济阳坳陷第三纪火成岩地球化学特征研究

Geochemical features of Tertiary igneous rocks from the Jiyang Basin

对济阳坳陷第三纪火成岩样品进行了系统的地球化学分析，分析结果表明：这些火成岩的SiO：含量较低（大部分低于50％），属于基性火成岩，岩石类型主要为玄武岩和粗面玄武岩。绝大部分样品的TiO2含量较高，为1．64％-2．09％，不同于TiO，含量较低的岛弧火山岩。碱性样品和亚碱性样品数量相当，Na2O含量都高于K20含量，Na2O／K20最高可达2．75。这些样品具有富集大离子亲石元素（LILE）如Rb和Ba，亏损重稀土元素（HREE）如Yb和Lu。具有右倾的球粒陨石标准化稀土元素配分模式和原始地幔标准化不相容元素分布模式。源区分析表明，这些火成岩的源区为富集的受过流体交代的岩石圈地幔。运用不活动元素对这些样品进行了构造环境的判别，结果表明这些样品的主体形成于板块内部环境。

Geochemical analyses were made for some Tertiary igneous rocks from the Jiyang Basin in this paper. The igneoug rocks are all mafic with SiO2 contents mostly below 50%, and are dominantly basalts and trachybasah. Most of the igneous rocks have higher TiO2 contents （1.64%-2.09%） in comparison with typical island-arc basalts. The volcanic strata include equal amounts of alkaline and sub-alkaline rock,with high Na20/K20 ratios（ up to 2.75）. The samples have enriched large ion lithophile elements（LILE） such as Rb and Ba, and depleted heavy rare earth elements （HREE）. They have strongly fractionated REE in chondrite normalized rare earth element distribution and primitive mantle normalized incompatible elements diagrams. It is proposed that the source of the igneous rocks is lithospheric mantle that have been metasomatised by fluids enriched in LILE. Discrimination diagrams using immobile elements indicate that the volcanics were likely formed in a within-plate environment.