ABSTRACT: Thrust Propagation Experiments

COLLETTA, BERNARD, JEAN LETOUZEY, and WILLIAM SASSI, Institut Francais du Petrole, Rueil Malmaison, France, PASCAL BALE, Lithologic, Rennes, France, and LAURENT VALLET, Elf-SNEA(P), Boussens, France

A series of simple sand-box experiments using cohesionless granular materials were performed to define the main parameters that control thrust spacing and propagation in thin-skinned systems with flats and ramps geometry. The effects of various parameters such as basal friction conditions, depth to detachment, precut faults, and erosion were tested and analyzed by X-ray tomography. This technique

gives a complete kinematic record of the deformation that can be visualized in video movies. In brittle material, thrust propagation is controlled by the coeval activation of two conjugate thrusts that merge at the basal decollement and produce an initial pop-up structure. Due to basal friction, the conjugate set is always tilted toward the foreland. The higher the basal friction is, the greater the tilt of the conjugate set will be. This tilt is responsible for the systematic forward propagation observed in the experiments. Under high basal friction conditions, horizontal displacement of thrusts is larger and thrust sheets are longer than under low friction conditions. Precut faults poorly affect thrust spacing, which is strongly constrained by the depth to detachment. Lateral variat ons in the depth to detachment or changes in the basal friction conditions produce oblique and transverse lateral ramps. Over horizontal flat lying decollement, forward propagation and passive piggy-back transport is the rule in most of the experiments. Erosion during thrusting induces out-of-sequence propagation or reactivation of previously inactive thrusts.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)