Preprints
https://doi.org/10.5194/sed-4-203-2012
https://doi.org/10.5194/sed-4-203-2012

  27 Jan 2012

27 Jan 2012

Review status: this preprint was under review for the journal SE but the revision was not accepted.

Possibility of titanium transportation within a mantle wedge: formation process of titanoclinohumite in Fujiwara dunite in Sanbagawa belt, Japan

S. Ishimaru1,2 and S. Arai2 S. Ishimaru and S. Arai
  • 1Guraduate School of Science and Technology, Department of Earth and Environmental Sciences, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860–8555, Japan
  • 2Earth Science Course, School of Natural System, College of Science and Engineering, Kanazawa University, Kakuma, Kanazawa 920–1192, Japan

Abstract. Titinoclinohumite-bearing dunites from Fujiwara, the Sanbagawa metamorphic belt of high-pressure type, Japan, were described to examine the possibility of Ti mobility during metasomatism within the mantle wedge. The Fujiwara dunite body and surrounding high-pressure Sanbagawa schists possibly form a subduction complex, and the dunites are a good analogue to the mantle wedge overlying the slab. The Fujiwara dunites are of deserpentinization origin; the deserpentinized olivine is high in Fo (up to 96) and low in NiO (0.2 to 0.3 wt %), and contains magnetite inclusions. Titanoclinohumites are associated with the deserpentinized olivine, as lamellar intergrowth or veinlets, up to 1 cm in width. Other metamorphic minerals include antigorite, brucite, chlorite, ilmenite, perovskite, Ti-rich ludwigite, and carbonates. The protolith of the Fujiwara dunite was partially serpentinized cumulative dunites from intra-plate magma, containing relatively low-Fo (85 to 86) olivines and TiO2-rich (up to 3 wt %) chromian spinels. The metamorphic olivines and titanoclinohumites contain micro-inclusions of methane (CH4) with or without serpentine and brucite. The source of Ti for titanoclinohumite was possibly the Ti-rich chromian spinel, but Ti was mobile through hydrocarbon-rich fluids, which were activated during the metamorphism. The hydrocarbons, of which remnants are carbonates and methane micro-inclusions, were derived from carbonaceous materials or bitumen, possibly incorporated in the precursory serpentinized and brecciated peridotite (= the protolith for the Fujiwara dunites) before subduction. Ti can be mobile in the mantle wedge if hydrocarbons are available from the subducted slab.

S. Ishimaru and S. Arai

 
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

S. Ishimaru and S. Arai

S. Ishimaru and S. Arai

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