Publication Date:
2022-05-25
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 September 2007
Description:
I provide constraints on mantle convection through observations of the rheology and
composition of the oceanic upper mantle. Convection cannot be directly observed, yet is
a fundamental part of the plate tectonic cycle. Relative motion among plates is accommodated
by localized deformation at their boundaries. I demonstrate that in the ductile regime,
strain localization occurs when different mineral phases are mixed together, limiting grain
annealing. Upper mantle flow is by dislocation creep, resulting in seismic anisotropy due
to mineral alignment. I use a shear zone in the Josephine Peridotite to quantify the relationship
between mineral orientation and shear strain, providing an improved framework
for the interpretation of seismic anisotropy. The upper mantle is generally assumed to be
homogeneous in composition. From detailed isotopic and chemical analyses of abyssal
peridotites from the Southwest Indian Ridge, I show that the mantle is heterogeneous at a
range of length-scales. Abyssal peridotites recovered at ocean ridges are generally interpreted
as the depleted residues of melt extraction. I find that melt-rock reaction is a significant
part of the melt extraction process, modifying the composition of the lithospheric
mantle. The generation of heterogeneous lithosphere provides a source for asthenospheric
heterogeneity, via subduction and mantle convection.
Description:
This work has been supported financially by a variety of sources, including a Hollister
Fellowship from WHOI, the Richard Vanstone Fund at WHOI and student travel assistance
funds at both WHOI and MIT. Funding from the National Science Foundation was
provided by grants OCE-0526905 and OCE-0624408 to H.J.B.D., EAR-0230267, EAR-
0405709 and EAR-0409609 to G.H., and EAR-0115433 and EAR-0106578 to N.S. Research
at ISEI, Japan, was supported by COE-21 funding to E.N.
Keywords:
Ocean bottom
;
Core-mantle boundary
;
Melville (Ship) Cruise Vancouver Expedition Leg 7
;
Islas Orcadas (Ship) Cruise IO11/76
;
Agulhas (Ship) Cruise AG22
;
Polarstern (Ship) Cruise PS86
;
Knorr (Ship : 1970-) Cruise KN162
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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