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1.
The composition of a reduced C–O–H fluid was studied by the method of chromatography–mass spectrometry under the conditions of 6.3 GPa, 1300–1400°C, and fO2 typical of the base of the subcratonic lithosphere. Fluids containing water (4.4–96.3 rel. %), methane (37.6–0.06 rel. %), and variable concentrations of ethane, propane, and butane were obtained in experiments. With increasing fO2, the proportion of the CH4/C2H6 peak areas on chromatograms first increases and then decreases, whereas the CH4/C3H8 and CH4/C4H10 ratios continually decrease. The new data show that ethane and heavier HCs may be more stable to oxidation, than previously thought. Therefore, when reduced fluids pass the “redox-front,” carbon is not completely released from the fluid and may be involved in diamond formation.  相似文献   

2.
Interactions in a Fe–C–O–H–N system that controls the mobility of siderophile nitrogen and carbon in the Fe0-saturated upper mantle are investigated in experiments at 6.3–7.8 GPa and 1200–1400 °C. The results show that the γ-Fe and metal melt phases equilibrated with the fluid in a system unsaturated with carbon and nitrogen are stable at 1300 °C. The interactions of Fe3C with an N-rich fluid in a graphite-saturated system produce the ε-Fe3N phase (space group P63/mmc or P6322) at subsolidus conditions of 1200–1300 °C, while N-rich melts form at 1400 °C. At IW- and MMO-buffered hydrogen fugacity (fH2), fluids vary from NH3- to H2O-rich compositions (NH3/N2?>?1 in all cases) with relatively high contents of alkanes. The fluid derived from N-poor samples contains less H2O and more carbon which mainly reside in oxygenated hydrocarbons, i.e., alcohols and esters at MMO-buffered fH2 and carboxylic acids at unbuffered fH2 conditions. In unbuffered conditions, N2 is the principal nitrogen host (NH3/N2?≤?0.1) in the fluid equilibrated with the metal phase. Relatively C- and N-rich fluids in equilibrium with the metal phase (γ-Fe, melt, or Fe3N) are stable at the upper mantle pressures and temperatures. According to our estimates, the metal/fluid partition coefficient of nitrogen is higher than that of carbon. Thus, nitrogen has a greater affinity for iron than carbon. The general inference is that reduced fluids can successfully transport volatiles from the metal-saturated mantle to metal-free shallow mantle domains. However, nitrogen has a higher affinity for iron and selectively accumulates in the metal phase, while highly mobile carbon resides in the fluid phase. This may be a controlling mechanism of the deep carbon and nitrogen cycles.  相似文献   

3.
Doklady Earth Sciences - The first results on diamond growth in the Fe–С–S system with 1 wt % S (relative to Fe) at 6 GPa and 1450°C have been reported. The diamonds obtained...  相似文献   

4.
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   

5.
Doklady Earth Sciences - The liquid phases are represented by immiscible Fe–S and Fe–C melts under partial melting of the graphite-saturated Fe–S–C system at P = 0.5 GPa and...  相似文献   

6.
Metasomatism of the lithospheric mantle sometimes produces unusual assemblages containing native metals and alloys, which provide important insight into metasomatic processes in the mantle. In this study, we describe the metasomatic enrichment of a refractory harzburgite xenolith in Ni, Fe and, to a lesser extent, Cu, Co, As and Sb. The xenolith (XM1/422) derives from the Bultfontein kimberlite (Kimberley, South Africa) and hosts Ni mineralisation that includes native nickel (Ni84.5-98.0), heazlewoodite (Ni3S2) and Ni-rich silicates (e.g. up to 37.5 wt % NiO in olivine, and 22.4 wt % NiO in phlogopite). The presence of several mineral phases enriched in alkali and volatile species (e.g. phlogopite, phosphates, carbonates, chlorides, djerfisherite) indicates that the transition metal cations were likely introduced during metasomatism by alkali-rich C–O–H fluids or alkali-carbonate melts. It is postulated that sulphide breakdown and fluid reaction with refractory mantle rocks contributed to the fluid’s enrichment in Ni and other metallic cations. The Ni-rich assemblages of xenolith XM1/422 show local chemical disequilibrium, and modelling of the Ni diffusion profiles adjacent to olivine-native nickel and olivine-heazlewoodite grain boundaries, suggests a close temporal relationship between Ni-rich metasomatism and subsequent entrainment by the kimberlite magma. However, metal-rich metasomatism has also been observed in other lithospheric mantle domains, including orogenic peridotitic massifs and the suboceanic mantle; regions unaffected by kimberlite magmatsim. As micro-scale occurrences of metallic phases are easily overlooked, it is possible that metal-rich metasomatism is more widespread in the Earth’s mantle than previously recognised.  相似文献   

7.
We recorded the photoelectron spectra of various crystalline calcium silicate hydrates (C–S–Hs) and have examined their O 1 s photoelectron spectra. The spectra are asymmetric, with contributions assigned primarily to bridging and non-bridging oxygen species. There is an increased contribution due to the presence of non-bonding oxygen atoms with increasing calcium:silicon ratio. Additionally, there are slight changes in theO 1s-binding energies with changes in calcium:silicon ratio. These changes are explained in terms of bonding and silicate structure.  相似文献   

8.
Experimental data is provided for the transport of platinum in a supercritical C–O–H fluid system. The transfer of platinum in space with its condensation on the surface of native carbon (diamond and amorphous carbon) in the form of micro- and nanocrystals, shapeless particles, and filamentous formations is established for the first time. The dominant participation of platinum in the formation of carbon micro- and nanotubes is demonstrated. The results are important in modeling the formation of noble metal deposits with deep fluid carbon systems.  相似文献   

9.
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   

10.
Reliable thermodynamic models assessing the interaction of radionuclides with cementitious materials are important in connection with long-term predictions of the safe disposal of radioactive waste in cement-based repositories. In this study, a geochemical model of U(VI) interaction with calcium silicate hydrates (C–S–H phases), the main component of hardened cement paste (HCP), has been developed. Uranium(VI) sorption isotherms on C–S–H phases of different Ca:Si ratios (C:S) and structural data from spectroscopic studies provided the indispensable set of experimental data required for the model development. This information suggested that U(VI) is neither adsorbed nor incorporated in the Ca–O octahedral layers of the C–S–H structure, but rather is located in the interlayer, similar to Ca2+ and other cations. With a view to the high recrystallisation rates and the cryptocrystalline ‘gel-like’ structure of the C–S–H phases, these observations indicated a U(VI) uptake driven by the formation of a solid solution.  相似文献   

11.
The sound velocity (V P) of liquid Fe–10 wt% Ni and Fe–10 wt% Ni–4 wt% C up to 6.6 GPa was studied using the ultrasonic pulse-echo method combined with synchrotron X-ray techniques. The obtained V P of liquid Fe–Ni is insensitive to temperature, whereas that of liquid Fe–Ni–C tends to decrease with increasing temperature. The V P values of both liquid Fe–Ni and Fe–Ni–C increase with pressure. Alloying with 10 wt% of Ni slightly reduces the V P of liquid Fe, whereas alloying with C is likely to increase the V P. However, a difference in V P between liquid Fe–Ni and Fe–Ni–C becomes to be smaller at higher temperature. By fitting the measured V P data with the Murnaghan equation of state, the adiabatic bulk modulus (K S0) and its pressure derivative (K S ′ ) were obtained to be K S0 = 103 GPa and K S ′  = 5.7 for liquid Fe–Ni and K S0 = 110 GPa and K S ′  = 7.6 for liquid Fe–Ni–C. The calculated density of liquid Fe–Ni–C using the obtained elastic parameters was consistent with the density values measured directly using the X-ray computed tomography technique. In the relation between the density (ρ) and sound velocity (V P) at 5 GPa (the lunar core condition), it was found that the effect of alloying Fe with Ni was that ρ increased mildly and V P decreased, whereas the effect of C dissolution was to decrease ρ but increase V P. In contrast, alloying with S significantly reduces both ρ and V P. Therefore, the effects of light elements (C and S) and Ni on the ρ and V P of liquid Fe are quite different under the lunar core conditions, providing a clue to constrain the light element in the lunar core by comparing with lunar seismic data.  相似文献   

12.
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13.
The phase and melting relations of the C-saturated C–Mg–Fe–Si–O system were investigated at high pressure and temperature to understand the role of carbon in the structure of the Earth, terrestrial planets, and carbon-enriched extraterrestrial planets. The phase relations were studied using two types of experiments at 4 GPa: analyses of recovered samples and in situ X-ray diffractions. Our experiments revealed that the composition of metallic iron melts changes from a C-rich composition with up to about 5 wt.% C under oxidizing conditions (ΔIW = ?1.7 to ?1.2, where ΔIW is the deviation of the oxygen fugacity (fO2) from an iron-wüstite (IW) buffer) to a C-depleted composition with 21 wt.% Si under reducing conditions (ΔIW < ?3.3) at 4 GPa and 1,873 K. SiC grains also coexisted with the Fe–Si melt under the most reducing conditions. The solubility of C in liquid Fe increased with increasing fO2, whereas the solubility of Si decreased with increasing fO2. The carbon-bearing phases were graphite, Fe3C, SiC, and Fe alloy melt (Fe–C or Fe–Si–C melts) under the redox conditions applied at 4 GPa, but carbonate was not observed under our experimental conditions. The phase relations observed in this study can be applicable to the Earth and other planets. In hypothetical reducing carbon planets (ΔIW < ?6.2), graphite/diamond and/or SiC exist in the mantle, whereas the core would be an Fe–Si alloy containing very small amount of C even in the carbon-enriched planets. The mutually exclusive nature of C and Si may be important also for considering the light elements of the Earth’s core.  相似文献   

14.
Integrated data are presented on structure–morphology features, as well as on the material and phase composition, of a fluid-produced carbonaceous substance (CS) formed under known thermodynamic conditions of the experiment (C–O–H system, 500–800°C, and 500–1000 atm). Solid products of the synthesis were examined by means of X-ray phase and thermal analyses, scanning electron microscopy combined with microprobe analysis, transmission electron microscopy, high-resolution Raman spectroscopy, IR spectroscopy, and CHN-analysis. The characteristics of the experimental CS may be applicable in genetic modeling of natural ore-bearing fluidal carbonaceous systems.  相似文献   

15.
Carbon-saturated crustal fluids in the C–O–H system comprise H2O, CO2 and CH4 as the most important fluid species. Graphite precipitation from a cooling C–O–H is discussed for two different systems, namely for a fluid–rock system in which no transfer of atomic oxygen and hydrogen between the fluid and the rock is possible (closed fluid system), and for an open fluid system. Thermodynamic model calculations show that the graphite-forming reactions and the graphite precipitation potential are different for these two systems. Furthermore, the calculations demonstrate that for both systems, the following factors play a role in determining the graphite precipitation potential, i.e. (1) the redox state of the fluid, (2) the initial pressure and temperature conditions and (3) whether cooling is combined with decompression. Open and closed fluid system graphite precipitation can be distinguished from each other using fluid inclusion and stable carbon isotope studies. The results of this study provide insight in the formation of hydrothermal graphite deposits.  相似文献   

16.
Located in the western Yangtze Block, the Qingshan Pb–Zn deposit, part of the Sichuan–Yunnan–Guizhou Pb–Zn metallogenic province, contains 0.3 million tonnes of 9.86 wt.% Pb and 22.27 wt.% Zn. Ore bodies are hosted in Carboniferous and Permian carbonate rocks, structurally controlled by the Weining–Shuicheng anticline and its intraformational faults. Ores composed of sphalerite, galena, pyrite, dolomite, and calcite occur as massive, brecciated, veinlets, and disseminations in dolomitic limestones.

The C–O isotope compositions of hydrothermal calcite and S–Pb–Sr isotope compositions of Qingshan sulphide minerals were analysed in order to trace the sources of reduced sulphur and metals for the Pb–Zn deposit. δ13CPDB and δ18OSMOW values of calcite range from –5.0‰ to –3.4‰ and +18.9‰ to +19.6‰, respectively, and fall in the field between mantle and marine carbonate rocks. They display a negative correlation, suggesting that CO2 in the hydrothermal fluid had a mixed origin of mantle, marine carbonate rocks, and sedimentary organic matter. δ34S values of sulphide minerals range from +10.7‰ to +19.6‰, similar to Devonian-to-Permian seawater sulphate (+20‰ to +35‰) and evaporite rocks (+23‰ to +28‰) in Carboniferous-to-Permian strata, suggesting that the reduced sulphur in hydrothermal fluids was derived from host-strata evaporites. Ores and sulphide minerals have homogeneous and low radiogenic Pb isotope compositions (206Pb/204Pb = 18.561 to 18.768, 207Pb/204Pb = 15.701 to 15.920, and 208Pb/204Pb = 38.831 to 39.641) that plot in the upper crust Pb evolution curve, and are similar to those of Devonian-to-Permian carbonate rocks. Pb isotope compositions suggest derivation of Pb metal from the host rocks. 87Sr/86Sr ratios of sphalerite range from 0.7107 to 0.7136 and (87Sr/86Sr)200Ma ratios range from 0.7099 to 0.7126, higher than Sinian-to-Permian sedimentary rocks and Permian Emeishan flood basalts, but lower than Proterozoic basement rocks. This indicates that the ore strontium has a mixture source of the older basement rocks and the younger cover sequence. C–O–S–Pb–Sr isotope compositions of the Qingshan Pb–Zn deposit indicate a mixed origin of the ore-forming fluids and metals.  相似文献   

17.
The results of photometric (BV RIJHK) and polarimetric (R)monitoring of the blazar 3C 66A performed at the St. Petersburg State University and the Central AstronomicalObservatory of the Russian Academy of Sciences in 2007–2015, radio observations performed by the Boston University team with the Very Long Baseline Array at 43 GHz, and a gamma-ray light curve based on observations with the Fermi SpaceObservatory are presented. Color variations of the object are studied. Changes in the optical spectral energy distribution are observed at some times, indicating the appearance and disappearance of individual variable sources. A variable source with a degree of polarization of 36% is identified, which is responsible for the polarization variations observed during one episode. The correlations between the variations in the different spectral ranges indicate that the optical and gamma-ray radiation originates near the radio core detected at 43 GHz. The presence of five superluminal components emerging from the core is detected.  相似文献   

18.
《地学前缘(英文版)》2020,11(4):1369-1380
This paper reports new geochronological (U–Pb) and isotope (C, O, and S) data to investigate the timing of mineralization and mode of ore genesis for the recently discovered Changtuxili Mn–Ag–Pb–Zn deposit, located on the western slopes of the southern Great Hinggan Range in NE China. The mineralization is hosted by intermediate–acidic lavas and pyroclastic rocks of the Baiyingaolao Formation. Three stages of mineralization are identified: quartz–pyrite (Stage I), galena–sphalerite–tetrahedrite–rhodochrosite (Stage II), and quartz–pyrite (Stage III). δ13C and δ18O values for carbonate from the ore vary from −8.51‰ to −4.96‰ and 3.97‰ to 15.90‰, respectively, which are indicative of a low-temperature alteration environment. δ34SV-CDT values of sulfides range from −1.77‰ to 4.16‰ and show a trend of equilibrium fractionation (δ34SPy ​> ​δ34SSp ​> ​δ34SGn). These features indicate that pyrite, sphalerite, and galena precipitated during the period of mineralization. The alteration mineral assemblage and isotope data indicate that the weakly acidic to weakly alkaline ore-forming fluid was derived largely from meteoric water and the ore-forming elements C and S originated from magma. During the mineralization, a geochemical barrier was formed by changes in the pH of the ore-forming fluid, leading to the precipitation of rhodochrosite. On the basis of the mineralization characteristics, new isotope data, and comparison with adjacent deposits, we propose that the Changtuxili Mn–Ag–Pb–Zn deposit is an intermediate-to low-sulfidation epithermal deposit whose formation was controlled by fractures and variability in the pH of the ore-forming fluid. The surrounding volcanic rocks yield zircon U–Pb ages of 160−146 ​Ma (Late Jurassic), indicating that the mineralization is younger than 146 ​Ma.  相似文献   

19.
Here, we present the first analytical technique (the quartz tube system technique—QTS) to directly analyze H2O and CO2 contents in liquids following high-pressure, high-temperature experiments in capsules containing mantle minerals and a diamond layer serving as a fluid/melt trap. In this technique, the capsule is frozen prior to opening; the diamond trap is cut out of the capsule and placed inside a N2-filled quartz tube. The diamond trap is heated up to 900 °C to release the gases to an Infrared Gas Analyzer, which determines the CO2 and H2O contents. Three sets of experiments containing SiO2 and CaCO3 powders were performed at 6 GPa and 1,000 °C in order to calibrate and validate the technique. These experiments demonstrated that when samples are prepared in a N2 environment, CO2 and H2O can be directly measured with an accuracy and precision of 2–3 and 3–4 %, respectively. The QTS technique (for H2O and CO2 determination) together with the cryogenic technique (total dissolved solids content) can be applied to diamond-trap capsules following HP–HT experiments in order to provide direct and complete liquid compositions coexisting with mantle material. The principal advantage of the QTS technique of direct analysis of volatile content in liquids over the indirect approach of mass balance calculations is the possibility of studying carbonated and hydrous liquid compositions in equilibrium with mantle material regardless of chemistry and pressure–temperature experimental conditions.  相似文献   

20.
《International Geology Review》2012,54(10):1300-1310
The Tianbaoshan Pb–Zn deposit, part of the Sichuan–Yunnan–Guizhou (SYG) Pb–Zn metallogenic province, is located in the western Yangtze Block and contains 2.6 million tonnes of 10–15 wt.% Pb + Zn metals. Ore bodies occur as vein or tubular types and are hosted in Sinian (late Proterozoic) carbonate rocks and are structurally controlled by the SN-trending Anninghe tectonic belt and NW-trending concealed fractures. The deposits are simple in mineralogy, with sphalerite, galena, pyrite, chalcopyrite, arsenopyrite, freibergite, and pyrargyrite as ore minerals and dolomite, calcite, and quartz as gangue minerals. These phases occur as massive, brecciated, veinlet, and dissemination in dolostone of the upper Sinian Dengying Formation. Hydrogen and oxygen isotope compositions of hydrothermal fluids range from –47.6 to –51.2‰ and –1.7 to +3.7‰, respectively. These data suggest that H2O in hydrothermal fluids had a mixed origin of metamorphic and meteoric waters. Carbon and oxygen isotope compositions range from –6.5 to –4.9‰ and +19.3 to +20.2‰, respectively. These compositions plot in the field between mantle and marine carbonate rocks with a negative correlation, suggesting that CO2 in the ore-forming fluids had multiple sources, including the Permian Emeishan flood basalts, Sinian-to-Permian marine carbonate rocks, and organic matters in Cambrian-to-Permian sedimentary rocks. Sulphur isotope compositions range from –0.4 to +9.6‰, significantly lower than Cambrian-to-Permian seawater sulphate (+15 to +35‰) and sulphate (+15 to +28‰) from evaporates in Cambrian-to-Permian strata, implicating that the S was derived from host-strata evaporates by thermal–chemical sulphate reduction. 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios range from 18.110 to 18.596, 15.514 to 15.878, and 38.032 to 39.221, respectively, which plot in field of the upper crust Pb evolution curve, unlike those of Proterozoic basement rocks, Sinian dolostone, Devonian-to-Permian carbonate rocks, and the Permian Emeishan flood basalts, implying complex derivation of Pb metal in the ore-forming fluids. Geological and isotopic studies of the Tianbaoshan Pb–Zn deposit reveal that constituents in the hydrothermal fluids were derived from multiple sources and that fluid mixing was a possible metallogenic mechanism. The studied deposit is not distal magmatic–hydrothermal, sedimentary exhalative (SEDEX), or Mississippi Valley (MVT) types, rather, it represents a unique ore deposit type, named in this article the SYG type.  相似文献   

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