Rb-Sr and Pb-Pb dating of the Anhalt leucotonalite, northern Natal

Rb-Sr and Pb-Pb isotope data are presented for the Anhalt leucotonalite, an intrusive granitoid from the Piet Retief area of northern Natal. The Rb-Sr data define an isochron date of 3 250 ± 39 Ma whereas the Pb-Pb data define an errorchron date of 3 402 + 166/-188 Ma. The 87Sr/86Sr for this suite is low (0,7001 ± 3) whereas the model source 238U/204Pb is high. The results are interpreted to indicate that the Anhalt leucotonalite was formed at approximately 3,25 Ga, the age suggested by the Rb-Sr systematics, and that the Pb isotopes are disturbed, although the timing of disturbance is not certain. The high 238U/204Pb is considered to be an artefact of incomplete Pb isotope homogenisation. 21 refs., 5 tabs., 3 figs