SHRIMP U–Pb zircon dating of the Kinshozan Quartz Diorite from the Kanto Mountains, Japan: Implications for late Paleozoic granitic activity in Japanese Islands

Abstract

The new result of SHRIMP U–Pb zircon dating of the Kinshozan Quartz Diorite from the Kanto Mountains, Japan, provides 281.5 ± 1.8 Ma. The age is 30 m.y. older than the available age of the Kinshozan Quartz Diorite obtained by hornblende K–Ar method. The new U–Pb zircon age represents the time of crystallization of the Kinshozan Quartz Diorite. The hornblende K–Ar age indicates the time that the Kinshozan Quartz Diorite cooled down to 500 °C which is the closure temperature of the systematics. Permian granites are found in small exposures in Japan, and frequently referred to as 250 Ma granites. The Kinshozan Quartz Diorite is considered as a type of the 250 Ma granites, and the age was influential in establishing a model of Paleozoic tectonic evolution for the Japanese Islands. The new age of the Kinshozan Quartz Diorite provides the opportunity to re‐examine the model. The Kinshozan Quartz Diorite and other Permian granites in the south of the Median Tectonic Line of Japan were constituents of the Paleo‐Ryoke Belt. The geochemical characteristics of the granitic rocks in the Paleo‐Ryoke Belt indicated that the granitic rocks were formed in a primitive island arc environment, and the new trace element data also support this interpretation. Examination of the available data and results of the present study suggests the late Paleozoic granitic activity in Japan as follows. At about 310–290 Ma, arc magmatism generated adakitic granites and other granites in the South Kitakami Belt. Quartz diorite and tonalites of primitive characteristic, such as the Kinshozan Quartz Diorite and granites in the Maizuru Belt appear to have been formed at the immature island arc, and accreted to the Japanese Islands at the end of Paleozoic or early Mesozoic era. During 260–240 Ma, granitic activity took place in the Hida and Maizuru Belts as a part of the Asian continent.

LateTriassic A‐type granite boulders in Lower Cretaceous conglomerate of theHida belt, Japan: Their origin and bearing on theYamatotectonic line inFar East Asia

“…M‐type ones, for example, ca. 400 Ma Dai plagiogranite (Ishizaka & Yanagi, 1975; Kawano et al, 1966), 280 Ma Kinshozan quartz diorite (Ogasawara et al, 2016; Ono, 1983), and 290–240 Ma Maizuru tonalite/granodiorite (Fujii et al, 2008; Tsutsumi et al, 2014), are extremely rare and small in amount. These Paleozoic granitoids may have primarily formed parts of full‐sized arc upper crusts for each or accreted intra‐oceanic arc crusts; however, they were almost totally removed afterwards probably due to subduction erosion (Isozaki et al, 2010; Suzuki et al, 2010).…”

Detrital zircon multi‐chronology, provenance, and low‐grade metamorphism of the Cretaceous Shimanto accretionary complex, eastern Shikoku, Southwest Japan: Tectonic evolution in response to igneous activity within a subduction zone

“…The major clusters of Permian to Early Jurassic detrital zircons within the KS1 sandstone are coincident with the three peaks of batholith‐related ages at 290–210 Ma, 190–160 Ma, and 110–90 Ma. Permian granitic rocks in Southwest Japan (Ogasawara, Fukuyama, & Horie, ), thought to be the source of the 290–210 Ma zircon peak, are identified only in a few areas in eastern Kyushu (e.g. the Usukigawa quartz diorite; Figure ; Kobayashi, Takagi, Katoh, Sango, & Shibata, ; Sakashima, Terada, Takeshita, & Sano, ), in the Maizuru belt (e.g.…”

U-Pb ages and Hf isotope composition of zircon from the Shimanto accretionary complex: Evidence for heterogeneous sources

“…As for the zircons of Permian age, they considered the few Permian intrusive complexes known within Japan as potential sources. Examples are the older Funatsu Granites occurring in the Hida Belt that yield U-Pb zircon ages in the range 240-250 Ma (Takahashi et al, 2010;Zhao et al, 2013) and the Kinshozan Quartz Diorite in the Kanto Mountains, which is, however older (dated at 282 ± 2 Ma Ogasawara et al, 2016). The Usukigawa Granodiorite (Sakashima et al, 2003) dated at 292 ± 12 Ma is another example and we actually prefer an age of 276 ± 6 Ma age for this pluton based on the younger group of analyses.…”