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1.
Based on the thermodynamic perturbation theory an equation of state (EOS) for molecular fluids has been formulated which can be used for many fluid species in geological systems. The EOS takes into account four substance specific parameters. These are the molecular dipole moment, the molar polarizability and the two parameters of the Lennard-Jones potential. For many fluids these parameters can be evaluated directly or indirectly from experimental measurements. In the absence of direct experimental determinations, as a first approximation, for a pure fluid the parameters of the Lennard-Jones potential can be evaluated using the critical temperature and the critical density if for polar molecules in addition the dipole moment is known with reasonable accuracy. The EOS with its model potential has the appropriate asymptotic behaviour at high pressures and temperatures and can be used to calculate both vapor-liquid equilibria and thermodynamic properties of single phase fluids up to at least 10 GPa and 2000 K. Currently, parameters for 98 inorganic and organic compounds are available. In this article the EOS for pure fluids is presented. In a further communication the EOS is extended to fluid mixtures (Churakov and Gottschalk, 2003). 相似文献
2.
《Geochimica et cosmochimica acta》1996,60(7):1209-1216
A general Equation of State (EOS), which we previously developed for pure nonpolar systems, is extended to polar systems such as water and to mixtures in this study. This EOS contains only two parameters for each pure component and two additional parameters for each binary mixture (no higher order parameters are needed for more complicated mixture systems). The two mixing parameters can be eliminated for nonaqueous mixtures with a slight loss of accuracy in both total mole volume and in excess volume (or nonideal mixing). Comparison with a large amount of experimental PVTX data in pure systems (including H2O) and in the mixtures, H2O-CO2, CO2-N2, CH4-CO2, and N2-CO2-CH4 results in an average error of 1.6% in density. Comparison with commonly used EOS for supercritical fluids shows that the EOS of this study covers far more T-P-X space with higher accuracy. We believe that it is accurate from supercritical temperature to 2000 K and from 0 to 25,000 bar or higher with an average error in density of less than 2% for both pure members and mixtures in the system H2O-CO2-CH4-N2-CO-H2-O2-H2S-Ar and possibly with additional gases. Comparison with the published simulated data suggests that this EOS is approximately correct up to 300,000 bar and 2800 K.We also simulated the PVTX properties of a number of supercritical fluid mixtures using molecular dynamics (MD) simulation. These results and those of other authors are well predicted by the EOS of this study. 相似文献
3.
Rui Sun 《Geochimica et cosmochimica acta》2010,74(7):1982-9617
Molecular based equations of state (EOS) are attractive because they can take into account the energetic contribution of the main types of molecular interactions. This study models vapor-liquid equilibrium (VLE) and PVTx properties of the H2O-CO2 binary system using a Lennard-Jones (LJ) referenced SAFT (Statistical Associating Fluid Theory) EOS. The improved SAFT-LJ EOS is defined in terms of the residual molar Helmholtz energy, which is a sum of four terms representing the contributions from LJ segment-segment interactions, chain-forming among the LJ segments, short-range associations and long-range multi-polar interactions. CO2 is modeled as a linear chain molecule with a constant quadrupole moment, and H2O is modeled as a spherical molecule with four association sites and a dipole moment. The multi-polar contribution to Helmholtz energy, including the dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole contribution for H2O-CO2 system, is calculated using the theory of Gubbins and Twu (1978). Six parameters for pure H2O and four parameters for pure CO2 are needed in our model. The Van der Waals one-fluid mixing rule is used to calculate the Lennard-Jones energy parameter and volume parameter for the mixture. Two or three binary parameters are needed for CO2-H2O mixtures, which are evaluated from phase equilibrium data of the binary system. Comparison with the experimental data shows that our model represents the PVT properties of CO2 better than other SAFT EOS without a quadrupole contribution. For the CO2-H2O system, our model agrees well with the vapor-liquid equilibrium data from 323-623 K. The average relative deviation for CO2 solubility (expressed in mole fraction) in water is within 6%. Our model can also predict the PVTx properties of CO2-H2O mixtures up to 1073 K and 3000 bar. The good performance of this model indicates that: (1) taking account of the multi-polar contribution explicitly improves the agreement of calculated properties with experimental data at high temperatures and high pressures, (2) the molecular-based EOS with just a few parameters fit to data in the sub-critical region can predict the thermodynamic properties of fluids over a wide range of P-T conditions. 相似文献
4.
5.
An equation of state (EOS) based on thermodynamic perturbation theory is presented for the NaCl-H2O-CH4 system. This equation consistently reproduces PvTX properties and phase equilibria with an accuracy close to that of data in the temperature, pressure and concentration ranges from 648 K to 873 K, 0 to 2500 bar and up to 2.37 mol % NaCl. Good agreement with recent ternary immiscibility data from 673 K to 873 K suggests that the EOS may provide accurate predictions for NaCl concentrations as high as 40 mol %. We could not find any experimental data above 873 K that can be used to validate the predictions of the EOS inside the ternary. However, parameters for the mixed ternary system were established from parameters evaluated for pure and binary systems and accurate combination rules. Therefore, predictions in the ternary should be reliable to the high temperatures and pressures where the EOS for the lower order systems are valid (about 1300 K and 5000 bar). Using the same combining approach, an EOS for the quaternary NaCl-H2O-CO2-CH4 is constructed on the basis of parameters from our earlier model for the NaCl-H2O-CO2 system and the present NaCl-H2O-CH4 model. This suggests that predictions of the quaternary EOS are reliable also to about 1300 K and 5000 bar. 相似文献
6.
超临界流体热力学函数的理论计算 总被引：10，自引：1，他引：9
Ｄｕａｎ等（１９９２。１９９６）基于分子间相互作用势能模型,建立了一个适合于超临界流体的状态方程,此方程能反演出世界上几十个实验室测定的成千上万个纯组分及混合物的ＰＶＴ（压力、体积、温度）数据（温压范围：Ｐ〈２ＧＰａ,Ｔｃ〈Ｔ〈２０００Ｋ）。最近的研究发现,此方程能准确预测Ｈ２Ｏ、ＣＯ２、ＣＨ４、Ｎ２及它们的混合物在Ｔ＝１．３Ｔｃ,Ｐ＝０到Ｔ＝２０００Ｋ,Ｐ＝１０ＧＰａ这一温压范围内的压力、体积、 相似文献
7.
An improved and extended internally consistent thermodynamic dataset for phases of petrological interest,involving a new equation of state for solids 总被引：15，自引：0，他引：15
The thermodynamic properties of 254 end‐members, including 210 mineral end‐members, 18 silicate liquid end‐members and 26 aqueous fluid species are presented in a revised and updated internally consistent thermodynamic data set. The PVT properties of the data set phases are now based on a modified Tait equation of state (EOS) for the solids and the Pitzer & Sterner (1995) equation for gaseous components. Thermal expansion and compressibility are linked within the modified Tait EOS (TEOS) by a thermal pressure formulation using an Einstein temperature to model the temperature dependence of both the thermal expansion and bulk modulus in a consistent way. The new EOS has led to improved fitting of the phase equilibrium experiments. Many new end‐members have been added, including several deep mantle phases and, for the first time, sulphur‐bearing minerals. Silicate liquid end‐members are in good agreement with both phase equilibrium experiments and measured heat of melting. The new dataset considerably enhances the capabilities for thermodynamic calculation on rocks, melts and aqueous fluids under crustal to deep mantle conditions. Implementations are already available in thermocalc to take advantage of the new data set and its methodologies, as illustrated by example calculations on sapphirine‐bearing equilibria, sulphur‐bearing equilibria and calculations to 300 kbar and 2000 °C to extend to lower mantle conditions. 相似文献
8.
Based on our previous study of the intermolecular potential for pure H2O and the strict evaluation of the competitive potential models for pure CH4 and the ab initio fitting potential surface across CH4-H2O molecules in this study, we carried out more than two thousand molecular dynamics simulations for the PVTx properties of pure CH4 and the CH4-H2O mixtures up to 2573 K and 10 GPa. Comparison of 1941 simulations with experimental PVT data for pure CH4 shows an average deviation of 0.96% and a maximum deviation of 2.82%. The comparison of the results of 519 simulations of the mixtures with the experimental measurements reveals that the PVTx properties of the CH4-H2O mixtures generally agree with the extensive experimental data with an average deviation of 0.83% and 4% in maximum, which is equivalent to the experimental uncertainty. Moreover, the maximum deviation between the experimental data and the simulation results decreases to about 2% as temperature and pressure increase, indicating that the high accuracy of the simulation is well retained in the high temperature and pressure region.After the validation of the simulation method and the intermolecular potential models, we systematically simulated the PVTx properties of this binary system from 673 K and 0.05 GPa to 2573 K and 10 GPa. In order to integrate all the simulation results and the experimental data for the calculation of thermodynamic properties, an equation of state (EOS) is developed for the CH4-H2O system covering 673-2573 K and 0.01-10 GPa. Isochores for compositions <4 mol% CH4 up to 773 K and 600 MPa are also determined in this paper. The program for the EOS can be downloaded from www.geochem-model.org/programs.htm. 相似文献
9.
Fluid inclusions from a biotite-garnet schist in the Southern Aravalli Mountain Belt (India) give information on both peak
metamorphic conditions and post-peak metamorphic processes during uplift. A combination of careful petrography, microthermometry
and Raman spectroscopy reveals the presence of at least five generations of enclosed fluids. Lower amphibolite-facies pressure-temperature
conditions of the growth of garnet rims are reproduced by the highest fluid density of the relatively oldest inclusion type
of CO2 (±N2)-rich compositions. A calculated fluid composition in the COH system, in equilibrium with the graphite buffer corresponds
to a CO2-rich fluid at metamorphic conditions. However, the results of these calculations are very sensitive to small fluctuations
in oxygen fugacity and the accuracy of thermodynamic properties of mineral equilibria. Re-equilibration, conceived by specific
size-density distribution and the absence of an aqueous phase in inclusions that contain nahcolite crystals, is monitored
in these inclusions as post-peak metamorphic processes, like partial decrepitation and preferential leakage. The other fluid
types represent heterogeneous fluid trapping of coexisting aqueous NaCl-bearing solutions with CO2-CH4-rich vapour bubbles in healed cracks, and probably the introduction of external fluids containing high salinity aqueous CaCl2-rich solutions in nearly pure N2 vapour bubbles, at lower P-T conditions. This study illustrates that fluid inclusions remain a valuable database of peak metamorphic conditions, moreover,
alterations of the entrapped fluids and surrounding crystals are illustrative for specific exhumation evolutions.
Received: 24 March 1999 / Accepted: 13 January 2000 相似文献
10.
Phase equilibria in the system CaO–MgO–SiO2–CO2–H2O–NaCl are calculated to illustrate phase relations in metacarbonates over a wide-range of P–T–X[H2O–CO2–NaCl] conditions. Calculations are performed using the equation of state of Duan et al. (Geochim Cosmochim Acta 59:2869–2882, 1995) for H2O–CO2–NaCl fluids and the internally consistent data set of Gottschalk (Eur J Mineral 9:175–223, 1997) for thermodynamic properties of solids. Results are presented in isothermal-isobarical plots showing stable mineral assemblages as a function of fluid composition. It is shown that in contact-metamorphic P–T regimes the presence of very small concentrations of NaCl in the fluid causes almost all decarbonation reactions to proceed within the two fluid solvus of the H2O–CO2–NaCl system. Substantial flow of magma-derived fluids into marbles has been documented for many contact aureoles by shifts in stable isotope geochemistry of the host rocks and by the progress of volatile-producing mineral reactions controlled by fluid compositions. Time-integrated fluid fluxes have been estimated by combining fluid advection/dispersion models with the spatial arrangement of mineral reactions and isotopic resetting. All existing models assume that minerals react in the presence of a single phase H2O–CO2 fluid and do not allow for the effect that fluid immiscibility has on the flow patterns. It is shown that fluids emanating from calc-alkaline melts that crystallize at shallow depths are brines. Their salinity may vary depending mainly on pressure and fraction of crystallized melt. Infiltration-driven decarbonation reactions in the host rocks inevitably proceed at the boundaries of the two fluid solvus where the produced CO2 is immiscible and may separate from the brine as a low salinity, low density H2O–CO2 fluid. Most parameters of fluid–rock interaction in contact aureoles that are derived from progress of mineral reactions and stable isotope resetting are probably incorrect because fluid phase separation is disregarded. 相似文献
11.
L. Ya. Aranovich 《Petrology》2017,25(5):486-497
The paper discusses petrological effects related to interaction between rocks and concentrated aqueous salt fluids (brines) at lower crustal metamorphism. These effects arise mainly from the low H2O activity typical of brines, while preserving and even increasing transport properties relative to pure H2O or H2O–nonpolar gas fluids. The paper presents thermodynamic properties of the halogen-bearing end members of the biotite solid solution based on experimental data, and examples illustrating how they can be employed to calculate the activities (concentrations) of alkali halides in the fluid. Action of brines significantly changes conventional views on the solubility of several minerals and on the distribution of elements (including trace elements) between minerals, melts, and fluids. The specific role of brines is also in bringing to interaction zones not only water but also alkali metals and Ca, which results in numerous metasomatic net-transfer reactions involving mafic minerals and/or exchange reactions with feldspars that produce new mineral assemblages with lower melting temperature, i.e., cause granitization of rocks as defined by D.S. Korzhinskii. Brines also exert fine “tuning” of metasomatic and melting processes: even at equal pressure, temperature, and water activity values metasomatism may or may not trigger melting depending on the Na/K/Ca ratio in the fluid phase. 相似文献
12.
An equation of state (EOS) explicit in Helmholtz free energy has been improved to calculate the PVTx and vapor–liquid phase equilibrium properties of CH4–CO2 fluid mixture. This EOS, where four mixing parameters are used, is based on highly accurate EOSs recommended by NIST for pure components (CH4 and CO2) and contains a simple generalized departure function presented by Lemmon and Jacobsen (1999). Comparison with experimental data available indicates that the EOS can calculate both vapor–liquid phase equilibrium and volumetric properties of this binary fluid system with accuracy close to that of experimental data up to high temperature and pressure within full range of composition. The EOS of CH4–CO2 fluid, together with the updated Gibbs free energy model of solid CO2 (dry ice), is applied to calculate the CH4 content (xCH4) and molar volume (Vm) of the CH4–CO2 fluid inclusion based on the assumption that the volume of an inclusion keeps constant during heating and cooling. diagrams are presented, which describe phase transitions involving vapor, liquid and CO2 solid phases of CH4–CO2 fluid inclusions. Isochores of CH4–CO2 inclusions at given and Vm can be easily calculated from the improved EOS. 相似文献
13.
V. López Sánchez-Vizcaíno J. A. D. Connolly M. T. Gómez-Pugnaire 《Contributions to Mineralogy and Petrology》1997,126(3):292-302
Phase relations and metamorphic conditions have been studied in metacarbonate rocks from the Nevado-Filábride Complex (Cordilleras
Béticas) through forward modeling. In many rock samples, the assemblage titanite + rutile + calcite + quartz + graphite buffered
the composition of the C-O-H fluid present during metamorphism. Over a wide range of P-T conditions, fluid compositions computed for this buffer are essentially binary H2O-CO2 mixtures. This buffer also constrains the chemical potentials of TiO2, CaO and SiO2. Consequently it is possible to make a thermodynamic projection through these components to predict the stable phase relations
consistent with the buffer. Using this method, phase relations have been analyzed in a rock containing the buffer assemblage
and paragonite, albite, phengite, epidote, and chlorite. The equilibrium P-T conditions for this assemblage are constrained, by minimization of the differences between predicted and observed mineral
compositions, to be 560 ± 15 °C and 9.5 ± 1 kbar. Conditions obtained compare well with those estimated from other studies
in different lithologic units. The inferred metamorphic fluid composition is H2O-rich ().
Received: 11 October 1995 / Accepted 5 August 1996 相似文献
14.
Non-aqueous CO2 and CO2-rich fluid inclusions are found in the vein quartz hosting mesothermal gold-sulphide mineralization at Bin Yauri, northwestern
Nigeria. Although mineralizing fluids responsible for gold mineralization are thought to be CO2-rich, the occurrence of predominantly pure to nearly pure CO2 inclusions is nevertheless unusual for a hydrothermal fluid system. Many studies of similar CO2-rich fluid inclusions, mainly in metamorphic rocks, proposed preferential loss (leakage) of H2O from H2O-CO2 inclusions after entrapment. In this study however, it is proposed that phase separation (fluid immiscibility) of low salinity
CO2-rich hydrothermal fluids during deposition of the gold mineralization led to the loss of the H2O phase and selective entrapment of the CO2. The loss of H2O to the wallrocks resulted in increasing oxidizing effects. There is evidence to suggest that the original CO2-rich fluid was intrinsically oxidized, or perhaps in equilibrium with oxidizing conditions in the source rocks. The source
of the implicated fluid is thought to be subducted metasediments, subjected to dehydration and devolatilization reactions
along a transcurrent Anka fault/shear system, which has been described as a Pan-African (450–750 Ma) crustal suture. 相似文献
15.
This work reports the application of thermodynamic models, including equations of state, to binary (salt-free) CH4-H2O fluid inclusions. A general method is presented to calculate the compositions of CH4-H2O inclusions using the phase volume fractions and dissolution temperatures of CH4 hydrate. To calculate the homogenization pressures and isolines of the CH4-H2O inclusions, an improved activity-fugacity model is developed to predict the vapor-liquid phase equilibrium. The phase equilibrium model can predict methane solubility in the liquid phase and water content in the vapor phase from 273 to 623 K and from 1 to 1000 bar (up to 2000 bar for the liquid phase), within or close to experimental uncertainties. Compared to reliable experimental phase equilibrium data, the average deviation of the water content in the vapor phase and methane solubility in the liquid phase is 4.29% and 3.63%, respectively. In the near-critical region, the predicted composition deviations increase to over 10%. The vapor-liquid phase equilibrium model together with the updated volumetric model of homogenous (single-phase) CH4-H2O fluid mixtures (Mao S., Duan Z., Hu J. and Zhang D. (2010) A model for single-phase PVTx properties of CO2-CH4-C2H6-N2-H2O-NaCl fluid mixtures from 273 to 1273 K and from 1 to 5000 bar. Chem. Geol.275, 148-160), is applied to calculate the isolines, homogenization pressures, homogenization volumes, and isochores at specified homogenization temperatures and compositions. Online calculation is on the website: http://www.geochem-model.org/. 相似文献
16.
I. Kenis Ph. Muchez G. Verhaert A. Boyce M. Sintubin 《Contributions to Mineralogy and Petrology》2005,150(1):102-118
Fluid inclusions in quartz veins of the High-Ardenne slate belt have preserved remnants of prograde and retrograde metamorphic
fluids. These fluids were examined by petrography, microthermometry and Raman analysis to define the chemical and spatial
evolution of the fluids that circulated through the metamorphic area of the High-Ardenne slate belt. The earliest fluid type
was a mixed aqueous/gaseous fluid (H2O–NaCl–CO2–(CH4–N2)) occurring in growth zones and as isolated fluid inclusions in both the epizonal and anchizonal part of the metamorphic
area. In the central part of the metamorphic area (epizone), in addition to this mixed aqueous/gaseous fluid, primary and
isolated fluid inclusions are also filled with a purely gaseous fluid (CO2–N2–CH4). During the Variscan orogeny, the chemical composition of gaseous fluids circulating through the Lower Devonian rocks in
the epizonal part of the slate belt, evolved from an earlier CO2–CH4–N2 composition to a later composition enriched in N2. Finally, a late, Variscan aqueous fluid system with a H2O–NaCl composition migrated through the Lower Devonian rocks. This latest type of fluid can be observed in and outside the
epizonal metamorphic part of the High-Ardenne slate belt. The chemical composition of the fluids throughout the metamorphic
area, shows a direct correlation with the metamorphic grade of the host rock. In general, the proportion of non-polar species
(i.e. CO2, CH4, N2) with respect to water and the proportion of non-polar species other than CO2 increase with increasing metamorphic grade within the slate belt. In addition to this spatial evolution of the fluids, the
temporal evolution of the gaseous fluids is indicative for a gradual maturation due to metamorphism in the central part of
the basin. In addition to the maturity of the metamorphic fluids, the salinity of the aqueous fluids also shows a link with
the metamorphic grade of the host-rock. For the earliest and latest fluid inclusions in the anchizonal part of the High-Ardenne
slate belt the salinity varies respectively between 0 and 3.5 eq.wt% NaCl and between 0 and 2.7 eq.wt% NaCl, while in the
epizonal part the salinity varies between 0.6 and 17 eq.wt% NaCl and between 3 and 10.6 eq.wt% for the earliest and latest
aqueous fluid inclusions, respectively. Although high salinity fluids are often attributed to the original sedimentary setting,
the increasing salinity of the fluids that circulated through the Lower Devonian rocks in the High-Ardenne slate belt can
be directly attributed to regional metamorphism. More specifically the salinity of the primary fluid inclusions is related
to hydrolysis reactions of Cl-bearing minerals during prograde metamorphism, while the salinity of the secondary fluid inclusions
is rather related to hydration reactions during retrograde metamorphism. The temporal and spatial distribution of the fluids
in the High-Ardenne slate belt are indicative for a closed fluid flow system present in the Lower Devonian rocks during burial
and Variscan deformation, where fluids were in thermal and chemical equilibrium with the host rock. Such a closed fluid flow
system is confirmed by stable isotope study of the veins and their adjacent host rock for which uniform δ180 values of both the veins and their host rock demonstrate a rock-buffered fluid flow system. 相似文献
17.
Abstract C-O-H fluid produced by the equilibration of H2O and excess graphite must maintain the atomic H/O ratio of water, 2:1. This constraint implies that all thermodynamic properties of the fluid are uniquely determined at isobaric-isothermal conditions. The O2, H2O and CO2 fugacities (fo2, fH2O and fCO2) of such fluids have been estimated from equations of state and fit as a function of pressure and temperature. These fugacities can be taken as characteristic for graphitic metamorphic systems in which the dominant fluid source is dehydration, e.g. pelitic lithologies. Because there are no compositional degrees of freedom for graphite-saturated fluids produced entirely by dehydration, the variance of the dehydration process is not increased in comparison with that in non-graphitic systems. Thus, compositional ‘buffering’of C-O-H fluids by dehydration equilibria, a common petrological model, requires that redox reactions, decarbonation reactions or external, H/O ± 2, fluid sources perturb the evolution of the metamorphic system. Such perturbations are not likely to be significant in metapelitic environments, but their tendency will be to increase the fO2 of the fluid phase. At high metamorphic grades, pyrite desulphidation reactions may cause a substantial reduction of fH2O and slight increases in fO2 and fCO2 relative to sulphur-free fluid. At low metamorphic grade, sulphur solubility in H/O ± 2 fluids is so low that pyrite decomposition must occur by sulphur-conserving reactions that cause iron depletion in silicates, a common feature of sulphidic pelites. With increasing temperature and sulphur solubility, pyrite desulphidation may be driven by dehydration reactions or infiltration of H2O-rich fluids. The absence of magnetite and the assemblages carbonate + aluminosilicate or pyrite + pyrrhotite + ilmenite from most graphitic metapelites is consistent with an H/O = 2 model for GCOH(S) fluid. For graphitic rocks in which such a model is inapplicable, a phase diagram variable that defines the H/O ratio of GCOH(S) fluid is more useful than the conventional fO2 variable. 相似文献
18.
Metamorphic assemblages and the direction of flow of metamorphic fluids in four instances of serpentinization 总被引：3，自引：0，他引：3
Ivan Barnes John B. Rapp James R. O'Neil Richard A. Sheppard Arthur J. Gude III 《Contributions to Mineralogy and Petrology》1972,35(3):263-276
Fluids related to Serpentinization are of at least three types. The first reported (Barnes and O'Neil, 1969) is a fluid of local meteoric origin, the chemical and thermodynamic properties of which are entirely controlled by olivine, orthopyroxene, brucite, and serpentine reactions. It is a Ca+2-OH–1 type and is shown experimentally to be capable of reacting with albite to yield calcium hydroxy silicates. Rodingites may form where the Ca+2-OH–1 type waters flow across the ultramafic contact and react with siliceous country rock.The second type of fluid has its chemical composition largely controlled before it enters the ultramafic rocks, but reactions within the ultramafic rocks fix the thermodynamic properties by reactions of orthopyroxene, olivine, calcite, brucite, and serpentine. The precipitation of brucite from this fluid clearly shows that fluid flow allows reaction products to be deposited at a distance from the point of solution. Thus, textural evidence for volume relations during Serpentinization may not be valid.The third type of fluid has its chemical properties fixed in part before the reactions with ultramafic rocks, in part by the reactions of orthopyroxene, olivine, and serpentine and in part by reactions with siliceous country rock at the contact. The reactions of the ultramafic rock and country rock with the fluid must be contemporaneous and require flow to be along the contact. This third type of fluid is grossly supersaturated with talc and tremolite, both found along the contact. The occurrence of magadiite, kenyaite, mountainite, and rhodesite along the contact is probably due to a late stage low-temperature reaction of fluids of the same thermodynamic properties as those that formed the talc and tremolite at higher temperatures. Oxygen isotope analyses of some of these minerals supports this conclusion.Rodingites form from Ca+2-rich fluids flowing across the contact; talc and tremolite form from silica-rich fluids flowing along the contact.Isotopic analyses of the fluids indicate varied origins including unaltered local meteoric water and connate water. Complexion Spring water may be a sample of only slightly altered Jurassic or Cretaceous sea water.Publication authorized by the Director, U.S. Geological Survey. 相似文献
19.
The Khtada Lake. British Columbia, metamorphic complex consists of high grade amphibolite and metasedimentary units with development of gneiss, migmatite and homogeneous autochthonous plutons. Maximum metamorphic conditions are estimated to have exceeded 5 kbar and 700°C.Fluid inclusions in matrix quartz are highly variable in density and composition, ranging from apparently pure CO2 (gas or liquid or both at room temperature) through CO2 + H2O ± CH4 mixtures to inclusions which are entirely aqueous. They occur along cracks, in groups without planar features and as isolated inclusions. The latter and some which occur in groups, are interpreted to most nearly approximate, in density and composition, the fluids present during the peak of metamorphism.The density and fluid composition data are derived from direct observations of phase changes between ? 180 and + 380°C and from the application of published experimental data in the system CH4-CO2-H2O-NaCl. The most dense, pure CO2 inclusions indicate a pressure of entrapment at 5 kbar, if a temperature of 700°C is assumed. This is in close agreement with the minimum P-T estimates from the mineral assemblages. Methane was positively identified in inclusions in graphite-bearing specimens. Salt content is concluded to be about 5–6 wt% NaCl equivalent in the aqueous phase in both aqueous and CO2 + H2O inclusions. There is evidence of immiscible separation of CO2-rich and H2O-rich fluids at temperatures at least as high as 375°C. 相似文献
20.
Martin J. Gole Stephen J. Barnes Robin E. T. Hill 《Contributions to Mineralogy and Petrology》1987,96(2):151-162
The Agnew nickel sulfide deposit is spatially associated with a lenticular body of ultramafic rocks which shows a concentric zonation in metamorphic mineralogy. Olivine + tremolite + chlorite + cummingtonite ±enstatite assemblages occur at the margin of the ultramafic lens, giving way to olivine + anthophyllite, olivine + talc and olivine + antigorite assemblages successively inwards. These rocks are interpreted as having crystallized from komatiitic lavas, and exhibit a spectrum of compositions from those of original flow tops to pure olivine adcumulates. The relative modal abundances of metamorphic olivine, tremolite and chlorite reflect original proportions of cumulus olivine and komatiite liquid in the protolith. Peak metamorphic conditions are estimated at 550° C, based on garnet-biotite thermometry, at a maximum pressure of 3 kb. This temperature falls within the narrow range over which metamorphic olivine may co-exist with enstatite, anthophyllite, talc or antigorite depending upon the fugacity of water in the metamorphic fluid. The observed mineralogical zonation is therefore attributed to infiltration by CO2-rich fluids, generated by decarbonation of talc-carbonate rocks formed during pre-metamorphic marginal alteration of the ultramafic lens. Metamorphic fluids were essentially binary mixtures of water and CO2, with minor H2S having a maximum partial pressure less than 1 percent of total pressure. Enstatite-bearing assemblages formed in the presence of CO2-rich fluids at fluid: rock volume ratios close to one, while anthophyllite, talc and antigorite bearing assemblages formed in the presence of progressively more water-rich fluids at progressively lower fluid-rock ratios. 相似文献