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1.
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   

2.
Flux-grown Fe3+-bearing spinel s.s.–hercynite solid-solution crystals, (Mg 1-y Fe2+ y )Al2O4 (0 < y≤ 1), have been investigated by means of electron microprobe technique and Mössbauer and electronic spectroscopy. Obtained results show that different electronic processes cause intense optical absorption bands in the near-infrared spectral region. In addition to an electronic d–d transition in single-ion IVFe2+, observed at 5200 cm?1, intense and broad bands at 9500 and 14 500 cm?1 are assigned to exchange-coupled pair (ECP) and intervalence charge-transfer (IVCT) transitions in VI Fe 2+ VI Fe3+clusters, respectively. The net linear extinction coefficients of these bands (α) were calibrated against Fe2+ and Fe3+ concentrations and site distributions previously defined by combined microchemical, Mössbauer, and XRD structural refinement data. The following expressions were obtained: where α is measured in cm?1 and concentrations are expressed in mol?l?1. The present results show that optical absorption spectroscopy may be used as a probe to obtain high spatial resolution (?～ 10 μm) information on Fe2+ ordering as well as on Fe3+ concentrations in minerals belonging to the spinel group.  相似文献   

3.
《Chemical Geology》2003,193(1-2):93-107
In situ atomic force microscopy (AFM) experiments, scanning electron microscopy (SEM) imaging and composition analysis, and X-ray diffraction have provided information about the growth, dissolution and transformation processes promoted by Sr2+–Ca2+–CO32− aqueous solutions in contact with calcite {101̄4} surfaces. Experiments have shown a wide variety of surface phenomena, such as the influence of the Sr-bearing newly-formed surface on the subsequent growth (template effect), the growth and subsequent dissolution of surfaces and the nucleation of secondary three-dimensional nuclei on calcite surfaces. These phenomena reveal the metastability of the crystallisation system and are a consequence of the interplay between thermodynamics (the relative stability of the two calcite and aragonite structure solid solutions that can be formed), supersaturation of the aqueous solution with respect to the two possible solid solutions, and the crystallographic control of the surfaces on cation incorporation.  相似文献   

4.
The influence on the spinel structure of Fe3+ → Cr substitution was studied in flux-grown synthetic single crystals of the magnesiochromite–magnesioferrite (MgCr2O4–MgFe2O4) solid solution series. Samples were analysed by single-crystal X-ray diffraction, electron microprobe analyses, optical absorption and Mössbauer spectroscopy. With the exception of iron-poor samples (3–12 mol-% MgFe2O4), optical absorption and Mössbauer spectra show that iron occurs almost exclusively as trivalent Fe in the present samples. A very intense and broad absorption band at ca 7,800 cm?1 dominates the optical absorption spectra of samples with higher Fe-contents. The appearance of this band is related to a distinct structural disorder of Fe3+ and a development of magnetic ordering as demonstrated by Mössbauer spectra. Profound composition-related changes are observed in the Mössbauer spectra, which are magnetically unsplit in the range 2–41 mol-% magnesioferrite, but become magnetically split in the range 59–100 mol-% magnesioferrite. Structural parameters a 0 and M–O increase with magnesioferrite content and inversion degree, while u and T–O decrease. Our study confirms the previously reported (Lavina et al. 2002) influence of Fe3+ at the M site on T–O bond lengths in the spinel structure.  相似文献   

5.
To elaborate physicochemical models for the origin of crystalline rocks, experimental studies of the field of high-alumina assemblages of the system CaO–MgO–Al2O3–SiO2 were carried out at 10–30 kbar and 1250–1535 °C. We have determined the phase relations between the melt (L) and An, Sp, Cpx, Cor, and Ga, the slope of the rays of the monovariant reactions An + Sp = Cpx + Cor + (Ga) and L = Cpx +Ga + Cor + Sp, the position of the nonvariant point (An, Sp, Cpx, Cor, Ga, L), and the compositions of phases participating in these reactions. Based on a topological analysis of the studied segment of the system CaO–MgO–Al2O3–SiO2, we have substantiated that “eclogitization” must follow the reaction Opx + An + Sp = Cpx + Ga. A fundamental continuous series of eutectic monovariant equilibria was observed: L = Cpx + Opx + Fo + An, L = Cpx + Opx + An + Sp, L = Cpx (+ Ga) + An + Sp, and L = Cpx + Cor (+ Ga) + An. A change in the melt composition in this series of eutectic reactions depending on pressure must reflect the most likely magma genesis trend in nature. Comparision of the composition fields in which the above series of reactions is observed with the composition fields of the rocks of magmatic formations showed that this series is most similar to the alkali-earth series of rocks. The mineralogical compositions of cumulates and phenocrysts found in the effusive and dike varieties of these rocks correspond to unique sets of subsolidus phase associations and individual subsolidus phases crystallizing in this fundamental eutectic series.  相似文献   

6.

To characterize the influence of alkaline metal chlorides on the phase ratios under melting of upper mantle eclogites, the eclogite–CaCO3–NaCl–KCl system with Н2О + СО2-fluid was studied in the experiments under 4 GPa and 1200–1300°C. A low difference in temperatures (<100°C) was registered between the eclogite solidus and liquidus (>1200 and <1300°C, respectively), which is characteristic for the near-eutectic compositions. The phase proportions were peculiar for the absence of any silicate melt over the entire temperature range considered. The carbonate melt coexisted with clinopyroxene and garnet within 1200–1250°C, whereas a carbonate melt exclusively occurred under above-liquidus conditions at 1300°C. The melt quenching resulted in the formation of a multiphase fine-grained mixture of Ca, Na, and K carbonates and chlorides containing microinclusions of clinopyroxene and garnet. The occurrence of a high-calcium carbonate melt in Cl-containing eclogite systems might play a significant role in the mantle metasomatism of subduction zones characterized by the water–alkaline–chloride type of fluids.

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7.
Geotechnical and Geological Engineering - The solidification technology of sludge can effectively solve the problem of environmental pollution and resource shortage. Whereas, the current study...  相似文献   

8.
Based on state-space method and component analysis, this paper builds a comprehensive evaluation system of carrying capacity for the Beijing–Tianjin–Hebei region from four aspects, namely economy, environment, ecology and energy. The results show that the comprehensive carrying capacity in this region gradually rises in recent years and the economic carrying capacity plays an important role in this situation. Ecological and environmental carrying capacity are gradually enhanced but still affected by water shortages. The energy carrying capacity of this region is low, which is the major factor restricting its sustainable development. Based on the empirical results, following policy suggestions should be adopted: Firstly, local government should accelerate technological progress, promoting the optimization and upgrading of industrial structure; Secondly, the contradiction between supply and demand of water resource should be solved gradually; thirdly, government should develop recycling economy, realizing the coordinated development of economy and environment; last but not least, saving energy and improving energy efficiency.  相似文献   

9.
Bai  Ruiqiang  Lai  Yuanming  Pei  Wansheng  Zhang  Mingyi 《Acta Geotechnica》2020,15(11):3295-3306
Acta Geotechnica - Frost heave is a process of coupled heat–water–mechanics, which refers to heat transfer, water migration, water–ice phase change, deformation, etc. The...  相似文献   

10.
In the present paper, dynamic response of rigid pavements subjected to moving vehicular loads is presented using an analytical procedure based on the finite element method. The vehicle–pavement interaction effects are taken into account while developing the solution algorithm. The concrete pavement is discretized by finite and infinite beam elements. Infinite elements are helpful in appropriate modeling of end conditions. The main purpose of the development of infinite elements is to model the unbounded domain. The underlying soil medium is modeled by Pasternak model which assumes the existence of shear interaction between the spring elements. The moving vehicle is represented by a mass supported by a spring-dashpot system. The vehicle -pavement interaction force is modeled with Dirac-delta function. Dynamic equilibrium equation is solved with Newmark-Beta integration scheme. It has been observed that the dynamic interaction between the moving load and the pavement has significant effect on pavement response. Parametric study is carried out to investigate the effect of vehicle–pavement interaction (VPI) and soil parameters on the response of pavement.  相似文献   

11.
In the present study, influence of wetting–drying cycles on swelling pressures of sand–bentonite mixtures used in the construction of sanitary landfills to have an impermeable liner was investigated before and after lime treatment of the mixtures. Swelling pressure tests were conducted to see if the swelling pressures were affected by wetting–drying cycles. First series of specimens were prepared as a mixture of sand and bentonite only. In the first series of specimens, sand was mixed with bentonite in various proportions with their optimum water contents and compacted by using standard proctor energy. In the second series of the specimens, lime in various proportions was added to the mixtures of sand–bentonite. Then, the sand–bentonite mixtures stabilized by lime were compacted with the standard proctor energy at their optimum moisture contents. Five wetting–drying cycles were performed on each specimen and values of swelling pressures were measured at the end of each cycle. Results of swelling pressure tests indicated that the swelling pressure is decreased when lime is added to the mixtures. In addition, decrements were observed on swelling pressures by wetting–drying cycles. The results of the experiments of this investigation showed that the beneficial effect of lime stabilization to control the swelling pressures was partly lost by the wetting–drying cycles. However, the test results indicated that the swelling pressures of the specimens made of sand–bentonite mixtures stabilized by lime were lower than the swelling pressures of the specimens made of only sand–bentonite mixtures.  相似文献   

12.
The crystal structure of chromite FeCr2O4 was investigated to 13.7 GPa and ambient temperature with single-crystal X-ray diffraction techniques. The unit-cell parameter decreases continuously from 8.3832 (5) to 8.2398 (11) Å up to 11.8 GPa. A fit to the Birch–Murnaghan equation of state (EoS) based on the P–V data gives: K 0 = 209 (13) GPa, K′ = 4.0 (fixed), and V 0 = 588 (1) Å3. The FeO4 tetrahedra and CrO6 octahedra are compressed isotropically with pressure with their Fe–O and Cr–O bond distances decreasing from 1.996 (6) to 1.949 (7) Å and from 1.997 (3) to 1.969 (7) Å, respectively. The tetrahedral site occupied by the Fe2+ cation is more compressible than the octahedral site occupied by the Cr3+ cation. The resulting EoS parameters for the tetrahedral and the octahedral sites are K 0 = 147 (9) GPa, K′ = 4.0 (fixed), V 0 = 4.07 (1) Å3 and K 0 = 275 (24) GPa, K′ = 4.0 (fixed), V 0 = 10.42 (2) Å3, respectively. A discontinuous volume change is observed between 11.8 and 12.6 GPa. This change indicates a phase transition from a cubic (space group Fd-[`3]{\overline{3}} m) to a tetragonal structure (space group I41 /amd). At the phase transition boundary, the two Cr–O bonds parallel to the c-axis shorten from 1.969 (7) to 1.922 (17) Å and the other four Cr–O bonds parallel to the ab plane elongate from 1.969 (7) to 1.987 (9) Å. This anisotropic deformation of the octahedra leads to tetragonal compression of the unit cell along the c-axis. The angular distortion in the octahedron decreases continuously up to 13.7 GPa, whereas the distortion in the tetrahedron rises dramatically after the phase transition. At the pressure of the phase transition, the tetrahedral bond angles along the c-axis direction of the unit cell begin decreasing from 109.5° to 106.6 (7)°, which generates a “stretched” tetrahedral geometry. It is proposed that the Jahn–Teller effect at the tetrahedrally coordinated Fe2+ cation becomes active with compression and gives rise to the tetrahedral angular distortion, which in turn induces the cubic-to-tetragonal transition. A qualitative molecular orbital model is proposed to explain the origin and nature of the Jahn–Teller effect observed in this structure and its role in the pressure-induced phase transition.  相似文献   

13.
We define and calibrate a new model of molar volume as a function of pressure, temperature, ordering state, and composition for spinels in the supersystem (Mg, Fe2+)(Al, Cr, Fe3+)2O4 ? (Mg, Fe2+)2TiO4. We use 832 X-ray and neutron diffraction measurements performed on spinels at ambient and in situ high-P, T conditions to calibrate end-member equations of state and an excess volume model for this system. The effect on molar volume of cation ordering over the octahedral and tetrahedral sites is captured with linear dependence on Mg2+, Al3+, and Fe3+ site occupancy terms. We allow standard-state volumes and coefficients of thermal expansion of the end members to vary within their uncertainties during extraction of the mixing properties, in order to achieve the best fit. Published equations of state of the various spinel end members are analyzed to obtain optimal values of the bulk modulus and its pressure derivative, for each explicit end member. For any spinel composition in the supersystem, the model molar volume is obtained by adding excess volume and cation order-dependent terms to a linear combination of the five end-member volumes, estimated at pressure and temperature using the high-T Vinet equation of state. The preferred model has a total of 9 excess volume and order-dependent parameters and fits nearly all experiments to within 0.02 J/bar/mol, or better than 0.5 % in volume. The model is compared to the current MELTS spinel model with a demonstration of the impact of the model difference on the estimated spinel-garnet lherzolite transition pressure.  相似文献   

14.
Applying Fe2+–Mg exchange geothermometers to natural samples may lead to incorrect temperature estimates if significant Fe3+ is present. In order to quantify this effect, high-pressure experiments were carried out in a belt apparatus in a natural system close to CFMAS at 5 GPa and 1,100–1,400 °C. The oxygen fugacity in the experiments was at or below the Re–ReO2 buffer. This is at significantly more oxidized conditions than in previous experiments, and, as consequence, higher Fe3+/Fe2+ ratios were generated. The Fe3+ content of garnet in the experiments was quantified by electron microprobe using the flank method. Making the usual assumption that Fetotal = Fe2+, the two-pyroxene thermometer of Brey and Köhler (J Pet 31:1353–1378, 1990) reproduced the experimental temperature to ±35 °C and the garnet–clinopyroxene Fe2+–Mg exchange thermometer of Krogh (Contrib Miner Pet 99:44–48, 1988) overestimated the temperatures on average by only 25 °C. On the other hand, application of the garnet–olivine (O’Neill and Wood in Contrib Miner Pet 70:59–70, 1979) and garnet–orthopyroxene (Harley in Contrib Miner Pet 86:359–373, 1984) exchange geothermometers yielded an underestimation in calculated temperatures of >200 °C. However, making explicit accounting for Fe3+ in garnet (i.e. using only measured Fe2+) leads to a vast improvement in the agreement between calculated and experimental temperatures, generally to within ±70 °C for the garnet–orthopyroxene geothermometer as well as noticeable improvement of calculated temperatures for the garnet–olivine geothermometer. Our results demonstrate that the two-pyroxene and garnet–clinopyroxene thermometers are rather insensitive to the presence of Fe3+ whilst direct accounting of Fe3+ in garnet is essential when applying the garnet–olivine and garnet–orthopyroxene thermometers.  相似文献   

15.
正1 Introduction Lithium resources are widely distributed in the oilfield brine from the Nanyishan district in the Qaidam Basin(Fan et al.,2007).The investigation of the thermodynamics and phase diagram of the brine system is valuable in providing the theoretic foundation and scientific guidance in the comprehensive exploitation of the mixture salts effectively.Comprehensive  相似文献   

16.
The Linghou deposit, located near Hangzhou City of Zhejiang Province, eastern China, is a medium-sized polymetallic sulfide deposit associated with granitic intrusion. This deposit is structurally and lithologically controlled and commonly characterized by ore veins or irregular ore lenses. In this deposit, two mineralization events were identified, of which the former produced the Cu–Au–Ag orebodies, while the latter formed Pb–Zn–Cu orebodies. Silicification and calc-silicate (skarn type), phyllic, and carbonate alternation are four principal types of hydrothermal alteration. The early Cu–Au–Ag and late Pb–Zn–Cu mineralizations are characterized by quartz ± sericite + pyrite + chalcopyrite + bornite ± Au–Ag minerals ± magnetite ± molybdenite and calcite + dolomite + sphalerite + pyrite + chalcopyrite + galena, respectively. Calcite clusters and calcite ± quartz vein are formed during the late hydrothermal stage.The NaCl–H2O–CO2 system fluid, coexisting with NaCl–H2O system fluid and showing the similar homogenization temperatures (385 °C and 356 °C, respectively) and different salinities (16.89–21.68 wt.% NaCl eqv. and 7.70–15.53 wt.% NaCl eqv.), suggests that fluid immiscibility occurred during the Cu–Au–Ag mineralization stage and might have given rise to the ore-metal precipitation. The ore-forming fluid of the Pb–Zn–Cu mineralization mainly belongs to the NaCl–H2O–CO2 system of high temperature (~ 401 °C) and mid-high salinity (10.79 wt.% NaCl eqv.).Fluids trapped in the quartz-chalcopyrite vein, Cu–Au–Ag ores, Pb–Zn–Cu ores and calcite clusters yielded δ18OH2O and δD values varying from 5.54‰ to 13.11‰ and from − 71.8‰ to − 105.1‰, respectively, indicating that magmatic fluids may have played an important role in two mineralization events. The δ13CPDB values of the calcite change from − 2.78‰ to − 4.63‰, indicating that the CO32 − or CO2 in the ore-forming fluid of the Pb–Zn–Cu mineralization was mainly sourced from the magmatic system, although dissolution of minor marine carbonate may have also occurred during the ore-forming processes. The sulfide minerals have homogeneous lead isotopic compositions with 206Pb/204Pb ranging from 17.958 to 18.587, 207Pb/204Pb ranging from 15.549 to 15.701, and 208Pb/204Pb ranging from 37.976 to 39.052, indicating that metallic elements of the Linghou deposit came from a mixed source involving mantle and crustal components.Based on geological evidence, fluid inclusions, and H–O–C–S–Pb isotopic data, the Linghou polymetallic deposit is interpreted as a high-temperature, skarn-carbonate replacement type. Two types of mineralization are both related to the magmatic–hydrothermal system, with the Cu–Au–Ag mineralization having a close relationship with granodiorite.  相似文献   

17.
Hydrogen gas produced in the subsurface from the hydration of mafic rocks is known to be a major energy source for chemolithotrophic life in extreme environments such as hydrothermal vents. The possibility that in situ anaerobic microorganisms present in the deep subsurface are sustained by low temperature H2-generating water–rock reactions taking place around them is being investigated. Whether the growth and activity of H2-utilizing microbes directly influences aqueous geochemistry, rates of mineral dissolution, and the chemical composition of the alteration products is also being quantitatively evaluated.To explore how microorganisms are affected by water–rock reactions, and how their activity may in turn affect reaction progress, laboratory experiments have been conducted to monitor the growth of a methanogenic Archaea in the presence of H2(g) produced from low temperature water–Fe0–basalt reactions. In these systems, the conversion of Fe(II) to Fe(III) and subsequent hydrolysis of water is responsible for the production of H2(g). To characterize key components of the geochemical system, time series measurements of H2 and CH4 gas concentrations, Fe and Si aqueous concentrations, and spatially resolved synchrotron-based analyses of microscale Fe distribution and speciation were conducted. Culture experiments were compared with an abiotic control to document changes in the geochemistry both in the presence and absence of the methanogen.In the control abiotic batch experiment, H2 was continuously produced, until the headspace became saturated, while in the biotic experiments, microbial consumption of H2 for methanogenesis draws H2 down and produces CH4. Purging the headspace gas reinitiates H2 and CH4 production in abiotic and culture experiments, respectively. Mass balance analysis of the amount of CH4 produced suggests that the total H2 production in microbial experiments does not exceed the abiotic experiment. Soluble Si concentrations, while buffered to relatively constant values, were higher in culture experiments than the abiotic control.Iron(aq) concentrations appear to respond to perturbations of H2 and CH4 gas concentrations in both culture experiments and the abiotic control. A pulse of Fe preceded the rise in either H2 or CH4 production, and as the gas concentrations increased the Fe(aq) decreased. Iron-bearing mineral assemblages change with increasing reaction time and mineral assemblages vary between culture experiments and the abiotic control. These geochemical trends suggest that there are different reaction paths between the culture experiments and the abiotic control.The hydration of mafic rocks is a common geologic reaction and one that has taken place on Earth for the majority of its history and is postulated to occur on Mars. These reactions are important because of their effect on the rheology and geochemistry of the ocean crust. While most often studied at temperatures of ～250 °C, this work suggests that at lower temperatures microorganisms may have a profound effect on what has long been thought to be solely an abiotic reaction, and may produce diagnostic mineral assemblages that will be preserved in the geological record.  相似文献   

18.
Doklady Earth Sciences - The results of instrumental observations for meteoparameters, microbaric variations, and variations in an electric field are analyzed at the Mikhnevo Observatory and the...  相似文献   

19.
Observations on the RadioAstron ground–space interferometer with the participation of the Green Bank and Arecibo ground telescopes at 1668 MHz have enabled studies of the characteristics of the interstellar plasma in the direction of the pulsar PSR B0525+21. The maximum projected baseline for the ground–space interferometer was 233 600 km. The scintillations in these observations were strong, and the spectrum of inhomogeneties in the interstellar plasma was a power law with index n = 3.74, corresponding to a Kolmogorov spectrum. A new method for estimating the size of the scattering disk was applied to estimate the scattering angle (scattering disk radius) in the direction toward PSR B0525+21, θ scat = 0.028 ± 0.002 milliarcsecond. The scattering in this direction occurs in a plasma layer located at a distance of 0.1Z from the pulsar, where Z is the distance from the pulsar to the observer. For the adopted distance Z = 1.6 kpc, the screen is located at a distance of 1.44 kpc from the observer.  相似文献   

20.
Arc–continent collision is a key process of continental growth through accretion of newly grown magmatic arc crust to older continental margin. We present 2D petrological–thermo-mechanical models of arc–continent collision and investigate geodynamic regimes of this process. The model includes spontaneous slab bending, dehydration of subducted crust, aqueous fluid transport, partial melting of the crustal and mantle rocks and magmatic crustal growth stemming from melt extraction processes. Results point to two end-member types of subsequent arc–continent collisional orogens: (I) orogens with remnants of accretion prism, detached fragments of the overriding plate and magmatic rocks formed from molten subducted sediments; and (II) orogens mainly consisting of the closed back-arc basin suture, detached fragments of the overriding plate with leftovers of the accretion prism and quasi insignificant amount of sediment-derived magmatic rocks. Transitional orogens between these two endmembers include both the suture of the collapsed back-arc basin and variable amounts of magmatic production. The orogenic variability mainly reflects the age of the subducting oceanic plate. Older, therefore colder and denser oceanic plates trigger subduction retreat, which in turn triggers necking of the overriding plate and opening of a backarc basin in which new oceanic lithosphere is formed from voluminous decompression melting of the rising hot asthenosphere. In this case, subducted sediments are not heated enough to melt and generate magmatic plumes. On the other hand, young and less dense slabs do not retreat, which hampers opening of a backarc basin in the overriding plate while subducted sediments may reach their melting temperature and develop trans-lithospheric plumes. We have also investigated the influences of convergence rate and volcanic/plutonic rocks' ratio in newly forming lithosphere. The predicted gross-scale orogenic structures find similarities with some natural orogens, in particular with deeply eroded orogens such as the Variscides in the Bohemian Massif.  相似文献   

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