Structural Evolution of Antigorite by High‐Velocity Impacts
Yuhei Umeda, Yusuke Seto, Naotaka Tomioka, Hiroshi Arima‐Osonoi, Yoichiro Hironaka, Yuichi Inubushi, Kento Katagiri, Ryosuke Kodama, Kohei Miyanishi, Hirotaka Nakamura, Norimasa Ozaki, Tomoko Sato, Keiichi Sueda, Tadashi Togashi, Toshinori Yabuuchi, Makina Yabashi, Toshimori Sekine, Takuo OkuchiAbstract
Serpentine is a major hydrous mineral present in hydrous asteroids that have evolved through planetary impacts. Understanding its dynamic behavior is essential to elucidate the redistribution and retention of water during high‐velocity impact processes. The shock response of antigorite was examined at pressures up to 106 GPa using laser‐driven shock compression combined with ultrafast time‐resolved X‐ray diffraction measurements. Results show that shock‐compressed antigorite remained crystalline up to 44 GPa (impact velocity ∼4.7 km/s), whereas it transformed to an amorphous state above 66 GPa (∼6.4 km/s). This transformation was completed within a few nanoseconds during compression, and recrystallization from the amorphous state did not occur during subsequent decompression, indicating that shock‐induced amorphization is the dominant structural response of antigorite. Adiabatic release calculations further indicate that the decompression path of shocked antigorite from a peak shock pressure of 60 GPa intersects the stability fields of several high‐pressure nominally anhydrous minerals (NAMs). On the other hand, the decompression path from peak pressures of 80 to 100 GPa is predicted to remain above the liquidus until ambient pressure is reached. These findings have significant implications for the impact thermal histories of serpentine‐rich hydrous asteroids, such as Ryugu and Bennu.