Armel Menant (Université de Nice)

Whereas long-term deformations in subduction zones are usually considered as stable over Myr-long periods, an increasing number of observations suggest a long-term pulsing evolution of active margins. To appraise this emerging view of a highly dynamic subduction system and identify the driving mechanisms, detailed studies on now-exhumed, high pressure-low temperature (HP-LT) accretionary complexes are crucial as they open a window on the deformation history from the plate interface to the surface.

In this study, we combine structural and petrological observations, Raman spectroscopy on carbonaceous material, Rb/Sr multi-mineral geochronology and thermo-mechanical models to unravel with an unprecedented resolution the tectono-metamorphic evolution of the Late-Cenozoic HP-LT nappe stack cropping out in western Crete (Hellenic subduction zone). In light of these results, we propose that a succession of basal-accretion events triggered (i) pulses in the strain rate, sometimes associated with a switch of the stress regime (i.e., compressional/extensional) and (ii) vertical surface oscillations eventually resulting in the growth of a high forearc topography. This accretion-controlled, Myr-scale tectonic and topographic signal plays a part in active deformations monitored at active margins, though it may remain invisible to most of geodetic methods because of superimposed shorter-timescale transients, such as seismic-cycle-related events.