内蒙古东乌旗泥盆纪塔尔巴格特组凝灰岩锆石U-Pb年龄及其地质意义

摘要

内蒙古东乌珠穆沁旗地区是中国北方造山带内泥盆系最为发育地区之一.前人运用古生物化石确定了该区泥盆纪地层的相对年代,但缺少精确的同位素年龄.本文采用LA-ICP-MS测年技术,对发育在泥盆纪塔尔巴格特组上部的凝灰岩夹层进行了锆石U-Pb同位素测年,获得206 pb/238U加权平均年龄为380.8±1.6 Ma(MSWD=2.7),确定其时代为晚泥盆世早期,为本区泥盆系提供了精确的年代学数据.结合古生物化石组合资料,将塔尔巴格特组时代确定为中泥盆世吉维特期—晚泥盆世弗拉期.%Dong Ujimqin Banner in Inner Mongolia is one of the most developed Devonian strata areas along the orogenic belt in northern China.Previous researchers determined the relative age of strata by fossils;however,there is no accurate isotopic age.In this paper,using LA-ICP-MS dating method,the authors determined zircon U-Pb ages of tuff interlayers in the upper part of Devonian Tarbaget Formation and acquired 206Pb/238U weighted average age of 380.8 ± 1.6 Ma(MSWD =2.7),indicating an early Late Devonian age.This provides accurate geochronological data for Devonian strata in this area.Combined with the data of the fossil assemblage,the authors determined the age of Tarbaget Formation,which is middle Devonian Givetian period-late Devonian Frasnian period.