¹Naotaka Tomioka,^2,3Kosuke Kurosawa,⁴Akira Miyake,⁴Yohei Igami,⁵Takayoshi Nagaya,⁴Takaaki Noguchi,⁴Toru Matsumoto,⁶Masaaki Miyahara,⁷Yusuke Seto
American Mineralogist 110, 945-955 Link to Article [https://doi.org/10.2138/am-2024-9540]
¹Kochi Institute for Core Sample Research, X-star, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Nankoku, Kochi 783-8502, Japan
²Department of Human Environmental Science, Graduate School of Human Development and Environment, Kobe University, 3-11, Tsurukabuto, Nada-ku, Kobe, Hyogo 657-8501, Japan
³Planetary Exploration Research Center, Chiba Institute of Technology, Narashino, Chiba 275-0016,Japan
⁴Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
⁵Department of Environmental Sciences, Tokyo Gakugei University, Koganei, Tokyo 184-8501, Japan
⁶Earth and Planetary Systems Science Program, Graduate School of Advanced Science and Engineering, Hiroshima University, Higashihiroshima, Hiroshima 739-8526, Japan
⁷Department of Geosciences, Graduate School of Science & School of Science, Osaka Metropolitan University, Sumiyoshi-ku, Osaka 558-8585, Japan
Copyright: The Mineralogical Society of America

Shock recovery experiments were performed using a two-stage light gas gun to clarify the progressive deformation microstructures of calcite at the submicrometer 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 [108–9 (cm−2)] is comparable to that of unshocked Carrara calcite grains. Subparallel bands of entangled dislocations <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. 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 ∼6 GPa, the dislocations nucleated homogeneously throughout the calcite crystals. The dislocation microstructure in a calcite grain collected from the asteroid Ryugu particle is similar to that of the experimentally shocked calcite at 4.2 GPa. The estimated pressure of 2–3 GPa, determined through fault mechanics analyses and the presence of dense sulfide minerals in the Ryugu particles, is in line with this pressure.