Akademik Veri Yönetim Sistemi
Yerbilimleri/ Earth Sciences, cilt.26, sa.1, ss.25-47, 2005 (Scopus)
The lowermost unit in the studied area, located at the west of Eastern Pontids, is the Late Cretaceous-Paleocene Tekkiraz Member of Akveren Formation. Paleocene (?)-Eocene Koçevyani basalt overlies this unit unconformably. Eocene Tekkeköy Formation consisting of Çaybaşi Member, Kurttaşli Tepe andesite, Kale Member, İkizce andesite and Teknecik andesite porphyr overlies this unit unconformably. The studied volcanic rocks are composed of mainly andesite, andesite porphyr and pyroclastics, rarely basalt and basaltic andesite, and show generally porphyric, microlitic porphyric, hyalo-microlitic porphyric, hyalopilitic and rarely intersertal, intergranular, fluidal and glomeroporphyric textures. The rocks include clinopyroxene (Wo44- 48En45- 39Fs10 -13), plagioclase (An31- 80), olivine (Fo83 -84), hornblende (Mg# = 0.49-0.82), biotite (Mg# = 0.48-0.60), rarely magnetite, apatite and zircon. In these rocks, disequilibrium textures are observed such as oscillatory zoning, sieve texture and corrosion in plagioclase phenocrysts, breakdown and opaque in hornblendes and biotites, and dissolution in clinopyroxenes. Volcanics are generally calcalkaline and tholeiitic-alkaline transitional in character, and have medium-K contents. Major oxide and trace element variations indicate a significant role of clinopyroxene, olivine, hornblende, plagioclase, magnetite and apatite fractionation during the evolution of rocks. High LILE (Sr, K2O, Rb, Ba) and LREE (La, Ce), and low HFSE (Nb, Zr, Y, TiO2) contents show that the rocks have evolved from a parental magma derived from an enriched source of mixed subducted slab and asthenospheric melts. Besides Koçevyani Basalt evolved by olivine + augite controlled fractionation whereas andesitic rocks developed augite + hornblende ± plagioclase controlled fractionation and assimilation ± magma mixing.