Geochemistry and U-Pb geochronology of K-bentonites from the Pingliang Formation of the Upper Ordovician in Gansu, North China, and their tectonic implications
Geochemistry and U-Pb geochronology of K-bentonites from the Pingliang Formation of the Upper Ordovician in Gansu, North China, and their tectonic implications
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甘肃上奥陶统平凉组钾膨润土地球化学、U-Pb年代学及其构造意义
DOI：
10.1002/gj.3609
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发表时间：
2020
影响因子：
1.8
通讯作者：
Li Haiyan
中科院分区：
文献类型：
--
作者：
Xu Junjie;Wu Huaichun;Chu Zhuyin;Fang Qiang;Zhang Shihong;Yang Tianshui;Li Haiyan
鄂尔多斯盆地西南部官庄剖面晚奥陶世平凉组中含有多个钾质膨润土层，对研究鄂尔多斯盆地西南部的构造演化具有重要意义。该研究为建立鄂尔多斯盆地奥陶纪高分辨率年代地层格架和提供主要火山-岩浆活动的时间约束提供了新的钾镁矾地球化学和西姆斯U-Pb年代学数据。该系列中的钾镁矾岩的锆石U-Pb年龄分别为457.6 ± 3.8 Ma和454.8 ± 3.8 Ma（2σ分析不确定度），显示其沉积时代为晚奥陶世砂变期。结果与生物地层和天体年代学框架相一致，实现了不同测年方法的相互校准。全岩Na 2 O + K2 O对SiO2、Zr/TiO 2对Nb/Y、Th/Yb对Nb/Yb、Th-Hf-Ta判别图解表明，钾镁矾具有明显的弧亲合性。结合地质背景，认为鄂尔多斯盆地西南部钾镁矾主要是在北祁连-北秦岭火山弧发育的砂质期沉积的。
The Late Ordovician Pingliang Formation in the Guanzhuang section, located in the south‐western Ordos Basin, North China, contains several K‐bentonite layers, which are important for understanding the tectonic evolution of the south‐western Ordos Basin. This study provides new geochemical and SIMS U–Pb geochronological data for the K‐bentonites to establish the Ordovician high‐resolution chronostratigraphic framework for the Ordos Basin and to provide temporal constraints of major volcanic–magmatic activity. K‐bentonites in the succession yield U–Pb zircon ages of 457.6 ± 3.8 Ma and 454.8 ± 3.8 Ma (2σ analytical uncertainty), showing a depositional age in the Sandbian Stage (Late Ordovician). The result is consistent with the biostratigraphic and astrochronologic framework, achieving the intercalibration of different dating methods. The discrimination diagrams of whole‐rock Na2O+K2O against SiO2and Zr/TiO2against Nb/Y and Th/Yb against Nb/Yb and Th‐Hf‐Ta indicate that the K‐bentonites have obvious arc affinities. Based on the geological background, we conclude that the K‐bentonites in the south‐western Ordos Basin were mainly deposited during the development of the North Qilian‐North Qinling volcanic arc in the Sandbian.