THE LIMPOPO BELT: A RESULT OF ARCHEAN TO PROTEROZOIC, TURKIC-TYPE OROGENESIS?

Abstract

Evidence is presented relating to the tectonic evolution of the Limpopo Belt of southern Africa. It is demonstrated that this evolution was protracted, lasting at least 700 m.y. between ca. 2.7 and ca. 2.04 Ga, and comprised the complex assembly of terranes along shear zones through processes involving compression, extension, and strike-slip strain (transpression and transtension). It is argued that this evolution is more akin to Turkic-type craton building than to Himalayan-or Alpine-type collision between the Kaapvaal and Zimbabwe cratons at either ca. 2.7 Ga or ca. 2.04 Ga, to which most earlier workers have subscribed. The steeply dipping shear zones separating terranes are tens of kilometers wide with gradational contacts, as opposed to narrow (<1 km) shear zones with relatively sharp contacts that characterize the Himalayas and Alps. Ductile deformation with both subvertical and horizontal transport directions is common in the Turkic-type orogenesis rather than thin skin, thrust tectonics. The shear zones are interpreted to be artifacts of long-lived subduction zones. Relics of calc-alkaline (I-type) magmatic arcs that formed both on continental and oceanic crust are identified and are related to subduction-accretion of the various terranes. In contrast, S-type magmatism (melts derived from sedimentary protoliths) characterizes deformation after continent-continent collision in the Alps and Himalayas. Individual terranes are characterized by distinct P-T-time (pressure-temperature) paths that show they experienced different tectonic histories under high-grade amphibolite-to granulite-facies conditions instead of lower-grade, greenschist-to amphibolite-grade conditions, which are more common in the Alps and Himalayas. Individual terranes also have distinct metallogenic signatures. © 2006 Geological Society of America.