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

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)。

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

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).