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Integrated Fe- and S-isotope study of seafloor hydrothermal vents at East Pacific Rise 9-10°N

Chemical Geology

By:
, , , and
DOI: 10.1016/j.chemgeo.2008.03.009

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Abstract

In this study, we report on coupled Fe- and S-isotope systematics of hydrothermal fluids and sulfide deposits from the East Pacific Rise at 9–10°N to better constrain processes affecting Fe-isotope fractionation in hydrothermal environments. We aim to address three fundamental questions: (1) Is there significant Fe-isotope fractionation during sulfide precipitation? (2) Is there significant variability of Fe-isotope composition of the hydrothermal fluids reflecting sulfide precipitation in subsurface environments? (3) Are there any systematics between Fe- and S-isotopes in sulfide minerals? The results show that chalcopyrite, precipitating in the interior wall of a hydrothermal chimney displays a limited range of δ56Fe values and δ34S values, between − 0.11 to − 0.33‰ and 2.2 to 2.6‰ respectively. The δ56Fe values are, on average, slightly higher by 0.14‰ relative to coeval vent fluid composition while δ34S values suggest significant S-isotope fractionation (− 0.6 ± 0.2‰) during chalcopyrite precipitation. In contrast, systematically lower δ56Fe and δ34S values relative to hydrothermal fluids, by up to 0.91‰ and 2.0‰ respectively, are observed in pyrite and marcasite precipitating in the interior of active chimneys. These results suggest isotope disequilibrium in both Fe- and S-isotopes due to S-isotopic exchange between hydrothermal H2S and seawater SO42− followed by rapid formation of pyrite from FeS precursors, thus preserving the effects of a strong kinetic Fe-isotope fractionation during FeS precipitation. In contrast, δ56Fe and δ34S values of pyrite from inactive massive sulfides, which show evidence of extensive late-stage reworking, are essentially similar to the hydrothermal fluids. Multiple stages of remineralization of ancient chimney deposits at the seafloor appear to produce minimal Fe-isotope fractionation. Similar affects are indicated during subsurface sulfide precipitation as demonstrated by the lack of systematic differences between δ56Fe values in both high-temperature, Fe-rich black smokers and lower-temperature, Fe-depleted vents.

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Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Integrated Fe- and S-isotope study of seafloor hydrothermal vents at East Pacific Rise 9-10°N
Series title:
Chemical Geology
DOI:
10.1016/j.chemgeo.2008.03.009
Volume
252
Issue:
3-4
Year Published:
2008
Language:
English
Publisher:
Elsevier
Description:
14 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Chemical Geology
First page:
214
Last page:
227
Other Geospatial:
East Pacific Rise