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At least 685 records · Page 38Linked to original sources
USGS1975

Tectonics of the western Valley and Ridge foldbelt, Pendleton County, West Virginia - a summary report

A belt of high anticlines, the Nittany anticlinorium, occupies the western Valley and Ridge foldbelt in the central Appalachians. It extends southwestward from the Nittany arch of central Pennsylvania into the Virginias. An investigation of the tectonics of this anticlinorium in Pendleton County, W. Va., rules out active basement involvement in the deformation of the area. Cross-sectional models consistent with the accumulated data show that Middle Cambrian through Middle Ordovician carbonate rocks are technically stacked, shingle-fashion, from southeast to northwest below predominantly folded younger strata that have undergone less lateral shortening. Differential shortening in this area is of the proper order to balance cover deformation in the Allegheny synclinorium to the west. Field relations suggest a long period of abnormally high fluid pressures in Lower Devonian and older strata during deformation. At this time, the area was under sufficient northwest, near-horizontal compressive stress for abundant quartz deformation lamellae to form. Gravity sliding is ruled out as the deforming mechanism for this part of the Appalachian foldbelt. No significant tectonism appears to have occurred prior to Pennsylvanian time in this area.

West Virginia↗
USGS1975

Quaternary faults at San Diego Bay, California

Acoustic-reflection profiles of subbottom strata reveal numerous faults that cut Quaternary deposits within and directly outside of San Diego Bay. These faults, together with previously mapped onshore faults, constitute the Rose Canyon fault zone that forms the local west boundary of the Santa Ana tectonic block, which is bounded on the east by the Elsinore fault zone. The minor earthquakes that have been felt in San Diego during historic time and accurately recorded during the past 41 yr are too infrequent to explain the observed rate of slip. The principal faulting is inferred to take place during moderate earthquakes similar to previous ones recorded along the west side of the Santa Ana block in 1933 at Long Beach, Calif., and in 1956 at San Miguel, Baja California. The known magnitudes of these previous events suggest that earthquakes in San Diego could attain a magnitude of approximately 6.5. An offset of the coast at Point La Jolla, when divided by the offset associated with previously studied earthquakes of magnitude 6.5, suggests that such events occur there at an average of approximately once every 600 yr.

California↗
USGS1975

Age of volcanism, intrusion, and mineralization in the Thomas Range, Keg Mountain, and Desert Mountain, western Utah

Twenty-six new age determinations by the fission-track method establish a chronology for volcanism, intrusion, and mineralization in the Thomas Range, Keg Mountain, and Desert Mountain, in western Utah. The fission-track ages confirm D. R. Shawe's three-fold classification of igneous rocks. The oldest group of rocks consists of flows, agglomerates, and some ash-flow tuffs that were deposited 38-39 m.y. ago. The middle group contains widespread rhyolitic ash-flow tuffs that originated from local volcanic centers 30-32 m.y. ago. A dike emplaced along the probable ring-fracture zone of the Keg caldera about 31 m.y. ago indicates that caldera collapse occurred soon after eruption of ash-flow tuffs. Rocks believed to belong-to the middle group also were intruded by the quartz monzonite of Desert Mountain 27-30 m.y. ago. Little or no igneous activity took place within the next 20 m.y., during which time the region was strongly broken by Basin-and-Range faulting. Rhyolites of the youngest group were extruded 8-10 m.y. ago in the Keg Mountain area and 6-7 m.y. ago in the Thomas Range. The beryllium-fluorite mineralization at Spor Mountain occurred after the rhyolitic volcanism in the Thomas Range.

Utah↗
USGS1975

The Oligocene volcanic center at Eureka, Nevada

A volcanic center covering an area of about 80 km 2 near Eureka, Nev., and active in the early Oligocene, is characterized by rhyolitic, rhyodacitic. and andesitic pyroclastic rocks, lava flows, and shallow intrusive bodies. These rocks were emplaced as intertonguing and interpenetrative units during a 5-m.y. interval; most of the volcanism was in the last 3 million years of this period (36 to 33 m.y. ago).

Nevada↗
USGS1975

Geomorphic evidence for late Holocene tilting in southern San Mateo County, California

Relations between the stream channels and the alluvial deposits along Bradley Creek and the lower part of Butano Creek suggest that the area has been tilted very recently, and localized swampy conditions supply additional supporting evidence. Radiocarbon dates show that some of the valley alluvium along Butano Creek was deposited no more than 750-800 yr ago, and tilting must have Occurred since that time.

California↗
USGS1975

Fossil fishes from the Pliocene or Pleistocene Cache Formation, Lake County, California

The remains of fossil fishes comprising three species were found in the Cache Formation in Lake County, Calif. The rocks containing the fossils are considered to be late Pliocene or early Pleistocene. The species are all freshwater and primarily quiet-water types that now live in Clear Lake and the waters of the surrounding area, suggesting continuity between the present lake and a lake represented by the rocks of the Cache Formation.

California↗
USGS1975

Spectrochemical determination of trace elements in galena

A semiquantitative spectrochemical method is described by means of which 10-mg samples of galena can be analyzed for their trace element content. Results on 40 elements are reported as six logarithmically spaced intervals per order of magnitude and obtained by visual comparison with standards prepared in spectrographically pure lead sulfide. Detection limits are generally between 1 and 20 ppm (except for Ce, Na, Sr, Ta, and Zn, which are 50 to 100 ppm). Replicate analyses of galena samples indicate a precision comparable to other semiquantitative spectrochemical methods used for the analysis of geochemical samples. Results obtained from the analysis of 129 galena samples are summarized.

Journal of Research of the U.S. Geological Survey↗
USGS1976

Fracturing and subsidence of the land surface caused by the withdrawal of ground water in the Milford area, Utah

Fracturing and subsidence of the land surface in the Milford area of Utah have resulted from the decline of water levels due to pumping in unconsolidated deposits of Quaternary age. To the writers' knowledge, these are the first such effects of ground-water withdrawal reported in Utah. The fracturing is in an area about 1 mile (1.6 km) wide and 11 miles (18 km) long near Milford, in an unsaturated clay-silt zone (locally peaty at top) in the upper part of the principal ground-water reservoir. The fractures range in length from several feet to more than 100 feet (30 m), and their maximum measured depth in 1972 was 4 feet (1.2 m). Land subsidence in the Milford area is demonstrated by three lines of evidence: (1) collapse structures, (2) well casings that protrude higher above the land surface than when first placed in the borehole, and (3) lower elevations at National Ocean Survey (formerly U.S. Coast and Geodetic Survey) bench marks in 1970 than in 1908. This evidence shows that land subsidence in the Milford area is of two types, each having a different origin. One type has a near-surface origin in the clay-silt zone in the upper part of the principal groundwater reservoir, and the other is in the lower artesian aquifers of the principal ground-water reservoir. The amount of observed subsidence ranges from 0.05 foot (0.015 m) at the bench mark at Read to about 6 feet (1.8 m) at collapse structures in the Hay Springs area.

Utah↗
USGS1976

Fresh ground water found deep beneath Nantucket Island, Masachusetts

In a deep water-resources and stratigraphic test well near the center of Nantucket Island, about 30 miles (48 kilometres) off the New England coast, freshwater has been found at greater depths than predicted by the Ghyben-Herzberg principle. An uppermost lens of freshwater, which occupies relatively permeable glacial-outwash sand and gravel to a depth of 520 feet (158 metres), is believed to be in hydrodynamic equilibrium with the present level of the sea and the height of the water table. However, two zones of freshwater at 730 to 820 ft (222-249 m) and 900 to 930 ft (274-283 m) are anomalously deep. Although several explanations are possible, the most likely is that the entire surface of the Continental Shelf was exposed to recharge by precipitation during long periods of low sea level in Pleistocene time. After the last retreat of glacial ice, seawater rapidly drowned the shelf around Nantucket Island. Since then, about 8,000 years ago, the deep freshwater zones which underlie dense clay layers have not had time to adjust to a new equilibrium. Under similar circumstances, freshwater may remain trapped under extensive areas of the Continental Shelf wherever clay confining beds have not permitted saltwater to intrude rapidly to new hydrodynamic equilibria positions. The implications are far reaching because all continental shelves worldwide were exposed to similar hydrologic influences during Pleistocene time.

Massachusetts↗
USGS1976

Improving estimates of streamflow characteristics by using Landsat-1 imagery

Imagery from the first Earth Resources Technology Satellite (renamed Landsat-1) was used to discriminate physical features of drainage basins in an effort to improve equations used to estimate streamflow characteristics at gaged and ungaged sites. Records of 20 gaged basins in the Delmarva Peninsula of Maryland, Delaware, and Virginia were analyzed for 40 statistical streamflow characteristics. Equations relating these characteristics to basin characteristics were obtained by a technique of multiple linear regression. A control group of equations contains basin characteristics derived from maps. An experimental group of equations contains basin characteristics derived from maps and imagery. Characteristics from imagery were forest, riparian (streambank) vegetation, water, and combined agricultural and urban land use. These basin characteristics were isolated photographically by techniques of film-density discrimination. The area of each characteristic in each basin was measured photometrically. Comparison of equations in the control group with corresponding equations in the experimental group reveals that for 12 out of 40 equations the standard error of estimate was reduced by more than 10 percent. As an example, the standard error of estimate of the equation for the 5-year recurrence-interval flood peak was reduced from 46 to 32 percent. Similarly, the standard error of the equation for the mean monthly flow for September was reduced from 32 to 24 percent, the standard error for the 7-day, 2-year recurrence low flow was reduced from 136 to 102 percent, and the standard error for the 3-day, 2-year flood volume was reduced from 30 to 12 percent. It is concluded that data from Landsat imagery can substantially improve the accuracy of estimates of some streamflow characteristics at sites in the Delmarva Peninsula.

Maryland, Delaware, Virginia↗
USGS1976

Field verification of method for distributing flow through multiple-bridge openings

Field data collected at three sites in Louisiana having multiple-bridge openings were used to check a method of distribution of flow through two or more bridges. Actual peak discharges in the various main and overflow bridges ranged from 878 to 11,055 cubic feet per second (24.9 to 313 m 2 /s). The error of the computed discharge to the actual discharge ranged between -20 and +6 percent, with the exception of one opening that had an error of +101 percent.

Louisiana↗
USGS1976

Confidence limits for flood-frequency curves computed from samples from Pearson type III populations

A study of T -year events computed from samples drawn from Pearson type III populations of known skew indicates that for skew coefficients between -1.0 and 1.0, confidence limits can be derived from the confidence limits computed for frequency curves based on samples from normal distributions. For samples from populations with skew coefficients between -0.5 and 0.5, the ratios of the standard deviates of the confidence limits to the standard deviates of the underlying frequency curve are approximately the same as for samples from normal distributions. A table provides adjustments required to make the ratios for normal distributions more applicable to distributions with skews in the range -1.0 to 1.0.

Journal of Research of the U.S. Geological Survey↗
USGS1976

Volcanic rocks of the eastern and northern parts of the San Francisco volcanic field, Arizona

The eastern and northern parts of the San Francisco volcanic field, between San Francisco Mountain and the Little Colorado River, contain about 175 cinder cones, many with one or more associated lava flows, and one center of silicic volcanism, O'Leary Peak. Basaltic flows and cones are divided into five groups, primarily on the bases of stratigraphic and physiographic relations, degree of weathering and erosion, K-Ar and tree-ring age determinations, and, in part, chemical and petrographic data: Basaltic rocks of Sunset age -------- A.D. 1064-1065 Holocene. Basaltic rocks of Merriam age ----- <100,100 years Pleistocene. Basaltic rocks of Tappan age ------- 0.2-0.7 m.y. Do. Basaltic rocks of Woodhouse age --- 0.8-3.0 m.y. Pliocene and Pleistocene. Basalt of Cedar Ranch --------------- 5.5 m.y. Pliocene. The flows and cones are predominantly alkali olivine basalt, commonly nepheline normative, and characterized by a single Ca-rich pyroxene phase and the absence of the olivine-pyroxene reaction relation. By depletion in olivine and pyroxene these basalts grade into alkali-rich high-alumina basalts; the most silicic of which contain both Ca-rich and Ca-poor pyroxene but show no olivine reaction. By relative enrichment in K 2 O and SiO 2 , alkali olivine basalts grade into intersertal basaltic andesites that contain, in addition to olivine, two pyroxene phases and minor primary cristobalite. Volcanic rocks of O'Leary Peak consist largely of rhyodacite domes, flows, and minor pyroclastic deposits. An andesite flow underlies the rhyodacites and andesitic cinders mantle the rhyodacite porphyry dome that forms O'Leary Peak. This dome, 0.23&plusmn;0.04 m.y. old, is both underlain and overlain by Tappan-age basaltic rocks. Variation diagrams that include data from the dominantly andesitic to rhyolitic San Francisco Mountain as well as from the mapped area show the differentiated and consanguineous character of the lavas, which are chemically intermediate between typical calc-alkalic and alkalic suites. Sr 87 /Sr 86 ratios of 0.7026 to 0.7050 suggest a mantle origin with little contamination by upper crustal material. Ultramafic and mafic xenoliths with cumulus texture may represent crustal intrusions related to the volcanic rocks. Eruption of intermediate to silicic magmas was generally localized in a few centers such as San Francisco Mountain and O'Leary Peak. In the same general time interval, basaltic eruptions dominated in the surrounding areas.

Arizona↗
USGS1976

Prehnite in plutonic and metamorphic rocks of the northern Santa Lucia Range, Salinian block, California

Prehnite is abundant as monomineralic veins, as lenses in biotite, and as discrete patches and apparent primary crystals in both plutonic and metamorphic rocks along the west edge of the Salinian block in the northern Santa Lucia Range. The prehnite appears to be concentrated near the Sur fault zone but is very rare in Franciscan rocks west of the fault zone. The prehnite does not appear to have been derived by local alteration of minerals in the country rocks (either plutonic or metamorphic). I suggest that solutions, derived from a "substratum" (possibly Franciscan graywacke) beneath the tectonically thinned west margin of the Salinian block, migrated through the fractured rocks of the Salinian block near the Sur fault zone and that the chemical and physical nature of these rocks favored selective prehnite deposition.

California↗
USGS1976

Bulk chemical analyses of petrographic thin sections of rocks of the Samli area, western Turkey

Petrographic thin sections have been analyzed for their major-element composition using a fusion-dilution technique and measuring the intensity of X-rays by means of the electron microprobe. The balsam-mounted thin sections were removed from the glass slides by soaking them in methylene chloride. The freed sections were mixed with twice their weight of Li 2 B 4 O 7 , and fused at 1100&deg; C. A fragment of the resulting glasslike bead was mounted for probe analysis. Both wavelength and energy-dispersive detector systems were used for quantitative determinations of elements sodium through iron. Because the samples and standards are diluted and fused, powdered rock standards may be used as reference materials. The calibration curves obtained by plotting X-ray intensity versus concentration of the analyte are linear over the concentration ranges used in this work and have an overall range of error of 2 to 8 percent. Although some of the analytical values show excessive scatter for petrographically similar rocks, in general the analyses are acceptable given the sample size and analytical uncertainties. Bulk chemical analyses were made of 18 thin sections, including altered diabase, amphibolite, and calc-silicate hornfels produced by progressive contact metamorphism and associated with metasomatic magnetite deposits in the Samli area, western Turkey. Normative plots indicate that (1) diabase and amphibolite are compositionally related and are similar to average compositions of basalts and orthoamphibolites, and (2) calc-silicate hornfels appears to have been derived in part from amphibolite and in part from crystalline limestone that underlies much of the region.

Journal of Research of the U.S. Geological Survey↗
USGS1976

Brown, yellow, orange, and greenish-black thorites from the Seerie pegmatite, Colorado

Four types of thorite - brown, yellow, orange, and greenish-black - occur together in narrow fracture fillings rich in brown fluorite near the outer edge of the Seerie pegmatite. The brown thorite is by far the most abundant. The thorites are remarkably similar in composition except for their Fe 2 O 3 and UO 2 contents. The common brown thorite contains about 5 percent Fe 2 O 3 , but the other types have only about 0.3 percent. The greenish-black thorite contains about 15 percent UO 2 ; the yellow and orange, about 7 percent; and the brown, about 3 percent. All four thorites have high total rare-earth oxide contents, which vary from 17.3 to 20 percent. The rare-earth assemblage is unusual in that the heavy rare earths predominate, ytterbium being the most abundant lanthanide. Unheated brown and yellow thorites gave thorite X-ray patterns, but the orange and greenish-black types are metamict. All the thorites gave a ThO 2 -UO 2 X-ray pattern as well as a thorite pattern after heating in air for 1- and 2-hour periods at 1,000&deg;C. In addition, the pattern of the greenish-black thorite contained peaks which we ascribe to a second UO 2 compound. Minute black inclusions present in the greenish-black thorite were identified as uraninite by microprobe analysis.

Colorado↗
USGS1976

Compositional variations in wolframite from the Hamme (Tungsten Queen) mine, North Carolina

A microprobe study of wolframite from the Tungsten Queen mine, Hamme district, North Carolina, proves it to be almost pure huebnerite. Concentric zoning, which shows up as light-brown and dark-brown bands, indicates small variations in the content of FeO. There is no apparent correlation between the small variations in the composition of the wolframite and its position in the mine. The Fe/Mn ratio of the wolframite is not indicative of the temperature of crystallization.

North Carolina↗