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1.
Garnet–melt trace element partitioning experiments were performed in the system FeO–CaO–MgO–Al2O3–SiO2 (FCMAS) at 3 GPa and 1540°C, aimed specifically at studying the effect of garnet Fe2+ content on partition coefficients (DGrt/Melt). DGrt/Melt, measured by SIMS, for trivalent elements entering the garnet X-site show a small but significant dependence on garnet almandine content. This dependence is rationalised using the lattice strain model of Blundy and Wood [Blundy, J.D., Wood, B.J., 1994. Prediction of crystal–melt partition coefficients from elastic moduli. Nature 372, 452–454], which describes partitioning of an element i with radius ri and valency Z in terms of three parameters: the effective radius of the site r0(Z), the strain-free partition coefficient D0(Z) for a cation with radius r0(Z), and the apparent compressibility of the garnet X-site given by its Young's modulus EX(Z). Combination of these results with data in Fe-free systems [Van Westrenen, W., Blundy, J.D., Wood, B.J., 1999. Crystal-chemical controls on trace element partitioning between garnet and anhydrous silicate melt. Am. Mineral. 84, 838–847] and crystal structure data for spessartine, andradite, and uvarovite, leads to the following equations for r0(3+) and EX(3+) as a function of garnet composition (X) and pressure (P):Accuracy of these equations is shown by application to the existing garnet–melt partitioning database, covering a wide range of P and T conditions (1.8 GPa<P<5.0 GPa; 975°C<T<1640°C). DGrt/Melt for all 3+ elements entering the X-site (REE, Sc and Y) are predicted to within 10–40% at given P, T, and X, when DGrt/Melt for just one of these elements is known. In the absence of such knowledge, relative element fractionation (e.g. DSmGrt/Melt/DNdGrt/Melt) can be predicted. As an example, we predict that during partial melting of garnet peridotite, group A eclogite, and garnet pyroxenite, r0(3+) for garnets ranges from 0.939±0.005 to 0.953±0.009 Å. These values are consistently smaller than the ionic radius of the heaviest REE, Lu. The above equations quantify the crystal-chemical controls on garnet–melt partitioning for the REE, Y and Sc. As such, they represent a major advance en route to predicting DGrt/Melt for these elements as a function of P, T and X. 相似文献
r0(3+) [Å]=0.930XPy+0.993XGr+0.916XAlm+0.946XSpes+1.05(XAnd+XUv)−0.005(P [GPa]−3.0)(±0.005 Å)
EX(3+) [GPa]=3.5×1012(1.38+r0(3+) [Å])−26.7(±30 GPa)
2.
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
3.
Status report on stability of K-rich phases at mantle conditions 总被引：1，自引：0，他引：1
Experimental research on K-rich phases and observations from diamond inclusions, UHP metamorphic rocks, and xenoliths provide insights about the hosts for potassium at mantle conditions. K-rich clinopyroxene (Kcpx–KM3+Si2O6) can be an important component in clinopyroxenes at P>4 GPa, dependent upon coexisting K-bearing phases (solid or liquid) but not, apparently, upon temperature. Maximum Kcpx content can reach 25 mol%, with 17 mol% the highest reported in nature. Partitioning (K)D(cpx/liquid) above 7 GPa=0.1–0.2 require ultrapotassic liquids to form highly potassic cpx or critical solid reactions, e.g., between Kspar and Di. Phlogopite can be stable to about 8 GPa at 1250 °C where either amphibole or liquid forms. When fluorine is present, it generally increases in Phl upon increasing P (and probably T) to about 6 GPa, but reactions forming amphibole and/or KMgF3 limit F content between 6 and 8 GPa. The perovskite KMgF3 is stable up to 10 GPa and 1400 °C as subsolidus breakdown products of phlogopite upon increasing P. (M4)K-substituted potassic richterite (ideally K(KCa)Mg5Si8O22(OH,F)2) is produced in K-rich peridotites above 6 GPa and in Di+Phl from 6 to 13 GPa. K content of amphibole is positively correlated with P; Al and F content decrease with P. In the system 1Kspar+1H2O K-cymrite (hydrous hexasanidine–KAlSi3O8·nH2O–Kcym) is stable from 2.5 GPa at 400 to 1200 °C and 9 GPa; Kcym can be a supersolidus phase. Formation of Kcym is sensitive to water content, not forming within experiments with H2O2O>Kspar. Phase X, a potassium di-magnesium acid disilicate ((K1−x−n)2(Mg1−nMn3+)2Si2O7H2x), forms in mafic compositions at T=1150–1400 °C and P=9–17 GPa and is a potential host for K and H2O at mantle conditions with a low-T geotherm or in subducting slabs. The composition of phase-X is not fixed but actually represents a solid solution in the stoichiometries □2Mg2Si2O7H2–(K□)Mg2Si2O7H–K2Mg2Si2O7 (□=vacancy), apparently stable only near the central composition. K-hollandite, KAlSi3O8, is possibly the most important K-rich phase at very high pressure, as it appears to be stable to conditions near the core–mantle boundary, 95 GPa and 2300 °C. Other K-rich phases are considered. 相似文献
4.
Metamorphic evolution, mineral chemistry and thermobarometry of schists and orthogneisses hosting ultra-high pressure eclogites in the Dabieshan of central China 总被引：55，自引：0，他引：55
As is typical of ultra-high pressure (UHP) terrains, the regional extent of the UHP terrain in the Dabieshan of central China is highly speculative, since the volume of eclogites and paragneisses preserving unequivocal evidence of coesite and/or diamond stability is very small. By contrast, the common garnet (XMn=0.18–0.45)–phengite (Si=3.2–3.35)–zoned epidote (Ps38–97)–biotite–titanite–two feldspars–quartz assemblages in the more extensive orthogneisses have been previously thought to have formed under low P–T conditions of ca. 400±50°C at 4 kbar. However, certain orthogneiss samples preserve garnets with XCa up to 0.50, rutile inclusions within titanite or epidote and relict phengite inclusions within epidote with Si contents p.f.u. of up to 3.49 — overlapping with the highest values (3.49–3.62) recorded for phengites in samples of undoubted UHP schists. These and other mineral composition features (such as A-site deficiencies in the highest Si phengites, Na in garnets linked to Y+Yb substitution and Al F Ti−1 O−1 substitution in titanites) are taken to be pointers towards the orthogneisses having experienced a similar metamorphic evolution to the associated UHP schists and eclogites. Re-evaluated garnet–phengite and garnet–biotite Fe/Mg exchange thermometry and calculated 5 rutile+3 grossular+2SiO2+H2O=5 titanite+2 zoisite equilibria indicate that the orthogneisses may indeed have followed a common subduction-related clockwise P–T path with the UHP paragneisses and eclogites through conditions of Pmax at ca. 690°C–715°C and 36 kbar to Tmax at ca. 710°C–755°C and 18 kbar, prior to extensive re-crystallisation and re-equilibration of these ductile orthogneisses at ca. 400°C–450°C and 6 kbar. The consequential conclusion, that it is no longer necessary to resort to models of tectonic juxtapositioning to explain the spatial association of these Dabieshan orthogneisses with undoubted UHP lithologies, has far-reaching implications for the interpretation of controversial gneiss–eclogite relationships in other UHP metamorphic terrains. 相似文献
5.
Christian Bertoldi Alexander Proyer Dieter Garbe-Schnberg Harald Behrens Edgar Dachs 《Lithos》2004,78(4):389-409
Cordierite samples from pegmatites and metamorphic rocks have been analysed for major [electron microprobe analysis (EMPA)] and trace elements [inductively coupled plasma mass spectrometry (ICP-MS), secondary ion mass spectrometry analyses (SIMS)] as well as for H2O and CO2 (coulometric titration), and the results evaluated in conjunction with published data in order to determine which exchange mechanisms are significant. Apart from the homovalent substitutions FeMg−1 and MnMg−1 on the octahedral site, some minor KNa−1 on the Ch0 channel site, and Fe3+Al−1 on the T11 tetrahedral site, the three most important substitution mechanisms are those for the incorporation of Li on the octahedral sites (NaLi□−1Mg−1), and of Be and other divalent cations on the tetrahedral T11 site (NaBe□−1Al−1 and Na(Mg,Fe2+)□−1Al−1). The dominant role of the last vector is clearly demonstrated. We propose a new generalized formula for cordierite: Ch(Na,K)0–1 VI(Mg,Fe2+,Mn,Li)2 IVSi5 IVAl3 IV(Al, Be, Mg, Fe2+, Fe3+)O18 *xCh(H2O, CO2…). Our results show that the population of (Mg, Fe2+) on the T11-site is limited to about 0.08 a.p.f.u. Other exchange mechanisms that were encountered in experiments operate only under P–T conditions or in bulk compositions that are rarely realized in nature. Routine analyses by electron microprobe in which Li and Be are not determined can be plotted as (Mg+Fe+Mn) versus (Si+Al) to assess whether significant amounts of Li and Be could be present. These amounts can be calculated as Li (a.p.f.u.)=Al+Na–4 and Be (a.p.f.u.)=10–2Al–M2+–Na. 相似文献
6.
Marcasite precipitation from hydrothermal solutions 总被引：3，自引：0，他引：3
Pyrite and marcasite were precipitated by both slow addition of aqueous Fe2+ and SiO32− to an H2S solution and by mixing aqueous Fe2+ and Na2S4 solutions at 75°C. H2S2 or HS2− and H2S4 or HS4− were formed in the S2O32− and Na2S4 experiments, respectively. Marcasite formed at pH < pK1 of the polysulfide species present (for H2S2, pK1 = 5.0; for H2S4, pK1 = 3.8 at 25°C). Marcasite forms when the neutral sulfane is the dominant polysulfide, whereas pyrite forms when mono-or divalent polysulfides are dominant. In natural solutions where H2S2 and HS2 are likely to be the dominant polysulfides, marcasite will form only below pH 5 at all temperatures.
The pH-dependent precipitation of pyrite and marcasite may be caused by electrostatic interactions between polysulfide species and pyrite or marcasite growth surfaces: the protonated ends of H2S2 and HS2 are repelled from pyrite growth sites but not from marcasite growth sites. The negative ions HS2 and S22− are strongly attracted to the positive pyrite growth sites. Masking of 1πg* electrons in the S2 group by the protons makes HS2 and H2S2 isoelectronic with AsS2− and As22−, respectively ( et al., 1981). Thus, the loellingitederivative structure (marcasite) results when both ends of the polysulfide are protonated.
Marcasite occurs abundantly only for conditions below pH 5 and where H2S2 was formed near the site of deposition by either partial oxidation of aqueous H2S by O2 or by the reaction of higher oxidation state sulfur species that are reactive with H2S at the conditions of formation e.g., S2O32− but not SO42−. The temperature of formation of natural marcasite may be as high as 240°C ( and , 1985), but preservation on a multimillion-year scale seems to require post-depositional temperatures of below about 160°C ( , 1973; and , 1985). 相似文献
7.
R. Schmid M. Wilke R. Oberhnsli K. Janssens G. Falkenberg L. Franz A. Gaab 《Lithos》2003,70(3-4):381-392
Micro-X-ray absorption near-edge structure (XANES) analysis was employed to determine the content of ferric iron in minerals formed in ultrahigh-pressure (UHP) eclogites. It is observed that omphacite and phengite contain significant amounts of Fe3+/Fetot (0.2–0.6), whereas only very low contents are present in garnet (Fe3+/Fetot=0.0–0.03), the latter being consistent with results from stoichiometric charge-balance calculations. Furthermore, considerable variations in the Fe3+/Fetot ratios of omphacite and phengite are observed depending on the textural sites and local bulk chemistry (eclogite and calc-silicate matrix) within one thin section. The oxidation state of isofacial minerals is thus likely to depend on the local fluid composition, which, in the studied case, is controlled by calcareous and meta-basic mineral compositions. These first in-situ measurements of ferric iron in an eclogite sample from the Dabie Shan, E China, are used to recalculate geothermobarometric data. Calculations demonstrate that the temperature during UHP metamorphism was as high as 780 °C, about 80–100 °C higher than previously estimated. Temperatures based on charge balance calculations often give erroneous results. Pressure estimates are in good agreement with former results and confirm metamorphism in the stability field of diamond (43.7 kbar at 750 °C). These P–T data result in a geothermal gradient of ca. 6 °C/km during UHP metamorphism in the Dabie Shan. However, accounting for ferric iron contents in geothermobarometry creates new difficulties inasmuch as calibrations of geothermometers may not be correctable for Fe3+ and the actual effect on Mg–Fe2+ partitioning is unknown. The present study further shows that micro-XANES is a promising technique for the in situ determination of ferric iron contents without destroying the textural context of the sample: a clear advantage compared to bulk methods. 相似文献
8.
We investigate the use of a ductile material with temperature-sensitive viscosity for thermomechanical modelling of the lithosphere. First, we consider the scaling of mechanical and thermal properties. For a normal field of gravity, the balance of stresses and body forces sets the stress scale, in proportion to the linear dimensions and the densities. The equation of thermal conduction sets the time scale. The activation enthalpy for creep sets the temperature scale; but the thermal expansivity provides an additional constraint on this temperature scale.
Gum rosin appears to be a suitable material for lithospheric modelling. We have measured its flow properties, at various temperatures, in a specially designed rotary viscometer with unusually low machine friction. The rosin is almost Newtonian. Strain rate depends upon stress to the power n, where 1.0 <n < 1.14. The viscosity varies over 5 orders of magnitude, from about 102 Pa s at 80°C, to about 107 Pa s at 40°C. The activation enthalphy is thus about 250 kJ/mol. Measured with a needle probe, the thermal conductivity is 0.113 ± 0.001 W m−1K−1; the thermal diffusivity, (6±3) ×10−7 m2 s−1. Calculated from X-ray profiles, the thermal expansivity is about 3 × 10−4 K−1. These thermal and mechanical properties make gum rosin suitable for thermomechanical models, where linear dimensions scale down by a factor of 106; time, by 1011; viscosity, by 1017; and temperature change, by 101. 相似文献
9.
Because of late metamorphic and tectonic overprints, the reconstruction of prograde parts of P–T paths is often difficult. In the SW Variscan French Massif Central, the Thiviers-Payzac Unit (TPU) is the uppermost allochthon emplaced above underlying units. The TPU experienced a Barrovian metamorphism coeval with a top-to-the-NW ductile shearing (D2 event) in Early Carboniferous times (ca. 360–350 Ma). The tectonic setting of the D2 event, compression or synconvergence extension, remains unclear. Using the THERMOCALC software and the model system MnNCKFMASH, the peak P–T conditions are estimated from garnet rims and matrix minerals and the prograde evolution is deduced from garnet core compositions. The combination of these two approaches demonstrates that the TPU experienced pressure and temperature increases before reaching peak conditions at 6.6–9.0 +/− 1.2 kbar and 615–655 +/− 35 °C. This kind of P–T path shows that the regional D2 event corresponds to crustal thickening. 相似文献
10.
We present results of computations on the interaction of solid-phase electrum–argentite–pyrite (weight ratios 210−5/ 210−3/1 and 210−5/410−2/1) association with Cl-containing aqueous moderately acid solutions (0.5m NaCl, pH = 3.08) at 300 °C and 500 bars. These data are a physicochemical basis for predicting the geochemical behavior of Au and Ag during the hydrothermal-metasomatic transformation of Au-Ag-pyrite. We also propose a technique of study of this process based on the phase equilibria of the subsystem Au–Ag–S with the aqueous solution at different liquid/solid (l/s) ratios, with the use of new graphic diagrams. The relationship of the composition of the solid-phase association with l/s ratio in real boundary conditions (Au = 17 ppm, mAu/mAg = 10–3.57–10–2.28) is shown. The maximum l/s values for complete leaching of gold and silver (l/smax = 200–800) are estimated. It has been established that argentite is the first to dissolve when mAu/mAg(s) > mAu/mAg(sol), and electrum, when mAu/mAg(s) < mAu/mAg(sol).
The experimental results showed that at 300 °C, the conversion of electrum (NAu = 300‰) nonequilibrated with pyrite into an Au-richer form (NAu = 730‰) and argentite follows an intricate kinetic scheme. Using the Pilling-Bedwords kinetic equation for processing data yielded the process rate constant K = 2.8(±0.5)10−5 g2cm−4day−1. With this equation, the time of the complete conversion of 200 μm thick flat gold grains is 604 days. These data evidence a significant role of kinetic factors in hydrothermal-metasomatic processes involving native gold, which requires combination of thermodynamic and kinetic approaches on the construction of geologo-genetic models for hydrothermal sulfide formation. 相似文献
11.
A. L. Martin-Del Pozzo F. Aceves R. Espinasa A. Aguayo S. Inguaggiato P. Morales E. Cienfuegos 《Chemical Geology》2002,190(1-4):207-229
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
12.
花岗伟晶岩型矿床是稀有金属矿床重要的类型之一。在花岗伟晶岩中,稀有金属元素Li、Be、Nb和Ta主要以独立矿物的形式存在,前人对稀有金属独立矿物在硅酸盐熔体中的溶解度及其影响因素展开了系统研究。本文综合分析了已有的实验数据,其结果表明,影响稀有金属独立矿物溶解度最为重要的2个参数是温度(T)和铝饱和指数(ASI)。因此本文建立了稀有金属独立矿物,尤其是铌锰矿和钽锰矿溶解度,与温度(T)和铝饱和指数(ASI)之间的定量关系: lg [w(Li)/10-6]=-0.37×[1 000/(T/K)]+4.56,R2=0.44 lg [w(BeO)/10-6]=-4.21×[1 000/(T/K)]+6.86,R2=0.91 lg [Ksp(Nb)/(mg2·kg-2)]=-(2.86±0.14)×ASI(Mn+Li)-(4.95±0.31)×[1 000/(T/K)]+(4.20+0.28),R2=0.86 lg [Ksp(Ta)/(mg2·kg-2)]=-(2.46±0.11)×ASI(Mn+Li)-(4.86±0.30)×[1 000/(T/K)]+(4.00+0.30),R2=0.80 式中,温度T为热力学温度,ASI(Mn+Li)(ASI=Al2O3/(CaO+Na2O+K2O+Li2O+MnO),摩尔分数比)和T的适用范围分别为0.6~1.2和1 073~1 373 K的范围内。上述公式为估算硅酸盐熔体中稀有金属含量提供了便利,为量化花岗伟晶岩成矿模型提供了基础。 稀有金属独立矿物溶解度随温度降低和铝饱和指数的增加而急剧降低,因此,在岩浆演化过程中,由岩浆侵位、分离结晶以及流体作用等因素引起的岩浆温度降低和铝饱和指数的增加,是导致稀有金属独立矿物结晶的主要机制。 相似文献
13.
The strength of a frozen soil increases with decreasing temperature. Furthermore, the speed it takes to form a frozen wall increases on lowering the temperature of the freezing liquid.
With the traditional freezing systems using brine it is difficult to work with temperatures below −30°C. To go lower than this limit, it is necessary to substitute the brine by using freezing liquids that maintain good hydraulic and thermal characteristics at much lower temperatures.
Different organic liquids have been tested and good results have been obtained with some aromatic hydrocarbon mixes from the terpene family.
As a result of the research, for practical purposes a by-product ofa distilling citrus fruit skins has been selected. This liquid solidifies at −100°C approx. and maintains a low viscosity rate below −30°C.
The present paper describes the thermal and hydraulic properties of this product as a function of the temperature concerned and compares them to the same properties of classic brines of CaCl2. 相似文献
14.
Qiuli Li Shuguang Li Yong-Fei Zheng Huimin Li Hans Joachim Massonne Qingchen Wang 《Chemical Geology》2003,200(3-4):255-265
This paper first reports a high precision U–Pb age of 218±1.2 Ma for rutile in coesite-bearing eclogite from Jinheqiao in the Dabie Mounteins, east–central China. This work shows that the U–Pb mineral (rutile+omphacite) isochron age of 218±2.5 Ma and conventional rutile U–Pb concordia age of 218±1.2 Ma obtained by common Pb correction based on the Pb isotopic composition of omphacite in the same eclogite sample are consistent, proving that the omphacite with low U/Pb ratio (μ=2.8) can be used for common Pb correction in U–Pb dating of rutile. Oxygen isotope analysis of rutile aliquots gave the consistent δ18O values of −6.1±0.1%, demonstrating oxygen isotope homogenization in the rutile of different grains as inclusion in garnet and grain in matrix. Oxygen isotope thermometry yields temperatures of 695±35 and 460±15 °C for quartz–garnet and quartz–rutile pairs, respectively. These oxygen isotopic observations suggest that the diffusion of oxygen in rutile as inclusion in garnet is not controlled by garnet. According to field-based thermochronological studies of rutile, an estimate of the Tc of about 460 °C for U–Pb system in rutile under rapid cooling conditions (20 °C/Ma) was advised. Based on this U–Pb age as well as the reported chronological data with their corresponding metamorphic and/or closure temperature, an improved T–t path has been constructed. The T–t path confirms that the UHPM rocks in South Dabie experienced a rapid cooling following the peak metamorphism before 220 Ma and a long isothermal stage from 213 to 180 Ma around 425 °C. 相似文献
15.
As a result of the collapse of a mine tailing dam, a large extension of the Guadiamar valley was covered with a layer of pyritic sludge. Despite the removal of most of the sludge, a small amount remained in the soil, constituting a potential risk of water contamination. The kinetics of the sludge oxidation was studied by means of laboratory flow-through experiments at different pH and oxygen pressures. The sludge is composed mainly of pyrite (76%), together with quartz, gypsum, clays, and sulphides of zinc, copper, and lead. Trace elements, such as arsenic and cadmium, also constitute a potential source of pollution. The sludge is fine grained (median of 12 μm) and exhibits a large surface (BET area of 1.4±0.2 m2 g−1).
The dissolution rate law of sludge obtained is r=10−6.1(±0.3) [O2(aq)]0.41(±0.04) aH+0.09(±0.06) gsludge m−2 s−1 (22 °C, pH=2.5–4.7). The dissolution rate law of pyrite obtained is r=10−7.8(±0.3) [O2(aq)]0.50(±0.04) aH+0.10(±0.08) mol m−2 s−1 (22 °C, pH=2.5–4.7). Under the same experimental conditions, sphalerite dissolved faster than pyrite but chalcopyrite dissolves at a rate similar to that of pyrite. No clear dependence on pH or oxygen pressure was observed. Only galena dissolution seemed to be promoted by proton activity. Arsenic and antimony were released consistently with sulphate, except at low pH conditions under which they were released faster, suggesting that additional sources other than pyrite such as arsenopyrite could be present in the sludge. Cobalt dissolved congruently with pyrite, but Tl and Cd seemed to be related to galena and sphalerite, respectively.
A mechanism for pyrite dissolution where the rate-limiting step is the surface oxidation of sulphide to sulphate after the adsorption of O2 onto pyrite surface is proposed. 相似文献
16.
Sr and Nd isotopic compositions, age and petrogenesis of A-type granitoids of the Vernon Supersuite, New Jersey Highlands, USA 总被引：3，自引：0，他引：3
Richard A. Volkert Mark D. Feigenson Lina C. Patino Jeremy S. Delaney Avery Ala Drake Jr. 《Lithos》2000,50(4):895-347
Voluminous late Mesoproterozoic monzonite through granite of the Vernon Supersuite underlies an area of approximately 1300 km2 in the Highlands of northern New Jersey. The Vernon Supersuite consists of hastingsite±biotite-bearing granitoids of the Byram Intrusive Suite (BIS) and hedenbergite-bearing granitoids of the Lake Hopatcong Intrusive Suite (LHIS). These rocks have similar major and trace element abundances over a range of SiO2 from 58 to 75 wt.%, are metaluminous to weakly peraluminous, and have a distinctive A-type chemistry characterized by high contents of Y, Nb, Zr, LREE, and Ga/Al ratios, and low MgO, CaO, Sr and HREE. Whole-rock Rb–Sr isochrons of BIS granite yield an age of 1116±41 Ma and initial 87Sr/86Sr ratio of 0.70389, and of LHIS granite an age of 1095±9 Ma and initial 87Sr/86Sr ratio of 0.70520. Both suites have similar initial 143Nd/144Nd ratios of 0.511267 to 0.511345 (BIS) and 0.511359 to 0.511395 (LHIS). Values of Nd are moderately high and range from +1.21 to +2.74 in the BIS and +2.24 to +2.95 in the LHIS. Petrographic evidence, field relationships, geochemistry, and isotopic data support an interpretation of comagmatism and the derivation of both suites from a mantle-derived or a juvenile lower crustal parent with little crustal assimilation. Both suites crystallized under overlapping conditions controlled by P–T–fH2O. Lake Hopatcong magma crystallized at a liquidus temperature that approached 900°C and a pressure of about 6 kbar, and remained relatively anhydrous throughout its evolution. Initial P–T conditions of the Byram magma were ≥850°C and about 5.5 kbar. BIS magma was emplaced contemporaneous with, or slightly preceding LHIS magma, and both magmas were emplaced during a compressional tectonic event prior to granulite facies metamorphism that occurred in the Highlands between 1080 and 1030 Ma. 相似文献
17.
The geochemical cycle of boron: Constraints from boron isotope partitioning experiments between mica and fluid 总被引：8，自引：0，他引：8
Bernd Wunder Anette Meixner Rolf L. Romer Richard Wirth Wilhelm Heinrich 《Lithos》2005,84(3-4):206-216
The fractionation of boron isotopes between synthetic boromuscovite and fluid was experimentally determined at 3.0 GPa/500 °C and 3.0 GPa/700 °C. For near-neutral fluids Δ11B(mica-fluid) = δ11B(mica) − δ11B(fluid) is − 10.9 ± 1.3‰ at 500 °C, and − 6.5 ± 0.4‰ at 700 °C. This supports earlier assumptions that the main fractionation effect is due to the change from trigonal coordination of boron in neutral fluids to tetrahedrally coordinated boron in micas, clays and melts. The T-dependence of this effect is approximated by the equation Δ11B(mica,clay,melt–neutral fluid) = − 10.69 · (1000/T [K]) + 3.88; R2 = 0.992, valid from 25 °C for fluid–clay up to about 1000 °C for fluid–silicate melt. Experiments at 0.4 GPa that used strongly basic fluids produced significantly lower fractionations with Δ11B(mica–fluid) of − 7.4 ± 1.0‰ at 400 °C, and − 4.8 ± 1.0‰ at 500 °C, showing the reduced fractionation effect when large amounts of boron in basic fluids are tetrahedrally coordinated. Field studies have shown that boron concentrations and 11B/10B-ratios in volcanic arcs systematically decrease across the arc with increasing distance from the trench, thus reflecting the thermal structure of the subducting slab. Our experiments show that the boron isotopic signature in volcanic arcs probably results from continuous dehydration of micas along a distinct P–T range. Continuous slab dehydration and boron transport via fluid into the mantle wedge is responsible for the boron isotopic signature in volcanic arcs. 相似文献
18.
Grossular–wollastonite–scapolite calc–silicate granulites from Maligawila in the Buttala klippe, which form part of the overthrusted rocks of the Highland Complex of Sri Lanka, preserve a number of spectacular coronas and replacement textures that could be effectively used to infer their P–T–fluid history. These textures include coronas of garnet, garnet–quartz, and garnet–quartz–calcite at the grain boundaries of wollastonite, scapolite, and calcite as well as calcite–plagioclase and calcite–quartz symplectites or finer grains after scapolite and wollastonite respectively. Other textures include a double rind of coronal scapolite and coronal garnet between matrix garnet and calcite. The reactions that produced these coronas and replacement textures, except those involving clinopyroxene, are modelled in the CaO–Al2O3–SiO2–CO2 system using the reduced activities. Calculated examples of T–XCO2 and P–XCO2 projections indicate that the peak metamorphic temperature of about 900–875 °C at a pressure of 9 kbar and the peak metamorphic fluid composition is constrained to be low in XCO2 (0.1<XCO2<0.30). Interpretation of the textural features on the basis of the partial grids revealed that the calc–silicate granulites underwent high-temperature isobaric cooling, from about 900–875 °C to a temperature below 675 °C, following the peak metamorphism. The late-stage cooling was accompanied by an influx of hydrous fluids. The calc–silicate granulites provide evidence for high-temperature isobaric cooling in the meta-sediments of the Highland Complex, earlier considered by some workers to be confined exclusively to the meta-igneous rocks. The coronal scapolite may have formed under open-system metasomatism. 相似文献
19.
Spinel-sapphirine-corundum-rutile parageneses in metapelitic xenoliths from the lamprophyric Popes Harbour dyke are enclosed by feldspathic (±rare quartz) haloes that embay aluminosilicates and biotite. These feldspathic haloes contain plagioclase (An20–40) and/or an alkali or ternary (hypersolvus) feldspar, and show a variety of igneous and devitrification textures, suggesting an anatectic origin. The spinel-bearing parageneses are interpreted as the refractory residue formed by the incongruent melting of biotite, aluminosilicates and associated phases.
Equilibration temperatures of these assemblages are estimated from an empirical sapphirine-spinel Mg---Fe exchange thermometer derived from literature data on both silica-saturated and undersaturated sapphirine granulites. Linear regression (R=0.81) of the calibrant data yields the expression T(°C) = [800 + (228*InKd)] − 273 where
Kd=(XspFe/XspMg)/(XsaFe/XsaMg)
Precision is estimated at ± 100°C, but will likely be less for highly oxidized sapphirine granulites owing to (1) errors in the stoichiometric estimation of XFe3+ from microprobe data and (2) the formation of magnetite at the expense of spinel or sapphirine, leading to an increase in XMg in either or both phases during cooling. Application of this expression to the reduced (graphite-bearing) Popes Harbour xenoliths yields T of 725–795°C. Anatexis is attributed to thermal metamorphism by the lamprophyric magma prior to and/or during entrainment of xenolith material in the dyke. Higher-T assemblages were quenched before the xenoliths attained thermal equilibrium with the magma, consequently prograde reaction textures and compositional zoning patterns are preserved. 相似文献
20.
D.J. Cherniak 《Geochimica et cosmochimica acta》1996,60(24):5037-5043
Strontium chemical diffusion has been measured in albite and sanidine under dry, 1 atm, and QFM buffered conditions. Strontium oxide-aluminosilicate powdered sources were used to introduce the diffusant and Rutherford Backscattering Spectroscopy (RBS) used to measure diffusion profiles. For the 1 atm experiments, the following Arrhenius relations were obtained: The alkali feldspars in this and earlier work display a broad range of activation energies for Sr diffusion, which may be a consequence of the thermodynamic non-ideality of the alkali feldspar system and/or the mixed alkali effect. 相似文献
Sanidine (Or61), temperature range 725–1075°C, diffusion normal to (001): D=8.4 exp(−450±13 kJ mol−1/RT) m2s−1. Albite (Or1), temperature range 675–1025°C, diffusion normal to (001): D=2.9 × exp(−224±11 kJ mol−1/RT) m2s−1.