A major problem posed by the geology of Crete is the horizontal contact of an upper unit without Miocene metamorphism onto a metamorphosed lower one with Early Miocene high pressure/low temperature (HP/LT) parageneses. This very sharp contact is roughly parallel to the major Oligo-Miocene thrust planes which were reactivated as a large-scale detachment which allowed exhumation of high-pressure units. We describe the extensional deformation and the metamorphic evolution of the lower plate. Most first-order deformation features relate to the retrogression from high-pressure to low-pressure conditions. A N-S pervasive stretching is observed everywhere, often associated with a top-to-the-north sense of shear. The extreme variation of thickness of the Phyllite-Quartzite nappe (upper part of the lower plate) is probably the result of large-scale boudinage similar to the one seen in large outcrops. The most important observation is the systematic occurrence of fresh carpholite immediately below the base of the Tripolitza nappe except in northwestern Crete where a late extensional shear zone is present. Deeper in the nappe pile carpholite is systematically retrograded. This observation reveals a drastically different PT history for the upper part of the Phyllite-Quartzite nappe. It also suggests that the late extensional shear zone found along the northern side of Crete cuts inside the metamorphic structure and brings the nonmetamorphosed Tripolitza nappe directly in contact with the deeper parts of the Phyllite-Quartzite nappe. PT-t paths suggest a fast temperature decrease in the top of the Phyllite-Quartzite during retrogression and, hence, during the top-to-the-north shear. The deeper part of the Phyllite-Quartzite nappe shows a low-temperature regime throughout, but its PT path includes an isothermal decompression in the first stage. We produce a tentative map of domains having experienced similar PT trajectories during decompression. The overall cool regime is related to the continuous underthrusting of cold continental units during exhumation. Isothermal decompression observed in the core of the Phyllite-Quartzite Nappe implies fast exhumation during extension and the faster cooling of the upper part is related to a continuous displacement toward the north of a cooler unit during exhumation. Single grain 39Ar-40Ar ages obtained on phengites (15--25 Ma) in various structural sites are in good agreement with these conclusions and with the geological context suggesting that underthrusting of cold units at the front the accretionnary complex occurred contemporaneously with unroofing below a north dipping detachment near the top of the wedge. The age of this detachment is bracketed between the end of the high-pressure event (20 Ma) and the deposition of the breccia (Early to Middle Miocene) in the Neogene basins. ¿ American Geophysical Union 1996