Provenance of the Neoproterozoic deep-water Zerrissene Group of the Damara Orogen, Namibia, and paleogeographic implications for the closing of the Adamastor Ocean and assembly of the Gondwana supercontinent

The upper Neoproterozoic Zerrissene Group of the Damara Orogen in southwestern Africa records some of the final contributions of sediment to the oceans between the converging Kalahari, Congo, and Rio de la Plata cratons before closure, suturing, and formation of the Gondwana supercontinent. The configuration of source terranes and the provenance and timing of sediment dispersal of the Zerrissene Group have remained poorly constrained due to structural and stratigraphic complexities, metamorphic recrystallization and metasomatism, and challenges in resolving recrystallization effects upon the U-Pb systematics of Precambrian detrital zircon. This study utilizes sandstone petrography, whole-rock geochemistry, and U-Pb detrital zircon geochronology to constrain provenance and depositional age of the Upper Neoproterozoic deep-water Zerrissene Group exposed in the Ugab Region in central-western Namibia. Detrital zircon U-Pb age data acquired by multicollector laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was augmented by sensitive high-resolution ion microprobe with reverse geometry (SHRIMP-RG) measurements to differentiate detrital versus recrystallization ages of highly zoned Zerrissene Group zircon grains that preserve a record of the tectonic and metamorphic development of the Damara Orogen and the suturing of the Gondwana supercontinent. New detrital zircon U-Pb age results yield maximum bounds upon the depositional age of the Zerrissene Group that systematically decrease from 662 Ma to 624 Ma, supporting correlation of a carbonate unit contained within the upper Zerrissene Group (Gemsbok Formation) to regional glaciogenic units that record the Marinoan Glaciation. Our results indicate a minor contribution from the Congo Craton to the Zerrissene Group and rule out sediment contributions from the Rio de la Plata and Kalahari cratons. The most abundant age component throughout the Zerrissene Group is Mesoproterozoic (maxima between 1000 and 1100 Ma) followed by Neoproterozoic (various maxima between 850 and 625 Ma). While the Mesoproterozoic zircon grains could have been eroded from orogenic belts bordering the Congo Craton, the Neoproterozoic zircon was most likely supplied by a large influx of sediment shed either westward from the East African Orogen and/or eastward from a magmatic arc terrane represented by the Dom Feliciano Belt of Uruguay. The latter records the Pan-African collision of the Rio de la Plata Craton of South America and the Congo and Kalahari cratons of Africa. Whole-rock geochemical analyses and petrographic study of Zerrissene detritus suggest derivation from uplifted passive margin sequences with possible continental magmatic arc contribution and are thus consistent with either scenario. The provenance data presented in this study help to refine pre-Gondwana paleogeographic settings, generalized sediment transport directions, and regional lithostratigraphic correlations of the Zerrissene Group with respect to the development of the western African continental margin during Neoproterozoic time.