Title Information
Title
Dehydration-Induced Weakening at Sub-Seismic and Seismic Strain-Rates and Experimental Constraints on the Rheology of Serpentine and Olivine at Mantle Pressures
Name: Personal
Name Part
Proctor, Brooks Pierce
Role
Role Term: Text
creator
Origin Information
Copyright Date
2016
Physical Description
Extent
xii, 204 p.
digitalOrigin
born digital
Note
Thesis (Ph.D. -- Brown University (2016)
Name: Personal
Name Part
Hirth, Greg
Role
Role Term: Text
Director
Name: Personal
Name Part
Cooper, Reid
Role
Role Term: Text
Reader
Name: Personal
Name Part
Forsyth, Don
Role
Role Term: Text
Reader
Name: Personal
Name Part
Saal, Alberto
Role
Role Term: Text
Reader
Name: Personal
Name Part
Goldsby, David
Role
Role Term: Text
Reader
Name: Corporate
Name Part
Brown University. Geological Sciences
Role
Role Term: Text
sponsor
Genre (aat)
theses
Abstract
Serpentine is a common mineral in many seismically active regions of the crust and mantle. In this dissertation, rock deformation experiments were conducted on serpentine over a broad range of pressures, temperatures and strain-rates to explore how the rheology might be linked to seismicity. Rotary shear experiments were conducted on initially bare-rock surfaces of serpentinite and powdered serpentinite (gouge) at seismic-slip rates (> 0.1 m/s). Using 1-D thermal modeling, X-ray diffraction and microstructural analysis, I constrained the effects of velocity, normal stress, shear heating, strain localization and dehydration reactions on frictional weakening. I concluded that dynamic frictional weakening, observed in bare-surface and gouge samples, is caused by flash heating at asperity contacts. Slow strain rate experiments (10-5/s-10-7/s) were conducted on serpentine gouge at mantle pressures (1-2 GPa) in a Griggs-type deformation apparatus. At stable temperatures, serpentine undergoes a distinct transition from ductile to brittle deformation with increasing temperature. These samples exhibit a low velocity dependence that decreases with increasing temperature. This ‘high-temperature’ embrittlement may explain the occurrence of seismicity in serpentinized regions of subduction zones not undergoing dehydration. To explore the role of pore fluid pressure during dehydration, temperature ramping experiments were conducted in conjunction with a new experimental method that allows fluid pressure to be varied during dehydration. These experiments demonstrated that pore fluid imparts both a strong mechanical and chemical effect; increasing pore pressure is the dominant driver of weakening and pore water enhances the reaction-rate and grain-growth during metamorphism. I concluded that dehydration reactions are not directly generating earthquakes in subduction zones. Experiments conducted on pure olivine aggregates and fully dehydrated serpentine showed that talc promotes flow of olivine at 700 °C and 1 GPa at hydrothermal conditions. Based on microstructural observations, I concluded that pressure-solution along olivine-talc surfaces is causing olivine flow at differential stresses significantly lower than predicted by existing flow laws. Pressure-solution might be an important weakening mechanism in olivine-rich regions of the mantle wedge that contain talc.
Subject
Topic
dehydration weakening
Subject
Topic
pressure solution
Subject (FAST) (authorityURI="http://id.worldcat.org/fast", valueURI="http://id.worldcat.org/fast/1113344")
Topic
Serpentine
Subject (FAST) (authorityURI="http://id.worldcat.org/fast", valueURI="http://id.worldcat.org/fast/935123")
Topic
Friction
Record Information
Record Content Source (marcorg)
RPB
Record Creation Date (encoding="iso8601")
20160629
Language
Language Term: Code (ISO639-2B)
eng
Language Term: Text
English
Identifier: DOI
10.7301/Z079433F
Access Condition: rights statement (href="http://rightsstatements.org/vocab/InC/1.0/")
In Copyright
Access Condition: restriction on access
Collection is open for research.
Type of Resource (primo)
dissertations