The effect of shearing on the onset and vigor of small‐scale convection in a Newtonian rheology

Abstract

As an oceanic plate cools with time, the bottom part of the plate may undergo gravitational instabilities and lead to sub‐lithospheric small‐scale convection (SSC). While numerous previous studies have examined the dynamics of SSC below a fixed top boundary, in this study we investigate the effects of shearing due to plate motion on the onset and time evolution of SSC with 2‐D and 3‐D finite element models with a prescribed surface plate motion and a Newtonian rheology. Our 3‐D models show that plate motion moderately enhances the SSC that displays plate‐motion‐parallel convective roll‐structures. However, plate motion significantly hinders SSC in 2‐D models with plate motion that produces plate‐motion‐perpendicular convective roll‐structures. In spite of moderate influences of plate motion on the dynamics of SSC, our results suggest that for Newtonian rheology the onset time of SSC predicted from previous studies with a fixed top boundary is to the first order valid.