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"
Contributors:Donnelly-Nolan, Julie M; Lanphere, Marvin A
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"
Contributors: Parat, Fleurice; Dungan, Michael A; Lipman, Peter W
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"
Contributors:Sherrod, David R; Taylor, Edward M; Ferns, Mark L; Scott, William E;Conrey, Richard M; Smith, Gary A
Reference Number: 661
GeoREF Number: 2004-076790
Publication Year: 2004
Abstract: "This map presents the stratigraphic and structural setting of volcanicand sedimentary strata deposited during the past 35 million yearsacross 4,430 km (super 2) in central Oregon. Snowfall in the CascadeRange (west part of map area) recharges important aquifers in theDeschutes basin (central part of map). The area includes the majesticpeaks of the Three Sisters volcanoes, where continued eruptions ofbasalt and rhyolite in the past 3,000 years indicate an ongoingvolcanic hazard. The Sisters fault zone, with several potentiallyactive faults, crosses the map from southeast to northwest."
Descriptors: areal geology; Bend Quadrangle; central Oregon; geochemistry; geologicmaps; intrusions; lithostratigraphy; maps; Oregon; petrology;stratigraphic units; surficial geology; tectonic elements; UnitedStates; USGS; volcanism
Classification: "13, Areal geology"
Source: "Geologic Investigations Series - U. S. Geological Survey, Report:I-2683, 48 pp., 2 sheets, 2004"
map_coordinates: "Latitude:N440000,N443000 Longitude:W1210000,W1220000"
Contributors:McMillan, Nancy J.
Reference Number: 7639
GeoREF Number: 2007-000986
Publication Year: 2004
Descriptors: absolute age Ar/Ar Cenozoic Cretaceous extension Grant County New Mexico Hidalgo County New Mexico Hillsboro New Mexico igneous rocks Laramide Orogeny magmatism Mesozoic New Mexico Paleogene plate tectonics Sierra County New Mexico Silver City New Mexico subduction tectonics Tertiary United States Upper Cretaceous
Classification: 16 Structural geology; 03 Geochronology
Source: "Special Publication - New Mexico Geological Society, vol.11, pp.249-270, 2004"
Reference Number: 2052
GeoREF Number: 2006-029607
Publication Year: 2003
Abstract: "Recent work in the Sierra Nevada batholith suggests that plutonism isepisodic, with large volumes of granodiorite emplaced in relativelyshort time periods ( approximately 10-15 m.y.). Two major magmaticepisodes are now recognized in the eastern Sierra and White/InyoMountains--one in the Jurassic ( approximately 180-165 Ma) and one inthe Cretaceous (the Sierra crest magmatic episode approximately 98-88Ma). The later event is responsible for growth of a large part of thehigh Sierra and comes toward the end of a general eastward sweep ofmagmatism. We present new U-Pb zircon ages for four high-silicagranites exposed across the central Sierra Nevada batholith thatdemonstrate the importance of these high silica rocks in the overallpattern of magmatism. In the west-central Sierra, a new U-Pb zirconage for the granite of Grant Grove is approximately 98 Ma, and for thegranite of Lodgepole is approximately 115 Ma. To the east, theEvolution Basin Alaskite yields a preliminary age of 92-94 Ma and agarnetiferous phase of the granite mapped as the leucogranite ofRawson Creek gives an age of approximately 165 Ma. This last agedistinguishes the garnetiferous phase from the leucogranite of RawsonCreek proper, which has been dated at about approximately 95 Ma (Sternet al., 1981). These new ages bear on the question of the generationand modification of crust in continental arcs. Several studies suggestthat the voluminous granodiorites in the Sierran arc are the productsof mixing between coexisting dioritic and granitic magmas. The U-Pbdates presented here demonstrate that the history of high-silicamagmatism in the arc mirrors that of diorites and granodioritesexposed nearby. Consequently, the geochronology permits thecoexistence of the three magma types. This combined with fieldevidence for mixing, the bulk geochemistry, and the isotopegeochemistry of rocks across the range of composition stronglysupports the hypothesis that magma mixing is an important process ingeneration of the intermediate composition rocks. Isotope geochemistryalso suggests very little involvement of old crustal material, even inthe most siliceous lithologies, consistent with the idea that theSierra crest magmatic event was responsible for growth of a largevolume of new crust in the arc."
Descriptors: absolute age; batholiths; California; continental crust; Cretaceous;crust; dates; geochemistry; granites; Grant Grove; igneous rocks;intrusions; Inyo County California; Inyo Mountains; island arcs; magmacontamination; magmas; Mesozoic; mixing; nesosilicates;orthosilicates; plutonic rocks; provenance; Rawson Creek; SierraNevada Batholith; silicates; siliceous composition; U/Pb; UnitedStates; White Mountains; zircon; zircon group
Classification: 05A Igneous and metamorphic petrology; 03 Geochronology
Source: "Abstracts with Programs - Geological Society of America, vol.35, no.6,pp.326, Nov 2003"
map_coordinates: "Latitude:N354500,N373000 Longitude:W1154000,W1184500"
Contributors:Miller, Jonathan; Miller, Robert J; Wooden, Joseph L; Harper, Gregory