U–Pb ages of detrital zircons from the Basal allochthonous units of NW Iberia: Provenance and paleoposition on the northern margin of Gondwana during the Neoproterozoic and Paleozoic

Abstract

Keywords: NW Iberia Variscan allochthonous terranes Detrital zircons JA-ICP-MS U-Pb dating GeodynamicsLA-ICP-MS U-Ph ages of detrital zircons from eight silicic1astic samples from the Basal units of the Variscan allochthonous complexes of NW Iberia are used to establish the maximum depositional age and provenance of two tectonically-stacked metasedimentary sequences deposited on the outermost margin of Gondwana, and subsequently involved in the Rheic Ocean suture. The maximum depositionai ages for the two sequences is latest Neoproterozoicand latest Cambrian, respectively. The age spectra are also used to discuss the paleoposition of the NW Iberian basement on the continental margin ofGondwana prior to the opening of the Rheic Ocean, which is tentatively placed in northern Africa, between the West African and Saharan cratons. Based on similarities and differences with age data from the NW Iberian autochthon and other allochthonous terranes involved in the Rheic suture, the relative proportions of Mesoproterozoic zircons in both assemblages are proposed as markers of proximity to the eastern part of the West African craton during late Neoproterozoic and late Cambrian. The geodynamic processes that took place along this part ofGondwana during the late Neoproterozoic, late Cambrian and Early Ordovician are discussed in the light of the LA-ICP-MS results, as well as the sedimentological record, magmatic evolution and plate tectonic setting of NW Iberia. These processes are linked to late Neoproterozoic and Cambro-Ordovician subduction events beneath the northern Gondwanan margin.

SHRIMP U–Pb geochronological constraints on the timing of the intra-Alcudian (Cadomian) angular unconformity in the Central Iberian Zone (Iberian Massif, Spain)

“…This age range matches the one of the Mesoproterozoic inherited zircons of the Alcudian sediments and suggests that the Saharan Metacraton could have been the source of these sediments. The hypothesis, that links the Neoproterozoic sediments of the SGC with the Saharan Metacraton, has been recently made by Talavera et al (2012) and is in agreement with the previous UPb dating in sedimentary rocks from the NW Iberian and Bohemian massifs (Díez Fernández et al 2010;Drost et al 2011). …”

Detrital zircons from the Ordovician rocks of the Pyrenees: Geochronological constraints and provenance

“…Similar conclusions have been reached by Williams et al (2012) that proposes an East African origin for Sicily based on the presence of Grenvillian-aged detrital/ inherited zircons, and on the scarcity of zircon in the age range 2.2-1.9 Ga, in the basement of the Peloritani Mountains. Finally, the Basal allochthonous Units and the parautochthonous complexes of NW Iberia (Díez-Fernández et al, 2010, 2012 would be located in an intermediate position, between the West African Craton and the Sahara Metacraton, due to the minor relative proportions of Mesoproterozoic zircons compared to those of the NW Iberian autochthon.…”

The Central Iberian arc, an orocline centered in the Iberian Massif and some implications for the Variscan belt

“…The zoning shows an arcuate pattern, very tight in the Cantabrian Zone, which forms the Cantabrian arc and the core of the Ibero-Armorican arc. Most of the zones consist of Paleozoic and Neoproterozoic sequences lying above a pre-Variscan (Cadomian and older), more or less reworked basement, which formed part of the Gondwanan continental crust (Eguíluz et al 2000;Fernández-Suárez et al 2000Martínez Catalán et al 2004;Díez Fernández et al 2010).…”