U-Pb age and Lu-Hf isotopic data of detrital zircons from the Neoproterozoic Damara Sequence: Implications for Congo and Kalahari before Gondwana

The proximity of the Congo and Kalahari cratons during the Neoproterozoic breakup of the supercontinent Rodinia and during subsequent assembly of Gondwana is unclear. Neoproterozoic metasedimentary rocks from the rifted margins of Congo and Kalahari in the Damara Orogen yield distinctive detrital zircon U-Pb age distributions that correspond to the ages of prominent crustal components within the respective cratons. The most abundant zircons from Neoproterozoic strata deposited on the Congo margin give ages of 1150-1000 and 800-600 Ma, whereas, the most abundant zircons from the Kalahari margin strata range from 1350 to 1100 Ma. A 1350-1200 Ma detrital zircon population in the Kalahari margin strata is absent in the Damara-Congo strata. A prominent c. 1050-1000 Ma detrital zircon age population from Damara-Congo strata is nearly absent from the Damara-Kalahari strata, even though orogenic events of this age are found on both cratons. Damara strata on the Kalahari margin also lack detrital zircons with U-Pb ages of 900-600 Ma. The differences in detrital zircon age distributions are robust when comparing strata of the same age on both cratons, and remains so, even when younger, deeper water facies are excluded, which could have been biased by other sediment sources. These data suggest that the Congo and Kalahari cratons were not proximal in Rodinia, and did not establish their current relative positions until the end of the Neoproterozoic when they were sutured together during the collisional orogenies that formed Gondwana.