My blogging will be light through this coming week - unless I find some unexpected free time - so I'm going to post some links I found recently about rheomorphic tuffs and voluminous silicic lava flows. My first exposure to these kinds of rocks - ash-flow tuffs or ignimbrites that are so strongly welded that they can be mistaken for rhyolite flows and domes - was in the High Rock country north of Gerlach, NV, and near Soldier Meadow, back during my days of uranium exploration. The rocks in question in that area were peralkaline (or peralkalic) ash-flow tuffs that showed laminated textures more typical of flows. Rheomorphic tuffs (RT - my abbreviation) can apparently be difficult to distinguish from extensive or voluminous silicic lava flows (VSLF - my abbreviation). The rhyolite of Dorsey Creek (Tdc) - which we saw here and here near Jarbidge, NV, and which erupted about 8 million years ago from the Bruneau-Jarbidge eruptive center - is a voluminous rhyolite flow. I'm not sure I'd be able to tell these things apart - RT v. VSLF - without doing some real research and going on a good field trip or two.
Volcanological aspects of peralkaline silicic welded ash-flow tuffs (1974): Bulletin of Volcanology [abs].
Mid-Tertiary silicic alkalic magmatism of Trans-Pecos Texas: Rheomorphic tuffs and extensive silicic lavas (1989): NM Bureau of Geology and Mineral Resources [buy Memoir 46, it looks good!]. NOTE: the silicic magmatism of the region is "commonly peralkaline" and includes "strongly rheomorphic welded tuffs, and unusually widespread silicic lavas." This is a field guide.
In situ formation of welded tuff-like textures in the carapace of a voluminous silicic lava flow, Owyhee County, SW Idaho (1996): Bulletin of Volcanology [abs]. NOTE: this is about the Badlands Rhyolite, a VSLF with textures similar to rheomorphic tuffs.
Field guide to the Rattlesnake Tuff and High lava Plains near Burns, Oregon (1999): Oregon Geology. NOTE: This is the only full article in the batch, and it not only mentions rheomorphic tuffs and peralkaline magmatism, but it is also a field guide.
Distinguishing strongly rheomorphic tuffs from extensive silicic lavas (1992): Bulletin of Volcanology [abs] - wherein Chris Henry and John Wolff state that, "Extensive silicic lavas could be appropriately termed flood rhyolites."
Rhyolitic ignimbrites in the Rogerson Graben, southern Snake River Plain volcanic province: volcanic stratigraphy, eruption history and basin evolution (2008): Bulletin of Volcanology [abs].
Northwestern Nevada: An early caldera-focused system of the Yellowstone hotspot track (2009): 2009 Portland GSA Annual Meeting [abs]. NOTE: About the Soldier Meadow Tuff and the peralkaline rhyolite flows and tuffs of the High Rock Canyon volcanic center.
The Soldier Meadow Tuff of the High Rock Caldera, northwestern Nevada (2009): 2009 Portland GSA Annual Meeting [abs]. I'm sorry I missed this session!