Lithospheric Deformation, Rebound, and Orogenesis along Southeastern Caribbean Plate Boundary

We summarize the results of seismic investigations in the southeastern Caribbean plate boundary region, including onshore-offshore active source profiles and broadband array measurements yielding 3D volumes of CCP stacked receiver functions and surface-wave tomography velocities. The area of investigation extends from the Guayana shield northward through the fold and thrust belts in coastal Venezuela, across the major plate boundary strike-slip faults (the El Pilar-San Sebastian system) and ends in the Caribbean sea. Active source profiles were acquired along the 64, 65, 67, and 70W meridians.

The seismic images document the evolution of the southeastern Caribbean plate boundary from west to east as South America has collided with and moved westward past the Caribbean plate since ~55 Ma. This motion has torn the South American plate between the subducting Atlantic oceanic lithosphere and buoyant continental South America. Near the eastern edge of the plate boundary at the 64W profile the South American continent is depressed ~15-20 km more than its reference state as the subducting Atlantic drags down the northern margin of South America, making space for a moderately shortened fold and thrust belt. The Moho shows abrupt changes in depth in traversing from the continental interior (at ~37km depth) to the plate boundary (~50km), across the island arc/metamorphic terranes in the near offshore region (~25km), to the Caribbean Large Igneous Province (~15km). A shear tear in the plate offshore northeastern Venezuela, is manifest by a column of mantle seismicity extending from ~50-110km depth. The western profiles (65, 67, and 70W) show a relaxing South American lithosphere and a shallowing Moho, resulting in uplift of the onshore and near offshore terranes, and exhuming both HP/LT subduction complex rocks and Paleogene basins. The systematic rebound of the South American continental lithosphere is responsible for significant aspects of the plate boundary tectonics.