An Early Ordovician tonalitic–granodioritic belt along the Schistose-Greywacke Domain of the Central Iberian Zone (Iberian Massif, Variscan Belt)

Abstract

The Zarza la Mayor and Zarza de Montánchez tonalites and Arroyo de la Luz granodiorite are part of a tonalitic–granodioritic belt located along the Schistose-Greywacke Domain of the Central Iberian Zone. These intrusions are also part of the Central Extremadura Batholith, a set of plutons ranging from tonalite to leucogranite that have been considered a prime example of Variscan syn-kinematic plutonism. New LA-ICP-MS and CA-ID-TIMS U–Pb dating reveals that the Zarza la Mayor tonalite–granodiorite is an Early Ordovician intrusion. The LA-ICP-MS data show that there is an absence of inherited cores, despite some complex internal zoning with obvious resorption features in some of the zircon crystals. Dating of monazite and zircon by CA-ID-TIMS provides a concordant age of 478.1 ± 0.8 Ma. This age coincides with electron microprobe analysis (EMPA) monazite chemical ages for the Zarza de Montánchez (482 ± 10 Ma) and Arroyo de la Luz (470 ± 15 Ma) intrusions. These new data indicate the presence of an Early Ordovician belt of calc-alkaline tonalite–granodiorite in the Schistose-Greywacke Domain – the Beira Baixa–Central Extremadura tonalite–granodiorite belt – which resembles a continental magmatic arc. This belt is contemporaneous with the Ollo de Sapo magmatic event further north in the Central Iberian Zone.

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 only Ordovician age (ca. 447 Ma) could be related to the Ordovician magmatism described along the Central Iberian Zone (e.g., Rubio-Ordóñez et al, 2012;Neiva et al, 2009;Solá et al, 2008;Bea et al, 2007). In general, the probability density curve of the Logrosán granite inheritances shows a broad overlap with the zircon U-Pb age distribution previously reported for the Schist Greywacke Complex ages Teixeira et al, 2011) and the Spanish Central System granitoids (Talavera et al, 2012;Teixeira et al, 2011;Gutiérrez-Alonso et al, 2003) (Fig.…”

“…High Sn contents found in this granite with respect to the crustal average (i.e. granites with Sn contents higher than 10 ppm, as defined by interval (for further analytical details see Rubio-Ordóñez et al, 2012). Data reduction was done using the PbMacDat spreadsheet (Isacksen et al, 2007;www.earth-time.org).…”

Magmatic evolution in the N-Gondwana margin related to the opening of the Rheic Ocean—evidence from the Upper Parautochthon of the Galicia-Trás-os-Montes Zone and from the Central Iberian Zone (NW Iberian Massif)

“…Also, the discrimination diagrams used to determine the tectonic setting suggest two different geodynamic scenarios, namely a volcanic arc and a rifted continental margin. Both options have been arguably considered as possible tectonic settings for the northern margin of Gondwana during the late Neoproterozoic and lower Paleozoic, both in Iberia (e.g., Rodríguez Alonso et al 2004;Chichorro et al 2008;Sánchez-García et al 2008;Andonaegui et al 2012;Pereira et al 2012;Rubio-Ordóñez et al 2012) or elsewhere along the Variscan belt (e.g., Kröner et al 2000;von Raumer et al 2003;Linnemann et al 2007). For this reason, we need to rely on additional regional data in order to interpret the geochemical results properly.…”

“…In the northern and central part of the CIZ, the oldest Paleozoic events are represented by Cambro-Ordovician calc-alkaline magmatism ("Ollo de Sapo" gneisses and correlatives), which include large felsic plutons (Valverde-Vaquero and Dunning 2000; Bea et al 2006;Zeck et al 2007;Antunes et al 2009) and volcanic rocks intercalated within the sedimentary succession ; Díez-Montes 2010) or unconformably overlying Neoproterozoic-early Cambrian strata (Sá et al 2005;Coke et al 2011). In the southern part of the CIZ, there is a tonalitic-granodioritic belt of similar age (Rubio-Ordóñez et al 2012), as well as igneous suites that resemble the "Ollo de Sapo" formation (Urra Topping the UP sequence, and stratigraphically above the local equivalent to the Armorican Quartzite facies (Algoso Formation), there is a bimodal volcano-sedimentary complex, the Peso formation (PFm) of suspected Middle Ordovician age (Dias da Silva et al , 2015. This complex is the object of study of this contribution.…”

“…Villadepera Gneiss ages:Montero et al 2007 Miranda do Douro Gneiss ages:Bea et al (2006) andZeck et al (2007) ◂ Formation;Solá et al 2008). Two different geodynamic settings have been proposed for the emplacement of these magmatic rocks, one relating them to the formation of a magmatic arc (e.g.,Rubio-Ordóñez et al 2012) and the other associating their formation with fast crustal melting of Cadomian-related graywackes and calk-alkaline felsic rocks during the initial rifting stages in the N-Gondwana margin (e.g.,Montero et al 2007; Díez-Montes 2010). Mafic and felsic magmatism can be observed after deposition of the Armorican Quartzite (c. 477 Ma; Gutiérrez-Alonso et al 2007).…”