Constraining the timing of volatile arrival on Earth using Ru and Mo isotopes in the Archean mantle

使用太古代地幔中的钌和钼同位素限制挥发物到达地球的时间

• 批准号: 404676364
• 负责人: Dr. Mario Fischer-Gödde
• 金额: --
• 依托单位: Institut für Geologie und Mineralogie
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/404676364?language=en
• 关键词: Constraining; timing; volatile; arrival; Earth

Volatile elements represent a crucial prerequisite for the birth and evolution of life on Earth. While it is largely accepted that water and other volatiles were brought to the Earth by the accretion of carbonaceous chondrite-like materials originating from the outer solar system, the timing of this accretion remains highly debated. It has long been suggested that volatile elements were added to the Earth by late accretion of a volatile-rich late veneer after core formation had ceased. However, this hypothesis was recently refuted by a Ru isotope study, which shows that the late veneer was made of reduced and volatile-poor material originating from the inner solar system. Hence, the Earth’s volatiles must have been added during the main accretion, i.e. before the cessation of core formation, but exactly when remains unconstrained. This proposal aims at providing new constraints on the timing of volatile arrival on Earth during its main accretion stage. This will be tackled by the investigation of the Ru and Mo isotopic signature of early Archean komatiites suggested to have preserved the pre-late veneer isotopic composition of the mantle. The approach builds on the results of recent nucleosynthetic isotope anomaly studies on meteorites, which show that volatile-rich carbonaceous chondrites exhibit Ru and Mo isotope signatures clearly distinct from volatile-poor meteorites. Hence, the particular genetic fingerprints of these meteorites can be used to assess whether significant amounts of volatile-rich material was present in the source of early Archean komatiites. This would be visible in their Ru and Mo isotope composition, which would be different from that of the modern mantle. The results of this study should ultimately provide critical insights for the discrimination between the two main models of the Earth’s accretion: heterogeneous and homogeneous.

挥发性元素是地球上生命诞生和进化的关键先决条件。虽然人们普遍认为，水和其他挥发物是由来自外太阳系的碳质类陨石物质的吸积带到地球的，但这种吸积的时间仍然存在很大争议。长期以来，人们一直认为，挥发性元素是在地核形成停止后，富含挥发性物质的晚期单板的晚期吸积作用中加入地球的。然而，这一假设最近被一项钌同位素研究反驳，该研究表明，晚期的单板是由来自内太阳系的还原和挥发性较差的材料制成的。因此，地球的挥发物一定是在主要的吸积过程中加入的，也就是说，在核心形成停止之前，但正是在不受约束的时候。这一提议旨在对不稳定物质在其主要吸积阶段到达地球的时间提出新的限制。这将解决的早期太古代科马提岩的Ru和Mo同位素签名的调查建议保存前晚单板的地幔同位素组成。该方法建立在最近对陨石的核合成同位素异常研究的结果的基础上，这些研究表明，富含挥发物的碳质陨石表现出明显不同于挥发物贫乏的陨石的Ru和Mo同位素特征。因此，这些陨石的特定遗传指纹可以用来评估是否有大量富含挥发性物质的物质存在于早期太古代科马提岩的来源中。这在它们的Ru和Mo同位素组成中是可见的，这与现代地幔不同。这项研究的结果应最终提供关键的见解之间的歧视地球的吸积的两个主要模型：异质和同质。