The WNW-trending Demirköy pluton has an elliptical shape and a concentrically zoned internal structure. In this structure, gabbro/diorites and quartz diorites are only seen in the SW corner of the pluton, while granodiorites form the main body of the pluton surrounded by a zone of granite. The granodiorites contain dioritic mafic microgranular enclaves. Small quartz monzonite lenses and/or bodies and mafic dykes are also observed in the Demirköy Igneous Complex.
Geochemically, the Demirköy Igneous Complex has calc-alkaline, metaluminous and medium-K characteristics. There is a significant correlation between the LREE/HREE ratios and SiO2 values. Chondrite-normalized REE patterns are relatively flat (LaN/LuN = 2) in gabbros. This ratio ranges from 3 to 11 for the diorite/granodiorites, and from 14 to 35 for the granites. Dioritic enclaves have REE patterns similar to those of the main body and have LaN/LuN values between 3 and 6. Relatively enriched LILE (Sr, K, Rb, Ba and Th) and relatively depleted HFSE (Ta, Nb and Ti) values indicate the classic subduction-related origin of the complex. The initial isotopic signatures range from εNd(i) = − 0.45 to − 2.57 and 87Sr/86Sr(i) = 0.7042–0.7064 for gabbros and εNd(i) = − 0.43 to − 2.67 and 87Sr/86Sr(i) = 0.7048–0.7059 for granodiorites and granites. δ18O values range from + 6.18 to + 7.80‰ (VSMOW) for gabbros and from + 6.86 to + 8.89‰ (VSMOW) for granodiorites and granites.
Based on geochemical and isotopic characteristics this magmatic complex can be subdivided into 4 groups: a) gabbro, b) diorite to alkali granite (main body), c) syenite/monzonite and d) mafic dykes. Geochemical data and modelling results favour a typical subduction-related enriched lithospheric mantle and lower crustal source for the Demirköy Igneous Complex. Slab-derived fluids and crustal contamination also played a key role in the petrogenesis of this magmatic suite.