新疆东天山哈尔里克奥陶纪的构造属性:来自火山岩LAICPMS锆石UPb年代学与地球化学的制约
Ordovician Tectonic Evolution of Harlik in Eastern Tianshan of Xinjiang:Constraints from LAICPMS Zircon UPb Geochronology and Geochemistry of Volcanic Rocks

摘要： 新疆东天山哈尔里克造山带火山岩为一套酸性—基性岩(流纹岩、英安岩、安山岩、玄武岩)夹火山碎屑岩(凝灰岩)的岩石组合。流纹岩样品的LAICPMS锆石UPb定年结果显示，时代为中奥陶世大坪期((4688±91) Ma)，代表了该套火山岩的形成年龄。岩石地球化学分析结果显示，该套火山岩SiO2含量介于4912%～7824%，TiO2介于012%～100%，Al2O3介于1131%～2086%；铝饱和指数A/CNK值为080～131(均值为099)，里特曼指数σ值为019～386(均值为129)，Mg#值为887～4929(均值为3120)；富集大离子亲石元素(LILE)Ba、Rb以及轻稀土元素(∑LREE)La、Ce，亏损高场强元素(HFSE)Nb、Ta、Ti等。微量元素和稀土元素的相关图解与比值以及发育的捕获锆石反映了俯冲带岛弧钙碱性火山岩特征，且存在大陆地壳混染作用。综合区域地质资料分析，在早古生代期间(中奥陶世—早志留世)，哈尔里克造山带存在大面积的与岛弧演化有关的加里东期岩浆活动，此期间哈尔里克造山带的构造背景为洋壳俯冲有关的岛弧环境，其形成可能与东准噶尔南部克拉麦里洋向南俯冲作用有关。
Abstract: The volcanic rocks in the Harlik orogenic belt of eastern Tianshan, Xinjiang are combined with a set of acid to basic rocks (rhyolite, dacite, andesite, basalt) intercalated with pyroclastic rocks(dacite tuff). UPb dating of zircons from the samples of rhyolite by LAICPMS yields weighed mean 206Pb/238U ages of (4688±91) Ma, which indicates that these volcanic rocks formed in Middle Ordovician. Geochemical analysis results show that the SiO2 contents are from 4912% to 7824%; TiO2 contents are from 012% to 100%; Al2O3 contents are from 1131% to 2086%; A/CNK ratios are from 080 to 131(with an average of 099); and Rittmann indexes (σ) are from 019 to 386(with an average of 129); Mg# values are from 887 to 4929(with an average of 3120). The rocks are rich in large ion lithophile elements(LILEs, eg, Rb, Ba) and light rare earth elements(LREEs,eg, La, Ce) and depleted in high fieldstrength elements(HFSEs, eg, Nb, Ta, Ti). According to the relevant diagrams, the ratios about the trace elements and rare earth elements, and xenocrystic zircon, it indicates that there are typical arc volcanic rocks in suppersubduction zone, and that the magma intruded the continental crust. Moreover, based on the analysis of regional geological data, during the Early Paleozoic (Middle Ordovician to Early Silurian), we can claim that there is a large island arc evolution related to the Caledonian tectonic magmatism, which tectonic background is the oceanic crust subduction of island arc environment, and its formation may be related to east Junggar Kelamaili ocean of the south subduction