New Pb-Pb Single Zircon Age Constraints on the Timing of Neoproterozoic Glaciation and Continental Break-up in Namibia

Dating of single zircons from low-grade metamorphosed rhyolites in the Rosh Pinah Formation of the Gariep Belt in southwestern Namibia, using the Pb evaporation technique, yielded a primary crystallization age of 741 ± 6 Ma. Both the stratigraphic position and the geochemistry of the volcanic rocks indicate an early continental rift environment. The new data not only provide an age for the massive Zn-Pb-Cu sulfide mineralization associated with these volcanic rocks, but they also set a maximum age limit for Neoproterozoic continental break-up in southern Namibia. This age is statistically indistinguishable from a recently reported age of 748 ± 3 Ma for stratigraphically equivalent volcanic rocks in the northern rift of the Damara Belt, suggesting that the onset of the formation of the N-S-trending Adamastor ocean and of the NE-trending Khomas ocean in central and northern Namibia occurred at the same time. The volcanic unit directly overlies, in both rift grabens, a diamictite horizon with glaciogenic features. Our new results further constrain the age of this glacial epoch, which may be correlated with the Sturtian glaciation, to around 750 Ma.