Abstract:

The geochemical properties of volcanic rocks bear close relations with structural background.It has been proved by analysis result that volcanic rocks in Zhangqiang and its neighbouning Dawa Changtu Depressions have following characteristics:(1)the volcanic rocks are neutral acid,and most of them are alkaline basalt;(2)the volcanic rocks are sodium alkaline basalts in Dawa Changtu Depression,but sodium and potassium alkaline basalts as well as calc alkali and continental tholeiitic basalts in Zhangqiang Depression;(3)the standard rare earth element distribution curves of chondrite in the volcanic rocks tilted rightwards and light rare earth element are rich in the rocks.(4)Zr-Ce and Zr-La diagrams show distinct differences between the two depressions.It is suggested that the volcanic rocks in the two depressions are all resulted from continental rift,the magma sources are different and should belong to different tectonic units.