Date of Award

1-1-2011

Document Type

Campus Access Dissertation

Department

Earth and Ocean Sciences

Sub-Department

Geology

First Advisor

James Kellogg

Abstract

Analyses of Global Positioning System (GPS) results, estimates of slip, seismic reflection data, and a variety of stress indicators (including borehole breakouts, natural fractures, and earthquake focal mechanism solutions) suggest that the Eastern Cordillera region in Colombia is an active zone of deformation that has undergone various stages of deformation. Knowledge of the tectonic processes and stress evolution in the area is important in understanding the geodynamic processes at work in the region, as well as the kinematics of hydrocarbon reservoirs in the flanks of the range.

GPS results show that the North Andes is escaping northeastward relative to stable South America. The driving mechanism for this "escape" is subduction of the aseismic Carnegie Ridge in the Colombia-Ecuador trench. Slip estimates suggest that the ridge arrived at the trench prior to 1.8 Ma. In the Eastern Cordillera, strike-slip displacement is obscured by rapid NW-SE permanent shortening and uplift associated with the on-going Panama Arc-South America collision.

Based on structural analyses and modeling, we propose a new structural model for the Piedemonte Llanero, a triangle zone located in the eastern flank of the Eastern Cordillera. This model is constrained by 3-D and 2-D seismic reflection profiles, surface geology, and well data. We propose that thin-skinned in-sequence imbricate thrust stack deformation produced most of the shortening of the range. This was followed by an out-of-sequence Laramide-style thick-skinned basement-uplift that produced much of the uplift in the Eastern Cordillera.

The primary present-day maximum principal stress direction in the Eastern Cordillera is WNW-ESE to NW-SE, and is in the direction of maximum shortening in the mountain range. A secondary E-W to ENE-WSW maximum principal stress direction is also observed. This is associated with the "escape" of the North Andes. In the Cupiagua hydrocarbon field located southwest of the Piedemonte Llanero, the dominant NNE-SSW fractures are produced by range-normal compression. However, less well developed asymmetrical shear fractures oriented E-W to WSW-ENE and NNW-SSE are also present, and are likely related to pre-folding stresses in the foreland basin of the Central Cordillera or to present-day shear which is associated with the "escape" of the northern Andes.

Rights

© 2011, Obi Egbue

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