Emplacement mechanism, petrogenesis and geodynamic setting of tertiary basaltic dikes and sills in the southern part of eastern black sea mountain belt (Ne Turkey)

This study focuses on the petrogenesis, emplacement time and geodynamic setting of the basaltic andesites that occur as dikes and sills within the Eocene sequence in Karaşeyh area that is situated in immediately east of Şiran town of Gümüşhane city and aims to contribute to the solution of the problem. The dikes range in length from 2 km to 6 km. Their trends (N20E) are perpendicular to the fold axes, indicating that dike emplacement was controlled by pre-existing extensional fractures that are approximately parallel to the maximum principal stress causing intensive folding in Eocene sedimentary rocks. The rocks consist predominantly of plagioclase and clinopyroxene, and minor olivine. Alteration products are represented by chlorite, epidotite, calcite and sericite. Apatite and zircon occur as accessory phases. Their major-trace-rare earth element concentrations indicate that they are basaltic andesite in composition and calc-alkaline in character. Primitive mantle and chondrite-normalized trace and rare earth element patterns indicate that basaltic andesites are enriched in LILE and LREE with respect to HFSE and HREE, respectively, and dare characterized by negative Nb, Ta and Ti and positive Pb anomalies, suggesting subduction- related processes played an important role during their petrogenetic evolution. Considering all geological and geochemical data we suggest that magmas that formed the studied basaltic andesites were derived from subcontinental lithospheric mantle source, enriched by subduction related fluids during the southward subduction of Paleo-Tethyan oceanic lithosphere, in the back-arc region of the Eastern Black Sea Mountain Belt.