西藏班戈地区侵入岩年代学和地球化学:对班公湖-怒江洋盆演化时限的制约

The geochronology and geochemistry of intrusive rocks in Bange area: Constraints on the evolution time of the Bangong Lake-Nujiang ocean basin

详细的野外地质调查、室内锆石U-Pb年代学和岩石地球化学研究显示,班戈地区侵入岩可以分为4期：早白垩世早期石英闪长岩和英云闪长岩（138Ma±）,早白垩世中期花岗闪长岩（132-128Ma）,早白垩世中晚期二云二长花岗岩（130-114Ma）,晚白垩世二长花岗岩（80Ma±）,从北到南各期次侵入岩具有成岩年龄逐渐变新,形成环境由岛弧环境→同碰撞造山环境→后碰撞环境演变。这一成果为确定班公湖-怒江洋盆的俯冲极性及演化时限提供了新的资料。班戈地区班公湖-怒江洋盆在中侏罗世之前已开始向南俯冲消减,这种俯冲消减活动一直持续至早白垩世中期最终闭合（130-125Ma）,拉萨地体与羌塘地体开始发生碰撞作用,这种碰撞作用大约持续了20-30Myr,在晚白垩世早期进入后碰撞阶段（100-80Ma）。

Field geological survey, U-Pb zircon chronology and rock geochemistry study shows that the intrusive rock of Bange region can be divided into four periods： early Early-Cretaceous quartz diorite and tonalite （138Ma±）, the middle Early-Cretaceous granodiorite （132-128Ma）, the middle-late Early-Cretaceous two-mica adamellite （130-114Ma）, Late-Cretaceous adamellite （80Ma±）. From the north to south, the petrogenic age of intrusive rock is from late to early, and the formation environment is from island-arc environment to syn-collosional orogenic environment to post-collisional environment. This result provides new information about the subduction polarity and evolution time of Bangong Lake-Nujiang ocean basin. The southward subduction of the Bangong Lake-Nujiang Ocean Basin is beginning before Middle Jurassic in Bange area, and it lasts to the middle Early-Cretaceous （130-125Ma）, and finally close in the middle Early-Cretaceous （125Ma±）. Then the collision of the Lhasa terrane and the Qiangtang terrane started, after 20-30Myr enter to post-collosional stage in early Late-Cretaceous （100-80Ma）.