东天山吐哈盆地南缘企鹅山群玄武岩锆石U-Pb年代学、地球化学及其对北天山洋闭合时限的约束  

Zircon U-Pb geochronology and geochemistry of basalts from the Qi'eshan Group in the southern Turpan-Hami Basin,East Tianshan: Constraints on closure time of the North Tianshan Ocean

作　　者：白建科 刘池阳[1] 张少华[1] 卢进才[2] 孙吉明[2] BAI JianKe;LIU ChiYang;ZHANG ShaoHua;LU JinCai;SUN JiMing(State Key of Continental Dynamics,Department of Geology,Northwest University,Xi＇an 710069,China;Research Center of Orogenic Geology,CGS,Xi＇an Center of Geological Survey,Xi＇an 710054,China)

机构地区：[1]大陆动力学国家重点实验室西北大学地质学系,西安710069 [2]中国地质调查局造山带地质研究中心西安地质调查中心,西安710054

出　　处：《岩石学报》2018年第10期2995-3010,共16页Acta Petrologica Sinica

基　　金：中国地质调查局地质调查项目(DD20160006;DD20179608);国家自然科学基金项目(41202077;41402051;41502061);陕西省自然科学基金项目(2018JM4001)联合资助

摘　　要：东天山吐哈盆地南缘广泛发育企鹅山群火山-沉积岩系,其形成时代及构造环境一直存在争议。本文对其进行了岩相序列、同位素年代学和地球化学研究。结果表明,企鹅山群自下而上分为三个岩性段,并可划分出7种岩相类型。2件玄武岩样品LA-ICP-MS锆石U-Pb定年结果显示,玄武岩喷发年龄分别为314. 0±3. 5Ma和316. 0±2. 3Ma,表明企鹅山群形成时代为晚石炭世早期。同时获得大量具有浅表碎屑成因的前寒武纪(589～2652Ma)捕获锆石,其物源来自中天山地块,表明该时期分割中天山地块与觉罗塔格构造带之间北天山洋已经闭合。玄武岩Si O2含量为46. 54%～52. 64%,以亚碱性拉斑系列为主;岩石亏损Nb、Ta等高场强元素,轻度富集轻稀土元素(LREE);(La/Yb)N=1. 87～5. 22,Eu异常不明显(δEu=0. 85～1. 06),稀土配分曲线右倾较缓。这些地球化学特征暗示该火山岩在上升过程中可能遭受了地壳的混染。综合区域地质资料与前人研究成果,认为吐哈盆地南缘企鹅山群形成于北天山洋闭合后的后碰撞裂谷构造环境。V0lcanic-sedimentary rocks of the Qi＇eshan Group are widely exposed along the southern edge of the Turpan-Hami basin,East Tianshan. However,the depositional age and tectonic setting of the Qi＇eshan Group are still in dispute. In this paper,lithofacies sequences,geochronology and geochemistry of the Qi＇eshan Group volcanic-sedimentary rocks are studied. The results show that the Qi＇eshan Group can be divided into three lithologic members,and furtherly divided into 7 types of lithofacies. By LA-ICP-MS zircon UPb dating,the ages of two basalt samples are 314. 0 ± 3. 5 Ma and 316. 0 ± 2. 3 Ma,respectively,indicating that the Qi＇eshan Group was deposited in the early Late Carboniferous. Moreover,we also obtained several pre-Cambrian zircon ages with detrital origin from above two basalt samples. These pre-Cambrian zircons were sourced from the Central Tianshan terrane,indicating the North Tianshan Ocean,which separated the Central Tianshan terrane and Jueluotage tectonic belt,has been closed prior to the early Late Carboniferous. In addition,the volcanic rocks mainly belong to sub-alkaline tholeiitic series,with Si O2 ranging from 46. 54% - 52. 64%. These volcanic rocks exhibit depletion in the high strength element Nb,Ta and Ti,and minor enrichment in the LREE. In terms of REE,（ La/Yb）N ranges from 1. 87 to 5. 22,showing less obvious Eu depletion（ δEu = 0. 85 - 1. 06） and slightly right-inclined REE distribution patterns. These geochemical characteristics suggest that the volcanic rocks of the Qi＇eshan Group may have been contaminated by the lithosphere during magma upwelling. Collectively,we suggest that the Qi＇eshan Group was deposited in a post-collision rift after the closure of the North Tianshan Ocean.

关 键 词：企鹅山群 地球化学 锆石U-Pb定年 后碰撞裂谷 东天山 

分 类 号：P588.145[天文地球—岩石学]