内蒙古阿鲁科尔沁旗林西组碎屑岩LA-ICP-MS锆石U-Pb年龄及构造意义

LA-ICP-MS Zircon U-Pb Age and Its Tectonic Significance of Clastic Rocks from Late Permian Linxi Formation in Aluke'erqin Qi, Inner Mogolia

阿鲁科尔沁旗陶海营子剖面以灰、灰黑、黄绿色的砂板岩组合为特征,是林西组典型剖面之一,含双壳、叶肢介、植物和孢粉化石,时代为晚二叠世晚期。对采自剖面上部第61层的长石岩屑砂岩中的锆石进行了LA-ICP-MS U-Pb同位素测试,获得了96颗锆石的谐和-近谐和年龄,同时引用该剖面第1层已发表碎屑岩97颗锆石数据,共计193个碎屑锆石数据年龄统一分析。193颗碎屑锆石按年龄值和频率分布特征可分为五组:248～302 Ma (80颗,41%),峰值年龄为263 Ma;312～388 Ma(24颗,12%); 417～523 Ma(26颗,13%);564～991 Ma(38颗,20%);1000～2775 Ma (25颗,13%,^(207)Pb/^(206)Pb年龄)。最小年龄段年龄的加权平均值为263±1.7 Ma (MSWD=1.7, n=80),与最小的峰值263Ma年龄相吻合,推测测年样品沉积时间下限为263 Ma,表明其沉积时代应为晚二叠世。碎屑锆石年龄谱值表明其沉积物源具多样性和复杂性,主体应来自东北各地块,同时存在华北板块和西伯利亚板块的物源信息(1637±26 Ma,1791±24 Ma,1927±31 Ma,1954±24 Ma,2089±31 Ma,2671±21 Ma,2775±21 Ma)。本次获得最年轻的一组碎屑锆石的峰值年龄为263 Ma,表明华北板块与西伯利亚板块的最终闭合时间应该在晚二叠世之后。

The Taohaiyingzi section at Aluke'erqin Qi, Inner Mongolia is one of typical Linxi Formation in north eastern China. The age of the section is late Late Permian according to the newly discovered conchostracans, pollen, and spores. The Linxi Formation in Taohaiyingzi consists mainly of black and gray-black sandstone and slate associations. The LA-ICP-MS U-Pb isotope analysis was performed on zircons of the feldspar lithic sandstone from the 61st layer of the profile. The obtained concordant ages from 96 zircons and the published 97 zircon data of clastic rocks from the first layer, amounting to a total of 193 detrital zircon data ages, were analyzed. The 193 detrital zircons can be divided into five groups according to age and frequency distribution characteristics: 248-302 Ma (n=80, ca. 41%) with peak ages at 263 Ma, 312-388 Ma (n=24, ca. 12%), 417-523 Ma (n=26, ca.13%), 564-991 Ma (n=38, ca. 20%), and 1000-2775 Ma (n=25, ca.13%, 207Pb /206Pb age). The weighted average age for the youngest age group is 263±1.7 Ma (MSWD=1.7, n=80), which coincided with the minimum peak age of 263 Ma. It was speculated that the maximum depositional age of the Linxi Formation is 263 Ma. The detrital zircon age spectrum indicates the diversity and complexity of its sediment source. The main source should come from all over the northeast and there is provenance information of North China plate and Siberian plate (1637±26 Ma, 1791±24 Ma, 1927±31 Ma, 1954 ±24 Ma, 2089 ±31 Ma, 2671 ±21 Ma, 2775 ±21 Ma). The peak age of the youngest group of detrital zircons obtained is 263 Ma, indicating that the final closure between North China plate and Siberian plate occurred after Late Permian.