The Cadomian orogeny in the Iberian Massif revisited

The exposed basement of the Variscan Iberian Massif includes various remains of the accretionary Cadomian orogen that fringed the northwestern margin of Gondwana in the late Neoproterozoic–Terreneuvian. Subduction of the Mirovoi Ocean beneath Gondwana was responsible for the formation of an arc system that was finally accreted to the continental margin. In the Iberian Massif, a complex Cryogenian–Fortunian arc/backarc system is preserved in the Ossa-Morena Zone, whereas a thick Ediacaran–Fortunian infill of a vast retroarc basin, developed as a result of arc accretion, is exposed in the Central Iberian, West-Asturian-Leonese and Cantabrian zones, defining a proximal (hinterland) to distal (foreland) transect. Wedge-top, foredeep and forebulge basin domains may be recognised in the foreland basin, but the basement of these Ediacaran–Fortunian successions is nowhere exposed. The Cadomian suture zone is currently exposed along the Variscan-age Badajoz-Córdoba shear zone that separates the Ossa-Morena Zone from the Central Iberian Zone. The suture is defined by an ‘accretionary unit’ consisting of high pressure metamorphic rocks and dismembered ophiolites, which is sandwiched between an underlying Gondwana margin Parautochthon (lower plate) and an overlying Ossa-Morena-like arc/backarc unit (upper plate). This geometric superposition implies southward polarity of the subduction responsible for the accretion, i.e. antithetic to the main subduction beneath Gondwana responsible for the development of the Cadomian arc. This double subduction system requires the existence and closure of a backarc basin, which is documented by the development of a secondary arc in the northern half of the Ossa-Morena Zone.