40Ar39Ar and K-Ar age constraints on the timing of regional deformation, south coast of New South Wales, Lachlan Fold Belt: Problems and implications

Abstract

Four slate samples from subduction complex rocks exposed on the south coast of New South Wales, south of Batemans Bay, were analysed by K-Ar and 40Ar/39Ar step-heating methods. One sample contains relatively abundant detrital muscovite flakes that are locally oblique to the regional cleavage in the rock, whereas the remaining samples appear to contain sparse detrital muscovite. Separates of detrital muscovite yielded plateau ages of 505 ± 3 Ma and 513 ± 3 Ma indicating that inheritance has not been eliminated by metamorphism and recrystallisation. Step-heating analyses of whole-rock chips from all four slate samples produced discordant apparent age spectra with 'saddle shapes' following youn..