GD7.2 | Long-term rheology , heat budget and dynamic permeability of deforming and reacting rocks: from laboratory to geological scales
Long-term rheology , heat budget and dynamic permeability of deforming and reacting rocks: from laboratory to geological scales
Co-organized by GMPV4
Convener: Yury Podladchikov | Co-conveners: Lucie Tajcmanova, Shun-ichiro Karato, Evangelos MoulasECSECS, Leni Scheck-Wenderoth
Orals
| Mon, 15 Apr, 16:15–18:00 (CEST)
 
Room -2.47/48
Posters on site
| Attendance Mon, 15 Apr, 10:45–12:30 (CEST) | Display Mon, 15 Apr, 08:30–12:30
 
Hall X2
Posters virtual
| Attendance Mon, 15 Apr, 14:00–15:45 (CEST) | Display Mon, 15 Apr, 08:30–18:00
 
vHall X2
Orals |
Mon, 16:15
Mon, 10:45
Mon, 14:00
The goal of this session is to reconcile short-time/small-scale and long-time/large-scale observations, including geodynamic processes such as subduction, collision, rifting, or mantle lithosphere interactions. Despite the remarkable advances in experimental rock mechanics, the implications of rock-mechanics data for large temporal and spatial scale tectonic processes are still not straightforward, since the latter are strongly controlled by local lithological stratification of the lithosphere, its thermal structure, fluid content, tectonic heritage, metamorphic reactions, and deformation rates.

Mineral reactions have mechanical effects that may result in the development of pressure variations and thus are critical for interpreting microstructural and mineral composition observations. Such effects may fundamentally influence element transport properties and rheological behavior.
Here, we encourage presentations focused on the interplay between metamorphic processes and deformation on all scales, on the rheological behavior of crustal and mantle rocks, and time scales of metamorphic reactions in order to discuss
(1) how and when up to GPa-level differential stress and pressure variations can be built and maintained at geological timescales and modeling of such systems,
(2) deviations from lithostatic pressure during metamorphism: fact or fiction?
(3) the impact of deviations from lithostatic pressure on geodynamic reconstructions.
(4) the effect of porous fluid and partial melting on the long-term strength.
We, therefore, invite the researchers from different domains (rock mechanics, petrographic observations, geodynamic and thermo-mechanical modeling) to share their views on the way forward for improving our knowledge of the long-term rheology and chemo-thermo-mechanical behavior of the lithosphere and mantle.

Orals: Mon, 15 Apr | Room -2.47/48

Chairpersons: Yury Podladchikov, Lucie Tajcmanova
Strain and fluid flow localization
16:15–16:25
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EGU24-1660
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ECS
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On-site presentation
Yury Alkhimenkov and Ruben Juanes

Structural softening is a well-known phenomenon in single-phase materials. If we consider a single-phase material, assume an elastoplastic rheology, and perform a strain-driven loading under pure shear boundary conditions, the evolution of the integrated stress will exhibit a softening beyond its peak. This is true for non-associated flow rules considering an ideal plasticity model with, for example, Mohr-Coulomb or Drucker-Prager yield criteria. The post-peak softening is usually associated with the development of the localized shear zones. However, this phenomenon hasn’t been properly analyzed for the case of porous rocks modeled with the quasi-static Biot’s poroelastic equations.

In this contribution, we present numerical results considering the poro-elasto-plastic rheology with a focus on structural softening. We show that the post-peak structural softening might be significant and exhibit large stress drops. The most important outcome is that even a little fluid overpressure leads to much larger stress drops compared to scenarios without any kind of fluid overpressure. This result may shed some light on the phenomenon of large earthquakes associated with small injection rates in geothermal or CO2 sequestration fields.

 

References:

Vermeer, P. A. (1990). The orientation of shear bands in biaxial tests. Géotechnique40(2), 223-236.

How to cite: Alkhimenkov, Y. and Juanes, R.: Structural softening in poro-elasto-plastic media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1660, https://doi.org/10.5194/egusphere-egu24-1660, 2024.

16:25–16:35
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EGU24-17292
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ECS
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On-site presentation
Ivan Utkin

Numerous studies emphasize the significance of thermal softening induced by shear heating and the concurrent generation of ductile shear zones in geological processes spanning various spatial and temporal scales. Thermal softening is proposed as a primary mechanism in the formation of tectonic plate boundaries and as a potential mechanism of intermediate-depth and deep-focused earthquakes, where large confining pressure inhibits brittle fracture. In the latter scenario, seismic velocities during shearing are achieved through the spontaneous viscous dissipation of stored elastic energy, a phenomenon known as self-localizing thermal runaway (SLTR) [1].

Resolving SLTR poses a formidable numerical challenge due to the multiscale nature of the process. The slow initial stage of differential stress buildup and strain localization is succeeded by the rapid development of a thin shear zone, necessitating high spatial and temporal resolution. Prior numerical studies of self-localizing thermal runaway were confined to 1D, restricting applications to less realistic geometries and simpler model setups.

In this study, we explore the viscoelastic effects of spontaneous flow localization through numerical modeling in 2D. We develop a fully coupled thermo-mechanical solver utilizing a novel conservative energy formulation. Our work demonstrates the potential for SLTR instability in various 2D model setups. Through systematic numerical experiments, we compare the onset of localization with 1D predictions. Additionally, we investigate the role of heterogeneities in the distribution of material properties on the development of a ductile shear zone.

[1] Braeck, S., & Podladchikov, Y. Y. (2007). Spontaneous thermal runaway as an ultimate failure mechanism of materials. Physical Review Letters98(9), 095504.

How to cite: Utkin, I.: Spontaneous strain localisation in a viscoelastic material owing to thermal softening , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17292, https://doi.org/10.5194/egusphere-egu24-17292, 2024.

16:35–16:45
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EGU24-22551
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Highlight
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On-site presentation
Dániel Kiss

Plate tectonics on Earth is characterized by a largely localized distribution of lithospheric strain, both in the ductile and in the brittle regimes. While deformation in brittle or elastic materials is generally localized, in homogenous ductile or viscous materials some strain localization requires a softening mechanism. Here we will focus on thermal softening, a consequence of the conversion of mechanical work into heat (i.e. shear heating) and the temperature dependence of rock viscosities.
First, I briefly list the fundamental features of ductile shear zone evolution due to thermal softening driven by steady-state background deformation. (1) After an initial transient period, the maximum temperature and stress in the shear zone converges to a (quasi-)constant value (temperature increase and stress drop). (2) The steady-state maximum temperature can be estimated using a scaling law. (3) With ongoing deformation, the high-temperature zone and consequently the shear zone widen, which indicates that shear zone width is controlled by conduction time scales.
Second, I demonstrate that thermal softening is a feasible mechanism of lithospheric scale ductile strain localization by comparing geological observations and model results of subduction initiation, ophiolite emplacement, and high-temperature metamorphic nappes.
Finally, I will investigate the possible occurrence and importance of thermal softening in the brittle, elastoplastic domain, often associated with much shorter time scales such as slow slip events and earthquakes. Data from rock deformation experiments indicate that steady-state friction angle becomes primarily velocity-dependent at high slip rates, which is consistent with thermal softening. Numerical models of Maxwell visco-elastic deformation show that thermal softening can be an efficient mechanism of limiting elastic stress build-up, often resulting in a rapid stress release, often referred to as thermal runaway.  

How to cite: Kiss, D.: Thermal softening in the ductile and brittle lithosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22551, https://doi.org/10.5194/egusphere-egu24-22551, 2024.

16:45–16:55
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EGU24-10931
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ECS
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On-site presentation
Thomas P. Ferrand and Damien Deldicque

Seeking to better investigate the mechanism of transformational faulting (i.e. dynamic olivine phase transition considered as the main earthquake mechanism in the deep Upper Mantle), experiments were carried out in a 1-atm rig using synthetic samples of peridotite analogues. The samples consisted of Mg2GeO4 with minor MgGeO3. In brief, using Ge instead of Si allows studying deep processes without increasing the confining pressure. At 1 atm, γ-Mg2GeO4 (high-pressure olivine polymorph) transitions to α-Mg2GeO4 (olivine) at 810 °C. The hope was to generate and document strain localization features due to local phase transition and/or locally nucleate the phase transition due to strain localization. Working with this material in this apparatus between 760 and 860 °C could have appeared clever.

The experimental setup allowed runs lasting a few hours up to a full day. However, after one day at 800 °C and an axial stress > 300 MPa, the synthetic samples, characterized by a small grain size and a high homogeneity, remained perfectly elastic. Runs were too cold and dry for any nucleation of the high-pressure phase γ-Mg2GeO4. Due to both kinetic and rheological issues, beginning to observe strain localization would have taken months, which would most probably have killed the apparatus in only one run due to the corrosion of the external furnace. 

This failed experimental journey turned into an opportunity to study something else: the temperature window was shifted to 950-1250°C. Some experiments revieled a significant viscosity reduction in a narrow temperature window (1000-1150°C), which we propose to interpret as an analogue of the lithosphere-Asthenosphere boundary (LAB). Until recently, melting was the only “transformation” considered in the interrogations about the reduced viscosity of the LAB. In this study, based on our unexpected experimental results, we document a solid-state viscosity reduction that seems to be associated with grain-boundary instability in the context of a competition between diffusive and displacive processes (i.e. premelting). We propose to broaden the discussion including solid-state transformations and potential metastable phases that are not yet fully understood. Although the most studied mineral, olivine has not revealed all its secrets. Additional experiments are required to fully understand what happened.

How to cite: Ferrand, T. P. and Deldicque, D.: Unexpected softening of a synthetic peridotite analogue (magnesium germanate) in a narrow temperature window: the Lithosphere-Asthenosphere Boundary accidentally reproduced?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10931, https://doi.org/10.5194/egusphere-egu24-10931, 2024.

16:55–17:05
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EGU24-10501
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Highlight
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On-site presentation
Lawrence Hongliang Wang and Viktoriya Yarushina

Seismic chimneys, prevalent along continental margins, intricately contribute to Earth's degassing processes, facilitating fluid migration from the deep Earth to the surface. This phenomenon carries significant implications for subsurface storage utilization. Among the principal mechanisms driving seismic chimney formation is the fluid flow instability within porous subsurface rocks. While numerical studies of geodynamical two-phase flow have successfully replicated vertical fluid flow structures, many of these models overlook elastic compaction, advection of solid and poro-space, and geological heterogeneity, thereby limiting their applicability in subsurface scenarios. In addressing these limitations, this study incorporates a viscoelastic rheology into the geodynamical two-phase flow model to explore the controlling factors influencing the formation of focused fluid flow, accounting for various rock properties, including geological heterogeneity. Initial investigations into the impact of elastic compaction by varying Deborah numbers reveal a limited influence on fluid flow compared to viscous compaction. Through a comparative analysis of models with and without advection, we observe the potential importance of solid advection in fluid migration, particularly under conditions of high background porosity (≥0.1) and relatively low permeability. This effect is accentuated when the solid matrix undergoes significant deformation. Channel widths range from 2-3 compaction lengths to a maximum of 5-10 compaction lengths, primarily contingent on the viscosity ratio between shear and bulk viscosity and the fluid supply. Further simulations involving fluid flow encountering a horizontal block with rock heterogeneity and geological heterogeneity demonstrate the potential for fluid penetration through the structure or deflection to the side, contingent upon rock properties and block size. Finally, we apply our model to a specific seismic chimney at Loyal Field in Scotland, UK, successfully reproducing the observed upward-bending structure in the seismic image with a consistent width-height ratio. This comprehensive investigation sheds light on the complex interplay of various factors influencing focused fluid flow, including geological heterogeneity, thereby contributing valuable insights to the understanding of seismic chimney formation in real-world geological settings.

 

How to cite: Wang, L. H. and Yarushina, V.: Modelling focused fluid flow in the subsurface: its controlling factors and the formation of seismic chimney , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10501, https://doi.org/10.5194/egusphere-egu24-10501, 2024.

Reactive flows
17:05–17:15
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EGU24-8478
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On-site presentation
Viktoriya Yarushina, Johannes C. Vrijmoed, and Lawrence H. Wang

Addressing climate change necessitates shifting from fossil fuels to renewables and implementing carbon capture and storage (CCS). Storing CO2 in mafic and ultramafic rocks is appealing due to the potential for mineral conversion. Recent pilot studies showed the feasibility of mineral CO2 storage in basalts. However, combating climate change requires increasing injection volumes by several orders of magnitude. Discussion continues on whether mineralization processes will still be as efficient at larger scales. One foreseen issue is the potential pore clogging due to mineral precipitation, eventually impeding the reaction. While reactive transport models based on dissolution-precipitation mechanism predict pore clogging and thus the limited extent of reaction, there is clear field evidence for complete reactions in natural analog systems. Besides, developing new injection sites requires pre-injection feasibility studies based on numerical simulations. These simulations aim to provide an initial evaluation of the potential success and challenges associated with the proposed CO2 injection project. They require large-scale, high-resolution simulations, which are challenging for commercially available codes. Recent success in using GPUs for scientific computing combined with matrix-free numerical methods stimulates the development of new numerical models and the revisiting of underlying theoretical approaches. CCS in depleted reservoirs, especially with old plugged-and-abandoned wells, also presents challenges. CO2 interacting with old cement compositions may compromise well integrity, leading to potential CO2 leakage along wellbores. Chemical reactions, fluid flow, and deformation are intricately coupled processes. Studies highlight the dependence of reaction progress both on assumed kinetics and constitutive hydro-mechano-chemical models. While conventional knowledge suggests transport-dominated reactions leading to pore clogging, recent observations challenge this, indicating that reaction-induced alterations occur in the solid phase without changing pore volume. A novel model addressing reaction-driven mineral expansion is presented, preserving porosity while allowing solid volume change. Examining fluid-rock interaction at the pore scale, we derive effective rheology for reacting porous media. The micromechanical model assumes rocks or cement as assemblies of solid reactive grains, accommodating externally applied and reaction-induced stresses through elastic, viscous, and plastic deformation mechanisms. Depending on the level of reaction-induced stresses, the model predicts either pore clogging or porosity-preserving solid volume increase as dominant mechanisms, with the latter facilitating complete reactions. Macroscopic stress-strain constitute laws account for chemical alteration and viscoelastic deformation, elucidating the dependence of mechanical rock properties on fluid chemistry [1]. We use a two-phase continuum medium approach and local equilibrium thermodynamic models [2] to investigate the coupling between reaction, deformation, and fluid flow on a larger scale. We consider two simple examples of the carbonation of portlandite and the hydration of mantle rocks. Both reactions are associated with a change in solid volume. We show how reaction-driven mineral expansion affects the porosity evolution and reaction progress.

References:

1. Yarushina, V.M., Y.Y. Podladchikov, and H.L. Wang, On the Constitutive Equations for Coupled Flow, Chemical Reaction, and Deformation of Porous Media. Journal of Geophysical Research-Solid Earth, 2023. 128(12).

2. Vrijmoed, J.C. and Y.Y. Podladchikov, Thermolab: A Thermodynamics Laboratory for Nonlinear Transport Processes in Open Systems. Geochemistry Geophysics Geosystems, 2022. 23(4).

How to cite: Yarushina, V., Vrijmoed, J. C., and Wang, L. H.: Reaction-driven mineral expansion and its impact on fluid flow, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8478, https://doi.org/10.5194/egusphere-egu24-8478, 2024.

17:15–17:25
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EGU24-22560
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ECS
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Highlight
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On-site presentation
Jo Moore, Sandra Piazolo, Andreas Beinlich, Håkon Austrheim, and Andrew Putnis

Fluid inflitration along brittle presursors is commonly with associated with hydration and deformation of the host rock. In many cases the relative timing of fracturing, fluid infiltration, reaction, and deformation is unclear, making it difficult to disentangle the relative importance of processes that facilitate advancement of the hydration front. Here we present the transition from an anhydrous and relatively undeformed precursor rock into a highly deformed and hydrated plagioclase-rich rock. The studied outcrop preserves both (1) the interface between the anhydrous granulite-facies parent lithology and a statically hydrated amphibolite-facies rock, and (2) a transition from statically hydrated amphibolite to the sheared amphibolite-facies lithologies. Detailed petrography, quantitative mineral chemistry and bulk rock analyses have been applied to investigate compositional variations and assemblage microstructure across both interfaces. Here, we produce hydro-chemical numerical models based on local equilibrium thermodynamics in an attempt to reproduce the characteristics of the hydration and deformation interfaces. Here, we present a comparison between the observed characteristics of the hydration front and those produced by modelling of the reaction front propagation.

How to cite: Moore, J., Piazolo, S., Beinlich, A., Austrheim, H., and Putnis, A.: Application of reaction front propagation modelling to amphibolite-facies plagioclase hydration: an example from the Bergen arcs, Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22560, https://doi.org/10.5194/egusphere-egu24-22560, 2024.

Geodynamics
17:25–17:35
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EGU24-4132
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ECS
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On-site presentation
Manon Pépin, Gianluca Gerardi, Hugo Remise-Charlot, Christiane Alba-Simionesco, and Anne Davaille

Strain-localization along plate boundaries and subduction of the lithosphere are key-features of Earth’s mantle plate tectonics and convective dynamics. Numerous mechanisms, operating on various time and length-scales, are able to produce strain localization. But the exact process(es) that control lithospheric subduction from convection in a viscous mantle remain debated. Laboratory experiments, where one can 1) characterize and control the fluid rheology, and 2) determine the structure/texture of the resulting lithosphere, can give valuable constraints to the ongoing discussion. To date, we have found only one fluid able to produce in the laboratory self-consistent subduction during convection: colloidal dispersions of silica nanoparticles (‘NP’). These fluids encompass a large diversity of rheological behavior, from viscous to elasto-visco-plastic to brittle, depending on the nanoparticles volume fraction. But we can now go one step further, and investigate the links between the rheological properties and the nanoparticles’organization.

 

So we studied Ludox® dispersions with NP of two different diameters (16 and 28 nm) and vary the water concentration, while keeping the ionic content constant. The rheology is characterized using shear rate and oscillatory tests. The organization of the nanoparticles is probed with Small-Angle Neutron Scattering (SANS) and Small-Angle X-ray Scattering (SAXS) measurements, and the solvent (water) state thanks to thermal analysis (ThermoGravimetric Analysis, TGA, and Differential Scanning Calorimetry, DSC). These measurements allow us to identify three types of water, (i) water adsorbed at the surface of the particles, (ii) water confined in nano-cavities and (iii) free water, and to determine the evolution of their amounts with increasing particle volume fraction. Rheology seems mainly controlled by the amount of free water. As the fraction of the latter decreases, the material becomes more heterogeneous at the meso-scale, with the formation of particle aggregates and free water channels. The rheology becomes more non-newtonian with the apparition of a yield stress, which value increases with decreasing free water. In convection-evaporation experiments, this results in the formation of a lithospheric « skin » floating on a less concentrated solution, and strong localization of deformation on this heterogeneous skin that can induce its break-up and subduction. Interestingly enough, subduction is observed for skins still containing a little amount of free water (0.2-1%). On a rocky planet, this suggests that the existence of partial melt in the asthenosphere and the lithosphere could be important to allow subduction. This could explain why localized subduction may exist on present-day Venus: eventhough there is no liquid water ocean on the surface of Venus today, there is plenty of evidence of active volcanism, which indicate the existence of a sizable amount of partial melt.  

How to cite: Pépin, M., Gerardi, G., Remise-Charlot, H., Alba-Simionesco, C., and Davaille, A.: On the link between subduction and lithospheric texture : insights from convection in colloidal dispersions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4132, https://doi.org/10.5194/egusphere-egu24-4132, 2024.

17:35–17:45
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EGU24-5497
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ECS
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On-site presentation
Iskander Ibragimov and Evangelos Moulas

Ophiolites are remnants of oceanic crust and mantle, now typically found within continental mountain ranges. Particularly in areas once part of the Tethys Ocean, ophiolites are often accompanied by narrow strips of metamorphic rocks, commonly referred to as metamorphic soles. These rocks exhibit peak metamorphic conditions characteristic of either granulite or amphibolite facies. Geochronological studies of Tethyan ophiolites indicate that the development of these metamorphic soles occurred almost simultaneously with the crystallization of the ophiolite's crustal sequence. Geological evidence also suggests that the metamorphism of the sole rocks took place concurrently with deformation, likely at the same time as the ophiolite's obduction. In our research, we explore the metamorphic effects of shearing in an ophiolite sequence overlying a crustal sequence. Our findings reveal that a strong crustal lithology can produce additional heat through the dissipation of mechanical energy, which can explain the high temperatures found in metamorphic-sole rocks. In addition, heating of the footwall rocks eventually leads to the migration of the active shear zone from the mantle sequence into the upper crustal domain. This migration is responsible for the metamorphic sole incorporation at the base of the ophiolite. Finally, we demonstrate that stopping the shearing process rapidly cools these rocks, corresponding with the findings from thermochronological studies from Oman ophiolite.

How to cite: Ibragimov, I. and Moulas, E.: A thermo-mechanical model of the thermal evolution and incorporation of the metamorphic sole in the Oman ophiolite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5497, https://doi.org/10.5194/egusphere-egu24-5497, 2024.

17:45–17:55
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EGU24-14329
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Highlight
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On-site presentation
Leonid Aranovich, Lyudmila Khakimova, Andrey Frendak, and Yury Podladchikov

Continental crust consists mainly of felsic rocks rich in silicon and aluminum, and is formed in subduction zones via processes linked to plate tectonics. Most recent models of the felsic crust formation rely on differentiation of basaltic magma generated via partial melting of mantle wedge peridotite under influence of a fluid phase liberated from subducting hydrated oceanic crust. Here we present an alternative model that invokes metasomatic alteration of mantle peridotite due to interaction with a water-rich fluid phase. The model is based on calculations of solid phase assemblages in equilibrium with a fluid saturated in major elements at varying pressure-temperature conditions. Calculations employed THERMOLAB software [1] along with thermodynamic properties of solids (both the standard state and mixing) according to [2,3] and aqueous solution models [4]. The calculations reveal that the SiO2 content in the fluid exerts major control on the solid phase assemblage. On decompression path from 2.5 to 0.2 GPa at 700oC in the model system NCMASH it changes from a six-mineral assemblage olivine (Ol) + orthopyroxene (Opx) + pargasite(Parg) + diopside + biotite + clinochlore to a three-phase Ol+Opx+Parg. The system Si/O ratio along the path increases from 0.26 (close to that of Ol, Si/O=0.25) to 0.28, thus pre-conditioning mantle protolith for subsequent melting that would generate diorite-granodiorite-granite melts.

How to cite: Aranovich, L., Khakimova, L., Frendak, A., and Podladchikov, Y.: Generation of Felsic Crust: A Fluid Transport Perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14329, https://doi.org/10.5194/egusphere-egu24-14329, 2024.

17:55–18:00

Posters on site: Mon, 15 Apr, 10:45–12:30 | Hall X2

Display time: Mon, 15 Apr 08:30–Mon, 15 Apr 12:30
Chairpersons: Evangelos Moulas, Leni Scheck-Wenderoth
Effective rheology and strain localization
X2.23
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EGU24-19434
Maxim Yakovlev and Victoriya Yarushina

The coupled process models incorporate fluid flow, chemical transport, and mechanical deformation equations. These equations adhere to the thermodynamic principles ensuring the preservation of mass and energy within the system. However, for accurate predictions, it is crucial to establish closure equations that provide additional information and ensure the model's completeness. Closure equations are derived either from extrapolating experimental data or from micromechanical models that consider processes at the scale of individual grains or particles. Microscale models are often based on simplified analytical solutions obtained for idealized conditions, which may not fully capture the complexity of real-world situations. For instance, these models may assume a dilute concentration of voids or pores, neglecting interactions between the pores. While this assumption may be suitable for very small porosities below 1%, it may not accurately reflect interactions at porosities around 10%, influencing the compaction process. One approach to address this challenge is to derive more sophisticated analytical solutions, which may sometimes be impractical. Alternatively, a common strategy is to retain simplified solutions and validate them against numerical simulations that include multiple interacting voids. Effective bulk modulus, frequently employed to describe compaction-driven fluid flow in porous rocks, relies on effective media models. We propose a new effective media model based on a Representative Volume Element consisting of multiple interacting pores. To address stress and strain field interactions caused by multiple pores in an elastoplastic matrix, we utilize the numerical simulator CAE Fidesys, implementing classical associated plastic flow laws with von Mises and Tresca yield criteria. For viscoplastic rocks, the correspondence principle is applied. We derive 2D effective stress-strain relations for porous viscoelastoplastic rocks under a general non-hydrostatic stress field and compare the results with existing and novel analytical solutions.

How to cite: Yakovlev, M. and Yarushina, V.: Numerical assessment of effective bulk moduli of porous rocks using high-performance computing on GPUs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19434, https://doi.org/10.5194/egusphere-egu24-19434, 2024.

X2.24
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EGU24-14851
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ECS
Spontaneous localization of inelastic deformation of geomaterials as a consequence of structural pressure drop in localized shear bands
(withdrawn)
Elvira Gizatullina, Yury Alkhimenkov, and Yury Podladchikov
X2.25
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EGU24-15095
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ECS
Olga Dubina, Stefan Schmalholz, and Yury Podladchikov

A characteristic feature of some collisional orogens, such as the Alps, are low-angle thrust sheets. The most prominent thrust sheet in the Alps is likely the Glarus nappe that has been displaced at least 30 to 40 km. The Glarus thrust has been studied for more than 150 years and these studies created much knowledge of, for example, rock deformation, strain localization, and softening mechanisms. However, the type of forces and the mechanisms that drive the tens of kilometers displacement at a low angle during continental collision remain unclear. Furthermore, the relative importance of softening mechanisms at the base of the thrust sheet is still disputed and proposed mechanisms include fluid overpressure, grain size reduction, or fluid release caused by shear heating.

In this study, we investigate the formation of low-angle thrust sheets and nappes with two-dimensional thermo-mechanical numerical models. We consider a lithosphere-mantle system with a continental crust that exhibits initially a horizontal variation in crustal thickness. The lithosphere is shortened by far-field convergence velocities. For simplicity, we apply thermal softening due to shear heating as the only softening mechanism since this mechanism requires the least assumptions in our thermo-mechanical model. The applied numerical algorithm is based on a staggered finite difference discretization and a matrix-free iterative pseudo-transient solver.

Preliminary numerical results indicate that buoyancy forces due to lateral crustal thickness variations can trigger the formation of sub-horizontal thrusting and a switch from a locally pure shear-dominated to a simple shear-dominated deformation. Without lateral thickness variations and associated buoyancy forces, thermal softening causes thrusting with 45-degree angles and, hence, no low-angle thrusting. We perform systematic numerical simulations and dimensional analysis to evaluate the conditions that are required to generate low-angle thrusting during lithospheric shortening.

How to cite: Dubina, O., Schmalholz, S., and Podladchikov, Y.: Control of buoyancy forces and thermal softening on the emplacement of low-angle thrust sheets during continental collision, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15095, https://doi.org/10.5194/egusphere-egu24-15095, 2024.

Pressure rise mechanisms
X2.26
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EGU24-14561
Yury Podladchikov and Ilya Bindeman

We present undated results of a numerical model of pressure increase in a quasi-isochoric magma system due to the flotation of bubble-crystal clusters (vesicular mafic enclaves), that are common in silicic rocks that experience magma chamber refill by water and CO2-saturated basaltic magma. The model accounts for water solubility and diffusion and utilizes measured size distributions of mafic enclaves in volcanic and plutonic rocks around the world. These mafic enclaves have sizes ranging from (~1 to >30 cm), lognormal size distribution that we explain by flotation. They have lower densities (density difference =10-30%) than silicic hosts due to bubbles. The principal results of the model are: 1) enclaves are capable of rapid (days-months) flotation leading to pressurization of shallow magma chambers over cracking limit (100 MPa) using fluid rise mechanisms below; 2) The dynamics of pressure increase is strongly non-linear and is determined by the initial size distribution of enclaves, and other parameters; 3) Diffusion of water out of enclaves is slower than the rise time for most realistic viscosities of the silicic host melt. We consider cases when overpressuring causes density reversal due to solubility increase, and consider the role of convection. We present examples of high concentrations of enclaves within silicic domes that we explain by pre-eruption accumulation by flotation to the roof 

Bindeman I.N., Podladchikov Y.Y., Inclusions in volcanic rocks and a mechanism for triggering volcanic eruptions, Modern Geology, 19, 1-11, 1993.
Steinberg, G.S., Steinberg, A.S., Merzhanov A.G., Fluid mechanism of pressure growth in volcanic (magmatic) systems, Modern Geology, 13, 257-265, 1989a.
Steinberg, G.S., Steinberg, A.S., Merzhanov A.G., Fluid mechanism of pressure growth and the seismic regime of volcanous prior to eruption, Modern Geology, 13, 267-274, 1989b.
Steinberg, G.S., Steinberg, A.S., Merzhanov A.G., Fluid mechanism of pressure rise in volcanic (magmatic) systems with mass exchange, Modern Geology, 13, 275-281, 1989c.

How to cite: Podladchikov, Y. and Bindeman, I.: Vesiculated basaltic enclave flotation as a mechanism of fluid pressure increase in magma chambers during silicic-basaltic magma mixing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14561, https://doi.org/10.5194/egusphere-egu24-14561, 2024.

X2.27
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EGU24-15739
Johannes C. Vrijmoed, Yury Y. Podladchikov, Marcin Dabrowski, and Lyudmila Khakimova

The occurrence of eclogite enclosed in felsic continental rocks have been subject of intense discussion over several decades. The eclogite facies mineralogy preserves the only evidence that the rocks were buried to great depth and therefore this has significant consequences for the understanding of geodynamic processes in continental collision zones. However, often the enclosing felsic gneiss lacks evidence of this high-pressure metamorphism.

This apparent conflict in metamorphic pressure is founded on experimental phase equilibria studies in which pyroxene and plagioclase in igneous mafic rocks transform at high pressure to the characteristic garnet and omphacite assemblage of eclogite. In contrast, the felsic rocks preserve a mineral assemblage expected to equilibrate at lower pressure. A common explanation is that the enclosing felsic gneiss was retrogressed on the exhumation path, whereas eclogite has been preserved due to slower reaction kinetics in mafic rocks. The preservation of original igneous structures of various mafic rocks and incomplete reactions in metagabbro may also be attributed to metastability. Subsequently, it has been shown that large areas of the enclosing felsic gneiss have retained their original low-pressure mineral assemblage (e.g. Peterman et al., 2009). Consequently, large areas of felsic gneiss were never metamorphosed in the eclogite facies. It is firmly established that fluids play an important role in metamorphic reactions. In contrast, the role of mechanics and the heterogeneity of rock mechanical properties during metamorphism has received less attention.

Mechanical properties of mafic rocks can be different from the surrounding felsic lithologies. Therefore, a mechanical model was proposed for a mafic inclusion in felsic continental rock in which the entire domain was subjected to burial (Podladchikov & Dabrowski, 2017). The model predicted a much higher pressure in the mafic inclusion than in the felsic matrix. The overpressure in the mafic inclusion resulted from difference in compressibility between the mafic and felsic lithologies. This may explain the contrast in high pressure eclogite compared to the enclosing lower pressure felsic continental rocks.

In this study, we combine the mechanical model with thermodynamic calculations using Thermolab (Vrijmoed & Podladchikov, 2022) and apply it to ultra-high-pressure rocks in western Norway. We retrieve density, compressibility, and thermal expansivity for observed rocks from phase equilibria calculations as input into the mechanical models. With Thermolab, complex fluids including more than 40 aqueous species, and multi-component melt and solid solution models, can be conveniently coupled to reactive transport and mechanical models to quantify the effect of burial overpressure.

References:

Podladchikov, Y. Y., Dabrowski, M., (2017), Overpressure by burial, Geophysical Research Abstracts, Vol. 19, EGU2017-18976, 2017, EGU General Assembly 2017.

Vrijmoed, J.C. and Y.Y. Podladchikov, (2022), Thermolab: A Thermodynamics Laboratory for Nonlinear Transport Processes in Open Systems. Geochemistry Geophysics Geosystems, 2022. 23(4).

Peterman, E. M., Hacker, B.R., Baxter, E. F. (2009), Phase transformations of continental crust during subduction and exhumation:Western Gneiss Region, Norway, Eur. J. Mineral. 2009, 21, pp. 1097-1118

How to cite: Vrijmoed, J. C., Podladchikov, Y. Y., Dabrowski, M., and Khakimova, L.: Occurrence of eclogite in felsic continental rocks as a natural consequence of burial, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15739, https://doi.org/10.5194/egusphere-egu24-15739, 2024.

Regimes of convective flows and porosity waves
X2.28
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EGU24-17074
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ECS
Ludovic Räss, Ivan Utkin, and Yuri Podladchikov

Fast vertical fluid transfers in the crust play a crucial role in transporting elements and energy from deep environments into the shallow subsurface. These fluid transfers also impact magmatic processes, metamorphism, and heat distribution. Heat distribution in the subsurface is key for temperature-dependent geological processes, geothermal energy, and reservoir operations. Therefore, assessing the efficiency of heat transport by localised fluid flow is important.

Nonlinear porosity waves, resulting from hydro-mechanical interactions, provide a mechanism for fast vertical fluid transfers in the subsurface. However, their ability to transport heat has not been fully explored yet.

In this study, we investigate the coupling of hydro-mechanical processes with thermal processes to assess the efficiency of heat transport by porosity waves in a porous subsurface environment. We use numerical simulations to solve the coupled thermo-hydro-mechanical equations and present high-resolution modeling results. We also evaluate the role of a consistent and conservative formulation. Our preliminary findings suggest that porosity waves do not significantly enhance heat transfer in the subsurface. Additionally, we discuss the influence of parameters such as porosity, permeability, and fluid properties on the efficiency of heat transport.

How to cite: Räss, L., Utkin, I., and Podladchikov, Y.: Thermal porosity waves, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17074, https://doi.org/10.5194/egusphere-egu24-17074, 2024.

X2.29
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EGU24-15242
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ECS
Boris Antonenko, Lyudmila Khakimova, and Yury Podladchikov

The simulation and visualization of geodynamical processes poses a major challenge for due to spatial and time scales spanning many orders of magnitude and highly nonlinear phenomena. Modeling and solving such processes are necessary in order to accurately predict changes in natural systems. Two-phase models of fluid flow in deformable porous media are widely used to explain the various processes that occur in the Earth’s interior and subsurface. However, thermal processes, especially volume changes caused by thermal expansion, are typically ignored.

In this study, numerical simulation methods were used to describe a mathematical model of heat transfer processes in a porous media. The purpose of these studies is to determine the influence of nondimensional parameters (Rayleigh numbers) on the convection regimes (free and porous convections). To study these problems, numerical modeling of a nonlinear thermo-hydro-mechanical processes in porous materials filled with a fluid under gravity. The finite difference staggered grid discretization and a graphics processing unit based pseudo-transient solver are utilized in the numerical simulation.

We perform systematic numerical simulations and dimensional analysis to classify the regimes of convection.

How to cite: Antonenko, B., Khakimova, L., and Podladchikov, Y.: Numerical modelling and classification of thermo-hydro-mechanical convective regimes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15242, https://doi.org/10.5194/egusphere-egu24-15242, 2024.

Reactive porosity waves
X2.30
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EGU24-15613
Anna Isaeva, Lyudmila Khakimova, and Yury Podladchikov

Multicomponent multiphase reactive transport in porous media controls various phenomena in geological formations such as carbonization, fluid flow in a petroleum reservoir, mobility of radioactive waste in repositories, etc. Despite the obvious differences between these geological processes, they have much in common from a numerical simulation point of view.

We draw parallels between mathematical models of processes from two different areas of research. Firstly, we study the process of carbonization. Secondly, we consider the process of retrograde condensation, which is known to occur when natural gas flows in reservoir rock (during isothermal pressure reduction). Retrograde condensation is a property of multicomponent mixtures, such as natural gas. 

Both systems considered exhibit complex behavior and phase  transitions. But both systems can be described by the same generalized equations. We discuss the differences and similarities between these mathematical models.

How to cite: Isaeva, A., Khakimova, L., and Podladchikov, Y.: Numerical simulation of multicomponent multiphase reactive fluid flow in porous media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15613, https://doi.org/10.5194/egusphere-egu24-15613, 2024.

X2.31
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EGU24-14845
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ECS
Lyudmila Khakimova, Andrey Frendak, Leonid Aranovich, and Yury Podladchikov

Revealing of continental crust formation mechanism is a fundamental problem. There are metamorphic based theories and leading magmatic ones. Most recent models rely on differentiation of basaltic magma generated by partial melting of peridotite under influence of a fluid escape from subducting hydrated oceanic crust.

Here we present hypothesis of alternative mechanism of continental crust formation which invokes the multicomponent pore fluid transport by reactive porosity waves through the base of the Lithosphere. It includes partial hydration of mantle peridotite due to interaction with aqueous solutions transported through fluid-rich channels-like structures in rocks undergoing visco-elastic deformation coupled with reactions, phase transformations, volume and density changes.

To support the hypothesis, we propose a coupled hydro-mechanical-chemical model for simulating the filtration of multicomponent fluid through deforming mineral matrix treating zero porosity limit. Along with a number of constitutive relations, this model is closed by tabulated thermodynamic data, which are to be preliminarily calculated using linprog minimization in ThermoLab. We present 2D numerical implementation utilizing accelerated pseudo-transient numerical scheme. Results illustrate hydration porosity wave propagation witj peridotite alteration and the visco-elastic deformation of the zero porosity mineral matrix, with reference to the system up to 12 components including the corresponding solid and aqueous solutions.

How to cite: Khakimova, L., Frendak, A., Aranovich, L., and Podladchikov, Y.: Multicomponent Pore Fluid Transport by Hydration Porosity Waves in the Litosphere: A Model for Continental Crust Formation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14845, https://doi.org/10.5194/egusphere-egu24-14845, 2024.

X2.32
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EGU24-8862
Andrey Frendak, Lyudmila Khakimova, Leonid Aranovich, and Yury Podladchikov

We propose a coupled hydro-mechanical-chemical model and its 1D numerical implementation. We demonstrate its application to the model filtration of a multicomponent fluid in deforming and reacting host rocks, considering changes in the densities, phase proportions, and the chemical compositions of the coexisting phases.

The numerical results show the propagation of a porosity wave by means of a viscous (de)compaction mechanism accompanied by the formation of an elongated zone with higher filtration properties. After the formation of such a channel, the formation and propagation of the reaction fronts occurs and are associated with the transformation of the mineral composition of the original rock.

How to cite: Frendak, A., Khakimova, L., Aranovich, L., and Podladchikov, Y.: Multicomponent Fluid Flow in Deforming and Reacting Porous Rock in the Earth’s crust: hydro-mechanical-chemical model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8862, https://doi.org/10.5194/egusphere-egu24-8862, 2024.

X2.33
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EGU24-19341
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Highlight
Timm John, Liudmila Khakimova, Konstantin Huber, Johannes Vrijmoed, Yuri Podladchikov, and Marco Scambelluri

Subduction of hydrated lithosphere slabs into the mantle leads to the release of hydrous fluids, which contribute to a wide range of subduction zone phenomena, such as arc volcanism and seismicity. The efficiency of slab devolatilization is crucial for maintaining the overall stability of the Earth's chemical reservoirs over geological timescales. The formation of channelized fluid flow structures during dehydration, such as olivine veins observed in the Erro Tobbio meta-serpentinites (Italy), enhances the efficiency of fluid release from the subducting slab and might be crucial for devolatilization to keep up with the rate of plate subduction.

Observed olivine-rich vein assemblages and the presence of mineral-bound H2O in the matrix is indicative of high temperatures and partial dehydration. Porosity structures develop into vein-like structures at the onset of dehydration due to intrinsic chemical heterogeneities [1], with connectivity being already reached at low porosities [2]. As dehydration progresses, the fluid pressure in the porous network rises, and buoyancy forces lead to an upward fluid flow in the rock. Porosity waves are a potential mechanism to explain fluid flow focusing structures in rocks undergoing viscous deformation.

This work presents a 2D hydro-mechanical-chemical model for reactive porosity waves in a dehydrating and deforming serpentinite that is part of a subducting slab. Based on [3], we chose SiO2 as the metasomatic agent in a MgO-FeO-SiO2 system with H2O in excess. As model input, we use chemical data of serpentinites from the Mirdita ophiolite (Albania) that has not entered a subduction zone. The 2D chemical mapping of the sample from outcrop down to µm-scale shows scale-invariant heterogeneities of SiO2 and FeO. Similar heterogeneities occur on the km-scale where they manifest as lithological differences between serpentinized harzburgites and dunites. This dataset of chemical maps ranging continuously from the µm- to dm-scale represents a scale-independent pattern of chemical heterogeneities in a dehydrating slab.

Numerical results using this data as input show spontaneous formation of fluid-rich high-permeable channels in deforming and dehydrating serpentinite associated with further olivine formation during the reactive flow of Н2О−SiО2 fluid carrying low SiO2 concentration. The numerical simulations show similar pattern to field observations from Erro Tobbio. We conclude that the formation of a fluid channeling network takes place from the µm- up to km-scale and provides the main fluid escape mechanism in subduction zones.

 

[1] Plümper, O. et al. Fluid escape from subduction zones controlled by channel-forming reactive porosity. Nat Geosci 10, 150–156 (2017).

[2] Bloch, W. et al. Watching dehydration: Seismic Indication for Transient Fluid Pathways in the Oceanic Mantle of the Subducting Nazca Slab. Geochem Geophy Geosy 19, doi:10.1029/2018gc007703 (2018)

[3] Huber, K. et al. Formation of olivine veins by reactive fluid flow in a dehydrating serpentinite. Geochem Geophy Geosy, 23, e2021GC010267 (2022).

How to cite: John, T., Khakimova, L., Huber, K., Vrijmoed, J., Podladchikov, Y., and Scambelluri, M.: Reactive porosity waves in a dehydrating and deforming slab: a scale invariant fluid release process, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19341, https://doi.org/10.5194/egusphere-egu24-19341, 2024.

X2.34
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EGU24-16643
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ECS
Marko Repac, Lyudmila Khakimova, Yury Podladchikov, Kurt Panter, Stefan Schmalholz, and Sebastien Pilet

Ongoing debates persist regarding the role of the lithospheric mantle in the generation of intraplate volcanoes. Most geochemical models propose that these volcanoes originate from magmas formed in the asthenosphere. Intraplate basalt composition, particularly their high content of trace elements, implies that these magmas are produced at low degree of partial melting. However, the melt migration through the lithospheric mantle remains largely unexplored. As these small quantities of magma traverse the lithosphere, their limited heat transport results in rapid cooling due to the lithosphere's strong geotherm (McKenzie, 1989), casting doubt on their ability to directly reach the surface. In contrast, this process induces a chemical effect characterized by the metasomatic enrichment of the lithospheric mantle, observed across oceanic, continental, and cratonic environments.

Here, we developed a numerical finite difference model, incorporating thermo-hydro-chemical-thermal (THMC) processes, to investigate melt migration across the lithosphere. The model includes conservation equations for mass, fluid, and solid momentum, featuring a non-linear porosity-permeability relation for decompaction weakening and reactive porosity waves essential for flow channelization. Thermodynamic calculations employed Thermolab (Vrijmoed & Podladchikov, 2022), a versatile Gibbs energy minimizer. Amphiboles and phlogopites are crucial phases for mantle metasomatism and alkaline magma generation. We successfully model these phases within expected PT ranges. Using both solution models and fixed composition phases.

The model progresses through multiple steps, initiating at the asthenosphere-lithosphere boundary. Initial melt, present there if volatile content is sufficient, migrates upward with a decreasing volume but increasing volatile content as the pressure and temperature decrease. At a given point, the freezing effect of volatiles on mantle melting temperature is no longer sufficient to stabilize melt in equilibrium with the surrounding mantle. Melt migration concludes with the formation of hydrous phases like pargasite or phlogopite depending on the pressure. The second step, addressing excess volatiles after hydrous phases crystallization, involves their further upward transport as fluid, metasomatizing the overlying mantle until depletion of fluid. This process explains several aspects of metasomatism, such as hydrated phase formation and cryptic metasomatism associated with fluid migration. On the other hand, our model confirms that magma does not seem capable of crossing the lithosphere without reacting with the surrounding mantle and crystallizing. To take this further, we consider the hypothesis that the process of melt transport in the lithosphere occurs through the repeated migration of several pulses of magma from the asthenosphere. The emplacement of the first porosity wave is fundamental in establishing a pathway through which all successive pulses will traverse. Following this intricate process, a more extensive segment of the lithosphere undergoes metasomatism. Additionally, the recurrent influx of melt/fluid gradually elevates temperatures in the metasomatized area, potentially leading to the subsequent re-melting of hydrous phases, thereby engendering alkaline melts observed at the surface.

  • McKenzie, D. (1989). Some remarks on the movement of small melt fractions in the mantle. Earth and Planetary Science Letters, 53-72.
  • Vrijmoed & Podladchikov. (2022). Thermolab: A Thermodynamics Laboratory for Nonlinear Transport Processes in Open Systems .G3, 23, e2021GC010303

How to cite: Repac, M., Khakimova, L., Podladchikov, Y., Panter, K., Schmalholz, S., and Pilet, S.: Multistep Numerical THMC Reactive Porosity Waves Transport Model to Explain Intraplate Volcanism and Mantle Metasomatism., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16643, https://doi.org/10.5194/egusphere-egu24-16643, 2024.

Microstructures
X2.35
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EGU24-16982
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ECS
Malgorzata Nowak, Lucie Tajcmanova, Jacek Szczepanski, and Marcin Dabrowski

The Snieznik eclogites experienced peak ultrahigh-pressure (UHP) metamorphism in around ~770°C at ~3.2 GPa followed by isothermal decompression and amphibolite-facies retrogression during Variscan Orogeny. The well-preserved peak metamorphic assemblage of these UHP eclogites comprises garnet + omphacite + kyanite + phengite + rutile + coesite. The mineral assemblage connected with the isothermal decompression episode is present in the form of diopside-amphibole-plagioclase symplectites that are locally disintegrating the main foliation.

Here, we investigate plagioclase rims developed around kyanite at the interface with quartz and diopside-plagioclase symplectite. They are present only around kyanite occurring in the vicinity of zones developed during the isothermal decompression event. In some parts, the plagioclase rims are locally replaced by the diopside-plagioclase symplectite. The monomineralic plagioclase rims, having max. 20 µm radial thickness, are polycrystalline. They consist of individual plagioclase grains (each 2-15 µm in diameter) with different crystallographic orientations. The rims as a whole exhibit zoning with the highest Ca content observed at the contact with the kyanite grains. The measured CaO content increases from ~2% near quartz and diopside-plagioclase symplectite to ~6% at the kyanite boundary.

In this contribution we investigate the chemical and mechanical effects, that might have contributed to the preservation of the observed zoning and the microstructural heterogeneity of the rims.

How to cite: Nowak, M., Tajcmanova, L., Szczepanski, J., and Dabrowski, M.: Microstructural relationships from locally equilibrated domains in UHP eclogites (Snieznik Massif, NE Bohemian Massif), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16982, https://doi.org/10.5194/egusphere-egu24-16982, 2024.

X2.36
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EGU24-22558
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ECS
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Highlight
Cindy Luisier, Lucie Tajcmanova, Thibault Duretz, Larissa Lenz Lenz, and Liudmila Khakimova

Coesite inclusions in garnets are emblematic observations, typical of Ultra-High-Pressure (UHP) rocks.  While small inclusions may fully preserve coesite, sufficiently large inclusions undergo partial transition of coesite to quartz. Here, we focus on samples from UHP rocks from Dora Maira Massif (Western Alps). Classical petrographic analysis indeed reveals the coexistence of quartz and coesite as well as deformation of the surrounding garnet (radial fractures). In addition, microprobe analysis further shows chemical zoning in garnet around partially transformed inclusions. This observation suggests a link between chemical zoning and deformation related to the phase transition. Such an observation provides a unique opportunity to investigate the relation between multi-component diffusion and garnet deformation using both microprobe analysis and quantitative modelling.

How to cite: Luisier, C., Tajcmanova, L., Duretz, T., Lenz, L. L., and Khakimova, L.: Influence of intracrystalline deformation on chemical diffusion in garnet around coesite inclusions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22558, https://doi.org/10.5194/egusphere-egu24-22558, 2024.

X2.37
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EGU24-15390
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ECS
Kristóf Porkoláb, Evangelos Moulas, and Stefan Schmalholz

Dehydration reactions at high pressures are considered as sources of stress perturbations potentially leading to the nucleation of intermediate-depth earthquakes. Dehydration reactions entail the release of water and significant solid volume changes, while solid deformation, fluid flow, and the migration of the reaction front interact with each other. Observation-based quantification of such complex interactions is challenging; hence, the exact mechanisms of dehydration-induced seismicity remain unclear. One of the most prominent dehydration reactions in subducted slabs, that may contribute to intermediate-depth seismicity, is the breakdown of antigorite at high pressures. To improve the understanding of this process, we quantify interactions between the metamorphic reaction, solid deformation, and fluid flow for the phase transformation of antigorite --> enstatite + forsterite + water. We present a two-phase, hydro-mechanical-chemical model that is based on the coupled solution of rock deformation, Darcy-flow of pore fluids, and equilibrium thermodynamics of the dehydration reaction (assuming isothermal conditions). We consider total and non-volatile mass conservation, while solid and fluid densities are based on thermodynamic lookup tables. We investigate the magnitude of reaction-induced stresses and test the effects of kinematic boundary conditions and rheological heterogeneities via a broad parameter study. We relate our findings to natural examples of antigorite dehydration and discuss implications for dehydration-induced earthquakes.

Acknowledgements

The reported investigation was financially supported by the National Research, Development and Innovation Fund, Hungary (PD143377).

How to cite: Porkoláb, K., Moulas, E., and Schmalholz, S.: Numerical modelling of antigorite dehydration at 3 GPa: reaction-induced stress variations and effects of tectonic forcing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15390, https://doi.org/10.5194/egusphere-egu24-15390, 2024.

Posters virtual: Mon, 15 Apr, 14:00–15:45 | vHall X2

Display time: Mon, 15 Apr 08:30–Mon, 15 Apr 18:00
Chairperson: Yury Podladchikov
vX2.2
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EGU24-19660
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ECS
Nikita Bondarenko, Roman Makhnenko, and Yury Podladchikov

Rock underground may be exposed to elevated deviatoric stress over prolonged time period resulting in time-dependent deformation and microcracking. This process of subcritical time-dependent deformation is sensitive to environmental conditions, such as applied state of stress, presence and chemical composition of pore fluids, and drainage conditions. To improve the understanding of processes occurring at subcritical stress, the laboratory brittle creep experiments are conducted on Berea sandstone specimens under various conditions. Strong correlation between time-dependent deformation and microcracking activity is observed in all conducted tests. Significant variation of magnitude-frequency relation of the acoustic emission signals occurs during macroscopic failure preparation, which can serve as a potential prognostic feature. The collected data on time-dependent deformation is interpreted by introducing viscosity as a coefficient of proportionality between deviatoric strain rate and applied deviatoric stress. It appears that viscosity is exponentially decreasing when the state of stress is approaching critical conditions associated with macroscopic failure. Empirically-based relationship is established describing the impact of mean and deviatoric stress on viscosity in wide range of applied stress. The presence of non-aqueous fluids (oil or CO2) appears to have significantly weaker impact on the creep deformation compared to aqueous fluids (deionized water and water with dissolved CO2). Finally, the drainage condition appears to be essential. If the mass of pore fluid inside the specimen remains constant throughout the experiment (undrained condition), the microcracking results in phenomena similar to dilatant hardening of the material observed at constant applied state of stress. This effect might be qualitatively similar to the ones occurring in the off-fault plasticity zones and provide the fault stabilization mechanism.

How to cite: Bondarenko, N., Makhnenko, R., and Podladchikov, Y.: Role of pore fluids in time-dependent deformation and microcracking of rock under high deviatoric stress, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19660, https://doi.org/10.5194/egusphere-egu24-19660, 2024.