Orthogonal folding of extensional detachments: Structure and origin of the Sierra Nevada elongated dome (Betics, SE Spain)

Abstract

A close relationship of the kinematics and timing between low‐angle extensional faulting and upright folding is established for the Miocene detachment systems in the hinterland of the Betics in southeastern Spain. Folding accompanied tectonic denudation developing elongated domes with fold axes both parallel and perpendicular to the direction of extension. The geometry, kinematics, and tectonic evolution of two major sequentially developed extensional fault systems have been characterized in several E‐W elongated mountain ranges of the central Betics on the basis of new cartographic and structural data and a comprehensive revision of other available geological and geophysical observations. The extensional systems have an average WSW direction of extension and led to exhumation of the two lower metamorphic complexes of the Betics, the Nevado‐Filabride and the Alpujarride, during the middle and upper Miocene (Serravallian to Tortonian). The extended domain contains a core complex, with distal and proximal antiformal hinges separated by around 60 km and with a fold amplitude of ∼6 km (measured parallel to the direction of extension). The total amount of extension across the core complex is about 109–116 km, corresponding to a stretching factor (β) of 3.5–3.9, estimated using the distance between fold axial surfaces and a geometrical model accomplishing footwall deformation during tectonic denudation via subvertical simple shear. The elongated domal and basinal geometry of the detachments and their respective footwalls is due to the interference between two sets of orthogonal large‐scale open folds, trending N‐S and E‐W. Longitudinal, N‐S trending folds are interpreted as isostatic folds, i.e., folds that developed in response to differential unloading of the extensional detachment footwalls inducing ductile flow in the middle crust. These folds formed in a rolling‐hinge anticline in which rotation migrates westward through the footwall as it is progressively unroofed. In contrast, E‐W trending folds, being subparallel to the direction of extension, have a contractional origin and progressively affect to the west the isostatically readjusted segments of the detachments once they are inactive. Orthogonal folding occurred since the Serravallian to lower Pliocene. Extension is still active from the rolling‐hinge anticline in Sierra Nevada to the west. The middle Miocene to Pliocene tectonic evolution of the Sierra Nevada elongated dome at the core of the Betic hinterland is another example of the coexistence of extension and contraction during continued overall convergence and mountain‐building.

Active tectonics in the central and eastern Betic Cordillera through morphotectonic analysis: the case of Sierra Nevada and Sierra Alhamilla

“…Montenat and Ott d' Estevou, 1990) or in synclines between E/W to ENE/WSW-elongated antiformal ridges, where the metamorphic basement is bounded by folded extensional detachments (Martínez-Martínez and Azañón, 1997;Martínez-Martínez et al, 2002;Booth-Rea et al, 2005). This basement is made up of several metamorphic complexes belonging to the Alboran domain, a terrain that collided with the South Iberian and Maghrebian passive margins during the Miocene, forming the Gibraltar arc and the Betic and Rif cordilleras (Balanyá and García-Dueñas, 1987;Martínez-Martínez and Azañón, 1997;Platt et al, 2003;Booth-Rea et al, 2007).…”

Recent and active faults and folds in the central-eastern Internal Zones of the Betic Cordillera

“…The folds have been interpreted as caused by isostatic rebound in response to extensional denudation along the regional extensional detachments (e.g., Martínez-Martínez et al, 2002;Augier et al, 2005;Meigninger and Vissers, 2006). Alternatively, we consider them as contractional folds developed above upper-crustal detachments developed in a collisional framework (e.g., Weijermars et al, 1985;Montenat and Ott d'Estevou, 1990;Sanz de Galdeano and Vera, 1992;Martínez-Martínez et al, 1995;Galindo-Zaldívar et al, 2003;Sanz de Galdeano and Alfaro, 2004;Pedrera et al, 2009b).…”

Uppermost Tortonian to Quaternary depocentre migration related with segmentation of the strike-slip Palomares Fault Zone, Vera Basin (SE Spain)

“…Consequently we have not found any evidence of preUppermost Tortonian activity of the PFZ. Although, contractive structures (reverse faults and folds with NW vergence) are sealed by Tortonian sediments in the northern foothills of Sierra Cabrera [4], which date the earliest convergent structures developed after well documented Lower and Middle Miocene extensional tectonics in the Internal Betics [4,5,12,15,16,20,21]. The Tortonian NW-SE convergence would constitute a reasonable tectonic scenario for the activity of the PFZ during the Tortonian, as proposed by several authors [1,13,24,36].…”

“…Le secteur sud-est des cordillères Bétiques est caractérisé par la présence de bassins sédimentaires dont l'âge va du Néogène au Quaternaire, le long d'une ligne de reliefs est-ouest à ENE-WSW, correspondant à des antiformes où affleure le socle métamorphique du domaine d'Alboran [20][21][22]35].…”

“…The southeastern Betics are characterized by the presence of Neogene to Quaternary sedimentary basins that outcrop among east-west-to ENE/WSW-elongated mountain ranges, which coincide with antiformal highs where metamorphic basement of the Alboran domain outcrops [20][21][22]35]. These basins were initiated by extensional tectonics that greatly attenuated the previous Palaeogene Betic Orogen during the Lower and Middle Miocene [5,15,16,20], in an evolution parallel to that of the formation of the Alboran Sea [12].…”