Mineral and Whole-rock Geochemistry of the Kestanbol Granitoid (Ezine-Çanakkale) and its Mafic Microgranular Enclaves in Northwestern Anatolia: Evidence of Felsic and Mafic Magma Interaction

Abstract

The Miocene Kestanbol granitoid, in Ezine-Çanakkale, Turkey, is one of post-collision granitoids of western Anatolia, which have been related to the the late Cretaceous collision between the Anatolide-Tauride platform and the Pontides. Magmatism began during the early Miocene, with coeval alkaline to calc-alkaline plutonism and volcanism, controlled by the regional tectonic evolution. The Kestanbol pluton intruded regionally metamorphosed basement rocks. Volcanic and volcano-clastic sedimentary rocks overlie the pluton, which is bounded in the west and east by major faults. The pluton is frequently cut by felsic and mafic dykes and includes mafic microgranular enclaves (MMEs) that are mixing products of coeval felsic and mafic magmas. The Kestanbol granitoid is quartz monzonitic but the MMEs include monzonite, monzodiorite, and quartz monzodiorite. There are some special mixing textures such as antirapakivi, blade-shaped biotite, acicular apatite, spongy-cellular plagioclase and spike-zoned plagioclase in MME-host rock pairs. MME and host rock pairs display mineralogical similarities and they indicate some interactions and parallel evolution with each other. However, they have distinct major and trace element behaviour. The mineralogical and petrographical properties of the felsic and mafic dykes resemble the felsic host rocks and MMEs respectively. The results of the mineral chemistry showed that plagioclases are albite-labradorite (An_{8-50}), amphiboles are magnesio-hornblende and biotites are Mg-biotites in MME-host rock pairs. The amphibole compositions of the Kestanbol granitoid and its MMEs are somewhat similar (Mg/Mg+Fe^{+2} = 0.55-0.87 and 0.55-0.74). The FeO^t/MgO ratio of biotites in these rocks is between 1.01 and 1.55. These rocks are post-collisional, subalkaline, metaluminous and high-K calc-alkaline, I-type in character, and derived from hybrid magma that originated from the mixing of coeval mafic and felsic magmas in different ratios and at different depths.