Stratigraphy of the Koekoepkop thrust sheet in the Grünau Terrane, Mesoproterozoic Namaqua Province

Abstract

Abstract The Koekoepkop Formation (KKP), near Kakamas, represents a thrust sheet (~25km2) of supracrustal rocks between granite-gneiss sheets on the southern boundary of the Riemvasmaak-Kenhardt Mega Sheath Fold within the eastern Namaqua Metamorphic Province. The formation with an outcrop strike-length of 106 km, is stratigraphically divided into four main units of which the Upper and Middle Units are laterally continuous. The KKP underwent deformation and metamorphism during the Namaqua Orogeny (1200 to 1100 Ma) resulting in thrust related imbricate structures and wedging-out of lithologies along strike. The four units represent an interbanded sequence of mafic, felsic and quartzo-feldspathic gneisses, with an unduplicated maximum thickness of 57 m. The younging direction in the four units on the south-dipping limb is northwards, as deduced from interpreted primary sedimentary structures of different scales (i.e. grading, load structures and upwards fining bedding cycles). The precursors of the four units are deduced to represent volcano-clastic sediments, a sequence of mafic and felsic pyroclastic tuffs of rhyolitic to dacitic composition. The interpreted primary structures suggest low energy subaqueous depositional environments that are distal from an unidentified source. The upper-most pyroclastic flow unit probably represents a change in depositional environment from low to high energy during syn-eruptive periods. The KKP cannot be directly correlated with other supracrustal sequences in the Grünau Terrane such as the Goede Hoop and Biesje Poort/Puntsit Formations owing to its probably allochthonous nature.