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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Structure of the Eastern Cordillera
of Colombia: A Tectonic Model
for the Colombian Andes
By
The tectonic history and structure of the Eastern
Cordillera is discussed with a view towards describing 1)
trap
styles and 2) a tectonic model that relates the Eastern
Cordillera to the adjacent Colombian Andes and the entire
orogen to the convergent plate margin in the Pacific. The
northern Andes in Colombia comprise the Western, Central
and Eastern Cordilleras, separated from each other by
intermontaine basins. A regional balanced cross section -
across the Eastern Cordillera shows that uplift of the
cordillera on high-angle, basement-involved reverse faults
was preceded by thin-skinned deformation, which generated
the majority of the structures present within the range.
During the Late Jurassic through Early Cretaceous, a
graben system formed in the area presently occupied by the
Eastern Cordillera. Late Cretaceous deposition in the
region was part of a passive margin that extended across the
northern and northwestern margin of South America.
Paleogene tectonism along the western South American
margin created a foreland basin that extended between the
Central Cordillera and the Guayana Shield, including the
Eastern Cordillera area. Compressional deformation began
in the Eastern Cordillera in Miocene-Pliocene time,
characterized by thin-skinned deformation on multiple
detachment levels within the Cretaceous section. This
deformation rooted in a deep, gently-dipping detachment
that extends beneath the Middle Magdalena Basin and the
Central Cordillera. Backthrusts splaying from this deep
detachment verge west toward the Middle Magdalena
Basin. Regional uplift of the Eastern Cordillera deformed
belt occurred in Plio-Pleistocene time along basement-involved
reverse faults, some of which are inverted Jura-Cretaceous graben-edge normal faults. Basement uplift
occurred as strike-slip along the Santa Marta-Bucaramanga
Fault
was transferred to the Guacaraimo, Soapaga, Boyaca,
and other reverse faults.
Trap
styles are
fault
-ramp folds
that involve one or both potential Cretaceous sandstone
reservoirs. Disharmonic folding of Cretaceous shales -
located between both reservoirs is commonly observed.
Based on a palinspastic restoration of the regional cross section, the amount of shortening across the Eastern Cordillera is about 40%, with 105 km of eastward-directed thrusting and 45 km of westward-directed thrusting. This shortening approximates closely that calculated by summing microplate motions for the northwest corner of South America. Shortening in the cover rocks greatly exceeds that for the high-angle basement-involved faults. The imbalance in shortening can be resolved with a deep, gently-dipping crustal detachment that extends beneath the Middle Magdalena Basin and Central and Western Cordilleras and which roots in the Benioff zone in the Pacific. The midcrustal detachment model provides a structural link between the three Andean ranges; it provides a mechanism to transmit crustal shortening from the convergent plate margin to the Llanos foreland; it explains the eastward progression of deformation in both space and time; and, it implies that the Colombian Andes have been tectonically transported eastwards a minimum of 150 km.
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