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Volcanism in the Afar Rift sustained by decompression melting with minimal plume influence


Continental breakup is caused by some combination of heating and stretching1,2. The Afar Rift system in Africa is an example of active continental rifting, where a mantle plume probably weakened the lithosphere through thermal erosion and magma infiltration. However, the location and degree of plume influence today are debated2,3. Here we use seismic S-to-P receiver functions to image the mantle structure beneath Afar. We identify the transition between the lithosphere and underlying asthenosphere at about 75 km depth beneath the flanks of the continental rift. However, this boundary is absent beneath the rift itself and we instead observe a strong increase in seismic velocities with depth, at about 75 km. We use geodynamic modelling to show that the velocity increase at this depth is best explained by decompression melting of the mantle in the absence of a strong thermal plume. So, although the absence of mantle lithosphere beneath the rift implies a plume may have once been active, we conclude that the influence of a thermal plume directly beneath Afar today is minimal.

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Figure 1: Stations, bins and phase polarity at 75 km depth from simultaneous deconvolution.
Figure 2: Cross-sections from extended multitaper and migration.
Figure 3: Summary and waveform modelling.

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We acknowledge financial support for personnel and data acquisition and analysis from the Natural Environment Research Council, UK (NE/E005284/1, NE/G013438/1 and NE/E007414/1) and the National Science Foundation, USA (EAR-0635789). Additional data came from the Incorporated Research Institutions for Seismology Data Management Center. We thank everyone who helped with the field work. This work would not have been possible without the continued support and collaboration from the University of Addis Ababa, for which we are very appreciative.

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Authors and Affiliations



C.A.R. developed the seismic methodology, carried out imaging and modelling and wrote the paper. N.H. carried out geodynamic modelling and corresponding seismic predictions. N.H. and C.A.R. developed the interpretations and decompression melting hypotheses and made the figures. J.O.S.H. compiled data and provided advice on stations, Moho structure and migration. J.M.K. initiated the project. J.M.K., J.O.S.H., C.E., D.K., I.D.B. and M.B. provided advice on regional tectonics and geodynamics. All authors discussed results and commented on the manuscript.

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Correspondence to Catherine A. Rychert.

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The authors declare no competing financial interests.

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Rychert, C., Hammond, J., Harmon, N. et al. Volcanism in the Afar Rift sustained by decompression melting with minimal plume influence. Nature Geosci 5, 406–409 (2012).

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