shear-induced metal segregation in ordinary chondrites: implications for planetary core formation

这个项目涉及不断增长的行星体中核心的形成过程。样品材料是一块陨石(严格地说是H6普通球粒陨石)，它含有Ni-Fe-S形式的“金属”。目前，我们基于实验的理解是，在非静力条件下，变形机制(剪切)为液态金属偏析提供了局部高渗透通道，而不受表面张力的影响。变形在部分熔融的硅酸盐基质中促进偏析(有时称为渗流)的作用挑战了长期以来的观点，即在行星体内形成核心需要岩浆海洋。然而，到目前为止，只对自然样品进行了少量的实验室实验。尽管它们很重要，但这些实验无法提供有关剪切过程中液态金属运输的详细流体动力学的可靠信息，也无法对岩心地层中变形驱动的多孔流动的更广泛规模的影响发表重大评论，而不是通过推测。所需的信息水平只能从数值模拟中获得。然而，实验确实提供了关键的纹理和几何信息，并在自然样品中提供了与孔隙尺度流动有关的地球化学数据。我们提供了一种组合方法，使用在实验室条件下变形的真实陨石的纹理数据作为我们的数值模型的输入数据。这一结果将使我们能够在更广泛的行星核形成背景下探索铁金属硅酸盐熔体分离的微观物理和化学后果。

This project is concerned with the process of core formation in growing planetary bodies. The sample material is a meteorite (technically an H6 ordinary chondrite) that contaims 'metal' in the form Ni-Fe-S. Presently, our understanding based on experiments is that under non-hydrostatic conditions, deformation mechanisms (shearing) provide local high permeability pathways for liquid metal segregation independent of surface tension effects. The role of deformation in promoting segregation (sometimes referred to as percolation) in a partially-molten silicate matrix challenges the long-standing idea that core formation in planetary bodies requires a magma ocean. However, only a small number of laboratory experiments on natural samples have been done to date. As important as they are, these experiments cannot provide robust information on the detailed fluid dynamics of liquid metal transport during shear, nor comment significantly on the wider scale implications of deformation driven porous flow in core formation other than through speculation. The required level of information can only be obtained from numerical modelling. Experiments do however provide critical textural and geometrical information and in natural samples, geochemical data pertinent to pore-scale flow. We offer a combined approach that uses textural data from real meteorites, deformed under laboratory conditions, as input data for our numerical models. The result will allow us to explore the microscale physics and chemical ramifications of Fe metal-silicate melt segregation in the wider context of planetary core formation.