Superposed Hercynian and Cadomian orogenic cycles in the Ossa-Morena zone and related areas of the Iberian Massif

Polyphase ductile deformation and metamorphism in the Ossa-Morena zone of t he Iberian Massif are related to a complex evolution including two major te ctonothermal episodes of Cadomian (Late Proterozoic to Early Cambrian) and Hercynian age (middle to late Paleozoic), Petrological, structural, and geo chronological data attest to a number of tectonic episodes in the 620-480 M a interval, The model presented for this orogeny comprises stages of volcan ic are generation, backarc extension, tectonic inversion, crustal thickenin g, and cratonization in an Andean-type continental margin, The Hercynian cy cle began in the early Paleozoic with episodes of continental rifting. Orog enic events occurred in the 390-300 Ma interval and affected both the Cadom ian basement, which was heterogeneously reworked and overprinted, and the P aleozoic cover. Hercynian regional metamorphism was generally of low grade. High-pressure assemblages and thermal domes developed locally, and were re lated to subduction and late extensional events. The geodynamic model propo sed for the Cadomian and Hercynian orogenies and the correlation with compa rable areas from pre-Mesozoic massifs elsewhere in western Europe account f or the geodynamic scenarios that drove the fate of Cadomian terranes.