U–Pb detrital zircon analysis of the lower allochthon of NW Iberia: age constraints, provenance and links with the Variscan mobile belt and Gondwanan cratons

Abstract

Detrital U-Pb laser ablation inductively coupled plasma mass spectrometry zircon ages from six siliciclastic samples from the lower allochthon of N\V Iberia are analysed to constrain their maximum sedi mentation age and provenance, and to evaluate the connections to the adjacent tectonostratigraphic domains. Deposited in the external sections of the Gondwana platform, their maximum depositional age is latest Neo proterozoic (c. 560Ma). Comparison of the age populations of the lower allochthon with those of the rest of the allochthonous and autochthonous units of NW Iberia suggests that the terranes located in the footwall of the Variscan suture should not be considered as exotic elements, but as contiguous pieces of the same conti nental margin transported onto the adjacent Gondwana mainland in Variscan times. The data are in agreement with the regional trend defined by the drop in Early Neoproterozoic and Mesoproterozoic zircon content upward in the tectonic pile, which had been previously proposed as a marrer of proximity to the eastern part of the West African Craton. Based on the age spectra, the palaeoposition for the time of sedimentation is placed in northern Africa, between the West African and Saharan cratons. Particular attention is paid to the occurr ence of an Early Neoproterozoic input, probably derived from the Pan-African Hoggar suture.Detennining the age and provenance of sedimentary rocks provides hints to place the processes that affected the Earth's crust in time and space. Access to such information in mobile belts surrOll llding stable cratons is limited by the fact that these belts usually are involved in active plate boundaries, where both defonnation and metamorphism blur some of the age (fossils) and palaeogeographical (palaeomagnetism) indicators. Zircon is a connn on constituent of most sedimentary rocks, and it is very resistant and largely survives metamorphism and defonnation.

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

“…7). The samples chosen were: 1) samples S-5 and S-14 from Sardinia ; 2) sample FIU-07 form Sicily ) and 3) samples GCH-PA-5, OD-3 and IBR-2 from the Iberian Massif (Díez-Fernández et al, 2012;Fernández-Suárez et al, 2014;Shaw et al, 2014 respectively). We have overlaid the markers derived from the main age populations from the Pyrenees on the relative probability plots of these samples (Fig.…”

“…After the early works by Fernández-Suárez et al (2000) and Linnemann et al (2000), the age signatures of detrital zircons have been widely used in the European Variscan belt and in the basement rocks involved in the Mediterranean Alpine orogenic belt to determine the potential provenance areas for the metasediments and thus to assess Ediacaran-early Paleozoic paleogeographic models (see discussion in Avigad et al, 2012;Meinhold et al 2013). Zircon age spectra have also been used to determine the maximum depositional age of the thick unfossiliferous lowermost preVariscan series (Díez-Fernández et al, 2012;Talavera et al, 2012) and to determine the time gap involved in certain unconformities in the Iberian Massif (Talavera et al, 2015).…”

Variscan ophiolites in NW Iberia: Tracking lost Paleozoic oceans and the assembly of Pangea

“…Maximum depositional ages for the metasedimentary series range between Ediacaran and Early Ordovician , 2012a with Nd model ages of between 1.78 and 2.22 Ga (Fuenlabrada et al, 2012). Major and trace element geochemistry of the metagreywackes suggests deposition in association with a peri-Gondwanan arc system built upon a thinned continental margin.…”

The relations between Gondwana and the adjacent peripheral Cadomian domain—constrains on the origin, history, and paleogeography of the peripheral domain

“…The detrital zircons age spectra also show regional differences, although ca. 550-650 Ma grains are most abundant in most of the basin and in the lower allochthon in the NW corner of Iberia, and the zircons are often abraded, which indicates long-distance transport (Gutiérrez-Alonso et al, 2003;Pereira et al, 2012;Talavera et al, 2012;Diez-Fernández et al, 2012). Commonly, a small number of b 580 Ma and 0.9-1.2 Ma zircons are also present, but they form a prominent cluster only in the Narcea antiform (Section 4.1).…”

“…and in late Ediacaran sediments in the para-autochthon of NW Iberia to the west(Diez-Fernández et al, 2012). Thus on many sides of the area where ca.…”