Exploitation methods of the metamorphic rock memory in the continental crust of orogenic belts to infer subduction history

The narrow axial zone of collisional belts, where ocean closure apparently generates the highest tectonic complexity, paradoxically provides in the petro-structural memory of polydeformed tectonites structural and petrological data critical to undertake on a new physical base the reconstruction of nappe trajectories. As a matter of fact, subduction-collision zones are characterized by repeated coupling and decoupling of lithospheric slices, acting in competition during building up of tectonic units of a metamorphic belt. Contours of these mobile units are transient and can be inferred integrating structural and petrologic analysis. Due to its propensity to be exhumed, continental crust in such a scenario represents the repository of rocks characterised by the longest memory preserving, in the same structural domain, tectonic and metamorphic imprints recorded during superposed subduction cycles. This makes continental crust, repeatedly forged along active margins, a key to unravel significant variations in thermal state and mechanical devices along subduction zones through time. Due to competing amalgamation and disaggregation of lithospheric slices in the construction of the tectonic architecture of subduction-collision belts, the reconstruction of the structural and metamorphic history requires an integrated field and laboratory approach implying geometrical and kinematic analysis of tectonic units, together with a joint reconstruction of quantitative P-T-d-t paths. The inferred translational trajectories and shape changes during P-prograde and P-retrograde paths are characterised by a marked thermo-tectonic connotation that, through the comparison with numerical modelling predictions, can shed light on the still largely unknown aspects (e.g. burial and exhumation of continental crust during oceanic subduction) of the deep dynamics of subduction systems.