Study Of Mineralogy Of Shock Metamorphism In Antarctic Chondrite GRV 022115

In this paper,we mainly study the characteristics of high-pressure minerals and shock metamorphism of shock-induced melt vein in L chondrite GRV 022115 by micro-analysis.The main experimental analysis methods include optical microscopy,focused-ion beam microscopy,scanning electron microscopy,electron probe microscopy analysis,field-emission transmission electron microscopy,and laser Raman spectroscopy.Shock metamorphism was the most important geological process in the early stage of the formation of the solar system,and the formation of shock-induced melt veins was the most prominent feature in the process of strong shock metamorphism.In this thesis we conduct a basic and guiding study on the shock-induced melt vein from the perspective of mineralogy,in order to lay the foundation for inland further and deeper research on melt vein.We mainly discuss the following topics:the petrologic and mineralogical characteristics of host rock and shock-induced melt vein;classification of the chondrite;the formation mechanism of shock-induced melt vein;the phase transformation of main silicate minerals in shock-induced melt vein,which mainly including solid phase transformation of olivine,pyroxene and feldspar in host rock fragment inclusions;the shock condition defined by crystallization pressure of high-pressure mineral combination in melt vein.We mainly got the following conclusions:(1)The host rock is mainly composed of minerals such as olivine,pyroxene,feldspar,iron-nickel metal and sulfide,they are organized in poikilitic texture and undergo a considerable degree of thermal metamorphism.There are several melt veins,they range in width from tens of micrometers to hundreds of micrometers.They are composed of two lithofacies:vein matrix and host rock fragment inclusion.The vein matrix is mainly composed of 10??m size majorite and nano-scale magnesiowustite.The host rock fragment inclusion is mainly composed of minerals such as olivine,pyroxene and feldspar,which mostly went through solid phase transformation at high temperature and high pressure,including partial phase transition and full phase changes.Olivine particles phase changed to ringwoodites.Smaller particles were completely transformed into ringwoodite,while larger ones were formed to ringwoodite belt by the temperature decayed from the particle edge location to the inner location.Pyroxene particles phase changed into perovskite-phase glass(Bridgemanite).Feldspar particles phase changed into maskelynite and lingunite.(2)The classification of the meteor:ite is determined as:L6 type ordinary chondrite with impact grade S6 and weathering level W1.(3)The shock pressure of GRV 022115's parent body can be inferred to be 23-27 GPa,according to the combination of majorite and magnesiowustite in the vein matrix.