地学前缘 ›› 2016, Vol. 23 ›› Issue (6): 186-201.DOI: 10.13745/j.esf.2016.06.013

• 前寒武纪地质及早期生命—环境相互作用 • 上一篇    下一篇

扬子克拉通北缘大洪山地区打鼓石群与神农架地区神农架群的对比:锆石SHRIMP U-Pb年龄及Hf同位素证据

李怀坤，田辉，周红英，张健，刘欢，耿建珍，叶丽娟，相振群，瞿乐生   

  1. 1.中国地质调查局 天津地质调查中心， 天津 300170 2. 湖北省区域地质矿产调查所， 湖北 武汉 430034
  • 收稿日期:2016-01-12 修回日期:2016-03-08 出版日期:2016-11-15 发布日期:2016-11-15
  • 通讯作者: 田辉(1985—)，男，硕士，工程师，地层学专业，主要从事前寒武纪地质调查与研究。E-mail:309702629@qq.com
  • 作者简介:李怀坤(1963—)，男，博士，研究员，地层学专业，主要从事前寒武纪年代学研究。E-mail:huaikunli@sina.com
  • 基金资助:

    中国地质调查局项目(12120115070501，1212011120142)；湖北省国土资源厅项目“神农架群岩石地层序列和年代格架研究”

Correlation between the Dagushi Group in the Dahongshan Area and the Shennongjia Group in the Shennongjia Area on the northern margin of the Yangtze Craton: Constraints from zircon UPb ages and LuHf isotopic systematics.

LI Huaikun,TIAN Hui,ZHOU Hongying,ZHANG Jian,LIU Huan,GENG Jianzhen,YE Lijuan,XIANG Zhenqun,QU Lesheng   

  1. 1.Tianjin Center of China Geological Survey, Tianjin 300170, China 2. Hubei Institute of Regional Geology and Mineral Resources Survey, Wuhan 430034, China
  • Received:2016-01-12 Revised:2016-03-08 Online:2016-11-15 Published:2016-11-15

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摘要：

出露于扬子克拉通北缘大洪山地区的打鼓石群一直被认为是一套中元古代沉积地层，其上被花山群不整合覆盖。但是由于缺少可靠的年龄依据，打鼓石群与同属扬子克拉通北缘的神农架群以及其他相关地层的对比关系一直存有争议。本文作者利用高精度高分辨率离子探针质谱仪(SHRIMP)测定了打鼓石群中凝灰岩的锆石U-Pb年龄，并利用激光烧蚀多接收器电感耦合等离子体质谱仪(LA-MC-ICPMS)测定了打鼓石群凝灰岩和基本同时代的神农架地区神农架群上亚群凝灰岩的锆石Lu-Hf同位素。这是迄今为止第一次测得了打鼓石群罗汉岭组凝灰岩年龄(1 225±19) Ma和(1 239±23) Ma；锆石Lu-Hf同位素结果显示打鼓石群罗汉岭组凝灰岩与神农架群上亚群野马河组凝灰岩具有相似的Lu-Hf同位素特征：176Hf/177Hf初始值介于0.282 172~0.282 397，εHf(t)值为4.9~12.0， TCDM=1 150~1 943 Ma。结合现有区域地质资料，我们认为打鼓石群与神农架群上亚群属于同时期沉积物，形成于超级地幔柱主导的哥伦比亚超大陆裂解背景。

关键词: 打鼓石群, 神农架群, 凝灰岩, 锆石SHRIMP U-Pb年龄, LuHf同位素, 扬子克拉通

Abstract:

The Dagushi Group in the Dahongshan Area, at the northern margin of the Yangtze Craton, has long been considered as a Mesoproterozoic sedimentary succession unconformably overlain by the Huashan Group. Owing to lacking of accurate and reliable isotopic ages, the correlation between the Dagushi Group and the Shennongjia Group that also occurred on the northern margin of the Yangtze Craton about 260 km to the west of the Dahongshan Area and other relevant strata in China, still remains as an enigmatic issue. In this study, using Sensitive and High Resolution Ion MicroProbe (SHRIMP) and Laser Ablasion coupled with MultiCollector Inductively Coupled Plasma Mass Spectrometer (LAMCICPMS), we analyzed U-Pb ages and LuHf isotopic compositions for zircons from the tuff beds in the Dagushi and Shennongjia groups, respectively. Two precise zircon UPb ages, 1225±19 Ma and 1239±23 Ma, from the tuff beds in the Luohanling Formation of the Dagushi Group were obtained for the first time. On the other hand, zircons from the two tuff samples of the Luohanling Formation show comparable LuHf isotopic compositions with (176Hf/177Hf)i varying from 0.282172 to 0.282397, corresponding to εHf(t) from 4.9 to 12.0 and TCDM from 1150 Ma to 1943 Ma. The LuHf results of the Dagushi Group are consistent with those of the zircons from a tuff sample from the Yemahe Formation of the Shennongjia Group. Integrating the data obtained in this study with the available regional geological data, we suggest that the Dagushi Group and the Upper Shennongjia Subgroup are coeval sedimentary succesion formed during the breakup of the Columbia Supercontinent, possibly geodynamically related to a super plume.

Key words: Dagushi Group, Shennongjia Group, tuff, zircon SHRIMP-U-Pb ages, Lu-Hf isotope, Yangtze Craton

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