刘超，梁天，杨文涛,等. 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[J].河南理工大学学报(自然科学版), doi:10.16186/j.cnki.1673-9787. 2023110026.

LIU C，LIANG T，YANG W T,et al. Zircon U-Pb dating of a volcanic tuff from the lower Taishanmiao Formation in the Nanzhao Basin, North Qinling and its geological significance[J].Journal of Henan Polytechnic University( Natural Science),doi:10.16186/j.cnki. 1673-9787. 2023110026.

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(网络首发)

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

（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）

摘要: 目的 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，海水温度上升了大约6～8 ℃，大量陆源碎屑物质输入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。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，阴极发光图像显示明显的振荡环带结构。根据阴极发光图像和Th/U元素比值，认为太山庙组下部凝灰岩中的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，太山庙组底界年龄大约为246 Ma。 结论 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。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，并有助于研究探讨南召盆地对卡尼期洪水事件的沉积响应。

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

中图分类号：P534.51

doi: 10.16186/j.cnki.1673-9787.2023110026

基金项目: 国家自然科学基金资助项目（42172120,41902102）；广西科技基地与人才专项项目（AD20159027）；教育部高等学校专项课题（ZJXF2022144）

收稿日期：2023-11-13

修回日期：2024-02-04

网络首发日期：2024-04-11

Zircon U-Pb dating of a volcanic tuff from the lower Taishanmiao Formation in the Nanzhao Basin, North Qinling and its geological（Online）

LIU Chao¹，LIANG Tian¹，YANG Wentao¹，CHEN Hao¹，LIU Xiaoxiao¹，AN Haihua¹，LI Xin¹，MA Qiangfen²

（1.School of Resource and Environment，Henan Polytechnic University，Jiaozuo 454000，Henan，China；2.College of Earth Sciences，Guilin Univer⁃ sity of Technology，Guilin 541004，Guangxi，China）

Abstract: Objectives During the Late Triassic Carnian Period, the global paleoclimate changed significantly, i.e. global precipitation increased, seawater temperature rose by about 6 to 8 °C, and a large amount of terrigenous detrital material led to a crisis of carbonate production in the ocean. This Carnian pluvial event might have been recorded in the Taishanmiao Formation of the Nanzhao Basin, North Qinling. In order to accurately determine the depositional age of the Taishanmiao Formation and highlight its geological significance, Methods laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to conduct U-Pb isotopic dating on zircons from a tuff bed in the lower part of the Taishanmiao Formation. Results The results show that zircons from the tuff are granular and short columnar in shape, without rounding, and their cathodoluminescence images exhibit obvious oscillating ring structure. According to 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 the zircons with high light rare earth element contents were removed, 15 zircons were selected for calculation, and the weighted average age was 241.4 ± 1.3 Ma (1σ; MSWD = 0.27), representing the crystallization age of the zircon in the tuff. Combined with previous studies, the average depositional rate of the lower Taishanmiao Formation was calculated to be 20.6 m/Ma, and the age of the bottom of the Taishanmiao Formation is about 246 Ma. Conclusions Therefore, the initial deposition of the Taishanmiao Formation occurred as early as the Anisian Age (Middle Triassic), and this formation then had a successive sedimentation till the end of the Carnian Age (Late Triassic). According to the evolution of trace fossil and plant pollen assemblage in the Nanzhao Basin, we conclude that the paleoclimate during the deposition of the Taishanmiao Formation in the Nanzhao Basin has undergone a significant change, from a dry and hot climate to a warm and humid climate. This study sheds new light on the chronostratigraphic division of the Triassic System in the Nanzhao Basin and is helpful to investigate the sedimentary response of the basin to the Carnian Pluvial Episode.

Key words：Carnian Pluvial Episode；U-Pb isotopic dating；Triassic；Nanzhao Basin；Taishanmiao Formation；terrestrial deposits；volcanic tuff

CLC: P534.51；