望天鹅火山喷发时限的激光 ^(40)Ar/ ^(39)Ar年代学  

Laser ^(40)Ar/ ^(39)Ar geochronology of the eruptiontiming of Wangtian’e volcano

作　　者：周鑫 周晶[1] ANDREEVA Olga A ANDREEVA Irina A 季建清[1] ZHOU Xin;ZHOU Jing;ANDREEVA Olga A;ANDREEVA Irina A;JI JianQing(MOE Key Laboratory of Orogenic Belts and Crustal Evolution,School of Earth and Space Sciences,Peking University,Beijing 100871,China;Institute of Geology of Ore Deposits,Petrography,Mineralogy,and Geochemistry,Russian Academy of Sciences,Moscow 119017,Russia)

机构地区：[1]北京大学地球与空间科学学院,造山带与地壳演化教育部重点实验室,北京100871 [2]俄罗斯科学院矿床岩石矿物与地球化学研究所,莫斯科119017

出　　处：《岩石学报》2021年第8期2521-2530,I0001-I0004,共14页Acta Petrologica Sinica

基　　金：中国地质调查局地质调查项目(12120113013700)资助.

摘　　要：在中国东北地区,望天鹅火山的覆盖范围仅次于长白山,前人测得的K-Ar年龄主要集中在2~3Ma,但其精确的喷发年代一直没有很好的限定。这是因为第四纪以来的火山岩40 Ar/39 Ar定年与较老的地质样品有显著的不同,测试过程中极其微小的偏差会呈指数方式放大,带来测年结果的极大误差,难以严格限定火山喷发的年代。本文选用的激光40 Ar/39 Ar年代学方法具有样品用量小、精度高、自动化测试稳定等优点。通过增加测试次数,在数据处理中引入高斯混合模型进行统计分析,可以更准确地判别火山喷发期次。在此基础上,提出符合等时线计算要求的同位素体系“同源、同时、封闭”的数学表达是表观年龄的正态分布,对构成同一正态分布的数据计算等时线年龄,能够实现对望天鹅火山喷发时代的精细限定。结果显示,在测试精度尺度内,望天鹅火山可以看作是一期喷发的结果,喷发时限为2.73±0.18Ma。这一时限可以帮助解释北太平洋深海钻探中同一时期火山凝灰质沉积层的出现,并由此可以把2.73Ma前后的北半球大冰期事件与望天鹅火山喷发联系起来,为研究火山喷发与气候变冷效应提供一个新的实证案例。Wangtian’e volcano is located at Northeast China and extends to a large area that is only smaller than that of Changbai.Previous K-Ar ages of the volcano mainly range from 2Ma to 3Ma and the eruptive age of Wangtian’e has not been precisely determined.This is because the 40 Ar/39 Ar dating of Quaternary volcanic rocks is different from that of the old samples and a minor deviation in isotopic analysis may lead to exponential increase of age error,making it difficult to date the eruption event accurately.This paper uses the laser fusion 40 Ar/39 Ar dating method which has the advantages of testing minor samples with high precision and stable automatic test process.By increasing the number of tests,apparent ages could be clustering analyzed by using Gaussian Mixture model.It is proposed that the normal distribution of apparent age is the mathematical expression of“homologous,simultaneous and closed”of isotopic system,and the normally distributed data could be used to calculate the isochron age.By this way,eruptive age of Wangtian’e volcano could be better determined.Our dating result shew that Wangtian’e volcano was formed from one eruptive stage under the testing scale,and the eruptive age is 2.73±0.18Ma.This result could help to explain the appearance of ash deposits at the same time under the North Pacific,and thus link the Wangtian’e eruption to the Northern Hemisphere Glaciation(NHG)around 2.73Ma,providing a new case for studying the cooling effect of volcanic eruption.

关 键 词：40 Ar/39 Ar定年 等时线年龄 高斯混合模型 望天鹅火山 

分 类 号：P588.14[天文地球—岩石学] P597.3[天文地球—地质学]