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Abstract Subduction-induced mantle flow has a considerable geodynamic impact on Earth. It can deflect mantle plumes, transport geochemical signatures and produce upwellings that generate atypical intraplate volcanism. The mantle flow produced by slab rollover subduction, however, remains unstudied, yet it may have a comparable geodynamic significance. Here, we present analogue models of buoyancy-driven subduction in which we image, using a state-of-the-art Particle Image Velocimetry (PIV) technique, the three-dimensional mantle flow induced by two contrasting subduction styles: slab rollback (trench retreat) and slab rollover (trench advance). Our model results show that the advancing subduction mode develops a slab rollover geometry that generates a large-scale upwelling in a broad mantle wedge domain. Based on a comparison between the location of this upwelling and Cenozoic volcanics in Tibet, we propose that slab rollover subduction of the Tethyan and Indian slabs generated a comparably broad mantle upwelling, which drove widespread Cenozoic volcanism in Tibet.

Abstract The origin of Samoan volcanism in the southwest Pacific remains enigmatic. Whether mantle melting is solely caused by a mantle plume is questionable because some volcanism, here referred to as non-hotspot volcanism, defies the plume model and its linear age-progression trend. Indeed, non-hotspot volcanism occurred as far as 740 km west of the predicted Samoan hotspot after 5 Ma. Here we use fully-dynamic laboratory subduction models and a tectonic reconstruction to show that the nearby Tonga-Kermadec-Hikurangi (TKH) subduction zone induces a broad mantle upwelling around the northern slab edge that coincides with the non-hotspot volcanic activity after 5 Ma. Using published potential mantle temperatures for the ambient mantle and Samoan mantle plume, we find that two geodynamic processes can explain mantle melting responsible for intraplate volcanism in the Samoan region. We propose that before 5 Ma, the volcanism is consistent with the plume model, whereas afterwards non-hotspot volcanism resulted from interaction between the Subduction-Induced Mantle Upwelling (SIMU) and Samoan mantle plume material that propagated west from the hotspot due to the toroidal component of slab rollback-induced mantle flow. In this geodynamic scenario, the SIMU drives decompression melting in the westward-swept plume material, thus producing the non-hotpot volcanism.