首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 125 毫秒
1.
Solubilities of corundum (Al2O3) and wollastonite (CaSiO3) were measured in H2O-NaCl solutions at 800 °C and 10 kbar and NaCl concentrations up to halite saturation by weight-loss methods. Additional data on quartz solubility at a single NaCl concentration were obtained as a supplement to previous work. Single crystals of synthetic corundum, natural wollastonite or natural quartz were equilibrated with H2O and NaCl at pressure (P) and temperature (T) in a piston-cylinder apparatus with NaCl pressure medium and graphite heater sleeves. The three minerals show fundamentally different dissolution behavior. Corundum solubility undergoes large enhancement with NaCl concentration, rising rapidly from Al2O3 molality (mAl2O3) of 0.0013(1) (1σ error) in pure H2O and then leveling off to a maximum of ∼0.015 at halite saturation (XNaCl ≈ 0.58, where X is mole fraction). Solubility enhancement relative to that in pure H2O, , passes through a maximum at XNaCl ≈ 0.15 and then declines towards halite saturation. Quenched fluids have neutral pH at 25 °C. Wollastonite has low solubility in pure H2O at this P and T(mCaSiO3=0.0167(6)). It undergoes great enhancement, with a maximum solubility relative to that in H2O at XNaCl ≈ 0.33, and solubility >0.5 molal at halite saturation. Solute silica is 2.5 times higher than at quartz saturation in the system H2O-NaCl-SiO2, and quenched fluids are very basic (pH 11). Quartz shows monotonically decreasing solubility from mSiO2=1.248 in pure H2O to 0.202 at halite saturation. Quenched fluids are pH neutral. A simple ideal-mixing model for quartz-saturated solutions that requires as input only the solubility and speciation of silica in pure H2O reproduces the data and indicates that hydrogen bonding of molecular H2O to dissolved silica species is thermodynamically negligible. The maxima in for corundum and wollastonite indicate that the solute products include hydrates and Na+ and/or Cl− species produced by molar ratios of reactant H2O to NaCl of 6:1 and 2:1, respectively. Our results imply that quite simple mechanisms may exist in the dissolution of common rock-forming minerals in saline fluids at high P and T and allow assessment of the interaction of simple, congruently soluble rock-forming minerals with brines associated with deep-crustal metamorphism.  相似文献   

2.
Fluid inclusion analyses leave little doubt that solutions containing large concentrations of H2O, CO2, and electrolytes are involved in a wide range of geologic processes. Although the miscibility gap in the system H2O-CO2 occurs only at low temperatures, experimental data reported by Takenouchi and Kennedy (1965) and Gehrig (1980) indicate that the addition of 6 weight percent NaCl relative to H2O + Nacl extends the region of immiscibility in the system H2O-CO2-NaC] to ≥700°C at 500 bars and mole fractions of CO2 (XCO2) ? 0.1. In contrast, addition of 20 weight percent NaCl relative to H2O + NaCl at 700°C and 500 bars expands the miscibility gap to XCO2 ? 0.2. At 2000 bars, addition of 20 and 35 weight percent NaCl relative to H2O + NaCl causes the miscibility gap to extend to ~500° and ~700°C, respectively, at XCO2 ? 0.3. The existence of the immiscible region in this high-pressure/temperature environment has a profound effect on temperatures of equilibration for metamorphic mineral assemblages (Bowers and Helgeson, 1983). To determine the extent to which nonideality in the ternary system affects these equilibria, the modified Redlich-Kwong (MRK.) equation of state was fit to pressure-volume-temperature data taken from Gehrig (1980) along pseudobinaries for which XNaClXH2O is constant. Fugacity coefficients of the components were then generated from the fugacity coefficient analog of the MRK equation of state and these coefficients were used together with solubility data to determine the compositions of the coexisting immiscible phases. The tie lines connecting the coexisting phases shift in orientation from nearly parallel to the H2O-CO2 binary at low temperatures to almost perpendicular to this binary at high temperatures.  相似文献   

3.
Reactions and partial melting of peraluminous rocks in the presence of H2O-CO2–salt fluids under parameters of granulite-facies metamorphism were modeled in experiments on interaction between orthopyroxene–cordierite–biotite–plagioclase–quartz metapelite with H2O, H2O-CO2, H2O-CO2-NaCl, and H2O-CO2-KCl fluids at 600 MPa and 850°C. Rock melting in the presence of H2O and equimolar H2O-CO2 fluids generates peraluminous (A/CNK1 > 1.1) melts whose composition corresponds to magnesian calcic or calc–alkaline S-type granitoids. The melts are associated with peritectic phases: magnesian spinel and orthopyroxene containing up to 9 wt % Al2O3. In the presence of H2O-CO2-NaCl fluid, cordierite and orthopyroxene are replaced by the association of K-Na biotite, Na-bearing gedrite, spinel, and albite. The Na2O concentrations in the biotite and gedrite are functions of the NaCl concentrations in the starting fluid. Fluids of the composition H2O-CO2-KCl induce cordierite replacement by biotite with corundum and spinel and by these phases in association with potassium feldspar at X KCl = 0.02 in the fluid. When replaced by these phases, cordierite is excluded from the melting reactions, and the overall melting of the metapelite is controlled by peritectic reactions of biotite and orthopyroxene with plagioclase and quartz. These reactions produce such minerals atypical of metapelites as Ca-Na amphibole and clinopyroxene. The compositions of melts derived in the presence of salt-bearing fluids are shifted toward the region with A/CNK < 1.1, as is typical of so-called peraluminous granites of type I. An increase in the concentrations of salts in the fluids leads to depletion of the melts in Al2O3 and CaO and enrichment in alkalis. These relations suggest that the protoliths of I-type peraluminous granites might have been metapelites that were melted when interacting with H2O-CO2-salt fluids. The compositions of the melts can evolve from those with A/CNK > 1.1 (typical of S-type granites) toward those with A/CNK = 1.0–1.1 in response to an increase in the concentrations of alkali salts in the fluids within a few mole percent. Our experiments demonstrate that the origin of new mineral assemblages in metapelite in equilibrium with H2O-CO2-salt fluids is controlled by the activities of alkaline components, while the H2O and CO2 activities play subordinate roles. This conclusion is consistent with the results obtained by simulating metapelite mineral assemblages by Gibbs free energy minimization (using the PERPE_X software), as shown in log(\({a_{{H_2}O}}\))–log(\({a_{N{a_2}O}}\)) and log(\({a_{{H_2}O}}\))–log(\({a_{{K_2}O}}\)) diagrams.  相似文献   

4.
The solubility and stability of synthetic grossular were determined at 800 °C and 10 kbar in NaCl-H2O solutions over a large range of salinity. The measurements were made by evaluating the weight losses of grossular, corundum, and wollastonite crystals equilibrated with fluid for up to one week in Pt capsules and a piston-cylinder apparatus. Grossular dissolves congruently over the entire salinity range and displays a large solubility increase of 0.0053 to 0.132 molal Ca3Al2Si3O12 with increasing NaCl mole fraction (XNaCl) from 0 to 0.4. There is thus a solubility enhancement 25 times the pure H2O value over the investigated range, indicating strong solute interaction with NaCl. The Ca3Al2Si3O12 mole fraction versus NaCl mole fraction curve has a broad plateau between XNaCl = 0.2 and 0.4, indicating that the solute products are hydrous; the enhancement effect of NaCl interaction is eventually overtaken by the destabilizing effect of lowering H2O activity. In this respect, the solubility behavior of grossular in NaCl solutions is similar to that of corundum and wollastonite. There is a substantial field of stability of grossular at 800 °C and 10 kbar in the system CaSiO3-Al2O3-H2O-NaCl. At high Al2O3/CaSiO3 bulk compositions the grossular + fluid field is limited by the appearance of corundum. Zoisite appears metastably with corundum in initially pure H2O, but disappears once grossular is nucleated. At XNaCl = 0.3, however, zoisite is stable with corundum and fluid; this is the only departure from the quaternary system encountered in this study. Corundum solubility is very high in solutions containing both NaCl and CaSiO3: Al2O3 molality increases from 0.0013 in initially pure H2O to near 0.15 at XNaCl = 0.4 in CaSiO3-saturated solutions, a >100-fold enhancement. In contrast, addition of Al2O3 to wollastonite-saturated NaCl solutions increases CaSiO3 molality by only 12%. This suggests that at high pH (quench pH is 11-12), the stability of solute Ca chloride and Na-Al ± Si complexes account for high Al2O3 solubility, and that Ca-Al ± Si complexes are minor. The high solubility and basic dissolution reaction of grossular suggest that Al may be a very mobile component in calcareous rocks in the deep crust and upper mantle when migrating saline solutions are present.  相似文献   

5.
Hydrothermal experiments with H2O-CO2 fluids at Pfluid = 6 kbar yielded the following quilibrium conditions for reactions important in metamorphosed siliceous dolomites (T = °C; X = Xco2): (3) dolomite + 2 quartz = diopside + 2 CO2T = 620 ± 8X = 0.73 ± 0.03 (5) 5 dolomite + 8 quartz + H2O = tremolite + 3 calcite + 7 CO2T = 600 ± 5 550 ±5 540±5 500±5X = 0.66 ± 0.03 0.21 ± 0.03 0.21 ± 0.04 0.06 ± 0.02 (7) 3 dolomite + 4 quartz + H2O = talc + 3 calcite + 3 CO2T = 550±5 500±5 450 ±5X = 0.25 ± 0.05 0.07 ± 0.02 0.03 ± 0.02 (8) 2 dolomite + talc + 4 quartz = tremolite + 4 CO2T = 550 ± 5 540 ±5 500 ± 5X = 0.22 ± 0.03 0.21 ± 0.02 0.06 ± 0.02 A thermodynamically self-consistent 6 kbar T-XCO2, topology results by extrapolating equilibria from experimental brackets using a modified Redlich-Kwong equation for activities in H2O-CO2 mixtures. This topology restricts the assemblage talc + calcite to a narrow stability band in T-XCO2 space at XCO2 < 0.55 and T < 590°C. Accordingly, the occurrence of talc + calcite in pure siliceous dolomites metamorphosed at Pfluid = 6 kbar implies correspondingly water-rich fluids.  相似文献   

6.
 H2O activities in concentrated NaCl solutions were measured in the ranges 600°–900° C and 2–15 kbar and at NaCl concentrations up to halite saturation by depression of the brucite (Mg(OH)2) – periclase (MgO) dehydration equilibrium. Experiments were made in internally heated Ar pressure apparatus at 2 and 4.2 kbar and in 1.91-cm-diameter piston-cylinder apparatus with NaCl pressure medium at 4.2, 7, 10 and 15 kbar. Fluid compositions in equilibrium with brucite and periclase were reversed to closures of less than 2 mol% by measuring weight changes after drying of punctured Pt capsules. Brucite-periclase equilibrium in the binary system was redetermined using coarsely crystalline synthetic brucite and periclase to inhibit back-reaction in quenching. These data lead to a linear expression for the standard Gibbs free energy of the brucite dehydration reaction in the experimental temperature range: ΔG° (±120J)=73418–134.95T(K). Using this function as a baseline, the experimental dehydration points in the system MgO−H2O−NaCl lead to a simple systematic relationship of high-temperature H2O activity in NaCl solution. At low pressure and low fluid densities near 2 kbar the H2O activity is closely approximated by its mole fraction. At pressures of 10 kbar and greater, with fluid densities approaching those of condensed H2O, the H2O activity becomes nearly equal to the square of its mole fraction. Isobaric halite saturation points terminating the univariant brucite-periclase curves were determined at each experimental pressure. The five temperature-composition points in the system NaCl−H2O are in close agreement with the halite saturation curves (liquidus curves) given by existing data from differential thermal analysis to 6 kbar. Solubility of MgO in the vapor phase near halite saturation is much less than one mole percent and could not have influenced our determinations. Activity concentration relations in the experimental P-T range may be retrieved for the binary system H2O-NaCl from our brucite-periclase data and from halite liquidus data with minor extrapolation. At two kbar, solutions closely approach an ideal gas mixture, whereas at 10 kbar and above the solutions closely approximate an ideal fused salt mixture, where the activities of H2O and NaCl correspond to an ideal activity formulation. This profound pressure-induced change of state may be characterized by the activity (a) – concentration (X) expression: a H 2O=X H 2O/(1+αX NaCl), and a NaCl=(1+α)(1+α)[X NaCl/(1+αX NaCl)](1+α). The parameter α is determined by regression of the brucite-periclase H2O activity data: α=exp[A–B/ϱH 2O ]-CP/T, where A=4.226, B=2.9605, C=164.984, and P is in kbar, T is in Kelvins, and ϱH 2O is the density of H2O at given P and T in g/cm3. These formulas reproduce both the H2O activity data and the NaCl activity data with a standard deviation of ±0.010. The thermodynamic behavior of concentrated NaCl solutions at high temperature and pressure is thus much simpler than portrayed by extended Debye-Hückel theory. The low H2O activity at high pressures in concentrated supercritical NaCl solutions (or hydrosaline melts) indicates that such solutions should be feasible as chemically active fluids capable of coexisting with solid rocks and silicate liquids (and a CO2-rich vapor) in many processes of deep crustal and upper mantle metamorphism and metasomatism. Received: 1 September 1995 / Accepted: 24 March 1996  相似文献   

7.
Thermal analysis of the halite liquidus in the system NaCl-H2O has been conducted for NaCl mole fractions (XNaCl) greater than 0.25 (i.e., > 50 wt. % NaCl) at pressures between 0.3 and 4.1 kb and temperatures greater than 450°C. The position of the liquidus was located by differential thermal analysis (DTA) of cooling scans only, as heating scans did not produce definitive DTA peaks. The dP/dT slope of the liquidus is positive and steep at high pressures, but at high XNaCl, and pressures below 0.5 kb it appears to reverse slope and intersects the three-phase curve (liquid-halite-vapour) at a shallow angle. However, due to the complex nature of the DTA signal when P <- 0.5 kb, there is considerable doubt about exactly what event has been recorded in the experiments conducted at these low pressures.The solubility of halite can be expressed as a function of the mole-fractional-based activity of NaCl in the liquid phase (L) in temperature (T, °K) and pressure (P, bars) In αNaCl(L.T.P) = ?19.884 ? 0.001275T ? 1388T + 3.2305 In (T) ? 0.07574PT Our liquidus data (based on 10 compositions) above 500 bars for these brines were combined with this equation to generate activity coefficients of NaCl which were fit within their experimental uncertainties to the following one parameter Margules equation In γNaCl(L.T.P) = (0.7268 ? 695.7T ? 0.1217PT)(1 ? XNaCl)2. Concentrated solutions of NaCl show negative deviations from ideality which rapidly increase in magnitude with decreasing XNaCl.  相似文献   

8.
Calculated phase equilibria involving minerals and H2O–CO2–NaCl fluid lead to predictions of how infiltration of rock by H2O–NaCl fluids with X NaCl in the range 0–0.3 (0–58 wt% NaCl) drives the reactions calcite + quartz = wollastonite + CO2 and dolomite = periclase + calcite + CO2. Calculations focus on metamorphism in four aureoles that together are representative of the normal P–T conditions and processes of infiltration-driven contact metamorphic reactions. The effect of salinity on the spatial extent of oxygen isotope alteration was also computed. The time-integrated input fluid flux (q°) that displaces the mineral reaction front an increment of distance along the flow path always increases with increasing X NaCl. For input fluids with salinity up to approximately five times that of seawater (X NaCl ≤ 0.05), values of q° required to explain the spatial extent of decarbonation reaction are no more than 1.1–1.5 times that computed assuming the input fluid was pure H2O. For more saline fluids, values of q° may be up to 1.4–7.9 times that for pure H2O. Except for reaction in the presence of halite and vapor (V), infiltration of H2O–NaCl fluids expands the region of oxygen isotope alteration relative to the size of the region of mineral reaction. The expansion is significant only for saline fluids with X NaCl ≥ ~0.1. Immiscible fluid phase separation and differential loss of the liquid (L) or V phase from the mineral reaction site increases the amount of reactive fluid required to advance the mineral reaction front compared to conditions under which equilibration of minerals and fluid is attained with no loss of L or V. Decarbonation reactions driven by infiltration of fluids with even modest seawater-like salinity can explain the occurrence of salt-saturated fluid and solid halide inclusions in contact metamorphosed carbonate rocks.  相似文献   

9.
  相似文献   

10.
Interaction between natural pargasite [Prg, SiO2 = 43.89 wt %, FeO/(FeO + MgO) = 0.35, (Na + K)A = 0.51] and H2O–NaCl fluid, whose composition (NaCl mole fraction) varied within the range X NaCl = NaCl/(NaCl + H2O) = 0–0.45, was experimentally studied in an internally heated apparatus at 900°C and 500 MPa. Natural pargasite begins to melt at a temperature 120–150°C lower than its synthetic analogue. In the presence of pure H2O, the subliquidus mineral assemblage involves amphibole Hbl 1, whose composition is closely similar to the starting Prg, clinopyroxene Cpx, calcic plagioclase Pl, and minor amounts of hercynite-magnetite spinel. With increasing X NaCl, the subliquidus assemblage systematically changed: calcic plagioclase disappeared and more Fe- rich amphibole Hbl 2 appeared at X NaCl = 0.07; Cpx disappeared at X NaCl = 0.14; and appearance of Na-Phl compositionally close to wonesite and almost complete disappearance of Hbl 1 was observed at X NaCl = 0.31. The composition of the melt also changed: its Na2O gradually increased (from 1.5 to 9–10 wt %), and CaO and SiO2 decreased(from 8.6 to 2 wt % and from 64 to 60 wt %, respectively, in recalculation to the anhydrous basis); at X NaCl ≥ 0.35, the melt was transformed from quartz- to nepheline-normative. The maximum Cl concentration of 1.2 wt % was measured in the melt poorest in SiO2. The experimental products contained spherical objects less than 10 μm in diameter that consisted of material that precipitated from the quenched fluid. These particles are richer than the melt in SiO2 (62–80 wt %) and poorer in Al2O3 (11–19 wt %) in experiments with X NaCl ≤ 0.24, but the differences between the compositions of the melt and particles decreased with increasing XNaCl. The relatively high concentrations of aluminosilicate material in the fluid is most likely explained by the high solubility of the melt in the fluid phase, with the formation in the fluid aqueous Si, Al–Si, Na–Al–Si, and other polymeric species. It is suggested that interaction of host rocks with such fluids, rich in granitic components, might be responsible for granitization (charnockitization) of mafic, and, particularly, ultramafic rocks described in the literature.  相似文献   

11.
Petrological and geochemical study of volatile bearing phases (fluid inclusions, amphibole, and nominally anhydrous minerals) in a spinel lherzolite xenolith suite from Quaternary lavas at Injibara (Lake Tana region, Ethiopian plateau) shows compelling evidence for metasomatism in the lithospheric mantle in a region of mantle upwelling and continental flood basalts. The xenolith suite consists of deformed (i.e., protogranular to porphyroclastic texture) Cl-rich pargasite lherzolites, metasomatized (LILE and Pb enrichment in clinopyroxene and amphibole) at T ? 1000 °C. Lherzolites contain chlorine-rich H2O-CO2 fluid inclusions, but no melt inclusions. Fluid inclusions are preserved only in orthopyroxene, while in olivine, they underwent extensive interaction with the host mineral. The metasomatic fluid composition is estimated: XCO2 = 0.64, XH2O = 0.33, XNa = 0.006, XMg = 0.006, XCl = 0.018, (salinity = 14-10 NaCl eq. wt.%, aH2O = 0.2, Cl = 4-5 mol.%). Fluid isochores correspond to trapping pressures of 1.4-1.5 GPa or 50-54 km depth (at T = 950 °C). Synchrotron sourced micro-infrared mapping (ELECTRA, Trieste) shows gradients for H2O-distribution in nominally anhydrous minerals, with considerable enrichment at grain boundaries, along intragranular microfractures, and around fluid inclusions. Total water amounts in lherzolites are variable from about 150 up to 400 ppm. Calculated trace-element pattern of metasomatic fluid phases, combined with distribution and amount of H2O in nominally anhydrous minerals, delineate a metasomatic Cl- and LILE-rich fluid phase heterogeneously distributed in the continental lithosphere. Present data suggest that Cl-rich aqueous fluids were important metasomatic agents beneath the Ethiopian plateau, locally forming a source of high water content in the peridotite, which may be easily melted. High Cl, LILE, and Pb in metasomatic fluid phases suggest the contribution of recycled altered oceanic lithosphere component in their source.  相似文献   

12.
Aqueous-carbonaceous and later pure aqueous fluid inclusions in quartz from a ferberite (Fe.95Mn.05 WO4) vein within the low-grade metamorphic aureole of the Borne granite (French Massif Central) have been studied by microthermometry and Raman spectrometry. The bulk V?-X properties of the aqueous-carbonaceous inclusions have been derived using the equation of state of Heyenet al. (1982) for the low-temperature CO2-CH4 system. A P-T path has been proposed for their trapping using the equations of state of Jacobs and Kerrick (1981a) for the H2O-CO2-CH4 system. Two main episodes were reconstructed for the history of the aqueous-carbonaceous fluid. (1) Primary H2O-CO2-CH4 vapourrich inclusions in quartz indicated the early circulation of a low-density fluid (65 mole% H2O-34 mole% CO2-1 mole% CH4 and traces of N2: d = 0.35 gcm?3) at around 550° ± 50°C and 700 ± 100 bar. Fluid cooled approximately isobarically to 450°-400°C and was progressively diluted by H2O with a concomitant increase in density. The fO2 of the H2OCO2-CH4 fluid, estimated from the equilibrium CO2 + 2H2O CH4 + 2O2, first ranged from 10?22 to 10?27 bar, close to the Q-F-M buffer. Within analytical errors, these values were consistent with the presence of graphite in equilibrium with the fluid. (2) A drop in PCO2, and therefore a drop in fO2, was recorded by the secondary liquid-rich inclusions in quartz. The inclusions, formed at and below 400°C, were composed of H2O and CH4 only, and fO2 at that stage was below that fixed by the graphite-fluid equilibrium. This second episode in the fluid-rock system could be explained by the drop of temperature below the blocking temperature of the graphite-fluid equilibrium. According to this interpretation, the blocking of the graphite-fluid equilibrium occurred at T ≥ 370°C and probably at 400°C on account of the pressure correction. Mass spectrometric data show that ferberite contains H2O, CO2 and CH4 in fluid inclusions, which lie in the gap of the V?-X properties of the aqueouscarbonaceous fluid in quartz. Deposition of ferberite probably occurred at around 400°C, the previously inferred blocking temperature, resulting from either the drop in PCO2, the drop fO2 and/or the related pH-increase.It is concluded that the existence of a blocking-temperature for the graphite-fluid chemical equilibrium may be a critical factor for maintaining a stable fluid pressure gradient in geothermal systems occurring under greenschist facies conditions in graphite-bearing rocks.  相似文献   

13.
New experimental data on the solubility of NaCl in gaseous CO2 were obtained at pressures (P) of 30–70 MPa and temperatures of 623 and 673 K on experimental equipment making possible to sample a portion of the gas in the course of the experiment. The new measures have demonstrated that the NaCl solubility increases with increasing temperature (T) and pressure and is approximately four to five orders of magnitude higher than the saturated vapor pressure of NaCl at the corresponding temperature. The paper also reports newly obtained experimental data on the equilibrium conditions of the reaction of talc decomposition into enstatite and quartz at a variable H2O/NaCl ratio in the fluid. The results of the experiments validate the empirical equations previously suggested for H2O and NaCl activities in concentrated aqueous salt solutions that can be used in describing silica-saturated fluids at high T-P parameters. A new empirical equation is suggested for the Gibbs free mixing energy in the H2O-CO2-NaCl ternary system, with the parameters of the equation calibrated against experimental data on phase equilibria in marginal binary systems and on the location of the boundary of the region of homogeneous three-component fluid according to data on synthetic fluid inclusions in quartz.  相似文献   

14.
Sapphirine, coexisting with quartz, is an indicator mineral for ultrahigh‐temperature metamorphism in aluminous rock compositions. Here a new activity‐composition model for sapphirine is combined with the internally consistent thermodynamic dataset used by THERMOCALC, for calculations primarily in K2O‐FeO‐MgO‐Al2O3‐SiO2‐H2O (KFMASH). A discrepancy between published experimentally derived FMAS grids and our calculations is understood with reference to H2O. Published FMAS grids effectively represent constant aH2O sections, thereby limiting their detailed use for the interpretation of mineral reaction textures in compositions with differing H2O. For the calculated KFMASH univariant reaction grid, sapphirine + quartz assemblages occur at P–T in excess of 6–7 kbar and 1005 °C. Sapphirine compositions and composition ranges are consistent with natural examples. However, as many univariant equilibria are typically not ‘seen’ by a specific bulk composition, the univariant reaction grid may reveal little about the detailed topology of multi‐variant equilibria, and therefore is of limited use for interpreting the P–T evolution of mineral assemblages and reaction sequences. Calculated pseudosections, which quantify bulk composition and multi‐variant equilibria, predict experimentally determined KFMASH mineral assemblages with consistent topology, and also indicate that sapphirine stabilizes at increasingly higher pressure and temperature as XMg increases. Although coexisting sapphirine and quartz can occur in relatively iron‐rich rocks if the bulk chemistry is sufficiently aluminous, the P–T window of stability shrinks with decreasing XMg. An array of mineral assemblages and mineral reaction sequences from natural sapphirine + quartz and other rocks from Enderby Land, Antarctica, are reproducible with calculated pseudosections. That consistent phase diagram calculations involving sapphirine can be performed allows for a more thorough assessment of the metamorphic evolution of high‐temperature granulite facies terranes than was previously possible. The establishment of a a‐x model for sapphirine provides the basis for expansion to larger, more geologically realistic chemical systems (e.g. involving Fe3+).  相似文献   

15.
Fluid inclusions approximated by the system H2O-CO2-NaCl are common in many geologic environments. In order to apply microthermometric data from these inclusions to infer P-T (pressure-temperature) trapping conditions, the composition of the inclusions, including the salinity, must be known. Normally, salinities of aqueous inclusions are determined from ice-melting temperatures obtained during microthermometry. However, when CO2-bearing aqueous fluid inclusions are cooled they often form a hydrate that incorporates H2O into the structure, and salinities estimated from ice-melting temperatures are therefore higher than the actual salinity. A technique that combines data from Raman spectroscopic and microthermometric analyses of individual inclusions was developed to determine the salinity of CO2-bearing aqueous inclusions based on measured clathrate melting temperatures and CO2 pressures obtained from Raman analyses. In this study, the pressure within inclusions was determined using Raman spectroscopy based on the splitting of the Fermi diad of CO2, measured at the clathrate melting temperature. The CO2 densities (and pressures) predicted by the equation developed in this study are in relatively good agreement with previously published equations, except for very low densities and correspondingly low pressures. The combined Raman spectroscopy - microthermometry technique thus provides both the temperature and the pressure in the inclusion at clathrate melting. For inclusions in which the clathrate melts in the presence of CO2 liquid, the salinity can be determined with a precision of a few tenths of a wt% NaCl, whereas for inclusions in which clathrate melts in the presence of CO2 vapor the salinity error may be a few wt% NaCl. Applying the method to synthetic fluid inclusions with known salinity suggests that the technique is valid for determining salinity of H2O-CO2-NaCl fluid inclusions in which clathrate melts in the presence of liquid CO2 only or vapor CO2 only.  相似文献   

16.
Traditionally, the application of stable isotopes in Carbon Capture and Storage (CCS) projects has focused on δ13C values of CO2 to trace the migration of injected CO2 in the subsurface. More recently the use of δ18O values of both CO2 and reservoir fluids has been proposed as a method for quantifying in situ CO2 reservoir saturations due to O isotope exchange between CO2 and H2O and subsequent changes in δ18OH2O values in the presence of high concentrations of CO2. To verify that O isotope exchange between CO2 and H2O reaches equilibrium within days, and that δ18OH2O values indeed change predictably due to the presence of CO2, a laboratory study was conducted during which the isotope composition of H2O, CO2, and dissolved inorganic C (DIC) was determined at representative reservoir conditions (50 °C and up to 19 MPa) and varying CO2 pressures. Conditions typical for the Pembina Cardium CO2 Monitoring Pilot in Alberta (Canada) were chosen for the experiments. Results obtained showed that δ18O values of CO2 were on average 36.4 ± 2.2‰ (1σ, n = 15) higher than those of water at all pressures up to and including reservoir pressure (19 MPa), in excellent agreement with the theoretically predicted isotope enrichment factor of 35.5‰ for the experimental temperatures of 50 °C. By using 18O enriched water for the experiments it was demonstrated that changes in the δ18O values of water were predictably related to the fraction of O in the system sourced from CO2 in excellent agreement with theoretical predictions. Since the fraction of O sourced from CO2 is related to the total volumetric saturation of CO2 and water as a fraction of the total volume of the system, it is concluded that changes in δ18O values of reservoir fluids can be used to calculate reservoir saturations of CO2 in CCS settings given that the δ18O values of CO2 and water are sufficiently distinct.  相似文献   

17.
Realistic simulations of fluid flow in geologic systems have severely been hampered by the lack of a consistent formulation for fluid properties for binary salt-water fluids over the temperature-pressure-composition ranges encountered in the Earth’s crust. As the first of two companion studies, a set of correlations describing the phase stability relations in the system H2O-NaCl is developed. Pure water is described by the IAPS-84 equation of state. New correlations comprise the vapor pressure of halite and molten NaCl, the NaCl melting curve, the composition of halite-saturated liquid and vapor, the pressure of vapor + liquid + halite coexistence, the temperature-pressure and temperature-composition relations for the critical curve, and the compositions of liquid and vapor on the vapor + liquid coexistence surface. The correlations yield accurate values for temperatures from 0 to 1000 °C, pressures from 0 to 5000 bar, and compositions from 0 to 1 XNaCl (mole fraction of NaCl). To facilitate their use in fluid flow simulations, the correlations are entirely formulated as functions of temperature, pressure and composition.  相似文献   

18.
The stability of the amphibole pargasite [NaCa2Mg4Al(Al2Si6))O22(OH)2] in the melting range has been determined at total pressures (P) of 1.2 to 8 kbar. The activity of H2O was controlled independently of P by using mixtures of H2O + CO2 in the fluid phase. The mole fraction of H2O in the fluid (XH2O1fl) ranged from 1.0 to 0.2.At P < 4 kbar the stability temperature (T) of pargasite decreases with decreasing XH2O1fl at constant P. Above P ? 4 kbar stability T increases as XH2O1fl is decreased below one, passes through a T maximum and then decreases with a further decrease in XH2O1fl. This behavior is due to a decrease in the H2O content of the silicate liquid as XH2O1fl decreases. The magnitude of the T maximum increases from about 10°C (relative to the stability T for XH2O1fl= 1) at P = 5 kbar to about 30°C at P = 8 kbar, and the position of the maximum shifts from XH2O1fl ? 0.6 at P = 5 kbar to XH2O1fl? 0.4 at P = 8 kbar.The H2O content of liquid coexisting with pargasite has been estimated as a function of XH2O1fl at 5 and 8 kbar P, and can be used to estimate the H2O content of magmas. Because pargasite is stable at low values of XH2O1fl at high P and T, hornblende can be an important phase in igneous processes even at relatively low H2O fugacities.  相似文献   

19.
Phase equilibria in the ternary system H2O-CO2-NaCl were studied at 800 °C and 9 kbar in internally heated gas pressure vessels using a modified synthetic fluid inclusion technique. The low rate of quartz overgrowth along the `b' and `a' axes of quartz crystals was used to avoid fluid inclusion formation during heating, prior to attainment of equilibrium run conditions. The density of CO2 in the synthetic fluid inclusions was calibrated using inclusions in the binary H2O-CO2 system synthesised by the same method and measured on the same heating-freezing stage. In the two-phase field, two types of fluid inclusions with different densities of CO2 were observed. Using mass balance calculations, these inclusions are used to constrain the miscibility gap and the orientation of two-phase tie-lines in the H2O-CO2-NaCl system at 800 °C and 9 kbar. The equation of state of Duan et al. (1995) approximately describes the P-T section of the ternary system up to about 40 wt% of NaCl. At higher NaCl concentrations the measured solubility of CO2 in the brine is much smaller than predicted by the EOS. A “salting out” effect must be added to the equation of state to include coulomb interaction in the model of Anderko and Pitzer (1993) and Pitzer and Jiang (1996). The new experimental data together with published data up to 5 kbar (Shmulovich et al. 1995) encompass practically all subsolidus crustal P-T conditions. A feature of the new experimental results is the large compositional range in the H2O-CO2-NaCl system occupied by the stability fields of halite + CO2-rich fluid ± H2O-NaCl brine. The prediction of halite stability in equilibrium with CO2-rich fluid in deep-crustal rocks is supported by recent petrological and fluid inclusion studies of granulites. Received: 29 June 1998 / Accepted: 17 March 1999  相似文献   

20.
In order to model the processes of formation of the highly alkaline (potassic) melts during the partial melting of the eclogite nodules in kimberlites, experiments on the melting of the model and natural eclogites in presence of the H2O-CO2 and H2O-CO2-KCl fluids at 5 GPa and 1200 and 1300°C are performed. A comparative analysis of the phase relations in the systems with H2O-CO2 and H2O-CO2-KCl demonstrate that KCl in the fluid equilibrated with eclogites intensifies their melting. It is related to both high Cl concentration in the forming silicate melt (2.0–5.5 wt %) and its enrichment in K2O owing to the K-Na exchange reactions with the immiscible chloride melt. Because of these reactions, the K2O/Cl ratio in the melts increases with the KCl content in the system and reaches 2.5–3.5 in the silicate melts coexisting with the immiscible chloride liquid. However, the ratio KCl/(H2O + CO2 + KCl) in the fluid does not influence on the ratio K2O/Cl in the melts. Thus, the solubility KCl in the melts, apparently, does not depend on presence of the H2O-CO2 fluid, at least, within the concentration range used in the experiments (up to 20 wt %). The experiments show that the deliberated chloride liquid is necessary to form the potassium-rich chlorine-bearing silicate melts during the eclogite melting. It corresponds to the KCl content in the system above 5 wt %.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号