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1.
Middle Miocene (17-9 Ma) volcanism in northeast Israel migrated from eastern Lower Galilee (Poria, west of the Sea of Galilee) to the southwest (Yizre'el Valley) in association with the development of an extensional basin in that area. The Yizre'el Valley magmas are highly undersaturated in silica (basanites and nephelinites), while those of Poria are alkali-basaltic. Scarce Middle Miocene basalts from the Golan, further to the east, are also alkali-basaltic. Magmas from Kaukab (southeastern Lower Galilee) show a range of compositions from alkali-basalts to basanites. The patterns defined by ratios versus concentrations of incompatible elements in Kaukab basalts (e.g. versus La), as well as the scatter observed in Sr isotope ratios, are interpreted in terms of binary mixing. It is suggested that the Kaukab magmas were derived from veined lithospheric peridotites, melts of the veins and of the peridotites being the two end-members. Accordingly, alkali-basaltic- and basanite-dominated areas are underlain by vein-poor and vein-rich lithosphere, respectively. It is also suggested that melting during the Middle Miocene mainly occurred in response to extension, and that it followed the propagation of the Yizre'el-Galilee Basin from northeast to southwest.  相似文献   

2.
Geochemical characteristics of Cretaceous carbonatites from Angola   总被引：1，自引：0，他引：1  
The Early Cretaceous (138–130 Ma) carbonatites and associated alkaline rocks of Angola belong to the Paraná-Angola-Etendeka Province and occur as ring complexes and other central-type intrusions along northeast trending tectonic lineaments, parallel to the trend of coeval Namibian alkaline complexes. Most of the Angolan carbonatite-alkaline bodies are located along the apical part of the Moçamedes Arch, a structure representing the African counterpart of the Ponta Grossa Arch in southern Brazil, where several alkaline-carbonatite complexes were also emplaced in the Early Cretaceous. Geochemical and isotopic (C, 0, Sr and Nd) characteristics determined for five carbonatitic occurrences indicate that: (1) the overall geochemical composition, including the O---C isotopes, is within the range of the Early and Late Cretaceous Brazilian occurrences from the Paraná Basin; (2) the La versus relationships are consistent with the exsolution of COi2-rich melts from trachyphonolitic magmas; and (3) the and initial ratios are similar to the initial isotopic ratios (129 Ma) of alkaline complexes in northwest Namibia. In contrast, the Lupongola carbonatites have a distinctly different initial ratio, suggesting a different source.The Angolan carbonatites have Sr---Nd isotopic compositions ranging from bulk earth to time-integrated depleted sources. Since those from eastern Paraguay (at the western fringe of the Paraná-Angola-Etendeka Province) and Brazil appear to be related to mantle-derived melts with time-integrated enriched or B.E. isotopic characteristics, it is concluded that the carbonatites of the Paraná-Angola-Etendeka Province have compositionally distinct mantle sources. Such mantle heterogeneity is attributed to ‘metasomatic processes’, which would have occurred at ca 0.6–0.7 Ga (Angola, northwest Namibia and Brazil) and ca 1.8 Ga (eastern Paraguay), as suggested by Nd-model ages.  相似文献   

3.
The Upper Proterozoic granitoids of the western part of the Siroua Massif (central Anti-Atlas, Morocco) are cut by doleritic dykes injected along submeridian and equatorial directions. These dykes were emplaced before deposition of late Neoproterozoic formations (PIII). According to and incompatible element ratios, these dolerites constitue two discrete chemical groups unrelated to orientation and thickness. They are both enriched in large ion lithophile elements, Zr, Th and light rare earth elements, and correspond to continental tholeiites displaying an alkaline affinity. This alkaline affinity is also confirmed by clinopyroxene and amphibole chemistry. Emplacement of these doleritic dykes occurred under an extensional regime active in the Anti-Atlas range during the Upper Proterozoic.  相似文献   

4.
Crystalline rocks from the western Ethiopian Precambrian terrain comprise two major rock groups: (1) the often migmatised eastern and western high-grade gneisses; and (2) the central low-grade metavolcanosedimentary rocks. Granitoid bodies of different ages and compositions intrude these rocks. Field observations, petrographic investigations, and geochemical features support a two-fold classification of the granitoid rocks. The volcanic arc granitoids (VAG) are most common and include the Ujjukka granite and granodiorite, and the Dhagaa Booqa and Guttin K-feldspar megacrystic granites. The second and geographically more restricted group represents within-plate or anorogenic (A-type) granitoids, typified by the Tullu Kapii syenite. Geochemically, the Tullu Kapii syenite is characterised by moderate to high contents of SiO2, total alkalis, Y, Nb, Ta, Hf, Zn, Zr, Ga, ΣREE, higher ratios of Fe2O3(total)/MgO, , , and lower contents of CaO, MgO, Sr, and Ba, compared to the other granitoids. The VAG group shows chondrite-normalised REE patterns with slightly enriched LREE and flat HREE patterns without significant Eu anomalies. In contrast, the Tullu Kapii A-type granitoid is characterised by a nearly horizontal REE pattern with variable negative Eu anomalies. The Ujjukka granite and granodiorite; and the Dhagaa Booqa and Guttin K-feldspar megacrystic granites originated in a two-step process, which involves batch equilibrium melting of basaltic or andesitic material producing tonalitic magma, followed by fractional crystallisation. The Tullu Kapii syenite was the product of partial melting of source rocks enriched in high field strength elements.  相似文献   

5.
In this paper, a sequence of five Late Quaternary tephras occurring as discrete, well-preserved horizons in lake sediments on the northeastern flank of Mount Kenya are characterised and their ages determined by a combination of high-resolution indirect radiocarbon dating and direct dating. The grain size characteristics suggest that the tephras are of fairly local origin. These Na---K-rich alkali pyroclasts with a trachytic chemical composition have a highly correlated chemistry and mineralogy, suggesting that they were probably derived from the same genetic series and possibly erupted from a single source vent. Morphological differences are attributed to the peculiar characteristics of each eruption episode. The magma source was probably a small, highly differentiated magma chamber following the olivine basalt-trachyandesite-trachyte-phonolite series, which broadly reflects the Quaternary rock suite of Mount Kenya.  相似文献   

6.
This work studies the water quality of the Pergamino–Arrecifes River zone in the Rolling Pampa, northeast Buenos Aires Province, Argentina. Temperature, pH, specific conductivity, Na, K, Mg, Ca, , Cl−, , , Si, Ag, Al, As, B, Ba, Be, Br, Cd, Co, Cr, Cu, Fe, Hg, Li, Mn, Mo, Ni, P, Pb, Se, Tl, U, V, Zn, and the environmental stable δ18O and δ2H isotope ratios were determined in 18 sampling stations. Natural and anthropogenic features influence surface and groundwater quality. Point pollution sources (septic wells and other domestic and farming effluents) increase the nitrate concentration. The values of pH, , Al, As, B, Fe, and Mn exceed the respective Argentine reference thresholds in different sampling stations for human drinking water; B, Mo, U, and V for irrigation; and V and Zn for cattle consumption.  相似文献   

7.
Nitrate-contaminated groundwater from an aquifer in the Osona region (NE Spain) was chemically and isotopically (δ15NNO3,δ18ONO3,δ34SSO4,δ18OSO4, δD, δ18OH2O and δ13CDIC) characterized. Diffuse- contamination reached values of 366 mg/L. Nearly 75% of the 37 sampled sites had higher concentrations than the 50 mg/L in limit for drinking water. To identify the source of pollution δ15NNO3 and δ18ONO3 were used with results, for most samples, in the range of pig manure . Nitrification processes were evaluated by means of the δ18O of and water. Isotopic data suggested that natural attenuation of was taking place. This process was confirmed using the δ18ONO3 coupled with the ratio, avoiding the influence of continuous inputs. A further insight on denitrification processes was obtained by analyzing the ions involved in denitrification reactions. Although the role of organic matter oxidation could neither be confirmed nor discarded, this approach showed a link between denitrification and pyrite oxidation. Therefore, in areas with no adequate infrastructure (e.g. multipiezometers), such as the one studied, this approach could be useful for implementing better water management.  相似文献   

8.
Gradients controlling natural attenuation of ammonium   总被引：1，自引：0，他引：1  
Oxidation of reduced pollutants such as in groundwater often takes place at steep redox gradients where oxygenated water is being mixed into polluted water such as landfill leachate. In order to identify controlling parameters and quantify the influence of environmental factors for degradation, sensitivity analysis was performed by means of scenario specific numerical modelling. Geometrical factors such as aquifer thickness have been shown to be very influential on the capability of natural attenuation of pollutants in groundwater. The scenarios investigated here include biodegradation at redox gradients in groundwater, so called fringe processes, for (i) a partly contaminated aquifer with two reaction fronts, (ii) and a spatially variable aquifer thickness. In addition, (iii) the influence of groundwater recharge and (iv) restricted supply of O2 to contaminated water by slow dispersion and diffusion across the capillary fringe are investigated. Contaminated aquifer thickness, zones of enhanced mixing due to flow focussing and diffusion/dispersion coefficients in the capillary fringe are identified qualitatively as controlling factors for natural attenuation under complex conditions, whereas predictive functions will require further research.  相似文献   

9.
This paper presents the first paleostress results from fault-slip data on Cretaceous limestone at the eastern rim of the Dead Sea transform (DST) in Jordan. Stress inversion of fault-slip data is performed using an improved right dieder method, followed by rotational optimization (Delvaux, TENSOR Program). The orientation of the principal stress axes (σ1, σ2 and σ3) and the ratio of the principal stress differences ( ) show two main paleostress fields marking two main stress regimes, strike-slip and extensional. The first is characterized by NNW–SSE compression and ENE–WSW extension and related to Middle Miocene-Recent sinistral movement along the Dead Sea transform and the opening of the Red Sea. The second paleostress field is a WNW–ESE compression and NNE–SSW extension restricted to the northern part of the investigated area. This stress field could be associated with the development of the Syrian Arc fold belt which started during the Turonian, or it may be due to an anticlockwise rotation of the first stress field.  相似文献   

10.
Recent experimental determinations of the solubility products of common rare earth minerals such as monazite and xenotime and stability constants for chloride, sulfate, carbonate and hydroxide complexes provide a basis to model quantitatively the solubility, and therefore the mobility, of rare earth elements (REE) at near surface conditions. Data on the mobility of REE and stabilities of REE complexes at near-neutral conditions are of importance to safe nuclear waste disposal, and environmental monitoring. The aim of this study is to understand REE speciation and solubility of a given REE in natural environments. In this study, a series of formation constants for La aqueous complexes are recommended by using the specific interaction theory (SIT) for extrapolation to infinite dilution. Then, a thermodynamic model has been employed for calculation of the solubility and speciation of La in soil solutions reacted with the La end-member of mineral monazite (LaPO4), and other La-bearing solid phases including amorphous lanthanum hydroxide (La(OH)3, am) and different La carbonates, as a function of various inorganic and organic ligand concentrations. Calculations were carried out at near-neutral pH (pH 5.5–8.5) and 25 °C at atmospheric CO2 partial pressure. The model takes account of the species: La3+, LaCl2+, , , , , , , , , La(OH)2+, LaOx+, , LaAc2+ and (where Ox2− = oxalate and Ac− = acetate).The calculations indicate that the La species that dominate at pH 5.5–8.5 in the baseline model soil solution (BMSS) include La3+, LaOx+, , and in order of increasing importance as pH rises. The solubility of monazite in the BMSS remains less than 3 × 10−9 M, exhibiting a minimum of 2 × 10−12 M at pH 7.5. The calculations quantitatively demonstrate that the concentrations of La controlled by the solubility of other La-bearing solid phases are many orders of magnitude higher than those controlled by monazite in the pH range from 5.5 to 8.5, suggesting that monazite is likely to be the solubility-controlling phase at this pH range. The calculations also suggest that significant mobility of La (and other REE) is unlikely because high water–rock ratios on the order of at least 104 (mass ratio) are required to move 50% of the La from a soil. An increase in concentration of oxalate by one order of magnitude from that of the baseline model solution results in the dominance of LaOx+ at pH 5.5–7.5. Similarly, the increase in concentration of by one order of magnitude makes the dominant species at pH 5.5–7.5. Above pH 7.5, carbonate complexes are important. The increase in oxalate or concentrations by one order of magnitude can enhance the solubility of monazite by a factor of up to about 6 below neutral pH, in comparison with that in the baseline model soil solution. From pH 7.0 to 8.5, the solubility of monazite in the soil solutions with higher concentrations of oxalate or is similar, or almost identical, to that in the BMSS.  相似文献   

11.
Various isotope studies require accurate fractionation factors (α’s) between different chemical compounds in thermodynamic equilibrium. Although numerous isotope systems involve aqueous solutions, the conventional theory is formulated for the gas-phase and predicts incorrect α’s for many compounds dissolved in water. Here I show that quantum-chemistry calculations, which take into account solute–water interactions, accurately predict, for instance, oxygen isotope fractionation between dissolved and H2O (hereafter ). Simple force field and quantum-chemistry calculations for the ‘gas-phase’ ion predict (15‰) at 25 °C. However, based on -clusters with up to 22 H2O molecules, I calculate a value of 25‰, which agrees with the experimental value of 24.5 ± 0.5‰. Effects of geometry and anharmonicity on the calculated α were also examined. The calculations reveal the critical role of hydration in solution, which is ignored in the gas-phase theory. The approach presented provides an adequate framework for calculating fractionation factors involving dissolved compounds; it may also be used to predict α’s that cannot (or have not yet been) determined experimentally.  相似文献   

12.
Clinopyroxene dissolution in basaltic melt   总被引：1，自引：0，他引：1  
The history of magmatic systems may be inferred from reactions between mantle xenoliths and host basalt if the thermodynamics and kinetics of the reactions are quantified. To study diffusive and convective clinopyroxene dissolution in silicate melts, diffusive clinopyroxene dissolution experiments were conducted at 0.47–1.90 GPa and 1509–1790 K in a piston-cylinder apparatus. Clinopyroxene saturation is found to be roughly determined by MgO and CaO content. The effective binary diffusivities, DMgO and DCaO, and the interface melt saturation condition, , are extracted from the experiments. DMgO and DCaO show Arrhenian dependence on temperature. The pressure dependence is small and not resolved within 0.47–1.90 GPa. in the interface melt increases with increasing temperature, but decreases with increasing pressure. Convective clinopyroxene dissolution, where the convection is driven by the density difference between the crystal and melt, is modeled using the diffusivities and interface melt saturation condition. Previous studies showed that the convective dissolution rate depends on the thermodynamics, kinetics and fluid dynamics of the system. Comparing our results for clinopyroxene dissolution to results from a previous study on convective olivine dissolution shows that the kinetic and fluid dynamic aspects of the two minerals are quite similar. However, the thermodynamics of clinopyroxene dissolution depends more strongly on the degree of superheating and composition of the host melt than that of olivine dissolution. The models for clinopyroxene and olivine dissolution are tested against literature experiments on mineral–melt interaction. They are then applied to previously proposed reactions between Hawaii basalts and mantle minerals, mid-ocean ridge basalts and mantle minerals, and xenoliths digestion in a basalt at Kuandian, Northeast China.  相似文献   

13.
Twelve massive sulphide deposits from the Iberian Pyrite Belt (IPB) show well-preserved iron caps, some of which were mined during the last century to recover precious metals (e.g., Tharsis, Rio Tinto, San Miguel). Field observations and correlation assays between the distinct mineral sequences at different deposits suggest that all the gossans were developed under similar conditions and have undergone the same geological events. All the gossans have a mushroom-like morphology in sharp contact with the underlying massive sulphide orebodies. In most cases these are located over an apparent supergene enrichment zone rich in secondary sulphides. Some gossans extend into tongues of alluvial heterolithic breccias consisting of eroded transported gossans displaced as far as several hundred meters away from their sources. The distribution of major minerals throughout the gossan profiles (goethite, hematite, quartz and jarosite) and the statistical analysis of the geochemical data distinguish three separate zones, with gradual contacts roughly parallel to the current topography: (1) the lower zone dominated by goethite and subordinate jarosite, with significant enrichment in S, As, P, Pb, Sn, Sb, Ag and Au; (2) the middle or principal zone dominated by goethite and lacking jarosite, which is depleted in S, and As, as well as heavy and precious metals; and (3) the upper zone near the surface, mainly composed of hematite and quartz with only weak anomalies in P, Pb and Sn. The origin and variations occurred in the profiles are explained by a three-stage process. This involves an initial acidic stage of gossan development centred on the oxidation of sulphides that lead to the formation of the first Fe-rich oxyhydroxides and sulphates (mainly goethite and jarosite, respectively). Over time, a progressive stage of maturity is reached progressively downwards through the gossan profile due to the intensification of the oxidation and leaching processes. The ongoing gossan formation produced alteration and reprecipitation of pre-existing oxyhydroxides, the loss of the majority of the previously sorbed heavy metals, and a major dilution of trace elements especially in the zones near the surface. The main results of this stage of formation are the production of heavy metal-depleted oxyhydroxides, most commonly goethite and hematite, and the disappearance of jarosite. Subsequently, local uplift of the gossanous rocks by neotectonic movements facilitated the rejuvenation of the oxidation of the ores. This final stage complicated the previously developed zonation with the formation of jarosite in mature areas. Possible major breaks in this gossan development ocurred in Messinian times (7–8 Ma) and at the beginning of the Early Quaternary (1–2 Ma?).  相似文献   

14.
The Songpan-Ganze terrane of the Tibetan plateau is underlain by Neoproterozoic crystalline basement rocks of the Yangtze block. These basement rocks are exposed as a series of extensional tectonic domes that form a nearly north–south trending extensional belt more than 1000 km long in the eastern margin of the Tibetan plateau. In the Danba area, detachment faults separate the basement core complexes (e.g., the Gezong and Gongcai complexes) from the Paleozoic strata which have been thinned or removed completely. The cover sequences have undergone upper greenschist to lower amphibolite facies metamorphism to form the Danba schist and are overlain by the Triassic Xikang Group, a thick flysch sequence. Both the basement rocks and the Paleozoic rocks have undergone multiple stages of deformation and thus provide an excellent opportunity to study the tectono-thermal evolution of the eastern margin of the Tibetan plateau. Two stages of deformation, corresponding to three generations of foliation (S1, , and ), have been recognized on the basis of structural and microscopic observations. We selected amphibole and biotite separates associated with distinct generations of foliation for 40Ar/39Ar dating using laser microprobe incremental heating technique to place numerical constraints on the major tectono-thermal events within the Danba area. The geochronogical results reveal an earliest metamorphic event at 258.6 ± 0.5 Ma (S1 biotite) and 263.6 ± 0.8 Ma (S1 amphibole), coinciding temporally with the mantle plume that produced the voluminous Emeishan flood basalts. The second event was a progressive extensional deformation first occurred at 159–166 Ma ( amphibole) responsible for the earlier tectonic doming of the crystalline basement, and then the final tectono-thermal overprint recorded by foliation and metamorphism locally in the core complexes at 47–58 Ma for the Gezong complex and 64–81 Ma for the Gongcai complex. This major post-orogenic extensional event is believed to be a consequence of collision between the North China and South China blocks. The apparent discrepancy of the 40Ar/39Ar ages observed between localities suggests a slow cooling process associated with progressive uplift.  相似文献   

15.
We determined concentrations and isotopic composition of nitrate in five German rivers (Rhine, Elbe, Weser, Ems, and Eider) that discharge into the North Sea. Samples were obtained on a biweekly to monthly basis and chemical and isotopic analyses were conducted for the period January 2006 to March 2007 at sampling stations situated before estuarine mixing with North Sea water. We observed maximum nitrate loads in winter and fall, when both discharge and concentration of nitrate are highest. Mean annual isotope values in nitrate ranged from 8.2‰ to 11.3‰ for and 0.4‰ to 2.2‰ for . The ranges of isotope values suggest that nitrate in these rivers derives from soil nitrification, sewage, and/or manure. These and published data on other rivers in northern Europe and northern America reveal a correlation between agricultural land use (>60% in the catchment areas of rivers examined) and values. The rivers Rhine, Elbe, Weser and Ems show similar seasonal patterns of the isotopic fractionation of nitrate with increasing values and simultaneously decreasing concentrations during summer months, indicating that assimilation of nitrate is the main fractionation process of riverine nitrate. Isotopic signals in winter are more depleted than the mean summer isotope values, attributed to less microbial activity and assimilative processes. Load weighted nitrate δ15N of the riverine input to the German Bight Coastal Water mass before estuarine mixing and processing is between 8‰ and 12‰. The high δ15N value of river nitrate is matched by high δ15N of nitrate in surface sediments in the German Bight.  相似文献   

16.
The petrographic and palynologic compositions of coal seams of the acler formation (Upper Carboniferous, Westphalian A) from northwestern and southeastern part of the Lower Silesian Coal Basin (LSCB) were examined. Coals studied are highly volatile bituminous coal, where Ro ranges from 0.91% to 1.09%. Seam 430 from the northwestern part of the basin contains high vitrinite percentage with rather low inertinite and liptinite contents, while percentage of mineral matter is variable. This petrographic composition is associated either with a predominance of Lycospora in miospore assemblage, or with a miospore assemblage of mixed character. The abundance of Lycospora reflects vegetation composed of the arborescent lycopsids while the mixed miospore assemblage is connected with diverse palaeoplant communities, namely, arborescent lycopsids, calamites and ferns. Seams 409 and 412/413 from the southeastern part of the LSCB are rich in inertinite and liptinite, while the vitrinite content is moderate. Their characteristic feature is the occurrence of a diagnostic crassisporinite (densosporinite). Amount of the mineral components in these coals is very low. Densosporites and related crassicingulate genera are main components of these miospore assemblages and were produced by herbaceous and/or sub-arborescent lycopsids. These petrographic and palynologic features were the basis for distinguishing three maceral–miospore associations: an arborescent lycopsid and mixed associations, occurring in the seam 430 and a herbaceous and/or sub-arborescent lycopsid association which was recorded in seams 409 and 412/413. The first two assemblages are interpreted as having been deposited in a planar rheotrophic mire, whereas the herbaceous and/or sub-arborescent lycopsid association is thought to have developed in an ombrotrophic, domed mire.  相似文献   

17.
Solubility and dissolution rate of silica in acid fluoride solutions   总被引：1，自引：0，他引：1  
We performed 57 batch reactor experiments in acidic fluoride solutions to measure the dissolution rate of quartz. These rate data along with rate data from published studies were fit using multiple linear regression to produce the following non-unique rate law for quartz
where 10−5.13 < aHF < 101.60, −0.28 < pH < 7.18, and 298 < T < 373 K. Similarly, 97 amorphous silica dissolution rate data from published studies were fit by multiple linear regression to produce the following non-unique rate law for amorphous silica
where 10−2.37 < aHF < 101.61, −0.32 < pH < 4.76 and 296 < T < 343 K. Regression of the rates versus other combinations of solution species, e.g.  + H+, F− + H+, HF + , HF + F−, or  + F−, produced equally good fits. Any of these rate laws can be interpreted to mean that the rate-determining step for silica dissolution in fluoride solutions involves a coordinated attack of a Lewis acid, on the bridging O atom and a Lewis base on the Si atom. This allows a redistribution of electrons from the Si–O bond to form a O–H group and a Si–FH group.  相似文献   

18.
Values of overall Gibbs free energy of 144 organic oxidation (respiration) and disproportionation (fermentation) reactions are calculated at the temperatures and chemical compositions that exist in nine submarine vents, sediment seeps and geothermal wells in the hydrothermal system of Vulcano Island, Italy. The organic compounds considered here include four carboxylic acids (formic, acetic, propanoic and lactic), two C5 aldoses (arabinose and xylose), three C6 aldoses (galactose, glucose and mannose), and 15 protein-forming amino acids (Ala, Arg, Asp, Glu, Gly, His, Ile, Leu, Lys, Met, Phe, Ser, Thr, Tyr, and Val). Oxidation of these compounds is coupled to five redox pairs: O2/H2O, , S0/H2S, and Fe3O4/Fe2+. Energy yields from potential respiration reactions range from 6 to 118 kJ/mol of electrons transferred and show systematic behavior with respect to the terminal electron acceptor. Overall, respiration with O2 yields the most energy (98–118 kJ/mol e−), followed by reactions with (53– 86 kJ/mol e−), magnetite (29–91 kJ/mol e−), S0 (11–33 kJ/mol e−) and (6–34 kJ/mol e−). Energy yields show little correlation with organic compound family, but are correlated with fluid pH. Variability in energy yields across the nine sites is greatest for Fe(III) reduction and is primarily influenced by pH and the activity of Fe2+. In addition to the potential respiration reactions, the energetics of 24 potential fermentation reactions are also calculated. As expected, fermentation reactions generally yield much less energy than respiration. Normalized to the number of moles of carbon transferred, fermentation yields−8 to 71 kJ/mol C, compared with 16 to 531 kJ/mol C for respiration reactions. All respiration and fermentation reactions, except for methionine (Met) fermentation, are exergonic under the in situ hydrothermal conditions and represent a plethora of potential metabolisms for Vulcano’s diverse thermophilic heterotrophs.  相似文献   

19.
The spatial and temporal variation of major ions (Ca2+, Mg2+, Na+, K+, , , and Cl−) in Himalayan snow and ice is investigated by using two snow pits from the East Rongbuk glacier (28°01′N, 86°58′E, 6500 m a.s.l.), one snow pit from the Nangpai Gosum glacier (28°03′N, 86°39′E, 5700 m a.s.l.), one snow pit from the Gyabrag glacier (28°11′N, 86°38′E, 6303 m a.s.l.), and three ice cores from the Sentik (35°59′N, 75°58′E, 4908 m a.s.l.), Dasuopu (28°33′N, 85°44′E, 7000 m a.s.l.), and East Rongbuk (27°59′N, 86°55′E, 6450 m a.s.l.) glaciers, respectively. In general, the major ions show a significant seasonal variation, with high concentrations during the non-monsoon (pre-monsoon and post-monsoon) season and relatively low concentrations during the monsoon season. Monsoon precipitation with high local/regional dust loading related to summer circulation is possibly responsible for the high concentrations occurring sporadically during the monsoon season. The crest of the Himalayas is an effective barrier to the spatial distribution of Na+, Cl− and concentrations, but not to the major ions associated with dust influx (e.g. Ca2+ and Mg2+). Atmospheric backward trajectories from the HYSPLIT_4 model used in identifying chemical species sourcing suggest that the major ions in the Himalayan snow and ice come mainly from the Thar Desert located in the North India, as well as West Asia, or even the distant Sahara Desert in the North Africa during the winter and spring seasons. This is different from the conventionally assumed arid and semi-arid regions of the central Asia. Factors, such as different vapor sources due to atmospheric circulation patterns and geographical features (e.g. altitude, topography), may contribute to the differences in major ionic concentrations between the western and eastern Himalayas.  相似文献   

20.
The partitioning of Pt in sulphide melt (matte) has been studied as a function of fS2 and fO2 at 1200 and 1300 °C. The results show that the solubility of Pt in mattes increases strongly with increasing fS2 and decreases weakly with increasing fO2. The increase in Pt solubility with increasing fS2 is attributed to Pt dissolving in the melt as a sulphide species and the weak inverse dependence of Pt solubility on fO2 to the diluting effect of increasing O in the melt at high fO2. These results, coupled with measurements of Pt solubility in silicate melts taken from the literature, allow the calculation of Pt matte/silicate-melt partition coefficients () for a range of conditions pertinent to the formation of Pt-rich horizons in layered intrusions. The calculated values range between 107 and 1011, depending on fO2 and fS2, several orders of magnitude higher than previously published values. Our preferred value for for conditions appropriate to the Merensky Reef is 107 and for the Stillwater Pt-rich horizon 108. The new results are consistent with the magmatic hypothesis for Pt-rich horizons in layered intrusions.  相似文献   

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