Geothermometry and geobarometry

Herzberg C. T. (1978b). Pyroxene geothermometry and geobarometry Experimental and thermodynamic evaluation of some subsolidus phase relations involving pyroxenes in the system CaO-MgO-AljOj-SiOj. Geochim. Cosmochim. Acta, 42 945-957. 

Ross M. and Huebner J. S. (1975). A pyroxene geothermometer based on composition temperature relationship of naturally occurring orthopyroxene, pigeonite and augite. In International Conference on Geothermometry and Geobarometry, The Pennsylvania State University. 

As an example, the phase diagram of the aluminosilicate Al2Si05 minerals sillimanite, andalusite and kyanite is important in geothermometry and geobarometry. The transformations amongst the pol)miorphs involve a change in coordination of one of the aluminium atoms, which is tetrahedral in sillimanite, five-coordinated in andalusite and octahedral in kyanite. The observed (from 0.25 mol) and calculated INS spectra [10] are shown in Fig. 11.5a and 11.5b. The individual... 

In situations where trace element abimdance variations are large, the use of these distribution coefficients will certainly help to limit the possible ways in which the variations were generated. The fact that these distribution coefficients, particularly the Berthelot-Nernst coefficients, vary with P, T and composition, greatly limits their usefulness in situations where the variations in trace element chemistry are more subtle as could arise from P and T variations. For geothermometry and geobarometry, it is necessary to calculate true equilibrium constants and some possible approaches to this problem have been discussed here. 

Chiodini, G., Cioni, R., Guidi, M., and Marini, L. (1991) Chemical geothermometry and geobarometry in hydrothermal aqueous solutions. A theoretical investigation based on a mineral-solution equilibrium model. Geochim. Cosmochim. Acta, 55, 2709-2727. 

Metamorphic facies is a more sophisticated extension of the grade concept to include pressure (i.e., geobarometry) as well as temperature (i.e., geothermometry) in the interpretation of metamorphic rocks. The indicator minerals become groups of minerals or mineral assemblages that characterize a particular region of pressure and temperature. 

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