The origin of large scale structure in mantle convection: Effects of plate motions and viscosity stratification

Abstract

Convection in Earth's mantle is dominated by long‐wavelength structure, as evidenced by the very “red” spectra of both seismic velocity heterogeneity in the deep mantle and the non‐hydrostatic gravity field, or geoid. Here we show that this large‐scale structure may be a consequence of two factors that influence the scale of mantle convection. First, the existence of surface plates, which tend to organize the flow. Second, a substantial increase in lower mantle viscosity for which there is considerable independent geophysical evidence. Combining these two factors in 3‐D spherical mantle convection models explains rather well the observed seismic spectrum of mantle heterogeneity.