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1.
Various zircons of Proterozoic to Oligocene ages (1060-31 Ma) were analysed by laser ablation-inductively coupled plasma-mass spectrometry. Calibration was performed using Harvard reference zircon 91500 or Australian National University reference zircon TEMORA 1 as external calibrant. The results agree with those obtained by SIMS within 2s error. Twenty-four trace and rare earth elements (P, Ti, Cr, Y, Nb, fourteen REE, Hf, Ta, Pb, Th and U) were analysed on four fragments of zircon 91500. NIST SRM 610 was used as the reference material and 29Si was used as internal calibrant. Based on determinations of four fragments, this zircon shows significant intra-and inter-fragment variations in the range from 10% to 85% on a scale of 120 μm, with the variation of REE concentrations up to 38.7%, although the chondrite-normalised REE distributions are very similar. In contrast, the determined age values for zircon 91500 agree with TIMS data and are homogeneous within 8.7 Ma (2 s ). A two-stage ablation strategy was developed for optimising U-Pb age determinations with satisfactory trace element and REE results. The first cycle of ablation was used to collect data for age determination only, which was followed by continuous ablation on the same spot to determine REE and trace element concentrations. Based on this procedure, it was possible to measure zircon ages as low as 30.37 0.39 Ma (MSWD = 1.4; 2 s ). Other examples for older zircons are also given.  相似文献   

2.
利用自然资源部古地磁与古构造重建重点实验室新引进的GeoLas HD型193nm ArF准分子激光剥蚀系统和Agilent 7900型四极杆电感耦合等离子质谱仪,成功建立了LA-ICP-MS锆石微区U-Pb定年及微量元素分析测试方法。以标准锆石91500为外标,在32 μm束斑直径、5.0 J/cm2能量密度和5 Hz剥蚀频率等实验条件下,对Ple?ovice、Temora1和Qinghu锆石标样开展了U-Pb定年实验,所测年龄结果与各标样推荐值在误差范围允许的条件下一致,并且Ple?ovice年龄结果在不同时间段内保持稳定。同时对未知年龄样品11-5开展了不同实验室测年结果对比研究,所测结果与中国地质大学(武汉)地质过程与矿产资源国家重点实验室所测年龄在误差允许范围内一致。以NIST SRM 610为外标,29Si为内标,分析测试了锆石91500和NIST SRM 612标准样品的微量元素含量,实验测试结果与推荐值一致。在此基础上探索总结了不同剥蚀斑束直径对U-Pb年龄结果的影响,认为在同样的能量密度和剥蚀频率条件下,16~44 μm的剥蚀直径可以获取可靠的锆石U-Pb年龄,但32~44 μm相比16~24 μm小斑束直径所测得的年龄更加精准。   相似文献   

3.
锆石是地质学研究中最重要的副矿物,其分布广泛、物理、化学性质稳定,记录了结晶时的年龄、温度、氧逸度以及O-Hf-Si-Zr-Li等多元同位素和微量元素信息,被广泛运用于地球科学的研究中。近年来,随着分析技术的发展,研究者在获取锆石年龄的同时也获取了大量锆石微量元素数据,这些数据的积累推动着研究者对锆石微量元素理论研究的不断深入,并取得了一系列重要进展,如发现锆石微量元素组成受锆石本身的晶格特点主导,符合晶格应变模型和类质同象替代机制;发现锆石微量元素组成受到熔体成分演化影响,锆石结晶时的熔体微量元素组成往往不等同于全岩;发现锆石内部的微量元素不均一特征(矿物包裹体、热点、蜕晶化作用等)可能会严重影响锆石的微量元素组成,继而建立了"干净锆石"的判别指标和筛选机制。此外,锆石微量元素的应用研究也取得了长足进展,研究者们不断尝试通过各类锆石微量元素指标、图解、分配系数,识别母岩浆物理化学性质、反演母岩浆组成,大大推动了锆石微量元素在示踪岩浆源区和岩浆过程中的应用。然而,由于锆石微量元素组成受控于多种因素,使得锆石微量元素在实际应用当中常常面临着多解性问题、重叠问题和分配系数的选择问题,在一定程度上影响了锆石微量元素应用研究的可靠性。未来的锆石微量元素研究将不满足于使用传统的低维指标和图解以及分配系数,而将在充分吸收传统方法精华的基础上,从海量数据与更高的维度中寻找元素之间相关性,基于热力学定律揭示新原理,基于更高空间分辨率揭示动力学因素的影响,从数据驱动和理论驱动的全新视角下深入揭示隐藏在锆石微量元素中的信息。  相似文献   

4.
Analytical protocols for SHRIMP‐SI oxygen isotope analysis (δ18O) of a suite of zircon reference materials (RMs) are presented. Data reduction involved a robust estimate of uncertainties associated with the individual spot as well as for groups where the spot data are combined. The repeatability of δ18O measurements is dependent on both the analytical conditions and the choice of the primary reference material. Under optimised conditions, repeatability was often better than 0.4‰ (2s) allowing sample uncertainties to be obtained to better than 0.2‰ (at 95% confidence limit). Single spot uncertainty combined the within‐spot precision with the scatter associated with repeated measurements of the primary zircon reference material during a measurement session. The uncertainty for individual spots measured under optimised conditions was between 0.3 and 0.4‰ (at 95% confidence). The analytical protocols described were used to assess a variety of zircon RMs that have been used for geochronology and for which laser fluorination oxygen isotope data are available (Temora 2, FC1, R33, QGNG and Ple?ovice), as well as zircons that have been used as RMs for trace element or other types of determination (Mud Tank, Monastery, 91500, AS57, AS3, KIM‐5, OG1, SL13, CZ3 and several other Sri Lankan zircons). Repeated analyses over nine sessions and seven different mounts show agreement within analytical uncertainty for Temora 2, FC1, R33, QGNG, Ple?ovice and 91500, when normalised to Mud Tank. For existing ion microprobe mounts with these materials, an appropriate δ18O can be determined. However, care should be taken when using zircons from the Duluth Complex (i.e., FC1, AS57 and AS3) as reference materials as our data indicated an excess scatter on δ18O values associated with low‐U zircon grains.  相似文献   

5.
Multi-Collector SIMS Determination of Trace Lanthanides in Zircon   总被引：3，自引：1，他引：3  
A method is presented for the determination of rare earth elements (REE) in zircon (ZrSiO4) using a multi-collector equipped ion-microprobe operating at moderately high mass resolution (M/ΔM ˜ 3900). The low abundance light REE (La-Eu) were measured simultaneously in six ion counting electron multipliers, reducing analytical time to less than half of that in a monocollection routine. Effective mass filtering, moderate energy filtering and careful set up of detector parameters in order to minimise background counts, yielded a highly coherent set of analyses from the 91500 zircon reference sample.  相似文献   

6.
In this contribution we evaluate the capabilities of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) using a 12 μm spot size. Precision, accuracy and detection limits were assessed on the USGS BCR-2G reference material. We demonstrate that the 12 μm LA-ICP-MS analyses of experimentally-grown amphibole and garnet are in excellent agreement with secondary ion mass spectrometry (SIMS) trace element determinations on the same crystals. The 12 μm spot size configuration was subsequently used to determine trace element crystal-melt partition coefficients (Dc/m) for a wide range of trace elements in amphibole in equilibrium with a basanitic melt. The following strategy to determine accurately and evaluate Dc/m is proposed. One or more major elements determined previously by electron probe microanalysis (EPMA) was used to ensure consistency between EPMA and the composition of the aerosol produced by the laser ablation. Measured Dc/m values were successively evaluated using the lattice strain model. The use of this strategy significantly improved the precision and accuracy of Dc/m determination when a LA-ICP-MS configuration with a high spatial resolution was employed.  相似文献   

7.
We have developed a new database named GeoReM ( http://georem.mpch-mainz.gwdg.de ) for reference materials and isotopic standards of geochemical and mineralogical interest. Reference samples include rock powders originating from the USGS, GSJ, GIT-IWG, synthetic and natural reference glasses originating from NIST, USGS, MPI-DING, as well as mineral (e.g., 91500 zircon), isotopic (e.g., La Jolla, E&A, NIST SRM 981), river water and seawater reference materials. GeoReM is a relational database, which strongly follows the concept of the three EARTHCHEM databases. It contains published analytical and compilation values (major and trace element concentrations, radiogenic and stable isotope ratios), important metadata about the analytical values, such as uncertainty, uncertainty type, method and laboratory. Sample information and references are also included. Three different ways of interrogating the database are possible: (1) sample names or material types, (2) chemical criteria and (3) bibliography. Some typical applications are described. GeoReM currently (October 2005) contains more than 750 geological reference materials, 6000 individual sets of results and references to 650 publications.  相似文献   

8.
A combined geochronological and geochemical investigation for the same domain of zircon provides valuable information on timing and genesis, particularly in the case of multi‐growth metamorphic zircon. A high spatial resolution concurrent analytical method for zircon U‐Pb age and rare earth element content was successfully achieved in this study, using a multi‐collector secondary ion mass spectrometer (SIMS) at a ~ 8 μm diameter scale. Special instrument parameters were employed, including a high mass resolution of approximately 15000 applied to replace the previous energy filter method, and a dynamic multi‐collector mode used to reduce the measurement time to 18 min per analysis. Six zircon reference materials yielded precise and accurate 206Pb/238U ages, which are comparable to those obtained by the ordinary mono‐collector method, but with 2–3 times higher spatial resolution. All zircon grains measured in this study showed enriched heavy‐REE (HREE) contents consistent with previously reported values determined by LA and solution ICP‐MS methods. The light‐REE (LREE) mass fractions measured using both SIMS and LA‐ICP‐MS methods in this study, although with quite different volume, show consistent results within uncertainties.  相似文献   

9.
贺娟  王启宇  王保弟  段瑶瑶 《地球科学》2020,45(8):2857-2867
前人对西藏拉萨地体则弄群的时代仍存在晚侏罗世与早白垩世的争议，且缺乏东西方向上的对比研究.对位于西段的狮泉河则弄群凝灰岩进行了系统的锆石U-Pb年代学、锆石微量元素和Hf同位素研究，完善了则弄群的年代学格架.狮泉河则弄群凝灰岩的锆石多为自形长柱状，发育明显的振荡环带，其微量元素特征显示为岩浆锆石.2件凝灰岩样品LA-ICP-MS锆石U-Pb测年结果显示其成岩年龄分别为157.5±0.9 Ma和159.2±1.3 Ma.结合前人研究成果，确定则弄群时代为晚侏罗-早白垩世.凝灰岩的锆石微量元素与Hf同位素特征表明其形成于大陆弧环境，源区可能由古老的陆壳基底与少量幔源物质混合形成.区域资料表明，Slainajap洋盆在东西延伸方向上俯冲起始时间不同，可能存在西早东晚的特征.   相似文献   

10.
Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used to determine K, Sc, Ti, V, Cr, Mn, Co, Ni and Zn in geological samples. Because the isotopes of these elements and the internal standard element (Ca) often have interferences from molecular ions when determined using quadrupole or sector-field ICP-MS in low mass resolution mode, ion intensities were measured at a high mass resolution of 4000. We investigated dynamic element fractionation, type and abundance of molecular ions using different geological reference materials. Highly resolved mass spectra were especially important for accurate low-abundance measurements. As a result, maximum "critical" concentration limits for each isotope were obtained, where a mass resolution of 4000 was necessary for reliable LA-ICP-MS analysis. To test the LA-ICP-MS technique, different international reference material glasses and powdered rock reference materials were analysed. Rock powders were fused to glass beads using an Ir-strip heater. Nearly all concentration values for the reference materials agreed with the reference values at the 95% confidence level. To demonstrate routine LA-ICP-MS analysis at a mass resolution of 4000, trace element data for Hawaiian basalts are also presented.  相似文献   

11.
The attractive physical and chemical properties of corundum lend to this material’s importance in both its natural and synthetic forms. However, much of the quantitative work performed on this material is plagued by unknown inaccuracy as non‐matrix‐matched reference materials are used. To conduct accurate quantitative analysis using SIMS, matrix‐specific relative sensitivity factors (RSFs) were determined for eighteen trace elements in corundum using dose‐verified ion implants. The RSF values ranged from 2.56 × 1022 to 3.29 × 1024 cm‐1 with total combined uncertainty values ranging from 7 to 10%. The RSF values, which are related to ionisation potentials, showed trends consistent with expectations for an insulating oxide. The developed values were applied to calibrate reference materials for LA‐ICP‐MS and to study other natural and synthetic corundum samples. A measurement reference material calibrated for Mg, Si, Ti, V, Fe and Ga produced consistent results over ten sessions in 4 years with relative standard deviations per trace element of 5% or less, confirming the repeatability of our process. A key finding was that calibrating LA‐ICP‐MS with NIST SRM 610 and 612 glasses to analyse corundum resulted in under‐reporting trace elements Be, Ti, V, Fe, Co, Ni and Ga compared with using matrix‐matched reference materials.  相似文献   

12.
We describe an in situ method for simultaneous measurement of U–Pb–Hf isotopes and trace element compositions of zircons using a quadrupole and multiple-collector inductively-coupled-plasma mass spectrometer (Q-ICP-MS and MC-ICP-MS, respectively) connected to a single excimer laser-ablation system. A laser-generated zircon aerosol was split behind the ablation cell into two transport tubes via a Y-shaped connector and simultaneously introduced into the two mass spectrometers. Hafnium isotopes were measured on the MC-ICP-MS instrument, while U–Pb ages and trace element compositions were determined using the Q-ICP-MS. The precision and accuracy of this method was evaluated using six well-known and widely used zircon standards (91500, Temora-2, GJ-1, Mud Tank, BR266 and Monastery). Analyses were carried out using spot sizes of 32, 44 and 60 μm. For the 44 and 60 μm spot, the resulting U–Pb ages, Hf isotopic and rare earth element (REE) compositions of these six zircons agree with recommended/reported values within 2σ error. The difference in relative standard deviations (RSD) of 206Pb/238U ages between split-flow measurements and those obtained separately on the Q-ICP-MS is within ～ 20% for 91500, Temora-2 and GJ-1, and ～ 60% for Mud Tank (due to its lower U and Pb concentrations). Our method provides a precise approach for determining the U–Pb age and the Hf isotopic and trace element compositions of zircon within a single ablation event. This is in particular important for analysis of zircons that are small or contain complicated zoning patterns. Finally, the REE composition of zircon BR266 is more homogeneous than other zircons and could be a suitable standard by which to benchmark new standards for microprobe analyses of zircons.  相似文献   

13.
To understand and/or avoid small-scale chemical heterogeneities within geological materials prepared as normal thin sections, in situ multiple trace element determination coupled with the simultaneous microscopic observation of the sample during analysis is preferable. We have examined fifty trace elements in thin (< 30 μm) layers of the NIST SRM 614 and 616 glass reference materials by LA-ICP-MS using different pit diameters and internal standard elements (Ca and Si). Compositional heterogeneities of Tl, Bi, As and Cd were found in NIST SRM 614 and 616 at the spatial resolution of ca. 10 0 μm. Except for these elements, the RSDs of six determinations for most elements were better than 10% in NIST SRM 614 when ablation diameters were < 50 μm. The measured concentrations for most elements in NIST SRM 614 and 616 agree with previous values in the literature at the 95% confidence level with the exception of W and Bi. New LA-ICP-MS data for K, As and Cd are also reported. The results support the view that the latest LA-ICP-MS is a powerful and flexible analytical technique for the determination of multiple ultra-trace element compositions in geological materials prepared as normal thin sections of the type that has been used for polarising optical microscopic observations since the end of the 19th century.  相似文献   

14.
Zircon populations of Neoproterozoic and early Paleozoic age occur in metabasites of a high-pressure amphibolite-facies unit of the Austroalpine basement south of the Tauern Window. The host rocks for these zircons are eclogitic amphibolites of N-MORB-type character, hornblende gneisses with volcanic-arc basalt signature, and alkaline within-plate-basalt amphibolites. Bulk rock magmatic trace element patterns were preserved during amphibolite-facies high-pressure and subsequent high-temperature events, as well as a greenschist-facies overprint. Positive Ce and negative Eu anomalies and enrichment of HREE in normalized zircon REE patterns, as analysed by LA-ICP-MS, are typical for an igneous origin of these zircon suites. Zircon Y is well correlated to HREE, Ce, Th, U, Nb, and Ta and allows discrimination of compositional fields for each host rock type. Low Th/U ratios are correlated to low Y and HREE abundances in zircon from low bulk Th/U host rocks. This is likely a primary igneous characteristic that cannot be attributed to metamorphic recrystallization. Variations of zircon/host rock element ratios confirm that ionic radii and charges control abundances of many trace elements in zircon. The trace element ratios—presented as mineral/melt distribution coefficients—indicate a selectively inhibited substitution of Zr and Si by HREE and Y in zircon which crystallized from a N-MORB melt. Correlated host rock and zircon trace element concentrations indicate that the metabasite zircons are not xenocrysts but crystallized from mafic melts, represented by the actual host rocks.  相似文献   

15.
锡石原位微区U-Pb同位素测年,样品制备简单,具有高空间分辨率、高性价比、高效率等显著优势,是锡多金属矿床直接定年的有效手段。然而,基体效应的影响和标样的缺乏是制约该方法发展的关键。本次研究在He做载气以及加入不同辅助气(N_2、水蒸气)条件下使用锆石作为外部标准物质对锡石标准和样品进行元素、同位素分馏校准,并采用TeraWasserburg图解法和~(207)Pb法对普通铅进行校正。分析结果显示,氮气和水蒸气的引入,可以不同程度的提升Pb、U信号强度;3个不同的锡石标准和样品在He做载气及不同辅助气(N_2、水蒸气)条件下获得的Tera-Wasserburg U-Pb下交点年龄及~(207)Pb法普通铅校正后的~(206)Pb/~(238)U加权平均年龄在误差范围内都与文献报道值一致,并未发现明显基体效应的影响,显示采用锆石标准物质对不同类型锡矿床的锡石样品进行原位LA-ICP-MS U-Pb定年是可行的。  相似文献   

16.
大型硅质火山作用(喷发体积约102～104km~3)的岩浆系统是地壳尺度的,经历了复杂的起源、运移、存储、补给和喷发等过程。揭示岩浆从起源到喷发过程中的结晶分异、堆晶、晶体-熔体分离、地壳混染、岩浆补给、晶粥活化等岩浆作用的细节是认识硅质火山岩浆系统演化的关键。锆石中Th、U、Ti、Hf和REE等微量元素的含量和系统变化反映了锆石结晶熔体的成分、温度、氧逸度和水含量等以及共生的矿物相特征,对示踪火山岩浆系统的演化过程具有重要研究意义。随着岩浆温度降低过程中结晶分异作用的进行,锆石微量元素呈现出Hf含量升高、Ti含量降低以及Th/U、Eu/Eu~*和Zr/Hf等比值降低的趋势,这些元素含量和比值可以作为岩浆分异演化程度的指标。成矿斑岩中的锆石一般具有高的Ce~(4+)/Ce~(3+)和Eu/Eu~*值,反映了岩浆具有高的氧逸度和水含量。火山岩锆石可能经历多阶段结晶过程,因而形成复杂的核-边结构特征,核部具有熔蚀现象,边部CL较亮并具有低的Hf、U和高的Ti含量以及Eu/Eu~*值等,反映了岩浆补给作用和晶粥活化过程。由于锆石颗粒比较微小,在晶体-熔体分离过程可能随提取的熔体进入喷发岩浆房,从而可以连续记录岩浆成分的变化,或者残留在晶粥中记录晶体-熔体的分离。锆石微量元素结合高精度年代学分析,可以精细制约火山岩浆系统的多阶段演化过程及其时间尺度。在锆石微量元素数据的解释和筛选过程中,需注意扇形分区、锆石褪晶化和其他矿物包裹体对分析结果的影响,并同时开展岩相学研究,结合锆石产状和共生矿物组合特征,为制约火山岩浆系统的演化过程提供可靠信息。  相似文献   

17.
The character of oscillatory zoning within a zircon crystal from the syenite Kipawa Complex, Quebec, varies with scale of observation. Analysis of an scanning electron microscopy (SEM) back-scatter gray-scale traverse at a resolution of one pixel = 2.43 μm revealed 145 zones over 5130 μm, whereas a detailed high-resolution (one pixel = 0.195 μm) section near the crystal rim revealed 225 zones over 795 μm. In order to mathematically characterize the zoning pattern, wavelet, Fourier, and nonlinear analysis techniques were used on profiles of the SEM gray-scale data, and a series constructed was from the zone widths. Results demonstrate that the zircon oscillatory zoning preserves nonlinear and periodic components. Secondary ion mass spectrometry, electron microprobe, and SEM analyses of trace elements show the SEM back-scatter bright zones are enriched in U, Th, and rare earth elements (REE) in comparison to the darker zones. REE patterns are sharply heavy REE enriched and have negative Eu anomalies and prominent positive Ce anomalies. We model the oscillatory zoning, including a measure of its chemical variation, by use of a periodically forced nonlinear system. Results of this data-driven model are quantitatively similar to the natural data. We envisage that the small-scale oscillatory zoning was the result of a nonlinear feedback process wherein the crystal growth modified the adjacent melt, which in turn affected the crystal composition. The large-scale harmonic zones likely reflect changes in the bulk geochemistry of the system from which the zircon grew.  相似文献   

18.
Although in situ analysis by LA-ICP-MS is considered a rapid technique with minimal sample preparation and data reduction, mapping areas of millimetres in size using a small beam (< 15 μm) can be time consuming (several hours) when a quadrupole ICP-MS is used. In addition, fully quantitative imaging using internal standardisation by LA-ICP-MS is challenging in samples with more than one mineral phase present due to varying ablation rates. A new protocol for the quantification of multiple coexisting phases, mapped at a rate of about 12 mm2 h-1 and a resolution of 12 μm × 12 μm per pixel, is presented. The protocol allows mapping of most atomic masses, ranging from 23Na to 238U, using a time-of-flight mass spectrometer (ICP-ToF-MS, TOFWERK) connected to a 193 nm excimer laser. A fast-funnel device was successfully used to increase the aerosol transport speed, reducing the time usually required for mapping by a factor of about ten compared with a quadrupole ICP-MS. The lower limits of detection for mid and heavy masses are in the range 0.1–10 μg g-1, allowing determination of trace to ultra-trace elements. The presented protocol is intended to be a routine analytical tool that can provide greater access to the spatial distribution of major and trace elements in geological materials.  相似文献   

19.
研究了人工合成锆石并加入微量元素的实验方法和条件。人工合成锆石是以氧化锆和硅酸锂为原料,以钼酸锂和氧化钼为助熔剂,并加入其他元素如Hf、Lu、Yb、U、Th、Pb等元素,充分混匀后转入带盖铂金坩埚中,在高温马弗炉中连续加热生长形成锆石晶体。利用激光剥蚀系统与电感耦合等离子体质谱技术分析了合成锆石晶体中微量元素含量和Lu-Hf同位素组成,结果表明合成锆石晶体中Lu、Yb、U、Th、Pb等微量元素含量不均一,而Hf的含量和Lu-Hf同位素组成有很好的均一性。  相似文献   

20.
外标物质及内标元素的选择是激光剥蚀-电感耦合等离子体质谱(LA-ICP-MS)准确测定元素含量的关键因素之一。文章选用玻璃标准参考物质NIST 610、GSE-1G、BHVO-2G、BCR-2G、ATHO-G、KL2-G和T1-G作为外标,Si或Zr作为内标,对锆石M257中的Ti进行LA-ICP-MS微区原位测定。结果显示,选择Si或Zr作内标,采用BCR-2G、ATHO-G、KL2-G和T1-G作外标时,Ti含量测定值与参考值之间差异均较大,因此它们不适合作外标物质。采用BHVO-2G作外标和Si作内标,NIST 610作外标和Zr作内标,Ti含量测定值与参考值之间的差异均小于4%,因此BHVO-2G和NIST 610可有条件地作为外标物质。选择Si还是Zr作内标,GSE-1G作外标时,Ti含量的测定值与参考值之间的差异均小于3%,说明GSE-1G是较为合适的外标物质。选用GSE-1G作为外标,Si作内标,对5个标准锆石中的Ti含量进行了测定,结果显示,Ti元素在锆石91500中分布不均匀,而在锆石GJ-1、M257、PENGLAI和MUDTANK中分布均匀。在Ti元素分布均匀的GJ-1、M257、PENGLAI和MUDTANK等4个锆石中,由于Ti的含量均小于5μg/g,不适合作为锆石中Ti元素测定用的外标物质,但可作为测定时的质量监控样品。  相似文献   

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