U-Pb zircon dating of granulite metamorphism in the Sludyanskiy Complex, Eastern Siberia

Conventional multigrain and single-grain zircon U-Pb ages were obtained for syn- and post-metamorphic granitoids from the Sludyanskiy Complex in the South-Western Baikal region regarded as a classical Precambrian terrain in the Eastern Siberia. Single grains of magmatic zircon from the syn-metamorphic hypersthene-bearing biotite trondhjemite and two-pyroxene trondhjemite have yielded concordant U-Pb ages of 488.5 +/- 0.6 Ma and 488 +/- 0.5 Ma. Concordant U-Pb data for zircons of metamorphic origin in the syn-metamorphic two-pyroxene trondhjemite yield an age for the peak of the granulite-facies metamorphism in the Sludyanskiy Complex as 477.6 +/- 2 Ma. The pattern of multigrain magmatic zircon samples from syn-metamorphic granitoids reflects significant Pb loss during the metamorphic episode. This came to an end before 471.1 +/- 2 Ma as demonstrated by concordant zircon data for the intrusion of post-metamorphic amphibole-two-pyroxene quartz syenite. Our zircon data establish that the granulite-facies reworking of the Sludyanskiy Complex took place during the Palaeozoic, and not during the Paleoproterozoic as was previously suggested. The age span between the intrusions of syn-metamorphic and post-metamorphic granitoids constrains the duration of the metamorphic episode to about 20 Ma.