A TIME-TRANSGRESSIVE OPHIOLITE-PLATFORM COLLISION (LATE MIDDLE JURASSIC TO EARLY CRETACEOUS, PELAGONIAN ZONE, EVVOIA, GREECE)

A carbonate platform complex and an overthrust ophiolite nappe-pile are being investigated in the Pelagonian zone of the Hellenides. The carbonate platform evolved on top of one of the microplates that formed as Pangaea broke up. The ophiolite originated in an intervening, spreading branch of the Neotethys. The general opinion is that plate convergence took place during the Early and Middle Jurassic along an intra-oceanic subduction zone and the ophiolite nappes were emplaced onto the platform in the Early Cretaceous. However, the actual collision between slices of oceanic lithosphere and the Pelagonian carbonate platform began around the late Middle Jurassic with folding and thrusting and a 25 ma. period of seesaw-tectonics characterised by oceanic-crust and platform-exposures followed by platform drowning below the CCD and finally by distal granitic basement uplifts prior to the ophiolite emplacement.

Sinemurian-Bathonian convergence

During early plate convergence, the Pelagonian carbonate platform was incipiently drowned. Simultaneously, the oceanic plate and was uplifted above the CCD and served as a pedestal which harboured a piggy-back, pelagic, carbonate-platform.

Bathonian-Callovian collision

The collision between the Pelagonian carbonate platform and the ophiolite began with folding, thrusting and uplifting, marked by a widespread unconformity with karstic dissolution and laterite deposits, having an ophiolitic geochemical signature.

Oxfordian-Tithonian drowning

A period of subsidence began with an Oxfordian transgression over the laterite and the deposition of shallow marine carbonates. Patch reefs and later "catch-up" pinnacle reefs temporarily survived initial drowning and shed debris into adjacent, basins. During the late Tithonian, the platform drowned below the CCD and became the site of carbonate-free radiolarite deposition.

Tithonian-Valanginian Turbidite and ophiolite emplacement

Arkosic turbidites of granitic provenience were deposited over the Tithonian radiolarite prior to the final ophiolite emplacement. At the base of the ophiolite nappe-pile a tectonic mélange accumulated which is composed of material that was scraped off the substrates over which the ophiolite had advanced.

Recent counterparts of the collision described above can be found in the vicinity of Papua New Guinea.