Jurassic ridge collapse, subduction initiation and ophiolite obduction in the southern Greek Tethys

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The Migdhalitsa Ophiolite is the southernmost of the Hellenic ophiolites, and was emplaced on to the Pelagonian microcontinent during the Upper Jurassic from an adjacent Tethyan ocean basin. Despite its small size the ophiolite comprises a series of distinct lava sequences, erupted over a relatively short period. These principally comprise N-MORBs and basalts enriched in incompatible trace elements, generated by melting of a normal and a depleted source at a slow-spreading oceanic ridge. In contrast, small volumes of picritic and boninitic lavas suggest the ophiolite was soon placed in a forearc position above a newly initiated subduction zone. This implies overthrusting at or close to the ridge, possibly due to ridge collapse. As subduction continued the ophiolite was emplaced over the Pelagonian platform following its collision with the trench and the resultant flexural collapse of the margin. Final obduction resulted in deposition of a turbiditic and olistostromal flysch, within a flexural trough created ahead of the advancing nappe. Composition of the flysch indicates erosion of a tectonically dissected, probably imbricated, ophiolite thrust sheet in which a variety of different structural levels were exposed. Deformation during obduction was largely thin-skinned, although locally the metamorphic basement and Paleozoic carbonate cover of the Pelagonian Continent were exposed to erosion due to out-of-sequence thrusting or structural culminations. Paleomagnetic reconstructions linked with structural studies indicate obduction towards the SSW, corresponding to the ESE in Kimmeridgian times due to relative rotation of the Argolis Peninsula. It thus seems most likely that the Migdhalitsa Ophiolite was derived from the western, Pindos oceanic suture.

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Eclogae Geologicae Helvetiae

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