2026-09-20T23:25:32Zhttps://dspace.mit.edu/server/oai/requestoai:dspace.mit.edu:1721.1/346652022-01-13T21:16:16Zcom_1721.1_7582com_1721.1_7581col_1721.1_131022
Henry J.B. Dick.
Standish, Jared Jeffrey
Woods Hole Oceanographic Institution.
Joint Program in Oceanography
Woods Hole Oceanographic Institution
Massachusetts Institute of Technology. Department of Ocean Engineering
2006-11-07T16:52:37Z
2006-11-07T16:52:37Z
2006
2006
http://hdl.handle.net/1721.1/34665
71197031
Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2006.
Includes bibliographical references.
Between 90-25° E on the ultraslow-spreading Southwest Indian Ridge lie two sharply contrasting supersegments. One 630 km long supersegment erupts N-MORB that is progressively enriched in incompatible element concentrations from east to west. The second 400 km long supersegment contains three separate volcanic centers erupting E-MORB and connected by long amagmatic accretionary segments, where mantle is emplaced directly to the seafloor with only scattered N-MORB and E-MORB erupted. Rather than a major break in mantle composition at the discontinuity between the supersegments, this sharp contrast in geometry, physiography, and chemistry reflects "source" versus "process" dominated generation of basalt. Robust along-axis correlation of ridge characteristics (i.e. morphology, upwelling rate, lithospheric thickness), basalt chemistry, and crustal thickness (estimated from gravity) provides a unique opportunity to compare the influence of spreading geometry and rate on MORB generation. What had not been well established until now is the importance of melting processes rather than source at spreading rates < 20 mm/yr.
(cont.) Along the orthogonally spreading supersegment (14 mm/yr) moderate degrees of partial melting effectively sample the bulk mantle source, while on the obliquely spreading supersegment (7-14 mm/yr) suppression of mantle melting to low degrees means that the bulk source is not uniformly sampled, and thus "process" rather than "source" dominates melt chemistry.
by Jared Jeffrey Standish.
Ph.D.
286 p.
71489623 bytes
71488786 bytes
application/pdf
application/pdf
eng
Massachusetts Institute of Technology
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http://dspace.mit.edu/handle/1721.1/7582
Joint Program in Oceanography.
Earth, Atmospheric, and Planetary Sciences.
Woods Hole Oceanographic Institution.
Geochemistry
The influence of ridge geometry at the ultraslow-spreading Southwest Indian Ridge (9⁰-25⁰E) : basalt composition sensitivity to variations in source and process
Thesis
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<Abstract>Between 90-25° E on the ultraslow-spreading Southwest Indian Ridge lie two sharply contrasting supersegments. One 630 km long supersegment erupts N-MORB that is progressively enriched in incompatible element concentrations from east to west. The second 400 km long supersegment contains three separate volcanic centers erupting E-MORB and connected by long amagmatic accretionary segments, where mantle is emplaced directly to the seafloor with only scattered N-MORB and E-MORB erupted. Rather than a major break in mantle composition at the discontinuity between the supersegments, this sharp contrast in geometry, physiography, and chemistry reflects "source" versus "process" dominated generation of basalt. Robust along-axis correlation of ridge characteristics (i.e. morphology, upwelling rate, lithospheric thickness), basalt chemistry, and crustal thickness (estimated from gravity) provides a unique opportunity to compare the influence of spreading geometry and rate on MORB generation. What had not been well established until now is the importance of melting processes rather than source at spreading rates < 20 mm/yr.</Abstract>
<Abstract>(cont.) Along the orthogonally spreading supersegment (14 mm/yr) moderate degrees of partial melting effectively sample the bulk mantle source, while on the obliquely spreading supersegment (7-14 mm/yr) suppression of mantle melting to low degrees means that the bulk source is not uniformly sampled, and thus "process" rather than "source" dominates melt chemistry.</Abstract>
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