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

Abstract

The 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.

Genesis and emplacement of felsic Variscan plutons within a deep crustal lineation, the Penacova-Régua-Verín fault: An integrated geophysics and geochemical study (NW Iberian Peninsula)

“…However the field relations, late-tectonic emplacement along the same tectonic lineation, led us to suppose that they have similar intrusion ages. The available U-Pb and Rb-Sr ages clearly indicate a post-D 3 emplacement for these granites which agree with the geological data and the AMS studies (Sant'Ovaia, 2000;Sant'Ovaia et al, 2000), as well as to the geochronologic data available for post-D 3 Variscan granitoids in Northern Portugal (Pinto et al, 1987;Dias et al, 1998;Martins et al, 2001;Mendes and Dias, 2004). In terms of Sr and Nd compositions, the VPAG and the AFG present the same rather little evolved isotope composition with ( 87 Sr/ 86 Sr) 299 between 0.7067 to 0.7071 and 0.7076 to 0.7079, respectively, whereas εNd 299 is very similar in both granites around to −2.5 ( Table 2).…”

“…These granites are significantly less radiogenic in Sr but more radiogenic in Nd than most of the Variscan granitoid rocks of Iberian Peninsula as well as most of the European Variscan granites (Cuesta, 1991;Schaltegger and Corfu, 1992;Cocherie et al, 1994;Forster et al, 1999;Paquette et al, 2003 and references therein). However, we must note that the post-D 3 granites from Northern Portugal, all have a weakly evolved isotopic composition (Silva and Neiva, 2004;Mendes and Dias, 2004).…”

Multiple crustal sources for post-tectonic I-type granites in the Hercynian Iberian Belt

“…SCS sector: 11 = Villacastin, 12 = La Cabrera, 13 = La granites (e.g. Capdevila and Floor 1970;Capdevila et al 1 973;Mendes and Dias 2004;Cuesta and Gallastegui 2004). The markedly felsic composition and the peralumi nous character of most of these granites make a direct comparison to the typical calc-alkaline series of subduction zones diffi cult.…”

Late-Variscan emplacement and genesis of the Vieira do Minho composite pluton, Central Iberian Zone: Constraints from U–Pb zircon geochronology, AMS data and Sr–Nd–O isotope geochemistry

“…1B), this pluton crosscuts the peraluminous two-mica syn-D 3 granites of Cabeceiras de Basto Complex (Almeida et al, 2002) and a metasedimentary sequence Silurian in age (Ribeiro et al, 2001). At the northern part it was intruded by the post-D 3 Gerês Massif (Mendes and Dias, 2004). Contact metamorphism of the studied granitoid pluton is marked by neoformation of biotite and cordierite (P: 2 kb, T: 550°C) (Ramos et al, 1981) and is superimposed to a regional metamorphism which reaches biotite-andalusite zone (Ramos et al, 1981).…”