高圧下でのマグマ物性：地球深部でのマグマの挙動解明

抄録

Magma has been deeply related to the evolution and dynamics of the Earth from the magma ocean in the early Earth to present magmatism. Especially, a hot topic is a pressure-induced change in the property/structure of magma and its correlation to the macroscopic property and microscopic structure, with the goal of understanding the deep magma. This article introduces our studies about high-pressure measurements of magma properties with focusing on three topics. First one is the gravitational stability of hydrous magma at the base of the upper mantle based on density measurements at high pressure. Our results indicated a rapid reduction of the partial molar volume of H₂O in magma with pressure, which causes enough densification of hydrous magma to be stagnant. Second, we proposed the ponded magma model at the lithosphere-asthenosphere boundary due to a decrease in the segregation rate. This model can illustrate the geophysically observed anomaly around the boundary. For density measurement of magmas under desired conditions, we succeeded in applying an X-ray absorption technique, which could provide a better understanding of magma behavior. Last topic is lunar magmatism. Compression behavior of lunar basaltic magma with high TiO₂ content indicated the density crossover between the magma and lunar mantle at a certain depth. Based on this result, subducted magma could create lateral chemical heterogeneities in the lunar mantle and, moreover, it could form the low-velocity/low-viscosity layer at the base of lunar mantle.