Carbonaceous xenoliths in the Krymka LL3.1 chondrite: Mysteries and established facts
Carbonaceous xenoliths in the Krymka LL3.1 chondrite: Mysteries and established facts
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Krymka LL3.1 球粒陨石中的碳质捕虏体：谜团和既定事实
DOI：
10.1016/j.gca.2004.10.027
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发表时间：
2005
影响因子：
5
通讯作者：
C. Wies
中科院分区：
文献类型：
--
作者：
V. Semenenko;E. Jessberger;M. Chaussidon;I. Weber;T. Stephan;C. Wies
本文介绍了对两种外来 Krymka 碳质捕虏体的矿物学、化学以及碳和氧同位素的详细研究结果。所研究的捕虏体经过变质和冲击，具有以下与 Krymka 宿主区分开的特征： 1. 其 SiO2/MgO 比率与碳质球粒陨石相似； 2.较高的Fe含量和FeO/(FeO+MgO)比； 3. Si、Ca、Al 浓度较低，S 和可能还有 Ag 富集； 4. 球粒及其碎屑尺寸较小，含量较低（10 vol%），基质含量相应较高； 5. 斑状球粒占主导地位，非斑状球粒较少； 6.富含16O成分的变形虫橄榄石颗粒的出现； 7.碳以三种不同的形式存在：石墨、富碳物质和有机化合物。捕虏体的整体化学性质与碳质球粒陨石相似，但不相同，这表明它们代表了之前未曾取样的球粒陨石母体。在任何已知类型的陨石材料中，捕虏体的矿物学仅对应于其他克林卡含石墨的捕虏体。然而，它与后者的不同之处在于其变质作用程度较低。我们推断，捕虏体原生碳质体的变质作用和/或 Krymka 母体的冲击是导致捕虏体主要变质变化的原因，包括原生有机化合物中石墨的结晶。将克林卡捕虏体的特征与彗星陨石的推断特征进行比较，证明它们与彗星物质的遗传关系仍然高度不确定。
The results of a detailed study on mineralogy, chemistry, and the carbon and oxygen isotopes of two exotic Krymka carbonaceous xenoliths are presented in this article. The investigated xenoliths are metamorphosed and shocked and have the following characteristics, which distinguish them from the Krymka host: 1. resemblance of their SiO2/MgO ratio to that of carbonaceous chondrites; 2. higher Fe content and FeO/(FeO + MgO) ratio; 3. lower concentration of Si, Ca, Al and an enrichment of S and probably of Ag; 4. smaller sizes and lower content (10 vol%) of chondrules and their clasts, and correspondingly higher content of matrix; 5. dominance of porphyritic chondrules and lack of nonporphyritic chondrules; 6. occurrence of an amoeboid olivine grain with16O-rich composition; 7. existence of carbon in three different forms: graphite, carbon-rich material, and organic compounds. The bulk chemistry of the xenoliths is similar, but not identical, to that of carbonaceous chondrites, suggesting that they represent a chondrite parent body that has not been previously sampled. Among any known type of meteoritic material the mineralogy of the xenoliths corresponds only to that of other Krymka graphite-containing xenoliths. It differs, however, from the latter by having a lower grade of metamorphism. We infer that metamorphism of the primary carbonaceous body of the xenoliths and/or shock of the Krymka parent body are responsible for the major metamorphic alteration of the xenoliths, including the crystallization of graphite from primary organic compounds. A comparison of the features of the Krymka xenoliths with the inferred characteristics of cometary meteorites attests that their genetic relationship to cometary material remains highly inconclusive.