The nature and origin of fine-scale sea-floor relief
Citable URI
https://hdl.handle.net/1912/1832Location
Mid-Atlantic RidgeEast Pacific Rise
DOI
10.1575/1912/1832Keyword
Mid-ocean ridges; Ocean bottom; Submarine topographyAbstract
Bathymetric profiles of mid-ocean ridges show that the
morphology of ridge crests and the roughness of sea-floor
relief created there is commonly related to the spreading
rate. To study the creation of fine-scale sea-floor relief
at mid-ocean ridges, detailed bathymetric profiles of
mid-ocean rid£es collected with the deep tow instrument
package were compiled. Tectonic features were identified in
order to provide an estimate of the zone over which tectonic
relief is created. The results suggest the age of the sea-floor to which tectonism is active is considerably greater at the slow spreading Mid-Atlantic Ridge though not noticeably
variable among faster spreading centers. The roughness of
sea-floor relief was measured using longer deep tow profiles.
Surprisingly, the sea-floor relief created at slow spreading
centers is not noticeably rougher than that created at faster
spreading centers, contrary to the often noted inverse
relationship between sea-floor roughness and spreading rate.
It is postulated that the apparent smooth sea-floor relief created at fast spreading centers is due to the inability of
typical surface ship profiling systems to resolve the small
amplitude/ short wavelength relief created there.
Surface ship bathymetric profiles of mid-ocean ridges were
also compiled to better define the relationships between the
dimensions of median rifts or central highs at spreading
centers and the roughness of sea-floor relief as seen by
surface ship profiling systems with spreading rate. The
measurement of ridge crest dimensions shows that though the
slow spreading Mid-Atlantic Ridge commonly does have medium
rifts and the fast spreading East Pacific Rise has central
highs, when ridge crest dimensions are plotted versus
spreading rate, no clear correlation can be seen in the
individual oceans. The roughness of sea-floor relief was
measured using the compiled surface ship profiles. A good
inverse correlation between roughness and spreading rate can
be seen in the Atlantic but not in the Pacific.
The hypothesis that the roughness of sea-floor relief created
at spreading centers is related to the ability of the lithosphere
to support relief within the zone of relief formation
was considered. The strength of the lithosphere at spreading
centers was estimated from measured strengths of rocks and
theoretical thermal models of the lithosphere near spreading
axes. The load imposed on the lithosphere by sea-floor relief
was estimated using deep tow bathymetric profiles. The
calculations show the lithosphere should achieve much higher
strengths within the zone of relief formation at slow
spreading centers compared to fast spreading centers.
Furthermore, the calculated lithospheric strengths within the
zone of relief formation increase exponentially for spreading
centers of lower spreading rates. This can explain why an
inverse correlation between sea-floor roughness and spreading
rate could be seen along the slow spreading Mid-Atlantic Ridge
but not along the fast spreading East Pacific Rise. Finally,
the extent of tectonism, or the width of the zone of relief
formation, at spreading centers is suggested to be controlled
by the width of magma chambers at faster spreading centers and
the extent of viscous forces at deeply rifted slow spreading centers.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution December 1979
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Suggested Citation
Thesis: Shih, John Shai-Fu, "The nature and origin of fine-scale sea-floor relief", 1979-12, DOI:10.1575/1912/1832, https://hdl.handle.net/1912/1832Related items
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