Petrogenesis of Late Cretaceous Adakitic Magmatism in the İstanbul Zone (Çavuşbaşı Granodiorite, NW Turkey)

Authors : Sabah Yilmaz ŞAHİN, Namik Aysal Yildirim GÜNGÖR

Pages : 1029-1045

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Publication Date : 0000-00-00

Article Type : Research Paper

Abstract :The Çavuşbaşı granodiorite intrudes Ordovician sedimentary rocks in the western part of the İstanbul Zone insert ignore into journalissuearticles values(NW Turkey);. The intrusion is made up mainly of granodiorite, and subordinate tonalite and quartz diorite, and has a granular texture and some special mixing textures such as antirapakivi, blade-shaped biotite, acicular apatite, spongy cellular dissolution/melting plagioclase textures. The main mafic minerals are hornblende and biotite. U-Pb in-situ dating of zircons from two samples via SHRIMP yielded weighted age values of ~68 Ma, suggesting emplacement during the Late Cretaceous. Geochemically the Çavuşbaşı granodiorite resembles adakites with high Sr/Y and La/Yb ratios, low Y and HREE contents and no Eu anomaly. It contains 63.4 insert ignore into journalissuearticles values(wt%); >SiO2, and is I-type, metaluminous, middle-K calc-alkaline. These adakitic rocks have high values of MgO insert ignore into journalissuearticles values(0.77-2.56 wt%);, Mg# insert ignore into journalissuearticles values(45.3-59.3); and LILE insert ignore into journalissuearticles values(e.g., Rb, K, Ba, Sr);. Initial eNd and 87Sr/86Sr values are 3.2-3.7 and 0.7035-0.7036, respectively. Based on the continuing subduction along the İzmir-Ankara and Intra-Pontide Neo-Tethyan oceanic domains and depleted Sr-Nd isotopic signatures, we suggest that the adakitic magmas may be derived from the partial melting of an oceanic slab under amphibole-eclogite facies conditions.
Keywords : İstanbul Zone, adakite, SHRIMP dating, Sr Nd isotops, arc related, slab melting, Neo Tethyan Ocean