Publication Date:
2022-05-25
Description:
Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1998
Description:
Stable sulfur isotopes (δ34S) and trace Co are analyzed in sulfide and sulfate minerals
from six sample types collected from the TAG active mound, 26°N Mid-Atlantic Ridge.
δ34S values range from 2.7 to 2O.9%, with sulfate minerals isotopically indistinguishable
from seawater (21%), and sulfide minerals reflecting input of 1/3 seawater and 2/3
basaltic sulfur (~0%). Co concentrations in pyrite analyzed by ion microprobe primarily
reflect depositional temperatures. The δ34S and Co data are combined to provide
information regarding the sources and temperatures of parent fluids, the genetic
relationships among sample types, and the circulation of hydrothermal fluids and
seawater in the mound. δ34S values and Co concentrations vary by sample type.
Chalcopyrite from black smoker samples exhibits invariant δ34S values, indicating direct
precipitation from black smoker fluids. Crust samples contain chalcopyrite with a mean
δ34S indistinguishable from that of black smoker samples, and pyrite with some light δ34S
and moderately high Co values, consistent with crust samples precipitating from cooled
black smoker fluids. Massive anhydrite samples are a mixture of anhydrite with high
δ34S, and pyrite with variable δ34S and Co values, indicative of deposition from
disequilibrium mixing between black smoker fluids and seawater. White smoker samples
contain chalcopyrite and sphalerite with high δ34S, and pyrite with low Co values,
reflecting deposition from cooler fluids formed from mixtures of seawater and black
smoker fluid, with some reduction of sulfate. Mound samples contain chalcopyrite with a
mean δ34S indistinguishable from that of black smoker and crust samples, and pyrite with
low Co values, suggesting deposition from a fluid isotopically similar to black smoker
fluid at temperatures similar to those of white smoker fluid. Massive sulfide samples
exhibit pyrite with high δ34S values and very high Co, indicating deposition from and
recrystallization with very hot fluids contaminated with seawater-derived sulfate. The
data demonstrate that direct precipitation from black smoker fluids, conductive cooling,
disequilibrium mixing with entrained seawater, sulfate reduction, and recrystallization all
contribute to the formation of the TAG mound deposit. The successful preliminary Co
analyses demonstrate that ion microprobe analyses are a viable technique for measuring
trace elements in sulfides.
Keywords:
Hydrothermal vents
;
Submarine geology
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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