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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 marginThe East Alboran Basin is floored by magmatic arc crust, while the southern area of the Alboran Basin is floored by continental crustSeismic activity is constrained to the upper‐middle continental crust; crustal domains are likely bounded by active faults [ABSTRACT FROM AUTHOR]

Quaternary volcanism in the Central Cordillera of Costa Rica has created an orographic barrier that concentrates rainfall on its northern side. This humid climate produces weathered bedrock prone to landsliding. Ash fall from explosive eruptions kills the vegetation cover and intensifies erosion processes. These eruptions, hydrothermal activity and associated earthquakes destabilize the slopes of river valleys, and even the volcanic edifices, producing landslides and large debris avalanches. All these processes mobilize an extra sediment input that is deposited in the piedmont lowlands forming the Santa Clara megafan. The megafans described in the literature mainly grow according to climatic fluctuations; however, sedimentation in the Santa Clara megafan is also controlled by endogenic processes with longer recurrence periods. Analysis of this megafan provides new insight into the origin and evolution of these landforms. In volcanic regions, active volcanism should be considered when investigating the formation of some megafans. [ABSTRACT FROM AUTHOR]

We map the lithospheric structure under the westernmost Mediterranean convergent setting interpreting P-receiver functions obtained from a dense seismic network. No orogenic root occurs under the eastern and great part of the central Betics. However, the subducted South Iberian continental lithosphere is found beneath the western Betics where the Iberian Moho reaches depths of approximately 65 km, dipping gently towards the SE. Meanwhile, at the Rif, strong crustal and lithospheric thickness contrasts occur across the Nekor NW-SE sinistral fault that overlies the region of present slab tearing. East of the Nekor fault there is no orogenic root and the crust has been thinned to approximately 22 km, whilst to the west the crust reaches 55 km thickness and the Maghrebian continental lithosphere is attached to the lithospheric slab imaged by tomography under the Alboran basin. These data suggest that subduction rollback under the Alboran and Algerian basins, together with continental slab tearing or detachment producing edge delamination under the Betics and Rif have been the main tectonic mechanisms driving extension, magmatism and regional uplift in the westernmost Mediterranean since the Late Miocene until present. The surface expression of edge-delamination and slab tearing is marked by regional uplift, denudation of HP rocks in elongated core-complex type domes, late Miocene volcanism in the Eastern Betics and Rif, and by large NE-SW strike-slip transfer faults like the Alpujarras, Crevillente, Torcal or Nekor faults that accommodate strong gradients in crustal displacements. The Iberian slab is still attached to the oceanic slab imaged under the Alboran basin at the western Betics where intermediate depth seismicity, recent dextral strike-slip faulting and folding, could reflect slab tearing. Meanwhile, active faulting and differential GPS-measured displacements would mark slab tearing beneath the Rif coinciding with the trace of the sinistral Nekor fault. [ABSTRACT FROM AUTHOR]

The complex present-day drainage network of the Lorca–Totana area records the changing tectonic setting, from extension to transpression, in the eastern Betics. Through a detailed morphometric analysis we evaluate the topographic response to this major change in the tectonic setting and the influence in the drainage of Miocene extension and middle Pleistocene to present day transpression. The present-day drainage network preserves geomorphic features inherited from Late Miocene extension that are being overprinted by a new transverse fluvial system. This new system advanced towards the NW since the middle Pleistocene in response to a localized base-level drop related to the NE–SW oriented Alhama de Murcia sinistral-reverse fault. Geomorphic indexes calculated in this work suggest the present-day activity of the Alhama de Murcia fault and the Sierra de la Tercia anticline, the two major tectonic structures in the area. The landscape rejuvenation associated with this process results in: contrasting mountain front sinuosity values between old and new mountain fronts, high SLk index anomalies, convex-shaped and complex hypsometric curves, knickpoints in river profiles, contrasting slope–area plots and high steepness index values. This fluvial reorganization was driven progressively by successive fluvial captures preserved as wind-gaps in the present-day drainage network. [ABSTRACT FROM AUTHOR]

Abstract: The Samaná complex exposes a segment of a high-P metasedimentary collisional accretionary wedge, built during Caribbean island arc-North America continental margin convergence. Combined detailed mapping, metamorphic mineral assemblages, multi-equilibrium calculations and thermodynamical modelling of garnet zoning, together with isotopic ages, allow proposing a tectonothermal evolution of the complex involving three major stages (M1 to M3). M1 metamorphism was characterised by a prograde P–T path towards the pressure-peak in the lawsonite-blueschists (Santa Bárbara Schists and Rincón Marbles lower structural nappes) and garnet-blueschists to eclogite-facies conditions (Punta Balandra upper nappe). This high-P metamorphism and related D1 deformation took place from the Eocene to Late Oligocene, when the different nappes were buried along a cold subduction-zone gradient. Contemporary to the D2 deformation, M2 retrograde metamorphism was associated in all nappes with substantial decompression under nearly isothermal or cooling conditions to the epidote-blueschists and greenchists facies conditions. D2 deformation produced ENE-directed folding, thrusting and nappe stacking in the complex, when nappes went sequentially incorporated to a growing collisional accretionary complex between the Late Eocene and the earliest Miocene. D2 deformation is thus responsible for much of the exhumation of the subducted rocks and for the thinning of the nappe pile. As the continuity of the P–T conditions within the accreted metasedimentary material were in this case preserved, the exhumation mechanisms for Samaná complex high-P rocks was most probably driven by underthrusting/underplating and erosion. Non-penetrative fabrics associated with D3 and D4 late deformations indicate M3 cooling in the greenschists and subgreenchists-facies conditions. D5 sinistral strike-slip brittle faults cut and laterally displaced the whole nappe pile of the Samaná complex from the Lower Miocene to the Present. [Copyright &y& Elsevier]

We present new Sr-Nd-Pb isotope data of the western Alpujárride metamorphic basement and the pre-Miocene Flysch sediments of the Betic Cordillera (southern Spain). Nd model ages are consistent with an increasing detrital input from the Alborán domain to the Flysch Trough in the western Mediterranean during the late Oligocene. The Alpujárride metamorphic crustal rocks derived from Archean-Paleoproterozoic terranes located along the northern margin of Gondwana in the Neoproterozoic. The heterogeneous isotopic signatures of the Alpujárride units indicate that they have different sedimentary protoliths and underwent contrasted Variscan and pre-Variscan tectono-magmatic evolutions. Melts/fluids derived from the western Alpujárride gneisses contaminated the mantle source of the Ronda high-Mg pyroxenite dykes, implying that the Alpujárride lower crust underthrusted the subcontinental lithospheric mantle of the Alborán domain generating subduction-like magmatism in the late Oligocene. The western Alpujárride upper crust is involved in the Neogene volcanism of the Alborán Sea basin, but only contaminated some LREE-enriched calc-alkaline lavas erupted along the continental margins. On the other hand, tholeiitic lavas in the center of the basin show no isotopic evidence of crustal assimilation. This indicates that most of the crust in the central Alborán Sea accreted by Miocene tholeiitic magmatism and that Alpujárride lower crust is absent and likely foundered close to the continental margins of the basin. [ABSTRACT FROM AUTHOR]

Based on more than 4,500 km of new and re-processed multichannel seismic lines, high-resolution seafloor bathymetry, available well data, and basement dredge samples, we have re-evaluated the entire stratigraphy and the tectonic evolution of the Alboran and western Algerian basins. We have correlated the sediment units deposited since the beginning of the formation of the different sub-basins, and we present for the first time a coherent stratigraphy and large-scale tectonic evolution of the whole region. The results provide the information to test and refine models of the geodynamic evolution of the westernmost Mediterranean. The data analysis supports an independent evolution of the sub-basins through the latemost Oligocene and Miocene, and a common Plio-Holocene evolution. The latemost Oligocene and Miocene evolution was controlled by the evolution of the Gibraltar subduction system. The oldest sedimentary unit is restricted to the West Alboran and Malaga basins depocenter that during the latemost Oligocene and early Miocene connected to some smaller marine basins currently uplifted and located onshore on the Betics range. Later, during the middle Miocene, the Habibas and Pytheas sub-basins formed a second depocenter on the North African margin. The different sedimentary units found in both depocenters, together with their different deformation patterns, support that the West Alboran-Malaga and the Habibas-Pytheas depocenters were separated by a major tectonic boundary. The early Tortonian initial arc magmatic activity produced the formation of new areas floored by a volcanic basement by the end of the late Tortonian, when the first sedimentary units deposited in the East Alboran sub-basin, and probably during the late Tortonian-early Messinian in the South Alboran sub-basin. Extension of the back-arc setting created oceanic crust flooring the Algero Balearic Basin. The extensional formation of the westernmost Mediterranean basins ended in the latemost Miocene. The western migration of the subduction system stopped and the convergence between the African and the European tectonic plates started to dominate the tectonic evolution of the region. During the Plio-Holocene, the sub-basins did not further subside individually so that these sediments have spread out across the whole Alboran Basin. A new tectonic contractional and strike-slip fault system developed that is active nowadays. The integration of our results together with the most recent tomographic studies has been used to test and refine the existing kinematic models of the area. None of the existing models explains all our large-scale observations. • We present the first unified stratigraphy of the westernmost Mediterranean. • Miocene marine basins currently onshore are integrated. • We present a kinematic model for the Alboran and Algero-Balearic basins. • We evaluate western Mediterranean geodynamic models in the framework of basin evolution. [ABSTRACT FROM AUTHOR]