Re-evaluating the P-T-t history of the metamorphic terranes of western New England with novel thermobarometry methods

Abstract

Affinities for garnet nucleation were calculated as the difference between the free energy of a fictive garnet composition based on the matrix assemblage and the free energy of the nucleated garnet. The calculated nucleation affinity varied from 300–600 kJ/mol O for St-Ky grade samples. These results suggest that the assumption that metamorphism proceeds as a sequence of near-equilibrium conditions cannot, in general, be made for regional metamorphic terranes. This body of work agrees with numerous recent studies showing that garnet producing reactions must be overstepped in order to for garnet to nucleate.