Rates of shortening, propagation, underthrusting, and flexural wave migration in continental orogenic systems

The rate of horizontal shortening in an orogenic wedge is the rate at which the length of undeformed crust decreases as it is incorporated into the or ogen, This rate equals the rate of convergence of the foreland lithosphere toward the central surface of the orogenic belt and the rate of subduction of foreland lithosphere beneath the central surface. The rate of propagatio n of an orogenic wedge is the rate at which it elongates in the direction o f horizontal shortening. This rate is controlled by the rates of mass accre tion to the orogenic wedge and erosion. The orogenic belt drives a flexural isostatic wave through the foreland lithosphere at a velocity equal to the rate of propagation plus the rate of subduction (or convergence or shorten ing). In orogenic belts where the total amount of shortening cannot be reli ably estimated from balanced regional cross sections, it may be possible to determine total shortening from the distance of flexural wave migration in the foreland basin and the width of the orogenic wedge. In addition, oroge nic wedges may accelerate solely in response to a reduction in taper.