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Study of Widespread Tephras Derived from Northeast Japan

日本东北部广泛分布的火山灰的研究

基本信息

批准号：
13680105
负责人：
SUZUKI Takehiko
金额：
$ 1.41万
依托单位：
Tokyo Metropolitan University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

项目摘要

The purpose of this study is to recognize widespread tephras derived from Northeast Japan for providing time-markers to the precise Quaternary chronology. Research was done by collecting many samples in distal and proximal areas and describing characteristic properties of them. Results are shown as follows.(1) Two ignimbrites were newly identified in Hakkoda area. Stratigraphy of these ignimbrites and Hakkoda 1^<st> and 2^<nd> pyroclastic flow deposits previously identified was established and characteristic properties of these were determined. Moreover, paleo-magnetic investigation revealed that Hakkoda 1^<st> pyroclastic flow deposits have normal polarity and Hakkoda 0 and Ose pyroclastic flow deposits have reverse polarity. This result is concordant with the correlation of the distal tephra associated with Hakkoda 1^<st> pyroclastic flow.(2) A widespread tephra named Seiganji-Toga Tephra (0.6-0.7 Ma) previously recognized in Boso peninsula is newly recognized in Northeast Japan, and this tephra derived from Kyushu will be a favorable time-marker in this study. Chemical composition of rare earth element in volcanic glass shards shows reliability of the correlation of this tephra from Kyushu to Boso and Oga peninsulas.(3) To investigate widespread tephras from Northeast Japan, comparisons of chemical compositions among tephras including vitric tephras layers and ignimbrites in Northeast Japan were carried out. No vitric tephra correlative to ignimbrites in Hokkaido was found. It is clarified that several properties of Ose pyroclastic flow deposits in Hakkoda area and Ashino pyroclastic flow deposits in Shirakawa area are similar to those of U8 tephra in Boso peninsula. It is difficult to judge which is the tephra correlative to U8 tephra. This problem is left for a further study.

本研究的目的是认识来自日本东北部的广泛分布的火山灰，为精确的第四纪年代学提供时间标记。研究是通过收集远端和近端区域的许多样本并描述它们的特征来完成的。结果如下： (1)八甲田地区新发现了两种熔结岩。建立了先前确定的这些熔结岩和 Hakkoda 1^<st> 和 2^<nd> 火山碎屑流沉积物的地层学，并确定了它们的特征性质。此外，古地磁调查显示，Hakkoda 1^<st>火山碎屑流沉积物具有正常极性，而Hakkoda 0和Ose火山碎屑流沉积物具有相反极性。这一结果与八甲田1^<st>火山碎屑流相关的远端火山碎屑流的相关性一致。(2)先前在房总半岛发现的一种广泛分布的火山灰，名为Seiganji-Toga Tephra (0.6-0.7 Ma)，在日本东北部新发现，这种来自九州的火山灰将成为本研究中有利的时间标记。火山玻璃碎片中稀土元素的化学成分显示了九州至房总和男鹿半岛的这种火山灰的相关性的可靠性。(3)为了调查日本东北部广泛分布的火山灰，对日本东北部的玻璃质火山灰层和熔结岩等火山灰的化学成分进行了比较。在北海道没有发现与熔结岩相关的玻璃质火山灰。明确了八甲田地区的大濑火山碎屑流沉积物和白川地区的芦野火山碎屑流沉积物的一些性质与房总半岛的U8火山碎屑流沉积物相似。很难判断哪个是与 U8 火山灰相关的火山灰。这个问题留待进一步研究。