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

Abstract

The Spanish Central System (SCS) batholith. located in the Central Iberian Zone, is one of the largest masses of granite in the European Variscan Belt. This batholith is a composite unit of late-and post-kinematic granitoids dominated by S-and I-type series granite. with subordinate leucogranite and granodiorite. Zircon trace element contents, from two representative S-type and three I-type granitoids from the eastern portion of the SCS batholith, indicate a heterogeneous composition due to magma differentiation and co-crystallisation of other trace element-rich accessory phases. In situ. U-Pb dating of these zircons by SHRIMP and LA-ICP-MS shows 479-462-Ma inherited zircon ages in the I-type intrusions. indicating the involvement of an Ordovician rnetaigneolls protolith, while the S-type intrusions exclusively contain Cadornian and older zircon ages. The zircon crystallisation ages show that these granites have been emplaced at ca. 300 Ma with a time span between 303 ± 3 Ma and 298 ± 3 Ma. Precise dating by CA-ID-TIMS reveals a pulse at 305.7 ± 0.4 Ma and confirms the major pulse at 300.7 ± 0.6 Ma. These ages match the Permo-Carbonif erous age for granulite-fades metamorphism of the lower crust under the SCS batholith and coincide with a wide spread granitic event throughout the Southern Variscides. Ti-in zircon thermometry indicates temperatures between 844 and 784°C for both the S-and I-type granites. rein forcing the hypothesis that these granites are derived from deep crustal sources.

Zircon U-Pb and Hf isotopic constraints on the genesis of a post-kinematic S-type Variscan tin granite: the Logrosán cupola (Central Iberian Zone)

“…The average temperatures obtained for the Logrosán Variscan-age zircon crystallization is 836 ºC, similar to other temperature estimates on S-type granites of the Central Iberian Zone (788 to 844ºC after Orejana et al, 2012). Lower temperature estimates (699-777 ºC, Table 1) have been obtained based on whole-rock zircon saturation.…”

“…Widespread granite generation occurred across the Central Iberian Zone over 325-300 Ma time interval (e.g., Dias et al, 1998;Fernández Suárez et al, 2000;Bea et al, 2003;Orejana et al, 2012). Most of the felsic magmatism in the CIZ is synto post-tectonic with respect to the last ductile deformation phase (D 3 ) (Dias et al, 1998) with three peaks at 320 (mainly syn-D 3 leucogranites of Galicia and northern Portugal), 308-306 and 301 Ma Teixeira et al, 2011;Fernández-Suárez et al, 2000;Dias et al, 1998).…”

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

“…Therefore we propose that the felsic granulites could be a potential source for the studied granites. Recent studies on U-Pb zircon ages in the Spanish Central System granulites seem to reinforce this conclusion, showing an abundant population of metamorphic zircons formed in the range 320-275 Ma (Orejana et al, 2012) which match the age of crystallisation of the analysed granites.…”

Mineral chemistry of late Variscan gabbros from central Spain: constraints on crystallisation processes and nature of the parental magmas

“…The last events of the Variscan orogeny are characterised in central Spain (and in many other western Variscan massifs) by a widespread felsic magmatism, with abundant granite intrusions emplaced in the range ~310-298 Ma (e.g., Orejana et al, 2012;Merino Martínez et al, 2014, and references therein). Late Variscan magmatism, including both the felsic magmas and the accompanying scarce basic melts, could have been originated by adiabatic decompression as lithosphere experienced considerable thinning during the orogen collapse (e.g., Orejana et al, 2009;.…”

“…The calc-alkaline gabbroic intrusions, which are mainly concentrated in the western SCS (Franco and García de Figuerola, 1986;Franco and Sánchez-García, 1987), are small (usually < 1 km in length) Variscan post-tectonic plutons with ages mainly in the range 305-300 Ma (Zeck et al, 2007;Villaseca et al, 2011). According to recent data, they are coeval with the main SCS granitoid intrusions (~308-298 Ma; Zeck et al, 2007;Díaz-Alvarado et al, 2011;Orejana et al, 2012).…”