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

Abstract

Polyphase ductile deformation and metamorphism in the Ossa-Morena zone of the Iberian Massif are related to a complex evolution including two major tectonothermal episodes of Cadomian (Late Proterozoic to Early Cambrian) and Hercynian age (middle to late Paleozoic). Petrological, structural, and geochronological data attest to a number of tectonic episodes in the 620–480 Ma interval. The model presented for this orogeny comprises stages of volcanic arc generation, backarc extension, tectonic inversion, crustal thickening, and cratonization in an Andean-type continental margin. The Hercynian cycle began in the early Paleozoic with episodes of continental rifting. Orogenic events occurred in the 390–300 Ma interval and affected both the Cadomian basement, which was heterogeneously reworked and overprinted, and the Paleozoic cover. Hercynian regional metamorphism was generally of low grade. High-pressure assemblages and thermal domes developed locally, and were related to subduction and late extensional events. The geodynamic model proposed for the Cadomian and Hercynian orogenies and the correlation with comparable areas from pre-Mesozoic massifs elsewhere in western Europe account for the geodynamic scenarios that drove the fate of Cadomian terranes.