CRUSTAL STRUCTURE FROM THE FAROES SHELF TO THE
NORWEGIAN BASIN
A.W. Roberts (1), R.S. White (1), N.J. Kusznir (2), P.A.F. Christie (3), A.M.Roberts
(4) & iSIMM team
(1) Dept. of Earth Sciences, University of Cambridge, CB3 0EZ UK; (2) Dept. of
Earth Sciences, University of Liverpool, L69 3GP UK; (3) Schlumberger Cambridge
Research, Madingley Road, Cambridge, CB3 0EL UK; (4) Badleys, Spilsby, Lincs.
PE23 5NB UK
roberts@esc.cam.ac.uk
We show the crustal structure along a 400km seismic profile extending
across a prime example of a volcanically rifted margin, from the Faroes shelf across
the continent-ocean boundary northeast of the Faroe Islands, and 100km into oceanic
crust of the Norwegian Sea formed immediately after continental break-up.
85 4-component OBS were used on the survey, giving wide-angle arrivals
visible to beyond 120km offset. The survey was complemented by a 12 km Qstreamer profile along the same line. Integration of the normal incidence through
wide-angle arrivals for the OBS and streamer data allow us to make a constrained
velocity model through the active crust and into the upper mantle. We used a large
airgun source comprising 14 guns with a total volume of 6,300 cu. in. towed at 20m
depth. The resulting output was dominated by low frequencies (peak at 9Hz) to allow
improved imaging through the basalts.
A thickened oceanic crust is found, indicative of high temperatures caused
by the Iceland mantle plume, and the presence of clear seaward dipping reflectors is
evidence of extrusive lavas. Underplating is also inferred on the margin from the
high seismic velocities in the lower crust.
Academia and industry seek to understand magmatic margin evolution for
its impact on deep water hydrocarbon prospecting. The NE Atlantic has been chosen
as our research area because of its accessibility, wealth of related data and current
exploration on the Atlantic margin. The iSIMM programme’s long term goals are to
characterise volcanically rifted margins and to develop theoretical models of the
formation and subsidence of rifted margins.
iSIMM investigators are: R.S. White (1), N.J. Kusznir (2), P.A.F. Christie
(3), A.M. Roberts (4), N. Hurst (2), Z.C. Lunnon (1,3), C.J. Parkin (1), A.W. Roberts
(1), L.K. Smith (1), R. Spitzer (1), V. Tymms (2), A. Davies (1), A. Surendra (1),
with funding from NERC, Agip UK, BP, Amerada Hess Ltd., Anadarko, Conoco,
Phillips, Shell, Statoil, and WesternGeco.