ON THE DESTRUCTIVE TENDENCIES OF CRATONS: INSIGHTS FROM 3D GEODYNAMIC MODELING

Cratons are the strongest regions of Earth’s lithosphere. Yet, there are several examples of confirmed (North China Craton) or suspected (Wyoming Craton) removal of cratonic lithosphere indicating that, in some regions, stability is impermanent. Flat slab subduction beneath a craton is often proposed as a mechanism for destroying the overriding lithosphere, yet a slab subducting adjacent to a continental margin, such as in northeastern South America, may also cause lithospheric removal by directing mantle flow along the boundary. The pattern of plate boundary parallel shear-wave splitting observations used to infer seismic anisotropy, decays in magnitude from large ~2 second delay times near the plate boundary to less than 1 second within the Amazonia craton. This anisotropic fabric, interpreted to be due from directed mantle flow, could carve and shape the margins of the craton. However, it is unclear whether present day craton margin shape reflects the processes that formed the craton or of post-formation events, and how the margin shape contributes to the overall (in)stability. To unravel these complexities, we computed a series of three-dimensional geodynamic models in Underworld to investigate how subduction-driven directed flow interacts with cratonic lithosphere with differing shapes. We find that the shape of the margin controls both the channelization of the flow around the craton as well as its potential for destruction.