Geometry and kinematics of the Nuncios detachment fold complex: implications for lithotectonics in northeastern Mexico
Fischer, Mark P.
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Using recent geologic mapping combined with digital elevation data, aerial photo interpretation, and cross section balancing, we describe the threedimensional (3-D) geometry and kinematics of the Nuncios Fold Complex in the Monterrey Salient of northeastern Mexico. This map-scale, evaporite-cored detachment fold structure involves Upper Jurassic through Cretaceous rocks deformed during the Laramide orogeny and comprises two westward plunging anticlines and an intervening, eastward plunging syncline. Seven balanced cross sections and a 3-D model of this north vergent structure document substantial along-strike variations in both fold geometry and detachment depth, suggesting that 3-D flow of the detachment layer may have occurred during folding. Comparison of folds in the Monterrey Salient with those in the neighboring Parras Basin suggests that the latter south vergent folds root to a shallower detachment. We suggest that northward transport of the Monterrey Salient folds on the lower evaporite detachment may have been inhibited by a thick sequence of foreland basin rocks in the northeastern Parras and southern La Popa basins and that the smaller, south verging folds formed where the lower detachment was abandoned and slip was transferred to the shallower detachment, forming a triangle zone at the front of the Sierra Madre orogenic wedge.