Source and deposition age of the Dialé-Daléma metasedimentary series (Kédougou-Kéniéba Inlier, Senegal) constrained by U–Pb geochronology on detrital zircon grains

Abstract : The Dialé-Daléma metasedimentary series is exposed in the Kédougou-Kéniéba Inlier that corresponds to the northwestern branch of the Eburnean orogenic belt in the southern West African Craton. Here we conducted a U–Pb geochronological study on metapelites, metagraywackes and metavolcanic breccia of the Dialé-Daléma metasedimentary series in order to identify the sedimentary sources and establish the lithostratigraphic sequence of the Kedougou-Kenieba Inlier. This new U–Pb geochronological dataset from five samples representing different stratigraphic levels yield a dominant population of Paleoproterozoic detrital zircon grains with ages ranging from c. 2200 to 2100 Ma. The youngest weighted mean ages at c. 2120 Ma are identical for all five samples within error and provide a maximum deposition age for the sediments of the Dialé-Daléma series. The dominant ages are similar to those obtained on metamorphosed plutonic and volcanic rocks of the Mako belt and thus suggest a dominant proximal source for the clastic sediments of the Dialé-Daléma series and a distal or geographically isolated position relative to the Archean Leo-Man or Réguibat craton nuclei. Deposition ages are only a few Myr older than available ages for metamorphism and intrusion of plutons forming the Saraya batholith. This is consistent with deposition along an active convergence zone marked by the succession, within a few tens of Myr, of (1) magmatic accretion of the Mako plutonic and volcanic rocks in the context of volcanic arc, associated with local uplift, exhumation and erosion at c. 2200-2160 Ma, (2) deposition of clastic sediments forming the Dialé-Daléma series at c. 2120-2110 Ma followed by (3) their burial and exhumation at c. 2090–2060 partially contemporaneous with (4) the intrusion of the Saraya batholith at c. 2080–2070 Ma.