| Summary: | Industry and university goals coincide in the integrated Seismic Imaging and Modeling of Margins (iSIMM) project whereby low frequency seismic energy, together with high-density, long-offset, single-sensor recordings, are used to penetrate volcanic overburdens and illuminate both the deep structure of magmatic margins and sub-basalt sediments in adjoining basins. Intracratonic basin models can successfully predict heat-flow and subsidence, and hence broad-brush hydrocarbon maturation, from basin stretching. However, these models cannot easily be extended to magmatic margins due to melt underplating and extrusion (i.e. crustal non-conservation), and depth dependent stretching. The North Atlantic continental margin was formed by continental break-up in the early Tertiary above the Iceland mantle plume. This led to stretching and thinning of the continental lithosphere, accompanied by massive magmatism, producing flood basalts which covered pre-existing sediments and extensive igneous intrusion. The seismic components of iSIMM seek to develop a structural model from seabed to Moho to image the stretched crust and the extruded, intruded and under-plated igneous material, and to use these constraints in magmatic margin basin modeling. In summer 2002, seismic data were acquired successfully over two magmatic ocean margins: the Hatton-Rockall margin and the margin to the northeast of the Faroe Islands, using a combination of towed streamers and Ocean-Bottom Seismometers (OBS). We focus on the surveys over the Faroe margin, where a 385 km profile was acquired by Cambridge University using OBS and by WesternGeco using three Q-Marine streamers. The profile passes over the complete range of basalt environments from no basalt at all on the southeast flank of the Faroe-Shetland Trough, through increasing basalt cover and the basalt escarpment, over the Fugløy Ridge, across the continent-ocean transition east of the Faroe Islands and out over oceanic crust. Each acquisition used a source array tuned for low frequencies, building upon reported experiences of imaging below shallow basalts west of Ireland, and seismic characterisation of Lower Series basalts in the Lopra borehole on the Faroes. In this paper, we describe the key features of the acquisition and the processing, we review the results to date from both OBS and streamer data and we show how the two datasets complement each other in estimating the base of the basalt sequence. A comparison with an earlier long-offset survey shows the benefit of the low frequency bandwidth and we speculate on the applicability of the method to other regions.
|
|---|