Paleoweathering, provenance and tectonic setting of the Kyandamu diamictite in the Lukutwe area (Katanga Supergroup, Democratic Republic of Congo)

Abstract The Katanga Supergroup in the Congolese Copperbelt (CCB) is characterized by two stratigraphical markers, the Mwale and the Kyandamu diamictic formations. A detailed study of the Kyandamu Subgroup in the Lukutwe area was conducted to understand its depositional environment by using new petrographic and geochemical data. The Kyandamu Subgroup is identified as an imbedded matrix supported diamictite with a low-carbonate content. The dominant clasts in this formation are quartz fragments, followed by carbonates, quartzites, feldspars, and granitoids. Smaller amounts of micaschist and conglomerate clasts also occur. Both petrographic and geochemical data suggests two major sources of sediment supply: the Neo- to Post-Archean Bangweulu block and the Neoproterozoic Katanga Supergroup (Roan and Nguba groups). Paleoweathering was assessed using various indicators such as the Nesbitt–Young alteration index, Parker index, plagioclase alteration index, Ruxton index, silica-titanium index, and Garzanti modified alteration index. These results indicate a low-drainage setting and weak chemical weathering, suggesting an arid climate. In addition, the V/Cr, U/Th, Ni/Co, and authigenic U ratios suggest an oxidizing environment during deposition of the Kyandamu diamictite. The presence of a predominant matrix, and the absence of striations and dropstones, allows us to envisage a gravity-flow process of transportation within a proglacial environment. The tectonic setting of the deposition is unstable and active, as highlighted by the index of compositional variability (ICV values). Such tectonic context indicates an active continental margin (ACM) evolving from extensive to compressive phase. This result suggest that the Kyandamu Subgroup deposited between the late rifting stage and the early stages of the Lufilian orogeny in the Katanga basin.