Gravity model and structural implications of the Goddard Pendant, Sierra Nevada, California
du Bray, H. W. Oliver
1981, Journal of Geophysical Research Solid Earth (86) 9279-9286
A subsurface model for the Goddard pendant is constructed from a residual gravity high of about 7 mGal over the pendant. The model, which is the simplest and most geologically reasonable possibility, shows a metamorphic block that tapers with depth and extends about 3.5 km below the surface. The structures...
Chemical modifications accompanying blueschist facies metamorphism of Franciscan conglomerates, Diablo Range, California
Diane E. Moore, J. G. Liou, B.-S. King
1981, Chemical Geology (33) 237-263
As part of an investigation of blueschist-facies mineral parageneses in pebbles and matrix of some Franciscan metaconglomerates of the Diablo Range, California, textural and major-element chemical analyses were conducted on a number of igneous pebbles that comprise a range of rock types from granite and dacite to gabbro and basalt....
The Redskin granite: Evidence for thermogravitational diffusion in a Precambrian granite batholith
S. Ludington
1981, Journal of Geophysical Research Solid Earth (86) 10423-10430
The 1000-Ma-old composite Pikes Peak batholith consists largely of medium- to coarse-grained biotite granite but is intruded by several smaller granite plutons. Two of these, the Tarryall Mountains batholith and the Redskin Granite (Hawley, 1969; Hawley and Wobus, 1977), are here interpreted as cupolas atop the main mass of the...
The origin and isotopic composition of dissolved sulfide in groundwater from carbonate aquifers in Florida and Texas
R. O. Rye, W. Back, B.B. Hanshaw, C.T. Rightmire, F. J. Pearson Jr.
1981, Geochimica et Cosmochimica Acta (45) 1941-1950
The δ34S values of dissolved sulfide and the sulfur isotope fractionations between dissolved sulfide and sulfate species in Floridan ground water generally correlate with dissolved sulfate concentrations which are related to flow patterns and residence time within the aquifer. The dissolved sulfide derives from the slow in situ biogenic reduction of sulfate dissolved from...
First manned submersible dives on the East Pacific Rise at 21°N (project RITA): general results
Jean Francheteau, H.D. Needham, P. Choukroune, Tierre Juteau, M. Seguret, Richard D. Ballard, P.J. Fox, W. R. Normark, A. Carranza, D. Cordoba, J. Guerrero, C. Rangin
1981, Marine Geophysical Research (4) 345-379
A submersible study has been conducted in February–March 1978 at the axis of the East Pacific Rise near 21°N. The expedition CYAMEX, the first submersible program to be conducted on the East Pacific Rise, is part of the French-American-Mexican project RITA (Rivera-Tamayo), a 3-year study devoted to detailed geological and...
Minor and trace element geochemistry of volcanic rocks dredged from the Galapagos spreading center: Role of crystal fractionation and mantle heterogeneity
D.A. Clague, F.A. Frey, G. Thompson, S. Rindge
1981, Journal of Geophysical Research Solid Earth (86) 9469-9482
A wide range of rock types (abyssal tholeiite, Fe-Ti-rich basalt, andesite, and rhyodacite) were dredged from near 95°W and 85°W on the Galapagos spreading center. Computer modeling of major element compositions has shown that these rocks could be derived from common parental magmas by successive degrees of fractional crystallization. However,...
Chrysophyte cysts as potential environmental indicators
D.P. Adam, A.D. Mahood
1981, Geological Society of America Bulletin (92) 839-844
Many Chrysophyte algae produce morphologically distinctive, siliceous, microscopic cysts during a resting stage of their life cycles; these cysts are often preserved in sediments. Scanning electron microscopy and Nomarski optics permit much more detailed observation of these cysts than was heretofore possible. We...
Geodetic strain measurements in Washington
J.C. Savage, M. Lisowski, W.H. Prescott
1981, Journal of Geophysical Research Solid Earth (86) 4929-4940
Two new geodetic measurements of strain accumulation in the state of Washington for the interval 1972–1979 are reported. Near Seattle the average principal strain rates are 0.07 ± 0.03 μstrain/yr N 19°W and −0.13 ± 0.02 μstrain/yr N71°E, and near Richland (south central Washington) the average principal strain rates are...
New maps of Federal coal
R. G. Wayland
1981, Geological Society of America Bulletin (92) 542-550
Compilation and analysis of publicly available data on Federal coal are resulting in voluminous map sets showing coal isopachs, structure contours, and overburden isopachs on each known minable coal bed. As of the spring of 1981, there are available from the U.S. Geological...
Cretaceous Arctic silicoflagellates
D. Bukry
1981, Geo-Marine Letters (1) 57-63
Cretaceous silicoflagellate assemblages from Arctic Ocean USGS Core 437 show Vallacerta siderea the most abundant species; most species of Lyramula disappear halfway up the core; only L. burchardae, n. sp., persists into the upper sections. These occurrences are untypical of the few documented Cretaceous assemblages from other areas. A Campanian...
13C 12C exchange between calcite and graphite: A possible thermometer in Grenville marbles
J.W. Valley, J. R. O’Neil
1981, Geochimica et Cosmochimica Acta (45) 411-419
The fractionation of 13C between calcite and graphite, Δ(Cc-Gr). is consistently small (2.6–4.8 permil) in 34 assemblages from upper amphibolite- and granulite-facies marbles of the Grenville Province. In 25 samples from the Adirondack Mountains, New York, it decreases regularly with increasing metamorphic temperature. The fractionations are independent of absolute δ13C values...
Estimation of surface temperature variations due to changes in sky and solar flux with elevation
S. Hummer-Miller
1981, Geophysical Research Letters (8) 595-598
Sky and solar radiance are of major importance in determining the ground temperature. Knowledge of their behavior is a fundamental part of surface temperature models. These two fluxes vary with elevation and this variation produces temperature changes. Therefore, when using thermal-property differences to discriminate geologic materials,...
Interpretation of changes in water level accompanying fault creep and implications for earthquake prediction
R. L. Wesson
1981, Journal of Geophysical Research Solid Earth (86) 9259-9267
Quantitative calculations for the effect of a fault creep event on observations of changes in water level in wells provide an approach to the tectonic interpretation of these phenomena. For the pore pressure field associated with an idealized creep event having an exponential displacement versus time curve, an analytic expression...
Systems for measuring thickness of temperate and polar ice from the ground or from the air.
R.D. Watts, D.L. Wright
1981, Journal of Glaciology (27) 459-469
Equipment has been designed and tested for ground-based and airborne sounding of temperate glaciers. The transmitter is a free-running pulse generator that uses avalanche-mode transistor breakdown to create high-voltage pulses. The transmit and receive antennas are resistively loaded dipoles; for the airborne system, a twin-lead transmit element...
Storm-built sand ridges on the Maryland inner shelf: a preliminary report
D.J.P. Swift, M.E. Field
1981, Geo-Marine Letters (1) 33-37
Several aspects of the Maryland ridge field are pertinent to the problem of ridge genesis in response to Holocene sea-level rise. There is a systematic morphologic change from shoreface ridges through nearshore ridges to offshore ridges, which reflects the changing hydraulic regime. Grain size is 90?? out of phase with...
Experimental seawater-basalt interaction at 300°C, 500 bars, chemical exchange, secondary mineral formation and implications for the transport of heavy metals
W.E. Seyfried Jr., J. L. Bischoff
1981, Geochimica et Cosmochimica Acta (45) 135-147
Seawater and NaCl solutions were reacted with basalt (basalt glass and diabase) for several months at 300°C, 500 bars and a water/rock ratio of 10. During reaction, seawater was significantly modified, increasing in Ca, H2S, CO2. SiO2, K. Fe, Mn. Ba, Al and H+, and decreasing in Mg and...
Computer-assisted photogrammetric mapping systems for geologic studies-A progress report
C. L. Pillmore, K.S. Dueholm, H.S. Jepsen, C.H. Schuch
1981, Photogrammetria (36) 159-171
Photogrammetry has played an important role in geologic mapping for many years; however, only recently have attempts been made to automate mapping functions for geology. Computer-assisted photogrammetric mapping systems for geologic studies have been developed and are currently in use in offices of the Geological Survey of Greenland at Copenhagen,...
Crystal growth of calcite from calcium bicarbonate solutions at constant PCO2 and 25°C: a test of a calcite dissolution model
Michael M. Reddy, Niel Plummer, E. Busenberg
1981, Geochimica et Cosmochimica Acta (45) 1281-1289
A highly reproducible seeded growth technique was used to study calcite crystallization from calcium bicarbonate solutions at 25°C and fixed carbon dioxide partial pressures between 0.03 and 0.3 atm. The results are not consistent with empirical crystallization models that have successfully described calcite growth at low PCO2 (< 10−3 atm). Good agreement was...
The late-Neoglacial histories of the Agassiz and Jackson glaciers, Glacier National Park, Montana.
P. E. Carrara, R. G. McGimsey
1981, Arctic and Alpine Research (13) 183-196
Twenty-one tree-ring stations, totaling 116 trees, were sampled at various localities within the forest trimlines fronting the Agassiz and Jackson glaciers, Glacier National Park, Montana. Tree ages within these zones became progressively younger from the region of the maximum late-Neoglacial position to the bases of the bedrock slopes on which...
Seawater sulfate reduction and sulfur isotope fractionation in basaltic systems: interaction of seawater with fayalite and magnetite at 200–350°C
Wayne C. Shanks III, James L. Bischoff, Robert J. Rosenbauer
1981, Geochimica et Cosmochimica Acta (45) 1977-1995
Sulfate reduction during seawater reaction with fayalite and with magnetite was rapid at 350°C, producing equilibrium assemblages of talc-pyrite-hematite-magnetite at low water/rock ratios and talc-pyrite-hematite-anhydrite at higher water/rock ratios. At 250°C, seawater reacting with fayalite produced detectable amounts of dissolved H2S, but extent of reaction of solid phases was...
Correlation of natural gas content to iron species in the New Albany shale group
R.H. Shiley, R.M. Cluff, D. R. Dickerson, C.C. Hinckley, Gerard V. Smith, H. Twardowska, Mykola Saporoschenko
1981, Fuel (60) 732-738
Mössbauer parameters were obtained for four Illinois Basin shales and their corresponding < 2μm clay fractions from wells drilled through the New Albany Shale Group in Henderson, Tazewell, and Effingham counties in Illinois and Christian County in Kentucky. Off-gas analysis indicated that the Illinois cores were in an area of...
Aeromagnetic and radio echo ice-sounding measurements over the Dufek intrusion, Antarctica
John C. Behrendt, D.J. Drewry, E. Jankowski, M. S. Grim
1981, Journal of Geophysical Research Solid Earth (86) 3014-3020
A combined aeromagnetic and radio echo ice-sounding survey (4200 km of traverse) made in 1978 in Antarctica over the Dufek layered mafic intrusion of Jurassic age suggests a minimum area of about 50,000 km2, making it comparable in size with the Bushveld Complex of Africa. Comparisons of the magnetic and...
Seismic amplitude anomalies associated with thick First Leo sandstone lenses, eastern Powder River basin, Wyoming
A. H. Balch, Myung W. Lee, J. J. Miller, R. T. Ryder
1981, Geophysics (46) 1519-1527
Several new discoveries of oil production in the Leo sandstone, an economic unit in the Pennsylvanian middle member of the Minnelusa formation, eastern Powder River basin, Wyoming-Nebraska-South Dakota, have renewed exploration interest in this area. Vertical seismic profiles (VSP) and model studies suggested that a measurable seismic amplitude anomaly is...
Sm-Nd systematics of a tonalitic augen gneiss and its constituent minerals from northern Michigan
K. Futa
1981, Geochimica et Cosmochimica Acta (45) 1245-1249
The Sm-Nd isotopic system of a tonalitic augen gneiss and its constituent minerals from northern Michigan was disturbed during metamorphism. Sm-Nd zircon ages are lower than the wholerock Sm-Nd model age. However, closely associated pairs of minerals (for example, sphene and biotite or apatite and plagioclase) retain their apparent metamorphic...
Dating of Archean basement in northeastern Wyoming and southern Montana.
Z. E. Peterman
1981, Geological Society of America Bulletin (92) 139-146
Rb-Sr whole-rock and U-Pb zircon ages of granite and gneiss cores from three deep drill holes extend known occurrences of Archean rocks in the subsurface of NE Wyoming and S Montanta. Rb-Sr and K- Ar mineral ages are discordant and reflect early or middle Proterozoic disturbance. Highly altered rocks occur...
