【摘要】 用K -Ar和4 0 Ar- 39Ar方法测定年轻火山岩年龄的技术关键在于如何有效规避过剩氩的影响和提高放射成因氩的相对含量。通过去除火山岩中可能含过剩氩的成分、选取样品中高钾成分作为测量对象、在实验中合理去气等措施 ,完全可以准确测定几万a至几千a期间的火山活动年龄。例如Renne等利用4 0 Ar - 39Ar法测定意大利威苏威火山公元 79年大喷发的熔岩年龄为距今(192 5± 94 )a ,与历史记载惊人的一致 ;Gillot等人测定Roccamonfina火山的白色粗面质凝灰岩(WTT)中透长石的4 0 Ar- 39Ar年龄为 32 8～ 333ka ,与透长石和黑云母的K -Ar年龄一致。更多还原

【Abstract】 The key technique to determine the ages of young volcanic rocks by K-Ar and 40Ar- 39Ar methods is how to avoid effects of excess argon and to raise the relative component of radiogenic argon. It is possible to obtain the ages of volcanic activity in the order of tens of thousand to thousands years by distinguishing compositions with excess argon in volcanic rocks and through selecting high-K materials as measuring factors and rational gassing in the experiment processes. Examples are as follows: Using 40Ar- 39Ar method, Renne et al. dated sanidine from the pumice deposited by the Plinian eruption of Vesuvius in 79 A. D. and obtained a 40Ar- 39Ar isochron age of (1925±94) years ago, in good agreement with the history record. Gillot et al. determined sanidine in the white trachytic tuff in Roccamonfina Volcano and yielded a 40Ar- 39Ar age of 328～333ka,perfectly agreeing with the results from K-Ar age of sanidine and biotite minerals.更多还原