山东临朐玄武岩微量元素地球化学特征

本文测定了山东临朐一带新生代玄武岩的稀土和某些微量元素含量。玄武岩的稀土元素含量较高,特别是轻稀土富集,同时可能存在微弱的铕正异常。在不相容元素丰度图形上,其特点和洋岛碱性玄武岩接近,和大陆裂谷玄武岩有一定差别。根据稀土元素和不相容元素含量特点,认为玄武岩是地幔部分熔融产物。根据作者提出的采用简单二元组分混合、锶同位素混合和部分熔融方程的共同制约及有关参数,计算了岩石形成时两种典型的地幔源区即MORB源和Plume源的可能混合比例。

Trace Elements Geochemistry Characteristics for Linju Basalts

This paper deals with concentrations and characteristics of rare earth elements and other incompatible elements for Linju basalts. According to their chondrite-normalized distribution patterns, they show the LREE enrichment which is common for most continental basalts.In incompatible elements diagram, compared with continental rift basalts, they show depleted in Rb, relative high in K and lower in total REE. The general pattern is similar with ocean island alkali basalts, and differs from continental rift basalts and other various deep source rocks. It is implied that the genesis of Linju basalts was probably resemble with ocean islands. This feature of Linju basalts was suited to their tectonic setting.We proposed that Linju basalts can be formed by mixing of melting of deep plume source with MORB-like source sited subcontinental lithosphere bottom. In terms of three constraint equations containing isotopes and trace elements. we calculated the rate of mixing of two magma sources and degree of partial melting. It is denoted that Linju basalts could be generated by partial melting of less than 1% for MORB source and 9--23% of partial melting for plume source, and about 9--50% rate of mixing.