Published 1995 as part of Memoir 62
Copyright © 1995 The American Association of Petroleum Geologists.   All Rights Reserved.

The eastern Venezuelan Coast Ranges result from oblique convergence along the South American-Caribbean plate boundary, expressed at the surface by the El Pilar dextral strike-slip fault. A crustal-scale, balanced NNW-SSE cross section has been constructed across this major transfer zone that links oceanic subduction of the Lesser Antilles with continental subduction of the Andes. It shows a major discrepancy between the cover and basement lengths, which can be explained by tectonic inheritance from the Tethyan margin and an initially thinned crust and basement tilted blocks. The section, interpreted down to the Moho, is constrained by magnetic and gravimetric profiles. A major gravimetric low along the axis of the Maturín basin shows the progressive northward deepening of the Moho. Positive magnetic anomalies on the southern flank of this basin probably result from shallow basaltic intrusions along the thinned part of the paleomargin or from crustal heterogeneities. A high-density intracrustal wedge is needed to fit the gravimetric high north of the Serranía; the solution requires a deep crustal root beneath the belt and a northward-dipping South American Moho. The results of successive gravimetric and magnetic modeling studies are compared with the present-day seismicity of the South American-Caribbean plate boundary. Shallow seismicity is restricted to the eastern part of the El Pilar fault, whereas deep focal mechanisms pick out a northwestward-dipping subduction slab off the northeastern Venezuelan and Trinidad coasts.

A consistent geodynamic model involving northward-dipping subduction of at least 70 km of South American continental lithosphere is thus proposed for the area. The El Pilar fault is a shallow structure that branches at depth on an intracrustal backstop and at the surface transfers the lateral motion required to balance the northward-dipping subduction in an oblique convergence regime. Petroleum generation was initiated in the early stages of the flexural evolution of the eastern Venezuelan basin, and early generated oils migrated over long distances from the inner parts of the belt toward the Orinoco to fill the traps of the Faja Petrolífera. Tectonic overburial also induced a late stage petroleum generation, with shorter migration of oil toward the frontal structures (the El Furrial and Orocual trends).