东天山党罗塔格构造带晚古生代火山岩地球化学特征及意义

本文报道了觉罗塔格构造带中企鹅山群和雅满苏组火山岩的元素和Sr-Nd同位素地球化学研究结果。企鹅山群和雅满苏组火山岩分别以低钾拉斑系列和钙碱性系列为主，玄武岩和安山岩均相对于N-MORB富集轻稀土元素和Sr、Ba、Th等大离子亲石元素，而亏损Nb、Zr和Ti等高场强元素，具有较高的Th/Ta和Ta/Yb比值，表明这些火山岩形成于具有陆壳基底的岛弧环境。但是，雅满苏组比企鹅山群具有偏高的K2O、Rb、Th、U、Nb、Zr和REE等不相容元素含量和较高的K2O／Na2O比值。Sr-Nd同位素组成表明企鹅山群和雅满苏组都来自亏损的地幔源区，但后者遭受了明显的陆壳物质混染。这种地球化学组成的差异反映了陆壳基底性质和厚度的不同。结合已有的地质调查结果，我们认为康古尔断裂作为俯冲带是比较合理的，早石炭世存在康古尔洋，而且它很可能发生了南北双向俯冲作用。企鹅山群火山岩是向北侧俯冲在大南湖泥盆纪岛弧南侧增生的产物，而雅满苏组火山岩是通过向南俯冲在中天山地块北缘形成的陆缘弧火山岩。

Geochemical characteristics of the Late Paleozoic Volcanics in Jueluotage tectonic belt, eastern Tianshan and its implications

This paper presents the geochemical data including major and trace elements and Sr,Nd isotopes of the volcanics from Qi'eshan Group and Yamansu Formation,occuring in the Jueluotage tectonic belt.The basalts and andesites of Qi'eshan Group and Yamansu Formation are mainly of low-K tholeiite series and calc-alkaline series,respectively.Compared to N-MORB all of these volcanics exhibit relative enrichment in large ion lithophile elements and depletion in high strength field elements(Nb,Zr and Ti), with higher Th/Ta and Ta/Yb ratios,suggesting that Qi'eshan Group and Yamansu Formation were formed at arc settings with continental basement.However,Yamansu Formation has higher abundances of K_2 O,Rb,Th,U,Nb,Zr,REE and K_2O/Na_2O ratio than Qi'eshan Group.Initial Sr and Nd isotopic compositions show that the basalts from both Qi'eshan Group and Yamansu Formation were derived from depleted mantle,and the basalts in Yamansu Formation were contaminated by continent crust to some extent.The geochemical difference between Qi'eshan Group and Yamansu Formation might reflect the different basement nature and thickness within each arc.Combining with the previous geological investigation,we propose that Kanggur fault is a probable suture.In the Early Carboniferous there was most likely an ocean in Kanggur and it bilaterally subducted.The northward subduction resulted in the volcanics of Qi'eshan Group accreted to the south of Dananhu island-arc,while the southward subduction formed the voleanics of Yamansu Formation with the nature of continental arc at the north of Central Tianshan Block.