Deformation vs. metamorphic re-equilibration heterogeneities in polymetamorphic rocks : a key to infer quality P-T-d-t path

The interaction between fabric gradients and reaction rate as a tool for individuating volumes carrying the longest «rock memory» is discussed through some examples from continental units of the Alpine chain. Here quality P-T-d-t paths have been inferred using a sampling strategy based on reconstruction of the metamorphic evolution, supported by a regionally valid deformation history and on the choice of sites for investigations on compositional variations, where mineral growth and sequences of overprinting fabrics are known. The examples show that correlation between degree of fabric evolution and progress of metamorphic transformation is positive and influence of strain partitioning on tectono-thermal rock memory must be taken into account during P-T-d-t reconstruction to avoid errors in determining the sequence of P-T re-equilibration steps and to obtain clustered P-T estimates relative to each step.