摘要： 为查明川西南盐津地区志留系龙马溪组页岩元素地球化学特征以及页岩形成时的物质来源和构造背景,对盐津牛寨剖面19件页岩样品岩石矿物学和地球化学进行测试分析,主要应用了稀土元素来探讨龙马溪组页岩的形成环境、沉积速率、物质来源和构造背景。研究表明: 盐津牛寨剖面龙马溪组页矿物成分以石英、碳酸盐矿物和黏土矿物为主,矿物三角图显示盐津地区龙马溪组页岩主要为黏土相页岩和混合相页岩的组合;整体??REE值较高,稀土元素标准化配分模式图呈Ce亏损和微弱Eu富集的右倾特点;样品δCe值和Ni/Co值、V/Cr值变化趋势表明古水深呈现早期突然增加后期逐渐变浅,含氧量由早期的缺氧还原状态逐渐演变为后期的弱氧化状态;La_N/Yb_N值变化表明页岩沉积速率受海平面升降及陆源碎屑输入影响呈现先增后减的变化特点;物源分析表明源岩以长英质火成岩及花岗岩类的中—酸性地质体为主;La-Th-Sc图解和构造背景特征表明源岩主体构造背景为被动大陆边缘,结合前人研究及其大地构造背景,推断川西南盐津地区龙马溪组页岩主体形成于缺氧的被动大陆边缘,且物源主要来自于西侧康滇古陆,黔中隆起次之。

关键词: 川西南, 盐津地区, 龙马溪组, 稀土元素, 物源分析, 构造背景

Abstract: In order to find out the element geochemical characteristics of Silurian Longmaxi Formation shale in Yanjin area,southwestern Sichuan Basin,as well as the material source and structural background of shale formation,the petromineralogy and geochemistry of 19 shale samples from Niuzhai section of Yanjin area were tested and analyzed. Combined with the previous research results and adjacent areas,the rare earth elements were mainly applied to discuss the sedimentary environment, the accumulation rate,material source and tectonic setting of the Longmaxi Formation shale in the study area. The results show that the mineral composition of the Longmaxi Formation in Niuzhai section of Yanjin is mainly quartz,carbonate minerals and clay minerals. The mineral triangle diagram shows that the Longmaxi Formation shale is mainly a combination of clay shale and mixed shale. The normalized partition pattern of rare earth elements is characterized by Ce deficit and weak Eu enrichment. The δCe values,Ni/Co and V/Cr values of the samples indicate that the paleo-water depth increases suddenly in the early stage and becomes shallow gradually in the later stage. Oxygen content gradually changes from anoxic reduction state in the early stage to weak oxidation state in the later stage. La_N/Yb_N values show that the shale deposition rate increases firstly and then decreases under the influence of sea level and terrigenous debris input. Provenance analysis shows that the source rocks area are mainly felsic igneous rocks and intermediate-acid geological bodies of granitoids. The La-Th-Sc diagram and tectonic setting characteristics show that the main tectonic setting of the source rocks is passive continental margin. Combined with previous studies and tectonic setting,it is inferred that the main source of the Longmaxi Formation shale is formed in the Passive continental margin of hypoxia,and the provenance is mainly from the Kang-Dian ancient land to the west of the study area,followed by the Central Guizhou uplift.

Key words: southwestern Sichuan Basin, Yanjin area, Longmaxi Formation, REE, provenance analysis, tectonic setting

中图分类号: 

• P59