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Reference Number: 7026 GeoREF Number: 2007-128477 Publication Year: 2007 Descriptors: "absolute age, Ar/Ar, Arizona, basalt flows, basalts, bedrock, canyons, Cenozoic, Coconino County Arizona, Colorado Plateau, Colorado River, dates, erosion, faults, field studies, fluvial features, Grand Canyon, igneous rocks, incised valleys, lava flows, Mohave County Arizona, neotectonics, quantitative, analysis, Quaternary, rivers, slip rates, structural controls, tectonics, United States, volcanic rocks, volcanism, water erosion" Classification: 24 Quaternary geology; 03 Geochronology Source: "Geological Society of America Bulletin, vol. 119, no. 11-12, pp.1283-1312, Dec 2007"
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The timing and petrogenesis of mid-Miocene flood basalt volcanism in the northwest United States has been extensively addressed, yet the chemical characteristics and temporal details of the Steens Basalt, exposed on the Oregon Plateau, are poorly defined. Steens Basalt volcanism has generally been accepted to have occurred at ∼ 16.6 Ma, coeval and/or just prior to the onset of Columbia River Basalt Group volcanism to the north. New major and trace element analyses and nine40Ar/39Ar ages ranging from 15.51 ± 0.28 to 16.58 ± 0.18 Ma were obtained on Oregon Plateau flood basalt lava flows from stratigraphic sections in close proximity to Steens Mountain. Additionally, new40Ar/39Ar ages were obtained on the uppermost and thirty-first lava flow down from the top of the ∼ 1 km section of Steens Basalt exposed at Steens Mountain and yield eruption ages of 16.59 ± 0.10 and 16.55 ±0.10 Ma, respectively. Field relations between these basalt sections suggest that multiple eruptive centers were present in the vicinity of Steens Mountain. The chemical and chronologic data presented in this study illustrate that flood basalts with the "Steens Basalt" chemical signature erupted across the southern Oregon Plateau over a much greater timespan than what is typically quoted for the Steens Mountain type section. These data suggest that the main volume of Steens Basalt volcanism erupted over at least an ∼ 1 m.y. duration from eruptive loci in the vicinity of Steens Mountain, while likely much less voluminous volcanism and lithospheric input of mafic magma appears to have occurred for > 2 Ma across the Oregon Plateau. These new geochemical and geochronological constraints verify a common temporal link between Steens, Malheur Gorge-region, and Columbia River Basalt Group (CRBG) volcanism. This direct temporal link requires that petrogenetic and tectonic models of mid-Miocene northwestern U.S. flood basalt volcanism recognize that the northern (Columbia Plateau) and southern (Oregon Plateau) portions of this mid-Miocene basalt province were erupting simultaneously during portions of the regional event. © 2007 Elsevier B.V. All rights reserved.
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Reference Number: 8667 GeoREF Number: 2008-109892 Publication Year: 2007 Abstract: "Gradients in the products of voluminous (10 (super 2) -10 (super 3) km (super 3) ) silicic eruptions are widely attributed to magmatic stratification developed by in situ differentiation over long periods of time (10 (super 4) -10 (super 5) years) in sub-volcanic chambers. Although the pattern of chemical and mineralogical variations may support magmatic zonation in the source reservoir at the time of eruption, evidence for protracted chamber differentiation is often equivocal. We report trace-element concentrations of sanidine phenocrysts measured by inductively coupled plasma mass spectrometry in the rapidly effused lavas of the 100 km (super 3) Taylor Creek Rhyolite, New Mexico, which link much of the eruptive heterogeneity of the domes and flows to mixing of fresh, crystal-poor, incompatible-element-rich, low- (super 87) Sr/ (super 86) Sr magma from below with partially crystallized, roof-rock contaminated, compatible-element-rich, high- (super 87) Sr/ (super 86) Sr magma resident in the shallow crust. Time constraints provided by high-resolution (super 40) Ar/ (super 39) Ar geochronology, reconstruction of the path of geomagnetic secular variation, and calculated cooling histories of overlapping eruptive units suggest that inputs from both above and below modified magma compositions during the lifespan of the dome field over periods as brief as a few hundred years or less. These domes thereby provide evidence that chemical gradients need not exist for protracted periods of time prior to eruption of zoned silica-rich magma. Comparisons with some ignimbrites reinforce this view and highlight the importance of processes occurring both at and below the pre-eruptive storage chamber in production of the chemical zonation in silicic systems." Classification: "05A, Igneous and metamorphic petrology" Source: "Journal of Volcanology and Geothermal Research, vol. 167, pp. 181-197, Nov 2007"
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  • Tabular Data
Reference Number: 2048 GeoREF Number: 2007-035831 Publication Year: 2007 Abstract: "Contiguous ring faults of the 8 x 3.5 km Hannegan caldera enclose theHannegan volcanics in the Cascade arc of northern Washington. Thecaldera collapsed in two phases, which each erupted rhyoliticignimbrite (72.3%-75.2% SiO (sub 2) ). The first collapse phase,probably trap-door style, erupted the > or =900-m-thick ignimbriteof Hannegan Peak at 3.722+ or -0.020 Ma. This single cooling unit,generally welded, has an uppermost facies of nonwelded ignimbrite andfine ash. A short period of localized sedimentation followed. Eruptionof the ignimbrite of Ruth Mountain then led to a second trap-doorcollapse as the first-phase partial ring fault propagated to the southto completely enclose the caldera. Wall-rock breccias are intercalatedas lenses and megabreccia blocks in both ignimbrites. The minimumintracaldera volume is 55-60 km (super 3) . No base is exposed, norare outflow sheets preserved. Caldera collapse and glacial erosionhave removed precaldera volcanic rocks, which survive only asintracaldera breccias. Rhyolite dikes and pods, one of which yielded a(super 40) Ar/ (super 39) Ar age of 3.72+ or -0.34 Ma, intrude thering fault and caldera fill. Dacite-andesite domes, dikes, and lavaflows were emplaced subsequently; one lava flow gives a (super 40) Ar/(super 39) Ar age of 2.96+ or -0.20 Ma. The quartz diorite of Icy Peakand the granite of Nooksack Cirque (plutons with (super 206) Pb/(super 238) U zircon ages of 3.42+ or -0.10 Ma and 3.36+ or -0.20 Ma,respectively) intrude caldera fill and basement rocks on the southwestmargin of the caldera. Both plutons are now exceptionally well exposedon high, glacially sculpted peaks within the caldera, indicatingerosion of at least 1 km of intracaldera fill. Hannegan calderaanchors the northeast end of a linear NE-SW age-progressive migrationof magmatic focus from the Chilliwack batholith to the active MountBaker volcano." Descriptors: absolute age; andesites; Ar/Ar; ash flows; breccia; calderas; CascadeRange; Cenozoic; collapse structures; dacites; dates; dikes; diorites;erosion; eruptions; experimental studies; faults; geochemistry;geomorphology; glacial erosion; glaciated terrains; granites; HanneganCaldera; igneous rocks; ignimbrite; intrusions; lava;lithostratigraphy; major elements; megabreccia; Neogene;nesosilicates; orthosilicates; Pliocene; plutonic rocks; plutons;pyroclastics; quartz diorites; rhyolites; ring faults; silicates;snow; spectra; Tertiary; U/Pb; United States; volcanic centers;volcanic features; volcanic rocks; Washington; Whatcom CountyWashington; X-ray fluorescence spectra; zircon; zircon group Classification: 12 Stratigraphy; 03 Geochronology Source: "Geological Society of America Bulletin, vol.119, no.3-4, pp.329-342,Apr 2007" map_coordinates: "Latitude:N484900,N485400 Longitude:W1212800,W1214000"
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  • Tabular Data
Reference Number: 7568 GeoREF Number: 2007-011011 Publication Year: 2007 Abstract: "Accurate ages for young (e.g., Pleistocene) volcanic eruptions areimportant for geomorphic, tectonic, climatic, and hazard studies.Existing techniques can be time-consuming and expensive when many agesare needed, and in the case of K/Ar and (super 40) Ar/ (super 39) Ardating, extraneous Ar often can limit precision, especially forcontinental basalts erupted through old lithosphere. We present a newtechnique for dating young basaltic eruptions by (U-Th)/He dating ofzircons (ZHe) from crustal xenoliths. Single-crystal ZHe datesgenerally have lower precision than typical (super 40) Ar/ (super 39)Ar dates, but can be determined relatively easily on multiplereplicate grain aliquots. We dated zircons from xenoliths from fourvolcanic centers in western North America: Little Bear Mountain,British Columbia (157+ or -3.5 [2.2%] ka weighted 95% confidenceinterval [CI], mean square of weighted deviates [MSWD] = 1.7) andPrindle Volcano, Alaska (176+ or -16 [8.9%] ka, MSWD = 13), in thenorthern Cordilleran volcanic province, and Fish Springs (273+ or -23[8.6%], MSWD = 43) and Oak Creek (179+ or -8.1 [4.5%] ka, MSWD = 12),in the Big Pine Volcanic Field, California. All ZHe ages are eitherequivalent to or younger than previously determined K/Ar or (super 40)Ar/ (super 39) Ar ages, indicating the possibility of inherited (super40) Ar in some of the previous measurements. Zircons from uppercrustal xenoliths in the Oak Creek and Fish Springs vents show poorerreproducibility and multiple apparent age distribution peaks,consistent with either intracrystalline U-Th zonation or <99.99% Hedegassing (assuming ca. 100 Ma pre-entrainment ZHe ages) of somezircons during magmatic entrainment. Removal of clear outliers in theolder age-distribution peaks of the upper crustal xenoliths, most ofwhich have extremely high U compared to other zircons of the samexenolith, improve the reproducibilities of Fish Springs to 4.7% (95%CI, MSWD = 4.8) and Oak Creek to 3.4% (95% CI, MSWD = 6.2). Coupledthermal and He diffusion modeling using appropriate xenolith sizes andmagma temperatures and assuming published diffusion kinetics forzircon indicate that incomplete He degassing would require entrainmenttimes <1 h. However, the observation of extremely high U in mostzircons with older ages raises the possibility that zircons with highradiation dosages may have more retentive He diffusioncharacteristics." Descriptors: (U-Th)/He; absolute age; Alaska; Big Pine volcanic field; BritishColumbia; California; Canada; Canadian Cordillera; Cenozoic; dates;diffusion; Fish Springs Vent; helium; inclusions; Little BearMountains; nesosilicates; noble gases; North America; North AmericanCordillera; Oak Creek Vent; orthosilicates; Pleistocene; Prindle;Quaternary; silicates; Southern Alaska; techniques; thermochronology;United States; vents; volcanic fields; volcanoes; Western Canada;xenoliths; zircon; zircon group Classification: 24 Quaternary geology; 03 Geochronology Source: "Geology (Boulder), vol.35, no.1, pp.17-20, Jan 2007"
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  • Tabular Data
Neogene magmatic activity in Central Baja California underwent a major change at ca. 12.5 Ma, when the Pacific-Farallon active oceanic ridge collided with the trench east of Vizcaíno Peninsula. The calc-alkaline magmatism which built the Comondú volcanic arc vanished and was replaced by unusual volcanic associations, which were erupted within six Late Miocene to Quaternary volcanic fields (Jaraguay, San Borja, San Ignacio, Santa Rosalía, Santa Clara, La Purísima), delineating a 600 km array along the Baja California Peninsula. New fieldwork, K-Ar datings and geochemical analyses on Jaraguay and San Borja lavas, combined with previous data, allow us to show that these associations include: (1) adakites emplaced between 12.5 and 8.2 Ma in the Santa Clara, Santa Rosalía and Jaraguay volcanic fields; (2) niobium-enriched basalts (NEB) in Santa Clara and Santa Rosalía (11.2 to 7.4 Ma); (3) tholeiitic basalts and basaltic andesites (11.3 to 7.2 Ma) displaying a very weak subduction imprint in La Purísima and San Ignacio; (4) alkali trachybasalts in Mesas San Carlos and Santa Catarina, northwest of Jaraguay (9.3 to 7.5 Ma), and finally (5) basalts and associated magnesian basaltic andesites and andesites. Locally referred to as "bajaites", the latter lavas display very specific geochemical characteristics, including very high Sr and Ba contents. They were emplaced in all the above-mentioned volcanic fields between 14.6 and 5.3 Ma. The origin of these Late Miocene volcanics has been considered linked either to the opening of an asthenospheric window through which they ascended (tholeiites and alkali trachybasalts), or to the melting of its edges due to thermal erosion (adakites) and the subsequent reaction between adakitic melts and the supraslab mantle (NEB and "bajaites"). However, the identification of the remnants of the Pacific-Farallon fossil ridge south of Vizcaíno Peninsula indicates that active ridge subduction was not responsible for the opening of the asthenospheric window. We propose that the emplacement of slab window-related volcanic rocks between 13 and 7 Ma from ca. 25°N to 30°N, was due to a process of slab-tearing, which started when the active ridge collided with the trench east of Vizcaíno Peninsula. The oldest part of the downgoing plate sunk into the mantle, leading to the opening of a tear-in-the-slab, which likely started from the southern limit of the already existing Southern California slab window. It propagated parallel to the trench over about 600 km and developed into an asthenospheric window. © 2006 Elsevier B.V. All rights reserved.
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Reference Number: 2040 GeoREF Number: 2006-900111 Publication Year: 2006 Source: Idaho Geological Survey Digital Analytical Data 2; part 1
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  • Tabular Data
Reference Number: 2050 GeoREF Number: 2007-043674 Publication Year: 2006 Descriptors: accessory minerals; alkaline earth metals; California; chemicalcomposition; chemical ratios; crystal chemistry; Dinkey Dome;diorites; garnet group; geochemistry; Goddard Terrane; Grant Grove;Idaho Batholith; igneous rocks; intrusions; isotope ratios; isotopes;Jurassic; Kings Sequence; magma contamination; magmas; major elements;melange; Mesozoic; metals; mineral composition; models; nesosilicates;O-18/O-16; ophiolite; orthosilicates; oxygen; peralkalic composition;petrography; plutonic rocks; plutons; provenance; Sierra NevadaBatholith; silicates; spectra; Sr-87/Sr-86; stable isotopes;strontium; textures; Tharps Peak; trace elements; United States; X-rayfluorescence spectra Classification: 05A Igneous and metamorphic petrology; 02D Isotope geochemistry Source: "Contributions to Mineralogy and Petrology, vol.151, no.1, pp.20-44,Jan 2006" map_coordinates: "Latitude:N361500,N371500 Longitude:W1183000,W1200000"
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Reference Number: 8090 GeoREF Number: 2007-046225 Publication Year: 2006 Classification: "05A, Igneous and metamorphic petrology" Source: "Journal of Volcanology and Geothermal Research, vol.152, no.3-4, pp.253-272, 15 Apr 2006"
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  • Other
Reference Number: 2011 GeoREF Number: 2006-013198 Publication Year: 2006 Abstract: "Eocene-middle Miocene volcanic rocks in the northern Pine ForestRange, Nevada, are ideally situated for reconstructing the timing andstyle of volcanism and extensional faulting in the northwesternmostpart of the Basin and Range province. A conformable sequence ofCenozoic volcanic and sedimentary strata in the northern Pine ForestRange dips approximately 30 degrees W, and 11 new (super 40) Ar/(super 39) Ar ages from this sequence define 3 major episodes ofvolcanic activity. Pre-Tertiary basement and older (ca. 38 Ma)Tertiary intrusive rocks are overlain unconformably by Oligocene (ca.30-23 Ma) basalt flows and dacitic to rhyolitic ash-flow tuffsinterbedded with fine-grained tuffaceous sedimentary rocks. Oligocenerocks are overlain by approximately 550 m of ca. 17-16 Ma basalt flowsequivalent to the Steens Basalt in southern Oregon, and basalt flowsare capped by a thin 16.3 Ma ignimbrite that likely is correlativewith either the Idaho Canyon Tuff or the Tuff of Oregon Cany!" Descriptors: absolute age; apatite; Ar/Ar; basalts; Basin and Range Province; basinrange structure; Cenozoic; correlation; dates; dip-slip faults;Eocene; exhumation; extension; extension faults; faults; fission-trackdating; geochemistry; Humboldt County Nevada; igneous rocks; lava;lava flows; major elements; Miocene; Neogene; Nevada; normal faults;North America; Oligocene; Paleogene; phosphates; Pine Forest Range;Tertiary; trace elements; United States; uplifts; volcanic rocks;volcanism Classification: 16 Structural geology; 03 Geochronology Source: "Geological Society of America Bulletin, vol.118, no.1-2, pp.126-139,Feb 2006" map_coordinates: "Latitude:N413000,N420000 Longitude:W1183000,W1185230"
Data Types:
  • Tabular Data
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