Petrologic and Geochemical Characteristics of K-Bentonites from the Basal Ediacaran in Yangtze Platform, South China and Their Geological Significance

详细信息   

• 责任者：Wan Bin (State Key Laboratory of Palaeobiology and Stratigraphy ; Nanjing Institute of Geology and Palaeontology ; Chinese Academy of Sciences ; Nanjing 210008 ; China) ; Guan Chengguo
• 刊名：Acta Petrologica Sinica
• 出版年：2013
• 卷期：29(12)
• 关键词：膨润土 ; bentonite ; 岩石地球化学 ; lithogeochemistry ; 华南地区 ; South China
• 页码：p.4373-4386
• 图表：6 illus., 1 table, 71 refs.
• 分类号：0803
• issnNo：ISSN1000-0569
• isbnNo：CN11-1922/P

摘要

     Light-coloured claystone layers occur in the basal Ediacaran cap carbonate in Yichang, Hubei Province and in Xiuning, Anhui Province of Yangtze Platform, South China. Petrologic studies including thin section and SEM observations, as well as XRD analysis, indicate that the claystones mainly consist of illite and mixed-layer illite-smectite, and some phenocryst minerals, such as vericular quartz, glassy feldspar and magmatic zircon. Geochemical analysis using XRE and ICP-MS indicates that claystones from Yichang and Xiuning have similar elemental composition and distribution patterns, which are characterized by high K2O and low TiO2, and rich in lithophile elements Nb, Ta, Zr, Hf, Th, and Y. Al2O3/TiO2, Zr/Hf and Ti/Th values suggest that they are acidic volcanic ash in origin, and REE distribution patterns resemble that of granite. Both petrologic and geochemical data indicate that the claystones from the cap carbonates in South China are K-bentonites, which can be used for stratigraphic correlation. The ages of the K-bentonites from Xiuning area are ~635Ma by correlating with Yichang section. Application of various chemical discrimination diagrams and characteristics of trace elements implie that these K-bentonites were possibly derived from high K subalkaline rhyodacite formed in continental arc environment provisory. The regional distribution of these K-bentonites in the Yangtze Platform suggests a widespread volcanic event at the beginning of the Ediacaran, which may have been triggered by sudden meltdown of the Snowball Earth.