OPHIOLITES: EXTENSION IN A CONVERGENT SETTING, WITH PARTICULAR REFERENCE TO THE WESTERN HELLENIC OPHIOLITES

Reference to some of the western Hellenic ophiolites (Vourinos, Pindos and Othris) as serpentine and dolerite eruptions by Boué dates from at least 1840; the observation of tuffs and pillow lavas(?), possibly not ophiolitic, in Othris in 1880 led Neumayr to suggest an origin as large submarine eruptions. A submarine setting was reinforced by Brunn's mapping of the Pindos and Vourinos ophiolites in the 1950s. He concluded that they were in situ; formed an entity; had been emplaced in late Jurassic time along feeders concealed under the Meso-Hellenic trough and had flowed outward to the NE (Vourinos) and SW (Pindos). Sheared serpentinite at the base of the ophiolites was attributed to post-consolidation effects related to later tectonics, with the required water possibly being derived from the underlying sediments. The amphibolites and garnet-mica schists at the base of the ophiolites were interpreted as slivers of the underlying Paleozoic metamorphic basement. In 1960 Brunn made the first analogy between these ophiolites and the rocks of the mid-Atlantic ridge. Moores (1969) recognized the fundamental difference between magmatic and tectonized ultramafics in the Vourinos and suggested that many of the ultramafic rocks had been emplaced by solid flow about a NE-trending symmetry axis . All of these interpretations were made in an essentially fixist framework.

Subsequent interpretations assume a plate tectonic setting. Like many other ophiolites, the main problems have been the 'root zone' of the ophiolites; the location and dip direction of associated subduction zones; the tectonic setting(s) indicated by their marked variations in composition; the relationship between extension and convergence; how they were emplaced onto a continent; and significance of the metamorphic sole; and the spatial and temporal relations of the Hellenic ophiolites to contiguous ophiolites in Albania and former Yugoslavia. The Hellenic ophiolites are a critical link between the Tethyan ophiolites in the eastern Mediterranean and the Alpine-Apennine ophiolites to the W. Detailed age dating and geochemical analyses will probably give significant insights into how extension has taken place in this particular convergent setting.