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GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L24307, doi:10.1029/2007GL031067, 2007

Mantle flow and melting underneath oblique and ultraslow mid-ocean ridges

Laurent G. J. Montési

Department of Marine Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA


Mark D. Behn

Department of Marine Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA


Abstract

Mid-ocean ridge morphology correlates strongly with spreading rate. As the spreading rate decreases, conductive cooling becomes more important in controlling ridge thermal structure and the axial lithosphere thickens. At ultraslow spreading rates, the ridge axis becomes sufficiently cold that peridotite blocks are emplaced directly at the seafloor and volcanism is limited to localized volcanic centers widely spaced along the ridge axis. Some slow-spreading ridges adopt an ultraslow morphology when their axis is oblique to the spreading direction. We present an analytical solution for mantle flow beneath an oblique ridge and demonstrate that the thermal structure and crustal thickness are controlled by the effective spreading rate (product of the plate separation velocity and the cosine of obliquity). A global compilation of oblique ridges reveals that ultraslow morphology corresponds to effective half rates less than 6.5 mm/yr, resulting in lithosphere that is thicker than ∼30 km. We conclude that the transition from slow to ultraslow spreading is not related to a change of melt productivity but rather in the efficiency of vertical melt extraction.

Received 20 June 2007; accepted 25 October 2007; published 25 December 2007.

Keywords: mid-ocean ridge; mantle flow; melting.

Index Terms: 3035 Marine Geology and Geophysics: Midocean ridge processes; 8120 Tectonophysics: Dynamics of lithosphere and mantle: general (1213); 3045 Marine Geology and Geophysics: Seafloor morphology, geology, and geophysics; 8416 Volcanology: Mid-oceanic ridge processes (1032, 3614); 1037 Geochemistry: Magma genesis and partial melting (3619).

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Citation: Montési, L. G. J., and M. D. Behn (2007), Mantle flow and melting underneath oblique and ultraslow mid-ocean ridges, Geophys. Res. Lett., 34, L24307, doi:10.1029/2007GL031067.