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Abstract: Geochronologic Constraints for the Serrania del Interior Foreland Fold and Thrust Belt, North-Central Venezuela

Jaime Perez De Armas, Hans Ave Lallemant

The Serrania del Interior fold-thrust belt in north-central Venezuela, consists of carbonates and clastic sedimentary rocks of Late Cretaceous and Tertiary age. It has been proposed that the belt was thrust southward onto the South American craton during two main events in the Eocene and Miocene. The present study quantifies the deformational history by carrying out field work (mapping and structural analysis), by interpreting seismic reflection lines, and by dating (fission-track and Ar/Ar) of samples from the states of Guarico and Aragua.

Field work centers on two north-south transects: (1) along Valle Morin (Aragua) and (2) Rio Platillon (Guarico). The rocks have been deformed into asymmetric SSE-vergent folds. Upper Cretaceous and Paleocene rocks in the north are much more heavily deformed than Miocene rocks in the south suggesting that most of the folding is of Eocene age, but that during the Miocene the rocks were mildly refolded in a displacement field similar to the Eocene one. The older rocks are also faulted: ENE-striking thrust faults, two sets of conjugate strike-slip faults indicating NW-SE and N-S shortening, and N-S-striking normal faults.

Preliminary fission-track data indicate that the sampled rocks cooled through the apatite fission-track blocking temperature (110°C) about 14 Ma (Miocene). None of the rocks attained temperatures above the zircon fission-track blocking temperature (225°C) although some have approached it between 40 and 50 Ma (Eocene).

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela