On most ancient geologic events on the Anabar Shield

The Anabar Shield is considered in geologic literature as one of the oldest formations of the Earth. In present work a special selection of two series of samples was undertaken: crystallic schists of the Daldynskaya Series and plagio-granito-gneisses from the basin of the Knyasevaya River. Concentrations of Rb, Sr, K and 87Sr/86Sr, 87Rb/86Sr isotope ratios were determined. A Rb-Sr isochron for plagio-granito-gneisses gives ages 1.1 and 1.8 by (depending on interpretation). According to the data obtained the plagio-granito-gneisses may not be regarded as oldest formations of the Earth. In contrast to these, the crystallic schists allow to obtain a reliable Rb-Sr isochron age of 3.8 ± 0.2 by with (87Sr/86Sr)0 = 0.7010. Thus, on the Anabar shield one of the oldest events of the Earth is detected. It is stated that K/Rb and 87Rb/86Sr ratios are correlated and are quite specific for oldest formations of the Earth. (author)