Evidence for Internal Zone unroofing from foreland basin sediments, Betic Cordillera, SE Spain

Abstract

Tertiary sediments at the boundary of the Internal and External Zones in the eastern Betic Cordillera record evidence of compressive deformation in the Internal Zone and its subsequent exhumation. Sediments on the north side of the Sierra Espun associated with the structurally highest unit of the Internal Zone, the Malaguide Complex, are interpreted as a foreland or piggyback basin which formed in response to the deforming Internal Zone. Basin evolution has been reconstructed using an integrated analysis of sedimentary facies, petrography, heavy minerals and structural data. The basin fill contains Eocene shallow-marine carbonate shelf/ramp sediments, early Oligocene fan conglomerates and coralgal reefs transitional to probable slope deposits of the late Oligocene, and a late Oligocene to mid-Miocene deep-water sequence with pelagic faunas. The provenance analyses illustrate an unroofing history of the Internal Zone orogenic edifice. Locally uplifted Mesozoic to Eocene carbonates at the thrust front were the source of lower Oligocene conglomerates. Clastic detritus supplied to the late Oligocene to Aquitanian basinal sediments was mainly derived from the Permo-Triassic and Palaeozoic basement of the Malaguide Complex. The presence of small amounts of first-cycle metamorphic minerals indicates the start of exhumation of the deeper metamorphic Alpujarride Complex. From the Burdigalian onwards a metamorphic terrane dominated the source area of the deep-water sediments, and by the Langhian high pressure minerals from the deepest parts of the Internal Zone orogenic edifice appear in the sedimentary sequence. Rapid exhumation recorded in the early Miocene sediments may be the result of extensional exhumation of the Internal Zone metamorphic complexes.