Juvenile crust formation in the northeastern Kaapvaal Craton at 2.97 Ga¡ªImplications for Archean terrane accretion, and the source of the Pietersburg gold

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• 作者：Armin Zeh ; Justine Jaguin ; Marc Poujol ; Philippe Boulvais ; Sylvain Block ; Jean-Louis Paquette
• 关键词：Archean terrane accretion ; Kaapvaal Craton ; Murchison Greenstone Belt ; U&ndash ; Pb&ndash ; Hf isotopes ; Pietersburg gold source ; Provenance
• 刊名：Precambrian Research
• 出版年：2013
• 出版时间：August, 2013
• 年：2013
• 卷：233
• 期：Complete
• 页码：20-43
• 全文大小：4998 K

文摘

Combined U-Pb and Lu-Hf isotope data of detrital and magmatic zircon grains provide evidence that the Murchison Greenstone Belt, NE Kaapvaal Craton (South Africa), hosts an important Archean suture zone, which primarily formed by a collision 2.97 Ga ago between a back arc system to the north and an evolved terrane, the proto-Kaapvaal Craton, to the south. This model is supported by the observations that igneous rocks of the northern terrane, comprising mafic rocks and tonalites of the Rooiwater Complex and felsic volcanics of the Rubbervale Formation, were both emplaced at about 2.97 Ga and show highly superchondritic ?Hf_t of +4.4 to +5.1. In contrast, U-Pb-Hf isotope data of detrital zircon grains from quartzitic schists of the Murchison Unit and the La France Formation, both part of the southern terrane, provide evidence for a southern provenance, which was affected by granitoid intrusions accompanied by crust re-working at 3.53-3.42 Ga (?Hf_t = +1.8 to ?4.8), 3.30-3.20 Ga (?Hf_t = +1.8 to ?6.3), and 3.13-3.05 Ga (?Hf_t = +1.3 to ?5.6); pointing to a connection with the Barberton Greenstone Belt and Swaziland. A spatial separation of the two terranes prior to 2.97 Ga, is furthermore supported by the facts that the youngest detrital zircon grains of the southern terrane, having ages between 2.99 and 2.97 Ga, show subchondritic ?Hf_t between ?6.5 and ?1.5, in contrast to the highly superchondritic ?Hf_t obtained from the contemporaneous magmatic rocks of the northern terrane. The juvenile character of the Rooiwater and Rubbervale magmatic rocks, along with the occurrence of VMS deposits, makes them a likely candidate for the source of the gold-pyrite bearing conglomerates exposed in the adjacent Pietersburg Greenstone Belt.