Abstract not available

Perched water zones have been identified in the fractured, welded tuff in the semiarid to arid environments of Yucca Mountain, Nevada and near Superior, Arizona. An understanding of the formation of such zones is necessary in order to predict where future perched water might form at Yucca Mountain, the proposed site of a high-level nuclear waste repository. The formation or growth of a perched zone above a repository is one factor of the factors to be considered in the risk assessment of the Yucca Mountain site. The Apache Leap Research Site (ALRS) near Superior, Arizona is a natural analog to the Yucca Mountain site in terms of geology, hydrology, and climate. Perched water has been identified over an area of at least 16 km² in the Apache Leap Tuff, a mid- Miocene fractured, welded ash-flow tuff. A primary goal of this investigation was to characterize the physical and hydrologic properties of the tuff in the region above and including the perched zone, and to evaluate those characteristics to develop a model for a perching mechanism in the tuff. A second goal was to determine what fraction of water entering a watershed reaches the subsurface, to potentially recharge the perched zone. The Apache Leap Tuff has been subject to considerable devitrification and vapor phase crystallization, which dominate the character of the rock. With depth to the perched zone, pumice fragments become increasingly flattened and segregated; the pumice fragments are the primary locations of porosity in the rock, therefore porosity also becomes greatly reduced with depth, to the extent that the rock matrix is virtually impermeable at the perched water zone. Fractures are the primary pathways by which water moves through the rock; fracture hydraulic conductivity values were determined to be nine orders of magnitude greater than measured matrix hydraulic conductivity at the perched zone. An increase in fracture filling by silica mineralization beneath the perched zone reduces the secondary permeability, enhancing the formation of perched water. Thus, the primary mechanisms for the formation of the perched zone include fracture flow bringing water into the subsurface, combined with extremely low matrix hydraulic conductivity at depth, and reduced secondary permeability by filled fractures and lower fracture density. Water budgets were calculated for two years in a 51.4-ha watershed. Direct measurements were made of precipitation and runoff', evapotranspiration was both directly measured, and modeled based on measurement of a number of weather parameters. Infiltration was calculated as the residual of precipitation after runoff and evapotranspiration were removed. Infiltration was determined to be less than 10% of the annual water budget; evapotranspiration removes on the order of 90% of precipitation on an annual basis.

No description available.

No description available.

[Truncated abstract] The Neoarchean (2800 to 2600 Ma) Eastern Goldfields Superterrane (EGST) comprises elongated belts of deformed and metamorphosed volcanic and sedimentary rocks intruded by granitoids. The Superterrane is made up of five distinct tectonostratigraphic terranes. From west to east these are the Kalgoorlie, Gindalbie, Kurnalpi, Laverton and Duketon Terranes. The Kalgoorlie Terrane is characterised by 2720 to 2680 Ma marine mafic-ultramafic volcanic successions interlayered with, and overlain by, 2710 to 2660 Ma dominantly trondhjemite-tonalite-dacite (TTD) dacititic volcaniclastic rocks (Black Flag Group). The adjacent Gindalbie and Kurnalpi terranes are characterised by 2720 to 2680 Ma calc-alkaline volcanic successions representing oceanic island arcs. To the west of the EGST, the Youanmi Terrane is characterised by older, dominantly 3000 to 2900 Ma greenstone rocks and complex granitoid batholiths derived from older crustal sources. The southern Kalgoorlie Terrane comprises five elongate NNW-trending tectono-stratigraphic domains. Three principal marine komatiitic to basaltic suites, collectively referred to as the Kambalda Sequence, are present, including the wellpreserved massive to pillowed Lower and Upper Basalt Sequences, separated by the Komatiite Unit, as well as numerous dyke suites. The Lower Basalt Sequence comprises the Woolyeenyer Formation, Lunnon, Wongi, Scotia, Missouri Basalts and Burbanks and Penneshaw Formations, whereas the Upper Basalt Sequence contains the Paringa, Coolgardie, Big Dick, Devon Consols, Bent Tree, and Victorious basalts. ... Instead, the data suggest that discrete PGE-bearing phase (s) fractionated from the basaltic magmas. Such phases could be platinum group minerals (PGM; e.g. laurite) and/or alloys, or discrete PGE-rich nuggets. In summary, data on the three magmatic sequences record decompression melting of three distinct mantle sources: (1) long-term depleted asthenosphere for prevalent depleted tholeiitic and komatiitic basalts, and komatiites; (2) long-term enriched asthenosphere for Paringa Basalts and similarly enriched rocks; and (3) shortterm enriched continental lithospheric mantle (CLM) for HREE and Al-depleted dykes. Some of these rocks were contaminated by TTD-type melts. Taken with the existing geophysical and xenocrystic zircon data, the most straightforward interpretation is eruption of a zoned mantle plume at the margin of rifted continental lithosphere. The Kalgoorlie Terrane extensional basin was subsequently tectonically juxtaposed with the adjacent arc-like Gindalbie and Kurnalpi Terranes at approximately 2660 Ma at the start of orogeny in a Cordilleran-style orogen to form the EGST. Collectively, uncontaminated basalts have Nb/Th of 8-16, compared to 8-12 reported for the Lunnon basalts in a previous study. To a first approximation these asthenosphere melts are complementary to average Archean upper continental crust with Nb/Th =2, consistent with early growth of large volumes of continental crust rather than models of steady progressive growth.

Mémoire (M.Sc.A.)-- Université du Québec à Chicoutimi ; 1986. / "Mémoire présenté pour l'obtention du grade de maîtrise es sciences appliquées" CaQCU Document électronique également accessible en format PDF. CaQCU

Thesis (Ph. D.)--Centre Universitaire de Perpignan, 1977. / Errata sheet inserted, v. 1. Includes bibliographical references (Vol. 1, p. [i]-xxxix).

Thesis (M.S.)--Brigham Young University. Dept. of Geology, 2006. / Includes bibliographical references (p. 42-46).

The tertiary history of the Chiricahua volcanic field of southeastern Arizona is essentially that of rhyolitic ash-flow deposition and concomitant block faulting in the period from 29 to 25 m.y., as determined by K-Ar analysis. The Rhyolite Canyon ash-flow sheet is the youngest of three sheets, each more than 1000 feet thick. Its distribution is limited mainly to the Chiricahua and northern Pedregosa Mountains with a lesser amount of deposits in the neighboring Swisshelm and Peloncillo Mountains. It is estimated that the original areal extent was of the order of 700 square miles and that the volume of deposits was around 100 cubic miles. The source area of the Rhyolite Canyon sheet is identified as a 13-mile diameter caldera, named the Turkey Creek caldera. This is the first major caldera of the Valles type described in the Mexican Highland and Sonoran Desert sections of the Basin and Range. It is unique because of its denudation. Erosion to 5000-foot depth locally has exposed thick sections of moat deposits and a fine grained monzonite pluton associated with central doming. Rhyolite Canyon tuff in the caldera, some 3000 feet thick, is domed and intruded by the monzonite. More than 1500 feet of tuff breccia, tuffaceous sediments, and rhyolite flows are exposed in the moat, along with 3000 feet of monzonite forming annular segments a couple miles wide abutting or overlying rocks forming the caldera wall. The most monzonite is similar to that in the dome and was emplaced amidst the period of deposition in the caldera. Petrographic and trace element analyses indicate a cogenetic relation between the Rhyolite Canyon sequence and the moat rhyolites. The K-Ar age of the Rhyolite Canyon tuff is very close to that of the monzonite. The ash-flow sheet immediately underlying the Rhyolite Canyon sheet is also very close in age as indicated by K-Ar analyses. Block faulting and tilting took place between the two sheets and also following the deposition of the Rhyolite Canyon sheet. There is evidence that the present basin-range structure was not established until after the Rhyolite Canyon sheet had been emplaced.

The Ellensburg Formation, preserved in the Nile basin 50 km northwest of Yakima, Washington, consists of a series of middle to late Miocene epiclastic and pyroclastic rock assemblages rich in porphyritic hornblende-biotite dacite. Geochemical, petrographic, and stratigraphic correlations indicate that Old Scab Mountain, a dacite porphyry intrusion, located at the western margin of the basin (lat. 46°53'30", long. 121°13'00"), is the probable source for much of the upper Ellensburg volcaniclastic material in the basin. The dacite intrusion exposed at Old Scab Mountain was emplaced at depths of 1 to 3 km and underlaid a now eroded volcanic edifice. This volcanic center is interpreted to have been active during the time of deposition of the upper Ellensburg Formation. AK-Ar age of 8.75 ± 0.20 Ma for an adjacent sill of similar dacite suggests an age for Old Scab Mountain between 9 to 7 Ma (Smith, 1988a). This age corresponds with the upper Ellensburg Formation which stratigraphically overlies Grande Ronde Basalt lava flows of the Columbia River Basalt Group, within the basin. Stratigraphic reconstruction of the Nile basin deposits indicates a dome collapse eruptive style. Progressive dome growth was punctuated by short-lived eruptions resulting in dome collapse and deposition of debris-avalanche and lahar deposits. These deposits were remobilized by fluvial processes which generated thick conglomerates and interstratified volcanic sandstones. Upper Ellensburg deposits and dacite of Old Scab Mountain are calc-alkaline and medium-K in composition. Silica content ranges from 53 to 67 weight percent Si02 for upper Ellensburg deposits and 66 to 67 weight percent Si02 for dacite of Old Scab Mountain. Older deposits composing the lower Ellensburg Formation are interbedded with and underlie the Grande Ronde Basalt. The lower Ellensburg deposits are typically more tholeiitic, range from 56 to 74 weight percent Si02 , and show slightly higher trace element concentrations than the upper Ellensburg deposits. These deposits were possibly derived from other dacite centers located near the headwaters of the adjacent Naches basin.