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1.
Ice core δ18O records from the No. 1 glacier at the head of the ürümqi River were used to characterize the relationship between δ18O and contemporaneous surface air temperature (Ta) nearby the Daxigou Meteorological Station (3539 m above sea level, ∼2km away from the ice core drilling site). Although the ice core records of annually averaged δ18O are positively correlated with contemporaneous surface air temperature, especially summer air temperature, the correlation is less significant than that for the precipitation samples due to depositional and post-depositional modification processes. However, the climatological significance of the ice core δ18O records can be still preserved to a certain degree, which might extend the application of high altitude and sub-tropical ice core δ18O records to paleoclimate reconstruction. 相似文献
2.
M. K. Bera Kasturi Bhattacharya A. Sarkar A. Samanta Kishor Kumar Ashok Sahni 《Journal of the Geological Society of India》2010,76(3):275-282
Oxygen isotope composition (δ18O) of fossil bone and tooth enamel phosphate (bioapatite) is an important tool for estimating the isotopic composition of
past environmental water. Lack of analytical facility was a hindrance for studying such bioapatites in spite of large number
of fossil materials reported from various geological ages in India. We have established in our laboratory, based on available
methods, the chemical procedure for extraction of very small amount (<1000 μg) PO4
−3 from bioapatite and on-line mass spectrometric measurement of its δ18O composition by high temperature (∼1450°C) pyrolysis. The achieved precision is ∼± 0.3 ‰ similar to obtained elsewhere, with
interlaboratory calibration showing excellent agreement of standard phosphates. Inferred δ18O values of environmental water, based on the analysis of teeth and bones of sharks, fish and terrestrial mammals from the
Paleogene successions of the northwest sub-Himalayan and the Peninsular India show strong correspondence with animal habitats.
The freshwater δ18O values are much depleted having range similar to modern monsoon precipitation. However, owing to our small dataset it is
not possible at this stage to infer about the existence of monsoon over the Indian sub-continent during the Eocene-Oligocene
time. 相似文献
3.
V. N. Nijampurkar D. K. Rao H. B. Clausen M. K. Kaul A. Chaturvedi 《Journal of Earth System Science》2002,111(1):39-49
The depth profiles of electrical conductance, δ18O,210Pb and cosmogenic radio isotopes10Be and36Cl have been measured in a 30 m ice core from east Antarctica near the Indian station, Dakshin Gangotri. Using210Pb and δ18O, the mean annual accumulation rates have been calculated to be 20 and 21 cm of ice equivalent per year during the past ∼
150 years. Using these acumulation rates, the volcanic event that occurred in 1815 AD, has been identified based on electrical
conductance measurements. Based on δ18O measurements, the mean annual surface air temperatures (MASAT) data observed during the last 150 years indicates that the
beginning of the 19th century was cooler by about 2‡ C than the recent past and the middle of 18th century. The fallout of
cosmogenic radio isotope10Be compares reasonably well with those obtained on other stations (73‡ S to 90‡ S) from Antarctica and higher latitudes beyond
77‡N. The fallout of36Cl calculated based on the present work agrees well with the mean global production rate estimated earlier by Lal and Peters
(1967). The bomb pulse of36Cl observed in Greenland is not observed in the present studies – a result which is puzzling and needs to be studied on neighbouring
ice cores from the same region. 相似文献
4.
Åke Fagereng Chris Harris Mandy La Grange Gary Stevens 《Contributions to Mineralogy and Petrology》2008,155(1):63-78
The Vredefort dome in the Kaapvaal Craton was formed as a result of the impact of a large meteorite at 2.02 Ga. The central
core of Archaean granitic basement rocks is surrounded by a collar of uplifted and overturned strata of the Witwatersrand
Supergroup, exposing a substantial depth section of the Archaean crust. Orthogneisses of the core show little variation in
whole-rock δ
18O value, with the majority being between 8 and 10‰, with a mean of 9.2‰ (n = 35). Quartz and feldspar have per mil differences that are consistent with O-isotope equilibrium at high temperatures,
suggesting minimal interaction with fluids during subsequent cooling. These data refute previous suggestions that the Outer
Granite Gneiss (OGG) and Inlandsee Leucogranofels (ILG) of the core represent middle and lower crust, respectively. Granulite-facies
greenstone remnants from the ILG have δ
18O values that are on average 1.5‰ higher than the ILG host rocks and are unlikely, therefore, to represent the residuum from
the partial melting event that formed the host rock. Witwatersrand Supergroup sedimentary rocks of the collar, which were
metamorphosed at greenschist-to amphibolite-facies conditions, generally have lower δ
18O values than the core rocks with a mean value for metapelites of 7.7‰ (n = 45). Overall, through an ∼20 km thick section of crust, there is a general increase in whole-rock δ
18O value with increasing depth. This is the reverse of what is normal in the crust, largely because the collar rocks have δ
18O values that are unusually low in comparison with metamorphosed sedimentary rocks worldwide. The collar rocks have δD values ranging from −35 to −115‰ (average −62‰, n = 29), which are consistent with interaction with water of meteoric origin, having a δD of about −25 to −45‰. We suggest that fluid movement through the collar rocks was enhanced by impact-induced secondary permeability
in the dome structure.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
5.
Groundwater nitrate contamination and risk assessment in an agricultural area,South Korea 总被引:2,自引:1,他引:1
Jae-Yeol Cheong Se-Yeong Hamm Jeong-Hwan Lee Kwang-Sik Lee Nam-Chil Woo 《Environmental Earth Sciences》2012,66(4):1127-1136
The nitrate of groundwater in the Gimpo agricultural area, South Korea, was characterized by means of nitrate concentration,
nitrogen-isotope analysis, and the risk assessment of nitrogen. The groundwaters belonging to Ca–(Cl + NO3) and Na–(Cl + NO3) types displayed a higher average NO3
− concentration (79.4 mg/L), exceeding the Korean drinking water standard (<44.3 mg/L NO3
−). The relationship between δ18O–NO3
− values and δ15N–NO3
− values revealed that nearly all groundwater samples with δ15N–NO3
− of +7.57 to +13.5‰ were affected by nitrate from manure/sewage as well as microbial nitrification and negligible denitrification.
The risk assessment of nitrate for groundwater in the study area was carried out using the risk-based corrective action model
since it was recognized that there is a necessity of a quantitative assessment of health hazard, as well as a simple estimation
of nitrate concentration. All the groundwaters of higher nitrate concentration than the Korean drinking water standard (<44.3 mg/L NO3
−) belonged to the domain of the hazard index <1, indicating no health hazard by nitrate in groundwater in the study area.
Further, the human exposure to the nitrate-contaminated soil was below the critical limit of non-carcinogenic risk. 相似文献
6.
Tracing the sources of nitrate in karstic groundwater in Zunyi,Southwest China: a combined nitrogen isotope and water chemistry approach 总被引:1,自引:0,他引:1
Si-Liang Li Cong-Qiang Liu Yun-Chao Lang Zhi-Qi Zhao Zhi-Hua Zhou 《Environmental Earth Sciences》2010,60(7):1415-1423
Nitrate (NO3
−) is major pollutant in groundwater worldwide. Karst aquifers are particularly vulnerable to nitrate contamination from anthropogenic
sources due to the rapid movement of water in their conduit networks. In this study, the isotopic compositions (δ15N–NO3
−, δ15N–NH4
+) and chemical compositions(e.g., NO3
−, NH4
+, NO2
−, K+) were measured in groundwater in the Zunyi area of Southwest China during summer and winter to identify the primary sources
of contamination and characterize the processes affecting nitrate in the groundwater. It was found that nitrate was the dominant
species of nitrogen in most of the water samples. In addition, the δ15N–NO3
− values of water samples collected in summer were lower than those collected in winter, suggesting that the groundwater received
a significant contribution of NO3
− from agricultural fertilizer during the summer. Furthermore, the spatial variation in the concentration of nitrate and the
δ15N–NO3
− value indicated that some of the urban groundwater was contaminated with pollution from point sources. In addition, the distribution
of δ15N–NO3
− values and the relationship between ions in the groundwater indicated that synthetic and organic fertilizers (cattle manure)
were the two primary sources of nitrate in the study area, except in a few cases where the water had been contaminated by
urban anthropogenic inputs. Finally, the temporal and spatial variation of the water chemistry and isotopic data indicated
that denitrification has no significant effect on the nitrogen isotopic values in Zunyi groundwater. 相似文献
7.
S. W. A. Naqvi T. Yoshinari J. A. Brandes A. H. Devol D. A. Jayakumar P. V. Narvekar M. A. Altabet L. A. Codispoti 《Journal of Earth System Science》1998,107(4):367-378
Measurements of15N/14N in dissolved molecular nitrogen (N2), nitrate (NO
3
−
) and nitrous oxide (N2O) and18O/16O in N2O [expressed as δ15N and δ18O, relative to atmospheric N2 and oxygen (O2), respectively] have been made in water column at several locations in the Arabian Sea, a region with one of the thickest
and most intense O2 minima observed in the open ocean. Microbially-mediated reduction of NO
3
−
to N2 (denitrification) in the oxygen minimum zone (OMZ) appears to greatly affect the natural isotopic abundances. The δ15N of NO
3
−
increases from 6‰ in deep waters (2500 m) to 15‰ within the core of the denitrifying layer (250–350 m); the δ15N of N2 concurrently decreases from 0.6‰ to 0.20‰ Values of the isotopic fractionation factor (ε) during denitrification estimated
using simple advection-reaction and diffusion-reaction models are 22‰ and 25‰, respectively. A strong decrease in δ15N of NO
3
−
is observed from ∼ 200m (> 11‰) to 80m (∼ 6‰); this is attributed to the input of isotopically light nitrogen through nitrogen
fixation. Isotopic analysis of N2O reveals extremely large enrichments of both15N and18O within the OMZ, presumably due to the preferential reduction of lighter N2O to N2. However, isotopically light N2O is observed to accumulate in high concentrations above the OMZ indicating that the N2O emitted to the atmosphere from this region cannot be very heavy. The isotope data from the intense upwelling zone off the
southwest coast of India, where some of the highest concentrations of N2O ever found at the sea surface are observed, show moderate depletion of15N, but slight enrichment of18O relative to air. These results suggest that the ocean-atmosphere exchange cannot counter inputs of heavier isotopes (particularly18O) associated with the stratospheric back flux, as proposed by previous workers. This calls for additional sources and/or
sinks of N2O in the atmosphere. Also, the N2O isotope data cannot be explained by production through either nitrification or denitrification, suggesting a possible coupling
between the two processes as an important mechanism of N2O production. 相似文献
8.
Ozcan Yigit Albert H. Hofstra Murray W. Hitzman Eric P. Nelson 《Mineralium Deposita》2006,41(6):527-547
Gold Bar is one of several Carlin-type gold mining districts located in the Battle Mountain–Eureka trend, Nevada. It is composed of one main deposit, Gold Bar; five satellite deposits; and four resources that contain 1.6 Moz (50 t) of gold. All of the deposits and resources occur at the intersection of north-northwest- and northeast-trending high-angle faults in slope facies limestones of the Devonian Nevada Group exposed in windows through Ordovician basin facies siliciclastic rocks of the Roberts Mountains allochthon. Igneous intrusions and magnetic anomalies are notably absent. The Gold Bar district contains a variety of discordant and stratabound jasperoid bodies, especially along the Wall Fault zone, that were mapped and studied in some detail to identify the attributes of those most closely associated with gold ore and to constrain genetic models. Four types of jasperoids, J0, J1, J2, and J3, were distinguished on the basis of their geologic and structural settings and appearance. Field relations suggest that J0 formed during an early event. Petrographic observations, geochemistry, and δ18O values of quartz suggest it was overprinted by the hydrothermal event that produced ore-related J1, J2, and J3 jasperoids and associated gold deposits. The greater amount of siliciclastic detritus present in J0 jasperoids caused them to have higher δ18O values than J1,2,3 jasperoids hosted in underlying limestones. Ore-related jasperoids are composed of main-ore-stage replacements and late-ore-stage open-space filling quartz with variable geochemistry and an enormous range of δ18O values (24.5 and −3.7‰). Jasperoids hosted in limestones with the most anomalous Au, Ag, Hg, ±(As, Sb, Tl) concentrations and the highest δ18O values are associated with the largest deposits. The 28‰ range of jasperoid δ18O values is best explained by mixing between an 18O-enriched fluid and an 18O-depleted fluid. The positive correlation between the sizes of gold deposits and the δ18O composition of jasperoids indicates that gold was introduced by the 18O-enriched fluid. The lowest calculated δ18O value for water in equilibrium with late-ore-stage quartz at 200°C (−15‰) and the measured δD value of fluid inclusion water extracted from late-ore-stage orpiment and realgar (−116‰) indicate that the 18O-depleted fluid was composed of relatively unexchanged meteoric water. The source of the 18O-enriched ore fluid is not constrained. The δ34S values of late-ore-stage realgar, orpiment, and stibnite (5.7–15.5‰) and barite (31.5–40.9‰) suggest that H2S and sulfate were derived from sedimentary sources. Likewise, the δ13C and δ18O values of late-stage calcite (−4.8 to 1.5‰ and 11.5 to 17.4‰, respectively) suggest that CO2 was derived from marine limestones. Based on these data and the apparent absence of any Eocene intrusions in the district, Gold Bar may be the product of a nonmagmatic hydrothermal system. 相似文献
9.
Emma A. A. Versteegh Hubert B. Vonhof Simon R. Troelstra Dick Kroon 《International Journal of Earth Sciences》2011,100(6):1423-1432
This paper examines if shell oxygen isotope ratios (δ18Oar) of Unio sp. can be used as a proxy of past discharge of the river Meuse. The proxy was developed from a modern dataset for the reference
time interval 1997–2007, which showed a logarithmic relationship between discharge and measured water oxygen isotope ratios
(δ18Ow). To test this relationship for past time intervals, δ18Oar values were measured in the aragonite of the growth increments of four Unio sp. shells; two from a relatively wet period and two from a very dry time interval (1910–1918 and 1969–1977, respectively).
Shell δ18Oar records were converted into δ18Ow values using existing water temperature records. Summer δ18Ow values, reconstructed from δ18Oar of 1910–1918, showed a similar range as the summer δ18Ow values for the reference time interval 1997–2007, whilst summer reconstructed δ18Ow values for the time interval 1969–1977 were anomalously high. These high δ18Ow values suggest that the river Meuse experienced severe summer droughts during the latter time interval. δ18Ow values were then applied to calculate discharge values. It was attempted to estimate discharge from the reconstructed δ18Ow values using the logarithmic relationship between δ18Ow and discharge. A comparison of the calculated summer discharge results with observed discharge data showed that Meuse low-discharge
events below a threshold value of 6 m3/s can be detected in the reconstructed δ18Ow records, but true quantification remains problematic. 相似文献
10.
The stable isotopic analyses (δ18O and δ13C) of a coralFavia speciosa spanning forty two years (1948–89 A.D.), collected from the Pirotan island (22.6°N, 70°E) in the Gulf of Kutch have been
carried out to assess its potential for retrieving past environmental changes in this region. It is seen that the summer (minima)
δ18O variations in the coral CaCO3 are negatively correlated with seasonal (summer) monsoon rainfall in the adjoining region of Kutch and Saurashtra and a qualitative
reconstruction of historical rainfall variations in this region can be obtained by analyzing the δ18O in this species of coral. The observed mean seasonal range of δ18O variations is 0.34 ±0.17‰ (n = 42), whereas the expected range calculated (from available SST and measured δ18O of sea water) is ∼ 1.1 ±0.15‰ The difference is due to the coarse resolution of sampling, which can be corrected. The seasonal
range in δ13C is ∼ l‰ and is explained by changes in: a) the light intensity related to the cloudiness during monsoons and b) phytoplankton
productivity. 相似文献
11.
Mid-Proterozoic anorthosite-suite magmatism is a major volumetric component of the southern Grenville Province, and provides
an important probe of the compositions and types of lower crustal rocks. The ∼1.15 Ga Morin Complex (Quebec) consists of two
anorthosite plutons with distinct compositions. Plagioclase from the western lobe of the anorthosite has δ18O values that average 9.6 ± 0.7‰, which is ∼3‰ higher than the values found in “normal” anorthosites and in mantle-derived
mafic igneous rocks worldwide. Plagioclase from the eastern lobe of the massif (deformed by the Morin Shear Zone) has δ18O values that average 8.7 ± 0.6‰, also high compared to mantle-derived rocks. Numerous lines of evidence, including homogeneity
of δ18O values within individual plutons, O–Sr–Nd mixing relations, and preservation of igneous δ18O in adjacent mangerite units argue against anorthosite interaction with high δ18O fluids as the cause of the high δ18O values seen in both anorthosite lobes. High δ18O values are best explained as primary magmatic compositions resulting from melting and assimilation of crustal materials
by the anorthosite's parent magma. The Morin and Marcy massifs are located in the Allochthonous Monocyclic Belt of the Grenville
Province, and have the highest known δ18O values for anorthosites in the Grenville. Although the Monocyclic Belt is juvenile in terms of radiogenic isotope systematics,
the new oxygen isotope data indicate the presence high δ18O supracrustal materials at the base of the crust, probably buried during the ∼1.2 Ga Elzevirian orogeny in the Monocyclic
Belt prior to anorthosite magmatism. This process is not recognized in other parts of the Grenville Province and points to
differences in the pre-1.2-Ga continental margins.
Received: 29 September 1999 / Accepted: 7 March 2000 相似文献
12.
THEJINLONGSHANGOLDOREBELTINZHEN’ANCOUN TY,SOUTHERNSHAANXIPROVINCE,ISLOCATEDINTHEWEST ERNQINLINGGOLDPROVINCE(NO.16INFIG.1;CHEN YANJINGETAL.,2004).ITWASDISCOVEREDINTHEDEVO NIANSTRATAINTHELATE1980S).ITSGEOLOGICALSETTING ANDMETALLOGENICEVOLUTIONARESIMILARTOT… 相似文献
13.
Mark E. Brandriss Richard J. Nevle Dennis K. Bird James R. O’Neil 《Contributions to Mineralogy and Petrology》1995,121(1):74-86
Hydrogen and oxygen isotope analyses have been made of hydrous minerals in gabbros and basaltic xenoliths from the Eocene
Kap Edvard Holm intrusive complex of East Greenland. The analyzed samples are of three types: (1) primary igneous hornblendes
and phlogopites that crystallized from partial melts of hydrothermally altered basaltic xenoliths, (2) primary igneous hornblendes
that formed during late–magmatic recrystallization of layered gabbroic cumulates, and (3) secondary actinolite, epidote and
chlorite that formed during subsolidus alteration of both xenoliths and gabbros. Secondary actinolite has a δ18O value of −5.8‰ and a δD value of −158‰. These low values reflect subsolidus alteration by low–δ18O, low–δD hydrothermal fluids of meteoric origin. The δD value is lower than the −146 to −112‰ values previously reported
for amphiboles from other early Tertiary meteoric–hydrothermal systems in East Greenland and Scotland, indicating that the
meteoric waters at Kap Edvard Holm were isotopically lighter than typical early Tertiary meteoric waters in the North Atlantic
region. This probably reflects local climatic variations caused by formation of a major topographic dome at about the time
of plutonism and hydrothermal activity. The calculated isotopic composition of the meteoric water is δD=−110 ± 10‰, δ18O ≈−15‰. Igneous hornblendes and phlogopites from pegmatitic pods in hornfelsed basaltic xenoliths have δ18O values between −6.0 and −3.8‰ and δD values between −155 and −140‰. These are both much lower than typical values of fresh
basalts. The oxygen isotope fractionations between pegmatitic hornblendes and surrounding hornfelsic minerals are close to
equilibrium fractionations for magmatic temperatures, indicating that the pegmatites crystallized from low–δ18O partial melts of xenoliths that had been hydrothermally altered and depleted in 18O prior to stoping. The pegmatitic minerals may have crystallized with low primary δD values inherited from the altered country
rocks, but these values were probably overprinted extensively by subsolidus isotopic exchange with low–δD meteoric–hydrothermal
fluids. This exchange was facilitated by rapid self–diffusion of hydrogen through the crystal structures. Primary igneous
hornblendes from the plutonic rocks have δ18O values between +2.0 and +3.2‰ and δD values between −166 and −146‰. The 18O fractionations between hornblendes and coexisting augites are close to equilibrium fractionations for magmatic temperatures,
indicating that the hornblendes crystallized directly from the magma and subsequently underwent little or no oxygen exchange.
The hornblendes may have crystallized with low primary δD values, due to contamination of the magma with altered xenolithic
material, but the final δD values were probably controlled largely by subsolidus isotopic exchange. This inference is based
partly on the observation that coexisting plagioclase has been extensively depleted in 18O via a mineral–fluid exchange reaction that is much slower than the hydrogen exchange reaction in hornblende. It is concluded
that all hydrous minerals in the study area, whether igneous or secondary, have δD values that reflect extensive subsolidus
isotopic equilibration with meteoric–hydrothermal fluids.
Received: 22 March 1994 / Accepted: 26 January 1995 相似文献
14.
Edward M. Ripley Nur Iskandar Taib Chusi Li Craig H. Moore 《Contributions to Mineralogy and Petrology》2007,154(1):35-54
Copper–nickel sulfide mineralization in the Partridge River Intrusion of the 1.1 Ga Duluth Complex is restricted primarily
to a 100 m thick zone near the base of the intrusion, which is heterogeneous at meter scales in terms of both sulfide contents
and rock types, which include dunite, melatroctolite, troctolite, leucotroctolite, gabbro, olivine gabbro, gabbronorite, and
rare norite. Olivine-rich troctolites and melatroctolites appear to have required mineral accumulation on a substrate, whereas
augite troctolite and gabbros are thought to have formed via in situ crystallization of magmas ranging in composition from
high-Al olivine tholeiite to high-Ti tholeiite. δ18O values of orthopyroxene-poor rocks in the Partridge River Intrusion range from 5.2 to 6.7‰. δ18O values of 6.7‰ are consistent with less than 20% contamination by high-18O metasedimentary country rock, either via devolatilization or local partial melting. Rocks with greater than ∼15% orthopyroxene,
gabbronorites, and norites, are characterized by δ18O values in excess of 6.9‰, and required the assimilation of larger amounts of siliceous country rocks. Sulfur isotopic values
in leucotroctolitic rocks that contain less than ∼400 ppm S and that overlie the basal zone range between −1.5 and 2‰, values
that are consistent with those of mantle-derived sulfur. In contrast, δ34S values in the basal zone range from −1.4 to 10.5‰, where the 34S-enriched samples require an input of sulfur from metasedimentary country rocks. δ34S values of the rocks in the basal zone correlate with variations in olivine Fo content but not with S abundance. The wide
range in δ34S values of rocks in the basal zone strongly suggests that magmas interacted with layers in the sedimentary country rocks
that were themselves characterized by variable sulfide contents and δ34S values. The S isotopic data suggest that the heterogeneity observed in the basal zone results from the emplacement of relatively
thin sheets of compositionally distinct magma. All rock types present in the basal zone can be produced as a result of variable
degrees of fractionation of a parental high-Al olivine tholeiite, followed by varying degrees of contamination of derivative
liquids by country rocks. The S-contamination process was essential for the development of Cu–Ni mineralization, and was restricted
to the earliest stages in the development of the Duluth Complex at a time when volatile species such as S and H2O, and low-T partial melts of country rocks, were available to magmas.
Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users. 相似文献
15.
Recharge source and hydrogeochemical evolution of shallow groundwater in a complex alluvial fan system,southwest of North China Plain 总被引:4,自引:0,他引:4
Fadong Li Guoying Pan Changyuan Tang Qiuying Zhang Jingjie Yu 《Environmental Geology》2008,55(5):1109-1122
Many cities around the world are developed at alluvial fans. With economic and industrial development and increase in population,
quality and quantity of groundwater are often damaged by over-exploitation in these areas. In order to realistically assess
these groundwater resources and their sustainability, it is vital to understand the recharge sources and hydrogeochemical
evolution of groundwater in alluvial fans. In March 2006, groundwater and surface water were sampled for major element analysis
and stable isotope (oxygen-18 and deuterium) compositions in Xinxiang, which is located at a complex alluvial fan system composed
of a mountainous area, Taihang Mt. alluvial fan and Yellow River alluvial fan. In the Taihang mountainous area, the groundwater
was recharged by precipitation and was characterized by Ca–HCO3 type water with depleted δ18O and δD (mean value of −8.8‰ δ18O). Along the flow path from the mountainous area to Taihang Mt. alluvial fan, the groundwater became geochemically complex
(Ca–Na–Mg–HCO3–Cl–SO4 type), and heavier δ18O and δD were observed (around −8‰ δ18O). Before the surface water with mean δ18O of −8.7‰ recharged to groundwater, it underwent isotopic enrichment in Taihang Mt. alluvial fan. Chemical mixture and ion
exchange are expected to be responsible for the chemical evolution of groundwater in Yellow River alluvial fan. Transferred
water from the Yellow River is the main source of the groundwater in the Yellow River alluvial fan in the south of the study
area, and stable isotopic compositions of the groundwater (mean value of −8.8‰ δ18O) were similar to those of transferred water (−8.9‰), increasing from the southern boundary of the study area to the distal
end of the fan. The groundwater underwent chemical evolution from Ca–HCO3, Na–HCO3, to Na–SO4. A conceptual model, integrating stiff diagrams, is used to describe the spatial variation of recharge sources, chemical
evolution, and groundwater flow paths in the complex alluvial fan aquifer system. 相似文献
16.
The Eastern Iberian Central System has abundant ore showings hosted by a wide variety of hydrothermal rocks; they include
Sn-W, Fe and Zn-(W) calcic and magnesian skarns, shear zone- and episyenite-hosted Cu-Zn-Sn-W orebodies, Cu-W-Sn greisens
and W-(Sn), base metal and fluorite-barite veins. Systematic dating and fluid inclusion studies show that they can be grouped
into several hydrothermal episodes related with the waning Variscan orogeny. The first event was at about 295 Ma followed
by younger pulses associated with Early Alpine rifting and extension and dated near 277, 150 and 100 to 20 Ma, respectively
(events II–IV). The δ18O-δD and δ34S studies of hydrothermal rocks have elucidated the hydrological evolution of these systems. The event I fluids are of mixed
origin. They are metamorphic fluids (H2O-CO2-CH4-NaCl; δ18O=4.7 to 9.3‰; δD ab.−34‰) related to W-(Sn) veins and modified meteoric waters in the deep magnesian Sn-W skarns (H2O-NaCl, 4.5–6.4 wt% NaCl eq.; δ18O=7.3–7.8‰; δD=−77 to −74‰) and epizonal shallow calcic Zn-(W) and Fe skarns (H2O-NaCl, <8 wt% NaCl eq.; δ18O=−0.4 to 3.4‰; δD=−75 to −58‰). They were probably formed by local hydrothermal cells that were spatially and temporally
related to the youngest Variscan granites, the metals precipitating by fluid unmixing and fluid-rock reactions. The minor
influence of magmatic fluids confirms that the intrusion of these granites was essentially water-undersaturated, as most of
the hydrothermal fluids were external to the igneous rocks. The fluids involved in the younger hydrothermal systems (events
II–III) are very similar. The waters involved in the formation of episyenites, chlorite-rich greisens, retrograde skarns and
phyllic and chlorite-rich alterations in the shear zones show no major chemical or isotopic differences. Interaction of the
hydrothermal fluids with the host rocks was the main mechanism of ore formation. The composition (H2O-NaCl fluids with original salinities below 6.2 wt% NaCl eq.) and the δ18O (−4.6 to 6.3‰) and δD (−51 to −40‰) values are consistent with a meteoric origin, with a δ18O-shift caused by the interaction with the, mostly igneous, host rocks. These fluids circulated within regional-scale convective
cells and were then channelled along major crustal discontinuities. In these shear zones the more easily altered minerals
such as feldspars, actinolite and chlorite had their δ18O signatures overprinted by low temperature younger events while the quartz inherited the original signature. In the shallower
portions of the hydrothermal systems, basement-cover fluorite-barite-base metal veins formed by mixing of these deep fluids
with downwards percolating brines. These brines are also interpreted as of meteoric origin (δ18O< ≈ −4‰; δD=−65 to −36‰) that leached the solutes (salinity >14 wt% NaCl eq.) from evaporites hosted in the post-Variscan
sequence. The δD values are very similar to most of those recorded by Kelly and Rye in Panasqueira and confirm that the Upper
Paleozoic meteoric waters in central Iberia had very negative δD values (≤−52‰) whereas those of Early Mesozoic age ranged
between −65 and −36‰.
Received: 9 June 1999 / Accepted: 19 January 2000 相似文献
17.
Chris Harris H. Stuart Smith Anton P. le Roex 《Contributions to Mineralogy and Petrology》2000,138(2):164-175
We have measured the δ18O values of the major phenocrysts (olivine, clinopyroxene and plagioclase) present in lavas from Tristan da Cunha and Gough
Island. These islands, which result from the same mantle plume, have enriched radiogenic isotope ratios and are, therefore,
prime candidates for an oxygen isotope signature that is distinct from that of MORB. Consistent differences between the δ18O values of olivine, pyroxene and feldspar in the Gough lavas show that the phenocrysts in the mafic Gough Island lavas are
in oxygen isotope equilibrium. The olivines in lavas with SiO2 <50 wt% have a mean δ18O value of 5.19‰, consistent with crystallization from a magma having the same oxygen isotope composition as MORB. Phenocrysts
in all the Gough lavas show a systematic increase in δ18O value as silica content increases, which is consistent with closed-system fractional crystallization. The lack of enrichment
in δ18O of the Gough magmas suggests that the mantle source contained <2% recycled sediment. In contrast, the Tristan lavas with
SiO2 >48 wt% contain phenocrysts which have δ18O values that are systematically ∼0.3‰ lower than their counterparts from Gough. We suggest that the parental mafic Tristan
magmas were contaminated by material from the volcanic edifice that acquired low δ18O values by interaction with water at high temperatures. The highly porphyritic SiO2-poor lavas show a negative correlation between olivine δ18O value and whole-rock silica content rather than the expected positive correlation. The minimum δ18O value occurs at an SiO2 content of about 45 wt%. Below 45 wt% SiO2, magmas evolved via a combination of assimilation, fractionational crystallization and crystal accumulation; above 45 wt%
SiO2, magmas appeared to have evolved via closed-system fractional crystallization.
Received: 23 November 1998 / Accepted: 27 September 1999 相似文献
18.
Jin-Hyeob Kwak Woo-Jung Choi Sang-Sun Lim Seung-Heon Lee Sang-Mo Lee Scott X. Chang Jae-Woon Jung Kwang-Sik Yoon Soo-Myung Choi 《Environmental Geology》2008,53(6):1331-1338
Electrical conductivity of saturated soil extracts (ECe) in three reclaimed tideland (RTL) soils on the west coast of Korea decreased with time since reclamation, indicating natural
desalinization through leaching of salts by precipitation water. Soil N concentration increased with decreasing ECe. With the increase in soil N concentration, the δ15N decreased, likely caused by the input of 15N-depleted N sources. As N2-fixing plant species were found in the oldest RTL, atmospheric N2 fixation likely contributed to the increase in soil N concentration in the oldest RTL. Negative δ15N (−7.1 to −2.0‰) of total inorganic N (NH4
++NO3
−) and published data on N deposition near the study area indicate that atmospheric N deposition might be another source of
N in the RTLs. Meanwhile, the consistently negative δ15N of soil NO3
− excluded N input from chemical fertilizer through groundwater flow as a potential N source, since NO3
− in groundwater generally have a positive δ15N. The patterns of δ15N of NH4
+ (+2.3 to +5.1‰) and NO3
− (−9.2 to −5.0‰) suggested that nitrification was an active process that caused 15N enrichment in NH4
+ but denitrification was probably minimal which would otherwise have caused 15N enrichment in NO3
−. A quantitative approach on N budget would provide a better understanding of soil N dynamics in the studied RTLs. 相似文献
19.
Geologic framework and isotope tracing of the arsenious Quaternary Aquifer of the southwestern North Bengal Plain,West Bengal,India 总被引:2,自引:2,他引:0
The aim of the paper is to understand the geological control of groundwater, the recharge sources, the relative age of groundwater
and the interaction between surface water and groundwater of the southwestern part of North Bengal Plain in the alluvium filled
gap between the Rajmahal hills on the west and the Garo hills on the east. The area is covered by Quaternary alluvia of two
different ages, viz. the Older Alluvium and the Newer Alluvium. The Older Alluvium of Pleistocene age is made up of argillaceous
bed reddish brown in color and interspread with ‘kankar’ and laterite debris and the Newer Alluvium is dark, loosely compacted
and has a high moisture content. A hydrostarigraphic model of the top 120 m geological column has been built by direct field
observation, constructing Fence diagram, lithofacies and isotope analyses. The model indicates an oscillating environment
of deposition of sediments from bottom to top with oxidizing at the bottom followed by reducing and then oxidizing environment
at the top. The hydrogeochemistry of groundwater also suggests a predominantly reducing condition of the aquifer with high
HCO3
−, low SO4
2− and NO3
− concentrations. The shallow groundwater at places contains heavy metals such as copper, cadmium, manganese, iron, chromium
and arsenic. The δ18O and tritium values of groundwater are within the range of monsoon precipitation composition which indicates that groundwater
is probably recharged primarily from precipitation. The plots of δ18O and δD show slight deviation from the Local Mean Water Lines suggesting that some evaporation of rainfall occurs prior to
or during infiltration. Therefore groundwater occurs under unconfined condition. Lithofacies analysis indicates that the sediments
below the depth of 40 m are the potential water bearing formation. Depletion or enrichment of δ18O and δD with depth was not observed and tritium content is also similar at various depths indicating possibility of mixing
of groundwater from various depths due to pumping which may lead to contamination of the deeper aquifer by heavy metals and
arsenic. 相似文献
20.
Ian Cartwright Ian S. Buick Roland Maas 《Contributions to Mineralogy and Petrology》1997,128(4):335-351
The Jervois region of the Arunta Inlier, central Australia, contains para- and orthogneisses that underwent low-pressure
amphibolite facies metamorphism (P = 200–300 MPa, T = 520–600 °C). Marble layers cut by metre-wide quartz + garnet ± epidote veins comprise calcite, quartz, epidote, clinopyroxene,
grandite garnet, and locally wollastonite. The marbles also contain locally discordant decimetre-thick garnet and epidote
skarn layers. The mineral assemblages imply that the rocks were infiltrated by water-rich fluids (XCO2 = 0.1–0.3) at ∼600 °C. The fluids were probably derived from the quartz-garnet vein systems that represent conduits for fluids
exsolved from crystallizing pegmatites emplaced close to the metamorphic peak. At one locality, the marble has calcite (Cc)
δ18O values of 9–18‰ and garnet (Gnt) δ18O values of 10–14‰. The δ18O(Gnt) values are only poorly correlated with δ18O(Cc), and the δ18O values of some garnet cores are higher than the rims. The isotopic disequilibrium indicates that garnet grew before the
δ18O values of the rock were reset. The marbles contain ≤15% garnet and, for water-rich fluids, garnet-forming reactions are
predicted to propagate faster than O-isotopes are reset. The Sm-Nd and Pb-Pb ages of garnets imply that fluid flow occurred
at 1750–1720 Ma. There are no significant age differences between garnet cores and rims, suggesting that fluid flow was relatively
rapid. Texturally late epidote has δ18O values of 1.5–6.2‰ implying δ18O(H2O) values of 2–7‰. Waters with such low-δ18O values are probably at least partly meteoric in origin, and the epidote may be recording the late influx of meteoric water
into a cooling hydrothermal system.
Received: 29 April 1996 / Accepted: 12 March 1997 相似文献