Nr.2 - ALPA - Albanian Papers

Elezaj et al.cases its tectonic fragments outcrop withinophiolites (Xhomo et al. 2002). In Kosova, itoccurs at the basement of Korishe, Lubizhde,Koxhi Ballkan, Brezovice etc., and small ophiolitemassifs (Elezaj et al. 2000, Elezaj and Kodra2008).The soles reflect a time when the base of a hotoceanic sheet was first detached from itssubstratum and overrode the rocks that havebeen metamorphosed, commonly to green schistor amphibolite grade (Jones et al. 1991, Smith,1993). In example of Albania, it is inferred thatthis formation is issued during the intraoceanicstage. Bidivergent and North-North Westernthrusting and the displacement of Middle Jurassicyoung hot oceanic lithosphere onto MiddleTriassic-Lower Jurassic old cold oceaniclithosphere produced the metamorphic sole(Kodra and Gjata 1982, Kodra et al 2000, etc.).The metamorphic sole is an important geologicalindicator because it preserves a key record on theophiolite evolution. The geological evidence ofthe metamorphic sole in Kosova provides ulterioralternatives on the driving forces and ophioliteemplacement in the most northeastern segmentof Mirdita-Gjakove-Rahovec ophiolite belt. Thepaper doesn’t address the metamorphic sole ofVardar Zone.Geological evidenceIn Kosova area, the ophiolite metamorphic sole iswidely exposed along the edge of the ophiolites,but in several cases it is found sporadically astectonic slices at the basement of the ultrabasicsheets. Its thickness ranges from several metersto 200 - 300 m. Generally, at the contact withultrabasics, the metamorphic sequence iscomposed of amphibolites or garnetamphibolites. These facies grade downward togarnet-mica schists and green schists. Locally, agradual transition to the underlying volcanosedimentaryformation is documented.On the basis of several chemical analyses, theamphibolites are originated from basaltic andgabbroic protoliths, and seem to includemembers of high Ti series. The protoliths of micaschists were probably siliciclastic sediments withpelitic components.At the bottom of the ophiolite massifs, asqueezed strip of serpentinites, 10 -100 m thickcrops out. Upward, the ultrabasic rocks arerepresented of fresh and mylonitized faciescorresponding to low-temperaturemetamorphism, probably related to the ophiolitepaleo displacement onto the continental margins.In general, two successive metamorphicsequences are distinguished: the upper and thelower sequence. The upper sequence isrepresented of garnet amphibolites (almandineamphibolites), amphibolites, almandinemuscovite-micaschists. The metamorphic faciesbelong to temperatures 500-700 ºC and pressure6-8,2 kbar. (Dimo, 1997). The Lower sequence iscomposed of green schists of the temperature300-400º and pressure 3-4 kbar.Downward the metamorphic sole passesgradually to Middle Triassic - Lower Jurassicunmetamorphosed basalt radiolarite series.In Albania, in several places the metamorphicsole shows a steep apparent invertedmetamorphic gradient, with granuliteassemblages preserved close to the contact withobducted ophiolites, going downward intoalmandine-amphibolite subfacies assemblages,amphibolite facies, then greenschist facies(Bebien et al. 2000). The granulites correspond toP-T conditions: 800-850 º C and 0,9- 1,2 GPa(Dimo, 1997).In Kosova area, the ophiolite massifs set onto themetamorphic sole are represented of lithosphericmetamorphosed peridotites. The peridotitesshow foliated porphyroclastic structure of lowtemperature and high pressure. Such typestructures are identified also in neighboring areas(Meshi, 1995, Gjata et al. 1995, Nicolas et al.1999).According to Fejza, 2004, in the example ofGoleshi massif, an eastern orientationdisplacement is documented (fig. 1). At theophiolite massif basement, the squeezed andhighly foliated serpentinite schists of severalmeters to 100 - 200 m thick are developed. Theyare widespread at the basement of the ultrabasicAKTET Vol. IV, Nr 2, 2011 241