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)

Abstract

Multidisciplinary studies integrating, U-Pb geochronology, whole-rock geochemical data, isotope geochemistry, anisotropy of magnetic susceptibility (AMS) studies and gravimetry were carried out on the Vila Pouca de Aguiar and the Águas Frias-Chaves porphyritic biotite granite plutons. Both plutons occur independently in a distance of about 20 km. The Vila Pouca de Aguiar and Águas Frias-Chaves plutons are examples of late to post-orogenic felsic Variscan granites in northern Portugal (NW Iberian Peninsula). The U-Pb zircon analyses yield a consistent age of 299 ± 3 Ma which is considered to be the emplacement age of the two plutons. These granites are weakly peraluminous, show high HREE and Y (and low P) contents which are consistent with them being I-type. This is also supported by their weakly evolved isotopic compositions, 87 Sr/ 86 Sr i = 0.7044-0.7077 and εNd = − 2.0 to − 2.6, as well as by the whole rock oxygen isotope (δ 18 O VSMOW) ranging from + 9.7‰ to + 11.0‰. The emplacement of granite magma took place after the third Variscan deformation phase (D 3 ) in an extensional tectonic regime, large scale uplift and crustal thinning. The integration of different data suggests that both plutons have the same feeding zone aligned within the Penacova-Régua-Verin fault (PRVF) and that both have the same structure which is related to late Variscan phases. The thicker shape for the Águas Frias-Chaves pluton comparing to that of the Vila Pouca de Aguiar pluton is compatible with different depths of PRVF sectors. The available data led us to propose a model of partial melting of a meta-igneous lower crustal source rather than an open-system of mantle-crust interaction. The interaction between the continental crust and invading mafic magmas could have been limited to mere heat transfer and, perhaps, local intermingling.

U–Pb geochronology and zircon composition of late Variscan S- and I-type granitoids from the Spanish Central System batholith

“…(5 Carracedo et al 2009;Martins et al 2009;Neiva et al 2009;Sola et al 2009;Diaz-Alvarado et al 2011 ;unpublished data) and from the Spanish Central System (Zeck et al 2007b;Diaz Alvarado et al 2011;this study) (Fig. 9b).…”

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

“…The late deformation phase, D 3 , Namurian-Westphalian in age, is correlated to the post-thickening and extension which marked the end of the collision process (Dias and Ribeiro, 1995;Lagarde et al, 1992). The events related to this tectonic phase were marked by vertical folds with subhorizontal axes and strike-slip sinistral and dextral, subvertical shear zones which controlled the large volume of orogenic granitic rocks emplaced in the Central Iberian Zone, (Aguado et al, 2005;Almeida et al, 2002;Dias et al, 1998Dias et al, , 2002Ferreira et al, 1987;Martins et al, 2009Martins et al, , 2011Noronha et al, 1979). Based on field and geochronological data, these Variscan granites were divided into two main groups (Dias et al, 1998;Ferreira et al, 1987;Martins et al, 2009Martins et al, , 2011: synorogenic (syn-late and late to post-D 3 ; 320-300 Ma) and late to post-orogenic (post-D 3 ; 299-290 Ma).…”

“…The lack of appropriate sources in terms of isotopic composition has led to consider several models for the origin of the peraluminous granites: (i) mixing or assimilation between crustal melts and mantle-derived magmas (Castro et al, 1999;Dias and Leterrier, 1994;Dias et al, 2002Dias et al, , 2009Moreno-Ventas et al, 1995) (ii) partial melting of essentially crustal sources either from mid-crustal levels (Bea et al, 2003;Neiva, 1998) or from infracrustal materials, namely metaigneous rocks (Dias et al, 2002(Dias et al, , 2009Martins et al, 2009;Villaseca and Herreros, 2000;Villaseca et al, 1998Villaseca et al, , 1999.…”

Emplacement of the Lavadores granite (NW Portugal): U/Pb and AMS results

“…This granite is porphyritic, coarse-grained biotite granodiorite-monzogranite and contains quartz + plagioclase (andesine/oligoclase) + perthitic orthoclase and microcline + biotite + zircon+ sphene + apatite + allanite AE amphibole. The main petrographic feature that distinguishes this granite is the presence of the accessory phase magnetite, which is uncommon in Late Variscan granites in northern Portugal (Dias et al, 2002;Martins et al, 2009;Mendes and Dias, 2004) and can be considered a magnetite-type granite (Ishihara, 1977). No clear shape preferential orientation of the main minerals was observed in the studied sites.…”

“…Outstanding features of the internal zone of the Iberian Variscides, the Central Iberian Zone, are a complex shear zone network and a intensive late to post-orogenic Variscan magmatism with the most active period spanning broadly the time between c. 320 and 290 Ma (Dias et al, 1998(Dias et al, , 2009Ferná ndez-Suá rez et al, 2011;Martins et al, 2009). In northern Portugal, this magmatic activity has left large granitoid plutons which presented highly contrasted compositions and whose emplacement was in most cases associated to major Variscan structures, namely shear zones and strike slip faults.…”