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1.
Geothermal resources are very rich in Yunnan, China. However, source of dissolved solutes in geothermal water and chemical evolution processes remain unclear. Geochemical and isotopic studies on geothermal springs and river waters were conducted in different petrological-tectonic units of western Yunnan, China. Geothermal waters contain Ca–HCO3, Na–HCO3, and Na (Ca)–SO4 type, and demonstrate strong rock-related trace elemental distributions. Enhanced water–rock interaction increases the concentration of major and trace elements of geothermal waters. The chemical compositions of geothermal waters in the Rehai geothermal field are very complicated and different because of the magma chamber developed at the shallow depth in this area. In this geothermal field, neutral-alkaline geothermal waters with high Cl, B, Li, Rb Cs, As, Sb, and Tl contents and acid–sulfate waters with high Al, Mn, Fe, and Pb contents are both controlled by magma degassing and water–rock interaction. Geothermal waters from metamorphic, granite, and sedimentary regions (except in the Rehai area) exhibit varying B contents ranging from 3.31 mg/L to 4.49 mg/L, 0.23 mg/L to 1.24 mg/L, and <0.07 mg/L, respectively, and their corresponding δ11B values range from −4.95‰ to −9.45‰, −2.57‰ to −8.85‰, and −4.02‰ to +0.06‰. The B contents of these geothermal waters are mainly controlled by leaching host rocks in the reservoir, and their δ11B values usually decrease and achieve further equilibrium with its surrounding rocks, which can also be proven by the positive δ18O-shift. In addition to fluid–rock reactions, the geothermal waters from Rehai hot springs exhibit higher δ11B values (−3.43‰ to +1.54‰) than those yielded from other areas because mixing with the magmatic fluids from the shallow magma. The highest δ11B of steam–heated waters (pH 3.25) from the Zhenzhu spring in Rehai is caused by the fractionation induced by pH and the phase separation of coexisting steam and fluids. Given the strong water–rock interaction, some geothermal springs in western Yunnan show reservoir temperatures higher than 180 °C, which demonstrate potential for electricity generation and direct-use applications. The most potential geothermal field in western Yunnan is located in the Rehai area because of the heat transfer from the shallow magma chamber.  相似文献   

2.
Chemical and isotopic data for 23 geothermal water samples collected in New Zealand within the Taupo Volcanic Zone (TVZ) are reported. Major and trace elements including Li, B and Sr and their isotopic compositions (δ7Li, δ11B, 87Sr/86Sr) were determined in high temperature geothermal waters collected from deep boreholes in different geothermal fields (Ohaaki, Wairakei, Mokai, Kawerau and Rotokawa geothermal systems). Lithium concentrations are high (from 4.5 to 19.9 mg/L) and Li isotopic compositions (δ7Li) are homogeneous, ranging between −0.5‰ and +1.4‰. In particular, it is noteworthy that, except for the samples from the Kawerau geothermal field having slightly higher δ7Li values (+1.4%), the other geothermal waters have a near constant δ7Li signature around a mean value of 0‰ ± 0.6 (2σ, n = 21). Boron concentrations are also high and relatively homogeneous for the geothermal samples, falling between 17.5 and 82.1 mg/L. Boron isotopic compositions (δ11B) are all negative, and display a range between −6.7‰ and −1.9‰. These B isotope compositions are in agreement with those of the Ngawha geothermal field in New Zealand. Lithium and B isotope signatures are in a good agreement with a fluid signature mainly derived from water/rock interaction involving magmatic rocks with no evidence of seawater input. On the other hand, Sr concentrations are lower and more heterogeneous and fall between 2 and 165 μg/L. The 87Sr/86Sr ratios range from 0.70549 to 0.70961. These Sr isotope compositions overlap those of the Rotorua geothermal field in New Zealand, confirming that some geothermal waters (with more radiogenic Sr) have interacted with bedrocks from the metasedimentary basement. Each of these isotope systems on their own reveals important information about particular aspects of either water source or water/rock interaction processes, but, considered together, provide a more integrated understanding of the geothermal systems from the TVZ in New Zealand.  相似文献   

3.
Zhang  Hongjie  Fan  Haifeng  Xiao  Chaoyi  Wen  Hanjie  Ye  Lin  Huang  Zhilong  Zhou  Jiaxi  Guo  Qingjun 《中国地球化学学报》2019,38(5):642-653

The Sichuan–Yunnan–Guizhou (SYG) metallogenic province of southwest China is one of the most important Zn–Pb ore zones in China, with ~ 200 Mt Zn–Pb ores at mean grades of 10 wt.% Zn and 5 wt.% Pb. The source and mechanism of the regional Zn–Pb mineralization remain controversial despite many investigations that have been conducted. The Wusihe Zn–Pb deposit is a representative large-scale Zn–Pb deposit in the northern SYG, which mainly occurs in the Dengying Formation and yields Zn–Pb resources of ~ 3.7 Mt. In this paper, Zn and S isotopes, and Fe and Cd contents of sphalerite from the Wusihe deposit were investigated in an attempt to constrain the controls on Zn and S isotopic variations, the potential sources of ore-forming components, and the possible mineralization mechanisms. Both the δ66Zn and δ34S values in sphalerite from the Wusihe deposit increase systematically from the bottom to the top of the strata-bound orebodies. Such spatial evolution in δ66Zn and δ34S values of sphalerite can be attributed to isotopic Rayleigh fractionation during sphalerite precipitation with temperature variations. The strong correlations between the Zn–S isotopic compositions and Fe–Cd concentrations in sphalerite suggest that their variations were dominated by a similar mechanism. However, the Rayleigh fractionation mechanism cannot explain the spatial variations of Fe and Cd concentrations of sphalerite in this deposit. It is noted that the bottom and top sphalerites from the strata-bound orebodies document contrasting Zn and S isotopic compositions which correspond to the Zn and S isotopic characteristics of basement rocks and host rocks, respectively. Therefore, the mixing of two-source fluids with distinct Zn–S isotopic signatures was responsible for the spatial variations of Zn–S isotopic compositions of sphalerite from the Wusihe deposit. The fluids from basement rocks are characterized by relatively lighter Zn (~ 0.2 ‰) and S (~ 5 ‰) isotopic compositions while the fluids from host rocks are marked by relatively heavier Zn (~ 0.6 ‰) and S (~ 15 ‰) isotopic compositions.

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4.
Large variations are reported in the B concentrations and isotopic ratios of river and thermal spring waters in Guadeloupe, Lesser Antilles. Rivers have δ11B values around 40‰ and B concentrations lower than 30 μg/L, while thermal springs have δ11B of 8–15‰ and B concentrations of 250–1000 μg/L. River samples strongly impacted by hydrothermal inputs have intermediate δ11B and B contents. None of these surface water samples have δ11B comparable to the local unweathered volcanic rocks (around 0‰), implying that a huge isotopic fractionation of 40‰ takes place during rock weathering, which could be explained by preferential incorporation of 10B during secondary mineral formation and adsorption on clays, during rock weathering or in the soils. The soil-vegetation B cycle could also be a cause for such a fractionation. Atmospheric B with δ11B of 45‰ represents 25–95% of the river B content. The variety of the thermal spring chemical composition renders the understanding of B behavior in Guadeloupe hydrothermal system quite difficult. Complementary geochemical tracers would be helpful.  相似文献   

5.
The Qiman Tagh W-Sn belt lies in the westernmost section of the East Kunlun Orogen, NW China, and is associated with early Paleozoic monzogranites, tourmaline is present throughout this belt. In this paper we report chemical and boron isotopic compositions of tourmaline from wall rocks, monzogranites, and quartz veins within the belt, for studying the evolution of ore-forming fluids. Tourmaline crystals hosted in the monzogranite and wall rocks belong to the alkali group, while those hosted in quartz veins belong to both the alkali and X-site vacancy groups. Tourmaline in the walk rocks lies within the schorl-dravite series and becomes increasingly schorlitic in the monzogranite and quartz veins. Detrital tourmaline in the wall rocks is commonly both optically and chemically zoned,with cores being enriched in Mg compared with the rims. In the Al-Fe-Mg and Ca-Fe-Mg diagrams,tourmaline from the wall rocks plots in the fields of Al-saturated and Ca-poor metapelite, and extends into the field of Li-poor granites, while those from the monzogranite and quartz veins lie within the field of Li-poor granites. Compositional substitution is best represented by the MgFe_(-1), Al(NaR)_(-1), and AlO(Fe(OH))_(-1) exchange vectors. A wider range of δ~(11)B values from -11.1‰ to -7.1‰ is observed in the wall-rock tourmaline crystals, the B isotopic values combining with elemental diagrams indicate a source of metasediments without marine evaporates for the wall rocks in the Qiman Tagh belt. The δ~(11)B values of monzogranite-hosted tourmaline range from -10.7‰ and-9.2‰, corresponding to the continental crust sediments, and indicate a possible connection between the wall rocks and the monzogranite. The overlap in δ~(11)B values between wall rocks and monzogranite implies that a transfer of δ~(11)B values by anataxis with little isotopic fractionation between tourmaline and melts. Tourmaline crystals from quartz veins have δ~(11)B values between -11.0‰ and-9.6‰, combining with the elemental diagrams and geological features, thus indicating a common granite-derived source for the quartz veins and little B isotopic fractionation occurred. Tourmalinite in the wall rocks was formed by metasomatism by a granite-derived hydrothermal fluid, as confirmed by the compositional and geological features.Therefore, we propose a single B-rich sedimentary source in the Qiman Tagh belt, and little boron isotopic fractionation occurred during systematic fluid evolution from the wall rocks, through monzogranite, to quartz veins and tourmalinite.  相似文献   

6.
Geothermal fields distributed in the southern Tibet Plateau rifts such as Yangbajing - Dangxiong basin, and the Yaluzangbu suture are characterized by intensive hydrothermal activity and high enrichment of trace elements (e.g., Li, Rb, Cs, B and Br) in geothermal springs. However, the origin of these elements and their enrichment mechanisms in those geothermal waters remain unclear. This study presents data for the enriched elements, incompatible elements, and B and Sr isotopes, in the geothermal water in the Tibetan Plateau and compares them with some typical geothermal fields worldwide, in an attempt to provide new insights into the origin and mechanism of the enrichment of these trace elements. The results indicate that all geothermal water samples from the Tibetan Plateau show more negative δ11B values than those from local precipitation and rivers. Considering the wide existence of a high-conductivity zone in the middle or even upper-crust interpreted to correspond to re-melt magmatic fluids in the Tibet, the main sources of the typical chemical composition of geothermal waters in the Tibetan Plateau can be classified into two main types: residual magmatic fluids derived from crustal partial remelting and deep circulated groundwater modified by water–rock interactions. In particular, the possible source of magmatic fluids may play a more significant role for special geochemical compositions of geothermal water in the Tibet. Such resources are beneficial for the development and utilization of the geothermal water itself and also serve as a stable source for feeding the salt lake resources.  相似文献   

7.
作为一种“非传统稳定同位素”,锂同位素地球化学研究已经成为近年来国际上研究的热点之一.文章成功应用锂同位素对青藏高原西南部赛利普超钾质火山岩进行了示范研究.研究表明,赛利普超钾质火出岩的w(Li)为11.2×10-6～22.9× 10-6,同位素组成δ7Li为1.2‰～+3.5‰,平均值为0 2‰,与平均上地壳的相当.超钾质火山岩的锂同位素组成与岩浆结晶分异程度参数之间不存在任何相关性,这表明在超钾质火山岩结晶分异过程中没有发生明显的锂同位素分馏,锂同位素组成特征反映了其形成时的源区特征.超钾质火山岩的锂同位素组成变化范围达4.7‰,并且与pb-Sr-Nd同位素和岩浆结晶分异参数之间亦无任何相关性,表明锂同位素异常可能反映了不均匀源区岩石特征.通过计算模拟以及与前人的类似研究成果进行对比,笔者认为俯冲印度地壳而不是特提斯洋壳(包括沉积物)的流体/熔体参与了超钾质火山岩的源区富集,并在此基础上提出了超钾质火山岩成因模式.  相似文献   

8.
The Cangyuan Pb-Zn-Ag polymetallic deposit is located in the Baoshan Block, southern Sanjiang Orogen. The orebodies are hosted in low-grade metamorphic rocks and skarn in contact with Cenozoic granitic rocks. Studies on fluid inclusions (FIs) of the deposit indicate that the ore-forming fluids are CO2-bearing, NaCl-H2O. The initial fluids evolved from high temperatures (462–498 °C) and high salinities (54.5–58.4 wt% NaCl equiv) during the skarn stage into mesothermal (260–397 °C) and low salinities (1.2–9.5 wt% NaCl equiv) during the sulfide stage. The oxygen and hydrogen isotopic compositions (δ18OH2O: 2.7–8.8‰; δD: −82 to −120‰) suggest that the ore-forming fluids are mixture of magmatic fluids and meteoric water. Sulfur isotopic compositions of the sulfides yield δ34S values of −2.3 to 3.2‰; lead isotopic compositions of ore sulfides are similar to those of granitic rocks, indicating that the sulfur and ore-metals are derived from the granitic magma. We propose that the Cangyuan Pb-Zn-Ag deposit formed from magmatic hydrothermal fluids. These Cenozoic deposits situated in the west of Lanping-Changdu Basin share many similarities with the Cangyuan in isotopic compositions, including the Laochang, Lanuoma and Jinman deposits. This reveals that the Cenozoic granites could have contributed to Pb-Zn-Cu mineralization in the Sanjiang region despite the abundance of Cenozoic Pb-Zn deposits in the region, such as the Jingding Pb-Zn deposit, that is thought to be of basin brine origin.  相似文献   

9.
《Applied Geochemistry》1996,11(3):471-479
Thermal waters with discharge temperatures ranging from 32 to 70°C are being discharged along the Gulf of Suez (Egypt) from springs and shallow artesian wells. A comprehensive chemical and isotopic study of these waters supports previous suggestions that the waters are paleometeoric waters from the Nubian sandstone aquifer. The chemical and isotopic compositions of solutes indicate possible contributions from Tertiary sedimentary aquifer rocks and windblown deposits (marine aerosols and/or evaporite dust) in the recharge area. There is no chemical or isotopic evidence for mixing with Red Sea water. Gas effervescence from the Hammam Faraoun thermal water contains about 4% CH4 (δ13C = −32.6‰) and 0.03% He having an isotopic ratio consistent with a mixture of crustal and magmatic He (3He/4He = 0.26 Re). Geothermometers for the thermal waters indicate maximum equilibration temperatures near 100°C. The waters could have been heated by percolation to a depth of several km along the regional geothermal gradient.  相似文献   

10.
The Burma Terrane is a microplate at the eastern edge of the Tibetan-Himalayan orogen, the origin of which remains poorly understood. Its basement comprises metamorphic and igneous rocks forming the Wuntho-Popa Arc (WPA) and has been correlated with Tibetan, Gondwana or Transtethyan rocks. Yet, little is known about the magmatic history of the WPA. We report elemental and Sr-Nd isotopic compositions of magmatic rocks, crystallization (zircon and apatite U-Pb) and exhumation (apatite fission-track) ages from rocks and river sands, and structural measurements from the Wuntho Ranges, central Myanmar, where the WPA is best exposed. We show that the WPA in the Wuntho Ranges is characterized by two magmatic events at 108–90 Ma and 46–32 Ma. Magmatism is subduction-related for both events, characterized by depleted Nd and Sr isotopic compositions, with more enriched values with time. Apatite fission-track data suggest arc exhumation during the 39–22 Ma time interval, partly overlapping with the last magmatic event. Structural data indicate NW-SE-striking tilting, folding, and thrusting that we associate with at least two phases of deformation, in the Cretaceous and the late Paleogene. Correlating the WPA with Tibetan, Gondwana or Transtethyan rocks based on its magmatic history remains ambiguous; however, models arguing for a Transtethyan origin for the WPA are most compatible with our results combined with available Burmese geological data.  相似文献   

11.
Chemical and isotopic data were measured for 51 leached brine springs in the Changdu-Lanping-Simao Basin (CD-LP-SM), China. The predominance of Cl and Na, saturation indices of carbonate minerals, and Na/Cl and Ca/SO4 ratios of ~1 suggest that halite, sulphate, and carbonate are the solute sources. Integration of geochemical, δ18O, and δD values suggests that springs are mainly derived from meteoric water, ice-snow melt, and water-rock interactions. B concentrations range from 0.18 to 11.9 mg/L, with δ11B values of ?4.37‰ to +32.39‰, indicating a terrestrial source. The δ11B-B relationships suggest B sources of crustal origin (marine carbonates with minor crust-derived volcanics); we did not identify a marine or deep mantle origin. The δ11B values of saline springs (+4.61‰ to +32.39‰) exceed those of hot (?4.37‰ to +4.53‰) and cold (?3.47‰ to +14.84‰) springs; this has contributed to strong water-rock interactions and strong saturation of dissolved carbonates. Conversely, the global geothermal δ11B-Cl/B relationship suggests mixing of marine and non-marine sources. The δ11B-Cl/B relationships of the CD-LP-SM are similar to those of the Tibet geothermal belt and the Nangqen Basin, indicating the same B origin. These differ from thermal waters controlled by magmatic fluids and seawater, suggesting that B in CD-LP-SM springs has a crustal origin.  相似文献   

12.
《Applied Geochemistry》2003,18(4):615-627
A study was conducted at the Fresh Kills landfill, Staten Island, New York to investigate the use of B and Li isotopes as tracers of mixing and flow in the groundwater environment. Four end-member waters are present at the Fresh Kills: freshwater, seawater, a geochemically distinct transitional groundwater (that occurs in the zone of mixing between seawater and freshwater) and landfill leachate. The δ11B and δ6Li values of end-member waters are distinct and have isotopic compositions that reflect the solute sources: freshwater δ11B∼+30‰, δ6Li∼−22‰; transition zone groundwaters δ11B∼+20‰, δ6Li∼−27‰; seawater δ11B+40 to +75‰, δ6Li−37 to−44‰; leachate δ11B∼+10‰ (δ6Li not determined). Those wells influenced by seawater exhibited a clear chemical mixing trend, with seawater contributions ranging from 3 to 85%. Well waters with a high percentage of seawater (>30%) had δ11B values that were within 1‰ of the seawater value (+40‰), whereas a trend of increasing δ11B values (+55 to +75‰) was observed for wells with a lower percentage of seawater (<30%). δ6Li values for well waters impacted by mixing with seawater ranged from−37 to−44‰, significantly more negative than pure seawater (−31‰). This deviation from the isotopic composition of seawater, for both δ11B and δ6Li values, represents non-conservative behavior and is likely the result of isotopic fractionation during ion exchange reactions. The wide range of δ11B and δ6Li values and the distinct isotopic compositions of end-member waters makes B and Li isotopes useful for recognizing solute sources, however isotopic fractionation may limit their use as simple tracers of groundwater flow and mixing.  相似文献   

13.
The Houxianyu borate deposit in northeastern China is one of the largest boron sources of China, hosted mainly in the Paleoproterozoic meta-volcanic and sedimentary rocks (known as the Liaohe Group) that are characterized by high boron concentrations. The borate ore-body has intimate spatial relationship with the Mg-rich carbonates/silicates of the Group, with fine-grained gneisses (meta-felsic volcanic rocks) as main country rocks. The presence of abundant tourmalinites and tourmaline-rich quartz veins in the borate orebody provides an opportunity to study the origin of boron, the nature of ore-forming fluids, and possible mineralization mechanism. We report the chemical and boron isotopic compositions of tourmalines from the tourmaline-rich rocks in the borate deposit and from the tourmaline-bearing fine-grained gneisses.Tourmalines from the fine-grained gneisses are chemically homogeneous, showing relatively high Fe and Na and low Mg, with δ11B values in a narrow range from +1.22‰ to +2.63‰. Tourmalines from the tourmaline-rich rocks, however, commonly show compositional zoning, with an irregular detrital core and a euhedral overgrowth, and have significantly higher Mg, REE (and more pronounced positive Eu anomalies), V (229–1852 ppm) and Sr (208–1191 ppm) than those from the fine-grained gneisses. They show varied B isotope values ranging from +4.51‰ to +12.43‰, which plot intermediate between those of the terrigenous sediments and arc rocks with low boron isotope values (as represented by the δ11B = +1.22‰ to +2.63‰ of the fine-grained gneisses of this study) and those of marine carbonates and evaporates with high boron isotope values. In addition, the rim of the zoned tourmaline shows notably higher Mg, Ti, V, Sn, and Pb, and REE (particularly LREEs), but lower Fe, Co, Cr, Ni, Zn, Mn, and lower δ11B values than the core. These data suggest that (1) the sources of boron of the borate ore-body are mainly the Paleoproterozoic meta-volcanic and sedimentary rocks, and (2) the ore-forming fluids should be the high temperature metamorphic fluids related to the amphibolite-facies metamorphism of the Paleoproterozoic foldbelt, which leach boron from the boron-rich meta-volcanic and sedimentary rocks of the Liaohe Group, and the boron-rich metamorphic fluids subsequently interacted with the marine Mg-rich carbonates and evaporates, forming borate deposit, the tourmaline overgrowth in the rim and the tourmaline-rich rocks.  相似文献   

14.
This contribution reports our preliminary work to determine Cu isotope ratios for various granite rocks and examine the Cu isotope systematics within granite suites. A chemical procedure, modified from Maréchal [Maréchal, C.N., Télouk, P. and Albarède, F., 1999. Precise analysis of copper and zinc isotopic compositions by plasma-source mass spectrometry. Chemical Geology, 156(1–4): 251–273.], was used to separate Cu from rock matrix. Quantitative recovery (100.6 ± 1.6%), with a low total procedural blank (2.65 ± 0.66 ng) for Cu, has been achieved, allowing Cu isotopic measurements on samples with as little as 10 ppm Cu. The Cu isotope ratios (δ65Cu relative to NIST SRM 976) of 32 rock samples, ranging from mafic to felsic compositions, from 3 batholiths (2 I-type, 1 S-type) from the Lachlan Fold Belt in southeastern Australia, vary from ? 0.46‰ to 1.51‰. Most of them cluster around zero, with mean values for the I-type and S-type granites of 0.03 ± 0.15‰ and ? 0.03 ± 0.42‰ (2 sigma) respectively. These data, together with Cu isotope ratios of two loess samples, provide preliminary evidence that the baseline Cu isotopic composition of the crystalline part of upper continental crust is close to zero. The tight clustering of Cu isotope ratios of rocks from the I-type suites suggests that high-temperature magmatic processes do not produce significant Cu isotope fractionation. However, two granites with abnormally heavy Cu isotope signatures (up to 1.51‰) appears to be the result of localized hydrothermal alteration. Measurable variation in Cu isotopic composition of the S-type granite may reflect isotopic heterogeneity in the sedimentary source region as a result of redox processes or may be due to hydrothermal overprinting. Thus, Cu isotope geochemistry may be a useful tracer for studying hydrothermal alteration and source heterogeneity of granitic rocks.  相似文献   

15.
Magnesium isotopic compositions, along with new Sr–Nd–Pb isotopic data and elemental analyses, are reported for 12 Miocene tourmaline-bearing leucogranites, 15 Eocene two-mica granites and 40 metamorphic rocks to investigate magnesium isotopic behaviors during metamorphic processes and associated magmatism and constrain the tectonic-magmatic-metamorphic evolution of the Himalayan orogeny. The gneisses, granulites and amphibolites represent samples of the Indian lower crust and display large range in δ26Mg from −0.44‰ to −0.09‰ in mafic granulites, −0.44‰ to −0.10‰ in amphibolites, and −0.70‰ to −0.03‰ in granitic gneisses. The average Mg isotopic compositions of the granitic gneisses (−0.19 ± 0.34‰), mafic granulites (−0.22 ± 0.17‰) and amphibolites (−0.25 ± 0.24‰) are similar, indicating the limited Mg isotope fractionation during prograde metamorphism from granitic gneisses to mafic granulites and retrograde metamorphism from mafic granulites to amphibolites. The Eocene two-mica granites and Miocene leucogranites are characterized by large variations in elemental and Sr–Nd–Pb isotopic compositions. The leucogranites and two-mica granites have their corresponding (87Sr/86Sr)i varying from 0.7282 to 0.7860 and 0.7163 to 0.7191, (143Nd/144Nd)i from 0.511888 to 0.512040 and 0.511953 to 0.512076, 207Pb/204Pb from 15.7215 to 15.7891 and 15.7031 to 15.7317, 208Pb/204Pb from 38.8521 to 39.5286 and 39.2710 to 39.4035, and 206Pb/204Pb from 18.4748 to 19.0139 and 18.7834 to 18.9339. However, they have similar Mg isotopic compositions (−0.21‰ to +0.06‰ versus −0.24‰ to +0.09‰), which did not originate from fractional crystallization nor source heterogeneity. Based on hornblende/biotite/muscovite dehydration melting reaction and Mg isotopic variations in two-mica granites and leucogranites with the proceeding metamorphism, along with elemental discrimination diagrams, Eocene two-mica granites and Miocene leucogranites could be related to hornblende dehydration melting and muscovite dehydration melting, respectively. Mg isotopic compositions of Eocene two-mica granites become heavier compared to the source because of residues of isotopically light garnet in the source; while those of Miocene leucogranites become lighter because of entrainment of isotopically light garnet from the source region. Thus, a new model for crustal anatexis and Himalayan orogenesis was proposed based on the Mg isotope fractionation in the leucogranites and metamorphic rocks. This model emphasizes a successive process from Indian continental subduction to rapid exhumation of the Higher Himalayan Crystalline Series (HHCS). The former underwent high-temperature (HT) and high-pressure (HP) granulite-facies prograde metamorphism, which resulted in the hornblende dehydration melting and the formation of Eocene two-mica granites; while the latter experienced amphibolite-facies retrogression and decompression, which resulted in the muscovite dehydration melting and the formation of Miocene leucogranites.  相似文献   

16.
为探究青藏高原搭格架地热区地热水、湖水、河水、冰雪融水等天然水体的水化学组成及物质来源控制因子,于2014年8月对该地区进行了考察和取样。利用紫外-可见光分光光度计和ICP-OES测定了水样中各阴、阳离子含量,利用Gas Bench连接同位素质谱仪测定了水样中溶解无机碳（DIC）同位素比值。结果表明,地热水中总溶解固体（TDS）含量为977.13~1 279.50 mg/L,阳离子以K+和Na+为主,阴离子以HCO3-和Cl-为主,湖水的TDS含量为77.81~810.94 mg/L,阳离子以Na+和Ca2+为主,阴离子以HCO3-(CO32-)和SO42-为主,地热水和湖水的水化学类型为HCO3-Na型;河水和冰雪融水的各离子含量较低,水化学类型为HCO3-Ca型;地热水的DIC浓度范围为9.2~15.4 mmol/L,δ13CDIC值为-9.09‰~-0.95‰;湖水的DIC浓度为1.1~9.7 mmol/L,δ13CDIC值为-8.84‰~-0.27‰。根据水化学Gibbs分布模式图判断出区域水化学特征主要受硅酸盐岩风化控制,以钠长石和钾长石风化为主,但是地热水的水化学组分受到硅酸盐岩和蒸发盐岩共同控制。通过碳同位素比值分析对区域主要风化过程中CO2的来源示踪表明,湖区周围的硅酸盐风化其碳源主要为土壤CO2,热泉区硅酸盐水解其碳源为地球深部CO2输入。   相似文献   

17.
The Han-Xing iron mineralization in the central North China Craton is a typical Fe skarn deposit associated with altered diorites. Here we report the Fe isotopic compositions of whole rocks and mineral separates from this deposit with a view to evaluate the Fe isotope fractionation during the formation of Fe skarn deposit, and to constrain the metal source. The Fe isotopes show a large variation both in whole rocks and mineral separates. Altered diorites show a wide range in δ56Fe values (− 0.07‰ to + 0.21‰ relative to the Fe isotope standard IRMM-014) which positively correlate with their TFe2O3/TiO2 ratios (Fe2O3 and FeO calculated as TFe2O3). The positive correlation indicates that heavy Fe isotopes were preferentially leached from diorites during the skarn-type alteration. Among the metallic minerals, pyrite and pyrrhotite are isotopically heavier (+ 0.12‰ to + 0.48‰) than the magnetite (+ 0.07‰ to + 0.21‰). Fe isotope fractionation between mineral pairs demonstrates that magnetite did not attain Fe isotopic equilibrium with pyrite and pyrrhotite, whereas pyrite and pyrrhotite might have attained isotopic equilibrium. Petrological observations and major element data also suggest that iron was leached from the diorites during the skarn-type alteration. If the leached iron provides the main Fe budget of the Han-Xing Fe skarn deposit, magnetite in ores would be isotopically heavier than the unaltered diorite. However, our results are in contrast with the magnetite being isotopically lighter than the unaltered diorite. This suggests that the major Fe source of the Han-Xing Fe skarn deposit is not from the leaching of diorites, and might be from magmatic fluid which is isotopically lighter than the silicate melt. Our data demonstrate that Fe isotopes can be used as important tracers in deciphering the metal source of Fe skarn deposits.  相似文献   

18.
腾冲地热区高温热泉水中稀土元素特征   总被引：2，自引：2，他引：0  
腾冲地热区位于印度-欧亚板块碰撞带东北缘,构造和岩浆活动频繁,地热作用明显,热泉广泛分布,是现代热泉研究的天然实验室。热泉水中的稀土元素特征是指示浅层水岩反应的重要指标。由于热泉水中稀土元素含量较低且变化范围大,腾冲地区热泉水稀土元素组成的报道比较罕见。本文尝试研究了腾冲高温热泉水中稀土元素组成特征,并与美国内华达州贝奥沃韦地热田和加利福尼亚希伯地热田热泉水的稀土元素特征进行了对比。本文选取腾冲地区的高温热泉,应用ICP-MS,测试了热泉水中稀土元素。分析结果表明热泉水中稀土元素含量相对较低且变化范围较大,其变化范围为球粒陨石的10-5～10-2倍。稀土元素球粒陨石标准化配分模式整体为轻微右倾型或平坦型,显示轻重稀土分异不明显;δEu既有正异常也有负异常;各热泉点热泉水稀土配分模式之间存在差异。虽然腾冲地热区热泉水的REE含量比美国贝奥沃韦地热田和希伯地热田热泉水的高10倍,两者之间的稀土元素分布特征具有一致性。热泉水中的δEu负异常为深循环的大气降水与具有负铕异常火山岩水岩反应的结果,正铕异常可能是由快速上返的大气降水与蒸发岩中的石膏反应导致。  相似文献   

19.
Over the last decade it has become apparent that Li isotopes may be a good proxy to trace silicate weathering. However, the exact mechanisms which drive the behaviour of Li isotopes in surface environments are not totally understood and there is a need to better calibrate and characterize this proxy. In this study, we analysed the Li concentrations and isotopic compositions in the various surface reservoirs (soils, rocks, waters and plants) of a small forested granitic catchment located in the Vosges Mountains (Strengbach catchment, France, OHGE http://ohge.u-strasbg.fr). Li fluxes were calculated in both soil profiles and at the basin scale and it was found that even in this forested basin, atmospheric inputs and litter fall represented a minor flux compared to input derived from the weathering of rocks and soil minerals (which together represent a minimum of 70% of dissolved Li). Li isotope ratios in soil pore waters show large depth dependent variations. Average dissolved δ7Li decreases from −1.1‰ to −14.4‰ between 0 and −30 cm, but is +30.7‰ at −60 cm. This range of Li isotopic compositions is very large and it encompasses almost the entire range of terrestrial Li isotope compositions that have been previously reported. We interpret these variations to result from both the dissolution and precipitation of secondary phases. Large isotopic variations were also measured in the springs and stream waters, with δ7Li varying from +5.3‰ to +19.6‰. δ7Li increases from the top to the bottom of the basin and also covaries with discharge at the outlet. These variations are interpreted to reflect isotopic fractionations occurring during secondary phase precipitation along the water pathway through the rocks. We suggest that the dissolved δ7Li increases with increasing residence time of waters through the rocks, and so with increasing time of interaction between waters and solids. A dissolution precipitation model was used to fit the dissolved Li isotopic compositions. It was found that the isotopic compositions of springs and stream waters are explicable by an isotopic fractionation of −5‰ to −14‰ (best fit −10.8‰), in agreement with Li incorporation into clay. In soil solutions, it was found that isotopic fractionation during secondary precipitation is larger (at least −23‰), suggesting a major role for different secondary phases, such as iron oxides that maybe incorporate Li with a higher isotope fractionation.  相似文献   

20.
 In order to investigate the application of the elemental abundance of boron and its stable isotopes, 10B and 11B, for tracing anthropogenic contamination of variably mineralized thermal and mineral waters, B concentrations and isotopic compositions (δ11B) were determined for sample pairs collected during surveys in 1984–1986 and 1995 from representative wells discharging water from deep crustal reservoirs within the central European crystalline basement and sedimentary cover (SW Germany and N Switzerland). The data presented show that natural temporal variations in the total B contents of thermal and mineral waters are a common feature, which makes it difficult to recognize admixture of extraneous (anthropogenic) components from B concentrations alone. Delineation of the natural versus anthropogenic origin of solutes and quantification of the relative mixing proportions may thus benefit considerably from the utilization of boron isotopes as an additional parameter. Hypothetical mixing scenarios involving various thermal waters and municipal wastewater effluents from the study area, with the latter being characterized by conspicuously light boron isotopic compositions, reveal that, in certain cases, δ11B values provide a superior diagnostic tool for detection of objectionable substances derived from the discharge of man-made boron products. Received: 14 September 1999 · Accepted: 8 March 2000  相似文献   

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