Fluid flow patterns and infiltration isograds in melilite marbles from the Bufa del Diente contact metamorphic aureole, north-east Mexico   总被引：2，自引：0，他引：2  

W. HEINRICH  M. GOTTSCHALK 《Journal of Metamorphic Geology》1994,12(4):345-359

In the inner aureole of the Bufa del Diente alkali syenite (north-east Mexico), thin calcareous argillite bands horizontally embedded in impure marbles acted as contact-metamorphic aquifers for hypersaline brines of magmatic origin. Thick-bedded marbles were largely impervious. From 180 m up to the intrusion contact, argillites were completely decarbonated, resulting in melilite + wollastonite + phlogopite + perovskite-bearing parageneses. In marbles, this assemblage is confined to a narrow 7-12-m-wide infiltration zone adjacent to the contact. Up to this distance, calcite + wollastonite + diopside + alkali feldspar + titanite was stable, indicating that the fluid evolution in these marbles was internally buffered. Brine infiltration from the metaargillite aquifer into the marbles occurred perpendicular to the marble-metaargillite boundaries and was confined to a zone 4-6 cm wide above the boundaries. This is documented by the three reactions Cc + Di = Mel + CO₂, (1) Cc + Kfs + Di + H₂O = Phl + Wo + CO₂, (2) Cc + Ttn = Prv + Wo + CO₂, (3) Melilites (Ak_32-45Gh_13-32Sm_32-40 to Ak_52-72Gh_0-1Sm_28-48) occur as rims around diopsides and become continuously thicker towards the metaargillite beds. Fluid inclusion observations suggest that the infiltrating brine was hypersaline (NaCl + KCl_cq～ 65 wt%) and that the reactions took place at the water-rich side of the H₂O-CO₂-salts immiscibility field at about 600d? C (2, 3) and 660 to 680d? C (1) at P～ 1200 bar and X_co2～ 0.02. Mass balance calculations show that the amount of brine infiltrated from the aquifer into the marble was very low and decreased continuously with increasing distance from the boundary. The maximum width of brine infiltration was about 6 cm. This confirms that brine flow was largely parallel to the aquifer, not perpendicular to it. The CO₂ produced by the decarbonation reactions probably escaped as an immiscible low-density H₂O-CO₂ fluid of X_co2≤ 0.5 into overlying marble via grain-edge flow. The metaargillite-marble boundary acted as a semipermeable membrane 6 cm in thickness keeping back the brine in the aquifer and losing the in-situ produced low-density CO₂-rich fluid.  相似文献   

Metamorphic equilibria in the siliceous dolomite system: 6 kbar experimental data and geologic implications     

R.G. Eggert  D.M. Kerrick 《Geochimica et cosmochimica acta》1981,45(7):1039-1049

Hydrothermal experiments with H₂O-CO₂ fluids at P_fluid = 6 kbar yielded the following quilibrium conditions for reactions important in metamorphosed siliceous dolomites (T = °C; X = X_co2): (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-X_CO2, 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-X_CO2 space at X_CO2 < 0.55 and T < 590°C. Accordingly, the occurrence of talc + calcite in pure siliceous dolomites metamorphosed at P_fluid = 6 kbar implies correspondingly water-rich fluids.  相似文献   

Experiments on the phase transition calcite+wollastonite+ +epidote=grossular-andraditess+CO2+H2O     

Dr. Niranjan D. Chatterjee 《Contributions to Mineralogy and Petrology》1967,14(2):114-122

The reaction 2 epidote+2 calcite+3 wollastonite3 grossular-andradite_ss+ 2 CO₂+1 H₂O has been explored by hydrothermal experiments at a total fluid pressure of 1000 bars. For a grossular-andradite_ss of andradite ₂₅ composition, the isobaric univariant curve passes through the points 458°C: X_CO2=0.00; 521°C: X_CO2=0.026; 523°C: X_CO2=0.052; 526°C: 0.088; 528°C: X_CO2=0.104. This curve intersects the isobaric univariant curve of the reaction calcite+quartz+[H₂O] wollastonite+CO₂+[H₂O] at the isobaric invariant point around 528°C and X_CO2=0.12. At higher values of X_CO2, this reaction is replaced by another one, namely: 2 epidote+5 calcite+3 quartz3 grossular-andradite_ss+5 CO₂+ 1 H₂O. It is demonstrated that both the reactions do actually take place during the metamorphism of calcareous rocks. The petrologic significance of contrasted sequence of reactions within this system observed by various workers is also discussed.  相似文献   

Metamorphic reactions between fluid inclusions and mineral hosts. I. Progress of the reaction calcite+quartz=wollastonite+CO2 in natural wollastonite-hosted fluid inclusions     

W. Heinrich  Matthias Gottschalk 《Contributions to Mineralogy and Petrology》1995,122(1-2):51-61

 At the Bufa del Diente contact-metamorphic aureole, brine infiltration through metachert layers embedded in limestones produced thick wollastonite rims, according to Cc+Qz=Wo+CO₂. Fluid inclusions trapped in recrystallized quartz hosts include: (1) high salinity four phase inclusions [Th(V-L)=460–573° C; Td(salts)=350–400° C; (Na+K)_Cleq=64–73 wt%; X _{CO 2}≤0.02]; (2) low density vapour-rich CO₂-bearing inclusions [Th(L-V)≈500±100° C; X _{CO 2}=0.22–0.44; X _NaCl≤0.01], corresponding to densities of 0.27± 0.05 gcm⁻³. Petrographical observations, phase compositions and densities show that the two fluids were simultaneously trapped in the solvus of the H₂O-CO₂-salts system at 500–600° C and 700±200 bars. The low density fluid was generated during brine infiltration at the solvus via the wollastonite producing reaction. Identical fluid types were also trapped as inclusion populations in wollastonite hosts 3 cm adjacent to quartz crystals. At room temperature, both fluid types additionally contain one quartz and one calcite crystal, generated by the back-reaction Wo+CO₂=Cc+Qz of the host with the CO₂-proportion of the fluid during retrogression. All of the CO₂ was removed from the fluid. On heating in the microstage, the reaction progress of the prograde reaction was estimated via volume loss of the calcites. In vapour-rich fluids, 50% progress is reached at 490–530° C; 80% at 520–560° C; and 100% at 540–590° C, the latter representing the trapping temperatures of the original fluid at the two fluid solvus. The progress is volume controlled. With knowledge of compositions and densities from unmodified inclusions in quartz and using the equation of state of Duan et al. (1995) for H₂O-CO₂-NaCl, along with f _{CO 2}-values extracted from it, the reaction progress curve was recalculated in the P-T-X-space. The calculated progress curve passes through the two fluid solvus up to 380° C/210 bars, continues in the one fluid field and meets the solvus again at trapping conditions. The P-T slope is steep, most of the reaction occurs above 450° C and there is high correspondence between calculated and measured reaction progress. We emphasize that with the exception of quartz, back-reactions between inclusion fluids and mineral hosts is a common process. For almost any prograde metamorphic mineral that was formed by a devolatilization reaction and that trapped the equilibrium fluid or any peak metamorphic fluid as an inclusion, a fluid-host back-reaction exists which must occur somewhere along the retrograde path. Such retrograde reactions may cause drastic changes in density and composition of the fluid. In most cases, however, evidence of the evolving mineral assemblages is not given for they might form submicroscopical layers at the inclusion walls. Received: 15 March 1995 / Accepted: 1 June 1995  相似文献   

Paragenesis of sodic pyroxene-bearing quartz schists: implications for the P-T history of the Sanbagawa belt     

Masaki Enami  Simon R. Wallis  Yasuyuki Banno 《Contributions to Mineralogy and Petrology》1994,116(1-2):182-198

Sodic pyroxene (jadeite content X _jd=0.1–0.3) occurs locally as small inclusions within, albite porphyroblasts and in the matrix of hematite-bearing quartz schists in the Sanbagawa (Sambagawa) metamorphic belt, central Shikoku, Japan. The sodic, pyroxene-bearing samples are characteristically free from chlorite and their typical mineral assemblage is sodic pyroxene+subcalcic (or sodic) amphibole+phengitic mica+albite+quartz+hematite+titanite±epidote. Spessartine-rich garnet occurs in Mn-rich samples. Sodic pyroxene in epidote-bearing samples tends to be poorer in acmite content (average X _Acm=0.26–0.50) than that in the epidote-free samples (X _Acm=0.45–0.47). X _Jd shows no systematic relationship to metamorphic grade, and is different among the three sampling regions [Saruta-gawa, Asemi-gawa and Bessi (Besshi)]. The average X _Jd of the Saruta-gawa samples (0.21–0.29) is higher than that of the Asemi-gawa (0.13–0.17) and Bessi (0.14–0.23). The P-T conditions of the Asemi-gawa and Bessi regions are estimated at 5.5–6.5 kbar, >360°C in the chlorite zone, 7–8.5 kbar, 440±15°C in the garnet zone and 8–9.5 kbar, 520±25°C in the albite-biotite zone. Metamorphic pressure of the Saruta-gawa region is systematically 1–1.5 kbar higher than that of the Asemi-gawa and Bessi regions, and materials of the Saruta-gawa region have been subducted to a level 3–5 km deeper than materials that underwent metamorphism at equivalent temperatures and are now exposed in the Asemi-gawa and Bessi regions. Pressure slightly increases toward the north (structurally high levels) through the Sanbagawa belt of central shikoku. Two types of zonal structure were observed in relatively coarse-grained sodic pyroxenes in the matrix. One type is characterized by increasing X _Jd from core to rim, the other type by decreasing X _Jd from core to rim. Both types of zoned pyroxenes show an increase in X _{Fe 2+}[=Fe²⁺/(Fe²⁺+Mg)] from core to rim. The first type of zoning was observed in a sample from the chlorite zone of lowest grade, whereas the latter occurs in the garnet and albite-biotite zones of higher grade. The contrast in zonal structure implies that dP/dT during prograde metamorphism decreased with increasing metamorphic grade and may have been negative in some samples from the higher-grade zones. The estimated dP/dT of the prograde stage of the chlorite zone is 3.2 kbar/100°C, and that of the garnet and albite-biotite zones is -1.8 to 0.9 kbar/100°C. The variation of dP/dT at shallow and deep levels of a subduction system probably reflects the difference of heating duration and/or change in thermal gradient of the subduction zone by continuous cooling of the surrounding mantle.  相似文献   

Modelling phase–assemblage diagrams for magnesian metapelites in the system K2O–FeO–MgO–Al2O3–SiO2–H2O: geodynamic consequences for the Monte Rosa nappe, Western Alps     

R. Le Bayon  C. de Capitani  M. Frey 《Contributions to Mineralogy and Petrology》2006,151(4):395-412

Magnesian metamorphic rocks with metapelitic mineral assemblage and composition are of great interest in metamorphic petrology for their ability to constrain P–T conditions in terranes where metamorphism is not easily visible. Phase–assemblage diagrams for natural and model magnesian metapelites in the system KFMASH are presented to document how phase relationships respond to water activity, bulk composition, pressure and temperature. The phase assemblages displayed on these phase diagrams are consistent with natural mineral assemblages occurring in magnesian metapelites. It is shown that the equilibrium assemblages at high pressure conditions are very sensitive to a(H₂O). Specifically, the appearance of the characteristic HP assemblage chloritoid–talc–phengite–quartz (with excess H₂O) in the magnesian metapelites of the Monte Rosa nappe (Western Alps) is due to the reduction of a(H₂O). Furthermore, the mineral assemblages are determined by the whole-rock FeO/(FeO+MgO) ratio and effective Al content X _A as well as P and T. The predicted mineral associations for the low- and high-X _A model bulk compositions of magnesian metapelites at high pressure are not dependent on the X _A variations as they show a similar sequence of mineral assemblages. Above 20 kbar, the prograde sequence of assemblages associated with phengite (with excess SiO₂ and H₂O) for low- and high-X _A bulk compositions of magnesian metapelites is: carpholite–chlorite → chlorite–chloritoid → chloritoid–talc → chloritoid–talc–kyanite → talc–garnet–kyanite → garnet–kyanite ± biotite. At low to medium P–T conditions, a low-X _A stabilises the phengite-bearing assemblages associated with chlorite, chlorite + K-feldspar and chlorite + biotite while a high-X _A results in the chlorite–phengite bearing assemblages associated with pyrophyllite, andalusite, kyanite and carpholite. A high-X _A magnesian metapelite with nearly iron-free content stabilises the talc–kyanite–phengite assemblage at moderate to high P–T conditions. Taking into account the effective bulk composition and a(H₂O) involved in the metamorphic history, the phase–assemblage diagrams presented here may be applied to all magnesian metapelites that have compositions within the system KFMASH and therefore may contribute to gaining insights into the metamorphic evolution of terranes. As an example, the magnesian metapelites of the Monte Rosa nappe have been investigated, and an exhumation path with P–T conditions for the western roof of the Monte Rosa nappe has been derived for the first time. The exhumation shows first a near-isothermal decompression from the Alpine eclogite peak conditions around 24 kbar and 505°C down to approximately 8 kbar and 475°C followed by a second decompression with concomitant cooling.M. Frey: deceased  相似文献   

The reaction chlorite+dolomite=spinel+forsterite+calcite+carbon dioxide+water     

E. Torbjörn Widmark 《Contributions to Mineralogy and Petrology》1980,72(2):175-179

The reaction chlorite+dolomite=spinel+ forsterite+calcite+CO₂+H₂O has been studied with hydrothermal equipment technique in a C-O-H fluid at P _fluid=1,000, 2,000 and 3,000 bars and fo₂ controlled by NB or QFM buffer. The equilibrium conditions for the reaction has been determined as log K=–57,119/T+95.77+0.9860(P-1)/T(bar,°K). The mineral mixtures had an excess of dolomite. The composition of the chlorite among the reaction products has been analysed and found to have a higher Al/Si ratio than clinochlore.  相似文献   

The P-T-fO 2 stability of deerite,Fe 12 2+ Fe 6 3+ [Si12O40](OH)10     

Dominique Lattard  Nicole Le Breton 《Contributions to Mineralogy and Petrology》1994,115(4):474-487

New equilibrium experiments have been performed in the 20–27 kbar range to determine the upper thermal stability limit of endmember deerite, Fe ₁₂ ²⁺ Fe ₆ ³⁺ [Si₁₂O₄₀](OH)₁₀. In this pressure range, the maximum thermal stability limit is represented by the oxygen-conserving reaction: deerite(De)=9 ferrosilite(Fs)+3 magnetite(Mag)+3 quartz(Qtz)+5 H₂O(W) (1). Under the oxygen fugacities of the Ni-NiO buffer the breakdown-reduction reaction: De=12 Fs+2 Mag+5 W+1/2 O₂ (10) takes place at lower temperatures (e.g. T=63° at 27 kbar). The experimental brackets can be fitted using thermodynamic data for ferrosilite, magnetite and quartz from Berman (1988) and the following 1 bar, 298 K data for deerite (per gfw): V^o=55.74 J.bar^-1, S^o=1670 J.K^-1, H _f ^o =-18334 kJ, =2.5x10^-5K^-1, =-0.18x10^-5 bar^-1. Using these data in conjunction with literature data on coesite, grunerite, minnesotaite, and greenalite, the P-T stability field of endmember deerite has been calculated for P _s=P _{H 2}O. This field is limited by 6 univariant oxygenconserving dehydration curves, from which three have positive dP/dT slopes, the other three negative slopes. The lower pressure end of the stability field of endmember deerite is thus located at an invariant point at 250±70°C and 10+-1.5 kbar. Deerite rich in the endmember can thus appear only in environments with geothermal gradients lower than 10°C/km and at pressures higher than about 10 kbar, which is in agreement with 4 out of 5 independent P-T estimates for known occurrences. The presence of such deerite places good constraints on minimum pressure and maximum temperature conditions. From log f _{O 2}-T diagrams constructed with the same data base at different pressures, it appears that endmember deerite is, at temperatures near those of its upper stability limit, stable only over a narrow range of oxygen fugacities within the magnetite field. With decreasing temperatures, deerite becomes stable towards slightly higher oxygen fugacities but reaches the hematite field only at temperatures more than 200°C lower than the upper stability limit. This practically precludes the coexistence deerite-hematite with near-endmember deerite in natural environments.  相似文献   

CO2-metasomatism of a metabasite block in a serpentine melange from the Nishisonogi metamorphic rocks,southwest Japan     

Tadao Nishiyama 《Contributions to Mineralogy and Petrology》1990,104(1):35-46

Local fluid migration through a serpentine melange caused successive carbonation of a metabasite block (about 80 meter in diameter) during the uplift stage of the glaucophanitic metamorphic rocks, the Nishisonogi metamorphics, southwest Japan. The block shows a zonal sequence as follows. Zone 1: original greenschist (Am+Ep+ Chl+Ab+Sph+Qtz). Zone 2: epidote disappears by the reaction Ep+Am+CO₂+H₂O=Chl+Cc+Qtz. Zone 3: balc appears by the reaction Am+CO₂+H₂O=Ta+Cc+ Qtz. Zone 4:sphene breakdowns by the reaction Sph+ CO₂=Rt+Cc+Qtz. Zone 5: amphibole disappears by the two simultaneous reactions, Am+CO₂=Do+Ta+Qtz and Ta+Cc+CO₂=Do+Qtz+H₂O. Zone 7: albite is replaced by chlorite, calcite, dolomite and quartz, and the assemblage of Do+Cc+Chl+Rt+Qtz is stable. Analyses of phase relations indicate an introduction of CO₂-rich fluid into the greenschist body during regional metamorphism. The CO₂-rich fluid may have formed by devolatilization reactions between serpentinite and graphite-bearing metasediments. The fluid migrated within the melange through a channelized pathway and into the greenschist body from a deeper part of the melange.  相似文献   

The solubility of calcite in water at 6–16 kbar and 500–800 °C     

Natalie?C.?CaciagliEmail author  Craig?E.?Manning 《Contributions to Mineralogy and Petrology》2003,146(3):275-285

The solubility of calcite in H₂O was measured at 6–16 kbar, 500–800 °C, using a piston-cylinder apparatus. The solubility was determined by the weight loss of a single crystal and by direct analysis of the quench fluid. Calcite dissolves congruently in the pressure (P) and temperature (T) range of this study. At 10 kbar, calcite solubility increases with increasing temperature from 0.016±0.005 molal at 500 °C to 0.057±0.022 molal at 750 °C. The experiments reveal evidence for hydrous melting of calcite between 750 and 800 °C. Solubilities show only a slight increase with increasing P over the range investigated. Comparison with work at low P demonstrates that the P dependence of calcite solubility is large between 1 and 6 kbar, increasing at 500 °C from 1.8×10^–5 molal at 1 kbar to 6.4×10^–3 molal at 6 kbar. The experimental results are described by:where T is in Kelvin and _H2O is the density of pure water in g/cm³. The equation is applicable at 1–20 kbar and 400–800 °C, where calcite and H₂O stably coexist. Extrapolated thermodynamic data for indicates that the dominant dissolved carbon species is CO_2,aq at all experimental conditions. The results require that equilibrium constant for the reaction:increases by several orders of magnitude between 1 and 6 kbar, and also rises with isobaric T increase. Published thermodynamic data for aqueous species fail to predict this behavior. The increase in calcite solubility with P and T demonstrates that there is a strong potential for calcite precipitation during cooling and decompression of water-rich metamorphic fluids sourced in the middle to lower crust.Editorial responsibility: T.L. Grove  相似文献   

High-temperature metamorphic imprint on calc-silicate granulites of Rayagada,Eastern Ghats,India: implication for the isobaric cooling path     

R. K. Shaw  M. Arima 《Contributions to Mineralogy and Petrology》1996,126(1-2):169-180

 Calc-silicate granulites from Rayagada, north-central sector of Eastern Ghats granulite belt show a wide range of mineral assemblages and chemical compositions, which can be grouped as Gr. I (grossular- rich garnet-wollastonite-scapolite-calcite-clinopyroxene), Gr. II (andradite-rich garnet-scapolite-calcite-clinopyr- oxene), and Gr. III (scapolite-calcite-clinopyroxene-plagioclase) assemblages. Petrographic features suggest the following several reactions in the CaO–Al₂O₃–SiO₂-vapor system: Mei+4Wo+Cal=3Grs+Qtz +2CO₂, Mei+3Wo+2Cal=3Grs+CO₂, Mei= 3An+Cal, Wo+CO₂=Cal+Qtz, Mei+5Wo =3Grs+2Qtz+CO₂, An+Wo=Grs+Qtz, Mei+ 5Cal+3Qtz=3Grs+6CO₂, and the following reactions in the CaO–FeO–MgO–Al₂O₃–SiO₂-vapor system: Cpx_ss+Scp+Wo=Grt_ss+Qtz+CO₂, 4Hd+ 2Cal+O₂=2Adr+2Qtz+2CO₂, Cpx_ss+Scp= Grt_ss+Cal+Qtz. These reactions have been used to estimate peak T-X _CO2 condition for these granulites. A maximum temperature of ∼920 °C has been calculated at an estimated pressure of 9 kbar. A T-X _CO2 diagram shows an isobaric cooling from ∼920 °C to ∼815 °C. A range of X _CO2 (0.50 at 920 °C to 0.25 at 815 °C) has been observed for Gr. I calc-silicate granulites based on the reaction sequences including coronal garnet-forming reactions. This sequence is suggestive of internal fluid buffering rather than external fluid influx and the differences in X _CO2 conditions has been thought to be due to local buffering of fluid phases. Group II and Gr. III calc-silicate granulites, on the other hand, exhibit relatively lower temperature conditions. Received: 11 September 1995/Accepted: 20 June 1996  相似文献   

Experimental study of chloritoid stability at high pressure and various fO2 conditions     

Olivier Vidal  Thomas Theye  Christian Chopin 《Contributions to Mineralogy and Petrology》1994,118(3):256-270

The reaction chloritoid (ctd)=almandine (alm)+diaspore+H₂O (CAD) has been reversed using Fe³⁺-free synthetic chloritoid and almandine, under fO₂ conditions of the solid oxygen buffer Fe/FeO (CADWI), and using partially oxidized synthetic minerals under fO₂ conditions of the solid oxygen buffer Ni/NiO (CADNNO). Experiments have been conducted between 550 and 700°C, 25 and 45 kbar. The equilibrium pressure and temperature conditions are strongly dependent on the fO₂ conditions (CADNNO lies some-what 50°C higher than CADWI). This can be explained by a decrease in aH₂O for experiments conducted on the Fe/FeO buffer, and a decrease in actd and aalm (through incorporation of ferric iron preferentially in chloritoid) for experiments conducted on the Ni/NiO buffer. The H₂O activity has been calculated using the MRK equation of state, and the values obtained checked against the shift of the equilibrium diaspore=corundum+H₂O bracketed on the Fe/FeO buffer and under unbuffered fO₂ conditions. For fO₂ buffered by the assemblage Fe/FeO, aH₂O increases with pressure from about 0.85 at 600°C, 12 kbar to about 0.9 at 605°C, 25 kbar and 1 above 28 kbar. For fO₂ buffered by the assemblage Ni/NiO, aH₂O=1. The aH₂O decrease from Ni/NiO to Fe/FeO is, however, too small to be entirely responsible for the temperature shift between CADNNO and CADWI. In consequence, the amount of ferric iron in almandine and chloritoid growing in the CADNNO experiments must be significant and change along the CADNNO, precluding calculation of the thermodynamic properties of chloritoid from this reaction. Our experimental data obtained on the Fe/FeO buffer are combined, using a thermodynamic analysis, with Ganguly's (1969) reversal of the reaction chloritoid=almandine+corundum +H₂O (CAC) on the same oxygen buffer. Experimental brackets are mutually consistent and allow extraction of the thermodynamic parameters H ^o f,ctd and S ^octd. Our thermodynamic data are compared with others, generally calculated using Ganguly's bracketing of CACNNO. The agreement between the different data sets is relatively good at low pressure, but becomes rapidly very poor toward high pressure conditions. Using our thermodynamic data for chloritoid and K_D=(Fe³⁺/Al)ctd/(Fe³⁺/Al)alm estimated from natural assemblages, we have calculated the composition of chloritoid and almandine growing from CADNNO and CACNNO. The Fe³⁺ content in chloritoid and almandine increases with pressure, from less than 0.038 per FeAl₂SiO₅(OH)₂ formula unit at 10 kbar to at least 0.2 per formula unit above 30 kbar. This implies that chloritoid and almandine do contain Fe³⁺ in most natural assemblages. The reliability of our results compared to natural systems and thermodynamic data for Mg-chloritoid is tested by comparing the equilibrium conditions for the reaction chloritoid+quartz=garnet (gt)+kyanite+H₂O (CQGK), calculated for intermediate Fe–Mg chloritoid and garnet compositions, from the system FASH and from the system MASH. For 0.65<(XFe)gt<0.8, CQKG calculated from FASH and MASH overlap for K_D=(Mg/Fe)ctd/(Mg/Fe)gt=2. This is in good agreement with the K_D values reported from chloritoid+garnet+quartz+kyanite natural assemblages.  相似文献   

Gehlenite stability in the system CaO-Al2O3-SiO2-H2O-CO2     

Gert Hoschek 《Contributions to Mineralogy and Petrology》1974,47(4):245-254

P, T, \(X_{{\text{CO}}_{\text{2}} }\) relations of gehlenite, anorthite, grossularite, wollastonite, corundum and calcite have been determined experimentally at P _f =1 and 4 kb. Using synthetic starting minerals the following reactions have been demonstrated reversibly

1. 2 anorthite+3 calcite=gehlenite+grossularite+3 CO₂.
2. anorthite+corundum+3 calcite=2 gehlenite+3 CO₂.
3. 3anorthite+3 calcite=2 grossularite+corundum+3CO₂.
4. grossularite+2 corundum+3 calcite=3 gehlenite+3 CO₂.
5. anorthite+2 calcite=gehlenite+wollastonite+2CO₂.
6. anorthite+wollastonite+calcite=grossularite+CO₂.
7. grossularite+calcite=gehlenite+2 wollastonite+CO₂.

In the T, \(X_{{\text{CO}}_{\text{2}} }\) diagram at P _f =1 kb two isobaric invariant points have been located at 770±10°C, \(X_{{\text{CO}}_{\text{2}} }\) =0.27 and at 840±10°C, \(X_{{\text{CO}}_{\text{2}} }\) =0.55. Formation of gehlenite from low temperature assemblages according to (4) and (2) takes place at 1 kb and 715–855° C, \(X_{{\text{CO}}_{\text{2}} }\) =0.1–1.0. In agreement with experimental results the formation of gehlenite in natural metamorphic rocks is restricted to shallow, high temperature contact aureoles.  相似文献   

Experimental investigation of the metamorphism of siliceous dolomites III. Equilibrium data for the reaction: 1 Tremolite + 11 dolomite ⇌ 8 forsterite + 13 calcite + 9 CO2 +1H2O for the total pressures of 3,000 and 5,000 bars     

Paul Metz 《Contributions to Mineralogy and Petrology》1976,58(2):137-148

The temperature-X _{CO 2}-equilibrium data for the reaction 1 tremolite + 11 dolomite 8 forsterite + 13 calcite + 9 CO₂ +1H₂O have been determined at total pressures (P _{CO 2} + P _H2_O) of 3,000 and 5,000 bars. The results are shown in Figure 2 along with the data for the total pressure of 1,000 bars (Metz, 1967).The MgCO₃ contents of the magnesian-calcites formed during the experiments agree very well with the calcite-dolomite-solvus which can be recalculated from Equation (1) and the activity coefficients for MgCO₃ in magnesiancalcite as given by Gordon and Greenwood (1970).If the T-X _{CO 2}-equilibrium data are calculated from the equilibrium constant as given by Skippen (1974), assuming ideal mixing of CO₂ and H₂O, good agreement is achieved for the total pressure of 1,000 bars (see Figs. 4 and 5). At a total pressure of 3,000 bars, however, the calculated equilibrium temperatures are about 40 ° C below the experimentally determined values (see Fig. 6). This difference increases up to 70 ° C for a total pressure of 5,000 bars (see Fig. 7).From the experimentally determined equilibrium conditions of the assemblage: tremolite + dolomite + forsterite + magnesian calcite (see Fig. 8) the pressure of metamorphism can be estimated if the temperature is determined by the MgCO₃-content of the magnesian-calcite from the calcite-dolomite solvus. However, when using the data of Figure 8, attention has to be drawn to the limiting condition of X _{CO 2}0.2.Simplified reaction equation not considering solid solution in the carbonates  相似文献   

Stability of sapphirine-bearing mineral assemblages in the system FeO-MgO-Al₂O₃-SiO₂ and metamorphic P-T parameters of aluminous granulites     

K. K. Podlesskii 《Petrology》2010,18(4):350-368

Consistent thermodynamic data on the properties of pure mineral end members and the mixing properties of solid solutions in the system FeO-MgO-Al₂O₃-SiO₂ were employed to simulate phase relations of sapphirine, garnet, spinel, orthopyroxene, cordierite, quartz, Al silicates, and corundum. Compositional variations of the solid solutions with temperature notably modify the topology of the P-T diagrams, which differ from the petrogenetic grids widely used in the literature. It is worth noting that the evaluation of P-T metamorphic conditions based on reaction relations in sapphirine-bearing assemblages cannot be so far considered reliable enough. The lower stability limit of the sapphirine + quartz assemblage in the system in question is possibly located at much lower P-T parameters: at least 835°C and ∼6 kbar. The sapphirine + kyanite assemblage can be stable at temperatures below 860°C and a pressure of ∼11 kbar, and the stability field of the sapphirine + olivine assemblage is narrow and constrained to temperatures no higher than ∼800°C.  相似文献   

Interdiffusion of H₂O and CO₂ in metamorphic fluids at ∼490 to 690°C and 1 GPa     

David A. Wark  E.Bruce Watson 《Geochimica et cosmochimica acta》2004,68(12):2693-2698

Interdiffusion coefficients have been determined for H₂O-CO₂ mixtures by quantifying the flux of CO₂ between two fluid-filled chambers in a specially designed piston-cylinder cell. The two chambers, which are maintained at 1.0 GPa and at temperatures differing by ∼100°C, each contain the X_CO2-buffering assemblage calcite + quartz + wollastonite, in H₂O. The positive dependence of X_CO2 on temperature results in a down-temperature, steady-state flux of CO₂ through a capillary tube that connects the two chambers. This flux drives the wollastonite = calcite + quartz equilibrium to the right in the cooler chamber, producing a measurable amount of calcite that is directly related to CO₂-H₂O interdiffusion rates. Diffusivities calculated from seven experiments range from 1.0 × 10⁻⁸ to 6.1 × 10⁻⁸ m²/s for mean capillary temperatures between ∼490 and 690°C. The data set can be approximated by an Arrhenius-type relation: