极地研究

极地研究 ›› 2020, Vol. 32 ›› Issue (2): 212-225.DOI: 10.13679/j.jdyj.20190027

• 研究论文 • 上一篇    下一篇

南极GRV 090196普通球粒陨石熔壳特征及其成因探讨

孙云龙1,2,3,缪秉魁1,2,3,黄丽霖1,2,3,张川统1,2,3,夏志鹏1,2,3   

  1. 1.广西隐伏金属矿产勘查重点实验室, 桂林理工大学, 广西 桂林 541004;
    2.陨石与行星物质研究中心, 桂林理工大学, 广西 桂林 541004;
    3.行星地质演化广西高校重点实验室, 桂林理工大学, 广西 桂林 541004
  • 收稿日期:2019-04-26 修回日期:2019-07-04 出版日期:2020-06-30 发布日期:2020-06-30
  • 通讯作者: 缪秉魁
  • 基金资助:
    国家自然科学基金项目(41776196, 41173077)、科技部国家科技基础条件平台项目(2005DKA21406)、广西科技基地及人才专项(桂科AD1850007)资助

Features and formation of fusion crusts on an ordinary chondrite(GRV 090196) from Antarctica

Sun Yunlong1,2,3, Miao Bingkui1,2,3, Huang Lilin1,2,3, Zhang Chuantong1,2,3, Xia Zhipeng1,2,3   

  1. 1.Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, Guilin University of Technology, Guilin 541004, China;
    2.Institute of Meteorites and Planetary Materials Research, Guilin University of Technology, Guilin 541004, China;
    3.Key Laboratory of Planetary Geological Evolution at Universities of Guangxi Province, Guilin University of Technology,Guilin 541004, China
  • Received:2019-04-26 Revised:2019-07-04 Online:2020-06-30 Published:2020-06-30
  • Contact: Bingkui Miao

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摘要： 熔壳是陨石在穿过大气层时因摩擦发热熔融所形成的，由于陨石的进入速度差异和大气层的结构变化，它可能产生不同的熔壳结构特征和类型，熔壳的研究对探索陨石穿过大气层过程和反映当时的大气层结构具有重要意义。由于南极特殊的地理气候条件，很多南极陨石样品保持了原始或完整的熔壳结构，因此，南极陨石是理想的熔壳研究对象。GRV090196是南极格罗夫山H4型普通球粒陨石。该陨石具有完整的熔壳结构，而且存在定向飞行的特征，陨石薄片保留了两段结构和厚薄不一（厚度分别为 1.3mm、0.4mm）的熔壳，是一块研究熔壳特征的理想样品。本文对GRV090196的熔壳开展了系统的岩石学和矿物学研究，将Ⅰ号熔壳由外向里分为四个不同结构层。一二层为玻璃质熔壳，发生了完全熔融后的重结晶作用，形成了主要由橄榄石斑晶和辉石质玻璃组成玻基斑状结构，一二层熔壳橄榄石斑晶的形态与成分有明显的差别，它们在下降的过程中经历了不同密度的大气层。三层熔壳发生部分熔融，大部分矿物颗粒发生圆化，其中含有少量气泡。四层熔壳产生热变质，单偏光下不透明发黑，出现了可能是细小铁质还原析出形成的暗化现象，该层结构特征与陨石内部相似。而Ⅱ号熔壳由外向里分为三层，第一层硅酸盐颗粒部分熔融且富含金属颗粒，二三层特征与Ⅰ号熔壳三四层基本相同。通过对比研究，提出了熔壳可以由陨石熔融物堆积作用产生并且可以利用其判断陨石降落的方向性，根据Ⅰ号熔壳存在两层玻璃质层且橄榄石斑晶发生了重结晶，判断在陨石降落过程中，陨石头部因摩擦发热而产生的熔融物质受到气流驱动而在陨石定向飞行的尾部产生堆积。熔壳经过两种不同密度的大气层 ，形成了两层不同堆积特征的玻璃质熔壳层，而Ⅱ号熔壳位于陨石的前侧部，熔化物质仅有少量保留，形成了很薄的玻璃质熔壳。

关键词: 普通球粒陨石, 熔壳, 堆积成因, 南极

Abstract: Meteorite fusion crusts are formed during atmospheric entry and show different textural characteristics based on differences in entry velocity and structural changes in the atmosphere. Therefore, fusion crust study is important to understand atmospheric entry processes and atmospheric structure at that time. Many Antarctic meteorites have retained their original or complete fusion crust because of the region’s unique geographical and climatic conditions, so they are ideal samples for fusion crust research. An ordinary H5 chondrite (GRV 090196) from the Grove Mountains region (Antarctica) was investigated in this study. It has a complete molten fusion crust with some flow lines showing its flying direction. Thin sections showed two intact fusion crusts with thicknesses of 1.3 mm and 0.4 mm. Petrology and mineralogy showed that the first fusion crust (Ⅰ) could be divided into four structural layers (outside to inside). Layers 1 and 2 were melted completely and recrystallized to form porphyritic structures in a glassy matrix, but the morphology and chemical composition of olivine phenocrysts in these layers were very different. This indicates it experienced different atmospheric layers of various densities. In layer 3, partial melting was obvious and mineral residues were observed; crystals were rounded with some bubbles. Thermal metamorphism occurred in layer 4, appearing opaque and black under plane polarized light, with a darkening phenomenon that may be from fine iron precipitation. Its texture was similar to those inside the meteorite. The second fusion crust (Ⅱ) was divided into three layers (outside to inside). Silicates in layer 1 were partially melted and rich in metallic grains. Layers 2 and 3 were similar to layers 3 and 4 in fusion crustⅠ. We suggest that fusion crusts were caused by accumulation and can be used to judge the landing direction of a meteorite. The two glassy layers and olivine phenocrysts in fusion crustⅠas well as the recrystallized olivine phenocrysts indicate that fusion crust melt was moved along the meteorite body by air. The fusion crusts experienced two relatively denser atmosphere layers that formed two glassy layers, and fusion crustⅡwas located in the side of the front. Only a small amount of the molten material remained and formed a very thin glassy fusion crust.

Key words: ordinary chondrite, fusion crust, accumulation cause, Antarctica