Petrogenetic evolution of the Koziakas ophiolite complex (W. Thessaly, Greece) |
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| Authors: | P Pomonis B Tsikouras K Hatzipanagiotou |
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| Institution: | (1) Department of Geology, University of Patras, Section of Earth Materials, Patras, Greece |
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| Abstract: | Summary The Koziakas ophiolitic complex is situated in W. Thessaly and is interpreted as an incomplete ophiolite sequence, thrust
over the Western Thessaly Unit (W.T.U.). Two tectonically distinct units represent it: (1) the lower unit with a metamorphic
sole and a tectonosedimentary mélange and (2) the upper unit including mantle peridotites and basaltic lavas. The mantle peridotites
are composed by harzburgite, lherzolite and plagioclase lherzolite intruded by a sparse network of gabbroic, plagiogranitic
and doleritic dykes. The volcanic sequence of the upper unit can be geochemically subdivided into four groups of basalts with:
(1) tholeiitic N-type MORB affinities, (2) low-Ti boninitic affinities, (3) subalkalic E-MORB type affinities and (4) alkali
characteristics displaying a different petrogenetic evolution with respect to the other groups. The magmatic history of the
Koziakas ophiolite is in agreement with extensive fractional crystallization and variable degrees of partial melting of a
heterogeneous mantle source, yielding, magmas mainly of MORB composition. Modal and cryptic metasomatic phenomena of the mantle
peridotites as well as Sr-Nd isotopic ratios imply that this melt contained also a hydrous component derived from melting
of a subducted lithosphere. The above geochemical characteristics and the correlation with the adjacent ophiolite suites of
Pindos, Othris and Vourinos indicate that Koziakas ophiolitic complex formed in a small backarc basin situated at the eastern
margin of the greater Pindos Ocean, between the Western Thessaly Unit (W.T.U.) and the Pelagonian continent. |
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