A shock-produced (Mg, Fe)SiO3 glass in the Suizhou meteorite

Abstract

Ovoid grains consisting of glass of stoichiometric (Mg, Fe)SiO 3 composition that is intimately associated with majorite were identified in the shock veins of the Suizhou meteorite. The glass is surrounded by a thick rim of polycrystalline majorite and is identical in composition to the parental low-Ca pyroxene and majorite. These ovoid grains are surrounded by a fine-grained matrix composed of majorite-pyrope garnet, ringwoodite, magnesiowüstite, metal, and troilite. This study strongly suggests that some precursor pyroxene grains inside the shock veins were transformed to perovskite within the pyroxene due to a relatively low temperature, while at the rim region pyroxene grains transformed to majorite due to a higher temperature. After pressure release, perovskite vitrified at post-shock temperature. The existence of vitrified perovskite indicates that the peak pressure in the shock veins exceeds 23 GPa. The post-shock temperature in the meteorite could have been above 477°C. This study indicates that the occurrence of high-pressure minerals in the shock veins could not be used as a ubiquitous criterion for evaluating the shock stage of meteorites. © Meteoritical Society, 2004.