Recent and active deformation structures in the central-eastern sector of the Betic Cordillera and the Alboran Sea: indentation processes and roll-back

Abstract

A multidisciplinary study that combines geology, geophysics and geodesy in an integrated land-sea approach is crucial for the analysis of the active and recent tectonic structures in the Alboran Sea and central-eastern Betic Cordillera. Such a study, presented in this Ph.D. Thesis, reveals new insights in the geodynamics of the Gibraltar Arc. The interaction between indentation tectonics caused by the Eurasia- Africa convergence and the active extension, and westwards displacement, related to subduction with roll-back, controls the active tectonics of the central Alboran Domain. To study these structures, geological, geodetical and geophysical methods have been applied, and marine and terrestrial data are integrated. In the central Alboran Sea indentation, the magnetic anomalies reveal large igneous intrusions related to the AlKaPeCa Domain rift that have conditioned the development of strike-slip faults and the indentation tectonics. In fact, these rigid bodies act as a backstop where the indenter of south Alboran Sea collides and has generated the Alboran Ridge. The magnetic anomalies also point to the inherited origin of the dextral Yusuf fault (north-eastern boundary of the indenter) and a very recent formation of the sinistral Al Idrissi fault zone (western boundary of the indenter). The southern termination of the Al Idrissi fault zone in the transtensional Nekor basin shows the interaction between the southwestwards motion of the Rif Cordillera and the indentation of the central Alboran Sea. The faults studied at the Al Hoceima Bay (Nekor basin) show a westward migration caused by the SW motion of the Rif. The deformation of the northern Alboran Sea is characterized by two conjugate sets of strike-slip faults that are propagating towards the coast. In the Campo de Dalías zone, the results of GNSS measurements show that the southern points of the GNSS network move WNW, while the northern ones move WSW. This zone is affected by normal-dextral faults with NW-SE orientation. Their dextral component, together with the GNSS results, implicate an influence of both the ENE-WSW extension, which is dominant in the central Betic, combined with the propagation of the tectonic indentation of the Alboran Sea. Thus, a transition zone can be defined in the western and northern boundaries of the Alboran Sea indentation. Such a transition happens between the indentation tectonics related to the continental collision in the central Alboran Sea, and the westwards motion with extension due to roll-back in the west Alboran Domain. In the eastern Betic, the active tectonics is marked by the transpressive and strike-slip faults of the Eastern Betic Shear Zone. A few of these faults, such as the Palomares one, are originated by the Águilas Arc indentation, where a rigid fragment of the Algerian crust collides with the deformed Betic Internal Zones. The gravity modeling next to the Palomares fault shows that the basin geometries are controlled by rotated synforms, whose fragmentation originated the Palomares fault during the indentation. In addition, the length of the Palomares fault is shorter than previously considered and it is constrained by the folding deformation. Consequently, it disrupts the continuity of the EBSZ. In addition, the data show a NW propagation of the Águilas Arc indentation. The high coupling in the eastern Betics between the Alboran Domain and the underlying Iberian crust favors the stress transmission towards the Iberian massif. This explains the strike-slip seismicity located inside the Iberian basement of the easternmost Guadalquivir foreland basin. Geophysical, seismological and geological data show a NNE-SSW sinistral fault in the Iberian basement and, combined with the compression structures located northwards, support an incipient indentation tectonics. The compression and strike-slip tectonics in the basement combined with the small westwards displacement at the surface, all point to an interaction between the collision tectonics of the eastern Betics and the roll-back in the central Betics. The boundary zone between areas affected by indentation tectonics and roll-back has variable features. Whilst in the Alboran Sea it is a transition zone, in the centraleastern Betics it manifests as a sharp boundary located west of the Águilas Arc indentation. Alternatively, in the Betic Cordillera, the boundary zone could be an area of progressive transition, eventually affected by other lithospheric processes related to the rupture of the slab between the western and eastern Betics. In the Guadalquivir foreland basin, transitional areas are also observed. The advancement of indentation, and the development of the Gibraltar Arc by roll-back processes, produces a progressive westwards migration of the boundary of the areas affected by these tectonic processes.