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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.