The Betic Cordilleras (SE Spain). Anatomy of a dualistic collision-type orogenic belt

Abstract

The first of three main tectonic events in the orogenic evolution of the Betic Cordilleras of southern Spain involved crustal subduction during the Late Cretaceous. It included the stacking of nappes in a deep crustal environment, accompanied by HP-metamorphism and polyphase ductile deformation. It has only been recorded in the nappes of the Internal Zone of the Betic Cordilleras and took place after a Middle Jurassic initial phase of rifting and break-up of a Triassic and Early Jurassic carbonate platform. The second phase in the development of the orogenic belt starts with an important regional phase of extension in Late Oligocene-earliest Miocene time. Crustal thinning during this extensional phase and updoming of the subcrustal lithosphere in the Betic-Alboran domain resulted in heating of the extended crust. Heating has been recorded in the metamorphic nappes of the Internal Zone. Extension of the Betic-Alboran domain resulted in low-angle normal faulting in the nappe pile of the Internal Zone. In the Early Miocene an abrupt transition from regional tension to compression is responsible for the final thrusting of elements of the Betic nappe complex towards the passive continental margin of the Iberian plate. This 'final emplacement' of the nappes marks the beginning of Neogene thin-skinned deformation in the External 7nne. In the Internal Zone, continuing convergence between the African and Iberian plates, resulted in strike-slip deformation from the latest Burdigalian onwards. Deformation in the eastern Internal Zone during this third tectonic phase is mainly characterised by basin subsidence and basement uplift in a strike-slip controlled regime under changing orientations of the main compressive stress. Theoretical lithospheric strength profiles predict differences in lithospheric strength between the eastern and western Betic Cordilleras, caused by differences in thermal structure and crustal thickness of the lithosphere. These differences are an inherited effect of the Late Oligocene-earliest Miocene extensional phase that influenced in particular the eastern part of the Betic Cordilleras. In the western Betic Cordilleras tectonic modelling predicts bending of the lithosphere and development of the Guadalquivir foreland basin under the load of the nappes, emplaced during the Early Miocene. In the eastern Betics lithospheric strength was restricted to the brittle upper crust, resulting in brittle strike-slip deformation and the development of pull-apart basins and basement uplifts.