Geochemistry and Source Characters of the Concealed Eogene Basalts in North Jiangsu Basin
苏北盆地隐伏早第三纪玄武岩地球化学及源区特征

The Eogene basalts, predominantly olivine tholeiites which have no surface exposures in north Jiangsu Basin, form thick sequences of many thin flows interfingered with inland lacustrine sediment beneath a sedimentary cover and were sampled through oil well prospecting. Detailed petrographical, petrological, trace element geochemical and Sr and Nd isotopic studies on them show that the primary magma was derived from a subcontinental lithospheric mantle which had been modified by subducted and altered oceanic crust through rather high degree partial melting and later underwent in situ certain degree of clinopyroxene and olivine fractionation.However the parent magma was not obviously contaminated by crustal material during its ascenting to the surface. The transitional characters of the olivine tholeiites indicate that the region was then in an important transforming period from an active continental margin to an intra continental rift in Eogene time.