In the central sector of the Sanandaj-Sirjan zone of Iran, the Triassic-to-Jurassic ‘Hamedan Phyllites’ metamorphic complex shows a polymetamorphic evolution characterised by a main Barrovian- to Buchan-type garnet+staurolite+kyanite/andalusite regional sequence, locally overprinted by a low-pressure thermal event generated by vigorous Jurassic magmatic activity and the emplacement of voluminous composite plutonic complexes (e.g., Alvand). In this work, we explore the Hamedan phyllites envel- oping the Jurassic Alvand granite batholith, particularly in the eastern sector at the transition from cordierite-bearing hornfels to staurolite-bearing schists. In this study, we present for the first time the textural characterisation and mineral chemistry of a previously undescribed minor population of post-kinematic Mn-rich garnet from the staurolite schists. We developed phase equilibria modelling to define the pressure-temperature condition of its genesis. We then integrated the existing literature on metapelites from the study area to develop new thermobarometric models with those data to propose a revised evolution of the metapelites enveloping the Alvand batholith and the extent of its contact aureole. On a wider scale, this study provides evidence for the relevance of garnet, as chemical-physical archive, in deciphering complex polymetamorphic histories where thermal events affect previously regional metamorphosed rocks under relatively hot gradients.

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