Petrology of the Plio-Quaternary Gobekoren Volcanics (Kangal-Sivas)

Abstract

The study area is located at 15 km W-SW of Kangal district of Sivas province. Lithological units are observed in the study area ranging from Late Miocene to Plio-Quaternary in age. The rock units start with Late Miocene-Pliocene Kangal Formation and Upper Pliocene Uzunyayla Formation conformably overlies this unite. Uzunyayla Formation is uncomfortably overlain by the Plio-Quaternary Gobekoren volcanics and again uncomfortably over the Quaternary alluvium. The Late Miocene-Pliocene Kangal Formation has a thickness of about 200 m in the study are and consists of sandstone, mudstone and lignite bands in some places. Uzunyayla Formation forms of marl and lacustrine limestone which was placed in conformity to Kangal Formation. Above units, Late Pliocene Gobekoren Volcanics with dark brown-black colour, porous, air-bubbled, massive columnar and an approximate thickness of 10 m is composed mostly from basalt and less from trachybasalt. Gobekoren volcanics characterizes alkaline as geochemically. Both geochemical analyses and mineralogical observations show that there are olivine and clinopyroxene fractionation from basalts to trachybasalt. As a result of the geochemical investigations, it was observed that Gobekoren volcanics has more enriched light rare earth elements than heavy rare earth elements which suggest that the crustal material may be added during the crystallization in the magmatism. In addition, the amount of partial melts increases from trachybasalt to basalts. Gobekoren volcanics which is located in Sivas Basin is continental plate basalts which is formed as a result of lithospheric thinning.