U-Pb zircon ages and petrogenesis of the Late Cretaceous I-type granitoids in arc setting, Eastern Pontides, NE Turkey

Abstract

The Eastern Pontides Orogenic Belt (EPOB) as a well-preserved ancient magmatic arc situated in the eastern part of the Sakarya Zone and has key importance to allow for proper reconstruction of the geodynamic evolution of the region. The region accepted as important part of Alpine-Himalayan Belt comprises of many granitoids of the Late Cretaceous age. This paper presents new mineral chemistry, bulk-rock petrochemistry, U-Pb geochronology and radiogenic and stable isotope geochemistry data from the Arpakoy and Oyman granitoids in the north part of the EPOB to interpretation of the igneous activity and geodynamic evolution of the region in Late Cretaceous era. Emplacement ages of 86.82 +/- 0.58 Ma for the Oyman granitoid and 82.0 +/- 2.3 Ma for the Arpakoy granitoid according to laser ablation ICP-MS U-Pb zircon dating. The Arpakoy granitoid are gabbro diorite, diorite and granite, whereas the Oyman granitoid are tonalite and granite in composition. They show metaluminous-peraluminous transitional (ASI = 0.79-1.20) low to medium-K calc-alkaline features. The rock samples from granitoids are characterized by enrichment in large ion lithophile elements (LILE) and high field strength elements (HFSE) depletion with concave-upward shapes (La-N/Lu-N = 1.88 to 6.04). The crystallization temperatures are 648 degrees C-913 degrees C and the pressure values are 0.2-3.0 kbar, which indicates emplacement depth of the studied granitoids varying from similar to 1 to 9 km correspond to shallow crustal depths. They show considerable variations in epsilon Nd-(i) (-4.02 to 1.50) and Sr-87/Sr-86((i)) (0.70478-0.70689). The Pb-206/Pb-204 ratios are between 17.97 and 18.65, and 8180 are varying from +5.4 to +9.3 parts per thousand. The parental magma of the Arpakoy and Oyman granitoids originated from a melt of the enriched lithospheric mantle and the fractional crystallization and lesser assimilation processes has important role on the evolution of magmas in the shallow crustal levels.