Workshop Report - Ridge 2000 Program

4. Regional Surveys. Variations in crustal thickness,
which may indicate variations in magma supply from the mantle,
are most efficiently mapped over large regions by combined
gravity and bathymetric surveys. In addition, gravity
measurements may provide some constraints on the thermal
structure of the mantle. Surveys may indicate the presence of
small-scale secondary convection which could influence the
melting process. Of particular importance is a determination of
the distribution of off-axis volcanism that may reflect spatial
variations in melt production in the vicinity of the ridge.
Laboratory Experiments
1. High Temperature/Pressure Experiments on Mantle
Materials. Experimental determination of the physical and
chemical behavior of mantle materials and melt-rock aggregates
over the range of relevant temperature (800-1400 0 C), pressure
(1-30 kbar), and strain rate conditions is critical to meaningful
interpretation of data obtained by field studies, as well as
to the parameterization of models which simulate components of
the upper mantle flow/melt regime beneath spreading centers.
Needed studies include characterization of: equilibrium and
non-equilibrium chemical interactions between melt and rock;
physical properties such as seismic velocities, electrical
conductivity, and rheology (particularly at low deviatoric
stress); and, the distribution of melt in, and permeability
of. partially molten peridotite.
2. Laboratory and Numerical Fluid Dynamic Experiments.
Laboratory and numerical fluid mechanics experiments on idealized
and analogue mantle systems result in testable predictions
about the behavior of the system they describe, directly
stimulate the design of field experiments, and show how the
integrated system might work. Laboratory experiments can give
direct information about fluid instabilities, episodicity of
transport phenomena, and complicated flows that are beyond the
range of present calculations. Numerical experiments, which can
involve more realistic geometries than laboratory analogues and
yield extensive quantitative predictions, can be developed in
three dimensions with supercomputers. Future experiments can
investigate: episodicity in melt and transport phenomena,
diapirism; flow with large variations in temperature, pressure
and temperature-dependent viscosity; two-phase flow including
compaction; coupling between two-phase flow and sub-solidus
thermal convection; and, interaction of mantle flow with the
lithosphere.
3. Numerical Modeling of Wave Propagation. Tomographic and
electromagnetic experiments require development of numerical
simulations of seismic and electromagnetic wave propagation in
three-dimensional, inhomogeneous, anisotropic media.
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