关键词: 拉斑玄武岩, 大陆溢流玄武岩, 部分熔融, 分离结晶, 中新世

Abstract: The Cenozoic basalt from Chifeng region, North China, are characterized by Al₂O₃=12.51%-14.42%, Na₂O>K₂O, and TiO₂>2.00%. They are continental flood basalt, produced by fissure-type volcanism in the Miocene. The basalts chemically belong to the tholeiitic series and were derived from asthenospheric source regions. Two processes would be responsible for the generation of the basalts. The basaltic magma was first generated by partial melting of peridotites in the mantle, followed by fractionation of olivine from the magma. The magma formed at depth of the mantle ascended into a chamber within the continental crust, where it could cease moving up further and concentrated to some extent. It was in the chamber that some of olivine crystallized early was fractionated from the magma. Then, the remaining olivine would reacted with the magma, resulting in the development of clinopyroxene rim around olivine. It is suggested that the fractional crystallization of olivine from the magma is probably a common process to the formation of continental flood basalts.

Key words: basalt, continental flood basalt, tholeiite, partial melting, fractional crystallization