Impact-induced melting, magma ocean evolution and core-mantle differentiation during accretion of the Earth

地球吸积过程中撞击引起的融化、岩浆海洋演化和核幔分异

• 批准号: 275826910
• 负责人: Professor Dr. David Rubie
• 金额: --
• 依托单位: Bayerisches Forschungsinstitut für Experimentelle Geochemie und Geophysik (BGI)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2015
• 资助国家: 德国
• 起止时间: 2014-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/275826910?language=en
• 关键词: Impact; induced; melting; magma; ocean

During the early history of the Solar System, the Earth differentiated into its metallic core and silicate mantle by a multistage process that was strongly coupled to accretion of the planet. Accretion occurred through numerous collisions with other smaller planetary bodies, each of which delivered both energy and metal to the growing planet. The high energies involved in accretional impacts caused large scale melting of the early Earth and magma ocean formation which facilitated the segregation of iron-rich metal from silicate to produce the core and mantle. Major questions about this early period of Earth's history remain unanswered. For example, was there a single long-lasting deep magma ocean during accretion (as is often assumed) and, if so, how did its depth evolve with time? Alternatively was there a series of short-lived deep magma oceans and, if so, how did their depths evolve with time? Such questions depend on magma ocean cooling/crystallization timescales which, in turn, depend critically on the presence or absence of an insulating atmosphere. Although an insulating atmosphere has been postulated to be present after the Moon-forming giant impact, it has also been shown that accretional impacts cause atmospheric loss. Magma ocean evolution and how it is coupled to insulating atmospheres will be investigated in this project using a novel approach. We have previously integrated a multistage core formation model with numerical simulations of planetary accretion that is based on highly simplified assumptions about magma ocean depths. Employing this integrated approach we propose to actually calculate the depth of melting during each of thousands of accretional impacts based on kinetic energies and impact angles. The depth of melting is of critical importance because it determines the pressure-temperature conditions at which chemical equilibration between liquid metal and liquid silicate occurs, which, in turn, determines the chemical evolution of Earth's mantle and core. Furthermore the cooling/crystallization timescale of resulting global magma oceans will be determined and included in the model for different insulating atmosphere scenarios. The combined accretion/differentiation model will also enable the compositions of Earth's building materials to be determined as a function of their heliocentric distances of origin in the proto-planetary disk.

在太阳系的早期历史上，地球通过多阶段的过程与地球的积聚相结合。通过与其他较小的行星体发生众多碰撞发生，每个行星都将能量和金属传递到生长的星球。涉及吸收影响的高能量导致了早期地球和岩浆海洋形成的大规模熔化，从而促进了富含铁的金属从硅酸盐中隔离，从而产生了核心和地幔。关于地球历史早期的主要问题仍然没有得到答复。例如，在积聚过程中是否有一个持久的深岩浆海洋（通常是假设），如果是这样，它的深度如何随着时间而变化？另外，是否有一系列短暂的深岩浆海洋，如果是的话，它们的深度如何随着时间的流逝而发展？这些问题取决于岩浆海洋冷却/结晶时间尺度，而时间尺度又取决于绝缘气氛的存在或不存在。尽管已经假定在形成月球的巨型撞击之后存在绝缘气氛，但还表明吸收影响会导致大气损失。岩浆海洋的进化及其如何与它结合在一起，将在该项目中使用一种新颖的方法进行研究。我们以前已经将多阶段核心形成模型与行星积聚的数值模拟集成在一起，该模拟基于对岩浆海洋深度的高度简化假设。我们提出采用这种综合方法，以实际计算基于动能和冲击角度的成千上万个吸收影响的熔化深度。熔化的深度至关重要，因为它决定了发生液体金属和液态硅酸盐之间化学平衡的压力温度条件，这反过来决定了地球地幔和核心的化学演化。此外，将确定所产生的全球岩浆海洋的冷却/结晶时间尺度，并将其包括在模型中，以用于不同的绝缘大气场景。组合的积聚/分化模型还将使地球建筑材料的组成能够确定原始磁盘中其原始距离的函数。