Geotectonics

The Mesohellenic ophiolites (MHO) in the Western Hellenides are part of an oceanic slab emplaced onto Pelagonian (Pangaean) continental rocks in the mid Jurassic with a documented NE ophiolite emplacement: the MHO root zone is probably preserved as a deep ultramafic mass within the Mesohellenic Trough. Ophiolitic outliers to the east of the MHO and west of the Chalkidiki ophiolitic formations are oceanic lithospheric fragments, not complete ophiolite bodies: these are incoherent blocks preserved above exhumed Pelagonian continental rocks and not remnants of a continuous ophiolitic nappe. As these fragments lack connection to original root zone provenance, we refer to these as the “rootless” ophiolites. Pelagonian continental exhumation, possibly triggered by transcurrent shear along its continental margin with the Pindos basin, began by the Late Jurassic and continued into the mid-Cretaceous. Exhumation affected the previously emplaced oceanic slab in the following ways: i) The metamorphic facies of the basal mélange separating the ophiolite from the Pelagonian basement grades from phyllitic to schist and amphibolite-schist over the exhumed Pelagonia ii) Ophiolitic remnants are metasomatized where in contact with the exhumed Pelagonian rocks. iii) Remnant ophiolitic fragments are rotated and largely disassociated from their original relative pseudostratigraphic positions in their parent slab iv) No amphibolite emplacement soles are preserved beneath ophiolitic remnants found directly above Pelagonia. East of Vourinos, remnants of the slab were tectonically entrapped between the exhuming Pelagonian core and its sedimentary overburden, and demonstrate extensional, largely gravitational displacements as well as rotation from original emplacement vectors. Primary constrictive slab emplacement features are obscured, but a general westerly sense of kinematics via listric and extensional faults have been imprinted on these fragments. In the Pelagonian exhumation model, this "SW topping" direction cannot be interpreted as indicative of an eastern origin of the Pindos Basin ophiolites from the Vardar Zone, but rather as a local response to the uplift of Pelagonia and active deformation of the sedimentary overburden.