Volcanism in the Afar Rift sustained by decompression melting with minimal plume influence, Rychert et al 2012

Non-technical summary

Continental breakup is caused by some combination of heating and stretching of the crust and uppermost mantle (the lithosphere). The Afar Rift system in Africa is an example of active continental rifting, where a mantle plume (a plume of unusually hot material rising towards the surface from the core-mantle boundary) weakened the lithosphere through heating and magma infiltration. The presence of the plume ~30 million years ago can be seen in the geochemistry of the flood basalts on the Ethiopian plateau. However, the location and degree of plume influence on volcanism today are debated.

Here we use seismic receiver functions to image the mantle structure beneath Afar. A receiver function is produced by processing information on how seismic waves, generated by earthquakes, interact with boundaries (such as the base of the crust or lithosphere) beneath a seismometer. The velocity of the seismic waves relates to the temperature and the amount of partial melt in the rocks they pass through. Our results show the best model for the data is of magma ponding under the lithosphere beneath the rift margins. However, beneath Afar the mantle lithosphere has been removed, and replaced by upwelling and melting. The depth of the onset of melting beneath Afar suggests that a strong temperature anomaly does not exist. This indicates, that whilst a plume was present beneath Afar as rifting was initiated, it is no longer active today.

Cross section through Afar depths of the lithosphere, asthenosphere and the location of melts and partial melting

Figure 1: Cross section through the Afar Rift system showing depths of the lithosphere, asthenosphere and the location of melts and partial melting

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