Magnetic Chart Deduced from Paleomagnetism of Widespread Marker Tephras

从广泛分布的标记火山石的古地磁学推导出的磁图

基本信息

批准号：
12680158
负责人：
NAKAJIMA Tadashi
金额：
$ 2.05万
依托单位：
Fukui University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-12680158/
关键词：
Paleomagnetism Aso-4 Tephra Aso-4 Co-ignimbrite Ash-fall Deposit Magnetic Chart Age Determination Aso Pyroclastic-flow Deposit Late Pleistocene 阿蘇4火山灰

项目摘要

The Aso pyroclastic-flow deposits are divided into four eruptive units : Aso-1, Aso-2, Aso-3, and Aso-4 in ascending order. The paleomagnetic directions of welded tuff samples determined for these units, which are distributed in central Kyushu, are characteristic of the individual units, and are all of normal polarity. The unit-mean directions for Aso-1 and Aso-4 are similar to the direction of the present geomagnetic field. On the other hand, the unit-mean direction for Aso-2 is characterized by a steep inclination, and that for Aso-3 by an extremely easterly declination. It appears that the distinctive directions of Aso-2 and Aso-3 could be useful in identifying these tephras. The mean VGP for the Aso-4 co-ignimbrite ash-fall deposit is identical to those for subunits of the Aso-4 tephra : the Aso-4A welded tuff in Oita Prefecture, the lower part of the Ube volcanic ash layer in Yamaguchi Prefecture, and the distal ash-flow deposit in Miyazaki Prefecture. From the identical VGPs and … More other stratigraphic evidences, the subunits are inferred to have been deposited at the same time. This indicates that the magnetizations were acquired in a geomagnetic field dominated by the same dipole field (DF) component in all regions of the Japanese Islands ; the DF pole is assumed to coincide with the overall-mean VGP ; declinations and inclinations over the Japanese Islands calculated from the pole range between - 3.5° and - 1.5°, and between 44.0° and 59.0°, respectively.In order to clarify the configuration of the geomagnetic field at the time of the Aso-4A eruption, the surveyed area was divided into eight regions, and the local geomagnetic field (LF) direction of each region was calculated from the regional-mean VGP. Local geomagnetic anomalies, exceeding the a_<95>s of the (LF) directions, could not be detected by comparing DF and LF in all of the eight regions. Had local geomagnetic anomalies existed at the time of the Aso-4A eruption, they have been in the narrower zones than the eight regions of this study Less

将ASO碎屑流沉积物分为四个四四四个四四个四个四个四个四个四个针对这些单位的焊接凝灰岩样品，这些单位分布在中央九州，是单个单位的特征，并且都是正常的极性另一方面，ASO-2的单位均值的特征是当前的地磁领域，而ASO-3的倾斜度是非常东方的-2和ASO-3。 Tepras。从相同的VGP和...同时进行的其他地层表明。与整个均值的VGP相吻合； Anes群岛从-3.5°和-1.5°之间以及44.0°和59.0°之间钙化，ASO -4A爆发时间到八个区域的配置每个区域的局部地磁场（LF）方向是从局部均值的元素中钙化的。 ASO -4A喷发，它们进入了较窄的区域，这项研究的八个区域较少