HR: 13:40h
AN: T23E-01 INVITED    [Abstracts]
TI: Seismic Evidence for a Vertical Tear in the South American Lithosphere Offshore Venezuela
AU: * Clark, S A
EM: s.a.clark@geo.uio.no
AF: Dept. of Earth Science, Rice Univ., MS 126 POBox 1892, Houston, TX 77251-1892, United States
AU: * Clark, S A
EM: s.a.clark@geo.uio.no
AF: now at Dept. of Geosciences, Univ. of Oslo, POBox 1047 Blindern, Oslo, N-0316, Norway
AU: Levander, A
EM: alan@rice.edu
AF: Dept. of Earth Science, Rice Univ., MS 126 POBox 1892, Houston, TX 77251-1892, United States
AU: Niu, F
EM: niu@rice.edu
AF: Dept. of Earth Science, Rice Univ., MS 126 POBox 1892, Houston, TX 77251-1892, United States
AU: Zelt, C A
EM: czelt@rice.edu
AF: Dept. of Earth Science, Rice Univ., MS 126 POBox 1892, Houston, TX 77251-1892, United States
AU: Sobiesiak, M
EM: polar@gfz-potsdam.de
AF: GFZ Potsdam, Telegrafenberg, Potsdam, D-14473, Germany
AU: Magnani, M
EM: mmagnani@memphis.edu
AF: CERI, Univ. of Memphis, 3876 Central Ave, Memphis, TN 38152, United States
AB: In the southeast corner of the Caribbean plate, westward subduction of oceanic (Atlantic) South America transitions to east-west transform with continental South America, forcing the South American lithosphere to tear along its former passive margin. The most widely accepted model for lithospheric detachment, the tensile tear model, envisages oblique convergence causing northwest-dipping subduction. In this model, tensile stress on the subducting slab results in detachment orthogonal to the motion vectors. Conversely, the less commonly accepted shear tear model predicts detachment parallel to the motion vectors along a vertical plane, with shear stress focused at the edge of the propagating transform boundary. The tensile tear model requires significant crustal shortening to produce the 7 km of uplift in the coastal Serrania del Interior and 10 km of subsidence in the Maturin Basin onshore Venezuela. These features have been widely interpreted as the foreland fold and thrust belt and foreland basin of a collisional orogeny. Recent numerical modeling of the lithospheric response to shear tearing has shown, however, that much of the topography of eastern Venezuela can be generated from the propagating detachment, requiring relatively little shortening. We present five types of initially independent seismic data analyses to resolve the lithospheric tear: local seismicity locations, fault plane solutions, receiver functions, wide-angle seismic data inverted for velocity structure, and a regional, balanced cross-section constrained by petroleum industry data. These five datasets image a shear tear extending near-vertically through the entire lithosphere. Confirmation of this type of detachment has implications for diverse locations with similar plate boundary geometries, such as Tonga or the Carpathians, and improves our general understanding of vertical tectonics and associated mantle driving forces.
DE: 7218 Lithosphere (1236)
DE: 8038 Regional crustal structure
DE: 8111 Continental tectonics: strike-slip and transform
DE: 8138 Lithospheric flexure
DE: 8160 Rheology: general (1236, 8032)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting