西天山阿吾拉勒西段早二叠世粗安岩年代学和地球化学特征  

Geochronology and geochemistry of the Early Permian trachyandesites in the western Awulale area,West Tianshan Mountains

作　　者：丁振信 薛春纪[2] 赵晓波[2] 田建吉[3] 闫永红 罗晖 DING Zhen-xin;XUE Chun-ji;ZHAO Xiao-bo;TIAN Jian-ji;YAN Yong-hong;LUO Hui(Peking University Press Co.,Ltd,Beijing 100871,China;State Key Laboratory of Geological Processes and Mineral Resources,School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China;CNNC Key Laboratory of Uranium Resource Exploration and Evaluation Technology,Beijing Research Institute of Uranium Geology,Beijing 100029,China;CITIC Mining Science and Technology Development Co.,Ltd .,Beijing 100004,China;Geological Survey Institute of Gansu Province,Lanzhou 730000,China)

机构地区：[1]北京大学出版社有限公司,北京100871 [2]中国地质大学地质过程与矿产资源国家重点实验室,中国地质大学(北京)地球科学与资源学院,北京100083 [3]核工业北京地质研究院中核集团铀资源勘查与评价技术重点实验室,北京100029 [4]中信矿业科技发展有限公司,北京100004 [5]甘肃省地质调查院,甘肃兰州730000

出　　处：《岩石矿物学杂志》2019年第5期587-605,共19页Acta Petrologica et Mineralogica

基　　金：国家科技支撑计划(2011BAB06B02);国家自然科学基金项目(U1303292,41072069);中国地质调查局项目(12120113057300,1212011220926)~~

摘　　要：阿吾拉勒构造岩浆带(ATMB)是西天山重要的Fe-Cu多金属矿带,尤其阿吾拉勒西段多见Cu矿床/矿点,但对该地区二叠纪的地球动力学背景和成矿环境的认识还存在分歧。本文在阿吾拉勒西段群吉萨依地区乌郎组火山岩的下部发现了中高钾钙碱性粗安岩,LA-ICP-MS锆石U-Pb测年显示该粗安岩的206Pb/238U加权平均年龄为300±11 Ma。群吉萨依粗安岩富集轻稀土元素(LREE)和大离子亲石元素(LILE,如Rb、Ba、K),重稀土元素(HREE)配分平坦,具有Nb、Ta、Ti的强烈亏损,同时Nd同位素相对亏损,εNd(t)=+4. 5^+4. 9,Nd同位素模式年龄(tDM)为808~765 Ma,具有受俯冲流体交代的地幔岩浆源区特征。群吉萨依粗安岩与中亚造山带北部出露的大量花岗岩具有相似的较为年轻的tDM年龄,与研究区内酸性岩具有相似的同位素地球化学特征,岩浆很可能来源于新生玄武质下地壳的部分熔融。西天山在早二叠世已经进入后碰撞演化阶段,很可能在北天山洋岩石圈南向俯冲的地球动力学背景下,俯冲板片尾部发生断离,软流圈上涌,触发新生玄武质下地壳发生部分熔融,引发具有岛弧特征的高钾钙碱性粗安岩岩浆的喷发,从而形成群吉萨依粗安岩,其为造山过程演化到最后阶段的标志,此时构造体制也相应地由俯冲挤压转换为伸展拉张背景。The Awulale tectonic magmatic belt is an important Fe-Cu metallogenic zone in western Tianshan Mountains,with especially lots of Cu deposits and ore spots discovered in the western Awulale. Nevertheless,the Permian geodynamic background and the metallogenic environments in this area remain unclear. Middle-high potassium calc-alkaline trachyandensite newly discovered at the bottom of Wulang Formation section of volcanic rocks in Qunjisayi area was studied in this paper. La-ICP-MS zircon U-Pb dating of trachyandesite yielded a206 Pb/238 U weighted average age of 300 ± 11 Ma. Trachyandesites in Qunjisayi area are geochemically characterized by enrichment of light rare earth elements( LREE) and large-ion lithophile elements( LILE,such as Rb,Ba,and K) and flat distribution of heavy rare earth elements( HREE),together with strong negative Nb,Ta,Ti anomalies. The rocks have whole-rock εNd( t) values of + 4. 5 to + 4. 9,and Nd isotopic model ages( tDM) of 808 ~ 765 Ma,indicating that the rocks originated from a fluid metasomatic mantle magma source. Similar to features of a large amount of granite exposed in the northern part of the central Asian orogenic belt,the tDMvalues are relatively young,and the acidic rocks in the study area have similar isotope geochemical characteristics. The magma probably came from the partial melting of the new basaltic lower crust. The West Tianshan Mountains entered the past-collision evolution stage in the Early Permian,and the formation of the high potassium calc-alkaline trachyandesite magma with arc features might have been related to the partial melting process of the new basaltic lower crust during the upwelling of asthenosphere material and energy that resulted from the break-off of the oceanic lithosphere plate tail that postdated the closure of the North Tianshan Ocean,which was the mark of the final stage of the evolution of the orogenic process. Meanwhile,the tectonic system correspondingly changed from the subduction extrusion background to the extensional tension background.

关 键 词：中高钾钙碱性粗安岩 早二叠世 阿吾拉勒西段 西天山 年代学 地球化学 

分 类 号：P588.14[天文地球—岩石学] P597[天文地球—地质学]