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云南哀牢山构造带仰宗流纹斑岩锆石U-Pb年龄、地球化学特征及其构造意义

孙崇波, 李忠权, 王道永, 许远平, 李滔, 赵云川

孙崇波, 李忠权, 王道永, 许远平, 李滔, 赵云川. 2017: 云南哀牢山构造带仰宗流纹斑岩锆石U-Pb年龄、地球化学特征及其构造意义. 地质通报, 36(2-3): 190-198.
引用本文: 孙崇波, 李忠权, 王道永, 许远平, 李滔, 赵云川. 2017: 云南哀牢山构造带仰宗流纹斑岩锆石U-Pb年龄、地球化学特征及其构造意义. 地质通报, 36(2-3): 190-198.
SUN Chongbo, LI Zhongquan, WANG Daoyong, XU Yuanping, LI Tao, ZHAO Yunchuan. 2017: Petrogeochemistry and zircon U-Pb chronology of the Yangzong rhyolite porphyry along Ailao Mountain tectonic belt. Geological Bulletin of China, 36(2-3): 190-198.
Citation: SUN Chongbo, LI Zhongquan, WANG Daoyong, XU Yuanping, LI Tao, ZHAO Yunchuan. 2017: Petrogeochemistry and zircon U-Pb chronology of the Yangzong rhyolite porphyry along Ailao Mountain tectonic belt. Geological Bulletin of China, 36(2-3): 190-198.

云南哀牢山构造带仰宗流纹斑岩锆石U-Pb年龄、地球化学特征及其构造意义

基金项目: 

中国地质调查局项目《西南三江成矿带南段基础地质调查》 1212010880406、1212011120582

详细信息
    作者简介:

    孙崇波 (1985-), 男, 在读博士生, 构造地质学专业。E-mail:1315333036@qq.com

  • 中图分类号: P588.14+1; P597+.3

Petrogeochemistry and zircon U-Pb chronology of the Yangzong rhyolite porphyry along Ailao Mountain tectonic belt

  • 摘要:

    对云南绿春县仰宗流纹斑岩进行了锆石U-Pb年龄、岩石地球化学分析。LA-ICP-MS锆石U-Pb测年显示,仰宗流纹斑岩年龄为263.1±2.3Ma,形成于晚二叠世。岩石地球化学分析显示,仰宗流纹斑岩SiO2含量为71.08%~80.26%,全碱(Na2O+K2O)含量为4.67%~8.67%,且Na2O<K2O;岩石轻、重稀土元素存在一定的分馏,负Eu异常明显(δEu=0.05~0.57),相对富集Rb、Th、U、Ni、Cs、Zr、Hf、As、K等元素,亏损Sr、Ta、Ba、Cr、Zn、W等元素。结果显示,仰宗流纹斑岩形成于碰撞期后的陆内构造环境,表明哀牢山构造带的古特提斯支洋或弧后盆地在晚二叠世(263.1±2.3Ma)可能已经闭合。

    Abstract:

    This paper presents bulk petrogeochemistry and zircon U-Pb dating results for the Yangzong rhyolite porphyry in Luchun County, Yunnan Province. LA-ICP-MS zircon U-Pb dating results show that the Yangzong rhyolite porphyry was formed in the Late Permian (263.1±2.3Ma). The Yangzong rhyolite porphyry is characterized by SiO2 content of 71.08%~80.26%, alkali (Na2O+ K2O) 4.67%~8.67%, and Na2O<K2O. It is enriched in LREE and Rb, Th, U, Ni, Cs, Zr, Hf, As, K and depleted in Sr, Ta, Ba, Cr, Zn, W with negative Eu anomalies (δEu=0.05~0.57). According to the diagrams, the Yangzong rhyolit porphyry was formed in the tectonic environment of island arc-continent or continental-arc collision, indicating that the branch of Paleo-Tethys Ocean or arc basin in Ailao Mountain tectonic belt might have been closed in the Late Permian (263.1±2.3Ma).

  • 滇西特提斯造山带以发育线性延伸构造行迹和岩浆带为特征,是研究多个岩石圈块体相互作用过程与动力学机制的典型地区[1-3]。哀牢山构造带位于特提斯-喜马拉雅构造区与滨太平洋构造区的结合部位,同时具有印支思茅地块及扬子地块构造单元的特征[4-5],被尤为重视。昌宁-孟连带位于亲扬子的思茅地块和亲冈瓦纳的缅泰马地块之间,被认为是古特提斯多岛洋格局的主洋盆遗迹分布区,代表了古特提斯的缝合线[6-7],而目前对金沙江-哀牢山带在晚古生代是否存在古特提斯支洋盆还存在争议。部分学者认为,在金沙江-哀牢山-松马构造带发育上古特提斯支洋盆,并在二叠纪发生了洋壳俯冲[6, 8-9];另一部分学者则认为,泥盆纪前思茅地块与扬子地块是一体的,在晚古生代两者之间发育了古特提斯洋东缘弧后盆地[5, 10]

    目前对哀牢山构造带火山岩的研究主要集中于中-基性岩石,关于该区酸性岩的研究报道较少[10-11]。本文在前人研究的基础上,对哀牢山南段的仰宗流纹斑岩 (图 1) 进行了主量、微量元素地球化学分析及LA-ICP-MS锆石U-Pb定年,进而讨论其形成环境和形成时代,以期为认识哀牢山-李仙江-松马构造带的演化提供新的证据。

    图  1  区域构造图 (a) 及仰宗地区地质略图 (b)
    Figure  1.  Regional structure (a) and geological sketch map of Yangzong area (b)

    哀牢山构造带整体呈NW—SE向,北西窄、南东宽,分布于云南省中南部,向南东经元阳和金平县延伸进入越南境内与松马构造带连接,向北西经点苍山与金沙江构造带对应[1, 12]。该构造带主要由4条主断裂及其分割的3套不同性质的岩石建造组成,断裂自南西向北东依次为李仙江断裂、九甲-安定断裂、哀牢山断裂及红河断裂[3]。哀牢山变质岩系是本区最古老的地层[1],构成哀牢山的主体[11]。哀牢山断裂带东侧为扬子地块,西侧为思茅地块。

    本次研究的仰宗流纹斑岩位于云南红河州绿春县九甲-安定断裂北东侧仰宗断片内,总面积84km2,岩体呈不规则的似椭圆状,长宽比大于3:1,岩体长轴受断裂构造控制明显,呈NW—SE向延伸,岩体中部及边缘多被断裂切割,侵入下志留统砂岩中,岩体南侧与上三叠统歪古村组砂泥岩呈断裂接触。岩石呈浅棕色、棕灰色,风化面呈黄棕色、黄褐色,含斑-斑状结构,斑晶熔蚀结构发育,基质为隐晶质,局部含脱玻化玻璃质,部分具球粒结构,块状构造,局部变余珍珠构造 (图 2-a)。斑晶无序,不均匀分布,主要成分为中长石 (含量≤15%,An=30~32)、石英 (分布不均,少时≤5%,多时达10%~15%)、钾长石 (分布不均,少时≤5%,多时可达10%~15%,最多可达20%),暗色矿物黑云母、角闪石偶见。中长石为中细粒自形板状,常熔蚀呈港湾状,局部呈聚合斑状,可见聚片双晶,但多因蚀变而模糊,裂隙发育,局部被绢云母取代并构成交代假象,也见铁质浸染。钾长石与中长石形态相似,也为中细粒自形板状,常熔蚀呈港湾状 (图 2-b),局部有聚合斑状,未见双晶,表面因粘土化而模糊,裂隙发育;暗色矿物少见,其中黑云母为不规则片状,蚀变强烈,光性较弱,多色性不明显,几乎全被绿泥石交代而残存;偶见细粒角闪石,绿色,包裹与斜长石变晶边缘。基质含量变化于70%~95%之间,由隐晶质状长英质组成,部分可见脱玻化,在粒度上可以区分,且见于玻璃质转变的长英质分布处,在单偏光显微镜下仍可见残余珍珠状构造;部分长英质也可组成球粒结构。副矿物为磁铁矿、褐铁矿,偶见锆石,局部见晚期石英细脉穿插,裂隙及粒间常为铁染。

    图  2  样品野外(a)和镜下照片(b)
    a—流纹斑岩;b—中长石斑晶呈熔蚀样状(-)
    Figure  2.  Macroscopic (a) and microscopic (b) photographs of samples

    对新鲜的样品通过人工重砂法选出锆石,在双目显微镜下挑选出晶形较好、无裂隙或裂隙较少、无包体、较干净透明的锆石颗粒,在玻璃板上将其用环氧树脂固定、抛光,然后拍摄反射光、透射光及阴极发光 (CL) 图像,以此为依据选择最佳分析点——避开裂纹和包裹体的区域及可能为不同时代过渡的晶域。锆石U-Pb同位素分析在中国科学院广州地球化学研究所同位素地球化学国家重点实验室的ICP-MS Elan6100DRC激光探针上完成,同位素比值的计算采用Gliter4.0程序[13],普通Pb校正采用Anderson[14]的方法,年龄计算及U-Pb谐和图绘制用Isoplot (ver2.49)[15]程序完成。

    全岩的主量和微量元素分析在四川省冶金地质岩矿测试中心的国家重点实验室完成。主量元素分析用Rigaku RIX 2000型荧光光谱仪 (XRF) 分析,分析精度优于1%~5%,具体实验流程见参考文献[16]。微量元素分析采用Perkin-Elmer Sciex ELAN 6000型电感耦合等离子体质谱仪 (ICP-MS),分析精度优于2%~5%,详细实验方法见参考文献[17]。

    仰宗流纹斑岩样品PM2915Z中锆石呈无色-淡黄色,部分为浅褐色,以自形短柱状为主,少数呈长柱状或近粒状 (图 3)。CL图像中柱状锆石多具清晰的振荡环带,部分具边-核内部结构。18个测点中的3、7及12号点为核部,其余测点均在振荡环带上。18个测点的206Pb/238U年龄值范围为257~269Ma (表 1),206Pb/238U年龄加权平均值为263.1±2.3Ma,置信度为95%(图 4),代表流纹斑岩的形成年龄,以此确定该岩体为晚二叠世岩浆的产物。

    图  3  样品PM15Z流纹斑岩锆石颗粒阴极发光(CL)图像
    Figure  3.  CL images of zircons in rhyolite porphyry
    图  4  仰宗流纹斑岩锆石U-Pb年龄谐和图 (a) 及加权平均年龄图 (b)
    Figure  4.  U-Pb concordia diagram (a) and weighted mean age diagram (b) for zircons of the Yangzong rhyolite porphyry
    表  1  仰宗流纹斑岩LA-ICP-MS锆石U-Th-Pb同位素测试结果
    Table  1.  LA-ICP-MS zircon U-Th-Pb analytical results of the Yangzong rhyolite porphyry
    测点含量/10-6Th/U207Pb/206Pb206Pb/238U207Pb/235U同位素年龄/Ma
    PbThU206Pb/238U207Pb/235U206Pb/206Pb
    1141413170.450.053430.000830.042580.000400.31370.0053268.82.5277.04.7347.235.11
    215853780.230.051020.000720.041540.000360.29220.0044262.42.3260.33.9241.832.6
    3161453810.380.051560.000740.040900.000340.29080.0042258.42.2259.23.7266.232.8
    4161433710.390.057680.001820.041970.000440.33380.0130265.02.8292.411.9517.769.2
    5151453540.410.050510.000740.042370.000380.29510.0047267.52.4262.64.2218.733.8
    64324610780.230.050600.000270.040990.000370.28600.0022259.02.4255.42.0222.512.4
    7252985910.500.050440.000600.040610.000330.28240.0036256.62.1252.63.2215.227.5
    8171804220.430.049010.000740.040820.000320.27590.0043257.92.0247.43.9148.435.2
    9141523340.450.050590.000830.040720.000330.28400.0049257.32.1253.84.4222.038.0
    10151143580.320.052990.000890.042530.000390.31070.0058268.52.5274.75.1328.337.9
    11121392820.490.053720.001280.041740.000420.30920.0074263.62.7273.56.5359.453.7
    1214223480.060.052270.000810.041960.000360.30240.0048265.02.3268.24.3297.035.3
    13191354630.290.051700.000670.041210.000440.29380.0046260.42.8261.54.1272.029.8
    149652210.290.052500.001150.042450.000410.30730.0073268.02.6272.16.5307.150.1
    15211275110.250.054140.000560.042330.000430.31600.0040267.22.7278.83.5376.923.4
    1620974780.200.056830.000620.042090.000520.32980.0057265.83.3289.45.0484.924.2
    17141233250.380.051570.000730.042670.000390.30340.0045269.32.4269.14.0266.632.6
    18121242730.450.053090.000860.042210.000360.30900.0054266.52.3273.44.7332.436.9
    下载: 导出CSV 
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    仰宗流纹斑岩的主量元素含量、CIPW标准矿物分子及主要参数见表 2。SiO2含量为71.08%~80.26%、平均74.38%,全碱 (Na2O + K2O) 含量为4.67%~8.67%、平均7.40%,且Na2O<K2O。与中国流纹岩[18]相比,具有贫钙、富硅钾的特点。其CIPW标准矿物分子中多含C;A/NCK值多大于1.0,为铝过饱和型;σ<3.3,属高钾钙碱性系列,AR数值特征也表明此特点;根据阳离子参数特征 (图 5),样品投点落于同碰撞 (S型) 花岗岩及造山期后A型花岗岩附近;在Pearce图解 (图 6) 上,投点全部落入板内型花岗岩区。因此,认为其形成于碰撞期后陆内环境。

    表  2  仰宗流纹斑岩主量、微量和稀土元素分析数据
    Table  2.  Major, trace elements and REE compositions of the Yangzong rhyolite porphyry
    样号PM2904H2PM2904H4PM2904H5PM3305H1PM2905H2PM2907H1PM2908H3PM2910H2PM2911H1PM2912H1
    SiO278.1275.0475.7881.8874.4070.3072.0472.0870.3873.94
    Al2O311.613.4013.959.9511.7513.4513.3513.1013.2513.65
    Fe2O30.100.310.510.022.382.032.391.992.671.44
    FeO0.280.520.220.150.601.490.452.531.710.67
    P2O50.0150.0150.0190.0270.0390.0420.0240.050.0540.011
    K2O4.144.825.852.926.366.797.424.415.536.05
    Na2O4.344.700.223.320.431.630.583.452.730.21
    MgO0.110.230.680.050.500.580.520.730.660.58
    CaO0.080.040.030.040.060.110.050.270.190.02
    TiO20.060.080.070.050.400.630.480.610.620.49
    MnO0.0260.0160.0320.0070.0330.0430.0350.0620.0490.026
    烧失量0.680.692.170.542.572.142.580.371.952.49
    总量99.5599.8699.5398.9599.5299.2399.9299.6599.8099.58
    Q47.6534.3340.1132.8832.0149.8145.6739.2142.5244.48
    An0.040.280.091.020.60.030.030.3300
    Ab3.7614.215.0529.423.631.831.4914.791.910.97
    Or38.8141.3545.1026.2533.4236.8540.1636.7644.8942.25
    C4.283.424.452.302.626.956.044.154.946.19
    Di0000000000
    Hy2.772.692.353.963.472.303.582.193.003.31
    Il0.791.230.951.171.210.960.940.850.860.87
    Mt1.812.391.832.912.911.252.021.661.841.87
    Ap0.090.100.060.120.130.030.060.060.060.07
    DI90.2289.8990.2688.5389.0688.4987.3290.7689.3287.70
    SI4.924.654.625.574.996.526.844.386.296.69
    AR3.714.283.963.854.192.693.063.653.733.11
    σ1.452.562.182.122.461.251.542.021.941.69
    NK6.798.428.007.868.266.266.727.757.636.97
    A/CNK1.5261.3151.4711.1971.2241.971.7741.4171.5641.773
    Sc7.089.798.109.919.695.667.045.876.777.07
    Cr17.6213.5915.0014.9812.7814.1213.0413.2613.8911.94
    Co5.315.546.566.795.873.924.193.644.955.07
    Ni10.816.0210.188.266.025.775.835.877.006.09
    Zn93.7051.0864.7877.2268.5235.7777.1437.4974.5342.14
    Rb313.5327.8340.2218.7263532.8499.5327.5387.1528.6
    Sr34.7553.9156.8446.4844.2831.6549.8078.8243.2653.01
    Cs5.664.635.243.154.149.1310.9610.6410.2813.62
    Ba796.3939.3955.8674.7820.3634.4867.1876.2783.4958.4
    Zr208.9393.5248.2402.3401.3333.8324.0307.1280.2301.9
    Ta1.051.341.211.311.361.361.311.221.271.25
    Th24.7932.7028.4732.4032.9534.8634.3132.6231.9032.60
    U5.206.675.996.656.976.897.026.336.526.35
    Hf5.8111.007.2010.9310.789.448.958.697.928.55
    Cu3.692.3517.242.492.681.924.233.090.925.02
     注:主量元素含量单位为%,微量和稀土元素为10-6;Q为CIPW标准矿物石英;σ为里特曼指数
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    图  5  R1-R2图解[19]
    Figure  5.  R1-R2 diagram
    图  6  构造环境图解[20]
    syn-COLG—同碰撞期花岗岩;VAG—火山弧花岗岩;ORG—洋脊型花岗岩;WPG—板内型花岗岩
    Figure  6.  Diagram of tectonic environment

    岩石的微量元素含量与世界相应岩类相比,具有Rb、Au、Th、U相对富集,Zr、Hf、K、As趋于富集,而Sr、Ta、Ba、Cr、Zn、W相对贫化的特点。

    岩石中大离子亲石元素丰度及稀土元素含量 (表 3) 变化特点反映了元素的迁移活动特征。岩石的地球化学型式 (图 7) 显示,岩石具有Cr强烈亏损的特点,可能暗示源区经历强烈分异或属于非下地壳-地幔源区。Sr负异常表明,Sr主要进入斜长石中,并经历结晶分异。Rb、Th、U、Yb等元素趋于富集,显示出不相容性。这些元素的变化不仅符合岩浆的一般演化规律,而且也表明了各单元之间存在成因联系和演化关系。

    表  3  仰宗流纹斑岩稀土元素丰度及主要参数
    Table  3.  REE analyses of the Yangzong rhyolite porphyry
    样号PM2904H2PM2904H4PM2904H5PM3305H1PM2905H2PM2907H1PM2908H3PM2910H2PM2911H1PM2912H1
    La40.2049.0242.2659.9950.6225.4960.1847.1042.9660.79
    Ce69.8294.5182.87109.8089.1972.5895.8587.989.02101.4
    Pr9.1312.499.2214.0413.086.0313.9811.778.8315.01
    Nd31.4547.4031.1551.7348.8022.6650.7044.5932.7358.93
    Sm6.7310.326.5010.7211.024.7011.659.686.3313.74
    Eu1.011.471.061.641.640.671.551.370.901.95
    Gd5.278.885.459.9010.274.849.288.895.6913.81
    Tb0.971.600.901.771.830.951.591.500.942.59
    Dy6.0010.325.9511.2611.687.089.979.465.9916.77
    Ho1.071.951.122.042.231.441.721.711.153.09
    Er3.065.653.345.726.24.275.034.873.398.00
    Tm0.480.910.530.910.940.710.840.750.571.18
    Yb2.945.383.255.585.764.185.014.363.346.66
    Lu0.430.810.490.870.860.630.790.680.520.95
    Y27.6150.1528.7357.0358.7838.0845.8745.5428.8889.56
    ΣREE178.56250.70194.10285.96254.11156.21268.15234.62202.35304.89
    LREE158.33215.2173.07247.89214.34132.12233.92202.41180.77251.84
    HREE20.2335.5021.0338.0739.7724.0934.2332.2121.5853.06
    LREE/ LaN7.836.068.236.515.395.486.836.288.384.75
    HREE/ YbN9.816.539.327.716.304.378.627.769.236.55
    δEu0.500.460.530.480.460.420.440.440.450.43
    δCe0.860.910.980.890.831.390.780.891.060.80
     注:样品从左到右序号为1~10,与图 7中序号对应
    下载: 导出CSV 
    | 显示表格
    图  7  稀土元素配分模式图 (a) 和原始地幔标准化蛛网图(b)(标准值据参考文献[21],样品序号见表 3
    Figure  7.  Chondrite-normalized REE patterns (a) and primitive mantle-normalized spider diagram (b) for Yangzong monzogranite porphyry

    稀土元素含量及参数 (表 3) 表明,除2个样品外,岩石稀土元素总量 (ΣREE) 均低于世界花岗岩,反映源区稀土元素亏损的特点;ΣREE平均值为232.97×10-6,重稀土元素 (HREE) 平均值为31.98 × 10-6,LREE/HREE平均值为6.57。岩石δCe大多小于1.0;δEu值在0.42~0.53之间,平均值为0.46,具负Eu异常。稀土元素配分模式均为富集“Eu谷”右倾型 (图 7)。

    目前关于哀牢山构造带南段火山岩形成时代的观点还存在争议。云南地矿局[3]对巴德轰花岗岩体测得黑云母K-Ar年龄为207Ma和217Ma;刘翠等[22]对绿春地区的流纹岩所测年龄为247.3Ma;云南地矿局[3]对新安寨花岗岩体研究,认为其侵位于晚三叠世;而刘汇川等[23]对其进行了修正,认为其侵位于晚二叠世—早三叠世 (251.6Ma)。本文对哀牢山构造带南段仰宗流纹斑岩进行的LAICP-MS锆石U-Pb定年结果显示,其年龄加权平均值为263.1±2.3Ma,说明其侵位于晚二叠世,与刘翠等[22]及刘汇川等[23]获得的结果相近。

    花岗岩成因类型的判定是花岗岩研究的一个基础问题,自19世纪70年代以来,以花岗岩物质来源为基础的分类方案受到学者们的普遍认同。根据物质来源将花岗岩划分为I型、S型、M型及A型[24]。一系列地球化学图解被广泛应用于花岗岩成因类型的判别[25];也有学者提出根据矿物组成划分,如角闪石、堇青石及碱性暗色矿物的出现分别被认为是判定I型、S型和A型花岗岩的矿物学标志[26]。对于经历过高程度分异演化的花岗岩,需要结合岩石学、矿物学、地球化学等多种证据进行综合判定[27]。本次研究的仰宗流纹斑岩,从矿物学及主、微量元素特征看,具有S型或A型花岗岩的特征。

    样品主量、微量元素特征显示,A/CNK值大于1.1,属过铝质花岗岩,符合A型花岗岩判别标志[27]。从微量元素特征看,样品的Rb/Sr值和Rb/Nd值均在4.16~16.83和4.23~23.51范围内,平均值分别为8.17和9.89,均明显高于中国东部的Rb/Sr值、Rb/Nd值 (分别为0.31和6.8)[28]和全球上地壳平均值 (分别为0.32和4.5)[29],表明晚二叠世仰宗流纹斑岩可能源自成熟度较高的地壳物质。

    目前学术界对昌宁孟连带作为古特提斯洋主洋的观点较一致,对其构造演化的各个阶段也做了大量的研究,如Jian等[30]、Li等[31]等。但是对位于扬子地块和思茅印支板块之间的金沙江-哀牢山-松马构造带,在古生代—早中生代是古特提斯支洋还是弧后盆地还存在争议。刘翠等[22]认为,绿春地区247.3Ma的流纹岩形成于成熟岛弧向陆陆碰撞过渡的构造环境;Zi等[32]认为,金沙江白马雪山的花岗质侵入体 (249Ma) 形成于岛弧向弧陆或陆陆碰撞转化的构造环境;刘汇川等[29]则认为,新安寨花岗岩体 (251.6Ma) 形成于岛弧向陆陆碰撞转化或陆陆 (陆弧) 碰撞环境。本次研究的仰宗流纹斑岩岩体与上述岩体同处于哀牢山构造带中,其形成时代也与之相近,在花岗岩构造环境判别图上同样投点于板内型花岗岩区,说明该岩体形成于碰撞期后陆内构造环境。

    前人对哀牢山构造带的古特提斯支洋或弧后盆地做了大量的研究,但晚古生代—早中生代的构造演化时限仍不确定。本次研究表明,哀牢山支洋或弧后盆地在古特提斯主洋向思茅印支板块之下俯冲及扬子地块西缘峨眉山地幔柱上侵的动力下,在晚二叠世 (263.1±2.3Ma) 可能已经闭合。

    (1) 仰宗流纹斑岩样品中锆石U-Pb年龄加权平均值为263.1±2.3Ma,即其形成于晚二叠世。

    (2) 岩石地球化学特征显示,云南绿春县仰宗流纹斑岩样品为贫钙、富钾,为过铝质高钾钙碱系列,具负Eu异常,轻、重稀土元素分馏明显,Rb、Th、U相对富集,Hf、Ni、Cs、Zr、As、K趋于富集,而Sr、Ta、Ba、Cr、Zn、W相对贫化,说明岩浆在后期演化过程中经历了较强的结晶分异作用。岩石类型多为S型或A型花岗岩,物质来源可能为地壳的部分熔融。

    (3) 仰宗流纹斑岩属过铝饱和型,形成于碰撞期后陆内构造环境,表明哀牢山构造带的古特提斯支洋或弧后盆地在晚二叠世 (263.1±2.3Ma) 可能已经闭合。

    致谢: 野外工作得到成都理工大学邓江红、吴德超等教授的大力支持,中国科学院广州地球化学研究所邵同宾博士提供了很多宝贵意见和建议,在此表示诚挚的感谢。
  • 图  1   区域构造图 (a) 及仰宗地区地质略图 (b)

    Figure  1.   Regional structure (a) and geological sketch map of Yangzong area (b)

    图  2   样品野外(a)和镜下照片(b)

    a—流纹斑岩;b—中长石斑晶呈熔蚀样状(-)

    Figure  2.   Macroscopic (a) and microscopic (b) photographs of samples

    图  3   样品PM15Z流纹斑岩锆石颗粒阴极发光(CL)图像

    Figure  3.   CL images of zircons in rhyolite porphyry

    图  4   仰宗流纹斑岩锆石U-Pb年龄谐和图 (a) 及加权平均年龄图 (b)

    Figure  4.   U-Pb concordia diagram (a) and weighted mean age diagram (b) for zircons of the Yangzong rhyolite porphyry

    图  5   R1-R2图解[19]

    Figure  5.   R1-R2 diagram

    图  6   构造环境图解[20]

    syn-COLG—同碰撞期花岗岩;VAG—火山弧花岗岩;ORG—洋脊型花岗岩;WPG—板内型花岗岩

    Figure  6.   Diagram of tectonic environment

    图  7   稀土元素配分模式图 (a) 和原始地幔标准化蛛网图(b)(标准值据参考文献[21],样品序号见表 3

    Figure  7.   Chondrite-normalized REE patterns (a) and primitive mantle-normalized spider diagram (b) for Yangzong monzogranite porphyry

    表  1   仰宗流纹斑岩LA-ICP-MS锆石U-Th-Pb同位素测试结果

    Table  1   LA-ICP-MS zircon U-Th-Pb analytical results of the Yangzong rhyolite porphyry

    测点含量/10-6Th/U207Pb/206Pb206Pb/238U207Pb/235U同位素年龄/Ma
    PbThU206Pb/238U207Pb/235U206Pb/206Pb
    1141413170.450.053430.000830.042580.000400.31370.0053268.82.5277.04.7347.235.11
    215853780.230.051020.000720.041540.000360.29220.0044262.42.3260.33.9241.832.6
    3161453810.380.051560.000740.040900.000340.29080.0042258.42.2259.23.7266.232.8
    4161433710.390.057680.001820.041970.000440.33380.0130265.02.8292.411.9517.769.2
    5151453540.410.050510.000740.042370.000380.29510.0047267.52.4262.64.2218.733.8
    64324610780.230.050600.000270.040990.000370.28600.0022259.02.4255.42.0222.512.4
    7252985910.500.050440.000600.040610.000330.28240.0036256.62.1252.63.2215.227.5
    8171804220.430.049010.000740.040820.000320.27590.0043257.92.0247.43.9148.435.2
    9141523340.450.050590.000830.040720.000330.28400.0049257.32.1253.84.4222.038.0
    10151143580.320.052990.000890.042530.000390.31070.0058268.52.5274.75.1328.337.9
    11121392820.490.053720.001280.041740.000420.30920.0074263.62.7273.56.5359.453.7
    1214223480.060.052270.000810.041960.000360.30240.0048265.02.3268.24.3297.035.3
    13191354630.290.051700.000670.041210.000440.29380.0046260.42.8261.54.1272.029.8
    149652210.290.052500.001150.042450.000410.30730.0073268.02.6272.16.5307.150.1
    15211275110.250.054140.000560.042330.000430.31600.0040267.22.7278.83.5376.923.4
    1620974780.200.056830.000620.042090.000520.32980.0057265.83.3289.45.0484.924.2
    17141233250.380.051570.000730.042670.000390.30340.0045269.32.4269.14.0266.632.6
    18121242730.450.053090.000860.042210.000360.30900.0054266.52.3273.44.7332.436.9
    下载: 导出CSV

    表  2   仰宗流纹斑岩主量、微量和稀土元素分析数据

    Table  2   Major, trace elements and REE compositions of the Yangzong rhyolite porphyry

    样号PM2904H2PM2904H4PM2904H5PM3305H1PM2905H2PM2907H1PM2908H3PM2910H2PM2911H1PM2912H1
    SiO278.1275.0475.7881.8874.4070.3072.0472.0870.3873.94
    Al2O311.613.4013.959.9511.7513.4513.3513.1013.2513.65
    Fe2O30.100.310.510.022.382.032.391.992.671.44
    FeO0.280.520.220.150.601.490.452.531.710.67
    P2O50.0150.0150.0190.0270.0390.0420.0240.050.0540.011
    K2O4.144.825.852.926.366.797.424.415.536.05
    Na2O4.344.700.223.320.431.630.583.452.730.21
    MgO0.110.230.680.050.500.580.520.730.660.58
    CaO0.080.040.030.040.060.110.050.270.190.02
    TiO20.060.080.070.050.400.630.480.610.620.49
    MnO0.0260.0160.0320.0070.0330.0430.0350.0620.0490.026
    烧失量0.680.692.170.542.572.142.580.371.952.49
    总量99.5599.8699.5398.9599.5299.2399.9299.6599.8099.58
    Q47.6534.3340.1132.8832.0149.8145.6739.2142.5244.48
    An0.040.280.091.020.60.030.030.3300
    Ab3.7614.215.0529.423.631.831.4914.791.910.97
    Or38.8141.3545.1026.2533.4236.8540.1636.7644.8942.25
    C4.283.424.452.302.626.956.044.154.946.19
    Di0000000000
    Hy2.772.692.353.963.472.303.582.193.003.31
    Il0.791.230.951.171.210.960.940.850.860.87
    Mt1.812.391.832.912.911.252.021.661.841.87
    Ap0.090.100.060.120.130.030.060.060.060.07
    DI90.2289.8990.2688.5389.0688.4987.3290.7689.3287.70
    SI4.924.654.625.574.996.526.844.386.296.69
    AR3.714.283.963.854.192.693.063.653.733.11
    σ1.452.562.182.122.461.251.542.021.941.69
    NK6.798.428.007.868.266.266.727.757.636.97
    A/CNK1.5261.3151.4711.1971.2241.971.7741.4171.5641.773
    Sc7.089.798.109.919.695.667.045.876.777.07
    Cr17.6213.5915.0014.9812.7814.1213.0413.2613.8911.94
    Co5.315.546.566.795.873.924.193.644.955.07
    Ni10.816.0210.188.266.025.775.835.877.006.09
    Zn93.7051.0864.7877.2268.5235.7777.1437.4974.5342.14
    Rb313.5327.8340.2218.7263532.8499.5327.5387.1528.6
    Sr34.7553.9156.8446.4844.2831.6549.8078.8243.2653.01
    Cs5.664.635.243.154.149.1310.9610.6410.2813.62
    Ba796.3939.3955.8674.7820.3634.4867.1876.2783.4958.4
    Zr208.9393.5248.2402.3401.3333.8324.0307.1280.2301.9
    Ta1.051.341.211.311.361.361.311.221.271.25
    Th24.7932.7028.4732.4032.9534.8634.3132.6231.9032.60
    U5.206.675.996.656.976.897.026.336.526.35
    Hf5.8111.007.2010.9310.789.448.958.697.928.55
    Cu3.692.3517.242.492.681.924.233.090.925.02
     注:主量元素含量单位为%,微量和稀土元素为10-6;Q为CIPW标准矿物石英;σ为里特曼指数
    下载: 导出CSV

    表  3   仰宗流纹斑岩稀土元素丰度及主要参数

    Table  3   REE analyses of the Yangzong rhyolite porphyry

    样号PM2904H2PM2904H4PM2904H5PM3305H1PM2905H2PM2907H1PM2908H3PM2910H2PM2911H1PM2912H1
    La40.2049.0242.2659.9950.6225.4960.1847.1042.9660.79
    Ce69.8294.5182.87109.8089.1972.5895.8587.989.02101.4
    Pr9.1312.499.2214.0413.086.0313.9811.778.8315.01
    Nd31.4547.4031.1551.7348.8022.6650.7044.5932.7358.93
    Sm6.7310.326.5010.7211.024.7011.659.686.3313.74
    Eu1.011.471.061.641.640.671.551.370.901.95
    Gd5.278.885.459.9010.274.849.288.895.6913.81
    Tb0.971.600.901.771.830.951.591.500.942.59
    Dy6.0010.325.9511.2611.687.089.979.465.9916.77
    Ho1.071.951.122.042.231.441.721.711.153.09
    Er3.065.653.345.726.24.275.034.873.398.00
    Tm0.480.910.530.910.940.710.840.750.571.18
    Yb2.945.383.255.585.764.185.014.363.346.66
    Lu0.430.810.490.870.860.630.790.680.520.95
    Y27.6150.1528.7357.0358.7838.0845.8745.5428.8889.56
    ΣREE178.56250.70194.10285.96254.11156.21268.15234.62202.35304.89
    LREE158.33215.2173.07247.89214.34132.12233.92202.41180.77251.84
    HREE20.2335.5021.0338.0739.7724.0934.2332.2121.5853.06
    LREE/ LaN7.836.068.236.515.395.486.836.288.384.75
    HREE/ YbN9.816.539.327.716.304.378.627.769.236.55
    δEu0.500.460.530.480.460.420.440.440.450.43
    δCe0.860.910.980.890.831.390.780.891.060.80
     注:样品从左到右序号为1~10,与图 7中序号对应
    下载: 导出CSV
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  • 收稿日期:  2015-12-08
  • 修回日期:  2016-09-10
  • 网络出版日期:  2023-08-15
  • 刊出日期:  2017-02-28

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