The tectono-metamorphic evolution of a dismembered ophiolite (Tinos, Cyclades, Greece)

Abstract

-The six exposures of the Upper tectonic Unit of the Cycladic Massif occurring on the island of Tinos are shown to comprise a metamorphosed dismembered ophiolite complex. The common stratigraphic section consisting of tens-of-metres-thick tectonic slices of mafic phyllites overlain by serpentinites and gabbros is considered to have been derived by a combination of thrusting during obduction and subsequent attenuation by low-angle normal faults. All rock types show evidence of a phase of regional greenschistfacies metamorphism, which in the case of the phyllites is accompanied by penetrative deformation. The greenschist-facies metamorphism in gabbros is preceded by high temperature sea-floor amphibolite-facies alteration, whereas in the serpentinites, the antigorite + forsterite greenschist-facies assemblage overprinted an earlier low temperature lizardite serpentinite. Trace element patterns of the mafic phyllites and a harzburgitic origin of meta-serpentinites suggest a supra subduction zone (SSZ) affinity for the ophiolitic suite. 5"O values of phyllites, gabbros and serpentinites range from 6 to 15%o. Model calculations indicate that such values are consistent with low temperature (50-200 °C) alteration of parent rocks by sea-water at varying water/rock ratios. This would agree with the early low temperature mineralogy of the serpentinites, but the early high temperature alteration of the gabbros would require the presence of "O-enriched sea-water.The following overall history is suggested for Tinos ophiolitic slices.(1) Oceanic crust was generated at a supra-subduction zone spreading centre with high temperature alteration of gabbros. (2) Tectonic disturbance (its early hot stages recorded in an amphibolitic shear zone at the base of serpentinites) brought the already cooled ultramafics into direct contact with sea-water and caused low-7* serpentinization. (3) Tectonism after cooling involved thrusting which caused repetition and inversion of the original order of the oceanic suite. (4) Regional metamorphism of all the ophiolite components at greenschist-facies conditions (~450 °C) overprinted the early alteration mineralogy. It was probably induced by continued thrusting and piling up of nappes. The Tinos ophiolite, dated as late Cretaceous and genetically related to other low pressure rock-units of the same age in the Aegean, differs in age and degree of dismemberment and metamorphism from ophiolites in mainland Greece.

Kinematic reconstructions and magmatic evolution illuminating crustal and mantle dynamics of the eastern Mediterranean region since the late Cretaceous

“…26 part of the Inner-Tauride oceanic domain was obducted over the Tauride and the eastern Pelagonian platforms forming the Lycian and Tauride ophiolites [Şengör and Yilmaz, 1981;Katzir et al, 1996;Dilek et al, 1999]. A similar process also occurred over the southern Tauride margin with the northward overthrusting of the Antalya ophiolites belonging to the Mesogean oceanic domain [Robertson, 2002].…”

“…in Crete) [Koepke et al, 2002] or to the late Cretaceous Lycian and Tauride ophiolites (e.g. in Tinos) [Katzir et al, 1996]. In Mykonos, Ikaria and Naxos, syn-tectonic sedimentary basins were also deposited in the hanging wall of these detachments during the Miocene [Photiades, 2002;Sánchez-Gómez et al, 2002;Lecomte et al, 2010;Laurent et al, 2015].…”

Cenozoic geodynamic evolution of the Aegean

“…8).The Upper Cycladic unit is represented by several large units (Melidonis 1980;Avigad and Garfunkel 1989;Katzir et al 1996;Stolz et al 1997) with a basal contact defining a broad open antiform as well as the metamorphic foliation of metapelites, metabasites and marbles in the underlying Cycladic Blueschists. HP-LT parageneses are best preserved to the southwest but pristine blueschists still occur in small lenses in the rest of the island (Jolivet and Patriat 1999;Jolivet et al 2004a).…”

Thermochronometric constraints on the tectonic evolution of the Serifos detachment, Aegean Sea, Greece

“…3. The Upper unit is rarely exposed and mainly consists of rocks of the Cycladic ophiolite nappe (Reinecke 1982;Maluski et al 1987;Altherr et al 1994;Patzak et al 1994;Katzir et al 1996). 4.…”