Abstract

Critical-wedge models for foreland thrust belts, although popular paradigms for thrust mechanics, also predict definite progressive changes within the orogenic belt. The most important constraint on critical-wedge models is the need for deformation of the interior of the wedge when new sheets are accreted to its front. Well-dated foreland thrust belts have sequential formation of new thrust sheets in the front of the belt. Thus, they also require continued superimposed deformation within the wedge. Geologic mapping and fabric studies provide evidence of only minor later intra-wedge shortening, severely reducing the acceptability of an accreting critically tapered wedge model. To apply critically tapered wedge models to foreland fold-and-thrust belts, one must relax requirements for constant wedge strengths and basal sliding laws. The wedge will need to strengthen after initial thrust emplacement, and the fault zones will probably need to progressively weaken. It is most likely that critical-wedge models which apply well to accretionary wedges do not apply in simple ways to foreland fold-and-thrust belts.

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