2024/12/25 by Hiroshi Yamamoto, Hiroshi YAMAMOTO, Yukio ISOZAKI +3 · 1 citation
Computer Science · Earth and Planetary Sciences · #Geochemistry and Geologic Mapping #Geological and Geochemical Analysis #earthquake and tectonic studies
paper · pdf · doi:10.5026/jgeography.133.447
crossref issued 2024/12/25 · crossref published 2024/12/25 · crossref published-print 2024/12/25 · openalex publication_date 2024/12/25 · crossref created 2025/01/15 · crossref deposited 2025/01/18 · openalex created_date 2025/10/10 · crossref indexed 2026/07/25 · openalex updated_date 2026/07/25
The latest geological and geotectonic aspects of Tokunoshima Island in Central Ryukyus are reviewed. The pre-Quaternary basement geology of the island is two-fold; i.e., the Cretaceous accretionary complex (Amagidake and Omo units) and the high-grade metamorphic unit newly named the Inokawadake metamorphic complex (IMC). The former is correlated with the northern subbelt of the Shimanto belt in SW Japan. The IMC is composed of high-grade metamorphic rocks composed of pelitic–psammitic schists, with minor lenses of serpentinite and “dioritic gneiss” with Paleoproterozoic (ca. 1.8 Ga) zircons. In the southern half of the island, the IMC structurally overlies the Cretaceous AC as a klippe, which is separated probably by a subhorizontal fault. The IMC suffered from high-grade metamorphism up to the amphibolite facies, which is extremely rare in the Shimanto belt. A new geotectonic unit, the Tokunoshima belt, is newly proposed for the area of the IMC, which is limited to a mountainous domain in southern Tokunoshima Island. Based on the youngest detrital zircon U–Pb ages (ca. 60 Ma) from psammitic schists, the metamorphism of the IMC probably occurred in the Paleocene or later. Possible sites for the Paleocene or later heat source may include the San-in (Paleogene batholith) belt in SW Japan on the north and/or an unknown collided island arc system from the south.