11:45 AM - 12:00 PM
[HGM02-10] Fracture systems and landform of the Okueyama batholith
Keywords:Granite, ColuColumnar joints, Rock tower
We have been studying fractures in 3D using an UAV for Kofu Granite and Hiroshima Granite, and found that the rock towers in the Mt. Mizugaki and Mt. Jizogadake are shaped by columnar joints that formed in the upper part of plutons by rapid cooling (Chigira, 2021; Chigira, 2022). However, the roofs of these granite plutons were removed by erosion so that the relationships between columnar joints and the probable roofs have not been clarified.
The Okueyama batholith is a Miocene pluton in the north of Miyazaki prefecture, Kyushu, and provides outcrops from its roof down to 1000 m from the bottom of the roof. Takahashi (1986) investigated the petrology of the pluton and reported that the granite pluton has zonal structures in a vertical profile. Its fracture systems, however, have never been studied. We made field survey for the fracture systems of the Okueyama pluton using UAV; we found that the granite and granodiorite are fractured with columnar joints in the upper part of the pluton from the base of the roof to 200-300 m below it. The granodiorite farther down is much less joints and almost massive. Such structures likely formed during the cooling of the pluton with faster rate in its upper part.
The Okueyama batholith is a Miocene pluton in the north of Miyazaki prefecture, Kyushu, and provides outcrops from its roof down to 1000 m from the bottom of the roof. Takahashi (1986) investigated the petrology of the pluton and reported that the granite pluton has zonal structures in a vertical profile. Its fracture systems, however, have never been studied. We made field survey for the fracture systems of the Okueyama pluton using UAV; we found that the granite and granodiorite are fractured with columnar joints in the upper part of the pluton from the base of the roof to 200-300 m below it. The granodiorite farther down is much less joints and almost massive. Such structures likely formed during the cooling of the pluton with faster rate in its upper part.