Geochronology of gneissic plagioclase-amphibolite from Beidahe Group-complex in western segment of Qilian Mountains, China.

SHRIMP U-Pb dating of detrital zircons from Beidahe Group-complex, one of the oldest metamorphic series in western segment of Qilian orogenic belt, shows the deposition occurred from 1400Ma to 863Ma rather than Paleoproterozoic previously studied. High resolution LA-ICP-MS in situ dating yields the age of 724.4±3.7 Ma from gneissic amphibolite in Beidahe Group-complex located in Dang River, Subei County, Gansu Province, which indicates the protolith age of gabbro. The age equals to the geological record of Rodinia supercontinent break-down event. Furthermore, the ages of 1949～1184 Ma for captured zircons also are yielded in Beidahe Group-complex. The study is of great significance to the existence of Rodinia supercontinent break-down event in the Qilian orogenic belt, and has further restricted the formation age of Beidahe Group-complex between 1400 and 724Ma.