Curved fold‐and‐thrust accretion during the extrusion of a synorogenic viscous allochthonous sheet: The Estepa Range (External Zones, Western Betic Cordillera, Spain)

Abstract

New structural, borehole, and time domain electromagnetic data allow us to reconstruct the 3‐D geometry of the Estepa range (External Zones of the Western Betic Cordillera), which constitutes an isolated curved fold‐and‐thrust range made up of Jurassic shallow marine carbonates and Cretaceous to Paleocene marls and marly limestones. Contraction and rising load linked to the accretion of the Subbetic nappe enhanced the expulsion of Triassic evaporites and overpressured clays during the early and middle Miocene, finally forming part of a highly deformed mélange unit. This plastic extrusion favored the disconnection of External and Middle Subbetic blocks, including the Sierra de Estepa Range. There, deformation is characterized by northwest‐vergent curved folds‐and‐thrusts associated with NE‐SW frontal ramps and NW‐SE lateral transfer faults that segmented the folds active between 18 and 12 Ma. At a local scale, curvature was achieved under a nearly uniform NW/WNW transport direction suggesting a primary arc type. Friction variation across the heterogeneous detached plastic basal Triassic unit mainly controlled the curvature and segmentation of the fold systems. Transport direction is consistent with previously published slip data from the Internal Subbetic and the Campo de Gibraltar units. After the Late Serravallian, accretion slowed down and a shallow marine unit deposited unconformably placed over the main thrust and folds. The sequence of deformation and emplacement of these ranges is interpreted as a continuous process linked to the early Miocene E continental collision of the Iberian margin thin continental crust and subduction of the Flysch trough oceanic crust beneath the Alboran continental domain.

Constraints on the frontal crustal structure of a continental collision from an integrated geophysical research: The central‐western Betic Cordillera (SW Spain)

“…Below several Jurassic‐Cretaceous Subbetic reliefs of the more frontal part (such as Sierra de Estepa; sites 6–7, eastern profile), the resistivity profile shows additional underlying repeated sequences of more resistive Subbetic sheets separated by the conductive mélange matrix bands (clays, sandstones and gypsum). Furthermore, the Subbetic of the Estepa range has a well‐defined structure characterized by curved folds mainly developed above NW–WNW directed thrusts [ Pedrera et al , 2012]. These ranges, apparently chaotically placed within the mélange unit, were previously described as large isolated blocks floating over the plastic mélange.…”

“…The Prebetic outcrops eastward of the study area, and is characterized by a typical imbricate thrust system of para‐autochthonous shallow‐water carbonate facies with terrigenous continental deposits [ García‐Hernández et al , 1980]. The Subbetic is constituted by allocthonous pelagic units detached from its Variscan basement and was folded and thrusted under a nearly uniform WNW‐NW transport direction during Early to Middle Miocene [ Pedrera et al , 2012]. It may be subdivided into External, Median and Internal zones on the basis of paleogeographic criteria.…”

“…It may be subdivided into External, Median and Internal zones on the basis of paleogeographic criteria. Accretion styles vary between the well‐structured Internal Subbetics and the more complex Median and External Subbetics [ Pedrera et al , 2012]. The accretion process induced the extrusion of a synorogenic viscous tectonic mélange mainly constituted by Triassic clays and evaporites, also including carbonate and marly Jurassic, Cretaceous, and Tertiary rocks.…”

“…In the literature, the name and the processed involved in the formation of these chaotic units has been source of controversy [ Staub , 1934; Cruz‐San Julián , 1974; Pérez López and Sanz de Galdeano , 1994; Roldán García , 1995; Berástegui et al , 1998; Vera , 2004; Roldán et al , 2012]. In an attempt to unify definitions, we will refer to this unit as the frontal mélange unit [ Pedrera et al , 2012].…”

Structural controls on karstic conduits in a collisional orogen (Sierra de las Nieves, Betic Cordillera, S Spain)

“…A thin-skin foldand-thrust belt developed along the South Iberian margin. Main deformation events in the western segment of the South Iberian margin range from the post-early Burdigalian to the Serravallian (Crespo- Blanco and Campos, 2001;Pedrera et al, 2012). Coeval to accretion within the frontal part of the cordillera, extension occurs at the rear of the hinterland, leading to the formation of the Alboran Basin, with an important depocenter in its western part (Comas et al, 1992(Comas et al, , 1999.…”