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Reference Number: 1962 GeoREF Number: 2004-900100 Publication Year: 2004 Abstract: _NULL_ Descriptors: _NULL_ Classification: _NULL_ Source: Idaho Geological Survey DAD-1
Data Types:
  • Tabular Data
New B and Li isotopic data are presented for well-characterized basalts from a transect across the Cascades volcanic arc, S. Washington, for a sediment core on the incoming Juan de Fuca plate, and for dacites from Mt. St. Helens. The basalts define two compositional groups, one (I) having affinities to those from intraplate settings and the other (II) resembling typical volcanic arc calcalkalic lavas. These groups are inferred to have distinct sources. Group I lavas have low Li/Y (0.25-0.6) and B/Nb (∼0.1-0.45), near-constant Ba/Nb (7-18), and show little cross-arc variation in fluid-mobile/immobile element ratios. In contrast, Group II lavas have slightly elevated Li/Y (∼0.5) and higher Ba/Nb (21-100) regardless of location; B/Nb is enriched (to ∼2.2) in the frontal arc, but toward the backarc drops to lower values (<0.4) overlapping with intraplate basalts. δ11B values are among the lowest reported for volcanic arcs. In detail, δ11B exhibits spatial variation, being highest (∼-3‰ to -0.4‰) in frontal arc lavas then decreasing sharply to OIB-like values (-8‰ to -9‰) in the backarc region; no systematic variation with magma types is apparent. δ7Li values (2.5‰ to 5‰) are MORB-like and show no systematic spatial variation. Combined with Sr-Nd-Pb isotopic and other trace element data, these results are consistent with weak slab contributions beneath the frontal arc ranging to negligible inputs below the backarc. This pattern is attributed to progressive dehydration of the subducting slab in an unusually warm subduction zone (SZ); initial inventories of fluid-mobile elements (FMEs) apparently were reduced extensively before the slab reached subarc depths, and essentially depleted as it moved beneath the backarc. Slab contributions appear to be superimposed on a compositionally layered mantle structure consisting of two domains sampled by the distinct basalt groups. Group I lavas appear to form by decompression melting of convectively upwelling deeper mantle that is little modified from an OIB-MORB source composition, except for the relatively small effect on B composition beneath the frontal arc. Group II lavas may form by melting of enriched domains within shallower lithospheric mantle. Because both groups have similar δ11B, production of Group II magmas need not involve modern inputs of slab fluid. This interpretation differs from the standard paradigm for arc magmatism in that flux melting is not invoked as the dominant cause for partial melting; efficient dehydration of the slab may remove the impetus to drive this mechanism. © 2004 Elsevier B.V. All rights reserved.
Data Types:
  • Tabular Data
Reference Number: 2704 GeoREF Number: 2004-069377 Publication Year: 2004 Descriptors: areal-geology; Clark-County-Washington; Cowlitz-County-Washington; geologic-maps; lithostratigraphy-; maps-; mass-movements; mineral-resources; paleoenvironment-; petrology-; surficial-geology; tectonic-elements; United-States; USGS-; Washington-; Woodland-Quadrangle Source: Scientific Investigations Map. 2004. map_coordinates: LAT: N455230; N460000; LONG: W1223730; W1224500.
Data Types:
  • Tabular Data
Reference Number: 1974 GeoREF Number: 2005-033633 Publication Year: 2004 Descriptors: absolute age; Ar/Ar; Cenozoic; dates; Idaho; igneous rocks; JuniperMountain; lava flows; mineral composition; Miocene; Neogene; OwyheeCounty Idaho; phenocrysts; pyroclastics; rhyolites; Snake River plain;Tertiary; tuff; United States; volcanic centers; volcanic features;volcanic fields; volcanic rocks; volcanism; Yellowstone Hot Spot Classification: "05A, Igneous and metamorphic petrology" Source: "Bulletin - Idaho Geological Survey, Report: 30, pp.205-228, May 2004" map_coordinates: "Latitude:N420000,N430000 Longitude:W1163000,W1173000"
Data Types:
  • Tabular Data
Reference Number: 1984 GeoREF Number: 2005-058227 Publication Year: 2004 Descriptors: absolute age; acidic composition; Ar/Ar; ash-flow tuff; Cenozoic; dates; domes; geochronology; High Lava Plains; Idaho; igneous rocks; Miocene; Neogene; Oregon; plate tectonics; Pliocene; plumes; pyroclastics; rhyolitic composition; Snake River Plain; southeastern Oregon; Tertiary; United States; volcanic rocks; volcanism; volcanoes; Yellowstone Hot Spot Classification: 03 Geochronology; 18 Solid-earth geophysics Source: "Journal of Geophysical Research, vol.109, no.B10, 19 pp., 10 Oct 2004" map_coordinates: "Latitude:N400000,N450000 Longitude:W1100000,W1300000"
Data Types:
  • Tabular Data
Reference Number: 425 GeoREF Number: 2004-068538 Publication Year: 2004 Abstract: "The 12.7-10.5 Ma Cougar Point Tuff in southern Idaho, USA, consists of10 large-volume <10 super 2 -10 super 3 km super 3 each,high-temperature 800-1000 degrees C, rhyolitic ash-flow tuffserupted from the Bruneau-Farbidge volcanic center of the Yellow-stonehotspot. These tuffs provide evidence for compositional and thermalzonation in pre-eruptive rhyolite magma, and suggest the presence of along-lived reservoir that was tapped by numerous large explosiveeruptions. Pyroxene compositions exhibit discrete compositional modeswith respect to Fe and Mg that define a linear spectrum punctuated byconspicuous gaps. Airfall glass compositions also cluster into modes,and the presence of multiple modes indicates tapping of differentmagma volumes during early phases of eruption. Equilibrium assemblagesof pigeonite and augite are used to reconstruct compositional andthermal gradients in the pre-eruptive reservoir. The recurrence ofidentical compositional modes and of mineral pairs equilibrated athigh temperatures in successive eruptive units is consistent with thepersistence of their respective liquids in the magma reservoir.Recurrence intervals of identical modes range from 0.3 to 0.9 Myr andsuggest possible magma residence times of similar duration. Eruptionages, magma temperatures, Nd isotopes, and pyroxene and glasscompositions are consistent with a long-lived, dynamically evolvingmagma reservoir that was chemically and thermally zoned and composedof multiple discrete magma volumes." Descriptors: Bruneau-Jarbidge volcanic center; Cenozoic; Cougar Point Tuff;geochemistry; high temperature; hot spots; Idaho; igneous rocks;lithogeochemistry; magmas; Miocene; Neogene; Owyhee County Idaho;plate tectonics; pyroclastics; rhyolite tuff; rhyolites; temperature;Tertiary; thermochemical properties; tuff; United States; volcanicrocks; Yellowstone Hot Spot; zoning Classification: "02C Geochemistry of rocks, soils, and sediments; 05A Igneous andmetamorphic petrology" Source: "Journal of Petrology, vol.45, no.1, pp.27-58, Jan 2004" map_coordinates: "Latitude:N420000,N434000 Longitude:W1150400,W1170200"
Data Types:
  • Tabular Data
Reference Number: 1975 GeoREF Number: 2005-033634 Publication Year: 2004 Descriptors: alkaline earth metals; basalts; Bruneau Idaho; Cenozoic; cratons;flood basalts; Idaho; igneous rocks; isotope ratios; isotopes;Jarbridge River; metals; Miocene; Neogene; Nevada; Oregon; OwyheeCounty Idaho; Owyhee Plateau; Pleistocene; Pliocene; Quaternary; SnakeRiver plain; Sr-87/Sr-86; stable isotopes; strontium; Tertiary; TwinFalls County Idaho; United States; volcanic rocks; Wyoming Province Classification: 05A, Igneous and metamorphic petrology Source: Bulletin - Idaho Geological Survey, Report: 30, pp.229-312, May 2004 map_coordinates: Latitude:N420000,N425000 Longitude:W1140000,W1150500 ;Latitude:N420000,N434000 Longitude:W1150400,W1170200
Data Types:
  • Tabular Data
Reference Number: 7666 GeoREF Number: 2004-084878 Publication Year: 2004 Descriptors: absolute age; batholiths; California; Cenozoic; chronostratigraphy;cleavage; contraction; Cretaceous; dates; Death Valley; deformation;faults; fold and thrust belts; folds; foliation; Garlock Fault;geochemistry; igneous rocks; intrusions; ion probe data; island arcs;isotope ratios; mass spectra; Mesozoic; Mono County California;Nevada; Nevadan Orogeny; orogeny; plutonic rocks; Sevier orogenicbelt; SHRIMP data; Sierra Nevada; spectra; strain; strike-slip faults;structural analysis; systems; tectonics; Tertiary; thermal ionizationmass spectra; thrust faults; U/Pb; United States Classification: 16 Structural geology; 03 Geochronology Source: "Tectonics, vol.23, no.4, 23 pp., Aug 2004" map_coordinates: "Latitude:N373000,N384000 Longitude:W1175000,W1193000"
Data Types:
  • Tabular Data
Reference Number: 1976 GeoREF Number: 2005-033635 Publication Year: 2004 Descriptors: absolute age; alkaline earth metals; Ar/Ar; basalts; Cenozoic;chemical composition; Columbia Plateau; concentration; dates;eruptions; genesis; geochemistry; Harney County Oregon; Idaho; igneousrocks; isotope ratios; isotopes; K/Ar; lithosphere; lithostratigraphy;magmatism; Malheur County Oregon; mantle; mantle plumes; metals;Miocene; Neogene; Oregon; Owyhee County Idaho; Owyhee Plateau; SnakeRiver plain; Sr-87/Sr-86; stable isotopes; strontium; Tertiary; UnitedStates; volcanic fields; volcanic rocks; volcanism; Yellowstone HotSpot Classification: "02C Geochemistry of rocks, soils, and sediments; 05A Igneous andmetamorphic petrology" Source: "Bulletin - Idaho Geological Survey, Report: 30, pp.313-328, May 2004" map_coordinates: "Latitude:N420000,N440000 Longitude:W1160000,W1190000"
Data Types:
  • Tabular Data
Reference Number: 207 GeoREF Number: 2004-049375 Publication Year: 2004 Descriptors: ash-flows; Cenozoic-; chemical-composition; Colorado-; experimental-studies; geochemistry-; igneous-rocks; laboratory-studies; lithostratigraphy-; pyroclastics-; San-Juan-Caldera; southwestern-Colorado; Tertiary-; tuff-; United-States; USGS-; volcanic-rocks Source: Open-File Report - U. S. Geological Survey. 2004. .
Data Types:
  • Tabular Data
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