Geochemical correlation of three large-volume ignimbrites from the Yellowstone hotspot track,Idaho, USA |
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Authors: | Ben S Ellis M J Branney T L Barry D Barfod I Bindeman J A Wolff B Bonnichsen |
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Institution: | (1) Department of Geology, University of Leicester, University Road, Leicester, LE1 7RH, UK;(2) SUERC, NERC Argon Isotope Facility, Rankine Avenue, Scottish Enterprise Technology Park, East Kilbride, GL75 OQF, UK;(3) Geological Sciences, 1272 University of Oregon, Eugene, OR 97403, USA;(4) School of Earth and Environmental Sciences, Washington State University, Pullman, WA, USA;(5) 927 East 7th Street, Moscow, ID 83834, USA |
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Abstract: | Three voluminous rhyolitic ignimbrites have been identified along the southern margin of the central Snake River Plain. As
a result of wide-scale correlations, new volume estimates can be made for these deposits: ~350 km3 for the Steer Basin Tuff and Cougar Point Tuff XI, and ~1,000 km3 for Cougar Point Tuff XIII. These volumes exclude any associated regional ashfalls and correlation across to the north side
of the plain, which has yet to be attempted. Each correlation was achieved using a combination of methods including field
logging, whole rock and mineral chemistry, magnetic polarity, oxygen isotope signature and high-precision 40Ar/39Ar geochronology. The Steer Basin Tuff, Cougar Point Tuff XI and Cougar Point Tuff XIII have deposit characteristics typical
of ‘Snake River (SR)-type’ volcanism: they are very dense, intensely welded and rheomorphic, unusually well sorted with scarce
pumice and lithic lapilli. These features differ significantly from those of deposits from the better-known younger eruptions
of Yellowstone. The ignimbrites also exhibit marked depletion in δ18O, which is known to characterise the SR-type rhyolites of the central Snake River Plain, and cumulatively represent ~1,700 km3 of low δ18O rhyolitic magma (feldspar values 2.3–2.9‰) erupted within 800,000 years. Our work reduces the total number of ignimbrites
recognised in the central Snake River Plain by 6, improves the link with the ashfall record of Yellowstone hotspot volcanism
and suggests that more large-volume ignimbrites await discovery through detailed correlation work amidst the vast ignimbrite
record of volcanism in this bimodal large igneous province. |
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