Recent and active tectonics of the central-eastern betic cordillera internal zone and comparison with the external zone front

Resumen

The study of the intramontane basins southward Sierra Nevada and the central-eastern Betic Cordillera External Zone Front provides new essential data to understand the western Mediterranean alpine tectonic evolution. This research integrates new acquired geological, geophysical and geodetical data to contribute to the main geodynamic models proposed for the Gibraltar Arc development. The Betic Cordillera present-day relief begun to develop since the late Serravalian due to the Africa-Eurasia convergence. This setting induced the development of tectonic structures that isolated the intramontane basins as the Alpujarran Corridor, the Tabernas basin or the Gádor-Almería basin. Alhabia basin was formed by the interaction of these three basins and shows a cross-shaped depocentre were a faulted E-W synform is intersected by NW-SE normal faults. The intramontane basins interaction helps to unravel the effects of the Neogene-Quaternary counter-clockwise rotation in the convergence setting between Africa and Eurasia. Active folds and faults accommodate the present-day deformations. New CGPS data show a present-day regional westward displacement with higher rates in the western sites. In addition, the southern sites undergo a south-westward displacement accommodated by the E-W and NW-SE normal faults south of Sierra Nevada. These faults are contributing to the dismantling of a thickened crust in the frame of the current N-S to NW-SE convergence. In this setting, the large E-W folds of the Internal Zone stopped their activity whilst the new convergence setting favours the developing of NE-SW folds. These structures are responsible of the highest ranges of the Iberian Peninsula in westernmost Sierra Nevada. Several active faults are located south and west the Sierra Nevada edges. The E-W oriented Laujar Fault Zone is located in the Alpujarran Corridor central part. It shows a N-S relative extension according to recent dip-slip striations and CGPS data. This fault zone evidences the gravitational collapse of Sierra Nevada whilst the southern region is folded by NW-SE shortening. The Padul normal fault plays an important role in the regional deformation since it accommodates most of the present-day NE-SW extension in the south-western end of Sierra Nevada. According to the fault length and rate, a maximum 6 magnitude earthquake might be expected every 154 years. However, the absence of historical seismic events suggests a creep activity rather than seismic activity for the Padul Fault. In the Alborán Sea northern coast, buried marine-cut terraces onshore are correlated with marine terraces offshore. Their origin is consequence of sea-level changes rather than tectonic vertical displacements. The External Zone front developed with NNE-SSW and roughly E-W orientations separated by the Tíscar Fault. Whilst the NNE-SSW oriented front in Sierra de Cazorla is relatively straight, the roughly E-W front in the Jódar area is highly sinuous due to heterogeneous displacement of the fold-and-thrust belt on the main detachment level. At the present-day, tectonic activity in this area is related to an E-W extension accommodated by NW-SE normal faults. All the data support an active subduction with associated roll-back in the Gibraltar Arc.