Experimental Investigations of Chemical Interaction at the Core-Mantle Boundary

核幔边界化学相互作用的实验研究

• 批准号: 0838141
• 负责人: James Van Orman
• 金额: $ 27.1万
• 依托单位: Case Western Reserve University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-01-01 至 2012-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0838141&HistoricalAwards=false
• 关键词: Experimental; Investigations; Chemical; Interaction; Core

A fundamental event in Earth's history was its early differentiation into a silicate mantle and dense metallic core. Whether there has been significant chemical exchange between the core and mantle subsequently is a long-standing question that has broad implications for geochemistry and geophysics. It is possible that complex seismic structures observed at the base of the mantle, and possibly also near the top of the core, relate to chemical reactions at the core-mantle boundary. Geochemical signatures observed in ocean island basalts, based primarily on osmium isotopes, also have been interpreted to reflect material contributions from the outer core. This study will address the importance of chemical exchange between the core and mantle through two different lines of experimental investigation, one aimed toward resolving whether the outer core is a plausible source of the radiogenic osmium isotope signature in ocean island basalts, and the other at constraining the kinetics of chemical exchange across the core-mantle boundary. The hypothesis that the outer core is a source of radiogenic osmium is based on the idea that Pt/Os and Re/Os ratios in the outer core are raised significantly by crystallization of the inner core. The proposed study will expand on previous experimental work that has cast doubt on this notion, because the differences in solid-metal/liquid-metal partition coefficients among Os, Re and Pt are too small and decrease with pressure. The new study will investigate partitioning of these elements in the Fe-FeO and Ni-NiO systems at high pressures, to determine whether oxygen-bearing systems may be capable of producing the appropriate partition coefficients. Experimental studies of reactions at the core-mantle boundary have focused primarily on equilibrium phase relations and element partitioning. The kinetics of the reactions are equally important for evaluating their relevance to the Earth. It is planned to pursue experiments to determine the mechanisms and rates of reactions between lower-mantle analog materials and liquid metals, and to determine the diffusion rates of transition metals through periclase. The proposed study will further test the results of recent experimental work by this group that indicates that the crystal field effect has a strong influence on the diffusion rates of transition metals with partially filled d orbitals, and it is a central goal of the project to investigate this effect in detail.

地球历史上的一个基本事件是它早期分化为硅酸盐地幔和致密的金属核心。 随后地核和地幔之间是否发生了显着的化学交换是一个长期存在的问题，对地球化学和地球物理学具有广泛的影响。 在地幔底部以及在地核顶部附近观察到的复杂地震结构可能与地核-地幔边界处的化学反应有关。 在海岛玄武岩中观察到的地球化学特征主要基于锇同位素，也被解释为反映了外核的物质贡献。 这项研究将通过两项不同的实验研究来解决地核和地幔之间化学交换的重要性，一项旨在解决外核是否是洋岛玄武岩中放射性锇同位素特征的合理来源，另一项旨在限制跨核-地幔边界的化学交换动力学。 外核是放射性锇来源的假设是基于外核中的 Pt/Os 和 Re/Os 比率因内核结晶而显着升高的想法。 这项研究将扩展之前对这一概念提出质疑的实验工作，因为 Os、Re 和 Pt 之间的固-金属/液-金属分配系数差异太小，并且随着压力而减小。 这项新研究将研究高压下这些元素在 Fe-FeO 和 Ni-NiO 系统中的分配，以确定含氧系统是否能够产生适当的分配系数。 核幔边界反应的实验研究主要集中在平衡相关系和元素分配上。 反应动力学对于评估其与地球的相关性同样重要。 计划进行实验以确定下地幔模拟材料和液态金属之间的反应机制和速率，并确定过渡金属通过方镁石的扩散速率。 拟议的研究将进一步测试该小组最近的实验工作结果，该结果表明晶体场效应对具有部分填充d轨道的过渡金属的扩散速率有很大影响，详细研究这种效应是该项目的中心目标。