四川理塘地区二叠-三叠纪硅质岩的地球化学特征及地质意义  

Geochemical Characteristics and Geological Significance of Permian–Triassic Siliceous Rocks in Litang Area, Sichuan Province

作　　者：严松涛[1] 谭昌海 秦蒙 李虎 段阳海 YAN Song-tao;TAN Chang-hai;QIN Meng;LI Hu;DUAN Yang-hai(No.12 Gold Party of Chinese People’s Armed Police,Chengdu,Sichuan 610000)

机构地区：[1]中国人民武装警察部队黄金第十二支队,四川成都610000

出　　处：《地球学报》2020年第4期504-514,共11页Acta Geoscientica Sinica

基　　金：中国地质调查局项目(编号:12120115041701)资助。

摘　　要：甘孜-理塘蛇绿混杂岩带位于西南"三江"东缘,为义敦-理塘弧盆系的重要组成部分,其内部发育大量不同时代不同类型的硅质岩。本次研究在理塘县理觉公路硅质岩夹层泥岩、泥灰岩中发现含有大量的中二叠-晚二叠世牙形石,在查日查东村附近硅质岩中采获中三叠世放射虫。通过对研究区硅质岩岩石学、地球化学特征研究,探讨硅质岩的成因类型及其沉积环境。结果表明,理塘地区硅质岩SiO2质量分数为66.13%~85.89%, Al2O3质量分数为4.69%~7.85%, Al/(Al+Fe+Mn)值介于0.44~0.73之间, U/Th比值为0.10~0.19,δCe值为1.00~1.63,这些特征共同指示其为生物成因硅质岩。Al2O3/(Al2O3+Fe2O3)质量比为0.52~0.79, MnO/TiO2质量比为0.05~0.27,∑REE为(49.26~165.41)×10–6,平均为94.37×10–6,(La/Yb)N比值为0.78~2.32,(La/Ce)N比值为0.72~1.26,指示其应形成于大陆边缘环境。理塘地区理觉公路和查日查东村二叠-三叠纪大陆边缘型硅质岩的厘定,不仅丰富了甘孜-理塘蛇绿混杂岩带的物质组成,也为甘孜-理塘洋盆二叠-三叠纪地质演化提供了新的证据。Located on the eastern margin of the "Three Rivers" region in Southwest China, the Ganzi–Litang ophiolite melange belt is an important part of the Yidun–Litang arc basin system, where a large number of siliceous rocks of different ages and types are developed. In this study, lots of conodonts in Middle Permian to Late Permian strata were found in the intercalated mudstone and marl of the siliceous rocks from Lijie Highway in Litang County, and Radiolaria in Middle Triassic strata was found in the siliceous rocks near Charichadong Village. Based on the study of the petrological and geochemical characteristics of siliceous rocks in the study area, the authors investigated the genetic type and sedimentary environment of siliceous rocks. The results show that the SiO2 content is 66.13%~85.89%, Al2O3 content is 4.69%~7.85%, Al/(Al+Fe+Mn) value is between 0.44 and 0.73, U/Th ratio is 0.10~0.19, and δCe value is 1.00~1.63, which indicates that the siliceous rocks are biogenetic. Al2O3/(Al2O3+Fe2O3) mass ratio is 0.52~0.79, MnO/TiO2 mass ratio is 0.05~0.27, ΣREE is(49.26~165.41)×10–6, 94.37×10–6 on average,(La/Yb)N ratio is 0.78~2.32, and(La/Ce)N ratio is 0.72~1.26, indicating that the rocks might have been formed in a continental marginal environment. The determination of Permian–Triassic continental margin siliceous rocks from Lijue Highway and Charichadong Village in Litang area not only enriches the material composition of the Ganzi–Litang ophiolite melange belt but also provides new evidence for the Permian–Triassic geological evolution of the Ganzi–Litang Ocean basin.

关 键 词：古生物化石 地球化学 沉积环境 硅质岩 甘孜-理塘蛇绿混杂岩带 

分 类 号：P596[天文地球—地球化学]