Devonian-Triassic brittle deformcition based on dyke geometry and fault kinematics in the Sunnhordland region, SW Norway
pp. 3-17

The coastal area south of Bergen exhibits fracture systems and lineaments that can be grouped in to N-S to NNW-SSE, NW-SE and NE-SW trends. Faults and Permo-Triassic Alkaline dykes along N-S to NNW-SSE lineaments in Sunnhordland have been subjected to kinematic analysis and used as absolute and relative age markers in this study. Observations suggest early, semi-brittle dip-slip movements associated chiefly with NE-SW striking faults, and later (re-) opening of N-S to NNW-SSE striking fractures associated with dyke intrusion. Kinematic analysis of faults and fractures gave a sub-horizontal extension axis trending 130°-310° for the early (pre-dyke) faults. Comparison of field observations with regional information indicates that this extensional episode is likely to have been Devonian. Dyke geometry has been utilized to estimate extension direction in the Perm o-Triassic stress field. The study indicates a fairly consistent extension direction, and a horizontal minimum principal stress o-3 of the regional Permo-Triassic stress field is found to trend 079"-259°. Hence, the regional stretching (and o-3 ) direction has rotated from a NW-SE orientation in pre-dyke (?Devonian) time to E(NE)-W(SW) in the Permo-Triassic. Dyke intrusion is connected to the contemporaneous crustal stretching and basin formation in the northern North Sea. Thus, the 079"-259° Permo-Triassic stretching direction calculated for the Sunnhordland area is considered to be a good estimate also for the North Sea basin west of the study area

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ISSN 029-196X