摘要
我国南方扬子板块是国际上新元古代冰期地层最具代表性的地区之一,冰期地层出露广泛,为国内外学者所关注。对扬子地块东南缘湘中大乘山地区长安组二段底部的凝灰质板岩中所获得的碎屑锆石的U-PbLA-ICP-MS同位素年代分析研究结果显示,长安组碎屑锆石年龄主要为831～720Ma,少数为新元古早期1005～842Ma,含有少量古元古—中元古的2500～1933Ma的锆石。长安组较年轻的两组锆石加权年龄为769Ma(2σ,n=9,MSWD=11.3)和828Ma(2σ,n=16,MSWD=7.9),最小年龄720.2±12Ma(206Pb/238U表面年龄)。长安组碎屑锆石的U-Pb年代学表明,该地层最早形成时代<770Ma,那么长安冰期的启动年龄应不大于770Ma。组成碎屑锆石年龄谱中最大碎屑锆石群体的年龄组构750～830Ma为华南在新元古代时期的生长和再造时代,可能与Rodinia超大陆的裂解有关。古元古代2500～1933Ma年龄信息在长安组碎屑锆石的出现,则暗示了湘中大乘山地区或扬子东南缘的一次地壳再造事件。
The Yangtze Block in South China is one of the important regions in the world where the Neoproterozoic glacial sediments are well developed and well studied. In this paper, we report and analyse the LA- ICP-MS U-Pb ages of detrital Zircon grains from the Jiangkou Group in the Central Hunan, Southeastern Yangtze Block. Together with compilations of all available high precision zircon U - Pb data on tuff beds in the Nanhua Basin, our work demonstrates that the Cryogenian deposition in South China had three depositional cycles at 831 ~ 720 Ma, 1005 -842 Ma and 2500 - 1933 Ma. The dominant age group can be further divided into two sub-groups with weighted mean age of 769 and 828 Ma, the youngest grain gives a 2~6pb/23SU age of 720 Ma. The youngest age population gives a mean 206pb/238 U age of 769 Ma that constrains the onset time of the Sturtian （Chang＇ an ） glaciation to 〈 770 Ma. The largest age group 750 - 830 Ma from the Cryogenian sedimentary rocks maybe compare global episodic continental growth and reworking events with possibly coupled Rodinia supercontinent break up. The late Paleoproterozoic （ 1.9 -2.5 Ga） thus appears to have witnessed significant of continental reworking in central Hunan Province.
出处
《地质论评》
CAS
CSCD
北大核心
2013年第2期334-344,共11页
Geological Review
基金
国家自然科学基金重点资助项目(编号41030315)
国家自然科学基金资助项目(编号41072088)
中国地质调查局基础地质科研项目(编号1212011121111)的成果
关键词
扬子东南缘
新元古代
冰期地层
长安组
碎屑锆石LA-ICP—MS年龄
The Yangtze Block of South China
Neoproterozoic
Cryogenian sedimentary
Chang＇ anFormation
detrital zircon LA-ICP-MS U-Pb Ages
