Geodynamic evolution of the Bangweulu Block, northern Zambia

Abstract

The Bangweulu Block is a cratonic unit underlying most of northern Zambia and adjacent parts of Tanzania and Zaire. Its geodynamic evolution is shown to be entirely Proterozoic except for Cainozoic rifting and related sedimentation. The Block has a crystalline basement of schists, acid metavolcanics and granitoids, which formed during a deformational and magmatic event of Eburnian age between 2000 and 1800 Ma ago. The metavolcanics have affinities with high-K calc-alkaline suites from modern subduction-controllled tectonic regimes suggesting an Eburnian plate margin to the northwest of the Block. The polyphase sedimentary cover of the Bangweulu Block comprises: The Mporokoso Group, a 5000 m thick sequence of fluvial, aeolian and lacustrine sediments deposited in the intracratonic Mporokoso basin in response to the final phase of the Eburnian tectogenic cycle. The Kasama Formation, a sequence of fluvial sediments, which is 100–300 m thick on the Bangweulu Block but increases in thickness to nearly 400 m in the downfaulted pericratonic Irumide basin, formed in the initial phase of the Kibaran tectogenic cycle. The Luitikila Beds, a 3000 m thick unit of post-orogenic molasse of the Kibaran Irumide belt, which encroaches with reduced thickness on the Bangweulu Block. The Luapula Beds deposited on the margins of the Bangweulu Block, and representing parts of the Kundelungu sedimentary sequence accumulated in the Pan-African pericratonic basin. Faults and shear zones bordering the Bangweulu Block developed in sequence during the Eburnian, Kibaran and Pan-African orogenies. The older ones are invariably reactivated during the younger tectogenetic events, resulting in substantial lateral and rotational movement of the Bangweulu Block with respect to adjacent structural terranes.