CSEDI Collaborative Research: Understanding the nature of water and melt transport between the transition zone and the lower mantle combining mineral physics and seismology

水和其他挥发性成分在地球内部循环，这种循环控制着地球将海洋和大气保持在表面的方式。现在已经确定，过渡带（410至660公里深度之间的一层）可以包含大量的水，如果过渡带有大量的水，那么从该区域向上输送到上地幔或向下输送到下地幔的富水物质将引起部分熔融。如果发生熔融，物质的化学成分将发生改变，这对地球的化学演化具有重要意义。在本研究中，我们将通过矿物物理学和地震学等跨学科的方法来研究过渡带和下地幔边界附近的熔融性质。只有当一些挥发性（不相容的）元素（如氢和碳）存在时，下地幔才会熔化。当挥发物（如氢）的数量超过临界值时，就会发生部分熔化。确定该值的关键因素是(a)水（氢）在下地幔矿物中的溶解度和(b)下地幔中金属铁的含量。目前矿物物理实验对这两个因素的约束都很差，研究人员建议开展实验工作以更好地了解这些过程。部分熔融的结果取决于熔体的密度（相对于共存的矿物）和它的几何形状（二面角），研究小组计划对这些问题进行理论和实验研究。同样重要的是对熔化的地震探测。在这个项目中，研究小组计划进行一项地震学研究，利用频率相关和各向异性接收函数来调查融化的证据。结合这些研究，跨学科团队将研究过渡带-下地幔边界附近地幔挥发性输运的性质。

Water and other volatile components circulate in the Earth's interior and this circulation controls the way in which Earth keeps its oceans and atmosphere on its surface. It is now well established that the transition zone (a layer between 410 to 660 km depth) can contain a substantial mount of water, and if the transition zone has a large amount of water, then the transportation of water-rich materials from that region up into the upper mantle or down to the lower mantle would induce partial melting. If melting occurs, chemical composition of materials will be modified and it has an important implication for the chemical evolution of this planet. In this proposal, we will investigate the nature of melting near the boundary between the transition zone and the lower mantle through an interdisciplinary approach including mineral physics and seismology. Melting in the lower mantle occurs only when some volatile (incompatible) elements (such as hydrogen and carbon) are present. When the amount of volatiles (such as hydrogen) exceeds a critical value, then partial melting should occur. The critical factors that define this value are (a) the solubility of water (hydrogen) in the lower mantle minerals and (b) the amount of metallic Fe in the lower mantle. Both of these factors are poorly constrained by mineral physics experiments at present, and the investigators propose to conduct experimental work to better understand these processes. The consequence of partial melting depends on the density of melt (relative to the co-existing minerals) and its geometry (dihedral angle), and the team plans to conduct theoretical and experimental studies on these issues. Also important is seismological detection of melting. In this project, the team plans to conduct a seismological study to investigate the evidence of melting using the frequency-dependent and anisotropic receiver functions. Combining these studies, the interdisciplinary team will investigate the nature of volatile transport in the Earth's mantle near the transition zone-lower mantle boundary.