内蒙古中部巴彦乌拉地区晚石炭世-早二叠世火山岩锆石SHRIMPU-Pb定年及其地质意义  

Zircon SHRIMP U-Pb dating and its geological significance of the Late-Carboniferous to Early-Permian volcanic rocks in Bayanwula area,the central of Inner Mongolia

作　　者：李可[1,2] 张志诚[1,2] 冯志硕[1,2] 李建锋[1,2] 汤文豪[1,2] 罗志文[1,2] 

机构地区：[1]北京大学造山带和地壳演化教育部重点实验室 [2]北京大学地球与空间科学学院,北京100871

出　　处：《岩石学报》2014年第7期2041-2054,共14页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划项目(2013CB429801);中国地质调查局项目(1212010050503)联合资助

摘　　要：内蒙古巴彦乌拉地区广泛出露宝力格组火山-沉积地层。其中流纹岩样品的锆石SHRIMP U-Pb年龄分别为307.1±6.3Ma和308.9±1.8Ma,结合前人研究结果,宝力格组火山岩确切喷发时间应为晚石炭世到早二叠世。样品位于碱性-钙碱性系列岩石过渡区域,在TAS图中,中基性火山岩落入玄武质粗安岩、粗安岩和安山岩区,REE分馏明显,LILE富集,HFSE明显亏损,Nb、Ta、Ti、P负异常,Zr、Hf正异常,形成于岩石圈地幔部分熔融作用;流纹岩LILE(Rb、Th、U)富集,HFSE(Nb、Ta、Ti)明显亏损,具有高正εNd(t)和年轻tDM1值,是新增生的陆壳部分熔融的结果,并具有I型和A型两类花岗岩的地球化学属性。综合区域地质特征和前人研究资料表明,宝力格组火山岩形成于后造山构造环境。The Inner Mongolia-Da Hinggan Orogenic Belt （ IMDOB）, located in the east of Central Asian Orogenic Belt （ CAOB）, records the boundary between the North China Craton and the Siberian Craton, and is the key area to reconstruct the tectonic history of the CAOB. However many essential issues still remain uncertain at present, such as the evolution of the tectonic environment, especially during Paleozoic period, and the final closure time of the Paleo-Asian Ocean. The Bayanwula area, situated in the northwest of Sonid Zuoqi, the west of the IMDOB, is characterized by the volcano-sedimentary strata of the Baolige Formation. The strata formed in the Late Paleozoic period is represented by typical intermediate-basic, felsic volcanic rocks and pyroclastic rocks. Some people consider these volcanic rocks display a bimodal geochemical distribution. They constitute one part of the Late Paleozoic magma in the IMDOB. So knowing the characteristics of the volcanic rocks is very important and helpful for understanding the tectonic setting and the evolution of the Paleo-Asian Ocean in Paleozoic. Therefore the geochronological and geochemical study has been done in order to solve these problems. By means of SHRIMP zircon U-Pb dating, the ages of two rhyolite samples are 307. 1 ±6. 3Ma and 308. 9 ± 1.8Ma, which are consistent with the ages of the Baolige Formation in the eastern area and about 20Myr earlier than the intrusive alkaline granite around Bayanwula village in the south. Combined with previous research results, it is suggested that the Baolige Formation was not erupted during Early Permian, but between Late Carboniferous and Early Permian. By the geochemical analysis, the intermediate to mafic rocks fall into basaltic trachyandesite, trachyandesite and andesite field and locate in the transition area between alkaline and subalkaline rock series in the TAS diagram. In the chondrite-normalized REE and primary mantle-normalized trace element fractional diagrams, they all exhibit enrichment in LILE and LREE, deplet

关 键 词：晚古生代火山岩 锆石SHRIMP U-PB定年 后造山环境 古亚洲洋 

分 类 号：P588.14[天文地球—岩石学] P597.3[天文地球—地质学]