Calibration of a new Ar analytical system for the K-Ar dating method and analytical results of K-Ar age known samples

Abstract

A new Ar analytical system at Kyoto University by sensitivity method which is suitable for dating of Neogene to Quaternary volcanic and tectonic events has been constructed and calibrated. Calibration has been performed using biotite mineral standard, Soni 93, in which the amount of radiogenic 40Ar is known. The system consists of a VG Isotech 3600 mass spectrometer and the main sample handling system both for the extraction by tantalum resistance furnace and for the purification of sample gases. The errors of 40Ar intensity, 40Ar/36Ar and 38Ar/36Ar of the system have been estimated to be 1.5%, 0.16% and 0.53%, respectively, by repeated standard air Ar analyses. The duplicate analyses have been done by the system using six K-Ar age mineral standards or K-Ar age known samples whose ages belong to Neogene or Quaternary. Most obtained K-Ar ages agree well with those in the literatures. There are no systematic errors among them. The ages of four Neogene samples (Bern4B, Bern4M, Baba Tuff biotite and NST30 biotite) has been obtained within about ±2-3% errors and that of one Quaternary sample (YZ1) within about ±25-30% errors. These implies that the Ar analytical system may be sufficiently useful for K-Ar dating of geological samples with younger ages than Neogene age.