Abstract
Abstract
The coupling between the surface and deep Earth is fundamental to the dynamics of the planet, yet the nature of these interactions remain incompletely understood. These processes are elusive, in part, because of a lack of constraints on the nature and evolution large low shear-velocity provinces (LLSVPs) near the core-mantle boundary (CMB), and their role in mantle circulation. Here we use a suite of 24 3D mantle circulation models, spanning a wide parameter space of CMB temperature, plate velocity, viscosity structure, and basal layer properties, to assess the stability of LLSVP-like structures and their relationships to upwellings, downwellings, and plate tectonics. We propose the hypothesis of a `superpile cycle' (named after its close ties to the supercontinent cycle, and usage of the term `super-pile' to describe LLSVPs beneath Africa and Pacific Ocean) that 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, new subduction zones form, slabs induce more complex mantle flow and disrupt the stable degree 2 structure in the lowermost mantle during a brief `rearrangement event', in which mantle plumes become more numerous and widely distributed. As subduction zone locations stabilise, LLSVP-like structures tend back to antipodal piles, plume activity becomes more focussed, and a new supercontinent assembles. This cyclicity, and the relative ordering of events, is consistent across the model suite , suggesting a coupled relationship between supercontinent dynamics, basal mantle structures, and distribution of upwellings through time.