Kunugiza, Keitaro et al. (2017) In–situ U–Pb zircon age dating deciphering the formation event of the omphacite growth over relict edenitic pargasite in omphacite–bearing jadeitite of the Itoigawa–Omi area of the Hida–Gaien belt, central Japan, Journal of Mineralogical and Petrological Sciences, 112, 256-270, doi: 10.2465/jmps.170402a. < 20191217154351-079566 > pub

Map on Earth or stone. Places and analyses are shown.

  • abstract:

    Omphacite replacing after relic edenitic pargasite has been found in an omphacite–bearing jadeitite block of the Itoigawa–Omi area in the Hida–Gaien belt. Omphacite occurs sporadically as fine–grained aggregate reaching a few cm in length in a jadeite–albite matrix, and sometimes contains edenitic pargasite as a core. The edenitic pargasite is chemically and optically homogeneous and does not show direct contact with jadeite and albite. An irregular shaped omphacite–diopside mixed area occurs near edenitic pargasite in a coarse omphacite aggregate. The texture suggests that the breakdown of edenitic pargasite was triggered by the addition of a hydrothermal fluid, from which jadeite and albite were precipitated later, passing through diopside and omphacite by the reaction:
    NaCa2Mg5(AlSi7)O22(OH)2 → (NaAlSi2O6 + CaMgSi2O6) + CaMgSi2O6 + Mg3SiO5 + H2O.
    At the periphery of pseudomorphic omphacite, a hydrothermal fluid removed the breakdown components of the reaction other than omphacite.
    New in–situ LA–ICP–MS U–Pb dating revealed that zircons in edenitic pargasite yield apparent age up to ~ 590 Ma, with mean ages of 560 ± 16 Ma, interpreted as the minimum age of a precursor rock. A zircon age of 519 ± 21 Ma from jadeitite without omphacite corresponds to a timing of crystallization of omphacite, jadeite, and albite. The studied jadeitite is a typical R–type jadeitite, and the nearly total replacement from a precursor rock to the omphacite–bearing jadeitite has been attributed to hydrothermal activity at Middle Cambrian times.

  • doi: 10.2465/jmps.170402a
  • modified at 16 h ago
Na03 thumb NA03 < 20170217111903-746253 >pub
  • classification: metamorphic
  • physical-form: thin section
  • status: (unknown)
  • description: Hida-Gaien belt, Itoigawa-Omi area; jadeitized meta-granitic rock
  • modified at 2020-03-26
201110203a thumb 201110203A < 20170217111950-355960 >pub
  • classification: metamorphic
  • physical-form: thin section
  • status: (unknown)
  • description: Hida-Gaien belt, Itoigawa-Omi area; jadeitized meta-gabbro
  • modified at 2020-03-26
name device size global-id
203A X1-5 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102212-487657
203A X2-1 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102212-150476
203A Y1-4 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102213-371786
203A Y2-3 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102214-880484
NA03 X1-1 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102214-290540
NA03 X2-4 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102215-683024
NA03 X3-3 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102215-857001
203A Y1-1 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102213-980542
203A Y1-2 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102213-483302
203A Y1-3 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102213-726816
203A Y2-4 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102214-568664
NA03 X1-3 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102214-711882
NA03 X2-2 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102215-127320
NA03 X3-4 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102215-496768
NA03 X5-3 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102216-199805
NA03 X5-4 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102218-001367
203A Y1-5 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102213-096894
203A Y2-2 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102214-988028
NA03 X3-5 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102215-764259
NA03 X4-1 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102216-298650
NA03 X4-4 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102216-330630
NA03 X5-1 pub Q-ICP-MS Photon Machines Analyte G2 7 20191218102216-993555
name spots global-id
caption ID assembly stone
Table 2.In–situ LA–ICP MS U–Pb zircon ages of omphacite–bearing jadeitite of the Itoigawa–Omi area pub 20191218102350-370396 U-series (Kunugiza et al., 2017) 22
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  • name
  • Kunugiza, Keitaro
  • Nakamura, Eizo
  • Goto, Atsushi
  • Kobayashi, Katsura
  • Ota, Tsutomu
  • Miyajima, Hiroshi
  • Yokoyama, Kazumi