The Lithophile Element Budget of Earth's Core
The Lithophile Element Budget of Earth's Core
复制标题
DOI：
10.1029/2021gc009986
复制
发表时间：
2022-02-01
影响因子：
3.5
通讯作者：
Campbell, A. J.
中科院分区：
文献类型：
--
作者：
Chidester, B. A.;Lock, S. J.;Campbell, A. J.
地球地核和地幔的相对组成在核形成过程中就已确定。通过确定元素在高压和高温下在金属和硅酸盐之间的分配方式，对地幔组成的测量以及对地核的地球物理观测可用于了解地球形成的机制。在此，我们展示了一系列名义上的亲石元素（铝、钙、钾、镁、氧、硅、钍和铀）以及硫在高达85吉帕和5400开尔文条件下的金属 - 硅酸盐分配实验结果。结合我们的结果以及文献数据的汇总，我们开发了一种分配参数化方法，该方法考虑了金属相和硅酸盐相中的成分依赖性。在一系列行星生长模型中使用这一参数化方法，我们发现，一般来说，亲石元素在高温下向金属相的分配会增强。地幔中氧化亚铁、二氧化硅和氧化镁的相对丰度在不同的行星生长模型之间存在显著差异，这些元素在地幔中的丰度可用于对地球的吸积过程提供重要约束。为了与地球的地核质量和地幔组成相匹配，与CI型球粒陨石相比，地球的组成物质必须富含铁且贫硅。最后，进入地核的镁、硅和氧太少，以至于氧化物沉淀无法成为地球发电机的主要能量来源。相比之下，在高温下，几 ppb的铀可进入地核，在热演化模型中必须考虑这一能量来源。
The relative composition of Earth's core and mantle were set during core formation. By determining how elements partition between metal and silicate at high pressures and temperatures, measurements of the mantle composition and geophysical observations of the core can be used to understand the mechanisms by which Earth formed. Here we present the results of metal-silicate partitioning experiments for a range of nominally lithophile elements (Al, Ca, K, Mg, O, Si, Th, and U) and S to 85 GPa and up to 5400 K. With our results and a compilation of literature data, we developed a parameterization for partitioning that accounts for compositional dependencies in both the metal and silicate phases. Using this parameterization in a range of planetary growth models, we find that, in general, lithophile element partitioning into the metallic phase is enhanced at high temperatures. The relative abundances of FeO, SiO2, and MgO in the mantle vary significantly between planetary growth models, and the mantle abundances of these elements can be used to provide important constraints on Earth's accretion. To match Earth's core mass and mantle composition, Earth's building blocks must have been enriched in Fe and depleted in Si compared with CI chondrites. Finally, too little Mg, Si, and O are partitioned into the core for precipitation of oxides to be a major source of energy for the geodynamo. In contrast, several ppb of U can be partitioned into the core at high temperatures, and this energy source must be accounted for in thermal evolution models.