U–Pb Geochronology of Paleoproterozoic Rocks in the Southern Part of the Kedougou-Kéniéba Inlier, Senegal, West Africa: Evidence for Diachronous Accretionary Development of the Eburnean Province

Abstract

The Kedougou-Kéniéba Inlier (KKI) in eastern Senegal is the westernmost exposed part of the Paleoproterozoic (Birimian/Eburnean) Baoulé-Mossi domain on the West African craton. Regional mapping indicates that the southern, relatively well preserved part of the KKI contains two northeast trending volcanic belts, the Mako and Falémé belts with associated Na-rich granitoid stocks. These belts are separated by the Diale-Dalema metasedimentary basin, containing the extensive syn- to late-kinematic K-rich Saraya batholith and other basin-type plutons. A similar pattern of northeast trending volcanic belts and sedimentary basins is also seen in Ghana and eastern Côte d'Ivoire, i.e. in the eastern part of the Baoulé-Mossi domain, as well as in central Côte d'Ivoire where, however, primary lithological relationships seem to be more obliterated by later tectono-thermal overprint. U–Pb ages were determined on single zircon and monazite from rocks in the KKI to investigate its relationship with the rest of the Baoulé-Mossi domain. A rhyolite from the Falémé belt gave a zircon age of 2099±4 Ma. Granitoid rocks from the Falémé (2) and Mako (1) volcanic belts possess zircon ages of 2082±1, 2080±1 and 2076±3 Ma, respectively. Reversely discordant monazites from a muscovite-bearing phase of the Saraya batholith in the Diale-Dalema basin yielded an interpreted igneous age of 2079±2 Ma and a metamorphic age of 2064±4 Ma. Detrital zircons from a quartz wacke in the Diale-Dalema basin all gave the same age within error, defining an average age of 2165±1 Ma for the source. Inherited zircon, 2155±34 Ma in age, was seen in the felsic flow from the Falémé belt while the Mako belt granitoid rock contains inheritance at least as old as 2122±5 Ma. These data indicate that volcanic belts in the KKI are substantially younger than the 2150–2190 Ma Birimian volcanic and associated plutonic rocks of the eastern Baoulé-Mossi domain, despite their geological similarities. Syn- to late-kinematic basin-type plutons in the KKI are also younger than lithologically similar 2090–2115 Ma old plutons in Ghana and eastern Côte d'Ivoire (eastern part of the Baoulé-Mossi domain). These relationships are consistent with previous suggestions that Paleoproterozoic rocks of the Baoulé-Mossi domain may be divided into an older eastern subprovince and an approximately 50–100 Ma younger western subprovince. They also show that supracrustal and intrusive Paleoproterozoic rocks in both subprovinces as well as over the entire domain developed diachronously from east to west. The data support an accretionary tectonic model for Paleoproterozoic growth of the West African craton.