Effect of Hydrous Mantle on a Coupled Core-Mantle Evolution

Abstract:

The water in the mantle is also important for dynamics, evolution, composition and structure of deep Earth’s interior [e.g. Karato, 2011]. However, the hydrous mantle was not assumed for thermo-chemical evolution model in numerical mantle convection simulations [e.g. Nakagawa and Tackley, 2014]. To assess the effect of hydrous mantle in thermo-chemical evolution of deep Earth’s interior, we develop a coupled core-mantle evolution model including water transportation system based on Iwamori [1998; 2004]. The important ingredient of this model is the rheological property of hydrous mantle and dehydration processes. Here we assume this taken from deformation experiments on hydrous olivine [e.g. Mei and Kohlsteadt, 2000; Korenaga and Karato, 2008; Fei et al., 2013], which ranges from weak to extremely strong viscosity dependence due to the water content. We also assume the reduction of solidus temperature of mantle minerals based on Katz et al. [2003].

Preliminary results suggested that the best-fit scenario of thermo-chemical evolution of Earth’s mantle and core could be found in the weak rheological dependence due to the water content. In the successful model, the lower mantle would be close to water-saturated situation less than 1.0 Gyrs from initial condition assuming the completely dry mantle. In the presentation, we will also discuss the possibility on hydrous basalt in the lowermost mantle and geochemical evolution in the deep mantle.