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    塔里木盆地盐下地区奥陶系火山碎屑物质特征

    侯明才 江文剑 邓敏 蔡鹏程

    侯明才, 江文剑, 邓敏, 蔡鹏程, 2019. 塔里木盆地盐下地区奥陶系火山碎屑物质特征. 地球科学, 44(3): 822-832. doi: 10.3799/dqkx.2019.001
    引用本文: 侯明才, 江文剑, 邓敏, 蔡鹏程, 2019. 塔里木盆地盐下地区奥陶系火山碎屑物质特征. 地球科学, 44(3): 822-832. doi: 10.3799/dqkx.2019.001
    Hou Mingcai, Jiang Wenjian, Deng Min, Cai Pengcheng, 2019. Characteristics of Ordovician Volcaniclastic Materials in Yanxia Area of Northern Tarim Basin and Their Geological Significance. Earth Science, 44(3): 822-832. doi: 10.3799/dqkx.2019.001
    Citation: Hou Mingcai, Jiang Wenjian, Deng Min, Cai Pengcheng, 2019. Characteristics of Ordovician Volcaniclastic Materials in Yanxia Area of Northern Tarim Basin and Their Geological Significance. Earth Science, 44(3): 822-832. doi: 10.3799/dqkx.2019.001

    塔里木盆地盐下地区奥陶系火山碎屑物质特征

    doi: 10.3799/dqkx.2019.001
    基金项目: 

    国家自然科学基金面上项目 41672102

    油气藏地质及开发工程国家重点实验室开放基金 PLC20180302

    详细信息
      作者简介:

      侯明才(1968-), 男, 教授, 博导, 主要从事大地构造沉积学和层序岩相古地理学的教学和科研工作

    • 中图分类号: P59

    Characteristics of Ordovician Volcaniclastic Materials in Yanxia Area of Northern Tarim Basin and Their Geological Significance

    • 摘要: 奥陶纪是古亚洲洋演化的关键时期,也是塔里木盆地周缘板块构造环境转换的重要时期.然而,南天山洋向北俯冲-消减的时间一直存在争议.通过对保存在塔里木盆地盐下地区奥陶系鹰山组和良里塔格组的火山碎屑物质的岩石学和地球化学特征研究,结合岩相古地理演化格局,约束了南天山洋向北俯冲削减的时间.研究表明,鹰山组碳酸盐岩中主要发育基性沉凝灰岩薄夹层,良里塔格组火山碎屑物质主要为基性火山岩屑.鹰山组和良里塔格组火山碎屑物质的Th/Yb-Ta/Yb图解指示它们来源于活动大陆边缘弧环境.U/Th-Th图解显示大部分样品落在典型弧火山岩区,且多数位于混有沉积物来源的弧火山岩与典型弧火山岩重叠区域,表明研究区火山物质源区曾受到与俯冲相关流体或熔体的改造.Ba/Th-(La/Sm)n图解进一步表明火山碎屑物质源区具有上地壳沉积物质起源的熔体混染,且良里塔格组沉积时期,火山碎屑物质源区受沉积物起源熔体混染的程度更深,改造得更加明显和强烈.上述地球化学特征表明,在早奥陶世鹰山组沉积时期南天山洋已经俯冲消减,且在晚奥陶世良里塔格组沉积时期处于强烈俯冲期.
    • 图 1  塔里木盆地构造分区及取样位置

      Figure 1.  Tectonic units and sampling location of Tarim Basin

      图 2  塔里木盆地盐下地区奥陶系综合柱状图

      Figure 2.  Integrated stratigraphic column in the study areas during the Ordovician

      于炳松等(2011)修改

      图 3  塔里木盆地及邻区早-中奥陶世(a)和晚奥陶世(b)原型盆地

      Figure 3.  Prototype of Tarim Basin and adjacent areas in Early-Middle Ordovician (a) and Late Ordovician (b)

      张光亚等(2015)修改

      图 4  盐下地区奥陶系火山碎屑物质岩石学特征

      Figure 4.  Petrological characteristics of Ordovician volcaniclastic materials in the Yanxia area

      a.碳酸盐化玻屑沉凝灰岩, 单偏光,鹰山组,T914井,6 230.98 m;b.碳酸盐化玻屑沉凝灰岩, 玻屑边缘和内部可见毛发状、丝状的水云母粘土矿物集合体,正交光,鹰山组,T914井,6 230.98 m;c.碳酸盐化玻屑沉凝灰岩经盐酸处理后,残余的水云母粘土矿物,正交光,鹰山组,T914井,6 230.98 m;d.含玄武岩屑亮晶粒屑灰岩,玄武岩屑呈纹层状富集,单偏光,良里塔格组,S108井,5 868.03 m;e.火山岩屑显示玻基斑状结构,正交光,良里塔格组,S108井,5 869 m;f.亮晶鲕粒灰岩,鲕粒同心纹层绿泥石化,单偏光,良里塔格组,S110井,6 084.31 m

      图 5  盐下地区火山碎屑物质CaO与SiO2含量相关性

      Figure 5.  The correlation between CaO and SiO2 concentrations of volcaniclastic materials in the Yanxia area

      图 6  盐下地区火山碎屑物质Zr/TiO2×10-4-Nb/Y图解(a)和Zr-TiO2图解(b)

      Figure 6.  Plots of Zr /TiO2×10-4 vs. Nb/Y (a) and Zr vs.TiO2 (b) of volcaniclastic materials in the Yanxia area

      图 7  盐下地区火山碎屑物质稀土元素球粒陨石标准化配分图(a)和微量元素原始地幔标准化蛛网图(b)

      Figure 7.  Chondrite-normalized REE pattern (a) and primitive mantle-normalized trace element spidergram (b) of volcaniclastic materials in the Yanxia area

      图 8  盐下地区火山碎屑物质样品Th/Yb-Ta/Yb图解

      Figure 8.  Th/Yb vs. Ta/Yb plot of volcaniclastic materials in the Yanxia area

      图 9  塔河南盐下地区玄武质火山碎屑物质样品U/Th-Th图解(a)和Ba/Th-(La/Sm)n图解(b)

      Figure 9.  Plots of U/Th vs.Th (a) and Ba/Th vs. (La/Sm)n (b) of basaltic volcaniclastic materials in the Yanxia area

      表 1  塔里木盆地奥陶系鹰山组和良里塔格组主量(%)、微量(10-6)、稀土元素(10-6)含量及特征比值

      Table 1.  Major element (%), trace element (10-6) and rare earth element (10-6) concentrations and typical values of Yingshan Formation and Lianglitage Formation in the Tarim Basin

      取样井号T914T914S110S110S110S110S110S108S108S108S108S108
      岩性AABBBBBBBBBB
      样品号T1T2S1S3S4S5S6S9S10S7S8S11
      SiO24.7510.4411.3216.7418.3931.1534.8015.7818.162.352.802.08
      Al2O31.804.721.202.071.753.520.915.916.620.570.730.57
      TiO20.060.140.160.330.260.420.071.261.450.050.070.06
      Fe2O30.390.731.332.461.942.470.817.544.840.520.910.40
      MgO0.280.750.300.370.320.450.173.294.020.720.660.91
      K2O0.631.500.500.790.691.340.270.910.950.140.200.14
      Na2O0.050.150.040.110.080.140.030.781.220.040.050.04
      CaO51.7045.3047.4044.1043.2034.3035.3037.1034.1052.7052.6053.20
      MnO0.010.010.110.080.070.040.030.090.080.050.050.04
      P2O5<0.010.010.050.090.070.100.020.180.250.030.030.02
      BaO0.010.01<0.010.010.010.090.010.020.020.01<0.010.01
      Cr2O3<0.01<0.010.010.010.010.020.010.090.080.010.010.01
      SO30.641.352.094.393.464.101.107.010.490.441.200.21
      SrO0.030.040.040.040.040.040.040.040.040.050.050.04
      LOI40.1135.1835.7730.7631.1524.3526.9125.0728.3942.2841.0342.64
      Li2.094.434.696.837.5413.5419.1841.9748.282.112.582.59
      Be0.200.460.210.270.260.590.190.740.680.120.210.14
      Sc2.544.012.996.695.106.013.5319.8113.511.332.531.42
      V4.367.3215.9732.8325.1641.7213.94155.99159.548.1911.5210.22
      Cr1.472.0925.1961.1544.7885.7914.22533.57421.377.4714.2511.05
      Co1.661.724.877.365.497.175.8723.3419.962.452.932.67
      Ni8.097.4018.6630.9224.1025.7614.71172.42152.6115.0316.3317.79
      Cu2.921.407.7212.217.9613.277.2212.0412.692.343.311.33
      Zn6.4514.1922.9839.5331.2040.7129.6130.6447.0812.2519.7313.01
      Ga2.075.542.073.493.135.861.727.879.490.951.140.89
      Rb10.4825.1611.1916.6614.8135.7210.2019.3015.356.088.176.31
      Sr197.47292.44276.46307.07314.19236.72263.74300.65304.81399.56435.23319.07
      Y8.2619.3817.7227.6428.1724.1320.0021.9922.626.9618.449.49
      Zr30.0174.2722.7033.4428.7365.0214.10102.15130.1215.7913.959.67
      Nb1.363.204.807.656.3410.371.3725.6340.710.981.321.28
      Cs0.822.230.330.430.381.200.420.840.600.260.390.29
      Ba16.8724.3520.5582.0323.25697.5214.86112.8995.0315.2425.4930.32
      La9.9318.7012.7819.2819.3121.5312.7921.6826.714.338.455.87
      Ce23.6942.0223.5438.4237.8939.5425.9541.9649.308.4921.4111.92
      Pr2.754.852.644.524.504.352.944.995.761.112.361.43
      Nd10.7119.0910.7618.6418.1617.4911.7320.7023.314.509.395.97
      Sm2.213.872.344.123.973.682.664.674.951.112.391.27
      Eu0.490.810.550.870.840.710.461.231.360.230.530.32
      Gd1.723.102.564.324.223.962.704.374.721.162.641.32
      Tb0.260.500.390.680.690.630.480.640.660.180.420.22
      Dy1.433.092.464.184.063.633.003.753.731.052.471.33
      Ho0.310.660.460.840.810.730.590.710.730.210.490.27
      Er0.942.161.312.332.292.051.741.871.910.571.320.79
      Tm0.140.340.190.360.330.330.280.280.290.080.210.12
      岩性AABBBBBBBBBB
      样品号T1T2S1S3S4S5S6S9S10S7S8S11
      Yb1.052.431.122.102.022.001.791.631.620.511.250.63
      Lu0.180.380.160.300.270.300.270.240.230.070.170.09
      Hf0.701.820.570.860.711.660.372.983.350.390.360.25
      Ta0.100.220.330.520.430.740.121.562.230.070.100.09
      Pb2.064.354.798.676.828.574.8213.017.445.368.602.01
      Th1.653.431.452.352.094.832.884.775.751.562.201.15
      U0.831.400.300.480.450.940.581.080.931.130.861.04
      ∑REE55.80102.0061.23100.9599.35100.9167.37108.71125.2723.6053.4931.56
      (La/Yb)N6.765.528.226.576.857.735.149.5511.866.094.866.64
      Eu*0.740.690.680.620.620.570.520.820.850.610.640.74
      Nb/Y0.160.170.270.280.230.430.071.171.800.140.070.14
      Zr/TiO20.050.050.010.010.010.020.020.010.010.030.020.02
      Th/Yb1.571.411.301.121.032.421.612.933.563.061.761.82
      Ta/Yb0.100.090.300.250.210.370.070.961.380.140.080.14
      U/Th0.500.410.200.210.210.190.200.230.160.730.390.91
      Ba/Th10.207.1014.1434.8411.14144.375.1623.6516.529.7911.6026.33
      (La/Sm)n2.833.043.442.943.063.683.032.923.402.462.232.90
      注:A代表碳酸盐化玻屑沉凝灰岩;B代表火山碎屑灰岩.
      下载: 导出CSV
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    • 收稿日期:  2019-01-07
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    塔里木盆地盐下地区奥陶系火山碎屑物质特征

      作者简介: 侯明才(1968-), 男, 教授, 博导, 主要从事大地构造沉积学和层序岩相古地理学的教学和科研工作
    • 1. 成都理工大学油气藏地质及开发工程国家重点实验室, 四川成都 610059
    • 2. 成都理工大学沉积地质研究院, 四川成都 610059
    • 3. 东华理工大学核资源与环境国家重点实验室, 江西南昌 330013
    • 4. 中国地质调查局成都地质调查中心, 四川成都 610081
    基金项目:  国家自然科学基金面上项目 41672102油气藏地质及开发工程国家重点实验室开放基金 PLC20180302

    摘要: 奥陶纪是古亚洲洋演化的关键时期,也是塔里木盆地周缘板块构造环境转换的重要时期.然而,南天山洋向北俯冲-消减的时间一直存在争议.通过对保存在塔里木盆地盐下地区奥陶系鹰山组和良里塔格组的火山碎屑物质的岩石学和地球化学特征研究,结合岩相古地理演化格局,约束了南天山洋向北俯冲削减的时间.研究表明,鹰山组碳酸盐岩中主要发育基性沉凝灰岩薄夹层,良里塔格组火山碎屑物质主要为基性火山岩屑.鹰山组和良里塔格组火山碎屑物质的Th/Yb-Ta/Yb图解指示它们来源于活动大陆边缘弧环境.U/Th-Th图解显示大部分样品落在典型弧火山岩区,且多数位于混有沉积物来源的弧火山岩与典型弧火山岩重叠区域,表明研究区火山物质源区曾受到与俯冲相关流体或熔体的改造.Ba/Th-(La/Sm)n图解进一步表明火山碎屑物质源区具有上地壳沉积物质起源的熔体混染,且良里塔格组沉积时期,火山碎屑物质源区受沉积物起源熔体混染的程度更深,改造得更加明显和强烈.上述地球化学特征表明,在早奥陶世鹰山组沉积时期南天山洋已经俯冲消减,且在晚奥陶世良里塔格组沉积时期处于强烈俯冲期.

    English Abstract

    • 塔里木盆地是中国西部大型叠合复合盆地,位于中亚造山带西段南部,而中亚造山带作为西伯利亚板块与中朝、塔里木板块之间由古亚洲洋削减而形成的巨型缝,其复杂洋-陆格局演化与造山作用一直是前人研究的热点和难点(Dobretsov et al., 1995; Xu et al., 2013; Zhang et al., 2013; 张光亚等, 2015).塔里木盆地内部地层记录着塔里木板块、伊犁-中天山微地块、西伯利亚板块之间的拼合作用过程以及古亚洲洋的演化历史.奥陶纪时期是古亚洲洋演化关键时期,作为古亚洲洋的一部分,南天山洋盆开始逐渐由拉张转变为俯冲削减,但是其俯冲-削减开始的时间和洋盆最终关闭的时间一直存在着较大争议(汤良杰, 1994, 1997a, 1997b; 何登发等,2007于炳松等,2011),如肖序常等(1991)认为南天山洋在志留纪仍处于拉张作用时期,直到晚志留世-早泥盆世才开始向北俯冲;朱志新等(2006)通过对中天山南缘那拉提山闪长花岗岩锆石年龄测定(436 Ma),认为南天山洋至少在早志留世就已经开始向伊犁-中天山板块俯冲;汤良杰(1997a)认为南天山洋东段从早奥陶世开始发生俯冲作用,至早二叠世才闭合;何登发等(2007)认为奥陶纪时南天山洋盆仍处于扩展发育时期.Hopson et al.(1989)杨天南等(2006)通过对南天山造山带产出黑云母花岗岩、二长花岗岩、花岗闪长岩等俯冲型花岗岩类年龄测试(其年龄分布在436~355 Ma之间),认为南天山洋在晚古生代时期一直处于俯冲过程;于炳松等(2011)综合现有的蛇绿岩、高压变质岩和花岗岩类-火山岩类的年龄资料,认为我国境内南天山造山带西段(塔里木与伊犁-中天山地块)的碰撞起始时间在早石炭世(345 Ma),结束时间为石炭纪末(300 Ma左右).近年来,笔者对塔里木盆地北部的盐下地区奥陶系碳酸盐岩进行研究时,首次在鹰山组和良里塔格组中发现了火山碎屑物质.这些火山碎屑物质可能会记录同时期的板块构造活动状态,从而可能为平息南天山洋向北俯冲消减时间的争议提供新的证据.本文通过对保存在碳酸盐岩内部的火山碎屑物质的岩石学特征、地球化学特征所揭示的构造环境的判识,探讨奥陶纪塔里木盆地北缘南天山洋的板块构造活动状态.

      • 盐下地区位于新疆塔里木盆地北部,地理位置位于新疆库车县和轮台县境内.构造上主体位于沙雅隆起阿克库勒凸起中南部,西与哈拉哈塘凹陷相接,南面过渡为满加尔坳陷(图 1).奥陶系自下而上可划分为下奥陶统蓬莱坝组、鹰山组,中奥陶统一间房组、恰尔巴克组和上奥陶统良里塔格组、桑塔木组(图 2).奥陶纪时期,塔里木盆地逐渐由区域拉张环境向挤压环境转变,盆地边缘由被动大陆边缘向活动大陆边缘转换.在盆地东部为半深海-深海相深水沉积,西部为碳酸盐岩台地和浅海陆棚相环境(图 3)(何登发等,2007).研究区自早寒武世开始,直到奥陶纪末期,一直接受碳酸盐岩沉积,其沉积环境主要为碳酸盐台地.全球海平面变化在纵向上控制了碳酸盐台地的发育与淹没消亡,加里东运动则在空间上控制着碳酸盐台地亚相及微相的分布(张丽娟等, 2007赵宗举等,2009; 林畅松等,2013赵宗举,2015岳勇等,2018).本文研究目的层鹰山组和良里塔格组主要为碳酸盐岩沉积,其中鹰山组沉积环境为开阔台地相(图 2图 3),主要发育泥晶灰岩、含生物碎屑泥微晶灰岩、生物碎屑灰岩、砂屑灰岩等,同时局部地区发育云质灰岩(高华华等,2018);良里塔格组为台地边缘浅滩亚相(图 2图 3),主要发育鲕粒灰岩和粒屑灰岩,可见大型腹足类和双壳类化石碎片(侯明才等,2006赵宗举,2015).但是笔者在对盐下地区鹰山组和良里塔格组的钻井岩心进行岩石矿物鉴定时,在多口井岩心中首次发现大量火山碎屑物质,这些火山碎屑物质表明在鹰山组和良里塔格组沉积时期研究区附近存在着较为活跃的火山活动.

        图  1  塔里木盆地构造分区及取样位置

        Figure 1.  Tectonic units and sampling location of Tarim Basin

        图  2  塔里木盆地盐下地区奥陶系综合柱状图

        Figure 2.  Integrated stratigraphic column in the study areas during the Ordovician

        图  3  塔里木盆地及邻区早-中奥陶世(a)和晚奥陶世(b)原型盆地

        Figure 3.  Prototype of Tarim Basin and adjacent areas in Early-Middle Ordovician (a) and Late Ordovician (b)

      • 研究区火山碎屑物质赋存状态主要表现为两种:(1)碳酸盐化玻屑沉凝灰岩,主要发育在鹰山组中;(2)火山碎屑灰岩,主要发育在良里塔格组中.

      • 样品采集于T914井,该类型岩石主要出现在下奥陶统鹰山组,呈灰白色,块状构造,沉凝灰结构.在显微镜下观察,其物质成分主要为火山碎屑物质,含量约为85%~90%,成分主要为玻屑(图 4a4b).其次为深灰色泥微晶灰岩岩屑,约为10%~15%.大部分玻屑已经蚀变,被微晶方解石交代,在玻屑边缘和内部可见毛发状、丝状的水云母粘土矿物集合体(图 4b).这种围绕玻屑呈梳状产出的结构特征表明水云母粘土矿物由玻屑蚀变而来,而非沉积形成的.虽然大部分玻屑被粘土化或碳酸盐化,但残余玻屑幻影结构仍清晰可见,形态呈骨针状,不规则尖角状.具有弱的塑性定向排列.将岩石样品经稀盐酸浸泡,碳酸盐岩化后形成的方解石被除掉后,玻屑蚀变形成的粘土矿物保持原始结构特征.残余玻屑与蚀变形成的水云母粘土矿物呈现典型的凝灰结构(图 4c),玻屑含量约为50%,未见晶屑.

        图  4  盐下地区奥陶系火山碎屑物质岩石学特征

        Figure 4.  Petrological characteristics of Ordovician volcaniclastic materials in the Yanxia area

      • 该类型岩石主要出现在上奥陶统良里塔格组,样品采集于S108和S110井,火山岩屑主要赋存在高能环境下形成的亮晶鲕粒灰岩、砂屑灰岩中.火山岩屑含量为5%~12%,粒径为0.1~0.3 mm,次圆状,以分散状产出为主,偶见呈纹层状富集(图 4d).可见间隐结构,斜长石呈长条状微晶,杂乱分布于火山玻璃中(图 4d).也可见典型的玻基斑状结构,斑晶主要为长板状的斜长石,呈不规则的格架状杂乱分布于玻璃质中(图 4e).基质火山玻璃具有脱玻化现象,形成微晶长英质物质.岩石学特征表明其岩屑主要为中基性火山岩岩屑.与火山岩屑同层的鲕粒灰岩中,同心纹层可见绿泥石矿物(图 4f),且具有疏松多微孔特征,这些绿泥石可能为同时期降落的中基性火山灰与方解石在形成同心纹层后经绿泥石化形成的.同时,在赋存有火山岩屑的灰岩中未见到其他陆源碎屑沉积物,表明火山岩屑不是来自中基性火山岩陆源区,而是来自同沉积期的火山喷发物.

      • 本文样品主要来自于研究区的T914井、S108和S110井的钻井岩心,共获得岩石样品25件.所有样品均进行岩石薄片鉴定,然后挑选出12件样品进行地球化学测试.在玛瑙磨样机中将样品磨成200目以下的岩石粉末,送至中国地质大学(武汉)地质过程与矿产资源国家重点实验室进行主量、微量和稀土元素分析测试.主量元素采用X射线荧光光谱仪(XRF)分析,微量元素和稀土元素采用电感耦合等离子体质谱仪(ICP-MS)和等离子体发射光谱仪(ICP-AES)分析.对国际标样BCR-2(玄武岩)、BHVO-1(玄武岩)和AGV-1(安山岩)的分析结果表明,主量元素分析精度和准确度优于5%,微量和稀土元素的分析精度和准确度一般优于10%(Ramsey et al., 1995).

      • 表 1所示,来自T914井的碳酸盐化玻屑沉凝灰岩SiO2含量低,为4.75%~10.44%;CaO含量高,为51.70%~45.30%;TiO2含量为0.06%~0.14%;Al2O3含量为1.80%~4.72%;Na2O含量低,为0.05%~0.15%,K2O含量较高,为0.16%~1.50%,表现出明显钠含量低、钾含量高的特征.烧失量LOI高(35.18%~40.11%),稀土元素总量ΣREE为55.80×10-6~102.00×10-6,经球粒陨石化后显示轻稀土较富集、重稀土平坦的特征,Eu显示负异常.来自S110井样品SiO2含量为11.32%~34.80%,CaO含量为34.30%~47.40%,TiO 2含量为0.07%~0.42%,Al2O3含量为0.91%~3.52%,Na2O含量为0.03%~0.14%,K2O含量为0.27%~1.34%,烧失量LOI为24.35%~35.77%,稀土元素总量ΣREE为61.23×10-6~10.95×10-6,经球粒陨石化后也显示轻稀土较富集、重稀土平坦的特征,Eu显示负异常(表 1).来自S108井样品SiO2含量为2.08%~18.16%,CaO含量为34.10%~53.20%,TiO2含量为0.06%~1.45%,Al2O3含量为0.57%~6.62%,Na2O含量为0.04%~1.22%,K2O含量为0.14%~0.95%,烧失量LOI为25.07%~42.64%,稀土元素总量ΣREE为23.60×10-6~125.27×10-6,经球粒陨石化后也显示轻稀土较富集、重稀土平坦的特征,Eu显示负异常(表 1).

        取样井号T914T914S110S110S110S110S110S108S108S108S108S108
        岩性AABBBBBBBBBB
        样品号T1T2S1S3S4S5S6S9S10S7S8S11
        SiO24.7510.4411.3216.7418.3931.1534.8015.7818.162.352.802.08
        Al2O31.804.721.202.071.753.520.915.916.620.570.730.57
        TiO20.060.140.160.330.260.420.071.261.450.050.070.06
        Fe2O30.390.731.332.461.942.470.817.544.840.520.910.40
        MgO0.280.750.300.370.320.450.173.294.020.720.660.91
        K2O0.631.500.500.790.691.340.270.910.950.140.200.14
        Na2O0.050.150.040.110.080.140.030.781.220.040.050.04
        CaO51.7045.3047.4044.1043.2034.3035.3037.1034.1052.7052.6053.20
        MnO0.010.010.110.080.070.040.030.090.080.050.050.04
        P2O5<0.010.010.050.090.070.100.020.180.250.030.030.02
        BaO0.010.01<0.010.010.010.090.010.020.020.01<0.010.01
        Cr2O3<0.01<0.010.010.010.010.020.010.090.080.010.010.01
        SO30.641.352.094.393.464.101.107.010.490.441.200.21
        SrO0.030.040.040.040.040.040.040.040.040.050.050.04
        LOI40.1135.1835.7730.7631.1524.3526.9125.0728.3942.2841.0342.64
        Li2.094.434.696.837.5413.5419.1841.9748.282.112.582.59
        Be0.200.460.210.270.260.590.190.740.680.120.210.14
        Sc2.544.012.996.695.106.013.5319.8113.511.332.531.42
        V4.367.3215.9732.8325.1641.7213.94155.99159.548.1911.5210.22
        Cr1.472.0925.1961.1544.7885.7914.22533.57421.377.4714.2511.05
        Co1.661.724.877.365.497.175.8723.3419.962.452.932.67
        Ni8.097.4018.6630.9224.1025.7614.71172.42152.6115.0316.3317.79
        Cu2.921.407.7212.217.9613.277.2212.0412.692.343.311.33
        Zn6.4514.1922.9839.5331.2040.7129.6130.6447.0812.2519.7313.01
        Ga2.075.542.073.493.135.861.727.879.490.951.140.89
        Rb10.4825.1611.1916.6614.8135.7210.2019.3015.356.088.176.31
        Sr197.47292.44276.46307.07314.19236.72263.74300.65304.81399.56435.23319.07
        Y8.2619.3817.7227.6428.1724.1320.0021.9922.626.9618.449.49
        Zr30.0174.2722.7033.4428.7365.0214.10102.15130.1215.7913.959.67
        Nb1.363.204.807.656.3410.371.3725.6340.710.981.321.28
        Cs0.822.230.330.430.381.200.420.840.600.260.390.29
        Ba16.8724.3520.5582.0323.25697.5214.86112.8995.0315.2425.4930.32
        La9.9318.7012.7819.2819.3121.5312.7921.6826.714.338.455.87
        Ce23.6942.0223.5438.4237.8939.5425.9541.9649.308.4921.4111.92
        Pr2.754.852.644.524.504.352.944.995.761.112.361.43
        Nd10.7119.0910.7618.6418.1617.4911.7320.7023.314.509.395.97
        Sm2.213.872.344.123.973.682.664.674.951.112.391.27
        Eu0.490.810.550.870.840.710.461.231.360.230.530.32
        Gd1.723.102.564.324.223.962.704.374.721.162.641.32
        Tb0.260.500.390.680.690.630.480.640.660.180.420.22
        Dy1.433.092.464.184.063.633.003.753.731.052.471.33
        Ho0.310.660.460.840.810.730.590.710.730.210.490.27
        Er0.942.161.312.332.292.051.741.871.910.571.320.79
        Tm0.140.340.190.360.330.330.280.280.290.080.210.12
        岩性AABBBBBBBBBB
        样品号T1T2S1S3S4S5S6S9S10S7S8S11
        Yb1.052.431.122.102.022.001.791.631.620.511.250.63
        Lu0.180.380.160.300.270.300.270.240.230.070.170.09
        Hf0.701.820.570.860.711.660.372.983.350.390.360.25
        Ta0.100.220.330.520.430.740.121.562.230.070.100.09
        Pb2.064.354.798.676.828.574.8213.017.445.368.602.01
        Th1.653.431.452.352.094.832.884.775.751.562.201.15
        U0.831.400.300.480.450.940.581.080.931.130.861.04
        ∑REE55.80102.0061.23100.9599.35100.9167.37108.71125.2723.6053.4931.56
        (La/Yb)N6.765.528.226.576.857.735.149.5511.866.094.866.64
        Eu*0.740.690.680.620.620.570.520.820.850.610.640.74
        Nb/Y0.160.170.270.280.230.430.071.171.800.140.070.14
        Zr/TiO20.050.050.010.010.010.020.020.010.010.030.020.02
        Th/Yb1.571.411.301.121.032.421.612.933.563.061.761.82
        Ta/Yb0.100.090.300.250.210.370.070.961.380.140.080.14
        U/Th0.500.410.200.210.210.190.200.230.160.730.390.91
        Ba/Th10.207.1014.1434.8411.14144.375.1623.6516.529.7911.6026.33
        (La/Sm)n2.833.043.442.943.063.683.032.923.402.462.232.90
        注:A代表碳酸盐化玻屑沉凝灰岩;B代表火山碎屑灰岩.

        表 1  塔里木盆地奥陶系鹰山组和良里塔格组主量(%)、微量(10-6)、稀土元素(10-6)含量及特征比值

        Table 1.  Major element (%), trace element (10-6) and rare earth element (10-6) concentrations and typical values of Yingshan Formation and Lianglitage Formation in the Tarim Basin

      • 表 1可以看出,样品的SiO2含量均较低而CaO含量高,CaO含量与SiO2含量具有很好的线性负相关性(图 5),这可能与岩石样品在沉积时混入火山碎屑物质量有关,当同期混入火山物质越多时,岩石中SiO2含量越高、钙质含量越少.由于样品烧失量均较大(24.35%~35.77%),岩石蚀变程度较高,因此一些活动性较强的元素如Ba、K、Na、Rb、Sr、U等不宜用来进行岩石类型判别,而一些高场强的元素(Nb、Ta、Zr、Hf等)、不活泼的元素受此影响较小,可以代表原岩特征,因此可用来判断蚀变岩石的类型和成因(Winchester and Floyd, 1977; Hastie et al., 2007).本文选用不活泼元素(Ti、Zr、Y、Nb)进行岩石分类(Winchester and Floyd, 1977Hall-berg,1984),在Zr/TiO2×10-4-Nb/Y判别图中(图 6a),来自T914井的样品落在亚碱性玄武岩范围;S110井和S108井样品基本落在亚碱性玄武岩和碱性玄武岩范围内,表明研究区火山碎屑物质主要来源于基性火山岩.在Zr-TiO 2图解中(图 6b),样品也均落在玄武岩区域内,也表明其主要来源于基性火山岩.

        图  5  盐下地区火山碎屑物质CaO与SiO2含量相关性

        Figure 5.  The correlation between CaO and SiO2 concentrations of volcaniclastic materials in the Yanxia area

        图  6  盐下地区火山碎屑物质Zr/TiO2×10-4-Nb/Y图解(a)和Zr-TiO2图解(b)

        Figure 6.  Plots of Zr /TiO2×10-4 vs. Nb/Y (a) and Zr vs.TiO2 (b) of volcaniclastic materials in the Yanxia area

        表 1还可以看出,研究区样品TiO2含量较低(0.06%~1.45%),并且明显富集Rb、Th、K等大离子亲石元素和轻稀土富集,而亏损Nb、Ta、Ti、P等高场强元素,Eu负异常(图 7a7b),显示弧火山岩地球化学特征(Bailey,1981孙赛军等,2015).从图 6可以看出研究区火山碎屑物质来源于玄武岩;研究表明基性火山岩Ta/Yb-Th/Yb图解可以有效地判别玄武岩形成的构造环境,图 8显示样品大多数落在活动大陆边缘弧环境中(Pearce, 1983).在U/Th-Th图解中(图 9a),大部分样品落在典型弧火山岩区域内,且多数位于混有沉积物来源的弧火山岩与典型弧火山岩重叠区域,表明研究区火山物质源区曾受到与俯冲相关流体或熔体的改造(Basta et al., 2011).Ba/Th-(La/Sm)n图解(图 9b)进一步表明火山碎屑物质源区具有上地壳沉积物质起源的熔体混染,且良里塔格组沉积时期,火山碎屑物质源区受沉积物起源熔体混染的程度更深,改造得更加明显和强烈(Tatsumi,2006).

        图  7  盐下地区火山碎屑物质稀土元素球粒陨石标准化配分图(a)和微量元素原始地幔标准化蛛网图(b)

        Figure 7.  Chondrite-normalized REE pattern (a) and primitive mantle-normalized trace element spidergram (b) of volcaniclastic materials in the Yanxia area

        图  8  盐下地区火山碎屑物质样品Th/Yb-Ta/Yb图解

        Figure 8.  Th/Yb vs. Ta/Yb plot of volcaniclastic materials in the Yanxia area

        图  9  塔河南盐下地区玄武质火山碎屑物质样品U/Th-Th图解(a)和Ba/Th-(La/Sm)n图解(b)

        Figure 9.  Plots of U/Th vs.Th (a) and Ba/Th vs. (La/Sm)n (b) of basaltic volcaniclastic materials in the Yanxia area

      • 元古代晚期由塔里木运动形成古塔里木板块,在南华纪时期(约800 Ma)(汤良杰,1997a于炳松等,2011)开始发生裂解,在其边缘和内部发育大陆裂谷盆地,在寒武纪-埃迪卡拉纪时期(510~570 Ma)(汤良杰,1997b于炳松等,2011),大陆裂谷带进一步扩张,在塔里木南、北两侧分别形成北昆仑洋和南天山洋,塔里木主体则为大型克拉通内拉张盆地,其边界为被动大陆边缘,在盆地内主要发育稳定台地相碳酸盐岩建造(Li et al., 1996Lin et al., 2014石开波等,2017).寒武纪到早奥陶世,塔里木盆地古地理格局呈现西台东盆的特征,即中西部地区主要为稳定碳酸盐岩台地沉积(以晚寒武世下丘里塔格群巨厚碳酸盐岩沉积为代表),东部的满加尔和库鲁克塔格地区则持续表现为欠补偿的深水盆地沉积(以晚寒武世突尔沙克组和早奥陶世黑土凹组黑色碳、硅质灰泥岩沉积组合为代表)(楼雄英和许效松,2004张光亚等,2015).但是从早奥陶世晚期开始,以近东西向展布的塔中隆起、塔北隆起、阿瓦提隆间坳陷、满加尔隆间坳陷的形成为标志,塔里木盆地沉积格局发生了重要转变,由前期西浅东深的台-盆体系转化为南北向隆坳相间的格局(图 3a)(楼雄英和许效松,2004张丽娟等,2007林畅松等,2013).这种盆地古地理格局的改变明显与盆地构造应力场转变有关(表明塔里木盆地从早奥陶世晚期开始明显受到南北向挤压构造应力场作用),而盆地构造应力场转变又与盆地周边洋-陆之间发生重大地质构造事件密切相关(楼雄英和许效松,2004).而本文的数据表明,在早奥陶世鹰山组沉积时期,塔里木板块周边开始出现由于板块俯冲作用而导致的火山活动,且处于俯冲削减初期.区域地质背景表明,本次火山活动可能与南天山洋开始向北俯冲有关,而研究区鹰山组发育的基性玻屑沉凝灰岩正是俯冲作用导致的塔里木盆地早奥陶世晚期应力场转变过程中大陆弧火山活动的良好记录;也证明了在早奥陶世晚期,塔里木北侧就已经存在活动大陆边缘弧,也即南天山洋已经开始俯冲、削减,从而形成盆地南北向挤压构造应力场,控制早-中奥陶世塔里木盆地沉积古地理格局.到了晚奥陶世良里塔格组沉积时期,本文的数据表明南天山洋可能已经进入强烈俯冲期,从而造成了良里塔格组火山碎屑物质受到上地壳沉积物强烈混染改造作用,也表明该时期塔里木板块北缘的大陆边缘弧环境发展越来越成熟,而研究区良里塔格组中出现基性火山碎屑岩屑就是该时期大陆边缘弧火山活动良好的记录.而塔里木良里塔格组沉积时期岩相古地理分布特征也印证了这一点.该时期塔里木盆地内部地形进一步分化,盆地拗陷作用进一步加剧,如西部阿瓦提坳陷与东部满加尔隆间坳陷连为一体(图 3b)(王恕一等,2006张丽娟等,2007),表明该时期塔里木盆地周缘受到的挤压应力增强,南天山洋俯冲更加强烈,即印证了本文所得出的结论.因此,结合塔里木盆地奥陶系古地理沉积格局的演化和研究区火山碎屑物质的岩石学、地球化学特征,表明南天山洋俯冲削减最早应该发生在早奥陶世晚期的鹰山组沉积时期,而到了晚奥陶世良里塔格组沉积时期,南天山洋已经进入强烈俯冲阶段,而塔里木盆地北缘南天山洋盆的最终关闭应该在晚奥陶世凯迪阶之后.

      • 通过对塔里木北部盐下地区奥陶系鹰山组和良里塔格组碳酸盐岩地层中火山碎屑物质进行岩石学和地球化学特征分析,揭示了奥陶纪时期塔里木板块北部的南天山洋俯冲活动特征.鹰山组碳酸盐岩中火山碎屑物质主要为碳酸盐化玻屑沉凝灰岩,良里塔格组中火山碎屑物质主要为中基性火山岩岩屑;地球化学特征表明研究区火山碎屑物质主要来源于基性火山岩,形成于活动大陆边缘弧环境,且受到与俯冲相关流体或熔体的改造,良里塔格组沉积时混染的程度更深,改造得更加明显.结合塔里木盆地奥陶系古地理沉积格局的演化,本文认为南天山洋在早奥陶世晚期已经开始俯冲,而到了晚奥陶世,南天山洋已经进入强烈俯冲阶段.

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