Recalibration of the Fe-Mg exchange reaction between garnet and cordierite as a thermometer
Dwivedi, Shyam B.; Mohan, Anand; Lal, Ravindra K.
European Journal of Mineralogy Volume 10 Number 2 (1998), p. 281 - 290
published: Mar 31, 1998
manuscript accepted: Oct 13, 1997
manuscript received: Jan 24, 1996
ArtNo. ESP147051002008, Price: 29.00 €
Abstract The continuous Fe-Mg exchange reaction, 1/2 Fe-cordierite + 1/3 pyrope = 1/2 Mg-cordierite + 1/3 almandine, between garnet and cordierite is recalibrated as a thermometer. The thermodynamic parameters for this reaction are derived from experimentally determined Fe-Mg fractionation data (n= 177) in the P-T range of 650-1000°C and 4-12 kbar in the FeO-MgO-Al2O3-SiO2-H2O system. The Margules parameters for Fe-Mg binary symmetric mixing in cordierite are also derived from the experimental data by adopting WFeMg and WMgFe interaction parameters of the Fe-Mg-Ca ternary (Mukhopadhyay et al, 1997) and Fe-Mg-Ca-Mn quaternary Berman (1990) mixing models of garnet. The respective values of WFeMg of cordierite (on a onecation basis) are 2024 ±248 and 887 ± 108 joule. Based on these mixing models of garnet and derived WFeMg of cordierite, two thermodynamic equations (T1 and T2) are accordingly formulated: Application of these formulations to experimental and natural data provides better temperature estimates compared to the previous calibrations for coexisting garnet-cordierite pairs.