Trace Element Analysis of NIST SRM 614 and 616 Glass Reference Materials by Laser Ablation Microprobe-Inductively Coupled Plasma-Mass Spectrometry

Fifty elements in NIST SRM 614 and 616 glass reference materials were determined by laser ablation microprobe-inductively coupled plasma-mass spectrometry (LAM-ICP-MS). The values determined for NIST SRM 614 agreed well with the NIST-certified and information values (mean relative difference ± 3.6%), except for B, Sc and Sb. The values determined for NIST SRM 616 agreed with the NIST-certified and information values within a mean relative difference of ± 1.5%, except for B, Sc and Ga. In addition, at an 80 μm sampling scale, NIST SRM 614 and 616 glass discs were homogeneous for trace elements within the observed precisions of 5 and 15% (mean), respectively. Detection limits were in the range 0.01 - 0.3 μg g⁻¹ for elements of lower mass numbers (amu < 80) and 1 - 10 ng g⁻¹ for heavy elements (amu > 80). Detection at the sub ng g⁻¹ level is possible for most of the heavy elements by using an ablation pit size larger than 10 0 μm.     

<Emphasis Type="Italic">In-situ</Emphasis> trace element analyses and Pb-Pb dating of zircons in granulite from Huangtuling,Dabieshan by LAM-ICP-MS

It is revealed by CL images that there are multi-stage growth internal structures of zircons in the Huangtuling granulite, including the inherited zircons, protolith zircons, sector and planar zone zircons and retrograde zircons. In-situ trace element compositions and Pb-Pb ages have been analyzed by LAM-ICP-MS. The sector and the planar zone domains show typical trace element characteristics of granulite zircon (low Th, U, Th/U, total REEs, clear negative Eu anomalies, relatively depleted HREE and small differential degree between MREE and HREE, etc.), indicating that they formed during granulite-facies metamorphism. The protolith zircons have trace element characteristics of crustal zircon (high Th, U, Th/U, total REEs and enriched HREEs, etc.). 12 analyzed spots on granulite-facies domains give a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of (2154±26) Ma (MSWD = 3.8), which is the best estimated age of granulite-facies metamorphism of this sample. The weighted mean ²⁰⁷Pb/²⁰⁶Pb age of 5 analyzed spots on protolith zircon domains is (2714 ± 22) Ma (MSWD = 1.4), which represents the protolith forming time. The discovery of ca. 3.4 Ga inherited zircon indicates that there are Palaeoarchean continental materials in this area. The interpretation of formation conditions and the ages of zircons can be constrained by simultaneous in-situ analysis of trace elements and ages.     

金绿宝石和变石中的微量元素研究

SRXRF微探针分析结果表明:金绿宝石和变石中主要的微量元素组成分别是Fe、Ga、Ti、Ca和Fe、Cr、Ti、Ca;Cr含量及Cr/Fe比不同是两种宝石微量元素的主要区别及形成不同颜色的原因。金绿宝石中的Ga含量达1600×10-6,说明它是又一载Ga矿物。SRXRF实验分析还得到了两种宝石中微量元素的相关性关系和浓度变化规律,结果表明在金绿宝石中主要是Ga、在变石中主要是Cr与其它微量元素负相关而相互替代;自金绿宝石或变石的中心到边缘处,Ti含量逐渐降低,Ga或Cr含量逐渐增加,Ti优先被Ga或Cr替代出晶格而形成猫眼;这两种宝石的形成还有富Ga或富Cr的成矿物质的加入。     

大别山黄土岭麻粒岩中锆石LAM-ICP-MS微区微量元素分析和Pb-Pb定年

阴极发光显微图像显示, 大别山黄土岭麻粒岩中的锆石有多期生长的复杂结构, 包括古老的残留锆石、原岩中的岩浆锆石、扇形和面形分带的变质锆石及后期退变质锆石. 利用激光等离子体质谱技术对不同区域锆石进行了微区微量元素分析和Pb-Pb定年. 扇形和面形分带锆石具有低Th和U含量及Th/U比值, 稀土总量低, 明显的Eu负异常、重稀土相对亏损和分异小等微量元素特征. 这两种类型锆石的稀土元素配分模式中明显的Eu异常及重稀土相对亏损和分异小, 表明这两类变质锆石与长石和石榴石平衡共生, 形成于麻粒岩相变质阶段. 原岩的岩浆锆石则具有典型的壳源锆石的微量元素特征(Th, U, Th/U比值及稀土总量高, 稀土总量变化范围大, 重稀土明显富集等). 12个麻粒岩相变质锆石分析点的²⁰⁷Pb/²⁰⁶Pb年龄平均结果为2154±26 Ma(MSWD＝3.8). 5个原岩岩浆锆石的分析点给出了2741±22Ma (MSWD＝1.4)的²⁰⁷Pb/²⁰⁶Pb年龄. 这一结果表明, 该样品原岩形成时代为晚太古代(2741±22 Ma), 麻粒岩相变质作用发生在2154±26 Ma. 该样品中还发现有约3.4 Ga的残留锆石, 证明该地区存在古太古代的陆壳物质. 对锆石进行微区定年的同时进行微区微量元素分析, 会对锆石不同区域的形成环境及不同区域获得年龄的解释提供重要的地球化学制约.     

A study of inherited zircons in granitoid rocks from the South Portuguese and Ossa-Morena Zones, Iberian Massif: support for the exotic origin of the South Portuguese Zone

Trace element and U–Pb isotopic analyses of inherited zircon cores from a sample of Gil Márquez granodiorite (South Portuguese Zone, SPZ) and Almonaster nebulite (Ossa-Morena Zone, OMZ, in the Aracena Metamorphic Belt) have been obtained using laser ablation-inductively coupled plasma-mass spectrometry. These data reveal differences in the age of deep continental crust in these two zones. Inherited zircon cores from the Ossa-Morena Zone range at 600±100 Ma, 1.7–2 Ga and 2.65–2.95 Ga, while those from the South Portuguese Zone range at 400–500 and 700–800 Ma. These data support the “exotic” origin of the South Portuguese Zone basement relative to the rest of Iberian Massif. The young ages of inherited zircon cores and Nd model ages of magmatic rocks of the South Portuguese Zone are comparable to results from granulite facies xenoliths and granitic rocks from the Meguma Terrane and Avalonia and support a correlation between the basement of the southernmost part of the Iberian Massif and the northern Appalachians.     

In-situ trace element analyses and Pb-Pb dating of zircons in granulite from Huangtuling, Dabieshan by LAM-ICP-MS

Zircon is an accessory mineral occurring in many types of rocks. For the rich content of U and low content of common Pb, it is the principal mineral used for U-Th-Pb dating. It can be sur-vived during weathering, transiting, high-grade metamorphism and ev…     

存在比桑日群弧火山岩更早的新特提斯洋俯冲记录么？

新特提斯洋的演化过程对于青藏高原的形成具有重要的意义,一直以来桑日群火山岩被认为是其俯冲作用的代表性岩浆记录.在拉萨以东发育的叶巴组火山岩,虽被认为早于桑日群的火山岩,但一直缺乏年代学的证据.本次研究选取了叶巴组的样品做了单颗粒锆石的LAM-ICP-MS定年,获得了174Ma左右的年龄,明显老于桑日群.同时,叶巴组火山岩具有与岛弧火成岩类似的地球化学特点：如大离子亲石元素相对富集,中基性火山岩表现明显的高场强元素HFSE的亏损.综合来看,叶巴组火山岩很可能是新特提斯洋向北俯冲作用的产物.如果这一点能够确证的话,新特提斯洋开始俯冲的时代将可以前推至早中侏罗纪或更早.