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Abstract:
Intraplate volcanism has long been linked to deep mantle plumes. However, recent studies showed that intraplate magmatism can originate from transition zone dynamics, where lower-mantle plumes might be ponding, creating a Thermal Boundary Layer (TBL). Inspired by intraplate volcanoes in Eifel, Massif Central and Hainan that are distributed near tips of stagnant slabs imaged at transition zone depth, we hypothesize that subducted slabs might destabilize the TBL and trigger upper mantle plumes (secondary plumes), leading to intraplate volcanism. So far, the generation of such secondary plumes and the influence of slabs on plumes remain poorly understood. In this study, we perform 2D upper-mantle geodynamic models with a TBL imposed at 670 km depth interacting with a slab of an intra-oceanic subduction zone. The effects of various slab geometries (rollback, rollover and intermediate), TBL temperature and heating time are tested. Our models show that slabs of all geometries can destabilize the TBL, initiating secondary plumes ahead of and behind the slab. All plumes are deflected by the slab-induced mantle flow and a sinking slab may even suppress plumes beneath it. However, a higher TBL temperature and a longer pre-subduction heating duration may increase buoyancy flux of secondary plumes, making them more resistant to slab-driven flow. Under all conditions explored in this study, the strength of secondary plumes produced in our models is comparable to that of the Eifel plume. This paper elucidates slab-plume interaction and their impact on intraplate volcanism with applications to the Eifel, Massif Central and Hainan volcanic areas.
