钙长辉长无球粒陨石GRV 13001中SiO_(2)相的特征及其成因

Characteristics and genesis of the SiO_(2) phases in eucrite GRV 13001

钙长辉长无球粒陨石中SiO_(2)相的形成与母体经历的热改造作用密切相关,能在一定程度上指示母体的热变质历史。以中国第30次南极科学考察队发现的一块钙长辉长无球粒陨石GRV 13001为研究对象,重点分析了不同产状的SiO_(2)相,发现其可分为成分较纯的不规则粒状方石英和石英、富Al和K的板条状鳞石英以及高钙辉石边部的蠕虫状SiO_(2)相3种类型。不同产状SiO_(2)相的成因及其指示的陨石母体热变质历史为:(1)母星体浅表层岩浆快速冷却结晶,形成充填型不规则粒状方石英;(2)经历缓慢热变质作用形成4型热变质程度辉石,同时导致充填物中部分方石英转变为石英;(3)缓慢热变质作用期间,相对短暂且高温的重新加热事件引起充填物区域物质部分熔融,从而形成板条状鳞石英,亦导致原生辉石颗粒边缘高钙辉石次生边的形成,生长过程中蠕虫状SiO_(2)相被包裹进次生边。不同产状SiO_(2)相的成因为其陨石母体经历的热改造过程提供了依据。

The formation of SiO_(2) 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 analyzes the different occurrence SiO_(2) phases,and finds three types:irregular granular cristobalite and quartz with relatively pure composition,Al-and K-rich lath-shaped tridymite,and vermicular SiO_(2) phase contained in high-Ca pyroxene rim.The genesis of SiO_(2) 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 mesostasis to normal quartz;(3)during the slow thermal metamorphism,a relatively short and high-temperature reheating 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 vermicular SiO_(2) phase is included in the accretive rims during the growth process.The genesis of the SiO_(2) phases with different occurrences provides a basis for the thermal transformation process of the meteorite parent body.