2025-03-21 産業技術総合研究所
＜関連情報＞
- https://www.aist.go.jp/aist_j/press_release/pr2025/pr20250321/pr20250321.html
- https://www.sciencedirect.com/science/article/abs/pii/S1367912020301231
- https://www.sciencedirect.com/science/article/abs/pii/S1367912021001292
紀伊半島東部、三波川帯の堆積史と産地分析-砕屑ジルコンのU-Pb年代から Sedimentary history and provenance analysis of the Sanbagawa Belt in eastern Kii Peninsula, Southwest Japan, based on detrital zircon U–Pb ages
Sui Jia, Makoto Takeuchi
Journal of Asian Earth Sciences Available: online 11 April 2020
DOI:https://doi.org/10.1016/j.jseaes.2020.104342
Graphical abstract
Highlight
- There are four types of detrital zircon age spectra from Cretaceous accretionary complexes (AC).
- Depositional basin of the Sanbagawa AC is different to that of the Shimanto AC.
- The two ACs juxtaposed with each other by lateral-slip faulting in the Kii Peninsula.
Abstract
U–Pb isotope ages of detrital zircons from psammitic rocks of the Sanbagawa Belt in eastern Kii Peninsula, Japan, were determined by laser ablation–inductively coupled plasma–mass spectrometry. The age spectra patterns allow four sedimentary types to be distinguished on the basis of dominant zircon age proportions: Permian–Jurassic, Cretaceous, Precambrian and Mixed types. Combining the age data with geological features in the area, we subdivide this belt into the Mayoidake, Hachisu, Kayumi, and Haze complexes, with their deposition–accretion ages estimated as 116–95, 103–84, 98–76, and 76–73 Ma, respectively. The Mayoidake Complex is dominated by Permian–Jurassic-type sediments, whereas the Haze Complex is dominated by Precambrian-type sediments. Cretaceous-type and Mixed-type sediments are found in the Kayumi and Hachisu complexes. Most of the Cretaceous zircons are inferred to have been derived from a Late Cretaceous volcanic arc on the eastern margin of the Eurasian continent, whereas the Precambrian zircons are interpreted to have been sourced from basement of the North China Block. By also considering results of previous studies, we conclude that the Mayoidake Complex belongs to the neighboring Shimanto Accretionary Complex rather than the Sanbagawa Metamorphic Rocks. Furthermore, detrital zircon U–Pb age spectra for the interval 100–95 Ma differ between the Mayoidake and Hachisu complexes. This difference suggests that the depositional basin of the Sanbagawa Metamorphic Rocks was separate and lay some distance from that of the Shimanto Accretionary Complex, with the two belts finally being juxtaposed by lateral displacement along a steeply dipping strike-slip.
紀伊半島中部の三波川変成岩と四万十付加体の変形特性とピーク温度 Deformation characteristics and peak temperatures of the Sanbagawa Metamorphic and Shimanto Accretionary complexes on the central Kii Peninsula, SW Japan
Yusuke Shimura, Tetsuya Tokiwa, Hiroshi Mori, Makoto Takeuchi, Yui Kouketsu
Journal of Asian Earth Sciences Available online: 21 April 2021
DOI:https://doi.org/10.1016/j.jseaes.2021.104791
Graphical abstract
Highlights
- Deformation and temperature were examined in Cretaceous subduction complexes.
- The complex at 280–440 °C records exhumation-related deformation.
- The complex at 280–290 °C records accretion- and exhumation-related deformations.
- The two deformations occurred in different tectonic settings in the subduction zone.
- The generation of exhumation-related deformation involved ridge approach.
Abstract
Structural analyses based on field survey and peak-temperature estimations using Raman spectra of carbonaceous-material thermometry were conducted for the Cretaceous subduction complexes on the central Kii Peninsula, southwest Japan, where there is a direct contact region between the Sanbagawa high-P/low-T Metamorphic Complex (MC) and the Shimanto Accretionary Complex (AC). In the study area, the Kosoku, Iro, and Mugitani complexes are arranged in descending order of structural position. The Kosoku and Iro complexes record exhumation-related deformation, which produced schistosity, stretching lineation, and folds, and peak temperatures of 280–440 °C. In contrast, the Mugitani Complex records both earlier accretion-related deformation which produced block-in-matrix structures and later exhumation-related deformation, as well as peak temperatures of 280–290 °C. The Mugitani Complex shares deformation characteristics with both the Shimanto AC and the Sanbagawa MC, and covers the interval from the upper temperatures of the Shimanto AC to the lower temperatures of the Sanbagawa MC. In addition, the two types of deformation differ in their kinematic patterns, suggesting that they took place diachronously in different tectonic settings in the subduction zone. We propose that exhumation-related Sanbagawa deformation occurred in a warm tectonic environment, such as ridge approach to the subduction zone.
