地质论评2017，Vol.63Issue(5)：1309-1327,19.DOI:10.16509/j.georeview.2017.05.013
鄂尔多斯盆地西北缘奥陶纪凝灰岩锆石U-Pb年龄、Hf同位素特征及地质意义
Zircon U-Pb Ages and Hf Isotope Characterestics and Their Geological Significance of Tuff in Wulalike Formation in the Northwestern Ordos Basin
摘要
Abstract
Thin-layered and laminated tuff was developed in the Wulalike Formation in the northwestern Ordos Basin.This tuff bed was produced by volcanic ash-fall deposits which can reclassify the Ordovician stratigraphic framework of Ordos Basin and provide importantconstrains on the plate tectonic setting of the northwestern Ordos Basin as well as major volcanism—magma activities.In this contribution,wecarried SHRIMP U-Pb dating and Hf isotope on tuff sample collected from Zhuozishan area,located in Wuhai City,Inner Mongolia.LA-ICP-MS U-Pb dating on zircons has yielded a weighted average of 454.9 ± 3.4Ma (MSWD =002).SHRIMP U-Pb dating on zircons from the tuff sample has yielded a set of concordant ages of 433.2 ± 3.3 ～ 464.2 ± 3.5 Ma with the mean age 456.4 ± 4.2Ma (MSWD =1.9).Accordingly,the main depositional period of Wulalike Formation,which is still controversial,is redefined to Darriwilian—Sandbian,Middle—Late Ordovician.In situ zircon isotope analysis yielded εHf(t) =+4.02 ～ + 10.98,n(176Hf)/rt(177Hf) ratios of 0.282 619 ～ 0.282 806 and two-stage model age of 729 ～ 1178Ma.According to their regional distribution,it is thought that these ruffs derive from volcanic eruption in the North Qinling or/ and North Qilian region.The zircon age and magmas source are in accordance with the tuffs from Wuhai city to the tuffs (or K-bentonites) from the southwestern Ordos Basin,which means all the western and southern Ordos Basin affected by the North Qilian or/and North Qinling Early Paleozoic orogenic belt during Middle—Late Ordovician.关键词
鄂尔多斯盆地/火山凝灰岩/奥陶纪/锆石U-Pb年龄/Hf同位素Key words
Ordos Basin/volcanic tuff/Ordovician/zircon U-Pb dating/Hf isotope引用本文复制引用
吴素娟,张永生,邢恩袁..鄂尔多斯盆地西北缘奥陶纪凝灰岩锆石U-Pb年龄、Hf同位素特征及地质意义[J].地质论评,2017,63(5):1309-1327,19.基金项目
本文为国家重大基础研究计划(973)项目(编号:2011CB403001)和中国地质调查局地调工作项目(编号:1212011085516)的成果.This work was supported by the National Basic Program of China (No.2011CB403001)and Geological Survey Project of China Geological survey (No.1212011085516). （973）
