Seismic tomography, surface uplift, and the breakup of Gondwanaland: Integrating mantle convection backwards in time

Abstract

[1] Mantle density heterogeneities, imaged using seismic tomography, contain information about timedependent mantle flow and mantle structures that existed in the past. We model the history of mantle flow using a tomographic image of the mantle beneath southern Africa as an initial condition while reversing the direction of flow and analytically incorporating cooling plates as a boundary condition. If the resulting (backwards integrated) model for structures is used as a starting point for a forwards convection model, today's mantle can be adequately reconstructed if we do not integrate backwards more than than about 50-75 Ma. Flow can also be reliably reversed through the Mesozoic, but only if instability of the lower boundary layer can be suppressed. Our model predicts that the large seismically-slow and presumably hot structure beneath southern Africa produced 500-700 m of dynamic topography throughout the Cenozoic. Since ̃30 Ma, uplift has moved from eastern to southern Africa, where uplift rates are ̃10 m/Myr, consistent with observations. During the Mesozoic, the modeled topographic high is situated near Gondwanaland rifting, raising the possibility that this buoyant structure may have been involved with this breakup. © 2003 by the American Geophysical Union.