新疆阿尔泰造山带乌希里克地区奥陶纪岩浆活动及其地质意义

The Ordovician magmatism and implication in Wuxilike,Altay orogenic belt,Xinjiang

阿尔泰乌希里克地区位于阿尔泰造山带的核心部位,本文首次报导该地区出露的早古生代奥陶纪花岗质侵入岩和火山岩。年代学结果表明该地区原来划为中-上奥陶统哈巴河群中的英安岩时代为486±7Ma,斜长角闪岩的原岩时代为482±5Ma,属早奥陶世,而侵位于这套地层中的阿斯恰套岩体、杜洛埃岩体和哈拉尔次岩体的结晶年龄分别为461±2Ma、452±5Ma、455±3Ma,属中-晚奥陶世。这些岩体和围岩的时空关系表明乌希里克地区哈巴河群应属下奥陶统。现有资料表明哈巴河群时间跨度很大,应该通过详细工作将其解体。这些侵入岩和喷出岩均属钙碱性到高钾钙碱性系列,准铝质到过铝质,具有相似的右倾稀土配分模式,亏损高场强元素Nb、Ta、Zr、Hf,富集大离子亲石元素K、Rb、Ba等,具弧岩浆岩的地球化学特征。哈拉尔次岩体和英安岩富K贫Na,尔齐斯-斋桑洋向北俯冲作用的产物。

Here we report the Ordovician arc setting igneous rocks in Wuxilike located in the core area of Chinese Altay orogenic belt. Zircons from dacite and amphibolite of Habahe Group,which had been considered as Middle to Upper Ordovician,yielded mean ages of 486 ± 7Ma and 482 ± 5Ma respectively,which show an Early Ordovician eruption age. The Asiqiatao diorite,Duluoai tonalite and Halaerci granodiorite intruded into the Habahe Group,and with intrusion ages of 461 ± 2Ma,452 ± 5Ma and 455 ± 3Ma,respectively. Thus,the strata near Wuxilike should be separated out from the originally named Middle-Upper Ordovician Habahe Group. Both the intrusive and extrusive rocks are calc-alkaline to high-K calc-alkaline,metaluminous to peraluminous,depleted in Nb,Ta,Zr and Hf and enriched in K,Rb and Ba,and show right incline REE patterns. These features are similar to arc rocks. But the variable Na and K contents with Na2O/K2 O values from 0. 73 to 2. 14 and enriched Sr-Nd isotopic compositions with ISrfrom 0. 7050 to 0. 7098,εNd（ t） from-2. 0 to ＋ 0. 5 and tDMfrom 1. 6Ga to 1. 2Ga implied a continental arc setting. We propose that the Ordovician Wuxilike igneous rocks were generated in an active continental margin when the Irtysh-Zhaisan Ocean plate subducted under the Altay-Mongolian microcontinent.