Melt-poor spreading in the Shikoku back-arc basin: widespread occurrence of oceanic core complexes and associated features
Abstract The Shikoku Basin, a Miocene back-arc basin in the Philippine Sea, hosts numerous oceanic core complexes (OCCs) that reflect melt-poor lithospheric extension. Based on bathymetric mapping, gravity and magnetic surveys, dredging, and submersible dives conducted between 2007 and 2023, we identified multiple OCCs in its southern part, including the Mado, Sui-Shin, Tosa, Sanuki, and Awa Megamullions. These OCCs expose mantle and lower crustal rocks and are associated with high mantle Bouguer anomalies, indicating thin crust. Geochemical and geochronological data from the Sui-Shin Megamullion suggest its formation immediately after rifting of the proto-Izu-Bonin arc (~24 Ma). The Tosa Megamullion, dominated by plagioclase-peridotites with only minor gabbros, exemplifies melt-poor lithospheric conditions and may represent Hess-type oceanic crust. The spatial and temporal distribution of OCCs, including the triplet OCCs (Tosa, Sanuki, and Awa), implies multiple ridge jumps during basin evolution. These findings suggest that a significant portion of the Shikoku Basin formed largely through amagmatic or melt-poor processes, contrasting with typical mid-ocean ridge settings. The OCCs serve as tectonic windows into back-arc lithosphere evolution and provide a framework for future investigations into the role of melt supply and slab-derived fluids in shaping oceanic crustal architecture.
Authors
- Camilla Sani
- Valentin Basch (ORCID: https://orcid.org/0000-0002-0069-4490)
- Kohei Nimura (ORCID: https://orcid.org/0000-0002-6492-9498)
- Yumiko Harigane (ORCID: https://orcid.org/0000-0002-8133-0700)
- Marco Cuffaro (ORCID: https://orcid.org/0000-0003-0626-1378)
- J. E. Snow (ORCID: https://orcid.org/0000-0003-4244-7700)
- Kenichiro Tani (ORCID: https://orcid.org/0000-0003-3374-8608)
- Kyoko Okino (ORCID: https://orcid.org/0000-0001-7070-7982)
- Alessio Sanfilippo (ORCID: https://orcid.org/0000-0002-4112-3643)
- Ken‐ichi Hirauchi (ORCID: https://orcid.org/0000-0002-5318-4646)
- Hiroyuki Yamashita (ORCID: https://orcid.org/0009-0009-3037-6862)
- Atlanta Sen (ORCID: https://orcid.org/0000-0001-9232-5088)
- Katsuyoshi Michibayashi (ORCID: https://orcid.org/0000-0003-1845-7298)
- So Inoue
- Takaaki Moriguchi
- Ryosuke Oyanagi
- Masakazu Fujii
- Osamu Ishizuka
- Shiki Machida
- Yasuhiko Ohara (ORCID: https://orcid.org/0000-0002-9567-0802)
- Norikatsu Akizawa
Institutions
- Hiroshima University (JP)
- Louisiana State University (US)
- Shizuoka University (JP)
- Japan Agency for Marine-Earth Science and Technology (JP)
- Kokushikan University (JP)
- University of Pavia (IT)
- Service Hydrographique et Océanographique de la Marine (FR)
- National Institute of Polar Research (JP)
- Institute of Environmental Geology and Geoengineering (IT)
- Kanagawa Prefectural Museum of Natural History (JP)
- Geological Survey of Japan (JP)
- National Museum of Nature and Science (JP)
- University of Houston (US)
- Nagoya University (JP)
- The University of Tokyo (JP)
- Chiba Institute of Technology (JP)
Publication Details
- Journal
- Progress in Earth and Planetary Science
- Published
- 2026-05-21
- DOI
- https://doi.org/10.1186/s40645-026-00818-7
- Citations
- 1
- Primary Topic
- Geological and Geochemical Analysis
- Type
- article
- Field-Weighted Citation Impact
- 19.70
Funders
- Louisiana State University
- Research Organization of Information and Systems
- Ministero dell’Istruzione, dell’Università e della Ricerca
- Consiglio Nazionale delle Ricerche
- Office of Research and Economic Development, Louisiana State University
- Japan Society for the Promotion of Science
- Japan Agency for Marine-Earth Science and Technology