Experimental Studies of Early Differentiation and Evolution of the Earth

为了模拟深度超过1000公里的岩浆海洋中的岩心分凝，我们的目标是在超高压下实验研究铁水和硅酸盐之间的反应和元素分配。利用烧结金刚石作为劈球式多砧器的顶锤材料，可进行压力高于30 Gpa的熔炼实验。使用二次离子质谱仪的分析方法的创新使在直径5微米的区域内测定小于1ppm的元素浓度成为可能。根据这些新发展的方法，研究了硅酸盐和硅酸铁体系的熔融关系，确定了常量元素和微量元素在MI与硅酸盐液体(SL)或共存固相之间的分配是压力的函数。本研究取得的重要成果概括如下：(1)原生地球物质的液相为镁闪锌矿(MW)…更多位于墨尔盖底部，深度为600-1000公里。然而，SL+MW场的一个很窄的温度区间表明，在成核之前，钙钛矿(PV)也可能与MI共存。(2)在高于20 Gpa的压力下，Si和O从SL的MI中的溶解随着压力的增加而显著增加。(3)Mi与SL、Mw、Pv之间的配分系数达到26 Gpa，说明地幔的Ni、Co丰度可以解释地幔物质与Sl、Mw在900 km以下深度的平衡。然而，PV的共存需要更深层次的MO。(4)已发现在高于20 Gpa的压力下，相当数量的稀土元素(REE)从SL的MI中溶解，轻稀土和重稀土之间存在显著的分馏，导致核心形成后原始地幔中轻稀土元素的亏损。这一结果对地幔化学具有重要意义，因为到目前为止，人们直观地认为原始地幔的稀土元素相对丰度与球粒陨石的稀土元素相对丰度相同。较少

In order to simulate the core segregation in a magma ocean (MO) extended deeper than 1000 km depth, we aimed to examine experimentally reactions and elemental partitioning between molten iron (MI) and silicates at ultrahigh pressures. Melting experiment at pressures higher than 30 GPa can be carried out by utilizing sintered diamond as anvil material of the splitsphere multi-anvil apparatus. Innovation of analytical method using a secondary ion mass spectrometer has made it possible to determine concentration of elements less than 1ppm over an area of 5mum diameter. Based on these newly developed methods, melting relations of silicate and iron silicate systems have been examined and the partitioning of major and trace elements between MI and silicate liquid (SL) or coexisting solid phases has been determined as function of pressure. Important results obtained in the present research are summarized as follows : (1) Liquidus phase of the primary Earth's material is magnesiow ustite (Mw) … More at the bottom of MO with depths of 600-1000 km. However, a very narrow temperature interval of the SL+Mw field suggests that perovskite (Pv) would also have coexisted with MI prior to core formation. (2) At higher than 20 GPa, dissolution of Si and O in MI from SL proceeds noticeably with pressure. Thus Mg/Si ratio of the mantle could remarkably be increased by the core segregation in a deep MO.(3) Partition co efficients of Mn, Ni, and Co between MI and SL,Mw, and Pv to 26 GPa indicate that Ni and Co abundance of the mantle can be explained if the core material would have been equilibrated with SL and Mw at the bottom of MO deeper than 900 km. However, the coexistence of Pv demands a much deeper MO.(4) It has been found that appreciable amounts of rare earth elements (REE) dissolve in MI from SL at pressures higher than 20 GPa with a remarkable fractionation between light and heavy REE,resulting in depletion in light REE in the primitive mantle after the core formation. The results are of crucial importance for the mantle chemistry because the relative abundace of REE for the primitive mantle have intuitively assumed so far to be same as those of chondrites. Less