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1.
Nanosilica particles modified by Schiff base ligands 3-methoxy salicylaldimine propyl triethoxysilane (MNS1), 5-bromo salicylaldimine propyl triethoxysilane (MNS2) and 3-hydroxy salicylaldimine propyl triethoxysilane (MNS3) were prepared, and their potential for separation of copper, lead, zinc, cadmium, cobalt and nickel ions from aqueous solutions was examined. The effect of parameters influencing adsorption efficiency including aqueous-phase pH, amount of adsorbent, stirring time and initial concentration of the metal ions was assessed and discussed. Although MNS1 and MNS3 removed lead ions efficiently, all adsorbents showed strong selectivity toward copper ions. It was shown that, under some circumstances, MNS3 decreased the amount of other ions, particularly cobalt, in the aqueous phase. The adsorbents were also applied for removal of copper and lead ions from real samples. Possible quantitative desorption of the metal ions loaded onto the adsorbents suggests their multiple uses in adsorption–desorption process. Investigation of temperature dependency of the process led to determination of the ΔH°, ΔS° and ΔG° values. This investigation indicates that the adsorption of copper ions onto the all studied adsorbents and lead ions onto MNS1 and MNS3 is endothermic. The Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms were tested to describe the equilibrium data. Pseudo-first-order, pseudo-second-order, Elovich and intra-particle diffusion equations were applied to study the kinetics of copper and lead adsorption onto the modified nanoparticles. This investigation indicates that the process for all adsorbents follows pseudo-second-order kinetics and suggests a chemisorption mechanism for the adsorption processes by the studied adsorbents.  相似文献   

2.
In studying the conditions of formation of stony meteorites, we assume that 1) they are fragments of asteroids fallen to the surface of the earth. During their flight through the atmosphere, the meteorites develop a melted surface layer but their texture and mineralogic composition remain unchanged. 2) According to V. M. Goldschmidt, stone meteorites crystallize in a lesser gravity field than that of the earth, which is the reason for their chondritic texture and high porosity (about 4%). 3) Meteorites were formed in a medium with a deficiency of free oxygen. As a result, part of their iron and nickel was segregated as native metal; in addition, lawrencite and oldhamite, sulfides typical of meteorites, were formed.

We identify three stages of meteorite formation: magmatic, pneumatolytic, and hydrothermal. The interval 1450-850°C. corresponds to the magmatic stage at which a silicate phase and native iron with nickel were formed. As a result of thermal dissociation of water and because of the deficiency of oxygen required for a complete oxidation of metals and carbon, in the gaseous phase, free oxygen and H2O were absent and the phase consisted probably of H2, CH4, CO2, and CO.

The temperature interval 750-500°C. corresponds to the pneumatolytic phase. Here, H2S, CH4, CO2, and CO were the principal agents of the gaseous phase. CH4 was formed in a high temperature reaction between hydrogen and elementary carbon. As the temperature dropped to 750°C., electrolytic dissociation of H2O rendered possible the formation of sulfides, especially of troilite.

Mineralization at the hydrothermal stage with a temperature interval of 400 to 300°C. has been observed only in carbon meteorites with a considerable graphitic carbon content. Here, a small portion of the ferrous iron is oxidized to the ferric, in the presence of CO2 and at a temperature of 450° to 500°C.; the iron sulfide so formed is represented by pyrrhotite. Simultaneously, colored silicates are chloritized, with a separation of CaCO3.—Auth. English summ.  相似文献   

3.
Ammonia-ammonium leaching of samples of nodules from several different locations was carried out after reduction of the nodules under COCO2 gas mixtures at 400, 600, and 800°C. In accordance with thermodynamic analysis, nickel, copper and cobalt oxides in the nodules are preferentially reduced with a 6040 gas mixture of COCO2. After an initial reduction step with COCO2 at 600°C, leaching at room temperature and atmospheric pressure with aqueous ammonia-ammonium carbonate and ammonia-ammonium sulfate solutions yielded high extractions of copper and nickel (> 80%), and close to 50% for cobalt. The nature of the pores in nodules from different locations appears to affect the extraction process. A lower reduction temperature is required to obtain the same extraction of nickel, copper and cobalt in a sulfate system than is necessary in a carbonate system. However, a higher manganese content results in the sulfate leaching solutions as compared to the carbonate system, where essentially none of the manganese and iron are extracted.  相似文献   

4.
Unfertilizable fruiting buds of mango plant Mangifera Indica L, an agrowaste, is used as a biomass in this study. The efficacy of the biosorbent was tested for the removal of lead, copper, zinc and nickel metal ions using batch experiments in single and binary metal solution under controlled experimental conditions. It is found that metal sorption increases when the equilibrium metal concentration rises. At highest experimental solution concentration used (150 mg/L), the removal of metal ions were 82.76 % for lead, 76.60 % for copper, 63.35 % for zinc and 59.35 % for nickel while at lowest experimental solution concentration (25 mg/L), the removal of metal ions were 92.00% for lead, 86.84 % for copper, 83.96 % for zinc and 82.29 % for nickel. Biosorption equilibrium isotherms were plotted for metal uptake capacity (q) against residual metal concentrations (Cf) in solution. The q versus Cf sorption isotherm relationship was mathematically expressed by Langmuir and Freundlich models. The values of separation factor were between zero and one indicating favourable sorption for four tested metals on the biosorbent. The surface coverage values were approaching unity with increasing solution concentration indicating effectiveness of biosorbent under investigation. The non-living biomass of Mangifera indica L present comparable biosorption capacity for lead, copper, zinc and nickel metal ions with other types of biosorbent materials found in literature and is effective to remove metal ions from single metal solutions as well as in the presence of other co-ions with the main metal of solution.  相似文献   

5.
27Al,29Si MAS NMR studies of kaolinite and its thermal transformation products show that in the kaolinite-mullite reaction series there is an extensive segregation of Al2O3 and SiO2 and the reaction of Al2O3 with SiO2 to form mullite is the main path of mullite formation. At about 850° C, the peak intensity of A1(V) reaches its maximum and with the further rise of temperature the A1(V) signal completely disappears. At about 950°C, γ-Al2O3 accounts for about 71% of the material phases containing Al atoms. In the series there is no obvious presence of Al-Si spinel. The27Al and29Si MAS NMR spectra show that there is an obvious difference between the temperature points for Al-O2(OH)4 octahedral sheet collapsing and Si-O4 tetrahedral sheet breaking down.  相似文献   

6.
Metal-cystine complexes of iron, lead, zinc, copper and nickel under mild artificial diagenesis give rise to crystalline metal sulphides and insoluble organic matter as well as gaseous and “oily” organic products. Under confined reducing conditions at 200°C for 100 h a virtual 100% conversion of metal complex to metal sulphide occurs, while < 10% of the associated organic material may remain as kerogen. Such a mechanism could account for the formation of metal sulphides and in particular pyrite from protein- or amino acid-rich material in carbonaceous sediments during diagenesis.  相似文献   

7.
Dehydration melting of tonalites. Part II. Composition of melts and solids   总被引：6，自引：0，他引：6  
 Dehydration melting of tonalitic compositions (phlogopite or biotite-plagioclase-quartz assemblages) is investigated within a temperature range of 700–1000°C and pressure range of 2–15 kbar. The solid reaction products in the case of the phlogopite-plagioclase(An45)-quartz starting material are enstatite, clinopyroxene and potassium feldspar, with amphiboles occurring occasionally. At 12 kbar, zoisite is observed below 800°C, and garnet at 900°C. The reaction products of dehydration melting of the biotite (Ann50)-plagioclase (An45)-quartz assemblage are melt, orthopyroxene, clinopyroxene, amphibole and potassium feldspar. At pressures > 8 kbar and temperatures below 800°C, epidote is also formed. Almandine-rich garnet appears above 10 kbar at temperatures ≥ 750°C. The composition of melts is granitic to granodioritic, hence showing the importance of dehydration melting of tonalites for the formation of granitic melts and granulitic restites at pressure-temperature conditions within the continental crust. The melt compositions plot close to the cotectic line dividing the liquidus surfaces between quartz and potassium feldspar in the haplogranite system at 5 kbar and a H 2O = 1. The composition of the melts changes with the composition of the starting material, temperature and pressure. With increasing temperature, the melt becomes enriched in Al2O3 and FeO+MgO. Potash in the melt is highest just when biotite disappears. The amount of CaO decreases up to 900°C at 5 kbar whereas at higher temperatures it increases as amphibole, clinopyroxene and more An-component dissolve in the melt. The Na2O content of the melt increases slightly with increase in temperature. The composition of the melt at temperatures > 900°C approaches that of the starting assemblage. The melt fraction varies with composition and proportion of hydrous phases in the starting composition as well as temperature and pressure. With increasing modal biotite from 20 to 30 wt%, the melt proportion increases from 19.8 to 22.3 vol.% (850°C and 5 kbar). With increasing temperature from 800 to 950°C (at 5 kbar), the increase in melt fraction is from 11 to 25.8 vol.%. The effect of pressure on the melt fraction is observed to be relatively small and the melt proportion in the same assemblage decreases at 850°C from 19.8 vol.% at 5 kbar to 15.3 vol.% at 15 kbar. Selected experiments were reversed at 2 and 5 kbar to demonstrate that near equilibrium compositions were obtained in runs of longer duration. Received: 27 December 1995 / Accepted: 7 May 1996  相似文献   

8.
Crack healing experiments were conducted at 780°, 815°, and 850° C in dry carbon dioxide over periods of 0.5 to 1320 h on small penny-shaped cracks of known geometry in Stahl calcite. As observed by previous investigators, healing initiates with the formation of tubes around the leading edge of the crack, followed by the pinching off of spherical bubbles from these tubes. Pillars and peninsular structures formed and grew at cleavage steps and other surface irregularities, greatly accelerating the healing process in some cracks. The crack tip regression distance at constant temperature follows a simple power law in time; although, with the exception of one crack at 850° C, the time exponent systematically decreases from 0.59 at 780° C to 0.15 and 0.07 at 815° and 850° C, respectively. Only the largest exponent is consistent with existing theory: the two smaller time exponents are, as yet, unexplained. Healing rates are strongly inversely dependent upon crack aperture, in qualitative agreement with theory. For example, cracks with maximum apertures of less than 60 nm (6×10?8 m) healed completely in 0.5 to 25 h at 850° C; while fatter cracks, with maximum apertures of about 700 nm, showed very little healing after up to 1320 h at the same temperature. At 780° C, the functional dependence of healing rate upon crack aperture was consistent with several aspects of the present model.  相似文献   

9.
Ten brands of spent portable rechargeable batteries used in mobile phones (lithium-ion and nickel metal hydride) were collected and disassembled and the battery electrode and printed wiring board prepared using the EPA Method 3050B. The metal concentrations were determined by atomic absorption spectrometry. The mean (± standard deviation) concentrations and range of cobalt, chromium, nickel and cadmium in the battery electrodes were 361284±32281mg/kg (range 20870–575330 mg/kg); 25.3 ± 4.6 mg/kg (7.9–149 mg/kg); 75272 ± 14630 mg/kg (3589–266607 mg/kg) and 2.8 ± 0.6 mg/kg (0.2–16.3 mg/kg), respectively. Similarly, the mean values of cobalt, chromium, nickel and cadmium in the PWB were 564 ± 165 mg/kg (56.1–4068 mg/kg); 28.1 ± 4.0 mg/kg (ND-97.2 mg/kg); 735 ± 188 mg/kg (22.7–2727 mg/kg) and 1.8 ± 0.3 mg/kg (ND-7.2 mg/kg), respectively. The Li-ion battery electrodes contained significantly higher levels of cobalt (p < 0.01) whereas, the NiMH battery contained significantly higher nickel (P < 0.01). All the results for the cobalt and nickel levels in the battery electrodes exceeded the toxicity threshold limit concentration used in the toxicity characterization of solid wastes (cobalt, 8000 mg/kg; nickel, 2000 mg/kg). In fact, the mean cobalt level of the battery electrode is about 45 times the toxicity threshold limit concentration limit for cobalt while the mean nickel result is about 38 times the toxicity threshold limit concentration. Spent portable rechargeable batteries should be handled as toxic materials that require special treatment. Implementation of a well-coordinated management strategy for spent batteries is urgently required to check the dissipation of large doses of toxic heavy metals and rare earth into the environment.  相似文献   

10.
 Experiments were performed in the three phase system high-silica rhyolite melt+low-salinity aqueous vapor+hydrosaline brine, to investigate the partitioning equilibria for copper in magmatic-hydrothermal systems at 800° C and 1 kbar, and 850° C and 0.5 kbar. Daqm/mlt Cu and apparent equilibrium constants, Kaqm/mlt Cu,Na, between the aqueous mixture (aqm=quenched vapor+brine) and the silicate melt (mlt) are calculated. Daqm/mlt Cu increases with increasing aqueous chloride concentration and is a function of pressure. Kaqm/mlt Cu,Na=215(±73) at 1 kbar and 800° C and Kaqm/mlt Cu,Na=11(±6) at 0.5 kbar and 850°C. Decreasing pressure from 1 to 0.5 kbar lowers Kaqm/mlt Cu,Na by a factor of approximately 20. Data revealed no difference in Kaqm/mlt Cu,Na or Daqm/mlt Cu as a function of the melt aluminium saturation index. Within the 2-phase field the Kaqm/mlt Cu,Na show no variation with total aqueous chloride, indicating that copper-sodium exchange between the vapor, brine and silicate melt is independent of the mass proportion of vapor and brine. Model copper-sodium apparent equilibrium constants for the hydrosaline brine and the silicate melt revealed a negative dependence on pressure. Model apparent equilibrium constants for copper-sodium exchange between the brine and vapor were close to unity at 1 kbar and 800° C. Received: 27 June 1994/Accepted: 30 March 1995  相似文献   

11.
The Jingbaoshan platinum-palladium deposit is China＇s largest independent PGM （platinum-group metals） deposit so far discovered. There are eleven kinds of useful components in the ore： Pt, Pd, Os, Ir, Ru, Rh, Au, Ag, Cu, Ni, and Co. The platinum-group elements, gold and silver occur in the form of minerals in ores. twenty-five kinds of precious metal minerals have been found, of which twenty one belong to the platinum-group minerals. The minerals are very small in grain size. Copper occurs mainly as copper sulfide with a small amount of free copper oxide, and the beneficiated copper accounts for 95.21%. Nickel occurs mainly as nickel sulfide, and some nickel silicate and nickel oxide occur in the ore. The beneficiated nickel accounts for 72.03%. Cobalt occurs mainly as cobalt sulfide, and there are some cobalt oxide and other kinds of cobalt. The beneficiated cobalt accounts for 77.58%.  相似文献   

12.
In the present study sediment and water samples collected from Kowsar Dam reservoir in Kohkiluye and Boyerahmad Province, southwest of Iran, are subjected to bulk digestion and chemical partitioning. The concentrations of nickel, lead, zinc, copper, cobalt, cadmium, manganese and iron in water and bed sediment were determined by atomic absorption spectrometry. The concentrations of metals bounded to five sedimentary phases were estimated. On this basis, the proportions of natural and anthropogenic elements were calculated.The anthropogenic portion of elements are as follows: zinc (96 %)> cobalt (88 %)> iron (78 %)> magnesium (78 %)> nickel (78 %)> copper (66 %)> lead (63 %)> cadmium (59 %). The results show sediment contamination by nickel, cadmium and lead, according to the world aquatic sediments and mean earth crust values. Manganese and copper have strong association with organic matter and are of high portion of sulfide bounded ions. Finally, The degree of sediment contamination was evaluated using enrichment factor, geo-accumulation index (Igeo) and pollution index (IPoll). The sediments were identified to be of high cadmium and lead pollution index. The pattern of pollution intensity according to enrichment factor is as follows; manganese (1.25) < copper (1.63) < zinc (1.93) < cobalt (2.35) < nickel (3.83) < lead (12.63) < cadmium (78.32). Cluster analysis was performed in order to assess heavy metal interactions between water and sediment. Accordingly, nickel, cadmium and copper are earth originated. Zinc, copper and manganese are dominated by pH. All the elemental concentrations in water and sediment are correlated except for sedimental copper.  相似文献   

13.
Organic materials dissolved in surface waters have long been implicated in metal binding and transport. In particular, fulvic and humic acids are considered to have a significant impact on speciation, total metal levels in solution and on the persistence of those metals. This work emphasizes the role played by dissolved organic matter (DOM) on the complexation of nickel, copper and cobalt and on its application to interpretation of surface water hydrogeochemical survey data. Waters from a number of well-known mining districts in Canada have been studied; in particular from Cobalt (Ontario), Sackville (New Brunswick) and Thetford Mines (Quebec). The diafiltration binding technique was used and shows that nickel, copper and cobalt are complexed significantly by DOM in natural waters. The tendency towards complexation was found to be Cu > Ni > Co. The binding functions determined were observed to be highly sensitive to pH and ligand:metal ratios; a gradation of binding site strength is evident.Data from some hydrogeochemical surveys conducted in the Kenora, Algoma and Ottawa districts of Ontario have been reinterpreted in the light of available data on the complexation behaviour of nickel, copper and cobalt. Occurrence of large water-borne anomalies unsupported by lake sediment loadings is most likely for cobalt and nickel and least likely for copper according to both field observations and experimental data. These studies provide good evidence for the formation of strong solution stable metal-organic species; the principal differences in persistence and migration behaviour are probably due to rates of coagulation and adsorption-precipitation processes which preferentially remove copper from solution. It is fair to conclude that these metals can be of use in mineral exploxation surveys using surface waters provided caution is exercised in interpretation of anomalies, especially in the absence of supporting sediment anomalies. Dissolved organic matter concentrations should always be determined when nickel, copper and cobalt are to be employed.  相似文献   

14.
Water and sediment samples were collected from 20 location of the Buriganga river of Bangladesh during Summer and Winter 2009 to determine the spatial distribution, seasonal and temporal variation of different heavy metal contents. Sequential extraction procedure was employed in sediment samples for the geochemical partitioning of the metals. Total trace metal content in water and sediment samples were analyzed and compared with different standard and reference values. Concentration of total chromium, lead, cadmium, zinc, copper, nickel, cobalt and arsenic in water samples were greatly exceeded the toxicity reference values in both season. Concentration of chromium, lead, copper and nickel in sediment samples were mostly higher than that of severe effect level values, at which the sediment is considered heavily polluted. On average 72 % chromium, 92 % lead, 88 % zinc, 73 % copper, 63 % nickel and 68 % of total cobalt were associated with the first three labile sequential extraction phases, which portion is readily bioavailable and might be associated with frequent negative biological effects. Enrichment factor values demonstrated that the lead, cadmium, zinc, chromium and copper in most of the sediment samples were enriched sever to very severely. The pollution load index value for the total area was as high as 21.1 in Summer and 24.6 in Winter season; while values above one indicates progressive deterioration of the sites and estuarine quality. The extent of heavy metals pollution in the Buriganga river system implies that the condition is much frightening and may severely affect the aquatic ecology of the river.  相似文献   

15.
中国岩浆铜镍钴硫化物矿床是国家镍、钴、铂族元素等战略性关键金属资源的主要来源,是需要特别关注的具有未来价值的重要矿床类型。该类矿床来源于上地幔,特别是软流圈的部分熔融形成的镁铁质、超镁铁质岩浆,硫化物液相?硅酸盐熔体的不混溶（熔离）作用是成矿的主要机制。它们主要形成于两种背景:大陆裂谷和造山带中的伸展环境。中国是岩浆铜镍钴硫化物矿床的产出大国,但与国外相比,形成背景和成矿动力学机制比较独特。世界上绝大多数岩浆铜镍钴硫化物矿床都形成于古老的克拉通,是地幔柱地球动力作用的结果,太古代—早元古代的科马提岩镍钴硫化物矿床是鲜明的产出特点。中国缺少古老的科马提岩有关的镍钴硫化物矿床,成矿时代相对较晚,主要形成于新元古代、晚古生代早期和晚期三个时期,新元古代以镍金属资源量居世界第三的金川超大型矿床为代表,晚古生代早期以近年来找矿突破发现的夏日哈木超大型矿床为代表。夏日哈木矿床也是迄今世界上特提斯造山带中发现的唯一一例超大型岩浆铜镍钴硫化物矿床。中国学者基于中国找矿实际提出的“大岩浆?深部熔离?贯入”表现为“小岩体成大矿”的成矿理论,广泛为野外地质勘查工作者接受并应用,取得了重要的找矿突破性成果,同时为国外同行认可,改变了岩浆铜镍钴硫化物矿床传统的成矿认识。造山带中岩浆铜镍钴硫化物矿床的广泛分布是中国该类矿床的一个重要特色,按形成造山带演化和成矿历史的不同,可分为特提斯型和中亚型两种重要的类型。特提斯型以夏日哈木矿床为代表,它是特提斯构造转换,原特提斯造山后,古特提斯裂解的产物;中亚型以中亚造山带中东天山?北山、阿尔泰分布的大批晚古生代晚期早二叠世岩浆铜镍钴硫化物矿床为代表,是板块构造和地幔柱双重地球动力学机制作用的结果。中国岩浆铜镍钴硫化物矿床找矿潜力巨大,金川矿床作为水平的“岩床”被推覆至地表呈倾斜的“岩墙”产出的结果,深边部仍具有重要找矿潜力,目前已在含矿岩体两端发现了重要的新矿体;夏日哈木矿床所在的东昆仑及其邻区已发现十余处新的矿床（点）。区域上,塔里木陆块东南缘、塔里木陆块北缘、扬子陆块西缘和华北陆块东北缘是亟待加强勘查的找矿远景区,而扬子陆块北缘、华北陆块北缘是急需调查的找矿新区。   相似文献   

16.
The coprecipitation of cobalt(II) and nickel(II) with manganese in ammoniacal solutions has been studied. It was found that cobalt and nickel were precipitated with the aid of manganese at pH 9.3–10.2. However, the rate of precipitation of manganese was about five times that of cobalt. The recovery of these divalent ions by precipitation increased as the pH of the solution increased, while the selectivity of cobalt against nickel decreased with the increase of pH. The partial pressure of oxygen had also an important role in the precipitation of manganese and cobalt but little effect on the up-take of nickel. As the oxygen pressure increased, manganese and cobalt oxidized at a fast rate and the rate of coprecipitation of cobalt with manganese increased. Typically, more than 90% of cobalt was recovered readily by coprecipitation with manganese, while very little nickel was removed from the solution.  相似文献   

17.
Metal levels (cadmium, cobalt, chromium, copper, iron, nickel, lead and zinc) of seventeen different edible wild fungi species (Agaricus campestris, Calocybe gambosa, Coprinus comatus, Hericium coralloides, Hydnum repandum, H. repandum var. rufescens, Lactarius deliciosus, L. salminocolor, Macrolepiota procera, Pleurotus ostreatus, P. ostreatus var. columbinus, Ramaria aurea, R. stricta, Rhizopogon luteolus, Sparassis crispa, Suillus bovinus, Tricholoma terreum) growing in Bolu-Turkey were measured by inductively coupled plasma optical emission spectrocopy. The obtained data were analyzed with “statistical package for the social sciences” statistics program. In addition, relation between metal concentrations in both soil and fungi samples were investigated. The highest metal concentrations in Bolu District, Turkey were measured in A. campestris (cadmium 0.270, chromium 2.735 and zinc 7.683), C. comatus (iron 160.12), M. procera (copper 15.990, cobalt 0.352 and nickel 3.645), R. luteolus (Pb 4.756) mg/kg dw (dry weight). As a result of the measurements, it was observed that metal uptake is related with the species of fungi and is also affected by pH and organic contents of the soil.  相似文献   

18.
The pressure–temperature (P–T) conditions for producing adakite/tonalite–trondhjemite–granodiorite (TTG) magmas from lower crust compositions are still open to debate. We have carried out partial melting experiments of mafic lower crust in the piston-cylinder apparatus at 10–15 kbar and 800–1,050 °C to investigate the major and trace elements of melts and residual minerals and further constrain the P–T range appropriate for adakite/TTG formation. The experimental residues include the following: amphibolite (plagioclase + amphibole ± garnet) at 10–15 kbar and 800 °C, garnet granulite (plagioclase + amphibole + garnet + clinopyroxene + orthopyroxene) at 12.5 kbar and 900 °C, two-pyroxene granulite (plagioclase + clinopyroxene + orthopyroxene ± amphibole) at 10 kbar and 900 °C and 10–12.5 kbar and 1,000 °C, garnet pyroxenite (garnet + clinopyroxene ± amphibole) at 13.5–15 kbar and 900–1,000 °C, and pyroxenite (clinopyroxene + orthopyroxene) at 15 kbar and 1,050 °C. The partial melts change from granodiorite to tonalite with increasing melt proportions. Sr enrichment occurs in partial melts in equilibrium with <20 wt% plagioclase, whereas depletions of Ti, Sr, and heavy rare earth elements (HREE) occur relative to the starting material when the amounts of residual amphibole, plagioclase, and garnet are >20 wt%, respectively. Major elements and trace element patterns of partial melts produced by 10–40 wt% melting of lower crust composition at 10–12.5 kbar and 800–900 °C and 15 kbar and 800 °C closely resemble adakite/TTG rocks. TiO2 contents of the 1,000–1,050 °C melts are higher than that of pristine adakite/TTG. In comparison with natural adakite/TTG, partial melts produced at 10–12.5 kbar and 1,000 °C and 15 kbar and 1,050 °C have elevated HREE, whereas partial melts at 13.5–15 kbar and 900–1,000 °C in equilibrium with >20 wt% garnet have depressed Yb and elevated La/Yb and Gd/Yb. It is suggested that the most appropriate P–T conditions for producing adakite/TTG from mafic lower crust are 800–950 °C and 10–12.5 kbar (corresponding to a depth of 30–40 km), whereas a depth of >45–50 km is unfavorable. Consequently, an overthickened crust and eclogite residue are not necessarily required for producing adakite/TTG from lower crust. The lower crust delamination model, which has been embraced for intra-continental adakite/TTG formation, should be reappraised.  相似文献   

19.
Distribution coefficients have been experimentally determined for the partitioning of nickel, cobalt and manganese between calcium-rich clinopyroxenes and coexisting silicate liquids. Temperatures ranged from 1110–1360°C and oxygen fugacities in the furnaces were controlled by gas mixtures at one atmosphere total pressure. Bulk compositions used include synthetic compositions in the system albite-anorthite-diopside and a natural basalt. Charges were doped with a few percent transition metal oxides and analyzed by electron microprobe. Measured clinopyroxene/liquid distribution coefficients range from 1.5–14 for Ni, 0.5–2.0 for Co and 0.3–1.2 for Mn. Diopside/liquid distribution coefficients for nickel are shown to be independent of Ni content over a range of from 3 ppm to 3 wt.% Ni in the liquid and to increase with decreasing temperature. From analyses of pyroxenes grown from experimental charges differing only in the amounts of transition metals present, nickel and cobalt are shown to occupy the M1 site of diopside while manganese occupies both M1 and M2.Ordinary weight ratio distribution coefficients are strongly dependent on liquid composition as well as temperature. For example, experiments on synthetic Ab-An-Di compositions give clinopyroxene/liquid distribution coefficients higher by about a factor of five than those from experiments at the same temperature on a natural basalt. For Ni and Co, which occupy only the M1 site of clinopyroxene, an equilibrium constant can be defined in terms of activities of components in the liquid and solid phases. Activities of components in the solid are approximated by their mole fractions. An activity/concentration model based on the viscosity model of BOTTINGA and WEILL (1972) is used for the liquid. This model approximates the activity of silica as its mole fraction among the network-forming components SiO2, TiO2, KAlO2, NaAlO2 and Ca0.5AlO2.Activities of network modifiers such as CaO are approximated as their mole fractions among the network-modifying components CaO, MgO, FeO, FeO1.5, etc. When these estimated activities are used in the expression for the equilibrium constant, the effects of compositional differences on trace element distribution coefficients can be understood and the results of experiments on synthetic and natural compositions reconciled.  相似文献   

20.
A detailed mineralogic and chemical study of Zelda, a gigantic (1mm diameter) Fremdling from the Allende CAI, Egg 6, was performed in an attempt to understand the mode of formation of sulfide-rich Fremdlinge and their relation to other types of Fremdlinge. Zelda is composed primarily of pentlandite, pyrrhotite and V-Cr-rich magnetite. Minor phases include NiFePt metal, molybdenite, whitiockite and refractory metal nuggets (RMN) of OsRu and PtIr. The refractory siderophile abundances in Zelda are about 20,000 to 70,000 times chondritic.NiFe grains are highly embayed and are surrounded by a mixture of pentlandite and PtIr RMN. PtIr RMN are found exclusively at the embayed boundaries of NiFe, while OsRu RMN are found distributed throughout the entire Fremdlinge. The texture and mineral and bulk chemistry of Zelda are consistent with closed system sulfidization of a metal-magnetite precursor, with the metal reacting to form a mixture of pentlandite and PtIr, and the magnetite reacting to form pyrrhotite. The evidence suggests that this sulfidization approached equilibrium at a temperature of 800–900°C.Examination of Egg 6 in the vicinity of Zelda indicates that the Fremdling underwent extensive reaction with its surroundings, losing perhaps 40% of its original mass. The reaction involved partial melting, breakdown of NiFe, magnetite and sulfide, formation of V-magnetite-rich veins, and diffusion of Fe, V and Cr into neighboring spinels. Compositional profiles measured in a large spinel near Zelda suggest a diffusion time of approximately 1 hour at a temperature of about 1150°C. Examination of other Fremdlinge indicates that the presence of V-fassaite rims around Fremdlinge helps to protect them from undergoing such types of reaction.The most likely formation of Fremdlinge appears to have involved relatively cold accretion of previously formed grains of magnetite, NiFe and RMN, followed by partial sintering and in some cases sulfidization before incorporation into proto-CAIs. Following incorporation, further sulfidization and reaction of some Fremdlinge with their surroundings occurred. The common coexistence of very high concentrations of refractory aderophiles and low-T metal-magnetite-sulfide assemblages, as well as the evidence that Fremdlinge were incorporated into proto-CAI as solid objects, underscore the complexity of early solar nebula processes and require local mixing of phases formed at considerably different T and fO2. Many of the phase relations observed in Fremdlinge point to CAIs existing for reasonable periods of time at temperatures of about 850°C and cooler, but only for very short times at temperatures greater than 1000°C, although some of these phase assemblages may have been created by exsolution during lower temperature reequilibration.  相似文献   

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