[S-MP29] Physics and Chemistry of Minerals

[SMP29-01] Progressive change in dislocation microstructures in shocked calcite with pressure

★Invited Papers

*Naotaka Tomioka¹, Kosuke Kurosawa², Akira Miyake³, Yohei Igami³, Takayoshi Nagaya^4,5, Takaaki Noguchi³, Toru Matsumoto³, Masaaki Miyahara⁶, Seto Yusuke⁷ (1.Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, 2.Graduate School of Human Development and Environment, Kobe University, 3.Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, 4.Department of Environmental Sciences, Tokyo Gakugei University, 5.Faculty of Education and Integrated Arts and Sciences, Waseda University, 6.Graduate School of Advanced Science and Engineering, Hiroshima University, 7.Graduate School of Science & School of Science, Osaka Metropolitan University)

Keywords:calcite, shock deformation, dislocation, transmission electron microscopy

Shock recovery experiments were performed using a two-stage light gas gun to clarify the progressive deformation microstructures of calcite at the submicron scale concerning pressure. Decaying compression pulses were produced using a projectile that was smaller than the natural marble target. In two experiments, natural marble samples were shocked to 13 and 18 GPa at the epicenters of the targets. Calcite grains shocked in the pressure range of 1.1–18 GPa were examined using polarized light microscopy and (scanning) transmission electron microscopy. The density of free dislocations in the grains shocked at 1.1–2.2 GPa [10^8–9 (cm^-2)] is comparable to that of unshocked Carrara calcite grains. Subparallel bands of entangled dislocations less than 1 µm are formed at 4.2 GPa, and strongly entangled dislocations spread throughout the focused ion beam (FIB) sections at 7.3–18 GPa pressures. Dislocations selectively nucleate and entangle near the slip planes at pressures above ~3 GPa, corresponding to the transition from sharp extinction to undulatory extinction, according to the microstructural evolution with shock pressure. Above approximately 6 GPa, the dislocations nucleated homogeneously throughout the calcite crystals.