An Upper Devonian foredeep basin in the Southern Central Iberian Zone (Variscan Iberian Massif): Consequences for Variscan plate dynamics

Abstract

New field research and revision of previous works in the Variscan Iberian Massif unravel the existence of an Upper Devonian foredeep basin in the southern Central Iberian Zone, close to the suture area with the Ossa-Morena Zone. Superimposed Tournaisian-Visean extensional basins, a Serpukhovian-Bashkirian foreland basin, and the Late Variscan wrench tectonics obscure this foredeep basin. This synorogenic sedimentation is related to the Late Devonian continental subduction featured by a high-pressure metamorphic belt exposed to the south of this area. The unravelling of this trough with marine turbiditic sedimentation and fragments of terrestrial plant fossils, allows the reinterpretation of the Upper Devonian deposits along the northern half of the Iberian Massif. It also explains the lack of Middle Devonian sedimentary rocks in most of the massif. The geometry and stratigraphy correspond to a collisional foreland basin with its classical depozonal elements. The structure of the foreland basin solves discussions about tectonic polarity in the Ossa-Morena - Central Iberian Variscan collision, the upper plate thus corresponds to the Upper Allochthon of the Ossa-Morena Zone. The tracking of the NE migration (current coordinates) of the bulge area suggests a ∼ 5.5 cm/yr rate of Upper Devonian convergence and up to ∼800 km of continental underplating. We also propose a correlation with the Upper Devonian high-pressure Basal Units and the synorogenic sediments of the NW Iberian Massif. Conclusions can be extended to the plate architecture between other peri-Gondwana terranes of the Armorican assemblage and the northern Gondwana margin.