贵州水城二叠纪钠质粗面玄武岩的地球化学特征及其源区  

Geochemistry of the Shuicheng Permian sodium trachybasalts in Guizhou Province and constraints on the mantle sources

作　　者：廖宝丽[1,2] 张招崇[1] 寇彩化[1] 李宏博[1] 

机构地区：[1]中国地质大学,地质过程与矿产资源国家重点实验室,北京100083 [2]桂林理工大学,广西隐伏金属矿产勘查重点实验室

出　　处：《岩石学报》2012年第4期1238-1250,共13页Acta Petrologica Sinica

基　　金：国家自然科学基金(40925006);教育部博士点基金(20090022110006);111计划(B07011)联合资助

摘　　要：贵州水城二叠纪玄武岩位于峨眉山大火成岩省东部。该玄武岩全岩SiO2的含量为44.5%～50.04%,TiO2的含量为2.38%～2.74%,MgO的含量为5.74%～7.96%,Mg#值较低为0.40～0.49,Na2O含量高,为4.81%～7.19%,并且Na2O/K2O>4,属于钠质粗面玄武岩即夏威夷岩。具有ΣREE富集的右倾型稀土元素分布模式,稀土和微量元素特征和Pb同位素特征显示洋岛玄武岩OIB的地球化学特征,(87Sr/86Sr)i=0.70482～0.70503,εNd(t)和(206Pb/204Pb)t变化范围较窄:1.3～1.8和17.21～17.62。与贵州威宁黑石头和织金二叠纪玄武岩比较,水城玄武岩富碱,TiO2含量低,Na2O、MgO和Al2O3含量高,造成峨眉山大火成岩省东部贵州境内三个地方玄武岩不同性质的主要原因是由于地幔源区不同,分离结晶程度和地壳混染程度的不同,水城玄武岩来源于交代富集地幔,是峨眉山地幔柱上升至石榴石稳定区发生部分熔融,地幔柱的部分熔融体和富含挥发分的大陆岩石圈地幔混合,在上升到地表过程中受到轻微的地壳混染所形成。The Shuicheng Permian basalts in Guizhou Province lie in the eastern Emeishan large igneous province（ELIP）,They have SiO2 contents between 44.5%～50.04%,2.38%～2.74% for TiO2,5.74%～7.96% for MgO,with Mg# [Mg/（Mg＋Fe2＋） of 0.40～0.49,The basaltic rocks are higher in Na2O,and have right-inclined chrondrite-nomalized rare-earth element（REE） patterns with total rare earth elements（ΣREE）,The geochemical characteristics indicate an affinity of alkaline basalt series,belonging to sodium trachybasalt or to Hawaiite,They are characterized by slightly radiogenic（87Sr/86Sr）i ratios（0.70482～0.70503）,the εNd（t） and（206Pb/204Pb）t ratios define a small range of 1.3 to 1.8,and 17.21 to 17.62 respectively,and they are geochemically similar with those of ocean island basalts（OIB）,Compared with the basalts in Heishitou and Zhijin in Guizhou Province,the Shuicheng basalts have much lower TiO2 contents,but higher Na2O,Al2O3 and MgO,These differences can be attributed to distinct mantle sources,fractional crystallization and crustal contamination,The Shuicheng basalts possibly resulted from the interaction between the plume-derived partial melts in the garnet stability field and volatile-rich metasomatized subcontinental lithospheric mantle,with minor crustal contamination.

关 键 词：玄武岩 地球化学 地幔柱 峨眉山大火成岩省 

分 类 号：P5[天文地球—地质学]