Scheduled Cruises in 2000

Summary of a recent cruise on margins research (UK.001)

Location :   Western Approaches to the English Channel, North Atlantic

Research ship and cruise identifier :   RRS Charles Darwin

Sailed :   Sep. 2000 from: Southampton

Docked :   Oct. 2000 in: Southampton

PI :   Tim Minshull

Laboratory :   Southampton Oceanography Centre, UK

Other investigators :   Rex Taylor

E-mail :   tmin@soc.soton.ac.uk

Scientific objectives :   Based on Deep Sea Drilling Project (DSDP) drilling and previous geophysical work, including reconnaissance seismic refraction, the Western Approaches margin at Goban Spur has been interpreted to have a relatively simple structure in which thinned continental crust without significant igneous addition is juxtaposed directly against normal oceanic crust. Such a structure would contrast with the volcanic margins to the north, with evidence for large volumes of igneous material at breakup time, and the non-volcanic margins to the south which typically have a broad transition zone of serpentinised mantle between oceanic and continental crust. However, the basement relief of the abyssal plain immediately adjacent to the Goban Spur margin resembles that of transition zones to the south, and the reconnaissance refraction data does not allow unequivocal identification of basement type in this region. The main objective of the cruise was to identify the nature of the basement in this region by detailed seismic refraction work and by dredging of basement highs which penetrate the sediment cover in several places. Unfortunately, most of the time on site was lost to poor weather, involving wind speeds of 40-70 knts. However, a 100 km wide-angle profile was shot with a 12-gun, 6286 cu. in. airgun array, which extended an existing wide-angle profile out to unequivocal oceanic crust at magnetic anomaly 34. Useful data on this profile were obtained from seven ocean bottom instruments, supplemented by data from six sonobuoys. Dredging goals were partially achieved during an opportunistic two-day exercise in August 2001.