Modeling of geochemical processes in the submarine discharge zone of hydrothermal solutions
- Saint-Petersburg Mining University
Abstract
The paper reviews the main methods and analyzes modeling results for geochemical processes in the submarine discharge zone of hydrothermal solutions of mid-ocean ridges. Initial data for modeling have been obtained during several marine expeditions, including Russian-French expedition SERPENTINE on the research vessel «Pourquoi Рas?» (2007). Results of field observations, laboratory experiments and theoretical developments are supported by the analysis of regression model of mixing between hydrothermal solutions and sea water. Verification of the model has been carried out and the quality of chemical analysis has been assessed; degree and character of participation of solution components in the hydrothermal process have been defined; the content of end members has been calculated basing on reverse forecasting of element concentration, depending on regression character; data for thermodynamic modeling have been prepared. Regression model of acid-base properties and chloridity of mineralizing thermal springs confirms adequacy of the model of double-diffusive convection for forming the composition of hydrothermal solutions. Differentiation of solutions according to concentrations of chloride-ion, depending on temperature and pH indicator within this model, is associated with phase conversions and mixing of fluids from two convection cells, one of which is a zone of brine circulation. In order to carry out computer thermodynamic modeling, hydro-geochemical and physicochemical models of hydrothermal discharge zone have been created. Verification of the model has been carried out basing on changes of Mn concentration in the hydrothermal plume. Prevailing forms of Mn migration in the plume are Mn 2+ , MnCl + , MnCl 2 . Two zones have been identified in the geochemical structure of the plume: 1) high-temperature zone (350-100 °С) with prevalence of chloride complexes – ascending plume; 2) low-temperature zone (100-2 °С), where predominant form of transfer is a free divalent ion – lateral plume. Sulfate complex in insignificant quantities (1.5 %) is detected in the lateral plume, whereas hydroxide complex is stable at temperatures 325-125 °С and can only be found in the ascending plume. Results of modeling almost fully correspond to field observations. Verification of thermodynamic model proves its adequacy and allows to make a transition to the next stage of research – examination of geochemical dissipation for key ore components of hydrothermal solutions – Fe, Cu, Zn etc.
References
- Bogdanov Yu.A. Hydrothermal Mineralizations of Mid-Atlantic Ridge Rifts. Мoscow: Nauchnyi mir, 1997, p. 167
- (in Russian).
- Hydrothermal Sulfide Ores and Metal-Bearing Sediments of the Ocean. Ed. by I.S.Gramberg. St. Petersburg: Nedra, 1992, p. 278 (in Russian).
- Grichuk D.V. Thermodynamic Models of Submarine Hydrothermal Systems. Мoscow: Nauchnyi mir, 2000, p. 304
- (in Russian).
- Rona P. Hydrothermal Mineralization of Spreading Areas in the Ocean. Мoscow: Mir, 1986, p. 159 (in Russian).
- Sudarikov S.M., Zmievskii M.V. Geochemistry of Ore-Forming Hydrothermal Fluids of the World Ocean. Zapiski Gornogo instituta. 2015. Vol. 215, р. 5-15 (in Russian).
- Sudarikov S.M. Hydromineral Occurrences in the Ocean. Geodinamika i rudogenez Mirovogo okeana. Nauch. red. akad. I.S.Gramberg. St. Petersburg: VNIIOkeangeologiya, 1999, p. 62-72 (in Russian).
- Sudarikov S.M., Kaminskii D.V., Narkevskii E.V. Hydrothermal Dispersion Halos in the Natural Waters of Mid-Atlantic Ridge. St. Petersburg: FGUP «VNIIOkeangeologiya im. I.S.Gramberga», 2014, p. 161 (in Russian).
- Sudarikov S.M., Zmievskii M.V. Study on Migration Forms of Ore Elements in Hydrothermal Solutions of the Mid-Atlantic Ridge. Izvestiya vysshikh uchebnykh zavedenii. Geologiya i razvedka, 2016. N 3, p. 31-35 (in Russian).
- Sudarikov S.M., Krivitskaya M.V. Forming of Hydrogeochemical Dispersion Halos in Discharge Zones of Thermal Solutions on the Mid-Atlantic Ridge. Zapiski Gornogo instituta. 2011. Vol. 189, p. 68-71 (in Russian).
- Shvarov Yu.V. On Thermodynamic Models of Actual Solutions. Geokhimiya. 2007. N 6, р. 670-679 (in Russian).
- Shvarov Yu.V. HCh: New Possibilities in Thermodynamic Modeling of Geochemical Systems, Available for Windows. Geokhimiya. 2008. N 8, p. 898-903 (in Russian).
- Bischoff J.L., Rosenbauer R.J. Phase Separation in Seafloor Geothermal Systems by Layered Double-Diffusive Convection. J. Geol. 1989. Vol. 97, p. 613-623.
- Bowers T.S., Von Damm K.L., Edmond J.M. Chemical Evolution of Mid-Ocean Ridge Hot Springs. Geochimica et Cos-mochimica Acta. 1985. Vol. 49 (19/20), p. 2239-2252.
- Charlou J.-L., Donval J.-P., Konn C., Birot D., Sudarikov S., Jean-Baptiste P. High Hydrogen and Abiotic Hydrocarbons from New Ultramafic Hydrothermal Sites Between 12 N and 15 N on the Mid-Atlantic Ridge. Results of the Serpentine Cruise (March 2007). EOS, Transactions of the American Geophysical Union. 2007. Vol. 88, p. 52.
- Charlou J.-L., Donval J.-P., Konn C., Ondreas H., Fouquet Y. High Production and Fluxes of H2 and CH4 and Evidence of Abiotic Hydrocarbon Synthesis by Serpentinization in Ultramafic-Hosted Hydrothermal Systems on the Mid-Atlantic Ridge. Diversity of Hydrothermal Systems on Slow Spreading Ocean Ridges. Geophysical Monograph Series 188. American Geophysical Union. 2010, p. 265-295.
- Garrels R.M., Christ C.L. Solutions, Minerals and Equilibria. New York: Harper & Row, 1965, p. 368.
- Mottl M.J. Metabasalts, Axial Hot Springs and the Structure of Hydrothermal Systems at Mid-Ocean Ridges. Geol. Soc. Amer. Bull. 1983. Vol. 94. N 2, p. 161-180.
- Sudarikov S.M., Roumiantsev A.B. Structure of Hydrothermal Plumes at the Logatchev Vent Field, 14°45' N, Mid-Atlantic Ridge: Evidence from Geochemical and Geophysical Data. Journal of Volcanology and Geothermal Research. 2000. Vol. 101, p. 245-252.
- Sudarikov S.M., Zhirnov E. Hydrothermal Plumes along the Mid-Atlantic Ridge: Preliminary Results of the CTD Investi-gations During the DIVERS Expedition (July 2001). InterRidge News. 2001. 10 (2). 33-36.
- Von Damm K. Seafloor Hydrothermal Activity: Black Smoker Chemistry and Chimneys. Annu. Rev. Earth Planet. Sci. 1990. Vol. 18, p. 173-204.