High-pressure-temperature phase relations of basaltic crust under lower-mantle conditions: implications for chemical heterogeneity in the lower mantle

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The chemical structure of the lower mantle remains under debate. The fate of subducting slabs is a key to answering the debate. In order to constrain dynamics of subducting slabs, phase relations of MORB under lower mantle conditions will be determined at pressures up to 50 GPa and temperatures of 1700, 2000 and 2300 K by means of the applicant’s original novel high-pressure generation technology of a Kawai-type multi-anvil press with tungsten carbide anvils. Using the compositions and proportions of constituent minerals in the MORB system determined in this project, density and seismic wave velocities of basaltic crust will be estimated. Based on these investigations, the roles of basaltic fragments of subducted slabs in mantle dynamics and possibility of the seismic detection of such fragments will be discussed.