Structural and kinematic analysis of the Corredoiras detachment: evidence for early Variscan synconvergent extension in the Ordenes Complex, NW Spain

An important detachment is described in the allochthonous Ordenes Complex, in the NW Iberian Massif, and its meaning is related to the kinematics of c ontemporaneous convergent structures. The Corredoiras Detachment (CD) separ ates a hangingwall unit, characterised by a medium-pressure metamorphic gra dient, from a footwall high-pressure and high-temperature unit and an under lying ophiolitic unit. An associated ductile shear zone, nearly 2000m thick , developed in the lower part of the hangingwall unit, where the Corredoira s Orthogneiss, a Lower Ordovician metagranite, was progressively transforme d into augengneisses, mylonitic and ultramylonitic gneisses. The attitude o f 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 ro ughly top to the SE. According to crosscutting relationships, the CD develo ped subsequent to the thrusting of the high-pressure/high-temperature unit onto the ophiolitic unit, and prior to younger extensional detachments, upr ight folding and strike-slip tectonics. The geometric relationships of the CD with the: previous structures in the footwall unit, the subtractive char acter of the metamorphic gap between its hangingwall and footwall, and the available isotopic data suggest that the CD is an early Variscan, ductile e xtensional detachment, the movement of which was roughly simultaneous with the onset of thrusting of the allochthonous complexes over their relative a utochthon.