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1.
Burkhard C. Schmidt François Holtz Michel Pichavant 《Contributions to Mineralogy and Petrology》1999,136(3):213-224
The water solubility in haplogranitic melts (normative composition Ab39Or32Qz29) coexisting with H2O-H2 fluids at 800 and 950 °C and 1, 2 and 3 kbar vapour pressure has been determined using IR spectroscopy. The experiments were
performed in internally heated pressure vessels and the hydrogen fugacity (f
H2) was controlled using the double capsule technique and oxygen buffer assemblages (WM and IW). Due to the limited lifetimes
of these oxygen buffers the water solubility was determined from diffusion profiles (concentration-distance profiles) measured
with IR spectroscopy in the quenched glasses. The reliability of the experimental strategy was demonstrated by comparing the
results of short- and long-duration experiments performed with pure H2O fluids. The water solubility in Ab39Or32Qz29 melts equilibrated with H2O-H2 fluids decreases progressively with decreasing f
H2O, as f
H2 (or X
H2) increases in the fluid phase. The effect of H2 on the evolution of the water solubility is similar to that of CO2 or another volatile with a low solubility in the melt and can be calculated in a first approximation with the Burnham water
solubility model. Recalculation of high temperature water speciation for AOQ melts coexisting with H2O-H2 fluids at 800 °C, 2 kbar suggests that the concentrations of molecular H2O are proportional to f
H2O (calculated using available mixing models), indicating Henrian behaviour for the solubility of molecular H2O in haplogranitic melts.
Received: 29 June 1998 / Accepted: 10 March 1999 相似文献
2.
The melting reaction: albite(solid)+ H2O(fluid) =albite-H2O(melt) has been determined in the presence of H2O–NaCl fluids at 5 and 9.2 kbar, and results compared with those obtained in presence of H2O–CO2 fluids. To a good approximation, albite melts congruently at 9 kbar, indicating that the melting temperature at constant
pressure is principally determined by water activity. At 5 kbar, the temperature (T)- mole fraction (X
(H2O) ) melting relations in the two systems are almost coincident. By contrast, H2O–NaCl mixing at 9 kbar is quite non-ideal; albite melts ∼70 °C higher in H2O–NaCl brines than in H2O–CO2 fluids for X
(H2O) =0.8 and ∼100 °C higher for X
(H2O) =0.5. The melting temperature of albite in H2O–NaCl fluids of X
(H2O)=0.8 is ∼100 °C higher than in pure water. The P–T curves for albite melting at constant H2O–NaCl show a temperature minimum at about 5 kbar. Water activities in H2O–NaCl fluids calculated from these results, from new experimental data on the dehydration of brucite in presence of H2O–NaCl fluid at 9 kbar, and from previously published experimental data, indicate a large decrease with increasing fluid pressure
at pressures up to 10 kbar. Aqueous brines with dissolved chloride salt contents comparable to those of real crustal fluids
provide a mechanism for reducing water activities, buffering and limiting crustal melting, and generating anhydrous mineral
assemblages during deep crustal metamorphism in the granulite facies and in subduction-related metamorphism. Low water activity
in high pressure-temperature metamorphic mineral assemblages is not necessarily a criterion of fluid absence or melting, but
may be due to the presence of low a
(H2O) brines.
Received: 17 March 1995/Accepted: 9 April 1996 相似文献
3.
Liquidus temperatures and phase compositions in the system Qz-Ab-Or at 5 kbar and very low water activities 总被引:1,自引:0,他引:1
Andreas Becker Francois Holtz Wilhelm Johannes 《Contributions to Mineralogy and Petrology》1998,130(3-4):213-224
Liquidus phase relations have been experimentally determined in the systems Qz-Ab-Or-(H2O), Qz-Ab-(H2O) and Qz-Or-(H2O) at H2O-undersaturated conditions (a
H2O = 0.07) and P = 5 kbar. Starting materials were homogeneous synthetic glasses containing 1 wt% H2O. The liquidus temperatures were bracketed by crystallization and dissolution experiments. The results of kinetic studies
showed that crushed glasses are the best starting materials to overcome undercooling and to minimize the temperature difference
between the lowest temperature of complete dissolution (melting) and the highest temperature at which crystallization can
be observed. At P = 5 kbar and a
H2O = 0.07, the Qz-Ab eutectic composition is Qz32Ab68 at 1095 °C (±10 °C) and the Qz-Or eutectic is Qz38Or62 at 1030 °C (±10 °C). The minimum temperature of the ternary system Qz-Ab-Or is 990 °C (±10 °C) and the minimum composition
is Qz32Ab35‐ Or33. The Qz content of the minimum composition in the system Qz-Ab-Or-H2O remains constant with changing a
H2O. The normative Or content, however, increases by approximately 10 wt% with decreasing a
H2O from 1 to 0.07. Such an increase has already been observed in the system Qz-Ab-Or-H2O-CO2 at high a
H2O and it is concluded that the use of CO2 to reduce water activities does not influence the composition of the minima in quartz-feldspar systems. The determined liquidus
temperature in melts with 1 wt% H2O is very similar to that obtained in previous nominally “dry” experiments. This discrepancy is interpreted to be due to problems
in obtaining absolutely dry conditions. Thus, the hitherto published solidus and liquidus temperatures for “dry” conditions
are probably underestimated.
Received: 27 March 1997 / Accepted: 1 October 1997 相似文献
4.
Meta-sedimentary rocks including marbles and calcsilicates in Central Dronning Maud Land (CDML) in East Antarctica experienced
a Pan-African granulite facies metamorphism with peak metamorphic conditions around 830 ± 20 °C at 6.8 ± 0.5 kbar which was
accompanied by the post-kinematic intrusion of huge amounts of syenitic (charnockitic) magmas at 4.5 ± 0.7 kbar. The marbles
and calcsilicates may represent meta-evaporites as indicated by the occurrence of metamorphic gypsum/anhydrite and Cl-rich
scapolite that formed in the presence of saline fluids with X
NaCl in the range 0.15–0.27. The marbles and calcsilicates bear biotite, tremolite and/or hornblende and humite group minerals
(clinohumite, chondrodite and humite) which are inferred to have crystallized at about 650 °C and 4.5 kbar. The syenitic intrusives
contain late-magmatic biotite and amphibole (formed between 750 and 800 °C) as well as relictic magmatic fayalite, orthopyroxene
and clinopyroxene. Two syenite and two calcsilicate samples contain fluorite. Corona textures in the marbles and calcsilicates
suggest very low fluid-rock ratios during the formation of the retrograde (650 °C) assemblages. Biotite in all but two syenite
samples crystallized at log(f
H
2
O/f
HF) ratios of 2.9 ± 0.4, while in the calcsilicates, both biotite and humite group minerals indicate generally higher log(f
H
2
O/f
HF) values of up to 5.2. A few samples, though, overlap with the syenite values. Log(f
H
2
O/f
HCl) derived from biotite covers the range 0.5–2.6 in all rock types. Within a single sample, the calculated values for both
parameters vary typically by 0.1 to 0.8 log units. Water and halogen acid fugacities calculated from biotite-olivine/orthopyroxene-feldspar-quartz
equilibria and the above fugacity ratios are 1510–2790 bars for H2O, 1.3–5.3 bars for HF and 7–600 bars for HCl. The results are interpreted to reflect the reaction of relatively homogeneous
magmatic fluids [in terms of log(f
H
2
O
/f
HF)] derived from the late-magmatic stages of the syenites with both earlier crystallized, still hotter parts of the syenites
and with adjacent country rocks during down-temperature fluid flow. Fluorine is successively removed from the fluid and incorporated
into F-bearing minerals (close to the syenite into metamorphic fluorite). In the course of this process log(f
H
2
O
/f
HF) increases significantly. Chlorine preferably partitions into the fluid and hence log(f
H
2
O
/f
HCl) does not change markedly during fluid-rock interaction.
Received: 28 November 1997 / Accepted: 27 April 1998 相似文献
5.
Jay J. Ague 《Contributions to Mineralogy and Petrology》1998,132(2):180-197
Simple one-dimensional numerical models are presented for coupled advection-hydrodynamic dispersion and kinetically controlled
oxidatioin-reduction reactions in graphite-free porous media containing magnetite coexisting with silicate assemblages. Fluid-solid
interactions involving either OH (O2-H2O-H2) or COH (O2-H2O-H2-CO2-CO-CH4) fluids are considered at ∼500 ∘C and 5 kbar. The major implications of the modeling are as follows: (1) Regional (km scale) reduction of typical magnetite-bearing
rocks originally at f
O2 near NNO may be possible during long-term metamorphic fluid flow if the infiltrating fluids have sufficiently low f
O2 and sufficiently large concentrations of CH4 and/or H2. Regional oxidation of such rocks by highly oxidized OH or COH fluids appears to be difficult to achieve. (2) Nearly identical
mineral assemblages and modes may be produced by very different kinetic reaction pathways. The model implies that “equilibrium”
assemblages preserved in rocks may not always reflect the true kinetic reaction path that evolved during fluid flow, and highlights
the need for quantitative measurements of metamorphic reaction rates. (3) Preservation of sharp lithologic contacts between
rocks of very different redox states containing accessory amounts of oxides may be unlikely if fluid-rock interaction times
exceed 103104 years. Substantial contact disruption over these times scales is predicted even for oxide-rich rocks if redox contrasts between
layers are large. Flow across lithologic contacts may produce asymmetric patterns of metasomatic mineral zonation that may
prove useful for mapping flow directions in metamorphic sequences. (4) For fluid flow in typical T gradients through originally homogeneous rock, significant major element metasomatism (e.g., K, Na, Ca) may be possible without
producing large changes in oxide abundances.
Received:12 November 1997 / Accepted: 9 March 1998 相似文献
6.
V. López Sánchez-Vizcaíno J. A. D. Connolly M. T. Gómez-Pugnaire 《Contributions to Mineralogy and Petrology》1997,126(3):292-302
Phase relations and metamorphic conditions have been studied in metacarbonate rocks from the Nevado-Filábride Complex (Cordilleras
Béticas) through forward modeling. In many rock samples, the assemblage titanite + rutile + calcite + quartz + graphite buffered
the composition of the C-O-H fluid present during metamorphism. Over a wide range of P-T conditions, fluid compositions computed for this buffer are essentially binary H2O-CO2 mixtures. This buffer also constrains the chemical potentials of TiO2, CaO and SiO2. Consequently it is possible to make a thermodynamic projection through these components to predict the stable phase relations
consistent with the buffer. Using this method, phase relations have been analyzed in a rock containing the buffer assemblage
and paragonite, albite, phengite, epidote, and chlorite. The equilibrium P-T conditions for this assemblage are constrained, by minimization of the differences between predicted and observed mineral
compositions, to be 560 ± 15 °C and 9.5 ± 1 kbar. Conditions obtained compare well with those estimated from other studies
in different lithologic units. The inferred metamorphic fluid composition is H2O-rich ().
Received: 11 October 1995 / Accepted 5 August 1996 相似文献
7.
H2O activities in supercritical fluids in the system KCl-H2O-(MgO) were measured at pressures of 1, 2, 4, 7, 10 and 15 kbar by numerous reversals of vapor compositions in equilibrium
with brucite and periclase. Measurements spanned the range 550–900 °C. A change of state of solute KCl occurs as pressures
increase above 2 kbar, by which H2O activity becomes very low and, at pressures of 4 kbar and above, nearly coincident with the square of the mole fraction
(x
H2O). The effect undoubtedly results primarily from ionic dissociation as H2O density (ρH2O) approaches 1 gm/cm3, and is more pronounced than in the NaCl-H2O system at the same P-T-X conditions. Six values of solute KCl activity were yielded by terminal points of the isobaric brucite-periclase T-x
H2O curves where sylvite saturation occurs. The H2O mole fraction of the isobaric invariant assemblage brucite-periclase-sylvite-fluid is near 0.52 at all pressures, and the
corresponding temperatures span only 100 °C between 1 and 15 kbar. This remarkable convergence of the isobaric equilibrium
curves reflects the great influence of pressure on lowering of both KCl and H2O activities. The H2O and KCl activities can be expressed by the formulas: a
H2O = γH2O[x
H2O+(1 + (1 + α)x
KCl)], and a
KCL = γKCl[(1 + α)x
KCl/(x
H2O +(1 + α)x
KCl)](1 + α), where α is a degree of dissociation parameter which increases from zero at the lowest pressures to near one at high pressures
and the γ's are activity coefficients based on an empirical regular solution parameter W: ln γi = (1 − xi)2W. Least squares fitting of our H2O and KCl activity data evaluates the parameters: α = exp(4.166 −2.709/ρH2O) − 212.1P/T, and W = (−589.6 − 23.10P) /T, with ρH2O in gm/cm3, P in kbar and T in K. The standard deviation from the measured activities is only ± 0.014. The equations define isobaric liquidus curves,
which are in perfect agreement with previous DTA liquidus measurements at 0.5–2 kbar, but which depart progressively from
their extrapolation to higher pressures because of the pressure-induced dissociation effect. The great similarity of the NaCl-H2O and KCl-H2O systems suggests that H2O activities in the ternary NaCl-KCl-H2O system can be described with reasonable accuracy by assuming proportionality between the binary systems. This assumption
was verified by a few reconnaissance measurements at 10 kbar of the brucite-periclase equilibrium with a Na/(Na + K) ratio
of 0.5 and of the saturation temperature for Na/(Na + K) of 0.35 and 0.50. At that pressure the brucite-periclase curves reach
a lowest x
H2O of 0.45 and a temperature of 587 °C before salt saturation occurs, values considerably lower than in either binary. This
double-salt eutectic effect may have a significant application to natural polyionic hypersaline solutions in the deep crust
and upper mantle in that higher solute concentrations and very low H2O activities may be realized in complex solutions before salt saturation occurs. Concentrated salt solutions seem, from this
standpoint, and also because of high mechanical mobility and alkali-exchanging potential, feasible as metasomatic fluids for
a variety of deep-crust and upper mantle processes.
Received: 9 August 1996 / Accepted: 15 November 1996 相似文献
8.
Stability and chemical composition of pargasitic amphibole in MORB pyrolite under upper mantle conditions 总被引:18,自引:1,他引:17
The stability field of pargasitic amphibole in a model mantle composition (MORB pyrolite) has been experimentally determined
for a fixed water content. A solidus for a pargasite-bearing lherzolite has been defined at pressures below the limit of amphibole
stability of 30 kbar at T = 925 °C. The maximum temperature for pargasitic amphibole in MORB pyrolite occurs at 1075 °C between P = 18 and 25 kbar. This maximum lies between that determined for a fertile peridotite composition (Hawaiian pyrolite) and
a depleted peridotite composition (Tinaquillo lherzolite). A comparison of the new results with those from earlier studies
suggests that the stability for a particular bulk H2O content is mostly controlled by alkali content of the lherzolite composition. The systematic compositional variation of
pargasitic amphibole as a function of pressure and temperature can be represented as an increase of the richterite component
with increase in both pressure and temperature. For a given pressure the tschermakite component increases with increasing
temperature. The compositions of coexisting clinopyroxenes also show a systematic variation with pressure and temperature.
The phase relationships in MORB pyrolite combined with the modal abundance of coexisting phases show that the breakdown reactions
of pargasitic amphibole occur continuously throughout the subsolidus region studied. The temperature stability limit of pargasitic
amphibole coincides with the water-undersaturated solidus (amphibole-dehydration solidus) at pressures below 30 kbar. The
experimental results are applicable to pargasitic amphibole-bearing natural peridotites. Cooling and decompression paths and
heating events observed in natural peridotites can be interpreted from changes in the composition of pargasitic amphibole.
The data are also applicable to a model for peridotite melting and hydration process in the subduction environment.
Received: 27 October 1997 / Accepted: 6 November 1998 相似文献
9.
E. Schmädicke M. Okrusch W. Schubert B. Elwart U. Görke 《Mineralogy and Petrology》2001,72(1-3):77-111
Summary In the Odenwald Crystalline Complex, calc-silicate rocks are concentrated at the margins of the marble layer of Auerbach.
They were presumably formed by metasomatic exchange between the calcite marble and the neighbouring granodioritic and quartz-dioritic
intrusives. The investigated samples contain the characteristic mineral assemblages: garnet + clinopyroxene + epidote/clinozoisite + calcite + quartz ± titanite
(1) and wollastonite + clinopyroxene + garnet + calcite ± quartz ± epidote/clinozoisite ± titanite (2). Microprobe analyses
revealed the following compositional ranges: garnet grs40–98adr2–55alm<5.5sps<5.5pyp<1; clinopyroxene di46–88hed9–47joh0–5cats0–6; epidote/clinozoisite ps20–80. Different phase diagrams were calculated in the system CaO-MgO-Al2O3-TiO2-SiO2-CO2-H2O (CMATSCH) to decipher the P-T-XCO2 parameters of metamorphism: isobaric T-XCO2 sections and a P-T projection with mixed volatiles. The phase diagrams illustrate that the observed assemblages can only
form in the presence of an H2O-rich volatile phase. The assemblages are stable over a large range of temperatures, from 580 °C to < 400 °C (at 4 kbar)
and at XCO2 values of less than 0.055 (at 4 kbar). Higher temperatures can be inferred from reaction textures which indicate that garnet + plagioclase
(T > 580 °C, at 4 kbar) and wollastonite + plagioclase (T > 660 °C, at 4 kbar) coexisted during an early metamorphic stage. A minimum pressure of 3.5 kbar can be inferred for the
early high-temperature stage. Furthermore, on the basis of the calculated phase diagrams, combined with modal abundances in
thin sections, it is possible to evaluate fluid behaviour; in the investigated specimens, infiltration of fluids from an external
reservoir occurred. A minimum fluid:rock ratio of 3.6:1 can be estimated.
Received July 29, 1999; accepted March 28, 2000 相似文献
Zusammenfassung Phasenbeziehungen in Kalksilikat-Paragenesen des Marmorzuges von Auerbach, Odenwald-Kristallin-Komplex, Deutschland Im kristallinen Odenwald konzentrieren sich kalksilikatische Gesteine in den Randbereichen des Marmorzuges von Auerbach. Die kalksilikatischen Partien wurden vermutlich duch metasomatischen Austausch zwischen dem Calcit-Marmor und benachbarten Granodioriten und Quarzdioriten gebildet. Die untersuchten Proben enthalten die charakteristischen Mineralparagenesen: Granat + Klinopyroxen + Epidot/Klinozoisit + Calcit + Quarz + Titanit (1) und Wollastonit + Klinopyroxen + Granat + Calcit ± Quarz ± Epidot/Klinozoisit ± Titanit (2). Mikrosondenanalysen ergaben folgendes Zusammensetzungsspektrum: Granat grs40–98adr2–55alm<5.5sps<5.5pyp<1; Klinopyroxen di46–88hed9–47joh0–5cats0–6s; Epidot/Klinozoisit ps20–80. Verschiedene Phasendiagramme wurden für das Modellsystem CaO-MgO-Al2O3-TiO2-SiO2-CO2-H2O (CMATSCH) berechnet, um die P-T-XCO2-Parameter der Metamorphose einzugrenzen: Isobare T-XCO2-Schnitte und eine P-T-Projektion mit einer Fluid-Mischphase. Die Phasendiagramme verdeutlichen, da? die beobachteten Paragenesen nur in Anwesenheit eines H2O-reichen Fluids gebildet werden k?nnen. Die Paragenesen sind über einen gro?en Temperaturbereich hinweg stabil, von 580 °C bis < 400 °C (bei 4 kbar) und bei XCO2-Gehalten von < 0.055 (bei 4 kbar). Ursprünglich h?here Temperaturen k?nnen anhand von Reaktions-Texturen rekonstruiert werden, die zeigen, da? Granat + Plagioklas (T > 580 °C, bei 4 kbar) und Wollastonit + Plagioklas (T > 660 °C, bei 4 kbar) w?hrend eines früheren Metamorphosestadiums koexistierten. Ein Minimaldruck von 3.5 kbar kann für dieses frühe Hochtemperatur-Stadium abgeleitet werden. Mit Hilfe der berechneten Phasendiagramme, in Kombination mit beobachteten Modalgehalten, ist es m?glich, das Verhalten der fluiden Phase abzusch?tzen. Die untersuchten Gesteine implizieren Fluidinfiltration, wobei ein minimales Verh?ltnis Fluid:Gestein von 3.6:1 abgesch?tzt werden kann.
Received July 29, 1999; accepted March 28, 2000 相似文献
10.
The diffusivity of water has been investigated for a haplogranitic melt of anhydrous composition Qz28Ab38Or34 (in wt %) at temperatures of 800–1200°C and at pressures of 0.5–5.0 kbar using the diffusion couple technique. Water contents
of the starting glass pairs varied between 0 and 9 wt %. Concentration-distance profiles for the different water species (molecular
water and hydroxyl groups) were determined by near-infrared microspectroscopy. Because the water speciation of the melt is
not quenchable (Nowak 1995; Nowak and Behrens 1995; Shen and Keppler 1995), the diffusivities of the individual species can
not be evaluated directly from these profiles. Therefore, apparent chemical diffusion coefficients of water (D
water) were determined from the total water profiles using a modified Boltzmann-Matano analysis. The diffusivity of water increases
linearly with water content <3 wt % but exponentially at higher water contents. The activation energy decreases from 64 ± 10 kJ/mole
for 0.5 wt % water to 46 ± 5 kJ/mole for 4 wt % water but remains constant at higher water contents. A small but systematic
decrease of D
water with pressure indicates an average activation volume of about 9 cm3/mole. The diffusivity (in cm2/s) can be calculated for given water content (in wt %), T (in K) and P (in kbar) by
in the ranges 1073 K ≤ T ≤ 1473 K; 0.5 kbar ≤ P≤ 5␣kbar; 0.5 wt % ≤ C
water ≤ 6 wt %. The absence of alkali concentration gradients in the glasses after the experiments shows that interdiffusion of
alkali and H+ or H3O+ gives no contribution to the transport of water in aluminosilicate melts. The H/D interdiffusion coefficients obtained at
800°C and 5 kbar using glass pieces with almost the same molar content of either water or deuterium oxide are almost identical
to the chemical diffusivities of water. This indicates that protons are transported by the neutral component H2O under these conditions.
Received: 26 March 1996 / Accepted: 23 August 1996 相似文献
11.
Hans Keppler 《Contributions to Mineralogy and Petrology》1989,102(3):321-327
The solidus temperatures in the haplogranite-system NaAlSi3O8-KAlSi3O8-SiO2-H2O-CO2 have been determined up to 15 kbar for a constant molar ratio of sodium to potassium of 11 and for fluid compositions ranging from pure water to pure carbon dioxide. The data for the water-saturated solidus are virtually identical with those of previous studies. At constant pressure, the solidus curve as a function of the fluid phase composition exhibits a point of inflection in the range of the water-rich compositions. This phenomenon is attributed to chemical interactions between the CO2 and the H2O in the silicate melt. The point of inflection disappears if the CO2 in the gas phase is replaced by molecular nitrogen. The CO2-saturated solidi have been measured at 2 and 5 kbars. The data at 5 kbar indicate a melting point depression in the order of 40° C compared to the dry solidus of Huang and Wyllie (1975). The experimental data can be used to estimate the melting temperatures of common quartz and feldspar bearing crustal rocks under the conditions of granulite facies metamorphism. Since for most fluid phase compositions, the solidus curves are very steep in the P, T-diagram, the beginning of melting is nearly exclusively determined by the fluid composition and almost independent of pressure between about 2 and more than 10 kbar. Therefore, the onset of partial melting in quartz and feldspar containing rocks under granulite facies conditions can be used to estimate the composition of a coexisting H2O-CO2 fluid phase if geothermometric data are available. The temperature range between the beginning of granulite facies metamorphism and the initiation of melting expands with increasing carbon dioxide content in the H2O-CO2 fluid phase. At a CO2 molar fraction of 0.9, this range extends from about 600° C to 900° C and is almost independent of pressure. 相似文献
12.
The Archean Shawmere anorthosite lies within the granulite facies portion of the Kapuskasing Structural Zone (KSZ), Ontario,
and is crosscut by numerous linear alteration veins containing calcite + quartz ± dolomite ± zoisite ± clinozoisite ± margarite ±paragonite ± chlorite.
These veins roughly parallel the trend of the Ivanhoe Lake Cataclastic Zone. Equilibria involving clinozoisite + margarite + quartz ± calcite
± plagioclase show that the vein minerals were stable at T < 600 °C, XCO2 < 0.4 at P ≈ 6 kbar. The stabilities of margarite and paragonite in equilibrium with quartz are also consistent with T < 600 °C and XCO2 < 0.4 at 6 kbar. Additional assemblages consisting of calcite + clinochlore + quartz + talc + margarite indicate T < 500 °C with XCO2 > 0.9. Thus, vein formation, while clearly retrograde, spanned a range of temperatures, and fluid compositions evolved from
H2O-rich to CO2-rich. The calcite in the retrograde veins has δ18O values that range from 8.4 to 11.2‰ (average = +9.7 ± 0.9‰) and δ13C values that range from −3.9 to −1.6‰ (average = −3.1 ± 0.6‰). These values indicate that the fluids from which calcite precipitated
underwent extensive exchange with the anorthosite and other crustal lithologies. The fluids may have been initially derived
either from devolatilization of metamorphic rocks or crystallization of igneous rocks in the adjacent Abitibi subprovince.
Vein quartz contains CO2-rich fluid inclusions (final melting T = −57.0 to −58.7 °C) that range in size from 5 to 17 μm. Measured homogenization temperatures (T h) range from −44.0 to 14.5 °C, however for most inclusions (46 of S1), T h = −44.0 to −21.1 °C (ρCO2 ≈ 1.13 to 1.05 g/cm3). At 400 to 600 °C, these densities correspond to pressures of 3.5 to 7 kbar, which is the best estimate of pressures of
vein formation. It has been argued that some high density CO2-rich fluid inclusions found in the KSZ were formed during peak metamorphism and thus document the presence of a CO2-rich fluid during peak granulite facies metamorphism (Rudnick et al. 1984). The association of high density CO2-rich fluid inclusions with clearly retrograde veins documents the formation of similar composition and density inclusions
after the peak of metamorphism. Thus, the coincidence of entrapment pressures calculated from fluid inclusion density measurements
with peak metamorphic pressures alone should not be considered strong evidence for peak metamorphic inclusion entrapment.
All fluid inclusion results are consistent with an initially semi-isobaric retrograde P–T path.
Received: 2 April 1996 / Accepted: 15 November 1996 相似文献
13.
Phase relations of a phonolite (K1) and a tephri-phonolite (K2) from the Upper Miocene lavas in the Southeast Province of the Kerguelen Archipelago have been investigated in the P/T range 100–500 MPa and 700–900 °C at two fO2 conditions (~ NNO and ~ NNO+2.3) to clarify the differentiation and pre-eruptive conditions of these magmas. Crystallization experiments were performed in cold seal pressure vessels (CSPV) and internally heated pressure vessels (IHPV) at various XH2O, under reducing (log fO2 ~ NNO) and oxidizing conditions (log fO2 ~ NNO+2.3). Under reducing conditions, the resulting phase assemblage for K1 was: titanomagnetite, nepheline, alkali feldspar, clinopyroxene and biotite; under oxidizing conditions, the assemblage was: magnetite, plagioclase, alkali feldspar, nepheline, titanite (minerals given in the order of appearance with decreasing T at 200 MPa for 4 wt% water in the melt). It is emphasized that an effect of fO2 on the phase stability of feldspars and feldspathoides was observed. Comparison of the natural and experimental phase assemblages shows that the pre-eruptive conditions for K1 must have been in the log fO2 range NNO+1–NNO+2, at pressures above 200–250 MPa. Assuming a temperature of 800 °C, the water content of the melt is constrained to be between 4 and 6 wt% H2O. The pre-eruptive fO2 conditions for the less evolved sample K2 are more oxidizing with log fO2 close to NNO+2.3. The experimental results show that the enrichment of alkalis in residual melts during differentiation of tephri-phonolites is enhanced at high fO2.Editorial responsibility: J. Hoefs 相似文献
14.
Wilhelm Johannes 《Contributions to Mineralogy and Petrology》1984,86(3):264-273
The beginning of melting in the system Qz-Or-Ab-An-H2 O was experimentally reversed in the pressure range
kbar using starting materials made up of mixtures of quartz and synthetic feldspars. With increasing pressure the melting
temperature decreases from 690° C at 2 kbar to 630° C at 17 kbar in the An-free alkalifeldspar granite system Qz-Or-Ab-H2O. In the granite system Qz-Or-Ab-An-H2O the increase of the solidus temperature with increasing An-content is only very small. In comparison to the alkalifeldspar
granite system the solidus temperature increases by 3° C (7° C) if albite is replaced by plagioclase An 20 (An 40). The difference
between the solidus temperatures of the alkalifeldspar granite system and of quartz — anorthite — sanidine assemblages (system
Qz-Or-An-H2O) is approximately 50° C.
With increasing water pressures plagioclase and plagioclase-alkalifeldspar assemblages become unstable and are replaced by
zoisite+kyanite+quartz and zoisite+muscovite-paragonitess +quartz, respectively. The pressure stability limits of these assemblages are found to lie between 6 and 16 kbar at 600°
C. At high water pressures (10–18 kbar) zoisite — muscovite — quartz assemblages are stable up to 700 and 720° C. The solidus
curve of this assemblage is 10–20° C above the beginning of melting of sanidine — zoisite — muscovite — quartz mixtures.
The amount of water necessary to produce sufficient amounts of melt to change a metamorphic rock into a magmatic looking one
is only small. In case of layered migmatites it is shown that 1 % of water (or even less) is sufficient to transform portions
of a gneiss into (magmatic looking) leucosomes. High grade metamorphic rocks were probably relatively dry, and anatectic magmas
of granitic or granodioritic composition are usually not saturated with water. 相似文献
15.
Clinopyroxene geobarometry of magmatic rocks. Part 2. Structural geobarometers for basic to acid, tholeiitic and mildly alkaline magmatic systems 总被引:12,自引:0,他引:12
Paolo Nimis 《Contributions to Mineralogy and Petrology》1999,135(1):62-74
The crystal structures of 212 experimentally synthesized, igneous clinopyroxenes were modeled from electronprobe chemical
data. The coexisting melts span a wide range of petrologically relevant, dry and hydrous compositions, characterized by variable
enrichment in silica and alkalis. Experimental conditions pertain to Earth's crust and uppermost mantle (P = 0–24 kbar; garnet absent) and a variety of f
O2 values (from CCO-buffered to air-buffered) and mineral assemblages (Cpx ± Opx ± Pig ± Ol ± Plag ± Spl ± Mt ± Amp ± Ilm).
Unit-cell volume (Vcell) versus M1-polyhedron volume (VM1) relations were investigated over a range of pressures and temperatures using data derived from structure modeling and corrected
for thermal expansivity and compressibility. The relationships between pressure and clinopyroxene structural parameters were
found to be dependent on the nature of the coexisting melt. To reduce compositional effects, only clinopyroxenes belonging
to mildly alkaline (MA) and tholeiitic (TH) series were considered. Pressure was modeled as a linear function of Vcell, VM1, and Mg/(Mg + Fe2+)Cpx ratio. A calibration based on the whole data set (MA + TH) reproduced the experimental pressures within 1.4 kbar at the 1-σ level. The maximum residuals were 3.5 kbar and 3.9 kbar
for MA- and TH-clinopyroxenes, respectively. Better statistics were obtained by considering MA- and TH-clinopyroxenes separately.
A calibration based on the 69 MA-clinopyroxenes reproduced the experimental pressures within 1.1 kbar (1σ) and with a maximum
residual of 2.7 kbar. A calibration based on the 143 TH-clinopyroxenes reproduced the experimental pressures within 1.0 kbar
(1σ) and with a maximum residual of 3.4 kbar. When these geobarometers are applied to natural samples for which P is unknown, the correction for compressibility is necessarily made through a trial-and-error procedure. This expedient propagates
an additional error that increases the above uncertainties and residuals by a factor of about 2. Applications to natural,
igneous rocks for which the pressures of crystallization could be constrained based on experimental, petrological or geological
evidence yielded pressure estimates that reproduced the expected values to within ca. 2 kbar. Compared to the MA-formulation,
the TH-formulation appears to be less robust to variations in magma composition. When applied to high-pressure (>10 kbar)
clinopyroxenes synthesized from very low Na (Na2O < 1.5%) melts, the latter geobarometer can underestimate P by as much as 6 kbar. Calculation of P through the present geobarometers requires clinopyroxene major-element composition and an independent, accurate estimate
of crystallization T. Underestimating T by 20 °C propagates into a 1-kbar increase in calculated P. The proposed geobarometers are incorporated in the CpxBar software program, which is designed to retrieve the pressure of
crystallization from a clinopyroxene chemical analysis.
Received: 11 June 1998 / Accepted: 12 November 1998 相似文献
16.
An experimental investigation on the P-T stability of Mg-staurolite in the system MgO-Al2O3-SiO2-H2O
Thomas Fockenberg 《Contributions to Mineralogy and Petrology》1998,130(2):187-198
The pressure-temperature stability field of Mg-staurolite, ideally Mg4Al18Si8O46(OH)2, was bracketed for six possible breakdown reactions in the system MgO-Al2O3-SiO2-H2O (MASH). Mg-staurolite is stable at water pressures between 12 and 66 kbar and temperatures of 608–918 °C, requiring linear
geotherms between 3 and 18 °C/km. This phase occurs in rocks that were metamorphosed at high-pressure, low-temperature conditions,
e.g. in subducted crustal material, provided they are of appropriate chemical composition. Mg-staurolite is formed from the
assemblage chlorite + kyanite + corundum at pressures <24 kbar, whereas at pressures up to 27 kbar staurolite becomes stable
by the breakdown of the assemblage Mg-chloritoid + kyanite + corundum. Beyond 27 kbar the reaction Mg-chloritoid + kyanite + diaspore
= Mg-staurolite + vapour limits the staurolite field on its low-temperature side. The upper pressure limit of Mg-staurolite
is marked by alternative assemblages containing pyrope + topaz-OH with either corundum or diaspore. At higher temperatures
Mg-staurolite breaks down by complete dehydration to pyrope + kyanite + corundum and at pressures below 14 kbar to enstatite +
kyanite + corundum. The reaction curve Mg-staurolite = talc + kyanite + corundum marks the low-pressure stability of staurolite
at 12 kbar. Mg-staurolite does not coexist with quartz because alternative assemblages such as chlorite-kyanite, enstatite-kyanite,
talc-kyanite, pyrope-kyanite, and MgMgAl-pumpellyite-kyanite are stable over the entire field of Mg-staurolite.
Received: 16 April 1997 / Accepted: 24 September 1997 相似文献
17.
Olivine and augite minette powders have been equilibrated from one bar to nearly 2.0 kbar (water-saturated), and from 900
to 1300° C, and then quenched rapidly, at oxygen fugacities controlled between the nickel-nickel oxide (NNO) and hematite-magnetite
(HM) oxygen buffers. The liquidus of both samples is suppressed ∼100° C at water-saturated conditions and 1500 bar. Both lavas
contained between 3 and 4 wt% water at the stage of phenocryst precipitation. The partitioning of ferric and ferrous iron
between phlogopite and liquid has been determined on eight samples across 3 log f O2 units; when these determinations are combined with previous studies, Fe2O3/(Σ FeO total) of Mg-rich biotite can be calculated knowing log f
O2, T, and X
Fe. Thermodynamic modelling of biotite-liquid equilibria results in two expressions for calculating activity coefficients (γ)
for annite and phlogopite in natural biotites. Based on the partitioning of BaO and TiO2 between biotite and liquid, we have formulated a thermometer and barometer. Over the range of 400° C, TiO2 partitioning between phlogopite and liquid is a function of temperature (±50° C), and is insensitive to pressure and H2O and O2 activities. BaO partitioning between phlogopite and liquid is a function of both temperature and pressure (±4 kbar), the
latter being most important. Applying the TiO2 and BaO partitioning expressions to lamprophyre and lamproite suites shows that Mexican minettes equilibrated at low pressures
(5 to 15 kbar;±4 kbar) and temperatures (1090 to 1160° C; ±50° C), while Australian lamproites equilibrated at higher P (up to 30 kbar; ±4 kbar) and T (1125 to 1400° C; ±50° C). Experimental glass compositions and phenocryst fractionation calculations, together with the BaO-
and TiO2- based pressure calculations indicate that felsic minettes from the Mexican suite of lavas can be generated by simple fractionation
of a more mafic parent minette at mid to lower crustal pressures.
Received: 1 August 1994/Accepted: 30 June 1995 相似文献
18.
The beginning of dehydration melting in the tonalite system (biotite-plagioclase-quartz) is investigated in the pressure
range of 2–12 kbar. A special method consisting of surrounding a crystal of natural plagioclase (An45) with a biotite-quartz mixture, and observing reactions at the plagioclase margin was employed for precise determination
of the solidus for dehydration melting. The beginning of dehydration melting was worked out at 5 kbar for a range of compositions
of biotite varying from iron-free phlogopite to iron-rich Ann70, with and without titanium, fluorine and extra aluminium in the biotite. The dehydration melting of phlogopite + plagioclase
(An45) + quartz begins between 750 and 770°C at pressures of 2 and 5 kbar, at approximately 740°C at 8 kbar and between 700 and
730°C at 10 kbar. At 12 kbar, the first melts are observed at temperatures as low as 700°C. The data indicate an almost vertical
dehydration melting solidus curve at low pressures which bends backward to lower temperatures at higher pressures (> 5 kbar).
The new phases observed at pressures ≤ 10 kbar are melt + enstatite + clinopyroxene + potassium feldspar ± amphibole. In addition
to these, zoisite was also observed at 12 kbar. With increasing temperature, phlogopite becomes enriched in aluminium and
deficient in potassium. Substitution of octahedral magnesium by aluminium and titanium in the phlogopite, as well as substitution
of hydroxyl by fluorine, have little effect on the beginning of dehydration melting temperatures in this system. The dehydration
melting of biotite (Ann50) + plagioclase (An45) + quartz begins 50°C below that of phlogopite bearing starting composition. Solid reaction products are orthopyroxene +
clinopyroxene + potassium feldspar ± amphibole. Epidote was also observed above 8 kbar, and garnet at 12 kbar (750°C). The
experiments on the iron-bearing system performed at ≤ 5 kbar were buffered with NiNiO. The f
O
2 in high pressure runs lies close to CoCoO. With the substitution of octahedral magnesium and iron by aluminium and titanium,
and replacement of hydroxyl by fluorine in biotite, the beginning of dehydration melting temperatures in this system increase
up to 780°C at 5 kbar, which is 70°C above the beginning of dehydration melting of the assemblage containing biotite (Ann50) of ideal composition. The dehydration melting at 5 kbar in the more iron-rich Ann70-bearing starting composition begins at 730°C, and in the Ann25-bearing assemblage at 710°C. This indicates that quartz-biotite-plagioclase assemblages with intermediate compositions of
biotite (Ann25 and Ann50) melt at lower temperatures as compared to those containing Fe-richer or Mg-richer biotites. This study shows that the dehydration
melting of tonalites may begin at considerably lower temperatures than previously thought, especially at high pressures (>5
kbar).
Received: 27 December 1995 / Accepted: 7 May 1996 相似文献
19.
W. Johannes 《Contributions to Mineralogy and Petrology》1980,72(1):73-80
Time studies were performed in the quinary system Qz-Or-Ab-An-H2O at
kbars and T=665 ° and 660 ° C. Starting material was a mixture of quartz, alkali feldspar Or80 and plagioclase An31. The compositions of plagioclases of run products were determined and compared with the plagioclase of stable solidus conditions.The solidus of the granite system was fixed at P
HäO=5 kbars using various plagioclase — and appropriate alkali feldspar — compositions besides quartz in the starting mixture (Fig. 1).The results of time studies (Table 3 and Fig. 3) reveal metastable melting in the granite system Qz-Or-Ab-An-H2O. Plagioclase melts almost stoichiometrically. The new plagioclase compositions formed during melting of cotectic compositions approach the theoretically expected stable plagioclase compositions only extremely slowly. An extrapolation of the data achieved in run times of 5–1,500 h indicates attainment of equilibrium after 1014 years. Metastable melting of granitic compositions is not only considered as an experimental problem but also as a rock forming process in nature. 相似文献
20.
The stability of merwinite (Mw) and its equivalent assemblages, akermanite (Ak)+calcite (Cc), diopside (Di)+calcite, and wollastonite (Wo)+monticellite (Mc)+calcite was determined at T=500–900° C and P
f=0.5–2.0 kbar under H2O–CO2 fluid conditions with X
CO
2=0.5, 0.1, 0.05, and 0.02. Merwinite is stable at P
f=0.5 kbar with T>700° C and X
CO
2<0.1. At P
f=2.0 kbar, the assemblage Di+Cc replaces merwinite at all T and X
CO
2 conditions. At intermediate P
f=1 kbar, the assemblage Ak+Cc is stable above 707° C and Wo+Mc+Cc is stable below 707° C. The univariant curve for the reaction Di+Cc=Wo+Mc+CO2 is almost parallel to the T axis and shifts to low P
f with increasing X
CO
2, with the assemblage Di+Cc on the high-P
f side. The implications of the experimental results in regard to contact metamorphism of limestone are discussed using the aureole at Crestmore, California as an example. 相似文献