Evidence of a common source component for east Australian Cenozoic mafic magmatism

Abstract

Eastern Australia includes Cenozoic mafic volcanic provinces that are commonly divided into age-progressive and non-age-progressive groups. The former group is typically ascribed to the Cenozoic northward motion of Australia over fixed thermal anomalies in the mantle (i.e., “hotspots”), while the latter group is traditionally attributed to the opening of the Tasman and Coral Seas, though more recent interpretations have linked its formation to edge-driven convection or other processes. However, the initial criteria used to define the groups based on morphological and lithological features are neither robust nor consistently able to be applied to individual provinces. Despite their importance in the Cenozoic tectonic history of eastern Australia and, more broadly, the SW Pacific, geochemical distinctions between the two groups have been underexplored. Based on examination of an extensive database of new and previous major element, trace element, and radiogenic isotope data and principal component analysisfrom key volcanic exposures in Queensland and New South Wales, we find no systematic geochemical differences between the two groups. Both age-progressive and non-age-progressive Cenozoic mafic volcanic rocks in eastern Australia have an EM1-like source signature that could have originated in the asthenosphere and interacted with SCLM upon ascent. Our work underpins the necessity of understanding the magma generation mechanisms and the geodynamic context of individual volcanoes across eastern Australia.