Constraining the style of magma-ocean crystallisation by present-day Earth structure: a coupled thermodynamic-geodynamic approach

当前地球结构限制岩浆-海洋结晶的方式：热力学-地球动力学耦合方法

• 批准号: NE/X000508/1
• 负责人: Maxim Ballmer
• 金额: $ 61.11万
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FX000508%2F1
• 关键词: Constraining; style; magma; ocean; crystallisation

Earth began life as a globally molten ball, a "magma ocean", following the vast energy release of its accretion. While evidence for such a magma ocean is preserved on the Moon's surface, there is no direct geochemical or geophysical evidence preserved on the Earth's surface.As the magma ocean cooled and froze, crystals settled to form the first solid mantle, and the shrinking magma ocean is thought to have become progressively enriched in iron and e.g. radioactive trace elements. Accordingly, the last droplets of the magma ocean, which ultimately stabilized the first crust on Earth, are thought to be extremely enriched in these elements. The differentiation of the rocky Earth in the magma-ocean stage has far-reaching implications for the long-term evolution of the Earth interior, the dynamics of which sustain life-friendly conditions on its surface. In this project, we propose to address an important, but previously neglected process during magma-ocean crystallization. Recent work has established that the crystal package already undergoes solid-state churning, or convection, while the magma ocean is still in the process of progressive freezing. This convection leads to upwellings of hot material, and the associated pressure decrease will bring about partial melting. However, the consequences of this melting for magma-ocean compositional evolution have not yet been explored. Using newly coupled thermodynamic-geodynamic models, our goal is to quantify these consequences of partial melting of the crystal package, and of related material exchange with the magma ocean. We hypothesize that this exchange completely changes the compositional structure of the first solid mantle and the chemistry of the primary crust. For example, it may reconcile the rather moderate compositional stratification of the present-day Earth mantle, which is not addressed by previous models of magma-ocean crystallization at all. The predictions of our new models will be tested, for example by interrogating the seismic structure of the deep mantle, which may host the remnants of the primary crust.

地球开始生命作为一个全球性的熔融球，一个“岩浆海洋”，随着其吸积的巨大能量释放。虽然月球表面保存了岩浆海洋的证据，但地球表面没有直接的地球化学或地球物理证据。当岩浆海洋冷却和冻结时，晶体沉淀形成第一个固体地幔，收缩的岩浆海洋被认为逐渐富含铁和放射性微量元素。因此，岩浆海洋的最后一滴，最终稳定了地球上的第一个地壳，被认为是在这些元素中非常丰富。岩石地球在岩浆-海洋阶段的分化对地球内部的长期演变具有深远的影响，地球内部的动态维持着地球表面适宜生命的条件。在这个项目中，我们建议解决一个重要的，但以前被忽视的过程中岩浆海洋结晶。最近的工作已经确定，晶体包已经经历了固态搅动，或对流，而岩浆海洋仍在逐步冻结的过程中。这种对流导致热材料的上升，并且相关联的压力降低将导致部分熔化。然而，这种熔融对岩浆海洋成分演化的影响尚未被探索。使用新耦合的地球动力学模型，我们的目标是量化这些后果的部分熔融的晶体包，以及相关的物质交换与岩浆海洋。我们假设，这种交换完全改变了第一固体地幔的组成结构和原生地壳的化学成分。例如，它可以调和现今地幔相当温和的成分分层，这是以前的岩浆海洋结晶模型根本没有解决的问题。我们的新模型的预测将被测试，例如，通过询问深地幔的地震结构，它可能容纳原始地壳的残留物。

项目成果

Multi-scale anisotropy in NE China: Evidence for localized mantle upwelling

• DOI: 10.1016/j.epsl.2023.118495
• 发表时间: 2024-01
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Cunrui Han;James O.S. Hammond;M. Ballmer;Wei Wei-Wei;Mijian Xu;Zhouchuan Huang;Liangshu Wang