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

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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.