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1.
Daisuke Yamazaki Eiji Ito Yoshinori Tange Takashi Yoshino Shuangmeng Zhai Hiroshi Fukui Anton Shatskiy Tomoo Katsura Ken-ichi Funakoshi 《Physics and Chemistry of Minerals》2007,34(4):269-273
In situ X-ray observations of the phase transition from ilmenite to perovskite structure in MnGeO3 were carried out in a Kawai-type high-pressure apparatus interfaced with synchrotron radiation. The phase boundary between
the ilmenite and perovskite structures in the temperature range of 700–1,400°C was determined to be P (GPa) = 16.5(±0.6) − 0.0034(±0.0006)T (°C) based on Anderson’s gold pressure scale. The Clapeyron slope, dP/dT, determined in this study is consistent with that for the transition boundary between the ilmenite and the perovskite structure
in MgSiO3. 相似文献
2.
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
3.
M. Akaogi H. Kojitani T. Morita H. Kawaji T. Atake 《Physics and Chemistry of Minerals》2008,35(5):287-297
Low-temperature isobaric heat capacities (C
p
) of MgSiO3 ilmenite and perovskite were measured in the temperature range of 1.9–302.4 K with a thermal relaxation method using the
Physical Properties Measurement System. The measured C
p
of perovskite was higher than that of ilmenite in the whole temperature range studied. From the measured C
p
, standard entropies at 298.15 K of MgSiO3 ilmenite and perovskite were determined to be 53.7 ± 0.4 and 57.9 ± 0.3 J/mol K, respectively. The positive entropy change
(4.2 ± 0.5 J/mol K) of the ilmenite–perovskite transition in MgSiO3 is compatible with structural change across the transition in which coordination of Mg atoms is changed from sixfold to eightfold.
Calculation of the ilmenite–perovskite transition boundary using the measured entropies and published enthalpy data gives
an equilibrium transition boundary at about 20–23 GPa at 1,000–2,000 K with a Clapeyron slope of −2.4 ± 0.4 MPa/K at 1,600 K.
The calculated boundary is almost consistent within the errors with those determined by high-pressure high-temperature in
situ X-ray diffraction experiments. 相似文献
4.
In situ X-ray diffraction experiments at high pressure were carried out up to 8.9 GPa and 1100 °C to study phase transformations
of iron and two iron-silicon alloys Fe0.91Si0.09 and Fe0.83Si0.17. For iron, the transformation from the bcc phase to the fcc phase was observed at pressures 3.8–8.2 GPa and temperatures
that are consistent with previous in situ X-ray diffraction studies. Reversal of the transformation of iron was found to be
sensitive to temperature; hysteresis of the transformation increased from 25 °C at 3.8 GPa to 100 °C at 7.0 GPa, primarily
because the bcc-fcc phase boundary has a negative Clayperon slope. In the binary system Fe-Si, the observations of the present
study indicate that the ferrite (bcc phase)-stabilizing behavior of silicon persists at high pressures and that the maximum
solubility of silicon in the fcc phase increases with increasing pressure: (1) the transformation from the bcc phase to the
fcc phase was observed in Fe0.91Si0.09 at 6.0, 7.4 and 8.9 GPa and the temperatures measured at the onset of the transformations were 300 °C higher than those in
iron at similar pressures, (2) the transformation rate in Fe0.91Si0.09 was extremely sluggish compared to that of iron, and (3) the bcc-fcc phase transformation was not observed in Fe0.91Si0.09 at 4.7 GPa up to 1000 °C and in Fe0.83Si0.17 at 8.2 GPa and 1100 °C.
Received: 1 June 1998 / Revised, accepted: 9 October 1998 相似文献
5.
The crystal structure of MgFe2O4 was investigated by in situ X-ray diffraction at high pressure, using YAG laser annealing in a diamond anvil cell. Magnesioferrite
undergoes a phase transformation at about 25 GPa, which leads to a CaMn2O4-type polymorph about 8% denser, as determined using Rietveld analysis. The consequences of the occurrence of this dense MgFe2O4 form on the high-pressure phase transformations in the (MgSi)0.75(FeIII)0.5O3 system were investigated. After laser annealing at about 20 GPa, we observe decomposition to two phases: stishovite and a
spinel-derived structure with orthorhombic symmetry and probably intermediate composition between MgFe2O4 and Mg2SiO4. At pressures above 35 GPa, we observe recombination of these products to a single phase with Pbnm perovskite structure.
We thus conclude for the formation of Mg3Fe2Si3O12 perovskite.
Received: 27 March 2000 / Accepted: 1 October 2000 相似文献
6.
Hitoshi Yusa Masaki Akaogi Nagayoshi Sata Hiroshi Kojitani Ryo Yamamoto Yasuo Ohishi 《Physics and Chemistry of Minerals》2006,33(3):217-226
In-situ X-ray powder diffraction measurements conducted under high pressure confirmed the existence of an unquenchable orthorhombic perovskite in ZnGeO3. ZnGeO3 ilmenite transformed into perovskite at 30.0 GPa and 1300±150 K in a laser-heated diamond anvil cell. After releasing the pressure, the lithium niobate phase was recovered as a quenched product. The perovskite was also obtained by recompression of the lithium niobate phase at room temperature under a lower pressure than the equilibrium phase boundary of the ilmenite–perovskite transition. Bulk moduli of ilmenite, lithium niobate, and perovskite phases were calculated on the basis of the refined X-ray diffraction data. The structural relations among these phases are considered in terms of the rotation of GeO6 octahedra. A slight rotation of the octahedra plays an important role for the transition from lithium niobate to perovskite at ambient temperature. On the other hand, high temperature is needed to rearrange GeO6 octahedra in the ilmenite–perovskite transition. The correlation of quenchability with rotation angle of GeO6 octahedra for other germanate perovskites is also discussed. 相似文献
7.
In order to elucidate high-pressure transformations of high-P clinopyroxene (C2/c) at kinetically low temperature where atoms are not thermally activated, the transformation processes of FeGeO3 clinopyroxene (C2/c) have been investigated at pressures up to 20 GPa and 365 °C by powder X-ray diffraction using a synchrotron radiation source
and TEM observation. With increasing pressure up to 20 GPa at room temperature, FeGeO3 high-P clinopyroxene (C2/c) reversibly transforms into a new high-pressure phase, FeGeO3(II). On increasing the temperature up to 365 °C, this phase rapidly transforms into FeGeO3 ilmenite within about 2 h. Intensity analysis of the X-ray diffraction pattern reveals that the high-pressure phase of FeGeO3(II) has an intermediate structure between clinopyroxene and ilmenite: the cation arrangement is similar to that of clinopyroxene
and the oxygen arrangement is similar to that of ilmenite. The comparison of the crystal structures of these polymorphs suggests
that clinopyroxene to FeGeO3(II) and FeGeO3(II) to ilmenite transformations are performed by the slight deformation of the oxygen packing and the short-range movement
of cations, respectively. It is shown that this high-P clinopyroxene transforms into ilmenite through a low-activation energy
path under the low-temperature condition.
Received: 30 August 2000 / Accepted: 10 February 2001 相似文献
8.
We conducted high-pressure phase equilibrium experiments in the systems MgSiO3 with 15 wt% H2O and Mg2SiO4 with 5 wt% and 11 wt% H2O at 20 ∼ 27 GPa. Based on the phase relations in these systems, together with the previous works on the related systems,
we have clarified the stability relations of dense hydrous magnesium silicates in the system MgO-SiO2-H2O in the pressure range from 10 to 27 GPa. The results show that the stability field of phase G, which is identical to phase
D and phase F, expands with increasing water contents. Water stored in serpentine in the descending cold slabs is transported
into depths greater than 200 km, where serpentine decomposes to a mixture of phase A, enstatite, and fluid. Reaction sequences
of the hydrous phases which appear at higher pressures vary with water content. In the slabs with a water content less than
about 2 wt%, phase A carries water to a depth of 450 km. Hydrous wadsleyite, hydrous ringwoodite, and ilmenite are the main
water reservoirs in the transition zone from 450 to 660 km. Superhydrous phase B is the water reservoir in the uppermost part
of the lower mantle from 670 to 800 km, whereas phase G appears in the lower mantle only at depths greater than 800 km. In
cold slabs with local water enrichment greater than 2 wt%, the following hydrous phases appear with increasing depths; phase
A to 450 km, phase A and phase G from 450 km to 550 km, brucite, superhydrous phase B, and phase G from 550 km to 800 km,
and phase G at depths greater than 800 km.
Received: 4 August 1999 / Accepted: 1 March 2000 相似文献
9.
Phase transformations in a natural sample of hedenbergite ((Ca0.93Fe0.61Mn0.34Mg0.08Na0.01Zn0.02Al0.003)Si2O6) have been studied by X-ray diffraction up to 40 GPa at ∼ 1200°C in a diamond anvil cell interfaced with a laser heating
system. The starting hedenbergite phase decomposed into a garnet plus γ-spinel and stishovite at ∼ 14 GPa; then into garnet plus stishovite and wüstite at ∼ 18 GPa; and finally into perovskite
plus stishovite and wüstite at pressures higher than ∼ 24 GPa. On decompression to 0.1 MPa, all the high pressure phases are
retained except for the cubic perovskite, which reverts back into the ɛ-CaSiO3 phase, in accordance with previous reports. Energy-dispersive SEM analyses show that the garnet is present as a calcium-rich
ABO
3-type phase. As no garnet phase has been previously observed either in pure CaSiO3 or in pure CaMgSi2O6, it appears that the observed calcium-rich garnet phase has been stabilized by the presence of other cations such as the
Na+, Zn2+, Mn2+, Fe2+, Mn3+, Fe3+ and Al3+. 相似文献
10.
Tomoo Katsura Sho Yokoshi Kazuyuki Kawabe Anton Shatskiy Maki Okube Hiroshi Fukui Eiji Ito Akifumi Nozawa Ken-ichi Funakoshi 《Physics and Chemistry of Minerals》2007,34(4):249-255
The electrical conductivity of (Mg0.93Fe0.07)SiO3 ilmenite was measured at temperatures of 500–1,200 K and pressures of 25–35 GPa in a Kawai-type multi-anvil apparatus equipped
with sintered diamond anvils. In order to verify the reliability of this study, the electrical conductivity of (Mg0.93Fe0.07)SiO3 perovskite was also measured at temperatures of 500–1,400 K and pressures of 30–35 GPa. The pressure calibration was carried
out using in situ X-ray diffraction of MgO as pressure marker. The oxidation conditions of the samples were controlled by
the Fe disk. The activation energy at zero pressure and activation volume for ilmenite are 0.82(6) eV and −1.5(2) cm3/mol, respectively. Those for perovskite were 0.5(1) eV and −0.4(4) cm3/mol, respectively, which are in agreement with the experimental results reported previously. It is concluded that ilmenite
conductivity has a large pressure dependence in the investigated P–T range. 相似文献
11.
Jennifer Linton Alexandra Navrotsky Yingwei Fei 《Physics and Chemistry of Minerals》1998,25(8):591-596
The enthalpies of formation from ilmenite, FeTiO3, and perovskite, CaTiO3, of two intermediate ordered perovskite phases, CaFeTi2O6 and CaFe3Ti4O12, have been measured at 801°C using oxide melt solution calorimetry. These data, in combination with experiments at high pressure
and temperature, indicate that below 1518±50°C CaFe3Ti4O12 is stable at lower pressures (∼7 GPa at 1200°C) than CaFeTi2O6 (∼13 GPa at 1200°C). This relationship should be reversed, and CaFeTi2O6 should become stable at lower pressures than CaFe3Ti4O12, at temperatures above 1518±50°C. These intermediate phases are of petrological interest because they form as a reaction
between two minerals, ilmenite and perovskite, which are commonly associated in kimberlites, and because their pressure-temperature
range of formation overlaps that of origin of kimberlites.
Received: 10 November 1997 / Revised; accepted: 15 January 1998 相似文献
12.
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
13.
T. Okada W. Utsumi H. Kaneko M. Yamakata O. Shimomura 《Physics and Chemistry of Minerals》2002,29(7):439-445
An experimental technique to make real-time observations at high pressure and temperature of the diamond-forming process
in candidate material of mantle fluids as a catalyst has been established for the first time. In situ X-ray diffraction experiments
using synchrotron radiation have been performed upon a mixture of brucite [Mg(OH)2] and graphite as starting material. Brucite decomposes into periclase (MgO) and H2O at 3.6 GPa and 1050 °C while no periclase is formed after the decomposition of brucite at 6.2 GPa and 1150 °C, indicating
that the solubility of the MgO component in H2O greatly increases with increasing pressure. The conversion of graphite to diamond in aqueous fluid has been observed at
7.7 GPa and 1835 °C. Time-dependent X-ray diffraction profiles for this transformation have been successfully obtained.
Received: 17 July 2001 / Accepted: 18 February 2002 相似文献
14.
M. Akaogi H. Takayama H. Kojitani H. Kawaji T. Atake 《Physics and Chemistry of Minerals》2007,34(3):169-183
The low-temperature isobaric heat capacities (C
p) of β- and γ-Mg2SiO4 were measured at the range of 1.8–304.7 K with a thermal relaxation method using the Physical Property Measurement System.
The obtained standard entropies (S°298) of β- and γ-Mg2SiO4 are 86.4 ± 0.4 and 82.7 ± 0.5 J/mol K, respectively. Enthalpies of transitions among α-, β- and γ-Mg2SiO4 were measured by high-temperature drop-solution calorimetry with gas-bubbling technique. The enthalpies of the α−β and β−γ
transitions at 298 K (ΔH°298) in Mg2SiO4 are 27.2 ± 3.6 and 12.9 ± 3.3 kJ/mol, respectively. Calculated α−β and β−γ transition boundaries were generally consistent
with those determined by high-pressure experiments within the errors. Combining the measured ΔH°298 and ΔS°298 with selected data of in situ X-ray diffraction experiments at high pressure, the ΔH°298 and ΔS°298 of the α−β and β−γ transitions were optimized. Calculation using the optimized data tightly constrained the α−β and β−γ transition
boundaries in the P, T space. The slope of α−β transition boundary is 3.1 MPa/K at 13.4 GPa and 1,400 K, and that of β−γ boundary 5.2 MPa/K at 18.7 GPa
and 1,600 K. The post-spinel transition boundary of γ-Mg2SiO4 to MgSiO3 perovskite plus MgO was also calculated, using the optimized data on γ-Mg2SiO4 and available enthalpy and entropy data on MgSiO3 perovskite and MgO. The calculated post-spinel boundary with a Clapeyron slope of −2.6 ± 0.2 MPa/K is located at pressure
consistent with the 660 km discontinuity, considering the error of the thermodynamic data. 相似文献
15.
The crystal structures and energies of SiO2 stishovite, MgO periclase, Mg2SiO4 spinel, and MgSiO3 perovskite were calculated as a function of pressure with the polarization-included electron gas (PEG) model. The calculated pressures of the spinel to perovskite phase transitions in the Mg2SiO4 and MgSiO3 systems are 26.0 GPa and 27.0 GPa, respectively, compared to the experimental zero temperature extrapolations of 27.4 GPa and 27.7 GPa. The two oxide phases are found to be the most stable form in the pressure range 24.5 GPa to 31.5 GPa, compared to the experimental zero temperature extrapolation of 26.7 GPa to 28.0 GPa. The volume changes associated with the phase transitions are in good agreement with experiment. The transition pressures calculated with the PEG model, which allows the ions to distort from spherical symmetry, are in much better agreement with experiment than those calculated with the modified electron gas (MEG) model, which constrains the ions to be spherical. 相似文献
16.
T. Inoue T. Irifune Y. Higo T. Sanehira Y. Sueda A. Yamada T. Shinmei D. Yamazaki J. Ando K. Funakoshi W. Utsumi 《Physics and Chemistry of Minerals》2006,33(2):106-114
The phase boundary between wadsleyite and ringwoodite in Mg2SiO4 has been determined in situ using a multi-anvil apparatus and synchrotron X-rays radiation at SPring-8. In spite of the similar X-ray diffraction profiles of these high-pressure phases with closely related structures, we were able to identify the occurrence of the mutual phase transformations based on the change in the difference profile by utilizing a newly introduced press-oscillation system. The boundary was located at ~18.9 GPa and 1,400°C when we used Shim’s gold pressure scale (Shim et al. in Earth Planet Sci Lett 203:729–739, 2002), which was slightly (~0.8 GPa) lower than the pressure as determined from the quench experiments of Katsura and Ito (J Geophys Res 94:15663–15670, 1989). Although it was difficult to constrain the Clapeyron slope based solely on the present data due to the kinetic problem, the phase boundary [P (GPa)=13.1+4.11×10−3×T (K)] calculated by a combination of a P–T position well constrained by the present experiment and the calorimetric data of Akaogi et al. (J Geophys Res 94:15671–15685, 1989) reasonably explains all the present data within the experimental error. When we used Anderson’s gold pressure scale (Anderson et al. in J Appl Phys 65:1535–1543, 1989), our phase boundary was located in ~18.1 GPa and 1,400°C, and the extrapolation boundary was consistent with that of Kuroda et al. (Phys Chem Miner 27:523–532, 2000), which was determined at high temperature (1,800–2,000°C) using a calibration based on the same pressure scale. Our new phase boundary is marginally consistent with that of Suzuki et al. (Geophys Res Lett 27:803–806, 2000) based on in situ X-ray experiments at lower temperatures (<1,000°C) using Brown’s and Decker’s NaCl pressure scales. 相似文献
17.
Olga B. Fabrichnaya 《Physics and Chemistry of Minerals》1995,22(5):323-332
Based on the available experimental data on phase equilibria in the FeO -MgO -SiO2 system the mixing properties of the solid solutions (olivine, β- and γ-spinel, pyroxene, majorite, ilmenite and perovskite and magnesiowustite), the enthalpies of FeO and fictive FeSiO3 phases with ilmenite and majorite structures have been assessed. The entropies, temperature dependance of heat capacities for fictive FeSiO3 end-members were estimated from structural analogies. The calculated phase diagrams for Mg2SiO4-Fe2SiO4 and MgSiO3 — FeSiO3 systems at pressures up to 30 GPa and temperatures between 1000 and 2100 K are quite consistent with the available experimental determinations except for the fine features of the phase diagram at 2073 K. 相似文献
18.
Lin Li Takaya Nagai Tomoki Ishido Satoko Motai Kiyoshi Fujino Shoichi Itoh 《Physics and Chemistry of Minerals》2014,41(6):431-437
Experiments using laser-heated diamond anvil cells combined with synchrotron X-ray diffraction and SEM–EDS chemical analyses have confirmed the existence of a complete solid solution in the MgSiO3–MnSiO3 perovskite system at high pressure and high temperature. The (Mg, Mn)SiO3 perovskite produced is orthorhombic, and a linear relationship between the unit cell parameters of this perovskite and the proportion of MnSiO3 components incorporated seems to obey Vegard’s rule at about 50 GPa. The orthorhombic distortion, judged from the axial ratios of a/b and \( \sqrt{2}\,a/c, \) monotonically decreases from MgSiO3 to MnSiO3 perovskite at about 50 GPa. The orthorhombic distortion in (Mg0.5, Mn0.5)SiO3 perovskite is almost unchanged with increasing pressure from 30 to 50 GPa. On the other hand, that distortion in (Mg0.9, Mn0.1)SiO3 perovskite increases with pressure. (Mg, Mn)SiO3 perovskite incorporating less than 10 mol% of MnSiO3 component is quenchable. A value of the bulk modulus of 256(2) GPa with a fixed first pressure derivative of four is obtained for (Mg0.9, Mn0.1)SiO3. MnSiO3 is the first chemical component confirmed to form a complete solid solution with MgSiO3 perovskite at the P–T conditions present in the lower mantle. 相似文献
19.
The crystal structure of ScAlO3 has been refined at temperatures up to 1100° C on the basis of x-ray powder diffraction data. The thermal expansion is adequately
described by a Grüneisen-Debye model with the elastic Debye temperature and an effective Grüneisen parameter of 1.6. The volumetric
thermal expansion of 3.0% between 10 and 1100° C, corresponding to a mean thermal expansion coefficient of 2.7 × 10−5 K−1, is entirely attributable to the expansion of the AlO6 octahedra. The interoctahedral angles, though not fixed by symmetry, do not vary significantly with temperature —indicating
that the expansivities of the constituent AlO6 and distorted ScO8 polyhedra are well matched. Similar considerations of polyhedral expansivity suggest thermal expansion coefficients of ∼2
× 10−5K−1 for cubic CaSiO3 perovskite and a value between 2 × 10−5 K−1 and 4 × 10−5 K−1 for MgSiO3 perovskite. The lower value is consistent with the reconnaissance measurements for Mg0.9Fe0.1SiO3 (Knittle et al. 1986) below 350° C, with low-temperature measurements of single-crystal MgSiO3 (Ross and Hazen 1989), and with the results of some recent calculations. The markedly greater expansivity ∼4 × 10−5 K−1 measured at higher temperatures (350–570° C) by Knittle et al. is inconsistent with the simple Grüneisen-Debye quasiharmonic
model and may reflect the marginal metastability of the orthorhombic perovskite phase. Under these circumstances, extrapolation
of the measured expansivity is hazardous and may result in the under-estimation of lower mantle densities and the drawing
of inappropriate inferences concerning the need for chemical stratification of the Earth's mantle. 相似文献
20.
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