关键词: 南极陨石, 冲击熔融脉, 高压矿物, 冲击相变, GRV 022115

Abstract: By micro-analytical techniques, such as electron probe microscopy analysis, scanning electron microscopy，laser Raman pectroscopy and transmission electron microscope, this paper mainly study the mineralogical characteristics of host rock and shock-induced melt vein of the Antarctic meteorite GRV 022115, and discuss the formation mechanism of shock-induced melt veins and the shock conditions of its parent bodies. The host rock of the meteorite GRV 022115 is mainly composed of minerals of olivine, pyroxene, feldspar, and some iron-nickel metal and sulfide. Based on the mineralogical features of the major silicates of the meteorite host rock, the meteorite is classified as L6 type ordinary chondrite with low weathering level (W1) which is similar to the previous classification. While the impact degree for meteorite GRV 022115 is modified as S6 from original S5 based on abundant ringwoodite fragments occurring in several shock-induced melt veins in GRV 022115 meteorite. The shock-induced melt veins are composed of two lithofacies: the melt-vein matrix and host rock fragment inclusions. The vein matrix is mainly composed of μm-scale majorite and nano-scale magnesiowüstite, which were crystallized under equilibrium shock pressure. The original low-pressure silicate minerals of the host rock fragment inclusions in melt-veins, such as olivine, pyroxene and feldspar, mostly went through solid phase transformations under high shock pressure and high temperature. Small olivine grains transformed to ringwoodite completely, while larger olivine grains have ringwoodite rim formed in outside edge of the fragment, and olivine in core part. Some pyroxene grains transformed to perovskite-structured bridgmanite. Feldspar grains transformed to the high-pressure phases of maskelynite and lingunite. Almost all host rock fragments show rounded edges by high temperature effects. The differences of elements’content of same mineral inside and outside melt veins reflects the effects of high temperature mixing and diffusion under high temperature and pressure. Based on the mineral assemblages of majorite and magnesiowüstite in the melt vein matrix of GRV 022115, and the phase diagram of the static high-pressure experiment, combing the formation and crystallization model of the shock-induced melt vein, the shock pressure of the GRV022115 chondrite can be constrained to 23-27 GPa.

Key words: Antarctic meteorites, shock-induced melt veins, high-pressure minerals, shock-induced phase transformation, GRV 022115