| 中国大陆科学钻探工程主孔斜长角闪岩中锆石的SHRIMPU-Pb定年及其地质意义 |
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| 引用本文： | 叶建国,刘福来.中国大陆科学钻探工程主孔斜长角闪岩中锆石的SHRIMPU-Pb定年及其地质意义[J].中国区域地质,2008(5):589-598. |
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| 作者姓名： | 叶建国 刘福来 |
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| 作者单位： | 中国地质科学院地质研究所,北京100037 |
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| 基金项目： | 国家杰出青年基金项目（编号：40725007）和国家重点基础研究发展规划项目（编号：2003CB716502）资助. |
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| 摘 要： | 矿物包裹体激光拉曼测试、阴极发光图像分析和SHILIMPU—Pb定年综合研究结果表明，中国大陆科学钻探主孔斜长角闪岩（样品G12）中的锆石可划分为2种类型：第一类颗粒粗大，舍有大量矿物包裹体和杂质；第二类颗粒细小，舍有少量矿物包裹体且十分干净。第一类锆石具有明显的双层结构。核部阴极发光图像显示典型的岩浆结晶环带，相应的矿物包裹体为单斜辉石（Cpx）＋斜长石（P1）＋磷灰石（Ap）±石英（Qtz），表明其寄主岩石的原岩为基性岩浆岩；边部阴极发光图像十分均匀，保存柯石英（Coe）＋石榴子石（Grt）＋绿辉石（Omp）＋多硅白云母（Phe）＋磷灰石（Ap）等标志性超高压包裹体矿物组合，记录的变质温压条件为T=732-839℃、p=3．0-4．0GPa，表明该类变质增生锆石微区形成于超高压变质阶段。第二类锆石阴极发光图像十分均匀，发光性明显增强，保存角闪石（Amp）＋斜长石（P1）等标志性角闪岩相包裹体矿物组合，记录的变质温压条件为T=612-698℃、p=0．76-1．05GPa，表明该类锆石形成于后期角闪岩相退变质阶段。SHRIMPU-Pb定年结果显示，继承性岩浆结晶锆石核部记录的^206Pb／灿的年龄为685-650Ma．表明其原岩形成于新元古代；舍柯石英等超高压矿物包裹体的边部记录的^206Pb／^238U年龄为243-225Ma，表明超高压变质时代应归属于晚三叠世。第二类舍低压包裹体矿物的锆石微区记录的^206Pb／^238U年龄为219-210Ma．应代表后期角闪岩相退变质作用的时代。上述研究结果表明，苏鲁地体斜长角闪岩的原岩在晚三叠世深俯冲至上地幔100-120km的地幔深处并经历了超高压变质作用。约15Ma之后，这些超高压岩石抬升到约25km的中部地壳，并经历了后期角闪岩相退变质作用的改造。相应的折返速率为0．57cm／y。
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| 关 键 词： | 锆石 矿物包裹体 SHRIMP U-Pb定年 斜长角闪岩 中国大陆科学钻探工程 |
Ye JG,Liu FL. SHRIMP U-Pb dating of zircons from amphibolite in the main hole of the Chinese Continental Scientific Drilling Project |
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| YE Jian-guo,LIU Fu-lai.Ye JG,Liu FL. SHRIMP U-Pb dating of zircons from amphibolite in the main hole of the Chinese Continental Scientific Drilling Project[J].Regional Geology of China,2008(5):589-598. |
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| Authors: | YE Jian-guo LIU Fu-lai |
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| Institution: | (Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037) |
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| Abstract: | An integrated study of mineral inclusions, trace elements and U-Pb ages was accomplished for complex zircons from amphibolite in the main hole of the Chinese Continental Scientific Drilling Project （CCSD-MH）. Zircon grains separated from amphibolite G12 may be subdivided into two types based on cathodoluminescence （CL） and laser Raman spectroscopy; they are big dusty zircons with an inherited （magmatic） core and a UHP metamorphic rim and small clear zircons. Zoned, grey-white luminescent inherited cores preserve mineral inclusions of clinopyroxene ＋ plagioclase ＋ apatite＋quartz indicative of a mafic igneous protolith. Grey-dark luminescent overgrowth rims contain the coesite eclogite-facies mineral inclusion assemblage of coesite ＋ garnet ＋ omphacite ＋ phengite ＋ apatite and formed at T = 732-839℃ and p= 3.0-4.0 GPa. In contrast, white luminescent, small clear zircons preserve amphibolitefacies mineral inclusions of amphibole ＋ plagioclase and formed at T = 612-698℃ and p= 0.76-1.05 GPa. Inherited zircons of sample G12 yielded SHRIMP ^206Pb/^238U ages of 685-650 Ma. The UHP rims yielded consistent Triassic ages around 243-225 Ma with aweighted mean of 229±3 Ma. Small clear zircon gave ^206pb/238^U ages around 219-210 Ma with a weighted mean of 214±3 Ma, interpreted as late-stage amphibolite-faeies retrogression. The data suggest deep subduetion of the protoliths of amphibolite in the Sulu terrane to＇the deep interior of the mande at 100-120 km depth in the Late Triassic （-229 Ma）, and -15 Ma later （at-214 Ma）, these UHP rocks was uplifted to the middle crust at -25 km depth and underwent reworking of late-stage amphibolite-faeies retrogressive metamorphism, with an average rate of exhumation of 0.57 cm/y. |
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| Keywords: | zircon mineral inclusion SHRIMP U-Pb dating amphibolite Chinese Continental Scientific Drilling Project |
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