Geology and stratigraphy of the Mount Bennett Hills, and the origin of west-central Snake River Plain rhyolites

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dc.contributor.advisorLeeman, William P.en_US
dc.creatorHonjo, Norioen_US
dc.date.accessioned2009-06-04T00:18:48Zen_US
dc.date.available2009-06-04T00:18:48Zen_US
dc.date.issued1990en_US
dc.description.abstractVoluminous mid-Miocene (8-13 Ma) rhyolitic ash-flows and lava flows (Idavada volcanics) are exposed continuously along the northern (Mount Bennett Hills or MBH) and southern margins of the west-central Snake River Plain (SRP). These rhyolites unconformably rest on Cretaceous granitic rocks of Idaho batholith and Eocene Challis volcanics and are locally overlain by (or intercalated with) minor Tertiary basalt flows and fluvial and lacustrine sediments. At both margins, the rhyolites dip gently and thicken toward the SRP. NW-to EW-trending normal faults drop the western SRP forming a graben-like structure where the inferred source vents of the rhyolites are buried by younger basalt flows (Pliocene to Recent) and sediments. The stratigraphy of Idavada volcanics in the MBH and evaluation of correlations with those exposed in the adjacent areas suggest that the rhyolites exposed in the northern margin of the west-central SRP are different from the southern margin counterparts and that the majority of west-central SRP rhyolites were erupted almost concurrently with the formations of the normal faults that formf"d the western SRP graben. Idavada volcanics range in composition from quartz latite to high-silica rhyolite and are characterized by anhydrous mineral assemblages (Plagioclase ±Sanidine ±Quartz + Augite + Pigeonite ± Hypersthene + Fe-Ti Oxides ± Fayalite + accessory Zircon and Apatite), suggesting that the rhyolites were formed under dry conditions. Pyroxene temperatures of Davidson and Lindsley (1985) range from 800 (high-silica rhyolites) to lOOO°C (quartz latites). Major and trace element, and isotopic (87Sr/86Sr = 0.709-0.713; 143Nd/144Nd = 0.51219-0.51230) compositions of the rhyolites suggest that the rhyolites may have formed by partial melting (caused by intrusions of hotspot-related basaltic magmas into the lower crust) of sialic lower crust with significant Juvenile component under dry conditions. Major and trace element variations observed in the west-central SRP rhyolites can be explained by differences in residence times which resulted in variable degrees of fractional crystallization. Variations of isotopic compositions and estimated magmatic temperatures of the rhyolites suggest that higher temperature rhyolitic magmas assimilated more Archean upper crustal material than lower temperature ones.en_US
dc.format.extent268 p.en_US
dc.format.mimetypeapplication/pdfen_US
dc.identifier.callnoThesis Geol. 1990 Honjoen_US
dc.identifier.citationHonjo, Norio. "Geology and stratigraphy of the Mount Bennett Hills, and the origin of west-central Snake River Plain rhyolites." (1990) Diss., Rice University. <a href="https://hdl.handle.net/1911/16351">https://hdl.handle.net/1911/16351</a>.en_US
dc.identifier.urihttps://hdl.handle.net/1911/16351en_US
dc.language.isoengen_US
dc.rightsCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.en_US
dc.subjectGeochemistryen_US
dc.subjectGeologyen_US
dc.subjectMineralogyen_US
dc.titleGeology and stratigraphy of the Mount Bennett Hills, and the origin of west-central Snake River Plain rhyolitesen_US
dc.typeThesisen_US
dc.type.materialTexten_US
thesis.degree.departmentEarth Scienceen_US
thesis.degree.disciplineNatural Sciencesen_US
thesis.degree.grantorRice Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophyen_US
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GEOLOGY AND STRATIGRAPHY OF THE MOUNT BENNETT HILLS, AND THE ORIGIN OF WEST-CENTRAL SNAKE RIVER PLAIN RHYOLITES
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