Tracing the Cambro-Ordovician ferrosilicic to calc-alkaline magmatic association in Iberia by in situ U–Pb SHRIMP zircon geochronology (Gredos massif, Spanish Central System batholith)

Abstract

18 U-Pb geochronological study of zircons from nodular granites and Qtz-diorites comprising part of 19Variscan high-grade metamorphic complexes in Gredos massif (Spanish Central System batholith) 20 points out the significant presence of Cambro-Ordovician protoliths among the Variscan migmatitic 21 rocks that host the Late Carboniferous intrusive granitoids. Indeed, the studied zone was affected by 22 two contrasted tectono-magmatic episodes, Carboniferous (Variscan) and Cambro-Ordovician. The European Variscan Chain resulted from the closure of the Rheic Ocean and the ensuing 50 collision of Gondwana and Laurussia (Matte, 1991; Martínez Catalán et al., 2007, Nance et al., 51 2010. In NW Iberian Massif, several allochthonous complexes are thrust onto parautochthonous 52 and autochthonous terranes (western part of the European Variscan Chain; e.g., Martínez Catalán et 53 al., 2002). These terranes belong to the North-Gondwana margin (e.g., Martínez Catalán et al., 54 2002Catalán et al., 54 , 2007 Abati et al., 2007; Díez Fernández et al., 2010, 2012a. The pre-Variscan Paleozoic 55 evolution of this tectonic realm includes the formation of a Cambro-Ordovician peri-Gondwanan 56 magmatic arc presumably linked to the subduction of the Iapetus-Tornquist Ocean, and 57 simultaneous opening of the Rheic Ocean triggered by back-arc extension and rifting (e.g., van 58 Staal et al., 1998; Abati et al., 1999 Abati et al., , 2007 Winchester et al., 2002; Stampfli and Borel, 2002; 59 Fernández-Suárez et al., 2003; Fuenlabrada et al., 2010; Sánchez Martínez et al., 2012; Díez 60 Fernández et al., 2012b). The analysis of the Cambro-Ordovician magmatism in the Iberian Massif 61 is essential to properly understand the building of the arc and its bearing on the inception of the 62 Rheic Ocean. This widespread magmatism along the northern Gondwana margin comprises rift-63 related mafic rocks: continental tholeiites (Murphy et al., 2008) and N-MORB, E-MORB and OIB 64 basalts (Sánchez-García et al., 2010), alkaline to peralkaline granites (Pin et al., 1992; Díez 65 Fernández et al., 2012b, 2015, and silicic peraluminous volcanic and plutonic rocks (e.g., 66Fernández et al., 2008, Díez Montes et al., 2010. These silicic rocks have been associated with the 67 onset of rifting and the formation of migmatites and a core-complex setting in the middle crust (e.g., 68 3 Fernández et al., 2008, Díez Montes et al., 2010 Silva et al., 2014Silva et al., , 2015. 73During the past decade, many Variscan metaigneous domains of the Central Iberian Zone (central 74 part of the Iberian Massif) have been ascribed to a late Cambrian to Middle Ordovician (ca. 500-75 460 Ma) long lasting magmatic event that occurred in North-Gondwana margin (Fig. 1a, Table 1): 76 1) the so-called "Ollo de Sapo" Formation (Hernández Sampelayo, 1922; Parga Pondal et al., 1964; 77 Martínez Catalán et al., 2004), the best known and most voluminous unit adscribed to Cambro-78Ordovician magmatism (Fernández et al., 2008) dated at 495...

Poly-Orogenic Melting of Metasedimentary Crust From a Granite Geochemistry and Inherited Zircon Perspective (Southern Calabria-Peloritani Orogen, Italy)

“…Therefore, the late Cadomian granites formed by melting of the same meta-greywacke source as the late Variscan granites, but at higher temperatures. This interpretation is consistent with the high content in ferromagnesian components observed in Figure 7 and reinforces the possibility that the most mafic late Cadomian granitoids resulted from particularly high degrees of melting, as proposed for the Cambro-Ordovician ferrosilicic magmatism defined in the central Iberian Massif (Fernández et al, 2008;Castro et al, 2009;Díaz-Alvarado et al, 2016). The CPO late Cadomian granitoids show indeed many geochemical features of the high-silica ferrosilicic magmatic rocks, as defined by Castro et al (2009), such as high FeO and MgO contents (FeOt > 2.5 wt.…”

“…The analysis of age patterns of detrital and inherited zircon in metasedimentary and igneous rocks, respectively, is commonly used in provenance studies aimed at reconstructing the geodynamic evolution of continents (e.g., Nance et al, 2014 and references therein). On the other hand, zircon inheritance patterns in igneous rocks have been employed relatively little as a petrogenetic tool, despite their considerable potential to provide key information on both magma sources and petrogenetic processes (e.g., Chen and Williams, 1990;Paterson et al, 1992;Williams, 1992Williams, , 2001Zeck and Williams, 2002;Fiannacca et al, 2008Fiannacca et al, , 2013Fiannacca et al, , 2017Jeon et al, 2012;Samperton et al, 2015;Díaz-Alvarado et al, 2016;Jeon and Williams, 2018;Schaltegger and Davies, 2018).…”

Atypical peri-Gondwanan granodiorite–tonalite magmatism from Southern Iberia. Origin of magmas and implications

“…passive margin) plate margin setting (Díez Montes et al, 2010;Martínez Catalán et al, 2004;Montero et al, 2009), and (2) the 'continuous' model that considers a protracted evolution of an active margin (i.e. back-arc basin) that has extended over time from the Ediacaran to the Ordovician (Abati et al, 2010;Díaz-Alvarado et al, 2016;Díez Fernández et al, 2010, 2012Fernandez et al, 2008;Pereira et al, 2018). The above-mentioned tectonic models agree that the Cambro-Ordovician magmatism is related to the development of an intracontinental rifting.…”

“…However, this study will focus on the Neoproterozoic-Ordovician CIZ stratigraphy and related magmatism. The oldest Ediacaran to Early Cambrian siliciclastic rocks (Schist Greywacke Complex; SGC,) are unconformably overlain by a Cambro-Ordovician felsic igneous-sedimentary complex, named "Ollo de Sapo Formation" in the north of the CIZ (Díez Montes et al, 2010;Fernandez et al, 2008;Montero et al, 2009), the Urra Formation in the south of the CIZ (Gonçalves, 1971;Solá et al, 2008)and/orOrdovician siliciclastic rocks (including the Armorican quartzites), all intruded by Cambro-Ordovician granitic rocks (Antunes et al, 2009;Bea et al, 2006;Ferreira et al, 2018;Montero et al, 2007Montero et al, , 2009Neiva et al, 2009;Pereira et al, 2018;Talavera et al, 2013), and a few gabbrodioritic rocks (Díaz-Alvarado et al, 2016;Gonçalves, 1971;Solá, 2007).…”

“…There is now a broad consensus regarding the Cambro-Ordovician tectonic setting of the CIZ as essentially extensional (e.g., Abati et al, 2010;Díaz-Alvarado et al, 2016;Díez Fernández et al, 2010, 2012Díez Montes et al, 2010;Fernandez et al, 2008;Martínez Catalán et al, 2004;Montero et al, 2009;Pereira et al, 2018). Regardless of whether this extension was related to the evolution of a passive margin that ultimately led to the Rheic Ocean, or to a back-arc basin associated with an active margin, the divergence process had profound petrogenetic consequences.…”