T49 Mantle Dynamics and Crust-Mantle Interactions in Collisional Orogens

Sunday, 28 October 2007
1:30 PM - 5:30 PM

IMAGES OF CONTINENTAL LITHOSPHERIC BENDING, TEARING, AND REBOUND IN THE SOUTHEASTERN CARIBBEAN PLATE BOUNDARY

Paper number: T49-10
Program: Technical Sessions
Time: 3:55 PM – 4:10 PM

Authors

Abstract

Using BOLIVAR Project and other seismic data, we have constructed a number of cross-sections of the southeastern Caribbean plate boundary based on active source seismic profiles, and slices from 3D volumes of common conversion point stacked receiver functions and surface-wave tomography velocities. The profiles extend from the Guayana shield northward through the fold and thrust belts near the coast, cross the major plate boundary strike-slip faults (the El Pilar-San Sebastian-Moron system) and end in the Caribbean sea, approximately along the 64, 65, 67, and 70W meridians. We include local seismicity data from FUNVISIS and the GFZ-Potsdam.

The profiles 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 from ~55 Ma to the present. This motion has forced a tear to develop in the South American plate between the subducting Atlantic oceanic lithosphere and buoyant continental South America. This plate boundary has been characterized as a Subduction-Transform Edge Propagator (STEP fault) by Govers and Wortel, 2005. 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 with ~65km shortening. 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 at approximately (62.5o,W, 11.0o,N), 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.