巴颜喀拉北部江日嘎玛花岗侵入岩地球化学特征及锆石年龄

江日嘎玛花岗侵入岩位于巴颜喀拉-松潘-甘孜造山带北部,侵位于中三叠世甘德组三段地层中。本文通过对江日嘎玛花岗侵入岩进行岩相学、岩石地球化学及年代学研究,探讨其成因及构造环境。研究表明,江日嘎玛花岗侵入岩,具有较高的SiO₂(w(SiO₂)=69.63%~71.05%),A/CNK=1.017~1.043,铝饱和指数<1.1,属弱过铝质高钾钙碱性Ⅰ型花岗岩;岩石具有明显富集Zr、Hf、Ba,亏损Nb、U、Ta、Ti、Rb、K的特征,并且具有负Eu异常;花岗岩锆石SHRIMP U-Pb测年为222.5 Ma±1.9 Ma,表明岩浆侵位时代为中生代晚三叠世,形成于碰撞造山后期地壳减薄环境中。

Geochemical characteristics and zircon age of Jiangri Gama intrusive granite in the North Bayan Hara area

The Jiangri Gama intrusive granite is located in the North Bayan Hara-Songpan-Ganzi orogenic belt occurring in the Member 3 of the Middle Triassic Gande formation. This paper deals with petrography, petrochemistry and chronology of the intrusive granite and discusses the genesis and tectonic environment. It is characterized by high silica (w(SiO₂=69.63%-71.05%), A/CNK=1.017-1.043, Al saturation index<1.1, enrichment of Zr, Hf and Ba, depletion of Nb, U, Ta, Ti, Rb and K and negative Eu anomaly. The zircon age is 222.5 Ma ±1.9 Ma. It is the high K, Ca-alkaline I type granite formed in the post-orogenic crust-thinning environment in the Middle Mesozoic Late Triassoc Epoch.