大兴安岭北段泥盆系泥鳅河组地球化学特征及沉积环境

GEOCHEMICAL CHARACTERISTIC AND SEDIMENTARY ENVIRONMENT OF THE DEVONIAN NIQIUHE FORMATION IN NORTHERN DAXINGANLING RANGE

通过对大兴安岭北段泥盆系泥鳅河组岩石组合特征和碎屑岩样品地球化学的分析,对泥鳅河组沉积环境进行了分析研究.泥鳅河组岩性为石英杂砂岩、粉砂岩、粉砂质板岩、板岩等.样品中Al2O3的含量较高（3.74％～17.13％）,即泥质矿物含量较多,碎屑岩的成熟度较低,反映沉积物为近物源堆积.稀土、微量元素地球化学性质分析显示,碎屑物质为长英质物源区,铕具有明显的亏损,δEu为0.65～0.73,Ce具有较弱的异常,δCe介于0.87～0.94间,Tb/Yb介于0.30～0.37之间,La/Th在2.84～6.73范围内,Th/U比值介于3.53～5.38之间.稀土元素分布曲线总体呈现右倾形式,轻稀土富集,重稀土分布平坦,与典型的上地壳相似.因此,泥鳅河组岩性成熟度相对较低,沉积环境为滨浅海,沉积体系可进一步划分为扇三角洲及滨浅海相.

Based on the study of rock assemblage with geochemical analysis of clastic rock samples,the sedimentary environment of Devonian Niqiuhe Formation is researched.Lithologically,the Niqiuhe Formation includes quartz greywacke,siltstone,silty slate and slate.The high A12O3 content （3.74％-17.13％）,i.e.more clay mineral content,means the low maturity of clastic rocks,reflecting that the sediment is accumulated near the source.The geochemical analysis of rare earth and trace elements indicates that the detrital material is from feldspar and quartz areas.Eu is of obviously deficient,with δEu between 0.65 and 0.73.Ce is slightly abnormal,with δCe from 0.87 to 0.94.Tb/Yb value is 0.30-0.37.La/Th is in the range of 2.84-6.73.Th/U is 3.53-5.38.REE distribution patterns generally show rightward incline,with enriched LREE and flat HREE,which is similar to those of the typical upper crnst source.It is concluded that the maturity of Niqiuhe Formation is relatively low,with a sedimentary environment of offshore shallow sea.The depositional system can be subdivided into fan delta and shore-shallow marine facies.