Lithostratigraphy of the Mesoproterozoic Twakputs Gneiss

Abstract The Twakputs Gneiss is a garnetiferous, K-feldspar megacrystic, biotite granite-granodiorite orthogneiss. It represents major unit in the Kakamas Domain of Mesoproterozoic Namaqua-Natal Metamorphic Province extending about 250 km between Riemvasmaak South Africa and Grünau southern Namibia. occurs as foliation-parallel, sheet-like bodies tightly infolded together with granulite-facies paragneisses into which it intrudes along variety other pre-tectonic granite leucogranite orthogneisses. These rocks were subsequently intruded by late-tectonic garnet-leucogranites, granites charnockites. distinctive characterised large ovoid to elongate megacrysts twinned perthitic K-feldspar, set coarse-grained matrix garnet, biotite, quartz feldspar. contains penetrative foliation defined alignment K-feldspars streaks that developed during main phase D2 Namaqua Orogeny (~1.2 1.1 Ga). an accompanying elongation lineation are more intensely lithological contacts, especially at margins mega-scale F3 domes basins refold regional fabrics. U-Pb zircon dating has yielded concordia ages ~1192 1208 Ma. Whole-rock geochemistry shows consistent major, trace REE elemental trends, thus reflect chemical variability from single fractionating magma. granitic granodiorite composition strongly peraluminous. ubiquitous presence garnet pelitic xenoliths indicate S-type protolith. most voluminous widespread member Eendoorn Suite comprises seven textural variants K-feldspar-megacrystic granitoid orthogneiss same age.