Mineralogical characteristics of plagioclase in a CK chondrite: Relationship with thermal and shock metamorphism

Abstract

Mineralogical characteristics of CK chondrites reflect the complex metamorphic history of this group. We here present the mineralogical features of plagioclase in LEW87009. Our goal is to reveal the thermal and shock history of CK chondrites. Shock melt veins are observed in LEW87009, and plagioclase near the largest shock vein is partially vitrified. Pervasive fractures are omnipresent in crystal regions, but glass regions are smooth and lack fractures. It suggests that plagioclase glass was formed by shock-induced melting and subsequent quenching. Thermal metamorphism is so progressed in LEW87009, but plagioclase glass near shock vein is not recrystallized. It suggests that the shock event was occurred following thermal metamorphism, and then thermal metamorphism was not progressed.