Survival of majoritic garnet in diamond by direct kimberlite ascent from deep mantle

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  • Masayuki Nishi
    Department of Earth and Planetary Sciences, Graduate school of Sciences Kyushu University Fukuoka Japan
  • Tomoaki Kubo
    Department of Earth and Planetary Sciences, Faculty of Sciences Kyushu University Fukuoka Japan
  • Takumi Kato
    Department of Earth and Planetary Sciences, Faculty of Sciences Kyushu University Fukuoka Japan
  • Aiko Tominaga
    Department of Earth and Planetary Sciences, Graduate school of Sciences Kyushu University Fukuoka Japan
  • Akira Shimojuku
    Department of Earth and Planetary Sciences, Faculty of Sciences Kyushu University Fukuoka Japan
  • Naoko Doi
    Department of Earth and Planetary Sciences, Graduate school of Sciences Kyushu University Fukuoka Japan
  • Ken‐ichi Funakoshi
    Japan Synchrotron Radiation Research Institute Hyogo Japan
  • Yuji Higo
    Japan Synchrotron Radiation Research Institute Hyogo Japan

書誌事項

公開日
2010-05
資源種別
journal article
権利情報
  • http://onlinelibrary.wiley.com/termsAndConditions#vor
DOI
  • 10.1029/2010gl042706
公開者
American Geophysical Union (AGU)

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説明

<jats:p>Majoritic garnets discovered as diamond inclusion in several localities originated from the deep upper mantle or the mantle transition zone. Some of them show evidence of partial transformation to low‐pressure phases of pyropic garnet and clinopyroxene during transportation to the Earth's surface. The degree of partial transformation can be used potentially as a unique speedometer on the average ascent rate of diamond through the entire upper mantle. Here we present experimental results on the back transformation kinetics of majoritic garnet into pyropic garnet and clinopyroxene by time‐resolved in‐situ synchrotron X‐ray diffraction measurements. We observed that back transformation occurs by grain‐boundary nucleation and diffusion‐controlled growth at 6.5–7.5 GPa and 1020–1300°C. The transformation mechanisms are similar to those observed in natural diamond. The temperature dependence of diffusion‐controlled growth rates were determined from the kinetic data obtained, which was used to constrain the survival time of majoritic garnet in diamond. We found that the ascending velocity in the normal mantle convection is far too slow to satisfy the time limitation for the survival of majoritic garnet, indicating that such diamonds have been transported directly from the deep mantle by the rapid kimberlite magma within a few days.</jats:p>

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