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

本研究主要分析从极少量的地质体和从年轻火山岩中分离出来的斑晶中提取的稀有气体同位素，如氩。为此，我们购买了激光探针加热装置，并使用该装置和高精度增量加热装置以及温度控制系统进行了基础实验。我们系统地收集了浅间、赤城、宫崎岛、樱岛、萨摩-伊沃岛、三原山（大岛）和九州-麻生的火山岩，包括历史熔岩，并对其火山地层学进行了很好的记录。对这些岩石进行了岩石学研究，并对其地质体和斑晶进行了分离，进行了K-Ar分析。用单粒或晶体分析地质体和斑晶。结果表明，由于氩含量极低，对<40>Ar/ <36>Ar的分析误差约为40%，对<38>Ar/ <36>Ar的分析误差大于50%。在利用电阻炉对岩石进行大面积地质量分析时，由于误差小于1%，检测出了氩同位素的质量分馏。对原有的气体抽净化生产线进行了全面改造，采用计算机自动控制信号检测和阀门控制。在Windows上使用HP-VEE处理程序进行编程。采用该系统对新建的萃取纯化生产线进行了控制。并编制了用峰高比较法分析氩气的程序。所有的分析工作都在计算机上完成。使用HP-VEE程序的独特分析系统将很快在某处报道。虽然没有进行岩石的K-Ar定年，但进行这项研究计划的基础已经完成。用旧质谱仪测定岩石K-Ar年代的结果已部分发表。

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.