The Superpile Cycle: the mobility of LLSVPs in response to plate tectonics

The coupling between the surface and deep Earth is fundamental to the dynamics of the planet, yet the nature of these interactions remain poorly understood through space and time. These processes are elusive, in part, because of a lack of constraint on the nature and evolution of two antipodal large low shear-velocity provinces (LLSVPs) near the core-mantle boundary (CMB), and the role they play in mantle circulation. The origins and long-term stability of these features are debated. This study aims to assess the relative stability of LLSVP-like structures in 3D mantle circulation models, through the coupling between these structures, upwellings and downwellings. The 'superpile cycle', named after its close ties to the supercontinent cycle, depicts the evolution of the deep Earth in response to supercontinent dynamics. Supercontinents assemble with stable subduction girdles and antipodal basal mantle structures, then break apart. During dispersal, as new subduction zones form, slabs induce more complex mantle flow and disrupt the stable degree 2 structure in the lowermost mantle. As subduction zones stabilise, LLSVP-like structures tend back to two antipodal piles, and a new supercontinent may assemble. These findings highlights the cyclical and coupled nature of structures in the deep Earth and at the surface.