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Structural and kinematic analysis of the Corredoiras detachment: evidence for early Variscan synconvergent extension in the Ordenes Complex, NW Spain
Authors:F Díaz García  J R Martínez Catalán  R Arenas  P González Cuadra
Institution:(1) Departamento de Geología, Universidad de Oviedo, E-33005 Oviedo, Spain e-mail: floro@asturias.geol.uniovi.es, Tel.: +34-98-5103114, Fax: +34-98-5103103, ES;(2) Departamento de Geología, Universidad de Salamanca, E-37008 Salamanca, Spain, ES;(3) Departamento de Petrología y Geoquímica, Universidad Complutense, E-28040 Madrid, Spain, ES
Abstract: An important detachment is described in the allochthonous Ordenes Complex, in the NW Iberian Massif, and its meaning is related to the kinematics of contemporaneous convergent structures. The Corredoiras Detachment (CD) separates a hangingwall unit, characterised by a medium-pressure metamorphic gradient, from a footwall high-pressure and high-temperature unit and an underlying ophiolitic unit. An associated ductile shear zone, nearly 2000 m thick, developed in the lower part of the hangingwall unit, where the Corredoiras Orthogneiss, a Lower Ordovician metagranite, was progressively transformed into augengneisses, mylonitic and ultramylonitic gneisses. The attitude of the stretching and mineral lineation in the mylonites varies due to late refolding at map scale, but the sense of movement can be estimated, being roughly top to the SE. According to crosscutting relationships, the CD developed subsequent to the thrusting of the high-pressure/high-temperature unit onto the ophiolitic unit, and prior to younger extensional detachments, upright folding and strike-slip tectonics. The geometric relationships of the CD with the previous structures in the footwall unit, the subtractive character of the metamorphic gap between its hangingwall and footwall, and the available isotopic data suggest that the CD is an early Variscan, ductile extensional detachment, the movement of which was roughly simultaneous with the onset of thrusting of the allochthonous complexes over their relative autochthon. Received: 17 November 1998 / Accepted: 4 April 1999
Keywords:  Extensional detachment  Synconvergent extension  Allochthonous complexes  Ordenes Complex  Iberian Massif
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