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Solid Earth An interactive open-access journal of the European Geosciences Union

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doi:10.5194/sed-4-203-2012
© Author(s) 2012. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
27 Jan 2012
Review status
This discussion paper has been under review for the journal Solid Earth (SE). The revised manuscript 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 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.

Citation: Ishimaru, S. and Arai, S.: Possibility of titanium transportation within a mantle wedge: formation process of titanoclinohumite in Fujiwara dunite in Sanbagawa belt, Japan, Solid Earth Discuss., 4, 203-239, doi:10.5194/sed-4-203-2012, 2012.
S. Ishimaru and S. Arai
S. Ishimaru and S. Arai

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