Structure, age, and geodynamic settings of early Neoproterozoic magmatic complexes of the Central Asian fold belt exemplified by the Holbo Nur zone of Songin terrane

摘要

The Holbo Nur zone of Songin terrane in the Central Asian fold belt is a rare example of slightly metamorphosed paleoceanic complexes that were formed at the initial stages of the Paleoasian ocean evolution. The zone encompasses three tectonic slices. Rhyolites of the island arc series have been dated back to 888 +/- 2 Ma; the formation of the island arc lasted from 888 to 859 Ma. The differences in the geological structure, geochemical and isotopic characteristics of igneous rocks constituting the tectonic slices of the Holbo Nur zone imply spatial isolation of these complexes during their formation in the Paleoasian ocean. They were tectonically juxtaposed between 859 and 790 Ma ago, which is evident from postkinematic granitoids.