早第三纪玄武岩在苏北盆地以橄榄拉斑玄武岩为主，在地表基本无出露，均为钻井揭示，呈夹层产出。对它们详细的岩相岩石学、微量元素地球化学及锶钕同位素研究表明，玄武岩原始岩浆源于受俯冲洋壳影响的陆下岩石圈地幔较高程度部分熔融并在源区经历了一定程度的单斜辉石和橄榄石的结晶分异，岩浆上升至喷出地表过程中没有发生明显地壳物质的混染，其所表现出的过渡特征暗示区域在古新世时处在一个由活动大陆边缘向大陆板内裂谷转换的关键时期。 Early Tertiary basalts were mainly composed of olive tholeiite basalts in the Northern Jiangsu Basin, and were basically not exposed on the surface of the earth. They were all revealed by drilling and showed a mezzanine output. Their detailed lithofacies, trace element geochemistry and strontium-neodymium isotope studies show that the basaltic primitive magma originated from the submarine lithospheric mantle that was partially subducted by the subducted oceanic crust and experienced a certain degree of The crystal differentiation of clinopyroxene and olivine did not result in obvious contamination of crustal material during the magma uplifting to the surface of the earth. The transitional characteristics of the transitional region suggested that the region was located at the margin of active continental margin The key period of continental rift transformation.