The central part of Sanjiang region can be divided into Yangtze(_phile) geochemical province and Gondwana(_phile) geochemical province. In the former province, the upper mantle rocks consist of harzburgite and lherzolite, characterized by the concentration of mantle type elements (KT) and the smooth_weak enrichment type REE patterns; the ocean volcanic rocks are dominated by basic rocks of subalkaline and oceanic ridge type; lead isotopes are noted for 206Pb/204Pb<18.5,208Pb/204Pb<38.65,μ<9.35,ω<38.60, V1<75 and V2<65. In the latter province, the upper mantle rock is mainly harzburgite characterized by impoverishment of mantle type elements ( KT) and the weak enrichment type REE patterns ; the ocean volcanic rocks are comprised of ultrabasic, basic and intermediate_basic rocks, being both subalkaline and alkaline in nature and assuming both oceanic island type and oceanic ridge type; the characteristic lead isotope values are all higher than the bove_mentioned values.