WESTWARD CONTINUATION OF THE CRATON LIMPOPO BELT TECTONIC BREAK IN ZIMBABWE AND NEW-AGE CONSTRAINTS ON THE TIMING OF THE THRUSTING

The Umlali Thrust Zone has been mapped between the granite-greenstone rocks of the Zimbabwe craton and the granulite-facies rocks of the Lim popo Belt. A tectonic break had not been previously recognized in the southwest because of the intrusion of syn- to post-kinematic porphyrit ic granites. These intrusions locally obliterate evidence for the tect onic break, although in some localities the associated mylonites are p reserved as xenoliths within the intrusive porphyritic granite bodies. The porphyritic granite bodies were emplaced during and after the mai n regional fabric forming event. A U-Pb zircon age of 2627 +/- 7 Ma ob tained from a late-kinematic microgranite is interpreted to be the min imum time of thrusting. A whole-rock Rb-Sr age of 2583 +/- 52Ma obtain ed from plutonic rocks and retrogressed zones within the North Margina l Zone falls within error of the zircon age, suggesting widespread mag matic and hydrothermal activity coeval with the thrusting.