CHEMICAL COMPOSITIONS, RB-SR ISOTOPIC SYSTEMATICS AND TECTONIC SETTING OF CERTAIN POST-KINEMATIC MAFIC IGNEOUS ROCKS, LIMPOPO MOBILE BELT, SOUTHERN-AFRICA

The results of a reconnaissance chemical and Rb-Sr isotopic investigation of some mafic igneous rocks from within the Limpopo Mobile Belt of the northern Transvaal suggest that these rocks are, for the most part, tholeiitic in composition and that they often have anomalous contents of Rb and K. They further indicate that two previously unrecognized episodes of dyke emplacement may have occurred in this area about 2200 Ma ago and again about 1900 Ma ago and that the initial stages of formation of the Soutpansberg Trough began about 1770 Ma ago. The episodes of dyke emplacement correspond, respectively, to the formation of the Transvaal Basin and to either the intrusion of the Bushveld Granite or to the formation of the Waterberg Basin. The Soutpansberg Trough likely formed subsequently as an aulacogen. The igneous activity documented expands the recognized spans of time over which the Limpopo Mobile Belt has been tectonically active. © 1979.