PROVENANCE OF THE ANYABONI FORMATION OF THE VOLTAIAN SUPERGROUP IN GHANA

Petrographic and whole-rock geochemical studies were carried out on 20 sandstone samples collected from the Anyaboni Formation (Asesewa area) of the Voltaian Supergroup, to determine its provenance. Petrographically, the Anyaboni sandstones can be classified as quartz arenite and subarkose. The dominant framework grain is quartz; monocrystalline quartz dominates over polycrystalline quartz. Lithic fragments constitute up to 8% of the rock volume and are mostly sedimentary and metamorphic in origin. These suggest derivation from granitic and recycled sedimentary rocks. Geochemically, the sandstones show high SiO₂ content (∼90 wt%). The Th/U values are mostly higher than 4.0 and High Field Strength Elements, (Zr, Hf), show enrichment over the ferromagnesian elements (Cr, V) on Neoproterozoic Upper Crust normalized trace element plot. On chondrite-normalized REE diagram the sandstones show fractionated LREE patterns, negative Euanomalies and a fairly flat but slightly depleted HREE patterns. These favor a dominantly felsic source. The most likely source lithology, compatible with the observed petrographic and geochemical features, is metasedimentary and associated granitic rocks of the Paleoproterozoic Biriman sedimentary basins. Quartz dominance in mineralogy, QFL and major element discrimination diagrams, suggest the tectonic setting of the depositional basin was a passive margin. Pre-metasomatized high CIW values (75 to 99) and high PIA values (71 to 98) suggest intense chemical weathering at the sediment source area, which further suggests a warm, moist climate prevalent during the deposition of the Formation.