Chemical evolution of planetesimal cores during the early history of the solar system

太阳系早期历史中星子核心的化学演化

• 批准号: 248632057
• 负责人: Professor Dr. David Rubie
• 金额: --
• 依托单位: Max-Planck-Institut für Sonnensystemforschung (MPS)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2014
• 资助国家: 德国
• 起止时间: 2013-12-31 至 2015-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/248632057?language=en
• 关键词: Chemical; evolution; planetesimal; cores; during

The Earth formed by the accretion of numerous small 10-100 km-sized planetesimals together with a smaller number of larger Moon- to Mars-sized embryos. According to current models of Earth's core formation, the bodies that accreted early to the Earth should have undergone core-mantle differentiation under highly reducing conditions, such that significant amounts of silicon, chromium and vanadium partitioned into their metallic Fe-Ni cores. Iron meteorites are derived from the metallic cores of early-formed planetesimals, and, in contrast to the predictions, the concentrations of Si and Cr in these meteorites are extremely low (e.g. <1 ppm). The aim of this proposal is to test the following hypothesis: Molten planetesimal cores originally contained high concentrations of the weakly siderophile elements Si and Cr but during cooling these elements became increasingly lithophile and partitioned back into the overlying molten mantle (magma ocean). This hypothesis will be tested by first determining the chemical diffusivities of Si and Cr in molten iron both experimentally (at 1-25 Gigapascals) and theoretically (using molecular dynamics simulations over a larger pressure range). Second we will develop models of chemical interaction at planetesimal core-mantle boundaries for realistic cooling histories, assuming that both the liquid core and overlying magma ocean are in a state of convection. The rate of chemical evolution will be controlled by diffusion through boundary layers for which the diffusion results will be required.

地球是由许多10-100公里大小的小行星体和数量较少的较大的月球到火星大小的胚胎共同形成的。根据目前的地核形成模型，早期附着到地球上的天体应该在高度还原的条件下经历核幔分化，从而使大量的硅、铬和钒分配到它们的金属Fe-Ni核中。铁陨石来自早期形成的行星体的金属核心，与预测相反，这些陨石中的硅和铬浓度极低(例如&lt；1ppm)。这一提议的目的是检验以下假设：熔融的行星小核心最初含有高浓度的弱亲铁元素Si和Cr，但在冷却过程中，这些元素变得越来越亲石，并重新分配到上面的熔融地幔(岩浆海洋)中。这一假设将通过首先从实验上(在1-25千兆帕斯卡)和理论上(在更大的压力范围内使用分子动力学模拟)确定硅和铬在铁液中的化学扩散系数来验证。第二，假设液核和上覆的岩浆海洋都处于对流状态，我们将建立行星微小核-地幔边界上的化学相互作用模型，用于真实的冷却历史。化学演化的速度将由通过边界层的扩散控制，这将需要扩散结果。