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1.
We performed comparative study of phase relations in Fe1−x Ni x (0.10 ≤ x ≤ 0.22 atomic fraction) and Fe0.90Ni0.10−x C x (0.1 ≤ x ≤ 0.5 atomic fraction) systems at pressures to 45 GPa and temperatures to 2,600 K using laser-heated diamond anvil cell and large-volume press (LVP) techniques. We show that laser heating of Fe,Ni alloys in DAC even to relatively low temperatures can lead to the contamination of the sample with the carbon coming from diamond anvils, which results in the decomposition of the alloy into iron- and nickel-rich phases. Based on the results of LVP experiments with Fe–Ni–C system (at pressures up to 20 GPa and temperatures to 2,300 K) we demonstrate decrease of carbon solubility in Fe,Ni alloy with pressure.  相似文献   

2.
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   

3.
We have investigated melting relations in the Fe–O–S ternary system in the pressure range of 15–27 GPa and 1873 K. Subsolidus phase relations are Fe, Fe3S2, and FeO up to 17 GPa and Fe, Fe3S, and FeO above this pressure. The eutectic temperature slightly decreases from ambient pressure to 17 GPa, whereas increases above this pressure. The eutectic temperature in this study is 100 K lower than that in the Fe–S binary system. The oxygen content in the Fe–O–S eutectic liquid drops when the coexisting solid phases changes from FeS to Fe3S2. The cotectic lines in the ternary phase diagram lie close to the Fe–FeS binary axis. The isothermal sections indicate that oxygen solubility in the Fe–O–S liquid increases with increasing temperature, and with increasing sulfur content. The solubility of sulfur in the solid Fe has a maximum value at the eutectic temperature, and decreases with increasing temperature. Our results could have important implications for formation and composition of the Martian core.  相似文献   

4.
The graphite-diamond transformation was investigated by in situ time-resolved X-ray diffraction experiments using aqueous fluid containing dissolved MgO as the diamond-forming catalyst under conditions of 6.6–8.9 GPa and 1400–1835 °C. The transformed volume fractions of diamond as a function of time under various pressure-temperature conditions were obtained and analyzed using the JMAK rate equation. Variations in the nucleation and growth processes during diamond formation as a function of pressure and temperature were clarified.  相似文献   

5.
Shuidonggou site has abundant Paleolithic remains of Late Pleistocene deposition. Studying the evolution of depositional environments is essential to the comprehensive understanding of the living conditions of ancient populations. To reconstruct the depositional environment at Shuidonggou, we carried out archaeological excavations and collected systematic deposition samples at the key position of Shuidonggou Locality 2 for grain size analysis and sporopollen statistics. The environmental evolution around the Shuidonggou site generally underwent four stages at ~72–18 kaBP. During the first stage (~72–41 kaBP), the river developed with gravel and sand stratums. During the second stage (41~34 kaBP), a swamp with numerous aquatic plants formed. In the third stage (34–29 kaBP), site formation was characterized by shallow lake depositional conditions; the climate was relatively warm and humid. The marginal bank depositional conditions deteriorated during the fourth stage (29–18 kaBP), and the site underwent several dry events; the climate also became drier and colder.  相似文献   

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High pressure melting behavior of three Fe-alloys containing 5 wt% Ni and (1) 10 wt% Si, (2) 15 wt% Si or (3) 12 wt% S was investigated up to megabar pressures by in situ X-ray diffraction and laser-heated diamond anvil cell techniques. We observe a decrease in melting temperature with increasing Si content over the entire investigated pressure range. This trend is used to discuss the melting curve of pure Fe. Moreover, our measurements of eutectic melting in the Fe–Fe3S system show a change in slope around 50 GPa concomitant with the fcc–hcp phase transition in pure solid iron. Extrapolations of our melting curve up to the core–mantle boundary pressure yield values of 3,600–3,750 K for the freezing temperature of plausible outer core compositions.  相似文献   

8.
The objective of the present study was to demonstrate the possibility of application of high-pressure equipment in combination with the solid state EMF technique. The equilibrium reaction 3?Ag+Sb?Ag3Sb was chosen for the studies. The experiments were carried out under argon gas pressure and the majority of data points were measured in the pressure range 4000–8000?bar at temperatures 550–725?K. The solid electrolyte consisted of AgI. Reproducible results were obtained along seven isotherms and one isobar at 7100?bar. The molar volume change for the reaction studied was calculated and compared with corresponding literature data at one bar.  相似文献   

9.
Diamond crystallization has been studied in the SiO2–H2O–С, Mg2SiO4–H2O–С and H2O–С subsystems at 7.5 GPa and 1,600°C. We found that dissolution of initial graphite is followed by spontaneous nucleation of diamond and growth of diamond on seed crystals. In 15-h runs, the degree of graphite to diamond transformation [α = MDm/(MDm + MGr)100, where MDm is mass of obtained diamond and MGr mass of residual graphite] reached 100% in H2O-rich fluids but was only 35–50% in water-saturated silicate melts. In 40-h runs, an abrupt decrease of α has been established at the weight ratio H2O/(H2O + SiO2) ≤ 0.16 or H2O/(H2O + Mg2SiO4) ≤ 0.15. Our results indicate that α is a function of the concentration of water, which controls both the kinetics of diamond nucleation and the intensity of carbon mass transfer in the systems. The most favorable conditions for diamond crystallization in the mantle silicate environment at reliable PT-parameters occur in the fluid phase with low concentration of silicates solute. In H2O-poor silicate melts diamond formation is questionable.  相似文献   

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We present the results of a series of density experiments in the system O–S–Fe–Ni–Cu. These experiments were designed to extend our understanding of the physical properties of sulfide liquids, and to extend one-bar thermochemical models for sulfide liquids to apply to low to moderate pressures. Density measurements indicate both positive and negative deviations from linear mixing of partial molar volumes across this five-dimensional composition space. In terms of the homogeneous speciation model of Kress (in Contrib Mineral Petrol 154:191–204, 2007), the best fit to experimental data can be achieved by starting with a model where the volume of formation reaction for associated species initially is set to zero. Further refinement of this first-order fit yields a volume mixing model which reproduces experimental data to within nearly the estimated experimental uncertainty. Experimental ultrasonic and X-ray absorption data from the literature, along with the bulk modulus–volume relation of Anderson and Nafe (J Geophys Res 16:3951–3963, 1965), allow the estimation of the pressure dependence of partial molar volumes for sulfide liquid species. The resulting combined thermochemical model should be valid to about 2,000 K and 3 GPa. Application of this thermochemical model in a simple adiabatic magma ascent scenario confirms earlier work suggesting that the pressure dependence of sulfur solubility in sulfide-saturated magma will decrease with increasing pressure along geologically reasonable paths in PT–– space.  相似文献   

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14.
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   

15.
The incorporation of hydrogen in enstatite in a hydrous system containing various amounts of NaCl was investigated at 25 kbar. The hydrogen content in enstatite shows a clear negative correlation to the NaCl-concentration in the system. The most favourable explanation is the reduction of water fugacity due to dilution. Other reasons for the limited hydrogen incorporation at high NaCl levels, such as a significant influence of Na+ on the defect chemistry or an exchange between OH- and Clin enstatite, appear much less important. A partition coefficient D Na En/Fluid = 0.0013 could be determined, demonstrating that Na is less incompatible in enstatite than H. The new results support the idea that dissolved components have to be considered when the total hydrogen storage capacity in nominally anhydrous minerals is estimated, especially in geological settings with high levels of halogens, such as subduction zones.  相似文献   

16.
Magnesite, siderite and ferromagnesites Mg1?x Fe x CO3 (x = 0.05, 0.09, 0.2, 0.4) were characterized using in situ Raman spectroscopy at high pressures up to 55 GPa. For the Mg–Fe-carbonates, the Raman peak positions of six modes (T, L, ν4, ν1, ν3 and 2ν2) in the dependence of iron content in the carbonates at ambient conditions are presented. High-pressure Raman spectroscopy shows that siderite undergoes a spin transition at ~40 GPa. The examination of the solid solutions with compositions Mg0.6Fe0.4CO3, Mg0.8Fe0.2CO3, Mg0.91Fe0.09CO3 and Mg0.95Fe0.05CO3 indicates that with increase in the amount of the Fe spin transition pressure increases up to ~45 GPa.  相似文献   

17.
According to the compositions of the underground gasfield brines in the west of Sichuan Basin,the phase equilibria in the ternary systems KBr-K2B4O7-H2O and KCl-K2B4O7-H2O at 373 K were studied using the isothermal dissolution equilibrium method.The solubilities of salts and the densities of saturated solutions in these ternary systems were determined.Using the experimental data,phase diagrams and density-composition diagrams were constructed.The two phase diagrams were simple co-saturation type,each having an invariant point,two univariant curves and two crystallization regions.The equilibrium solid phases in the ternary system KBr-K2B4O7-H2O are potassium bromide (KBr) and potassium tetraborate tetrahydrate (K2B4O7·4H2O),and those in the ternary system KCl-K2B4O7-H2O are potassium chloride (KCl) and potassium tetraborate tetrahydrate (K2B4O7·4H2O).Comparisons of the phase diagrams of the two systems at different temperatures show that there is no change in the crystallization phases,but there are changes in the size of the crystallization regions.As temperature increases,the solubility of K2B4O7·4H2O increases rapidly,so the crystallization field of K2B4O7·4H2O becomes smaller.  相似文献   

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正1 Introduction The underground brine resources distributing widely in Sichuan Basin,China have drawn worldwide attention due to their unusual element abundance and excellent quality.  相似文献   

20.
Hydrous K-rich kimberlite-like systems are studied experimentally at 5.5–7.5 GPa and 1200–1450?°C in terms of phase relations and conditions for formation and stability of phlogopite. The starting samples are phlogopite–carbonatite–phlogopite sandwiches and harzburgite–carbonatite mixtures consisting of Ol?+?Grt?+?Cpx?+?L (±Opx), according to the previous experimental results obtained at the same PT parameters but in water-free systems. Carbonatite is represented by a K- and Ca-rich composition that may form at the top of a slab. In the presence of carbonatitic melt, phlogopite can partly melt in a peritectic reaction at 5.5 GPa and 1200–1350?°C, as well as at 6.3–7.0 GPa and 1200?°C: 2Phl?+?CaCO3 (L)?Cpx?+?Ol?+?Grt?+?K2CO3 (L)?+?2H2O (L). Synthesis of phlogopite at 5.5 GPa and 1200–1350?°C, with an initial mixture of H2O-bearing harzburgite and carbonatite, demonstrates experimentally that equilibrium in this reaction can be shifted from right to left. Therefore, phlogopite can equilibrate with ultrapotassic carbonate–silicate melts in a?≥?150?°C region between 1200 and 1350?°C at 5.5 GPa. On the other hand, it can exist but cannot nucleate spontaneously and crystallize in the presence of such melts in quite a large pressure range in experiments at 6.3–7.0 GPa and 1200?°C. Thus, phlogopite can result from metasomatism of peridotite at the base of continental lithospheric mantle (CLM) by ultrapotassic carbonatite agents at depths shallower than 180–195 km, which creates a mechanism of water retaining in CLM. Kimberlite formation can begin at 5.5 GPa and 1350?°C in a phlogopite-bearing peridotite source generating a hydrous carbonate–silicate melt with 10–15 wt% SiO2, Ca# from 45 to 60, and high K enrichment. Upon further heating to 1450?°C due to the effect of a mantle plume at the CLM base, phlogopite disappears and a kimberlite-like melt forms with SiO2 to 20 wt% and Ca#?=?35–40.  相似文献   

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