Maximum depositional ages and provenance analysis of the Precambrian Manyovu redbeds, Tanzania: Implications for Neoproterozoic tectonics

The Manyovu redbeds are an up to 600 m succession of fine-grained, siliciclastic strata in northwestern Tanzania and are part of the Neo­proterozoic Bukoban Supergroup. Previous authors estimated the age of the Manyovu redbeds to be Neoproterozoic or older based on the K-Ar dates of underlying volcanic rocks (ca. 800 Ma). However, no other age constraints exist for these Neoproterozoic units. U-Pb detrital zircon results from six stratigraphic intervals of the Manyovu units, including both sandstone and siltstone samples, indicate maximum depositional ages as young as 614 ± 6 Ma, almost 200 m.y. younger than the underlying volcanics, with primary detrital contributions from Pan-African orogens, which indicates that these units are syn-tectonic accumulations associated with the assembly of Greater Gondwana/Pannotia. Detrital zircon spectra and modal compositions reveal that the sediment that formed these strata was sourced from a range of terranes, including continental blocks (i.e., Tanzania Craton), magmatic arcs (i.e., Mozambique Belt and Arabian-Nubian Shield), and recycled orogens (e.g., Ubendian-Usagaran belts). Together, these data indicate that the Manyovu redbeds accumulated following the Marinoan Snowball Earth event (ca. 635 Ma) and record the initiation of collision along the Mozambique Belt during Pan-African orogenesis and the formation of greater Gondwana.