The Listafjorden–Drangedal Fault Complex of the Agder–Telemark Lineament Zone, southern Norway. A structural analysis based on remote sensing and potential field data

ABSTRACT

The Listafjord–Drangedal Fault Complex is a central structure in the NE-SW-trending Agder–Telemark Lineament Zone that dominates the structural grain and topography of southernmost tip of Norway. The fault can be followed for a distance of more than 170 km from the shelf area off Listafjorden–Fedafjorden in Vest Agder county to Drangedal in Telemark county. It has been analyzed by the use of digital topographic, remote sensing and potential field data, supported by field investigations. At least seven separate left-stepping fault segments have been identified. These are characterized by numerous internal fault lenses, separate fault strands and fault splays, partly displaying contrasting fault attitude and style of deformation. The northeastern termination of the Listafjord–Drangedal Fault Complex consists of fanning fault branches (horse-tailing), whereas its southwestern termination is buried below sediments in the continental shelf and remains obscure. The fault rocks of the various fault segments include cataclasites and mylonites that in places are interlayered with zones of fault gouge. By tentative correlation to the Hunnedalen dyke system in Rogaland, the age of initiation for the Listafjord–Drangedal Fault Complex is suggested to be Late Proterozoic. Parts of the fault complex were affected by at least two stages of faulting including (dextral?) shear and top-to-the-SE extension. The latter stage is assumed to be of post-Caledonian age, and recent seismic activity suggests that this ancient structural grain is still seismically active.

KEYWORDS:

• Lineament zones
• composite fault complex
• multiple reactivation
• fault segmentation
• fault rocks
• southern Norway

Acknowledgments

The authors would like to thank Dr John Dehls (Geological Survey of Norway) for company and discussions at an early stage of the field work. Professor Bob Holdsworth made valuable comments and suggestions on an early version of the manuscript and also sparked a new field campaign, which resulted in a detailed study published elsewhere. Norsk Hydro ASA and Staoil (Equinor) are thanked for financial support for the first part of the field study. The Department of Geoscience, University of Oslo supported the last part of the study through a “Småforsk”-grant. The Geological Survey of Norway is thanked for making some of the potential field data available through their data bases. AkerBP, BayernGas, Centrica, ConocoPhillips, DONG, Engie, Eni, Lundin Norway, Maersk Oil, NGU, Noreco, NPD, Repsol, Dea, Statoil (Equinor), Suncor, Total, VNG and Wintershall funded the Coop Project and the acquisition of funthe high-resolution fixed-wing aeromagnetic data.

The manuscript benefited from valuable reviews and comments from Dr Tobias Bauer and Dr Javier Fernández-Lozano and from kind advices from the associate editor of GFF, Dr Magnus Ripa.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Norsk Hydro ASA and Staoil (Equinor) are thanked for financial support for the first part of the field study. The Department of Geoscience, University of Oslo supported the last part of the study through a “Småforsk”-grant. Aker BP, Bayerngas, Centrica, ConocoPhillips, DONG, Engie, Eni, Lundin Norway, Maersk Oil, NGU, Noreco, NPD, Repsol, Dea, Statoil (Equinor), Suncor, Total, VNG and Wintershall funded the Coop Project and the acquisition of the high-resolution fixed-wing aeromagnetic data.