Stepwise dissolution and grain size separation for obtaining the Rb-Sr internal isochron

In this paper, the method for obtaining the internal Rb-Sr system of enstatite chondrite is presented. The mineral separation was carried out by stepwise dissolution combined with grain size separation. Such method as well as the stepwise dissolution using 1 M HF was applied to the age determination for the first time. The details of analytical procedures including chemistry and mass spectrometry are also described. The blank levels of Rb and Sr during mineral separations and chemical treatments are negligibly low. The result of Rb-Sr data of Khairpur enstatite chondrite represents the performance of this method. The silicate phases separated by grain sizes and 1 M HF dissolution showed the precise isochron. The statistical errors of the age and the initial 87Sr/86Sr ratio are as good as 1 % and 0.05 %, respectively. This is the clear evidence that the stepwise dissolution does not dissolve recoiled atoms by nuclear decay process, nor leach elements selectively between Rb and Sr, thus could be used on the internal Rb-Sr isochron studies, as a strong means. (author)