Petrogenetic evolution of an ophiolite fragment in an ensialic marginal basin, northern Aegean (Samothraki Island, Greece)
Tsikouras, Basilios; Hatzipanagiotou, Konstantin
European Journal of Mineralogy Volume 10 Number 3 (1998), p. 551 - 568
published: Jun 22, 1998
manuscript accepted: Dec 8, 1997
manuscript received: Nov 19, 1996
ArtNo. ESP147051003014, Price: 29.00 €
Abstract Ophiolitic rocks on Samothraki Island comprise gabbros, diorite with associated plagiogranite pods and veins, massive dolerite and basalt; doleritic dykes are rooted in the gabbro and have acted as feeders for the basalt. The mineralogy and chemistry of clinopyroxenes from the gabbro and basalt suggest that both were crystallized under low pressure. Minimum equilibrium temperatures were ~950°C for the clinopyroxenes of gabbros and 1050-1250°C for those of basalt. Hornblende-plagioclase pairs in the diorite yield equilibrium temperatures of 690-740 °C. The petrogenetic evolution of the ophiolite suite was controlled by plagioclase and clinopyroxene fractionation under increasing /02; olivine was probably eliminated as an early stage of fractionation. Whole-rock chemistry indicates that the diorites have bimodal or at least transitional affinities between MORB and IAT. Two generations of dolerite dykes are recognized: a younger set with a strong signature of a subduction component and an older set, more differentiated and chemically similar to MORB. The chemistry of the younger set of dykes is compatible with mixing of an evolved magma with a more primitive one, derived from the melting of a subducted slab. Both basalts and massive dolerites have MORB affinities with a weak arc imprint. The chemical variability of the ophiolitic lithologies is also consistent with magma mixing. Field evidence coupled with mineralogical and petrochemical data suggest that the Samothraki ophiolite originated in an ensialic back-arc basin. This basin was probably developed in the broad area of the northern Aegean Sea region; the Guevgueli, Chalkidiki, Evros and Lesvos ophiolites, which are located in this area, are thought to have been formed during the evolution of this basin.