Petrology and geodynamic significance of the Cagirankaya (Ikizdere-Rize) trachytes

Whole-rock major and trace element compositions and dating of the first time adakitic trachytes from the eastern part of the Sakarya Zone were investigated to understand their origin and geodynamic processes. The obtained age data by SIMS zircon U-Pb technique is 5.16 ± 0.11 Ma. The adakitic trachytes consist of andesite and dacites. The rocks are characterized by high La/Yb and Sr/Y ratios. They have metaluminous features. All the samples show high-K calc-alkaline characters. The trachytes have enrichments of large ion lithophile elements (LILE) (Rb, Ba, K ve Th), light rare earth elements [(LREE) (La/Yb)n= 18-24) and depletion of high field strange elements [(HFSE) (Ta, Nb, Hf, Sm ve Yb)], negative Nb and Ti anomalies and no significant Eu anomalies. Their compositions, with low Mg# (42-46) are consistent with an origin as partial melts of a mafic continental lower crust beneath the region. All the geochemical data combined with regional data, Late Miocene adakitic trachytes was generated by partial fusion of mafic lower continental crust due to local extension and then their magmas may use the deep faults as a pathway.