西准噶尔包古图地区地层火山岩锆石LA-ICP-MSU-Pb年代学研究

The zircon U-Pb LA-ICP-MS geochronology of volcanic rocks in Baogutu areas,western Junggar

包古图地区位于西准噶尔东南部,区内出露地层主要为石炭系太勒古拉组、包古图组和希贝库拉斯组,为一套巨厚的半深海相-大陆坡相火山-火山碎屑沉积建造。这套地层的时代归属和地层层序长期以来一直存在争议。本文报导了包古图地区实测地层剖面,并从太勒古拉组玄武岩和包古图组及希贝库拉斯组凝灰岩中分别选出锆石,进行了LA-ICP-MS U-Pb年代学研究,获得^(206)Pb/^(238)U加权平均年龄分别为357.5±5.4Ma、332.1±3.0Ma和336.3±2.5Ma。由此确定这套地层属于早石炭世的杜内阶到维宪阶,由下到上依次为太勒古拉组、包古图组和希贝库拉斯组。

There is a great thickness of bathyal- and slope-facies volcanic-volcaniclastic sedimentary sequence at Baogutu area in southeast of western Junggar,which are named as Tailegula Formation,Baogutu Formation and Xibeikulas Formation,respectively. There have been controversies about the geological ages and stratigraphic subdivision about these strata for a long time.So we surveyed the stratum section at Baogutu area and separated zircons from basalt of the Tailegula Formation and tuff of Baogutu Formation and Xibeikulas Formation.LA-ICP-MS U-Pb dating on these zircon grains gives the ^(2060Pb/^(238)U weighted mean ages of 357.5±5.4Ma, 332.1±3.OMa and 336.3±2.5Ma,respectively,indicating that the strata sequence from bottom to top should be Tailegula Formation,Baogutu Formation and Xibeikulas Formation in turn,which were formed from Tournaisian to Visean of Early Carboniferous.