Microstructural evolution during strain localization in dolomite aggregates |
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| Institution: | 1. Department of Earth Science, Rice University, Houston, TX 77005, USA;2. State Key Laboratory of Petroleum Resource and Prospecting, and Unconventional Natural Gas Institute, China University of Petroleum, Beijing, China;3. FUNVISIS, Caracas, Venezuela;1. Grupo de Espectroscopia de Materiales Avanzados y Nanoestructurados (GEMANA), Centro de Investigaciones en Óptica, A.P. 1-948, León, Gto. 37150, Mexico;2. Centro de Nanociencias y Nanotecnología UNAM, Km 107 Carretera Tijuana-Ensenada, Ensenada, B.C. 22860, Mexico;1. GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany;2. Centre for Earth Evolution and Dynamics, University of Oslo, PO Box 1028, 0315 Oslo, Norway;3. Department of Geophysics, Tohoku University, Sendai 980-8578, Japan;1. Department of Earth Sciences, Western University, London N6A 5B7, Canada;2. School of Resource and Environmental Engineering, Hefei University of Technology, Hefei 230009, China;3. Department of Geology, Northwest University, Xi''an 710069, China;4. Department of Earth Sciences, China University of Geosciences, Wuhan 430074, China;1. Department of Earth and Atmospheric Sciences, University of Houston, TX 77204, USA;2. School of Geography & Earth Sciences, McMaster University, Hamilton, ON, Canada |
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| Abstract: | Dolomite aggregates deformed by dislocation creep over a wide range of conditions (T = 700–1000 °C, effective pressure of 900 MPa, strain rates of 10?7 – 10?4/s) strain weaken by up to 75% of the peak differential stress. Microstructural study of samples shortened to different finite strains beyond the peak differential stress shows that strain becomes highly localized within shear zones by high-temperature creep processes, with no contribution of brittle cracking. At low strains (8%), dolomite deforms homogeneously by recrystallization-accommodated dislocation creep. At progressively higher sample strains, deformation is localized into narrow shear zones made up of very fine (～3 μm) recrystallized grains and relict porphyroclasts (20–100 μm). Finely-recrystallized dolomite grains in the shear zones are largely dislocation free and localized shear is facilitated by diffusion creep. In contrast, original dolomite grains and porphyroclasts in shear zones have high dislocation densities and do not deform after shear zone formation. Calculated strain rates in the shear zones are two to three orders of magnitude faster than the imposed bulk strain rate of the samples and these strain rates are consistent with predictions of the diffusion creep flow law for fine-grained dolomite. |
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| Keywords: | Strain localization Dolomite Carbonate Transient creep |
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