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1.
Tibor Gasparik 《Geochimica et cosmochimica acta》1984,48(12):2537-2545
Subsolidus phase relations in the system CaO-Al2O3-SiO2 (CAS) were experimentally determined with tight reversals of several univariant curves and with 14 equilibration experiments containing the assemblage pyroxene + anorthite, where pyroxene is a binary solid solution of Ca-Tschermak (CaTs-CaAl2SiO6) and Ca-Eskola (CaEs-Ca0.5AlSi2O6) endmembers.Reversals were obtained on the following reactions (bar, °C): 3An = Gr + 2Ky + Q (P = 22T ? 700), 3An + Cor = Gr + 3Ky (P = 21.8T ? 950), 3CaTs= Gr + 2Cor(P = 55T ? 53900), and 6CaTs(1 ? x)CaEsx = 2(1 ? 2x)Gr + 4(1 ? 2x)Cor + 9xAn. Observed slopes indicate 9.8 J/mol · K of Al-Si disorder in Ca-Tschermak pyroxene and 5.3 J/mol·K of Al-Si disorder in anorthite, at 1300°C. It is suggested that Al-Si disorder in anorthite increases by 1.9 J/mol · K from 700°C to 1300°C.Compositions of CaTs-CaEs pyroxene in equilibrium with anorthite and PbO-rich liquid were experimentally determined at 1400–1430°C and 22.7–30.8 kbar. Microprobe measurements gave compositions which are consistent with an ideal pyroxene solution and the following parameters for the reaction 3An = 2CaTs + 2CaEs (J, bar, K): 2RTln(XCaTs · XCaEs) + 60200 + 86.4T ? (5.06 + 13 × 10?7P)P = 0, resulting in ΔH0j = ?39.8 kJ/mol and S0 = 461.8 J/mol · K for the Ca-Eskola endmember at 1300°C. The obtained properties of the Ca-Eskola component are necessary for thermobarometry based on pyroxene bearing assemblages containing plagioclase, quartz, or kyanite. 相似文献
2.
Wilhelm Johannes 《Contributions to Mineralogy and Petrology》1980,74(1):29-34
Beginning of melting and subsolidus relationships in the system K2O-CaO-Al2O3-SiO2-H2O have been experimentally investigated at pressures up to 20 kbars. The equilibria discussed involve the phases anorthite, sanidine, zoisite, muscovite, quartz, kyanite, gas, and melt and two invariant points: Point [Ky] with the phases An, Or, Zo, Ms, Qz, Vapor, and Melt; point [Or] with An, Zo, Ms, Ky, Qz, Vapor, and Melt.The invariant point [Ky] at 675° C and 8.7 kbars marks the lowest solidus temperature of the system investigated. At pressures above this point the hydrated phases zoisite and muscovite are liquidus phases and the solidus temperatures increase with increasing pressure. At 20 kbars beginning of melting occurs at 740 °C. The solidus temperatures of the quinary system K2O-CaO-Al2O3-SiO2-H2O are almost 60° C (at 20 kbars) and 170° C (at 2kbars) below those of the limiting quaternary system CaO-Al2O3-SiO2-H2O.The maximum water pressure at which anorthite is stable is lowered from 14 to 8.7 kbars in the presence of sanidine. The stability limits of anorthite+ vapor and anorthite+sanidine+vapor at temperatures below 700° C are almost parallel and do not intersect. In the wide temperature — pressure range at pressures above the reaction An+Or+Vapor = Zo+Ms+Qz and temperatures below the melting curve of Zo+Ms+Ky+Qz+Vapor, the feldspar assemblage anorthite+sanidine is replaced by the hydrated phases zoisite and muscovite plus quartz. CaO-Al2O3-SiO2-H2O. Knowledge of the melting relationships involving the minerals zoisite and muscovite contributes to our understanding of the melting processes occuring in the deeper parts of the crust. Beginning of melting in granites and granodiorites depends on the composition of plagioclase. The solidus temperatures of all granites and granodiorites containing plagioclases of intermediate composition are higher than those of the Ca-free alkali feldspar granite system and below those of the Na-free system discussed in this paper.The investigated system also provides information about the width of the P-T field in which zoisite can be stable together with an Al2SiO5 polymorph plus quartz and in which zoisite plus muscovite and quartz can be formed at the expense of anorthite and potassium feldspar. Addition of sodium will shift the boundaries of these fields to higher pressures (at given temperatures), because the pressure stability of albite is almost 10kbars above that of anorthite. Assemblages with zoisite+muscovite or zoisite+kyanite are often considered to be products of secondary or retrograde reactions. The P-T range in which hydration of granitic compositions may occur in nature is of special interest. The present paper documents the highest temperatures at which this hydration can occur in the earth's crust. 相似文献
3.
Melting and subsolidus reactions in the system K2O-CaO-Al2O3-SiO2-H2O: corrections and additional experimental data 总被引:2,自引:0,他引:2
Melting relationships in the system K2O-CaO-Al2O3-SiO2-H2O have been reinvestigated using Schreinemakers analysis and hydrothermal experiments. The reaction sanidine+muscovite+zoisite+quartz+vapor =melt has been bracketed at 10, 15, and 20 kbars and 670–680, 680–690, and 690–700° C, respectively and it marks the lowest solidus temperatures in the system investigated.Below 10 kbars, experimental data on the beginning of melting in zoisite- or muscovite-bearing anorthite+sanidine assemblages have been obtained, which are not showing any differences and therefore point to melt compositions close to the feldspar-quartz join. 相似文献
4.
The heat capacities of lawsonite, margante, prehnite and zoisite have been measured from 5 to 350 K with an adiabatic-shield calorimeter and from 320 to 999.9 K with a differential-scanning calorimeter. At 298.15 K, their heat capacities, corrected to end-member compositions, are 66.35, 77.30, 79.13 and 83.84 cal K?1 mol?1; their entropies are 54.98, 63.01, 69.97 and 70.71 cal K?1 mol?1, respectively. Their high-temperature heat capacities are described by the following equations (in calories, K, mol): Lawsonite (298–600 K): Cp° = 66.28 + 55.95 × 10?3T ? 15.27 × 105T?2 Margarite (298–1000 K): Cp° = 101.83 + 24.17 × 10?3T ? 30.24 × 105T?2 Prehnite (298–800 K): Cp° = 97.04 + 29.99 × 10?3T ? 25.02 × 105T?2 Zoisite (298–730 K): Cp° = 98.92 + 36.36 × 10?3T ? 24.08 × 105T?2 Calculated Clapeyron slopes for univariant equilibria in the CaO-Al2O3-SiO2-H2O system compare well with experimental results in most cases. However, the reaction zoisite + quartz = anorthite + grossular + H2O and some reactions involving prehnite or margarite show disagreements between the experimentally determined and the calculated slopes which may possibly be due to disorder in experimental run products. A phase diagram, calculated from the measured thermodynamic values in conjunction with selected experimental results places strict limits on the stabilities of prehnite and assemblages such as prehnite + aragonite, grossular + lawsonite, grossular + quartz, zoisite + quartz, and zoisite + kyanite + quartz. The presence of this last assemblage in eclogites indicates that they were formed at moderate to high water pressure. 相似文献
5.
David M. Jenkins 《Contributions to Mineralogy and Petrology》1981,77(2):166-176
The hydration of peridotites modelled by the system H2O-CaO-MgO-Al2O3-SiO2 has been treated theoretically after the method of Schreinemakers, and has been investigated experimentally in the temperature range 700°–900° C and in the pressure range of 8–14 kbar. In the presence of excess forsterite and water, the garnet- to spinel-peridotite transition boundary intersects the chlorite dehydration boundary at an invariant point situated at 865±5° C and 15.2±0.3 kbar. At lower pressures, a model spinel lherzolite hydrates to both chlorite- and amphibole-bearing assemblages at an invariant point located at 825±10° C and 9.3±0.5 kbar. At even lower pressures the spinel-to plagioclase-peridotite transition boundary intersects the dehydration curve for amphibole+forsterite at an invariant point estimated to lie at 855±10° C and 6.5±0.5 kbar.Both chlorite and amphibole were characterized along their respective dehydration curves. Chlorite was found to shift continuously from clinochlore, with increasing temperature, to more aluminous compositions. Amphibole was found to be tremolitic with a maximmum of 6 wt.% Al2O3.The experimentally determined curves in this study were combined with the determined or estimated stability curves for hydrous melting, plagioclase, talc, anthophyllite, and antigorite to obtain a petrogenetic grid applicable to peridotites, modelled by the system H2O-CaO-MgO-Al2O3-SiO2, that covers a wide range of geological conditions. Direct applications of this grid, although quite limited, can be made for ultramafic assemblages that have been extensively re-equilibrated at greenschist to amphibolite facies metamorphism and for some highgrade ultramafic assemblages that display clear signs of retrogressive metamorphism. 相似文献
6.
Theoretical phase relations involving cordierite and garnet in the system MgO-FeO-Al2O3-SiO2 总被引:1,自引:0,他引:1
B. J. Hensen 《Contributions to Mineralogy and Petrology》1971,33(3):191-214
Theoretical stability relations have been derived between the phases cordierite (Cd), garnet (Ga), hypersthene (Hy), olivine (Ol), sapphirine (Sa), spinel (Sp), sillimanite (Si) and quartz (Qz) in the system MgO-FeO-Al2O3-SiO2. Natural rock data and experimental evidence suggest that the Mg/Mg+Fe2+ ratio (X) of coexisting ferromagnesian phases decreases as follows: X
Cd>X
Sa>X
Hy>X
Ol>X
Sp>X
Ga. By use of this information four stable invariant points are proposed involving the phases: Cd, Hy, Sa, Ga, Si, Qz; Cd, Sa, Ga, Sp, Si, Qz; Cd, Hy, Sa, Ga, Sp, Qz; Cd, Ga, Hy, Ol, Sp, Qz. All univariant curves in the system are nonterminal, representing the breakdown of a join rather than the stability limit of an individual phase. A detailed treatment of divariant equilibria involving two and three ferromagnesian solid solutions illustrates the potential of these equilibria as Pressure-Temperature indicators. Interactions between solid-solid reactions and dehydration reactions involving biotite in the system MgO-FeO-Al2O3-SiO2-K2O-H2O have been graphically analysed. The addition of biotite to anhydrous divariant assemblages does not affect the composition of coexisting phases at constant P and T but can affect their relative proportions. 相似文献
7.
Niranjan D. Chatterjee Ludger Terhart 《Contributions to Mineralogy and Petrology》1985,89(2-3):273-284
The system MgO-Al2O3-SiO2(MAS) comprises 88–90% of the bulk composition of an average peridotite. The MAS ternary is thus a suitable starting point for exploring peridotite phase relations in multicomponent natural systems. The basic MAS phase relations may be treated in terms of the reactions (see list of symbols etc).
- py (in Gt)=en (in Opx)+mats (in Opx),
- en (in Opx)+sp (in Sp)=mats (in Opx)+fo (in Ol), and
- py (in Gt)+fo (in Ol)=en (in Opx)+sp (in Sp).
- binary Sp (sp-pc) crystalline solution (Oka et al. 1984),
- ternary Opx (en-mats-mcts) crystalline solution (this study), and
- binary Gt (py-kn) crystalline solution (this study).
- With increasing incorporation of Cr+3 into Sp and Gt, the X mats isopleths of the reactions (1) and (2) are shifted to higher temperatures (Fig. 3a); simultaneously, the spinel-peridotite to garnet-peridotite phase transition is moved to higher pressures (Fig. 3b).
- At identical P and T, the X mats values of Opx coexisting in equilibrium with Ol and Sp is strongly dependent upon the X pc value in the latter phase (Figs. 4a and b). Accurate correction for the composition of Sp is, therefore, a necessary precondition for geothermometry of the spinelperidotites.
- The discrepant temperatures reported by Sachtleben und Seck (1981, Fig. 5) from the spinel-peridotites of the Eifel area (systematically too high temperatures as a function of X pc in Sp) are demonstrated to be the result of ignoring the nonideality in the chromian spinels.
8.
9.
The chemical interaction between fluorine and highly polymerized sodium aluminosilicate melts [Al/(Al+Si)= 0.125–0.250 on the join NaAlO2-SiO2] has been studied with Raman spectroscopy. Fluorine is dissolved to form F– ions that are electrically neutralized with Na+ or Al3+. There is no evidence for association of fluorine with either Si4+ or Al3+ in four-fold coordination and no evidence of fluorine in six-fold coordination with Si4+ in these melt compositions. Upon solution of fluorine nonbridging oxygens are formed and are a part of structural units with nonbridging oxygen per tetrahedral cations (NBO/T) about 2 and 1. The proportions of these two depolymerized units in the melts increase systematically with increasing F/(F+O) at constant Al/(Al+Si) and with decreasing Al/(Al+Si) at constant F/(F+O). Depolymerization (increasing NBO/T) of silicate melts results from a fraction of aluminum and alkalies (in the present study; Na+) reacting to form fluoride complexes. In this process an equivalent amount of Na+ (orginally required for Al-3+charge-balance) or Al3+ (originally required Na+ to exist in tetrahedral coordination) become network-modifiers.The structural data have been used to develop a method for calculating the viscosity of fluorine-bearing sodium aluminosilicate melts at 1 atm. Where experimental viscosity data are available, the calculated and measured values are within 5% of each other.A method is also suggested by which the liquidus phase equilibria of fluorine-bearing aluminosilicate melts may be predicted. In accord with published experimental data it is suggested, for example, that — on the basis of the determined solubility mechanism of fluorine in aluminosilicate melts — with increasing fluorine content of feldspar-quartz systems, the liquidus boundaries between aluminosilicate minerals (e.g., feldspars) and quartz shift away from silica. 相似文献
10.
Stability of manganocordierite and related phase equilibria in part of the system MnO-Al2O3-SiO2-H2O
The pressure temperature stability of the phase Mn-cordierite hitherto not recorded as a mineral has been determined at temperatures ranging from 400° C up to the melting mainly using standard hydrothermal techniques at the oxygen fugacities provided by the buffering power of the bomb walls. Manganocordierite is a pronounced low-pressure phase with a maximum pressure stability of about 1 kb near 400° C and decreasing pressure limits at higher temperatures. Throughout the temperature range investigated the stable high-pressure breakdown assemblage of Mn-cordierite is spessartine, an Al-silicate, and a SiO2-polymorph. Due to the variable water contents of Mn-cordierite and spessartine there is a pronounced curvature in the negative dP/dT-slope of the requisite upper pressure breakdown curve of Mn-cordierite. Only theoretical deductions were possible concerning the stable hydrous low-temperature breakdown assemblage of Mn-cordierite below about 400° C.The manganocordierites synthesized are orthorhombic low-cordierites with distortion indices increasing with temperature, water pressure, and duration of heating. Their mean refractive indices increase with rising contents of absorbed water in the structural channels. Based on experiments with natural material the upper temperature stability limit of the mineral carpholite must lie at temperatures below about 400° C for water pressures up to 2.5 kb.The absence of Mn-cordierite from natural rocks studied thus far cannot be explained on chemical grounds, but must be due to its narrow pressure temperature stability range. The phase may yet be discovered as a mineral in manganiferous metasediments formed by lowpressure contact metamorphism. 相似文献
11.
Birger Hansen 《Contributions to Mineralogy and Petrology》1981,76(2):234-242
The pressure-temperature curve for the equilibrium anorthite+2enstatite=pyrope+diopside+quartz has been determined in the system CaO-MgO-Al2O2-SiO2 to be between 13.4 and 14.0 kbars at 900° C. The slope up to 1,240° C is 8.5 bar/K. The entropy change at 1,200 K is 20 kJ. These data, combined with data from the literature, lead to a geobarometer equation which, when applied to rocks from the Agto area (West Greenland), gives pressure estimates of 6–10 kbars at 800° C. The results are consistent for rocks of differing Fe/Mg ratios and are consistent with independent pressure estimates. 相似文献
12.
This formulation of the free energy of mixing in a binary system takes as parameters a Bragg-Williams type cooperative disordering energy and the difference in free energy between different structures for the end-members. Subsolidus phase relations in carbonate systems such as CaCO3—MgCO3 and CdCO3—MgCO3 are calculated. Similar equations also reproduce the topologies of subsolidus phase relations in pyroxenes, including orthopyroxene-clinopyroxene phase boundaries in the enstatitediopside and ferrosilite-hedenbergite systems, the pigeonite-augite solvus, and the stability field of iron-free pigeonite. 相似文献
13.
Thomas Will Martin Okrusch Esther Schmädicke Guoli Chen 《Contributions to Mineralogy and Petrology》1998,132(1):85-102
Calculated phase equilibria among the minerals sodic amphibole, calcic amphibole, garnet, chloritoid, talc, chlorite, paragonite,
margarite, omphacite, plagioclase, carpholite, zoisite/clinozoisite, lawsonite, pyrophyllite, kyanite, sillimanite, quartz
and H2O are presented for the model system Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O (NCFMASH), which is relevant for many greenschist, blueschist, amphibolite and eclogite facies rocks. Using the activity-composition
relationships for multicomponent amphiboles constrained by Will and Powell (1992), equilibria containing coexisting calcic
and sodic amphiboles could be determined. The blueschist–greenschist transition reaction in the NCFMASH system, for example,
is defined by the univariant reaction sodic amphibole + zoisite = calcic amphibole + chlorite + paragonite + plagioclase (+
quartz + H2O) occurring between approximately 420 and 450 °C at 9.5 to 10 kbar. The calculated petrogenetic grid is a valuable tool for
reconstructing the PT-evolution of metabasic rocks. This is shown for rocks from the island of Samos, Greece. On the basis of mineral and whole
rock analyses, PT-pseudosections were calculated and, together with the observed mineral assemblages and reaction textures, are used to reconstruct
PT-paths. For rocks from northern Samos, pseudomorphs after lawsonite preserved in garnet, the assemblage sodic amphibole-garnet-paragonite-chlorite-zoisite-quartz
and the retrograde appearance of albitic plagioclase and the formation of calcic amphibole around sodic amphibole constrain
a clockwise PT-path that reaches its thermal maximum at some 520 °C and 19 kbar. The derived PT-trajectory indicates cooling during exhumation of the rocks and is similar to paths for rocks from the western part of the
Attic-Cycladic crystalline complex. Rocks from eastern Samos indicate lower pressures and are probably related to high-pressure
rocks from the Menderes Massif in western Turkey.
Received: 8 July 1997 / Accepted: 11 February 1998 相似文献
14.
Andrew G. Christy 《Contributions to Mineralogy and Petrology》1989,102(4):422-428
Reaction textures and chemographic relations in sapphirine-bearing basic granulites at Finero, Italy, suggest that sapphirine and aluminous diopside were formed in mutual equilibrium from an inferred early spinel-bearing assemblage. Finero appears to be the only known locality where this association has been found in situ, although it is also known from kimberlite and breccia pipe nodules elsewhere. The reactions deduced to have occurred in these rocks suggest the existence of stable invariant points involving the phases sapphirine-spinel-orthopyroxene-clinopyroxene-garnet-anorthite and sapphirine-two pyroxenes-garnetanorthite-kyanite (or sillimanite) in the CMAS end-member system. P-T estimates for the relevant rocks, and the available experimental data, suggest that these points lie at around 800°–900° C, 9–11 kbar. A semi-quantitative petrogenetic grid, incorporating these invariant points with previously determined univariant reactions, is proposed. It is inferred that sapphirine+diopside are stable relative to spinel-bearing assemblages below 900° C. The relatively low temperature explains why sapphirine has not to date been reported from experimental work on the CMAS system. It also suggests that sapphirine may be an important aluminous phase in Mg-rich metagabbros under conditions corresponding to the base of the continental crust, despite the observed rarity of such rocks at the surface. 相似文献
15.
16.
17.
18.
Pyrope and quartz are stable with respect to aluminous enstatite and sillimanite at 1400 °C, 20 kb and at 1100 °C, 16 kb. The phase boundary limiting the coexistence of pyrope and quartz towards lower pressures is probably slightly curved. A slope of 15 bars/°C at 1400° and of 10 bars/°C at 1000 °C has been estimated from the experimental data. Between 1050 and 1100 °C the curve is intersected by the kyanite-sillimanite phase boundary. The calculated slope of the reaction aluminous enstatite + kyanite pyrope + quartz is negative (ca. 18–25 bars/°C). The existence of a negative slope has been demonstrated experimentally. Experimental evidence indicates that the assemblage aluminous enstatite and sillimanite is metastable with respect to sapphirine + quartz at high temperature. The invariant point involving the phases pyrope-sapphirine-aluminous enstatite-sillimanite-quartz is estimated to occur at 1125°±25 °C and 16±1 kb. A model phase diagram for the silicasaturated part of the system MgO-Al2O3-SiO2 has been constructed. The position of three invariant points in this system has been estimated on the basis of presently available data. 相似文献
19.
Crystal-melt relations at a water vapour pressure of 1 kilobar have been determined for planes at 3, 5, 7.5, and 10 weight per cent anorthite in the system NaAlSi3O8KAlSi3O8-CaAl2Si2O8-SiO2. The ratio of the silicate components in the liquids which are in univariant equilibrium with plagioclase, alkali feldspar, quartz and gas are Ab31Or28Q38An3 (weight per cent) at 730°±5–10° C, Ab21Or34Q40An5 at 745°±5–10° C and Ab10Or39 Q43.5An7.5 at 780°±10° C. The univariant curve on which the above compositions lieoriginates on the H2O-saturated Or-An-Q plane at a composition containing less than 10 weight per cent An and terminates within 1.5 weight per cent An of the H2O-saturated Or-Ab-Q plane. Experimental data for the synthetic system have been used to illustrate a discussion on the partial melting of metasediments and the possible significance of such a process with respect to the genesis of granitic rocks. Data taken from the literature (Winkler and v. Platen, 1960, 1961a) have been used to illustrate that the normative salic composition of a sediment has a strong influence on the composition of any melt which form when such a rock is subjected to high temperatures and pressures. 相似文献