大兴安岭中生代火山活动构造背景

Tectonic Setting of Mesozoic Volcanism in Da Hinggan Mountains,Northeastern China

大兴安岭中生代火山岩主要为高钾粗面质火山岩,属于一套碱质含量比较高的钙碱性火山岩系,随时间从酸性向中基性方向演化。其元素地球化学特征和Sr、Nd同位素组成揭示火山岩具有壳源和幔源两部分源区特点,玄武质岩石来源于相对未亏损的地幔,中酸性火山岩则成因于地壳物质的混染或下地壳的重熔作用,暗示火山岩的形成与陆内深部软流体上涌引起的壳-幔相互作用有关。此外,本文还从火山活动中心的迁移,以及东邻洋陆板块之间的相互运动角度,阐述了大兴安岭中生代火山活动与大洋板块的俯冲作用无直接联系。

Mesozoic volcanic rocks developed in the Da Hinggan Mts. , Northeastern China are characterized by high-K, high-alkali trachytic calc-alkaline series and evoluted from acid to intermediate -basic with the progressive time. Their REE, trace element features and isotopic Sr, Nd compositions distinctly reveal two magma sources,a lower crust and a relatively undepleted or primary mantle one, indicating that petrogenesis of the Mesozoic volcanic rocks in the area is associated with crust-mantle interaction resulted from upwelling of deep intracontinental asthenolith. In addition , taking into consideration the migration of volcanic center and characteristics of the movement between neighboring continental and oceanic plates in the east,it is proposed that there is no direct relationship between Mesozoic volcanism in the Da Hinggan Mts. and subduction of the oceanic plate.