Workshop Report - Ridge 2000 Program

GROUP 4:
SUBSEAFLOOR HYDROTHERMAL PROCESSES
Members:
Johnson Cann. Co-Chairman
John Edmond. Co-Chairman
Alan Chave. John Delaney. David Janecky.
Marc Langseth. Robert Lowell. Russell McDuff.
Peter Rona. William Seyfried. Wayne Shanks.
Norman Sleep. Geoffrey Thompson. Richard von Herzen
Motivation and Goals
Seafloor hydrothermal systems are a central component of a
dynamic process that transfers energy and mass through the crust
of the earth. Chemical and thermal exchanges between the ocean
and the oceanic crust in hydrothermal systems play a major role
in the cooling of the earth. the genesis of many types of ore
deposits. control of geochemical mass balances that influence
the composition of the oceans. and the ecology of associated
chemosynthetic animal communities. An order of magnitude
estimate of the flow rate of seawater shows that the entire
ocean is cycled through the oceanic crust every few million
years. equivalent to a flow rate of several million gallons per
second. The thermal power output of this system is about 10
million megawatts. Previous and current research on seafloor
hydrothermal systems has begun to address the complexity of the
physical. chemical. and biological components involved in the
interactions between circulating seawater and the lithosphere.
New approaches are required to understand the physics and
chemistry of t.he individual processes which produce t.emporal and
spatial variability of hydrothermal circulation. and the
geological products of rock-water interactions.
Rocks and sediments which make up the seafloor are permeable.
allowing wat.er to penetrate t.hrough t.he seafloor and into
the oceanic lithosphere. The downwelling seawater is heated
when it. flows near the magmat.ic sources which drive hydrothermal
circulation. The most prominent locus of magmatic activity is
the ridge system which extends through all the ocean basins. In
addition. magmatic activity is associated with volcanic centers.
Research into hydrothermal flow complements the investigations
of magmatic systems proposed by Working Groups 1 and 2 and will
reveal the intertwined dynamics of the magma-hydrothermal system.
In fact. it is likely that hydrothermal activity strongly
affects the depth and geometry of crustal magma chambers on
mid-ocean ridges. A primary objective in the future study of
the global mid-ocean ridge system is to understand the physical.
chemical. and biological processes involved in the interactions
between circulating seawater and the lithosphere.
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