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现代地质 ›› 2022, Vol. 36 ›› Issue (01): 347-361.DOI: 10.19657/j.geoscience.1000-8527.2022.01.31

• 地球化学 • 上一篇    下一篇

北秦岭二郎坪群抱树坪组碎屑锆石LA-MC-ICP-MS U-Pb定年及物源特征

欧伟程1,2(), 李承东3(), 张永清3, 赵利刚3, 许腾3, 许雅雯3, 孙烜烨4   

  1. 1. 中国地质科学院,北京 100037
    2. 中国地质大学(北京),北京 100083
    3. 中国地质调查局 天津地质调查中心,天津 300170
    4. 中钢集团天津地质研究院有限公司,天津 300061
  • 收稿日期:2021-03-09 修回日期:2021-07-07 出版日期:2022-02-10 发布日期:2022-03-08
  • 通讯作者: 李承东
  • 作者简介:李承东,男,教授级高级工程师,1963年出生, 构造地质学专业,从事造山带地质及岩石大地构造研究。Email: tjlcd99@163.com
    欧伟程,男,硕士研究生,1995年出生,地质工程专业,主要从事岩石大地构造研究。Email: 2120190010@cugb.edu.cn
  • 基金资助:
    中国地质调查局项目“全国陆域及海区地质图件更新与共享”(DD20190371);国家自然科学青年基金项目“锐钛矿U-Pb同位素定年方法及其在桂西那豆铝土矿矿床中的应用”(41803047)

LA-MC-ICP-MS Zircon U-Pb Dating and Provenance Characteristic from Baoshuping Formation of Erlangping Group of the North Qinling

OU Weicheng1,2(), LI Chengdong3(), ZHANG Yongqing3, ZHAO Ligang3, XU Teng3, XU Yawen3, SUN Xuanye4   

  1. 1. Chinese Academy of Geological Sciences,Beijing 100037,China
    2. China University of Geosciences, Beijing 100083,China
    3. Tianjin Center of Geological Survey,China Geological Survey,Tianjin 300170,China
    4. Sinosteel Tianjin Geology Co.,Ltd.,Tianjin 300061,China
  • Received:2021-03-09 Revised:2021-07-07 Online:2022-02-10 Published:2022-03-08
  • Contact: LI Chengdong

摘要:

北秦岭造山带中二郎坪群构造属性及形成时代一直存在争议,其中的抱树坪组更是缺少年代学数据报道。为了进一步厘定抱树坪组时代及形成的构造环境,对其碎屑锆石开展LA-MC-ICP-MS定年及物源研究。结果表明,取自原划分为抱树坪组中的斜长黑云石英岩(18P3TW2)和含透辉黑云阳起斜长变粒岩(18P3TW3)具有完全不同的锆石年龄谱特征,揭示它们属于不同时代的地层。18P3TW2碎屑锆石年龄谱为多峰,锆石来源于北秦岭微陆块及华北地块,缺乏早古生代岩浆弧锆石,最年轻的一组锆石年龄为493~972 Ma。18P3TW3碎屑锆石年龄谱为单峰,其中最年轻一组锆石年龄为420~440 Ma,主体来源于二郎坪岛弧岩浆岩。通过野外特征、锆石年龄组成和物源特征综合分析,18P3TW2所代表的地层形成于盆地初期,没有大规模火山活动,不应归属于抱树坪组。18P3TW3所代表的抱树坪组地层形成于盆地晚期,主体沉积时代为奥陶纪—志留纪,最晚地层可能延续到早泥盆世。结合区域地质背景,抱树坪组形成于早古生代商丹洋向北俯冲所产生的弧后伸展盆地构造环境。

关键词: 北秦岭, 二郎坪群, 抱树坪组, 碎屑锆石, LA-MC-ICP-MS锆石U-Pb定年

Abstract:

The tectonic attributes and age of Erlangping Group in the North Qinling orogenic belt have been controversial,and Baoshuping Formation lacks chronological data.In order to further determine the age and tectonic setting of Baoshuping Formation,detrital zircon dating and provenance studies by LA-MC-ICP-MS were carried out. The results show that the plagioclase biotite quartzite (18P3TW2) and the diopside-bearing biotite actinolite plagioclase granulite (18P3TW3) from Baoshuping Formation have completely different zircon age spectrum characteristics,indicate that they belong to the strata of different ages. The detrital zircons age spectrum of 18P3TW2,which originates from the North Qinling micro-continental block and North China block,is multi-peaked but short of the data about Early Paleozoic magmatic arc. The youngest group of zircons range from 493 Ma to 972 Ma. The detrital zircons age spectrum of the 18P3TW3 is unimodal,and the main source of zircons is the Erlangping arc magmatic rocks,of while the youngest group of zircons is 420-440 Ma. With comprehensive analysis of field characteristics,age spectrum of zircons and provenance characteristics,the strata represented by 18P3TW2 was formed in the early stage of the basin without large-scale volcanic action,so it should not be attributed to Baoshuping Formation. Baoshuping Formation, represented by the 18P3TW3,was formed in the late period of the basin,the main sedimentary age is Ordovician-Silurian,and the latest strata may extend to Early Devonian. Combined with the regional geological background,Baoshuping Formation was formed in the tectonic environment of the back-arc extensional basin caused by the northward subduction of Shangdan Ocean in Early Paleozoic.

Key words: the North Qinling, Erlangping Group, Baoshuping Formation, detrital zircon, LA-MC-ICP-MS zircon U-Pb dating

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