LATE HERCYNIAN EXTENSIONAL AND TRANSCURRENT TECTONICS IN CENTRAL IBERIA

At the end of the Hercynian orogeny, the central Iberian crust, which had been thickened by nappe tectonics, and heated/weakened/overthickened by massive granitic intrusions, was subjected to extensional tectonics through lithosphere-scale low-angle detachment systems, thus releasing the gravitational potential inherent in thickened crust. These detachment faults evolved by tectonic denudation, isostatic rebound, and upward arching, to define an Extensional-Tardi-Hercynian (ETH) "Basin and Range-type province", with upper-plate listric high-angle normal faults delimiting tilted blocks and asymmetric troughs (occasionally filled with Permian sediments and volcanics), N-S-oriented transfer faults, and synform/antiform pairs (with denuded "Metamorphic Core Complexes" in the antiforms, and local compressional features in the synforms). Postdating the gravitational collapse of the thickened crust, the residual late Hercynian E-W-oriented compressional stresses triggered a Ductile-Transcurrent-Tardi-Hercynian (DTTH) event. This is expressed by two major shear zones, and by the extrusion and deformation of porphyry dyke swarms along the previously thinned and weakened antiformal trends. Finally, interplate stresses related to a continental-scale shear zone gave rise to a Brittle-Transcurrent-Tardi-Hercynian (BTTH) event, with different sets of brittle faults indicating a N-S-oriented compression. The present geological features are the result of these events, overprinted by the Alpine reactivation of the entire complex.