Mafic dykes represent a possible event of crustal break-off and can constrain the time of land-rebuilding and dynamics in this area. The authors found rome unreported mafic dykes in the Qinling and Longshan Groups between the Qinling and the Qilian orogenic belts. A 440 Ma U-Pb age was measured for these dykes using zircon LA ICPMS, which indicates that a regional extension might have occurred in the Qinling and the Qilian orogenic belts. The data is very important in the study of the evolution and mineralization of the Qinling and the Qilian orogenic belts.