Reference Number: 1968
GeoREF Number: 2005-004738
Publication Year: 2004
Abstract: "The Long Valley Volcanic Field in east-central California straddles the East Sierran frontal fault zone, overlapping the Sierra Nevada and western Basin and Range Provinces. Long Valley volcanism began about 4 Ma during Pliocene time and has continued intermittently through the Holocene. The current (post-1980) seismic unrest at Long Valley, accompanied by uplift of the resurgent dome, may signal the onset of a new episode of regional extension and basalt injection into the residual magma chamber."
Descriptors: basalts-; California-; Cenozoic-; dacites-; eruptions-; geochemistry-; Holocene-; igneous-rocks; lava-; Long-Valley-Caldera; magmas-; major-elements; metals-; Mono-County-California; Mono-Inyo-Suite; Neogene-; Pliocene-; Quaternary-; rare-earths; seismicity-; Tertiary-; trace-elements; trachyandesites-; United-States; USGS-; volcanic-fields; volcanic-rocks; volcanism-
Source: U. S. Geological Survey Professional Paper. 2004.
map_coordinates: LAT: N374500; N380000; LONG: W1183000; W1190000.
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"
Contributors:White, Craig M; Hart, William K; Bonnichsen, Bill; Matthews, Debra
Reference Number: 1979
GeoREF Number: 2005-033636
Publication Year: 2004
Descriptors: Ada County Idaho; alkaline earth metals; basalts; Canyon County Idaho;chemical composition; concentration; genesis; geochemistry; Idaho;igneous rocks; isotope ratios; isotopes; magmas; metals; ocean-islandbasalts; Owyhee County Idaho; rare earths; Snake River plain;Sr-87/Sr-86; stable isotopes; strontium; tholeiitic basalt; UnitedStates; variations; volcanic rocks
Classification: 02C Geochemistry of rocks, soils, and sediments; 05A Igneous andmetamorphic petrology
Source: Bulletin - Idaho Geological Survey, Report: 30, pp.329-342, May 2004
map_coordinates: Latitude:N431200,N433000 Longitude:W1161800,W1164200
Contributors:Mihai, Ducea N.; Kidder, Steven; Zandt, George
Reference Number: 2710
GeoREF Number: 2004-085330
Publication Year: 2003
Abstract:  The Coast Ridge Belt (CRB, Santa Lucia Mts., central California) comprises mid-crustal rocks (750-800degreesC and 0.8 GPa) of the California magmatic arc. We estimated the bulk composition of the CRB and converted our results to seismic velocities expected at the observed pressures and temperatures. The bulk composition of this arc section changes abruptly at 25 km depth from a granodiorite to a quartz-diorite or diorite. These data are in agreement with results from other Cordilleran batholiths suggesting 1.5 to 2 times thicker felsic columns than interpreted for modern continental arcs, and a relatively sharp transition from a felsic upper crustal batholith, and a mafic deep crust. This implied rheological boundary may have significant implications for intracrustal faulting or convective removal of the roots of batholiths.
Descriptors: batholiths; California; Coast Ridge Belt; crust; diorites; emplacement; faults; granites; granodiorites; igneous rocks; intrusions; mafic composition; plutonic rocks; rheology; Santa Lucia Range; United States
Classification: Igneous and metamorphic petrology
Source: 30(13) (July 01, 2003)
Reference Number: 2540
GeoREF Number: 2005-006849
Publication Year: 2003
Abstract: "The eastern Snake River Plain (ESRP) volcanic basin in southeast Idaho is underlain by approximately 1 km of dominantly Pliocene-Quaternary olivine tholeiite basalt and interbedded sediment. The F basalt flow group is a stratigraphic marker bed near the top of the regional aquifer and underlies a portion of the Idaho National Engineering and Environmental Laboratory, where radiochemical and chemical wastewater has been discharged to the aquifer. This flow group erupted during an unusual, short-lived period of reversed magnetic polarity approximately 565 ka, probably in < or =200 years. This study uses new petrographic, geochemical, and isotopic analyses of the flow group to refine the subsurface stratigraphy. This sequence of lava flows is uneroded, apparently comagmatic, and is observed in drill core over an area of approximately 75 km (super 2) between approximately 120-220 m depth. Lithologic logs for six sections of F flows in drill-core reveal textural discordance within the sequence and that the thickest ( approximately 55 m) lie in the southwest part of the study region and contain an upper portion ( approximately 15-23 m) that is texturally coarser and significantly enriched in incompatible elements relative to the remainder of the sequence. In addition, lava flows in the lower sequence have lower initial (super 87) Sr/ (super 86) Sr isotopic ratios than the upper flows (0.7068 vs. 0.7071) while all exhibit similar (super 143) Nd/ (super 144) Nd isotope ratios ( approximately 0.5124; epsilon (sub Nd) approximately -4.3). Petrographic, isotopic, and geochemical features support correlations between sampled sections and define two flow groups within the F sequence. Variations in the texture and stratigraphy of the two flow groups indicate that they were derived from multiple coeval eruptive centers aligned along a common rift or fissure system, and not from a central vent complex. The stratigraphy of the entire F sequence is consistent with formation by constructional volcanic processes and is unaffected by post depositional structural offsets."
Descriptors: alkaline-earth-metals; basalts-; Cenozoic-; cores-; correlation-; F-Basalt; geochemistry-; Idaho-; igneous-rocks; INEEL-; isotope-ratios; isotopes-; lithofacies-; lithostratigraphy-; metals-; Nd-144-Nd-143; neodymium-; petrography-; Quaternary-; rare-earths; Snake-River-plain; Sr-87-Sr-86; stable-isotopes; strontium-; textures-; tholeiitic-basalt; United-States; volcanic-rocks; volcanism-
map_coordinates: LAT: N432200; N440200; LONG: W1122600; W1131000.
Reference Number: 1850
GeoREF Number: 2004-026604
Publication Year: 2003
Abstract: "Biotite and K-feldspar (super 40) Ar/ (super 39) Ar systems from the east-central Peninsular Ranges batholith near 33 degrees N were affected by two distinct phases of Late Cretaceous rapid cooling. The 85-Ma biotite K-Ar isochron separates comparatively shallow rocks in the southwest that record earlier cooling (91-86 Ma) from deeper rocks in the northeast that record later cooling (78-68 Ma). Samples close to 85 Ma isochron record both episodes of rapid cooling as well as slower cooling between 86 and 78 Ma. Although the 85 Ma isochron also coincides with a steep (1-2 m.y./km) K-Ar age gradient, only localized faulting has been detected along it. We attribute 91-86 Ma cooling to denudation related to emplacement of the voluminous suite of 96+ or -3 Ma La Posta plutons. In contrast, we link cooling after 78 Ma to Laramide shallow subduction beneath the Peninsular Ranges batholith. Our numerical simulations indicate that the latter cooling phase can be explained by either pure erosional denudation or by subduction refrigeration beginning at 80 Ma. In the latter case, erosional denudation occurs during steady-state shallow subduction. While final erosion depths predicted by the two models differ significantly (as much as 20 km for pure erosional denudation but only 11 km for subduction refrigeration followed by erosion), both are within the range indicated by independent thermobarometry of the eastern batholith. Based upon the similarity of independently determined denudation histories from Peninsular Ranges batholith basement rocks and forearc sediments that onlap the northern Peninsular Ranges batholith, we conclude that erosional denudation was probably the most important process between 78 and 68 Ma. We speculate that removal of lower crust and lithospheric mantle beneath the east-central Peninsular Ranges batholith during Laramide shallow subduction triggered erosional denudation and localized thrusting until the density balance between the crust and mantle was restored in latest Cretaceous-early Tertiary time."
Descriptors: absolute-age; Ar-Ar; Baja-California; basins-; batholiths-; California-; Cenozoic-; chemical-composition; cooling-; Cretaceous-; dates-; deformation-; denudation-; diorites-; emplacement-; erosion-; faults-; fore-arc-basins; geochemistry-; igneous-rocks; intrusions-; isotope-ratios; La-Posta-Pluton; Laramide-Orogeny; Little-Blair-Valley; magmas-; Mason-Valley; melts-; Mesozoic-; metamorphic-rocks; Mexico-; mineral-assemblages; mineral-composition; North-America; paleoenvironment-; Peninsular-Ranges; Peninsular-Ranges-Batholith; petrology-; plate-tectonics; plutonic-rocks; sedimentation-; stratigraphic-units; subduction-; tectonics-; Tertiary-; tonalite-; United-States; uplifts-; Upper-Cretaceous; Vallecito-Valley
Source: Special Paper - Geological Society of America. 374; Pages 355-379. 2003.
map_coordinates: LAT: N323000; N331500; LONG: W1160000; W1170000.