西藏切穷地区早侏罗世花岗岩年代学特征及其构造意义

西藏切穷地区早侏罗世花岗岩岩体位于西藏冈底斯构造—岩浆带之中带。其主要岩性为不等粒二长花岗岩+花岗闪长岩。LA-ICP-MS锆石U-Pb定年结果表明，研究区花岗岩岩体侵位年龄主要集中在（192.8±1.3 Ma～189.1±0.66 Ma），属早侏罗世。花岗岩SiO₂ = 65.58%～75.57%，K₂O+Na₂O = 7.00%～8.25%，铝饱和指数A/CNK = 0.81～1.33；轻重稀土元素分馏较明显，（La/Yb）_N = 2.47～42.03，负Eu异常，δEu = 0.27～0.72；微量元素表现出Rb、Th、U、La和Ce的强烈富集，Nd、Hf、Sm、Y、Yb和Lu相对富集，K、Nb、Sr、P和Ti元素相对亏损的特点，属高钾钙碱性S型花岗岩系列。根据岩体的成因类型并结合区域构造环境演化，分析认为研究区花岗岩形成于同碰撞环境，是壳源岩石重熔作用的产物。

The chronology characteristics and tectonic significance of Early Jurassic granite in Qieqiong area in Tibet

The Early Jurassic granite body in Qieqiong area of Tibet lies in the middle of Gangdise tectonic-magmatic belt. The main lithology is unequal granitic monzonite and granodiorite. The dating results of U-Pb from LA-ICP-MS zircon indicate that the emplacement ages of granite bodies in the study area are mainly 192.8±1.3 Ma～189.1±0.66 Ma, which belongs to the Early Jurassic. SiO₂ = 65.58%～75.57%, K₂O+Na₂O = 7.00%～8.25%, aluminum saturation index A/CNK = 0.81～1.33. The fractionation of heavy and light rare earth elements is obvious, （La/Yb）_N = 2.47～42.03, negative Eu anomaly, δEu = 0.27～0.72. Early Jurassic acid intrusive rocks showed strong enrichment of Rb, Th, U, La and Ce, relatively enrichment of Nd, Hf, Sm, Y, Yb and Lu, and relative deficit of K, Nb, Sr, P and Ti. According to the genetic type of rock mass and the evolution of regional tectonic environment, it is concluded that the granite in the study area was formed in the same collision environment. It is the product of shell source rock remelting.