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磷灰石LA-ICP-MS U-Pb定年直接校准方法研究

赵令浩, 詹秀春, 曾令森, 胡明月, 孙冬阳, 袁继海

赵令浩, 詹秀春, 曾令森, 胡明月, 孙冬阳, 袁继海. 磷灰石LA-ICP-MS U-Pb定年直接校准方法研究[J]. 岩矿测试, 2022, 41(5): 744-753. DOI: 10.15898/j.cnki.11-2131/td.202202260035
引用本文: 赵令浩, 詹秀春, 曾令森, 胡明月, 孙冬阳, 袁继海. 磷灰石LA-ICP-MS U-Pb定年直接校准方法研究[J]. 岩矿测试, 2022, 41(5): 744-753. DOI: 10.15898/j.cnki.11-2131/td.202202260035
shu
ZHAO Linghao, ZHAN Xiuchun, ZENG Lingsen, HU Mingyue, SUN Dongyang, YUAN Jihai. Direct Calibration Method for LA-HR-ICP-MS Apatite U-Pb Dating[J]. Rock and Mineral Analysis, 2022, 41(5): 744-753. DOI: 10.15898/j.cnki.11-2131/td.202202260035
Citation: ZHAO Linghao, ZHAN Xiuchun, ZENG Lingsen, HU Mingyue, SUN Dongyang, YUAN Jihai. Direct Calibration Method for LA-HR-ICP-MS Apatite U-Pb Dating[J]. Rock and Mineral Analysis, 2022, 41(5): 744-753. DOI: 10.15898/j.cnki.11-2131/td.202202260035
shu

磷灰石LA-ICP-MS U-Pb定年直接校准方法研究

  • 1.

    中国地质调查局元素微区与形态分析重点实验室，国家地质实验测试中心，北京 100037

  • 2.

    自然资源部深部动力学重点实验室，中国地质科学院地质研究所，北京 100037

基金项目: 

中国地质科学院基本科研业务费项目 CSJ201901

中国地质科学院基本科研业务费项目 CSJ202201

中国地质调查局地质调查项目 DD20221838

国家重点研发计划项目 2021YFC2903101

详细信息
    作者简介:

    赵令浩，博士，副研究员，从事地球化学及构造地质学研究。E-mail：linghaozhao@126.com

  • 中图分类号: P597;O657.63

Direct Calibration Method for LA-HR-ICP-MS Apatite U-Pb Dating

  • 1.

    Key Laboratory of in-situ Elemental Micro-probe and Speciation Analysis, China Geological Survey; National Research Center for Geoanalysis, Beijing 100037, China

  • 2.

    Key Laboratory of Deep-Earth Dynamics, Ministry of Natural Resources; Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China

摘要

    摘要
  • 摘要:

    磷灰石作为含铀副矿物在各种类型地质样品中广泛存在，其U-Pb封闭温度~500℃，是良好的热年代学研究对象。但是磷灰石相对较低的铀含量和较高普通铅含量以及缺少基体匹配标准样品等问题限制了磷灰石LA-ICP-MS U-Pb定年技术的发展和应用。本文采用激光剥蚀高分辨电感耦合等离子体质谱(LA-HR-ICP-MS)针对Madagascar磷灰石样品MAD2进行U-Pb定年分析，探讨其U-Pb同位素均一性及直接用作磷灰石LA-ICP-MS U-Pb定年标准样品的可行性。结果表明：该样品U、Pb含量均值分别为23.8×10-6和13.5×10-6，颗粒内207Pb/206Pb和206Pb/238U比值均一性较好，加权平均值分别为0.0943±0.0006和0.0794±0.0004，可以用于直接校准磷灰石LA-ICP-MS U-Pb同位素分析过程中的元素分馏效应，无需普通铅校正。以MAD2为标准样品，结合207Pb普通铅扣除法，测定了不同年龄磷灰石样品U-Pb年龄，结果为：McClure Moutain(521±5Ma)、Tory Hill-apt(1021±16Ma)、Durango(30.7±1.5Ma)、房山岩体闪长岩磷灰石(~131Ma)，各样品年龄测定值与推荐值在误差范围内一致，表明本文建立的LA-ICP-MS U-Pb定年方法和同位素比值校准方案的可行性和准确性。本文采用的校准和数据处理方案有效地降低了磷灰石LA-ICP-MS U-Pb定年数据处理难度，有利于方法的推广和应用。

    要点

    (1) Madagascar磷灰石样品MAD2具有较好的U-Pb同位素均一性，可用于直接校准磷灰石LA-ICP-MS U-Pb同位素比值，无需普通铅校正。

    (2) 以MAD2为标准样品，结合207Pb普通铅扣除法，准确测定了McClure Moutain、Tory Hill-apt和Durango磷灰石U-Pb年龄。

    (3) 基于MAD2的校准和数据处理方案，满足磷灰石LA-ICP-MS U-Pb定年精确度要求，同时有效地降低了数据处理难度。

    HIGHLIGHTS

    (1) Madagascar apatite sample MAD2 shows stable U-Pb isotope ratios, which can be used to calibrate apatite U-Pb isotope ratio measured by LA-ICP-MS directly, without common-Pb correction.

    (2) Taking MAD2 as a reference mineral, combined with207Pb-correction method, the ages of apatite samples from McClure Mountain, Tory-Hill-apt and Durango were determined accurately.

    (3) The calibration and data processing scheme based on MAD2 meets the accuracy requirements of apatite LA-ICP-MS U-Pb dating, while effectively reducing the difficulty of data processing.

    Abstract:
    BACKGROUND 

    Apatite is a common U-bearing accessory mineral with a U-Pb closure temperature of ~500℃, making U-Pb dating of apatite a potentially valuable thermochronometer. However, its low U concentration, high common lead concentration and lack of reference material has limited widespread application to LA-ICP-MS dating.

    OBJECTIVES 

    To develop a technique for U-Pb dating of apatite using laser ablation sector field inductively coupled plasma-mass spectrometry (LA-HR-ICP-MS).

    METHODS 

    The U-Pb isotope ratio in apatite samples was determined by LA-HR-ICP-MS, with apatite MAD2 as the external standard to correct U-Pb and Pb-Pb elemental fractionation directly without a common Pb correction.

    RESULTS 

    Long-term U-Pb analysis of Madagascar apatite sample (MAD2) showed homogeneous distribution of U, Pb and U-Pb isotope ratios, with average contents of U and Pb ~23.8×10-6 and ~13.5×10-6, respectively and weighted average 207Pb/206Pb and 206Pb/238U ratios of 0.0941±0.0006 and 0.0794±0.0004, respectively. Taking MAD2 apatite as a reference mineral, combined with 207Pb-correction method, the ages of apatite samples, McClure Mountain (521±5Ma), Tory-Hill-apt (1021±16Ma), a Durango (30.7±1.5Ma) and Fagnshan diorite apatite (~131Ma) can be determined accurately.

    CONCLUSIONS 

    The Madagascar apatite sample (MAD2) can be used to calibrate apatite U-Pb isotope ratio measured by LA-ICP-MS directly, without common-Pb correction, similar to the calibration strategy in zircon U-Pb dating. The method greatly reduces the difficulty of data processing during apatite U-Pb dating by LA-ICP-MS, which is conducive to the wide application of the method.

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  • 斑岩铜矿作为最重要的铜矿类型之一，为世界提供了50%以上的金属铜资源[1]。自斑岩铜矿概念提出后，众多地质矿产学者对斑岩铜矿进行了大量的研究工作。前人在斑岩铜矿形成大地构造背景[2-4]、成矿斑岩特征[3-5]、斑岩铜矿与埃达克岩关系[3-4, 6-7]、斑岩铜矿中金属来源[3, 8]、成矿流体特征[8-9]等方面取得重大成果。研究表明，斑岩型铜(金或钼)成矿体系倾向于出现在线性的、典型的平行造山带中，它们与钙碱性岩基和火山链一起，常产于板块汇聚边缘活动俯冲带之上的岩浆弧中。斑岩铜(金或钼)成矿体系在空间上常与中性-酸性成分的同岩浆来源的钙碱性火山岩相关联。

    乌努格吐山斑岩型铜钼矿床位于额尔古纳—呼伦断裂北西侧(图 1)，是中国东北地区最为重要的斑岩型铜钼矿床之一，也是中国探明的第四大铜钼伴生矿床。前人对该矿床的地质特征[10]、成岩成矿年代学[11-19]、岩石地球化学[14, 16-18]、围岩蚀变[20]、矿石矿物特征[20]、稳定同位素[14, 16-18]、流体包裹体[14, 21]等方面开展了大量的工作。其中，对围岩和成矿母岩进行了许多同位素年代学研究，包括绢云母K-Ar和Ar-Ar、全岩Rb-Sr、锆石U-Pb等测年方法。然而，由于前人研究时的采样对象、测试方法、实验室的标准和精度均有区别，所取得的年龄存在较大差异，进而导致对岩石成因和形成背景也存在不同的认识。本文在系统地质调查的基础上，选取了蚀变较弱的赋矿围岩不等粒二长花岗岩和成矿母岩流纹质碎斑熔岩的样品，通过LA(MC)-ICP-MS方法对锆石U-Pb同位素、微量元素和Lu-Hf同位素进行研究，精确限定了赋矿围岩和成矿母岩的形成时代，查明了岩浆岩的成因和源区特征。

    图  1  研究区(a)大地构造位置和(b)地质略图及乌努格吐山斑岩型铜钼矿床地质图(据文献[13-14, 22]修改)
    Figure  1.  Geotectonic location of (a) the research area, and (b) its geological sketch map, and geological map of the Wunugetushan porphyry Cu-Mo deposit (Modified after Reference [13-14, 22])
    下载: 全尺寸图片 幻灯片

    1.   地质概况

    乌努格吐山斑岩型铜钼矿床大地构造位置上位于北东向额尔古纳—呼伦断裂的北西侧之额尔古纳地块西部。区域地层由老到新主要为古生代泥盆系，中生代侏罗系、白垩系，以及新生界[14](图 1)。区域构造受额尔古纳—呼伦深断裂的影响，主要构造线为北东向[11, 13]。本区岩浆活动频繁，时代分为海西晚期、燕山早期和燕山晚期，而以燕山早期为最广泛[22]。

    矿区地层出露较为简单，主要为泥盆系上统乌奴耳组和第四系全新统，其岩性与区域上基本一致。矿区内岩浆岩较为发育，主要形成于燕山早期和燕山晚期。区域性北东向额尔古纳—呼伦深断裂位于矿区东南约25km处，受其影响，次一级断裂构造十分发育。赋矿围岩和成矿母岩的成岩时代及岩石成因研究可以对成矿作用有所启示。

    2.   实验部分

    2.1   实验样品

    在系统野外地质调查的基础上，结合前人在该地区的岩浆岩研究成果，选择赋矿围岩不等粒二长花岗岩(WS05)和成矿母岩流纹质碎斑熔岩(WS02)进行锆石U-Pb同位素和Hf同位素进行研究，所选取的样品较为新鲜且蚀变较弱，采样位置具体见图 1。

    不等粒二长花岗岩(WS05)手标本呈显浅灰色，具不等粒花岗结构，块状构造；岩石蚀变较弱，以绿泥石化为主，并发生较弱的矿化(图 2中a、b)。主要组成矿物为斜长石、钾长石、石英，黑云母仅保留假像。斜长石约占35%~45%，呈半自形-近半自形板状，粒径为0.2~2.0mm；聚片双晶多较细密平直，为更长石，可见交代港湾结构等；常发育绢云母化、高岭土化等。钾长石约占35%，呈近半自形板状-他形粒状，为正长石；粒径为2~5mm，常呈杂乱状或填隙状分布，具高岭土化；粒内常见斜长石和黑云母嵌布，交代斜长石。石英约占25%，呈他形粒状，粒内具波状、斑块状消光；呈填隙状分布于长石粒间，直径小于5.0mm，常见集合体呈堆状聚集分布。黑云母约占3~5%，直径小于3.0mm，常呈叶片状零散分布，有的嵌布于钾长石粒内；发生绢云母和白云母化后常呈假像。岩石内偶见裂隙、细脉、锥状集合体发育，主要被石英、白云石、钾长石、白云母、黄铁矿、黄铜矿等矿物充填。

    图  2  矿区围岩及成矿母岩野外与显微照片
    Figure  2.  Field photos and hand specimen photograph of the surrounding rock and ore-forming parent rock
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    流纹质碎斑熔岩(WS02)手标本显浅灰色，主要为斑结构-基质霏细结构，具块状构造(图 2中c、d)。其中斑晶约占40%，基质约占60%。斑晶由长石、石英、暗色矿物构成，其中长石和暗色矿物常发生蚀变而呈假象；粒径一般0.1~4.5mm，略显方向性排列。长石多呈半自形-近半自形板状，较少量显棱角状、尖棱角状等，具绢云母化、少量石英化等主呈假像，局部见少量斜长石、钾长石残留，含量35%~40%。石英多呈自形-半自形粒状，较少量显棱角状、尖棱角状，有的具熔蚀特征，含量约15%。暗色矿物具绢云母化、白云母化等，主呈黑云母假像，少量似角闪石假像，含量3%~5%。基质主由长英质构成。长英质具霏细结构，颗粒细小，粒径一般＜0.01mm，少量0.01~0.03mm，略具定向特征，具较明显绢云母化，含量约45%。岩内较多见由石英、白云石、黄铁矿、黄铜矿、少量闪锌矿、白云母等充填的细脉及裂隙，另见较少量黄铁矿、黄铜矿呈星散状交代岩石。

    2.2   实验方法

    2.2.1   锆石U-Pb年龄测试

    锆石的分选、制靶及透反射和阴极发光(CL)由河北省区域地质调查院实验室完成，样品经常规粉碎、磁选和重选，选出高纯度锆石，在双目镜下经人工挑选出纯度在99%以上的锆石。将挑选好的锆石粘贴在环氧树脂表面，打磨抛光后露出锆石的表面，制成靶样。

    锆石U-Pb年龄测试在北京锆年领航科技有限公司完成。分析仪器为Finnigan Neptune型MC-ICP MS及配套的New Wave UP213激光剥蚀系统，采用激光剥蚀多接收电感耦合等离子体质谱法(MC-ICP-MS)对锆石进行U-Pb同位素分析。激光剥蚀束斑直径为25μm，剥蚀深度为20~40μm，能量密度为13~14J/cm2，频率为10Hz，激光剥蚀物以氦为载气进入Neptune，利用动态变焦扩大色散可以同时接收质量数相差较大的U-Pb同位素。采用Plešovice(年龄为337±0.37Ma)[23]作为外标样进行基体校正，普通铅校正采用ComPbCorr#3.17校正程序[24]。信号较小的207Pb、206Pb、204Pb(+204Hg)、202Hg用离子计数器(multi-ion-counters)接收，208Pb、232Th、238U信号用法拉第杯接收，实现了所有目标同位素信号的同时接受。对采集的数据采用中国地质大学(武汉)刘勇胜博士研发的ICP-MS DataCal程序和Kenneth R.Ludwig的Isoplot程序进行处理，并绘制谐和图等图件，置信度为95%。详细的仪器操作条件和数据处理方法见文献[25]。

    2.2.2   锆石Lu-Hf年龄测试

    锆石Hf同位素测试在北京锆年领航科技有限公司完成。锆石Hf同位素分析测试工作通过激光剥蚀电感耦合等离子体质谱法(LA-ICP-MS)进行。激光剥蚀系统为美国NewWave公司生产的UP193FX型193nm ArF准分子系统，激光器来自于德国ATL公司，ICP-MS仪器型号为Agilent 7500a。激光器波长为193nm，脉冲宽度 < 4ns，束斑直径为35μm。采用锆石标样91500[176Hf/177Hf=0.282308±12(2σ)]作为外标样进行基体校正[26]。Hf的地幔模式年龄计算中，亏损地幔176Hf/177Hf值现在值采用0.28325，176Lu/177Hf值采用0.0384[27]，地壳模式年龄计算时采用平均地壳的176Lu/177Hf=0.015[28]。数据计算和处理采用ICP-MS DataCal程序完成[25]。

    3.   结果与讨论

    3.1   锆石U-Pb同位素特征

    用于测试的锆石自形程度较好，多为长柱状，整体较完整，发育震荡环带，具岩浆成因特征[29]。选择不发育裂隙和包裹体的锆石进行年龄测试，在发育震荡环带的位置测试(图 3中a、c)。

    图  3  矿区围岩及成矿母岩锆石CL图像及年龄图
    Figure  3.  Zircon CL images and age maps of surrounding rocks and ore-forming parent rocks in the mining area
    下载: 全尺寸图片 幻灯片

    弱矿化蚀变不等粒二长花岗岩(WS05)锆石Pb含量为8.17×10-6~105.40×10-6，Th含量为60.44×10-6~988.45×10-6，U含量为177.56×10-6~2090.24×10-6；矿化蚀变流纹质碎斑熔岩(WS02)锆石Pb含量为6.63×10-6~38.32×10-6，Th含量为90.78×10-6~701.01×10-6，U含量为106.28×10-6~575.53×10-6(表 1)。Th/U比值均大于0.1，为岩浆成因锆石[30-31]。样品U-Pb年龄＜1.0Ga，因而采用锆石206Pb/238U年龄[32]。WS05样品锆石206Pb/238U年龄值为197.19±1.32~203.63±1.38Ma，加权平均值为200.96±0.88Ma，MSWD=3.0(图 3b)；WS02样品锆石206Pb/238U年龄值为175.31±1.46~183.89±1.29Ma，加权平均值为179.58±0.91Ma，MSWD=2.7(图 3d)。表明两类岩体均形成于早侏罗世。

    表  1  乌努格吐山岩体LA-MC-ICP-MS锆石U-Pb同位素分析结果
    Table  1.  LA-MC-ICP-MS zircon U-Pb isotopic analysis of the Wunugetushan rocks
    样品名 元素含量(×10-6) Th/U 元素比值 年龄(Ma)
    Pb Th U 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ
    WS02-1 6.63 99.33 106.28 0.93 0.054800689 0.002451556 0.21777954 0.009825907 0.028920427 0.0002901 466.71 99.99 200.06 8.19 183.79 1.82
    WS02-2 21.18 360.70 357.46 1.01 0.052139056 0.001611966 0.19929428 0.005904684 0.027904962 0.0002414 300.06 70.36 184.53 5.00 177.42 1.51
    WS02-3 9.71 127.12 187.62 0.68 0.053187486 0.001725981 0.20737534 0.006527215 0.028589719 0.0002581 344.50 74.07 191.35 5.49 181.72 1.62
    WS02-4 23.29 335.12 435.58 0.77 0.0523526 0.001072423 0.2014723 0.00400281 0.028002268 0.0001724 301.91 46.29 186.37 3.38 178.03 1.08
    WS02-5 8.61 90.78 183.57 0.49 0.055145614 0.001930204 0.21747196 0.007653397 0.028658462 0.0002537 416.72 77.77 199.80 6.38 182.15 1.59
    WS02-6 20.64 291.00 376.00 0.77 0.054660963 0.001447771 0.2124608 0.005765492 0.028240433 0.0002631 398.20 59.25 195.62 4.83 179.53 1.65
    WS02-8 8.18 135.96 138.07 0.98 0.054630817 0.002674734 0.20791517 0.009586314 0.028118499 0.0003531 398.20 109.25 191.80 8.06 178.76 2.21
    WS02-9 26.43 382.25 491.17 0.78 0.052954664 0.000994737 0.20600679 0.003891296 0.028261949 0.000183 327.84 42.59 190.20 3.28 179.66 1.15
    WS02-10 10.38 130.90 207.45 0.63 0.049377333 0.001784532 0.18873552 0.006546347 0.027953044 0.0002377 164.90 87.95 175.55 5.59 177.72 1.49
    WS02-11 22.22 300.23 410.94 0.73 0.052497602 0.001023893 0.20769834 0.004161734 0.028732664 0.0001882 305.62 44.44 191.62 3.50 182.61 1.18
    WS02-12 38.32 701.01 575.53 1.22 0.050521629 0.000821741 0.19443142 0.003348741 0.027897904 0.0001672 220.44 34.25 180.40 2.85 177.38 1.05
    WS02-13 15.41 248.04 256.19 0.97 0.050553309 0.001345129 0.19415114 0.005059312 0.02803746 0.0002147 220.44 56.47 180.17 4.30 178.25 1.35
    WS02-14 16.30 256.91 298.04 0.86 0.050617744 0.001296767 0.19604288 0.004959068 0.028254753 0.0002041 233.40 59.25 181.77 4.21 179.62 1.28
    WS02-15 9.86 128.93 197.58 0.65 0.053200153 0.001778239 0.20301776 0.006439848 0.027963384 0.0002068 344.50 75.92 187.68 5.44 177.79 1.30
    WS02-16 11.93 159.19 228.39 0.70 0.051343842 0.001688606 0.20303925 0.006728144 0.028755703 0.0002669 257.47 71.29 187.69 5.68 182.76 1.67
    WS02-17 23.68 362.75 419.53 0.86 0.054711601 0.001166784 0.21235292 0.00470457 0.028205027 0.0002095 466.71 50.92 195.53 3.94 179.30 1.31
    WS02-18 10.80 134.97 212.47 0.64 0.055085188 0.00186445 0.21549537 0.007139035 0.028663977 0.0002485 416.72 80.55 198.15 5.96 182.18 1.56
    WS02-19 22.29 417.16 350.97 1.19 0.051618269 0.002041641 0.19860798 0.007722468 0.02798546 0.0002789 333.39 95.36 183.95 6.54 177.93 1.75
    WS02-21 28.22 505.10 401.58 1.26 0.053629164 0.001209577 0.20969736 0.004457275 0.028636014 0.0002611 353.76 51.85 193.30 3.74 182.01 1.64
    WS02-22 13.76 199.73 247.98 0.81 0.050498539 0.001704943 0.19981518 0.007007338 0.028780503 0.0003232 216.74 47.22 184.97 5.93 182.91 2.03
    WS02-23 15.67 233.95 279.27 0.84 0.053609854 0.001945143 0.20426492 0.006872007 0.027979173 0.0002475 353.76 50.92 188.73 5.79 177.89 1.55
    WS02-24 12.13 155.47 242.85 0.64 0.048139881 0.001435921 0.18517718 0.005419974 0.028059585 0.0002194 105.65 70.37 172.51 4.64 178.39 1.38
    WS02-25 21.94 294.47 456.44 0.65 0.05015908 0.001703097 0.18973048 0.006066855 0.027568544 0.0002324 211.19 79.62 176.40 5.18 175.31 1.46
    WS02-26 11.03 202.63 163.39 1.24 0.048642808 0.001868937 0.18622353 0.007027353 0.028034949 0.0002515 131.57 90.73 173.40 6.02 178.24 1.58
    WS02-27 18.79 270.47 307.16 0.88 0.0592801 0.001671102 0.23539905 0.006493675 0.02893611 0.0002062 575.96 58.32 214.65 5.34 183.89 1.29
    WS02-28 15.65 205.15 290.46 0.71 0.050701322 0.001279128 0.20087159 0.005146519 0.028781368 0.0002166 227.85 57.40 185.86 4.35 182.92 1.36
    WS02-29 17.27 254.50 308.03 0.83 0.051600767 0.001357782 0.19851122 0.005220095 0.028089674 0.0002205 333.39 61.10 183.87 4.42 178.58 1.38
    WS02-30 15.90 246.27 276.75 0.89 0.051720434 0.001294036 0.19826738 0.004938912 0.027877092 0.0001995 272.29 57.40 183.66 4.19 177.25 1.25
    WS05-1 64.67 982.05 957.01 1.03 0.049821594 0.000679027 0.21445247 0.003309532 0.031186237 0.0002163 187.12 31.48 197.28 2.77 197.97 1.35
    WS05-2 57.13 549.94 1168.26 0.47 0.051369046 0.00067504 0.22227668 0.003450735 0.031302054 0.0002225 257.47 29.63 203.80 2.87 198.69 1.39
    WS05-3 47.18 434.72 1006.50 0.43 0.0506981 0.000730666 0.2174262 0.003523028 0.031061297 0.0002109 227.85 33.33 199.77 2.94 197.19 1.32
    WS05-4 34.20 444.49 539.30 0.82 0.050076452 0.00089561 0.21978911 0.003838643 0.031905458 0.0002253 198.23 36.10 201.73 3.20 202.46 1.41
    WS05-5 27.24 293.62 512.29 0.57 0.050704918 0.000898261 0.2223234 0.004083565 0.03180311 0.0002221 227.85 73.14 203.84 3.39 201.82 1.39
    WS05-6 36.62 406.81 627.91 0.65 0.053227511 0.000811598 0.23413474 0.003583162 0.031928406 0.0001706 338.95 35.18 213.61 2.95 202.61 1.07
    WS05-7 83.00 979.16 1509.58 0.65 0.050594466 0.00081154 0.21775243 0.003377792 0.031220547 0.0001736 233.40 37.03 200.04 2.82 198.18 1.09
    WS05-8 32.42 390.91 580.70 0.67 0.050650678 0.000990998 0.21692246 0.004238077 0.031130835 0.000211 233.40 72.21 199.35 3.54 197.62 1.32
    WS05-9 29.94 328.98 562.17 0.59 0.052125927 0.000943859 0.22710559 0.004118635 0.031673079 0.0002015 300.06 40.74 207.81 3.41 201.01 1.26
    WS05-11 44.07 450.63 852.34 0.53 0.050493385 0.000603843 0.22279877 0.002627975 0.03205128 0.000192 216.74 32.40 204.24 2.18 203.37 1.20
    WS05-12 11.55 105.13 237.06 0.44 0.051080959 0.001477309 0.22439572 0.00633483 0.032046799 0.0002526 242.66 66.66 205.56 5.25 203.35 1.58
    WS05-14 42.65 589.47 697.76 0.84 0.05127644 0.001010592 0.22059852 0.004252904 0.031231933 0.000197 253.77 46.29 202.41 3.54 198.25 1.23
    WS05-15 39.70 446.39 683.49 0.65 0.052426052 0.001056312 0.23066064 0.004658531 0.031933659 0.0002448 305.62 46.29 210.74 3.84 202.64 1.53
    WS05-16 30.83 351.35 540.24 0.65 0.05575571 0.001034747 0.24554158 0.004129216 0.032092859 0.0002217 442.64 8.33 222.95 3.37 203.63 1.38
    WS05-17 31.36 393.76 522.41 0.75 0.050483307 0.001147105 0.22167031 0.004880911 0.031926872 0.0002473 216.74 84.25 203.30 4.06 202.60 1.54
    WS05-18 105.40 988.45 2090.24 0.47 0.055715982 0.000922293 0.2396987 0.003938731 0.031188268 0.0002232 442.64 4.63 218.17 3.23 197.98 1.40
    WS05-19 41.50 594.60 650.78 0.91 0.052764976 0.000837416 0.22901688 0.00383827 0.031430675 0.0001724 320.43 35.18 209.39 3.17 199.50 1.08
    WS05-20 32.81 439.05 545.05 0.81 0.050598044 0.001078644 0.22137187 0.004978527 0.031761313 0.0002199 233.40 80.54 203.05 4.14 201.56 1.37
    WS05-21 35.38 283.00 748.80 0.38 0.053983443 0.000743583 0.23800768 0.003481432 0.031971686 0.0002069 368.57 63.88 216.79 2.86 202.88 1.29
    WS05-22 28.57 328.62 500.85 0.66 0.050519726 0.001050105 0.22322756 0.004803931 0.032029526 0.0002293 220.44 48.14 204.59 3.99 203.24 1.43
    WS05-23 42.59 608.47 643.73 0.95 0.049834093 0.000955096 0.22053286 0.004450034 0.032048558 0.0002182 187.12 44.44 202.35 3.70 203.36 1.36
    WS05-24 8.17 60.44 177.56 0.34 0.052461445 0.001898692 0.22941335 0.00798765 0.032038934 0.0002929 305.62 83.33 209.71 6.60 203.30 1.83
    WS05-25 24.90 213.14 529.34 0.40 0.053206234 0.000909342 0.23360332 0.004100044 0.031832937 0.0002027 344.50 38.89 213.17 3.37 202.01 1.27
    WS05-26 30.48 333.52 561.03 0.59 0.050610366 0.00098056 0.22392893 0.004444282 0.032039082 0.0001895 233.40 78.69 205.17 3.69 203.30 1.18
    WS05-27 42.92 359.80 939.57 0.38 0.053112655 0.000673233 0.23125454 0.003331502 0.031536009 0.0002358 344.50 27.78 211.23 2.75 200.15 1.47
    WS05-28 24.77 245.33 487.82 0.50 0.05240212 0.001044812 0.23207116 0.004988243 0.032062634 0.0002458 301.91 44.44 211.91 4.11 203.44 1.54
    WS05-29 88.23 961.68 1634.70 0.59 0.051403159 0.000521454 0.22632576 0.00277416 0.03194678 0.0002878 257.47 24.07 207.16 2.30 202.72 1.80
    WS05-30 45.76 621.40 772.57 0.80 0.050900004 0.00083911 0.21961879 0.00358115 0.03129567 0.0001579 235.25 37.03 201.59 2.98 198.65 0.99
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    3.2   锆石稀土元素特征

    两类岩体锆石的稀土含量较高，弱矿化蚀变不等粒二长花岗岩(WS05)的ΣREE为1036.03×10-6~3489.37×10-6，轻稀土LREE含量为13.76×10-6~158.11×10-6，重稀土HREE含量为1022.28×10-6~3415.31×10-6，轻/重稀土比值为0.01~0.09；矿化蚀变流纹质碎斑熔岩(WS02)的ΣREE为579.83×10-6~1110.14×10-6(表 2)，轻稀土LREE含量为28.83×10-6~85.54×10-6，重稀土HREE含量为535.47×10-6~1049.04×10-6，轻/重稀土比值为0.05~0.11。轻重稀土分异程度较高，具岩浆锆石稀土元素特征[33-35]。WS05样品锆石δEu值为0.13~0.38，WS02样品δEu值为0.39~0.67，具负异常；WS05样品锆石δCe值为1.57~476.84，WS02样品δCe值为10.48~1613.59，具强正异常，与典型热液锆石差异较大[36]。两类岩体锆石稀土配分曲线具左倾特征，轻稀土亏损、重稀土富集，具岩浆锆石特征(图 4)。

    表  2  锆石稀土元素(×10-6)组成
    Table  2.  REE element (×10-6) compositions of the zircons
    样品编号 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Y ΣREE LREE HREE LREE/HREE δEu δCe
    WS05-1 0.009 30.818 0.109 2.207 5.808 1.336 37.462 14.819 189.182 78.302 365.255 82.336 775.232 155.907 2317.566 1738.78 40.29 1698.50 0.02 0.28 243.55
    WS05-2 0.136 31.651 0.383 3.864 6.669 0.940 38.640 16.064 209.545 91.003 450.613 107.613 1082.980 229.910 2788.147 2270.01 43.64 2226.37 0.02 0.18 33.96
    WS05-4 0.033 26.488 0.276 4.746 10.352 3.109 61.401 22.084 281.410 113.924 528.866 118.980 1130.763 227.279 3457.657 2529.71 45.00 2484.71 0.02 0.38 68.45
    WS05-5 1.985 26.801 0.971 5.922 5.631 1.404 38.216 15.136 206.981 89.074 430.765 100.296 995.993 206.695 2738.920 2125.87 42.71 2083.16 0.02 0.29 4.73
    WS05-6 7.588 48.479 4.041 22.978 9.309 1.237 35.817 12.572 166.430 71.866 347.266 81.181 817.296 167.611 2167.755 1793.67 93.63 1700.04 0.06 0.21 2.15
    WS05-7 0.410 34.403 0.259 2.745 5.160 0.656 36.139 14.704 194.596 81.371 391.476 88.285 871.715 179.856 2485.255 1901.77 43.63 1858.14 0.02 0.15 25.90
    WS05-8 0.071 26.437 0.180 3.754 6.534 1.671 45.710 17.406 241.011 104.037 496.093 114.322 1096.435 226.859 3098.375 2380.52 38.65 2341.87 0.02 0.30 57.53
    WS05-9 0.634 19.833 0.405 4.501 6.978 1.302 43.246 15.843 207.008 86.747 414.299 94.644 940.131 191.090 2642.584 2026.66 33.65 1993.01 0.02 0.23 9.60
    WS05-11 0.132 22.938 0.122 1.732 3.547 0.468 29.152 11.791 165.304 72.780 361.164 85.935 859.033 177.858 2241.112 1791.96 28.94 1763.02 0.02 0.14 44.37
    WS05-12 0.004 8.790 0.057 1.131 3.136 0.640 19.128 7.017 97.977 41.175 206.170 48.490 497.626 104.694 1221.775 1036.03 13.76 1022.28 0.01 0.25 138.94
    WS05-14 0.009 32.244 0.147 2.820 7.772 2.330 55.584 21.225 286.814 119.502 561.039 124.996 1187.688 245.743 3612.210 2647.91 45.32 2602.59 0.02 0.34 212.89
    WS05-15 21.426 79.810 7.266 36.278 11.865 1.461 39.927 13.963 180.198 75.958 375.290 87.983 872.939 179.036 2355.693 1983.40 158.11 1825.29 0.09 0.21 1.57
    WS05-16 0.293 20.491 0.259 4.083 8.775 1.680 49.344 17.701 216.112 87.518 406.557 90.786 878.944 176.341 2581.778 1958.88 35.58 1923.30 0.02 0.25 18.24
    WS05-17 0.010 21.905 0.154 2.594 6.575 1.483 39.647 15.071 197.835 83.773 397.977 91.152 885.319 176.519 2547.626 1920.01 32.72 1887.29 0.02 0.28 133.88
    WS05-18 0.236 45.705 0.646 6.351 8.428 0.844 47.397 19.589 265.616 113.368 545.382 128.379 1250.060 255.596 3519.237 2687.60 62.21 2625.39 0.02 0.13 28.68
    WS05-19 0.106 31.726 0.695 12.497 23.102 5.938 113.735 37.357 433.393 165.370 720.022 158.983 1491.171 295.277 4901.935 3489.37 74.06 3415.31 0.02 0.35 28.69
    WS05-20 0.018 21.968 0.154 2.858 6.418 1.727 45.681 17.085 223.461 92.612 432.575 100.645 974.587 198.240 2787.431 2118.03 33.14 2084.89 0.02 0.31 103.06
    WS05-21 0.004 21.146 0.046 1.445 3.019 0.626 24.090 10.259 142.687 63.075 325.911 77.391 790.708 167.260 1970.759 1627.67 26.29 1601.38 0.02 0.22 407.07
    WS05-22 0.009 21.816 0.142 3.198 6.343 1.554 41.438 15.424 207.699 87.686 414.011 96.134 937.960 194.215 2622.130 2027.63 33.06 1994.57 0.02 0.29 151.73
    WS05-23 0.003 22.911 0.098 1.891 3.940 1.176 29.171 11.371 149.383 61.629 293.179 65.118 632.896 128.904 1849.730 1401.67 30.02 1371.65 0.02 0.34 316.29
    WS05-25 0.002 16.515 0.045 1.028 3.357 0.484 23.728 10.029 137.925 61.334 312.802 75.410 763.433 161.320 1887.306 1567.41 21.43 1545.98 0.01 0.17 393.39
    WS05-26 1.008 24.326 0.398 2.601 4.114 0.720 25.298 9.861 133.470 56.062 278.105 65.256 647.789 133.518 1756.502 1382.53 33.17 1349.36 0.02 0.22 9.41
    WS05-27 0.092 25.471 0.132 1.488 3.234 0.412 22.485 9.565 134.435 59.983 305.314 76.238 761.997 161.823 1859.903 1562.67 30.83 1531.84 0.02 0.15 56.82
    WS05-28 0.003 18.423 0.075 1.262 3.754 0.691 25.768 9.865 134.315 59.939 296.515 71.285 712.008 147.629 1821.177 1481.53 24.21 1457.32 0.02 0.21 300.82
    WS05-29 0.004 35.127 0.083 1.768 4.805 0.560 36.981 14.534 195.832 83.381 406.337 94.943 902.927 182.187 2596.732 1959.47 42.35 1917.12 0.02 0.13 476.84
    WS05-30 0.036 28.599 0.176 3.424 7.606 1.394 51.304 19.131 240.823 97.181 453.263 101.128 968.755 193.054 2897.227 2165.87 41.24 2124.64 0.02 0.22 88.05
    WS02-1 0.012 34.124 0.201 3.717 7.501 2.472 33.922 10.145 110.736 40.545 175.905 38.370 354.954 72.500 1190.890 885.10 48.03 837.08 0.06 0.47 171.62
    WS02-2 0.004 47.559 0.028 0.832 1.807 0.754 11.337 3.437 45.540 19.866 103.023 26.165 283.910 69.933 671.635 614.20 50.98 563.21 0.09 0.51 1098.02
    WS02-3 0.036 38.471 0.057 1.129 1.884 0.852 13.736 4.517 57.026 24.387 123.912 31.368 334.975 77.953 794.007 710.30 42.43 667.87 0.06 0.51 208.54
    WS02-4 0.012 50.641 0.028 0.917 2.720 1.204 23.208 8.413 108.997 44.986 213.779 49.899 493.407 105.741 1389.597 1103.95 55.52 1048.43 0.05 0.46 663.38
    WS02-5 0.028 25.975 0.035 0.491 1.696 0.609 9.999 3.803 50.945 22.719 116.668 30.012 320.913 76.685 716.429 660.58 28.83 631.74 0.05 0.45 204.19
    WS02-6 0.002 39.230 0.043 1.074 1.639 0.847 14.867 5.382 65.972 26.461 127.859 29.241 297.651 61.893 825.531 672.16 42.83 629.32 0.07 0.52 1165.23
    WS02-8 0.022 49.184 0.100 1.682 4.625 1.492 25.052 8.713 107.265 41.207 186.206 42.565 411.247 85.181 1270.296 964.54 57.11 907.44 0.06 0.42 255.34
    WS02-10 0.037 39.545 0.062 0.682 1.360 0.751 9.690 3.256 44.980 21.913 123.529 33.255 385.436 97.691 775.348 762.19 42.44 719.75 0.06 0.63 201.55
    WS02-11 0.021 50.670 0.048 0.923 3.155 1.071 21.971 7.807 103.572 42.221 202.132 45.845 453.713 95.438 1281.416 1028.59 55.89 972.70 0.06 0.39 393.96
    WS02-12 0.058 79.046 0.052 1.273 3.551 1.560 23.297 8.214 102.291 40.931 194.555 45.875 471.126 105.613 1292.794 1077.44 85.54 991.90 0.09 0.52 351.83
    WS02-13 0.007 41.369 0.031 0.585 1.481 0.882 10.855 3.720 45.719 19.385 103.144 24.923 266.428 61.299 660.738 579.83 44.36 535.47 0.08 0.67 678.70
    WS02-14 0.090 42.582 0.057 0.907 2.388 0.960 15.585 5.242 67.882 29.502 146.837 35.601 377.324 83.402 952.952 808.36 46.98 761.37 0.06 0.48 145.43
    WS02-15 0.001 36.232 0.025 0.652 1.487 0.687 10.554 3.614 47.289 21.155 108.615 27.361 292.008 67.054 706.786 616.73 39.08 577.65 0.07 0.53 1613.59
    WS02-16 0.006 34.544 0.034 0.576 1.889 0.791 11.415 3.799 49.643 20.958 111.258 28.462 308.290 73.409 720.434 645.07 37.84 607.23 0.06 0.52 592.69
    WS02-17 0.019 55.315 0.094 1.178 3.093 1.401 22.447 8.198 105.758 43.429 211.144 49.744 502.611 105.706 1372.515 1110.14 61.10 1049.04 0.06 0.51 317.77
    WS02-18 0.114 33.968 0.085 0.792 2.304 0.919 14.432 5.286 72.123 29.318 141.600 33.361 341.146 71.884 906.553 747.33 38.18 709.15 0.05 0.49 84.73
    WS02-21 3.329 70.750 0.675 4.084 2.962 1.097 16.614 5.693 71.338 29.382 145.671 35.768 374.958 86.700 942.341 849.02 82.90 766.12 0.11 0.48 11.57
    WS02-22 0.016 34.745 0.029 0.489 1.662 0.649 11.137 3.800 52.177 22.416 116.877 28.201 305.484 70.054 710.722 647.73 37.59 610.14 0.06 0.46 403.25
    WS02-23 0.107 62.564 0.076 1.118 2.358 1.186 17.166 6.850 88.307 38.545 193.851 47.299 498.511 118.403 1243.373 1076.34 67.41 1008.93 0.07 0.57 170.98
    WS02-24 2.004 48.432 0.640 3.362 2.621 0.843 14.286 5.148 70.194 31.348 160.890 41.314 434.070 97.581 1022.773 912.73 57.90 854.83 0.07 0.42 10.48
    WS02-26 0.005 46.151 0.095 1.871 5.035 1.709 25.118 7.616 91.112 34.882 155.620 35.799 330.432 66.691 1025.318 802.14 54.87 747.27 0.07 0.46 517.34
    WS02-27 2.028 56.031 0.752 4.134 4.097 1.387 22.082 7.776 94.715 39.040 181.422 42.463 422.544 89.574 1187.650 968.05 68.43 899.62 0.08 0.45 11.12
    WS02-28 0.008 47.547 0.023 0.658 2.307 0.831 14.808 5.122 69.094 31.174 158.314 38.944 424.423 95.861 1005.799 889.11 51.37 837.74 0.06 0.43 873.10
    WS02-29 0.032 49.428 0.052 0.873 2.233 1.023 17.366 6.285 84.980 36.660 184.098 44.561 457.590 101.390 1191.673 986.57 53.64 932.93 0.06 0.50 297.46
    WS02-30 0.004 59.507 0.064 0.916 2.714 1.230 17.426 6.273 80.858 35.278 178.230 44.319 468.570 107.968 1157.665 1003.36 64.43 938.92 0.07 0.55 961.76
    下载: 导出CSV 
    | 显示表格
    图  4  稀土元素球粒陨石标准化配分型式(标准化数据据文献[38])
    Figure  4.  Chondrite-normalized REE patterns (Normalization values after Reference [38])
    下载: 全尺寸图片 幻灯片

    3.3   锆石Lu-Hf同位素特征

    弱矿化蚀变不等粒二长花岗岩(WS05)、矿化蚀变流纹质碎斑熔岩(WS02)锆石176Lu/177Hf比值分别为0.001688~0.003588、0.000831~0.001292，176Lu/177Hf比值均较小，表明锆石在形成后，仅具有少量的放射性成因Hf积累，因而可以用初始176Hf/177Hf比值代表形成时的Hf同位素组成[37]。176Hf/177Hf初始比值和εHf(t)值根据同一锆石U-Pb测年数据计算；二阶段模式年龄(TDMC)根据亏损幔源计算[27]。测定结果显示，WS05锆石Hf同位素176Hf/177Hf比值为0.282659~0.282820(表 3)，176Yb/177Hf比值为0.099606~0.046370，fLu/Hf为-0.95~-0.89，锆石εHf(0)为-4.0~-0.7，εHf(t)为0.1~5.8(图 5)；WS02锆石Hf同位素176Hf/177Hf比值为0.282783~0.282850，176Yb/177Hf比值为0.020042~0.035646，fLu/Hf为-0.97~-0.96，锆石εHf(0)为0.4~2.8，εHf(t)为4.3~6.6(图 6)。WS05锆石Hf单阶段模式年龄(TDM)为643~882Ma，二阶段模式年龄(TDMC)为874~1235Ma；WS02锆石Hf单阶段模式年龄(TDM)为570~663Ma，二阶段模式年龄(TDMC)为802~952Ma。

    表  3  乌努格吐山岩体LA-ICP-MS锆石Lu-Hf同位素分析结果
    Table  3.  LA-ICP-MS Zircon Lu-Hf isotopic analysis of Wunugetushan rocks
    样品编号 年龄(Ma) 176Yb/177Hf 176Lu/177Hf 176Hf/177Hf εHf(0) εHf(t) TDM (Ma) TDMC(Ma) fLu/Hf
    WS02-001 183.79 0.035646 0.001292 0.282829 2.0 5.9 604 850 -0.96
    WS02-002 181.72 0.022735 0.000914 0.282783 0.4 4.3 663 952 -0.97
    WS02-003 178.76 0.023283 0.000875 0.282837 2.3 6.1 587 833 -0.97
    WS02-004 177.72 0.024778 0.000996 0.282818 1.6 5.4 616 878 -0.97
    WS02-005 177.38 0.030802 0.001225 0.282803 1.1 4.8 641 914 -0.96
    WS02-006 178.25 0.022562 0.000964 0.282825 1.9 5.7 604 860 -0.97
    WS02-007 179.62 0.020253 0.000831 0.282831 2.1 5.9 595 846 -0.97
    WS02-008 177.79 0.026337 0.001096 0.282842 2.5 6.3 582 822 -0.97
    WS02-009 182.76 0.022090 0.000917 0.282804 1.1 5.0 634 905 -0.97
    WS02-010 182.18 0.026716 0.000988 0.282850 2.8 6.6 570 802 -0.97
    WS02-011 182.91 0.023562 0.000917 0.282834 2.2 6.1 591 837 -0.97
    WS02-012 177.89 0.020042 0.000854 0.282819 1.7 5.5 611 873 -0.97
    WS02-013 178.39 0.026401 0.001009 0.282829 2.0 5.8 599 851 -0.97
    WS02-014 178.24 0.024919 0.000902 0.282803 1.1 4.9 634 909 -0.97
    WS02-015 178.58 0.027675 0.001052 0.282809 1.3 5.1 629 897 -0.97
    WS02-016 177.25 0.025114 0.001094 0.282813 1.5 5.2 623 888 -0.97
    WS05-001 197.97 0.067606 0.002426 0.282738 -1.2 2.8 756 1057 -0.93
    WS05-002 197.19 0.060028 0.002184 0.282694 -2.8 1.3 816 1155 -0.93
    WS05-003 201.82 0.073935 0.002745 0.282820 1.7 5.8 643 874 -0.92
    WS05-004 202.61 0.059110 0.002155 0.282728 -1.5 2.6 765 1074 -0.94
    WS05-005 197.62 0.067911 0.002509 0.282731 -1.4 2.6 768 1073 -0.92
    WS05-006 201.01 0.052678 0.002027 0.282712 -2.1 2.0 786 1110 -0.94
    WS05-007 203.37 0.046370 0.001688 0.282703 -2.4 1.8 792 1127 -0.95
    WS05-008 199.5 0.099606 0.003588 0.282743 -1.0 2.9 775 1055 -0.89
    WS05-009 201.56 0.047960 0.001782 0.282714 -2.0 2.1 778 1103 -0.95
    WS05-010 202.88 0.058686 0.002184 0.282702 -2.5 1.7 805 1135 -0.93
    WS05-011 202.01 0.059888 0.002143 0.282712 -2.1 2.0 789 1111 -0.94
    WS05-012 203.3 0.077946 0.002817 0.282659 -4.0 0.1 882 1235 -0.92
    WS05-013 200.15 0.056164 0.002059 0.282711 -2.1 2.0 788 1113 -0.94
    WS05-014 202.72 0.085910 0.003052 0.282701 -2.5 1.5 825 1143 -0.91
    WS05-015 198.65 0.091676 0.003159 0.282751 -0.7 3.2 753 1034 -0.90
    注：εHf(t)=10000×{[(176Hf/177Hf)S-(176Lu/177Hf)S×(eλt-1)]/[(176Hf/177Hf)CHUR，0-(176Lu/177Hf)CHUR×(eλt-1)]-1}；
    TDM=1/λ×ln{1 +[(176Hf/177Hf)S-(176Hf/177Hf)DM]/[(176Hf/177Hf)S-(176Hf/177Hf)DM]}；
    TDMC=TDM-(TDM-t)×[(fcc-fs)/(fcc-fDM)]，fLu/Hf=(176Lu/177Hf)S/(176Lu/177Hf)CHUR-1。
    其中：λ=1.867×10-11/a[41]；(176Lu/177Hf)S和(176Hf/177Hf)S为样品测量值；(176Lu/177Hf)CHUR=0.0332，(176Hf/177Hf)CHUR，0=0.282772[26]；(176Lu/177Hf)DM=0.0384，(176Hf/177Hf)DM=0.28325[27]；(176Lu/177Hf)平均地壳=0.015；fcc=[(176Lu/177Hf)平均地壳/(176Lu/177Hf)CHUR]-1；fs= fLu/Hf；fDM=[(176Lu/177Hf)DM/(176Lu/177Hf)CHUR]-1；t为锆石结晶年龄。
    下载: 导出CSV 
    | 显示表格
    图  5  不等粒二长花岗岩(WS05)锆石εHf(t)-t图(底图据文献[33])
    Figure  5.  εHf(t) versus age diagrams of unequal-grained monzogranite (WS05). Base image according to Reference[33]
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    图  6  流纹质碎斑熔岩(WS02)锆石εHf(t)-t图(底图据文献[33])
    Figure  6.  εHf(t) versus age diagrams of rhyolite porphyritic lava (WS02). Base image according to Reference [33]
    下载: 全尺寸图片 幻灯片

    3.4   成岩时代对成矿作用的约束

    乌努格吐山成岩成矿年代学取得大量成果，也存在较大争议[11-15]。本次工作在系统野外地质调查的基础上，选择代表性围岩和成矿母岩进行同位素年龄测试，测试单位为北京锆年领航科技有限公司，测试方法为LA-ICP-MS。锆石U-Pb年龄具有成熟有效，锆石易挑选，封闭体系温度高等优点[39-40]，所测年龄结果真实有效，能够有效地代表岩体形成年龄。

    本次工作所测围岩(WS05)不等粒二长花岗岩样品锆石具震荡环带，Tu/U比值较大，锆石稀土强烈富集重稀土、亏损轻稀土，δEu负异常；δCe正异常特征，表明测试用锆石为岩浆成因锆石，测试结果为200.96±0.88Ma，该测试结果与秦克章等[12]测得的矿区黑云二长花岗岩全岩Rb-Sr等时线年龄(211±21Ma)、谭刚[14]获得的外围黑云母花岗岩锆石U-Pb年龄(198.1±2.9Ma)、Wang等[16]获得的矿区黑云花岗岩SIMS锆石U-Pb年龄(203.5±1.6Ma)、Zhang等[17]测得的花岗斑岩脉的SHRIMP锆石U-Pb年龄(201.4±3.1Ma)和Mi等[18]获得的矿区黑云母花岗岩锆石U-Pb年龄(206.9±1.9Ma)在误差范围内，表明了200Ma左右是本区重要的成岩时期，主体为大面积展布的黑云母花岗岩和二长花岗岩，其次为花岗斑岩脉体。其中，本次研究的不等粒二长花岗岩为新报道的一类赋矿围岩，与黑云母花岗岩属于同期形成的岩体在不同部位的岩性过渡。因此，本次所测得的不等粒二长花岗岩年龄(200.96±0.88Ma)可代表赋矿围岩岩体形成的时代，该岩体在靠近斑岩体的部位发育一定程度的蚀变和矿化，表明成矿作用晚于大面积展布的二长花岗岩-黑云母花岗岩围岩的形成时代。

    成矿母岩(WS02)流纹质碎斑熔岩样品锆石具震荡环带，Tu/U比值较大，锆石稀土强烈富集重稀土、亏损轻稀土，δEu负异常；δCe正异常特征，表明测试用锆石为岩浆成因锆石，加权平均值为179.58±0.91Ma，表明矿化蚀变流纹质碎斑熔岩形成于早侏罗世。该测试结果与秦克章等[11]获得的蚀变绢云母K-Ar年龄(183.5±1.7Ma)、Wang等[16]获得的二长花岗斑岩SIMS锆石U-Pb年龄(180.4±1.4Ma)和Mi等[18]获得的流纹斑岩锆石U-Pb年龄(180.4±4.5Ma)年龄在地质误差范围内，也与Zhang等[17]获得的辉钼矿Re-Os加权平均年龄(179.8±1.0Ma)在误差内一致，稍早于谭钢[14]测得的辉钼矿Re-Os等时线年龄(177.4±2.4Ma)，说明除了二长花岗斑岩和流纹斑岩，本次研究的流纹质碎斑熔岩也为一种重要的成矿母岩体，其形成年龄可代表矿区的成矿时代。

    赋矿围岩锆石Hf同位素特征表明岩浆源区以新生陆壳物质或幔源物质为主，混有少量古老壳源物质。成矿母岩锆石Hf同位素特征表明岩浆源区主要为新生陆壳物质或幔源物质为主，仅含极少数古老壳源物质。

    4.   结论

    本文采用LA-MC-ICP-MS和LA-ICP-MS证实不等粒二长花岗岩和流纹质碎斑熔岩为早侏罗世不同阶段的产物。锆石εHf(t)值及二阶段模式年龄(TDMC)的细微区别反映了岩浆源区的异同。通过对比赋矿围岩和成矿母岩成岩时代和Lu-Hf同位素之间的差异，指示了赋矿围岩岩浆源区为幔源物质和少量古老壳源物质的混合；成矿母岩岩浆源区主要为幔源物质。从赋矿围岩到成矿母岩岩浆源区幔源物质增加，壳源物质减少。

    致谢: 感谢Trinity College Dublin的David Chew博士提供McClure Mountain磷灰石样品；感谢两位审稿人对本文审阅提出的宝贵修改意见。

  • 图  1   Madagascar磷灰石(MAD2) LA-ICP-MS U-Pb定年结果

    (a)和(b)为多次实验质量监控样品NIST612 207Pb/206Pb和206Pb/238U比值；(c)和(d)为磷灰石MAD2校准207Pb/206Pb和206Pb/238U比值；(e)和(f)为MAD2磷灰石Tera-Wasserburg图解和206Pb/238U加权平均年龄(限于绘图软件数据上限，随机选择200点数据绘制图e)。

    Figure  1.   U-Pb isotope ratios for Madagascar apatite (MAD2) measured by LA-ICP-MS; (a) and (b) 207Pb/206Pb and 206Pb/238U ratios of monitoring sample NIST612; (c) and (d) calibrated 207Pb/206Pb and 206Pb/238U ratios of apatite MAD2; (e) and (f) Tera-Wasserburg diagram and the weighted average age of apatite MAD2

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    图  2   磷灰石样品LA-ICP-MS U-Pb定年结果

    (a)和(b)为McClure Mountain磷灰石；(c)和(d)为Tory Hill-apt-1磷灰石；(e)和(f)为Durango磷灰石；(b)、(d)、(f)为207Pb法普通铅校正206Pb/238U加权平均年龄。

    Figure  2.   U-Pb dating of apatite by LA-ICP-MS with MAD2 apatite as the external standard. (a) and (b) McClure Mountain apatite; (c) and (d) Tory Hill-apt-1 apatite; (e) and (f) Durango apatite; (b), (d) and (f) 207Pb-corrected age

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    图  3   房山花岗闪长岩样品19FS-01、19FS-03中锆石、榍石和磷灰石定年结果

    Figure  3.   U-Pb dating of zircon, titanite and apatite in granodiorite sample 19FS-01 and 19FS-03 from Fangshan Pluton

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    表  1   LA-ICP-MS仪器参数和工作条件

    Table  1   Instrumental setup and operating conditions

    高分辨电感耦合等离子体质谱
    (Thermo Scientific Element XR)    		 激光剥蚀系统
    (NWR 193ArF准分子激光器)
    参数 工作条件 参数 工作条件
    RF功率 1400W 波长 193nm
    冷却气(Ar)流速 16L/min 脉冲时间 15ns
    辅助气(Ar)流速 0.9L/min 激光斑束 25μm, 30μm, 40μm
    样品气(Ar)流速 0.98L/min 激光频率 10Hz
    分辨率 低(M/ΔM=300) 激光能量 7mJ
    扫描模式 E-Scan 剥蚀模式 点剥蚀
    扫描质量
    积分时间    		 202Hg(16ms), 204Pb(16ms),
    206Pb(24ms), 207Pb(24ms), 208Pb(16ms), 232Th(16ms), 238U(24ms)    		 载气(He) 流速 0.87L/min
    接收器模式 Counting: 202Hg, 204Pb, 207Pb, 208Pb Analog: 206Pb, 232Th, 238U 剥蚀时间 40s
    下载: 导出CSV
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  • 被引次数: 5
出版历程
  • 收稿日期:  2022-02-25
  • 修回日期:  2022-04-22
  • 录用日期:  2022-04-29
  • 网络出版日期:  2022-11-10
  • 刊出日期:  2022-09-28

目录

摘要
HTML全文

  • 1.   地质概况

  • 2.   实验部分

  • 2.1   实验样品

  • 2.2   实验方法

  • 2.2.1   锆石U-Pb年龄测试
  • 2.2.2   锆石Lu-Hf年龄测试

  • 3.   结果与讨论

  • 3.1   锆石U-Pb同位素特征

  • 3.2   锆石稀土元素特征

  • 3.3   锆石Lu-Hf同位素特征

  • 3.4   成岩时代对成矿作用的约束

  • 4.   结论

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