Order/disorder phase transition in cordierite and its possible relationship to the development of symplectite reaction textures in granulites
MetadataShow full item record
The original publication is available at http://link.springer.com/article/10.1134%2FS0869591107050013
© Pleiades Publishing, Ltd. 2007.
Based on a consistent set of empirical interatomic potentials, static structure energy calculations of various Al/Si configurations in the supercell of Mg-cordierite and Monte Carlo simulations the phase transition between the orthorhombic and hexagonal modifications of cordierite (Crd) is predicted at 1623 K. The temperature dependences of the enthalpy, entropy, and free energy of the Al/Si disorder were calculated using the method of thermodynamic integration. The simulations suggest that the commonly observed crystallization of cordierite in the disordered hexagonal form could be related to a tendency of Al to occupy T1 site, which is driven by local charge balance. The increase in the Al fraction in the T1 site over the ratio of 2/3(T1): 1/3(T2), that characterizes the ordered state, precludes formation of the domains of the orthorhombic phase. This intrinsic tendency to the crystallization of the metastable hexagonal phase could have significantly postponed the formation of the association of orthorhombic cordierite and orthopyroxene over the association of quartz and garnet in metapelites subjected to granulite facies metamorphism. The textures of local metasomatic replacement (the formation of Crd + Opx or Spr + Crd symplectites between the grains of garnet and quartz) indicate the thermodynamic instability of the association of Qtz + Grt at the moment of the metasomatic reaction. This instability could have been caused by the difficulty of equilibrium nucleation of orthorhombic cordierite.
Showing items related by title, author, creator and subject.
Hövelmann, J.; Austrheim, H.; Putnis, Andrew (2014)The reaction between plagioclase (labradorite and oligoclase) and Mg-rich aqueous solutions was studied experimentally at hydrothermal conditions (600–700 °C, 2 kbar). During the experiments, plagioclase grains were readily ...
Mechanical and thermodynamic properties of the monoclinic andorthorhombic phases of SiC2N4 under high pressurefrom first principles*Miao, N.; Pu, C.; He, C.; Zhang, Feiwu; Lu, C.; Lu, Z.; Zhou, D. (2014)First principles calculations are preformed to systematically investigate the electronic structures, elastic and thermodynamic properties of the monoclinic and orthorhombic phases of SiC2N4 under pressure. The calculated ...
New constraints on UHT metamorphism in the Eastern Ghats Province through the application of mineral equilibria modelling and in situ geochronologyKorhonen, Fawna; Saw, A.; Clark, Christopher; Brown, M.; Bhattacharya, S. (2011)High Mg–Al granulites from the Sunki locality in the central portion of the Eastern Ghats Province record evidence for the high-temperature peak and retrograde evolution. Peak metamorphic phase assemblages from two samples ...