SHRIMP U-Pb ages and REE patterns for zircon from an anatectic Variscan two-mica granite from the Bemposta Migmatite Complex (Central Iberian Zone)

Abstract

The Variscan Bemposta Migmatite Complex (BMC) in northern Portugal (Central Iberian Zone) is a NE–SW-trending high-grade metamorphic core complex comprising upper-amphibolite- to lower-granulite-facies metapelites and metagreywackes of Ediacaran-Cambrian age and subordinate Ordovician orthogneisses showing evidence of intense migmatization. The available petrological data indicate that these rocks attained peak metamorphic conditions at the end of the first Variscan contractional deformation event (D1), followed an isothermal decompression path during D2 crustal extension, and underwent subsequent retrogression during D3 shearing. The whole BMC complex hosts numerous concordant intrusive bodies (sheets several meters thick) of syn-D2 two-mica granites, genetically linked to the leucosomes, suggesting that the emplacement of these magmas was synchronous with core complex extension. U-Pb SHRIMP ages obtained from zircons from one of these syn-D2 tabular plutons (the Faia d'Água Alta granite) yielded a crystallization age of 324 ± 3 Ma, providing a good estimate for the age of the D2 anatectic event in the region.