Vein architecture in the Devonian sandstones of the Hornelen basin, western Norway, and implications for the palaeostrain history

Systems of veins in the Devonian sandstones of the Hornelen basin are descr ibed. These veins range from an early generation of anastomosing networks o f thin veins and breccia zones with a fine-grained matrix to a later genera tion of veins with fibrous quartz fill. The presence of cataclasite: fragme nts in the breecias suggests the existence of an earlier deformation phase still, possibly associated with shearing and grain size reduction of weakly consolidated sediments (deformation bands). 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 wit h time. Correlation with other indications of the palaeostrain field orient ation in western Norway from the literature suggests that this rotation too l; place between Middle Devonian and Late Permian times. The textures, mine ralogy and morphology of the veins are used to interpret the history of bri ttle deformation, stress/strain system and fluid pressures in the Hornelen basin through these times.