AQUEOUS ALTERATION IN CARBONACEOUS CHONDRITES - MASS BALANCE CONSTRAINTS ON MATRIX MINERALOGY
AQUEOUS ALTERATION IN CARBONACEOUS CHONDRITES - MASS BALANCE CONSTRAINTS ON MATRIX MINERALOGY
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DOI：
10.1016/0016-7037(87)90298-5
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发表时间：
1987-09-01
影响因子：
5
通讯作者：
MCSWEEN, HY
中科院分区：
文献类型：
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作者：
MCSWEEN, HY
用微探针散焦束技术测定了南极CM陨石和其他非南极CM和CI陨石中基质物质的整体化学成分。这些都是使用，沿着与先前发表的矿物学研究的结果，提供质量平衡的碳质球粒陨石基质中共生和混合层状硅酸盐相的相对比例的限制。这些计算的结果表明，五氯苯酚（约25%的氯镍石和75%的氯镍石的混合物）和蛇纹岩（不同比例的富镁和富铁品种或中间成分品种）的含量不同。另外的硫化物相也可能是必要的，以解释过量的Ni和S。单个陨石基质的Fe/Si比值为1.21至2.77，对应的PCP/（PCP + SERF）比值为0.16至0.58。基质的渐进性水蚀变似乎是通过形成托奇利石，然后是铬铁矿和富镁蛇纹石，最后是富铁蛇纹石和硫化物而发生的。CM矩阵显然没有表现为一个孤立的系统在改造。CI球粒陨石基质中似乎几乎不含五氯苯酚，这可能是在未发生变化的前体材料中缺乏球粒伴生金属（五氯苯酚的形成来源）的自然结果。这些数据提供了一个更定量的图片低温水蚀变过程中的碳质球粒陨石母体比迄今为止可能从TEM研究。
Bulk chemical compositions of matrix material in Antarctic CM chondrites and other non-Antarctic CM and CI chondrites have been determined using microprobe defocused beam techniques. These are used, along with the results of previously published mineralogical studies, to provide mass balance constraints on the relative proportions of intergrown and intermixed phyllosilicate phases in carbonaceous chondrite matrices. Results of these calculations indicate differing amounts of PCP (a mixture of approximately 25% tochilinite and 75% cronstedtite) and serpentines (Mg-rich and Fe-rich varieties in varying proportions or intermediate compositional varieties). Additional sulfide phases are also probably necessary to account for excess Ni and S. Fe/Si ratios for matrices of individual meteorites range from 1.21 to 2.77, corresponding to PCP/(PCP + SERF) ratios of 0.16 to 0.58. Progressive aqueous alteration of matrix appears to have occurred by formation of tochilinite, then cronstedtite and Mg-rich serpentine, and finally Fe-rich serpentine and sulfides. CM matrix clearly did not behave as an isolated system during alteration. CI chondrite matrices appear to contain little if any PCP; this may be a natural consequence of the absence of chondrule-associated metal, from which PCP forms, in the unaltered precursor material. These data provide a more quantitative picture of low-temperature aqueous alteration processes in carbonaceous chondrite parent bodies than has heretofore been possible from TEM studies alone.