大兴安岭北段龙江盆地光华组碱流岩LA-ICP-MS锆石U-Pb年龄及其地质意义

对大兴安岭北段龙江盆地光华组碱流岩进行了岩石地球化学及锆石U-Pb年龄研究,并对其岩石成因及构造意义进行了讨论。结果表明,龙江盆地碱流岩的锆石具有典型的岩浆振荡生长环带和较高的Th/U值(0.71~2.12),反映了岩浆成因特征,LAICP-MS锆石U-Pb年龄为122.4±1.7Ma(n=19,MSWD=0.77)。岩石富硅、富碱,贫Mg、Ca;稀土元素配分曲线呈现右倾"V"字形特征,显示强烈的负Eu异常;微量元素显示具有较低的Sr和Ba丰度,以及较高的Rb、Th、U、Zr等特点。以上特征表明,龙江盆地碱流岩类似于铝质A1型花岗岩,为长英质地壳部分熔融及其后斜长石和Ti、Fe氧化物分离结晶作用的产物,代表了伸展的构造环境。

LA-ICP-MS zircon U-Pb dating and geochemical characteristics of the pantellerite of Guanghua Formation from Longjiang basin in northern Da Hinggan Mountains and their geological implica-tions

In this paper, geochemistry and zircon U-Pb isotope chronology of the pantellerite of Guanghua Formation from Longji-ang basin in northern Da Hinggan Mountains were studied and their petrogenesis and tectonic significance were discussed. The zir-cons from pantellerite of Longjiang basin show oscillatory growth zonation of typical magmatic origin and high Th/U ratios (0.71~2.12), indicating a magmatic origin for the zircons. LA-ICP-MS zircon U-Pb weighted average age is 122.4 ±1.7Ma (n=19, MSWD=0.77). The pantellerite is characterized by high SiO₂ content, high alkali content but low Mg, Ca content. The REE pat-terns are characterized by enrichment of LREEs relative to HREEs and distinct negative Eu anomalies in the chondrite-normalized REE patterns, characterized by right-inclined and "V" -shaped feature. These rocks are depleted in Sr and Ba but enriched in Rb, Th, U, Zr. All these characteristics are similar to features of A-type granites which originated from the partial melting of felsic crust under high temperature and low pressure conditions and the subsequent fractional crystallization of plagioclase and Ti and Fe oxides, thus representing an extensional tectonic environment.