Study on the identification of Quaternary tephras in southern Kyushu based on EPMA analysis

利用EPMA对九州南部地区第四纪泥岩进行了化学成分分析，获得了泥岩对比和年代学的基础资料。在本研究中，我重点研究了包括托卡拉群岛在内的Satsunan群岛的晚更新世和全新世tephras，这些岛屿的tephras的系统年代学研究很少。EPMA分析明确了Tokara群岛Kuchierabujima、Kuchinoshima和Akusekijima岛的大型plinian tephras和Yakushioma岛中更新世标志tephras的化学性质。此外，通过对其他泥质岩的鉴定和年代学，明确了泥质岩的地貌演化和古环境历史，并对泥质岩的特征进行了分析。主要结果如下：根据其化学性质，可以对Kuchierabujima、Kuchinoshima和Akusekijima三处标志性浮石瀑布进行区分。这些富含sio2的泥岩均为流纹岩，是普林尼期大喷发的产物，表明这些泥岩分布在远离火山岛的萨苏南群岛、大sumi和萨摩半岛上。中更新世玻璃灰岩-安博火山碎屑岩和巨火山碎屑岩-古久岛火山碎屑岩的玻璃碎片具有明显的化学性质，表明这些火山碎屑岩可以在日本全岛及其周围广泛分布。

This study airas to characterize Quaternary tephras in southern Kyushu based on the chemical compositions of their volcanic glass shards using EPMA, and to get fundamental data on the correlation and chronology of those tephras. In this study, I focused on the late Pleistocene and Holocene tephras of Satsunan Islands including Tokara islands, in which there have been few systematic tephrochronological studies. EPMA analysis made it clear the chemical properties of large plinian tephras in Kuchierabujima, Kuchinoshima and Akusekijima Islands of Tokara Islands, and of middle Pleistocene marker tephras in Yakushioma Island.In addition, Landform evolution and palaeo-environment history were clarified based on the identification and chronolog on other tephras relevant to tephra characterizations of those tephras. The main results are as follows. Three marker pumice falls recognized in Kuchierabujima, Kuchinoshima, Akusekijima Islands, can be distinguished based on their chemical properties. Those tephras rich in Si02 are all rhyolitic and the products of big plinian eruptions, suggesting that those tephras are distributed over Satsunan Islands, Osumi and Satsuma peninsulas far distant from the volcanic islands. Middle Pleistocene vitric ash-Anbo tephra-and gigantic pyroclastic flow-Koseda pyroclastic flow-in Yakushima Island have distinct chemical properties in their glass shards, suggesting that those tephras can be identified in extensive area across and around the Japanese Island.