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

本文提出了一种量化高亲铁元素Au、Pt、Ir和Os在高温高压淬火球粒状材料中硅酸盐液体和硫化铁液体之间分配的方法。这样的划分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25gpa， T高达2500℃）包括的数值与假定在地球形成的早期阶段产生的岩浆海洋相适应。因为地球是由挥发物耗尽的球粒陨石形成的，我们将使用5级或6级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研究压力和温度对类似于吸积的地球的大块成分的划分的影响。虽然对中等亲铁元素进行了大量的高压研究，但对高亲铁元素在高压下的配分行为的研究却很少。如果我们的研究结果表明，HSEs并没有高度分馏到硫化铁熔体中，那么亲铁试剂的丰度可以用深部岩浆海洋中金属-硅酸盐平衡的均匀吸积模型来解释。如果我们的数据显示了强强的HSEs在金属-硫化物阶段的划分，那么HSEs的地幔丰度必须用核幔之间缺乏平衡和非均质吸积来解释。为了估计均匀或非均匀吸积模型的贡献，我们必须知道在适合球粒物质吸积和岩心形成的条件下亲铁元素的分配行为。除了测量分割系数外，我们还将使用高分辨率电子显微镜来表征运行产物，以确定HSEs是溶解在硅酸盐中还是以微块的形式出现。

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.