Using SHRIMP zircon dating to unravel tectonothermal events inudarc environments. The early Palaeozoic arc of NW Iberia revisited

摘要

Dating of zircon cores and rims from granulites developed in audshear zone provides insights into the complex relationshipudbetween magmatism and metamorphism in the deep roots ofudarc environments. The granulites belong to the uppermostudallochthonous terrane of the NW Iberian Massif, which formsudpart of a Cambro-Ordovician magmatic arc developed in theudperi-Gondwanan realm. The obtained zircon ages confirm thatudvoluminous calc-alkaline magmatism peaked around 500 Maudand was shortly followed by granulite facies metamorphismudaccompanied by deformation at c. 480 Ma, giving a timeudframework for crustal heating, regional metamorphism, deformationudand partial melting, the main processes that control theudtectonothermal evolution of arc systems. Traces of this arc canudbe discontinuously followed in different massifs throughout theudEuropean Variscan Belt, and we propose that the uppermostudallochthonous units of the NW Iberian Massif, together with theudrelated terranes in Europe, constitute an independent andudcoherent terrane that drifted away from northern Gondwanaudprior to the Variscan collisional orogenesis.