Reply to comment on “How diverse is the source? Age, provenance, reworking, and overprint of Precambrian meta-sedimentary rocks of West Gondwana, Cameroon, from zircon U-Pb geochronology’’ by Hubert Mvondo and Thierry Bineli Betsi

Abstract

The Congo craton hosts banded iron formations (BIFs) in southern Cameroon. The Gouap iron deposit is in the central part of the Nyong Complex, next to the Ntem Complex in the northwestern part of the East Gabonian Block of the Congo craton. The Gouap BIFs are interbedded with metasiliciclastic rocks consisting of gneisses, schists, and quartzites. We present the first integrated study combining whole-rock and Sm-Nd isotope geochemistry with SIMS and LA-ICP-MS U-Pb-Hf-O isotope analyses of detrital zircons from metasiliciclastic rocks from the Gouap iron deposit to assess the provenance and tectonic setting during deposition of BIFs as well as the crustal evolution at the northwestern margin of the East Gabonian Block. Geochemical data for the metasiliciclastic rocks indicate that their protolith comprised a sequence of greywacke. Along with regional geology, our U-Pb-Hf-O detrital zircon and Sm-Nd whole-rock isotope data suggest that these rocks were predominantly derived from Neoarchean charnockite and TTG suites of the Ntem Complex with a variable and episodic contribution from ca. 2.2–2.0 Ga charnockites of the Nyong and Ogooué complexes. Metasiliciclastic rocks and BIFs were deposited between ca. 2.1 and 2.0 Ga in a foreland basin developed along the northwestern continental margin of the East Gabonian Block. So far unrecognized ca. 2.50–2.45 and 2.45–2.22 Ga magmatic rocks were exposed in their provenance. The Gouap succession experienced amphibolite-facies metamorphism when the Congo and São Francisco cratons collided during the Eburnean-Transamazonian orogeny to form the core of the Nuna/Columbia supercontinent. With the subduction dipping to the west, under the West Gabonian Block, slices of Paleoproterozoic oceanic crust and sediments scraped off the margin of the East Gabonian Block formed an accretionary prism. BIFs of the Nyong Complex likely represent a deep-water temporal equivalent of shallow-marine Mn-deposits of the Francevillian basin, Gabon, and together they belong to the same redox-fractionated deep-water upwelling system that was charged with iron and manganese via hydrothermal alteration of oceanic crust.