Kythnos lies between Kea and Serifos in the Western Cyclades, both of which were critical in our understanding of Miocene top-SSW directed deformation associated with the West Cycladic Detachment System. Kythnos itself, however, is less well studied, although the West Cycladic Detachment crops out in theSW of the island. The detachment footwall on Kythnos underwent Eocene high pressure (blueschist facies) metamorphism, associated with top-W to -WSW directed deformation. Although evidence of the HP metamorphism has been almost completely overprinted, the structural grain on the island varies from W- to WSW-directed in the NE, likely a relic of the Eocene HP-deformation, to SSW-directed in the W and S. In the SE, Kythnos has a well-defined stratigraphy of epidote schists overlain by sericite-albite schists; within the latter, a blue grey marble and associated yellow quartz-carbonate mica schists occur, becoming progressively more deformed and thinner to the west. An upper marble is sporadically developed at the highest topographic levels of the island and also directly under the detachment in the SW. The hanging wall comprises brittle deformed quartz-rich rocks of uncertain origin.
The guide documents five excursions on Kythnos, each requiring a full day to complete. These show the small-scale structures that formed in the Cycladic Blueschist Unit during extension (folds, boudins, flanking structures, winged inclusions and marble ultramylonites and mylonites), with Miocene strains in the marbles increasing markedly to the west.
Other outcrops that can be visited by the more interested geoscientist are listed and briefly described in an Appendix