EVOLUTION OF CONTINENTAL-CRUST IN THE WESTERN ALDAN SHIELD - EVIDENCEFROM SM-ND SYSTEMATICS OF GRANITOIDS

The Sm-Nd evolution of granitoid rocks of various ages was studied to date major crust-formation events in the geologic history of the weste rn Aldan Shield: 2.0-2.4, 3.0-3.1, 3.3-3.5, and 3.5-3.8 Ga. It was fou nd that the continental crust formation had occurred 3.0-3.5 Ga ago in the eastern Olekma granulite-greenstone terrain and 3.5-3.8 Ga ago in the northwestern Aldan granulite-gneiss terrain. At least two events of continental crust formation were identified in the central Aldan gr anulite-gneiss terrain: an Early Proterozoic event of approximately 2. 0-2.4 Ga and an Archaean event of not less than 2.8 Ga.