Comparative petrogenetic investigation of Composite Kaçkar Batholith granitoids in Eastern Pontide magmatic arc—Northern Turkey

Abstract

The Pontides are an east-west trending orogenic belt which is subdivided into west, middle and eastern sectors according to their different tectonostratigraphy. The Eastern Pontides are represented by west-east-trending tectonic zones resulted from a common Mesozoic-Tertiary history, comprises dominantly of magmatic rocks. The magmatic belt in the Eastern Pontides includes a large batholith, termed the Composite Kaçkar Batholith (CKB) in which there are various granitic facies. The emplacement of CKB occurred in pulses between the Early Cretaceous and Eocene period during the development of the eastern Pontide magmatic arc and following collisional events. The members of the CKB are Dereli-Şebinkarahisar (Giresun) in the west, southern Araklı (Trabzon) in the middle and Kaçkar Mountain and its surrounding area (Rize) in the east. The plutons ranging from syenite through monzonite to granite are typically medium-high K calc-alkaline rarely tholeiitic and metaluminous I-type. The studied members of the CKB intrudes into the Late Cretaceous arc volcanics and are determined to be Late Cretaceous-Eocene (75.7 ± 1.55; 41.2 ± 0.89) in K-Ar age. The tectono-magmatic setting of the granitoids has been interpreted as an arc-related granitic suite, a post-collisional granitic suite and a post-orogenic granitic suite. Some plutons including mafic magmatic enclaves (MME) and K-feldspar megacrystals suggest magma mixing/mingling. HFS and LIL element geochemistry of the granitic intrusions also suggest that fractional crystallization, magma mixing/mingling and crustal contamination played an important role in the evolution of the CKB. All the data mentioned above show that the granitoids in the three different regions may have been derived from an arc, developed in response to the northward subduction of the northern branch of neo-Tethyan oceanic crust beneath the Eurasian plate in Late Cretaceous and a collision between the Pontide arc and the Anatolide-Tauride platform in Paleocene.