Amini, Marghaleray

Augustin, Nico

Eisenhauer, Anton

Garbe-Schönberg, C.-Dieter

Krabbenhöft, André

English

OceanRep

Geophysical Research Abstracts,Vol. 11, EGU2009-4328-3, 2009EGU General Assembly 2009© Author(s) 2009Calcium and strontium isotope (δ44/40Ca, δ88/86Sr) fractionation in hightemperature hydrothermal systems: First insights from 4°48’S, MARN. Augustin (1), A. Eisenhauer (1), M. Amini (2), D. Garbe-Schönberg (3), and A. Krabbenhöft (1)(1) IFM-GEOMAR, Leibniz Institute of Marine Sciences, Wischhofstr. 1-3, 24148 Kiel, Germany, (2) University ofSaskatchewan, 114 Science Place, Saskatoon, SK, S7N 5E2, Canada, (3) Institute of Geosciences, University of Kiel,Ludewig-Meyn-Straße 10, 24118 Kiel, GermanyCa isotope fractionation in hydrothermal systems has been recently demonstrated as a result of fluid flow andmineral precipitation (Amini et al., 2008). In this study, we investigate the Ca and Sr isotopic systematic of threehydrothermal vent sites in order to further constrain potential isotopic effects along hydrothermal pathways inparticular during phase separation at temperatures>400˚C. Therefore, the Ca (δ44/40Ca) and Sr (δ88/86Sr) isotopiccompositions of high-temperature vent fluids of the hydrothermal vent sites Turtle Pits (TP), Comfortless Cove(CC) and Red Lion (RL) at the 4˚48´ S Mid-Atlantic Ridge were determined and compared. Both, Ca and Srisotope ratios were measured by thermal ionization mass spectrometry using double spike technique (48Ca/43Ca-,and 87Sr/84Sr-double spike, respectively) and reported in δ notation relative to seawater.At the non-boiling system RL, the Ca concentration of pristine seawater ([Ca]SW ) changes from about 10.2 mMto about 16 mM (RL) in the hydrothermal end-member ([Ca]HydEnd) adopting thereby a δ44/40CaHydEnd of-0.91±0.09h (RL) relative to seawater. This value is in good agreement with previously reported data for non-phase separated fluids from the Logatchev hydrothermal field (LHF; 15˚N) (Amini et al., 2008). In contrast, the Caconcentration of hydrothermal fluids from the two boiling vent sites Comfortless Cove and Turtle Pits ([Ca]HydEnd=10.5 mM) rather resemble that of seawater, and with a δ44/40CaHydEnd of -1.14±0.08h relative to seawaterthey are isotopically significantly lighter than fluids from the non-boiling systems, RL and LHF. This suggeststhat Ca isotope fractionation along hydrothermal pathways is influenced by the thermal conditions prevailing in ahydrothermal system. Amini et al. (2008) indicate a negative correlation between Ca isotope fractionation duringthe precipitation of anhydrite and the mineral formation temperature. We, therefore suggest hydrothermal anhydriteprecipitation being a controlling factor for Ca isotope fractionation in hydrothermal systems.Likewise, the Sr concentrations and isotopic compositions of the fluids differ between seawater, the non-boilinghydrothermal vent site RL and the boiling systems CC and TP. While the strontium concentration of seawater([Sr]SW ) change during the transformation to a hydrothermal fluid from about 90 µM to ∼70 µM at RF andadopt a δ88/86SrHydEnd of -0.17±0.01h relative to seawater, [Sr]HydEnd of fluids from CC and TP is ∼50 µMlower with δ88/86SrHydEnd = -0.14±0.01h). Changes in the Sr composition in hydrothermal systems are due towater/rock interaction and fluid-mineral reactions during ocean crust alteration.. The mechanism underlying theseprocesses to fractionate Sr isotopes and their meaning for the global Sr cycling is not known yet and has to befurther constrained.References:Amini, M., Eisenhauer, A., Böhm, F., Fietzke, J., Bach, W., Garbe-Schönberg, D., Rosner, M., Bock, B., Lacksche-witz, K. S., and Hauff, F., 2008. Calcium isotope (δ44/40Ca) fractionation along hydrothermal pathways, Logatchevfield (Mid-Atlantic Ridge, 14˚45´N). Geochimica et Cosmochimica Acta 72, pp. 4107–4122.

Calcium and strontium isotope (d44/40Ca, d88/86Sr) fractionation in high temperature hydrothermal systems: First insights from 4°48'S, MAR

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