Structural, geochronological, and geochemical analysis of a Cycladic detachment system II: Results from the Lavrion Unit, Greece

English Abstract:

The West Cycladic islands comprise the footwall of the West Cycladic Detachment System (WCDS), characterized by a system of high and low angle normal faults that cuts different structural levels of the Cycladic Blueschist Unit (CBU). Whereas the hanging wall has mostly been eroded on the islands, the Lavrion peninsula preserves the Lavrion Unit, interpreted to be the upper structural levels of the WCDS. The main foliation is a compressional crenulation cleavage with ENE-WSW to NE-SW stretching and intersection lineations. Kinematic indicators reveal top-to-SSW sense of shear, and along the detachment both units are overprinted by cataclastic deformation and high-temperature metallic ore mineralization. Glaucophane and chlorite pseudomorphs of glacophane are preserved. New single-crystal Ar-Ar geochronology on muscovite from the Lavrion Unit yields ages between 35-28 Ma, and together with published zircon (U-Th)/He dates of 16-12 Ma and preservation of glaucophane suggests these rocks did not witness the dominant Miocene greenschist facies deformation that characterizes the WCDS. One muscovite sample along the west coast at Thimari yielded an Ar-Ar age of c. 175 Ma and maybe part of the Sub-Pelagonian Berzekos Unit. Moreover, the geology of Lavrion peninsula is strikingly similar to Serifos island on the southeast termination of the WCDS. Pinning the ends of the detachment system, the geology of Lavrion and Serifos both include late-tectonic granodiorite plutons intruded at c. 10 Ma into the low-angle normal fault that cuts different structural levels of the CBU, which preserves an Eocene-Oligocene cooling signature and ENE-WSW trending lineations. The western Cyclades including the Lavrion peninsula can be resolved into a coherent and uniform tectonic progression commencing in the Eocene involving ENE-WSW to NNE-SSW ductile to brittle extension through the Miocene, localized plutonism at the tips of the detachment system, and relatively rapid cooling of the footwall.