Shear localization,velocity weakening behavior,and development of cataclastic foliation in experimental granite gouge |
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| Institution: | 1. 212 Lutz Hall, Department of Geography and Geosciences, University of Louisville, Louisville, KY 40292, USA;2. Brown University, Department of Earth, Environmental, and Planetary Sciences, Providence, RI 02912, USA;3. University of New Brunswick, Fredericton, New Brunswick, Canada E3B 5A3;1. Department of Earth & Environmental Sciences, KULeuven, Celestijnenlaan 200E, B-3001 Heverlee, Belgium;2. Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA;3. FROGTECH Ltd., 2 King Street, 2600 Deakin West, ACT, Australia;1. Departamento de Geología, Universidad de Salamanca, Pza. de los Caídos s/n, 37008 Salamanca, Spain;2. Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA;3. Los Alamos Neutron Science Center, Los Alamos National Laboratory, NM 87545, USA;1. Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel;2. School of Geology and Geophysics, University of Oklahoma, Norman, OK 73019, USA;1. Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, 00143, Roma, Italy;2. School of Geology and Geophysics, University of Oklahoma, Norman, USA;3. Dipartimento di Scienze della Terra, Università La Sapienza di Roma, Italy;4. Geological Survey of Israel, Jerusalem, Israel;1. Department of Geology, University of Otago, Dunedin 9054, New Zealand;2. Rock Mechanics Laboratory, Department of Earth Sciences, Durham University, Durham, England, United Kingdom;3. Istituto Nazionale di Geofisica e Vulcanologia (INGV), Rome 00143, Italy;4. Dipartimento di Geoscienze, Università degli Studi di Padova, Via G. Gradenigo 6, 35131 Padova, Italy |
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| Abstract: | Microstructural aspects of room-temperature deformation in experimental Westerly granite gouge were studied by a set of velocity stepping rotary-shear experiments at 25 MPa normal stress. The experiments were terminated at: (a) 44 mm, (b) 79 mm, and (c) 387 mm of sliding, all involving variable-amplitude fluctuations in friction. Microstructural attributes of the gouge were studied using scanning (SEM) and scanning transmission electron microscopy (STEM), image processing, and energy dispersive X-ray (EDX) analyses. The gouge was velocity weakening at sliding distances >10 mm as a core of cataclasites along a through-going shear zone developed within a mantle of less deformed gouge in all experiments. Unlike in experiment (a), the cataclasites in experiments (b) and (c) progressively developed a foliation defined by stacks of shear bands. The individual bands showed an asymmetric particle-size grading normal to shearing direction. These microstructures were subsequently disrupted and reworked by high-angle Riedel shears. While the microstructural evolution affected the effective thickness and frictional strength of the gouge, it did not affect its overall velocity dependence behavior. We suggest that the foliation resulted from competing shear localization and frictional slip hardening and that the velocity dependence of natural fault gouge depends upon compositional as well as microstructural evolution of the gouge. |
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| Keywords: | Experimental gouge Shear localization Cataclastic foliation Velocity weakening |
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