Crystallizing the terrestrial magma ocean: thermo- and geodynamics

可能起源于月球形成撞击的岩浆海洋的冷却和结晶决定了固体地幔的初始热结构和化学结构，从而决定了随后受热成分对流控制的内部演化的条件。要对岩浆海洋结晶产生的成分进行模拟，需要详细描述整个地幔压力范围内的液线和相图、主要元素在晶体和熔体之间的分配系数以及残留液体和新形成的固体的密度。我们将通过有针对性的多顶锤高压实验，将熔融相关系的热力学模型推广到FeO-MgO-SiO_2(FMS)和CaO-MgO-SiO_2(CMS)系统。重点将放在在FeO存在的情况下更好地约束共晶MgSiO_3一侧的液相线，并获得可靠的关于CMS系统中共晶的数据，在该系统中存在Low的所有主要相：方镁石、布里奇曼石和钙钙钛矿。这些实验还将被用来确定熔体和下地幔相之间的分配系数，特别是铁的分配系数。附加的约束条件将被纳入岩浆海洋的分离结晶模型，建立陆地岩浆海洋的结晶序列和密度结构。新获得的关于CMS、FMS和含Al_2O_3的地幔成分中熔体密度的MD结果将被包括在内，以计算结晶岩性的浮力。由此产生的密度分层将为我们提供地幔凝固后立即热状态和成分状态的物理和化学上一致的图景，并将作为内部动力学数值模型的新起点。我们将利用这些模型来模拟整个地球历史上地幔和核的耦合演化，并从一个新的角度描述基本过程，如板块构造和磁场产生的开始和维持，以及大规模地球化学库的形成和随后的混合。

Cooling and crystallization of the magma ocean that likely originated from the Moon-forming impact set the initial thermal and chemical structure of the solid mantle and thus the conditions for the subsequent evolution of the interior controlled by thermo-compositional convection. Modelling of the composition resulting from magma ocean crystallization requires a detailed description of the liquidus and phase diagram - over the entire mantle pressure-range-, of the distribution coefficients of major elements between crystals and melts, and of the density of residual liquids and newly formed solids. We will extend thermodynamic models of melting phase relations in the MgO-SiO2 system to the FeO-MgO-SiO2 (FMS) and CaO-MgO-SiO2 (CMS) systems by performing targeted multianvil high-pressure experiments. The focus will be on better constraining the liquidus on the MgSiO3 side of the eutectic in the presence of FeO and to obtain reliable data on the eutectic in the CMS system in which all major phase of the lower exists: periclase, bridgmanite and Ca-perovskite. These experiments will also be used to establish partition coefficients, in particular of Fe, between the melt and lower mantle phases. The additional constraints will be incorporated into a model of fractional crystallization of the magma ocean, establishing the crystallization sequence and the density structure of the terrestrial magma ocean. Newly obtained MD results on melt densities in the CMS, the FMS and Al2O3-bearing mantle compositions will be included to compute buoyancy of crystallizing lithologies. The resulting density stratification will provide us with a physically and chemically consistent picture of the thermal and compositional state of the mantle immediately after its solidification and will serve as a novel starting point for numerical models of the dynamics of the interior. We will employ these models to simulate the coupled evolution of the mantle and core over the entire history of the Earth and characterize from a new perspective fundamental processes such as the onset and maintenance of plate tectonics and magnetic field generation, and the formation and subsequent mixing of large scale geochemical reservoirs.