五台群是新太古代还是古元古代?同位素年代学研究评述  

Is the Wutai Group of Neoarchean or Paleoproterozoic?A Review of Isotope Chronological Studies

作　　者：赵飞凡 陈衍景[1,2] Zhao Feifan;Chen Yanjing(MOE Key Laboratory of Orogenic Belts and Crustal Evolution,Peking University,Beijing 100871,China;Faculty of Earth Resources,China University of Geosicences,Wuhan 430074,China)

机构地区：[1]北京大学造山带与地壳演化教育部重点实验室,北京100871 [2]中国地质大学资源学院,湖北武汉430074

出　　处：《地球科学》2021年第1期1-12,共12页Earth Science

基　　金：国家自然科学基金项目(Nos.U1906207,41890833);国家重点基础研究发展计划(“973”计划)(No.2012CB416602).

摘　　要：五台群长期被多数学者作为新太古代地层,自下而上分为石咀亚群、台怀亚群和高凡亚群,但同位素年代学研究给出了一些古元古代年龄,致使五台群形成时代及地层划分对比方案悬而未决.全面收集了五台群已有同位素年龄数据,仅锆石U⁃Pb谐和年龄数据就有800多组.数据显示,高凡亚群包括洪寺组和羊蹄沟组,沉积时间不早于2331±38 Ma,属于古元古代层侵纪.台怀亚群包括柏枝岩组和鸿门岩组,鸿门岩组结晶年龄约为2435±64 Ma,柏枝岩组沉积年龄为2435±64~2468±61 Ma,故台怀亚群形成于2435±64~2468±61 Ma,属古元古代成铁纪.石咀亚群自下而上分为板峪口组、金岗库组、庄旺组、文溪组,其中,文溪组和板峪口组缺乏同位素年龄数据,庄旺组形成于2468±61 Ma,金岗库组形成于2468±61~2494±29 Ma,属于古元古界底部.结合五台花岗绿岩地体之花岗岩类的年龄(>2520 Ma),认为五台群之下存在花岗质岩石基底.五台地区锆石年龄还表现出了~2.7 Ga和~2.5 Ga的年龄峰值,指示新太古代发生了两次地壳快速生长.五台地区2.52~2.56 Ga的花岗质岩石显示岛弧特征,表明板块俯冲作用在新太古代地壳生长中扮演了重要角色.The Wutai Group includes the Shizui,Taihuai and Gaofan subgroups in ascending sequence and has always been considered as Neoarchean strata.However,results from isotopic chronology studies of the Wutai Group have frequently shown a Paleoproterozoic age,making its formation age and stratigraphic subdivision controversial.In this contribution,we have collected all the available isotopic ages obtained from the Wutai Group,including more than 800 groups of zircon U⁃Pb concordant age.The age dataset indicates that the Gaofan Subgroup,consisting of the Hongsi Formation and the Yangtigou Formation,is no earlier than 2331±38 Ma and belongs to the Rhyacian Period.The Taihuai Subgroup,consisting of the Baizhiyan and Hongmenyan formations whose deposition ages are constrained 2435±64 to 2468±61 Ma and 2435±64 Ma,respectively,has deposited during 2435±64 to 2468±61 Ma,belonging to the Siderian Period of the Paleoproterozoic Era.The Shizui Subgroup is upwardly divided into the Banyukou,Jin’gangku,Zhuangwang and Wenxi formations.The Wenxi and Banyukou formations are lacking of isotopic dating data.The Zhuangwang and Jin’gangku formations are defined to have formed around 2468±61 Ma and 2468±61 to 2494±29 Ma,respectively.This shows that the Shizui Subgroup was formed at the beginning of the Paleoproterozoic Era,i.e.,the lower Siderian Period.Considering that the granitoids in the Wutai granite⁃greenstone terrain generally yielded zircon U⁃Pb ages of>2520 Ma,it is inferred that the Wutai Group was likely deposited on an Archean granitic basement.The zircon U⁃Pb ages from the Wutai terrain show two peaks around 2.7 Ga and 2.5 Ga,implying two crustal growth events.The island⁃arc affinity of the 2.52-2.56 Ga granitoids in the Wutai granite⁃greenstone terrain indicates that plate subduction played an important role in the late Neoarchean.

关 键 词：五台群 同位素年龄 沉积时代 成铁纪 层侵纪 地壳生长 

分 类 号：P597[天文地球—地球化学]