Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Lake Mweru, located between the Northern Province of Zambia and the south-eastern Katanga Province of the Democratic Republic of Congo, is part of the southwest extension of the East African Rift System (EARS). Fault analyses have revealed that the Mweru-Mweru Wantipa fault system (MMFS) was formed due to the NW-SE rotation of the extension direction of the EARS and is responsible for the reorganization of the drainage system of the area since the Miocene, creating knickpoints as a result of intense seismic activity. Twenty-six quartzitic bedrock samples were collected predominantly from knickpoints across the Mporokoso Plateau (south of Lake Mweru, Zambia) and the eastern part of the Kundelungu Plateau (north of Lake Mweru, DRC). These samples were analyzed for in-situ cosmogenic ¹⁰Be and ²⁶Al using Accelerator Mass Spectrometry. Samples from the Mporokoso Plateau and close to the MMFS provide evidence of temporary cover. Samples located far from the MMFS have consistent ¹⁰Be and ²⁶Al exposure ages ranging up to ~830 ka, indicating that these surfaces were never covered since their initial exposure. The observed burial patterns, combined with morphotectonic analyses of the drainage system and evidence of lacustrine sediments, reveal the existence of an extensive paleo-lake during the Pleistocene.
Elevational analyses of the dated knickpoints constrain the level of the paleo-lake to around 1200 m asl and its area to around 40000 km².
Calculated high denudation rates (up to ~40 mm ka^-1) along the eastern Kundelungu Plateau suggest that tectonic forcing caused the breaching of the paleo-lake. Ensuing outflow gouged a deep-sided canyon, today occupied by the underfitting Luvua River. The complex exposure histories recorded in our study area by ¹⁰Be and ²⁶Al can be a result of waterlevel fluctuations caused by intense climate variations across southeastern Africa, coupled with active rifting along the MMFS.