Elemental geochemistry and Nd isotope constraints on the provenance of the basal siliciclastic succession of the middle Paleoproterozoic Francevillian Group, Gabon

Olabode Bankole (1) , Abderrazak El Albani (1) , Alain Meunier (1) , Marc Poujol (2) , Andrey Bekker (3, 4)

1 IC2MP [Poitiers] - Institut de chimie des milieux et matériaux de Poitiers [UMR 7285]
2 GR - Géosciences Rennes
3 UC Riverside - University of California [Riverside]
4 UJ - University of Johannesburg [South Africa]

Whole-rock elemental geochemistry and Nd isotope composition of siliciclastic rocks from the basal part of the unmetamorphosed middle Paleoproterozoic Francevillian Group, Gabon (FA Formation and FB1 Member) were examined to provide insights into their provenance and its crustal evolution. Chemical weathering index diagrams suggest moderate degree of weathering in the provenance and secondary K-addition during illitization. Trace element geochemical proxies including the REEs provide evidence for sediment derivation from felsic-dominated upper continental crust (UCC) similar to Archean trondhjemite-tonalite-granodiorite (TTG) with minor contribution of mafic components. The low 143Nd/144Nd and negative εNd values (-10.83 to -5.76) provide further evidence for old and evolved upper continental crust components in detrital sources. The depleted mantle model ages for the provenance protolith (2.73-3.05 Ga) are consistent with sediments sourced from the Mesoarchean granitoids of East Gabonian block exposed in the northern and southern parts of Gabon. We infer that the evolved, Mesoarchean felsic TTG-like granitoids were the main source for the sediments of the basal Francevillian Group, while minor mafic inputs from the contemporaneous greenstone belt with the Belinga Group cannot be completely discounted. The predominantly old crustal sources for the sediments suggest crustal addition and recycling of differentiated granitoid plutons instead of formation of juvenile crust during deposition in the Francevillian basin.

Mots clés: Elemental geochemistry; Nd isotope; provenance; Mesoarchean; Francevillian Group; Gabon

Domaines: Géochimie

Olabode Bankole, Abderrazak El Albani, Alain Meunier, Marc Poujol, Andrey Bekker. Elemental geochemistry and Nd isotope constraints on the provenance of the basal siliciclastic succession of the middle Paleoproterozoic Francevillian Group, Gabon. Precambrian Research, 2020, 348, pp.105874. ⟨10.1016/j.precamres.2020.105874⟩. ⟨insu-02903479⟩