Miocene ductile thinning below the Folegandros Detachment System, Cyclades, Greece

Folegandros island lies between the established SW-directed West Cycladic and S-directed Santorini detachment systems. Preserving shear-sense indicators with opposing kinematics, the geodynamics and timing of kinematics are debated. Using white mica ⁴⁰Ar/³⁹Ar geochronology complemented by structural data, we report a new Miocene top-to-S detachment system, the Folegandros Detachment System (FDS), that is coupled with pure-shear flattening and juxtaposes the Cycladic Blueschist Unit below Early Cretaceous to early Eocene low-grade marble and quartzitic-phyllitic sequences, topped by a metaflysch. Chronostratigraphic correlation and detrital zircon geochronology reveal the low-grade rocks from the hanging wall of the FDS likely belong to the Pelagonian Zone. Middle Miocene zircon and apatite (U-Th)/He cooling ages correspond to the latest stages of exhumation. Observations of opposing kinematics on Sikinos, Ios and now Folegandros reveal that ductile thinning played a more significant role in accommodating Miocene exhumation of high-pressure rocks in the southern Cyclades than previously postulated.