HR: 1340h
AN: T33C-0579    [Abstracts]
TI: Evidence of Nicoya Ophiolite Material Drilled at ODP Site 1042
AU: Steiger, T
EM: T_Steiger@gmx.de
AF: TU Bergakademie Freiberg, Bernhard-von-Cotta-Str. 2, Freiberg, D-09596 Germany
AU: * Meschede, M
EM: meschede@uni-greifswald.de
AF: University of Greifswald, Institute of Geography and Geology, Friedrich-Ludwig-Jahn-Str. 17a, Greifswald, D-17487 Germany
AU: Gawlick, H
EM: gawlick@unileoben.ac.at
AF: University of Leoben, Institute of Geosciences, Franz-Josef-Str. 18, Leoben, A-8700 Austria
AB: The convergent plate margin off Costa Rica has been intensely studied during the last two decades to understand the process of subduction along the Central American margin. Based on high- resolution 3D seismic data and results from ODP drilling, it has recently been recognized that the Costa Rican forearc wedge on the upper plate is currently undergoing active subduction erosion (Meschede et al., 1999; Ranero and von Huene, 2000) rather than tectonic accretion by underplating. The model of subduction erosion implies that the forearc wedge of the upper plate is progressively reduced at its base and that the offscraped material is transported downward into the subduction zone. Removal of material from the base of the forearc causes extensional deformation of the upper plate, which results in subsidence of the forearc wedge and leads to landward migration of the coastline. Subsidence of the Costa Rican forearc wedge has been proven by benthic foraminifera which clearly indicate subsidence from shallow water deposition about 10-12 Myr ago to the present deep sea deposition in a depth of more than 4000 m at the location of ODP Site 1042 (Meschede et al., 2001). At the base of this drill hole a breccia dated as 14 Myr old has been encountered. It contains basaltic rocks and radiolarites as components. Rocks of these types occur in the nearby Nicoya ophiolite complex at the Nicoya peninsula in a distance of about 60 km. Radiolarians found in a sample from the breccia coincide with radiolarians from the Nicoya ophiolite complex thus indicating the provenance of the breccia. We therefore argue that the breccia represents a coastal breccia formed at the coastline of the Nicoya peninsula 14 Myr ago.
DE: 3042 Ophiolites (8140)
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
DE: 9355 Pacific Ocean
DE: 9609 Mesozoic
SC: Tectonophysics [T]
MN: Fall Meeting 2005