24 research outputs found
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Chemical and textural surface features of pyroclasts from hydrovolcanic eruption sequences
Hydrovolcanic pyroclasts are produced by the interaction of erupting magma with surface or near-surface water. Eruption energy determining pyroclast transport and depositional modes is dependent upon the amount of water interacting with magma. Grain morphologies, size distributions, surface textures, and chemical effects studied record the history of eruption cycles for volcanoes under consideration. Samples of crater-rim stratigraphic sequences from Crater Elegante and Cerro Colorado, Mexico, and from Panum Crater and Obsidian Dome, California, illustrate a basaltic tuff ring and tuff cone and two rhyolitic tuff rings respectively. Grain morphologies observed by scanning electron microscopy (SEM) reveal information on the process of melt fragmentation. Surface alteration and diagenesis have greater effect on pyroclasts from wet eruptions compared to dry ones. These textures are patchy overgrowths of microcrystalline and hydrated materials. Surface chemical characteristics observed with energy dispersive spectral analysis (EDS) show relative gains or losses of elements and an apparent enrichment of silica on altered surfaces
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Origin of accretionary lapilli from the Pompeii and Avellino deposits of Vesuvius
Accretionary lapilli from the Pompeii and Avellino Plinian ash deposits of Vesuvius consist of centimeter-sized spheroids composed of glass, crystal, and lithic fragments of submillimeter size. The typical structure of the lapilli consists of a central massive core surrounded by concentric layers of fine ash with concentrations of larger clasts and vesicles and a thin outer layer of dust. Clasts within the lapilli larger than 125 ..mu..m are extremely rare. The median grain-size of the fine ash is about 50 ..mu..m and the size-distribution is well sorted. Most constituent particles of accretionary lapilli display blocky shapes characteristic of grains produced by phreatomagmatic hydroexplosions. We have used the scanning electron microscope (SEM) in conjunction with energy dispersive spectral analysis (EDS) to investigate the textural and chemical variation along traverses from the core to the rim of lapilli from Vesuvius
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Fracture characterizatioin of the Bandelier tuff in OU-1098 (TA-2 and TA-41)
Rock fracture characterization documents a total of 1496 fractures in unit 2 of the Tshirege Member of the Bandelier Tuff along 6013 feet of Los Alamos Canyon`s north wall adjacent to Operational Unit 1098. Geologically termed joints, these fractures likely owe their primary origin to brittle failure during the cooling contraction of the tuff after its emplacement nearly 1 million years ago. Subsequent tectonic movement along the Pajarito Fault system has modified fracture strikes, dips, apertures, and linear density. From a background linear density of approximately 20 fractures per 100-foot interval along the canyon wall, fracture density increases to values in excess of 50 fractures per 100-foot interval in a zone at and immediately east of the Omega West reactor building TA-2-1. This increase in fracture density is coincident with the mapped trace of the Guaje Mountain Fault (GMFZ) that apparently bifurcates with a branch running through the canyon at Building TA-2-1 and another about 200 feet east of the Omega site east gate. With it occurs notable slump failure of the canyon wall, increased cumulative fracture aperture, and slight rotation of fracture orientations. Fractures show average strikes of either N35W or N47E, average dips between 75N and 82N, and average apertures of 0.7 cm. Calculations, based on the assumption that fracture apertures are produced by vertical movement along each fracture, suggest approximately 3 m of westward downdrop has occurred over the GMFZ is this area. While fracture character is not documented for Bandelier Tuff units above and below unit 2, observations indicate that inferred tectonic movement has likely influenced fracture permeability in the Bandelier Tuff in Los Alamos Canyon along the trace of the Guaje Mountain Fault. Because of increased fracture permeability, groundwater movement is expected to show greater penetration into bedrock units in that area just east of the Omega West reactor
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Origin of a sanidine-coesite grospydite
A grospydite xenolith from the Roberts Victor kimberlite pipe in South Africa presents an unusual phase assemblage of clinopyroxene, garnet, kyanite, coesite, and sanidine. The rock as previously described (Smyth and Hatton, 1977) consists of 50% omphocitic clinopyroxene, 28% garnet (Gr/sub 50/Py/sub 28/Alm/sub 22/), 9% kyanite, 65 coesite, and 1% sanidine (Or/sub 99/). Assuming the addition of three additional compatible phases (phlogopite, enstatite, and H/sub 2/O vapor) and a simplified chemistry of the phases present, a Schreinemakers thermodynamic analysis was attempted in order to estimate the pressure and temperature of equilibrium of the rock. Four reactions involving six components are likely to have determined an invariant point for the assemblage: (1) Kyn + 2 Cpx reversible Cos + Gt + En; (2) 3 Cos + Phl reversible San + 3 En + H/sub 2/O; (3) 3 Kyn + 6 Cpx + Phl reversible San + 3 Gt + 6 En + H/sub 2/O; and (4) 6 Cos + 3 gt + Phl reversible San + 3 Kyn + 6 Cpx + H/sub 2/O. Using tabulated as well as estimated thermodynamic data for the phases, the calculated values for equilibrium temperatures and pressures for the reactions yield an invariant point for the assemblage at a depth of about 160 km (40 kbars) and a temperature of about 1060/sup 0/C. This point likely represents a subsolidus recrystallization stage of origin
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Geothermal resource evaluation of Castle Hot Springs, Arizona
The purpose of this report is to define the geothermal system that supplies the hot water for Castle Hot Spring. An attempt was made to specify the "reservoir" temperature and to model possible sources of heat. This report summarizes our findings and presents the important supporting information in the various tables and figures. Additional data, including details of the techniques and methodologies used in the investigation, will be recorded in an Arizona State University MS thesis (Satkin, in preparation, 1980). Appendices I and II are two papers resulting from the funded work on Castle Hot Spring. Our geologic feasibility study consisted of five parts: 1) construction of a detailed geologic map of hot spring area, 2) production of geologic cross sections, 3) calculation of water geothermometry based on repeated analyses, 4) measurement of geothermal profiles in shallow wells, and 5) speculation on models for the heat source. p.51Documents in the AZGS Documents Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected])
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Geothermal resource evaluation of Castle Hot Springs, Arizona
The purpose of this report is to define the geothermal system that supplies the hot water for Castle Hot Spring. An attempt was made to specify the "reservoir" temperature and to model possible sources of heat. This report summarizes our findings and presents the important supporting information in the various tables and figures. Additional data, including details of the techniques and methodologies used in the investigation, will be recorded in an Arizona State University MS thesis (Satkin, in preparation, 1980). Appendices I and II are two papers resulting from the funded work on Castle Hot Spring. Our geologic feasibility study consisted of five parts: 1) construction of a detailed geologic map of hot spring area, 2) production of geologic cross sections, 3) calculation of water geothermometry based on repeated analyses, 4) measurement of geothermal profiles in shallow wells, and 5) speculation on models for the heat source. p.51Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]
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Status of volcanic hazard studies for the Nevada Nuclear Waste Storage Investigations. Volume II
Volcanic hazard investigations during FY 1984 focused on five topics: the emplacement mechanism of shallow basalt intrusions, geochemical trends through time for volcanic fields of the Death Valley-Pancake Range volcanic zone, the possibility of bimodal basalt-rhyolite volcanism, the age and process of enrichment for incompatible elements in young basalts of the Nevada Test Site (NTS) region, and the possibility of hydrovolcanic activity. The stress regime of Yucca Mountain may favor formation of shallow basalt intrusions. However, combined field and drill-hole studies suggest shallow basalt intrusions are rare in the geologic record of the southern Great Basin. The geochemical patterns of basaltic volcanism through time in the NTS region provide no evidence for evolution toward a large-volume volcanic field or increases in future rates of volcanism. Existing data are consistent with a declining volcanic system comparable to the late stages of the southern Death Valley volcanic field. The hazards of bimodal volcanism in this area are judged to be low. The source of a 6-Myr pumice discovered in alluvial deposits of Crater Flat has not been found. Geochemical studies show that the enrichment of trace elements in the younger rift basalts must be related to an enrichment of their mantle source rocks. This geochemical enrichment event, which may have been metasomatic alteration, predates the basalts of the silicic episode and is, therefore, not a young event. Studies of crater dimensions of hydrovolcanic landforms indicate that the worst case scenario (exhumation of a repository at Yucca Mountain by hydrovolcanic explosions) is unlikely. Theoretical models of melt-water vapor explosions, particularly the thermal detonation model, suggest hydrovolcanic explosion are possible at Yucca Mountain. 80 refs., 21 figs., 5 tabs
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Analyses of sweep-up, ejecta, and fallback material from the 4250 metric ton high explosive test ''MISTY PICTURE'
The MISTY PICTURE surface burst was detonated at the White Sands Missle range in May of 1987. The Los Alamos National Laboratory dust characterization program was expanded to help correlate and interrelate aspects of the overall MISTY PICTURE dust and ejecta characterization program. Pre-shot sampling of the test bed included composite samples from 15 to 75 m distance from Surface Ground Zero (SGZ) representing depths down to 2.5 m, interval samples from 15 to 25 m from SGZ representing depths down to 3m, and samples of surface material (top 0.5 cm) out to distances of 190 m from SGZ. Sweep-up samples were collected in GREG/SNOB gages located within the DPR. All samples were dry-sieved between 8.0 mm and 0.045 mm (16 size fractures); selected samples were analyzed for fines by a contrifugal settling technique. The size distributions were analyzed using spectral decomposition based upon a sequential fragmentation model. Results suggest that the same particle size subpopulations are present in the ejecta, fallout, and sweep-up samples as are present in the pre-shot test bed. The particle size distribution in post-shot environments apparently can be modelled taking into account heterogeneities in the pre-shot test bed and dominant wind direction during and following the shot. 13 refs., 12 figs., 2 tabs