北秦岭南召盆地太山庙组下部凝灰岩锆石U-Pb年龄及其地质意义
Zircon U-Pb dating of a tuff from the lower Taishanmiao Formation in the Nanzhao Basin,Northern Qinling and its geological significance
刘超 1梁天 1杨文涛 1陈浩 1刘萧萧 1安海花 1李昕 1马强分2
作者信息
- 1. 河南理工大学 资源环境学院,河南 焦作 454000
- 2. 桂林理工大学 地球科学学院,广西 桂林 541004
- 折叠
摘要
晚三叠世卡尼期全球古气候发生明显转变,全球降水量增加,海水温度上升了6～8℃,大量陆源碎屑物质输入海洋,导致海洋中出现碳酸盐生产危机.北秦岭南召盆地太山庙组可能记录了卡尼期洪水事件.目的 为精确限定太山庙组沉积时代,凸显其地质意义,方法 采用激光剥蚀电感耦合等离子体质谱法(LA-ICP-MS)对太山庙组下部凝灰岩进行锆石U-Pb同位素定年分析.结果 结果表明:凝灰岩锆石颗粒呈粒状、短柱状,无磨圆;阴极发光图像显示振荡环带结构明显;根据阴极发光图像和Th/U,认为太山庙组下部凝灰岩中18颗锆石均为火山来源,剔除轻稀土富集的锆石后,选择其中 15 颗锆石进行计算,得到其加权平均年龄为(241.4±1.3)Ma(1σ;MSWD=0.27),代表凝灰岩中锆石的结晶年龄;结合前人研究成果,计算出太山庙组下部平均沉积速率为20.6 m/Ma,太山庙组底界年龄约246 Ma,因此,太山庙组至少自中三叠世安尼期就开始沉积,至晚三叠世卡尼期末结束;根据南召盆地遗迹化石组合演化规律和植物孢粉变化,认为太山庙组沉积时期古气候发生了明显转变,由干旱炎热气候转变为温暖、湿润气候.结论 研究结果对北秦岭南召盆地三叠纪地层划分产生了新认识,有助于研究探讨南召盆地对卡尼期洪水事件的沉积响应.
Abstract
During the Late Triassic Carnian Period,there were significant global paleoclimate changes,in-cluding increased global precipitation and a rise in seawater temperature by about 6 to 8 ℃.Additionally,a large amount of terrigenous detrital material led to a crisis in carbonate production in the ocean.It is possible that this Carnian pluvial event was recorded in the Taishanmiao Formation of the Nanzhao Basin,Northern Qinling.Objectives To accurately determine the sedimentary age of the Taishanmiao Formation and highlight its geological significance,Methods laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS)was used for U-Pb isotopic dating analysis on zircons from a tuff bed located in the lower part of the Taishanmiao Formation.Results The results show that zircons from the tuff are granular and short columnar in shape,non-rounded,and exhibit an obvious oscillating ring structure in their cathodoluminescence images.Based on the CL image and Th/U ratios,it is considered that the 18 zircons from the tuff in the lower part of the Taishanmiao Formation are of volcanic origin.After removing zircons with high light rare earth element contents,15 zircons were selected for calculation,and their weighted average age was(241.4±1.3)Ma(1σ;MSWD=0.27),representing the crystallization age of the zircon in the tuff.According to previous studies,the average sedimentary rate of the lower Taishanmiao Formation was calculated to be 20.6 m/Ma,and it is estimated that the bottom of the Taishanmiao Formation has an age of about 246 Ma.Conclusions Therefore,it can be concluded that initial deposition of the Taishanmiao Formation occurred as early as Anisian Age(Middle Triassic),followed by successive sedimentation until end of Carnian Age(Late Triassic).Considering trace fossil evolution and plant pollen assemblage in the Nanzhao Basin during sedimentation of the Tai-shanmiao Formation,significant changes in paleoclimate from a dry and hot climate to a warm and humid one was observed.This study provides new insights into chronostratigraphic division within Triassic System in the Nanzhao Basin while also helping investigate basin's sedimentary response to Carnian Pluvial Episode.
关键词
卡尼期洪水幕/U-Pb同位素定年/三叠纪/南召盆地/太山庙组/陆相沉积/火山凝灰岩Key words
Carnian Pluvial Episode/U-Pb isotopic dating/Triassic/Nanzhao Basin/Taishanmiao Forma-tion/terrestrial sedimentation/volcanic tuff引用本文复制引用
出版年
2025
国家科技期刊平台
NSTL
万方数据