离子探针第四纪锆石U-Pb和U-Th定年方法及应用

SIMS U-Pb AND U-Th ZIRCON AGE DETERMINATION FOR QUATERNARY ROCKS

第四纪年代学是第四纪地质研究的重要组成部分。高精度、高效率第四纪U—Th-Pb定年技术已在气候一环境演化、全球变化、火山-岩浆作用、生物迁徙-灭绝等研究中得到广泛应用并取得重大成果。本文以离子探针（SIMS）第四纪锆石U—Th—Ph定年方法为主，对其定年的原理和方法、分析技术与误差校正以及国内外研究进展进行介绍。相较于其他定年方法，SIMS微区原位定年可以提供样品内部的微观年龄信息。对于〉350ka的锆石，可以用常规SIMSU—Pb方法定年，经过适当的普通Pb和^230Th校正，得到准确的年龄；对于〈350ka的锆石，不平衡U系（^238U-^230Th）定年精度高于^238U-^206pb定年，可以根据样品Th—U含量情况选择微区原位定年方法或者通过对样品。^230Th进行富集后再进行测定。在过去10余年里，SIMS第四纪锆石U-Th—Pb定年技术取得了长足进步，在矿物结晶机制、岩浆过程以及火山活动中显示出巨大的应用前景。我国已有3个实验室装备了大型高分辨率高灵敏度SIMS，迅速建立SIMS第四纪锆石U—Th定年方法并推广应用，对提高我国高分辨率第四纪年代学以及第四纪地质研究有重要的意义。

Quaternary geochronology is a fundamental part for Quaternary studies. High resolution and high precision U-Th-Pb dating techniques are increasingly being used and have obtained revolutionary achievements in the study of climate-environment evolution, global change, volcanism-magmatism, and the biota migration-extinction studies. In this paper we introduce the principles, analytical techniques, as well as error correction of secondary ion mass spectrometry （SIMS） in situ U-Th-Pb dating method on Quaternary zircon and review a selection of applications. Compared to bulk dating methods, SIMS in situ dating provides micrometre-scale age information of the samples. For zircons〉350ka, conventional SIMS U-Pb dating method with proper common Pb and ^230Th correction can be used to accurately determine the age of the samples. For zircons 〈350ka, U-series （^238U-^230Th） dates become more precise than ^238U-^206Pb dates. According to Th-U concentration of the samples, one can chose between SIMS high spatial resolution in situ dating or chemical purification of ^230Th before SIMS dating. In the past 10 years, SIMS U-Th-Pb dating technology has made considerable progress and showing great prospect in deciphering mineral crystallization mechanism, magmatic processes and volcanic activities. Three laboratories in China have been equipped with large, high resolution and high sensitivity SIMS. It is important to establish SIMS U-Th zircon dating techniques for Quaternary rocks to promote the study and application of high resolution Quaternary geochronology as well as Quaternary geology in our country.