1992 年 87 巻 7 号 p. 291-299
Three samples of hornblende and ten of biotite from seven granitic masses in Awaji Island, Inner Zone of Southwest Japan, were dated by the K-Ar method. The hornblende and biotite ages for granitic rocks range from 87.7 to 89.6 Ma and 69.5 to 88.0 Ma, respectively.
Eleven granitic masses in Awaji Island were classified into three age groups by intrusive relations; Granitic Rocks I, Granitic Rocks II and Granitic Rocks III. The Granitic Rocks I are more or less deformed, exhibiting foliations. Mylonite is formed in strongly deformed part of the Granitic Rocks I, indicating a dextral shear movement. The Granitic Rocks II are massive hornblende-biotite granodiorite. They are emplaced to the north and the south of the Granitic Rocks I, and cause cotact metamorphism to the Granitic Rocks I. The Granitic Rocks III are massive stocks of biotite granite, intruding into the Granitic Rocks I and II.
Foliations imprinted in the Granitic Rocks I were formed by mylonitization prior to intrusion (before 87.7 Ma) of the non-deformed Nojima Granodiorite (Granitic Rocks II), because the Nojima Granodiorite intruded into the Granitic Rocks I and caused contact metamorphism to them.