Geochemical zonation of the Miocene Alboran Basin volcanism (westernmost Mediterranean):: geodynamic implications

We present new major and trace element and O-Sr-Nd-isotope data for igneous rocks from the western Mediterranean Alboran Sea, collected during the METEOR 51/1 cruise, and for high-grade schists and gneisses from the continental Alboran basement, drilled during the Ocean Drilling Programme (ODP Leg 161, Site 976). The geochemical data allow a detailed examination of crustal and mantle processes involved in the petrogenesis of the lavas and for the first time reveal a zonation of the Miocene Alboran Sea volcanism: (1) a keel-shaped area of LREE-depleted (mainly tholeiitic series) lavas in the central Alboran Sea, generated by high degrees of partial melting of a depleted mantle source and involving hydrous fluids from subducted marine sediments, that is surrounded by (2) a horseshoe-shaped zone with LREE-enriched (mainly calc-alkaline series) lavas subparallel to the arcuate Betic-Gibraltar-Rif mountain belt. We propose that the geochemical zonation of the Miocene Alboran Basin volcanism results from eastward subduction of Tethys oceanic lithosphere coupled with increasing lithospheric thickness between the central Alboran Sea and the continental margins of Iberia and Africa.