Deflection of mantle flow controlled by slab-cratonic keel interactions: insights from shear-wave splitting in the southeastern Caribbean

Subduction and recycling of oceanic lithosphere is a major control on the thermal evolution of the Earth. Cratonic continental lithosphere, conversely, can resist mechanical erosion for billions of years, moves coherently with plates, and deflects flow in the asthenosphere. We investigate the mechanical interactions between these two components of mantle convection in the Caribbean-South American plate margin which hosts a complex subduction system and continental transform fault adjacent to the Guyana Shield. Along the northern margin of the South American continent, shear-wave splitting measurements display anomalously large (1.5-2.5 s) delay times and fast polarization directions are oriented orthogonal to the Antilles trench and parallel to the transform plate boundary. Analysis of various seismological data, including seismicity, tomography, and SK(K)S splitting, and 176 global geodynamical models with lateral viscosity and density variations adapted to this unique region allow for quantitative testing of how mantle flow, as induced by the oceanic slab of the Antilles volcanic arc and mediated by a weak asthenosphere, is influenced by the stiff South American cratonic keel. We explore for the first time how slab-craton interactions affect tectonic force transmission to produce this narrow region of abnormally strong seismic anisotropy parallel to the coastline, change regional plate velocities, and localize intra-plate deformation.