Graduate Thesis Or Dissertation
 

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5q47rt364

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  • Steens Mountain is a major horst block near the northern terminus of the Basin and Range geomorphic province of southeastern Oregon. A section of Miocene volcanic rocks totaling 5000 feet in thickness are exposed in a fault escarpment on the eastern side of Steens Nountain. These include: the Pike Creek Formation, consisting of rhyolite and dacite flows and tuffs about 1000 feet in thickness, including one rhyolite ignimbrite locally 900 feet thick; the Andesite Series (also known as Steens Mountain Volcanics), a sequence of andesite and basaltic andesite flows totaling about 1500 feet in thickness; Steens Basalt, a series of 15 million year old high-alumina olivine basalt flows totaling about 3000 feet in thickness, which crop out extensively in southeastern Oregon. Steens Basalt also crops out in the Mickey Hot Springs area, 16 miles east of Steens Mountain, where it is overlain by a thin, continuous ignimbrite and a younger basalt, here informally named Mickey basalt. The basalts of Steens Mountain were compared to those o the Mickey Rot Springs area. Correlation is established on the basis of a paleomagnetic reversal observed in the two areas, and supported by petrologic observations and chemical analysis. A large circular fault basin north of Mickey Hot Springs is suggestive of a collapsed caldera structure. The great thickness of a rhyolite ignimbrite in the Pike Creek formation may have been deposited in a rhyolite-flood eruption associated with a caldera collapse, creating a structure such as the one north of Mickey Hot Springs.
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file details Map.jpg 2017-10-25 Public Télécharger