‘Eclogitic’ minerals in a shocked basaltic meteorite

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 the shock veins. The microtexture of the veins and zoning of the clinopyroxene indicate the formation of minerals by crystallization from a high-pressure melt. Using calibration data from shock and multi-anvil experiments we infer that frictional melting occurred in veins at minimum temperatures of 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.