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TURKISH JOURNAL OF EARTH SCIENCES, vol.16, no.4, pp.523-539, 2007 (SCI-Expanded)
The Jurassic volcanic rocks in the centre of the northern zone ( south of Trabzon City) provide important constraints on the evolution of Pontides. The investigated volcanic rocks form a transitional series between tholeiitic and calc- alkaline, and is dominated by basalt, basaltic andesite and andesite. Geochemically, they are enriched in LILE and LREE contents and depleted in HFSE [(La/Yb)(N)= 2.2 - 8.5; (Nb/La)(N)= 0.1 - 0.77)] compared to mid- ocean ridge basalts and have radiogenic Nd isotope ratios of epsilon Nd( 210 Ma)= - 0.72 to 3.24. These trace element and isotope data suggest that these rocks were derived from low degrees of partial melting of spinel lherzolite that was metasomatized by subduction- related fluids and further underwent a degree of fractional crystallization in magma chambers before being extruded at the surface.