Stretching lineation and transport direction in the Ibero-Armorican arc during the siluro-devonian collision

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Abstract
Large structures, lineations, foliations and sense of shear criteria are examined on the scale of the whole Ibero-Armorican Arc. Four sections (Galicia, Brittany-Vendée, Limousin and Eastern Massif Central) exemplify the major thrust sheets observed around the Arc. Stretching lineations are contemporaneous with the siluro-devonian metamorphism and are either transverse, oblique or parallel to the collision zone. A kinematic analysis shows that these lineations have resulted from a dominanüy transverse shear deformation which was followed by, or combined with, a longitudinal shear direction. On the scale of the entire Arc, this variation in the shear direction is interpreted as resulting from an early head on thrusting relative movement evolving to large scale movements parallel to the plate boundaries. Experiments with sand-silicone models support a model which generates the Arc by interaction between a transform sinistral direction, and a converning zone at a high angle to the transform direction.

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