Geochemistry of the Neoproterozoic sandstone associated with the Buem Structural Unit ophiolite of Northwestern Benin Republic: Implications for geodynamic evolution and paleoenvironment

This study involves the petrographic and geochemical assessment of Neoproterozoic metasandstones associated with the Buem Structural Unit (BSU) ophiolite in northwest Benin Republic in order to infer their tectonic setting, provenance history, and weathering in the source area. Petrographically, the metasandstones are quartz-rich with subordinate K-feldspar content and classified as quartz-rich and sublitharenite on the relevant geochemical scheme. The REE spider diagram of the rocks exhibits positive peaks for Ba, Hf and Zr and a negative peak for Sr on the chondrite profile. The chemical indexes of alteration, including CIA (23.06–80.92), PIA (16.07–62.64) and K₂O/Na₂O (average: 18.89) values, suggest minor to moderate weathering for the metasandstones of the BSU. On the provenance discrimination diagrams of La/Yb versus Ce, La/Th versus Hf and La/Sc versus Th/Co, BSU metasandstone samples plot predominantly in the felsic parentage field. This implies that the sediments mainly derive from felsic igneous rocks with a minor contribution from intermediate and mafic igneous sources. Tectonic setting discrimination diagrams suggest a passive continental margin in a collisional setting. The paleoclimatic condition evaluation based on major elements indicates semihumid to humid conditions. The petrographic and geochemical features of the metasandstones are consistent with siliciclastic rocks formed in a passive continental margin, similar to the West African Craton terrane. The deposition of these sediments may have started from the early stage of rifting until the Pan-African collision involving the WAC, Sahara metacraton, and Benin-Nigerian Shield, from which the Dahomeyide orogenic belt formed. These results place positive constraints on the rift–subduction–collision geodynamic model proposed for the evolution of the Dahomeyide orogen.