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分布于甘肃北山北亚带的奥陶纪火山岩是一套由浅变质的富碱玄武安山岩、粗面英安岩以及少量钾玄岩岩石组合。岩石稀土总量偏低,属轻稀土富集型,稀土分布模式为右倾曲线;微量元素的球粒陨石标准化配分模式显示岩石富集K、Rb、Th等元素,而亏损Nb、Ti,表明火山岩形成与板块俯冲作用有关。综合分析火山岩的岩石学、岩石地球化学特征,并结合区域构造背景,认为该套火山岩产于活动大陆边缘岛弧带环境,为俯冲造山带的构造背景。
Ordovician volcanic rocks distributed in the northern subtropical zone of the Beishan Gansu are a combination of supergene alkali-rich basaltic andesite, rough dacite and a small amount of potash rock. The total amount of rare earth rocks is low, which belongs to the light rare earth enrichment and the distribution pattern of rare earth is right-angled. The normalized distribution pattern of trace elements chondrites shows that the rocks are enriched in elements such as K, Rb, Th and depleted in Nb and Ti, indicating volcanic rocks Formation and subduction plate related. Based on a comprehensive analysis of the petrological and petrogeochemical characteristics of volcanic rocks and combined with regional tectonic setting, the volcanic rocks are believed to be produced in the active continental marginal island arc environment and are the tectonic setting of the subducted orogenic belt.