HR: 1340h
AN: T13C-1478    [Abstracts]
TI: BOLIVAR: Crustal Structure of the Caribbean-South America Plate Boundary at 65W
AU: * Bezada, M
EM: maxbezada@rice.edu
AF: Rice University, 6100 Main st. MS-126, Houston, TX 77005, United States
AU: Magnani, M
EM: mmagnani@memphis.edu
AF: Center for Earthquake Research and Info - University of Memphis, 3890 Central Ave., Memphis, TN 38152, United States
AU: Zelt, C A
EM: czelt@rice.edu
AF: Rice University, 6100 Main st. MS-126, Houston, TX 77005, United States
AU: Levander, A
EM: alan@rice.edu
AF: Rice University, 6100 Main st. MS-126, Houston, TX 77005, United States
AU: Schmitz, M
EM: mschmitz@funvisis.gob.ve
AF: FUNVISIS, Prolongacion Calle Mara, El Llanito., Caracas, DC 1070, Venezuela
AB: We describe a ~550 km long, N-S oriented, onshore-offshore profile that crosses the SE Caribbean plate boundary at approximately 65W longitude. The profile 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. The transect starts ~330 km offshore northern Venezuela and crosses the plate boundary from the stable Caribbean (CAR) plate to the stable South America (SA) continent crossing the El Pilar continental strike-slip fault system. High quality multi-channel seismic (MCS) reflection data were acquired along the 330 km offshore portion of the profile. The airgun shots from the MCS vessel and two land shots were also recorded by 7 OBS's and 514 single channel land receivers for wide-angle analysis. We have analyzed the wide-angle data using a tomographic inversion of first arrival travel times to obtain upper and mid-crustal P wave velocities, followed by simultaneous inversion of PmP and Pn to obtain Moho depth and lower crustal and upper mantle P wave velocities. The P-Wave velocity model was converted to density using a 5^th order polynomial fit to global experimental data, and the calculated gravity response was compared to an observed gravity curve resulting from averaging a swath 50 km wide about the profile. The calculated gravity response fits the observed locations and wavelengths of local highs and lows well, although the anomaly amplitudes do not fit exactly using the automatic velocity-density conversion. The model suggests a Caribbean crust that is over 10 km thick and shows South American crust of variable thickness ranging from 30 to 40 km. Structures imaged in the model include the Cariaco trough offshore, a sedimentary basin that reaches a depth of ~9 km; and the Espino Graben onshore, that reaches a maximum depth of ~8 km. The MCS data image the stable CAR plate and the thrusting of the CAR plate under the South Caribbean Deformed Belt (SCDB) prism. The accretionary prism is highly deformed although the seismic data suggest limited recent tectonic activity: The frontal thrust faults are draped by an apron of recent sediments, mostly deformed by slumping above the steepest slope of the prism. Wide-angle data corroborate a limited amount of thrusting of the CAR plate under the Leeward Antilles arc region. To the south, the reflection data cross the El Pilar continental strike-slip system along the northern edge of the Cariaco basin. At this longitude the dextral strike-slip system accommodates ~50% of the strike-slip displacement between the CAR and SA plate and is characterized by transtensional motion. The Cariaco basin appears as a narrow, deep trough, bounded to the north by the nearly vertical El Pilar strike slip fault, which juxtaposes crustal rocks with an average velocity of 5.7 km/s against sedimentary sequences with an average velocity of 3.0 km/s.
DE: 0905 Continental structures (8109, 8110)
DE: 0935 Seismic methods (3025, 7294)
DE: 1219 Gravity anomalies and Earth structure (0920, 7205, 7240)
DE: 7205 Continental crust (1219)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting