摘要:
鄂拉山岩浆岩地处东昆仑、西秦岭、南祁连造山带交汇部位,内部结构复杂,是中国西部重要的构造结和矿集区之一。海相火山岩出露广泛,岩石类型主要由杏仁状玄武安山岩、杏仁状安山岩、安山质火山角砾岩、安山质晶屑岩屑凝灰岩、安山质角砾凝灰熔岩及英安岩、流纹岩等组成,以火山地层、夹层状、透镜状等形式赋存于洪水川组索拉曲砂岩、幸福村细浊积岩、河卡山粗浊积岩中,属海相喷发环境的产物。火山岩岩石化学成分与岛弧钙碱性安山岩平均化学成分相似,δEu平均为0.75,显示为弱负异常,(La/Sm)N、(Gd/Yb)N值平均分别为5.09、1.76,轻重稀土元素之间分馏程度显著,轻稀土元素分馏程度较高且富集。Ba、Rb、Th元素强烈富集,Ti、Cr等元素较亏损。Th×Ta/Hf2值在0.029～0.162,平均为0.079,具有陆缘火山弧的特性。由上所述,洪水川组火山岩产于碰撞后的拉伸环境。
Abstract:
Elashan magmatic belt,an intersection location for East Kunlun,West Qinling and South Qilian orogenic belt,has complex internal structure and is an important junction in western China and ore concentration area in Qinghai.Marine volcanic widely outcrops in Elashan area and the rock types are ainly amygdaloidal basaltic andesite,amygdaloidal andesite,andesitic volcanic breccia,andesitic crystal-vitric tuff debris,andesitic breccia tuff lava,dacite and rhyolite.Marine volcanic rocks occurs by the volcanic strata,or laminated and lenticular shapes in the Suolaqu sandstone,Xingfucun fine-turbidite and Hekashan coarse-turbidite of the Hongshuichuan Formation,which is the product of a marine environment eruption.Chemical composition of volcanic rocks similar with the average chemical composition of island arc calc-alkaline andesite,The average δEu value is 0.75 indicating a weak negative anomalies,(La/Sm)N,(Gd/Yb)N values of the average were 5.09,1.76,and There are significantly fractionated between light and heavy rare earth elements and enrich in LREE.The trace elements such as Ba,Rb and Th are strongly enriched and Ti,Cr and other elements are depleted.The Th×Ta/Hf2 value is between 0.029 to 0.162,shows volcanic arc character.From the above,volcanic rocks of the Hongchuichuan Formation produced in stretching after the collision environment.
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