Elezaj et al.retardation of the ophiolite forming processesand the intraoceanic paleo displacement of thedifferent ophiolite segment limited by thetransform faults largely developed into theMirdita-Gjakove ophiolite belt (Kodra et al.1995).In the light of the age data provided by themetamorphic sole, the radiolarite chertsequences found within the Mirdita-Gjakoveophiolite belt and by its primary radiolarite cover,a very close age span is evidenced (Kodra et al.1995, Xhomo et al. 2002). The time span of themetamorphic soles indicates that its production ismade parallel to ophiolite forming processes andradiolarite chert sedimentation.Figura. 4. Metamorphich sole and its deformationsSimilar age indicate also the garnet pyroxenitesenclaves in a serpentinite breccia that crosscutsthe ophiolite volcanics near Derveni (Albania)(Gjata et al. 1992). According to geochemicaldata, the garnet pyroxenites probably originatefrom oceanic gabbro protoliths.Thermobarometric considerations show hightemperature (1200º C) and high pressure 1.5GPa). It s inferred that they are formed on theinitiation of a subduction process or near theoceanic ridge. Analogous age span show also theplagiogranites of SSZ type ophiolites (Ivanaj,1992).Genetic implicationsSummarizing the available data, it is inferred thatthe oceanic spreading producing the Jurassicophiolites, the successive intraoceanicsubduction and the ophiolite paleo emplacementonto the Middle Triassic-Lower Jurassic volcanosedimentary diabas radiolarite formation leadingto the metamorphic sole generation areAKTET Vol. IV, Nr 2, 2011 245
Elezaj et al.developed in very short time interval (Kodra andGjata 1982, Kodra et al. 2000, Elezaj and Kodra,2008).It seems that in the Mirdite - Gjakove narrowoceanic basin, the ophiolite detachment and thetwo margins decoupling of the young oceaniclithosphere is not developed above the oceanicridge. However, in the oceanic crust sequence ispreserved the necessary thermal flux for themetamorphic sole formation. Its setting may be isclose to the oceanic ridge or intraoceanicsubduction zone. As consequence, the suggestedscenario implies that the initial displacement ofyoung, hot, ocean crust and mantle occur withinan oceanic setting.The petrological and structural evidence from themetamorphic sole supports also theinterpretation that during the intraoceanic stage,the ophiolite emplacement (thrusting anddecoupling) is developed. The Early Jurassic-Middle Jurassic young and thick oceaniclithosphere is set onto the Middle Triassic-EarlyJurassic precedent oceanic lithosphere. Theemplacement movement is associated withproduction of the amphibolites, gneisses andmica schists with or without garnet.On the other side, the obducted ultramafics aresubjected at their basement to intensivemetamorphism. It is expressed by rockdehydration and the mylonitization. In moreadvanced phases the intensive serpentinizationprocesses are developed. At the lowest part ofthe ultramafic sheets a strong serpentinizationand the squeezing phenomena occurred and theshear zones are developed (Fig. 4). At theultrabasic massif bottom the cutting deformationpasses to ductile deformation, which iscontemporaneous to ophiolite solemetamorphism. The last one is affected by thefoliation S1, splitting schistosity S2 andmultiphase micro folds (Meshi 1995, Nicolas et al.1999).Some time, the metamorphic sole is cross cut bythe garnet, quartz-garnet etc. thin veins (from 2-5cm, to 10-15 cm). They are considered asproducts related to the metamorphic processesoccurred during the ophiolite emplacement.In general, a structural concordance between theultrabasic allochthonous massifs foliation,metamorphic sequence foliation, the structurallyunderlying basalt radiolarite series (βT 2 -J 1 )stratification and the Jurassic ophiolitesemplacement plane on volcano-sedimentaryseries is observed (βT 2 - J 1 ). Some time, it isdifficult to retrace the boundary between themetamorphic sequence and the underlyingvolcano sedimentary formation, because a lightmetamorphic imprint is evidenced also into thevolcano sedimentary members.CONCLUSIONS1. In the example of the Mirdita – Gjakovaophiolite, it is inferred that during the MiddleJurassic, the bidivergent emplacement of theyoung oceanic lithosphere onto the oldlithosphere (Triassic-Lower Jurassic ophiolites)occurred. The ophiolite displacement producedthe subjacent metamorphic sole developed alongside the ophiolite margins.2. The initial displacement of the oceanic andmantle crust occurs within an oceanic setting.3. The time span of the metamorphic solesindicates that its production is made parallel toophiolite forming processes and radiolarite chertsedimentation.4. The very short age span of the Jurassicophiolites, accompanied with their bidivergentemplacement onto Triassic-Liassic ophiolites(volcano-sedimentary formation, βT 2 -J 1 ) supportsthe suggestion on the existence of very narrowoceanic basin suggested by Kodra and Gjata1982, Vergély et al. 1998, Kodra et al. 1994, 1995,2000 etc.REFERENCES1. Ciric B.A., Eric V. (1996) – Contactmetamorphism beneath the peridotite of BorovVrh-Brezovica, Eds. Knezhevic et al. 359-264.2. Dimo A. (1997) – Le mécanisme de mise enplace des ophiolites d’Albanie. Ph.D. thesis, Univ.Paris-Sud, 307.3. Dimo A., Monie, Vergely P., Kodra A., andGjata K. (1998) – Mosha radiometrike eshkembinjve te shtrojes metamorfike dhe te246AKTET Vol. IV, Nr 2, 2011
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