Differences in decompression of a high-pressure unit: A case study from the Cycladic Blueschist Unit on Naxos Island, Greece

Determining the tectonic evolution and thermal structure of a unit that experiences subduction-related pressure temperature (P-T) loop is challenging. Within single unit, P-T conditions can vary from top to bottom which only be revealed by detailed petrological work. We present micropetrological data middle section Cycladic Blueschist Unit (CBU) in Naxos, Greece, indicates different than for sequence. Using Zr-in-rutile Ti-in-biotite thermometry coupled with quartz-in-garnet elastic barometry phase equilibrium thermodynamic modeling, we identify prograde path 15.4 ± 0.8 kbar 19.9 0.6 496 16 °C 572 7 (2σ uncertainty), equilibration during decompression at 8.3 1.5 519 12 followed near-isobaric heating 9.2 550 10 (or even 584 19 °C), final greenschist-facies stage 3.8 0.3 520 4 °C. compare these estimates published also CBU find half on Naxos records higher peak high-pressure (HP) about defining thickness 15 km Eocene. determine crustal thickening up ~15% occurs upper exhumation HP rocks an extrusion wedge convergence setting. At 30 Ma, was finally thrust onto radiogenic basement. Subsequently this underwent isobaric 9–96 between c. 32–28 23–21 Ma. Isobaric occurred below thickened commenced when metamorphism Cyclades ended. This suggests relaxation following accretion controlled evolving orogen tectonically quiescent period before lithospheric extension 23–20.5