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					Brittle fault zones in North Norway: Onshore-offshore link and regional

John-Are Hansen*, Steffen G. Bergh*, Tormod Henningsen** and Corine Davids*

*Department of Geology, University of Tromsø, 9037 Tromsø. **Statoil, Harstad

Preliminary mapping and data compilation indicates that the brittle fault zones bounding the
offshore rift basins on the mid-Norwegian passive margin continues onshore, and may be
traced as a series of topographic lineaments across coastal Nordland, Troms and Finnmark,
and into the SW Barents Sea margin, where they link up with the Troms-Finnmark Fault
Complex and other basin bounding fault zones. The largest of these faults define the fjords
and sounds in coastal areas. The direct link between the onshore fault zones and the major rift
basins offshore, offer the possibility to study basement control on faulting, in addition to fault
architecture and kinematics. We show that the major fault zones are arranged in a pattern of
dominantly N-S to NNE-SSW striking, right-stepping en echelon faults which are linked by
NE-SW to E-W striking soft- and hard-linked transfer zones, some of which caused
segmentation of whole rift-basin domains. In onshore areas many of the NE-SW to E-W
striking faults, interpreted to represent transfer zones, follow pre-existing weakness zones in
the basement. This indicates basement controlled faulting and rift-basin segmentation. The
offshore fault zones developed through multiple rift events since the collapse of the
Caledonian mountain chain, leading to final separation and passive margin development in the
Eocene. Similar time constraints are also inferred from onshore areas, and are partly
confirmed by direct correlation and by ongoing dating of fault gouges. The onshore fault
zones seems to have played an important role in the preservation and distribution of
Caledonian and Precambrian basement rocks, for instance, the West Troms Basement
Complex seems to be situated on a horst of a similar affinity as that defining the Lofoten
Ridge. They also represent major zones of weakness more susceptible to erosion, and may
have had an impact on pre-glacial, glacial and recent drainage paths in addition to the
localization and distribution of rock avalanches.

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