文档共享_Beijing SHRIMP Center

Evolution of Pre-1.8 Ga basement rocks in the western Mt Isa Inlier,northeastern Australia—Insights from SHRIMP U-Pb dating and in-situ Lu-Hf analysis of zircons [查看] FrankP.Bierlein、LanceP.Black、JanetHergt、GeordieMark

We present new SHRIMP zircon U–Pb data from pre 1.8 Ga basement rocks (Yaringa Metamorphics, Kurbayia Migmatite) on both sides of the Mt Isa Fault in the western Mt Isa Inlier. These data confirm that felsic intrusions were emplaced into the western Kalkadoon-Leichhardt Belt at 1849±4Ma (2σ), and constrain the Barramundi Orogeny in the western Fold Belt to ca. 1.87 Ga, at the bottom part of the previously reported range of ca. 1.90–1.87 Ga. Integration of in situ Hf isotope analysis and SHRIMP zircon age data support the notion that there is no lithospheric break across the Mount Isa Fault. Furthermore, the 176Hf/177Hf isotope data confirm that Archaean–Palaeoproterozoic magmatic zircons on both sides of the Mount Isa Fault were sourced from the same parental lithospheric reservoir which evolved over time from more primitive mantle to supracrustal compositions, without significant contributions from juvenile sources in the Palaeoproterozoic. The oldest inherited zircons in samples from the Yaringa Metamorphics reflect the participation of Archaean (ca. 3300–3600 Ma) crustal components in the western Mt Isa Inlier. These zircons, together with isotopic data from other studies, may allow for a tectonic reconstruction involving Archaean crust underlying much of the Proterozoic succession at least in the western Mt Isa Inlier. Alternatively, the Archaean zircons could represent detrital components incorporated from Palaeoproterozoic metasedimentary rocks. As detrital zircons can be transported laterally for hundreds of kilometres, these grains cannot be diagnostic of the nature and age of the basement beneath the western Mt Isa Inlier. Consequently, neither model can be conclusively excluded given the current data set.