长白山天池火山晚更新世以来的喷发活动：

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：＞350ka、70ka、18－25ka、10ka、4－5ka和1－0．75ka。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，讨论了样品封闭等问题。

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

Eleven samples of lava and pumice from the cone of ChangbaishanTianchi 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 TianZhi volvanivs and the results are reliable.