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