina Geyer, Meritxell Aulinas, Gemma Ercilla, and Antonio Álvarez-Valero

The chemical and textural characterization of ash layers allows relating them to their volcanic source, provides information regarding an eruptive event and its impact; and pictures more accurate scenarios in case of future activity. Deception Island, located in central Bransfield strait (South Shetland Islands, Antarctica), consists of a horseshoe-shaped composite volcano, whose central part is occupied by a collapse caldera (8.5 x 10 km). It is considered to be among the most active volcanoes in Antarctica and a future eruption is very likely to happen, affecting the military and scientific research stations located nearby. The characterisation of volcanic ash layers found in marine sediment cores outside Deception Island can provide valuable information to: (i) determine the size and explosiveness of past eruptive events, (ii) assess the extent of their related hazards; and (iii) complete the eruption record of the island. Here, we present results of the characterization of the ash layers found on five marine sediment cores (TG-40, 41,43, 48 and 50) drilled proximal to Deception Island (less than 40 km) during the Antarctic Campaign of the MAGIA project (ANT-584/97). The final aim is to trace isochronous tephra horizons between the studied cores and try associating them to their respective eruptive events on the island. First, we carried out a granulometry analysis of each sampled layer and characterized the morphology of the fragments using as parameters: elongation, sphericity, solidity, and length/width ratio. Results obtained indicate that most of the layers are moderate to well sorted coarse ash. Minor amounts of lapilli and fine ash appear in the shallower (0 to 50 cm depth) layers. The granulometry and the morphology indicate that the layers have been reworked by turbiditic currents after the eruption, but not enough to destroy the information necessary for correlation. The petrographical study via optical microscope has highlighted the presence of three different types of volcanic glasses based on: (i) the colour of the ash particles under non-crossed polarized light; (ii) microcrystal content; (iii) texture; and (iv) vesicle abundance. Type 1 glasses, with black colour and generally shard shaped, show a low content in microcrystals and vesicles. Type 2, with brown colour and more spherical shapes, have a higher content in microcrystals and the fragments usually have a fluidal texture; the vesicle abundance is variable. Type 3, with yellow colour and variably shaped, are usually rich in microcrystals and vesicles, and have fluidal texture. In all families, the mineralogy of the microcrystals is mainly plagioclase (90%), pyroxene and olivine. The longest core (TG-48, 120 cm long) contains 15 layers, the deepest ones (113, 115 and 120 cm depth) may be correlated to the ones found in previous studies associated with a period of abundant volcanic activity around 2000 years BP.

This research is part of POLARCSIC and PTIVolcan research initiatives. This research was partially funded by the MINECO grants VOLCLIMA (CGL2015-72629-EXP), POSVOLDEC(CTM2016-79617-P)(AEI/FEDER-UE) and VOLGASDEC (PGC2018-095693-B-I00)(AEI/FEDER, UE). Analyzed tephra samples and sediment cores were provided by the rock repository of the Instituto de Ciencias del Mar del CSIC (ICM-CSIC) (http://gma.icm.csic.es/ca/dades).

How to cite: Polo Sánchez, A., Hopfenblatt, J., Geyer, A., Aulinas, M., Ercilla, G., and Álvarez-Valero, A.: Completing the eruptive record of Deception Island (South Shetland Islands, Antarctica) by characterizing ash layers in proximal marine sediments cores., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2402, https://doi.org/10.5194/egusphere-egu21-2402, 2021.

EGU21-2840 | vPICO presentations | GMPV9.4

Characterization of the Outer Coast Tuff Formation- A way to unravelling the magmatic processes preceding and triggering Deception Island’s caldera - forming eruption (Antarctica)

Oriol Vilanova, Meritxell Aulinas, Adelina Geyer, Joan Marti, Antonio Álvarez-Valero, Helena Albert, and Guillem Gisbert

Deception Island (South Shetland Islands), discovered in 1820, is one of the most active volcanoes in Antarctica with more than 20 eruptions (including the historic eruptions of 1967, 1969 and 1970) and three documented volcanic unrest events (1992, 1999 and 2014-15) over the past two centuries. Deception Island currently hosts two scientific bases, which operate every year during the Austral summer, and is also one of the most popular tourist destinations in Antarctica. The island is a composite volcano with a centrally located caldera of 8.5 x 10 km dated at 3,980 ± 125 yr. BP. During the caldera-forming event, between 30 and 60 km3 (Dense Rock Equivalent-DRE) of magma, erupted in the form of dense basaltic-andesitic pyroclastic density current deposits. During the last decades, Deception Island has been intensively investigated but some aspects regarding the magmatic processes associated with the formation of its caldera collapse are still under research and debate. For instance, characterizing the magmatic conditions and processes that triggered the huge explosive event is crucial to understand the past (and in turn the future) magmatic and volcanic evolution of the island.

This study is performing an exhaustive petrological and geochemical characterization (mineral and juvenile glass geochemistry) of the Outer Coast Tuff Formation (OCTF), the main syn-caldera depositional unit. The preliminary results confirm the existence of two different magmas coexisting, and interacting, prior to (and during) the caldera-forming event. Mineral analyses also allow shedding further light on the magmatic processes occurring in the magma system before the eruption (e.g. fractional crystallization, magma mixing). The presence of alteration minerals such as palagonite and zeolites indicate different magma-water interaction mechanisms occurred during the syn- and post-eruptive episodes in the island.

This research is part of POLARCSIC and PTIVolcan research initiatives. This research was partially funded by the MINECO grants POSVOLDEC(CTM2016-79617-P)(AEI/FEDER-UE) and VOLGASDEC (PGC2018-095693-B-I00)(AEI/FEDER, UE). This research is also supported by the PREDOCS-UB grant.

How to cite: Vilanova, O., Aulinas, M., Geyer, A., Marti, J., Álvarez-Valero, A., Albert, H., and Gisbert, G.: Characterization of the Outer Coast Tuff Formation- A way to unravelling the magmatic processes preceding and triggering Deception Island’s caldera - forming eruption (Antarctica), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2840, https://doi.org/10.5194/egusphere-egu21-2840, 2021.

EGU21-9003 | vPICO presentations | GMPV9.4

Rhyolite volcanism in the Marie Byrd Land volcanic province, Antarctica: New evidence for pyroclastic eruptions during latest Pliocene icesheet expansion 

Nels Iverson, Christine Siddoway, Matthew Zimmerer, John Smellie, Nelia Dunbar, and Karsten Gohl and the IODP Expedition 379 Scientists

       IODP Expedition 379 deep-sea drilling in 2019 (Gohl et al. 2021, doi:10.14379/iodp.proc.379.2021), offered an opportunity to obtain chronostratigraphic control for seismic reflection data for Amundsen Sea shelf and slope deposits that record Miocene to Present fluctuations in volume of the West Antarctic ice sheet. Here we report the age and interpret the provenance of a volcanic ash bed recovered at/near the Plio-Pleistocene boundary at 31.51 meters below sea level in Hole U1533B and 33.94 mbsf in Hole U1533D. With distinctive geochemistry and inferred wide regional distribution, the bed may serve as a reliable age marker.

       In Hole 1533B, the fresh tephra forms a discrete layer interstratified within uniform brown marine mud. The layer has a sharp base and upper boundary that is gradational over 5 cm into overlying mud. Color reflectance and density data aided identification of the tephra horizon (diffuse) in Hole 1533D, ~1000m away. A possible on-land source for ash is the Miocene to Pleistocene Marie Byrd Land volcanic province, comprising 18 large alkaline volcanoes dominated by effusive lavas. Products of pyroclastic eruptions are uncommon, mainly occurring as distal englacial, and probably marine, tephra.

       We undertook an offshore-onshore comparison by first characterizing samples of Site U1533 tephra from a petrographic and geochemical standpoint, using thin section observations, EMPA-WDS glass compositions, and 40Ar/39Ar dating. We then identified onshore exposures with similar characteristics. The offshore tephra are composed of coarse (50-300µm) cuspate glass shards with elongated vesicles.  The glass composition is rhyolite, with 75-79wt.% SiO2, ~4wt.% FeO and 0.0wt.% MgO. Single-crystal feldspar 40Ar/39Ar dates are 2.55±0.12 and 2.92±0.02 Ma for U1533B and 2.87 ±0.45 Ma for U1533D. The geochemistry, shard morphology, discrete bed expression, and lateral continuity between Holes U1533B-U1533D indicate that the rhyolite tephra formed as airfall settled to the deep seabed. The ca. 2.55 Ma age based on youngest feldspar grains differs slightly from the 2.1 to 2.2 Ma result obtained from in-progress core bio-magnetostratigraphy.

       Rare exposures of rhyolite are found in the Chang Peak/Mt. Waesche centers, 1080 km from Site U1533. We obtained pumice sample MB.7.3 (prior-published age of 1.6±0.2 Ma), which displays elevated FeO and F content, and MB.8.1, a specimen of porphyritic cryptocrystalline lava. Single-crystal sanidine 40Ar/39Ar dates are 1.315±0.007 Ma (MB.7.3) and 1.385±0.003 Ma (MB.8.1). Site U1533 samples share a geochemical affinity with these on-land rhyolites, expressed as similar SiO2, CaO, TiO2, MgO and FeO content, suggesting an origin for Site U1533 tephra in the Chang-Waesche volcanoes. A possible explanation for the distinctly greater age, and observed contrasts in Al2O3, Na2O and F percentages, is that Site U1533 tephra are older and erupted from a source entirely concealed beneath subsequent eruptions and the ice sheet.  Our results suggest that rhyolite volcanism initiated earlier, was of longer duration than previously known (2.92 to 1.315 Ma), and dispersed tephra far offshore. The finding is significant because ash and aerosols produced by large eruptions may influence regional climate. Antarctica cooled significantly and ice sheets expanded in latest Pliocene time (McKay et al. 2012, doi:10.1073/pnas.1112248109).

How to cite: Iverson, N., Siddoway, C., Zimmerer, M., Smellie, J., Dunbar, N., and Gohl, K. and the IODP Expedition 379 Scientists: Rhyolite volcanism in the Marie Byrd Land volcanic province, Antarctica: New evidence for pyroclastic eruptions during latest Pliocene icesheet expansion , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9003, https://doi.org/10.5194/egusphere-egu21-9003, 2021.

EGU21-2075 | vPICO presentations | GMPV9.4

DecTephra: A new database of Deception Island’s tephra record (Antarctica

Joaquin Hopfenblatt, Adelina Geyer, Meritxell Aulinas, Antonio Polo Sánchez, and Antonio Álvarez-Valero

Deception Island is the most active volcano in the South Shetland Islands (Antarctica) with more than 20 eruptions in the in the last two centuries, including the 1967, 1969 and 1970 most recent eruptive events, and three episodes of volcanic unrest since 1990 (1992, 1999 and 2014-2015). Since the discovery of Deception island in 1820, the number of scientific bases, touristic activities, and air and vessel traffic in the region, have considerably increased. Only the Antarctic Peninsula region, together with the South Shetland Islands, hosts 25 research stations and 3 summer field camps, which are located inside or within a 150 km radius distance from this active volcano. Nearby, the Palmer Archipelago and the north-western coast of the Antarctic Peninsula are both important tourist destinations exceeding 30,000 visitors per year with a significant increase in vessel traffic during the tourist season. This escalation in the amount of exposed infrastructure and population to a future eruption of Deception Island clearly urges the need to advancing our knowledge of the island’s volcanic and magmatic history and developing improved vulnerability analyses and long-term volcanic hazard assessments. However, past attempts to construct a volcanic hazard map of Deception have always been limited by the lack of a complete eruption record. In this sense, volcanic ash layers found in marine and lacustrine sediment cores, and glaciers outside Deception Island can provide valuable information to: (i) determine the size and explosiveness of past eruptive events; (ii) assess the extent of their related hazards (e.g. ash fall out); (iii) complete the eruption record of the island; and (iv) estimate the island’s eruption recurrence over time.

In this work, we provide a detailed, and up-to-date, revision of the current knowledge on Deception Island’s tephra record.  For this, we have compiled the DecTephra (Deception Island Tephra Record) database, which seeks recording the most relevant information of all up today known tephra layers with Deception Island as presumed source vent. DecTephra database includes 335 tephra layers (including cryptotephras) found in marine/lacustrine sediment and ice cores. For each tephra layer, we have compiled information regarding: (i) location (e.g. latitude, longitude, region) and characteristics of the sampling site (e.g. length of the sediment or ice core); and (ii) tephra characteristics (e.g. age, chemistry, granulometry). The analysis of the information included in this new database shows that Deception Island’s tephras can be observed at numerous proximal (< 150 km) sampling sites distributed all along the South Shetland Islands but also as far as in the Scotia Sea (> 1,000 km) and the South Pole (> 2,900 km). Also, identified isochronous tephra horizons allow defining periods of higher explosive eruptive activity in the island during the Holocene.

This research is part of POLARCSIC and PTIVolcan research initiatives. This research was partially funded by the MINECO projects VOLCLIMA (CGL2015-72629-EXP) and VOLGASDEC (PGC2018-095693-B-I00)(AEI/FEDER, UE). A.P.S is grateful for his JAE_Intro scholarship (JAEINT_20_00670).

How to cite: Hopfenblatt, J., Geyer, A., Aulinas, M., Polo Sánchez, A., and Álvarez-Valero, A.: DecTephra: A new database of Deception Island’s tephra record (Antarctica, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2075, https://doi.org/10.5194/egusphere-egu21-2075, 2021.

EGU21-5347 | vPICO presentations | GMPV9.4

Tephra layers in Perunika Glacier, Livingston Island, Antarctica

Stefan Velev and Tsveta Stanimirova

Perunika Glacier is an 8 km long and 3 km wide roughly crescent-shaped glacier in Livingston Island, South Shetland Islands, Antarctica. The glacier is heavily crevassed in its lower half receiving ice influx from snowfields and from part of the islands ice cap.

Tephra layers recorded in the ice caps are very common in Antarctica, and Perunika Glacier is not an exception. The glacier contains several dark layers of unconsolidated ash (tephra), resulting the most probably from volcanic activities at Deception Island, a large active volcano in Bransfield Strait situated 40 km south of the tephra outcrops on Livingston Island (Pallas et al., 2001). Three eruptions have been documented in recent history – 1967, 1969 and 1970. The most powerful and intensive of which was in 1970.

The ice and tephra stratigraphy seen in the ice cliffs is the result of deposition within the accumulation zone in the interior of the island. The distortion of tephra layers during glacial transport and ablation may result in different local tephra stratigraphies. The distinctive grouping and spacing of the multiple tephra layers is repeated at many localities.

In the cliff of Perunika Glacier there are 10 tephra layers. During the 26th Bulgarian Antarctic Expedition 7 of them were observed, the other were inaccessible. The lower six levels are located at relatively equal intervals and have thicknesses between 3 cm and 5 cm. The layer 7 is situated about 10 m above the others and is 10–12 cm thick. All tephra layers consist predominantly of black and subordinately of red components. In this research is shown data about phase composition of the tephra layers, based on X-ray diffraction analysis.

The obtained phase composition by Powder X-ray diffraction corresponds with basalt and basaltic andesite from the published data on chemical content of the tephroid levels by Pallas et al. (2001). As main phases of samples at 7 assayed levels were determained plagioclase (34–47%) and pyroxene (7–10%). Diffraction lines analysis defines two types of plagioclase – anorthite and sodic anorthite. Comparison between registered diffraction lines and different pyroxene types from the reference database identifies pyroxene from all samples as ferrian diopside. In three of the levels was discovered andalusite (2–6%) and mica (5–7%). Due to low mica content in the samples, it is difficult to define its type by powder analysis. However, in samples from levels 1, 2, 3, 5, and 7 the mica is probably sericite type and in levels 4 and 6 – biotite type. The presence of xenocrystals of andalusite and micas (biotite and sericite) is interesting. Considering their metamorphic genesis, the most reasonable source is the metamorphic fundament of this Antarctic area. The lithotypes it is built are represented by phyllites, schists, Ca-silicate rock types, marbles, rare amphibolites and fine layers of volcanic metaconglomerates (Marsh, Thompson, 1985).

How to cite: Velev, S. and Stanimirova, T.: Tephra layers in Perunika Glacier, Livingston Island, Antarctica, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5347, https://doi.org/10.5194/egusphere-egu21-5347, 2021.

EGU21-16038 | vPICO presentations | GMPV9.4

Deciphering the fallout of tephra on glaciers in past eruptions, the case history of the Katla 1918 eruption

Magnus Tumi Gudmundsson, Gudrun Larsen, Maria H. Janebo, Thordis Hognadottir, and Tinna Jonsdottir

Explosive eruptions in ice-covered volcanoes may deposit large volumes of tephra on the glaciated slopes.  The tephra can influence surface ablation and alter mass balance.  Ice melting by an eruption can change glacier geometry and temporarily alter the flow of outlet glaciers.  Conversely, when assessing the size of past tephra-producing eruptions in an ice-covered volcano the glacier complicates such estimates.  The effects of ice flow, dilation and shear need to be considered.  A tephra layer may get buried in the accumulation area, be transported by glacier flow and progressively removed over years-to-centuries by ice flow, eolian transport of exposed tephras and sediment transport in glacial rivers.  Here we report on a case study from the Mýrdalsjökull ice cap that covers the upper parts of the large Katla central volcano in south Iceland.  Most eruptions start beneath the 300-700 m thick ice cover within the Katla caldera, melt large volumes of ice and cause major jökulhlaups.  They also produce tephra layers that are preserved in soils around the volcano.  The most recent eruption in Katla occurred in October-November 1918, when a large tephra layer was deposited in a 3-weeks long eruption. By using a combination of (1) data obtained at or near the vent area within the SE-part of the Katla caldera in the year following the eruption, (2) mapping of the tephra as exposed at the present time in the ablation areas in the lower parts of the outlet glaciers, and (3) simple models of ice flow based on balance velocities and knowledge of mass balance, we estimate the location of fallout and the original thickness of the presently exposed tephra.  Photos taken in the vent area in 1919 indicate a tephra thickness of 20-30 m on the ice surface proximal to the vents.  The greatest thicknesses presently observed, 30-35 cm, occur where the layer outcrops in the lowermost parts of the ablation areas of the Kötlujökull and Sólheimajökull outlet glaciers.  A fallout location within the Katla caldera is inferred for the presently exposed tephra, as estimates of balance velocities imply lateral transport since 1918 of ~15 km for Kötlujökull, ~11 km for Sólheimajökull and about 2 km for the broad northern lobe of Sléttjökull.  The calculations indicate that ice transport with associated dilation of the glacier through the accumulation areas has resulted in significant thinning.   Thus, the layer that is now 0.3-0.35 m thick in the fastest flowing outlets is estimated to have been four to seven times thicker when it fell on the accumulation area within the ice-filled caldera.  In contrast, changes have been minor in the slowly moving Sléttjökull.  These findings allow for the construction of an isopach map for the glacier.  The results indicate that just under half of the total airborne tephra produced in the eruption fell within the Mýrdalsjökull glacier, with the remaining half spread out over a large part of Iceland.  These methods potentially allow for reconstruction of several tephra layers from ice-covered volcanoes in Iceland and elsewhere. 

How to cite: Gudmundsson, M. T., Larsen, G., Janebo, M. H., Hognadottir, T., and Jonsdottir, T.: Deciphering the fallout of tephra on glaciers in past eruptions, the case history of the Katla 1918 eruption, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16038, https://doi.org/10.5194/egusphere-egu21-16038, 2021.

EGU21-3728 | vPICO presentations | GMPV9.4

Monitoring Volcanic Activity of Baekdu Mountain based on Ice Area Changes During the Winters of 2015-2020

Arip Syaripudin Nur, Sungjae Park, Seulki Lee, and Chang-Wook Lee

Baekdu Mountain is a 2,744 m high stratovolcano, located on the border of China and North Korea. The mountain has a caldera lake, Lake Cheonji, as a result of past volcanic activity. The ice area changes during winter in Lake Cheonji could act as a proxy for volcanic activity monitoring in Baekdu. As Baekdu laid on a political border, remote sensing allows us to quantify attributes of otherwise inaccessible or dangerous places. We assessed changes in winter (October–April) ice area in a high-altitude groundwater-fed caldera lake using Sentinel-1 synthetic aperture radar (SAR) data acquired from 2015 to 2020. To calculate the ice-covered area, 10 gray level co-occurrence matrix (GLCM) texture features were computed from SAR images obtained with VH (vertical transmission and horizontal reception) and VV (vertical transmission and vertical reception) polarizations. A support vector machine (SVM) algorithm was used to classify ice and water pixels from the GLCM layers, and the results from VH and VV imagery were combined to calculate the total area covered by ice. We examined the relationship between ice area and air temperature from the closest weather station, Samjiyeon using fixed period regression. The ice area was inversely proportional to 30-day averaged air temperature and these variables were highly correlated (-0.86). Our results show that there were no significant ice changes during the period, which indicates that there was no significant volcanic activity in Baekdu Mountain during the winters of 2015–2020. This study is expected to be useful for a better understanding of whether and how ice area changes in volcano lakes aid in eruption forecasting.

How to cite: Nur, A. S., Park, S., Lee, S., and Lee, C.-W.: Monitoring Volcanic Activity of Baekdu Mountain based on Ice Area Changes During the Winters of 2015-2020, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3728, https://doi.org/10.5194/egusphere-egu21-3728, 2021.

EGU21-7940 | vPICO presentations | GMPV9.4 | Highlight

Discriminating glacial and volcanic seismicity at Llaima and Villarrica volcanoes, Chile

Oliver Lamb, Jonathan Lees, Luis Franco Marin, Jonathan Lazo, Andres Rivera, Michael Shore, and Stephen Lee

The monitoring of seismic activity at active glacier-hosting volcanoes is challenging as volcanic and glacial earthquakes (i.e. icequakes) can have overlapping characteristics (i.e. frequencies, waveform shape and magnitude). Here we present results from the first study to target glacial activity at active ice-covered volcanoes in the Southern Chile. The primary focus so far has been on Llaima volcano, one of the largest and most active volcanoes in the region while hosting >14 km2 of glacial ice on the flanks. We use a combination of automatic multi-station event detection and waveform cross-correlation to find candidate repeating icequakes in seismic data from the permanent volcano monitoring network recorded in early 2019. We identified dozens of low magnitude families of repeating seismic events across two months, the largest of which included over 200 events. These findings are comparable to results from analysis of seismic data recorded at Llaima volcano during the same time period in 2015. The persistent, repetitive nature of these events combined with their waveform characteristics and source locations suggest they originated from multiple sub-glacial stick-slip sources around the upper flanks of the volcano. We also deployed a network of seismo-acoustic sensors at Villarrica volcano in early 2020 to record glacial activity in concurrence with the lava lake and strombolian activity at the summit. We conclude that icequakes at Llaima volcano may be more common than previously thought and has implications for how seismic data at ice-covered volcanoes may be used for assessing future volcanic and glacial hazard potential.

How to cite: Lamb, O., Lees, J., Franco Marin, L., Lazo, J., Rivera, A., Shore, M., and Lee, S.: Discriminating glacial and volcanic seismicity at Llaima and Villarrica volcanoes, Chile, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7940, https://doi.org/10.5194/egusphere-egu21-7940, 2021.

GMPV9.5 – Volcanic processes: tectonics, deformation, geodesy, unrest

EGU21-15987 | vPICO presentations | GMPV9.5

The volcanic provinces of the Lennon-Picasso basin (Mercury)

Sabrina Ferrari, Matteo Massironi, Riccardo Pozzobon, and Simone Bedon

The volcanic provinces are embedded between the NE margin of b56 /Lennon-Picasso basin and high terrain bounding structures. Resulting plains are interested by endogenic pits associated with pyroclastic activity, in agreement with the observation that Mercury's explosive volcanic vents tend to be located along major fold and thrust belts (Byrne et al 2014) and around large impact basins. Recent large scale mapping defined them intercrater plains partly covered by smooth plains (Malliband et al 2019; Whitten et al 2020). In addition to endogenic pits, these provinces display several 10-km diameter prominent cones, sometimes aligned forming high-relief ridges, resembling  constructional edifices. In colour composite images, cone tops are peculiarly darker (blue) or, alternatively, brighter (and yellow) with respect to the surrounding material. On the surface Mercury, Wright et al. (2019) interpreted two randomly located constructional edifices of similar size, attributing their origin to a late highly viscous  stage of volcanism that followed lower-viscous stage that are thought to provide typical smooth plains. Wider et al. (2016) proposed that the encounter of highly-viscous lavas with C-rich material during the magma ascent can easily provide volatiles (Zolotov et al. 2011) that progressively accumulate and lead to explosive eruptions. The resulting high reflectance of pyroclastic deposits would arise from removal of graphite as it was consumed during oxidation. The study aims to reveal the nature of cones at the margin of the Lennon-Picasso basin and to explain the relationship between a potential long-lasting volcanic activity and the concurrent global contractional regime.

Authors received funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2017-47 and from European Union’s Horizon 2020 research grant under agreement 776276- PLANMAP.

How to cite: Ferrari, S., Massironi, M., Pozzobon, R., and Bedon, S.: The volcanic provinces of the Lennon-Picasso basin (Mercury), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15987, https://doi.org/10.5194/egusphere-egu21-15987, 2021.

EGU21-1486 | vPICO presentations | GMPV9.5

Volcano dynamics vs tectonics on Mars: evidence from Pavonis Mons

Riccardo Pozzobon, Diana Orlandi, Carolina Pagli, and Francesco Mazzarini

EGU21-8497 | vPICO presentations | GMPV9.5

Tectonic control on monogenetic volcanism in the Michoacán-Guanajuato Volcanic Field, México

Martha Gabriela Gómez Vasconcelos, José Luis Macías, Denis Ramón Avellán, Giovanni Sosa-Ceballos, and Víctor Hugo Garduño-Monroy

Aligned volcanism is very common in many monogenetic volcanic fields around the world, which can reveal volcano-tectonic interactions at different scales. For instance, volcanic distribution discloses the tectonic stress orientation on regional scales. On more local scales, preexisting faults or fractures may control magma intrusions and their propagation through the upper crust, as faults are zones of crustal weakness that magma intrusions can intercept during its ascent, partly controlling the volcanic vent spatial distribution. But it is not quite understood how do these alignments occur; if they erupted at the same time (within a few dozens of years), if they erupted during a short time interval (hundreds of years) or during a long time interval (thousands of years); if the eruptive style and magma volumes are controlled by these faults and the regional tectonic stress regime, etc.

This study aims to understand the magmatic and structural conditions that favored the emission of a lava plateau followed by Strombolian explosions that built 13 aligned and six dispersed scoria cones through preexisting E-W– to ENE-striking faults in the Queréndaro area. Our results indicate that volcanism in the Michoacán-Guanajuato Volcanic Field occurs as intermittent magma fluxes, sometimes represented by independent volcanic vents and sometimes by clustered or aligned volcanoes. Moreover, preexisting faults exert a strong influence on volcanic spatial and temporal distribution, volcanic morphology, magma volume, and eruptive dynamics in this area.

How to cite: Gómez Vasconcelos, M. G., Macías, J. L., Avellán, D. R., Sosa-Ceballos, G., and Garduño-Monroy, V. H.: Tectonic control on monogenetic volcanism in the Michoacán-Guanajuato Volcanic Field, México, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8497, https://doi.org/10.5194/egusphere-egu21-8497, 2021.

EGU21-7534 | vPICO presentations | GMPV9.5

The 2020 volcano-tectonic unrest at Reykjanes Peninsula, Iceland: stress triggering and reactivation of several volcanic systems

Halldór Geirsson, Michelle Parks, Kristín Vogfjörd, Páll Einarsson, Freysteinn Sigmundsson, Kristín Jónsdóttir, Vincent Drouin, Benedikt G. Ófeigsson, Sigrún Hreinsdóttir, and Cécile Ducrocq

The Reykjanes Peninsula in south-west Iceland straddles the North-America - Eurasia plate boundary and hosts several active volcanic systems, including the Svartsengi volcanic system. The last eruption in this area took place around 1240 CE, with eruptive episodes recurring every 800-1000 years, affecting one volcanic system at a time, but spanning multiple systems  with activity spaced ~100 to 200 years. In January 2020, unrest was identified in Svartsengi, characterized by intense seismicity and inflation at a rate of 3-4 mm per day. This area is located within 5 km of several important infrastructures: a) the town of Grindavík; b) the Svartsengi geothermal power plant; c) and the Blue Lagoon geothermal spa, which had over a million annual visits before the Covid pandemy.

 

Two continuously recording GNSS stations were installed in the Svartsengi geothermal area in 2013-2015 to monitor geothermally-induced subsidence.  Coinciding with the onset of an earthquake swarm starting on January 21 (M<4), uplift of about 3-4 mm/day was noticed in automated GNSS and InSAR results. The uplift rates in this first inflation phase decreased after January 31 and reverted to slight subsidence in early February. Interestingly, the most intense seismicity was offset from the uplift center by about 2-4 km to the southeast. Geodetic source models from the initial two weeks indicate the deformation is the result of a sill intrusion at a depth of about 4 km  with a volume change of approximately 3  million m3. The resulting stress changes from this intrusion act to increase seismicity at the sill edges, thus offering an explanation for why the seismicity is offset from the center of uplift. The location of the sill coincides roughly with a crustal volume with a high Vp/Vs ratio.

 

Two more inflation-deflation episodes have occurred at Svartsengi in 2020 and the total uplift amounts to approximately 12 cm. Additionally, at least one inflation episode occurred in the Reykjanes system, in February 2020, and inflation started in the Krýsuvík system in mid-July 2020, culminating in a M5.6 earthquake on October 20. The Fagradalsfjall system, between Krýsuvík and Svartsengi, has shown high seismicity in 2020, but does not display detectable inflation nor deflation. Therefore, the volcano-tectonic activity in 2020 spans the entire western part of the Reykjanes Peninsula. The stress changes for each of these events are too small to explain the cross-system activity, hence we suggest the entire unrest is  by deep magma migration beneath the entire western Reykjanes Peninsula.  

How to cite: Geirsson, H., Parks, M., Vogfjörd, K., Einarsson, P., Sigmundsson, F., Jónsdóttir, K., Drouin, V., Ófeigsson, B. G., Hreinsdóttir, S., and Ducrocq, C.: The 2020 volcano-tectonic unrest at Reykjanes Peninsula, Iceland: stress triggering and reactivation of several volcanic systems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7534, https://doi.org/10.5194/egusphere-egu21-7534, 2021.

EGU21-9052 | vPICO presentations | GMPV9.5

Mapping and dynamic analysis of faults in the Hengill volcanic area, SW-Iceland 

Hanna Blanck, Kristín Vogfjörd, Halldór Geirsson, and Vala Hjörleifsdóttir

From 1993 to 1998, the Hengill volcanic area in SW-Iceland was subjected to a volcano-tectonic event which caused a local uplift of the crust of 8 cm and triggered over 90.000 earthquakes. Relocating a sub-set of 12.000 earthquakes in the direct vicinity of the uplift centre improved resolution and enabled the mapping of 25, mostly NNE-SSW and ENE-WSW oriented sub-vertical groups of earthquake which are interpreted as faults. Focal mechanisms were calculated, using the best fitting plane through a group of earthquakes as additional constraint. Slip on the interpreted faults could be estimated averaging slip of all earthquakes within that group. Most faults show strike-slip movement with a small normal component. Right-lateral slip prevails. We modelled Coulomb stress changes that the uplift would have caused and compared them to out results. The Coulomb stress changes can only explain the observed movement on some of the faults but on others fault movements is impeded, that is, the Coulomb stress change is negative. Varying the location of the uplift within its error margin increases the number of faults on which the observed movement is promoted but the slip on a number of faults remains unexplained.  

How to cite: Blanck, H., Vogfjörd, K., Geirsson, H., and Hjörleifsdóttir, V.: Mapping and dynamic analysis of faults in the Hengill volcanic area, SW-Iceland , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9052, https://doi.org/10.5194/egusphere-egu21-9052, 2021.

EGU21-5571 | vPICO presentations | GMPV9.5

An elastic 3D Finite-Element-Model for Grímsvötn, Iceland

Sonja Heidi Maria Greiner and Halldór Geirsson

Deformation models are an important tool to study and monitor active volcanoes. However, in many cases models are strongly simplified either due to a lack of data or for the sake of speed and computational demands. The assumption of a magma body embedded in a homogeneous elastic half-space for example neglects the topography and heterogeneous crustal structures found at some volcanoes. This oversimplification can lead to a poor representation of individual systems and result in erroneous estimates of deformation source parameters like the location and geometry of a magma chamber.  The Finite Element Method (FEM) is a powerful tool to include complex heterogeneous structures and existing data sets into deformation models in order to create more realistic representations of individual volcanic systems.
In this study, the FEM-software COMSOL was used to build a three-dimensional elastic model of the subglacial volcano Grímsvötn, Iceland, accounting for the steep topography at the caldera rim, using a digital elevation model, as well as crustal heterogeneity. The elastic structure developed for this model is based on a density-structure, a seismic-velocity-structure and a pressure-dependent relation between the dynamic and static elastic moduli. The main feature of the elastic structure is a weak material (static shear modulus of Gstat=0.6-9.8 GPa from 1 km above to 2 km below sea level) filing the caldera, which is surrounded by a stiffer, ring-like structure underneath the caldera rim (Gstat=1.6-18 GPa from 1 km above to 2 km below sea level). The source parameters and geometry of forward models including the topography and elastic structure (individually and combined) were varied to fit the deformation observed at the nunatak GPS station GFUM, located at the caldera rim, during the last eruption (2011). While the topography has limited influence at the deformation at GFUM, the elastic structure requires the magma chamber to be significantly deeper than previous models suggested.

How to cite: Greiner, S. H. M. and Geirsson, H.: An elastic 3D Finite-Element-Model for Grímsvötn, Iceland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5571, https://doi.org/10.5194/egusphere-egu21-5571, 2021.

Laccoliths play a significant role in the transport and storage of magma in sub-volcanic systems. The construction and geometry of laccoliths can influence host rock and surface deformation patterns that may precede and provide warning of active magmatism and impending eruptions. Yet how laccolith construction and internal magma dynamics controls the location and form of magma ascent conduits (e.g., dykes and inclined sheets), which facilitate magma evacuation and may feed volcanic eruptions, remains poorly documented in natural examples.

The excellently exposed silicic, sub-volcanic Miocene Reyðarártindur Laccolith in SE Iceland offers an opportunity to investigate how magma ascent within inclined sheets, which emanated from the laccolith, related to intrusion construction and deformation in the surrounding host rock. We combine detailed structural mapping with anisotropy of magnetic susceptibility (AMS) analyses, which allow us to map magnetic rock fabrics that reflect magma flow patterns, to show that the laccolith comprises of several distinct magma lobes that intruded laterally towards the south-west. Each lobe intruded, inflated, and coalesced along a NE-SW primary axis facilitated by doming (i.e., forced folding) of the host rock. We also shown that pre-existing NNE-striking, left-stepping, en-echelon fault/fractures, as well as those generated during intrusion-induced host rock uplift, host moderately to steeply inclined rhyolitic/granophyric sheets that emanate from the lateral terminations of some flow lobes.

Based on the observed geometrical relationships between AMS fabrics and the sheet margins where magnetic foliations subparallel sheet contacts, or characterize an imbrication fabric, we suggest that magma evacuated moderately to steeply upward via these fault/fracture-controlled sheets. As these inclined sheets dip towards the laccolith, any eruptions they may have fed would have been laterally offset from the laccolith and any overlying surface deformation driven by forced folding. Our study shows that magma evacuation and ascent from laccoliths can be facilitated by inclined sheets that form at the lateral terminations of magma lobes that are spatially controlled by laccolith construction (e.g., flow direction and doming of the host rock) and the presence of pre-existing structures.

How to cite: Twomey, V., McCarthy, W., and Magee, C.: Structural controls on the emplacement and evacuation of magma from a sub-volcanic laccolith: Reyðarártindur Laccolith, SE Iceland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14930, https://doi.org/10.5194/egusphere-egu21-14930, 2021.

EGU21-15769 | vPICO presentations | GMPV9.5

3D Gravity modeling of the volcanic island of Surtsey, Iceland

sara sayyadi, Magnús T. Gudmundsson, Thórdís Högnadóttir, James White, Joaquín M.C. Belart, and Marie D. Jackson

The formation of the oceanic island Surtsey in the shallow ocean off the south coast of Iceland in 1963-1967 remains one of the best-studied examples of basaltic emergent volcanism to date. The island was built by both explosive, phreatomagmatic phases and by effusive activity forming lava shields covering parts of the explosively formed tuff cones.  Constraints on the subsurface structure of Surtsey achieved mainly based on the documented evolution during eruption and from drill cores in 1979 and in the ICDP-supported SUSTAIN drilling expedition in 2017(an inclined hole, directed 35° from the vertical). The 2017 drilling confirmed the existence of a diatreme, cut into the sedimentary pre-eruption seafloor (Jackson et al., 2019). 

We use 3D-gravity modeling, constrained by the stratigraphy from the drillholes to study the structure of the island and the underlying diatreme.  Detailed gravity data were obtained on Surtsey in July 2014 with a gravity station spacing of ~100 m. Density measurements for the seafloor sedimentary and tephra samples of the surface were carried out using the ASTM1 protocol. By comparing the results with specific gravity measurements of cores from drillhole in 2017, a density contrast of about 200 kg m-3 was found between the lapilli tuffs of the diatreme and the seafloor sediments.  Our approach is to divide the island into four main units of distinct density: (1) tuffs above sea level, (2) tuffs below sea level, (3) lavas above sea level, and (4) a lava delta below sea level, composed of breccias over which the lava advanced during the effusive eruption.  The boundaries between the bodies are defined from the eruption history and mapping done during the eruption, aided by the drill cores. 

A complete Bouguer anomaly map is obtained by calculating a total terrain correction by applying the Nagy formula to dense DEMs (5 m spacing out to 1.2 km from station, 200 m spacing between 1.2 km and 50 km) of both island topography and ocean bathymetry.  Through the application of both forward and inverse modeling, using the GM-SYS 3D software, the results provide a 3-D model of the island itself, as well as constraints on diatreme shape and depth.

How to cite: sayyadi, S., T. Gudmundsson, M., Högnadóttir, T., White, J., M.C. Belart, J., and D. Jackson, M.: 3D Gravity modeling of the volcanic island of Surtsey, Iceland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15769, https://doi.org/10.5194/egusphere-egu21-15769, 2021.

EGU21-13845 | vPICO presentations | GMPV9.5

Crustal folds alter local stress fields as demonstrated by magma sheet – fold interactions in the Central Andes

Matías Clunes, John Browning, José Cembrano, Carlos Marquardt, and Agust Gudmundsson

For magma chambers to form or volcanic eruptions to occur magma must propagate through the crust as dikes, inclined sheets and sills. The vast majority of models that investigate magma paths assume the crust to be either homogeneous or horizontally layered, often composed of rocks of contrasting mechanical properties. In subduction regions that have experienced orogenesis, like the Andes, the crust has been deformed over several million years, resulting in rock layers that are commonly folded and steeply dipping. The assumption of homogeneous properties or horizontal layering then does not capture all of the potential magma path crustal interactions. Here we tackle this problem by determining the effect of a crust made of steeply inclined layers in which sills and inclined sheets are emplaced. We combine field observations from a sill emplaced in the core of an anticlinal fold at El Juncal in the Chilean Central Andes, such as lithologies, sill and fold limbs attitude, sill length and layers and sill thickness, with a suite of finite element method models to explore the mechanical interactions between inclined layers and magma paths. Our results demonstrate that the properties of the host rock layers as well as the contacts between the layers and the crustal geometry all play an important role on magma propagation and emplacement at shallow levels. Sill propagation and emplacement through heterogeneous and anisotropic crustal segments changes the crustal stress field promoting sill arrest, deflection or propagation. Specifically, sills are more likely to be deflected when encountering shallow dipping layers rather than steeply dipping layers of a fold. Mechanically weak contacts encourage sill deflection due to the related rotation of the maximum principal compressive stress and this effect is attenuated when the fold layers are more steeply dipping. This processes may change the amount and style of surface deformation recorded, with significant implications for monitoring of active volcanoes.

How to cite: Clunes, M., Browning, J., Cembrano, J., Marquardt, C., and Gudmundsson, A.: Crustal folds alter local stress fields as demonstrated by magma sheet – fold interactions in the Central Andes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13845, https://doi.org/10.5194/egusphere-egu21-13845, 2021.

EGU21-9519 | vPICO presentations | GMPV9.5

Could the Liquiñe-Ofqui fault zone promote the 2011 Cordon Caulle eruption ?

Camila Novoa Lizama, Muriel Gerbault, Dominique Rémy, José Cembrano, Luis Lara, Andres Tassara, riad Hassani, Juan Carlos Baez, and Javiera Ruz

The 2011-2012 Cordon-Caulle eruption was the largest subaerial eruption of the 21th century. An inflation captured from InSAR between 2007 and 2009 was related to a volume of magma injection too small to have triggered this eruption. Here, we benefit from SAR imagery acquired by ALOS-1, ENVISAT and SENTINEL-1 data, to analyze the temporal and spatial behavior of ground displacements before, during and after the eruption. We find that a similar prolate spheroidal source explains the data for the pre-eruptive and post-eruptive periods. Then we explore two tectonically-related hypotheses to explain the observed displacements during the explosive phase of the eruption. Therefore, first we model InSAR data using standard inversion models to evaluate how slip motion along specific structures explain surface observations. Our results show that the explosive phase's ground displacements could have been produced either by the collapse of the caldera and the graben overriding the reservoir, or by slip motion along a dextral-strike slip fault zone related to the North-South trending Liquiñe-Ofqui fault zone. Second, we use 3D numerical models and elasto-plasticity to assess the failure conditions along both structures resulting from an overpressure applied at the wall of the prolate-spheroidal reservoir. Our results show that a magma injection consistent with the 2007-2009  inflation signal rather promotes constriction at the roof of the reservoir, which tends to impede fluid flow towards the surface. The presence of a relatively weak graben-caldera structure in our models show that this constrictional area is enhanced. On the other hand, the elasto-plastic pattern resulting from the application of a dextral-slip motion along the LOFZ branch-fault generates a dilatational plastic zone that connects the reservoir wall to the surface, where it coincides with the location of the 2011 eruption. Hence we propose that the LOFZ branch-fault, weakened during the pre-eruptive inflation phase, destabilized and slipped two years later in a way that it served as open channels for fluid migration from the magma reservoir up to the surface.

How to cite: Novoa Lizama, C., Gerbault, M., Rémy, D., Cembrano, J., Lara, L., Tassara, A., Hassani, R., Baez, J. C., and Ruz, J.: Could the Liquiñe-Ofqui fault zone promote the 2011 Cordon Caulle eruption ?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9519, https://doi.org/10.5194/egusphere-egu21-9519, 2021.

EGU21-9211 | vPICO presentations | GMPV9.5

The continued 2008-2010 subsidence of Dallol on the spreading Erta Ale ridge: InSAR observations and source models

Maurizio Battaglia, Carolina Pagli, and Stefano Meuti

Volcanoes commonly subside during eruptions as magma flows out of a chamber, but continued subsidence during non-eruptive episodes is not easy to explain. In this work, we use InSAR and source modelling to understand the causes of the continued subsidence of Dallol, a nascent volcano along the spreading Erta Ale ridge of Afar (Ethiopia). The Dallol volcano never erupted and no volcanic deposits originating from the volcano exists at the surface. Recent seismicity, diking and continuous deformation of a crustal magma chamber indicate the Dallol is a nascent central volcano with its own rift segment. An active magma plumbing exists and the injection of a dike beneath the volcano was imaged in 2004 from InSAR data. This unrest episode was followed by complete quiescence until subsidence started in 2008. We analysed InSAR data from 2004-2010 to create time-series of line-of-sight (LOS) surface deformation. Average velocity maps show that subsidence centred at Dallol initiated in October 2008 and continued as far as February 2010 at an approximately regular rate of up to 10 cm/yr. The inversion of InSAR average velocities found that a sill-like source, located a depth between 1.2 and 1.5 km under Dallol with a mean volume change of  -0.62 to -0.53 106 km3/yr and a radius of approximately 1.6 km, best fits the InSAR observations. The observed volume change could be explained by changes in pore fluid pressure in a confined hydrothermal aquifer or by thermoelastic deformation caused by changes in temperature in a volume of rock. Simple models of poro-elastic and thermo-elastic contraction indicates that the observed deformation would require either a decrease in pore fluid pressure of the order of 10-2G, where G is the rock shear modulus, or a decrease in temperature between 60 °C and 80 °C.  

How to cite: Battaglia, M., Pagli, C., and Meuti, S.: The continued 2008-2010 subsidence of Dallol on the spreading Erta Ale ridge: InSAR observations and source models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9211, https://doi.org/10.5194/egusphere-egu21-9211, 2021.

EGU21-8464 | vPICO presentations | GMPV9.5

Deformation patterns in Canary Islands volcanic area from GNSS data analysis

Umberto Riccardi, Josè Arnoso, Maite Benavent, Umberto Tammaro, Fuensanta G. Montesinos, Isabel Blanco-Montenegro, and Emilio Vélez

We present a study of the deformation pattern along the Canary archipelago through the analysis of continuous GNSS data. We use data spanning 2011–2017 period to retrieve precise horizontal displacements and a broad calculation of the strain. Geodetic data are interpreted in light of the regional tectonics, which is proven to play a key role in the volcanic eruptions that take place in the archipelago. The common-mode component filtering technique is applied to improve the signal-to-noise ratio of the time series of the GNSS daily solutions before retrieving the geodetic velocities. Through a triangular segmentation approach, we retrieve the 2D infinitesimal strain from the velocities along the Canaries and map deformation patterns in various sectors of the volcanic archipelago. We found areas of maximum deformation west of Tenerife, Gran Canaria and Fuerteventura Islands. A sharp change in shear strain between Tenerife and Gran Canaria is recognized, delineating a sector of intense seismicity, which is mostly associated with a well-known major submarine fault that separates the two insular edifices. On this submarine tectonic structure, we have performed a tentative simulation of the horizontal deformation and strain caused by one of the strongest (mbLg 5.2) earthquakes of the region. Our strain analysis supports the possibility that the main tectonic lineaments are being influenced by the regional stress field. Furthermore, the seismic areas between islands seem mainly influenced by the regional tectonic stress, rather than by the local volcanic activity. This is in accordance with the extensional and compressional tectonic regimes, already identified by other authors, which might favour episodes of volcanism in this volcanic archipelago.

How to cite: Riccardi, U., Arnoso, J., Benavent, M., Tammaro, U., Montesinos, F. G., Blanco-Montenegro, I., and Vélez, E.: Deformation patterns in Canary Islands volcanic area from GNSS data analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8464, https://doi.org/10.5194/egusphere-egu21-8464, 2021.

EGU21-9702 | vPICO presentations | GMPV9.5

Thermal history of the Siberian platform: Apatite Fission-Track data from the Permian-Triassic magmatic complexes

Tatyana Bagdasaryan, Roman Veselovskiy, Viktor Zaitsev, and Anton Latyshev

The largest continental igneous province, the Siberian Traps, was formed within the Siberian platform at the Paleozoic-Mesozoic boundary, ca. 252 million years ago. Despite the continuous and extensive investigation of the duration and rate of trap magmatism on the Siberian platform, these questions are still debated. Moreover, the post-Paleozoic thermal history of the Siberian platform is almost unknown. This study aims to reconstruct the thermal history of the Siberian platform during the last 250 Myr using the low-temperature thermochronometry. We have studied intrusive complexes from different parts of the Siberian platform, such as the Kotuy dike, the Odikhincha, Magan and Essey ultrabasic alkaline massifs, the Norilsk-1 and Kontayskaya intrusions, and the Padunsky sill. We use apatite fission-track (AFT) thermochronology to assess the time since the rocks were cooled below 110℃. Obtained AFT ages (207-173 Ma) are much younger than available U-Pb and Ar/Ar ages of the traps. This pattern might be interpreted as a long cooling of the studied rocks after their emplacement ca. 250 Ma, but this looks quite unlikely because contradicts to the geological observations. Most likely, the rocks were buried under a thick volcanic-sedimentary cover and then exhumed and cooled below 110℃ ca. 207-173 Ma. Considering the increased geothermal gradient up to 50℃/km at that times, we can estimate the thickness of the removed overlying volcanic-sedimentary cover up to 207-173 Ma as about 2-3 km.

The research was carried out with the support of RFBR (grants 20-35-90066, 18-35-20058, 18-05-00590 and 18-05-70094) and the Program of development of Lomonosov Moscow State University.

How to cite: Bagdasaryan, T., Veselovskiy, R., Zaitsev, V., and Latyshev, A.: Thermal history of the Siberian platform: Apatite Fission-Track data from the Permian-Triassic magmatic complexes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9702, https://doi.org/10.5194/egusphere-egu21-9702, 2021.

EGU21-11191 | vPICO presentations | GMPV9.5

Thermomechanical Controls on the Timing of Magma Reservoir Failure in a Viscoelastic Crust

Matthew Head, James Hickey, Joe Thompson, Joachim Gottsmann, and Nicolas Fournier

As volcanic systems undergo unrest, understanding the conditions required for reservoir failure, the associated timescales, and the links to geophysical observations are critical when evaluating the potential for eruption. The characteristics and dynamics of a pressurised magmatic system can be inferred from episodes of surface deformation, but this process is heavily reliant on the assumed crustal rheology. In volcanic regions, shallow or long-lived magmatic systems can significantly perturb the regional geothermal gradient, altering the rheology of the surrounding crustal rock. Viscoelasticity incorporates a time-dependent viscous deformation response, accounting for the increased ductility and thermomechanical heterogeneity induced by the modelled reservoir.

Here, we investigate the influence of an imposed thermal regime on the critical reservoir overpressure (OPc) required to facilitate failure in elastic and viscoelastic models, alongside the predicted critical surface uplift (Uc). By evaluating tensile and Mohr-Coulomb failure criteria on the reservoir walls, we can determine the mechanical stability of the magma reservoir and identify the conditions that are susceptible to failure. We explore a range of reservoir temperatures (representing felsic, intermediate, and mafic magma compositions) and background geothermal gradients, to simulate varied volcanic regions, and use the Standard Linear Solid viscoelastic rheology together with a temperature-dependent viscosity structure, calculated from the thermal constraints. The models incorporate mechanical heterogeneity in the form of a temperature-dependent Young’s modulus, accounting for the thermal weakening of the surrounding crustal rock. We use an overpressure rate of 10 MPa yr-1, in excess of lithostatic pressure, that produces an average elastic volumetric strain rate of ~3-7x10-12 s-1, depending on the imposed thermal regime.

We show that reservoir failure is systematically inhibited by incorporating viscoelasticity, with OPc for Mohr-Coulomb failure increasing by up to 65% with respect to the corresponding elastic model. The greatest increases in OPc, and Uc, are observed when pairing cool reservoir temperatures (i.e., felsic composition) with low background geothermal gradients. In contrast, stress partitioning due to the viscoelastic crustal rheology promotes failure at the ground surface, decreasing the required OPc for tensile failure by up to 32%. The greatest reductions in OPc are produced in models that couple a hot reservoir temperature (i.e., mafic composition) with low background geothermal gradients. By resisting mechanical failure on the reservoir wall, temperature-dependent viscoelasticity impacts the conditions required for dyke nucleation and propagation. Further to this, a viscoelastic crustal rheology dramatically reduces the timescales for throughgoing failure; complete brittle failure connecting the reservoir to the ground surface. This occurs much earlier than suggested by elastic models, which could have implications for interpreting the conditions, and onset, of a potential eruption.

How to cite: Head, M., Hickey, J., Thompson, J., Gottsmann, J., and Fournier, N.: Thermomechanical Controls on the Timing of Magma Reservoir Failure in a Viscoelastic Crust, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11191, https://doi.org/10.5194/egusphere-egu21-11191, 2021.

EGU21-1397 | vPICO presentations | GMPV9.5

Deformation driven magma ascent in stratified magma reservoirs: an experimental study

Amy Ryan, Mark Zimmerman, and Lars Hansen

Mature volcanic systems (e.g., Yellowstone, USA; Campi Flegrei, Italy) are fed by stratified magma reservoirs – small bodies of eruptible, crystal-poor silicic magma are suspended within a larger volume of non-eruptible, crystal-rich mush. Lavas erupted from these systems record geochemical evidence for long-term (103 to 105 years) deep storage followed by short (<1 to 103 years) residences in shallow chambers prior to eruption. Evidence for protracted magma ascent is frequently absent, suggesting deep-seated magmas rise quickly in reservoirs despite the high viscosity and low permeability of crystal-rich mushes. We hypothesize that deformation of a reservoir (by intrusion of new magma, passing seismic waves, tectonic stresses, etc.) allows low viscosity magmas to intrude high viscosity mush, creating mechanical instabilities that focus magma migration and facilitate rapid magma ascent through the reservoir.

To test this hypothesis, we are conducting high-temperature and high-pressure deformation experiments in a gas-medium, Paterson apparatus. Samples consist of a disk of soda lime glass (“magma”) stacked in series with a disk of a composite (“mush”) composed of borosilicate glass and fine quartz sand (44-106 μm). The mush has a crystal fraction of 80%. The stacked magma and mush disks are overlain by permeable ceramics. Sample assemblies are heated to 900°C (above the glass transition temperatures for soda lime and borosilicate glasses) and pressurized to 200 MPa confining pressure. At 900°C the magma viscosity is 104 Pa s and the mush viscosity is ~1012-1014 Pa s. Following heating and pressurization, samples either dwell at high P-T conditions for extended time or are subjected to axial compression (strain rates of 10-5-10-3 s-1; shortening up to 50% of the length of the mush disk) or pore pressure gradients (a pressure difference across the sample of 10-150 MPa, equivalent to 2-30 MPa/mm over the length of the mush disk). After dwelling or deformation, samples are rapidly quenched and decompressed, cut in longitudinal sections and polished. Polished samples are analyzed in an SEM to collect back-scatter electron images and compositional maps. BSE images can be used to look for melt structures (e.g., viscous channels, dikes) that form in the mush during deformation. The compositions of magma (soda lime) and mush (borosilicate) melts are different, therefore compositional maps can be used to look for their respective spatial distributions. In static experiments, no magma intrudes the mush. We expect deformation to facilitate magma intrusion and that the volume of intruding magma will increase with increasing strain rate, strain and pore pressure gradient. These experiments will shed light on the role deformation plays in instigating magma ascent in stratified magma reservoirs.

How to cite: Ryan, A., Zimmerman, M., and Hansen, L.: Deformation driven magma ascent in stratified magma reservoirs: an experimental study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1397, https://doi.org/10.5194/egusphere-egu21-1397, 2021.

EGU21-976 | vPICO presentations | GMPV9.5

Influence of geometry on eruptive behaviour of magma reservoirs

Martin Letourneur, John O'Sullivan, Darren Gravley, Guilherme Gualda, and David Dempsey

All active polygenetic volcanoes erupt magma sourced from a shallow crustal reservoir.  Those chambers are complex entities that act as a collector of magma originating from deeper crustal sources. The geometry of those active storage systems depends on the rheology of the magma and on the rock properties of the host. Studying how the geometry influences the eruptive behaviour of a magma chamber has implications for our understanding of volcanic hazard.
We introduced a simple model where a magma reservoir is cooled by an overlying geothermal system and recharged by a deeper magma source. The geometry of the chamber is defined by its volume and aspect ratio. The model tracked changes in pressure, mixture enthalpy and composition, and implemented parameterisations of eruption, hydrothermal cooling, viscoelastic relaxation, and volatile leakage. The thermodynamic properties of the melt, crystals and water were computed using rhyolite-MELTS.
A large number of simulations sweeping our parameter space gave us insight into how the different magmatic processes trade off with respect to the geometry of the inclusion. An example of the complex control of geometry on the eruptive behaviour can be made regarding cooling and the effective compressibility of an ellipsoidal inclusion. On the one hand, a larger aspect ratio will favor eruptibility by offering a larger area for cooling therefore increasing the exsolution of water and pressure build up. On the other hand, a larger aspect ratio will work against eruptibility by decreasing the compressibility making it harder to build overpressures within the chamber. We found that a specific geometry is required in order for a chamber to erupt without any external stimuli (such as a large recharge event).
A limiting factor of our model is the assumption of a perfect mixing. Whereas, in reality, we would expect recharge, cooling and leakage to occur within specific regions of the chamber. In a model where mixing is not considered perfect, those processes would be a source of heterogeneity. We could conjecture that under the right conditions, eruptible regions would appear within the chamber. A model focusing more on the flows within the chamber might be able to give additional insights on the eruptive behaviour of magma chambers.

How to cite: Letourneur, M., O'Sullivan, J., Gravley, D., Gualda, G., and Dempsey, D.: Influence of geometry on eruptive behaviour of magma reservoirs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-976, https://doi.org/10.5194/egusphere-egu21-976, 2021.

EGU21-9258 | vPICO presentations | GMPV9.5

Insights into the poroelastic mechanical behaviour of a crystalline magma reservoir and its influence on modelling volcano surface deformation 

Rami Alshembari, James Hickey, Ben Williamson, and Katharine Cashman

Understanding the physical properties of magma reservoirs and their fluid/mechanical behaviour is crucial for improving geophysical models. New evidence suggests that large bodies of magma are difficult to maintain for an extended time period and that melts may instead reside within crystal-mush reservoirs which consist of variably packed frameworks of crystals and interstitial melt. Most existing volcano deformation models assume a pressurized cavity embedded in a homogeneous or heterogenous elastic half-space and therefore ignore the presence of crystals and the possible poroelastic mechanical response to melt intrusion or withdrawal. Here, we consider the magma reservoir to be entirely porous, comprising melt distributed between solid crystals. We investigate the influence of poroelastic mechanical behaviour on reservoir pressure development and resultant spatio-temporal surface deformation. We examine the post-intrusion and post-eruption time-dependent pressure evolution in the magma reservoir due to melt diffusion in the porous domain. Unlike the classic (cavity) models for volcanic surface deformation, an observable post-eruptive or post-intrusion time-dependent inflation can occur without an additional mass change if the reservoir is sufficiently permeable. Post-intrusion and post-eruption timescales vary depending on the porosity of the mush (melt fraction), permeability and magma viscosity. Our study confirms that reservoir inflation and surface deformation can occur without an intrusion or withdrawal of melt but are instead controlled by the mush's poroelastic behaviour. 

 

How to cite: Alshembari, R., Hickey, J., Williamson, B., and Cashman, K.: Insights into the poroelastic mechanical behaviour of a crystalline magma reservoir and its influence on modelling volcano surface deformation , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9258, https://doi.org/10.5194/egusphere-egu21-9258, 2021.

EGU21-8628 | vPICO presentations | GMPV9.5

Propagation velocity of magma intrusions, a new 2D numerical approach

Severine Furst, Virginie Pinel, and Francesco Maccaferri

The tortuous travel of magma through the crust may sometimes result in volcanic eruptions at the surface. In the brittle crust, magma propagation usually occurs by fracturing the rock and opening its own way through them. This process of diking is controlled by the interaction of many complex physical processes including rock fracture, flow of compressible fluids, phase transitions, heat exchange. Current models of dikes consider either a fracturing-dominated approach, that neglects the viscous flow and allow to estimate the trajectory of dike propagation, or a viscous-dominated approach that neglects the fracturing at the dike tip allowing to infer the propagation velocity of the dike. Here we propose a new numerical approach aiming at modeling both the magma path and velocity. We start from a two-dimensional Boundary Element model solving for the trajectory of a quasi-static crack in an elastic medium subjected to external stress (Maccaferri et al, 2011), and implement the effects of the viscous fluid flow assuming a Poiseuille flow. We build on the previous work by Dahm (2000) but relaxing the assumption of stationarity, and thus allowing to take into account heterogeneous crustal stresses, complex dike paths, and dike velocity variations. The fluid flow results in a viscous pressure drop applied to the crack wall, which modifies the crack shape and contributes to the energy balance of the propagating dike. In fact, the energy dissipated by viscous flow is linearly dependant on the viscosity of the fluid and the crack velocity. It follows that the velocity can be inferred from the total energy budget by imposing that the viscous energy dissipation and the energy spent to fracture the rocks equals the strain-plus-gravitational energy release. However, the viscous dissipation strongly depends on the opening of each dislocation element, causing numerical instabilities in the calculation of the dike velocity due to the fracture closure at the dike tail. We will present first results of velocities derived with this approach considering only a static crack shape (that is to say neglecting the modification of the crack shape induced by the flow). We will discuss the influence of various parameters (crack size, Young’s modulus value...), and will compare the numerical velocities obtained with observations, first considering velocities measured in analogue experiments when injecting fluids of various viscosity (air and oils) in gelatin tanks, and secondly using diking events documented at basaltic volcanoes (such as Piton de la Fournaise (Réunion) and Mount Etna (Sicily)).

How to cite: Furst, S., Pinel, V., and Maccaferri, F.: Propagation velocity of magma intrusions, a new 2D numerical approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8628, https://doi.org/10.5194/egusphere-egu21-8628, 2021.

EGU21-9810 | vPICO presentations | GMPV9.5

Flow and fracturing conditions before the segmentation of experimental dikes 

Jazmin Chavez and Mariano Cerca

The uprise of  magma dikes that split in branches  are regularly outcropping as en echelon structures, segmented dikes, or finger like intrusions are documented examples. Dike segmentation and finger formation at different scales have been attributed commonly to effects of the host rock: 1) crustal heterogeneities that interact with the magma such as faults, fractures, and joints; 2) local rotation of the principal stress axes orientations during emplacement;  3) changes in the host rock elastic properties due to chemical corrosion, unconsolidation and weathering. Less attention has been devoted to the effect of the magma flow in leading to segmentation and formation of fingers, but the effect of fluid flow might be relevant due to the complex flow dynamics of magmas.  In past experiments presented by  Chavez-Alvarez et al.  (2020a) and Chavez-Alvarez and Cerca (2020b), he relevance of viscous forces in hydrofracturing was analyzed by quantitatively comparing the evolution of experimental dikes of contrasting rheology (Newtonian and shear thinning), where segmentation was documented for the case of shear thinning fluids. Here we provide an analysis of the hydrofracturing conditions that prevail before the segmentation of hydrofractures that transport shear thinning fluids. We evaluated parameters of toughness and viscous regimes in conditions of the hydrocrack inception, early development and propagation before segmentation. Furthermore some aspects of the flow such as Reynolds number and flow trajectories inside the experimental dikes are presented. 

References

Chàvez-Alvarez, M. J., Cerca-Martìnez, M. Bustos-Cervantes N. 2020a. Contrasting emplacement modes of water (Newtonian) and Carbopol suspension (shear thinning) injected in gelatin: insights for magma dikes.   (In revision).

Chàvez-Alvarez, M. J. and Cerca-Martìnez, M. 2020b: Dyke segmentation: an experimental approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13768, https://doi.org/10.5194/egusphere-egu2020-13768, 2020

 

How to cite: Chavez, J. and Cerca, M.: Flow and fracturing conditions before the segmentation of experimental dikes , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9810, https://doi.org/10.5194/egusphere-egu21-9810, 2021.

EGU21-8749 | vPICO presentations | GMPV9.5

Elliptical Versus Cylindrical Magma Conduits

Eliot Eaton, Jurgen Neuberg, and Luke Marsden

By modelling the magnitude and spatial distribution of surface displacement induced by different representations of magma conduits, more informed decisions can be made for the deployment of real-time monitoring devices, such as tiltmeters, and aid interpretations of stress changes within the subsurface. The existence of varying forms of magma conduit is widely known, despite this, the effect of laterally elongated conduits on magma flow processes and resulting surface deformation at volcanoes has not been systematically explored.

By varying the ellipticity of the volcanic conduit cross-section we assess the relative importance of laterally elongated conduits when considering flow processes and surface deformation. The scenario of magma ascent through a dyke that changes into a cylindrical conduit closer to the surface is also considered, herein referred to as a complex conduit. Both shear stress on the conduit walls due to viscous magma flow resistance and the pressurisation of conduits are used as source mechanisms.

When considering the pressurisation of different conduit geometries, the displacement field induced by an elongated conduit (where semi-axes a and b of the elliptical cross-section equal a=10b) is an order of magnitude larger than that of a cylindrical conduit. Moreover, for the case of the complex conduit, the displacement field is dominated by the dyke form of the deeper conduit, with little influence from the transition region between elongated and cylindrical conduit. When considering shear stress as a source mechanism, the displacement field induced is primarily vertical and radially symmetric even at the smallest spatial scales ($<1$ km), independent of ellipticity of conduit origin. The ellipticity of conduits with equal cross-sectional area has a significant control on the flow rate, and therefore, the magnitude of shear stress achieved under equal pressure gradients. The deformation resulting from shear stress on the conduit walls is also influenced by the depth of rheological changes within the magma and the inter-dependency with conduit geometry.

How to cite: Eaton, E., Neuberg, J., and Marsden, L.: Elliptical Versus Cylindrical Magma Conduits, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8749, https://doi.org/10.5194/egusphere-egu21-8749, 2021.

EGU21-13325 | vPICO presentations | GMPV9.5

Beyond elasticity: Are Coulomb properties of the Earth’s crust important for volcano geodesy?

Håvard Svanes Bertelsen, Frank Guldstrand, Sigmundsson Freysteinn, Rikke Pedersen, Karen Mair, and Olivier Galland

Geodetic modelling has become an established procedure to interpret the dynamics of active volcanic plumbing systems. Most established geodetic models implemented for inverting geodetic data share similar physical assumptions: (1) the Earth's crust is modelled as an infinite, homogeneous elastic half-space with a flat surface, (2) there is no anisotropic horizontal stress to simulate tectonic stresses, (3) the source boundary conditions are kinematic, i.e., they account for an instantaneous inflation or deflation of the source. Field and geophysical observations, however, provide evidence that significant inelastic shear deformation of the host rock can accommodate the propagation of dykes and sills. We show that inelastic processes accommodating the emplacement of dykes in the brittle crust have large implications for dyke-induced surface deformation patterns.

We present two quantitative laboratory experiments that simulate two distinct dyke emplacement mechanisms, in agreement with geological and geophysical observations: (1) dyke propagation as a tensile fracture through a dominantly elastic host in gelatin, and (2) dyke propagation in the silica flour as viscous indenter, which pushes its ahead plastic host that dominantly fails in shear. The syn-emplacement surface deformation is monitored during each experiment. Each dyke emplacement mechanism triggers drastically distinct surface deformation patterns: two uplifting bulges separated by a trough in the gelatin experiment, in good agreement with the expected dyke-induced deformation predicted by the rectangular dislocation model, versus a single uplifting elongated bulge above the apex of the dyke in the silica flour experiment. This first-order difference shows that (1) the rheology of the host and the emplacement mechanisms of dykes are key factors for interpreting dyke-induced geodetic data at active volcanoes, and (2) static, kinematic geodetic models, such as the rectangular dislocation model, have limitations for revealing the physics and dynamics of volcanic plumbing systems.

There is no geodetic model associated with dyke emplacement able to reproduce the single uplifting bulge measured in our silica flour experiment. Instead, such surface deformation pattern is usually fitted with geodetic models of inflating spherical, ellipsoidal or horizontal planar sources. Our silica flour experiment thus shows that (1) a successful data fit is not sufficient and does not imply a physically relevant interpretation, and (2) dykes emplaced as viscous indenters should be considered as an alternative interpretation of single uplifting bulges measured at active volcanoes. This implies that novel geodetic models accounting for dykes emplaced as viscous indenters should be designed to interpret dyke-induced surface deformation patterns in favorable geological settings, e.g. felsic volcanoes.

In summary, our study motivates the design of new geodetic models that move beyond elasticity, i.e. that account for the realistic elasto-plastic mechanical behavior we know occurs in the Earth's brittle crust. In addition, it highlights the added value of our laboratory volcano geodesy approach, which can be the foundation for designing novel geodetic models that accounts for processes that cannot be implemented in numerical models.

How to cite: Bertelsen, H. S., Guldstrand, F., Freysteinn, S., Pedersen, R., Mair, K., and Galland, O.: Beyond elasticity: Are Coulomb properties of the Earth’s crust important for volcano geodesy?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13325, https://doi.org/10.5194/egusphere-egu21-13325, 2021.

EGU21-8282 | vPICO presentations | GMPV9.5

A numerical approach for modeling thermo-poro-elastic deformation sources in volcanic and hydrothermal regions.

Massimo Nespoli, Maria Elina Belardinelli, and Maurizio Bonafede

The Thermo-Poro-Elastic (TPE) inclusions contribute to deformation and stress in volcanic and hydrothermal areas. Differently from other deformation source models (e.g. magma chambers), the TPE sources effects are due to pore-pressure and temperature changes of the fluid within the inclusion. So that the TPE inclusions can allow large deformations even in those volcanic environments in which there is no evidence of a shallow magmatic body. This kind of sources also provides large deviatoric stresses, promoting different types of focal mechanisms both inside and around them. With respect to a previous work, we propose a numerical model that allows for a more realistic representation of TPE sources: we can represent inclusions with an arbitrary geometry and we take into account the elastic stratification of the crust, thanks to a modified version of the EDGRN/EDCMP code. We can also represent the case of a depth dependent distribution of pore pressure and temperature changes within inclusions, as expected during the transient stage of fluid propagation and temperature diffusion. We found that elastic layering and transient changes of the TPE source can promote both normal and thrust earthquakes in its interior. For the 1982-84 unrest episode at Campi Flegrei the inversion of geodetic data leads to a lower misfit between modeled and measured deformation data, with respect to a homogeneous medium and the retrieved geometry and location of the thermo-poro-elastic are in good agreement with the observed distribution of seismicity.

How to cite: Nespoli, M., Belardinelli, M. E., and Bonafede, M.: A numerical approach for modeling thermo-poro-elastic deformation sources in volcanic and hydrothermal regions., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8282, https://doi.org/10.5194/egusphere-egu21-8282, 2021.

EGU21-4887 | vPICO presentations | GMPV9.5

Analytical modelling and joint inversion of surface displacements and gravity changes at volcanoes

Mehdi Nikkhoo and Eleonora Rivalta

Gravity change observations at volcanoes provide information on the location and mass change of intruded magma bodies. Gravity change and surface displacement observations are often combined in order to infer the density of the intruded materials. Previous studies have highlighted that it is crucial to account for magma compressibility and the shape of the gravity change and deformation source to avoid large biases in the density estimate. Currently, an analytical model for the deformation field and gravity change due to a source of arbitrary shape is lacking, affecting our ability to perform rapid inversions and assess the nature of volcanic unrest.  

Here, we propose an efficient approach for rapid joint-inversions of surface displacement and gravity change observations associated with underground pressurized reservoirs. We derive analytical solutions for deformations and gravity changes due to the volume changes of triaxial point-sources in an isotropic elastic half-space. The method can be applied to  volcanic reservoirs that are deep compared to their size (far field approximation). We show that the gravity changes not only allow inferring mass changes within the reservoirs, but also help better constrain location, shape and the volume change of the source. We discuss how the inherent uncertainties in the realistic shape of volcanic reservoirs are reflected in large uncertainties on the density estimates. We apply our approach to the surface displacements and gravity changes at Long Valley caldera over the 1985-1999 time period. We show that gravity changes together with only vertical displacements are sufficient to constrain the mass change and all the other source parameters. We also show that while mass change is well constrained by gravity change observations the density estimate is more uncertain even if the magma compressibility is accounted for in the model.

How to cite: Nikkhoo, M. and Rivalta, E.: Analytical modelling and joint inversion of surface displacements and gravity changes at volcanoes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4887, https://doi.org/10.5194/egusphere-egu21-4887, 2021.

EGU21-503 | vPICO presentations | GMPV9.5 | Highlight

Pore fluid pressure evolution in volcanic environments: the role of rainfall

Jamie Farquharson and Falk Amelung

There is mounting evidence that rainfall can be instrumental in triggering or otherwise modulating primary volcanic activity. Individual case studies have revealed a link between rainfall and volcanism at Piton de la Fournaise (La Réunion), Mount St. Helens, Kīlauea (both USA), Las Pilas volcano (Nicaragua), and Soufrière Hills volcano (Montserrat), among others. Additionally, there exists a wealth of anecdotal evidence of rainfall-induced volcanism around the world. Do these discrete examples reflect a prevalent underlying link between rainfall and volcanic activity?

We extract and analyse multi-decadal rainfall timeseries from satellite data to assess whether the duration and timing of annual rainfall plays a role in modulating eruption frequency at different volcanoes. By comparing observed eruption distributions over time with the theoretical probability of those distributions, we identify around three dozen volcanic systems—~15 % of the volcanoes in our pre-filtered catalogue—where the eruption record appears to be strongly correlated with the wettest parts of the year. Our analyses reconfirm previous observations at several volcanoes and suggests that they are indeed symptomatic of a broader link between volcanism and the hydrological cycle.

Shallow-seated physical explanations often involve either the thermal contraction of recently-emplaced lava, fluid-induced pressurisation of the interior of a dome, or a combination of both. Deeper-seated mechanisms  include rainfall perturbing the regional stress within or applied by the volcanic edifice in one of two primary different ways: (a) by changing the load overlying the magma chamber, or (b) by changing the threshold for mechanical failure (either prompting opportunistic dyke propagation or directly facilitating magma chamber rupture).These mechanisms are underpinned by a single common process: the infiltration of meteoric water into the edifice.

We demonstrate that pressure transfer models yield pressure fluctuations at magma-relevant depths in line with previously theorised trigger stresses. Infiltration-induced quasistatic stresses can bring about a long-lived increase of pore pressure above hydrostatic, in contrast to the short-lived dynamic stress pulses observed at shallow depths. Assuming realistic fluid transport properties, we model pressure perturbations of order 10 kPa in the immediate subsurface, attenuating rapidly in the uppermost couple of kilometers. These pressure changes are a non-negligible fraction of the tensile strength of material thought to be important in dyke propagation, highlighting that the potential for time-variant fluid pressure within the edifice is an important consideration.

We anticipate that satellite-derived precipitation data will prove invaluable in integrating rainfall into future quantitative studies, volcano monitoring programs, and probabilistic hazard assessment. Aside from the possibility for initiation of primary volcanic activity, rainfall is a demonstrable driver of many secondary hazards, such as lahars, debris flows, mass movement, acid rain.  As ongoing climate change is projected to result in increasingly extreme rainfall patterns over the coming century, the potential for rainfall-triggered volcanic activity may be set to increase in the future. Rainfall is both measurable and, to a degree, forecastable: the inclusion of continuous ground- and satellite-based meteorological monitoring—in tandem with simple models of pressure transfer—could prove invaluable in providing some advance warning of these hazards.

How to cite: Farquharson, J. and Amelung, F.: Pore fluid pressure evolution in volcanic environments: the role of rainfall, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-503, https://doi.org/10.5194/egusphere-egu21-503, 2021.

EGU21-3204 | vPICO presentations | GMPV9.5

From permanent flank sliding to catastrophic collapse and explosive eruptions at basaltic volcanoes: the role of shallow intrusive magma bodies.

Andrea Di Muro, Ulrich Kueppers, Michael Heap, Fabian Scharzlmueller, and Donald Dingwell

Caldera collapses and flank failures, eventually associated with violent explosive eruptions, punctuate the history of volcanoes worldwide and represent major highly hazardous events in their evolution. Nevertheless, their link to magma transfer and storage in the plumbing system, together with the nature of weakness zones responsible for volcano collapses still need to be fully elucidated. We performed rapid decompression experiments on a set of basaltic rocks (lavas, dolerite dikes, gabbros) from Piton de la Fournaise, La Réunion, spanning a very large range of petrophysical properties. Samples derived from the most recent  caldera-related explosive breccias of this volcano. Petrophysical measurements revealed a corresponding variability in density, porosity, P-wave velocity (dry and wet), and uniaxial compressive strength. The large variation in P-wave velocity and strength is interpreted to be the result of the wide ranges in texture (porosity/vesicularity) and lithology. Notably, some of the dense gabbroic units that have remained intact despite likely having experienced several natural cycles of heating and cooling are comparatively weak. We infer that volcano instability should not be interpreted solely in terms of altered rock units. On one side, the interface between shallow intrusive bodies and the vesicular lava pile represents a potential interface for repeated sill emplacement, which favour flank sliding. On the other side, weak shallow seated granular intrusive rocks with variable amounts of interstitial melt respond in a brittle fashion to rapid decompression during caldera and flank collapse events. The large petrophysical heterogeneity of crustal rocks together with the occurrence of shallow intrusive bodies must be considered when interpreting monitoring data and assessing potential hazards related to the stability of basaltic volcanoes.

How to cite: Di Muro, A., Kueppers, U., Heap, M., Scharzlmueller, F., and Dingwell, D.: From permanent flank sliding to catastrophic collapse and explosive eruptions at basaltic volcanoes: the role of shallow intrusive magma bodies., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3204, https://doi.org/10.5194/egusphere-egu21-3204, 2021.

EGU21-3475 | vPICO presentations | GMPV9.5

Flank motion detected between 2010 and 2014 through InSAR time-series analysis at Pacaya Volcano, Guatemala

Judit Gonzalez Santana and Christelle Wauthier

Volcanic flank collapse has caused over 20,000 casualties in the past 400 years, and is one of the most dangerous hazards affecting communities and infrastructure near volcanoes. Flank instability has mostly been investigated at ocean volcanoes, due to their ability to trigger deadly tsunamis, however, these collapses are prevalent across volcanic settings, with all but one volcano in Guatemala with elevation over 2000m having experienced flank collapse, like Pacaya Volcano. At Pacaya, there is evidence for at least one past collapse, and transient SW flank motion has been identified accompanying vigorous eruptions in 2010 and 2014. We use InSAR time-series analysis to reveal, for the first time, long-term displacement of the SW flank of Pacaya during a period of volcanic quiescence from 2011-2013. This motion extended into 2014, with increased displacement rate attributed to dike intrusion during a major eruption. Subsequent static stress change analyses investigated the interactions between the modeled dike intrusion and detachment slip. Our research highlights that long-term flank motion might be more prevalent than currently recognized and that an awareness of existing structural weaknesses such as detachment faults and of possible magma-faulting interactions is vital when assessing the likelihood and style of volcanic flank collapse.

How to cite: Gonzalez Santana, J. and Wauthier, C.: Flank motion detected between 2010 and 2014 through InSAR time-series analysis at Pacaya Volcano, Guatemala, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3475, https://doi.org/10.5194/egusphere-egu21-3475, 2021.

EGU21-13573 | vPICO presentations | GMPV9.5

Characterising fracture patterns at growing lava domes

Amy Myers, Claire Harnett, Michael Heap, Eoghan Holohan, and Thomas Walter

Volcanic domes form when lava is too viscous to flow away from an active volcanic vent; instead, the lava accumulates into a mound consisting of a hotter, ductile core and a colder, brittle outer layer. An existing lava dome grows when new material is injected into the core of the dome, causing the  outer layer to stretch and develop tensile fractures. With continued dome growth, these weaknesses can propagate to form an extensive fracture network and the dome may fail. Collapse events often generate rock falls and debris avalanches, lahars, and high-speed pyroclastic flows, endangering populations residing at the base of a volcano. Since such fractures represent potential failure planes, in this project we aim to understand the role they have in destabilising lava domes.

This project will build on the work published by Harnett et al. (2018), which demonstrates the suitability of a discrete element modelling approach to simulate dome emplacement and evolution. Specifically, this project is designed to:

1. Use high-resolution photogrammetry to characterise the possible fracture states of a dome;

2. Establish up-scaled rock-mass properties by performing geomechanical experiments on both fractured and non-fractured samples of dome rock from prior collapses;

3. Develop a numerical model to investigate how the presence and properties of fracture networks influence dome stability.

The model, developed using PFC, will be used to identify critical fracture states that can signify a dome collapse is likely to occur. Under the current model, parallel bonds simulate the fluid magma core and flat joints simulate the solid talus material. This project will build on this original model by incorporating discrete fracture networks into the smooth-joint model to implement dome fracturing. The new model will look to investigate the effect  of a fracture network on a static dome that, when in its unfractured state, is stable under gravity. Additionally, the model will be designed such that inputs can include experimentally derived rock-mass properties. It is hoped that, by incorporating observational and experimental data into a more  complex model, the dynamic evolution of fractures in a growing lava dome can be investigated and the ongoing likelihood of a dome collapse event can be assessed.

 

Harnett, C. E. et al., 2018. J. Volcanol. Geoth. Res., 359: 68-77.

How to cite: Myers, A., Harnett, C., Heap, M., Holohan, E., and Walter, T.: Characterising fracture patterns at growing lava domes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13573, https://doi.org/10.5194/egusphere-egu21-13573, 2021.

EGU21-3200 | vPICO presentations | GMPV9.5

Using minimal spanning tree based ICA optimization for volcanic unrest determination

Binayak Ghosh, Mahdi Motagh, Mahmud Haghshenas Haghshenas, and Thomas Walter

Over the years, various satellites like ERS-1, ERS-2 and Envisat has been in use for the interferometric capability for a wide range of geophysical and environmental applications. With the launches of Sentinel-1A and 1B satellites in 2014 and 2016 respectively, the availability of SAR data from every part of the world has been increased many folds. With short revisit times of 1-6 days, the Sentinel-1 and the planned Tandem-Land NISAR missions provide an unprecedented wealth of topography and surface change data using InSAR technique. Utilizing these Synthetic Aperture Radar (SAR) acquisitions, repeated approximately from the same point in space at different times, it is possible to produce measurements of ground deformations at some of the world’s active volcanoes and can be used to detect signs of volcanic unrest. Most of the existing traditional algorithms like Permanent Scatterer (PS) analysis and Small Baseline Subset (SBAS) technique are computationally extensive and cannot be applied in near real time to detect  precursory deformation and transient deformations. To overcome this problem, we have adapted a minimum spanning tree (MST) based spatial independent component analysis (ICA) method to automatically detect deformation signals of volcanic unrest. We utilize the algorithm’s capability to isolate signals of geophysical interest from atmospheric artifacts, topography and other noise signals, before monitoring the evolution of these signals through time in order to detect the onset of a period of volcanic unrest, in near real time. We demonstrate our approach on synthetic datasets having different signal strengths, varying temporally. We also present the results of our approach on the volcanic unrest of Mt. Thorbjörn in Iceland on 2020 and also the volcanic unrest of a volcano in Mexico from 2017 to 2019.

How to cite: Ghosh, B., Motagh, M., Haghshenas Haghshenas, M., and Walter, T.: Using minimal spanning tree based ICA optimization for volcanic unrest determination, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3200, https://doi.org/10.5194/egusphere-egu21-3200, 2021.

EGU21-5394 | vPICO presentations | GMPV9.5

The 2011-2020 long-term sustained inflation at Long Valley Caldera:  investigation of the interaction of magmatic and tectonic processes

Erica De Paolo, Elisa Trasatti, Cristiano Tolomei, and Emily K. Montgomery-Brown

The Long Valley Caldera, California (USA), has been restless over the past few decades, experiencing seismic swarms and ground deformation episodes. The last inflation began in late 2011, when a radially symmetric tumescence was detected coinciding with a large resurgent dome within the caldera. Since then, a continuous inflation with quasi-steady rate of ~1.5 cm/yr has been observed.  Earthquakes mostly occur within the caldera along the South Moat Seismic Zone, to the south of the maximum deformation area. Although the area is tectonically active, increased seismic activity has been documented during periods of renewed inflation since the onset of this tumescence in 1978. In this study, we aim to investigate the nature and dynamics of the long-term unrest at Long Valley Caldera, as well as to provide new insights into the interaction between magmatic and tectonic processes. For this purpose, we consider a variety of datasets including geodetic and seismic records over the period spanning from late 2011 to the end of 2020. A complete seismic catalog supports our study, with more than 200 M2.5-4.5 earthquakes recorded since 2011, most with epicenters located within the caldera. Measurements from a dense network of continuous GPS stations collected in the last 10 years are analyzed in combination with high resolution Interferometric Synthetic Aperture Radar (InSAR) data. For full temporal coverage, we integrate InSAR velocities obtained from the acquisition of different satellite missions. We use, in particular, data from SAR systems operating with X and C-bands such as TerraSAR-X, COSMO-SkyMed and Sentinel-1. The multi-sensor dataset (i.e., GPS and multi-mission InSAR data) compensate the limitations of each technique, with reliable mapping of the deformation pattern evolving over several years. Data analysis highlights uplift velocities with peaks of ~2 cm/yr within the caldera and beyond its southern rim. Moreover, compared to the first half of the period of analysis (2011-2014), the area affected by high deformation rates is broader in the last several years (2017-2020). Models based on the geodetic data are developed to constrain the deformation source and to better interpret the observed signals. This study is motivated as a contribution to the understanding of this long-lived caldera unrest, for a more reliable hazard assessment.

How to cite: De Paolo, E., Trasatti, E., Tolomei, C., and Montgomery-Brown, E. K.: The 2011-2020 long-term sustained inflation at Long Valley Caldera:  investigation of the interaction of magmatic and tectonic processes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5394, https://doi.org/10.5194/egusphere-egu21-5394, 2021.

EGU21-988 | vPICO presentations | GMPV9.5 | Highlight

Axial Seamount: A Wired Submarine Volcano Observatory in the NE Pacific

William W. Chadwick, Scott L. Nooner, William S. D. Wilcock, Maya Tolstoy, Felix Waldhauser, Deborah S. Kelley, Adrien F. Arnulf, Suzanne M. Carbotte, and Jeff W. Beeson

Axial Seamount is the most active submarine volcano in the NE Pacific Ocean, and is monitored by instruments connected to a cabled observatory (the US Ocean Observatories Initiative Cabled Array), supplemented by autonomous battery-powered instruments on the seafloor at ~1500 m depth.  Axial Seamount is a basaltic hot spot volcano superimposed on the Juan de Fuca spreading ridge, giving it a robust and apparently continuous magma supply.  It has had three effusive eruptions in the last 23 years in 1998, 2011, and 2015.  Deformation measurements have been conducted at Axial Seamount since the late 1980’s with bottom pressure recorders (BPRs) that can detect vertical movements of the seafloor with a resolution of ~1 cm.  This monitoring has produced a long-term time-series including co-eruption rapid deflation events of 2.5-3.2 meters, separated by continuous gradual inter-eruption inflation at rates that have varied between 15-80 cm/yr.  The overall pattern appears to be inflation-predictable, with eruptions repeatedly triggered at or near a critical level of inflation.  Using this pattern, the 2015 eruption was successfully forecast within a one-year time window, 7 months in advance.  As of January 2021, Axial Seamount has re-inflated ~2.1 m (~83%) of the 2.54 m it deflated during the 2015 eruption, but the rate of inflation has been decreasing since then.  Our current eruption forecast window is between 2022-2026, based on the latest rate of inflation.  Modeling of the seafloor deformation data along with other recent results from ocean bottom seismometers and multichannel seismic surveys inform our interpretation of the subsurface structure of the volcano and the geometry and depth of the shallow magma storage system.

How to cite: Chadwick, W. W., Nooner, S. L., Wilcock, W. S. D., Tolstoy, M., Waldhauser, F., Kelley, D. S., Arnulf, A. F., Carbotte, S. M., and Beeson, J. W.: Axial Seamount: A Wired Submarine Volcano Observatory in the NE Pacific, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-988, https://doi.org/10.5194/egusphere-egu21-988, 2021.

EGU21-12301 | vPICO presentations | GMPV9.5

Resurgent uplift at large calderas and relationship to caldera-forming faults and the magma reservoir: new insights from the Neapolitan Yellow Tuff caldera (Italy) 

Marta Corradino, Fabrizio Pepe, Marco Sacchi, Giuseppe Solaro, Henrique Duarte, Luigi Ferranti, and Ivana Zinno

Resurgence uplift is the rising of the caldera floor, mainly due to pressure or volume changes in the magma reservoir. Identifying resurgence structures and understanding their relationship to the magmatic reservoir is challenging. We investigate the resurgence structures of the Neapolitan Yellow Tuff (NYT) caldera (Italy) by integrating bathymetric data, high-resolution seismic profiles and Differential Synthetic-Aperture Radar Interferometry data. Our results show that the resurgent area is manifested as 1) a central dome constituted by two main blocks bounded by NNE-SSW trending faults, 2) an apical graben developed on top of the most uplifted block, 3) a peripheral zone including several uplifted and tilted blocks, bounded by inward-dipping faults. The onset of the uplift of the central dome occurred through re-activation, in reverse motion, of normal faults formed during the caldera collapse, and located in the peripheral zone. During periods of unrests, the blocks of the central dome move independently at different velocities, and the peripheral zone accommodates the deformation. The restless behaviour of the NYT caldera is the result of a shallow magmatic reservoir located at 3.5 ± 0.7 km, and characterised by a width that roughly corresponds to the extension of the overlaying resurgent area. Defining the caldera-forming fault system and identifying the area involved by the resurgence is crucial for estimating depth and width of the magma reservoir, and predicting the caldera behaviour during periods of unrest by localising possible vents and sectors that will deform. This knowledge contributes to the evaluation of the volcanic hazard.

How to cite: Corradino, M., Pepe, F., Sacchi, M., Solaro, G., Duarte, H., Ferranti, L., and Zinno, I.: Resurgent uplift at large calderas and relationship to caldera-forming faults and the magma reservoir: new insights from the Neapolitan Yellow Tuff caldera (Italy) , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12301, https://doi.org/10.5194/egusphere-egu21-12301, 2021.

EGU21-15220 | vPICO presentations | GMPV9.5

Offshore ground movements in the Campi Flegrei caldera during the last ~12 ka

Camilla Marino, Luigi Ferranti, Jacopo Natale, Marco Sacchi, and Marco Anzidei

Appraisal of morphodepositional markers tied to ancient sea-levels in high-resolution seismic profiles together with geo-archaeological markers along the coast of the Pozzuoli Bay provided insights into the vertical deformation of the submerged part of the Campi Flegrei caldera (Southern Italy).

The collapse of the central part of the Campi Flegrei caldera is associated with the eruption of the Neapolitan Yellow Tuff (NYT) at ~15 ka. The NYT caldera collapse was followed by central dome resurgence associated with alternations of fast uplift and subsidence displacements that accompanied with discrete phases of intra-caldera volcanic activity. Previously, the evolution of ground movement in the Campi Flegrei caldera has been reconstructed using marine deposits uplifted onland or archaeological evidence and historical accounts and thus offers a mainly 2D appraisal of the deformation pattern. However, a complete reconstruction of post-collapse deformation suffers of the limitation that nearly two-thirds of the caldera are submerged beneath the Pozzuoli Bay.

We contribute to fill this gap by providing a reconstruction of offshore and coastal deformation through estimation of the vertical displacement of morphodepositional markers in high-resolution seismic reflection profiles and geoarchaeological markers directly surveyed at shallow depths. Our interpretation reveals the occurrence of different sediment stacking pattern whose provides evidence of rapid and oscillating ground movements. Whereas the offshore morphodepositional markers provide displacement information for the last ~12 ka, for the last ~2 ka our interpretation is supported by ancient Roman sea-level indicators. The multi-dataset analysis has allowed disentangling the signal related to the post-caldera dynamics from a broader deformation signal that affects this part of the extensional margin of the Apennines.

The integration of offshore data in the study of past episodes of ground deformation, by yielding a more complete picture of the ground motions associated to the post-collapse evolution of the Campi Flegrei caldera, bears a significant contribution for a 3D reconstruction of this high-risk resurgence caldera. Besides, the multidisciplinary approach presented here can be relevant for investigations of other calderas spanning the sea-land transition.

How to cite: Marino, C., Ferranti, L., Natale, J., Sacchi, M., and Anzidei, M.: Offshore ground movements in the Campi Flegrei caldera during the last ~12 ka, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15220, https://doi.org/10.5194/egusphere-egu21-15220, 2021.

EGU21-14799 | vPICO presentations | GMPV9.5

Assessing the Multiple Pressure Source Hypothesis for the Sakurajima Volcano and Aira Caldera Magmatic System

Robert Backhurst, James Hickey, and Ben Williamson

Sakurajima, located on the southern rim of Aira caldera, is one of the most active volcanoes in Japan. From long term deformation trends, the volcano is showing an increased risk of large-scale eruption, emphasizing the need to better understand the magmatic system.

Deformation modelling, primarily using the Mogi method, has dominated the geodetic assessment history of Sakurajima. These methods, however, contain limitations, such as the assumption of a homogeneous crust, and have therefore not accurately depicted the magmatic system. Numerical modelling techniques have reduced this limitation by accounting for subsurface heterogeneity.

Analytical modelling studies have suggested multiple magmatic sources beneath Aira caldera and Sakurajima volcano, whilst the only numerical study undertaken so far indicated a single source. Here, we test the multiple deformation source hypothesis, whilst also incorporating subsurface heterogeneity and topography, using Finite Element (FE) numerical modelling, and geodetic data from Sakurajima.

Using a full 3D model geometry for Sakurajima and Aira caldera, preliminary forward modelling suggests a second deformation source produces our best fit to the measured geodetic data. Optimum results indicate a shallow prolate source 7-10 km below sea level (bsl), in addition to a deeper oblate source at ~13 km bsl. These preliminary findings produce greater shallow storage depths than the previous analytical models (3-6 km) and ties in with the trans-crustal magmatic system hypothesis.

Increasing our understanding of the Sakurajima magmatic system will enable improved interpretations of geodetic data prior to eruptions and will inform models for a range of similar volcanoes world-wide.

How to cite: Backhurst, R., Hickey, J., and Williamson, B.: Assessing the Multiple Pressure Source Hypothesis for the Sakurajima Volcano and Aira Caldera Magmatic System, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14799, https://doi.org/10.5194/egusphere-egu21-14799, 2021.

EGU21-13355 | vPICO presentations | GMPV9.5

Volcanic deformation at Sakurajima between 2015 and 2020 revealed by Sentinel-1 InSAR time series

Alejandra Vásquez-Castillo and Matthias Hort

Surface displacements recorded in volcanically active regions are often driven by magmatic, hydrothermal or tectonic processes. Measuring the deformation experienced by the ground as a result of these processes allows to constrain the changing volcanic conditions and to infer quantitative estimates of the subsurface magmatic storage, thus increasing the knowledge of volcanic hazards for the closest local population. Interferometric synthetic aperture radar (InSAR) has proven to be an useful tool to observe ground deformation in volcanically active areas like the Sakurajima volcano, southern Japan, one of the most active volcanoes worldwide. Its current activity is characterized by degassing and almost daily explosive eruptions. We performed an InSAR time series analysis to identify and characterize time-dependent ground deformation using Sentinel-1 data between 2015 and 2020. During this period several large explosions with plume heights of up to 6000 m occurred. We found evidence of ground deformation associated with precursory inflation connected to major explosions. In addition, we processed interferograms spanning a remarkable event that occurred on August 15 2015, in which we identified strong deformation around the Showa crater, in agreement with previous studies.

How to cite: Vásquez-Castillo, A. and Hort, M.: Volcanic deformation at Sakurajima between 2015 and 2020 revealed by Sentinel-1 InSAR time series, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13355, https://doi.org/10.5194/egusphere-egu21-13355, 2021.

EGU21-7998 | vPICO presentations | GMPV9.5

Can high rates of passive volcanic gas emissions induce reservoir depressurization at Ambrym volcano (Vanuatu)?

Tara Shreve, Raphaël Grandin, and Marie Boichu

Satellite-based UV spectrometers can constrain sulphur dioxide (SO2) fluxes at passively degassing volcanoes over decadal time scales. From 2005 to 2015, more than 15 volcanoes had mean passive SO2 fluxes greater than 1 kiloton per day. Although the processes responsible for such high emission rates are not clearly established, this study aims to investigate the impact of strong degassing on the pressurization state of volcanic systems and the resulting ground deformation. One possible result of high degassing rates is the depressurization of the region where the melt releasing gas is stored, which may result in subsidence at the Earth’s surface. Passive degassing may depressurize pathways between deep and shallow magma storage regions, resulting in magma ascent and possibly eruption.

A lumped-parameter model developed by Girona et al., 2014 couples the mass loss by passive degassing with reservoir depressurization in an open volcanic system. However, this model has yet to be tested using real measurements of gas emissions and ground deformation. In our study, we focus on Ambrym volcano, the past decade’s top passive emitter of volcanic SO2, which exhibits intriguing long-term subsidence patterns and no obvious pressurization preceding eruptive periods. We compare subsidence rates measured by InSAR to the system’s average daily SO2 flux, focusing on a subsidence episode spanning 2015 to 2017 that is not clearly linked to magma removal from the system. Using realistic input parameters for Ambrym’s system constrained by petrology and gas geochemistry, a range of reservoir volumes and conduit radii are explored. Large reservoir volumes (greater than 30 km3) and large conduit radii (greater than 300 m) are consistent with depressurization rates obtained from geodetic modelling of InSAR measurements using the Boundary Element method. By comparing these values of reservoir volume and conduit radius with those estimated from geodesy, gas geochemistry, and seismology, we test the applicability and discuss uncertainties of the aforementioned lumped-parameter physical model to interpret the long-term subsidence at Ambrym volcano as a result of sustained passive degassing.

How to cite: Shreve, T., Grandin, R., and Boichu, M.: Can high rates of passive volcanic gas emissions induce reservoir depressurization at Ambrym volcano (Vanuatu)?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7998, https://doi.org/10.5194/egusphere-egu21-7998, 2021.

EGU21-3623 | vPICO presentations | GMPV9.5

Architecture and dynamics of the magmatic system feeding the 2018 offshore Mayotte eruption from satellite gravity data

Hélène Le Mével, Craig A. Miller, and Yan Zhan

In May 2018, a submarine eruption started offshore Mayotte (Comoros archipelago, Indian Ocean), and was first detected as a series of earthquake swarms. Since then, at least 6.4 km3 of lava has erupted from a newly mapped volcanic edifice (MAYOBS campaigns), about 50 km east of Mayotte island. Since the onset of the eruption, GNSS stations on the island have recorded subsidence (up to 17 cm) and eastward displacement (up to 23 cm). We combine marine gravity data derived from satellite altimetry with finite element models to examine the magmatic system structure and its dynamics. First, we calculate the Mantle Bouguer Anomaly (MBA) by taking into account the gravitational effect of the bathymetry and the Moho interfaces, assuming a crust of constant thickness of 17.5 km and correction densities of 2.8 g/cm3 and 3.3 g/cm3 for the crust and mantle, respectively. We then invert the MBA to determine the anomalous density structures within the lithosphere, using the mixed Lp-norm inversion and Gauss-Newton optimization implemented in the SimPEG framework. The gravity inversion reveals two zones of low density, east of Mayotte island. The first is located NE of Petite Terre island between ~15 and 35 km depth, and the second is located further east, south of La Jumelle seamounts and extends from ~25 to 35 km depth. We interpret these low density regions as regions of partial melt stored in the lithosphere and estimate the volume of stored magma. Finally, we use the newly imaged low density bodies to constrain the magma reservoir geometry and simulate magma flow from this reservoir to the eruptive vent in a 3D, time-dependent, numerical model. The model parameters are adjusted by minimizing the misfit between the modeled surface displacement and that measured at the 6 GPS sites, between May 2018 and 2020. The deformation modeling reveals the temporal evolution of the magma flux during the eruption, and the resulting stress distribution in the crust explains the patterns of recorded seismicity. Together with the existing seismic and geodetic studies, the gravity data analysis and FEM models bring new constraints on the architecture of the magma plumbing system and the magmatic processes behind the largest submarine eruption ever documented.

How to cite: Le Mével, H., Miller, C. A., and Zhan, Y.: Architecture and dynamics of the magmatic system feeding the 2018 offshore Mayotte eruption from satellite gravity data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3623, https://doi.org/10.5194/egusphere-egu21-3623, 2021.

EGU21-13865 | vPICO presentations | GMPV9.5

Reconciling the location of lava domes and eruption centers in Paleocene-Eocene calderas in northern Chile

Matías Clunes, John Browning, Carlos Marquardt, José Cembrano, Matías Villarroel, Orlando Rivera, and Constantino Mpodozis

In the Atacama Desert, at the Precordillera of northern Chile, a series of Paleocene-Eocene caldera deposits and ring-faults are exceptionally well-preserved1. Here we aim to build on previous mapping efforts to consider the location, timing and style of pre, syn and post caldera volcanism in the region. We focus on the partially nested caldera complexes of Lomas Bayas and El Durazno2,3 where deposits record several stages of caldera evolution (pre-collapse, collapse/intra-caldera and extra-caldera, resurgence and post-collapse eruptive deposits). The pre-caldera basement is a thick sequence of early Paleocene mafic lavas4, 5. The caldera complex formed between around 63 and 54 Ma4, 5. Both calderas constitute subcircular structures approximately 13 km in diameter and are cut by several NNW to NNE-trending felsic dikes which are spatially related to felsic domes interpreted as resulting from post caldera formation unrest1,4. These calderas have been interpreted as part of the Carrizalillo megacaldera complex2 . We combine field observations, such as the attitude of dikes, as well as information on their dimension and composition, the size, location and composition of domes and lava flows, as well as the evidence of the regional stress field operating during the caldera evolution from measurements of fault kinematics. This data will be used as the input to finite element method models to investigate the effect of nested caldera geometry, ring-faults and crustal heterogeneities on the location of domes and eruptive centers generated during caldera unrest. The results will be potentially useful for constraining models of eruption forecasting during periods of unrest in calderas and ore deposition models which have been shown to be linked to caldera structure and magma emplacement.

References

1 Rivera, O. and Falcón, M. (2000). Calderas tipo colapso-resurgentes del Terciario inferior en la Pre-Cordillera de la Región de Atacama: Emplazamiento de complejos volcano-plutónicos en las cuencas volcano-tectónicas extensionales Hornitos y Indio Muerto: IX Congreso Geológico Chileno, v. 2. Soc. Geol. de Chile, Puerto Varas.

2 Rivera, O., and Mpodozis, C. (1994). La megacaldera Carrizalillo y sus calderas anidadas: Volcanismo sinextensional Cretácico Superior-Terciario inferior en la Precordillera de Copiapó, paper presented at VII Congreso Geológico Chileno. Acad. de Cienc. del Inst. Chilecol. de Geol. de Chile, Concepción.

3 Rivera, O. (1992). El complejo volcano-plutónico Paleoceno-Eoceno del Cerro Durazno Alto: las calderas El Durazno y Lomas Bayas, Región de Atacama, Chile. Tesis Departamento de Geología, Universidad de Chile, 242. (Unpublished).

4 Arévalo, C. (2005). Carta Los Loros, Región de Atacama. Servicio Nacional de Geología y Minería, Carta Geológica de Chile, 92, 1(100.000), 53 p.

5 Iriarte, S., Arévalo, C., Mpodozis, C. (1999). Mapa Geológico de la Hoja La Guardia, Región de Atacama. Servicio Nacional de Geología y Minería. Mapas Geológicos, 13, 1(100.000).

How to cite: Clunes, M., Browning, J., Marquardt, C., Cembrano, J., Villarroel, M., Rivera, O., and Mpodozis, C.: Reconciling the location of lava domes and eruption centers in Paleocene-Eocene calderas in northern Chile, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13865, https://doi.org/10.5194/egusphere-egu21-13865, 2021.

EGU21-2939 | vPICO presentations | GMPV9.5

Subsidence of the lava flow formed during 2012-2013 Tolbachik fissure eruption: SAR data and thermal model

Valentin Mikhailov, Maria Volkova, Elena Timoshkina, Nikolay Shapiro, Vladimir Smirnov, Pavel Dmitriev, and Igor Babayantz

During the Tolbachik fissure eruption which took place from November 27, 2012 to September 15, 2013 a lava flow of area about 45.8 km2 and total lava volume ~0.6 km3 was formed. We applied method of persistent scatterers to the satellite Sentinel-1A SAR images and estimated the rates of displacement of the lava field surface for 2017–2019. The surface mainly subsides along the satellite’s line-of-sight, with the exception of the periphery of the Toludski and Leningradski lava flows, where small uplifts are observed. Assuming that the displacements occur mainly along the vertical, the maximum average displacement rates for the snowless period of 2017–2019 were 285, 249, and 261 mm/year, respectively. On the Leningradski and Toludski lava flows the maximum subsidence was registered in areas with the maximum lava thickness.

To estimate the thermal subsidence of the lava surface we constructed a thermal model of lava cooling. It provides subsidence rate which are generally close to the real one over a significant part of the lava field, but in a number of areas of its central part, the real subsidence values are much higher than the thermal estimates. According to the thermal model when lava thickness exceeds 40 meters, even 5 years after eruption under the solidified surface there can be a hot, ductile layer, which temperature exceeds 2/3 of the melting one. Since on the Leningradski flow, the maximum subsidence is observed in the area of the fissure along which the eruption took place, one could assume that the retreat of lava down the fissure could contribute to the observed displacements of the flow surface. Subsidence can also be associated with compaction of rocks under the weight of the overlying strata. Migration of non-solidified lava under the solidified cover, also can contribute to the observed distribution of displacements - subsidence of the surface of the lava field in the upper part of the slope and a slight uplift at its periphery.

The work was supported partly by the mega-grant program of the Russian Federation Ministry of Science and Education under the project no. 14.W03.31.0033 and partly by the Interdisciplinary Scientific and Educational School of Moscow University «Fundamental and Applied Space Research».

How to cite: Mikhailov, V., Volkova, M., Timoshkina, E., Shapiro, N., Smirnov, V., Dmitriev, P., and Babayantz, I.: Subsidence of the lava flow formed during 2012-2013 Tolbachik fissure eruption: SAR data and thermal model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2939, https://doi.org/10.5194/egusphere-egu21-2939, 2021.

EGU21-14889 | vPICO presentations | GMPV9.5

Magma system pressurisation and long-term surface deformation at Soufrière Hills Volcano, Montserrat

James Hickey, Karen Pascal, Matthew Head, Jo Gottsmann, Nico Fournier, Sigrun Hreinsdottir, and Racquel Syers

Soufrière Hills Volcano (SHV) is an andesitic dome-building volcano on the island of Montserrat (British West Indies). SHV began its current, and anomalously long, eruption in 1995, but eruptive activity has been intermittent with phases of lava extrusion separated by periods of relative quiescence. The current pause in eruption started in February 2010 and is the longest yet recorded, 10 years and 11 months at the time of writing (January 2021). Continuous GPS measurements show island-wide inflation from 2010 onwards, with the rate of inflation slowly decreasing with time. However, the length of the eruptive pause raises questions as to whether there have been significant changes to the magmatic system and/or the eruption at SHV might have ended. To assess the behaviour and evolution of the SHV magmatic system since 2010 and the relation to ongoing hazard assessment, we analyse the continuous GPS temporal deformation trends using a suite of geodetic numerical models. Our models incorporate a temperature-dependent viscoelastic rheology, topography derived from a Digital Elevation Model and three-dimensional variations in mechanical properties derived from seismic tomography. The models are driven using one of four possible time-dependent source functions, to simulate differences in the temporal evolution of the magmatic system. The results show that the observed deformation data requires a temporal source function whereby the magmatic system pressure is increasing with time. A viscoelastic crustal response cannot explain the long-term deformation trends alone. The nature of the source pressurisation is unclear, and could be due, for example, to one or a combination of, magma supply, degassing/volatile influx, or overturning within a transcrustal magmatic system. Continued pressurisation within the magmatic system highlights the need for sustained vigilance in the monitoring and management of the volcano and its surroundings.

How to cite: Hickey, J., Pascal, K., Head, M., Gottsmann, J., Fournier, N., Hreinsdottir, S., and Syers, R.: Magma system pressurisation and long-term surface deformation at Soufrière Hills Volcano, Montserrat, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14889, https://doi.org/10.5194/egusphere-egu21-14889, 2021.

Identifying driving mechanisms behind volcano deformation is one the key challenges of volcanology. Many geodetic models rely on simplified assumptions on source shape and the mechanical behaviour of surrounding rocks. However, geochemical, petrological and geophysical data illustrate complex architectures of sub-volcanic plumbing systems and crustal rocks. Mechanical heterogeneities fundamentally influence the stress vs. strain relationship and therefore require detailed analysis beyond the isotropic, homogenous, and elastic (IHE) half-space approximation embodied in traditional models.  
Here, we invert intra-eruptive ground displacements recorded between 2003-2005 on Montserrat to shed light on the magmatic plumbing system of Soufrière Hills Volcano.  Incorporating 3-dimensional crustal mechanical and topographic data in a finite-element model we show that the recorded displacements are best explained by a southeastward dipping (plunge angle of 9.3˚) vertically extended tri-axial ellipsoidal pressure source with semi-axis lengths of 1.9 and 2.0 km horizontally, and 5.0 km vertically.  The source is centred at 9.35 km depth below main sea level and embedded in independently imaged anomalously weak crustal rocks.  The source orientation appears to be controlled by the local stress field at the intersection of two major WNW-ESE and NW-SE striking tectonic lineaments. We derive an average volumetric strain rate of 8.4 x10-12 s-1 by transcrustal pressurisation which may have contributed to flank instability and mass wasting events in the southern and eastern sectors of the island.

How to cite: Gottsmann, J., Flynn, M., and Hickey, J.: 2003-2005 intra-eruptive  deformation at Soufrière Hills Volcano (Montserrat) modulated  by volcano-tectonics and weak crustal rocks  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10709, https://doi.org/10.5194/egusphere-egu21-10709, 2021.

EGU21-7517 | vPICO presentations | GMPV9.5

Modelling the Soufrière Hills Volcano; Investigating the Montserrat magmatic system with co-analysis of EDM and GPS data

Alexander Johnson, James Hickey, Karen Pascal, Ben Williamson, and Racquel Syers

Ground deformation offers vital insight into the activity of volcanoes, as well as the characteristics of the magmatic systems that feed them. The extended eruption of the Soufrière Hills Volcano (SHV) has allowed for the development of a comprehensive multi-disciplinary monitoring network, which has aided extensive research into the magmatic system underlying the volcano. The modern network comprises GPS, strainmeters, and cheaper Electronic Distance Measurement (EDM). However, the island’s EDM network has to date only being used for monitoring the SHV. Here, for the first time, we co-analyse the EDM dataset from 2010-19 with the GPS data from the same period. This study aims to delineate the modern magmatic system conditions by building 3D Finite Element Models, as well as assessing the best use of EDM data in modelling the SHV.

The island-wide deformation recorded over the past decade at the GPS network is broadly radial relative to the SHV dome, with a decreasing deformation rate. The EDM data shows line lengthening on the west and east flanks of the volcano, but minor line length shortening on the northern flank. We utilise Finite Element Modelling to model the SHV magmatic system as a single elongated prolate with 3D topography incorporated. We systematically test a wide range of parameters to explore how both EDM and GPS record perturbations to the magmatic system. Our preliminary results show that variations of certain parameters to the deeper magmatic system have an impact on both EDM and GPS timeseries, while some parameters (e.g., source pressure, source depth, and source location) have a more significant effect on EDM measurements than others (e.g., source shape).

How to cite: Johnson, A., Hickey, J., Pascal, K., Williamson, B., and Syers, R.: Modelling the Soufrière Hills Volcano; Investigating the Montserrat magmatic system with co-analysis of EDM and GPS data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7517, https://doi.org/10.5194/egusphere-egu21-7517, 2021.

EGU21-14952 | vPICO presentations | GMPV9.5

Explaining the continuing inflation of Montserrat

Jurgen Neuberg and Benoit Taisne

Soufrière Hills volcano on Montserrat in the West Indies showed five episodes of magma extrusion and as many pauses in its 25 years of volcanic activity. This eruptive behaviour exhibited cyclic deformation pattern where extrusive “phases” showed island-wide deflation and all “pauses” have been linked to inflation, the last of which remains ongoing. Several models have been developed over the years; all based on magma intrusion and extrusion, into, or from one or several reservoirs, respectively. Addressing the entire eruptive history, we explore in this presentation several alternative models ranging from the continuous magma influx at depth to the extreme case where intrusion of fresh magma has ceased years ago, while the inflation is continuing. Both, purely elastic and visco-elastic rheologies are explored.

How to cite: Neuberg, J. and Taisne, B.: Explaining the continuing inflation of Montserrat, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14952, https://doi.org/10.5194/egusphere-egu21-14952, 2021.

Seamounts are isolated, underwater volcanoes with more than 100 m in relief. This kind of volcanism arises from the lithosphere or asthenosphere through fractional melt and is a direct manifestation of the tectonic-magmatic activity of the interior of the earth. While previous studies have quantified the global distribution of seamounts by their physical properties (e.g., height, semimajor axis, angle, etc.), these studies usually (1) assume an elliptical cone to model seamount shape, and (2) neglect the sediment coverage on the seamount, which results in significant uncertainties when comparing properties of seamounts near the continents covered with thick sediments to those in the open ocean covered with thin sediments.

We apply a large-scale Gaussian Process regression to recover the seamount topography covered by sediments for an accurate distribution of volcanism in the South China Sea basin (with an average thickness of 1.5 km sediments) and the entire Pacific Ocean (with < 300 m thick sediments). Specifically, we first use Tophat filtering to isolate short-spatial-wavelength seamount topography above long-wavelength seafloor. Subsequently, we apply Gaussian Process regression to learn the seamount structure above the seafloor in order to extrapolate the structure beneath the sediment. Lastly, we compute the seamount volume above the sedimentary basement (i.e., top boundary of the oceanic crust) and compare it to the volume above the seafloor. Our results show that for the South China Sea, there is a significant increase in estimated seamount volume above the basement as compared to above the seafloor. For the Pacific Ocean, due to the thin sediment coverage, we observe negligible differences between the two volume estimates. Thus, analysis of seamount properties in marginal basins in the West Pacific with thick sediment coverage can lead to significant underestimation of volcanism intensity if sub-seafloor topography is not accounted for. For these marginal basins, without massive hotspots or apparent evidence of mantle plumes, normal plate tectonic processes are likely responsible for the intensive oceanic volcanism.

How to cite: Zhao, Y. and Riel, B.: Accurate Quantification of Seamount Volcanism in Abyssal  Sediments Using Gaussian Process Regression, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4073, https://doi.org/10.5194/egusphere-egu21-4073, 2021.

EGU21-12060 | vPICO presentations | GMPV9.5

Mineral chemistry and geothermobarometry of the Balıkesir Volcanites (NW Anatolia, Turkey) 

Alp Ünal and Şafak Altunkaynak

Balıkesir Volcanites (BV) are included into the Balıkesir Volcanic Province and contain various products of Oligo-Miocene volcanic activity in NW Anatolia. BV are formed from trachyandesite, andesite and dacite lavas with associated pyroclastic rocks. In this study, we report the petrographical investigations, mineral chemistry results and geothermobarometry calculations of the Balıkesir Volcanites in order to deduce the magma chamber processes and crystallization conditions. Andesites present a mineral composition of plagioclase (An35–50) + amphibole (edenitic hornblende) +biotite ± quartz and opaque minerals. The major phenocryst phases in dacite lavas are plagioclase (An39–53), quartz, amphibole (magnesio-hornblende), biotite, sanidine and opaque minerals. The mineral composition of the trachyandesites, on the other hand, is represented by plagioclase (An38–57) + amphibole (pargasitic hornblende) + biotite + clinopyroxene (endiopside- augite) ± sanidine ± quartz ± opaque minerals. Balıkesir Volcanites present distinct textural properties such as rounded plagioclase phenocrysts with reaction rims, oscillatory zoning, honeycomb and sieve textures in plagioclase, reverse mantled biotite and hornblende crystals. The plagioclase- amphibole geothermobarometry calculations of Balıkesir volcanites indicate that, andesite and dacite lavas present similar crystallization temperature and pressures conditions of 798- 813°C and 1,98- 2.17 kbar. Oppositely, trachyandesites were crystallized under 857°C and 3,72 kbar temperature and pressure conditions. These results show that the andesite and dacite lavas were originated from the same magma chamber with the depth of 7km whereas trachyandesites were evolved in a deeper magma chamber with 13 km depth. Combined mineral chemistry, petrography and geothermobarometry studies indicate that the open system processes such as magma mixing/mingling and/or assimilation fractional crystallization (AFC) were responsible for the textural and compositional variations of the Balıkesir Volcanites.

How to cite: Ünal, A. and Altunkaynak, Ş.: Mineral chemistry and geothermobarometry of the Balıkesir Volcanites (NW Anatolia, Turkey) , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12060, https://doi.org/10.5194/egusphere-egu21-12060, 2021.

GMPV9.6 – Magma ascent, degassing and eruptive dynamics: linking experiments, models and observations

EGU21-60 | vPICO presentations | GMPV9.6

Bubbles and element clusters in rock melts: A chicken and egg problem

Renelle Dubosq, Pia Pleše, Brian Langelier, Baptiste Gault, and David Schneider

The nucleation and growth dynamics of gas bubbles and crystals play a vital function in determining the eruptive behaviour of a magma. Their rate and relative timing, among other factors, are controlled by the magma’s ascent rate. Investigating the kinetics of decompression-induced degassing and crystallization processes can thus give us insight into the rheology of magmas. For example, the rapid decompression of magmas inhibits microlite crystallization and bubble nucleation during ascent leading to crystallization and degassing at shallow levels. This results in a drastic increase in viscosity and an over pressured system, which can lead to violent eruptions. Although many experiments and numerical simulations of magma decompression have been carried out, nascent and initial bubble nucleation remain poorly understood. It is widely accepted that there are two ways bubbles can nucleate within a melt: heterogeneous (on a pre-existing surface) and homogeneous nucleation (within the melt), where homogeneous nucleation requires a higher volatile supersaturation. It has since been tentatively suggested that homogeneous nucleation is simply a variety of heterogeneous nucleation where nucleation occurs on the surface of submicroscopic crystals. However, evidence of these crystals is equivocal. Thus, we have combined novel 2D and 3D structural and chemical microscopy techniques including scanning transmission electron microscopy (STEM), electron energy-loss spectroscopy (EELS) mapping, and atom probe tomography (APT) to investigate the presence of sub-nanometer scale chemical heterogeneities in the vicinity of gas bubbles within an experimental andesitic melt. The combined STEM and EELS data reveal a heterogeneous distribution of bubbles within the melt ranging between 20-100 nm in diameter, some of which have Fe and/or Ca element clusters at the bubble-melt interface. Element clusters enriched in Fe, Ca, and Na are also observed heterogeneously distributed within the melt. The reconstructed APT data reveals bubbles as low ionic density regions overlain by a Na-, Ca-, and K-rich cluster and heterogeneously distributed Fe clusters within the bulk of the melt. Based on these observations, our data demonstrate the existence of nano-scale chemical heterogeneities within the melt and at the bubble-melt interface of bubbles that were previously interpreted to be nucleated homogeneously within the melt, therefore contributing to the proposed hypothesis that homogeneous nucleation could in fact be a variety of heterogeneous nucleation. These results highlight the need to redefine homogeneous nucleation and revisit whether bubbles or crystals occur first within volcanic melts. 

How to cite: Dubosq, R., Pleše, P., Langelier, B., Gault, B., and Schneider, D.: Bubbles and element clusters in rock melts: A chicken and egg problem, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-60, https://doi.org/10.5194/egusphere-egu21-60, 2021.

EGU21-3018 | vPICO presentations | GMPV9.6

The effect of anisotropic vesiculation on the porous-permeable evolution in magmatic foams

Jenny Schauroth, Joshua Weaver, Jackie E. Kendrick, Anthony Lamur, and Yan Lavallée

Volcanoes can undergo rapid transitions between effusive and explosive eruptions that are often dependant on the melt’s ability to devolatilise and outgas. Eruptive products show widely contrasting permeability values for a given porosity owing to the fact that magma properties evolve over time and space, hence porosity and permeability vary depending on transport and deformation history, scale and orientation. The vesicularity that enables bubble coalescence and permeability development, termed the percolation threshold, is experimentally determined to be at ~30-80 %, depending on the microstructure of magma (i.e. bubble size and shape distribution, crystal content, dominant mode of rheological deformation during vesiculation and flow). During ascent of magma pressure decreases and the magma adapts to these new conditions by vesiculating and expanding against wall rocks. Friction between the vesicular magma and the conduit wall encourages shear, which modifies the architecture of the vesicular network. The geometrical constriction associated with conduits, dykes or fractures which host magma thus prevents or limits the isotropic growth of vesicles; we hypothesise that geometrical constraints instead lead to different ratios of isotropic to anisotropic expansion, which impacts vesicle coalescence and the onset and development of permeable gas flow in magma. We present experimental results detailing the impact of constricting geometry on the development of a permeable porous network, by combining various diameter basalt crucibles with different sized cylindrical cores of aphyric rhyolitic glass (0.12 wt.% H2O). We vesiculate the samples in a furnace at 1009 °C for different isothermal dwell increments, before cooling our sample assembly and determining porosity, strain and gas permeability. The vesiculated rhyolites host an impervious glass rind (due to near-surface bubble resorption via diffusion) surrounding a vesicular core; as such, we measure gas permeability of the assembly after cutting the upper and lower glassy rind, to expose the permeability of the internal porous network developed experimentally. The findings indicate that increasing anisotropy, caused by minimising the extent of isotropic vesiculation and maximising vesiculation under constricted conditions, lowers the porosity at which the percolation threshold occurs by ~30 %. We postulate that pure and simple shear, developed parallel to the constricting walls, increase bubble aspect ratios and enhance coalescence. This suggests magmatic foams form connected networks at lower porosities when they vesiculate in constricted conduits, dykes and fractures, thus impacting outgassing efficiency. This implies that the physico-chemical evolution of vesiculating magma may be more strongly linked to structural and rheological controls than previously anticipated, with important implications on ascending magma evolution and eruptive processes, such as degassing, outgassing and fragmentation.

How to cite: Schauroth, J., Weaver, J., Kendrick, J. E., Lamur, A., and Lavallée, Y.: The effect of anisotropic vesiculation on the porous-permeable evolution in magmatic foams, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3018, https://doi.org/10.5194/egusphere-egu21-3018, 2021.

The non-in-situ analysis of H2O degassing of silicate melt at high temperature and pressure is conducted using synthetic, decompressed melt samples quenched to glass. Interpretations regarding the degassing behavior are based on the number of H2O filled vesicles and the porosity of the vitrified samples. These properties of the glass samples may not represent the vesiculation at experiment temperature Texp and target pressure Pfinal. Even at high quench rates q, a decrease of vesicle volumes during cooling occurs, facilitated by resorption of H2O fluid back into the melt (McIntosh et al., 2014) and by the decrease of molar volume of H2O (Marxer et al., 2015) in the vesicles. This vesicle shrinkage introduces uncertainty regarding the true q-dependent “freezing” temperature Tf, at which shrinkage stops, represented by the vesiculated glass sample. While often neglected, knowledge of Tf is useful for improved sample interpretation.

McIntosh et al. (2015) developed a computer tomography (CT) based method to determine Tf. This approach infers Tf from the volume fraction of liquid H2O in vesicles (whose volumes are comprised of a liquid and a gaseous H2O phase) which decreases for increasing Tf.

Using their theoretical foundations, we developed a simple, transmitted light microscopy (TLM) image-based approach for the determination of this intra-vesicle phase ratio, applying two different model calculations: 1) Approximation of phase boundaries using polynomial functions. 2) Calculation of total vesicle and gas-phase volumes from ellipsoid axes measurements, approximating the vesicle and gas-phase volumes with symmetrical spheroids. In our analyzed hydrous, haplogranitic samples, we found mean Tf’s up to ~250 to ~300 K lower than Texp, at which quench was initiated, for q’s of ~40 and ~90 K/s. These values are close to the estimated Tf’s obtained using an independent glass porosity equation (Gardner et al., 1999). The large scatter of volume fractions and thus Tf for individual vesicles cannot be attributed to our image-based approach as data obtained from phonolitic samples using the CT method (Allabar et al., 2020) depict a similar scatter. At present, no correlation of Tf with vesicle size or position within the sample could be made. The method is, for the range of vesicle sizes investigated (20 to 50 µm in diameter), limited to liquid volume fractions larger than ~10 vol% as a distinction between phases is limited by optical resolution.

Nevertheless, our TLM based approach provides a simple, readily available method to constrain Tf of vitrified vesiculated samples which significantly improves the quality and comparability of derived interpretations. Our method uses standard polished sections for FTIR, making it even applicable to already existing samples.

 

 

Allabar, A. et al. (2020), Contrib. Mineral. Petrol, 175, 21, 1-19

Gardner, J.E., Hilton, M. and Carroll, M.R. (1999), Earth Planet. Sci. Lett, 168, 201-218

Marxer, H., Bellucci, P. and Nowak, M. (2015), J. Volcanol. Geotherm. Res, 297, 109-124

McIntosh, I.M. et al. (2014), Earth Planet. Sci. Lett, 401, 1-11

McIntosh et al. (2015): ‘Practical’ glass transition temperatures of vesicular glasses: a combined FTIR-XRCT approach. Abstract, 10th Silicate melt workshop. La Petite Pierre, France

How to cite: Eul, D., Allabar, A., and Nowak, M.: An image-based technique to determine the freezing temperature Tf of vesicle volumes in decompressed, synthetic melt samples, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10227, https://doi.org/10.5194/egusphere-egu21-10227, 2021.

EGU21-6511 | vPICO presentations | GMPV9.6

Melt degassing triggered by magma injection?

Patricia Petri, Anja Allabar, and Marcus Nowak

Explosive eruptions of silicic magmas depend mainly on the amount and the degassing behavior of soluble volatile components like H2O and CO2. The injection of a hot mafic magma into a cooler volatile-rich rhyolitic magma chamber might initiate mingling and mixing processes at the interface of the two melt reservoirs (Paredes-Marino et al. 2017). An accompanying increase in temperature and a buoyant ascent of the H2O-saturated rhyolitic melt may cause a sufficiently high decrease in solubility at pressures < 300 MPa (e.g. Holtz et al. 1995) to trigger vesicle formation. Furthermore, the interface between different melt compositions might act as a site for enhanced vesicle formation. To test this hypothesis, bimodal decompression experiments were conducted. Basaltic and rhyolitic compositions similar to the Askja eruption 1875 in Iceland (Sparks and Sigurdsson 1977) were used for this purpose. For the preparation of the experiments, rhyolitic and basaltic glass cylinders were molten and hydrated separately in an internally heated argon pressure vessel with H2O excess at 200 MPa and 1523 K for 96–168 h and then isobarically quenched with 16 K∙s‑1. The hydrated glass samples were cut perpendicular to the cylinder axis. The cylinder faces were polished to enable a perfect contact of the rhyolite cylinder with the basalt cylinder. An additional decompression experiment with two contacted hydrated rhyolite cylinders was conducted as a reference to test the experimental setup.

Each pair of cylinders was heated isobarically with 25 K·s-1 to 1348 K at 210 MPa and equilibrated for 10 min. To simulate the magma ascent, three bimodal samples and the reference sample were decompressed with rates of 0.17 MPa∙s-1 or 1.7 MPa∙s-1 to the final pressure of 100 MPa and then quenched with 44 K∙s-1. H2O vesicle number and spatial distribution as well as the H2O contents in the decompressed samples were analysed by microscope, quantitative BSE image analysis, and FTIR-spectroscopy, respectively.

All decompression experiments resulted in vesiculated samples. In the rhyolite reference experiment, the H2O vesicles are homogeneously distributed within the whole sample. The former interface of the cylinders is no longer visible. This confirms that the former contact plane of the cylinders does not influence the degassing behaviour during decompression.

Optical examination and electron microprobe analysis of oxide diffusion profiles of the decompressed bimodal samples expose the development of a hybrid melt zone between the rhyolite and the partially crystallized basalt, documenting mixing processes during the decompression experiments (Petri 2020). The hybrid zone in the rhyolitic compositional dominated region is decorated with an enhanced number of H2O vesicles compared to the rhyolitic and basaltic glass volumes. This suggests that the injection of a basaltic melt into a rhyolitic melt reservoir may lead to significantly enhanced homogeneous H2O vesicle formation in the hybrid zone and, therefore, enhanced degassing with the concomitant triggering of explosive eruptions.

 

Holtz F. et al. (1995) American Mineralogist 80: 84-108.

Paredes-Marino J. et al. (2017) Scientific Reports 7: 16897.

Petri P. (2020) Master thesis University of Tübingen.

Sparks S.R.J. and Sigurdsson H. (1977) Nature 267: 315-318.

How to cite: Petri, P., Allabar, A., and Nowak, M.: Melt degassing triggered by magma injection?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6511, https://doi.org/10.5194/egusphere-egu21-6511, 2021.

EGU21-9650 | vPICO presentations | GMPV9.6

Phase relations and pre-eruptive conditions at low f(O2) in Pantelleria peralkaline rhyolites

Ernestina Appiah, Paola Stabile, Fabio Arzilli, Alessandro Fabbrizio, and Michael Robert Carroll

The volcanic system of Pantelleria is an example of volcanism in a continental rift basin which over the years has attracted much researcher due to the different eruptive styles it exhibits, ranging from effusive to explosive. Investigating the cooling history as well as the magma transport dynamics of peralkaline rhyolitic magma is useful to understand the eruptive behaviour of the pantelleritic magma system.

The present work seeks to obtain information on the liquidus temperature of alkali feldspar in pantellerite from the Fastuca pumice fall unit (PAN13) under water-saturated conditions. Alkali feldspar is one of the most abundant crystalline phases in peralkaline rhyolitic melts as well as in evolved, alkali-rich magma compositions (e.g., trachyte, phonolite).

A series of water-saturated isobaric single-step cooling experiments were performed at reducing conditions (graphite filler rod, water P-medium, ~NNO-2) with final temperature range of 670 °C-880 °C and water pressure of 20-150 MPa. Phase equilibria show that clinopyroxene is the first liquidus phase always appearing by 750 °C, followed by alkali feldspar over the entire pressure and temperature (P-T) range investigated, with also the presence of aenigmatite crystallizing near the liquidus at P of 50 MPa. Providing experimental constraints on pre- and syn-eruptive magma crystallization is fundamental to better understand the eruptive dynamics of peralkaline rhyolitic magmas. This is important for volcanic hazard assessments of peralkaline rhyolitic magmatic systems.

How to cite: Appiah, E., Stabile, P., Arzilli, F., Fabbrizio, A., and Carroll, M. R.: Phase relations and pre-eruptive conditions at low f(O2) in Pantelleria peralkaline rhyolites, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9650, https://doi.org/10.5194/egusphere-egu21-9650, 2021.

EGU21-8094 | vPICO presentations | GMPV9.6

CO2 favours the accumulation of excess fluids in felsic magmas

Mattia Pistone, Luca Caricchi, and Peter Ulmer

Volcano deformation and gas emissions provide insights into subsurface magmatic systems. Large discrepancies are observed between the volumes calculated from deformation data, mass of emitted gases, and volumes of erupted magmas. Such discrepancies hinder our capacity to predict the magnitude and intensity of imminent eruptions and are ascribed to the amount of excess fluids stored in magma reservoirs. High-pressure (1240 bar) and high-temperature (1200 °C) hot isostatic press experiments show that the amount of trapped excess fluids in haplogranitic magmas with variable crystal contents (30, 50, 60, and 70 vol.%) depends strongly on fluid composition. Magmas with CO2 excess fluids become permeable at much larger porosities (44% higher) with respect to the H2O-rich counterparts at equivalent crystallinity. Available excess gas geochemistry data calculated from volatile-saturated melt inclusion record, syn-eruptive SO2 emission, and erupted juvenile porosity data collected for crystal-rich andesite and crystal-poor dacite/rhyolite volcanoes with known eruption magnitude and intensity (Mt St Helens 1980, Pinatubo 1991, Soufrière Hills 1996, and Merapi 2010) reveal that the discrepancy between erupted magma volume and SO2 released during the eruption increases with CO2 excess in magmas. In agreement with our experiments, these data highlight that CO2-rich fluids enhance magma’s capacity to store excess volatiles and shed light on the largest discrepancies between pre-eruptive deformation, gas emissions, and eruption intensity and magnitude.

How to cite: Pistone, M., Caricchi, L., and Ulmer, P.: CO2 favours the accumulation of excess fluids in felsic magmas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8094, https://doi.org/10.5194/egusphere-egu21-8094, 2021.

EGU21-8568 | vPICO presentations | GMPV9.6

Experimental constraints on volcanic ash generation and clast morphometrics in pyroclastic density currents and granular flows

Adrian Hornby, Ulrich Kueppers, Benedikt Maurer, Carina Poetsch, and Donald Dingwell

Pyroclastic density currents (PDCs) present perhaps the greatest proximal primary hazard of volcanic activity and produce abundant fine ash that can present a range of health, environment and infrastructure hazards. However, direct, fully quantitative observation of ash production in PDCs is lacking, and little direct evidence exists to constrain the parameters controlling ash generation in PDCs. Here, we use an experimental approach to investigate the effects of starting mass, material density and ash removal on the efficiency of ash generation and concurrent clast rounding in the dense basal flow of PDCs. We employ a rotary drum to tumble pumice and scoria lapilli clasts over multiple transport “distance” steps (from 0.2 to 6 km). We observe increased ash generation rates with the periodic removal of ash during the experiments and with increasing starting mass. By scaling to the bed height and clast diameter we obtain a general description for ash production in all experiments as a function of flow distance, bed height and average clast diameter. We confirm that changes in lapilli shape factors correlate with the ash fraction generated and that the grain size of ash produced decreases with distance. Finally, we estimate shear rate in our experiments and calculate the inertial number, which describes the ratio between clast-scale and flow-scale rearrangement during flow. We show that, under certain conditions, fractional ash production can be calculated accurately for any starting mass solely as a function of the inertial number and the flow distance. This work sheds light on some of the first systematic and generalizable experimental parameterizations of ash production and associated clast evolution in PDCs and should advance our ability to understand flow mobility and associated hazards.

How to cite: Hornby, A., Kueppers, U., Maurer, B., Poetsch, C., and Dingwell, D.: Experimental constraints on volcanic ash generation and clast morphometrics in pyroclastic density currents and granular flows, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8568, https://doi.org/10.5194/egusphere-egu21-8568, 2021.

EGU21-2652 | vPICO presentations | GMPV9.6

Insights into lava dome and spine extrusion using analogue sandbox experiments

Edgar Zorn, Thomas Walter, Michael Heap, and Ulrich Kueppers

Lava dome formation is a common process at stratovolcanoes involving the shallow intrusion or extrusion of viscous lava and may lead to the rise of spines. Spines are protrusions observed to extrude episodically during lava dome growth, yet the structural and mechanical factors controlling their formation are only partially understood. Here, we provide new, detailed insight into lava dome growth and the production of spines using a novel set of analogue experiments extruding sand-plaster mixtures from a fixed-diameter conduit under isothermal conditions. We trace displacement and strain with photogrammetric methods for precise and detailed monitoring of the extrusion process. Results show initial dome growth forming a steep-sided and flat-topped shape through extrusion of new material, leading to slumping of oversteepening slopes, forming a talus. Spines are found to protrude at a later stage through the dome surface along discrete circular faults that originate from the conduit walls, starting a cycle of spine growth and collapse. As our spines only appear after prolonged extrusion, we relate their appearance to the compaction and strengthening of material within the conduit. We find that spine diameter, height and volume are positively correlated with increasing cohesion and therefore material strength. The spine diameter was also observed to be smaller or equal to the diameter of the underlying conduit, as shear extrusion occurs along vertical to outward-dipping fault planes. For natural domes, our findings imply that spine growth may be the consequence of compaction and densification via porosity loss, shearing and/or outgassing of conduit magma during ascent. More efficient compaction will yield wider and taller spines as a result of increasing rock strength. Our study further highlights the relevance of analogue experiments in the study of lava domes and spines, which remain one of the most hazardous and unpredictable features at dome-forming volcanoes worldwide.

How to cite: Zorn, E., Walter, T., Heap, M., and Kueppers, U.: Insights into lava dome and spine extrusion using analogue sandbox experiments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2652, https://doi.org/10.5194/egusphere-egu21-2652, 2021.

EGU21-10633 | vPICO presentations | GMPV9.6

Volcanic supersonic jets: an experimental study of the effect of particles on the shock cell structure and acoustic emissions.

Stefano Panunzi, Jacopo Taddeucci, Valeria Cigala, Ulrich Kueppers, Danilo Mauro Palladino, Juan José Peña Fernández, Piergiorgio Scarlato, and Jörn Sesterhenn

Explosive volcanic eruptions eject a mixture of gas and pyroclasts into the atmosphere at a range of velocities. Directly above the vent, in the gas-thrust region, a supersonic jet may be generated that strongly controls the eruptive dynamics. To improve our quantitative understanding of volcanic supersonic jets, the effect on particles within them, and their acoustic emission, we have performed small-scale explosive eruptions in the laboratory using a shock-tube. The shock-tube is composed of 3 parts, a bottom (5.6 m long, elevated pressure) and a top (48mm long, ambient pressure) plexiglass cylinder (5 mm inner diameter), separated by an electrovalve.

We have run experiments using ambient air as gas and sand, with diameter between 0.1 and 0.3 mm, as particles. The gas volume was fixed while the pressure ratio (the shock-tube reservoir to ambient pressure ratio) was varied from about 4 to 8.4 to obtain supersonic flows. During the experiments, the jet was recorded with a high-speed camera operating at 34660 fps, and the resulting noise acoustic emission with microphones (6 Hz-140 kHz; 1000 kfps) positioned at 90° from the jet axis.

Among the acoustic signals produced by a supersonic jet (jet noise) we have particularly focussed on the broad-band shock noise (BBSN) that is emitted by the interaction between shock cells and the turbulence in the jet. We estimated the jet velocity using an acoustic model based on the identification of the peak frequency of the BBSN. We also identified the BBSN frequency and its variation over time by applying the complex Morlet wavelet transformation. As expected, the BBSN frequency is inversely proportional to the gas velocity. Concerning the video recording, we analysed the shock cells behaviour and their temporal oscillation due to the presence of particles. Finally, the particle ejection rate was calculated in every video frame.

We found that the acoustic signal and shock cells are influenced by the presence of particles. In fact, fluctuations in particle concentration are well visible and decelerate the flowing gas. As a consequence, there is a temporary decrease of the stand-off-distance between the vent and the first shock-cell and concurrent rise of the BBSN frequency. We noticed, in some cases, that the shock-cells disappear during a short time interval. The BBSN frequency and the stand-off-distance behaviour over time follow the oscillation of the particle ejection rate confirming their sensitivity to particle load variation.

The future prospectives of this embryonal study could lead to new instruments for determining either the amount of pyroclasts inside the volcanic jets and their exit velocity on the basis of the recorded acoustic signals.

How to cite: Panunzi, S., Taddeucci, J., Cigala, V., Kueppers, U., Palladino, D. M., Peña Fernández, J. J., Scarlato, P., and Sesterhenn, J.: Volcanic supersonic jets: an experimental study of the effect of particles on the shock cell structure and acoustic emissions., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10633, https://doi.org/10.5194/egusphere-egu21-10633, 2021.

EGU21-10275 | vPICO presentations | GMPV9.6

Experimental determination of fragmentation efficiency for Plinian and Pelean eruptions of Mt. Pelée, Martinique

Mila Huebsch, Ulrich Kueppers, Guillaume Carazzo, Anne-Marie Lejeune, Audrey Michaud-Dubuy, and Donald B. Dingwell

Mt. Pelée is a historically active volcano, situated on the island of Martinique (Lesser Antilles), that has shown a variety of explosive styles in the recent past, ranging from dome-forming (Pelean) to open-vent (Plinian) eruptions.  The 1902-1905 eruption is infamous for the pyroclastic density currents (PDCs) that destroyed the towns of St. Pierre and Morne Rouge, killing 30 000 residents.  Since the last eruption (dome-forming) in 1929-1932, Mt. Pelée was quiet and considered dormant until recently.  In late 2020, the local Volcanological Observatory (OVSM) raised the alert level following a noticeable increase in seismicity, bringing into effect a reinforcement of monitoring resources.  As St. Pierre is long since re-established, along with several other towns along the volcano’s flanks, it is of utmost importance to understand the possible range of eruptive activity to improve the preparedness strategies of local communities.

The precise controls on eruption dynamics vary across volcanic systems and cannot be constrained via direct observation. However, crucial inferences can be made based on petrophysical properties and mechanical behaviours of erupted materials.  For this study, we collected samples from PDC deposits of Mt. Pelée, from the two historic Pelean (1902-1905, and 1929-1932) and three pre-Columbian Plinian eruptions (1300 CE P1, 280 CE P2, and 79 CE P3). We measured petrophysical properties (density, porosity, permeability) of cylindrical samples drilled from bomb-sized clasts and investigated their fragmentation behaviour via grain size and high-speed video analysis. These results are used in comparison with field data of grain-size distribution (GSD) of individual outcrops and calculated total GSD data.  We investigated the effects of transport-related sorting or fining.

The “Pelean” samples are found to be denser (32-47% open porosity) than the pumiceous “Plinian” samples (55-66% open porosity).  Moreover, these two classes are distinctly different in their crystallinity as samples underwent different ascent conditions.  In our experiments, distinct fragmentation behaviour and resulting GSDs are observed for samples from each eruption style, regardless of experimental pressure conditions (5-20 MPa). Our results show the paramount importance of open porosity on fragmentation efficiency in pumiceous samples, alongside a strong influence of crystallinity.  The fractal dimension of fragmentation calculated from weight fractions, independent of grain shape, shows clear differences in fragmentation efficiency as a function of sample properties and experimental starting conditions.

Our results suggest that (i) the variability in porosity and permeability is too low to cause the increased explosivity exhibited during the 1902 eruption compared to the 1929 event, (ii) open porosity has a major control on fragmentation efficiency in pumiceous samples, (iii) fragmentation efficiency can be effectively evaluated by calculating the fractal dimension of the cumulative weight fractions of experimental products.

The influence of crystallinity and pore textures on fragmentation efficiency must be further investigated to aid hazard model development for future eruptions of Mt. Pelée. Future work will constrain these textural parameters of naturally and experimentally fragmented materials from Mt. Pelée, to further elucidate the controls on eruptive dynamics at this hazardous volcano.

How to cite: Huebsch, M., Kueppers, U., Carazzo, G., Lejeune, A.-M., Michaud-Dubuy, A., and Dingwell, D. B.: Experimental determination of fragmentation efficiency for Plinian and Pelean eruptions of Mt. Pelée, Martinique, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10275, https://doi.org/10.5194/egusphere-egu21-10275, 2021.

EGU21-4545 | vPICO presentations | GMPV9.6

Controls on Eruption Style at La Soufrière de Guadeloupe from Melt Inclusions and Mineral Diffusion Timescales.

Abigail Metcalfe, Séverine Moune, and Jean-Christophe Komorowski

Signals of volcanic unrest do not usually provide insights into the timing, size and style of future eruptions. However, analysis of past eruptions provides useful information in order to understand the evolution, magma storage and onset of future eruptions, Here, we examine basaltic-andesitic to andesitic eruption deposits from La Soufrière de Guadeloupe, covering a range of eruption styles, ages and magnitudes. Our work is timely given unrest at this system has increased over the last 25 years, with a potential eruption capable of directly impacting ~70,000 people in Southern Basse-Terre.

Here, we study the geochemistry of pre-eruptive magmas and timescales of magmatic processes preceding four explosive eruptions: 1657 Cal. CE (Vulcanian), 1010 Cal. CE (Plinian), ca. 341 Cal. CE (Strombolian) and 5680 Cal. BCE (Plinian). Using diffusion timescale studies of orthopyroxene phenocrysts, we constrain the timing of magma injections into the La Soufrière de Guadeloupe magmatic reservoir. These range from 35 ± 0.37 to 848 ± 0.4 days before eruption. Diffusion timescales do not appear to correlate with eruption style/size, but may correlate with other parameters (e.g., magma interactions in the reservoir and/or volatile content of the magma).

Major element concentrations in whole rock (WR), groundmass glasses (GM) and melt inclusions (MI) show a strong linear trend. However, this evolution cannot be resolved through fractional crystallisation alone, as there is no clear temporal trend. MIs reveal a relatively homogenous melt composition from the first to the most recent eruptions, ranging from 63.6 – 78.7 wt% SiO2. Volatiles, including H­2O (2.3-4.4 wt%), CO2 (35-866 ppm) and sulphur (30-202 ppm), are also consistent across the various eruptions. MIs are often more evolved than the GM, indicating they cooled prior to their entrainment. This, along with the different crystal populations observed, suggests a recharge magma has intruded through a mush system and entrained crystals stored there. Crystals in different regions of the mush therefore experience different interactions with magmatic processes.

The major element compositional homogeneity across the eruptions indicates that composition does not have a large control on eruption style at this system. However, MI pre-eruptive volatile contents are more concentrated in the larger Plinian eruptions (e.g., CO­2 – 866 ppm) than the smaller Vulcanian and Strombolian eruptions (e.g., CO­2 – 674 ppm). Volatile emissions calculated through the petrologic method also differ, with higher total volatile emissions observed in the Plinian eruptions (12 Mt) than the smaller eruptions (0.1 Mt). The Plinian eruptions also have a faster magma ascent rate (0.3-22 m/s) than the vulcanian eruptions (3 m/s) as calculated from mass flux estimates. 

Though the composition of the La Soufrière de Guadeloupe system has remained constant over time, changes in eruption style can result from variations: (i) in the way magma interacts with the mush system, (ii) in the pre-eruptive volatile contents and (iii) in the ascent rates. Understanding the controls on eruption style is important, especially during the current phase of unrest, in order to improve early-warning system efficiency, forecast models, eruption scenario crisis response and long-term risk reduction planning.

How to cite: Metcalfe, A., Moune, S., and Komorowski, J.-C.: Controls on Eruption Style at La Soufrière de Guadeloupe from Melt Inclusions and Mineral Diffusion Timescales., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4545, https://doi.org/10.5194/egusphere-egu21-4545, 2021.

EGU21-14665 | vPICO presentations | GMPV9.6

Conduit processes of the Sf. Ana (TGS) sub-Plinian-Vulcanian eruption sequence of the Ciomadul volcano (SE Carpathians)

Balázs Kiss, Dávid Karátson, László Aradi, János Szepesi, Tamás Biró, Tamás Sági, Veronika Szilágyi, and Zoltán Kis

The Sf. Ana crater is the young volcanic crater of the dacitic Ciomadul volcano located at the SE end of the Călimani-Gurghiu-Harghita volcanic chain in the Eastern Carpathians. The crater was formed at ~60-30 kyr-s ago probably by several eruptions. The Sf. Ana also called as TGS eruption sequence was the main event that shaped the crater to the present form. The eruption produced fall and PDC deposits, but it is unclear what caused the change in the eruption style. The stratigraphically controlled analyses of the Mohos Layered Pyrolcalstic Sequence (MLPS) provide deep insight into the evolution of the eruption. Assuming that juvenile clast density is primarily controlled by the magma vesiculation within the conduit, the processes close to the fragmentation level can be studied. The vesicularity, vesicle texture, microlite texture, and glass H2O content of the juvenile pyroclasts were studied to reveal the conduit processes. The juvenile clasts show textural evidence for different stages of the vesiculation from bubble nucleation to collapse indicating degassing and outgassing processes in the conduit. The increase of the juvenile clast density upward in the MLPS and the sharp increase of the dense clasts in the PDC deposits indicate the effect of magma column heterogeneity on the eruption style. The conduit heterogeneity was induced by the effective outgassing of the slowly ascending magma portion due to the evolution of vesicle textures together with localized shearing. The eruption column collapse was preceded by a vent failure event which caused densification in the conduit. Banded pumices suggest that the observed conduit heterogeneity was small scale.

 

The study is supported by the PD130214 project National Research, Development, and Innovation Fund of Hungary.

How to cite: Kiss, B., Karátson, D., Aradi, L., Szepesi, J., Biró, T., Sági, T., Szilágyi, V., and Kis, Z.: Conduit processes of the Sf. Ana (TGS) sub-Plinian-Vulcanian eruption sequence of the Ciomadul volcano (SE Carpathians), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14665, https://doi.org/10.5194/egusphere-egu21-14665, 2021.

EGU21-107 | vPICO presentations | GMPV9.6

Hydrothermal alteration and sealing at Turrialba as a mechanism for phreatic eruption triggering

Emily Mick, John Stix, J. Maarten de Moor, and Geoffroy Avard

Turrialba is a basaltic to andesitic Holocene stratovolcano that after decades of quiescence re-activated in 1996 and has been highly active ever since. Turrialba is characterized by a highly active magmatic-hydrothermal system, and we propose that hydrothermal sealing and volatile accumulation are the mechanisms responsible for the reactivation and persistent phreatic activity at Turrialba since 2010. Evidence of sealing is found in pyroclastic breccias from phreatic eruptions as high concentrations of hydrothermal minerals coupled with low intrinsic permeability. The suite of volcanic breccias studied erupted from the main vent between 2014 and 2019 and has an alteration mineral assemblage of SiO2polymorphs ± gypsum ± natroalunite ± pyrite. The mineral assemblage is indicative of acid sulphate alteration within the advanced-argillic alteration facies characterized by temperatures of approximately 200-350°C as indicated by the presence of gypsum and natroalunite, the high temperature endmember of the alunite series. Acid sulphate alteration is the result of extreme base leaching by acidic fluids (pH<4) with a high sulphate content. Measurements of permeability and porosity yielded variable porosity and very low to non-existent permeability in all hydrothermal breccia samples. Back-scatter electron (BSE) images reveal nano-, micro- and macro-scale fracture networks discontinuously filled with hydrothermal gypsum and pyrite which are responsible for diminished permeability, supporting the conclusion that hydrothermal sealing is active at Turrialba. Diminished permeability associated with the formation of a seal inhibits the escape of gases, causing them to accumulate below the seal and pressurize the system. Eventual seal failure releasing overpressure and possibly dynamic rapid seal formation result in the frequent phreatic eruptions seen at Turrialba.

How to cite: Mick, E., Stix, J., de Moor, J. M., and Avard, G.: Hydrothermal alteration and sealing at Turrialba as a mechanism for phreatic eruption triggering, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-107, https://doi.org/10.5194/egusphere-egu21-107, 2021.

EGU21-6916 | vPICO presentations | GMPV9.6

Using apatite records of volatile budget and magma ascent rates to investigate eruption dynamics

Olivier Bernard, Weiran Li, Fidel Costa, and Caroline Bouvet de Maisonneuve

One of the major challenges faced by volcanologists to investigate controls on eruption dynamics is to quantify both pre-eruptive volatile budgets and timescales of magma ascent. Indeed, petrological investigations of the two parameters usually rely on different methods/analytical techniques that are not always applicable/accessible. Recent studies have shown that the abundance and zoning pattern of F, Cl, and OH in apatite can be used to determine both pre-eruptive volatile budget and magma degassing rates that can, under some conditions, be related to magma ascent rates ([1],[2]).

Here we apply the two methods to apatite in the Rabaul 2006 eruption deposits (Papua-New-Guinea). This was a VEI-4 eruption and occurred in three main phases: (1) a sub-plinian onset followed 12h after its start by (2) a mixed strombolian-effusive phase, which subsequently evolved into (3) discrete vulcanian explosions. We sampled deposits of the three phases: (1) pumices, (2) fragments of lava flow, and (3) fragments of cow-pad bombs.

We calculated pre-eruptive water contents using apatite included in clinopyroxene as they keep a better record of reservoir conditions from the time of entrapment. We found that the magma that fed the sub-plinian phase contained the highest water content of about 2 wt.%, while magmas that fed the lava flow and the vulcanian phase were drier, with 0.2 to 0.5 wt.% less H2O. X-ray maps acquired with an EPMA show that only apatite crystals in the groundmass of the vulcanian and effusive deposits are zoned in F and Cl at the crystal rims, whereas those from the sub-plinian deposits and included in clinopyroxenes are not zoned. This indicates that the zoning is related to syn- or immediately pre-eruptive changes of Cl-F-H2O during magma ascent towards the surface and can thus be modelled as diffusive reequilibration of the crystal and the melt. We obtained maximum diffusion timescales of <8 hours for the unzoned apatite in sub-plinian deposits, timescales of 20–22 hours for apatite in vulcanian deposits, and 600–1500 hours for those in the lava flow. Thus, the time scales increase with decreasing explosivity of the eruptions, as it could be expected if magma ascent rate played the key role of eruption dynamics. However, the degassing timescales of the effusive phase are significantly longer than the eruption duration itself, which can be explained if the magma started rising in the system 1–3 months prior to the onset of the eruption. The volatile-rich, fast-rising magma that fed the initial sub-plinian phase propagated through, disturbed and remobilized the shallower, more degassed batch of magma, which was erupted during the following effusive phase. Deeper, volatile-poor magma that kept moving up the open conduit, was responsible for the late vulcanian explosions.

Our results show that apatite is a powerful tool for probing slight changes in magma volatile chemistry and ascent rates that can vary between different phases of the same eruption and produce different eruption styles.

 

[1] Li and Costa, 2020, GCA [2] Li et al. 2020, EPSL

How to cite: Bernard, O., Li, W., Costa, F., and Bouvet de Maisonneuve, C.: Using apatite records of volatile budget and magma ascent rates to investigate eruption dynamics, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6916, https://doi.org/10.5194/egusphere-egu21-6916, 2021.

EGU21-13287 | vPICO presentations | GMPV9.6

A myriad of melt inclusions: a synchrotron microtomography study of melt inclusions and vapour bubbles from Colli Albani (Italy)

Corin Jorgenson, Luca Caricchi, Michael Stueckelberger, Giovanni Fevola, and Gregor Weber

Melt inclusions provide a window into the inner workings of magmatic systems. Both mineral chemistry and volatile distributions within melt inclusions can provide valuable information about the processes modulating magma ascent and preceding volcanic eruptions. Many melt inclusions host vapour bubbles which can be rich in CO2 and H2O and must be taken into consideration when assessing the volatile budget of magmatic reservoirs. These vapour bubbles can be the product of differential volumetric contraction between the melt inclusion and host phase during an eruption or indicate an excess fluid phase in the magma reservoir. Thus, determining the distribution of volatiles between melt and vapour bubbles is integral to our fundamental understanding of melt inclusions, and by extension the evolution of volatiles within magmatic systems.

A large dataset of 79 high-resolution tomographic scans of clinopyroxene and leucite phenocrysts from the Colli Albani Caldera Complex (Italy) was recently acquired at the German Electron Synchrotron (DESY). These tomograms allow us to quantify the volume of melt inclusions and associated vapour bubble both glassy and microcrystalline melt inclusions. Notably, in the glassy melt inclusions the vapour bubbles exist either as a single large vapour bubble in the middle of the melt inclusion or as several smaller vapour bubbles distributed around the edge of the melt inclusion. These two types of melt inclusions can coexist within a single crystal. We suggest that the occurrence of these rim- bubbles is caused by one of two exsolution pathways, either pre-entrapment and bubble migration or post entrapment with preferential exsolution at the rims. By combining the analysis of hundreds of melt inclusions with the chemistry of the host phase we aim to unveil magma ascent rates and distribution of excess fluids within the magmatic system of Colli Albani, which produced several mafic-alkaline large volume ignimbrites.

How to cite: Jorgenson, C., Caricchi, L., Stueckelberger, M., Fevola, G., and Weber, G.: A myriad of melt inclusions: a synchrotron microtomography study of melt inclusions and vapour bubbles from Colli Albani (Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13287, https://doi.org/10.5194/egusphere-egu21-13287, 2021.

EGU21-15199 | vPICO presentations | GMPV9.6

Chemical-physical constraints of the 2015 eruptive activity of Mt. Etna: new insights from thermo-barometry and geochemistry of olivine-hosted melt inclusions

Pier Paolo Giacomoni, Federico Casetta, Virginia Valenti, Carmelo Ferlito, Gabriele Lanzafame, and Manuela Nazzari

The concomitant activation off all four summit craters of Mt. Etna during the December 2015 eruptive event allow us to investigate the chemical-physical crystallization conditions and magma dynamics in the shallower portion of the open-conduit feeding system. In this study, we discuss new petrological, geochemical and thermo-barometric data as well as the composition of major element and volatile content (H2O, CO2, F, Cl and S) of olivine-hosted melt inclusions from the explosive and effusive products emitted during the December 2015 eruptive event.

Results and rhyolite-MELTS thermodynamic modelling of mineral phase stability highlight the relatively shallow crystal equilibrium depth prior to the eruption ranging from 400-500 MPa for Central Crater and North East Crater, up to 200 MPa below the New South East Crater. The study of high-pressure and high-temperature homogenized olivine-hosted melt inclusions allowed us to identify the composition of the almost primary alkali-basalt magma (11.8 wt% MgO) containing up to 4.9 wt% and 8151 ppm of H2O and CO2 respectively. The results, together with those already reported for the previous paroxystic events of the 2011-2012 (Giacomoni et al., 2018), reinforce the model of a vertically extended feeding system and highlight that the activity at the New South East Crater was fed by a magma residing at significant shallower depth with respect to Central Craters and North East Crater, although all conduits are fed by a common deep (P = 530-440 MPa) basic magmatic refilling. Plagioclase stability model and dissolution and resorption textures confirm its dependence on H2O content, thus suggesting that further studies on the effect that flushing from fluids with different H2O/CO2 ratio are needed in order to understand the eruption triggering mechanisms of paroxystic fountaining.

 

References

Giacomoni P., Coltorti M., Mollo S., Ferlito C., Braiato M., Scarlato P. 2018. The 2011-2012 paroxysmal eruptions at Mt. Etna volcano: Insights on the vertically zoned plumbing system. JVGR 349, 370-391.

How to cite: Giacomoni, P. P., Casetta, F., Valenti, V., Ferlito, C., Lanzafame, G., and Nazzari, M.: Chemical-physical constraints of the 2015 eruptive activity of Mt. Etna: new insights from thermo-barometry and geochemistry of olivine-hosted melt inclusions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15199, https://doi.org/10.5194/egusphere-egu21-15199, 2021.

EGU21-6746 | vPICO presentations | GMPV9.6

Decrease in Volcano Jet Noise Peak Frequency from Crater Expansion

Kathleen McKee, Eveanjelene Snee, Sean Maher, Cassandra Smith, Kevin Reath, Diana Roman, Robin S. Matoza, Simon Carn, Larry Mastin, Kyle Anderson, David Damby, Anna Perttu, Jelle Assink, Rodrigo de Negri Leiva, Artem Degterev, Alexander Rybin, Marina Chibisova, Ima Itikarai, Kila Mulina, and Steve Saunders

Volcanic jet noise is the sound, often below the human audible range (<20 Hz and termed infrasound), generated by momentum-driven fluid flow through a volcanic vent. Assuming the self-similarity of jet flows and audible jet noise extends to infrasonic volcanic jet noise, the Strouhal number, St=Djf/Uj, connects frequency changes, f, to changes in the jet length (expanded jet diameter, Dj) and/or velocity scale (jet velocity, Uj). We examine the infrasound signal characteristics from the June 2019 VEI 4 eruptions of Raikoke, Kuril Islands and Ulawun, Papua New Guinea volcanoes with changes in crater geometry. We use data from the International Monitoring System (IMS) infrasound network and pre- and post-eruption satellite data (RADARSAT-2 and PlanetScope imaging for Raikoke and Ulawun, respectively). During both eruptions we observe a decrease in infrasound peak frequency during the transition to a Plinian phase, which remains through the end of the eruptions. The RADARSAT-2 data show a qualitative increase in the crater area at Raikoke; quantitative analysis is limited by shadows. At Ulawun, however, we estimate an increase in crater area from ~35,000 m2 on May 25, 2019 to ~66,000 m2 on July 17, 2019. We assume a constant Strouhal number and use the crater diameter as a proxy for expanded jet diameter. Our analysis suggests that the increase in crater diameter alone cannot account for the decrease in peak frequency during the Ulawun eruption. This suggests that the jet velocity also increased, which fits satellite data, and or the fluid properties (e.g. particle loading, nozzle geometry and roughness, etc.) changed. This is reasonable as the Ulawun eruption went Plinian, which likely involved an increase in jet velocity and erosion of the crater walls. This is the first study to corroborate the decrease in infrasound peak frequency with documented increase in crater area. The fortuitous satellite overpass timing, clear skies, and high spatial resolution enabled the quantitative examination of the Ulawun eruption.

How to cite: McKee, K., Snee, E., Maher, S., Smith, C., Reath, K., Roman, D., Matoza, R. S., Carn, S., Mastin, L., Anderson, K., Damby, D., Perttu, A., Assink, J., de Negri Leiva, R., Degterev, A., Rybin, A., Chibisova, M., Itikarai, I., Mulina, K., and Saunders, S.: Decrease in Volcano Jet Noise Peak Frequency from Crater Expansion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6746, https://doi.org/10.5194/egusphere-egu21-6746, 2021.

EGU21-12049 | vPICO presentations | GMPV9.6

New insights into magmatic processes from integrated satellite observation, trajectory analysis and magma ascent modelling

Mike Burton, Giuseppe La Spina, Catherine Hayer, and Benjamin Esse

Analysis of TROPOMI data with plume trajectory tools opens the possibility of new insights into volcanic / magmatic processes from two data sources: SO2 flux time series and plume height time series. In this paper we investigate results from explosive eruptions and attempt to explain the results with a magma ascent conduit model. The combination of plume height and gas flux data with a model of the magma ascent process provides a toolkit which allows us to constrain magma reservoir processes from satellite monitoring data. The combination of modelling and observations opens a new volcanological research frontier, because the TROPOMI sensor has daily global coverage, a high spatial resolution and is sensitive enough to detect many small-medium explosions globally, so that a large inventory of explosive activity can be characterised. 

How to cite: Burton, M., La Spina, G., Hayer, C., and Esse, B.: New insights into magmatic processes from integrated satellite observation, trajectory analysis and magma ascent modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12049, https://doi.org/10.5194/egusphere-egu21-12049, 2021.

EGU21-10661 | vPICO presentations | GMPV9.6

Role of rheology, ascent rate and outgassing on fragmentation: implications for basaltic lava fountains

Giuseppe La Spina, Fabio Arzilli, Ed Llewellin, Mike Burton, Amanda Clarke, Mattia de’ Michieli Vitturi, Margherita Polacci, Margaret Hartley, Danilo Di Genova, and Heidy Mader

Basaltic volcanoes exhibit a wide range of eruptive styles, from relatively gentle effusive eruptions (producing lava flows and lava domes) to highly explosive activity (where pyroclastic materials are ejected from the vent as a jet or plume). The difference between explosive and effusive eruptions is dictated by the ability of magma to fragment during ascent. For lava fountains the distinction is unclear, as the liquid phase in the rising magma may remain continuous to the vent, fragment in the fountain, then re-weld on deposition to feed rheomorphic lava flows.

Here we use a magma ascent model to constrain the controls on basaltic eruption style, using Kilauea and Etna as case studies. Following our results, we suggest that lava fountaining is a distinct style, separate from effusive and explosive eruption styles, that is produced when magma ascends quickly and fragments above the vent, rather than within the conduit. Performing sensitivity analyses of Kilauea and Etna case studies we found that high lava fountains (> 50 m high) occur when the Reynolds number of the bubbly magma is greater than ~0.1, the bulk viscosity is less than 106 Pa s, and the gas is well-coupled to the melt. According to our results, explosive eruptions (Plinian and sub-Plinian) are expected over a wide region of parameter space for higher viscosity basalts, typical of Etna, but over a much narrower region of parameter space for lower viscosity basalts, typical of Kilauea. Numerical simulations indicate also that the magma that feeds high lava fountains ascends more quickly than the magma that feeds explosive eruptions, thanks to its lower viscosity. For the Kilauea case study, a decreasing ascent velocity is expected to produce a progressive evolution from high to weak fountaining, to ultimate effusion. For the Etna case study, instead, small changes in parameter values lead to transitions to and from explosive activity, indicating that eruption transitions may occur with little warning.

How to cite: La Spina, G., Arzilli, F., Llewellin, E., Burton, M., Clarke, A., de’ Michieli Vitturi, M., Polacci, M., Hartley, M., Di Genova, D., and Mader, H.: Role of rheology, ascent rate and outgassing on fragmentation: implications for basaltic lava fountains, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10661, https://doi.org/10.5194/egusphere-egu21-10661, 2021.

EGU21-15923 | vPICO presentations | GMPV9.6

Open volcanic systems: evidence for deep gas loss

Marielle Collombet, Alain Burgisser, Mathieu Colombier, and Elizabeth Gaunt

Previous studies of Vulcanian eruptive products have shown that the respective volcanic conduits were filled for the
most part with low-porosity magma prior to eruption. Comparison with the theoretical porosity distribution
expected from closed-system degassing suggests that gas loss must have taken place at great depth within the
magmatic column. At such high pressures, however, porosities are low enough to rule out traditional gas loss
mechanisms. We tested if channelling, an outgassing mechanism based on bubble connection due to high crystal
content proposed to occur in mushy magma reservoirs, could also happen in volcanic conduits. We reanalysed
phenocryst, microlite, and porosity data from recent eruptions of Merapi volcano, Indonesia, Soufrière Hills
volcano, Montserrat, and Tungurahua volcano, Ecuador. Overall, these magmas had crystal contents high enough
for outgassing to occur by channelling. Gases could be channelled out of the magma columns at various levels
during ascent to yield mostly gas-depleted magma columns prior to explosive behaviour. Such outgassing by
channelling has thus the capacity to influence eruptive style. Depending on the phenocryst content, microlite
growth during ascent can either foster, or impede gas escape by channelling. Considering the pervasive occurrence
of microlites and ensuing high crystal contents in volcanic conduits, the high likelihood of channelling implies that
other outgassing mechanisms might not be as dominant as previously envisioned.

How to cite: Collombet, M., Burgisser, A., Colombier, M., and Gaunt, E.: Open volcanic systems: evidence for deep gas loss, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15923, https://doi.org/10.5194/egusphere-egu21-15923, 2021.

GMPV10.1 – Volcano hazard modelling

EGU21-3212 | vPICO presentations | GMPV10.1 | Highlight

Ensemble-based volcanic ash forecasts using satellite retrievals for quantitative verification

Antonio Capponi, Natalie J. Harvey, Helen F. Dacre, Keith Beven, and Mike R. James

Volcanic ash poses a significant hazard for aviation. If an ash cloud forms as result of an eruption, it forces a series of flight planning decisions that consider important safety and economic factors. These decisions are made using a combination of satellite retrievals and volcanic ash forecasts issued by Volcanic Ash Advisory Centres.  However, forecasts of ash hazard remain deterministic, and lack quantification of the uncertainty that arises from the estimation of eruption source parameters, meteorology and uncertainties within the dispersion model used to perform the simulations. Quantification of these uncertainties is fundamental and could be achieved by using ensemble simulations. Here, we explore how ensemble-based forecasts — performed using the Met Office dispersion model NAME — together with sequential satellite retrievals of ash column loading, may improve forecast accuracy and uncertainty characterization.

We have developed a new methodology to evaluate each member of the ensemble based on its agreement with the satellite retrievals available at the time. An initial ensemble is passed through a filter of verification metrics and compared with the first available set of satellite observations. Members far from the observations are rejected. The members within a limit of acceptability are used to resample the parameters used in the initial ensemble, and design a new ensemble to compare with the next available set of satellite observations. The filtering process and parameter resampling are applied whenever new satellite observations are available, to create new ensembles propagating forward in time, until all available observations are covered.

Although the method requires the run of many ensemble batches, and it is not yet suited for operational use, it shows how combining ensemble simulations and sequential satellite retrievals can be used to quantify confidence in ash forecasts. We demonstrate the method by applying it to the recent Raikoke (Kurii Islands, Russia) eruption, which occurred on the 22nd July 2019. Each ensemble consists of 1000 members and it is evaluated against 6-hourly HIMAWARI satellite ash retrievals.

How to cite: Capponi, A., Harvey, N. J., Dacre, H. F., Beven, K., and James, M. R.: Ensemble-based volcanic ash forecasts using satellite retrievals for quantitative verification, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3212, https://doi.org/10.5194/egusphere-egu21-3212, 2021.

EGU21-7594 | vPICO presentations | GMPV10.1 | Highlight

Assessing potential impacts on the air traffic routes due to an ash-producing eruption on Jan Mayen Island (Norway)

Manuel Titos, Beatriz Martínez, Sara Barsotti, Laura Sandri, Arnau Folch, Leonardo Mingari, Antonio Costa, and Giovanni Macedonio

Jan Mayen Island (Norway), located in the North Atlantic, is considered the world’s northernmost active subaerial volcano, with at least five eruptive periods recorded during the last 200 years. Explosive activity of the volcano may seriously affects the nearby important air traffic routes. However, no quantitative studies on the possible impact of a new explosive volcanic eruption on the air traffic have been conducted.  In this work, we statistically characterise the spatial and temporal distribution of airborne volcanic ash cloud and its persistence at different flight levels. Since current operational forecast products do not always meet the requirements of the aviation sector and related stakeholders (using coarse time and space scales, with outputs on a 40 km horizontal resolution grid and 6 hour time averages), and they neglect epistemic/aleatory uncertainties in quantitative forecasts on real time, we propose hourly high resolution hazard maps over a 3D-grid covering a 2 km-resolution spatial domain 2000 km x 2000 km wide. We present the use of high-performance computing (HPC) to overcome the computational limitations associated with unbiased long-term probabilistic volcanic hazard assessment (PVHA) .Considering a continuum of possible combinations of Eruptive Source Parameters (ESP) to assess and quantify the uncertainty, and the natural variability associated with wind fields over 20 years of data, from 1999 to 2019, we run thousands of analytical solutions (numerical simulations) using the most recent version of the FALL3D model. As a result, the first comprehensive long-term PVHA for Jan Mayen volcanic island is presented.

How to cite: Titos, M., Martínez, B., Barsotti, S., Sandri, L., Folch, A., Mingari, L., Costa, A., and Macedonio, G.: Assessing potential impacts on the air traffic routes due to an ash-producing eruption on Jan Mayen Island (Norway), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7594, https://doi.org/10.5194/egusphere-egu21-7594, 2021.

EGU21-13871 | vPICO presentations | GMPV10.1

Forecasting the dispersion and fallout of volcanic ash during a crisis: Assessment of the September 20, 2020 eruption at Sangay volcano in Ecuador

Benjamin Bernard, Pablo Samaniego, and Marjorie Encalada Simbaña

Sangay volcano (2.00°S, 78.34°W, 5326 m asl), located at the southern end of the Northern Volcanic Zone of the Andes (Morona Santiago province, Ecuador), has frequently been referred as one of the most active volcanoes in the world. Its most recent eruptive period began on May 7, 2019 and is still ongoing. It is characterized by a semi-continuous viscous lava flow emission accompanied by frequent low magnitude explosions (Vasconez et al., this meeting). This eruptive episode is the first in more than two decades to produce significant impacts both locally and regionally, and reached its paroxysm on September 20, 2020 without clear precursory signals. The eruption started at 9:20 (UTC) and lasted about one and a half hours. The eruptive column rapidly split into a high-altitude (15 km asl) gas-rich cloud, drifting eastward at 5-8 m/s and a lower (12 km asl) ash-rich cloud, drifting westward at 10-14 m/s. The ash began to fall at 11:00 (UTC) in the communities near the volcano and reached the city of Guayaquil, the second largest city in Ecuador, at 13:00 (UTC), forcing the closure of the international airport.

In this work, we evaluate the ash dispersion simulations performed by the IG-EPN using the Ash3D model before, during and after the eruption using different eruptive source parameters (ESP), by comparison with the available satellite images (GOES-16). The simulated ash fallout for each set of ESP is compared to reports from the community and volcanic observers, as well as with a fallout map obtained from a four-days field trip initiated immediately after the eruption to ensure good quality of samples and measurements (September 20-23). Ash fallout was estimated using thickness measurements where possible and area density at 40 sites located between 30 and 180 km from the volcano. The grain size distribution of 35 samples was obtained by laser diffraction.

Our results show that the general westward direction and speed of the ash cloud in the simulations is coherent with the satellite images, except for the high-altitude, gas-rich cloud. However, large discrepancies were found when comparing the simulated and measured ash fallout. Field data shows that the first simulation using ESP based on the previous activity at Sangay, underestimated the eruption size, while the second simulation using the eruption column height estimated in near-real time overestimated it. As expected, the simulation carried out immediately after the eruption, based on the first field results shows the best correlation with field data, although there are still some second-order discrepancies. In particular, the plume axis was shifted about 12° northward in the simulation, which is attributed to the atmospheric model. We also noted that the deposition pattern was slightly different between the field data and the simulation. Grain size analysis reveals uni- to multimodal distributions, associated with complex eruptive dynamics and aggregation that probably influenced the sedimentation process. Further research is needed to better understand the eruptive dynamics at Sangay in order to improve forecasts.

How to cite: Bernard, B., Samaniego, P., and Encalada Simbaña, M.: Forecasting the dispersion and fallout of volcanic ash during a crisis: Assessment of the September 20, 2020 eruption at Sangay volcano in Ecuador, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13871, https://doi.org/10.5194/egusphere-egu21-13871, 2021.

EGU21-2309 | vPICO presentations | GMPV10.1 | Highlight

Ashfall hazard: modelling volcanic ash roof loading and revisions to European Building Codes 

Nick Petford, Philip Quainoo, and Stefan Kaczmarczyk

This paper presents a numerical procedure for testing the effects of both static and dynamic loading of volcanic ash deposition on concrete roofs. The study aims to propose, a revision to the building regulations to make existing and future European buildings more resilient. The investigation uses a multi-physics simulation approach. Mathematical modelling is developed to investigate the volcanic ash effects in the context of the EN1991 code. A numerical modelling tool (EDEM software) for the Discrete Element Method (DEM) and structural analysis tool (ANSYS) for the Finite Element Method (FEM) is used to investigate 1 m x 1 m x 0.0154 m concrete slab plate subjected to pressure load considering the wind and no-wind effects. The modelled wind velocity was held constant at 0. 2 m/s. The density of the volcanic ash is low compared to natural systems but can be changed to reflect a range of relevant (measured) eruptive products. The key parameters and the results are illustrated as follows. With the initial results only, it is clear that our modelling technique has the potential to explore the loading effects of ash over a range of geological and environmental conditions during deposition.

The number of simulated volcanic particle loads is 80000, Volcanic ash particle density of 1000 (kg/m3). The simulated particle variables results for wind effects in the horizontal direction of (0.2 m/s) are as follows: The maximum pressures as 220042(Pa), the maximum deformation as 0.177 (mm) and the maximum was stress as 10.3 (MPa). The no wind effect (controlled condition) simulations particle variable results are as follows: the maximum pressures as 6411.3 (Pa), the maximum deformation as 0.061 (mm) and the maximum stress as 3.44 (MPa). 

As expected, the wind effect resulted in an uneven distribution of the ash on the roof surface, which in turn produced areas of high-pressure load and stress levels. These results will have a possible impact on the designs of buildings on flat roof considerations. We aim to continue with further investigations to determine the stress impact and collapse failure due to loading over a wide range of relevant volcanic ash particle size compositions.

How to cite: Petford, N., Quainoo, P., and Kaczmarczyk, S.: Ashfall hazard: modelling volcanic ash roof loading and revisions to European Building Codes , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2309, https://doi.org/10.5194/egusphere-egu21-2309, 2021.

EGU21-14206 | vPICO presentations | GMPV10.1

Plinian eruption of the Middle Pleistocene Irind volcano, Armenia

Khachatur Meliksetian, Hripsime Gevorgyan, Ivan Savov, Charles Connor, Laura Connor, Ralf Halama, Ruben Jrbashyan, Gevorg Navasardyan, Edmond Grigoryan, and Osamu Ishizuka

Large (VEI= 4-6) Quaternary explosive eruptions have repeatedly occurred in Armenia and the neighboring territories. Worth noting are the Plinian eruptions of Aragats stratovolcano (4096m), located in the vicinity of the Armenian capital city Yerevan (pop. >1 million) and producing lava flows variable in composition and size, pyroclastic density currents (PDCs) and fallout deposits (Connor et al., 2011; Gevorgyan et al., 2020). The youngest lavas from Aragats are 0.52 million years (myr) old and the youngest ignimbrites are 0.65 myr old. (Connor et al., 2011, Gevorgyan et al., 2020).

Here we present some features of a violent explosive Plinian eruption (VEI=4) from the relatively small, subsidiary Irind vent on the slopes of Aragats stratovolcano. We report results from newly mapped thick pumice fall deposits and pumice-rich welded lapilli-tuff and vitrophyres. Formation of up to ~10 m thick pumice fall deposits is related to a sustained Plinian eruption, while the formation of overlaying pumice tuffs (age= 0.490±0.028 M.yrs, Connor et al., 2011) and vitrophyre cover is interpreted as result of collapse of the eruption column due to a decrease of the magma supply.

Following the pyroclastic eruption, a voluminous (2.9-3.6 km3) effusive eruption of Irind created up to 120 m thick trachydacite lava flows that extended 18 km from the vent. Such long and thick lava flows are not typical for viscous felsic lavas. The Irind eruption products are characterized by a plagioclase-two pyroxene mineral association that is atypical for Aragats. The Irind magmas are trachydacitic  (SiO2= 66 wt; MgO= 0.7 wt%) with high- K2O contents (5.2 wt%) and enrichments in U, Th, LILE and LREE compared to Aragats. Geothermobarometry and hygrometry based on detailed textural analysis and mineral chemistry (Cpx, Opx, plagioclase, glass) reveals that Irind magmas also have elevated H2O, increased alkalinity and high T (~970 °C)- all features capable to generate magmas with much lower viscosity (4.2–4.5 log η Pa·s) in respect to typical dacites.

Our results support the view that often small eruptive vents (Irind) on the slopes of large coeval stratovolcanoes (Aragats) are not necessarily tapping their voluminous magma mushes underneath and are capable to deliver independent Plinian eruptions. We speculate that these are triggered by intrusions of hot, volatile-rich, alkaline felsic magmas, presumably emplaced fast, similar to the Chaiten eruption in 2008, and did not mix well with the otherwise dominant and older magmatic system under Aragats.

References

Connor C., Connor L., Halama, R., Meliksetian, K., Savov, I., 2011. Volcanic Hazard Assessment of the Armenia Nuclear Power Plant Site, Final Report, 278 pp.

Gevorgyan, H., Breitkreuz, C., Meliksetian, K, et al., 2020. Quaternary ring plain- and valley-confined pyroclastic deposits of Aragats stratovolcano (Lesser Caucasus): Lithofacies, geochronology and eruption history, JVGR 401, 1-22. 

How to cite: Meliksetian, K., Gevorgyan, H., Savov, I., Connor, C., Connor, L., Halama, R., Jrbashyan, R., Navasardyan, G., Grigoryan, E., and Ishizuka, O.: Plinian eruption of the Middle Pleistocene Irind volcano, Armenia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14206, https://doi.org/10.5194/egusphere-egu21-14206, 2021.

EGU21-9334 | vPICO presentations | GMPV10.1

The Effects of the Quasi-Biannual Oscillation on Tephra Distribution from a Plinian Eruption

Steffen Eisele, Yang Qingyuan, Caroline Bouvet de Maissoneuve, and Susanna F. Jenkins

The quasi-biannual oscillation (QBO) dominates the equatorial zonal wind in the tropical stratosphere. Alternating easterly and westerly wind regimes form in the upper stratosphere and propagate downwards to the tropopause with a mean period of approximately 28 months. The westerly phase of the QBO is characterized by faster and more regular downward propagation, while the easterly phase has higher intensity (up to double the wind speed) and longer duration. Long-term lower stratospheric wind records indicate prevailing easterly winds (~60 % of the time) for the tropical regions. However, during westerly phases of the QBO, the wind is exclusively blowing towards the east. This leads to different but well predictable tephra distributions during the two phases. The QBO is effectively controlling the variations of the lower stratospheric wind regimes between 15º N and 15º S. Therefore, the effects of the QBO on spatial tephra distribution impact all tropical volcanic regions, including Central America, SE-Asia, the Andean Northern Volcanic Zone and the African Rift. We use the Tephra2 model in a case study from Tandikat volcano in West Sumatra to analyse the different QBO phases' effects on tephra distribution from Plinian eruptions. Incorporating the QBO in probabilistic hazard assessments for Plinian eruptions improves the accuracy of the hazard assessments. Understanding the effects of the QBO on the spatial tephra distribution will also help re-evaluate distal tephra records.   

How to cite: Eisele, S., Qingyuan, Y., Bouvet de Maissoneuve, C., and Jenkins, S. F.: The Effects of the Quasi-Biannual Oscillation on Tephra Distribution from a Plinian Eruption, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9334, https://doi.org/10.5194/egusphere-egu21-9334, 2021.

EGU21-7833 | vPICO presentations | GMPV10.1

Particle size, leaf pubescence and condition of humidity at leaf surfaces are key factors determining the retention of volcanic ash on crop foliage.

Noa Ligot, Benoît Pereira, Patrick Bogaert, Guillaume Lobet, and Pierre Delmelle

Volcanic ashfall negatively affects crops, causing major economic losses and jeopardising the livelihood of farmers in developing countries where agriculture is at volcanic risk. Ash on plant foliage reduces the amount of incident light, thereby limiting photosynthesis and plant yield. An excessive ash load may also result in mechanical plant damages, such as defoliation and breakage of the stem and twigs. Characterising crop vulnerability to ashfall is critical to conduct a comprehensive volcanic risk analysis. This is normally done by describing the relationship between the ash deposit thickness and the corresponding reduction in crop yield, i.e. a fragility function. However, ash depth measured on the ground surface is a crude proxy of ash retention on plant foliage as this metrics neglects other factors, such as ash particle size, leaf pubescence and condition of humidity at leaf surfaces, which are likely to influence the amount of ash that stays on leaves.

Here we report the results of greenhouse experiments in which we measured the percentage of leaf surface area covered by ash particles for one hairy leaf plant (tomato, Solanum lycopersicum L.) and one hairless leaf plant (chilli pepper, Capsicum annuum L.) exposed to simulated ashfalls. We tested six particle size ranges (≤ 90, 90-125, 125-250, 250-500, 500-1000, 1000-2000 µm) and two conditions of humidity at leaf surfaces, i.e. dry and wet. Each treatment consisted of 15 replicates. The tomato and chilli pepper plants exposed to ash were at the seven- and eight-leaf stage, respectively. An ash load of ~570 g m-2 was applied to each plant using a homemade ashfall simulator. We estimated the leaf surface area covered by ash from pictures taken before and immediately after the simulated ashfall. The ImageJ software was used for image processing and analysis.

Our results show that leaf coverage by ash increases with decreasing particle size. Exposure of tomato and chilli pepper to ash ≤ 90 μm always led to ~90% coverage of the leaf surface area. For coarser particles sizes (i.e. between 125 and 500 µm) and dry condition at leaf surfaces, a significantly higher percentage (on average 29 and 16%) of the leaf surface area was covered by ash in the case of tomato compared to chilli pepper, highlighting the influence of leaf pubescence on ash retention. In addition, for particle sizes between 90 and 500 µm, wetting of the leaf surfaces prior to ashfall enhanced the ash cover by 19 ± 5% and 34 ± 11% for tomato and chilli pepper, respectively.

These findings highlight that ash deposit thickness alone cannot describe the hazard intensity accurately. A thin deposit of fine ash (≤ 90 µm) will likely cover the entire leaf surface area, thereby eliciting a disproportionate effect on plant foliage compared to a thicker but coarser deposit. Similarly, for a same ash depth, leaf pubescence and humid conditions at the leaf surfaces will enhance ash retention, thereby increasing the likelihood of damage. Our study will contribute to improve the reliability of crop fragility functions used in volcanic risk assessment.

How to cite: Ligot, N., Pereira, B., Bogaert, P., Lobet, G., and Delmelle, P.: Particle size, leaf pubescence and condition of humidity at leaf surfaces are key factors determining the retention of volcanic ash on crop foliage., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7833, https://doi.org/10.5194/egusphere-egu21-7833, 2021.

EGU21-10575 | vPICO presentations | GMPV10.1

The numerical reconstruction of three past eruptions at Gede volcano (Indonesia)

Eleanor Tennant, Susanna Jenkins, Annie Winson, Christina Widiwijayanti, Hendra Gunawan, Nia Haerani, Nugraha Kartadinata, Wilfridus Banggur, and Hetty Triastuti

Understanding past eruption dynamics at a volcano is crucial for forecasting the range of possible future eruptions and their associated hazards and risk. In this work we reconstructed pyroclastic density currents and tephra fall from three eruptions at Gede volcano, Indonesia with the aim of gaining further insight into past eruptions and identifying suitable eruption source parameters for future hazard and risk assessment. Gede has the largest number of people living within 100 km of any volcano worldwide, and has exhibited recent unrest activity, yet little is known about its eruption history. For pyroclastic density currents, we used Titan2D to reconstruct geological deposits dated at 1200 and c. 1000 years BP. An objective and quantitative multi-criteria method was developed to evaluate the fit of over 300 pyroclastic density current (PDC) model simulations to field observations. We found that the 1200 years BP geological deposits could be reproduced with either a dome collapse or column collapse as the generation mechanism although a relatively low basal friction of 6 degrees would suggest that the PDCs were markedly mobile. Lower basal frictions may reflect the occurrence of previous PDCs that smoothed the path, reducing frictional resistance and enabling greater runout for the reconstructed unit. For the 1,000 years BP PDC, a column collapse mechanism and higher basal friction was required to fit the geological deposits. In agreement with previous studies, we found that Titan2D simulations were most sensitive to the basal friction; however, we also found that the internal friction – often fixed and considered of low influence on outputs - can have a moderate effect on the simulated average deposit thickness. We used Tephra2 to reconstruct historic observations of tephra dispersed to Jakarta and other towns during the last known magmatic eruption of Gede in 1948. In the absence of observable field deposits, or detailed information from the published literature, we stochastically sampled eruption source parameters from wide ranges informed by analogous volcanic systems. Our modelling suggests that the deposition of tephra in Jakarta during the November 1948 eruption was a very low probability event, with approximately a 0.03 % chance of occurrence. Through this work, we exemplify the reconstruction of past eruptions when faced with epistemic uncertainty, and improve our understanding of past eruption dynamics at Gede volcano, providing a crucial step towards the reduction of risk to nearby populations through volcanic hazard assessment.

How to cite: Tennant, E., Jenkins, S., Winson, A., Widiwijayanti, C., Gunawan, H., Haerani, N., Kartadinata, N., Banggur, W., and Triastuti, H.: The numerical reconstruction of three past eruptions at Gede volcano (Indonesia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10575, https://doi.org/10.5194/egusphere-egu21-10575, 2021.

EGU21-16402 | vPICO presentations | GMPV10.1

The muesli effect in pyroclastic density currents - what does reverse grading in an ignimbrite mean? 

Matthew Johnson, Natasha Dowey, Rebecca Williams, and Pete Rowley

Pyroclastic density currents (PDCs) are hot, density-driven flows of gas, rock and ash generated during explosive volcanic eruptions, or from the collapse of lava domes (e.g. Fisher, 1979; Branney and Kokelaar, 2002; Cas et al. 2011). They pose a catastrophic geological hazard and have caused >90 000 deaths since 1600AD (Auker et al. 2013). Improved understanding of PDCs will enable us to better understand the explosive eruptions that generate them, improving our preparedness for future volcanic events. However, these deadly hazards are rarely observed up close and are difficult to analyse in real-time. To understand the flow dynamics of density currents we must use models and interpretations of their deposits (e.g. Smith N and Kokelaar, 2013; Rowley et al. 2014, Williams et al. 2014, Sulpizio et al. 2014; Lube et al. 2019, Smith G 2018, 2020).

The deposits of pyroclastic density currents, known as ‘ignimbrites’ can reveal important clues about how these deadly volcanic hazards behave in time and space Reverse grading in an ignimbrite can be interpreted in different ways (Branney & Kokelaar, 2002). It could record a growing eruption intensity through time - where increasingly larger clasts are introduced into the pyroclastic density current. Alternatively, it could record Kinematic sorting (the ‘muesli effect’) and transport processes within the current where larger particles became increasingly likely to be deposited as the current wanes (Palladino & Valentine,1995). The link between current dynamics and reverse grading is currently untested in aerated granular currents.

This project seeks to investigate the relationship between current dynamics and deposit architecture, specifically by considering granular sorting mechanisms in unidirectional flow. We will use an analogue flume (following methods in Rowley et. al., 2014, and Smith G et al., 2018, 2020) to explore how reverse grading and lateral grading may be related to changes in grain sizes at source versus kinematic sorting processes. A mix of grain sizes will be incorporated into the current via a hopper which allows for the starting composition of the current to be varied e.g. homogenous mix versus layered. Photographs of the deposit will be taken through the transparent sidewall of the flume and analysed using image analysis software. These experiments will be complimented by static tests of kinematic sorting, where a Perspex column will be sliced to reveal internal 3d architecture. This project will contribute to our understanding of lithofacies architecture in the field, and help to quantity how we interpret the sedimentation of ignimbrites.

References

Auker et al. (2013) https://doi.org/10.1186/2191-5040-2-2

Branney and Kokelaar (2002) https://doi.org/10.1144/GSL.MEM.2003.027

Cas et al. (2011) Bulletin of Volcanology 731583 https://doi.org/10.1007/s00445-011-0564-y

Fisher (1979) https://doi.org/10.1016/0377- 0273(79)90008-8    

Lube et al. (2019) https://doi.org/10.1038/s41561-019-0338-2

Palladino & Valentine (1995). https://doi.org/10.1016/0377-0273(95)00036-4

Rowley et al. (2014) https://doi.org/10.1007/s00445-014-0855-1

Smith N. and Kokelaar (2013) https://doi.org/10.1007/s00445-013-0768-4

Smith G. et al. (2018) https://doi.org/10.1007/s00445-018-1241-1

Smith, G. et al. (2020). https://doi.org/10.1038/s41467-020-16657-z

How to cite: Johnson, M., Dowey, N., Williams, R., and Rowley, P.: The muesli effect in pyroclastic density currents - what does reverse grading in an ignimbrite mean? , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16402, https://doi.org/10.5194/egusphere-egu21-16402, 2021.

EGU21-12266 | vPICO presentations | GMPV10.1 | Highlight

Lava flow hazard map of Piton de la Fournaise volcano 

Oryaëlle Chevrel, Massimiliano Favalli, Villeneuve Nicolas, Andrew Harris, Alessandro Fornaciai, Nicole Richter, Allan Derrien, Patrice Boissier, Andrea Di Muro, and Aline Peltier

Piton de la Fournaise, situated on La Réunion Island (France), is one of the most active hot spot basaltic shield volcanoes worldwide, experiencing at least two eruptions per year since the establishment of the observatory in 1979. Eruptions are typically fissure-fed and form extensive lava flow fields. About 95 % of some ~250 historical events (since the first confidently dated eruption in 1708) have occurred inside an uninhabited horse-shoe shaped caldera (hereafter referred to as the Enclos) which is open to the ocean on its eastern side. Rarely (12 times since the 18th century), fissures have opened outside of the Enclos where housing units, population centers and infrastructure are at risk. In such a situation, lava flow hazard maps are a useful way of visualizing lava flow inundation probabilities over large areas. Here, we present a lava flow hazard map for Piton de la Fournaise volcano based on: i) vent distribution, ii) statistics of lava flow lengths, iii) lava flow recurrence times, and iv) simulations of lava flow paths across multi-temporal (i.e., regularly updated) topography using the DOWNFLOW stochastic numerical model. A map of the entire volcano highlights that the most probable (up to 12 %) location for future lava flow inundation is within the Enclos, where about 100,000 visitors are present each year. Hazard distribution changes throughout the analysis period due to the high frequency of eruptions that constantly modifies the vent opening distribution as well as the topography and the lava flow dimensional characteristics. Outside of the Enclos, probabilities reach 0.5 % along the well-defined rift zones and, although hazard occurrence in inhabited areas is deemed to be very low (<0.1 %), it may be underestimated here, as our study is only based on post-18th century records and neglects cycles of activity at the volcano. Specific hazard maps considering different event scenarios (i.e., events fed by different combinations of temporally evolving superficial and deep sources) are required to better assess affected areas in the future – especially by atypical, but potentially extremely hazardous, large volume eruptions. At such an active site, our method supports the need for regular updates of DEMs and associated lava flow hazard maps if we are to be effective in mitigating the associated risks.

How to cite: Chevrel, O., Favalli, M., Nicolas, V., Harris, A., Fornaciai, A., Richter, N., Derrien, A., Boissier, P., Di Muro, A., and Peltier, A.: Lava flow hazard map of Piton de la Fournaise volcano , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12266, https://doi.org/10.5194/egusphere-egu21-12266, 2021.

An active phase of Soufrière Hills Volcano (Montserrat, Lesser Antilles) has started in 1995 and had its most intense period between 1995 and 2010, when phases of lava dome growth were interrupted by dome collapses triggering ash clouds and different types of pyroclastic flows. These flows were released in various directions, so that two thirds of the island were left in an inhabitable state. The material deposited was later remobilized through lahar flows, burying the centre of the former capital town of Plymouth. In the present work, we attempt to back-calculate the sequences of dome growth – pyroclastic flows, and the subsequent lahar flows, in an integrated way, using the mass flow simulation tool r.avaflow. Thereby, we build on the reconstruction of the pre-event topography as well as on various reference data obtained from the large amount of available literature – mainly, the peak elevation and volumes of the lava domes, the impact areas of the flow processes, and ash fall characteristics. Most observations are successfully reproduced with physically plausible, though calibrated, parameter sets and temporal scaling of lava dome growth. Due to the complexity and multi-stage nature of the volcanic crisis, a number of simplifications had to be introduced, such as considering only the twelve largest sequences of dome growth and pyroclastic flows, and evaluating some of the results on the basis of aggregated impact areas for more than one event. Consequently, the results reflect a strong conceptual component, but can - at least in part - be considered useful for predictive modelling of similar events. Another scope of the simulation results, however, is its educational use. Appropriately presented, they greatly facilitate the generation of a better understanding for complex chains of volcanic processes and their consequences to learners at various levels in different educational contexts, from school and university all the way to targeted awareness-building campaigns.

How to cite: Mergili, M. and Pudasaini, S. P.: Landscape and hazard evolution during the Montserrat volcanic crisis 1995–2010: an integrated simulation with r.avaflow, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13407, https://doi.org/10.5194/egusphere-egu21-13407, 2021.

EGU21-4448 | vPICO presentations | GMPV10.1

Lava flow hazard of the 2018 Etna eruption: What happened and what could happen

Giuseppe Bilotta, Sonia Calvari, Annalisa Cappello, Claudia Corradino, Ciro Del Negro, Gaetana Ganci, and Alexis Hérault

On 24 December 2018 a flank eruption started on Etna from an eruptive fissure opened on the eastern side of the New Southeast Crater (NCSE) at about 3,100 m asl, which in few minutes, propagated to the south-east, overcoming the edge of the western wall of the Valle del Bove (VdB), reaching an altitude of 2,400 m asl and a total length of about 2 km. The eruption, which lasted only three days, produced lava flows from different vents along the eruptive fissure that reached a distance of about 4.2 km and covered an area of about 1 km2. The satellite monitoring of the 2018 Etna eruption was performed using the HOTSAT system using mid and thermal infrared data acquired by the Spinning Enhanced Visible and InfraRed Imager (SEVIRI), which provided minimum and maximum estimates for the lava thermal flux, the effusion rate and the lava volume. The SEVIRI-derived effusion rate estimates were used as input of the MAGFLOW model to simulate the actual lava flow field, obtaining a very good fit. We also simulated different eruptive scenarios assuming the lava emission wouldn’t run out in only three days to forecast if, when and how the lava flow could reach the inhabited areas, causing possible significant damage. 

How to cite: Bilotta, G., Calvari, S., Cappello, A., Corradino, C., Del Negro, C., Ganci, G., and Hérault, A.: Lava flow hazard of the 2018 Etna eruption: What happened and what could happen, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4448, https://doi.org/10.5194/egusphere-egu21-4448, 2021.

EGU21-13608 | vPICO presentations | GMPV10.1

Lava flow modelling at El Hierro (Canary Islands): the case of Montaña Aguarijo volcano

Alejandro Rodriguez-Gonzalez, Claudia Prieto-Torrell, Meritxell Aulinas, Francisco José Perez-Torrado, Jose-Luis Fernandez-Turiel, Constantino Criado Hernández, and María del Carmen Cabrera

Lava flow simulations are valuable tools for forecasting and assessing the areas that may be potentially affected by new eruptions, but also for interpreting past volcanic events and understanding the controls on lava flow behaviour. The plugin Q-LavHA v3.0 (Mossoux et al., 2016), integrated into QGIS, allows simulating the inundation probability of an a’a lava flow from one or more eruptive vents spatially distributed in a Digital Elevation Model (DEM). Q-LavHA allows running probabilistic and deterministic methods to calculate the spatial propagation and the maximum length of lava flows, considering a number of morphometric and/or thermo-rheological parameters.

El Hierro is the smallest and westernmost island of the Canary Archipelago where basaltic lava flows infer the major volcanic hazard. However, no lava flow emplacement modelling has been carried out yet on the island. Here we present Montaña Aguarijo's lava flow simulation, a monogenetic volcano located on the NW rift of El Hierro. Detailed geological fieldwork and current topographic-bathymetric data were used to reconstruct the pre-eruption (before the eruption modifies the relief) and post-eruption (at the end of the eruption, prior to erosive processes) DEMs. The obtained morphometric parameters of the lava flow (2,268m long; 5m medium thickness; 422,560m3) were used to run probabilistic (Maximum Length) and deterministic (FLOWGO) models. The latter also considers a set of thermo-rheological properties of the lava flow such as initial viscosity, phenocryst content, or vesicle proportion.

Results obtained show a high degree of overlap between the real and simulated lava flows. Therefore, the thermo-rheological parameters considered in the deterministic approach are close to the real ones that constrained Montaña Aguarijo lava flow propagation. Moreover, this work evidence the effectiveness of Q-LavHA plugin when simulating complex lava flows such as Montaña Aguarijo’s lava which runs through a coastal platform, a typical morphology of oceanic volcanic islands.     

Financial support was provided by Project LAJIAL (ref. PGC2018-101027-B-I00, MCIU/AEI/FEDER, EU). This study was carried out in the framework of the Research Consolidated Groups GEOVOL (Canary Islands Government, ULPGC) and GEOPAM (Generalitat de Catalunya, 2017 SGR 1494).

References

Mossoux, S., Saey, M., Bartolini, S., Poppe, S., Canters F., Kervyn, M. (2016). Q-LAVHA: A flexible GIS plugin to simulate lava flows. Computers & Geosciences, 97, 98-109.

How to cite: Rodriguez-Gonzalez, A., Prieto-Torrell, C., Aulinas, M., Perez-Torrado, F. J., Fernandez-Turiel, J.-L., Criado Hernández, C., and Cabrera, M. C.: Lava flow modelling at El Hierro (Canary Islands): the case of Montaña Aguarijo volcano, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13608, https://doi.org/10.5194/egusphere-egu21-13608, 2021.

EGU21-14717 | vPICO presentations | GMPV10.1 | Highlight

SPH model for the simulation of lava-buildings interactions

Vito Zago, Giuseppe Bilotta, Annalisa Cappello, Robert Dalrymple, Luigi Fortuna, Gaetana Ganci, Alexis Herault, and Ciro Del Negro

Numerical simulation is a fundamental aspect of modern volcanology, providing tools for the forecasting of lava flows behavior, so as to assist in the design of mitigation actions for volcanic risk. In addition to the prediction of the emplacement topology, numerical simulation can be useful to study the possible outcomes of the interaction between a lava flow and a building. This kind of information can help to estimate the vulnerability of buildings so as to produce more accurate risk evaluations. Smoothed Particle Hydrodynamics (SPH) is a particle-based numerical method, particularly suited for the simulation of fluids with a high level of complexity, that can intrinsically deal with all of the physical properties of lava. GPUSPH is a simulation engine based on the SPH method that has been developed in order to take into account the challenging aspects of lava simulations and has been successfully applied to the simulation of lava-related benchmark tests. Here we use the SPH method, coupled within the framework of GPUSPH with a rigid body mechanics solver provided by the Project Chrono engine, for the realistic study of lava-buildings interaction. The resulting coupled model is able to simulate masonry with a brick-level accurate description, providing insights on any damages happening to the structure. We will show the simulation of a lava flow interacting with an elementary masonry piece, where a total collapse of the structure is induced by the action of the lava.

How to cite: Zago, V., Bilotta, G., Cappello, A., Dalrymple, R., Fortuna, L., Ganci, G., Herault, A., and Del Negro, C.: SPH model for the simulation of lava-buildings interactions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14717, https://doi.org/10.5194/egusphere-egu21-14717, 2021.

EGU21-714 | vPICO presentations | GMPV10.1

Exploring the in situ high temperature emissivity of 2014–2015 Bardarbunga magmas

Jonas Biren, Lionel Cosson, Leire del Campo, Cécile Genevois, Emmanuel Veron, Sandra Ory, Hao Li, Aneta Slodczyk, and Joan Andújar

Abstract: Temperature is a key parameter controlling the rheology of lava flows. Unfortunately, the hazardous behavior of eruptions prevents direct measurements of hot magmatic bodies. Hence, the temperature of magma is mostly retrieved by using remote sensing methods (ground-based or satellite-based detectors) build on measuring the infrared (IR) radiance of the body [1]. These well-established techniques are however subjected to important errors related to, among others, the poor knowledge of the spectral emissivity (ε), which is one of the most critical parameters in IR radiance measurement [2, 3]. In this study, we performed in situ optical measurements at relevant magmatic temperatures of basaltic magma from the 2014–2015 Holuhraun eruption (Bardarbunga volcano, Iceland). Spectral emissivity has been systematically determined over a wide spectral range (400–15000 cm−1) covering TIR, MIR and SWIR regions, from room temperature up to 1473 K using a non-contact in situ IR emissivity apparatus [4]. SEM, EMPA, Raman spectroscopy, DSC, XRD and TEM techniques helped characterize and understand the complex radiative behavior of this natural magmatic composition. The results show not only that spectral emissivity varies accordingly with temperature and wavenumber but also that small changes in bulk rock composition or texture produce drastic changes in emissivity at given temperature, with iron content and its oxidation state being the main agents controlling this parameter. Appropriate emissivity values can then be used to refine current radiative data from IR remote sensing and to implement the thermo-rheological models of lava flows [5] as to support hazard assessment and risk mitigation.


References: [1] Kolzenburg et al. 2017. Bull. Volc. 79:45. [2] Harris, A. 2013: Cambridge University press. 728. [3] Rogic et al. 2019 Remote Sens., 11, 662 [4] De Sousa Meneses et al. 2015. Infrared Physics & Technology 69. [5] Ramsey et al. 2019. Annals of Geophysics, 62, 2.


Keywords: Spectral emissivity, temperature, IR spectroscopy, remote sensing, basalt

How to cite: Biren, J., Cosson, L., del Campo, L., Genevois, C., Veron, E., Ory, S., Li, H., Slodczyk, A., and Andújar, J.: Exploring the in situ high temperature emissivity of 2014–2015 Bardarbunga magmas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-714, https://doi.org/10.5194/egusphere-egu21-714, 2021.

EGU21-13166 | vPICO presentations | GMPV10.1

Machine Learning analysis of seismic signals recorded at Stromboli Volcano

Darius Fenner, Georg Rümpker, Horst Stöcker, Megha Chakraborty, Wei Li, Johannes Faber, Kai Zhou, Jan Steinheimer, and Nishtha Srivastava

At Stromboli, minor volcanic eruptions occur at time intervals of approximately five minutes on average, making it one of the most active volcanoes worldwide. In addition to these mostly harmless events, there are also stronger eruptions and paroxysms which pose a serious threat to residents and tourists. In light of recent developments in Machine Learning, this study attempts to apply these new tools for the analysis of the time-varying volcanic eruptions at Stromboli. As input for the Machine-Learning approach, we use continuous recordings of seismic signals from two seismometers on the island. The data is available from IRIS  and includes records starting in 2012 up to the present. 

One primary challenge is to label and classify the data, i.e., to discriminate events of interest from noise. The variety of signal-appearance in the recorded data is wide, in some periods the events are clearly distinguishable from noise whereas, in other cases relevant events are obscured by the high noise level. To enable the event-detection in all cases, we developed the following algorithm: in the first step, the seismic data is pre-processed with an STA/LTA-Filter, which allows detection of events based on a prominence threshold. However, due to the diversity of signal patterns, a fixed set of hyperparameters (STA- and LTA-window length, prominence threshold, correlation coefficient) fails to reliably extract the relevant events in a consistent manner. Therefore, the (time-varying) noise level of the recordings is used as an additional key indicator. After this, the hyperparameters are optimized. The automatic adaptation is then used for labeling the continuous seismic data.

After extracting the events based on this approach, a machine learning model is trained to analyze the recordings for possible patterns in the interval times and the event amplitudes. This study is expected to provide constraints on the possibility to detect complex time-dependent patterns of the eruption history at Stromboli.

How to cite: Fenner, D., Rümpker, G., Stöcker, H., Chakraborty, M., Li, W., Faber, J., Zhou, K., Steinheimer, J., and Srivastava, N.: Machine Learning analysis of seismic signals recorded at Stromboli Volcano, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13166, https://doi.org/10.5194/egusphere-egu21-13166, 2021.

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