青岛崂山劈石口深源脉岩的岩石地球化学及成因研究

Study of the Geochemistry and Genesis of Deep Dikes in Pishikou of Laoshan Mountain,Qingdao

对青岛劈石口含地幔橄榄岩包体的超基性煌斑岩的岩相学、岩石地球化学和矿物化学等方面的研究表明,劈石口煌斑岩贫硅（SiO2=33.72%～36.70%）,富碱,富TiO2（2.08%～2.57%）,Mg#=25.23～37.32,SI=21.53～30.14,FL=30.25～40.64,DI=16.4～31.1,均显示煌斑岩岩浆演化程度不高,与玄武安山岩类相当;明显富集大离子亲石元素和轻稀土,相对亏损高场强元素,轻重稀土分异明显,微量元素配分模式和比值指示煌斑岩与OIB相似,具有明显的Cr、Ni负异常而Eu负异常不明显,Nb＊值大于1,Nb/U=30.32～41.04,说明煌斑岩具有富集地幔源区特征,岩浆上升过程中没有受到明显的陆壳物质的混染,主要进行了以橄榄石和单斜辉石为主的分离结晶作用。劈石口煌斑岩富集地幔源区的形成可能与中生代中国东部软流圈的上涌有关,华北克拉通岩石圈拉张减薄,形成造山后期拉张环境是引起富集地幔部分熔融和煌斑岩岩浆侵位的原因。

The study of the petrography,hthogeochemistry and mineral chemistry of the lamprophyre in Pishikou,which contains predictive inclusions of mantle,showed that the lamprophyre lacks silicon（SiO2 = 33.72%-36.70%） but rich in alkali,especially TiO2（2.08%-2.57%）.Mg# =25.23-37.32,SI= 21.53-30.14,FL = 30.25-40.64,DI=16.4-31.1.All of these indicate that the degree of magma evolution of lamprophyre was low,and it was equivalent to basaltic andesitic.It was significantly enriched in LILE and LREE,and was relatively loss of HFSE.The differentiation between LREE and HREE was obvious.Nb＊〉1,Nb/U = 30.32-41.04,and the distribution patterns and the ratioes of trace elements showed the similarity to OIB.Cr and Ni have obvious negative anomalies,while Eu＇ negative anomalies were not obvious.All of these indicated that the lamprophyre had enriched mantle source characteristics.The magma was not significantly contaminated by the continental crust and undergoes the crystal fractionation of olivine and clinopyroxene.The formation of enriched mantle source may be connected with the upwelling of asthenosphere in Mesozoic in Eastern China.The lithospheric thinning of the North China Craton,which causes extensional environment,lead to the partial melting of enriched mantle as well as the lamprophyre magma emplacement.