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Geochemical study of cherts and mudstones in the Chichibu Southern Belt and the Shimanto Belt in Shikoku

秩父南部带和四国四万十带燧石和泥岩的地球化学研究

基本信息

批准号：
02452071
负责人：
SUZUKI Takashi
金额：
$ 4.35万
依托单位：
Kochi University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1991
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-02452071/
关键词：
the Aouthern Chichibu Terrane Shimanto belt X-ray fluorescence sedimentary environment the Ogawa belt the Kobiura belt the Nishiyama II belt K-Ar method チャ-ト泥質岩蛍岩X線分析装置熱水起源陸源砕屑物堆積深度

项目摘要

In the Southern Chichibu Terrane of the western part in Kochi Prefecture, the Mesozoic strata are widel-V distributed. The Togano Group (middle Triassic - late Jurassic) in the studied area consists mainly of chert, mudstone, silicious claystone, sandstone and acidic tuff. This Group divided into three belts, namely, the Ogawa belt, the Kobiura belt and Nishiyama II belt in order to the lower unit. The purpose of this study is to analyse bedded cherts and mudstones in their units chemically based on their paleontological data and to elucidate their sedimentary environments in detail. From theiy. samples, 10 major and 9 minor elements are analysed by the X-ray fluorecence. The authors investigated their chemical compositions within each columnar section, and behavior and relationship among each element bythe clustering technique, and composed their characteristics of the chemical. composition-of the various siliceous rocks with those of modern marine sediments detected from various environments.From the results, it is considered that the rocks of the Ogawa belt are of pelagic type with influence of oceanic tholeiite and twice times hydrothermal environment in early Early Jurassic and late Early Jurassic, and those of Nishiyama II belt are hemipelagic type from Middle Jurassic to Late Jurassic in age, and the bed ded cherts of the Kobiura belt are of pelagic to hemipelagic type with weak hydrothermal environment in early Early Jurassic.The cherts of the Kobiura belt might have been formed under the deeper condition than those of the Ogawa and Nishivama II belts from late Triassic to Early jurassic. In the Shimanto belt, field survey and sampling of cherts and mudstones were finished, and chemical analyses are in proaress at present.Age determination of mudstone by K-Ar method was finished from Cretaceous to Tertiary strata. It is tendency that the ages are younger towards the south gradually.

在高知县西部的秩父地体南部，中生代地层广泛分布。研究区中三叠世-晚侏罗世渡加诺群主要由硅质岩、泥岩、硅质粘土岩、砂岩和酸性凝灰岩组成。该群以下为单位分为三个带，即小川带、小井浦带和西山Ⅱ带。本研究的目的是在古生物资料的基础上，对层状硅质岩和泥岩进行化学分析，并详细阐明其沉积环境。从他们那里。用X射线荧光法分析了10种主量元素和9种次量元素。作者利用聚类分析技术研究了各柱剖面的化学组成、各元素之间的行为和相互关系，并综合了它们的化学特征。结果表明，小川带的硅质岩为远洋型，受大洋拉斑玄武岩的影响，形成于早侏罗世早期和晚侏罗世晚期的两次热液环境，西山Ⅱ带的硅质岩形成于中侏罗世至晚侏罗世的半远洋型，小尾浦带的层状硅质岩在早侏罗世早期为弱热液环境的远洋-半远洋型硅质岩，其形成环境可能比小川带和西瓦马Ⅱ带的硅质岩在晚三叠世-早侏罗世的形成环境更深。在四万十带，完成了硅质岩和泥岩的野外调查和取样，目前正在进行化学分析，并完成了白垩纪至第三纪泥岩的K-Ar法年龄测定。年龄有向南逐渐年轻化的趋势。