LATE ARCHEAN GRANITOIDS OF THE DAMBUKINSKIǐ BLOCK OF THE DZHUGDZHUR-STANOVOY FOLD BELT: FORMATION AND TRANSFORMATION OF THE CONTINENTAL CRUST IN THE EARLY PRECAMBRIAN

Abstract

This paper presents new data on the age and composition of granitoids from the Charnokitovyǐ and Drevnestanovoy complexes of the Dambukinskiǐ block in the eastern Dzhugdzhur-Stanovoy fold belt. Based on the results of U-Pb zircon geochronology, including single grain dating, it was shown that these granitoids are 2833±15 and 2828±34 Ma old, respectively, and experienced structural and metamorphic transformations corresponding to at least two events of high-temperature regional metamorphism of Late Archean (2647 ± 3 Ma) and Early Proterozoic (1884 ± 9 Ma) ages. The former was probably related to the accretion of the small terranes that now build up the ancient granulite basement of the Dzhugdzhur-Stanovoy fold belt and their attachment to the Olekma-Aldan continental microplate. The second metamorphic event was probably caused by the collision of the Dzhugdzhur-Stanovoy microplate and the Siberian craton, when the Early Proterozoic ocean basin between them closed. Our geochronological, isotopic (Sm-Nd and Pb-Pb), and geochemical results suggest that the generation of the parental melts of the Charnokitovyǐ and Drevnestanovoy granitoids reflected the occurrence of crust-forming processes 2.9-2.8 Ga ago. They were younger than the Late Archean crust-forming events that have been recognized up to now in the Aldan shield.