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Black smoker
anhydrite
chimney
Collapsed
chimney
Mainly sulfides
Impermeable
crust
Sea floor basalt
hydrothermal fluid
Sea water
Cold (2°C)
Alkaline (pH~7-8)
Oxidizing
SO
4
-rich
Metal-deficient
Hydrothermal fluid
Hot (up to 400°C)
Acidic (pH~4-6)
Reducing
H
2
S-rich
Metal-rich
(Fe, Mn, Zn, Cu)
Fig. 4.3 Characteristics and general pattern of circulation of fluids at mid-ocean ridges. These
fluids are responsible for the construction of black smokers and lead to the accumulation of sulfides
on the seafloor (Modified from Robb 2007)
precipitation of sulfides from granite-sourced fluids. However, in the 1950s and
1960s geologists in Norway, Canada, and Australia developed the hypothesis that
these deposits in fact had formed on the ocean floor, an idea vindicated by the
subsequent discovery of the black smokers (Fig.
4.3
). Strengthened by important
contributions from Japanese geologists who undertook detailed studies of the
Besshi deposits around the same time, a volcanic exhalative model for the forma-
tion of this class of deposits is now widely accepted.
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