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

LA-ICP-MS U–Pb ages of detrital zircons from eight siliciclastic 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. Themaximumdepositional ages for the two sequences is latest
Neoproterozoic and latest Cambrian, respectively. The age spectra are also used to discuss the paleoposition of the
NWIberian basement on the continentalmargin of Gondwana 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
differenceswith age data fromtheNWIberian autochthon and other allochthonous terranes involved inthe 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 of Gondwana 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 ofNWIberia. These processes are linked to late Neoproterozoic and
Cambro-Ordovician subduction events beneath the northern Gondwanan margin.