Geologic tools on the ocean floor

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Geologic tools on the ocean floor

• Indirect methods
• Satellite Altimetry
• Airborne Magnetometry
• Seagoing Bathymetric mapping
• Gravity
• Magnetics
• Seismic Reflection
• Seismic Refraction
• Direct methods
• Deep tow
• Photography
• Bathymetry
• Gravity
• Magnetics
• ROV
• Submersible
• Dredging/Grabbing
• Coring
• Drilling

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• The Earths crust is divided into 7 major plates
  and a number of minor ones.

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• Plate motions are determined by rotations of the
  two plates about a pole (the Euler pole) on a
  spherical surface.
• Spreading ridges (and magnetic isochrons)
  describe great circles that converge at the pole
  of rotation.
• Transform faults lie on small circles with the
  Euler pole
• The velocity of rotation is described by ?, given
  in degrees per million years.

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Where ? and ? are the colatitude (90- latitude)
of the Euler pole and the point on the plate
boundary, ? and ? are their respective
longitudes, ? is the rotational velocity in
degrees/million years and a is the radius of the
Earth.
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Worked example The North America-Pacific plate
boundary in Alaska
If ? is .85 /myr, then ? 36.8 and u 3.2
km/myr (cm/yr).
In San Francisco, the latitude and longitude are
52.2 and -122, with the same pole Then ?30.15
and u2.7 km/myr.
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Morphology of the ridge axis The primary
determining factor is the spreading rate.
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Vertical Structure
Seismic structure varies strongly from place to
place.
However, an idealized seismic cross-section of
the crust is still possible.
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The depth-age correlation is a thermal
phenomenon, due to the cooling of the lithosphere.
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Rayleigh-Taylor instability
Laboratory experiments suggest that melt
upwelling beneath ridges may be concentrated into
periodically spaced upwelling centers. Geologic
observations were just beginning to arrive at the
same conclusion (Whitehead, et al. 1984).
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Focussed Accretion
Mantle Bouguer anomaly at the MAR near the Kane
Fracture Zone. Bullseyes indicate zones of hot
melt upwelling (Lin et al., 1990).
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Axial magma chambers