共查询到20条相似文献，搜索用时 171 毫秒
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近些年来,人们广泛地利用火山岩的主元素或微量元素的特征对火山岩进行地球化学、成因岩石学和构造岩石学的研究。Mullen(1983)利用玄武岩的 MnO、TiO2和P2O5建立大洋型玄武岩的 MnO×10-TiO2-P2O5×10的构造背景判别图(以下简称MTP图)和圈出了大陆拉斑玄武岩在 MTP 图中的分布范围。他选择了能反映玄武岩形成过程中的重要地球化学特征和成因机制的元素组作为该图的端元组分。 相似文献
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我們在前一篇文章里曾討論了Ca2+-HPO42--F1--H2O体系中氟对磷酸盐矿物形成影响的若干方面。为了使該項模拟試驗工作更符合于表生作用条件,我們在叶連俊教授的指导下,在上述实驗体系中增加了一个組分--HCO31-,进行了Ca2+-HPO42--HCO31-F1--H2O体系的試驗研究。其目的为进一步探索在合有HCO31-組分的体系中氟对磷酸盐矿物形成的影响,以及CO32-能否进入磷灰石晶格和磷酸盐矿物与碳酸盐矿物的沉积分异順序等問題。 相似文献
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地球大气圈中40Ar/36Ar的现代比值被公认为295.5,在利用K-Ar法测定地球物质年龄时,它是校正大气氩混染量的重要参数。陨石中原始捕获(trapped)的(40Ar/36Ar)t比值是否和地球大气圈中氩同位素丰度相一致,这个问题不但在地质年龄测定中具有现实意义,而且对探索太阳系的形成和演化也有重要理论价值。近十几年,随着质谱分析技术的提高以及登月计划的实施,国外出现了一批有关月岩中氩同位素原始组分的资料,但至今对陨石中原始氩同位素丰度的报道很少。笔者采用40Ar/39Ar快中子活化技术和约克方程[3,4],对吉林陨石雨2号标本进行了原始捕获的(40Ar/36Ar)t比值进行了测定,并探讨了它的地质意义。 相似文献
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引言戈斯（Ghose,S.）在测定斜方辉石的结构时,首次发现Fe2+离子择优占据M2晶位,而Mg2+离子择优占据M1晶位。这一事实,引起了矿物学家的极大注意。 相似文献
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氟碳钡铈矿(Cordylite)BaCe2(CO3)3 F2本世纪初首先发现于格陵兰纳尔萨尔苏克(Narssarssuk)的碱性正长伟晶岩脉中,与霓石、氟碳铈钙矿、柱星叶石和碳锶铈矿共生。1965年该矿物又发现于我国白云鄂博西矿区热液交代的元古代白云岩中。1975年,加拿大魁北克省圣赫莱山(Mont st. Hilaire,Quebec)的霞石正长岩中的伟晶岩脉中也发现了这一矿物,它与方沸石、霓石和钠闪石共生。 相似文献
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利用配有电阻炉外加热装置的金刚石对顶砧及紧装式六面顶高压容器,在500—1700℃和常压至17.8GPa温压范围内,对AlPO4进行了实验研究。常压下,磷铝石(石英型AlPO4)向鳞石英型AlPO4转变的温度约为778℃,鳞石英型向方英石型AlPO4转变的温度约为1100℃,块磷铝石α-β相转变的温度为586℃。在5.4 GPa和1300℃以下,块磷铝石保持稳定,在5GPa和大于1700℃时,发现AlPO4分解为Al2O3,(刚玉)和P2O5鳞石英型AlPO4在6GPa及500℃转变成斜方晶系新相,新相在室温常压下的晶胞参数为:a=4.930Å,b=7.200Å和c=6.165Å,鳞石英型AlPO4及块磷铝石在11GPa以上均变为NiSO4型结构。文中讨论了AlPO4与SiO2的异同,并给出了一个AlPO4可能的相图。 相似文献
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在夏季分层期间对红枫湖南、北湖湖心的水样进行分层采集,同时测定了分层水样的温度、pH、HCO3-浓度、溶解氧(DO)、叶绿素a(Chl-a)及铵根离子(NH4+)、硝酸根离子(NO3-)、磷酸根离子(PO43-)的浓度,水体中CO2的分压(pCO2)由化学平衡及亨利定律求得。研究结果表明:光合作用、有机质降解及水体热分层是影响红枫湖夏季pCO2分布的主要因素。其中,温水层CO2欠饱和是光合作用吸收CO2引起的,温跃层中pCO2的急剧增加是光合产物降解产生CO2引起的。静水层沉积物附近pCO2最高并且还有持续增加的趋势,说明沉积物中有机质降解是静水层中CO2增加的主要原因,夏季湖底水温较高加快了沉积物中有机质的降解。分层现象使pCO2在水体中的分布差别明显,并且使静水层中CO2得到积累。此外,夏季红枫湖水体中pCO2的变化与NH4+、PO43-的变化密不可分,表现为温水层中光合作用消耗NH4+、PO43-,有机质降解过程伴随NH4+、PO43-的释放。 相似文献
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Domain twinning of laihunite has been investigated based on diffracton phenomena, and its crystal structure has then been refined. Space group with respect to the domain isP21/c, and cell parametersa=5.813,b=4,812,c=10.211(A), β=90.87°. Atomic coordinate and bond length have been recalculated. Discussions are made of the Fe2+ distribution, lattice distortion, degree of order of laihunite and the relationship of this mineral with fayalite and ferrifayalite. The authors still hold that laih unite should be considered as a new silicate mineral with dominant Fe3+ and less amount of Fe2+. 相似文献
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Susan A WelchJillian F Banfield 《Geochimica et cosmochimica acta》2002,66(2):213-221
Prior transmission electron microscope studies showed that the surface geometry of olivine changes dramatically during natural chemical weathering. However, similar morphological evolution has not been reported in laboratory studies of olivine dissolution. In this study, we examined the development of fayalite (Fe2SiO4) surface morphology during both abiotic and biotic (using Acidithiobacillus ferrooxidans) laboratory dissolution experiments at an initial pH of 2.0. The fayalite came from Cheyenne Canyon, Colorado (Smithsonian # R 3516) and contains a few percent laihunite (olivine structure with ordered ferric iron and vacancies, ∼Fe0.82+Fe0.83+SiO4). High-resolution field emission low voltage scanning electron microscope (SEM) characterization of all reacted samples showed etch patterns consistent with those reported from naturally reacted olivine. High-resolution transmission electron microscope (HRTEM) data demonstrated pervasive channeling on (001), with channel spacings that range down to < 10 nm. Formation of channels on (001) is probably initiated by preferential removal of cations from olivine M1 sites. Channeling confers at least an order of magnitude increase in surface area. Relict strips of olivine between channels contain laihunite layers that are oriented parallel to channel margins. X-ray diffraction analyses indicated that the relative abundance of laihunite is higher in reacted compared to unreacted samples. This result is consistent with prior studies of naturally weathered olivine that suggest that laihunite is far less readily dissolved than olivine.Samples reacted in the presence of A. ferrooxidans cells that enzymatically oxidized iron, or in solutions where ferric iron was added to simulate biological activity, dissolve at a much slower rate than samples reacted abiotically. We attribute suppression of the olivine dissolution rate to surface adsorption of Fe3+. It is probable that ferric iron adsorption is controlled by M2 sites in the underlying olivine structure. If this is coupled with removal of M1 cations during channel formation, then a modified laihunite-like surface will develop (vacancies in laihunite are on M1 sites). Although surface modification might only penetrate a few atomic layers, an inherently unreactive laihunite-like surface structure could explain both the pervasive channeling and the dramatic suppression of the measured dissolution rate. 相似文献
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Six natural chloritoid crystals with Fe2+ and Fe3+ contents ranging from 4.15 to 12.81 and from 0.411 to 0.849g-atoms/l, respectively, as determined by means of microprobe and Mössbauer techniques, served as reference material to develop non-destructive microscope-spectrophotometric methods for quantitative Fe2+ – Fe3+ determinations in chloritoids from unpolarized spectra of (001) platelets. Fe2+ concentrations in g-atom/l can be obtained from [ [Fe3+]=C1xD1/t where D1 = log10(I0/I at 28,000 cm-1 and t=crystal thickness in cm; C1 is a conttant that may be influenced somewhat by experimental conditions and is found to be 0.002289 with the experimental set-up used in this study. Fe2+ concentrations in g-atom/l can be obtained from [Fe2+]=C1xD1/D1-C3 with D2=log10(I0/I) at 16,300 cm?1 and constants C4 = 45.36 and C5 = 3.540. Due to the uncertainties in absorbance measurements, D1 and D2 and the thickness measurements, the accuracies are ±0.05 and ±0.15 g-atom/l for [Fe3+] and [Fe2+], respectively. The determinations may be carried out on chloritoid grains in normal thin sections with an areal resolution of ～10 μm. 相似文献
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本文进行了莱河矿3C超结构和4.2K穆斯堡尔谱的对比研究。研究表明。莱河矿的非等效位置M2A+M2C,M2B,M1B,M1A和VB能够分别与Kan等(1985)测定的莱河矿穆斯堡尔谱的吸收双峰A,B,C,D和E对应,不仅解决了超结构位置和吸收双峰之间的对应,而且圆满解释了吸收双峰A:B和C:D的强度比为2:1的关系。另外,还利用莱河矿超结构的资料讨论了莱河矿的反铁磁性内部作用。 相似文献
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Reversals for the reaction 2 annite+3 quartz=2 sanidine+3 fayalite+2 H2O have been experimentally determined in cold-seal pressure vessels at pressures of 2, 3, 4 and 5?kbar, limiting annite +quartz stability towards higher temperatures. The equilibrium passes through the temperature intervals 500–540°?C (2?kbar), 550–570°?C (3?kbar), 570–590°?C (4?kbar) and 590–610°?C (5?kbar). Starting materials for most experiments were mixtures of synthetic annite +fayalite+sanidine+quartz and in some runs annite+quartz alone. Microprobe analyses of the reacted mixtures showed that the annites deviate slightly from their ideal Si/Al ratio (Si per formula unit ranges between 2.85 and 2.92, AlVI between 0.06 and 0.15). As determined by Mössbauer spectroscopy, the Fe3+ content of annite in the assemblage annite+fayalite +sanidine+quartz is around 5–7%. The experimental data were used to extract the thermodynamic standard state enthalpy and entropy of annite as follows: H 0 f,?Ann =?5125.896±8.319 [kJ/mol] and S 0 Ann=432.62±8.89 [J/mol/K] (consistent with the Holland and Powell 1990 data set), and H 0 f,Ann =?5130.971±7.939 [kJ/mol] and S 0 Ann=424.02±8.39 [J/mol/K] (consistent with the TWEEQ data base, Berman 1991). The preceeding values are close to the standard state properties derived from hydrogen sensor data of the redox reaction annite=sanidine+magnetite+H 2 (Dachs 1994). The experimental half-reversal of Eugster and Wones (1962) on the annite +quartz breakdown reaction could not be reproduced experimentally (formation of annite from sanidine+fayalite+quartz at 540°?C/1.035?kbar/magnetite-iron buffer) and probable reasons for this discrepancy remain unclear. The extracted thermodynamic standard state properties of annite were used to calculate annite and annite+quartz stabilities for pressures between 2 and 5?kbar. 相似文献
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Frances N. Skomurski Sebastien Kerisit Kevin M. Rosso 《Geochimica et cosmochimica acta》2010,74(15):4234-7290
For the purpose of improving fundamental understanding of the redox reactivity of magnetite, quantum-mechanical calculations were applied to predict Fe2+ availability and electron hopping rates at magnetite (1 0 0) surfaces, with and without the presence of adsorbed water. Using a low free energy surface reconstruction (½-Fetet layer relaxed into the Feoct (1 0 0) plane), the relaxed outermost layer of both the hydrated and vacuum-terminated surfaces were found to be predominantly enriched in Fe2+ within the octahedral sublattice, irrespective of the presence of adsorbed water. At room temperature, mobile electrons move through the octahedral sublattice by Fe2+-Fe3+ valence interchange small polaron hopping, calculated at 1010-1012 hops/s for bulk and bulk-like (i.e., near-surface) environments. This process is envisioned to control sustainable overall rates of interfacial redox reactions. These rates decrease by up to three orders of magnitude (109 hops/s) at the (1 0 0) surface, and no significant difference is observed for vacuum-terminated versus hydrated cases. Slower hopping rates at the surface appear to arise primarily from larger reorganization energies associated with octahedral Fe2+-Fe3+ valence interchange in relaxed surface configurations, and secondarily on local charge distribution patterns surrounding Fe2+-Fe3+ valence interchange pairs. These results suggest that, with respect to the possibility that the rate and extent of surface redox reactions depend on Fe2+ availability and its replenishment rate, bulk electron hopping mobility is an upper-limit for magnetite and slower surface rates may need to be considered as potentially rate-limiting. They also suggest that slower hopping mobilities calculated for surface environments may be amenable to Fe2+-Fe3+ site discrimination by conventional spectroscopic probes. 相似文献
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Jillian F. Banfield David R. Veblen Blair F. Jones 《Contributions to Mineralogy and Petrology》1990,106(1):110-123
Olivine crystals in basaltic andesites which crop out in the Abert Rim, south-central Oregon have been studied by high-resolution and analytical transmission electron microscopy. The observations reveal three distinct assemblages of alteration products that seem to correspond to three episodes of olivine oxidation. The olivine crystals contain rare, dense arrays of coherently intergrown Ti-free magnetite and inclusions of a phase inferred to be amorphous silica. We interpret this first assemblage to be the product of an early subsolidus oxidation event in the lava. The second olivine alteration assemblage contains complex ordered intergrowths on (001) of forsterite-rich olivine and laihunite (distorted olivine structure with Fe3+ charge balanced by vacancies). Based on experimental results for laihunite synthesis (Kondoh et al. 1985), these intergrowths probably formed by olivine oxidation between 400 and 800°C. The third episode of alteration involves the destruction of olivine by low-temperature hydrothermal alteration and weathering. Elongate etch-pits and channels in the margins of fresh olivine crystals contain semi-oriented bands of smectite. Olivine weathers to smectite and hematite, and subsequently to arrays of oriented hematite crystals. The textures resemble those reported by Eggleton (1984) and Smith et al. (1987). We find no evidence for a metastable phase intermediate between olivine and smectite (M — Eggleton 1984). The presence of laihunite exerts a strong control on the geometry of olivine weathering. Single laihunite layers and laihunite-forsteritic olivine intergrowths increase the resistance of crystals to weathering. Preferential development of channels between laihunite layers occurs where growth of laihunite produced compositional variations in olivine, rather than where coherency-strain is associated with laihunite-olivine interfaces. 相似文献
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A. C. Doriguetto N. G. Fernandes A. I. C. Persiano E. Nunes Filho J. M. Grenèche J. D. Fabris 《Physics and Chemistry of Minerals》2003,30(5):249-255
Single crystals of a rock magnetite were separated from steatite cobbles collected in a geological site near the city of Serro (18° 36′ 47′′ S 43° 22′ 46′′ W), Minas Gerais, Brazil. A typically well-shaped magnetite single crystal was characterized by chemical analysis, 57Fe Mössbauer spectrometry at 300, 77 and 4 K and under an applied magnetic field of 6 T at 10 K, magnetization measurements and electronic microprobe. From Mössbauer data, the sample is stoichiometric with a tetrahedral and octahedral site occupancy ratio of 1:2. Elemental chemical analysis and point-to-point electron microscope probing show some inclusions of lamellar ilmenite (≤ 1 mass%) randomly distributed throughout the magnetite matrix, and also that the magnetite matrix is constituted only by Fe2+ and Fe3+, with no isomorphic substitution. Results are discussed on the basis of the magnetization curve and of the temperature dependence of the AC magnetic susceptibility. The Verwey transition occurs in the temperature range of 100–115 K, observed by a sudden change in the temperature dependence of the magnetization. 相似文献
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Shengyuan Wang 《中国地球化学学报》1982,1(2):233-245
Laihunite, a mineral of ferric and ferrous iron silicate discovered in China in recent years, occurs in high grade metamorphic BIF coexisting with magnetite, quartz, fayalite, ferrosilite and almandinc. Complete nets based on Schreinemakers bundles and partial nets with maximum closure after the method described by H. W. Day have been constructed by taking into account the existence of this mineral in order to illustrate phase relations for the (n+3) multisystem in the system Fe2O3-FeO-SiO2. Judging from Lindsley’s experimental data on ferrosilite, laihunite-ferrosilite assemblage is expected to be stable at pressures probably higher than 15 kb. Two-pyroxene and garnet-clinopyroxene geothermometers gave the temperatures of formation between 600–700°C. The free energy of laihunite calculated according to Chen’s method and estimated heat capacity power-function coeficients allow oxygen fugacity to be plotted against temperature at different total pressure swith respect to a number of univariant reactions in which laihunite is involved. The logfo 2-T diagram demonstrates that to a first approximation the stability field of laihunite overlaps the upper part of the magnetite field, but its upper limit is a little beyond the hematite-magnetite equilibrium. The three major requirements for laihunite stability, i.e., an unusual high pressure, a temperature in the order of 600°C–700°C and a relatively higher oxygen fugacity, are mutually exclusive in common geological environment, which may probably account for the rare occurrence of this mineral in nature. For the BIF in which laihunite occurs, the pressure caused by the weight of overlying strata is not high enough to give rise to its formation even in the extreme case of geothermal gradient. So it is suggested that additional tectonic pressure in response to plate activity might have been involved. 相似文献