Manteldynamik und das Aufbrechen von Gondwana

Abstract

Southern Africa was part of Gondwanaland until the Mesozoic, when this supercontinent broke up into fragments that evolved into today’s southern continents. In particular, around 140 Ma, rifting started between southern Africa and South America, followed by the opening of the South Atlantic after ~130 Ma. What caused this breakup is a subject of ongoing research. In particular, it is unclear whether, and to what extent, plumes from the deep mantle are a cause for, or at least assisted in the breakup, or whether, on the contrary, the flood basalt provinces attributed to plumes are a consequence of breakup. The Paraná and Etendeka flood basalts erupted ~132 Ma ago at a location nearly vertically above the margin of the African “Large Low Shear Velocity Province” in the lowermost mantle, indicative of a deep mantle plume. Plate reconstructions show that the plume was initially beneath the South American plate, but close to the breakup location, such that plume material could flow to and erupt at the developing spreading ridge. The plume was overridden by the ridge at ~90 Ma and has been under the African plate ever since. Plume-lithosphere interaction can also be addressed through active seismic surveys on land, and in combination with petrologic and geochemical studies of the flood basalts and dyke swarms, this work has led to many important new insights. In particular, it has been shown that mantle temperatures beneath Etendeka province were about 150 °C higher than the global mid-oceanic ridge average, thus further supporting the mantle plume hypothesis.