Geological Characteristics And Tectonic Significance Of Fengshuigouhe Group In The Northwestern Lesser Xing’an Range

The formation time of the Fengshuigouhe Group in the northwestern Lesser Xing’an Range, NE China, remains controversial owing to the lake of the precise dating data. This article reports zircon U-Pb ages for the leptynite, gneissic granitoids from the Fengshuigouhe Group in the northwestern Lesser Xing’an Range. The aim is to constrain the formation time and provenance of Fengshuigouhe Group. Field observation indicates that the Fengshuigouhe Group consists of a suit of metamorphic rocks(leptynite) and gneissic granitoids intruding the leptynite, and that both of them are cut by late granitic pegmatite. Zircons from two leptynites are euhedral-subhedral in shape and display oscillatory zoning in CL images. These detrital zircons give weighted mean ages of 453,284, 302, and 261 Ma. The youngest age of them is interpreted to maximum depositional age of the protoliths of these leptynites. Zircons from gneissic granites are euhedral and subhedral in shape and exhibit typical oscillatory zoning in CL images. The dating results indicate that the gneissic granites were formed in the Early Permian, rather than Neoproterozoic as previously believed, and that the sediments in the Fengshuigouhe Group were sourced directly from geological bodies in the study area and adjacent regions.In addition, the geochemical characteristics suggest that the Fengshuigouhe Group is developed in active continental margin environment. Therefore, we concluded that the Fengshuigouhe Group is not belong to the Precambrian crystal basement of Xing’an terrain.