BOLIVAR & GEODINOS: INVESTIGATING ISLAND ARC ACCRETION ALONG THE SOUTHEASTERN CARIBBEAN PLATE BOUNDARY

Post-Archean continental growth is presumed to result from accretion of island arcs to older continental masses. Along the Caribbean-South American (CAR-SA) plate boundary zone the Antilles Arc has collided obliquely with the northern SA margin since the Late Cretaceous. Neogene motions combine right-lateral strike-slip faulting along the coastal faults (El Pilar-San Sebastian-Oca), underthrusting of CAR plate beneath SA, and folding and thrusting and foredeep sedimentation at the southern edge of the plate boundary.

We provide a progress report on the components of the U.S. BOLIVAR and Venezuelan GEODINOS projects. The goals of these projects are understanding the mechanisms for accretion of arc-related terranes to the northern SA continent, and assessing earthquake hazard in the SE Caribbean. The project includes geological, geochemical, and geophysical investigations involving ~30 scientists at 9 institutions in the U.S. and Venezuela. The study area extends from the Atlantic Ocean to the 71°W meridian, and from the Guyana Shield (60°N) into the eastern Caribbean basin (14°N). This immense area (>0.7M km2) is comparable in size to California and its continental margin, and rivals the San Andreas plate boundary zone in geologic complexity.

Geologic studies have included mapping and age dating of igneous rocks of the Leeward Antilles from Aruba to Los Testigos, mapping of brittle deformation structures on the ABC islands, and mapping in the Villa de Cura blueschist belt in Venezuela, basin analysis and analysis of uplift and subsidence patterns in the onshore and offshore region, and 3-D reconstruction of palegeographic evolution.

The BOLIVAR passive seismology group has completed two years of recording with 84 land and OBS broadband instruments. The BOLIVAR active seismology group acquired marine reflection, land refraction, and wide-angle onshore-offshore/OBS profiles along 5 principal reflection/wide-angle profiles. Four of these are along meridians (64°W, 65°W, 67°W, 70°W), extending from the Caribbean basin to the front of the fold-thrust belts onland in Venezuela. The fifth profile was oriented NW and extended from the Venezuela Basin to the Atlantic Ocean, crossing the Lesser Antilles arc and Aves Ridge. We also recorded reflection profiles and wide-angle data along the length of the Leeward Antilles arc.