Abstract: Tectonic Inheritance, Crustal Architecture and Contrasting Structural Styles Along the Northern and Southern Andean Flanks, Venezuela

Bernard Colletta, Francois Roure, Bruno De Toni, Daniel Loureiro, Herminio Passalacqua, Yves Gou

Regional seismic profiles, exploration wells, geological maps and field studies image contrasting structural styles of the northern and southern flank of the Venezuelan Andes.

In the north, a flexural basin developed in Neogene times between the Andes and the Maracaibo Lake. North verging thrusts are mainly detached in the pre-Cretaceous substratum and form a deeply buried antiformal stack, whereas secondary decollement levels occur either in the Lower Cretaceous or in the Tertiary, accounting for the passive roof thrusting of the frontal triangle zone.

In the south, the Barinas basin can hardly be compared with a flexural basin. It is largely dominated by basement involved structures, either north or south verging. Tectonic inheritance is obvious, as Paleocene normal faults have been locally inverted, and early Caribbean nappes (Paleocene structures) are frequently reactivated or refolded by younger oblique Andean (Neogene) structures.

All these data have been integrated to compile two crustal scale balanced sections which have been constrained by an inversion of the gravimetric data. The Present relief of sections is directly inherited from the Jurassic (Tethyan) rifting event. The southern low land results from the structural inversion of Jurassic extensional structures (thin initial crust), whereas the northern culmination relates to newly created Andean structures (thick Jurassic crust).

Whether the Hercynian structures have been or not reactivated during the Tethyan rifting or the Andean deformation, remains an open question. The Hercynian thrusts trend more or less parallels to the younger structures, especially Mesozoic extensional ones which could thus partially result from the negative inversion (collapse) of the Paleozoic edifice.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France