[S-IT14] Deep Earth Sciences

[SIT14-P19] Structures and mechanical stabilities of various kinds of melts under the ULVZ condition based on first-principles calculations

*Kan Kitano¹, Taku Tsuchiya^1,2 (1.Faculty of science,Ehime University , 2.Geodynamics Research Center)

Keywords:First principles MD calculation, Ultra Low Velocity Zones, Physical properties of melts

At the core-mantle boundary (CMB) in the deep Earth, there are seismically observed ultra-low velocity zones (ULVZ), which have been proposed to be caused by the existence of melts (e.g., Garnero et al., 1998). If the partially molten mantle is the cause of the ULVZ, the magma must be mechanically stable under the CMB condition and have a density intermediate between those of the core and the mantle. It however remains unclear what chemical composition would produce such a dense magma and what is the nature of ULVZ. Several questions still unresolved since it is quite difficult to experimentally measure the physical properties of liquids under the CMB condition (pressure 135.8 GPa, temperature 4000-5000 K). Therefore, in this study, we quantitatively determine the densities and atomic structures of melts in several different rock compositions including pyrolite, MORB, KREEP basalt, etc. using the first-principles MD method. By comparing calculated physical propaties, the major factors that control the densities of melts under the CMB condition are discussed, and these factors are applied to constrain the composition of the ULVZ which have appropriate densities.