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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 77 (1993)

Issue: 8. (August)

First Page: 1315

Last Page: 1337

Title: Structure of the Eastern Cordillera of Colombia: Implications for Trap Styles and Regional Tectonics

Author(s): Carlos A. Dengo (2), Michael C. Covey (3)


The northwest margin of South America has undergone multiple phases of compressional deformation beginning in the Late Cretaceous and culminating in the Pliocene-Pleistocene. The latest phases (Miocene to Pleistocene) of this deformation created the Eastern Cordillera of Colombia. Compressional structures in the Eastern Cordillera formed traps that have petroleum exploration potential; these are generally in the form of fault-bend and fault-propagation folds containing top-sealed reservoir and mature source rocks. Trap delineation, although difficult to achieve because of the poor seismic quality obtained in the region, can be accomplished by supplementing the seismic data with geometric analysis of surficial structures.

The Eastern Cordillera is asymmetrical, with the dominant tectonic transport direction towards the east. West-directed thrust faults are localized along the western flank of the Eastern Cordillera and are interpreted to be back thrusts splaying off a deep mid-crustal detachment. A regional, retrodeformable cross section across the Eastern Cordillera shows that basement-detached deformation of late Miocene to Pliocene age was followed by Pliocene to Holocene uplift of the Cordillera on high-angle, basement-involved reverse faults. These two structural styles were superimposed on preexisting Jurassic and Lower Cretaceous grabens, whose normal faults were partially inverted during the later stages of compressional deformation.

A palinspastic restoration of this regional cross section indicates that approximately 150 km of shortening (40% shortening) has occurred: 105 km eastward-directed towards the Llanos basin and 45 km westward-directed towards the Middle Magdalena basin. This calculated shortening is very close to that calculated by summing microplate motions for the northwest corner of South America. Shortening in the sedimentary cover rocks exceeds that in the basement rocks by about three times. This shortening can be regionally balanced with a gently dipping, mid-crustal detachment that extends beneath the Middle Magdalena basin and Central Cordillera and which roots in the Benioff zone beneath the Western Cordillera. The presence of a mid-crustal detachment, as postulated here, provides a mechanism to transmit the shortening from the convergent plate margin in the Pacific to the Andean foreland, and is interpreted to have provided the structural link between the three ranges of the Colombian Andes. The detachment also provides a mechanism to explain the imbalance of shortening seen between Eastern Cordillera basement and the overlying strata, and implies that the Western and Central Colombian Andes have been tectonically transported eastwards a distance of at least 150 km.

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