Variance in Measurements of Rb and Sr Isotopic Ratios of the Some Sample, and Its Effect to the Age Determi nation(as to the Standard Sample JG-I)

Abstract

A standard sample JG-I, a granodiorite from Sori, Gunma Prefecture indicates the following isotopic compositions:Rb content has a range of178. 9to183. 4ppm;Sr content has a range of182. 5to187. 5ppm;the ratio of Sr⁸⁷/Sr⁸⁶ has a range of0. 7113to 0. 7121. The ratio of Rb⁸⁷/Sr⁸⁶, calculated from above data, has a range of2. 692to2. 839. In an isochron diagram, the error in vertical axis is ±0. 06%, and that in horizontal axis is±2. 6%. Thus, the error in the calculated age is?±10. 6%, in a case of the rock of which age is approximately100million years. When the correction of the multiplier was not adequate, the initial ratio of Sr⁸⁷/Sr⁸⁶ in isochron is also effected.