Cooling of the Earth's Mantle by Plate Subduction -Importance of Pressure- and Stress-Dependent Rheology-

Abstract

Numerical simulation of 2-D mantle convection with variable viscosity is performed to examine the effect of plate subduction on cooling of the Earth's mantle. We employ temperature-, pressure-, and stress-dependent viscosity in order to realize plate-like motion and subduction of a cold thermal boundary layer at the surface. Our model predicts that the velocity of surface plates strongly depends on the viscosity of the mantle interior, at least when the viscosity of the mantle strongly depends on the pressure. As a result, the heat transfer of the Earth's mantle strongly couples with the temperature, and the Earth cools slowly. This is consistent with past mantle temperatures derived from petrological data. It also suggests the possibility that the Earth has a higher Urey ratio than that inferred from measurements of terrestrial heat flow combined with geochemical data.