西藏江玛地区闪长玢岩锆石U-Pb年龄、地球化学特征及其地质意义  

Zircon U-Pb Ages,Geochemistry and Geological Significance of Diorite Porphyrite in Jiangma Area,Tibet

作　　者：尹滔[1] 张伟[1] 尹显科[1] 裴亚伦[1] Yin Tao;Zhang Wei;Yin Xianke;Pei Yalun(Evaluation and Utilization of Strategic Rare Metals and Rare Earth Resources Key Laboratory of Sichuan Geological Survey,Chengdu 610081,China)

机构地区：[1]四川省地质调查院稀有稀土战略资源评价与利用四川省重点实验室,四川成都610081

出　　处：《地球科学》2020年第11期4128-4142,共15页Earth Science

基　　金：中国地质调查局项目(Nos.DD20160026,DD20191029)。

摘　　要：目前对班公湖-怒江蛇绿混杂岩带的中酸性侵入岩的报道相对较少,对其成因和形成机制的研究有助于揭示班公湖-怒江特提斯洋构造带的岩浆作用过程和动力学背景.对西藏班公湖-怒江蛇绿混杂岩带江玛地区的闪长玢岩进行了年龄分析、岩石地球化学研究.闪长玢岩的LA-ICP-MS锆石U-Pb年龄为121±1 Ma,表明其形成于早白垩世晚期.岩石地球化学特征表明,闪长玢岩具高Al2O3含量(18.2%~19.3%),属高铝玄武岩,岩石富集轻稀土元素和大离子亲石元素Rb、K等,亏损高场强元素Nb、Ta、Ti,属典型的岛弧玄武岩.综合区域地质资料认为,江玛地区闪长玢岩可能形成于俯冲带前缘增生的岛弧环境,是早白垩世期班公湖-怒江特提斯洋壳岩石圈南向俯冲消减背景下,板片脱水形成的流体与地幔楔橄榄岩发生交代作用的产物.There are relatively few reports on the intermediate-acid intrusive rocks in the Bangonghu-Nujiang ophiolitic melange belt,the study on the petrogenesis and tectonic setting of this rocks is important to define the geodynamic evolution of Bangonghu-Nujiang Tethys oceanic.It reports zircon U-Pb age and major-trace elements for the diorite porphyrite from the Jiangma area in the Bangonghu-Nujiang suture zone.Zircon LA-ICP-MS U-Pb dating of the diorite porphyrite yields an Early Cretaceous age of a 121±1 Ma,indicating that the intruded rocks were formed in the late Early Cretaceous period.Geochemical studies show that diorite porphyrite has typical geochemical characteristics similar to the high-alumina basalts.They are characterized by high Al2 O3 contents(18.2%-19.3%),and enriched in light rare earth elements and large ion lithophile elements(Rb and K),but depleted in high field strength elements(Nb,Ta and Ti).All of these geochemistry characteristics of the rocks are the same as the typically island arc basalts.Combined with the regional geological setting,the diorite porphyrite may be formed in an accretive arc environment related to the southward subduction of Bangonghu-Nujiang Tethys oceanic crust in late Early Cretaceous.The fluids derived from the subducted oceanic crust would metasomatize the overlying mantle peridotite to generate the mantle source of the studied diorite porphyrite.

关 键 词：班公湖-怒江蛇绿混杂岩带 闪长玢岩 高铝玄武岩 俯冲消减 锆石U-PB年龄 地球化学 

分 类 号：P581[天文地球—岩石学]