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

English Abstract:

The Lavrion peninsula of Greece marks the northern terminus of the West Cycladic Detachment System (WCDS), a low-angle normal fault system accommodating extension under ductile-brittle condition. The Kamariza unit comprises the lowest structural levels, and is composed mainly of greenschist facies marble and schist recording SSW-directed kinematics. We have collected samples to conduct Ar-Ar geochronology on white mica in an attempt to better understand the thermal history of this extensional terrane. In the schists, white mica is abundant, defining the main foliation and locally forming a secondary SC foliation with mica fish structures; in the marble samples, white mica is rare. In all samples, the quartz and calcite crystals are recrystallized and quartz often has bulging grain boundaries. Chemical maps show that the white mica has a dominant muscovite composition and is strongly zoned within samples yielding younger cooling ages. Mica from the Kamariza unit yields Early to Middle Miocene Ar-Ar ages, and coupled with Late Miocene zircon (U-Th)/He ages and top-to-SSW shear sense, suggests these rocks experienced the same extensional tectonism as the other WCDS footwall exposures on Makronisos, Kea, and Kythnos. Relatively rapid exhumation initiated decompressional melting in the Late Miocene generating the Plaka pluton as well as attendant hydrothermal fluids. Fluid infiltration along the brittle detachment metasomatized the host marbles resulting in high-temperature Mississippi Valley Type deposits. Some of our mica ages may reflect reheating associated with mineralization. Similar to the tectonic history on Serifos, the final extensional movements along the low-angle normal faults took place at rather shallow depths, postdating the intrusion and illustrating the >10 m.y. evolution of the detachment system.