Characteristics and genesis of the SiO2 phases in eucrite GRV 13001
The formation of SiO2 phase in eucrite is closely related to the thermal transformation of the parent body,which can indicate the thermal metamorphic history of the parent body to a certain extent.Taking GRV 13001,a eucrite discovered by the 30th Chinese Antarctic expedition,as the research object.This research analy-zes the different occurrence SiO2 phases,and finds three types:irregular granular cristobalite and quartz with rela-tively pure composition,Al-and K-rich lath-shaped tridymite,and vermicular SiO2 phase contained in high-Ca pyroxene rim.The genesis of SiO2 phases with different occurrences and the thermal metamorphism history of the parent body of GRV 13001 are as follows:(1)the shallow surface magma of the parent body cooled rapidly and crystallized to form filling irregular granular cristobalite;(2)slow thermal metamorphism to form pyroxene with type 4 thermally metamorphosed degree,which also results in the transformation of some cristobalite in the me-sostasis to normal quartz;(3)during the slow thermal metamorphism,a relatively short and high-temperature re-heating event causes the formation of lath-shaped tridymite by partial melting of the mesostasis area,which also leads to the formation of high-Ca pyroxene accretive rims at the edges of the primitive pyroxene grains.The ver-micular SiO2 phase is included in the accretive rims during the growth process.The genesis of the SiO2 phases with different occurrences provides a basis for the thermal transformation process of the meteorite parent body.
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