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1.
The deep well MV5A, drilled in the western part of the Larderello geothermal field, crossed a 20-cm-thick hydraulic fracture breccia unit at a depth of 1090 m below ground level (b.g.l.). This breccia occurs in a fine-grained Triassic metasandstone and consists of angular to subangular clasts of up to some centimeters in size. Pervasive alteration has affected the breccia clasts and wall rock around the breccia, with the formation of Mg–Fe chlorite. After such alteration, hydrothermal circulation caused the precipitation of two generations of calcite cement. Then, ankerite partially replaced these two calcite generations. Ankerite also precipitated in late veinlets with chlorite. Late hydrothermal activity led to the crystallization of albite, quartz and finally, anhydrite. The calcite contains vapor-rich inclusions and two populations of liquid-rich (L1 and L2) inclusions. L1 inclusions are characterized by homogenization temperatures between 304 and 361°C and salinities from 7.4 to 11.6 wt.% NaCl equivalent; L2 inclusions revealed homogenization temperatures in the range of 189–245°C and salinities from 2.6 to 6.3 wt.% NaCl equivalent. The fluids contained in L2 inclusions were probably trapped coevally with some vapor-rich inclusions under boiling conditions after the L1 inclusions formed. Some of the abundant vapor-rich inclusions in calcite may also represent early, low-temperature inclusions affected by decrepitation and/or stretching and/or leaking during L1 trapping. The liquid-rich (L) inclusions trapped at later stages in ankerite, albite and anhydrite display, respectively, homogenization temperature ranges of 189–198°C, 132–145°C, and 139–171°C, and salinities ranging from 1.6 to 1.7 wt.% NaCl equivalent, 1.4 to 2.1 wt.% NaCl equivalent and 3.7 to 6.2 wt.% NaCl equivalent. The inclusions studied record the evolution, over time, of the fluids flowing in the breccia level: L1 inclusions capture high-temperature fluid (about 300 to 350°C) of high salinity (around 10 wt.% NaCl equivalent) at above-hydrostatic pressures (up to about 150 bar). The L2 inclusions in calcite and liquid-rich inclusions in ankerite and albite represent subsequent hydrothermal fluid evolution toward lower temperatures (about 250 to 130°C), pressures (45 to a few bar) and salinities (6.3 to 1.4 wt.% NaCl equivalent). During this stage, boiling processes and infiltration of meteoric waters probably occurred. Finally, moderately saline fluids (around 5 wt.% NaCl equivalent) at a temperature (about 160°C) close to that of present-day in-hole measurements was trapped in the anhydrite inclusions. The liquids trapped in liquid-rich inclusions circulated at 41,000 years (maximum age of calcite) or later. This age represents an upper limit for the development of vapor-dominated condition, in this part of the geothermal system. The fluids circulating at the breccia level were probably meteoric and/or connate waters. These fluids may have interacted with the anhydrite and carbonate bearing formations present in the Larderello area. The occurrence of the hot and saline fluids, trapped in L1 inclusions at above-hydrostatic pressure, suggests that similar fluids but with higher pressure (≥167 bar) and temperature (≥360°C) may have been responsible for rock fracturing.  相似文献   

2.
The Platanares geothermal area in western Honduras consists of more than 100 hot springs that issue from numerous hot-spring groups along the banks or within the streambed of the Quebrada de Agua Caliente (brook of hot water). Evaluation of this geothermal area included drilling a 650-m deep PLTG-1 drill hole which penetrated a surface mantling of stream terrace deposits, about 550 m of Tertiary andesitic lava flows, and Cretaceous to lower Tertiary sedimentary rocks in the lower 90 m of the drill core.Fractures and cavities in the drill core are partly to completely filled by hydrothermal minerals that include quartz, kaolinite, mixed-layer illite-smectite, barite, fluorite, chlorite, calcite, laumontite, biotite, hematite, marcasite, pyrite, arsenopyrite, stibnite, and sphalerite; the most common open-space fillings are calcite and quartz. Biotite from 138.9-m depth, dated at 37.41 Ma by replicate 40Ar/39 Ar analyses using a continuous laser system, is the earliest hydrothermal mineral deposited in the PLTG-1 drill core. This mid-Tertiary age indicates that at least some of the hydrothermal alteration encountered in the PLTG-1 drill core occured in the distant past and is unrelated to the present geothermal system. Furthermore, homogenization temperatures (Th) and melting-point temperatures (Tm) for fluid inclusions in two of the later-formed hydrothermal minerals, calcite and barite, suggest that the temperatures and concentration of dissolved solids of the fluids present at the time these fluid inclusions formed were very different from the present temperatures and fluid chemistry measured in the drill hole.Liquid-rich secondary fluid inclusions in barite and caicite from drill hole PLTG-1 have Th values that range from about 20°C less than the present measured temperature curve at 590.1-m depth to as much as 90°C higher than the temperature curve at 46.75-m depth. Many of the barite Th measurements (ranging between 114° and 265°C) plot above the reference surface boiling-point curve for pure water assuming hydrostatic conditions; however, the absence of evidence for boiling in the fluid inclusions indicates that at the time the minerals formed, the ground surface must have been at least 80 m higher than at present and underwent stream erosion to the current elevation. Near-surface mixed-layer illite-smectite is closely associated with barite and appears to have formed at about the same temperature range (about 120° to 200°C) as the fluid-inclusion Thvalues for barite. Fluid-inclusion Th values for calcite range between about 136° and 213°C. Several of the calcite Th values are significantly lower than the present measured temperature curve. The melting-point temperatures (Tm) of fluid-inclusion ice yield calculated salinities, ranging from near zero to as much as 5.4 wt. % NaCl equivalent, which suggest that much of the barite and calcite precipitated from fluids of significantly greater salinity than the present low salinity Platanares hot-spring water or water produced from the drill hole.  相似文献   

3.
Abundant fluid inclusions in olivine of dunite xenoliths (～1–3 cm) in basalt dredged from the young Loihi Seamount, 30 km southeast of Hawaii, are evidence for three coexisting immiscible fluid phases—silicate melt (now glass), sulfide melt (now solid), and dense supercritical CO2 (now liquid + gas)—during growth and later fracturing of some of these olivine crystals. Some olivine xenocrysts, probably from disaggregation of xenoliths, contain similar inclusions.Most of the inclusions (2–10 μm) are on secondary planes, trapped during healing of fractures after the original crystal growth. Some such planes end abruptly within single crystals and are termed pseudosecondary, because they formed during the growth of the host olivine crystals. The “vapor” bubble in a few large (20–60 μm), isolated, and hence primary, silicate melt inclusions is too large to be the result of simple differential shrinkage. Under correct viewing conditions, these bubbles are seen to consist of CO2 liquid and gas, with an aggregate ? = ～ 0.5–0.75 g cm?3, and represent trapped globules of dense supercritical CO2 (i.e., incipient “vesiculation” at depth). Some spinel crystals enclosed within olivine have attached CO2 blebs. Spherical sulfide blebs having widely variable volume ratios to CO2 and silicate glass are found in both primary and pseudosecondary inclusions, demonstrating that an immiscible sulfide melt was also present.Assuming olivine growth at ～ 1200°C and hydrostatic pressure from a liquid lava column, extrapolation of CO2P-V-T data indicates that the primary inclusions were trapped at ～ 220–470 MPa (2200–4700 bars), or ～ 8–17 km depth in basalt magma of ? = 2.7 g cm?3. Because the temperature cannot change much during the rise to eruption, the range of CO2 densities reveals the change in pressure from that during original olivine growth to later deformation and rise to eruption on the sea floor. The presence of numerous decrepitated inclusions indicates that the inclusion sample studied is biased by the loss of higher-density inclusions and suggests that some part of these olivine xenoliths formed at greater depths.  相似文献   

4.
Microthermometric measurements were obtained for 618 fluid inclusions in hydrothermal quartz, fluorite and calcite and magmatic quartz phenocrysts in intracaldera tuffs from the VC-2A core hole in order to study evolutionary processes of the Sulphur Springs hydrothermal system in the Valles caldera. Relatively high Th values in samples from shallow depths indicate erosion of about 200 m of caldera fill since deposition of hydrothermal minerals at shallow depths in the Sulphur Springs hydrothermal system, accompanied by a descent in the water table of the liquid-dominated reservoir. For samples collected below the current water level of the well, the minimum values of homogenization temperature (Th) fit the present thermal profile, whereas minimum Th values of samples from above the water level are several tens of degrees higher than the present thermal profile and fit a paleo-thermal profile following the boiling point curve for pure water, as adjusted to 92 °C at 20 m below the present land surface. This is attributed to development of an evolving vapor zone that formed subsequent to a sudden drop in the water table of the liquid-dominated reservoir. We suggest that these events were caused by the drainage of an intracaldera lake when the southwestern wall of the caldera was breached about 0.5 Ma. This model indicates that vapor zones above major liquid-dominated geothermal reservoirs can be formed due to dramatic changes in geohydrology and not just from simple boiling.  相似文献   

5.
Major-element, Cl, S, F analyses have been performed on a wide selection of melt inclusions trapped in olivine (Fo81–87) from scoria and crystal-rich lapilli samples of Piton de la Fournaise volcano. As a whole, they display a transitional basaltic composition. The melt inclusions (8–9 wt.% MgO, 0.62–0.73 wt.% K2O) are in equilibrium with olivines (Fo81–85) in the samples from the Central Feeding Zone and the South-East Feeding Zone and show a slight alkaline affinity. The melt inclusions in olivines (Fo85–87) from the North-West Rift (NWR) contain 9.3–9.7 wt.% MgO and 0.54–0.58 wt.% K2O, with a more tholeiitic tendency. In oceanitic lavas and crystal-rich lapilli, the olivine xenocrysts are recognisable by the presence of one or more secondary shear plane fracture(s) filled up with CO2 and alkali-rich basaltic melt inclusions. In dunite nodules, olivines present also contain several secondary shear plane fracture(s) filled up with CO2 and high-SiO2 melt inclusions. Secondary CO2-rich fluid inclusions in olivine (Fo85–87) from the NWR samples indicate PCO2 up to 500 MPa whereas, PCO2 ranges from 95 MPa to few tenths of bars in the other samples. Both the primary melt inclusions and the secondary fluid inclusions strongly suggest that the olivine crystallises and accumulates over a wide depth range (15 km). It is envisioned that cumulative pockets with low residual porosity are repeatedly percolated with a CO2-rich fluid phase, possibly associated with basaltic to SiO2-rich melts, and are finally disrupted and entrained to the surface when vigorous magma transfer occurs. The SiO2-rich residual melts in early-formed dunitic or gabbroic bodies may have acted as contaminant agents for the more alkali character of magmas vented through the central feeding system, where a well-developed cumulative system is thought to exist. Finally, the existence of secondary fluid and melt inclusions in olivines implies that the dunitic bodies are weakened on the micrometric scale.  相似文献   

6.
Fluids supplied in alpine-type mantle peridotites and trapped as fluid inclusions in olivines have been fixed by low-temperature reactions, and theirCO2/H2O ratios can be deduced from the minerals in the inclusions. Relic fluid inclusions were commonly observed by the optical microscope in olivines from almost all examined solid intrusive ultramafic complexes (Papua, Oman, Troodos and eleven alpine-type complexes of Japan). Such complexes were emplaced into the crust in a solid state. Electron microscopic studies of olivines from three complexes, Higashiakaishi, Horoman and Iwanai-dake, showed that relic fluid inclusions in these olivines have distinctive mineral parageneses: serpentine + magnesite + talc, serpentine + magnesite + brucite, and serpentine + brucite, respectively, depending on theCO2/(H2O+CO2) ratio of the trapped fluid.It is deduced that the fluids had been supplied to peridotites, at least partly, but almost wholly in some case, when the peridotites were still hot, probably at the upper mantle for the following reasons: (1) the curved surfaces along which the inclusions are distributed are cut by post-emplacement serpentine veins; (2) for the Higashiakaishi dunite, the relic fluid inclusions are exclusively found in porphyroclast olivines and are totally absent in matrix olivines recrystallized during the Sanbagawa metamorphism.Recent models on the derivation of ophiolitic or some alpine-type peridotites favor the island-arc or fore-arc settings. Dehydration of the descending oceanic slab may supply H2OCO2 vapor to the overlying mantle wedge. Fluid inclusions trapped in such mantle wedge may abound in H2O component. H2O-bearing fluid inclusions may, therefore, be important H2O containers in the upper mantle, especially near the edge of the mantle wedge above downgoing oceanic slabs.  相似文献   

7.

This paper presents gas compositions and H-, O-isotope compositions of sulfide- and quartz-hosted fluid inclusions, and S-, Pb-isotope compositions of sulfide separates collected from the principal Stage 2 ores in Veins 3 and 210 of the Jinwozi lode gold deposit, eastern Tianshan Mountains of China. Fluid inclusions trapped in quartz and sphalerite are dominantly primary. H-and O-isotopic compositions of pyrite-hosted fluid inclusions indicate two major contributions to the ore-forming fluid that include the degassed magma and the meteoric-derived but rock 18O-buffered groundwater. However, H- and O-isotopic compositions of quartz-hosted fluid inclusions essentially suggest the presence of groundwater. Sulfide-hosted fluid inclusions show considerably higher abundances of gaseous species CO2, N2, H2S, etc. than quartz-hosted ones. The linear trends among inclusion gaseous species reflect the mixing tendency between the gas-rich magmatic fluid and the groundwater. The relative enrichment of gaseous species in sulfide-hosted fluid inclusions, coupled with the banded ore structure indicating alternate precipitation of quartz with sulfide minerals, suggests that the magmatic fluid has been inputted to the ore-forming fluid in pulsation. Sulfur and lead isotope compositions of pyrite and galena separates indicate an essential magma derivation for sulfur but the multiple sources for metallic materials from the mantle to the bulk crust.

  相似文献   

8.
This paper presents gas compositions and H-, O-isotope compositions of sulfide- and quartz-hosted fluid inclusions, and S-, Pb-isotope compositions of sulfide separates collected from the principal Stage 2 ores in Veins 3 and 210 of the Jinwozi lode gold deposit, eastern Tianshan Mountains of China. Fluid inclusions trapped in quartz and sphalerite are dominantly primary. H-and O-isotopic compositions of pyrite-hosted fluid inclusions indicate two major contributions to the ore-forming fluid that include the degassed magma and the meteoric-derived but rock 18O-buffered groundwater. However, H- and O-isotopic compositions of quartz-hosted fluid inclusions essentially suggest the presence of groundwater. Sulfide-hosted fluid inclusions show considerably higher abundances of gaseous species CO2, N2, H2S, etc. than quartz-hosted ones. The linear trends among inclusion gaseous species reflect the mixing tendency between the gas-rich magmatic fluid and the groundwater. The relative enrichment of gaseous species in sulfide-hosted fluid inclusions, coupled with the banded ore structure indicating alternate precipitation of quartz with sulfide minerals, suggests that the magmatic fluid has been inputted to the ore-forming fluid in pulsation. Sulfur and lead isotope compositions of pyrite and galena separates indicate an essential magma derivation for sulfur but the multiple sources for metallic materials from the mantle to the bulk crust.  相似文献   

9.
Methods used previously to remove compositional modifications from volcanic gas analyses for Mount Etna and Erta'Ale lava lake have bean employed to estimate the gas phase composition at Nyiragongo lava lake, based on samples obtained in 1959. H2O data were not reported in 11 of the 13 original analyses. The restoration methods have been used to estimate the H2O contents of the samples and to correct the analyses for atmospheric contamination, loss of sulfur and for pre- and pest-collection oxidation of H2S, S2, and H2. The estimated gas compositions are relatively CO2-rich, low in total sulfur and reduced. They contain approximately 35–50% CO2 45–55% H2O, 1–2% SO2, 1–2% H2., 2–3% CO, 1.5–2.5% H2S, 0.5% S2 and 0.1% COS over,he collection temperature range 102° to 960° C. The oxygen fugacities of the gases are consistently about half an order of magnitude below quartz-magnetite-fayalite. The low total sulfur content and resulting low atomic S/C of the Nyiragongo gases appear to be related to the relatively low fO2 of the crystallizing lava. At temperatures above 800°C and pressures of 1–1.5 k bar, the Nyiragongo gas compositions resemble those observed in primary fluid inclusions believed to have formed at similar temperatures and pressures in nephelines of intrusive alkaline rocks. Cooling to 300°C, with fO2 buffered by the rock, results in gas compositions very rich in CH4 (50–70%) and resembling secondary fluid inclusions formed at 200–500°C in alkaline rocks. Below 600°C the gases become supersaturated in carbon as graphite. These inferences are corroborated by several reports of hydrocarbons in plutonic alkaline rocks, and by the presence of CH4-rich waters in Lake Kivu — a lake on the flanks of Nyiragongo volcano.  相似文献   

10.
Masanori  Kurosawa  Satoshi  Ishii  Kimikazu  Sasa 《Island Arc》2010,19(1):40-59
Fluid inclusions in quartz from miarolitic cavities, pegmatites, and quartz veins in Miocene biotite-granite plutons, Kofu, Japan, were analyzed by particle-induced X-ray emission to examine chemistries and behaviors of granite-derived fluids in island-arc granite. Most inclusions are aqueous two-phase inclusions, and halite-bearing polyphase inclusions are also observed in quartz veins in the upper part of the plutons. From element contents of fluid inclusions in the miarolitic cavities, the original fluid released from the granite plutons during solidification is inferred to have concentrations of Mn, Fe, Cu, Zn, Ge, Br, Rb, Pb, and Ba of several tens to hundreds of parts per million by weight (ppm) and a salinity of about 10 wt% NaCl equivalent. We estimated the formation conditions of the fluid to have been at about 1.3–1.9 kb and 530–600°C on the basis of the homogenization temperatures of the inclusions and the solidification conditions of the plutons. The polyphase inclusions probably originated from hypersaline fluid by boiling of part of the released fluid during its ascent in the plutons. The polyphase inclusions contain several hundreds to tens of thousands of ppm of Fe and Mn, and tens to several hundreds of ppm of Cu, Zn, Br, Rb, and Pb. The salinities are about 35 wt% NaCl equivalent. Compositional variations in two-phase inclusions from the miarolitic cavities and quartz veins are primarily explained by mineral precipitation with dilution by surface water exerting a secondary influence. Thus, chemistries and behaviors of the granite-derived fluids in the plutons can be explained by mineral precipitation, boiling, and dilution of the originally released fluid.  相似文献   

11.
Appalachian Deep Core Hole 2 (ADCOH-2) penetrated part of one of the most persistent and important tectonostratigraphic belts in the southern Appalachians—the Brevard-Chauga belt in South Carolina. The Brevard-Chauga belt is a subdivision of the Inner Piedmont and it includes the Brevard fault zone. The 307 m core contains four imbricated slices of Early Ordovician Henderson Gneiss and metasedimentary rocks of the Chauga River Formation. Aqueous (NaCl–CaCl2) inclusions and CO2–CH4-rich inclusions present in syntectonic quartz veins in the metasedimentary units, together with garnet-biotite geothermometry, provide information on the P-T conditions during uplift. Garnet-biotite geothermometry in the Brevard metasiltstone indicates a crystallization temperature of 466±52 °C, which together with published 40Ar/39Ar hornblende data from the Chauga belt, are interpreted as a Neoacadian (late Devonian) garnet crystallization age. High-density CO2-rich fluid inclusion isochores indicate a pressure of 4.5 kbar at 466±52 °C at this time. A Rb–Sr muscovite model age of 302 Ma in retrograde mylonitic Henderson Gneiss is interpreted as an Alleghanian recrystallization age. Fluid inclusions record a 2.5 kbar decompression event at this time, consistent with thrust assembly of the tectonostratigraphic units in the core.  相似文献   

12.
Microthermometric analyses of fluid inclusions on a suite of hydrothermally altered gabbros recovered just south of the eastern intersection of the Kane Fracture Zone and the Mid-Atlantic Ridge, record the highest homogenization temperatures yet reported for mid-ocean ridge hydrothermal systems. Fluid salinities in the high temperature inclusions are more than ten times that of seawater. Multiple generations of fluid inclusions entrapped along healed microfractures exhibit three distinct temperature-compositional groups. We interpret these populations as having been trapped during three separate fracturing events.The earliest episode of brittle failure in the gabbros is represented by coplanar, conjugate vapor-dominated and brine-dominated fluid inclusion arrays in primary apatite. Vapor-dominated inclusions exhibit apparent homogenization temperatures of 400°C and contain equivalent salinities of 1–2 wt.% NaCl. These inclusions are interspersed with liquid-dominated, sulfide-bearing inclusions containing salinities of 50 wt.% NaCl equivalent. These high salinity inclusions remain unhomogenized at temperatures greater than 700°C.Compositional and phase relationships of the fluid inclusions may be accounted for by two-phase separation of a fluid under 1000–1200 bars pressure. These pressures require that fluid entrapment occurred under a significant lithostatic component and indicate a minimum entrapmentdepth of 2 km below the axial valley floor. This depth corresponds to a minimum tectonic uplift of 3 km, in order to emplace the samples at the 3100 m recovery depth. The microfracture networks within magmatic apatites represent fluid flow paths for either highly modified, deeply penetrating seawater or a late stage magmatic aqueous fluid. The inclusions may have formed close to the brittle-ductile transition zone adjacent to an active magma chamber.Following collapse of the high temperature front, lower temperature fluids of definite seawater origin circulated through the open fracture networks, pervasively altering portions of the gabbros. This stage is represented by low-to-moderate (1–7 wt.% NaCl equivalent) salinity inclusions in plagioclase, apatite, epidote, and augite, which homogenize at temperatures of approximately 200–300°C and 400°C. Formation of hydrous mineral assemblages, under greenschist to lower amphibolite facies conditions, resulted in sealing of the vein system and may have resulted in modification of seawater salinities by as much as a factor of two. During or following these later stages of hydrothermal activity the gabbros were emplaced high on the axial walls by differential uplift attending formation of the flanking mountains.  相似文献   

13.
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   

14.
The Dongping gold deposit is contained within an inner contacting zone of the Hercynian Shuiquangou alkali syenite. The ores occur as veins or as replacement bodies. Fluid inclusion observation shows that in early and main mineralizing stages inclusion types are gas and gas-liquid inclusions, respectively. Gas inclusions occur in isolation in vein quartz, their homog-enization temperature is 372-306°C, and salinity 3.7-1.0 wt% NaCl. Gas-liquid inclusions occur in clusters or healed fractures but do not cut quartz boundary with homogenization temperature 342-267°C and salinity 1.9-0.8 wt% NaCl. Stable isotope measurements show that at main gold mineralization, hydrogen and oxygen isotopic ratios of the mineralizing fluids are -70.8‰-108.4‰ and 2.44‰-4.05‰, respectively. Primary ore fluids in Dongping are higher temperature and lower salinity NaCl-CO2-H2O fluids, and come from Yanshanian granitic magmatism. Fluid im-miscibility, fluid-rock interactions and meteoric water adding were main reasons for gold deposition.  相似文献   

15.
Detailed geochemistry supported by geologic mapping has been used to investigate Sulphur Springs, an acid-sulfate hot spring system that issues from the western flank of the resurgent dome inside Valles Caldera. The most intense activity occurs at the intersection of faults offsetting caldera-fill deposits and post-caldera rhyolites. Three geothermal wells in the area have encountered pressures <1 MPa and temperatures of 200°C at depths of 600 to 1000 m. Hot spring and fumarole fluids may discharge at boiling temperatures with pH 1.0 and SO4 8000 mg/l. These conditions cause argillic alterations throughout a large area.Non-condensible gases consist of roughly 99% CO2 with minor amounts of H2S, H2, and CH4. Empirical gas geothermometry suggests a deep reservoir temperature of 215 to 280°C. Comparison of 13C and 18O between CaCO3 from well cuttings and CO2 from fumarole steam indicates a fractionation temperature between 200 and 300°C by decarbonation of hydrothermally altered Paleozoic limestone and vein calcite in the reservoir rocks. Tritium concentrations obtained from steam condensed in a mudpot and deep reservoir fluids (Baca #13, 278°C) are 2.1 and 1.0 T.U. respectively, suggesting the steam originates from a reservoir whose water is mostly >50 yrs old. Deuterium contents of fumarole steam, deep reservoir fluid, and local meteoric water are practically identical even though 18O contents range through 4‰, thus, precipitation on the resurgent dome of the caldera could recharge the hydrothermal system by slow percolation. From analysis of D and 18O values between fumarol steam and deep reservoir fluid, steam reaches the surface either (1) by vaporizing relatively shallow groundwater at 200°C or (2) by means of a two-stage boiling process through an intermediate level reservoir at roughly 200°C.Although many characteristics of known vapor-dominated geothermal systems are found at Sulphur Springs, fundamental differences exist in temperature and pressure of our postulated vapor-zone. We propose that the reservoir beneath Sulphur Springs is too small or too poorly confined to sustain a “true” vapor-dominated system and that the Sulphur Springs system may be a “dying” vapor-dominated system that has practically boiled itself dry.  相似文献   

16.
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   

17.
We characterize and quantify volatile emissions at Hot Spring Basin (HSB), a large acid-sulfate region that lies just outside the northeastern edge of the 640 ka Yellowstone Caldera. Relative to other thermal areas in Yellowstone, HSB gases are rich in He and H2, and mildly enriched in CH4 and H2S. Gas compositions are consistent with boiling directly off a deep geothermal liquid at depth as it migrates toward the surface. This fluid, and the gases evolved from it, carries geochemical signatures of magmatic volatiles and water–rock reactions with multiple crustal sources, including limestones or quartz-rich sediments with low K/U (or 40?Ar/4?He). Variations in gas chemistry across the region reflect reservoir heterogeneity and variable degrees of boiling. Gas-geothermometer temperatures approach 300 °C and suggest that the reservoir feeding HSB is one of the hottest at Yellowstone. Diffuse CO2 flux in the western basin of HSB, as measured by accumulation-chamber methods, is similar in magnitude to other acid-sulfate areas of Yellowstone and is well correlated to shallow soil temperatures. The extrapolation of diffuse CO2 fluxes across all the thermal/altered area suggests that 410 ± 140 t d− 1 CO2 are emitted at HSB (vent emissions not included). Diffuse fluxes of H2S were measured in Yellowstone for the first time and likely exceed 2.4 t d− 1 at HSB. Comparing estimates of the total estimated diffuse H2S emission to the amount of sulfur as SO42− in streams indicates ~ 50% of the original H2S in the gas emission is lost into shallow groundwater, precipitated as native sulfur, or vented through fumaroles. We estimate the heat output of HSB as ~ 140–370 MW using CO2 as a tracer for steam condensate, but not including the contribution from fumaroles and hydrothermal vents. Overall, the diffuse heat and volatile fluxes of HSB are as great as some active volcanoes, but they are a small fraction (1–3% for CO2, 2–8% for heat) of that estimated for the entire Yellowstone system.  相似文献   

18.
A fluid-inclusion study has been performed on quartzite nodules of stromboli volcano hosted by calc-alkaline lavas of both the Strombolicchio (200 ka) and Paleostromboli II (60 ka) periods. The nodules are mainly composed of quartz crystals with subordinate plagioclase and K-feldspar. Small interstitial minerals such as plagioclase, K-feldspar, clinopyroxene, biotite, and quartz are also found, together with glass. Muscovite, epidote and zircon occur as accessory minerals. Different quartzite nodules occur: (1) equigranular polygonal granoblastic quartzite nodules forming a polygonal texture with clear triple points; (2) inequigranular polygonal granoblastic quartzite nodules; and (3) break-up nodules with strongly resorbed quartz. These quartzites are restites from partial melting, involving felsic crustal rocks at the magma/wall rock contact. Restitic quartz re-crystallises at variable and generally high temperatures, leading to the formation of quartzites with different textures. Quartz grains contain five types of fluid inclusions distinguished on the basis of both fluid type and textural/phase relationships at room temperature. Type I are two-phase (liquid+vapour) CO 2-rich fluid inclusions. They are primary and subordinately pseudosecondary in origin and have undergone re-equilibration processes. Type II mono-phase/two-phase (vapour/liquid+vapour) CO 2-rich fluid inclusions are the most common and, based on their spatial distribution and shape, they can be divided into two subclasses: type IIa and type IIb. Type II inclusions are secondary or pseudosecondary and they are assumed to have formed after decrepitation of type I inclusions and cracking of the host quartz. Type III inclusions are mono-phase (vapour); they possibly contain CO 2 at very low density and surround the inner rims of quartz grains. Type IV two-phase silicate-melt inclusions contain glass±CO 2-rich fluid. Some of them are cogenetic with type II inclusions. Finally, type V two-phase (liquid+vapour) aqueous inclusions are both vapour-rich and liquid-rich aqueous inclusions. Microthermometric experiments were performed on both type I and II inclusions. Type I inclusions homogenise to liquid between 20 and 30.5 °C. Type IIa inclusions homogenise to vapour in the 24 to 30 °C range, with a maximum peak of frequency at 29 °C. Type IIb inclusions also homogenise to vapour between 14 and 25 °C. There appears to be no difference in homogenisation temperature distribution between the Strombolicchio and Paleostromboli II samples. The trapping pressures of the fluid inclusions have been obtained by combining the microthermometric data of the Strombolicchio and Paleostromboli II samples with the pressure–temperature–volume (i.e. density) characteristics for a pure CO 2 system. The data on the early inclusions (type I) suggest an important magma rest at a pressure of about 290 MPa (i.e. about 11-km depth). Type IIa CO 2 inclusions suggest that a second magma rest occurred at a pressure of about 100 MPa (i.e. about 3.5-km depth), whereas type IIb inclusions were trapped later at a shallower depth during the final magma upwelling. No pressure/depth differences seem to occur between the Strombolicchio and Paleostromboli II periods, indicating the same polybaric rests for the calc-alkaline magmas of Stromboli, despite their significantly different ages. This persistence in magma stagnation conditions from 200 to 60 ka suggests a similar plumbing system for the present-day Strombolian activity.  相似文献   

19.
The Okinawa trough is a spreading back-are basin featuring emitting hydrothermal solutions (black chimney type) and modem sulfide precipitation on the sea floor. The study of fluid inclusions in water-rock interaction products in the Jade hydrothermal field indicates that the deep hydrothermal system beneath the sea floor is fairly rich in gas and there are two independent and coexisting fluids-CO2-hydrocarbon fluid and salt aqueous fluid. On the whole, the composition of CO2-hydrocarbon fluid inclusions is similar to that of the fluid inclusions in natural gas fields. The dominant composition of the inclusions in aqueous fluid is H2O with CO2 and CH4 being oversaturated. The salt aqueous fluid of the Jade hydrothermal system might be emitted through a black chimney, whereas CO2-rich fluids discharge CO2 bubbles and CO2 hydrate through fissures. Hydrocarbons in gas phase or in fluid might be enclosed somewhere under the sea. Large storage of CO2-CH4-H2S gas or fluid and reaction of this gas or fluid with salt water will lead to commercial sulfide deposits.  相似文献   

20.
Two kinds of inclusions, fluid-melting inclusion and gas-liquid inclusion, are present in the Huanggangliang deposit in eastern Inner Mongolia. Temperature ranges from 1050°C of fluid-melting inclusion to 150°C of liquid inclusion. Away from intrusion, the inclusions of orebodies intend to be characterized by simpler type, lower temperature and lower salinity, as well as weakened relation to intrusion. The metallization of the Huanggangliang deposit is characterized by multiple activities of ore-forming fluid, multi-source, multi-stage accumulation of ore-forming material, F-rich environment, enrichment of F, organic gas, CO2 and N2, and involving of residual magma.  相似文献   

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