Francisco M. Alonso-Chaves

Palaeokarst and rauhwacke development, mountain uplift and subaerial sliding of tectonic sheets (northern Sierra de los Filabres, Betic Cordilleras, Spain)

The rauhwackes near Serón in the northern Sierra de los Filabres (S Spain), previously considered as true tectonic breccias, are reinterpreted on the basis of sedimentological, geomorphological and geometrical evidence as subaerial or nearly subaerial sedimentary deposits. Channel fills, parallel lamination, cross-lamination, graded bedding, sedimentary clastic dykes and other sedimentary structures and features occur in the rauhwacke body. These sedimentary rocks correspond to continental deposits of alluvial and karstic origin deposited over a karstified erosional surface of Nevado–Filabride marbles. Although no fossils have been found in the rauhwackes, a Tortonian age for these rocks is suggested on the basis of structural arguments and lithostratigraphic data from the nearby Almanzora basin. The rauhwackes were buried by slabs of Alpujarride rocks that gravitationally slid over them during the uplifting of the Sierra de los Filabres.

Tectonic style and structural analysis of the Puebla de Guzmán Antiform (Iberian Pyrite Belt, South Portuguese Zone, SW Spain)

Abstract In the South Portuguese Zone (Iberian Massif), thin-skinned tectonics linked to the collision with the Ossa-Morena Zone produced the inversion of previous extensional basins in Carboniferous times. Its central domain, namely the Iberian Pyrite Belt, underwent two deformation phases at mostly low-grade metamorphic conditions linked to a progressive deformation migrating upwards from a basal detachment and from north to south. The Puebla de Guzmán Antiform is one of the most outstanding cartographic structures in the Iberian Pyrite Belt, representing a imbricate fan thrust system developed during the second regional deformation phase. In the Puebla de Guzmán Antiform, the first deformation phase gave rise to a penetrative slaty cleavage (S1), which is also recognized in the whole Iberian Pyrite Belt and constitutes the main foliation all over the region. Its genesis is possibly linked to the coetaneous development of thrusts at deeper crustal levels and SSW-vergent folds at all levels above these thrusts. First phase structures were deformed by large-scale imbricated thrust systems with lateral (NNE–SSW) and frontal (WNW–ESE) ramps, which constitute the most relevant regional cartographic structures. This second deformation phase generated thrusts, two set of folds with WNW–ESE and NNE–SSW-oriented axes, as well as two related axial plane crenulation cleavages. These relatively brittle to ductile-brittle second phase structures have been identified in many areas of the Iberian Pyrite Belt, and especially in the southern limb of the Puebla de Guzmán Antiform. The second phase thrusts reported from the Puebla de Guzmán Antiform have not been folded according to both the geological map of the area and the analysis of maximum shortening and stretching axes.

Gravity-induced recumbent folds and low-angle normal faults in the Alpujarras region (Betic Cordilleras, Spain): indications of Miocene extensional tectonics in the western Mediterranean

Large north-facing recumbent folds found in the Alpujarride Domain of the Betic orogen, heretofore related with a contractional nappe-stacking episode predating the early- to middle-Miocene extension, can be reinterpreted as gravitational folds, their development being connected with the extensional event that produced the low-angle normal faults and extensional detachments in Miocene times. This conclusion is based on detailed research carried out in the eastern part of the Alpujarras region (southern Betics) and includes the establishment of the fold geometry and metamorphic frame by means of field and mineralogical techniques, and the analysis of the relationships between recumbent folds and extension-related structures such as low-angle normal faults, stretching lineations, boudinage structures, etc.

Subsidence tectonique et sédimentation synrift associée au rifting du domaine d'Alboran au Miocène inférieur (Chaîne bétique, Espagne)

Abstract The sedimentary units described constitute the La Vinuela Formation, situated at the eastern end of the Colmenar Depression. The lowest unit, formed of massive continental breccias, has been interpreted as arising from slope deposits of ‘sturzstrom’-type or rock avalanches. Higher up, progressive subsidence resulted in a terrigenous-carbonated series, typical of marine material. It is a transgressive sequence, formed in an extensional synorogenic basin, associated with the first episode of Neogene rifting in the Betic Cordilleras. The direction of extension is deduced as N-S.