AN EXPERIENCE OF THE RB-SR SYSTEMS STUDY IN INTRUSIVE PYROCLASTS

The Rb-Sr isotope systems have used for the first time to reconstruct geological history of intrusive pyroclastic rocks - later Variscian rh yolite ''intrusive tuffs'' of Peredovoi Ridge of Great Caucasus. In ha s been stated that the Rb-Sr systems of melt inclusions in quartz as w ell as that of nonaltered biotite can be an indicator of magmatic stag e of formation of intrusive pyroclastic rocks, whereas that of albite and potassium feldspar - indicators of hydrothermal stage, Rb-Sr syste m of chlorite - indicator of diagenetic stage of desintegrated materia l. Hydrothermal alteration of rhyolitic intrusive tuffs occurred simul taneously with its intrusion whereas the diagenesis of desintegrated m aterial occurred not at the same time with intrusion and hydrothermal alteration. A conclusion has been made that the Rb-Sr method is suitab le for the time determination of intrusion of these specific formation s.