Description: 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.

Description: Processes near the Earth’s surface are linked to the deep mantle and core. From plate reconstructions, we can infer where slabs have been subducted through geologic time and the distribution of slabs throughout the mantle, which can be compared with seismic tomographic images. When slabs approach the core-mantle boundary (CMB), they push the thermal boundary layer ahead, leading to large lateral variations in heat flux from the core to the mantle: Beneath regions of subduction, we compute heat flux of several hundred mW/m2, whereas in areas where hot material has resided for long times, it is 〈 10 mW/m2. CMB heat flux likely influences the geodynamo, yet we are only beginning to understand such core-mantle processes. Seismology indicates there are large domes of geochemically distinct materials in the lowermost mantle which possibly represent old oceanic crust that was subducted during the billions of years of plate tectonics. Hot mantle plumes are mainly generated from the margins of lower mantle heterogenieties, where hot material pushed ahead of slabs is forced to rise. The largest and hottest plumes entrain a large amount (up to 20 %) of the former oceanic crust and carry it to the base of the lithosphere. This material has lower melting temperature than “normal” peridotitic mantle and contains huge amounts of CO2, HCl and other components that are toxic for the environment. Mantle plumes rich in such material produce exceptional volume of melts and cause extreme pollution of the atmosphere and hydrosphere. This happened 252 Mln years ago, when millions of cubic km of lava were erupted in Siberia in the time of a few hundred thousand years or less. That led to the Permo-Triassic mass extinction, the largest environmental catastrophe in Earth history when more than 90 % of all species on land and in the ocean became extinct.