Towards a new understanding of the Neoproterozoic-Early Palaezoic Lufilianand northern Zambezi Belts in Zambia and the Democratic Republic of Congo

The Lufilian Belt is of geological significance and economic importance due to rich Cu-Co mineralisation in the Katanga Province of the Democratic Rep ublic of Congo and the Copperbelt of Zambia. Though thorough exploration ha s yielded much information on the mines districts, the understanding of the belt as a whole appears, to some extent, historically charged and confused . In the first part of this article, basic knowledge and assumptions are re viewed and existing models critically assessed. Results include recognition of standard lithostratigraphies of the Katanga Supergroup comprising the R oan, Mwashia, Lower and Upper Kudelungu Groups in the Copperbelt and Katang a, a lower limit for the onset of deposition at about 880 Ma, and a major o rogenetic event involving northeast directed thrusting (Lufilian Orogeny) a t 560-550 Ma. The depositional history of the Lufilian Belt was controlled by continental rifting leading to formation of a passive continental margin . Continental rifting related to the dispersal of Rodinia began ca 880 Ma a go and was accompanied by magmatism (Kafue rhyolites: 879 Ma; Nchanga Grani te: 877 Ma; Lusaka Granite: 865 Ma). Differential subsidence of the northwe stward propagating rift soon allowed invasion by the sea advancing from the southeast, and subsequent development of marine rift-basin and platform do mains. The standard stratigraphies for the Roan Group are restricted to the platform domain that bordered the rift-basin on its northeastern side. Thi s domain included the Domes region of the Lufilian Belt and extended southe astwards into the northern Zambezi Belt. The platform was differentiated in to a carbonate platform (barrier) represented by the Bancroft Subgroup (pre viously 'Upper Roan') in Zambia and Kambove Dolomite Formation in Katanga a nd a lagoon-basin (lower Kitwe Subgroup/Zambia; Dolomitic Shale Formation/K atanga) with mudflats (R.A.T. Subgroup/Katanga) and a siliciclastic margin towards the hinterland. The mineralised horizons of the 'Ore Formation' in Zambia and 'Series des Mines' in Katanga are related to temporarily anoxic conditions prevailing in the Roan Lagoon-Basin which had a southwest-northe ast extent of ca 400 km. The lagoon-basin was subsequently filled by clasti cs derived from mainly northeastern sources (upper Kitwe Subgroup/Zambia; D ipeta Subgroup/Katanga). Possibly due to continental rupture in the southeastern, more advanced, seg ment of the rift and concomitant differential movement in the rupturing pla te, the Kundelungu Basin started to open during deposition of the Mwashia G roup. Opening of the extensional basin was accompanied by rifting, rapid su bsidence of the affected platform segment and widespread mafic magmatism, w hich lasted until deposition of the Lower Kundelungu Group. The elevated ma rgins of the rapidly subsiding Kundelungu Basin offered favourable conditio ns for inland glaciation during the Sturtian-Rapitan global glaciation epoc h. The diamictites of the Grand Conglomerat are thus dated at ca 750 Ma. Tectonogenesis in the Lufilian and Zambezi Belts is related to ca 560-550 M a collision of the 'Angola-Kalahari Plate' (comprising the Kalahari Craton and southwestern part of the Congo Craton) and the 'Congo-Tanzania Plate' ( comprising the remaining part of the Congo Craton) along a southeast-northw est trending suture linking up the southern Mozambique Belt with the West C ongo Belt. Collision was accompanied by northeast directed thrusting involv ing deep crustal detachments and forward-propagating thrust faults that dev eloped in platform and slope deposits below a high level thrust. In the Dom es region, the platform sequence was detached from its basement and displac ed for ca 150 km into the External Fold-Thrust Belt of Katanga. The large d isplacement was enhanced by fluids liberated from evaporite-rich mudflat de posits of the R.A.T. Subgroup. In the Zambezi Belt, northeast directed thrusting was succeeded by southwes t directed backfolding and backthrusting, due to greater shortening or thic kening of the thrust wedge. The Mwembeshi Shear Zone accommodated greater s hortening in the Zambezi Belt relative to the Lufilian Belt by sinistral tr anscurrent movement. The Mwembeshi Shear Zone is a reactivated pre-existing zone of weakness in the lithosphere of possibly Palaeoproterozoic age. The re is no evidence of Neoproterozoic collision along this zone in the Lufili an Belt/Zambezi Belt domain. (C) 2000 Elsevier Science Limited. All rights reserved.