Seafloor spreading centers

Lister, C.R.B. (1973) Hydrothermal convection at seafloor spreading centers source of power or geophysical nightmare Geol. Soc. Am. Ab.st. Programs, 5, 74. 

Hydrothermal vents are another source of water entering the ocean. These vents are submarine hot-water geysers that are part of seafloor spreading centers. The hydrothermal fluids contain some major ions, such as magnesium and sulfete, in significantly different ratios than foimd in seawater. The importance of hydrothermal venting in determining the chemical composition of seawater is described in Chapters 19 and 21. 

Von Damm, K.L., Grant, B., Edmond, J.M. 1983. Preliminary report on the chemistry of hydrothermal solutions at 20°N, East Pacific Rise. In Rona, P.A., Bostrom, K., Smith, K.L., Jr. (eds.) Hydrothermal Processes at Seafloor Spreading Centers. Plenum, New York, 369-389. 

Thompson G. (1983a) Basalt-seawater interaction. In Hydrothermal Processes at Seafloor Spreading Centers (eds. P.A. Rona, K. Bostrom, L. Laubjer and K.L. Smith), pp. 225-278. Plenum Press, New York. 

Fleet A. J., Bostrom K., Laubier L., and Smith K. L. (1983) Hydrothermal and hydrogenous ferro-manganese deposits do they form a continuum The rare earth element evidence. In Hydrothermal Processes at Seafloor Spreading Centers (ed. P. A. Rona). Plenum, New York, pp. 535-555. 

Lilley MD, Butterfield DA, Olson EJ, Lupton JE, Macko SA, Mcduff RE (1993)Anomalous CH4 and NH/ concentrations at an unsedimented mid-ocean-ridge hydrothermal system. Nature 364 45-47 Lister CRB (1983) The basic physics of water penetration into hot rock In PA Rona, K Bostrom, L Laubier, KL Smith Jr (eds) Hydrothermal Processes at Seafloor Spreading Centers. Plenum Press, New York, p 141-168... 

Welhan JA, Craig H (1983) Methane, hydrogen and helium in hydrothermal flttids at 21°N on the East Pacific Rise. In Rona, PA, Bostrom, K, Laubier, L, Smith, KL, Jr (eds) Hydrothermal Processes at Seafloor Spreading Centers. NATO conference series IV, Marine Sciences. Plenum Press, New York, p 391-409... 

Fleet, A.J. 1983. Hydrothermal and hydrogenous ferromanganese deposits Do they form a continuum In Rona, P., Bostrom, K., Laubier, L. and Smith, K.L. (eds) Hydrothermal processes at seafloor spreading centers. NATO Conference Series, 12 535-555. 

Bulk chemical composition data of the Besshi-type deposits (Besshi), the seafloor sulfide deposits from the Mid-Atlantic Ridge at 23°N (MAR), the Galapagos Spreading Center at 86 W (GSC) and the East Pacific Rise at 21 N (EPR) (Kase and Yamamoto, 1988)... 

Pillow basalts Large mounds of basalt that form when lava is extruded onto the seafloor at active spreading centers. 

The objective of this chapter is to review available stable isotopic data on seafloor hydrothermal systems. However, this goes far beyond a simple literature review because much new, previously unpublished data, collected by the author, is included. In addition, an important goal of this chapter is to interpret the stable isotope systematics of seafloor hydrothermal systems in the context of fluid-rock reactions and geochemical reaction calculations. Boiling and supercritical phase-separation, volcanic eruption and dike-emplacement events, addition of magmatic volatiles, and bacterial fractionation processes will be discussed where applicable. In addition to the commonly measured stable isotopes of C, O, H, and S, stable isotope ratios of B, Li, N, Cl, Cu, and Fe are included where data are available. Much new data has appeared since the last comprehensive overview of stable isotopes in seafloor hydrothermal systems (Shanks et al. 1995). This includes a wealth of information on hydrothermal systems related to volcanic arcs, back-arc spreading centers, seamounts, and serpentinized ultramafics. 

Seafloor hydrothermal systems that are reasonably well studied in terms of stable isotope values of fluids, hydrothermal precipitates and hydrothermal alteration are presented as case studies in this section. Ranges of sulfur isotope values from given deposits are summarized in Figure 11. It is clear that most of the mid-ocean ridge sulfides (designated S SmbS to indicate metal sulfide minerals), ) us those from Manus and Mariana back-arc spreading centers, are quite similar with ranges of about l-5%o. 

Seafloor hydrothermal activity at mid-ocean ridges and back-arc spreading centers has a major impact on the chemistry of the oceans (Edmond et al. 1979a, 1982) and has been responsible for... 

Fig. 13.3 Seismic profile showing the top of a high-level magma chamber at a depth of 3.5 km below the seafloor at a spreading center in the southwest Pacific (after Collier and Sinha 1992 provided by M.C. Sinha).

Fig. 13.13 Schematic diagram showing the geotectonic setting of a seafloor back-arc spreading center, showing the relationship to the active volcanic front of the arc and the subducting slab.

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