Deciphering the shoshonitic monzonites with I-type characteristic, the Sisdagi pluton, NE Turkey: Magmatic response to continental lithospheric thinning

Large-scale late Mesozoic to early Cenozoic plutons in the Eastern Pontide orogenic belt mostly show calc-alkaline and I-type geochemical features. However, we identify the Sisdagi pluton that has shoshonitic affinity and I-type character in the region. The pluton was emplaced at shallow depths (<5 km), revealed by Al-in hornblende barometry, in the northern margin of the orogenic belt, with SHRIMP zircon U-Pb age of 41.55 +/- 0.31 Ma, interpreted as dating magma crystallization. It is composed of monzonite, monzodiorite and monzogabbro. The samples show low zircon saturation temperature (T-zr) ranging from 603 to 769 degrees C compared to A-type rocks. They exhibit SiO2 contents of 47.6-61.4 wt.%, and high K2O + Na2O (5.0-8.8 wt.%) and K2O/Na2O (0.8-1.8). All the samples are characterized by low Mg# (<47) and relatively high but variable Al2O3 content (16.9-22.2 wt.%). They are also enriched in light rare earth elements (LREE), large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE), with a weak negative Eu anomaly (Eu/Eu-center dot = 0.58-1.26) in mantle-normalized trace element patterns.