The tectono-metamorphic event at 2 Ga in the Limpopo Belt and the resetting behaviour of chronometers at high temperature

Structural observations with garnet and monazite dates from the Messina area, Central Zone of the Limpopo Belt, are presented, as well as Rb-Sr and zircon ages from the Transition Zone between the Triangle shear zone and the Northern Marginal zone. It is shown that the 2.57 Ga Bulai pluton NW of Messina is deformed by a later high grade event involving minor local remelting. Within samples, monazite concordia ages broadly concur with garnet-feldspar Pb-Pb results. In some samples they document full resetting of both chronometers at 2.0 Ga, but in some they display mixed ages indicating pre-existing parageneses of at least 2.6 Ga. An overview in histogram form of available age results from the Limpopo Belt shows peaks at 2.6-2.7 Ga in the Northern and Southern Marginal Zones but not in the Central Zone, and a peak at 2.0 in all three zones, indicating that the 2.0 Ga event is the first episode common to the three zones of the Limpopo Belt.