Zirconology of Navysh Volcanic Rocks of the Ai Suite and the Problem of the Age of the Lower Riphean Boundary in the Southern Urals

摘要

Volcanic rocks of the Navysh Complex occur in the base of the Lower Riphean Ai Formation of the Burzyan Series within the Bashkirian meganticlinorium (Southern Urals). They represent practically the only object suitable by the material—geological and geochronolog-ical criteria for estimation of the age of the lower boundary of not only the Ai Formation, but the whole strato-typical Riphean section of the Southern Urals.