A series of isothermal annealing experiments at 750°C has been carried out on an orthopyroxene single crystal from Johnstown diogenite containing (100) exsolved augite lamellae and Gp zones. After each annealing experiment the Fe-Mg ordering degree has been measured by X-ray single-crystal diffraction. The disordering rate constant, calculated using Mueller's equation (Mineralogical Society American Special Paper, 2, 83-93, 1969.), resulted to be K+ = 0.00116 min-1. This value is much lower than that expected on the basis of the relation derived by Ganguly and Tazzoli (American Mineralogist, 79, 930-937, 1994.) using all the previous data available in literature. This suggests an influence of exsolutions on the kinetics of the Fe-Mg exchange reaction in orthopyroxene.
Do exsolutions influence the kinetics of the order-disorder reaction in orthopyroxene?
M. Zema
;
1999-01-01
Abstract
A series of isothermal annealing experiments at 750°C has been carried out on an orthopyroxene single crystal from Johnstown diogenite containing (100) exsolved augite lamellae and Gp zones. After each annealing experiment the Fe-Mg ordering degree has been measured by X-ray single-crystal diffraction. The disordering rate constant, calculated using Mueller's equation (Mineralogical Society American Special Paper, 2, 83-93, 1969.), resulted to be K+ = 0.00116 min-1. This value is much lower than that expected on the basis of the relation derived by Ganguly and Tazzoli (American Mineralogist, 79, 930-937, 1994.) using all the previous data available in literature. This suggests an influence of exsolutions on the kinetics of the Fe-Mg exchange reaction in orthopyroxene.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
