The Magondi Belt in northeast Botswana: regional relations and new geochronological data from the Sua Pan area

Available data bearing on the extent of the 2.0-1.8 Ga Magondi Orogenic Bel t beneath Phanerozoic cover in Botswana are reviewed. Also, new U-Pb and Sm -Nd geochronological data from isolated outcrops of granite on Kubu Island in Sua Pan, ca 60 km west of the main exposures of Precambrian basement in northeast Botswana, are presented. The Kubu Island Granite previously has b een considered as a continuation of the Archaean Zimbabwe Craton exposed to the east. U-Pb isotopic analyses of single zircons from the granite yield a crystallisation age of 2039.2 +/- 1.4 Ma, indicating that the granite was intruded during Palaeoproterozoic orogenesis. One zircon grain interpreted as a xenocryst has a Pb-207/Pb-206 date of 2673 Ma. Sm-Nd isotopic data fo r the granite yield a T-dm model age of 2682 Ma. These data indicate the pr esence of Archaean crustal components in the lithospheric column sampled by the granite magma, consistent with intrusion of the granite near the edge of the Zimbabwe Craton. Together with regional geophysical evidence, the U- Pb zircon age for the Kubu Island Granite constrains the eastern margin of the Magondi Orogenic Belt to lie between Kubu Island and exposed parts of t he Zimbabwe Craton farther east. (C) 2001 Elsevier Science Limited. All rig hts reserved.