HR: 09:00h
AN: T11D-05    [Abstracts]
TI: Upper mantle structure beneath the Caribbean – South American plate boundary from surface wave tomography
AU: * Miller, M S
EM: meghan.s.miller@rice.edu
AF: Rice University, Department of Earth Science, Houston, TX 77005, United States
AU: * Miller, M S
EM: meghan.s.miller@rice.edu
AF: University of British Columbia, Department of Earth and Ocean Sciences, Vancouver, BC V6T 1Z4, Canada
AU: Niu, F
EM: niu@rice.edu
AF: Rice University, Department of Earth Science, Houston, TX 77005, United States
AU: Levander, A
EM: alan@rice.edu
AF: Rice University, Department of Earth Science, Houston, TX 77005, United States
AB: The shear wave velocity structure of the crust and upper mantle beneath the Caribbean-South American boundary was determined by analysis of fundamental mode Rayleigh waves in the 20-100s band that were recorded at the BOLIVAR/GEODINOS stations between 2003-2005. The 84 station array included 1 GSN station, 27 PASSCAL broadband (BB) seismographs, 15 OBSIP BB instruments and 8 Rice BB seismometers, as well as 34 BB stations of the Venezuelan national seismological network. Earthquakes in the distance range 20° to 60°, with magnitudes greater than 5.1, were used to invert for the upper mantle structure using the method of Forsyth and Li (2005). The model contains lateral variations that primarily correspond to tectonic provinces and plate boundaries. A clear linear velocity change parallels the plate bounding strike-slip fault systems along the northern coast of Venezuela, illustrating the differences between the continental lithosphere of the South American plate and the lithosphere of the Caribbean large igneous province. At depths up to 120 km beneath the Venezuelan Andes and the Maracaibo block there is evidence of underthrusting of the Caribbean plate a few hundred kilometers inland, but there is no other evidence of subduction of the Caribbean plate beneath the South American plate. Shallow low velocities associated with the basins near the coast are clearly imaged, as are higher velocities in the crust and upper mantle associated with the Guayana shield in southeastern Venezuela. The subducting Atlantic plate is imaged beneath the Antilles Arc as a shear tear where the subducting Atlantic plate tears away from the buoyant continental plate at the western end of the Caribbean-South American plate boundary. A low velocity "column" at the edge of the tear may be associated with asthenospheric flow from the Lesser Antilles arc mantle wedge. The complex structure of the plate boundary is best imaged and interpreted with three-dimensional modeling. We have combined the surface wave model, receiver functions, relocated local seismicity, and interpretations from active source profiling to more completely understand the geometry and upper mantle structure of the region.
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 7270 Tomography (6982, 8180)
DE: 8104 Continental margins: convergent
DE: 8138 Lithospheric flexure
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting