The crustal architecture of Archaean terranes in Northeastern Botswana

Abstract

New and published geological, geochemical and U-Pb zircon age data are combined to model the architecture and evolution of the Archaean crust in north-eastern Botswana. Four distinct crustal terranes are identified. The Francistown granite-greenstone terrane at the south-western margin of the Zimbabwe craton, is interpreted as a continental-margin arc complex (the Francistown Arc Complex) that developed between ~2710 and ~2647Ma. Outboard of this arc complex, and separated from it by the Shashe shear zone, is the allochthonous Matsitama-Motloutse Complex. SHRIMP U-Pb zircon data from quartzite units in this terrane distinguish the supracrustal rocks from similar material in the Central Zone of the Limpopo belt to the east. The Matsitama-Motloutse Complex was accreted to the Francistown Arc Complex between ~2661 and ~2647Ma. The third terrane is the Phikwe Complex, which is part of the Central Zone to the Limpopo belt. The Mahalapye Complex is the fourth terrane and comprises Archaean rocks of the Central Zone reworked and remobilised during the Palaeoproterozoic. The Francistown Arc Complex, the Matsitama-Motloutse Complex and the Phikwe and Mahalapye sectors of the Central Zone were juxtaposed during the Neoarchaean.