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Quantitative assessment of the Quaternary tectonic movement based on paleomagnetism of widespread tephra and large-scale pyroclastic flow deposit

基于广泛分布的火山灰和大规模火山碎屑流沉积的古地磁定量评价第四纪构造运动

基本信息

批准号：
15540440
负责人：
ITOH Yasuto
金额：
$ 1.92万
依托单位：
Osaka Prefecture University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

项目摘要

This study aimed at assessment of the Quaternary tectonic movements around the central part of the Honshu arc on the basis of paleomagnetism. Mountainous range of the central Honshu arc is characterized by quite high strain and uplift rate of the upper crust as a result of an arc-arc collision. We identified topographic lineaments indicative of active faults, and collected paleomagnetic samples along transects crossing the target faults. Samples are taken from Nyukawa and Kamitakara Pyroclastic Flow Deposits, which emplaced in the early and late Quaternary, respectively. Their correlative widespread tephras have been discovered around the central Honshu. Detailed analysis of magnetic vector preserved in the Nyukawa Pyroclastic Flow Deposit demonstrated that a Quaternary basin had been developed associated with highly complicated crustal rotation around vertical axes reflecting relaxation process of strain in crust blocks sheared under the influence of fault movements. Detailed analysis of magnetic vector preserved in the Kamitakara Pyroclastic Flow Deposit demonstrated that the deformation has continued through the late Quaternary. It is amazing that small amount of recent deformation can be significantly detected on the basis of paleomagnetic approach. Stable detrital remanent magnetization of widespread tephras correlative with the above-stated pyroclastic flow deposits delineates pattern of seismological activity of the studied active faults. It is also noted that the Quaternary cumulative deformation of the upper crust resembles with instanteneous strain distribution exactly determined on the basis of satellite research during the last decade.

本研究以古地磁为基础，对本州弧中部第四纪构造运动进行了评价。由于弧-弧碰撞，本州弧中部山脉的上地壳应变和抬升速率相当高。我们确定了指示活动断层的地形特征，并沿着穿过目标断层的样带收集了古地磁样品。样品分别采自早第四纪和晚第四纪的新川火山碎屑流沉积和Kamitakara火山碎屑流沉积。在本州中部地区发现了与之相关的广泛分布的tephras。对新川火山碎屑流沉积中保存的磁矢量的详细分析表明，第四纪盆地的发育与高度复杂的地壳绕垂直轴旋转有关，反映了地壳块体在断裂运动的影响下剪切应变的松弛过程。详细分析了Kamitakara火山碎屑流沉积中保存的磁矢量，表明其变形持续到晚第四纪。令人惊奇的是，在古地磁方法的基础上，可以明显地探测到少量的近代变形。与上述火山碎屑流沉积相关的广布断层的稳定碎屑残余磁化描述了所研究的活动断层的地震活动模式。第四纪上地壳的累积变形与近十年来卫星观测精确确定的瞬时应变分布相似。