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1 Department of Geology, University of Zimbabwe, Box MP 167, Mt Pleasant, Harare, Zimbabwe
2 Mineralogisch-petrographisches Institut, Gruppe Isotopengeologie, Universitaet Bern, Erlachstr. 9a, 3012 Bern, Switzerland
The Umlali Thrust Zone has been mapped between the granite–greenstone rocks of the Zimbabwe craton and the granulite-facies rocks of the Limpopo Belt. A tectonic break had not been previously recognized in the southwest because of the intrusion of syn- to post-kinematic porphyritic granites. These intrusions locally obliterate evidence for the tectonic break, although in some localities the associated mylonites are preserved as xenoliths within the intrusive porphyritic granite bodies.
The porphyritic granite bodies were emplaced during and after the main regional fabric forming event. A U–Pb zircon age of 2627 ± 7 Ma obtained from a late-kinematic microgranite is interpreted to be the minimum time of thrusting. A whole-rock Rb–Sr age of 2583 ± 52 Ma obtained from plutonic rocks and retrogressed zones within the North Marginal Zone falls within error of the zircon age, suggesting widespread magmatic and hydrothermal activity coeval with the thrusting.
Key Words: Zimbabwe • Limpopo Belt • Archaean • granite porphyry
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