TY - JOUR
T1 - Thermodynamic modelling of sodic pyroxene solid-solution and its application in a garnet-omphacite-kyanite-coesite geothermobarometer for UHP metamorphic rocks
AU - Nakamura, Daisuke
AU - Banno, Shohei
N1 - Funding Information:
Acknowledgements We would like to thank Dr. T. Hirajima for his helpful suggestions and offering his precious sample from the Dora Maira Massif. We also thank Dr. S. Wallis for his critical reading, Dr. T. Mori for his useful advice, H. Tsutumi and K. Yoshida for making of thin sections. Critical comments from Prof. M.A. Carpenter and Prof. N.D. Chatterjee are gratefully acknowledged. The sample from Rongcheng County used in this study was collected as part of a cooperative project between Kyoto University and Academia Sinica supported by JSPS and CNNSF, and we also thank the members of the project, Dr. M. Enami, Dr. A. Ishiwatari, Dr. K. Ye and the other members, for their discussion and advice. This study was supported financially in part by a JSPS Research Fellowship for Young Scientists.
PY - 1997
Y1 - 1997
N2 - A garnet-omphacite-kyanite-coesite geothermobarometer is constructed to estimate the peak metamorphic pressure of ultrahigh-pressure (UHP) eclogites. For this we use a quaternary regular solution model for garnet, and propose a new model for sodic pyroxene that assumes double site solid-solution (Na,Ca)M2(Al,Fe3+,Fe2+,Mg)M1Si2O6, where cations in the M2- and the M1-sites mix randomly but with intersite interactions, not only between nearest neighboring cations but also bewteen next nearest neighboring cations. In the new model, overall excess interaction parameters are quantitatively deduced from the previous experimental data and critical temperature, and the activity of the jadeite component agrees reasonbly with that based on the Landau theory. Furthermore, the relations of the calculated order parameter to temperature and composition are consistent with other experimental works. These facts support the usefulness of the new model. Application of our geothermobarometer to kyanite eclogite gave metamorphic conditions around 3.4 GPa and 800°C for both samples from the Dora Maira Massif, Western Alps, and from Rongcheng County, in the Su-Lu region of Eastern China.
AB - A garnet-omphacite-kyanite-coesite geothermobarometer is constructed to estimate the peak metamorphic pressure of ultrahigh-pressure (UHP) eclogites. For this we use a quaternary regular solution model for garnet, and propose a new model for sodic pyroxene that assumes double site solid-solution (Na,Ca)M2(Al,Fe3+,Fe2+,Mg)M1Si2O6, where cations in the M2- and the M1-sites mix randomly but with intersite interactions, not only between nearest neighboring cations but also bewteen next nearest neighboring cations. In the new model, overall excess interaction parameters are quantitatively deduced from the previous experimental data and critical temperature, and the activity of the jadeite component agrees reasonbly with that based on the Landau theory. Furthermore, the relations of the calculated order parameter to temperature and composition are consistent with other experimental works. These facts support the usefulness of the new model. Application of our geothermobarometer to kyanite eclogite gave metamorphic conditions around 3.4 GPa and 800°C for both samples from the Dora Maira Massif, Western Alps, and from Rongcheng County, in the Su-Lu region of Eastern China.
UR - http://www.scopus.com/inward/record.url?scp=0031389814&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0031389814&partnerID=8YFLogxK
U2 - 10.1007/s004100050352
DO - 10.1007/s004100050352
M3 - Article
AN - SCOPUS:0031389814
SN - 0010-7999
VL - 130
SP - 93
EP - 102
JO - Contributions of Mineralogy and Petrology
JF - Contributions of Mineralogy and Petrology
IS - 1
ER -