The present geological data indicate that the age of the diabasic subvolcanic rock in Changma area is Lower Cambrian. The rock is characterized by high Na, Mg and Ti, but low K contents, it belongs to the series of alkaline with low total REE contents, and obvious fractionation between LREEs and HREEs. REE pattern normalized by chondrite are slightly inclined, while N-MORB normalized trace element spider diagram show enrichment in LILEs. In comparison with the case of primitive mantle, the value of trace elements is about 10~100 times higher than that for primitive mantle, and the trace element data for the diabase show relative depletion in K, Sr and enrichment in Nb, Ta. All data indicate that the diabase was formed under intraplate rift setting.