长白山天池火山晚更新世以来的喷发活动:高精度铀系TIMS年代学制约  

Activity of Cangbaishan Tianchi Volcano since Late Pleistocene: The constrain from geochronology of high precision U- series TIMS method

作　　者：王非[1] 陈文寄[1] 彭子成[2] 李齐[1] 

机构地区：[1]中国地震局地质研究所,北京100029 [2]中国科学技术大学地球与空间科学系,安徽合肥230026

出　　处：《地球化学》2001年第1期88-94,共7页Geochimica

基　　金：中国地震局重点项目资助! (95- 11)

摘　　要：应用高精度铀系不平衡 TIMS法测定了吉林长白山天池火山岩锥体中上部的 11个熔岩、浮岩样品的年龄，并据此划分出晚更新世、全新世以来 6个喷发活动期次，分别为： >350 ka、 70 ka、 18～ 25 ka、 10 ka、 4～ 5 ka和 1～ 0.75 ka。此外，还介绍了铀系不平衡法火山岩年代学的基本原理和试验流程，讨论了样品封闭性等问题。Eleven samples of lava and pumice from the cone of Changbaishan Tianchi Volcano, Jiling, China, were dated by using high precision U- series TIMS method. The results show that the bottom of the cone formed before 350 ka, the middle part in 70～ 80 ka, the upper during 20～ 1 ka, and the top less than 1 ka, and the age based periods of the volcano eruption since Late Pleistocene is given as follows: >350 ka, 70 ka, 18～ 25 ka, 10 ka, 4～ 5 ka, 1～ 0.75 ka, which may offer the basis for the study of volcanic disaster in future. In addition, the principle of dating young volcanic rocks by using U- series TIMS method is introduced briefly. Differentiation characteristics of U and Th in different minerals of the volcanic rocks are discussed, and the ability producing isochrons, based on U and Th differentiation, are discussed. In the last part of the paper, the closure of samples to the elements U and Th, which is important for age results, is discussed by using (234U/238U) radioactivity ratio which can be used to monitor if the samples have been weathered or eroded or leached since the time they formed. In this study, all samples have (234U/238U) activity ratios within 1％ of secular equilibrium [(234U/238U) radioactivity ratios are unity), indicating no disturbance of the 234U- 238U system. All of these discussions show that the TIMS method is good to date Tianchi volcanics and the results are reliable.

关 键 词：铀系不平衡TIMS法 火山喷发 晚更新世 长白山天池火山 火山岩测年法 

分 类 号：P317.3[天文地球—固体地球物理学]