Coupled phengite 40Ar–39Ar geochronology and thermobarometry: P-T-t evolution of Andros Island (Cyclades, Greece)
2015
Andros is a key island for understanding both the timing of high-pressure–low-temperature
(HP-LT) metamorphism and the dynamics of crustal-scale detachment systems exhuming high-grade
units in the Cyclades (Greece). Using phengite 40Ar–39Ar geochronology coupled with thermobarometry,
as well as data from literature, we constrain the pressure–temperature–time (P-T-t) paths of the
Makrotantalon and Attic–Cycladic Blueschist units on Andros. Peak conditions of the HP-LT episode
in the Makrotantalon unit are 550 °C and 18.5 kbar, dated at 116 Ma. We correlate this episode with
Early Cretaceous blueschist facies metamorphism recognized in the Pelagonian zone of continental
Greece. This is a new argument favouring a Pelagonian origin for the Makrotantalon unit. In the Attic–
Cycladic Blueschist unit, the P-T-t path is characterized by: (1) exhumation after peak conditions in
HP-LT conditions between 55 and 35 Ma; (2) isobaric heating at 7 kbar until 30 Ma; and (3) isothermal
decompression until 21 Ma. This thermal evolution and timing are similar to those of the neighbouring
Tinos Island, emphasizing major thermal re-equilibration at the transition between stable and retreating
subduction. Modifications of the crustal thermal state played a major role in the evolution of the North
Cycladic Detachment System, below which Andros HP-LT units were exhumed.
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