川西道孚地区三叠系细碎屑岩的地球化学特征及成生背景  

GEOCHEMICAL CHARACTERS AND FORMATION SETTING OF THE TRIASSIC FINE GRAINED CLASTIC ROCKS IN DAOFU AREA,WESTERN SICHUAN

作　　者：于远山[1] 廖声萍 潘忠习[1] 金灿海[1] 张海[1] YU Yuanshan;LIAO Shengping;PAN Zhongxi;JIN Canhai;ZHANG Hai(Chengdu Centert of China Geological Survey ,Chengdu 610081,China)

机构地区：[1]中国地质调查局成都地质调查中心,四川成都610081

出　　处：《矿物岩石》2018年第2期94-103,共10页Mineralogy and Petrology

基　　金：中国地质调查局西南三江有色金属资源基地调查项目(DD20160016)

摘　　要：道孚地区位于松潘-甘孜造山带的中心部位,该区发育一套以三叠系西康群浊积岩为代表的碎屑岩系。通过对该区金川和雅江盆地所采细碎屑岩样品地球化学特征的分析,结果显示,其w(SiO_2)集中在61%~68%之间,w(Al2O3)为7.58%~10%,w(CaO)多大于7%,w(K_2O/Na_2O)为1.11~1.82;化学性质活泼的大离子亲石元素Rb,Sr,Ba及不活泼元素Zr,Hf,Sc等含量大多低于上地壳丰度;而铁族元素Cr,Co,Ni含量较高;稀土元素总量相差不大(ΣREE=140.67×10^(-6)~179.57×10^(-6)),LREE/HREE多为7.07~9.27,δEu为0.62~0.67,La/Yb为10.15~16.14,稀土元素曲线基本相似,以轻稀土富集、重稀土平坦和较显著的负铕异常为特征;表明该区两盆地细碎屑岩常、微量元素及稀土元素地球化学特征均具有一定相似性,反映出其在物源和沉积环境上的一致性。研究认为,道孚地区三叠系浊积细碎屑岩的地球化学特征主要与大陆岛弧及活动大陆边缘沉积物特征较一致,个别样品或部分地球化学元素参数指标具被动陆缘构造环境砂岩的某些特点;反映其物源区性质主要为大陆岛弧和活动大陆边缘,并具有被动大陆边缘的构造背景。综合前人研究,认为研究区金川与雅江盆地的细碎屑岩是由前印支期的被动大陆边缘环境转化为晚三叠世具有多岛弧盆特征的活动大陆边缘环境下浊流沉积的产物,在其之间和周缘分布着与火山活动有关的岛屿或陆缘岛弧,为盆地充填提供相关物源。The Triassic Xikang Group in the Daofu area,central Songpan-Ganzi orogenic belt,is composed of turbidite elastic rocks. Geochemical analysis of these fine grained elastic rocks in the Jinchuan and Yajiang basin shows that the w（SiO2） content ranges from 61% to 68% ,w（Al2O3） from 7.58% to 10%,w（K2O/NazO） from 1.11 to 1.82 and w（CaO） content is over 7%. The large ionic stone elements of active chemical properties, such as Rb, Sr, Ba, and the contents of chemically inactive elements, such as Zr,Hf,Sc are lower than the upper crust abundance,while the contents of iron elements Cr,Co,Ni is relatively high. There is no obvious difference for the total amount of rare earth elements （∑REE= 140.67 × 10.6 ～179.57 × 10-6） ,LREE/HREE is in the range of 7.07～9.27,8Eu is 0.62～0. 67,La/Yb is 10.15～16.14. The REE curves are basically similar, characterized by enrichment of light rare earth, flat of heavy rare earth, and obvious negative Eu anomaly. The geochemical characteristics of major, trace elements and REE of the fine grained elastic rocks in the two basins are basically similar, indication of the consistency of its provenance and sedimentary environment. It reveals that the Triassic turbidite clastic rocks are consistent with continental arc and active continental margin sediments, and some of the collected and analyzed samples have the same geochemical parameters as the typical elastic rocks in the passive continental marginal environment. Therefore,the main provenance of these Triassic turbidite elastic rocks is the continental arc and active continental margin with certain passive continental margin setting. It is considered that the fine elastic rocks in Jinchuan and Yajiang Basins was products of turbidite deposition during the environment transition from passive continental margin in the early Indosinian period to the active continental margin in the late Triassic period. The volcanic rocks originated from islands or continental marginal arcs within and on the periphery of the study a

关 键 词：三叠系 细碎屑岩 地球化学 成生背景 道孚地区 西康群 

分 类 号：P588.212.3[天文地球—岩石学] P591.1[天文地球—地质学]