寺巷口普通球粒陨石的热变质和冲击变质历史研究  

Thermal and Shock Metamorphism of the Sixiangkou Ordinary Chondrite

作　　者：丁明伟[1] 张爱铖[1] 徐伟彪[1] 

机构地区：[1]中国科学院紫金山天文台天体化学和行星科学实验室

出　　处：《天文学报》2008年第1期55-66,共12页Acta Astronomica Sinica

基　　金：国家杰出青年科学基金(40325009);小行星基金会;南京大学成矿机制研究国家重点实验室的开放课题(12-06-14)资助项目

摘　　要：寺巷口陨石是一块经历强冲击变质的普通球粒陨石.系统研究陨石主体和冲击熔融脉的岩相学和矿物学.该陨石中球粒较少且轮廓和内部结构均模糊不清,基质重结晶程度高,橄榄石和辉石的成分非常均一.单斜辉石-斜方辉石矿物对计算得到的平衡温度峰值为891±36℃.说明寺巷口陨石的热变质程度与6型一致.陨石主体中的橄榄石具有明显的波状消光和面状变形裂隙,熔长石广泛存在,在冲击熔融脉中含有粗粒的林伍德石和镁铁榴石以及细粒的高压矿物组合,这些特征预示了寺巷口陨石经历了S6级的冲击变质作用且形成冲击脉的峰期压力可能在20GPa—24GPa左右,而温度可能高于2000℃.冲击熔融脉中白磷钙矿和铬铁矿的存在可能是因为经历了较长的退火时间,导致其高压矿物的回退.The Sixiangkou meteorite is merous shock-induced melt veins of various a heavily shocked chondrite that contains nuwidths. This paper focuses on the petrography and mineralogy of the host portion and shock veins of Sixiangkou. This meteorite contains relict chondrules with obscure structures and shapes. We calculate the peak equilibration temperature （891±36℃） recorded in the Sixiangkou L6 chondrite using the two-pyroxene geothermometer. The thermal metamorphic features of Sixiangkou are in accordance with the petrologic type 6. Olivine in the host portion of the chondrite shows obvious undulatory extinction and planar deformation features. Abundant maskelynite occurs in the chondrite. The shock veins contain numerous coarse-grained ringwoodite, majorite, and fine-grained high-pressure mineral assemblages. On the basis of these observations, Sixiangkou can be graded as $6 on the shock metamorphism scale. And it can also be inferred that the peak pressure which melt veins experienced is about 20GPa-24GPa and the temperature is higher than 2000℃. Merrilite and chromite in the shock veins are possibly transformed back from their high-pressure to low-pressure phases during the prolonged shock event Sixiangkou experienced.

关 键 词：流星和陨星 天体化学 方法 实验室 

分 类 号：P148[天文地球—天体物理]