Study of low-relief surfaces development using volcanic products, Japan

本研究的目的是利用火山产物估算日本低起伏地表的年龄，并重建山内及周边地区的古地理。它旨在促进对山地建筑的年代学研究。本研究以日本关东、飞驒等地区的新生代火山产物为研究对象，采用温度年代学、辐射年龄和基底地貌等方法进行研究。结果如下：首先，通过古地磁测量和K-Ar测年，确定了覆盖在武间山西北部的火山碎屑流沉积与前人研究的白川火山碎屑流沉积群的年龄比预期的要早；另一方面，在郡山盆地及郡山盆地与武间山交界处发现了2个火山碎屑流沉积，属于白川火山碎屑流沉积群。建立了阿布库马山脉周边低起伏面发育与地貌发育模型。其次，对关东平原西缘几个丘陵和关东平原西部地下的温层地层进行了修正。第三，厘清了火山碎屑流沉积的特征，为飞驒山周围古地理重建提供了若干资料。

The purpose of this study is to estimate the ages of low-relief surfaces using volcanic products in Japan, and to reconstruct the paleogeography in and around mountain area. It aims to promote the chronological study of mountain buildings. For this study, tephrochronological method, radiometric ages and basal landforms of Cenozoic volcanic products were used in Abukuma, Kanto, Hida Mountains. The results are as follows. First, pyroclastic flow deposit covering the northwest part of Abukuma Mountains, correlated to the Shirakawa Pyroclastic Flow Deposit Group by previous study, was identified as older one than expected using paleomagnetic survey and K-Ar dating. One the other hand, two pyroclastic flow deposits belonging to the Shirakawa Pyroclastic Flow Deposit Group were found in Koriyama Basin and along the boundary of Koriyama Basin and Abukuma Mountains. The model of development of low-relief surfaces and geomorphic development around the Abukuma Mountains were established. Second, stratigraphy of tephra layers in several hills along the west margin of the Kanto Plain and underground of the west part of the Kanto Plain were revised. Third, characteristic properties of pyroclastic flow deposits providing several data for reconstruction of paleogeography around the Hida Mountains were clarified.