Reference Number: 1812
GeoREF Number: 2003-047638
Publication Year: 2003
Abstract: Deleted in this version
Descriptors: "absolute-age; active-faults; adularia-; alkali-feldspar; Ar-Ar; Cenozoic-; chemically-precipitated-rocks; dates-; disseminated-deposits; epithermal-processes; faults-; feldspar-group; framework-silicates; gold-ores; high-angle-faults; Ivanhoe-mining-district; K-Ar; lacustrine-environment; mercury-ores; metal-ores; Midas-mining-district; middle-Miocene; mineral-deposits,-genesis; mineral-exploration; mineralization-; Miocene-; Neogene-; Nevada-; northern-Nevada; ore-forming-fluids; oxidation-; paleogeography-; plagioclase-; sanidine-; sedimentary-rocks; silicates-; siliceous-sinter; Tertiary-; United-States; volcanism-"
Source: "Economic Geology and the Bulletin of the Society of Economic Geologists. 98; 2, Pages 409-424. 2003."
map_coordinates: LAT| N400000; N402000; LONG: W1162000; W1165500.
Contributors:Nutt, C J; Ludington, Steve
Reference Number: 1842
GeoREF Number: 2004-020759
Publication Year: 2003
Descriptors: data bases; data processing; digital data; geographic information systems; igneous rocks; information systems; intrusions; mapping; plutonic rocks; spatial data; United States; USGS; Utah
Classification: "05A, Igneous and metamorphic petrology"
Source: "Open-File Report - U. S. Geological Survey, Report: OF 03-0486, 41 pp., 2003"
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
Reference Number: 1803
GeoREF Number: 2003-031234
Publication Year: 2003
Abstract: "The north-northwest-trending White-Inyo Range locally defines the western edge of the Great Basin. The northeast-trending Barcroft structural break lies astride the province boundary. Along this preintrusive, high-angle reverse fault, middle Mesozoic White Mountain Peak alkaline volcanic and intercalated volcaniclastic rocks on the north are separated from uppermost Proterozoic--Lower Cambrian miogeoclinal quartzite and carbonate strata on the south by the 165 + or - 1 Ma (SHRIMP-RG, [sensitive, high-resolution ion microprobe--reverse geometry], U-Pb zircon) Barcroft pluton. Although locally faulted, the subparallel southeast and northwest borders of the body display intrusive contacts. Finer-grained comagmatic metadiorite occurs as early-stage dikes in the wall rocks. Eastward, the 100 Ma McAfee Creek granite intrudes the Barcroft pluton. Tertiary diabase dikes crosscut the section. The two granitic series, reflecting local evolution of the Mesozoic arc system, are described in this paper: (1) mafic granitoid rocks of the calc-alkaline Barcroft series, including chemically intergradational granodiorite, gabbro/diorite, metadiorite, and rare alaskite-aplite-all rich in large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs), and (2) granite of the felsic McAfee Creek series, which has even greater enrichment of LILEs and greater depletion in HFSEs than the Barcroft pluton. Rocks rich in hornblende+ or -clinopyroxene and belonging to the Ca-rich, metaluminous Barcroft series exhibit a broad range of chemical and mineral compositions and represent products of both mixing between high- and low-silica members of the series to generate intermediate compositions and fractional crystallization to generate the most mafic (cumulate) rocks. The younger, more homogeneous, K-rich McAfee Creek-type muscovite granite possesses mildly peraluminous, minimum-melt compositions. Field evidence for magma mixing and isotopic data for the Barcroft series (epsilon (sub Nd(t)) = -1.53 to -5.50, (super 87) Sr/ (super 86) Sr (sub (i)) = 0.7053-0.7063) and the McAfee Creek granite (epsilon (sub Nd(t)) = -5.64 to -9.76, (super 87) Sr/ (super 86) Sr (sub (i)) = 0.7062-0.7116) require open-system processes and involvement of preexisting crustal rocks in their genesis. The Barcroft series is one of several shallow-level magma systems now recognized in the Sierran arc that include significant amounts of reworked, preexisting crustal material. These magma series are distinct from those that represent demonstrably deeper levels of Mesozoic magma systems and lack isotopic evidence for significant involvement of older crust. Despite these differences in magma sources and evolution, both magma series evolved along indistinguishable petrologic and chemical trends. Igneous rocks in the White Mountains record post-Paleozoic growth of this part of the Californian margin: (1) Jurassic and younger subduction, partial fusion of the overlying mantle wedge, and/or deep-seated mafic crust, ascent of mildly alkaline and later calc-alkaline magmas attending Andean-style volcanic-plutonic arc production, with significant involvement of preexisting crustal rocks; (2) Late Cretaceous thickening, heating, and crustal contamination, followed by rise of peraluminous granite-minimum melts; and (3) Neogene Basin and Range lithospheric transtension, tapping of upper-mantle diabasic melt, and dike emplacement."
Descriptors: alkaline-earth-metals; Barcroft-Pluton; calc-alkalic-composition; California-; concentration-; continental-margin; crust-; crustal-thickening; dikes-; field-studies; geochemistry-; granites-; granodiorites-; high-field-strength-elements; igneous-rocks; intrusions-; Inyo-County-California; isotope-ratios; isotopes-; lithogeochemistry-; lithophile-elements; magma-contamination; magmas-; major-elements; mantle-wedges; Mesozoic-; metadiabase-; metaigneous-rocks; metals-; metaluminous-composition; metamorphic-rocks; mineral-composition; mixing-; Mono-County-California; Mount-Barcroft; open-systems; peraluminous-composition; plate-tectonics; plutonic-rocks; plutons-; shallow-depth; Sierra-Nevada; Sr-87-Sr-86; stable-isotopes; strontium-; subduction-; trace-elements; United-States; White-Mountains
Source: "Geological Society of America Bulletin. 115; 4, Pages 499-512. 2003."
map_coordinates: LAT: N372900; N374000; LONG: W1181000; W1182200.