Small-Scale Convection in the Earth's Mantle

Abstract

Small-scale convection (SSC) in the Earth‘s mantle contributes to intraplate deformation, heat flow, and volcanism. In this article, I give an overview over the causes and effects of SSC. SSC is a boundary layer instability that is driven by a density inversion, and mostly restricted to low-viscosity layers such as the asthenosphere. The density inversion that supports SSC can be related to thermal and/or chemical stratification. SSC is thought to occur beneath mature oceanic basins to restrict their subsidence and stabilize geothermal heat flux. The onset of SSC is preferentially triggered near lateral heterogeneity such as fracture zones or other steps in lithospheric thickness. SSC may also occur beneath continents, and seismic evidence for related perturbations has indeed been found. Both in continental and oceanic environments, SSC can cause dynamic topography and intraplate deformation, as well as melting of mantle rocks. Mantle melting can boost SSC through a positive-feedback mechanism, and most importantly, feeds intraplate volcanism. While plate tectonics and related natural hazards are mostly caused by large-scale whole-mantle circulation, intraplate geologic activity may be sustained by SSC in the upper mantle.