Petrology and mineralogy of (retrograded) eclogites from Mengku area, Shuangjiang County, western Yunnan Provinc
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摘要:
滇西双江县勐库镇以北的那卡河、控角等地出露的（退变）榴辉岩以构造岩片的形式产于奥陶纪湾河蛇绿岩混杂岩带中。根据退变质程度差异依次划分为退变榴辉岩、榴闪岩、含石榴斜长角闪岩，主要矿物成分为角闪石、石榴子石、单斜辉石、斜长石，次要矿物成分为金红石、多硅白云母、硬玉、绿帘石、黑云母、磷灰石、石英等，特征的高压-超高压变质矿物绿辉石仅残余在少量的石榴子石、角闪石中，以包裹体形式产出。岩石学和矿物学研究显示，该榴辉岩峰期变质矿物组合为：绿辉石+石榴子石+金红石+石英+多硅白云母。石榴子石中的部分石英包裹体周围发育放射状的胀裂纹，暗示其可能由柯石英转化而成。由此推断，该榴辉岩可能经历了超高压变质作用。
Abstract:Retrograded eclogites are exposed in structural-sheet form in Naka River, Kongjiao and some other areas north of Mengku Town, Shuangjiang County of west Yunnan Province and occur in Ordovician Wanhe ophiolite mélange belt. According to different retrograde degrees, the exlogites can be divided into retrograded eclogites, garnet-amphibolite and garnet-bearing am-phibolite. The main minerals include garnet, clinopyroxene, amphibole, and plagioclase together with minor rutile, phengite, jade-ite, epidote, biotite, apatite, quartz etc. Omphacite, which is a typical HP-UHP metamorphic mineral, only exists as inclusions in a small amount of garnet and amphibole. Petrological and mineralogical characteristics show that the mineral assemblage at the meta-morphic peak is Omp+Gt+Ru+Q+Phen. Due to the growth of radial bulging cracks around some quartz inclusions in garnet, it is held that some quartz inclusions belong to retrograded coesite. The retrograded eclogite therefore must have undergone UHP meta-morphism.
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致谢: 云南省地质调查院李静总工程师认真审阅本文并提出了许多宝贵的修改意见，在此表示诚挚的谢意。
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图 1 研究区地质简图及退变质榴辉岩的出露位置
N—新近系；J—侏罗系；T3—上三叠统；Pz2a—西部上古生界被动陆缘沉积；Pz2b—东部上古生界被动-主动陆缘沉积；Pz1—下古生界澜沧岩群；Pt1—古元古界崇山岩群；Eξγ—古近纪正长花岗岩；T2ηγ—中三叠世二长花岗岩；Pγδ—二叠纪花岗闪长岩；1—石炭纪铜厂街蛇绿混杂岩；2—奥陶纪湾河蛇绿混杂岩；3—同位素采样位置及年龄值；4—正长花岗岩；5—二长花岗岩；6—花岗闪长岩；7—地质界线；8—角度不整合界线；9—断层；10—退变质榴辉岩出露位置
Figure 1. Geological map of the study area and outcrop location of retrograded eclogite
表 1 单斜辉石电子探针分析结果
Table 1 Electron microprobe analyses of clinopyroxene
% 样品矿物 D0302-1-1 KJH-1-2 MNH-1-7 MNH-1-6 D0502-9-1 Omp Omp Jd Omp Omp Omp Jd Omp Omp Aug Dio Dio Dio Dio Dio Dio SiO2 53.310 53.682 62.596 57.935 58.650 55.899 60.561 60.109 56.585 55.402 55.140 54.402 56.045 55.787 54.932 54.948 TiO2 0.060 0.064 0.047 0.011 0.000 0.141 0.013 1.311 0.049 0.079 0.048 0.107 0.127 0.013 0.068 0.087 Al2O3 9.383 12.925 20.189 13.938 15.412 9.128 22.256 17.593 19.076 0.304 0.724 1.197 1.064 0.239 0.331 0.862 FeO 5.276 3.802 1.696 4.472 3.987 11.241 1.184 3.505 7.039 10.340 11.130 10.493 7.894 12.024 12.485 10.541 MnO 0.056 0.087 0.000 0.048 0.053 0.160 0.021 0.071 0.062 1.500 1.178 1.206 0.831 1.424 1.240 1.172 MgO 9.068 6.490 1.624 6.507 3.794 9.924 0.402 3.651 2.187 11.796 10.973 10.684 12.634 10.246 10.204 10.597 CaO 12.309 12.466 4.313 6.674 6.837 9.951 5.449 3.762 7.254 20.713 21.994 21.677 23.154 21.699 20.438 22.282 Na2O 5.323 2.900 8.763 4.433 7.815 4.225 9.029 7.010 8.370 0.104 0.006 0.065 0.046 0.039 0.033 0.055 K2O 0.029 0.037 0.083 0.045 0.081 0.110 0.168 0.121 0.326 0.011 0.003 0.016 0.006 0.015 0.000 0.000 合计 94.814 92.453 99.311 94.063 96.631 100.778 99.083 97.171 100.977 100.249 101.196 99.847 101.801 101.486 99.731 100.544 Wo 43.071 50.814 54.620 34.659 44.774 30.469 78.413 32.336 45.795 44.657 46.915 47.447 48.692 46.698 45.056 48.249 En 44.149 36.809 28.616 47.017 34.571 42.279 8.049 43.665 19.210 35.386 32.567 32.539 36.968 30.681 31.299 31.928 Fs 12.780 12.377 16.765 18.324 20.655 27.252 13.538 23.998 34.995 19.957 20.518 20.014 14.339 22.621 23.644 19.823 Quad 59.647 69.861 19.836 54.385 34.905 67.741 17.361 31.196 33.768 99.139 99.938 99.405 99.621 99.621 99.737 99.571 Jd 38.213 30.139 80.164 45.615 65.095 32.259 82.639 68.804 66.232 0.861 0.062 0.595 0.379 0.379 0.263 0.429 Ae 2.140 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 注:Omp—绿辉石; Jd—硬玉; Dio—透辉石; Aug—普通辉石; Wo—硅灰石; En—顽火辉石; Fs—铁辉石; Quad—普通辉石; Ae—霓石 
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表 2 石榴子石电子探针分析结果
Table 2 Electron microprobe analyses of garnet
% 样品 D0302-1-1 D1502-9-1 KJH-1-2 MNH-1-5 D0502-9-1 SiO2 37.483 32.292 38.004 38.477 38.848 38.034 38.091 37.936 38.485 38.880 38.619 39.541 39.856 40.044 39.760 40.083 38.922 TiO2 0.097 0.071 0.110 0.088 0.129 0.134 0.261 0.202 0.152 0.139 0.112 0.280 0.159 0.102 0.191 0.041 0.203 Al2O3 21.146 20.753 20.816 20.347 20.978 21.868 21.396 21.255 20.785 18.070 18.348 19.884 20.390 20.546 20.607 20.779 20.464 FeO 29.473 26.898 28.462 27.788 29.431 28.846 28.786 26.108 30.195 30.062 29.115 31.353 30.616 31.837 30.515 32.550 31.178 MnO 0.449 0.356 0.492 0.551 0.523 0.540 0.479 2.239 0.385 2.016 1.945 1.175 1.311 1.452 1.593 1.268 1.294 MgO 1.634 8.478 2.433 2.731 2.468 1.835 1.990 2.347 1.274 1.728 0.815 0.723 0.687 1.193 0.853 1.685 0.672 CaO 9.459 6.057 9.748 9.630 9.574 9.753 9.556 10.517 10.031 7.754 9.333 7.922 8.429 6.821 8.351 5.973 8.202 Na2O 0.025 0.062 0.032 0.009 0.003 0.012 0.005 0.000 0.002 0.000 0.000 0.066 0.035 0.024 0.052 0.057 0.034 K2O 0.007 0.019 0.000 0.007 0.008 0.000 0.000 0.000 0.000 0.010 0.000 0.009 0.014 0.007 0.018 0.000 0.012 合计 99.773 94.988 100.097 99.628 101.962 101.022 100.564 100.604 101.309 98.659 98.287 100.953 102.026 102.026 101.940 102.436 100.981 Py 6.480 30.146 9.474 10.689 9.437 7.244 7.873 9.090 4.969 6.828 3.266 2.931 2.786 4.815 3.429 6.752 2.711 Alm 65.554 53.655 62.161 61.001 63.120 63.875 63.880 56.714 66.061 66.628 65.434 71.286 69.633 72.072 68.807 73.161 70.546 Gro 26.955 15.479 27.277 27.085 26.307 27.670 27.170 29.270 28.117 22.018 26.873 23.077 24.562 19.783 24.126 17.200 23.777 SP 1.011 0.719 1.088 1.225 1.136 1.211 1.077 4.926 0.853 4.525 4.427 2.706 3.020 3.329 3.638 2.887 2.965 注:Py—镁铝榴石; Alm—铁铝榴石; Gro—钙铝榴石; Sp—锰铝榴石
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表 3 角闪石电子探针分析结果
Table 3 Electron microprobe analyses of amphibole
样品矿物 D0302-1-1 D1502-9-1 KJH-1-2 D0502-9-1 Fts Tre Fpar Mhb Ts Mhb Tre Mhb Tre Act Bar Act Mhb Tre Win Mhb Fts Tre Bar Mhb Act Fhb SiO2 38.167 55.517 40.629 50.223 42.412 49.343 53.925 45.973 56.566 54.005 53.212 56.079 51.531 54.462 55.186 50.374 40.642 55.41 47.439 51.518 53.622 52.111 TO2 1.243 0.049 0.102 0.02 0.029 0.081 0.126 0.178 0.017 0.085 0.039 0.011 0.073 0.034 0.03 0.082 0.421 0.021 0.06 0.281 0.284 0.4 Al2O3 16.198 1.468 14.889 3.857 11.351 6.986 3.524 10.183 1.269 2.753 4.514 1.253 3.341 1.504 3.288 5.254 15.593 1.589 9.005 6.92 5.115 4.065 FeO 19.177 9.121 19.589 14.171 19.156 11.783 9.512 16.853 8.356 11.699 11.425 9.425 11.906 9.228 8.067 15.163 17.249 10.576 13.822 15.428 15.295 21.431 MnO 0.377 0.038 0.245 0.28 0.377 0.265 0.13 0.171 0.003 0.145 0.101 0.133 0.125 0.066 0.064 0.214 0.149 0.124 0.123 0.905 1.329 1.037 MgO 6.311 19.117 7.512 14.887 9.015 14.65 16.886 10.777 18.879 16.207 18.089 17.888 16.501 18.93 19.232 13.456 9.45 18.234 13.648 11.651 12.238 8.988 CaO 10.381 10.584 10.894 10.085 10.393 11.3 10.974 10.451 10.612 11.635 8.996 11.718 11.695 10.629 10.173 11.339 10.74 10.774 9.775 10.149 10.394 10.224 Na2O 2.175 0.517 2.217 0.79 2.023 1.195 0.848 1.591 0.529 0.318 0.878 0.397 0.6 0.602 0.907 0.807 2.405 0.483 1.697 0.518 0.454 0.323 K2O 0.22 0.065 0.494 0.071 0.264 0.155 0.051 0.254 0.083 0.037 0.08 0.06 0.071 0.049 0.074 0.124 0.53 0.05 0.178 0.258 0.121 0.206 合计 94.249 96.476 96.571 94.384 95.02 95.75 95.976 96.431 96.314 96.884 97.334 96.964 95.843 95.504 97.021 96.813 97.179 97.261 95.747 97.628 98.852 98.785 Si 5.91 7.724 6.139 7.331 6.442 7.163 7.669 6.76 7.889 7.683 7.269 7.905 7.414 7.675 7.587 7.21 5.784 7.71 6.79 7.366 7.575 7.466 AlⅣ 2.09 0.241 1.861 0.663 1.558 0.837 0.331 1.24 0.111 0.317 0.727 0.095 0.566 0.25 0.413 0.79 2.216 0.261 1.21 0.634 0.425 0.534 AlⅥ 0.866 0 0.79 0 0.474 0.358 0.26 0.524 0.098 0.144 0 0.113 0 0 0.12 0.097 0.399 0 0.309 0.532 0.427 0.153 Fe3+ 0.794 0.996 0.777 1.73 1.048 0.582 1.131 0.509 0.975 0.513 1.305 0.44 0 0.944 0.927 0 0 1.027 0 0.741 0.646 0 Ti 0.145 0.005 0.012 0.002 0.003 0.009 0.013 0.02 0.002 0.009 0.004 0.001 0.008 0.004 0.003 0.009 0.045 0.002 0.006 0.03 0.03 0.043 Fe2+ 1.689 0.065 1.698 0 1.385 0.848 0 1.563 0 0.878 0 0.671 1.432 0.143 0 1.815 2.053 0.203 1.654 1.103 1.161 2.568 Mn 0.049 0.004 0.031 0.035 0.048 0.033 0.016 0.021 0 0.017 0.012 0.016 0.015 0.008 0.007 0.026 0.018 0.015 0.015 0.11 0.159 0.126 Mg 1.457 3.965 1.692 3.239 2.041 3.17 3.58 2.362 3.925 3.437 3.684 3.759 3.539 3.977 3.942 2.871 2.005 3.782 2.912 2.484 2.577 1.92 Ca 1.722 1.577 1.763 1.577 1.691 1.757 1.672 1.646 1.586 1.773 1.317 1.77 1.803 1.605 1.498 1.739 1.638 1.606 1.499 1.555 1.573 1.569 Na 0.653 0.139 0.649 0.224 0.596 0.336 0.234 0.454 0.143 0.088 0.233 0.108 0.167 0.164 0.242 0.224 0.664 0.13 0.471 0.144 0.124 0.09 K 0.043 0.012 0.095 0.013 0.051 0.029 0.009 0.048 0.015 0.007 0.014 0.011 0.013 0.009 0.013 0.023 0.096 0.009 0.033 0.047 0.022 0.038 TOTAL 15.418 14.728 15.508 14.814 15.338 15.122 14.915 15.148 14.743 14.868 14.563 14.889 14.958 14.778 14.753 14.803 14.918 14.745 14.9 14.745 14.719 14.506 Mg/(Mg+Fe2+) 0.463 0.984 0.499 1 0.596 0.789 1 0.602 1 0.797 1 0.897 0.848 0.965 1 0.613 0.494 0.949 0.638 0.692 0.689 0.428 注:Fts—铁镁钙闪石; Tre—透闪石; Fpai—铁韭闪石; Mhb—镁角闪石; Ts—镁钙闪石; Act—阳起石; Bar—冻蓝闪石; Win一蓝透闪石；Fhb—铁角闪石
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表 4 多硅白云母电子探针分析结果
Table 4 Electron microprobe analyses of phengite
样品号 SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O F 合计 Si AlⅣ AlⅥ Ti Fe(ii) Mn Mg Ca Na K F TOTAL KJH-1-5 54.168 0.253 24.388 2.52 0.066 4.063 0.084 0.123 6.518 0.353 92.535 3.763 1.76 0.237 0.013 0.146 0.004 0.421 0.006 0.016 0.577 0 6.943 KJH-1-5 56.142 0.268 23.329 2.723 0.013 4.601 0.017 0.115 6.737 0.106 94.051 3.846 1.73 0.154 0.014 0.156 0.001 0.47 0.001 0.015 0.589 0 6.976 PM029-26-2 55.034 0.212 23.871 4.006 0 3.744 0.013 0.138 7.243 0 94.307 3.807 1.746 0.183 0.011 0.231 0 0.385 0.001 0.018 0.638 0 7.020 PM029-26-2 54.33 0.221 24.083 3.295 0 3.667 0.015 0.187 7.918 0 93.716 3.786 1.763 0.214 0.011 0.192 0 0.386 0.001 0.025 0.704 0 7.082 注:以11个氧原子为基数, KJH-1-5—石榴子石中的包裹体, KJH-1-5—多硅白云母Phe1、Phe2，PM029-26-2—石榴白云母石英片岩中的多硅白云母（Phe3）。勐库（退变）榴辉岩的矿物电子探针分析在中国地质调查局天津地质调查中心完成，加速电压为15kV，测试电流2.50×10-8A，电子束直径为5μm
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