Abstract: Five fresh MORBs samples collected from the 50°E of the SWIR have been studied for petrology and geochemistry. The major elements, TAS and AFM diagrams suggest that the samples from the SWIR are dominated by low potassic tholeiite. The primitive mantle-normalized sprider diagram shows negative anomalies of Ba, Nb and Sr, while K is positive in all of the samples. The MORBs of the SWIR show a depleted pattern of light REE in chondrite-normalized REE diagram, with slightly positive Eu and Ce anomalies; The MORBs from the SWIR are all derived from the upper mantle and obviously migrate to the end member of EMII. Most of the SWIR basalts enriched in the region are sourced from mantle. It is composed of both DM and EMII, includes small amount of continental crustal components. The basaltic magmas of SWIR are originated from the spinel peridotite zone. The samples of the SWIR are formed under a moderate reducing environment, experienced obvious fractional crystallization from olivine, clinopyroxene to plagioclase.