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Meaning of Rocks Basic Enclaves in the Eburnean Granitoids of Mako Area (Kédougou-Kéniéba Inlier, Senegal): Petrogenetic Implications

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Document pages: 18 pages

Abstract: The Makoarea, located in eastern Sénégal, constitutes a segment of Paleoproterozoic (Birimian) formations of theKédougou-Kéniéba Inliers (KKI) in the western part of the West African craton. The basicvolcanism of the Birimian formations of the KKI has long been considered to berelated to a single magmatic event associated with a Mid Oceanic Ridge Basalts(MORB) setting. The aim of this paper is to demonstrate on the basis of the architecturalcharacteristics of the granitoids dark enclaves, the occurrence of at least twodistinct phases of basic Magamtism in the Birimian of the KKI. Themethodology consists of a cartography, a petrographic and architecturalcharacterization of the dark enclaves within the Mako granitoids, in order toconstrain their spatial and temporal relationships with the granitic magma. Theresults obtained are compared with those of the bibliography. We havepinpointed two types of enclaves depending on their shapes and thecharacteristics of their edge with the enclosing rocks: angular enclaves withstraight edges (ante-granitoids) and the soft enclaves with uneven edges(syn-granitoids). The enclaves with straight and well-defined rectilinear edges(ante-granitoids) would be linked to a basic magma which is alreadyconsolidated before being fragmented, torn and carried away as enclaves in thegranitoids. These enclaves would come from enclosing outcrops of metabasaltsand metagabbros which are locally cross-cut by thegranitoids. The soft enclaves with uneven edges (syn-granitoids) were co-magmatic andnot solid during their incorporation into the granitoids. They come from abasic magma which is contemporaneous to the granitic one. Thus, theoccurrence of two generations of dark enclaves is relatedto, at last, two different phases of basic magmatism in the Birimian formationsof the KKI.

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