BOLIVAR: The SE Caribbean Continental Dynamics Project

Alan Levander, Paul Mann, Hans G. Ave Lallemant, Michael Schmitz

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 (pbz) the Antilles Arc has obliquely collided with the northern SA margin since the Late Cretaceous. Neogene motions across the pbz combine right-lateral strike-slip faulting along the coastal faults (El Pilar-Oca), underthrusting of CAR seafloor beneath SA, and folding and thrusting and foredeep sedimentation at the southern edge of the pbz.

We provide a progress report on the components of the NSF Continental Dynamics BOLIVAR project ("Broadband Ocean-Land Investigations of Venezuela and the Antilles arc Region"). The focus of this study is the mechanism for accretion of arc-related terranes to the northern SA continent. The project includes geological, geochemical, and geophysical investigations involving more than 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 installation of a network of 35 PASSCAL broadband seismographs in central and eastern Venezuela, and 14 long-term OBSIP recorders along the Leeward Antilles arc and in the southeastern Caribbean basin. The PASSCAL and OBSIP instruments complement the 35 satellite-telemetered broadband stations operated by FUNVISIS, giving a broadband array of 84 stations.

In June, 2004, the BOLIVAR active seismology group completed marine reflection profiling, and joint land refraction, wide-angle onshore-offshore and OBS recording. We acquired ~6000 km of reflection data, including 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, and crossing the South Caribbean deformed belt, the Oca-El Pilar fault system, and most of the fold-thrust belt onland in Venezuela. The fifth profile was oriented northwest and extended from the Atlantic Ocean east of Trinidad and Tobago to the eastern Caribbean Sea and spanned the Lesser Antilles arc and associated structures. The R/V Ewing provided the sound source for much of the wide-angle program as well as acquired the reflection data. Dense wide-angle data were recorded using 49 OBSIP instruments deployed 169 times from the R/V Seward Johnson II, and 550 Reftek Texans deployed along each profile on the SA mainland. We also recorded reflection profiles and wide-angle data along the length of the Leeward Antilles arc.

We summarize the progress made in interpreting the geological and geophysical data, with a goal toward developing a unified model for development of the southeastern Caribbean plate boundary zone.