新疆东天山中段玉林花岗岩体锆石U-Pb测年及地球化学特征

摘要

The Yulin granitoids located in the Qoltag belt in middle section of the eastern Tianshan.This paper conducted zircon U-Pb dating and lithogeochemistry for the Yulin granitoids.The result of the LA-ICP-MS zircon U-Pb age is (327.1±6.6) Ma,was the products of magmation in Late Carboniferous.Geochemical result shows that SiO2 content of the Yulin granitoids is 66.34％～67.52％,Al2O3 content is 15.21％～15.7％,total alkalis content is 5.39％～7.57％,A/CNK values are ranging from 0.877 to 0.988,less than 1.1,suggesting that they are quasi alumina-low K and calc-alkali series granodiorite.The rock have distinctly REE difference,are enrich in LILE,such as K,Sr,and depleted in HFSE,such as Nb,Th,Ti,suggesting that they are VAG,showing geochemical affinities similar to adakites.Combined with the geochemical and isotopic characteristics,it is believed that the Yulin granitoids were probably formed in the island arc environment and were formed in melting of subducted oceanic crust,and affected by the mantle wedge during the ascent.%玉林花岗岩体位于东天山中段觉罗塔格构造带,对玉林花岗岩体开展了锆石U-Pb年代学及岩石地球化学研究.LA-ICP-MS锆石U-Pb测年结果为(327.1±6.6) Ma,为早石炭世岩浆活动的产物.岩石地球化学结果表明,玉林花岗岩体SiO2含量为66.34％～67.52％,Al2O3含量为15.21％～15.7％,全碱含量为5.39％～7.57％,A/CNK为0.877～0.988,小于1.1,属准铝质-低钾钙碱性系列的花岗闪长岩类.岩石具有明显的轻重稀土分异,富集K,Sr等大离子亲石元素,相对亏损Nb,Th,Ti等高场强元素,为火山弧花岗岩,显示与埃达克岩相似的地球化学性质.结合岩石地球化学及同位素特征,认为玉林花岗岩体可能来源于俯冲洋壳的熔融,并在上升过程中受到地幔楔物质的影响,形成于洋壳俯冲下的岛弧环境.