SM-ND AGE AND REE GEOCHEMISTRY OF PROTEROZOIC ARC-RELATED IGNEOUS ROCKS IN THE RICHTERSVELD SUBPROVINCE, NAMAQUA MOBILE BELT, SOUTHERN AFRICA

Igneous rocks of the Richtersveld Subprovince in South Africa and Nami bia form a Palaeo-Mesoproterozoic are complex, dominated by extrusive andesites and their plutonic equivalents (diorites, tonalites), althou gh the whole spectrum of rock types from ultramafic to felsic is prese nt. Sm-Nd isotope data indicate an extrusion age of 2000 Ma, thereby c onfirming previously published Rb-Sr and U-Th-Pb ages. Initial Nd, Sr and Pb isotope ratios indicate a juvenile crust-producing episode at t his time, with rapid recycling of young crust to generate rhyolitic an d granitic components within the are complex. The Richtersveld Subprov ince represents the oldest crust in the western Namaqua Province, whic h was subsequently recycled during post 2.0 Ga tectonothermal events, especially the 1200-1000 Ma Kibaran episode. (C) 1997 Elsevier Science Limited.