Timing and sources of pre-collisional Neoproterozoic sedimentation along the SW margin of the Congo Craton (Kaoko Belt, NW Namibia)

Abstract

Isotopic dating of detrital zircon populations from metasediments and of magmatic zircon from intercalated metavolcanic layers in the medium- to high-grade part of the Kaoko Belt in Namibia provides first robust constraints on the age of Neoproterozoic sedimentation along the southwestern margin of the Congo Craton. Dating of detrital zircons from metasediments directly overlying the cratonic basement shows maximum sedimentary ages of c. 1.00 and c. 1.45Ga, and age populations comparable with known protolith ages from the gneisses of the Congo/Kalahari cratons. Dating of zircon from associated metavolcanics constrains the age of the earliest preserved sediments at c. 740–710Ma.Detrital zircon populations from the samples collected from the upper parts of the metasedimentary succession contain only small proportion of grains with ages similar to those from the Congo Craton. These samples show dominance of c. 1.00Ga, c. 750Ma and c. 650Ma old zircon grains that are probably derived from the Punta del Este – Coastal Terrane (Dom Feliciano and Kaoko belts) that acted as an arc/back-arc domain at c. 650–630Ma. Neodymium model ages for the samples of metasedimentary cover of the cratonic basement provide another evidence that the youngest preserved sediments could not have been derived from the Congo Craton.Recognition of the Punta del Este – Coastal Terrane crust as a source region for the youngest pre-collisional sediments of the Kaoko Belt suggests that this terrane must have been in close proximity to the Congo Craton passive margin already some time prior to their mutual collision at c. 570–550Ma. This is in accord with an interpretation that the c. 650–630Ma arc/back-arc Punta del Este – Coastal Terrane has developed directly on top of, or very close to, the attenuated Congo Craton passive margin.