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1.
The Valles caldera in New Mexico hosts a high-temperature geothermal system, which is manifested in a number of hot springs discharging in and around the caldera. In order to determine the fluid pathways and the origin of chloride in this system, we measured 36Cl/Cl ratios in waters from high-temperature drill holes and from surface springs in this region. The waters fall into two general categories: recent meteoric water samples with low Cl− concentrations (< 10 mg/L) and relatively high 36Cl/Cl ratios [(300–1000) × 10−15]; and geothermal brines with high Cl− concentrations (800–9400 mg/L) but low 36Cl/Cl ratios [(11–26) × 10−15]. The 36Cl/Cl ratios for meteoric waters are slightly higher than expected for this region, suggesting a small addition of anthropogenic 36Cl. Because of low 36Cl/Cl ratios and high Cl− concentrations in the brines, chloride in these waters must be derived from subsurface sources. A comparison between the observed 36Cl/Cl ratios in the brines and those calculated for potential source formations in this region indicates that the present host formations, mainly volcanic tuffs, cannot be major sources of chloride, and that formations at greater depth, such as the Paleozoic and Precambrian formations are more likely to be sources of chloride in the brines. The results suggest that brines are meteoric waters which penetrated into the basement where they derive chloride from leaching of basement rocks and/or from saline pore fluids trapped there, along with likely addition of chloride from Paleozoic strata. Although these fluids have since come to reside in the intracaldera volcanic sequence after convective upwelling, they do not derive much Cl− from the volcanic strata; and residence times of fluids in the volcanics are < 100,000 years.  相似文献   

2.
Temperatures of aquifers feeding thermal springs and wells in Long Valley, California, estimated using silica and Na-K-Ca geothermometers and warm spring mixing models, range from 160/dg to about 220°C. This information was used to construct a diagram showing enthalpy-chloride relations for the various thermal waters in the Long Valley region. The enthalpy-chloride information suggests that a 282 ± 10°C aquifer with water containing about 375 mg chloride per kilogram of water is present somewhere deep in the system. That deep water would be related to 220°C Casa Diablo water by mixing with cold water, and to Hot Creek water by first boiling with steam loss and then mixing with cold water. Oxygen and deuterium isotopic data are consistent with that interpretation. An aquifer at 282°C with 375 mg/kg chloride implies a convective heat flow in Long Valley of 6.6 × 107 cal/s.  相似文献   

3.
The Ischia geothermal system is hosted by silicic rocks of the Quaternary Potassic Roman Province, in southern Italy. Exploration drilling down to 1156 m depth in the mid-1950s provided information on boiling profiles (up to 250°C) and on the depth and permeability of the potential reservoirs. Discharge fluid samples were collected and analyzed to define the inflow of surrounding seawater (C1 ranges from 2.5 to 20 g/kg) into the system.Analyses of samples from surface manifestations and shallow wells collected during 1983 and 1988 point to the existence of three distinct mixing regimes, involving three water components. A dishomogeneous body of diluted water (Cl less than 2.5 g/kg), that occurs at depths > 700 m and reequilibrates at 240°C at least, is overlain by an aquifer of groundwater variably mixed with variably seawater (Cl from 4 to 10 g/kg), which tends to reequilibrate at 160°C. Steam-heated waters locally develop and act as dilutants of the rising geothermal fluids.Dilution, mixing, and evaporation of the ascending chloride fluids are supported by oxygen and hydrogen isotopic data the thermal waters being enriched in 18O and D with respect to local meteoric water by up to 7 and 30‰, respectively. The relative composition of the major cations in thermal solutions was used to discriminate the two main groups of thermal waters, the reservoir temperatures of which are estimated from the Na/K-gethermometer. K-Mg geothermometer indicates reequilibration in near-surface conditions.The isotopic composition of the fumarolic steam varies from −7 to −12‰ in ∂8O and from − 35 to − 70‰ in ∂D, in agreement with a deep mixed fluid that boils adiabatically from 240 to 80°C. The deuterium content of the H2O-H2 pair gives enrichment factor of about 830‰, corresponding to equilibrium temperature conditions slightly higher than the surface boiling temperatures. The ∂13C of CO2is almost constant at −4.5‰ (1δ=0.4), suggesting an important magmatic contribution, and the ∂18O values of CO2appears to in equilibrium with accompanying steam at the measured temperatures.The CO2/Ar and H2/Ar chemical ratios have been used to derive aquifer temperatures, the values obtained being consistent with those of solute geothermometers.  相似文献   

4.
The Campi Flegrei (Naples, Campanian Plain, southern Italy) geothermal system is hosted by Quaternary volcanic rocks erupted before, during and after the formation of the caldera that represents one of the major structural features in the Neapolitan area. The volcanic products rest on a Mesozoic carbonate basement, cropping out north, east and south of the area. Chemical (major, minor and trace elements) and stable isotope (C, H, O) analyses were conducted on drill-core samples recovered from geothermal wells MF-1, MF-5, SV-1 and SV-3, at depths of ˜ 1100 to 2900 m. The study was complemented by petrographic and SEM examination of thin sections. The water which feeds the system is both marine and meteoric in origin. Mineral zonation typical of a high-temperature geothermal system exists in all the geothermal wells; measured temperatures in wells are as high as ˜ 400 °C. The chemical composition of the waters suggests the existence of two reservoirs: a shallow reservoir (depth < 2000 m) fed by seawater that boiled at 320 °C and became progressively diluted by steam-heated local meteoric water during its ascent; and a deeper reservoir (depth > 2000 m) of hypersaline water. The drill-cores are mainly hydrothermally altered volcanics of trachy-latitic affinity, but some altered pelites and limestones are also present. Published Na, Mg and K concentrations of selected geothermal waters indicate that the hydrothermal fluids are in equilibrium with their host rocks, with respect to K-feldspar, albite, sericite and chlorite. The measured δ18O(SMOW) values of rocks range from +4.3 to + 16.5%. The measured δD(SMOW) values range from − 79 to − 46%. The calculated isotopic composition of the fluids at equilibrium with the samples vary from + 1 to + 8.3%. δ18O and from − 52 to + 1%. δD. The estimated isotopic composition of the waters at equilibrium with the studied samples confirmed the existence of two distinct fluid types circulating in the geothermal system. The shallower has a marine water signature, while the deeper water has a signature consistent both with magmatic and meteoric origins. In the latter case, the recharge of this aquifer likely occurs at the outcrop of the Mesozoic Limestones surrounding the Campanian Plain; after infiltration, the water percolates through evaporitic layers, becoming hypersaline and D-depleted.  相似文献   

5.
Thermal springs associated with normal faults in Utah have been analyzed for major cations and anions, and oxygen and hydrogen isotopes. Springs with measured temperatures averaging greater than 40°C are characterized by Na + K- and SO4 + Cl-rich waters containing 103 to 104 mg/l of dissolved solids. Lower temperature springs, averaging less than 40°C, are more enriched in Ca + Mg relative to Na + K. Chemical variations monitored through time in selected thermal springs are probably produced by mixing with non-thermal waters. During the summer months at times of maximum flow, selected hot springs exhibit their highest temperatures and maximum enrichments in most chemical constituents.Cation ratios and silica concentrations remain relatively constant through time for selected Utah thermal springs assuring the applicability of the geothermometer calculations regardless of the time of year. Geothermometer calculations utilizing either the quartz (no steam loss), chalcedony or Mg-corrected Na/K/Ca methods indicate that most thermal springs in Utah associated with normal faults have subsurface temperatures in the range of 25 to less than 120°C. This temperature range suggests fluid circulation is restricted to depths less than about three kilometers assuming an average thermal gradient of about 40°C/km.Thermodynamic calculations suggest that most thermal springs are oversaturated with respect to calcite, quartz, pyrophyllite, (Fe, Mg)-montmorillonite, microcline and hematite, and undersaturated with respect to anhydrite, gypsum, fluorite and anorthite. Chalcedony and cristobalite appear to be the only phases consistently at or near saturation in most waters. Theoretical evaluation of mixing on mineral saturation trends indicates that anhydrite and calcite become increasingly more undersaturated as cold, dilute groundwater mixes with a hot (150°C), NaCl-rich fluid. The evolution of these thermal waters issuing from faults appears to be one involving the dissolution of silicates such as feldspars and micas by CO2-enriched groundwaters that become more reactive with increasing temperature and/or time. Solution compositions plotted on mineral equilibrium diagrams trend from product phases such as kaolinite or montmorillonite toward reactant phases dominated by alkali feldspars.Isotopic compositions indicate that these springs are of local surface origin, either meteoric (low TDS, < 5000 mg/l) or connate ground water (high TDS, > 5000 mg/l). Deviations from the meteoric water line are the result of rock-water isotopic exchange, mixing or evaporation. Fluid source regions and residence times of selected thermal spring systems (Red Hill, Thermo) have been evaluated through the use of a σ D-contour map of central and western Utah. Ages for waters in these areas range from about 13 years to over 500 years. These estimates are comparable to those made for low-temperature hydrothermal systems in Iceland.  相似文献   

6.
Thermal and cold waters from Castellammare–Alcamo (Western Sicily-Italy) were collected between May 1994 and May 1995 and studied for their chemical and isotopic composition. During the same period, mean monthly samples of meteoric water were also collected and measured for their isotopic composition. The main purpose of this study was the characterization of the acquifers and, if possible, of their recharge areas. According to the results obtained, the acquifers were divided into three main groups: (a) selenitic waters, (b) cold carbonatic waters, and (c) deep thermal waters resulting from the mixing of the other two types. Besides a mixing process between carbonatic and selenitic waters, contamination processes of thermal waters by seawater take place during their ascent. The water temperature of the acquifer feeding the thermal springs was estimated by means of various geothermometers to range between 60°C and 97°C. Isotope data on rainwater samples show a wide seasonal variation of both δ and δD values. The fairly constant values of thermal waters through time and the lack of an apparent correlation with the isotopic values of rainwater suggest the existence of a deep circuit determining an almost complete homogenisation of the seasonal variations of the isotopic values.  相似文献   

7.
Isotopic compositions were determined for hydrothermal quartz, calcite, and siderite from core samples of the Newberry 2 drill hole, Oregon. The δ15O values for these minerals decrease with increasing temperatures. The values indicate that these hydrothermal minerals precipitated in isotopic equilibrium with water currently present in the reservoirs. The δ18O values of quartz and calcite from the andesite and basalt flows (700–932 m) have isotopic values which require that the equilibrated water δ18O values increase slightly (− 11.3 to −9.2‰) with increasing measured temperatures (150–265°C). The lithic tuffs and brecciated lava flows (300–700 m) contain widespread siderite. Calculated oxygen isotopic compositions of waters in equilibrium with siderite generally increase with increasing temperatures (76–100°C). The δ18O values of siderite probably result from precipitation in water produced by mixing various amounts of the deep hydrothermal water (− 10.5 ‰) with meteoric water (− 15.5 ‰) recharged within the caldera. The δ13C values of calcite and siderite decrease with increasing temperatures and show that these minerals precipitated in isotopic equilibrium with CO2 of about −8 ‰.The δ18O values of weakly altered (<5% alteration of plagioclase) whole-rock samples decrease with increasing temperatures above 100°C, indicating that exchange between water and rock is kinetically controlled. The water/rock mass ratios decrease with decreasing temperatures. The δ18O values of rocks from the bottom of Newberry 2 show about 40% isotopic exchange with the reservoir water.The calculated δ18O and δD values of bottom hole water determined from the fluid produced during the 20 hour flow test are −10.2 and −109‰, respectively. The δD value of the hydrothermal water indicates recharge from outside the caldera.  相似文献   

8.
Kawah Putih is a summit crater of Patuha volcano, West Java, Indonesia, which contains a shallow, 300 m-wide lake with strongly mineralized acid–sulfate–chloride water. The lake water has a temperature of 26–34°C, pH=<0.5–1.3, Stot=2500–4600 ppm and Cl=5300–12 600 ppm, and floating sulfur globules with sulfide inclusions are common. Sulfur oxyanion concentrations are unusually high, with S4O62−+S5O62−+S6O62−=2400 – 4200 ppm. Subaerial fumaroles (<93°C) on the lake shore have low molar SO2/H2S ratios (<2), which is a favorable condition to produce the observed distribution of sulfur oxyanion species. Sulfur isotope data of dissolved sulfate and native sulfur show a significant 34S fractionation (ΔSO4–Se of 20‰), probably the result of SO2 disproportionation in or below the lake. The lake waters show strong enrichments in 18O and D relative to local meteoric waters, a result of the combined effects of mixing between isotopically heavy fluids of deep origin and meteoric water, and evaporation-induced fractionation at the lake surface. The stable-isotope systematics combined with energy-balance considerations support very rapid fluid cycling through the lake system. Lake levels and element concentrations show strong seasonal fluctuations, indicative of a short water residence time in the lake as well.Thermodynamic modeling of the lake fluids indicates that the lake water is saturated with silica phases, barite, pyrite and various Pb, Sb, Cu, As, Bi-bearing sulfides when sulfur saturation is assumed. Precipitating phases predicted by the model calculations are consistent with the bulk chemistry of the sulfur-rich bottom sediments and their identified mineral phases. Much of the lake water chemistry can be explained by congruent rock dissolution in combination with preferential enrichments from entering fumarolic gases or brines and element removal by precipitating mineral phases, as indicated by a comparison of the fluids, volcanic rocks and lake bed sediment.Flank springs on the mountain at different elevations vary in composition, and are consistent with local rock dissolution as a dominant factor and pH-dependent element mobility. Discharges of warm sulfate- and chloride-rich water at the highest elevation and a near-neutral spring at lower level may contain a small contribution of crater-lake water. The acid fluid-induced processes at Patuha have led to the accumulation of elements that are commonly associated with volcano-hosted epithermal ore deposits. The dispersal of heavy metals and other potentially toxic elements from the volcano via the local drainage system is a matter of serious environmental concern.  相似文献   

9.
Most thermal spring discharges of Rajasthan and Gujarat in northwestern India have been sampled and analysed for major and trace elements in both the liquid and associated gas phase, and for 18O/16O, D/H (in water), 3He/4He and 13C/12C in CO2 (in gas) isotopic ratios. Most thermal springs in Rajasthan are tightly associated to the several regional NE–SW strike-slip faults bordering NE–SW ridges formed by Archaean rocks at the contact with Quaternary alluvial and aeolian sedimentary deposits of the Rajasthan desert. Their Ca–HCO3 immature character and isotopic composition reveals: (1) meteoric origin, (2) relatively shallow circulation inside the crystalline Archaean formations, (3) very fast rise along faults, and (4) deep storage temperatures of the same order of magnitude as discharging temperatures (50–90°C). Thermal spring discharges in Gujarat are spread over a larger area than in Rajasthan and are associated both with the NNW–SSE fault systems bordering the Cambay basin and the ENE–WSW strike-slip fault systems in the Saurashtra province, west of the Cambay basin. Chemical and isotopic compositions of springs in both areas suggest a meteoric origin of deep thermal waters. They mix with fresh or fossil seawater entering the thermal paths of the spring systems through both the fault systems bordering the Cambay basin, as well as faults and fractures occurring inside the permeable Deccan Basalt Trap in the Saurashtra province. The associated gas phase, at all sampled sites, shows similar features: (1) it is dominated by the presence of atmospheric components (N2 and Ar), (2) it has high crustal 4He enrichment, (3) it shows crustal 3He/4He signature, (4) it has low CO2 concentration, and (5) the only analysed sample for 13C/12C isotopic ratio in CO2 suggests that CO2 has a strong, isotopically light organic imprint. All these features and chemical geothermometer estimates of spring waters suggest that any active deep hydrothermal system at the base of the Cambay basin (about 2000–3000 m) has low-to-medium enthalpy characteristics, with maximum deep temperature in the storage zone of about 150°C. In a regional overview, both thermal emergences of Rajasthan and Gujarat could be controlled by the counter-clockwise rotation of India.  相似文献   

10.
Shallow submarine hydrothermal activity has been observed in the Bahía Concepción bay, located at the Gulf coast of the Baja California Peninsula, along faults probably related to the extensional tectonics of the Gulf of California region. Diffuse and focused venting of hydrothermal water and gas occurs in the intertidal and shallow subtidal areas down to 15 m along a NW–SE-trending onshore–offshore fault. Temperatures in the fluid discharge area vary from 50 °C at the sea bottom up to 87 °C at a depth of 10 cm in the sediments.Chemical analyses revealed that thermal water is enriched in Ca, As, Hg, Mn, Ba, HCO3, Li, Sr, B, I, Cs, Fe and Si, and it has lower concentrations of Cl, Na, SO4 and Br than seawater. The chemical characteristics of the water samples indicate the occurrence of mixing between seawater and a thermal end-member. Stable isotopic oxygen and hydrogen composition of thermal samples plot close to the Local Meteoric Water Line on a mixing trend between a thermal end-member and seawater. The composition of the thermal end-member was calculated from the chemistry of the submarine samples data by assuming a negligible amount of Mg for the thermal end-member. The results of the mixing model based on the chemical and isotopic composition indicate a maximum of 40% of the thermal end-member in the submarine vent fluid.Chemical geothermometers (Na/Li, Na–K–Ca and Si) were applied to the thermal end-member concentration and indicate a reservoir temperature of approximately 200 °C. The application of K–Mg and Na/Li geothermometers for vent fluids points to a shallow equilibrium temperature of about 120 °C.Results were integrated in a hydrogeological conceptual model that describes formation of thermal fluids by infiltration and subsequent heating of meteoric water. Vent fluid is generated by further mixing with seawater.  相似文献   

11.
A 23-m.y.-old, fossil meteoric-hydrothermal system in the Lake City caldera (11 × 14 km) has been mapped out by measuring δ 18O values of 300 rock and mineral samples. δ 18O varies systematically throughout the caldera, reaching values as low as −2. Great topographic relief, regional tilting, and variable degrees of erosion within the caldera all combine to give us a very complete section through the hydrothermal system, from the surface down to a depth of more than 2000 m. The initial δ 18O value of the caldera-fill Sunshine Peak Tuff was very uniform (+7.2 ± 0.1), making it easy to determine the exact amount of 18O depletion experienced by each sample during hydrothermal alteration. Also, we have excellent stratigraphic control on depths beneath the mid-Tertiary surface, quantitative information on mineralogical alteration products, and accurate data on the shape of the central resurgent intrusion, which was the principal ‘heat engine’ that drove the hydrothermal circulation. Major conclusions are: (1) Although pristine mid-Tertiary meteoric waters in this area had δ 18O −14, these fluids were 18O-shifted upward to about δ18O = −8 to −5 prior to entering the shallow convective system associated with the resurgent intrusive rocks. Although there was undoubtedly radial inflow toward the caldera from all directions, the highly fractured Eureka Graben, southwest of the caldera, was probably the principal source of recharge groundwater for the Lake City system. (2) Fluid flow within the caldera was dominated by three major categories of permeable zones: the porous megabreccia units (which dip outward from the resurgent dome), vertical fractures and faults related to resurgence, and the caldera ring fault itself. All of these zones exhibit marked 18O depletions, and they are also typically intensely mineralogically altered. (3) The resurgent intrusive stock and its contact metamorphic aureole of hornfels both experienced water/rock ratios lower than the permeable zones; however, they have similarly low δ 18O values because they were altered at higher temperatures. (4) Throughout the caldera, the δ 18O of Sunshine Peak Tuff decreases with increasing depth (about 6 per mil/km), indicative of a shallow thermal gradient, typical of a convective hydrothermal system. The near-surface portion of this gradient was controlled by the temperature drop associated with boiling in the uprising fluid. (5) Deeply circulating meteoric water rose along permeable ring fractures 3 to 5 km beneath the mid-Tertiary surface. These fluids were drawn into the shallow convective system through the lower, porous, megabreccia units. Near the resurgent intrusions, fluid flow was again directed upward where resurgence-related, near-vertical fractures intersect the megabreccia units.  相似文献   

12.
Meteoric waters from cold springs and streams outside of the 1912 eruptive deposits filling the Valley of Ten Thousand Smokes (VTTS) and in the upper parts of the two major rivers draining the 1912 deposits have similar chemical trends. Thermal springs issue in the mid-valley area along a 300-m lateral section of ash-flow tuff, and range in temperature from 21 to 29.8°C in early summer and from 15 to 17°C in mid-summer. Concentrations of major and minor chemical constituents in the thermal waters are nearly identical regardless of temperature. Waters in the downvalley parts of the rivers draining the 1912 deposits are mainly mixtures of cold meteoric waters and thermal waters of which the mid-valley thermal spring waters are representative. The weathering reactions of cold waters with the 1912 deposits appear to have stabilized and add only subordinate amounts of chemical constituents to the rivers relative to those contributed by the thermal waters. Isotopic data indicate that the mid-valley thermal spring waters are meteoric, but data is inconclusive regarding the heat source. The thermal waters could be either from a shallow part of a hydrothermal system beneath the 1912 vent region or from an incompletely cooled, welded tuff lens deep in the 1912 ash-flow sheet of the upper River Lethe area.Bicarbonate-sulfate waters resulting from interaction of near-surface waters and the cooling 1953–1968 southwest Trident plug issue from thermal springs south of Katmai Pass and near Mageik Creek, although the Mageik Creek spring waters are from a well-established, more deeply circulating hydrothermal system. Katmai caldera lake waters are a result of acid gases from vigorous drowned fumaroles dissolving in lake waters composed of snowmelt and precipitation.  相似文献   

13.
Distribution, abundance and life history characteristics of Mysis relicta were studied in the Feldberg Lake District (Lake Breiter Luzin, Lake Schmaler Luzin, Lake Zansen) located in northeastern Germany. Between July 2001 and November 2002 mysids were collected by vertical net hauls. In order to determine the impact of the current trophic conditions on the distribution of mysids in these lakes, oxygen concentration, total phosphorus, chlorophyll a and water transparency were also measured. All investigated lakes are mesotrophic at present. Lake Breiter Luzin exhibited great seasonal and spatial variations in mysid abundance. Density of adults and juveniles had a mean of 44.9 ± 57.1 and 68.7 ± 99.6 m−2, respectively. Highest abundance of adults was 110.4 ± 76.5 m−2 in summer, lowest abundances of 2.0 ± 4.0 m−2 occurred in spring. For juveniles, highest density of 218.4 ± 174.6 m−2 was detected in summer and lowest of 0.8 ± 1.8 m−2 in winter. No mysids were caught in any of the daytime hauls, but they were widely distributed throughout the water column at night. Size frequency distribution of mysids suggested that reproduction occurred year-round, the most consistent influx of juveniles occurred in early summer and a smaller second cohort in autumn. Highest mysid abundance was 189.2 ± 318.6 adults and 127.0 ± 66.3 juveniles m−2 in Lake Schmaler Luzin, and 59.6 ± 5.6 adults and 79.4 ± 11.2 juveniles m−2 in Lake Zansen. There were great spatial differences in abundance in both lakes.  相似文献   

14.
Stable isotope compositions (δD, δ18O and δ34S) of volcanic lake waters, gas condensates and spring waters from Indonesia, Italy, Japan, and Russia were measured. The spring fluids and gas samples plot in a broad array between meteoric waters and local high-temperature volcanic gas compositions. The δD and δ18O data from volcanic lakes in East Indonesia plot in a concave band ranging from local meteoric waters to evaporated fluids to waters heavier than local high-temperature volcanic gases. We investigated isotopic fractionation processes in volcanic lakes at elevated temperatures with simultaneous mixing of meteoric waters and volcanic gases. An elevated lake water temperature gives enhanced kinetic isotope fractionation and changes in equilibrium fractionation factors, providing relatively flat isotope evolution curves in δ18O–δD diagrams. A numerical simulation model is used to derive the timescales of isotopic evolution of crater lakes as a function of atmospheric parameters, lake water temperature and fluxes of meteoric water, volcanic gas input, evaporation, and seepage losses. The same model is used to derive the flux magnitude of the Keli Mutu lakes in Indonesia. The calculated volcanic gas fluxes are of the same order as those derived from energy budget models or direct gas flux measurements in open craters (several 100 m3 volcanic water/day) and indicate a water residence time of 1–2 decades. The δ34S data from the Keli Mutu lakes show a much wider range than those from gases and springs, which is probably related to the precipitation of sulfur in these acid brine lakes. The isotopic mass balance and S/Cl values suggest that about half of the sulfur input in the hottest Keli Mutu lake is converted into native sulfur.  相似文献   

15.
The Blackfoot Reservoir region in southeastern Idaho is recognized as a potential geothermal area because of the presence of several young rhyolite domes (50,000 years old), Quaternary basalt flows, and warm springs. North- to northwest-trending high-angle normal faults of Tertiary to Holocene age appear to be the dominant structural control of spring activity. Surface spring-water temperatures average 14°C except for a group of springs west of the Reservoir Mountains which average 33°C. Chemical geothermometers applied to fifty water samples give temperatures less than 75°C except for eight springs along the Corral Creek drainage. The springs along Corral Creek have Na-K-Ca temperatures that average 354°C, a direct result of high potassium concentrations in the water. A correction for carbon dioxide applied to the Na-K-Ca geothermometer lowers the estimated temperatures of the anomalous springs to near the measured surface temperatures, and Na-K-Ca-Mg temperatures for the anomalous springs are near 100°C. Mixing model calculations suggest that hot water with a temperature of approximately 120°C may be mixing with cooler, more dilute water in the springs from the Corral Creek drainage, a temperature supported by Na-K-Ca-Mg temperatures and mineral saturation temperatures.Stability relations of low-temperature phases in the system indicate that the large concentrations of potassium in the eight anomalous springs are derived from reactions with the potassium-bearing minerals muscovite and K-feldspar. Carbon dioxide and hydrogen sulfide gases may be derived through the oxidation of organic matter accompanied by the reduction of sulfate. Concentrations of major and minor elements, and gases found in springs of the Blackfoot Reservoir region are due to water-rock reactions at temperatures less than 100°C.Based on spring geochemistry, a geothermal reservoir of 100°C up to 120°C may exist at shallow (less than 2 km) depths in the Blackfoot Reservoir region.  相似文献   

16.
The D/H and 18O/16O ratios of water in the active crater lake situated on the Kusatsu-Shirane volcano, Japan are about 20 and 6‰, respectively, higher than local meteoric water. The ratios show seasonal variations superimposed on a gradual change over nine years. The isotopic ratios started to increase in early 1990 and decrease in the spring of 1995. The seasonal variation which is high in winter and low in summer correlates with the temperature difference between lake water and ambient air. The large temperature difference in winter enhances the evaporation of lake water and produces the enriched isotopic ratios relative to the ratios in summer. The accumulation of snow and the decrease in the flux of meteoric water into the lake strengthens the winter-time isotopic enrichment. The enriched isotopic ratios of the lake water over a long time result from the addition of an end member with heavy isotopic ratios contained in a thermal fluid supplied to the lake. Considering the water balance in the lake, the isotopic ratios of the thermal fluid were found to be close to the lake water itself, suggesting the circulation of the lake water seeping through lake floor. Based on the correlation between Cl−concentration and the isotopic ratios, the contribution by the heavy end member was estimated to be 25–36% relative to the enrichment by evaporation. The heavy end member could be a liquid phase evolved from a parental fluid, which is a mixture of local meteoric water and a magmatic fluid as found in high-temperature volcanic gases.  相似文献   

17.
The edifice of Mount Rainier, an active stratovolcano, has episodically collapsed leading to major debris flows. The largest debris flows are related to argillically altered rock which leave areas of the edifice prone to failure. The argillic alteration results from the neutralization of acidic magmatic gases that condense in a meteoric water hydrothermal system fed by the melting of a thick mantle of glacial ice. Two craters atop a 2000-year-old cone on the summit of the volcano contain the world's largest volcanic ice-cave system. In the spring of 1997 two active fumaroles (T=62°C) in the caves were sampled for stable isotopic, gas, and geochemical studies.Stable isotope data on fumarole condensates show significant excess deuterium with calculated δD and δ18O values (−234 and −33.2‰, respectively) for the vapor that are consistent with an origin as secondary steam from a shallow water table which has been heated by underlying magmatic–hydrothermal steam. Between 1982 and 1997, δD of the fumarole vapor may have decreased by 30‰.The compositions of fumarole gases vary in time and space but typically consist of air components slightly modified by their solubilities in water and additions of CO2 and CH4. The elevated CO2 contents (δ13CCO2=−11.8±0.7‰), with spikes of over 10,000 ppm, require the episodic addition of magmatic components into the underlying hydrothermal system. Although only traces of H2S were detected in the fumaroles, most notably in a sample which had an air δ13CCO2 signature (−8.8‰), incrustations around a dormant vent containing small amounts of acid sulfate minerals (natroalunite, minamiite, and woodhouseite) indicate higher H2S (or possibly SO2) concentrations in past fumarolic gases.Condensate samples from fumaroles are very dilute, slightly acidic, and enriched in elements observed in the much higher temperature fumaroles at Mount St. Helens (K and Na up to the ppm level; metals such as Al, Pb, Zn Fe and Mn up to the ppb level and volatiles such as Cl, S, and F up to the ppb level).The data indicate that the hydrothermal system in the edifice at Mount Rainier consists of meteoric water reservoirs, which receive gas and steam from an underlying magmatic system. At present the magmatic system is largely flooded by the meteoric water system. However, magmatic components have episodically vented at the surface as witnessed by the mineralogy of incrustations around inactive vents and gas compositions in the active fumaroles. The composition of fumarole gases during magmatic degassing is distinct and, if sustained, could be lethal. The extent to which hydrothermal alteration is currently occurring at depth, and its possible influence on future edifice collapse, may be determined with the aid of on site analyses of fumarole gases and seismic monitoring in the ice caves.  相似文献   

18.
Application of various chemical geothermometers and mixing models indicate underground temperatures of 260°C, 280°C and 265°C in the Geysir, Hveravellir and Landmannalaugar geothermal fields in Iceland, respectively. Mixing of the hot water with cold water occurs in the upflow zones of all these geothermal systems. Linear relations between chloride, boron and δ18O constitute the main evidence for mixing, which is further substantiated by chloride, silica and sulphate relations in the Geysir and Hveravellir fields.A new carbonate-silica mixing model is proposed which is useful in distinguishing boiled and non-boiled geothermal waters. This model can also be used to estimate underground temperatures using data from warm springs. This model, as well as the chloride-enthalpy model and the Na-Li, and CO2-gas geothermometers, invariably yield similar results as the quartz geothermometer sometimes also does. By contrast, the Na-K and the Na-K-Ca geothermometers yield low values in the case of boiling hot springs, largely due to loss of potassium from solution in the upflow. The results of these geothermometers are unreliable for mixed waters due to leaching subsequent to mixing.  相似文献   

19.
The meteoric input of36Cl due to cosmogenic or nuclear-weapon-produced36Cl cannot contribute significantly to the36Cl present in the saline groundwaters (up to 700 mg l−1 Cl−) from the Stripa granite. The extent of in-situ production of36Cl has been estimated on the basis of the neutron fluxes within the granite and its surrounding leptite. The36Cl present in the groundwaters is attributed to either admixture of labelled Cl− from the leptite with Cl− from the granite or to the total derivation of groundwater chlorinity within the leptite followed by radiochemical ingrowth of36Cl during subsequent groundwater residence within the granite. The chloride derived from the leptite may be either matrix chloride or chloride from an external source which has had a long residence time within the leptite. The implications of36Cl in-situ production for the estimation of groundwater residence times and for the geochemical evolution of groundwater chlorinity are discussed.  相似文献   

20.
Sulfur isotope effects during the SO2 disproportionation reaction to form elemental sulfur (3SO2+3H2O→2HSO4−+S+2H+) at 200–330°C and saturated water vapor pressures were experimentally determined. Initially, a large kinetic isotopic fractionation takes place between HSO4− and S, followed by a slow approach to equilibrium. The equilibrium fractionation factors, estimated from the longest run results, are expressed by 1000 ln αHSO4−–S=6.21×106/T2+3.62. The rates at which the initial kinetic fractionation factors approach the equilibrium ones were evaluated at the experimental conditions.δ34S values of HSO4− and elemental sulfur were examined for active crater lakes including Noboribetsu and Niseko, (Hokkaido, Japan), Khloridnoe, Bannoe and Maly Semiachik (Kamchatka), Poás (Costa Rica), Ruapehu (New Zealand) and Kawah Ijen and Keli Mutu (Indonesia). ΔHSO4−–S values are 28‰ for Keli Mutu, 26‰ for Kawah Ijen, 24‰ for Ruapehu, 23‰ for Poás, 22‰ for Maly Semiachik, 21‰ for Yugama, 13‰ for Bannoe, 9‰ for Niseko, 4‰ for Khloridonoe, and 0‰ for Noboribetsu, in the decreasing order. The SO2 disproportionation reaction in the magmatic hydrothermal system below crater lakes where magmatic gases condense is responsible for high ΔHSO4−–S values, whereas contribution of HSO4− produced through bacterial oxidation of reduced sulfur becomes progressively dominant for lakes with lower ΔHSO4−–S values. Currently, Noboribetsu crater lake contains no HSO4− of magmatic origin. A 40-year period observation of δ34SHSO4− and δ34SS values at Yugama indicated that the isotopic variations reflect changes in the supply rate of SO2 to the magmatic hydrothermal system. This implies a possibility of volcano monitoring by continuous observation of δ34SHSO4− values. The δ18O values of HSO4− and lake water from the studied lakes covary, indicating oxygen isotopic equilibration between them. The covariance gives strong evidence that lake water circulates through the sublimnic zone at temperatures of 140±30°C.  相似文献   

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