Detachment Faulting in the South-eastern Sorbas Basin, SE Spain

The Betic domain of the Alpine orogenic belt of S. Spain is characterised by a number of tectonic contacts, recently reinterpreted as low angle detachment faults (e.g. the Betic Movement Zone, BMZ) that displace lower grade metamorphic rocks onto higher grade metamorphic rocks, excising part of the sequence.The Betic domain is bounded on its south-eastern side by a steeply-dipping complex of strike-slip fault zones that comprises the linked sequence of the Alhama de Murcia, Palomares, and Carboneras fault zones (Trans-Alborán Shear zone, off-shore). This linked fault system, which extends across the Alborán Sea into N. Africa behaves as a velocity discontinuity, separating NE-SW stretched crust to the north from less deformed crust to the south. Rutter et al., 2012 (JSG, 45, 68-86, 2012).In the most internal zone of the Betic domain, metamorphic basement rocks are exposed in the core complexes that have been uplifted as a result of late-orogenic extension. This was coupled with the formation of post-orogenic sedimentary basins (such as the Sorbas Basin) filled dominantly with upper Miocene sediments. Recent studies have shown that accommodation space was created through extensional faulting taking place at the same time as the uplift of the basement massifs. Steeply-dipping strike-slip faults also play a major role, acting as transfer faults linking the extensional detachments. Most previous work has focused on the fact that the basin is clearly fault-bounded against uplifted basement rocks of the S. Alhamilla to the south. Details of the geometry of the northern edge of the Sorbas basin are unclear owing to burial under overlying Messinian and Pliocene deposits.This project is aimed at reconstructing the evolution of the Sorbas and neighbouring basins and the south-eastern part of the Betic Cordillera throughout the Neogene era, by the means of an in-depth analysis of the tectono-stratigraphic setting based on the collection of original structural data and K-Ar isotopic dating of authigenic clays from fault gouge. The occurrence of extensional faulting in the Sorbas basin, highlighted recently by authors of the University of Granada, has here been further studied and interpreted in the context of the wider, regional setting. New fault systems have been identified and an hypothesis concerning the so-called Gafarillos, and possibly Polopos fault zones is proposed, by which the coeval Miocene NE-SW directed stretching and NW-SE directed shortening would have driven a significant reorientation of originally detachment faults to assume a strike-slip character.Extensive mapping, coupled with data manipulation with ArcGIS ® software, allowed identification of sealing of the early-active extensional faults beneath at least one previously unrecognized intra-basinal unconformity. Furthermore, our current data indicates that the lower part of the Sorbas basin fill (Chozas Fm) was likely not confined only to what is now perceived as the Sorbas basin, but extended over the presently uplifted Sierras and into the lower part of what is now the Nijar basin (to the SW of the Sorbas basin).