Geochemistry of vent fluid particles formed during initial hydrothermal fluid–seawater mixing along the Mid-Atlantic Ridge

Klevenz, Verena, Bach, Wolfgang, Schmidt, Katja, Hentscher, Michael, Koschinsky, Andrea and Petersen, Sven (2011) Geochemistry of vent fluid particles formed during initial hydrothermal fluid–seawater mixing along the Mid-Atlantic Ridge Geochemistry Geophysics Geosystems, 12 . Q0AE05. DOI 10.1029/2011GC003704.

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We present geochemical data of black smoker particulates filtered from hydrothermal fluids with seawater-dilutions ranging from 0–99%. Results indicate the dominance of sulphide minerals (Fe, Cu, and Zn sulphides) in all samples taken at different hydrothermal sites on the Mid-Atlantic Ridge. Pronounced differences in the geochemistry of the particles between Logatchev I and 5°S hydrothermal fields could be attributed to differences in fluid chemistry. Lower metal/sulphur ratios (Me/H2S < 1) compared to Logatchev I result in a larger amount of particles precipitated per liter fluid and the occurrence of elemental sulphur at 5°S, while at Logatchev I Fe oxides occur in larger amounts. Systematic trends with dilution degree of the fluid include the precipitation of large amounts of Cu sulphides at a low dilution and a pronounced drop with increasing dilution. Moreover, Fe (sulphides or oxides) precipitation increases with dilution of the vent fluid by seawater. Geochemical reaction path modeling of hydrothermal fluid–seawater mixing and conductive cooling indicates that Cu sulphide formation at Logatchev I and 5°S mainly occurs at high temperatures and low dilution of the hydrothermal fluid by seawater. Iron precipitation is enhanced at higher fluid dilution, and the different amounts of minerals forming at 5°S and Logatchev I are thermodynamically controlled. Larger total amounts of minerals and larger amounts of sulphide precipitate during the mixing path when compared to the cooling path. Differences between model and field observations do occur and are attributable to closed system modeling, to kinetic influences and possibly to organic constituents of the hydrothermal fluids not accounted for by the model.

Document Type: Article
Keywords: Mid-Atlantic Ridge ; geochemical modeling ; geochemistry ; hydrothermal fluids ; hydrothermal mixing zone particles; RV Meteor; RV Maria S. Merian, RV Atlalante; ROV Quest, ROV Kiel6000
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
Refereed: Yes
DOI etc.: 10.1029/2011GC003704
ISSN: 1525-2027
Projects: Future Ocean, SPP 1144 "From Mantle to Ocean"
Date Deposited: 25 Oct 2011 07:43
Last Modified: 13 Mar 2018 08:07

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