Localisation of Mantle Upwelling Beneath Recent Intra-Plate Volcanism in Australia

Abstract:

The widespread occurrence of intraplate volcanism is difficult to explain using the primary features of plate tectonics, such as subduction at convergent boundaries or upwelling at rifted margins, which are responsible for most volcanism on Earth. Instead, other mechanisms are invoked, foremost of which is the mantle plume model, typically characterised by a localised thermal upwelling that brings material from the deep mantle up to the base of the lithosphere to form a volcanic hotspot at Earth's surface. However, it is becoming increasingly apparent that many instances of intraplate volcanism do not adhere to this model, which has lead to a variety of other causes being postulated, including edge driven convection (EDC), shear driven upwelling (SDU) of the asthenosphere, lithospheric cracking, ductile removal of lithosphere via gravitational instability, glacial rebound and slab tear. Here, we use a combination of seismic tomography and geodynamic modelling to show that the source of the most recent volcanism within the Australian continent is restricted to the upper mentle and is unlikely to be plume-fed. Moreover, we demonstrate, for the first time, that mantle upwelling induced by EDC can be localised and intensified as a result of 3-D variations in lithospheric thickness and SDU caused by plate motion. In this case, geodynamic modelling constrained by seismic imaging results predicts a localised zone of mantle upwelling beneath the Quaternary Newer Volcanics Province (NVP) in southeast Australia. This helps to solve the puzzle of why EDC - which occurs at step changes in lithospheric thickness - only manifests at isolated locations along craton edges and passive margins.