High-pressure metamorphism and cooling on SE Naxos (Cyclades, Greece)

The island of Naxos, in the centre of the Aegean Sea, is a Cordillera-type metamorphic core complex formed by the collapse of the Alpine orogenic belt of the Hellenides. The island is dominated by Early-Miocene (M2) Barrovian metamorphic assemblages that overprinted Eocene (M1) high-pressure (HP) rocks. A P-T path, which integrates data from a new, unique occurrence of jadeite-bearing blueschists, shows that the rocks of SE Naxos near the top of the lower plate sequence reached M1 P-T conditions of at least 12 kbar and ca. 470°C, and then cooled during decompression. This P-T path strongly differs from P-T paths recorded in the lower part of the section exposed in central Naxos, where M2 heating caused migmatization and anatexis and completely obliterated the high-pressure mineral assemblages. It is postulated that the contrasting P-T paths on Naxos reflect the effect of heat launched from below the section and cooling caused by unroofing and denudation of the section from above. Peak P-T conditions estimated on SE Naxos may be used to set constraints on the high-pressure M1 conditions that prevailed in the centre of the island (where no traces of M1 have been preserved). Because the rock sequence separating SE Naxos from the core of the island is ca. 7 km thick, it is likely that the core reached M1 pressure conditions of at least 14 kbar. Extrapolation of the M1 field geothermal gradient defined on SE Naxos (12 kbar, 470°C; ca. 13°C/km) yields M1 temperatures of at least 550°C in the core of the island.