Distribution and evolution of the Palaeocene-Eocene stress fields on Spitsbergen support a two-stage model of development of the West Spitsbergen Orogenic Belt, within a transpressive setting. A wrench-type tectonic regime developed first, adjacent to the intra-continental transform, then followed by a superimposed and widespread regime of strictly transverse compression. The tectonic nature of the belt is therefore composite. The clockwise change of trend of the average maximum horizontal stress from 10-20° N to 70-80 °N (oblique to subnormal to the transform fault) is interpreted in terms of a progressive decrease in friction and shear stress along the plate boundary, and supports the idea of a partitioning of the components of transcurrent and convergent motions. Such a phenomenon is aided by the presence of deep ductile horizons.

Claude Lepvrier, URA CNRS 718, Departement de Geotectonique, Universite P. et M. Curie, Case 129, 4 Place Jussieu 75230 Paris cedex 05, France.