関東平野温泉ボーリングのカッティングスの岩石記載とその帰属―つくば市下原および野田市花井

概要

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This report describes the subsurface geology, based on the petrography of rock cuttings taken from bore holes at spa sites, at Shimohara, Tsukuba City, Ibaraki Prefecture, and at Hanai, Noda City, Chiba Prefecture, both upon the Kanto Plain. The cutting samples from Tsukuba (four samples from 1241–1210 m depth) are hornfels, biotite-muscovite schist, and sillimanite-andalusite gneisses that resemble the Tsukuba metamorphic rocks. A single cutting sample from Noda (1295–1300 m depth) is mylonitized biotite granite that is similar in lithology to the Late Cretaceous Name Granite in the Shimonita area, Gunma Prefecture. These results provide new information on the eastern extension of the Ryoke Metamorphic Belt and the southern extension of the Tsukuba Metamorphic Belt. The occurrence of mylonite from Noda also provides important information in terms of constraining the eastern extension of the Median Tectonic Line.