Tectono-magmatic significance of volcanic rocks from the Albanide-Hellenide ophiolitic mélanges

Ophiolites of the Albanide-Hellenide Subpelagonian Zone are widely associated with mélange units, which consist of polygenetic thrust sheets formed by various combination of tectonic and sedimentary processes operating at subduction zones during tectonic emplacement of ophiolites. Subpelagonian mélanges incorporate tectonically eroded and/or fragmented blocks of the subducting oceanic plate, as well as materials derived from the forearc region in the upper plate plate. Composition and petrology of volcanics included in these mélanges record the magmatic activities developed from the early stages of generation of oceanic lithosphere (including seamounts) up to its consumption in a converging margin setting and also provide information on the mélange formation and evolution. The Rubik Complex (Albanides) and the Avdella Mélange (Pindos, Hellenides) are typical tectono-sedimentary mélanges, which include Triassic-Jurassic basalts with both mid-ocean ridge (MORB) and ocean island (OIB) affinities. This suggests that they formed by incorporation of oceanic materials from the subducting plate. The tectono-sedimentary Koziakas Mélange (Hellenides) consists of a variety of different volcanic rocks: (1) transitional to alkaline basalts, trachyandesites, and trachytes; (2) both normal (N-) and transitional (T-) MORBs; (3) boninitic volcanics. No datings are available for these litho-types, although blocks of associated radiolarian chert indicate both Triassic and Jurassic ages. The Agoriani Mélange (Othrys, Hellenides), originated mainly through sedimentary processes, includes N-MORBs, alkaline OIBs, boninitic clasts and blocks, and MORB/IAT intermediate basalts. The mélange from the Argolis Peninsula (Hellenides) can be subdivided into four different mappable units. In the Lower and Upper Units sedimentary processes prevail with volcanics largely predominated by boninitic rocks, whereas N- and T-MORBs and alkaline OIBs are rare. By contrast, tectonic processes mainly characterize the Middle and Wedged Units. Volcanics in the Middle Unit are alkaline OIBs and Triassic and Jurassic N- and T-MORBs, whereas the Wedged Unit is exclusively composed of OIBs, thus representing a seamount fragment. In the Rubik and Koziakas Mélanges some boninitic dykes crosscut different tectonic slices, referred to both MORB and OIB sequences. This implies that tectonic incorporation of MORB-type and OIB-type materials occurred prior to the development of boninitic magmatism