Internal isochrone method in accessory zircon dating

Validity of initial ideas of dating on the basis of internal isochrone and geological situations at which such dating is possible are checked up. Probability of obtaining the false isochrones when dating of various fractions of accessory zircon is revealed for the case of multiple transformations of zircon-containing rock. The dating with respect to terrigenous zircon of metamorphic rocks probably due to the content of different quantities of terrigenous component in various zircon fractions may correspond only to minimum ages, if one-stage alteration of zircon is not proved. The method of dating based on the internal isochrone may be used for late-Pre-Cambrian and even younger formations, for which the danger of multiple disturbances of the U-Pb system in accessory zircons is absent. For the dating of more ancient rocks the above method is usable only at proved lack of multiple metamorphism phenomena in the region under investigation