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1.
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
2.
Wenjun Yong E. Dachs A. C. Withers E. J. Essene 《Physics and Chemistry of Minerals》2006,33(3):167-177
The low-temperature heat capacity (C
p
) of KAlSi3O8 with a hollandite structure was measured over the range of 5–303 K with a physical properties measurement system. The standard entropy of KAlSi3O8 hollandite is 166.2±0.2 J mol−1 K−1, including an 18.7 J mol−1 K−1 contribution from the configurational entropy due to disorder of Al and Si in the octahedral sites. The entropy of K2Si4O9 with a wadeite structure (Si-wadeite) was also estimated to facilitate calculation of phase equilibria in the system K2O–Al2O3–SiO2. The calculated phase equilibria obtained using Perple_x are in general agreement with experimental studies. Calculated phase relations in the system K2O–Al2O3–SiO2 confirm a substantial stability field for kyanite–stishovite/coesite–Si-wadeite intervening between KAlSi3O8 hollandite and sanidine. The upper stability of kyanite is bounded by the reaction kyanite (Al2SiO5) = corundum (Al2O3) + stishovite (SiO2), which is located at 13–14 GPa for 1,100–1,400 K. The entropy and enthalpy of formation for K-cymrite (KAlSi3O8·H2O) were modified to better fit global best-fit compilations of thermodynamic data and experimental studies. Thermodynamic calculations were undertaken on the reaction of K-cymrite to KAlSi3O8 hollandite + H2O, which is located at 8.3–10.0 GPa for the temperature range 800–1,600 K, well inside the stability field of stishovite. The reaction of muscovite to KAlSi3O8 hollandite + corundum + H2O is placed at 10.0–10.6 GPa for the temperature range 900–1,500 K, in reasonable agreement with some but not all experiments on this reaction. 相似文献
3.
Yusuke Seto Daisuke Hamane Takaya Nagai Kiyoshi Fujino 《Physics and Chemistry of Minerals》2008,35(4):223-229
We report on high-pressure and high-temperature experiments involving carbonates and silicates at 30–80 GPa and 1,600–3,200 K,
corresponding to depths within the Earth of approximately 800–2,200 km. The experiments are intended to represent the decomposition
process of carbonates contained within oceanic plates subducted into the lower mantle. In basaltic composition, CaCO3 (calcite and aragonite), the major carbonate phase in marine sediments, is altered into MgCO3 (magnesite) via reactions with Mg-bearing silicates under conditions that are 200–300°C colder than the mantle geotherm.
With increasing temperature and pressure, the magnesite decomposes into an assemblage of CO2 + perovskite via reactions with SiO2. Magnesite is not the only host phase for subducted carbon—solid CO2 also carries carbon in the lower mantle. Furthermore, CO2 itself breaks down to diamond and oxygen under geotherm conditions over 70 GPa, which might imply a possible mechanism for
diamond formation in the lower mantle. 相似文献
4.
The stability field of Mg3Al2Si3O12-pyrope was examined for the first time under hydrostatic pressure conditions in a CO2-laser heated diamond cell in the pressure range 21–30 GPa between 2300 and 3200 K. The phases were characterized using Raman
and fluorescence spectroscopy. With increasing pressure pyrope transforms to an ilmenite phase above ∼21.5 GPa, to perovskite
plus ilmenite above ∼24 GPa, and to perovskite above 29 GPa. The pressures of the first occurrence of perovskite in this study
are about 2 GPa above the corresponding phase boundary between end-member MgSiO3-ilmenite and perovskite. A small amount of Al2O3 coexists with perovskite up to 43 GPa, as evident from fluorescence spectra resembling those of ruby, but above 43 GPa the
entire Al2O3 content of the pyrope starting material is accommodated in the perovskite structure.
Received: 6 March 1997 / Revised, accepted: 23 July 1997 相似文献
5.
High PT experiments were performed in the range 2.5–19 GPa and 800–1,500°C using a synthetic peridotite doped with trace elements
and OH-apatite or with Cl-apatite + phlogopite. The aim of the study was (1) to investigate the stability and phase relations
of apatite and its high PT breakdown products, (2) to study the compositional evolution with P and T of phosphate and coexisting
silicate phases and (3) to measure the Cl-OH partitioning between apatite and coexisting calcic amphibole, phlogopite and
K-richterite. Apatite is stable in a garnet-lherzolite assemblage in the range 2.5–8.7 GPa and 800–1,100°C. The high-P breakdown
product of apatite is tuite γ-Ca3 (PO4)2, which is stable in the range 8–15 GPa and 1,100–1,300°C. Coexisting apatite and tuite were observed at 8 GPa/1,050°C and
8.7 GPa/1,000°C. MgO in apatite increases with P from 0.8 wt% at 2.5 GPa to 3.2 wt% at 8.7 GPa. Both apatite and tuite may
contain significant Na, Sr and REE with a correlation indicating 2 Ca2+=Na+ + REE3+. Tuite has always higher Sr and REE and lower Fe and Mg than apatite. Phosphorus in the peridotite phases decreases in the
order Pmelt ≫ Pgrt ≫ PMg2SiO4 > Pcpx > Popx. The phosphate-saturated P2O5 content of garnet increases from 0.07 wt% at 2.5 GPa to 1.5 wt% at 12.8 GPa. Due to the low bulk Na content of the peridotite,
[8]Na[4]P[8]M2+
−1
[4]Si−1 only plays a minor role in controlling the phosphorus content of garnet. Instead, element correlations indicate a major contribution
of [6]M2+[4]P[6]M3+
−1
[4]Si−1. Pyroxenes contain ~200–500 ppm P and olivine has 0.14–0.23 wt% P2O5 in the P range 4–8.7 GPa without correlation with P, T or XMg. At ≥12.7 GPa, all Mg2SiO4 polymorphs have <200 ppm P. Coexisting olivine and wadsleyite show an equal preference for phosphorus. In case of coexisting
wadsleyite and ringwoodite, the latter fractionates phosphorus. Although garnet shows by far the highest phosphorus concentrations
of any peridotite silicate phase, olivine is no less important as phosphorus carrier and could store the entire bulk phosphorus
budget of primitive mantle. In the Cl-apatite + phlogopite-doped peridotite, apatite contains 0.65–1.35 wt% Cl in the PT range
2.5–8.7 GPa/800–1,000°C. Apatite coexists with calcic amphibole at 2.5 GPa, phlogopite at 2.5–5 GPa and K-richterite at 7 GPa,
and all silicates contain between 0.2 and 0.6 wt% Cl. No solid potassic phase is stable between 5 and 8.7 GPa. Cl strongly
increases the solubility of K in hydrous fluids. This may lead to the breakdown of phlogopite and give rise to the local presence
in the mantle of fluids strongly enriched in K, Cl, P and incompatible trace elements. Such fluids may get trapped as micro-inclusions
in diamonds and provide bulk compositions suitable for the formation of unusual phases such as KCl or hypersilicic Cl-rich
mica. 相似文献
6.
R. G. Trønnes 《Mineralogy and Petrology》2002,74(2-4):129-148
Summary The phase relations of K-richterite, KNaCaMg5Si8O22(OH)2, and phlogopite, K3Mg6 Al2Si6O20(OH)2, have been investigated at pressures of 5–15 GPa and temperatures of 1000–1500 °C. K-richterite is stable to about 1450 °C
at 9–10 GPa, where the dp/dT-slope of the decomposition curve changes from positive to negative. At 1000 °C the alkali-rich,
low-Al amphibole is stable to more than 14 GPa. Phlogopite has a more limited stability range with a maximum thermal stability
limit of 1350 °C at 4–5 GPa and a pressure stability limit of 9–10 GPa at 1000 °C. The high-pressure decomposition reactions
for both of the phases produce relatively small amounts of highly alkaline water-dominated fluids, in combination with mineral
assemblages that are relatively close to the decomposing hydrous phase in bulk composition. In contrast, the incongruent melting
of K-richterite and phlogopite in the 1–3 GPa range involves a larger proportion of hydrous silicate melts.
The K-richterite breakdown produces high-Ca pyroxene and orthoenstatite or clinoenstatite at all pressures above 4 GPa. At
higher pressures additional phases are: wadeite-structured K2SiVISiIV
3O9 at 10 GPa and 1500 °C, wadeite-structured K2SiVISiIV
3O9 and phase X at 15 GPa and 1500 °C, and stishovite at 15 GPa and 1100 °C. The solid breakdown phases of phlogopite are dominated
by pyrope and forsterite. At 9–10 GPa and 1100–1400 °C phase X is an additional phase, partly accompanied by clinoenstatite
close to the decomposition curve. Phase X has variable composition. In the KCMSH-system (K2CaMg5Si8O22(OH)2) investigated by Inoue et al. (1998) and in the KMASH-system investigated in this report the compositions are approximately K4Mg8Si8O25(OH)2 and K3.7Mg7.4Al0.6Si8.0O25(OH)2, respectively.
Observations from natural compositions and from the phlogopite-diopside system indicate that phlogopite-clinopyroxene assemblages
are stable along common geothermal gradients (including subduction zones) to 8–9 GPa and are replaced by K-richterite at higher
pressures. The stability relations of the pure end member phases of K-richterite and phlogopite are consistent with these
observations, suggesting that K-richterite may be stable into the mantle transition zone, at least along colder slab geotherms.
The breakdown of moderate proportions of K-richterite in peridotite in the upper part of the transition zone may be accompanied
by the formation of the potassic and hydrous phase X. Additional hydrogen released by this breakdown may dissolve in wadsleyite.
Therefore, very small amounts of hydrous fluids may be released during such a decomposition.
Received April 10, 2000; revised version accepted November 6, 2000 相似文献
7.
The phase relations and the element partitioning in a mid-oceanic ridge basalt composition were determined for both above-solidus and subsolidus conditions at 22 to 27.5 GPa by means of a multianvil apparatus. The mineral assemblage at the solidus changes remarkably with pressure; majorite and stishovite at 22 GPa, joined by Ca-perovskite at 23 GPa, further joined by CaAl4Si2O11-rich CAS phase at 25.5 GPa, and Mg-perovskite, stishovite, Ca-perovskite, CF phase (approximately on the join NaAlSiO4-MgAl2O4), and NAL phase ([Na,K,Ca]1[Mg,Fe2+]2[Al,Fe3+,Si]5.5-6.0O12) above 27 GPa. The liquidus phase is Ca-perovskite, and stishovite, a CAS phase, a NAL phase, Mg-perovskite, and a CF phase appear with decreasing temperature at 27.5 GPa. Partial melt at 27 to 27.5 GPa is significantly depleted in SiO2 and CaO and enriched in FeO and MgO compared with those formed at lower pressures, reflecting the narrow stability of (Fe,Mg)-rich phases (majorite or Mg-perovskite) above solidus temperature. The basaltic composition has a lower melting temperature than the peridotitic composition at high pressures except at 13 to 18 GPa (Yasuda et al., 1994) and therefore can preferentially melt in the Earth’s interior. Recycled basaltic crusts were possibly included in hot Archean plumes, and they might have melted in the uppermost lower mantle. In this case, Ca-perovskite plays a dominant role in the trace element partitioning between melt and solid. This contrasts remarkably with the case of partial melting of a peridotitic composition in which magnesiowüstite is the liquidus phase at this depth. 相似文献
8.
M. Catti 《Physics and Chemistry of Minerals》2001,28(10):729-736
Quantum-mechanical solid-state calculations have been performed on the highest-pressure polymorph of magnesium aluminate
(CaTi2O4-type structure, Cmcm space group), as well as on the low-pressure (Fd3ˉm) spinel phase and on MgO and Al2O3. An ab initio all-electron periodic scheme with localized basis functions (Gaussian-type atomic orbitals) has been used,
employing density-functional-theory Hamiltonians based on LDA and B3LYP functionals. Least-enthalpy structure optimizations
in the pressure range 0 to 60 GPa have allowed us to predict: (1) the full crystal structure, the pV equation of state and the compressibility of Cmcm-MgAl2O4 as a function of pressure; (2) the phase diagram of the MgO–Al2O3–MgAl2O4 system (with exclusion of CaFe2O4-type Pmcn-MgAl2O4), and the equilibrium pressures for the reactions of formation/decomposition of the Fd3ˉm and Cmcm polymorphs of MgAl2O4 from the MgO + Al2O3 assemblage. Cmcm-MgAl2O4 is predicted to form at 39 and 57 GPa by LDA and B3LYP calculations, with K
0=248 (K′=3.3) and 222 GPa (K′=3.8), respectively. Results are compared to experimental data, where available, and the performance of different DFT functionals
is discussed.
Received: 31 January 2001 / Accepted: 16 May 2001 相似文献
9.
The phase relations in the Fe2SiO4–Fe3O4 binary system have been determined between 900 and 1200 °C and from 2.0 to 9.0 GPa. At low to moderate pressures magnetite
can accommodate significant Si, reaching XFe2SiO4=0.1 and 0.2 at 3.0 and 5.0 GPa respectively, with temperature having only a secondary influence. At pressures below 3.5 GPa
at 900 °C and 2.6 GPa at 1100 °C magnetite-rich spinel coexists with pure fayalite. This assemblage becomes unstable at higher
pressures with respect to three intermediate phases that are spinelloid polytypes isostructural to spinelloids II, III and
V in the Ni-aluminosilicate system. The phase relations between the spinelloid phases are complex. At pressures above ≈8.0 GPa
at 1100 °C, the spinelloid phases give way to a complete spinel solid solution between Fe3O4 and Fe2SiO4. The presence of small amounts of Fe3+ stabilises the spinel structure to lower pressures compared to the Fe2SiO4 end member. This means that the fayalite–γ-spinel transition is generally unsuitable as a pressure calibration point for
experimental apparatuses. The molar volumes of the spinel solid solutions vary nearly linearly with composition, having a
small negative deviation from ideal behaviour described by Wv=−0.15(6) cm3. Extrapolation yields V°(298) = 41.981(14) cm3 for the Fe2SiO4-spinel end member. The cell parameters and molar volumes of the three spinelloid polytypes vary systematically with composition.
Cation disorder is an important factor in stabilising the spinelloid polytypes. Each polytype exhibits a particular solid
solution range that is directly influenced by the interplay between its structure and the cation distributions that are energetically
favourable. In the FeO–FeO1.5–SiO2 ternary system Fe7SiO10 (“iscorite”) coexists with the spinelloid phases at intermediate pressures on the SiO2-poor, or Fe3+-poor side of the Fe2SiO4–Fe3O4 join. On the SiO2 and Fe3+-rich side of the join, orthopyroxene or high-P clinopyroxene coexists with the spinelloids and spinel solid solutions. The
assemblage pyroxene+spinel+SiO2 is stable over a wide range of bulk composition. The stability of spinelloid III is of particular petrologic interest since
this phase has the same structure as (Mg,Fe)2SiO4–wadsleyite, indicating that Fe3+ can be easily incorporated in this important phase in the Earth's transition zone, in addition to silicate spinel. This has
important implications for the redox state of the Earth's transition zone and for the depth at which the olivine to spinel
transition occurs in the mantle, potentially leading to a shift in the “410 km” seismic discontinuity to shallower depths
depending on the prevailing redox state. In addition, a coupled tetrahedral substitution of Fe3++OH for Si+O could provide a further mechanism for the incorporation of H2O in wadsleyite.
Received: 10 January 2000 / Accepted: 12 May 2000 相似文献
10.
The greenschist to amphibolite transition as modeled by the reaction zoisite+tremolite + quartz= anorthite+diopside+water
has been experimentally investigated in the chemical system H2O−CaO− MgO−Al2O3−SiO2 over the range of 0.4–0.8 GPa. This reaction is observed to lie within the stability fields of anorthite + water and of zoisite
+ quartz, in accord with phase equilibrium principles, and its position is in excellent agreement with the boundary calculated
from current internally-consistent data bases. The small dP/dT slope of 0.00216 GPa/K (21.6 bars/K) observed for this reaction supports the pressure-dependency of this transition in this
chemical system. Experimental reversals of the Al content in tremolitic amphibole coexisting with zoisite, diopside, quartz,
and water were obtained at 600, 650, and 700°C and indicated Al total cations (atoms per formula unit, apfu) of only up to 0.5±0.08 at the highest temperature. Thermodynamic
analysis of these and previous compositional reversal data for tremolitic amphibole indicated that, of the activity/composition
relationships considered, a two-site-coupled cation substitution model yielded the best fit to the data and a S
0 (1 bar, 298 K) of 575.4±1.6 J/K · mol for magnesio-hornblende. The calculated isopleths of constant Al content in the amphibole
are relatively temperature sensitive with Al content increasing with increasing temperature and pressure. Finally, several
experiments in the range of 1.0–1.3 GPa were conducted to define the onset of melting, and thus the upper-thermal limit, for
this mineral assemblage, which must involve an invariant point located at approximately 1.05 GPa and 770°C.
Received: 24 January 1997 / Accepted: 2 October 1997 相似文献
11.
Jürgen Konzett Daniel J. Frost Alexander Proyer Peter Ulmer 《Contributions to Mineralogy and Petrology》2008,155(2):215-228
Experiments have been conducted in the P-T range 2.5–15 GPa and 850–1,500°C using bulk compositions in the systems SiO2–TiO2–Al2O3–Fe2O3–FeO–MnO–MgO–CaO–Na2O–K2O–P2O5 and SiO2–TiO2–Al2O3–MgO–CaO–Na2O to investigate the Ca-Eskola (CaEs Ca0.5□0.5AlSi2O6) content of clinopyroxene in eclogitic assemblages containing garnet + clinopyroxene + SiO2 ± TiO2 ± kyanite as a function of P, T, and bulk composition. The results show that CaEsss in clinopyroxene increases with increasing T and is strongly bulk composition dependent whereby high CaEs-contents are favoured by bulk compositions with high normative
anorthite and low diopside contents. In this study, a maximum of 18 mol% CaEsss was found at 6 GPa and 1,350°C in a kyanite-eclogite assemblage garnet + clinopyroxene + kyanite + rutile + coesite. By comparison,
no significant increase in CaEsss with increasing P could be observed. If the formation of oriented SiO2-rods frequently observed in eclogititc clinopyroxenes is due to the retrogressive breakdown of a CaEs-component then these
textures are a cooling rather than a decompression phenomenon and are most likely to be found in kyanite-bearing eclogites
cooled from temperatures ≥750°C. The presence of clinopyroxene with approx. 4 mol% CaEsss in an experiment conducted at 2.5 GPa/850°C confirms earlier suggestions based on field data that vacancy-rich clinopyroxenes
are not necessarily restricted to ultrahigh pressure metamorphic conditions.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
12.
High pressure phase relation of the system Fe2SiO4–Fe3O4 was investigated by synthesis experiments using multi-anvil high pressure apparatus. A complete solid solution with spinel
structure along Fe2SiO4–Fe3O4 join occurs above 9 GPa at 1200 °C. Lattice constants of the solid solution show almost linear variation with composition.
A spinelloid phase is stable for intermediate compositions in the pressure range from 3 to 9 GPa. the synthesized spinelloid
phase is successfully indexed assuming nickel aluminosilicate V type structure.
Received: October 16, 1995 / Revised, accepted: March 19, 1997 相似文献
13.
S. Ono E. Ito T. Katsura A. Yoneda M. J. Walter S. Urakawa W. Utsumi K. Funakoshi 《Physics and Chemistry of Minerals》2000,27(9):618-622
In situ synchrotron X-ray experiments in the system SnO2 were made at pressures of 4–29 GPa and temperatures of 300–1400 K using sintered diamond anvils in a 6–8 type high-pressure
apparatus. Orthorhombic phase (α-PbO2 structure) underwent a transition to a cubic phase (Pa3ˉ structure) at 18 GPa. This transition was observed at significantly lower pressures in DAC experiments. We obtained the
isothermal bulk modulus of cubic phase K
0 = 252(28) GPa and its pressure derivative K
′=3.5(2.2). The thermal expansion coefficient of cubic phase at 25 GPa up to 1300 K was determined from interpolation of the
P-V-T data obtained, and is 1.7(±0.7) × 10−5 K−1 at 25 GPa.
Received: 7 December 1999 / Accepted: 27 April 2000 相似文献
14.
Xi Liu Norimasa Nishiyama Takeshi Sanehira Toru Inoue Yuji Higo Shizue Sakamoto 《Physics and Chemistry of Minerals》2006,33(10):711-721
In order to constrain the high-pressure behavior of kyanite, multi-anvil experiments have been carried out from 15 to 25 GPa, and 1,350 to 2,500°C. Both forward and reversal approaches to phase equilibria were adopted in these experiments. We find that kyanite breaks down to stishovite + corundum at pressures above ∼15 GPa, and stishovite + corundum should be the stable phase assemblage at the pressure–temperature conditions of the transition zone and the uppermost part of the lower mantle of the Earth, in agreement with previous multi-anvil experimental studies and ab initio calculation results, but in disagreement with some of the diamond-anvil cell experimental studies in the literature. The Al2O3 solubility in nominally dry stishovite has been tightly bracketed by forward and reversal experiments; it is slightly but consistently reduced by pressure increase. Its response to temperature increase, however, is more complicated: increases at low temperatures, maximizes at around 2,000°C, and perhaps decreases at higher temperatures. Consequently, the Al2O3 solubility in dry stishovite at conditions of high temperature–high pressure is very limited. 相似文献
15.
Resulting from static experiments performed to study the phase state of CaCO3, it was found that its melting is congruent at 20–22 GPa and 3500 K. The obtained experiment data show that the field of
congruent melting of calcium carbonate is rather broad (form 2300 to 3500–3800 K at 20–22 GPa). However, the potential presence
of a high-temperature phase boundary at which CaCO3 is decomposed into CaO and CO2 is not ruled out. The existence of a wide area of congruent melting of calcium carbonate (a common primary inclusion in diamonds
of the transition zone and lower mantle of the Earth) allow one to consider deep-seated melts as potential parental media
for ultradeep diamonds. 相似文献
16.
Wenjun Yong E. Dachs A. C. Withers E. J. Essene 《Contributions to Mineralogy and Petrology》2008,155(2):137-146
The low-temperature heat capacity (C
p) of Si-wadeite (K2Si4O9) synthesized with a piston cylinder device was measured over the range of 5–303 K using the heat capacity option of a physical
properties measurement system. The entropy of Si-wadeite at standard temperature and pressure calculated from the measured
heat capacity data is 253.8 ± 0.6 J mol−1 K−1, which is considerably larger than some of the previous estimated values. The calculated phase transition boundaries in the
system K2O–Al2O3–SiO2 are generally consistent with previous experimental results. Together with our calculated phase boundaries, seven multi-anvil
experiments at 1,400 K and 6.0–7.7 GPa suggest that no equilibrium stability field of kalsilite + coesite intervenes between
the stability field of sanidine and that of coesite + kyanite + Si-wadeite, in contrast to previous predictions. First-order
approximations were undertaken to calculate the phase diagram in the system K2Si4O9 at lower pressure and temperature. Large discrepancies were shown between the calculated diagram compared with previously
published versions, suggesting that further experimental or/and calorimetric work is needed to better constrain the low-pressure
phase relations of the K2Si4O9 polymorphs.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
17.
P. Tropper I. Deibl F. Finger R. Kaindl 《International Journal of Earth Sciences》2006,95(6):1019-1037
The Sauwald Zone, located at the southern rim of the Bohemian Massif in Upper Austria, belongs to the Moldanubian Unit. It exposes uniform biotite + plagioclase ± cordierite paragneisses that formed during the post-collisional high-T/low-P stage of the Variscan orogeny. Rare metapelitic inlayers contain the mineral assemblage garnet + cordierite + green spinel + sillimanite + K-feldspar + plagioclase + biotite + quartz. Mineral chemical and textural data indicate four stages of mineral growth: (1) peak assemblage as inclusions in garnet (stage 1): garnet core + cordierite + green spinel + sillimanite + plagioclase (An35–65); (2) post-peak assemblages in the matrix (stages 2, 3): cordierite + spinel (brown-green and brown) ± sillimanite ± garnet rim + plagioclase (An10–45); and (3) late-stage growth of fibrolite, muscovite and albite (An0–15) during stage 4. Calculation of the P–T conditions of the peak assemblage (stage 1) yields 750–840°C, 0.29–0.53 GPa and for the stage 2 matrix assemblage garnet + cordierite + green spinel + sillimanite + plagioclase 620–730°C, 0.27–0.36 GPa. The observed phase relations indicate a clockwise P–T path, which terminates below 0.38 GPa. The P–T evolution of the Sauwald Zone and the Monotonous Unit are very similar, however, monazite ages of the former are younger (321 ± 9 Ma vs. 334 ± 1 Ma). This indicates that high-T/low-P metamorphism in the Sauwald Zone was either of longer duration or there were two independent phases of late-Variscan low-P/high-T metamorphism in the Moldanubian Unit. 相似文献
18.
In order to clarify Al2O3 content and phase stability of aluminous CaSiO3-perovskite, high-pressure and high-temperature transformations of Ca3Al2Si3O12 garnet (grossular) were studied using a MA8-type high-pressure apparatus combined with synchrotron radiation. Recovered samples
were examined by analytical transmission electron microscopy. At pressures of 23–25 GPa and temperatures of 1000–1600 K, grossular
garnet decomposed into a mixture of aluminum-bearing Ca-perovskite and corundum, although a metastable perovskite with grossular
composition was formed when the heating duration was not long enough at 1000 K. On release of pressure, this aluminum-bearing
CaSiO3-perovskite transformed to the “LiNbO3-type phase” and/or amorphous phase depending on its Al2O3 content. The structure of this LiNbO3-type phase is very similar to that of LiNbO3 but is not identical. CaSiO3-perovskite with 8 to 25 mol% Al2O3 was quenched to alternating lamellae of amorphous layer and LiNbO3-type phase. On the other hand, a quenched product from CaSiO3-perovskite with less than 6 mol% consisted only of amorphous phase. Most of the inconsistencies amongst previous studies
could be explained by the formation of perovskite with grossular composition, amorphous phase, and the LiNbO3-type phase.
Received: 11 April 2001 / Accepted: 5 July 2002 相似文献
19.
Andrea Orlando Yves Thibault Alan D. Edgar 《Contributions to Mineralogy and Petrology》2000,139(2):136-145
Experiments ranging from 2 to 3 GPa and 800 to 1300 °C and at 0.15 GPa and 770 °C were performed to investigate the stability
and mutual solubility of the K2ZrSi3O9 (wadeite) and K2TiSi3O9 cyclosilicates under upper mantle conditions. The K2ZrSi3O9–K2TiSi3O9 join exhibits complete miscibility in the P–T interval investigated. With increasing degree of melting the solid solution becomes progressively enriched in Zr, indicating
that K2ZrSi3O9 is the more refractory end member. At 2 GPa, in the more complex K2ZrSi3O9–K2TiSi3O9–K2Mg6Al2Si6O20(OH)4 system, the presence of phlogopite clearly limits the extent of solid solution of the cyclosilicate to more Zr-rich compositions
[Zr/(Zr + Ti) > 0.85], comparable to wadeite found in nature, with TiO2 partitioning strongly into the coexisting mica and/or liquid. However, at 1200 °C, with increasing pressure from 2 to 3 GPa,
the partitioning behaviour of TiO2 changes in favour of the cyclosilicate, with Zr/(Zr + Ti) of the K2(Zr,Ti)Si3O9 phase decreasing from ∼0.9 to ∼0.6. The variation in the Ti content of the coexisting phlogopite is related to its degree
of melting to forsterite and liquid, following the major substitution VITi+VI□=2VIMg.
Received: 26 January 1999 / Accepted: 10 January 2000 相似文献
20.
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