Application of nuclear analytical techniques to trace elements in Cenozoic basalt and their mantle xenoliths from Aershan area in Inner Mongolia,China

Basaltic samples from different locations in Aershan area determined by instrumental neutron activation analysis (INAA) have the same distribution patterns of REE and trace elements. The similar REE contents of the same minerals without inclusions from different xenolith suggest that the mantle source region under different active volcanoes have the same composition. The REE content differences between the same minerals with and without melt inclusions selected from the same mantle xenolith indicate that the melt inclusions are rich in REE. The same patterns of trace elements of inclusions and host minerals from different xenolith analyzed by SRXRF suggest that the mantle fluid has no notable heterogeneity in Aershan area.

内蒙古阿尔山地区新生代玄武岩及其幔源包体微量元素组成特征

内蒙古阿尔山地区新生代火山活动频繁，喷发期次可划分为上新世、更新世、全新世，最新喷发时间约为1900aBP，具有再次喷发的可能。为了探讨活火山源区地幔流体的分布特征，利用中子活化分析和同步辐射X射线荧光微探针分析技术，对阿尔山地区全新世玄武岩及其幔源包体的稀土、微量元素组成特征、地幔包体矿物及其熔融包裹体的微量元素组成特征进行了分析。中子活化分析结果表明，不同产地玄武岩具有相同的稀土配分模式，其中，∑8REE=96．93～114．94，Eu／Sm=0．32～0．37，（La／Lu）N=8.89～12.52；不相客元素蛛网曲线整体右倾，Ba，Ta，Sm具正异常，Th，Zr具负异常，没有明显的Sr异常，说明岩浆上升过程中很少演化和分离结晶；不同产地地幔岩包体中不含包裹体的同类矿物的REE组成相近，反映了不同活火山的地幔源区REE组成特征相同；不同产地地幔岩包体同类矿物及其内部包裹体同步辐射X射线荧光微探针分析表明具有相同的微量元素曲线分布形态；这些特征说明阿尔山活火山群分布区地幔流体不存在显著的不均一性。