华北东部青岛地区煌斑岩岩石地球化学特征与成因

华北东部青岛地区煌斑岩广泛发育,其岩石成因、构造环境等方面研究程度较低。本文通过研究其岩石学和地球化学特征,讨论岩浆的源区性质、形成的构造环境,进而推断研究区的地质演化过程。研究区内煌斑岩的SiO2含量(W(SiO2))为39.13%~51.26%,属于钾玄质碱性岩。样品的稀土元素整体表现出轻稀土元素富集、重稀土元素亏损的特征,Ce和Eu异常(分别用δCe和δEu表示)不显著。样品微量元素总体表现出大离子亲石元素(Ba、K、Pb)和轻稀土元素富集(LREE),而高场强元素(Nb、Ta和Ti)亏损的特征,具有典型的俯冲特征。源区为三叠纪时北向俯冲的扬子板块析出的熔体,交代上覆华北板块地幔橄榄岩而形成的地幔交代岩。白垩纪时,俯冲带岩石圈大范围坍塌,软流圈上涌形成伸展环境,地幔源区发生部分熔融,岩浆上升侵位形成煌斑岩。

Geochemical Characteristics and Petrogenesis of the Lamprophyres of Qingdao,Eastern North China

The lamprophyres widely present as intrusions in Qingdao,the study degree of which is still low,especially its petrogenesis and tectonic context.Based on the petrological and geochemical characteristics,the nature of magma source and tectonic setting were discussed to deduce the geological evolution of the study area.The rocks contain 39.13%~51.26%SiO2,which show alkaline and shoshonitic signatures.Combined with the LREEenrichment with no Eu and Ce anomalies,the enrichment of LILE and depletion of HFSE suggest the subduction influence.The lithology of magma source is pyrolite,which was modified by subduction metasomatic melt/fluid released from the Yangtze plate subducted continuously beneath the North China Plate in Triassic.Accompanied with asthenosphere upwelling,the lithosphere regionally destructed in the extensional environment during Cretaceous,and the lamprophyres formed after emplacement of the magma generated by the partial melting of mantle source.