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51.
Hazel Rymer Corinne A. Locke rea Borgia Maria Martinez Jorge Brenes Rodolfo Van der Laat Glyn Williams-Jones 《地学学报》2009,21(4):304-309
Acidic crater lakes at persistently active volcanoes act as both an index and a moderator of volcanic processes. A catastrophic drop in lake level can therefore lead to serious local environmental damage. In the early 1990s, the crater lake at Poás volcano, Costa Rica diminished, and acid aerosols erupted with devastating consequences for local health, environment and economy. The first indications of this event can be retrospectively identified to have started from 1985, on the basis of our unique 20-year data time series, which provides evidence for the shallow intrusion of magma. New data presented in this article show similar trends and we conclude that Poás has now entered another active period with renewed intrusion. Severe environmental damage in this region is expected within the next few years if the current trend continues. 相似文献
52.
Tamar Elias A. Jeff Sutton Clive Oppenheimer Keith A. Horton Harold Garbeil Vitchko Tsanev Andrew J. S. McGonigle Glyn Williams-Jones 《Bulletin of Volcanology》2006,68(4):313-322
The correlation spectrometer (COSPEC), the principal tool for remote measurements of volcanic SO2, is rapidly being replaced by low-cost, miniature, ultraviolet (UV) spectrometers. We compared two of these new systems with
a COSPEC by measuring SO2 column amounts at Kīlauea Volcano, Hawaii. The two systems, one calibrated using in-situ SO2 cells, and the other using a calibrated laboratory reference spectrum, employ similar spectrometer hardware, but different
foreoptics and spectral retrieval algorithms. Accuracy, signal-to-noise, retrieval parameters, and precision were investigated
for the two configurations of new miniature spectrometer. Measurements included traverses beneath the plumes from the summit
and east rift zone of Kīlauea, and testing with calibration cells of known SO2 concentration. The results obtained from the different methods were consistent with each other, with <8% difference in estimated
SO2 column amounts up to 800 ppm m. A further comparison between the COSPEC and one of the miniature spectrometer configurations,
the ‘FLYSPEC’, spans an eight month period and showed agreement of measured emission rates to within 10% for SO2 column amounts up to 1,600 ppm m. The topic of measuring high SO2 burdens accurately is addressed for the Kīlauea measurements. In comparing the foreoptics, retrieval methods, and resultant
implications for data quality, we aim to consolidate the various experiences to date, and improve the application and development
of miniature spectrometer systems. 相似文献
53.
The nature, origin and physicochemical controls of hydrothermal Mo-Bi mineralization in the Cadillac deposit, Quebec, Canada 总被引:2,自引:0,他引:2
Mo-Bi mineralization occurs in subvertical and subhorizontal quartz-muscovite-± K-feldspar veins surrounded by early albitic
and later K-feldspathic alteration halos in monzogranite of the Archean Preissac pluton, Abitibi region, Québec, Canada. Molybdenite
is intergrown with muscovite in the veins or associated with K-feldspar in the alteration halos. Mineralized veins contain
five main types of fluid inclusions: aqueous liquid and liquid-vapor inclusions, aqueous carbonic liquid-liquid-vapor inclusions,
carbonic liquid and vapor inclusions, halite-bearing aqueous liquid and liquid-vapor inclusions, trapped mineral-bearing aqueous
liquid and liquid-vapor inclusions. The carbonic solid in frozen carbonic and aqueous-carbonic inclusions melts in most cases
at −56.7 ± 0.1 °C indicating that the carbonic fluid consists largely of CO2. All aqueous inclusion types and the aqueous phase in carbonic inclusions have low initial melting temperatures (≥70 °C),
requiring the presence of salts other than NaCl. Leachate analyses show that the bulk fluid contains variable proportions
of Na, K, Ca, Cl, and traces of Mg and Li. The following solids were identified in the fluid inclusions by SEM-EDS analysis:
halite, calcite, muscovite, millerite (NiS), barite and antarcticite (CaCl2 · 6H2O). All are interpreted to be trapped phases except halite which is a daughter mineral, and antarcticite which formed during
sample preparation (freezing). Aqueous inclusions homogenize to liquid at temperatures between 75 °C and 400 °C; the mode
is 375 °C. Aqueous-carbonic inclusions homogenize to liquid or vapor between 210 °C and 400 °C. Halite-bearing aqueous inclusions
homogenize by halite dissolution at approximately 170 °C. Aqueous inclusions containing trapped solids exhibit liquid-vapor
homogenization at temperatures similar to those of halite-bearing aqueous inclusions. Temperatures of vein formation, based
on oxygen isotopic fractionation between quartz and muscovite, range from 342 °C to 584 °C. The corresponding oxygen isotope
composition of the aqueous fluid in equilibrium with these minerals ranges from 1.2 to 5.5 per mil with a mean of 3.9 per
mil, suggesting that the liquid had a significant meteoric component. Isochores for aqueous fluid inclusions intersect the
modal isotopic isotherm of 425 °C at pressures between 590 and 1900 bar. A model is proposed in which molybdenite was deposited
owing to decreasing temperature and/or pressure from CO2-bearing, moderate to high salinity fluids of mixed magmatic-meteoric origin that were in equilibrium with K-feldspar and
muscovite. These fluids resulted from the degassing of a monzogranitic magma and evolved through interaction with volcanic
(komatiitic) and sedimentary country rocks.
Received: 6 February 1997 / Accepted: 28 January 1998 相似文献
54.
S. F. Tombros K. St. Seymour A. E. Williams-Jones P. G. Spry 《Mineralogy and Petrology》2008,94(3-4):175-194
Precious metals accompany all types of epithermal deposits. In general, the largest of these deposits occur in intrusive or extrusive rocks of alkaline or calc-alkaline affinity. The Apigania Bay vein system and Au–Ag mineralization is hosted in Mesozoic marbles and schists, and is composed primarily of five nearly parallel, high-angle quartz veins that extend for at least 200 m. Gold–silver mineralization, in association with more than thirty ore and vein minerals, is developed in three stages and occurs at the contact of marbles and schists. Zones of epidote–chlorite–calcite and sericite–albite alteration are associated with precious metal-bearing milky and clear quartz veins. Fluid inclusion studies suggest that hydrothermal mineralization was deposited under hydrostatic pressures of ~100 bars, at temperature of 120–235°C, from low to moderate, calcium-bearing, saline fluids of 0.2 to 6.8 equiv. wt.% NaCl. Calculated isotope compositions (δ18O?=??4.7‰ to 1.7‰ and δD?=??120‰ to ?80‰) for waters in equilibrium with milky and clear quartz are consistent with mixing with dilute, low temperature meteoric ore fluids. Calculated δ 13CCO2 (0.6‰ to 1.1‰) and δ 34SH2S (?7.3 to ?0.3‰) compositions of the ore fluids indicate exchange, in an open system, with a metasedimentary source. Gold and silver deposition was associated with degassing of hydrogen due to intense uplift of the mineralizing area. The physicochemical conditions of mineralization stages I to III range between 200°C and 150°C, $f_{{\text{S}}_2 } = 10^{ - 18.1} $ to 10?16.8, $f_{{\text{O}}_2 } = 10^{ - 44.0} $ to 10?41.5, pH?=?6.9 to7.6, $f_{{\text{H}}_{\text{2}} {\text{S}}} = 10^{ - 3.4} $ to 10?2.6 and $a_{{\text{H}}_{\text{2}} {\text{S}}} = 10^{ - 2.7} $ to 10?2.6. Apigania Bay could be possibly considered the latest evolutional phase of Tinos hydrothermal system. 相似文献
55.
A series of 707 measurements at Masaya in 2005, 2006, and 2007 reveals that SO2 emissions 15km downwind of the active vent appear to be ~33% to ~50% less than those measured only 5km from the vent. Measurements
from this and previous studies indicate that dry deposition of sulfur from the plume and conversion of SO2 to sulfate aerosols within the plume each may amount to a maximum of 10% loss, and are not sufficient to account for the
larger apparent loss measured. However, the SO2 measurement site 15km downwind is located on a ridge over which local trade winds, and the entrained plume, accelerate. Greater
wind speeds cause localized dilution of the plume along the axis of propagation. The lower concentrations of SO2 measured on the ridge therefore lead to calculations of lower fluxes when calculated at the same plume speed as measurements
from only 5km downwind, and is responsible for the apparent loss of SO2. Due to the importance of SO2 emission rates with respect to hazard mitigation, petrologic studies, and sulfur budget calculations, measured fluxes of
SO2 must be as accurate as possible. Future campaigns to measure SO2 flux at Masaya and similar volcanoes will require individual plume speed measurements to be taken at each flux measurement
site to compensate for dilution and subsequent calculation of lower fluxes. This study highlights the importance of a comprehensive
understanding of a volcano’s interaction with its surroundings, especially for low, boundary layer volcanoes. 相似文献