Internal structure of a collapsed terrain: The Lújar syncline and its significance for the fold- and sheet-structure of the Alborán Domain (Betic Cordilleras, Spain) |
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Authors: | Miguel Orozco, Antonio M lvarez-Valero, Francisco M Alonso-Chaves,John P Platt |
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Affiliation: | aDepartamento de Geodinámica e I.A.C.T., Universidad de Granada, Granada, Spain;bDepartamento de Geodinámica y Paleontologı́a, Universidad de Huelva, Huelva, Spain;cResearch School of Earth Sciences, UCL and Birkbeck College, Gower Street, London WC1E 6BT, UK |
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Abstract: | Detailed structural analysis of the Sierra de Lújar in the western Alpujarras region (Betic Cordilleras, S Spain), a very representative area of the terrain known as the Alborán Domain, has revealed the existence of a very large N-vergent recumbent syncline which involves the whole mountain massif and neighbouring areas. The Lújar syncline and, probably, the associated recumbent anticline which crops out southeast of Sierra de Lújar show a great variation in the orientation of the hinge line. Although having a curved shape, the hinge line is contained in a plane whose attitude coincides with the main attitude of the axial-plane crenulation foliation (Sc), suggesting that it is a sheath fold.The strongly deformed overturned limb of the syncline is cut by two low-angle normal faults displacing towards the north. Similarity in the kinematics between the faults and the fold, and the association between the faults and the high-strain zone in the overturned limb of the fold, suggest that they are related. Regional constraints on the age of the crenulation cleavage and the low-angle normal faults indicate that they formed during the early Miocene late-orogenic extensional event in the Alborán Domain.We propose an alternate explanation for the structure of the Alpujarras region in which the Lújar syncline forms part of a recumbent syncline–anticline pair that extends along much of the Alpujarride outcrop in the southern Betic Cordillera. In several places, the fold is disrupted by low-angle normal faults, and it is overlain by an upper Alpujárride extensional sheet mainly composed of medium- to high-grade metamorphic rocks. We suggest that all these structures arose from the extensional deformation under decreasing temperature conditions of a previously thickened and metamorphosed orogenic crust. |
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Keywords: | Collapsed terrains Extension-related folds Mediterranean Belt Alborá n Domain |
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