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Petroleum Geoscience; October 2005; v. 11; no. 4; p. 291-308; DOI: 10.1144/1354-079304-627
© 2005 Geological Society of London
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Original Article

Sub-basalt structures east of the Faroe Islands revealed from wide-angle seismic and gravity data

T. Raum1, R. Mjelde1, A. M. Berge1, 2, J. T. Paulsen1, 3, P. Digranes1, 4, H. Shimamura5, H. Shiobara5, 6, S. Kodaira5, 7, V. B. Larsen8, R. Fredsted9, D. J. Harrison10 and M. Johnson11

1 Institute for Geoscience, University of Bergen, Allegt. 41, 5007 Bergen, Norway (e-mail: thomas.raum@geo.uib.no)
2 Present address: Norsk Hydro, 5020 Bergen, Norway
3 Present address: Talisman Energy, Stavanger, Norway
4 Present address: Statoil, 5020 Bergen, Norway
5 Institute for Seismology and Volcanology, Hokkaido University, Sapporo 060, Japan
6 Present address: Tokyo University, Japan
7 Present address: JAMSTEC, Yokosuka, Japan
8 Statoil, Trondheim, Norway (Present address: Statoil, 4035 Stavanger, Norway)
9 Statoil, Denmark (Present address: Statoil, 4035 Stavanger, Norway)
10 Exxon-Mobil, UK
11 Exxon-Mobil, Dallas USA

Two semi-regional wide-angle Ocean Bottom Seismograph (OBS) profiles, acquired east of the Faroe Islands, have been analysed by use of forward and inverse modelling to map the crustal structures. In the present wide-angle data, the Tertiary basalt shows a maximum thickness of 3 km under the Faroe Islands, decreasing towards the Faroe–Shetland Channel where it terminates. Sedimentary rocks are present below the basalts and vary in thickness from 2 km to a maximum of 8 km towards the Faroe–Shetland Channel. These sedimentary rocks appear mainly as a low-velocity zone, and the presence of high-velocity intrusions in these layers generate several step-back features in the wide-angle refraction data. Pre-Cretaceous sedimentary rocks are only inferred north of the Clair fracture zone, while Cretaceous rocks dominate southeast of the Westray fracture zone. The crystalline basement is divided into an upper granitic and a lower granodioritic part. P-wave velocities around 7.0 km s–1 are modelled in the lowermost part of the crust, indicating that magmatic underplating is not present below the Faroe Islands. The depth to the Moho is modelled with a maximum depth of 29–30 km below the northern part of the Faroe Islands, decreasing both southeastwards and southwestwards to 25 km and 17 km, respectively.

KEYWORDS: wide-angle seismic data, sub-basalt, crustal structure, Faroe–Shetland Channel, sedimentary rocks






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