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1.
Ajaz Karim  Jan Veizer   《Chemical Geology》2000,170(1-4):153-177
This study deals with the major ions and isotope systematics for C, O, S, and Sr in the Indus River Basin (IRB). Major ion chemistry of the Indus, and most of its headwater tributaries, follow the order Ca2+>Mg2+>(Na++K+) and HCO3−>(SO42−+Cl−)>Si. In the lowland tributaries and in some of the Punjab rivers, however, (Na++K+) and (SO42−+Cl−) predominate. Cyclic salts, important locally for Na+ in dilute headwater tributaries, constitute about 5% of the annual solutes transported by the Indus. Weathering of two lithologies, sedimentary carbonates and crystalline rocks, controls the dissolved inorganic carbon (DIC) concentrations and its carbon isotope systematics throughout the Indus, but turbulent flow and lower temperatures in the headwaters, and storage in reservoirs in the middle and lower Indus promote some equlibration with atmospheric carbon dioxide. Combined evidence from sulfur and oxygen isotopic composition of sulfates refutes the proposition that dissolution of these minerals plays a significant role in the IRB hydrochemistry and suggests that any dissolved sulfates were derived by oxidation of sulfide minerals.

In the upper Indus, silicate weathering contributes as much as 75% (or even higher in some tributaries) of the total Na+ and K+, declining to less than 40% as the Indus exits the orogen. In contrast, about two-thirds of Ca2+ and Mg2+ in the upper Indus (over 70% in some tributaries) and three-fourth in the lower Indus, are derived from sedimentary carbonates. The 87Sr/86Sr ratios tend to rise with increasing proportions of silicate derived cations in the headwater tributaries and in the upper and middle Indus, but are out of phase or reversed in the lower Indus. Finally, close to the river mouth, the discharge weighted average contribution of silicate derived Ca2++Mg2+ and silicate derived Na++K+ are, respectively, about one-fourth and two-thirds of their total concentrations.  相似文献   


2.
Atmospheric precipitation samples were collected in the Bohemian Karst (30 km SW from Prague, Czech Republic) at six localities in the vicinity of the limestone-quarry Čertovy schody during years 1996–2003. Samples were analyzed for major components (Na+, K+, Mg2+, Ca2+, F−, Cl−, NO3−, HCO3−, SO42−) and trace metals (Cu, Mn, Fe, Zn, Pb, Be, As, Sr, Cd, Al, Cr). Deposition fluxes were calculated from more than 10 000 elemental analyses of samples collected monthly. The fluxes of monitored substances show temporal and spatial variability. The most marked attribute is the strong affection by local emission sources confirmed by the investigation of seasonal variability, temporal trend and correlation analysis.  相似文献   

3.
The spatial and temporal distributions of major elements were investigated in the surface waters and in associated suspended matter at two sites of the upper Loire basin (Orleans and Brehemont) between 1995 and 1998.According to geochemical and isotopic patterns, the dissolved load appears to result from a process of mixing rainwater inputs, weathering processes of carbonate and silicate bedrock, and agricultural and urban inputs. Natural inputs influence 60% of water chemical composition at both sites. Annual dissolved fluxes were estimated to be 1300 103 t/y at Orleans and 1620 103 t/y at Brehemont. Major elements are transported mainly in the dissolved fraction. After correcting for atmospheric and anthropogenic inputs, the silicate specific export rate was calculated to be 11 t/y/km2 throughout the basin and the carbonate specific export rate to be from 47 t/y/km2 at Orleans to 23 t/y/km2 at Brehemont.The suspended load appears to result from at least two particle reservoirs: a silicate reservoir and a carbonate reservoir. The silicate reservoir has a detrital origin, mainly during periods of high flow, while the carbonate reservoir has a detrital origin during periods of high flow and an authigenic origin during periods of low flow. Of the total annual flow of suspended matter, this authigenic material represents 16% at Orleans, 25% at Brehemont and 37% in the fluvial part of the estuary. After correcting authigenic inputs, the specific export rate due to mechanical weathering was estimated to be 8 t/y/km2 throughout the Loire basin.  相似文献   

4.
额尔齐斯河源春季水化学及稳定同位素特征研究   总被引：2，自引：0，他引：2  
基于2018年4月额尔齐斯河源至富蕴段的河水样品, 综合运用Gibbs图、 Piper三线图、 相关矩阵分析等方法对河水中主要的化学离子、 pH值、 电导率、 TDS和氢、 氧稳定同位素等物理化学指标进行了分析。结果表明： 额尔齐斯河源春季河水呈弱碱性, TDS平均值为72.02 mg·L-1, 整体属于低矿化度水。河水中主要离子浓度序列为HCO3- > SO42- > Ca2+ > Na+ > Cl- > NO3- > Mg2+ > K+, 其中HCO3-、 SO42-和Ca2+是最主要的阴阳离子。水化学类型从库依尔特河的HCO3--Ca2+型转变为额尔齐斯河富蕴段的（HCO3-, SO42-）-Ca2+型。从源区至富蕴段各离子含量整体呈增大趋势, 但其增加过程受到复杂因素的影响而出现差异。河水离子主要受水-岩风化作用控制, 且以碳酸盐岩（石灰岩、 白云岩）为主的风化水解是离子的主要来源, 其次是长石类矿物的风化, 还包括下游人类活动的离子输入等。δD和δ18O沿程逐渐增大, 在下游出现了富集现象。  相似文献   

5.
以疏勒河源区为研究区,自2018年12月至2019年11月分别采集河水、泉水和雪样样品44个、4个和7个,综合运用Piper三线图、Gibbs图、离子比值法定性分析不同水体水化学特征及控制因素,利用质量平衡法（正向地球化学模型）量化不同来源对不同季节河水水化学成分的贡献率。结果表明：疏勒河源区不同水体水化学特征存在差异,TDS含量为泉水>河水>冰川融水>雪水,河水水化学类型冬季为HCO3--Mg2+?Ca2+型,春季为HCO3--Ca2+?Mg2+?Na+型,夏、秋季均为HCO3--Ca2+?Mg2+型,泉水和雪水分别为HCO3--Ca2+?Mg2+型、HCO3--Ca2+型;受多种因素共同影响,不同季节河水主离子时空变化均存在差异;河水和泉水水化学组成受岩石风化作用控制,主离子来源于以白云石为主的碳酸盐岩风化、硅酸盐岩风化和盐岩、石膏、硫酸盐矿物等蒸发岩溶解;正向地球化学模型计算结果表明冬春季河水阳离子主要来源于硅酸盐岩风化溶解,夏秋季碳酸盐岩对河水阳离子贡献率大于硅酸盐岩,总体河水阳离子主要来源于碳酸盐岩和硅酸盐岩风化。  相似文献   

6.
人工回灌过程中所发生的水-岩相互作用是影响回灌层位地下水环境质量的重要因素。采用室内实验和水文地球化学模拟等技术对人工回灌过程中的水-岩相互作用机理进行了分析。研究结果表明：受混合作用影响,随着回灌水比例的增加,混合水中TDS质量浓度降低,水化学类型由Cl·HCO3-Na型水逐渐转变为HCO3·Cl-Na·Ca型水;受水-岩作用影响,在同一混合比例条件下,随着水-岩作用的进行,混合水中TDS质量浓度升高,各主要离子质量浓度呈现升高的趋势,但只有回灌水比例占10%时,混合水TDS质量浓度才大于原始地下水（涨幅约5%）。实验介质溶解于水的离子中,Ca2+、Mg2+和HCO-3主要来源于碳酸盐矿物的溶解, Na+主要来自岩盐的溶解。在人工回灌过程中,发生的水-岩相互作用主要包括方解石、白云石、钾长石、岩盐、CO2的溶解和伊利石的沉淀。其中:钾长石溶解量与伊利石沉淀量、碳酸盐矿物溶解量与CO2溶解量的相关性较强,其相关系数分别为1.00和0.78（显著性水平为0.05）;硅酸盐矿物反应量和回灌水比例之间的相关系数为0.97（显著性水平为0.01）,相关性极强;而碳酸盐矿物反应量和回灌水比例之间的相关系数为0.52（显著性水平为0.01）,相关性较弱。上述相关性分析为确定人工回灌过程中的水-岩相互作用机理、地下水中主要离子组分的来源途径以及定量分析人工回灌对含水层介质的影响提供了依据。  相似文献   

7.
在调查取样的基础上,充分利用前人成果资料,应用SPSS及地下水污染分析软件,对莲花山地区区域地质条件、水化学参数空间分布特征、地下水化学类型、地下水化学成因进行分析研究,认为：莲花山地区地下水的硬度较高且矿化度较大;HCO3-浓度的平均值最大,在地下水的离子中占据主导地位;TDS（溶解性总固体）浓度较高且不同区域间浓度相差较大;莲花山地区部分区域偏硅酸、锶达到矿泉水标准,是矿泉水开发潜力区;研究区Na+和K+同时来自岩盐和硅酸岩的溶解;研究区浅层地下水中的Ca2+和Mg2+主要来源于碳酸盐的溶解;莲花山地区浅层地下水发生了阳离子交换作用.  相似文献   

8.
A displacement history and slip rates were determined for the Reelfoot fault in the New Madrid seismic zone from a seismic reflection profile and trench data. Based on calculations from the seismic reflection line the average slip rate over the last 80 million years is 0.0009 mm year−1. Slip rate during the Late Cretaceous was 0.0007 mm year−1, 0.002 mm year−1 during the Paleocene Midway Group, 0.001 mm year−1 during Paleocene–Eocene Wilcox Formation time, 0.0003 mm year−1 during the post-Wilcox/pre-Holocene period, and a Holocene slip rate of 1.8 mm year−1. Based on trench data, slip rate on the Reelfoot fault has been 4.4 mm year−1 over the last 2400 years and a maximum of 6.2 mm year−1 during the two most recent earthquake cycles between AD 900 and AD 1812. The Holocene slip rate is at least four orders of magnitude higher than the average Late Cretaceous and Cenozoic slip rates for the Reelfoot fault. It would appear that there has been a Quaternary change in the stress field in the central United States or the Reelfoot fault is experiencing a short-lived burst of seismic activity.  相似文献   

9.
Geomorphic effects observed in the Barranco (creek) de Arás basin are used to characterize the flood. Sediment features allow to qualify the flood as essentially a water flow. Using the critical section method, the peak flood discharge is estimated to be between 400 and 600 m3 s−1. Similar results were obtained using a paleohydraulic formula based on the size of the largest mobilized clasts. Using the rational method with available rainfall data, the discharge for a recurrence interval of 500 years is estimated to be between 150 and 200 m3 s−1. These results agree with predictions obtained using curves of peak discharge versus basin area based on regional data. Several trenches dug on the fan showed that the size of boulders mobilized by the event is larger that those left by previous floods at the same place. When the estimated peak flood discharge is related to the basin area, values between 20 and 30 m3 s−1 km−2 are obtained, demonstrating that the Barranco de Arás flood was most unusual.  相似文献   

10.
Dissolution rates of single calcite crystals were determined from sample weight loss using free-drift rotating disk techniques. Experiments were performed at 25 °C in aqueous HCl solutions over the bulk solution pH range −1 to 3 and in the presence of trace concentrations of aqueous NaPO3 and MgCl2. These salts were chosen for this study because aqueous magnesium and phosphate are known to strongly inhibit calcite dissolution at neutral to basic pH. Reactive solutions were undersaturated with respect to possible secondary phases. Neither an inhibition or enhancement of calcite dissolution rates was observed in the presence of aqueous MgCl2 at pH 1 and 3. The presence of trace quantities of NaPO3, which dissociates in solution to Na+ and H2PO4−, decreased the overall calcite dissolution rate at pH≤2. This contrasting behavior could be attributed to the different adsorption behavior of these dissolved species. As calcite surfaces are positively charged in acidic solutions, aqueous Mg2+ may not adsorb, whereas aqueous phosphate, present as either the anion H2PO4− or the neutral species H3PO40, readily adsorbs on calcite surfaces leading to significant dissolution inhibition.  相似文献   

11.
We determine seismic strain rate of tectonic earthquakes along the Central America Volcanic Arc. We then compare this result to those obtained from earthquakes related to the convergence of the Cocos and Caribbean plates and to earthquakes in the back-arc region of northern Central America.

The seismic strain-rate tensor for shallow-focus earthquakes along the Central America volcanic arc since 1700, has a compressive eigenvector with a magnitude of 0.7 × 10−8 year−1, and oriented in a 357° azimuth. The extensive eigenvector is oriented in a 86° azimuth, with a magnitude of 0.82 × 10−8 year−1. When only Centroid Moment-tensor solutions (CMT) are considered, the respective eigenvectors are 1.2 × 10−8 year−1 and 1.0 × 10−8 year−1.

The compressive eigenvector from the seismic strain-rate tensor for earthquakes along the Cocos-Caribbean convergent margin is 2.0 × 10−8 year−1, plunging at 25°, and oriented in a 29° azimuth. Its magnitude and direction are similar to those of the compressive eigenvector for earthquakes along the volcanic arc. The extensive eigenvector along the convergent margin, on the other hand, has a large vertical component. The compressive and extensive eigevenvectors are 4.9 × 10−8 year−1 and 4.6 × 10−8 year−1, using only CMTs as the database.

Earthquakes along the grabens of northern Central America yield a seismic strain-rate tensor whose extensive eigenvector has a magnitude of 2.4 × 10−8 year−1, oriented in a 109° azimuth. Magnitude and direction are similar to those of the extensive eigenvector for earthquakes along the volcanic arc. The compressive eigenvector along the grabens is practically vertical.

Similarities in magnitudes and directions for compressive and extensive eigenvectors suggest to us that the strain field along the Central America volcanic arc is the result of compression along the convergent Cocos-Caribbean margin, and extension in the back-arc region, along the grabens of northern Central America. This field is resolved as strike-slip faulting along the arc.  相似文献   


12.
The results of the 7 years (1994–2000) of monthly monitoring of spring water before and during eruptions show response to volcanic activity. Low salinity and temperature characterize most of the springs, which are located on the flanks of Popocatepetl Volcano. The pH ranges from 5.8 to 7.8 and temperature from 3 to 36 °C. Oxygen and hydrogen isotopic data show that the water is of meteoric origin, but SO42−, Cl−, F−, HCO3−, B, and SO42−/Cl− variations precede main eruptive activity, which is considered linked to influx of magmatic gases and acid fluids that react with sublimates and host rock and mix with the large water system. Na+, Ca2+, SiO2 and Mg2+ concentrations in the water also increased before eruptive activity. The computed partial pressure of CO2 in equilibrium with spring waters shows values higher than air-saturated water (ASW), with the highest values up to 0.73 bar of pCO2. Boron is detected in the water only preceding the larger eruptions. When present, boron concentration is normally under health standard limits, but in two cases the concentration was slightly above. Other components are within health standard limits, except for F− in one spring.  相似文献   

13.
Measured pore-water concentrations of iron in interbedded pelagic and turbiditic sediments from the Nares Abyssal Plain are in excellent agreement with sediment colour and measured redox potential. The organic carbon content of these sediments appears to define the redox conditions and consequently the porewater and solid-phase concentration of constituents that are involved in early diagenetic reactions. In the turbiditic sediments the concentration of NO3− generally goes to zero within a sediment depth of 1 m, whereas at 8 m in a pelagic core from the same area the concentration of NO3− is still higher than it is in the bottom water. The pore-water concentration of Mn2+ in the turbiditic sediments increases sharply down to a depth of approximately 3 m and from thereon remains nearly constant due to saturation with respect to Mn, Ca-CO3. The pore water of the turbiditic sediments is also saturated with respect to calcite. The few “diagenetic spikes” in the pore-water concentration of NO3− and Mn2+ and the concentration/depth profile of dissolved iron, H4SiO4 and phosphate all clearly demonstrate the inhomogeneous nature of interbedded pelagic and turbiditic sediments. The simultaneous occurrence of peaks of dissolved iron/silica and of sediment intervals with a relatively high organic carbon content is attributed to enhanced early diagenetic reactions associated with the decomposition of organic matter in these specific intervals. Linked with these reactions is the irregular pore-water concentration of phosphate, which is shown to originate partly from the oxidation of organic matter, but mainly from the desorption of phosphate from iron oxide. Potential concentrations of phosphate are calculated from the stoichiometric early diagenetic reactions and compared with measured concentrations. Due to the unique combination of low porosity and relatively high sedimentation rates, the sediments from the Nares Abyssal Plain are an ideal basis for the study of such interbedded sequences of pelagic and turbiditic deposits.  相似文献   

14.
Urs Eggenberger  Daniel Kurz   《Chemical Geology》2000,170(1-4):243-257
The steady-state soil chemistry model PROFILE was used to calculate the chemical status of forest soils under present deposition loads for two areas with dissimilar ecosystem properties. Two regions in Switzerland, with contrasting bedrock geology were selected to be investigated in detail: 88 locations in the Jura Mountains, representative for carbonate bedrock and 91 locations in the Ticino Area dominated by metamorphic crystalline host rocks. Weathering rates calculated for the key regions cover the tremendous range between 0.013 and 25 keq ha−1 yr−1. In the Ticino Area, the effect of increased abundance of relatively fast weathering silicates (epidote, hornblende and plagioclase) on the weathering rate is apparently masked by the total effects of the physical conditions applied and by the variation in the deposition load. In the Jura Mountains, generally high weathering rates occur with about 50% of the sites yielding rates above 1 keq ha−1 yr−1. In many of the sites investigated, however, carbonates have already been dissolved completely in the soil horizons of interest resulting in very low weathering rates. The critical load of actual acidity was calculated according to: CLAcidity=RWeathering−ANCLeaching, where alkalinity leaching is estimated by keeping the base cation to aluminum molar ratio at the critical limit of 1 at steady-state. The minimum critical load calculated was 0.2 keq ha−1 yr−1 and the maximum was 6.2 keq ha−1 yr−1. Comparing the cumulative frequency distributions of critical loads of actual acidity for forest soils in the individual areas it can be seen that the differences between the key regions are less substantial than with the weathering rates. Critical loads of acidity for the Ticino Area range from 1 to 3.9 keq ha−1 yr−1. Sites yielding the lowest critical loads of acidity are observed in the Jura Mountains. Among these apparent sensitive soils are soils with intermediate or high weathering rates, although it has depleted topsoil layers. Within the context of this model application, it becomes apparent that the sensitivity of these soils with respect to acidification is also governed by the alkalinity leaching term and not only by the susceptibility of its minerals to weathering.  相似文献   

15.
碳酸盐岩的Fe/Mn元素比值,作为一项新的地球化学指标,可以用于恢复海洋的氧化还原状态.在氧化条件下,Fe3+和Mn4+均不可溶,因此氧化海水中的溶解Fe和Mn的含量均很低.Fe3+和Mn4+在还原条件下可以被细菌还原为可溶的Fe2+和Mn2+,而氧化还原电位的计算表明,Mn4+的还原要早于Fe3+的还原,因此细菌的Mn还原过程发生在沉积物的更浅层.可溶的Fe2+和Mn2+向上扩散到海水中,替代碳酸盐岩晶格里的Ca2+,因此碳酸盐岩晶格中的Fe2+和Mn2+的含量受控于来自沉积物孔隙水的扩散,而后者又与水岩界面的氧化还原状态相关.因此可以预测,随着海水变得逐渐缺氧,碳酸盐岩中的Fe/Mn比值会逐渐增高.为了验证这一假说,我们分析了中元古代高于庄组白云岩的Fe/Mn比值.研究发现,几乎所有的样品的Fe/Mn比值介于20～30之间,显著高于泥盆纪末期深水碳酸盐岩和浅水台地碳酸盐岩的Fe/Mn比值.高于庄组碳酸盐岩高的Fe/Mn比值一方面可能指示了中元古代低的大气氧气浓度和海洋的广泛缺氧,也可能反映了白云岩形成于缺氧的沉积物空隙水里.  相似文献   

16.
I. Th. Rosenqvist 《Lithos》1970,3(4):327-334
Concretions of vivianite attaining 0.5 g occur in the upper 4 m of the bottom sediments of the Åsrum lake, Vestfold, S. Norway. The vivianite-bearing zone is of lacustrine origin. Vivianite is absent in the underlying lagunal and marine sediments. Electro-chemical and chemical data are given for the interstitial water and the clay.

Solubility product of vivianite is determined. The equilibrium constant is K = 10−40 for the reaction 3 Fe++ + 2 HPO4− + 2 OH− = vivianite. The concretions grew by diffusion from a slightly supersaturated interstitial water phase. The degree of supersaturation is calculated. The stability relations of vivianite and hydroxyl apatite are discussed.  相似文献   


17.
雅鲁藏布江丰水期河水离子组成特征及其控制因素   总被引：1，自引：0，他引：1  
为了解雅鲁藏布江丰水期河水离子组成特征及其控制因素,利用2015年采集的8个河水水样,运用数理统计、聚类分析、Piper三线图、Gibbs模型以及离子比值等方法,分析了雅鲁藏布江丰水期河水水化学特征,并探讨了其主要控制因素。结果表明：河水中阳离子以Ca2+、Mg2+为主,阴离子则以HCO3-和SO42-为主,阴、阳离子分别约占其总量的96%和85%。河水水化学类型均为HCO3·SO4-Ca·Mg型。TDS含量介于202.46~371.27 mg·L-1,均值为299.30 mg·L-1,较世界河流平均值高。自上至下,河水水化学特征表现出一定的差异性,河水中主要离子以及TDS、TH、EC的含量沿程表现出下降的趋势,其原因主要有支流河水汇入和降水增加的稀释作用。河水水样均落在Gibbs模型图中部偏左,表明河水中主要离子化学组分主要受水岩作用控制。离子比值法分析表明研究区碳酸盐岩以及蒸发岩的风化溶解是河水水化学的主要控制因素,且存在硅酸盐类矿物的风化。  相似文献   

18.
Several types of fluid immiscibility may affect the evolution of volatile-rich magmatic systems at the magmatic–hydrothermal transition. The topology of silicate–salt–H2O systems implies that three-fluid immiscibility (silicate melt+hydrosaline melt+vapour) should be stable in a broad range of compositions and P–T conditions. The most important factor controlling the immiscibility appears to be the Coulombic properties (electric charges Z and ionic radii r) of the main network-modifying cations and the capacity for immiscibility appears to decrease in the following sequence: Mg>Ca>Sr>Ba>Li>Na>K. Liquid immiscibility is enhanced in peralkaline compositions and in the presence of nonsilicate anions such as F−, Cl−, CO32− and BO33−. In volatile-rich magmatic systems, the H2O is likely to react with the chloride, fluoride, borate and carbonate species and the chemical effects of high-temperature hydrolysis may be greatly enhanced by phase separation in systems with multiple immiscible fluid phases. Natural granitic magmas can thus exsolve a range of chemically and physically diverse hydrosaline liquids and the role of these fluid phases is likely to be especially significant in pegmatites and Li–F rare-metal granites.  相似文献   

19.
马莲河流域地处鄂尔多斯盆地南部黄土高原区,按储水介质和埋藏条件可将地下水分为黄土潜水、基岩潜水和基岩承压水三类,利用2015—2018年流域的295组地下水水化学数据,分析了地下水中锶(Sr2+)的质量浓度水平、垂向分布及沿流向分布的特征,并采用因子相关性研究地下水中Sr2+的来源和富集成因。结果表明:马莲河流域地下水富锶现象显著,黄土潜水、基岩潜水和基岩承压水中锶的平均质量浓度分别为1.14 mg/l、1.39 mg/l和5.24 mg/l;地下水中锶富集成因主要是含锶矿物天然状态下的水-岩作用,黄土潜水、基岩潜水和基岩承压水三类地下水中Sr2+的主要来源分别为碳酸盐岩与铝硅酸盐岩、碳酸盐岩与硫酸盐和碳酸盐矿物的溶滤作用;地下水中Sr2+的质量浓度沿流向呈逐渐增大的趋势,在不同区域中随深度变化的趋势不一致。  相似文献   

20.
Within the framework of Pitzer's specific interaction model, interaction parameters for aqueous silica in concentrated electrolyte solutions have been derived from Marshall and co-authors amorphous silica solubility measurements. The values, at 25°C, of the Pitzer interaction parameter (λSiO2(aq)−i) determined in this study are the following: 0.092 (i = Na+), 0.032 (K+), 0.165 (Li+), 0.292 (Ca2+, Mg2+), −0.139 (SO42−), and −0.009 (NO3−). A set of polynomial equations has been derived which can be used to calculate λSiO2(aq)−i for these ions at any temperature up to 250°C. A linear relationship between the aqueous silica-ion interaction parameters (λSiO2(aq)−i) and the surface electrostatic field (Zi/re,i) of ions was obtained. This empirical equation can be used to estimate, in first approximation, λSiO2(aq)−i if no measurements are available. From this parameterisation, the calculated activity coefficient of aqueous silica is 2.52 at 25°C and 1.45 at 250°C in 5 m NaCl solution. At lower concentrations, e.g. 2 m NaCl, the activity coefficient of silica is 1.45 at 25°C and 1.2 at 250°C. Hence, in practice, it is necessary to take into account the activity coefficient of aqueous silica (λSiO2(aq)≠1) in hydrothermal solutions and basinal brines where the ionic strength exceeds 1. A comparison of measured [Marshall, W.L., Chen, C.-T.A., 1982. Amorphous silica solubilities, V. Prediction of solubility behaviour in aqueous mixed electrolyte solutions to 300°C. Geochim. Cosmochim. Acta 46, 289–291.] and computed amorphous silica solubility, using this parameterisation, shows a good agreement. Because the effect of individual ions on silicate and silica polymorph solubilities are additive, the present study has permitted to derive Pitzer interaction parameters that allow a precise computation of γSiO2(aq) in the Na---K---Ca---Mg---Cl---SO4---HCO3---SiO2---H2O system, over a large range of salt concentrations and up to temperatures of 250°C.  相似文献   

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