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1.
B. C. Schmidt François Holtz Bruno Scaillet Michel Pichavant 《Contributions to Mineralogy and Petrology》1997,126(4):386-400
Solidus temperatures of quartz–alkali feldspar assemblages in the haplogranite system (Qz-Ab-Or) and subsystems in the presence
of H2O-H2 fluids have been determined at 1, 2, 5 and 8 kbar vapour pressure to constrain the effects of redox conditions on phase relations
in quartzofeldspathic assemblages. The hydrogen fugacity (f
H2) in the fluid phase has been controlled using the Shaw membrane technique for moderately reducing conditions (f
H2 < 60 bars) at 1 and 2 kbar total pressure. Solid oxygen buffer assemblages in double capsule experiments have been used to
obtain more reducing conditions at 1 and 2 kbar and for all investigations at 5 and 8 kbar. The systems Qz-Or-H2O-H2 and Qz-Ab-H2O-H2 have only been investigated at moderately reducing conditions (1 and 5 kbar) and the system Qz-Ab-Or-H2O-H2 has been investigated at redox conditions down to IW (1 to 8 kbar). The results obtained for the water saturated solidi are
in good agreement with those of previous studies. At a given pressure, the solidus temperature is found to be constant (within
the experimental precision of ± 5°C) in the f
H2 range of 0–75 bars. At higher f
H2, generated by the oxygen buffers FeO-Fe3O4 (WM) and Fe-FeO (IW), the solidus temperatures increase with increasing H2 content in the vapour phase. The solidus curves obtained at 2 and 5 kbar have similar shapes to those determined for the
same quartz - alkali feldspar assemblages with H2O-CO2- or H2O-N2-bearing systems. This suggests that H2 has the behaviour of an inert diluent of the fluid phase and that H2 solubility in aluminosilicate melts is very low. The application of the results to geological relevant conditions [HM (hematite-magnetite) > f
O2 > WM] shows that increasing f
H2 produces a slight increase of the solidus temperatures (up to 30 °C) of quartz–alkali feldspar assemblages in the presence
of H2O-H2 fluids between 1 and 5 kbar total pressure.
Received: 4 March 1996 / Accepted: 22 August 1996 相似文献
2.
Differentiation and crystallization conditions of basalts from the Kerguelen large igneous province: an experimental study 总被引:2,自引:2,他引:0
Marcus Freise Francois Holtz Marcus Nowak James S. Scoates Holger Strauss 《Contributions to Mineralogy and Petrology》2009,158(4):505-527
Phase relations of basalts from the Kerguelen large igneous province have been investigated experimentally to understand the
effect of temperature, fO2, and fugacity of volatiles (e.g., H2O and CO2) on the differentiation path of LIP basalts. The starting rock samples were a tholeiitic basalt from the Northern Kerguelen
Plateau (ODP Leg 183 Site 1140) and mildly alkalic basalt evolved from the Kerguelen Archipelago (Mt. Crozier on the Courbet
Peninsula), representing different differentiation stages of basalts related to the Kerguelen mantle plume. The influence
of temperature, water and oxygen fugacity on phase stability and composition was investigated at 500 MPa and all experiments
were fluid-saturated. Crystallization experiments were performed at temperatures between 900 and 1,160°C under oxidizing (log
fO2 ~ ΔQFM + 4) and reducing conditions (log fO2 ~ QFM) in an internally heated gas-pressure vessel equipped with a rapid quench device and a Pt-Membrane for monitoring the
fH2. In all experiments, a significant influence of the fO2 on the composition and stability of the Mg/Fe-bearing mineral phases could be observed. Under reducing conditions, the residual
melts follow a tholeiitic differentiation trend. In contrast, melts have high Mg# [Mg2+/(Mg2+ + Fe2+)] and follow a calk-alkalic differentiation trend at oxidizing conditions. The comparison of the natural phenocryst assemblages
with the experimental products allows us to constrain the differentiation and pre-eruptive conditions of these magmas. The
pre-eruptive temperature of the alkalic basalt was about 950–1,050°C. The water content of the melt was below 2.5 wt% H2O and strongly oxidizing conditions (log fO2 ~ ΔQFM + 2) were prevailing in the magma chamber prior to eruption. The temperature of the tholeiitic melt was above 1,060°C,
with a water content below 2 wt% H2O and a log fO2 ~ ΔQFM + 1. Early fractionation of clinopyroxene is a crucial step resulting in the generation of silica-poor and alkali-rich
residual melts (e.g., alkali basalt). The enrichment of alkalis in residual melts is enhanced at high fO2 and low aH2O. 相似文献
3.
N. W. A. Odling D. H. Green B. Harte 《Contributions to Mineralogy and Petrology》1997,129(2-3):209-221
An experimental method of melt inclusion synthesis within olivine crystals has been developed to determine the composition
of the melt present in a partially molten peridotite assemblage. Trace element doped peridotite was equilibrated with 5 wt%
of a C-O-H volatile source at 20 kbar/1175 °C in a piston-cylinder apparatus under buffered oxygen and sulphur fugacity conditions
[log(f
O2) ∼ IW +1 log unit, log (f
S2) ∼ Fe/FeS > +1 log unit]. A single crystal of olivine, which had been cut to a disc shape, was included in the sample capsule.
At run conditions the peridotite charge formed olivine, orthopyroxene, clinopyroxene, Fe-Ni sulphide and a volatile-bearing
melt. The melt phase is preserved as homogeneous glass inclusions up to 50 μm in size, trapped in situ in the olivine disc.
The major element composition of the glass inclusions showed them to be of broadly basaltic character, but with a low Mg/(Mg + ΣFe),
which is associated with precipitation of olivine from the melt inclusion onto the walls of the olivine disc during quenching.
Thus the equilibrium melt composition has been calculated from the glass inclusion composition by addition of olivine component
using the Fe/Mg exchange coefficient of Roeder and Emslie (1970); the desired Mg/(Mg + ΣFe) being determined from the composition
of olivine formed at run conditions in the peridotite section of the charge. The melt composition obtained is close to the
trend for dry melting established by Falloon and Green (1988), and it is evident that although the reduced volatiles in this
case have induced a liquidus depression of some 250 °C, there has been only a small shift in melt composition. Trace element,
carbon and hydrogen contents of thirteen melt inclusions have been determined by secondary ion mass spectrometry (SIMS). The
trace element signature is consistent with ∼29% melting in equilibrium with a lherzolitic assemblage. The equilibrium melt
has a C/H of 0.48 by weight. Carbon solubility in partial melts is thus significant under reducing conditions in the presence
of dissolved “water components” and establishes a major melt fluxing role for carbon in the upper mantle. The ubiquitous presence
of carbon and hydrogen in basaltic magmas underscores the importance of determining both the position of vapour-present solidi
and the composition of melts generated, when developing petrogenetic models.
Received: 1 July 1996 / Accepted: 25 June 1997 相似文献
4.
Experimental comparison of trace element partitioning between clinopyroxene and melt in carbonate and silicate systems, and implications for mantle metasomatism 总被引:13,自引:2,他引:11
Experiments in the systems diopside-albite (Di-Ab) and diopside-albite-dolomite (Di-Ab-Dmt), doped with a wide range of trace
elements, have been used to characterise the difference between clinopyroxene-silicate melt and clinopyroxene-carbonate melt
partitioning. Experiments in Di-Ab-Dmt yielded clinopyroxene and olivine in equilibrium with CO2-saturated dolomitic carbonate melt at 3 GPa, 1375 °C. The experiments in Di-Ab were designed to bracket those conditions
(3 GPa, 1640 °C and 0.8 GPa, 1375 °C), and so minimise the contribution of differential temperature and pressure to partitioning.
Partition coefficients, determined by SIMS analysis of run products, differ markedly for some elements between Di-Ab and Di-Ab-Dmt
systems. Notably, in the carbonate system clinopyroxene-melt partition coefficients for Si, Al, Ga, heavy REE, Ti and Zr are
higher by factors of 5 to 200 than in the silicate system. Conversely, partition coefficients for Nb, light REE, alkali metals
and alkaline earths show much less fractionation (<3). The observed differences compare quantitatively with experimental data
on partitioning between immiscible carbonate and silicate melts, indicating that changes in melt chemistry provide the dominant
control on variation in partition coefficients in this case. The importance of melt chemistry in controlling several aspects
of element partitioning is discussed in light of the energetics of the partitioning process. The compositions of clinopyroxene
and carbonate melt in our experiments closely match those of near-solidus melts and crystals in CMAS-CO2 at 3 GPa, suggesting that our partition coefficients have direct relevance to melting of carbonated mantle lherzolite. Melts
so produced will be characterised by elevated incompatible trace element concentrations, due to the low degrees of melting
involved, but marked depletions of Ti and Zr, and fractionated REE patterns. These are common features of natural carbonatites.
The different behaviour of trace elements in carbonate and silicate systems will lead to contrasted styles of trace element
metasomatism in the mantle.
Received: 15 July 1999 / Accepted: 18 February 2000 相似文献
5.
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
6.
In order to develop models simulating the crystallization of Fe-Ti oxides in natural lavas, we have processed published experimental
data on magnetite-melt and ilmenite-melt equilibria. These data include 62 Mt-melt and 75 Ilm-melt pairs at temperatures 1040–1150 °C, oxygen fugacities from IW to NNO+2, and bulk compositions ranging from ferrobasalts to andesites and dacites. Five major cations (Fe3+, Fe2+, Ti4+, Mg2+ and Al3+) were considered for the purpose of describing Fe-Ti oxide saturation as a function of melt composition, temperature and
oxygen fugacity at 1 atmosphere pressure. The empirically calibrated mineral-melt expression based on multiple linear regressions
is: ln D
i
= a/T + blog f
O2 + c + d
1
X
Na + d
2
X
K + d
3
X
P, where D
i
represents molar distribution coefficients of the given cations between Mt/Ilm and melt; X
Na, X
K, and X
P are the molar fractions of Na, K, and P in the melt. The empirically calibrated Mt-melt and Ilm-melt equilibria equations allowed us to develop two models for calculating crystallization temperatures of the Fe-Ti oxides
in the melts with an accuracy of 10–15 °C, and compositions with an accuracy of 0.5–2 mol%. These models have been integrated
into the COMAGMAT-3.5 program, improving our ability to study numerically the effects of temperature and oxygen fugacity on
the stability and phase equilibria of Fe-Ti oxides. Application of this approach to the tholeiitic series of Chazhma Sill
from Eastern Kamchatka (Russia) indicates oxygen fugacity conditions near NNO + 0.5. Numerical simulation of fractional crystallization of an iron-enriched basaltic andesite parent at these oxidizing
conditions accurately reproduces the FeO-SiO2 relations observed in the Chazhma suite.
Received: 3 March 1998 / Accepted: 7 August 1998 相似文献
7.
Jasper Berndt François Holtz Jürgen Koepke 《Contributions to Mineralogy and Petrology》2001,140(4):469-486
Phase relations of three samples of the Laacher See Tephra (LST) have been determined experimentally as a function of temperature
(760 to 880 °C), pressure (200, 300 and 400 MPa), water content of the melt and oxygen fugacity (ƒO2). The crystallization experiments were carried out at ƒO2=NNO buffer and at NNO=+ 2.3 log units. The melt water contents varied between 6 and more than 8 wt% H2O, corresponding to water-undersaturated and water saturated conditions respectively. The synthetic products are compared
to the natural phases to constrain pre-eruptive conditions in the Laacher See magma chamber. The major phases occurring in
the LST have been reproduced. The stability of hauyne is favoured at high ƒO2 (≈NNO + 2.3). The CaO contents in melt and plagioclase synthesized under water-saturated conditions are significantly higher
than in the natural phases, implying that most of the differentiation of the phonolites took place under water-undersaturated
conditions. However, this does not exclude the presence of a S-, Cl- and CO2-rich fluid phase in the upper parts of the magma chamber. The phase relationships and the TiO2 contents of melts show that the temperature was lower than 760 °C in the upper part of the magma column (probably down to
720 °C in the most differentiated levels) and that temperatures above 840–860 °C prevailed in the lower part. The variation
of the X
Mg of ferromagnesian minerals observed in both natural and experimental phases reflects the strong variations in ƒO2 in the lower magma chamber just prior to eruption (probably variation of about 2 log units). The most probable explanation
for these ƒO2 variations is the injection of an oxidized alkali-rich magma, containing Mg-rich phenocrysts, at the base of a chemically
zoned and more reduced magma column prior to eruption. Although the amount of injected magma may not have been very important,
it was sufficient to change the ƒO2 conditions locally, explaining the heterogeneous X
Mg of ferromagnesian minerals and the formation of hauyne at the base of the chamber.
Received: 30 May 2000 / Accepted: 12 August 2000 相似文献
8.
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
9.
Laser Ablation ICPMS study of trace element partitioning between plagioclase and basaltic melts: an experimental approach 总被引:3,自引:1,他引:3
Mario Aigner-Torres Jon Blundy Peter Ulmer Thomas Pettke 《Contributions to Mineralogy and Petrology》2007,153(6):647-667
Plagioclase-melt partition coefficients (D) for 34 trace elements at natural concentration levels were determined experimentally in a natural MORB composition at atmospheric
pressure using thin Pt-wire loops. Experiments were carried out at three temperatures (1,220, 1,200, and 1,180°C), and at
three different oxygen fugacities (fO2 = IW, QFM, air) in order to assess the effect of fO2 on the partitioning of elements with multiple valence (Fe, Eu, Cr). Run products were analyzed by laser-ablation ICP-MS.
Most trace element Ds increase slightly as temperature decreases, except for D
Zr, D
Fe, D
Eu and D
Cr that vary systematically with fO2. Applying the Lattice Strain Model to our data suggests the presence of Fe2+ entirely in the octahedral site at highly to moderate reducing conditions, while Fe3+ was assigned wholly to the tetrahedral site of the plagioclase structure. Furthermore, we provide a new quantitative framework
for understanding the partitioning behaviour of Eu, which occurs as both 2+ and 3+ cations, depending on fO2and confirm the greater compatibility of Eu2+, which has an ionic radius similar to Sr, relative to Eu3+ in plagioclase and the higher Eu2+/ Eu3+ under reducing conditions. For petrogenetic basaltic processes, a combined fractionation of Eu2+–Sr and Fe–Mg by plagioclase has considerable potential as an oxybarometer for natural magmatic rocks. 相似文献
10.
Victor Kress 《Contributions to Mineralogy and Petrology》1997,127(1-2):176-186
Recrystallized globules representing former immiscible sulfide liquids are found in a variety of igneous environments. Relatively
little is known about the physical properties and thermochemistry of sulfide liquids, despite their importance in igneous
systems. This study presents results of a series of experiments designed to calibrate a thermodynamic model for sulfide liquids
in the system O-S-Fe at one atmosphere pressure. Sulfide liquids were equilibrated under controlled oxygen and sulfur fugacities
at temperatures between 1100 and 1350 ° C in equilibrium with a silica mineral and a silicate melt. Experiments were quenched
in a high-speed double-roller “splat” quencher in order to assure that measured compositions were as close to equilibrium
liquid values as possible. Sulfide liquids are not stable in equilibrium with a silica-saturated silicate melt at log10(f
O2) > FMQ-1 at 1250 °C and log10(f
S2)=−3. Iron content of the sulfide changes little with variations in oxygen and sulfur fugacity at a given temperature. Consequently,
oxygen and sulfur contents are inversely correlated in these liquids. Sulfur is present entirely as sulfide. Iron appears
to be present in both its ferric and ferrous states. Data from this study were combined with data compiled from the literature
to calibrate an asymmetric regular solution thermodynamic mixing model for O-S-Fe liquids. This model reproduces miscibility
gaps and data from this study quite well, but exhibits minor but systematic errors at the O-Fe binary. The observed inverse
correlation between sulfur and oxygen is reflected in the predicted free-energy surface by a sharp energy valley running along
a line of constant Fe content.
Received: 10 April 1996 / Accepted: 15 November 1996 相似文献
11.
The Ordovician stratiform iron deposits at Zamora (NW Iberia) are arranged in several levels ranging between 0.2 and 1.5 m
in thickness, which are interstratified in the upper member of the “Pielgo” Quartzites Formation (Arenig). The sandy nature,
and trace-fossils corresponding to the ichnogenus Cruziana and Daedalus, together with major and trace element contents of this formation suggest an inter and subtidal, shallow marine depositional
environment, which on a global scale formed part of a broad shelf situated in the northern margin of the Gondwana continent.
The iron mineralization displays a foliated and banded structure due to the alternation of quartzitic, phosphatic (apatite),
chamositic, chamositic-biotitic and ferriferous (magnetite and hematite) beds. They have high TiO2, Ta, Sc, V, Nb, Co, Zn and Y contents. The magnetite contains unusually large amounts of TiO2, V, Cr and Ni; there is also a clear depletion in Eu and the (Eu/Sm)CN ratio is <1 and the (Sm/Yb)CN ratio is >1. The chamosite contains high concentrations of Cr and V. These results suggest that iron was supplied from the
weathering of a continental source, in combination with volcanic activity, such as within-basin basic volcanism or the presence
of basic volcanic rocks in the exposed land. The physicochemical conditions of iron mineral crystallization calculated from
chamosite compositions are the following: log f O2: −38.8 to −30.7, log f S2: −13.2 to −9.5 and T: 200 to 330 °C. These results together with the δ18O value (∼2‰) of the magnetite suggest that chamosite and magnetite were crystallized during later diagenesis and early low-grade
metamorphism under redox conditions below the magnetite-hematite buffer.
Received: 25 September 1996 / Accepted: 2 February 1998 相似文献
12.
Systematics of calcium partitioning between olivine and silicate melt: implications for melt structure and calcium content of magmatic olivines 总被引:8,自引:0,他引:8
Guy Libourel 《Contributions to Mineralogy and Petrology》1999,136(1-2):63-80
A systematic characterization of the chemical factors that control calcium partitioning between olivine and melt in a magmatic
environment was undertaken using experiments performed on compositionally simple systems (CaO-MgO-SiO2, CaO-MgO-Al2O3-SiO2, CaO-MgO-Al2O3-SiO2-Cr2O3, CaO-MgO-Al2O3-SiO2-TiO2, CaO-MgO-Al2O3-SiO2-Na2O, CaO-MgO-Al2O3-SiO2-FeO, CaO-MgO-Al2O3-SiO2-FeO-Na2O) over a wide range of temperature (1050–1530 °C) at one bar pressure. The calcium concentration of olivines is shown to
be dependent not only on the forsterite content of the olivine but to a large extent on melt composition. For a fixed CaO
content of the melt, these results show that the CaO concentration of olivine is strongly sensitive to the amount of alumina,
alkali and ferrous iron present in the coexisting melt. Oxygen fugacity and temperature are not found directly to affect Ca
partitioning. It is thus proposed that the systematic variations of the calcium content of olivine may be used as an “in-situ
chemical potentiometer” of the lime activity of the melt. Based upon these data in synthetic systems, an empirical model describing
Ca partitioning between olivine and melt is developed. When applied to natural olivines this model reproduces their Ca content,
where melt composition is known, to within ±10% relative. The model may therefore be used to predict changes in melt composition
during olivine crystallization and/or to assess whether an olivine is in equilibrium with its host magma. Finally, the wide
range of Ca partitioning observed at fixed crystal composition confirms that minor element partitioning between crystal and
melt cannot be predicted from the physical characteristics of the crystal alone, and that the non-ideality of the melt has
to be taken into account.
Received: 12 June 1998 / Accepted: 1 February 1999 相似文献
13.
Jürgen Konzett 《Contributions to Mineralogy and Petrology》1997,128(4):385-404
Experiments have been conducted in a peralkaline Ti-KNCMASH system representative of MARID-type bulk compositions to delimit
the stability field of K-richterite in a Ti-rich hydrous mantle assemblage, to assess the compositional variation of amphibole
and coexisting phases as a function of P and T, and to characterise the composition of partial melts derived from the hydrous assemblage. K-richterite is stable in experiments
from 0.5 to 8.0 GPa coexisting with phlogopite, clinopyroxene and a Ti-phase (titanite, rutile or rutile + perovskite). At
8.0 GPa, garnet appears as an additional phase. The upper T stability limit of K-richterite is 1200–1250 °C at 4.0 GPa and 1300–1400 °C at 8.0 GPa. In the presence of phlogopite, K-richterite
shows a systematic increase in K with increasing P to 1.03 pfu (per formula unit) at 8.0 GPa/1100 °C. In the absence of phlogopite, K-richterite attains a maximum of 1.14 K
pfu at 8.0 GPa/1200 °C. Titanium in both amphibole and mica decreases continuously towards high P with a nearly constant partitioning while Ti in clinopyroxene remains more or less constant. In all experiments below 6.0 GPa
ΣSi + Al in K-richterite is less than 8.0 when normalised to 23 oxygens+stoichiometric OH. Rutiles in the Ti-KNCMASH system
are characterised by minor Al and Mg contents that show a systematic variation in concentration with P(T) and the coexisting assemblage. Partial melts produced in the Ti-KNCMASH system are extremely peralkaline [(K2O+Na2O)/Al2O3 = 1.7–3.7], Si-poor (40–45 wt% SiO2), and Ti-rich (5.6–9.2 wt% TiO2) and are very similar to certain Ti-rich lamproite glasses. At 4.0 GPa, the solidus is thought to coincide with the K-richterite-out
reaction, the first melt is saturated in a phlogopite-rutile-lherzolite assemblage. Both phlogopite and rutile disappear ca.
150 °C above the solidus. At 8.0 GPa, the solidus must be located at T≤1400 °C. At this temperature, a melt is in equilibrium with a garnet- rutile-lherzolite assemblage. As opposed to 4.0 GPa, phlogopite
does not buffer the melt composition at 8.0 GPa. The experimental results suggest that partial melting of MARID-type assemblages
at pressures ≥4.0 GPa can generate Si-poor and partly ultrapotassic melts similar in composition to that of olivine lamproites.
Received: 23 December 1996 / Accepted: 20 March 1997 相似文献
14.
Experiments at 750 °C, 200 MPa(H2O), a
(H2O)=1, and fO2∼Ni-NiO established that the equilibrium among tourmaline, biotite, cordierite, and melt (± spinel, aluminosilicate, or corundum)
occurs with ∼2 wt% B2O3 in strongly peraluminous melt with an aluminosity, measured by the parameter ASI, of >1.2. The experiments demonstrate the
relationship of tourmaline stability to the activity product of the tourmaline components boron and aluminum, which are inversely
related to one another. Tourmaline is unstable in metaluminous to mildly peraluminous melts (ASI <1.2) at 750 °C regardless
of their boron content. For a given aluminosity, addition of components such as F requires a greater boron content of melt
at this equilibrium. The stability of tourmaline increases with decreasing temperatures below 750 °C. At the inception of
melting, tourmaline breaks down incongruently to assemblages containing crystalline AFM silicates (biotite, cordierite, garnet,
sillimanite), aluminates (spinel, corundum), and B-enriched but Fe-Mg-poor melt. Granitic melts are likely to be undersaturated
in tourmaline from the start of their crystallization, and their initial boron contents will be limited by the abundance of
tourmaline in their source rocks. Quartzofeldspathic (gneissic, metapelitic) rocks that reached conditions of the granulite
facies and still contain (prograde) tourmaline are rare, and probably have never yielded a partial melt. Most leucogranitic
magmas will initially crystallize biotite, cordierite, or garnet, but not tourmaline. With crystallization, the Fe-Mg content
of melt decreases, and the B2O3 content increases until the tourmaline-biotite and/or tourmaline-cordierite (or garnet) equilibria are attained. The B2O3 content of melt is buffered as long as these equilibria continue to operate, but low initial Fe-Mg contents of the magmas
limit the quantity of boron that can be consumed by these reactions to <1 wt% B2O3. Normally, leucogranitic magmas contain insufficient Fe and Mg to conserve all boron as tourmaline and thus lose a large
fraction of magmatic boron to wallrocks. Leucogranites and pegmatites with tourmaline as an early and only AFM silicate mineral
probably contained >2 wt% B2O3 in their bulk magmas.
Received: 6 August 1996 / Accepted: 21 July 1997 相似文献
15.
Melt inclusions in pegmatite quartz: complete miscibility between silicate melts and hydrous fluids at low pressure 总被引:10,自引:1,他引:9
Fluorine-, boron- and phosphorus-rich pegmatites of the Variscan Ehrenfriedersdorf complex crystallized over a temperature
range from about 700 to 500 °C at a pressure of about 1 kbar. Pegmatite quartz crystals continuously trapped two different
types of melt inclusions during cooling and growth: a silicate-rich H2O-poor melt and a silicate-poor H2O-rich melt. Both melts were simultaneously trapped on the solvus boundaries of the silicate (+ fluorine + boron + phosphorus) − water
system. The partially crystallized melt inclusions were rehomogenized at 1 kbar between 500 and 712 °C in steps of 50 °C by
conventional rapid-quench hydrothermal experiments. Glasses of completely rehomogenized inclusions were analyzed for H2O by Raman spectroscopy, and for major and some trace elements by EMP (electron microprobe). Both types of melt inclusions
define a solvus boundary in an XH2O–T pseudobinary system. At 500 °C, the silicate-rich melt contains about 2.5 wt% H2O, and the conjugate water-rich melt about 47 wt% H2O. The solvus closes rapidly with increasing temperature. At 650 °C, the water contents are about 10 and 32 wt%, respectively.
Complete miscibility is attained at the critical point: 712 °C and 21.5 wt% H2O. Many pegmatites show high concentrations of F, B, and P, this is particularly true for those pegmatites associated with
highly evolved peraluminous granites. The presence of these elements dramatically reduces the critical pressure for fluid–melt
systems. At shallow intrusion levels, at T ≥ 720 °C, water is infinitely soluble in a F-, B-, and P-rich melt. Simple cooling
induces a separation into two coexisting melts, accompanied with strong element fractionation. On the water-rich side of the
solvus, very volatile-rich melts are produced that have vastly different physical properties as compared to “normal” silicate
melts. The density, viscosity, diffusivity, and mobility of such hyper-aqueous melts under these conditions are more comparable
to an aqueous fluid.
Received: 15 September 1999 / Accepted: 10 December 1999 相似文献
16.
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
17.
A. A. Kadik N. A. Kurovskaya Yu. A. Ignat’ev N. N. Kononkova V. V. Koltashev V. G. Plotnichenko 《Geochemistry International》2010,48(10):953-960
Equilibria in the model melt (NaAlSi3O8(80) + FeO(20))-C-H2 system were experimentally studied at ΔlogfO2(IW) from −2.2 to −5.6, a pressure of 1.5 GPa, and a temperature of 1400°C. The experiments were conducted in a piston-cylinder
apparatus using Pt capsules. The low fO2 values were imposed during the experiments by adding 2, 5, and 7 wt % of finely dispersed SiC to NaAlSi3O8(80) + FeO(20) powder. The experimental products were investigated by electron microprobe analysis and Raman spectroscopy.
The investigations showed that melting at 1.5 GPa and 1400°C in the stability field of a metallic iron phase produces silicate
liquids containing both oxidized and reduced H and C species. Carbon and hydrogen are dissolved in the melt as C-H (CH4) complexes. In addition, OH− groups, molecular hydrogen H2, and molecular water H2O were observed in the melts. The proportions of dissolved C and H species strongly depend on oxygen fugacity. With decreasing
fO2, the content of O-H species decreases and that of H-C species increases. The obtained data and previous results (Kadik et
al., 2004, 2006) allow us to suppose a fundamental change in the character of magmatic transfer of C-O-H components during
the evolution of the redox state of the Earth’s mantle in geologic time toward higher fO2 in its interiors. 相似文献
18.
The equilibrium water content of cordierite has been measured for 31 samples synthesized at pressures of 1000 and 2000 bars
and temperatures from 600 to 750° C using the cold-seal hydrothermal technique. Ten data points are presented for pure magnesian
cordierite, 11 data points for intermediate iron/magnesium ratios from 0.25 to 0.65 and 10 data points for pure iron cordierite.
By representing the contribution of H2O to the heat capacity of cordierite as steam at the same temperature and pressure, it is possible to calculate a standard
enthalpy and entropy of reaction at 298.18° K and 1 bar for,
(Mg,Fe)2Al4Si5O18+H2O ⇄ (Fe,Mg)2Al4Si5O18.H2O
Combining the 31 new data points with 89 previously published experimental measurements gives: ΔH
°
r
=–37141±3520 J and ΔS
°
r
=–99.2±4 J/degree. This enthalpy of reaction is within experimental uncertainty of calorimetric data. The enthalpy and entropy
of hydration derived separately for magnesian cordierite (–34400±3016 J, –96.5±3.4 J/degree) and iron cordierite (–39613±2475,
–99.5±2.5 J/degree) cannot be distinguished within the present experimental uncertainty. The water content as a function of
temperature, T(K), and water fugacity, f(bars), is given by n
H2O=1/[1+1/(K ⋅ f
H2O)] where the equilibrium constant for the hydration reaction as written above is, ln K=4466.4/T–11.906 with the standard state for H2O as the gas at 1 bar and T, and for cordierite components, the hydrous and anhydrous endmembers at P and T.
Received: 2 August 1994/Accepted: 7 February 1996 相似文献
19.
The effects of pressure and oxygen fugacity (fO2) on trace element partitioning between pargasitic amphibole and alkali-basaltic melts have been determined at pressures from
1.5 to 2.5 GPa and oxygen fugacities at 2 log units above and below the nickel–nickel oxide buffer. Amphibole crystallization
experiments were performed in a piston cylinder apparatus and partition coefficients between amphibole and quenched melt of
large-ion-lithophile elements (LILE: Rb, Sr, Ba), high-field-strength elements (HFSE: Zr, Nb, Ta, Hf, U, Th) and rare-earth
elements (REE: La to Lu; +Y) were measured with a LASER ablation inductively coupled plasma – mass spectrometer. Increasing
pressure from 1.5 to 2.5 GPa at similar temperatures and approximately constant fO2 increases D
Rb but decreases D
Zr and D
Hf and D
REE (D
La, D
Ce, D
Pr). An empirical relationship was observed between D
Zr and (Ti/Al)M2 in the amphibole, which can be described by:
Increasing the fO2 by ∼4 log units (∼NNO–2.0 to ∼NNO+2.2) at similar temperatures and constant pressure increases D
Ba and D
Nd but decreases D
Ti. An increase in pressure or fO2 decreases the maximum partition coefficient (D
o
), the Young's modulus (E) and the optimum ionic radius (r
o
) of the A-, M2- and M4-lattice sites. The calculated r
o
values from the monovalent cations (Na, K, Rb) in the A site and the quadrivalent cations (Ti, Hf, Zr) in the M2 lattice
sites suggests that amphiboles crystallized from alkaline basalt material have smaller 〈A-O〉 and 〈M2-O〉, mean bond-lengths
than those formed from pargasitic materials at identical pressures and fO2's. The measured partition coefficients were used to calculate trace element concentrations in melts formed by partial melting
of amphibole-bearing peridotite. This modeling demonstrates those changes in either the pressure or fO2 of melting can exert a significant effect on Rb/HFSE ratios in the melts and thus help explain the wide variations of these
ratios sometimes observed in basaltic rock suites.
Received: 7 August 1998 / Accepted: 7 June 2000 相似文献
20.
Summary Mineral chemistry and petrological data of chromites from chromitite bands in the N–S trending schist belt of Nuggihalli (southern
Karnataka, India), belonging to the Dharwar craton of South India, are presented in this paper. Crystal chemical data indicate
a komatiitic affinity of the chromitite. P–T calculations of the chromite-hosting peridotites yielded a pressure range of 13 to 28 kbar and temperatures ranging from
775 to 1080 °C; the oxygen fugacity (log fO2) varies from +0.5 to +1.6 above the QFM buffer. The P, T and fO2 data indicate that Nuggihalli chromitites crystallized in an environment akin to the upper mantle. The studied samples also
show partial resetting; the lower temperatures ranging from 515 to 680 °C are ascribed to subsequent metamorphism of the area. 相似文献