BODC Cruise Metadata Report for RRS James Cook (740H) cruise JC021

Introduction

This report collates information from the BODC cruise inventory and oceanographic databases. It presents

Cruise Inventory Information
A summary of BODC data holdings for the cruise from the
- National Oceanographic Database
- Projects Database
References - including cruise tracks and cruise reports

Cruise Inventory Information

Long name	RRS James Cook (740H) cruise JC021
Short name	JC021
Objectives and Narrative	RRS James Cook Cruise JC21 (6th January to10th February 2008) investigated exposures of lower oceanic crust that crop out at Hess Deep (~2�15'N, 101�30'W); a rifted depression formed by the westward propagation of the Cocos-Nazca plate boundary towards the East Pacific Rise. Hess Deep provides unique exposures of the deeper levels of ocean crust formed at a fast spreading mid-ocean ridge, one of the fundamental processes in the solid Earth cycle. Our principal aims were to provide detailed site survey for future Integrated Ocean Drilling Program (IODP) drilling, and to collect a suite of deep crustal rocks with good geological context to test hypotheses of mid-ocean ridge accretion. The specific objectives were as follows: 1. To find suitable locations for the drill sites proposed in the highly-ranked IODP proposal #551. This requires use of a remotely-operated vehicle or autonomous underwater vehicle to collect accurately navigated high-resolution bathymetry and seafloor photographs in order to identify areas of outcrop and/or flat benches suitable for spud-in by a non-riser drillship. 2. To characterise the lithologies present at these potential sites, and provide geological context on a broader scale, by surveying and sampling in as much detail as possible the lower crustal section exposed on the southern slope of the intra-rift ridge of Hess Deep. This we intend to do by using the British Geological Survey's 'BRIDGE' seabed rock drill to collect geographically orientated core material, supplemented if appropriate with sampling using an ROV and/or dredging. The broader scientific objectives were defined as follows: 3. To quantify as far as possible the heat and mass flux between mantle and crust and crust and ocean by constraining the structure, composition and alteration history of gabbroic rocks from the Hess Deep section. 4. To test the hypothesis that the Oman ophiolite is an appropriate analogue for fastspread ocean lithosphere. 5. To test competing models for the accretion of the lower ocean crust at fast-spreading ridges.
Ship	RRS James Cook
Departure Port	Panama, Panama
Departure Date	2008-01-04
Arrival Port	Caldera, Costa Rica
Arrival Date	2008-02-10
Principal Scientist(s)	Christopher J MacLeod (University of Cardiff School of Earth and Ocean Sciences)
Responsible Organisation	University of Cardiff School of Earth and Ocean Sciences
Associated Project(s)
IHB Sea Areas Visited	North East Pacific Ocean (limit 180W)
Marsden Squares Visited	11
Work Area Description	Hess Deep
Unable to lookup cruise bounds at this time
Work Area Bounding Polygon
Southern Limit	unknown
Northern Limit	unknown
Western Limit	unknown
Eastern Limit	unknown

Cruise Inventory Datasets

Geology and geophysics
Bottom photography	Quantity: number of dives = 8 Description: ISIS ROV deployed near bottom to acquire digital imagery of basement exposures and to collect outcrop samples using the vehicle's manipulator arms
Core - rock	Quantity: number of deployments = 3 Description: BRIDGE drill deployment, no cores recovered
Grab	Quantity: number of samples = 145 Description: 760kg of sample collected, rock types includedharzburgite, dunite, troctolite, olivine and other gabbro, dolorites and basalts
Grab	Quantity: number of dives = 12 Description: ISIS ROV dives over an aggregate of 14.5 days from depths between 3000 and 5400m to do swath mapping and sample collection
Multi-beam echosounding	Quantity: number of dives = 12 Description: ISIS ROV dives over an aggregate of 14.5 days from depths between 3000 and 5400m to do swath mapping and sample collection
Multi-beam echosounding	Quantity: survey square kilometres = 11 Description: Bathymetric survey of the slop north of the nadir of Hess Deep and the intra-rift ridge horst block further north within the rift valley