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Abstract: Structural Inversion and the Development of the Serrania del Interior, Eastern Venezuela

Robert J. Hooper, James W. Granath, Don C. Foley, James H. Ballard, Ken C. Abdulah, Moon J. Lee

Advances in computer-aided restoration and visualization, combined with new insights into contractional tectonics derived from scaled analog- and numerical-model studies, prompt a reevaluation of the development of the Serrania del Interior and its associated external fold-thrust belt. All models for the development of the Serrania del Interior need to provide an explanation for the variations in structural relief both across and along the mountain front. Traditional models assume that the Serrania del Interior developed as a thin skinned fold-thrust belt. Variations in the degree of imbrication and overthrusting within the passive margin section are used to produce the variations in relief across the mountain front. Such models require Tertiary shortening in excess of 50 , and use out-of-sequence and backward-imbricated thrusting to explain timing relations.

Basin inversion provides a simpler model. We consider that the architecture of the Mesozoic passive margin of northern South America controlled both the location and character of the subsequent Tertiary contractional deformation. The most important factors controlling the final "inversion style" were the preinversion configuration of the margin and the resolved inversion direction. Contractional deformation was focused initially in the post-rift section, and created a series of dominantly southeast-verging folds and thrusts. Further contraction within the thrust wedge reactivated preexisting extensional faults, and led to localized footwall-shortcuts, some potentially involving pre-rift basement. Syn-rift basin-fill was expelled to the southeast over the platform, creating a series of southeast-vergent thrusts and lobate folds within the foreland. Reactivation of basement faults controlling the trend of structures on the old passive margin, led to localized crosscutting relations between the trends of dominant folds and major contractional faults. Later shortening caused minor reactivation of the frontal folds and thrusts and the local development of new in- and out-of-sequence thrusts as the post-rift and syn-inversion sections continued to be expelled toward the foreland. Basin inversion downplays the importance of imbrication and overthrusting within the post-rift passive margin section in favor of the reactivation of preexisting extensional faults linked to deeper detachment levels. A basin-inversion model would require only 10 to 15% shortening across the Serrani del Interior as a result of Tertiary contraction.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela