云南怒江河流沉积物碎屑锆石LA-ICP-MS U-Pb年龄和Hf同位素组成及其地质意义

LA-ICP-MS U-Pb ages and Hf isotopic compositions of detrital zircons in the sediments of the Nujiang River, Yunnan Province, and their geological significance

采用LA-MC-ICP-MS测定技术,对怒江河流沉积物中的碎屑锆石进行了U-Pb和Lu-Hf同位素测定。结果显示,碎屑锆石U-Pb年龄可分为6个组段:50~74Ma、84~235Ma、275~413Ma、451~569Ma、657~1429Ma和1602~3436Ma,其中最主要的年龄组段为50~74Ma和84~235Ma。50~74Ma的年龄段为新特提斯洋从俯冲到碰撞闭合的阶段,约65Ma的年龄峰值可能是印度大陆与欧亚大陆主体碰撞的远程地质记录。84~235Ma年龄段代表了中特提斯洋演化阶段,年龄峰值约为110Ma,可能指示羌塘地块与拉萨地块的碰撞拼接此时已经完成,通过U-Pb年龄分布对比,羌塘地块几乎没有给怒江河流沉积物提供物质。怒江河流沉积物中碎屑锆石的εHf(t)值介于-18.7^+11.7之间,模式年龄分布于0.65~4.05Ga之间,其中中生代碎屑锆石的εHf(t)值分布于-16.4^+2.9之间,与中拉萨地块有密切的亲缘性,同时含有少量北拉萨地块的特征。因此,怒江河流沉积物代表了中拉萨地块与北拉萨地块的特征。

In this paper, LA-ICP-MS technology was used to perform U-Pb dating and analyze Lu-Hf isotopic composition. U-Pb ages of the detrital zircons in the sediments of the Nujiang River can be divided into 6 groups： 50～74Ma, 84～235Ma, 275～413Ma, 451～569Ma, 657～1429Ma and 1602～3436Ma, with the most important age populations being 50～74Ma and 84～235Ma. The ages of 50～74Ma reflect the history of the subduction and the closure of the Neo-Tethys Ocean, and the age peak of ca.65Ma reveals the main collision stage between India and Eurasian continents. The 84～235Ma might reveal the evolution of the Meso-Tethys Ocean, and the age peak of ca.110Ma is the geological record of the post collisional stage between the Qiangtang block and the Lhasa block. A comparison of the U-Pb ages distribution with that of the Qiangtang block suggests that sediments of the Nujiang River are not derived from the Qiangtang block. In addition, theεHf（t） values and the two-stage model ages of the detrital zircons from the Nujiang River range from-18.7 to＋11.7 and from 0.65Ga to 4.05Ga, respectively. Meanwhile,εHf（t） values of the Mesozoic detrital zircons range from-16.4 to＋2.9, which is consistent with the data from the Middle Lhasa block and the North Lhasa block.