New U-Pb zircon ages of (reworked) tuffs from the Moodies Group of the Barberton Greenstone Belt (3.22 Ga) confirm an unusually high-resolution Paleoarchean sedimentary record

Eleven new U-Pb LA-ICP-MS zircon ages of the Moodies Group of the Barberton Greenstone Belt from tuffs, felsic lava flows, and aquatically reworked tuffaceous siltstones confirm that this up to 3.7 km thick siliciclastic unit in dominantly coastal-plain and tidal facies was deposited within only a few million years while being deformed into tight, steeply plunging folds. LA-ICP-MS dating of the Moodies Group gradually reaches its limits because (1) analytical uncertainty approaches the time scale of the research questions, and (2) xenocrystic and reworked zircons in the tuffs are commonly hydrothermally altered and subjected to multiple metamorphic events, resulting in complex populations. A diachronous onset of Moodies deposition is not discernible. The onset (ca. 3224±3 Ma) is statistically indistinguishable from the end (ca. 3217±8 Ma) of Moodies deposition. Deformation began at ca. 3221±3 Ma and had ended prior to ca. 3210±10 Ma. The large granodioritic Lomati River Intrusive laccolith is likely of Moodies ages (ca. 3220±8 Ma) and was folded while still viscoplastic. Its syndepositional character at only ca. 1 km depth below the surface is consistent with a dike stockwork, extensive hydrothermal alteration, and the eruption of the basaltic Moodies Lava. Hydrothermal silicification of Moodies sandstones in its halo preserved a large microbial lagerstätte. Moodies stratigraphy thus appears to be dominated by rapid subsidence, balanced by high depositional rates and accompanied by significant mafic to felsic magmatism. Sediment in the central BGB was mainly sourced from the erosion of intermediate to felsic volcanics in the rising Onverwacht Anticline.