Carbon isotopic compositions of Antarctic carbonaceous chondrites with relevance to the alteration and existence of organic matter
Carbon isotopic compositions of Antarctic carbonaceous chondrites with relevance to the alteration and existence of organic matter
复制标题
南极碳质球粒陨石的碳同位素组成与有机质的蚀变和存在的关系
DOI：
10.2343/geochemj.31.155
复制
发表时间：
1997
影响因子：
0.8
通讯作者：
K. Harada
中科院分区：
文献类型：
--
作者：
H. Naraoka;A. Shimoyama;O. Matsubaya;K. Harada
本文报道了26个南极碳质玄武岩（33个样品）的碳同位素组成，并讨论了它们的蚀变过程和溶剂可提取有机质的存在。δ 13 C值（相对于PDB）变化范围为-16.6 ~+0.9‰。平均值（-6.2‰）比非南极碳质玄武岩高出-6‰。这种差异可能是由于陆地有机碳污染了非南极洲的南极洲和/或母体的不同种群。大多数南极碳质玄武岩具有δ 13 C值随碳含量增加而变高的明显趋势（“主序列”）。这一趋势可能由两种组分的混合模型来解释：同位素重的和不稳定的组分（溶剂可提取的有机物和碳酸盐），以及同位素轻的和惰性的酸不溶性组分（干酪根样物质）。此外，一个独特的组（蚀变标本）的特点是相对高的含量和同位素轻碳。还报道了7种CM沸石经热H_2O和HCl/HF处理后的残余物的δ ~（13）C值。尽管体碳的同位素变化相当大，但酸不溶性残渣的δ 13 C值可分为两类：同位素轻的（-15至-13‰）和同位素重的（-9至-7‰）。大多数类干酪根物质属于轻族，其同位素与非南极类干酪根物质相似。蚀变标本具有同位素轻体碳（10 - 15 ‰），这与它们的干酪根样物质相似;它们可能失去了重组分，如溶剂可提取的有机物质（例如，氨基酸和羧酸）和碳酸盐。这与矿物学和氧同位素研究结果雅阁。溶剂可提取有机质的存在是控制碳质玄武岩体相碳同位素的重要因素之一。
Bulk carbon isotopic compositions of 26 Antarctic carbonaceous chondrites (33 specimens) are reported and discussed with relevance to the processes involved in their alteration and the existence of solvent-extractable organic matter. The δ13C values (relative to PDB) vary from -16.6 to +0.9‰. The average value (-6.2‰) is higher than that for non-Antarctic carbonaceous chondrites by -6‰. The difference may be explained by contamination of terrestrial organic carbon on non-Antarctic chondrites and/or different populations of parent bodies. Most Antarctic carbonaceous chondrites have an apparent trend (“a major sequence”) that the δ13C value becomes higher with increasing carbon content. The trend is likely to beexplained by a mixing model of two components; isotopically heavy and labile component (solvent-extractable organic matter and carbonate), and isotopically light and inert acid-insoluble component (kerogen-like matter). In addition, an unique group (altered specimens) is characterized by relatively high content and isotopically light carbon. For seven CM chondrites, δ13C values of residues after the hot H2O and HCl/HF treatment are also reported. Despite considerable isotopic variations of bulk carbon, the δ13C values of acid-insoluble residues may be classified into two groups; isotopically light (-15 to -13‰) and heavy (-9 to -7‰) ones. Most kerogen-like matters belong to the light group, which are isotopically similar to non-Antarctic kerogen-like matter. The altered specimens have isotopically light bulk carbon (∼-15‰), which is similar to those of their kerogen-like matter; they probably lost heavy components such as solvent-extractable organic matters (e.g., amino acid and carboxylic acid) and carbonates during aqueous alteration and thermal metamorphism on parent bodies. This is in accord with mineralogical and oxygen isotope studies. The presence of solvent-extractable organic matter is one of the important factors controlling bulk carbon isotopes in carbonaceous chondrites.