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

Metamorphic soles are key petrotectonic units that offer valuable insights into the processes governing ophiolite emplacement. Ophiolite obduction involves complex thermomechanical phenomena and is associated with limited petrological data. 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. We mainly focused on two lithologies: a garnet-mica metapelite and an amphibolite. Petrographic investigation of the metapelite revealed quartz inclusions in garnet indicating syn-kinematic growth, asymmetric quartz ribbons and S-C shear bands of syn-kinematic mica, all being consistent with top-to-the-NE shearing. Petrographic and textural evidence, temperature calculations (Fe-Mg garnet-biotite exchange and paragonite-muscovite solvus thermometry), and phase-equilibria modelling using an effective bulk composition bracket metamorphism at amphibolite-facies conditions (ca. 620-640°C and 1.1-1.2 GPa). Moreover, Quartz-in-Garnet (QuiG) barometry yielded a pressure of ~1.2 GPa for 635°C demonstrating that the syn-kinematic growth of garnet took place under high-pressure conditions. New ⁴⁰Ar/³⁹Ar geochronology of syn-kinematic muscovite from the metapelite and amphibole from the amphibolite showed 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 exhibited no evidence of argon loss, suggesting its apparent age closely represents the time of formation. The muscovite age, by contrast, should be considered a minimum apparent age due to the potential influence of argon diffusion. Despite this limitation, the studied metapelite represents, in all probability, metamorphosed pelagic sediments in association with oceanic crust of N-MORB affinity. A combination of heat conduction from the overlying peridotite and shear heating developed during emplacement are considered responsible for the formation of the metapelite. Our joint petrological, geochronological and structural data indicate that the Pindos metamorphic sole records evidence of rapid thrusting (<2.5Myr) of the ophiolite from a westerly oceanic tract (Pindos Ocean) onto the Pelagonian margin over to the east in Callovian times (uppermost mid-Jurassic).