游离态Fe(Ⅱ)驱动赤铁矿晶相重组的Fe原子交换机制:稳定Fe同位素示踪研究

土壤中游离态Fe(Ⅱ)与铁(氢)氧化物矿物之间的原子交换是最近发现的重要的铁循环化学过程.但是,结晶度高、性质稳定的赤铁矿,与游离态Fe(Ⅱ)之间的原子交换过程及其矿物晶相变化仍然未知.本研究中,我们采用控制实验,以~(5 7)Fe同位素示踪方法研究厌氧体系中游离态Fe(Ⅱ)与赤铁矿中结构态Fe(Ⅲ)之间的原子交换机制.结果表明,游离态Fe(Ⅱ)与赤铁矿中的结构态Fe(Ⅲ)能发生明显的Fe原子交换,即游离态Fe(Ⅱ)进入到赤铁矿结构形成结构态Fe(Ⅲ),而赤铁矿中原来的部分结构态Fe(Ⅲ)被还原释放,进入到溶液体系形成游离态Fe(Ⅱ).这一反应体系中Fe原子交换率受pH和游离态Fe(Ⅱ)初始浓度的影响;与酸性环境相比,pH 7.5的中性环境更有利于Fe原子交换的发生;在相同pH条件下,Fe原子交换率首先随游离态Fe(Ⅱ)初始浓度的升高而提高,但是过高的Fe(Ⅱ)浓度导致在赤铁矿表面吸附的Fe(Ⅱ)超过单层吸附位覆盖量,在一定程度上抑制Fe原子交换.Fe(Ⅱ)作用下Fe原子交换发生的同时,赤铁矿晶相发生重组.更为重要的是,通过X射线衍射表征研究发现,游离态Fe(Ⅱ)驱动赤铁矿晶相重组过程中形成新的赤铁矿和针铁矿;进一步通过穆斯堡尔谱研究证实,新的赤铁矿晶体主要形成机制为晶体同质外延生长,针铁矿形成机制为异质外延生长.本研究发现的游离态Fe(Ⅱ)驱动性质稳定的赤铁矿晶相转变及其Fe原子交换过程,可为揭示以稳定态铁(氢)氧化物为主要含铁矿物分布的热带亚热带土壤元素环境地球化学过程机制提供重要理论基础.     

对PH敏感的顺磁性造影剂—Fe—EDTA

目的探讨ＰＨ值对Ｆｅ－ＥＤＴＡ造影效果的影响。方法;配制ＰＨ梯度５０－８０的０．５和０．１ｍｍｏｌ／Ｌ的Ｆｅ－ＥＤＴＡ液,观察ＳＥ序列「ＴＲ（ｍｓ）／ＴＥ（ｍｓ）２００／１５,２５００／８０」,信号变化,结果：Ｆｅ－ＥＤＴＡ的ＭＲ信号随ＰＨ值提高而减弱。     

The transformation of γ Fe2O3 to α Fe2O3: thermal activation and the effect of elevated pressure

The transformation of acicular γ Fe₂O₃ particles to α Fe₂O₃ has been monitored using magnetic properties as a proxy for γ Fe₂O₃ concentration during the inversion process. The transformation is thermally activated, the height of the barrier opposing inversion being 3.7 eV at atmospheric pressure and 0.5 eV at a pressure of about 100 MPa. The barrier arises from the combination of a term representing the reduction in lattice energy in an inverted region, and the strain energy associated with the interface between the inverted and non-inverted phases. The sensitivity of the inversion process to pressure can be understood in terms of the dependence of these energy terms, and the energy barrier, on interatomic spacing. Extrapolation of these laboratory data to the conditions of the submarine crust at Site 504B of the Deep Sea Drilling Project is consistent with the inferred magnetic mineralogy of the recovered material.     

中国东部新生代玄武岩高Fe/Mn比值的成因意义

中国东部新生代玄武岩普遍具有的高Fe/Mn比值(平均 = 68.6 ± 11.5)与OIB型微量元素特征暗示高Fe/Mn比值与OIB型特征之间具有耦合关系. 尽管单斜辉石分离结晶作用会引起玄武岩Fe/Mn比值增加, 但对华北克拉通北缘的汉诺坝和南缘安徽境内新生代玄武岩的详细研究, 发现这些玄武岩的高Fe/Mn比值无法单独用单斜辉石分离结晶作用解释, 而必须存在高Fe/Mn比值原始岩浆. 橄榄岩和辉石岩部分熔融实验研究和模拟计算结果表明, 高Fe/Mn比值与OIB型特征之间的耦合关系应反映了地幔源区中存在的辉石岩组分, 而不必求助于核-幔作用或高度亏损岩石圈地幔的再熔融作用. 结合中国东部的岩石圈演化历史和新生代玄武岩Sr-Nd-Pb同位素组成, 新生代玄武岩的高Fe/Mn比值和OIB型微量元素组成之间的耦合特征应是中国东部岩石圈演化过程中广泛的岩石圈物质再循环作用的记录.     

Asymmetry of the contours of the Fe X 6374-Å coronal line

The east-west asymmetry has been analyzed using the 1946–2000 corona observation data for the green line at the Kislovodsk station. A positive east-west asymmetry has been revealed throughout the entire observation period except for three years, 1994–1996. Time variations of the east-west asymmetry for certain periods coincide with those for flares. Seasonal variations of the east-west asymmetry revealed earlier by other authors are not confirmed. If seasonal variations of the east-west asymmetry in the corona exist, their amplitudes are smaller than or comparable to the instrumental errors, errors caused by atmospheric variations during the observation period and to differences between the corona-intensity measuring systems used at different observatories.     

Melting and thermal expansion in the Fe–FeO system at high pressure

Melting in the Fe–FeO system was investigated at pressures up to 93 GPa using synchrotron X-ray diffraction (XRD) and a laser heated diamond anvil cell (DAC). The criteria for melting were the disappearance of reflections associated with one of the end-member phases upon raising the temperature above the eutectic and the reappearance of those reflections on dropping the temperature below the eutectic. The Fe–FeO system is a simple eutectic at 50 GPa and remains eutectic to at least 93 GPa. The eutectic temperature was bound at several pressure points between 19 and 93 GPa, and in some cases the liquidus temperature was also determined. The eutectic temperature rises rapidly with pressure closely following the melting curve of pure Fe. A detailed phase diagram at 50 GPa is presented; the eutectic temperature is 2500 ± 150 K and the eutectic composition is bound between 7.6 ± 1.0 and 9.5 ± 1.0 wt.% O. The coefficient of thermal expansion of FeO is a strong function of volume and decreases with pressure according to a simple power law.     

阿哈湖Fe、Mn沉积后再迁移的生物地球化学机理

贵州阿哈湖是一底层滞水带季节性缺氧的中型人工湖。由于长期积累。沉积物顶部微粒悬浮层出现了Ｆｅ、Ｍｎ富集。湖底缺氧时,经生物氧化作用形成的Ｆｅ＾２＋、Ｍｎ＾２＋自沉积物向上覆水体扩散,水体Ｆｅ＾２＋浓度增高比Ｍｎ＾２＋滞后出现且超过前结束。     

Fe(Ⅲ)改性土壤用于微囊藻细胞及微囊藻毒素的去除

蓝藻水华及其释放的蓝藻毒素给我国很多地区的饮用水安全带来较大威胁.尽管去除蓝藻和净化藻毒素的技术目前已有较多报道,但能同时对二者起作用的技术方法还较少,发展能够同时去除蓝藻和蓝藻毒素的技术显得十分必要.根据前期Fe(Ⅲ)化合物去除微囊藻毒素的工作基础,选取4种不同的土壤对其进行Fe(Ⅲ)改性,并应用于微囊藻毒素的去除.结果表明,黏土含量高低决定土壤本身对毒素的吸附能力强弱;土壤经过离子改性后,其毒素吸附能力与其阳离子交换量大小直接相关,且毒素去除能力较未改性前有显著提高,其中效率提升最高的一种土壤离子改性后其吸附能力增加了约148倍.离子改性土壤对微囊藻细胞同样具有絮凝沉降功能,沉降能力同样随土壤对Fe(Ⅲ)负载能力的提高而上升,使用剂量提高时微囊藻沉降平衡时间明显缩短.在野外蓝藻水华去除实验中,蓝藻细胞去除可以保持与室内实验相近的高去除率,但蓝藻毒素的去除效率有一定的下降,可能与天然水体中其它杂质的竞争作用有关.     

Thermal equation of state of magnesiowüstite (Mg0.6Fe0.4)O

Volume measurements for magnesiowüstite (Mg_0.6Fe_0.4)O, were carried out up to pressures of 10.1 GPa in the temperature range 300–1273 K, using energy-dispersive synchrotron X-ray diffraction. These data allow reliable determination of the temperature dependence of the bulk modulus and good constraint on the thermal expansitivity at ambient pressure which was previously not known for magnesiowüstite. From these data, thermal and elastic parameters were derived from various approaches based on the Birch–Murnaghan equation of state (EOS) and on the relevant thermodynamic relations. The results from three different equations of state are remarkably consistent. With (∂K_T/∂P)_T fixed at 4, we obtained K₀=158(2) GPa, (∂K_T/∂T)_P=−0.029(3) GPa K⁻¹, (∂K_T/∂T)_V=−3.9(±2.3)×10⁻³ GPa K⁻¹, and α_T=3.45(18)×10⁻⁵+1.14(28)×10⁻⁸T. The K₀, (∂K_T/∂T)_P, and (∂K_T/∂T)_V values are in agreement with those of Fei et al. (1992) and are similar to previously determined values for MgO. The zero pressure thermal expansitivity of (Mg_0.6Fe_0.4)O is found to be similar to that for MgO (Suzuki, 1975). These results indicate that, for the compositional range x=0–0.4 in (Mg_1−xFe_x)O, the thermal and elastic properties of magnesiowüstite exhibit a dependence on the iron content that is negligibly small, within uncertainties of the experiments. They are consequently insensitive to the Fe–Mg partitioning between (Mg, Fe)SiO₃ perovskite and magnesiowüstite when applied to compositional models of the lower mantle. With the assumption that (Mg_0.6Fe_0.4)O is a Debye-like solid, a modified equation of heat capacity at constant pressure is proposed and thermodynamic properties of geophysically importance are calculated and tabulated at high temperatures.     

High-altitude sporadic metal atom layers observed with Na and Fe lidars at 30°N

The seasonal/annual characteristics of the high-altitude sporadic metal atom layers are presented on the basis of extensive Na and Fe lidar measurements at 30°N during the past several years. It is found that the extremely high sporadic Na (Na_s) and Fe (Fe_s) layers above 105 km occurred mostly during summer. They had long durations (a few hours) and broad layer widths (much larger than 2 km). Their absolute peak densities could be comparable to or even larger than those of the corresponding main layers on a few nights. By using all the raw data profiles including sporadic layers, we have constructed the contour plots of Na and Fe densities versus month and altitude at 30°N. The Na and Fe layers both exhibit evidence for summer topside extension, which is consistent with the earlier observations for K and Ca at different latitudes. The summer topside extension of mean metal atom layers might represent a universal phenomenon that is alike for different atom species, different geographic locations and different measurement years. The extremely high sporadic metal atom layers above 105 km occurring during summer give rise to the phenomenon.     

鄱阳湖湿地土壤中Fe、Mn的迁移特征及其与水位周期变动的关系

对鄱阳湖地区蚌湖水下沉积物、滩地草甸土柱状样品不同深度土壤的酸度、氧化还原电位进行了现场测定;对剖面各层次的Ｆｅ、Ｍｎ总量,还原性Ｆｅ、Ｍｎ含量,以及有机质等进行了分析。实验表明：鄱阳湖湿地土壤中Ｆｅ、Ｍｎ有其独特的分布规律和迁移特征。元素Ｆｅ仅在水土界面轻微富集,Ｍｎ则向界面和深层双向富集;还原性Ｆｅ、Ｍｎ受氧化还原边界层的控制呈垂向分布。另外,元素Ｆｅ、Ｍｎ的水平迁移与水位变动相关,退水时Ｆｅ     

Microaerobic Fe (Ⅱ) oxidation coupled to carbon assimilation processes driven by microbes from paddy soil

Microaerobic Fe(Ⅱ) oxidation process at neutral pH, driven by microbes can couple to carbon assimilation process in iron-rich freshwater and marine environments; however, few studies report such coupled processes in paddy soil of the critical zone in South China. In this study, rhizosphere soil from flooded paddy field was used as the inoculum to enrich the microaerophilic Fe(Ⅱ)-oxidizing bacteria(FeOB) in gradient tubes with different Fe(Ⅱ) substrates(FeS and FeCO_3) and ~(13)C-biocarbonate as inorganic carbon source to track the carbon assimilation. Kinetics of Fe(Ⅱ) oxidation and biomineralization were analyzed, and the composition and abundance of the microbial community were profiled using 16 S rRNA gene-based highthroughput sequencing. Results showed that microbial cell bands were formed 0.5–1.0 cm below the medium surface in the inoculated tubes with Fe(Ⅱ) substances, while no cell band was found in the non-inocula controls. The protein concentrations in the cell bands reached the highest values at 18.7–22.9 mg m~L(-1) on 6 d in the inocula tubes with Fe(Ⅱ) substrates. A plateau of the yields of ~(13)C-biocarbonate incorporation was observed during 6–15 d at 0.44–0.54% and 1.61–1.98% in the inocula tubes with FeS and FeCO_3, respectively. The inocula tube with FeS showed a higher Fe(Ⅱ) oxidation rate of 0.156 mmol L~(-1) d~(-1) than that with FeCO_3(0.106 mmol L~(-1) d~(-1)). Analyses of X-ray diffraction and scanning electron microscopy with energy-dispersive X-ray spectroscopy revealed that amorphous iron oxide was formed on the surface of rod-shaped bacteria after Fe(Ⅱ) oxidation.Relative to the agar only control, the abundances of Clostridium and Pseudogulbenkiania increased in the inocula tube with FeS,while those of Vogesella, Magnetospirillum, Solitalea, and Oxalicibacterium increased in the inocula tube with FeCO_3, all of which might be the potential microaerophilic FeOB in paddy soil. The findings in this study suggest that microbes that couple microaerobic Fe(Ⅱ) oxidation to carbon assimilation existed in the paddy soil, which provides an insight into the iron-carbon coupling transformation under microaerobic conditions in the critical zone of the iron-rich red soil.     

Correlation of rhyolitic pyroclastic eruptive units from the Taupo volcanic zone by Fe–Ti oxide compositional data

Grain-specific analyses of Fe–Ti oxides and estimates of eruption temperature (T) and oxygen fugacity (fO₂) have been used to fingerprint rhyolitic fall and flow deposits that are important for tephrostratigraphic studies in and around the Taupo volcanic zone of North Island, New Zealand. The analysed Fe–Ti oxides commonly occur in the rims of orthopyroxene crystals and appear to reflect equilibrium immediately prior to eruption because of geochemical correlation with the co-existing glass phase. The composition of the spinel phase is particularly diagnostic of eruptive centre for post-65 ka events and can be used to distinguish many tephra beds from the same volcano. The 29 different units examined were erupted over a wide range in T (690–990°C) and Δ log fO₂ (–0.1 to 2.0). These parameters are closely related to the mafic mineral assemblage, with hydrous mineral-bearing units displaying higher fO₂. Such trends are superimposed on larger differences in fO₂ that are related to eruptive centre. At any given temperature, all post-65 ka Okataina centre tephra have higher fO₂ values than post-65 ka Taupo centre tephra. This provides a useful criterion for identifying the volcanic source. There are no temporal T and fO₂ trends in the tephra record; over intervals >20 ka, however, tephra sequences from Taupo centre form characteristic T-fO₂ buffer trends mirroring the glass chemistry. Individual eruptive events display uniform spinel and rhombohedral phase compositions and thus narrow ranges in T (± <20°C) and log fO₂ (± <0.5), allowing these features to identify individual magma batches. These criteria can help distinguish tephra deposits of similar bulk or glass composition that originated from the same volcano. Distal fall deposits record the same T-fO₂ conditions as the proximal ignimbrite and enable distal–proximal correlation. Lateral and vertical compositional and T-fO₂ variability displayed in large volume (>100 km³) ignimbrites, such as the Oruanui, Rotoiti and Ongatiti, is similar to that found in a single pumice clast and thus mainly reflects analytical error; however, thermal gradients of ca. 50°C may occur in some units. Received: 6 April 1998 / Accepted: 16 June 1998     

含Fe3+的硅酸盐尖晶石γ-Fe2SiO4的M(o)ssbauer效应研究

对3个合成的含Fe3+的铁硅酸盐尖晶石γ-Fe2SiO4进行了电子探针分析, 并在298, 150和95 K的温度下对它们进行了M(o)ssbauer谱的测试. 每个温度下的M(o)ssbauer谱均由两个双峰组成. 这两个双峰分别被指派给八面体位置上的Fe2+和四面体位置上的Fe3+, 并且根据M(o)ssbauer吸收面积给出了占位. 结果表明, Fe3+和少量的Si4+分别占据在四面体和八面体位置上. 根据M(o)ssbauer分析所得到的占位, 使用经过修正的公式, 计算了八面体和四面体位置的平均键长. 在此基础上, 八面体和四面体的平均键长进而被用来计算含Fe3+的γ-Fe2SiO4的晶胞参数和氧参数. 此外, 使用次近邻效应解释了含Fe3+的γ-Fe2SiO4 M(o)ssbauer谱的Fe3+谱线的宽化现象.     

球粒陨石冲击脉体冷却速率对(Mg,Fe)_2SiO_4多型转变的制约

发生在寺巷口陨石冲击脉体的较大冷却速率 ( >1 0 0 0 0℃·s-1)使得橄榄石(α 相 )的高压多型γ相被保存了下来 ;冷却速率中等的和平河陨石冲击脉体 ( 1 0 0 0～ 2 0 0 0℃·s-1) ,γ相部分逆转为β相 ,但β相向α相的进一步逆转受阻 ,脉体保存了β相 ;冷却速率较慢的蒙巴喇陨石冲击脉体 ( <5 0 0℃·s-1) ,γ相几乎全部逆转为α相 .冲击脉体的热散失滞后于陨石母体冲击压缩阶段 ,发生在陨石母体崩解成碎块以后 .脉体的冷却速率制约了 (Mg ,Fe) 2 SiO4高压多型的逆向转变过程 .     

Formation of the Late Permian Panzhihua plutonic-hypabyssal-volcanic igneous complex: Implications for the genesis of Fe–Ti oxide deposits and A-type granites of SW China

The Late Permian (260 Ma) Emeishan large igneous province of SW China contains numerous magmatic Fe–Ti oxide deposits. The Fe–Ti oxide deposits occur in the lower parts of evolved layered gabbroic intrusions which are spatially and temporally associated with A-type granitic rocks. The 260 Ma Panzhihua layered gabbroic intrusion hosts one of the largest magmatic Fe–Ti oxide deposits in China and is coeval with a peralkaline A-type granitic pluton. The granite has intruded the overlying Emeishan flood basalts and fed at least one dyke which erupted onto the surface producing columnar jointed trachytes. The presence of syenodiorite between the layered gabbro and granite is evidence for compositional evolution from mafic to intermediate to felsic rocks. The syenodiorites have intermediate to felsic composition with SiO₂ = 61 to 65 wt.%, MgO = 0.27 to 0.6 wt.% and CaO = 1.0 to 2.5 wt.% as compared to the granite SiO₂ = 65 to 72 wt.%, MgO = 0.1 to 0.4 wt.%, CaO = < 1.0 wt.%. Primitive-mantle-normalized incompatible element plots show corresponding reciprocal patterns between the mafic and felsic rocks. The chondrite-normalized REE patterns show Eu anomalies changing from > 1(Eu/Eu? = 1.1 to 2.6) in the gabbroic intrusion, to < 1 in the syenodiorite (Eu/Eu? = 0.75 to 0.83), granites and trachytes (Eu/Eu? = 0.55–0.87). Previously published εNd_(T) values from clinopyroxenes (εNd_(T) = + 1.1 to + 3.2) of the gabbroic intrusion match the whole-rock values of the syenodiorite (εNd_(T) = + 2.1 to + 2.5), granite and trachyte (εNd_(T) = + 2.2 to + 2.9), suggesting that all rock types originated from the same mantle source. MELTS and trace element modeling confirm that all rock types can be generated by fractional crystallization of high-Ti Emeishan basalt. The jump in SiO₂ from the gabbro to the syenodiorite is attributed to the en masse crystallization of the Fe–Ti oxides. The geological and geochemical data indicate that fractional crystallization of a common parental magma produced the layered gabbroic intrusion and Fe–Ti oxide deposit, the syenodiorite, granites and trachyte of the Panzhihua region, which thus form a genetically related plutonic-hypabyssal-volcanic complex. Other granite–gabbro complexes in the region likely formed in a similar manner.     

大冶-九江地区Fe, Cu(Au)和Au(Cu)矿床夕卡岩矿物里的熔融包裹体特征

在大冶-九江沿长江分布的Fe, Cu(Au)和Au(Cu)矿床的夕卡岩矿物中, 除含气-液包裹体外, 还含大量熔融包裹体和流体-熔融包裹体. 熔融包裹体形态多样, 它们主要由不同相比例的晶质硅酸盐(C_Si)、铁质(Fe)、非晶质硅酸盐(A_Si)及气体(V)多相组成. 其中有的含有几个结晶硅酸盐相. 所研究的熔融包裹体大小一般为(10~46) mm×(6~15) mm. 流体-熔融包裹体与熔融包裹体的区别是在前者中出现液体(L)相, 均一温度较低. 在所获得的48个温度数据中, 夕卡岩石榴石和辉石中熔融包裹体有39个均一温度数据, 流体-熔融包裹体有两个数据, 其余属流体包裹体所有. 石榴石和辉石中的熔融包裹体具有890~1115℃均一温度, 流体-熔融包裹体具有745~750℃均一温度, 流体包裹体的均一温度介于580~675℃之间. 39个熔融包裹体的均一温度平均值为1029.9℃. 现有包裹体相态特征及其均一温度表明, 所研究的夕卡岩应为岩浆成因.     

Silicon isotope fractionation during the precipitation of quartz and the adsorption of H_4SiO_(4(aq))on Fe(Ⅲ)-oxyhydroxide surfaces

Equilibrium Si isotope fractionation factors among orthosilicic acid(i.e.,H4 Si O4(aq)), quartz and the adsorption complexes of H4 Si O4(aq)on Fe(III)-oxyhydroxide surface were calculated using the full-electron wave-function quantum chemistry methods [i.e., B3LYP/6-311G(2df,p)]with a new cluster-model-based treatment. Solvation effects were carefully included in our calculations via water-droplet method combined with implicit solvent models(e.g., PCM).The results revealed that, if it is under equilibrium conditions,heavy Si isotopes would be significantly enriched in quartz in comparison to H4 Si O4(aq). However, most of the field observations suggested that quartz would have identical or even depleted d30 Si values compared to that of H4 Si O4(aq). To explain this discrepancy between the equilibrium calculation results and the field observations, the kinetic isotope effect(KIE) associated with the formation of amorphous silica,which usually is the precursor of crystalline quartz, was investigated using quantum chemistry methods. The KIE results showed that amorphous silica would be significantly enriched in light Si isotopes during its formation. Our equilibrium fractionation results, however, matched a special type of quartz(i.e., Herkimer ‘‘diamond') very well, due to its nearly equilibrated precipitation condition. Opposite to the case of precipitated quartz, a large equilibrium Si isotope fractionation(i.e.,-3.0 %) was found between the absorbed bidentate Si surface complexes(i.e.,2C [ Fe2O2Si(OH)2) and H4 Si O4(aq). This calculated equilibrium Si isotope fractionation factor largely differed from a previous experimental result(ca.-1.08 %). We found that the formation of transient or temporary surface complexes [e.g.,1V [ Fe2OSi(OH)3] may have accounted for the smaller net fractionation observed.With the equilibrium and kinetic Si isotope fractionation factors provided here, the distributions and changes of Si isotope compositions in the Earth's surface systems can be better understood.     

Geochemistry,mineral paragenesis and geothermal conditions of oreforming fluids from the Ain El Bey Cu–Fe deposit: potential occurrence of native gold and precious metal traces(North African orogenic belt,Northern Tunisia)

The Ain El Bey abandoned mine, in North-West Tunisia, fits into the geodynamic context of the European and African plate boundary. Ore deposit corresponds to veins and breccia of multiphase Cu–Fe-rich mineralization related to various hydrothermal fluid circulations. Petromineralogical studies indicate a rich mineral paragenesis with a minimum of seven mineralization phases and, at least, six pyrite generations. As is also the case for galena and native silver, native gold is observed for the fi...