山东昌乐蕴含中国最大的宝石级刚玉—蓝宝石矿床.昌乐刚玉巨晶与玄武岩界限截然,边缘圆化,沿巨晶溶蚀圆化的边缘发育富铝的尖晶石和钛磁铁矿反应环边,显示其为深源捕虏晶的岩相学特征.对刚玉等巨晶及其反应边矿物进行岩相学、电子探针和LA-ICP-MS(Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry)分析能有效揭示其成因及演化历程.昌乐刚玉2组样品(CL-1和CL-2)矿物化学和关键元素特征及Ga/Mg、Cr/Ga、Fe/Ti、Fe/Mg等关键元素比值显示为岩浆型来源,而CL-2组样品明显叠加了后期熔体交代作用的特征.反应边尖晶石具刚玉巨晶向尖晶石巨晶过渡的成分特征,关键元素特征指示两者具强烈亲缘性,尖晶石巨晶是刚玉经历复杂交代作用的产物.昌乐刚玉呈现碱性熔体中结晶的化学成分特征,极有可能源于交代富集的地幔岩低度熔融形成的富铝的碱性熔体.%Objectives:The Chinese largest gem quality corundum—sapphire deposits is located in Changle,Shandong Province.Changle corundum occurs as megacryst in the Cenozonic basalt,showing roundish shape and having sharp boundary contact with host basalt.The well developed reaction rim of Al-riched spinel and titanium magnetite,around corundum megacrysts indicate they are deep mantle derived xenocryst.The study of corundum megacryst and its reaction rim can reveal their genesis and evolution information.Methods:The petrography,electron microprobe and LA-ICP-MS (Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry) study methods are applied in this paper.Results:The major and trace mineral compositions,key elements such as Ga/Mg、Cr/Ga、Fe/Ti、Fe/Mg ratios of two groups samples of the corundum megacrysts (CL-1 and CL-2) indicate they are magmatic origin.In compared with the the CL-1 group samples,the CL-2 group samples of Changle corundum obviously overprint the features of late melt infiltration metasomatism.The reaction spinel rim diaplays transitional compsition characteristics from corundum megacryst to spinel megacryst,and the key element data of corundum and spinel megacrysts exhibit obvious affinity.Conclusions:The spinel megacryst is the product of corundum after complicated metasomatic evolution.In adation,Changle corundums present mineral chemical features of crystallization from alkali melt that most likely derive from low extraction of metasomatic enriched mantle rocks.
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