AGE DETERMINATION OF ROCKS BY THE RUBIDIUM-STRONTIUM METHOD

Age determination measurements by the rubidium-strontium method have given widely varying results. In an attempt to improve the reproducibility of this method an optical spectrographic determination of the strontium-rubidium ratio was made on feldspar. The ratio obtained was Sr/Rb- (10 9 plus or minus 0 2) x 10/sup -3/. The ratio of the radioactive Sr/sup 87/ to the total strontium content of the feldspar was determined to be Sr/sup 87//Sr = 0.745 plus or minus 0.0006. Using a half life of 5.0 x 10/sup 9/ for Rb/sup 87/, the age of the feldspar was calculated as (2.08 x 0.04) x 10/sup 9/ years, a result in good agreement with the vaiue 2.06 x 10/sup 9/ obtained by the potassium-- argon method. (J.S.R.)