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ISSN 0016-7029, Geochemistry International, 2006, Vol. 44, No. 4, pp. 419–421. © Pleiades Publishing, Inc., 2006.Original Russian Text © S.A. Silantyev, 2006, published in Geokhimiya, 2006, No. 4, pp. 462–464.

A workshop of the Russian branch of the InterRidgeInternational program was held this summer, on July 6and 7, 2005, in St. Petersburg. The workshop wasattended by leading Russian specialists dealing withprocesses in the crest zones of mid-oceanic ridges thatcontrol the origin and geochemistry of mineral depositsrelated to the hydrothermal alterations of the oceaniclithosphere. The workshop was also participated byprominent researchers from Germany and France andby K. Freitag, a coordinator of the Organizing Commit-tee of the project.

A conspicuous achievement of Russian researchersin studying the Ocean that was related to the mappingand examination of ore-producing MOR systems andthe processes that control their origin and evolution wasthe recent discovery of a number of large hydrothermalfields that occur as a chain extending along the Mid-Atlantic Ridge axis from

12°58

′

N to 16

°

38

′

N.Because of this, discussions at the St. Petersburg work-shop were focused mainly on the petrological,geochemical, and geodynamic factors responsible forthe development of such clusters of hydrothermal fieldsand on the outlooks of their future discovery. Inasmuchas most active hydrothermal fields of the MAR segmentbetween 12

°

and 17

°

N lie within the crest zone of theridge, which is made up of the Hess-type crust (mantleperidotites with volumetrically subordinate gabbroids),several presentations at the workshop were devoted tovarious aspects of petrogenesis in slow-spreading mid-oceanic ridges.

The workshop comprised two thematic blocks. Oneof them dealt with the main problem discussed at thisworkshop and included reports of the preliminaryresults of Cruise 26 of the R/V

Professor Logachev.

The presentations were made by researchers from NPPPMGRE. The other block included talks devoted to thefundamental problems of oceanic lithospheric accre-

tion in MOR and various aspects of the genesis andexploration of oceanic hydrothermal ore fields.

V.N. Ivanov and V.E. Bel’tenev (NPP PMGRE)reported the discovery of two new ore occurrences,Ashadze 2 and Ashadze 3, which were found within thepreviously known Ashadze hydrothermal field duringCruise 26 of the R/V

Professor Logachev

and whichpossibly compose, together with the Ashadze 1 hydro-thermal field, a newly found cluster of ore occurrences,whose reserves are comparable with those of theLogachev field to the north of these fields. As followsfrom the data reported in this presentation, activehydrothermal systems in the study area (at 12

°

58

′

Nand slightly south of it, 20 km north of the MarathonFZ) are spatially restricted to the oceanic basementconsisting of peridotites with subordinate amounts ofgabbro. The composition of the sulfide ore mineraliza-tion at the Ashadze 1 field was discussed in the paper byL.I. Lazareva et al. (NPP PMGRE). It was demon-strated that a distinctive feature of the ore mineralogyof this field are elevated concentrations of Zn and Ag.Judging by the composition of the mineralized sedi-ments from the same segment of the MAR crest zone(13

°

N), which were presented in the talk by V.V. Shilovet al. (VNIIOkeangeologiya, St. Petersburg State Uni-versity, and NPP PMGRE), the first indications ofhydrothermal activity in this area have an age of morethan 200 ka and are the oldest among all known hydro-thermal fields in MAR. T.V. Stepanov, T.A. Semkov,and G.A. Cherkashev (VNIIOkeangeologiya) dis-cussed the materials of “shallow” drilling at theLogachev hydrothermal field in the context of theextreme compositional variability of the ores and themosaic structure of the orebodies examined in detail. A.Koschinsky with colleagues of the International Uni-versity of Bremen, Westfälische Wilhelms-UniversitätMünster, and IFM-GEOMAR demonstrated the effi-

Workshop “A Hydrothermal Cluster of the MAR Axisbetween 12

°

and 17

°

N: A Unique Natural Phenomenonor a Common Feature of the Hydrothermal Systems

of Mid-Oceanic Ridges?” of the Russian Branch of the InterRidge International Program

S. A. Silantyev

Vernadsky Institute of Geochemistry and Analytical Chemistry (GEOKhI),Russian Academy of Sciences, ul. Kosygina 19, Moscow, 119991 Russia

Received July 21, 2005

DOI:

10.1134/S0016702906040082

CHRONICLE

420

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SILANTYEV

ciency of the application of the in-situ fine geochemicalparameters of the fluid to the assessment of the materialbalance in MOR hydrothermal systems. Theseresearchers have identified the major geochemical res-ervoirs that contributed to the composition of thehydrothermal source of the Logachev field. T. Kuhnet al. (IFM-GEOMAR; TU Bergakademie, Freiberg;and Max-Plank-Institut für Chemie) have demonstratedthat massive sulfides from the Logachev hydrothermalfiled, which are related to ultramafic rocks, are enrichedin Cu, Au, and Os. S.A. Silantyev and his colleagues(GEOKhI, Russ. Acad. Sci.; NPP PMGRE; and theHobart University) discussed the first data on thegeochemistry of quenched glasses from the MAR riftvalley near the base-metal sulfide occurrence at

16°38

′

N.The variations of the

H

2

O/K

2

O

and Cl/K indicatorparameters in the sulfide samples seem to be explainedas resulting from the interaction of the basaltic glasseswith a seawater-derived fluid of low salinity. Theadvantageousness of the application of computer-basedtechnologies to the analysis of the topography of the riftvalley surface of MAR between

12°58

′

N and

16°38

′

Nwas convincingly demonstrated in the talk byS.I. Andreev and coauthors (VNIIOkeangeologiya).

In their report, N.S. Bortnikov with colleagues(IGEM Rus. Acad. Sci., and IG OIGGM, Sib. Branch,Russ. Acad. Sci.) presented a comparative analysis oforiginal authors' data on fluid inclusions in mineralsfrom hydrothermal ore-forming systems in slow- andfast-spreading mid-oceanic ridges. This research hasdemonstrated that the maximum temperatures of solu-tions (deduced from the analysis of fluid inclusions) inboth slow- and fast-spreading mid-oceanic ridges are ingood agreement with the results obtained by mannedsubmersibles via direct measurements at the oceanicfloor. S.A. Silantyev and his coauthors (GEOKhI, Russ.Acad. Sci., and IGGD Russ. Acad. Sci.) presentednewly obtained data indicating that the distinctivegeochemical features of hydrothermal ore occur-rences on the Hess crust depend more strongly on thecomposition of the peridotite rocks that host thehydrothermal systems. The report by S.M. Sudarikov(VNIIOkeangeologiya) presented the results obtainedon geochemical links in the system of a hydrothermalfluid–ascending hydrothermal plume—lateral hydro-thermal plume. M.P. Davydov (VNIIOkean-geologiya) discussed in this talk the possibility ofusing Fe–Mn deposits as an exploration guide for sul-fide ore mineralization in the MAR rift valley. Theprospects of the application of electrical surveyingto the study and prediction of massive sulfidedeposits in the MAR axial zones were considered inthe talks given by S.I. Andreev et al. (VNIIOkean-geologiya) and E.D. Lisitsyn (Sevmorgeo).

L.V. Dmitriev and his coauthors (GEOKhI, GIN,and the Smithsonian Institute) presented a review ofpetrological studies of magmatism in mid-oceanicridges and highlighted the tasks for further investiga-tions. The presentation by J. Koepke et al. (

Universit

ä

t

Hannover, Max-Plank-Institut

f

ü

r

Chemie) wasdevoted to the investigation of the root zones of thedescending branches of hydrothermal systems andincluded petrological arguments in support of thehypothesis that the hydrothermal alterations of thelower levels in the oceanic crust begin at temperaturescorresponding to the late evolution of crustal magmachambers beneath MOR. R. Almeev et al. (GEOKhI, Rus.Acad. Sci.;

Universit

ä

t

Hannover; Universität Kiel)explored the problem of the cotectic crystallizationpressure of MORB in the context of the simulations ofphase equilibria in basalts from MAR segmentsbetween

6°

and

10°

S. G.N. Savelieva et al. (GIN Rus.Acad. Sci., IGEM Rus. Acad. Sci., and GIN, KolaResearch Center, Rus. Acad. Sci.) reported the first zir-con ages of plutonic rocks from MAR near its intersec-tion with the Sierra Leone FZ. A petrogenetic model forthe genesis of the plutonic complex in the same MARsegment was proposed by E.V. Sharkov et al. (IGEMRus. Acad. Sci., and NPP MPMGRE). The presenta-tions by B.A. Bazylev (GEOKhI, Rus. Acad. Sci.) weredevoted to the comparative analysis of petrological andgeochemical characteristics of mantle residues fromtwo anomalous MAR segments: from the vicinity of itsintersecttion with the Fifteen-Twenty FZ and fromabove the Azores superplume. S.A. Merkur’ev andN.A. Sochevanova (SPbF IZMIRAN) presented geo-physical (magnetic survey) evidence for the small-scalejump of the MAR axis in the TAG area (

26°–26°40

′

N).An attempt of reconstructing the geodynamic evolutionof the Gakkel ultraslow-spreading ridge was presentedin the talk by A. Minakov and his colleagues (VNI-IOkeangeologiya).

At the workshop in St. Petersburg, representatives ofthe Stirring Committee came forward, on behalf of itschair Prof. Colin Devi, with the initiative to raise thestatus of Russia in the international InterRidge commu-nity.

The international InterRidge project is one of themost authoritative world-class programs devoted toEarth sciences and comprises researchers from27 countries. Much of its activities are centered on thecoordination of interdisciplinary studies in all scientificand technological fields related to the investigations ofthe system of mid-oceanic ridges and the developmentof projects and recommendations for their efficientimplementation in cooperation with other researchprojects. The activities within the scope of this projectsignificantly influence the choice strategy of first-prior-ity target areas for deep sea drilling within the frame-work of the ODP Project (Ocean Drilling Program).The infrastructure of the project includes three levels:its principal members are the United States, Great Brit-ain, France, and Japan; the associate members are eightcountries; and the corresponding members are fifteencountries, including Russia. Representatives of associ-ate-member countries do not attend the meeting of theplanning committee of the InterRidge Project and can-not head working groups of this project (the activities

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WORKSHOP “A HYDROTHERMAL CLUSTER OF THE MAR AXIS 421

of these groups are of interdisciplinary character). Atthe same time, the planning committee of InterRidgeinvited the national correspondent of Russia to itsannual meetings over the past five years, and this testi-fies to the high appreciation of activities of R-RIDGE(Russian RIDGE), the Russian branch of the InterRidgeProject. The Russian branch was established in 1995,and its activities were participated by researchers fromGEOKhi, Rus. Acad. Sci. (which is the head organiza-tion); GIN Rus. Acad. Sci.; IO Rus. Acad. Sci.; GGMRus. Acad. Sci.; IGEM Rus. Acad. Sci.; IZMI Rus.Acad. Sci.; IGGD Rus. Acad. Sci.; OIGGM Sib.Branch, Rus. Acad. Sci.; Moscow State University,VNIIOkeanologiya, and NPP PMGRE. Meetings withthe discussion of the newly obtained results and issuesrelated to the planning and coordination with the Inter-Ridge Project are held systematically.

In recent years, the members of the OrganizingCommittee of InterRidge repeatedly expressed theirfirm belief that the current status of Russia in thisproject does not correspond to the actual contributionof this country to the study of the World Ocean. Uponchanging Russia’s status in InterRidge, researchersfrom this country will acquire the unique possibility ofparticipating in the elaboration of strategic avenues forthe future studies of mid-oceanic ridges. Research cen-

ters of Russia will be able to actively influence theselection of high-priority targets for deep-sea drilling,will participate in the exploitation of the bottom cablenetworks used to operate monitoring systems of geo-logical processes in spreading zones, and will acquireaccess to the fullest databases and collections owned byvarious working groups of the project. The newlyobtained status of Russia will facilitate the appointmentof Russian researchers to newly established workinggroups of the InterRidge Project.

In general, both Russian and foreign participants ofthe meeting highly estimated its organization and thescientific level of its presentations. One of the impor-tant outcomes of this meeting was the initiative of K.Freitag, a coordinator of the Organizing Committee, toestablish a new workshop of InterRidge that will be ori-ented on the studying of massive sulfide hydrothermalsystems of MAR. The head of this group could be a rep-resentative of Russia.

The next regular meeting of the Russian branch ofthe InterRidge International Project is planned to beheld, according to the tradition, in September 2007, inMoscow, at the Vernadsky Institute of Geochemistryand Analytical Chemistry (GEOKhI), Russian Acad-emy of Sciences.