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1.
Characteristics and origins of primary fluids and noble gases in mantle-derived minerals from the Yishu area, Shandong Province, China 总被引:3,自引:1,他引:3
springerlink.com Studies of mantle fluids are currently one of the hot topics in the earth science, greatly contributing to re-vealing origins and evolutions of fluids. In general, the concept of mantle fluids refers to their active compo-nents, such as CO2, H2O, N2, etc., while the noble gases inert in chemical properties belong to another research system. Due to their marked differences in various fluid sources of the Earth[1], the isotopic sig-natures of He and Ar have been widely used a… 相似文献
2.
Material sources of escaped gases from Tianchi volcanic geothermal area, Changbai Mountains 总被引:4,自引:0,他引:4
On the basis of the chemical components and stable isotopic compositions of escaped gases from the Tianchi volcanic geothermal
area, the material sources of these gases are discussed, presenting that they are mainly derived from the residual mantle-derived
magma in the crust; Changbai geothermal area may be directly interlinked with the eruption canal in history; there is a stable
reservoir of the geothermal water and the deep-seated gases under the Changbai geothermal area, with water temperature of
the reservoir being about (166 ± 9)°C.
Project supported by the National Natural Science Foundation of China. 相似文献
3.
We have analysed volatiles (H2O, He, Ar, CO2) in differentiated (basaltic andesite, dacite) volcanic glasses dredged at a depth of ca. 2000 m in the eastern part of the Manus Basin between 151°20′ and 152°10′ E. These samples have Sr–O–B isotopic ratios that show that they most likely represent lavas evolved from a common magma source. Since these glasses are very fresh, they provide a unique opportunity to study the behaviour of magmatic volatiles during assimilation–fractional crystallisation–degassing (AFCD). The samples are highly vesicular (up to 18%) and the volatiles trapped in vesicles consist predominantly of H2O with minor amounts of CO2, and the concentration of water in the glasses indicates that H2O saturation was attained. Rare gases except helium are atmospheric in origin, and the 3He/4He ratios and the CO2/3He ratios are respectively lower and higher than those typical of Mid-Ocean Ridge Basalt (MORB), and appear to correlate with the degree of differentiation. AFCD allows efficient degassing of mantle-derived volatiles and contribution of crust-derived and atmosphere-derived volatiles. Given the widespread occurrence of differentiated magmatism at arcs, we suggest that AFCD is responsible for large-scale occurrence of 3He-rich crustal fluids and of atmospheric-like rare gases in arc emanations, and that most of the volatiles are lost continuously during fractional crystallisation, rather than catastrophically during eruptions. 相似文献
4.
The chemical and isotopic compositions (δDH2O, δ18OH2O, δ18OCO2, δ13CCO2, δ34S, and He/N2 and He/Ar ratios) of fumarolic gases from Nisyros, Greece, indicate that both arc-type magmatic water and local seawater feed the hydrothermal system. Isotopic composition of the deep fluid is estimated to be +4.9±0.5‰ for δ18O and ?11±5‰ for δD corresponding to a magmatic water fraction of 0.7. Interpretation of the stable water isotopes was based on liquid–vapor separation conditions obtained through gas geothermometry. The H2–Ar, H2–N2, and H2–H2O geothermometers suggest reservoir temperatures of 345±15 °C, in agreement with temperatures measured in deep geothermal wells, whereas a vapor/liquid separation temperature of 260±30 °C is indicated by gas equilibria in the H2O–H2–CO2–CO–CH4 system. The largest magmatic inputs seem to occur below the Stephanos–Polybotes Micros crater, whereas the marginal fumarolic areas of Phlegeton–Polybotes Megalos craters receive a smaller contribution of magmatic gases. 相似文献
5.
Yuri A. Taran 《Bulletin of Volcanology》2011,73(4):395-408
A detailed analysis of published data on the N2, Ar, and He content and Ar and He isotopic composition of fumarolic fluids from Vulcano crater (south Italy) supports a model
with two endmembers comprising magmatic and hydrothermal fluids with correspondingly low and high H2O content. The magmatic component with the highest 3He/4He and highest absolute concentrations of N2, Ar, and He also has the lowest N2/Ar and N2/He ratios (∼300 and ∼500, respectively). In contrast, the hydrothermal endmember, with the lower 3He/4He and lower absolute N2, Ar, and He abundances, has high N2/Ar (∼1,000) and high N2/He (>3,000) ratios. The hydrothermal component is also characterized by the highest 40Ar/36Ar ratios (>1,000) and is proposed to be the main carrier of metamorphic gases from the arc crust. 相似文献
6.
Noncondensible gases from hot springs, fumaroles, and deep wells within the Valles caldera geothermal system (210–300°C) consist of roughly 98.5 mol% CO2, 0.5 mol% H2S, and 1 mol% other components. 3He/4He ratios indicate a deep magmatic source (R/Ra up to 6) whereas δ13C–CO2 values (−3 to −5‰) do not discriminate between a mantle/magmatic source and a source from subjacent, hydrothermally altered Paleozoic carbonate rocks. Regional gases from sites within a 50-km radius beyond Valles caldera are relatively enriched in CO2 and He, but depleted in H2S compared to Valles gases. Regional gases have R/Ra values ≤1.2 due to more interaction with the crust and/or less contribution from the mantle. Carbon sources for regional CO2 are varied. During 1982–1998, repeat analyses of gases from intracaldera sites at Sulphur Springs showed relatively constant CH4, H2, and H2S contents. The only exception was gas from Footbath Spring (1987–1993), which experienced increases in these three components during drilling and testing of scientific wells VC-2a and VC-2b. Present-day Valles gases contain substantially less N2 than fluid inclusion gases trapped in deep, early-stage, post-caldera vein minerals. This suggests that the long-lived Valles hydrothermal system (ca. 1 Myr) has depleted subsurface Paleozoic sedimentary rocks of nitrogen. When compared with gases from many other geothermal systems, Valles caldera gases are relatively enriched in He but depleted in CH4, N2 and Ar. In this respect, Valles gases resemble end-member hydrothermal and magmatic gases discharged at hot spots (Galapagos, Kilauea, and Yellowstone). 相似文献
7.
Recent Geochemical Variation of the Hot-Spring Gases from the Tianchi Volcano, Changbai Mountains, Northeast China 总被引:1,自引:0,他引:1
Recent fluid monitoring work shows that the contents of mantle-derived CO_2,He and CH_4 increased anomalously in 2002 and 2003. The 3He/4He ratio of the deep-fault-type Jinjiang hot springs increased highly anomalously in 2003, and then decreased in 2004. The 3He/4He ratio from the thermal-reservoir-type Changbaijulong hot springs increased slowly in 2003, and the increase continued in 2004. The mantle-derived He content of the He released from the Changbaijulong springs increased obviously in 2004. The anomaly of the released gases and the isotopic He was consistent with the trends of seismic activities in the Tianchi volcanic area between 2002 and 2004. The abnormal release of the Jinjiang hot springs apparently decreased after the seismic activities ceased in the second half of 2004, while the abnormal release from the Changbaijulong increased significantly after these seismic activities. It shows that the abnormal release of magmas-derived gases from the thermal-reservoir-type springs lags behind that of the deep-fault-type springs. These characteristics may be of great significance for identifying deep magmatic activity and predicting volcanic earthquakes in the future. 相似文献
8.
Study on the carbonate ocelli-bearing lamprophyre dykes in the Ailaoshan gold deposit zone, Yunnan Province 总被引:1,自引:0,他引:1
Three carbonate ocelli-bearing lamprophyre dykes have been found in the Laowangzhai and Beiya gold orefields in the northern
sector of the Ailaoshan gold deposit zone, Yunnan Province. Ocelli in the lamprophyre dykes are carbonates composed mainly
of dolomite and calcite. Their trace elements, REE and C isotopic compositions are characteristic of carbonatite and the main
mineral assemblages, major elements, trace elements and REE in the matrix are similar to those in the carbonate ocelli-barren
lamprophyre dykes in the orefields, which are calc-alkaline lamprophyres that derived from the fertile mantle. The results
indicate that the carbonate ocelli-bearing lamprophyre dykes in this area were produced at the time when the Himalayan lamprophyre
magma evolved to a relatively late stage of silicate-carbonate liquid immiscibility. In the process of magmatic evolution
there took place magmatic degassing with CO2 and H2O as the dominant released gases. 相似文献
9.
Petrogenesis of the Mesozoic intrusive rocks in the Tongling area,Anhui Province,China and their constraint on geodynamic process 总被引:39,自引:0,他引:39
TheTonglingarea,whichiscalledtheChineseCopperCapital,isoneofthemostimportantnon-ferrousmetalproducersinChina(e.g.Cu,AuandAg,especiallyCu).ManyresearchershavenotedthatthemetaldepositsarecloselyrelatedtotheMesozoicintrusiverocksinthisarea.Therefore,theTongl… 相似文献
10.
Hsiao-Fen Lee Tsanyao Frank Yang Tefang Faith Lan Cheng-Hong Chen Sheng-Rong Song Shuhjong Tsao 《Journal of Volcanology and Geothermal Research》2008
Hydrothermal activity is common in the Tatun Volcano Group of northern Taiwan. Helium isotopic compositions of fumarolic samples show that mantle component occupies more than 60% in the previous study. Along with recent seismic results, a magma reservoir is inferred to have existed beneath the area of Da-you-keng, where fumarolic venting is the most active in Tatun Volcano Group. Progressive increases of HCl concentrations and SO2/H2S ratio in fumaroles from Da-you-keng have been observed since August 2004. The HCl concentration changed from almost the detection limit to thousands of ppm, even up to 30,000 ppm. SO2/H2S ratios varied from almost 0 to 3; hence SO2 became the dominated S species in this area. These variations were accompanied by rising temperature of fumaroles in the Tatun Volcano Group, especially in the area of Da-you-keng (from boiling point to 131 °C). Meanwhile, 3He/4He ratios showed a decreasing trend but returned to normal values shortly thereafter. We propose two possible processes, 1) new magma supply and 2) recent opening of fractures in local area, to explain these observations. Based on the change of 3He/4He ratio and lack of ground deformation, we consider the latter might be more plausible. 相似文献
11.
Takeshi Ohba Yasushi Daita Takeshi Sawa Noriyasu Taira Yusuke Kakuage 《Bulletin of Volcanology》2011,73(4):457-469
The chemical and isotopic compositions of volcanic gases at a borehole and a natural fumarole in the Owakudani geothermal
area, Hakone volcano, Japan, have been repeatedly measured since 2001, when a seismic swarm occurred in the area. The CO2/H2O and CO2/H2S ratios were high in 2001. It increased in 2006 and again in 2008 when seismic swarms occurred beneath the geothermal area.
The observed increases suggest the injection of CO2- and SO2-rich magmatic gas into the underlying hydrothermal reservoir, implying that the magmatic gas was episodically supplied to
the hydrothermal system in 2006 and 2008. The earthquake swarms probably resulted from the injection of gas through the shallow
crust accompanying the break of the sealing zone. 相似文献
12.
Giovanni Chiodini Stefano Caliro Giorgio Caramanna Domenico Granieri Carmine Minopoli Roberto Moretti Lavinia Perotta Guido Ventura 《Pure and Applied Geophysics》2006,163(4):759-780
The marine sector surrounding Panarea Island (Aeolian Islands, South Italy) is affected by widespread submarine emissions
of CO2 -rich gases and thermal water discharges which have been known since the Roman Age. On November 3rd, 2002 an anomalous degassing event affected the area, probably in response to a submarine explosion. The concentrations of
minor reactive gases (CO, CH4 and H2) of samples collected in November and December, 2002 show drastic compositional changes when compared to previous samples
collected from the same area in the 1980s. In particular the samples collected after the November 3rd phenomenon display relative increases in H2 and CO and a strong decrease in the CH4 contents, while other gas species show no significant change. The interaction of the original gas with seawater explains
the variable contents of CO2, H2S, N2, Ar and He which characterize the different samples, but cannot explain the large variations of CO, CH4 and H2 which are instead compatible with changes in the redox, temperature and pressure conditions of the system. Two models, both
implying an increasing input of magmatic fluids are compatible with the observed variations of minor reactive species. In
the first one, the input of magmatic fluids drives the hydrothermal system towards atypical (more oxidizing) redox conditions,
slowly pressurizing the system up to a critical state. In the second one, the hydrothermal system is flashed by the rising
high-T volcanic fluid, suddenly released by a magmatic body at depth. The two models have different implications for volcanic
surveillance and risk assessment: In the first case, the November 3rd event may represent both the culmination of a relatively slow process which caused the overpressurization of the hydrothermal
system and the beginning of a new phase of quiescence. The possible evolution of the second model is unforeseeable because
it is mainly related to the thermal, baric and compositional state of the deep magmatic system that is poorly known. 相似文献
13.
Marie-Lise Bernard Jack Molini Rose-Helen Petit Franois Beauducel Gilbert Hammouya Guy Marion 《Journal of Volcanology and Geothermal Research》2006,150(4):395-409
This paper presents the first remote measurements of La Soufrière gas emissions since the fumarolic and seismic reactivation in 1992. The chemical composition of the plumes has been measured from May 2003 to September 2004 using an Open Path Fourier Transform InfraRed (OP-FTIR) spectrometer, up to 15 m downwind the South Crater. HCl is clearly detected (concentration between 2.4 and 12 ppmv) whereas SO2 and H2S generally remain below the detection limit of the OP-FTIR. Direct measurements of SO2 and H2S near the South Crater with a Lancom III analyzer show a fast decrease of their concentrations with the distance. Calculated Cl / S mass ratios are high: from 9.4 ± 1.7 at 15 m from the vent to 2.8 ± 0.6 at 140 m. The enrichment in HCl of the gas emitted at La Soufrière, observed since 1998, corresponds to the degassing of a magma enriched in Cl and depleted in S. This result agrees with isotopic measurements which suggest a magmatic origin of the gases. Readjustments inside the volcanic system may have taken place during the seismic activity beginning in 1992 and enhance the transfer of magmatic gases to the summit. 相似文献
14.
Jean-Paul Toutain Jean-Claude Baubron Joseph Le Bronec Patrick Allard Pierre Briole Bernard Marty Gerarda Miele Dario Tedesco Giuseppe Luongo 《Bulletin of Volcanology》1992,54(2):147-155
The increasing activity of Vulcano Island (Italy) since 1985 led to the initiation of continuous geochemical monitoring of the lateral soil gas emissions. On the basis both of their relative geochemical characteristics and of local considerations, three gaseous components were selected for monitoring, namely CO2, He and 222Rn. Monitoring has been performed by means of specific analysers. Gases extracted from a water well located at the foot of the active cone were selected for monitoring, on the basis of their geochemical and isotopic characters that indicate their genetic link with central high temperature fumarolic gases emitted at the crater. Very strong variations of gas composition can be observed within one day (from 1 to about 94% for CO2). Some variations display a daily character and can be correlated with that of atmospheric pressure. The three monitored gases are highly correlated, suggesting very high kinetics of gas transfer in the system. Because of these considerable variations of chemical composition, bulk concentrations obviously are not suitable for monitoring at Vulcano. However, the evolution with time of ratios such as 222Rn/CO2 and He/CO2 (the latter being corrected for atmospheric contamination) supplies numerical parameters that the expected to characterize the intensity of the degassing process. A new input of magmatic gases, that would lead to an increase in the 222Rn/CO2 and He/CO2 ratios, should therefore be detected by such a monitoring station. 相似文献
15.
G.M. Sawyer C. Oppenheimer V.I. Tsanev G. Yirgu 《Journal of Volcanology and Geothermal Research》2008
Here we report measurements of the chemical composition and flux of gas emitted from the central lava lake at Erta 'Ale volcano (Ethiopia) made on 15 October 2005. We determined an average SO2 flux of ∼ 0.69 ± 0.17 kg s− 1 using zenith sky ultraviolet spectroscopy of the plume, and molar proportions of magmatic H2O, CO2, SO2, CO, HCl and HF gases to be 93.58, 3.66, 2.47, 0.06, 0.19 and 0.04%, respectively, by open-path Fourier transform infrared (FTIR) spectrometry. Together, these data imply fluxes of 7.3, 0.7, 0.008, 0.03 and 0.004 kg s− 1 for H2O, CO2, CO, HCl and HF, respectively. These are the first FTIR spectroscopic observations at Erta 'Ale, and are also some of the very few gas measurements made at the volcano since the early 1970s (Gerlach, T.M., 1980b. Investigation of volcanic gas analyses and magma outgassing from Erta 'Ale lava lake, Afar, Ethiopia. Journal of Volcanology and Geothermal Research, 7(3–4): 415–441). We identify significant increases in the proportion of H2O in the plume with respect to both CO2 and SO2 across this 30-year interval, which we attribute to the depletion of volatiles in magma that sourced effusive eruptions during the early 1970s and/or to fractional magma degassing between the two active pit craters located in the summit caldera. 相似文献
16.
Magmatic gas scrubbing: implications for volcano monitoring 总被引:1,自引:0,他引:1
R. B. Symonds T. M. Gerlach M. H. Reed 《Journal of Volcanology and Geothermal Research》2001,108(1-4)
Despite the abundance of SO2(g) in magmatic gases, precursory increases in magmatic SO2(g) are not always observed prior to volcanic eruption, probably because many terrestrial volcanoes contain abundant groundwater or surface water that scrubs magmatic gases until a dry pathway to the atmosphere is established. To better understand scrubbing and its implications for volcano monitoring, we model thermochemically the reaction of magmatic gases with water. First, we inject a 915°C magmatic gas from Merapi volcano into 25°C air-saturated water (ASW) over a wide range of gas/water mass ratios from 0.0002 to 100 and at a total pressure of 0.1 MPa. Then we model closed-system cooling of the magmatic gas, magmatic gas-ASW mixing at 5.0 MPa, runs with varied temperature and composition of the ASW, a case with a wide range of magmatic–gas compositions, and a reaction of a magmatic gas–ASW mixture with rock. The modeling predicts gas and water compositions, and, in one case, alteration assemblages for a wide range of scrubbing conditions; these results can be compared directly with samples from degassing volcanoes. The modeling suggests that CO2(g) is the main species to monitor when scrubbing exists; another candidate is H2S(g), but it can be affected by reactions with aqueous ferrous iron. In contrast, scrubbing by water will prevent significant SO2(g) and most HCl(g) emissions until dry pathways are established, except for moderate HCl(g) degassing from pH<0.5 hydrothermal waters. Furthermore, it appears that scrubbing will prevent much, if any, SO2(g) degassing from long-resident boiling hydrothermal systems. Several processes can also decrease or increase H2(g) emissions during scrubbing making H2(g) a poor choice to detect changes in magma degassing.We applied the model results to interpret field observations and emission rate data from four eruptions: (1) Crater Peak on Mount Spurr (1992) where, except for a short post-eruptive period, scrubbing appears to have drastically diminished pre-, inter-, and post-eruptive SO2(g) emissions, but had much less impact on CO2(g) emissions. (2) Mount St. Helens where scrubbing of SO2(g) was important prior to and three weeks after the 18 May 1980 eruption. Scrubbing was also active during a period of unrest in the summer of 1998. (3) Mount Pinatubo where early drying out prevented SO2(g) scrubbing before the climactic 15 June 1991 eruption. (4) The ongoing eruption at Popocatépetl in an arid region of Mexico where there is little evidence of scrubbing.In most eruptive cycles, the impact of scrubbing will be greater during pre- and post-eruptive periods than during the main eruptive and intense passive degassing stages. Therefore, we recommend monitoring the following gases: CO2(g) and H2S(g) in precursory stages; CO2(g), H2S(g), SO2(g), HCl(g), and HF(g) in eruptive and intense passive degassing stages; and CO2(g) and H2S(g) again in the declining stages. CO2(g) is clearly the main candidate for early emission rate monitoring, although significant early increases in the intensity and geographic distribution of H2S(g) emissions should be taken as an important sign of volcanic unrest and a potential precursor. Owing to the difficulty of extracting SO2(g) from hydrothermal waters, the emergence of >100 t/d (tons per day) of SO2(g) in addition to CO2(g) and H2S(g) should be taken as a criterion of magma intrusion. Finally, the modeling suggests that the interpretation of gas-ratio data requires a case-by-case evaluation since ratio changes can often be produced by several mechanisms; nevertheless, several gas ratios may provide useful indices for monitoring the drying out of gas pathways. 相似文献
17.
Rare gas constraints on hydrocarbon accumulation, crustal degassing and groundwater flow in the Pannonian Basin 总被引:2,自引:0,他引:2
C.J. Ballentine R.K. O'Nions E.R. Oxburgh F. Horvath J. Deak 《Earth and Planetary Science Letters》1991,105(1-3)
The isotopic composition and abundances of He, Ne and Ar have been measured in a sequence of vertically stacked gas reservoirs at Hajduszoboszlo and Ebes, in the Pannonian Basin of Hungary. The gas reservoirs occur at depths ranging from 727 to 1331 m, are CH4 dominated and occupy a total rock volume of approximately 1.5 km3. There are systematic variations in both major species abundances and rare gas isotopic composition with depth: CO2 and N2 both increase from 0.47 and 1.76% to 14.1 and 30.5%, respectively, and 40Ar/36Ar and 21Ne/22Ne increase systematically from 340 and 0.02990 at 727 m to 1680 and 0.04290 at 1331 m. A mantle-derived He component between 2 and 5% is present in all samples, the remainder is crustal-radiogenic He. The Ar and Ne isotope variations arise from mixing between atmosphere-derived components in groundwater, and crustally produced radiogenic Ar and Ne. The atmosphere-derived 40Ar and 21Ne decreases from 85 and 97% of the total 40Ar and 21Ne at 727 m to 18 and 68% at 1331 m. The deepest samples are shown to have both atmosphere-derived and radiogenic components close to the air-saturated water and radiogenic production ratios. The shallowest samples show significant fractionation of He/Ar and Ne/Ar ratios in atmosphere-derived and radiogenic rare gas components, but little or no fractionation of He/Ne ratios. This suggests that diffusive fractionation of rare gases is relatively unimportant and that rare gas solubility partitioning between CH4 and H2O phases controls the observed rare gas elemental abundances.The total abundance of atmosphere-derived and radiogenic rare gas components in the Hajduszoboszlo gas field place limits on the minimum volume of groundwater that has interacted with the natural gas, and the amount of crust that has degassed and supplied radiogenic rare gases. The radiogenic mass balance cannot be accounted for by steady state production either within the basin sediments or the basement complex since basin formation. The results require that radiogenic rare gases are stored at their production ratios on a regional scale and transported to the near surface with minimal fractionation. The minimum volume of groundwater required to supply the atmosphere-derived rare gases would occupy a rock volume of some 1000 km3 (assuming an average basin porosity of 5%), a factor of 670 greater than the reservoir volume. Interactions between groundwater and the Hajduszoboszlo hydrocarbons has been on a greater scale than often envisaged in models of hydrocarbon formation and migration. 相似文献
18.
Results are presented on scubadiving investigations carried out on thermal manifestations in the area of Panarea (Aeolian Islands). The area investigated falls inside a caldera which extends from the main island to the group of islets located to the northeast. The distribution of the gaseous manifestations is regulated by the NE-SW, NW-SE and N-S regional tectonic directrices, through which the more recent basic magma intruded, giving rise to dikes and pillow lavas. fO2-temperature relation of the gases sampled in the investigated area was calculated to be: logfO2 = 11−24,593/T which indicates that a buffering mechanism acted on the gases as they cooled down during their ascent. The high 3He/4He ratio (6 × 10−6) and the δ13C = −3.2%. (PDB), suggest the presence of a magmatic component in the gas feeding the investigated manifestations. The above relations and the almost constant high He/N2 ratio suggest that all the fumaroles are fed by the same deep hot fluids. On the basis of both the chemical characters of the fluids and the geothermo-barometric data, a deep geothermal body, having a temperature of about 240°C, is recognized. Two other shallower thermal aquifers, with a temperature of 170–210°C, are identified. A circulation pattern of the geothermal fluids is also proposed. On the basis of calculations regarding the convective energy released by the geothermal system of Panarea, and the magmatic mass responsible for the positive gravimetric anomaly of the area, it was estimated that the last volcanic activity took place less then 10,000 years ago. 相似文献
19.
J.F. Albert-Beltrn V. Araa J.L. Diez A. Valentin 《Journal of Volcanology and Geothermal Research》1990,43(1-4)
The Teide volcano (3717 m) is the central structure of the island of Tenerife and at present its morphology is that of a stratovolcano which has grown on a large caldera with a collapse 17 km in diameter, which was generated some 0.6 million years ago.The different studies that have been carried out seem to indicate that, in a oversimplified model, there is an intermediate magma chamber with an approximate volume of 30 km3 and located 2–3 km below the actual base of the caldera, i.e., almost at sea level, with a temperature of 430 ± 50°C, and a pressure of 400 ± 100 bar.The summit fumarole emissions are 85°C and are formed mainly of CO2 with small amounts of sulphur species, H2, CH4 and He. The water vapor (68–82%) emitted with the gases comes from the vaporization of a perched aquifer in the upper cone, as shown by the isotopic analyses. 相似文献
20.
Excess degassing of magmatic H2O and SO2 was observed at Izu-Oshima volcano during its latest degassing activity from January 1988 to March 1990. The minimum production rate for degassed magma was calculated to be about 1×104 kg/s using emission rates of magmatic H2O and SO2, and H2O and S contents of the magma. The minimum total volume of magma degassed during the 27-month period is estimated to be 2.6×108 m3. This volume is 20 times larger than that of the magma ejected during the 1986 summit eruption. Convective transport of magma through a conduit is proposed as the mechanism that causes degassing from a magma reservoir at several kilometers depth. The magma transport rate is quantitatively evaluated based on two fluid-dynamic models: Poiseuille flow in a concentric double-walled pipe, and ascent of non-degassed magma spheres through a conduit filled with degassed magma. This process is further tested for an andesitic volcano and is concluded to be a common process for volcanoes that discharge excess volatiles. 相似文献