贵州省大方地区二叠纪玄武岩地球化学特征

Geochemical Characteristics of the Permian Basalts in Dafang Area in Guizhou Province

分布于贵州省大方地区的玄武岩属亚碱性拉班玄武岩系列岩石。通过对其主量元素、稀土微量元素及同位素特征进行分析,显示具有与洋岛玄武岩(OIB)相似的源区,与地幔柱活动有关。大方玄武岩具有Nb、Ta负异常特征,表明其为大陆拉班玄武岩,同时Sr、Eu显示负异常特征,说明岩石中发生了广泛的斜长石结晶分离。大方玄武岩Th/Nb<1,Nb/La<1,说明大方玄武岩在形成过程中受到强烈的岩石圈地幔组分的混染。采用构造环境判别图解法对大方玄武岩的地球化学特征进行分析,从而确定该地区玄武岩的喷发构造环境为大陆裂谷区。

The basahs in Dafang area is located in Guizhou province, which is belongs to the type of subalkaline tholeiitic basalt. Based on analyzing the characteristics of the major elements, trace ele- ments and isotope of the basalts, the analysis results show that, the characteristics that is analyzed is simi- lar to the oceanic island basalt（OIB） source region and related to the mantle plume activity. The Dafang basahs has the negative anomaly characteristics of Nb and Ta, so, it show that, the generous basalts is be- longs to continental tholeiitic basalts, at the same time, the negative anomaly characteristics of Sr and Eu is displayed, so,it is show that, a wide range of plagioclase crystallization separation is happened in these rocks. The values of Th/Nb and Nb/La of Dafang basalts are both lover than 1, which show that, the basalts is strongly contaminated by the lithospheric mantle components in the process of formation. The tec- tonic discrimination diagrams is applied to analyze the geochemical characteristics of Dafang basalts, it is ensured that the tectonic environment of Dafang basahs is continental rift zone.