[H-GM03] Geomorphology

[HGM03-05] Internal structures of granitic plutons and their topographic expression

*Masahiro Chigira¹, Hironori Katou² (1.Fukada Geological Institute, 2.Aratani Civil Engineering Consultants, Co. Ltd.)

Keywords:Granite, ColuColumnar joints, Cooling, Corestone

We have reported on the internal structure and topography of granitic plutons at multiple locations. Here, we will organize and summarize them. The areas investigated from the north are as follows: Mt. Mizugaki, Mt. Kinpo, Mt. Jizoga in Yamanashi Prefecture, Mt. Gozaisho in Mie Prefecture, Tenguiwa in Hiroshima Prefecture, Mt. Migata in Yamaguchi Prefecture, Mt. Takatsuki in Ehime Prefecture, Tsushima in Nagasaki Prefecture, Mt. Okure in Miyazaki Prefecture, Yakushima in Kagoshima Prefecture, Mt. Kinabalu in Malaysia, and Monsanto in Portugal. These afes are from the Cretaceous to the Neogene. The common feature of these structures was that columnar joints developed at the edges of the granite, that is, under the roof and near the walls, and the center was massive or had parallel joints. High angle columnar joints often form rock towers. Columnar joints near the wall of a pluton have low-angle axes, but they have never been noticed or reported. This is probably due to its difficulty in certification. In the lecture, I will show examples of these. Corestones are often formed in rock columns surrounded by columnar joints, supporting that a corestone prototype is formed inside the column upon cooling, as suggested by Hirata et al (2016). Based on these facts, it is highly likely that the rock towers and corestones characteristic of granite are caused by columnar joints at the margins of granitic plutons.