Geochemistry and ion microprobe (SHRIMP) age of a quartz porphyry sill in the Mozaan Group of the Pongola Supergroup: implications for the Pongola and Witwatersrand Supergroups

The Mozaan Group of the Pongola Supergroup is one of the oldest known cratonic supracrustal successions in the world. In the Mooihoek area, south central Swaziland, the Mozaan Group is preserved in an open syncline with axial traces trending north-northwest. A pretectonic quartz porphyry sill, folded with the sedimentary strata, gives a SHRIMP U-Pb zircon age of 2837 +/- 5 Ma, providing a minimum age limit for the deposition of the Mozaan Group. In contrast, the Mooihoek granitic pluton, which cross-cuts the folding, has a known single-zircon evaporation Pb-207/Pb-206 age of 2824 +/- 6 Ma, suggesting that the deformation of the Mozaan strata took place sometime between similar to 2824 Ma and similar to 2837 Ma. Correlation between the Mozaan and Witwatersrand Supergroups suggests that most of the latter succession was also deposited prior to 2837 +/- 5 Ma.