Age of the Irkut block of the Prisayan uplift of the Siberian platform basement: Dating minerals from metamorphic rocks

New geochronological (U-Pb, Pb-LS, Sm-Nd) studies were carried out for minerals from metamorphic rocks (aluminous plagiogneisses with sillimanite (kinzigites) and potassium shadow migmatites) to establish the sequence of metamorphic events in the Irkut block of the Prisayan marginal uplift of the Siberian platform basement. Obtained data permit the distinguishing of two main stages of regional metamorphism under the granulite and amphibolite facies conditions: 2480–2560 and 1860–1900 Ma. New age data in general are consistent with previously published zircon estimates of the Neoarchean and Paleoproterozoic ages of the granulite-facies metamorphism of the Irkut block. This gives grounds to consider the geochronological studies of garnet and monazite as promising tool for distinguishing age boundaries of metamorphic transformations in the areas of polycyclic evolution.