山东昌乐新生代玄武岩内的刚玉巨晶(蓝宝石)中含有多种类型熔融包裹体,其成分对了解华北深部地幔交代过程中的流/熔体性质和刚玉母岩浆特点具有重要意义。详细的岩相学和激光拉曼分析鉴定出一类富碳酸盐和硫酸盐成分的原生熔融包裹体以及一类含硫酸盐和氯化物等成分的次生熔融包裹体,二者同时还含有CO2和H2O。碳酸盐和硫酸盐成分在世界范围玄武岩内刚玉巨晶中是首次发现,结合已有的包裹体稀有气体同位素和测温资料,反映两种成分可能来源于交代地幔的碳酸岩熔体,预示着华北深部地幔不仅经历了硅酸盐成分的交代还经历了富碳酸盐和硫酸盐成分(碳酸岩)的交代,同时也显示刚玉母岩浆成分复杂,至少有富这两类成分物质的参与,刚玉很可能是硅酸盐岩浆/岩石和幔源碳酸岩岩浆相互作用的产物,后被玄武岩喷发携带至地表。
Corundum megacrysts (sapphires) hosted by Changle Cenozoic basalts of Shandong Province contain various melt inclusions, whose compositions are of significance in understanding the mantle metasornatism beneath the North China Craton and the parent magma of the corundum megacrysts. Based on petrographic observation and detailed laser Raman analysis, the authors identified two types of melt inclusions: one is primary melt inclusion rich in carbonates and sulfates and the other is secondary melt inclusion containing sulfates and chloride, with CO2 and H2O existent in both of them. This is the first time that sulfate and carbonate are recognized in fluid/melt inclusions from basalt-hosted eorudum megacrysts. The compositions, combined with existing isotopic compositons of noble gases and microthermometry of the inclusions, imply that they are a kind of carbonatite that propably originated from metasomatized mantle. The authors thus hold that the mantle beneath the North China Craton might have experienced metasomatism of carbonates and sulfates-bearing melts (carbonititic magma) besides silicic melts. The carbonates and sulfates identifed in primary inclusions suggest that they must have played an important role in corundum crystallization. The corundums probably resulted from the interaction between mantlederived carbonatites andsilicic magmas/rocks, and were transported to the surface by subsequent basaltic lava.