Tectonic inheritance, crustal architecture, and contrasting structural styles in the Venezuela Andes

Abstract

Surface and subsurface data image contrasting structural styles for the two flanks of the Venezuela Andes. In the north, a flexural basin developed in Neogene times between the Andes and the Lake Maracaibo. North verging thrusts are mainly detached in the pre‐Cretaceous substratum and form a deeply buried antiformal stack. Secondary décollement levels occur both in the Upper Cretaceous and Tertiary strata, accounting for the passive roof thrust of a conventional frontal triangle zone. In the south, the Barinas basin hardly compares with a flexural basin. It is largely dominated by both north and south verging basement‐involving structures. Paleogene normal faults are locally inverted, and Caribbean nappes are frequently reactivated or refolded by younger oblique Neogene Andean structures. Seismic profiles in this area also attest to the strong Neogene structural inversion of Upper Jurassic‐Lower Cretaceous grabens. Hercynian, or more likely Early Paleozoic structures account for local preexisting crustal heterogeneities, reactivated during both the Tethyan rifting and the Andean deformations. Two trans‐Andean regional profiles have been balanced and constrained by an inversion of the gravimetric data. They imply a progressive deepening of the northern Moho and a south dipping subduction of the infracontinental lithospheric mantle of the Maracaibo block. The shortening for both sections averages 60 km. Palinspastic restorations assume a relative cylindricity for the deep crustal architecture of the Andes and minimize the possible effects of a progressive right‐lateral escape of the Maracaibo block with respect to stable South America along the Bocono Fault. Strain partitioning during Neogene oblique convergence induced surficial thrust fronts parallel to the plate boundary, strike‐slip motion in the allochthon along the Bocono Fault, and an asymmetric subduction (wedging) at depth.