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

Recent hypotheses of the Miocene-Pliocene structural evolution of the Eastern Cordillera of the Andes in Colombia have proposed a divergent fan model combining a system of southeast-verging, basement-rooted thrust faults beneath the eastern edge of the Cordillera with a system of northwest-verging thrusts rooted in the basement beneath its western edge. However, structural relationships within the western thrust system indicate that its faults are superficial posttectonic gravity-driven features. This leads to an alternative hypothesis for the evolution of the Colombian Andes, which has significant structural, stratigraphic, and temporal implications for hydrocarbon exploration.

In the new model, the Eastern Cordillera and Perija Andes are interpreted as elements of a single southeast-verging thrust sheet with minor imbrications. Initially, this thrust sheet moved east-southeastward as a blind thrust sheet with triangle zone (buried thrust front) geometry, creating the continuous uplifted area of the Eastern Cordillera, Santandar massif, and Perija Andes. The overthrust sheet was subsequently transported "piggy-back" farther southeast to its present location by emplacement of the underlying Merida Andes thrust system, for a total shortening of approximately 185 km. According to the new model, the incipient leading edge of this overthrust sheet was offset by an oblique lateral ramp. After deformation, the resultant lateral step in the footwall was accommodated by normal fault movement in the overthrust sheet, forming the Bucaramanga fault, with an apparent strike-slip offset of 210 km.