Petrology, geothermobarometry and C-O-H-S fluid compositions in the environs of Rampura-Agucha Zn-(Pb) ore deposit, Bhilwara District, Rajasthan     

M. Deb  Uma Sehgal 《Journal of Earth System Science》1997,106(4):343-356

The massive Zn-(Pb) sulfide ore body at Rampura-Agucha in Bhilwara district, Rajasthan, occurs within graphitic metapelites surrounded by garnet-biotite-sillimanite gneiss containing concordant bodies of amphibolite. These rocks and the sulfide ores have been studied to estimate the pressure, temperature and fluid composition associated with upper amphibolite facies metamorphism. Geothermobarometric calculations involving garnet-biotite and garnet-hornblende pairs, as well as sphalerite-hexagonal pyrrhotite-pyrite and garnet-plagioclase-sillimanite-quartz assemblages indicate that the most pervasive P-T condition during peak of regional metamorphism was 650°C and 6 kb, and was attained between the first and second deformations in the region. Some temperature-pressure estimates also cluster around 500°C–5.1 kb which probably represent retrograde cooling during unloading. Consideration of devolatilization equilibria in the C-O-H-S system at the pervasive metamorphic conditions mentioned above shows that the metamorphic fluid was H₂O-rich ( ) but also had a substantial component of . and were the other important phases in the fluid. CO (X_CO = 0.002) and were the minor phases in the fluid. It is probable that a part of this aqueous fluid was consumed by re-/neocrystallization of hydrous silicate phases like chlorite during the retrogressive metamorphic path, so that fluid entrapped in quartz below 450°C was rendered CO₂-rich (Holleret al 1996).  相似文献   

Charnockitization and enderbitization of mafic granulites in the Porya Bay area,Lapland Granulite Belt,Southern Kola Peninsula: I. Petrology and geothermobarometry     

S. P. Korikovsky  L. Ya. Aranovich 《Petrology》2010,18(4):320-349

Charnockitization of mafic Opx-Cpx-Grt-Hbl-Bt-Pl ± Qtz granulites and Hbl-Opx-Bt hornblendites was studied in the southeastern part of the Lapland Granulite Belt. The evolutionary trends of the whole-rock compositions and mineral assemblages indicate that the rocks were affected by Na-K-Si-H₂O-CO₂-Cl brines, which came from outside, alkalinized and debasified the granulites, introduced Na, K, and Si into them, and depleted them in Mg, Fe, and Ca prior to the onset of charnockite melting; the latter began in the granulites only in their most extensively debasified domains. In the course of alkaline metasomatism, pyroxene were replaced by secondary hornblende and biotite with high Ti concentrations, analogous to those in the unaltered granulites. This suggests that the pre-charnockite amphibolization and biotitization were induced not by a temperature decrease but by the effect of Na- and K-bearing fluid during the metamorphic culmination. The metasomatically altered granulites, which were transformed into leucocratic disintegrated amphibolite skialiths, were gradually resorbed and dissolved in the charnockite melt, whose bulk composition corresponded to low-alkaline granites and tonalites. Hence, no contamination took place, and the excess Mg, Fe, and Ca amounts with respect to the eutectic composition were removed from the reaction zone. Variation diagrams indicate that the whole-rock composition of the granulites is gradually shifted toward the composition of charnockitoids. In certain instances, however, melanocratic Hbl-Grt-Opx-Cpx-Pl rims were formed along the granulite-charnockite interface, with the bulk composition of these fringes richer in Mg, Fe, and Ca than that of the ambient granulites. The reason for this was the sporadic redeposition of Mg, Fe, and Ca, which were mobilized from during charnbockitization and redeposited immediately in the reaction zone. In addition, rocks around the charnockite veins bear autonomous melanocratic Grt-Opx-Cpx-Hbl ± Mag ± Ilm ± Scp ± Pl ± Qtz veins whose mineral assemblages and bulk composition are close to those of the melanocratic rims around charnockitoids. The veins were formed via the transportation of Mg, Fe, and Ca for long distances outside the charnockitization zones. TWQ thermobarometric calculations indicate that the pre-charnockite alkaline metasomatism and debasification (amphibolization, biotitization, and feldspathization), anatectic formation of charnockite migma or magma, and the development of the melanocratic veins took place at the peak of the high-pressure granulite metamorphism at the same P-T parameters: approximately 800°C and 9–9.5 kbar. The calculated composition of the charnockitizing fluids suggests that they were homogeneous brines with $ X_{H_2 O} = 0.45 $ X_{H_2 O} = 0.45 , $ X_{CO_2 } = 0.10 $ X_{CO_2 } = 0.10 , X _NaCl = 0.30, and X _KCl = 0.15.  相似文献   

H2O–CO2 solubility in mafic alkaline magma: applications to volatile sources and degassing behavior at Erebus volcano, Antarctica     

Kayla Iacovino  Gordon Moore  Kurt Roggensack  Clive Oppenheimer  Philip Kyle 《Contributions to Mineralogy and Petrology》2013,166(3):845-860

We present new equilibrium mixed-volatile (H₂O–CO₂) solubility data for a phonotephrite from Erebus volcano, Antarctica. H₂O–CO₂-saturated experiments were conducted at 400–700 MPa, 1,190 °C, and ~NNO + 1 in non-end-loaded piston cylinders. Equilibrium H₂O–CO₂ fluid compositions were determined using low-temperature vacuum manometry, and the volatile and major element compositions of the glassy run products were determined by Fourier transform infrared spectroscopy and electron microprobe. Results show that the phonotephrite used in this study will dissolve ~0.8 wt% CO₂ at 700 MPa and a fluid composition of $ X_{{{\text{H}}_{ 2} {\text{O}}}} $ ~0.4, in agreement with previous experimental studies on mafic alkaline rocks. Furthermore, the dissolution of CO₂ at moderate to high $ X_{{{\text{H}}_{ 2} {\text{O}}}}^{\text{fluid}} $ in our experiments exceeds that predicted using lower-pressure experiments on similar melts from the literature, suggesting a departure from Henrian behavior of volatiles in the melt at pressures above 400 MPa. With these data, we place new constraints on the modeling of Erebus melt inclusion and gas emission data and thus the interpretation of its magma plumbing system and the contributions of primitive magmas to passive and explosive degassing from the Erebus phonolite lava lake.  相似文献   

Petrology of the early Proterozoic platinum-bearing massif of Fedorov Tundra,Kola Peninsula     

M. I. Dubrovsky  T. V. Rundqvist 《Geology of Ore Deposits》2009,51(7):577-587

The massif of Fedorov Tundra was formed as part of the Paleoproterozoic (2.5 Ga) Fedorov-Pana platinum-bearing layered complex as a result of consecutive emplacement of two intrusive phases. The emplacement of the first phase resulted in the formation of a large layered intrusive body composed of amphibole gabbro, gabbronorite, norite, pyroxenite, olivine pyroxenite, and harzburgite. The second phase gave birth to a gabbronorite intrusion smaller in volume and enriched in sulfides and PGM. Magmatic breccia has been observed in the contact zone between two phases. The rocks of the massif are referred to the series of normal alkalinity and to the quartz- and olivine-normative groups differing in saturation with silica. Using isoplethic and isobaric joins of the q-fo-fa-di-hd-ab-an-aq phase diagram, the stages of rock formation are considered. The thermodynamic conditions of rock crystallization were determined as T = 1000−800°C and $ P_{H_2 O} $ P_{H_2 O} = 1000−2500 bar for the first intrusive phase and T = 1000–900°C and $ P_{H_2 O} $ P_{H_2 O} = 800−1000 bar for the second intrusive phase.  相似文献   

Solubility of platinum and palladium in silicate melts under high water pressure as a function of redox conditions     

N. I. Bezmen  P. N. Gorbachev  A. I. Shalynin  M. Asif  A. J. Naldrett 《Petrology》2008,16(2):161-176

The solubility of platinum and palladium in a silicate melt of the composition Di ₅₅ An ₃₅ Ab ₁₀ was determined at 1200°C and 2 kbar pressure in the presence of H₂O-H₂ fluid at an oxygen fugacity ranging from the HM to WI buffer equilibria. The influence of sulfur on the solubility of platinum in fluid-bearing silicate melt was investigated at a sulfur fugacity controlled by the Pt-PtS equilibrium at 1200°C and a pressure defined in such a way that the \(f_{H_2 O} \) and \(f_{O_2 } \) values were identical to those of the experiments without sulfur. The experiments were conducted in a high pressure gas vessel with controlled hydrogen content in the fluid. Oxygen fugacity values above the NNO buffer were controlled by solid-phase buffer mixtures using the two-capsule technique. Under more reducing conditions, the contents of H₂O and H₂ were directly controlled by the argon to hydrogen ratio in a special chamber. The hydrogen fugacity varied from 5.2 × 10^?2 bar (HM buffer) to 1230 bar (\(X_{H_2 } \) = 0.5). Pt and Pd contents were measured in quenched glass samples by neutron activation analysis. The results of these investigations showed that the solubility of Pt and Pd increases significantly in the presence of water compared with experiments in dry systems. The content of Pd within the whole range of redox conditions and that of Pt at an oxygen fugacity between the HM to MW buffer reactions are weakly dependent on \(f_{O_2 } \) and controlled mainly by water fugacity. This suggests that, in addition to oxide Pt and Pd species soluble at the ppb level in haplobasaltic melts, much more soluble (ppm level) hydroxide complexes of these metals are formed under fluid-excess conditions. Despite a decrease in water fugacity under reducing conditions, Pt solubility increases sharply near the MW buffer. It was shown by electron paramagnetic resonance spectrometry that, in contrast to dry melts, fluid-saturated silicate melts do not contain a pure metal phase (micronuggets). Therefore, the increase in Pt solubility under reducing conditions can be explained by the formation of Pt hydride complexes or Pt-fluid-silicate clusters. At a sulfur fugacity controlled by the Pt-PtS equilibrium, the solubility of Pt in iron-free silicate melts as a function of redox conditions is almost identical to that obtained in the experiments without sulfur at the same water and oxygen fugacity values. These observations also support Pt dissolution in iron-free silicate melts as hydroxide species.  相似文献   

Non-ideal Mg-Fe binary mixing in cordierite: Constraints from experimental data on Mg-Fe partitioning in garnet and cordierite and a reformulation of garnet-cordierite geothermometer     

S. B. Dwivedi 《Journal of Earth System Science》1996,105(4):365-377

The non-ideal regular Mg-Fe binary in cordierite has been derived through multivariate linear regression of the expressionRT InK_D +(P- 1)ΔVK ₁ ⁰ , 298 along with updated subfegular mixing parameter of almandine-pyrope solution (Hackler and Wood 1989; Berman 1990). The data base used for multivariate analyses consists of published experimental data (n = 177) on Mg-Fe partitioning between garnet and cordierite in theP-T range 650–1050°C and 4–12 K bar. The non-ideality can be approximated by temperature-dependent Margules parameters. The retrieved values of ΔH_<T> ^o and ΔH_<T> ^o of exchange reaction between garnet and cordierite and enthalpy and entropy of mixing of Mg-Fe cordierite were combined with recent quaternary (Fe-Mg-Ca-Mn) mixing data in garnet to obtain the geothermometric expressions to determine temperature (T Kelvin): $$\begin{gathered} T(WH) = 6832 + 0.031(P - 1) - \{ 166(X_{Mg}^{Gt} )^2 - 506(X_{Fe}^{Gt} )^2 + 680X_{Fe}^{Gt} X_{Mg}^{Gt} + 336(X_{Ca} + X_{Mn} ) \hfill \\ (X_{Mg} - X_{Fe} )^{Gt} - 3300X_{Ca}^{Gt} - 358X_{Mn}^{Gt} \} + 954(X_{Fe} - X_{Mg} )^{Crd} /1.987\ln K_D + 3.41 + 1.5X_{Ca}^{Gt} \hfill \\ + 1.23(X_{Fe} - X_{Mg} )^{Crd} \hfill \\ \end{gathered} $$ $$\begin{gathered} T(Br) = 6920 + 0.031(p - 1) - \{ 18(X_{Mg}^{Gt} )^2 - 296(X_{Fe}^{Gt} )^2 + 556X_{Fe}^{Gt} X_{Mg}^{Gt} - 6339X_{Ca}^{Gt} X_{Mg}^{Gt} \hfill \\ - 99(X_{Ca}^{Gt} )^2 + 4687X_{Ca}^{Gt} (X_{Mg} - X_{Fe}^{Gt} ) - 4269X_{Ca}^{Gt} X_{Fe}^{Gt} - 358X_{Mn}^{Gt} \} + 640(X_{Fe} - X_{Mg} )^{Crd} \hfill \\ + 1.90X_{Ca}^{Gt} (X_{Mg} - X_{Ca} )^{Gt} . \hfill \\ \end{gathered} $$   相似文献   

Fluid-magmatic interactions at oceanic islands as a possible source for the sodic agpaitic Trend     

A. G. Simakin  T. P. Salova  V. I. Kovalenko 《Petrology》2011,19(7):641-652

Experiments on spilite melting at P = 3 kbar and T = 950−850°C indicate that partial melting in the presence of aqueous fluid (P_{H2 O}P_{H_2 O} = 3 kbar) produces a series of melts of normal alkalinity with up to 77 wt % SiO₂. The partial melts derived from spilite in the presence of aqueous fluid generated in the system NaCl-CaCO₃-H₂O have an agpaitic coefficient increasing to a level sufficient for the origin of alkaline granite in the course of fractional crystallization. An increase in the alkalinity of the melt is explained by soda synthesis in the fluid due to an exchange reaction between CaCO₃ and NaCl. In contrast to NaCl, soda in highly soluble in aluminosilicate melts. We discovered that partial melting in the presence of a soda-bearing fluid results in BaO concentrating from a level of 0.05 wt % in the original spilite to 1 wt % in the partial melt. Conceivably, magmatism in the environment of oceanic islands can occur under conditions favorable for the synthesis of soda-bearing fluids. CO₂ that carbonizes the mafic rocks is provided by mantle plumes, whereas seawater penetrating to depths greater than those of intermediate chambers serves as a source of NaCl. The activity of a fluid-magmatic system is able to generate subalkaline sodic rocks, such as benmoreite and pantellerite.  相似文献   

H<Subscript>2</Subscript>O diffusion in peralkaline to peraluminous rhyolitic melts     

Harald Behrens  Youxue Zhang 《Contributions to Mineralogy and Petrology》2009,157(6):765-780

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   

The H<Subscript>2</Subscript>O solubility of alkali basaltic melts: an experimental study     

Priscille Lesne  Bruno Scaillet  Michel Pichavant  Giada Iacono-Marziano  Jean-Michel Beny 《Contributions to Mineralogy and Petrology》2011,162(1):133-151

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 H₂O_MORB 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   

Simulation of the molecular mass distributions of Si anions on the liquidus of the Na<Subscript>2</Subscript>O-SiO<Subscript>2</Subscript> system with regard for the disproportionation of <Emphasis Type="Italic">Q</Emphasis> structons     

A. A. Ariskin  A. V. Shil’dt  V. B. Polyakov 《Geochemistry International》2011,49(4):355-374

A new version of the STRUCTON (2009) computer model is proposed for the simulation of the molecular mass distributions (MMD) characterizing the diversity of anions in silicate melts depending on their polymerization and temperature. In contrast to earlier versions, the new version of the model accounts for disproportionation reactions of Q ⁿ species and makes use of their proportions in the statistical simulations of the origin of real Si-O complexes. The new potentialities of the STRUCTON program package are illustrated by its application to studying the structural-chemical characteristics of melts in the Na₂O-SiO₂ system along its liquidus line, including the points of eutectics and phase transitions at 0.333 ≤ $ N_{SiO_2 } $ N_{SiO_2 } < 0.500. This problem is solved with the use of a temperature-composition dependence of polymerization constants K _p ^Na in the Toop-Samis approximation. The variations in K _p ^Na were proved to be as large as three orders of magnitude due to both the temperature effect at a constant composition and the composition effect at a constant temperature. The results of the MMD simulations on the liquidus show that the concentration of the SiO₄⁴⁻ ion strongly decreases, and the proportion of chain species increases compared to those at a stochastic distribution. The concentration of the Si₂O₇⁶⁻ anion reaches its maximum (∼42%) at 40 mol % in the liquid, i.e., the composition of Na₆Si₂O₇. At $ N_{SiO_2 } $ N_{SiO_2 } > 0.40, this ion dominates over the SiO₄⁴⁻ monomer. More silicic melts with $ N_{SiO_2 } $ N_{SiO_2 } ≥ 0.45, are dominated by (Si _n O_3n )³ⁿ⁻ ring species, and the concentrations of these species are related as (Si₃O₉)⁶⁻ > (Si₄O₁₂)⁸⁻ > (Si₅O₁₅)¹⁰⁻. The maximum concentration of these flat rings also occurs near the composition of stoichiometric metasilicate with Si/O = 0.333. The comparison of the dependence of the average size of anions i _av and the average number of their species on depolymerization indicates that a change in the proportion of Q ⁿ species in melt at decreasing temperature results in structural restyling and an increase in the average size of Si-O complexes. The average number of anion species thereby decreases compared to that in a stochastic MMD. The results presented in this publication direct the progress in the thermodynamic theory of silicate melts to a new avenue that makes use of the capabilities and advantages of the ion-polymer model, the theory of associated solutions, spectroscopic data, and the experimental study of variations in oxide activities depending on composition and temperature.  相似文献   

The probable occurrence of interstitial Al in hydrous,F-bearing and F-free aluminosilicate melts   总被引：1，自引：0，他引：1  

D. A. C. Manning  D. L. Hamilton  C. M. B. Henderson  M. J. Dempsey 《Contributions to Mineralogy and Petrology》1981,75(3):257-262

Experiments carried out on the system SiO₂-NaAlSi₃O₈-KAlSi₃O₈(Qz-Ab-Or) at 1 kbar in the presence of H₂O and F show that the quartz-alkali feldspar field boundary is progressively displaced towards the feldspar join as F contents increase from 0 to 4 wt. %F. Increasing , in the absence of F, has already been shown to have a similar effect (Tuttle and Bowen 1958; Luth, Jahns, and Tuttle 1964). The increased size of the quartz field in the F-bearing system compared to the hydrous system is believed to be caused by progressive removal of Al from the tetrahedral network of the melt by complexing with F. The residual network in the melt is thus enriched in Si and this stabilizes precipitation of quartz rather than feldspar for certain bulk compositions. The common presence of quench cryolite (Na₃AlF₆) in certain experiments carried out with 4 wt.% F supports this interpretation and indicates that some Al in the melt may be present in six-fold coordination with F^–. The effect of H₂O in the absence of F may be similar, with Al being progressively removed from four-fold coordination as more H₂O is dissolved in the melt. Although a proportion of Al in hydrous melts may occur in six-fold coordination, dry melts predominantly contain Al in four-fold coordination. This major difference in Al complexing may be one of the main causes for differences in the high-pressure phase relations of wet and dry Albearing silicate systems.  相似文献   

(Ca,Mg)2Si2O6 clinopyroxenes: A solution model based on nonconvergent site-disorder     

Paula M. Davidson  John Grover  Donald H. Lindsley 《Contributions to Mineralogy and Petrology》1982,80(1):88-102

Experiments at high pressure and temperature indicate that excess Ca may be dissolved in diopside. If the (Ca, Mg)₂Si₂O₆ clinopyroxene solution extends to more Ca-rich compositions than CaMgSi₂O₆, macroscopic regular solution models cannot strictly be applied to this system. A nonconvergent site-disorder model, such as that proposed by Thompson (1969, 1970), may be more appropriate. We have modified Thompson's model to include asymmetric excess parameters and have used a linear least-squares technique to fit the available experimental data for Ca-Mg orthopyroxene-clinopyroxene equilibria and Fe-free pigeonite stability to this model. The model expressions for equilibrium conditions \(\mu _{{\text{Mg}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} }^{{\text{opx}}} = \mu _{{\text{Mg}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} }^{{\text{cpx}}} \) (reaction A) and \(\mu _{{\text{Ca}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} }^{{\text{opx}}} = \mu _{{\text{Ca}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} }^{{\text{cpx}}} \) (reaction B) are given by: 1 $$\begin{gathered} \Delta \mu _{\text{A}}^{\text{O}} = {\text{RT 1n}}\left[ {\frac{{(X_{{\text{Mg}}}^{{\text{opx}}} )^2 }}{{X_{{\text{Mg}}}^{{\text{M1}}} \cdot X_{{\text{Mg}}}^{{\text{M2}}} }}} \right] - \frac{1}{2}\{ W_{21} [2(X_{{\text{Ca}}}^{{\text{M2}}} )^3 - (X_{{\text{Ca}}}^{{\text{M2}}} ] \hfill \\ {\text{ + 2W}}_{{\text{22}}} [X_{{\text{Ca}}}^{{\text{M2}}} )^2 - (X_{{\text{Ca}}}^{{\text{M2}}} )^3 + \Delta {\text{G}}_{\text{*}}^{\text{0}} (X_{{\text{Ca}}}^{{\text{M1}}} \cdot X_{{\text{Ca}}}^{{\text{M2}}} )\} \hfill \\ {\text{ + W}}^{{\text{opx}}} (X_{{\text{Wo}}}^{{\text{opx}}} )^2 \hfill \\ \Delta \mu _{\text{B}}^{\text{O}} = {\text{RT 1n}}\left[ {\frac{{(X_{{\text{Ca}}}^{{\text{opx}}} )^2 }}{{X_{{\text{Ca}}}^{{\text{M1}}} \cdot X_{{\text{Ca}}}^{{\text{M2}}} }}} \right] - \frac{1}{2}\{ 2W_{21} [2(X_{{\text{Mg}}}^{{\text{M2}}} )^2 - (X_{{\text{Mg}}}^{{\text{M2}}} )^3 ] \hfill \\ {\text{ + W}}_{{\text{22}}} [2(X_{{\text{Mg}}}^{{\text{M2}}} )^3 - (X_{{\text{Mg}}}^{{\text{M2}}} )^2 + \Delta {\text{G}}_{\text{*}}^{\text{0}} (X_{{\text{Mg}}}^{{\text{M1}}} \cdot X_{{\text{Mg}}}^{{\text{M2}}} )\} \hfill \\ {\text{ + W}}^{{\text{opx}}} (X_{{\text{En}}}^{{\text{opx}}} )^2 \hfill \\ \hfill \\ \end{gathered} $$ where 1 $$\begin{gathered} \Delta \mu _{\text{A}}^{\text{O}} = 2.953 + 0.0602{\text{P}} - 0.00179{\text{T}} \hfill \\ \Delta \mu _{\text{B}}^{\text{O}} = 24.64 + 0.958{\text{P}} - (0.0286){\text{T}} \hfill \\ {\text{W}}_{{\text{21}}} = 47.12 + 0.273{\text{P}} \hfill \\ {\text{W}}_{{\text{22}}} = 66.11 + ( - 0.249){\text{P}} \hfill \\ {\text{W}}^{{\text{opx}}} = 40 \hfill \\ \Delta {\text{G}}_*^0 = 155{\text{ (all values are in kJ/gfw)}}{\text{.}} \hfill \\ \end{gathered} $$ . Site occupancies in clinopyroxene were determined from the internal equilibrium condition 1 $$\begin{gathered} \Delta G_{\text{E}}^{\text{O}} = - {\text{RT 1n}}\left[ {\frac{{X_{{\text{Ca}}}^{{\text{M1}}} \cdot X_{{\text{Mg}}}^{{\text{M2}}} }}{{X_{{\text{Ca}}}^{{\text{M2}}} \cdot X_{{\text{Mg}}}^{{\text{M1}}} }}} \right] + \tfrac{1}{2}[(2{\text{W}}_{{\text{21}}} - {\text{W}}_{{\text{22}}} )(2{\text{X}}_{{\text{Ca}}}^{{\text{M2}}} - 1) \hfill \\ {\text{ + }}\Delta G_*^0 (X_{{\text{Ca}}}^{{\text{M1}}} - X_{{\text{Ca}}}^{{\text{M2}}} ) + \tfrac{3}{2}(2{\text{W}}_{{\text{21}}} - {\text{W}}_{{\text{22}}} ) \hfill \\ {\text{ (1}} - 2X_{{\text{Ca}}}^{{\text{M1}}} )(X_{{\text{Ca}}}^{{\text{M1}}} + \tfrac{1}{2})] \hfill \\ \end{gathered} $$ where δG _E ⁰ =153+0.023T+1.2P. The predicted concentrations of Ca on the clinopyroxene Ml site are low enough to be compatible with crystallographic studies. Temperatures calculated from the model for coexisting ortho- and clinopyroxene pairs fit the experimental data to within 10° in most cases; the worst discrepancy is 30°. Phase relations for clinopyroxene, orthopyroxene and pigeonite are successfully described by this model at temperatures up to 1,600° C and pressures from 0.001 to 40 kbar. Predicted enthalpies of solution agree well with the calorimetric measurements of Newton et al. (1979). The nonconvergent site disorder model affords good approximations to both the free energy and enthalpy of clinopyroxenes, and, therefore, the configurational entropy as well. This approach may provide an example for Febearing pyroxenes in which cation site exchange has an even more profound effect on the thermodynamic properties.  相似文献   

The influence of fluid unmixing on cation exchange between plagioclases and aqueous chloride solutions at 700° C, 1 kbar     

Saint Clair Dujon  Martine Lagache 《Contributions to Mineralogy and Petrology》1986,92(1):128-134

Experimental exchanges between plagioclases (synthesized from gels) and aqueous solutions (0.5N–8N) were carried out according to the reaction $$\begin{gathered} 2NaA1Si_3 O_8 + CaC1_2 \hfill \\ \leftrightarrow CaA1_2 Si_2 O_8 + 4SiO_2 + 2NaC1. \hfill \\ \end{gathered}$$ Distribution coefficients defined by $$K_D = \frac{{X_{An} }}{{(X_{Ab} )^2 }}\frac{{(X_{NaC1} )^2 }}{{X_{CaC1_2 } }}$$ were determined at 700° C and 1 kbar. From previous studies it is known that variations in the concentration of the aqueous solutions have no influence upon K _D if the fluid is a single phase. In this study, variation of K _D with the concentration of the solutions is interpreted as the result of fluid unmixing to vapour and brine phases. This implies boiling of CaCl₂-NaCl-H₂O fluids analogous to that known for the system NaCl-H₂O. Experimental data permit calculation of the compositions of vapours and estimation of those of the brines for fluids in which Ca/Na<0.5. Boiling has an effect upon the exchange between feldspars and solutions (metasomatism) and must be considered when determining the activity coefficients.  相似文献   

Experimental determination of liquidus H<Subscript>2</Subscript>O contents of haplogranite at deep-crustal conditions     

A.?R.?MakhlufEmail author  R.?C.?Newton  C.?E.?Manning 《Contributions to Mineralogy and Petrology》2017,172(9):77

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 Ab_36.25Or_36.25Qz_27.5 (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