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 June 2017
Description:
This thesis investigates the formation and subsequent motion of oceanic lithospheric plates
through geophysical and petrological methods. Ocean crust and lithosphere forms at mid-ocean
ridges as the underlying asthenosphere rises, melts, and flows away from the ridge axis. In
Chapters 2 and 3, I present the results from partial melting experiments of mantle peridotite that
were conducted in order to examine the mantle melting point, or solidus, beneath a mid-ocean
ridge. Chapter 2 determines the peridotite solidus at a single pressure of 1.5 GPa and concludes
that the oceanic mantle potential temperature must be ~60ºC hotter than current estimates.
Chapter 3 goes further to provide a more accurate parameterization of the anhydrous mantle
solidus from experiments over a range of pressures. This chapter concludes that the range of
potential temperatures of the mantle beneath mid-ocean ridges and plumes is smaller than
currently estimated. Once formed, the oceanic plate moves atop the underlying asthenosphere
away from the ridge axis. Chapter 4 uses seafloor magnetotelluric data to investigate the
mechanism responsible for plate motion at the lithosphere-asthenosphere boundary. The
resulting two dimensional conductivity model shows a simple layered structure. By applying
petrological constraints, I conclude that the upper asthenosphere does not contain substantial
melt, which suggests that either a thermal or hydration mechanism supports plate motion.
Oceanic plate motion has dramatically changed the surface of the Earth over time, and evidence
for ancient plate motion is obvious from detailed studies of the longer lived continental
lithosphere. In Chapter 5, I investigate past plate motion by inverting magnetotelluric data
collected over eastern Zambia. The conductivity model probes the Zambian lithosphere and
reveals an ancient subduction zone previously suspected from surface studies. This chapter
elucidates the complex lithospheric structure of eastern Zambia and the geometry of the tectonic
elements in the region, which collided as a result of past oceanic plate motion. Combined, the
chapters of this thesis provide critical constraints on ocean plate dynamics.
Description:
Funding for this research was provided by the National Science Foundation Division of Earth
Sciences (EAR) grant number 1010432, Division of Ocean Sciences (OCE) grant numbers
1459649 and 0928663, WHOI Deep Ocean Exploration Institute, and the WHOI Academic
Programs Office.
Keywords:
Lithosphere
;
Ocean
;
Temperature
;
Mid-Atlantic Ridge
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
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