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Discussion papers
https://doi.org/10.5194/se-2019-116
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/se-2019-116
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 25 Jul 2019

Submitted as: research article | 25 Jul 2019

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This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Solid Earth (SE) and is expected to appear here in due course.

Alkali basalt from the Seifu seamount of the Japan Sea: post-spreading magmatism in the back-arc region

Tomoaki Morishita1,2, Naoto Hirano3, Hirochika Sumino4, Hiroshi Sato5, Tomoyuki Shibata6, Masako Yoshikawa6, Shoji Arai7, Rie Nauchi7, and Akihiro Tamura7 Tomoaki Morishita et al.
  • 1Faculty of Geosciences and Civil Engineering, Kanazawa University, Kanazawa 920-1192, Japan
  • 2Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA
  • 3Center for Northeast Asian Studies, Tohoku University, 41 Kawauchi, Aoba-ku, Sendai 980-8576, Japan
  • 4Graduate School of Arts and Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-0041, Japan
  • 5Department of Business Administration, Senshu University, 2-1-1, Higashimita, Tama-ku, Kawasaki-shi, Kanagawa 214-8580, Japan
  • 6Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, 1-3-2 Kagamiyama, Higashi-Hiroshima City, Hiroshima 739-8511, Japan
  • 7School of Natural System, Kanazawa University, Kanazawa 920-1192, Japan

Abstract. We report geochemical characteristics and Ar-Ar dating of a basalt dredged from the Seifu Seamount (SSM-basalt), located at northeast of the Tsushima Basin in the southwest Japan Sea, which is one of the western Pacific back-arc basin swarm. A plateau age of 8.33 ± 0.15 Ma (2σ) was obtained by the 40Ar-39Ar age spectrum of SSM-basalt. The SSM-basalt (8.3 Ma) was formed at an early stage after the termination of the Japan Sea back-arc opening. The SSM-basalt is high-K to shoshonitic alkaline basalt and is characterized by enrichment of light rare earth element (REE). The trace element pattern of the SSM-basalt is similar to Ocean island-type basalt (OIB) whereas YbPM (= 6) is distinctively higher than that of OIB, indicating of its formation by the low degree melting of the source mantle under spinel peridotite stability field. The Nd-Sr and Pb isotope compositions of the SSM-basalt are offset from the compositional trend of the Japan Sea back-arc basin basalts. The Sr-Nd isotope relationship of the SSM-basalt suggest its source can be formed by deplete MORB mantle source mixing with EM1-like component. The SSM basalt was formed as a post-back-arc spreading magmatism by low degree of partial melting of a portion that is easily melted in the upwelling asthenosphere associated with the main back-arc magmatism.

Tomoaki Morishita et al.
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Tomoaki Morishita et al.
Tomoaki Morishita et al.
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Short summary
We report a basalt dredged from the Seifu Seamount (SSM-basalt), located at northeast of the Tsushima Basin in the southwest Japan Sea, which is one of the western Pacific back-arc basin swarm. A plateau Ar-Ar age of 8.33 ± 0.15 Ma (2σ) was obtained by the 40Ar-39Ar age spectrum. The SSM basalt was formed as a post-back-arc spreading magmatism by low degree of partial melting of a portion that is easily melted in the upwelling asthenosphere associated with the main back-arc magmatism.
We report a basalt dredged from the Seifu Seamount (SSM-basalt), located at northeast of the...
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