Setting the Sequence of Slicing Events Along Deep Subduction Interfaces: 1. The Tectonic and Thermal Structure of the High-P Duplex in Western Crete (Hellenic Margin)
Résumé
Basal accretion at active subduction margins occurs through a series of tectonic slicing events at varying depths along the plate interface, shaping the forearc domain. To assess the spatial and temporal scale of the accretion-controlled forearc dynamics, it is crucial to constrain the sequence of basal-accretion episodes that form deep accretionary duplexes. This requires identifying the successive tectono-metamorphic units constituting paleo-duplexes and dating the accretion and exhumation events that expose high-pressure rocks at the surface. This, the first of two companion papers in this issue of Tektonika, presents a detailed reconstruction of the tectonic and thermal structure of a high-pressure/low-temperature paleo-accretionary duplex in western Crete (Greece) that formed along the active Hellenic margin during the Oligocene-Miocene. Combining field observations, structural measurements and Raman spectroscopy on carbonaceous material (RSCM), we identify five tectono-metamorphic slices (i) bounded by shear zones often reworked during exhumation and (ii) characterized by a down-stepping of peak metamorphic temperatures towards lower structural levels. Our geological and structural mapping reveals the overall geometry of the nappe stack forming a dome-like structure, exhumed beneath major top-to-the-N and subordinate top-to-the-S detachments that accommodated N-S-directed crustal extension. This trench-perpendicular extension was intermittently rotated into an E-W direction (trench-parallel), as evidenced by a newly recognized top-to-the-W ductile-brittle detachment. Minor compressional events did not significantly alter the 3D architecture of the paleo-duplex. Reported RSCM peak metamorphic temperatures of ~350-450 °C from the nappe stack align with the typical temperature range for the downdip limit of the seismogenic zones, suggesting a first-order thermo-mechanical control on the depth of basal accretion along the subduction interface. These findings provide crucial constraints for interpreting the deep-accretion and exhumation dynamics that shaped the long-term evolution of the Hellenic forearc domain.
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