Geochemical and rheological constraints on the dynamics of the oceanic upper mantle
Warren, Jessica M.
MetadataShow full item record
LocationSouthwest Indian Ridge
KeywordOcean 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
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.
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
Showing items related by title, author, creator and subject.
Trace element geochemistry of oceanic peridotites and silicate melt inclusions : implications for mantle melting and ocean ridge magmagenesis Johnson, Kevin T. M. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1990-06-15)The mantle melting process is fundamental to basalt genesis and crustal accretion at mid-ocean ridges. It is believed that melts ascend more rapidly than the surrounding mantle, implying a process similar to fractional ...
Interactions between mantle plumes and mid-ocean ridges : constraints from geophysics, geochemistry, and geodynamical modeling Georgen, Jennifer E. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2001-09)This thesis studies interactions between mid-ocean ridges and mantle plumes using geophysics, geochemistry, and geodynamical modeling. Chapter 1 investigates the effects of the Marion and Bouvet hotspots on the ultra-slow ...
Helium isotope geochemistry of oceanic volcanic rocks : implications for mantle heterogeneity and degassing Kurz, Mark D. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1982-06)The concentrations and isotopic compositions of helium have been measured in a number of mantle derived oceanic basalts. The goal of this research is to use the helium isotopic systematics to constrain the nature and ...