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1.
Ilya V. Veksler Yana M. Fedorchuk Troels F. D. Nielsen 《Contributions to Mineralogy and Petrology》1998,131(4):347-363
The evolution of nephelinitic melts in equilibrium with mica-bearing liquidus assemblages and melting relations have been
studied on two silica-undersaturated joins of the KAlSiO4– Mg2SiO4– Ca2SiO4– SiO2– F system at atmospheric pressure by quench runs in sealed platinum capsules. Fluorine has been added to the batch compositions
by the direct exchange of fluorine for oxygen (2F− = O2−). The first join is the pseudo-ternary Forsterite – Diopside – KAlSiO3F2 system. Forsterite, diopside, F-phlogopite and leucite crystallisation fields and a fluoride-silicate liquid immiscibility
solvus are present on the liquidus surface of the join. Sub-liquidus and sub-solidus phases include akermanite, cuspidine,
spinel, fluorite and some other minor fluorine phases. The second system is the pseudo-binary Akermanite – F-phlogopite join
that intersects the Forsterite – Diopside – KAlSiO3F2 join. Akermanite, forsterite, diopside, F-phlogopite, leucite and cuspidine are found to crystallise on the join. Forsterite
(fo) and leucite (lc) are related to F-phlogopite (phl) by a reaction with the fluorine-bearing liquid: fo + lc + l = phl,
and the reaction proceeds until forsterite or leucite are completely consumed. The reaction temperature and resulting phase
association depend on batch composition. Thus, leucite is not stable in the sub-solidus of the Akermanite – F-phlogopite join,
but is preserved in a part of the Forsterite – Diopside – KAlSiO3F2 system where forsterite reacts out, or does not crystallise at all. The phlogopite-in reaction has an important effect on
the composition of the coexisting liquid. The liquids initially saturated in forsterite evolve to extremely Ca rich, larnite-normative
residuals. The experimental data show that larnite-normative melilitolites can crystallise from evolved melilititic melts
generated from “normal” melanephelinitic parental magmas with no normative larnite. The evolution towards melilitites requires fractionation of phlogopite-bearing assemblages under volatile pressure.
Received: 3 June 1997 / Accepted: 5 January 1998 相似文献
2.
K.D. Litasov A.F. Shatskiy Yu.N. Pal’yanov A.G. Sokol T. Katsura E. Ohtani 《Russian Geology and Geophysics》2009,50(12):1129-1138
Experiments on water solubility in forsterite in the systems Mg2SiO4–K2Mg(CO3)2–H2O and Mg2SiO4–H2O–C were conducted at 7.5–14.0 GPa and 1200–1600 °C. The resulting crystals contain 448 to 1480 ppm water, which is 40–70% less than in the forsterite–water system under the same conditions. This can be attributed to lower water activity in the carbonate-bearing melt. The water content of forsterite was found to vary systematically with temperature and pressure. For instance, at 14 GPa in the system forsterite–carbonate–H2O the H2O content of forsterite drops from 1140 ppm at 1200 °C to 450 ppm at 1600 °C, and at 8 GPa it remains constant or increases from 550 to 870 ppm at 1300–1600 °C. Preliminary data for D-H-bearing forsterite are reported. Considerable differences were found between IR spectra of D-H- and H-bearing forsterite. The results suggest that CO2 can significantly affect the width of the olivine-wadsleyite transition, i.e., the 410-km seismic discontinuity, which is a function of the water content of olivine and wadsleyite. 相似文献
3.
The second-order elastic constants up to 30 GPa, which encompass the stability field of the spinel forms, their pressure derivatives and the third-order elastic constants of both hydrous and anhydrous -Mg2SiO4 have been obtained theoretically. A combination of deformation theory and finite strain elasticity theory has been employed to arrive at the expressions for second-order and third-order elastic constants from the strain energy of the lattice. The strain energy is calculated by taking into account the interactions up to second nearest neighbours in the -Mg2SiO4 lattice. This is then compared with the strain-dependent lattice energy from continuum model approximation to obtain the expression of elastic constants. The second-order elastic constants Cij compare favourably with the measurements in the case of anhydrous as well as hydrous -Mg2SiO4 and with other calculations on the anhydrous phase. All the third-order elastic constants of both the compounds are negative. The third-order elastic constant C144(–52.41 and –45.07 GPa for anhydrous and hydrous -Mg2SiO4, respectively) representing the anisotropy of shear mode has a smaller value than C111 (–2443.94 and –2101.25 GPa for anhydrous and hydrous phases, respectively), which corresponds to the longitudinal mode. The pressure-induced variations in the longitudinal elastic constants (i.e.,dC11/dp) are relatively large (4.08 and 4.09 for dry and hydrous ringwoodite, respectively) compared with those for the shear (0.22 and 0.32 for dry and hydrous ringwoodite, respectively) and off-diagonal constants (1.40 and 1.41 for dry and hydrous ringwoodite, respectively). The variation of the shear moduli Cs
and anisotropy factor A with pressure have also been studied. The average value of elastic anisotropy is 0.835 in the case of anhydrous -Mg2SiO4 and 0.830 in the hydrous phase. The reversal of sign of the Cauchy pressure C12
– C44, which describes the angular character of atomic bonding in metals and other compounds, at around 21 GPa for both the compounds may be a precursor to the phase transition from ringwoodite to periclase and perovskite at an elevated temperature. The aggregate elastic properties like the adiabatic bulk modulus K (175.4 and 150.2 GPa for anhydrous and hydrous phases, respectively), and the isotropic compressional (P) and shear (S) wave velocities were calculated and the mode Grüneisen Parameters (GPs) of the acoustic waves were determined based on the quasi-harmonic approximation. The low temperature limit
of both hydrous and anhydrous phases of -Mg2SiO4 are positive (1.69 and 1.78, respectively, for hydrous and anhydrous phases) and hence we expect the thermal expansion to be positive down to absolute zero. The Anderson–Grüneisen parameter obtained for hydrous as well as anhydrous phases of -Mg2SiO4 from the second-order and third-order elastic constants are 2.30 and 2.29, respectively. 相似文献
4.
Xiaozhi Yang Leonid Dubrovinsky M. A. G. M. Manthilake Qingguo Wei 《Physics and Chemistry of Minerals》2012,39(1):57-64
In situ Raman spectra of hydrous wadsleyite (β-Mg2SiO4) with ~1.5 wt% H2O, synthesized at 18 GPa and 1,400°C, have been measured in an externally heated diamond anvil cell up to 15.5 GPa and 673 K.
With increasing pressure (at room temperature), the three most intense bands at ~549, 720 and 917 cm−1 shift continuously to higher frequencies, while with increasing temperature at 14.5 GPa, these bands generally shift to lower
frequencies. The temperature-induced frequency shifts at 14.5 GPa are significantly different from those at ambient pressure.
Moreover, two new bands at ~714 and ~550 cm−1 become progressively significant above 333 and 553 K, respectively, and disappear upon cooling to room temperature. No corresponding
Raman modes of these two new bands were reported for wadsleyite at ambient conditions, and they are thus probably related
to thermally activated processes (vibration modes) at high-pressure and temperature conditions. 相似文献
5.
6.
采用多顶砧高压实验装置研究了Mg2SiO4-MgAl2O4体系在压力为22 GPa,温度为1550～1750℃条件下的相变,并考查了Al2O3在γ相中的固溶度.结果表明,随着体系中MgAl2O4组分含量的增加,相组合发生了变化,依次为γ相+镁铝硅酸盐固溶体+方镁石→镁铝硅酸盐固溶体+方镁石→镁铝硅酸盐固溶体+方镁石+刚玉固溶体;镁铝硅酸盐固溶体具有石榴子石结构,其化学成分随着体系中共存相的改变而有所变化;Al2O3在γ相中的固溶度很低(其重量百分比＜0.8%),因此,在Mg2SiO4-MgAl2O4体系中Al2O3可能对γ相超尖晶石分解转变的压力不会有很大的影响. 相似文献
7.
We report the crystal structures determined under ambient condition for two Zn2SiO4 polymorphs synthesized at 6.5 GPa and 1,273 K (phase III) and 8 GPa and 1,273 K (phase IV) and also compare their 29Si MAS NMR spectroscopic characteristics with those of other Zn2SiO4 polymorphs (phases I, II and V). Electron microprobe analysis revealed that both of phases III and IV are stoichiometric like the lower-pressure polymorphs (phases I and II), contrary to previous report. The crystal structures were solved using an ab initio structure determination technique from synchrotron powder X-ray diffraction data utilizing local structural information from 29Si MAS NMR as constraints and were further refined with the Rietveld technique. Phase III is orthorhombic (Pnma) with a = 10.2897(5), b = 6.6711(3), c = 5.0691(2) Å. It is isostructural with the high-temperature (Zn1.1Li0.6Si0.3)SiO4 phase and may be regarded as a ‘tetrahedral olivine’ type that resembles the ‘octahedral olivine’ structure in the (approximately hexagonally close packed) oxygen arrangement and tetrahedral Si positions, but has Zn in tetrahedral, rather than octahedral coordination. Phase IV is orthorhombic (Pbca) with a = 10.9179(4), b = 9.6728(4), c = 6.1184(2) Å. It also consists of tetrahedrally coordinated Zn and Si and features unique edge-shared Zn2O6 dimers. The volumes per formula under ambient condition for phases III and IV are both somewhat larger than that of the lower-pressure polymorph, phase II, suggesting that the two phases may have undergone structural changes during temperature quench and/or pressure release. 相似文献
8.
通过CNDO/2量子化学计算,得到了M_2SiO_4型矿物的结构特征。根据不同阳离子对硅氧四面体骨架的影响程度,对M_2SiO_4型矿物的类质同象现象、熔点、深成岩浆作用中的结晶次序,熔融状态的导电性及M_2SiO_4型炉渣的热力学性质作了系统研究。 相似文献
9.
Data on the mechanisms of mantle phase transformations have come primarily from studies of analogue systems reacted experimentally at low pressures. In order to study transformation mechanisms in Mg2SiO4 at mantle pressures, forsterite () has been reacted in the stability field of -phase, at 15 GPa and temperatures up to 900° C, using a multianvil split-sphere apparatus. Transmission electron microscope studies of samples reacted for times ranging from 0.25–5.0 h show that forsterite transforms to -phase by an incoherent nucleation and growth mechanism involving nucleation on olivine grain boundaries. This mechanism and the resultant microstructures are very similar to those observed at much lower pressures in analogue systems (Mg2GeO4 and Ni2SiO4) as the result of the olivine to spinel () transformation. Metastable spinel () also forms from Mg2SiO4 olivine at 15 GPa, in addition to -phase, by the incoherent nucleation and growth mechanism. With time, the spinel progressively transforms to the stable -phase. After 1 h, spinels exhibit a highly striated microstructure along {110} and electron diffraction patterns show streaking parallel to [110] which indicates a high degree of structural disorder. High resolution imaging shows that the streaking results from thin lamellae of -phase intergrown with the spinel. The two phases have the orientation relationship [001]//[001] and [010]//[110] so that the quasi cubic-close-packed oxygen sublattices are continuous between both phases. These microstructures are similar to those observed in shocked meteorites and show that spinel transforms to -phase by a martensitic (shear) mechanism. There is also evidence that the mechanism changes to one involving diffusion-controlled growth at conditions close to equilibrium. 相似文献
10.
Liquid–liquid immiscibility has crucial influences on geological processes, such as magma degassing and formation of ore deposits. Sulfate, as an important component, associates with many kinds of deposits. Two types of immiscibility, including (i) fluid–melt immiscibility between an aqueous solution and a sulfate melt, and (ii) fluid–fluid immiscibility between two aqueous fluids with different sulfate concentrations, have been identified for sulfate–water systems. In this study, we investigated the immiscibility behaviors of a sulfate- and quartz-saturated Na2SO4–SiO2–H2O system at elevated temperature, to explore the phase relationships involving both types of immiscibility. The fluid–melt immiscibility appeared first when the Na2SO4–SiO2–H2O sample was heated to ~270°C, and then fluid–fluid immiscibility emerged while the sample was further heated to ~450°C. At this stage, the coexistence of one water-saturated sulfate melt and two aqueous fluids with distinct sulfate concentrations was observed. The three immiscible phases remain stable over a wide pressure–temperature range, and the appearance temperature of the fluid–fluid immiscibility increases with the increased pressure. Considering that sulfate components occur extensively in carbonatite-related deposits, the fluid–fluid immiscibility can result in significant sulfate fractionation and provides implications for understanding the formation of carbonatite-related rare earth deposits. 相似文献
11.
The configurational heat capacity, shear modulus and shear viscosity of a series of Na2O–Fe2O3–Al2O3–SiO2 melts have been determined as a function of composition. A change in composition dependence of each of the physical properties
is observed as Na2O/(Na2O + Al2O3) is decreased, and the peralkaline melts become peraluminous and a new charge-balanced Al-structure appears in the melts.
Of special interest are the frequency dependent (1 mHz–1 Hz) measurements of the shear modulus. These forced oscillation measurements
determine the lifetimes of Si–O bonds and Na–O bonds in the melt. The lifetime of the Al–O bonds could not, however, be resolved
from the mechanical spectrum. Therefore, it appears that the lifetime of Al–O bonds in these melts is similar to that of Si–O
bonds with the Al–O relaxation peak being subsumed by the Si–O relaxation peak. The appearance of a new Al-structure in the
peraluminous melts also cannot be resolved from the mechanical spectra, although a change in elastic shear modulus is determined
as a function of composition. The structural shear-relaxation time of some of these melts is not that which is predicted by
the Maxwell equation, but up to 1.5 orders of magnitude faster. Although the configurational heat capacity, density and shear
modulus of the melts show a change in trend as a function of composition at the boundary between peralkaline and peraluminous,
the deviation in relaxation time from the Maxwell equation occurs in the peralkaline regime. The measured relaxation times
for both the very peralkaline melts and the peraluminous melts are identical with the calculated Maxwell relaxation time.
As the Maxwell equation was created to describe the timescale of flow of a mono-structure material, a deviation from the prediction
would indicate that the structure of the melt is too complex to be described by this simple flow equation. One possibility
is that Al-rich channels form and then disappear with decreasing Si/Al, and that the flow is dominated by the lifetime of
Si–O bonds in the Al-poor peralkaline melts, and by the lifetime of Al–O bonds in the relatively Si-poor peralkaline and peraluminous
melts with a complex flow mechanism occurring in the mid-compositions. This anomalous deviation from the calculated relaxation
time appears to be independent of the change in structure expected to occur at the peralkaline/peraluminous boundary due to
the lack of charge-balancing cations for the Al-tetrahedra. 相似文献
12.
Ｘ射线单晶衍射测定了高压合成的完全含水的黄玉类Ａｌ２ＳｉＯ４（ＯＨ）２中Ｈ的位置。两个非等效的Ｈ位置相距２．４Ａ。两个Ｈ的位置明显地代替了在天然的含ＯＨ的氟黄玉中所发现的单个Ｈ位，并至少局部地影响了空间群ｐｂｎｍ的对称面。 相似文献
13.
New internally consistent interpretations of the phases represented by the high pressure phase shock wave data for an albite-rich rock, Jadeite, and nepheline in the system NaAlSiO4-SiO2, are obtained using the results of static high pressure investigations, and the recent discovery of the hollandite phase in a shocked meteorite. We conclude that nepheline transforms directly to the calcium ferrite structure, whereas albite transforms possibly to the hollandite structure. Shock Hugoniots for the other plagioclase and alkali feldspars also indicate that these transform to hollandite structures. The pressure-volume data at high pressure could alternatively represent the compression of an amorphous phase. Moreover, the shock Hugoniot data are expected to reflect the properties of the melt above shock stresses of 60–80 GPa. The third order Birch-Murnaghan equation of state parameters are: Kos=275±38 GPa and Kos=1.6±1.5 for the calcium ferrite type NaAlSiO4, Kos=186±33 GPA and Kos=2.6±1.7 for the albite-rich hollandite, Kos=236±45 GPa and Kos=2.3±2.0 for the orthoclase-rich hollandite, and Kos=190 to 210 GPa and Kos2.2 for the anorthite-rich hollandite. 相似文献
14.
Liquidus phase relations in the system diopside–kalsilite–forsterite–quartz with 3 wt% F were examined at 1 bar and the locations
of important invariant points were determined at 18 kbar. At all pressures within this range a large liquidus field for fluorphlogopite
(Phl) exists, and has a large influence on both melting and fractionation processes. One eutectic point was found to the silica-rich
side of the plane Lc–Fo–Di at Di1Ks30Fo2Qz67, where a melt coexists with San, Qz, Phl and Di at 840 °C and 1 bar. Another eutectic point must exist in the silica-poor
part of the system because the phase topology determines that thermal barriers must exist. At this point a feldspathoid, either
Lc or Ks, must coexist with Fo, Phl and a Ca-bearing phase such as Di. The exact location and phase assemblage were not determined,
but the equilibrium melt must have a composition rich in Di (>29 wt%) and extremely poor in Qz (<8 wt%). The composition of
the first eutectic moves towards lower SiO2 contents with increasing pressure (Di3Ks40Fo1Qz56 at 18 kbar), whereas the second does not exist at 18 kbar due to the disappearance of Lc as a stable liquidus phase. Liquids
which coexist with mafic minerals such as En, Fo, Phl and Di are important for the genesis of potassium-rich mafic rocks by
partial melting in the mantle and for the early stages of fractional crystallisation. The equilibrium melt at the invariant
point Fo + En + Phl + Di + L at 1125 °C is very poor in Fo and Di components at atmospheric pressure (Di5Ks37Fo5Qz53), whereas at 18 kbar the melt contains large amounts of Fo and Di (Di19Ks31- Fo28Qz21), and has a composition close to that of natural lamproites. Kamafugites do not correspond to melts in this system under
any of the studied conditions, and appear to require CO2 in the source. Fractionation processes from primitive potassic basanite melts are controlled principally by the size (and
not the mere presence) of the liquidus phase field for phlogopite: at high pressures where the Phl field is large, olivine
is eliminated early from the fractionating assemblage and Cpx + Phl fractionation may lead to relatively silica-rich rock
differentiates such as trachytes. At low pressures, extensive olivine and restricted Phl crystallisation prevents silica enrichment
in the melt, resulting in phonolitic differentiates. Later crystallisation of alkali feldspar accentuates the trends laid
down in the early stages of fractionation.
Received: 2 February 1999 / Accepted: 14 October 1999 相似文献
15.
１金属基板上ＳｉＯ２ ＴｉＯ２ ＺｒＯ２陶瓷涂层工艺的研究现状在金属基板上进行Ｓｏｌ ｇｅｌ涂层是国外在９０年代发展起来的一项新工艺。根据金属陶瓷复合材料这一新兴工业的应用前景,一些工业发达国家的政府研究部门和工业界都十分重视这项新工艺的开发与研究,... 相似文献
16.
正确测定地下热水中的SiO_2含量是很重要,而且也很必要。因为SiO_2的浓度用作地热温标,可估算地下热储的温度,为地热能的开发提供信息。因此地下热水中SiO_2的取样方法是至关重要的。 传统的SiO_2取样方法是在现场直接取原水样带口实验室,通常用分光光度法(比色法)进行测定。这对于一般天然水和中低温地热水来讲是合理的,因为它们中的SiO_2含量一般小于100mg/L,SiO_2以可溶性状态(单体)存在于水中。但对于高温地下热水(大于80℃), 相似文献
17.
Two synthetic series of spinels, MgCr2O4–Fe2+Cr2O4 and MgCr2O4–MgFe2 3+O4 have been studied by Raman spectroscopy to investigate the effects of Fe2+ and Fe3+ on their structure. In the first case, where Fe2+ substitutes Mg within the tetrahedral site, there is a continuous and monotonic shift of the Raman modes A1g and Eg toward lower wavenumbers with the increase of the chromite component into the spinel, while the F2g modes remain nearly in the same position. In the second series, for low Mg-ferrite content, Fe3+ substitutes for Cr in the octahedral site; when the Mg-ferrite content nears 40 %, a drastic change in the Raman spectra occurs as Fe3+ starts entering the tetrahedral site as well, consequently pushing Mg to occupy the octahedral one. The Raman spectral region between 620 and 700 cm?1 is associated to the octahedral site, where three peaks are present and it is possible to observe the Cr–Fe3+ substitution and the effects of order–disorder in the tetrahedral site. The spectral range at 500–620 cm?1 region shows that there is a shift of modes toward lower values with the increase of the Mg-ferrite content. The peaks in the region at 200–500 cm?1, when observed, show little or negligible Raman shift. 相似文献
18.
Kevin J. Grant Simon C. Kohn Richard A. Brooker 《Contributions to Mineralogy and Petrology》2006,151(6):651-664
The solubility of water in coexisting enstatite and forsterite was investigated by simultaneously synthesizing the two phases in a series of high pressure and temperature piston cylinder experiments. Experiments were performed at 1.0 and 2.0 GPa at temperatures between 1,100 and 1,420°C. Integrated OH absorbances were determined using polarized infrared spectroscopy on orientated single crystals of each phase. Phase water contents were estimated using the calibration of Libowitzky and Rossman (Am Mineral 82:1111–1115, 1997). Enstatite crystals, synthesized in equilibrium with forsterite and an aqueous phase at 1,350°C and 2.0 GPa, contain 114 ppm H2O. This is reduced to 59 ppm at 1,100°C, under otherwise identical conditions, suggesting a strong temperature dependence. At 1,350°C and 1.0 GPa water solubility in enstatite is 89 ppm, significantly lower than that at 2.0 GPa. In contrast water solubility in forsterite is essentially constant, being in the range 36–41 ppm for all conditions studied. These data give partition coefficients
in the range 2.28–3.31 for all experiments at 1,350°C and 1.34 for one experiment at 1,100°C. The incorporation of Al2O3 in enstatite modifies the OH stretching spectrum in a systematic way, and slightly increases the water solubility. 相似文献
19.
Sol-gel法制备SiO2-TiO2复合薄膜，进行甲醛的光催化降解实验，研究了SiO2掺杂量、薄膜焙烧温度、甲醛溶液pH值及初始浓度对光催化性能的影响。结果表明，500℃焙烧1h，掺杂质量SiO2：TiO2=12：100时，SiO2-TiO2薄膜的光催化活性最高，150min后甲醛降解率达76％，是单纯TiO2薄膜的1．3倍，该薄膜稳定性较好，经重复8次使用，最大降解率只下降4％。 相似文献
20.
The synthesis boundaries of the phase transformation; ++ in (Mg0.9, Fe0.1)SiO4, have been clarified at temperatures to 2000° C and pressures up to 20 GPa in order to synthesize single crystals of high quality. A single crystal of (Mg0.9, Fe0.1)2SiO4 was grown successfully to a size of 500 m. The crystal structure has been refined from single-crystal X-ray intensities. The ferrous ions prefer M1 and M3 sites to over the larger M2 site. The volume change of all the occupied polyhedra does not contribute to the decrease of total volume in the transformation; rather it tends to increase the bulk volume through the expansion of occupied tetrahedra. The volume reduction in the phase transformations is accounted for by unoccupied polyhedra, with the octahedra contributory 60% and the tetrahedra 40% to the V of the transition. The volume change in the transformation is caused also partly by the volume decrease of MO
6 (25%), partly the unoccupied tetrahedra (45%) and octahedra (30%). 相似文献