HR: 1340h
AN: T13C-1477    [Abstracts]
TI: BOLIVAR: Crustal structure of the Caribbean-South America plate boundary between 60W and 70W from wide-angle seismic data
AU: * Zelt, C A
EM: czelt@rice.edu
AF: Rice Univeristy, Dept Earth Science, MS-126, 6100 Main street, Houston, TX 77251, United States
AU: Christeson, G L
EM: gail@ig.utexas.edu
AF: Institute for Geophysics, University of Texas, J.J. Pickle Research Campus, Bldg 196, 10100 Burnet Road, Austin, TX 78758, United States
AU: Magnani, M B
EM: mmagnani@memphis.edu
AF: Center for Earthquake Research and Information (CERI), University of Memphis, 3876 Central Ave., Memphis, TN 38152, United States
AU: Clark, S A
EM: s.a.clark@geo.uio.no
AF: University of Oslo, Dept Geosciences, Oslo, NO-0316, Norway
AU: Guedez, M C
EM: maria.c.guedez@exxonmobil.com
AF: ExxonMobil Production Company, 800 Bell, Houston, TX 77060, United States
AU: Bezada, M
EM: maxbezada@rice.edu
AF: Rice Univeristy, Dept Earth Science, MS-126, 6100 Main street, Houston, TX 77251, United States
AU: Levander, A
EM: alan@rice.edu
AF: Rice Univeristy, Dept Earth Science, MS-126, 6100 Main street, Houston, TX 77251, United States
AU: Schmitz, M
EM: mschmitz@funvisis.gob.ve
AF: Fundación Venezolana de Investigaciones Sismológicas (FUNVISIS), Seismology Dept, Caracas, 1070, Venezuela
AB: We present the results from five wide-angle seismic profiles collected onshore and offshore Venezuela in 2004 as part of the Broadband Ocean Land Investigation of Venezuela and the Antilles arc Region project (BOLIVAR). The study area is the diffuse plate boundary between South America (SA) and the SE Caribbean plate (CAR) covering roughly 1000 km by 500 km. Over the past 55 My the Leeward Antilles island arc that borders the CAR plate has been colliding obliquely with the SA continent resulting in a collision front that has migrated from west to east. The five wide-angle profiles sample different stages of the time-transgressive margin from west to east, each crossing the margin roughly perpendicularly. The main purpose of this presentation is to contrast and compare the crustal velocity structure along these profiles to better understand the tectonic processes that are responsible for the evolution and present-day configuration of the plate boundary. Each of the wide-angle profiles is about 500 km in length and includes both onshore and offshore shots and receivers, except the easternmost profile, which is entirely offshore. The dense wide-angle data were modeled in the same way along each profile using a two-step, layer-stripping approach: (1) the first-arrival times were tomographically inverted for a smooth velocity model, and (2) the lower crust, Moho, and uppermost mantle were determined by simultaneous inversion of the PmP refection and Pn refraction phases while keeping the upper and middle crust from the first step fixed. The five models show tremendous lateral heterogeneity, as they cross features such as normal oceanic crust, oceanic plateau crust, an accretionary wedge, active and remnant island arcs, forearc and foreland basins, a major strike-slip system, a fold and thrust belt, and the edge of cratonic continental crust. Two of the main contributions of the wide-angle models to the BOLIVAR project, and the focus of this presentation, are the Moho structure, which is generally not imaged in the coincident reflection data (see Magnani et al., this session), and the 1-D velocity structure of the tectonic units that make up the diffuse plate boundary. The first-order results are (1) a general smoothing and flattening of Moho topography from the youngest to oldest parts of the margin (east to west), suggesting a "relaxation" of the Moho, (2) an offset in the Moho roughly beneath the strike-slip fault system, more pronounced in the east, suggesting that the deformation is not confined to the crust, and (3) high crustal velocities at all depths within the island arc.
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 7205 Continental crust (1219)
DE: 7270 Tomography (6982, 8180)
DE: 8111 Continental tectonics: strike-slip and transform
DE: 9360 South America
SC: Tectonophysics [T]
MN: 2007 Fall Meeting