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保持海洋和大气层的方式。现在已经确定的是，过渡带（410至660公里深的一层）可能含有大量的水，如果过渡带有大量的水，那么富含水的物质从该地区向上进入上地幔或向下进入下地幔将引起部分熔融。如果熔化发生，物质的化学成分将被改变，这对这个星球的化学演化有重要的影响。在这个提议中，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之间边界附近的熔融性质。 下地幔的熔融只有在某些挥发性（不相容）元素（如氢和碳）存在时才会发生。当挥发物（例如氢）的量超过临界值时，则应发生部分熔融。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）下地幔中金属铁的量。这两个因素目前都没有受到矿物物理实验的约束，研究人员建议进行实验工作以更好地了解这些过程。部分熔融的后果取决于熔体的密度（相对于共存矿物）及其几何形状（二面角），该团队计划对这些问题进行理论和实验研究。同样重要的是地震学对融化的探测。在这个项目中，该团队计划进行地震学研究，使用频率相关和各向异性的接收器函数来调查融化的证据。结合这些研究，跨学科团队将调查过渡带-下地幔边界附近地幔中挥发性物质传输的性质。

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.