“Rootless” ophiolites above the Pelagonian core complex of north central Greece

More than twenty ophiolitic fragments ranging in size from meter-scale to several tens of km² occur strato-tectonically above the Pelagonian continental massif (mid-Neoproterozoic and Permo-Carboniferous crystalline basement plus Triassic-Jurassic platform carbonate cover) in the region between the mid-late Jurassic Mesohellenic ophiolites (rooted within the Mesohellenic Trough in the west) and the Vardar Zone ophiolites (rooted in the Vardar Zone in the east). Formerly presumed to be part of a single, initially continuous mid-upper Jurassic ophiolite nappe, we have begun documentation of these fragments within the context of their role in the exhumation model of Pelagonia.
   A “rootless” ophiolite is a piece of oceanic lithosphere that is no longer contiguous with an ophiolitic complex emanating and emplaced from a plate suture zone. The Rodiani complex has long been considered tectonically continuous to the Vourinos massif, but rather appears to be more alike to Aspropotamos-Pindos lithosphere. Extension from Vourinos would require tectonic thinning of about eleven km of ophiolitic lithosphere, and rotation of the Rodiani section that cannot be explained by a simple antiformal structure between Vourinos and Rodiani within the interceding Triassic-Jurassic Pelagonian platform carbonates. Zindani, also apparently tectonically continuous with Vourinos, is severely altered to a massive serpentinite (predominantly antigorite) body, imbricated with Pelagonian schist. The Livadi ophiolite, once included as part of the Paleozoic (Pelagonian), crops out as a nappe above the Pelagonian gneissic core complex. The contact comprises a metamorphic discontinuity with the much lower T-P lithologies of the ophiolite. Primary ophiolitic fabrics and ridge-crest structures are still recognizable in the Livadi complex. The smallest ophiolitic fragment that includes a complete Steinmann Trinity occurs near Lefkovrisi, Kozani (the “IGME” ophiolite): less than three meters of section including serpentinite, pillow lava, and Upper Jurassic oceanic sediments crop out over a pebbly mudstone mélange similar to that of the Vourinos ophiolite, and beneath the Lower Cretaceous lateritic rocks to Upper Cretaceous reefal limestone and flysch.
   Most of these “rootless” bodies are overlain by Upper Cretaceous transgressional limestone that allows rotation to their pre-Upper Cretaceous orientations. This aids in delineating older constrictional structures from exhumation structures. The pre-Upper Cretaceous interval includes formation of laterite deposits and extensively striated cobble formations (olistolithic or tectonic in origin). The provenance of supra-ophiolitic sedimentation is consistently “towards the east,” that is, towards the area of the Pelagonian core complex. Structures within the ophiolitic fragments themselves are generally too highly overprinted by exhumation structures to determine the constrictive or emplacement origins of the nappe. The apparent continuation of a pebbly mudstone from the west to higher metamorphosed equivalent (amphibolite schist) towards the east and above the Pelagonian core suggests derivation from the NE-emplacing Mesohellenic slab.
   Compared to the “rooted” Mesohellenic ophiolites that exhibit abundant constrictional structures associated with emplacement, all these small complexes are overprinted by “extensional” or transtensional structures. The thickness of these rootless ophiolites is so small compared to the distance of displacement from either potential root zone that an emplacement as a single, once contiguous, obduction nappe is probably not possible. Their outcrops over a long distance from a root zone can only result from thrusting within the Jurassic subduction followed by later extensional exhumation. Our study questions what these bodies show as representative portions of the roof zone above the exhuming complex. The metasomatic veining and heavy alteration of serpentinite is probably a remnant of exhumation beneath these “rootless” oceanic remnants.