Provenance of Ediacaran-Ordovician sediments of the Medio Armorican Domain, Brittany, West France: Constraints from U/Pb detrital zircon and Sm–Nd isotope data

Dabard, Marie Pierre;Loi, Alfredo

Writing - Original Draft Preparation

;Pavanetto, Pamela

Formal Analysis

;Meloni, Mattia Alessio

Formal Analysis

;Hauser, Natalia;Matteini, Massimo;Funedda, Antonio

Member of the Collaboration Group

2021-01-01

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Abstract

The temporal evolution of the sedimentary source areas of the Armorican Massif, involving Ediacaran to Upper Ordovician strata, is investigated to gain insight into the palaeogeographic affinities and changes that occurred as a result of Cadomian orogenesis. Until now, palaeogeographic reconstructions based on geodynamic, stratigraphic and paleontological data have shown geological continuity between the Armorican Massif and the Iberian and Bohemian massifs and have allowed researchers to locate the Armorican Massif near the West African Craton and the Trans-Saharan Belt. This study goes beyond the interpretations based on lithostratigraphic correlation, which may be influenced by allocyclic factors (e.g., sea-level change) or fauna assemblages that have a wide provincial distribution, to provide a correct assessment of sediment flux. To determine the palaeogeographic location more accurately, the provenance of the siliciclastic sediments was examined in this study using U–Pb LA-MC-ICP–MS geochronology on detrital zircons coupledwith whole-rock Sm–Nd and zircon Lu–Hf isotope analysis. This work was carried out on the sedimentary succession of the Medio Armorican Domain. The oldest studied sedimentary rocks were shown to belong to the Brioverian succession, which contains mainly 519–781Ma old zircons, likely derived fromsources that are still present in the Armorican basement. Successively, the lower Paleozoic succession was deposited in the rift stages of the Rheic Ocean, with contributions from a new source of 827–1120 Ma old zircons. A comparison of the zircon populations showed an increase in negative εNd(t) and εHf(t) values of the sedimentary supply in the post-Cadomian samples. Moreover, it revealed that the Medio and North Armorican domains had different locations during the Lower Ordovician, and that some areas of the IberianMassif and theMedio Armorican Domain close to the Sahara Metacraton and Arabian-Nubian Shield were contiguous.