Description
- 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.
- Notes:
- Thesis (Ph.D. -- Brown University (2016)
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Citation
Proctor, Brooks Pierce,
"Dehydration-Induced Weakening at Sub-Seismic and Seismic Strain-Rates and Experimental Constraints on the Rheology of Serpentine and Olivine at Mantle Pressures"
(2016).
Earth, Environmental and Planetary Sciences Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://doi.org/10.7301/Z079433F
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Earth, Environmental and Planetary Sciences Theses and Dissertations
Theses and Dissertations for the Earth, Environmental and Planetary Sciences department....