Transformation of Brown Olivine in Martian meteorites to high-pressure polymorphs

Abstract

It is considered that olivine in Martian meteorites is darkened by strong shock. However, their detailed processes and conditions are not clear. Our previous study implies that they are formed with transformation to high-pressure polymorphs. In this study, our Raman analyses of darkened olivine and lamellar textures observed in slightly darkened olivine in Tissint show that there are extra Raman shift peaks in 650 ~ 680 cm^-1. These peaks indicate that they have been high-pressure polymorph. Although Martian meteorites with brown olivine rarely contain high-pressure polymorphs, they have undergone higher temperature and pressure than those the other meteorites done.