french-japanese starmer project...
TRANSCRIPT
FRENCH-JAPANESE STARMER PROJECT
STARMER SYMPOSIUM
GEOLOGY AND BIOLOGY OF THE RIFT SYSTEM
IN THE NORTH FIJI AND LAU BASINS
7 - 11 February 1991
ORSTOM Center
Noumea, New Caledonia
Dear colleagues,
We are gratified by the number of responses of the project of a STARMER Symposium although the organization began only very few times before the dates chosen.
Sixty two participants and thirty nine communications and posters demonstrate the interest concerning this meeting.
There are probably many reasons to this success. One is the very good coordination
between the Scientific Committee of STARMER, the Executive Committee of STARMER
and the Organizing Committee of this symposium. But the most important reason is the
enthousiasm of all the participants to the STARMER programme and all the scientists
interested by the theme. We have to remember that this project on the study of the rift system in the Pacific
was initiated only four years ago. The strategy chosen was to focus a systematic studies on a typical opening marginal
basin, the North Fiji Basin, and of a typical recent or aborted tensional structure, the Vanuatu
back arc trough. Many cruises using geophysical, hydrological, bottom sampling tools, and
submersibles have associated geoscience and bioscience scientists. Furthermore, two more cruises are skeduled for this year.
Preliminary and mature results will be presented and discussed. Opportunity to print
papers will be decided before the end of the symposium.
The last part of the meeting will be devoted to a workshop.
Provision is made for ample discussion time. The objective will be to identify major insolved
problems in the field of geoscience and bioscience and further research work needed to solve this problem using the scientific strategy which was already successful for the STARMER
programme.
On behalf of the Organizing Committee of the Starmer symposium sponsored by
ORSTOM, IFREMER, INSU/CNRS, GSJ, JAMSTEC, MSA/HDJ, SOPAC, it is our
pleasure to extend our warmest welcome to all the participants.
Kiyoyuki KISIMOTO, Jacques RECY Co-chairmen of the Organizing Committee
SrARMERSymposium 7-11 l3ixuary 1991, OlXS-IDMcenter, Noun-a New (Ihkbia
Programme
Thursday 7 February
0890 to 09:OO Opening of the Secretary in the Entrance Hall of the ORSTOM Center
09:oo to 1O:lO Welcome and official allocutions in the ORSTOM Center Auditorium
co-Chairman of the STARMER Symposium Organizing Committee co-Chairman of the STARMER Excecutive Committee for the french party co-Chairman of the STARMER Excecutive Committee for the japanese party
Government Representantive
1O:lO to 10:40 Coflee Break chairman : RCcy
lo:40 to 11 :OO AUZENDE Jean-Marie, Eiichi HONZA, Jean-Pierre MAZE, and STARMER Group - Seabeam Maps of the North Fiji Basin Ridge - New Constraints on the Recent Spreading Phase.
ll:oo to 11:20 HONZA Eiichi - Spreading in Backarc Basin.
11:40 to 13:30 Lunch
Session 1 : North Fiji Basin; general and detailed survey chairman : Auzende
13:30 to 1350 RUELLAN Etienne: Jean-Marie AUZENDE, Patrick MAILLET - Propagating Rift Combined wrth Fossile Overlapping Spreading Center ; The Tectonic Relay Between the N15 and the NS Axis in the North Fiji Basin at 18 o3O’S.
13:50 to 14:lO KROENKE Loren, and Philip JARVIS - Rift propagation in the North Fiji Basin : Evolution of the Fiji Fracture Zone. - University of Hawaii - School of Ocean and Earth Sciences and Technonoly - Hawaii Institute of Geophysics - Honolulu, Hawaii.
14:lO to 14:30 HUCHON Philippe, Etienne RUELLAN, Jean-Marie AUZENDE, Yves LAFOY and Yves LAGABRIELLE - Kinematics of the Active Opening of the North Fiji Basin from Magnetic and Structural Data.
14:30 to 1450 TANAHASHI Manabu, Kiyoyuki KISIMOTO, Masato JOSHIMA and Jean-Marie AUZENDE - Development of a Triple Junction, Central North Fiji Basin.
1450 to 15:20 Co#ee Break
SrARMERSymposium,7-11E;eb1~a.q491, ORSI-OMcentea,Nouma,Newcaledonia
Session 1 : North Fiji Basin; general and detailed survey (following) chairman : Honza
15:20 to 1530 NOJIRI Yukihiro, and Jun-ichiro ISHIBASHI - Hydrothermal Plumes Observed in the North Fiji Basin.
15:40 to 16:00 MOMMA Hiroyasu, Takeo TANAKA, Jun HASHIMOTO, Hiroshi HO’ITA, and JAMSTEC Deep Sea Research Group - Deep Tow Surveys to Search for Hydrothermal Activities in the North Fiji Basin Rift Axis.
16:00 to 16:20 MITSUZAWA Kyohiko, Kiyoshi OTSUKA, Hiroyasu MOMMA, Hiroshi HOTTA, and JAMSTEC Deep Sea Research Group. - Deployment of Stationary Sea Floor Observation System.
16:20 to 16:40 NAKA Jiro, Kyohiko MITSUZAWA, Takeshi MATSUMOTO, Takeo TANAKA, Katsunori FUJIKURA, Jun HASHIMOTO, Hiroyasu Momma, and Hiroshi Hotta - Stationary Sea Floor Observation around the Hydrothermal Area in the North Fiji Basin.
18:00 Official Reception at ORSTOM Hall
Friday 8 February
Session 2 : Biological communities associated with hydrothermalism
chairman : Eade
0890 to 08:20 DESBRUYERES Daniel, Anne-Marie ALAYSE, Suguru OHTA, and the participants of STARMER II and BIOLAU cruises - Deep-Sea Hydrothermal Communities in Two Back Arc Basins of the South West Pacific : Composition, Microdistribution and Food-Web.
08:20 to 08:40 ALAYSE Anne-Marie, Christine LADRAT, and Michel MARCHAND - Submarine Hydrothermal Ecosystems as a Source of Thermostable Enzymes : Prospects and Preliminary Results of Screening of Bacteria Isolated !?om Lau and North Fiji Basins.
08:4O to 09:oO HESSLER Robert R., and Peter F. LONSDALE - Biogeography of Mariana Trough Hydrothermal Vent Communities.
09:20 to 0950 OHTA Suguru, Jun HASHIMOTO, Daniel DESBRUYERES, Hitoshi SAKAI, and KH-90-3 Cruise members - Comparison and Some Ecological Notes on the Hydrothermal Vents Communities of the Southwestern and Western Pacific.
09:20 to 09:50 Posters Session :
Co#ee Break and Posters
EISSEN Jean-Philippe, Masato NOHARA, Jo COTTEN, and STARMER I scientific team - Petrology and Geochemistry of the North Fiji Basin Spreading Center between 16’S and 22’S .
MONZIER Michel - The boninitic trend of the southern terminaison of the New Hebrides island arc (SW Pacific).
5
TIFFIN Don L., J.H. CLARKE, P. HILL, Phil1 JARVIS, David JOHNSON, Patrick MAILLET, L. PARSON, and Ric PRICE - GLORIA Data from the North Fiji and Lau Basins : a Summary of Results.
Session 2 : Biological communities associated with hydrothermalism (following) chairman : Ohta
0950 to 1O:lO FIALA-MEDIONI Aline, V. PRANAL, Jean GUEZENNEC, J.C. COLOMINES, and P. ALBERIC - Structural and Biochemical Characteristics of the Mussel Bathyrnodiolus sp. from the Lau Basin.
1O:lO to 10:30 NAGANUMA Takeshi, and Humitake SEKI - A Sulfur Bacterium, NFB04, from a Hydrothermal Plume in the North Fiji Basin.
10:30 to 1050 ANTOINE Elisabeth, Georges BARBIER, Jean-Claude CAPRAIS, Gael ERAUSO, Anne GODFROY, Jean GUEZENNEC, Daniel PRIEUR, and G&ard RAGUENES - Isolation of Anaerobic Sulfur Dependent Thermophilic Bacteria from Two New Hydrothermal Sites in SW Pacific (Lau Basin and North Fiji Basin).
10:50 to 11:lO DESBRUYERES Daniel, and Lucien LAUBIER - New Species of Alvinellids (Polychaeta) from the North Fiji Back-Arc Basin Hydrothermal Vents (South West Pacific) and Notes on Related Species.
11:lO to 13:30 Lunch
Session 3 : Tectonics, Magmatism and Vanuatu Rear arc Troughs chairman : Matsumoto
13:30 to 139 IWABUSHI Yo, Takeshi MATSUMOTO, and Tadahiko KATSURA - Tectonics in the Central Axial Area of North Fiji Basin as Derived from Precise Bottom Topography.
13:50 to 14:lO RUELLAN Etienne, Jean-Marie AUZENDE, Yves LAFOY and Eiichi HONZA - The Southern End of the Seafloor Spreading in the North Fiji Basin.
14:lO to 14% LAGABRIELLE Yves, Jean-Marie AUZENDE, and Jean-Philippe EISSEN - A 800 m Thick Section of Upper Oceanic Crust in the North Fiji Basin (NFB). Results of Nautile dive No7 of the STARMER cruise.
14:30 to 149 CRAWFORD Anthony J. and Steve M. EGGINS - Boninites from the North Fiji Basin - Hunter “Fracture Zone”
14:50 to 1590 Coffee Break
Session 3 : Tectonics, Magmatism and Vanuatu Rear arc Troughs (following)
chairman : Kisimoto
1520 to 15:40 NOHARA Masato, Jean-Philippe EISSEN, Tetsuro URABE, and Masato JOSHIMA - Isotopic and Geochemical Characteristics of Basalts from the Spreading Center of the North Fiji Basin.
15:40 to 16:oO RECY Jacques, Philippe CHARVIS, Bernard PELLETIER, Martine GERARD, Marie-Claire MONJARET, and Patrick MAILLET - The New Hebrides Back Arc Troughs : an Example of Permanent Slow Tensional Structure.
6
16:00 to l&20 MATSUMOTO Takeshi, and Yo IWABUSHI - Tectonics in the Northern Part of Vanuatu Back-arc Basin as Derived from Precise Bottom Topography.
16:20 to 1640 MAILLET Patrick, Etienne RUELLAN, Tetsuro URABE et al. - Magmatic and Tectonic Activities in the Northern Vanuatu Back-Arc Troughs. Results of the STARMER /Kaiyo 89 Cruise.
1640 to 17:00 AUZENDE Jean-Marie, Jean-Philippe EISSEN, Yoshihisa OKUDA and YOKOSUKA 90 scientific team - Preliminary results of the YOKOSUKA 90 cruise in the Coriolis troughs and North Fiji basin spreading center.
Saturday 9 February
Session 4 : Hydrothermal deposits and Geophysics chairman : Desbruyeres
08:OO to 0820 BENDEL Valerie, Yves FOUQUET, Tetsuro URABE, Jean-Marie AUZENDE, and Yves LAGABRIELLE - Hydrothermal Deposits in the North Fiji Basin : Petrology and Geochemistry (STARMER).
08:20 to 08:40 HERZIG Peter M., Yves FOUQUET, Mark D. HANNINGTON, and Ulrich von Stackelberg - Visible Gold in Primary Polymetallic Sulfides from the Lau Back-Arc.
0840 to 09:OO URABE Tetsuro, and S.W. ELDRIDGE - Geochemical and Isotopic Studies on Sulfides and Sulfates from North Fiji Basin Spreading Center.
09:20 to 0950 GRIMAUD Daniel, and Jun-Ishiro ISHIBASHI - Chemical Features of the Hot Waters Emitted at the White Lady Active Vents.
09:20 to 0950 Coflee Break
Session 4 : Hydrothermal deposits and Geophysics (following) chairman : Urabe
0950 to 1O:lO Basin.
EADE Jim V., and M.R. GREGORY - Sediments of the North Fiji
1O:lO to 10:30 MATSUMOTO Takeshi - Gravity Anomaly and Sub-bottom Structures in the North Fiji Basin.
10:30 to 1050 KISIMOTO Kiyoyuki, Takanobu YOKOKURA, Manabu TANANASHI, and Yves LAFOY - Crustal Structure along the Rift Axis of the North Fiji Basin.
1050 to 11:lO JOSHIMA Masato - Heat Flow Measurements and Magnetic Anomalies in the North Fiji Basin.
11:lO to 11:30 PAUTOT Guy, Robert Le SUAVE, and Pierre COCHONAT - In Situ Observations of Deep Sea Manganese Nodules Environments.
from 11:30 Lunch Afternoon free
Sunday 10 February
Day free
Monday 11 February
Post-STARMER Programme Session
08:oo to 09:45 plenary session
09:45 to 10:15 Coffee Break
10:15 to 1120 working groups
chairman : Pautot
11:30 to 139 Lunch
13:30 to 15:oo
15:oo to 1520
15:30 to 17:oo
working groups
Coflee Break
plenary session chairman : Pautot
Publication of Papers
FullName:................................................
Address: ................................................. .................................................... ....................................................
Phone: ..............................
Fax: ................................
Telex:...............................
E-mail:..............................
Please make your choice :
I am / I am not interested in contribuing Special Volume in a journal to be selected.
to a STARMER Symposium
Several journals (Deep Sea Reasearch, Oceanologica Acta,...) or special edition (ORSTOM Editions , . ..) have been approached, but the final choice of journal will be done during the Symposium.
Tentative deadline for paper submission will be March 3 lst, 1991.
Tentative title of your contribution : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . .
. . . . *
Authors : . .
. . . . .
Approximate length of your manuscript (figures and tables included) :
...............................................
...............................................
...............................................
...............................................
. . . . . . .pages
Please to be returned to the Secretatriat of the Symposium in the ORSTOM Hall as soon as possible. Thank you.
Additionnal informations will be given during the Symposium.
9
Sl’~Rsymposium, 7-11 l?dxuq 1991, ORsroMcenter, Noun-a, New (Iakchb
ABSTRACTS
11
Submarine Hydrothermal Ecosystems as a Source of Thermostable Enzymes : Prospects and Preliminary Results of
Screening of Bacteria Isolated from Lau and North Fiji Basins
Anne Marie ALAYSE-DANET, Christine LADRAT,
and Michel MARCHAND (IFREMER, Brest)
Enzyme-catalysed industrial processes are largely run at relatively high temperature
(50-1OOOC) : starch hydrolysis, food processing, detergent for example but, most of the
enzymes used now in industry are produced from mesophilic organisms. This situation is in part a consequence of the relatively little knowledges acquired about other thermophiles than
those of the two more used genera Bacillus and Thermus.
Submarine hydrothermal ecosystems’offer new prospects to discover novel species of
thermophiles in particular extremely thermophilic bacteria (organism with growth temperature
optimum above 8OOC) which may possess unique properties because of their extreme thermostability.
At the sight of these considerations a program of research of thermostable enzymes is running with bacteria isolated from Lau and North Fiji basins. Five activities (p galactosidase,
p glucosidase, alcohol dehydrogenase, lipase and protease) are now screened, preliminary
results will be presented.
13
Isolation of Anaerobic Sulfur Dependent Thermophilic Bacteria from Two New Hydrothermal Sites
in SW Pacific (Lau Basin and North Fiji Basin)
Elisabeth ANTOINE (IFREMER, Brest), Georges BARBIER (IFREMER, Brest), Jean-Claude CAPRAIS (IFREMER, Brest), Gael ERAUSO (CNRS, Roscoff),
Anne GODFROY (IFREMER, Brest), Jean GUEZENNEC (IFREMER, Brest),
Daniel PRIEUR (CNRS, Roscoff), and Gerard RAGUENES (IFREMER, Brest)
Hydrothermal activities have been recently discovered in back arc basins of the SW
Pacific and depths ranging from 1800 to 2800 m. During the French biological cruise (Biolau)
in the Lau Basin and the French-Japanese cruise (Starmer) in the North Fiji Basin, samples of
hydrothermal fluids (with temperatures up to 400°C), chimney and rock debris, invertebrates, were collected by the man-operated submersible “Nautile”.
Enrichment cultures were performed using two sulfur-containing media, at
temperatures up to 97OC, under anaerobic conditions. Twenty seven thermophilic isolates were
obtained by streaking on gelrite medium at 80 and 97OC. Twenty one isolates were also obtained
from cultures incubated at 8590°C by the dilution method. Using phase contrast microscopy, isolates appeared regular or irregular shaped coccoid cells. Cells were from 1 to 3 pm in
diameter, occuring singly, by pairs, or in aggregates of 10 to 20 cells.
From preliminary lipid analysis and antibiotic sensitivity, six of those isolates could be
assigned to Archaebacteria.
In addition, nine isolates of different morphological types were isolated at 60-65OC.
These isolates were of two types of rod-shaped rigid cells, one with a diameter of 0.4 p.m
(8 isolates), the other with a diameter of 0.8 pm. Both showed varying length up to 70 pm.
Nutritional characterization is now undertaken and further investigations using molecular tools are considered.
14
Seabeam Maps of the North Fiji Basin Ridge - New Constraints on the Recent Spreading Phase
Jean-Marie AUZENDE (GDR GEDO, IFREMER Brest), Eiichi HONZA (GSJ, Tsulcuba),
Jean-Pierre MAZE (GDR GEDO, IFREMER Brest) and STARMER Group*
One of the main features of the STARMER project was the Seabeam mapping of the North Fiji
Basin ridge. After the Seapso 3 cruise of the R.V. Jean Charcot (December 1985), the Kaiyo 87 and 88
cruises allow to present a quite complete coverage map of the North Fiji Basin ridge between 16OS and
22’s. This map recently published at the l/200.000 scale shows the complexity of the structure and the
functioning of the North Fiji Basin ridge since 3 Ma.
From the South to the North we distinguish four main segments exhibiting peculiar features :
Between 22’S and 20’30s the axial area is characterized by a double ridge flanking an axial deep
graben. This whole area is dotted by numerous isolated volcanoes probably related to the vicinity of the
Matthew-Hunter subduction zone. To the North, this axial area is limited by V shape faults suggesting that it is propagating northward.
Between 20’30s and 18’30s the present-day accretion is concentrated on a NS axial flat-topped
dome at 2800 m depth. This type of dome is very similar to the EPR axis around 14’N for example. On both sides of the axis the oceanic bottom shows a typical alternation of ridges and depressions.
From 18’30s to the 16’40s triple junction the present-day axis trend becomes N15 and the
accretion zone is constituted by a double ridge flanking an axial graben 100 to 200 m deep. To its southern tip this N15 axis is propagating toward the Southwest within a large fossil overlapping spreading center which was probably active during a previous phase. From the analysis of magnetic data, we estimate that
this N15 axis has been functioning since 1 Ma. In that case the age of the OSC is a little bit more than 1 Ma and has been abandoned on the western side by a spreading axis jump. A similar fossil OSC is also visible
on the western side of the present-day axis around 17’S just West of the large axial dome constituting the
northern tip of the N15 axis.
From 16’40’s to 16’S, the N160 branch of the triple junction is formed by two ridges flanking a
3400 m deep graben. Toward the North, this axis is more complicated and the Seamarc II data of the
Moana Wave cruise (Kroenke et al., 1987) suggest an “en echelon” propagating system. East of 16’40s the western end of the North Fiji Fracture zone is characterized by a deep graben
partly occupied by a small SW-NE propagating ridge. In conclusion, the seabeam map of the North Fiji Basin axis illustrates a polyphased accretion in
the last 2 Ma probably related to the large scale deformation of the whole North Fiji Basin due to its
location between two active subduction zones (New Hebrides to the West and Tonga to the East).
* STARMER Group : France : X. BOESPFLUG, J.P. EISSEN, P. HUCHON, Y. LAFOY, H. ONDREAS, E. RUELLAN, M. SIBUET, D. JOLLIVET; Japan : J. HASHIMOTO, J. ISHIBASHI, Y. IWABUCHI, M. JOSHIMA, T. KAWAI, T. KAWAMOTO, K. KISIMOTO, Y. KUWAHATA, T. MATSUMOTO, K. MITSUZAWA, H. MOMMA, T. NAGANUMA, J. NAKA, Y. NOJIRI, S. OHTA, K. OTSUKA, A. OTSUKI, M. TANAHASHI, T. TANAKA, T. URABE, T. YOKOKURA; SOPAC
countries : S. DEO, P. JARVIS, S. DUTT, B. RAO, J.S. TEMAKON, T. VEIVAU.
15
Hydrothermal Deposits in the North Fiji Basin :
Petrology and Geochemistry (STARMER)
Valerie BENDEL (GDR GEDO, UBO Brest),
Yves FOUQUET (GDR GEDO, IFREMER Brest),
Tetsuro URABE (GSJ, Tsukuba),
Jean-Marie AUZENDE (GDR GEDO, JFREMER Brest)
and Yves LAGABRIELLE (GDR GEDO, UBO Brest)
Hydrothermal deposits were sampled during the STARMER diving cruise at Station 4
on the N15 branch of the North Fiji Basin spreading axis.
The White Lady active chimney was located at 16’59’s in the central graben of the
axial area. This three meters high white chimney is mainly made of anhydrite but also contains
talc and opal. Oxide deposits were observed on fault scarps, or as patches in sediments and building
fossil chimneys. They are totally amorphous and rich in silica.
Sulfide deposits were sampled on a small sulfide mound beneath the active smoker, but also on dead chimneys which surround this active site. They were also sampled one
kilometer northward in the “Pet-e Lachaise” fossil field. They are all Cu-Fe-Zn s&ides. They show a chemical diversity which is based on the Cu, Fe and Zn amounts and also on the silica content which can reach 25 percent in weight in some case.
Although mound sulfides are
better crystalized than the chimneys fragments, and though the chemical
variability, all sulfides show the same
mineralogical sequence which can be
summarized as follows :
First, the iron sulfides crystalize in numerous stages which are outlined by
sphalerite precipitation. These iron
sulfide crystals are brecciated and a hot
temperature assemblage of chalcopyrite and sphalerite crystallizes after them in
conduits. The brecciation and fissuration
of these sulfides are the result of a tectonic event. At last, opal fills all
cavities, pores and fissures, and in some
case, iron oxides precipitate with this
opal. Irn The “White Lady” chimney
16
SIARMJXRSymposium, 7-11 I%lxuq 1991, ORStDMCaer, &mea, New -
Boninites from the North Fiji Basin - Hunter “Fracture Zone”
Anthony J. CRAWFORD and Steve M. EGGINS (University of Tasmania, Hobart)
Rocks of the boninite association (>53 % Si02 at >8 % MgO) are currently the subject of much research interest for a number of reasons :
1. Boninites are generally quite primitive lavas, and as such can yield useful information about subduction zone magma generation and the nature of the sub-arc mantle and fluids.
2. Boninites are being recorded with increasing regularity from ancient foldbelts (Cambrian to Early Tertiary), where they occur in greenstone belts and ophiolites. The Troodos Complex in Cyprus, once considered the ‘type-location’ mid-ocean ridge-generated section of ocean crust, has been found to contain boninites, and demands a reexamination of the ophiolite concept and definition.
3. Boninites have anomalously hig levels of precious metals and platinum group elements, and the parental magmas of both the Bushveld and Stillwater Complexes, the largest PGE deposits in the world, have been shown to be broadly boninitic (Sun et al. 1989).
Lavas of the boninite association are apparently not a ubiquitous component of convergent plate boundary magmatism, being unrecorded from many well-studied arcs (eg. Aleutians, Lesser Antilles, Indonesia). Probably, temperatures sufficiently high to generate boninites (>1200°C) are not attained in the mantle wedge above the subducted slab at appropriate depths (40 km) in such arcs, even in the presence of slab-derived, solidus-lowering hydrous fluids. Normally, temperatures necessary to generate arc magmas (> 1100°C) are not attained until the subducted slab reaches depths of 100 km or more. At these levels, compared to the situation at 50 km or less, the stability field of olivine has shrunk considerably relative to that of orthopyroxene, and picritic precursors of normal arc basalts are generated. To generate boninites at shallower levels than 50 km, we hypothesize that the prime requirement is input of a considerable amount of extra heat.
The heat supply for boninitic magmatism may derive from diapirs of backarc basin source mantle ascending beneath the arc. Alternatively, Crawford et al. (1989) argue that the extra heat required in boninite generation from sub-arc mantle could be provided by trench-parallel subduction of an active spreading centre. Support for the former model comes from the report by J.B. Gill (pers. comm. 1986) of lavas with boninitic affinities in the outer Lau Is. Group of Fiji, thought to have been generated during initial opening of the Lau Basin. Support for the second model comes from two locations where modern active spreading centres have been subducted. Unusual high-Si, high-Mg lavas with affinities to boninites have been dredged recently from the intersection of the Woodlark spreading centre and the Solomons trench. Similar lavas were predicted to occur where the southern end of the N Fiji Basin main spreading centre abuts the cooler, fractured crust of the Hunter Fracture Zone (Crawford et al. 1989). Recent dredging at this location (R/V Nesmeyanov, Soviet Academy of Science) has yielded boninites, and abundant andesites and dacites of possible boninitic parentage. Theses andesites and dactites are geochemical similar to the distinctive, very low-Ti lavas of nearby Hunter and Mathew Islands.
The Hunter Fracture Zone boninites are also associated with unusual Na-rich dacites (plagiogranites). The latter occur directly at the intersection of the North Fiji Basin spreading centre and the Hunter Fracture Zone. They are consistent with being the melting products of Hunter Fracture Zone crust, generated in response to the presence of upwelling hot mantle at very shallow levels in this zone of active rifting. The occurrence of relatively widespread boninite generation along the Hunter Ridge is further suggested by reported dolerite inclusions from Hunter Island (Maillet et al., 1987) which are geochemically identical to the dredged boninites.
17
Deep-Sea Hydrothermal Communities in Two Back Arc Basins of the South West Pacific : Composition, Microdistribution and Food-Web
Daniel DESBRUYERES (IFREMER, Brest), Anne-Marie ALAYSE (IFREMER, Brest),
Suguru OHTA (ORI, Tokyo) and the participants of STARMER II and BIOLAU cruises*
During spring and early summer of 1989, two biological cruises, BIOLAU (05/12/89 to 05/27/89) and STARMER II (06/30/89 to 07/19/89) were devoted to the study of biological communities associated with deep sea hydrothermal vents in south western Pacific, in the Lau Basin and in the North Fiji Basin. The french research submersible “Nautile”, operated from R/V “Le Nadir”, dove sucessfully 24 times in active areas. Four active hydrothermal fields were explored at depths ranging from 1730 m to 2700 m on the Valu Fa ridge and on the North Fiji Basin spreading axis. (A) In the Lau Basin (LB) warm venting (2-19OC) was observed in Hine Hina vent field (22”32’S and 176’43’W) although hot fluid (up to 400°C ?) was seen in Vailili vent field (22’13’s and 176’36’W); in the last area, warm venting (2-33°C) was also observed. Two “cold venting” areas were also located according to blota (bacterial mats and vestimentiferans) southward to Hine Hina vent field. (B) In the North Fiji Basin (NFEQ, two active vent fields were explored. White Lady vent field, displaying temperature up to 288OC, is located by 16’59’s and 173’55’W. Mussel Valley (18’49’s and 173’29’W) in the southern most part of the explored zone, displays only warm venting (up to 8.5”C).
In all sites, the fauna is dominated by molluscs : Mussel beds (Bathymodiolus spp) thrive in warm waters ranging from 4.38OC to 18.80°C in Lau Vasin and from 8.51”C to 22.36OC in the NFB; a polynoid worm belonging to Branchipolynoe lives commensal to the mussel. Gastropods belonging to two different species (Alvinichonca hessferi and a viviparus-like snail) are abundant in the central area of warm venting. Temperature time series recorded in NFB populations range from 5.26”C to 12.18”C (mean 7.35OC) inside a clump of Alvinichonca and from 3.67OC to 17OC (mean 7.12OC) in viviparus-like gastropods. Discrete temperature measurements in LB in such clumps displays temperature of 15 to 33°C for the first species and 6°C to 20°C for the second.
These three species are the dominant base of the food web : all of them harbour symbiotic bacteria inside
the cells of their gills. Alvinichoncha display high RuBPcase activity (0.1 - 0.2 u.g-’ of WW) on the same range than previously published in other sympiont bearing grastropod species. The RuBPcase activity in the viviparus-
like gastropod gills displays a more variable activity (0.003-0.03 u.g-’ of WW in LB and 0.044 - 0.632 in NFB).
Bathymodiolus symbionts in LB has a RuBPcase activity of the same order of magnitude (0.007 to 0.018 u.g-’ of WW) in LB but has a lower activity in NFB (at the detection limits).
Other primary consumers are present although less prominent in biomass : Vestimentiferans belonging to two underscribed species (one is refered to Lameflibrachia n.sp. and the other is no refered to existing taxa) are present in one cold venting area. A Pogonophoran was sampled in the same area and belongs to Siphonobrachia. At the edge of all sites, where temperature range from 3 to 4OC (NFB) or to 6OC (BL), a dense population of cirripeds belonging to Eochlonalasmus ohtal and Neolepas sp. covers the basalts. In White Lady hydrothermal field, alvinellid worms belonging to new species of Paralvinelfa are dwelling in the anhydrite wall of the chimney. Carnivorous animals are mainly belonging to decapods : crabs (Austinograea alaysae, Austinograea n.sp.), shrimps (Chorocaris sp., Alvinocaris sp., Lebbeus sp.), galatheids (Munidopsis sp.) and lithodids (Uroptychus sp.). A new angulliform fish is abundant only in Lau basin dwelling inside gastropod clumps; It is a new genus and species of synaphobranchid. The fauna from the two back arc basins is roughly similar but differs by the occurence of rare species. The comparison with other back arc basins of the western Pacicic would point out the relative unicity of ecosystem fauna1 composition and the difference with Eastern Pacific populations at least at specific level.
* Anne-Marie ALAYSE, Elisabeth ANTOINE, Georges BARBIER, Patrick BRIAND, Philippe CRASSOUS, Evelyne DERELLE, Daniel DESBRUYERES, Alain DINET, Aline FIALA-MEDIONI, Anne GODFROY, Jun HASHIMOTO, Didier JOLLIVET, Jacques KER.DONCUFF, Alexis KHRIPOUNOFF, Lucien LAUBIER, Michel MARCHAND, Yuihiro NOJIRI, Suguru OHTA, Roger PERRON, Daniel PRIEUR, Etienne RUELLAN, Sione SOAKAI.
18
New Species of Alvinellids (Polychaeta) from the North Fiji Back-arc Basin Hydrothermal Vents
(South West Pacific) and Notes on Related Species
Daniel DESBRUYERES and Lucien LAUBIER
(IFREMER, Brest)
Alvinellid polychaets have been recently discovered on hydrothermal vents of the East
Pacific Rise (DESBRUYERES & LAUBIER, 1980, 1982). First considered as a sub-family of
the Terebellidae, they have been recently erected at the family level (DESBRUYERES & LAUBIER, 1986). The number of new species described has rapidly increased and reaches at
present nine species belonging to two genera : the genus Alvinella D. & L., 1980, comprising
two species, and the genus Paralvinelfa D. & L., 1982, comprising seven species or subspecies, plus another undescribed species. Except for P. hessleri D. & L., 1989, collected
in the Mariana trench hydrothermal field, all other species come from the East Pacific Rise, the Galapagos Ridge and the Juan de Fuca and Ex-plorer Ridges. One species lives in sediments percolated by hydrothermal fluids in the Guaymas Basin. Other species build honeycomb-like
masses of tubes, while some others settle on the parchment-like tubes of different
Vestimentiferan species. Alvinellids are unknown in non-hydrothermal deep-sea environments.
From a biogeographical point of view, the relationship between evolu-tionary trends,
phylogeny and distribution in Alvinellids is of a great interest. Pairs of sister species or
subspecies have been discovered North and South of the Oregon Subduction Zone
(DESBRUYERES & LAUBlER, 1986). One of them, P. pandorae pandorae and P. p. irlandei, differs from all other Alvinellids by the occurrence of uncinigerous rows in front of the
modified anterior segment. No simple relationship occurs in the other species of the family.
The recent dives of the submersible Nautile in July 1989 in the North Fijian Basin
during STARMER cruise made it possible to discover two new species of the genus
Paralvinella. Both have been collected on the White Lady hydrothermal site, at 2 000 meters
depth (16’59’50s and 173°5S’47W). One of these new species is related to the main stem of
Parafvinelfa species. On the other hand, the second species exhibits apomorphic features such
as flattened leaf-shaped secondary branchial filaments. This species is also characterized by the absence of secondary tooth of the uncini, which does not seem of phylogenetic significance.
19
Sediments of the North Fiji Basin
Jim V. EADE (SOPAC Technical Secretariat, Suva) and
M.R. GREGORY (Geology Department, University of Auckland)
Sediments of the North Fiji Basin are either calcareous pelagic material, or airborne
volcanic, and turbidity current material derived from the adjacent island arcs. The study is based
on a detailed examination of five piston cores which have sampled a continuous sedimentary
record of the past 0.8 my. Three cores are from the sediment covered, abyssal hill terrain in the central part of the Basin and two from an archipelagic apron (New Hebrides Apron) which
extends east from Vanuatu into the western part of the North Fiji Basin.
In the central part of the Basin calcareous pelagic oozes (nannofossil oozes) are the
predominent sediment. Volcanic glass is also common, occurring in a single ash bed in each core, in ashy intervals where glass is less than 50 %, and in pelagic ooze where it is persistantly
present as a few percent of the total sediment. From its physical and chemical characteristics the
glass appears to be mostly airfall ash, derived from the Central Chain volcanoes of the New
Hebrides Arc to the west. A westerly origin is supported by the existence of strong tropospheric
westerlies which dominate the structure of the atmosphere.
Bioturbation is moderate to intense throughout all the central Basin cores, the upper 5- 20 cm commonly being continually churned over. Only the thickest ashes (greater than 2 cm)
have survived this biological mixing moderately intact. Thinner ashes have either been partially
mixed with ooze to form an ashy interval, or completely mixed and lost as recognisable layers.
Three stratigraphic units are recognised in the central Basin cores. The middle unit, approximately 0.5 -0.25 my in age, has significantly more ash than the other two units and
represents a period of increased volcanic activity in Vanuatu. Sediment accumulation rates are as
low as 9 m/my for the ooze and has high as 20 m/my for the midle unit in one core where as well as ooze and ash there has also been some reworking of sediment from an adjacent
topographic high.
In the western part of the North Fiji Basin sediments are predominantly alternating
ashy pelagic ooze and volcaniclastic graded beds of the New Hebrides Apron. Sediment in the
graded beds was derived from shallow water along the eastern side of the New Hebrides Arc and transported by turbidity currents eastward into the western part of the North Fiji Basin.
20
ST’ARMERZ!$qmium,7-11 l33xuq 1991, ORSlDMCmter, Ncxma,New~
Petrology and Geochemistry of the North Fiji Basin Spreading Center Between 16”s and 22”s
Jean-Philippe EISSEN (GDR GEDO, ORSTOM Noumea), Masato NOHARA (GS J, Tsukaba),
Jo CO’ITEN (GDR GEDG, UBO Brest) and STARMER I scientific team
The North Fiji Basin (NFB) is a 12 MY old back arc basin which has a complex multi-stage history. The presently active spreading system can be divided into four segments between 16’S and 22’S which from N to S are successively N160, N15, N-S oriented segments located near 173’East. South of 21’S, a N-S segment is offset near 174’East. The N- S segment is morphologically similar to other medium-rate oceanic ridges, whereas the other segments have rougher morphologies, strongly perturbed by a triple junction at 16’45’s and several instability features as overlapping spreading centers (O.S.C.) and propagating rifts. Spreading rate seems to decline from 7.8 cm/y near 20’S to 4.6 cm/y near 18”s.
The petrogenesis of the basalts collected on 24 new stations located all along the four segments is essentially controlled by low pressure crystal fractionation of plagioclase >& olivine >& clinopyroxene with some 52% of the NFB basalts reaching the 4-phase cotectic. Locally some magma mixing occurs, limited to magma batches of closely related compositions, as might be expected to occur inside a magma reservoir.
The N-S segment, which is the only steady-state one since 3 MY, is also petrologically and geochemically very comparable to other medium-rate oceanic spreading centers, producing LILE- and LREE-depleted moderately evolved N-MORB.
In contrast, the three other segments produce basalts of much more variable petrology and geochemistry. They are characterized by LILE and LREE slightly enriched magmas of BABB affinity (but not as enriched as e.g. the Mariana BABB) although MORB are also found on the N160, N15, and 174E segments. Diagrams using Ba, Rb, K/P and (K/TQN (normalized
to the chondrites) plotted vs latitude clearly show along-strike variations. Beneath the recently formed segments, the mantle source is heterogeneous, and has locally some BABB affinities, whereas beneath the more steady-state N-S segment the magma source is more homogeneous, being generally depleted in LILE and REE as is the case for classical N-MORB mantle sources.
Furtherrmore, samples collected near 17’S (station 4) eather by dredging, deep towing or submersible Nautile (during the STARMER I cruise) exhibit, along this 20 km long, 4 km wide area studied in more detailed, a variability quite similar to the one observed along the entire N15 segment. This fact confirms the heterogeneous nature of the local upper mantle.
Evolution from an early stage of BABB production to MORB described in the Lau basin and proposed for the NFB does not seem to occur merely. Present day activity still produces large amounts of BABB along the less stable and more recently created segments, and MORB have been produced in earlier stages of the NFB development. But relative origin and relationship of N-MORB, BABB and/or E-MORB types of magmas present in the NFB still needs to state precisely as well geographically as during the NFB opening.
21
ORSIOM Fends Documentaire
N O g .,,34, as- 4)i 3 Co& 1 ‘# ’
Structural and Biochemical Characteristics of the Mussel
Bathymodiolus sp. from the Lau Basin (Southwest Pacific)
Aline FIALA-MEDIONI (C.N.R.S. Banyuls) ,V. PRANAL,
Jean GUEZENNEC ( IFREMER Brest), J.C. COLOMINES, and P. ALBERIC
The mussel Bathymodiolus sp. observed in dense populations in the Lau Basin was studied from samples collected during the BIOLAU cruise (1989, IFREMER), between 1750
and 1880 m. The ultrastructural analysis of the gill allows distinction of two kinds of mussels :
in “Hine Hina” site the mussels gills present one kind of symbiont (0.4-0.6 pm) similar to
those found in Bathymodiolus thermophilus from 13’N in the East Pacific Rise; in “Vailili Fields” site mussels, two types of bacteria are simultaneously present : same bacteria that found
in “Hine Hina” mussels (0.4-0.6 pm) but less abundant and larger ones (l-l.3 I.trn) also
surrounded by peribacterial membranes. A hemoautotrophic metabolism associated with the symbiosis is demonstrated by the
presence of Rubisco (RuBPCase) activities from 0.007 to 0.018 international units
(pmoles.mn-‘.g-’ fresh weight).
A common feature, unusual in the lipid composition of marine animals, is the absence
of polyinsaturated fatty acids C205w3 and C22:6w3 taken from phytoplancton or algae. This
confirms the independence of the food webs of these hydrothermal vents sites from the
photosynthetic production elaborated in the euphotic zone. The phospholipid composition demonstrates specific bacterial indicators with high
concentrations of the monounsatured palmitoleic acid C16:lw7. The percentage of
polyunsatured fatty acids with mean values of 32 +/- 6% is weak compared to the values obtained with littoral mussels (50 +/- 5%). The low diversity of fatty acids reflects the low
diversity of trophic sources and the predominance of bacyteria-bivalve symbiotic relationships.
Samples from “Vailili Fields” gave different results from other samples with lower
bacterial ratios.
The free aminoacids composition of the mantle and other organs (without gill and
mantle) is comparable to those of littoral molluscs. In contrast, gill tissues show high
concentrations of aminoacids whose composition is close to the bacterial type. Diaminopimelic
(DAP) and muramic acids, synthetized only by bacteria, have been demonstrated in the tissues
and could be used for estimation of the bacterial biomass associated with the gill.
22
Chemical Features of the Hot Waters Emitted at the White Lady Active Vents
Daniel GRIMAUD (UPME, Paris) and
Jun-Ishiro ISHIBASHI (Univ. of Tokyo)
Water samples of 285°C transparen fluid were collected using titanium syringes at the active vents located at 16’59’s in the axial graben. Measurements of non conservative parameters (pH and H2S) were completed within half an hour. Alkalinity and chloride concentration were performed on 0,45 um filtered aliquot of the sample within 1-2 hours. Samples were analysed, back to the lab, using atomic absorption spectrometry (cations), High Pressure Liquid Chromatography (anions) and calorimetry for silica. Isotopic dilution and mass spectrometry were used by A. Michard (CRPG Nancy) to determine Sr concentrations and 87Sr/s6Sr ratios. The 7 samples compositions range from some percents of hydrothermal water to nearly pure 285OC fluid. The element concentrations of the end-member were calculated assuming that Mg = 0 mmol/kg as well as sulfate in the pure end-member.
All the concentrations are among the lowest observed in any seafloor hydrothermal systems : Na and Cl concentration close to 210 and 255 mmol/kg are lower by 60 ok, from the sea water concentration; the alkaline earth have the lowest levels including the MARK system : Ca* (6.55 mmol/kg) is depleted by a factor of 1.5 and Sr++ (25 pmol/kg) is depleted by a factor of 3. These features could be explain by the removal from the solution by anhydrite precipitation at the time of mixing with sea water with high sulfate concentrations (28 mmol/kg).
Silica concentration (14 mmol/kg) is about 6-7 mmol/kg lower than for the other hydrothermal systems and the solution is undersaturated with respect to quartz at 340-35OOC. pH is < 4.7 and alkalinity should be zero or slightly negative.
Fe and Mn concentrations (lo- 15 pmol/kg and 12 pmol/kg are lower by a factor of at least 100 compared
with the waters of the other systems. These values, asociated with Mg* and Sod-- relatively high concentrations in the most depleted samples may originate from oxydation of millimolal concentrated hot water during the mixing with oxygenated bottom seawater in the upper part of the plumbing system of the vents. According with the 285°C output temperature and the linear relationship between Mg++ and Sod-- these low values prompted us to consider
that the 285’C fuid results from a mixing of about 15 ok, of sea water and 85 % of a 340-350°C parent endmember. The 87Sr/s6Sr ratios of the samples are in agreement with this hypothesis, assuming that the parent hydrothermal fluid have a 87SrS6Sr ratio close to the basalt ratio as for other known hydrothermal systems.
In spite of these low concentrations, the caracteristic elemental ratios K/Na+K (0.048), Ca/Sr (205-3 10) and the temperatures calculated using classical geothermometers Na-K-Ca (21O’C) and Na-Li (140°C) are close to the usual values which were found for the other seafloor hydrothermal systems. The constancy of these elemental ratios and calculated temperatures suggests that the subseafloor conditions are very similar at all of the sites studied and that the major cations would be controlled by a greenschist-type assemblage of minerals at temperature close to 340-350°C.
The low salinity of the NFB hydrothermal water could be explain by phase separation which would results in the formation of one vaporlike phase with lowered salinity and one liquidlike phase with increased salinity (a brine). Dissolved species would be depleted in the vapor but phase separation would not significantly modify the elemental ratios. That is what we observe in the NFB hydrothermal waters where the concentrations are very low and the concentration ratios quite similar comparing with EPR and MAR hydrothermal waters. So we can estimate that the NFB waters partly originate from the condensation of the vaporlike phase created during the transit somewhere below the seafloor. According with Von Damm 1988, we can conclude that the NFB hydrothermal waters could result of a three-component mixing including “normal” hydrothermal water, low salinity fluid from condensed vapor and brine. The last 285OC transparent NFB hydrothermal water would then originates from the mixing with bottom seawater in the last part of the plumbing system of the vent.
23
.
Visible Gold in Primary Polymetallic Sulfides from the Lau Back-Arc
Peter M. HERZIG (Inst. of Mineralogy & Eton. Geology, RWTH Aachen)
Yves FOUQUET (IFREMER, Brest)
Mark D. HANNINGTON (GSC, Ottawa) Uhich von STACKELBERG (BRG, Hannover)
Bulk chemical analyses of polymetallic sulfides recovered with the submersible
NAUTILE from the Valu Fa Ridge (22” 13’S) in the Lau back-arc have revealed gold contents of up 20.1 ppm Au. These samples contain the highest gold concentrations yet reported from
hydrothermal precipitates on the seafloor, and they are the first known examples of visible
primary gold in polymetallic sulfides at active vents. High contents of primary gold (up to 7 ppm Au) have previously been reported from black smoker deposits on the Juan de Fuca and
Mid-Atlantic ridges, but no discrete gold-bearing phases were identified.
On the Central Valu Fa Ridge (Vai Lili Hydrothermal Field, 1700 m depth), high gold values occur locally in unoxidized Zn-Ba-Si02 precipitates from the outer rim of some inactive
chimneys. The gold-rich chimneys were found close to active white smokers venting at 285 32OOC. The samples consist of massive, low-Fe (< 1.0 mol.% FeS) sphalerite (40%), barite
(35%), and opaline silica (lo%), with disseminated chalcopyrite (5%) and tennantite (5%), and
minor pyrite and galena. Numerous grains of native gold (< 10 wt% Ag) are also clearly visible
at a magnification of 500x in polished specimens from two samples containing 20.1 and
12.9 ppm Au. The gold grains are apparent colloidal aggregates (SEM) and range in size from
1 to 5 microns. They occur as inclusions in massive sphalerite (70%), at grain boundaries between sphalerite / chalcopyrite / tennantite (15%), and as inclusions in disseminated
chalcopyrite and tennantite (15%). The average gold content for analyses of bulk sulfides from the Valu Fa Ridge, including Fe-rich, Cu-rich, and gold-bearing Zn-rich samples (n = 54) is
2.8 ppm Au with a median value of 2.1 ppm Au.
The identification of a gold phase within primary polymetallic sulfides confirms that
gold can occur as a discrete mineral and not simply as a trace element within the sulfides or absorbed onto sulfide surfaces. High gold grades in Zn-Ba-SiO;! samples associated with
tennantite and galena appear to be consistent with recent solubility models explaining the late- stage enrichment of gold with low-temperature (c 3OOOC) mineral assemblages due to oxidation
of Au(HS&-.
24
.
Biogeography of Mariana Trough Hydrothermal Vent Communities
Robert R. HESSLER
and
Peter F. LONSDALE
(Scripps Institution of Oceanography, La Jolla)
Although the Mariana Trough contains a spreading center geographically isolated from the global mid-ocean ridge system, 59% of the 27 identified Mariana vent species (out of a total 30 - 3 1 species) demonstrate interchange with the fauna of mid-ocean ridge vents.
Other western Pacific back-arc spreading centers harbor vent communities, and
preliminary evidence indicates the likelihood that there has been dispersal within this back-arc
complex.
.
A gap of 7600 km separates the western Pacific complex from the Juan de Fuca Ridge to the north and 3200 km from the Southeast Indian Ridge to the south. Past gaps have been
narrower, and two now-extinct portions of the mid-ocean ridge system would have allowed
comparatively easy interchange 43 and 55 millions years ago.
Hydrothermal vents at isolated volcanoes, cold-water seeps and rotting whale carcasses are also potential “stepping stones” that might bridge larger gaps; however, there is
little information to document the degree of their importance.
25
Spreading in the Backarc Basin
Eiichi HONZA (GSJ, Tsukuba)
Spreading of a backarc basin seems to occur originally along the volcanic chain or
immediately backarc side of the chain. This is illustrated in the original formations of backarc troughs in many arcs along the western Pacific rim, especially in the formation of backarc
depressions in the Bonin Arc which are geomorphologically traced to the southern Mariana Trough.
Volcanic chain seems to be association with subduction under the arc. However later phase
spreading in the backarc basin seems to be not controlled by the arc volcanism. This is well
illustrated in the North Fiji and West Philippine Basins. Therefore there may be two process to form
a backarc basin. The first is the formation of backarc rifting along the volcanic chain. The second is convection current inside backarc basin for spreading.
For the formation of backarc basin, there may be associated with tensional field in the arc
area. The tensional field may be formed by distortion of major plates movements or upwelling in a
hot region. This is possibly the first order’condition for the formation of a backarc basin. The
second may be the formation of the subduction under the arc which causes upwelling in the volcanic chain and following rifting to form backarc basin. If there is no subducting slab where the tensional
field is formed, normal spreading is hard to form as is observed in the initial rifting of continents.
This suggests that the initial backarc rifting is also formed by a small convection current in the backarc side. Once it was formed, the second phase convection is easily rearranged to form backarc
basin.
26
Kinematics of the Active Opening of the North Fiji Basin from Magnetic and Structural Data
Philippe HUCHON (Ecole Nor-male SupCrieure, Paris), Etienne RUELLAN (C.N.R.S, Nice -
Sophia Antipolis), Jean-Marie AUZENDE (GDR GEDO IFREMER, Brest), Yves LAFOY (MRD, Fiji), and Yves LAGABRIELLE (GRD GEDO, UBO-CNRS, Brest).
Kinematics of the north-south trending accreting plate boundary in the North Fiji basin
was examined using magnetic and structural data obtained during ORSTOM and IFREMER cruises as well as during the STARMER project (Kaiyo 87,88 and 89 cruises).
Magnetic data processing includes an attempt to remove discrepancies between various data sources, most especially important at track crossings. This processing was done in order to
avoid systematic biases which would induce possible mislocation of magnetic lineations. It has
been performed using various techniques (Fourier filtering, least-squares minimization, kriging . . . ).
Identification of individual magnetic anomalies has been obtained by direct modeling using a FFI algorithm. Identification of magnetic lineations has been controlled using structural
data. Such an identification provides, in turn, a control on the location of active and fossil ridge
segments and of particular features such as offsets and propagators. The resulting magnetic lineation map shows evidences for complex, although minor, reorganizations such as ridge
jumps and propagators, which would correlate with the activity of the North Fiji Fracture Zone.
Finally, an attempt will be presented to reconstruct the detailled evolution of the North Fiji basin rift system during Plio-Quaternary. Its causes and consequences will be discussed
with respect to the plate kinematics at a regional scale, the North Fiji basin being considered as a
large left-lateral pull-apart basin sandwiched between the Pacific and Australian plates.
27
Tectonics in the Central Axis Area of North Fiji Basin as Derived from Precise Bottom Topography
Yo IWABUSHI (JHD), Takeshi MATSUMOTO (JAMSTEC), and Tadahiko KATSURA (JHD)
Precise sea bottom survey has been conducted under the cooperative research program
“STARMER” between Japan and France, from 1987 to 1989 by the R/V KAIYO. One of the
purpose of the survey is geomorphological research of the North Fiji basin (NFB). The survey was carried out with multi-narrow-beam echo sounder, and differential GPS method was used for
positioning throughout all cruises, KAIYO 87, 88 and 89. Before the survey, French research
program “SEAPSO 3” was conducted in 1985. Multi-narrow-beam echo sounding data of the three
boxes and zig-zag lines were acquired in the NFB.
The precise topographic maps in the central axis of the NFB were drawn from the data of KAIYO 87,88 and 89 and SEAPSO 3 cruises. These maps show some geomorphological features
of the rift systems. Triple junction of rift systems, overlapping spreading center and rift propagation were admitted in the axial area of the basin. The southern rift on the triple junction can be divided
into several segments whose length are about 100 km to 150 km. Rift propagation suggests the
spreading rate changes between the each segment. The triple junction and its adjacent area is one of
the shallowest areas in the basin, because there are some topographic highs. Considering the
topographic features these topographic highs can be restored as one block. Later, this one block
might be split into several topographic highs by the activities of the central rifts. This hypothesis
leads that the area had thick and old crust. Because of thick crust, spreading rate of the triple junction and its adjacent area are shallower than that of the southern rift. Therefore, the central rift is
propagating from south to north. Spreading late and direction of ocean floor spreading in the NFB
may be sensitive to the relative motion changes between two giant plates, the Pacific plate and the Australia-India plate. Because, the gap between two giant plates is filled up by the growth of north
Fiji micro plate. Segmentation of central rift of the NFB, at least in the past may suggest not only the
size of magma chamber but also the relative motion changes between the Pacific plate and the
Australia-India plate.
28
Heat flow measurement and magnetic anomalies in the North Fiji Basin
Masato JOSHIMA (GSJ, Tsukuba)
Data sets of aeromagnetic survey are the most common in the North Fiji Basin due to its broad coverage. Marine magnetic surveys were done by French and Japanese vessels from 1985
mainly around the central ridge axis, whose cruises were named as SEAPSO 3, KAIYO 87, KAIYO 88 and KAIYO 89. We have studied mainly these marine magnetic data corrected in the
Japan-France cooperative study in the North Fiji Basin and compared our results with those of
aeromagnetic ones. The difference should be due to the accuracy of positionings.
The main feature is the central high lineation which continues from Latitude 22’S to 16’s. The positive anomaly line shifts from Longitude 174’1O’E between 22 to 21’S, to 173’3O’E between
21 to 18’S, and finally changes the direction from S-N to SSW-NNE and makes T shape at the triple junction area. And it also continues northward, changing its width to much narrower and direction to SSE-NNW. According to these magnetic and topographic patterns the central high anomalies can be
divided into the above mentioned 4 blocks, hereafter named A, B, C, and D, respectively.
The northernmost SSE-NNW trending depressed area, A area, has negative anomaly
around the deepest area and it may mean the area had been produced at Matuyama epoch and reversely magnetized.
The area B has SSW-NNE trending lineation and it becomes broader to the south and looks
like a fan shape, but topographically not so fan shape like. The apparent topographical center goes to
the southern direction and encounters to the magnetic low at the eastern edge of the broad positive lineation.
The area C has almost S-N direction of central topographic high and north to south
enlarging fan shape like positive magnetic anomaly and northernmost part, where fan shape like
topography exists and spire like shaped topography s visible, shows rather high anomaly and it may
be caused by edge effect of the lineation.
The area D has a N-S directional topographical depression in the broad topographic high
and it corresponds to positive magnetic high.
In C and D area the central broad positive magnetic high has negative anomaly in the midst
part, which may be caused by hydrothermal effect which acts on the magnetic mineral and depress
the intensity.
Between these blocks there exists a short lineation of SW-NE trending, which may have some relation to transform fault which seems to have strong linear anomaly sometimes.
29
Crustal Structure along the Rift Axis of NFB
Kiyoyuki KISIMOTO (GSJ, Tsukuba), Takanobu YOKORURA (GSJ, Tsukuba), Manabu TANAHASHI (GSJ, Tsukuba), and Yves LAFOY (MRD, Suva)
Extensive bathymetric surveys done by multi-narrow-beam echo sounder, SEAPSO 3 and
KAIYO cruises, have revealed the clear accretionary topographical structure in the axial domain of
North Fiji Basin. Seismic reflection and refraction survey have been also conducted along and
across the axial areas in the region to clarify the deeper geological structure and its evolutional
mechanism. During the cruises of KAIYO 87 and KAIYO 88, multichannel seismic reflection
survey (MCS) and refraction seismic survey using sonobuoys and OBS’s (Ocean Bottom Seismometers) have been carried out in the selected axial areas. Seismic reflection profiles obtained by MCS method show little or lack of sedimentary layers in the axial domain indicating the existence
of very young oceanic crustal layers with few sediments. Even from the MCS profiles, subbottom
geological structure is not clear along the central axial area because of the high reflectivity at the sea
bottom and partly because of the less differentiation in the layers. Although sporadical discontinuous
strong reflectors can be seen on the processed profile along the axis, it is difficult to tell whether they are reflection events from low-velocity-layer boundary, e.g. top of the magma chamber, or simply
topographical effects, such as side echo.
Several seismic refraction stations were chosen along with the MCS lines. During
KANO 87 cruise, useful refraction data were obtained at two sonobuoy stations in the N15 trend
axial segment (between latitudes of 17’S and 17’35’s). In 1988, two OBS’s were deployed as well
as expendable sonobuoys near the Station 14 (18’50’s - 173’3O’E). Features of reduced crustal
velocity structures along the axial area in the central NFB are;
(1) In the northern part of the axis (KAIYO 87 data), thickness of the sedimental layer is
very thin if any and quite high velocity layer (4.3km/s - 4.9km/s) can be recognized at rather shallow depth (less than 1 km). This feature can also be seen at nearby crustal velocity data compiled by Larue et al., 1982. Moho phase cannot be recorded in 1987 cruise.
(2) On the other hand, both sonobuoy and OBS records obtained in KAIYO 88 cruise
show clear refraction phase from Moho boundary (7.7km/s - 7.9km/s). Estimated depth of Moho
from the sea bottom is less than 3 km. No sedimentary layer was discernible from sonobuoy data.
30
Rift propagation in the North Fiji Basin :
Evolution of the Fiji Fracture Zone
Loren W. KROENKE (HIG, Hawaii), and Philip A. JARVIS (HIG, Hawaii).
SeaMARC II imagery and bathymetry together with recently acquired GLORIA
imagery of the Fiji Fracture Zone (FFZ) reveals the structure of the fracture zone adjacent to the
Fiji Platform. Along most of its length, The FFZ is an east-west trending sinistral,
transtensional transform fault which runs from the northern Lau Basin across the northern end of the Fiji Platform into the North Fiji Basin. Left-stepping offsets occurring along the trace of
the fault result in realy zones, or pull-apart basins, containing short spreading centers. These spreading centers are characterized by recent basalt effusion and magnetic anomalies over their axes. North and west of the active transform fault are the Balmoral and Braemar Ridges rising
more than 2000 m above average depth of the basin. These ridges are postulated to be
fragments of the Fiji Platform separated from it by jumps in the location of the transform fault.
There is no evidence, however, that the fault is currently active in this area. Seismicity farther
west is believed to be related to eastward propagation of the Central North Fiji Triple Junction.
31
A 800 m Thick Section of Upper Oceanic Crust in the North Fiji Basin (NFB) ; Results of
Nautile Dive No 7 of the STARMER I Cruise
Yves LAGABRIELLE (CNRS UBO Brest, GDR GEDO), Jean-Marie AUZENDE (IFREMER Brest, GDR GEDO)
and Jean-Philippe EISSEN (ORSTOM Nourn& GDR GEDO)
One of the objectives of the STARMER I Cruise of the french submersible Nautile in
the NFB was the geological and structural study of a triangular shaped deep basin located along
the eastern arm of the 17’S - 174’E triple junction, in the central part of the basin. This flat-
floored trough is thought to represent an eastward propagating rift with a typical V shaped apex
developed in the western end of the North Fiji Fracture Zone. The northern boundary of the
basin is a N60 trending, 1200 m high, steep wall.
Dive no 7 allowed a complete survey of the northern wall of the triangular basin, providing a remarkably complete section. Oceanic crust is exposed almost continuously from
2600 m to 1800 m depth. The dive started at 2880 m along a steep talus located at the base of
the wall. From 2600 m to 2040 m, we observed a succession of 100 m high vertical cliffs,
separated by steep slopes dusted with pelagic sediments or covered with talus. A succession of
large plateaus and smaller scarps occur from 2040 m to 1800 m.
Outcrops are composed of basaltic formations including pillowed and massive lavas as well as spectacular prismatic massive lava observed at different levels along the basal part of the section. Sheeted dikes (1 m thick) arc present from 2260 m to 2210 m depth. Despite a slight
alteration, three units can be petro-chemically distinguished in this section : the lower one
(samples 7-l and 7-2) consists of relatively unevolved typical N-MORB; the middle one
(samples 7-4, 7-5, 7-6, and 7-7) is made of unevolved to evolved basalts, showing a slight
enrichment in incompatible elements, which could be related to BABB type of lavas; the upper
one (sample 7-8) is again a more typical N-MORB. This North Fiji Basin upper crust section
seems to indicate that the type of geochemical heterogeneities observed along the North Fiji
Basin spreading center has also been variable through time.
Tectonic features observed during the dive include vertical fault breccias, tight
cleavages within massive lavas, fresh section of pillows and folding of the sedimentary cover
exposed on top of the upper plateaus. All these features clearly confirm that the northern wall of the eastern basin of the triple junction is a major normal (strike slip ?) fault scarp with at least a
1000 m vertical offset.
oiwofvi Fonds Documentai@,
_’ N” ,: 94 . d’i36 AC 3
Cote : A 32
Magmatic and Tectonic Activities in the Jean-Charcot Trough (Northern Vanuatu Rear-Arc). Results of the STARMER/KAIYO 89 Cruise
Patrick MAILLET (ORSTOM, La Trobe), Etienne RUELLAN (CNRS, Nice-Sophia),
Tetsuro URABE (GSJ, Tsukuba), and the KAIYO 89 scientific crew
The Jean-Charcot trough (JCT) is a N-S trending rear-arc basin located in the northern part of the
Vanuatu arc-trench system. The JCT, and its southern counterpart, the Coriolis trough (CT), have been
extensively studied since the SEAPSO 2 cruise (1985). Structural and geophysical data show that both
troughs (JCT and CT) correspond to extensional structures emplaced on the Vanuatu arc substratum.
Petrological studies of dredged samples (from the flanks of the troughs or from isolated volcanic cones on
the trough bottoms) emphasize a general arc-related affinity for most samples. K-Ar ages of volcanics may
vary from south (CT) to north (JCT). However, most of the dredged volcanics have been emplaced during
the last 5 Ma.
During the KAIYO 89 cruise (Dec. 1989 - Jan. 1990), a complementary detailed survey of the JCT
has been added to the two areas previously studied during the SEAPSO 2 cruise (i.e. the “Vanikoro” and
“Vot Tande” areas). With these new data from the so-called “Tikopia” area, we now have a ca. 50%
seabeam coverage of the whole JCT, from 12o1O’S to 13’25’s. Besides, single-channel seismic surveys,
deep-tow camera observations (5 surveys), dredgings (6 dredging sites), corings and heat-flow
measurements (5 sites), and hydrocasts (5 stations) were also conducted during the KAIYO 89 cruise.
Although data from this cruise are still being processed, some results can be emphasized.
1) The JCT (including from north to south the Vanikoro, Tikopia, and Vot Tande areas) is composed
of a succession of small troughs, ridges and knolls, showing a general N-S topographic trend. A N45’E
trend appearing in the central JCT may mark a regional right-lateral strike-slip accident, with a displacement
of ca. 3-4 km. 2) We found no direct evidence of active spreading in the JCT. However, a distinct methane (CH,)
anomaly was recorded in the northern JCT (Vanikoro area; station 31: 12O12.50 S; 167’38.77 E), at a depth of about 1200 m (the trough bottom being at 1617 m at that station). This CH, anomaly, unaccompanied
with any temperature anomaly, likely originates from an hydrothermal plume. Deep-tow surveys, however,
did not show any evidence of such an active hydrothermalism.
3) Strong magnetic anomalies recorded in the JCT usually correspond to young isolated seamounts
(some of them as young as 0.3 Ma). The lack of strong anomalies in the central part of the JCT is likely due to the complexity of the structural pattern of the JCT.
4) Preliminary petrological data from dredged samples confirm the results of the SEAPSO 2 cruise:
basalts, andesites, and dacites show petrographic and geochemical characteristics which are typical of an
island arc environment.
Therefore, the JCT is not a classical active back-arc basin. It rather corresponds to a complex
extensional structure, which formed between the Vanuatu island arc and the active North Fiji Basin. The
JCT presently displays active tectonism and seismicity, whereas mainly arc-related volcanic activity ceased
only very recently (less than 0.3 Ma). The formation of the Jean-Charcot trough likely reflects a reajustment
in the regional stress regime, induced by antagonistic forces, i.e. subduction (along the Vanuatu arc) and
spreading (in the North Fiji Basin).
33
SURMERSympium,7-11 l%bruq 1991,0l?SIOM~~, Notmm,NewCaledonia
Tectonics in the Northern Part of Vanuatu Back-arc Basin as Derived from Precise Bottom Topography
Takeshi MATSUMOTO (JAMSTEC)
and Yo IWABUCHI (JHD)
The Jean-Charcot Trough is a back-arc basin situated in the northern part of the Vanuatu
arc-trench system. It is located at 12’S - 13’3O’S, 167’3O’E - 168’1O’E. This trough is divided
into two parts, the eastern trough and the western trough. They are separated by a 167’3O’E ridge which is the northern extension of the islands of Mota Lava and Vot Tande. The northern
and southern borders of the trough were surveyed during the SEAPSO 2 Cruise in 1985, and were subsequently named the “Vanikoro Box” and the “Vot Tande Box” respectively.
During the KAIYO 89 Cruise, a SEABEAM survey was conducted along the E-W
tracks in the eastern part of the trough to make a complementary topographic map together with data obtained from SEAPSO 2 Cruise. The surveyed area was named “Tikopia Box”.
Topographic map and gradient map thus obtained shows that the survey area is
character&d by four major strikes of structure. They are:
(1) N-S: The N-S structure is dominant in the central part of the survey area, around 12o4O’S, where it is characterized by rather flat bottom topography.
(2) N20’E: This structure is limited to the eastern part of the area between latitudes 13’S
- 12O2O’S. At the southernmost part of the survey area (12’55’S, 167’5O’E), the structure overrides the N-S structure.
(3) N30°-45’W: This trend cuts the N20°E structure at l2o5O’S, 167’55’E and cuts the
N-S structure at 12’2O’N, 167’52’E.
(4) N45’E: The N45’E structure is recognized from 12’55’S, 167’4O’E to 12’25’S,
168’1O’E and completely bifurcates the Jean Charcot Trough area. This structure
is considered to be a large-scale right lateral fault, and its displacement is about 3- 4 km. Some other smaller right lateral faults are also lacated throughout the
entire survey area.
Hazel Holme Fracture Zone, placed just south of the survey area presents a large-scale left lateral fault. The area south of HI-IF2 is affected by the collision of d’Entrecasteaux Ridge
from the west beyond the New Hebrides Trench, then the direction of maximum compression
axis is E-W. The area north of I-IHFZ has the tention axis of N-S direction according to the existence of the right lateral fault found in the cruise. This agrees well with the result of the
regional focal mechanisms and seismicity observed around the survey area.
34
Gravity Anomalies and Sub-bottom Structures in the North Fiji Basin
Takeshi MATSUMOTO (JAMSTEC)
Satellite altimetry data such as GEOS-3, SEASAT and GEOSAT provides informations on the marine geoid in equal density of observation, so they are quite useful to complement the conventional surface ship gravimetry. Several methods of conversion from geoid to gravity are
presented and applied to these altimetry data. A gravity map of the world ocean thus compiled by Segawa and Matsumoto (1987) covers the NFB area. This map is derived from altimetric
geoid data of SEASAT and GEOS-3. Recently GEOSAT altimetric data became available. The
precise periodicity of the GEOSAT data, as compared to the SEASAT data, has resulted in increased accuracy of analysis.
The author recalculated the altimetric gravity distribution of NFB by use of GEOS-3, SEASAT and GEOSAT data. In this article, the author would like to discuss the characteristics of the gravity distribution, estimate the thickness anomalies of the lithosphere below NFB
together with the seismic refraction survey data, and discuss the tectonic structures of NFB from
the viewpoint of gravity anomalies. ’
The whole area of the NFB presents positive free air anomalies of several tens of
milligals. This is the same characteristics as those of the typical back arc basins such as
Philippine Sea, Japan Sea, Manus Basin and so forth.
Anomaly values become maximum near the island arc of New Hebrides, and go up to
about 100 mgal. This distribution is considered to be due to the gravity effect of the subducting slab of the New Hebrides Trench. The area of the free air anomaly value greater than +50 mgal
is wider towards the south, corresponding to the slab angle estimated by seismicity.
On the other hand, in this area, a seismic refraction survey has been carried out by
ORSTOM, and some results show the sub-bottom structure up to the Moho surface (Lame et al., 1982). According to this result, the oceanic crust is thinner in the NFB than that of the
surrounding oceanic area. At the point where gravity and crustai structure up to the Moho,
Residual Gravity Anomaly (RGA) can be calculated and the thickness anomaly can be estimated using RGA if the relation between density and P wave velocity is assumed. RGA shows the
shape of tire boundary between lithosphere and asthenosphere.
The whole area of NFB presents RGA values lower than that of the surrounding ocean, such as the Pacific and the South Fiji Basin. This means that the lithosphere of the whole NFB is a few tens of kilometers thinner than that of the surrounding ocean and suggests the opening of the basin. In NFB, the RGA values tends to decrease towards the central spreading axis running at N-S direction, so those values express that the lithosphere thickens apart from the central
spreading axis.
35
Deployment of Stationary Sea Floor Observation System
Kyohiko MITSUZAWA, Kiyoshi OHTSUKA, Hiroyasu MOMMA,
Hiroshi HOTTA and Deep Sea Research Group*
(JAMSTEC)
Recently, we obtained interesting results about deep sea phenomena from real-time
observations using manned research submersible, ROV and deep tow surveys. However some
deep sea phenomena show sporadic changes such as transportation of submarine deposits with
turbidity current, submarine volcanic activities, appearance and disappearance of biological
communities depending on hydrothermal activities, earthquake, etc. It is difficult to observe
these sporadic phenomena using the above mentioned survey techniques. We need long term observations to investigate changes over time of deep sea phenomena on a fixed point.
Therefore, we developed two kinds of stationary observation systems that collect visual
information about the deep sea floor. Each type composes of an open frame with a deep sea still
camera and strobe, a current meter, a CTD sensor, an acoustic transponder with releaser and
glass spherical buoys. One system, deployed by means of free fall from the surface, was located
in the Suruga Trough, central Japan to observe time change of ripple marks on the seafloor caused by bottom current at a depth of 1975 meters. Another system is attached under the deep
tow camera frame and is carried until an appropriate deployment location is found. This system was deployed at Station 4 in the North Fiji Basin at a depth of 1990 meters and within cold seep
communities in Sagami Bay, central Japan at a depth of 1060 meters.
In the hydrothermal active area of the North Fiji Basin, the stationary observation
system was used two times while “KAIYO 88” and “KAIYO 89” cruises to observe time
changes of hydrothermal activity and biological communities, it was called “LHOS (Long-term
Hydrothermalism Observation System)“.
In this report, we present how to develop and manage the stationary observation
systems.
* Deep Sea Research Group: Jun HASHIMOTO, Takeshi MATSUMOTO,
Takeo TANAKA, Jiro NAKA, and Katsunori FUJIKURA
36
Deep Tow Surveys to Search for Hydrothermal Activities in the North Fiji Basin Rift Axis
Hiroyasu MOMMA, Takeo TANAKA, Jun HASHIMOTO, Hiroshi HOTTA and Deep Sea Research Group* (JAMSTEC)
1. Introduction
During the last three years, between 1987 and 1989, joint sea floor surveys with Japan
and France (STARMER) were conducted by R/V KAIYO in the North Fiji Basin. It was one of
the main targets of the STARMER project to search for the hydrothermal activity. Systematic surveys with Sea Beam, water sampling and JAMSTEC / Deep Tow sonar and camera were carried out all along the rift axis.
Sampling for water chemistry, to detect methane and manganese anomalies in the sea
water, was conducted prior to deep tow survey to determine the most likely area where
hydrothermal activity could be found.
2. Deep Tow Surveys in 1987 and 1988
In 1987, deep tow surveys were carried out at three stations (Stations 4, 6 and 6), where large methane or manganese anomaly in the sea water was detected by water sampling. At every station, a l:lO.OOO scale Sea Beam map was produced within three or four miles square.
Among these stations, hydrothermalism and associated biological community were discovered at
Station 4 to the south of the triple junction, which was located at 16’59’s and 173’55’E. A
temperature anomaly of 0.2OC was detected at the vent site 2 m above the sea floor. There were
several indications of hydrothermalism at Station 4, such as yellow or reddish stains of
sediments, scattered dead shells etc. In 1988, deep tow surveys were carried out at stations 4, 14 and 22 (Stations 4, 14 and
22). During reconnaisance survey to search for the site to deploy a long-term observatory
(LHOS) at Station 4, the deep tow camera passed directry over the venting chimney. Other
hydrothermal activity was discovered at Station 14 (approximately 18o5O’S and 17’3O’E), where
the largest methane and manganese anomalies in the sea water were detected along the rift axis.
The sea floor at Station 14 was flat and covered by very fresh sheet flow lava with a glassy surface. This was quite different from Station 4, where the sea floor was covered by sediments.
A large community of giant clams was discovered in the collapsed pit with a temperature
anomaly of 0. l°C.
3 Summarv .
Systematic surveys with Sea Beam, water sampling and deep tow resulted in the first discovery of hydrothermalism in the North Fiji Basin. Also, this lead to the successful dives with French submersible “Nautile” and Japanese deep ROV “Dolphin 3K”.
* Deep Sea Research Group: Kiyoshi OHTSUKA, Takeshi MATSUMOTO,
Jiro NAKA, Kyohiko MITSUZAWA and Katsunori FUJIKURA
37
A Sulfur Bacterium, NFB04, from a Hydrothermal Pluhe in the North Fiji Basin
Takeshi NAGANUMA (JAMSTEC)
and Humitake SEKI (University of Tsukuba)
Sulfur bacteria make up the major group of organisms that chemosynthetically support the dense biological communities at hydrothermal vent areas. We recovered a sulfur bacterial
species from hydrothermal plume water in the North Fiji Basin (Station 04). The sulfur bacterium, NFB04, is a gram-negative motile rod, forming yellowish white colonies on both
inorganic and organic media. These characteristics tentatively suggest the NEB04 to be a species
of Thiobucillux Other characteristics, e.g. oxidative/fermentative growth and oxidase activity,
were examined for classifying the NEB04 in detail.
Growth response of NFB04 against temperature, salinity and pressure was investigated. The NFB04 showed a mesophilic and moderately halophilic growth with the maximum at 30 C and 30% salinity. The growth rates at 1 and 200 atm were almost equal, showing moderately barophilic or barotolerant nature. These physiological characteristics are possibly advantageous
for inhabiting deep-sea hydrothermal vent areas.
During the cultivation of NFB04, bacterial cells attached to each other and built up in
chains. The chains further connected and resulted in network-like formation. The networks then aggregated in bacterial clusters. The formation of such networks and clusters would greatly
facilitate the ingestion by filter-feeding animals. This suggests free-living bacteria, like NFB04,
in plume waters could make much more of a contribution to the hydrothermal food-chains than
previously expected.
38
Stationary Sea Floor Observation around the Hydrothermal Area in the North Fiji Basin
Jim NAKA, Kyohiko MITSUZAWA, Takeshi MATSUMOTO, Take0 TANAKA,
Katsunori FUJIKUBA, Jun HASHIMOTO, Hiroyasu MOMMA and Hiroshi HOTI’A
(JAMSTEC)
During the KAIYO 87 cruise, a hydrothermal vent field and biological community were discovered in the central graben of the North Fiji rift system (16”59S’S, 173’53.8’E, 1970 m)
by JAMSTEC Deep Tow camera survey. During the KAIYO 88 and KAIYO 89 cruise, after conformation of the existence of the hydrothermal area, we deployed the Long term Hyrothermalism Obsevation System (LHOS) at the hydrothermal area about 20 days for each
cruise (KAIYO 88 data were not complete because of the trouble of current meter). LHOS was
composed of a deep sea steel camera and strobe, a self memoried CID, a self memoried electromagnetic current meter and an acoustic transponder.
In the first leg of KAIYO 89 cruise, we observed the bottom feature around LHOS
deployment site by Deep Tow camera prior to the LHOS deployment. The dominant bottom
materials were sheet and pillow lava which were thinly covered with pelagic sediments. In the
sheet flow area 2 to 5 meter deep depressions which thought to be collapsed lava lake was observed. Hydrothermal biological communities were distributed inside this depression. LHOS
was deployed in the depression within communies area which occupied 5 to 10 square meter
(16’59.45’S, 173’54.92’E). A 2 or 3 meter hight standing chimney, shimmering water on the sea bottom and about a one degree sea water temparature anomoly were observed by Deep Tow
camera at this deployment site.
LHOS photographed the foot of the chimney, biological community and white colored
deposit around it. Tiny white colored suspended material which were probably discharged from
a crack in the sea bottom were recorded in a photos. LHOS CTD recorded about l°C sea
temperature anomaly during about 12 intervals. These intervals were correlated with the tidal
northward current by earth tide which was recorded by the current meter, and thus do not
indicate a change of hydrothermal activity. Because the anomaly was so clearly defined, the hot water source was probably close to LHOS, perhaps standing chimney. The amplitude of the
anomaly is comparatively constant, therefore, the hydrothermal activity of this source was stable
during the observation period.
39
Isotopic and Geochemical Characteristics of Basalts from the Spreading Center in the North Fiji Basin
Masato NOHARA (GS J, Tsukuba), Jean-Philippe EISSEN (GDR GEDG, ORSTOM Noumea),
Tetsuro URABE (GSJ, Tsukuba), and Masato JOSHIMA (GSJ, Tsukuba)
The Sr, Nd and trace elements were analyzed for porphyric and aphyric basalts from
the active spreading axis in the North Fiji Basin (NFB). *7Sr/%r ratios vary from 0.7028 to
0.7034, whereas 14sNd/t44Nd ratios cover a small range from 0.51286 to 0.51316 which fall within the cluster of the N-type MORB. The average abundance of Y is 27 ppm which is the
range of N-MORB (17 to 37 ppm), while Zr concentrations (60 to 150 ppm) are slightly
higher than those of N-MORB. The isotopic data show that the NFB spreading axial area has
reached a mature stage remarkably similar to the mid-oceanic ridges.
The Sr, Nd isotopic and rare earth data for basahs from the triple junction (16’48’S, 17’4O’E) suggest that they are less fractionated and more primitive, as being results of injection
of a mantle plume or hotspot component.
In spite of a large-scale isotope homogeneity in the NFB, small but distinct variations
occur in the NFB basalts at a regional scales of several kilometers to several tens of kilometers.
The spreading axial ridge of the NFB is a least divided into three to four isotopic domains
which imply that large scale magma chambers do not occur beneath the NFB.
Hydrothermal plumes observed in the Nor@ Fiji Basin
Yukihiro NOJIRI (Natl. Inst. Environ. Stud.)
and Jun-ichiro ISHIBASHI (Univ. Tokyo)
Emanation of hydrothermal fluid transports heat and chemical components from the
magmatic source beneath the ocean ridge spreading axis into the deep ocean. Water column
survey, including CTD measurements and chemical analysis, is an efficient way to detect the vent activity on board ship. In STARMER Japanese-French cooperative survey cruises for the North Fiji Basin (NFB), we carried out hydrocasts to discover the ocean bottom hydrothermalism. Along the spreading axis, hydrothermal plumes having anomalies of temperature, manganese and
methane were observed.
First, we will report the recent development of chemical analysis for components related
to hydrothermal activity as manganese and methane. An onboard analyzing system of methane in
seawater sample was developed. Dissolved methane is purged out, trapped on cooled activated
charcoal, and determined with FID-GC. The .operation is fully automated with a micro computer. A hydrothermal plume in the Vanuatu back-arc trough was detected on board in ‘Kaiyo 89’
cruise.
The characteristics of hydrothermal plumes observed in the NEB are discussed in
respect of heat, manganese and methane flux ratios. The gigantic hydrothermal plume with large
temperature anomaly was discovered at station 14 in the central NEB during ‘Kaiyo 87’ cruise,
which showed the nature of ‘megaplume’ first observed in the Juan de Fuca Ridge. The plume had disappeared at the time of the next year cruise, suggesting the discontinuous emission of
hydrothermal fluid. The plume observed in the Vanuatu back-arc trough had an extremely high
methane / manganese ratio compared with those observed in the central NEB. The methane /
manganese ratio of 8 was similar with that observed in the Okinawa back-arc trough, having
analogous geological condition.
41
Comparison and Some EcoIogical Notes on the Hydrothermal Vent Communities of the Southwestern and Western Pacific
Suguru OHTA (ORI, Tokyo), Jun HASHIMOTO (JAMSTEC),
Daniel DESBRUYERES (IFREMER, Brest), Hitoshi SAKAI (ORI, Tokyo)
and KH-90-3 Cruise members
During the past few years we have got rather good sets of information on hydrothermal vents
and associated communities in the Western and Southwestern Pacific to pursue the global-scale
comparison and characterization of hydrothermal vents and biological communities in those regions.
Based on several explorations, preliminary categorization of the hydrothermal vents and brief summary
of the zoogeographical distribution of representative vent-specific organisms can be drawn.
“White Lady Chimney” at Station 4 (ca. 2000 m deep) in the North Fiji Basin now emits clear
water and consists of anhydrite chimney: dominant associated organisms are gastropods (Alviniconcha
and trochids), Bathymodiolid mussels and ancestral form of balanomorph cirripeds. “Mussels Valley”
at Station 14 (ca. 2600 m) is characterized by cleft emissions and filled with Bathymodiolus-
consociation. Occurrence of vestimentiferans and myriothrochid holothurians is noteworthy.
Vents in the Mariana Backarc Basin are rather deep 3600 m and emit 28OOC clear water, and are
characterized by pyrite-chalcopyrite deposition. Dominant organisms bearing chemosynthetic
symbionts are hairy gastropod called Alviniconcha. The ancestor of Verrucomorph cirripeds and
anemones dominated in number over the other components. Absence of vestimentiferan tube worms
and lithodids might be explained by its depth.
Vents in Okinawa Backarc Trough can be divided into two typical subunits. “Black Smoker”
zone in the Izena Cauldron (1400 m) which emits turbid jets of ca. 3OOOC water. Munidopsis and
paralvinellid polychactes were the dominant members. “Clam Site” at the Iheya Ridge is very peculiar;
although no pronounced shimmering and thermal anomalies were recognized. Calyptogena dominates
in the sedimented bottom, and Neolepds, vestimentiferan tube worms and hexactinellids thrive on the
hard rocks. “Pyramid Site” of the Iheya Ridge is intermediate between the two sites, and Munidopsis
and bresiliid-hippolytid shrimps predominated. COZ-rich water and the occurrence of most ancient-type
lepadomorph cirripeds, Neolepas spp. in the very young backarc basin must be notified.
Vents in the eastern Manus Basin were explored during KH-90-3 cruise by means of
sophisticated deep-tow system named “DESMOS”. Those discovered in the “DESMOS Cauldron” (ca.
2ooO m) were composed of Calyptogena buried in rather thick sediments covered by red precipitates,
and at least two species of vestimentiferan tube worms. bathymodiolus and thyasilid bivalves were the
subordinate members. Neolepas-type cirripeds were also dominant based on TV observations. The
scenery of the vents of central Manus basin is reported to be characterized by dead chimneys and heaps
of gastropods (probably Alviniconcha and trochids) which again emphasize chimney-sulphide crust vs.
sediment-covered subzones in the backarc vent systems.
42
In Situ Observations of Deep Sea Manganese Nodules Environments
Guy PAUTOT, Robert Le SUAVE, and Pierre COCHONAT
(IFREMER, Brest)
Since 1970, marine geologists from CNEXO-IFREMER national research body have been involved in an important manganese nodule program. The assessment of these potential mineral resources was conducted in the South Pacific (Polynesia area) during a first phase and in
the North Pacific (Clarion-Clipperton area) until now.
This last phase of exploration was able to define a “French Claim” where detailed
studies were performed : multibeam survey, continuous photograph track lines, deep towed side scan sonar SAR, samplings and finally dives with the French submersible Nautile.
The videotape shows the different and successive stages of survey and mainly the NIXONAUTE cruise results.
This cruise was the first direct observation of polymetallic nodule fields in the world by
5000 meters depth. Different kinds of environments were studied : NS elongated hills and
valleys, deep plateaus, nodule fields around seamounts. Thanks to the previous survey, dive
targets were very carefully choosen in key areas.
The first observations were devoted to the nodules : size, shape, contact with the
sediment, density on the bottom, bioturbation, boundaries of the nodule fields. The nodule
distribution and the variability of their morphology and size are clearly related to the sea-floor
physiography and to the thickness of the Plio-Quaternary siliceous pelagic clays.
The substrate of the Plio-Quaternary pelagic clays was outcropping on different places :
steep flanks of hills, top axis of the hills, valley axis. Ovdid depressions with steep cliffs were observed mainly on the hill crests. The geological observations along the cliffs showed a well-
defined stratigraphic sequence which we sampled. The sequence from the base upwards is
basalt, metalliferous sediments, massive beds of chalk (Oligicene to Upper Miocene), stiff Fe/Mn impregnated clay markig a Mio-Pliocene hiatus and Plio-Quatemary siliceous pelagic clays.
In situ measurements of cohesion were made by a vane shear device operated from the
submersible. Within the upper acoustically transparent unit different geotechnical facies exist
which do not correspond to any apparent change in lithology.
43
!3TARMFiRSymposium,7-11 I%bruary 1!291,OR!3TOMGznter, Noumea,,NewQledonia
The New Hebrides Back Arc Troughs :
an Example of Slow Tensional Structure
Jacques RECY* (ORSTOM, Villefranche), Philippe CHARVIS (ORSTOM, Villefranche), Bernard PELLETIER* (ORSTOM, Noumea),
Martine GERARD (ORSTOM, Bondy), Marie-Claire MONJARET* (UBO, Brest),
and Patrick MAILLET* (ORSTOM, Melbourne)
The New Hebrides back-arc troughs are restricted to the southern and northern rear of
the arc. Lack of trough in the central part is related to the compression induced by the collision of
the Entrecasteaux ridge and the New Hebrides arc.
The southern troughs are 50-60 km wide and are composed of one or two grabens
striking N130-140°, while the northern troughs extend over 70 km wide and are composed of a
succession of N-S trending grabens, horsts and half-grabens. Although the location and the
main trend (N150’) of the troughs indicate that they are largely guided by the subduction, the
direction of extension (N30’ to N40° for the southern troughs, N45’ to N60° for the northern
trough) is clearly oblique to the volcanic line and thus does not seem only leaded by the New
Hebrides subduction process. Lack of island arc tholeiitic lavas in the volcanoclastic series
outcropping along the eastern scarps of the different troughs since 2.7-2.2 Ma, can be
considered as an evidence of the initiation of the troughs structuration, which is not necessary
synchronous all along the back-arc domain. The formation of the troughs is polyphased and the tectonics is still active. The thickness of the sedimentary filling inside the half grabens of the northern troughs is in good accordance with the Pre 2 Ma age proposed for the onset of the
extensional tectonics. The geometry of this filling indicates that the tectonic activity has been
continuous with accelerated phases underlined by unconformities The volcanism developed on the flanks and bottom of the troughs presents no
important geochemical difference with the New Hebrides arc volcanism. However, a low-K acid
volcanism emplaced since 1.8 Ma could be associated with punctiform initiation of opening in
the northern troughs.
Formation of the New Hebrides back arc troughs may result from extensional tectonics
induced by a major reorganization at 3 Ma of the seafloor spreading of the North Fiji basin,
which since this time appears to be developed independently of the subduction process.
Although the strain is continuous from 3 Ma the rate of extension in the troughs is very low. In
the studied area there is no young crust related to a recent back arc spreading. The thoughs are
largely developed on the oldest part of the North Fiji basin oceanic crust. In that particular environment the volcanism activity initiated 1.8 Ma ago into the northern troughs and still recently active might be considered as a pun&form spreading.
* member of the GDR GEDO
ORSTOM Fends Documentaire
44 Cote 5 A
;
The Tectonic Between the and the Axis in North Fiji at 18
Etienne RUELLAN ( C.N.R.S, Nice-Sophia), Jean-Marie AUZENDE ( IFREMER, Brest),
and Patrick MAILLET ( ORSTOM, La Trobe)
The North Fiji Basin (SW Pacific) is a marginal basin opened close to the Pacific Indo- Australian plate boundary. It is delimited by the Vanuatu active island arc to the west, the Fiji islands to th east, The Vitiaz inactive system to the north and the Hunter fracture zone to the
south. The present day geometry of the North Fiji Basin results from a polyphased tectonic
evolution since the begining of the spreading. The oceanic opening of the basin is generally considered as the consequence of two rotations : the clockwise rotation of the Vanuatu volcanic arc system and the anti-clockwise rotation of the Fiji platform.
Since the beginning of the opening,the spreading occurred along several axis ridges that are characterized by highly variable trends : N140, NS, N15, N160, N120 (?) and NlOO (?). From 15’S to 21040’S, the present day trends of the axis are mainly N160 (north of l6o5O’S), N15 (between 16’50’s and 18’30’s) and about NS (south of 18’30’s).
The structural analysis of multi-beam echosounder and seismic data combined with the in
situ submersible observations allow to study precisely the NS and N15 axis relationships near
18’3O’S. The tectonic analysis of the seabeam and of sinle channel seismic profiles display two
main oceanic features in this area. First, on the N15 axis, we observe a typical large overlapping
spreading center. But this one is now inactive. East and southeast of this OSC, lies the NS axis. It is located on 173’30’s and is characterized by a northern “V” shape and drawing a propagating rift. Moreover, the youngest axis trends inside the N15 axial domain suggest a northward
propagation of the NS trends. Five dives, three with Nautile submersible and two with Dolphin ROV, have been
conducted on the NS North Fiji Basin spreading axis near 18”5O’S. The observation data allow to
precise the recent spreading activity of the NFB in this area. The studied area is located in the middle of a wide flat dome that constitute the spreading axial domain. On the bottom, the axis is
underlined by a narrow elongated graben, 20 to 30 m deep and 40 to 50 m wide. It is limited by
two normal fault scarps that are tectonically very active. Inside the graben lies hollowed out lava lakes from which remain only many pilars and large collapsed pannels of the top. Going to the outer parts of the axial graben we observe sheet flow lavas and lobate lavas more or less hollowed out and tectonically very active. Outside of the graben lies a large area of pillows lavas without
any fracturation. The hydrothermal activity is located mainly on the lobate lavas and characterized only by active vents through fractures without chimneys.
In conclusion, this study provide new arguments for NFB kinematic models. It confirm the present day full magmatic and tectonic activities of the NS spreading axis located between 18o1O’S and 20’30’s and its northward propagating to the detriment of the N15 axis. In addition, for the first time a fossile overlapping spreading center is described. Trough all those elements, the NFB spreading system appears to be highly instable, due probabl
OJs* i_liij hiius to double sphenoch
a smic
opening of the basin. Lh,curile:l~ am
45 BJ” ; 3~‘cL;3si, q 3
The Southern End of the Seafloor Spreading in the North Fiji Basin
Etienne RUELLAN ( C.N.R.S, Nice-Sophia), Jean-Marie AUZENDE (IFREMER, Brest), Yves LAFOY ( M.R.D, Suva), and Elchi HONZA ( G.S.J, Tsukuda)
The North Fiji Basin (SW Pacific) is a marginal basin opened close to the Pacific and Indo-Australian plate boundary. It is delimited by the Vanuatu active island arc to the west, the Fiji islands to the east, the Vitiaz inactive system to the north and the Hunter fracture zone to the south. The present day geometry of the NFB results from a polyphased tectonic evolution since the
begining of the spreading. Since 3 to 4 Ma, the spreading occurs along a NS axis located in the central part of the basin. Since about 1 Ma, the spreading centers located between 18”lO’S and 16”4O’S, and between 15’S and 16’40’s shift respectively to N15 and N160 directions, due to the functioning of the North Fiji Fracture Zone and of the triple junction of 16’40’s. The newly formed area is only 120 km wide and only 1 and J (Jamarilo) magnetic anomalies can be recognized, which infers a 5.6 cm/y opening rate. On the other hand, from 18o1O’S to 20030’S, the accretionary area, always running NS, is 200 km wide and the identification of 1, J, 2 and 2A magnetic anomalies involve an opening rate of 7.2 cm/y since 3 Ma.
The STARMER Project, especially the Kaiyo 88 cruise (Nov. 13 - Dec. 19, 1988), was
focused partly on geological and geophysical investigations on the southernmost end of the spreading axis of the basin.
A spreading axis area is identified in the NFB, from 20’50% to 21040’S. It is roughly centered on 174’10’E and trends NS to N15. Compared with the central spreading axis of the basin, this axis is offset 80 km eastward by the “Jean Charcot Fracture Zone”, trending N60. The structure exhibits a relative dispersion on the structural trends and an along strike morpho-structural
variability. But often, it has a dome shape bounded by two elongated troughs and two high scarps, that are very similar to those previously described for the central spreading area of the NFB. The entire structure is closely controled by a normal fault network and several N45 or N60 strike-slip faults. The major N60 tranverse faults divide the axial domain into three main segments. The newly-formed area related to this axis is narrow, which suggests a recent beginning of activity. It occurs inside an older domain related to the first opening stages of the basin.
All the structural and magnetic data show that the southern shifted axis could be an incipient spreading axis. The oldest oceanic area was certainly created during the previous opening stages of the NFB, between 10 and 0.7 Ma. Nevertheless, the location of the active axis is not precise. The dispersion of the structural trends, the “V” shaped of the northern segment and the lightness of the newly formed area reflect a very young and unstable spreading system, which probably start less than 1 Ma ago, perhaps at the last change in the whole NFB at 0.7 Ma. In this
case, the total opening rate should be 2.5 cm/y, which is very low compared with the northern and central part of the basin. Last, the spreading could not be concentrated along a well determined axis but disseminated in some places of the newly formed area.
46
Development of a Triple Junction, Central North Fiji Basin.
Manabu TANAHASHI (GSJ, Tsukuba), Kiyoyuki KISIMOTO (GSJ, Tsukuba), Masato JOSHIMA (GSJ, Tsukuba), and Jean-Marie AUZENDE (IFREMER, Brest)
Detailed bathymetric, magnetic and seismic reflection data which were obtained during
STARMER survey cruises (KAIYO 87, 88, and 89), revealed a detailed structural configuration
and history of development of a triple junction at about 17’S, 174’E in the central North Fiji Basin. The triple junction connects N15 typical fast spreading system to SSW, N340 slow oblique
spreading system to NNW and N40 embryo or slow spreading system.
N15 spreading system has 15 to 35 km wide swelled axial domain and 0.7 to 3.5 km axial
graben. It means it is a typical fast spreading system resembles to East Pacific Rise. It shows
symmetrical morphological features. It suggests the spreading direction about NllO, normal to the axis.
N340 spreading system consists of linear, rugged, deep graben. It shows several offsets of linearity and their orientation, N310, suggesis the spreading direction of the system. It means the
spreading is highly oblique at the system. The system is volcanic starved and slow spreading one.
N40 spreading system is the western end of sinistral strike-slip fault system, the North Fiji
Fracture Zone, which borders Pacific and Eastern North Fiji Basin plates. It consists of spreading
system of pull apart basin under the transtensional stress condition. A volcanic high developed at
the triple junction. It is split by the N15 trending axial graben of the SSW spreading system. It morphologically elongates to N310 about 25 km. The elongated part is interpreted as a short
transform fault system connects N15 and N340 spreading system.
The volcanic high developed on the floor of a 35 km wide graben, which possibly
dismembered an old high volcanic high at this position with the steep cliffs. The morphology of the
graben and lineaments on the graben floor suggest that it had been developed by the NW-SE
extensions. And the extension had not been accompanied with extensive volcanic activity.
Present triple junction volcanic structure and N15 spreading system started its activity in late
Quaternaly. The spreading system replaced the NW-SE extensional activity which dismembered the
old volcanic high at this location at possibly early Quaternaly.
47
GLORIA Data from the North Fiji and Lau Basins :
a Summary of Results
Don L. TIFFIN (SOPAC, Suva), J.H. CLARKE, P. HILL,
Phil1 JARVIS (HIG, Hawaii), David JOHNSON (HIG, Hawaii),
Patrick MAILLET (GRSTOM, La Trobe Univ., Melbourne), L. PARSON,
and Ric PRICE (La Trobe Univ., Melbourne)
One swath of GLORIA data about 35 - 45 km in width crosses the North Fiji Basin from the junction of the Hazel Holme Fracture Zone with New Hebrides arc to the triple junction west of Fiji. Two parallel tracks give a swath about 60 - 90 km wide from the triple junction to Peggy Ridge in the Lau Basin, passing north of Fiji. The northeastern Lau Basin and the
northern end of the Tonga arc are almost fully surveyed.
The processed GLORIA data provides information on the structure, sediments, and
tectonics of the region. Although it provides answers to many problems, it also raises questions.
For example, the Hazel Holme Fracture Zone is enigmatic. Does it really exist ?
Also, the Fiji Transform Fault is readily identified in some regions, but it does not connect directly to the North Fiji Basin triple junction. Where does it go ?
Similarly, north of Vanua Levu, the transform fault trace is not so apparent - other
features occur that could be propagators.
The northeastern end of Lau Basin east of Niuafo’ou Island is characterised by an
incipient triple junction, and an extensive broad sheeet-like neo-volcanic zone indicates activity
extends northeast from Peggy Ridge, passing west of Niuafo’ou.
These features, highly visible on the GLORIA mosaics, indicate the complexity of
young backarc basins.
ORSTOM Fonds Documentaire
N” I: wm 4% 3 Cote : A
48
SIARMERSymposium,7-11 l3bn1q 1991, ORS-IDMCimter, Noumea,NewC&donia
Geochemical and Isotopic Studies on Sulfides and Sulfates from North Fiji Basin Spreading Center
Tetsuro URABE (GSJ, Tsukuba)
and S.W. ELDRIDGE (ANU, Canberra)
Active chimneys were located during Nautile dives (STARMER cruise) about 3 km south of a triple junction of the spreading center of the North Fiji Basin. They were found sitting
on a solidified lava lake of the central axial rift. One of the active chimneys, called White Lady,
has two-storied structure; white, dendritic anhydrite (CaSO4) chimney on top of dead sulfide chimney and mound. The maximum measured temperature of the venting fluid is 285°C.
According to the chemical analysis (Ishibashi et al., in press), the hydrothermal fluid shows an evidence of boiling and is heavily depleted in ore-forming elements like iron and
manganese. They also suggested the reduced nature of the fluid, that is, absence of sulfate ion in
spite of their possible origin of down-circulated seawater.
However, the detailed sulfur isotopic analyses using SHRIMP indicate that anhydrite
has wide range of 634s composition (18 - 24 per mil) which is significantly larger than the
reproducibility limit (about 3 per mil). This result suggests that at least a part of the sulfate in anhydrite came from ascending fluid rather than from ambient seawater sulfate.
On the other hand, the sulfur isotopic compositions of sulfides are quite homogeneous; about 0 per mil which is common among sulfide chimneys in East Pacific Rise and other mid-
oceanic ridge hydrothermal areas.
Mineral assemblages of the sulfide chimneys are relatively simple; predominant
marcasite, pyrite, and subordinate amount of wurtzite, sphalerite, chalcopyrite, and covelline.
Average ore grade is : Cu 2.75 %, Zn 5.50 %, Au 1.2 ppm, and Ag 47.7 ppm. There
observed no systematic difference in these compositions between White Lady and large dead
chimneys about 1 km north of the former.
The overall characteristics of the chimneys are very similar to those found in EPR and
other mid-oceanic ridges. This indicates that the process involved in the formation of
hydrothermal deposits in matured marginal basin like North Fiji Basin is also similar to that of MOR.
49
POSTER SESSION
The Boninitic Trend of the Southern Termination of the New Hebrides Island Arc (SW Pacific)
Michel MONZIER (ORSTOM, Noumda )
During the VOLSMAR/GEMINI cruises (1989), the submarine volcanoes of the southern New Hebrides island arc have been sampled quite regularly by dredging and scubadiving. Basalts, basic andesites and dacites from seamounts located between Anatom and 22’S, as well as basic andesites recovered in the same area during one Nautile dive on the inner wall of the trench (SUBPSO I, 1989), are quite similar to the lavas of Anatom and Tanna islands (Vanuatu). These rocks belong to the usual lava trend of the New Hebrides arc. On the other hand, boninites (SiO2=55%; MgO=&9%) and related Mg-rich (Mg0=6-1%) acid andesites and dacites, from southernmost seamounts and islands of the arc, define a high-Mg trend quite distinct of the usual lava trend of the New Hebrides.
This high-Mg character of the lavas of the southern southern termination of the arc appears to be in relation to the peculiar geodynamic evolution of this area during the opening of the North Fiji Basin. The formation of the boninitic volcanoes could have begun a few Ma ago during the propagation of the subduction along the evolutionary sinistral transform zone linking the trench and the North Fiji Basin spreading axis. The Mg-rich andesitic and dacitic volcanoes are younger than the dominantly boninitic volcanoes (some of them are presently active: Matthew and Hunter) and their formation took place in an increasing ridge/arc collision context (Loyalty Ridge vs. New Hebrides arc), with the formation along 22’S of a new E-W sinistral transform zone in the overthrusting plate, isolating the southernmost part of the arc.
Thus, the unusual high-Mg character of the lavas of the southern part of the New Hebrides arc probably results from the unusual geodynamic evolution of this area; this character decreases with time as the spreading axis of the North Fiji Basin shifts away but still remains noticeable in the lavas and inclusions of Matthew and Hunter active volcanoes (Maillet et al., 1986).
lo-
6.
hnds Documentair 0~~10~
NO’: 34.%4\ !L$S Cote ? 13(
’ ’ 50 55 60 66 70
50
SOUTHERN NEW HEBRIDES ISLAND ARC
B I BA I AA 1 D ~ p02
LIST AND ADDRESS OF
THE PARTICIPANTS
51
BRG
CNRS
DMR
ENS
GDR
GEDO
GSJ
HDJ
HIG
IFREMER
INSU
IPGP
JAMSTEC
JEA
MSA
NIES
OOV
ORI
ORSTOM
RWTH
SOPAC
STA
UA
UBO
UR
URA
Abbrevations used
with their country of origin
: Bundesanstalt fur Geowissenschaften und Rohstroffe (FRG)
: Centre National de la Recherche Scientifique (France)
Department of Mineral Resources (Fiji)
: Geological
: Institut
: Marine
: Rheinisch-Westfalischen Technischen Hochschule (FRG)
: South Pacific Applied Geoscience Commission (Fiji)
: Science and Technology Agency (Japan)
: Unite Associee (CNRS France)
:
. ALAYSE Anne-Marie IFREMER Brest
B.P. 70,29280 PLOUZANE, France Phone : (33) 98-22-40-40 Fax : (33) 98-22-45-47 Telex : 940627F E-mail :
AUZENDE Jean-Marie IFREMER Brest
B.P. 70,29280 PLOUZANE, France Phone : (33) 98-22-42-29 Fax : (33) 98-22-45-49 Telex : 940627F E-mail : c/o [email protected]
BARBIER Georges IFREMER Brest
B.P. 70,29280 PLOUZANE, France Phone : (33) 98-22-45-21 Fax : (33) 98-22-45-47 Telex : 940627F E-mail :
BENDEL Valkie U.B.O. c/o IFREMER Brest
B.P. 70,29280 PLOUZANE, France Phone : (33) 98-22-48-62 Fax : (33) 98-22-45-49 Telex : 940627F E-mail : c/o [email protected]
CADETDaniel INSU-CNRS
117 Avenue Denfert Rochereau, 75014 PARIS, France Phone : (33) 1 40-51-21-21 Fax : (33) 140-51-21-01 Telex : 27007OF E-mail :
CIABRINI Jean-Pierre Universite Paris VII - IPGP, Laboratoire de Geochimie des Eaux,
T.54-53 - 5e &age, 2, place Jussieu, 75251 PARIS Cedex 05, France Phone : (33) 144-27-60-36 Fax : (33) 144-27-33-73 Telex : 20081OF E-mail :
53
CRAWFORD Tony University of Tasmania,
Geology Department, GPO Box 252C, HOBART, Tasmania, Australia Phone : (61) 02 202 490 Fax : (61) 02 232 547 Telex : E-mail :
CRESSARD Alain IFREMER TECHNOPGLIS 40
155, rue J.J. Rousseau 92138 ISSY-LES-MOULINEAUX Cbdex, France Phone : (33) l- 46-48-22-20 Fax : (33) l-46-48-22-24 and (33) 1-46-48-21-88 Telex : 631912F E-mail :
DANIEL Jacques ORSTGM Noumea
BP A5 Noumea Cbdex, New Caledonia Phone : (687) 26-10-00 ext. 1139 Fax : (687) 26-43-26 Telex : 3193 NM E-mail : daniel @orstom.orstom.fr
DESBRUYERES Daniel IFREMER Brest
B.P. 70,29280 PLOUZANE, France Phone : (33) 98-22-40-40 Fax : (33) 98-22-45-47 Telex : 940627F E-mail :
DUPONT Jacques ORSTGM Noumt?a
BP A5 Noumea C&lex, New Caledonia Phone : (687) 26-10-00 ext. 1171 Fax : (687) 26-43-26 Telex : 3193 NM E-mail : c/o [email protected]
EADE Jim SOPAC Technical Secretariat
Private Mail Bag, G P 0 SUVA, Fiji Phone : (679) 38-13-77 or (679) 38-l l-39 Fax : (679) 37-00-40 Telex : 2330 SOPACPRO FJ E-mail :
54
,
EGGINS Steve University of Tasmania,
Geology Department, GPO Box 252C, HOBART, Tasmania, Australia Phone : (61) 02 202 490 Fax
:
E-mail :
EISSEN Jean-Philippe ORSTOM Not&a
B.P. AS, NOUMEA C&lex, New Caledonia Phone : (687) 26-10-00 ext. 1165 Fax : (687) 26-43-26 Telex : 3193 NM E-mail : [email protected]
FIALA-MEDIONI Aline Universite P. et M. Curie Paris VI, Observatoire OcCanologique de Banyuls,
CNRS UA 117,66650 BANYULS sur Mer, France Phone : (33) 68-88-00-40 Fax : (33) 68-88-19-99 Telex : 50502OF ARAGOBA E-mail :
FUCHIDA Koichi Hydrographic Department of Japan, Satellite Geodesy Office
M.S.A.Tsukiji 5-3-1, Chuo-ku, TOKYO 104, Japan Phone (81) 33-541-3811 Fax : (81) 33-545-2885 Telex : 2522452 HDJODC J E-mail :
FUJIKURA Katsunori JAMSTEC
2- 15, Natsushima-Cho, Y OKOSUKA 237, Japan Phone : (81) 468-66-3811 Fax : (81) 468-66-4600 Telex : E-mail :
GRACIA Eulalia UBO Brest, GDR910 “GEDO”,
6 Av Le Gorgeu, 29287 BREST Ct!dex,France Phone : (33) 98-03-16-94 Fax : (33) 98-31-61-31 Telex : 941439F SEGALEN E-mail : c/o [email protected]
55
GRIMAUD Daniel Universite Paris VII - IPGP, Laboratoire de GCochimie des Eaux,
T. 54-53 - 5e &age, 2, place Jussieu, 75251 PARIS C&lex 05, France Phone : (33) l-44-27-60-36 Fax : (33) l-44-27-33-73 Telex : 20081OF
:
HELU Saimone SOPAC - Tonga
Private Mail Bag, G.P.O. SUVA, Fiji Phone : (679) 38-13-77 or (679) 38-l l-39 Fax : (679) 37-00-40 Telex : 2330 SOPACPRO FJ E-mail :
HENOCQUE Yves IFREMER TECHNOPOLIS 40
155, rue J.J. Rousseau 92138 ISSY-LES-MOULINEAUX Cklex, France Phone : (1) 46-48-21-00 Fax : (1) 46-48-22-24 or (1) 46-48-21-88 .
Telex : 631912F E-mail :
HERZIG Peter Institut fti Mineralogie und Lagerstittenlehre RWTH Aachen
Wiillnerstrasse 2, 5100 AACHEN, F.R.G. Phone : (49) 241-80-5773 Fax : (49) 241-80-5771 Telex : 0832704 E-mail :
HESSLER Robert R. Scripps Institution of Oceanography
La Jolla, California 92093-0202, U.S.A. Phone : (1) 619-534-2665 Fax : (1) 619-534-7313 Telex : E-mail :
HIROSE Kei University of Tokyo, Geological Institute
7-3- 1 Hongo, Bunkyo, TOKYO, Japan Phone : (81) 33-812-2111 ext. 4538 Fax : (81) 33-815-9490 Telex : E-mail :
56
HONZA Eiichi Geological Survey of Japan, Geophysics Department,
l-l-3 Higashi, Tsukuba, IBARAKI 305, Japan Phone : (8 1) 298-54-3591 Fax : (81) 298-54-3533 Telex : 3652570 GSJ J E-mail :
HUCHON Philippe Ecole Normale Sup&ieure, Paris
Laboratoire de Geologic, 24, rue Lhomond, 7523 1 PARIS C&&x 05, France Phone : (33) 143-29-12-25 ext. 3514 Fax : (33) 1 43-31-67-54 Telex : 202601F E-mail :
IWABUCHI Yo Hydrographic Department of Japan, Ocean Survey Division,
M.S.A. -Tsukiji 5-3-1, Chuo-ku, TOKYO 104, Japan Phone (81) 33-541-38111 Fax : (81) 33-545-2885 Telex : 2522452 HDJODC J E-mail :
JARRIGE Franqois ORSTOM Paris
Dt?partement TOA, 213, rue La Fayette, 75480 PARIS C&lex 10, France Phone : (33) 148-03-76-68 Fax : (33) 1 48-03-08-29 Telex : 214627F E-mail : [email protected]
JOSHIMA Masato Geological Survey of Japan, Marine Geology Department,
l-l-3 Higashi, Tsukuba, IBARAKI 305, Japan Phone : (81) 298-54-3768 Fax : (81) 298-54-3533 Telex : 3652570 GSJ J E-mail : gOl58@jpnaist
KISIMOTO Kiyoyuki Geological Survey of Japan, Marine Geology Department,
l-l-3 Higashi, Tsukuba, IBARAKI 305, Japan Phone : (81) 298-54-3795 Fax : (81) 298-54-3533 Telex : 3652570 GSJ J E-mail : [email protected] or gOl58@jpnaist
57
KROENKE Loren Hawai Institute of Geophysics
2525 Correa Road, Honolulu, Hawaii 96822, U.S.A. Phone : (1) 808-948-78-45 Fax : ( 1) 808-949-02-43 Telex : 7238861 HIGCY MR E-mail : GTETLMHAWAILJNST
LAFOY Yves Department of Mineral Resources
Private Mail Bag, G.P.O. SUVA, Fiji Phone : (679) 38-19-79 Fax : (679) 37-10-39 Telex : 2330 SOPACPRO FJ E-mail :
LAGABRIELLE Yves UBO Brest, URA CNRS 1278, GDR910 “GEDO”,
6 Av Le Gorgeu, 29287 BREST C&lex,France Phone : (33) 98-03- 16-94 Fax : (33) 98-31-61-31 Telex : 941439F SEGALEN E-mail : c/o [email protected]
LARUE Michel ORSTOM Noumea
BP A5 Noumea CXdex, New Caledonia Phone : (687) 26-10-00 ext. 1164 Fax : (687) 26-43-26 Telex : 3193 NM E-mail : [email protected]
MALLET Patrick (until March lst, 1991) ORSTOM La Trobe University
Department of Geology, Bundoora Victoria, 3083 Australia Phone : (61) 3-479-2490 Fax : (61) 3-479-1272 Telex : AA 33 143 E-mail :
MALLET Patrick (from March lst, 1991) ORSTOM, Observatoire Oc&nologique de Villefranche, Laboratoire de Geodynamique, B.P. 48,06230 VILLEFRANCHE sur Mer, France Phone : (33) 93-76-37-40 Fax : (33) 93-76-37-68 Telex :
E-mail : c/o [email protected]
58
t MARUMO Katsumi University of Toronto / GSJ, Marine Geology Research Lab., Department of Geology,
Earth Sciences Centre, 22 Russel Street, TORONTO, Ontario, M5S 3B 1, CANADA Phone : ( 1) 416-978-2975 or 6554 or 6807 Fax : ( 1) 416-978-3938 Telex : 06-23887 GEOLOGY TOR E-mail :
MATSUMOTO Takeshi JAMSTEC
2- 15, Natsushima-Cho, YOKOSUKA 237, Japan Phone : (8 1) 468-66-3811 Fax : (81) 468-66-4600 Telex : E-mail :
MEVELCatherine Universite P. et M. Curie Paris VI, Laboratoire de P&rologie et Magmatologie,
T. 26 - 3e &age, 4, place Jussieu, 75252 PARIS Cedex 05, France Phone : (33) l-43-36-25-25 Fax : (33) l-44-27-39-11 Telex : 200145F UPMCSIX E-mail :
MISSEGUE Fraqois ORSTOM Nourn&
BP A5 Noumea Cklex, New Caledonia Phone : (687) 26-10-00 ext. 1168 Fax : (687) 26-43-26 Telex : 3193 NM E-mail : [email protected]
MITSUZAWA Kyohiko JAMSTEC
2- 15, Natsushima-Cho, YOKOSUKA 237, Japan Phone : (81) 468-66-3811 Fax : (81) 468664600 Telex : E-mail :
MOMMA Himyasu JAMSTEC
2- 15, Natsushima-Cho, YOKOSUKA 237, Japan Phone : (81) 468-66-38 11 Fax : (81) 468-66-4600 Telex : E-mail :
59
MONZIER Michel ORSTOM Noun&
BP A5 Noumea C&iex, New Caledonia Phone : (687) 26-10-00 ext. 1165 Fax : (687) 26-43-26 Telex : 3193 NM E-mail : c/o [email protected]
MOREL Yann SOPAC Data Management
Private Mail Bag, GPO SUVA, Fiji Phone : (679) 38-13-77 or (679) 38-l 1-59 Fax : (679) 37-00-40 Telex : 2330 SOPACPROFJ E-mail :
MUKAI Hitoshi NIES-JEA
16-2 Onogawa, Tsukuba, IBARAKI 305, Japan Phone : (81) 298-51-6111 Fax : (8 1) 298-5 l-4732 Telex : E-mail :
NAGANUMA Takeshi JAMSTEC
2-15, Natsushima-Cho, YOKOSUKA 237, Japan Phone : (81) 468-66-3811 Fax : (81) 468-66-4600 Telex : E-mail
NAKA Jiro JAMSTEC
2- 15, Natsushimla-Cho, YOKOSUKA 237, Japan Phone : (81) 468-66-3811 Fax : (81) 468-66-4600 Telex : E-mail
NOHARA Masato Geological Survey of Japan, Marine Geology Department,
l-l-3 Higashi, Tsukuba, IBARAKI 305, Japan Phone : (81) 298-54-3769 Fax : (81) 298-54-3533 Telex : 3652570 GSJ J E-mail :
60
NOJIRI Yukihiro N-IES-JEA
16-2 Onogawa, Tsukuba, IBARAKI 305, Japan Phone : (81) 298-51-6111 Fax : (81) 298-51-4732 Telex : E-mail :
OHTA Suguru Ocean Research Institute, University of Tokyo
Ninamidai l- 15-1, Nakano-ku, TOKYO 164, Japan Phone : (81) 33-376-1251 Fax: Telex : 25607 ORIUT E-mail :
OKUDA Yoshihisa Geological Survey of Japan Marine geology Department,
l-1-3 Higashi, Tsukuba, IBARAKI 305, Japan Phone : (81) 298-54-3594 Fax : (81) 298-54-3533 Telex : 3652570 GSJ J E-mail :
ORTEGA-OSORIO Alejandm Marine Geology Research Lab., Department of Geology, Earth Sciences Centre,
University of Toronto, 22 Russel Street, TORONTO, Ontario, M5S 3B1, CANADA Phone : ( 1) 416-978-2975 or 6554 or 6807 Fax : ( 1) 416-978-3938 Telex : 06-23887 GEOLOGY TOR E-mail :
PAUTOT Guy IFREMER Brest
B.P. 70 - 29280 PLOUZANE, France Phone : (33) 98-22-42-22 Fax : (33) 98-22-45-49 Telex : 940627F E-mail :
PELLETIER Bernard ORSTOM Noun&a
B.P. A 5, NOUMEA C&lex, New Caledonia Phone : (687) 26-10-00 ext. 1166 Fax : (687) 26-43-26 Telex : 3193 NM E-mail : c/o [email protected]
61
PRIEUR Daniel Observatoire Oceanologique de Roscoff,Universite P. et M. Curie Paris VI,
CNRS-INSU, Place Georges Teissier, 29680 ROSCOFF, France Phone : (33) 98-29-23-33 Fax : (33) 98-29-23-24 Telex : E-mail :
RECY Jacques ORSTOM, Observatoire Oct!anologique de Villefranche,
Laboratoire de Geodynamique, B.P. 48,06230 VILLEFRANCHE sur Mer, France Phone : (33) 93-76-37-40 Fax : (33) 93-76-37-68 Telex : E-mail : [email protected]
ROBIN Claude ORSTOM Noum6a
BP A5 Noumea C&lex, New Caledonia Phone : (687) 26-10-00 ext. 1159 Fax : (687) 26-43-26 Telex : 3193 NM E-mail : c/o [email protected]
RUELLAN Etienne Institut de Geodynamique
Rue A. Einstein, Sophia Antipolis 1,06560 VALBONNE, France Phone : (33) 93-95-42-44 Fax : (33) 93-65-27-17 Telex : 970006F CNRS GRP E-mail :
SIMPSON Alfred Department of Mineral Resources, FIJI
Private Mail Bag, G.P.O. SUVA, Fiji Phone : (679) 38-19-79 Fax : (679) 37-10-39 Telex : 2330 SOPACPRO FJ E-mail :
TANAHASHI Manabu Geological Survey of Japan, Marine Geology Department,
l-1-3 Higashi, Tsukuba, Ibaraki, 305, Japan Phone : (81) 298-54-3767 Fax : (81) 298-54-3533 Telex : 3652570 GSJ J E-mail : [email protected]
62
, TEMAKON Stanley SOPAC VANUATU
Private Mail Bag, G.P.O. SUVA, Fiji Phone : (679) 38- 13-77 or (679) 38-l l-39 Fax : (679) 37-O-40 Telex : 2330 SOPACPRO FJ E-mail :
TIFFIN Don SOPAC Technical Secretariat FIJI
Private Mail Bag, G.P.O. SUVA, Fiji Phone : (679) 38- 13-77 or (679) 38-l l-39 Fax : (679) 37-00-40 Telex : 2330 SOPACPRO FJ E-mail :
TUPUA Eroni Department of Mineral Resources, FIJI
Private Mail Bag, G.P.O. SUVA, Fiji Phone : (679) 38-19-79 Fax : (679) 37-10-39 Telex : 2330 SOPACPRO FJ E-mail :
URABE Tetsuro Geological Survey of Japan, Mineral Deposit Department,
l-l-3 Higashi, Tsukuba, IBARAKI 305, Japan Phone : (8 1) 298-54-3634 Fax : (81) 298-54-3533 Telex : 3652570 GSJ J E-mail :
YAMAGUCHI Kazuo Geological Survey of Japan, Geophysics Department,
l-1-3 Higashi, Tsukuba, IBARAKI 305, Japan Phone : (81) 298-54-3588 Fax : (81) 298-54-3533 Telex : 3652570 GSJ J E-mail :
63