In Situ SHRIMP U-Pb Geochronology and Petrography of Mafic Dykes in the Yilgarn Craton, Western Australia, and Vestfold Hills and Bunger Hills, East Antarctica

Abstract:

Large Igneous Provinces (LIPs) are believed to result from major mantle melting events. Mafic dyke swarms associated with LIPs are therefore important for testing plume and non-plume related models for their formation as well as for understanding global tectonics and geodynamics. The Archean Yilgarn Craton in Western Australia and the Archean and Proterozoic Vestfold Hills and Bunger Hills cratonic blocks in East Antarctica are intruded by a large number of mafic and ultramafic dykes of different ages, orientations and magnetic signatures. Only a small fraction of these dykes have precise isotopic ages or systematic geochemical and paleomagnetic data. In the Yilgarn, previous studies have identified several dyke generations with two major suites at ca. 2.4 Ga and 1.2 Ga. At Vestfold Hills, geochronology and geochemical data have shown presence of at least five different dyke generations. No precise isotope ages for mafic dykes at Bunger Hills exist but previous work suggest that five compositionally distinctive dyke suites exist. We present new in situ SHRIMP U-Pb data for two previously unreported dyke suites in the southern Yilgarn and provide first high precision isotope ages for two dykes at Bunger Hills. Petrography and Ar/Ar ages from mafic dykes at Vestfold Hills reveal metamorphic and metasomatic events with implications for interpretation of paleomagnetic data.