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<p>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&#xa0;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.</p><p></p>

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Melt-poor spreading in the Shikoku back-arc basin: widespread occurrence of oceanic core complexes and associated features

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月21日

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  • Yasuhiko Ohara,
  • Kyoko Okino,
  • Norikatsu Akizawa,
  • Valentin Basch,
  • Marco Cuffaro,
  • Masakazu Fujii,
  • Yumiko Harigane,
  • Ken-ichi Hirauchi,
  • So Inoue,
  • Osamu Ishizuka,
  • Shiki Machida,
  • Katsuyoshi Michibayashi,
  • Takaaki Moriguchi,
  • Kohei Nimura,
  • Ryosuke Oyanagi,
  • Alessio Sanfilippo,
  • Camilla Sani,
  • Atlanta Sen,
  • Jonathan E. Snow,
  • Kenichiro Tani,
  • Hiroyuki Yamashita

摘要

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.