The Betic Intramontane Basins (Se Spain): Stratigraphy, Subsidence, And Tectonic History

One of the most striking features of the Betic Cordillera in Southern Spain is the importance of Late Miocene extensional tectonics, representing a late stage subsequent to a rather poorly characterized compressional stage. Low-angle normal faults have been responsible for the exhumation of the metamorphic rocks constituting the Internal Zone or Alboran domain, as well as for the formation of sedimentary basins, commonly referred to as Betic intramontane basins.The Betic intramontane basins are located either on the Alboran domain or at the contact between the Alboran domain and the External Zone. All of these basins have a common sedimentary evolution, characterized by three main sequences separated by unconformities of regional significance. The lower (Upper Serravallian-Lower Tortonian) and upper sequences (uppermost Tortonian-Pleistocene) consist of continental clastic sedimentary rocks. The intermediate sequence (Upper-Tortonian-Upper Messinian) is made of marine sedimentary rocks, representing a very short-lived diachronic inundation, which lasted longer in the eastern and southern parts of the Betics. Subsidence rates in the basins reached maximum values during Late Serravallian-Early Tortonian times (13-7 Ma), and gradually decreased toward Pleistocene time. Uplift in the sierras surrounding the basins was roughly in accordance with the subsidence in the basins.The onset of subsidence of the Betic intramontane basins was coeval with the onset of extension in the deeper tectonometamorphic units of the Alboran domain, in Late Serravallian-Early Tortonian times. From latemost Tortonian on, the Africa-Europe convergence direction changed, giving way to E-W trending compressional folds, NW-SE oriented high-angle normal faults, as well as E-W and NE-SW trending strike-slip faults. These structures deformed the basins and their basements in a complex way, with coeval compression, exhumation and extension. Later on, strike-slip faults strongly affected some of the basin margins, obliterating the previous extensional structures. A lithosphere-scale scenario characterized by mantle delamination and/or subduction roll-back/slab-detachment provides the framework to explain the Betic intramontane basins.