Bishop Tuff Explained

Bishop eruption
Date:764,800 ± 600 years ago
Location:California, United States
Coordinates:37.7167°N -118.8842°W
Volume:Approx. 200km3
Vei:7
Map:Geologic map of Long Valley and Mono Basin region (USGS).png

The Bishop Tuff is a welded tuff which formed 764,800 ± 600 years ago as a rhyolitic pyroclastic flow during the approximately six-day eruption that formed 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]

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 2200km2, and are as thick as 200m (700feet).[5]

The Owens River cuts through the Volcanic Tableland, an ignimbrite plateau which is a principal sector of the Bishop Tuff outflow sheet. Erosion of the plateau by the Owens River has carved the Owens River Gorge.[6]

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%), followed by Al2O3 (12.7%).

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".[9]

See also

External links

Notes and References

  1. Andersen . Nathan L. . Jicha . Brian R. . Singer . Brad S. . Hildreth . Wes . Wes Hildreth . 2017 . Incremental heating of Bishop Tuff sanidine reveals preeruptive radiogenic Ar and rapid remobilization from cold storage . Proceedings of the National Academy of Sciences . en . 114 . 47 . 12407–12412 . 2017PNAS..11412407A . 10.1073/pnas.1709581114 . 0027-8424 . 5703294 . 29114056 . free.
  2. 10.1130/G24017A.1. Crowley. J.L.. B. . Schoene. S.A.. Bowring. U-Pb dating of zircon in the Bishop Tuff at the millennial scale. Geology. December 2007. 35. 1123–1126. 12. 2007Geo....35.1123C.
  3. Hildreth . Wes . Wes Hildreth . Wilson . Colin J. N. . 2007 . Compositional Zoning of the Bishop Tuff . Journal of Petrology . 48 . 5 . 951–999 . 10.1093/petrology/egm007 . 1460-2415. free .
  4. Web site: Bishop Tuff in Long Valley Caldera, California . 2021-12-06 . Long Valley Caldera . U.S. Geological Survey.
  5. Web site: Bishop Tuff in Long Valley Caldera, California. USGS. October 24, 2023.
  6. Hildreth . Wes . Wes Hildreth . Fierstein . Judy . Judy Fierstein . 2016 . Long Valley Caldera Lake and Reincision of Owens River Gorge . U.S. Geological Survey Scientific Investigations Report 2016–5120 . Scientific Investigations Report . 10.3133/sir20165120 . 2328-031X . 1007736792 . . free .
  7. Wilson . C. J. N. . Hildreth . Wes . Wes Hildreth . 1997-07-01 . The Bishop Tuff: New Insights from Eruptive Stratigraphy . The Journal of Geology . 105 . 4 . 407–440 . 10.1086/515937 . 1997JG....105..407W . 0022-1376 . 129371841.
  8. Gualda . Guilherme A. R. . Ghiorso . Mark S. . Mark S. Ghiorso . September 2013 . The Bishop Tuff giant magma body: an alternative to the Standard Model . Contributions to Mineralogy and Petrology . en . 166 . 3 . 755–775 . 2013CoMP..166..755G . 10.1007/s00410-013-0901-6 . 0010-7999 . 129644681.
  9. 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 . en . 41 . 3 . 449–473 . 10.1093/petrology/41.3.449 . 1460-2415. free .

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