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

Abstract

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.