Author(s)

Nelson Lekeba Makamba^1,2*, Vicky Tendresse Télange Bouenitela¹, Ulrich Verne Matiaba-Bazika^1,2, Florent Boudzoumou^1,2

¹Geodynamics Laboratory, Faculty of Science and Technology, Marien Ngouabi University, Brazzaville, Republic of the Congo.
²Department of Geosciences, National Institute for Research in Exact and Natural Sciences, Brazzaville, Republic of the Congo.

The Elogo complex is a greenstone belt portion located on the Eastern edge of the Archean Congo craton at the junction with the Paleoproterozoic to Neoproterozoic Sembe Ouesso basin. This study was carried out on this complex to determine the context of the placement of basaltic rocks. Metaluminous tholeiitic basalts (basic and ultrabasic), calc-alkaline basalts, andesitic basalts, and peraluminous calc-alkaline dacites represent greenstones. Tholeiitic and calc-alkaline basalts come from deep enriched and depleted mantle sources, including garnet in fusion residues [Al₂O₃/TiO₂ > 16 (16.5 to 35.12) and in some samples between 12.45 to 14.48; CaO/Al₂O₃ < 1 (0.52 to 0.97) and >1 (1.04 to 1.35) in ten samples and (Gb/Yb)_PM > 1]. The calc-alkaline dacites come from a shallow depleted mantle source [Al₂O₃/TiO₂ > 16; CaO/Al₂O₃ < 1 and (Gb/Yb)_PM > 1]. Tholeiitic and calc-alkaline basalts have a negative Rb, Ba, Ce, and Nb anomaly without negative Ti anomaly, positive Ta, Pb anomalies, and a lack of significant REE [(La/Yb)n = 0.36 to 0.97 and 1 to 2.15; (Ce/Yb)n = 0.27 to 0.96 and 1.04 to 1.72, respectively] fractionation. High Nb/Th (2 to 10) and Nb/U (1.82 to 26) ratios and low La/Ta (5 to 27) ratios are characteristic of divergent margin magmatic sources. Tholeiitic and calc-alkaline basalts correspond to an extensive back-arc basin-type tectonic setting. Calc-alkaline andesitic basalts and dacites show positive Ba, U, Th, K, La, Ce, Pb, and Li anomalies and negative Nb, Ta, and Ti anomalies reflecting crustal contamination and hydrothermal alteration in a compressive tectonic context as a volcanic arc in a subduction regime marking the interruption of the meso-neoarchean Elogo’s opening. Elogo’s opening and closing are probably associated with the emplacement of the greenstone of the meso-neoarchean Gabon Belinga group and the relics of the Mesoarchean greenstones of the Cameroun Ntem complex.

Elogo, Greenstone, Archean, Tholeiitic, Andesitic Basalts, Dacites, Magma Source

Makamba, N. , Bouenitela, V. , Matiaba-Bazika, U. and Boudzoumou, F. (2023) Geochemistry and Petrogenesis of Basic and Ultrabasic Rocks Elogo Complex in Ivindo Archean Block (Congo Craton): Geodynamic Implications. Open Journal of Geology, 13, 107-135. doi: 10.4236/ojg.2023.132006.