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INFLUENCE OF THE ICELAND MANTLE PLUME ON NORTH
ATLANTIC CONTINENTAL MARGINS
R.S. White (1) & iSIMM team
(1) Dept. of Earth Sciences, University of Cambridge, CB3 0EZ, UK
[email protected]
Early Tertiary breakup of the North Atlantic was accompanied by widespread
magmatism. The histories of the Iceland mantle plume, of rifting and of magmatism
are intimately related. The magmatism provides a challenge both to imaging
structure, and to modelling the subsidence and development of the continental
margins. We report new work which integrates state-of-the-art seismic imaging and
new acquisition on the Atlantic volcanic margins with new techniques for modelling
their evolution. We discuss the distribution of igneous rocks along the North
Atlantic margins and discuss the temporal and spatial variations in the Iceland mantle
plume in the early Tertiary, which have largely controlled this pattern of magmatism.
Igneous rocks are added to the crust on rifted margins as extrusive lavas, as sills
intruded into the sub-surface and as lower crustal intrusions or underplate. Each
provide different, but tractable problems to seismic imaging. We show that many of
these difficulties can be surmounted by using very long offsets (long streamers or
two-ship methods) with a broad-band, low-frequency source, and by using fixed
ocean bottom receivers. We report results from surveys on the North Atlantic
continental margins using these methods. Imaging results are shown from the recent
FLARE project and from the iSIMM project, which recorded new seismic data
recorded in summer 2002.
The iSIMM project acquired two seismic surveys, using 85 4-component ocean
bottom seismometers with long streamers for wide-angle data, and vertical arrays for
far-field source signature recording. One survey crosses the Faroes Shelf and
adjacent continental margin, and a second the Hatton-Rockall Basin, Hatton Bank
and adjacent oceanic crust. The Faroes wide-angle profiles were overshot by
WesternGeco's Topaz using three single-sensor, Q-Marine streamers, 12km plus two
4km. We designed deep-towed, broad-band low-frequency sources tuned to enhance
the bubble pulses, with peak frequencies at 8-11 Hz. The OBS survey used a 14-gun,
6,300 cu. in. array towed at 20 m depth, and the Q-marine survey used a 48-gun,
10,170 cu. in. array, with shot-by-shot signature recording. They provided excellent
arrivals to ranges beyond 120 km, with penetration through the basalts and well into
the upper mantle.
iSIMM investigators are R.S. White, N.J. Kusznir, P.A.F. Christie, A.M. Roberts, N.
Hurst, Z.C. Lunnon, C.J. Parkin, A.W. Roberts, L.K. Smith, R. Spitzer , V. Tymms,
A. Davies and A. Surendra, with funding from NERC, DTI, Agip UK, BP, Amerada
Hess Ltd., Anadarko, Conoco, Phillips, Shell, Statoil, and WesternGeco.
RS White1, NJ Kusznir², PAF Christie³, A Roberts4, N Hurst², Z
Lunnon¹, CJ Parkin¹, AW Roberts¹, LK Smith¹, R Spitzer¹ & V
Tymms²
1
Bullard Laboratories, Cambridge University, Madingley Rd, Cambridge CB3 0EZ,
UK
2
Department of Earth Sciences, University of Liverpool, Liverpool, L69 3BX, UK
3
Schlumberger Cambridge Research, Cambridge, CB3 0EL, UK
4
Badley Technology Ltd, Hundleby, Spilsby, Lincolnshire, PE23 5NB, UK