冈底斯带中北部色日绒地区早白垩世花岗岩的LA-ICP-MS锆石U-Pb年龄、地球化学特征及其地质意义  

LA-ICP-MS zircon U-Pb dating,geochemical characteristics and geological significance of Early Cretaceous granites in the Serirong area of north-central Gangdese,Tibet

作　　者：秦松[1,2] 孙传敏[1] 张剑波[2] 张伟[2] 丁代国 尼玛次仁 

机构地区：[1]成都理工大学地球科学学院,四川成都610059 [2]四川省地质矿产勘查开发局区域地质调查队,四川成都610213 [3]西藏自治区地质矿产勘查局第二地质大队,西藏拉萨851400

出　　处：《地球化学》2018年第2期182-195,共14页Geochimica

基　　金：中国地质调查局项目(1212011221077);国家自然科学基金(41272046)

摘　　要：色日绒地区崔绝果和寒空达岩体位于冈底斯带中北部的隆格尔-工布江达弧背断隆带东段,主要岩性分别为黑云母花岗岩和黑云母二长花岗岩。对寒空达岩体进行了LA-ICP-MS锆石U-Pb测年,其年龄值为(136.0±1.4)Ma,与同时期崔绝果岩体共同代表了该地区早白垩世大规模的中酸性岩浆活动。据岩石学、主元素特征分析,两个岩体均属钾玄岩-高钾钙碱性强过铝S型花岗岩系列。微量元素Sr、P、Ti、Nb元素亏损,具后碰撞花岗岩特征;Th元素具高丰度值(绝大多数大于20μg/g),指示岩体源岩来自地壳物质;两个岩体均显示轻、重稀土元素之间分异明显,具右倾型分布模式,反映了源区地壳成熟度较高的特征。结合地球化学特征、构造图解判别以及区域构造演化分析,得出该地区早白垩世花岗岩是在班公湖-怒江缝合带主造山作用结束后,色日绒地区由挤压转变为伸展、拉张为主应力的后碰撞环境下,部分熔融念青唐古拉群变质砂屑岩形成的。该地区两个岩体的发现及其形成时代的确定,将冈底斯中北部后碰撞构造环境的时限约束在136.0~139.2 Ma之前。The Cuijueguo and Hankongda granites are found in the Serirong area, in the eastern section of the Longgaer-Gongbujiangda uplift, north-central Gangdese; they mainly comprise biotite adamellite, and biotite granite. The Hankongda granites have been analyzed using the LA-ICP-MS zircon U-Pb techniques; their U-Pb age is （136.0±1.4） Ma, which is similar to that of the Cuijueguo granite, representing large-scale middle-acid magmatic activity of the Early Cretaceous in the region. The two granites belong to the shoshonites to high-K calc-alkaline and strongly peraluminous S-granite series, based on the analysis of the petrology and major elements. They display typical geochemical signatures of post-collisional granites, including the depletion of Sr, P, Ti, and Nb. The two granites have high Th abundance values （the vast majority are more than 20）, indicating their source to be crustal material. Both granites show significant differentiation between LREE and HREE with a right-leaning pattern, reflecting high maturity of the crust. Based on the geochemical analysis, the trace element discrimination diagrams for tectonic interpretation, and regional tectonic evolution, it can be established that the Serirong granites have been formed after the main orogenic event in the Bangonghu-Nujiang suture, in a post-collisional tectonic setting transitioning from the compressional system to the tensional system. They are derived from the partial melting of the metamorphosed basement of psammitolite from Nyainqentanglha Group. The discovery and age determination of these two granites in the Serirong area constrains of the post-collisional tectonic setting in the north-central Gangdese to before 136.0-139.2 Ma.

关 键 词：早白垩世 花岗岩 LA-ICP-MS锆石U-PB定年 岩石地球化学特征 色日绒地区 冈底斯中北部 

分 类 号：P597[天文地球—地球化学] P581[天文地球—地质学]