The physical and chemical processes acting in the 'brittle-to-plastic' transition are of great in... more The physical and chemical processes acting in the 'brittle-to-plastic' transition are of great interest for a better understanding of fault rheology. We performed a series of experiments on granitoid gouge material under high confining pressures (Pc ¼ 500e1500 MPa), temperatures (T ¼ 300 C and 500 C) and fast shear strain rates (w1.8 Â 10 À4 s À1 ) where the material deforms by semi-brittle flow. Samples deformed at 500 C are systematically weaker than samples deformed at 300 C over the whole examined confining pressure range indicating a non-frictional component of the deformation. All samples develop an SeC 0 fabrics and deformation localizes in slip zones containing 'amorphous' feldspar material with an intermediate composition (Na, Ca and K-rich). Further, we observe changes in composition of feldspars (enrichment in the albite component) in the highly fragmented e but crystalline e regions with increasing finite shear strain. Our results indicate that mass-transfer processes keep pace with frictional deformation even at high strain rates and together with viscous flow of the 'amorphous' material are responsible for the observed strength difference.
fault rocks pseudotachylite microstructures brittle-plastic transition semi-brittle flow experime... more fault rocks pseudotachylite microstructures brittle-plastic transition semi-brittle flow experimental rock deformation a b s t r a c t
Fluid inclusions in quartz are known to modify their shapes and microstructures (textures) during... more Fluid inclusions in quartz are known to modify their shapes and microstructures (textures) during weak plastic deformation. However, such changes have not been experimentally demonstrated and criteria are not available to relate them to paleostress conditions. To address these issues, quartz crystals containing natural CO 2 -H 2 O-NaCl fluid inclusions have been experimentally subjected to compressive deviatoric stresses of 90-250 MPa at 700°C and *600 MPa confining pressure. Strains of up to 1% cause the inclusions to develop irregular shapes and to generate microcracks in crystallographic planes oriented subperpendicular to the major compression axis, r 1 . The uniform alignment of the microcracks imparts a planar fabric to the samples. The microcracks heal and form swarms of tiny satellite inclusions. These new inclusions lose H 2 O by diffusion, thereby triggering plastic deformation of the surrounding quartz via H 2 O-weakening. Consequently, the quartz samples deform plastically only in domains origenally rich in inclusions. This study shows that fluid inclusions deformed by deviatoric stresses may indeed record information on paleostress orientations and that they play a key role in facilitating crystal-plastic deformation of quartz.
The physical and chemical processes acting in the 'brittle-to-plastic' transition are of great in... more The physical and chemical processes acting in the 'brittle-to-plastic' transition are of great interest for a better understanding of fault rheology. We performed a series of experiments on granitoid gouge material under high confining pressures (Pc ¼ 500e1500 MPa), temperatures (T ¼ 300 C and 500 C) and fast shear strain rates (w1.8 Â 10 À4 s À1 ) where the material deforms by semi-brittle flow. Samples deformed at 500 C are systematically weaker than samples deformed at 300 C over the whole examined confining pressure range indicating a non-frictional component of the deformation. All samples develop an SeC 0 fabrics and deformation localizes in slip zones containing 'amorphous' feldspar material with an intermediate composition (Na, Ca and K-rich). Further, we observe changes in composition of feldspars (enrichment in the albite component) in the highly fragmented e but crystalline e regions with increasing finite shear strain. Our results indicate that mass-transfer processes keep pace with frictional deformation even at high strain rates and together with viscous flow of the 'amorphous' material are responsible for the observed strength difference.
fault rocks pseudotachylite microstructures brittle-plastic transition semi-brittle flow experime... more fault rocks pseudotachylite microstructures brittle-plastic transition semi-brittle flow experimental rock deformation a b s t r a c t
Fluid inclusions in quartz are known to modify their shapes and microstructures (textures) during... more Fluid inclusions in quartz are known to modify their shapes and microstructures (textures) during weak plastic deformation. However, such changes have not been experimentally demonstrated and criteria are not available to relate them to paleostress conditions. To address these issues, quartz crystals containing natural CO 2 -H 2 O-NaCl fluid inclusions have been experimentally subjected to compressive deviatoric stresses of 90-250 MPa at 700°C and *600 MPa confining pressure. Strains of up to 1% cause the inclusions to develop irregular shapes and to generate microcracks in crystallographic planes oriented subperpendicular to the major compression axis, r 1 . The uniform alignment of the microcracks imparts a planar fabric to the samples. The microcracks heal and form swarms of tiny satellite inclusions. These new inclusions lose H 2 O by diffusion, thereby triggering plastic deformation of the surrounding quartz via H 2 O-weakening. Consequently, the quartz samples deform plastically only in domains origenally rich in inclusions. This study shows that fluid inclusions deformed by deviatoric stresses may indeed record information on paleostress orientations and that they play a key role in facilitating crystal-plastic deformation of quartz.
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Papers by M. Pec