Hydrothermal phase separation

Phase separation and segregation are occurring in some hydrothermal systems (Gamo, 1995) which modify the chemistry of initial hydrothermal solution. Von Damm and Bischoff (1987) and Butterfield et al. (1994) obtained high chloride concentration of more than twice of the seawater value for the hydrothermal solution at the North Cleft Segment and the South Cleft Segment of the Juan de Fuca Ridge. 

Cowan, J.E. and Cann, J. (1988) Supercritical two-phase separation of hydrothermal fluids in the Troodos ophiolite. Nature, 333, 259-261. 

Ishibashi, J., Grimaud, D., Nojiri, Y. Auzende, J.M. and Urabe, T. (1994a) Fluctuation of chemical compositions of the phase-separated hydrothermal fluid from the North Fuji Basin Ridge. Marine GeoL, 116, 215-226. 

Seawater and marine pore fluids. As discussed above, the chlorine isotopic composition of modem seawater does not vary measurably. This is not surprising in light of its long residence hme (approximately 90 million years) and its conservative behavior in the water column. In contrast, marine pore fluids have been demonstrated to vary considerably. There is also the likelihood that hydrothermal fluids may be fractionated as a result of exchange with mineral phases, as phase separation under marine hydrothermal conditions does not appear to lead to measurable fractionation (e.g., Magenheim et al. 1995). However, to date no stable-chlorine isotopic compositions of marine hydrothermal fluids have been reported in the literature. 

Vapor and brine from the Brandon vent of the East Pacific Rise have identical Fe isotope compositions, implying that phase separation does not produce an isotopic fractionation (Beard et al. 2003a). The role that sulfide precipitation plays in controlling the Fe isotope composition of the fluid remains unknown. The precision of the two sulfide analyses reported by Sharma et al. (2001) was not sufficient to resolve if sulfide precipitation would produce Fe isotope fractionation in the vent fluid. In a detailed study of sulfldes from the Lucky Strike hydrothermal field from the mid Atlantic Ridge, however, Rouxel et al. (2004) found that sulfldes span a range in 5 Fe values from -2.0 to +0.2%o, and that pyrite/marcasite has lower 5 Fe values ( l%o) as compared to chalcopyrite. The variations in mineralogy and isotope composition are inferred to represent open-system equilibrium fractionation of Fe whereby... 

Phase separation greatly affects the chemistry of the hydrothermal emissions. More information on the fractionation of chemicals that occurs during phase separation is provided in the supplemental information for Chapter 19 available at http //elsevierdirect.com/ companions/9780120885305. 

Bermin J, Vance D, Archer C, Statham PJ (2006) The determination of the isotopic composition of Cu and Zn in seawater. Chem Geol 226 280-297 Berndt ME, Seal RR, Shanks WC, Seyfried WE (1996) Hydrogen isotope systematics of phase separation in submarine hydrothermal systems experimental calibration and theoretical models. 

There are, however, two limitations associated with preparation and application of zeolite based catalysts. First, hydrothermal syntheses Umit the extent to which zeolites can be tailored with respect to intended appUcation. Many recipes involving metals that are interesting in terms of catalysis lead to disruption of the balance needed for template-directed pore formation rather than phase separation that produces macroscopic domains of zeoUte and metal oxide without incorporating the metal into the zeohte. When this happens, the benefits of catalysis in confined chambers are lost. Second, hydrothermal synthesis of zeoHtic, silicate based soHds is also currently Hmited to microporous materials. While the wonderfully useful molecular sieving abihty is derived precisely from this property, it also Hmits the sizes of substrates that can access catalyst sites as weU as mass transfer rates of substrates and products to and from internal active sites. 

Here we are concerned with changes in the solid structure of the waste form, such as devitrification and phase separation in waste-containing glasses. Thus we need to understand the mechanisms and kinetics of the solid-state transformations and the effect of these changes on the solubility of the wastes. Besides the transformations that might occur in the dry state, we also need to know what hydrothermal changes might occur. 

This gel is then hydrothermally treated to convert it to the oxide. The gel helps to trap the cations and prevent phase separation. 

In all known cases the starting fluid for a submarine hydrothermal system is predominantly, if not entirely, seawater, which is then modified by processes occurring within the oceanic crust. Four factors have been identified the two most important are (i) phase separation and (ii) water-rock interaction the importance of (iii) biological processes and (iv) magmatic degassing has yet to be established. 

Water-rock interaction and phase separation are processes that are inextricably finked. As water passes through the hydrothermal system it wiU react with the rock and/or sediment substrate that is present (Figure 5). These reactions begin in the downflow zone, and continue throughout. When... 

The pressure conditions at any hydrothermal field are largely controlled by the depth of the overlying water column. Pressure is most critical in terms of phase separation and vent fluids are particularly sensitive to small changes in pressure when close to the critical point. It is in this region, close to the critical point, when fluids are very expanded (i.e., at very low density) that small changes in pressure can cause significant changes in vent-fluid composition. 

Bray A. M. and Von Damm K. L. (2003a) The role of phase separation and water—rock reactions in controlling the boron content of mid-ocean ridge hydrothermal vent fluids. Geochim. Cosmochim. Acta (in revision). 

Butterfield D. A., McDuff R. E., Mottl M. J., Lilley M. D., Lupton J. E., and Massoth G. J. (1994) Gradients in the composition of hydrothermal fluids from the endeavour segment vent field phase separation and brine loss. J. Geophys. Res. 99, 9561-9583. 

Charlou J.-L., Fouquet Y., Donval J. P., Auzende J. M., Jean Baptiste P., Stievenard M., and Michel S. (1996) Mineral and gas chemistry of hydrothermal fluids on an ultrafast spreading ridge East Pacific Rise, 17° to 19°S (NAUDUR cruise, 1993) phase separation processes controlled by volcanic and tectonic activity. J. Geophys. Res. 101, 15899-15919. 

DouviUe E., Charlou J. L., OeUcers E. H., Bienvenu P., Colon C. E. J., Donval J. P., Fouquet Y., Prieur D., and Appriou P. (2002) The rainbow vent fluids (36 degrees 14 N, MAR) the influence of ultramafic rocks and phase separation on trace metal content in Mid-Atlantic Ridge hydrothermal fluids. Chem. Geol. 184, 37-48. 

Von Damm K. L., Parker C. M., Gallant R. M., Loveless J. P., and the AdVenture 9 Science Party, (2002) Chemical evolution of hydrothermal fluids from EPR 21°N 23 years later in a phase separating world. EOS Trans. AGU (abstr.) 83, V61B-1365. 

You C.-F., Butterfield D. A., Spivack A. J., Gieskes J. M., Gamo T., and Campbell A. J. (1994) Boron and halide systematics in submarine hydrothermal systems effects of phase separation and sedimentary contributions. Earth Planet. Sci. Lett. 123, 227-238. 

Schematic diagram of hydrothermal convection. The left half is a cross section of a spreading center with a shallow heat source indicating the water flow. The right half is a schematic description of the relative locations of water-rock reactions (W-R Rxn) and phase separation along the flow of hydrothermal circulation. Adapted from German and Von Damm (2003).

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