早三叠世北澜沧江结合带碰撞作用：类乌齐花岗质片麻岩年代学、地球化学及Hf同位素证据  

Early Triassic collision of northern Lancangjiang suture:Geochronological,geochemical and Hf isotope evidences from the granitic gneiss in Leiwuqi area,East Tibet

作　　者：王保弟[1] 王立全[1] 强巴扎西 曾庆高 张万平[1] 王冬兵[1] 程万华[1] 

机构地区：[1]成都地质矿产研究所,成都610081 [2]西藏地勘局区域地质调查大队,拉萨850000

出　　处：《岩石学报》2011年第9期2752-2762,共11页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目(2009CB421003);国家自然科学基金(41073033、40872055);中国地质调查局项目(1212011121259、1212011085119)联合资助

摘　　要：西藏东部类乌齐一带吉塘岩群中新识别出一套花岗质片麻岩,其Cameca锆石U-Pb年龄为246.3±0.8Ma,表明该变质花岗岩形成于早三叠世。该套变质侵入体具高SiO2(68.21%～74.82%)、富K2O(K2O/Na2O>1)和低P2O5(<0.26%)特征,铝饱和指数(ACNK)为1.01～1.19,属准铝质到过铝质岩石;富集Rb、Th和U,亏损Ba、Nb、Ta、Sr、P和Eu等;并具不均一的锆石εHf(t)值(-1.3～+3.7)和古老的锆石Hf同位素地壳模式年龄(1.0～1.4Ga),具有碰撞型花岗岩的地球化学特征。类乌齐变质侵入体很可能形成于澜沧江结合带所代表的洋盆闭合后碰撞的地球动力学背景,可能是幔源岩浆诱发古老地壳物质重熔并与之混合形成母岩浆,再经历高程度分离结晶作用而形成,为北澜沧江结合带碰撞造山过程的产物,暗示澜沧江结合带在早三叠世存在岩浆增生事件,藏东类乌齐地区在246Ma之前己进入陆-陆碰撞时期。A suit of granitic gneiss was recognized in the Jitang rock group from Leiwuqi area in the East Tibet.Cameca U-Pb zircon analyses suggest that the granitic gneiss was dated at 246.3±0.8Ma,suggesting the metamorphic granite was formed in the Early Triassic.The metamorphic intrusive rocks are characterized by high SiO2（68.21%~74.82%）,K2O（K2O/Na2O1） and low P2O5（0.26%）.ACNK are ranging from 1.01 to 1.19,belonging to aluminous-peraluminous rocks.They are enrichment of Rb,Th and U,and strong negative anomalies of Ba,Nb,Ta,Sr,P and Eu,with variable εHf（t）（-1.3~＋3.7） and ancient tCDM（1.0~1.4Ga）.These features suggest that the granitic gneiss is similar to collision type granite.The Leiwuqi granitic gneiss was most likely formed at post-collision setting in the Lancangjiang belt.They were probably generated by highly fractional crystallization of parent magma,which mixing with melts from remelting of ancient crust materials induced by mantle-derive magma underplating and mantle-derive magma melts,product of collisional orogenesis.The results indicate that magmatic growth in Lancangjiang suture during Early Triassic,and had entered a continental collision stage by the Early Triassic（~ 246Ma） in the Leiwuqi area of the east Tibet.

关 键 词：花岗质片麻岩 碰撞型花岗岩 锆石U-PB年龄 澜沧江结合带 类乌齐 西藏 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]