Petrological and geochemical study of Birimian ultramafic rocks within the West African Craton: Insights from Mako (Senegal) and Loraboué (Burkina Faso) lherzolite/harzburgite/wehrlite associations

Abstract

In Archean and Paleoproterozoic greenstone belts, ultrabasic (UB) rock occurrences are commonly found in close association within basic and differentiated magmatic series. In the Kedougou inlier (West African Craton), UB rocks are interbeded within the Birimian (2.1 Ga) Mako tholeiitic series (basalts, gabbros). UBs are typically lherzolite, harzburgite and wehrlite, characterized by their cumulative textures and relative proportions of chromite, olivine, clinopyroxene, amphibole ± orthopyroxene. Geochemical study (Major, REE and trace elements in whole rocks and mineral (mainly clinopyroxene and amphibole) and Sr/Nd isotopic records suggest the existence of different types of complexes. The first one consists of lherzolite + harzburgite assemblages whereas the second one consists of isolated wehrlite massifs. Both complexes highlight two different geodynamic environments, the first association being significantly more juvenile or mantle-related than isolated wehrlites which show more evolved geochemical signatures. UB rocks (dunite + wehrlite) of Loraboué (greenstone belt of Boromo, Burkina Faso) associated with calc-alcaline series display the same mineralogical composition as the Mako UB rocks but exhibit a different whole rock composition characteristics of mature island-arc magmas and showing U-shaped REE pattern for both clinopyroxene and host rock, and a clear negative Nb anomaly. The Mako UBs suggest that this portion of the Birimian crust was built in an oceanic context evolving from a MORB-like domain to an increasingly mature volcanic arc domain.

Geochemistry of Mafic Rocks from the Birimian Basement of Doropo (Northeast of Côte d’Ivoire): Petrogenetic and Geodynamic Implications

“…These rocks, composed of gabbro dykes and amphibolite enclaves are characterized by a paragenesis mainly composed of green hornblende, plagioclase and clinopyroxene. This mineralogical composition is typical of mafic rocks described in the Birimian domain of the West African craton [10] [40] [41] [42].…”

Paleoproterozoic gold events in the southern West African Craton: review and synopsis

“…-2200 Tholeiitic basalts are the oldest supracrustal rocks in the Baoulé-Mossi Domain and dominate the basal part of the lithostratigraphic record in each of the older belts of volcanic and volcano-sedimentary rocks (Fig. 1) across the region (Houndé-Boromo belt, Baratoux et al 2011;Nangodi belt, Sylvester and Attoh 1992; Sefwi belt, Hirdes et al 1993;Ashanti belt, Dampare et al 2008;Mako belt, Dioh 1986;Diallo 1994;Dia et al 1997;Abouchami et al 1990;Labou et al 2020). The timing of the onset of tholeiitic volcanism remains poorly constrained, but the presence of inherited zircons ca.…”

“…2200 Ma (De Kock et al 2011;Parra-Avila et al 2017). The geodynamic context of the juvenile tholeiitic oceanic crust remains uncertain, although plume-related oceanic plateau (Abouchami et al 1990;Boher et al 1992;, island arc (Sylvester and Attoh 1992;Baratoux et al 2011;Labou et al 2020), back-arc basin (Vidal and Alric 1994), and mid-ocean ridge (Pouclet et al 2006;Labou et al 2020) settings have been proposed.…”

A Sentinel-2 based multispectral convolutional neural network for detecting artisanal small-scale mining in Ghana: Applying deep learning to shallow mining

“…The study area boundary chosen is the Ghanaian territory corresponding to the Precambrian West African Craton (Labou et al, 2020), shown in Fig. 1.…”