ISOTOPE-GEOCHRONOLOGICAL DATA ON GRANULITES OF THE ILYINSKAYA BLOCK AS AN EVIDENCE OF THE ANABAR SHIELD HETEROGENEITY

N. I. Gusev

A.P. Karpinsky Russian Geological Research Institute, Saint Petersburg, Russia

The paper presents the results of analysing petrographic and chemical composition of rocks, zircon U-Pb dating (SHRIMP-II), and the Sm-Nd isotope system of granulites from the Ambardakhskaya Series of the Ilyinskaya block of the Anabar shield. The magmatic protolith of granulites in the Ilyinskaya block had been formed ca. 2.9 Ga, with the involvement of a mantle component, which is much later than the formation of the protolith of granulites of the Daldynskaya Series in the Daldynskaya block. Being exposed to the Late Archean granulite methamorphism, the rocks were subjected to anatexis with the age of 2.7 Ga. The Ambardakhskaya Series contains Proterozoic hypersthenic plagiogneisses and mafic two-pyroxene crystalline schists with a Nd-model age of protolith of 2.27–2.12 Ма. They were formed being subjected to juvenile mantle matter. The age of the Proterozoic granulite magmatism was identified within 1970±21–1927±7 Ma. Small bodies of garnet granite gneisses of a potassic series have an age of 1883±5 Ma. They were formed together with the potassic granitoids of the Kotuykan-Monkholinskaya zone of shearing, metamorphism, and granitisation. The authors came to the conclusion that the source rocks of the Ilyinskaya (2.9 Ga) and Daldynskaya (3 Ga) blocks, being genetically different and of different ages, were subjected to granulite metamorphism at approximately the same time — about 2.75 Ма — probably, due to the collision of the Daldynsky and Magansky terrains.

Key words: Anabar Shield, granulites, granite gneisses, SHRIMP zircon U-Pb age, Sm-Nd isotope system.

DOI 10.20403/2078-0575-2017-1-66-79

Download PDF