Effect of Rheological Structure on Flow Patterns Driven by Density Anomaly in the Mantle

Abstract

A new model is employed to investigate the effects of viscous structures on the convection patterns in the mantle, which is driven by density anomaly and plate motion. We use the seismic tomography models of Grands and S12-WM13 to estimate the density distribution in the mantle and take the 660 km discontinuity as a boundary between the upper and lower mantle. We take ρ=5500kg/m3 as the average density of the mantle and μ=1021Pa·s as the average viscosity of the upper mantle and calculate the convection patterns of the mantle with different viscous rations of 1, 10, 100 and 1000 between the lower and upper mantle. Computation results show that when the viscous ration between lower and upper mantle is more than 100 the flow speed in the lower mantle decreases obviously. But the convection patterns still exhibit a single cell style and not layered. This feature suggests that there is a large scale convection in the mantle. The relationship between convection patterns and global tectonics is also discussed in this paper.