The Alpine orogenic belt of the Hellenides has been strongly reworked by ductile and brittle
extensional tectonics. Extensional structures have affected the central Aegean region and obliterated
much of the original orogenic architecture since at least early Miocene times. In the area of
Almyropotamos (on the island of Evia, flanking the western part of the Aegean) a unique remnant
compressional nappe stack involving Tertiary metamorphic rocks has been preserved. This nappe
sequence comprises a high-pressure rock unit on top of a lower grade unit. The upper unit (South Evia
Blueschist Belt) is thought to be the westward continuation of the Cycladic blueschist belt metamorphosed
at high-pressure conditions during Late Cretaceous–Eocene times. The underlying unit (the
Almyropotamos Unit) is a continental margin sequence covered by a flysch and containing Lutetian
nummulites, indicating that this unit accumulated sediments until at least late Eocene times.
In the present study we analyse the petrology of the Almyropotamos nappe stack and define the
P–T conditions of each of the different rock units exposed there. The presence of glaucophane, lawsonite
rimmed by epidote, and jadeite (70 mol.%) suggest that peak P–T conditions in the South Evia
Blueschist Belt reached approximately 10–12 kbar and 350–450 °C. Unlike previous studies, which
estimated that the underlying Almyropotamos Unit reached only greenschist-facies conditions, glaucophane
relics and Si-rich phengites were found by us in this unit. These indicate that high-pressure
metamorphism and crustal thickening in this part of the Aegean lasted until at least the late Eocene or
early Oligocene. We note that in this respect the architecture of southern Evia resembles that of northern
Greece (Olympos, Ossa). Our structural data indicate that rock units in the Almyropotamos area
record different folding phases, with the South Evia Blueschist Belt having a more complex fold history
than the underlying Almyropotamos Unit. The entire nappe stack shares large-scale folds which
are E–W trending, and locally overturned-to-the-south, and which may represent (at present coordinates)
N–S contraction and nappe transport.