STRUCTURE AND TECTONICS OF SUBOPHIOLITIC MÉLANGES IN THE WESTERN HELLENIDES (GREECE) AND IMPLICATIONS FOR OPHIOLITE EMPLACEMENT TECTONICS

The Jurassic Vourinos ophiolite (VO), part of the Western Hellenic ophiolite belt in Greece, rests tectonically on the Pelagonian subcontinent. The Vourinos & the coeval Pindos ophiolite (PO) to the west display SSZ affinities & represent remnants of a rifted forearc Tethyan oceanic crust developed in the Pindos basin. The subophiolitic Zavordas mélange (ZM) beneath the VO contains a pebbly mudstone unit (Agios Nikolaos Formation, ANF), blocks of lava with hemipelagic chert & carbonate intercalations, gabbro-diabase & brecciated serpentinite. The ANF constitutes the matrix of the ZM & comprises a scaly mudstone with pebbles, cobbles & boulders of arenite & wacke derived from Pelagonia. Imbricated along E-NE-directed thrust faults & metamorphosed up to lower amphibolite facies, the ANF represents continental rise deposits of the Pelagonian passive margin. Lavas display MORB-WPB affinities & represent Upper Triassic rift units that formed during the separation of Pelagonia from Apulia. The gabbro, diabase & brecciated serpentinite in the easternmost part of the ZM are tectonically intercalated with the Pelagonian carbonates, although primary intrusive relations are locally preserved. These gabbro-diabase intrusions are the products of a magmatic rifting episode prior to the onset of seafloor spreading in the Pindos basin. The ZM is a subophiolitic mélange made of passive margin & rift assemblages overridden by VO during ophiolite emplacement in the Middle Jurassic. The Avdella mélange (AM) beneath the PO to the W includes a chaotic matrix clasts & blocks of ophiolitic rocks, reefal to pelagic limestones & olistostromal turbidites, ranging in age from Triassic to J-K. The AM rests tectonically on a K-Eocene flysch unit and the K-Eocene shelf & slope deposits of the Apulian margin along W-directed back-thrusts. The evolutionary history of the ZM & AM subophiolitic mélanges indicates a diachronous emplacement tectonics of the VO & PO and their mélanges, first in the east as a result of a trench-continent (Pelagonia) collision in the Middle Jurassic & then in the west due to the collision of Apulia with Eurasia in the Eocene. Subophiolitic mélanges beneath Tethyan ophiolites consist mainly of rifted passive margin units, whereas those beneath Cordilleran ophiolites are made of subduction-accretion complexes.