Title:
 The Cougar Point Tuff; implications for thermochemical zonation andlongevity of high-temperature, large-volume silicic magmas of theMiocene Yellowstone Hotspot 
Reference Number:
 425 
ISSN:
 0022-3530
Publication Year:
 2004
GeoREF Number:
 2004-068538 (View Original Data File)
Authors:
 Cathey, Henrietta E; Nash, Barbara P
Descriptors:
 Bruneau-Jarbidge volcanic center; Cenozoic; Cougar Point Tuff;geochemistry; high temperature; hot spots; Idaho; igneous rocks;lithogeochemistry; magmas; Miocene; Neogene; Owyhee County Idaho;plate tectonics; pyroclastics; rhyolite tuff; rhyolites; temperature;Tertiary; thermochemical properties; tuff; United States; volcanicrocks; Yellowstone Hot Spot; zoning
Source:
 Journal of Petrology, vol.45, no.1, pp.27-58, Jan 2004
Abstract:
 The 12.7-10.5 Ma Cougar Point Tuff in southern Idaho, USA, consists of10 large-volume <10 super 2 -10 super 3 km super 3 each,high-temperature 800-1000 degrees C, rhyolitic ash-flow tuffserupted from the Bruneau-Farbidge volcanic center of the Yellow-stonehotspot. These tuffs provide evidence for compositional and thermalzonation in pre-eruptive rhyolite magma, and suggest the presence of along-lived reservoir that was tapped by numerous large explosiveeruptions. Pyroxene compositions exhibit discrete compositional modeswith respect to Fe and Mg that define a linear spectrum punctuated byconspicuous gaps. Airfall glass compositions also cluster into modes,and the presence of multiple modes indicates tapping of differentmagma volumes during early phases of eruption. Equilibrium assemblagesof pigeonite and augite are used to reconstruct compositional andthermal gradients in the pre-eruptive reservoir. The recurrence ofidentical compositional modes and of mineral pairs equilibrated athigh temperatures in successive eruptive units is consistent with thepersistence of their respective liquids in the magma reservoir.Recurrence intervals of identical modes range from 0.3 to 0.9 Myr andsuggest possible magma residence times of similar duration. Eruptionages, magma temperatures, Nd isotopes, and pyroxene and glasscompositions are consistent with a long-lived, dynamically evolvingmagma reservoir that was chemically and thermally zoned and composedof multiple discrete magma volumes.
Copyright:
 GeoRef, Copyright 2004, American Geological Institute.

Sample Summary:
Sample ID: Major Data: Trace Data: Isotope Data:
tc89-12 Yes Yes No
95cpt/sr27 Yes Yes No
95cpt/sr81 Yes Yes No
tc89-18a Yes Yes No
95cpt/j83 Yes Yes No
95cpt/j85 Yes Yes No
brv93-429 Yes Yes No
95cpt/sr57 Yes Yes No
95cpt/sr61 Yes Yes No
tc89-25a Yes Yes No
95cpt/sr63 Yes Yes No
95cpt/sr66 Yes Yes No
95cpt/sr38 Yes Yes No
95cpt/sr39 Yes Yes No
brv93-431a Yes Yes No
95cpt/sr67 Yes Yes No
95cpt/sr75 Yes Yes No
wjr93-538 Yes Yes No
95cpt/hg98 Yes Yes No
95cpt/hg97.5 No Yes No
95cpt/j10 Yes Yes No
95cpt/j16 Yes Yes No
tc89-31a Yes Yes No
95cpt/hg96 Yes Yes No
95cpt/hg90 Yes Yes No
brv95-840 Yes Yes No
95cpt/hg89 Yes Yes No
95cpt/hg87 Yes Yes No
ejr93-532a Yes Yes No
95cpt/mhs2 Yes Yes No
95cpt/mhs6 Yes Yes No