TECTONIC LINKS BETWEEN PROTEROZOIC OROGENIC BELTS IN SOUTHERN AFRICA BENEATH THE KALAHARI DESERT

Proterozoic crustal evolution in southern Africa is recorded by a network of orogenic belts that formed at ca. 2.1-1.8, 1.35-1.0, and 0.65-0.5 Ga. A complete understanding of the regional tectonic relations within and between these belts has been hindered by extensive cover in the Kalahari region of Botswana and adjacent countries. Here we combine recently available geochronological data from isolated exposures and drill cores in the Kalahari region together with geophysical data from subsurface basement terranes to arrive at the following conclusions: (1) The western margins of the Archean Kaapvaal and Zimbabwe cratons in southern Africa are delimited by a major Paleoproterozoic orogen that records a diachronous history of plutonism, contractional deformation, and rifting at 2.06-1.9 Ga, partly coinciding with the 2.06 Ga within-plate Bushveld magmatic event to the east. Development of this orogen was linked to transpressional reactivation of Archean structures in the Limpopo belt between the Zimbabwe and Kaapvaal cratons. (2) The Paleoproterozoic orogen is succeeded outward by a NE-trending Mesoproterozoic orogen that records granitoid plutonism and amphibolite-grade ductile deformation at 1.35-1.1 Ga and links with the Namaqua belt exposed to the south. Bimodal magmatic rocks were emplaced at 1.1 Ga in a rift zone that formed within this orogen following compressional deformation. These rocks are part of the Umkondo large igneous province that was emplaced across southern Africa at 1.1 Ga. (3) The Mesoproterozoic orogen is delimited to the west by a NE-trending continuation of the Damara belt exposed in Namibia. Neoproterozoic Damaran structures wrap a major promontory in the Congo craton margin to the north to connect with the coeval Lufilian arc along strike to the northeast in Zambia. These two belts represent exposed segments of a single, transcontinental, 0.65-0.5 Ga orogen that connects with the Zambezi belt farther east.