Chemistry of solutions from the 13°N East Pacific Rise hydrothermal site |
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| Authors: | G Michard F Albarède A Michard J-F Minster J-L Charlou N Tan |
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| Institution: | 1. Laboratoire de Géochimie des Eaux, Universitéde Paris 7, Paris France;2. C.R.P.G./E.N.S.G., Vandoeuvre-les-Nancy France;3. Institut de Physique du Globe de Paris, UniversitéPierre et Marie Curie, Paris France;4. Centre National pour l''Exploitation des Océans, Centre Océanologique de Bretagne, Brest France;5. E.N.S.E.M., Nancy France |
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| Abstract: | Ten samples were recovered by the submersible “Cyana” submersible from two groups of hydrothermal vents located 2600 m deep along the East Pacific Rise at 13°N. The maximum measured temperature was 317°C and minimum pH 3.8. A systematic determination of major and trace elements has been carried out and mixing lines between a high-temperature component (HTC) and seawater are observed. The water chemistry of the HTC slightly differs for several elements at the two sites. This HTC is deprived of SO4 and Mg and is greatly enriched in most other species. Maximum concentrations are (in units per kg):Cl = 0.72mol; Br = 1.1mmol; Na = 0.55mol; K = 29mmol; Rb = 14 μmol; Ca = 52mmol; Sr = 170 μmol; Mn = 750 μmol; Fe = 1mmol; Al = 15 μmol; Si = 21mmol. For many elements, the magnitude of the anomaly relative to seawater does not compare with the results obtained from the Galapagos or East Pacific Rise 21°N. The enrichment of cations relative to seawater is likely related to the huge Cl excess through charge balance. TheBr/Cl ratio is close to that for seawater. However, it is not clear whether the Cl excess is due to gas release or basalt hydration (formation of amphibole chlorite or epidote).P-T dependence of SiO2 solubility suggests that water-rock interaction last occurred at a depth in excess of 1 km below the sea floor. A mixing line of87Sr/86Sr vs. Mg/Sr demonstrates that the HTCs have a nearly identical87Sr/86Sr ratio of 0.7041 for both sites. A water/rock ratio of about 5 is inferred, which differs from the 1.5 value obtained at 21°N. |
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