Combined thrusting and wrenching in the Ibero-Armorican arc: A corner effect during continental collision

Abstract

This paper is an attempt to reconcile strain pattern and deformation history, in an overall arcuate structure, with continental collision processes. Geological data are first presented for the early history (400 Ma) of the Variscan orogenic belt in France. Principal stretch trajectories are, on a large scale, more or less parallel with the trend of the belt. They became strongly oblique to this trend near the basal surfaces of the nappes. A kinematic model combining two orthogonal shear components is proposed to explain such a strain pattern. It is concluded that the observed strain trajectories result from a combination of a southward thrusting and a sinistral wrenching. This conclusion is in good agreement with previous conclusions gained by several local microtectonic studies. The geodynamic significance of combined thrusting and wrenching at the scale of the Ibero-Armorican arc is discussed, and a progressive deformation model is proposed.