Systems of veins in the Devonian sandstones of the Hornelen basin are described. These veins range from an early generation of anastomosing networks of thin veins and breccia zones with a fine grained matrix to a later generation of veins with fibrous quartz fill. The presence of cataclasite fragments in the breccias suggests the existence of an earlier deformation phase still, possibly associated with shearing and grain size reduction of weakly consolidated sediments (deformation hands). The orientations, reactivation textures and cross-cutting relationships of these veins are interpreted as indicating a rotation of the extension direction from NW-SE to WSW-ENE with time. Correlation with other indications of the palaeostrain field orientation in western Norway from the literature suggests that this rotation took place between Middle Devonian and Late Permian times. The textures, mineralogy and morphology of the veins are used to interpret the history of brittle deformation, stress/strain system and fluid pressures in the Hornelen basin through these times.

N. E. Odling, NERSC, Edv. Griegsvei JA, N-5037 Bergen, Norway. Present address: RDR, School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK;
Ø. Larsen, Geologisk Institutt, Realfagbygget, Allégt. 41, N-5007 Bergen, Norway