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.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:530567 |
| Date | January 2006 |
| Creators | Andrews, Graham Douglas Michael |
| Contributors | Branney, Michael ; Bonnichsen, Bill ; Temperley, Steve ; McCurry, Mike ; Godchaux, Martha |
| Publisher | University of Leicester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/2381/7933 |
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