New insights on proterozoic tectonics and sedimentation along the peri-Gondwanan West African margin based on zircon U-Pb SHRIMP geochronology

To the west of the Archaean craton, the Rokel-Kasila Belt occurs, which incorporates two tectonic terranes: the Palaeoproterozoic Kasila terrane, accreted to the Archaean craton and comprised of granulite-facies paragneiss units of the Kasila Group, and the Meso- to Neoproterozoic Marampa terrane, thrust on top of the Archaean basement, and comprised of greenschist-facies schists and metabasites of the Marampa Group. A metavolcanic unit in the Kasila Group provides an age of 1941 ± 4 Ma interpreted to date the emplacement of the Kasila succession. Xenocrystic zircon in the sample suggest the presence of cryptic older crust with components of 2.7-2.6 Ga and 2.2 Ga, and the Kasila Terrane is interpreted to represent a Ganderian-type peri-Gondwanan terrane left attached to the West African Craton. Detrital age data on two schist units of the Marampa Group suggest a maximum age of deposition of between 1076-1030 Ma. The detrital age peaks indicate source terranes in part consistent with a West African affinity, but also comprising significant sources of between 2.0 and 1.0 Ga for which no suitable source terranes are known in West Africa. We suggest that at the time the Marampa Group was deposited along the West African margin at ∼1.05 Ga, a source terrane with significant matching components of Palaeoproterozoic and Mesoproterozoic source rocks, was present to provide the sedimentary input, possibly the Amazonian Craton.