Garcia, X., Seillé, H., Elsenbeck, J., Evans, R. L., Jegen, Marion , Hölz, Sebastian , Ledo, J., Lovatini, A., Marti, A., Marcuello, A., Queralt, P., Ranero, César R. and Ungarelli, C. (2015) Structure of the mantle beneath the Alboran basin from magnetotelluric soundings. Geochemistry, Geophysics, Geosystems, 16 . pp. 4261-4274. DOI 10.1002/2015GC006100.

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Abstract

We present results of marine MT acquisition in the Alboran sea that also incorporates
previously acquired land MT from southern Spain into our analysis. The marine data
show complex MT response functions with strong distortion due to seafloor
topography and the coastline, but inclusion of high resolution topography and
bathymetry and a seismically defined sediment unit into a 3D inversion model has
allowed us to image the structure in the underlying mantle. The resulting resistivity
model is broadly consistent with a geodynamic scenario that includes subduction of
an eastward trending plate beneath Gibraltar, which plunges nearly vertically beneath
the Alboran. Our model contains three primary features of interest: a resistive body beneath the
central Alboran, which extends to a depth of ~150 km. At this depth, the mantle
resistivity decreases to values of ~100 Ohm-m, slightly higher than those seen in
typical asthenosphere at the same depth. This transition suggests a change in slab
properties with depth, perhaps reflecting a change in the nature of the seafloor
subducted in the past.
Two conductive features in our model suggest the presence of fluids released by the
subducting slab or a small amount of partial melt in the upper mantle (or both). Of
these, the one in the center of the Alboran basin, in the uppermost-mantle (20-30km
depth) beneath Neogene volcanics and west of the termination of the Nekkor Fault, is
consistent with geochemical models, which infer highly thinned lithosphere and
shallow melting in order to explain the petrology of seafloor volcanics.

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