Paleomagnetic secular variation study using young volcanic rocks in Kyushu Island

地磁的磁电流体动力学模型与古地磁资料之间仍有较大差距。一些古地磁参数的全球分布，将是弥合这一空白的关键观测。多年来研究的参数之一是虚拟地磁极(VGP)的角标准偏差(ASD)。换言之，它是对古分子变化强度的研究，通常使用熔岩作为样品，因此被称为PSVL研究。在PSVL的标准模型中，ASD是纬度的函数，但不取决于经度。然而，在整个研究历史中，一直存在反对意见。该项目的首席调查员提供了新西兰北部的ASD，并发现它比标准模型小得多。如果日本的ASD在不同半球的近经带和近纬度范围内得到很好的确定，那将是一件有趣的事情。我们已经有了S…日本年轻火山岩的更多古地磁年代，但远不能得出结论。在日本群岛西端的九州岛，我们有许多不同时代的火山。我们对这些年轻火山的熔岩和焊接凝灰岩进行了古地磁测量。我们主要关注麻生火山、库州火山和玉佛火山，因为这些地区的构造活动似乎没有九州南部的火山那么活跃，但一些非常年轻(不到0.1 Ma)的焊接凝灰岩也来自九州南部。在古地磁方向上测量了约60个独立的时间层位。同时，我们试图从当地的期刊和论文中收集整理该地区的古地磁数据，并建立了一个120多个独立层位的数据集，其中很大一部分具有一致的多个站点。该数据集的房间隔缺损和正常、反向、布朗尼、布朗尼前等子集的房间隔缺损范围为17°至21°。所有这些ASD值都明显大于新西兰、11.5°和太平洋其他岛屿。这一事实意味着PSV随纬度或半球的不同而不同。较少

The gap between the magnetoelectoric fluid dynamic models_ of the geomagnetism and the paleomagnetic data is still large. The global distribution of some paleomagnetic parameters, would be the key observations bridging over the gap. One of those parameters studied for years is the angular standard deviation (ASD) of the virtual geomagnetic poles (VGPs). As it is, in another word, the study of the intensity of the paleosecular variation, and usually uses lavas for the samples, it is called as the PSVL studies. In the standard models of the PSVL, the ASD is function of the latitude, but does not depend on the longitude. However, there have been objections throughout the research history. The head investigator of this project had provided the ASD in northern New Zealand, and found it significantly smaller than the standard models. It would be interesting if the ASD in Japan, in the close longitudinal band and close latitude in different hemisphere, is well determined. We already had had s … More ome paleomagnetic date of young volcanic rocks in Japan, but was far less to be conclusive.In Kyushu Island, at the western end of Japanese Islands, we have many volcanoes of various ages. We performed the paleomagnetic measurements of lavas and welded tuffs of those young volcanoes. We primarily focused on the Aso, Kuju and Yufu volcanoes, as those areas seemed to be less active in tectonics than those in southern Kyushu, some of very young (less then 0.1Ma) welded tuffs were also taken from southern Kyushu, though. About 60 independent time horizon were measured in their paleomagnetic directions. Mean while, we tried to compile paleomagnetic data in this area from local journals and theses, and build a dataset of more than 120 independent horizon, significant portion of which have concordant multiple sites. ASD of this dataset and subsets of normal, reversed, Brunhes, pre-Brunhes, etc. gave ASDs from 17° to 21°. All of those ASD value are significantly larger than that of New Zealand, 11.5° and other islands in the Pacific Ocean. This fact implies the PSV varies by the latitude or the hemisphere. Less