Taking advantage of petrostructural heterogeneities in subduction-collisional orogens, and effect on the scale of analysis

Since the beginning of the last century, tectonic history of polyphase metamorphic tectonites of orogenic basement complexes is often related to primary links with metasediments, of presumably known origin, and location of their original basins. However such history is worth to be compared with results of an alternative and independent investigation that pursues: i) an objective reconstruction of the evolutionary steps modifying the lithostratigraphic setting and of its deformation-metamorphism interactions during plate-scale events and ii) a privileged reconstruction of the rock memory for the structural and metamorphic correlation of crystalline basement units. Interpretative merging of data gathered from these affine rock properties made interpretations of orogenic zones more actualistic and based on recognition of tectonic trajectories of units through evolving geodynamic contexts. In this account a refinement of the analytical approach to inferring deformation and metamorphic paths and constructing geological histories of basements in axial zones of orogenic belts is presented and examples are synthesised from the Western Alps and the Canadian Cordillera, based on detailed structural and lithostratigraphic mapping in harmony with macro- and micro-structural techniques of analysis, are reported from the two belts.