南极格罗夫山球粒陨石冲击变质程度及特征

本文对93块南极格罗夫山普通球粒陨石的冲击变质特征进行了研究:在光学显微镜下观察并描述了橄榄石、辉石、长石等主要硅酸盐矿物的破裂、消光、熔融以及重结晶现象;在冲击熔脉和熔融囊中观察到了矿物的分解、相变,并确认了林伍德石、镁铁榴石、辉石玻璃和熔长石等多种硅酸盐矿物的高压多形。根据冲击变质特征以及高压矿物的组合对93块南极普通球粒陨石进行了冲击变质程度分类。冲击变质类型的统计结果表明,这批样品中共有23块陨石遭受了强烈的冲击变质作用(S4-S5),并且其中绝大部分为L群普通球粒陨石(22块),仅有1块H群陨石受到明显的冲击变质,并形成熔脉。H与L群陨石完全不同的冲击变质特征,可能反映了两者小行星母体表面不同的物性。此外,相同化学群陨石中,冲击变质程度的分布与岩石类型相关,平衡型(特别是5-6型)陨石具有最高比例的强烈冲击变质陨石。

SHOCK METAMORPHISM OF ORDINARY CHONDRITES FROM THE GROVE MOUNTAINS,ANTARCTICA

hock effects of 93 Grove Mountains(GRV) ordinary chondrites were studied in this paper,including fracture,various types of extinction,and recrystallization of silicates observed under optical microscopy.Shock-induced veins and pockets show various microtextures,decomposition and phase transformation of minerals.The confirmed high-pressure polymorphs of silicates are ringwoodite,majorite,pyroxene glass and maskelynite.Based on the shock effects and assemblages of high-pressure minerals,shock stages of all of 93 GRV chondrites were classified.In comparison with literature,the Grove Mountains meteorites have a higher fraction(23 out of 93) of heavily shocked samples(S4—S5).Most of the heavily shocked meteorites are L group(22 out of 23),except for one H chondrite.The distinct shock metamorphism between H and L groups may indicate different surface properties of their parent bodies.In addition,there is relationship between petrologic types and shock stages,with most heavily shocked samples observed in equilibrated ordinary chondrites(especially Type 5 and 6).