Workshop Report - Ridge 2000 Program

Strategies For Solving The Critical Problems
We envision a strategy with four major components.
1. Global Reconnaissance. The first component would
include reconnaissance studies of substantial lengths of the
mid-ocean ridge system in order to obtain a measure of the world
wide variability of ocean ridge morphologic, structural and
chemical characteristics. The reonnaissance would include
bathymetric surveys over a distance of approximately 1000 km
continuously along the strike of the ridge, with a swath width
of several times the active accretion zone; multichannel seismiC
(MCS) surveys along the axis to define the lateral continuity
and width of the axial low velocity zone and any variations in
seismically estimated crustal thickness; petrological sampling
with approximately one station for every 10 to 20 km of ridge
length, in order to determine the regional geochemical signature
and to explore quantitative relationships among petrology,
bathymetry, and the MCS axial reflector, and continuous
surveying of along-axis water column temperature and chemical
anomalies, in order to determine the distribution of
hydrothermal activity. Such reconnaissance surveys should cover
ridges which vary in their spreading rate, in their tectonic
style (i .e., fracture zone spacing, presence or absence of rift
valley, back-arc settings L and in the ambient mantle
temperature (i.e., hot spots such as Ic.:land and cold spots such
as the Australian!Antarctic Discordance). Approximately ten
such surveys will be necessary to obtain adequate global
coverage. These surveys will lead to coverage of about
20 percent of the entire system of ocean ridges. They will
determine the global distribution of magma chambers and provide
the data necessary to develop quantitative relationships among
spreading rate, gross tectonic fabric, magma chambers and
geochemistry.
2. Eruption Detection. The second component stems from
the recognition that the ocean ridge volcano observatory should
be located in an area of active volcanism. To find such a
location we need to know the periodicity in space and time of
volcanic eruptions on the sea floor, and the relationship of
such eruptions to hydrothermal activity. There is at the moment
no such information for submarine ocean ridges. Calculation of
magma production rates and analogy with terrestrial volcanos
suggests we should be able to find an active volcanic area which
would remain active on the time scale of a decade. To find such
a location, however, requires effective eruption monitoring.
Two approaches could be explored: (a) long term monitoring of
hydrothermal plumes and (b) acoustic monitoring. In addition to
locating active ridge segments, such monitoring will provide
data concerning regional eruption frequency and spatial
systematics.
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