Friday Seminar (Mar. 8th, 2019) by Prof. H. Iwamori (Division of Earth and Planetary Materials Science)

Earth's mantle constitutes ~70% of the total mass and more than 80% of the heat capacity of the whole Earth's system, in which mantle convection dominates material and thermal evolution of the whole system. Capturing how the convection has occurred and will occur is therefore important. Seismic tomography has revealed the modern snapshot. Another approach utilizes basalts erupted on the surface as a geochemical probe of the mantle, whose distributions in spatial and compositional domains may record the past convective patterns (like “SUMI NAGASHI” (Japanese marbling)) and the differentiation processes associated with convection. Based on the multivariate statistical analyses such as Independent Component Analysis, which are commonly used in machine learning and brain science, we have found an East-West hemispherical structure of the mantle (Iwamori and Nakamura, 2012; 2015; Iwamori et al., 2018). Modeling suggests that it was likely produced by aqueous fluid processes in subduction zones. Based on these, “top-down hemispherical dynamics” is proposed, which is consistent with both global seismic tomography, including the inner core structure, and convection theory of viscous fluid with internal heating (Iwamori and Nakamura, 2015; Iwamori, 2016).