昌都—兰坪思茅盆地含盐系地层地球化学特征及物源属性探讨

Geochemical Characteristics and Provenance Attributes of Salt Bearing Formation in Qamdo-Lanping-Simao-Basin

碎屑岩的地球化学特征对应于特定的源区和构造环境,本文利用主微量元素对昌都盆地的早白垩纪景星组地层进行了地球化学分析,并与兰坪思茅盆地的早白垩纪地层进行了物源对比研究。岩相学研究显示景星组沉积岩的成分成熟度较低,其物源以火山岩为主。昌都地区景星组的主量元素地球化学分析显示其源区为石英质沉积岩源区和长英质火成岩源区。相比兰坪思茅地区早白垩纪地层,景星组地层物源的输入比较单一。景星组地层的CIA在59~78之间,平均为67,明显低于扒沙河组地层,表明兰坪思茅盆地的早白垩纪地层的风化强度明显高于昌都盆地。主微量构造环境判别图解显示昌都—兰坪思茅盆地早白垩纪地层的物源构造环境主要为被动大陆边缘与活动大陆边缘,同时具有大陆岛弧的特征。

The geochemical characteristics of clastic rocks correspond to the specific source area and tectonic environment.In this paper,the geochemical analysis of the Early Cretaceous Jingxing Formation in Qamdo Basin is carried out by using major trace elements,and the provenance of the early Cretaceous jingxing Formation in Lanping Simao Basin is studied.Petrographic studies show that the sedimentary rocks of Jingxing Formation have low compositional maturity and their provenance is mainly volcanic rocks.The main element geochemical analysis of Jingxing Formation in Qamdo area shows that the source area is quartz sedimentary rock and felsic igneous rock.Compared with the early Cretaceous strata in Lanping Simao area,the provenance input of Jingxing Formation is relatively simple.The CIA of jingxing Formation is between 59 and 78,with an average of 67,which is significantly lower than that of Pashahe Formation,indicating that the weathering intensity of early Cretaceous strata in Lanping Simao Basin is obviously higher than that in Qamdo Basin.The discriminant diagram of main and micro tectonic environment shows that the provenance tectonic environment of the Early Cretaceous strata in Qamdo-Lanping Simao Basin is mainly passive continental margin and active continental margin,and has the characteristics of continental island arc.