Aborted oceanic basin during the Mesozoic rifting of the South-Iberian Palaeomargin and interactions with the sedimentation processes

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ABSTRACT During the Mesozoic, the South-Iberian Palaeomargin experienced successive phases of extensional tectonics related to the fragmentation of Pangea and the aperture of the Central Atlantic. During the Pliensbachian, the rifting favoured the fracturing and collapse of the Early Jurassic carbonate platform and delimited a subdomain characterized by high subsidence called Median Subbetic (Betic Cordillera, S Spain). The progression of the rifting and the related extension along ~ 102 Ma, from late Pliensbachian to Santonian, favoured the activity of lithospheric scale faulting and extensional basic magmatism in the Median Subbetic with alkaline affinity. The highest volume of lava emissions, represented by pillow-lava flows interbedded with hemipelagic sediments, occurred during the Middle Jurassic. The pillow-lavas show aphanitic texture with Ca-rich plagioclase and clinopyroxene, whereas subvolcanic rocks are aphanitic with high content of plagioclase to phaneritic with plagioclase, olivine and biotite. The rocks present low SiO2 (46.6–53.5 wt.%) and relatively high K2O (locally reaching 8.7 wt.%), and the content of trace elements generally ranges between those from E-MORB and OIB composition. Values of some ratios such as (Gd/Yb)N, (La/Yb)N, (La/Sm)N, and the Nb content increase in the Upper Cretaceous pillow-lava flows, whereas Yb and Y contents decrease, that point to more alkaline affinity. Low Yb and Y contents point to the presence of garnet as residual phase in the mantle source. We interpret that during the early Late Cretaceous, hyperextensional phase of the continental rifting throughout an aborted oceanic basin occurred and allowed lithospheric deeper asthenospheric mantle up-lift and the partial melting. The phases of extensional tectonic controlled the configuration of this palaeomargin in complex tectono-palaeogeographic subdomains, the sedimentary cycles, and the volcanic activity during the Jurassic and Cretaceous. Finally, the transition from passive margin to a convergent one began during the Campanian and no more volcanism is recorded in the Median Subbetic.