共查询到18条相似文献，搜索用时 140 毫秒
1.
以甘肃白银厂地区的7件锆石同位素年龄样品为例,根据其红外光谱中615cm-1吸收峰的高和半高宽度的比值,将锆石样品的变生程度量化,并将其分为晶质锆石、半变生锆石和变生锆石3类。参考相关资料,利用7件锆石样品的红外光谱特征对其铀钍含量和"红外年龄"做了估测,并将估测年龄与其U Th年龄和全岩Rb Sr年龄进行了比较和分析。 相似文献
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甘肃白银厂矿田锆石红外光谱特征和地质年龄估测 总被引：3，自引：0，他引：3
应用矿物红外光谱学的方法系统研究了白银厂地区7件锆石同位素年龄样品的红外光谱。测定结果表明，3件样品的吸收峰强而窄，整体线形与标准的晶质锆石谱线相符合；其余4件样品的吸收相对较弱，峰形圆钝；谱线均有不同程度向变生锆石特征谱线的演化，以变生程度最高的LGG-6为尤。根据615cm^-1吸收峰的H／M值可将所研究样品分为晶质锆石、半变生锆石和变生锆石三类，并利用锆石红外光谱特征估测了铀钍含量和地质年龄。同时还评估了相应样品的U-Pb同位素年龄的可靠性。 相似文献
3.
不同变生程度锆石的阴极射线发光谱 总被引：3，自引：0，他引：3
变生使矿物的物理、化学性质发生显著变化。本文着重研究变生对锆石阴极射线发光谱的影响。为此,对若干锆石样品进行了X射线粉晶分析,差热分析和室温阴极射线发光谱测量。衍射和差热分析结果表明,这些样品具有不同的变生程度,有些样品已完全变生,有些部分变生,有些则是晶质的。所研究样品的阴极射线发光谱中,主要的发光谱线均来源于Dy~(3+)离子的~4F9/2→~6H_(13/2)和~4F_(9/2)→~6H_(15/2)跃迁。与晶质锆石相比,变生锆石发光谱线的强度降低、宽度增加表明在变生过程中,锆的局部环境发生畸变,无序程度增加。根据发光谱的特征,可以定性地估计锆石的变生程度。 相似文献
4.
锆石变生程度与放射性元素含量间的定量研究 总被引：1，自引：0，他引：1
为获得锆石变生程度与放射性元素质量分数之间的相互关系,对来自山东蒙阴金伯利岩中的锆石进行了阴极发光、激光拉曼光谱、离子探针测试和研究.研究表明,锆石样品的年龄近于一致;按照拉曼光谱特征峰1000cm-1左右的强度/半高宽比值和放射元素质量分数(wB)可以将锆石分为全晶质锆石、弱变生锆石、变生锆石、强变生锆石4类.放射元素总质量分数(wB)与拉曼光谱特征峰1000cm-1左右的强度/半高宽比值(H/W,设为r)之间符合经验关系方程:(1/r)1/2=1.3×10-2·(wB/10-6)1/2—0.11,可以借助锆石在1000cm-1左右的拉曼光谱特征峰值强度/半高宽比值并采用这一经验关系方程来大致计算出拉曼测试位置的放射性元素的质量分数. 相似文献
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研究了不同程度变生褐帘石及其热处理样品的红外光谱变化特征，提出其变生的红外光谱定量标志－变生度Ｍ＝１／５（６－Ｎ）（Ｎ为７５０－２００Ｃｍ＾－１范围的谱带数）。分析了变生作用中褐帘石晶格内离子基团的变化，结合晶体结构分析，提出褐帘石红外光谱中４５０、５１０ｃｍ＾－１附近的两个谱带分别系结构内孤立硅氧四面体ＳｉＯ４及群体硅氧四面体Ｓｉ２Ｏ７的弯曲振动谱带。 相似文献
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研究了不同程度变生褐帘石及其热处理样品的红外光谱变化特征，提出其变生的红外光谱定量标志──变生反M＝■（6-N）（N为750-200Cm-1范围的谱带数）。分析了变生作用中褐帘石晶格内离子基团的变化，结合晶体结构分析，提出褐帘石红外光谱中450、510cm－1附近的两个谱带分别系结构内孤立硅氧四面体SiO4及群体硅氧四面体Si2O7的弯曲振动谱带。 相似文献
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宝石锆石改色改性的实验研究 总被引：2，自引：1，他引：2
锆石是一种可用作宝石的矿物。但天然锆石由于变晶作用往往呈现出红褐色,半透明或不透明,因而不能用作宝石。本文用高温实验研究了天然锆石改色改性的技术和方法。研究表明,热处理可以除去锆石的变晶结构,恢复其结晶结构。900—1300℃和氧化气氛条件下的热处理可将红褐色半透明的天然锆石改变成无色透明和金黄色透明的晶体,还原条件则将其改变为天蓝色。 相似文献
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苏皖凹凸棒石矿物红外光谱特征研究 总被引：13，自引：0，他引：13
苏皖凹凸捧石粘土矿物包括沉积、风化及火山碎屑蚀变三种成因类型。成矿物质来源于内陆浅水湖盆水下玄武岩风化蚀变及地表玄武岩的风化。不同成因类型的凹凸棒石在矿物晶体结晶程度上有较大差异。通常,由风化作用生成并与碳酸盐共生的沉积型凹凸棒石结晶程度低,较纯的并与硅质岩共生的沉积型凹凸棒石结晶程度高。它们在红外吸收光谱特征上表现为:前者红外振动吸收带分裂程度低,吸收峰弱且峰形钝。后者红外振动吸收带分裂程度高,吸收峰尖锐。因此研究凹凸捧石的红外吸收光谱特征可基本上区分出它们的成因类型。本文还对凹凸棒石红外吸收光谱振动波数带进行了划分,并对相应的振动类型作了探讨。 相似文献
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锆石的结构与化学稳定性 :核废料处置矿物类比物研究 总被引：6，自引：0，他引：6
锆石可作为核废料处置矿物类比物的重要矿物 ,近年来对此开展了大量的研究。在综合前人研究成果的基础上 ,文中对天然锆石遭受放射性照射所导致的晶格破坏、蜕晶质化以及锆石在各种热液条件下的稳定性、表面反应特性等几个方面进行了总结研究 ,特别是对各种热液条件下锆石的溶解动力学及元素传质进行全面讨论 ,进一步阐明了锆石作为核废料处置矿物类比物的优越性 ,指出今后一方面应着重对锆石的放射性破坏机制及蜕晶质化过程中的元素扩散、迁移和聚集进行系统的研究 ,另一方面着重研究不同变质程度锆石的淋滤机制和不同条件下淋滤溶液 (不同 pH值、无机溶液组分、有机溶液等 )对锆石中各种元素的影响。 相似文献
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Interpretation of discordant U-Pb zircon ages: An evaluation 总被引：36，自引：0，他引：36
The most widely used technique for the determination of high precision mineral growth ages in igneous and metamorphic rocks is dating of zircons with the U-Pb method. The interpretation of these ages, particularly in metamorphic settings, is hampered by an incomplete understanding of the common phenomenon of partial Pb-loss in zircon. In principle, this Pb-loss may occur in four very different ways: diffusion in metamict zircon, diffusion in pristine zircon, leaching from metamict zircon and recrystallization of metamict zircon. Here it is argued that, under conditions common in the continental crust, Pb-loss is only possible in partially to strongly metamict zircons. Pb-diffusion in the pristine zircon lattice is insignificant up to temperatures of at least 1000 °C. Pb-loss is only possible if the zircons experienced a time interval below their annealing temperature of about 600–650 °C, because only below this temperature can the lattice damage through α-decay and spontaneous fission accumulate. Zircons that remain above this temperature do not lose Pb by diffusion and will stay closed systems. Complete resetting of the U-Pb system in zircon under crustal conditions is only possible through dissolution and reprecipitation of zircon. Partial resetting results from recrystallization, leaching or diffusion in metamict zircon. As a consequence, special care has to be taken to interpret lower intercepts on concordia diagrams defined by discordant U-Pb data. Lower intercept ages may be significant only if they are defined by zircons with low U-content (<100 p.p.m.) or if confirmed by other geochronological methods. In addition, the accuracy of the lower intercept should be confirmed by abrading the zircon fractions that define the discordia. 相似文献
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N. Tomašić A. Gajović V. Bermanec D. S. Su M. Rajić Linarić T. Ntaflos R. Schlögl 《Physics and Chemistry of Minerals》2006,33(2):145-159
The metamict state and recrystallization of fergusonite in metamict natural samples were studied by thermal methods (TGA-DTA), X-ray powder diffraction (XRD), Raman spectroscopy (RS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and electron microprobe (EPMA). Two metamict mineral samples of fergusonite were investigated in order to identify the original premetamict crystal structure and to identify recrystallization mechanisms. The TEM data and RS provided evidence on the partial preservation of the original structure in the investigated minerals, which are X-ray amorphous. It was shown that fergusonite could recrystallize from a metamict mineral with original fergusonite structure or from metamictized pyrochlore, which was altered before or after metamictization. Two recrystallization mechanisms were recognized: (a) epitaxial growth occurring at the boundary between preserved premetamict structure fragments and completely metamictized areas, and (b) nucleation-crystal growth mechanism occurring in completely amorphous areas of the minerals, and resulting in recrystallization of the original mineral as well as in the crystallization of a new mineral with a modified chemical composition as compared to the initial matrix. 相似文献
14.
《地学前缘(英文版)》2022,13(4):101401
Magmatic-hydrothermal Sn deposits are commonly associated with high silica magmas, but why most global high silica granites do not bear economic Sn ore grades remains unclear. Two crucial factors controlling magmatic-hydrothermal Sn mineralization, including advanced fractionation and depressurization-induced rapid cooling, were revealed in the case study of the Guyong granitic pluton linked with the Xiaolonghe Sn deposit, in the Tengchong block, SW China. The Guyong granitic pluton comprises three petrological facies: less evolved biotite syenogranite, evolved alkali granite and leucogranite, and highly evolved facies (the protolith of greisenized granite). Similar crystallization ages (～77 Ma) and gradual contact between different petrological facies indicate the Guyong granitic pluton records a continuous fractionation process. Monte Carlo-revised Rayleigh fractionation model suggests the fractionation degree of the Guyong pluton is markedly high (>87 wt.%) that can only be achieved by a high initial water (≥4 wt.%) content in the parent granitic magma revealed by rhyolite-MELTS calculation. Advanced degree fractionation causes the first Sn enrichment but it also significantly increases the viscosity of evolved magmas, suppressing the exsolution and transport of hydrothermal fluids. Hence, it must be compensated by the second critical factor: depressurization-induced rapid cooling, reflected by the occurrence of highly metamict zircons in the greisenized granite. The highly metamict feature, indicated by the large full width at half maximum (FWHM) values of zircon ν3(SiO4) peak (>19.5 cm?1), suggests these zircons do not experience thermal annealing but rapidly ascend into a shallow cooling environment. Depressurization-induced rapid cooling facilitates exsolution and transport of hydrothermal fluids, interacting with wall rocks and resulting in Sn mineralization. 相似文献
15.
Recrystallization of zircons under the influence of fluids was studied using examples from Precambrian rocks (microcline granites, metasedimentary, and mafic rocks) of the Kola Peninsula. All zircon crystals showed complex internal textures visible by cathodoluminescence and backscattered electron (BSE) imaging. Detailed mineralogical and geochemical studies with subsequent secondary ion mass spectrometer U–Pb dating of different zircon domains show that secondary texture formation can be interpreted in terms of metasomatic replacement of zircon crystals on the base of crystallogenetic experimental models. Mechanisms of zircon replacement and interpretation of U–Pb ages for secondary zircon domains are dependent on the degree of damage of the zircon structure and the fluid composition. The recrystallization of metamict zircon without additional supply of new zircon substance (Zr, SiO2) goes with the dissolution of amorphous domains and precipitation of new polycrystalline zircon, which preserves the U–Pb initial age, but loses radiogenic lead, and the lower intercept of Discordia lines with the Concordia curve determines the time of fluid influence. The recrystallization of metamict zircon or crystalline zircon with high contents of impurities with additional supply of Si and Zr forms monocrystalline replacements. Dissolution of primary zircon is accompanied by growth of new zircon domains differing in the composition of isomorphic impurities and zones of transitional composition, whose ages have no geological sense. The study is of particular importance for zircons from Precambrian rocks with long and complex histories. 相似文献
16.
Zircon textures, chemistry and microstructures have been characterized in situ within Carboniferous sandstones from the Midland Valley of Scotland using back‐scattered electron and cathodoluminescence images, electron backscatter diffraction techniques and chemical analyses. The study of polished thin sections reveals a variety of zircon types including unmodified detrital zircon, zircon outgrowths and different forms of modified zircon that formed in low‐temperature conditions within the sedimentary rocks. These rocks have only experienced temperatures of <100 °C during burial; however, altered zircon is abundant and characterized by a low mean atomic number, with relatively high contents of non‐formula elements and a nano‐crystalline or microcrystalline structure. It forms by replacement of detrital zircon that subsequently became metamict. Two types of replacement mechanisms are effective in sedimentary environments and involve either dissolution–reprecipitation or solid‐state reaction, but both require fluid access to the radiation‐damaged areas. The former process appears to become the dominant replacement mechanism as temperature increases and produces highly porous, inclusion‐rich zircon. Metamict zircon is extremely reactive in near‐surface conditions and the production of low‐temperature zircon is sensitive to both parent zircon characteristics and environmental conditions. As such, the alteration of zircon has the potential to yield unique information on the diagenetic history of sedimentary rocks. Low‐temperature zircon would be unlikely to survive sedimentary transport or the rock crushing procedures that characterize many investigations of detrital zircon populations and consequently may generate severe biases in studies of this type. 相似文献
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18.
Zircon reaction and stability of the U-Pb isotope system during interaction with carbonate fluid: experimental hydrothermal study 总被引：4，自引：0，他引：4
N. G. Rizvanova O. A. Levchenkov A. E. Belous N. I. Bezmen A. V. Maslenikov A. N. Komarov A. F. Makeev L. K. Levskiy 《Contributions to Mineralogy and Petrology》2000,139(1):101-114
The interpretation of metamorphically induced U-Pb isotopic discordance requires a thorough understanding of zircon-fluid
interactions. With this aim we have studied the behaviour of metamict and crystalline zircon phases and their U-Pb systems
by cathodoluminescence after treatment by 2M Na2CO3 solution at T = 200–800 °C and P = 1–5 kbar for 3–14 days, X-ray diffraction, microprobe and isotope dilution analysis. The data indicate that zircon transformation
under hydrothermal conditions depends on the experimental conditions and the degree of structural damage. Reconstitution of
defective and impurity-enriched zones of metamict zircon (homogenization of impure element concentrations and increase of
crystallinity) was observed at 400 °C and P = 1 kbar. Considerable lead and uranium loss occurred under these conditions. As a result of zircon dissolution, newly formed
baddeleyite accommodating U from 2M Na2CO3 solution and Zr-Na-silicate were recognized. This process intensified with increasing pressure. Study of crystalline zircon
indicates that migration of U and Pb took place only during dissolution of zircon at T above 650 °C. In the presence of carbonate-ions essential U and Pb amounts are lost from metamict zircon at a lower P-T than is typical for greenschist facies metamorphism.
Received: 4 October 1997 / Accepted: 6 December 1999 相似文献