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1.
Abstract The Shinanogawa Seismic Belt in the Northern Fossa Magna, Honshu Island, Japan, extends along the Shinano River, bounding the Eurasian Plate and the Okhotsk Plate. The geopressured hydrothermal system occurs widely in the Northern Fossa Magna region. Many destructive earthquakes are related to the activity of this system in the Shinanogawa Seismic Belt. Expulsion of a geopressured hydrothermal system and rising from depth along an active fault triggers the occurrence of an earthquake and opens the fault as a pathway. Anomalous areas in temperature, electrical conductivity and Cl– concentration of groundwater trend north–east in a linear distribution, and convincingly demonstrate the presence of a buried active fault at the epicentral area of the destructive earthquake in the Shinanogawa Seismic Belt. The distribution of the major axis of the anomalous area in groundwater temperature shows a strong positive relationship with earthquake magnitude, which means that the distribution of this area may indicate the scale of earthquake fault. The linearly anomalous areas in groundwater temperature, resulting from the percolation of a geopressured hydrothermal system, that have no record of previous destructive earthquake are predicted to be areas where destructive earthquakes could occur in the future. Four potential earthquake areas are proposed and discussed in this paper, based on re-examination of active faults and seismicity in the Shinanogawa Seismic Belt. 相似文献
2.
The 1995 Northern Niigata Earthquake with special attention to a geopressured hydrothermal system 总被引：1，自引：0，他引：1
The 1995 Northern Niigata Earthquake of magnitude (M) 5.5 occurred at the eastern margin of the Niigata seismic gap and might have been a precursor of a large destructive earthquake. The anomaly areas in temperature, electrical conductivity and Cl- concentration of groundwater were approximately coincident with the area of the seismic intensity 6 on the Japan Meteorological Agency scale, and convincingly demonstrated the presence of a buried active fault beneath the epicentral area, as was suggested by a linear distribution of seismic intensity 6. These anomalies of groundwater were created by the expulsion of geopressured hydrothermal water along an active fault. Anomalies in local groundwater and hotspring systems associated with the earthquake and the proximity of the earthquake to the Niitsu oil field led to an interpretation that the earthquake might have been triggered by activity within the geopressured hydrothermal system. The accumulation of geopressured hydrothermal water in combination with high rock temperature might reduce fracture strength of the rock, and trigger earthquake occurrence. 相似文献
3.
信浓川地震带位于日本大地沟北部,地壳运动十分强烈,区内地震主要沿信浓川流域发生,并密集成带,大地构造上处于日本海板块向本州板块俯冲的边界线上。该地震带大多数地震为中强震,且均为浅源地震,地震发生伴随着明显的地下水前兆异常,震中区有强烈的超压热水系的喷溢活动。震中区地下水的温度、电导率以及主要地球化学成分呈线性异常分布,并与地震强弱或地震断裂规模有关,地震断层的规模控制了超压热水系喷溢活动的强度和规模。地震发生与超压热水系喷溢活动有着密切的成生关系,超压热水系喷溢活动使断层发生活动所需应力条件降低,诱发地震发生,同时断层活动为超压热水系向上喷溢提供通道。 相似文献
4.
D.M. Han X. Liang M.G. Jin M.J. Currell X.F. Song C.M. Liu 《Journal of Volcanology and Geothermal Research》2010,189(1-2):92-104
This paper examines groundwater hydrochemical characteristics during mixing between thermal and non-thermal groundwater in low-to-medium temperature geothermal fields. A case study is made of Daying and Qicun geothermal fields in the Xinzhou basin of Shanxi province, China. The two geothermal fields have similar flow patterns, with recharge sourced from precipitation in mountain areas heated through a deep cycle, before flowing into overlying Quaternary porous aquifers via fractures. Hydrochemical features of 60 ground- and surface water samples were examined in the context of hydrogeologic information. The average temperatures of the deep geothermal reservoirs are estimated to be 125 °C in Daying field, and 159 °C in Qicun field, based on Na–K–Mg geothermometry, while slightly lower estimates are obtained using silica geothermometers. Hydrochemical features of thermal water are distinct from cold water. Thermal groundwater is mainly Cl·SO4–Na type, with high TDS, while non-thermal groundwater is mostly HCO3–Ca·Mg and HCO3–Ca type in the Daying and Qicun regions, respectively. Hydrogeochemical processes are characterized by analyzing ion ratios in various waters. Higher contents of some minor elements in thermal waters, such as F, Si, B and Sr, are probably derived from extended water–rock interaction, and these elements can be regarded as indicators of flow paths and residence times. Mixing ratios between cold and thermal waters were estimated with Cl, Na, and B concentrations, using a mass balance approach. Mixing between ascending thermal waters and overlying cold waters is extensive. The proportion of water in the Quaternary aquifer derived from a deep thermal source is lower in Daying geothermal field than in Qicun field (5.3–7.3% vs. 6.3–49.3%). Mixing between thermal and non-thermal groundwater has been accelerated by groundwater exploitation practices and is enhanced near faults. Shallow groundwater composition has also been affected by irrigation with low-temperature thermal water. 相似文献
5.
中低温对流型地热资源在华北地区广泛分布,是一种清洁的替代能源.与活动断裂带相关的水热型地热资源是中低温地热系统的重要组成部分.本文基于高精度重力测量、微动测深及钻孔温度测量等数据,从热源、通道、储层和盖层四个方面探讨了南口—孙河断裂带水热系统特征.低重力异常揭示的燕山期花岗二长岩、闪长岩岩体范围为23.8 km~2和14.3 km~2,放射性测井数据计算得到其生热率均值为3.14μW·m~(-3),侏罗系火山岩生热率均值为1.65μW·m~(-3),隐伏岩体和火山岩均难以构成地热系统的附加热源.重力异常显示南口—孙河断裂带宽度约500~800 m,断裂带切割蓟县系雾迷山组白云岩热储层.钻井温度曲线显示断裂带内水热活动强烈,说明该断裂带是导水、导热的重要通道.断裂带南西侧马池口一带第四系松散层与侏罗系火山岩形成了热储盖层,微动测深显示火山岩最大厚度约1500 m.综上源、通、储、盖四个要素分析,该地热系统为热传导一对流复合型,来自京西北山区的大气降水经远距离径流深循环吸收地层热量后沿南口—孙河断裂上移到达裂隙发育的白云岩地层中形成热水.总之,沿南口—孙河断裂带具备了良好的地热地质条件,可达到规模开采的条件. 相似文献
6.
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
7.
Peter Blattner 《Earth and Planetary Science Letters》1993,120(3-4):511-518
On account of the low porosity of the lithosphere, intracrustal fluids behave very differently from surface fluids, in that they are changing their geochemical and isotopic labels according to the geological environment. Given a heat source, meteoric waters can be supplied plentifully and their rates of throughput in geothermal systems are sufficiently high to exhaust the compositional signals of a given rock buffer. In contrast, fluids exsolved from magma, and subducted fluids, would be supplied at less than about one tenth of the meteoric rate over the life time of a system. Based on up-to-date flow models, the isotopic evolution of meteoric water interacting with crustal rock follows a curved to L-shaped track in the δD versus δ18O plot. Instantaneous (present-day) tie-lines between recharge and discharge are secants of such tracks and can have a range of slopes. At the start of an interaction, waters have δD and δ18O values approaching equilibrium with the original rock composition (water “W1”). Using known hydrogen isotope fractionation factors, W1 values generally plot in the region of “andesite” or “andesitic” waters of various authors. Since the W1 waters have δD values that are on average more positive, and also less variable than those of the meteoric recharges, most tracks and tie-lines have positive slopes, and the plotting of a large number of tie-lines will produce a focus on the field of W1 waters, regardless of the original water source. 相似文献
8.
9.
Recovery of hydrocarbons commonly is associated with coproduction of water. This water may be put to beneficial use or may be reinjected into subsurface aquifers. In either case, it would be helpful to establish a fingerprint for that coproduced water so that it may be tracked following discharge on the surface or reintroduction to geologic reservoirs. This study explores the potential of using δ13 C of dissolved inorganic carbon (DIC) of coalbed natural gas (CBNG)–coproduced water as a fingerprint of its origin and to trace its fate once it is disposed on the surface. Our initial results for water samples coproduced with CBNG from the Powder River Basin show that this water has strongly positive δ13 CDIC (12‰ to 22‰) that is readily distinguished from the negative δ13 C of most surface and ground water (−8‰ to −11‰). Furthermore, the DIC concentrations in coproduced water samples are also high (more than 100 mg C/L) compared to the 20 to 50 mg C/L in ambient surface and ground water of the region. The distinctively high δ13 C and DIC concentrations allow us to identify surface and ground water that have incorporated CBNG-coproduced water. Accordingly, we suggest that the δ13 CDIC and DIC concentrations of water can be used for long-term monitoring of infiltration of CBNG-coproduced water into ground water and streams. Our results also show that the δ13 CDIC of CBNG-coproduced water from two different coal zones are distinct leading to the possibility of using δ13 CDIC to distinguish water produced from different coal zones. 相似文献
10.
The purpose of this work was to study jointly the volcanic-hydrothermal system of the high-risk volcano La Soufrière, in
the southern part of Basse-Terre, and the geothermal area of Bouillante, on its western coast, to derive an all-embracing
and coherent conceptual geochemical model that provides the necessary basis for adequate volcanic surveillance and further
geothermal exploration. The active andesitic dome of La Soufrière has erupted eight times since 1660, most recently in 1976–1977.
All these historic eruptions have been phreatic. High-salinity, Na–Cl geothermal liquids circulate in the Bouillante geothermal
reservoir, at temperatures close to 250 °C. These Na–Cl solutions rise toward the surface, undergo boiling and mixing with
groundwater and/or seawater, and feed most Na–Cl thermal springs in the central Bouillante area. The Na–Cl thermal springs
are surrounded by Na–HCO3 thermal springs and by the Na–Cl thermal spring of Anse à la Barque (a groundwater slightly mixed with seawater), which are
all heated through conductive transfer. The two main fumarolic fields of La Soufrière area discharge vapors formed through
boiling of hydrothermal aqueous solutions at temperatures of 190–215 °C below the "Ty" fault area and close to 260 °C below
the dome summit. The boiling liquid producing the vapors of the Ty fault area has δD and δ18O values relatively similar to those of the Na–Cl liquids of the Bouillante geothermal reservoir, whereas the liquid originating
the vapors of the summit fumaroles is strongly enriched in 18O, due to input of magmatic fluids from below. This process is also responsible for the paucity of CH4 in the fumaroles. The thermal features around La Soufrière dome include: (a) Ca–SO4 springs, produced through absorption of hydrothermal vapors in shallow groundwaters; (b) conductively heated, Ca–Na–HCO3 springs; and (c) two Ca–Na–Cl springs produced through mixing of shallow Ca–SO4 waters and deep Na–Cl hydrothermal liquids. The geographical distribution of the different thermal features of La Soufrière
area indicates the presence of: (a) a central zone dominated by the ascent of steam, which either discharges at the surface
in the fumarolic fields or is absorbed in shallow groundwaters; and (b) an outer zone, where the shallow groundwaters are
heated through conduction or addition of Na–Cl liquids coming from hydrothermal aquifer(s).
Received: 9 November 1998 / Accepted: 15 July 1999 相似文献
11.
ULRICH SCHIMSCHAL 《Geophysical Prospecting》1991,39(2):279-291
An integrated exploration study is presented to locate low-temperature geothermal reservoirs in the Honey Lake area of northern California. Regional studies to locate the geothermal resources included gravity, infra-red, water-temperature, and water-quality analyses. Five anomalies were mapped from resistivity surveys. Additional study of three anomalies by temperature-gradient and seismic methods was undertaken to define structure and potential of the geothermal resource. The gravity data show a graben structure in the area. Seismic reflection data indicate faults associated with surface-resistivity and temperature-gradient data. The data support the interpretation that the shallow reservoirs are replenished along the fault zones by deeply circulating heated meteoric waters. 相似文献
12.
Abstract The variation of sulphur isotopic composition during the 2000 eruption of the Miyakejima Volcano was examined in order to monitor the temporal change of the volcanic activity. The δ34 S values of water-soluble sulphate leached from volcanic ash effused during intermittent eruptions from July to September 2005 range from +5 to +11‰ with a fluctuation of ca 3‰ within a single eruption. The δ34 S value of sulphuric acid mist collected with 'Cu-metal trap' placed on the flank of the volcano from December 2000 to January 2001 is +6.2‰. These sulphur isotopic compositions of sulphate, which were isotopically equilibrated in the subvolcanic hydrothermal system, indicate that the temperature of the hydrothermal system beneath the caldera increased after the period of intermittent phreatic and phreatomagmatic eruptions. Then, the δ34 S value of sulphuric acid trapped from January to March 2001 was +9.0‰ and the δ34 S value of water-soluble sulphate on volcanic ash emitted with minor eruption in May 2001 was +11.0‰, suggesting a decrease in temperature of the subvolcanic hydrothermal system. 相似文献
13.
D. C. McDonald 《Bulletin of Volcanology》1966,29(1):691-707
The ratios of D/H and O18/O16 in natural waters from streams, boreholes, soda springs, hot pools, ponds and larger bodies of water in the Ngawha hydrothermal area were determined. The results are considered in relation to the isotopic changes known to occur in water subjected to evaporation. Where applicable chemical and other work was also considered. It is assumed that stream water isotope composition is the mean value for the isotopic composition of meteoric waters. Measurements on waters taken from boreholes drilled to 65 feet and 350 feet and from the other water sources mentioned, indicate that they were of meteoric origin as judged by stream isotope composition. The waters from the soda springs appeared to be isotopically the same as the stream water, a finding consistent with the absence of evaporative surface. These borehole waters were similar but slightly different in O18 due probably to exchange between rock and water. Heavy isotope enrichment of the ponds and larger bodies of water appeared to be due to non-equilibrium evaporation at ambient temperature. The hot pools in the Ngawha springs area proper were enriched in the heavier isotopes probably due to non-equilibrium evaporation at the usual hot pool temperature of about 40°C and also to exchange of O18 between water and rock. The water from a further borehole drilled to approximately 2,000 feet appeared also to be of meteoric origin but was changed in O18 content to an extent consistent with the assumption that oxygen isotope exchange with rock had taken place at approximately 230°C. The results are used to illustrate possibilities for the use of oxygen and hydrogen isotope measurements in hydrothermal investigations. 相似文献
14.
Graeme L. Scott 《Island Arc》2004,13(2):370-386
Abstract The influence of major active faults on rock alteration and stable isotope geochemistry is described for the Tongonan geothermal field, Leyte, the Philippines. In the Pliocene, acid alteration with characteristic iron enrichment (3 g/100 g) and calcium depletion (2 g/100 g) occurred along a Riedel shear fault in the Malitbog sector, and initial minor acid alteration also occurred along a similar shear in the Mahiao sector. Later, sodium metasomatism (5 g/100 g) coincided with the highest aquifer chloride (10 000 mg/kg) as a result of dissociation of saline magmatic fluids discharging through the reservoir rocks in the Upper Mahiao. The incursion of magmatic fluids (possibly δD 35‰, δ18O +7‰) set up a vigorous convection cell of meteoric water, which focused around low‐angle (L) shears centered in the Sambaloran sector. Meteoric water (δD ?35 to ?40‰, δ18O ?6 ± 1‰) depleted the reservoir in silica (6 g/100 g) and potassium (1–2 g/100 g). It also completely exchanged oxygen isotopes rapidly (within months) at high temperatures (300–400°C), and now does so continuously with fractured isotopically fresh or incompletely altered rock at small scales (centimeters or less) exposed by a 2 cm/year creep around the L shears to form a new component called geothermal water. Geothermal water mixes with meteoric water at lower temperatures (<300°C) to create the characteristic shift in δ18O of 6‰ at near constant δD (?35 ± 5‰). The 10‰ variation in δD is due to groundwater recharge derived from rain falling on steep terrain (5‰) and to enrichment of deuterium in boiling saline solutions (5‰); it is not due to two‐component mixing of meteoric with magmatic water. The low (～1) isotopic water/rock (W/R) ratios calculated from oxygen isotopes in previously published reports are meaningless, because the water contains four components (predominantly geothermal and meteoric water; <10% magmatic and rock water). W/R ratios of up to 1500 calculated from spring and rock chemistry are more realistic and, with a flow rate of approximately 50 L/s through a 30 km3 reservoir, can account for the estimated 3 My age of the system. 相似文献
15.
Groundwater flow-paths through shallow-perch and deep-regional basaltic aquifers at the Golan Heights, Israel, are reconstructed by using groundwater chemical and isotopic compositions. Groundwater chemical composition, which changes gradually along flow-paths due to mineral dissolution and water–rock interaction, is used to distinguish between shallow-perched and deep-regional aquifers. Groundwater replenishment areas of several springs are identified based on the regional depletion in rainwater δ18O values as a function of elevation (−0.25‰ per 100 m). Tritium concentrations assist in distinguishing between pre-bomb and post-bomb recharged rainwater.
It was found that waters emerging through the larger springs are lower in δ18O than surrounding meteoric water and poor in tritium; thus, they are inferred to originate in high-elevation regions up to 20 km away from their discharge points and at least several decades ago. These results verify the numerically simulated groundwater flow field proposed in a previous study, which considered the geological configuration, water mass balance and hydraulic head spatial distribution. 相似文献
16.
Grant Heiken Napoleon Ramos Wendell Duffield John Musgrave Kenneth Wohletz Sue Priest James Aldrich Wilmer Flores Alexander Ritchie Fraser Goff Dean Eppler Carlos Escobar 《Journal of Volcanology and Geothermal Research》1991,45(1-2)
The Platanares geothermal area, Departamento de Copán, Honduras, is located within a graben that is complexly faulted. The graben is bounded on the north by a highland composed of Paleozoic (?) metamorphic rocks in contact with Cretaceous - Tertiary redbeds of unknown thickness. These are unconformably overlain by Tertiary andesitic lavas, rhyolitic ignimbrites, and associated sedimentary rocks. The volcanic rocks are mostly older than 14 Ma, and thus are too old to represent the surface expression of an active crustal magma body. Thermal fluids that discharge in the area are heated during deep circulation of meteoric water along faults in a region of somewhat elevated heat flow. Geothermometry based upon the chemical composition of thermal fluids from hot springs and from geothermal gradient coreholes suggests that the reservoir equilibrated at temperatures as high as 225 to 240°C, within the Cretaceous redbed sequence. Three continuously cored geothermal gradient holes have been drilled; fluids of about 165°C have been produced from two drilled along a NW-trending fault zone, from depths of 250 to 680 m. A conductive thermal gradient of 139°C/km, at a depth of 400 m, was determined from the third well, drilled 0.6 km west of that fault zone. These data indicate that the Platanares geothermal area holds considerable promise for electrical generation by moderate- to hightemperature geothermal fluids. 相似文献
17.
by Denis Cohen Mark Person Peng Wang Carl W. Gable Deborah Hutchinson ee Marksamer Brandon Dugan Henk Kooi Koos Groen Daniel Lizarralde Robert L. Evans Frederick D. Day-Lewis John W. Lane Jr. 《Ground water》2010,48(1):143-158
While the existence of relatively fresh groundwater sequestered within permeable, porous sediments beneath the Atlantic continental shelf of North and South America has been known for some time, these waters have never been assessed as a potential resource. This fresh water was likely emplaced during Pleistocene sea-level low stands when the shelf was exposed to meteoric recharge and by elevated recharge in areas overrun by the Laurentide ice sheet at high latitudes. To test this hypothesis, we present results from a high-resolution paleohydrologic model of groundwater flow, heat and solute transport, ice sheet loading, and sea level fluctuations for the continental shelf from New Jersey to Maine over the last 2 million years. Our analysis suggests that the presence of fresh to brackish water within shallow Miocene sands more than 100 km offshore of New Jersey was facilitated by discharge of submarine springs along Baltimore and Hudson Canyons where these shallow aquifers crop out. Recharge rates four times modern levels were computed for portions of New England's continental shelf that were overrun by the Laurentide ice sheet during the last glacial maximum. We estimate the volume of emplaced Pleistocene continental shelf fresh water (less than 1 ppt) to be 1300 km3 in New England. We also present estimates of continental shelf fresh water resources for the U.S. Atlantic eastern seaboard (104 km3 ) and passive margins globally (3 × 105 km3 ). The simulation results support the hypothesis that offshore fresh water is a potentially valuable, albeit nonrenewable resource for coastal megacities faced with growing water shortages. 相似文献
18.
Geochemical studies on cold meteoric waters, post-1980 hot spring waters, fumarole emissions from the dacite dome, and volcanic rocks at Mount St. Helens (MSH) from 1985 to 1989 show that magmatic volatiles are involved in the formation of a new hydrothermal system. Hot spring waters are enriched in 18O by as much as 2 and display enrichments in D relative to cold waters. A well-defined isotopic trend is displayed by the isotopic composition of a>400°C fumarole condensate collected from the central crater in 1980 (-33 D, +6 18O), of condensate samples collected on the dome, and of cold meteoric and hot spring waters. The trend indicates that mixing occurs between local meteoric water and magmatic water degassing from the dacite dome. Between 30 and 70% magmatic water is present in the dome fumarole discharges and 10% magnatic water has been added to the waters of the hydrothermal system. Relations between Cl, SO4 and HCO3 indicate that the hot spring waters are immature volcanic waters formed by reaction of rocks with waters generated by absorption of acidic volcanic fluids. In addition, the B/Cl ratios of the spring waters are similar to the B/Cl ratios of the fumarole condensates (0.02), values of 13C in the HCO3 of the hot springs (-9.5 to-13.5) are similar to the magmatic value at MSH (-10.5), and the 3He/4He ratio, relative to air, in a hot spring water is 5.7, suggesting a magmatic origin for this component.managed by Martin Marietta Energy Systems, Inc., under contract DE-AC05-84OR21400 with the US Department of Energy 相似文献
19.
Geothermal data analysis at the high-temperature hydrothermal area in Western Sichuan 总被引：2，自引：0，他引：2
Jian Zhang WuYang Li XianChun Tang Jiao Tian YingChun Wang Qi Guo ZhongHe Pang 《中国科学:地球科学(英文版)》2017,60(8):1507-1521
The western Sichuan hydrothermal area is located at the northeastern margin of the eastern syntaxis of the Qinghai-Tibet Plateau, which is also the eastern end of the Mediterranean-Himalayan geothermal activity zone. There are 248 warm or hot springs in this area, and 11 have temperatures beyond the local boiling temperature. Most of these hot springs are distributed along the Jinshajiang, Dege-Xiangcheng, Ganzi-Litang, and Xianshuihe faults, forming a NW-SE hydrothermal belt. A geothermal analysis of this high-temperature hydrothermal area is an important basis for understanding the deep geodynamic process of the eastern syntaxis of the Qinghai-Tibet Plateau. In addition, this study offers an a priori view to utilize geothermal resources, which is important in both scientific research and application. We use gravity, magnetic, seismic, and helium isotope data to analyze the crust-mantle heat flow ratio and deep geothermal structure. The results show that the background terrestrial heat flow descends from southwest to northeast. The crustal heat ratio is not more than 60%. The high temperature hydrothermal active is related to crustal dynamics processes. Along the Batang-Litang-Kangding line, the Moho depth increases eastward, which is consistent with the changing Qc/Qm(crustal/mantle heat flow) ratio trend. The geoid in the hydrothermal zone is 4–6 km higher than the surroundings, forming a local "platform". The NW-SE striking local tensile stress zone and uplift structure in the upper and middle crust corresponds with the surface hydrothermal active zone. There is an average Curie Point Depth(CPD) of 19.5–22.5 km in Batang, Litang, and Kangding. The local shear-wave(S-wave) velocity is relatively low in the middle and lower crust. The S-wave shows a low velocity trap(Vs3.2 km s.1) at 15–30 km, which is considered a high-temperature partial melting magma, the crustal source of the hydrothermal active zone. We conclude that the hydrothermal system in this area can be divided into Batang-type and Kangding-type, both of which rely on a crustal heating cycle of atmospheric precipitation and surface water along the fracture zone. The heat is derived from the middle and lower crust: groundwater penetrates the deep faults bringing geothermal energy back to the surface and forming high-temperature springs. 相似文献
20.
《Ground Water Monitoring & Remediation》2001,21(2):108-116
Pore water collected from piezometers installed in a thick clay-rich till were used to compare and evaluate four techniques for obtaining δD and δ18 O values in these media. The techniques included mechanical squeezing, centrifugation, azeotropic distillation, and a direct soil-water equilibration technique. Direct CO2 -core equilibration yielded sufficiently accurate and reproducible δ18 O results of pore water in clay-rich tills. In addition, this method eliminated the need for labor-intensive complete extraction of water from the geologic media. Mechanical squeezing and centrifugation produced results similar to direct equilibration. However, both of these methods exhibited a greater degree of variability and were laborious and more time consuming. Small differences in δ18 O values between piezometer water and equilibrated, squeezed, and centhfuged samples suggested that each method collected different fractions of the clay-water reservoir. Although these subtle differences were not conclusive, they did suggest the presence of weakly bound water and highlighted the difference between these three techniques for determining the stable isotopic composition of pore water in clay-rich aquitards. Azeotropic distillation produced a high level of discrepancy in δD andδ18 O results compared to the other methods. Incomplete extraction was considered the most probable cause of this error. The results of this study suggested that direct equilibration is the best method for determining detailed δD and δ18 O values of pore water in clay-rich aquitards. 相似文献