藏北物玛错地区扎弄朗当日白垩纪复式岩体的地球化学特征及地质意义

Geochemical Characteristics and Their Geological Significance of the Zhalonglangdangri Complex Intrusivein the Oma Co Region,North Tibetan

扎弄朗当日复式岩体呈不规则状、近椭圆状侵位于早白垩世多尼组和去申拉组火山岩地层中。早白垩世闪长岩、二长闪长岩为钙碱性-高钾钙碱性准铝质岩,具有低K_(2)O、高CaO的特征;晚白垩世形成的石英闪长岩、石英二长岩为高钾钙碱性-钾玄岩、准铝质-过铝质岩,明显有K_(2)O升高、CaO降低的特点。复式岩体富集轻稀土和Rb、K等大离子亲石元素,强烈亏损Nb、Ta、P和Ti等高场强元素,从早白垩世以幔源成分为主向晚白垩世以壳源成分为主演化,形成于典型的活动大陆边缘环境,始于班公湖-怒江洋向南俯冲消减过程中,止于班公湖-怒江缝合带洋陆转换完成后的后碰撞伸展环境。

The Zhalonglangdangri complex intrusive in an irregular or nearly elliptical form was emplaced in volcanic rock of the Lower Cretaceous Duoni Formation and Qushenla Formation.The Early Cretaceous diorite and monzodiorite are calc-alkaline and K-rich calc-alkaline metaluminous rocks with low K_(2)O and high CaO and the Late Cretaceous quartz diorite and quartz monzonite are K-rich calc-alkalinedolerite and metaluminous and peraluminous rocks with high K_(2)O and low CaO.The complex intrusiveis rich in REE and LIL elementssuch as Rb and K and depleted in HFSE such as Nb,Ta and Ti which indicate that the complex intrusive was derived mainly from the mantle in the Early Cretaceous and mainly from the crust in the Late Cretaceous and emplaced in a typical active continental margin setting,and beginning during the southwards subduction of the Bangong Co-Nujiang Ocean and ending in post-collisional extensional setting of the Bangong Co-Nujiang suture zone.