Distinct sources for syntectonic Variscan granitoids: Insights from the Aguiar da Beira region, Central Portugal

The Variscan syntectonic granitoid plutons from the Aguiar da Beira region (central Portugal) were emplaced into metasediments of Late Proterozoic-Early Cambrian age during the last Variscan ductile tectonic event (D-3), which is related to dextral and sinistral shearing. The older intrusion, with a U-Pb ID-TIMS zircon age of 321.8 +/- 2.0 Ma, consists of porphyritic biotite granodiorite-granite with transitional I-S type geochemical signature, relatively low Sr-87/Sr-88(322) ratios (0.7070-0.7074), epsilon Nd-322 values of -3.9 to -4.6 and whole-rock and zircon delta O-18 values of 10.6 parts per thousand and 8.0 parts per thousand, respectively. By contrast, the younger intrusion is an S-type muscovite-biotite leucogranite, emplaced at 317.0 +/- 1.1 Ma, showing more radiogenic Sr-87/Sr-86(317) = 0.7104-0.7146, lower epsilon Nd-317 values of -7.7 to -8.7 and higher delta O-18-wr = 11.3 parts per thousand and delta O-18-zr = 9.5 parts per thousand. The combined isotopic and geochemical evidence supports a lower crustal origin for the biotite granodiorite-granite, involving the anatexis of lower crustal metaigneous protoliths, and possible hybridization with mantle-derived magmas. A shallower origin, at mid crustal levels, from pure crustal derivation, through moderate degrees of partial melting of Proterozoic-Cambrian metasediments is proposed instead for the muscovite-biotite leucogranite. (C) 2014 Elsevier B.V. All rights reserved.