Evaluation of the relationships among segmentation, hydrothermal activity and petrological diversity on the Mid-Atlantic Ridge : FAZAR (French American Zaps and Rocks) : R/V Atlantis II 127 legs 1 and 2, August 29-October 20, 1992

338 Pages·1992·14.5 MB·English

CRUISE REPORT
EVALUATION OF THE RELATIONSHIPS AMONG
SEGMENTATION, HYDROTHERMAL ACTIVITY
AND PETROLOGICAL DIVERSITY ON THE
MID-ATLANTIC RIDGE
FAZAR
(French American Zaps and Rocks)
R/V ATLANTIS II
127
Legs 1 and 2
August 29 - October 20, 1992
Lamont-Doherty Earth Observatory of Columbia University
Technical Report No. LDEO-92-3
Palisades, New York 10964

'
11
TABLE OF CONTENTS
Page
Title Page .i
Table of Contents . ii-iii
Participants .i v
INTRODUCTION .1
Cruise Plan .1
Discovery of "Lucky Strike" Vent Site .2
ROCK SAMPLING & ANALYSIS .3
Dredging Operations .3
Rock Core Operations .3
Free Fall Boomerang Cores .7
Shipboard Sample Processing .1 6
Shipboard Analysis by Plasma Spectrometry . 1 6
ROSETTE-CTD OPERATIONS .1 9
Objectives .1 9
Strategy .1 9
Equipment .2 0
Operations .2 0
Preliminary Results .2 1
ZAPS DEPLOYMENTS & SLED OPERATIONS .2 7
Introduction .2 7
Sled Frame .2 7
Conducting Cable and Traction Winch .2 7
ZAPS Sled Instrumentation .2 7
Navigational System . 29
Field Performance .2 9
Leg 1 Results .3 0
Introduction .3 0
ZAPS on the IFREMER Rosette .3 0
Results From Sled Lowerings During Leg 1 3 4
Leg 2 Results .4 4
Introduction .4 4
Stations north of the Azores .4 5
The Lucky Strike segment .4 6
The Southern AMAR Segment .4 7
The South of AMAR Segment .4 7
More Southerly Leg 2 Lowerings .4 7
Conclusions for Leg 2 Results .4 8

General Conclusions 48
SEA BEAM OPERATIONS - A127 Leg 1 4 9
Introduction .4 9
Hardware Modifications and Problems .4 9
Software .5 0
Data Processing .5 0
SEA BEAM OPERATIONS - A127 Leg 2 5 1
Introduction .5 1
Hardware Modifications and Problems .5 1
Software .5 2
Data Processing .5 2
Description of SeaBeam File System .5 3
ACKNOWLEDGMENTS .5 4
APPENDICES
Appendix 1. Dredge Log .5 5
Appendix 2. Freefall Core Log .71
Appendix 3. Dredge Inventory DRl-55 74
Appendix 4. Rock Core Inventory .8 0
Appendix 5. French Sample Selections .8 9
Appendix 6. Thin Sections .9 2
Appendix 7. Bagged Working Samples .9 3
Appendix 8. Rock Processing .9 4
Appendix 9. Steps to a Perfectly Executed Rock Core .101
Appendix 10. How To Run the Shipboard DCP .102
Appendix 11. Sled Log 1 ..1 05
Appendix 12. Sled Log 2 .119
Appendix 13. Hydrocast Log .140
Appendix 14. Helium Log .146
Appendix 15. UNOLS Research Vessel Cruise Assessment...1 61

IV
PARTICIPANTS
Principal Investigators:
Charles H. Langmuir, Lamont-Doherty Geological Observatory, Palisades, NY 10964
Gary Klinkhammer, College of Oceanography, Oregon State University, Corvallis, OR 97331
Henri Bougault, IFREMER, BP70 29263, Plouzane, France
Scientific Party:
Leg 1: Charles Langmuir1 - Chief Scientist, Gary Klinkhammer2, Henri Bougault3, Jean-Luc
Charlou3, Carol Chin2, Bobbi Conrad2, Shef Corey (Seabeam tech)4, Dana Desonie1, Jean
Pierre Donval3, Skip Gleason8, Kei Hirose5, Gautam Mandal1, Reuben Margolin1, Joyce
Miller (Seabeam tech)4, Jennifer Monteith1, Chris Moser2, Henri Pelle3, Jennifer Reynolds1,
Dana Stuart1, Michael Thatcher1, Cara Wilson2
Leg 2: Charles Langmuir1 - Chief Scientist, Gary Klinkhammer2, Henri Bougault3, Bernard
Bourdon1, Kathryn Brooksforce2, Jean-Luc Charlou 3, Carol Chin2, Shef Corey (Seabeam
tech)4, Dana Desonie1, Elisa Ferguson7, Chris German6, Skip Gleason 8, Pete Kalk2, Randy
Keller2, Chris Moser2, YaoLingNiu1, Henri Pelle3, Terry Plank1, Michael Thatcher1, Cara
Wilson2
1 Lamont-Doherty Geological Observatory, Palisades, NY 10964
2 College of Oceanography, (Ocean Admin. Bldg. HI 04), Oregon State University, Corvallis,
OR 97331-5503
3 IFREMER BP70 29263, Plouzane, Brest, France
4 Department of Geology, University of Rhode Island, Kingston, RI02881
5 Earthquake Research Institute, Geological Institute, University ofToyko, Mongo, Tokyo,
Japan
6 Institute of Oceanographic Sciences, Deacon Laboratory, Brook Rd., Wormley, Godaiming,
Surrey GU8 5UB, UK
7 Department of Geology, (103 Old Chem. Bldg.), Duke University, Durham, NC 27708
8 Woods Hole Oceanography Institution, Woods Hole, MA

INTRODUCTION
We carried out a multi-disciplinary exploration of an extensive length of the mid-
Atlantic Ridge that is affected by the Azores hot spot. Our study area extended from south of
the Hayes fracture zone at 32°N, to the Kurchatov fracture zone at 40°30'N. The program
had two major aims: first, to acquire data sets that would allow an evaluation of the
relationships among the petrological composition of the basalts of the ocean crust, the
presence of hydrothermal activity, and bathymetric and geophysical characteristics of the
ridge; second, to provide the regional framework for the FARA project (French American
Ridge Atlantic). This entailed identifying ridge segments with potential active hydrothermal
activity, and determining the petrological systematics of the youngest volcanism on the ridge.
Identifying hydrothermal segments would be the first step to discovering new hydrothermal
vent sites in shallower water and on more enriched basement than the two previously known
sites. The petrological studies would establish a baseline for future off-axis and more detailed
on-axis studies. The survey work of our FAZAR expedition was to lay the groundwork for
more detailed studies of individual ridge segments that are to take place in Phase II of the
FARA project, probably in 1994, as outlined in the FARA project plan. Because of logistical
considerations, our cruise consisted of two consecutive legs of ship time, which we
nonetheless refer to by a single name.
The FAZAR expedition was the second part of a team effort by French-American
investigators as part of the FARA program. An earlier cruise, SIGMA, took place in June
1991 on the French research vessel, Atalante. The purpose of the SIGMA cruise (David
Needham, Chief Scientist) was multibeam mapping and underway geophysics. The Atalante
mapped most of the mid-Atlantic Ridge (MAR) in the vicinity of the Azores, and collected data
on gravity and magnetics. The high quality maps, made available by David Needham and
others of our IFREMER colleagues, were essential for an efficient and precise sampling
program to take place during the FAZAR expedition.
Cruise Plan
Because of ship logistics, the expedition was divided into two consecutive legs, with
slightly more than half the time on the second leg. Roughly half the time was to be devoted to
rock and half to water work, exclusive of transits, with one extra day for testing of free fall
boomerang cores. The first leg was to be devoted to vertical profiling of the water column
and broadly spaced rock sampling. The water work was to be done primarily with the French
CTD/Rosette system adapted to carry the OSU ZAPS Mn sensor. Segments that seemed
active hydrothermally on the first leg were to be revisited and surveyed in more detail using
the OSU sled on the second leg, with more intensive rock sampling both in a regional
framework and of segments that exhibited end member characteristics in terms of their tectonic
style or gravity signature. Some portion of the water time on the second leg was to be
devoted to water sampling using the French CTD/rosette of areas that were particularly active,
and to a hydrographic experiment in an active segment.
The cruise followed this plan quite closely. However, the plan was modified on the
first leg to include work with the OSU sled. This was necessary because the French were
unable to bring their chemical analysis van to sea, and hence their system was not able to
provide the critical real time data that was necessary to unambiguously identify hydrothermal
activity. Data from the OSU sled were essential for planning the second leg. There was also
the desire to use the OSU sled during the first leg in order to test equipment and solve any