The Origin of Metal and Chondrules in CH and CB Chondrites - Evidence from Fe, Ni and Mg isotopes

CH 和 CB 球粒陨石中金属和球粒的起源 - 来自 Fe、Ni 和 Mg 同位素的证据

• 批准号: 248714675
• 负责人: Professor Dr. Stefan Weyer, Ph.D.
• 金额: --
• 依托单位: Institut für Geologie, Mineralogie und Geophysik
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2014
• 资助国家: 德国
• 起止时间: 2013-12-31 至 2017-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/248714675?language=en
• 关键词: Origin; Metal; Chondrules; CH; CB

CH and CB chondrites are unusual chondrite breccias that contain a range of objects that formed under different conditions and settings. In particular, the origin of chondrules of types SO and CC as well as of zoned and unzoned metal grains have been extensively studied as they carry mineralogical and chemical features consistent with a formation as condensates from a gas/melt mix or gas vapour at variable high temperatures. The preferred current model postulates a giant impact of two embryos, at about 4.5 m.y after CAI formation, to have lead to the formation of such a vapour plume. Alternatively, it was suggested that metal and SO and CC chondrules condensed from a solar gas in isolated compartments of the solar nebula. In order to better constraint the formation conditions we propose a study of insitu analyses by femtosecond LA-MC-ICP-MS of stable isotopes of Fe and Ni in metal and Fe and Mg in chondrule silicates in CH and CB chondrites. We showed in preliminary studies of CH and CB chondrites that silicates and metal display mass-dependent Fe isotopes fractionation, with silicates being isotopically heavier. We also showed that unzoned metal grains in CBb chondrite HaH 237 contain Fe isotopes of chondritic composition. Chemically zoned metal display a zonation of Fe isotopes that follows the chemical zonation of Ni, with light delta56Fe in cores and chondritic delta56Fe in rims. Rapid grain growth at high temperatures could cause the zoning and the observed kinetic fractionation of Fe isotopes. Fractionation signatures of stable isotopes are sensitive markers for condensation, evaporation and diffusion processes. Therefore, we plan a systematic study of Fe isotopes and, on selected grains, also Ni isotopes in order to trace condensation signatures and distinguish these from those generated by diffusion. Isotope and chemical zoning patterns will be modelled in order to gain information on time scales of condensation or diffusion. In addition, we propose to analyse Mg and Fe isotope systematics in silicates of SO and CC chondrules in order to test existing hypothesis and constrain their orgin further. An important part of this study is the careful petrologic characterization of the meteorites that will includes major and minor element analyses by EMP and insitu analyses of REE, Sc, etc. in siliactes and PGE, etc. elements in metal by LA-ICP-MS. These data will provide the basis for the selection of suitable grains and chondrules for stable isotope analyses. We expect this study to substantially expand our knowledge of the origin of CH and CB chondrites chondrites.

CH和CB软管是不寻常的软骨角砾岩，其中包含在不同条件和设置下形成的一系列物体。特别是，已经对类型和CC的软骨以及划分和未分布的金属晶粒的形式的起源进行了广泛的研究，因为它们携带矿物质学和化学特征与形成型的矿物质和化学特征，该特征与可变高的气体/熔体混合物中的冷凝物一致温度。首选的电流模型假设在CAI形成后约4.5 m.y的两个胚胎的巨大影响会导致形成这种蒸气羽流。另外，有人建议金属以及CC软管从太阳气中的太阳气中凝结在太阳星云的分离室中。为了更好地限制形成条件，我们提出了一项稳定的Fe和Ni同位素在CH和CB软骨中硅酸盐硅酸盐中的Fe和Ni稳定同位素的LA-MC-ICP-MS研究的研究。我们在对CH和CB软管的初步研究中表明，硅酸盐和金属表现出质量依赖性的Fe同位素分馏，而硅酸盐在同位素上较重。我们还表明，CBB软管中的未分区金属晶粒HAH 237包含软骨组成的Fe同位素。化学分区的金属显示了Ni化学分区的Fe同位素的分区，并在核心中带有光delta56fe和RIMS的软骨delta56fe。高温下的快速谷物生长可能导致分区和观察到的Fe同位素的动力学分馏。稳定同位素的分级特征是用于凝结，蒸发和扩散过程的敏感标记。因此，我们计划对Fe同位素的系统研究，并在选定的晶粒上也计划进行Ni同位素，以追踪凝结特征并将其与扩散产生的同位素区分开。同位素和化学分区模式将进行建模，以获取凝结或扩散时间的信息。此外，我们建议在SO和CC软骨中分析MG和Fe同位素系统学，以检验现有的假设并进一步限制其Orgin。这项研究的一个重要部分是对陨石的仔细的岩石学表征，其中包括eMP和REE，SC等的主要和次要元素分析。在Siliactes和pge中进行。 。这些数据将为选择合适的晶粒和软骨用于稳定同位素分析提供基础。我们希望这项研究将大大扩展我们对CH和CB软骨软骨的起源的了解。