冈底斯中段扎扎龙矿区闪长岩体锆石U-Pb年代学、岩石地球化学特征及其意义

扎扎龙矿区位于西藏冈底斯中段,隆格尔念青唐古拉铁、铜、铅、锌、银成矿带之西段。岩石学、LA-ICP-MS锆石U-Pb测年及岩石地球化学特征研究显示:扎扎龙矿区闪长岩体的岩石类型主要为闪长岩,个别为石英闪长岩,其LA-ICP-MS锆石U-Pb年龄为(64.15±0.52) Ma,形成于古新世(E₁)早期;闪长岩体属准铝质过铝质岩石(A/CNK值为0.89~1.06),具高钾钙碱性系列的特征;稀土元素表现为轻稀土弱富集的右倾斜型,绝大多数(La/Yb)_N为1.78~2.08,具弱的负铕异常(δEu=0.65~0.81);微量元素普遍表现出K、Th元素的富集和Nb、P、Ti元素的强烈亏损。扎扎龙闪长岩体源区为壳幔混合源区,形成于雅鲁藏布江洋高角度俯冲阶段,暗示了印度-亚洲大陆碰撞时间应晚于65 Ma。

Zircon U Pb Chronology,Geochemical Characteristics and Significance of Diorites in Mining Area of Zhazhalong in Mid-Gangdese

Zhazhalong area is located in the Middle of Gangdese and also on the west part of Longgeer Nyainqentanglha Fe ,Cu ,Pb ,Zn ,Ag metallogenic belt in Tibet . The petrology ,LA ICP MS zircon U Pb dating ,and lithogeochemical characteristics show that the main rock type is diorite with individual quartz diorite .The LA ICP MS zircon U Pb age of the diorites is (64 .15 ± 0 .52) Ma which indicates that the rocks were formed in the Early Paleocene .The diorites are meta‐aluminous to per‐aluminous (A /CNK date is 0 .89 1 .06 ) , and belong to the high‐K calc‐alkaline series . The characters of REE are right‐incline and LREE enrichment (LaN /YbN date is 1 .78 2 .08) with weak Eu anomaly(δEu date is 0 .65 0 .81) .The characters of trace elements are rich in K ,Th and depleted of Nb ,P ,Ti intensively .By synthesis analysis ,the origin of the rocks was a mixture of crust mantle , and they were formed in the subduction of Yarlung Zangbo Oceanic crust .This implies that the time of the collision between India and Asia land should be later than 65 Ma .