Seismic evidence for blind thrusting of the northwestern flank of the Venezuelan Andes

Author(s)

Bruno De Toni
James N. Kellogg, University of South Carolina - ColumbiaFollow

Document Type

Article

Abstract

Surface geology and seismic and well data from the northwestern flank of the Venezuelan Andes indicate overthrusting of Andean basement rocks toward the adjacent Maracaibo Basin along a blind thrust fault. The frontal monocline is interpreted as the forelimb of a northwestward verging fault-related fold deformed over a crustal-scarle map. The Andean block has been thrust 20 km to the northwest and uplifted 10 km on a ramp that dips about 20^o-30^o southeastward. The thrust fault ramps up through crystalline basement rocks to a decollement horizon within the shaly units of the Cretaceous Colon-Mito Juan formations. Backthrusts in the monocline produce a wedge geometry and reduce the amount of blind slip required on the decollement northwest of the Andes. The rigid Andean uplift was caused by northwest-southeast compressive tectonic forces related to the convergence of the Caribbean plate, the Panama volcanic arc, and northwestern South America. The thick (up to 6 km) molasse deposits accumulated in the foredeep basin indicate that the Venezuelan Andes started to rise as early as the early Miocene. However, a late Miocene intramolasse unconformity marks the beginning of the formation of the monocline and the greatest uplift. The crustal-scale fault-related fold model may explain structural features seen in other areas of basement-involved foreland deformation.

Publication Info

Published in Tectonics, Volume 12, Issue 6, 1993, pages 1393-1409.

Rights

De Toni, B. & Kellogg, J. N. (1993). Seismic evidence for blind thrusting of the northwestern flank of the Venezuelan Andes. Tectonics, 12 (6), 1393-1409.

©Tectonics 1993, American Geophysical Union