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Kenta Kawaguchi,早坂康隆,Pham Minh,Kaushik Das,Kosuke Kimura 한국지질과학협의회 2022 Geosciences Journal Vol.26 No.1
The Sambagawa Belt is a subduction-related high-pressure intermediate type metamorphic complex with its protoliths characterized by the ocean plate stratigraphy. The Iyo-nada Sea area of this belt at western Shikoku, Southwest Japan exposes lenticular bodies of metagabbro. Besides, low P/T type metamorphosed Karasaki mylonites occur in this area as an upper structural unit of the Sambagawa Belt. LA-ICP-MS zircon U-Pb dating of the metagabbros in the Sambagawa Belt revealed their crystallization ages of 139–135 Ma as a magmatic event. Trace element composition of zircon suggests that the metagabbros were formed under the arc tectonic setting. Metagabbros do not show any evidence of high P/T metamorphism, instead, they indicate low P/T metamorphism based on the chemical compositional analysis of the hornblende. From the present study, it is constrained that the 139–135 Ma metagabbros were possibly originated as the hanging-wall arc crust. Zircon U-Pb dating of the Karasaki mylonites revealed imprints of multiple tectono-thermal events of 114.3 ± 1.5 Ma (magmatic event), ~108–105 Ma (metamorphic with or without magmatic event), and 102.4 ± 0.9Ma (metamorphic event). The first two tectono-thermal events can be correlated with those of the Higo Belt, central Kyushu. However, the last metamorphic event is younger than the tectono-thermal events of the Higo Belt, instead, it coincides with the initial stage tectono-thermal events of Ryoke-San’yo igneous province. Detrital zircon age of the pelitic schist in Karasaki mylonites revealed their origin as Jurassic to earliest Cretaceous sedimentary rock and its age distribution pattern is likely comparable to the previously reported age spectra of Higo metasedimentary rocks and their equivalent rock units. The newly obtained dataset indicates that the Karasaki mylonites are the eastern extension of the late Early Cretaceous Higo Belt.
Kenta Kawaguchi,Chang Whan Oh,Masaya Furusho,Satoshi Shibata 대한지질학회 2021 대한지질학회 학술대회 Vol.2021 No.10
Tectonic correlation between the Korean Peninsula and the Japanese Islands have long been discussed, but is still under debate and a challenging issue. This is because the limited occurrences of the correlatable rock units between them. The basement of the Korean Peninsula and the Japanese Islands are markedly different; Precambrian basement is dominant in the Korean Peninsula, while the Phanerozoic accretionary orogen is dominant in the Japanese Islands. However, the Jurassic granitoids is one of the common rock types between them. In this study, we focus on the Jurassic granitoids with figuring out the paleo-geographical position of the Japanese Islands along the erstwhile Korean Peninsula. The zircon U-Pb age dating of the 10 cm scale granite pebbles within the Cenozoic sedimentary sequence in the Noto Peninsula, the less studied area of northern part of the Hida Belt, revealed the weighted average ages of 183.6 ± 1.0 Ma (MSWD = 2.0, n = 25), 183.6 ± 1.1 Ma (MSWD = 2.0, n = 27), and 182.8 ± 1.4 Ma (MSWD = 2.6, n = 24). Zircon CL images, REE pattern, and Th/U ratio suggest that the obtained weighted average ages are the magmatic crystallization timing. Whole-rock geochemical data shows the moderately enriched LREE pattern with the weak Eu and Ce anomalies. In the primitive mantle-normalized multielement diagram, the granitoids display negative anomaly of the HFS elements such as Nb, Ta, P, and Ti. These geochemical features indicate that the 184–183 Ma granites were formed under the subduction related arc tectonic setting. Together with the previously reported data, the Jurassic granitoids in the Hida Belt show the age between 200–180 Ma and yield the arc tectonic setting. In the Korean Peninsula, Jurassic granitoids so-called “Daebo granites” (200–160 Ma) are widespread and formed under the arc tectonic setting. However, they show a clear selective trend in which the ~200–180 Ma granitoids are dominant in the southeastern (the Gyeongsang Basin and Yeongnam Massif) and northeastern (the Tumangang Belt) parts of the Korean Peninsula, while the later stage 180–160 Ma granitoids show the wide distribution on the continental side of the 200–180 Ma arc with northwest- and west-ward younging trend in the southern and northeastern parts of the Korean Peninsula (e.g., Kawaguchi and Oh, 2021). Considering those, the Hida Belt was located within the missing part of the 200–180 Ma arc belts between those developed in the southeastern and northeastern parts of the Korean Peninsula. Zircon Lu-Hf isotopic analysis of the 184–183 Ma granites revealed the εHf(t) values of –3 to +5 (an average of +1.4) in all the three dated samples. From the previous study, εHf(t) of zircon from the Early Jurassic granitoids (~200–180 Ma) in the Gyeonggi Massif and Ogcheon Belt show the negative values of ~–30 to –5, whereas those of the eastern part of the Yeongnam Massif yield the higher values of –5 to +10 (Lee et al ., 2016; Jo et al ., 2018; Cheong et al ., 2020). These isotopic features indicate that the 184–183 Ma Hida granites show the similar characteristics with those of the granitoids in the eastern part of the Yeongnam Massif. In addition, earliest to early Late Triassic zircons from the deformed granitic rocks in the Noto Peninsula area show the zircon εHf(t) value of –4.5 to –0.5 (an average of –2.0). These values are well matched to those of the Permo–Triassic granitoids in the Yeongnam Massif (Lee et al ., 2016). This study suggests that the zircon ages and εHf(t) values of the Hida granites show the common characteristics with the granitoids in the eastern part of the Yeongnam Massif. However, zircon εHf(t) value of the eastern part of the Gyeonggi Massif and the Taebaeksan Basin area are unclear, so the study in that area should have a key for further correlation between the Jurassic arc magmatism in the Korean Peninsula and the Japanese Islands.