摘要
大同火山群是第四纪火山,分布着近20个大小不等的火山地形。喷发类型以爆发为主,喷发溢流为辅。岩石类型为碧玄岩和碱性玄武岩两类。碧玄岩中含有极少量的二辉橄揽岩包体和单斜辉石、歪长石巨晶。本区碧玄岩的化学成分与世界碧玄岩平均化学成分相比,有较高的Mg/(Mg+Fe^(2+))值和较高的Al_2O_3/CaO值。可解释为本区玄武岩是地幔部分熔融产物,在上升过程中,有富镁组分和富钙辉石的结晶分异作用。本区LREE强烈富集的分配形式和高浓度的相容元素Ti、K、P等,说明本区玄武岩是熔融程度很低的产物。
Datong volcanic oltuster formed in the Quaternary period, in which area nearly twenty volcanic relief features are distributed. The dominant typy of volcanic eroption is explosion, and then extrusion. The rock types can be divided into basanite and alkali-basalt. The former contains a few inclusions of therzolite, monocinic pyroxene and giant crystals of anorthoclase. The chemical composition of basanite in the area possesses higher value of Mg/(Mg+Fe.^(2+)) and A1_2O_3 / CaO, comparing with mean chemical composition of basanite in global, which can be explained that the basalt in this area is a result from partial mantle melting, and there exists crystallization of rich magnesium and rich calcareous pyroxense, during the metting magma raising. The element distribution pattern of strong enrichment of LREE and high consistency of compatible elements Ti, K, P, etc. shows that the basalt is a product of melts with low extent.
关键词
玄武岩
火山群
结晶作用
Datong, basanite, crytallization.
