Spatiotemporal evolution of magmatic pulses and regional metamorphism during a Cretaceous flare-up event: Constraints from the Ryoke belt (Mikawa area, central Japan)

K-Ar ages of the Ryoke and related plutonic rocks in the Akechi area, Gifu-Aichi prefectures, central Japan

“…The dating result of the K-Ar biotite age for the Naegi-Agematsu-Toki Granite (64.1 1.4 Ma) in this study is substantially younger than that of the Toki Granite (74.0 1.8-72.3 1.8 Ma; Umeda, 2012, 2013) in the northern area. According to Takatsuka et al (2018), the K-Ar ages of biotite (ca. 71-68 Ma) are only slightly younger than the U-Pb age of the final stage of igneous activity (75-69 Ma pulse granitoids) in the Mikawa area.…”

“…Age data representing the timing of the solidification owing to the high-T closure temperature are as follows for the Inagawa Granite, CHIME monazite dating yields 83.5 1.5-81.9 1.4 Ma (Suzuki and Adachi, 1998;Miyake et al, 2016) and U-Pb zircon dating yields 76 4-67 4 Ma (Murakami et al, 2006) and 74.7 0.7-69.2 0.5 Ma (Takatsuka et al, 2018); for the Busetsu Granite, 78.5 2.6-75.3 4.9 Ma (CHIME: Suzuki et al, 1994;Nakai and Suzuki, 2003), and 70.9 0.9-69.5 0.4 Ma (U-Pb: Takatsuka et al, 2018); and for the Naegi and Toki Granite: 69.4 1.5-67.2 3.2 Ma (CHIME: Suzuki et al, 1994;Suzuki and Adachi, 1998;Yokoyama et al, 2016) and 71.3 1.6 Ma (U-Pb: Nakajima et al, 1993). As for K-Ar biotite ages, 70.1 1.8 Ma from the massive facies of the Inagawa Granite, 66.7 1.7 Ma from the gneissose facies of the Inagawa Granite (Yamasaki, 2013), and 71.1 1.8 Ma and 66.0 3.3 Ma (Nakai, 1982;Yamasaki, 2013) and 74.0 1.8-72.3 1.8 Ma Umeda, 2012, 2013) from the Toki Granite have been reported.…”

“…Many age data, mainly focused on the timing of the peak metamorphism and solidification of plutonic rocks, have been reported from the Mikawa area using chemical Th-U-total Pb isochron (CHIME) monazite and U-Pb zircon dating methods (see summary of Takatsuka et al, 2018). While the timing of exhumation constraining the termination of the igneous events (75-69 Ma;Takatsuka et al, 2018) relies largely on the K-Ar dating method which results in a lower closure temperature compared to the CHIME monazite and U-Pb zircon dating methods, the K-Ar age data from the Mikawa-Tono area are not necessarily sufficient (e.g., see summary of Yamasaki, 2013 andTakatsuka et al, 2018). This study provides new K-Ar biotite dating results from four plutonic rocks in the RPC, Mikawa-Tono area.…”

Whole-rock major and trace element geochemistry and geotectonic attribution of granitic rocks around the Higashigata, Akechi Town, Ena City, Gifu Prefecture, central Japan

“…黒雲母花崗岩との直接的な関係は不明である．固結年 代を示すと解釈される高温の閉鎖温度をもつ同位体及 び放射年代として，伊奈川花崗岩からは 83.5 ± 1.5-81.9 ± 1.4 MaのCHIMEモ ナ ザ イ ト 年 代 Adachi, 1998；三宅ほか，2016) と 76 ± 4-67 ± 4 Ma (Murakami et al, 2006) ，74.7 ± 0.7 Ma及び 69.2 ± 0.5 Ma (Takatsuka et al, 2018) の ジ ル コ ンU-Pb年 代， 武 節 花 崗 岩 か ら は， 78.5 ± 2.6-75.3 ± 4.9 MaのCHIMEモナザイト年代 (鈴木 ほか，1994；Nakai and Suzuki, 2003) と 70.9 ± 0.9, 70.8 ± 1.4 及び 69.5 ± 0.4 MaのジルコンU-Pb年代 (Takatsuka et al, 2018) M.V., 分析値;…”

“…Sr content (244 ppm) and Sr isotopic ratio (0.70965) of Inagawa Granite were averaged value of the Type I litho-facies by Tsuboi (2005). Gray-colored area denotes range of Sr initial isotopic ratio (corrected to 70 Ma; Takatsuka et al, 2018) reported by Shibata and Ishihara (1979). (b) Relationship between SiO 2 content (wt%) and alumina saturation index (ASI: A/CNK = Al 2 O 3 /[CaO + Na 2 O + K 2 O], in molar ratio) in assimilation of pelitic gneiss by Inagawa Granitic melt.…”