TIMING AND PROVENANCE OF NEOARCHEAN-PALEOPROTEROZOIC UNCONFORMITY BOUNDED SEQUENCES ON THE KAAPVAAL CRATON

In this contribution we report on SHRIMP detrital zircon age populations from selected Neoarchean to late Paleoproterozoic successions on the Kaapvaal Craton. The following stratigraphic trends are displayed:

a)Systematic younging of the youngest detrital zircons from one unconformity bounded sequence to the next, providing a framework for depositional ages.

b)Abrupt variations in detrital zircon populations across major sequence boundaries, allowing more robust lateral correlation of sequences, especially in the late Paleoproterozoic red bed successions on the craton.

c)Distinct gaps in detrital zircon age populations. Most interesting is the scarcity of middle to late Archean detrital zircons suggesting that the Kaapvaal Craton itself was not a major source for the Paleoproterozoic sedimentary successions preserved on it.

The results imply that most of the detrital zircons were sourced from areas outside the present limits of the Kaapvaal Craton. It is also apparent that formation of prominent unconformity bounded sequences was related to major plate tectonic and crust forming events, each providing new detrital zircon populations. There is also no indication that any of the Neoarchean to early Paleoproterozoic successions on the craton were sourced from the 2650-2700 Ma orogenic event preserved in the Limpopo Metamorphic Complex. However, younger late Paleoproterozoic red bed successions contain abundant zircons of this time interval as well as a dominant population of ~2000 Ma detrital zircons. This may imply that the Limpopo Complex together with the Zimbabwe craton only became attached to the Kaapvaal craton at ~2.0 Ga during formation of the Magondi Mobile Belt which in turn sourced the voluminous late Paleoproterozoic red beds of southern Africa.