九州離島域の地球化学図作成 Geochemical mapping of remote islands around Kyushu, Japan

Access this Article

Search this Article

Author(s)

Abstract

<p>本論文では,西南日本離島域を対象とした高密度地球化学図についての報告を行う.九州地方の陸海域地球化学図や現在作成中の広域Sr同位体図における研究調査を補完し強化する事を目的として,193試料の河川堆積物および3試料の火山灰降下堆積物を主に九州周辺の離島から採取し,53元素の分析を行った.堆積物試料中の元素広域分布と地質との関係を地理情報解析ソフトウェアを用いて詳細に調べた.非アルカリ苦鉄質火山岩や火砕岩由来の河川堆積物や火山灰降下堆積物はマグネシウム,カルシウム,スカンジウム,チタン,バナジウム,鉄,コバルト,ストロンチウムに富んでいた.アルカリ苦鉄質火山岩はさらに河川堆積物中のクロム,ニッケル,ニオブ,ランタン,セリウム,プラセオジム,ネオジム,タンタル濃度も増加させた.花崗岩由来の河川堆積物は,ベリリウム,ナトリウム,カリウム,カルシウム,ストロンチウム,イットリウム,スズ,ランタノイド元素,トリウム,ウランに富んでいた.付加帯・非付加帯堆積岩は河川堆積物中のニオブやタンタル濃度を増加させたが,ナトリウム,マグネシウム,カルシウム,ストロンチウム濃度を低下させた.これらの地球化学的な特徴は,砕屑物中の母岩から供給された主要造岩鉱物(例えば石英,斜長石,カリ長石,苦鉄質鉱物)や副成分鉱物(例えば,アパタイトやモナザイト)の相対的な存在量によって説明が可能である.また,亜鉛・鉛鉱床が対馬の河川堆積物中の亜鉛,カドミウム,鉛濃度を高め,アンチモン鉱床が天草下島の河川堆積物中のアンチモン濃度を高めたことが確認された.</p>

<p>This paper describes high-density geochemical mapping of isolated islands in southwest Japan. A total of 193 stream sediments and three volcanic ash deposits collected from isolated islands around Kyushu were analyzed to determine the content of 53 elements to supplement land and sea geochemical mapping of the Kyushu area and regional Sr isotope mapping. The relationship between the spatial distribution of elements in stream sediments and volcanic ash deposits and the geology was closely examined using geographical information system (GIS) software. Stream sediments derived from mafic volcanic and pyroclastic rocks and volcanic ash deposits were enriched with MgO, CaO, Sc, TiO<sub>2</sub>, V, T-Fe<sub>2</sub>O<sub>3</sub>, Co, and Sr. The presence of alkaline mafic volcanic rock increased the concentration of Cr, Ni, Nb, La, Ce, Pr, Nd, and Ta in stream sediments. Stream sediments originating from granitic rock were abundant in Be, Na<sub>2</sub>O, K<sub>2</sub>O, CaO, Sr, Y, Sn, Ln, Th, and U. Accretionary and non-accretionary sedimentary rocks caused an increase in Nb and Ta concentrations in stream sediments, and a reduction in Na<sub>2</sub>O, MgO, CaO, and Sr concentrations. These geochemical features could be explained by the relative abundance of major rock forming minerals (such as quartz, plagioclase, K-feldspar, and mafic minerals) and accessary minerals (such as apatite and monazite) derived from the host rocks. Also, Zn-Pb deposits increased Zn, Cd, and Pb concentrations in stream sediments on Tsushima Island, and Sb deposits enhanced the Sb concentration in stream sediments on Amakusa-Shimoshima Island.</p>

Journal

  • BULLETIN OF THE GEOLOGICAL SURVEY OF JAPAN

    BULLETIN OF THE GEOLOGICAL SURVEY OF JAPAN 69(5), 233-263, 2018

    National Institute of Advanced Industrial Science and Technology, Geological Survey of Japan

Codes

  • NII Article ID (NAID)
    130007529672
  • NII NACSIS-CAT ID (NCID)
    AA11587519
  • Text Lang
    ENG
  • ISSN
    1346-4272
  • NDL Article ID
    029477765
  • NDL Call No.
    Z15-177
  • Data Source
    NDL  J-STAGE 
Page Top