The high-pressure Iberian–Czech belt in the Variscan orogen: Extrusion into the upper (Gondwanan) plate?

Abstract

A Siluro-Devonian, high -pressure (HP) belt (the Iberian–Czech or IC belt) extends from Iberia (Cordoba–Coimbra Shear Zone) through Armorica and the Massif Central to the Bohemian Massif (Iberian–Czech [IC] belt), and includes arc and periarc rocks, MORB and supra-subduction ophiolites, and passive margin sequences. It has generally been interpreted to be either: (a) a suture of the Galician, South Brittany, Massif Central and Moldanubian ocean; (b) a nappe rooted to the north in the Rheic Ocean; or (c) the result of post-collisional strike-slip shuffling of the Gondwanan margin during which a slice of the Rheic Ocean was inserted into the Gondwanan margin. We agree with a Rheic Ocean origin, but propose that the IC belt represents a pre-collisional part of the Gondwanan continental–oceanic margin that was removed by subduction erosion, underwent HP metamorphism, and was then extruded into the overlying Gondwanan plate. This model explains: (i) the lack of paleolatitudinal and faunal differences across the IC belt, (ii) the juxtaposition of active margin tectonics within synchronous passive margin sequences, and (iii) the pre-collisional age of most of the HP metamorphism. The complete range of HP rocks in the IC belt, from blueschist to hot eclogites, indicates that previous correlations with B- and A-type subduction, respectively, cannot be sustained.