HR: 1340h
AN: T43C-1333    [Abstracts]
TI: Morphostructural Analysis of an Escape Tectonic Zone : the North-Western Venezuelan Andes
AU: * Dhont, D
EM: damien.dhont@niv-pau.fr
AF: Universite de Pau et des Pays de l'Adour, CNRS- FRE 2639: Laboratoire d'Imagerie Geophysique, CURS-IPRA, Avenue de l'Universite, Pau, 64000 France
AU: Backe, G
EM: guillaume.backe@univ-pau.fr
AF: Universite de Pau et des Pays de l'Adour, CNRS- FRE 2639: Laboratoire d'Imagerie Geophysique, CURS-IPRA, Avenue de l'Universite, Pau, 64000 France
AU: Hervouet, Y
EM: yves.hervouet@univ-pau.fr
AF: Universite de Pau et des Pays de l'Adour, CNRS- FRE 2639: Laboratoire d'Imagerie Geophysique, CURS-IPRA, Avenue de l'Universite, Pau, 64000 France
AU: Niviere, B
EM: bertrand.niviere@univ-pau.fr
AF: Universite de Pau et des Pays de l'Adour, CNRS- FRE 2639: Laboratoire d'Imagerie Geophysique, CURS-IPRA, Avenue de l'Universite, Pau, 64000 France
AB: Lateral motions in active collisional areas have been mainly described in the Asian and European belts. The most common view is that part of the intracontinental convergence between to plates is accommodated by major strike-slip faults bounding a lithospheric block that laterally moves away. This process, privileging horizontal compressional forces at boundaries of the moving block corresponds to an extrusion or escape of the continental landmass. Diffuse extensional deformation within the block implies that buoyancy forces, leading eventually to an extensional collapse, must be taken into account. Escape of the block is perpendicular to the convergence direction of the orogen and can only occur if a free lateral boundary exists. Our study concerns the analysis of the deformation in the northwestern part of the Venezuelan Andes, located in the northern part of South America. It is based on analysis of satellite and Digital Elevation Model imagery, complemented by field structural observations. We shall describe new tectonic features advocating that part of the belt is subjected to lateral escape tectonics during the Plio-Quaternary. The zone displays major active faults forming crustal blocks having a triangular shape pattern, and which are moving toward the north-east. The triangular corners are composed of smaller pluri-kilometre size crustal blocks bounded by normal faults. A major result is that in an area characterized by on-going intracontinental convergence, extension and strike-slip deformations predominate. In order to better constrain the depth of the deformation, we have generated a 3-D geologic model displaying the seismicity the area showing that the earthquakes are mainly restricted to the crust. The type and distribution of the deformation are not consitent with the behaviour of a simple rigid extrusion. The Venezuelan Andes are rather composed of crustal blocks that are tilted and move relative to each others. This is consistent with extensional crustal deformation related to the escape of a main triangular block (Trujillo block) towards the Caribbean plate that constitutes a free boundary towards which the Venezuelan belt landmass can easily flow.
DE: 8010 Fractures and faults
DE: 8015 Local crustal structure
DE: 8040 Remote sensing
DE: 8107 Continental neotectonics
DE: 8109 Continental tectonics--extensional (0905)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting