Litho-Stratigraphic Refinement of the Precambrian Rocks in the Kampti-Loropeni Greenstone Belt, South-West Burkina Faso (West African Craton)

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Résumé

The Kampti-Loropeni greenstone belt (KLB) in south-west Burkina Faso forms part of the paleoproterozoic Baoulé-Mossi domain of the West African Craton. Its lithostratigraphic chronology and magmatic sources remain insufficiently constrained. This study integrates field observations, petrography, whole-rock and trace element geochemistry, whole-rock Sm-Nd isotopes and zircon U-Pb geochronology to refine the timing and petrogenesis of the KLB suite. The KLB records a bimodal magmatic succession that comprises tholeiitic
basaltic rocks in the lower sequence and subordinate cal-alkaline andesite rocks together with tonalitic to potassic granitoids. The tholeiitic rocks display broadly flat REE patterns comparable to N-MORB like island arc composition, with slight negative εNd values at 2.2 Ga (−1.2 to −0.22) indicating a primary magma source from or in interaction with an older reworked crust or previously differentiated mantle component. Their whole-rock Sm-Nd isochron age of 2264 ± 0.1 Ma provides a timeline for the lower volcanic sequence, whereas depleted-mantle ages of 3.86 to 3.22 Ga indicate an older source history. Zircon U-Pb analyses date the crystallization of a muscovite granite at 2161 ± 2.4 Ma and a monzodiorite at 2120 ± 1.8 Ma, defining at least two generations of paleoproterozoic plutonism. These results support a multistage evolutionary model involving early tholeiitic volcanism followed by calc-alkaline plutonism consistent with subduction-related arc magmatism, mantle metasomatism and crustal assimilation during the eburnean evolution of the southern West Africa Craton.

Mots-clés

Kampti-Loropeni Greenstone, Sm-Nd Isotopes, U-Pb Zircon, West African Craton, Magmatic Arc