新疆东北部三塘湖盆地卡拉岗组火山岩的形成时代:锆石U-Pb定年  

The Age of Kalagang Formation in the Santanghu Basin,Northeast Xinjiang:Evidence from Zircons U-Pb Dating of Volcanic Rocks

作　　者：张明民[1,2] 陈红汉[3] 郑建平[2,4] 苏玉平[4] 

机构地区：[1]中国地质大学研究生院,武汉430074 [2]地质过程与矿产资源国家重点实验室,武汉430074 [3]中国地质大学资源学院,武汉430074 [4]中国地质大学地球科学学院,武汉430074

出　　处：《矿物岩石地球化学通报》2010年第4期400-408,共9页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：国家自然科学基金青年基金资助项目(40803007);国家973计划项目(2011CB808900)

摘　　要：新疆东北部三塘湖盆地卡拉岗组火山岩十分发育,但火山岩的形成时代,是二叠纪还是石炭纪一直存有争议。本文用LA-ICP-MS方法测定了该盆地的马朗凹陷中马17井卡拉岗组的3个层位的玄武岩的锆石U-Pb年龄,得到1543.1 m处的锆石加权平均年龄为343.5±2.4 Ma,1954.3 m处的锆石两组加权平均年龄为331.3±5.0 Ma和306.6±5.3 Ma,2327 m处的加权平均年龄为325.2±3.0 Ma。表明卡拉岗组时代可能不是二叠纪,而是石炭纪。其年龄分布大致有上老(早石炭世)和下新(晚石炭世)的特点。这种分布特点可能与马朗凹陷马17井火山岩较发育、有多期火山活动的特点有关。在排除地层倒转的情况下,层位高的火山岩锆石年龄老可解释为与上面层位的火山岩可能捕获早期岩浆结晶锆石有关。说明最小的年龄(306.6 Ma)可作为该组火山岩的喷发年龄:卡岗组时代定为晚石炭世更合适。Kalagang Formation is developed widely in the Santanghu basin,northeast Xinjiang.The eruption age of volcanic rocks in this Formation was considered as either Permian or Carboniferous.LA-ICP-MS U-Pb dating was made on the basaltic zircons for three samples,which were collected from drill hole（Ma 17） at different depths.Zircons in the basalt at 1543.1 m yield weighed mean age of 343.5±2.4 Ma（n=11,MSWD=0.74）.Those at 1954.3 m show two groups of weighted mean ages,331.3±5.0Ma（n=6,MSWD=1.4） and 306.6±5.3 Ma（n=9,MSWD=4.5）,respectively.Zircons in the sample at 2327.0 m give weighted mean age of 325.2±3.0 Ma（n=19,MSWD=2.2）.This study considers the minimum age,306.6 Ma,as the eruption age of the volcanic rocks in the Kalagang Formation,suggesting that this volcanic suite was formed in Carboniferous instead of formerly widely-accepted Permian.Zircons at the higher depth of the drill hole are old（early Carboniferous）,Zircons at the lower depth are younger（Late Carboniferous）.This may indicate that volcanic rocks in Malang depression developed within different ages,showing a characteristic of multi-stage eruption,old zircons at the higher depth of Kalagang Formation may represent the early magma crystallization.Therefore,Kalagang Formation should be formed at the Late Carboniferous.

关 键 词：三塘湖盆地 卡拉岗组 玄武岩 锆石U-PB定年 晚石炭世 

分 类 号：P597.3[天文地球—地球化学]