U-Pb and Hf isotope record of detrital zircons from gold-bearing sediments of the Pietersburg Greenstone Belt (South Africa)-Is there a common provenance with the Witwatersrand Basin?

Results of combined U-Pb and Hf isotope analyses on detrital zircons from coarse grained clastic sediments of the Pietersburg Greenstone Belt provide evidence for four major magmatic activities in the hinterland, at ca. 3.29, 3.26, 3.21, and 2.96 Ga, during which new crust was formed from depleted mantle sources. The latter interpretation is supported by mostly superchondritic epsilon Hf-t of -4.3 to +4.2 at 2.96 Ga, +0.1 to +5.3 at 3.21 Ga, +0.2 to +3.2 at 3.26 Ga, and 0.0 to +6.2 at 3.29 Ga. The observed epsilon Hf-t variations, and the finding of abundant magmatic but also metamorphic zircon overgrowths with ages at ca. 2.96 Ga furthermore suggests that the youngest magmatic event took place in a continental arc setting, whereby juvenile magmas were mixed with older reworked crust. A similar setting is also suggested for the three older magmatic events. Based on our datasets deposition and metamorphism of the Pietersburg sediments is bracketed between 2.88 and 2.69 Ga, in agreement with the deposition age of the gold-bearing Central Rand Group of the Witwatersrand Basin. The occurrence of 2.98-2.88 Ga zircon populations with mostly superchondritic but variable epsilon Hf-t in the Pietersburg and Central Rand Group sediments indicate that a vast amount of detritus for both areas was supplied from proximal, relative juvenile magmatic arc sources. However, the general absence of 3.15-3.00 Ga zircons in the Pietersburg sediments, but their abundant occurrence in the Witwatersrand Basin indicates that detritus supply for both basins came either from completely different sources, or that 3.15-3.00 Ga basement was additionally sampled during southward transport. (C) 2012 Elsevier B.V. All rights reserved.