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 February 2007
Description:
Oceanic spreading centers are sites of magmatic, tectonic, and hydrothermal processes. In
this thesis I present experimental and seismological constraints on the evolution of these
complex regions of focused crustal accretion and extension. Experimental results from
drained, triaxial deformation experiments on partially molten olivine reveal that melt
extraction rates are linearly dependent on effective mean stress when the effective mean
stress is low and non-linearly dependent on effective mean stress when it is high.
Microearthquakes recorded above an inferred magma reservoir along the TAG segment
of the Mid-Atlantic Ridge delineate for the first time the arcuate, subsurface structure of a
long-lived, active detachment fault. This fault penetrates the entire oceanic crust and
forms the high-permeability pathway necessary to sustain long-lived, high-temperature
hydrothermal venting in this region. Long-lived detachment faulting exhumes lower
crustal and mantle rocks. Residual stresses generated by thermal expansion anisotropy
and mismatch in the uplifting, cooling rock trigger grain boundary microfractures if stress
intensities at the tips of naturally occurring flaws exceed a critical stress intensity factor.
Experimental results coupled with geomechanical models indicate that pervasive grain
boundary cracking occurs in mantle peridotite when it is uplifted to within 4 km of the
seafloor. Whereas faults provide the high-permeability pathways necessary to sustain
high-temperature fluid circulation, grain boundary cracks form the interconnected
network required for pervasive alteration of the oceanic lithosphere. This thesis provides
fundamental constraints on the rheology, evolution, and alteration of the lithosphere at
oceanic spreading centers.
Description:
Research was funded by a MIT Presidential Fellowship and NSF grants OCE-0095936, OCE-9907224, OCE-0137329, OCE-6892222, and OCE-6897400.
Keywords:
Seismology
;
Sea-floor spreading
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
Permalink