Global coupling of Earth surface topography with hotspots, geoid and mantle heterogeneities

Abstract

REMARKABLE global correlations exist between the Earth's gravity field (the geoid), hotspot distribution and lower-mantle heterogeneities. The geoid has two conspicious long-wavelength highs centred on the Equator 180° apart ('degree 2 pattern'), which contain most of the world's hotspots^1-4. Seismic tomography of the lower mantle has revealed that low-velocity, presumably hot, regions are positively correlated with hotspot concentration and geoid highs^4-7. In a viscous, convective Earth, correspondence between geoid highs and hot (low-density) mantle implies dynamical uplift of mantle boundaries, particularly the Earth's surface^8,9. The gravitational effect of the surface deformation caused by the convective flow is opposite in sign and comparable in magnitude to that arising from the deep density contrast; geoid anomalies result from these mutually opposing contributions in a manner that depends critically on the dynamics of the mantle, that is, on viscosity stratification and style of convection. Here we show that the global surface topography, once corrected for shallow density variations inside the lithosphere, presents a strong degree 2 pattern, with uplifted regions well correlated with hotspot concentration, geoid highs and hot lower mantle. This long-wavelength topography probably represents the dynamic response of the Earth's surface to mantle convection; used together with geoid and seismic velocity anomalies, it should provide an important constraint on convection models.