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

Abstract

Dating of zircon cores and rims from granulites developed in a
shear zone provides insights into the complex relationship
between magmatism and metamorphism in the deep roots of
arc environments. The granulites belong to the uppermost
allochthonous terrane of the NW Iberian Massif, which forms
part of a Cambro-Ordovician magmatic arc developed in the
peri-Gondwanan realm. The obtained zircon ages confirm that
voluminous calc-alkaline magmatism peaked around 500 Ma
and was shortly followed by granulite facies metamorphism
accompanied by deformation at c. 480 Ma, giving a time
framework for crustal heating, regional metamorphism, deformation
and partial melting, the main processes that control the
tectonothermal evolution of arc systems. Traces of this arc can
be discontinuously followed in different massifs throughout the
European Variscan Belt, and we propose that the uppermost
allochthonous units of the NW Iberian Massif, together with the
related terranes in Europe, constitute an independent and
coherent terrane that drifted away from northern Gondwana
prior to the Variscan collisional orogenesis.