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的差距仍然很大。一些古地磁参数的全球分布将是填补这一空白的关键观测资料。其中一个研究多年的参数是虚拟地磁极（VGPs）的角标准差（ASD）。换句话说，它是对古长期变化强度的研究，通常使用熔岩作为样本，它被称为PSVL研究。在PSVL的标准模型中，ASD是纬度的函数，而不依赖于经度。然而，在整个研究过程中，一直存在反对意见。该项目的首席研究员提供了新西兰北部的自闭症谱系障碍，发现它比标准模型小得多。如果能很好地确定日本在近纵带和近纬度的不同半球的ASD，这将是一个有趣的问题。我们已经有了更多关于日本年轻火山岩的古地磁数据，但远没有得出结论。在九州岛，在日本群岛的西端，我们有许多不同年龄的火山。我们对那些年轻火山的熔岩和焊接凝灰岩进行了古地磁测量。我们主要关注的是阿苏火山、久州火山和鱼浮火山，因为这些地区的构造活动似乎不如九州南部的活跃，尽管一些非常年轻（小于0.1Ma）的焊接凝灰岩也来自九州南部。在它们的古地磁方向上测量了大约60个独立的时间范围。同时，我们尝试从当地期刊和论文中整理该地区的古地磁资料，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性的多站点。该数据集的ASD以及normal、reversed、Brunhes、pre-Brunhes等子集给出的ASD范围为17°~ 21°。这些地区的ASD值均明显大于新西兰、11.5°等太平洋岛屿。这一事实意味着PSV随纬度或半球而变化。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