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1.
Hydrometallurgical processing of spent hydrodesulphurisation (HDS) catalyst for the recovery of molybdenum using sodium carbonate and hydrogen peroxide mixtures was investigated. The results indicated that the recovery of molybdenum was largely dependent on the concentrations of Na2CO3 and H2O2 in the reaction medium, which controls the acidity of the leach liquor and carry over of impurities such as Al, Ni, P, Si and V. Leaching process was exothermic and leaching efficiency of molybdenum decreased with increasing solid to liquid ratio. Large scale leaching of spent catalyst, under optimum conditions: 20% pulp density, 85 g/L Na2CO3, 10 vol.% H2O2 and 1 h reaction, resulted a leaching efficiency of 84% Mo. The obtained leach liquor contained (g/L): Mo — 22.0, Ni — 0.015 and Al — 0.82, P — 1.1, Si — 0.094 and minor quantities of V — 8 mg/L, As and Co — < 1 mg/L. Recovery of Mo from leach solution as MoO3 of 97.30% purity was achieved by ammonium molybdate precipitation method.  相似文献   

2.
Supercritical gas sorption on moist coals   总被引：2，自引：1，他引：1  
The effect of moisture on the CO2 and CH4 sorption capacity of three bituminous coals from Australia and China was investigated at 55 °C and at pressures up to 20 MPa. A gravimetric apparatus was used to measure the gas adsorption isotherms of coal with moisture contents ranging from 0 to about 8%. A modified Dubinin–Radushkevich (DR) adsorption model was found to fit the experimental data under all conditions. Moisture adsorption isotherms of these coals were measured at 21 °C. The Guggenheim–Anderson–de Boer (GAB) model was capable of accurately representing the moisture isotherms over the full range of relative pressures.Moist coal had a significantly lower maximum sorption capacity for both CO2 and CH4 than dry coal. However, the extent to which the capacity was reduced was dependent upon the rank of the coal. Higher rank coals were less affected by the presence of moisture than low rank coals. All coals exhibited a certain moisture content beyond which further moisture did not affect the sorption capacity. This limiting moisture content was dependent on the rank of the coal and the sorbate gas and, for these coals, corresponded approximately to the equilibrium moisture content that would be attained by exposing the coal to about 40–80% relative humidity. The experimental results indicate that the loss of sorption capacity by the coal in the presence of water can be simply explained by volumetric displacement of the CO2 and CH4 by the water. Below the limiting moisture content, the CO2 sorption capacity reduced by about 7.3 kg t− 1 for each 1% increase in moisture. For CH4, sorption capacity was reduced by about 1.8 kg t− 1 for each 1% increase in moisture.The heat of sorption calculated from the DR model decreased slightly on addition of moisture. One explanation is that water is preferentially attracted to high energy adsorption sites (that have high energy by virtue of their electrostatic nature), expelling CO2 and CH4 molecules.  相似文献   

3.
Metamorphic decarbonation reactions and volcanic degassing lead to significant influx of CO2, a major greenhouse gas, into the ocean-atmosphere system from the solid Earth. Here we present quantitative estimates on CO2 derived through metamorphic degassing during ultrahigh-temperature (UHT) metamorphism in the Neoproterozoic through the mineralogical and geological analyses of the UHT decarbonation. Our computations show that an extra flux of CO2 was added to the atmosphere through a Himalayan scale UHT metamorphism to the extent of 6 × 1016 to 3.0 × 1018 mol/my, for a duration of 10 my. A calculation of the impact of the extra CO2 influx to the global mean temperature in the context of carbon cycle and greenhouse effect of CO2 shows that at the peak influx stage, the steady state temperature would be raised by 4 °C from 15 °C and by 13 °C from 4 °C. Our results have important bearing in evaluating the mechanism of melting and the duration of the Snowball Earth. Our estimate of the maximum degassing rate during UHT metamorphism suggests that the duration of the Marinoan snowball Earth was probably shorter, and the recovery from an ice-covered Earth to ocean-covered Earth was faster than previous estimates.  相似文献   

4.
To investigate the potential for the geologic storage of CO2 in saline sedimentary aquifers, 1600 ton of CO2 were injected at 1500 m depth into a 24-m sandstone section of the Frio Formation — a regional reservoir in the US Gulf Coast. Fluid samples obtained from the injection and observation wells before, during and after CO2 injection show a Na–Ca–Cl type brine with 93,000 mg/L TDS and near saturation of CH4 at reservoir conditions. As injected CO2 gas reached the observation well, results showed sharp drops in pH (6.5 to 5.7), pronounced increases in alkalinity (100 to 3000 mg/L as HCO3) and Fe (30 to 1100 mg/L), and significant shifts in the isotopic compositions of H2O and DIC. Geochemical modeling indicates that brine pH would have dropped lower, but for buffering by dissolution of calcite and Fe oxyhydroxides. Post-injection results show the brine gradually returning to its pre-injection composition.  相似文献   

5.
Motivated by the rapid increase in atmospheric CO2 due to human activities since the Industrial Revolution, and the climate changes it produced, the world’s concerned scientific community has made a huge effort to investigate the global carbon cycle. However, the results reveal that the global CO2 budget cannot be balanced, unless a “missing sink” is invoked. Although numerous studies claimed to find the “missing sink”, none of those claims has been widely accepted. This current study showed that alkaline soil on land are absorbing CO2 at a rate of 0.3–3.0 μmol m−2 s−1 with an inorganic, non-biological process. The intensity of this CO2 absorption is determined by the salinity, alkalinity, temperature and water content of the saline/alkaline soils, which are widely distributed on land. Further studies revealed that high salinity or alkalinity positively affected the CO2 absorbing intensity, while high temperature and water content had a negative effect on the CO2 absorbing intensity of these soils. This inorganic, non-biological process of CO2 absorption by alkaline soils might have significant implications to the global carbon budget accounting.  相似文献   

6.
Fluid inclusion microthermometry and structural data are presented for quartz vein systems of a major dextral transcurrent shear zone of Neoproterozoic–Cambrian age in the Ribeira River Valley area, southeastern Brazil. Geometric and microstructural constraints indicate that foliation–parallel and extensional veins were formed during dextral strike–slip faulting. Both vein systems are formed essentially by quartz and lesser contents of sulfides and carbonates, and were crystallized in the presence of CO2–CH4 and H2O–CO2–CH4–NaCl immiscible fluids following unmixing from a homogeneous parental fluid. Contrasting fluid entrapment conditions indicate that the two vein systems were formed in different structural levels. Foliation–parallel veins were precipitated beneath the seismogenic zone under pressure fluctuating from moderately sublithostatic to moderately subhydrostatic values (319–397 °C and 47–215 MPa), which is compatible with predicted fluid pressure cycle curves derived from fault–valve action. Growth of extensional veins occurred in shallower structural levels, under pressure fluctuating from near hydrostatic to moderately subhydrostatic values (207–218 °C and 18–74 MPa), which indicate that precipitation occurred within the near surface hydrostatically pressured seismogenic zone. Fluid immiscibility and precipitation of quartz in foliation–parallel veins resulted from fluid pressure drop immediately after earthquake rupture. Fluid immiscibility following a local pressure drop during extensional veining occurred in pre-seismic stages in response to the development of fracture porosity in the dilatant zone. Late stages of fluid circulation within the fault zone are represented dominantly by low to high salinity (0.2 to 44 wt.% equivalent NaCl) H2O–NaCl–CaCl2 fluid inclusions trapped in healed fractures mainly in foliation–parallel veins, which also exhibit subordinate H2O–NaCl–CaCl2, CO2–(CH4) and H2O–CO2–(CH4)–NaCl fluid inclusions trapped under subsolvus conditions in single healed microcracks. Recurrent circulation of aqueous–carbonic fluids and aqueous fluids of highly contrasting salinities during veining and post-veining stages suggests that fluids of different reservoirs were pumped to the ruptured fault zone during faulting episodes. A fluid evolution trending toward CH4 depletion for CO2–CH4–bearing fluids and salinity depletion and dilution (approximation of the system H2O–NaCl) for aqueous–saline fluids occurred concomitantly with decrease in temperature and pressure related to fluid entrapment in progressively shallower structural levels reflecting the shear zone exhumation history.  相似文献   

7.
To further our knowledge of the coupling between the hydraulic and mechanical behaviours of the swelling soils, this paper presents an experimental study on a bentonite/silt mixture using an osmotic odometer. A loading/unloading cycle was applied to samples with different initial dry densities (1.27, 1.48, and 1.55 Mg m− 3) at different constant suctions (0, 2, and 8 MPa). We noted that the initial state of the soils after compaction significantly influenced the values of the apparent preconsolidation stress p0(s), the virgin compression index λ(s), and the elastic compression index κ.These experimental results provided a sufficient database to interpret the mechanical behaviour of the swelling soil and define three yielding surfaces:
– the suction limit between micro- and macrostructure (sm/M) and the suction limit between nano- and microstructure (sn/m), which depend completely on the soil fabrics and the diameter separating the nano-, micro-, and macrostructure,
– the Loading Collapse (LC) curve, representing the preconsolidation stress variation as a function of suction,
– the Saturation Curve (SC), representing the variation of the saturation stress (Psat) as a function of suction.
In general, we can state that the increase of compaction pressure unified the LC and SC surfaces and decreased the (sm/M) value without modifying the (sn/m) value.  相似文献   

8.
Accurate measurements to assess the influence of soil moisture on CO2 flux requires the absolute estimates of soil CO2 flux. Thus, it was constructed a calibration system where CO2 with fixed concentration flowed through the different porous material. Previous to measurement, in order to verify the performance and reliability of a closed dynamic chamber, different discontinuous air-mixing rates and times were tested. The CO2 flux was estimated through sequential lectures and the best fit for flux measurements was obtained taking short readings every 3 min, during a total time of 12 min (R 2 = 0.99). The best mixing rate was attained for 250 mL min−1, allowing 25 s of mixing previous to CO2 extraction for an infrared gas analyzer. The deviation of the measured values for dry sand from the reference CO2 flux (0.097 and 0.071 g m−2 min−1) was 5 and 7%. On dry sandy loam soil (SLS) the deviation was 2%. The measured fluxes decreased 73 and 22% with content moisture of 20 and 10% (sand), and 78% with content moisture of 31% (SLS). This work allowed to estimate how much the measured emission rates deviate from the true ones for the specified chamber and sampling conditions.  相似文献   

9.
Accurate measurements of soil CO2 concentrations (pCO2) are important for understanding carbonic acid reaction pathways for continental weathering and the global carbon (C) cycle. While there have been many studies of soil pCO2, most sample or model only one, or at most a few, landscape positions and therefore do not account for complex topography. Here, we test the hypothesis that soil pCO2 distribution can predictably vary with topographic position. We measured soil pCO2 at the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO), Pennsylvania, where controls on soil pCO2 (e.g., depth, texture, porosity, and moisture) vary from ridge tops down to the valley floor, between planar slopes and slopes with convergent flow (i.e., swales), and between north and south-facing aspects. We quantified pCO2 generally at 0.1–0.2 m depth intervals down to bedrock from 2008 to 2010 and in 2013. Of the variables tested, topographic position along catenas was the best predictor of soil pCO2 because it controls soil depth, texture, porosity, and moisture, which govern soil CO2 diffusive fluxes. The highest pCO2 values were observed in the valley floor and swales where soils are deep (≥0.7 m) and wet, resulting in low CO2 diffusion through soil profiles. In contrast, the ridge top and planar slope soils have lower pCO2 because they are shallower (≤0.6 m) and drier, resulting in high CO2 diffusion through soil profiles. Aspect was a minor predictor of soil pCO2: the north (i.e., south-facing) swale generally had lower soil moisture content and pCO2 than its south (i.e., north-facing) counterpart. Seasonally, we observed that while the timing of peak soil pCO2 was similar across the watershed, the amplitude of the pCO2 peak was higher in the deep soils due to more variable moisture content. The high pCO2 observed in the deeper, wetter topographic positions could lower soil porewater pH by up to 1 pH unit compared to porewaters equilibrated with atmospheric CO2 alone. CO2 is generally the dominant acid driving weathering in soils: based on our observations, models of chemical weathering and CO2 dynamics would be improved by including landscape controls on soil pCO2.  相似文献   

10.
The 1.27 Ga old Ivigtut (Ivittuut) intrusion in South Greenland is world-famous for its hydrothermal cryolite deposit [Na3AlF6] situated within a strongly metasomatised A-type granite stock. This detailed fluid inclusion study characterises the fluid present during the formation of the cryolite deposit and thermodynamic modelling allows to constrain its formation conditions.Microthermometry revealed three different types of inclusions: (1) pure CO2, (2) aqueous-carbonic and (3) saline-aqueous inclusions. Melting temperatures range between − 23 and − 15 °C for type 2 and from − 15 to − 10 °C for type 3 inclusions. Most inclusions homogenise between 110 and 150 °C into the liquid.Stable isotope compositions of CO2 and H2O were measured from crushed inclusions in quartz, cryolite, fluorite and siderite. The δ13C values of about − 5‰ PDB are typical of mantle-derived magmas. The differences between δ18O of CO2 (+ 21 to + 42‰ VSMOW) and δ18O of H2O (− 1 to − 21.7‰ VSMOW) suggest low-temperature isotope exchange. δD (H2O) ranges from − 19 to − 144‰ VSMOW. The isotopic composition of inclusion water closely follows the meteoric water line and is comparable to Canadian Shield brines. Ion chromatography revealed the fluid's predominance in Na, Cl and F. Cl/Br ratios range between 56 and 110 and may imply intensive fluid–rock interaction with the host granite.Isochores deduced from microthermometry in conjunction with estimates for the solidification of the Ivigtut granite suggest a formation pressure of approximately 1–1.5 kbar for the fluid inclusions. Formation temperatures of different types of fluid inclusions vary between 100 and 400 °C. Thermodynamic modelling of phase assemblages and the extraordinary high concentration in F (and Na) may indicate that the cryolite body and its associated fluid inclusions could have formed during the continuous transition from a volatile-rich melt to a solute-rich fluid.  相似文献   

11.
This study investigates the potential risks associated with high levels and long term exposure of carbon dioxide (CO2) on the mobility and speciation of exchangeable metals in soils. CO2 incubation batch experiments at high pressure and temperature coupled with geochemical modelling were carried out to elucidate the behaviour and mobilisation of metals and the response of soil chemical parameters as a result of long term CO2 exposure. A t-Student analysis was performed to ascertain whether differences in the mean concentration of exchangeable metals in soils before and after CO2-incubations are attributable to increase of metal molibilisation because of the long term CO2 exposure. The t-Student revealed the CO2 long term incubation was statistically significant (p < 0.05) for the exchangeable concentration of Ni, Zn, and Pb. The CO2-soil incubation induces the acidification of the pore water of soils via CO2 hydrolysis and as a consequence, it increases the exchangeable concentration of Ni, Zn, and Pb in the soils. As, Al, Cr, Cu, and Fe show a different mobilisation pattern depending on the moisture content in soils. Al3+, Fe2+, Cr3+, and Cu2+ as free cations, As as HAsO2, Pb2+and PbHCO3−, Zn2+ and ZnHCO3−, are predicted to be the predominant aqueous complexes in the pore water of the incubated soils.  相似文献   

12.
A. Proyer  E. Mposkos  I. Baziotis  G. Hoinkes 《Lithos》2008,104(1-4):119-130
Four different types of parageneses of the minerals calcite, dolomite, diopside, forsterite, spinel, amphibole (pargasite), (Ti–)clinohumite and phlogopite were observed in calcite–dolomite marbles collected in the Kimi-Complex of the Rhodope Metamorphic Province (RMP). The presence of former aragonite can be inferred from carbonate inclusions, which, in combination with an analysis of phase relations in the simplified system CaO–MgO–Al2O3–SiO2–CO2 (CMAS–CO2) show that the mineral assemblages preserved in these marbles most likely equilibrated at the aragonite–calcite transition, slightly below the coesite stability field, at ca. 720 °C, 25 kbar and aCO2 ~ 0.01. The thermodynamic model predicts that no matter what activity of CO2, garnet has to be present in aluminous calcite–dolomite-marble at UHP conditions.  相似文献   

13.
A model is presented here, which attempts to determine interactions between change in land use and concentration of atmospheric CO2 over the 1700–2100 period. The main impact of the conversion of forests to agricultural areas is the increase of atmospheric CO2 because of the losses of biomass and soil carbon in favour of the atmosphere. This raise will probably increase in the next years, correlated with the proportion of cultivated areas. We show here that this first-order effect is amplified by the correlative decrease of terrestrial sinks of CO2; in fact, as forests are replaced by cultivated parcels, carbon residence time in biosphere decreases, as well as sequestration ability of these ecosystems. This amplification effect leads to an additional increase in atmospheric CO2, which could reach 100 ppm in 2100. The uncertainties on the range of such an increase are important since they cumulate both uncertainties on the behaviour (sink or source) of terrestrial ecosystems in the future and inherent uncertainties of the modeling of carbon fluxes linked to changing land uses… Such an additional increase in CO2 is partially limited by the ocean reservoir and by the existing CO2 sinks in primary non-anthropologically disturbed ecosystems. The results imply that conservation of primary forests, for which primary productivity and carbon time of residence are high, is an efficient strategy for greenhouse-effect mitigation. To cite this article: V. Gitz, P. Ciais, C. R. Geoscience 335 (2003).  相似文献   

14.
Stability of biomass-derived black carbon in soils   总被引：16，自引：0，他引：16  
Black carbon (BC) may play an important role in the global C budget, due to its potential to act as a significant sink of atmospheric CO2. In order to fully evaluate the influence of BC on the global C cycle, an understanding of the stability of BC is required. The biochemical stability of BC was assessed in a chronosequence of high-BC-containing Anthrosols from the central Amazon, Brazil, using a range of spectroscopic and biological methods. Results revealed that the Anthrosols had 61-80% lower (P < 0.05) CO2 evolution per unit C over 532 days compared to their respective adjacent soils with low BC contents. No significant (P > 0.05) difference in CO2 respiration per unit C was observed between Anthrosols with contrasting ages of BC (600-8700 years BP) and soil textures (0.3-36% clay). Similarly, the molecular composition of the core regions of micrometer-sized BC particles quantified by synchrotron-based Near-Edge X-ray Fine Structure (NEXAFS) spectroscopy coupled to Scanning Transmission X-ray Microscopy (STXM) remained similar regardless of their ages and closely resembled the spectral characteristics of fresh BC. BC decomposed extremely slowly to an extent that it was not possible to detect chemical changes between youngest and oldest samples, as also confirmed by X-ray Photoelectron Spectroscopy (XPS). Deconvolution of NEXAFS spectra revealed greater oxidation on the surfaces of BC particles with little penetration into the core of the particles. The similar C mineralization between different BC-rich soils regardless of soil texture underpins the importance of chemical recalcitrance for the stability of BC, in contrast to adjacent soils which showed the highest mineralization in the sandiest soil. However, the BC-rich Anthrosols had higher proportions (72-90%) of C in the more stable organo-mineral fraction than BC-poor adjacent soils (2-70%), suggesting some degree of physical stabilization.  相似文献   

15.
The positions of the liquidi and the near-liquidus phases of olivine-melilitite+CO2 have been determined under MH-buffered and furnace-buffered conditions up to 40 kb. It is found that CO2 alone lowers the liquidus compared to dry conditions, yet its influence is minor compared to H2O. The major role of CO2 is to favour the growth of orthopyroxene and garnet over that of olivine at least at high pressures. CO2-contents of glasses from experiments just above the liquidus (MH-buffered) were determined as 5.1 % at 10kb; 7.5 % at 20kb, 9.3 % at 30kb and 10–11 % (estimated) at 40 kb. Experiments on (pyrolite –40 % olivine)+H2O+CO2 show that CO2 occurs under mantle conditions as carbonate under subsolidus conditions and dissolved in a melt above the solidus. At 30kb, the solidus lies between 1,000 ° C and 1,050 ° C for vapour-saturated conditions, at and at .  相似文献   

16.
The objective of this study was to investigate the role of dissolved CO2 (H2CO3*) as a mechanism of cation removal from surface soils under secondary land uses in the tropics. Soil leachate columns were prepared with 0–10 cm soils from mature and secondary forest, and managed pastures, and extracted with H2CO3* from deionized water equilibrated with 0%, 0.5%, 1%, and 10% CO2 (g). Extraction of soil cations slowed over time following an exponential form for the cumulative data. The rate of cation concentration decline varied as a function of CO2 concentration with the 10% solution resulting in a greater percent decline with extraction volume. Potassium removal from the exchange sites of all soils and for all solutions was nearly complete ranging from 85% to 97% while removals of Mg (31% to 71%) and Ca (12% to 42%) were lower. The asymptotic patterns of cation loss observed in this study suggest that H2CO3* acid-driven losses of cations may become self-limiting over time. Other stronger acids from atmospheric deposition or organic sources may serve to perpetuate cation removal, and re-forestation on these cleared lands would certainly re-distribute cations from soils to vegetation.  相似文献   

17.
The interaction of organic compounds with the mineral phase is considered as one stabilization mechanism for organic carbon (OC) in soils. The objective of this study is to assess the role of mineral surfaces for the long-term stabilization of OC in arable soils, with special emphasis on iron oxides. Soil samples were taken from two contrasting treatment types, i.e. fertilized plots and C-depleted plots, in long-term agroecosystem experiments. The soil organic carbon pool of the C-depleted plots is considered to show a lower contribution of labile compounds and consequently to be relatively enriched in refractory compounds compared with the fertilized counterparts. In fractions <6 μm, OC was studied in relation to total mineral surface area, surface area contributed by oxides and silicates, and the content and type of iron oxides (dithionite and oxalate extractable iron, Fed and Feo). In two sandy soils, OC contents were linearly related to total mineral surface area and the content of the two iron oxide fractions (Fed and Feo). The surface area developed by the silicates was low and thus the surface area contribution from oxides was dominant in fractions <6 μm. In contrast to the sandy soils, in a loamy soil OC was not correlated with surface area or the iron oxide content. However, the different soils agreed with respect to the behavior of C in density fractions: losses of OC occurred mainly from the light fraction (2 g cm−3), whereas C in the heavy fraction (>2 g cm−3) proved to be stable. For the sandy soils, mineral surface area appears to control the storage of OC in fine fractions. Given the dominant surface area contribution from oxides, OC storage here primarily depends on the oxides. The C-depleted plots in particular show that surface area controls the accumulation of refractory C. The interaction of organic compounds with the mineral phase, mainly with the surface of oxides, seems to be a major mechanism for the long-term stabilization of OC in these sandy soils. An interaction with minerals seems to be important for stabilizing OC also in the loamy soil, although this is not reflected by a proportional relation between OC and surface area across the fractions.  相似文献   

18.
A simple process to produce fine and low soda α-alumina (α-Al2O3) from a commercial grade aluminium trihydroxide (gibbsite, Al(OH)3) produced by KC Corporation Ltd was developed. There are two options for this process with the first one producing low soda α-alumina (< 0.05% Na2O) having a mean particle size of 50 μm. The second option yields a fine product with a mean size of less than 10 μm. In the first option, a plant aluminium trihydroxide containing 0.20% Na2O was first fluidized with nitrogen at 400–600 °C to yield an amorphous activated alumina. This intermediate product was then treated with acetic or oxalic acid, washed with water and heated to 1200 °C to form calcined α-alumina, having a Na2O content of less than 0.05%. A 20 min leaching using 0.2 M acetic or oxalic acid could yield an alumina product containing 0.04% Na2O. In the second option, a new technique for the preparation of fine and low soda α-alumina was evaluated using an attrition mill working also as a leaching vessel at 80 °C. Fine (< 10 μm in mean particle size) and low soda (< 0.04% Na2O) alumina was produced by a 20 min leaching step with 0.2 M acetic acid and concurrent attrition milling.  相似文献   

19.
The nature of the near-liquidus phases for a mantle-derived olivine melilitite composition have been determined at high pressure under dry conditions and with various water contents. Olivine and clinopyroxene occur on or near the liquidus and there are no conditions where orthopyroxene crystallizes in equilibrium with the olivine melilitite. We have determined the effect on the liquidus temperature and liquidus phases of substituting CO2 for H2O on a mole for mole basis at 30 kb, using olivine melilitite + 20 wt% H2O at = 0 and = (CO2)/(H2+CO2) (mole fraction) = 0.25, 0.5, 0.75 and 1.0 (i.e. olivine melilitite + 38 wt% CO2). Experiments were buffered by the MH or NNO buffers. At 30 kb, CO2 is only slightly less soluble than water for <0.5 as judged by the slight increase in liquidus temperature on mole-for-mole substitution of CO2 for H2O and at 30 kb, 1200° C, = = 0.5 the olivine melilitite contains 8.8 wt% H2O and 21 wt% CO2 in solution. For 1 the CO2 saturated liquidus is depressed 70 ° C below the anhydrous liquidus and the magma dissolves approx. 17% CO2 at 30kb, 1400 ° C, 1, 0. Infrared spectra of quenched glasses have absorption bands characteristic of CO 3 = and OH- molecules and no evidence for HCO 3 - . The effect of CO 3 = molecules dissolved in the olivine melilitite at high pressure is to suppress the near-liquidus crystallization of olivine and clinopyroxene and bring orthopyroxene and garnet on to the liquidus. We infer that olivine melilitite magmas may be derived by equilibrium partial melting (<5%) of pyrolite at 30 kb, 1150–1200 ° C, provided that both H2O and CO2 are present in the source region in minor amounts. Preferred conditions are 0< <0.5, 0.5< <1, and at low oxygen fugacities (相似文献   

20.
Marble-hosted ruby deposits represent the most important source of colored gemstones from Central and South East Asia. These deposits are located in the Himalayan mountain belt which developed during Tertiary collision of the Indian plate northward into the Eurasian plate. They are spatially related to granitoid intrusions and are contained in platform carbonates series that underwent high-grade metamorphism. All occurrences are located close to major tectonic features formed during Himalayan orogenesis, directly in suture zones in the Himalayas, or in shear zones that guided extrusion of the Indochina block after the collision in South East Asia. Ar–Ar dating of micas syngenetic with ruby and U–Pb dating of zircon included in ruby gives evidence that these deposits formed during Himalayan orogenesis, and the ages document the extensional tectonics that were active, from Afghanistan to Vietnam, between the Oligocene and the Pliocene.The petrography shows that ruby-bearing marbles formed in the amphibolite facies (T = 610 to 790 °C and P ~ 6 kbar). A fluid inclusion study defines the conditions of gem ruby formation during the retrograde metamorphic path (620 < T < 670 °C and 2.6 < P < 3.3 kbar) for the deposits of Jegdalek, Hunza and northern Vietnam.Whole rock analyses of non-ruby-bearing marbles indicate that they contain enough aluminum and chromiferous elements to produce all the ruby crystals that they contain. In addition, (C, O)-isotopic analyses of carbonates from the marbles lead to the conclusion that the marbles acted as a metamorphic closed fluid system that were not infiltrated by externally-derived fluids. The carbon isotopic composition of graphite in marbles reveals that it is of organic origin and that it exchanged C-isotopes with the carbonates during metamorphism. Moreover, the O-isotopic composition of ruby was buffered by metamorphic CO2 released during devolatilisation of marble and the H-isotopic composition of mica is consistent with a metamorphic origin for water in equilibrium with the micas. The (C, O, H)-isotopic compositions of minerals associated with marble-hosted ruby are all in agreement with the hypothesis, drawn from the unusual chemistry of CO2–H2S–COS–S8–AlO(OH)-bearing fluids contained in fluid inclusions, that gem ruby formed at P ~ 3 kbar and 620 < T < 670 °C, during thermal reduction of evaporite by organic matter, at high temperature-medium pressure metamorphism of platform carbonates during the Tertiary India–Asia collision. The carbonates were enriched in Al- and chromiferous-bearing detrital minerals, such as clay minerals that were deposited on the platform with the carbonates, and in organic matter. Ruby formed during the retrograde metamorphic path, mainly by destabilization of muscovite or spinel. The metamorphic fluid system was rich in CO2 released from devolatilisation of carbonates, and in fluorine, chlorine and boron released by molten salts (NaCl, KCl, CaSO4). Evaporites are key to explaining the formation of these deposits. Molten salts mobilized in situ Al and metal transition elements contained in marbles, leading to crystallization of ruby.  相似文献   

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