RRS James Clark Ross JR20010414 (JR63)

Cruise summary report

Cruise Info. 
Ship name (ship code)RRS James Clark Ross (74JC)
Cruise identifierJR20010414 (JR63)
Cruise period2001-04-14 — 2001-05-22
Port of departureRecife, Brazil
Port of returnPonta Delgada, Portugal
ObjectivesRRS James Clark Ross cruise JR63 started in Recife, Brazil, on 14th April 2001 and ended in Ponta Delgada in the Azores on 23rd May 2001. Twenty-eight days were spent in scientific operations in the area around the Fifteen-Twenty fracture zone on the Mid-Atlantic Ridge. Effort was centred on an area around 15°45'N 46°55'W, ~30km the west of the present axis and ~35km north of the fracture zone. This region is well known as a 'magma starved' part of the Mid- Atlantic Ridge system.
Previous swath mapping of this region had revealed four anomalously shallow massifs, rising to ~1540m below sea level, with prominent spreading-parallel corrugations on their upper surfaces on a hundreds-of-metre to kilometre scale. These and other similarly striated massifs found in several places along the Mid-Atlantic Ridge have been interpreted as the surface exposures of sub-horizontal detachment faults.
The principal aim of cruise JR63 was to make a detailed geological investigation of the corrugated massifs at 15°45'N in order to test the detachment fault hypothesis and constrain the mechanisms of their formation and deformation. It was hoped that mapping and sampling of the surfaces would also offer insights into the processes of accretion of the lower crust at slowspreading mid-ocean ridges.
Chief scientistChristopher J MacLeod (University College Cardiff Geology Department), Javier E Escartin Guiral (CNRS Institute of Earth Physics, Paris)
Cruise reportRRS James Clark Ross JR20010414 (JR63) cruise report jr63.pdf (35.56 MB)  RRS James Clark Ross JR20010414 (JR63) cruise report jr63_bgspart.pdf (2.67 MB) 
Ocean/sea areas 
GeneralNorth West Atlantic Ocean (limit 40W)
SpecificMid-Atlantic Ridge centred on an area around 15 45'N 46 55'W
Track chartsRRS James Clark Ross JR20010414 (JR63) cruise track — jr63trk.pdf (1.83 MB) 
Physical oceanography 
Subsurface temperature and salinity measurementsQuantity: number of profiles = 4
Description: Invesitagtion of 4 massifs took place during the cruise.
Current metersQuantity: number of profiles = 4
Description: Invesitagtion of 4 massifs took place during the cruise.
Geology and geophysics 
DredgeQuantity: number of samples = 32
Description: A number of dredges were collected throughout the cruise, to gather material from the steep slopes.
Core - rockQuantity: number of cores = 63
Description: A number of rock cores were also made on the massifs.
Core - rockQuantity: number of samples = 73
Description: A number of rock samples from the massifs and surrounding areas using a drill.
Long/short range side scan sonarDescription: TOBI sonar imagery was gathered on the correated knolls. A large number of faults around the massif were made visible. No. of profiles not noted.