赤峰地区新生代玄武岩的基本特征及成因

General Features and Origin of Cenozoic Basalts from Chifeng Region,North China

赤峰地区新生代玄武岩是中新世裂隙式火山活动产生的大陆溢流玄武岩，属于拉斑玄武岩系列，源区是软流圈上地幔。玄武岩是部分熔融和分离结晶过程联合作用的结果。先由地幔橄榄岩部分熔融产生玄武质岩浆。但岩浆在上升到大陆地壳内一定深度的岩浆房时，发生部分橄榄石的分离结晶作用。在部分熔融作用之后发生橄榄石分离结晶作用，可能是大陆溢流玄武岩的一种普遍现象。

The Cenozoic basalt from Chifeng region,North China,are characterized by Al 2O 3=12.51%～14.42%,Na 2O>K 2O,and TiO 2>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.