甘肃省景泰正路下志留统复理石杂砂岩沉积地球化学特征

位于北祁连造山带东段甘肃省景泰正路一带的下志留统肮脏沟组为一套巨厚的浊流相陆源碎屑岩,以杂砂岩为主,夹有板岩,属典型的浊流沉积。薄片的镜下观察结果表明,其粒度为0.05~4.00 mm,岩性为细粒-中、粗粒砂岩、含砾砂岩。对5块采集于复理石中的杂砂岩样品进行岩性组合判定和主要元素地球化学分析结果表明,w(SiO2)为61.83%~69.90%,w(K2O)/w(Na2O)为0.89~1.46。利用数据对比及w(K2O)/w(Na2O)—w(SiO2)等判别图的分析结果对其物源区的性质及沉积大地构造背景进行分析和判别的研究结果表明,北祁连造山带东段甘肃省景泰正路一带下志留统肮脏沟组的陆源碎屑主要来源于活动大陆边缘岩浆岛弧源区和造山带源区,反映了卷入造山带的岛弧、活动大陆边缘的弧后盆地的物源背景。沉积地球化学特征揭示的沉积大地构造背景为弧后前陆盆地背景,与碰撞后的大地构造背景相吻合。

Geochemical Characteristics of the Lower Silurian Flysch Greywacke in Zhenglu, Jingtai County,Gansu Province

The North Qilian orogenic belt is an elongated unit situated between the North China Plate in the north and Qaidam Plate in the south.While the Zhenglu section of Jingtai County,Gansu Province is located in the eastern sector of the orogenic belt.The Lower Silurian Angzanggou Formation is dominated by terrestrial clastic deposits,which is typical turbidite deposit of flysch facies.Angzanggou Formation is composed of greywacke intercalated with slates.The observation of 11 thin sections by microscope indicates the grain ranges from 0.05 mm to 4 mm,and the rock is fine-midum grained and granule texture.5 samples of greywacke are collected from the lower part of Angzanggou Formation and analysed.The major elements they contained are w(SiO_2) ranging from 61.83% to 69.90% and w(K_2O)/w(Na_2O) ranging from 0.89 to(1.46.) The provenance analyses and tectonic setting distrimination indicate that the sedimentary basin is a multi-sources turbidite flysch basin in Silurian,whose terrigenous materials come from the volcanic island arc and orogenic belts.The tectonic setting of flysch from Angzanggou Formation is a back-arc foreland basin.