The Cu-Zn-S system     

J. R. Craig  G. Kullerud 《Mineralium Deposita》1973,8(1):81-91

The phase relations in the Cu-Zn-S system were studied at temperatures ranging from 100 ° to 1050 °C with emphasis on the 500 ° and 800 °C isotherms. All experiments were performed in closed, evacuated silica tubes in which vapor always is a phase. Ternary phases did not appear in any of these experiments. At 800 °C tie-lines exist between cubic ZnS (sphalerite) and the digenite-chalcoite solid solution, between ZnS and three CuZn alloys (, , ) and between ZnS and ZnCu liquid containing from zero to about 30 wt % Cu. Only the cubic, sphalerite, form of ZnS was encountered in the present study. At 800 °C the solid solution of ZnS in Cu₂S is 7.0 ± 1 wt % and the solid solution of Cu₂S in ZnS is less than 1.0 wt %. At lower temperatures ZnS coexists with all other phases once they become stable, i.e., -CuZn (<598 °C), CuS (<507 °C), and blue-remaining covellite (<157 °C). At 500 °C the solid solution of ZnS in Cu₂S is 1.5±0.5 wt % and that of Cu₂S in ZnS is less than 0.1 wt %. The presence of ZnS depresses the temperature of the hexagonal cubic inversion in Cu₂S by about 13 °C, but does not measurably affect the temperature of the monoclinic hexagonal inversion in Cu₂S nor that of the cubic cubic inversion in Cu₉S₅. The coexistence in nature of sphalerite and copper-sulfides is discussed in light of the low temperature phase relations in the Cu-Zn-S system.

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Zusammenfassung Die Phasengleichgewichtsredaktionen des Dreistoffsystems Cu-Zn-S wurden über einen weiten Temperaturbereich, nämlich von 100 °C bis zu 1050 °C und dabei besonders nachdrücklich die 500 ° und 800 °C-Isothermen, untersucht. Alle Experimente wurden in abgeschmolzenen und vorher evakuierten Quarzglasampullen durchgeführt, in welchen eine Dampfphase (vapor) stets gegenwärtig war. In keinem der Experimente war das Vorhandensein einer ternären Phase zu verzeichnen. Bei 800 °C verlaufen Konodenscharen vom kubischen ZnS (Zinkblende) zur Digenit-Kupferglanz-Mischkristallreihe, ferner Konoden zwischen ZnS und drei Cu-Zu-Legierungen (, , ) und zwischen ZnS und einer Zn-Cu-Schmelze von 0 bis ca. 30 Gew.-% Cu. In der hier vorliegenden Arbeit trat nur kubisches ZnS (Zinkblende) auf. Cu₂S vermag bei 800 °C 7,0±1 Gew.-% ZnS in fester Lösung aufzunehmen, während die Löslichkeit von Cu₂S in ZnS weniger als 1,0 Gew.-% beträgt. Mit zunehmender Temperaturerniedrigung koexistiert ZnS mit allen übrigen Phasen des Systems, sobald diese stabil werden, z. B. -CuZn (<598 °C), CuS (<507 °C) und blaubleibender Covellin (<157 °C). Bei 500 °C beträgt die Löslichkeit von ZnS in Cu₂S nur noch 1,5±0,5 Gew.-% und die von Cu₂S in ZnS weinger als 0,1 Gew.-%. Die Gegenwart von ZnS erniedright die Inversionstemperatur von hexagonalem kubischen Cu₂S um etwa 13 °C, hat aber weder einen meßbaren Einfluß auf die Inversionstemperatur des monoklinen hexagonalen Cu₂S noch auf die kubisch kubische Inversion des Cu₉S₅. Angeischts der im Cu-Zn-S-System ermittelten Phasenbeziehungen bei niedrigen Temperaturen werden die Koexistenz natürlicher Zinkblende mit Kupfersulfiden diskutiert.

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Sulfur isotopes and the origin of stibnite mineralisation in New England,Australia     

Brian W. Robinson  Michael G. Farrand 《Mineralium Deposita》1982,17(2):161-174

Stibnite mineralisation in the antimony province of New England can be divided into Central type ores (veins of stibnite + quartz ± berthierite) and Peripheral type ores of stibnite + quartz + native antimony ± berthierite. The Central stibnites have ³⁴S_CDT values of –5±2 (1) which may represent equilibrium precipitation from mantle sulfur at about 200°C. Peripheral stibnites have ³⁴S values between 0 and –25, with a large group at 0±2. They represent precipitation from a limited supply of mantle sulfur and the acquisition of sedimentary sulfur. We consider that the different ore types were produced from distinct ore solutions derived from two immiscible melts. These originated in the deep mantle, were mobilised by tectonic activity and supplied the antimony and most of the sulfur to the ores.  相似文献   

An experimental study of the diffusion of oxygen in quartz and albite using an overgrowth technique   总被引：1，自引：0，他引：1  

S. C. Elphick  P. F. Dennis  C. M. Graham 《Contributions to Mineralogy and Petrology》1986,92(3):322-330

Diffusion rates of¹⁸O tracer in quartz ( c, 1 Kb H₂O) and Amelia albite ( 001, 2 Kb H₂O) have been measured, using Secondary Ion Mass Spectrometry (SIMS). A new technique involving hydrothermal deposition of labelled materials has removed the possibility of pressure solution-reprecipitation processes adversely affecting the experiments. Reported diffusion constants are:-quartz ( c), ,Q=98±7 KJ mol^–1 (600–825° C, 1 Kb); Amelia albite ( 001), ,Q=85±7 KJ mol^–1, (400–600° C, 2 Kb). Measured quartz¹⁸O diffusivities decrease discontinuously at the- transition, reflecting strong structural influences. The reported albite data agree with previously recorded studies, but-quartz data indicate significantly lower activation energies. Possible causes of this discrepancy, and some geological consequences, are noted.  相似文献   

1Tc-Strontiohilgardit (Ca,Sr)2[B5O8(OH)2Cl] und seine Stellung in der Hilgarditgruppe X2/II[B5O8(OH)2Cl]     

Dr. Otto Braitsch 《Contributions to Mineralogy and Petrology》1959,6(4):233-247

Zusammenfassung 1Tc-Strontiohilgardit (Ca, Sr)₂ [B₅O₈(OH)₂,Cl] mit Ca : Sr etwa 1 : 1 ist ein neues Mineral der Hilgarditgruppe. Fundpunkt: Reyersbausen (9° 59,7 E, 51° 36,6 N), Grube Königshall-Hindenburg, Flöz Staßfurt in sylvinitischer Ausbildung.Konstanten : triklin-pedial,a ₀=6,38 Å,b ₀=6,480 Å,c ₀=6,608 Å, =75,4°,=61,2°, =60,5°; tafelige-gestreckte Links- und Re chtskristalle, farblos, wasserunlöslich, piezoelektrisch. Härte 5–7, Dichte 2,99 g cm^–3;n =1,638,n =1,639,n =1,670; 2V =19°.Neue Daten für die Hilgarditgruppe : 2 M (Cc)-Calciumhilgardit (=Hilgardit) =4 Ca₂[B₅O₃(OH)₂Cl], Raumgruppe Cc.3Tc-Calciumhilgardit (=Parahilgardit) = 3 Ca₂[B₅O₃(OH)₂Cl]; trinklin-pedial, ₀=6,31 Å,b =6,484 Å,c ₀=17,50 Å; =84,0°,=79,6°, =60,9°.Die Polymorphiebeziehungen sind geometrisch deutbar durch eine spezielle Art der Polytropie (Stapelung von Links- und Rechtskristallen im Elementarbereich).  相似文献   

Pitfalls in geothermobarometry of eclogites: Fe<Superscript>3+</Superscript> and changes in the mineral chemistry of omphacite at ultrahigh pressures   总被引：1，自引：0，他引：1  

Alexander?ProyerEmail author  Edgar?Dachs  Catherine?McCammon 《Contributions to Mineralogy and Petrology》2004,147(3):305-318

The relatively low-variance mineral assemblage of a talc-kyanite eclogite from Dabie Shan enabled application of both conventional geothermobarometers (garnet-clinopyroxene geothermometer and the garnet-omphacite-phengite geobarometer) and a multi-equilibrium method to determine peak P-T conditions (THERMOCALC, average PT). The results were highly discrepant: 840 °C / 31.1 kbar vs. 590 °C / 29.8 kbar. Mössbauer spectroscopy showed that Fe³⁺/Fe_total in omphacite was significantly higher than the value obtained from standard formula recalculation. When the activities were corrected for Fe endmembers, geothermobarometry gave consistent results (606 °C / 31.3 kbar vs. 585 °C / 30.8 kbar). These are close to those obtained earlier by average PT, confirming the robustness of the multi-equilibrium approach. The high Fe³⁺ concentration in omphacite is best explained using a Ca-eskola endmember Ca_0.5[]_0.5AlSi₂O₆ and allowing corresponding vacancies in the omphacite structure.Editorial responsibility: W. Schreyer  相似文献   

Metagranitoids from the eastern part of the Central Rhodopean Dome (Bulgaria): U–Pb, Rb–Sr and 40Ar/39Ar timing of emplacement and exhumation and isotope-geochemical features     

I. Peytcheva  A. von Quadt  M. Ovtcharova  R. Handler  F. Neubauer  E. Salnikova  Y. Kostitsyn  S. Sarov  K. Kolcheva 《Mineralogy and Petrology》2004,82(1-2):1-31

Summary Geochronological data (U–Pb, Rb–Sr and ⁴⁰Ar/³⁹Ar) are used to unravel the Late Alpine high-grade metamorphism, migmatisation and exhumation of Variscan granitoids within the core of the Central Rhodopean dome, Bulgaria. The age of the granitoid protolith is 300±11Ma, as determined by U–Pb analyses on single zircons selected from the core of the dome structure.Rb–Sr whole rock data define an errorchron with a large scatter of the data points due to the Late Alpine metamorphic overprint. The slope of the reference line indicates a Variscan magmatic event. Strontium characteristics are used to discriminate the samples most influenced by metamorphism from those, which reflect possible differences in the protolith age of the granitoids.Petrological-geochemical data, the initial strontium ratio of 0.708±0.001, and _Hf zircon values ranging from –2.58 to –3.82 point to a mixed, but crust-dominated origin of the Variscan magmas; young crustal material and mantle fragments were sources for the I-type metagranitoids.The exhumation of the granitoids from depths greater than 20–25km to about 5km below the surface was a rapid geological process. It started with the formation of granitic eutectic minimum melts at the temperature peak of metamorphism. Monazite crystallisation at about 650°C continued during isothermal decompression to possible depths of about 10–12km. An age of 35.83±0.40Ma was determined using conventional U–Pb isotope methods on four multigrain monazite fractions. A maximum average age of 36.6–37.5Ma (assuming same error uncertainties) for crystallisation of the metamorphic monazites was calculated assuming 10 to 20% monazite resetting during the subsequent Oligocene volcanism and hydrothermal activity in the region of the Central Rhodopean Dome. The rocks were then cooled to about 350–300°C at 35.35±0.22Ma according to ⁴⁰Ar/³⁹Ar ages of biotites and below 300°C at 35.31±0.25Ma (Rb–Sr data), as indicated by crystallisation of adularia in an open vein subsequent to pegmatite intrusion. A minimum exhumation rate of 3–5km per 1 million years can therefore be calculated for the exhumation of the metagranitoids during the period from 38–35Ma.  相似文献   

Petrographic and geochemical evidence for hydrothermal evolution of the North Deposit,Mt Tom Price,Western Australia     

Warren?Spencer?ThorneEmail author  Steffen?Gerd?Hagemann  Mark?Barley 《Mineralium Deposita》2004,39(7):766-783

High-grade iron mineralisation (>65%Fe) in the North Deposit occurs as an E-W trending synclinal sheet within banded iron formation (BIF) of the Early Proterozoic Dales Gorge Member and consists of martite-microplaty hematite ore. Three hypogene alteration zones between unmineralised BIF and high-grade iron ore are observed: (1) distal magnetite-siderite-iron silicate, (2) intermediate hematite-ankerite-magnetite, and (3) proximal martite-microplaty hematite-apatite alteration zones. Fluid inclusions trapped in ankerite within ankerite-hematite veins in the hematite-ankerite-magnetite alteration zone revealed mostly H₂O–CaCl₂ pseudosecondary and secondary inclusions with salinities of 23.9±1.5 (1, n=38) and 24.4±1.5 (1, n=66) eq.wt.% CaCl₂, respectively. Pseudosecondary inclusions homogenised at 253±59.9°C (1, n=34) and secondary inclusions at 117±10.0°C (1, n=66). The decrepitation of pseudosecondary inclusions above 350°C suggests that their trapping temperatures are likely to be higher (i.e. 400°C). Hypogene siderite and ankerite from magnetite-siderite-iron silicate and hematite-ankerite-magnetite alteration zones have similar oxygen isotope compositions, but increasingly enriched carbon isotopes from magnetite-siderite-iron silicate alteration (–8.8±0.7, 1, n=17) to hematite-ankerite-magnetite alteration zones (–4.9±2.2, 1, n=17) when compared to the dolomite in the Wittenoom Formation (0.9±0.7, 1, n=15) that underlies the deposit. A two-stage hydrothermal-supergene model is proposed for the formation of the North Deposit. Early 1a hypogene alteration involved the upward movement of hydrothermal, CaCl₂-rich brines (150–250°C), likely from the carbonate-rich Wittenoom Formation (¹³C signature of 0.9±0.7, 1, n=15), within large-scale folds of the Dales Gorge Member. Fluid rock reactions transformed unmineralised BIF to magnetite siderite-iron silicate BIF, with subsequent desilicification of the chert bands. Stage 1b hypogene alteration is characterised by an increase in temperature (possibly to 400°C), depleted ¹³C signature of –4.9±2.2 (1, n=17), and the formation of hematite-ankerite-magnetite alteration and finally the crystallisation of microplaty hematite. Late Stage 1c hypogene alteration involved the interaction of low temperature (~120°C) basinal brines with the hematite-ankerite-magnetite hydrothermal assemblage leaving a porous martite-microplaty hematite-apatite mineral assemblage. Stage 2 supergene enrichment in the Tertiary resulted in the removal of residual ankerite and apatite and the weathering of the shale bands to clay.Editorial handling: B. Lehmann  相似文献   

The genesis of Cu-bearing quartz veins by metamorphic remobilization from stratiform red bed deposits,SW County Cork,Ireland     

Dr. Ni Wen  Dr. A. J. Boyce  Dr. A. E. Fallick  Dr. J. R. Ashworth  Dr. R. A. Ixer 《Mineralogy and Petrology》1996,57(1-2):73-89

Summary Polymetallicmajor veins of the West Carbery district (County Cork) are compared with the nearby stratiform-disseminated copper mineralization in metasedimentary rocks, containingminor veins (metamorphic quartz veins and veinlets). These stratiform deposits are hosted by non-marine Devonian sediments (Old Red Sandstone), metamorphosed in the Hercynian orogeny. In sulphides from the stratiform deposits and minor veins, isotopic compositions of sulphur (³⁴S) range from – 21.00 to + 5.14%₀, consistent with the vein sulphide being remobilized stratiform-disseminated sulphide, and the latter being of diagenetic bacteriogenic origin. Sulphate (barite), found in veins separate from the sulphides, has ³⁴S + 12.3 to + 15.7%₀. consistent with groundwater origin. In minor-vein quartz, fluid inclusions have homogenization temperatures consistent with trapping under the estimated peak-metamorphic conditions (300–400°C, 1–3 kbar).In the major veins, sulphide ³⁴S (–15.8 to –4.2 0) suggest remobilization of diagenetic sulphide. Oxygen and hydrogen isotopes suggest deposition from metamorphic fluids (calculated ¹⁸O_H2O approximately + 8 to + l3%₀, measured range of D –52.2 to –27.3%₀). Immiscible C0₂-bearing fluids were trapped in the temperature range 280–350°C with fluid pressure < ca. 600 bar. The inferred pressure-temperature history is attributed to late-metamorphic uplift, with fluid pressures falling below lithostatic. The sulphide-bearing veins are interpreted as a small-scale example of redistribution of mineral deposits by metamorphic fluids.

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Die Genese Cu führender Quarzgdnge durch metamorphe Remobilisation aus stratiformen Rotsedimenten, SW County Cork, Irland

Zusammenfassung Polymetallische Erzgänge (major veins) des westlichen Carbery Distriktes (County Cork) werden mit kleineren Gängchen (minor veins), die in den benachbarten, eine disseminierte stratiforme Cu-Vererzung führenden, Metasedimenten liegen, verglichen. Diese stratiformen Lagerstätten sind an nichtmarine devonische Sedimente (Old Red Sandstone), die während der hercynischen Orogenese metamorphisiert wurden, gebunden. Die Zusammensetzung der Schwefelisotope (³⁴S) der Sulfide in der disseminierten Vererzung und in den kleineren Gängen variiert von –21.00 bis –5.14%₀. Diese Zusammensetzung ist mit der Interpretation, daß der Schwefel in den Gängchen aus den stratiformen disseminierten Sulfiden remobilisiert wurde, die ihrerseits diagenetischbakteriogene Signatur zeigen, konsistent: Die ³⁴5-Werte der Sulfate (Baryt) in den Gängchen variieren von + 12.3 bis + 15.7%₀, was mit einer Herkunft aus Grundwässern übereinstimmt. Die Homogenisierungs-Temperaturen der FlüsBigkeitseinschlüsse in Quarz der Gängchen sind mit einem Einschluß der Fluide während des Höhepunktes der Metamorphose (300–400°C, l-3 kbar) konsistent.In den polymetallischen Erzgängen weisen die ³⁴S-Werte (–15.8 bis –4.2%0) auf die Remobilisation diagenetischen Schwefels, die Sauerstoff und Wasserstoffisotope auf Ausfällung aus metamorphen Wässern hin. Die berechneten ¹⁸O-Werte liegen zwischen ca. +8 bis +13%₀ die gemessenen H-Werte zwischen –52.2 bis –27.3%₀. Nicht mischbare C0₂-führende Fluide wurden im Temperaturbereich von 280–350°C bei Fluid-Drucken < ca. 600 bar eingeschlossen. Der abgeleitete P-T Pfad wird mit spätmetamorpher Hebung, während der der Fluiddruck unter den lithostatischen Druck fiel, erklärt. Die Sulfid-führenden Gänge werden als kleinmaßstäbliche Beispiele für Wiederverteilung von Minerallagerstätten durch metamorphe Fluide gedeutet.

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With 6 Figures  相似文献   

The genesis of emeralds and their host rocks from Swat,northwestern Pakistan: a stable-isotope investigation     

M. Arif  A. E. Fallick  C. J. Moon 《Mineralium Deposita》1996,31(4):255-268

Emerald deposits in Swat, northwestern Pakistan, occurring in talc-magnesite and quartz-magnesite assemblages, have been investigated through stable isotope studies. Isotopic analyses were performed on a total of seven emeralds, associated quartz (seven samples), fuchsite (three samples) and tourmaline (two samples) from the Mingora emerald mines. The oxygen isotopic composition ( ¹⁸O SMOW) of emeralds shows a strong enrichment in¹⁸O and is remarkably uniform at + 15.6 ± 0.4 (1,n = 7). Each of the two components of water in emerald (channel and inclusion) has a different range of hydrogen isotopic composition: the channel waters being distinctly isotopically heavier (D = –51 to –32 SMOW) than the other inclusion waters (D = –96 to –70 SMOW). Similarly the oxygen isotopic compositions of tourmaline and fuchsite are relatively constant ( ¹⁸O = + 13 to + 14 SMOW) and show enrichment in¹⁸O. The ¹⁸O values of quartz, ranging from + 15.1 to + 19.1 SMOW, are also high (+ 16.9 ± 1.4 1, n = 7). The meanD of channel waters measured from emerald (–42 ± 6.6 SMOW) and that of fluid calculated from hydrous mineralsD_calculated (–47 ± 7.1 SMOW) are consistent with both metamorphic and magmatic origin. However, the close similarity between the measuredD values of the hydroxyl hydrogen in fuchsite (–74 to –6 SMOW) and tourmaline (–84 and –69 SMOW) with pegmatitic muscovite and tourmaline suggests that the mineralization was probably caused by modified (¹⁸O-enriched) hydrothermal solutions derived from an S-type granitic magma. The variation in the carbon and oxygen isotopic composition of magnesite, locally associated with emerald mineralization, is also very restricted ( ¹³ –3.2 ± 0.7%, PDB; ¹⁸O + 17.9 ± 1.27 SMOW). On the basis of the isotopic composition of fluid ( ¹³C –1.8 ± 0.7 PDB; ¹⁸O + 13.6 ± 1.2 SMOW calculated for the 250-550 °C temperature), it is proposed that the Swat magnesites formed due to the carbonation of previously serpentinized ultramafic rocks by a CO₂-bearing fluid of metamorphic origin.  相似文献   

Latest precambrian (Cadomian) zircon ages,Nd isotopic systematics and P-T evolution of granitoid orthogneisses of the Erzgebirge,Saxony and Czech Republic     

A. Kröner  A. P. Willner  E. Hegner  A. Frischbutter  J. Hofmann  R. Bergner 《International Journal of Earth Sciences》1995,84(3):437-456

Single zircons from two orthogneiss complexes, the Grey Gneiss and Red Gneiss, the lowermost tectonic units in the Erzgebirge, were dated. The grey Freiberg Gneiss is of igneous origin and has a ²⁰⁷Pb/²⁰⁶Pb emplacement age of 550±7 Ma. A quartz monzonite from Lauenstein contains idiomorphic zircons with a mean ²⁰⁷Pb/²⁰⁶Pb age of 555±7 Ma as well as xenocrysts ranging in age between 850 and 1910 Ma. Red gneisses from the central Erzgebirge contain complex zircon populations, including numerous xenocrysts up to 2464 Ma in age. The youngest, idiomorphic, zircons in all samples yielded uniform ²⁰⁷Pb/²⁰⁶Pb ages between 550±9 and 554±10 Ma. Nd isotopic data support the interpretation of crustal anatexis for the origin of both units. _Nd(t) values for the grey gneisses are –7.5 and –6.0 respectively, (mean crustal residence ages of 1.7–1.8 Ga). The red gneisses have a wider range in _Nd(t) values from –7.7 to –2.8 (T _DM ages of 1.4–1.8 Ga). The zircon ages document a distinct late Proterozoic phase of granitoid magmatism, similar in age to granitoids in the Lusatian block farther north-east. However, Palaeozoic deformation as well as medium pressure metamorphism ( 8 kbar/600–650° C) are identical in both gneiss units and distinguish these rocks from the Lusatian granitoids. The grey and red gneisses were overthrust by units with abundant high-pressure relicts and a contrasting P-T evolution. Zircon xenocryst and Nd model ages in the range 1000–1700 Ma are similar to those in granitoid rocks of Lusatia and the West-Sudetes, and document a pre-Cadomian basement in parts of east-central Europe that, chronologically, has similarities with the Sveconorwegian domain in the Baltic Shield.  相似文献   

Sapphirine/kornenipine-bearing rocks and crustal uplift history of the Limpopo belt,Southern Africa     

B. F. Windley  D. Ackermand  R. K. Herd 《Contributions to Mineralogy and Petrology》1984,86(4):342-358

Sapphirine/kornerupine-bearing rocks occur within the anorthosites of the Messina layered intrusion in the Limpopo mobile belt of Zimbabwe. The X_Mg range of the major minerals is as follows: cordierite (0.98-0.93); enstatite (0.97-0.86); chlorite (0.98-0.92); phlogopite (0.98-0.90); sapphirine (0.98-0.86); kornerupine (0.94-0.88); gedrite (0.96-0.85); spinel (0.92-0.78). There are four rock types, the constituent minerals of which have different values, which decrease in the above mineral order; other minerals are corundum, sillimanite and relict kyanite. We recognise twenty reactions without phlogopite and nine reactions involving phlogopite. The textural relations and the plots of the microprobe data of coexisting minerals in the MgO-Al₂O₃-SiO₂-(H₂O) system are consistent with the following sequence of main reactions: (1) enstatite+corundum cordierite+sapphirine; (4) sapphirine+sillimanite cordierite+corundum; (8) kornerupine+corundum cordierite+sapphirine; (13) kornerupine cordierite+sapphirine+enstatite; (15) enstatite+spinel chlorite+sapphirine; (18) cordierite+sapphirine chlorite+corundum; (20) sapphirine chlorite+corundum+spinel. The early reactions are shown by coarse-grained reaction intergrowths, kornerupine and gedrite breakdown is shown by finer-grained symplectites, and the latest reactions by very fine-grained products in micro-fractures. These selected reactions illustrate a remarkably steep trajectory from thePT peak close to 10 kbar and 800° C to the minimum observable at 3.5–4.5 kbar and 700° C as indicated by the pure MASH system. Very rapid uplift took place under nearly isothermal conditions. The protolith of this material was possibly sedimentary, derived from altered volcanic rocks. The bulk composition is close to the composition of kornerupine or to a mixture of alunite, chlorite and pyrophyllite. These texturally and mineralogically complex rocks contain a wealth of relevant data for documenting crustal uplift history.  相似文献   

The upper stability limit of the assemblage paragonite + quartz and its natural occurrences     

Niranjan D. Chatterjee 《Contributions to Mineralogy and Petrology》1972,34(4):288-303

The assemblage paragonite + quartz is encountered frequently in low- to medium-grade metamorphic rocks. With rising grade of metamorphism they react mutually to yield the condensed assemblage albite + Al₂SiO₅.The univariant curve pertaining to the equilibrium paragonite + quartz=albite + andalusite + H₂O has been located experimentally. The reversed P _{H 2 O}-T data are: 1 kb: 470–490° C 2 kb: 510–530° C 3 kb: 540–560° C 4 kb: 560–580° C 5 kb: 590–600° C The univariant curve pertaining to the equilibrium paragonite + quartz=albite + kyanite + H₂O runs through the following P _{H 2 O}-T-intervals: 5 kb: 570–625° C 6 kb: 600–630° C 7 kb: 620–640° C Thermodynamic calculations of S ₂₉₈ ⁰ , H _f,298 ⁰ and G _f,298 ⁰ of the phase paragonite from the experimental data presented above and those obtained from the equilibria of the reaction paragonite=albite + corundum + H₂O (Chatterjee, 1970), agree within the limits of uncertainty. This prompts the idea that Zen's (1969) suggestion of a possible error of approximately 7 kcal in G _f,298 ⁰ of the Al₂SiO₅ polymorphs may in fact be due to an error of similar magnitude in G _f,298 ⁰ of corundum.A best estimate of S ₂₉₈ ⁰ , H _f,298 ⁰ and G _f,298 ⁰ of paragonite based on these considerations yield: S ₂₉₈ ⁰ : 67.61±3.9 cal deg^–1 gfw^–1 H _f,298 ⁰ : –1411.4±2.7 kcal gfw^–1 G _f,298 ⁰ : –1320.9±4.0 kcal gfw^–1 These numbers will be subject to change when better thermochemical data on corundum and albite are available.In medium-grade metamorphic rocks the assemblage paragonite + quartz is commonly found in stable coexistence with such other phases as muscovite, staurolite, andalusite, kyanite, but not with cordierite or sillimanite. However, the assemblage paragonite-sillimanite has been reported to be stable in the absence of quartz. All these petrologic observations can be explained on the basis of the stability data of the phases and phase assemblages concerned.  相似文献   

A stable isotope study of retrograde alteration in SW Connemara,Ireland     

G. R. T. Jenkin  A. E. Fallick  B. E. Leake 《Contributions to Mineralogy and Petrology》1992,110(2-3):269-288

Dalradian metamorphic rocks, Lower Ordovician meta-igneous rocks (MGS) and Caledonian granites of the Connemara complex in SW Connemara all show intense retrograde alteration. Alteration primarily involves sericitization and saussuritization of plagioclase, the alteration of biotite and hornblende to chlorite and the formation of secondary epidote. The alteration is associated with sealed microcracks in all rocks and planes of secondary fluid inclusions in quartz where it occurs, and was the result of a phase of fluid influx into these rocks. In hand specimen K-feldspar becomes progressively reddened with increasing alteration. Mineralogical alteration in the MGS and Caledonian granites took place at temperatures 275±15°C and in the MGS P_fluid is estimated to be 1.5 kbar during alteration. The °D values of alteration phases are:-18 to-29 (fluid inclusions),-47 to-61 (chlorites) and-11 to-31 (epidotes). Chlorite ¹⁸O values are +0.2 to +4.3, while ¹⁸O values for quartz-K-feldspar pairs show both positively sloped (MGS) and highly unusual negatively sloped (Caledonian granites) arrays, diverging from the normal magmatic field on a - plot. The stable isotope data show that the fluid that caused retrogression continued to be present in most rocks until temperatures fell to 200–140°C. The retrograde fluid had D -20 to-30 in all lithologies, but the fluid ¹⁸O varied both spatially and temporally within the range-4 to +7. The fO₂ of the fluid that deposited the epidotes in the MGS varied with its ¹⁸O value, with the most ¹⁸O-depleted fluid being the most oxidizing. The D values, together with low (<0) ¹⁸O values for the retrograde fluid in some lithologies indicate that this fluid was of meteoric origin. This meteoric fluid was probably responsible for the alteration in all lithologies during a single phase of fluid infiltration. The variation in retrograde fluid ¹⁸O values is attributed to the effects of variable oxygen isotope shifting of this meteoric fluid by fluid-rock interaction. Infiltration of meteoric fluid into this area was most likely accomplished by convection of pore fluids around the heat anomaly of the Galway granite soon after intrusion at 400 Ma. However convective circulation of meteoric water and mineralogical alteration could possible have occurred considerably later.  相似文献   

18O-Enrichment of silicic magmas caused by crystal fractionation at the Galapagos Spreading Center   总被引：1，自引：1，他引：0  

Karlis Muehlenbachs  Gary Byerly 《Contributions to Mineralogy and Petrology》1982,79(1):76-79

An extremely differentiated suite of unaltered volcanic rocks dredged from the Galapagos Spreading Center ranges in ¹⁸O from 5.7 to 7.1 At 95°W, low K-tholeiites, FeTi-basalts, andesites and rhyodacites were recovered. Their lithologic and major element geochemical variation can be accounted for by crystal fractionation of plagioclase, pyroxenes, olivine and titanomagnetite in the same proportions and amounts needed to model the ¹⁸O variation by simple Rayleigh fractionation. More complicated behaviour was observed in a FeTi-basalt suite from 85°W. This study shows that 90% fractionation only enriches the residual melt by about 1.2 in ¹⁸O. It also implies that the magma chambers along parts of the Galapagos Spreading Center were static and isolated such that extreme differentiation could occur.  相似文献