Miocene high-pressure metamorphism in the Cyclades and Crete, Aegean Sea, Greece: Evidence for large-magnitude displacement on the Cretan detachment

The Cyclades in the backarc region of the present Hellenic subduction zone are known for widespread Late Cretaceous to Eocene high-pressure metamorphi sm in the Cycladic blueschist unit, We report Ar-40/Ar-39 and Rb/Sr phengit e ages of 24-21 Ma for high-pressure metamorphism (8-10 kbar, 350-400 degre esC) in the lowest tectonic unit in the Cyclades, the Basal unit, which str ucturally underlies the Cycladic bluesehist unit. The Basal unit is correla ted with the Tripolitza unit of the External Hellenides in the forearc regi on of the Hellenic subduction zone, The Tripolitza unit is unmetamorphosed on Crete, where it is separated from the underlying high-pressure (8-10 kba r, 300-400 degreesC) Plattenkalk and Phyllite-Quartzite units by the extens ional Cretan detachment. The age for high-pressure metamorphism in the latt er units is similar to our age for the Basal unit in the Cyclades. Because pressure-temperature conditions in the Plattenkalk and Phyllite-Quartzite u nits on Crete and the Basal unit in the Cyclades are also similar, they mus t have been in close proximity in the early Miocene Hellenic subduction zon e. A palinspastic reconstruction suggests a subsequent displacement of > 10 0 km on the Cretan detachment. This is one of the greatest displacement mag nitudes ever reported from detachment faults. Because of this large offset, the Cretan detachment was an efficient agent for exhuming high-pressure ro cks.