Sensitivity to initial CMB temperature of structure and evolution of the Earth's mantle and core based on 3-D spherical models of thermo-chemical mantle convection

The early thermal state of the Earth, just after core-mantle differentiation, is expected to be extremely high temperature, especially the temperature of the core, hence core-mantle boundary (CMB). To understand the evolution of the coupled core-mantle system, it is therefore important to test the effect of extremely high initial CMB temperature, which our previous studies did not do [e.g., Nakagawa and Tackley, 2005]. Here a range of 4500 K to 6000 K for the initial CMB temperature is used to investigate the thermal history of the Earth's mantle and core using 3-D spherical mantle convection models with yielding-induced place tectonics and a parameterized core heat balance, focusing particularly on the time-scale for formation of compositional anomalies near the CMB and the parameter combinations that lead to the correct present day inner core boundary (ICB) temperature. Preliminary results are as follows: 1. The final CMB temperature and heat flux are likely to converge a certain range regardless of initial CMB temperature, 2. The time scale for formation of compositional anomalies in the CMB region is likely to be longer when the initial CMB temperature is extremely high because then plume activity is more vigorous and entrains compositionally-anomalous material. In this presentation, we will also investigate the plausibility of the Basal Magma Ocean hypothesis, so far investigated using only simple models [Labrosse et al., 2007], in more realistic mantle convection models with core-cooling and realistic mineral physics.