Workshop Report - Ridge 2000 Program

fossil hydrothermal systems in ophiolites and in other terrains
must be integrated with seafloor studies.
2. Geophysical data related to the subseafloor geometry
and structure of porosity and permeability are essential. These
data include seismic imaging, controlled source electromagnetic
sounding, static magnetic properties of rocks. and density
contrasts using seafloor and borehole gravimeters, all with
instruments developed for high resolution.
3. Heat flow, pore pressure, thermo-physical property. and
chemical concentration gradient data in sediments associated
with sediment-hosted hydrothermal systems must be collected.
4. Measurements of vent flow parameters covering the full
range from diffusive to jet-like flow are needed. The required
observations include direct. non-intrusive measurements of fluid
flow rates and fluxes, accurate and representative temperature
data, and subseafloor pore lJressure and chemical concentration
gradient data. Determinations of mixing rates at the sea floor
and in sub-bottom regions, compositions of the different parts.
and fluxes of chemical species are also important. Measurements
of the total heat output of the entire exhalative zone of axial
hydrothermal systems over time should be combined with
observations of the acoustic and seismic signatures of active
vents.
5. The chemical composition of reactants and products.
such as fluid components. hydrothermal precipitates, and altered
rocks need to be measured. Inorganic. organic and isotopic
analyses of these components must be integrated with these data.
6. Measurements should be collected below the seafloor,
including within ODP drill holes, of in situ physical parameters
and chemical properties. These include standard and innovative
wireline logs, geophysical experiments and geochemical
measurements of many different kinds. Geophysical experiments
may be required between boreholes. New, high temperature
instruments are clearly necessary.
7. These types of data must be combined with geophysical
and petrological measurements of magma chamber properties, as
well as geochemical and physical oceanographic measurements of
surface plumes, to provide a coherent. large-scale picture of
the entire seafloor hydrothermal system.
In conjunction with field programs, laboratory. theoretical.
and numerical developments must focus on specific geologic,
geochemical and geophysical processes to constrain subseafloor
water-rock interactions.
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