Evidence for a welded tuff in the rhyolite of Calico Hills
- Science Applications International Corp., Golden, CO (United States)
- Geological Survey, Denver, CO (United States)
A welded pyroclastic deposit has been identified in the Rhyolite of Calico Hills near Yucca Mountain, Nevada, where only lava flows and nonwelded pyroclastic deposits were previously described. Field data from Fortymile Wash show that nonwelded, bedded tuff grades upward into partially welded massive tuff, and thence into densely welded vitrophyre. Petrographic data show a progressive decrease in inter- and intragranular porosity and amount of vapor-phase minerals, with increasing welding. Pumice fragments are first deformed, then develop diffuse boundaries which become increasingly obscure with progressive welding. The most densely welded rock is a perlitic vitrophyre. The origin of this welded tuff is not clear, as it could represent an ignimbrite or a tuff fused beneath a thick lava flow.
- Research Organization:
- American Society of Civil Engineers, New York, NY (United States); American Nuclear Society, La Grange Park, IL (United States)
- OSTI ID:
- 60926
- Report Number(s):
- CONF-940553--Vol.4
- Country of Publication:
- United States
- Language:
- English
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