AAPG Middle East Region Geoscience Technology Workshop, Rift Basin Evolution and Exploration

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Mantle Convection and Africa's Rift architecture: A General Model


A simple model of mantle convection is introduced that seeks to provide a mechanism for both the formation and development of the key structural characteristics observed on Africa's passive margins that allows extension to a general model for passive margin development. The basins on the passive margins of West and East Africa can be characterized in terms of their magmacity and the style of the syn-rift. Mapping out the basin character reveals both irregular spatial heterogeneiity along the margin, and asymmetry between conjugates. During rifting, style of extension reflects the supply of heat to the rift. Hot rifts have abrupt terminations to continental crust, narrow syn-rift margins, and often have wide seaward dipping reflector domains (SDRs). Cold rifted margins are wider, often display thick and wide syn-rift sections, and may become hyper-extended where serpentinized mantle is exposed at sea bed. Such margins are not associated with SDRs. During drifting, volcanism is either sub areal (flood basalts that build SDR complexes) or sub aqueous (sub marine or sub lake level), and the degree of "margin magmacity" reflects the position of the volcanic eruption relative to water level. We propose that the structure and character of both syn-rift and post-drift domain is controlled by the fabric of the underlying convecting mantle as revealed by dynamic topographic analysis. This is now represented globally, comprising numerous small scale mantle convection cells. This fabric provides topology to the rift laterally along a rift, controlling the development of either so called “magma-rich” or “magma-poor” domains, which are an expression of spreading centre elevation relative to sea level. These convection cells also provide heat to rifting processes that lead either to the development of abrupt margins, wide syn-rift domains or hyperextended crust. A model relating mantle convection to dynamic topography to observed asymmetry and rifting styles is proposed, and tested against observations of basin shelf and slope stability back through time in the context of plate tectonic movement. This allows some constraints to be placed on the stability of mantle convection cells and their interaction with the overlying crust.