TY - JOUR
T1 - Exsolution kinetics of majoritic garnet from clinopyroxene in subducting oceanic crust
AU - Nishi, Masayuki
AU - Kubo, Tomoaki
AU - Kato, Takumi
AU - Tominaga, Aiko
AU - Funakoshi, Ken ichi
AU - Higo, Yuji
N1 - Funding Information:
We thank S. Uehara and A. Toramaru for their helpful discussions and useful comments. We also acknowledge A. Shimojuku and N. Doi for their support with the in situ X-ray diffraction experiments. Constructive reviews by J. Ganguly and an anonymous referee were helpful in improving the manuscript. M. Nishi was supported by Research Fellowships of the Japan Society for the Promotion of Science for Young Scientists. This work was partially supported by a Front Researcher Development Program of Kyushu University and by a Grant-in-Aid for Scientific Research to T. Kubo from the Ministry of Education, Culture, Sports, Science, and Technology, Japan. In situ X-ray diffraction experiments were carried out at BL04B1 of SPring-8 (Proposal No. 2008A1716).
PY - 2011/11
Y1 - 2011/11
N2 - Mechanisms and kinetics of exsolution of majoritic garnet from Ca-Tschermak-rich clinopyroxene were examined at 14.0-15.6GPa, 1250-1590°C, and H2O-undersaturated conditions (800-1170wt. ppm H2O) by time-resolved in situ synchrotron X-ray diffraction measurements. Textural observations of recovered samples revealed that majoritic garnet had exsolved along the grain boundaries of parent clinopyroxene. Analyses of the kinetic data obtained indicate that exsolved majoritic garnet grew by diffusion-controlled growth, and the growth kinetics can be described by k2 (m2/s)=7.4×10-5 exp[-389(kJmol-1)/RT]. The exsolution of majoritic garnet from clinopyroxene would be kinetically inhibited at temperatures below ∼800°C in geological time scales (105-106years) when the parent grain size is larger than 1mm. We constructed possible phase relations of subducting mid-ocean ridge basalt (MORB) taking the exsolution kinetics into consideration. When the effect of reaction kinetics is considered, the density contrast between the MORB component of a subducting slab and surrounding mantle becomes significantly reduced relative to that calculated for the equilibrium MORB assemblage.
AB - Mechanisms and kinetics of exsolution of majoritic garnet from Ca-Tschermak-rich clinopyroxene were examined at 14.0-15.6GPa, 1250-1590°C, and H2O-undersaturated conditions (800-1170wt. ppm H2O) by time-resolved in situ synchrotron X-ray diffraction measurements. Textural observations of recovered samples revealed that majoritic garnet had exsolved along the grain boundaries of parent clinopyroxene. Analyses of the kinetic data obtained indicate that exsolved majoritic garnet grew by diffusion-controlled growth, and the growth kinetics can be described by k2 (m2/s)=7.4×10-5 exp[-389(kJmol-1)/RT]. The exsolution of majoritic garnet from clinopyroxene would be kinetically inhibited at temperatures below ∼800°C in geological time scales (105-106years) when the parent grain size is larger than 1mm. We constructed possible phase relations of subducting mid-ocean ridge basalt (MORB) taking the exsolution kinetics into consideration. When the effect of reaction kinetics is considered, the density contrast between the MORB component of a subducting slab and surrounding mantle becomes significantly reduced relative to that calculated for the equilibrium MORB assemblage.
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U2 - 10.1016/j.pepi.2011.07.002
DO - 10.1016/j.pepi.2011.07.002
M3 - Article
AN - SCOPUS:80955135034
SN - 0031-9201
VL - 189
SP - 47
EP - 55
JO - Physics of the Earth and Planetary Interiors
JF - Physics of the Earth and Planetary Interiors
IS - 1-2
ER -