The ophiolitic unit in the SE Lesvos constitutes the uppermost tectonic nap
pe, consisting of ultramafic rocks with minor gabbroic dykes and an amphibo
lite sole. The most abundant lithologies comprise Iherzolite and harzburgit
e with minor dunite. The harzburgite member and the dunite are intensively
serpentinized. The harzburgite has chemical affinity analogous to Alpine pe
ridotites while the Iherzolite is more fertile and resembles some abyssal p
eridotites. Both have undergone partial melting and depletion as indicated
by geochemical and mineralogical results. The exsolution of clinopyroxene a
nd spinel from orthopyroxene indicates elemental redistribution in the pyro
xenes and hence geothermometric calculations based on pyroxenes cannot give
the original temperatures of formation. Therefore, our geothermobarometric
calculations indicate a later cooling episode, which occurred after the fo
rmation of porphyroclasts in a temperature range of 1100-650 degrees C and
at pressures of about 6-7 kbars. Metasomatic phenomena that affected the Le
svos peridotites resulted in low MgO/FeOt ratios and enrichment in some inc
ompatible trace elements together with the formation of amphibole. Chemical
affinities and mineralogical compositions suggest that the Lesvos peridoti
tes originated in a marginal basin regime.