Workshop Report - Ridge 2000 Program

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FORMATION OF OCEAN CRUST AT SPREADING CENTER VOLCANISM HYDROTHERMAL ISM TECTON ISM \~.......I'-----"--/ DIFFERENTIATION AND CRYSTALLIZATION MAGMA FORMATION AND TRANSPORT FIGURE 1 23
Strategies For Solving The Critical Problems We envision a strategy with four major components. 1. Global Reconnaissance. The first component would include reconnaissance studies of substantial lengths of the mid-ocean ridge system in order to obtain a measure of the world wide variability of ocean ridge morphologic, structural and chemical characteristics. The reonnaissance would include bathymetric surveys over a distance of approximately 1000 km continuously along the strike of the ridge, with a swath width of several times the active accretion zone; multichannel seismiC (MCS) surveys along the axis to define the lateral continuity and width of the axial low velocity zone and any variations in seismically estimated crustal thickness; petrological sampling with approximately one station for every 10 to 20 km of ridge length, in order to determine the regional geochemical signature and to explore quantitative relationships among petrology, bathymetry, and the MCS axial reflector, and continuous surveying of along-axis water column temperature and chemical anomalies, in order to determine the distribution of hydrothermal activity. Such reconnaissance surveys should cover ridges which vary in their spreading rate, in their tectonic style (i .e., fracture zone spacing, presence or absence of rift valley, back-arc settings L and in the ambient mantle temperature (i.e., hot spots such as Ic.:land and cold spots such as the Australian!Antarctic Discordance). Approximately ten such surveys will be necessary to obtain adequate global coverage. These surveys will lead to coverage of about 20 percent of the entire system of ocean ridges. They will determine the global distribution of magma chambers and provide the data necessary to develop quantitative relationships among spreading rate, gross tectonic fabric, magma chambers and geochemistry. 2. Eruption Detection. The second component stems from the recognition that the ocean ridge volcano observatory should be located in an area of active volcanism. To find such a location we need to know the periodicity in space and time of volcanic eruptions on the sea floor, and the relationship of such eruptions to hydrothermal activity. There is at the moment no such information for submarine ocean ridges. Calculation of magma production rates and analogy with terrestrial volcanos suggests we should be able to find an active volcanic area which would remain active on the time scale of a decade. To find such a location, however, requires effective eruption monitoring. Two approaches could be explored: (a) long term monitoring of hydrothermal plumes and (b) acoustic monitoring. In addition to locating active ridge segments, such monitoring will provide data concerning regional eruption frequency and spatial systematics. 24
Page 2 and 3: The Mid-Oceanic Ridge A Dynamic G
Page 4 and 5: OCEAN STUDIES BOARD WALTER H. MUNK,
Page 6 and 7: PREFACE Recent discoveries of the w
Page 8 and 9: o Regional Scale: selected subsets
Page 10 and 11: 1 INTRODUCTION The global mid-ocean
Page 12 and 13: papers were compiled, printed, and
Page 14 and 15: 2 STATEMENT OF GOALS AND OBJECTIVES
Page 16 and 17: experience from land volcanic and m
Page 18 and 19: solid understanding of both the bio
Page 20 and 21: NEXT STEPS TOWARD A RIDGE INITIATIV
Page 22 and 23: 4 REPORTS OF THE WORKING GROUPS INT
Page 24 and 25: Critical Investigations The specifi
Page 26 and 27: Seismic refraction methods provide
Page 28 and 29: New Instrument and Laboratory Capab
Page 30 and 31: GROUP 2: GEOMETRY AND DYNAMICS OF M
Page 34 and 35: 3. Regional Surveys. The third comp
Page 36 and 37: provide efficient and economically
Page 38 and 39: 3. Adaptation of tomographic invers
Page 40 and 41: Consequently, the sin;J1e most impo
Page 42 and 43: Thermal stresses have been suggeste
Page 44 and 45: electromagnetic fields must be meas
Page 46 and 47: capability should include at least
Page 48 and 49: In order to understand subseafloor
Page 50 and 51: fossil hydrothermal systems in ophi
Page 52 and 53: instrumented to record the environm
Page 54 and 55: GROUP 5: BIOLOGY OF HYDROTHERMAL SY
Page 56 and 57: There are several key questions abo
Page 58 and 59: Dispersal of Organisms What are the
Page 60 and 61: Strategy Biological studies will em
Page 62 and 63: GROUP 6: WATER COLUMN DYNAMICS AND
Page 64 and 65: On the ridge segment scale, detaile
Page 66 and 67: standard transect sampling and Lagr
Page 68 and 69: APPENDIX I The Mid-Oceanic Ridge: A
Page 70 and 71: Forsyth, Donald Department of Geolo
Page 72 and 73: Lonsdale. Peter Scripps Institution
Page 74 and 75: Reeve, Michael National Science Fou
Page 76: Tunnicliffe, Verena University of V

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