A POSSIBLE EXPLANATION FOR FORELAND THRUST PROPAGATION

A common feature of thin-skinned fold and thrust belts is the sequential nature of foreland directed thrust systems. As a rule, younger thrusts develop in the footwalls of older thrusts, the whole sequence propagating towards the foreland in the transport direction. In an attempt to investigate the stresses in the frontal regions of thrustsheets, a numerical method has been devised from the algorithm given by McTigue and Mei [1981]. The numerical version of the McTigue and Mei algorithm shows that there is a region of increased maximum resolved shear stress, τ, directly beneath the toe of the overthrust sheet. Utilizing the Mohr-Coulomb failure criterion, predicted fault lines are computed. It is shown that they flatten and become horizontal in some portions of this zone of increased τ. Thrust sheets are known to advance upon weak decollement zones. If there is a coincidence of increased τ, a weak rock layer, and a potential fault line parallel to this weak layer, we have in place all the elements necessary to initiate a new thrusting event. Therefore, thrusts develop in sequence towards the foreland as a consequence of the stress concentrating abilities of the toe of the thrust sheet. -from Authors