(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2016-02)
Feng, Helen S.-H.
This thesis examines the structure of Pacific oceanic lithosphere that has been modified
by post-formation magmatism in order to better understand the processes of secondary
magmatic evolution of the lithosphere, which can have global-scale implications for
oceanic and atmospheric chemistry. In the western Pacific, widespread Cretaceous
magmatism has modified oceanic lithosphere over hundreds of millions of square
kilometers. Seismic models of the upper crust from within the Jurassic Quiet Zone and
the crust and upper mantle near the Mariana Trench reveal crust that is locally thickened
via focused extrusive volcanism and crust that is modestly but uniformly thickened over
broad regions. These distinct modes of magmatic emplacement suggest the operation of
both focused and diffuse modes of melt transport through the lithosphere. Analysis of
seismic observations from Guaymas Basin, in the Gulf of California, endeavor to advance
our understanding of sill-driven alteration of sediments, an important consequence of
secondary magmatism. We show that seismically imaged physical disruption to
sediments due to igneous sill intrusion can be related to changes in sediment physical
properties that reflect alteration processes. We also show how sill thickness can be
estimated, enabling alteration intensity to be related to sill thickness in a variety of
settings.
