Interaction between subducting slabs and an anomalous lower mantle as source of intraplate volcanism

A significant fraction of the Earth’s volcanism occurs within plates, and it is traditionally associated with mantle plumes. However, a number of intraplate volcanic provinces, including those emplaced in the Central Mediterranean, Northeast America and Southeast Asia, lack many of the characteristic features of the plume model. Other mechanisms include slab-induced upwelling of a wet mantle transition zone (MTZ), the Big Mantle Wedge model invoking the progressive dehydration of a slab stagnating into the MTZ and edge-driven convection. In this work, we investigate the interaction between a subducting slab and a thermochemical anomaly present within the uppermost lower mantle - possibly given by a ponding plume - as a potential source of secondary upwellings in the upper mantle. We used 2-D numerical simulations to test the effect of thermal and hydrous anomalies and show that, with a linear increase in viscosity through the mantle, a 100-200°C hotter lower mantle always cause volcanism, while the presence of water (0.1 wt%) alone is not enough. If a viscosity jump atop the lower mantle is assumed, then only thermochemical anomalies can produce volcanics. Overall, the results provide a new perspective on the petrological-thermomechanical interaction between the slab and the lower mantle that may explain several intraplate volcanic provinces in the world.