Transient weakening during the granulite to eclogite transformation within hydrous shear zones (Holsnøy, Norway)

Bras, Erwan; Baïsset, Marie; Yamato, Philippe; Labrousse, Loïc

doi:10.1016/j.tecto.2021.229026

Cited by 16 publications

(38 citation statements)

References 89 publications

(142 reference statements)

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“…In such a case, this pressure increase would extend the degree of overstepping of the rock. This is something that can be expected for the eclogitization process in specific cases, such as the granulite to eclogite transformation, as it is classically proposed that the eclogite is weaker, at least transiently, than its granulitic protolith (Labrousse et al, 2010;Bras et al, 2021;Kaatz et al, 2021).…”

Section: Modelling Perspectivesmentioning

confidence: 75%

“…It is associated with an important density change of ~ 400-500 kg.m -3 (Fig. 1f) and with a transient variations of material strength (Bras et al, 2021). Another major characteristic of densification reactions in fluid undersaturated lower crustal rocks, such as amphibolites and granulites, is that they usually take place far from the predicted thermodynamic equilibrium (e.g., Austrheim, 1987;Wayte et al, 1989;Wain et al, 2001;Jackson et al, 2004;Hetényi et al, 2007Hetényi et al, , 2021.…”

Section: Introductionmentioning

confidence: 98%

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Reaction-induced volume change triggers brittle failure at eclogite facies conditions

Yamato

Duretz

Baïsset

et al. 2022

Earth and Planetary Science Letters

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Section: Modelling Perspectivesmentioning

confidence: 75%

Section: Introductionmentioning

confidence: 98%

Reaction-induced volume change triggers brittle failure at eclogite facies conditions

Yamato

Duretz

Baïsset

et al. 2022

Earth and Planetary Science Letters

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“…Assuming such diffusivities, Bras et al. (2021) provided viscosity, η , ratios during progressive shearing, eclogitization, and hydration of η transient / η granulite < 1 and η transient / η eclogite < 1. However, an additional hydrogen influx accompanying the H 2 O inflow (e.g., Kaatz et al., 2022) might influence how hydration propagates into the wall rock and how it impacts the rheological behavior of the affected rocks.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, it has been suggested that the fluid infiltration on Holsnøy can be sufficiently approximated via bulk diffusion of aqueous fluid, mainly H 2 O, with bulk diffusivities of D b = 10 −14±2 m 2 /s (e.g., Bras et al., 2021; Kaatz et al., 2021). Assuming such diffusivities, Bras et al.…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulations Reproduce Field Observations Showing Transient Weakening During Shear Zone Formation by Diffusional Hydrogen Influx and H₂O Inflow

Kaatz

Schmalholz

John

2023

Geochem Geophys Geosyst

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Exposures on Holsnøy island (Bergen Arcs, Norway) indicate fluid infiltration through fractures into a dry, metastable granulite, which triggered a kinetically delayed eclogitization, a transient weakening during fluid‐rock interaction, and formation of shear zones that widened during shearing. It remains unclear whether the effects of grain boundary‐assisted aqueous fluid inflow on the duration of granulite hydration were influenced by a diffusional hydrogen influx accompanying the fluid inflow. To better estimate the fluid infiltration efficiencies and the parameter interdependencies, a 1D numerical model of a viscous shear zone is utilized and validated using measured mineral phase abundance distributions and H2O‐contents in nominally anhydrous minerals of the original granulite assemblage to constrain the hydration by aqueous fluid inflow and diffusional hydrogen influx, respectively. Both hydrations are described with a diffusion equation and affect the effective viscosity. Shear zone kinematics are constrained by the observed shear strain and thickness. The model fits the phase abundance and H2O‐content profiles if the effective hydrogen diffusivity is approximately one order of magnitude higher than the diffusivity for aqueous fluid inflow. The observed shear zone thickness is reproduced if the viscosity ratio between dry granulite and deforming, reequilibrating eclogite is ∼104 and that between dry granulite and hydrated granulite is ∼102. The results suggest shear velocities <10−2 cm/a, hydrogen diffusivities of ∼10−13±1 m2/s, and a shearing duration of <10 years. This study successfully links and validates field data to a shear zone model and highlights the importance of hydrogen diffusion for shear zone widening and eclogitization.

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“…The lower pressure experienced by brittle materials allows further localization of deformation and promotes fluid influx from the surroundings, if available. Fluid introduction to lower crustal rocks will invariably lead to metamorphic reactions and rheological weakening both due to a reduction in grain size and the formation of weaker hydrous minerals, such as micas 2,8,[30][31][32][33] . Sustained far-field (tectonic-) loading will then lead to viscous deformation and the development of shear zones along the weakened and reacted rock volumes 12 .…”

mentioning

confidence: 99%

Dynamic Pressure Variations in the Lower Crust Caused by Localized Fluid-Induced Weakening

Jamtveit

Moulas

Kaus

2023

Preprint

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When continents collide, the Earth&#8217;s crust experiences structural and metamorphic transformations that control the geodynamic evolution of the orogen. Metamorphism of dry, lower crust requires fluid supply and produce mechanically weaker rocks. Metamorphism is often localized in shear-zones, which provide the available fluid pathways. Several field-based studies show that shear zone development is preceded by brittle faults, frequently portraying evidence for seismic slip rates and introduction of externally derived fluids. However, despite the extensive documentation of lower crustal metamorphism and associated deformation features, a unifying model coupling deformation to fluid migration and metamorphic reactions does not exist. Here, we present a visco-elasto-plastic model where the most pertinent features observed in transformed lower crust emerge from basic mechanical principles during the deformation of a coherent rock volume with associated fluid introduction. Characteristic features include a strikingly dynamic and heterogeneous pressure distribution in the reacting and deforming rock volumes. Lower crustal pressure variations may reach 1 GPa at any given depth. This will have first order effects on the pattern of fluid migration in the lower crust, and may also explain the apparent discrepancies between the relevant tectonic settings and petrologically-inferred burial depths. An additional petrological consequence of the positive pressure variations is the generation of fluid-undersaturated high-pressure assemblages. For common bulk-rock compositions that are observed in the Bergen Arcs (Norway), and for finite amounts of fluid, phase equilibria modelling results suggest that the quasi-isothermal pressurization will lead to the formation of H2O-undersaturated metamorphic rocks. These results highlight the importance of coupling between metamorphic reaction progress and deformation at high-grade conditions. &#160; &#160; Acknowledgements: This project was supported by a research award from the Alexander von Humboldt foundation to BJ, by ERC Advanced Grant Agreement n&#176;669972 to Jamtveit and ERC Consolidator Grant Agreement n&#176;771143 to Kaus from the European Union&#8217;s Horizon 2020 Research and Innovation Programme. Parts of this research were conducted using the supercomputer MOGON2 and/or advisory services offered by Johannes Gutenberg University Mainz (hpc.uni-mainz.de), which is a member of the AHRP (Alliance for High Performance Computing in Rhineland Palatinate, www.ahrp.info) and the Gauss Alliance e.V. Andrew Putnis and H&#229;kon Austrheim are acknowledged for numerous discussions. &#160; References: Moulas, E., Kaus, B., Jamtveit, B., 2022. Dynamic pressure variations in the lower crust caused by localized fluid-induced weakening. Communications Earth & Environment 3, 157. https://doi.org/10.1038/s43247-022-00478-7

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Transient weakening during the granulite to eclogite transformation within hydrous shear zones (Holsnøy, Norway)

Cited by 16 publications

References 89 publications

Reaction-induced volume change triggers brittle failure at eclogite facies conditions

Reaction-induced volume change triggers brittle failure at eclogite facies conditions

Numerical Simulations Reproduce Field Observations Showing Transient Weakening During Shear Zone Formation by Diffusional Hydrogen Influx and H₂O Inflow

Dynamic Pressure Variations in the Lower Crust Caused by Localized Fluid-Induced Weakening

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Transient weakening during the granulite to eclogite transformation within hydrous shear zones (Holsnøy, Norway)

Cited by 16 publications

References 89 publications

Reaction-induced volume change triggers brittle failure at eclogite facies conditions

Reaction-induced volume change triggers brittle failure at eclogite facies conditions

Numerical Simulations Reproduce Field Observations Showing Transient Weakening During Shear Zone Formation by Diffusional Hydrogen Influx and H2O Inflow

Dynamic Pressure Variations in the Lower Crust Caused by Localized Fluid-Induced Weakening

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Numerical Simulations Reproduce Field Observations Showing Transient Weakening During Shear Zone Formation by Diffusional Hydrogen Influx and H₂O Inflow