Tectonics of the Ryoke-Izumi belt of the Izumi Mountains, Southwest Japan from thermochronological data

Abstract

The Late Cretaceous to early Paleogene evolution of the RyokeIzumi belt is examined using apatite and zircon fission-track (FT) dating of the Sennan Rhyolites, the Takijiri Adamellite, and the Izumi Group in the Izumi Mountains, southwestern Japan, together with pre-existing geochronological data and interpretation of geologic structures. The results reveal that the geology of the area can be divided into three blocks on the basis of different cooling histories and east-west-trending boundary faults; namely, blocks A, B, and C from south to north. Block A consists mainly of the Izumi Group, which accumulated over a part of the Sennan Rhyolites and the Takijiri Adamellite at ..

Kinematic Analyses and Radiometric Dating of the Large‐Scale Paleogene Two‐Phase Faulting Along the Median Tectonic Line, Southwest Japan

“…Note that the Izumi Group includes no detritus from the Sambagawa metamorphic rocks, indicating that the latter were never exposed at the surface during the sedimentation of the former. The Izumi Group was dated to the Late Cretaceous (82.7-70.3 Ma) based on the zircon fission track and U-Pb ages (e.g., Noda & Sato, 2018;Seike et al, 2013).…”

Abyssal Peridotite as a Component of Forearc Mantle: Inference from a New Mantle Xenolith Suite of Bankawa in the Southwest Japan Arc

“…This horizon can be correlated with the lower part of the Shindachi Formation (lithologic units Ss4 and Ss5) on the basis of lithological studies [36]. The Shindachi Formation has been considered to be of Maastrichtian age based on ammonoid biostratigraphy [37] and was dated by a fission track method at 70.9 ± 3.4 Ma [33].…”

“…We recognized the alkali basaltic dike extending over a distance of 50 m in the west-east direction along both Bankawa River and forest trails, and the thickness is less than a few meters. The alkali basaltic rocks thermally metamorphosed sandstone or mudstone of the Izumi Group adjacent to the In the Izumi Mountains, four geologic divisions, namely the late Pliocene-early Pleistocene Osaka Group, Cretaceous Ryoke granitoids and Sennan Rhyolites, Late Cretaceous Izumi Group, and Sanbagawa metamorphic belt, have been established from north to south [26,33]. The Izumi Group unconformably caps or is bounded with faults by the Ryoke granitoids and Sennan Rhyolites in the northern margin, and is in contact with a great boundary fault, the Median Tectonic Line (MTL), in the southern margin.…”

Submarine slope–fan sedimentation in an ancient forearc related to contemporaneous magmatism: The Upper Cretaceous Izumi Group, southwestern Japan

“…Abbreviations for stratigraphy: Coniac., Coniacian; Sant., Santonian. References for radiometric age data: [1] Aoki et al (), [2] Imaoka, Nakajima, and Itaya (), [3] Takagi et al (), [4] Takagi et al (), [5] Takagi, Soda, and Yoshimura (), [6] Kishi et al (), [7] Imaoka et al (), [8] Imaoka and Ikawa (), [9] Imaoka et al (), [10] Yuge, Imaoka, and Iizumi (), [11] Ikawa et al (), [12] Suzuki, Adachi, and Nureki (), [13] Suzuki and Adachi (), [14] Suzuki, Adachi, and Kajizuka (), [15] Umeda et al (), [16] Tazaki et al (), [17] Kagami et al (), [18] T. Sato et al (), [19] Aoki et al (), [20] Nakahata, Isozaki, and Tsutsumi (), [21] Sonehara and Yagi (), [22] Matsumoto, Sawada, and Kagami (), [23] K. Sato et al (), [24] A. Noda et al (), [25] A. Noda, Danhara, Iwano, and Hirata (2017a), [26] Nakajima et al (), [27] Iida et al (), [28] D. Sato, Matsuura, and Yamamoto (2016a), [29] D. Sato, Yamamoto, and Takagi (2016b), [30] D. Sato (), [31] Terakado and Nohda (), [32] D. Sato (), [33] H. Ito et al (), [34] Miyata (), [35] Shibata and Uchiumi (), [36] Seike et al (), [37] Morioka, Tainosho, and Kagami (), [38] Watanabe et al (), [39] Kawakami and Suzuki (). Detailed version of this figure is presented in supporting information…”

“…Miyazaki et al, ) that yield whole‐rock K–Ar ages of 81.2–82.7 Ma to the north of Matsuyama (Tazaki et al, ) and a fission‐track (FT) age of 80.1 ±6.4 Ma (2σ error) from the drilled core we used in this study (344.0–344.2 m depth; T. Sato et al, ). The felsic volcanic rocks (the Sennan rhyolites) yield radiometric ages of ca 80–93 Ma including errors (K–Ar ages of Shibata & Uchiumi, ; Rb–Sr ages of Terakado & Nohda, ; fission‐track ages of Seike et al, ), which occur on Awaji Island and the Kii Peninsula (Figure ).…”