HR: 0800h
AN: T11B-0388    [Abstracts]
TI: Imaging the SE Caribbean Accretionary Boundary: Results from the BOLIVAR Seismic Reflection and Refraction data at 65W
AU: * Magnani, M
EM: beatrice@rice.edu
AF: Rice University, 6100 Main Street, Houston, TX 77005 United States
AU: Zelt, C A
EM: czelt@rice.edu
AF: Rice University, 6100 Main Street, Houston, TX 77005 United States
AU: Sawyer, D
EM: dale@rice.edu
AF: Rice University, 6100 Main Street, Houston, TX 77005 United States
AU: Levander, A
EM: alan@rice.edu
AF: Rice University, 6100 Main Street, Houston, TX 77005 United States
AB: We describe a N-S, ~550 km long onshore-offshore profile at approximately 65oW., which is one of the principal seismic reflection and refraction transects acquired in 2004 as part of the Broadband Ocean and Land Investigation of Venezuela and the Antilles arc Region (BOLIVAR) experiment. Goals of BOLIVAR are to understand the complex history of the progressive oblique collision between the Leeward Antilles arc and South America that has taken place since the late Cretaceous, and to unravel the mechanisms responsible for continental growth of the South American continent through arc accretion. The transect starts ~330 km offshore northern Venezuela, in the Venezuela Basin, crosses the South America/Caribbean incipient subduction zone, the Los Roques canyon, the ABC ridge, the Tuy-Cariaco Trough (bounded by the El Pilar-Moron dextral strike-slip system), and crosses the coast east of Barcelona, Ve., continues south 175 km through the Espino Graben, and the Eastern Venezuela Basin. Multi-channel seismic reflection data were acquired by the R/V Ewing along the offshore portion of the profile, while 7 ocean bottoms seismometers (offshore) and 485 Reftek Texans (onland) recorded the Ewing airgun shots. In addition two large land shots (600 kg and 1000 kg of pentanol) were recorded by the land stations, providing reversed refraction coverage. The profile is located in a unique position along the South America/Caribbean plate boundary as it lies astride a transfer zone between the Southern Caribbean Deformed Belt, where the Caribbean plate is subducting beneath South America, and the eastern Venezuela strike-slip boundary and modern Antilles volcanic arc, where the South American plate subducts beneath the Caribbean. The structure and motion across this apparent transfer zone are unknown. The seismic data show that this area is characterized by a basement high, with little sediment coverage and velocities as high as 6.5-6.7 km/s at a depth of 8-10 km. North of the coast about 30 km, the profile images a the El Pilar Fault, part of the plate bounding strike-slip fault system, on the northern flank of the Tuy-Cariaco pull-apart basin. Here the fault is vertical to a depth of at least 10 km, where the signal on the reflection data becomes weak and the signature of the fault fades out. On land, the wide angle data image the Espino Graben, a Jurassic rift basin that extends from the Barcelona area, to the NE, to the Colombian border, to the SW. A prominent reflection in the northern land shot can be interpreted either as the base of the basin, suggesting a thickness of at least 9 km for the sedimentary sequences, or as a reflection from the Paleozoic pre-rift sedimentary sequences or from the crystalline Precambrian basement.
UR: http://earthscience.rice.edu/BOLIVAR.html
DE: 3025 Marine seismics (0935, 7294)
DE: 7205 Continental crust (1219)
DE: 8038 Regional crustal structure
DE: 8108 Continental tectonics: compressional
DE: 8111 Continental tectonics: strike-slip and transform
SC: Tectonophysics [T]
MN: Fall Meeting 2005