极地研究

极地研究 ›› 2008, Vol. 20 ›› Issue (2): 189-200.

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南极格罗夫山球粒陨石冲击变质程度及特征

冯璐;林杨挺;胡森;刘焘;   

  • 出版日期:2008-06-30 发布日期:2008-06-30

SHOCK METAMORPHISM OF ORDINARY CHONDRITES FROM THE GROVE MOUNTAINS,ANTARCTICA

  • Online:2008-06-30 Published:2008-06-30

PDF (PC)

2074

被引次数

6

摘要：

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。

关键词: 南极;格罗夫山;普通球粒陨石;冲击变质;高压矿物

Abstract:

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).