Basic research for K-Ar dating of volcanic rocks up to 10ka

本研究主要对极少量基岩中提取的Ar和年轻火山岩中分离出的斑晶等贵重气体同位素进行分析。为了完善它，我们购买了一台激光探头加热装置，然后利用它和带有温度控制系统的高精度增量加热装置进行了基本实验。我们系统地收集了浅间、赤城、宫城岛、樱岛、萨玛-1Wojima、宫山(Lzu Ohshima)和九州麻生的火山岩，包括历史上的熔岩，这些火山岩的火山地层学都有很好的记录。对这些岩石进行了岩石学研究，并分离了它们的基质和斑晶进行K-Ar分析。用单颗粒或晶体分析基质和斑晶。结果表明，由于极少量的Ar含量，~(40)Ar；Ar/~(36)Ar；Ar的分析误差约为40%，~(38)Ar；Ar/~(36)Ar的分析误差大于50%。在用电阻炉对岩石进行大块磨料分析时，检测到的Ar同位素质量分馏误差小于1%，对原抽气净化流水线进行了全面改造，实现了信号检测和阀门控制的计算机自动控制系统。编程采用Windows环境下的HP-VEE处理。利用该系统对新建的萃取线和纯化线进行了控制。编制了用峰高比较法进行Ar分析的程序。所有的分析工作都是在计算机上完成的。这种使用HP-VEE程序的独特分析系统将很快在某个地方报告。尽管没有对岩石进行K-Ar测年，但进行这一研究计划的基地已经完成。用原质谱仪对岩石进行K-Ar定年的结果已部分发表。

This study is to analyze noble gase isotopes such as mainly argon extracted from extremely small amount of groundmass and phenocrysts separated from young volcanic rocks. To perfome it, We have purchased an laser probe heating apparatus and then carried out the basic experiments using it and the high precision incremental heating device with the temperature control system.We have collected volcanic rocks including historical lavas systematicaly from Asama, Akagi, Miyakejima, Sakurajima, Satsuma-lwojima, Miharayama (lzu Ohshima) and Kyushu-Aso which have been documented well for their volcano stratigraphy. The rocks were studied petrographically and their groundmass and phenocrysts were separated for K-Ar analyses. Groundmass and phenocrysts were analysed using single grains or crystals. The results show that the analytical errors were ca. 40% for ^<40>Ar/^<36>Ar ratio and higher than 50% for ^<38>Ar/^<36>Ar one due to extremely small amount of argon content. In bulk groundmass analysis of the rocks using the resistance furnace, a mass fractionation for argon isotopes were detected because of small error less than 1%.We reformed completely the former gas extraction and purification line and then performed a computer systems controlling automatically the signal detection and valve control. HP-VEE processing on Windows was used for the programming. The newly constracted extraction and purification lines were controlled using the system. The program for argon analysis using the peak height comparison method was also developed. All the analytical works are done on a computer. This unique analytical system using HP-VEE program will be reported somewhere soon. The base to proceed this research program was completed although K-Ar dating of rocks was not carried out. K-Ar dating result of rocks using the former mass spectormeter has been published in part.