The Eastern Pontides in NE Turkey hosts a very limited number of plutonic rocks from the Jurassic period. Here we submit new geochemical, Sr-Nd-Pb and zircon Lu-Hf isotope data, and zircon U-Pb ages for plutonic rocks in this region. Zircon U-Pb dating for the Alemdar and Isikdere plutons yielded an age of 175-170 Ma (Middle Jurassic). The Alemdar and Isikdere plutons have I-type, medium to high-K calc-alkaline series, and metaluminous to slightly peraluminous characteristics. On PM-normalized diagrams, the plutons are enriched in large-ion lithophile elements (LILEs) with pronounced depletion of high field strength elements (HFSEs, Ta, Nb, Ti). Chondrite-normalized plots for the plutons show variable enrichment in light rare earth elements (LREEs) with depletion of heavy rare earth elements (HREEs). The rocks of the Alemdar Pluton have homogeneous I-Sr values (0.70585 to 0.70673), low epsilon Nd-(i) values (-3.9 to -1.6), pozitif epsilon Hf-(i) values (+3.3 to +9.1), and Hf single-stage model ages (563-712 Ma), whereas those of Isikdere have high I-Sr values (0.70666 to 0.70673), low epsilon Nd-(i) values (-3.9 to -3.8), epsilon Hf-(i) values (-3.1 to +1.1), and Hf single-stage model ages (791-969 Ma). These values imply that they have different sources. These results suggest that the magma of the Alemdar was formed by the partial melting of a relatively depleted lithospheric mantle wedge interaction of the OIB-like melts, while those of Isikdere have derived from the partial melting of an enriched mantle metasomatized by slab-derived sediments and then modified by fractional crystallization and crustal contamination in crustal magma chambers. Considering the available data, we conclude that the studied plutons were related to extensional tectonic events during the Middle Jurassic in response to the roll-back of the Paleotethys oceanic slab in the final stage of oceanic closure. These rocks are an example of the formation of deep subduction products following Early Jurassic subduction.

The Eastern Pontides comprise many intrusive bodies varying in composition, size and age from Palaeozoic to Cenozoic. Especially Cenozoic aged bodies are commonly observed in the southern part, while they are rarely exposed in the northern part of the Eastern Pontides. In this study, the petrography and mineral chemistry of the Cenozoic aged Cicekli, Somarova, Sorkunlu, Sasurluk, Aydintepe, Kemerlikdagi and Pelitli plutons located to the north of Bayburt are determined, and the crystallisation conditions of the studied bodies were estimated by means of thermobarometer calculations. The studied plutons extend mostly in NE-SW directions and are approximately ellipsoid in shape. The contacts between the plutons and surrounding rocks are sharp, and plutons commonly contain mafic microgranular enclaves (MMEs) of different sizes. Petrographic and mineral chemistry studies reveal some disequilibrium textures reflecting the magma mixing process. Based on modal mineralogy, the plutonic rocks are gabbroic diorite, diorite, tonalite, granodiorite and monzogranite in composition. The rocks have fine to medium granular, porphyric, monzonitic, poikilitic, occasionally myrmekitic and micrographic textures. The main minerals are labradorite and albite (An(68-02)), magnesiohornblende and actinolite (Mg# = 0.6-0.9), diopside and augite (Wo(44-46)), clinoenstatite (En(53-57)) and Fe-Ti oxide minerals. Crystallization temperatures calculated from amphibole, biotite, clinopyroxene, magnetite and ilmenite minerals are 405 degrees C to 1161 degrees C, pressure values are 0.1 to 2.7 kbar, and oxygen fugacity (log10 fO(2)) is -20 to -12. Estimation of water content calculated by using amphiboles is between 2.9 and 6.8%. Based on obtained data, it is suggested that the studied plutons were emplaced at shallow depths (similar to 1-8 km).

Doğu Pontidler, Paleozoyik’ten Senozoyik’e kadar farklı yaş aralığı, bileşim ve büyüklüğe sahip pek çok plütona ev sahipliği yapmaktadır. Bu plütonik kütlelerden özellikle Senozoyik yaşlı olanlar, Doğu Pontidler’in güney kısmında yaygın olarak gözlenirken, kuzey kısmında seyrek olarak gözlenirler. Bu çalışmada, Bayburt kuzeyinde yer alan Senozoyik yaşlı Çiçekli, Somarova, Sorkunlu, Şaşurluk, Aydıntepe, Kemerlikdağı ve Pelitli plütonlarının petrografik ve mineral kimyası özellikleri belirlenerek termobarometre hesaplamalarıyla kristallenme koşulları ortaya konulmuştur. İncelenen plütonlar, genelde KD-GB uzanımlı olup, yaklaşık elips şekillidirler. Genellikle yan kayaçlarla dokanakları keskin olup, değişik boyutlu mafik mikrogranüler anklavlar (MMA) içerirler. Petrografik ve mineral kimyası incelemelerinde magma karışımına ait dokusal özellikler saptanmıştır. Modal mineralojik bileşimlerine göre; incelenen plütonlar, gabroyik diyorit, diyorit, tonalit, granodiyorit ve monzogranit bileşimlidirler. Kayaçlarda ince-orta taneli, porfirik, monzonitik, poikilitik, yer yer de mirmekitik ve mikrografik dokular görülür. Labrador ve albit (An68-02), magnezyumlu hornblend ve tremolit (Mg# = 0.6-0.9), diyopsit ve ojit (Wo44-46), klinoenstatit (En53-57) ve Fe-Ti oksit başlıca mineralleri oluşturur. Amfibol, biyotit, klinopiroksen, manyetit ve ilmenit minerallerine göre hesaplanan kristallenme sıcaklıkları 405°C ile 1161°C, basınç değerleri 0.1 ile 2.7 kbar, oksijen fugasitesi (log10 ƒO2) -20 ile -12 ve amfibollerden hesaplanan su içerikleri ise % 2.9 ile 6.8 arasındadır. Tüm bu veriler dikkate alındığında, incelenen plütonların sığ derinliklere (~ 1-8 km) yerleşerek katılaştıkları ileri sürülebilir.