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Submarine Hot Springs, Cold Seeps, and Serpentinte Diapirs on the Pacific Rim


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Author Motti MJ


Fluid circulation occurs in oceanic crust of
all ages, at the seafloor spreading axis, on mid-
ocean ridge flanks, in the ocean basins, and in
subduction zones. In the first three settings
the fluid originates as seawater. At the axis
and on the ridge flanks, the circulating seawater
produces a major chemical exchange between the
oceans and the crust. Based on heat budget
constraints, between 10 and 40% of the river flux
of Mg can be taken up during high-temperature
alteration of the basaltic crust along the mid-
ocean ridge axis. Most of the hydrothermal -heat
loss, however, occurs on the mid-ocean ridge
flanks, where the temperatures are lower and the
seawater flux correspondingly larger. The
estimated heat loss on the flanks is so large
that upwelling must occur over a large fraction
(5-30%) of the seafloor less than 65 Ma in age,
at seepage velocities on the order of 10 to 100
cm/yr. The circulating seawater need lose less
than 1 to 2% of its Mg content in order to solve
the Mg mass balance for the oceans. Fluids in
subduction zones are commonly less saline than
seawater and are rich in methane and other light
hydrocarbons. These fluids may originate by
dewatering of the downgoing slab. If so, they
may close the geochemical cycle of H2O that began
with hydration of the basaltic crust at the ridge