Mantle‐like Sr–Nd isotope composition of Fe–K subalkaline granites: the Peneda–Gerês Variscan massif (NW Iberian Peninsula)

Abstract

AbstractThe Peneda–Gerês massif is one of the most representative NW Iberian late‐ to post‐orogenic Variscan granitic plutons. It resulted essentially from the subsynchronous emplacement, at 290–296 Ma, of two granitic magmas of Fe–K subalkaline affinity, with primitive isotopic composition: Sri = 0.703–0.707 and εNdi=−1.5 to −2.4. An origin by mantle input followed by mantle–crust interactions is proposed, implying the contribution of a less enriched mantle component than that involved in the genesis of synorogenic hybrid granitoids of Mg–K subalkaline affinity. A less voluminous aluminopotassic and isotopically more evolved magma (Sri=0.708–0.709 and εNdi=−3.5 to −3.9) with little or no mantle input was also generated, suggesting the involvement of lower crust materials. Therefore, this study suggests an input of juvenile magmas in late Variscan times, the mantle‐like isotope signature of Fe–K granitic magmatism being clearly related to a geodynamic setting of extensional processes, large‐scale uplift and thinning.