RRS Shackleton S3/75

Cruise summary report

Cruise Info. 
Ship name (ship code)RRS Shackleton (74SF)
Cruise identifierS3/75
Cruise period1975-03-27 — 1975-04-15
Port of departureDjibouti, Djibouti
Port of returnDubai, United Arab Emirates
Objectives1. Magnetic survey, western Gulf of Aden
Four days at the beginning of the cruise were reserved for completing a magnetic survey begun by the University of Newcastle during Shackleton Cruise 2/75. The object of the survey was to obtain profiles along the spreading direction in order to look for the two-stage spreading history already postulated for the Red Sea (Girdler and Styles, 1974).
2. Seismic refraction experiment, East Sheba Ridge
Following work done on the Mid-Atlantic Ridge (Whitmarsh, 1975) this experiment was designed to see whether a shallow zone of low-velocity material also underlay the median valley of the Sheba Ridge, using IOS pop-up bottom seismic recorders (PUBS).
3. Subduction zone off the Makran coast, Gulf of Oman
First motion studies of earthquakes near the Makran coast (McKenzie, in preparation), and other evidence, suggest that an incipient subduction zone should exist offshore. Participants from the University of Cambridge wished to obtain seismic reflection and gravity profiles over the continental margin in the search for a zone of compression. Two long seismic refraction lines were also planned.
4. Reflection profiles across the Murray Ridge
Since the work of Barker (1966) little more has been done to investigate Murray Ridge. Two reflection and gravity profiles were planned across the ridge to shed further light on its origin.
5. Passage track over Owen Basin
A long passage track, from the East Sheba Ridge to the Murray Ridge, down the axis of the Owen Basin, was planned as a preliminary investigation for the following cruise.
Chief scientistRobert B Whitmarsh (Institute of Oceanographic Sciences Wormley Laboratory)
Cruise reportRRS Shackleton S3/75 cruise report shackleton3_4_75_data_report.pdf (4.90 MB)  RRS Shackleton S3/75 cruise report shackleton3_75.pdf (11.23 MB)  RRS Shackleton S3/75 cruise report shackleton3and4_75.pdf (0.85 MB) 
Ocean/sea areas 
GeneralGulf of Aden
Arabian Sea
Gulf of Oman
Track chartsRRS Shackleton S3/75 cruise track — trk1419.html RRS Shackleton S3/75 cruise track — trk1774.html
Geology and geophysics 
Single-beam echosoundingQuantity: track kilometres = 5556
Single channel seismic reflectionQuantity: track kilometres = 2648
Seismic refractionQuantity: 150
Gravity measurementsQuantity: track kilometres = 5889
Magnetic measurementsQuantity: track kilometres = 5556