[an error occurred while processing this directive] 高校地质学报 2020, 26(3) 265-275 DOI:   10.16108/j.issn1006-7493.2019044  ISSN: 1006-7493 CN: 32-1440/P

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岩石.矿床.矿物.地球化学
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本文关键词相关文章
南极陨石
冲击熔融脉
高压矿物
冲击相变
GRV 022115
本文作者相关文章
司加鑫
谢志东
李阳
PubMed
Article by Si J
Article by Xie Z
Article by Li Y
南极陨石GRV 022115冲击熔融脉矿物学研究
司加鑫,谢志东,李阳
1. 南京大学 地球科学与工程学院,南京 210023;
2. 中国科学院 地球化学研究所月球与行星科学研究中心,贵阳 550081
摘要: 文章主要通过电子探针、扫描电镜、激光拉曼光谱、透射电镜等微区微分析技术研究GRV 022115球粒陨石的基础矿物学特征和冲击变质矿物学特征,探讨陨石冲击熔融脉的形成机制和界定其母体的冲击条件。陨石主岩主要由橄榄石、辉石、熔长石、铁镍金属和硫化物等矿物组成。根据主岩的硅酸盐矿物学特征,确定GRV 022115是风化程度较低(W1) 的L6型普通球粒陨石,与前期分类结果一致。根据熔融脉内含有大量林伍德石的现象,修正GRV 022115陨石的冲击级别为S6,比原定的S5高一个级别。GRV 022115球粒陨石中有多条冲击熔融脉,熔融脉由基质和主岩碎块包裹体两类岩相组组成。熔融脉基质的主要组成是微米级粒状镁铁榴石与纳米级的含铁方镁石,是在平衡冲击压力下结晶的产物。冲击熔融脉主岩碎块包裹体中的橄榄石、低钙辉石、长石碎块已部分或全部转为相对应的高压相。橄榄石相变为林伍德石;个别低钙辉石相变为钙钛矿结构布里奇曼石微晶的集合体;长石主要相变为熔长石与玲根石。几乎所有的主岩碎块都有高温熔融的圆滑边界。熔融脉内外同类矿物的主量和微量元素具有一定的差异性,该差异性可以反映高温高压下混溶作用和扩散作用的影响。结合陨石冲击熔融脉形成机制和结晶模型,根据熔脉基质中镁铁榴石+方镁石矿物组合及静态高温高压实验相图,界定该陨石经受的冲击压力为23~27 GPa。
关键词 南极陨石   冲击熔融脉   高压矿物   冲击相变   GRV 022115  
The Mineralogy Study of Shock-induced Melt-veins in Antarctic Meteorite GRV 022115
SI Jiaxin,XIE Zhidong,LI Yang
1. School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China;
2. Center for Lunar and Planetary Sciences, Institute of Geochemistry Chinese Academy of Sciences, Guiyang 550081,China
Abstract: By micro-analytical techniques, such as electron probe microscopy analysis, scanning electron microscopy,laser Raman pectroscopy and transmission electron microscope, this paper mainly study the mineralogical characteristics of host rock and shock-induced melt vein of the Antarctic meteorite GRV 022115, and discuss the formation mechanism of shock-induced melt veins and the shock conditions of its parent bodies. The host rock of the meteorite GRV 022115 is mainly composed of minerals of olivine, pyroxene, feldspar, and some iron-nickel metal and sulfide. Based on the mineralogical features of the major silicates of the meteorite host rock, the meteorite is classified as L6 type ordinary chondrite with low weathering level (W1) which is similar to the previous classification. While the impact degree for meteorite GRV 022115 is modified as S6 from original S5 based on abundant ringwoodite fragments occurring in several shock-induced melt veins in GRV 022115 meteorite. The shock-induced melt veins are composed of two lithofacies: the melt-vein matrix and host rock fragment inclusions. The vein matrix is mainly composed of μm-scale majorite and nano-scale magnesiowüstite, which were crystallized under equilibrium shock pressure. The original low-pressure silicate minerals of the host rock fragment inclusions in melt-veins, such as olivine, pyroxene and feldspar, mostly went through solid phase transformations under high shock pressure and high temperature. Small olivine grains transformed to ringwoodite completely, while larger olivine grains have ringwoodite rim formed in outside edge of the fragment, and olivine in core part. Some pyroxene grains transformed to perovskite-structured bridgmanite. Feldspar grains transformed to the high-pressure phases of maskelynite and lingunite. Almost all host rock fragments show rounded edges by high temperature effects. The differences of elements’content of same mineral inside and outside melt veins reflects the effects of high temperature mixing and diffusion under high temperature and pressure. Based on the mineral assemblages of majorite and magnesiowüstite in the melt vein matrix of GRV 022115, and the phase diagram of the static high-pressure experiment, combing the formation and crystallization model of the shock-induced melt vein, the shock pressure of the GRV022115 chondrite can be constrained to 23-27 GPa.
Keywords: Antarctic meteorites   shock-induced melt veins   high-pressure minerals   shock-induced phase transformation   GRV 022115  
收稿日期 2019-05-15 修回日期 2019-09-29 网络版发布日期  
DOI: 10.16108/j.issn1006-7493.2019044
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