Intraplate volcanism triggered by subducted volatiles during bursts in slab flux

Convective upwellings in the upper-mantle have been proposed to explain intraplate volcanic provinces not associated with a hotspot chain. Such upwellings have been alternatively attributed to edge-driven convection, asthenospheric shear, and lithospheric detachment to explain intraplate volcanism, but fail to account for episodes of non-plume related volcanism across large regions. Eastern Australia and Zealandia host one of the world’s largest intraplate volcanic fields that has been sporadically active throughout the Cenozoic. While some linear chains of volcanoes correlate with the direction of plate motion, the majority of volcanoes show no clear age-progression and exhibit eruption spikes at 4 Ma and 21 Ma. Here we show that these spikes in intraplate volcanism are likely triggered by the release of subducted volatiles from the transition zone during bursts in regional slab consumption rates, associated with abrupt changes in plate motion. Using tectonic reconstructions of the Australia-Zealandia domain, we show that thick piles of subducted slabs have stagnated in the transition zone and underlie the volcanic field. Relatively unimpeded subduction along the northern segment of the Tonga-Kermadec trench supplies a high flux of volatile-rich pelagic sediments into the transition zone, supported by high 87Sr/86Sr ratios in eruption products analogous to EM2. Further south the subduction zone is congested by the Campbell and Challenger Plateaux, which is manifested in a gradation to a more HIMU mantle reservoir due to longer slab residence times in the transition zone. We have identified a slab flux-driven upper mantle process which explains previously enigmatic space-time relationships of intraplate volcanism from east Australia and Zealandia, potentially applicable to many other intraplate regions underlain by subducted slabs in the transition zone.

Feb 4, 2020 2:15 PM — 2:30 PM