Tectonics of the Venezuelan Andes

The Venezuelan Andes form a 400 km long and 100 km wide belt which morphotectonic structures have been recognized in the field mostly in the 1970s-80s (Bellizia et al., 1976; Gonzalez de Juana et al., 1980; Schubert, 1980; Stéphan, 1982, 1985; Laubscher, 1987). These preliminary observations have served the basis for interpretations and discussions concerning the morphological and structural evolution of the belt (e.g., Audemard, 1993; De Toni and Kellogg, 1993; Colletta et al., 1997; Audemard and Audemard, 2002). Analysis of remote sensing images allowed implementing the geological mapping and to explicit the relationships between the main structures (Dhont et al., 2002, 2005). Recent GPS data (Freymuller et al., 1993, Perez et al., 2001; Trenkamp et al., 2002) illustrate the kinematics of the Northern Andes, which motion is directed NNE, obliquely to the E-W relative convergence between the South American and the Nazca plates (Fig. 21). More details have been observed in the field, permitting to precise the tectonic style and timing of deformation (Soulas et al., 1985; Dhont et al., 2005; Hervouët et al., 2001, 2005, Backé et al., this volume). Seismic surveys across the northern and southern foreland basins gave way to different interpretations on the structure of the belt (e.g., De Toni and Kellogg, 1993; Colletta et al., 1997). Among all these various approaches, none enabled to precisely constraint the geometry of the tectonic structures at depth, this being essentially due because the available data are limited to the surface or are interpreted cross-sections.

Faults

Once the 3D map has been calculated, graphical representations permit the user to examine it from various directions, slice it and disassemble it. Fault surfaces modelling (Fig. 22) shows that the Bocono and Valera faults are the only vertical structures. The other accidents cross-cutting the Venezuelan Andes correspond to normal faults with a listric shape. The Trujillo triangular block is subdivided in smaller wedges bounded to the east by SE-dipping normal faults and to the south by the Bocono fault. Each wedge is composed of elongate tilted blocks with dimension less than 20 km in width. They are compatible with a generalized décollement in the upper or middle crust.