Emplacement of the Pindos ophiolite, NW Greece : P-T-t-kinematic constraints from the metamorphic sole

Abstract

Metamorphic soles are key petrotectonic units that offer valuable insights into the processes governing ophiolite emplacement on continental margins (obduction). In this work, we have investigated the metamorphic sole of the Pindos ophiolite in northwestern Greece. In the studied locality, the sole is sandwiched between mantle peridotites and pillow lavas of N-MORB affinity. Our study focuses on two lithologies from the metamorphic sole: a garnet-mica schist (metapelite) and a mafic amphibolite. Kinematic indicators from the garnet-mica schists are consistent with top-to-the-NE shearing of the Pindos ophiolite on the Pelagonian zone. Petrographic and textural evidence, geothermometry results (Fesingle bondMg garnet-biotite exchange and paragonite-muscovite solvus thermometry), and phase-equilibria modelling bracket the upper-limit of metamorphism at amphibolite-facies conditions (630 ± 20 °C and 1.1 ± 0.2GPa). Moreover, Quartz-in-Garnet (QuiG) barometry yields a pressure of ∼1.2GPa for 630 °C demonstrating the equilibration of garnet inclusions at high-pressure conditions. New 40Ar/39Ar dating results from syn-kinematic muscovite from the metapelite and amphibole from the amphibolite indicate an apparent minimum age of 164.16 ± 0.37 Ma and a consistent age plateau at 165.5 ± 0.73 Ma respectively. Notably, the amphibole exhibits no evidence of argon loss. The muscovite age, by contrast, should be considered a minimum apparent age due to the potential influence of argon diffusion. Finally, Usingle bondPb geochronology of garnet was dominated by inclusions and did not result in a meaningful age. The measured ages imply cooling rates for the Pindos metamorphic sole ranging from 60 to 625 °C/Ma.