We present the results of a detailed structural study in the Cycladic Blueschist Unit at Fabrika on Syros Island, Greece, and discuss their significance for tectonic processes at the subduction interface. Some samples record top-to-the-west shear reflecting prograde (burial), peak high-pressure (HP) and initial decompression (exhumation) conditions. Other nearby samples record top-to-the-east shear during HP metamorphism and exhumation. Some rocks re-equilibrated at greenschist-facies conditions and record top-to-the-west shear. Greenschist-facies top-to-the-west shear is also found at the base of non-HP upper units above the Fabrika HP sequence. We interpret the HP structures to reflect forced return flow and incipient formation of an extrusion wedge in the subduction channel. The HP top-to-the-west structures resulted from thrusting along the base of the wedge and started to form during burial before the rocks reached their deepest point. The HP top-to-the-east structures reflect deformation near the top of the developing extrusion wedge. After considerable exhumation during ongoing subduction, out-of-sequence, top-to-thewest thrusts emplaced the non-HP upper units above the exhuming extrusion wedge~10 Myr after the wedge initially formed. Our work suggests that the HP rocks were considerably exhumed during sustained lithospheric shortening in the subduction channel by forced return flow. Because return flow is controlled by the velocity of the subducting slab, it may explain why HP rocks can be exhumed at subduction rates. On the regional scale we find that four distinct HP belts were sequentially accreted and exhumed between~50 and 20 Ma suggesting continuous subduction-channel return flow in the Hellenic subduction zone.

We constrain the fault pattern and the kinematics of faulting that facilitated the uplift of the Troodos Massif in Cyprus in the eastern Mediterranean. The fault pattern consists of E‐W striking reverse faults, N‐S striking normal faults, and NW striking dextral and NE striking sinistral strike/oblique‐slip faults. Fault‐slip analysis reveals that this overall pattern resulted from subhorizontal NNW directed shortening and coeval, subhorizontal ENE directed extension. Dated sediments affected by faulting reveal that the N‐S striking normal faults are, at least in part, younger than 2.14 Ma. This suggests that the entire fault pattern, or at least a large part of it, resulted or was reworked during post‐2.14‐Ma deformation. Published work further shows that the uplift of the Troodos Massif was controlled by underthrusting of the Eratosthenes Seamount, which entered the Cyprus subduction zone by about 2 Ma. The alleged E‐W extent of the underthrust segment of the seamount approximately matches the size of the high‐topography area of the Troodos Mountains. We interpret this geometry to have caused spatially limited crustal thickening underneath the high‐topography area by subhorizontal N‐S shortening in front of and above the underthrusting seamount and coeval, subhorizontal E‐W extension at its flanks, and that the uplift of the high‐topography area occurred in the footwall of the N‐S striking normal faults. This model is broadly in line with seismicity and may also explain why serpentinized mantle rocks and dense gabbro are now exposed on top of the Troodos Massif.