Mineral chemistry, crystallization conditions and petrography of Cenozoic volcanic rocks in the Bahcecik (Torul/Gumushane) area, Eastern Pontides (NE Turkey)

Abstract

Mineralogical, petrographical and mineral chemistry properties are presented for the Cenozoic aged Bahcecik volcanics in the Eastern Pontides (NE Turkey). The studied volcanic rocks are composed of basaltic andesitic, andesitic, dacitic and trachydacitic lavas and pyroclastics. Petrographic and mineral chemistry studies reveal some disequilibrium textures reflecting magma mixing process. These rocks contain labradorite (An67-50), andesine (An46-34), oligoclase (An29-15), and albite (An1-01), magnesio-hastingsite (Mg# = 0.73-0.9), pargasite (Mg# = 0.76-0.78) and edenite (Mg# = 0.76-0.85), augite (Wo43-45), diopside (Wo46) and clinoenstatite (En68-69), K-feldispar, biotite, quartz and Fe-Ti oxide minerals. Crystallization temperatures calculated from amphibole and clinopyroxene minerals are 834 °C to 1149 °C, pressure values are 1.4 to 6.5 kbar, oxygen fugacity (log10 ƒO2) are -11 to -9.6. Estimation of water content calculated by using amphiboles is between 6.6 and 8.5%. Based on the obtained data, it is suggested that the magmas had undergone hydrous and anhydrous crystallizations in the shallow to mid-crustal magma chambers.