The multistage crystallization of zircon in calc-alkaline granitoids: U–Pb age constraints on the timing of Variscan tectonic activity in SW Iberia

Abstract

explained by: (1) crystallization from melts with different compositions (felsic peraluminous to felsic-intermediate metaluminous; 0.001 < Th/U ratio < 0.5) and (2) transient temperature fluctuations in a system where anatectic felsic melts periodically underwent injection of more mafic magmas at higher temperatures. The two studied calc-alkaline granitoids do not include inherited zircons (pre-Carboniferous), probably because they were formed at the highest grade of metamorphism (T > 837 °C; granulite facies) and/or because they were derived from inheritance-poor felsic and mafic rocks from a previous cycle, as suggested by the internal structures of zircon cores. These Variscan magmatic rocks with crystallization ages estimated at ca. 336-335 Ma are spatially and temporally related to hightemperature metamorphism, anatexis, processes of interaction between crustal-and mantle-derived magmas and intra-orogenic extension that acted in SW Iberia during the Early Carboniferous.

An Active Seismic Zone in Intraplate West Iberia Inferred From High‐Resolution Geophysical Data

“…During the Carboniferous, after the collision between Gondwana and Laurussia, sedimentary basins developed within the OMZ (e.g., Eguiluz et al, ; Pereira et al, ). They formed in an extensional regime and were accompanied by deep crustal metamorphism and emplacement of voluminous magmatism (Giese & Bühn, ; Mata & Munhá, ; Pereira et al, ; Sánchez‐Garcıa et al, ). The IBERSEIS deep reflection profile (Carbonell et al, ; Simancas et al, ), wide angle transects (Palomeras et al, ), petrophysical analysis (Brown et al, ), and geophysical modeling (Palomeras et al, ) suggest that Carboniferous magmatism is responsible for the emplacement of a large amount of magma at midcrustal depths (12–14 km) in the region.…”

“…Most outcropping rocks in the ASZ and ESZ are part of the Évora Massif (Fernández et al, ; Pereira et al, ), a metamorphic dome mainly composed of gneisses, migmatites, schists, amphibolites, and minor gabbros and diorites (Figure c). This metamorphic complex is contemporaneous with the emplacement of igneous rocks, including calc‐alkaline felsic and mafic magmas represented by outcropping plutons of tonalites, gabbros, diorites, granodiorites, and granites (Pereira et al, ). Toward the west, the region is covered by the recent Cenozoic sediments of the Tagus and Sado river basins.…”

“…To the south, the Beja-Acebuches ophiolite marks the transition between the OMZ and the SPZ (Dallmeyer et al, 1993;Quesada, 1991;Ribeiro et al, 2010). (Giese & Bühn, 1994;Mata & Munhá, 1990;Pereira et al, 2015;Sánchez-Garcıa et al, 2003). The IBERSEIS deep reflection profile (Carbonell et al, 2004;Simancas et al, 2003), wide angle transects (Palomeras et al, 2009), petrophysical analysis (Brown et al, 2012), and geophysical modeling (Palomeras et al, 2011) suggest that Carboniferous magmatism is responsible for the emplacement of a large amount of magma at midcrustal depths (12-14 km) in the region.…”

Exhuming a cold case: The early granodiorites of the northwest Iberian Variscan belt—A Visean magmatic flare-up?

“…This early Carboniferous suite is widely represented in other areas of the WEVB (e.g., Schaltegger, 1997Schaltegger, , 2000Schulmann et al, 2002;Eichhorn et al, 2000;Cartannaz et al, 2007;Li et al, 2014;Mezger and Gerdes, 2016;Tabaud et al, 2015;Galán et al, 1997;Ledru et al, 2001;Rossi et al, 2009;Kubínová et al, 2017;Laurent et al, 2017;Žák et al, 2017), including the Ossa Morena zone of southwest Iberia (e.g., Dallmeyer et al, 1995;Ordóñez Casado, 1998;Montero et al, 2000;Ordóñez Casado et al, 2008;Romeo et al, 2006;Jesus et al, 2007;Pin et al, 2008;Pereira et al, 2009Pereira et al, , 2015Braid et al, 2012;Dupuis et al, 2014;Gladney et al, 2014;Cambeses et al, 2015). In the Ossa Morena zone rocks belonging to this suite are the volumetrically dominant granitoids, whereas in northwest Iberia the volumetrically dominant granitoids are both the previously described syntectonic leucogranites and the postorogenic granites (Fig.…”

Age of the basement beneath the Mesozoic Lusitanian Basin revealed by granitic xenoliths from the Papôa volcanic breccia (West Iberia)

“…Upper Devonian to Lower Carboniferous marine siliciclastic rocks are overlain by Upper Carboniferous terrestrial strata in the CIZ and OMZ (Martínez-Catalán et al, 2007;Quesada et al, 1990) and by Upper Carboniferous marine strata in the SPZ (Oliveira, 1990;Pereira et al, 2020). Carboniferous and Lower Permian magmatism (c. 350-290Ma) is widespread in the Iberian Massif (Castro et al, 2002;Dias da Silva et al, 2018;Fernández-Suarez et al, 2011;Pereira et al, 2015Pereira et al, , 2017a (Fig. 3).…”