| 华北克拉通孔兹岩带中段大青山-乌拉山变质杂岩立甲子基性麻粒岩年代学及地球化学研究 |
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| 引用本文： | 刘平华,刘福来,蔡佳,刘建辉,施建荣,王舫.华北克拉通孔兹岩带中段大青山-乌拉山变质杂岩立甲子基性麻粒岩年代学及地球化学研究[J].岩石学报,2013,29(2):462-484. |
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| 作者姓名： | 刘平华 刘福来 蔡佳 刘建辉 施建荣 王舫 |
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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： | 本文受科技部973项目(2012CB416603);国家杰出青年科学基金项目(40725007);中国地质调查局地质大调查项目(1212010811065、1212011120150)和中国地质科学院地质研究所基本科研业务经费(J1212)联合资助. |
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| 摘 要： | 大青山-乌拉山变质杂岩立甲子基性麻粒岩主要由角闪二辉麻粒岩、含榴角闪二辉麻粒岩和黑云角闪二辉麻粒岩所组成,并以变形岩墙和不规则透镜体形式赋存于富铝片麻岩和花岗质片麻岩之中.立甲子基性麻粒岩中变质锆石含有单斜辉石(Cpx)+角闪石(Amp)+斜长石(Pl)+磷灰石(Ap)的包体矿物,与寄主岩石——基性麻粒岩矿物组合及其化学成分十分一致,相应的207 pb/206 Pb表面年龄变化于1933±39Ma ～ 1834±40Ma,加权平均年龄为1892±7Ma(MSWD =0.50,n=46),应代表立甲子基性麻粒岩原岩经历中低压麻粒岩相的变质时代.在变质过程中,以大离子亲石元素(K、Na、Sr、Rb)为代表的活动元素发生了显著的改变；而高场强元素(Nb、Zr、Ti)和稀土元素基本无变化,保持稳定.立甲子基性麻粒岩原岩属于拉斑玄武质岩石系列,其SiO2集中变化于45.58％ ～51.40％,Mg#值集中介于41 ～54之间；在球粒陨石标准化稀土配分图中,立甲子基性麻粒岩具有平坦型的稀土配分曲线特征((La/Yb)cN=1.30～1.51),Eu异常不明显(Eu/Eu*=0.93～1.04).与显生宙岛孤拉斑玄武岩类似,立甲子基性麻粒岩所有样品皆具有Nb、Zr、Ti负异常特征.综合分析认为,立甲子基性麻粒岩原岩形成于2450～1930Ma,并于～1900Ma经历中低压麻粒岩相变质作用的改造,其主量元素和微量元素组成具有岛弧拉斑玄武质岩石的地球化学特征,其原岩可能是板块汇聚动力学背景下,岛弧构造环境中形成的辉长岩或辉绿岩.
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| 关 键 词： | 基性麻粒岩 年代学 地球化学 大青山-乌拉山变质杂岩 |
| 收稿时间： | 2012/9/18 0:00:00 |
| 修稿时间： | 1/7/2013 12:00:00 AM |
Geochronological and geochemical study of the Lijiazi mafic granulites from the Daqingshan-Wulashan metamorphic complex, the central Khondalite Belt in the North China Craton |
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| LIU PingHu,LIU FuLai,CAI Ji,LIU JianHui,SHI JianRong and WANG Fang.Geochronological and geochemical study of the Lijiazi mafic granulites from the Daqingshan-Wulashan metamorphic complex, the central Khondalite Belt in the North China Craton[J].Acta Petrologica Sinica,2013,29(2):462-484. |
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| Authors: | LIU PingHu LIU FuLai CAI Ji LIU JianHui SHI JianRong and WANG Fang |
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| Institution: | Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China |
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| Abstract: | The Lijiazi mafic granulites are predominantly composed of Amp Cpx-Opx granulite, Grt-bearing Amp Cpx-Opx granulite and Bt Amp Cpx-Opx granulite, and have been found as irregular lenses and deformed dykes within the Al-rich gneisses and granitic gneisses in the Daqingshan-Wulashan metamorphic complex. The apparent 207Pb/206Pb ages recorded by the metamorphic zircon domains with the middle-to low-pressure granulite-facies mineral inclusions of Cpx+Amp+Pl, which are consistent to the matrix-type metamorphic assemblages of the mafic granulites, range from 1933±39Ma to 1834±40Ma with a weighted mean age of 1892±7Ma, which are interpreted as the timing of the middle-to low-pressure granulite-facies metamorphism of the mafic granulites. Mobile elements such as the large ion lithophile elements (K, Na, Sr, Rb) of the mafic granulites changed in significant levels, high field strength elements (such as Nb, Zr, Ti) and rare earth elements basically unchanged and keep stable during the metamorphic process. The Lijiazi mafic granulites from the Daqingshan complex belong to tholeiitic-basaltic rock series, with the concentrations of SiO2 at 45.58%~51.40%, and Mg# value mainly ranging from 41 to 54. The composition of the rare earth elements of the mafic granulites is characterized by the flat, (La/Yb)CN=1.30~1.51) with no Eu anomalies (Eu/Eu*=0.93~1.04) on the chondrite-normalized patterns. All samples of the mafic granulites share obvious negative anomaly in Nb, Zr and Ti of the Phanerozoic island arc basalts. According to the geochemical and geochronological data of the Lijiazi mafic granulites, it is suggested that the protolith ages of the Lijiazi mafic granulites is 2450~1930Ma, the protoliths of the mafic granulites are undergone middle-to low-pressure granulite-facies metamorphism at ~1900Ma, the composition of the major and trace elements of the mafic granulites is characterized by the island arc tholeiitic basaltic rocks, and their protoliths may be gabbro or diabase dykes which formed in the island arc of the plate convergence dynamic setting. |
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| Keywords: | Mafic granulites Geochronology Geochemistry Daqingshan-Wulashan metamorphic complex |
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