Based on new SmNd isotope data of gneisses in Longshan Group , we come to t he conclusion that Longshan Group formed in the Middle Proterozoic with an SmNd isochron age of 1451±190Ma, indicating an inicial rift magmatism in the region. Two more basic magmatisms took place afterwards with amphibolite SmNd isochro nages of 983±22Ma and 756±97Ma respectively, namely during Jinning Movement (8 00～1000Ma), and with materials very depleted and similar to MORBtype mantle s ource, reflecting intensive rifting. It′s also mentioned that owing to its speci al geological site of the studying area where QilianQinling orgenes and Helan rift meet, all the achievements mentioned above have much more regional tectonic significance.