Structure of Paleosecular Variation : Relation to the Core Dynamics

用一种新引进的热去磁剂对日本温泉火山和大武火山的许多火山岩进行了实验研究。从温岑测得的布鲁内斯时区的古分子变化角标准差(ASD)与日本其他地区的相同，但年长的文仁比年轻的文仁大。古地磁方法也被应用于一些火山地层问题；火山碎屑流侵位温度的估计和熔岩的识别。日本翁竹火山古地磁研究的最重要成果之一是建立了日本最新更新世的地磁漂移。这种偏转的可靠性很高，因为它们来自两个安山岩熔岩流，其中剩磁的稳定性比来自沉积物的稳定性高得多。从两个熔岩流之一获得的古强度约为今天值的1/10，相关的虚拟地磁极(VGP)位于中太平洋附近。由于中太平洋的VGP位置也是从新西兰的奥克兰漂移中报告的，因此提出了赤道偶极矩在漂移过程中起主导作用的观点。为了解释PSV的结构，发展了一个新的统计模型，在该模型中，高斯涨落被赋予偏心偶极子。这个简单的模型解释了PSV的大部分结构；依赖于纬度的ASD和古强度直方图的形状。

Experimental studies with a newly introduced thermal demagnetizer were made on many volcanic rocks from the Unzen Volcano and the Ontake Volcano, Japan. Angular standard deviation(ASD) of the paleosecular variation(PSV) in the Brunhes Chron obtained from Unzen was in the same level as those from other areas of Japan, but it was larger for Older Unzen than Younger Unzen. Paleomagnetic methods were also applied to some volcanostratigrphic problems ; estimation of emplacement temperature of pyroclastic flows and lava identifications. One of the most important results obtained from the paleomagnetic studies of the Ontake Volcano is the establishment of the geomagnetic excursions in the latest Pleistocene in Japan. Reliability of the excursions is very high because they were found from two andesite lava flows, in which stabilities of the remanences are much higher than those from sediments. Paleointensities obtained from one of the two lava flows are abut 1/10 of the present-day value, and the associated virtual geomagnetic poles(VGPs) locate near the central Pacific Ocean. As the VGP positions in the central Pacific were also reported from the Auckland excursion in New Zealand, it was proposed that the equatorial dipole moment becomes dominant during the excursion. To explain the structure of PSV, a new statistical model was developed, in which Gaussian fluctuation was given to an eccentric dipole. This simple model explains most of the structures of PSV ; latitude dependent ASD and the shape of the histograms of the paleointensities.