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    The influence of ridge geometry at the ultraslow-spreading Southwest Indian Ridge (9º-25ºE) : basalt composition sensitivity to variations in source and process

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    Standish'05_Final_thesis.pdf (21.72Mb)
    Date
    2006-02
    Author
    Standish, Jared J.  Concept link
    Metadata
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    Citable URI
    https://hdl.handle.net/1912/1508
    Location
    9°-25°E
    Southwest Indian Ridge
    DOI
    10.1575/1912/1508
    Keyword
     Crust; Geochemistry; Knorr (Ship : 1970-) Cruise KN162; Melville (Ship) Cruise VAN-7; Agulhas (Ship) Cruise AG22 
    Abstract
    Between 9º-25º 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 EMORB 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. 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.
    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 February 2006
    Collections
    • WHOI Theses
    • Geology and Geophysics (G&G)
    Suggested Citation
    Thesis: Standish, Jared J., "The influence of ridge geometry at the ultraslow-spreading Southwest Indian Ridge (9º-25ºE) : basalt composition sensitivity to variations in source and process", 2006-02, DOI:10.1575/1912/1508, https://hdl.handle.net/1912/1508
     

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