Recycled metaigneous crustal sources for S- and I-type Variscan granitoids from theudSpanish Central System batholith: Constraints from Hf isotope zircon composition

摘要

The Spanish Central System (SCS) is one of the largest granite batholiths in the European Variscan Belt.udZircons from five granitic intrusions from the eastern SCS have been separated and analysed for Hf isotopesudby laser ablation MC-ICPMS, in order to evaluate the nature of granitic magma source. Two samples areudcordierite-bearing S-type granites, the rest are amphibole-bearing I-type monzogranites. Hf-isotopeudcomposition of zircons from these granites defines a narrow range of negative ɛHf values (−1.1 to −5.8),udtypical of crustal protoliths. The within-sample variation of zircon Hf isotope composition is slightly aboveudthe analytical uncertainty (±1.5 ɛ units), suggesting the mixing of different magma batches during plutonudassembly. The S- and I-type granites display the same range of initial ɛHf values, that is in agreement withudprevious data showing that both SCS granite types have similar (Sr, Nd, O, Pb) isotope signatures. Theseudisotopic data suggest that they derived from similar sources, while the variation in peraluminosity could beudrelated to different partial melting conditions.udThe presence of a Lower Ordovician inherited zircon population (478–462 Ma), at least in I-type granites,udsuggests the involvement of Cambro–Ordovician orthogneisses as components in the source of some SCSudgranites. Inherited zircon population of similar age has also been identified in the SCS lower crustaludgranulites. The Hf-isotope composition of the analysed granite zircons is within that of zircons from theudabove granulites. Moreover, some evidence of a juvenile input at 560–595 Ma is recorded by Hf-isotope dataudin zircons from both the SCS granites and granulite xenoliths. Hf-isotope signature, in conjunction with otherudchemical, isotopic (Sr, Nd, O, Pb) and geochronological evidences, suggests that SCS granites were probablyudderived from metaigneous lower crustal sources. The Variscan magmatism in central Spain is dominantly audcrustal reworking event.