Petrography and geochemistry of metasedimentary rocks from the Paleoproterozoic Birimian at the Chagupana area, North-West Ghana: implications for provenance and tectonic setting

This study uses petrographical and whole-rock geochemical data to determine the provenance, paleo-weathering conditions, tectonic settings, paleo-climate, and mixing proportions of the conglomerate and greywacke in the Chagupana area within the Paleoproterozoic Birimian in North-West Ghana. The conglomerate is foliated and composed of dominant metamorphosed clasts which are matrix-supported, poorly sorted, and polymictic. The greywacke is immature, medium to coarse-grained, poorly sorted, and rich in quartz (53%) and feldspar (46%). The major element contents of 30 greywacke samples were determined by X-ray fluorescence, while the trace element contents including rare earth elements (REEs) were analyzed by inductively coupled plasma mass spectrometer. SiO 2 , Na 2 O, and Fe 2 O 3 are slightly enriched while TiO 2 , MnO, MgO, CaO, K 2 O, and P 2 O 5 are depleted, compared with average upper continental crust values. The greywacke is sodic with K 2 O/Na 2 O ratio of 0.63. Average chemical index of alteration (53%) and chemical index of weathering (58%) values indicate weak chemical weathering, while Plagioclase index of alteration (53%) value suggests weak-moderate alteration of plagioclase. The greywacke is from intermediate-felsic source rocks with minimum recycling, incipient alteration, and underwent K-metasomatism during diagenesis. Tectonically, the rocks belong to an active continental plate margin of a rift basin with slight positive Eu anomaly suggesting derivation from young undifferentiated volcanic arc. Very low TiO 2 (