Basement recycling and orogenic influx during late ediacaran: A zircon U-Pb-Hf study from the southern Nama basin

The Nama Basin in southern Namibia preserves one of the most continuous and well-calibrated sedimentary records of the Ediacaran–Cambrian transition. However, reconstructing its geodynamic evolution remains hindered by a lack of integrated source-to-sink isotopic data, leaving the precise timing of the passive-to-foreland basin transition and its linkage to southwestern Gondwana assembly unresolved. To address this, the current study presents new detrital and magmatic zircon U–Pb ages combined with Hf isotopic data, alongside syn -depositional volcanic tuff ages, recovered from six drill cores from the GRIND-ECT (Geological Research through Integrated Neoproterozoic Drilling: The Ediacaran-Cambrian transition) project in the Witpütz sub-basin. The data show that the thick succession of marine-to-terrestrial sandstones, shales, and platform carbonates of the Nama Group were deposited onto a Mesoproterozoic crystalline basement characterized by evolved, crustal-type Hf isotopic signatures consistent with the Namaqua–Natal Complex. The lower members of the Kuibis Subgroup (Kanies, Kliphoek and Aar members) yield maximum depositional ages (MDAs) spanning ca.1111 ± 9 Ma and 1075 ± 8 Ma. Their unradiogenic, crustal Hf isotope compositions reflect intense recycling of Meso- and Palaeoproterozoic basement sources derived predominantly from the Namaqua, Gariep, and Ghanzi belts. These features suggest sedimentation in a stable passive-margin setting during the early evolutionary stages of the basin. In contrast, the overlying Schwarzrand Subgroup (Nudaus and Urusis formations) displays a major provenance shift dominated by Neoproterozoic detrital zircon populations clustered between 645 ± 7 Ma and 568 ± 7 Ma. New CA-ID-TIMS U–Pb zircon ages from volcanic ash layers at the lower Huns Member and the top of the Spitskop Member precisely bracket the deposition of this interval between 541.71 ± 0.12 Ma and 538.30 ± 0.10 Ma. The influx of young syn -orogenic detritus, coupled with a prominent transition toward more radiogenic, juvenile Hf signatures up-section, records the structural progradation and erosional unroofing of an active magmatic orogenic front (the Damara and/or Saldania belts). These new U–Pb–Hf datasets contextualize the rapid paleogeographic and geodynamic reorganization of Southwestern Gondwana during its final terminal assembly.