Collaborative Research: Ion Probe Analysis of O and C Isotope Ratios in ALH84001

摘要该奖项支持一项利用离子探针对“火星”陨石（SNC类陨石）ALH84001中碳酸盐、硅酸盐、氧化物和可能的还原性含碳相中氧同位素（18O/16O）和碳同位素（13C/12C）的微米尺度分布进行合作研究。它由极地项目办公室、化学部门和MPS多学科活动办公室提供支持。这项工作将为该岩石的热渗透历史和流体渗透历史以及ALH84001碳酸盐岩可能的生物成因提供约束。这项工作将建立在先前完成的试点研究的基础上，该研究包括对12种特征良好的碳酸盐标准进行500多次分析，对ALH84001硅酸盐进行11次氧同位素分析，对ALH84001碳酸盐结核进行9次氧同位素分析和4次碳同位素分析。这项初步研究表明，在ALH84001碳酸盐中，超过10微米的氧同位素组成中有超过10 / 10000的部分存在梯度，这表明这些矿物的细尺度稳定同位素变化中有足够的“信号”，使我们能够从我们提出的分析中提取有意义的信息。进一步表征氧同位素分带和寻找低碳-13相对于解释这些碳酸盐结核的形成环境至关重要。该样品中已经记录的异质性表明，大部分工作只能使用离子微探针技术。根据该合同完成的研究工作包括对各种碳酸盐、硅酸盐和含铁矿物中10-30微米（约5-10微米深）的大量分析，以建立氧和碳同位素的组成剖面。这些新的分析将允许以下内容：(1)测试核心到边缘氧带的固结；(2)检验和完善前人对各种碳酸盐矿物相形成温度的估计；(3)研究非碳酸盐相记录的流体渗透历史；(4)验证碳酸盐结块外部可能含有低碳-13成分的初步观测结果，这可能与ALH84001陨石中推断的结块边缘所谓的“生物膜”有关。这些分析将评估已发表的报告，即碳酸盐和相关还原碳之间的碳同位素分馏与生物过程是一致的。这些限制是解释ALH84001中碳酸盐起源的核心，既考虑到它们的生物起源的可能性，也考虑到它们提供的早期火星挥发物性质的证据。

9713978 Valley 9714028 Eiler, Stolper Abstract This award supports a collaborative study of the micron-scale distribution of oxygen isotopes (18O/16O) and carbon isotopes (13C/12C) in carbonates, silicates, oxides and possibly reduced carbon-bearing phases in the "Martian" meteorite (SNC class of meteorites), ALH84001, using the ion microprobe. It is supported by the Office of Polar Programs, the Chemistry Division, and the MPS Office of Multidisciplinary Activities. This work will provide constraints on the thermal and fluid-infiltration history experienced by this rock and the possible biogenic origin of ALH84001 carbonate. This work will build on a previously completed pilot study comprised of over 500 analyses of 12 well characterized carbonate standards, 11 oxygen isotope analyses in ALH84001 silicates, and 9 oxygen isotope analyses coupled with 4 carbon isotope analyses in ALH84001 carbonate concretions. This pilot study demonstrated the presence of gradients in the oxygen isotope composition of more than 10 parts in 10,000 in ALH84001 carbonates over 10's of microns, showing that there is sufficient `signal' in the fine- scale stable isotope variations of these minerals for us to extract meaningful information from our proposed analyses. Further characterization of the oxygen isotope zonation and search for low carbon-13 phases will be critical to interpreting the environment of formation of these carbonate concretions. The heterogeneity already documented in this sample indicates that much of this work will only be possible using ion microprobe techniques. The research work to be completed under this award includes a large number of analyses of 10-30 micron spots (about 5-10 microns deep) in a variety of carbonate, silicate and iron bearing minerals to establish compositional profiles for oxygen and carbon isotopes. These new analyses will allow the following: (1) test concretions for core-to-rim oxygen zonation; (2) test and refine previo us estimates of the temperatures of formation of the various carbonate mineral phases; (3) investigate the fluid-infiltration history recorded by non-carbonate phases, and (4) verify initial observations that the outer portions of carbonate concretions may contain low carbon-13 compositions, which may be related to purported `biofilms' at concretion margins that have been inferred in meteorite ALH84001. These analyses will evaluate published reports that the fractionation of carbon isotopes between carbonate and associated reduced carbon is consistent with biological processes. These constraints are central to the interpretation of the origin of carbonates in ALH84001, both with regard to the possibility of their biogenic origin and the evidence they provide of the nature of volatiles on early Mars.