There exists a large scale upwelling event of mantle source materials during late Paleoproterozoic in southwestern Yangtze block, China, and the detailed geochemistry of Paleoproterozoic diabase at the Yimin Luoxue mine of the Dongchuan copper deposit in the central Kangdian area is reported in this paper. The results show that the major elements of diabase have the characteristics of high MgO, 6.16%～9.65%(mean Mg# of 72.2), low SiO2(45.61%～49.34%), low TiO2(0.74%～2.74%), and FeO/MgO<1, implying that the initial magma of the diabase was relatively primitive. The correlations between MgO and the main major components and trace elements reflect that the primitive magma have experienced fractional crystallization of olinve，orthopyroxenite, chromite, and ilmenite in early stage. The diabse has (La/Yb)N of 1.66～4.37, and δEu of 1.04～1.22, and the chondrite normalized REE pattern slightly tilt to the right. The diabase enriches in large ion lithophile elements(LILE), such as Rb, Ba, U, etc., and the MORB normalized trace elements pattern steeply tilt to the right, with obviously positive anomaly of Rb, Ba, and slightly negative anomaly of Zr, Hf, and without obvious anomaly of Nb, Ta except few samples. The Paleoproterozoic diabase in the Dongchuan area displays －0.2～3.8 of εNdt and 0.7055～0.7084 of initial 87Sr/86Sri. The source area of the Dongchuan diabase exhibits the spinel lherzolite facies, indicating a product of partial melting of relatively deplete transitional mantle, and the slight contamination is derived from sub continental lithospheric mantle and little lower crust materials. The geochemical characteristics of intraplate basalt(WPB), E MORB, and OIB of Dongchuan diabase imply that a large scale intracontinental rift extensional event may occur contemporaneously with the breakup of the global Columbia supercontinent in the southwest of Yangtze block during late Paleopoterozoic, and may be caused by the mantle plume activity.