Progressive metamorphism of the Taitao ophiolite; evidence for axial and off-axis hydrothermal alterations

Takazo Shibuya, Tsuyoshi Komiya, Ryo Anma, Tsutomu Ota, Soichi Omori, Yoshiaki Kon, Shinji Yamamoto, Shigenori Maruyama

    Research output: Contribution to journalArticlepeer-review

    22 Citations (Scopus)


    We estimated metamorphic conditions for the ∼ 6 Ma Taitao ophiolite, associated with the Chile triple junction. The metamorphic grade of the ophiolite, estimated from secondary matrix minerals, changes stratigraphically downwards from the zeolite facies, through the prehnite-actinolite facies, greenschist facies and the greenschist-amphibolite transition, to the amphibolite facies. The metamorphic facies series corresponds to the low-pressure type. The metamorphic zone boundaries are subparallel to the internal lithological boundaries of the ophiolite, indicating that the metamorphism was due to axial hydrothermal alteration at a mid-ocean ridge. Mineral assemblages and the compositions of veins systematically change from quartz-dominated, through epidote-dominated, to prehnite-dominated with increasing depth. Temperatures estimated from the vein assemblages range from ∼ 230 °C in the volcanic unit to ∼ 380 °C at the bottom of the gabbro unit, systematically ∼ 200 °C lower than estimates from the adjoining matrix minerals. The late development of veins and the systematically lower temperatures suggest that the vein-forming alteration was due to off-axis hydrothermal alteration. Comparison between the Taitao ophiolite with its mid-ocean ridge (MOR) affinity, and other ophiolites and MOR crusts, suggests that the Taitao ophiolite has many hydrothermal alteration features similar to those of MOR crusts. This is consistent with the tectonic history that the Taitao ophiolite was formed at the South Chile ridge system near the South American continent (Anma, R., Armstrong, R., Danhara, T., Orihashi, Y. and Iwano, H., 2006. Zircon sensitive high mass-resolution ion microprobe U-Pb and fission-track ages for gabbros and sheeted dykes of the Taitao ophiolite, Southern Chile, and their tectonic implications. The Island Arc, 15(1): 130-142).

    Original languageEnglish
    Pages (from-to)233-260
    Number of pages28
    Issue number1-4
    Publication statusPublished - Oct 2007


    • Axial and off-axis hydrothermal alteration
    • Hydrothermal metamorphism
    • Mid-ocean ridge system
    • Ophiolite
    • Ridge subduction
    • Taitao

    ASJC Scopus subject areas

    • Geology
    • Geochemistry and Petrology


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