Phengite megacryst quasi-exsolving phlogopite, from Sulu ultra-high pressure metamorphic terrane, Qinglongshan, Donghai County (eastern China): New data for P-T-X conditions during exhumation

On the basis of energy modelling of the reaction process from phengite to phlogopite in presence of quartz and a matter exchanger, we determined that such a transformation is weakly dependent on T over the 500-930 °C thermal range. The intersection of the calculated P-T assemblage equilibrium curve with the country rock P-T metamorphic path occurs at P ~ 2.4 ± 0.2 GPa and T ~ 700 °C, thus reflecting an early stage of exhumation, close to the metamorphic peak of the Sulu UHP terrane.