PROTEROZOIC METAVOLCANIC ROCKS AND ASSOCIATED METASEDIMENTS ALONG THEORANGE RIVER IN THE POFADDER TERRANE, NAMAQUA MOBILE BELT

The Pofadder terrane in western Namaqualand is a continental margin is land are domain (Cordilleran-type) of Eburnian age (2.0 Ga). The 320 x 90 km terrane is situated between other thrust-bounded tectonostratig raphic terranes which underwent metamorphism and deformation during th e Namaqua (Kibaran) Orogeny (1.3 to 1.0 Ga). The Pofadder terrane cons ists of a supracrustal sequence of metavolcanic rocks (the Haib Subgro up), which are engulfed in granitic rocks (the Vioolsdrif Suite). The rocks comprising the Haib Subgroup and Vioolsdrif Suite define a major calk-alkaline igneous complex which are the magmatic products of the Orange River (Eburnian) Orogeny (2.0 Ga). The Haib Subgroup consists o f the Hom Formation at the base (felsic metavolcanic rocks with interb anded calcium-rich metasediments and minor mafic metavolcanic rocks), followed by the Tsams Formation (mixed felsic and mafic metavolcanic r ocks with interbanded metasediments), Boerputs/Gaidip Formation (metas ediments, quartzite/schist with minor meta-arkose and mafic metavolcan ic rocks), and Guadom Formation (mafic metavolcanic rocks and interban ded metasediments consisting mainly of schist within which pod-like bo dies of sillimanite occur). Wedges of sedimentary rock with cordierite /anthophyllite, calcium-rich rock (calc-silicates), peraluminous rock, and magnetite-quartzite/BIF associations form distinct units within t he volcanic rocks, for example, the Pella Subgroup, Boerputs Formation , and Abbasas Sequence. The area studied is interpreted to be distal w ith respect to the eruptive centres of the Haib in the west, because o f the absence of coarse volcaniclastic rocks and the presence of assoc iated metasedimentary rocks. The wedges of metasedimentary sequences a re interpreted as second-order basins generated during incipient rifti ng (back arc environment).