Provenance of metasedimentary rocks of the Kheis Terrane and Kakamas Domain: support for accretionary tectonics during the development of the western Namaqua-Natal metamorphic province.

Abstract

The ~1 200 to 1 000 Ma Namaqua-Natal Metamorphic Province (NNMP) is part of a major orogenic belt in the west-central parts of South Africa and most likely formed during the convergence of the Laurentia and Kalahari cratons during the assembly of Rodinia. Controversy exists regarding the mode of formation of the Namaqua sector of the NNMP, with some supporting the idea of accretion of different crustal fragments while others argue that it formed in a continental back-arc setting. Here we address this controversy and provide information regarding the provenance of two metasedimentary successions that are preserved to the east and west of the Trooilapspan shear zone, which represents the Eastern Namaqua Front. 207Pb/206Pb SHRIMP ages for detrital zircon grains sampled from the Keis supergroup, which is preserved in the Kheis Terrane and situated on the Kalahari Craton, support derivation from Archaean to Paleoproterozoic source areas on the Kaapvaal Craton. In contrast, SHRIMP ages from detrital zircon grains of the Korannaland Group, which forms the metamorphosed supracrustal sequence of the Kakamas Domain, show derivation from late-Paleoproterozoic to Mesoproterozoic source areas like the Bushmanland and Richtersveld domains as well as the gneissic basement of the Kakamas Domain. The zircon age distribution data show that the metasedimentary rocks of the Keis supergroup and Korannaland Group did not obtain detrital material from the same source areas during their deposition, and that the Keis supergroup never served as a source for the detrital material in the Korannaland Group. This indicates that these successions had different geological histories prior to the formation of the NNMP, which supports the accretionary model for the development of the Namaqua Sector of the NNMP.