中太平洋海山玄武岩的岩石学特征与年代

PETROLOGIC CHARACTERISTICS AND AGES OF BASALT IN MIDDLE PACIFIC MOUNTAINS

玄武岩在中太平洋海山分布广泛,且普遍存在风化蚀变现象。对测区内玄武岩样品的岩石学特征研究表明,玄武岩具斑状结构,基质以间粒结构为主。斑晶矿物为基性斜长石、单斜辉石和伊丁石化橄榄石。基质矿物为斜长石、辉石、橄榄石、铁矿物、磷灰石、玻璃及次生矿物等。各海山玄武岩同属碱性玄武岩系列,并为钾质类型玄武岩,它们的形成基本上处于同一地质构造环境中。稀土元素分析结果为轻稀土富集型,轻重稀土在岩石形成过程中发生了不同程度的分异作用。CM5海山玄武岩比其他海山年代相对较老(60 Ma)。

The basalt is widely distributed in the middle Pacific mountains,and has been weathered or altered to some extent. The study of petrologic characteristics of basalt in the area indicates that the basalt has porphyritic texture and matrix has intergranular texture. The mineral compositions of porphyritic crystals are basic plagioclase, monoclinic pyroxene and olivine. Mineral compositions of matrix include the above-mentioned minerals and magnetite,apatite,glass and secondary minerals etc. Chemical analysis of the basalt shows that it belongs to alkali-basalt series,and is basalt of potassic type. They formed basically in the similar environment of geologic structure. The distribution pattern diagram of rare-earth element shows it is LREE enrichment type. The separation effect of LREE and HREE occurred in the formative process of rock. The age （60Ma） of the basalt in Mountain CM5 is older than those in other mountains.