Variscan Suture Zone and Suspect Terranes in the NW Iberian Massif: Allochthonous Complexes of the Galicia-Trás os Montes Zone (NW Iberia)

Abstract

The NW Iberian Allochthon represents the suture of a peri-Gondwanan, Paleozoic ocean formed around the Cambro-Ordovician boundary but having registered renewed spreading during the Lower Devonian. The ocean separated a piece of continental crust detached from NW Gondwana from the northern and northwestern parts of present Africa. The separation was a consequence of slab roll-back of a wide, subducting oceanic lithosphere around 500 Ma. Early Variscan plate convergence closed the oceanic domain involving three subduction events between 400–365 Ma, and building an accretionary prism formed by the detached continental fragment, the new oceanic lithosphere and the external margin of Gondwana. The change of regime from subductive to collisional occurred at the Devonian-Carboniferous transition and was responsible for the emplacement of the Allochthon above the Central Iberian Autochthon.