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KAMMER, ANDREAS, Universidad Nacional de Colombia, Bogota, Colombia

ABSTRACT: Basement Tectonics of the Southem Termination of the Santander Massif, Eastern Cordillera, Colombian Andes

The Santander Massif is a broad, basement cored antiform which, where fully developed, is limited toward its eastern and western foreland basins by two oppositely dipping reverse faults, which involve minor thrusting within the foreland sediments. More internal faults, however, accommodated an east-west extension by limiting sedimentary wedges which have the structure of half-grabens. Both marginal and internal faults impart a near symmetrical fan structure to the massif. The alternating compressional and extensional deformation regimes are taken as evidence for a vertical flow model, in which laminar parts of the massif rose along slightly divergent movement paths, following the fan array of the faults, and triggered the extensional deformation at higher levels. Evidence for a steep ttitude of the faults is provided by (1) normal faults which, when bordering secondary basement highs, become reverse faults of an opposed dip, and (2) by the Bucaramanga fault, which between the Santander Massif on its eastern side and the more southerly Mogotes-Arcabuco Massif on its western side inverts both dip and displacement.

A further internal deformation, which controlled the massif's structural evolution, consists of a longitudinal stretch. This was mitigated within the basement itself by an internal arching, and, where transmitted to the foreland, was absorbed by minor transcurrent faults or by east-west trending normal faults, as is the case of the displaced plateaus in the Bucaramanga area.

Considering the deep-seated origin of the structures of the Santander Massif, it is suggested that the imbricate sheets of the Guaicaramo fold and thrust belt at the eastern foothills of the Cocuy Massif evolved out of steeply inclined synclines. Folding of these imbricate sheets reflects uplift of more foreland oriented basement blocks.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.