Precambrian Research, 47 (1990) 17-26 17 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands Geochemistry and origin of early Proterozoic volcanic rocks from the Transvaal and Soutpansberg successions, South Africa CLAY CROW and KENT C. CONDIE Department of Geology, University of Nevada, Las Vegas, Las Vegas, NV89154 (U.S.A.) Department of Geoscience, New Mexico Institute of Mining and Technology, Socorro, NM 87801 (U.S.A.) (Received July 12, 1988; revision accepted September 21, 1989) Abstract Crow, C. and Condie, K.C., 1990. Geochemistry and origin of early Proterozoic volcanic rocks from the Transvaal and Soutpansberg successions, South Africa, Precambrian Res., 47: 17-26. The early Proterozoic Transvaal (TR) and Soutpansberg (SB) successions in South Africa are composed of sedi- ments and variable amounts of volcanic rocks. Volcanic rocks are chiefly tholeiitic in character and in some formations range from mafic to felsic in composition. Except for Machadodorp basalts, all volcanics exhibit Nb-Ta depletion relative to Th and REE. Machadodorp basalts are relatively depleted in incompatible elements and some exhibit flat to depleted LREE patterns like MORB. Andesites and more felsic volcanics in the TR succession can be related to associated basalts by shallow fractional crystallization. In terms of incompatible trace-element ratios, two and perhaps three mantle sources are required for TR-SB basalts. These sources may be part of an ancient subcontinental litho- sphere beneath the Kaapvaal Craton which was variably enriched with a subduction-zone component during one or more episodes of arc collision prior to 3.0 Ga. Introduction Archean volcanic rocks from the Kaapvaal Craton in southern Africa commonly exhibit major- and trace-element distributions similar to volcanic rocks from modern arc systems (Crow and Condie, 1987, 1988; Crow et al., 1990). In addition, these volcanics appear to have been contaminated with large ion litho- phile elements (LILE) by upper continental crust. Results suggest that the mafic compo- nents of these Archean volcanic suites are de- rived from a LILE-enriched subcontinental lithosphere that acquired a subduction-zone geochemical signature prior to 3 Ga, perhaps during construction of the Kaapvaal Craton by arc collisions. To understand volcanic pro- cesses and the evolution of mantle sources be- neath the Kaapvaal Craton during the Proter- ozoic, we herein extend our geochemical studies to include early Proterozoic volcanic rocks from the Transvaal Supergroup and the Waterberg Supergroup in South Africa. Geologic setting The Transvaal Supergroup is a succession composed largely of shallow marine clastic sed- imentary rocks that covers an area about 5 × 105 km 2 and attains a maximum thickness of 12 km in the Transvaal region of South Africa (Fig. la). Although the Transvaal succession is cra- tonic in character in terms of sedimentary rocks (Button, 1973), four volcanic horizons occur in 0301-9268/90/$03.50 © 1990 Elsevier Science Publishers B.V.