Relamination in a Variscan subduction system: early structural evolution of the Central Unit (SW Iberia)

Despite the fact that Earth has numerous high-P belts, relamination remains as a poorly studied process. We describe a continental subduction zone in which exhumed high-P rocks became a relaminant beneath an upper plate. This study focuses on the Variscan Orogeny (SW Iberia). A Variscan lithospheric-scale thrust transported deeper sections of a continental slab onto shallower ones during the Devonian. This piece of exhuming slab reached the base of the upper plate, which locked the high-P rocks' exhumation course through the subduction zone. At this point, the high-P rocks became a relaminant, moving away from the trench and beneath the upper plate. Relamination was achieved by a combination of synthetic and anti-thetic shearing in relation to the subduction polarity. These shear zones were coeval with the constriction of the subduction system as more buoyant lithosphere gradually entered the subduction zone. The combination of these processes produced large-scale recumbent folds, which affected the early thrusts and contributed to the relamination process by channeling subhorizontal flow during fold amplification.