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Geologic units containing rhyodacite

Earth material > Volcanic rock > Felsic volcanic rock
A volcanic rock defined in the QAPF diagram as having Q/(Q+A+P) between 20 and 60% and P/(P+A) between 35 and 65%...

California - Idaho - Nevada - Oregon - Washington
Cretaceous marine rocks (in part nonmarine) (?), unit 1 (Blythe) (Middle Jurassic(?) to Late Cretaceous)
Undivided Cretaceous sandstone, shale, and conglomerate; minor nonmarine rocks in Peninsular Ranges (?)
Dacite to rhyolite (or rhodacite) ignimbrites; Eocene rhyodacitic cauldron complex; east-central Idaho, central Challis volcanic field (Eocene)
Eocene mixed silicic and basaltic volcanic ejecta, flows and reworked debris.
Intrusive rocks of mafic and intermediate composition (Miocene to Quaternary)
Volcanic sandstone, felsic ash-flow tuffs, rhyolite, and rhyodacite flows (Middle Jurassic to Early Cretaceous)
VOLCANIC SANDSTONE, FELSIC ASH-FLOW TUFFS, RHYOLITE, AND RHYODACITE FLOWS (Upper? Jurassic)-Pony Trail Group of Cortez Mountains, Eureka County
Mazama ash-flow deposits (Holocene) (Holocene)
Rhyodacitic to andesitic ash-flow deposits related to climactic eruptions of Mount Mazama about 6,845 yr B.P. (14C) (Bacon, 1983)
Mazama pumice deposits (Holocene) (Holocene)
Primary and reworked air-fall rhyodacite pumice related to climactic eruptions of Mount Mazama about 6,845 yr B.P.(14C). Mapped only where it extensively covers older units
Rhyolite and dacite (Pliocene? and Miocene) (Miocene to Pliocene)
Ash-flow tuff, lava flows, pumice-lapilli tuff, coarse pumicite, flow breccia, and domal complexes of rhyolitic, rhyodacitic, and dacitic composition; in places includes peralkaline rhyolite and some andesite and andesite breccia. Locally porphyritic with phenocrysts of alkali feldspar, plagioclase, and minor augite, ferro-hedenbergite, hornblende, hypersthene, or biotite. Commonly flow banded; locally glassy. Many of the ash--flow tuffs exhibit flow features and only obscure vitro-clastic textures. In places includes interlayers of silicic volcaniclastic rocks and tuffaceous sedimentary rocks. Includes rhyolite at Owyhee Dam, Jump Creek Rhyolite, and Littlefield Rhyolite, all of Kittleman and others (1965); Dooley Rhyolite Breccia of Gilluly (1937), radiometrically dated at 14.7 +/- 0.4 Ma by potassium-argon methods (Fiebelkorn and others, 1983); resurgent domal masses in McDermitt caldera area; and extensive unnamed flows and ash-flow tuffs in the central and southern part of the Owyhee Upland. Also includes isolated masses of dacitic and rhyodacitic flows, breccia, and ash-flow tuff along eastern slope of Cascade Range that are lapped by flows and sediments of the Madras (or Deschutes) Formation. Potassium-argon ages on rocks in unit from southeast Oregon range from about 13 to 16 Ma; lenses of interbedded tuffaceous sedimentary rocks locally contain a Miocene (Barstovian) vertebrate fauna
Eocene-Oligocene volcanic rocks (Eocene-Oligocene)
Predominantly light-green, bedded andesite breccia with interbedded andesite and basalt flows, mudflows, and tuff beds; becomes more tuffaceous near top of unit. Includes tuffaceous and arkosic sandstone, shale, and carbonaceous shale beds in central and southern Cascade Mountians. Rhyodacite and quartz latite flows in northwestern Ferry County.
Oligocene volcanic rocks (Oligocene)
Andesite and rhyodacite flows, tuff, and tuffaceous sandstones of northern Lincoln County and southwestern Stevens County.
Tertiary dikes, sills, and small intrusive bodies (Middle to Late Tertiary)
Dikes are commonly diabase; plugs and sills are generally andesite porphyry and dacite.

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Page Last modified: 15:10 on 07-Dec-2016