Bishop Tuff

The Bishop Tuff is a welded tuff that formed 764,800 ± 600 years ago as a rhyolitic pyroclastic flow during the approximately six day eruption that created the Long Valley Caldera.[1][2][3] Large outcrops of the tuff are located in Inyo and Mono Counties, California, United States. Approximately 200 cubic kilometers of ash and tuff erupted outside the caldera.[4]

Bishop eruption
Two layers of the Bishop Tuff: lower layer was from ashfall, upper layer was from the main pyroclastic flow.
VolcanoLong Valley Caldera
Date764,800 ± 600 years ago
TypeUltra-Plinian
LocationCalifornia, United States
37°43′00″N 118°53′03″W
VolumeApprox. 200 km3 (48 cu mi)
VEI7
Map of the Long Valley Caldera, with Bishop Tuff outlined.

Modern exposure

The Bishop Tuff caps a volcanic plateau in the northern Owens Valley in eastern California. The tableland formation is located east of U.S. Route 395 and west of the Nevada stateline, sitting northwest of Bishop and southeast of Crowley Lake and Mammoth Lakes. Another part of the flow is south of Mono Lake, and surrounding the Mono-Inyo Craters.

Deposits of Bishop Tuff in this area cover nearly 2,200 km2 (850 sq mi), and range in thickness from 150 m (490 ft) to 200 m (660 ft).

The Owens River cuts through the Volcanic Tableland, an ignimbrite plateau that is a principal sector of the Bishop Tuff outflow sheet. Erosion of the plateau by the Owens River has created the Owens River Gorge.[5]: 2 

Lithology

The Bishop Tuff is a high-silicate rhyolitic welded tuff, made up of ash and pumice clasts. The main minerals found in the pumice clasts are biotite, plagioclase, quartz, and sanidine. The main composition is SiO2 (73.4-77.9%),[3] followed by Al2O3 (12.7%).[6]

The Bishop Tuff is compositionally zoned. The lower section, formed from ash fall, is notated by pyroxene-free high-silica rhyolite pumice. The upper section, formed by pyroclastic flow, is notated by pyroxene-bearing high-silica rhyolite pumice.[7][8] The magma that formed the Bishop Tuff is suggested to be a "residual magma derived from some parental magma and not itself a primary or parental partial melt of common crustal rocks".[6]

See also

References
  1. Andersen, Nathan L.; Jicha, Brian R.; Singer, Brad S.; Hildreth, Wes (2017). "Incremental heating of Bishop Tuff sanidine reveals preeruptive radiogenic Ar and rapid remobilization from cold storage". Proceedings of the National Academy of Sciences. 114 (47): 12407–12412. Bibcode:2017PNAS..11412407A. doi:10.1073/pnas.1709581114. ISSN 0027-8424. PMC 5703294. PMID 29114056.
  2. Crowley, J.L.; Schoene, B.; Bowring, S.A. (December 2007). "U-Pb dating of zircon in the Bishop Tuff at the millennial scale". Geology. 35 (12): 1123–1126. Bibcode:2007Geo....35.1123C. doi:10.1130/G24017A.1.
  3. Hildreth, Wes; Wilson, Colin J. N. (2007). "Compositional Zoning of the Bishop Tuff". Journal of Petrology. 48 (5): 951–999. doi:10.1093/petrology/egm007. ISSN 1460-2415.
  4. "Bishop Tuff in Long Valley Caldera, California". Long Valley Caldera. U.S. Geological Survey. Retrieved 2021-12-06.
  5. Hildreth, Wes; Fierstein, Judy (2016). "Long Valley Caldera Lake and Reincision of Owens River Gorge". U.S. Geological Survey Scientific Investigations Report 2016–5120. doi:10.3133/sir20165120. ISSN 2328-031X. OCLC 1007736792. Catkey:12203311.
  6. Anderson, Alfred T.; Davis, Andrew M.; Lu, Fangqiong (2000-03-01). "Evolution of Bishop Tuff Rhyolitic Magma Based on Melt and Magnetite Inclusions and Zoned Phenocrysts". Journal of Petrology. 41 (3): 449–473. doi:10.1093/petrology/41.3.449. ISSN 1460-2415.
  7. Wilson, C. J. N.; Hildreth, Wes (1997-07-01). "The Bishop Tuff: New Insights from Eruptive Stratigraphy". The Journal of Geology. 105 (4): 407–440. doi:10.1086/515937. ISSN 0022-1376. S2CID 129371841.
  8. Gualda, Guilherme A. R.; Ghiorso, Mark S. (September 2013). "The Bishop Tuff giant magma body: an alternative to the Standard Model". Contributions to Mineralogy and Petrology. 166 (3): 755–775. Bibcode:2013CoMP..166..755G. doi:10.1007/s00410-013-0901-6. ISSN 0010-7999. S2CID 129644681.
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