Magma process of the Kibe Granite (One of the Younger granitoids) in the Yanai area of the Ryoke Belt, southwest Japan

Abstract

Magma process of the Kibe Granite (One of the Younger granitoids) in the Yanai area of the Ryoke Belt, southwest Japan 赤o 英里(Eri AKASAKI) 亀井 淳志(Atsushi KAMEI)  大和田 正明(Masaaki OWADA) Cretaceous granitic rocks in the Chugoku district, Southwest Japan arc, are divided into the following three groups; Older Ryoke granitoids, Younger Ryoke granitoids and San'yo granites. The Kibe Granite, a representative Younger Ryoke granitoids in the Yanai area, Yamaguchi Prefecture, occurs as an elliptic outcrop associated with a coeval quartz diorite, and intruded the high-grade Ryoke metamorphic rocks. The Kibe Granite is dominated by homogeneous biotite-granite that contain euhedral alkali-feldspar phenocrysts. These rocks also contain local micro-magmatic enclaves and have migmatitic structures in contact zones with the pelitic gneisses in the marginal parts of the granite. The mixing and mingling structures are developed at the contact between the granite and quartz diorite. The major and trace element variations of the Kibe Granite can be explained by a subtraction of plagioclase together with minor biotite and alkali-feldspar from a parental magma. The Kibe Granite was formed through the following processes: assimilation of the pelitic gneisses, magma mixing with the quartz diorite and fractional crystallization of a parental magma. These processes took place at the exhumation stage of the Ryoke metamorphism following its isothermal decompression path.

Oxygen isotope data of quartz from San-yo and Ryoke belt granites, schists, and siliceous veins: constraining the effects of 18O-rich fluids on granitic magma

“…Numerous authors have discussed the occurrence, emplacement order, and magma genesis of the granitoids of the Inner Zone, based on detailed structural relationships in the field, petrographic observations on individual granitic bodies, and geochemical and geochronological results (e.g., Kojima, 1953;Okamura, 1957Okamura, , 1960Koide, 1958;Kawano and Ueda, 1966;Shigeno and Yamaguchi, 1976;Hayasaka et al, 1983;Higashimoto et al, 1983;Okano and Honma, 1983;Kagami et al, 1992;Ikeda, 1993Ikeda, , 1998Owada et al, 1995;Suzuki et al, 1996;Suzuki and Adachi, 1998;Herzig et al, 1998;Nakajima et al, 1993;Ishihara and Matsuhisa, 2002;Ishihara and Chappell, 2007;Akasaki et al, 2013Akasaki et al, , 2015Skrzypek et al, 2016Skrzypek et al, , 2018Nakajima, 2018;Mateen et al, 2019 and references therein). In the forthcoming sections, a discussion is presented on the magma origin, effects of the metasedimentary sources on the magmatic rocks, and the role of fluids that precipitated the late-stage quartz veins.…”