东昆仑巴音呼都森晚三叠世中酸性侵入岩锆石LA-ICP-MS U-Pb定年及地质意义

摘要

巴音呼都森中酸性花岗岩位于东昆仑西段祁漫塔格山,处于北昆仑岩浆弧中,岩石类型由灰白色中细粒花岗闪长岩、灰白色中细粒二长花岗岩、浅肉红色细中粒似斑状二长花岗岩和浅灰肉红色二长花岗斑岩组成.笔者分别选取该地区多登似斑状二长花岗岩和景忍二长花岗斑岩进行LA-ICP-MS锆石微区定年,获得时间为(217±2)Ma、(212±1)Ma,表明该岩体成岩年龄为晚三叠世.岩石地球化学特征具有高SiO2含量(67.01％～76.61％)、K2O含量(3.47％～5.52％)、Na2O含量(1.55％～4.52％),而贫MgO(0.12％～1.37％),低TiO2(0.06％～0.84％)、P2O5(0.01％～0.36％)的特征,稀土元素特征具弱的Eu负异常(δEu值=0.17～0.72),A/CNK均小于1.1,岩石系列属过铝质的高钾钙碱性.综合分析认为该期花岗岩形成于后造山伸展环境.该型花岗岩的确定证明了祁漫塔格地区晚三叠世之前碰撞造山作用的存在.%The Bayinhudousen intrusive rocks are located at Qimantage Mountain in the western part of East Kunlun Mountains,and they are occurred in the North Kunlun magmatic arc.They are composed of gray white fine granite granodiorite,gray medium-fine grained monzonitic granite,flesh red fine-medium grained porphyritic monzogranite and light grey monzonitic granite porphyry.In this paper,the LA-ICP-MS Zircon U-Pb method has been used to date the samples of porphyritic monzogranite in Duodeng area and monzonitic granite porphyry in Jingren area.The obtained ages are (217.0±2.0) Ma and (212.0±1.0) Ma,respectively,suggesting that these plutons were formed in Late Triassic epoch.The geochemical results show that these rocks have highSiO2 (67.01％～76.61％),K20 (3.47％～5.52％) andNa2O (1.55％～4.52％) contents,but havelow MgO (0.12％～1.37％),TiO2 (0.06％～0.84％) and P2O5 (0.01％～0.36％) contents.Their rare earth elements have weak negative Eu anomaly (δEu values are 0.17～0.72),and their A/CNK ratios are less than 1.1,showing the features of peraluminous high-k calc-alkaline series.After analyzing the characteristics mentioned above,it's believed that these granites were formed in post orogenic extensional environment.Therefore,the existence of Bayinhudousen late triassic intrusive rocks has proved that the collision orogenesis was existed in Qimantage tectonic belt before Late Triassic epoch.