Abstract

The Mesoproterozoic metamorphic formations of the Wilgenhoutsdrif Group underlie a large area around the Orange River east of Upington. The quartzitic Grootdrink Formation occurs at the base of the sequence and contacts with older units are either unconformable or along thrusts. The Zonderhuis Formation is a sequence of low-grade pelitic phyllites and impure quartzites with subordinate lenses of metavolcanic rocks and serpentinite. The Leerkrans Formation is thought to follow conformably and consists of deformed basaltic and quartz-porphyritic lavas and volcanogenic metasediments. The entire group is isoclinally folded and foliated, with greenschist facies metamorphic parageneses, and is altered by carbonate veins and epidotisation. The age of felsic volcanic rocks is reliably established at 1289 or 1293 Ma with 2σ errors of 9 Ma. The Wilgenhoutsdrif Group now forms part of the Kaaien Terrane of the Namaqua-Natal Province. It may have formed in a continental back-arc basin at about the same time as the arc-related volcanic rocks of the Areachap Group formed by subduction of an ocean basin to the west, prior to ~1.2 Ga Namaqua terrane assembly by collisions with the Kaapvaal-Rehoboth Craton.

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