K–Ar ages of the Ryoke plutonic rocks in the Asuke area, Aichi prefecture, central Japan

Abstract

K-Ar ages of .. Ma (Kamihara Tonalite), . . Ma (Mitsuhashi Granodiorite), .. Ma (Inagawa Granite, massive facies), .. Ma (Inagawa Granite, gneissose porphyritic facies) and .. Ma (Busetsu Granite) were determined from the Ryoke plutonic rocks in the Asuke area, central Japan. All of these ages are interpreted to be cooling ages related to the blocking temperature of biotite. The coincident -Ma cooling ages of the Kamihara Tonalite, Mitsuhashi Granodiorite, massive facies of Inagawa Granite and Busetsu Granite in -Ma suggests that these plutonic rocks followed a common cooling path in this area after solidification of the Busetsu Granite (ca. -Ma). On the other hand, solidification age of the gneissose porphyritic facies of Inagwa Granite is ca. -Ma, and K-Ar age of .. Ma from the gneissose porphyritic facies of Inagawa Granite was younger than other plutonic rocks in the Asuke area. thus, the K-Ar age is concordantly interpreted as cooling age of the granite.

Age gap between the intrusion of gneissose granitoids and regional high‐temperature metamorphism in the Ryoke belt (Mikawa area), central Japan

“…For granitoids from northern Mikawa, the bulk-rock composition of sample GY88A agrees with previous analyses from the same pluton (Ishihara & Chappell, 2007;Ishihara & Terashima, 1977;Morishita & Suzuki, 1993;Nakai, 1976;Tsuboi & Asahara, 2009;Yamasaki, 2013;Figure 4). It is also compatible with bulk-rock data from Toyone (Kutsukake, 1993;Tsuboi & Asahara, 2009; Figure 4), which is the type locality of the Kamihara tonalite (Sakakibara, 1967).…”

“…Concordant 206 Pb/ 238 U ages obtained from FIGURE 4 Selected Harker diagrams for gneissose granitoids from the Mikawa and Toyone areas. The composition of the studied samples is plotted together with published data from Ishihara and Chappell (2007), Ishihara and Terashima (1977), Kutsukake (1993), Masumoto et al (2014), Morishita and Suzuki (1993), Nakai (1976), Asahara (2009), andYamasaki (2013). See text for detailed discussion 37 analyses range from 82 Ma to 74 Ma, and their weighted mean is 77.1 AE0.6 Ma (37 spots, MSWD = 1.2; Figure 6e).…”

“…Selected Harker diagrams for gneissose granitoids from the Mikawa and Toyone areas. The composition of the studied samples is plotted together with published data from Ishihara and Chappell (), Ishihara and Terashima (), Kutsukake (), Masumoto et al (), Morishita and Suzuki (), Nakai (), Tsuboi and Asahara (), and Yamasaki (). See text for detailed discussion…”

“…Bulk-rock analyses were performed for all samples except for sample GY98A and weathered sample GY90A. The results are summarized in Table 1 and plotted in Figure 4, together with data from previous studies of the Kamihara tonalite and Tenryukyo granite (Ishihara & Chappell, 2007;Ishihara & Terashima, 1977;Kutsukake, 1993;Masumoto et al, 2014;Morishita & Suzuki, 1993;Nakai, 1976;Tsuboi & Asahara, 2009;Yamasaki, 2013).…”

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

“…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.…”