科研之友
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摘要
U-Pb zircon analyses from a series of orthogneisses sampled in drill core in the northern Gawler Craton provide crystallisation ages at ca 1775-1750 Ma, which is an uncommon age in the Gawler Craton. Metamorphic zircon and monazite give ages of ca 1730-1710 Ma indicating that the igneous protoliths underwent metamorphism during the craton-wide Kimban Orogeny. Isotopic Hf zircon data show that 1780-1750 Ma zircons are somewhat evolved with initial epsilon(Hf) values -4 to +0.9, and model ages of ca 2.3 to 2.2 Ga. Isotopic whole rock Sm-Nd values from most samples have relatively evolved initial epsilon(Nd) values of -3.7 to -1.4. In contrast, a mafic unit from drill hole Middle Bore 1 has a juvenile isotopic signature with initial epsilon(Hf) zircon values of ca +5.2 to +8.2, and initial epsilon(Nd) values of similar to +3.5 to +3.8. The presence of 1775-1750 Ma zircon forming magmatic rocks in the northern Gawler Craton provides a possible source for similarly aged detrital zircons in Paleoproterozoic basin systems of the Gawler Craton and adjacent Curnamona Province. Previous provenance studies on these Paleoproterozoic basins have appealed to the Arunta Region of the North Australian Craton to provide 1780-1750 Ma detrital zircons, and isotopically and geochemically similar basin fill. The orthogneisses in the northern Gawler Craton also match the source criteria and display geochemical similarities between coeval magmatism in the Arunta Region of the North Australian Craton, providing further support for paleogeographic reconstructions that link the Gawler Craton and North Australian Craton during the Paleoproterozoic.
- 出版日期2011
