摘要
海南蓬莱锆石巨晶具有均一的U-Pb年龄(4.4±0.1Ma,95%置信度),而其寄主岩浆喷发形成的碱性玄武岩,具有较为分散的放射成因同位素年龄(K-Ar定年,4.4~3.6Ma)。变化较大K-Ar年龄与一致的U-Pb年龄形成鲜明的对比,预示着该套碱性玄武岩K-Ar定年结果的不确定性。本研究通过优化仪器参数及样品分析流程,提升测试自动化程度,建立年轻玄武岩^(40)Ar/^(39)Ar定年方法,并对海南蓬莱地区碱性玄武岩开展阶段升温^(40)Ar/^(39)Ar定年分析,以期获得蓬莱碱性玄武岩的高精度年龄。2个样品坪年龄分别为4.36±0.05(0.05)[0.19]Ma(2s,MSWD=0.53)和4.35±0.06(0.06)[0.19]Ma(2s,MSWD=1.32),其反等时线所计算的空气氩初始值分别为296.5±1.5(2s)和297.7±1.1(2s),样品不存在过剩40 Ar的干扰。一致的^(40)Ar/^(39)Ar年龄表明2个样品是同时形成、K-Ar体系封闭且未受后期热扰动,该结果可代表海南蓬莱玄武岩的喷发年龄。本研究不仅获得了海南蓬莱地区碱性玄武岩高精度^(40)Ar/^(39)Ar年龄,而且该结果与具有不同封闭温度的年代学方法(U-Pb法及U-Th/He法)所获放射成因同位素年龄在2 sigma范围内一致,表明海南蓬莱地区碱性玄武岩未受后期热事件影响,具有一致的喷发年龄。
Natural zircon megacrysts from Penglai,situated in northern Hainan Island,southern China,exhibit a homogeneous U-Pb age of 4.4±0.1Ma(95%confidence interval).However,the K-Ar ages for the host alkaline basalt display a broad range between 4.4Ma to 3.6Ma.This significant variation in K-Ar ages contrasts starkly with the consistent U-Pb age,suggesting potential factors influencing the K-Ar dating system in the alkaline basalt.In this study,we enhanced the instrument automation level and optimized instrument parameters and sample analysis procedures to establish a young basalt ^(40)Ar/^(39)Ar dating method.We then conducted stepwise heating ^(40)Ar/^(39)Ar dating analyses on alkaline basalts from the Penglai area of Hainan.The primary objective was to obtain a precise age for the Penglai alkaline basalts.Stepwise heating analyses yielded a highly concordant age of 4.36±0.05(0.05)[0.19]Ma(2s,MSWD=0.53)and 4.35±0.06(0.06)[0.19]Ma(2s,MSWD=1.32)for two samples,respectively.Inverse isochron calculations identified trapped 40 Ar/36 Ar components at 296.5±1.5(2s)and 297.7±1.1(2s),respectively,indicating an absence of detectable excess argon in the samples.The uniformity of the ^(40)Ar/^(39)Ar age suggests that the two samples possess a consistent K-Ar isotopic system,representing the time of the eruption.This study not only provides high-precision ^(40)Ar/^(39)Ar ages for the alkaline basalts in the Penglai area of Hainan but also reveals that these results are consistent within a 2 sigma range with radiogenic isotopic ages derived from other methods(U-Pb and U-Th/He)with different closure temperatures.This consistency suggests that the alkaline basalts in the Penglai area of Hainan were erupted simultaneously and have remained unaffected by subsequent thermal events.
作者
张万峰
汪俊杰
郑德文
徐义刚
崔泽贤
张彦强
ZHANG WanFeng;WANG JunJie;ZHENG DeWen;XU YiGang;CUI ZeXian;ZHANG YanQiang(State Key Laboratory of Deep Earth Processes and Resources,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China;State Key Laboratory of Earthquake Dynamics and Forecasting,Institute of Geology,China Earthquake Administration,Beijing 100029,China)
出处
《岩石学报》
北大核心
2025年第9期3190-3197,共8页
Acta Petrologica Sinica
基金
广州市科技计划项目(2025A04J4664)
中国科学院技术支撑人才和中国科学院仪器功能开发项目(GIGGNKF202201)联合资助
