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董宇超, 解超明, 于云鹏, 王斌, 李麟瀚, 曾孝文. 西藏工布江达县龙崖松多榴辉岩的发现及意义[J]. 地质通报, 2018, 37(8): 1464-1471.
引用本文: 董宇超, 解超明, 于云鹏, 王斌, 李麟瀚, 曾孝文. 西藏工布江达县龙崖松多榴辉岩的发现及意义[J]. 地质通报, 2018, 37(8): 1464-1471.
shu
DONG Yuchao, XIE Chaoming, YU Yunpeng, WANG Bin, LI Linhan, ZENG Xiaowen. The discovery of Longyasongduo eclogite from Gongbujiangda County, Tibet, and its significance[J]. Geological Bulletin of China, 2018, 37(8): 1464-1471.
Citation: DONG Yuchao, XIE Chaoming, YU Yunpeng, WANG Bin, LI Linhan, ZENG Xiaowen. The discovery of Longyasongduo eclogite from Gongbujiangda County, Tibet, and its significance[J]. Geological Bulletin of China, 2018, 37(8): 1464-1471.
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西藏工布江达县龙崖松多榴辉岩的发现及意义

  • 吉林大学地球科学学院, 吉林 长春 130061

  • 基金项目:
    中国地质调查局项目《冈底斯-喜马拉雅铜矿资源基地调查》(编号:DD20160015)、《班公湖-怒江成矿带铜多金属矿资源基地调查》(编号:DD20160026)与青年科学基金项目《藏北聂荣微陆块新元古代-寒武纪构造演化》(批准号:41402190)、《青藏高原羌塘南部埃迪卡拉纪地层研究》(批准号:41602230)
详细信息
    作者简介: 董宇超(1993-), 男, 在读博士生, 矿产普查及勘探。E-mail:dongyc123@hotmail.com
    通讯作者: 解超明(1983-), 男, 博士, 副教授, 从事构造地质学研究。E-mail:xcmxcm1983@126.com

  • 中图分类号: P588.3

The discovery of Longyasongduo eclogite from Gongbujiangda County, Tibet, and its significance

  • College of Earth Science, Jilin University, Changchun 130061, Jilin, China

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    摘要

  • 唐加-松多榴辉岩高压变质带位于冈底斯板块中部，对研究古特提斯构造演化具有至关重要的意义，但是榴辉岩的出露范围和规模尚不清楚。在龙崖松多地区新发现榴辉岩的出露点，通过详细的野外地质调查、岩石学及矿物学研究，发现其岩性为金红石榴辉岩和石英榴辉岩，以透镜体的形式产出，围岩以低绿片岩相岩石为主，少部分为石英白云母片岩。龙崖松多榴辉岩的主要矿物组合为石榴子石、绿辉石、多硅白云母、角闪石、金红石、石英及少量榍石、钛铁矿等，石榴子石的电子探针分析结果显示，从核部到边部，镁铝榴石和铁铝榴石含量逐渐增加，锰铝榴石含量显著减少，具有典型的进变质环带特征，同时榴辉岩边部石榴子石角闪岩的发现，说明该露头的榴辉岩可能经历了后期退变质作用改造。该榴辉岩的发现对探讨唐加-松多蛇绿混杂带的构造演化具有重要意义。

    Located in the central part of Gangdise plate, the Tangjia-Sumdo eclogite-bearing metamorphic belt played an important role in the evolution of the Paleo Tethys Ocean. However, the exposed scale of eclogites is still unclear. In this study, the authors found a new site of eclogite in Longyasongdo area. The detailed field survey and petrographic and mineralogical study show that the lithology of Longyasongduo eclogite includes rutile eclogite and quartz eclogite. The eclogite is in the form of lens. The surrounding rock of Longyasongduo eclogite is mainly greenschist, with a small part being muscovite quartz schist. The general mineral assemblage of eclogite is garnet+omphagite+phengite+amphibole+rutile+quartz, with minor sphene and ilmenite. The analysis of the EMPA composition profile of the garnet shows typical growth zoning, with Xpyr and Xalm increasing from core to rim but Xspe showing a tendency of decrease. Meanwhile, according to the discovery of garnet amphibolite from the edge of eclogite, it is inferred that Longyasongduo eclogite might have undergone retrograde process. The discovery of Longyasongduo eclogite is of great importance for the study of the tectonic evolution of the Tangjia-Sumdo ophiolite belt.

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  • 图 1  西藏工布江达县龙崖松多地区地质简图

    Figure 1. 

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    图 2  西藏工布江达县龙崖松多榴辉岩实测剖面

    Figure 2. 

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    图 图版Ⅰ   

    Figure 图版Ⅰ. 

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    图 3  龙崖松多金红石榴辉岩石榴子石成分（分类据参考文献[18]）和单斜辉石三元成分图解

    Figure 3. 

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    图 4  石榴子石电子探针成分剖面照片及各端元组分含量分布

    Figure 4. 

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    表 1  龙崖松多榴辉岩石榴子石（S17T3T4）剖面化学成分

    Table 1.  Chemical compositions of garnet(S17T3T4)from Longyasongduo eclogite in Tibet

    测试点 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15
    SiO2 38.962 38.291 38.711 38.518 38.568 38.49 38.103 37.873 38.327 37.762 38.54 38.029 36.691 38.47 38.078
    TiO2 0.0 0.034 0.011 0.078 0.169 0.169 0.101 0.101 0.169 0.135 0.135 0.0 0.157 0.158 0.224
    Al2O3 21.739 22.128 21.682 22.082 21.966 21.771 22.007 21.795 21.576 21.686 21.629 21.692 21.384 21.979 21.782
    Cr2O3 0.02 0.025 0.006 0.0 0.0 0.024 0.0 0.0 0.032 0.039 0.007 0.0 0.131 0.028 0.004
    FeO 24.305 22.448 22.891 23.129 22.253 21.887 21.296 22.104 20.913 20.704 21.874 22.104 20.981 21.508 23.497
    MnO 0.674 0.535 0.538 0.631 0.441 0.898 0.68 0.565 1.168 0.983 0.955 0.958 0.989 0.989 0.678
    MgO 6.151 6.468 5.937 5.891 5.766 5.726 5.793 5.641 5.313 5.473 5.4 5.108 5.281 5.518 5.76
    CaO 8.828 10.758 10.798 10.122 11.393 11.467 11.741 11.159 11.657 11.574 11.686 10.955 11.166 11.355 10.03
    Si 2.9948 2.9374 2.9752 2.9669 2.9630 2.9624 2.9498 2.9527 2.9842 2.9640 2.9744 2.9804 2.9382 2.9716 2.9523
    Ti 0.0 0.0020 0.0006 0.0045 0.0098 0.0098 0.0059 0.0059 0.0099 0.0080 0.0078 0.0 0.0095 0.0092 0.0131
    Al 1.9693 2.0006 1.9640 2.0046 1.9889 1.9749 2.0080 2.0026 1.9799 2.0061 1.9673 2.0036 2.0182 2.0009 1.9904
    Cr 0.0012 0.0015 0.0004 0.0 0.0 0.0015 0.0 0.0 0.0020 0.0024 0.0004 0.0 0.0083 0.0017 0.0003
    Fe3+ 0.0329 0.0383 0.0517 0.0144 0.0293 0.0422 0.0216 0.0249 0.0221 0.0102 0.0441 0.0095 0.0084 0.0102 0.0325
    Fe2+ 1.5295 1.4019 1.4197 1.4756 1.4004 1.3666 1.3572 1.4163 1.3397 1.3489 1.3677 1.4393 1.3968 1.3793 1.4911
    Mn 0.0439 0.0348 0.0350 0.0412 0.0287 0.0585 0.0446 0.0373 0.0770 0.0654 0.0624 0.0636 0.0671 0.0647 0.0445
    Mg 0.7048 0.7397 0.6802 0.6765 0.6604 0.6570 0.6686 0.6556 0.6167 0.6404 0.6213 0.5968 0.6305 0.6354 0.6658
    Ca 0.7270 0.8843 0.8892 0.8354 0.9378 0.9456 0.9739 0.9322 0.9725 0.9734 0.9663 0.9199 0.9581 0.9398 0.8332
    Ura 0.06 0.07 0.02 0.0 0.0 0.07 0.0 0.0 0.10 0.12 0.02 0.0 0.41 0.08 0.01
    And 1.64 1.88 2.57 0.71 1.45 2.09 1.06 1.23 1.10 0.50 2.19 0.47 0.41 0.50 1.60
    Pyr 23.45 24.17 22.49 22.34 21.81 21.70 21.96 21.56 20.52 21.15 20.59 19.76 20.65 21.05 21.94
    Spe 1.46 1.14 1.16 1.36 0.95 1.93 1.46 1.23 2.56 2.16 2.07 2.11 2.20 2.14 1.47
    Gro 22.49 26.94 26.82 26.87 29.53 29.07 30.93 29.42 31.15 31.52 29.81 30.00 30.57 30.54 25.84
    Alm 50.89 45.81 46.94 48.72 46.26 45.14 44.58 46.57 44.57 44.55 45.32 47.67 45.76 45.68 49.14
    注：氧化物含量单位为%，其他为阳离子数
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    表 2  龙崖松多榴辉岩绿辉石、多硅白云母化学成分

    Table 2.  Chemical compositions of omphacite and pehngite from Longyasongduo eclogite in Tibet

    样品号 S17T3T1-2 S17T3T1-3
    矿物名称 多硅白云母 多硅白云母 绿辉石 绿辉石 多硅白云母 多硅白云母 多硅白云母 绿辉石
    SiO2 54.260 54.462 52.151 53.492 53.489 50.437 53.395 53.069
    TiO2 0.081 0.116 0.186 0.116 0.151 0.266 0.081 0.046
    Al2O3 27.085 25.685 7.533 7.085 25.550 30.019 6.839 6.477
    Cr2O3 0.016 0.039 0.016 0.039 0.000 0.000 0.000 0.022
    FeO 2.228 2.155 8.028 7.989 2.425 2.721 7.121 7.216
    MnO 0.031 0.000 0.034 0.027 0.021 0.010 0.000 0.010
    MgO 3.959 4.357 9.492 9.551 4.255 3.140 10.006 10.121
    CaO 0.018 0.035 16.080 16.112 0.011 0.032 16.296 15.910
    Na2O 0.433 0.390 6.148 5.978 0.378 0.686 6.185 6.358
    K2O 8.480 8.437 0.013 0.006 8.808 8.942 0.000 0.013
    Si 3.5076 3.5533 1.931 1.960 3.5282 3.3081 1.961 1.965
    AlⅣ 0.4924 0.4467 0.069 0.040 0.4718 0.6919 0.039 0.035
    AlⅥ 1.5711 1.5283 0.260 0.266 1.5145 1.6286 0.258 0.248
    Al 2.0635 1.9750 0.000 0.000 1.9863 2.3205 0.000 0.000
    Ti 0.0039 0.0057 0.005 0.003 0.0075 0.0131 0.002 0.001
    Cr 0.0000 0.0000 0.000 0.001 0.0000 0.0000 0.000 0.001
    Fe3+ 0.1205 0.1176 0.349 0.280 0.1338 0.1493 0.317 0.351
    Mn 0.0017 0.0000 0.001 0.001 0.0012 0.0006 0.000 0.000
    Mg 0.3815 0.4238 0.524 0.522 0.4184 0.3070 0.548 0.559
    Ca 0.0012 0.0024 0.638 0.633 0.0008 0.0022 0.641 0.631
    Na 0.0543 0.0493 0.441 0.425 0.0483 0.0872 0.441 0.456
    K 0.6993 0.7022 0.0006 0.0003 0.7412 0.7482 0.000 0.001
    注：氧化物含量单位为%，其他为离子数
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    表 3  龙崖松多榴辉岩（S17T3T1）金红石、钛铁矿化学成分

    Table 3.  Chemical compositions of rutile and ilmenite from Longyasongduo eclogite in Tibet

    %
    矿物名称 金红石 金红石 钛铁矿 钛铁矿
    SiO2 0.065 0.065 0.016 0.044
    TiO2 98.973 99.381 51.426 51.243
    Al2O3 0.001 0.008 0.026 0.014
    Cr2O3 0.031 0 0.038 0.024
    FeO 0.322 0.348 44.459 44.912
    MnO 0 0.003 3.051 3.249
    MgO 0 0.007 0.014 0.043
    CaO 0.077 0.076 0.044 0.039
    K2O 0.034 0.01 0 0.013
    Na2O 0.079 0.008 0.066 0.055
    总量 99.582 99.906 99.14 99.636
    注：单矿物化学成分分析在中国地质科学院（北京）地质与矿物资源研究所，使用的电子探针型号为JXA-8800，分析条件为放射束电流的加速电压20kV、电流20nA、探针束斑直径5μm，石榴子石中的Fe3+依照Droop[20]计算，标准辉石各端元组分计算方法根据Morimoto[21]，硬玉(XJd)=AlⅥ/(Na+Ca), 霓石(XAe) = (Na-AlⅥ)/(Na+Ca)，普通辉石(XAu) = (Ca+Mg+Fe2+)/2，详细分析方法步骤参照Zhai等[22]
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收稿日期:  2018-01-05
修回日期:  2018-05-15
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