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

本文利用电子探针对九州南部第四纪冰盖的化学成分进行了研究，并获得了这些冰盖对比和年代学方面的基本数据。在这项研究中，我重点研究了包括托卡拉群岛在内的萨特孙南群岛的晚更新世和全新世的冰盖，但很少有系统的年代学研究。EPMA分析明确了托卡拉群岛Kuchierabujima、Kuchinoshima和Akusekijima群岛大型丛生岩石群的化学性质，以及Yakushioma岛中更新世标志性岩石群的化学性质，并根据与这些岩石群特征相关的其他岩石群的鉴定和年代学，阐明了地貌演化和古环境历史。主要研究结果如下。在库契亚布吉岛、库奇诺岛、Akusekijima群岛发现的三个标志性浮石瀑布，可以根据它们的化学性质加以区分。这些富含SiO_2的冰盖岩均为流纹岩，是大型普里宁火山喷发的产物，表明这些冰盖岩系分布在远离火山岛的萨特孙群岛、大须岛和萨苏马半岛。中更新世玻璃灰岩-安博火山灰岩-和巨大的火山碎屑流-Koseda火山碎屑流-在Yakushima岛的玻璃碎片中具有不同的化学性质，这表明可以在日本岛屿及其周围的大片地区发现这些玻璃碎屑。

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.