(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2004-06)
Braun, Michael Geoffrey
Observations at mid-ocean ridges indicate that magmas are focused to the ridge
axis by a network of porous dunites in near chemical isolation. This thesis investigates
several of the outstanding questions regarding the mechanisms of melt transport and its
effects on the shallow mantle. Chapter 1 details the current understanding of melt
migration from observations at mid-ocean ridges and ophiolites. Chapter 2 uses the size
distribution and abundance of dunites measured in the Oman ophiolite to place limits on
the potential mechanisms by which dunites form and subsequently estimate the flux of
chemically unequilbrated melt which a network of dunites can supply. Chapter 3
characterizes the chemical composition of dunites and harzburgites from Oman to further
constrain the process by which dunites form and relates the observed trends within
dunites to variations in the time-integrated meltrock ratio. Chapter 4 examines the
microstructures of peridotites in Oman to constrain the deformation mechanisms which
determine the viscosity of shallow mantle. Chapter 5 is a numerical investigation of
advection beneath ridges incorporating the rheology inferred from the observed
microstructures. Chapter 6 integrates the conclusions of the previous chapters,
reevaluating the potential melt flux through dunites and constraining the permeabilty of
the shallow mantle.
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