Vendeville, Bruno C.1, Christine R. Fox2
(1) University of Texas at Austin, Austin, TX
(2) Department of Geological Sciences, University of Texas at Austin, Austin, TX
ABSTRACT: Role of Curved Detachment Pinch-Outs on the Formation of Arcuate Fold-and-Thrust Belts
Many fold-and-thrust belts overlying weak detachment levels (overpressured or evaporitic) have highly arcuate traces. To date, geologists have focused on the role of obstacles, indenters, or the shape of the detachment’s pinch-out on the foreland side. We conducted two sets of experiments testing the role of curvature of the detachment pinch-out on the foreland side, as well as on the hinterland side. In both sets, the cover was brittle. In the first set, the foreland pinch-out of the detachment was convex forward, whereas shortening was imposed by a linear, rigid backstop on the hinterland side. The resulting belt did not comprise broad, arcuate structures. Instead, sublinear thrusts formed in the center and sharply linked along strike with oblique- or strike-slip faults above the lateral pinch-out of the detachment. In the second set, the hinterland pinch-out of the detachment was convex backward, and the area located between the detachment and the linear backstop had a high-friction base. As the backstop advanced, successive linear thrust sheets moved forward. Once their front reached the area underlain by the detachment, thin-skinned shortening propagated rapidly forward. Because of the detachment’s curved pinch-out, however, shortening propagated first only in the center of the model, whereas the lateral areas had not yet deformed. Detached folds and thrusts, having initially convex-forward traces formed first at the center. Younger, longer, arcuate folds formed during continued shortening. Kinematic models also confirm that a curved detachment pinch-out on the hinterland side leads to formation of convex-forward folds and thrusts.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.