Trondhjemitic, 1.35-1.31 Ga gneisses of the Mount Holly Complex of Vermont: evidence for an Elzevirian event in the Grenville Basement of the United States Appalachians
N. M. Ratcliffe, J. N. Aleinikoff, W.C. Burton, P. Karabinos
1991, Canadian Journal of Earth Sciences (28) 77-93
A newly recognized suite of trondhjemite–tonalite and dacitic gneiss forms a 10 km wide belt of rocks within the Mount Holly Complex in the central part of the Green Mountain massif of Vermont. Field relationships and chemistry indicate that these gneisses are calc-alkaline, volcanic, and hypabyssal plutonic rocks older than the...
An AEM-TEM study of weathering and diagenesis, Abert Lake, Oregon: II. Diagenetic modification of the sedimentary assemblage
J.F. Banfield, B.F. Jones, D.R. Veblen
1991, Geochimica et Cosmochimica Acta (55) 2795-2810
This paper compares the mineralogy and chemistry of clay minerals in sediments from various depths and positions in Abert Lake and surrounding playa with those of the weathered materials entering the lake in order to reveal the nature and extent of post-depositional mineralogical modification.Analytical electron microscope (AEM) data from individual...
Origin of xenoliths in the trachyte at Puu Waawaa, Hualalai Volcano, Hawaii
David A. Clague, Wendy A. Bohrson
1991, Contributions to Mineralogy and Petrology (108) 439-452
Rare dunite and 2-pyroxene gabbro xenoliths occur in banded trachyte at Puu Waawaa on Hualalai Volcano, Hawaii. Mineral compositions suggest that these xenoliths formed as cumulates of tholeiitic basalt at shallow depth in a subcaldera magma reservoir. Subsequently, the minerals in the xenoliths underwent subsolidus reequilibration that particularly affected chromite...
Cenozoic prograding sequences of the Antarctic continental margin: a record of glacio-eustatic and tectonic events
A. K. Cooper, P. J. Barrett, K. Hinz, V. Traube, G. Letichenkov, H.M.J. Stagg
1991, Marine Geology (102) 175-213
Sedimentary sections up to 6-14 km thick lie beneath many areas of the Antarctic continental margin. The upper parts of the sections contain up to 6 km of Cenozoic glacial and possibly non-glacial sequences that have prograded the continental shelf up to 85 km. We describe the Cenozoic sequences using...
The transition from hydrostatic to greater than hydrostatic fluid pressure in presently active continental hydrothermal systems in crystalline rock
R.O. Fournier
1991, Geophysical Research Letters (18) 955-958
Fluid flow at hydrostatic pressure (Ph) is relatively common through fractures in silicic and in mafic crystalline rocks where temperatures are less than about 350–370°C. In contrast, pore-fluid pressure (Pf) > Ph has been encountered at the bottom of 3 geothermal exploration wells that attained temperatures >370°C...
Wasatch fault zone, Utah - segmentation and history of Holocene earthquakes
Michael N. Machette, Stephen F. Personius, Alan R. Nelson, David P. Schwartz, William R. Lund
1991, Journal of Structural Geology (13) 151-164
The Wasatch fault zone (WFZ) forms the eastern boundary of the Basin and Range province and is the longest continuous, active normal fault (343 km) in the United States. It underlies an urban corridor of 1.6 million people (80% of Utah's population) representing the largest earthquake risk in the interior...
Seismic response of transamerical building. I. Data and preliminary analysis
M. Çelebi, E. Safak
1991, Journal of Structural Engineering (117) 2389-2404
The objective of this paper is to present preliminary analyses of a set of acceleration response records obtained during the October 17, 1989 Loma Prieta earthquake (Ms = 7.1) from the 60-story vertically tapered, pyramid-shaped Trans-america Building-a landmark of San Francisco. The building was instrumented in 1985 with 22 channels...
Photometric functions for photoclinometry and other applications
A. S. McEwen
1991, Icarus (92) 298-311
Least-squared fits to the brightness profiles across a disk or “limb darkening” described by Hapke's photometric function are found for the simpler Minnaert and lunar-Lambert functions. The simpler functions are needed to reduce the number of unknown parameters in photoclinometry, especially...
Re - Os isotopic constraints on the origin of volcanic rocks, Gorgona Island, Colombia: Os isotopic evidence for ancient heterogeneities in the mantle
R.J. Walker, L.M. Echeverria, S.B. Shirey, M.F. Horan
1991, Contributions to Mineralogy and Petrology (107) 150-162
The Re - Os isotopic systematics of komatiites and spatially associated basalts from Gorgona Island, Colombia, indicate that they were produced at 155??43 Ma. Subsequent episodes of volcanism produced basalts at 88.1??3.8 Ma and picritic and basaltic lavas at ca. 58 Ma. The age for the ultramafic rocks is important...
An empirical coverage test for the g-sample problem
L.A. Orlowski, W.D. Grundy, P.W. Mielke Jr.
1991, Mathematical Geology (23) 583-589
A nonparametric g-sample empirical coverage test has recently been developed for univariate continuous data. It is based upon the empirical coverages which are spacings of multiple random samples. The test is capable of detecting any distributional differences which may exist among the parent populations, without additional assumptions beyond randomness and...
Degassing and differentiation in subglacial volcanoes, Iceland
J.G. Moore, L. C. Calk
1991, Journal of Volcanology and Geothermal Research (46) 157-180
Within the neovolcanic zones of Iceland many volcanoes grew upward through icecaps that have subsequently melted. These steep-walled and flat-topped basaltic subglacial volcanoes, called tuyas, are composed of a lower sequence of subaqueously erupted, pillowed lavas overlain by breccias and hyaloclastites produced by phreatomagmatic explosions in shallow water, capped by...
The effects of noise due to random undetected tilts and paleosecular variation on regional paleomagnetic directions
G.J. Calderone, R.F. Butler
1991, Journal of Geophysical Research (96) 3973-3977
Random tilting of a single paleomagnetic vector produces a distribution of vectors which is not rotationally symmetric about the original vector and therefore not Fisherian. Monte Carlo simulations were performed on two types of vector distributions: (1) distributions of vectors formed by perturbing a single...
Cretaceous-Eocene (Laramide) landscape development and Oligocene- Pliocene drainage reorganization of transition zone and Colorado Plateau, Arizona
D. P. Elston, R.A. Young
1991, Journal of Geophysical Research (96) 12389-12406
Landscape development of central and northern Arizona can no longer be ascribed mainly to events of Miocene and Pliocene age. New information on the age and distribution of older Cenozoic deposits has led to the recognition of a regional Cretaceous-Paleocene(?) surface of erosion that conforms...
Infiltration of unconsumed irrigation water in Utah
William C. Brothers, Susan A. Thiros
1991, Conference Paper
The ground-water hydrology of Panguitch Valley and adjacent areas, south-central Utah, was studied during 1988-90. One objective of the study was to measure ground-water recharge from infiltration of unconsumed irrigation water. Water-level and soil-moisture data were used to estimate travel times for water moving down through the soil profile, and...
Late quaternary geologic framework, north-central Gulf of Mexico
Jack L. Kindinger, Shea Penland, S. Jeffress Williams, Gregg R. Brooks, John R. Suter, Randolph A. McBride
1991, Conference Paper, Coastal Sediments '91
The geologic framework of the north-central Gulf of Mexico shelf is composed of multiple, stacked, delta systems. Shelf and nearshore sedimentary facies were deposited by deltaic progradation, followed by shoreface erosion and submergence. A variety of sedimentary facies has been identified, including prodelta, delta fringe, distributary, lagoonal, barrier island, and...
Calibration of a texture-based model of a ground-water flow system, western San Joaquin Valley, California
Steven P. Phillips, Kenneth Belitz
1991, Ground Water (29) 702-715
The occurrence of selenium in agricultural drain water from the western San Joaquin Valley, California, has focused concern on the semiconfined ground-water flow system, which is underlain by the Corcoran Clay Member of the Tulare Formation. A two-step procedure is used to calibrate a preliminary model of the system for...
The possible role of thiosulfate in the precipitation of 34S-rich barite in some Mississippi Valley-type deposits
C.S. Spirakis
1991, Mineralium Deposita (26) 60-65
The precipitation of extremely 34S-rich barite in the late stage of mineralization in the Mississippi Valleytype deposits of the Illinois-Kentucky district (U.S.A.) may be explained by reactions involving thiosulfate (S2O3=). Inorganic processes are known to concentrate 34S in the sulfonate site of thiosulfate and 32S in the sulfate site. In...
A new approach to plane-sweep overlay: topological structuring and line-segment classification
Jan W. van Roessel
1991, Cartography and Geographic Information Systems (18) 49-67
An integrated approach to spatial overlay was developed with the objective of creating a single function that can perform most of the tasks now assigned to discrete functions in current systems. Two important components of this system are a unique method for topological structuring, and a method for attribute propagation...
Revised values for the thermodynamic properties of boehmite, AlO(OH) , and related species and phases in the system Al-H-O
B. S. Hemingway, R. A. Robie, J. A. Apps
1991, American Mineralogist (76) 445-457
Heat capacity measurements are reported for a well-characterized boehmite that differ significantly from results reported earlier by Shomate and Cook (1946) for a monohydrate of alumina. It is suggested that the earlier measurements were made on a sample that was a mixture of phases and that use of that heat-capacity...
Low sulfur content in submarine lavas: An unreliable indicator of subaerial eruption
A. S. Davis, D.A. Clague, M. S. Schulz, J.R. Hein
1991, Geology (19) 750-753
Low S content (<250 ppm) has been used to identify subaerially erupted Hawaiian and Icelandic lavas. Large differences in S content of submarine-erupted lavas from different tectonic settings indicate that the behavior of S is complex. Variations in S abundance in undegassed, submarine-erupted...
Uranium and minor-element partitioning in Fe-Ti oxides and zircon from partially melted granodiorite, Crater Lake, Oregon
T.Z.L. Tourrette, D.S. Burnett, C. R. Bacon
1991, Geochimica et Cosmochimica Acta (55) 457-469
Crystal-liquid partitioning in Fe-Ti oxides and zircon was studied in partially melted granodiorite blocks ejected during the climactic eruption of Mt. Mazama (Crater Lake), Oregon. The blocks, which contain up to 33% rhyolite glass (75 wt% SiO2), are interpreted to be portions of the magma chamber walls that were torn...
Landscape analysis: Theoretical considerations and practical needs
A.E. Godfrey, E.T. Cleaves
1991, Environmental Geology and Water Sciences (17) 141-155
Numerous systems of land classification have been proposed. Most have led directly to or have been driven by an author's philosophy of earth-forming processes. However, the practical need of classifying land for planning and management purposes requires that a system lead to predictions of the results of management activities. We...
Tritium as an indicator of ground-water age in Central Wisconsin
Kenneth R. Bradbury
1991, Groundwater (29) 398-404
In regions where ground water is generally younger than about 30 years, developing the tritium input history of an area for comparison with the current tritium content of ground water allows quantitative estimates of minimum ground-water age. The tritium input history for central Wisconsin has been constructed using precipitation tritium...
Gaylussite formation at Mono Lake, California
J. L. Bischoff, D.B. Herbst, R.J. Rosenbauer
1991, Geochimica et Cosmochimica Acta (55) 1743-1747
The salinity of Mono Lake has steadily increased since 1941 from 50%. to about 90%. due to diversion of tributary streams. This increase has resulted in the newly discovered precipitation of gaylussite (Na2Ca(CO3)2 · 5H2O). Chemical modeling of the lake water using Pitzer equations suggests that gaylussite has been forming year...
Backwater effects in the Amazon River basin of Brazil
R.H. Meade, J.M. Rayol, S.C. Da Conceicao, J.R.G. Natividade
1991, Environmental Geology and Water Sciences (18) 105-114
The Amazon River mainstem of Brazil is so regulated by differences in the timing of tributary inputs and by seasonal storage of water on floodplains that maximum discharges exceed minimum discharges by a factor of only 3. Large tributaries that drain the southern Amazon River basin reach their peak discharges...
