摘要
澄江组是晋宁不整合面之上最早沉积的地层之一,了解其物源对于认识扬子西缘早期地壳演化具有重要意义。对扬子西缘东川地区澄江组底部碎屑锆石进行了U-Pb定年和Lu-Hf同位素分析。结果显示,澄江组碎屑锆石的年龄谱具有780~900 Ma、约1000 Ma、约1800 Ma的峰值,最年轻一组碎屑锆石年龄加权平均值为801±5 Ma(MSWD=2.4,n=9),与区内澄江组底部火山岩的年龄十分接近,限定研究区澄江组的沉积下限为约800 Ma。综合碎屑锆石U-Pb年龄和Hf同位素组成、锆石形态及古地理特征,认为东川地区澄江组底部的物源主要来自于扬子地块西缘新元古代岩浆岩的剥蚀,其次为东川群的沉积再循环。通过扬子地块南华纪早期地层的区域对比发现,扬子西缘与北缘在新元古代之前可能具有不同的地壳演化历史。扬子西缘不同地区澄江组之间存在物源差异,与区域构造活动密切相关。
The Chengjiang Formation is one of the earliest stratigraphic units above the Jinning unconformity.Determining the sources is of great significance for the understanding of the early crustal evolution in the western Yangtze Block.U-Pb dating and Lu-Hf isotopic composition studies were carried out on the detrital zircons from the Lower Chengjiang Formation in the Dongchuan area of the western Yangtze Block.The U-Pb ages of the zircons are clustered at 780~900 Ma,~1000 Ma and~1800 Ma respectively,and the weighted mean age of the youngest group is 801±5 Ma(MSWD=2.4,n=9),which is consistent with the volcanic age of the Lower Chengjiang Formation.Thus,it is further confirmed that the lower age of the Chengjiang Formation should be limited at~800 Ma.Combined with the U-Pb age and Hf isotopic composition,zircon morphology and paleogeography,it is believed that the detritus was largely sourced from the widely distributed Neoproterozoic magmatic rock in the western Yangtze Block,and a small part from the recycled materials of the Dongchuan Group.Regional comparison of the early Nanhua strata of the Yangtze Block indicates that the western and northern margins of the Yangtze Block show different crustal evolution history.The provenance differences of the Chengjiang Formation in different regions of the western margin of the Yangtze are closely related to regional tectonic activities.
作者
高永娟
林仕良
秦雅东
任光明
庞维华
楼雄英
GAO Yongjuan;LIN Shiliang;QIN Yadong;REN Guangming;PANG Weihua;LOU Xiongying(Chengdu Center,China Geological Survey,Chengdu 610081,Sichuan,China)
出处
《地质通报》
CAS
CSCD
北大核心
2021年第11期1943-1956,共14页
Geological Bulletin of China
基金
国家自然科学基金项目《扬子西南缘东川地区前寒武纪地层Nd、Hf同位素示踪研究》(批准号:41503025)
《西藏那曲地区中晚侏罗世拉贡塘组沉积作用对班公湖-怒江构造带地质演化的制约》(批准号:41972113)
中国地质调查局项目《中尼铁路(境内段)沿线区域地质调查》(编号:DD20211195)
《扬子陆块攀枝花—玉溪地区与罗平生物群区域地质调查》(编号:DD20190054)
科技部青藏科考项目《深时特提斯生物与环境演变》(编号:2019QZKK0706)。
关键词
扬子西缘
澄江组
碎屑锆石
HF同位素
地壳演化
东川
western Yangtze Block
Chengjiang Formation
detrital zircon
Hf isotope
crustal evolution
Dongchuan
