Several distinct tectono-metamorphic slices in the Cycladic eclogite-blueschist belt, Greece

Abstract

Several relatively thin tectono-metamorphic slices have been recognized in the Cycladic eclogite-blueschist belt, through detailed studies on Ios, Sifnos, Syros, and Tinos. A sequence of distinct metamorphic mineral growth events has been documented. These recur in each tectonic slice, although individual slices are dominated by different events. To constrain the timing of these processes, the method of asymptotes and limits has been used to reanalyze published 40Ar/ 39Ar apparent age spectra. This reanalysis supports the concept that there were separate and quite distinct high-pressure metamorphic mineral growth events, and allows potential constraints as to the timing of some of these events to be developed. M1B eclogite-facies metamorphism is estimated to have occurred at some time in the period 53-49 Ma, the M1C blueschist-facies metamorphic event at some time in the period 44-38 Ma, and the M1D transitional blueschist-facies metamorphic event is estimated to have occurred at some time in the period 35-30 Ma. A kinematic model is proposed to explain the geometry of a thinly sliced tectono-metamorphic stratigraphy, as observed, and the reason as to why individual tectonic slices in this 'tectono-metamorphic stratigraphy' should display distinctive patterns of fabrics and micro-structures, as well as characteristic temperature-time curves as inferred by 40Ar/ 39Ar geochronology.