Abstract

Jurassic basalts cap the Karoo stratigraphic sequence in the Ellisras sub-basin of the Northern Province. The 75-metre section of basalt flows, obtained from a borehole, is probably a remnant of a thicker accumulation of unknown thickness. K-Ar ages of flows from top and bottom of the profile average 179+ or -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 another occurrence of the voluminous low Ti-Zr (or LTZ) type, which characterizes the Springbok Flats, central Botswana, and Lesotho. None of the 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 appeared to have been erupted from the Lebombo-Soutpansberg/Tuli-Nuanetsi triple junction. The Ellisras basalts represent part of the margins of a vast basalt lava field consisting of the LTZ magma type that was erupted from a separate centre (or centres) in Lesotho and/or Botswana.

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