⁴⁰Ar/³⁹Ar geochronology reveals rapid change from plume-assisted to stress-dependent volcanism in the Newer Volcanic Province, SE Australia

Abstract

© 2017. American Geophysical Union. All Rights Reserved.Here we present 40Ar/39Ar ages of volcanic features in the Cenozoic intraplate Newer Volcanic Province in southeast Australia. The <5 Ma volcanic products in the Newer Volcanic Province can be subdivided into tholeiitic, valley-filling Newer Plains basalts, and alkaline scoria cones, lava shields, and maars of the Newer Cones series. Plateau ages range from 3.76±0.01 to 4.32±0.03 Ma (2s; all sources of uncertainties included) for the Newer Plains series, with production rates of volcanism decreasing post 4 Ma. We suggest that magmatism is related to the complex interplay of magma upwelling due to edge-driven convection and the Cosgrove track mantle plume located in the northeast of the province at 6.5-5 Ma. Plateau ages range from 1290±20 to 41.1±2.2 ka (2s) for the Newer Cones series, with a diffuse age progression in the onset of volcanism for these features from east to west. Analyses of the distribution and geomorphology of these volcanic features indicates a strong control of basement faults on volcanism, reflected in alignment of volcanic features along Paleozoic north-south oriented basement faults in the east and Cretaceous northwest-southeast oriented extensional features in the west. This age progression can be explained by a westerly migration of stress derived from the left-lateral strike-slip Tasman Fracture Zone. This suggests that the general mechanism of volcanism changed from upwelling due to plume-assisted edge-driven convection prior to ~4 Ma to stress-dependent upwelling at around 1.3 Ma.