西藏唐加地区卓隆普斜长角闪岩锆石U-Pb年代学、地球化学及地质意义

Zircon U-Pb Geochronology,Geochemistry and Geological Significance of the Zhuolongpu Amphibolite in the Tangjia Area of Tibet

本文以西藏唐加地区卓隆普斜长角闪岩为研究对象,通过岩相学、锆石U-Pb年代学和全岩地球化学组成分析,探讨了其岩石成因以及对松多古特提斯洋演化的地质意义。结果显示,卓隆普斜长角闪岩原岩形成于264.7±1.3 Ma(n=28,MSWD=0.88),属中二叠世。全岩地球化学特征显示该套岩石呈钙碱性,富集轻稀土元素(LREE/HREE=4.69~4.88),弱铕异常(δEu=0.81);样品富集大离子亲石元素(LILEs),具有强烈的Nb-Ta负异常,表现出岛弧玄武岩亲缘性。多种判别图解显示斜长角闪岩原岩形成于俯冲相关的岛弧环境,原岩岩浆由俯冲大洋板片和洋壳物质融熔体以及其脱水过程中形成的俯冲流体交代上覆地幔楔形成,岩浆上升过程中可能受到轻微的地壳物质混染。结合区域资料,本次研究认为唐加-松多古特提斯洋在265 Ma(中二叠世)之前已经发生俯冲。

This work reports the petrography,zircon U-Pb chronology and whole-rock geochemical composition of the Zhuolongpu amphibolite in the Tangjia area of Tibet,and discusses its petrogenesis and the geological significance of the evolution of Sumdo Paleo-Tethys.Results show that the protolith of Zhuolongpu amphibolite was formed in the Middle Permian at 264.7±1.3 Ma(n=28,MSWD=0.88).The whole-rock geochemical characteristics indicate that the rocks are calc-alkaline,rich in light rare earths(LREE/HREE=4.69~4.88)and weak europium anomalies(δEu=0.81).Moreover,the samples are rich in large ion lithophiles(LILEs)and display strong negative Nb-Ta anomalies,showing the affinity with island arc basalt.Various discriminant diagrams show that the protolith of the amphibolite were formed under a subduction-related island arc setting.Magma of the protolith was formed by the melt of mantle wedge and subducting oceanic slabs,oceanic crust melts.The magma may be contaminated by crustal material slightly during ascending.In combination with previous studies,it is inferred that the subduction of the Tangjia-Sumdo Paleo-Tethys began before 265 Ma(Middle Permian).