Sequential deformation from serpentinite mylonite to metasomatic rocks along the Sashu Fault, SW Japan

Yusuke Soda, Hideo Takagi

    Research output: Contribution to journalArticle

    33 Citations (Scopus)

    Abstract

    The deformation of serpentinites along the Sashu Fault, Saganoseki Peninsula, SW Japan, involved both mylonitization and brecciation. The brecciation was accompanied by metasomatism, and the metasomatized rocks record additional ductile deformation. Serpentinite mylonite is composed mainly of antigorite, with minor magnetite and Cr-spinel. Foliation and lineation in this rock type are defined by the shape preferred orientation of antigorite and the alignment of fine-grained magnetite and carbonate minerals. The antigorite also shows a lattice preferred orientation (LPO), as measured with a universal stage, with c axes oriented near-perpendicular to the foliation and b axes oriented parallel to the lineation. Brecciation is concentrated in the reaction zone along the boundary between serpentinites and surrounding country rocks. Talc and chlorite schists developed in this zone as a result of associated metasomatism and deformation; consequently, they contain composite planar fabrics and drag folds. The breccias themselves are composed of serpentinite fragments cut by veins of calcite and talc. Analyses of fluid inclusions in calcite from the breccia indicate that brecciation occurred at 200-300 °C at depths of 3.8-11.8 km. Metasomatic reactions, particularly the formation of talc, contributed to weakening of this serpentinite-bearing fault zone.

    Original languageEnglish
    Pages (from-to)792-802
    Number of pages11
    JournalJournal of Structural Geology
    Volume32
    Issue number6
    DOIs
    Publication statusPublished - 2010 Jun

    Fingerprint

    metasomatic rock
    antigorite
    mylonite
    serpentinite
    talc
    preferred orientation
    lineation
    metasomatism
    foliation
    magnetite
    calcite
    mylonitization
    ductile deformation
    country rock
    breccia
    rock
    spinel
    schist
    fluid inclusion
    drag

    Keywords

    • LPO of antigorite
    • Metasomatic rocks
    • Serpentinite breccia
    • Serpentinite mylonite

    ASJC Scopus subject areas

    • Geology

    Cite this

    Sequential deformation from serpentinite mylonite to metasomatic rocks along the Sashu Fault, SW Japan. / Soda, Yusuke; Takagi, Hideo.

    In: Journal of Structural Geology, Vol. 32, No. 6, 06.2010, p. 792-802.

    Research output: Contribution to journalArticle

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