松辽盆地北部海伦-望奎地区姚家组灰色砂岩地球化学特征及地质意义

Geochemical Characteristics and Geological Significance of Gray Sandstones of the Yaojia Formation in the Hailun-Wangkui Area in Northern Songliao Basin

松辽盆地北部姚家组是主要的富铀层位,灰色砂岩普遍发育,但是其古沉积环境、构造背景及物源分析工作一直以来鲜有研究。文章基于高品质测井曲线、碎屑岩组成成分及元素地球化学特征,探讨了上白垩统姚家组灰色砂岩的物源组成、地球化学成分、源区风化特征及构造背景。结果表明:姚家组砂岩主要以长石砂岩为主,砂岩w(SiO_(2))变化较大,介于51.48%~82.95%之间,平均为73.07%,全碱含量较高w(Na_(2)O+K_(2)O)=4.76%~7.21%,平均为5.92%;稀土元素ΣREE介于(73.77~208.36)×10^(−6),平均为124.02×10^(−6),LREE/HREE介于7.06~14.34之间,Eu为微弱负异常(δEu=0.63~1.12),具有明显的壳源岩浆特征;姚家组灰色砂岩CIA值变化于31.77~66.86,ICV值介于0.73~1.92之间,PIA值变化大(27.93~72.55,平均为59.52),整体反映了姚家组砂岩沉积时期为干旱-半干旱气候背景下弱风化作用;w(Sr)/w(Ba)均小于1,w(Al_(2)O_(3))/w(MgO)大多数变化于11.48~53.19之间,反映了在姚家组沉积时期为富氧的淡水环境;在w(K_(2)O)/w(Na_(2)O)-w(SiO_(2))和w(TFe_(2)O_(3)+MgO)-w(K_(2)O)/w(Na_(2)O)图解上,样品几乎落入大陆边缘构造环境范围内,结合区域演化史,综合研究认为物源应为小兴安岭-张广才岭地区发育的长英质岩石。

Yaojia Formation in the northern Songliao Basin is the major uranium-rich formation with well developed gray sandstone.However,few study was finished on its depositional environment,tectonic background and source analysis.In this paper,the source composition,geochemical composition,weathering characteristics of the source area and tectonic setting of the Late Cretaceous Yaojia Formation gray sandstones were discussed based on highquality logging curves,clastic composition and elemental geochemical characteristics.The results showed that the sandstones of Yaojia Formation are mainly feldspathic sandstones,the w(SiO_(2))varies widely,ranging from 51.48%to 82.95%,with an average of 73.07%,and the total alkali content range from w(Na_(2)O+K_(2)O)4.76%to 7.21%,with an average of 5.92%;the REE ranges from 73.77×10^(-6) to 208.36×10^(-6),averaging 124.02×10^(-6) with the LREE/HREE between 7.06 and 14.34,weakly negative Eu anomaly(δEu=0.63~1.12),indicating the obvious crustal source magma characteristics.The gray sandstone of Yaojia Formation CIA values vary from 31.77 to 66.86,ICV values vary between 0.73 and 1.92,and PIA values are highly variable(27.93 to 72.55,with an average of 59.52),reflecting overall weak weathering in arid-semi-arid climatic context during the deposition of the sandstones.The w(Sr)/w(Ba)are all less than 1,and w(Al_(2)O_(3))/w(MgO)mostly vary between 11.48 and 53.19,indicating the rich oxygen shallow water environment.In the diagram of w(K_(2)O)/w(Na_(2)O)-w(SiO_(2))and w(TFe_(2)O_(3)+MgO)-w(K_(2)O)/w(Na_(2)O),almost samples fall within the tectonic environment of the continental margin.The source of the material was the felsic rocks developed in the Xiaoxing'anling-Zhangguangcailing area.