新疆东准乌须克劳格岩体LA-ICP-MS锆石U-Pb年龄、Hf同位素特征及其地质意义

LA-ICP-MS zircon U-Pb ages and Hf isotopic characteristics of Wuxukelaoge pluton in East Junggar Basin of Xinjiang and their geological significance

新疆东准噶尔琼河坝地区近年来找矿获得重大突破,发现了一系列重要的矿产,这些矿产基本上围绕该地区出露面积最大的乌须克劳格岩体分布。该岩体组成比较复杂,主要岩性为二长花岗岩和花岗闪长岩。采用LA-ICP-MS技术测得花岗闪长岩和二长花岗岩锆石^(206)Pb/^(238)U年龄分别为428.9±1.9Ma和427.2±1.7Ma,被解释为岩石的结晶年龄。2类岩石都属于过铝质-钙碱性系列花岗岩,具有较高的铝、钙含量,K_2O/Na_2O值普遍偏低,介于0.15~0.40之间;稀土元素配分曲线呈现右倾特征,稀土元素总量较低,轻稀土元素相对富集,负Eu异常不明显;在微量元素原始地幔标准化蛛网图上,高场强元素Th、Nb、Ta、P、Ti等相对亏损,大离子亲石元素Rb、Ba、U、K、Sr等相对富集,具有高Ba、Sr含量和高(La/Yb)_N、Sr/Y值,显示出高Ba-Sr花岗岩的特征;同时岩体具有高正ε_(Hf)(t)值和年轻的模式年龄。这些地球化学和同位素特征表明,晚志留世乌须克劳格岩体是大陆边缘弧环境下大洋板片熔融的产物。

Thanks to prospecting breakthrough in recent years, a series of important mineral resources have been found in Qiongheba area, East Junggar Basin, Xinjiang, which are essentially distributed around Wuxukelaoge pluton. The pluton is the largest in the re？ gion and it has a complex composition, mainly comprising granodiorite and monzonitic granite. In this paper, U-Pb dating of LA-ICP-MS zircon was used to investigate the age of the pluton. It is shown that granodiorite is 428.9±1.9Ma and monzonitic granite is 427.2±1.7Ma in age, suggesting that the two ages represent the ages of rocks that contain the zircon. Both the granodiorite and mon-zonitic granite are of peraluminous and calc-alkaline series with high Al2O3 （15.87%~18.77%）, CaO （2.92%~6.82%） and low K2O/Na2O ratios （0.15~0.40）;The pluton has low total REE content （57.33×10-6~72.13×10-6） with relative enrichment of LREE and ob-scure Eu negative anomaly （δEu=0.79~1.06）. The primitive mantle normalized trace element patterns are characterized by the deple-tion of the HFSE （Th, Nb, Ta, P, Ti） and enrichment of the LILE （Rb, Ba, U, K, Sr）. High Ba （230×10-6~682×10-6）, Sr（851.8×10-6~1020.1×10-6）, high （La/Yb）N（6.0~10.1）, Sr/Y（70.0~106.4） ratios, and distinct Nb all suggest features of high Ba-Sr granitoids. The test results of Hf isotope show that Wuxukelaoge pluton has high and positive εHf（t） values（14.28~17.54） and younger model age. These geochemical and Hf isotope characteristics indicate that the pluton was formed in a continental margin arc setting and related to partial melting of subducted oceanic crust.