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Giorgio Pennacchioni - One of the best experts on this subject based on the ideXlab platform.
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Fault plane processes and mesoscopic structure of a strong-type seismogenic fault in tonalites (Adamello batholith, Southern Alps)
Tectonophysics, 2020Co-Authors: Giulio Di Toro, Giorgio PennacchioniAbstract:The Gole Larghe Fault is an exhumed paleoseismic fault crosscutting the Adamello tonalites (Italian Southern Alps). Ambient conditions of faulting were 9-11 km in depth and 250-300 degrees C. In the study area the fault accommodates similar to 1100 in of dextral strike-slip over a fault thickness of 550 m. Displacement is partitioned into three hierarchically different sets of discrete subparallel cataclastic horizons (faults (1-2-3)). Fault displacement is in the range of few centimeters (faults(3)) to a maximum of a few tens of meters in major faults (1). Faults(1-2) nucleated on pre-existing joints, whereas faults(3) are newly generated fractures produced during slip along faults(1-2). Each fault within the Gole Larghe Fault records the same evolution with development of indurated Cataclasites precursory to pseudotachylyte production. Pseudotachylytes are usually generated at the host rock/ Cataclasite boundary and within Cataclasites the mean clast size decreases getting closer to pseudotachylyte fault veins. Pseudotachylytes and Cataclasites have a similar chemical composition which is enriched in Loss On Ignition, K, Rb, Ba, U and Fe(3+) compared to host rock. \ud \ud We envision two models for the evolution of the Gole Larghe Fault. In both models synkinematic fluid-rock interaction along a fault causes fault hardening by precipitation of abundant K-feldspar+epidote (and minor chlorite) in the Cataclasite matrix conducive to final production of pseudotachylyte. In the first model, induration occurs progressively by differential precipitation related to fabric evolution in Cataclasites. In the second model, induration occurs abruptly dependent on the development of full connectivity within the fault network and to fluid reservoir. Whatever the model, the Gole Larghe Fault represents a strong fault, where hardening processes resulted in a low displacement/fault thickness ratio and contrast with many mature weak faults where localized repeated seismic slip along the same weak horizons yields high displacement/fault thickness ratios. (c) 2005 Elsevier B.V All rights reserved
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Origin of hydrous fluids at seismogenic depth: Constraints from natural and experimental fault rocks
Earth and Planetary Science Letters, 2013Co-Authors: Silvia Mittempergher, Giorgio Pennacchioni, L. Dallai, François Renard, Giulio Di ToroAbstract:Abstract Fluids control the mechanical behavior of fault zones during the seismic cycle. We used geochemical, mineralogical, microstructural, hydrogen isotope compositions and Fourier Transform Infrared (FTIR) investigations to characterize the origin of hydrous fluids involved in ductile and brittle shear zones at the bottom of the seismogenic crust. Natural samples were collected from exhumed mylonitic shear zones and Cataclasite–pseudotachylyte bearing faults in the northern Adamello (Italian Southern Alps), which were active at 9–11 km depth. Pseudotachylytes, solidified coseismic friction-induced melts, testify to ancient seismogenic behavior of the faults. Natural pseudotachylytes were compared with artificial pseudotachylytes produced in high velocity friction experiments simulating seismic slip. Mylonites have mineralogical, elemental and hydrogen isotope compositions ( − 80 ‰ δ D − 78 ‰ ) similar to the host tonalite ( − 77 ‰ δ D − 73 ‰ ), within the analytical error of ± 5 ‰ . Cataclasites have instead mineralogical (chlorite, epidote, K-feldspar, no biotite), major and trace elements (enrichment in K2O, Ba, Rb; depletion in CaO, Na2O, SiO2) and hydrogen isotope ( − 69 ‰ δ D − 60 ‰ ) compositions suggesting interactions with a crustal metamorphic fluid. Pseudotachylytes are composed of high temperature minerals (plagioclase, biotite, dmisteinbergite, cordierite, and scapolite) and have elemental compositions resulting from mixing of tonalite and Cataclasite. Pseudotachylytes have complex microstructures, including: (i) microlitic domains, with well crystallized micrometric biotite, which have hydrogen isotope composition ( − 81 ‰ δ D − 59 ‰ ) similar to Cataclasites and tonalite; and (ii) cryptocrystalline domains, with poorly crystallized biotite, which have very high water content, release water upon heating at T > 50 ° C and have low δD value ( − 93 ‰ ). The hydrogen isotope composition of bulk samples is dominated by the composition of cryptocrystalline domains ( − 103 ‰ δ D − 88 ‰ ), where most of the water is hosted. Their hydrogen isotope composition is compatible with adsorption of present day rainfall water ( δ D = − 95 ‰ ). Artificial pseudotachylytes have the same hydrogen isotope compositions of the starting tonalite ( − 76 ‰ δ D − 74 ‰ ) or Cataclasite ( − 68 ‰ δ D − 62 ‰ ), with a slight decrease of the δD values in some samples ( − 85 ‰ δ D − 81 ‰ ). The first ingression of a crustal metamorphic fluid occurred in cataclastic faults. Natural pseudotachylytes, when not contaminated by present day rainfall water, have a hydrogen isotope composition similar to tonalite and Cataclasite, as reproduced in dry high velocity friction experiments. The fluids dissolved in coseismic melts are most likely derived from the breakdown of hydrous minerals of Cataclasite and tonalite undergone melting, and we could not identify the infiltration of an external fluid during earthquakes.
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fault plane processes and mesoscopic structure of a strong type seismogenic fault in tonalites adamello batholith southern alps
Tectonophysics, 2005Co-Authors: Giulio Di Toro, Giorgio PennacchioniAbstract:Abstract The Gole Larghe Fault is an exhumed paleoseismic fault crosscutting the Adamello tonalites (Italian Southern Alps). Ambient conditions of faulting were 9–11 km in depth and 250–300 °C. In the study area the fault accommodates ∼ 1100 m of dextral strike-slip over a fault thickness of 550 m. Displacement is partitioned into three hierarchically different sets of discrete subparallel cataclastic horizons (faults1–2–3). Fault displacement is in the range of few centimeters (faults3) to a maximum of a few tens of meters in major faults1. Faults1–2 nucleated on pre-existing joints, whereas faults3 are newly generated fractures produced during slip along faults1–2. Each fault within the Gole Larghe Fault records the same evolution with development of indurated Cataclasites precursory to pseudotachylyte production. Pseudotachylytes are usually generated at the host rock/Cataclasite boundary and within Cataclasites the mean clast size decreases getting closer to pseudotachylyte fault veins. Pseudotachylytes and Cataclasites have a similar chemical composition which is enriched in Loss On Ignition, K, Rb, Ba, U and Fe3+ compared to host rock. We envision two models for the evolution of the Gole Larghe Fault. In both models synkinematic fluid–rock interaction along a fault causes fault hardening by precipitation of abundant K-feldspar+epidote (and minor chlorite) in the Cataclasite matrix conducive to final production of pseudotachylyte. In the first model, induration occurs progressively by differential precipitation related to fabric evolution in Cataclasites. In the second model, induration occurs abruptly dependent on the development of full connectivity within the fault network and to fluid reservoir. Whatever the model, the Gole Larghe Fault represents a strong fault, where hardening processes resulted in a low displacement/fault thickness ratio and contrast with many mature weak faults where localized repeated seismic slip along the same weak horizons yields high displacement/fault thickness ratios.
Giulio Di Toro - One of the best experts on this subject based on the ideXlab platform.
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Fault plane processes and mesoscopic structure of a strong-type seismogenic fault in tonalites (Adamello batholith, Southern Alps)
Tectonophysics, 2020Co-Authors: Giulio Di Toro, Giorgio PennacchioniAbstract:The Gole Larghe Fault is an exhumed paleoseismic fault crosscutting the Adamello tonalites (Italian Southern Alps). Ambient conditions of faulting were 9-11 km in depth and 250-300 degrees C. In the study area the fault accommodates similar to 1100 in of dextral strike-slip over a fault thickness of 550 m. Displacement is partitioned into three hierarchically different sets of discrete subparallel cataclastic horizons (faults (1-2-3)). Fault displacement is in the range of few centimeters (faults(3)) to a maximum of a few tens of meters in major faults (1). Faults(1-2) nucleated on pre-existing joints, whereas faults(3) are newly generated fractures produced during slip along faults(1-2). Each fault within the Gole Larghe Fault records the same evolution with development of indurated Cataclasites precursory to pseudotachylyte production. Pseudotachylytes are usually generated at the host rock/ Cataclasite boundary and within Cataclasites the mean clast size decreases getting closer to pseudotachylyte fault veins. Pseudotachylytes and Cataclasites have a similar chemical composition which is enriched in Loss On Ignition, K, Rb, Ba, U and Fe(3+) compared to host rock. \ud \ud We envision two models for the evolution of the Gole Larghe Fault. In both models synkinematic fluid-rock interaction along a fault causes fault hardening by precipitation of abundant K-feldspar+epidote (and minor chlorite) in the Cataclasite matrix conducive to final production of pseudotachylyte. In the first model, induration occurs progressively by differential precipitation related to fabric evolution in Cataclasites. In the second model, induration occurs abruptly dependent on the development of full connectivity within the fault network and to fluid reservoir. Whatever the model, the Gole Larghe Fault represents a strong fault, where hardening processes resulted in a low displacement/fault thickness ratio and contrast with many mature weak faults where localized repeated seismic slip along the same weak horizons yields high displacement/fault thickness ratios. (c) 2005 Elsevier B.V All rights reserved
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Origin of hydrous fluids at seismogenic depth: Constraints from natural and experimental fault rocks
Earth and Planetary Science Letters, 2013Co-Authors: Silvia Mittempergher, Giorgio Pennacchioni, L. Dallai, François Renard, Giulio Di ToroAbstract:Abstract Fluids control the mechanical behavior of fault zones during the seismic cycle. We used geochemical, mineralogical, microstructural, hydrogen isotope compositions and Fourier Transform Infrared (FTIR) investigations to characterize the origin of hydrous fluids involved in ductile and brittle shear zones at the bottom of the seismogenic crust. Natural samples were collected from exhumed mylonitic shear zones and Cataclasite–pseudotachylyte bearing faults in the northern Adamello (Italian Southern Alps), which were active at 9–11 km depth. Pseudotachylytes, solidified coseismic friction-induced melts, testify to ancient seismogenic behavior of the faults. Natural pseudotachylytes were compared with artificial pseudotachylytes produced in high velocity friction experiments simulating seismic slip. Mylonites have mineralogical, elemental and hydrogen isotope compositions ( − 80 ‰ δ D − 78 ‰ ) similar to the host tonalite ( − 77 ‰ δ D − 73 ‰ ), within the analytical error of ± 5 ‰ . Cataclasites have instead mineralogical (chlorite, epidote, K-feldspar, no biotite), major and trace elements (enrichment in K2O, Ba, Rb; depletion in CaO, Na2O, SiO2) and hydrogen isotope ( − 69 ‰ δ D − 60 ‰ ) compositions suggesting interactions with a crustal metamorphic fluid. Pseudotachylytes are composed of high temperature minerals (plagioclase, biotite, dmisteinbergite, cordierite, and scapolite) and have elemental compositions resulting from mixing of tonalite and Cataclasite. Pseudotachylytes have complex microstructures, including: (i) microlitic domains, with well crystallized micrometric biotite, which have hydrogen isotope composition ( − 81 ‰ δ D − 59 ‰ ) similar to Cataclasites and tonalite; and (ii) cryptocrystalline domains, with poorly crystallized biotite, which have very high water content, release water upon heating at T > 50 ° C and have low δD value ( − 93 ‰ ). The hydrogen isotope composition of bulk samples is dominated by the composition of cryptocrystalline domains ( − 103 ‰ δ D − 88 ‰ ), where most of the water is hosted. Their hydrogen isotope composition is compatible with adsorption of present day rainfall water ( δ D = − 95 ‰ ). Artificial pseudotachylytes have the same hydrogen isotope compositions of the starting tonalite ( − 76 ‰ δ D − 74 ‰ ) or Cataclasite ( − 68 ‰ δ D − 62 ‰ ), with a slight decrease of the δD values in some samples ( − 85 ‰ δ D − 81 ‰ ). The first ingression of a crustal metamorphic fluid occurred in cataclastic faults. Natural pseudotachylytes, when not contaminated by present day rainfall water, have a hydrogen isotope composition similar to tonalite and Cataclasite, as reproduced in dry high velocity friction experiments. The fluids dissolved in coseismic melts are most likely derived from the breakdown of hydrous minerals of Cataclasite and tonalite undergone melting, and we could not identify the infiltration of an external fluid during earthquakes.
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fault plane processes and mesoscopic structure of a strong type seismogenic fault in tonalites adamello batholith southern alps
Tectonophysics, 2005Co-Authors: Giulio Di Toro, Giorgio PennacchioniAbstract:Abstract The Gole Larghe Fault is an exhumed paleoseismic fault crosscutting the Adamello tonalites (Italian Southern Alps). Ambient conditions of faulting were 9–11 km in depth and 250–300 °C. In the study area the fault accommodates ∼ 1100 m of dextral strike-slip over a fault thickness of 550 m. Displacement is partitioned into three hierarchically different sets of discrete subparallel cataclastic horizons (faults1–2–3). Fault displacement is in the range of few centimeters (faults3) to a maximum of a few tens of meters in major faults1. Faults1–2 nucleated on pre-existing joints, whereas faults3 are newly generated fractures produced during slip along faults1–2. Each fault within the Gole Larghe Fault records the same evolution with development of indurated Cataclasites precursory to pseudotachylyte production. Pseudotachylytes are usually generated at the host rock/Cataclasite boundary and within Cataclasites the mean clast size decreases getting closer to pseudotachylyte fault veins. Pseudotachylytes and Cataclasites have a similar chemical composition which is enriched in Loss On Ignition, K, Rb, Ba, U and Fe3+ compared to host rock. We envision two models for the evolution of the Gole Larghe Fault. In both models synkinematic fluid–rock interaction along a fault causes fault hardening by precipitation of abundant K-feldspar+epidote (and minor chlorite) in the Cataclasite matrix conducive to final production of pseudotachylyte. In the first model, induration occurs progressively by differential precipitation related to fabric evolution in Cataclasites. In the second model, induration occurs abruptly dependent on the development of full connectivity within the fault network and to fluid reservoir. Whatever the model, the Gole Larghe Fault represents a strong fault, where hardening processes resulted in a low displacement/fault thickness ratio and contrast with many mature weak faults where localized repeated seismic slip along the same weak horizons yields high displacement/fault thickness ratios.
Bernd Leiss - One of the best experts on this subject based on the ideXlab platform.
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fabrication of synthetic calcite muscovite rocks with variable texture an analogue to Cataclasite fabrics
Tectonophysics, 2008Co-Authors: Volkmar Schmidt, Luigi Burlini, Ann M Hirt, Bernd LeissAbstract:Abstract A series of large diameter calcite–muscovite aggregates has been prepared from calcite and muscovite powders, in order to gain a better understanding of how texture develops in impure carbonate rocks. The development of the microstructure and the crystallographic preferred orientation (CPO, texture) during the preparation process is described. The synthetic rocks have been fabricated from powders of calcite and muscovite by uniaxial cold-pressing at loads up to 400 MPa and subsequent hot isostatic pressing (HIPping) at pressures of 150 to 170 MPa and a temperature of 670 °C. The resulting textures and microstructures are homogeneous throughout the samples. The calcite CPO is generated by rigid body rotation and twinning during cold-pressing and is not significantly altered by recrystallization during HIPping. Grain growth during HIPping is observed in pure calcite samples, but is inhibited through high porosity and the presence of muscovite in the mixed aggregates. The preferred orientation of the calcite c -axes is found to increase with increasing uniaxial cold pressure, and to be independent of the muscovite content. The magnetic bulk susceptibility of the starting material has been changed by the formation of ferromagnetic impurities during fabrication. Comparison of the samples to natural calcite fabrics from fault zones show the potential of the experiments and fabric analyses presented to analyze and to better understand the deformation mechanisms of fault zones.
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Fabrication of synthetic calcite–muscovite rocks with variable texture — An analogue to Cataclasite fabrics?
Tectonophysics, 2008Co-Authors: Volkmar Schmidt, Luigi Burlini, Ann M Hirt, Bernd LeissAbstract:Abstract A series of large diameter calcite–muscovite aggregates has been prepared from calcite and muscovite powders, in order to gain a better understanding of how texture develops in impure carbonate rocks. The development of the microstructure and the crystallographic preferred orientation (CPO, texture) during the preparation process is described. The synthetic rocks have been fabricated from powders of calcite and muscovite by uniaxial cold-pressing at loads up to 400 MPa and subsequent hot isostatic pressing (HIPping) at pressures of 150 to 170 MPa and a temperature of 670 °C. The resulting textures and microstructures are homogeneous throughout the samples. The calcite CPO is generated by rigid body rotation and twinning during cold-pressing and is not significantly altered by recrystallization during HIPping. Grain growth during HIPping is observed in pure calcite samples, but is inhibited through high porosity and the presence of muscovite in the mixed aggregates. The preferred orientation of the calcite c -axes is found to increase with increasing uniaxial cold pressure, and to be independent of the muscovite content. The magnetic bulk susceptibility of the starting material has been changed by the formation of ferromagnetic impurities during fabrication. Comparison of the samples to natural calcite fabrics from fault zones show the potential of the experiments and fabric analyses presented to analyze and to better understand the deformation mechanisms of fault zones.
Fabrizio Storti - One of the best experts on this subject based on the ideXlab platform.
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Field and experimental evidence for coseismic ruptures along shallow creeping faults in forearc sediments of the Crotone Basin, South Italy
2014Co-Authors: Fabrizio Balsamo, Luca Aldega, Nicola De Paola, I. Faoro, Fabrizio StortiAbstract:Large seismic slip occurring along shallow creeping faults in tectonically active areas represents an unsolved paradox, which is largely due to our poor understanding of the mechanics governing creeping faults, and to the lack of documented geological evidence showing how coseismic rupturing overprints creep in near-surface conditions. In this contribution we integrate field, petrophysical, mineralogical and friction data to characterize the signature of coseismic ruptures propagating along shallow creeping faults affecting unconsolidated forearc sediments of the seismically active Crotone Basin, in South Italy. Field observations of fault zones show widespread foliated Cataclasites in fault cores, locally overprinted by sharp slip surfaces decorated by thin (0.5-1.5 cm) black gouge layers. Compared to foliated Cataclasites, black gouges have much lower grain size, porosity and permeability, which may have facilitated slip weakening by thermal fluid pressurization. Moreover, black gouges are characterized by distinct mineralogical assemblages compatible with high temperatures (180-200 C) due to frictional heating during seismic slip. Foliated Cataclasites and black gouges were also produced by laboratory friction experiments performed on host sediments at sub-seismic ( 0.1 m/s) and seismic (1 m/s) slip rates, respectively. Black gouges display low friction coefficients (0.3) and velocity-weakening behaviours, as opposed to high friction coefficients (0.65) and velocity-strengthening behaviours shown by the foliated Cataclasites. Our results show that narrow black gouges developed within foliated Cataclasites represent a potential diagnostic marker for episodic seismic activity in shallow creeping faults. These findings can help understanding the time-space partitioning between aseismic and seismic slip of faults at shallow crustal levels, impacting on seismic hazard evaluation of subduction zones and forearc regions affected by destructive earthquakes and tsunamis.
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the signature and mechanics of earthquake ruptures along shallow creeping faults in poorly lithified sediments
Geology, 2014Co-Authors: Fabrizio Balsamo, Luca Aldega, Nicola De Paola, I. Faoro, Fabrizio StortiAbstract:Seismic slip episodically occurring along shallow creeping faults in poorly lithified sediments represents an unsolved paradox, largely due to our poor understanding of the mechanics governing creeping faults and the lack of documented geological evidence showing how coseismic rupturing overprints creep in near-surface conditions. Here we describe the signature of seismic ruptures propagating along shallow creeping faults affecting unconsolidated forearc sediments. Field observations of deformation band–dominated fault zones show widespread foliated Cataclasites in fault cores, locally overprinted by sharp slip surfaces decorated by thin (0.5–1.5 cm) black gouge layers (herein, black gouge). Compared to foliated Cataclasites, black gouges have much lower grain size, porosity, and permeability. Moreover, they are characterized by distinct mineralogical assemblages compatible with high temperatures (180–200 °C) due to frictional heating during seismic slip. Foliated Cataclasites were also produced by laboratory experiments performed on host sediments at subseismic slip rates (≤0.1 m/s), displaying high residual friction (µf = 0.65) and strain-hardening behavior. Black gouges were produced during experiments performed at seismic (1 m/s) slip rates, displaying low residual friction (µf = 0.3) due to dynamic weakening. Our results show that black gouges represent a potential diagnostic marker for seismic faulting in shallow creeping faults. These findings can help understanding the time-space partitioning between aseismic and seismic behavior of faults at shallow crustal levels.
Volkmar Schmidt - One of the best experts on this subject based on the ideXlab platform.
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fabrication of synthetic calcite muscovite rocks with variable texture an analogue to Cataclasite fabrics
Tectonophysics, 2008Co-Authors: Volkmar Schmidt, Luigi Burlini, Ann M Hirt, Bernd LeissAbstract:Abstract A series of large diameter calcite–muscovite aggregates has been prepared from calcite and muscovite powders, in order to gain a better understanding of how texture develops in impure carbonate rocks. The development of the microstructure and the crystallographic preferred orientation (CPO, texture) during the preparation process is described. The synthetic rocks have been fabricated from powders of calcite and muscovite by uniaxial cold-pressing at loads up to 400 MPa and subsequent hot isostatic pressing (HIPping) at pressures of 150 to 170 MPa and a temperature of 670 °C. The resulting textures and microstructures are homogeneous throughout the samples. The calcite CPO is generated by rigid body rotation and twinning during cold-pressing and is not significantly altered by recrystallization during HIPping. Grain growth during HIPping is observed in pure calcite samples, but is inhibited through high porosity and the presence of muscovite in the mixed aggregates. The preferred orientation of the calcite c -axes is found to increase with increasing uniaxial cold pressure, and to be independent of the muscovite content. The magnetic bulk susceptibility of the starting material has been changed by the formation of ferromagnetic impurities during fabrication. Comparison of the samples to natural calcite fabrics from fault zones show the potential of the experiments and fabric analyses presented to analyze and to better understand the deformation mechanisms of fault zones.
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Fabrication of synthetic calcite–muscovite rocks with variable texture — An analogue to Cataclasite fabrics?
Tectonophysics, 2008Co-Authors: Volkmar Schmidt, Luigi Burlini, Ann M Hirt, Bernd LeissAbstract:Abstract A series of large diameter calcite–muscovite aggregates has been prepared from calcite and muscovite powders, in order to gain a better understanding of how texture develops in impure carbonate rocks. The development of the microstructure and the crystallographic preferred orientation (CPO, texture) during the preparation process is described. The synthetic rocks have been fabricated from powders of calcite and muscovite by uniaxial cold-pressing at loads up to 400 MPa and subsequent hot isostatic pressing (HIPping) at pressures of 150 to 170 MPa and a temperature of 670 °C. The resulting textures and microstructures are homogeneous throughout the samples. The calcite CPO is generated by rigid body rotation and twinning during cold-pressing and is not significantly altered by recrystallization during HIPping. Grain growth during HIPping is observed in pure calcite samples, but is inhibited through high porosity and the presence of muscovite in the mixed aggregates. The preferred orientation of the calcite c -axes is found to increase with increasing uniaxial cold pressure, and to be independent of the muscovite content. The magnetic bulk susceptibility of the starting material has been changed by the formation of ferromagnetic impurities during fabrication. Comparison of the samples to natural calcite fabrics from fault zones show the potential of the experiments and fabric analyses presented to analyze and to better understand the deformation mechanisms of fault zones.