Mesozoic to Cenozoic magmatism, Lorne Basin, NSW

Abstract

The Lorne Basin on the mid north coast region of New South Wales is a small circular-shaped basin within the southern margin of the New England Fold Belt. It comprises an Early Triassic terrestrial sedimentary sequence (the Camden Haven Group) overlain by rhyolitic volcanics which appear to be co-genetic with the Late Triassic granitoids (the Brothers) which intrude the Lorne Basin sedimentary sequence. Over the last few years, we have conducted fieldwork in the Lorne Basin, mainly investigating the magmatic rocks, as part of a larger project on the volcanic sequences of eastern Australia. Initial work resulted in the identification of a number of rhyolitic dykes intruding the Brothers granitoids, previously unrecorded. As a result of this, we then undertook detailed geochronological and geochemical investigations of the magmatic sequences throughout the basin to determine their relationship to each other, and other peripheral sequences, outside of the basin. Our results show that the Lorne Basin had a more complex and protracted magmatic history than previously thought, beginning with Late Triassic rhyolitic volcanics, followed by co-genetic rhyolitic volcanics and granitoids, then Late Jurassic and Early Cretaceous rhyolitic volcanics, terminating in Mid Miocene mafic volcanism.