Emplacement and deformation ages of the Wyangala Granite, Cowra, NSW

Abstract

New geochronological data from the Wyangala Granite in the Hill End Trough, Eastern Lachlan Fold Belt, constrain the timing of granite emplacement and subsequent deformation. SHRIMP U–Pb dating of zircon indicates that the granite crystallised in the late Silurian (425.2 ± 3.5 Ma). Subsequent west-over-east thrusting resulted in the development of mylonite along its eastern margin and cataclasis of megacrystic and groundmass feldspars, especially in pervasive shear zones within the granite. 40Ar/39Ar dating of feldspar from two deformed granite samples yielded ‘plateau’ ages in the range 375–365 Ma that are interpreted to reflect the timing of deformation associated with major shearing. These ages broadly overlap with the proposed age range of the late Middle Devonian Tabberabberan event and some biotite K–Ar and Rb–Sr ages in the nearby Sunset Hills Granite.