U–Pb zircon chronology and petrogenesis of Carboniferous plutons in the northern part of the Eastern Pontides, NE Turkey: Constraints for Paleozoic magmatism and geodynamic evolution

Abstract

Numerous intrusive rocks of varying ages and compositions exist in the Paleozoic to Tertiary periods in the Eastern Pontides. Carboniferous intrusive rocks are commonly observed in the southern part of the Eastern Pontides. The nature of the rocks in the northern part of the region has not been determined because of Upper Cretaceous and Tertiary volcano-sedimentary units. Whole-rock geochemical, isotopic and geochronological data obtained from five different mapped granitoid bodies located in the northern part of the Eastern Pontides allow for the proper reconstruction of Carboniferous magmatism and the geodynamic evolution of the region.According to laser ablation ICP-MS U–Pb zircon dating, the Özdil, Soğuksu, Seslikaya, Kızılağaç and Şahmetlik plutons have similar 206Pb/238U vs. 207Pb/235U concordia ages of 340.7±1.8Ma and 323.1±1.5Ma, 348.4±1.6Ma, 335.4±1.4Ma, 337.2±0.6Ma and 334.5±1.4Ma, respectively. The aluminium saturation index (ASI) values of all of the samples from the plutons are between 1.0 and 1.32, which indicate peraluminous melt compositions. The plutons have SiO2 contents between 59 and 79wt.% and show low- to high-K calc-alkaline characteristics. The plutons are enriched in large-ion lithophile and light rare earth elements and are depleted in high-field strength elements. Chondrite-normalized rare earth element patterns are characterized by concave-upward shapes and pronounced negative Eu anomalies, with LaCN/YbCN=1.9–46.8 and EuCN/Eu*=0.19–1.76. The studied plutons show considerable variations in 87Sr/86Sr(i) (0.70255 to 0.71006) and εNd(i) values (−4.8 to −7.1), as well as Nd model ages (1.15 to 2.47Ga). The Pb-isotopic ratios are 206Pb/204Pb=17.11–18.60, 207Pb/204Pb=15.58–15.64 and 208Pb/204Pb=36.95–38.62. The crystallization temperatures of the melts range from 676 to 993°C, as determined by zircon and apatite saturation thermometry.These data suggest that the Carboniferous granitic magmas were produced by the partial melting of meta-mafic to meta-felsic lower crustal source rocks, with minor contributions from the mantle. Collectively, these rocks represent a late stage of Hercynian magmatism in the northern part of the Eastern Pontides.