Setting the sequence of deep slicing events along the Hellenic subduction zone from the P-T-t evolution of the HP-LT Cretan paleo-accretionary duplex (Greece)

Subduction dynamics in the Mediterranean realm is largely controlled by the Eurasia-Africa convergence and by the protracted accretion, since the late Cretaceous, of successive oceanic domains and microcontinents to the overriding Eurasian margin. Among these processes, basal accretion of coherent tectonic slices at the base of the forearc domain is one of the most difficult to investigate, as it occurs at high depth along the subduction interface and is only rarely preserved in the geological record. Yet, basal accretion is of prime importance, as it is suspected to remain active beneath active Mediterranean subduction zones and to contribute to the deformation and topographic signals monitored along them. To assess the spatial and temporal scales of the accretion-controlled forearc dynamics, it is therefore crucial to constrain the sequence of slicing episodes forming deep accretionary duplexes.

We address this issue through an integrated structural, petro-metamorphic and geochronological study of a high-pressure/low-temperature paleo-duplex exposed in western Crete and formed along the Hellenic subduction zone during the Oligocene–Miocene. We combine field-based structural mapping, petrological characterization, Raman spectroscopy on carbonaceous material, thermodynamic modelling, Rb/Sr multi-mineral geochronology and zircon (U–Th–Sm)/He thermochronology to identify distinct tectono-metamorphic slices, quantify their peak pressure–temperature conditions and constrain their timing of accretion and exhumation.

Our results reveal a dome-shaped nappe stack composed of five tectono-metamorphic units bounded by major shear zones, with a systematic down-stepping of peak temperatures (~450 to ~350 °C), pressures (17–18 to 7–8.5 kbar) and Rb/Sr ages (~26 Ma and ~15 Ma) toward lower structural levels. These indicate five basal-accretion episodes that successively migrated to shallower depths (~55–60 km to ~25–30 km) between the late Oligocene and middle Miocene. Subsequent fast exhumation of the duplex, with rates of ~3-11 mm/yr, decreasing to ~2-4 mm/yr at shallow levels, was mainly accommodated by top-to-the-N and subordinate top-to-the-S detachments associated with trench-perpendicular extension, intermittently overprinted by trench-parallel deformation.

This study further suggests a sequence of ~2-3-Myr-long deep slicing events, providing a critical timescale for trackingthe tectonic and topographic signatures of deep mass fluxes along active forearc margins in the Mediterranean region and beyond.