TY - JOUR
T1 - Survival of pyropic garnet in subducting plates
AU - Nishi, Masayuki
AU - Kato, Takumi
AU - Kubo, Tomoaki
AU - Kikegawa, Takumi
N1 - Funding Information:
We thank A. Tominaga for assistance with in situ X-ray diffraction experiments and S. Uehara and A. Shimojuku for their helpful discussions and useful comments. We also acknowledge D.C. Rubie, E Ohtani, and two anonymous referees for valuable comments. In situ X-ray diffraction experiments were carried out using the MAX-III system at BL14C of the Photon Factory (Proposal no. 2004G225). This work was supported by a Front Researcher Development program of Kyushu University, and by a Grant-in-Aid for Scientific Research to T.K. from the Japan Society for the Promotion of Science.
PY - 2008/11
Y1 - 2008/11
N2 - An experimental study has been conducted to clarify the conditions and kinetic aspects of the pyroxene-garnet transformation by using synthetic polycrystals (two pyroxenes + garnet) in the CaO-MgO-Al2O3-SiO2 system. The run products recovered from the in situ X-ray diffraction experiments in a double-stage multi-anvil system at 15.5-20.4 GPa and 800-1600 °C were carefully analyzed by scanning electron microscopy. Our results show that the pyroxene-garnet transformation proceeds by overgrowth of garnet absorbing the surrounding pyroxene components above 1550 °C. At 18.4 GPa and 1320 °C, pyroxenes (enstatite + diopside) directly decomposed to the assemblages (wadsleyite + stishovite + Ca-perovskite) without dissolving in garnet. The pyroxene-garnet transformation requires much higher temperatures than those needed for transformation of olivine to wadsleyite (∼1000 °C) and of pyroxenes to their high-pressure phases (∼1300 °C) in laboratory time (∼103 s) and grain (∼10-5 m) scales. Therefore, the pyroxene-garnet transformation is likely to be kinetically inhibited at low temperatures in the subducting plate, and the pyropic garnet could survive in the transition zone instead of equilibrium majoritic garnet.
AB - An experimental study has been conducted to clarify the conditions and kinetic aspects of the pyroxene-garnet transformation by using synthetic polycrystals (two pyroxenes + garnet) in the CaO-MgO-Al2O3-SiO2 system. The run products recovered from the in situ X-ray diffraction experiments in a double-stage multi-anvil system at 15.5-20.4 GPa and 800-1600 °C were carefully analyzed by scanning electron microscopy. Our results show that the pyroxene-garnet transformation proceeds by overgrowth of garnet absorbing the surrounding pyroxene components above 1550 °C. At 18.4 GPa and 1320 °C, pyroxenes (enstatite + diopside) directly decomposed to the assemblages (wadsleyite + stishovite + Ca-perovskite) without dissolving in garnet. The pyroxene-garnet transformation requires much higher temperatures than those needed for transformation of olivine to wadsleyite (∼1000 °C) and of pyroxenes to their high-pressure phases (∼1300 °C) in laboratory time (∼103 s) and grain (∼10-5 m) scales. Therefore, the pyroxene-garnet transformation is likely to be kinetically inhibited at low temperatures in the subducting plate, and the pyropic garnet could survive in the transition zone instead of equilibrium majoritic garnet.
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U2 - 10.1016/j.pepi.2008.03.013
DO - 10.1016/j.pepi.2008.03.013
M3 - Article
AN - SCOPUS:54049093630
SN - 0031-9201
VL - 170
SP - 274
EP - 280
JO - Physics of the Earth and Planetary Interiors
JF - Physics of the Earth and Planetary Interiors
IS - 3-4
ER -