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    西昆仑东段宿营地晚三叠世中性脉岩的锆石U-Pb定年、岩石地球化学特征及其意义

    黎有为 魏启荣 王程 丁鹏飞 刘小念 张小强 王敬元 刘文平 农明智

    黎有为, 魏启荣, 王程, 丁鹏飞, 刘小念, 张小强, 王敬元, 刘文平, 农明智, 2017. 西昆仑东段宿营地晚三叠世中性脉岩的锆石U-Pb定年、岩石地球化学特征及其意义. 地球科学, 42(6): 909-926. doi: 10.3799/dqkx.2017.083
    引用本文: 黎有为, 魏启荣, 王程, 丁鹏飞, 刘小念, 张小强, 王敬元, 刘文平, 农明智, 2017. 西昆仑东段宿营地晚三叠世中性脉岩的锆石U-Pb定年、岩石地球化学特征及其意义. 地球科学, 42(6): 909-926. doi: 10.3799/dqkx.2017.083
    Li Youwei, Wei Qirong, Wang Cheng, Ding Pengfei, Liu Xiaonian, Zhang Xiaoqiang, Wang Jingyuan, Liu Wenping, Nong Mingzhi, 2017. Zircon U-Pb Dating and Geochemistry of Late Triassic Intermediate Dykes in Suyingdi, Eastern Section of West Kunlun and Their Geological Significance. Earth Science, 42(6): 909-926. doi: 10.3799/dqkx.2017.083
    Citation: Li Youwei, Wei Qirong, Wang Cheng, Ding Pengfei, Liu Xiaonian, Zhang Xiaoqiang, Wang Jingyuan, Liu Wenping, Nong Mingzhi, 2017. Zircon U-Pb Dating and Geochemistry of Late Triassic Intermediate Dykes in Suyingdi, Eastern Section of West Kunlun and Their Geological Significance. Earth Science, 42(6): 909-926. doi: 10.3799/dqkx.2017.083

    西昆仑东段宿营地晚三叠世中性脉岩的锆石U-Pb定年、岩石地球化学特征及其意义

    doi: 10.3799/dqkx.2017.083
    基金项目: 

    贵州省科技计划项目 黔科合SY字[2012]3031号

    贵州省工程技术研究中心项目 黔科合G字[2014]4004号

    中国地质调查局项目 1212011220636

    详细信息
      作者简介:

      黎有为(1990-),男,助理研究员,主要从事岩浆岩与成矿研究.ORCID:0000-0002-9446-1371.E-mail:liyouwei668@163.com

      通讯作者: 魏启荣,E-mail: weiqr1030@cug.edu.cn
    • 中图分类号: P588.1

    Zircon U-Pb Dating and Geochemistry of Late Triassic Intermediate Dykes in Suyingdi, Eastern Section of West Kunlun and Their Geological Significance

    • 摘要: 为了研究西昆仑造山带东段古特提斯构造-岩浆演化,提升区域研究程度,对宿营地脉岩进行系统的野外地质调查、岩相学、LA-ICP-MS锆石U-Pb定年、岩石地球化学研究.脉岩呈NE向成群成带分布;岩石类型为(含石榴)闪长玢岩、角闪安山玢岩及闪斜煌斑岩;获得(含石榴)闪长玢岩LA-ICP-MS锆石U-Pb加权平均年龄(214±1)~(219±1) Ma,形成于晚三叠世,是印支晚期构造-岩浆活动产物;脉岩主要为钙碱性系列岩石,表现出中Si(SiO2=53.92%~62.95%)、高Al(Al2O3=15.99%~17.69%)、富Na(Na2O=2.63%~6.09%、Na2O/K2O=1.09~8.30)、低Ti(Ti2O=0.50%~0.76%)、低P(P2O5=0.14%~0.23%)、Mg(Mg#=37.73~59.32) 变化大等主量元素特征,铝饱和指数(A/CNK)为0.92~1.36;脉岩富集LREE、Rb、Th、U、K,亏损HREE、Nb、Ta、P、Ti,(La/Yb)N=7.24~20.02,Ce、Eu异常不明显.结果表明,宿营地中性脉岩是西昆仑东段南缘晚三叠世古特提斯弧后拉张作用引起的壳-幔混合作用的产物.
    • 图 1  西昆仑东段宿营地地区地质简图

      Figure 1.  Geologic sketch of Suyingdi area, eastern section of West Kunlun

      WK.西昆仑地块;EK.东昆仑地块;QT.羌塘地块;BK.巴颜喀拉地块;AS.阿尔金断裂;ASN.阿尔金断裂北支;ASS.阿尔金断裂南支;HSS.红山顶-三道河子断裂;KMAS.康西瓦-木孜塔格-阿尼玛卿晚古生代结合带;XJS.西金乌兰-金沙江晚古生代结合带;1.第四系;2.下白垩统双伍山组;3.下三叠统西长沟组;4.中二叠统黄羊岭组;5.脉岩;6.断层;7.地质界线;8.产状;9.岩石化学分析样采样位置;10.锆石U-Pb年龄样采样位置;b图据(陈守建等,2011)

      图 2  西昆仑东段宿营地地区中性脉岩野外及镜下特征

      Figure 2.  Field photos and photomicrograph features of Suyingdi dykes

      a.闪长玢岩脉地貌特征;b.闪长玢岩脉与西长沟组的接触关系;c.闪长玢岩野外露头特征;d.含石榴闪长玢岩中的暗色包体;e.闪长玢岩镜下特征;f.含石榴闪长玢岩镜下特征;g.角闪安山玢岩镜下特征;h.闪斜煌斑岩镜下特征;Grt.石榴石;Mag.磁铁矿;Pl.斜长石;Qz.石英;Am.角闪石;下图同

      图 3  西昆仑东段宿营地中性脉岩中锆石阴极发光电子图像

      Figure 3.  CL image of zircon of Suyingdi dykes

      图 4  西昆仑东段宿营地中性脉岩中锆石U-Pb年龄谐和图

      Figure 4.  Zircon U-Pb concordia diagram of Suyingdi dykes

      图 5  西昆仑东段宿营地中性脉岩TAS图解(a)、FAM图解(b)、SiO2-K2O图解(c)和A/CNK-A/NK图解(d)

      Figure 5.  TAS (a), FAM (b), K2O-SiO2 (c) and A/NK-A/CNK (d) diagram of Suyingdi dykes

      1.橄榄辉长岩;2.辉长岩;3.辉长闪长岩;4.闪长岩;5.花岗闪长岩;6.花岗岩;7.硅英岩;8.二长辉长岩;9.二长闪长岩;10.二长岩;11.石英二长岩;12.正长岩;13.似长辉长岩;14.似长二长闪长岩;15.似长正长闪长岩;16.似长正长岩;17.似长岩;18.霓方钠岩/磷霞岩/粗白榴岩;Ir-Irvine分界线(Irvine and Baragar, 1971);A.碱性系列;S.亚碱性系列;TH.拉斑玄武岩系列;CA.钙碱性系列;数据来源:东昆仑同期石榴闪长玢岩(Yuan et al., 2008);a图据Cox et al.(1979);b图据Irvine and Baragar(1971);c图据Peccerillo and Taylor(1976);d图据Maniar and Piccolli(1989)

      图 6  西昆仑东段宿营地中性脉岩稀土元素球粒陨石标准化配分曲线(a)和微量元素原始地幔标准化蛛网图(b)

      Figure 6.  REE distribution pattern (a) and trace element spidergram (b) of Suyingdi dykes

      东昆仑同期石榴闪长玢岩数据同图 5;球粒陨石标准化值据Sun and McDonough(1989)

      图 7  西昆仑东段宿营地中性脉岩的SiO2-REE(a)和SiO2-Y(b)图解

      Figure 7.  SiO2-REE (a) and SiO2-Y (b) diagram of Suyingdi dykes

      图 8  西昆仑东段宿营地中性脉岩YbN-(La/Yb)N判别图解

      Figure 8.  YbN-(La/Yb)N diagram of Suyingdi dykes

      底图据Castillo(2006)

      图 9  西昆仑东段宿营地中性脉岩Y-Nb(a)和Yb+Ta-Rb(b)构造环境判别图解

      Figure 9.  Y-Nb diagram (a) and Yb+Ta-Rb diagram (b) of tectonic setting discrimination of Suyingdi dykes

      syn-COLG.同碰撞花岗岩;WPG.板内花岗岩;ORG.洋脊花岗岩;VAG.岛弧花岗岩;底图据Pearce et al.(1984);图中东昆仑同期石榴闪长玢岩数据同图 6b

      表 1  西昆仑东段宿营地中性脉岩LA-ICP-MS锆石U-Pb同位素分析结果

      Table 1.  LA-ICP-MS U-Pb data of zircon of Suyingdi dykes

      点号 元素(10-6) 同位素比值 年龄(Ma)
      Pb Th U Th/U 207Pb*/206Pb* 1σ 207Pb*/235U 1σ 206Pb*/238U 1σ 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ
       样品2065-1(含石榴石闪长玢岩)
      B2065-1-125.51102.62337.860.300.050 110.002 460.237 530.011 290.034 530.000 3621111321692192
      B2065-1-226.1392.35324.200.280.057 170.002 640.272 020.012 490.034 410.000 45498102244102183
      B2065-1-338.88165.39452.290.370.055 870.002 650.265 030.012 320.034 500.000 43456106239102193
      B2065-1-417.6474.63235.510.320.049 450.002 510.234 220.011 760.034 490.000 49169114214102193
      B2065-1-521.1572.01271.730.270.059 840.003 120.287 000.015 410.034 440.000 52598113256122183
      B2065-1-628.99114.20305.740.370.053 870.002 990.253 460.013 420.034 210.000 45365126229112173
      B2065-1-743.34180.59560.370.320.049 190.001 820.235 340.008 780.034 510.000 401678221572192
      B2065-1-838.35154.17353.870.440.055 700.002 610.263 320.012 150.034 500.000 44439106237102193
      B2065-1-926.21100.26385.560.260.051 930.002 740.246 050.012 540.034 710.000 46283116223102203
      B2065-1-1039.30166.05460.520.360.049 690.002 750.234 820.012960.034430.00048189125214112183
      B2065-1-1139.84154.29558.050.280.046 990.002 260.222 610.011 120.034 470.000 435611120492183
      B2065-1-1244.97156.47653.560.240.048 780.002 190.229 800.010 820.034 540.000 5520010621092193
      B2065-1-1324.4699.03306.030.320.050 010.002 530.235 300.011 770.034 670.000 46195119215102203
      B2065-1-1433.92138.01453.020.300.051 190.001 960.241 360.009 310.034 500.000 402508922082192
      B2065-1-1540.44155.31424.030.370.052 130.002 330.248 190.011 190.034 510.000 3930010222592192
      B2065-1-1631.36130.60414.280.320.048 880.001 960.227 120.008 690.033 840.000 341439020872152
      B2065-1-1725.7698.27317.960.310.051 110.002 670.241 380.012 660.034 370.000 36256120220102182
      B2065-1-1825.22105.30300.200.350.052270.002 550.248 530.012 200.034 350.000 45298108225102183
      B2065-1-1941.85184.45497.650.370.049120.002 460.235 420.012 020.034 570.000 48154151215102193
      B2065-1-2055.15249.35614.870.410.046 620.001 640.222 090.008 100.034 130.000 30329120472162
      B2065-1-2131.72126.89421.190.300.049 120.001 930.233 820.008 660.034 700.000 371549321372202
      B2065-1-2228.49126.21308.690.410.050 890.002 260.241 570.010 620.034 550.000 4523510622092193
      B2065-1-2337.33158.03458.200.340.052 430.002 060.251 280.009 940.034 570.000 373068922882192
      B2065-1-2424.79103.02313.030.330.051 530.002 150.244830.009 980.034 540.000 3926510122282192
      B2065-1-2563.92288.87787.030.370.049 500.001 710.234 470.007 840.034 420.000 311727521462182
      B2065-1-2635.31161.15360.750.450.049 620.002 130.235 100.009 810.034 460.000 4017610221482182
       样品7168-1(含石榴石闪长玢岩)
      B7168-1-132.17199.86420.770.470.053 430.002 280.245 030.009 790.033 670.000 433469422382133
      B7168-1-238.15192.66529.960.360.053 250.001 960.248 370.008 990.033 790.000 353398322572142
      B7168-1-333.21104.42552.860.190.053 390.002 310.247 170.011 340.033 360.000 523469222492123
      B7168-1-445.70247.48676.780.370.053 290.001 770.247 900.008 370.033 580.000 403437422572132
      B7168-1-514.5765.61231.360.280.053 840.003 910.247 120.017 560.033 610.000 46365165224142133
      B7168-1-624.30124.89363.190.340.053 280.002 020.244 230.009 110.033 330.000 383399022272112
      B7168-1-750.99296.69751.900.390.053 970.001 760.252 540.007 890.033 920.000 333697422962152
       样品7168-1(含石榴石闪长玢岩)
      B7168-1-815.7492.11228.110.40 0.049 930.003 450.239 920.016 100.034 620.000 55191156218132193
      B7168-1-938.75213.54554.950.380.055 780.002 550.262 090.011 840.033 910.000 47443102236102153
      B7168-1-1049.05357.46601.430.590.052 640.001 770.247 950.008 240.033 980.000 383227622572152
      B7168-1-1121.71103.29367.840.280.051 000.002 610.241 040.011 610.034 390.000 4324311721992183
      B7168-1-1262.92360.59992.790.360.054 910.002 260.259 870.010 840.034 060.000 404098823592163
      B7168-1-1317.8989.40294.700.300.053 390.003 580.244 360.015 820.033 270.000 53346156222132113
      B7168-1-1435.35237.20516.560.460.055 310.002 400.257 030.011 360.033 430.000 444339823292123
      B7168-1-1537.54232.83515.510.450.051 930.001 920.246 430.008 880.034 320.000 392838522472182
       样品7742-1(闪长玢岩)
      B7742-1-123.89143.12385.300.37 0.049 660.002 030.237 460.010 040.034 650.000 431899621682203
      B7742-1-231.81195.07550.410.350.048 420.001 590.231 690.007 770.034 610.000 371207621262192
      B7742-1-316.68107.61278.100.390.049 780.002 160.237 060.010 280.034 850.000 4418310221682213
      B7742-1-422.99136.32385.130.350.054 020.002 240.259 460.010 930.034 700.000 383729323492202
      B7742-1-511.8069.18235.260.290.049 440.002 390.234 850.011 150.034 660.000 4816911521492203
      B7742-1-611.7078.94205.120.380.052 510.002 840.253 980.015 040.034 440.000 58309122230122184
      B7742-1-713.5781.88271.730.300.050 280.002 730.239 670.012 900.034 690.000 53209126218112203
      B7742-1-812.7276.45226.640.340.057 910.003 090.277 810.014 860.034 880.000 50528117249122213
      B7742-1-913.3282.17265.330.310.049 760.002 630.239 490.013 250.034 690.000 57183122218112204
      B7742-1-1018.71118.28342.540.350.051 580.002 290.239 880.010 180.034 100.000 4333310221882163
      B7742-1-1111.3668.84204.930.340.052 000.002 750.246 100.013 370.034 440.000 55287150223112183
      B7742-1-1222.82141.16361.450.390.048 940.003 320.233 390.015 820.034 640.000 43146152213132203
      B7742-1-1317.20105.70276.350.380.053 610.002 610.254 790.012 460.034 580.000 47354111230102193
      B7742-1-1418.43115.58288.760.400.053 750.002 500.253 690.011 770.034 420.000 42361104230102183
      B7742-1-159.5054.70151.330.360.055 050.004 870.248 280.019 600.034 520.000 82413200225162195
      B7742-1-1614.8379.88201.090.400.062 210.004 220.293 010.020 170.034 230.000 57681146261162174
      B7742-1-1714.5182.68236.900.350.051 390.002 580.243 770.012 410.034 470.000 47257115222102183
      B7742-1-1820.24107.12333.310.320.051 850.002 520.242 800.011 380.034 440.000 4128011122192183
      B7742-1-1915.5595.32259.400.370.052 890.002 910.248 210.013 100.034 530.000 55324131225112193
      B7742-1-2020.80117.26338.380.350.054 290.003 000.259 940.014 350.034 590.000 49383124235122193
      B7742-1-2114.3280.15233.050.340.051 240.003 300.242 820.016 110.034 560.000 69250150221132194
      B7742-1-2225.55174.52352.100.500.055 660.003 080.264 780.017 650.033 820.000 49439129239142143
      B7742-1-2326.34134.93278.380.480.051 360.001 850.337 410.012 490.047 630.000 562578329593003
      B7742-1-248.7056.88146.000.390.057 950.003 230.260 530.013 930.033 640.000 5252894235112133
       样品8070-1(闪长玢岩)
      B8070-1-141.12146.12651.060.220.050 090.002 020.240 140.009 510.034 340.000 371989921982182
       样品8070-1(闪长玢岩)
      B8070-1-222.6493.70267.210.350.054 380.003 710.255 480.016 520.034 490.000 47387149231132193
      B8070-1-328.05103.85437.840.240.054 610.002 540.257 940.012 170.033 880.000 36394106233102152
      B8070-1-430.98133.77389.540.340.047 930.002 630.225 250.012 260.033 740.000 3995126206102142
      B8070-1-523.3788.22397.870.220.047 260.002 490.225 740.012 430.034 350.000 4261122207102183
      B8070-1-625.7989.60412.860.220.053 020.002 950.249 260.013 910.034 100.000 46328126226112163
      B8070-1-728.86141.37355.920.400.053 300.002 800.243 900.012 380.033 480.000 41343120222102123
      B8070-1-815.7366.05181.450.360.054 050.004 280.255 020.019 810.033 800.000 49372180231162143
      B8070-1-927.79117.99396.100.300.050 520.004 000.239 180.019 110.034 420.000 54220179218162183
      B8070-1-1028.57121.01323.590.370.050 260.003 150.229 330.013 840.033 430.000 40206146210112123
      B8070-1-1127.35112.34368.390.300.048 840.002 920.236 820.015 150.034 310.000 41139137216122173
      B8070-1-1224.19107.20255.290.420.049 960.003 960.233 500.017 980.034 410.000 47195174213152183
      B8070-1-13191.69708.401097.300.650.050 990.001 670.317 420.010 040.045 140.000 432398128082853
      B8070-1-1438.35160.30517.710.310.052 650.002 410.245 350.010 530.034 080.000 3732210422392162
      B8070-1-1522.87107.13298.360.360.055 030.003 550.250 820.015 920.033 300.000 40413144227132113
      B8070-1-1633.95143.41405.770.350.046 640.002 480.217 220.011 620.033 830.000 3932122200102142
      B8070-1-1728.06120.75415.180.290.050 190.002 460.234 290.011 210.033 940.000 3721111821492152
      B8070-1-1818.7267.66292.380.230.050 470.003 310.233 610.014 760.033 660.000 47217152213122133
      B8070-1-1934.84168.15416.520.400.047 530.002 480.224 350.011 890.033 960.000 4276119206102153
      B8070-1-2013.5551.40146.090.350.047 680.005 370.215 370.023 280.033 880.000 5383248198192153
      B8070-1-2139.12176.36437.650.400.045 680.002 300.214 430.010 680.033 910.000 3419792152
      B8070-1-22 45.73 224.50 467.05 0.48 0.050 21 0.002 54 0.232 87 0.011 69 0.033 56 0.000 36 211 117 213 10 213 2
      注:Pb*代表放射性铅.
      下载: 导出CSV

      表 2  西昆仑东段宿营地中性脉岩主量元素分析结果(%)

      Table 2.  Major element result of Suyingdi dykes (%)

      样号岩性SiO2TiO2Al2O3Fe2O3FeOMnOMgOCaONa2OK2OP2O5H2O+CO2TotalMg#σA/CNK
      B0141-1闪长玢岩62.500.5017.201.043.610.091.582.805.900.750.171.302.4399.8637.772.271.10
      BP2-18-1闪长玢岩58.790.6517.411.104.650.122.504.564.151.200.172.472.0199.7743.631.811.06
      B4180-1闪长玢岩60.580.6816.781.284.500.091.972.696.090.920.162.471.6599.8637.842.801.05
      B3712-2闪长玢岩55.970.7517.320.915.810.134.155.103.261.200.183.940.3599.0852.231.531.09
      D4306-2闪长玢岩62.950.5417.451.203.890.101.804.114.131.230.152.200.2299.9738.741.441.12
      B7742-1闪长玢岩57.360.6616.270.724.650.102.604.742.632.400.173.503.6899.4846.151.761.05
      B7661-2闪长玢岩58.370.6916.620.515.430.113.165.133.721.410.173.171.3499.8348.381.710.98
      B2065-1含石榴石闪长玢岩59.120.6717.690.934.850.112.003.245.381.010.232.212.0399.4838.052.531.12
      B5218-1含石榴石闪长玢岩62.020.5917.271.333.150.071.815.043.501.780.181.731.1599.6242.101.471.02
      B7168-1含石榴石闪长玢岩61.150.5115.990.903.970.081.803.375.251.300.142.812.6899.9639.672.360.99
      B8094-1角闪安山玢岩61.160.6217.670.894.300.082.431.645.061.590.181.952.1699.7445.412.441.36
      B3569-1角闪安山玢岩57.840.6616.900.625.530.134.582.695.500.660.213.091.2799.6856.782.561.15
      B8104-1闪斜煌斑岩53.920.7617.301.395.090.135.316.423.141.820.182.731.6499.8259.392.250.92
      下载: 导出CSV

      表 3  西昆仑东段宿营地中性脉岩稀土元素分析结果(10-6)

      Table 3.  Rare earth element result of Suyingdi dykes (10-6)

      样号LaCePrNdSmEuGdTbDyHoErTmYbLuYΣREELREEHREELaN/YbNEu/Eu*Ce/Ce*
      B0141-122.8542.705.0822.213.741.503.360.421.940.361.060.170.950.1410.45106.4898.088.4017.201.270.93
      BP2-18-124.1943.425.0422.104.241.364.220.623.410.661.970.331.920.2817.52113.77100.3513.419.030.970.91
      B4180-126.7447.505.7625.194.431.254.200.583.020.581.780.291.660.2316.05123.21110.8712.3411.560.870.89
      B3712-227.9249.996.6429.265.851.645.420.884.720.972.910.412.640.4019.10139.64121.318.357.580.870.87
      D4306-222.5844.135.6624.944.541.434.230.653.370.671.840.261.700.2613.93116.25103.2812.989.560.980.93
      B7742-125.0148.696.0426.015.031.275.030.804.380.882.580.362.300.3517.35128.71112.0516.687.810.760.94
      B7661-227.4953.566.7830.145.761.685.520.884.780.982.880.412.720.4118.63144.00125.4118.587.240.900.93
      B2065-122.7741.925.2122.904.301.754.010.552.650.501.450.231.300.1913.67109.7298.8510.8812.591.270.91
      B5218-124.8446.245.6724.664.201.483.640.441.920.341.040.160.890.129.99115.62107.098.5520.021.130.92
      B7168-127.7453.096.7028.985.281.504.870.703.370.631.780.241.420.2112.81136.49123.2913.2214.030.890.93
      B8094-125.5843.635.1822.263.911.193.920.532.820.561.730.291.690.2615.21113.54101.7511.810.880.920.88
      B3569-124.9745.305.8825.594.941.634.710.743.900.822.340.332.140.3318.40123.62108.3115.318.371.020.88
      B8104-120.1736.804.4219.923.911.493.850.593.390.682.040.341.940.2918.4599.8286.7113.127.461.160.91
      下载: 导出CSV

      表 4  西昆仑东段宿营地中性脉岩微量元素分析结果(10-6)

      Table 4.  Trace element result of Suyingdi dykes (10-6)

      样号RbSrBaThUNbTaZrHfScVCrCoNiCuPbZn
      B0141-125.86416637.051.569.260.591123.017.3152.98.967.142.964.7618.196.5
      BP2-18-137.43413296.191.496.890.621293.5113.680.412.710.98.215.5211.583.3
      B4180-143.15302026.581.507.690.5872.11.9512.781.211.810.03.606.3818.8102
      B3712-230.94434857.151.699.510.651183.1621.412968.818.217.77.7548.5185
      D4306-247.63361805.341.158.490.611263.4110.572.79.917.866.994.2516.670.5
      B7742-190.32903676.861.516.870.541253.4416.175.742.213.518.25.7711.973.9
      B7661-233.73954096.251.448.660.591313.5117.080.646.113.725.56.8635.5118
      B2065-130.584117095.161.248.140.521303.359.5454.49.818.873.713.8512.2102
      B5218-171.33705406.471.568.880.561303.597.5354.512.07.165.098.1318.390.6
      B7168-139.94091317.272.126.210.571193.2312.759.011.89.638.177.8117.180.1
      B8094-151.74733738.792.047.480.621373.7812.082.837.610.811.03.4310.878.8
      B3569-117.814341715.881.6010.10.731393.5215.510613219.045.27.9622.178.0
      B8104-150.54397435.881.527.470.5149.41.3222.715511018.246.425.610.975.6
      下载: 导出CSV
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    • 收稿日期:  2016-12-01
    • 刊出日期:  2017-06-01

    西昆仑东段宿营地晚三叠世中性脉岩的锆石U-Pb定年、岩石地球化学特征及其意义

      通讯作者: 魏启荣, weiqr1030@cug.edu.cn
      作者简介: 黎有为(1990-),男,助理研究员,主要从事岩浆岩与成矿研究.ORCID:0000-0002-9446-1371.E-mail:liyouwei668@163.com
    • 1. 中国地质大学资源学院,湖北 武汉 430074
    • 2. 贵州省山地资源研究所,贵州 贵阳 550001
    基金项目:  贵州省科技计划项目 黔科合SY字[2012]3031号贵州省工程技术研究中心项目 黔科合G字[2014]4004号中国地质调查局项目 1212011220636

    摘要: 为了研究西昆仑造山带东段古特提斯构造-岩浆演化,提升区域研究程度,对宿营地脉岩进行系统的野外地质调查、岩相学、LA-ICP-MS锆石U-Pb定年、岩石地球化学研究.脉岩呈NE向成群成带分布;岩石类型为(含石榴)闪长玢岩、角闪安山玢岩及闪斜煌斑岩;获得(含石榴)闪长玢岩LA-ICP-MS锆石U-Pb加权平均年龄(214±1)~(219±1) Ma,形成于晚三叠世,是印支晚期构造-岩浆活动产物;脉岩主要为钙碱性系列岩石,表现出中Si(SiO2=53.92%~62.95%)、高Al(Al2O3=15.99%~17.69%)、富Na(Na2O=2.63%~6.09%、Na2O/K2O=1.09~8.30)、低Ti(Ti2O=0.50%~0.76%)、低P(P2O5=0.14%~0.23%)、Mg(Mg#=37.73~59.32) 变化大等主量元素特征,铝饱和指数(A/CNK)为0.92~1.36;脉岩富集LREE、Rb、Th、U、K,亏损HREE、Nb、Ta、P、Ti,(La/Yb)N=7.24~20.02,Ce、Eu异常不明显.结果表明,宿营地中性脉岩是西昆仑东段南缘晚三叠世古特提斯弧后拉张作用引起的壳-幔混合作用的产物.

    English Abstract

    • 位于青藏高原的古特提斯构造域形成于复杂的增生造山体制下,其内部物质记录了大量的构造-岩浆演化信息(Pan et al., 2012许志琴等, 2012, 2013王程等,2014).昆仑山南缘的康西瓦-木孜塔格-阿尼玛卿缝合带被认为是青藏高原北部古特提斯洋存在的直接证据(陈守建等,2011).前人研究表明,沿该缝合带两侧发育大量的二叠-三叠纪岩浆活动(吕金刚等,2006Yuan et al., 2008康磊等,2012Ding et al., 2014刘金龙等,2015Xia et al., 2015Zhang et al., 2016).但由于缝合带中段(西、东昆仑接合部位)人烟稀少,自然环境极其恶劣,导致研究程度低,高质量岩浆岩研究成果罕见报道,限制了对古特提斯构造-岩浆演化过程的全面认识.

      脉岩通常是区域性地壳引张环境下的岩浆产物,对研究地质构造演化过程具有重要的意义(Halls, 1982Zhan et al., 2015).脉岩作为母岩浆的代表,通常被用以反映源区物质组成(Westerman et al., 2003Xu et al., 2007).脉岩的空间分布规律,对古构造应力场的恢复有着指示意义(Ancochea et al., 2003).脉岩是研究深部岩石圈动力演化过程的重要“探针”(Poland et al., 2004梁涛等,2005付乐兵等,2010).在新近完成的新疆西昆仑1:5万4幅区域地质调查过程中,笔者首次系统地对宿营地地区出露的脉岩进行锆石U-Pb年代学、岩石地球化学的研究,为重新认识西昆仑东段古特提斯的构造-岩浆演化提供新思路.

      • 研究区位于新疆民丰县西昆仑宿营地一带,构造上位于巴颜喀拉地块(BK)西北缘,阿尔金断裂带(AS)南侧.该区为东昆仑地块(EK)、西昆仑地块(WK)及巴颜喀拉地块(BK)三者夹持的地带(图 1b).区内地层从老到新依次出露有中二叠统黄羊岭组(P2h)、下三叠统西长沟组(T1x)以及下白垩统双伍山组(K1s)地层,黄羊岭组及西长沟组地层劈理化普遍发育.区内主要发育2条大型断裂,从北至南为阿尔金断裂(AS)及红山顶-三道河子断裂(HSS).在黄羊岭组及西长沟组地层中多见NEE向同劈理逆冲断层及紧闭褶皱,属巴颜喀拉印支褶皱系,主要受碰撞造山作用影响(许志琴等,2012).

        图  1  西昆仑东段宿营地地区地质简图

        Figure 1.  Geologic sketch of Suyingdi area, eastern section of West Kunlun

        区内岩浆岩仅见脉岩,呈NE向成群成带分布于黄羊岭组及西长沟组地层中(图 1a).脉岩在地貌上表现为断续分布的小山丘(图 2a).脉岩多呈透镜状产出,规模大小不一,走向大多数50°~80°,个别90°~100°,一般延伸200~300 m,最长延伸可达3 000 m,脉岩围岩发育烘烤边.脉岩倾向150°~170°、倾角70°~80°,其产状与邻近的断层、褶皱轴面及围岩中发育的劈理面基本一致(图 2b),反映脉岩侵位于该区印支碰撞造山期压性应力之后.

        图  2  西昆仑东段宿营地地区中性脉岩野外及镜下特征

        Figure 2.  Field photos and photomicrograph features of Suyingdi dykes

        宿营地地区出露的脉岩主要为3种岩石类型:(含石榴)闪长玢岩(90%)、角闪安山玢岩(5%)、闪斜煌斑岩(3%).在脉岩中可见少量的暗色包体(图 2d).

        闪长玢岩(含石榴)呈灰黑色、灰绿色(图 2c2d),斑状结构(图 2e),块状构造.斑晶矿物多呈熔蚀港湾结构,其中斜长石约35%~45%,自形板状,偶见环带结构,大小0.1~1.5 mm;角闪石约10%~15%,自形柱状,长径0.2~2.5 mm;石英0%~15%,他形粒状,粒径0.1~0.5 mm;特别值得注意的是,约半数以上的闪长玢岩脉中发育有石榴石晶体,其含量2%~15%,均匀分布在脉岩露头内,石榴石在手标本上呈灰红色,自形粒状,粒径3~8 mm,在石榴石中包裹有斜长石、磷灰石、磁铁矿、角闪石等颗粒(图 2f).基质含量35%~50%,由显微粒状、显微柱状的斜长石、角闪石、石英等组成.副矿物可见磷灰石、磁铁矿、锆石等.

        角闪安山玢岩呈灰黑色,斑状结构,熔蚀港湾结构,块状构造.斑晶矿物多呈熔蚀港湾结构,为10%~20%的角闪石及10%~20%的斜长石,粒度0.3~2.0 mm.基质含量约60%~80%,由显微柱状、针状、粒状的角闪石、斜长石及玻璃质等组成,基质具玻晶交织结构(图 2g).

        闪斜煌斑岩呈灰黑色,煌斑结构(图 2h),块状构造.斑晶矿物角闪石约占40%~50%,自形柱状、粒状,熔蚀结构、暗化边结构发育,粒度为0.2~3.0 mm;斜长石约占5%~10%,自形板状,粒度在0.5~1.5 mm.基质含量约占40%~55%,由显微柱状、粒状的角闪石、斜长石等组成.

      • 本文对样品B2065-1、B7168-1(含石榴闪长玢岩)和B7742-1、B8070-1(闪长玢岩)进行了LA-ICP-MS锆石U-Pb测年.锆石分选由河北廊坊区域地质矿产调查研究所实验室完成,用磁法和重力法挑选,再将待测锆石以环氧树脂固定,磨蚀并抛光至锆石中心部位暴露.随后进行阴极发光(cathodoluminescence,CL)显微照相,结合透射光、反射光观察锆石内部结构.锆石LA-ICP-MS微区原位测试由中国地质大学(武汉)地质过程与矿产资源国家重点实验室Agilent 7500a电感耦合等离子体质谱仪与GeoLas 2005准分子激光剥蚀系统联机完成,激光斑束直径为32 μm.分析采用标准锆石91500作为外标标准矿物,以GJ-1作为内标标准矿物,用NISTSRM610来校正微量元素的含量.原始数据处理和年龄计算分别用ICPMSDataCal8.0(Liu et al., 2008Liu et al., 2010)和ISOPLOT(Ver6.0)(Ludwing, 2012)完成,并采用Anderson(2002)方法对普通铅进行较正.锆石的LA-ICP-MS分析结果见表 1所示.

        点号 元素(10-6) 同位素比值 年龄(Ma)
        Pb Th U Th/U 207Pb*/206Pb* 1σ 207Pb*/235U 1σ 206Pb*/238U 1σ 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ
         样品2065-1(含石榴石闪长玢岩)
        B2065-1-125.51102.62337.860.300.050 110.002 460.237 530.011 290.034 530.000 3621111321692192
        B2065-1-226.1392.35324.200.280.057 170.002 640.272 020.012 490.034 410.000 45498102244102183
        B2065-1-338.88165.39452.290.370.055 870.002 650.265 030.012 320.034 500.000 43456106239102193
        B2065-1-417.6474.63235.510.320.049 450.002 510.234 220.011 760.034 490.000 49169114214102193
        B2065-1-521.1572.01271.730.270.059 840.003 120.287 000.015 410.034 440.000 52598113256122183
        B2065-1-628.99114.20305.740.370.053 870.002 990.253 460.013 420.034 210.000 45365126229112173
        B2065-1-743.34180.59560.370.320.049 190.001 820.235 340.008 780.034 510.000 401678221572192
        B2065-1-838.35154.17353.870.440.055 700.002 610.263 320.012 150.034 500.000 44439106237102193
        B2065-1-926.21100.26385.560.260.051 930.002 740.246 050.012 540.034 710.000 46283116223102203
        B2065-1-1039.30166.05460.520.360.049 690.002 750.234 820.012960.034430.00048189125214112183
        B2065-1-1139.84154.29558.050.280.046 990.002 260.222 610.011 120.034 470.000 435611120492183
        B2065-1-1244.97156.47653.560.240.048 780.002 190.229 800.010 820.034 540.000 5520010621092193
        B2065-1-1324.4699.03306.030.320.050 010.002 530.235 300.011 770.034 670.000 46195119215102203
        B2065-1-1433.92138.01453.020.300.051 190.001 960.241 360.009 310.034 500.000 402508922082192
        B2065-1-1540.44155.31424.030.370.052 130.002 330.248 190.011 190.034 510.000 3930010222592192
        B2065-1-1631.36130.60414.280.320.048 880.001 960.227 120.008 690.033 840.000 341439020872152
        B2065-1-1725.7698.27317.960.310.051 110.002 670.241 380.012 660.034 370.000 36256120220102182
        B2065-1-1825.22105.30300.200.350.052270.002 550.248 530.012 200.034 350.000 45298108225102183
        B2065-1-1941.85184.45497.650.370.049120.002 460.235 420.012 020.034 570.000 48154151215102193
        B2065-1-2055.15249.35614.870.410.046 620.001 640.222 090.008 100.034 130.000 30329120472162
        B2065-1-2131.72126.89421.190.300.049 120.001 930.233 820.008 660.034 700.000 371549321372202
        B2065-1-2228.49126.21308.690.410.050 890.002 260.241 570.010 620.034 550.000 4523510622092193
        B2065-1-2337.33158.03458.200.340.052 430.002 060.251 280.009 940.034 570.000 373068922882192
        B2065-1-2424.79103.02313.030.330.051 530.002 150.244830.009 980.034 540.000 3926510122282192
        B2065-1-2563.92288.87787.030.370.049 500.001 710.234 470.007 840.034 420.000 311727521462182
        B2065-1-2635.31161.15360.750.450.049 620.002 130.235 100.009 810.034 460.000 4017610221482182
         样品7168-1(含石榴石闪长玢岩)
        B7168-1-132.17199.86420.770.470.053 430.002 280.245 030.009 790.033 670.000 433469422382133
        B7168-1-238.15192.66529.960.360.053 250.001 960.248 370.008 990.033 790.000 353398322572142
        B7168-1-333.21104.42552.860.190.053 390.002 310.247 170.011 340.033 360.000 523469222492123
        B7168-1-445.70247.48676.780.370.053 290.001 770.247 900.008 370.033 580.000 403437422572132
        B7168-1-514.5765.61231.360.280.053 840.003 910.247 120.017 560.033 610.000 46365165224142133
        B7168-1-624.30124.89363.190.340.053 280.002 020.244 230.009 110.033 330.000 383399022272112
        B7168-1-750.99296.69751.900.390.053 970.001 760.252 540.007 890.033 920.000 333697422962152
         样品7168-1(含石榴石闪长玢岩)
        B7168-1-815.7492.11228.110.40 0.049 930.003 450.239 920.016 100.034 620.000 55191156218132193
        B7168-1-938.75213.54554.950.380.055 780.002 550.262 090.011 840.033 910.000 47443102236102153
        B7168-1-1049.05357.46601.430.590.052 640.001 770.247 950.008 240.033 980.000 383227622572152
        B7168-1-1121.71103.29367.840.280.051 000.002 610.241 040.011 610.034 390.000 4324311721992183
        B7168-1-1262.92360.59992.790.360.054 910.002 260.259 870.010 840.034 060.000 404098823592163
        B7168-1-1317.8989.40294.700.300.053 390.003 580.244 360.015 820.033 270.000 53346156222132113
        B7168-1-1435.35237.20516.560.460.055 310.002 400.257 030.011 360.033 430.000 444339823292123
        B7168-1-1537.54232.83515.510.450.051 930.001 920.246 430.008 880.034 320.000 392838522472182
         样品7742-1(闪长玢岩)
        B7742-1-123.89143.12385.300.37 0.049 660.002 030.237 460.010 040.034 650.000 431899621682203
        B7742-1-231.81195.07550.410.350.048 420.001 590.231 690.007 770.034 610.000 371207621262192
        B7742-1-316.68107.61278.100.390.049 780.002 160.237 060.010 280.034 850.000 4418310221682213
        B7742-1-422.99136.32385.130.350.054 020.002 240.259 460.010 930.034 700.000 383729323492202
        B7742-1-511.8069.18235.260.290.049 440.002 390.234 850.011 150.034 660.000 4816911521492203
        B7742-1-611.7078.94205.120.380.052 510.002 840.253 980.015 040.034 440.000 58309122230122184
        B7742-1-713.5781.88271.730.300.050 280.002 730.239 670.012 900.034 690.000 53209126218112203
        B7742-1-812.7276.45226.640.340.057 910.003 090.277 810.014 860.034 880.000 50528117249122213
        B7742-1-913.3282.17265.330.310.049 760.002 630.239 490.013 250.034 690.000 57183122218112204
        B7742-1-1018.71118.28342.540.350.051 580.002 290.239 880.010 180.034 100.000 4333310221882163
        B7742-1-1111.3668.84204.930.340.052 000.002 750.246 100.013 370.034 440.000 55287150223112183
        B7742-1-1222.82141.16361.450.390.048 940.003 320.233 390.015 820.034 640.000 43146152213132203
        B7742-1-1317.20105.70276.350.380.053 610.002 610.254 790.012 460.034 580.000 47354111230102193
        B7742-1-1418.43115.58288.760.400.053 750.002 500.253 690.011 770.034 420.000 42361104230102183
        B7742-1-159.5054.70151.330.360.055 050.004 870.248 280.019 600.034 520.000 82413200225162195
        B7742-1-1614.8379.88201.090.400.062 210.004 220.293 010.020 170.034 230.000 57681146261162174
        B7742-1-1714.5182.68236.900.350.051 390.002 580.243 770.012 410.034 470.000 47257115222102183
        B7742-1-1820.24107.12333.310.320.051 850.002 520.242 800.011 380.034 440.000 4128011122192183
        B7742-1-1915.5595.32259.400.370.052 890.002 910.248 210.013 100.034 530.000 55324131225112193
        B7742-1-2020.80117.26338.380.350.054 290.003 000.259 940.014 350.034 590.000 49383124235122193
        B7742-1-2114.3280.15233.050.340.051 240.003 300.242 820.016 110.034 560.000 69250150221132194
        B7742-1-2225.55174.52352.100.500.055 660.003 080.264 780.017 650.033 820.000 49439129239142143
        B7742-1-2326.34134.93278.380.480.051 360.001 850.337 410.012 490.047 630.000 562578329593003
        B7742-1-248.7056.88146.000.390.057 950.003 230.260 530.013 930.033 640.000 5252894235112133
         样品8070-1(闪长玢岩)
        B8070-1-141.12146.12651.060.220.050 090.002 020.240 140.009 510.034 340.000 371989921982182
         样品8070-1(闪长玢岩)
        B8070-1-222.6493.70267.210.350.054 380.003 710.255 480.016 520.034 490.000 47387149231132193
        B8070-1-328.05103.85437.840.240.054 610.002 540.257 940.012 170.033 880.000 36394106233102152
        B8070-1-430.98133.77389.540.340.047 930.002 630.225 250.012 260.033 740.000 3995126206102142
        B8070-1-523.3788.22397.870.220.047 260.002 490.225 740.012 430.034 350.000 4261122207102183
        B8070-1-625.7989.60412.860.220.053 020.002 950.249 260.013 910.034 100.000 46328126226112163
        B8070-1-728.86141.37355.920.400.053 300.002 800.243 900.012 380.033 480.000 41343120222102123
        B8070-1-815.7366.05181.450.360.054 050.004 280.255 020.019 810.033 800.000 49372180231162143
        B8070-1-927.79117.99396.100.300.050 520.004 000.239 180.019 110.034 420.000 54220179218162183
        B8070-1-1028.57121.01323.590.370.050 260.003 150.229 330.013 840.033 430.000 40206146210112123
        B8070-1-1127.35112.34368.390.300.048 840.002 920.236 820.015 150.034 310.000 41139137216122173
        B8070-1-1224.19107.20255.290.420.049 960.003 960.233 500.017 980.034 410.000 47195174213152183
        B8070-1-13191.69708.401097.300.650.050 990.001 670.317 420.010 040.045 140.000 432398128082853
        B8070-1-1438.35160.30517.710.310.052 650.002 410.245 350.010 530.034 080.000 3732210422392162
        B8070-1-1522.87107.13298.360.360.055 030.003 550.250 820.015 920.033 300.000 40413144227132113
        B8070-1-1633.95143.41405.770.350.046 640.002 480.217 220.011 620.033 830.000 3932122200102142
        B8070-1-1728.06120.75415.180.290.050 190.002 460.234 290.011 210.033 940.000 3721111821492152
        B8070-1-1818.7267.66292.380.230.050 470.003 310.233 610.014 760.033 660.000 47217152213122133
        B8070-1-1934.84168.15416.520.400.047 530.002 480.224 350.011 890.033 960.000 4276119206102153
        B8070-1-2013.5551.40146.090.350.047 680.005 370.215 370.023 280.033 880.000 5383248198192153
        B8070-1-2139.12176.36437.650.400.045 680.002 300.214 430.010 680.033 910.000 3419792152
        B8070-1-22 45.73 224.50 467.05 0.48 0.050 21 0.002 54 0.232 87 0.011 69 0.033 56 0.000 36 211 117 213 10 213 2
        注:Pb*代表放射性铅.

        表 1  西昆仑东段宿营地中性脉岩LA-ICP-MS锆石U-Pb同位素分析结果

        Table 1.  LA-ICP-MS U-Pb data of zircon of Suyingdi dykes

      • 在4件样品中挑选的锆石矿物学特征相似,呈浅黄色-无色透明,半自形-自形粒状,形态多为长-短柱状,少数为四方双锥状.锆石晶棱锋锐,长度一般为80~250 μm,长宽比1:1~5:1,显示岩浆锆石特征.阴极发光(CL)电子图像(图 3)显示,锆石发育清晰的岩浆震荡环带,属典型的岩浆锆石(吴元保和郑永飞,2004).

        图  3  西昆仑东段宿营地中性脉岩中锆石阴极发光电子图像

        Figure 3.  CL image of zircon of Suyingdi dykes

        样品B2065-1(含石榴闪长玢岩)成功测定了26颗锆石,Th/U比值介于0.24~0.45,206Pb/238U加权平均年龄为218±1 Ma(MSWD=0.24)(图 4a);样品B7168-1(含石榴石闪长玢岩)成功测定了15颗锆石,Th/U比值介于0.19~0.59,206Pb/238U加权平均年龄为214±1 Ma(MSWD=1.00)(图 4b);样品B7742-1(闪长玢岩)成功测定了24颗锆石,除1颗锆石(B7742-1-23) 年龄较大(300±3 Ma)外,其余23颗Th/U比值介于0.29~0.50,206Pb/238U加权平均年龄为219±1 Ma(MSWD=0.37)(图 4c);样品B8070-1(闪长玢岩)成功测定了22颗锆石,除1颗锆石(B8070-1-13) 年龄较大(285±3 Ma)外,其余21颗Th/U比值介于0.22~0.65,其206Pb/238U加权平均年龄为215±1 Ma(MSWD=0.68)(图 4d).4件样品分别在谐和曲线附近形成集中的锆石群(图 4),锆石U-Pb年龄为(214±1)~(219±1) Ma,代表了样品脉岩的侵位年龄,表明宿营地地区的脉岩形成于晚三叠世(T3),是印支晚期构造-岩浆活动的产物.这一时期与古特提斯洋闭合导致的造山运动时间一致,该造山运动在昆仑造山带内已有许多年龄记录(莫宣学和潘桂棠,2006Pullen etal., 2008康磊等,2012).

        图  4  西昆仑东段宿营地中性脉岩中锆石U-Pb年龄谐和图

        Figure 4.  Zircon U-Pb concordia diagram of Suyingdi dykes

      • 为了探讨脉岩的岩石地球化学特征,笔者对10件(含石榴)闪长玢岩、2件角闪安山岩及1件闪斜煌斑岩样品进行了主量元素、稀土元素和微量元素的配套分析.样品的分析测试在西南冶金测试所完成.主量元素采用X-射线荧光熔片法(X-ray fluorescence,XRF)测定,分析精度小于1%,其中FeO、H2O+和CO2采用湿化学分析法测定.稀土元素和微量元素在电感耦合等离子质谱仪(inductively coupled plasma mass spectrometry,ICP-MS)中完成,分析精度优于6%.

      • 表 2显示,脉岩的SiO2含量为53.92%~62.95%;Al2O3含量为15.99%~17.69%;铝饱和指数A/CNK为0.92~1.36,在图 5d中多数样品落入过铝质区域,显示准铝质-过铝质特征;Na2O含量为2.63%~6.09%;K2O含量为0.66%~2.40%,Na2O/K2O比值为1.09~8.32,显示高度富钠的特征;TiO2含量为0.50%~0.76%;MgO含量为1.58%~5.31%,Mg#为37.73~59.32;P2O5含量为0.14%~0.23%.总体来说,岩石表现出高CaO、Al2O3、Na2O、MgO,低K2O、TiO2、P2O5的特征.在图 5a中,13件样品全部落入亚碱性系列,其中6件样品落入闪长岩范围内,5件样品落入花岗闪长岩范围内,1件样品落入石英二长岩范围内,1件样品落入辉长闪长岩范围内;在图 5b中,样品全部落入钙碱性系列;在图 5c中,脉岩样品大部分落入钙碱性系列区域中.

        样号岩性SiO2TiO2Al2O3Fe2O3FeOMnOMgOCaONa2OK2OP2O5H2O+CO2TotalMg#σA/CNK
        B0141-1闪长玢岩62.500.5017.201.043.610.091.582.805.900.750.171.302.4399.8637.772.271.10
        BP2-18-1闪长玢岩58.790.6517.411.104.650.122.504.564.151.200.172.472.0199.7743.631.811.06
        B4180-1闪长玢岩60.580.6816.781.284.500.091.972.696.090.920.162.471.6599.8637.842.801.05
        B3712-2闪长玢岩55.970.7517.320.915.810.134.155.103.261.200.183.940.3599.0852.231.531.09
        D4306-2闪长玢岩62.950.5417.451.203.890.101.804.114.131.230.152.200.2299.9738.741.441.12
        B7742-1闪长玢岩57.360.6616.270.724.650.102.604.742.632.400.173.503.6899.4846.151.761.05
        B7661-2闪长玢岩58.370.6916.620.515.430.113.165.133.721.410.173.171.3499.8348.381.710.98
        B2065-1含石榴石闪长玢岩59.120.6717.690.934.850.112.003.245.381.010.232.212.0399.4838.052.531.12
        B5218-1含石榴石闪长玢岩62.020.5917.271.333.150.071.815.043.501.780.181.731.1599.6242.101.471.02
        B7168-1含石榴石闪长玢岩61.150.5115.990.903.970.081.803.375.251.300.142.812.6899.9639.672.360.99
        B8094-1角闪安山玢岩61.160.6217.670.894.300.082.431.645.061.590.181.952.1699.7445.412.441.36
        B3569-1角闪安山玢岩57.840.6616.900.625.530.134.582.695.500.660.213.091.2799.6856.782.561.15
        B8104-1闪斜煌斑岩53.920.7617.301.395.090.135.316.423.141.820.182.731.6499.8259.392.250.92

        表 2  西昆仑东段宿营地中性脉岩主量元素分析结果(%)

        Table 2.  Major element result of Suyingdi dykes (%)

        图  5  西昆仑东段宿营地中性脉岩TAS图解(a)、FAM图解(b)、SiO2-K2O图解(c)和A/CNK-A/NK图解(d)

        Figure 5.  TAS (a), FAM (b), K2O-SiO2 (c) and A/NK-A/CNK (d) diagram of Suyingdi dykes

      • 表 3显示,脉岩的稀土总量ΣREE为99.82×10-6~144.00×10-6.脉岩样品Ce/Ce*=0.87~0.93,Eu/Eu*=0.76~1.27,不具明显的Eu、Ce异常,可能与斜长石在岩浆中富集有关.在图 6a中可以看出,脉岩样品的分配模式相似,表现为轻稀土富集的右倾型模式,其(La/Yb)N为7.24~20.02.

        样号LaCePrNdSmEuGdTbDyHoErTmYbLuYΣREELREEHREELaN/YbNEu/Eu*Ce/Ce*
        B0141-122.8542.705.0822.213.741.503.360.421.940.361.060.170.950.1410.45106.4898.088.4017.201.270.93
        BP2-18-124.1943.425.0422.104.241.364.220.623.410.661.970.331.920.2817.52113.77100.3513.419.030.970.91
        B4180-126.7447.505.7625.194.431.254.200.583.020.581.780.291.660.2316.05123.21110.8712.3411.560.870.89
        B3712-227.9249.996.6429.265.851.645.420.884.720.972.910.412.640.4019.10139.64121.318.357.580.870.87
        D4306-222.5844.135.6624.944.541.434.230.653.370.671.840.261.700.2613.93116.25103.2812.989.560.980.93
        B7742-125.0148.696.0426.015.031.275.030.804.380.882.580.362.300.3517.35128.71112.0516.687.810.760.94
        B7661-227.4953.566.7830.145.761.685.520.884.780.982.880.412.720.4118.63144.00125.4118.587.240.900.93
        B2065-122.7741.925.2122.904.301.754.010.552.650.501.450.231.300.1913.67109.7298.8510.8812.591.270.91
        B5218-124.8446.245.6724.664.201.483.640.441.920.341.040.160.890.129.99115.62107.098.5520.021.130.92
        B7168-127.7453.096.7028.985.281.504.870.703.370.631.780.241.420.2112.81136.49123.2913.2214.030.890.93
        B8094-125.5843.635.1822.263.911.193.920.532.820.561.730.291.690.2615.21113.54101.7511.810.880.920.88
        B3569-124.9745.305.8825.594.941.634.710.743.900.822.340.332.140.3318.40123.62108.3115.318.371.020.88
        B8104-120.1736.804.4219.923.911.493.850.593.390.682.040.341.940.2918.4599.8286.7113.127.461.160.91

        表 3  西昆仑东段宿营地中性脉岩稀土元素分析结果(10-6)

        Table 3.  Rare earth element result of Suyingdi dykes (10-6)

        图  6  西昆仑东段宿营地中性脉岩稀土元素球粒陨石标准化配分曲线(a)和微量元素原始地幔标准化蛛网图(b)

        Figure 6.  REE distribution pattern (a) and trace element spidergram (b) of Suyingdi dykes

      • 表 4显示,脉岩大离子亲石元素(LILE)中Rb、Sr、Ba含量分别为17.8×10-6~90.3×10-6、290×10-6~1 434×10-6、131×10-6~1 709×10-6;放射性生热元素(RPH)中Th、U含量分别为5.16×10-6~8.79×10-6、1.15×10-6~2.12×10-6;高场强元素(HFSE)中Nb、Ta、Zr、Hf含量分别为6.21×10-6~10.10×10-6、0.51×10-6~0.73×10-6、49.4×10-6~139.2×10-6、1.32×10-6~3.78×10-6;过渡元素(TE)中Cr、Ni含量变化范围较大,分别为8.96×10-6~132.00×10-6、2.96×10-6~46.00×10-6,Co含量为7.14×10-6~19.00×10-6.从图 6b中可以看出,脉岩分配模式相近,整体表现为右倾趋势,相对富集Rb、Ba、K、Sr、Th、U,亏损Nb、Ta、Ti、P、Y.

        样号RbSrBaThUNbTaZrHfScVCrCoNiCuPbZn
        B0141-125.86416637.051.569.260.591123.017.3152.98.967.142.964.7618.196.5
        BP2-18-137.43413296.191.496.890.621293.5113.680.412.710.98.215.5211.583.3
        B4180-143.15302026.581.507.690.5872.11.9512.781.211.810.03.606.3818.8102
        B3712-230.94434857.151.699.510.651183.1621.412968.818.217.77.7548.5185
        D4306-247.63361805.341.158.490.611263.4110.572.79.917.866.994.2516.670.5
        B7742-190.32903676.861.516.870.541253.4416.175.742.213.518.25.7711.973.9
        B7661-233.73954096.251.448.660.591313.5117.080.646.113.725.56.8635.5118
        B2065-130.584117095.161.248.140.521303.359.5454.49.818.873.713.8512.2102
        B5218-171.33705406.471.568.880.561303.597.5354.512.07.165.098.1318.390.6
        B7168-139.94091317.272.126.210.571193.2312.759.011.89.638.177.8117.180.1
        B8094-151.74733738.792.047.480.621373.7812.082.837.610.811.03.4310.878.8
        B3569-117.814341715.881.6010.10.731393.5215.510613219.045.27.9622.178.0
        B8104-150.54397435.881.527.470.5149.41.3222.715511018.246.425.610.975.6

        表 4  西昆仑东段宿营地中性脉岩微量元素分析结果(10-6)

        Table 4.  Trace element result of Suyingdi dykes (10-6)

      • 石榴石常见于变质岩、碎屑岩内,岩浆岩内发育石榴石的现象较为罕见,其通常有以下几种成因:(1) 捕获围岩而形成的捕掳晶(Warren, 1970);(2) 岩浆结晶矿物(Lackey et al., 2011);(3) 部分熔融残留体(Birch and Gleadow, 1974);(4) 转熔产物(Zeng et al., 2005);(5) 矽卡岩矿物(赖健清等,2015).宿营地中性脉岩侵入于碎屑岩地层中,围岩基本未发生变质作用,脉岩内石榴石分布均匀,而并非分布于脉岩边部,并且石榴石内未发现包含变质矿物,暗示其不是矽卡岩矿物或与围岩发生交代作用形成矿物,来自于围岩的可能性也不大.在区调工作及邻区资料中,笔者在周边未见有较老的岩浆岩地质体内发育石榴石,在脉岩暗色包体中也未见有石榴石存在,说明石榴石是部分熔融残留体或捕掳晶的可能性不大.宿营地脉岩中的石榴石自形程度较高,包含有斜长石、磷灰石、磁铁矿、角闪石等颗粒(图 2f),包含矿物与脉岩中其他结晶矿物成分一致,而并未见到变质矿物,暗示石榴石很有可能是从母岩浆中结晶形成的(Kawabata and Takafuji, 2005Yuan et al., 2008Krippner et al., 2014Samadia et al., 2014),并且结晶较其他矿物晚.在脉岩的SiO2-HREE、SiO2-Y图解(图 7a7b)中,发现它们具有一定的线性关系,说明母岩浆可能经历了一定的石榴石分离结晶作用过程.结合邻区同期含石榴英云闪长玢岩(213 Ma)内石榴石斑晶(Yuan et al., 2008)的发现,笔者认为脉岩中石榴石最有可能是岩浆结晶矿物,同时也不排除有转熔作用发生的可能性.

        图  7  西昆仑东段宿营地中性脉岩的SiO2-REE(a)和SiO2-Y(b)图解

        Figure 7.  SiO2-REE (a) and SiO2-Y (b) diagram of Suyingdi dykes

      • 宿营地脉岩主要为中性,以钙碱性系列岩石为主,主量元素富Na、高Al,呈现出准铝质及轻微过铝质特征;微量元素富集LILE,亏损HFSE;富集轻稀土元素,亏损重稀土元素,La/Yb、(La/Yb)N、Sr/Y、Sr较高;Mg及过渡元素(TE)变化范围较大,部分含量较高.目前已有实验结果表明,下地壳熔融产物以Mg#<45为其特征(Rapp and Watson, 1995),显然与本区部分脉岩Mg#>45不符,因此脉岩成因不能单纯用下地壳部分熔融模式解释.这类富Mg闪长质岩浆还可能有如下几种成因模式:(1) 含水地幔橄榄岩部分熔融形成的幔源基性岩浆分离结晶作用(Tatsumi and Hanyu, 2003);(2) 俯冲板片部分熔融形成的熔体与地幔楔反应形成的高镁埃达克岩(Rapp et al., 1999);(3) 拆沉下地壳起源的熔体与软流圈地幔相互作用(Gao et al., 2004);(4) 壳-幔岩浆混合作用(刘金龙等,2015).

        宿营地脉岩的Al2O3、Na2O/K2O、Sr、Sr/Y和La/Yb较高,Eu异常不明显,并且Nb、Ta、Ti显著亏损,说明脉岩不太可能是幔源基性岩浆分离结晶作用形成(陈国超等,2013).研究表明,昆仑造山带南缘的古特提斯洋盆于晚古生代拉张裂解,并不断扩张至二叠纪开始北向俯冲于昆仑地体之下(许志琴等,2001Bian et al., 2004),于中三叠世之前就已发生碰撞造山作用(张传林等,2005陈守建等,2011康磊等,2012).宿营地脉岩形成于晚三叠世(214~219 Ma),如果是上述第(2) 种成因,俯冲板片形成的熔体应在中三叠世之前就已形成,不可能在晚三叠世才上升侵位,并且在图 8中,脉岩投点主要落入经典岛弧岩石区,因此第(2) 种成因模式不是脉岩主要的成因模式.下地壳拆沉经历了下地壳压力增加并转变为榴辉岩相、榴辉岩部分熔融及交代岩石圈地幔等过程(张旗等,2006陈国超等,2013).Foley et al.(2002)认为,角闪岩及石榴角闪岩部分熔融产生的熔体以低Nb/Ta(<17.5) 为特征,而榴辉岩部分熔融产生的熔体Nb/Ta>17.5,而形成的岩浆交代岩石圈地幔会使熔体Nb/Ta值升高.本文脉岩样品的Nb/Ta比值为10.89~15.69,说明脉岩母岩浆可能不是加厚下地壳拆沉引起的榴辉岩部分熔融来源.另外考虑到大红柳滩地区同碰撞二长花岗岩体年龄为220 Ma(乔耿彪等,2015),如此短暂的时间也很难有拆沉作用发生,因此排除第3种成因模式.

        图  8  西昆仑东段宿营地中性脉岩YbN-(La/Yb)N判别图解

        Figure 8.  YbN-(La/Yb)N diagram of Suyingdi dykes

        中性脉岩可能是壳-幔相互作用的体现,而壳-幔过渡带不仅是壳幔间的重要物理分界,也是壳幔间能量和物质传输的重要通道,幔源原始基性岩浆难以直接穿过地壳,而是底侵于壳-幔边界富集,与地壳物质混染.从地球化学特征看,脉岩具有较高的(La/Nb)N比值(2.56~4.64) 以及低的Sm/Nd(0.17~0.20) 比值,并且Al、Ba、Sr、Pb(10.8×10-6~48.5×10-6)含量高,指示地壳端元物质的存在.但脉岩的Nb/Ta(10.89~15.69) 值较地壳平均值(11.4) 高(Rudnik and Gao, 2003),指示可能有地幔端元组份的加入,另外脉岩的La/Ta值(33.98~48.77) 较高、部分脉岩Mg及过渡元素(TE)较高也指示了地幔端元的贡献.从岩相学特征看,宿营地发育大量的含石榴闪长玢岩,这种含石榴安山质岩类被认为是壳-幔过渡带的代表性岩浆(Yuan et al., 2008),部分脉岩中还发育暗色包体(图 2d).另外,Yuan et al.(2008)在东昆仑库木库里地区发现的石榴闪长玢岩(212 Ma)Nd-Sr同位素(εNd(t)=-2.33~-1.38,87Sr/86Sr=0.706 5~0.706 7),斜长石的反向分带发育,认为其形成与古特提斯洋板片北向俯冲及壳-幔岩浆混合作用有关.本文脉岩与该岩体形成年代接近,分布的构造位置相似,矿物组成及地球化学特征十分类似(图 5图 6),说明二者可能成因及构造背景类似.综上所述,壳-幔岩浆混合作用可能是宿营地中性脉岩最主要的成因机制.

        脉岩样品具有高Al、高Sr和较弱或无Eu异常的特征,暗示着斜长石在源区残留较少或是缺失的(张旗等,2001).样品亏损HREE,暗示着石榴石为源区残留矿物之一.脉岩的轻稀土及中稀土分异明显,HREE分配模式相对平缓,再加上样品具有强烈的Nb、Ta、Ti负异常,说明源区可能富集角闪石或金红石(Mahoney et al., 1998Moyen, 2009).实验岩石学表明,在熔体中Nb、Ta易于富集在角闪石内(Pearce and Norry, 1979),而在>15×105 kPa的压力条件下受金红石分离结晶影响,Nb/Ta会快速上升(Xiong et al., 2005).研究区脉岩具有低的Nb/Ta比值,暗示源区中角闪石、钛铁矿的富集,但金红石贫乏.已有相平衡实验(Xiong et al., 2006)结果证实,石榴石稳定在约10×105 kPa以上,由此将石榴石稳定区域限定在33 km以下,而金红石的稳定区域在50 km以上,由此可以将宿营地脉岩的岩浆源区深度限定在33~50 km,而当时昆仑山地壳厚度正处于一个正常范围(约35 km)(Yuan et al., 2008),因此这一深度很有可能是壳-幔过渡带所处位置.前人认为,东昆仑造山带在晚印支期时广泛发生了一起壳-幔岩浆混合作用(罗照华等,2002刘成东等,2004),而本文脉岩的岩相学及地球化学特征显示该起区域性壳-幔岩浆混合作用可能延伸至西昆仑东部地区.

      • 昆仑造山带位于青藏高原北缘,属于中央造山系的组成部分,昆仑山南缘至巴颜喀拉一带属古特提斯构造域,该区经历了包括古特提斯洋的扩张、消亡在内的一系列构造演化过程(Yang et al., 2009许志琴等,2012Zhang et al., 2014).前人研究表明,含石榴石安山质岩主要存在于与消减带有关的构造位置,形成于消减活动停止之后的环境(Day et al., 1992Harangi, 2001Nitoi et al., 2002Kawabata and Takafuji, 2005),因此宿营地地区发育大量的含石榴闪长玢岩指示着晚三叠世西昆仑东段古特提斯洋板片消减活动可能已经结束.另外,围岩地层劈理化及同劈理褶皱大面积发育,它们很可能为中-晚三叠世碰撞事件的产物,而脉岩劈理化不明显,也可以说明脉岩形成时代晚于主碰撞期.Yuan et al.(2008)认为,在压力降低的过程中,石榴石会变得不稳定而被溶蚀,而宿营地部分脉岩中石榴石斑晶较为自形完整,反映了岩浆迅速上升的过程,部分脉岩中未见石榴石发育,笔者认为这可能是因为岩浆部分上升通道打开时间滞后而造成石榴石被溶蚀所致.因此,宿营地脉岩的侵入时代可能代表一次应力场由挤压向伸展快速变化事件.

        宿营地中性脉岩以钙碱性系列岩石为主,主量元素富Na、高Al,呈现出准铝质及轻微过铝质特征,富集大离子亲石(LILE)元素,亏损高场强元素(HFSE),反映火山弧岩浆岩地球化学特征,13件样品在Y-Nb图解(图 9a)及Yb+Ta-Rb图解(图 9b)中全部落入火山弧岩浆岩范围内,显示其与弧岩浆岩的亲缘性.由于西昆仑古特提斯造山带于中三叠世(240 Ma)之前就已发生碰撞造山作用(张传林等,2005陈守建等,2011康磊等,2012),而宿营地脉岩形成年代为晚三叠世(214~219 Ma),主要为钙碱性系列岩石,具有弧岩浆岩地球化学特征,因此大规模俯冲作用、同碰撞及后碰撞作用都无法解释脉岩成因.最近,Zhang et al.(2014)通过对巴颜喀拉地体西部的埃达克岩(221~212 Ma)及I型花岗岩(225~193 Ma)成因进行研究,证实昆仑山中部南缘-巴颜喀拉西段古特提斯晚三叠世弧后盆地的存在.在陆缘弧后拉张环境下,玄武岩浆底侵可以造成下地壳岩石发生部分熔融,形成长英质岩浆并发生壳-幔岩浆混合作用(蒋少涌等,2008).综上所述,笔者倾向于认为宿营地中性脉岩形成于昆南古特提斯洋板片对昆仑地体北向俯冲引起的弧后拉张环境下,是弧后拉张引起幔源基性岩浆底侵,发生壳-幔岩浆混合作用并快速上升侵位形成的.

        图  9  西昆仑东段宿营地中性脉岩Y-Nb(a)和Yb+Ta-Rb(b)构造环境判别图解

        Figure 9.  Y-Nb diagram (a) and Yb+Ta-Rb diagram (b) of tectonic setting discrimination of Suyingdi dykes

      • (1) 宿营地脉岩的岩石类型为(含石榴)闪长玢岩、角闪安山岩、闪斜煌斑岩等浅成-超浅成岩石,LA-ICP-MS锆石U-Pb年龄为214~219 Ma,侵位于晚三叠世,为晚印支期构造-岩浆活动产物.

        (2) 脉岩主体为中性钙碱性系列岩石,主量元素表现中Si、高Al、富Na、低Ti、低P及Mg变化较大的特征.脉岩富集LREE、Rb、Th、U、K,亏损HREE、Nb、Ta、Ti、P,(La/Yb)N=7.24~20.02,Ce、Eu异常不明显.

        (3) 本文首次在西昆仑东段的宿营地一带发现中性脉岩,进一步确认了西昆仑南缘晚三叠世古特提斯弧后盆地的存在,而宿营地中性脉岩是弧后拉张引起基性岩浆底侵,继而发生壳-幔岩浆混合作用后,在拉张背景下快速上升侵位形成.

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