loading page

Modelling mantle geodynamics in the Ethiopian Rift and Afar through olivine thermometry and rare-earth element distributions
  • +3
  • Kevin Wong,
  • David Ferguson,
  • Dan Morgan,
  • Simon Matthews,
  • Amdemichael Tadesse,
  • Gezahegn Yirgu
Kevin Wong
University of Leeds

Corresponding Author:[email protected]

Author Profile
David Ferguson
University of Leeds
Author Profile
Dan Morgan
University of Leeds
Author Profile
Simon Matthews
University of Iceland
Author Profile
Amdemichael Tadesse
Université Libre de Bruxelles
Author Profile
Gezahegn Yirgu
Addis Ababa University
Author Profile


The Ethiopian sector of the East African Rift system (the Main Ethiopian Rift, MER) and Afar rift showcase advanced stages of continental breakup. Here the interplay between active continental rifting and rift-induced volcanism poses key questions regarding the mantle geodynamics of late-stage rift development. A particular subject of interest is the presence of hot mantle upwellings in the sub-rift mantle, which are inferred from geophysical imaging. Magma generation in the sub-rift asthenosphere depends on the temperature, lithology, and composition of the upwelling mantle material. Geophysical observations of the sub-rift mantle must therefore be supported by petrological studies aimed at understanding the physico-chemical conditions of melt production. In this study we investigate melt generation beneath the MER and Afar using a mantle melting model constrained by olivine crystallization temperatures and rare-earth element (REE) concentrations, both observed in rift zone lavas. Olivine crystallization, a proxy for magma liquidus temperature, is directly related to the thermodynamic and geochemical conditions of the melting mantle. Through application of an olivine-spinel aluminium exchange thermometer, we provide the first petrological olivine crystallization temperatures for MER and Afar basalts (1177±16°C and 1263±43°C respectively). A multi-lithology mantle melting model subsequently allows for inversion of our olivine crystallization temperatures and observed REE concentrations of rift magmas to estimate the temperature, lithology, and composition of the Ethiopian mantle. Our results suggest that the crystallization temperatures and REE distributions measured at the MER and Afar necessitate elevated mantle temperatures (Tp ≥ 1450 °C) relative to ambient mid-ocean ridge mantle. A thick mantle lithosphere (~60 km) is also required to provide deep garnet-field mantle melting inferred from REE distributions. We additionally conclude that an enriched and fusible pyroxenitic mantle component is necessary to match crustal melt thicknesses and observed REE concentrations. The composition of this pyroxenitic lithology is further explored through our inversions, and the contributions of enriched pyroxenitic melts to rift volcanism in the MER and Afar are subsequently compared.