The Cenozoic kamafugites in Lixian County of West Qinling are poor in SiO2and Al2O3but rich in MgO, CaO, TiO2and K2O+Na2O. The modal mineral assemblage is composed mainly of olivine, clinopyrox-ene, nepheline/ kalsilite, melilite/leucite and Ti-phlogopite. The trace isotopic compositions of Sr, Nd and traceelement characteristics of kamafugitic series show distinct geochemical features similar to those of N-OIB and MORB as well as an EMⅠend member caused by metasomatism of asthenospheric fluids. Based on the estima-tion results ofpandTfrom lherzolites, regional geophysical information, regional tectonic settings and the for-mation ages of volcanic rocks, it is held that the formation of kamafugitic series was closely related to the Ceno-zoic lithospheric extension in this area, and that the primitive kamafugitic magma was derived from the low-de-gree partial melting of the thermal boundary layer at the basement of lithosphere beneath the depth of 92 km