HR: 0800h
AN: T11B-0385    [Abstracts]
TI: Anomalous High Seismic Velocity Zones Along Major Strike-Slip Faults in the Collision Belt of Coastal Venezuela: Results of the BOLIVAR Project
AU: * Avé Lallemant, H G
EM: ave@rice.edu
AF: Department of Earth Science, MS-126, Rice University, 6100 Main Street, Houston, TX 77005 United States
AU: Levander, A
EM: alan@rice.edu
AF: Department of Earth Science, MS-126, Rice University, 6100 Main Street, Houston, TX 77005 United States
AU: Zelt, C A
EM: czelt@rice.edu
AF: Department of Earth Science, MS-126, Rice University, 6100 Main Street, Houston, TX 77005 United States
AU: Magnani, M B
EM: beatrice@rice.edu
AF: Department of Earth Science, MS-126, Rice University, 6100 Main Street, Houston, TX 77005 United States
AU: Guedez Parra, M C
EM: mcguedez@rice.edu
AF: Department of Earth Science, MS-126, Rice University, 6100 Main Street, Houston, TX 77005 United States
AU: Clark, S A
EM: stoney@rice.edu
AF: Department of Earth Science, MS-126, Rice University, 6100 Main Street, Houston, TX 77005 United States
AB: Interpretation of wide-angle seismic data, collected in 2004 on and offshore central Venezuela as part of the BOLIVAR Project, shows several high-velocity anomalies that coincide with major plate-boundary strike-slip fault zones. These fault zones high-velocity bodies extend from depths of about 2 to 15 km and are approximately 10 km wide. The associated fault zones (e.g., San Sebastian / Morón fault; Oca fault), generally, strike east-west and are steep at the surface. They were active during south-vergent thrusting in the foreland area (Serranía del Interior, and Barinas-Apure and Eastern Basins). Consequently, the strike-slip and thrust faults are connected and merge into a common decollement surface at depth. These structures indicate that displacement partitioning has occurred from the strongly right-oblique convergence between the South American and Caribbean plates. Many of the east-west striking fault zones contain heavily deformed assemblages of serpentinized peridotite, serpentinite, and other rock types (e.g., mica schist, graphite schist, marble, granite, gneiss, amphibolites). These zones often carry inclusions of HP/LT (High Pressure / Low Temperature) metamorphic rocks, such as eclogite and blueschist. Some of the eclogites have formed at depths exceeding 70 km. Several models have been proposed to explain the ascent and exhumation of these rocks. We prefer a model related to displacement partitioning along a curved plate boundary such as the Lesser Antilles arc (Avé Lallemant and Guth, 1990). The arc-normal component of the displacement rate vector causes arc-normal thrusting and the arc-parallel component results in arc-parallel strike-slip displacements. As the arc-parallel component increases along the arc, arc-parallel stretching results in exhumation of the HP/LT metamorphic rocks and peridotites in a manner analogous to exhumation of a metamorphic core complex. We take the ubiquitous appearance of high-velocity rocks with major strike-slip faults as evidence that this exhumation process involves the entire South American-Caribbean plate boundary. Despite the fact that ultramafic rocks are frequently found associated with fault zones, to our knowledge high-velocity zones associated with faults have rarely been recognized seismically worldwide.
DE: 8011 Kinematics of crustal and mantle deformation
DE: 8015 Local crustal structure
DE: 8021 Melanges
DE: 8104 Continental margins: convergent
DE: 8111 Continental tectonics: strike-slip and transform
SC: Tectonophysics [T]
MN: Fall Meeting 2005