Tectonic significance of P-T-t paths in metamorphic rocks: examples from Alpine and Variscan orogenic belts

The recognition of several metamorphic re-equilibration steps in a single metamorphic complex has been fruitfully app!ied to mobile or collisional belts for tracing their tectonic history. Case studies from the Alps and other orogenic belts are here reviewed. All these applications of metamorphic studies share a common strategy in selecting the samples to be considered the ones representative of the petrologic and structural history: a mesostructural evolutionary sequence is first determined, that guides the individuation of microstructural sites representing relics or advancing steps of metamorphic re-equilibration. The basic physical principles allowing this policy to be followed are mentioned and some applications of importance to the Alpine case are resumed. Construction of' P-T paths can acquire a geotectonic significance and suggest the geodynamic environment inducing the metamorphism, when established across nappe piles and confronted with current thermal models.