New U-Pb data on zircons from the Amalia greenstone belt Southern Africa: insights into the Neoarchaean evolution of the Kaapvaal Craton

Abstract

Evidence for the existence of Neoarchaean greenstone rocks in the western part of the Kaapvaal Craton is provided by ID-TIMS and SHRIMP U-Pb age data on zircons from supracrustal rocks of the Amalia greenstone belt. Although all the units described from the Amalia greenstone belt might not be coeval, an age of 2750.1 ± 4.6 Ma found for two samples appears to be the best estimate for the deposition of this part of the Amalia greenstone belt sequence. These samples also contain younger zircons, the majority of them yielding a 1099 ± 32 Ma upper intercept age. This date of ∼ 1.1 Ga might indicate that these rocks have been affected by the crustal thickening and magmatism event coeval with the peak of metamorphism during the Namaqua orogeny ∼1.1 Ga. These data provide the first evidence for the development of a Neoarchaean greenstone sequence in the western part of the Kaapvaal Craton. They also demonstrate that the Namaqua orogeny affected rocks within the craton itself.