Intra-plate volcanism in North Queensland and eastern new Guinea: A cryptic mantle plume?

Abstract

Intra-plate volcanism in NE Australia, the eastern Highlands of New Guinea and along the Papuan Peninsula has been reasonably continuous over the Pliocene and Quaternary, without age progression, despite rapid movement of the Australian plate towards the north (∼7 cm/yr). Global seismic tomography indicates a strong zone of reduced seismic wavespeed near the core-mantle boundary beneath the Coral Sea, between Australia and New Guinea, yet unlike the majority of such features, there is no obvious volcanic ‘hotspot’ at Earth’s surface. By analysing a combined global and regional tomography model, we suggest here that since 20 Ma, remnants of past subduction, imaged as fast wavespeed zones in seismic tomography, have impeded any direct upwelling from depth. The spatio-temporal patterns and geochemical signature of volcanism in this region, however, suggests that some plume material has made its way through this maze of slab remnants, to impinge on the strong lithospheric step associated with the edge of the thick North Australian craton, which extends into New Guinea. We suggest that following the arrival of the extended Australian continent into the zone of influence of this cryptic mantle plume at ∼10 Ma, the combination of largely blocked upward flow and shallow edge- and shear-driven processes modulates the regional flow regime to spawn volcanism at the observed locations in NE Australia and New Guinea.