Subduction, Underplating, and Return Flow Recorded in the Cycladic Blueschist Unit Exposed on Syros, Greece

Exhumed high-pressure/low-temperature (HP/LT) metamorphic rocks provide insights into deep (∼20–70 km) subduction interface dynamics. On Syros Island (Cyclades, Greece), the Cycladic Blueschist Unit preserves blueschist-to-eclogite facies oceanic- and continental-affinity that record structural thermal evolution linked to Eocene subduction. Despite decades of research, deformation history (P-T-D) timing exhumation are matters ongoing discussion. We suggest comprises three coherent tectonic slices each slice underwent subduction, underplating, syn-subduction return flow along similar P-T trajectories, but at progressively younger times. Subduction distinguished by lineations ductile fold axis orientations, kinematically consistent with previous studies document top-to-the-S-SW shear (prograde-to-peak subduction), top-to-the-NE (blueschist exhumation), then E-W coaxial stretching (greenschist exhumation). Amphibole zonations cooling during decompression, indicating above a cold slab. Multi-mineral Rb-Sr isochrons compiled geochronology show distinct stages peak (53–52, ∼50, 45 Ma) young depth. Retrograde blueschist greenschist fabrics span ∼50–40 ∼43–20 Ma, respectively, also Synthesized data sets support revised framework for Syros, involving structurally simultaneous previously accreted in channel zone. Distributed, ductile, dominantly an Eocene-Oligocene proceeded rates ∼1.5–5 mm/yr accommodated ∼80% total this HP/LT complex.