Partitioning of Highly Siderophile Elements at Elevated Pressure and Temperature: Constraints on Core Formation and Accretion of the Earth

Sharp和Herviglit-0087584提出了在高压和高温下淬火的实验中，对高亲铁性元素Au、Pt、Ir和Os在硅酸盐液体和硫化铁液体之间的分配进行量化。这种分区数据将使我们能够更好地约束早期地球的吸积和分化模型。实验条件（P = 1至25 GPa，T高达2500 C）包括适合于假定在地球形成早期阶段产生的岩浆海洋的值。由于地球是由挥发性贫化的球粒陨石物质堆积而成的，我们将使用5级或6级的H球粒陨石作为起始材料。所提出的条件范围将使我们能够调查的影响，压力和温度上的分区散装组成类似的吸积地球。虽然在高压下对中等亲铁性元素的研究已经做了很多，但对高亲铁性元素在高压下的分配行为的研究却很少。如果我们的研究结果表明，HSEs没有高度分馏成的铁硫化物熔体，那么今天丰富的亲铁矿物可以解释一个均匀的增生模型与金属硅酸盐平衡在深岩浆海洋。如果我们的数据显示出强烈的分区的HSEs到金属硫化物相，那么地幔丰度的HSEs必须解释为缺乏核幔之间的平衡和异质增生。为了估计均匀或非均匀吸积模型的贡献，我们必须知道亲铁元素的分配行为的吸积和核心的形成，从南极物质的条件下适当的。除了测量分配系数外，我们还将使用高分辨率电子显微镜来表征运行产品，以确定HSE是否溶解在硅酸盐中或作为微块出现。

Sharp and HervigEAR-0087584It is proposed to quantify the partitioning of the highly siderophile elements Au, Pt, Ir, and Os between silicate liquid and iron-sulfide liquid in chondritic material quenched from experiments at high pressures and temperatures. Such partitioning data will allow us to better constrain models for the accretion and differentiation of the early Earth. The conditions of the experiments (P = 1 to 25 GPa, T up to 2500 C) include values appropriate to a magma ocean presumed to have been generated during the early stages of formation of the Earth. Because the Earth accreted from volatile-depleted chondritic material, we will use a grade 5 or 6 H chondrite as the starting material. The range of conditions proposed will allow us to investigate the effect of pressure and temperature on partitioning for a bulk composition similar to the accreting Earth. Although much high-pressure work has been done on the moderately siderophile elements, little work has been done to measure the partitioning behavior of highly siderophile elements (HSEs) at high pressure. If our results show that the HSEs are not highly fractionated into the iron-sulfide melt, then the present-day abundance of siderophiles can be explained by a homogenous accretion model with metal-silicate equilibration in a deep magma ocean. If our data show strong partitioning of HSEs into the metal-sulfide phase then the mantle abundances of HSEs must be explained by a lack of equilibrium between core and mantle and heterogeneous accretion. In order to estimate the contributions of either homogeneous or heterogeneous accretion models, we must know the partitioning behavior of siderophile elements under conditions appropriate for accretion and core formation from chondritic material. In addition to measuring partition coefficients, we will use high-resolution electron microscopy to characterize the run products to determine if the HSEs are dissolved in the silicate or occur as micro nuggets.