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Title: The emplacement and deformation of high-temperature tuffs: a structural analysis of the Grey’s Landing ignimbrite, Snake River Plain, Idaho
Authors: Andrews, Graham Douglas Michael
Supervisors: Branney, Michael
Bonnichsen, Bill
Temperley, Steve
McCurry, Mike
Godchaux, Martha
Award date: Jan-2006
Presented at: University of Leicester
Abstract: The Grey’s Landing ignimbrite is an exceptionally well-preserved and well-exposed lava-like ignimbrite in the Snake River Plain volcanic province of southern Idaho, USA. High-grade tuffs are typically intensely welded and rheomorphic, preserving evidence of syn- and post-depositional ductile flow. The Grey’s Landing ignimbrite underwent two distinct phases of rheomorphism: (1) syn-depositional welding and rheomorphism as the deposit aggraded, producing a penetrative, mylonite-like L > S fabric including sheath folds, a strong elongation lineation, and shear-sense indicators; and (2) post-depositional, en masse, gravity-driven flow of parts of the deposit down palaeo-slopes, producing a fold-dominated deformation characterised by large-scale folds of the upper surface of the ignimbrite. Thermal and rheological modelling suggest that the original magma was hot (~ 950 °C), volatile-rich (≤ 5 wt % fluorine), and low viscosity (≥ 106 Pa.s-1). Syn-depositional rheomorphism had a strain rate of ~ 10-5 s-1 and deformed ignimbrite with a viscosity similar to the original magma. Postdepositional rheomorphism was limited to 6 months at the upper surface and ≤ 16 years in the centre of the thickest ignimbrite, at a strain rate of ~ 10-6 s-1.
Type: Thesis
Level: Doctoral
Qualification: PhD
Appears in Collections:Theses, Dept. of Geology
Leicester Theses

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