Paleoproterozoic Mafic and Ultramafic Rocks from the Mako Belt, Senegal: Implications for Back-Arc Basin Origin

Date

2025-10-01

Author

Dia, Ibrahima
Furman, Tanya
Sayıt, Kaan
Bowden, Shelby
Gueye, Mamadou
Faye, Cheikh Ibrahima
Vanderhaeghe, Olivier

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The Mako Belt in the Kédougou-Kéniéba Inlier (eastern Senegal) preserves Paleoproterozoic (2.3–1.9 Ga) mafic and ultramafic rocks that record early crustal growth processes within the southern West African Craton (WAC). Basalt bulk rock compositions preserve primary melt signatures, whereas the associated ultramafic cumulates are variably serpentinized and are better assessed through mineral chemistry. Basalts occur as massive and pillow lavas, with MgO contents of 5.9–9.1 wt.% and flat to slightly LREE-depleted patterns (La/Smₙ = 0.73–0.88). Primitive mantle-normalized diagrams show subduction-related signatures, including enrichment in Ba, Pb, and Rb and depletion in Nb and Ta. Most basalts and all ultramafic rocks display (Nb/La)PM > 1, consistent with enriched mantle melting in a back-arc setting. Harzburgites and lherzolites have cumulate textures, high Cr and Ni contents, and spinel with chromian cores (Cr# > 0.6) zoned sharply to Cr-rich magnetite rims that overlap basalt spinel compositions. Integration of the petrographic, mineralogical, and whole-rock geochemical data indicates the presence of mafic melts derived from a subduction-modified mantle wedge and likely formed in a back-arc basin above a subducting slab, rather than from a plume or mid-ocean ridge setting. Regional comparisons with other greenstone belts across the WAC suggest that the Mako Belt was part of a broader arc–back-arc system accreted during the Eburnean orogeny (~2.20–2.00 Ga). This study supports the view that modern-style plate tectonics—including subduction and back-arc magmatism—was already active by the Paleoproterozoic, and highlights the Mako Belt as a key archive of early lithospheric evolution in the WAC.

Subject Keywords

back-arc basin, mafic-ultramafic sequences, Mako Belt, Paleoproterozoic, plate tectonics, trace element geochemistry

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https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=105020203787&origin=inward
https://hdl.handle.net/11511/116800

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Department of Geological Engineering, Article