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A mantle magma reservoir beneath an incipient mid-ocean ridge in Afar, Ethiopia

Nature Geoscience volume 6, pages 861–865 (2013)Cite this article

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Abstract

Shallow magma reservoirs exist in the crust beneath volcanoes and mid-ocean ridges, yet there are no reports of extensive magma bodies within the uppermost mantle. Indeed the buoyancy of magma should cause it to intrude into the crust, preventing it from ponding in the mantle below. The Dabbahu magmatic segment in Afar, Ethiopia, marks the late stages of continental rifting. This segment has been active since 2005 and has experienced repeated magma intrusions1,2,3,4,5,6. Here we use magnetotelluric data to image magma bodies beneath it. We identify a 30-km-wide region of very high electrical conductivity that reaches down to about 35 km depth. We interpret this region as a large volume of magma of at least 500 km3 that extends well into the mantle and contains about 13% melt fraction. The magma volume is orders of magnitude larger than that intruded during a typical rifting episode, implying that the magma reservoir persists for several tens of thousands of years. This is in marked contrast to the situation beneath mid-ocean ridges, where melt supply is thought to be episodic7,8,9,10,11. Large magma reservoirs within the mantle may therefore be responsible for the localization of strain that accompanies the final stages of continental break-up.

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Figure 1: Tectonic setting of the area and magnetotelluric site distribution.
Figure 2: Data pseudo-sections and their predictions by the preferred model.
Figure 3: Preferred 2D resistivity model beneath the profile from joint inversion of the transverse electric and transverse magnetic mode data.

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  • 06 September 2013

    In the version of this Letter originally published online, the published online date should have read '5 September 2013'. This has been corrected in the PDF and HTML versions of the Letter.

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Acknowledgements

This research has been supported financially by NERC (grant NE/E007147/1 and PhD studentship for N.E.J.), the School of GeoSciences (MSc by Research MTEM Partial Scholarship to M.D.), CNRS (financial support for S.H.), and in-kind by equipment loans from the NERC Geophysical Equipment Facility (GEFSC loans 855 and 907), and the Geophysical Instrument Pool Potsdam (part of GeoForschungsZentrum) through the auspices of O. Ritter and U. Kalberkamp (BGR, Hannover). The Institute for Geophysics, Space Science and Astronomy, Addis Ababa University and the Geological Survey of Ethiopia are thanked for logistical support, as is Y. Lemma for help with the fieldwork. Helicopter access to the rift was provided by C. Stewart, Everett Aviation. We also acknowledge discussions with and results in advance of publication from Afar Rift Consortium colleagues and Project Partners, in the UK, Ethiopia, USA and New Zealand.

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Author notes

  1. M. Desissa

    Present address: Present address: Geological Survey of Northern Ireland, Colby House, Stranmillis Court, Belfast BT9 5BF, UK,

Authors and Affiliations

  1. School of GeoSciences, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, UK

    M. Desissa, N. E. Johnson, K. A. Whaler & G. J. K. Dawes

  2. Imagir, IUEM, 29280 Plouzané, France

    S. Hautot

  3. Institute of Geophysics, Space Sciences and Astronomy, Addis Ababa University, Addis Ababa, Ethiopia

    S. Fisseha

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Contributions

All authors participated in the fieldwork. M.D., S.H. and N.E.J. processed the data. M.D. and N.E.J. analysed their dimensionality and corrected for galvanic distortion. M.D., N.E.J. and S.F. performed 2D inversions. G.J.K.D. designed and constructed the data recording systems. K.A.W., S.H. and N.E.J. undertook most of the model interpretation, including estimating melt fractions and volumes. K.A.W. obtained the financial support, and wrote the article (with comments from co-authors).

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Correspondence to K. A. Whaler.

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The authors declare no competing financial interests.

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Desissa, M., Johnson, N., Whaler, K. et al. A mantle magma reservoir beneath an incipient mid-ocean ridge in Afar, Ethiopia. Nature Geosci 6, 861–865 (2013). https://doi.org/10.1038/ngeo1925

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