右江盆地富宁地区石炮组顶部凝灰岩的厘定及其对T1/T2界线划分的约束
投稿时间:2023-12-25  修订日期:2024-02-16  点此下载全文
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作者单位邮编
李维科 云南省地质调查院 650216
宛胜 江西省地质调查勘查院基础地质调查所 
刘军平* 云南省地质调查院 
晏海宝 云南省地质调查院 
何世军 中国冶金地质总局第二地质勘查院 
赵云江 云南省地质调查院 
赵江泰 云南省地质调查院 
卢晓萍 云南省地质调查院 
中文摘要:通过野外地质调查,笔者在右江盆地富宁地区中三叠统板纳组与下伏下三叠统石炮组之间新发现一套厚约5m凝灰岩关键层,对凝灰岩进行LA-ICP-MS U-Pb同位素定年,自下而上分别获得249.0±1.9 Ma、247.9±3.4 Ma、245.5±1.6Ma同位素年龄,在误差范围内较为一致,首次获得石炮组顶界年龄为下三叠统奥伦尼克阶;同时在凝灰岩层之下约100m采获早三叠世双壳类和菊石化石;本次新发现的关键层凝灰岩层及化石可作为早-中三叠世等时地层标志进行区域对比,丰富了右江盆地早三叠世火山岩分布范围;结合前人资料,这套凝灰岩(又称绿豆岩)被广泛认为是稳定的,可为华南陆块T1/T2界线的划分提供了重要年代学及古生物证据,认为安尼阶/奥伦尼克阶界线年龄应定为245.5Ma,可能更为合理。
中文关键词:华南陆块  右江盆地  早-中三叠统  凝灰岩  古生物  锆石U-Pb年龄
 
Determination of top tuff from Shipao Formation in the Funing area of the Youjiang Basin and its constraints on the T1/T2 boundary division
Abstract:Through field geological surveys, the author discovered a new key layer of tuff with a thickness of about 5m between the Banna Formation of the Middle Triassic and the underlying Youpao Formation of the Lower Triassic in the Funing area of the Youjiang Basin. LA-ICP-MS U-Pb isotope dating was performed on the tuff, and isotopic ages of 249.0 ± 1.9 Ma, 247.9 ± 3.4 Ma, and 245.5 ± 1.6 Ma were obtained from bottom to top, respectively. The age range of the top boundary of the Shipao Formation was relatively consistent within the error range. The age of the top boundary of the Shipao Formation was first obtained as the Olennian of the Lower Triassic; Simultaneously, early Triassic bivalve and ammonite fossils were collected approximately 100m below the tuff layer; The newly discovered key layers of tuff and fossils can be used as early to middle Triassic isochronous stratigraphic markers for regional comparison, enriching the distribution range of early Triassic volcanic rocks in the Youjiang Basin; Based on previous data, this set of tuff (also known as mung bean rock) is widely believed to be stable and provides important chronological and paleontological evidence for the division of the T1/T2 boundary of the South China landmass. It is believed that the age of the Anian/Orenician boundary should be set at 245.5Ma, which may be more reasonable.
keywords:South China block  Youjiang Basin  Early Middle Triassic  Tuff  Paleontology  Zircon U-Pb age
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