The initiation of segmented buoyancy driven melting during continental breakup

Posted by pkm at Mar 06, 2015 09:30 PM |
Ryan J. Gallacher (1), Derek Keir (1), Nicholas Harmon (1), Graham Stuart (2), Sylvie Leroy (3), James O. S. Hammond (4), J-Michael Kendall (5), Atalay Ayele (6), Berhe Goitom (5) & Ghebrebrhan Ogubazghi (7) - (1) University of Southampton, Southampton, UK; (2) School of Earth and Environment, University of Leeds, Leeds, UK; (3) ISTEP, Institut des Sciences de la Terre Paris, CNRS UPMC, Paris, France; (4) Department of Earth Science and Engineering, Imperial College London, London, UK; (5) School of Earth Sciences, University of Bristol, Bristol, UK; (6) Institute of Geophysics, Space & Astronomy, Addis Ababa University, Addis Ababa, Ethiopia; (7) Eritrea Institute of Technology, Asmara, Eritrea

Melting of the mantle during continental breakup leads to magma intrusion and volcanism, yet the locus and dominant cause of melt production remains poorly constrained due to the paucity of direct observations. Additionally, it is unclear at what stage during the rifting process the segmented nature of magma supply typical of seafloor spreading initiates. We use Rayleigh-wave tomography to construct the first high-resolution absolute 3-dimensional shear-wave velocity model of the upper 250 kilometres beneath Ethiopia in order to image the response of the mantle during progressive continental breakup. Our model suggests melt production is highest and melting depths are deepest early during the breakup process and decrease through to full breakup. Elevated melt production during continental rifting is likely due to localised plate thinning and melt focusing when the rift is narrow. Additionally, we find segmented zones of melt supply beneath the rift, indicating that buoyancy driven active upwelling of the mantle initiates early during continental rifting and persists through to full seafloor spreading.

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