--> Abstract: Influence of the Eastern Cordillera Exhumation on the Structural Evolution of the Eastern Part of Middle Magdalena Valley Basin, Colombia, by Carlos J. Sanchez, Eliseo Teson, Brian K. Horton, Andres R. Mora Bohorquez, Richard A. Ketcham, Daniel F. Stockli, and Nestor R. Moreno; #90124 (2011)

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AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Influence of the Eastern Cordillera Exhumation on the Structural Evolution of the Eastern Part of Middle Magdalena Valley Basin, Colombia

Carlos J. Sanchez1; Eliseo Teson2; Brian K. Horton1; Andres R. Mora Bohorquez2; Richard A. Ketcham1; Daniel F. Stockli3; Nestor R. Moreno2

(1) Department of Geological Sciences, University of Texas at Austin, Austin, TX.

(2) Instituto Colombiano del Petróleo, Ecopetrol, Bucaramanga, Colombia.

(3) Department of Geology, University of Kansas, Lawrence, KS.

The timing of deformation and uplift of the Eastern Cordillera in the northern Andes of Colombia has been being constrained by recent themochronological and geochronological results. These approaches allow linking of the process of thrusting-inducing denudation along the western front of the Eastern Cordillera fold-thrust belt to deformation in the eastern part of the Middle Magdalena Valley basin.

Structural analysis, based on subsurface and surface information, permits the construction of a kinematic model for the evolution of the deformation. Age control for the kinematic restorations is provided by thermochonological and petrographic provenance analyses. In the study area, the La Salina fault marks the boundary between the Paleogene foreland basin and thrust belt provinces. New apatite fission track and U-Th/He thermochronological results allow us to identify an early Miocene (~25-20 Ma) timing for initial exhumation of the La Salina hanging wall.

We propose a deep master fault system which accommodated the deformation in both provinces in response to shortening of the Cretaceous section as part of a duplex system. Although kinematically linked, shortening in the Cenozoic section is characterized by backthrust structures constituting the passive roof of the main duplex structure. The most recent deformation—an out-of-sequence event is suggested by irregular crosscutting relationships of the La Salina fault with some footwall structures.

Increased exhumation rates over the last 10 Myr in the hangingwall of the La Salina fault coincide with (a) the greatest thickness of the Upper Miocene Real Formation in the footwall and (b) increased sedimentary lithic fragments, evidence of sedimentary recycling of the lower part of Cenozoic succession. Additionally, the concealment (burial) of some faults, and the presence of growth strata in the Real Formation related to the northward structural plunge would indicate lateral variation in the development of the duplex system, the advance of a thrust front, and late-stage out-of-sequence faulting. Structures in the foreland display modestly different orientations relative to the La Salina fault and its associated structures, possibly suggesting a shift in the direction of maximum shortening. This proposed kinematic scenario may imply a coalescence of two generations of structures which could provide trapping configurations in the proximal foreland basin province along the eastern Magdalena Valley.