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iSIMM (INTEGRATED SEISMIC IMAGING AND MODELLING OF MARGINS):
THE NORTH ATLANTIC VOLCANIC CONTINENTAL MARGIN
R.S White1, N.J. Kusznir2, P.A.F. Christie3, A Roberts4, R. Spitzer1, Z. Lunnon1, A.W.Roberts1,
A. Surendra1, N. Hurst2, C. Parkin1 , L. Smith1 & V. Timms2
1
Bullard Labs, Department of Earth Sciences, University of Cambridge, Cambridge, CB3, 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, PE, UK)
Tel. +44 1223 337187 Fax. +44 1223 360779 email. [email protected]
The iSIMM project is investigating the structure of North Atlantic rifted continental margins
using state-of-the art seismic data recorded in summer 2002, integrated with new models of rifted
margin formation incorporating heterogeneous stretching, the effects of melt generation and
emplacement and varying thermal anomalies in the mantle. The addition of melt to the crust,
together with the rapid asthenospheric mantle temperature variations that accompany interaction
of a mantle plume with the onset of continental rifting, cause rapid uplift and subsidence
anomalies on the margin. The new seismic data enables us to image both the shallow basalt flows
and the lower-crustal igneous intrusions and underplate, and thus to place constraints on the
igneous distribution and volumes, that feed back into the modelling. We use both seismic and
subsidence results to show that there was a rapid drop in the temperature of the mantle plume
immediately following continental breakup.
We acquired two wide angle and normal incidence surveys, using 85 four-component ocean
bottom seismometers, and several vertical arrays for far-field source signature recording.
Coincident magnetics and gravity data were also recorded. The first survey crossed the Faroes
Shelf and adjacent continental margin, and the 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 deeptowed, broad-band low-frequency sources tuned to enhance the bubble pulses, with peak
frequencies at 9-11 HZ. They provided excellent arrivals to ranges beyond 100 km, penetrating
well into the upper mantle. 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.
The iSIMM project is supported by the NERC, WesternGeco, 8 oil companies and the DTI.