海拉尔盆地西北部火山岩地层划分的锆石U-Pb年代学证据

Division of volcanic strata in the northwestern part of Hailar basin: Evidence from zircon U-Pb dating

海拉尔盆地是中国东北地区的中生代断陷盆地,其中的火山岩地层是大兴安岭晚中生代火山岩的重要组成部分。本文对秃1井和红2井8个火山岩岩芯样品进行的LA-ICP-MS锆石U-Pb定年结果表明,所研究的火山岩时代明显分为145～151Ma和117～119Ma两期,分别与海拉尔盆地及大兴安岭地区的塔木兰沟组和上库力组火山岩的形成时间相当。根据本文测年结果,辅以前人近几年对邻区中生代火山岩测年数据的统计,认为海拉尔盆地晚中生代火山作用至少分为三期:117～125Ma、140～151Ma和～160Ma。根据火山岩的岩石学特征及锆石的U-Pb同位素年龄新资料,认为红2井原定为盆地基底布达特群的一套火山岩地层至少有一段实际是晚中生代火山岩。

Hailar basin is a Mesozoic fault basin in Northeast China,there the volcanic strata is an important part of Late Mesozoic volcanic rocks of the Great Xing’an Range. In this paper,we report zircon LA-ICP-MS U-Pb ages of the volcanic rock samples from Tu#1 and Hong#2 core wells in the northwestern part of Halar basin. Eight zircon U-Pb ages may be divided into two groups: 145 ～ 151Ma and 117 ～ 119Ma,indicating two episodes of Late Mesozoic volcanism in the northwestern part of Hailar basin,and both may be correlated well with the volcanic strata of Tamulangou and Shangkuli formations,respectively,not only within the basin but also in the Great Xing’an Range around the basin. Combined with the age compilations for the volcanic rocks from Hailar basin and adjacent area, at least three episodes of the Mesozoic volcanism may be identified: 117 ～ 125Ma,140 ～ 151Ma,and ～ 160Ma. In addition,zircon U- Pb ages from the volcanic rocks of Budate Group,which has been considered as a part of the basement of Hailar basin,show that those volcanic rocks are actually Late Jurassic in age.