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

9713978山谷9714028埃勒，斯托尔珀该奖项支持了一项合作研究，利用离子微探针对碳酸盐、硅酸盐、氧化物和可能还原的含碳相中的氧同位素(18O/16O)和碳同位素(13C/12C)在微米级的分布进行了研究。它得到了极地计划办公室、化学司和MPS多学科活动办公室的支持。这项工作将对这块岩石经历的热和流体渗入历史以及ALH84001碳酸盐可能的生物成因提供限制。这项工作将建立在之前完成的一项初步研究的基础上，该研究包括12个特征良好的碳酸盐标准的500多个分析，ALH84001硅酸盐中的11个氧同位素分析，以及ALH84001碳酸盐结核中的9个氧同位素分析和4个碳同位素分析。这项初步研究表明，在10‘S微米以上的ALH84001碳酸盐中，氧同位素组成存在10/10以上的梯度，表明这些矿物的精细稳定同位素变化中有足够的“信号”，我们可以从拟议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相将是解释这些碳酸盐结核形成环境的关键。本样本中已经记录的异质性表明，只有使用离子微探针技术才能完成大部分工作。根据该奖项将完成的研究工作包括对各种碳酸盐、硅酸盐和含铁矿物中的10-30微米(约5-10微米深)斑点进行大量分析，以建立氧和碳同位素的组成剖面。这些新的分析将使以下工作成为可能：(1)测试结核的核到缘氧分带作用；(2)测试和改进先前对各种碳酸盐矿物相形成温度的估计；(3)调查非碳酸盐相记录的流体渗入历史；以及(4)核实初步观察结果，即碳酸盐结核的外部可能含有低碳-13成分，这可能与陨石ALH84001中推断的结核边缘的所谓‘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一致。这些限制是解释ALH84001中碳酸盐起源的核心，既涉及它们生物起源的可能性，也涉及它们提供的关于早期火星上挥发物性质的证据。

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.