南极陨石GRV052483中岩石矿物学特征:撞击熔融型普通球粒陨石

南极陨石GRV052483样品为中国第22次南极科学考察队在蓝冰上发现的一块普通球粒陨石。初步研究发现,该样品中球粒结构并不发育。薄片中可见大量自形-半自形橄榄石斑晶镶嵌在细粒基质矿物中,具有典型的斑状结构。这些橄榄石斑晶大多为残留相,斑晶橄榄石和基质中主要矿物橄榄石、低钙辉石成分均一,平均橄榄石Fa值为24.7 mol%,而低钙辉石平均Fs值为21.1 mol%,斑晶中偶有粗粒长石玻璃化,根据岩相学及矿物成分特征,可确定此陨石为L6。不透明矿物含量较少,包括金属(铁纹石和镍纹石)与陨硫铁,此外可见少量的铬铁矿和磷灰石。冲击熔融脉发育、斑晶中粗粒长石玻璃化、基质中橄榄石、辉石、长石重结晶等现象说明该样品经历了强烈冲击,其冲击程度可能达到S6以上。因此,GRV052483可能为撞击熔融型L6普通球粒陨石。

PETROLOGY-MINERALOGY OF GRV 052483 FROM THE GROVE MOUNTAINS,ANTARCTICA:AN L-CHONDRITE IMPACT-MELT ROCK

An ordinary chondrite(Sample No.GRV052483) was recovered on blue ice during the 22nd Chinese Antarctic Research Exploration in Grove Mountains,Antarctica.In thin section,the sample shows a recrystallization texture and the texture is not particularly chondritic.Most euhedral to subhedral olivine crystals are set in a mesostasis of fine-grained olivine,pyroxene,and tiny spheres of Ni,Fe-rich metal and sulfides.Most olivine grains are essentially relicts.The major silicate phases are olivine,orthopyroxene,and plagioclase,with trace clinopyroxene.The mean Fa of olivine crystals and matrix are 24.7 mol%,and the mean Fs of low-Ca pyroxene is 21.1 mol% in GRV052483.These values are in the L chondrite range.Metal and sulfides are Fe–Ni metal(kamacite,taenite) and troilite.Minor phases are chromite and apatite.Abundant dark portions,numerous cracks and microfaults,as well as impact-melt veins,are also present.As a result,GRV052483 is an L6-chondrite impact-melt rock(i.e.,shocked L-6 chondrite).