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1.
Fractionations of carbon and oxygen isotopes and magnesium between coexisting dolomite and calcite have been determined for marbles and calcareous schists of a wide variety of metamorphic environments from Vermont and the Grenville Province of Ontario. Concordant equilibrium fractionations are given by 83% of the samples. Calibration of the isotopic thermometers using the Mg-calcite solvus thermometer gave in the temperature range: 650°>T°>100°C $$ \begin{gathered} 1,000\ln \alpha _{D - Ct}^{O^{18} } = 0.45 (10^6 T^{ - 2} ) - 0.40 \hfill \\ 1,000\ln \alpha _{D - Ct}^{O^{18} } = 0.18 (10^6 T^{ - 2} ) + 0.17. \hfill \\ \end{gathered} $$ These isotopic fractionation expressions differ significantly from the experimentally derived relations, including the dolomite-Mg-calcite C13 partial exchange experiments of this study. Temperature ranges obtained for the metamorphic zones of Vermont are: chlorite zone, 210° to 295° C; biotite zone, 255° to 400° C; staurolite-kyanite zone, 110° to 550° C. In amphibolite-facies rocks the quenched partition relations can be complex. The temperature of quench or recrystallization may be as large as 400° C below the inferred metamorphic maximum. Oxygen isotope disequilibrium in high grade rocks, particularly from the Chester dome area, Vermont, is characterized by large negative δO D 18 –δO Ct 18 values. The size of the equilibrium exchange system for carbon and oxygen isotopes and magnesium is small, less than a few inches across the inferred relict bedding. This is attributed to the lack of a mobile pore fluid except in systems undergoing decarbonation. C13/C12 ratios in Grenville and Vermont marbles and O18/O16 ratios in Grenville and greenschist-facies Vermont carbonates span the range of ancient limestones. Staurolite-kyanite zone calcareous schists and marbles from the Chester dome area, Vermont are depleted in O18(δO18=12 to 20‰) due to equilibrium or disequilibrium decarbonation and some partial exchange. Extrapolation of the dolomite-calcite fractionation expressions to 20° C indicates that dolomite is enriched in O18 by about 4.9‰ and in C13 by about 2.4‰.  相似文献   

2.
The liquidus water content of a haplogranite melt at high pressure (P) and temperature (T) is important, because it is a key parameter for constraining the volume of granite that could be produced by melting of the deep crust. Previous estimates based on melting experiments at low P (≤0.5 GPa) show substantial scatter when extrapolated to deep crustal P and T (700–1000 °C, 0.6–1.5 GPa). To improve the high-P constraints on H2O concentration at the granite liquidus, we performed experiments in a piston–cylinder apparatus at 1.0 GPa using a range of haplogranite compositions in the albite (Ab: NaAlSi3O8)—orthoclase (Or: KAlSi3O8)—quartz (Qz: SiO2)—H2O system. We used equal weight fractions of the feldspar components and varied the Qz between 20 and 30 wt%. In each experiment, synthetic granitic composition glass + H2O was homogenized well above the liquidus T, and T was lowered by increments until quartz and alkali feldspar crystalized from the liquid. To establish reversed equilibrium, we crystallized the homogenized melt at the lower T and then raised T until we found that the crystalline phases were completely resorbed into the liquid. The reversed liquidus minimum temperatures at 3.0, 4.1, 5.8, 8.0, and 12.0 wt% H2O are 935–985, 875–900, 775–800, 725–775, and 650–675 °C, respectively. Quenched charges were analyzed by petrographic microscope, scanning electron microscope (SEM), X-ray diffraction (XRD), and electron microprobe analysis (EMPA). The equation for the reversed haplogranite liquidus minimum curve for Ab36.25Or36.25Qz27.5 (wt% basis) at 1.0 GPa is \(T = - 0.0995 w_{{{\text{H}}_{ 2} {\text{O}}}}^{ 3} + 5.0242w_{{{\text{H}}_{ 2} {\text{O}}}}^{ 2} - 88.183 w_{{{\text{H}}_{ 2} {\text{O}}}} + 1171.0\) for \(0 \le w_{{{\text{H}}_{ 2} {\text{O}}}} \le 17\) wt% and \(T\) is in °C. We present a revised \(P - T\) diagram of liquidus minimum H2O isopleths which integrates data from previous determinations of vapor-saturated melting and the lower pressure vapor-undersaturated melting studies conducted by other workers on the haplogranite system. For lower H2O (<5.8 wt%) and higher temperature, our results plot on the high end of the extrapolated water contents at liquidus minima when compared to the previous estimates. As a consequence, amounts of metaluminous granites that can be produced from lower crustal biotite–amphibole gneisses by dehydration melting are more restricted than previously thought.  相似文献   

3.
祁连山冻土区含天然气水合物层段岩心热模拟实验研究   总被引:1,自引:0,他引:1  
以热模拟实验为手段,对祁连山冻土区DK-2和DK-3孔含天然气水合物层段岩心(泥岩、油页岩和煤)热模拟烃类气体的组分、碳同位素组成与天然气水合物进行对比,以探寻这些气源岩与天然气水合物气源之间的可能联系。实验结果显示:低温(300 ℃以下)条件下,产生的气体以非烃CO2为主,烃类气体含量少,且泥岩产生烃类气体量<油页岩产生烃类气体量<煤产生烃类气体量,表现出不同岩石吸附气体的差异性特征;随着热模拟温度增加,产生的烃类气体量明显增加,至500 ℃时达到最高,相反CO2产气量变化不大;随热模拟温度增加,泥岩、油页岩、煤所产生烃类气体的碳同位素值呈现先变轻后变重的演化趋势和δ13C1 <δ13C2<δ13C3的正碳同位素序列特征;泥岩在350~400 ℃条件下或油页岩在380~400 ℃条件下所产生的烃类气体在组成和同位素特征上与天然气水合物中烃类气体较为相似,推测天然气水合物气源与深部泥岩或油页岩具有地球化学成生联系,相反煤产生的烃类气体虽然在组成上与天然气水合物中烃类气体较为相近,但两者同位素值相差较远,推测煤与天然气水合物气源关系不大。  相似文献   

4.
Experiments were conducted to determine the water solubility of alkali basalts from Etna, Stromboli and Vesuvius volcanoes, Italy. The basaltic melts were equilibrated at 1,200°C with pure water, under oxidized conditions, and at pressures ranging from 163 to 3,842 bars. Our results show that at pressures above 1 kbar, alkali basalts dissolve more water than typical mid-ocean ridge basalts (MORB). Combination of our data with those from previous studies allows the following simple empirical model for the water solubility of basalts of varying alkalinity and fO2 to be derived: \textH 2 \textO( \textwt% ) = \text H 2 \textO\textMORB ( \textwt% ) + ( 5.84 ×10 - 5 *\textP - 2.29 ×10 - 2 ) ×( \textNa2 \textO + \textK2 \textO )( \textwt% ) + 4.67 ×10 - 2 ×\Updelta \textNNO - 2.29 ×10 - 1 {\text{H}}_{ 2} {\text{O}}\left( {{\text{wt}}\% } \right) = {\text{ H}}_{ 2} {\text{O}}_{\text{MORB}} \left( {{\text{wt}}\% } \right) + \left( {5.84 \times 10^{ - 5} *{\text{P}} - 2.29 \times 10^{ - 2} } \right) \times \left( {{\text{Na}}_{2} {\text{O}} + {\text{K}}_{2} {\text{O}}} \right)\left( {{\text{wt}}\% } \right) + 4.67 \times 10^{ - 2} \times \Updelta {\text{NNO}} - 2.29 \times 10^{ - 1} where H2OMORB is the water solubility at the calculated P, using the model of Dixon et al. (1995). This equation reproduces the existing database on water solubilities in basaltic melts to within 5%. Interpretation of the speciation data in the context of the glass transition theory shows that water speciation in basalt melts is severely modified during quench. At magmatic temperatures, more than 90% of dissolved water forms hydroxyl groups at all water contents, whilst in natural or synthetic glasses, the amount of molecular water is much larger. A regular solution model with an explicit temperature dependence reproduces well-observed water species. Derivation of the partial molar volume of molecular water using standard thermodynamic considerations yields values close to previous findings if room temperature water species are used. When high temperature species proportions are used, a negative partial molar volume is obtained for molecular water. Calculation of the partial molar volume of total water using H2O solubility data on basaltic melts at pressures above 1 kbar yields a value of 19 cm3/mol in reasonable agreement with estimates obtained from density measurements.  相似文献   

5.
The pressure–volume–temperature (PVT) relation of CaIrO3 post-perovskite (ppv) was measured at pressures and temperatures up to 8.6 GPa and 1,273 K, respectively, with energy-dispersive synchrotron X-ray diffraction using a DIA-type, cubic-anvil apparatus (SAM85). Unit-cell dimensions were derived from the Le Bail full profile refinement technique, and the results were fitted using the third-order Birth-Murnaghan equation of state. The derived bulk modulus \( K_{T0} \) at ambient pressure and temperature is 168.3 ± 7.1 GPa with a pressure derivative \( K_{T0}^{\prime } \) = 5.4 ± 0.7. All of the high temperature data, combined with previous experimental data, are fitted using the high-temperature Birch-Murnaghan equation of state, the thermal pressure approach, and the Mie-Grüneisen-Debye formalism. The refined thermoelastic parameters for CaIrO3 ppv are: temperature derivative of bulk modulus \( (\partial K_{T} /\partial T)_{P} \) = ?0.038 ± 0.011 GPa K?1, \( \alpha K_{T} \) = 0.0039 ± 0.0001 GPa K?1, \( \left( {\partial K_{T} /\partial T} \right)_{V} \) = ?0.012 ± 0.002 GPa K?1, and \( \left( {\partial^{2} P/\partial T^{2} } \right)_{V} \) = 1.9 ± 0.3 × 10?6 GPa2 K?2. Using the Mie-Grüneisen-Debye formalism, we obtain Grüneisen parameter \( \gamma_{0} \) = 0.92 ± 0.01 and its volume dependence q = 3.4 ± 0.6. The systematic variation of bulk moduli for several oxide post-perovskites can be described approximately by the relationship K T0  = 5406.0/V(molar) + 5.9 GPa.  相似文献   

6.
The water-saturated phase relations have been determined for a primitive magnesian andesite (57 wt% SiO2, 9 wt% MgO) from the Mt. Shasta, CA region over the pressure range 200–800 MPa, temperature range of 915–1,070 °C, and oxygen fugacities varying from the nickel–nickel oxide (NNO) buffer to three log units above NNO (NNO+3). The phase diagram of a primitive basaltic andesite (52 wt% SiO2, 10.5 wt% MgO) also from the Mt. Shasta region (Grove et al. in Contrib Miner Petrol 145:515–533; 2003) has been supplemented with additional experimental data at 500 MPa. Hydrous phase relations for these compositions allow a comparison of the dramatic effects of dissolved H2O on the crystallization sequence. Liquidus mineral phase stability and appearance temperatures vary sensitively in response to variation in pressure and H2O content, and this information is used to calibrate magmatic barometers-hygrometers for primitive arc magmas. H2O-saturated experiments on both compositions reveal the strong dependence of amphibole stability on the partial pressure of H2O. A narrow stability field is identified where olivine and amphibole are coexisting phases in the primitive andesite composition above 500 MPa and at least until 800 MPa, between 975–1,025 °C. With increasing H2O pressure (\({P}_{\text {H}_2{\rm O}}\)), the temperature difference between the liquidus and amphibole appearance decreases, causing a change in chemical composition of the first amphibole to crystallize. An empirical calibration is proposed for an amphibole first appearance barometer-hygrometer that uses Mg# of the amphibole and \(f_{\text {O}_2}\):
$$ P_{\text{H}_{2}{\rm O}}({\rm MPa})=\left[{\frac{{\rm Mg\#}}{52.7}}-0.014 * \Updelta {\rm NNO}\right]^{15.12} $$
This barometer gives a minimum \({P}_{\text{H}_{2}{\rm O}}\) recorded by the first appearance of amphibole in primitive arc basaltic andesite and andesite. We apply this barometer to amphibole antecrysts erupted in mixed andesite and dacite lavas from the Mt. Shasta, CA stratocone. Both high H2O pressures (500–900 MPa) and high pre-eruptive magmatic H2O contents (10–14 wt% H2O) are indicated for the primitive end members of magma mixing that are preserved in the Shasta lavas. We also use these new experimental data to explore and evaluate the empirical hornblende barometer of Larocque and Canil (2010).
  相似文献   

7.
The origin of epigenetic graphite: evidence from isotopes   总被引:1,自引:0,他引:1  
Stable carbon isotope ratios measured in syngenetic graphite, epigenetic graphite, and graphitic marble suggests that syngenetic graphite forms only by the metamorphism of carbonaceous detritus. Metamorphism of calcareous rocks with carbonaceous detritus is accompanied by an exchange of carbon between the two, which may result in large changes in isotopic composition of the non-carbonate phase but does not affect the relative proportions of the two reactants in the rock. Epigenetic graphite forms only from carbonaceous material or preexisting graphite. The reactions involved are the water gas reaction (C + H2O → CO + H2) at 800–900°C, and the Boudouard reaction (2CO → C + CO2), which probably takes place at temperatures about 50–100°C lower.  相似文献   

8.
The onset of hydrous partial melting in the mantle above the transition zone is dictated by the H2O storage capacity of peridotite, which is defined as the maximum concentration that the solid assemblage can store at P and T without stabilizing a hydrous fluid or melt. H2O storage capacities of minerals in simple systems do not adequately constrain the peridotite water storage capacity because simpler systems do not account for enhanced hydrous melt stability and reduced H2O activity facilitated by the additional components of multiply saturated peridotite. In this study, we determine peridotite-saturated olivine and pyroxene water storage capacities at 10–13 GPa and 1,350–1,450°C by employing layered experiments, in which the bottom ~2/3 of the capsule consists of hydrated KLB-1 oxide analog peridotite and the top ~1/3 of the capsule is a nearly monomineralic layer of hydrated Mg# 89.6 olivine. This method facilitates the growth of ~200-μm olivine crystals, as well as accessory low-Ca pyroxenes up to ~50 μm in diameter. The presence of small amounts of hydrous melt ensures that crystalline phases have maximal H2O contents possible, while in equilibrium with the full peridotite assemblage (melt + ol + pyx + gt). At 12 GPa, olivine and pyroxene water storage capacities decrease from ~1,000 to 650 ppm, and ~1,400 to 1,100 ppm, respectively, as temperature increases from 1,350 to 1,450°C. Combining our results with those from a companion study at 5–8 GPa (Ardia et al., in prep.) at 1,450°C, the olivine water storage capacity increases linearly with increasing pressure and is defined by the relation C\textH2 \textO\textolivine ( \textppm ) = 57.6( ±16 ) ×P( \textGPa ) - 169( ±18 ). C_{{{\text{H}}_{2} {\text{O}}}}^{\text{olivine}} \left( {\text{ppm}} \right) = 57.6\left( { \pm 16} \right) \times P\left( {\text{GPa}} \right) - 169\left( { \pm 18} \right). Adjustment of this trend for small increases in temperature along the mantle geotherm, combined with experimental determinations of D\textH2 \textO\textpyx/olivine D_{{{\text{H}}_{2} {\text{O}}}}^{\text{pyx/olivine}} from this study and estimates of D\textH2 \textO\textgt/\textolivine D_{{{\text{H}}_{2} {\text{O}}}}^{{{\text{gt}}/{\text{olivine}}}} , allows for estimation of peridotite H2O storage capacity, which is 440 ± 200 ppm at 400 km. This suggests that MORB source upper mantle, which contains 50–200 ppm bulk H2O, is not wet enough to incite a global melt layer above the 410-km discontinuity. However, OIB source mantle and residues of subducted slabs, which contain 300–1,000 ppm bulk H2O, can exceed the peridotite H2O storage capacity and incite localized hydrous partial melting in the deep upper mantle. Experimentally determined values of D\textH2 \textO\textpyx/\textolivine D_{{{\text{H}}_{2} {\text{O}}}}^{{{\text{pyx}}/{\text{olivine}}}} at 10–13 GPa have a narrow range of 1.35 ± 0.13, meaning that olivine is probably the most important host of H2O in the deep upper mantle. The increase in hydration of olivine with depth in the upper mantle may have significant influence on viscosity and other transport properties.  相似文献   

9.
The effect of alkalis on the solubility of H2O and CO2 in alkali-rich silicate melts was investigated at 500 MPa and 1,250 °C in the systems with H2O/(H2O + CO2) ratio varying from 0 to 1. Using a synthetic analog of phonotephritic magma from Alban Hills (AH1) as a base composition, the Na/(Na + K) ratio was varied from 0.28 (AH1) to 0.60 (AH2) and 0.85 (AH3) at roughly constant total alkali content. The obtained results were compared with the data for shoshonitic and latitic melts having similar total alkali content but different structural characteristics, e.g., NBO/T parameter (the ratio of non-bridging oxygens over tetrahedrally coordinated cations), as those of the AH compositions. Little variation was observed in H2O solubility (melt equilibrated with pure H2O fluid) for the whole compositional range in this study with values ranging between 9.7 and 10.2 wt. As previously shown, the maximum CO2 content in melts equilibrated with CO2-rich fluids increases strongly with the NBO/T from 0.29 wt % for latite (NBO/T = 0.17) to 0.45 wt % for shoshonite (NBO/T = 0.38) to 0.90 wt % for AH2 (NBO/T = 0.55). The highest CO2 contents determined for AH3 and AH1 are 1.18 ± 0.05 wt % and 0.86 ± 0.12 wt %, respectively, indicating that Na is promoting carbonate incorporation stronger than potassium. At near constant NBO/T, CO2 solubility increases from 0.86 ± 0.12 wt % in AH1 [Na/(Na + K)] = 0.28, to 1.18 ± 0.05 wt % in AH3 [Na/(Na + K)] = 0.85, suggesting that Na favors CO2 solubility on an equimolar basis. An empirical equation is proposed to predict the maximum CO2 solubility at 500 MPa and 1,100–1,300 °C in various silicate melts as a function of the NBO/T, (Na + K)/∑cations and Na/(Na + K) parameters: \({\text{wt}}\% \;{\text{CO}}_{2} = - 0.246 + 0.014\exp \left( {6.995 \cdot \frac{\text{NBO}}{T}} \right) + 3.150 \cdot \frac{{{\text{Na}} + {\text{K}}}}{{\varSigma {\text{cations}}}} + 0.222 \cdot \frac{\text{Na}}{{{\text{Na}} + {\text{K}}}}.\) This model is valid for melt compositions with NBO/T between 0.0 and 0.6, (Na + K)/∑cation between 0.08 and 0.36 and Na/(Na + K) ratio from 0.25 to 0.95 at oxygen fugacities around the quartz–fayalite–magnetite buffer and above.  相似文献   

10.
The equilibrium curve for the reaction 3 dolomite + 1 K-feldspar + 1 H2O=1 phlogopite + 3 calcite + 3 CO2 was determined experimentally at a total gas pressure of 2000 bars using two different methods.
  1. In the first case water alone was added to the reactants. The CO2 component of the gas phase was producted solely by the reaction under favourable P-T conditions. This manner of carrying out the reaction is called the “water method”. With this method sufficient time must be allowed for the gas phase to attain a constant composition (see Fig. 1). Reverse reactions were carried out using reaction products of the forward reaction.
  2. In the second case silver oxalate + water were added to the reactants. Breakdown of the silver oxalate leads to formation of a CO2-H2O gasphase of definite composition. At constant temperature and gas pressure the \(X_{{\text{CO}}_{\text{2}} } \) determines whether the reaction products will be phlogopite + calcite or dolomite + K-feldspar. In this case it is not necessary to wait for equilibrium to be attained. This method is abbreviated the “oxalate method”. Reactants for reverse reactions are not identical with the products of the forward reaction.
At high temperatures the results of the two different methods agree well (see Tables 1 and 2). Equilibrium was attained in one case at 490° C and \(X_{{\text{CO}}_{\text{2}} } \) of approximately 0.77, and in the other case at 520° C and \(X_{{\text{CO}}_{\text{2}} } \) of 0.90. At lower temperatures there are considerable differences in the results. With the water method an \(X_{{\text{CO}}_{\text{2}} } \) of about 0.25 was reached at 450° C. With the oxalate method dolomite K-feldspar and water still react with each other at even higher \(X_{{\text{CO}}_{\text{2}} } \) values. Phlogopite, calcite and CO2 are formed together with metastable talc. There are no criteria to indicate which of the methods is the correct one at lower temperatures and in Fig. 2, therefore, both equilibrium curves are plotted.  相似文献   

11.
Mineral-specific IR absorption coefficients were calculated for natural and synthetic olivine, SiO2 polymorphs, and GeO2 with specific isolated OH point defects using quantitative data from independent techniques such as proton–proton scattering, confocal Raman spectroscopy, and secondary ion mass spectrometry. Moreover, we present a routine to detect OH traces in anisotropic minerals using Raman spectroscopy combined with the “Comparator Technique”. In case of olivine and the SiO2 system, it turns out that the magnitude of ε for one structure is independent of the type of OH point defect and therewith the peak position (quartz ε = 89,000 ± 15,000  \textl \textmol\textH2\textO-1 \textcm-2\text{l}\,\text{mol}_{{\text{H}_2}\text{O}}^{-1}\,\text{cm}^{-2}), but it varies as a function of structure (coesite ε = 214,000 ± 14,000  \textl \textmol\textH2\textO-1 \textcm-2\text{l}\,\text{mol}_{{\text{H}_2}\text{O}}^{-1}\,\text{cm}^{-2}; stishovite ε = 485,000 ± 109,000  \textl \textmol\textH2\textO-1 \textcm-2\text{l}\,\text{mol}_{{\text{H}_2}\text{O}}^{-1}\,\text{cm}^{-2}). Evaluation of data from this study confirms that not using mineral-specific IR calibrations for the OH quantification in nominally anhydrous minerals leads to inaccurate estimations of OH concentrations, which constitute the basis for modeling the Earth’s deep water cycle.  相似文献   

12.
Hydrothermal reversal experiments have been performed on the upper pressure stability of paragonite in the temperature range 550–740 ° C. The reaction $$\begin{gathered} {\text{NaAl}}_{\text{3}} {\text{Si}}_{\text{3}} {\text{O}}_{{\text{1 0}}} ({\text{OH)}}_{\text{2}} \hfill \\ {\text{ paragonite}} \hfill \\ {\text{ = NaAlSi}}_{\text{2}} {\text{O}}_{\text{6}} + {\text{Al}}_{\text{2}} {\text{SiO}}_{\text{5}} + {\text{H}}_{\text{2}} {\text{O}} \hfill \\ {\text{ jadeite kyanite vapour}} \hfill \\ \end{gathered}$$ has been bracketed at 550 ° C, 600 ° C, 650 ° C, and 700 ° C, at pressures 24–26 kb, 24–25.5 kb, 24–25 kb, and 23–24.5 kb respectively. The reaction has a shallow negative slope (? 10 bar °C?1) and is of geobarometric significance to the stability of the eclogite assemblage, omphacite+kyanite. The experimental brackets are thermodynamically consistent with the lower pressure reversals of Chatterjee (1970, 1972), and a set of thermodynamic data is presented which satisfies all the reversal brackets for six reactions in the system Na2O-Al2O3-SiO2-H2O. The Modified Redlich Kwong equation for H2O (Holloway, 1977) predicts fugacities which are too high to satisfy the reversals of this study. The P-T stabilities of important eclogite and blueschist assemblages involving omphacite, kyanite, lawsonite, Jadeite, albite, chloritoid, and almandine with paragonite have been calculated using thermodynamic data derived from this study.  相似文献   

13.
The thermodynamic stability constants for the hydrolysis and formation of mercury (Hg2+) chloride complexes
have been used to calculate the activity coefficients for Hg(OH) n (2–n)+ and HgCl n (2–n)+ complexes using the Pitzer specific interaction model. These values have been used to determine the Pitzer parameters for the hydroxide and chloro complexes and C ML). The values of and have been determined for the neutral complexes (Hg(OH)2 and HgCl2). The resultant parameters yield calculated values for the measured values of log to  ±0.01 from I  =  0.1 to 3 m at 25°C. Since the activity coefficients of and are in reasonable agreement with the values for Pb(II), we have estimated the effect of temperature on the chloride constants for Hg(II) from 0 to 300°C and I = 0–6 m using the Pitzer parameters for complexes. The resulting parameters can be used to examine the speciation of Hg(II) with Cl in natural waters over a wide range of conditions.  相似文献   

14.
塔里木盆地侏罗系煤岩热模拟生物标志化合物特征研究   总被引:9,自引:0,他引:9  
通过对塔里木盆地侏罗系煤岩热模拟实验研究,其结果表明生物标志化合物的组成不仅受其母质的控制,而且还受热成熟度和生油岩的岩性影响。这与生油岩中生物标志化合物先质在不同演化阶段释放出不同碳数生物标志化合物的强度有关。同时,在烃源岩热演化过程中时,不能仅依靠OEP值作为热成熟度的判识指标;正构烷烃峰型在整个热演化过程中呈现出双峰型,前驼峰的主峰碳主要集中在nC16-nC18,而后驼峰则随着模拟温度的升高逐渐增大;煤岩的ΣC21-/ΣC22+值与热模拟温度之间呈现出规律性变化;原始煤岩的Pr/Ph值随热模拟温度由250℃~550℃升高,总体呈逐渐降低的趋势。  相似文献   

15.
Experiments were conducted to determine CO2 solubilities in alkali basalts from Vesuvius, Etna and Stromboli volcanoes. The basaltic melts were equilibrated with nearly pure CO2 at 1,200°C under oxidizing conditions and at pressures ranging from 269 to 2,060 bars. CO2 solubility was determined by FTIR measurements. The results show that alkalis have a strong effect on the CO2 solubility and confirm and refine the relationship between the compositional parameter Π devised by Dixon (Am Mineral 82:368–378, 1997) and the CO2 solubility. A general thermodynamic model for CO2 solubility in basaltic melts is defined for pressures up to 2 kbars. Based on the assumption that O2− and CO32− mix ideally, we have:
_boxclose_3^2 - ^m (P,T)X_^2 - ^m f__2 (P,T) K(P,T) = X__3^2 - ^m (P,T) ( X_^2 - ^m f__2 (P,T) ). \begin{gathered} K(P,T) = {\frac{{X_{{{\text{CO}}_{3}^{2 - } }}^{m} (P,T)}}{{X_{{{\text{O}}^{2 - } }}^{m} \times f_{{{\text{CO}}_{2} }} (P,T)}}} \hfill \\ K(P,T) = {{X_{{{\text{CO}}_{3}^{2 - } }}^{m} (P,T)} \mathord{\left/ {\vphantom {{X_{{{\text{CO}}_{3}^{2 - } }}^{m} (P,T)} {\left( {X_{{{\text{O}}^{2 - } }}^{m} \times f_{{{\text{CO}}_{2} }} (P,T)} \right).}}} \right. \kern-\nulldelimiterspace} {\left( {X_{{{\text{O}}^{2 - } }}^{m} \times f_{{{\text{CO}}_{2} }} (P,T)} \right).}} \hfill \\ \end{gathered}  相似文献   

16.
This paper presents the carbon isotopic values of individual n-alkanes in pyrolysates of algae,which are widely spread in marine and lacustrine environments.The carbon isotopic values of n-alkanes originated from different algal precursors vary greatly,and those of n-alka nes orginated from C.protothecoides,S.sp PCC 6803 and I.Galbana are even heavier than from higher plants,n-alkanes with different carbon numers derived from the sme organism may stem from different biomacromolecules.The dominant product nC31 diene yielded at 300℃ or lower temperature also is different from n-alkanes yielded at the same thermal evolution phase with respect to their origin.The catalysis of mineral components in limestone may lead to a lighter carbon isotope composition of n-alkanes.  相似文献   

17.
Dissolution Kinetics of Dolomite in Water at Elevated Temperatures   总被引:1,自引:0,他引:1  
Kinetic experiments of dolomite dissolution in water over a temperature range from 25 to 250°C were performed using a flow through packed bed reactor. Authors chose three different size fractions of dolomite samples: 18–35 mesh, 35–60 mesh, and 60–80 mesh. The dissolution rates of the three particle size samples of dolomite were measured. The dissolution rate values are changed with the variation of grain size of the sample. For the sample through 20–40 mesh, both the release rate of Ca and the release rate of Mg increase with increasing temperature until 200°C, then decrease with continued increasing temperature. Its maximum dissolution rate occurs at 200°C. The maximum dissolution rates for the sample through 40–60 mesh and 60–80 mesh happen at 100°C. Experimental results indicate that the dissolution of dolomite is incongruent in most cases. Dissolution of fresh dolomite was non-stoichiometric, the Ca/Mg ratio released to solution was greater than in the bulk solid, and the ratio increases with rising temperatures from 25 to 250°C. Observations on dolomite dissolution in water are presented as three parallel reactions, and each reaction occurs in consecutive steps as
where the second part is a slow reaction, and also the reaction could occur as follows:
The following rate equation was used to describe dolomite dissolution kinetics
where refers to one of each reaction among the above reactions; k ij is the rate constant for ith species in the jth reaction, a i stands for activity of ith aqueous species, n is the stoichimetric coefficience of ith species in the jth reaction, and define . The experiments prove that dissolved Ca is a strong inhibitor for dolomite dissolution (release of Ca) in most cases. Dissolved Mg was found to be an inhibitor for dolomite dissolution at low temperatures. But dissolution rates of dolomite increase with increasing the concentration of dissolved Mg in the temperature range of 200–250°C for 20–40 mesh sample, and in the temperature range of 100–250°C for 40–80 mesh sample, whereas the Mg2+ ion adsorption on dolomite surface becomes progressively the step controlling reaction. The following rate equation is suitable to dolomite dissolutions at high temperatures from 200 to 250°C.
where refers to dissolution rate (release of Ca), and are molar concentrations of dissolved Ca and Mg, k ad stands for adsorption reaction rate constant, K Mg refers to adsorption equilibrium constant. At 200°C for 40–60 mesh sample, the release rate of Ca can be described as:
  相似文献   

18.
We evaluate balanced metasomatic reactions and model coupled reactive and isotopic transport at a carbonatite-gneiss contact at Alnö, Sweden. We interpret structurally channelled fluid flow along the carbonatite-gneiss contact at ~640°C. This caused (1) metasomatism of the gneiss, by the reaction: ${\hbox{biotite} + \hbox{quartz} + \hbox{oligoclase} + \hbox{K}_{2} \hbox{O} +\,\hbox{Na}_{2}\hbox{O} \pm \hbox{CaO} \pm \hbox{MgO} \pm \hbox{FeO} = \hbox{albite} + \hbox{K-feldspar} + \hbox{arfvedsonite} + \hbox{aegirene-}\hbox{augite} + \hbox{H}_{2} \hbox{O} + \hbox{SiO}_{2}}We evaluate balanced metasomatic reactions and model coupled reactive and isotopic transport at a carbonatite-gneiss contact at Aln?, Sweden. We interpret structurally channelled fluid flow along the carbonatite-gneiss contact at ∼640°C. This caused (1) metasomatism of the gneiss, by the reaction: , (2) metasomatism of carbonatite by the reaction: calcite + SiO2 = wollastonite + CO2, and (3) isotopic homogenization of the metasomatised region. We suggest that reactive weakening caused the metasomatised region to widen and that the metasomatic reactions are chemically (and possibly mechanically) coupled. Spatial separation of reaction and isotope fronts in the carbonatite conforms to a chromatographic model which assumes local calcite–fluid equilibrium, yields a timescale of 102–104 years for fluid–rock interaction and confirms that chemical transport towards the carbonatite interior was mainly by diffusion. We conclude that most silicate phases present in the studied carbonatite were acquired by corrosion and assimilation of ijolite, as a reactive by-product of this process and by metasomatism. The carbonatite was thus a relatively pure calcite–H2O−CO2–salt melt or fluid.  相似文献   

19.
The diffusion of water in a peralkaline and a peraluminous rhyolitic melt was investigated at temperatures of 714–1,493 K and pressures of 100 and 500 MPa. At temperatures below 923 K dehydration experiments were performed on glasses containing about 2 wt% H2O t in cold seal pressure vessels. At high temperatures diffusion couples of water-poor (<0.5 wt% H2O t ) and water-rich (~2 wt% H2O t ) melts were run in an internally heated gas pressure vessel. Argon was the pressure medium in both cases. Concentration profiles of hydrous species (OH groups and H2O molecules) were measured along the diffusion direction using near-infrared (NIR) microspectroscopy. The bulk water diffusivity () was derived from profiles of total water () using a modified Boltzmann-Matano method as well as using fittings assuming a functional relationship between and Both methods consistently indicate that is proportional to in this range of water contents for both bulk compositions, in agreement with previous work on metaluminous rhyolite. The water diffusivity in the peraluminous melts agrees very well with data for metaluminous rhyolites implying that an excess of Al2O3 with respect to alkalis does not affect water diffusion. On the other hand, water diffusion is faster by roughly a factor of two in the peralkaline melt compared to the metaluminous melt. The following expression for the water diffusivity in the peralkaline rhyolite as a function of temperature and pressure was obtained by least-squares fitting:
where is the water diffusivity at 1 wt% H2O t in m2/s, T is the temperature in K and P is the pressure in MPa. The above equation reproduces the experimental data (14 runs in total) with a standard fit error of 0.15 log units. It can be employed to model degassing of peralkaline melts at water contents up to 2 wt%.  相似文献   

20.
Solubility curves of water-hydrogen fluid were studied using a high-pressure gas apparatus at a pressure of 200 MPa under variable fluid composition in haplogranite (Ab 39 Or 32 Qtz 29, 950°C), Na-disilicate (Na2Si2O5, 950°C), and albite melts (1200°C). The mole fraction of hydrogen in experiments was controlled directly by Ar-H2 mixtures using a specially designed cell with a Shaw membrane. $ X_{H_2 }^{Ar - H_2 } $ X_{H_2 }^{Ar - H_2 } ranged from 0 to 1. In some experiments with haplogranite and Na-disilicate melts under oxidizing conditions, in order to increase the accuracy of experimental parameters, the fugacities of oxygen and hydrogen were controlled using the double-capsule technique and the solid-phase buffer mixtures Ni-NiO (NNO) and Co-CoO (CCO). The addition of H2 to the H2O-saturated systems ($ X_{H_2 }^{H_2 O - H_2 } $ X_{H_2 }^{H_2 O - H_2 } ≥ 0.012) results in the appearance of a distinct maximum on the solubility curves at $ X_{H_2 }^{H_2 O - H_2 } $ X_{H_2 }^{H_2 O - H_2 } = 0.05–0.07 (H2 mole fractions were calculated for real H2O-H2 mixtures of real gases), and the maximum content of H2O-H2 fluid increases relative to the H2O-saturated melts by 1.51 wt % for haplogranite melt at $ X_{H_2 } $ X_{H_2 } = 0.063, 2.68 wt % for albite melt at $ X_{H_2 } $ X_{H_2 } = 0.066, and 3.54 wt % for Na-disilicate melt at $ X_{H_2 } $ X_{H_2 } = 0.067. A further increase in H2 content in the gas mixture decreases the solubility of H2O-H2 fluid in the melts, and under pure H2 pressure, the contents of fluid components are 0.08 wt % in haplogranite melt and 0.06 wt % in albite melt. The 1H NMR study of aluminosilicate and Na-silicate glasses obtained under the pressure of H2O and H2O-H2 fluids suggests different mechanisms of the dissolution of H2O and H2O-H2 fluids in magmatic melts. In addition to the spectra of dissolved water fluid, the spectra of quenched glasses synthesized under H2O-H2 fluid pressure exhibited a narrow line of molecular hydrogen with a width at half height of 1.8–2.0 kHz at $ X_{H_2 } $ X_{H_2 } ≥ 0.653 for albite and $ X_{H_2 } $ X_{H_2 } ≥ 0.063 for Na-disilicate and two lines at $ X_{H_2 } $ X_{H_2 } ≥ 0.063 for the haplogranite composition.  相似文献   

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