Wyznaczanie wieku bezwzględnego skał metodą rubidowo-strontową

Abstract

ABSOLUTE AGE DETERMINATIONS OF ROCKS BY RB-SR METHOD Summary The Rb-Sr method, discussed herein, was applied to estimate absolute ages of granites of Strzelin-Żulova and Strzegom-Sobótka massifs, Przedgórze Sudeckie. a migmatite from Sowie Mts., and a gneiss from Tatra Mts. Relative Sr and Rb content in these rock was determined by X-ray fluorescence and isotope dilution methods. Separation of Rb and Sr was performed by ion exchange in chromatographical cation columns. Isotope relations, Rb/Sr, were established by means of 90-degree mass spectrometer CH-5 of the Atlas Co.; the spectrometer works with two-belt two-carrier ion source, and the resulting ion currents are recorded by a single collector. In age determinations, β-87 Rb equalling λ = 1.47 • 10-11 years-1 was accepted as the value of half-life constant, and 87Sr/86Sr = 0.716 was accepted as the initial value (for the moment of rock formation). The average age of Przedgórze Sudeckie granites is 268 • 105 years, that of the examined migmatite - 329 • 106 years, and the age of the gneiss – 408 • 106 years. The absolute age data previously obtained for the granites of the Przedgórze Sudeckie by the use of K-Ar method by other authors appear to be remarkably consistent with the results presented herein.