Akademik Veri Yönetim Sistemi
CHEMIE DER ERDE-GEOCHEMISTRY, cilt.57, sa.2-3, ss.157-187, 1997 (SCI-Expanded)
The eastern Pontides are characterized by three volcanic cycles erupted in Liassic, Upper Cretaceous and Eocene times. Volcanic rocks of Liassic age are transitional, those of Upper Cretaceous age are subalkaline, and Eocene volcanic rocks are alkaline around Trabzon and Tonya, but subalkaline in the south of Gumushane. Geochemical variations indicate that fractional crystallization played a significant role in the evolution of more differentiated rocks, especially in Liassic and Upper Cretaceous volcanic rocks. Fractionation of olivine, clinopyroxene and plagioclase was the major control in the evolution of Liassic volcanic rocks, whereas fractionation of plagioclase and clinopyroxene dominated in the Upper Cretaceous volcanic rocks. Liassic volcanics show high to low pressure fractionation but Upper Cretaceous volcanic rocks low pressure fractionation. Eocene volcanic rocks from Tonya exhibit high to low pressure whereas those from Trabzon low pressure fractionation. The volcanic rocks were possibly derived from a tholeitic to an E-type MORE source. The Eocene volcanic rocks around Trabzon have very high LILE and LREE concentrations compared to those of Tonya. This may be due to varying degrees of partial melting from a common source.