大兴安岭呼中地区玛尼吐组火山岩锆石U- Pb年龄、地球化学特征及地质意义

大兴安岭北部地区大面积分布中生代火山岩，前人对呼中地区玛尼吐组火山岩研究的较少，本文通过年代学及地球化学等方面的研究，探讨玛尼吐组岩石形成年代、岩浆来源及构造背景。对玛尼吐组中—酸性火山岩进行了系统的LA- ICP- MS锆石U- Pb测年，显示同位素年龄为154. 5±8. 6 Ma，表明形成时代为晚侏罗世。岩石地球化学显示富集Rb、Ba、K、Th、La、Ce、Nd、Hf等元素和轻稀土元素，亏损Sr、Nb、P和Ti等元素，属准铝质—铝质高钾钙碱性岩系。玛尼吐组中—酸性火山岩岩浆可能来源于受俯冲板片流体加入引发下地壳部分熔融，进而发生分离结晶作用。构造背景为古太平洋板块向额尔古纳地块下的俯冲作用形成的活动陆缘环境。

Zircon U- Pb age, geochemical characteritics of volcanic rocks in the Manitu Formation in Huzhong area, Great Hinggan Mountains and geological significances

The volcanic rocks of the Manitu Formation were formed in the Late Jurassic—Early Cretaceous in the Great Hinggan Mountains. By petrological, geochemical and isotopic chronological study of the Manitu volcanic rocks in Huzhong area,the origin, formation age and tectonic setting of the rocks are discussed.Methods:Based on 1:50000 field work, the petrogeochemical test and LA- ICP- MS zircon U- Pb dating were carried out on the volcanic rocks of the Manitu Formation.Results: Systematic LA- ICP- MS zircon U- Pb dating of the medium—acidic volcanic rocks of the Manitu Formation yielded an isotopic age of 154.5±8.6 Ma, indicating a Late Jurassic age of formation. The rocks are enriched in Rb,Ba,Th,La,Ce,Nd and Hf elements, and light rare earth elements; loss Nb, P and Ti elements; belong to the metaluminous—alumina—high potassium—alkalic calcic rock sreies. The intermediate—acid volcanic magma in the Manitu Formation may be derived from the partial melting of the lower crust caused by the addition of subduction plate fluid, and then the separation crystallization occurred.Conclusions: The tectonic setting is an active continental margin formed by the subduction of the paleo-Pacific plate to the Erguna block.