'ECLOGITIC' MINERALS IN A SHOCKED BASALTIC METEORITE

Abstract

Analytical transmission electron microscopy (ATEM) was used to characterize mineral parageneses occurring in melt veins of shock origin in the Martian meteorite Zagami. We discovered a new ultra-high pressure 'eclogite facies' mineral assemblage consisting of omphacite, stishovite, and KAlSi3O8 hollandite. These tiny (<200-300 nm) high-pressure minerals are embedded in silicate glass, which forms the groundmass of shock veins. microtexture veins and zoning clinopyroxene indicate formation by crystallization from a melt. using calibration data multi-anvil experiments we infer that frictional melting occurred at minimum temperatures 2400-2500°C and at a pressure of ca. 30 GPa. Subsequently, the high-pressure phases crystallized during decompression in the pressure interval from 25-5 GPa.