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Strain softening and microstructural evolution of anorthite aggregates and quartz-anorthite layered composites deformed in torsion |
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| Authors: | Shaocheng Ji Zhenting Jiang Richard Wirth Bin Xia |
| Institution: | a Département des Génies Civil, Géologique et des Mines, École Polytechnique de Montréal, C.P. 6079, Succ. Centre-Ville, Montreal, QC, Canada H3C 3A7 b Department of Earth Sciences, University of Liverpool, L69 3BX, Liverpool, UK c GeoForschungsZentrum Potsdam, D-14473 Potsdam, Germany d Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry and South China Sea Institute of Oceanology, Chinese Academy of Sciences, Wushan, Guangzhou, PR China |
| Abstract: | Torsion experiments of anorthite (An) aggregates and layered composites with equal volume fractions of quartz (Qtz) and An were performed in a gas-medium apparatus at a confining pressure of 400 MPa, temperatures from 1373 to 1473 K, and twist rates from 1.0×10−4 to 3.0×10−4 rad/s. Dense specimens were fabricated from An glass and Qtz crystalline powder using hot isostatic pressing (HIP) techniques. Both An aggregates and Qtz-An layered composites show a continuous strain weakening from a peak stress at γ=0.2-0.3 to γ=3.2, and steady-state flow has not reached under the experimental conditions. The weakening is even more pronounced in the layered composites than the monolithic aggregates, suggesting channeling or localization of flow into the weak material between strong layers. The sheared An specimens developed pervasively C-S-C′ structures which are similar to those observed in natural ductile shear zones. TEM and electron backscattering diffraction (EBSD) fabric analyses suggest that grain boundary migration recrystallization-accommodated dislocation creep with (010)100] as the dominant slip system was operating in the An. The strain softening may be due to the development of crystallographic preferred orientation (CPO), the operation of dynamic recrystallization and the formation of extremely fine-grained recrystallized material in the narrow C′ shear bands. |
| Keywords: | anorthite quartz-anorthite composite simple shear crystallographic preferred orientation flow strength |
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