KAROO BASALTS IN THE ELLISRAS SUBBASIN, NORTHERN PROVINCE

Jurassic basalts cap the Karoo stratigraphic sequence in the Ellisras sub-basin of the Northern Province. The 75-metre section of basalt flo ws, obtained from a borehole, is probably a remnant of a thicker accum ulation of unknown thickness. K-Ar ages of flows from top and bottom o f the profile average 179 +/- 5 Ma, which is similar to ages obtained for the Lebombo and Lesotho lavas. Little geochemical variation can be detected in the lava section, and the basalts appear to represent ano ther occurrence of the voluminous low Ti-Zr (or LTZ) type, which chara cterizes the Springbok Flats, central Botswana, and Lesotho. None of t he Ellisras basalts resemble those of northern Lebombo, Nuanetsi, Tuli , and the area east of Soutpansberg, thereby providing a western limit to the geochemically enriched magma type (high Ti-Zr or HTZ) that app eared to have been erupted from the Lebombo-Soutpansberg/Tuli-Nuanetsi triple junction. The Ellisras basalts represent part of the margins o f a vast basalt lava field consisting of the LTZ magma type that was e rupted from a separate centre (or centres) in Lesotho and/or Botswana.