Rhyolitic ignimbrites in the Rogerson Graben, southern Snake River Plain volcanic province: volcanic stratigraphy, erupt
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RESEARCH ARTICLE
Rhyolitic ignimbrites in the Rogerson Graben, southern Snake River Plain volcanic province: volcanic stratigraphy, eruption history and basin evolution Graham D. M. Andrews & Michael J. Branney & Bill Bonnichsen & Michael McCurry
Received: 10 February 2005 / Accepted: 8 March 2007 / Published online: 20 June 2007 # Springer-Verlag 2007
Abstract The 80 km long NNE-trending Rogerson Graben on the southern margin of the central Snake River Plain, Idaho, USA, hosts a rhyolitic pyroclastic succession, 200 m thick, that records a period of successive, late-Miocene, large-volume explosive eruptions from the Yellowstone– Snake River Plain volcanic province, and contemporaneous extension. The succession, here termed the Rogerson Formation, comprises seven members (defined herein) and records at least eight large explosive eruptions with numerous repose periods. Five high-grade and extremely high-grade ignimbrites are intercalated with three nonwelded ignimbrites and two volcaniclastic deposits, with numerous repose periods (palaeosols) throughout. Two of This paper constitutes part of a special issue dedicated to Bill Bonnichsen on the petrogenesis and volcanology of anorogenic rhyolites. Editorial responsibility: M McCurry Electronic supplementary material The online version of this article (doi:10.1007/s00445-007-0139-0) contains supplementary material, which is available to authorized users. G. D. M. Andrews : M. J. Branney Department of Geology, University of Leicester, Leicester LE1 7RH, UK G. D. M. Andrews (*) Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC V6T 1Z4, Canada e-mail: [email protected] B. Bonnichsen 927 East 7th Street, Moscow, ID 83843, USA M. McCurry Department of Geosciences, Idaho State University, Pocatello, ID 83209-8072, USA
the ignimbrites are dominantly rheomorphic and lava-like but contain subordinate non-welded pyroclastic layers. The ignimbrites are typical Snake River Plain high-silica rhyolites, with anhydrous crystal assemblages and high inferred magmatic temperatures (≤ 1,025°C). We tentatively infer that the Jackpot and Rabbit Springs Members may have been emplaced from the Bruneau–Jarbidge eruptive centre on the basis of: (1) flow lineation trends, (2) crystal assemblage, and (3) radiometric age. We infer that the overlying Brown’s View, Grey’s Landing, and Sand Springs Members may have been emplaced from the Twin Falls eruptive centre on the basis of: (1) kinematic indicators (from the east), and (2) crystal assemblage. Furthermore, we have established the contemporaneous evolution of the Rogerson Graben from the emplacement of the Jackpot Member onwards, and infer that it is similar to younger half-graben along the southern margin of the Snake River Plain, formed by local reactivation of Basin and Range structures by the northeastwardly migration of the Yellowstone hot-spot. Keywords Snake River Plain volcanic province . Rheomorphic ignimbrite . Volcanic stratigraphy . Geothermometry . Rhyolite . Basin and range . Yellowstone h
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