年轻火山岩的定年:进展与问题

Advances of ^(40)Ar/^(39)Ar dating on young volcanic rocks

年轻火山岩定年对人类的起源与进化、地质年表建立、古环境演化、火山灾害、岩浆演化及地球动力学等研究非常重要。由于年轻样品放射性成因子体积累较少、大气氩含量高,微量的过剩氩极难识别,使得年轻火山岩及其沉积地层高精度定年一直是地质年代学中最具挑战性的课题之一。过去几年,年轻火山岩定年在技术上的进展主要体现在定年精度和准确度不断提升,尤其是利用新型多接收稀有气体质谱对单颗粒样品进行逐步升温^(40)Ar/^(39)Ar定年,是方法学上最重要的进展之一。本文总结了年轻火山岩^(40)Ar/^(39)Ar定年的现状、影响因素和相关定年技术及应用,以引起大家的关注和思考,共同提高我国年轻火山岩定年的技术水平。利用新型多接收质谱和创新的实验方法,通过对全球重要火山喷发事件和年轻国际标准样的研究,广泛开展实验室间的对比是提高国内^(40)Ar/^(39)Ar年代学水平并在年轻火山岩定年中取得突破的重要途径,也是当前^(40)Ar/^(39)Ar年代学研究的重要方向。

Dating on young volcanic rocks and ashes plays an important role in volcanology, magnetostratigraphy, biostratigraphy, paleoanthropology and paleoclimate studies. It is still a challenge due to many limitations, such as detecting small amount of radiogenic isotopes. The argon geochronology community has paid a lot of attention to improving precision and accuracy of 40Ar/39Ar dating. Recent advances in laboratory and instrumentation techniques result in higher precision and accuracy that allow for inter-calibrating other chronometers. Cross calibration and improving the precision as well as accuracy of these methods will be a main task in the future. We review recent advances in ^40Ar/^39Ar method and new results from selected volcanic eruptions which are of either global super eruptions or are the primitive standards in ^40Ar/^39Ar geochronology. Multi-collector noble gas mass spectrometer and new advanced technology greatly promote the analytical accuracy, precision and efficiency of 40Ar/39Ar dating, especially for those younger and smaller samples.