首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 312 毫秒
1.
Orthopyroxene reaction rims were synthesized between polished plates of natural olivine or synthetic forsterite and quartz at 1.9 GPa and temperatures of 750–950°C. The experiments were performed in a piston-cylinder apparatus after drying the samples at 600°C. Each experiment comprised 4 or 7 quartz-olivine contacts that were positioned along a temperature gradient. As a monitor for water content in the samples, the water concentration in the two olivines was determined by FTIR before and after the experiments. The orthopyroxene layers show two different structural variants. Type one (normal layers) has very constant thickness at each contact and formed with equal growth rates at both interfaces. Type two (bulging layers) comprises more irregular areas with 3–5 times thicker rims where porosity provides evidence for the local presence of a fluid. In the bulging layers the growth rate at the olivine-orthopyroxene interface exceeds that at the quartz-orthopyroxene interface. The relative growth rates at the interfaces are in accordance with SiO2-immobile growth of the normal layers and SiO2-mobile growth of the bulging layers. The natural olivine contains about 60 wt-ppm intracrystalline water before and after experiment and took up about 20 wt-ppm water molecular adsorbed to micro- and nanocracks and -pores during the runs. The synthetic forsterite contains about 7 wt-ppm internally adsorbed molecular water before and after experiment, and during the runs took up hydrogen equivalent to 3 wt-ppm adsorbed water. The IR spectra indicate that large parts of the point defects (possibly tetrahedral) were frozen-in at the conditions of the experiments. In both olivines a new band appeared at 3,355 or 3,357 cm?1, respectively, equivalent to about 3 wt-ppm water that at the high pressure of the experiments and opx-buffered aSiO2 of the experiments might already mean water saturation of the olivines. Despite the effective drying before experiment and the absence of porosity, the bulk diffusivity derived from the rim growth rates is perfectly in line with data from water-bearing piston-cylinder experiments at higher temperatures. The bulk diffusivity during rim growth is 4 to 7 orders of magnitude higher than an extrapolation of really dry experiments to the temperature range of this study.  相似文献   

2.
The thermal evolution of 10-Å phase Mg3Si4O10(OH)2·H2O, a phyllosilicate which may have an important role in the storage/release of water in subducting slabs, was studied by X-ray single-crystal diffraction in the temperature range 116–293 K. The lattice parameters were measured at several intervals both on cooling and heating. The structural model was refined with intensity data collected at 116 K and compared to the model refined at room temperature. As expected for a layer silicate on cooling in this temperature range, the a and b lattice parameters undergo a small linear decrease, α a  = 1.7(4) 10?6 K?1 and α b  = 1.9(4) 10?6 K?1, where α is the linear thermal expansion coefficient. The greater variation is along the c axis and can be modeled with the second order polynomial c T  = c 293(1 + 6.7(4)10?5 K?1ΔT + 9.5(2.5)10?8 K?2(ΔT)2) where ΔT = T ? 293 K; the monoclinic angle β slightly increased. The cell volume thermal expansion can be modeled with the polynomial V T  = V 293 (1 + 8.0 10?5 K?1 ΔT + 1.4 10?7 K?2 (ΔT)2) where ΔT = T ? 293 is in K and V in Å3. These variations were similar to those expected for a pressure increase, indicating that T and P effects are approximately inverse. The least-squares refinement with intensity data measured at 116 K shows that the volume of the SiO4 tetrahedra does not change significantly, whereas the volume of the Mg octahedra slightly decreases. To adjust for the increased misfit between the tetrahedral and octahedral sheets, the tetrahedral rotation angle α changes from 0.58° to 1.38°, increasing the ditrigonalization of the silicate sheet. This deformation has implications on the H-bonds between the water molecule and the basal oxygen atoms. Furthermore, the highly anisotropic thermal ellipsoid of the H2O oxygen indicates positional disorder, similar to the disorder observed at room temperature. The low-temperature results support the hypothesis that the disorder is static. It can be modeled with a splitting of the interlayer oxygen site with a statistical distribution of the H2O molecules into two positions, 0.6 Å apart. The resulting shortest Obas–OW distances are 2.97 Å, with a significant shortening with respect to the value at room temperature. The low-temperature behavior of the H-bond system is consistent with that hypothesized at high pressure on the basis of the Raman spectra evolution with P.  相似文献   

3.
The disk masses of four low-surface-brightness (LSB) galaxies are estimated using the criterion of marginal gravitational stability. The constructed mass models are close to those for a maximum disk. The results show that the disks of LSB galaxies may be significantly more massive than is usually believed based on their brightnesses. In this case, their surface densities and masses are fairly typical for higher-surface-brightness spirals. Alternatively, it may be that LSB disks are dynamically overheated.  相似文献   

4.
Low birth weight (LBW), defined as a live birth weighing <2,500 g, is a significant public health problem in the United States, especially a few states including Georgia. Although much work has been done to study the epidemiology of LBW in various regions, the spatial–temporal patterns of LBW prevalence in Georgia remain unclear to a large degree. This paper investigates the temporal trend of LBW rates over a time span of 11 years and the spatial clusters of LBW prevalence in the state of Georgia at the county level. Comparison is also made between race and gender groups, and between county groups of different socioeconomic statuses to uncover disparities. Results showed a steady and prevalent increase of LBW rate in the state over the study period. Three counties and two county clusters with significantly higher LBW rates than the state rate were detected for 1999–2001, while one more county and two more county clusters of high LBW rates were detected for 2007–2009. More urbanized counties were found to have a relatively lower LBW rate when compared with the less urbanized ones as groups. The findings from this paper are expected to provide valuable insights to better understanding the etiology of LBW and more effective allocating prenatal health care resources in the future.  相似文献   

5.
Groundwater with low total dissolved solids （less than 200 mg/L） occurs in the unconfined and confined aquifers near Beihai in southern Guangxi, China. Under natural conditions the groundwater ranges in pH from 3,33 to 7,0 with an average value of 5.12. The pH in the unconfined aquifer varies from 3.67 to 7.0 with an average value of 5.17 and the pH in the confined aquifer is in the range 3.33-6.97 with an average value of 5.07. The pH in the groundwater does not show significantly increasing or decreasing trends with time. Fluctuations in pH exist at some of the monitoring wells and the pH in groundwater is a bit higher in the rainy season than in the dry season, Monitoring data show that the pH in rainwater is higher than in groundwater in the unconfined aquifer, whereas the pH in the latter is a bit higher than in the confined aquifer. A slightly decreasing trend in the pH was also found from the inland area to the coastal zone. The occurrence of weakly acidic groundwater in this area is attributed to the recharge from low pH precipitation and the multi-aquifer and leaky groundwater system.  相似文献   

6.
Summary The investigations reported are concerned with the synthesis of simple sulphides, Tl-bearing sulphosalts, and antimony-iron sulphides in aqueous environment using a combination of clay/dolomite or clay/quartz buffer at a temperature range of 85–90°C. Clay minerals as catalyst have been employed because their K+, Na+, Ca2+, etc. contents have to be substituted by cations of Fe, Cu, As, Sb, Tl, Bi, etc. After substitution, the saturated clay minerals were in turn treated by aqueous H2S solution under controlled Eh-pH condition, where the heavy elements were extracted and precipitated as sulphide minerals.The data obtained show that the pH for simple sulphides varied between 6.46–9.70, and for sulphosalts from 4.14 up to 10.1. The antimony-copper and antimony-iron sulphides had an average pH value of 8.7. The combination clay/dolomite was characterized by high pH, that of clay/quartz by lower pH values. A linear relation between the Eh and pH is recognized for the sulphides, the sulphosalts, the antimony-copper and iron as well as the copper-arsenic sulphides in all environments.In most cases, the mineral assemblages obtained depend on the initial materials and on the environment available. Using this procedure, we were able to synthesise thallium-sulphosalts at temperatures below 100°C.
Hydrothermale Bildung von Sulf den und Sulfosalzen bei niedrigen Temperaturen<100°)
Zusammenfassung Bei den hier vorgelegten Ergebnissen geht es um die Synthese einfacher Sulfide, Tl-führender Sulfosalze und Antimon-Eisensulfide in wässerigen Milieus unter Benutzung einer Kombination von Ton/Dolomit oder Ton/Quarz Puffern bei Temperaturen von 85–90°C. Tonminerale als Katalyst wurden deshalb benützt, weil ihre K+, Na+, Ca2+, etc. Gehalte durch Kationen (Fe, Cu, As, Sb, TI, Bi etc.) ersetzt werden müssen. Nach dem Ersatz wurden die gesättigten Tonminerale mit einer wässerigen H2S-Lösung bei kontrollierten Eh-pH Bedingungen behandelt, wobei dann die Schwermetalle extrahiert und als Sulfidminerale ausgefällt wurden. Die Daten zeigen, daß die pH-Werte für einfache Sulfide von 6,46–9,70, und für Sulfosalze von 4,14 bis zu 10,1 schwanken. Die Antimon-Kupfer und Antimon-Eisen Sulfide hatten einen durchschnittlichen pH-Wert von 8,7. Die Kombination Ton/Dolomit war durch hohe pH-Werte charakterisiert, die von Ton/Quartz durch niedrige pH-Werte. Eine lineare Beziehung zwischen Eh und pH ist für Sulfide, Sulfosalze, Antimon-Kupfer und Eisen sowohl wie auch für die Kupfer-Arsensulfide in allen Milieus zu erkennen. In den meisten Fällen wird die bestehende Mineral-Assoziation durch die Ausgangsminerale und durch das Bildungsmilieu bestimmt. Mit dieser Methode war es möglich, Thallium-Sulfosalze bei Temperaturen unter 100°C zu synthetisieren.

With 3 Figures  相似文献   

7.
Continuous monitoring of a 15 m high heavily instrumented experimental waste rock pile (0.053 wt.% S) since 2006 at the Diavik diamond mine in northern Canada provided a unique opportunity to study the evolution of fresh run-of-mine waste rock as it evolved over annual freeze–thaw cycles. Samples were collected from soil water solution samplers to measure pore water properties, from twelve 4 to 16 m2 basal collection lysimeters to measure basal leachate properties in the region underlying the crest of the pile (the core), and from basal drains to measure aggregate total pile leachate properties. By 2012, monitoring of pore water geochemistry within the core structure of the test pile revealed an apparent steady state with respect to weathering geochemistry, represented by (i) a flush of pre-existing blasting residuals and applied tracers, (ii) declining pH, (iii) a stepwise progression and subsequent equilibrium with acid-neutralizing phases (depletion of available carbonates; equilibrium with respect to aluminum hydroxide phases and subsequent iron (III) hydroxide phases), and (iv) concordant release of SO4, major cations (Ca, Mg, K, Na, Si), and trace metals (Al, Fe, Ni, Co, Cu, Zn). Distinct, high concentration ‘spring flushes’, characteristic of drainage in northern environments and primarily explained by a combination of fluid residence time and the build-up of oxidation products over the winter, were released from core drainage each season. Following the initial flush, the concentration of all dissolved constituents steadily declined, with distinct minimums prior to freeze-up. The opposite trend was observed in the cumulative pile drainage, in which early season leachate dominated by snowmelt and batter flow had low concentrations and late season leachate dominated by contributions from the core of the pile (indicated by season end merging of core and cumulative drainage geochemistry) had higher concentrations. Northern waste rock pile drainage geochemistry is strongly influenced by freeze–thaw cycling and varying core and batter subsystem contributions to total drainage. A comprehensive understanding of thermal cycling in waste rock piles is an important component of temporal predictions of drainage water composition based on up-scaling or reactive transport modeling.  相似文献   

8.
Twenty-one iron meteorites with Ge contents below 1 μg/g, including nine belonging to groups IIIF and IVB, have been analyzed by instrumental neutron activation analysis (INAA) for the elements Co, Cr, As, Au, Re, Ir and W. Groups IIIF and IVB show positive correlations of Au, As and Co (IIIF only) with published Ni analyses, and negative correlations of Ir, Re, Cr (IVB only) and W (IIIF only) with Ni. On element-Ni plots, the gradients of the least squares lines are similar to those of many other groups, excluding IAB and IIICD. With the inclusion of a new member, Klamath Falls, group IIIF has the widest range of Au, As and Co contents of any group and the steepest gradients on plots of these elements against Ni. It is likely that these trends in groups IIIF and IVB were produced by fractionation of elements between solid and liquid metal, probably during fractional crystallization.It has been suggested that some of the 15 irons with <l μg/g Ge which lie outside the groups might be related. However, the INAA data indicate that no two are as strongly related as two group members. These low-Ge irons and the members of groups IIIF, IVA and IVB tend to have low concentrations of As, Au and P, low CoNi ratios and high Cr contents. The depletion of the more volatile elements probably results from incomplete condensation into the metal from the solar nebula.The structures of low-Ge irons generally reflect fast cooling rates (20–2000 K Myr?1). When data for all iron meteorites are plotted on a logarithmic graph of cooling rate against Ge concentration and results for related irons are averaged, there is a significant negative correlation. This suggests that metal grains which inefficiently condensed Ge and other volatile elements tended to accrete into small parent bodies.  相似文献   

9.
The adsorption capacity of high–over-matured shale has been widely investigated, but the adsorption capacity and the main factors influencing low–middle-matured, type II kerogen-containing, and organic-rich marine shale have been rarely explored. This research conducts organic geochemistry, mineralogical composition, adsorption isotherm tests to reveal the adsorption and main influencing factors of the different geochemistry characteristics, mineralogical compositions, temperature and pressure conditions of the low–middle-matured Neoproterozoic Xiamaling marine shale in Zhangjiakou, Hebei. The investigated shale is in a low–middle maturity stage, contains type II kerogen and is rich in organic matter. The results show that the total organic carbon (TOC) content of the Xiamaling shale is positively correlated with the methane adsorption capacity, which is the most important influencing factor on the adsorptive property of shale. The methane adsorption capacity first decreases to the minimum value as the temperature reaches 360°C equivalent Ro (EqRo = 1.0%), then increases and reaches the maximum value at 620°C (EqRo = 3.28%) and finally decreases again as the temperature rises at the last simulation stage. The mineral components exhibit an insignificant influence on the methane absorbability because of organic-matter coatings. The TOC-normalised methane adsorption capacity is positively correlated with the illite–smectite and clay-mineral contents but shows no significant correlation with brittle minerals, such as quartz. Soluble organic matter and kerogen caused the methane dissolution and adsorbtion, respectively. The strong dissolution property of the soluble organic matter is the most important cause of the larger adsorption capacity of the original shale compared with that of the residual samples. Moreover, the methane adsorption capacity of the Xiamaling shale decreases with increasing temperature, and increases with pressure below the critical pressure but decreases exceeding the critical pressure.  相似文献   

10.
Acid mine drainage (AMD) is treated at several points in the Lausitz lignite mine district (Saxony, Germany) in treatment plants. The remaining alkaline low density sludge (LDS) was deposited in acidic mining lakes without having an impact on the lake water quality. Batch experiments show that alkalinity can be raised using LDS from acid mine drainage treatment plants together with CO2. Batch experiments were conducted using lake water and deposited LDS from the mining lake Spreetal-Nordost with varying concentrations of CO2. Also the duration of gas contact as well as the LDS–water ratio was changed in the batch experiments. The gas contact time and the partial pressure of CO2 are the relevant parameters controlling the alkalinity in the lake water at the end of the experiments. The Ca and Mg concentrations of the pore water are relevant for higher pH values. Therefore, dissolved CO2 can form bicarbonate or carbonate complexes, thus alkalinity rises. A second factor for alkalinity gain is the calcite content of the sludge, because CO2 triggers the dissolution of carbonates. Therefore, unused calcite in the sludge can raise the alkalinity more effectively by the application of carbon dioxide. Furthermore, it was shown that remobilization of trace elements will not affect the water quality.  相似文献   

11.
Low molecular weight organic acids （LMWOAs） are important components of root exudates. They play an important role in immobilizing and remobilizing contaminants in rhizospheric soil. Effects of four LMWOAs on the sorption and desorption behavior of p-chlorophenol by yellow earth was studied in batch mode. The results showed that the previous application of LMWOAs to enhanced adsorption capacity of p-chlorophenol of the soil in the order of maleic acid〉malic acid〉oxalic acid〉citric acid. However, when LMWOAs were applied to soil where p-chlorophenol had been previously adsorbed, substantial p-chlorophenol was desorbed from soil by oxalic acid, whereas citric acid, malic acid and maleic acid didn＇t desorb as much p-chlorophenol from soil as deionized water.  相似文献   

12.
Hydrogen gas produced in the subsurface from the hydration of mafic rocks is known to be a major energy source for chemolithotrophic life in extreme environments such as hydrothermal vents. The possibility that in situ anaerobic microorganisms present in the deep subsurface are sustained by low temperature H2-generating water–rock reactions taking place around them is being investigated. Whether the growth and activity of H2-utilizing microbes directly influences aqueous geochemistry, rates of mineral dissolution, and the chemical composition of the alteration products is also being quantitatively evaluated.To explore how microorganisms are affected by water–rock reactions, and how their activity may in turn affect reaction progress, laboratory experiments have been conducted to monitor the growth of a methanogenic Archaea in the presence of H2(g) produced from low temperature water–Fe0–basalt reactions. In these systems, the conversion of Fe(II) to Fe(III) and subsequent hydrolysis of water is responsible for the production of H2(g). To characterize key components of the geochemical system, time series measurements of H2 and CH4 gas concentrations, Fe and Si aqueous concentrations, and spatially resolved synchrotron-based analyses of microscale Fe distribution and speciation were conducted. Culture experiments were compared with an abiotic control to document changes in the geochemistry both in the presence and absence of the methanogen.In the control abiotic batch experiment, H2 was continuously produced, until the headspace became saturated, while in the biotic experiments, microbial consumption of H2 for methanogenesis draws H2 down and produces CH4. Purging the headspace gas reinitiates H2 and CH4 production in abiotic and culture experiments, respectively. Mass balance analysis of the amount of CH4 produced suggests that the total H2 production in microbial experiments does not exceed the abiotic experiment. Soluble Si concentrations, while buffered to relatively constant values, were higher in culture experiments than the abiotic control.Iron(aq) concentrations appear to respond to perturbations of H2 and CH4 gas concentrations in both culture experiments and the abiotic control. A pulse of Fe preceded the rise in either H2 or CH4 production, and as the gas concentrations increased the Fe(aq) decreased. Iron-bearing mineral assemblages change with increasing reaction time and mineral assemblages vary between culture experiments and the abiotic control. These geochemical trends suggest that there are different reaction paths between the culture experiments and the abiotic control.The hydration of mafic rocks is a common geologic reaction and one that has taken place on Earth for the majority of its history and is postulated to occur on Mars. These reactions are important because of their effect on the rheology and geochemistry of the ocean crust. While most often studied at temperatures of ～250 °C, this work suggests that at lower temperatures microorganisms may have a profound effect on what has long been thought to be solely an abiotic reaction, and may produce diagnostic mineral assemblages that will be preserved in the geological record.  相似文献   

13.
The present work compares the performance of two alternative flow models for the simulation of thermal-hydraulic coupled processes in low permeable porous media: non-isothermal Richards’ and two-phase flow concepts. Both models take vaporization processes into account: however, the Richards’ model neglects dynamic pressure variations and bulk flow of the gaseous phase. For the comparison of the two approaches first published, data from a laboratory experiment are studied involving thermally driven moisture flow in a partially saturated bentonite sample. Then a benchmark test of longer-term thermal-hydraulic behavior in the engineered barrier system of a geological nuclear waste repository is analyzed (DECOVALEX project). It was found that both models can be used to reproduce the vaporization process if the intrinsic permeability is relative high. However, when a thermal-hydraulic coupled problem has the same low intrinsic permeability, only the two-phase flow approach provides reasonable results.  相似文献   

14.
We conducted melting experiments on a low MgO (3.29 wt.%) basaltic andesite (54.63 wt.% SiO2) from Westdahl volcano, Alaska, at XH2O = 0.7–1 and fO2 ~ Ni–NiO, at pressures = 0.1–180 MPa and temperatures = 900–1,200 °C. We examine the evolution of the melt along a liquid line of descent during equilibrium crystallization at high H2O and fO2 conditions, starting from a high FeOt/MgO, low MgO basaltic andesite. Ti-magnetite formed on the liquidus regardless of XH2O, followed by clinopyroxene, plagioclase, amphibole, and orthopyroxene. We observe slight but significant differences in the phase stability curves between the XH2O = 1 and 0.7 experiments. Early crystallization of Ti-magnetite and suppression of plagioclase at higher pressures and temperatures resulted in strongly decreasing melt FeOt/MgO with increasing SiO2, consistent with a “calc-alkaline” compositional trend, in agreement with prior phase equilibria studies on basalt at similar H2O and fO2. Our study helps quantify the impact of small amounts of CO2 and high fO2 on the evolution of melts formed during crystallization of a low MgO basaltic andesite magma stored at mid- to shallow crustal conditions. Like the prior studies, we conclude that H2O strongly influences melt evolution trends, through stabilization of Ti-magnetite on the liquidus and suppression of plagioclase at high P–T conditions.  相似文献   

15.
This study uses clay mineral assemblages, illite ??crystallinity?? (IC), chlorite ??crystallinity?? (CC), illite polytypes, the b cell-dimension of K-white mica, mineral geothermo-geobarometers and homogenization temperatures of fluid inclusions to investigate the transition from diagenesis to metamorphism in a 7?km thick Triassic flysch sequence in the well Hongcan 1, eastern Tibetan plateau. The 7,012.8?m deep borehole penetrated flysch of Upper to the Middle Triassic age and represents a unique chance to characterize low temperature metamorphic processes in an unusually thick sedimentary sequence developed on thickened continental crust. Mineral assemblage analysis reveals a burial metamorphic pattern with kaolinite and chlorite/smectite mix-layer phases present in the upper 1,500?m, and illite/smectite mixed-layer phases extending to a depth of 3,000?m. The metamorphic index mineral, graphite, was detected in sedimentary rock below 5,000?m using Raman spectroscopy. There exists a good correlation between IC and CC within the prograde burial sequence; with CC anchizonal boundaries of 0.242 and 0.314°2?? (upper and lower boundaries, respectively) corresponding to Kübler??s IC limits at 0.25 and 0.42°2??. Illite polytypism also shows an increase in the 2M 1 polytype with increasing depth, with ca. 60?% 2M 1 abundance compared to the 1M type at the surface, to 100?% 2M 1 at the bottom of the borehole. Fluid inclusion analysis show HHC-rich bearing fluids correspond to the diagenetic zone, CH4-rich bearing fluids appear at transitional zone from diagenetic to low anchizone and H2O-rich bearing fluids mark the high anchizone to epizone. Based on chlorite chemical geothermometer, calcite?Cdolomite geothermo-barometers as well as homogenization temperature of fluid inclusions, a paleotemperature range of 118?C348?°C is estimated for the well with a pressure facies of low to intermediate type.  相似文献   

16.
The hypothesis that much of the lithosphere of the Archaean Tanzania Craton was hydrated, by the dehydration of a buoyant subduction 2 Ga ago is presented in this study. Buoyant subduction is a potential mechanism for thermal erosion and metasomatism of extensive regions of the cold overlying continental lithosphere. This hypothesis could explain why the Tanzania Craton forms an undeformed island within the intensely deformed mobile belts. Furthermore, it would explain the formation of the eclogite and lherzolite bearing kimberlites within the Tanzania Craton far away from the trench. A buoyant, slow subduction is required because this would provide sufficient cooling from the overlying cratonic lithosphere and therefore the dipping slab could retain hydrous minerals such as antigorite in hydrated aureoles in peridotites. To test this hypothesis, the release of water during prograde metamorphism of a flat-subducting plate was modeled. It is shown that water can be transported ～800 km laterally, inboard of the trench, which is close to the north-south extension of the Archaean Tanzania Craton.  相似文献   

17.
Zircon outgrowths are present on detrital zircon grains in many very low to low-grade metasedimentary rocks worldwide, ranging in age from mid-Archaean to Palaeozoic. The outgrowths comprise minute (typically <3 μm) crystals that form an irregular fringe on detrital zircon grains, and in a few cases, on diagenetic xenotime outgrowths. Textural relationships indicate that while zircon growth postdates diagenetic xenotime precipitation, it precedes or is synchronous with metamorphic xenotime formation. Unlike xenotime, zircon outgrowths are absent in unmetamorphosed sedimentary rocks, and only appear in prehnite-pumpellyite facies rocks, suggesting that zircon growth commences at temperatures of ∼250°C. The greater abundance of zircon outgrowths in shales than in to other sedimentary rocks may relate to higher halogen concentrations, which have been linked to enhanced zirconium mobility in hydrothermal systems. The growth of zircon in metasedimentary rocks indicates that zirconium was transported in aqueous fluids, possibly as fluorine complexes, during very low-grade metamorphism.  相似文献   

18.
Low-temperature thermal waters (<20–40 °C) from Mesozoic carbonate formations of Outer and Inner Dinarides which outcrop along the margins of small Tertiary basins, are characterised by low content (commonly <500 mg/l) of total dissolved solids and the dominance of calcium-(magnesium) bicarbonate hydrogeochemical facies. Trace elements occur in the ppb to ppt range, and can be substantially enriched in carbon dioxide-rich thermomineral waters. Contacts of thermal waters with clastic sediments affect the abundance of many trace elements, like B, Ni, Mn, Fe, Se, Sr, Ba, REE and Th. The U/Th ratios are commonly very high for the waters from carbonate aquifers, although the U abundance is in the range of some ppb. The influence of clastic sediments is reflected in an increased abundance of Th, and therefore much lower U/Th ratio. Some waters are rich in strontium (over 1 ppm), which probably originates from aragonite in Cretaceous carbonate rocks.  相似文献   

19.
Abstract

The geochemistry of Early Proterozoic sedimentary rocks from the low‐grade metamorphic terrain W of the South Alligator Hinge Zone in the Pine Creek Geosyncline is reported and discussed in terms of the stratigraphy and differences in rock type. Major element trends are dominated by lithological and mineralogical variations; in particular, the dolomitic nature of pelites in the Mount Partridge and Namoona Groups, the presence of chlorite in Crater Formation pelites, and the volcanic affinity of pelites within the Gerowie Tuff. Concentration of Th, U, Zr, Y, Nb, Ce and La in the clastic sediments of the Finniss River and South Alligator Groups is probably related to the presence of felsic volcanics in these groups; high levels of Sn in these groups may be similarly related, and highlight the apparent volcanogenic source for this metal. The South Alligator Group is a preferred host for base‐metal mineralization, and the regional abundance of several metals in this group enhance its economic potential and support a syngenetic, possibly exhalative, origin for these deposits. Anomalous Co, Ni, and V values in Masson Formation pelites are probably related to the nearby mafic Stag Creek Volcanics. Detrital minerals derived from reworked Archaean basement account for high Zr and Th in the Crater Formation. The geochemical data support the shift in REE patterns related to changes in crustal composition about the Archaean‐Proterozoic boundary, though patterns within the Early Proterozoic have also been influenced by felsic volcanism in the South Alligator Group. The chemical index of alteration (which reflects the degree of weathering of sedimentary rocks) reflects the existence of a major unconformity between the Mount Partridge and Namoona Groups; however, other hiatuses observed in or inferred from the rock record are not evident. The dominant felsic volcanic component of the Gerowie Tuff pelites is also indicated by this technique.  相似文献   

20.
The biological impact of microwaves exposure on biosphere is presently an important research subject. With the significant increase of communications technology use, of industrial and military activities which involve radiofrequency radiation, electromagnetic pollution became very intense in the last years. The aim of the present work was to investigate the genotoxic influence of microwaves on Zea mays seeds. They were exposed in controlled conditions for different durations at 1 GHz continuous wave providing a low specific absorption rate of energy. Post-exposure the mitotic- and chromosomal aberrations indexes were determined. Qualitatively, a wide range of abnormal mitotic stages were detected in cells of exposed seeds in comparison with the control. Quantitatively, slight stimulatory effect on mitotic division process, expressed by an enhanced percentage of dividing cells (increased of 26% for 180 min exposure), for all exposed samples was revealed, while lowered level of induced chromosomal aberrant cells percentage (up to 2.14%) was also found. The aberrations percentage and mitotic index increased in time-dependent manner on exposure dose.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号