Alkali basalt from the Seifu Seamount in the Sea of Japan: post-spreading magmatism in a back-arc setting
T. Morishita,
T. Morishita,
T. Morishita,
N. Hirano,
H. Sumino,
H. Sato,
T. Shibata,
M. Yoshikawa,
S. Arai,
R. Nauchi,
A. Tamura
Affiliations
T. Morishita
Faculty of Geosciences and Civil Engineering, Kanazawa University,
Kanazawa 920-1192, Japan
T. Morishita
Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY
10964, USA
T. Morishita
Volcanoes and Earth's Interior Research Center, Japan Agency for
Marine-Earth Science and Technology, 2–15 Natsushima, Kanagawa, 237-0061,
Japan
N. Hirano
Center for Northeast Asian Studies, Tohoku University, 41 Kawauchi,
Aoba-ku, Sendai 980-8576, Japan
H. Sumino
Graduate School of Arts and Sciences, University of Tokyo, 3-8-1
Komaba, Meguro-ku, Tokyo 153-0041, Japan
H. Sato
Department of Business Administration, Senshu University, 2-1-1,
Higashimita, Tama-ku, Kawasaki, Kanagawa 214-8580, Japan
T. Shibata
Department of Earth and Planetary Systems Science, Graduate School of
Science, Hiroshima University,
1-3-2 Kagamiyama, Higashi-Hiroshima City, Hiroshima 739-8511, Japan
M. Yoshikawa
Department of Earth and Planetary Systems Science, Graduate School of
Science, Hiroshima University,
1-3-2 Kagamiyama, Higashi-Hiroshima City, Hiroshima 739-8511, Japan
S. Arai
School of Natural System, Kanazawa University, Kanazawa 920-1192,
Japan
R. Nauchi
School of Natural System, Kanazawa University, Kanazawa 920-1192,
Japan
A. Tamura
School of Natural System, Kanazawa University, Kanazawa 920-1192,
Japan
We present geochemical and 40Ar∕39Ar age data for a peridotite xenolith-bearing basalt dredged from the Seifu Seamount (SSM basalt) in the northeast Tsushima Basin, southwest Sea of Japan. An 40Ar∕39Ar plateau age of 8.33±0.15 Ma (2σ) was obtained for the SSM basalt, indicating that it erupted shortly after the termination of back-arc spreading in the Sea of Japan. The SSM basalt is a high-K to shoshonitic alkali basalt that is characterized by light rare earth element enrichment. The trace element features of the basalt are similar to those of ocean island basalt, although the Yb content is much higher, indicating formation by the low-degree partial melting of spinel peridotite. The Nd, Sr, and Pb isotopic compositions of the SSM basalt differ from those of back-arc basin basalts in the Sea of Japan. The Sr–Nd isotopic composition of the SSM basalt suggests its source was depleted mid-ocean ridge mantle containing an enriched mantle (EM1) component. The SSM basalt was formed in a post-back-arc extension setting by the low-degree partial melting of an upwelling asthenosphere that had previously been associated with the main phase of back-arc magmatism.
