A Discussion on Intrusion Epochs of Granodiorites along the Bagexia-Heidaban Zone in the Western Part of the North Qilian Mountains
No isotopic dating of granodiorites along the Bagexia-Heidaban zone in the western part of North Qilian Mountains was made by previous workers.They were commonly thought to be products of Late Variscan.Nevertheless,U-Pb single-zircon dating conducted by the authors show that these granodiorites are 481.6±3.3 Ma in age,thus belonging to Ordovician.The Altun fault belt might have been formed earlier than 481.6±3.3 Ma.Geological significance of these age data is also discussed in this paper.