Tectónica cenozoica en el dominio cortical de Alborán

La Tesis doctoral propone un modelo de evolución tectónica del dominio Cortical de Alborán (DCA), aflorante en la rama norte del Arco de Gibraltar, durante el Cenozoico, haciendo especial énfasis en la geometría, cinemática y cronología de las estructuras formadas en ese período de tiempo y difereciando los episodios tectónicos más relevantes. Para esto se han seleccionado, para su estudio, tres áreas emergidas representativas de distintas posiciones estructurales del Dominio Cortical de Alborán, poco estudiadas previamente, y con una cobertera sedimentaria que permitiese establecer la relación tectónica entre las estructuras que afectan al DCA y la geometría del relleno sedimentario. Además se ha determinado la estructura, mediante el procesado e interpretación de los perfiles sísmicos de reflexión profunda ESCI Alb 2b y 2c, de un área sumergida, representativa de la transición entre corteza continental adelgazada, constituida por rocas del DCA y volcánicas, y corteza oceánica de las cuencas de Alborán y Surbalear respectivamente. Las áreas emergidas seleccionadas han sido las siguientes: Un sector de las Béticas occidentales, situado al W del meridiano de Málaga y que incluye la cuenca de la Hoya de Málaga y las sierras de la Axarquía occidental, constituidas por rocas del Dominio Cortical de Alborán. En este área se han diferenciado dos sistemas extensionales con transporte tectónico hacia el SSW y NNW responsables del adelgazamiento del Dominio Cortical de Alborán hasta constituir el basamento de la Hoya de Málaga, especialmente subsidente durante el Mioceno inferior. Se ha seleccionado un área representativa de las Béticas nororientales que incluye a la Cuenca de Lorca y los relieves que la circundan, correspondientes a las sierras de las Estancias, de la Tercia y de Espuña. En este sector se ha estudiado la evolución tectonometamórfica de unidades del Dominio Cortical de Alborán, así como las estructuras frágiles que constituyen los contactos entre unidades, interpretados como al menos dos sistemas de fallas normales de bajo ángulo, y la relación entre estas estructuras y el relleno sedimentario de la Cuenca de Lorca. En esta área además se ha prestado una atención especial a estructuras relacionadas con la emersión de la Cuenca de Lorca como son pliegues y fallas transcurrentes activas durante el Neógeno superior-Cuaternario. El tercer área estudiada se encuentra en las Béticas surorientales al este del meridiano de Carboneras y al sur del pueblo de Águilas. Esta área incluye a la Cuenca de Vera y las sierras que la rodean, y en ella se ha determinado la evolución tectonometamórfica de algunas de las Unidades del Dominio de Alborán que constituyen el basamento de la Cuenca de Vera, en concreto del Complejo Alpujárride y de la Unidad de Almagro. Con los datos obtenidos en estas áreas se ha propuesto un modelo de evolución tectónica para el Dominio Cortical de Alborán, diferenciando los eventos tectónicos principales, que se resumen a continuación: Evento D1 de subducción del Complejo Alpujárride bajo el Malaguide, produciendo metamorfismo de baja gradiente en las unidades basales del Complejo Malaguide y en el Alpujárride, donde se encuentran asociaciones minerales de alta presión, como Mg-carfolita+clorita+pirofilita o distena. Evento D2 de aplastamiento dúctil del Complejo Alpujárride con un factor B cercano a 3, dando lugar a la formación de la foliación principal del complejo Alpujárride, coetáneamente a procesos extensionales frágiles en el Complejo Malaguide. Evento D3 contractivo durante el cual se producen pliegues recumbentes y cabalgamientos postmetamórficos que dan lugar a inversiones y recurrencias en el grado metamórfico, además de la imbricación intracortical de los perioditas de Ronda. En las áreas estudiadas este evento es especialmente manifiesto en la de Vera. Este evento habría dado lugar a la configuración definitiva del Dominio Cortical de Alborán. Evento D4 de rifting del Dominio Cortical de Alborán durante el Mioceno inferior y medio para dar lugar a la Cuenca de Alborán miocena, coetáneamente a la formación y migración hacia el W del Arco de Gibraltar. Relacionados con este evento se han diferenciado al menos dos sistemas extensionales frágiles con direcciones de extensión transversas en todas las áreas estudiadas. Evento D5, durante el Tortoniense se produce un evento contractivo que da lugar a la formación de grandes pliegues de dirección grosera E-W, que exhuman a los sistemas extensionales anteriores. Durante este evento se inicia la emersión de gran parte de las Cuenca de Alborán miocena, dando lugar a una discordancia erosiva denominada "intratortoniense". Evento D6, durante el Tortoniense superior se produce una cierta subsidencia y aumento de los depocentros sedimentarios a favor de fallas normales de alto ángulo con direcciones variadas. Evento D7, desde el Tortoniense terminal hasta el Cuaternario domina la tectónica transcurrenteTesis Univ. de Granada. Departamento de Geodinámica. Leída 13 de septiembre de 200

The Alboran volcanic-arc modulated the Messinian faunal exchange and salinity crisis

What process triggered the Mediterranean Sea restriction remains debated since the discovery of the Messinian Salinity Crisis (MSC). Recent hypotheses infer that the MSC initiated after the closure of the Atlantic-Mediterranean Betic and Rifean corridors, being modulated through restriction at the Gibraltar Strait. These hypotheses however, do not integrate contemporaneous speciation patterns of the faunal exchange between Iberia and Africa and several geological features like the evaporite distribution. Exchange of terrestrial biota occurred before, during and after the MSC, and speciation models support an exchange path across the East Alborán basin (EAB) located a few hundreds of km east of the Gibraltar Strait. Yet, a structure explaining jointly geological and biological observations has remained undiscovered. We present new seismic data showing the velocity structure of a welldifferentiated 14–17-km thick volcanic arc in the EAB. Isostatic considerations support that the arccrust buoyancy created an archipelago leading to a filter bridge across the EAB. Sub-aerial erosional unconformities and onlap relationships support that the arc was active between ~10–6 Ma. Progressive arc build-up leading to an archipelago and its later subsidence can explain the extended exchange of terrestrial biota between Iberia and Africa (~7–3 Ma), and agrees with patterns of biota speciation and terrestrial fossil distribution before the MSC (10–6.2 Ma).This study was supported by research projects CGL2015-67130-C2-1-R and was part of the EUROMARGINS and TOPO-EUROPE initiatives of the EUROCORES Programme of the European Science Foundation (ESF). Efforts benefitted from funding of the German Science Foundation (DFG grants GR1964/12-1; RA 925/2-1+2-2 and RE 873/17-1)

Role of the Alboran Sea volcanic arc choking the Mediterranean to the Messinian salinity crisis and foundering biota diversification in North Africa and Southeast Iberia

The Mediterranean Sea desiccated 5.96 million years ago when it became isolated from the world oceans during the Messinian salinity crisis. This event permitted the exchange of terrestrial biota between Africa and Iberia contributing to the present rich biodiversity of the Mediterranean region. The cause chocking the Mediterranean has been proposed to be tectonic uplift and dynamic topography but the driving mechanism still remains debated. We present a new wide-angle seismic profile that provides a detailed image of the thickness and seismic velocity distribution of the crust in the eastern Alboran basin. The velocity model shows a characteristic structure of a subduction-related volcanic arc with a high-velocity lower crust and a 16-18 km total-thickness igneous crust that magmatic accreted mostly between 10-6 Ma across the eastern Alboran basin. Estimation of the isostatically corrected depth of the arc crust taking into account the original thermal structure and sediment-loading subsidence since 6 Ma places a large area of the eastern Alboran basin above sea level at the time. This estimation is supported by geophysical data showing subaereal erosional unconformities for that time. This model may explain several up-to-now-disputed features of the Messinian salinity crisis, including: the progressive isolation of the Mediterranean since 7.1 Ma with the disappearance of open marine taxa, the existence of evaporites mostly to the east of the volcanic arc, the evidence that the Gibraltar straits were not a land bridge offered by continuous Messinian open marine sediments at ODP site 976 in the western Alboran basin, the importance of southeastern Iberia and North Africa as centres of biota diversification since before the salinity crisis, and patterns of speciation irradiating from SE Iberia and the eastern Rif in some taxons. Guillermo Booth-Rea (1), Cesar R. Ranero (2), and Ingo Grevemer (3

Metamorphic Domes in Northern Tunisia: Exhuming the Roots of Nappe Belts by Widespread Post-Subduction Delamination in the Western Mediterranean

Cenozoic extension in the Western Mediterranean has been related to the dynamics of back-arc domains. Although, in most of its orogenic belts extension propagated into the fore-arc nappe domains. Here we revisit the structure, metamorphism and radiometric ages of the Tunisian Tell, where HP/LT rocks (350°C at 0.8 GPa), were exhumed by the sequential activity of extensional detachments after heating and decompression (410°C–440°C at 0.6–0.3 GPa) in a plate convergent setting. Normal faults thinning the Tunisian Tell detached at two different crustal levels. The shallower one cuts down into the Atlas Mesozoic sequence, involving Tellian Triassic evaporites in the hanging-wall forming halokinetic structures in the Mejerda basin late Miocene. The deeper-detachment bounds metamorphic domes formed by marbles and metapsammites from the Atlas domain. Illite crystallinity on Triassic rocks shows epizonal to anchizonal values, at deep and intermediate structural depths of the Tell-Atlas nappe belt, respectively. New U-Pb 49.78 ± 1.28 Ma rutile ages from Tellian metabasites, together with existing phlogopite 23–17 Ma K-Ar ages in Atlas marbles from the footwall of the deepest detachment, indicate a polymetamorphic evolution. The Tell rocks underthrusted the Kabylian flysch in the early Eocene. Further, early Miocene shortening thrusted the metabasites over lower-grade sediments, producing HP/LT metamorphism and ductile stretching at the base of the Atlas belt. The exhumation of midcrustal roots of Western Mediterranean nappe belts after tectonic shortening is a common feature related to tearing at the edges of the subduction systems and inboard delamination of their subcontinental lithospheric mantle.Ministerio de Ciencia e innovación PID2019- 107138RB-I00P18-RT-3632 of the Junta de Andalucia,Erasmus Mundus External Cooperation Window and by Scientific Cooperation Agreement 0534 between the Office National des Mines (ONM)The Tunis el Manar University and the Group for Relief and Active Processes Analysis (ARPA) from the University of GranadaTunisian Company of Petroleum Activities (ETAP)Universidad de Granada / CBU

Is The Iberian-African plates boundary well defined in the Alboran Basin of the Westernmost Mediterranean?

European Geosciences Union (EGU) General Assembly 2018, 8-13 April 2018, Vienna, Austria.-- 1 pageThe Alboran Basin (Westernmost Mediterranean) hosts the boundary between the Iberian and African plates. Traditionally, this boundary has been described as a wide deformation zone, in which the convergence is accommodated by several onshore-offshore tectonic structures. Extensional processes that led to the Alboran Basin formation took place from the Early to the Late Miocene, led by slab roll-back and slab tearing. During the Plio-Quaternary, the basin has been deformed due to the Iberia – Africa tectonic plates convergence, producing the contractive reorganization of some structures at the basin. In this study, we estimate the total slip accommodated by the most prominent tectonic structures in the area of Ear-liest Pliocene in age. We use Pre-Stack Depth Migrated sections of the crustal structure, that allow us to analyzed the real geometry of these structures at depth and to measure strain. We use the deformation-related geometry of strata and faults to estimate slip on the main faults. Results show that estimated total slip accommodated by the main fault system may be similar (with error bounds) to the estimated plate convergence value since the Messinian time (∼24 km). Thus, slip on that faults may have accommodated most of the Iberian – African plate convergence during the Plio-Quaternary, revealing that the contractive reorganization of the Alboran basin is focused on a few first-order structures that act as lithospheric boundaries, rather than widespread and diffuse along the entire basinPeer Reviewe

Uppermost-Tortonian to present depocentre migration related with segmentation of the Palomares Fault Zone (PFZ), SE Betics, Spain

The Palomares Fault Zone (PFZ) is one of the main strike-slip brittle shear zones found in the Betics. It is segmented in several faults that have been active between the Upper Tortonian and present day. Data from drill cores in the The Palomares Fault Zone (PFZ) is one of the main strike-slip brittle shear zones found in the Betics. It is segmented in several faults that have been active between the Upper Tortonian and present day. Data from drill cores in the Palomares area have permitted us to define the geometry and location of sedimentary depocentres related with the PFZ. These data show an eastward displacement between the Upper Tortonian to Messinian and the Pliocene–Quaternary sedimentary depocentres, towards the presently active Arteal fault, which bounds the western mountain front of Sierra Almagrera, showing that deformation along this fault zone has migrated towards the east, from the Palomares segment, with its main activity during the Upper Tortonian and Messinian, towards the Arteal fault, active during the Pliocene and Quaternary

The lithospheric structure of the Gibraltar Arc System from Wide Angle Seismic data

In continental settings, seismic failure is generally restricted to crustal depth. Crustal structure is therefore an important proxy to evaluate seismic hazard of continental fault systems. Here we present a seismic velocity model across the Gibraltar Arc System, from the Eurasian Betics Range (South Iberian margin), across offshore East Alboran and Pytheas (African margin) basins, and ending onshore in North Morocco. Our results reveal the nature and configuration of the crust supporting the coexistence of three different crustal domains: the continental crust of the Betics, the continental crust of the Pytheas Basin (south Alboran Basin) and onshore Morocco, and a distinct domain formed of magmatic arc crust under the East Alboran Basin. The magmatic arc under the East Alboran Basin is characterized by a velocity structure containing a relatively high‐velocity lower crust (~7 km/s) bounded at the top and base by reflections. The lateral extension of this crust is mapped integrating a second perpendicular wide‐angle seismic profile along the Eastern Alboran basin, together with basement samples, multibeam bathymetry, and a grid of deep‐penetrating multichannel seismic profiles. The transition between crustal domains is currently unrelated to extensional and magmatic processes that formed the basin. The abrupt transition zones between the different crustal domains support that they are bounded by crustal‐scale active fault systems that reactivate inherited structures. Seismicity in the area is constrained to upper‐middle crust depths, and most earthquakes nucleate outside of the magmatic arc domain. Key Points New velocity model reveals the lithospheric structure under the Betics (South Iberia), the Alboran Basin and the North African margin The East Alboran Basin is floored by magmatic arc crust, while the southern area of the Alboran Basin is floored by continental crust Seismic activity is constrained to the upper‐middle continental crust. Crustal domains are likely bounded by active fault