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Reference Number: 1998 GeoREF Number: 2006-000010 Publication Year: 2006 Source: Idaho Geological Survey Digital Analytical Data 2; part 2
Data Types:
  • Tabular Data
Reference Number: 2039 GeoREF Number: 2006-900110 Publication Year: 2006 Source: Idaho Geological Survey Digital Analytical Data 2; part 2
Data Types:
  • Tabular Data
Reference Number: 7830 GeoREF Number: 2005-024533 Publication Year: 2005 Descriptors: alkaline earth metals; andesites; assimilation; California; CascadeRange; chemical composition; chemical ratios; crust; crystalchemistry; crystallization; dacites; fractional crystallization;geochemistry; hydration; ICP mass spectra; igneous rocks; island arcs;isotope ratios; isotopes; Klamath Mountains; lava; magmacontamination; magmas; magnesium; major elements; mantle; massspectra; melts; metals; mineral composition; mixing; Mount Shasta;Nd-144/Nd-143; neodymium; Northern California; peridotites;petrography; plutonic rocks; provenance; rare earths; silicate melts;silicates; Siskiyou County California; spectra; Sr-87/Sr-86; stableisotopes; strontium; textures; trace elements; ultramafics; UnitedStates; variations; volcanic rocks; volcanoes; water; X-rayfluorescence spectra Classification: 05A Igneous and metamorphic petrology; 02D Isotope geochemistry Source: "Contributions to Mineralogy and Petrology, vol.148, no.5, pp.542-565,Jan 2005" map_coordinates: "Latitude:N412400,N412600 Longitude:W1221100,W1221300"
Data Types:
  • Tabular Data
Reference Number: 1990 GeoREF Number: 2005-074713 Publication Year: 2005 Abstract: "The Golden Bear dike in the Sierra Nevada and the Coso dikes in theCoso Range crop out on opposite sides of Owens Valley, California, andstrike roughly perpendicular to it. Neither dike reappears alongstrike across the valley. New data demonstrate that the dike sets areca. 83 Ma in age, share nearly identical mineralogy and petrography,and intrude similar wall rocks including distinctive 102 Maleucogranite. Dike bulk-chemical and Sr and Nd isotope compositionsare nearly indistinguishable. These data suggest that the dike setswere originally continuous and were offset dextrally by approximately65 km. This displacement estimate is consistent with other recentestimates of total slip across Owens Valley. If faulting began duringthe Pliocene, the average slip rate was significantly faster than thecurrent rate. Alternatively, motion could have been episodic and havebegun as early as the Late Cretaceous." Descriptors: absolute age; alkali feldspar; California; Cenozoic; correlation; Cosodike swarm; Coso Range; Cretaceous; dates; dike swarms; dikes; faults;feldspar group; framework silicates; geochemistry; Golden Bear dikeswarm; igneous rocks; intrusions; Inyo County California; K-feldspar;lateral faults; Mesozoic; monzonites; nesosilicates; orthosilicates;Owens Valley; plutonic rocks; quartz porphyry; rhyolites;right-lateral faults; Sierra Nevada; silicates; slip rates; U/Pb;United States; volcanic rocks; zircon; zircon group Classification: 16 Structural geology; 03 Geochronology Source: "Geological Society of America Bulletin, vol.117, no.7-8, pp.962-968,Aug 2005" map_coordinates: "Latitude:N354500,N370000 Longitude:W1171500,W1190000"
Data Types:
  • Tabular Data
Four closely spaced volcanoes (Summer Coon; Twin Mountains; Del Norte; Carnero Creek) form the east-central cluster of Conejos volcanic centers. These Conejos rocks range from high-K basaltic andesite to rhyolite, with andesite volumetrically the most abundant. Summer Coon and Twin Mountains are composite volcanoes. The Del Norte and Carnero Creek volcanoes are deeply eroded dacite shields. Rhyolite (10% of our Conejos analyses but a much smaller percentage by volume) is only known from Summer Coon and Twin Mountains volcanoes, although high-SiO2dacite occurs in the Del Norte volcano. The younger Hinsdale Formation contains a related series ranging from transitional basalt to high-K andesite; we use Hinsdale Formation analyses to represent Conejos parental magmas. Conejos and Hinsdale magmas evolved through AFC processes: Basalt, after interacting with lower crust, assimilated low K/Rb crust, similar in some ways to Taylor and McLennan (Taylor, S.R., and McLennan, S.M., 1985, The continental crust: its composition and evolution. Oxford, Blackwell Scientific.) model upper crust; main series basaltic andesite fractionated to high-K andesite; rhyolite was produced by melting of high K/Ba upper crustal rocks similar to granite gneiss known from inclusions and basement outcrops. Some rhyolite may have been back-mixed into fractionating andesite and dacite. Field evidence for assimilation includes sanidinite-facies, partially melted, gneiss blocks up to 1 m in diameter. Temperature estimates (1100-0900 °C) from two-pyroxene equilibria are consistent with this interpretation, as are the sparsely porphyritic nature of the most-evolved rhyolites and the absence of phenocrystic alkali feldspar. Our study supports the conclusions of previous workers on AFC processes in similar, but generally more mafic, Conejos magmas of the southeastern San Juan Mountains. Our results, however, emphasize the importance of crustal melting in the generation of Conejos rhyolite. We further speculate that Conejos magmatism, and the San Juan Volcanic Field (SJVF) in general, may represent an early phase of Rio Grande rift magmatism, the orogenic geochemical signature of the series having been generated through multi-level and extensive assimilation of varied Precambrian orogenic and anorogenic rocks. © 2004 Elsevier B.V. All rights reserved.
Data Types:
  • Tabular Data
Reference Number: 2042 GeoREF Number: 2006-901011 Publication Year: 2005
Data Types:
  • Tabular Data
Reference Number: 2072 GeoREF Number: 2006-060936 Publication Year: 2005 Descriptors: absolute age; Ar/Ar; California; Cenozoic; K/Ar; mapping; Medicine Lake; Mesozoic; Paleozoic; Siskiyou County California; United States; USGS; volcanoes Source: "Open-File Report - U. S. Geological Survey, Report: OF 2005-1416, 37 pp., 2005"
Data Types:
  • Other
Reference Number: 1772 GeoREF Number: 2005-075954 Publication Year: 2005 Abstract: " Locally, voluminous andesitic volcanism both preceded and followed large eruptions of silicic ash-flow tuff from many calderas in the San Juan volcanic field. The most voluminous post-collapse lava suite of the central San Juan caldera cluster is the 28 Ma Huerto Andesite, adiverse assemblage erupted from at least 5-6 volcanic centres that were active around the southern margins of the La Garita caldera shortly after eruption of the Fish Canyon Tuff. These andesitic centres are inferred, in part, to represent eruptions of magma that ponded and differentiated within the crust below the La Garita caldera, thereby providing the thermal energy necessary for rejuvenation and remobilization of the Fish Canyon magma body. The multiple Huerto eruptive centres produced two magmatic series that differ in phenocryst mineralogy (hydrous vs anhydrous assemblages), whole-rock major and trace element chemistry and isotopic compositions. Hornblende-bearing lavas from three volcanic centres located close to the southeastern margin of the La Garita caldera (Eagle Mountain-Fourmile Creek, West Fork of the San Juan River, Table Mountain) define a high-K calc-alkaline series (57-65 wt % SiO (sub 2) ) that is oxidized, hydrous and sulphur rich. Trachyandesitic lavas from widely separated centres at Baldy Mountain-Red Lake (western margin), Sugarloaf Mountain (southern margin) and Ribbon Mesa (20 km east of the La Garita caldera) are mutually indistinguishable (55-61 wt % SiO (sub 2) ); they are characterized by higher and more variable concentrations of alkalis and many incompatible trace elements (e.g. Zr, Nb, heavy rare earth elements), and they contain anhydrous phenocryst assemblages (including olivine). These mildly alkaline magmas were less water rich and oxidized than the hornblende-bearing calc-alkaline suite. The same distinctions characterize the voluminous precaldera andesitic lavas of the Conejos Formation, indicating that these contrasting suites are long-term manifestations of San Juan volcanism. The favoured model for their origin involves contrasting ascent paths and differentiation histories through crustal columns with different thermal and density gradients. Magmas ascending into the main focus of the La Garita caldera were impeded, and they evolved at greater depths, retaining more of their primary volatile load. This model is supported by systematic differences in isotopic compositions suggestive of crust-magma interactions with contrasting lithologies." Descriptors: calc-alkalic composition; Cenozoic; Colorado; Conejos Formation; Eagle Mountain; Fish Canyon Tuff; Fourmile Creek; Huerto Andesite; igneous rocks; La Garita Caldera; lava; Oligocene; Paleogene; pyroclastics; San Juan River; San Juan volcanic field; Table Mountain; Tertiary; trachyandesites; tuff; United States; volcanic rocks; volcanism Classification: " 05A, Igneous and metamorphic petrology" Source: " Journal of Petrology, vol.46, no.5, pp.859-891, May 2005" map_coordinates: " Latitude;N373000,N380000 Longitude;W1064500,W1070000"
Data Types:
  • Other
Reference Number: 1982 GeoREF Number: 2005-046755 Publication Year: 2005 Abstract: "The Challis volcanic field is the largest of several Eocene volcanicfields in the Pacific Northwest of the United States and Canada. Inthe Little Wood River area of Idaho, rock types in the Eocene ChallisVolcanic Group include andesite lava flows and tuff breccia, dacitelava flows and flow breccia, volcaniclastic sedimentary rocks, lithictuff, nonvolcanic conglomerate, and rhyolite dikes." Descriptors: breccia; Cenozoic; Challis Volcanics; Eocene; Idaho; igneous rocks;lava flows; lithostratigraphy; Little Wood River valley; Paleogene;pyroclastics; south-central Idaho; Tertiary; tuff; United States;USGS; volcanic rocks; volcaniclastics Classification: 05A Igneous and metamorphic petrology; 12 Stratigraphy Source: "U. S. Geological Survey Bulletin, Report: B 2064-II, 22 pp., May 2005" map_coordinates: "Latitude:N432500,N434500 Longitude:W1135500,W1141500"
Data Types:
  • Tabular Data
Reference Number: 692 GeoREF Number: 2005-031004 Publication Year: 2005 Descriptors: absolute age; alkali feldspar; Ar/Ar; Arbon Valley Tuff Member;Blacktail Creek Tuff; calderas; Cenozoic; chronostratigraphy; ConantCreek Tuff; dates; explosive eruptions; Heise Group; Heise volcanic field; Idaho; igneous rocks;ignimbrite; Kilgore Tuff; lower Pliocene; Miocene; Neogene; paleogeography; Pliocene; pyroclastics; Snake River plain;Tertiary; tuff; vitrophyre; volcanic fields; volcanism; Walcott Tuff; Western U.S. Classification: 05A Igneous and metamorphic petrology; 03 Geochronology Source: "Geological Society of America Bulletin, vol.117, no.3-4, pp.288-306, Apr 2005"
Data Types:
  • Tabular Data
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